JP3997797B2 - Image forming apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming technique for forming a color image of a printer, a copying machine, a facsimile machine or the like.
[0002]
[Prior art]
Conventionally, an electrostatic latent image formed on a photosensitive member by an exposure unit is attached with toner by a developing unit to form a toner image, the toner image is transferred to a transfer sheet, and the toner image on the transfer sheet is transferred by a fixing unit. An electrophotographic image forming apparatus which is fixed on the transfer paper is known. In particular, as an apparatus capable of forming a color image, a toner image formed on a photoreceptor is primarily transferred to an intermediate transfer medium. A color image forming apparatus is known in which the toner image transferred to the intermediate transfer medium is secondarily transferred onto transfer paper.
[0003]
The image forming apparatus includes, for example, a single photoconductor, sequentially forms toner images of different colors on the photoconductor, and performs primary transfer onto an intermediate transfer medium every time a toner image of each color is formed. A color toner image on which the images are superimposed is formed on an intermediate transfer medium, and the color toner image is secondarily transferred onto a transfer sheet to obtain a color image.
[0004]
By the way, the primary transfer is performed, for example, by applying a primary transfer bias between the intermediate transfer medium and the photosensitive member, and the secondary transfer is opposed to the intermediate transfer medium with the transfer paper interposed therebetween, for example. This is performed by applying a secondary transfer bias between the intermediate transfer medium and the arranged secondary transfer member. In this case, conventionally, it is known that the output value of the primary transfer bias is different for each color.
[0005]
[Problems to be solved by the invention]
When the primary transfer bias is controlled at a constant voltage, the potential difference in the primary transfer portion is kept constant, so even if the output value of the secondary transfer bias changes during the application of the primary transfer bias. The change has little influence on the primary transfer.
[0006]
On the other hand, if the output value of the primary transfer bias changes during application of the secondary transfer bias, the electric field between the intermediate transfer medium and the secondary transfer member changes, so that the secondary transfer becomes unstable. There is a fear. In particular, when the intermediate transfer medium is composed of a plurality of layers including a conductive layer, the application of the primary transfer bias to the intermediate transfer medium is not limited to the primary transfer part, and the intermediate transfer medium includes a secondary transfer part. Therefore, the influence of the change in the output value of the primary transfer bias on the secondary transfer bias is large.
[0007]
Therefore, it is preferable to change the output value of the primary transfer bias, because the transfer efficiency changes due to the toner materials of each color being different and the toner of each color being laminated on the intermediate transfer medium. It is desirable to set the change timing so as not to adversely affect the secondary transfer. However, the output value of the primary transfer bias needs to be determined before the primary transfer is started.
[0008]
The present invention has been made in view of the above problems, and in the case where the intermediate transfer medium is composed of a plurality of layers including a conductive layer, the change in the output value of the primary transfer bias adversely affects the secondary transfer. An object of the present invention is to provide an image forming apparatus and method capable of preventing the above.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 is provided with one photoconductor and an intermediate transfer medium composed of a plurality of layers including a conductive layer, and the photoconductor has N (N is a positive integer). A color toner image is sequentially formed, and each time the toner image of each color is formed, the toner image is primarily transferred to the intermediate transfer medium in a primary transfer unit, and the toner images of each color are superimposed, and the superimposed N Primary transfer bias applying means for applying a preset primary transfer bias to the conductive layer of the intermediate transfer medium in an image forming apparatus in which a color toner image is secondarily transferred to transfer paper in a secondary transfer portion And bias control means for changing the output value of the primary transfer bias between the primary transfer of the first color toner image and the primary transfer of the N color toner image, the bias control means comprising: Secondary transfer to transfer paper is complete The output value of the primary transfer bias for the N color is maintained until the second transfer to the transfer paper and before the primary transfer of the next toner image for the first color. The output value of the primary transfer bias is changed to the output value of the primary transfer bias for the first color.
[0010]
According to this configuration, since the primary transfer bias set in advance is applied to the conductive layer of the intermediate transfer medium including a plurality of layers including the conductive layer, the primary transfer bias is an intermediate transfer medium including the secondary transfer unit. It will be applied to the whole. Accordingly, when the output value of the primary transfer bias is changed between the primary transfer of the first color toner image and the primary transfer of the N color toner image, the output value is changed during the secondary transfer. If this occurs, the effect of the change will affect the secondary transfer, but the output value of the primary transfer bias for the N color is maintained until the secondary transfer to the transfer paper is completed, and the secondary transfer to the transfer paper is performed. Since the output value of the primary transfer bias of the N color is changed from the output value of the primary transfer bias of the first color to the output value of the primary transfer bias of the first color before the primary transfer of the next first color toner image. It is possible to reliably avoid the change of the output value during the secondary transfer, thereby preventing the influence of the change of the output value from affecting the secondary transfer.
