JP3931667B2 - Image forming apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming technique such as a printer, a copying machine, and a facsimile machine.
[0002]
[Prior art]
Conventionally, a toner image is formed by attaching a toner to an electrostatic latent image formed on a photosensitive member by an exposure unit by a developing unit, 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 in which paper is fixed to the transfer paper while being transported is known. In particular, as an apparatus capable of forming a color image, a toner image formed on a photoconductor is intermediately transferred. There is known an image forming apparatus in which a primary transfer is performed on a medium and a primary transfer toner image on the intermediate transfer medium is secondarily transferred onto a transfer sheet.
[0003]
In this image forming apparatus, when a color image is formed, a plurality of color toner images are sequentially formed on a photoconductor, and each toner image of each color is primary-transferred to an intermediate transfer medium to form a plurality of color toners. 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. In the image forming apparatus configured as described above, it is possible to perform single color printing using a specific color among a plurality of colors, and in many cases, black toner.
[0004]
On the other hand, conventionally, an image forming apparatus that can use thick paper thicker than plain paper such as high-quality paper, postcards, envelopes, glossy paper, and high-definition paper in addition to plain paper has been put to practical use as transfer paper. However, if the thick paper as described above is conveyed at the same speed as that of the plain paper and the fixing unit is operated, sufficient fixing performance cannot be obtained, resulting in a deterioration in image quality. Such a situation can be prevented by improving the fixing performance by, for example, increasing the heat capacity of the fixing means, but as a result, the apparatus becomes larger, or conversely, the image quality is improved by excessive heat when fixing plain paper. In such an image forming apparatus, when using thick paper as transfer paper, it is sufficient to reduce the paper conveyance speed and increase the fixing time as compared with plain paper. Fixing performance is secured.
[0005]
In this case, at the time of secondary transfer, it is necessary to set the driving speed of the intermediate transfer medium to a low speed in accordance with the paper conveyance speed, but the process speed such as image formation on the photoreceptor and primary transfer to the intermediate transfer medium is also low. It is conceivable to use a device having a high speed and a device in which the process speed is kept at a normal speed and the driving speed is made low only at the time of secondary transfer. In the former apparatus, since the image forming process is performed at two types of speed, it takes twice as much labor to obtain a favorable process setting value for the development condition and transfer condition as compared with the case of one type. Although there is a problem that it takes time to check the apparatus design and operation, the latter apparatus does not have the above-mentioned problem because the speed of the image forming process is one type.
[0006]
[Problems to be solved by the invention]
However, when the latter device is adopted, it is necessary to sufficiently consider the timing for starting deceleration from the normal speed to the low speed. In general, the distance between the primary transfer portion and the secondary transfer portion is shorter than that of a large transfer paper in order to reduce the size of the apparatus. For this reason, in the case of the apparatus having such a configuration, at the end of the primary transfer, the leading edge of the primary transfer toner image has already passed through the secondary transfer portion. Therefore, immediately after the completion of the primary transfer, the intermediate transfer medium is rotated as it is without performing the secondary transfer, and then the secondary transfer is performed when passing through the secondary transfer portion. Therefore, it is only necessary to decelerate from the normal speed to the low speed before the leading edge of the primary transfer toner image reaches the secondary transfer portion.
[0007]
However, if the intermediate transfer medium starts decelerating while the primary transfer toner image passes through the primary transfer portion again, a difference occurs in the degree of reverse transfer from the intermediate transfer medium to the photosensitive member. There is a possibility that the toner image is uneven and the image quality is deteriorated. On the other hand, if the above-described deceleration start timing is too early and the driving time of the intermediate transfer medium at a low speed becomes long, the image forming throughput decreases.
[0008]
The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus and method capable of preventing a deterioration in image quality when a low-speed mode is provided as a transfer paper conveyance speed.
