JP6187149B2 - Image forming apparatus and program - Google Patents

Description

  The present invention relates to an image forming apparatus and a program.

  As a conventional technique, a region of a photosensitive drum that passes through a transfer portion and an electrostatic latent image is formed when there is no recording material between the transfer roller and the photosensitive drum, and the transfer roller and the photosensitive member There is an image forming apparatus that performs control to switch a transfer bias between a region of a photosensitive drum that passes through a transfer portion when a recording material is present between the drum and an electrostatic latent image is to be formed. (See Patent Document 1).

JP 2008-102329 A

  An object of the present invention is to suppress the occurrence of density unevenness along the rotation axis direction of an image carrier in an image formed on a recording material.

According to a first aspect of the present invention, there is provided a rotating image carrier, a transfer unit that is supplied with a transfer current or voltage having a predetermined magnitude, and transfers a toner image formed on the image carrier to a recording material; When the toner image is transferred to the second recording material having a width larger than that of the first recording material after the toner image is transferred to the first recording material in the transfer unit, the first recording is performed. After the material has passed through the transfer portion, before the second recording material is conveyed to the transfer portion, a correction current / voltage having the same polarity that is larger in absolute value than the transfer current / voltage is applied to the transfer portion. and a control unit for supplying Te, the control unit, the first according to the thickness and / or width of the recording material, said correction current / voltage image forming apparatus to change the supply time and / or magnitude of It is.
The invention according to claim 2 is characterized in that the control unit supplies the correction current / voltage to the transfer unit until the image carrier rotates at least once. Device.
According to a third aspect of the present invention, the control unit supplies the correction current / voltage to the transfer unit and then transfers the second recording material to the transfer unit before the second recording material is conveyed to the transfer unit. 2. The image forming apparatus according to claim 1, wherein a transfer current / voltage is supplied .
According to a fourth aspect of the present invention, the control unit transfers the toner image to the first recording material at the transfer unit, and then applies the third recording material having a width smaller than that of the first recording material. 2. The image forming apparatus according to claim 1, wherein when the toner image is transferred, the correction current / voltage is controlled not to be supplied.
According to a fifth aspect of the present invention, there is provided a computer having a function of receiving an instruction for image forming processing, a function of controlling a rotatable image carrier based on the instruction, and the image carrier based on the instruction. A function of supplying a transfer current or voltage for transferring the toner image formed on the recording material to the recording material, and a width compared to the first recording material after the image is formed on the first recording material. When an instruction to form an image is received for a large second recording material, after the first recording material passes through the transfer portion, before the second recording material is conveyed to the transfer portion, A function of supplying a correction current / voltage having the same polarity, which has an absolute value larger than that of the transfer current / voltage, to the transfer unit is realized, and the control function is the thickness of the first recording material and / or Or, depending on the width, the correction current / power Supply time of and / or a program to change the size.

According to the first aspect of the present invention, it is possible to suppress the occurrence of excessive density in the image formed on the recording material, compared to the case where this configuration is not provided.
According to the second aspect of the present invention, it is possible to suppress the occurrence of density unevenness along the recording material conveyance direction in the image formed on the recording material, as compared with the case where this configuration is not provided.
According to the third aspect of the present invention, it is possible to suppress the occurrence of excessive density in the image formed on the recording material, as compared with the case where this configuration is not provided .
According to the fourth aspect of the present invention, it is possible to suppress the deterioration of the image carrier as compared with the case where this configuration is not provided.
According to the fifth aspect of the present invention, it is possible to suppress the occurrence of excessive density in the image formed on the recording material as compared with the case where the present configuration is not provided.

1 is a diagram illustrating an example of a configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a figure showing an example of composition of an image forming part to which this embodiment is applied. 4 is a timing chart showing changes in the magnitude (absolute value) of current applied to a transfer roll by a transfer power supply in the present embodiment. (A)-(e) is the figure shown about the state of the transfer roll and photosensitive drum in the image formation operation | movement of this Embodiment, and the surface potential of a photosensitive drum. It is the flowchart which showed an example of the process which the control part of this Embodiment performs. (A)-(c) is a figure for demonstrating the states of a photoconductive drum etc. in the conventional image formation operation | movement.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a single-color printer, an image forming unit 10 that forms an image corresponding to image data, and a user interface (UI) 4 that receives instructions from the user and displays messages to the user. An image that is connected to an external device such as a personal computer (PC) 2 or an image reading device 3 for controlling the operation of the entire image forming apparatus 1 and performs image processing on image data received from these devices. A processing unit 6 is provided.
The image forming apparatus 1 also includes a recording material supply unit 40 that supplies a recording material to the image forming unit 10 and a toner cartridge 45 that supplies toner to the image forming unit 10.

