JP6907815B2 - Image forming device - Google Patents

Description

The present disclosure relates to an image forming apparatus, and more specifically to a transfer apparatus of an image forming apparatus.

Electrophotographic image forming apparatus is widespread. The electrophotographic image forming apparatus has, as a printing process, a charging step of charging the photoconductor as an image carrier, an exposure step of exposing the photoconductor according to an input image pattern, and an electrostatic charge formed by the exposure. A developing step of developing a latent image as a toner image and a transfer step of transferring the developed toner image to a transfer material such as paper are executed.

In recent years, a thick-film photoconductor has been used in order to extend the life of the photoconductor unit. In a thick-film photoconductor, an appropriate transfer bias value changes depending on the change in the film thickness of the photoconductor. As a technique for determining the transfer bias value, for example, Japanese Patent Application Laid-Open No. 2014-153410 (Patent Document 1) states, "While using a DC charging method or a pre-exposure-less method, the occurrence of positive ghosts is prevented. It discloses an image forming apparatus that does not cause harmful effects such as other abnormal images (see [Problem] in [Summary]).

Japanese Unexamined Patent Publication No. 2014-153410

However, in the above-mentioned conventional technique, a potential difference that cannot be completely removed occurs on the photoconductor as the film thickness of the photoconductor changes, and an event that causes a problem in subsequent image formation occurs. Therefore, there is a need for a technique for preventing the occurrence of defects in image formation.

The present disclosure has been made to solve the above problems, and an object in a certain aspect is to determine an appropriate transfer bias value according to the state of the photoconductor.

According to a certain aspect, the image forming apparatus is configured to apply a rotatably configured photoconductor and a charging bias for charging the surface of the rotating photoconductor to the photoconductor at the charging portion. A toner image is developed on the surface of the photoconductor exposed by the charging device, the exposure device configured to irradiate and expose the surface of the photoconductor charged by the charging device with laser light, and the surface of the photoconductor exposed by the exposure device. It is provided with a developing device configured as described above, a transfer device configured to transfer a toner image to an object to be transferred at a transfer unit, and a control device configured to apply a transfer bias to the transfer device. The control device changes the magnitude of the transfer bias and detects the transfer current generated in the region of the photoconductor passing through the transfer portion and the charging current generated in the region when the region passes through the charged portion. The change point at which the change characteristic of the charging current accompanying the change of the transfer current changes from the first characteristic to the second characteristic is calculated, and the magnitude of the transfer current corresponding to the change point is determined.

Preferably, when the toner image is transferred, the control device applies a transfer bias to the transfer device that generates a current equal to or less than the determined transfer current magnitude in the region.

Preferably, when the toner image is transferred, a transfer bias is applied to the transfer device to generate a current in the region equal to the determined transfer current.

Preferably, it further comprises a static eliminator that removes charges in the region after the region of the photoconductor has passed through the transfer section.

Preferably, the charging bias is a DC voltage.
Preferably, the image forming apparatus further comprises a humidity sensor that detects the humidity in the image forming apparatus, and the control device determines the magnitude of the transfer current when the calculated humidity is equal to or less than a predetermined threshold value. to correct.

Preferably, the control device controls the charging device to apply a predetermined charging bias to the photoconductor before changing the magnitude of the transfer bias to calculate the change point.

Preferably, the control device controls the charging device to apply a predetermined charging bias to the photoconductor after determining the magnitude of the transfer current corresponding to the change point.

The above and other objectives, features, aspects and advantages will become apparent from the following detailed description understood in connection with the accompanying drawings.

It is a figure which shows an example of the whole structure of an image forming apparatus. It is a block diagram which shows the main hardware composition of an image forming apparatus. It is a figure which shows the structure of the image formation unit in an electrophotographic system. It is a figure which shows the surface potential of the photoconductor at a predetermined timing. It is a figure which shows the outline of the image forming part schematically. It is a timing chart of the transfer current control processing in this embodiment. It is a graph which shows the change characteristic of the charge current with the change of the transfer current. It is a figure which shows the change of the potential on the photoconductor with the change of the transfer current. It is a figure which shows the outline of the image forming part which concerns on 2nd Embodiment. It is a graph which shows the change characteristic of the charge current with the change of the transfer current which concerns on 2nd Embodiment. It is a figure which shows the relationship between the humidity in an image forming apparatus, and the correction value of the determination value of a transfer current. It is a timing chart which showed the pre-processing and post-processing of the transfer current control processing.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following description, the same parts and components are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of these will not be repeated. In addition, each embodiment and each modification described below may be selectively combined as appropriate.