[0011]
Further, the bias control means may change the output value at the time of primary transfer of toner images of respective colors. According to this configuration, the toner images of different colors are sequentially formed on the photosensitive member, and the toner images of the respective colors overlap each other on the intermediate transfer medium so that the primary image is transferred from the photosensitive member to the intermediate transfer medium every time the toner image of each color is formed. Since the toner image is transferred, the transfer efficiency of the primary transfer may change depending on the thickness of the toner image on the intermediate transfer medium, but the output value of the primary transfer bias also changes during the primary transfer of each color toner image. As a result, primary transfer is suitably performed regardless of the change in the transfer efficiency.
[0012]
According to a third aspect of the present invention, there is provided an end determination means for determining an end timing of secondary transfer to the transfer paper based on the size of the transfer paper, and immediately after the end timing determined by the end determination means. Image forming control means for starting an image forming operation on the photoconductor during execution of the secondary transfer so that the next first color toner image on the photoconductor reaches the primary transfer portion. Furthermore, it is characterized by having prepared.
[0013]
According to this configuration, the end timing of the secondary transfer to the transfer paper is determined based on the size of the transfer paper, and immediately after the determined end timing, the next first color toner image on the photoconductor is primary. Since the image forming operation on the photosensitive member is started during the secondary transfer so as to reach the transfer portion, the image forming operation on the photosensitive member for the next image formation is completed after the secondary transfer is completed. The throughput can be improved compared to the start.
[0014]
According to a fourth aspect of the present invention, the image forming operation for each color on the photoconductor is repeated at a predetermined cycle, and the bias control unit is configured to perform the primary operation after a predetermined time from the start time of the image forming operation for each color. Each of the output values of the transfer bias is changed, and the image formation control unit turns on the secondary transfer bias after the predetermined time from the start time of the N-th color image formation operation after the predetermined period. Is determined based on the end timing, and if it is determined that the secondary transfer bias remains on, the next toner image is waited for a waiting time corresponding to the size of the transfer paper. The image forming operation for the first color on the photosensitive member is started.
[0015]
According to a fifth aspect of the present invention, a photoconductor and an intermediate transfer medium including a plurality of layers including a conductive layer are provided, and N (N is a positive integer) color toner image is sequentially applied to the photoconductor. Each time the toner image of each color is formed, the toner image is primarily transferred to the intermediate transfer medium in the primary transfer portion, the toner images of each color are superimposed, and the superimposed N color toner images are transferred. In an image forming method in which secondary transfer is performed on paper, primary transfer is applied to the conductive layer of the intermediate transfer medium during primary transfer of the first color toner image and primary transfer of the N color toner image. The output value of the bias is changed, the output value of the primary transfer bias for the N color is maintained until the secondary transfer to the transfer paper is completed, and after the secondary transfer to the transfer paper is completed, Before the primary transfer of the next toner image of the first color, the primary color of the N color It is characterized in that from the output values of the shooting bias was set to make changes to the output value of the primary transfer bias of the first color.
According to this configuration, since the primary transfer bias set in advance is applied to the conductive layer of the intermediate transfer medium including a plurality of layers including the conductive layer, the primary transfer bias is an intermediate transfer medium including the secondary transfer unit. It will be applied to the whole. Accordingly, when the output value of the primary transfer bias is changed between the primary transfer of the first color toner image and the primary transfer of the N color toner image, the output value is changed during the secondary transfer. If this occurs, the effect of the change will affect the secondary transfer, but the output value of the primary transfer bias for the N color is maintained until the secondary transfer to the transfer paper is completed, and the secondary transfer to the transfer paper is performed. Since the output value of the primary transfer bias of the N color is changed from the output value of the primary transfer bias of the first color to the output value of the primary transfer bias of the first color before the primary transfer of the next first color toner image. It is possible to reliably avoid the change of the output value during the secondary transfer, thereby preventing the influence of the change of the output value from affecting the secondary transfer.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
First, the configuration of a printer that is an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a diagram showing the internal configuration of the printer, FIG. 2 is a block diagram showing the electrical configuration of the printer, FIGS. 3 and 4 are sectional views and development views of the intermediate transfer belt, respectively, and FIG. 5 is a transfer bias generation circuit. It is a figure which shows typically the example of a structure.
[0017]
This printer forms a full color image by superposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K), or uses only black (K) toner, for example. A monochrome image is formed. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 causes each part of the engine unit 1 to respond to the control signal from the main control unit 100. And an image corresponding to the image signal is printed out on the transfer paper 4 conveyed from the paper feed cassette 3 disposed below the apparatus main body 2.