  The recording material supply unit 40 of the present embodiment has a plurality of paper feeding units in order to enable supply of a plurality of types of recording materials (paper) having different sizes and different directions to the image forming unit 10, for example. doing. In this example, the recording material supply unit 40 includes three paper feeding units 41 to 43 as shown in FIG.

FIG. 2 is a diagram illustrating an example of the configuration of the image forming unit 10 to which the exemplary embodiment is applied.
As shown in FIGS. 1 and 2, the image forming unit 10 includes a photosensitive drum 12 as an example of an image holding body that is rotatably provided and forms an electrostatic latent image and holds a toner image, and the photosensitive drum 12. A charger 13 for charging the surface of the toner, an exposure device 14 for exposing the photosensitive drum 12 charged by the charger 13 based on image data, and a developing device for developing an electrostatic latent image formed on the photosensitive drum 12. 15. A cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer is provided. Note that the photosensitive drum 12 in the present exemplary embodiment includes a rotation shaft (not shown) so that the axial direction is directed from the front side (front side in the figure) to the rear side (back side in the figure) of the image forming apparatus 1. Is arranged.

The image forming unit 10 also forms a transfer unit with the photosensitive drum 12, and transfers the toner image formed on the photosensitive drum 12 to a recording material, and records the transferred toner image. A fixing device 30 for fixing on the material is provided.
Further, the image forming unit 10 includes a peeling device 17 that peels the recording material onto which the toner image is transferred by the transfer device 20 from the surface of the photosensitive drum 12.

  The photosensitive drum 12 of the present embodiment is formed by forming a photosensitive layer on the outer peripheral surface of a metal thin cylindrical drum, and the photosensitive layer is made of a material having a negative charging polarity. Note that the cylindrical drum constituting the photosensitive drum 12 is grounded. The photosensitive drum 12 of the present embodiment is configured to rotate in the direction of arrow A in an image forming operation for forming an image on a recording material (paper).

The charger 13 of the present embodiment has a charging roll 13a that contacts the surface of the photosensitive drum 12, and employs a contact charging method in which the surface of the photosensitive drum 12 is charged by the charging roll 13a. . The surface of the charging roll 13a is made of, for example, a rubber material, and a negative charging bias is applied to the charging roll 13a by a charging power source (not shown).
Here, as a method of applying a voltage to the charging member for charging the photosensitive drum 12, generally, a direct current charging method in which only a direct current voltage is applied and an alternating current in which an alternating current voltage is applied to the direct current voltage are superimposed. And a superposition method. In the present embodiment, a DC charging method in which only a DC voltage is applied to the charging roll 13a is adopted.

  The exposure device 14 emits laser light corresponding to the image data to the outer peripheral surface of the photosensitive drum 12. Then, the exposure device 14 forms an electrostatic latent image by irradiating light to a position where a toner image is to be formed on the outer peripheral surface of the photosensitive drum 12 charged to a negative polarity by the charger 13. .

  The developing device 15 includes a developing roll 15 a disposed to face the photosensitive drum 12, and a developer containing black toner is accommodated in the developing device 15. In the developing device 15 of the present embodiment, a so-called two-component developer including a magnetic carrier is used as the developer. In this developer, the carrier has a positive charging polarity, and the toner has a negative charging polarity.

  In the present embodiment, the developing roll 15a incorporates a magnet (not shown), and holds the developer on the surface of the developing roll 15a by magnetic force. The developing unit 15 develops the electrostatic latent image on the photosensitive drum 12 with the developer (toner) held on the developing roll 15a. In the developing device 15 of the present embodiment, a developing bias for setting the developing roll 15a to a negative potential is supplied from a developing power source (not shown), so that the electrostatic latent image on the photosensitive drum 12 has a negative polarity. Development is performed by a so-called reversal development method in which a negatively charged toner is transferred to a charged image portion. Here, as a developing bias application method, there are a DC developing method for supplying only a DC voltage and an AC superimposed developing method for supplying an AC voltage superimposed on the DC voltage. In this embodiment, the DC developing method is used. The method is adopted.

  Further, the cleaner 16 of the present embodiment is configured by a blade, for example, and is pressed against the surface of the photosensitive drum 12 to scrape off transfer residual toner adhering to the surface of the photosensitive drum 12 from the surface of the photosensitive drum 12. ing.

The transfer device 20 according to the present embodiment includes a cylindrical transfer roll 20 a that is in contact with the outer peripheral surface of the photosensitive drum 12 and rotates following the rotation of the photosensitive drum 12. In the following description, a contact portion between the photosensitive drum 12 and the transfer roll 20a is referred to as a transfer position T.
A transfer roller 20a as an example of a transfer unit is supplied with a positive transfer bias (transfer current) controlled at a constant current by a transfer power source 25. Then, when a transfer current flows from the transfer power source 25 through the transfer roll 20a and the photosensitive drum 12, a transfer electric field is formed between the transfer roll 20a and the photosensitive drum 12, and the toner image on the photosensitive drum 12 is transferred. The image is transferred to the recording material (paper) conveyed to the position T.

