JP2018005090A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a picture quality defect due to a latent image ghost even when electricity cannot be removed by an anti-static lamp, as compared with the case where a potential difference is not adjusted.SOLUTION: A latent image ghost removing process during a preparation period is executed while both of a photoreceptor drum 14 and a primary transfer roll 24 are in a non-charged state (0 V). A control subject for the latent image ghost removing process in the preparation period the primary transfer roll 24. In the preparation period, is the primary transfer roll 24 is controlled to a voltage (positive voltage) of an image formation period or higher than that during the image formation period ("pre-transfer process control"). Also, during an interval period, the primary transfer roll 24 is charged with electricity in the immediately preceding image formation period so that a control subject for the latent image removing process during the interval period is the photoreceptor drum. In the interval period, the photoreceptor drum 14 is controlled to the same voltage (0 V to 300 V) as in the preparation period and a transfer voltage is thereby secured ("electric charge adjustment process").SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  A charging member (charging roll) is brought into contact with the surface of the photosensitive member as an image holding member, and the charging member is applied with a standard voltage to uniformly charge the surface of the photosensitive member, and then electrostatically based on image information. In an image forming apparatus that forms a latent image, supplies a developer (for example, toner), develops the image, and transfers the developed image to the transfer target, insufficient charge removal on the surface of the photoconductor may affect the image quality. Are known.

  Japanese Patent Application Laid-Open No. H10-228707 describes that image processing defects such as a latent image ghost are prevented by performing preprocessing such as charging and exposure on a photoconductor. More specifically, before forming an image on the photoconductor, the surface of the photoconductor is precharged by at least one of a transfer charging unit and a separation charging unit, and the surface of the photoconductor is exposed to an image exposure unit and a static elimination exposure. Pre-exposure is performed by at least one of the means.

Japanese Patent Laid-Open No. 10-186745

  No countermeasure has been established for image quality defects due to latent image ghosts in models that cannot be neutralized with a static elimination lamp.

  An object of the present invention is to obtain an image forming apparatus that can improve image quality defects due to a latent image ghost even when the neutralization by the neutralization lamp cannot be performed, as compared with the case where the potential difference is not adjusted.

  According to a first aspect of the present invention, an image formed by an image carrier having a grounded substrate and a developer charged on the image carrier whose surface of a photosensitive layer is charged is displayed on the image carrier. A transfer means for transferring to a transfer member charged at a different electric potential, a preparation period before an image forming period for forming an image on the image holding body, and an image intermittently on the image holding body in the image forming period. Adjustment means for adjusting the potential difference between the grounded image carrier base and the transfer member to be a predetermined potential difference in at least one of the interval periods during which no image is formed when formed. And an image forming apparatus.

  According to a second aspect of the present invention, in the first aspect of the present invention, the potential difference is equal to or greater than a potential difference when an image is transferred.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the adjusting means completes charging of the image carrier to the potential during the image forming period in the preparation period. Before the transfer, a voltage or current is supplied to the transfer member.

  According to a fourth aspect of the present invention, in the invention according to the third aspect, the adjusting means supplies a voltage or a current to the transfer member before the charging of the image carrier is started during the preparation period. .

  According to a fifth aspect of the present invention, in the invention of the third or fourth aspect, the image holding body has an image holding surface to be applied in a circle, and the transfer member during the preparation period. The period during which the voltage or current is supplied is an integer number of rounds of the image carrier.

  According to a sixth aspect of the invention, in the invention according to any one of the first to fifth aspects of the invention, the adjusting unit is configured so that the image holding member approaches a ground potential during the interval period. The voltage or current supplied to the charging means of the image carrier is adjusted.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects of the present invention, an image carrier whose voltage or current is adjusted during the interval period by the adjusting means is used as the interval. When the period ends and the image forming period is restarted, charging is performed at a potential that is higher in absolute value than the potential in the image forming period before the interval period.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the adjusting means adjusts stepwise to a target adjustment value.

  According to the first and second aspects of the present invention, image quality defects due to latent image ghosts can be improved even when static elimination by a static elimination lamp is not possible, compared to a case where the potential difference is not adjusted.

According to the third and fourth aspects of the invention, it is possible to improve image quality defects due to latent image ghosts during the preparation period. According to the fifth aspect of the invention, voltage or current is supplied to the transfer member. Compared with the case where the period is not an integral number of revolutions of the image carrier, the latent image ghost removal effect can be made uniform over the circumference of the image carrier.

  According to the sixth aspect of the present invention, even when the transfer member is under constant current control, the potential of the transfer member can be increased as an absolute value in the interval period compared to the image formation period. According to the seventh aspect of the present invention, the rise of the surface potential of the image carrier after the interval period is accelerated as compared with the case where the potential is equal to or lower than the potential in the image forming period before the interval period. be able to.