[0018]
The engine unit 1 includes a photoconductor unit 10, a rotary developing unit 20, an intermediate transfer unit 30, a fixing unit 40, and an exposure unit 50. The photoreceptor unit 10 includes a photoreceptor 11, a charging unit 12, and a cleaning unit 13. A rotary developing unit 20 includes a yellow developing unit 2Y that contains yellow toner, a magenta developing unit 2M that contains magenta toner, and cyan. The intermediate transfer unit 30 includes an intermediate transfer belt 31, a bias applying member 32, a belt cleaner 33, a pair of gate rollers 34, 2 and the like. A next transfer roller 35, a photoreceptor driving motor 36, and the like are provided. The seven units 10, 2Y, 2M, 2C, 2K, 30, 40 are each configured to be detachable from the apparatus main body 2.
[0019]
The printer forms a toner image of each color on the photoconductor 11, primarily transfers the toner image on the photoconductor 11 to the intermediate transfer belt 31, and secondary-transfers the primary transfer toner image to the transfer paper 4. It is configured to transfer, and the output value of the primary transfer bias is changed at the time of primary transfer of the toner images of the respective colors. This is performed after the completion and before the primary transfer of the next toner image of the first color.
[0020]
The photoconductor 11 of the photoconductor unit 10 is moved in the direction of arrow 5 by the photoconductor drive motor 36 in a state where the seven units 10, 2Y, 2M, 2C, 2K, 30, 40 are mounted on the apparatus main body 2. Rotate. Around the photoreceptor 11, a charging unit 12, a rotary developing unit 20, and a cleaning unit 13 are arranged along the rotation direction 5.
[0021]
The charging unit 12 includes a wire electrode to which a high voltage of a predetermined level is applied, and uniformly charges the outer peripheral surface of the photoreceptor 11 by, for example, corona discharge. The cleaning unit 13 is disposed on the upstream side of the charging unit 12 in the rotation direction 5 of the photoconductor 11 and remains on the outer peripheral surface of the photoconductor 11 after the primary transfer of the toner image from the photoconductor 11 to the intermediate transfer belt 31. The surface of the photoreceptor 11 is cleaned by scraping off the toner.
[0022]
The exposure unit 50 is reflected by a laser light source 51 made of, for example, a semiconductor laser, a polygon mirror 52 that reflects laser light from the laser light source 51, a scanner motor 53 that rotates the polygon mirror 52 at high speed, and the polygon mirror 52. A lens unit 54 for focusing the laser light, a plurality of reflection mirrors 55, a horizontal synchronization sensor 56, and the like are provided. The laser beam 57 reflected by the polygon mirror 52 and emitted through the lens unit 54 and the reflection mirror 55 is scanned in the main scanning direction (direction perpendicular to the paper surface of FIG. 1) on the surface of the photoreceptor 11. Then, an electrostatic latent image corresponding to the image signal is formed on the surface of the photoreceptor 11. At this time, the horizontal synchronization sensor 56 obtains a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal. The exposure unit 50 functions as an exposure unit.
[0023]
The rotary developing unit 20 develops the toner of each color by attaching it to the electrostatic latent image. The yellow developing unit 2Y, the magenta developing unit 2M, the cyan developing unit 2C, and the black developing unit 2K of the rotary developing unit 20 are provided to be rotatable about the axis, and these developing units 2Y, 2M, 2C, and 2K are determined in advance. The plurality of positions are movably disposed, and are selectively disposed at the contact position and the separation position with respect to the photoconductor 11. Then, a developing bias in which an alternating current component is superimposed on a direct current component or a direct current component is applied, and the toner of the color adheres to the surface of the photosensitive member 11 from the developing unit in contact with the photosensitive member 11. The rotary developing unit 20 functions as a developing unit.
[0024]
The intermediate transfer belt 31 of the intermediate transfer unit 30 is stretched around a plurality of rollers, and is rotationally driven together with the photosensitive member 11 by the photosensitive member driving motor 36. As shown in the cross-sectional view of FIG. 3, the intermediate transfer belt 31 includes a plurality of layers having a resistance layer 81 on the surface, an intermediate conductive layer 82, and a base material portion 83 as a lower layer. The resistance layer 81 is made of a synthetic resin (for example, urethane resin) having a predetermined thickness (for example, 20 μm), and is made of conductive particles (for example, SnO). ₂ ) 84, fluororesin (for example, polytetrafluoroethylene) particles 85, and the like. By including the conductive particles 84, the resistance value of the resistance layer 81 is 10 ⁸ -10 ¹⁴ The frictional resistance is suppressed by including the fluororesin particles 85 and the intermediate transfer belt 31 is prevented from being locked by the belt cleaner 33 (described later).
[0025]
The conductive layer 82 is formed by vapor deposition of aluminum, for example. The base material portion 83 has a predetermined thickness (for example, 100 μm) and is formed of a synthetic resin (for example, polyethylene terephthalate). In this manner, the cost is reduced by separating the resistance layer 81 and the conductive layer 82 which are layers that perform an electrical function and the base material portion 83 that is a layer for giving mechanical strength.