As a method for supplying a transfer current to the transfer roll 20a, there are a direct current transfer method for supplying only a direct current and an alternating current transfer method for supplying an alternating current superimposed on the direct current. The transfer power supply 25 employs a direct current transfer system.
The transfer power supply 25 supplies a transfer current including a direct current component set to a positive value to the transfer roll 20a. The magnitude of the transfer current supplied from the transfer power supply 25 can be adjusted by the control unit 5.

  The fixing device 30 is composed of a pair of rotating members arranged in contact with each other, and the recording material on which the image is transferred by the transfer device 20 is heated and pressed through the pair of rotating members, thereby forming a recording material. Fix the image.

  Here, the image forming unit 10 according to the present embodiment does not include a static eliminating device that neutralizes the surface of the photosensitive drum 12 after the transfer by the transfer device 20 and before the charging by the charger 13.

Next, an image forming operation (print process) using the image forming apparatus 1 shown in FIG. 1 will be described. The image forming operation described below is executed under the control of the control unit 5.
With the start of the image forming operation, driving of the photosensitive drum 12 and driving of the developing roll 15a provided in the developing device 15 are started, and the photosensitive drum 12 and the developing roll 15a respectively start to rotate. As the photosensitive drum 12 starts rotating, the charging roll 13a and the transfer roll 20a also start rotating. Further, supply of a charging bias to the charging roll 13a, supply of a developing bias to the developing roll 15a, and supply of a transfer current from the transfer power source 25 to the transfer roll 20a are started. Furthermore, driving of the heating roll in the fixing device 30 is started, and power supply to the heating roll is started.

Next, the photosensitive drum 12 rotating in the arrow A direction is charged to the charging potential VH by the charging bias supplied to the charging roll 13 a of the charger 13. The charging potential in this example is about −700 V, for example.
Next, exposure by the exposure device 14 is started, and the photosensitive drum 12 that rotates in the direction of the arrow A while being charged to the charged potential selectively selects a portion to be an image portion by light emitted from the exposure device 14. Exposed. As a result, an electrostatic latent image is formed on the photosensitive layer of the photosensitive drum 12 that has been charged and exposed, with the background portion being charged potential VH and the image portion being exposed potential VL. Note that the exposure potential VL in this example is, for example, about −100V.

  Subsequently, the electrostatic latent image formed on the photosensitive drum 12 is opposed to the developing roller 15a provided in the developing unit 15 (hereinafter referred to as a developing unit) as the photosensitive drum 12 rotates in the direction of arrow A. Reach the area). At this time, the developing roll 15a rotates with a developer (two-component developer) containing toner and a carrier on the surface thereof held by magnetic force, and a developing bias is supplied to the developing roll 15a. Yes. Therefore, the toner is selectively transferred from the developing roll 15a to the photosensitive drum 12 with respect to the image portion having the image potential in the electrostatic latent image. As a result, a black toner image corresponding to the electrostatic latent image is developed on the photosensitive drum 12 that has passed through the development area.

Then, the toner image developed on the photoconductive drum 12 moves toward the transfer position T facing the transfer roll 20a as the photoconductive drum 12 rotates in the direction of arrow A.
On the other hand, the recording material taken out from the recording material supply unit 40 is conveyed to the transfer position T in accordance with the timing when the toner image on the photosensitive drum 12 reaches the transfer position T.

  Then, at the transfer position T where the toner image and the recording material on the photosensitive drum 12 have arrived, a transfer current is supplied to the transfer roll 20a by the transfer power supply 25, whereby the photosensitive drum 12 rotating in the direction of arrow A is applied. The formed toner image is transferred onto a recording material conveyed at the transfer position T in the same direction as the arrow A direction.

  Thereafter, the recording material onto which the toner image has been transferred is conveyed to the fixing device 30. Then, the toner image on the recording material is fixed by being heated and pressed by the fixing device 30, and is discharged to a paper discharge stacking unit provided at the top of the image forming apparatus 1.

On the other hand, adhering matter such as toner remaining on the photosensitive drum 12 after passing through the transfer position T reaches a portion facing the cleaner 16 as the photosensitive drum 12 further rotates in the direction of arrow A, and the cleaner 16 is cleaned.
The above-described image forming operation is repeated for the required number of prints.