<First Embodiment>
[1. Configuration of image forming apparatus 100]
An image forming apparatus 100 according to an embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an example of the overall structure of the image forming apparatus 100.

FIG. 1 shows an image forming apparatus 100 as a color printer. Hereinafter, the image forming apparatus 100 as a color printer will be described, but the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be a monochrome printer, or may be a multifunction printer of a monochrome printer, a color printer, and a facsimile (so-called MFP (Multi Functional Peripheral)).

The image forming apparatus 100 includes a scanner 20 as an image reading unit and a printer 25 including an image forming unit 90 (specifically, image forming units 90Y, 90M, 90C, 90K). The scanner 20 includes a cover 21, a paper base 22, a tray 23, and an ADF (Auto Document Feeder) 24. One end of the cover 21 is fixed to the paper base 22, and the cover 21 is configured to be openable and closable with the one end as a fulcrum.

The user of the image forming apparatus 100 can set the original on the paper base 22 by opening the cover 21. When the image forming apparatus 100 receives a scan instruction while the original is set on the paper base 22, the image forming apparatus 100 starts scanning the original set on the paper base 22. Further, when the image forming apparatus 100 receives a scan instruction with the originals set in the tray 23, the ADF 24 automatically reads the originals one by one.

The printer 25 includes image forming units 90Y, 90M, 90C, 90K, an IDC sensor 19, a transfer belt 30, a primary transfer roller 31, a transfer drive 32, a secondary transfer roller 33, and cassettes 37A to 37C. The driven roller 38, the driving roller 39, the timing roller 40, the cleaning unit 43, the fixing device 60, and the control device 101 are provided.

The image forming portions 90Y, 90M, 90C, and 90K are arranged in order along the transfer belt 30. The image forming unit 90Y receives the toner supply from the toner bottle 15Y and forms a yellow (Y) toner image. The image forming unit 90M receives the toner supply from the toner bottle 15M and forms a toner image of magenta (M). The image forming unit 90C receives the toner supply from the toner bottle 15C and forms a toner image of cyan (C). The image forming unit 90K receives the toner supply from the toner bottle 15K and forms a black (BK) toner image.

The image forming portions 90Y, 90M, 90C, and 90K are arranged along the transfer belt 30 in the order of the rotation direction of the transfer belt 30, respectively. The image forming units 90Y, 90M, 90C, and 90K each include a photoconductor 10, a charging device 11, an exposure device 13, a developing device 14, a cleaning unit 17, and a static elimination device 18, which are rotatably configured. Be prepared.

After the image forming units 90Y, 90M, 90C, and 90K operate as described above, the transfer of the transfer drive 32 causes a yellow (Y) toner image, a magenta (M) toner image, and a cyan (C) toner image. The toner image and the black (BK) toner image are sequentially superimposed and transferred from the photoconductor 10 to the transfer belt 30. As a result, a color toner image is formed on the transfer belt 30.

The IDC sensor 19 detects the density of the toner image 35 formed on the transfer belt 30. Typically, the IDC sensor 19 is a light intensity sensor including a reflective photo sensor, which detects the reflected light intensity from the surface of the transfer belt 30.

The transfer belt 30 is stretched between the driven roller 38 and the driving roller 39. The drive roller 39 is connected to a motor (not shown). The drive roller 39 rotates when the control device 101 controls the motor. The transfer belt 30 and the driven roller 38 rotate in conjunction with the drive roller 39. As a result, the toner image 35 on the transfer belt 30 is sent to the secondary transfer roller 33.

Papers of different sizes are set in each of the cassettes 37A to 37C. The paper is fed one by one from any of the cassettes 37A to 37C to the secondary transfer roller 33 along the transport path 41 by the timing roller 40.

The control device 101 controls the transfer voltage applied to the secondary transfer roller 33 according to the timing at which the paper is fed. The secondary transfer roller 33 applies a transfer voltage having a polarity opposite to the charging polarity of the toner image 35 to the paper being conveyed. As a result, the toner image 35 is attracted from the transfer belt 30 to the secondary transfer roller 33, and the toner image 35 on the transfer belt 30 is transferred. Details of applying the transfer voltage to the secondary transfer roller 33 will be described later.