  According to the eighth aspect of the present invention, it can be avoided that a belt-like history remains.

(A) is a front view of the image forming apparatus according to the present embodiment, and (B) is a sectional view of the photosensitive drum. 3 is a control block diagram of an image forming processing engine of the image forming apparatus according to the present embodiment. FIG. FIG. 5 is a block diagram in which the flow of image formation processing including latent image ghost removal processing is classified by function in the image formation processing control unit according to the present embodiment. 5 is a flowchart showing a main routine showing a flow from a process preparation start to a process end for executing an image forming process in the image processing apparatus according to the present embodiment. 6 is a timing chart of latent image ghost removal (pre-transfer) processing for each color, which is executed in the image formation preparation period in FIG. 4. 5 is a flowchart showing details of an image forming processing routine in step 218 in FIG. 4. FIG. 7 is a timing chart of a latent image ghost removal (charging adjustment) process for each color, which is executed in the image formation interval period in FIG. 6. FIG. 11 is a characteristic diagram showing a result of a sensitivity evaluation as to whether or not a latent image ghost has been eliminated by a latent image ghost removal process according to the present embodiment.

  FIG. 1A is a schematic configuration diagram of an image forming apparatus 10 to which the exemplary embodiment is applied.

  The image forming apparatus 10 is capable of image formation (sometimes referred to as “printing”) in a quadruple tandem full color, and in order from the upstream side, yellow (Y), magenta, which are examples of image forming units, respectively. (M), cyan (C), and black (K) electrophotographic first image forming unit 12Y, second image forming unit 12M, third image forming unit 12C, and fourth image forming unit that output images of respective colors. 12K are arranged at a predetermined interval from each other.

  In the following, the four first image forming units 12Y, the second image forming unit 12M, the third image forming unit 12C, and the fourth image forming unit 12K have the same configuration. Unit 12 ”. Further, when the description is made without distinguishing the respective constituent members of the image forming unit 12, the end of the reference numerals (“Y”, “M”, “C”, “K”) of the respective constituent members described in the drawings is omitted. There is a case.

  The image forming unit 12 includes a photosensitive drum 14 as an example of a drum-shaped image carrier having a photosensitive layer on the surface, a charging roll 16 that uniformly charges the photosensitive drum 14, and a uniform charging. An exposure unit 18 that irradiates the photosensitive drum 14 with image light to form an electrostatic latent image, a developing unit 20 that transfers toner to the latent image to form a toner image, and remains on the photosensitive drum 14 after transfer. And a cleaning unit 26 for removing the toner.

  Further, the image forming apparatus 10 includes an endless belt-like intermediate transfer belt 22 as an image holding member, which is stretched around a path that contacts each of the photosensitive drums 14 of the four image forming units 12. And a primary transfer roll 24 as an example of a transfer member that transfers the toner image formed on the photosensitive drum 14 to the intermediate transfer belt 22. A region where the photosensitive drum 14 and the primary transfer roll 24 face each other is referred to as a primary transfer portion T1.

  Further, the image forming apparatus 10 includes a recording paper transport mechanism 28 that transports the recording paper P stored in the paper tray 29, and a fixing unit 30 that fixes the toner image on the recording paper P.

  The intermediate transfer belt 22 is wound around a drive roll 32 that is rotationally driven, a tension roll 34 that adjusts the tension, and a backup roll 36. The primary transfer roll 24 is disposed inside the intermediate transfer belt 22.

  Further, a secondary transfer roll 38 that transfers the toner image on the intermediate transfer belt 22 onto the recording paper P conveyed by the recording paper conveyance mechanism 28 at a position facing the backup roll 36 across the intermediate transfer belt 22. Is provided. A region where the backup roll 36 and the secondary transfer roll 38 are opposed to each other is referred to as a secondary transfer portion T2.

  Further, a toner that removes the toner remaining on the intermediate transfer belt 22 after the toner image is transferred onto the recording paper P by the secondary transfer roll 38 at a position facing the drive roll 32 across the intermediate transfer belt 22. A removal unit 40 is provided.

  The recording paper transport mechanism 28 includes a pickup roll 42, transport rolls 44 and 46, paper guides 48, 50, 52, 54 and 56 that guide the transport movement path, a paper discharge roll 58, and a paper discharge tray (not shown). Etc.). The recording paper transport mechanism 28 drives the recording paper P accommodated in the paper tray 29 to a secondary transfer position where the secondary transfer roll 38 and the backup roll 36 are opposed to each other with the intermediate transfer belt 22 interposed therebetween. It is transported from the secondary transfer position to the fixing unit 30 and then transported from the fixing unit 30 to the paper discharge tray.

