JP2009003483A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always discharge a fixed amount, irrespective of fluctuation of the resistance value of an charging member due to an environment and a manufacturing time, and to uniformly charge an image carrier 1 without causing troubles, such as deterioration in the image carrier, toner melt-sticking and image deletion with respect to an image forming apparatus where the image carrier 1 is charged by a charging means 2 with a voltage disposed in proximity or in contact with the image carrier. <P>SOLUTION: The image forming apparatus includes: a means S1 for applying a voltage to the charging means 2; a control means 13 for controlling a voltage value to be applied to the charging means; and a current value measuring means 14 for measuring the AC current value flowing in the charging means through the image carrier. During the non image formation period, current values are measured upon application of at least one or more peak-to-peak voltages less than two times a discharge start voltage Vth to the charging means and upon application of at least two or more peak-to-peak voltages not less than two times Vth, and a peak-to-peak voltage of the AC voltage to be applied to the charging means during an image formation period is determined based on the measured AC current values. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging control method and an image forming apparatus.

  More specifically, the present invention relates to a charging control method and an image forming apparatus in an image forming apparatus in which charging of an image carrier is performed by a charging unit that is arranged close to or in contact with the image carrier and to which voltage is applied.

  Conventionally, for example, as a method of charging the surface of an image carrier as a charged body such as a photoconductor or a dielectric in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, corona charging which is non-contact charging is generally used. It was the target. In this method, a corona generated by applying a high voltage to a thin corona discharge wire is applied to the surface of the image carrier to perform charging.

  In recent years, from the viewpoints of low-pressure process, low ozone generation, and low cost, a roller-type or blade-type charging member is brought into contact with the surface of the image carrier, and a voltage is applied to the charging member to Contact charging methods for charging are becoming mainstream. In particular, a roller-type charging member can perform stable charging over a long period of time.

  The voltage applied to the charging member may be only a DC voltage, but charging can be performed uniformly by applying an oscillating voltage and alternately causing discharge to the plus side and minus side.

  For example, a vibration in which an alternating voltage having a peak-to-peak voltage that is twice or more the discharge start threshold voltage (charging start voltage) of the object to be charged when a DC voltage is applied and a DC voltage (DC offset bias) are superimposed. Apply voltage. As a result, it is known that there is an effect of leveling the charge of the member to be charged and uniform charging is performed.

  The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. The oscillating voltage is a rectangular wave voltage formed by periodically turning on / off the DC voltage, or the same output as the superimposed voltage of the AC voltage and the DC voltage by periodically changing the value of the DC voltage. Including.

  As described above, a contact charging method in which an oscillating voltage is applied to the charging member for charging is hereinafter referred to as an “AC charging method”. A contact charging method in which only a DC voltage is applied for charging is referred to as a “DC charging method”.

  However, in the AC charging method, compared to the DC charging method, the amount of discharge to the image carrier increases, so that the image carrier deterioration such as scraping of the image carrier is promoted, and in the high temperature and high humidity environment due to the discharge product. Abnormal images such as image flow may occur.

  In order to improve this problem, it is necessary to minimize the discharge that occurs alternately on the positive side and the negative side by applying the minimum necessary voltage.

  However, in reality, the relationship between the voltage and the discharge amount is not always constant, and changes depending on the film thickness of the photosensitive layer and dielectric layer of the image carrier, the environmental variation of the charging member and air, and the like. In a low-temperature and low-humidity environment (L / L), the material dries and the resistance value increases, making it difficult to discharge. Therefore, in order to obtain uniform charging, a peak-to-peak voltage of a certain value or more is required. However, even when the charging operation is performed in a high-temperature and high-humidity environment (H / H) even at the lowest voltage value at which charging uniformity is obtained in this L / L environment, the material absorbs moisture and the resistance value decreases. For this reason, the charging member causes more discharge than necessary. As a result, when the discharge amount increases, problems such as image flow / blurring, toner fusion, and image carrier scraping / shortening due to deterioration of the surface of the image carrier occur.

  In order to suppress the increase / decrease in discharge due to environmental fluctuations, in addition to the “AC constant voltage control method” in which a constant AC voltage is always applied as described above, the AC current value that flows by applying an AC voltage to the charging member An “AC constant current control method” for controlling the above has been proposed. According to this AC constant current control system, the peak voltage value of the AC voltage is increased in an L / L environment where the material resistance increases, and conversely, the peak voltage value is decreased in an H / H environment where the material resistance decreases. Therefore, increase / decrease in discharge can be suppressed as compared with the AC constant voltage control method.

  Here, the charging member is not necessarily in contact with the image carrier surface. In other words, if even a dischargeable region determined by the gap voltage and the corrected Paschen curve is reliably ensured between the charging member and the image carrier, for example, a gap (gap) of several tens of μm exists and is arranged in a non-contact manner. (Proximity charging). In the present invention, this proximity charging also falls within the category of contact charging.

  However, when aiming to further extend the life of the image carrier, even in the AC constant current control system, the variation in the resistance value due to manufacturing variation and contamination of the charging member, the capacitance fluctuation of the image carrier due to durability, the main body high voltage device It is not perfect for suppressing the increase and decrease of the discharge amount due to the variation of the current. In order to suppress the increase / decrease in the discharge amount, it is necessary to take measures to suppress the manufacturing variation of the charging member and the environmental fluctuation and to eliminate the high-voltage fluctuation, thereby increasing the cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems with respect to an image forming apparatus in which charging of an image carrier is performed by a charging unit that is placed in proximity to or in contact with the image carrier and to which a voltage is applied. In other words, regardless of the variation in the resistance value of the charging member due to the environment or manufacturing, there is no problem of deterioration of the image carrier, toner fusion, image flow, etc. by always causing a certain amount of discharge without causing excessive discharge. The voltage and current applied to the charging means are appropriately controlled so that uniform charging can be performed. This aims to stably maintain high image quality and high quality over a long period of time.

  The present invention is a charge control method in an image forming apparatus and an image forming apparatus characterized by the following means and configuration.

(1) In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier.
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
Means for applying a superposed voltage of either or both of DC voltage and AC voltage to the charging means;
Means for controlling each voltage value of the DC voltage applied to the charging means and the peak-to-peak voltage of the AC voltage;
Means for measuring an alternating current value flowing to the charging means via the image carrier;
When the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, at the time of non-image formation, the charging means has at least one point between peaks less than twice Vth Measures the current value when a voltage is applied and the current value when a peak-to-peak voltage that is at least twice the Vth of at least two points is applied, and applies the measured alternating current value to the charging means during image formation A charging control method characterized by determining a peak-to-peak voltage of an alternating voltage to be applied.

(2) A peak-to-peak voltage-alternating current function obtained by connecting 0 to a current value when a peak-to-peak voltage less than twice Vth of one point is applied to the charging means with D being a predetermined constant. By comparing fI1 (Vpp) with the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of at least two points is applied.
fI2 (Vpp) −fI1 (Vpp) = D
The voltage according to (1) is characterized in that the peak-to-peak voltage value is determined, and the peak-to-peak voltage of the AC voltage applied to the charging means during image formation is controlled by the determined peak-to-peak voltage value. Control method.

(3) The peak-to-peak voltage-alternating current function fI1 (Vpp) obtained from the current value when D is a predetermined constant and a voltage less than twice the Vth of at least two points is applied to the charging means. And the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when at least two times the peak-to-peak voltage of Vth is applied.
fI2 (Vpp) −fI1 (Vpp) = D
The voltage according to (1) is characterized in that the peak-to-peak voltage value is determined, and the peak-to-peak voltage of the AC voltage applied to the charging means during image formation is controlled by the determined peak-to-peak voltage value. Control method.

  (4) An environment detection unit that detects an environment in which the image forming apparatus is installed has an environment detection unit that measures the peak-to-peak voltage values of multiple stages of AC voltage applied to the charging unit during AC current value measurement during non-image formation. The charging control method according to (2) or (3), wherein the charging is changed for each environment detected by the means.

