JP2017191264A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can ensure transferability of a recording material at a low cost.SOLUTION: An image forming apparatus comprises: a photoreceptor drum 121; a developing device 122 that supplies a toner t to an electrostatic latent image formed on the photoreceptor drum 121 to form a toner image; a transfer roller 17 that transfers the toner image formed on the photoreceptor drum 121 to a recording material 1; and a CPU 201 (control means) that attaches the toner t from the developing device 122 to a portion of the transfer roller 17 through which the recording material 1 does not pass according to a change in resistance value between the photoreceptor drum 121 and transfer roller 17.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  Conventionally, an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus first exposes a laser beam corresponding to image information onto a surface uniformly charged by a charging unit while rotating a photosensitive drum as an image carrier. To form an electrostatic latent image. Then, toner is supplied to the electrostatic latent image by a developing unit to form a toner image. In addition, the toner image is transferred to the recording material by a transfer separation unit in which the transfer unit and the photosensitive drum sandwich the recording material, the recording material is separated from the surface of the photosensitive drum, and the transferred toner image is recorded by a fixing unit such as a heating method. The image is formed by fixing on the material.

  When the constant current control is used when transferring the toner image to the recording material, the transferability changes depending on the size of the recording material. For example, when a recording material (small size sheet) having a width smaller than the width of the transfer means (transfer belt or transfer roller) is used, a non-passing portion where the recording material does not pass is a passing portion where the recording material passes. Compared with, the electrical resistance is relatively low. For this reason, the transfer current necessary for the transfer of the recording material may leak through the non-passing portion of the recording material.

  In Patent Document 1, transferability is ensured by switching the transfer bias applied to the transfer means according to the size of the recording material between constant voltage control and constant current control. In Patent Document 2, toner is developed in a non-passing portion where the recording material on the surface of the photosensitive drum does not pass. The toner in the non-passing portion where the recording material does not pass in the transfer nip portion plays a role of electric resistance, and the current leaking from the transfer roller to which the transfer bias is applied to the photosensitive drum is suppressed, and is necessary for transferring the toner image. Charge is secured. As a result, there is no deterioration in image quality due to the size of the recording material.

Japanese Patent Laid-Open No. 11-095579 JP 09-325624 A

  However, in Patent Document 1, since it is necessary to provide a power source for constant voltage control and a power source for constant current control, the cost increases. In Patent Document 2, in each print job, toner is attached to a non-passing portion where the recording material on the surface of the photosensitive drum does not pass, and is further cleaned each time. For this reason, if the toner is unconditionally attached to the non-passing portion, the amount of toner discarded after the transfer increases, resulting in an increase in cost.

  The present invention provides an image forming apparatus capable of ensuring transferability of a recording material at low cost.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image developed by a developing unit that supplies a developer, and the image carrier. A transfer unit that sandwiches the conveyed recording material at the nip portion and transfers the toner image to the recording material, and the transfer unit or the transfer unit according to a change in resistance value between the image carrier and the transfer unit. And a control unit that causes the developer to adhere to a non-passing portion of at least one recording material of the image carrier.

  According to the above configuration, the transferability of the recording material can be ensured at low cost.

1 is an explanatory cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus according to the present invention. (A) is a front explanatory view showing a state in which toner is adhered to a non-passing portion where the recording material on the surface of the image carrier does not pass when a small-size recording material passes through the transfer nip portion. (B) is a front explanatory view showing a state in which the toner on the surface of the image carrier is transferred and adhered to a non-passing portion where the recording material on the surface of the transfer means does not pass. (C) is a front explanatory view showing a state in which a small-sized recording material passes through a transfer nip portion. (A) is a diagram showing the direction and magnitude of the bias current that flows from the transfer means toward the image carrier when a small-sized recording material passes through the transfer nip and transfers the toner image. (B) is a diagram showing an equivalent circuit of the electrical resistance between the transfer means and the image carrier when a small size recording material passes through the transfer nip and transfers the toner image. (A), (b) is a figure explaining the principle which the transfer explosion generate | occur | produces by transfer current shortage. 3 is a flowchart illustrating an image forming operation of the first embodiment. (A) is a figure which shows the relationship between the electrical resistance value of a transfer means, and a transfer explosion level. (B) is a diagram comparing the transfer explosion level and the toner consumption amount in the first embodiment and Comparative Example 2. FIG. (C) shows the passage time of the recording material when the recording material passes through the transfer nip portion with the toner adhered to the non-passing portion where the recording material on the surface of the transfer device does not pass, and the surface of the transfer device. FIG. 6 is a diagram illustrating a relationship with a toner amount attached to a non-passing portion through which a recording material does not pass. It is a flowchart which shows the image formation operation | movement of 2nd Embodiment. It is a flowchart which shows the image formation operation | movement of 2nd Embodiment. 10 is a flowchart illustrating an image forming operation according to a third embodiment. It is a figure which shows a mode that the toner adhesion amount of a transfer means reduces with time. (A) is a figure which shows a mode that the timing which replenishes a toner is set according to the determination value of the charge amount of the toner in the image development means of 4th Embodiment. FIG. 6B is a diagram illustrating a charging transition in which the charge amount of the toner in the developing unit varies depending on the environmental conditions in accordance with the passing time of the recording material passing through the transfer nip portion. (C) is a diagram showing the discharge transition that varies depending on the environmental condition of the charge amount of the toner in the developing means according to the standby time. (A) is a figure which shows an example of the correction coefficient set according to environmental conditions, when determining the charge amount of the toner in the developing means of 4th Embodiment. FIG. 7B is a diagram illustrating the charge amount of toner in the developing unit according to the passing time for the recording material to pass through the transfer nip portion of the fourth embodiment. (C) is a diagram showing the charge amount of the toner in the developing means according to the standby time of the fourth embodiment. 10 is a flowchart illustrating an image forming operation according to a fourth embodiment. FIG. 10 is a diagram comparing transfer explosion and toner consumption in the fourth and fifth embodiments and Comparative Example 3. FIG. 10 is a diagram illustrating a state in which a toner supply amount is set according to a determination value of a toner charge amount in a developing unit according to a fifth embodiment. 10 is a flowchart illustrating an image forming operation according to a fifth embodiment. (A) is a diagram showing the relationship between the toner charge amount on the image carrier and the toner amount adhering to the conveyance guide. (B) is a diagram showing the relationship between the area of the dot image formed on the image carrier and the toner charge amount on the image carrier. (A) is a figure which shows an example of the dot image formed in the non-passing part through which the recording material of the image carrier of 6th Embodiment does not pass. (B) is a diagram showing the potential difference between the surface potential of the image carrier of the sixth embodiment and the developing bias voltage. 14 is a flowchart illustrating an image forming operation according to a sixth embodiment. (A) is a diagram comparing the amount of toner adhering to the conveyance guide in the sixth embodiment and Comparative Example 4. FIG. (B) is a diagram showing the relationship between the potential difference between the developing bias voltage and the surface potential of the image carrier and the toner charge amount on the image carrier. (A) is a figure which shows an example of the toner image formed in the non-passing part through which the recording material of the image carrier of 7th Embodiment does not pass. (B) is a diagram showing the potential difference between the surface potential of the image carrier of the seventh embodiment and the developing bias voltage. 18 is a flowchart illustrating an image forming operation according to a seventh embodiment. FIG. 10 is a diagram comparing the amount of toner adhered to a conveyance guide between a seventh embodiment and a comparative example. (A) is a diagram showing the relationship between the number of passing recording materials and the resistance value of the transfer means in a normal temperature / low humidity environment, a normal temperature / humidity environment, and a high temperature / high humidity environment. FIG. 6B is a diagram illustrating a relationship between a time during which the recording material has been left after the recording material has continuously passed through the transfer unit and a resistance value of the transfer unit.

  An embodiment of an image forming apparatus according to the present invention will be specifically described with reference to the drawings. In addition, the structure described in each following embodiment is an example, and the range of this invention is not limited only to them.

  First, the configuration of the first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory cross-sectional view showing the configuration of the image forming apparatus of the present embodiment. FIG. 2 is a block diagram showing the configuration of the control system of the image forming apparatus of this embodiment.

<Image forming apparatus>
An image forming apparatus 10 shown in FIG. 1 is an example of a laser beam printer using an electrostatic transfer process. The photosensitive drum 121 is rotationally driven in a direction indicated by an arrow a in FIG. 1 at a predetermined peripheral speed (process speed) by a motor as a driving source (not shown).

  A charging roller 123 serving as charging means for uniformly charging the surface of the photosensitive drum 121 is provided. Further, along the rotation direction of the photosensitive drum 121, the surface of the photosensitive drum 121 that is uniformly charged by the charging roller 123 is irradiated with a laser beam 11a corresponding to the image information to form an electrostatic latent image. A laser scanner 11 serving as an image exposure unit is provided.

  Further, the image forming apparatus includes a developing device 122 serving as a developing unit that supplies a developer (toner t) to the electrostatic latent image formed on the surface of the photosensitive drum 121 to form a toner image. Furthermore, a transfer roller 17 is provided as a transfer unit for transferring the toner image formed on the surface of the photosensitive drum 121 to a sheet-like recording material 1 such as paper. Further, a cleaning device 124 is provided as a cleaning unit that scrapes and collects untransferred toner remaining on the surface of the photosensitive drum 121 after the toner image is transferred by a cleaning blade. In the lower part of the main body of the image forming apparatus 10 shown in FIG. 1, a feeding cassette 7 containing the recording material 1 is disposed, and a fixing device 18 is disposed above the photosensitive drum 121.

<Control unit>
In the present embodiment, as shown in FIG. 2, a CPU (Central Processing Unit) 201 serving as a control means for controlling an image forming operation or the like is provided. A transfer bias power source 204 that applies a transfer bias to the transfer roller 17 shown in FIG. 2 is connected to the CPU 201. Further, a transfer voltage detection circuit 205 is connected to the CPU 201. A transfer current Idc flows from the transfer roller 17 to the photosensitive drum 121 by the transfer bias applied to the transfer roller 17 by the transfer bias power source 204. The transfer voltage detection circuit 205 detects a transfer voltage generated when the transfer current Idc flows.

  Further, the CPU 201 determines the width size W of the recording material 1 in the direction intersecting the conveying direction of the recording material 1 conveyed from the size of the recording material 1 selected by the operation panel (not shown) by the user (in the longitudinal direction of the transfer nip portion Nt). Parallel length) is determined. Note that a recording material width detection sensor 202 serving as a size detection means is disposed in the feeding cassette 7 or the recording material conveyance path, and the recording material width detection sensor 202 is parallel to the longitudinal direction of the transfer nip portion Nt. The size W may be detected.

  Further, the CPU 201 is connected with an environmental sensor 206 serving as an environmental detection unit that detects environmental conditions such as temperature and humidity where the image forming apparatus 10 shown in FIG. 2 is installed. Further, a charging bias power supply 123 a that applies a charging bias voltage to the charging roller 123 is connected to the CPU 201. Further, the CPU 201 is connected to a developing bias power source 122 b that applies a developing bias voltage Vdc to a developing sleeve 122 a provided in the developing device 122. The charging bias power source 123a and the developing bias power source 122b are constituted by a DC power source and an AC power source, respectively. The transfer bias power source 204 includes positive and negative DC power sources.

  Further, the CPU 201 is connected with an environment sensor 206 serving as an environment detection means for detecting environment information such as temperature and humidity where the main body of the image forming apparatus 10 is installed. Further, a time timer 207 serving as a standby time detecting means for detecting a standby time Tb between print jobs from the end time of the immediately preceding print job to the start time of the next print job is connected.

  Further, a memory 203 serving as a storage unit is connected to the CPU 201. The memory 203 includes a ROM (Read Only Memory) and a RAM (Randam Access Memory). The ROM stores various control programs for controlling the image forming apparatus 10, various settings, initial values, and the like.

  The RAM is used as a work area from which various control programs are read, or as a storage area for temporarily storing image data. The RAM provided in the memory 203 also serves as an operation time storage unit that stores the operation time from the start time to the end time of the previous print job counted by the time timer 207. Further, it also serves as a standby time storage unit that stores a standby time from the end time of the immediately preceding print job to the start time of the next print job.

  Information on the width size W parallel to the longitudinal direction of the transfer nip portion Nt of the recording material 1 is stored in the memory 203 as needed. Further, temperature / humidity information of the place where the main body of the image forming apparatus 10 detected by the environment sensor 206 is stored as needed. Further, the passage time information of the recording material 1 passing through the transfer nip portion Nt is stored at any time during the print job detected by the CPU 201 which also serves as a passage time detection means. Further, information on the waiting time Tb between print jobs is stored as needed.

The transfer roller 17 of this embodiment covers an elastic rubber (elastic body) such as urethane on a metal core such as stainless steel (SUS) having an outer diameter of 6 mm. Such an elastic rubber (elastic body) is adjusted to an electric resistance value of, for example, 1 × 10 ⁶ Ω to 1 × 10 ¹⁰ Ω with a conductive material. The transfer roller 17 of the present embodiment has an outer diameter of 16 mm and a longitudinal width of 306 mm.

  As a material for the elastic rubber used for the transfer roller 17, a material in which carbon is dispersed in urethane, a conductive roller made of nitrile butadiene rubber (NBR), or the like can be used. Furthermore, an ion conductive roller composed of hydrin or the like, an electronic conductive roller composed of ethylene propylene diene terpolymer (EPDM), or the like can be used. It is known that the resistance value of the transfer roller having such a configuration greatly varies depending on the environment in which it is used and the number of times of bias application depending on the use.

  At a timing when the recording material 1 is conveyed to the transfer nip portion Nt, a predetermined direct current (+10 μA in this embodiment) having a polarity opposite to the polarity of the toner t is applied from the transfer bias power source 204 to the transfer roller 17. As a result, the toner images attached to the surface of the photosensitive drum 121 are electrostatically transferred sequentially to the recording material 1. At this time, the width size W of the recording material 1 parallel to the longitudinal direction of the transfer nip portion Nt (the size of the width in the direction intersecting the recording material conveyance direction) may be as follows. That is, the width may be smaller than the maximum printable width size in the longitudinal direction of the transfer nip portion Nt (hereinafter referred to as “small size recording material 1”).

  In this embodiment, as a representative example of the small-size recording material 1, a sheet of LTR (Letter) size (279.4 mm × 215.9 mm) is fed longitudinally (the short direction of the recording material 1 is the transfer nip portion Nt). (LTR-R) is considered when transporting in parallel with the longitudinal direction. In the transfer nip portion Nt, as shown in FIG. 3C, in the non-passing portion where the recording material 1 does not pass in the region other than the width size of the small size recording material 1, the transfer roller 17 and the photosensitive drum 121 are provided. And are in direct contact.

  An arrow shown in FIG. 4A indicates a transfer current Idc that flows from the surface of the transfer roller 17 toward the surface of the photosensitive drum 121 when the small-sized recording material 1 passes the transfer nip portion Nt and transfers the toner image. Indicates the direction and size of FIG. 4B shows an equivalent circuit of an electrical resistance value between the surface of the transfer roller 17 and the surface of the photosensitive drum 121 when the small size recording material 1 passes the transfer nip portion Nt and transfers the toner image. FIG.

  As shown in FIG. 4B, the surface of the transfer roller 17 in the non-passing portion (the left and right end portions in FIG. 4A) through which the small size recording material 1 nipped and conveyed in the transfer nip portion Nt does not pass. And the electric resistance value R0 between the photosensitive drum 121 and the surface of the photosensitive drum 121 is as follows. The surface of the transfer roller 17 in the passing portion (center portion of FIG. 4A) where the small-sized recording material 1 having the electric resistance value Rp is nipped and conveyed between the transfer roller 17 and the photosensitive drum 121, and the photosensitive drum 121 It is smaller than the electric resistance (R0 + Rp) between the surface.