  FIG. 1B is an example of a cross-sectional view of the photosensitive drum 14.

  As the photosensitive drum 14, a cylindrical base material 100 serving as an axis is applied as an example of a substrate. The base material 100 is made of metal (made of aluminum) and is grounded. A subbing layer 102, a charge generation layer 104, and a charge transport layer 106 are provided as a photosensitive layer in order from the substrate 100 side around the substrate 100.

  The undercoat layer 102 has a role of a base for holding the charge generation layer 104 and is basically conductive, but may have a resistance as necessary.

  The charge generation layer 104 has a function of generating a positive charge when a voltage is applied to the photosensitive drum 22 from the charging unit 24 (see FIG. 1A).

  The charge transport layer 106 is an insulator, and a negative charge is charged on the surface of the surface according to the charge generation layer 104. When exposed, the charge transport layer 106 is a layer in which positive charge is transported. It is an important layer.

(Engine control system)
FIG. 2 is a block diagram illustrating an example of a control system of the image forming apparatus 10.

  A user interface 142 is connected to the main controller 120 which is a main control function of the image forming apparatus 10. The user interface 142 includes an input unit for inputting an instruction regarding image formation and the like, and an output unit for displaying information such as information at the time of image formation or informing by voice.

  The main controller 120 is connected to a network line with an external host computer (not shown), and image data is input via the network line.

  When the image data is input, the main controller 120 analyzes, for example, the print instruction information included in the image data and the image data, and converts them into a format suitable for the image forming apparatus 10 (for example, raster image data). The converted image data is sent to an image formation processing control unit 144 as an example of an adjustment unit that functions as a part of the MCU 118.

  In the image formation processing control unit 144, the drive system control unit 146, the charge control unit 148, the development control unit 150, and the exposure control unit 152 function as the MCU 118 together with the image formation processing control unit 144 based on the input image data. Each of the transfer control unit 154, the fixing control unit 156, and the cleaner control unit 158 (collectively referred to as “each control unit”), which is an example of the transfer unit, is synchronously controlled to execute image formation. In the present embodiment, the functions executed by the MCU 118 are classified and described as blocks, and the hardware configuration of the MCU 118 is not limited.

  The main controller 120 is connected to a temperature sensor 162, a humidity sensor 164, and the like, and may detect the environmental temperature / humidity in the housing of the image forming apparatus 10 based on the temperature sensor 162 and the humidity sensor 164.

(Generation of latent image ghost)
The image forming apparatus 10 according to the present exemplary embodiment does not include a static elimination lamp around the photosensitive drum 14. The static elimination lamp is a device having a function of eliminating the charge on the surface of the photosensitive drum 14 and making the charge accumulated therein uniform when the photosensitive drum 14 receives light.

  In theory, the surface of the photosensitive drum 14 is uniformly charged by the charging roll 16, so that the previous exposure state in the exposure unit 18 is eliminated. And black), the charge accumulated inside the photosensitive member 14 may not be removed even if it is uniformly charged by the charging roll 16, and may appear as an afterimage (latent image ghost).

  Therefore, in the present embodiment, in the image forming apparatus 10 that is not equipped with a static elimination lamp, the latent image ghost removal process is executed using the transfer voltage by the primary transfer roll 24 as a substitute for the static elimination lamp.

  It should be noted that the presence or absence of the static elimination lamp is irrelevant whether or not the latent image ghost removal function of the present embodiment is provided, and the image processing equipped with the static elimination lamp from the image processing apparatus having the latent image ghost elimination function. It does not exclude the device. For example, the latent image ghost removal function of the present embodiment can be applied in an auxiliary manner depending on power saving measures, fail-safe when the charge removal lamp fails, exposure image conditions, and the like.

  The latent image ghost removal using the transfer voltage is shown in the following (1) to (4), taking as an example the case where the primary transfer roll 24 is controlled with constant current.

  (1) For example, the charging voltage during the image forming period of the photosensitive drum 14 charged by the charging roll 16 is set to about −700V.

  (2) The charging voltage of the photosensitive drum 14 is set to 0 V to −300 V during the non-image forming period (the following preparation period and interval period).

  (3) On the other hand, the transfer roll (primary transfer roll 24) is set up so that it is equal to or higher than the transfer voltage when transferring during the image forming period (about +800 V to +1.3 KV).

  (4) Due to the potential difference between the base material 100 (grounding state) which is the base of the photoconductive drum 14 and the primary transfer roll 24, a function (static elimination function) of discharging the accumulated charge from the photoconductive drum 14 at the time of exposure works.

  Here, when the primary transfer roll 24 is controlled at a constant current, it is necessary to lower the charging voltage of the photosensitive drum 14 in order to ensure a transfer voltage higher than that during the image forming period in order to exhibit the charge eliminating function. Therefore, the state (2) is performed before the state (3).

