JP2020134608A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can suppress the transfer of toner between images and the occurrence of a photoreceptor memory and supply a sufficient amount of toner to a cleaning blade.SOLUTION: An image formation apparatus 1 for supplying toner as a lubricant to a cleaning blade 160K that scrapes off the toner remaining on an outer peripheral surface of a photoreceptor drum 122k after the primary transfer by forming a toner patch on the outer peripheral surface of the photoreceptor drum 122K between the images determines the charge amount of the toner patch from the exposure condition, development condition and environmental condition at the time when the toner patch is formed, conveys the toner patch to the cleaning blade 160K while performing the constant current control of the primary transfer bias when the charge amount of the toner patch is large, performs the constant voltage control of the primary transfer bias when the charge amount of the toner patch is small, and therefore prevents the toner from moving onto the intermediate transfer belt 125 and also prevents the occurrence of the photoreceptor memory.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus, and more particularly to a technique of supplying toner as a lubricant to protect a cleaning blade.

The electrophotographic image forming apparatus electrostatically transfers the toner image formed on the photoconductor to the image carrier at the transfer unit, and then removes the toner remaining on the photoconductor prior to the formation of the next toner image. For example, scrape with a cleaning blade and discard. At this time, if the cleaning blade is rolled up due to friction with the photoconductor, the residual toner cannot be sufficiently scraped off. In order to prevent such mekure, there is known a technique of supplying toner as a lubricant between the photoconductor and the cleaning blade and storing the toner in the blade edge portion.

The lubricating toner is supplied by forming a toner patch outside the image region, for example, between images from the rear end of the preceding image region to the tip of the succeeding image region. After being supplied by the developing unit, this toner patch passes through the transfer unit on the way to the cleaning blade. When passing through this transfer portion, the toner may move from the toner patch to the image carrier or the like.

In order to solve such a problem, for example, in order to allow the toner patch to pass through the transfer portion without being transferred to the image-carrying rotating body while being carried on the intermediate transfer belt, for example, in a tandem image forming apparatus, intermediate transfer is performed. It is conceivable to apply a conventional technique (see, for example, Patent Document 1) in which the transfer bias applied to transfer from the belt to the recording medium differs between the paper and the paper.

However, simply turning off the transfer bias between the images in correspondence with the papers according to the prior art does not work to hold the toner patch on the photoconductor, and therefore, due to the potential of the toner patch itself. A part of the toner patch may be electrostatically adsorbed from the photoconductor to the image carrier side, or may adhere to the image carrier due to mechanical action.

On the other hand, if the polarity of the transfer bias is reversed between the images and the image portion other than between the images, the toner is urged toward the photoconductor in the transfer portion, so that the toner loss due to the movement to the image carrier is suppressed. , The lubricant can be supplied to the cleaning blade.

JP-A-2017-207547 Japanese Unexamined Patent Publication No. 2014-123004

However, in the above-mentioned prior art, when the transfer bias is switched, the transfer bias is controlled by a constant current except that the transfer bias is temporarily controlled by a constant voltage. When constant current control is performed between images, the transfer bias is not stable when the amount of charge in the toner patch is small, so that the transfer of toner from the photoconductor to the image-bearing rotating body cannot be sufficiently suppressed. The amount of toner supplied to the cleaning blade is reduced.

On the other hand, if the transfer bias is controlled by a constant voltage between images, the transfer bias acting on the toner patch can be stabilized, but when the amount of charge in the toner patch is large, the transfer bias must be increased. However, when the transfer bias is increased, there is a problem that the surface potential of the region where the toner patch is not formed on the surface of the photoconductor is directly affected by the transfer bias, and the photoconductor memory is generated.

The present invention has been made in view of the above-mentioned problems, and supplies a sufficient amount of toner to the cleaning blade by suppressing the transfer of toner between images and the generation of the photoconductor memory. It is an object of the present invention to provide an image forming apparatus capable of performing.

In order to achieve the above object, the image forming apparatus according to the present invention applies a first transfer bias to the transfer body to generate a toner image from the first image-bearing rotating body onto the second image-bearing body. A transfer means that electrostatically transfers at the transfer position, a cleaning blade that scrapes off the toner remaining on the first image-bearing rotating body after the electrostatic transfer, and a toner that precedes when two or more toner images are formed. The first transfer between the toner patch forming means for forming a toner patch on the first image-bearing rotating body and the toner image between the toner images from the rear end of the image to the tip of the subsequent toner image. Toner is supplied to the cleaning blade by rotationally driving the first image-bearing rotating body between the bias control means for applying a second transfer bias having a polarity opposite to the bias to the transfer body and the toner image. The bias control means switches the control method of the second transfer bias to either constant current control or constant voltage control according to the amount of charge of the toner patch. It is characterized by.