Incidentally, in the image forming apparatus 1 according to the present embodiment, as described above, the image forming unit 10 can form images on recording materials (paper sheets) having different sizes and different orientations. . Here, when images are formed on recording materials of different sizes and orientations, the recording material along the direction orthogonal to the recording material conveyance direction (that is, the axial direction of the photosensitive drum 12) in the image forming unit 10 is used. May vary in width.
For example, in the case where the image forming unit 10 forms an image on a postcard as a recording material and the case where an image is formed on an A4 size paper as the recording material, the recording material along the axial direction of the photosensitive drum 12 is used. The width of is different. In the image forming unit 10, the photosensitive member is used when an image is formed on A4 size paper conveyed in the vertical direction and when an image is formed on A4 size paper conveyed in the horizontal direction. The width of the recording material along the axial direction of the drum 12 is different.
In the following description, the width of the recording material (paper) in the direction (axial direction of the photosensitive drum 12) orthogonal to the recording material conveyance direction conveyed through the image forming unit 10 is simply referred to as “recording material (paper)”. The length of the recording material (paper) along the recording material conveyance direction may be simply called “the length of the recording material (paper)”.

Conventionally, when an image forming operation is performed on a recording material having a wide width after an image forming operation is performed on a recording material having a narrow width in the image forming unit 10, as described below, the recording material is In some cases, defects such as uneven density and fogging may occur in the image formed on the surface.
6A to 6D are views for explaining the state of the photosensitive drum 12 and the like in the conventional image forming operation. 6A to 6C, after the image forming operation is performed on the first sheet P1, the image is continuously formed on the second sheet P2 having a width larger than that of the first sheet P1. The state of the photosensitive drum 12 and the like when performing the operation is shown. FIG. 6D shows an example of the state of an image formed on the second paper P2.

  As described above, when the image forming operation is started, the image forming unit 10 supplies the charging bias to the charging roll 13a, supplies the developing bias to the developing roll 15a, and the transfer roll based on the control by the control unit 5. Supply of a transfer current to 20a is started. As shown in FIG. 6A, the surface of the photosensitive drum 12 is charged to a negative charging potential VH by the charging bias supplied by the charging roll 13a.

In this example, as shown in FIG. 6A, a positive transfer current is applied to the transfer roll 20a in advance after the image forming operation is started and before the recording material is conveyed to the transfer position T. It has come to be. When a transfer current is applied to the transfer roll 20a, a current flows from the transfer roll 20a into the photosensitive drum 12 in contact with the transfer roll 20a. In this example, as a result of the supply of the charging bias by the charging roll 13a and the flow of current from the transfer roll 20a, the surface potential of the photosensitive drum 12 is the charging potential VH.
In the examples shown in FIGS. 6A to 6C, for the sake of simplicity, the description of the image portion that is exposed by the exposure device 14 and whose surface potential is the exposure potential VL is omitted, and exposure is performed. Only the state of the background portion is displayed.

Subsequently, when the first sheet P1 is conveyed to the transfer position T, the first electric field is generated by the transfer electric field between the transfer roll 20a and the photosensitive drum 12 formed by the transfer current applied to the transfer roll 20a. The toner image is transferred to the paper P1.
Here, as shown in FIG. 6B, when the first sheet P1 is conveyed to the transfer position T, the photosensitive drum 12 and the transfer roll 20a are directly connected to each other at both axial ends of the photosensitive drum 12. On the other hand, since the first sheet P1 exists in the central portion in the axial direction of the photosensitive drum 12, the photosensitive drum 12 and the transfer roll 20a are not in direct contact.
As a result, there is a difference in the amount of current flowing from the transfer roll 20a between the axial end portions and the axial center portion of the photosensitive drum 12. That is, as shown in FIG. 6B, both axial ends of the photosensitive drum 12 that are in direct contact with the transfer roll 20a are compared with the axial central portion of the photosensitive drum 12 that is not in direct contact with the transfer roll 20a. More current flows from the transfer roll 20a.

  At both axial ends of the photosensitive drum 12, the surface potential is lowered by the flow of positive current from the transfer roll 20a, while the surface potential is lowered at the axial central portion of the photosensitive drum 12 where the flow of current is small. Hardly goes down. As a result, in the photosensitive drum 12 after the first paper P1 has passed, as shown in FIG. 6B, a difference in surface potential occurs between the axial end portions and the axial center portion.

  In the case of the image forming unit 10 that does not have a static elimination mechanism, the photosensitive drum 12 that has passed the transfer position T after that has a surface potential difference as shown in FIG. It reaches the charger 13 (see FIG. 2) and is charged by the charging roll 13a (see FIG. 2). When the amount of decrease in the surface potential at both ends in the axial direction of the photosensitive drum 12 is large, even when charged by the charging roll 13a, as shown in FIG. The surface potential at both ends in the axial direction of 12 remains lower than the charging potential VH, and the difference in surface potential between the both ends in the axial direction and the central portion in the axial direction of the photosensitive drum 12 may not be eliminated.