[0026]
The intermediate transfer belt 31 is a seamless (seamless) endless belt, and has a total length L0 as shown in the developed view of FIG. In FIG. 4, an arrow 71 indicates the rotational drive direction, and an arrow 72 indicates the rotational axis direction. The transfer area 73 of the intermediate transfer belt 31 has a size larger than the A3 size in the long side direction in the rotational drive direction 71, for example, and the transfer area 73 is divided into two sub areas 73A and 73B. Further, two A4 size toner images 74 having a short side direction in the rotational driving direction 71 can be transferred on one rotation of the intermediate transfer belt 31.
[0027]
As shown in FIG. 4, the conductive layer 82 is exposed on the surface at one end side (the lower side in FIG. 4) of the intermediate transfer belt 31 in the rotation axis direction 72. Then, for example, a roller-shaped bias applying member 32 (see FIG. 2) is electrically connected to the exposed portion, and a primary transfer bias is applied through the bias applying member 32, and the photosensitive member is exposed to the primary transfer bias. The toner image on the body 11 is primarily transferred to the intermediate transfer belt 31, and the contact position of the photoreceptor 11 with the intermediate transfer belt 31 is set in the primary transfer portion 14.
[0028]
The belt cleaner 33 is disposed so as to be switchable between a contact state (solid line in FIG. 1) and a separation state (broken line in FIG. 1) with the cleaner separating clutch. The residual toner on the transfer belt 31 is scraped off. The gate roller pair 34 is driven to rotate when the driving force of the transport system driving motor 60 is transmitted by turning on the gate clutch.
[0029]
The secondary transfer roller 35 is switched between a contact state (solid line in FIG. 1) and a separation state (broken line in FIG. 1) with the intermediate transfer belt 31 by the secondary transfer roller separation / contact clutch. A predetermined secondary transfer bias is applied to the secondary transfer roller 35 in contact with the intermediate transfer belt 31, and the primary transfer toner image on the intermediate transfer belt 31 is transferred to the transfer paper while conveying the transfer paper 4. 4, the contact position is set in the secondary transfer portion 37.
[0030]
The fixing unit 40 includes a heating roller 41 and a pressure roller 42, and fixes the toner image on the transfer paper 4 to the transfer paper 4 while conveying the transfer paper 4 by a heat roller fixing method, and constitutes a fixing unit. To do.
[0031]
From the front end (right end in FIG. 1) of the paper feed cassette 3, a half-moon pickup roller 61 and a feed roller pair 62 are disposed, and the gate roller pair 34, the secondary transfer roller 35, and the fixing unit 40 are arranged. Further, a pair of conveying rollers 63 and a pair of discharging rollers 64 are disposed so as to form a conveying path for the transfer paper 4 (a chain line in FIG. 1). The transfer paper 4 discharged by the discharge roller pair 64 is stacked on the paper discharge unit 6.
[0032]
The pickup roller 61 is driven by a pickup solenoid. The feed roller pair 62, the gate roller pair 34, the secondary transfer roller 35, the heating roller 41 of the fixing unit 40, the transport roller pair 63, and the discharge roller pair 64 are respectively the same transport system driving motor via a driving force transmission mechanism. 60. The feed roller pair 62 is driven to rotate by the driving force of the conveyance system driving motor 60 being transmitted when the feed clutch is turned on. The transfer paper 4 is conveyed at a predetermined conveyance speed by the conveyance system driving motor 60. The feed roller pair 62, the gate roller pair 34, the transport roller pair 63, and the discharge roller pair 64 constitute transport means for the transfer paper 4.
[0033]
In FIG. 2, the main control unit 100 includes an interface 102 that transmits and receives control signals between the CPU 101 and an external device such as a host computer, and an image for storing an image signal given through the interface 102. And a memory 103. When the CPU 101 receives a print command signal including an image signal from an external device via the interface 102, the CPU 101 converts the job data into a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110.
[0034]
The engine control unit 110 includes a CPU 111, a ROM 112, a RAM 113, and the like. The ROM 112 stores a control program of the CPU 111 and the like, and the RAM 113 temporarily stores control data of the engine unit 1, a calculation result by the CPU 111, and the like.
[0035]
The CPU 111 receives a horizontal synchronization signal Hsync from the horizontal synchronization sensor 56 as an input signal from the engine unit 1 and receives predetermined detection signals from other sensors and the like. The CPU 111 controls the operation of each unit of the engine unit 1 based on these input signals and the control program.
[0036]
That is, the CPU 111 sends a control signal to the motor drive circuit 114 that drives the photoconductor drive motor 36 to rotate the photoconductor 11 and the intermediate transfer belt 31 in synchronization. In addition, a control signal is sent to the motor drive circuit 115 that drives the transport system driving motor 60 to control the transport of the transfer paper 4 from the paper feed cassette 3.