The timing of transferring the paper to the secondary transfer roller 33 is controlled by the timing roller 40 according to the position of the toner image 35 on the transfer belt 30. As a result, the toner image 35 on the transfer belt 30 is transferred to an appropriate position on the paper.

The fuser 60 pressurizes and heats the paper passing through the fuser 60. As a result, the toner image is fixed on the paper. After that, the paper is discharged to the tray 49.

The cleaning unit 43 collects the toner remaining on the surface of the transfer belt 30 after the toner image is transferred from the transfer belt 30 to the paper. The recovered toner is conveyed by a conveying screw (not shown) and stored in a waste toner container (not shown). Details of the cleaning unit 43 will be described later.

[2. Hardware configuration]
An example of the hardware configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 2 is a block diagram showing a hardware configuration of the image forming apparatus 100.

As shown in FIG. 2, the image forming apparatus 100 includes a control device 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a network interface 104, an operation panel 105, a scanner 20, and the like. It includes a temperature sensor 70, a humidity sensor 80, an image forming unit 90, and a storage device 120.

The control device 101 is composed of, for example, at least one integrated circuit. An integrated circuit is composed of, for example, at least one CPU (Central Processing Unit), at least one ASIC (Application Specific Integrated Circuit), at least one FPGA (Field Programmable Gate Array), or a combination thereof.

The control device 101 controls the operation of the image forming apparatus 100 by executing various programs such as a program 122 for adjusting the control parameters of the image forming apparatus 100. The control device 101 reads the program 122 from the storage device 120 into the RAM 103 based on the reception of the execution instruction of the program 122. The RAM 103 functions as a working memory and temporarily stores various data necessary for executing the program 122.

An antenna (not shown) or the like is connected to the network interface 104. The image forming apparatus 100 exchanges data with an external communication device via an antenna. External communication devices include, for example, mobile communication terminals such as smartphones, servers, and the like. The image forming apparatus 100 may be configured so that the program 122 can be downloaded from the server via the antenna.

The operation panel 105 includes a display (not shown) and a touch panel (not shown). The display and the touch panel are superposed on each other, and the image forming apparatus 100 receives an operation on the touch panel. As an example, the operation panel 105 accepts an operation for executing a control parameter adjustment process.

The storage device 120 is, for example, a hard disk, an SSD (Solid State Drive) or other storage device. The storage device 120 may be either a built-in type or an external type. The storage device 120 stores a program 122 or the like according to the present embodiment. However, the storage location of the program 122 is not limited to the storage device 120, and may be stored in the storage area of the control device 101 (for example, a cache or the like), the ROM 102, the RAM 103, an external device (for example, a server), or the like.

The program 122 may be provided as a part of an arbitrary program, not as a stand-alone program. In this case, the control process according to the present embodiment is realized in cooperation with an arbitrary program. Even a program that does not include such a part of modules does not deviate from the purpose of the program 122 according to the present embodiment.

Further, some or all of the functions provided by program 122 may be realized by dedicated hardware. Further, the image forming apparatus 100 may be configured in the form of a so-called cloud service in which at least one server executes a part of the processing of the program 122.

[3. Transfer current control process]
(3.1. Related technologies and problems)
With reference to FIGS. 3 and 4, related techniques and problems thereof in electrophotographic image formation will be described. FIG. 3 is a diagram showing a configuration of an image forming unit K in an electrophotographic system. FIG. 4 is a diagram showing the surface potential of the photoconductor D at a predetermined timing. In FIG. 4, the vertical axis indicates the potential (negative potential is a positive value), and the horizontal axis indicates the position.

As shown in FIG. 3, the image forming unit K includes a developing roller A, an exposure device B, a charging roller C, a photoconductor D, a static elimination device E, a transfer belt F, and a transfer device G.

In the image forming unit K, the surface of the photoconductor D is uniformly charged by the charging bias applied from the charging roller C in accordance with the rotation of the photoconductor D. After that, an electrostatic latent image due to a potential difference is formed on the surface of the photoconductor D by the laser light emitted from the exposure apparatus B based on the image data to be formed.

A toner image is formed on the surface of the photoconductor D on which the electrostatic latent image is formed by the developing roller A. Here, since the toner is negatively charged, development is performed by the toner adhering to a portion having a high potential in the electrostatic latent image.

FIG. 4A shows the surface potential of the photoconductor D after the development by the developing roller A is completed (t = T1). The potential V1 of the image portion is higher than the potential V0 of the non-image portion in order to attach the negatively charged toner.