  Consider the case where the recording material 1 of LTR-R size, which becomes the recording material 1 of small size, is sandwiched between the transfer nips Nt. The electrical resistance value R0 of the non-passing portion where the recording material 1 of LTR-R size is not sandwiched by the transfer nip portion Nt is greater than the electrical resistance (R0 + Rp) of the passing portion where the recording material 1 of LTR-R size is sandwiched. Is about 5 kΩ smaller.

  The electrical resistance difference between the electrical resistance value R0 of the non-passing portion where the recording material 1 of LTR-R size is not sandwiched between the transfer nip portion Nt and the electrical resistance (R0 + Rp) of the passing portion sandwiched between the transfer nip portion Nt. Is represented by the following formula 1.

[Formula 1]
ΔR = 5kΩ

  In this state, when a transfer current Idc is applied from the transfer bias power supply 204 to the transfer roller 17, the transfer current Idc applied to the transfer roller 17 is small in the non-passing portion of the recording material 1 on the surface of the transfer roller 17. It becomes easy to flow to the resistance value R0 side. As a result, the transfer current Idc leaks to the surface of the photosensitive drum 121 at the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  For this reason, the transfer current Idc flowing through the small-sized recording material 1 is reduced to half of the normal value (about +0.5 μA). As a result, the charge necessary for transferring the toner image on the surface of the photosensitive drum 121 onto the surface of the recording material 1 becomes insufficient. If the charge transferred onto the surface of the recording material 1 is insufficient, the toner image on the surface of the recording material 1 cannot be held. For this reason, the toner t is scattered around and a transfer explosion shown in FIGS. 5B and 7A occurs.

  Before forming the image of the small-size recording material 1, the laser beam 11 a emitted from the laser scanner 11 is emitted to a region corresponding to at least one turn of the transfer roller 17 in the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. Irradiate. 3A, the toner t carried on the surface of the developing sleeve 122a of the developing device 122 is attached to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121.

  Thereafter, as shown in FIG. 3B, the photosensitive drum 121 is rotated. A transfer bias having a polarity opposite to that of the toner t adhered on the surface of the photosensitive drum 121 is applied to the transfer roller 17. As a result, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is electrostatically attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  Thereafter, as shown in FIG. 3C, the small-sized recording material 1 is transferred to the photosensitive drum 121 and the transfer roller 17 with the toner t attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. And the transfer nip portion Nt. Here, there is no recording material 1 in the transfer nip portion Nt, and most of the transfer current Idc flows into the non-passing portion of the recording material 1 having a low electrical resistance value R0 and leaks. For this reason, the charge necessary for transferring the toner image formed on the surface of the photosensitive drum 121 to the recording material 1 is insufficient.

  Further, when the electric resistance value R of the transfer roller 17 is low, the toner formed on the surface of the photosensitive drum 121 due to Ohm's law (V = IR) even when the transfer current Idc is applied to the transfer roller 17. The charge required to transfer the image to the recording material 1 is relatively reduced.

  In this embodiment, the width size W information of the recording material 1 is sent to the CPU 201 serving as a control unit. The CPU 201 applies a transfer current Idc to the transfer roller 17 by the transfer bias power source 204 shown in FIG. From the transfer current Idc and the transfer voltage obtained by measuring the voltage induced by the transfer current Idc flowing through the detection resistor provided in the transfer voltage detection circuit 205 shown in FIG. The value R is determined. The electric resistance value R of the transfer roller 17 varies depending on the environment in which it is used, the number of times of bias application depending on the use, and the like.

  That is, a predetermined voltage or a predetermined current is applied to at least one of the photosensitive drum 121 (image carrier) and the transfer roller 17 (transfer means) by the transfer bias power source 204 shown in FIG. As a result, a current value or a voltage value flowing through at least one of the photosensitive drum 121 (image carrier) and the transfer roller 17 (transfer means) is detected by a detection means including the transfer voltage detection circuit 205 and the CPU 201. Then, the CPU 201 (control unit) determines a change in the resistance value from the resistance value obtained from the voltage value or current value detected by the CPU 201 (detection unit).

  Further, the CPU 201 as the control unit sets the following toner amount according to the change in the electrical resistance value R between the determined photosensitive drum 121 and the transfer roller 17 (between the transfer units). That is, the toner t is set by supplying toner t from the developing sleeve 122a of the developing device 122 serving as developing means to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  The developing method of this embodiment is a one-component reversal jumping developing method using a one-component magnetic negative toner. In addition, there is a method (one-component contact development) in which development is performed in contact with the surface of the photosensitive drum 121. Further, there is a method (two-component contact development method) in which a two-component developer in which a magnetic carrier is mixed with toner t is conveyed by magnetic force and developed in contact with the surface of the photosensitive drum 121. Further, there is a method (two-component non-contact development method) in which a two-component developer in which a magnetic carrier is mixed with toner t is developed in a non-contact state with respect to the surface of the photosensitive drum 121.

  Next, the control of the present embodiment will be described with reference to FIG. 6 which is a flowchart. In step S1 shown in FIG. 6, the CPU 201 as the control means starts a print job. Next, in step S2, the CPU 201 determines the width size W of the recording material 1 before the recording material 1 passes through the transfer nip portion Nt. When the width size W in the direction intersecting the conveyance direction of the recording material 1 is equal to or smaller than a predetermined size (A3 size; 297 mm × 420 mm), the process proceeds to step S3.

  In the present embodiment, the recording material 1 having a width size W equal to or smaller than the LTR-R size (the length in the direction intersecting the conveyance direction of the recording material 1 is 279 mm) is set as the small size recording material 1. The LTR-R size is a size when the recording material 1 of LTR (Letter) size is fed longitudinally (the transverse direction of the recording material 1 is conveyed in parallel with the longitudinal direction of the transfer nip portion Nt).

  In step S3, a transfer current Idc having a constant value is applied to the transfer roller 17 by the transfer bias power source 204 during, for example, a pre-rotation operation before image formation. The voltage induced by the transfer current Idc flowing through a detection resistor provided in the transfer voltage detection circuit 205 is measured as a transfer voltage.

  The CPU 201 detects the electric resistance between the transfer roller 17 and the photosensitive drum 121 from the transfer current Idc applied to the transfer roller 17 by the transfer bias power source 204 and the voltage detected by the transfer voltage detection circuit 205 based on the transfer current Idc. The value R is determined. Then, in steps S4 and S5, a case is considered in which the transfer explosion shown in FIGS. 5 and 7A occurs in the small-size recording material 1 stored in advance in the memory 203 shown in FIG.

In this case, the upper limit threshold value Ru, the lower limit threshold value Rl of the electric resistance value R, and the electric resistance value R determined in step S3 are respectively compared. The upper limit threshold Ru is appropriately set to a value larger than the lower limit threshold Rl. In the present embodiment, the electric resistance value of the upper threshold Ru is set to 4 × 10 ⁷ Ω, and the electric resistance value of the lower threshold R1 is set to 3 × 10 ⁷ Ω.

  In step S4, the electrical resistance value R determined in step S3 may be larger than the upper limit threshold Ru. In that case, the CPU 201 determines that the electrical resistance value R is sufficiently high. The CPU 201 determines that the charge necessary for transferring the toner image formed on the surface of the photosensitive drum 121 to the recording material 1 can be sufficiently supplied even when the small-size recording material 1 passes through the transfer nip portion Nt. . Then, the toner t does not adhere to the non-passing portion of the recording material 1 on the surface of the transfer roller 17, and the process proceeds to step S6 to perform a normal image forming operation.

  In step S4, if the electrical resistance value R determined in step S3 is equal to or lower than the upper threshold value Ru (lower than the first threshold value), the process proceeds to step S5. In step S5, when the electrical resistance value R determined in step S3 is equal to or lower than the upper limit threshold value Ru and larger than the lower limit threshold value R1, transfer is performed when the small-sized recording material 1 passes through the transfer nip portion Nt. There is a concern of explosion. For this reason, the process proceeds to step S7, where the laser scanner 11 irradiates the laser beam 11a to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 in the range of at least one round of the transfer roller 17 during the pre-rotation operation.

  Then, as shown in FIG. 3A, the CPU 201 as the control unit attaches the toner t to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 by the first toner amount X (2 g). Then, a transfer bias having a polarity opposite to that of the toner t is applied to the transfer roller 17. As shown in FIG. 3B, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is transferred to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. Electrostatic transfer to adhere. At this time, the CPU 201 adheres the first toner amount X (2 g) to the non-passing portion of the recording material 1 of the transfer roller 17.

  Next, in step S8, an image forming operation is performed in a state where the toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 by the first toner amount X (2 g). As shown in FIG. 3C, when the small-sized recording material 1 passes through the transfer nip portion Nt, the toner t attached to the surface of the transfer roller 17 in the non-passing portion of the recording material 1 is the first. It acts as an electric resistor having an electric resistance value corresponding to the toner amount X (2 g). As a result, the leakage current that directly flows from the transfer roller 17 to the photosensitive drum 121 at the non-passing portion of the recording material 1 is suppressed. As a result, a charge necessary for transferring the toner image formed on the surface of the photosensitive drum 121 to the recording material 1 is secured.

  Further, in step S5, when the electrical resistance value R determined in step S3 is equal to or lower than the lower threshold R1 that is the second threshold (lower than the second threshold), the process proceeds to step S9. When the electrical resistance value R obtained in step S3 is less than or equal to the lower limit threshold value R1, transfer explosion occurs when the recording material 1 having a smaller size passes through the transfer nip portion Nt than when the electrical resistance value R is greater than the lower limit threshold value R1. There is great concern. Furthermore, the generation level of the transfer explosion is also deteriorated.

Therefore, when the determined electric resistance value R is equal to or lower than the lower limit threshold value Rl (3 × 10 ⁷ Ω) that is the second threshold value, the CPU 201 detects the first toner amount X in the non-passing portion of the recording material 1 of the transfer roller 17. A second toner amount Y (4 g) that is 2 g more than (2 g) is deposited. As a result, the electrical resistance value R0 of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 can be further increased.

  Next, in step S10, an image forming operation is performed in a state where the toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 by the second toner amount Y (> X). As shown in FIG. 3C, when the small-size recording material 1 passes through the transfer nip portion Nt, the toner t adhering to the surface of the transfer roller 17 in the non-passing portion of the recording material 1 is the second. It plays the role of an electric resistor having an electric resistance value corresponding to the toner amount Y (> X). As a result, leakage current that directly flows from the transfer roller 17 to the photosensitive drum 121 at the non-passing portion of the recording material 1 is suppressed. As a result, a charge necessary for transferring the toner image formed on the surface of the photosensitive drum 121 to the recording material 1 is secured.

  In step S2, the width W of the recording material 1 detected by the recording material width detection sensor 202 may be larger than a predetermined size (A3 size). In that case, the CPU 201 proceeds to step S11 and performs a normal image forming operation without attaching the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. After performing the image forming operations in steps S6, S8, S10, and S11, the process proceeds to step S12 to end the print job.

  In the present embodiment, when the small-sized recording material 1 passes through the transfer nip portion Nt, the electrical resistance value R is determined in advance by the CPU 201. When the electric resistance value R is larger than the upper limit threshold Ru, the toner t does not adhere to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. For this reason, the toner consumption can be reduced. Further, even when the determined electrical resistance value R is equal to or less than the upper limit threshold value Ru and greater than the lower limit threshold value R1, the amount of toner attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is reduced. As a result, toner consumption can be suppressed.

  It is necessary to prevent leakage (flow) of the transfer current Idc flowing from the transfer roller 17 to the photosensitive drum 121 in the non-passing portion of the recording material 1 in the transfer nip portion Nt having a small electrical resistance value R0. Therefore, in this embodiment, the amount of toner to be attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is appropriately set according to the determined electric resistance value R.

  FIG. 7B shows the present embodiment in which the amount of toner to be adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is appropriately set according to the determined electric resistance value R, and Comparative Example 2. 5 and FIG. 7A is a comparison between the transfer explosion and the toner consumption. In Comparative Example 2, the amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is set to a constant amount regardless of the determined electrical resistance value R.

  As shown in FIG. 7B, the transfer explosion did not occur in Comparative Example 2, but the toner consumption was large. In this embodiment, the transfer explosion can be reduced with the minimum toner amount, and the consumption amount of the toner t can be suppressed. As a result, the toner consumption can be reduced.

  In the above-described embodiment, the CPU 201 as the control unit controls the amount of developer that is supplied from the developing unit to the non-passing portion of the recording material 1 in accordance with the determined electric resistance value R. However, the present invention is not limited to this, and the electric resistance difference ΔR may be adjusted by controlling the supply area of the developer supplied to the non-passing portion, the supply rate per fixed area, etc. according to the determined electric resistance value R. good.

  Next, the configuration of the second embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition, what was comprised similarly to the said 1st Embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description. In the present embodiment, the CPU 201 causes the transfer roller 17 to adhere to the toner during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt between the photosensitive drum 121 and the transfer roller 17 according to the obtained electric resistance value R. The electric resistance value R is corrected. This is reduced because the toner t adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is affected by the recording material 1 passing through the transfer nip portion Nt. Alternatively, the case where it decreases due to the centrifugal force accompanying the rotation of the transfer roller 17 is taken into consideration.

  The horizontal axis of FIG. 7C indicates when the recording material 1 passes through the transfer nip portion Nt with 4 g of toner t attached to a non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass. The passing time Ta of the recording material 1 is shown. The vertical axis of FIG. 7C indicates the amount of toner attached to the non-passing portion where the recording material 1 on the surface of the transfer roller 17 does not pass.

  As shown in FIG. 7C, 4 g of toner t was adhered to the non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass. In this state, the toner t adhered to the non-passing portion where the recording material 1 on the surface of the transfer roller 17 does not pass is reduced to 2 g 30 seconds after the recording material 1 starts to pass through the transfer nip portion Nt. .

  The toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the immediately preceding print job. The CPU 201 that also serves as the correction unit is configured to detect the transfer roller 17 detected by the CPU 201 that also serves as the resistance detection unit based on the passage time Ta of the transfer nip portion Nt of the recording material 1 detected by the CPU 201 that also serves as the passage time detection unit illustrated in FIG. The electric resistance value R is corrected. Then, the CPU 201 that also serves as a setting unit sets the amount of toner that adheres to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in accordance with the corrected electric resistance value Rc of the transfer roller 17.

  The CPU 201 causes the toner t to adhere to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. In addition, the CPU 201 lies between the preceding recording material 1 in which the recording material 1 does not pass through the transfer nip portion Nt between the photosensitive drum 121 and the transfer roller 17 and the immediately following recording material 1 (between the recording materials). Then, the toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. That is, the CPU 201 (control means) controls the surface of the transfer roller 17 before the recording material 1 that follows the recording material 1 passes through the transfer nip Nt (nip) and before the recording material 1 reaches the transfer nip Nt (nip). The toner t is adhered to the non-passing portion of the upper recording material 1.

  Also in this embodiment, the transfer voltage is detected by the transfer voltage detection circuit 205 in order to calculate the electric resistance value R of the transfer roller 17 before the small size recording material 1 passes through the transfer nip portion Nt, as in the first embodiment. Detect. In a state where the toner t adheres on the surface of the transfer roller 17, the transfer voltage detection circuit 205 detects the transfer voltage in order to calculate the electric resistance value R of the transfer roller 17. When the recording material 1 continuously passes through the transfer nip portion Nt, the amount of toner adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 decreases. This causes a transfer explosion.