(Latent image ghost removal process "Pre-transfer process")
The latent image ghost removal is impossible at least when the photosensitive drum 14 is exposed (electrostatic latent image formation) with a light beam from the exposure unit 18.

  On the other hand, under the control of the drive system control unit 146, the photosensitive drum 14 starts to rotate and the charging of the photosensitive drum 14 is completed (in the case where the potential is increased stepwise, the final potential increase is completed). However, there is a preparation period before the image formation period during which exposure can be started.

  In addition, when an image is formed on a plurality of recording sheets P in the image forming period, each recording sheet P is generally conveyed intermittently at a predetermined interval. In other words, There is an interval period when the image to be recorded on each recording paper P is exposed to the photosensitive drum 14.

  Therefore, in the present embodiment, the preparation period that exists before the image formation period starts and the interval period that exists during the image formation period are set as periods during which the latent image ghost removal process can be executed. .

  Note that “potential (or voltage) during the image forming period” refers to a potential (or voltage) during a period other than the interval period during the image forming period.

  The latent image ghost removal process during the preparation period is executed from a state in which the photosensitive drum 14 is not charged to a period during which the charging roller 16 is charged to a potential during the image formation period and enters the image formation period.

  In the present embodiment, specifically, it is executed during a period in which both the photosensitive drum 14 and the primary transfer roll 24 are in an uncharged state (0 V). Therefore, the main control body for the latent image ghost removal processing in the preparation period is the primary transfer roll 24. That is, during the preparation period, the primary transfer roll 24 is controlled to a voltage (plus voltage) higher during the image formation period or during the image formation period (“pre-transfer process control”).

  The pre-transfer is not limited to the period in which the photosensitive drum 14 is in an uncharged state, and the stage where the potential of the photosensitive drum 14 is not fully raised in the course of gradually raising the potential of the photosensitive drum 14 (about −300 V or less). In this state, pre-transfer may be performed.

(Latent image ghost removal processing “Charge adjustment processing”)
During the interval period, the primary transfer roll 24 is in a charged state in the immediately preceding image forming period, and therefore, the control subject for the latent image ghost removal process in the interval period is the photosensitive drum. That is, in the interval period, the transfer voltage is secured by controlling the photosensitive drum 14 to the same voltage (0 V to −300 V) as in the preparation period (“charging adjustment process”).

  FIG. 3 is a block diagram in which the flow of image formation processing including latent image ghost removal processing in the image formation processing control unit 144 is classified by function. Each block in FIG. 3 does not limit the hardware configuration of the image forming process control unit 144. In FIG. 3, alphabets (A to G) surrounded by a rectangular frame (□ frame) indicate a connection relationship of transmission systems that exchange signals with each control unit.

  As shown in FIG. 3, the user interface 142 is connected to the reception unit 170, and outputs an activation instruction to the reception unit 170 when executing the image forming process.

  The receiving unit 170 is connected to the photosensitive drum rotation instruction unit 172. Upon receiving the activation instruction, the reception unit 170 outputs a drive start instruction for a drive system device (for example, a motor) to the photosensitive drum rotation instruction unit 172. In response to the drive start instruction, the photosensitive drum rotation instruction unit 172 instructs the drive system control unit 146 to start rotation of the photosensitive drum 14.

  The photosensitive drum rotation instruction unit 172 is connected to the pre-transfer program reading unit 174. When the photosensitive drum rotation instruction unit 172 instructs the drive system control unit 146 to start rotation, the photoconductor drum rotation instruction unit 172 instructs the pre-transfer program reading unit 174 to read the pre-transfer program from the pre-transfer program memory 176.

  The pre-transfer program reading unit 174 is connected to the pre-transfer executing unit 178, and sends the read pre-transfer program to the pre-transfer executing unit 178.

  The pre-transfer execution unit 178 controls the charge control unit 148, the development control unit 150, and the transfer control unit 154 to execute pre-transfer processing. That is, the primary transfer roll 24 is controlled to a voltage (plus voltage) during the image formation period (“pre-transfer process control”). At this time, the voltage of the primary transfer roll 24 may be further set to the positive side than during the normal image forming period. The pre-transfer process is preferably current control, but voltage control is not denied.

  The pre-transfer execution unit 178 is connected to the image formation preparation process execution unit 180. The image formation preparation processing execution unit 180 controls the charging control unit 148, the development control unit 150, and the transfer control unit 154, and charges the photosensitive drum 14 and the developing unit 20 in parallel with the pre-transfer processing control.

  The image formation preparation process execution unit 180 is connected to the image data reading unit 182. When the image formation preparation processing execution unit 180 is ready to charge the photosensitive drum 14, the image data reading unit 182 is instructed to read image data.