Further, when the photoconductor D rotates, the transfer device D transfers the photoconductor D to the transfer belt F. Here, a voltage (plus voltage) having a polarity opposite to that of the toner is applied to the transfer device D as a transfer bias. As a result, the toner adhering to the surface of the photoconductor D is attracted to the transfer device D by the electrostatic attraction generated by the transfer bias and transferred to the transfer belt F.

FIG. 4B shows the surface potential of the photoconductor D after the transfer by the transfer device D is completed (t = T2). When a voltage having a polarity opposite to that of the toner is applied to the transfer device D, a current flows into a non-image portion having a low potential before transfer, and the potential becomes V2. Here, the case where V2 has a positive potential is shown. On the other hand, before transfer, a slight current flows into the image portion having a high potential, resulting in V1'.

Further, when the photoconductor D rotates, the surface potential of the photoconductor D is removed by the static elimination device E. Here, as shown in FIG. 4C, since the static elimination device E removes the negative charge, the positive potential remains on the surface of the photoconductor D. That is, the potential of the image portion becomes zero, but the potential of the non-image portion remains.

When the photoconductor D is further rotated, the surface of the photoconductor D is uniformly charged by the charging device C. As a result, as shown in FIG. 4 (D), the potential difference between the image portion and the non-image portion at the time of the previous image formation remains, and both become negative potentials.

Here, when the next image to be formed is an image having a uniform amount of toner, such as a so-called solid image, the exposure by the exposure apparatus B is limited to the extent that a uniform potential is applied. The image is developed by the developing roller A with the potential difference in the above remaining, and an event occurs in which the previous image is formed in the image to be formed. This event will be referred to as transfer memory below.

As described above, the cause of the transfer memory is that when the toner image formed on the photoconductor D is transferred, a large amount of current flows into the non-image portion where the transfer bias voltage is too large and the potential is low. As a result, as shown in FIG. 4B, there is a region having a positive potential on the photoconductor D.

(3.2. Transfer current control processing)
The configuration of the image forming unit 90 in the present embodiment will be described with reference to FIG. FIG. 5 is a diagram schematically showing an outline of the image forming unit 90.

As shown in FIG. 5, the image forming unit 90 includes a photoconductor 10, a charging roller 11a, a developing roller 14a, a transfer belt 30, a primary transfer roller 31, and a static elimination device 18. In the image forming unit 90, the photoconductor 10 is charged by the charging roller 11a in the charging unit R2. Further, in the image forming unit 90, the toner image formed on the photoconductor 10 is transferred to the transfer belt 30 by the primary transfer roller 31 in the transfer unit R1.

The transfer bias application unit 113 is realized by the control device 101, and applies a transfer bias, which is a DC voltage, to the primary transfer roller 31. The charging bias applying unit 111 is realized by the control device 101, and applies a charging bias, which is a DC voltage, to the charging roller 11a. The charge current detection unit 112 is realized by the control device 101 and detects the charge current generated in the charge unit R2.

The transfer current control process in the present embodiment will be described with reference to FIG. FIG. 6 is a timing chart of the transfer current control process in the present embodiment.

As shown in FIG. 6, the control device 101 applies a voltage as a charging bias to the primary transfer roller 31 as the transfer bias applying unit 113 (t = t1). The bias voltage is continuously applied with a constant magnitude.

When the region of the photoconductor 10 charged in the charging unit R2 reaches the transfer unit R1 (t = t2), the control device 101 applies a bias voltage to the primary transfer roller 31 as the transfer bias application unit 113. At this time, the control device 101 applies a bias voltage S1 so that the transfer current generated in the transfer unit R1 becomes I1.

When the region on the photoconductor 10 that has passed through the transfer unit R1 reaches the charging unit R2 when the bias voltage S1 is started to be applied (t = t3), the control device 101 is charged as the charging current detecting unit 112. The charging current generated in the unit R2 is detected. Then, the control device 101 increases the transfer bias from S1 to S2 such that the transfer current generated in the transfer unit R1 becomes I2 as the transfer bias application unit 113.