  In particular, when a thick paper such as a postcard is used as the first paper P1, the resistance of the first paper P1 is high, so that the first paper P1 is conveyed at the transfer position T in the axial direction. In the central portion, the flow of current from the transfer roll 20a to the photosensitive drum 12 is reduced. As a result, in the photosensitive drum 12 after the first paper P1 has passed, the difference in surface potential between the axial end portions and the axial center portion tends to increase.

Then, the second sheet P2 having a width larger than that of the first sheet P1 is set at the transfer position T in a state where the surface potential difference is generated between the both axial ends of the photosensitive drum 12 and the central portion in the axial direction. When the toner image is transferred and transferred, as shown in FIG. 6D, both end portions in the axial direction where the surface potential of the photosensitive drum 12 is low and the central portion in the axial direction where the surface potential of the photosensitive drum 12 is high. As a result, density unevenness, fogging, or the like may occur in the image transferred to the second paper P2.
Specifically, when a uniform halftone image or a solid image is formed on the second paper P2 in the axial direction, density unevenness may occur between the axial end portions and the axial center portion. In addition, when there are blank paper portions where no image is formed at both ends in the axial direction, so-called fogging or the like in which toner adheres to the blank paper portion of the second paper P2 may occur.

  On the other hand, in the present embodiment, when an image is formed on the first sheet P1, the image is formed on the second sheet P2, which is wider than the first sheet P1. Before the second sheet P2 is conveyed to the transfer position T, a process for eliminating the difference in surface potential generated on the photosensitive drum 12 is performed.

Subsequently, when the image is formed on the second sheet P2 having a width wider than that of the first sheet P1 after the image is formed on the first sheet P1, the image of the present embodiment is used. Processing performed in the forming unit 10 will be described. FIG. 3 is a timing chart showing changes in the magnitude (absolute value) of the current applied to the transfer roll 20a by the transfer power supply 25 in the present embodiment. 4A to 4E are diagrams showing the state of the transfer roll 20a and the photosensitive drum 12 and the surface potential of the photosensitive drum 12 in the image forming operation of the present embodiment.
Here, in FIG. 3 and FIGS. 4A to 4E, the width compared with the first paper P1 after the first job for forming an image on the three first papers P1 is performed. In this example, the second job for forming an image is performed on the second sheet P2 having a large.

  Note that the interval between the scale lines parallel to the vertical axis indicated by the broken line in FIG. 3 represents the time for one rotation of the photosensitive drum 12. 4A to 4E show states of the transfer roll 20a and the photosensitive drum 12 at timings I to V in the timing chart of FIG. 3, respectively. Further, in FIGS. 4A to 4E, for the sake of simplicity, the description of the image portion that is exposed by the exposure device 14 and whose surface potential becomes the exposure potential VL is omitted, and exposure is not performed. Only the state of the background is shown.

Also in the present embodiment, the image forming process for the first paper P1 in the image forming unit 10 (see FIG. 2) is performed in the same manner as in the above-described conventional example.
That is, when an instruction to perform the first job is issued, the image forming unit 10 supplies a charging bias to the charging roll 13a (see FIG. 2), supplies a developing bias to the developing roll 15a (see FIG. 2), and a transfer power source. The supply of the transfer current It to the transfer roll 20a by 25 (see FIG. 2) is started. In this example, as shown in FIG. 3, before the first sheet P1 reaches the transfer position T, the transfer current is transferred from the transfer power supply 25 to the transfer roll 20a by the transfer power supply 25 for a period until the photosensitive drum 12 makes five turns. It is supplied.
As a result of the supply of the charging bias by the charging roll 13a and the flow of current from the transfer roll 20a, the surface of the photosensitive drum 12 is charged to the charging potential VH as shown in FIG.

Subsequently, the first sheet P1 is conveyed to the transfer position T, and the toner image is transferred to the first sheet P1 by a transfer electric field formed between the transfer roll 20a and the photosensitive drum 12.
Here, as described above, when the first sheet P1 is transported to the transfer position T, the amount of current flowing from the transfer roll 20a at the axial end portions and the axial center portion of the photosensitive drum 12 is increased. There is a difference. As shown in FIG. 4B, when the first sheet P1 is transported to the transfer position T, the surface potential of both ends in the axial direction of the photosensitive drum 12 is transported by the first sheet P1. It will be in the state which fell compared with the surface potential of the axial direction center part. In this example, as shown in FIG. 4B, the surface potential at both ends in the axial direction of the photosensitive drum 12 is lowered to the lowering potential VD lower than the charging potential VH due to the current flowing from the transfer roll 20a. Shall be.