  (5) Having an environment detection means for detecting the environment in which the image forming apparatus is installed, and from the peak-to-peak voltage-alternating current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the alternating current value during non-image formation. , FI2 (Vpp) −fI1 (Vpp) = D, the constant D used when determining the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is changed for each environment detected by the environment detection unit. The charge control method according to (2) or (3), characterized in that:

  (6) It has an environment detection means for detecting the environment where the image forming apparatus is installed, and the environment detection means detects the multi-step peak-to-peak voltage value applied to the charging means when measuring the alternating current value during non-image formation. FI2 (Vpp) −fI1 (Vpp) = D from the peak-to-peak voltage-alternating current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the alternating current value during non-image formation. (2) or (3), wherein the constant D used to determine the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is changed for each environment detected by the environment detection unit. The charge control method described in 1.

(7) In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier.
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
Means for applying at least an alternating current to the charging means;
Means for controlling the AC current value applied to the charging means;
Means for measuring the peak-to-peak voltage value of the alternating voltage applied to the charging means;
When the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, the charging means has a peak interval less than twice Vth of at least one point during non-image formation. It is measured by measuring the voltage value when an alternating current that is a voltage is applied and the peak-to-peak voltage value of the alternating voltage when an alternating current that is a peak-to-peak voltage that is at least twice the Vth of at least two points is applied. A charge control method characterized in that an alternating current value to be applied to the charging means during image formation is determined based on the peak-to-peak voltage value.

(8) The peak-to-peak value obtained by connecting 0 to the voltage value when an alternating current value that is less than twice the Vth of one point is applied to the charging means with D being a predetermined constant. Voltage-alternating current function fI2 (Vpp) and peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the voltage value when applying an alternating current value that is a peak-to-peak voltage more than twice Vth at least two points ) And
fI2 (Vpp) = fI1 (Vpp) + D
The AC control value according to (7), wherein the AC current value to be applied is determined, and the AC current value applied to the charging means during image formation is controlled by the determined AC current value.

(9) The peak-to-peak voltage-alternating current obtained from the voltage value when D is a predetermined constant and an alternating current value that is less than twice the Vth of at least two points is applied to the charging means. Comparing the function fI1 (Vpp) with the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the voltage value when an alternating current value that is at least twice the peak voltage of Vth at least two points is applied By doing
fI2 (Vpp) = fI1 (Vpp) + D
The AC control value according to (7), wherein the AC current value to be applied is determined, and the AC current value applied to the charging means during image formation is controlled by the determined AC current value.

  (10) An environment detection unit that detects an environment in which the image forming apparatus is installed has a plurality of AC current values to be applied to the charging unit when measuring the AC peak-to-peak voltage value during non-image formation. The charging control method according to (8) or (9), wherein the charging is changed for each environment detected by the means.

  (11) It has an environment detection means for detecting the environment in which the image forming apparatus is installed, and the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 obtained by measuring the peak-to-peak voltage value of the AC voltage during non-image formation. From (Vpp), the constant D used to determine the alternating current applied to the charging means during image formation by fI2 (Vpp) = fI1 (Vpp) + D is changed for each environment detected by the environment detection means. (8) or (9).

  (12) An environment detection unit that detects an environment in which the image forming apparatus is installed has an environment detection unit that detects a plurality of AC current values applied to the charging unit when measuring the peak-to-peak voltage value of the AC voltage during non-image formation. It is changed for each environment detected by the means, and from the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value during non-image formation, fI2 (Vpp) = fI1 ( (8) or (9), characterized in that the constant D used when determining the alternating current applied to the charging means during image formation is changed for each environment detected by the environment detecting means by Vpp) + D. The charge control method as described.

  (13) The image forming apparatus includes an image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage, and an electrostatic latent image is applied to the charged image carrier. An information writing unit that forms an image, a developing unit that supplies toner to the electrostatic latent image to visualize the electrostatic latent image, and a transfer unit that transfers the visualized toner image to a transfer material (1) ) To (12).

  (14) The charging control method according to (13), wherein the information writing unit is an exposure unit.

(15) In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier.
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier, according to any one of (1) to (12) An image forming apparatus, wherein a charging process of an image carrier by a charging unit is controlled by a charging control method.

  (16) An image forming apparatus includes an image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage, and an electrostatic latent image is applied to the charged image carrier. An information writing unit that forms an image, a developing unit that supplies toner to the electrostatic latent image to visualize the electrostatic latent image, and a transfer unit that transfers the visualized toner image to a transfer material (15) ).

  (17) The image forming apparatus according to (16), wherein the information writing unit is an exposure unit.

  That is, the present invention controls the peak-to-peak voltage or current of the AC voltage applied to obtain a desired discharge in contact charging by the AC charging method. In other words, by measuring the relationship between voltage and current during non-image formation, the peak-to-peak voltage or the peak discharge voltage can always be obtained regardless of the environment, variations in manufacturing of the charging member, variations in the main body high voltage device, etc. An alternating current can be applied. As a result, it has become possible to perform image formation without causing problems due to excessive discharge and insufficient discharge, which are concerns of conventional AC constant voltage control and AC constant current control.

  Thus, according to the present invention, the above-described problems can be solved for an image forming apparatus in which charging of an image carrier is performed by a charging unit that is placed close to or in contact with the image carrier and to which a voltage is applied. In other words, regardless of the variation in the resistance value of the charging member due to the environment or manufacturing, there is no problem of deterioration of the image carrier, toner fusion, image flow, etc. by always generating a certain amount of discharge without causing excessive discharge. The voltage and current applied to the charging means can be appropriately controlled so that uniform charging can be performed. As a result, high image quality and high quality can be stably maintained over a long period of time.

<Example 1> (FIGS. 1 to 7)
FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer having a transfer type electrophotographic process, a contact charging method, a reverse development method, and a maximum sheet passing size of A3 size.

(1) Overall schematic configuration of printer a) Image carrier 1 is a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. This photosensitive drum 1 is a negatively charged organic photoconductor (OPC), has an outer diameter of 25 mm, and rotates in the counterclockwise direction indicated by an arrow with a process speed (peripheral speed) of 100 mm / sec around the center support shaft. Driven.

  The photosensitive drum 1 has a configuration as shown in a layer configuration model diagram of FIG. That is, on the surface of an aluminum cylinder (conductive drum base) 1a, three layers of an undercoat layer 1b for suppressing light interference and improving the adhesion of the upper layer, a photocharge generation layer 1c, and a charge transport layer 1d are provided. It is structured to be repainted in order from the bottom.

b) Charging means 2 is a contact charging device (contact charger) as a charging means for uniformly charging the peripheral surface of the photosensitive drum 1, and in this example, a charging roller (roller charger).

  The charging roller 2 holds both ends of the cored bar 2a rotatably by bearing members (not shown), and is urged in the direction of the photosensitive drum by a pressing spring 2e to be applied to the surface of the photosensitive drum 1. It is in pressure contact with a predetermined pressing force. The charging roller 2 rotates following the rotation of the photosensitive drum 1. A pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a.

  By applying a charging bias voltage of a predetermined condition from the power source S1 to the core 2a of the charging roller 2, the peripheral surface of the rotating photosensitive drum 1 is uniformly contact-charged to have a negative polarity in this example. .

  The configuration of the charging roller 2 and the charging control method will be described in detail in section (3).

c) Information writing means 3 is an exposure apparatus as information writing means for forming an electrostatic latent image on the surface of the charged photosensitive drum 1, and this example is a laser beam scanner using a semiconductor laser. A laser beam modulated in response to an image signal sent from a host device such as an image reading device (not shown) to the printer side is output to perform laser scanning on the uniformly charged surface of the rotating photosensitive drum 1 at the exposure position b. Exposure L (image scanning exposure) is performed. By this laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is lowered, so that an electrostatic latent image corresponding to the scanned and exposed image information is sequentially formed on the surface of the rotating photosensitive drum 1. It will be done.

d) Developing means 4 is a jumping developing device (developer) in this example as developing means for supplying a developer (toner) to the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. . The electrostatic latent image formed on the surface of the photosensitive drum 1 is reversely developed with the one-component magnetic toner (negative toner) negatively charged by the developing device 4.