When the region on the photoconductor 10 that has passed through the transfer unit R1 reaches the charging unit R2 when the bias voltage S2 is started to be applied (t = t4), the control device 101 is charged as the charging current detecting unit 112. The charging current generated in the unit R2 is detected. Then, the control device 101 increases the transfer bias from S2 to S3 such that the transfer current generated in the transfer unit R1 becomes I3 as the transfer bias application unit 113. Similarly, a plurality of transfer biases are repeated from S4 to S6 (t = t5 to t7). After that, the application of the transfer bias is terminated (t = T8), and the application of the charging bias is terminated (t = t9).

The control device 101 calculates the change characteristic of the charge current detected by the charge current detection unit 112 due to the change of the transfer current corresponding to the applied transfer bias. Then, the control device 101 calculates a change point at which the change characteristic changes from the first characteristic to the second characteristic.

With reference to FIGS. 7 and 8, the change characteristics of the charging current with the change of the transfer current will be described. FIG. 7 is a graph showing the change characteristics of the charging current with the change of the transfer current. FIG. 8 is a diagram showing a change in the potential on the photoconductor with a change in the transfer current.

As shown in FIG. 7, when the transfer current is increased, the charging current becomes almost constant for a while. However, when a certain critical value (hereinafter referred to as a change point) is exceeded, the charging current increases linearly. This change point is the slope L1 when the charging current shows a change characteristic (first characteristic) that is almost constant with respect to the change of the transfer current, and the characteristic that the charge current increases linearly with the change of the transfer current. It can be obtained as the intersection P with the slope L2 when showing (second characteristic). As described above, the change in the charging current accompanying the change in the transfer current exhibits two different characteristics, and whether or not the transfer memory is generated is determined by using the transfer current corresponding to the change point P as a threshold value. .. This will be described below with reference to FIG.

8 (A) to 8 (D) show the potentials on the photoconductor 10 after the transfer step and the static elimination step, respectively (corresponding to (B) and (C) in FIG. 4), (A). The transfer bias increases toward (D). As shown in FIGS. 8 (A) and 8 (B), when the transfer bias is small, the transfer current is also small, so that the voltage after transfer in the image portion has a negative polarity. In this case, since the static elimination device 18 uniformly eliminates static electricity to zero potential, the magnitude of the charging current does not change and no transfer memory is generated.

On the other hand, as shown in FIGS. 8C and 8D, when the transfer bias is large, the transfer current also increases, so that the voltage after transfer in the image portion becomes positive polarity. In this case, the positive potential remains even after static elimination by the static elimination device. The charging current increases by the amount of the remaining positive potential, and a transfer memory is generated.

Based on this, when the transfer current at the change point P is determined by the method described above, the control device 101 sets a transfer bias that generates a transfer current equal to or less than the determined transfer current value in the subsequent image formation by the primary transfer roller. It is applied to 31 to perform a transfer step. Here, preferably, a transfer bias that generates a transfer current equal to the stored transfer current is applied to the primary transfer roller 31. This makes it possible to prevent transfer defects due to insufficient transfer bias.

As described above, in the present embodiment, the control device 101 changes the magnitude of the transfer bias applied to the primary transfer roller 31, and determines the transfer current generated in the region of the photoconductor when passing through the transfer unit. When the region passes through the charged portion, the charging current generated in the region is detected. Then, the control device 101 calculates a change point at which the change characteristic of the charging current due to the change of the transfer current changes from the first characteristic to the second characteristic, and determines the magnitude of the transfer current corresponding to the change point. decide. In the subsequent transfer step, the control device 101 generates a transfer memory by applying a transfer bias that generates a transfer current having a magnitude equal to or smaller than the transfer current thus determined to the primary transfer roller 31. The transfer process can be performed without any problem.

<Second embodiment>
[overview]
Hereinafter, the second embodiment will be described. The second embodiment is different from the first embodiment in that the image forming unit 190 does not include the static elimination device 18. In this embodiment, the same components as those provided in the image forming apparatus 100 according to the above-described embodiment are designated by the same reference numerals as those of the image forming apparatus 100. Therefore, those explanations will not be repeated.

An outline of the image forming unit 190 according to the second embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 is a diagram showing an outline of the image forming unit 190 according to the second embodiment. FIG. 10 is a graph showing the change characteristic of the charging current with the change of the transfer current according to the second embodiment. In FIG. 10, a case where the film thickness of the photoconductor 10 is 40 μm and a case where the film thickness is 15 μm are shown.

As shown in FIG. 9, the image forming unit 190 according to the second embodiment does not include a static elimination device. The other configurations and the control by the control device 101 are the same as those in the first embodiment. In this case, the negative potential on the photoconductor 10 remains without being eliminated after the transfer step by the primary transfer roller 31.