[0037]
Further, the CPU 111 sends a control signal to a drive circuit that drives the cleaner separating clutch, and controls the separation and contact of the belt cleaner 33 with respect to the intermediate transfer belt 31. Further, a control signal is sent to a drive circuit that drives the secondary transfer roller separation clutch, and the separation and contact of the secondary transfer roller 35 with respect to the intermediate transfer belt 31 are controlled.
[0038]
Further, the CPU 111 receives, for example, the operation content for the operation keys of the operation display panel 7 disposed on the surface of the apparatus main body 2 and controls the display content of the display unit. When the CPU 111 forms two or more images having a size that allows two sheets to be taken (for example, a size of A4 size or less that is the short side direction in the rotational drive direction 71), the sub-region 73A in the transfer region 73 is formed. , 73B, the image forming operation on the photosensitive member 11 is controlled so that the toner images are transferred to the respective toner images.
[0039]
In addition, the CPU 111 sends a control signal to a primary transfer bias generation circuit 116 that generates a primary transfer bias, and controls application of the primary transfer bias to the intermediate transfer belt 31. In addition, the CPU 111 sends a control signal to a secondary transfer bias generation circuit 117 that generates a secondary transfer bias, and controls application of the secondary transfer bias to the secondary transfer roller 35.
[0040]
Here, as shown in FIG. 5, the CPU 111 sends control data to the D / A converter 121 of the primary transfer bias generation circuit 116. The D / A conversion unit 121 controls the drive unit 122 based on control data input from the CPU 111, and performs primary transfer by constant voltage (for example, a voltage value set in advance within a range of about 50 to 400V). The application of bias is controlled.
[0041]
In addition, the CPU 111 sends control data to the D / A conversion unit 123 of the secondary transfer bias generation circuit 117. The D / A conversion unit 123 controls the drive unit 124 based on control data input from the CPU 111, and takes into account a lower limit voltage (for example, a voltage value set in advance within a range of about 500 to 3000 V). Application of the secondary transfer bias is controlled by constant current control (for example, a current value set in advance within a range of about 1 to 100 μA). That is, voltage control is performed until the lower limit voltage is reached, and then constant current control is performed.
[0042]
In FIG. 5, the load 125 is equivalently composed of a resistance component such as the photosensitive member 11 and the bias applying member 32, and the load 126 is equivalently composed of a resistance component such as the secondary transfer roller 35 and the intermediate transfer belt 31. Is done.
[0043]
Further, the CPU 111 changes the output value of the primary transfer bias to the D / A converter 121 at the time of primary transfer of each color toner image, and the change of the output value is performed when the secondary transfer is not performed. To do. For example, when a plurality of image formations are performed continuously, the output value of the primary transfer bias for the fourth color (for example, K in FIG. 6 described later) for the previous image formation is used as the first image for the next image formation. The color (for example, Y in FIG. 6) is changed to the output value of the primary transfer bias after the secondary transfer for the previous image formation is completed.
[0044]
At this time, the CPU 111 determines the end timing of the secondary transfer to the transfer paper 4 based on the size of the transfer paper 4, and the next first color toner image on the photoconductor 11 is immediately after the determined end timing. An image forming operation on the photoconductor 11 is started during the secondary transfer so as to reach the primary transfer unit 14.
[0045]
The intermediate transfer belt 31 corresponds to an intermediate transfer medium, and the bias applying member 32 and the primary transfer bias generating circuit 116 correspond to a primary transfer bias applying unit. The CPU 111 corresponds to a bias control unit, an end determination unit, and an image formation control unit.
[0046]
Next, the operation of this printer will be described with reference to FIG. FIG. 6 is a timing chart showing the time change of the state of each part of the engine unit 1 and shows a case where four color images having a size that can be taken (for example, A4 size) are formed, and each toner image to be superimposed is shown. The output value of the primary transfer bias is changed for each primary transfer. The image signal and the development bias are turned on at a predetermined timing in response to the image request signal Vreq. The on timing is delayed for a predetermined time from the image request signal Vreq. In FIG. It is described that the signal is turned on in synchronization with the signal Vreq.
[0047]
When a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 starts operation of each unit of the engine unit 1 in response to the control signal from the main control unit 100. To do. At this time, if the size of the transfer paper 4 loaded in the paper feed cassette 3 does not match the size instructed by the print command signal, a message prompting the user to replace the paper feed cassette is displayed on the operation display panel 7. To do. In FIG. 1, the printer includes a single paper feed cassette 3. However, the printer is not limited to this, and a printer having a plurality of paper feed cassettes may be used.