In this case, when the charge amount of the toner patch is larger than a predetermined threshold value, the bias control means sets the transfer bias control method to constant current control, and the charge amount of the toner patch is the predetermined threshold value. If it is less than, the transfer bias control method may be constant voltage control.

Further, the bias control means may switch the transfer bias control method according to the charge amount of the toner patch at the transfer position where the toner image is electrostatically transferred.

Further, by applying an exposure means for exposing the first image-bearing rotating body to form an electrostatic latent image and a development bias, toner is supplied to the electrostatic latent image to form the toner patch. The bias control means includes a developing means, and the bias controlling means includes any one or more of the exposure amount, the exposure time, the developing bias, the application time of the developing bias, the coverage of the toner patch, and the environmental conditions when forming the toner patch. The amount of charge of the toner patch may be determined accordingly.

Further, the first image-bearing rotating body may be a photoconductor drum in which an electrostatic latent image is formed by exposure and a toner image is formed by developing the electrostatic latent image.

Further, the first image-supporting rotating body may be an intermediate transfer belt capable of supporting a toner image to be transferred on a recording sheet.

By doing so, it is possible to prevent the toner from moving from the toner patch and being separated from the first image-bearing rotating body depending on the state of the toner patch, or to prevent the occurrence of a memory phenomenon in the first image-bearing rotating body. Can be done.

It is a figure which shows the main structure of the image forming apparatus which concerns on 1st Embodiment of this invention. It is a block diagram which shows the main structure of the control part 150. It is a figure which shows the main structure of the transfer bias control unit 200. It is a flowchart explaining the control operation of the primary transfer bias. It is a figure which illustrates the control operation of the primary transfer bias when the charge amount of a toner patch is small. It is a figure which illustrates the control operation of the primary transfer bias when the charge amount of a toner patch is large. It is a figure which illustrates the control operation of the primary transfer bias when the charge amount of a toner patch changes. It is a control table which concerns on the modification of this invention, and shows the control table when the absolute humidity in an apparatus is 5 g / m ³ or less. It is a control table which concerns on the modification of this invention, and shows the control table when the absolute humidity in an apparatus is in the range of 5 to 18 g / m ³ . It is a control table which concerns on the modification of this invention, and shows the control table when the absolute humidity in an apparatus is 18 g / m ³ or more.

Hereinafter, embodiments of the image forming apparatus according to the present invention will be described with reference to the drawings.

The image forming apparatus according to the present embodiment is characterized in that the control method of the primary transfer bias is switched between the image portion and the image on the outer peripheral surface of the photoconductor drum.
[1] Configuration of Image Forming Device First, the configuration of the image forming apparatus according to the present embodiment will be described.

As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem color printer, and includes an image forming unit 120, a paper feeding unit 130, a fixing unit 140, and a control unit 150. When the control unit 150 receives a print job from an external device via a communication network such as a LAN (Local Area Network), the control unit 150 controls the image forming unit 120, the paper feeding unit 130, and the fixing unit 140 based on the instruction. Then, the image formation process is executed.

The image forming unit 120 includes image forming units 121Y, 121M, 121C and 121K, an exposure unit 123 and an intermediate transfer belt 125, and is a yellow (Y), magenta (M), cyan (C) and black (K) color toner. 128Y, 128M, 128C, 128K toner cartridges containing the above are installed. The image forming portions 121Y, 121M, 121C and 121K form toner images of each color of YMCK.

Since the image-forming units 121Y, 121M, 121C and 121K have the same configurations as each other, the image-creating unit 121K will be described below as a representative example. The image forming unit 121K is a combination of the photoconductor unit 124K and the developing unit 126K. The photoconductor unit 124K includes a photoconductor drum 122K, a cleaning blade 160K, a static elimination lamp 161K, a charging roller 162K, and the like.