  When the number of recording materials 1 passing through the transfer nip portion Nt is large in one printing job, the temperature inside the image forming apparatus 10 is raised by heat generated from the fixing device 18 and the electric resistance value of the transfer roller 17 R decreases. In the immediately preceding print job, toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 as shown in FIG. In that case, the CPU 201 corrects the electric resistance value R of the transfer roller 17 calculated in step S3 of FIG.

  Further, the CPU 201 calculates an electric resistance value R of the transfer roller 17 between the recording material 1 of the preceding recording material 1 and the recording material 1 subsequent thereto. The amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is appropriately set according to the electric resistance value R of the transfer roller 17 even between the recording materials 1.

<Image forming operation>
The image forming operation of the image forming apparatus 10 according to this embodiment will be described with reference to FIGS. In step S21 in FIG. 8, the user selects a small-size recording material 1, and the CPU 201 starts a print job. Next, in step S22, the width W of the recording material 1 (the size in the direction along the transfer nip portion Nt) is determined during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. If the determined width size W of the recording material 1 is a predetermined size (A3 size; 297 mm × 420 mm) or less, the process proceeds to step S23.

  Also in this embodiment, LTR-R (the length in the width direction of the recording material 1 is 279 mm) or less is defined as the small size recording material 1. In the LTR-R size, the recording material 1 having the recording material 1 whose width size W is LTR (Letter) size is longitudinally fed (the transverse direction of the recording material 1 is conveyed in parallel with the longitudinal direction of the transfer nip portion Nt). The size of the case.

  In step S23, the CPU 201 refers to the history data stored in the memory 203 as to whether or not the toner t has adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the immediately preceding print job. In step S23, the CPU 201 refers to the history data stored in the memory 203 and determines that the toner t is not attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the previous print job. There is a case. In that case, in steps S24 to S31 of FIG. 8, the same control as that shown in steps S3 to S10 of FIG. 6 in the first embodiment is performed.

  In step S23, the CPU 201 refers to the history data stored in the memory 203 and determines that the toner t is attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the previous print job. There is a case. In this case, the process proceeds to step S32, and the electric resistance value R of the transfer roller 17 is calculated.

  In step S32, during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip Nt, a transfer current Idc having a constant value is applied to the transfer roller 17 by the transfer bias power source 204 shown in FIG. Then, the voltage induced by the transfer current Idc flowing through the detection resistor provided in the transfer voltage detection circuit 205 shown in FIG. 2 is measured as the transfer voltage, and the electric current of the transfer roller 17 is determined from the transfer current Idc and the transfer voltage. The resistance value R is calculated according to Ohm's law.

  Next, proceeding to step S33, the CPU 201 considers the amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the immediately preceding print job. Further, the passage time Ta of the recording material 1 at the transfer nip portion Nt is considered. Then, the electric resistance value R of the transfer roller 17 calculated in step S32 is corrected from the toner amount and the passage time Ta.

  The toner adhering to the non-passing portion of the recording material 1 of the transfer roller 17 is gradually returned to the photosensitive drum 121 by the mechanical adhesion force as the recording material 1 passes continuously, and the amount of toner adhering to the transfer roller 17 Less. Therefore, the difference in resistance value of the transfer roller 17 when 2 g of toner is adhered to the non-passing portion of the recording material 1 after the transfer roller 17 is cleaned is stored.

  Further, as shown in FIG. 7C, the amount of toner adhering to the transfer roller 17 after passing for a predetermined time can be found from the graph of the passage time Ta and the toner adhesion amount stored in advance. Therefore, a resistance value corresponding to the remaining amount of toner adhesion is calculated from the difference between the remaining toner adhesion amount and the electric resistance value R of the transfer roller 17, and the electric resistance value R of the transfer roller 17 calculated in step S32 of FIG. Is corrected to the electrical resistance value Rc.

  The reason why the passage time Ta of the recording material 1 at the transfer nip portion Nt is included in the correction condition is as follows. In some cases, the recording material 1 passes through the transfer nip portion Nt after the toner t is attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the immediately preceding print job. In this case, retransfer of the toner t from the transfer roller 17 to the photosensitive drum 121 occurs due to a change in toner polarity due to a transfer bias (+ polarity bias) applied to the transfer roller 17. Further, the amount of toner attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 changes due to the centrifugal force caused by the rotation of the transfer roller 17. The change in the toner amount is estimated based on the passage time Ta of the recording material 1 at the transfer nip portion Nt.

  In this embodiment, the passage time Ta during which the recording material 1 passes through the transfer nip portion Nt after the toner t is attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is considered. Further, the amount of toner attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is considered. The relationship between the passage time Ta and the toner adhesion amount is stored in advance in the memory 203 shown in FIG.

  In this embodiment, the passage time Ta of the recording material 1 at the transfer nip portion Nt is the size (conveyance) of the recording material 1 that has passed through the transfer nip portion Nt stored in the memory 203 shown in FIG. Refer to the direction length information. Further, the number information for each size of the recording material 1 is referred to. Further, it is calculated with reference to speed (process speed) information of the recording material 1 passing through the transfer nip portion Nt. The CPU 201 also serves as a number detection unit that detects the number of recording materials 1 passing through the transfer nip Nt between the photosensitive drum 121 and the transfer roller 17.

  In step S33, the electrical resistance value Rc of the transfer roller 17 corrected by the CPU 201 shown in FIG. 2 is as follows. In steps S34 to S40 in FIG. 8, the same control is performed by replacing the electrical resistance value R of the transfer roller 17 with the corrected electrical resistance value Rc in the control shown in steps S4 to S10 in FIG. 6 in the first embodiment. Do.

  After performing the image forming operation in steps S27, S29, S31, S36, S38, and S40, in step S41 shown in FIG. 8, the CPU 201 determines whether or not the image forming operation is finished. If the image forming operation is finished in step S41, the process proceeds to step S42 and the process is finished. In this case, no cleaning (cleaning) is performed to remove the toner t adhering to the surface of the transfer roller 17 due to post-rotation or the like.

  If the image forming operation is not completed in step S41 shown in FIG. 8, the process proceeds to step S42 shown in FIG. In steps S42 to S51, the same control as in steps S32 to S41 is performed. In steps S37 and S39, the laser scanner 11 applies at least one turn of the transfer roller 17 to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 during the pre-rotation operation where the recording material 1 does not pass through the transfer nip portion Nt. The laser beam 11a is irradiated in the above range.

  In step S37, as shown in FIG. 3A, the CPU 201 causes the toner t to adhere to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 by the first toner amount X (2g). Then, a transfer current Idc having a polarity opposite to that of the toner t is applied to the transfer roller 17. As shown in FIG. 3B, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is transferred to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. Electrostatic transfer to adhere.

  When the recording material 1 is not passing through the transfer nip portion Nt, the toner is applied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation when the recording material 1 is not passing through the transfer nip portion Nt. t is adhered by the first toner amount X (2 g). As a result, as shown in FIG. 3C, the toner t flying to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 does not adhere to the recording material 1 passing through the transfer nip portion Nt.

  In step S39, the electrical resistance value Rc of the transfer roller 17 calculated by the CPU 201 in step S32 corrected by the CPU 201 in step S33 is equal to or less than the lower threshold R1. In that case, there is a greater concern that the transfer explosion shown in FIGS. 5 and 7A may occur when the recording material 1 having a smaller size passes through the transfer nip portion Nt than when the recording material 1 is larger than the lower limit threshold value Rl. Furthermore, the generation level of the transfer explosion is also deteriorated.

  The electrical resistance value Rc of the transfer roller 17 calculated by the CPU 201 in step S32 corrected by the CPU 201 in step S33 may be larger than the lower limit threshold value Rl. As shown in FIG. 3A, the CPU 201 performs the following control during the pre-rotation operation when the recording material 1 does not pass through the transfer nip portion Nt. The second toner amount Y (4 g) when the toner t is adhered to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is increased from the first toner amount X (2 g) in step S37 (2 g). )

  When the corrected electrical resistance value Rc of the transfer roller 17 is equal to or lower than the lower limit threshold value Rl, more toner t has jumped to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 and is recorded on the surface of the transfer roller 17. It adheres to the non-passing part of the material 1. As a result, the electrical resistance value of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 can be further increased.

  In steps S28, S30, S37, and S39, the CPU 201 performs the following control during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. A laser scanner 11 irradiates the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 with a laser beam 11a in a range of at least one round of the transfer roller 17 or more.

  In steps S47 and S49, the CPU 201 performs the following control between the preceding recording material 1 and the immediately following recording material 1 (between the recording materials). A laser scanner 11 irradiates the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 with a laser beam 11a in a range of at least one round of the transfer roller 17 or more.

  In step S47, as shown in FIG. 3A, the CPU 201 causes the toner t to adhere to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 by the first toner amount X (2g). Then, a bias having a polarity opposite to that of the toner t is applied to the transfer roller 17. As a result, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is transferred to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 as shown in FIG. Electrostatic transfer to adhere.

  The CPU 201 does not detect when the recording material 1 has passed through the transfer nip portion Nt, but instead of the preceding recording material 1 in which the recording material 1 has not passed through the transfer nip portion Nt and the recording material 1 that immediately follows. The following control is performed between the recording materials (between recording materials). The toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 by the first toner amount X (2 g). As a result, as shown in FIG. 3C, the toner t flying to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 does not adhere to the recording material 1 passing through the transfer nip portion Nt.

  In step S49, the electric resistance value Rc obtained by correcting the electric resistance value R of the transfer roller 17 calculated in step S42 in step S43 may be less than or equal to the lower threshold R1. In that case, there is a greater concern that the transfer explosion shown in FIGS. 5 and 7A may occur when the recording material 1 having a smaller size passes through the transfer nip portion Nt than when the recording material 1 is larger than the lower limit threshold value Rl. Furthermore, the generation level of the transfer explosion is also deteriorated.

  Also in this embodiment, the electrical resistance value Rc of the transfer roller 17 calculated by the CPU 201 in step S42 corrected by the CPU 201 in step S43 may be larger than the lower limit threshold value Rl. Instead, as shown in FIG. 3A, the CPU 201 performs the following control between the preceding recording material 1 and the immediately following recording material 1 (between the recording materials). The second toner amount Y (4 g) when the toner t is attached to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is increased from the first toner amount X (2 g) in the step S47 (2 g). )

  When the corrected electrical resistance value Rc of the transfer roller 17 is equal to or lower than the lower limit threshold value Rl, more toner t has jumped to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 and recording on the surface of the transfer roller 17 It adheres to the non-passing part of the material 1. As a result, the electrical resistance value of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 can be further increased.

  If the image forming operation is not completed in step S51, the process returns to step S41 and repeats steps S41 to S51. If the image forming operation is completed in step S51, the process proceeds to step S52 and the print job is completed.

  When the width size W of the recording material 1 is larger than the predetermined size (A3 size) in step S22, the process is as follows. The process advances to step S53 to perform a normal image forming operation without adhering the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. Thereafter, the process proceeds to step S52 to end the print job. Other configurations are the same as those in the first embodiment, and the same effects can be obtained.

  Next, the configuration of the third embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. In addition, what was comprised similarly to each said embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description. In the present embodiment, the CPU 201 that also serves as resistance detection means considers environmental information such as temperature and humidity at which the image forming apparatus 10 detected by the environment sensor 206 shown in FIG. Further, the number information of the recording material 1 passing through the transfer nip portion Nt detected by the CPU 201 also serving as the number detection means is considered. Then, the electrical resistance value R is corrected based on the environmental information and the number information.

  First, in step S61 shown in FIG. 10, a print job is started. Next, in step S62, the CPU 201 determines the width size W of the recording material 1 (size in the direction intersecting the recording material conveyance direction). When the width W of the recording material 1 is a predetermined size (A3 size; 297 mm × 420 mm) or less, the process proceeds to step S63.

  In the present embodiment, the recording material 1 having a width size W equal to or smaller than LTR-R (the length in the width direction of the recording material 1 is 279 mm) is defined as the small size recording material 1. The LTR-R size is a size when the recording material 1 of LTR (Letter) size is fed longitudinally (the short direction of the recording material 1 is conveyed in parallel to the longitudinal direction of the transfer nip portion Nt).

  In step S63, the CPU 201 detects environmental information such as temperature and humidity at which the image forming apparatus 10 is installed by the environmental sensor 206. Next, in step S64, the CPU 201 refers to the number information of the recording material 1 passing through the transfer nip portion Nt, which is stored in the memory 203 as needed. Next, in step S65, the CPU 201 obtains an electrical resistance value R from the environmental information such as temperature and humidity detected by the environmental sensor 206 and the number information of the recording material 1 passing through the transfer nip portion Nt.

  In the ion conductive transfer roller 17 of this embodiment, the electric resistance value R varies depending on the temperature and humidity. For this reason, the electrical resistance value R of the transfer roller 17 under typical environmental conditions is stored in the memory 203 in advance. Further, the electrical resistance value R of the transfer roller 17 increases when energized. For this reason, the electric resistance value R of the transfer roller 17 can be estimated from the number of recording materials 1 passing through. FIG. 25 (a) shows the relationship between the number of passing sheets of recording material 1 and the electric resistance value R of the transfer roller 17. NL is a normal temperature and low humidity environment curve, NN is a normal temperature and normal humidity environment curve, and HH is a high temperature and high humidity environment. It is a curve.

  Next, in step S66, the CPU 201 refers to the number information of the recording material 1 passing through the transfer nip portion Nt in the immediately preceding print job stored in the memory 203 as needed. Further, reference is made to idle time information from the time point when the immediately preceding print job detected by the time timer 207 serving as the idle time detection means ends to the present time.

  The CPU 201 that also serves as the second correction unit considers the number information of the recording material 1 that passes through the transfer nip portion Nt in the immediately preceding print job detected by the CPU 201 that also serves as the number detection unit. Furthermore, neglected time information from the time when the immediately preceding print job detected by the time timer 207 serving as the neglected time detecting means is considered. Then, based on the number information and the standing time information, the electric resistance value R of the transfer roller 17 detected by the CPU 201 which also serves as a resistance detecting means is corrected in the step S65.

  The electric resistance value R of the transfer roller 17 varies depending on the ambient temperature. As the recording material 1 passes continuously, the ambient temperature around the transfer roller 17 rises. Along with this, the electric resistance value R of the transfer roller 17 decreases. If the main body of the image forming apparatus 10 stops after the recording material 1 has passed continuously, the ambient temperature in the main body of the image forming apparatus 10 decreases. Along with this, the electric resistance value R of the transfer roller 17 increases.

  The transition of the electric resistance value R due to the temperature fluctuation of the transfer roller 17 is stored as needed, and the electric resistance value R of the transfer roller 17 is calculated from the standing time. FIG. 25B shows the relationship between the time when the image forming apparatus 10 was stopped after the recording material 1 continuously passed through the transfer roller 17 and the electrical resistance value R of the transfer roller 17. Indicates.

Next, in step S67, the CPU 201 compares the electric resistance value Rc of the transfer roller 17 corrected in step S66 with the upper limit threshold Ru (4 × 10 ⁷ Ω). In step S67, the corrected electric resistance value Rc of the transfer roller 17 may be equal to or lower than the upper limit threshold value Ru (4 × 10 ⁷ Ω). In that case, the process proceeds to step S68, and the CPU 201 applies the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. Only toner amount X (2 g) is adhered.

  The CPU 201 that also serves as the setting means corresponds to the amount of toner that adheres to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 corresponding to the electrical resistance value Rc of the transfer roller 17 corrected by the CPU 201 that also serves as the second correction means. Set. Thereafter, after an image forming operation is performed in step S69, the process proceeds to step S70 to end the print job.