[0048]
The size of the transfer paper 4 loaded on the paper feed cassette 3 matches the size indicated by the print command signal (or the size indicated by the print command signal among the plurality of paper feed cassettes). (A cassette for containing the transfer paper 4 is included) on the surface of the photoconductor 11 uniformly charged by the charging unit 12, the electrostatic latent image corresponding to the image signal is output by the laser light 57 from the exposure unit 50. An image is formed, and the electrostatic latent image is developed by the rotary developing unit 20 to form a toner image. The toner image on the photoreceptor 11 is primary transferred onto the intermediate transfer belt 31 in the primary transfer unit 14. Is done.
[0049]
That is, the intermediate transfer belt 31 is rotated at a predetermined peripheral speed by the photosensitive member driving motor 36, and as shown in FIG. 6, image request signals are respectively received at times t1, t2, t3, t4, t5, t6, t7, and t8. Vreq is output. If the output cycle of the image request signal Vreq is T1, and the peripheral speed of the intermediate transfer belt 31 is S1, in FIG.
L0 = 2 ・ T1 ・ S1
As shown in FIG. 4, two A4 size toner images are transferred around the intermediate transfer belt 31.
[0050]
In response to the image request signal Vreq at time t1, formation of an electrostatic latent image corresponding to the first image signal is started, and the developing bias is turned on. Subsequently, in response to the image request signal Vreq at time t2, formation of an electrostatic latent image corresponding to the second image signal is started.
[0051]
Then, the developing unit of the rotary developing unit 20 is switched at times t1, t3, t5, and t7, and toner images of the respective colors are formed on the photoconductor 11, and are sequentially primary-transferred to the intermediate transfer belt 31. At this time, the output value of the primary transfer bias generation circuit 116 is changed after a predetermined time T2 from time t1, t3, t5, t7.
[0052]
In this embodiment, the primary transfer bias is set such that the first color (here, Y) is set to the voltage V1 (for example, V1 = 220V), and the second color (here, C) is set to the voltage V2 (for example, V2 = 245V). The third color (here, M) is set to the voltage V3 (for example, V3 = 270V), and the last color (here, K for the fourth color) is set to the voltage V4 (for example, V4 = 300V).
[0053]
During the predetermined time T2, the primary transfer bias applied to the intermediate transfer belt 31 until the leading end of the toner image on the photoconductor 11 (the downstream end in the rotational drive direction 71) reaches the primary transfer unit 14. Is preset to complete the change.
[0054]
Here, since the primary transfer is not completed at the time after the predetermined time T2 from the times t1, t3, t5, and t7, the secondary transfer is not performed, so the output value of the primary transfer bias is changed. Will not cause any trouble. That is, during this period, the secondary transfer roller 35 is in a separated state with respect to the intermediate transfer belt 31, so that the toner images of the respective colors are superimposed on the intermediate transfer belt 31.
[0055]
The developing bias is turned off after a predetermined time determined in advance by the transfer paper size from the falling point of each image request signal Vreq at times t1, t3, t5, and t7.
[0056]
As a result, the color toner image obtained by superimposing the toner images Y1, C1, M1, and K1 is primarily transferred to the sub-region 73A downstream of the rotational drive direction 71 in the transfer region 73 of the intermediate transfer belt 31, and the toner is transferred. The color toner image obtained by superimposing the images Y2, C2, M2, and K2 is primarily transferred to the sub-region 73B that is upstream of the rotational drive direction 71 in the transfer region 73 of the intermediate transfer belt 31.
[0057]
On the other hand, the uppermost transfer sheet 4 in the bundle of transfer sheets loaded in the sheet feeding cassette 3 is taken out by the pickup roller 61, conveyed at a predetermined speed S 1 by the feed roller pair 62, and nipped by the gate roller pair 34. Then, the gate clutch is turned on in synchronization with the toner image on the intermediate transfer belt 31, and the transfer paper 4 is conveyed from the gate roller pair 34 toward the secondary transfer unit 37 at a predetermined speed S1.
[0058]
Then, at time t9 after a predetermined time from time t7, the secondary transfer roller separating clutch is turned on, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, the application of the secondary transfer bias from the secondary transfer bias generation circuit 117 to the secondary transfer roller 35 is turned on at time t10 after a predetermined time from time t7.
[0059]
As a result, the color toner image superimposed on the toner images Y1, C1, M1, and K1 that is primarily transferred to the sub-region 73A downstream of the rotational drive direction 71 in the transfer region 73 of the intermediate transfer belt 31 is obtained. The image is transferred to the first transfer paper 4.
[0060]
The gate clutch is temporarily turned off after the first transfer sheet 4 is carried out, and the application time of the secondary transfer bias is set in advance according to the size of the transfer sheet 4. At this time, the next transfer paper 4 is taken out by the pickup roller 61, conveyed at a predetermined speed S 1 by the feed roller pair 62, and nipped by the gate roller pair 34.