  4a is a developing container, 4b is a non-magnetic developing sleeve, and this developing sleeve 4b is rotatably arranged in the developing container 4a with a part of its outer peripheral surface exposed to the outside. 4c is a non-rotating magnet roller fixedly inserted in the developing sleeve 4b, 4d is a developer coating blade, 4e is a one-component magnetic toner as a developer contained in the developing container 4a, and S2 is a developing for the developing sleeve 4b. This is a bias application power source.

  Accordingly, the surface of the developing sleeve 4b rotating in the counterclockwise direction indicated by the arrow is coated as a thin layer, and the one-component magnetic toner conveyed to the developing unit c is electrostatically latentized on the surface of the photosensitive drum 1 by the electric field due to the developing bias. It selectively adheres corresponding to the image. As a result, the electrostatic latent image is developed as a toner image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

  The developer thin layer on the developing sleeve 4b that has passed through the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.

e) Transfer means / fixing means / cleaning means 5 is a transfer device, and in this example is a transfer roller. The transfer roller 5 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, and the pressure nip portion is a transfer portion d. A transfer material (a member to be transferred, a recording material) P is fed to the transfer portion d from a paper feeding mechanism portion (not shown) at a predetermined control timing.

  The transfer material P fed to the transfer part d is nipped between the rotating photosensitive drum 1 and the transfer roller 5 and conveyed. During the conveyance, a positive transfer bias having a polarity opposite to the negative polarity that is the normal charging polarity of the toner is applied to the transfer roller 5 from the power source S3. As a result, the toner image on the surface of the photosensitive drum 1 is sequentially electrostatically transferred onto the surface of the transfer material P that is nipped and conveyed by the transfer portion d.

  The transfer material P which has received the transfer of the toner image through the transfer portion d is sequentially separated from the surface of the rotating photosensitive drum 1 and conveyed to the fixing device 6 (for example, a heat roller fixing device) to receive the toner image fixing process. Output as an image formed product (print, copy).

  Reference numeral 7 denotes a cleaning device. The surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is rubbed by the cleaning blade 7a to be cleaned to remove the transfer residual toner, and repeatedly used for image formation. The e is a photosensitive drum surface contact portion of the cleaning blade 7a.

(2) Printer Operation Sequence FIG. 3 is an operation sequence diagram of the printer.

a. Initial rotation operation (front multiple rotation process)
This is a start operation period (start operation period, warming period) when the printer is started. When the power switch is turned on, the photosensitive drum is rotationally driven, and a preparatory operation of a predetermined process device such as starting up the fixing device to a predetermined temperature is executed.

b. Print preparation rotation operation (pre-rotation process)
Print signal-This is a preparatory rotation operation period before image formation from when the image formation (printing) process operation is actually performed, and is executed following the initial rotation operation when a print signal is input during the initial rotation operation. Is done. When the print signal is not input, the main motor is temporarily stopped after the initial rotation operation is completed, and the photosensitive drum is stopped from rotating. The printer is kept in a standby (standby) state until the print signal is input. When the print signal is input, the print preparation rotation operation is executed.

  In the present embodiment, during this printing preparation rotation operation period, an appropriate peak-to-peak voltage value (or alternating current value) calculation / determination program for the applied alternating voltage in the charging step of the printing step is executed. This will be described in detail in section (3) below.

c. Printing process (image forming process, image forming process)
When the predetermined print preparation rotation operation is completed, an image forming process for the rotating photosensitive drum is subsequently executed, and the toner image formed on the surface of the rotating photosensitive drum is transferred to a transfer material, and the fixing process of the toner image by the fixing device is performed. The image formation is printed out.

  In the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined set number of prints n.

d. Inter-sheet process In the continuous printing mode, after the trailing edge of one transfer material passes the transfer position d, the recording paper at the transfer position until the leading edge of the next transfer material reaches the transfer position d. This is a non-paper passing period.

e. Post-rotation operation This is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while after the last transfer material printing process is completed and rotating the photosensitive drum.

f. Standby When the predetermined post-rotation operation is completed, the drive of the main motor is stopped, the rotation of the photosensitive drum is stopped, and the printer is kept in a standby state until the next print start signal is input.

  In the case of printing only one sheet, after the printing is completed, the printer goes into a standby state through a post-rotation operation.

  When the print start signal is input in the standby state, the printer proceeds to the pre-rotation process.

  The printing process of c is the time of image formation, and the initial rotation operation of a, the pre-rotation operation of b, the paper gap process of d, and the post-rotation operation of e are non-image formation.

(3) Detailed description of charging means A) Charging roller 2
The longitudinal length of the charging roller 2 as the contact charging member is 320 mm. As shown in the layer configuration model diagram of FIG. 1, the lower layer 2b, the intermediate layer 2c, and the surface layer 2d are disposed around the core metal (support member) 2a. Is a three-layer structure in which are sequentially stacked from the bottom. The lower layer 2b is a foamed sponge layer for reducing charging noise, the intermediate layer 2c is a conductive layer for obtaining a uniform resistance as a whole of the charging roller, and the surface layer 2d has defects such as pinholes on the photosensitive drum 1. This is a protective layer provided to prevent the occurrence of leaks even if there is.

  More specifically, the specification of the charging roller 2 of this example is as follows.

Core metal 2a; stainless steel round bar with a diameter of 6 mm Lower layer 2b; Foamed EPDM with carbon dispersion, specific gravity 0.5 g / cm ³ , volume resistivity 10 ³ Ω
cm, layer thickness 3.0 mm, length 320 mm
Intermediate layer 2c: carbon-dispersed NBR rubber, volume resistivity 10 ⁵ Ωcm, layer thickness 700 μm
Surface layer 2d: tin oxide and carbon dispersed in a resin resin of fluorine compound, volume resistivity 10 ⁸
Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer
10 μm thick
B) Charging Bias Application System FIG. 4 is a block circuit diagram of a charging bias application system for the charging roller 2.

  A predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage of frequency f on a DC voltage from the power source S1 is applied to the charging roller 2 through the core metal 2a, so that the peripheral surface of the rotating photosensitive drum 1 is It is charged to a predetermined potential.

  A power source S 1 that is a voltage application unit for the charging roller 2 includes a direct current (DC) power source 11 and an alternating current (AC) power source 12.

  Reference numeral 13 denotes a control circuit which controls the DC power supply 11 and the AC power supply 12 of the power supply S1 so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 2. It has the function to do. The control circuit 13 has a function of controlling the DC voltage value applied to the charging roller 2 from the DC power source 11 and the peak-to-peak voltage value of the AC voltage applied from the AC power source 12 to the charging roller 2.

  Reference numeral 14 denotes an AC current value measurement circuit as means for measuring the AC current value flowing through the charging roller 2 via the photosensitive member 1. The measured AC current value information is input from the circuit 14 to the control circuit 13.

  Reference numeral 15 denotes an environment sensor (thermometer and hygrometer) as means for detecting the environment where the printer is installed. The detected environmental information is input from the environmental sensor 15 to the control circuit 13.

  The control circuit 13 has a function of executing a calculation / determination program. That is, the control circuit 13 determines an appropriate peak of the applied AC voltage to the charging roller 2 in the charging process of the printing process from the AC current value information input from the AC current value measuring circuit 14 and the environmental information input from the environment sensor 15. Execute the inter-voltage value calculation / determination program.

C) Control Method for Peak Voltage of AC Voltage Next, a control method for the peak voltage of the AC voltage applied to the charging roller 2 during printing will be described.

  Based on various studies, the inventors have shown that the amount of discharge current quantified according to the following definition represents the actual amount of AC discharge, and has a strong correlation with the photoconductor drum scraping, image flow, and charging uniformity. Found that there is.