In step S67, the electrical resistance value Rc of the transfer roller 17 corrected by the CPU 201 may be larger than the upper limit threshold Ru (4 × 10 ⁷ Ω). In this case, the CPU 201 proceeds to step S69 without performing toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17, and then proceeds to step S70. End the print job.

  In step S62, the detected width size W of the recording material 1 may be larger than a predetermined size (A3 size). Even in this case, the CPU 201 proceeds to step S69 without performing toner t on the non-passing portion of the recording material 1 on the surface of the transfer roller 17, and then proceeds to step S70 to perform a print job. Exit.

  The CPU 201, which also serves as a resistance detection unit that detects the electrical resistance value R of the transfer roller 17, is transferred to the detection resistor by applying the transfer current Idc to the transfer roller 17 as in the first and second embodiments. In some cases, the voltage is measured and detected directly.

  In addition, as in the present embodiment, the transfer roller is determined based on environmental information such as temperature and humidity where the image forming apparatus 10 is installed detected by the environmental sensor 206 and information on the number of recording materials 1 passing through the transfer nip portion Nt. It is also possible to indirectly detect and detect 17 electrical resistance values R.

  As a result, also in this embodiment, the surface of the transfer roller 17 according to the electric resistance value R of the transfer roller 17 when the small-sized recording material 1 passes through the transfer nip portion Nt, as in the first and second embodiments. The amount of toner adhered to the non-passing portion of the upper recording material 1 can be changed. Other configurations are the same as those in the above embodiments, and the same effects can be obtained.

  In the present embodiment, there is a cleaning means for cleaning the toner t adhering to the surface of the transfer roller 17 during the post-rotation. As an example of the cleaning means of this embodiment, a bias of −1700 V having the same polarity as the regular toner t is applied to the transfer roller 17. The application time is applied only for the movement time of one rotation of the rotating transfer roller 17.

  Next, a bias of +800 V having a reverse polarity is applied to the transfer roller 17. The application time is applied only for the movement time of one rotation of the rotating transfer roller 17. The toner flies to the surface of the photosensitive drum 121 due to the potential difference, and the transfer roller 17 can be cleaned. In the present embodiment, the case where the transfer roller 17 is used as an example of the transfer unit that transfers the toner image formed on the surface of the photosensitive drum 121 to the recording material 1 has been described. Can be applied similarly.

  Next, the configuration of the fourth embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition, what was comprised similarly to each said embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description. The CPU 201 of this embodiment also serves as a determination unit that determines the charge amount Q of the toner t stored in the developing device 122 (in the developing unit).

  The CPU 201 determines the charge amount Q of the toner t in the developing device 122 based on various detection data stored in the memory 203. In accordance with the determination result of the charge amount Q of the toner t in the developing device 122 determined by the CPU 201, a control signal is sent from the CPU 201 to the exposure control unit 208 that controls the drive of the laser scanner 11 and emitted from the laser scanner 11. The output intensity of the laser beam 11a is set.

  FIG. 11 shows how the rate at which the toner adhesion amount of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 decreases with time, depending on the magnitude of the charge amount Q of the toner t in the developing device 122. Show. A straight line c in FIG. 11 is a case where the charge amount Q of the toner t in the developing device 122 is smaller than −5.0 μC / g and larger than −7.0 μC / g.

  A straight line d in FIG. 11 corresponds to the case where the charge amount Q of the toner t in the developing device 122 is −7.0 μC / g or less. A straight line e is a case where the charge amount Q of the toner t in the developing device 122 is −5.0 μC / g or more. As shown in FIG. 11, the speed at which the toner adhesion amount of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 decreases with time depending on the magnitude of the charge amount Q of the toner t in the developing device 122. Change.

  As shown by the straight line c in FIG. 11, the charge amount Q of the toner t in the developing device 122 may be smaller than −5.0 μC / g and larger than −7.0 μC / g. In this case, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt may be 3 g. In this case, when the passage time Ta for passing the recording material 1 through the transfer nip portion Nt has elapsed for 60 seconds, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is reduced to 1 g.

  In this embodiment, when the amount of toner adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 indicated by the vertical axis in FIG. 11 is less than 1 g, the transfer explosion shown in FIG. 5 and FIG. Occurs. As indicated by the straight line d in FIG. 11, the charge amount Q of the toner t in the developing device 122 may be −7.0 μC / g or less. In that case, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is more than 1 g until the passing time Ta for passing the recording material 1 through the transfer nip portion Nt elapses 80 seconds. . Therefore, the transfer explosion shown in FIGS. 5 and 7A does not occur.

  As indicated by the straight line e in FIG. 11, the charge amount Q of the toner t in the developing device 122 may be −5.0 μC / g or more. In this case, when the passage time Ta for passing the recording material 1 through the transfer nip portion Nt has passed 40 seconds, the toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is reduced to 1 g. For this reason, the transfer explosion shown in FIGS. 5 and 7A occurs.

  As indicated by straight lines c to e in FIG. 11, the decrease rate of the toner t adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is the magnitude of the charge amount Q of the toner t in the developing device 122. Depends on. Therefore, in the present embodiment, when the small-sized recording material 1 passes through the transfer nip portion Nt, the CPU 201 first charges the toner t in the developing device 122 before the image forming operation of the image forming device 10 is started. The quantity Q is determined.

  In accordance with the determination result of the charge amount Q of the toner t in the developing device 122 determined by the CPU 201 that also serves as the judging means, the CPU 201 that also serves as the second setting means performs the following settings. An amount of toner t to be supplied from the developing sleeve 122a of the developing device 122 serving as developing means is set to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  In this embodiment, the CPU 201 that also serves as the second setting unit sets the timing for supplying the toner t from the developing sleeve 122a of the developing device 122 serving as the developing unit to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. To do. The CPU 201 reduces the amount of toner adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 and the transfer sleeve 122a of the developing device 122 before the transfer explosion shown in FIGS. 5 and 7A occurs. The timing for supplying new toner t from is calculated.

  The CPU 201 performs the following control while the recording material 1 is continuously passing through the transfer nip portion Nt after the print job is started. As shown by straight lines c to e in FIG. 12A, predetermined timing times T1 (80 seconds), T2 (60 seconds), T3 (40 seconds) corresponding to the charge amount Q of the toner t in the developing device 122. ) Is supplied to the surface of the transfer roller 17 every time.

  As shown by the straight lines c to e in FIG. 12A, the CPU 201 corresponds to the charge amount Q of the toner t in the developing device 122 for predetermined timing times T1 (80 seconds), T2 (60 seconds), T3. The following control is performed every time (40 seconds) elapses. The non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is irradiated with laser light 11a. Then, as shown in FIG. 3A, the toner t is caused to fly from the developing device 122 to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. Then, the photosensitive drum 121 is rotated, and the toner t is supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 as shown in FIG.

  As shown in FIG. 12A, the CPU 201 performs the following control during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt at the start of the print job of the small size recording material 1. After 3 g of toner t is supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17, the transfer operation in which the recording material 1 passes through the transfer nip portion Nt is started.

  At this time, the CPU 201, which also serves as a passage time detection means, detects the passage time Ta of the recording material 1 passing through the transfer nip portion Nt. The passing time Ta reaches predetermined timing times T1 (80 seconds), T2 (60 seconds), and T3 (40 seconds) set corresponding to the charge amount Q of the toner t in the developing device 122, respectively.

  The CPU 201 detects that the charge amount Q of the toner t in the developing device 122 is in a range smaller than −5.0 μC / g and larger than −7.0 μC / g as indicated by a straight line c in FIG. The At that time, the CPU 201 again transfers the transfer roller while the recording material 1 passes through the transfer nip Nt at the time when 60 seconds have elapsed from the time when the recording material 1 started to pass through the transfer nip Nt (timing time T2). The toner t is supplied to the non-passing portion of the recording material 1 on the surface 17.

  Every time the timing time T2 (60 seconds) elapses from the time when the recording material 1 starts to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt until the print job is completed. The following control is performed. The toner t is again supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. Thus, the occurrence of the transfer explosion shown in FIGS. 5 and 7A can be continuously suppressed until the print job is completed.

  Similarly, the CPU 201 detects that the charge amount Q of the toner t in the developing device 122 is −7.0 μC / g or less as indicated by the straight line d in FIG. At that time, the CPU 201 applies the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 at every timing time T1 when 80 seconds elapse from the time when the recording material 1 starts to pass through the transfer nip portion Nt. Supply.

  Further, the CPU 201 detects that the charge amount Q of the toner t in the developing device 122 is −5.0 μC / g or more as indicated by the straight line e in FIG. At that time, the CPU 201 applies the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 every timing time T3 when 40 seconds elapse from the time when the recording material 1 starts to pass through the transfer nip portion Nt. Supply.

<Determination of toner charge amount>
Next, a method for determining the charge amount Q of the toner t in the developing device 122 by the CPU 201 that also serves as a determination unit will be described with reference to FIGS. As shown in FIGS. 12B and 12C, the charge amount Q of the toner t in the developing device 122 is the passing time Ta during which the recording material 1 passes through the transfer nip portion Nt during the print job and the print job. This largely depends on the stand-by waiting time Tb.

  As shown in FIGS. 12B and 12C, the charge amount Q of the toner t in the developing device 122 at the start of the print job is the transit time for the recording material 1 to pass through the transfer nip portion Nt in the immediately preceding print job. The longer Ta is and the shorter the waiting time Tb during which the print job is stopped, the higher the value is.

  On the other hand, the charge amount Q of the toner t in the developing device 122 at the start of the print job is as follows. As shown in FIGS. 12B and 12C, the passing time Ta for the recording material 1 to pass through the transfer nip portion Nt in the immediately preceding print job is shorter and the waiting time Tb for which the print job is stopped is longer. Lower.

  Further, the degree of charging of the toner t in the developing device 122 depends on the temperature and humidity of the environment where the image forming apparatus 10 is installed. For example, as shown by curves HH in FIGS. 12B and 12C, when the image forming apparatus 10 is installed and used in a high temperature and high humidity environment (30 ° C., 80% RH), There is a lot of water. For this reason, since the charge of the toner t in the developing device 122 is easily discharged through moisture in the atmosphere, it is difficult to be charged.

  Further, as shown by the curves NN in FIGS. 12B and 12C, the image forming apparatus 10 may be used in a normal temperature and normal humidity environment (23 ° C., 50% RH). In that case, since the amount of moisture in the atmosphere is smaller than the curve HH in FIGS. 12B and 12C, the toner t in the developing device 122 is easily charged.

  Further, as shown by the curves NL in FIGS. 12B and 12C, the image forming apparatus 10 may be installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). In that case, the amount of water in the atmosphere is much smaller than the curve NN in FIGS. 12B and 12C, so that the toner t in the developing device 122 is more easily charged.

  Here, the image forming apparatus 10 may be used by being installed in a normal temperature and normal humidity environment (23 ° C., 50% RH) indicated by a curve NN in FIGS. In this case, the transition of the charge amount Q of the toner t in the developing device 122 with respect to the passing time Ta when the recording material 1 passes through the transfer nip portion Nt in the immediately preceding print job and the standby time Tb when the print job is stopped. Based on

  At that time, as shown in FIG. 12B, the relationship between the passing time Ta for the recording material 1 to pass through the transfer nip portion Nt in the immediately preceding print job and the charge amount Q of the toner t in the developing device 122 is as follows. It is as follows. In some cases, the image forming apparatus 10 indicated by the curve NL in FIG. 12B is installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). In that case, the image forming apparatus 10 indicated by the curve NN in FIG. 12B is 1.1 times faster than the case where the image forming apparatus 10 is installed and used in a normal temperature and humidity environment (23 ° C., 50% RH). The toner t in the developing device 122 is charged.

  On the other hand, the image forming apparatus 10 indicated by a curve HH in FIG. 12B may be used in a high temperature and high humidity environment (30 ° C., 80% RH). In that case, the image forming apparatus 10 indicated by the curve NN in FIG. 12B is 0.9 times faster than the case where it is used in a normal temperature and humidity environment (23 ° C., 50% RH). The toner t in the developing device 122 is charged.

  Further, as shown in FIG. 12C, the relationship between the waiting time Tb during which the print job is stopped and the charge amount Q of the toner t in the developing device 122 is as follows. In some cases, the image forming apparatus 10 indicated by the curve NL in FIG. 12C is installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). In that case, the image forming apparatus 10 indicated by a curve NN in FIG. 12C is 0.9 times faster than the case where the image forming apparatus 10 is used in a normal temperature and humidity environment (23 ° C., 50% RH). The toner t in the developing device 122 is discharged.

  On the other hand, the image forming apparatus 10 indicated by the curve HH in FIG. 12C may be used in a high temperature and high humidity environment (30 ° C., 80% RH). In that case, the image forming apparatus 10 indicated by the curve NN in FIG. 12C is 1.1 times faster than the case where the image forming apparatus 10 is installed and used in a normal temperature and humidity environment (23 ° C., 50% RH). The toner t in the developing device 122 is discharged.

  Consider the use environment conditions when the image forming apparatus 10 shown by the curve NL in FIGS. 12B and 12C is used in a normal temperature, low humidity environment (23 ° C., 15% RH). Furthermore, the use environment conditions when the image forming apparatus 10 indicated by the curve NN is installed and used in a normal temperature and normal humidity environment (23 ° C., 50% RH) are considered. Furthermore, consideration is given to each use environment condition when the image forming apparatus 10 indicated by the curve HH is used in a high temperature and high humidity environment (30 ° C., 80% RH).

  Then, environmental correction coefficients A and B are respectively set for the passage time Ta during which the recording material 1 passes through the transfer nip portion Nt and the waiting time Tb during which the print job is stopped in the immediately preceding print job shown in FIG. Set. As shown in FIG. 13 (a), the image forming apparatus 10 indicated by the curve NL in FIGS. 12 (b) and 12 (c) is installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). There is a case. In that case, the environmental correction coefficient A of the passing time Ta during which the recording material 1 passes through the transfer nip portion Nt in the immediately preceding print job is 1.1. The environmental correction coefficient B for the waiting time Tb when the print job is stopped is 0.9.

  Also, transfer is performed in a print job immediately before the image forming apparatus 10 indicated by a curve NN in FIGS. 12B and 12C is installed and used in a normal temperature and humidity environment (23 ° C., 50% RH). The environmental correction coefficient A of the passage time Ta for the recording material 1 to pass through the nip portion Nt is 1.0. Further, the environmental correction coefficient B for the standby time Tb during which the print job is stopped is 1.0.

  Also, the transfer nip in a print job immediately before the image forming apparatus 10 indicated by the curve HH in FIGS. 12B and 12C is installed and used in a high temperature and high humidity environment (30 ° C., 80% RH). The environmental correction coefficient A of the passage time Ta for the recording material 1 to pass through the portion Nt is 0.9. Further, the environmental correction coefficient B of the waiting time Tb when the print job is stopped is 1.1.

  Then, each environmental correction coefficient A shown in FIG. 13A is multiplied by the charge amount Q of the toner t in the developing device 122 determined from the passing time Ta through which the recording material 1 passes through the transfer nip portion Nt of the print job. The charge amount Q of the toner t in the developing device 122 is corrected. Alternatively, each environmental correction coefficient B shown in FIG. 13A is multiplied by the charge amount Q of the toner t in the developing device 122 determined from the standby time Tb during which the print job is stopped. The charge amount Q is corrected.