The photoconductor drum 122K rotates in the direction of arrow B when forming an image or forming a toner patch. The charging roller 162K uniformly charges the outer peripheral surface of the photoconductor drum 122K. The exposure unit 123 forms an electrostatic latent image by irradiating the outer peripheral surface of the photoconductor drum 122K with a laser beam LB modulated according to K color image data or toner patch data and performing exposure scanning. An electrostatic latent image is formed for each main scanning line. On the outer peripheral surface of the photoconductor drum 122K, the main scanning lines are orthogonal to the circumferential direction of the photoconductor drum 122K and parallel to the axial direction.

Since the exposure amount of the electrostatic latent image increases as the irradiation light amount of the laser light LB increases, the amount of toner adhering to the electrostatic latent image increases as described later. Further, the slower the rotation speed of the photoconductor drum 122K, the longer the exposure time for each main scanning line, so that the exposure amount increases and the toner adhesion amount also increases.

The developing unit 126K receives the supply of K-colored toner from the toner bottle 128K detachably mounted above the intermediate transfer belt 125, and supports the toner on the developing roller 171K. A development bias is applied to the developing roller 171K, and the toner carried by the developing roller 171K is supplied to the electrostatic latent image on the outer peripheral surface of the photoconductor drum 122K. As a result, the electrostatic latent image is developed and a K-color toner image is formed. The larger the development bias, the larger the amount of toner supplied.

The area where the developing roller 171K and the photoconductor drum 122K face each other and toner is supplied is called a developing nip. The application time of the development bias for each main scanning line is the time required for the main scanning line to pass through the development nip due to the rotation of the photoconductor drum 122K. If the photoconductor drum 122K rotates quickly, the application time of the development bias is shortened, so that the amount of toner adhered is reduced. On the contrary, if the rotation is slow, the length becomes long, so that the amount of toner adhered increases.

A primary transfer bias is applied to the primary transfer roller 127K, and a K-color toner image is electrostatically transferred from the outer peripheral surface of the photoconductor drum 122K onto the intermediate transfer belt 125 (primary transfer). The charging bias condition and the development bias condition are the same at the time of image formation and the time between images.

When forming a color toner image, the image forming portions 121Y, 121M and 121C also form a toner image of each color of YMC in the same manner, and primary transfer is performed so that the toner images of each color of YMCK overlap each other on the intermediate transfer belt 125. To do. Therefore, the image forming portions 121Y, 121M, 121C and 121K form a toner image at different timings from each other.

The intermediate transfer belt 125 is an endless belt, which is stretched on a driving roller 125a and a driven roller 125b and is rotationally driven in the direction of arrow A. As a result, the toner image is conveyed to the secondary transfer position T.

After the primary transfer, the toner remaining on the outer peripheral surfaces of the photoconductor drums 122Y, 122M, 122C and 122K is scraped off by the cleaning blade 160 and discarded. Further, by illuminating the outer peripheral surfaces of the photoconductor drums 122Y, 122M, 122C and 122K with a static elimination lamp, the electric charge remaining on the outer peripheral surface is removed.

The paper feed unit 130 accommodates the recording sheet S, and feeds out the recording sheet S using the paper feed roller 132 in parallel with the formation and transfer of the toner image. The unfolded recording sheet S is skew-corrected by the timing roller pair 134, and after adjusting the transfer timing, it is transferred to the secondary transfer position T. At the secondary transfer position T, the toner image is electrostatically transferred from the intermediate transfer belt 125 to the recording sheet S by the secondary transfer bias applied to the secondary transfer roller 129 (secondary transfer).

The toner remaining on the intermediate transfer belt 125 after the secondary transfer is conveyed by the rotational running of the intermediate transfer belt 125, then scraped off by the cleaning blade 190 and discarded in the waste toner box 191.

The fixing unit 140 includes a fixing roller 141, a pressure roller 142, and a temperature sensor 143, and by monitoring the temperature of the fixing roller 141 with a temperature sensor, the temperature of the fixing roller 141 becomes a predetermined target temperature. Control. A pressure roller 142 is pressure-welded to the fixing roller 141, and the toner image is heat-fixed to the recording sheet S by passing the recording sheet S through the fixing nip formed by the pressure welding.

The recording sheet S on which the toner image is heat-fixed is discharged onto the discharge tray 138 by the paper discharge roller pair 136. When performing double-sided printing, the paper ejection roller pair 136 is rotated in the reverse direction (switchback) with the recording sheet S bitten into the paper ejection roller pair 136, and the secondary transfer position is passed through the double-sided reversal path. The recording sheet S is conveyed to T. In this way, the toner image is secondarily transferred to the back surface of the recording sheet S and heat-fixed.