Subsequently, in the present embodiment, after the two first sheets P1 pass through the transfer position T in the first job, the second paper P2 reaches the transfer position T in the second job. In addition, a correction current Ir for correcting the surface potential difference generated on the photosensitive drum 12 is supplied to the transfer roll 20a.
Here, the correction current Ir is a current having the same polarity (in this example, positive polarity) as the transfer current It, and has a larger absolute value than the transfer current It.

As shown in FIG. 4C, after the first sheet P1 passes the transfer position T and until the second sheet P2 reaches the transfer position T, the transfer roll 20a and the photosensitive member are exposed at the transfer position T. The body drum 12 is in direct contact. Accordingly, the correction current Ir supplied to the transfer roll 20a flows into the surface of the photosensitive drum 12 from one axial end of the photosensitive drum 12 to the other axial end.
Then, at both ends in the axial direction of the photosensitive drum 12 where the surface potential has decreased to the decrease potential VD,
As the correction current Ir flows from the transfer roll 20a, the surface potential decreases to a correction potential VR lower than the decrease potential VD.
Also in the central portion of the photosensitive drum 12 in the axial direction, the surface potential is lowered to the correction potential VR as in the axial end portions due to the flow of the correction current Ir from the transfer roll 20a.

  That is, due to the flow of the correction current Ir from the transfer roll 20a, the surface potential of the photosensitive drum 12 becomes the correction potential VR from one end in the axial direction to the other end in the axial direction. Thus, the difference in surface potential is eliminated.

  The supply of the correction current Ir to the transfer roll 20a is performed for at least a period until the photosensitive drum 12 rotates once. As a result, the difference in surface potential between the axial end portions and the axial center portion can be eliminated over the entire outer peripheral surface of the photosensitive drum 12. In this example, as shown in FIG. 3, the correction current Ir is supplied to the transfer roll 20a during the period until the photosensitive drum 12 rotates five times.

Note that the supply time of the correction current Ir to the transfer roll 20a is preferably varied depending on, for example, the thickness and width of the first paper P1 used in the first job, the number of images formed in the first job, and the like.
That is, for example, the thicker the first sheet P1, the smaller the width of the first sheet P1, and the more the number of images formed in the first job, the more the axial end portions of the photosensitive drum 12 are. The difference in surface potential with the central portion in the axial direction tends to increase.

Thus, the longer the difference in surface potential generated on the photosensitive drum 12, the longer the supply time of the correction current Ir to the transfer roll 20a, and the smaller the difference in surface potential generated on the photosensitive drum 12, the more the transfer. It is preferable to shorten the supply time of the correction current Ir to the roll 20a.
When the difference in surface potential generated on the photosensitive drum 12 is large, the difference in surface potential generated on the photosensitive drum 12 is effectively eliminated by setting the supply time of the correction current Ir to the transfer roll 20a longer. can do.
When the difference in surface potential generated on the photoconductive drum 12 is small, the correction current Ir from the transfer roll 20a to the photoconductive drum 12 is set by shortening the supply time of the correction current Ir to the transfer roll 20a. It is possible to suppress the wear and deterioration of the photosensitive drum 12 due to the flow.

Also, the magnitude (absolute value) of the correction current Ir supplied to the transfer roll 20a differs depending on, for example, the thickness and size of the first paper P1 used in the first job, the number of images formed in the first job, and the like. It may be allowed.
For example, when the thickness of the first sheet P1 is large, the width of the first sheet P1 is narrow, or when the number of images formed in the first job is large, the surface potential generated on the photosensitive drum 12 is used. When the difference between the two values tends to increase, it is preferable to increase the magnitude (absolute value) of the correction current Ir supplied to the transfer roll 20a.

Next, as shown in FIG. 3, before the second sheet P2 is conveyed to the transfer position T, a transfer current It is supplied to the transfer roll 20a. In the example shown in FIG. 3, the transfer current It is supplied to the transfer roll 20a following the supply of the correction current Ir.
As described above, by supplying the correction current Ir to the transfer roll 20a, the surface potential of the photosensitive drum 12 becomes the correction potential VR lower than the charging potential VH. For this reason, when an image is formed on the second paper P2 immediately after the correction current Ir is supplied to the transfer roll 20a, the toner tends to adhere to the photosensitive drum 12 in the development by the developing device 15, for example. In some cases, the image density is high in a halftone image or the like.

On the other hand, as in the present embodiment, after the correction current Ir is supplied to the transfer roll 20a, the transfer current It is applied to the transfer roll 20a before the second sheet P2 is conveyed to the transfer position T. By supplying, as shown in FIG. 4D, the surface potential of the photosensitive drum 12 can be returned to the charging potential VH.
As a result, for the image formed on the second paper P2, it is possible to suppress the occurrence of problems such as a high image density.