<Changes in toner charge amount>
Next, the variation in the charge amount Q of the toner t in the developing device 122 with respect to the passing time Ta through which the recording material 1 passes through the transfer nip portion Nt will be described with reference to FIG. The toner in the developing device 122 immediately after the end of the print job when the image forming apparatus 10 indicated by the curve NN shown in FIG. 12B is installed and used in a normal temperature, normal humidity environment (23 ° C., 50% RH). The charge amount Q of t is, for example, −6.0 μC / g. At that time, as shown in FIG. 13B, when the passing time Ta for passing the recording material 1 through the transfer nip portion Nt is less than 3 minutes, the charge amount Q of the toner t in the developing device 122 is −6. 1 μC / g.

  As shown in FIG. 13B, when the passing time Ta for passing the recording material 1 through the transfer nip Nt is 3 minutes or more and less than 7 minutes, the charge amount Q of the toner t in the developing device 122 Is −6.3 μC / g. As shown in FIG. 13B, when the passing time Ta for passing the recording material 1 through the transfer nip portion Nt is 7 minutes or more, the charge amount Q of the toner t in the developing device 122 is −6.6 μC. / G.

  On the other hand, the variation coefficient α of the charge amount Q of the toner t in the developing device 122 with respect to the passing time Ta through which the recording material 1 passes through the transfer nip portion Nt is set as follows. As shown in FIG. 13B, the coefficient of variation α when the passage time Ta is less than 3 minutes is set to 1.02. The variation coefficient α when the passage time Ta is 3 minutes or more and less than 7 minutes is set to 1.05. The coefficient of variation α when the passage time Ta is 7 minutes or longer is set to 1.10.

  Then, the CPU 201 corresponds to the charge amount Q of the toner t in the developing device 122 when the immediately preceding print job is started, and the passage time Ta through which the recording material 1 passes through the transfer nip portion Nt, as shown in FIG. The coefficient of variation α shown in FIG. Then, immediately after that, the charge amount Q of the toner t in the developing device 122 when starting the subsequent print job is determined.

  In some cases, the image forming apparatus 10 indicated by the curve NL shown in FIG. 12B is installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). In that case, the CPU 201 uses the determination value of the charge amount Q of the toner t in the developing device 122 multiplied by the coefficient of variation α shown in FIG. 13B as an environment correction coefficient A shown in FIG. The judgment value of the charge amount Q of the toner t in the developing device 122 is corrected by multiplying by 1.1.

  Similarly, the image forming apparatus 10 indicated by a curve HH shown in FIG. 12B may be used in a high temperature and high humidity environment (30 ° C., 80% RH). In that case, the CPU 201 uses the determination value of the charge amount Q of the toner t in the developing device 122 multiplied by the coefficient of variation α shown in FIG. 13B as an environment correction coefficient A shown in FIG. The determination value of the charge amount Q of the toner t in the developing device 122 is corrected by multiplying by 0.9.

  Next, a change in the charge amount Q of the toner t in the developing device 122 with respect to the standby time Tb when the print job is stopped will be described with reference to FIG. The toner in the developing device 122 immediately after the end of the print job when the image forming apparatus 10 indicated by the curve NN shown in FIG. 12C is installed and used in a normal temperature and humidity environment (23 ° C., 50% RH). The charge amount Q of t is, for example, −6.0 μC / g. At that time, as shown in FIG. 13C, when the waiting time Tb during which the print job is stopped is less than 4 hours, the charge amount Q of the toner t in the developing device 122 is −5.9 μC / g. is there.

  As shown in FIG. 13C, when the waiting time Tb during which the print job is stopped is 4 hours or more and less than 8 hours, the charge amount Q of the toner t in the developing device 122 is -5. 7 μC / g. As shown in FIG. 13C, when the standby time Tb when the print job is stopped is 8 hours or more, the charge amount Q of the toner t in the developing device 122 is −5.4 μC / g. .

  On the other hand, the variation coefficient β of the charge amount Q of the toner t in the developing device 122 with respect to the waiting time Tb when the print job is stopped is set as follows. As shown in FIG. 13C, the variation coefficient β when the waiting time Tb is less than 4 hours is set to 0.98. The variation coefficient β when the waiting time Tb is 4 hours or more and less than 8 hours is set to 0.95. The coefficient of variation β when the standby time Tb is 8 hours or longer is set to 0.90.

  Then, the CPU 201 multiplies the charge amount Q of the toner t in the developing device 122 immediately after the end of the print job by a variation coefficient β shown in FIG. 13C corresponding to the standby time Tb during which the print job is stopped. Then, immediately after that, the charge amount Q of the toner t in the developing device 122 when starting the subsequent print job is determined.

  In some cases, the image forming apparatus 10 indicated by a curve NL shown in FIG. 12C is installed and used in a normal temperature, low humidity environment (23 ° C., 15% RH). In this case, the CPU 201 further adds an environmental correction coefficient B shown in FIG. 13A to the determination value of the charge amount Q of the toner t in the developing device 122 multiplied by the variation coefficient β shown in FIG. The determination value of the charge amount Q of the toner t in the developing device 122 is corrected by multiplying by 0.9.

  Similarly, the image forming apparatus 10 indicated by a curve HH shown in FIG. 12C may be used in a high temperature and high humidity environment (30 ° C., 80% RH). In this case, the CPU 201 further adds an environmental correction coefficient B shown in FIG. 13A to the determination value of the charge amount Q of the toner t in the developing device 122 multiplied by the variation coefficient β shown in FIG. The judgment value of the charge amount Q of the toner t in the developing device 122 is corrected by multiplying by 1.1.

  The CPU 201 that also serves as the determination unit considers the operation time of the immediately preceding print job stored in the memory 203 (operation time storage unit). Further, the standby time Tb stored in the memory 203 (standby time storage means) is considered. Then, the charge amount Q of the toner t in the developing device 122 based on the temperature / humidity result detected by the environment sensor 206 serving as the environment detection means from at least one of the operation time and the waiting time Tb of the immediately preceding print job. Correct.

The charge amount of the toner t at the start of the developing device 122 of the print job immediately preceding the Q _0. A coefficient of variation of the charge amount Q of the toner t in the developing device 122 with respect to the passing time Ta through which the recording material 1 passes through the transfer nip portion Nt is α. Let A be the environmental correction coefficient for the passage time Ta during which the recording material 1 passes through the transfer nip Nt in the immediately preceding print job.

  A variation coefficient of the charge amount Q of the toner t in the developing device 122 with respect to the waiting time Tb when the print job is stopped is represented by β. Let B be the environmental correction coefficient for the waiting time Tb when the print job is stopped. Then, the charge amount Q of the toner t in the developing device 122 at the start of the print job can be determined by the following Equation 2 or Equation 3.

[Formula 2]
Q = Q ₀ × α × A

[Formula 3]
Q = Q ₀ × β × B

The charge amount Q ₀ of the toner t in the developing device 122 at the start of the immediately preceding print job is the reference set at the time of designing the toner t when performing the first print job after installing the main body of the image forming apparatus 10. The charge amount Q of toner t is assumed. The charge amount Q of the reference toner t set at the time of designing the toner t is stored in the CPU 201 in advance. In this embodiment, −5.0 μC / g is used as the charge amount Q of the reference toner t, but the present invention is not limited to this.

  Consider the passage time Ta that the recording material 1 passes through the transfer nip Nt of the immediately preceding print job detected by the CPU 201 that also serves as the passage time detection means. Further, the temperature and humidity of the environment in which the image forming apparatus 10 is installed as measured by the environment sensor 206 are taken into consideration. By using these, it is possible to determine the charge amount Q of the toner t in the developing device 122 corrected by the equation 2.

  In addition, the standby time Tb from the end time of the immediately preceding print job measured by the time timer 207 shown in FIG. 2 to the start time of the subsequent print job is taken into consideration. Further, the temperature and humidity of the environment in which the image forming apparatus 10 is installed as measured by the environment sensor 206 are taken into consideration. By using these, it is possible to determine the charge amount Q of the toner t in the developing device 122 corrected by the equation 3.

In Equation 2, the variation coefficient α with respect to the passing time Ta when the recording material 1 passes through the transfer nip portion Nt to the charge amount Q ₀ of the toner t in the developing device 122 at the start of the immediately preceding print job, and the environmental correction coefficient A Multiply and to calculate.

Wherein the Equation 3, by multiplying the immediately preceding coefficient of variation for the standby time Tb that print job to the charge amount Q ₀ is stopped toner t of the print job is started in the developing device 122 beta, and environmental correction coefficient B Calculate. Alternatively, it is possible to determine the charge amount Q of the toner t in the developing device 122 at the start of the print job by using the following Equation 4 using both Equation 2 and Equation 3.

[Formula 4]
Q = Q ₀ × (α × A) × (β × B)

<Image forming operation>
Next, an image forming operation of the image forming apparatus 10 of the present embodiment will be described with reference to FIG. First, in step S81, after starting a print job, in step S82, the environment sensor 206 shown in FIG. 2 detects the temperature and humidity of the environment where the image forming apparatus 10 is installed. In step S83, the recording material width detection sensor 202 shown in FIG. 2 detects the width size W of the recording material 1 that passes through the transfer nip portion Nt in the print job.

  In step S83, the CPU 201 determines whether or not the width size W of the recording material 1 detected by the recording material width detection sensor 202 is equal to or less than LTR-R (the length in the width direction of the recording material 1 is 279 mm). In the present embodiment, LTR-R (recording) when the recording material 1 of LTR (Letter) size is longitudinally fed (the short direction of the recording material 1 is conveyed in parallel with the longitudinal direction of the transfer nip portion Nt). The length of the material 1 in the width direction is 279 mm or less is defined as a small size recording material 1.

  In step S83, if the width size W of the recording material 1 detected by the recording material width detection sensor 202 is equal to or smaller than the LTR-R size, the process proceeds to step S84. In step S84, the CPU 201 determines the charge amount Q of the toner t in the developing device 122.

  In step S84, the CPU 201 refers to the passage time Ta through which the recording material 1 passes through the transfer nip portion Nt in the immediately preceding print job stored in the memory 203 shown in FIG. 2 at the end of the immediately preceding print job. Furthermore, the standby time Tb from the end time of the immediately preceding print job to the start time of the immediately following print job is referred to. Further, reference is made to the temperature and humidity of the environment where the image forming apparatus 10 is detected, which is detected by the environment sensor 206 shown in FIG.

Then, the CPU 201 that also serves as a determination unit corrects the charge amount Q ₀ of the toner t in the developing device 122 at the start of the immediately preceding print job, using Equations 2 to 4. Then, the charge amount Q of the toner t in the developing device 122 at the start of the print job immediately after that is determined.

  Next, in step S85, the CPU 201 determines whether or not the charge amount Q of the toner t in the developing device 122 determined in step S84 is −7.0 μC / g or less indicated by a straight line d in FIG. In step S85, if the charge amount Q of the toner t in the developing device 122 determined in step S84 is −7.0 μC / g or less shown by the straight line d in FIG. 11, the process proceeds to step S87. In step S87, the timing time T1 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is set to 80 seconds.

  If it is determined in step S85 that the charge amount Q of the toner t in the developing device 122 determined in step S84 is greater than -7.0 μC / g, the process proceeds to step S86. In step S86, the CPU 201 determines that the charge amount Q of the toner t in the developing device 122 determined in step S84 is larger than −7.0 μC / g shown by the straight line c in FIG. 11 and −5.0 μC / g. Or less.

  In step S86, the charge amount Q of the toner t in the developing device 122 determined in step S84 is larger than −7.0 μC / g and smaller than −5.0 μC / g shown by the straight line c in FIG. In the case, the process proceeds to step S88. In step S88, the CPU 201 sets a timing time T2 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 to 60 seconds.

  In step S86, if the charge amount Q of the toner t in the developing device 122 determined in step S84 is −5.0 μC / g or more shown by the straight line e in FIG. 11, the process proceeds to step S89. In step S89, the CPU 201 sets a timing time T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 to 40 seconds.

  In steps S87 to S89, the CPU 201 appropriately sets timing times T1 to T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 corresponding to the straight lines d, c and e in FIG. To do. Next, in step S90, the CPU 201 outputs the laser beam 11a emitted from the laser scanner 11 to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. Irradiate.

  Then, as shown in FIG. 3A, the CPU 201 attaches the toner t from the developing sleeve 122a to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. Then, as shown in FIG. 3B, a non-passing portion of the recording material 1 on the surface of the transfer roller 17 to which a transfer bias having a polarity opposite to that of the toner t is applied by the transfer bias power source 204 shown in FIG. Toner t is electrostatically attached.

  Next, in step S91, as shown in FIG. 3C, the CPU 201 moves the transfer nip portion Nt to the recording material with the toner t attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. The image forming operation through which 1 passes is started. The width of the recording material 1 detected by the recording material width detection sensor 202 in the direction parallel to the longitudinal direction of the transfer roller 17 may be a predetermined value (LTR-R size) or less. In that case, the CPU 201 forms an electrostatic latent image on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 in the same manner as the passing portion of the recording material 1.

  Then, the toner t carried on the surface of the developing sleeve 122 a of the developing device 122 is supplied to develop the toner t on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. Then, the photosensitive drum 121 is rotated so that the recording material 1 reaches the non-passing portion of the recording material 1 on the surface of the transfer roller 17 before reaching the transfer nip portion Nt where the photosensitive drum 121 and the transfer roller 17 face each other. The image forming operation is performed in a state in which is attached.

  In step S92, the CPU 201 starts from the time when the recording material 1 starts to pass through the transfer nip portion Nt by the time timer 207 shown in FIG. In steps S87 to S89, timing times T1 to T3 for supplying the toner t to the non-passing portions of the recording material 1 on the surface of the transfer roller 17 respectively set corresponding to the straight lines d, c and e in FIG. It is determined whether or not elapses.

  If the timing times T1 to T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 are counted in step S92, the process proceeds to step S93. In step S93, the CPU 201 applies a laser beam to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 by the laser scanner 11 in parallel with the image forming operation in which the recording material 1 continuously passes through the transfer nip portion Nt. Irradiate 11a.

  Then, as shown in FIG. 3A, the CPU 201 attaches the toner t to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 by the developing sleeve 122a. Then, as shown in FIG. 3B, the toner t is statically applied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 to which a transfer bias having a polarity opposite to that of the toner t is applied by the transfer bias power source 204. Electrically attach.

  In step S94, the CPU 201 determines that the print job has been completed. Until then, steps S92 to S94 are repeated. The CPU 201 performs the following control each time the timing times T1 to T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 are repeatedly counted by the time timer 207 shown in FIG. In step S93, the toner t is continuously supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 in parallel with the image forming operation in which the recording material 1 continuously passes through the transfer nip portion Nt. .

  If the CPU 201 determines in step S94 that the print job has been completed, the process proceeds to step S95, where the CPU 201 cleans (cleans) the toner t adhering to the surface of the transfer roller 17 by the cleaning means during the post-rotation. A transfer bias of −1700 V having the same polarity as the regular toner t is applied to the transfer roller 17. The transfer bias is applied for the time required for the transfer roller 17 to rotate once.

  Next, a +800 V transfer bias having a reverse polarity is applied to the transfer roller 17. The transfer bias is applied for the time required for the transfer roller 17 to rotate once. Thus, the toner t adhering to the surface of the transfer roller 17 due to the potential difference of the transfer bias applied to the transfer roller 17 flies to the surface of the photosensitive drum 121, and the surface of the transfer roller 17 can be cleaned.

  In step S96, the passage time Ta for the recording material 1 to pass through the transfer nip portion Nt required for the current print job is stored in the memory 203 shown in FIG. Thereafter, the process proceeds to step S97 to end the print job. The time timer 207 shown in FIG. 2 measures the waiting time Tb until the next print job is started, as needed, starting from the time when the current print job is finished. The CPU 201 stores the standby time Tb measured by the time timer 207 in the memory 203 shown in FIG.