[0061]
After the gate clutch and the secondary transfer bias application are turned off, the gate clutch is turned on at the timing of the next toner image and the next transfer sheet 4 is conveyed, and the secondary transfer is performed at time t11 after a predetermined time from time t7. Bias application is turned on. Then, when the set application time of the secondary transfer bias has elapsed (time t12), the application of the secondary transfer bias is turned off, and then the secondary transfer roller separating clutch is turned on after a predetermined time from time t7. Accordingly, the secondary transfer roller 35 is separated from the intermediate transfer belt 31.
[0062]
As a result, the color toner image superposed on the toner images Y2, C2, M2, and K2 that is primarily transferred to the sub-region 73B on the upstream side in the rotational driving direction 71 in the transfer region 73 of the intermediate transfer belt 31 is obtained. It is transferred to the second transfer paper 4.
[0063]
In the fixing unit 40, the toner image is fixed to the transfer paper 4 while the transfer paper 4 is conveyed. The transfer paper 4 is further transported by a transport roller pair 63, and is discharged by a discharge roller pair 64 to a paper discharge unit 6 provided in the upper part of the apparatus main body 2.
[0064]
Subsequently, the third and fourth images are formed on the photoconductor 11, but the application time of the secondary transfer bias is set in advance according to the size of the transfer paper 4, and therefore after a predetermined period T1 from time t8. At the time (time t13), it is possible to determine whether or not the secondary transfer bias remains on (t13 + T2 is earlier than t12) after a predetermined time T2. Here, in FIG. 6, the secondary transfer bias is on at a time point after a predetermined time T2 from time t13, and the CPU 111 knows that point at the time t13, so the image request signal Vreq at time t13. Is not output and waits for a predetermined waiting time.
[0065]
Then, the image request signal Vreq is output again at a predetermined cycle T1 at times t14, t15,... To form toner images Y3 and Y4 for forming the third and fourth images, and after a predetermined time T2 from the time t14. At time t16, the output value of the primary transfer bias is changed to V1, and thereafter, the same operation as described above is performed. Here, time t14 is set to a time at which the secondary transfer bias is turned off at time t16 after the predetermined time T2 (time t16 is later than time t12).
[0066]
The third and fourth image formations after time t14 are delayed by the above-described waiting time with respect to the first and second image formations up to that point. The contact and separation timing with respect to the transfer belt 31 may be changed.
[0067]
As described above, according to the operation of FIG. 6, the primary transfer bias is changed for each primary transfer of the toner image. Therefore, the toner that changes in accordance with the toner stack thickness on the intermediate transfer belt 31. The toner of each color can be suitably primary-transferred to the intermediate transfer belt 31 in accordance with the transfer efficiency, whereby a high-quality color image can be obtained on the transfer paper 4.
[0068]
Further, since the output value of the primary transfer bias is changed when the secondary transfer is not performed (after the secondary transfer is completed), the change of the primary transfer bias has an adverse effect on the secondary transfer. It is possible to prevent the image quality transferred onto the transfer paper 4 from being deteriorated.
[0069]
Also, the time t14 at which the output of the image request signal Vreq is resumed is set to a time at which the secondary transfer bias is turned off at time t16 after the predetermined time T2 (time t16 becomes later than time t12). As a result, the waiting time can be increased or decreased according to the size of the transfer paper 4, thereby reducing the throughput as much as possible.
[0070]
The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention.
[0071]
For example, in the above embodiment, the intermediate transfer belt 31 including a seamless endless belt is used. However, the intermediate transfer medium of the present invention is not limited to this, and for example, a cylindrical intermediate transfer drum may be used.
[0072]
In the above-described embodiment, the primary transfer bias output value is changed in the primary transfer of the first to fourth color toner images, but the present invention is not limited to this. For example, the output value may be the same value during the primary transfer of the first to third toner images, and may be changed only during the primary transfer of the fourth toner image. Further, it may be changed only at the time of primary transfer of the first toner image, and the output value may be set to the same value at the time of primary transfer of the second to fourth toner images. That is, it is sufficient if the output value of the primary transfer bias is changed between the first primary transfer and the last primary transfer.
[0073]
In the above-described embodiment, the secondary transfer bias returns to OFF at time t14 when output of the image request signal Vreq is resumed, and at time t16 after the predetermined time T2 (time t16 becomes later than time t12). However, the present invention is not limited to this, and the output of the image request signal Vreq may be resumed in synchronization with the time t12 when the secondary transfer bias returns to off. According to this aspect, the control procedure is simplified, and the control program can be easily designed.
[0074]
In the above embodiment, a printer that prints an image provided from an external device such as a host computer on transfer paper is described. However, the present invention is not limited to this, and includes a copying machine, a facsimile machine, and the like. The present invention can be applied to a general electrophotographic image forming apparatus.