The supply of the transfer current It to the transfer roll 20a after the supply of the correction current Ir is preferably performed for at least a period until the photosensitive drum 12 rotates once. As a result, the surface potential can be returned to the charging potential VH over the entire outer peripheral surface of the photosensitive drum 12. In the present embodiment, as shown in FIG. 3, the transfer current It is supplied to the transfer roll 20a for a period until the photosensitive drum 12 rotates five times.
Note that the supply time of the transfer current It may be changed according to, for example, the supply time of the correction current Ir described above or the magnitude (absolute value) of the correction current Ir.

  Subsequently, the second job is started and the second sheet P is conveyed to the transfer position T. As shown in FIG. 4E, in the present embodiment, the surface potential of the photosensitive drum 12 is a charging potential VH from one end in the axial direction to the other end in the axial direction. The difference in surface potential is small between the portions. As a result, in the present embodiment, it is possible to suppress the occurrence of density unevenness, fogging, and the like in the image transferred to the second paper P2.

In the above-described example, after the first job that forms an image on the first sheet P1, the second job that forms an image on the second sheet P2 that is wider than the first sheet P1 is executed. The process when doing so has been described.
Here, for example, when an image is formed on a first sheet P1 and then formed on a third sheet having a width smaller than that of the first sheet P1, the above-described case is performed. It is not necessary to supply the correction current Ir to the transfer roll 20a. In this case, the boundary portion of the surface potential generated on the surface of the photosensitive drum 12 due to the image formation on the first paper P1 is located on the outer side in the axial direction than the third paper conveyed to the transfer position T. For this reason, when an image is formed on a third sheet having a width smaller than that of the first sheet P1, problems such as uneven density and fog due to the difference in surface potential of the photosensitive drum 12 are unlikely to occur. is there.

  As described above, in the present exemplary embodiment, after image formation is performed on the first sheet P1, image formation is performed on the second sheet P2 that is wider than the first sheet P1. In addition, by applying the correction current Ir to the transfer roll 20a, compared to the case where the correction current Ir is applied every time after the end of image formation regardless of the width of the paper, the transfer drum 20a to the photosensitive drum. Thus, the wear and deterioration of the photoconductive drum 12 due to the flow of the correction current Ir to 12 can be suppressed.

Next, processing executed by the control unit 5 of the present embodiment will be described. FIG. 5 is a flowchart showing an example of processing executed by the control unit 5 of the present embodiment.
As shown in FIG. 5, the control unit 5 first receives an instruction to execute a new image forming process via the UI 4 (see FIG. 1), the PC 2 (see FIG. 1), and the like (step 101). Here, when receiving an image formation instruction, the control unit 5 also acquires information regarding the type of paper on which an image is formed, the number of formed images, and the like. Information on the paper type includes information such as the paper transport direction, the paper size (paper width), and the paper thickness. Then, the control unit 5 stores information about the acquired sheet in association with the image forming process that has received the instruction. In the following, the new image forming process that has received an instruction in step 101 is referred to as a “new process”.

Next, the control unit 5 determines whether or not the image forming unit 10 is executing the image forming process received before the new process received in step 101 (step 102).
If the control unit 5 determines that the image forming process (hereinafter referred to as “current process”) received before the new process in the image forming unit 10 is being executed (YES in step 102). ), The width of the paper on which an image is formed by the current process is compared with the width of a paper on which an image is formed by a new process (step 103).
The comparison of the sheet width in step 103 is acquired when the control unit 5 receives a new process in step 101 and the information on the sheet acquired when the control unit 5 receives the current process. This is based on information on paper.

  If it is determined that the width of the paper on which the image is formed by the new processing is larger than the width of the paper on which the image is formed by the current processing (YES in step 103), the control unit 5 performs, for example, step 101 The magnitude (absolute value) of the correction current Ir supplied to the transfer roll 20a via the transfer power supply 25 and the supply time of the correction current Ir (the number of rotations of the photosensitive drum 12) based on the information on the sheet obtained in this way. Determine (step 104).

Subsequently, the control unit 5 determines whether or not the last sheet in the current process has passed the transfer position T in the image forming unit 10 (step 105).
If the last sheet in the current process has not passed the transfer position T (NO in step 105), the control unit 5 waits until the last sheet in the current process has passed the transfer position T.

  On the other hand, when the image forming unit 10 determines that the last sheet in the current process has passed the transfer position T (YES in step 105), the control unit 5 determines whether or not based on the condition determined in step 104. The correction power Ir is supplied from the transfer power supply 25 to the transfer roll 20a (step 106). As a result, the difference in surface potential generated on the surface of the photosensitive drum 12 is eliminated.

Then, after the supply time of the correction current Ir determined in step 104 has elapsed, the control unit 5 causes the transfer power supply 25 to supply the transfer current It to the transfer roll 20a (step 107).
Thereafter, the control unit 5 starts a new process in the image forming unit 10 (step 108), and ends the series of processes.