[0009]
It is another object of the present invention to provide an image forming apparatus and method capable of suppressing a decrease in image formation throughput when a low-speed mode is provided as a transfer paper conveyance speed.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 includes a developing unit that forms a toner image by attaching toner to an electrostatic latent image formed on a photosensitive member, a primary transfer unit that rotates, An intermediate transfer medium that cyclically passes through a secondary transfer section; a primary transfer means that primarily transfers the toner image to the intermediate transfer medium in the primary transfer section; and the intermediate transfer medium in the secondary transfer section. Secondary transfer means for secondary transfer of the primary transfer toner image on the transfer paper; and fixing means for fixing the secondary transfer toner image on the transfer paper to the transfer paper while transporting the transfer paper. In the image forming apparatus, the conveyance control has a normal mode for conveying the transfer paper at the first speed and a low speed mode for conveying the transfer paper at least at a second speed lower than the first speed from the secondary transfer unit to the end of fixing. Means and said normal mode Drives the intermediate transfer medium at the first speed, and in the low speed mode, drives the intermediate transfer medium at the first speed at least until the end of the toner image formation by the developing means, and after the end of the toner image formation. An intermediate transfer medium control means for controlling to drive the intermediate transfer medium at the second speed at least until the end of the secondary transfer, and reducing the driving speed of the intermediate transfer medium; The secondary transfer portion that passes immediately after the completion of the primary transfer in the secondary transfer portion does not perform the secondary transfer of the primary transfer toner image, and the primary transfer toner image re-opens the primary transfer portion. And a transfer control means for performing secondary transfer of the primary transfer toner image in the secondary transfer portion that passes next, and the intermediate transfer medium control means is in the low speed mode. After the completion of the primary transfer in the primary transfer portion, the leading edge of the primary transfer toner image is intermediated from the start of deceleration from the first speed to the second speed until the time when the leading edge is stabilized at the second speed. When the primary transfer portion reaches the upstream position in the rotational drive direction from the primary transfer portion by the distance traveled by the transfer medium, the primary transfer toner image is transferred to the primary transfer by starting deceleration from the first speed. The intermediate transfer medium is driven at the second speed when the leading edge of the primary transfer toner image reaches the primary transfer portion when passing through the portion again.
[0011]
According to this configuration, there is a normal mode in which the transfer paper is conveyed at the first speed, and a low speed mode in which the transfer paper is conveyed at a second speed lower than the first speed from the secondary transfer unit to the end of fixing. In the mode, the intermediate transfer medium is driven at the first speed. In the low speed mode, the intermediate transfer medium is driven at the first speed at least until the end of the toner image formation by the developing means, and after the toner image formation is completed, the intermediate transfer is performed. The driving speed of the medium decreases from the first speed to the second speed, and is maintained at the second speed at least until the end of the secondary transfer. In the low-speed mode, the primary transfer toner image is not transferred to the primary transfer toner image in the secondary transfer unit that passes immediately after the primary transfer in the primary transfer unit is completed. After passing through the transfer portion again, the secondary transfer of the primary transfer toner image is performed in the secondary transfer portion that passes next.
[0012]
Then, in the low speed mode, when the primary transfer toner image passes through the primary transfer portion again after the primary transfer in the primary transfer portion is completed by the intermediate transfer medium control means, the primary transfer toner image When the leading edge reaches the primary transfer portion, the intermediate transfer medium is driven at the second speed.
[0013]
Accordingly, since the driving speed of the intermediate transfer medium does not change while the primary transfer toner image passes through the first transfer portion again, the environmental condition between the intermediate transfer medium and the photosensitive member in the primary transfer portion is the primary transfer toner. Since there is no change in the middle of the image, the primary transfer toner image becomes uneven due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer portion, and the image quality deteriorates. The situation will be prevented beforehand.