  If the width W of the recording material 1 detected by the recording material width detection sensor 202 is larger than the LTR-R size in step S83, the process proceeds to step S98. In step S98, the CPU 201 performs a normal image forming operation in which the toner t is not attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. Thereafter, the process proceeds to step S95, where the CPU 201 performs cleaning (cleaning) of the toner t adhering to the surface of the transfer roller 17 by the cleaning means during post-rotation.

  In the present embodiment, before the small-sized recording material 1 passes through the transfer nip portion Nt, the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is irradiated with the laser light 11a emitted from the laser scanner 11. The toner t then flies and adheres to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 from the developing sleeve 122a provided in the developing device 122.

  Then, the photosensitive drum 121 to which the toner t is attached is rotated. The toner t is electrostatically attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 to which a transfer bias having a polarity opposite to that of the toner t is applied by the transfer bias power source 204. As a result, the transfer current Idc flowing from the transfer roller 17 to the photosensitive drum 121 due to the electrical resistance difference ΔR between the passage portion of the recording material 1 and the non-passage portion when the small size recording material 1 passes through the transfer nip portion Nt. Prevent leaks.

  In the image forming apparatus 10 using such an electrostatic transfer process, the charge amount Q of the toner t in the developing device 122 is determined by the CPU 201 that also serves as a determination unit. Depending on the determination result, timing times T1 to T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 are changed. Accordingly, it is possible to continuously suppress image defects such as transfer explosions shown in FIGS. 5 and 7A when the small-sized recording material 1 continuously passes through the transfer nip portion Nt.

  As shown in FIG. 15, in Comparative Example 3, 37 or more recording materials 1 of A4R size (210 mm × 297 mm) continuously passed through the transfer nip portion Nt. At that time, the transfer explosion shown in FIGS. 5 and 7A occurred due to a decrease in the amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. In Comparative Example 3, the toner t is attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 only once.

  In this embodiment, while the recording material 1 is passing through the transfer nip portion Nt, new toner t is supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. As a result, the transfer explosion shown in FIGS. 5 and 7A does not occur. Further, in Comparative Example 3, the toner t is attached to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 for each print job, and thereafter, on the surface of the photosensitive drum 121 after each print job is completed. Perform cleaning (cleaning). For this reason, the toner consumption also increases.

  In the present embodiment, the toner t is supplied at an appropriate timing while the recording material 1 passes through the transfer nip portion Nt. Thereby, the toner consumption can be suppressed. In the present embodiment, the transfer explosion shown in FIGS. 5 and 7A can be continuously suppressed even in a print job in which a plurality of recording materials 1 continuously pass through the transfer nip portion Nt with a small amount of toner consumption. Other configurations are the same as those in the above embodiments, and the same effects can be obtained.

  Next, the configuration of the fifth embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition, what was comprised similarly to each said embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description. In the fourth embodiment, the CPU 201 supplies the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 from the determination result of the charge amount Q of the toner t in the developing device 122. To change. Thus, the amount of toner t carried on the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is kept constant.

  In this embodiment, the CPU 201, which also serves as the second setting unit, develops the developing device 122 on the non-passing portion of the recording material 1 on the surface of the transfer roller 17 based on the determination result of the charge amount Q of the toner t in the developing device 122. The supply amount of the toner t supplied from the sleeve 122a is set. Thus, the amount of toner t carried on the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is kept constant.

  In the fourth embodiment, the CPU 201 attaches 3 g of toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. For example, a print job in which the passing time Ta for passing the recording material 1 through the transfer nip portion Nt is 60 seconds starts.

  Thereafter, the case where the charge amount Q of the toner t in the developing device 122 is −5.0 μC / g or more shown by the straight line e in FIG. 11 is as follows. Forty seconds after the recording material 1 starts to pass through the transfer nip portion Nt, the toner adhesion amount of the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is reduced to 1 g, as shown in FIGS. 5 and 7A. A transcription explosion occurs.

  For this reason, as shown in FIG. 12A, the CPU 201 again supplies 2 g (= 3 g-1 g) of toner t on the surface of the transfer roller 17 after 40 seconds from the start of passage of the recording material 1 through the transfer nip Nt. The non-passing portion of the recording material 1 is supplied. As a result, the toner t supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 consumes a total amount of 5 g (= 3 g + 2 g).

  Further, the case where the charge amount Q of the toner t in the developing device 122 is −7.0 μC / g or less shown by the straight line d in FIG. 11 is as follows. The transfer explosion shown in FIGS. 5 and 7A is prevented at the non-passing portion of the recording material 1 on the surface of the transfer roller 17 even in a print job in which the recording material 1 passes through the transfer nip portion Nt and the passing time Ta is 80 seconds. The toner amount can be maintained.

  For this reason, in a print job in which the recording material 1 passes through the transfer nip Nt and the passing time Ta is 60 seconds, the recording material 1 on the surface of the transfer roller 17 is rotated during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip Nt. 3 g of toner t adhering to the non-passing portion is excessively consumed.

  Therefore, in this embodiment, the excessive consumption amount of the toner t attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is suppressed. The CPU 201 supplies the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation where the recording material 1 does not pass through the transfer nip portion Nt from the determination result of the charge amount Q of the toner t in the developing device 122. Change the toner amount. Alternatively, the amount of toner supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is changed at every elapse of a predetermined time while the recording material 1 is continuously passing through the transfer nip portion Nt.

  As shown in FIG. 16, first, at the start of a print job for the small-sized recording material 1, the CPU 201 performs the following control according to the determination result of the charge amount Q of the toner t in the developing device 122. The amount of toner attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt is changed. Alternatively, the amount of toner supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is changed every time a predetermined time elapses while the recording material 1 passes through the transfer nip portion Nt.

  The CPU 201 determines that the charge amount Q of the toner t in the developing device 122 is smaller than −5.0 μC / g and larger than −7.0 μC / g shown by the straight line c in FIG. At that time, 3 g of toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt.

  Thereafter, the following control is performed every 60 seconds as the passing time Ta for the recording material 1 to pass through the transfer nip Nt while the recording material 1 passes through the transfer nip Nt until the print job is completed. Again, 2 g (= 3 g-1 g) of toner t is supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. As a result, the occurrence of the transfer explosion shown in FIGS. 5 and 7A can be prevented continuously, and the excessive toner consumption can be reduced.

  Similarly, the CPU 201 determines that the charge amount Q of the toner t in the developing device 122 is −7.0 μC / g or less indicated by the straight line d in FIG. At that time, 2 g of toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt.

  Further, the CPU 201 determines that the charge amount Q of the toner t in the developing device 122 is −5.0 μC / g or more as indicated by the straight line e in FIG. At that time, 4 g of toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt.

  Then, the CPU 201 performs the following control every 60 seconds as the passing time Ta for the recording material 1 to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt. If the straight line d in FIG. 16 is applied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 again, 1 g (= 2g-1g) of toner t is supplied. In the case of the straight line e in FIG. 16, 3 g (= 4 g-1 g) of toner t is supplied.

  That is, J (g) toner t is adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 during the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt. In that case, the following control is performed every 60 seconds as the passing time Ta for the recording material 1 to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt. When the amount of toner to be supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 again is M (g), the relationship shown in Expression 5 below is obtained.

[Formula 5]
M (g) = J (g) -1 (g)

<Image forming operation>
Next, an image forming operation of the image forming apparatus 10 of the present embodiment will be described with reference to FIG. Note that steps S101 to S106 shown in FIG. 17 are the same as steps S81 to S86 shown in FIG. In step S105, when the charge amount Q of the toner t in the developing device 122 determined by the CPU 201 is −7.0 μC / g or less shown by the straight line d in FIG. 16, the process proceeds to step S107.

  In step S107, the CPU 201 performs the following every 60 seconds as a passing time Ta for the recording material 1 to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt until the print job is completed. Control. Again, the toner amount M1 supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 1 g, and the toner amount adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 2 g. .

  In step S106, the charge amount Q of the toner t in the developing device 122 determined by the CPU 201 is larger than −7.0 μC / g and smaller than −5.0 μC / g shown by the straight line c in FIG. If so, the process proceeds to step S108. In step S108, the CPU 201 performs the following every 60 seconds as a passage time Ta for the recording material 1 to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt until the print job is completed. Control. Again, the toner amount M2 supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 2 g, and the toner amount adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 3 g. .

  Similarly, in step S106, when the charge amount Q of the toner t in the developing device 122 determined by the CPU 201 is −5.0 μC / g or more shown by the straight line e in FIG. 16, the process proceeds to step S109. In step S109, the CPU 201 performs the following every 60 seconds as a passage time Ta for the recording material 1 to pass through the transfer nip portion Nt while the recording material 1 passes through the transfer nip portion Nt until the print job is completed. Control. Again, the toner amount M3 supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 3 g, and the toner amount adhering to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is 4 g. .

  Thereafter, the process proceeds to steps S110 and S111. The steps S110 and S111 are the same as the steps S90 and S91 shown in FIG. In step S111, the CPU 201 starts an image forming operation with the toner t attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. In step S112, the CPU 201 determines whether the elapsed time from the time when the image forming operation is started in step S111 measured by the time timer 207 shown in FIG. 2 has reached 60 seconds.

  When the CPU 201 determines in step S112 that the elapsed time from the start time of the image forming operation measured by the time timer 207 shown in FIG. 2 has reached 60 seconds, the process proceeds to step S113. In step S113, in parallel with the printing operation in which the recording material 1 passes continuously through the transfer nip portion Nt, a laser of at least the circumference of the transfer roller 17 is provided in the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. Irradiate light 11a.

  Then, as shown in FIG. 3A, the toner amount M (g) expressed by the equation 5 is supplied to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121, and the transfer bias shown in FIG. A transfer bias having a polarity opposite to that of the toner t is applied to the transfer roller 17 by the power source 204. As a result, as shown in FIG. 3B, the toner t having the toner amount M (g) expressed by the above equation 5 is electrostatically attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. . Thereafter, in step S114, the CPU 201 determines whether or not the print job is finished, and repeats the steps S112 to S114 until the print job is finished.

  In step S112, the elapsed time from the time when the replenishment of the toner t in step S113 is completed is measured by the time timer 207 shown in FIG. When 60 seconds have passed again, the CPU 201 proceeds to step S113 again, and the toner of the toner amount M (g) expressed by the mathematical formula 5 at the non-passing portion of the recording material 1 on the surface of the transfer roller 17 is reached. The operation of replenishing t is performed.

  In step S114, the CPU 201 repeats steps S112 to S114 until the print job is completed, and continuously supplies toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17. If the CPU 201 determines in step S114 that the print job has been completed, the process proceeds to step S115. Steps S115 to S117 are the same as steps S95 to S97 shown in FIG.

  In this embodiment, the CPU 201 changes the amount of toner t supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 according to the determination result of the charge amount Q of the toner t in the developing device 122. . As a result, image defects such as the transfer explosion shown in FIGS. 5 and 7A when the small-sized recording material 1 continuously passes through the transfer nip portion Nt are continuously suppressed, and the toner consumption is also reduced. It becomes possible.

  As shown in FIG. 15, in Comparative Example 3 in which the toner t was attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 only once, 37 recording materials 1 of A4R size (210 mm × 297 mm) were obtained. The above is the following when the sheet passes through the transfer nip Nt continuously. The transfer explosion shown in FIGS. 5 and 7A occurred due to a decrease in the amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  In the present embodiment, similarly to the fourth embodiment, even when 37 or more A4R-sized recording materials 1 pass through the transfer nip portion Nt continuously, the transfer explosion shown in FIGS. 5 and 7A occurs. do not do. Further, in the present embodiment, the CPU 201 performs the following control from the determination result of the charge amount Q of the toner t in the developing device 122. During the pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt and at a predetermined elapsed time during which the recording material 1 continuously passes through the transfer nip portion Nt, the recording material 1 on the surface of the transfer roller 17 is not passed through. Change the amount of toner to be replenished. Thereby, the transfer explosion shown in FIG. 5 and FIG. 7A can be suppressed with a toner consumption smaller than that in the fourth embodiment.

  In the present embodiment, before the small size recording material 1 passes through the transfer nip portion Nt, the laser scanner 11 is placed on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 as shown in FIG. The laser beam 11a emitted from the laser beam is irradiated. The developing bias voltage Vdc is applied to the developing sleeve 122a of the developing device 122 by the developing bias power source 122b so that the toner t carried on the surface of the developing sleeve 122a does not pass through the recording material 1 on the surface of the photosensitive drum 121. Fly to the club.

  Then, the photosensitive drum 121 having the toner t adhered to the non-passing portion of the recording material 1 is rotated, and the recording material 1 on the surface of the transfer roller 17 to which a transfer bias having a polarity opposite to that of the toner t is applied by the transfer bias power source 204. The toner t is electrostatically adhered to the non-passing portion.

  As a result, the transfer current Idc flows (leaks) into the photosensitive drum 121 due to the electrical resistance difference ΔR between the passing portion of the recording material 1 and the non-passing portion when the small size recording material 1 passes through the transfer nip portion Nt. To prevent. The image forming apparatus 10 using such an electrostatic transfer process is as follows.

  The CPU 201 determines the timing times T1 to T3 for supplying the toner t to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 according to the determination result of the charge amount Q of the toner t in the developing device 122, or the toner At least one of the replenishment amounts of t is changed. This makes it possible to continuously suppress image defects such as a transfer explosion shown in FIGS. 5 and 7A when the small-sized recording material 1 continuously passes through the transfer nip portion Nt. .

  As shown in FIG. 15, in Comparative Example 3 in which the toner t was attached to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 only once, 37 recording materials 1 of A4R size (210 mm × 297 mm) were obtained. The above is the following when the sheet passes through the transfer nip Nt continuously. The transfer explosion shown in FIGS. 5 and 7A occurred due to a decrease in the amount of toner adhered to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  In the fourth and fifth embodiments, new toner t is appropriately supplied to the non-passing portion of the recording material 1 on the surface of the transfer roller 17 while the recording material 1 passes through the transfer nip portion Nt. Therefore, the transfer explosion shown in FIGS. 5 and 7A does not occur. Further, in Comparative Example 3, the toner t is attached to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 in each print job, and the surface of the photosensitive drum 121 is cleaned (cleaned) every time. It was. For this reason, the toner consumption also increases.

  In the fourth and fifth embodiments, the toner t is appropriately replenished while the recording material 1 passes through the transfer nip portion Nt. Thereby, the toner consumption can be suppressed. As a result, even in a print job in which the recording material 1 having a small size passes through the transfer nip portion Nt continuously, the transfer explosion shown in FIGS. 5 and 7A can be suppressed with a small amount of toner consumption. Other configurations are the same as those in the above embodiments, and the same effects can be obtained.

  Next, the configuration of the sixth embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition, what was comprised similarly to each said embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description.

  For example, the toner t is caused to fly from the developing sleeve 122 a of the developing device 122 shown in FIG. 1 to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. At that time, the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 may be stained with the toner t. In that case, the recording material 1 may be stained with the toner t adhering to the conveyance guide 41.

  The toner t having a low charge amount Q has a small electrical adhesion. Therefore, if the charge amount Q of the toner t carried on the surface of the photosensitive drum 121 is small, the toner t carried on the surface of the photosensitive drum 121 or the surface of the transfer roller 17 may be scattered. Further, when the charge amount Q of the toner t is small at the initial stage when the image forming apparatus 10 is installed or after being left for a long period of time, the conveyance guide 41 near the photosensitive drum 121 and the transfer roller 17 shown in FIG. It is.