As shown in FIG. 10, in this case, both the first characteristic in which the transfer memory is not generated and the second characteristic in which the transfer memory is not generated have an inclination. This is because, in the second embodiment, since static elimination is not performed after the transfer step, a negative potential corresponding to the magnitude of the transfer current remains on the photoconductor 10, and the magnitude of the charging current also changes accordingly. do. Then, when the transfer current exceeds a certain amount, the photoconductor 10 is positively charged. In this case, since the positive charge is trapped inside the photoconductor 10, even if the surface of the photoconductor 10 is charged by the charging roller 11a, it is canceled by the positive charge inside. As a result, it is considered that the charging current increases without increasing the potential on the photoconductor 10.

Also in this case, the transfer current corresponding to the change point can be obtained by finding the intersection of the slope in the first characteristic and the slope in the second characteristic. From FIG. 10, it can be considered that the larger the film thickness, the smaller the value of the transfer current corresponding to the change point, and the more easily the transfer memory is generated.

<Third embodiment>
[overview]
Hereinafter, the third embodiment will be described. In the third embodiment, the control device 101 calculates the absolute humidity in the image forming apparatus 100 based on the humidity detected by the humidity sensor 80 in the image forming apparatus 100, and the calculated absolute humidity is predetermined. It differs from the first embodiment in that the magnitude of the determined transfer current is corrected when the value is equal to or less than the threshold value. The image forming apparatus according to the present embodiment is realized by the same configuration as that provided in the image forming apparatus 100 according to the above-described embodiment. Therefore, their configuration is not repeated.

With reference to FIG. 11, correction of the determined value of the transfer current due to humidity will be described. FIG. 11 is a diagram showing the relationship between the humidity in the image forming apparatus 100 and the correction value of the determined value of the transfer current.

When the temperature inside the image forming apparatus 100 is low, the resistance of the charging roller 11a to the surface of the photoconductor 10 becomes high, and the charging uniformity is lowered due to the influence of the resistance unevenness generated on the surface. As a result, it becomes difficult to uniformly charge the potential step, so that a transfer memory is easily generated. Therefore, when the humidity in the image forming apparatus 100 is low, it is necessary to increase the correction value from the change point and decrease the transfer current when forming the toner image.

On the other hand, when the humidity in the image forming apparatus 100 is high, the chargeability of the toner is lowered, so that the transfer efficiency is lowered. It is necessary to apply a transfer current as large as possible without generating a transfer memory. Therefore, the transfer current value is set so that the correction value is made as small as possible from the change point where the transfer memory is generated.

As shown in FIG. 11, the higher the absolute humidity, the smaller the correction value, and the lower the absolute humidity, the larger the correction value. For example, when the absolute humidity is 5 g / m ³ , the control device 101 reduces the calculated transfer current value corresponding to the change point by 2 μA. By performing such correction, it is possible to set the transfer current so that the transfer memory does not occur at low humidity and transfer defects do not occur at high humidity.

<Fourth Embodiment>
[overview]
Hereinafter, the fourth embodiment will be described. In the fourth embodiment, the control device 101 is charged before changing the magnitude of the transfer bias in order to calculate the change point and after determining the magnitude of the transfer current corresponding to the change point. It differs from the first embodiment in that the roller 11a is controlled to apply a predetermined charging bias to the photoconductor 10. The image forming apparatus according to the present embodiment is realized by the same configuration as that provided in the image forming apparatus 100 according to the above-described embodiment. Therefore, their configuration is not repeated.

With reference to FIG. 12, the pretreatment and the posttreatment of the transfer current control processing according to a certain embodiment will be described. FIG. 12 is a timing chart showing the pre-processing and post-processing of the transfer current control process.

As shown in FIG. 12, the surface potential of the photoconductor 10 may not be uniform before the start of the transfer current control (time t2) or due to a defect in the preceding control. Further, there is a possibility that the electrostatic latent image formed on the photoconductor 10 before the control is performed remains on the surface of the photoconductor 10. As described above, when the surface potential of the photoconductor 10 is not uniform, an accurate charging current cannot be obtained. Therefore, in the control device 101 according to the present embodiment, the photoconductor 10 whose charge bias is rotated before the control is executed has a predetermined time (for example, the speed of the transfer belt 30 is 166 m / s and the diameter of the photoconductor 10 is 30φ. In this case, the photoconductor 10 rotates about 3 times for about 2 seconds). By this pretreatment, the surface potential of the photoconductor 10 is made uniform, an accurate charging current can be detected, and a change point at which the change characteristic of the charging current changes with a change in the transfer current can be accurately obtained.