[0017]
Further, the leading edge of the primary transfer toner image is upstream from the primary transfer portion in the rotational drive direction by the distance traveled by the intermediate transfer medium from the start of deceleration from the first speed to the second speed until the time when it stabilizes at the second speed. When the position on the intermediate transfer medium is reached, the deceleration from the first speed is started, so that the intermediate transfer medium is surely synchronized with the time when the intermediate transfer medium is driven at the second speed. The leading edge of the next transfer toner image reaches the primary transfer portion. In addition, since the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, a decrease in image formation throughput is suppressed as much as possible.
[0018]
According to a second aspect of the present invention, a toner image formed by adhering toner to an electrostatic latent image formed on a photosensitive member by a developing unit is transferred to a rotating intermediate transfer medium at a primary transfer portion. Then, the primary transfer toner image on the intermediate transfer medium is secondarily transferred to the transfer paper at the secondary transfer unit, and the secondary transfer toner image on the transfer paper is fixed to the transfer paper while transporting the transfer paper. The image forming method according to the present invention has a normal mode in which transfer paper is conveyed at a first speed and a low-speed mode in which transfer paper is conveyed at a second speed lower than the first speed from the secondary transfer unit to the end of fixing. In the normal mode, the intermediate transfer medium is driven at the first speed, and in the low speed mode, the intermediate transfer medium is driven at the first speed at least until completion of toner image formation by the developing unit. Both An intermediate transfer medium control step of controlling the intermediate transfer medium to be driven at the second speed at least until the end of the secondary transfer by reducing the driving speed of the intermediate transfer medium after the toner image formation is completed; In this case, the secondary transfer portion that passes immediately after the primary transfer in the primary transfer portion does not perform the secondary transfer of the primary transfer toner image, and the primary transfer toner image is A transfer control step of performing secondary transfer of the primary transfer toner image in the secondary transfer portion that passes again after passing through the primary transfer portion, and in the intermediate transfer medium control step, the low speed In the mode, after the primary transfer in the primary transfer portion is completed, the leading edge of the primary transfer toner image is from the start of deceleration from the first speed to the second speed until the time when the leading speed is stabilized at the second speed. In the above When the primary transfer portion reaches the upstream position in the rotational drive direction from the primary transfer portion by the distance traveled by the transfer medium, the primary transfer toner image is transferred to the primary transfer by starting deceleration from the first speed. The intermediate transfer medium is driven at the second speed when the leading edge of the primary transfer toner image reaches the primary transfer portion when passing through the portion again.
[0019]
According to this configuration, there is a normal mode in which the transfer paper is conveyed at the first speed, and a low speed mode in which the transfer paper is conveyed at a second speed lower than the first speed from the secondary transfer unit to the end of fixing. In the mode, the intermediate transfer medium is driven at the first speed. In the low speed mode, the intermediate transfer medium is driven at the first speed at least until the end of the toner image formation by the developing means, and after the toner image formation is completed, the intermediate transfer is performed. The driving speed of the medium decreases from the first speed to the second speed, and is maintained at the second speed at least until the end of the secondary transfer. In the low-speed mode, the primary transfer toner image is not transferred to the primary transfer toner image in the secondary transfer unit that passes immediately after the primary transfer in the primary transfer unit is completed. After passing through the transfer portion again, the secondary transfer of the primary transfer toner image is performed in the secondary transfer portion that passes next.
[0020]
Then, in the low speed mode, when the primary transfer toner image passes through the primary transfer portion again after the primary transfer in the primary transfer portion is completed by the intermediate transfer medium control means, the primary transfer toner image When the leading edge reaches the primary transfer portion, the intermediate transfer medium is driven at the second speed.
[0021]
Accordingly, since the driving speed of the intermediate transfer medium does not change while the primary transfer toner image passes through the primary transfer portion again, the environmental condition between the intermediate transfer medium and the photosensitive member in the primary transfer portion is the primary transfer toner. Since there is no change in the middle of the image, the primary transfer toner image becomes uneven due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer portion, and the image quality deteriorates. The situation will be prevented beforehand.