  That is, as shown in FIG. 5, the alternating current Iac is in a linear relationship with the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) (undischarged region), and gradually increases from that point toward the discharge region. In the direction of increasing current. In a similar experiment in a vacuum where no discharge occurs, a straight line is maintained, so this is considered to be the increment ΔIac of the current involved in the discharge.

Therefore, when the ratio of the current Iac to the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) is α, AC current such as current flowing to the contact portion (hereinafter referred to as nip current) other than current due to discharge The current becomes α · Vpp, and the difference between Iac measured when a voltage higher than the discharge start voltage Vth × 2 (V) is applied, and this α · Vpp,
Formula 1... ΔIac = Iac−α · Vpp
To ΔIac is defined as a discharge current amount that indicates the amount of discharge instead.

  The amount of discharge current changes as the environment and durability are increased when charging is performed under the control of a constant voltage or a constant current. This is because the relationship between the peak-to-peak voltage and the discharge current amount and the relationship between the alternating current value and the discharge current amount are fluctuating.

  In the AC constant current control method, control is performed with the total current flowing from the charging member to the member to be charged. As described above, the total current amount is the sum of the nip current α · Vpp and the discharge current amount ΔIac that flows by discharging at the non-contact portion. In constant current control, the charged object is actually charged. In addition to the discharge current, which is the current required for the control, the nip current is controlled.

  For this reason, the amount of discharge current cannot actually be controlled. Even when the constant current control is performed with the same current value, the discharge current amount naturally decreases as the nip current increases due to the environmental fluctuation of the material of the charging member. If the nip current decreases, the amount of discharge current increases. Therefore, even with the AC constant current control method, it is impossible to completely suppress the increase / decrease in the discharge current amount, and it is difficult to realize both the shading of the photosensitive drum and the charging uniformity when aiming for a long life. there were.

  Therefore, the present inventors performed control in the following manner in order to always obtain a desired discharge current amount.

  A method of determining the peak-to-peak voltage that becomes the discharge current amount D when the desired discharge current amount is D will be described.

  In this embodiment, the control circuit 13 executes an appropriate peak-to-peak voltage value calculation / determination program for the charging roller 2 in the charging process during the printing process during the printing preparation rotation operation.

  Concretely, it demonstrates with reference to the Vpp-Iac graph of FIG. 6, and the control flowchart of FIG.

  The control circuit 13 controls the AC power source 12, and as shown in FIG. 6, the charging roller 2 has three points of peak-to-peak voltage (Vpp) that is a discharge region and three points of peak-to-peak voltage that is an undischarged region. Apply to. Then, the alternating current value flowing through the charging roller 2 via the photosensitive member 1 at that time is measured by the alternating current value measuring circuit 14 and input to the control circuit 13.

  Next, the control circuit 13 linearly approximates the relationship between the peak-to-peak voltage in the discharged and undischarged regions and the alternating current from the measured current values at the three points using the least square method, Equation 3 is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX + A
Equation 3 ... Approximate straight line of undischarged region: Y _β = βX + B
After that, the peak-to-peak voltage Vpp at which the difference between the approximate straight line of the discharge area of Expression 2 and the approximate straight line of the undischarged area of Expression 3 becomes the discharge current amount D is determined by Expression 4.

Formula 4... Vpp = (D−A + B) / (α−β)
Here, the peak-to-peak voltage (Vpp) -alternating current (Iac) functions fI1 (Vpp) and fI2 (Vpp) in the undischarged region and the discharged region described in the claims are expressed by Y _β = βX _β Corresponds to + B and Y _α = αX _α + A in Equation 2. The constant D described in the claims corresponds to the desired discharge current amount D.

Therefore, fI2 (Vpp) −fI1 (Vpp) = D described in the claims is Y _α −Y _β = (αX _α + A) − (βX _β + B) = D
It becomes.

From fI2 (Vpp) -fI1 (Vpp) = D, Vpp = (D−A + B) / (α−β)
Induction is as follows.

fI2 (Vpp) −fI1 (Vpp) = Y _α −Y _β = D
(ΑX _α + A) − (βX _β + B) = D
Now looking for the value of X that becomes D, and if that point is Vpp,
(ΑVpp + A) − (βVpp + B) = D
Therefore, Vpp = (D−A + B) / (α−β).

  Then, the peak-to-peak voltage applied to the charging roller 2 is switched to Vpp obtained by the above equation 4, the constant voltage control is performed, and the process proceeds to the above-described printing process.

  In this manner, the peak-to-peak voltage necessary for obtaining a predetermined discharge current amount at the time of printing is calculated every time printing preparation is rotated. During printing, the obtained peak-to-peak voltage is applied by constant voltage control. As a result, it is possible to absorb the fluctuation of the resistance value caused by the manufacturing variation of the charging roller 2 and the environmental variation of the material and the high voltage variation of the main body device, and to obtain a desired discharge current amount with certainty.

  When durability was examined under this control, no deterioration or abrasion of the photosensitive drum as an image carrier occurred in any environment, and about 10% of the photosensitive drum compared with the conventional constant current control. Long service life can be realized.

  In this embodiment, the peak-to-peak voltage of the AC voltage applied to the charging roller is switched. This controlled the amount of discharge current. However, it is not limited to this. Conversely, by applying an alternating current, the peak-to-peak voltage of the alternating voltage is measured (the alternating current value measuring circuit 14 in FIG. 4 is changed to a peak-to-peak voltage value measuring circuit). The output AC current of the AC power source can be controlled at a constant current by the control circuit 13 so that an AC current necessary for obtaining a desired discharge current amount can always be applied during printing.

  Further, in this embodiment, the desired discharge current amount D and the peak-to-peak voltage value applied during the print preparation rotation are made constant in each environment. However, in a device in which the environment sensor (thermometer and hygrometer) 15 is installed, it is possible to perform more stable and uniform charging by changing each value for each environment.

  Thus, during printing preparation rotation, several points in the undischarged area and several points in the discharging area are sequentially applied to the charging roller 2 to measure the AC voltage value, and the peak-to-peak voltage applied during printing is determined. To do. As a result, by applying a peak-to-peak voltage or an alternating current that can always obtain the desired amount of discharge current, it is possible to achieve both deterioration and shaving of the photoconductor and charging uniformity, realizing a longer life and higher image quality. It has become possible.

  Furthermore, since variations at the time of manufacturing can be absorbed, the permissible range of materials and accuracy is widened, so that the cost of manufacturing can be reduced and products can be provided to users at low cost.

<Example 2> (FIG. 8)
This embodiment is a one-point control and constant voltage control system. As shown in FIG. 8, the image forming apparatus is configured to sequentially charge the charging roller with two points of peak-to-peak voltage (Vpp) that is a discharge region and one point of peak-to-peak voltage that is an undischarged region. Apply and measure the alternating current value at that time. The relationship between the peak-to-peak voltage and the alternating current is set in advance so that when the peak-to-peak voltage is zero, the alternating current value is also zero.

  Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current using the measurement value 2 points in the discharge region and the measurement value 0 point in the non-discharge region. Is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX _α + A
Formula 3 ... Approximate straight line of undischarged region: Y _β = βX _β
Then, the difference between the approximate line Y _beta approximate straight line Y _alpha and non-discharge region of the discharge region, the peak-to-peak voltage Vpp of the discharge current amount D is determined by Equation 4.

Formula 4... Vpp = (D−A) / (α−β)
Then, the peak-to-peak voltage applied to the charging member is switched to Vpp obtained (constant voltage control using Vpp), and the process proceeds to the image forming operation described above.

  By adopting such a control configuration, it is possible to obtain the same effect as in the first embodiment with a small number of measurement points.

  As for the one-point control system as in the present embodiment, as a broader meaning, it may not be zero here. For example, if the amount of current flowing at a certain Vpp is known in advance, the relationship between the peak-to-peak voltage and the alternating current can be obtained using that point and the measurement point. If at least one point is measured, the relationship between the peak-to-peak voltage and the alternating current can be obtained.