  When the image data reading unit 182 receives a reading instruction (reading instruction), the image data reading unit 182 reads the image data from the main controller 120 and sends it to the image forming process execution unit 184.

  The image forming process execution unit 184 controls each control unit to execute the image forming process.

  Further, the image forming process execution unit 184 is connected to the processing number acquisition unit 186. The processing number acquisition unit 186 acquires the processing number in real time from the image formation processing execution unit 184 and sends it to the latent image ghost removal necessity determination unit 188.

  The latent image ghost removal necessity determination unit 188 outputs a signal (execution signal) indicating that latent image ghost removal is necessary for each predetermined number of processing sheets (for example, 3 to 5 sheets). To send.

  Upon receiving the execution signal, the charge adjustment program reading unit 190 reads the charge adjustment program from the charge adjustment program memory 192 and sends the read charge adjustment program to the charge adjustment execution unit 194.

  The charge adjustment execution unit 194 controls the charge control unit 148, the development control unit 150, and the transfer control unit 154 to execute a charge adjustment process. That is, the photosensitive drum 14 is controlled to a voltage (0 V to −300 V) in an uncharged state that is equal to or close to the preparation period (“charging adjustment process”). At this time, the voltage of the primary transfer roll 24 may be set on the plus side of the normal image forming period. The charge adjustment processing is preferably current control, but voltage control is not denied.

  The operation of this embodiment will be described below.

(Flow of normal image formation processing mode)
Since the image forming unit 12 has substantially the same configuration, here, the first image forming unit 12Y that forms a yellow image disposed on the upstream side of the intermediate transfer belt 22 in the traveling direction will be described as a representative. . The same reference numerals with magenta (M), cyan (C), and black (K) are attached to the members having the same function as the first image unit 12Y instead of yellow (Y). The description of the second to fourth image forming units 12M, 12C, and 12K is omitted.

  First, in the preparation period, rotation of the photosensitive drum 14Y is started, and then, a voltage in which direct current and alternating current are superimposed is applied to the surface of the photosensitive drum 14Y by the charging roll 16Y in the present embodiment. It is charged to a predetermined potential that is a potential during the formation period. In general, it can be selected in the range of -400V to -800V, and in this embodiment, it is set to -700V. For example, when charging the photosensitive drum 14Y, a voltage obtained by superimposing an AC voltage having a specific amplitude Vpp and a specific frequency f on the DC voltage is applied to the charging roll 16Y.

  As shown in FIG. 1B, the photosensitive drum 14Y has a photosensitive layer (an undercoat layer 102, a charge generation layer 104, and a charge transport layer 106) on a conductive metal substrate 100 as a base. It is formed by laminating and usually has high resistance, but when irradiated with a light beam including laser light or LED light, it has a property that the resistance of the portion irradiated with the light beam changes.

  Therefore, in the MCU 118, an exposure light beam is output from the exposure unit 18Y to the surface of the charged photosensitive drum 14Y according to the yellow image data sent from the main controller 120. The light beam is applied to the photosensitive layer on the surface of the photoreceptor drum 14Y, whereby an electrostatic latent image of a yellow print pattern is formed on the surface of the photoreceptor drum 14Y.

  The electrostatic latent image is an image formed on the surface of the photosensitive drum 14Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is reduced by the light beam, and the charged charge on the surface of the photosensitive drum 14Y. On the other hand, it is a so-called negative latent image formed by the charge remaining in the portion not irradiated with the light beam.

  The electrostatic latent image formed on the photosensitive drum 14Y in this way is rotated to the developing position by the rotation of the photosensitive drum 14Y. At this development position, the electrostatic latent image on the photosensitive drum 14Y is made a visible image (toner image) by the developing unit 20Y.

  Yellow toner is accommodated in the developing unit 20Y. The yellow toner is triboelectrically charged by being stirred inside the developing unit 20Y, and has a charge of the same polarity (−) as that of the surface of the photosensitive drum 14Y.

  As the surface of the photosensitive drum 14Y passes through the developing portion 20Y, yellow toner is electrostatically attached only to the latent image portion on the surface of the photosensitive drum 14Y, and the latent image is developed with the yellow toner.

  The photosensitive drum 14Y continues to rotate, and the toner image developed on the surface of the photosensitive drum 14Y is conveyed to the primary transfer portion T1. When the yellow toner image on the surface of the photoreceptor drum 14Y is conveyed to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 24Y, and electrostatic force from the photoreceptor drum 14Y toward the primary transfer roll 24Y acts on the toner image. Then, the toner image on the surface of the photosensitive drum 14Y is transferred to the surface of the intermediate transfer belt 22.