Further, the leading edge of the primary transfer toner image is upstream from the primary transfer portion in the rotational drive direction by the distance traveled by the intermediate transfer medium from the start of deceleration from the first speed to the second speed until the time when it stabilizes at the second speed. When the position on the intermediate transfer medium is reached, the deceleration from the first speed is started, so that the intermediate transfer medium is surely synchronized with the time when the intermediate transfer medium is driven at the second speed. The leading edge of the next transfer toner image reaches the primary transfer portion. In addition, since the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, a decrease in image formation throughput is suppressed as much as possible.
[0022]
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. FIG. 1 is a diagram showing an internal configuration of the printer, and FIG. 2 is a block diagram showing an electrical configuration of the printer.
[0023]
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.
[0024]
As the transfer paper 4, in addition to plain paper, thick paper thicker than plain paper such as high-quality paper, postcards, envelopes, glossy paper, and high-definition paper (for example, white PET sheet), or a transparent sheet for OHP can be used. In this printer, plain paper or OHP transparent sheet is conveyed at a normal first speed, and as will be described later, in the case of thick paper, it is conveyed at a second speed lower than the first speed. Yes.
[0025]
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 photoconductor unit 10 includes a photoconductor 11, a charging unit 12, and a cleaning unit 13. A rotary developing unit 20 includes a yellow developing unit 2Y containing yellow toner, a magenta developing unit 2M containing magenta toner, and cyan. The intermediate transfer unit 30 includes an intermediate transfer belt 31, a vertical synchronization sensor 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.
[0026]
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.
[0027]
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.
[0028]
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.
[0029]
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 corresponds to a developing unit.
[0030]
The intermediate transfer belt 31 of the intermediate transfer unit 30 is stretched around a plurality of rollers including the primary transfer roller 31 </ b> A, and is rotationally driven together with the photoreceptor 11 by the photoreceptor driving motor 36. A predetermined primary transfer bias is applied to the primary transfer roller 31 </ b> A, and the toner image on the photoreceptor 11 is primarily transferred to the intermediate transfer belt 31 by the primary transfer bias. The photoreceptor 11 is in contact with the intermediate transfer belt 31 immediately downstream of the primary transfer roller 31A in the rotational drive direction 71 (see FIG. 5) of the intermediate transfer belt 31, and the contact position is in contact with the primary transfer unit 14. Is set.
[0031]
The intermediate transfer belt 31 is composed of an endless belt formed by joining substantially rectangular sheet bodies at seams. As shown in FIG. 5, the intermediate transfer belt 31 is provided with a protrusion 73 on one end side (upper side in FIG. 5) of the rotation axis direction 72 orthogonal to the rotation drive direction 71.
[0032]
The vertical synchronization sensor 32 is formed of, for example, a photo interrupter having a light emitting portion and a light receiving portion arranged to face each other, and is arranged on one end side in the rotation axis direction 72 of the rotating intermediate transfer belt 31 and detects the passage of the protrusion 73. Therefore, this detection signal is used as a vertical synchronization signal that serves as a reference for image formation control by the engine control unit 110. The belt cleaner 33 is arranged so that the contact state (solid line in FIG. 1) and the separation state (broken line in FIG. 1) and the separation state (broken line in FIG. 1) of the intermediate transfer belt 31 can be switched by the cleaning clutch 37. In the contact state, the residual toner on the intermediate 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.
[0033]
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 separating clutch 38. A predetermined secondary transfer bias is applied to the secondary transfer roller 35 in contact with the intermediate transfer belt 31, and the toner image on the intermediate transfer belt 31 is transferred to the transfer paper 4 while the transfer paper 4 is conveyed. The contact position is set in the secondary transfer portion 39 for the next transfer.
[0034]
The intermediate transfer belt 31 corresponds to an intermediate transfer medium, the primary transfer roller 31A and a transfer bias generation circuit 118 (described later) correspond to a primary transfer unit, and the secondary transfer roller 35 and the transfer bias generation circuit 118 correspond to a secondary transfer. Corresponds to the means.