[0075]
【The invention's effect】
As described above, according to the first and fifth aspects of the present invention, the first color image is applied to the conductive layer of the intermediate transfer medium during the primary transfer of the first color toner image and during the primary transfer of the N color toner image. The output value of the next transfer bias is changed, and the output value of the primary transfer bias for the N color is maintained until the secondary transfer to the transfer paper is completed. Before the primary transfer of the first color toner image, the output value of the primary transfer bias of the N color is changed from the output value of the primary transfer bias of the first color. This can surely be avoided during the secondary transfer, whereby the influence of the change in the output value on the secondary transfer can be prevented beforehand.
[0076]
According to the second aspect of the invention, since the output value of the primary transfer bias is changed also during the primary transfer of the toner images of the respective colors, the primary transfer depends on the thickness of the toner image on the intermediate transfer medium. Regardless of the transfer efficiency of the transfer, the primary transfer from the photoconductor to the intermediate transfer medium can be suitably performed.
[0077]
According to the third aspect of the present invention, the end timing of the secondary transfer to the transfer paper is determined based on the size of the transfer paper, and the next first color on the photoconductor is immediately after the determined end timing. Since the image forming operation on the photosensitive member is started during the secondary transfer so that the toner image reaches the primary transfer portion, the photosensitive member for the next image formation after the secondary transfer is completed. The throughput can be improved as compared to starting the image forming operation on the body.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the printer.
FIG. 3 is a cross-sectional view of an intermediate transfer belt.
FIG. 4 is a development view of an intermediate transfer belt.
FIG. 5 is a diagram schematically illustrating a configuration example of a transfer bias generation circuit.
FIG. 6 is a timing chart showing temporal changes in the state of each part of the engine part for explaining the operation.
[Explanation of symbols]
4 Transfer paper
11 photoconductor
14 Primary transfer section
31 Intermediate transfer belt (intermediate transfer medium)
32 Bias applying member (primary transfer bias applying means)
37 Secondary transfer section
71 Rotation drive direction
72 Direction of rotation axis
82 Conductive layer
110 Engine control unit
111 CPU (bias control means, end determination means, image formation control means)
116 Primary transfer bias generation circuit (primary transfer bias applying means)

Claims (5)

A single photosensitive member and an intermediate transfer medium comprising a plurality of layers including a conductive layer, and sequentially forming N (N is a positive integer) color toner image on the photosensitive member, and forming each color toner image Then, the toner image is primarily transferred to the intermediate transfer medium in the primary transfer portion to superimpose the toner images of the respective colors, and the superimposed N color toner images are secondarily transferred to the transfer paper in the secondary transfer portion. In the image forming apparatus as described above,
Primary transfer bias applying means for applying a preset primary transfer bias to the conductive layer of the intermediate transfer medium;
Bias control means for changing an output value of the primary transfer bias between the primary transfer of the first color toner image and the primary transfer of the N color toner image;
The bias control means maintains the output value of the primary transfer bias for the N color until the secondary transfer to the transfer paper is completed, and after the secondary transfer to the transfer paper is completed, Before the primary transfer of the first color toner image, the output value of the primary transfer bias for the N color is changed to the output value of the primary transfer bias for the first color. .   The image forming apparatus according to claim 1, wherein the bias control unit changes the output value at the time of primary transfer of toner images of respective colors. End determination means for determining the end timing of the secondary transfer to the transfer paper based on the size of the transfer paper;
Immediately after the end timing determined by the end determination means, the toner image of the next first color on the photoconductor reaches the primary transfer portion during the secondary transfer so that the image on the photoconductor The image forming apparatus according to claim 1, further comprising an image forming control unit that starts the image forming operation. The image forming operation of each color on the photoconductor is repeated at a predetermined cycle,
The bias control unit changes the output value of the primary transfer bias after a predetermined time from the start of the image forming operation for each color,
The image formation control means determines whether or not the secondary transfer bias remains on after the predetermined time from the start of the N-th color image formation operation at the end of the predetermined period. If the secondary transfer bias is determined to remain on, after waiting for a waiting time corresponding to the size of the transfer paper, the first color image on the photoreceptor of the next toner image is determined. The image forming apparatus according to claim 3, wherein a forming operation is started. A single photosensitive member and an intermediate transfer medium comprising a plurality of layers including a conductive layer, and sequentially forming N (N is a positive integer) color toner image on the photosensitive member, and forming each color toner image First, the toner image is primarily transferred to the intermediate transfer medium in the primary transfer portion, the toner images of the respective colors are superimposed, and the superimposed N color toner images are secondarily transferred to the transfer paper. In the method
Changing the output value of the primary transfer bias applied to the conductive layer of the intermediate transfer medium between the primary transfer of the first color toner image and the primary transfer of the N color toner image;
The output value of the primary transfer bias for the N color is maintained until the secondary transfer to the transfer paper is completed,
The primary transfer bias of the first color is determined from the output value of the primary transfer bias of the N color after the completion of the secondary transfer to the transfer paper and before the primary transfer of the next first color toner image. An image forming method characterized in that the output value is changed.

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