  The transfer bias applied at this time is a (+) polarity opposite to the polarity (−) of the toner. For example, in the first image forming unit 12Y, the transfer control unit 154 controls the constant current to about +20 to 30 μA. .

  On the other hand, the transfer residual toner on the surface of the photosensitive drum 14Y is cleaned by the cleaning unit 26Y.

  The primary transfer bias applied to the primary transfer rolls 24M, 24C, and 24K after the second image forming unit 12M is also controlled in the same manner as described above.

  Thus, the intermediate transfer belt 22 to which the yellow toner image is transferred by the first image forming unit 12Y is sequentially conveyed through the second to fourth image forming units 12M, 12C, and 12K, and the toner images of the respective colors are similarly overlapped. Multiple transfer.

  The intermediate transfer belt 22 on which the toner images of all colors are transferred in multiple numbers through all the image forming units 12 is conveyed in the direction of the arrow and holds the images of the backup roll 36 and the intermediate transfer belt 22 that are in contact with the inner surface of the intermediate transfer belt 22. It reaches the secondary transfer portion T2 constituted by the secondary transfer roll 38 arranged on the surface side.

  On the other hand, the recording paper P is fed at a predetermined timing between the secondary transfer roll 38 and the intermediate transfer belt 22 via the supply mechanism, and a secondary transfer bias is applied to the secondary transfer roll 38.

  The transfer bias applied at this time is the polarity (+) opposite to the polarity (−) of the toner, and the electrostatic force from the intermediate transfer belt 22 toward the recording paper P acts on the toner image, and the toner on the surface of the intermediate transfer belt 22 The image is transferred to the surface of the recording paper P.

  Thereafter, the recording paper P is sent to the fixing unit 30 where the toner image is heated and pressurized, and the color-superposed toner image is melted and permanently fixed on the surface of the recording paper P. The recording paper P on which the color image has been fixed is carried out toward the discharge unit, and a series of color image forming operations is completed.

  The flow of control for removing the latent image ghost according to the present embodiment will be described below with reference to FIGS.

(Latent image ghost removal processing during the preparation period "Pre-transfer processing")
FIG. 4 is a flowchart showing a main routine showing the flow from the start of processing preparation to the end of processing for executing image forming processing in the image processing apparatus 10 according to the present embodiment.

  In step 200, it is determined whether it is a preparation start time. If a negative determination is made, this routine ends. If an affirmative determination is made in step 200, it is determined that an activation instruction has been issued from the user interface 142, the process proceeds to step 202, the rotation of the photosensitive drum 14 is started, and the process proceeds to step 204.

  In step 204, charging of the primary transfer roll 24 is started. In this case, it is preferable to start up in stages.

  When the primary transfer roll 24 is charged, the photosensitive drum 14 is not charged by the charging roll 16 (for example, 0 V), and the primary transfer roll 24 has a voltage higher than the image forming period. The negative charge of the photosensitive drum 14 is attracted to the primary transfer roll 24. This negative charge movement has a function equivalent to charge removal, and the latent image ghost of the photosensitive drum 14 is eliminated (pre-transfer).

  In the next step 206, it is determined whether the photosensitive drum 14 has rotated a predetermined integer number of times (in this embodiment, one rotation) from the start of charging of the primary transfer roll 24, and affirmative. Then, the process proceeds to step 208, and the charging of the primary transfer roll 24 is finished. In this case, it is preferable to lower in a stepwise manner.

  The reason why the pre-transfer period (adjustment period) due to the charging of the primary transfer roll 24 is set to an integral number of revolutions of the photosensitive drum 14 is to equalize the effect of static elimination on the peripheral surface of the photosensitive drum 14. In other words, it is possible to neutralize static electricity in a specific area.

  In the next step 210, the delay time of each color set based on the arrangement relationship of the image forming units 12 of each color shown in FIG. 1A and the process speed is read, and then the process proceeds to step 212. The charging of each unit (photosensitive drum 14 and developing unit 20) is started at the delay time set for each color, and the process proceeds to step 214.

  In step 214, it is determined whether preparation of all colors (preparation until exposure is possible) is completed. If the determination is affirmative, the process proceeds to step 216, and the secondary transfer roll 38 is charged. Then, the transfer bias is applied, and the process proceeds to Step 218.

  In step 218, an image forming process (exposure process using a light beam) is executed. Details of the image forming process in step 218 will be described later based on the flowchart of FIG.

  In the next step 220, charging of each part is terminated, and then the routine proceeds to step 222, where the rotation of the photosensitive drum 14 is stopped, and this routine is terminated.