<Example 3> (FIG. 9)
The present embodiment is a system of three-point control and constant current control, and a method of determining an alternating current value that becomes the discharge current amount D when D is a desired discharge current amount will be described.

  As shown in FIG. 9, the image forming apparatus sequentially applies the charging roller to the charging roller with three points of alternating current (Iac) that is a discharge region and three points of alternating current that is an undischarged region to the charging roller during print preparation rotation. Measure the peak-to-peak voltage at that time.

  Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current in the discharged and undischarged regions from the measured current values at the three points using the least square method, Equation 3 is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX _α + A
Formula 3 ... Approximate straight line in the undischarged region: Y _β = βX _β + B
Then, the difference between the approximate line Y _beta approximate straight line Y _alpha and undischarged areas of the discharge region, the alternating current as a discharge current amount D a (Iac) is determined by Equation 4.

If the alternating current value for D is Iac1, and the peak-to-peak voltage at that time is Vpp, then Equations 2 and 3 are
Iac1 = αVpp + A Expression a
Iac2 = βVpp + B Formula b
It becomes. Here, Iac2 is an AC current value becomes the Vpp of the approximate straight line Y _beta undischarged areas.

Iac1 = Iac2 + D (Formula c)
From the equations a, b, and c, the alternating current (Iac) that becomes the discharge current amount D is determined by the equation 4.

Formula 4... Iac = (αD + αB−βA) / (α−β)
Then, the AC current applied to the charging member is switched to the obtained Iac, the constant current is controlled by the Iac, and the process proceeds to the above-described image forming operation.

<Example 4> (FIG. 10)
The present embodiment is a one-point control and constant current control system, and a method of determining an alternating current value that becomes the discharge current amount D when the desired discharge current amount is D will be described.

  As shown in FIG. 10, the image forming apparatus sequentially applies two points of alternating current (Iac) that is a discharge area to the charging roller and one point of alternating current that is an undischarged area to the charging roller during print preparation rotation. Then, the peak-to-peak voltage value at that time is measured.

  Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current using the measurement value 2 points in the discharge region and the measurement value 0 point in the non-discharge region. Is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX _α + A
Formula 3 ... Approximate straight line of undischarged region: Y _β = βX _β
Then, the difference between the approximate line Y _beta approximate straight line Y _alpha and undischarged areas of the discharge region, the alternating current as a discharge current amount D a (Iac) is determined by Equation 4.

When the alternating current value for D is Iac1, and the peak-to-peak voltage at that time is Vpp, Equations 2 and 3 are
Iac1 = αVpp + A Expression a
Iac2 = βVpp Formula b
It becomes. Here, Iac2 is an AC current value becomes the Vpp of the approximate straight line Y _beta undischarged areas.

Iac1-Iac2 = D... Formula c
From the equations a, b, and c, the alternating current (Iac) that becomes the discharge current amount D is determined by the equation 4.

Formula 4... Iac = (αD−βA) / (α−β)
Then, the AC current applied to the charging member is switched to the obtained Iac, the constant current is controlled by the Iac, and the process proceeds to the above-described image forming operation.

<Example 5> (FIG. 11)
FIG. 11 is a schematic configuration model diagram of the image forming apparatus in the present embodiment. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a contact charging method, a reversal development method, cleaner-less, and a maximum sheet passing size of A3 size.

  Constituent members / portions common to the printer of the first embodiment are denoted by the same reference numerals and description thereof is omitted, and constituent members / portions / items different from those of the printer of the first embodiment are described.

(1) Overall Schematic Configuration of Printer In the printer of this embodiment, the photosensitive drum 1 as an image carrier has an outer diameter of 50 mm.

  The developing device 4 which is a developing means is a reversal developing device of a two-component magnetic brush developing system, and the electrostatic latent image formed on the surface of the photosensitive drum 1 is sequentially converted into a toner image by the developing device 4 in this example. Reversal development is performed by negatively charged toner (negative toner). The developer 4e accommodated in the developing container 4a is a two-component developer. Reference numeral 4f denotes a developer stirring member disposed on the bottom side in the developing container 4a, and 4g denotes a toner hopper which accommodates replenishing toner.

The two-component developer 4e in the developing container 4a is a mixture of toner and a magnetic carrier and is stirred by the developer stirring member 4f. In this example, the average particle size of the toner is 6 μm, the resistance of the magnetic carrier is about 10 ¹³ Ωcm, and the particle size is about 40 μm. The toner is triboelectrically charged to negative polarity by rubbing with the magnetic carrier.

  The developing sleeve 4b is disposed opposite to the photosensitive drum 1 so that the closest distance (referred to as S-Dgap) to the photosensitive drum 1 is maintained at 350 μm. A facing portion between the photosensitive drum 1 and the developing sleeve 4a is a developing portion c. The developing sleeve 4b is driven to rotate in the direction opposite to the traveling direction of the photosensitive drum 1 in the developing portion c. A part of the two-component developer 4e in the developing container 4a is adsorbed and held on the outer peripheral surface of the developing sleeve 4b as a magnetic brush layer by the magnetic force of the magnet roller 4c in the sleeve. The sleeve is rotated and conveyed with the rotation of the sleeve, is layered into a predetermined thin layer by the developer coating blade 4d, and comes into contact with the surface of the photosensitive drum 1 at the developing portion c to appropriately rub the surface of the photosensitive drum. To do. A predetermined developing bias is applied to the developing sleeve 4b from the power source S2.

  Thus, the toner in the developer coated as a thin layer on the surface of the rotating developing sleeve 4b and conveyed to the developing unit c corresponds to the electrostatic latent image on the surface of the photosensitive drum 1 by the electric field due to the developing bias. As a result, the electrostatic latent image is developed as a toner image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

  The developer thin layer on the developing sleeve 4b that has passed through the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.

  In order to maintain the toner concentration of the two-component developer 4e in the developing container 4a within a predetermined substantially constant range, the toner concentration of the two-component developer 4e in the developing container 4a is adjusted by, for example, an optical toner concentration sensor (not shown). Detected. The toner hopper 4g is driven and controlled according to the detected information, and the toner in the toner hopper is supplied to the two-component developer 4e in the developing container 4a. The toner supplied to the two-component developer 4e is stirred by the stirring member 4f.

(2) Cleanerless system The printer of this example is cleanerless, and does not include a dedicated cleaning device that removes a small amount of transfer residual toner remaining on the surface of the photosensitive drum 1 after the toner image is transferred to the transfer material P. . After the transfer, the untransferred toner on the surface of the photosensitive drum 1 is carried to the developing portion c through the charging portion a and the exposing portion b as the photosensitive drum 1 continues to rotate. Recovered).

  The simultaneous development cleaning is as follows. In other words, the transfer residual toner on the photosensitive member after transfer is collected in the developing device in the developing step after the next step. More specifically, the photosensitive member is subsequently charged, exposed to form an electrostatic latent image, and a portion of the surface of the photosensitive member that should not be developed with toner by a fog removal bias during the developing process of the electrostatic latent image. The existing transfer residual toner is collected by the developing device. The fog removal bias is a fog removal potential difference Vback which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor. According to this method, the transfer residual toner is collected by the developing device and reused for development of the electrostatic latent image in the subsequent process, so that waste toner is eliminated and maintenance work is reduced. Can do. In addition, the cleaner-less configuration is advantageous for downsizing the image forming apparatus.

  A toner charging control unit 8 is disposed at a position downstream of the transfer portion d in the photosensitive drum rotation direction and at a position upstream of the charging portion a in the photosensitive drum rotation direction. This toner charge control means 7 is a brush-shaped member (auxiliary brush) having moderate conductivity, and is arranged with the brush portion in contact with the surface of the photosensitive drum 1, and a negative voltage is applied to the power source S4. Is applied. f is a contact portion between the brush portion and the photosensitive drum 1 surface. The untransferred toner on the photosensitive drum 1 that passes through the toner charge control means 7 is aligned to a negative polarity whose charge polarity is normal.