  The horizontal axis of FIG. 18A represents the toner carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 of the image forming apparatus 10 installed in an environment where the temperature is 23 ° C. and the humidity is 50%. The charge amount Q of t is shown. The vertical axis in FIG. 18A indicates the amount of toner attached to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. The charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 shown on the horizontal axis in FIG. 18A is the charge per gram of the toner t on the surface of the photosensitive drum 121. Indicates the amount.

  As shown in FIG. 18A, when the amount of toner adhering to the front surface of the conveyance guide 41 exceeds 20 mg, the toner t is soiled to the extent that the back surface of the recording material 1 is visible. In this embodiment, the charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 in an environment where the temperature is 23 ° C. and the humidity is 50% is 6.5 μC / g. It is. Further, the amount of toner adhering to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. 1 is 26 mg. In this case, the toner t adhering to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. 1 is transferred and adhered to the back surface of the recording material 1, and the toner t is contaminated.

  In the present embodiment, the charging bias voltage applied to the charging roller 123 is changed by the CPU 201 that also serves as the third setting unit. Alternatively, the exposure pattern by the laser beam 11a for exposing the surface of the photosensitive drum 121 is changed. Alternatively, the exposure intensity is changed by controlling the output of the laser beam 11a for exposing the surface of the photosensitive drum 121. Alternatively, the developing bias voltage Vdc applied to the developing sleeve 122a is changed. As a result, toner t having a charge amount Q higher than that during normal image formation is attached to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. As a result, the toner guide t in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. 1 before transferring the toner image on the surface of the photosensitive drum 121 to the recording material 1 is prevented from being contaminated.

  The CPU 201 of this embodiment also serves as a third setting unit, and can change the charging bias voltage applied to the charging roller 123 by controlling the charging bias power source 123a. Furthermore, the exposure pattern by the laser beam 11a for controlling the laser scanner 11 to expose the surface of the photosensitive drum 121 can be changed. Further, the exposure intensity can be changed by controlling the laser scanner 11 to control the output of the laser beam 11a for exposing the surface of the photosensitive drum 121. Further, the developing bias voltage Vdc applied to the developing sleeve 122a can be changed. The CPU 201 appropriately changes and sets at least one of these conditions.

  In the present embodiment, as a toner image formed on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121, a toner image having a dot pattern with a small dot (black portion) area is formed. FIG. 18B shows the area of the dot (black part) of the toner image formed on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 and the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. This represents the relationship with the charge amount Q of the toner t carried.

  As shown in FIG. 18B, the surface of the photosensitive drum 121 as the area of the dot (black portion) of the toner image formed on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 decreases. The charge amount Q of the toner t carried on the non-passing portion of the upper recording material 1 is increased. The toner t having a high charge amount Q has a large electrical adhesion. Therefore, it is easy to carry on the surface of the photosensitive drum 121. On the other hand, the toner t having a low charge amount Q returns from the surface of the photosensitive drum 121 to the developing sleeve 122a.

In this embodiment, the charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is maintained so as to be 8 μC / g or more. In the present embodiment, the area of one dot of the toner image formed on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is as follows. The resolution of the image data of the image forming apparatus 10 has an area of 0.002 mm ² corresponding to one pixel of 600 dpi (dots per inch). A toner image having such a dot pattern is formed on every non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 as shown in FIG.

  Next, a case where the recording material 1 of LTR-R size passes through the transfer nip portion Nt will be described with reference to FIG. When the resolution of the image data of the image forming apparatus 10 is 600 dpi, the image data when the recording material 1 is LTR-R size is 5100 pixels in the main scanning direction (longitudinal direction of the transfer nip portion Nt). The total length in the longitudinal direction of the transfer roller 17 of this embodiment is 306 mm, which is 7288 pixels in terms of the number of pixels. For this reason, when the recording material 1 of LTR-R size passes through the transfer nip portion Nt, the number of pixels in the non-passing portion where the recording material 1 of the transfer nip portion Nt does not pass is 2188 pixels (= 7288 pixels-5100 pixels). is there.

  In the present embodiment, the CPU 201 passes a laser beam 11a corresponding to an image signal from the laser scanner 11 on the surface of the photosensitive drum 121 to pass the laser beam 11a in order to form a toner image on the LTR-R size recording material 1. Irradiate. At the same time, a signal for irradiating the laser beam 11a from the laser scanner 11 to every other 2188 pixels of the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is input to the laser scanner 11. As a result, as shown in FIG. 19A, a dot pattern latent image is formed every other pixel in the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121.

Based on the signal emitted from the laser scanner 11 for irradiating the laser beam 11a from the CPU 201, the laser scanner 11 irradiates the laser beam 11a as follows. As shown in FIG. 19B, the laser beam 11a is irradiated every other pixel to the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 uniformly charged with the surface potential V _D of −600 V does not pass. To do. The surface potential V _L of the photosensitive drum 121 irradiated with the laser beam 11a becomes −150 V, and an electrostatic latent image is formed. On the other hand, a developing bias voltage Vdc of −400 V is applied to the developing sleeve 122a of the developing device 122.

As a result, the toner t charged to −400 V is carried on the surface of the developing sleeve 122a. The toner t charged to −400 V is converted into an electrostatic latent image on the surface of the photosensitive drum 121 by a potential difference Vs from the surface potential V _L (−150 V) of the electrostatic latent image formed on the surface of the photosensitive drum 121. Fly against. As a result, a toner image is formed on the surface of the photosensitive drum 121.

  When the width in the direction parallel to the longitudinal direction of the transfer roller 17 of the recording material 1 detected by the recording material width detection sensor 202 shown in FIG. 2 is equal to or less than a predetermined value (LTR-R size: 215.9 mm × 279.4 mm) Is as follows. A toner image having a dot pattern shown in FIG. 19A is formed on a non-passing portion on the surface of the photosensitive drum 121 where the recording material 1 does not pass, similarly to the passing portion where the recording material 1 passes.

  A toner image corresponding to the image information is formed on a passage portion on the surface of the photosensitive drum 121 where the recording material 1 passes. At the same time, a toner image having a dot pattern every other pixel shown in FIG. 19A is also formed in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass. The photosensitive drum 121 rotates while carrying these toner images.

The toner image on the surface of the photosensitive drum 121 is moved to the transfer nip portion Nt, and a transfer current Idc (+10 μA in this embodiment) having a polarity opposite to the polarity of the toner t is applied to the transfer roller 17. As a result, the toner image of the passage portion of the recording material 1 on the surface of the photosensitive drum 121 is electrostatically transferred to the recording material 1. Further, the toner t of the dot pattern toner image having an area of 0.002 mm ² at every other non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is recorded on the recording material 1 on the surface of the transfer roller 17. At the same time, electrostatic transfer is performed on the non-passing portion.

  When the recording material 1 passes through the transfer nip portion Nt, the toner t adhered to the non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass plays a role of electric resistance (about 5 kΩ). As a result, the electrical resistance difference ΔR between the surface of the photosensitive drum 121 and the surface of the transfer roller 17 in the longitudinal direction of the transfer nip portion Nt is reduced.

  In some cases, the surface of the photosensitive drum 121 and the surface of the transfer roller 17 are in direct contact with each other without the toner t adhering to a non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass. In this case, the electrical resistance difference ΔR between the surface of the photosensitive drum 121 and the surface of the transfer roller 17 in the longitudinal direction of the transfer nip portion Nt is about 5 kΩ.

  As a result, when the surface of the photosensitive drum 121 and the surface of the transfer roller 17 are in direct contact with each other without the toner t adhering to the non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass, is there. The transfer current Idc leaked from the transfer roller 17 to the photosensitive drum 121 at the non-passing portion where the recording material 1 did not pass.

  When the toner t is adhered to the non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass, the leakage current is reduced by about +0.5 μA. Thus, it was possible to suppress the occurrence of defective images such as the transfer explosion shown in FIGS. 5 and 7A due to the shortage of the transfer current Idc.

In this embodiment, a toner image of a dot pattern having an area of 0.002 mm ² every other pixel is carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121, thereby increasing the charge amount Q of the toner t. be able to. This prevents leakage of the transfer current Idc from the transfer roller 17 to the photosensitive drum 121 due to the electrical resistance difference ΔR between the passing portion and the non-passing portion when the small size recording material 1 passes through the transfer nip portion Nt. it can.

The recording material 1 reaches the transfer nip Nt between the photosensitive drum 121 and the transfer roller 17. Before that, in the present embodiment, as shown in FIG. 19A, a toner image of a dot pattern having an area of 0.002 mm ² every other pixel in a non-passing portion of the transfer roller 17 where the recording material 1 does not pass. Is carried. As a result, the image forming operation is performed with the toner t having a charge amount Q higher than that during normal image formation being adhered.

<Image forming operation>
Next, the image forming operation of this embodiment will be described with reference to FIG. When a print job is started in step S121, a pre-rotation operation in which the recording material 1 does not pass through the transfer nip portion Nt is performed in step S122. Thereafter, in step S123, the width size W of the recording material 1 (the size in the direction along the transfer nip portion Nt) is detected by the recording material width detection sensor 202 shown in FIG. The CPU 201 determines whether the width size W of the recording material 1 detected by the recording material width detection sensor 202 is equal to or less than the maximum width size W of the recording material 1 that can be printed by the image forming apparatus 10.

  In step S123, the width W of the recording material 1 detected by the recording material width detection sensor 202 may be a predetermined size (LTR-R size) or less. In that case, the process proceeds to step S124, and the CPU 201 performs an operation of reducing transfer defects such as transfer explosion shown in FIGS. 5 and 7A when the small-sized recording material 1 passes through the transfer nip portion Nt. carry out.

In step S124, the CPU 201 forms an image of a toner image corresponding to the image information on the passage portion on the surface of the photosensitive drum 121 through which the recording material 1 passes. At the same time, a dot pattern toner image having an area of 0.002 mm ² every other pixel as shown in FIG. 19A also in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass. Form.

  In step S123, the width W of the recording material 1 detected by the recording material width detection sensor 202 may be larger than a predetermined size (LTR-R size). In that case, the process proceeds to step S125, and the CPU 201 executes the image forming operation without attaching the toner t to the non-passing portion where the recording material 1 on the surface of the transfer roller 17 does not pass, as in the normal image forming operation. To do.

  When the image forming operation is completed in steps S124 and S125 (step S126), the process proceeds to step S127, and the CPU 201 cleans (cleans) the surface of the transfer roller 17 by a cleaning unit (not shown). Thereafter, the process proceeds to step S128 to end the print job.

  A transfer bias of −1700 V having the same polarity as the regular toner t is applied to the transfer roller 17. The transfer bias is applied for the time required for the transfer roller 17 to rotate once. Next, a +800 V transfer bias having a reverse polarity is applied to the transfer roller 17. The transfer bias is applied for the time required for the transfer roller 17 to rotate once. The toner t adhering to the surface of the transfer roller 17 due to the potential difference of the transfer bias flies to the surface of the photosensitive drum 121, and the surface of the transfer roller 17 can be cleaned.

In this embodiment, as shown in FIG. 19A, a toner image having a dot pattern having an area of 0.002 mm ² every other pixel is carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. . As a result, as shown in FIG. 18B, the charge amount Q of the toner t adhered to the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 can be increased to 8.5 μC / g.

  There is a case where the recording material 1 of LTR-R size continuously passes through the transfer nip portion Nt from the initial stage when the image forming apparatus 10 having a low charge amount Q of the toner t is installed. FIG. 21A shows the amount of toner adhered to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. A solid line m in FIG. 21A indicates the present embodiment, and a broken line n in FIG.

  The experiment shown in FIG. 21A is an experiment in which printing is continuously performed at a printing rate of 10% on the recording material 1 of LTR-R size from the initial stage when the image forming apparatus 10 is installed in an environment where the temperature is 23 ° C. and the humidity is 50%. It is data. Comparative Example 4 indicated by a broken line n in FIG. 21A is data when a toner image having a dot pattern is not carried on the non-passing area of the recording material 1 in the transfer roller 17.

In Comparative Example 4 indicated by a broken line n in FIG. 21A, when 3 × 10 ³ recording materials 1 continuously pass through the transfer nip portion Nt, the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. The amount of toner adhering to the transport guide 41 exceeded 20 mg.

On the other hand, in the present embodiment indicated by the solid line m in FIG. 21A, 20 × 10 ³ recording materials 1 continuously pass through the transfer nip portion Nt from the beginning when the image forming apparatus 10 having a low charge amount Q of toner t is installed. Then pass. Even in this case, the amount of toner adhering to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. 1 did not exceed 20 mg.

In this embodiment, as shown in FIG. 19A, a toner image having a dot pattern having an area of 0.002 mm ² every other pixel is carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121. . As a result, the charge amount Q of the toner t in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass can be increased.

  As a result, the toner t scatters in the main body of the image forming apparatus 10 while preventing a transfer failure such as a transfer explosion shown in FIGS. 5 and 7A when the small size recording material 1 passes through the transfer nip portion Nt. This prevents internal components and the recording material 1 from being contaminated by the toner t.

  When the small-sized recording material 1 passes through the transfer nip portion Nt, there is a possibility that a transfer failure such as a transfer explosion shown in FIGS. 5 and 7A may occur. In this case, in this embodiment, the laser beam 11a is also emitted from the laser scanner 11 to the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 other than the passing portion where the recording material 1 passes the transfer nip portion Nt does not pass. Irradiate.

  Then, the toner t is allowed to fly and adhere from the developing sleeve 122a of the developing device 122 to the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass. On the surface of the photosensitive drum 121 in the non-passing portion where the recording material 1 does not pass on the surface of the transfer roller 17 to which the transfer bias 17 having a polarity opposite to the polarity of the toner t is applied by rotating the photosensitive drum 121 to which the toner t is attached The toner t is electrostatically attached.

  The toner t attached to the non-passing portion where the recording material 1 on the surface of the transfer roller 17 does not pass plays a role of electric resistance. This prevents leakage of the transfer current Idc from the transfer roller 17 to the photosensitive drum 121 due to the electrical resistance difference ΔR between the passing portion and the non-passing portion when the small size recording material 1 passes through the transfer nip portion Nt. it can.

  As a result, even when the small-size recording material 1 passes through the transfer nip portion Nt, the charge necessary for transfer can be secured, and FIGS. 5 and 5 show the small-size recording material 1 passing through the transfer nip portion Nt. Image defects such as a transfer explosion shown in FIG. 7A can be suppressed. In the present embodiment, the toner t flies to the non-passing portion where the recording material 1 does not pass through the transfer nip portion Nt only when an image defect such as a transfer explosion shown in FIGS. 5 and 7A is likely to occur. Run. For this reason, the consumption amount of the toner t is reduced.

  The image forming apparatus 10 forms an image on the recording material 1 having a size smaller than the recording material 1 having a size capable of forming an image. In this embodiment, the transfer failure such as the transfer explosion shown in FIG. 5 and FIG. 7A is effectively prevented at that time, and the toner t in the image forming apparatus 10 and the recording material 1 due to the scattering of the toner t. Dirt caused by can be prevented. Other configurations are the same as those in the above embodiments, and the same effects can be obtained.

Next, the configuration of the seventh embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In addition, what was comprised similarly to each said embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description. In the sixth embodiment, as shown in FIG. 19A, a dot pattern toner having an area of 0.002 mm ² every other pixel in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass. Carry an image. As a result, the charge amount Q of the toner t in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass is increased.

  In the present embodiment, the CPU 201, which also serves as the third setting unit, performs the following control when an image is formed on the normal size recording material 1 and when an image is formed on the small size recording material 1. The developing bias voltage Vdc applied to the developing sleeve 122a of the developing device 122 is changed by the developing bias power source 122b shown in FIG. As a result, the charge amount Q of the toner t in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass is increased.