An operation panel (not shown) is provided on the upper part of the front surface of the image forming apparatus 1. The operation panel is equipped with a liquid crystal display (LCD: Liquid Crystal Display), a touch panel with a touch pad, and hard keys. Information can be presented to the user on the liquid crystal display, or the user can use the touch pad or hard key. To accept instruction input.

Further, the image forming apparatus 1 includes an environment sensor 180, and the control unit 150 acquires the temperature and the absolute humidity in the image forming apparatus 1 by referring to the output signal of the environment sensor 180.
[2] Configuration of Control Unit 150 Next, the configuration of the control unit 150 will be described.

As shown in FIG. 2, the control unit 150 includes a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, and the like, and when the power of the image forming apparatus 1 is turned on or the like. When the CPU 201 is reset, the CPU 201 reads the boot program from the ROM 202 and starts it, and executes the OS (Operating System) and the control program read from the HDD (Hard Disk Drive) 204 using the RAM 203 as the working storage area.

The CPU 201 controls the transfer bias control unit 206, the image forming unit 120, the paper feeding unit 130, and the fixing unit 140 by executing the control program. As a result, the exposure amount, exposure time, development bias, and development bias application time when the image forming portions 121Y, 121M, 121C, and 121K form a toner image on the outer peripheral surfaces of the photoconductor drums 122Y, 122M, 122C, and 122K. Can be controlled.

Further, the image forming unit 120 includes transfer bias control units 200Y, 200M, 200C and 200K as described later, and the primary transfer bias applied to the primary transfer rollers 127Y, 127M, 127C and 127K by a control signal from the CPU 201. It is possible to switch between constant current control and constant voltage control, and to set a target current value for constant current control and a target voltage value for constant voltage control.

In the NIC (Network Interface Card) 205, the control unit 150 communicates with another device via a communication network such as a LAN (Local Area Network), and executes, for example, a process for accepting a print job.
[3] Transfer bias control unit 200
As shown in FIG. 3, the transfer bias control unit 200 is provided for each of the primary transfer rollers 127Y, 127M, 127C and 127K, and has the same configuration as each other. Therefore, the transfer bias control unit 200K that controls the primary transfer bias applied to the primary transfer roller 127K will be described as an example.

The transfer bias control unit 200K includes a constant current (CC: Constant Current) control unit 301K, a constant voltage (CV: Constant Voltage) control unit 302K, and a changeover switch 303K. The CPU 201 sets a target current value of the constant current control unit 301K, sets a target voltage value of the constant voltage control unit 302K, or presses the changeover switch 303K by inputting a control signal to the transfer bias control unit 200K. To switch.

By providing such a configuration, the primary transfer is performed by constant current control having the same polarity as the toner at the time of image formation, and the toner patch is transferred onto the intermediate transfer belt 125 by constant voltage control or constant current control having the same polarity as the toner during image formation. Encourage them not to be transferred to. The target current value when the constant current control is performed during image formation and between images, and the target voltage value when the constant voltage control is performed during image spacing are preset and are stored in a table, for example.

In the present embodiment, a case where the toner is negatively charged will be described as an example. Therefore, positive constant current control is performed during image formation, and negative constant voltage control or negative constant current control is performed during image spacing. The target current value for positive constant current control is 20 μA, the target current value for negative constant current control is -5 μA, and the target voltage value for negative constant voltage control is -500 V.
[4] Control of Primary Transfer Bias Next, control of the primary transfer bias executed by the image forming apparatus 1 when executing a print job will be described. Since the following description is an operation common to each color of YMCK, the characters of YMCK are omitted from the reference numerals.

As shown in FIG. 4, when the image forming apparatus 1 receives the print job, as described above, the image forming apparatus 1 uses the charging roller 162, the exposure unit 123, and the developing unit 126 on the first page on the outer peripheral surface of the photoconductor drum 122. Toner image is formed (S401). Then, the transfer bias control unit 200 executes positive constant current control (S402). In this way, the toner image is primarily transferred from the outer peripheral surface of the photoconductor drum 122 onto the intermediate transfer belt 125 while the positive constant current control is being executed.

When forming the toner image of the second and subsequent pages after the primary transfer of the toner image of the first page (S404: YES), the space between the toner image of the first page and the toner image of the second page , Or a toner patch is formed at the timing of hitting between the papers of the first page and the second page (S405). This toner patch is for supplying toner as a lubricant to the cleaning blade 160. Since the toner can be supplied over the entire longitudinal direction of the cleaning blade 160, the distribution range of the toner patch in the longitudinal direction (main scanning direction) is the entire developable width.