  That is, the transfer residual toner on the surface of the photosensitive drum 1 after the transfer process includes a negative toner that cannot be completely transferred in the image portion, a positive fog toner that adheres to the non-image portion during development, and a positive transfer voltage. The toner whose polarity is reversed to positive polarity due to the influence of the toner is included. Such a transfer residual toner is uniformly charged to a negative polarity by the toner charge control means 8 described above. In this embodiment, the toner charge control means 8 is applied with −1000 V, which is a voltage at which discharge occurs on the transferred photoreceptor. As a result, the transfer residual toner that passes through the toner charge control means 8 is given a charge by discharging and direct charge injection, and is made negative in polarity.

  In the charging process described above, the surface of the photosensitive drum 1 is charged from above the untransferred toner. Since the polarity of the transfer residual toner is uniformly uniform to the negative polarity, the toner does not adhere to the charging roller 2 to which the negative DC voltage is applied. Even in the exposure process, the exposure is performed from the transfer residual toner, but since the amount of the transfer residual toner is small, there is no significant influence. In the developing process, the transfer residual toner present in the unexposed portion on the photosensitive drum 1 is collected by the developing device due to the electric field.

  As described above, the closest distance (S-Dgap) between the developing sleeve 2b and the photosensitive drum 1 is 350 μm. By maintaining this distance, the magnetic brush of the two-component developer formed on the developing sleeve 4b is appropriately rubbed against the surface of the photosensitive drum 1 to simultaneously collect the development residual toner on the photosensitive drum 1. Further, the developing sleeve 4b is rotated in the direction opposite to the traveling direction of the surface of the photosensitive drum 1 in the developing portion c so as to be advantageous for collecting the transfer residual toner.

(3) Control of peak-to-peak voltage of AC voltage When the AC charging method is used in the cleanerless system, the following problems occur. That is, image flow and blur caused by discharge products generated by AC charging.

  In the case of the AC charging method using contact charging, the amount of generated ozone is small in comparison with the charging process using a corona charger, but it is not completely absent. In the image forming apparatus, the discharge product adheres to the surface of the photoreceptor as the image carrier and further absorbs moisture. This lowers the resistance of the surface of the photosensitive member and reduces the resolution of the latent image. Further, in the image forming apparatus adopting the cleaner-less configuration as described above, the effect of renewing the photosensitive member by the cleaning device cannot be expected, and blurring, image flow, and the like are likely to occur.

  In order to achieve both the above-described problem and charging uniformity, it is necessary to always obtain a desired amount of discharge current, and for this purpose, it is necessary to use the means for controlling the voltage applied to the charging roller according to the present invention.

  The peak-to-peak voltage control of the AC voltage in the present embodiment is performed as follows.

  During printing preparation rotation, three points in the non-discharge region and three points in the discharge region are sequentially applied to the charging roller 2 to measure the AC voltage value, and the peak-to-peak voltage applied during printing is determined. The calculation method of the applied peak-to-peak voltage is the same as the method shown in the first embodiment.

  The apparatus main body used in this embodiment is provided with an environmental sensor 15 (FIG. 4). In each environment, the peak-to-peak voltage applied during printing preparation rotation is varied, and the resistance of the charging roller is reduced. In the environment, a peak-to-peak voltage which is about 10% lower than that in the L / L environment is applied. As a result, it was possible to measure at a value close to the peak-to-peak voltage actually applied at the time of printing, and it became possible to obtain a desired amount of discharge current more reliably.

  Further, the value of the discharge current amount D is also variable for each environment, and in an H / H environment where the amount of discharge current necessary for obtaining charging stability is small and image flow is likely to occur compared to the L / L environment, the L Control was performed to reduce the set discharge current amount D in the / L environment to about 2/3. As a result, even for the above problem, in the H / H environment, about 2/3 times the L / L environment, the image flow and the blurring are reliably prevented in the H / H environment. In the environment, it became possible to carry out stable and uniform charging without generating sand.

  By performing the above control, effects similar to those of the first embodiment are absorbed, that is, the resistance value fluctuation caused by the manufacturing variation of the charging roller and the environmental variation of the material, and the high voltage variation of the main body device are absorbed, and the charging roller is further contaminated. Even at times, it is possible to reliably obtain a desired amount of discharge current. In addition to the effects similar to those of the first embodiment, it is possible to perform fine control with a minimum and necessary discharge current amount in each environment by simultaneously performing environmental control.

  Thus, even when used in a cleaner-less device, it has become possible to stably maintain high image quality and high quality without causing problems such as image flow, charging failure, fusion, and image memory over a long period of time. .

  Of course, it is possible to adopt the control method as in the second to fourth embodiments.

  The configuration of the charge control method or the image forming apparatus of Embodiments 1 to 5 described above is summarized as follows.

  (1) In an image forming apparatus that performs image formation by applying an image forming process including a step of charging the image carrier to the image carrier, charging means for charging the image carrier is close to the image carrier or It is a charging means for charging the surface of the image carrier by being placed in contact and applied with a voltage. Means for applying a superimposed voltage of either DC voltage or AC voltage or both to the charging means, means for controlling each voltage value of the DC voltage and the peak voltage of the AC voltage applied to the charging means, and image bearing Means for measuring an alternating current value flowing through the body to the charging means. Applying a peak-to-peak voltage of at least one point and less than Vth, which is at least one point, at the time of non-image formation, when the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth Measure the current value. In addition, the current value is measured when a peak-to-peak voltage that is at least twice the Vth of at least two points is applied. The charge control method is characterized in that the peak-to-peak voltage of the AC voltage applied to the charging means during image formation is determined based on the measured AC current value.

  (2) Let D be a predetermined constant. Let fI1 (Vpp) be the peak-to-peak voltage-alternating current function obtained by connecting 0 to the current value when a peak-to-peak voltage less than twice Vth at one point is applied to the charging means. In addition, a peak-to-peak voltage-alternating current function obtained from a current value when a peak-to-peak voltage more than twice the Vth at least two points is applied is defined as fI2 (Vpp). Then, by comparing the function fI1 (Vpp) and the function fI2 (Vpp), the peak-to-peak voltage value at which fI2 (Vpp) −fI1 (Vpp) = D is determined. The charge control method according to (1), wherein the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled by the determined peak-to-peak voltage value.

  (3) Let D be a predetermined constant. Let fI1 (Vpp) be the peak-to-peak voltage-AC current function obtained from the current value when at least two points or more of the peak-to-peak voltage less than twice Vth are applied to the charging means. In addition, a peak-to-peak voltage-alternating current function obtained from a current value when a peak-to-peak voltage more than twice the Vth at least two points is applied is defined as fI2 (Vpp). Then, by comparing the function fI1 (Vpp) and the function fI2 (Vpp), the peak-to-peak voltage value at which fI2 (Vpp) −fI1 (Vpp) = D is determined. The charge control method according to (1), wherein the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled by the determined peak-to-peak voltage value.

  (4) It has an environment detection means for detecting the environment where the image forming apparatus is installed. The peak-to-peak voltage value of a plurality of stages of AC voltage applied to the charging unit when measuring the AC current value during non-image formation is changed for each environment detected by the environment detection unit (2) or The charge control method according to (3).

  (5) It has an environment detection means for detecting the environment where the image forming apparatus is installed. From the peak-to-peak voltage-alternating current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the alternating current value during non-image formation, fI2 (Vpp) −fI1 (Vpp) = D Determine the peak-to-peak voltage of the AC voltage to be applied. The charge control method according to (2) or (3), wherein the constant D used for the determination is changed for each environment detected by the environment detection means.