  The control unit 5 determines that the image forming process received before the new process is not executed in the above-described step 102 (NO in step 102), and in step 103, the new process is performed. If it is determined that the width of the paper on which the image is formed by the processing is equal to or smaller than the width of the paper on which the image is formed by the current processing (NO in step 103), execute steps 104 to 106. Instead, the processing after step 107 is performed.

In this embodiment, the correction current Ir is continuously supplied to the transfer roll 20a until the photosensitive drum 12 makes five revolutions. However, the correction current Ir is intermittently supplied to the transfer roll 20a. It may also be possible to supply them.
In this embodiment, the toner image is transferred using the transfer current It having the same magnitude between the first paper P1 and the second paper P2. However, the type (width, length) of the paper is used. The magnitude (absolute value) of the transfer current It may be changed depending on the thickness and the like.
Further, in the present embodiment, the transfer current It is supplied in advance to the transfer roll 20a before the sheet is conveyed to the transfer position T. However, the transfer current It may not necessarily be supplied. Further, a current having a current value different from the transfer current It may be supplied.

  In the present embodiment, the transfer power supply 25 is controlled so that the transfer current It is supplied to the transfer roll 20a during image formation, and the correction current Ir is supplied to the transfer roll 20a after image formation. Thus, the difference in surface potential between the axial end portions and the axial center portion of the photosensitive drum 12 is eliminated. However, the transfer power supply 25 may be controlled so that a transfer voltage is supplied to the transfer roll 20a during image formation and a correction voltage is supplied to the transfer roll 20a after image formation. In this case, the control part 5 should just control a voltage similarly to control of the electric current mentioned above. That is, when the image forming is performed on the second sheet P2 having a width wider than that of the first sheet P1 after the image forming is performed on the first sheet P1, the control unit 5 performs the transfer voltage. The transfer power supply 25 may be controlled so as to supply a correction voltage having a larger absolute value to the transfer roll 20a.

  Furthermore, in the present embodiment, the case where a two-component developer including a toner and a carrier is used as the developer has been described as an example. However, the present invention is not limited to this, and includes a toner and a carrier. A so-called one-component developer may be used.

  In this embodiment, the electrostatic latent image is formed on the photosensitive drum 12 by combining the image portion exposure method and the reverse development method. However, the present invention is not limited to this. A so-called background portion exposure method in which the background portion is exposed may be employed, or a so-called regular development method in which a portion that has not been exposed is developed as an image portion may be employed.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 5 ... Control part, 10 ... Image forming part, 12 ... Photosensitive drum, 13 ... Charger, 13a ... Developing roll, 14 ... Exposure apparatus, 15 ... Developing device, 20 ... Transfer device, 20a ... Transfer roll, 25 ... Transfer power supply, T ... Transfer position

Claims (5)

A rotating image carrier;
A transfer portion that is supplied with a transfer current or voltage of a predetermined size and transfers a toner image formed on the image carrier to a recording material;
When the toner image is transferred to the second recording material having a width larger than that of the first recording material after the toner image is transferred to the first recording material in the transfer unit, the first recording is performed. After the material has passed through the transfer portion, before the second recording material is conveyed to the transfer portion, a correction current / voltage having the same polarity that is larger in absolute value than the transfer current / voltage is applied to the transfer portion. and a control unit for supplying Te, the control unit, the first according to the thickness and / or width of the recording material, said correction current / voltage image forming apparatus to change the supply time and / or magnitude of .   The image forming apparatus according to claim 1, wherein the controller supplies the correction current / voltage to the transfer unit until the image carrier rotates at least once.   The control unit supplies the transfer current / voltage to the transfer unit after supplying the correction current / voltage to the transfer unit and before the second recording material is conveyed to the transfer unit. The image forming apparatus according to claim 1.   The control unit transfers the toner image to the third recording material having a width smaller than that of the first recording material after the toner image is transferred to the first recording material by the transfer unit. 2. The image forming apparatus according to claim 1, wherein the correction current / voltage is controlled not to be supplied. On the computer,
A function for receiving instructions on image formation processing;
A function of controlling the rotatable image carrier based on the instructions;
A function of supplying, to the transfer unit, a transfer current or voltage for transferring a toner image formed on the image carrier to a recording material based on the instructions;
When an instruction to form an image is received on a second recording material having a width larger than that of the first recording material after an image is formed on the first recording material, the first recording material is After passing through the section, before the second recording material is transported to the transfer section, a correction current / voltage having the same polarity having a larger absolute value than the transfer current / voltage is supplied to the transfer section. to realize the functions and the ability to the control, the first according to the thickness and / or width of the recording material, said correction current / voltage supply time and / or program to change the size of the.

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