[0035]
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. The fixing unit 40 corresponds to a fixing unit.
[0036]
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).
[0037]
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 rotation speed of the conveyance system driving motor 60 is switched between two types of conveyance speeds for the transfer paper 4: a normal first speed S1 for conveying plain paper and a second speed S2 (<S1) for conveying thick paper. It is possible.
[0038]
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.
[0039]
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.
[0040]
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.
[0041]
The CPU 111 receives a vertical synchronization signal Vsync from the vertical synchronization sensor 32 as an input signal from the engine unit 1 and a horizontal synchronization signal Hsync from the horizontal synchronization sensor 56. The CPU 111 controls the operation of each unit of the engine unit 1 based on these input signals and the control program.
[0042]
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 this embodiment, for example, a stepping motor is used as the photosensitive member driving motor 36, and the rotational driving speed of the photosensitive member driving motor 36 is controlled by an input control pulse signal.
[0043]
In addition, the CPU 111 sends a control signal to a motor drive circuit 115 that drives the conveyance system drive motor 60 to control the conveyance of the transfer paper 4 from the paper feed cassette 3. At this time, when the transfer paper 4 is a plain paper or an OHP transparent sheet, the transfer paper 4 is conveyed at a preset first speed S1, and the peripheral speed of the photoconductor 11 and the intermediate transfer belt 31 is the first speed. Control to match S1.
[0044]
On the other hand, when the transfer paper 4 is the above thick paper, the thick paper (transfer paper) 4 is conveyed at a preset second speed S2 (<S1). Thus, by increasing the passage time of the transfer paper 4 in the fixing unit 40, the shortage of the fixing capacity that occurs when the transfer paper 4 is thick paper is compensated. Here, the CPU 111 controls the photoreceptor 11 and the intermediate transfer belt 31 so that the peripheral speed thereof coincides with the first speed S1 when the development of the photoreceptor 11 is being performed. Deceleration is started at a preset time point, and the secondary transfer to the transfer paper 4 is performed at the peripheral speed of the second speed S2. This deceleration start time will be described later.
[0045]
Further, the CPU 111 sends a control signal to the contact / disengagement clutch drive circuit 116 that drives the cleaner contact / disengagement clutch 37 to control the separation and contact of the belt cleaner 33 with respect to the intermediate transfer belt 31. Further, the CPU 111 sends a control signal to a contact / separation clutch drive circuit 117 that drives the secondary transfer roller contact / separation clutch 38 to control separation and contact of the secondary transfer roller 35 with respect to the intermediate transfer belt 31.
[0046]
Further, the CPU 111 sends a control signal to a transfer bias generation circuit 118 that generates a transfer bias, applies a primary transfer bias (for example, several hundred volts) to the primary transfer roller 31A, and performs secondary transfer to the secondary transfer roller 35. Application of a bias (for example, several kV) is controlled.
[0047]
Further, the CPU 111 receives, for example, the operation content for the operation keys of the operation display panel 8 disposed on the surface of the apparatus main body 2 and controls the display content of the display unit. The CPU 111 corresponds to a conveyance control unit and an intermediate transfer medium control unit.
[0048]
Next, the operation when the transfer paper 4 is the above thick paper will be described with reference to FIGS. 3 and 4 are timing charts for explaining the operation of each part of the engine unit 1. FIG. 5 is a diagram for explaining the deceleration start time of the intermediate transfer belt 31. FIG.
[0049]
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 designated by the print command signal, a message prompting the user to replace the paper feed cassette is displayed on the operation display panel 8. 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.