There are variations in the timing at which the rear end of the toner image on the first page passes through the primary transfer nip. Therefore, the positive constant current control is continued from the timing at which the rear end of the toner image is estimated to have passed through the primary transfer nip until a predetermined margin of time elapses. By doing so, the toner image can be reliably primary-transferred.

Further, it takes a certain amount of time to switch the polarity of the high voltage applied to the charging roller 162. Therefore, the toner patch is formed at a timing when the distance from the rear end of the toner image to the tip of the toner patch becomes longer than the distance obtained by multiplying the rotation speed (tangential speed) of the photoconductor drum 122 by the fixed time. Is desirable.

After that, when the margin region passes through the primary transfer nip (S406: YES), the transfer bias control unit 200 switches the control method of the primary transfer bias according to the charge amount of the toner patch. That is, when the charge amount of the toner patch in the primary transfer nip (the portion of the toner patch in which the main scanning line is in the primary transfer nip) is larger than a predetermined threshold value (S407: YES), the transfer bias control unit 200 The negative constant current control is executed at (S408).

Here, the primary transfer nip is a nip region formed by pressing the primary transfer roller 127 against the photoconductor drum 122 with the intermediate transfer belt 125 interposed therebetween, and the toner in the primary transfer nip is the primary transfer. Under the influence of the bias, it is urged in the direction corresponding to the polarity of the primary transfer bias.

Further, until the toner patch reaches the primary transfer nip, the transfer bias control unit 200 switches the control method of the primary transfer bias according to the charge amount of the tip portion of the toner patch.

The amount of charge in the toner patch is determined by referring to the amount of irradiation light when forming the toner patch, the exposure time, the development bias, the application time of the development bias, the coverage information, and the environmental information. Here, the coverage information is the coverage ratio (B / W ratio) for each main scanning line, and when toner is adhered to the photoconductor drum corresponding to all the pixels constituting the main scanning line. It becomes 100%.

Further, the environmental information is the absolute humidity in the image forming apparatus 1, and is acquired by the control unit 150 by referring to the output signal of the environmental sensor 180 as described above. The lower the absolute humidity, the easier it is for the toner patch to be charged, so the amount of charge increases. The irradiation light amount, the exposure time, the development bias, the application time of the development bias, and the coverage information for each scanning line are acquired from the setting information when forming the toner patch. The amount of irradiation light, the exposure time, the development bias, and the application time of the development bias may be the same when the toner patch is formed and when the toner image is formed.

When determining the charge amount of the toner patch, the control unit 150 sets the charge amount for each combination of the irradiation light amount, the exposure time, the development bias, the application time of the development bias, the coverage information, and the environmental information. The charge amount for each main scanning line may be determined by storing the table in advance and referring to the charge amount table. In addition, even if the charge amount for each main scanning line is calculated using a function in which the irradiation light amount, the exposure time, the development bias, the application time of the development bias, the coverage information and the environmental information are set as independent variables and the charge amount is set as the dependent variable. Good.

After calculating the charge amount for each main scan line, the total charge amount of the main scan lines passing through the primary transfer nip is sequentially calculated, and the conditional branching in step S407 depends on whether or not the total charge is greater than a predetermined threshold value. I do.

When the charge amount of the toner patch in the primary transfer nip is smaller than a predetermined threshold value (S407: NO), the transfer bias control unit 200 executes negative constant voltage control (S409). After that, when the toner patch is completed (S410: YES), the process proceeds to step S402 to form the toner image on the next page. In this case, when the main scanning line crossing the toner patch disappears from the primary transfer nip, it is determined that the toner patch has been completed.

In this way, after the rear end of the toner patch has passed through the primary transfer nip, the positive constant current control is immediately started in step S402. As described above, it takes a certain amount of time to switch the polarity of the high voltage applied to the charging roller 162. Therefore, if the positive constant current control is started in step S402, the primary transfer of the toner image on the second page is performed. The polarity of the high voltage applied to the charging roller 162 can be reliably switched before the start of.