Further, as shown in FIG. 12, when the control device 101 executes the determination control of the transfer current at the time t2 to t8, the transfer current is set to a high transfer current generated by the transfer memory. Positive charge remains. In order to remove the positive charge, after time t8, the control device 101 performs post-processing. Specifically, after applying the final transfer current for control, the control device 101 rotates the photoconductor 10 for about 2 seconds while applying the charging bias. By this post-treatment, the positive charge of the photoconductor 10 is removed by natural discharge, and the photoconductor 10 can be charged to a normal surface potential. By doing so, the paper is ready to be image-formed after this.

<Other Embodiments>
The scope of application of the technical idea according to the present disclosure is not limited to the above embodiment. For example, in the above embodiment, the charging bias is a DC voltage, but an AC voltage may be used. Further, the humidity in the third embodiment may be relative humidity instead of absolute humidity. Even in this way, the same effect as that of the above embodiment can be obtained.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

10 Photoreceptor, 11 Charging device, 11a Charging roller, 13 Exposure device, 14 Developer, 15C, 15K, 15M, 15Y Toner bottle, 17,43 Cleaning unit, 18 Static eliminator, 19 Sensor, 20 Scanner, 21 Cover, 22 Paper stand, 23,49 trays, 25 printers, 30 transfer belts, 31 primary transfer rollers, 32 transfer drives, 33 secondary transfer rollers, 35 toner images, 37A, 37C cassettes, 38 driven rollers, 39 drive rollers, 40 timings. Roller, 41 transport path, 60 fuser, 70 temperature sensor, 80 humidity sensor, 90, 90C, 90K, 90M, 90Y, 190 image forming unit, 100 image forming device, 101 control device, 102 ROM, 103 RAM, 104 network Interface, 105 operation panel, 111 charge bias application unit, 112 charge current detector unit, 113 transfer bias application unit, 120 storage device, 122 program.

Claims (8)

With a rotatable photoconductor,
A charging device configured to apply a charging bias for charging the surface of the rotating photoconductor to the photoconductor at the charging unit, and a charging device.
An exposure device configured to irradiate and expose the surface of the photoconductor charged by the charging device with a laser beam, and an exposure device.
A developing device configured to develop a toner image on the surface of the photoconductor exposed by the exposure device, and a developing device.
A transfer device configured to transfer the toner image to the transfer target in the transfer unit,
A control device configured to apply a transfer bias to the transfer device is provided.
The control device is
By changing the magnitude of the transfer bias,
The transfer current generated in the region of the photoconductor that passes through the transfer portion and the charge current generated in the region when the region passes through the charge portion are detected.
The change point at which the change characteristic of the charge current accompanying the change of the transfer current changes from the first characteristic to the second characteristic is calculated.
An image forming apparatus that determines the magnitude of the transfer current corresponding to the change point. The image according to claim 1, wherein the control device applies a transfer bias to the transfer device to generate a current equal to or less than the determined transfer current magnitude in the region when the toner image is transferred. Forming device. The image forming apparatus according to claim 2, wherein the control device applies a transfer bias to the transfer device to generate a current equal to the determined transfer current in the region when the toner image is transferred. The image forming apparatus according to any one of claims 1 to 3, further comprising a static elimination device for removing electric charges in the region after the region of the photoconductor has passed through the transfer portion. The image forming apparatus according to any one of claims 1 to 4, wherein the charging bias is a DC voltage. The image forming apparatus further includes a humidity sensor for detecting the humidity in the image forming apparatus.
The image forming apparatus according to any one of claims 1 to 5, wherein the control device corrects the magnitude of the determined transfer current when the calculated humidity is equal to or less than a predetermined threshold value. Claims 1 to 6, wherein the control device controls the charging device to apply a predetermined charging bias to the photoconductor before changing the magnitude of the transfer bias in order to calculate the change point. The image forming apparatus according to any one of the above. Any one of claims 1 to 7, wherein the control device controls the charging device to apply a predetermined charging bias to the photoconductor after determining the magnitude of the transfer current corresponding to the change point. The image forming apparatus according to the section.

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