  (6) It has an environment detection means for detecting the environment where the image forming apparatus is installed. Then, a plurality of peak-to-peak voltage values applied to the charging unit when measuring the alternating current value during non-image formation are changed for each environment detected by the environment detection unit. At the same time, the charging means during image formation by fI2 (Vpp) −fI1 (Vpp) = D from the peak-to-peak voltage-alternating current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the alternating current value during non-image formation. The peak-to-peak voltage of the AC voltage applied to is determined. The charge control method according to (2) or (3), wherein the constant D used for the determination is changed for each environment detected by the environment detection means.

  (7) In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier, charging means for charging the image carrier is close to the image carrier or It is a charging means for charging the surface of the image carrier by being placed in contact and applied with a voltage. A means for applying at least an alternating current to the charging means; a means for controlling an alternating current value applied to the charging means; and a means for measuring a peak-to-peak voltage value of the alternating voltage applied to the charging means. Then, when the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, the peak-to-peak voltage less than twice the Vth of at least one point is applied to the charging means during non-image formation. Measure the voltage when an alternating current is applied. Further, the peak-to-peak voltage value of the alternating voltage is measured when an alternating current having a peak-to-peak voltage that is at least twice the Vth of at least two points is applied. A charging control method is characterized in that an alternating current value to be applied to the charging means during image formation is determined based on the measured peak-to-peak voltage value.

  (8) Let D be a predetermined constant. In addition, the peak-to-peak voltage-alternating current function obtained by connecting 0 to the voltage value when an alternating current value having a peak-to-peak voltage less than twice Vth at one point is applied to the charging means is fI1 (Vpp). And Further, a peak-to-peak voltage-alternating current function obtained from a voltage value when an alternating current value having a peak-to-peak voltage that is at least two times Vth at least two points is applied is defined as fI2 (Vpp). Then, by comparing the function fI1 (Vpp) and the function fI2 (Vpp), an alternating current value satisfying fI2 (Vpp) = fI1 (Vpp) + D is determined. The charging control method according to (7), wherein constant current control is performed on the alternating current value applied to the charging unit during image formation based on the determined alternating current value.

  (9) Let D be a predetermined constant. A peak-to-peak voltage-alternating current function obtained from a voltage value when an alternating current value having a peak-to-peak voltage less than twice the Vth of at least two points or more is applied to the charging means is defined as fI1 (Vpp). Further, a peak-to-peak voltage-alternating current function obtained from a voltage value when an alternating current value having a peak-to-peak voltage that is at least two times Vth at least two points is applied is defined as fI2 (Vpp). Then, by comparing the function fI1 (Vpp) and the function fI2 (Vpp), an alternating current value satisfying fI2 (Vpp) = fI1 (Vpp) + D is determined. The charging control method according to (7), wherein the AC current value applied to the charging unit during image formation is controlled by the determined AC current value at a constant current.

  (10) It has an environment detection means for detecting the environment where the image forming apparatus is installed. Then, the AC current values in a plurality of stages applied to the charging unit when measuring the peak-to-peak voltage value of the AC voltage during non-image formation are changed for each environment detected by the environment detecting unit (8). ) Or (9).

  It has environment detection means for detecting the environment where the image forming apparatus is installed. Then, from the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value of the AC voltage during non-image formation, fI2 (Vpp) = fI1 (Vpp) + D The alternating current applied to the charging means is determined. The charging control method according to (8) or (9), wherein the constant D used for the determination is changed for each environment detected by the environment detection means.

  (12) It has environment detection means for detecting the environment where the image forming apparatus is installed. Then, the AC current values in a plurality of stages applied to the charging unit when measuring the peak-to-peak voltage value of the AC voltage during non-image formation are changed for each environment detected by the environment detection unit. Along with this, charging means during image formation by fI2 (Vpp) = fI1 (Vpp) + D from the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value during non-image formation The alternating current to be applied to is determined. The charge control method according to (8) or (9), wherein the constant D used for the determination is changed for each environment detected by the environment detection means.

  (13) The image forming apparatus includes an image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage, and an electrostatic latent image is applied to the charged image carrier. Information writing means for forming an image. The image forming apparatus further includes a developing unit that supplies toner to the electrostatic latent image to visualize the electrostatic latent image, and a transfer unit that transfers the visualized toner image to a transfer material. The charging control method according to any one of (12).

  (14) The charging control method according to (13), wherein the information writing unit is an exposure unit.

  (15) An image forming apparatus that performs image formation by applying an image forming process including a step of charging the image carrier to the image carrier. The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage close to or in contact with the image carrier. The image forming apparatus is characterized in that the charging process of the image carrier by the charging means is controlled by the charging control method according to any one of (1) to (12).

  (16) An image forming apparatus includes an image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage, and an electrostatic latent image is applied to the charged image carrier. Information writing means for forming an image. The image forming apparatus according to (15), further comprising: a developing unit that supplies toner to the electrostatic latent image to visualize the electrostatic latent image; and a transfer unit that transfers the visualized toner image to a transfer material. It is.

  (17) The image forming apparatus according to (16), wherein the information writing unit is an exposure unit.

<Others>
1) In the embodiments, only the printing operation in mono color (single color) has been described. However, the present invention is not limited to this, and the same effect can be exhibited in the full color printing operation.

  2) In the embodiment, an appropriate peak-to-peak voltage value or AC current value calculation / determination program is executed in the charging process of the printing process during the printing preparation rotation operation period when the printer is not forming an image. It is not limited to examples. That is, it is not limited to the print preparation rotation operation period as in the printer of the embodiment, it can be during other non-image formation, that is, during the initial rotation operation, during the inter-sheet process, during the post-rotation process, It can also be executed when a plurality of non-images are formed.

3) The image carrier may be of a direct injection charging type provided with a charge injection layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm. Even when the charge injection layer is not used, for example, the same effect can be obtained when the charge transport layer is in the above resistance range. An amorphous silicon photoreceptor having a surface layer volume resistance of about 10 ¹³ Ω · cm may be used.

  4) In addition to the charging roller, a flexible contact charging member having a shape or material such as a fur brush, felt, or cloth can be used. Further, a combination of various materials can provide more appropriate elasticity, conductivity, surface property, and durability.

  5) As the waveform of the alternating voltage component (AC component, voltage whose voltage value periodically changes) of the oscillating electric field applied to the contact charging member and the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off a DC power supply.

  6) In addition to the laser scanning unit of the embodiment, the image exposure unit as the information writing unit for the charged surface of the photoconductor as the image carrier is a digital exposure unit using a solid light emitting element array such as an LED. May be. An analog image exposure unit using a halogen lamp or a fluorescent lamp as a document illumination light source may be used. In short, any device capable of forming an electrostatic latent image corresponding to image information may be used.

  7) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged, the charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information. .

  8) The toner developing method and means for the electrostatic latent image are arbitrary. A reversal development method or a regular development method may be used.

In general, the electrostatic latent image is developed by coating a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and magnetic toner on a developer carrying member. A method in which an electrostatic latent image is developed in a non-contact state with respect to an image carrier by coating and conveying by force (one-component non-contact development), and coating on a developer carrying member as described above A method for developing an electrostatic latent image by applying toner in contact with an image carrier (one-component contact development), and a developer obtained by mixing a magnetic carrier with toner particles (two-component developer) And a method of developing the electrostatic latent image by conveying it by magnetic force and applying it in contact with the image carrier (two-component contact development), and applying the above two-component developer to the image carrier. Apply electrostatic latent image in contact It is roughly divided into four 顛 the method (two-component non-contact development) to the image.

  9) The transfer means is not limited to the roller transfer in the embodiment, but may be a blade transfer, belt transfer, other contact transfer charging method, or a non-contact transfer charging method using a corona charger.

  10) The present invention can be applied not only to the formation of a single color image by using an intermediate transfer member such as a transfer drum or a transfer belt, but also to an image forming apparatus that forms a multicolor, full color image by multiple transfer or the like.