[0050]
When the size of the transfer paper 4 loaded on the paper feed cassette 3 matches the size specified by the print command signal, the exposure unit is placed on the surface of the photoconductor 11 uniformly charged by the charging unit 12. An electrostatic latent image corresponding to the image signal is formed by the laser light 57 from 50, and the electrostatic latent image is developed by the rotary developing unit 20 to form a toner image. The toner image is transferred to the primary transfer unit 14. 1 is primarily transferred onto the intermediate transfer belt 31.
[0051]
That is, in FIG. 3, the photosensitive member driving motor 36 is driven at the first speed S1, the intermediate transfer belt 31 rotates, and the vertical synchronization signal Vsync is output at times t1, t2, t3, and t4. The image request signal Vreq is output after a predetermined time T1 from the falling point of each vertical synchronization signal Vsync, and formation of an electrostatic latent image corresponding to the image signal is started in synchronization with the falling of the image request signal Vreq. At the same time, the developing bias is turned on.
[0052]
Then, the developing unit of the rotary developing unit 20 is switched at times t1, t2, t3, and t4, and toner images of the respective colors are formed on the photoconductor 11 and sequentially transferred onto the intermediate transfer belt 31 sequentially. During this time, the secondary transfer roller 35 is separated from the intermediate transfer belt 31, so that the toner images of the respective colors are superimposed on the intermediate transfer belt 31. The developing bias is turned off after a predetermined time T2 determined in advance by the transfer paper size from the falling point of each vertical synchronization signal Vsync at times t1, t2, t3, and t4.
[0053]
As a result, the color image on which the toner images Y, C, M, and K are superimposed is primarily transferred to a predetermined area on the intermediate transfer belt 31.
[0054]
Subsequently, in FIG. 4, when the development of the last electrostatic latent image (formation of the toner image K) is completed, the photosensitive member drive is performed at time t6 after a predetermined time T3 from time t5 (at the falling edge of the vertical synchronization signal Vsync). The motor 36 starts to decelerate. A procedure for determining the predetermined time T3 will be described. In FIG. 5, the time transition of the driving speed of the intermediate transfer belt 31 by the photoconductor driving motor 36 is associated with the position of the primary transfer toner image 74 and the position of the primary transfer unit 14 on the intermediate transfer belt 31. It shows.
[0055]
As shown in FIG. 5, the photosensitive member driving motor 36 composed of a stepping motor has a time T4 required to decrease from the first speed S1 to the second speed S2 when the deceleration starts at the deceleration start time t6. The time T5 required for stabilization at the second speed S2 is substantially constant, and the distance L1 traveling during this time is also substantially constant. These values are determined as known values when the motor is determined.
[0056]
Therefore, the leading end (downstream end in the rotational driving direction 71) 75 of the primary transfer toner image 74 on the intermediate transfer belt 31 reaches the upstream position in the rotational driving direction 71 from the primary transfer unit 14 by the distance L1. Elapsed time T0 from time t5 required in advance is obtained in advance, and a value obtained by subtracting a known time (T4 + T5) from this elapsed time T0 is stored in ROM 112 as predetermined time T3.
[0057]
As a result, the leading end 75 of the primary transfer toner image 74 on the intermediate transfer belt 31 is reliably transferred to the primary transfer in synchronization with time t7 when the intermediate transfer belt 31 is stably driven at the peripheral speed of the second speed S2. The part 14 is reached.
[0058]
In this operation, at the deceleration start time t6, the rear end (upstream end in the rotational drive direction 71) 76 of the primary transfer toner image 74 has already passed through the primary transfer unit 14, and at the first speed S1. The condition is that the primary transfer is completed. Accordingly, the total length L of the intermediate transfer belt 31 is
L> (L1 + L2 + L3)
Must be set. Here, as shown in FIG. 5, L2 is the dimension of the primary transfer toner image 74 in the rotational drive direction, and L3 is the dimension of the primary transfer unit 14 in the rotational drive direction.