  FIG. 5 is a current control timing chart of the latent image ghost removal (pre-transfer) process for each color, which is executed in the preparation period in FIG. 4, and the portion with a relatively high density is the pre-transfer process period. (Refer to the legend in FIG. 5). In FIG. 5, the pre-transfer process is executed at the same time for each color, but may be executed with a time difference as in the image forming process.

(Latent image ghost removal processing during the interval "Charge adjustment processing")
FIG. 6 is a flowchart showing details of the image forming processing routine in step 218 of FIG.

  In step 250, the image data is read out, and then the process proceeds to step 252 to set the delay time of each color set based on the arrangement relationship of the image forming units 12 of each color and the process speed shown in FIG. Then, the process proceeds to step 254 to start paper conveyance control. That is, the recording paper P is taken out from the paper tray 29, conveyed by the recording paper conveyance mechanism 28, and positioned at a position synchronized with the toner image at the secondary transfer position (T2).

  In the next step 256, it is determined whether or not the exposure start time of the first color (Y color in the present embodiment) is reached. If an affirmative determination is made, the process proceeds to step 258 and the delay time set for each color is reached. , Exposure is started.

  In the next step 260, it is determined whether or not the exposure of all the colors has been completed. If an affirmative determination is made, the process proceeds to step 262 to determine whether or not to continue the image forming process. That is, when an image is formed on N recording papers P, the image forming process is repeated N times.

  If a negative determination is made in step 262, it is determined that it is not necessary to continue the image forming process, the routine ends, and the process returns to step 220 in FIG.

  If the determination in step 262 is affirmative, it is determined that the image forming process needs to be continued, and the process proceeds to step 264.

  In step 264, it is determined whether or not the predetermined number of separators has been reached. The number of sheets to be processed is, for example, the number of processed sheets in which M sheets (about 3 to 5 sheets) are separated in terms of the number of processed sheets of recording paper P (A4 size). In step 264, an affirmative determination is made for each M sheets. Will be.

  If a negative determination is made in step 264, the process returns to step 254, and the image forming process for the next recording paper P is executed. If the determination in step 264 is affirmative, it is determined that it is time to execute the latent image ghost removal process (charging adjustment process), the process proceeds to step 266, and each unit (photosensitive) is set with the delay time set for each color. The charging of the body drum 14 and the developing unit 20) is stopped. The charging pause is preferably lowered step by step. The term “rest” means that the charging voltage is 0 V, but a voltage (for example, 0 V to −300 V) that shifts to a plus side from the charging voltage (−700 V) during the image forming period is an allowable range.

  When the charging of the photosensitive drum 14 is adjusted, the primary transfer roll 24 is controlled at a constant current. As a result, the voltage becomes higher than the voltage during the image formation period, and the negative charge on the photosensitive drum 14 is transferred to the primary transfer roll 24. A force attracted to the roll 24 works. This negative charge movement has a function equivalent to charge removal, and the latent image ghost of the photosensitive drum 14 is eliminated (charging adjustment).

  In the next step 268, it is determined whether or not the photosensitive drum 14 has made an integral number of revolutions (one revolution in the present embodiment) from the start of the charge adjustment process. Then, the charging of each unit (photosensitive drum 14 and developing unit 20) is resumed at the set delay time for each color, and the process proceeds to step 254 to continue the image forming process. In this case, it is preferable to start up in stages.

  The reason why charging of each part is resumed is an integer number of revolutions of the photosensitive drum 14 in order to equalize the influence of static elimination on the circumferential surface of the photosensitive drum 14. In other words, it is possible to neutralize static electricity in a specific area.

  Note that in the stepwise start-up in step 270 of FIG. 6 (when the image carrier whose voltage or current is adjusted during the interval period is used when the interval period ends and the image formation period is restarted), the image before the interval period is displayed. It is preferable to charge at a potential higher in absolute value than the potential in the formation period. As a result, it is possible to reduce or eliminate the standby time due to insufficient voltage immediately after the return.

  FIG. 7 is a current control timing chart of the latent image ghost removal (charge adjustment) processing for each color, which is executed in the image formation interval period in FIG. 6, and the portion subjected to oblique line processing is the charge adjustment processing period. (See legend in FIG. 7). In FIG. 7, the charge adjustment processing is executed in synchronization with the delay time of each color, but may be executed simultaneously after the end of the final color.

  FIG. 8 is a characteristic diagram showing a result of sensitively determining whether or not the latent image ghost has been eliminated by the latent image ghost removal processing according to the present embodiment. The horizontal axis of FIG. 8 is the number of processed sheets of recording paper P in A4 conversion, and the vertical axis of FIG. 8 is the sensitivity evaluation G, where G0 is the best and G3 is the worst. Evaluating.

  A characteristic A in FIG. 8 is an evaluation characteristic when the countermeasure against the latent image ghost is not taken. Almost the evaluation G2 is changed, and the latent image ghost is constantly generated.