The vertical axis of FIG. 21B represents the development bias voltage Vdc applied to the development sleeve 122a of the development device 122 by the development bias power source 122b shown in FIG. 2, and the surface potential V on which the electrostatic latent image on the photosensitive drum 121 is formed. A potential difference Vs from _L is shown. The horizontal axis of FIG. 21B shows the charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121.

As shown in FIG. 21B, the smaller the potential difference Vs between the developing bias voltage Vdc applied to the developing sleeve 122a and the surface potential _VL on which the electrostatic latent image of the photosensitive drum 121 is formed, the following is true. . It can be seen that the charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 increases.

The toner t having a low charge amount Q has a small electric adhesion force. For this reason, when the potential difference Vs between the developing bias voltage Vdc applied to the developing sleeve 122a and the surface potential _VL on which the electrostatic latent image of the photosensitive drum 121 is formed is small, the surface of the developing sleeve 122a is transferred to the surface of the photosensitive drum 121. The toner t is difficult to fly.

In this embodiment, the charging amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is set to be 8 μC / g or more. Therefore, the potential difference Vs between the developing bias voltage Vdc applied to the developing sleeve 122a of the developing device 122 by the developing bias power source 122b shown in FIG. 2 and the surface potential _VL on which the electrostatic latent image of the photosensitive drum 121 is formed is set to 150V. did.

Next, the case where the recording material 1 of LTR-R size passes through the transfer nip portion Nt will be described with reference to FIG. As shown in FIG. 22 (b), irradiating a laser beam 11a by the laser scanner 11 on the surface of the photosensitive drum 121 is uniformly charged at a surface potential V _D of -600 V. The surface potential V _L on which the electrostatic latent image of the photosensitive drum 121 irradiated with the laser beam 11a is formed becomes −150 V, and an electrostatic latent image is formed on the surface of the photosensitive drum 121 by the irradiation of the laser beam 11a.

A developing bias voltage Vdc of −300 V is applied to the developing sleeve 122a of the developing device 122. As a result, a potential difference Vs (150 V = | −300 V − (− 150 V) |) is generated between the surface potential V _L (−150 V) of the photosensitive drum 121 and the developing bias voltage Vdc (−300 V). The toner t charged on the surface of the developing sleeve 122a flies to the electrostatic latent image formed on the surface of the photosensitive drum 121 by the potential difference Vs. As a result, a toner image is formed on the surface of the photosensitive drum 121.

  After the toner image is formed on the surface of the photosensitive drum 121, the photosensitive drum 121 rotates while the toner image is carried on the surface of the photosensitive drum 121. As a result, the toner image formed on the surface of the photosensitive drum 121 is moved to the transfer nip portion Nt. The transfer bias power supply 204 applies a transfer current Idc (in this embodiment, +10 μA) having a polarity opposite to that of the toner t to the transfer roller 17.

  As a result, the toner image of the passage portion of the recording material 1 on the surface of the photosensitive drum 121 is electrostatically transferred to the recording material 1. On the other hand, the toner t in the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 is simultaneously electrostatically transferred to the non-passing portion of the recording material 1 on the surface of the transfer roller 17.

  Next, the image forming operation of this embodiment will be described with reference to FIG. Steps S131 to S133 shown in FIG. 23 are the same as steps S121 to S123 shown in FIG. In step S133, the width W of the recording material 1 detected by the recording material width detection sensor 202 shown in FIG. 2 may be a predetermined size (LTR-R size) or less. In that case, the process proceeds to step S134, and the CPU 201 performs an operation of reducing transfer defects such as transfer explosion shown in FIGS. 5 and 7A when the small-sized recording material 1 passes through the transfer nip portion Nt. carry out.

In step S134, the CPU 201 irradiates the laser scanner 11 with the laser beam 11a to the area corresponding to one rotation of the transfer roller 17 at the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass. At this time, the surface potential V _L of the photosensitive drum 121 irradiated with the laser beam 11a becomes −150 V as shown in FIG.

  In step S135, the CPU 201 applies a developing bias voltage Vdc of −300 V to the developing sleeve 122a of the developing device 122 by the developing bias power source 122b. As a result, the toner t carried on the surface of the developing sleeve 122a flies over the surface of the photosensitive drum 121.

  In step S136, the CPU 201 applies a transfer current Idc of +10 μA to the developing sleeve 122a of the developing device 122 by the developing bias power source 122b. As a result, the toner t in the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass is electrostatically transferred to the non-passing portion where the recording material 1 on the surface of the transfer roller 17 does not pass.

  In step S137, the CPU 201 executes an image forming operation by the image forming apparatus 10 in a state where the toner t is carried on a non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass. Thereafter, steps S138 to S140 in FIG. 23 are the same as steps S126 to S128 in FIG.

  In step S133, the width size W of the recording material 1 detected by the recording material width detection sensor 202 shown in FIG. 2 may be larger than a predetermined size (LTR-R size). In that case, the process proceeds to step S137, and the CPU 201 performs the image forming operation without attaching the toner t to the non-passing portion on the surface of the transfer roller 17 where the recording material 1 does not pass, as in the normal image forming operation. Run.

  In the sixth embodiment, as shown in FIG. 19B, the developing bias voltage Vdc applied to the developing sleeve 122a is set to −400V. In this embodiment, as shown in step S135 of FIG. 23 and FIG. 22B, the developing bias voltage Vdc applied to the developing sleeve 122a is set to −300V.

Thus, in the present embodiment, as shown in FIG. 21B, the developing bias voltage Vdc (−300 V) applied to the developing sleeve 122a is considered. The potential difference Vs (150 V = | −300 V − (− 150 V) |) between the developing bias voltage Vdc and the surface potential V _L (−150 V) of the photosensitive drum 121 was set small. As a result, the charge amount Q of the toner t carried on the non-passing portion of the recording material 1 on the surface of the photosensitive drum 121 can be set large (9 μC / g).

  FIG. 24 shows the result of comparing the amount of toner adhering to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. A solid line o in FIG. 24 indicates the present embodiment, and a broken line n in FIG. FIG. 24 shows a case where the recording material 1 of LTR-R size has passed through the transfer nip portion Nt continuously from the initial stage when the image forming apparatus 10 having a low charge amount Q of the toner t is installed. The horizontal axis of FIG. 24 indicates the number of LTR-R size recording materials 1 that pass through the transfer nip portion Nt continuously. The vertical axis in FIG. 24 is the amount of toner attached to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG.

  The experiment shown in FIG. 24 is experimental data in which printing is continuously performed at a printing rate of 10% on the recording material 1 of LTR-R size from the initial stage when the image forming apparatus 10 is installed in an environment where the temperature is 23 ° C. and the humidity is 50%. . Comparative Example 4 indicated by a broken line n in FIG. 24 is data when a toner image having a dot pattern is not carried on the non-passing area of the recording material 1 in the transfer roller 17.

In Comparative Example 4 indicated by a broken line n in FIG. 24, when 3 × 10 ³ recording materials 1 pass through the transfer nip portion Nt continuously, a conveyance guide in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. The amount of toner adhering to 41 exceeded 20 mg.

On the other hand, in the present embodiment indicated by a solid line o in FIG. 24, 20 × 10 ³ recording materials 1 continuously pass through the transfer nip portion Nt from the beginning when the image forming apparatus 10 having a low charge amount Q of toner t is installed. To do. Even in this case, the amount of toner adhering to the conveyance guide 41 in the vicinity of the photosensitive drum 121 and the transfer roller 17 shown in FIG. 1 did not exceed 20 mg.

In the present embodiment, the developing bias voltage Vdc applied to the developing sleeve 122a is changed from −400V in the sixth embodiment to −300V. Thus, as shown in FIG. 21B, the developing bias voltage Vdc (−300 V) applied to the developing sleeve 122a is taken into consideration. The potential difference Vs (150 V = | −300 V − (− 150 V) |) between the developing bias voltage Vdc and the surface potential V _L (−150 V) of the photosensitive drum 121 can be reduced. As a result, the charge amount Q of the toner t carried on the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass can be increased.

  As a result, scattering of the toner t in the main body of the image forming apparatus 10 is prevented while preventing image defects such as a transfer explosion shown in FIGS. 5 and 7A when the small size recording material 1 passes through the transfer nip portion Nt. It is possible to prevent the recording material 1 from being soiled by the toner t.

  In the present embodiment, only the developing bias voltage Vdc applied to the developing sleeve 122a is changed by the CPU 201 that also serves as the third setting means. In addition, the intensity of the laser beam 11a of the laser scanner 11 is changed with respect to the intensity of the laser beam 11a during normal image formation. Alternatively, the charging bias voltage applied to the charging roller 123 by the charging bias power source 123a can be changed with respect to the charging bias voltage during normal image formation.

As a result, the potential difference Vs between the developing bias voltage Vdc applied to the developing sleeve 122a and the surface potential _VL on which the electrostatic latent image on the photosensitive drum 121 is formed can be reduced. As a result, the charge amount Q of the toner t carried on the non-passing portion where the recording material 1 on the surface of the photosensitive drum 121 does not pass can be increased.

  The cleaning operation on the surface of the transfer roller 17 is set not to be performed until the width size W of the recording material 1 detected by the recording material width detection sensor 202 is changed in the direction parallel to the longitudinal direction of the transfer roller 17. You can also Other configurations are the same as those in the above embodiments, and the same effects can be obtained.

  In each of the above-described embodiments, the transfer nip portion Nt is formed by the photosensitive drum 121 as an image carrier and the transfer roller 17 as a transfer unit. Without being limited thereto, the transfer nip portion Nt may be formed by an intermediate transfer member such as a transfer belt as an image carrier and a secondary transfer roller as a transfer means instead of the photosensitive drum 121. .

  Further, in each of the above-described embodiments, the CPU 201 as the control unit attaches the developer to the non-passing portion of the recording material 1 of the transfer unit, but the invention is not limited thereto, and the transfer nip portion Nt is formed. A developer may be attached to the non-passing portion of the recording material 1 of the image carrier.

  Furthermore, in each of the above-described embodiments, the transfer current Idc applied to the transfer roller 17 and the voltage detected by the transfer voltage detection circuit 205 based on the transfer current Idc are used between the transfer roller 17 and the photosensitive drum 121. The electric resistance value R is determined. In addition, the resistance value of the transfer roller 17 may be obtained by a circuit without the photosensitive drum 121 and the resistance value may be set as the electric resistance value R.

t ... Toner 1 ... Recording material
17… Transfer roller (transfer means)
121… Photosensitive drum (image carrier)
122 ... Developing device (developing means)
201... CPU (control means, detection means, determination means, passage time detection means, number detection means, correction means, setting means)

Claims (15)

An image carrier for carrying a toner image developed by a developing means for supplying a developer;
A transfer means for transferring the toner image onto the recording material by holding the recording material conveyed at a nip formed by the image carrier;
Control means for attaching a developer to a non-passing portion of at least one recording material of the transfer means or the image carrier in accordance with a change in resistance value between the image carrier and the transfer means;
An image forming apparatus comprising: A detection unit that detects a current value or a voltage value that flows when a predetermined voltage or a predetermined current is applied to at least one of the image carrier and the transfer unit;
The control means includes
The image forming apparatus according to claim 1, wherein a change in the resistance value is determined from a resistance value obtained from a voltage value or a current value detected by the detection unit. The control means includes
When the resistance value is larger than the first threshold, toner is not attached to the non-passing portion,
When the resistance value is less than or equal to a first threshold value and greater than a second threshold value that is smaller than the first threshold value, a first toner amount is adhered to the non-passing portion;
3. The image forming apparatus according to claim 2, wherein when the resistance value is equal to or less than the second threshold value, a second toner amount larger than the first toner amount is adhered to the non-passing portion. . A passage time detecting means for detecting a passage time of the recording material passing through the nip portion;
The control unit is configured to detect the non-passing portion based on the passage time and the resistance value of the recording material detected by the passage time detecting unit when toner is attached to the non-passing portion in the immediately preceding print job. The image forming apparatus according to claim 1, wherein an amount of toner adhering to the toner is set. Environmental detection means for detecting environmental information;
A sheet number detecting means for detecting the number of recording materials passing through the nip portion;
Have
The said control means determines the said resistance value based on the environment information detected by the said environment detection means, and the number information detected by the said number detection means, The any one of Claims 1-4 characterized by the above-mentioned. The image forming apparatus described in 1. A sheet number detecting means for detecting the number of recording materials passing through a transfer nip between the image carrier and the transfer means;
A neglect time detection means for detecting the neglect time from the time when the previous print job was completed;
Correction means for correcting the resistance value based on the number information detected by the number detection means and the leaving time information detected by the leaving time detection means;
Have
The image forming apparatus according to claim 2, wherein the control unit attaches toner to the non-passing portion corresponding to the resistance value corrected by the correction unit.   The image forming apparatus according to claim 1, wherein the control unit adheres toner to the non-passing portion before forming an image in which a recording material does not pass through the nip portion.   The control means causes toner to adhere to the non-passing portion before the recording material that follows the recording material passes through the nip portion and before the recording material reaches the nip portion. 2. The image forming apparatus according to item 1.   The image forming apparatus according to claim 1, further comprising a cleaning unit that cleans toner adhering to the transfer unit. An image carrier that carries a toner image formed by developing means for supplying a developer;
Transfer means for holding the recording material at a nip formed by the image carrier and transferring the toner image to the recording material;
Determining means for determining the charge amount of toner in the developing means;
Control means for causing toner to adhere to a non-passing portion of at least one recording material of the transfer means or the image carrier in accordance with a determination result by the determination means;
An image forming apparatus comprising:   The image forming apparatus according to claim 10, wherein the control unit sets at least one of a timing for supplying toner from the developing unit and a supply amount of toner to the non-passing portion. Environmental detection means for detecting environmental information;
An operation time storage means for storing an operation time from the start time to the end time of the immediately preceding print job;
A standby time storage means for storing a standby time from the end time of the immediately preceding print job to the start time of the next print job;
Have
The control means includes
Based on the temperature / humidity result detected by the environment detection unit from at least one of the operation time of the immediately preceding print job stored in the operation time storage unit and the standby time stored in the standby time storage unit. The image forming apparatus according to claim 10, wherein the determination unit corrects a charge amount of toner in the developing unit. An image carrier for carrying a toner image developed by a developing means for supplying a developer;
Charging means for charging the image carrier;
Image exposing means for exposing the image carrier uniformly charged by the charging means to form an electrostatic latent image;
Developing means for supplying a developer to the electrostatic latent image formed on the image carrier to form a toner image;
A transfer means for transferring the toner image onto the recording material by holding the recording material conveyed at a nip formed by the image carrier;
A charging bias voltage applied to the charging unit, an exposure pattern for exposing the image carrier by the image exposure unit, an exposure intensity for exposing the image carrier by the image exposure unit, and a developing bias voltage applied to the developing unit. Setting means for setting at least one of the conditions;
Have
A charging bias voltage applied to the charging unit by the setting unit, an exposure pattern for exposing the image carrier by the image exposure unit, an exposure intensity for exposing the image carrier by the image exposure unit, and an application to the developing unit By changing at least one of the conditions of the developing bias voltage, a toner having a higher charge amount than that at the time of normal image formation is attached to a non-passing portion of the transfer unit or at least one recording material of the transfer unit. Control means;
An image forming apparatus comprising:   The image forming apparatus according to claim 13, wherein a toner having a charge amount higher than that during normal image formation is attached to the non-passing portion before the recording material reaches the nip portion.   The image forming apparatus according to claim 14, wherein the transfer unit is not cleaned until the width in the direction intersecting the conveyance direction of the recording material detected by the size detection unit is changed.

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