If the toner patch is not completed (S410: NO), the process proceeds to step S407 to determine the charge amount of the toner patch again. After that, when there is no toner image to be formed next (S404: NO), the process ends. Therefore, since the photoconductor drum 122 is rotationally driven to form the toner image on the next page, the toner patch surely reaches the cleaning blade 160 by the rotation of the photoconductor drum 122. Therefore, the toner as a lubricant is reliably supplied to the cleaning blade 160.
[5] Operation Example Next, the operation of the image forming apparatus 1 will be described with reference to an operation example.
(5-1) When the charge amount of the toner patch is small The charge amount of the toner patch is the time when the amount of irradiation light when forming the toner patch is small, the exposure time is short, the development bias is low, and the development bias is applied. When is short, when the coverage rate in the coverage information is low, the amount of toner is small, so that the amount is small. Further, when the absolute humidity related to the environmental information is high, the toner is less likely to be charged, so that the amount of charge of the toner patch is reduced.

FIG. 5 illustrates a case where the amount of charge is small because the amount of irradiation light when forming the toner patch is small, and the toner adhered state according to the position in the circumferential direction on the outer peripheral surface of the photoconductor drum 122. , The operating state of the exposed unit 123 and the amount of primary transfer current are shown.

As shown in FIG. 5, the toner adheres to the image portion 511 of the image region 501 on the outer peripheral surface of the photoconductor drum 122, while the toner does not adhere to the margin portion 512. The margin region 502 following the image region 501 is a portion for allowing an error in the image formation position as described above. Therefore, when the image region 501 and the margin region 502 are in the primary transfer nip, the transfer bias control unit 200 selects the positive constant current control in order to perform the primary transfer of the image.

The switching region 503 is a region for switching the primary transfer bias. When the exposure position enters the switching region 503 due to the rotation of the photoconductor drum 122, the exposure unit 123 sets the exposure conditions for forming the toner patch in the preparation 521. In this operation example, since the exposure conditions are set so that the light emission amount 522 of the exposure unit 123 is small, the charge amount of the toner patch 513 is small.

Therefore, the transfer bias control unit 200 switches the control method of the primary transfer bias to negative constant voltage control. As a result, the primary transfer current changes from 20 μA in the switching region 503 until the direction in which the primary transfer current flows is reversed. When the charge amount of the toner patch is small, it is possible to prevent the toner from moving to the intermediate transfer belt 125 without increasing the target voltage value of the negative constant voltage control, so that the target voltage value is set. It is kept low. Therefore, since the primary transfer bias applied to the portion of the outer peripheral surface of the photoconductor drum 122 where the toner patch does not exist is suppressed to a low level, the generation of an image memory is prevented.

The nip area 504 is a spare area for passing the primary transfer nip through the toner patch after the change of the primary transfer current is completed.

In the patch region 505, the exposure unit 123 forms the toner patch 513 by emitting light 522 under the exposure conditions set in the preparation 521. When the toner patch 513 passes through the primary transfer nip, the change in the primary transfer current is complete. Further, since the negative constant voltage control is performed, the voltage applied to the toner patch 513 is stabilized, so that it is possible to effectively prevent the toner from moving from the toner patch 513 to the intermediate transfer belt 125.

In the switching region 506, the transfer bias control unit 200 switches the primary transfer bias control method to positive constant current control. As a result, the primary transfer current changes up to 20 μA, and the image can be primary transferred.

The margin region 507 is a preliminary region for surely changing the primary transfer current up to 20 μA before the image is first transferred.

After that, in the next image area 508, the margin portion 514 first enters the primary transfer nip, and then the image portion 515 enters the primary transfer nip. As a result, the image portion 515 is primarily transferred.
(5-2) When the amount of charge of the toner patch is large FIG. 6 illustrates the operation when the amount of charge of the toner patch 601 is large because the amount of irradiation light 602 when forming the toner patch 601 is large. ..

As shown in FIG. 6, when the amount of charge of the toner patch 601 is large, the transfer bias control unit 200 switches the primary transfer bias control method to negative constant current control in the switching region 503. In this way, the portion of the outer peripheral surface of the photoconductor drum 122 where the toner patch does not exist has a lower electrical resistance than the portion where the toner patch 601 exists, and the primary transfer current is set to the target current value by negative constant current control. When it is maintained, the voltage drop (primary transfer bias) can be suppressed, so that the generation of the image memory can be prevented.

In the patch region 505, the amount of charge of the toner patch 601 is large, so if the primary transfer current is maintained at the target current value by negative constant current control, the voltage drop (primary transfer bias) caused by the electrical resistance of the toner patch 601 itself causes The movement of the toner to the intermediate transfer belt 125 is suppressed.
(5-3) When the charge amount of the toner patch changes In FIG. 7, the charge amount of the toner patch changes, especially when the charge amount of the toner patch is large in the tip portion 701 and decreases in the subsequent portion 702. The operation of is illustrated.