  Characteristic B in FIG. 8 is an evaluation characteristic when only pre-transfer countermeasures are taken. The highest evaluation G0 is maintained up to the first three sheets, but the evaluation gradually decreases after the fourth sheet. Transition to G2. That is, the pre-transfer process is effective up to about three sheets at the start of the process, but the effect is reduced as the number of processed sheets increases.

  A characteristic C in FIG. 8 is an evaluation characteristic when the pre-transfer countermeasure and the charge adjustment countermeasure are used together. The highest evaluation G0 is maintained up to about the first five sheets, and thereafter the evaluation G0 and G1 are evaluated. In other words, when the pre-transfer countermeasure and the charge adjustment countermeasure are used in combination, the effect of removing the latent image ghost can be maintained even if the number of processed sheets is increased.

  In the present embodiment, the preparation period and the interval period are set as periods during which the latent image ghost removal process can be executed.

  Execution of this latent image ghost removal processing can be performed in a single execution period in the preparation period, a single execution in the interval period, or a combined execution in the preparation period and the interval period.

  The execution pattern may be changed depending on the type of job.

  For example, a job (image forming process) with 3 to 5 recording sheets P (A4 size) may be selected to be executed alone during the preparation period.

  Further, for example, for a job (image forming process) having six or more recording sheets P (A4 size), it is only necessary to select the combined use of the preparation period and the interval period.

  Further, if the latent image ghost removal process is executed in the final interval period of the previous job execution, the execution in the preparation period can be omitted and the execution in the interval period can be performed independently.

P recording paper T1 primary transfer portion T2 secondary transfer portion 10 image forming apparatus 12 image forming unit 12Y first image forming unit 12M second image forming unit 12C third image forming unit 12K fourth image forming unit 14 photoconductor drum 16 charging Roll 18 Exposure section 20 Development section 22 Intermediate transfer belt 24 Primary transfer roll 26 Cleaning section 28 Recording paper transport mechanism 29 Paper tray 30 Fixing section 32 Drive roll 34 Tension roll 36 Backup roll 38 Secondary transfer roll 40 Toner removal section 42 Pickup roll 44, 46 Transport roll 48, 50, 52, 54, 56 Paper guide 58 Paper discharge roll 118 MCU
DESCRIPTION OF SYMBOLS 120 Main controller 142 User interface 144 Image formation process control part 146 Drive system control part 148 Charging control part 150 Development control part 152 Exposure control part 154 Transfer control part 156 Fixing control part 158 Cleaner control part 162 Temperature sensor 164 Humidity sensor 170 Reception part 172 Photosensitive drum rotation instructing unit 174 Pre-transfer program reading unit 176 Pre-transfer program memory 178 Pre-transfer executing unit 180 Image forming preparation process executing unit 182 Image data reading unit 184 Image forming process executing unit 186 Processed number acquiring unit 188 Latent image ghost Deletion necessity determination unit 190 Charge adjustment program reading unit 192 Charge adjustment program memory 194 Charge adjustment execution unit

Claims (8)

An image carrier having a grounded substrate;
A transfer means for transferring an image formed by a developer charged on the image carrier having the surface of the photosensitive layer charged to a transfer member charged to a potential different from that of the image carrier;
At least one of a preparation period before an image forming period for forming an image on the image carrier and an interval period during which an image is not formed when an image is intermittently formed on the image carrier in the image forming period. Adjusting means for adjusting the potential difference between the grounded image carrier and the transfer member to be a predetermined potential difference in the period of
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the potential difference is equal to or greater than a potential difference when an image is transferred. The adjusting means is
3. The image forming apparatus according to claim 1, wherein, in the preparation period, a voltage or a current is supplied to the transfer member before the charging of the image carrier to the potential during the image forming period is completed. The adjusting means is
The image forming apparatus according to claim 3, wherein a voltage or a current is supplied to the transfer member before the charging of the image carrier is started in the preparation period. The image holding body has an image holding surface to be applied around,
The image forming apparatus according to claim 3, wherein a period during which the voltage or current is supplied to the transfer member during the preparation period is an integer number of rounds of the image carrier. The adjusting means is
6. The image forming apparatus according to claim 1, wherein a voltage or a current supplied to a charging unit of the image carrier is adjusted so that the image carrier approaches a ground potential during the interval period. .   An image carrier whose voltage or current has been adjusted during the interval period by the adjusting means is adjusted to a potential in the image forming period before the interval period when the interval period ends and the image forming period is restarted. The image forming apparatus according to claim 1, wherein the image forming apparatus is charged with a high potential as an absolute value.   The image forming apparatus according to claim 1, wherein the adjusting unit adjusts stepwise up to a target adjustment value.