Schematic configuration model diagram of image forming apparatus of embodiment 1 Layer structure model of photoconductor Operation sequence diagram of image forming apparatus Block diagram of charging bias application system Measurement schematic of discharge current Relationship between peak-to-peak voltage and AC current measured during print preparation rotation Charge control flow chart Relationship diagram between peak-to-peak voltage and alternating current measured during print preparation rotation in Example 2 Relationship diagram between peak-to-peak voltage and AC current amount measured during printing preparation rotation in Example 3 Relationship diagram between peak-to-peak voltage and AC current measured during printing preparation rotation in Example 4 Schematic configuration model diagram of image forming apparatus (cleaner-less) of Example 5

Explanation of symbols

1 .... photosensitive drum (image carrier) 2 .... charging roller 3 .... laser beam scanner 4 .... developing device 5 .... transfer roller 6 .... fixing device 7 .... cleaning device 8 ..Toner charging control means, S1 to S4
11 .... DC power supply, 12 .... AC power supply, 13 .... Control circuit, 14 .... AC voltage or peak-to-peak voltage measurement circuit, 15 .... Environmental sensor

Claims (17)

In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
Means for applying a superposed voltage of either or both of DC voltage and AC voltage to the charging means;
Means for controlling each voltage value of the DC voltage applied to the charging means and the peak-to-peak voltage of the AC voltage;
Means for measuring an alternating current value flowing to the charging means via the image carrier;
When the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, at the time of non-image formation, the charging means has at least one point between peaks less than twice Vth Measures the current value when a voltage is applied and the current value when a peak-to-peak voltage that is at least twice the Vth of at least two points is applied, and applies the measured alternating current value to the charging means during image formation A charging control method characterized by determining a peak-to-peak voltage of an alternating voltage to be applied. D is a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 (Vpp obtained by connecting 0 to the current value when a peak-to-peak voltage less than twice Vth at one point is applied to the charging means. ) And the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when at least two times the peak-to-peak voltage of Vth is applied.
fI2 (Vpp) −fI1 (Vpp) = D
2. The charging according to claim 1, wherein the peak-to-peak voltage value is determined, and the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled at a constant voltage based on the determined peak-to-peak voltage value. Control method. Let D be a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 (Vpp) obtained from the current value when at least two points or more of the peak-to-peak voltage less than twice Vth are applied to the charging means; By comparing the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of two or more points is applied,
fI2 (Vpp) −fI1 (Vpp) = D
2. The charging according to claim 1, wherein the peak-to-peak voltage value is determined, and the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled at a constant voltage based on the determined peak-to-peak voltage value. Control method.   It has an environment detection means that detects the environment where the image forming apparatus is installed, and the environment detection means detects the peak-to-peak voltage values of multiple stages of AC voltage applied to the charging means when measuring the AC current value during non-image formation. The charge control method according to claim 2, wherein the charge control method is changed for each environment.   From the peak-to-peak voltage-alternating current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the alternating current value during non-image formation, fI2 ( Vpp) −fI1 (Vpp) = D, and the constant D used when determining the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is changed for each environment detected by the environment detection unit. The charge control method according to claim 2 or 3.   Environment detection means that detects the environment in which the image forming apparatus is installed, and the environment detection means detects the multi-step peak-to-peak voltage value applied to the charging means when measuring the alternating current value during non-image formation The image is formed by fI2 (Vpp) −fI1 (Vpp) = D from the peak-to-peak voltage-alternating current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the alternating current value during non-image formation. 4. The charge control according to claim 2, wherein a constant D used for determining a peak-to-peak voltage of the alternating voltage applied to the charging means is changed for each environment detected by the environment detecting means. Method. In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
The charging means for charging the image carrier is a charging means for charging the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier,
Means for applying at least an alternating current to the charging means;
Means for controlling the AC current value applied to the charging means;
Means for measuring the peak-to-peak voltage value of the alternating voltage applied to the charging means;
When the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, at the time of non-image formation, the charging means has at least one point between peaks less than twice Vth It is measured by measuring the voltage value when an alternating current that is a voltage is applied and the peak-to-peak voltage value of the alternating voltage when an alternating current that is a peak-to-peak voltage that is at least twice the Vth of at least two points is applied. A charge control method characterized in that an alternating current value to be applied to the charging means during image formation is determined based on the peak-to-peak voltage value. The peak-to-peak voltage obtained by connecting 0 to the voltage value when an alternating current value that gives a peak-to-peak voltage less than twice the Vth of one point is applied to the charging means with D being a predetermined constant. The current function fI1 (Vpp) and the peak-to-peak voltage-AC current function fI2 (Vpp) obtained from the voltage value when an alternating current value that is at least two times the peak-to-peak voltage of Vth is applied. By comparing,
fI2 (Vpp) = fI1 (Vpp) + D
The charging control method according to claim 7, wherein an alternating current value to be determined is determined, and the alternating current value applied to the charging unit at the time of image formation is controlled by a constant current based on the determined alternating current value. D is a predetermined constant, and the peak-to-peak voltage-alternating current function fI1 () obtained from the voltage value when an alternating current value that is less than twice the Vth of at least two points is applied to the charging means. Vpp) and the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the voltage value when applying an alternating current value that is at least two times the peak-to-peak voltage of Vth at least two points ,
fI2 (Vpp) = fI1 (Vpp) + D
The charging control method according to claim 7, wherein an alternating current value to be determined is determined, and the alternating current value applied to the charging unit at the time of image formation is controlled by a constant current based on the determined alternating current value.   It has an environment detection unit that detects the environment in which the image forming apparatus is installed, and the environment detection unit detects multiple levels of AC current applied to the charging unit when measuring the peak-to-peak voltage value of the AC voltage during non-image formation. The charge control method according to claim 8 or 9, wherein the charge control method is changed for each environment.   It has an environment detection means that detects the environment where the image forming apparatus is installed, and the peak-to-peak voltage-AC current function fI1 (Vpp), fI2 (Vpp) obtained by measuring the peak-to-peak voltage value of the AC voltage during non-image formation From the above, it is characterized in that the constant D used when determining the alternating current applied to the charging means at the time of image formation is changed for each environment detected by the environment detection means by fI2 (Vpp) = fI1 (Vpp) + D. The charge control method according to claim 8 or 9.   It has an environment detection unit that detects the environment in which the image forming apparatus is installed, and the environment detection unit detects multiple levels of AC current applied to the charging unit when measuring the peak-to-peak voltage value of the AC voltage during non-image formation. FI2 (Vpp) = fI1 (Vpp) + D from the peak-to-peak voltage-AC current functions fI1 (Vpp) and fI2 (Vpp) obtained by measuring the peak-to-peak voltage value during non-image formation. 10. The charging control method according to claim 8, wherein a constant D used for determining an alternating current applied to the charging unit during image formation is changed for each environment detected by the environment detecting unit. .   The image forming apparatus forms an electrostatic latent image on the image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage. 13. An information writing means for developing, a developing means for supplying toner to the electrostatic latent image to visualize the electrostatic latent image, and a transfer means for transferring the visualized toner image to a transfer material. The charge control method according to any one of the above.   14. The charging control method according to claim 13, wherein the information writing means is an exposure means. In an image forming apparatus that executes image formation by applying an image forming process including a step of charging the image carrier to the image carrier,
13. The charging control unit according to claim 1, wherein the charging unit that charges the image carrier is a charging unit that charges the surface of the image carrier by applying a voltage in the vicinity of or in contact with the image carrier. An image forming apparatus, wherein a charging process of an image carrier by a charging unit is controlled by a method.   The image forming apparatus forms an electrostatic latent image on the image carrier, a charging unit that is placed in close contact with or in contact with the image carrier, and charges the surface of the image carrier by applying a voltage. 16. The apparatus according to claim 15, further comprising: an information writing unit configured to supply information; a developing unit that supplies toner to the electrostatic latent image to visualize the electrostatic latent image; and a transfer unit that transfers the visualized toner image to a transfer material. Image forming apparatus.   The image forming apparatus according to claim 16, wherein the information writing unit is an exposure unit.