For example, in a toner patch, as the amount of toner increases, the force that pushes the cleaning blade 160 when plunging into the cleaning blade 160 increases, so that the edge of the cleaning blade 160 may lose the sudden input of the toner patch and be rolled up. is there. In order to weaken such bump input and prevent mekure of the cleaning blade 160, it is necessary to make the cross section L-shaped by increasing only the amount of toner at the beginning of the toner patch and decreasing the amount of toner at the subsequent part. It is valid.

In order to make the shape of the toner patch L-shaped in cross section, when forming the toner patch, at the beginning, one or more of the irradiation light amount, the exposure time, the development bias, the application time of the development bias, and the coverage rate should be set. It may be increased and any one or more of these may be decreased in the subsequent portion. Not limited to the L-shape, the cross-sectional shape of the toner patch can be made into a desired shape such as a concave shape or a convex shape by appropriately adjusting the exposure conditions, the development conditions and the coverage rate.

As shown in FIG. 7, in the switching region 503, since the charge amount of the tip portion 701 of the toner patch is large, the transfer bias control unit 200 selects the negative constant current control. By doing so, it is possible to prevent the occurrence of the photoconductor memory in the switching area 503. Further, with respect to the tip portion 701 of the toner patch, it is possible to prevent the toner from moving to the intermediate transfer belt 125.

After that, when the subsequent portion 702 of the toner patch reaches the primary transfer nip and the charge amount of the toner patch becomes less than a predetermined threshold value, the transfer bias control unit 200 changes the transfer bias control method to negative constant voltage control. Switch. In this way, since the primary transfer bias can be stabilized, it is possible to prevent the toner from moving to the intermediate transfer belt 125 also for the subsequent portion 702 of the toner patch.
[6] Modified Examples Although the present invention has been described above based on the embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and the following modified examples can be implemented. ..
(6-1) In the above embodiment, the case where the positive constant current control is performed in the image region has been described as an example, but it goes without saying that the present invention is not limited to this, and the positive constant voltage control is performed instead. May be done.
(6-2) In the above embodiment, the case where toner is supplied to the cleaning blade 160 for cleaning the outer peripheral surface of the photoconductor drum 122 has been described as an example, but it goes without saying that the present invention is not limited to this. Instead of this, the same effect can be obtained by applying the present invention to the case where the toner is supplied to the cleaning blade 190 for cleaning the outer peripheral surface of the intermediate transfer belt 125.

In this case, if the charge amount of the toner patch is small, the secondary transfer bias may be controlled by a constant voltage, and if the charge amount of the toner patch is large, the secondary transfer bias may be controlled by a constant current. By doing so, when the amount of charge of the toner patch is small, it is possible to prevent the toner from moving to the secondary transfer roller 129. Further, when the amount of charge of the toner patch is large, high image quality can be achieved by preventing the memory phenomenon in the intermediate transfer belt 125.
(6-3) In the above embodiment, a case where it is determined in S407 whether or not the toner charge amount is equal to or higher than the threshold value and the control method of the primary transfer bias is switched has been described as an example. Needless to say, the following may be used instead of the above.

For example, when the absolute humidity inside the machine of the image forming apparatus 1 is 5 g / m ³ or less with reference to the detection value of the environment sensor 180, the control method of the primary transfer bias is referred to with reference to the control table of FIG. , The target voltage value and the target current value may be determined. In the control table of FIG. 8, when the combination of the development bias value and the exposure amount is in the column surrounded by the thick line 801, the constant voltage control with the voltage value described in the corresponding column as the target voltage value is performed. Do. For example, when the development bias value is −200 V and the exposure amount is 0.3 mJ / m ² , constant voltage control is performed at the target voltage value −450 V.

On the other hand, when the combination of the development bias value and the exposure amount is in the column surrounded by the thick line 802, constant current control is performed with the voltage value described in the corresponding column as the target current value. For example, when the development bias value is −500 V and the exposure amount is 2.00 mJ / m ² , constant current control is performed with a target current value of −20 μA.

As described above, if the absolute value of the target voltage value and the target current value is increased as the toner charge amount corresponding to the combination of the development bias value and the exposure amount is increased, the movement of the toner can be effectively suppressed. In particular, when the absolute humidity inside the machine is low, the amount of toner charged increases even if the amount of toner is the same, as compared with the case where the absolute humidity inside the machine is high. Therefore, the movement of toner is suppressed by performing constant current control more often than when the absolute humidity in the machine is high as shown in the control tables of FIGS. 9 and 10.

When the absolute humidity in the machine of the image forming apparatus 1 is 5 to 18 g / m ³ , the control method of the primary transfer bias and its target voltage value and target current value are determined with reference to the control table of FIG. You may. Even in this case, it is desirable to increase the absolute value of the target voltage value and the target current value as the toner charge amount increases.

When the absolute humidity in the machine of the image forming apparatus 1 is 18 g / m ³ or more, the control method of the primary transfer bias and its target voltage value and target current value are determined with reference to the control table of FIG. May be good. In particular, when the absolute humidity inside the machine is high, the amount of toner charged is smaller than when the absolute humidity inside the machine is low, even if the toner amount is the same. Therefore, as shown in the control tables of FIGS. 8 and 9, if the constant voltage control is performed more often than when the absolute humidity in the machine is low, the generation of the photoconductor memory can be suppressed.
(6-4) In the above embodiment, the case where the image forming apparatus 1 is a tandem color printer has been described as an example, but it goes without saying that the present invention is not limited to this, and the image forming apparatus 1 is tandem. It may be a color printer other than the method, or it may be a monochrome printer. Further, even if the present invention is applied to a single-function device such as a copying device equipped with a scanner, a facsimile device equipped with a facsimile communication function, or a multi-function peripheral (MFP) having these functions, the same applies. The effect of can be obtained.

The image forming apparatus according to the present invention is useful as an image forming apparatus capable of suppressing the transfer of toner between images and the generation of a photoconductor memory and supplying a sufficient amount of toner to the cleaning blade.

1 ... Image forming apparatus 121 ... Image forming unit 122 ... Photoreceptor drum 123 ... Exposure unit 124 ... Photoreceptor unit 125 ... Intermediate transfer belt 126 ... Development unit 127 ... Primary transfer roller 129 ... Secondary transfer roller 150 ... Control unit 160, 190 ... Cleaning blade 162 ... Charging roller 180 ... Environmental sensor

Claims (6)

A transfer means for electrostatically transferring a toner image from the first image-supporting rotating body to the second image-supporting body at the transfer position by applying a first transfer bias to the transfer body.
A cleaning blade that scrapes off the toner remaining on the first image-supporting rotating body after the electrostatic transfer,
When forming two or more toner images, toner patch formation that forms a toner patch on the first image-carrying rotating body between the toner images from the rear end of the preceding toner image to the tip of the subsequent toner image. Means and
A bias control means for applying a second transfer bias having a polarity opposite to that of the first transfer bias to the transfer body between the toner images.
A lubricant supply means for rotationally driving the first image-carrying rotating body to supply toner to the cleaning blade is provided between the toner images.
The image forming apparatus is characterized in that the bias control means switches the control method of the second transfer bias to either constant current control or constant voltage control according to the amount of charge of the toner patch. When the charge amount of the toner patch is larger than a predetermined threshold value, the bias control means sets the transfer bias control method to constant current control, and when the charge amount of the toner patch is smaller than the predetermined threshold value. The image forming apparatus according to claim 1, wherein the transfer bias control method is constant voltage control. The image forming apparatus according to claim 2, wherein the bias control means switches the transfer bias control method according to the amount of charge of the toner patch at the transfer position where the toner image is electrostatically transferred. An exposure means for exposing the first image-supporting rotating body to form an electrostatic latent image,
A developing means for supplying toner to the electrostatic latent image and forming the toner patch by applying a developing bias is provided.
The bias control means charges the toner patch according to any one or more of the exposure amount, the exposure time, the development bias, the application time of the development bias, the coverage of the toner patch, and the environmental conditions when forming the toner patch. The image forming apparatus according to claim 2 or 3, wherein the amount is determined. The first image-bearing rotating body is a photoconductor drum in which an electrostatic latent image is formed by exposure and a toner image is formed by developing the electrostatic latent image, according to claim 1. The image forming apparatus according to any one of 4. The image forming apparatus according to any one of claims 1 to 4, wherein the first image-carrying rotating body is an intermediate transfer belt capable of carrying a toner image to be transferred on a recording sheet.

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