[0059]
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 the second speed S2 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 primary transfer toner image 74 on the intermediate transfer belt 31, and the transfer paper 4 is conveyed from the gate roller pair 34 toward the secondary transfer portion 39 at the second speed S2. The
[0060]
In FIG. 4, the secondary transfer roller contact / separation clutch 38 is turned on at time t <b> 8 after a predetermined time from time t <b> 5, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, the application of the secondary transfer bias from the transfer bias generation circuit 118 to the secondary transfer roller 35 is turned on at time t9 after a predetermined time from time t5.
[0061]
As a result, the color primary transfer toner image obtained by superimposing the toner images Y, C, M, and K on the intermediate transfer belt 31 is secondarily transferred to the transfer paper 4.
[0062]
The gate clutch is turned off after the transfer paper 4 is carried out, and the application time T6 of the secondary transfer bias is set in advance according to the size of the transfer paper 4. When the set application time T6 of the secondary transfer bias elapses, the application of the secondary transfer bias is turned off, and the secondary transfer roller contact clutch 38 is turned on, and the secondary transfer roller 35 is turned on. Is separated from the intermediate transfer belt 31.
[0063]
Then, in the fixing unit 40, the secondary transfer toner image is fixed to the transfer paper 4 while the transfer paper 4 is conveyed. At this time, since the transfer paper 4 is conveyed at the second speed S2 lower than the first speed S1, a sufficient fixing time is secured. The transfer paper 4 is further transported by a transport roller pair 63, and is discharged to a paper discharge unit 7 provided on the upper part of the apparatus main body 2 by a discharge roller pair 64.
[0064]
On the other hand, at time t10, which is a predetermined time after time t5, the cleaner separating clutch 37 is turned on and cleaning of residual toner on the intermediate transfer belt 31 is started. Then, at a time t12 after a predetermined time from the time t11 when the next vertical synchronization signal Vsync falls, the cleaner engagement / disengagement clutch 37 is turned on again, and the belt cleaner 33 is separated from the intermediate transfer belt 31.
[0065]
When the next print command signal is input from the external device via the main control unit 100 by time t11, the photosensitive member driving motor 36 is accelerated at time t13, which is a predetermined time after time t11, and the second speed is reached. The process returns from S2 to the first speed S1, and the next image formation control is performed with reference to the time t14, which is the time when the next vertical synchronization signal Vsync falls.
[0066]
As described above, according to the present embodiment, when the transfer paper 4 is thick paper, the transfer paper 4 is conveyed at the second speed S2 lower than the first speed S1, so that a sufficient fixing time is secured in the fixing unit 40. As a result, the toner image can be satisfactorily fixed on the transfer paper 4 which is a thick paper.
[0067]
Further, according to the present embodiment, when the primary transfer toner image 74 on the intermediate transfer belt 31 passes through the primary transfer unit 14 again, the driving speed does not change during the passage, and the second transfer toner image 74 does not change. Since the re-pass is performed at the speed S 2), the environmental condition between the intermediate transfer belt 31 and the photoconductor 11 in the primary transfer unit 14 does not change in the middle of the primary transfer toner image 74. Accordingly, it is possible to prevent a situation in which the primary transfer toner image 74 is uneven due to a change in the level of reverse transfer from the intermediate transfer belt 31 to the photoconductor 11 and the image quality is deteriorated. .
[0068]
Further, according to the present embodiment, at the time t7 when the intermediate transfer belt 31 is stably driven at the peripheral speed of the second speed S2, the leading end 75 of the primary transfer toner image 74 on the intermediate transfer belt 31 is primary. Since the deceleration start time t6 of the intermediate transfer belt 31 is set so as to reach the transfer unit 14, the drive speed of the intermediate transfer belt 31 is maintained at the first speed S1 as much as possible. Can be suppressed as much as possible.
[0069]
In addition, according to the present embodiment, since the stepping motor is used as the photosensitive member driving motor 36, the time T4 required to decrease from the first speed S1 to the second speed S2 is stabilized at the second speed S2. The time T5 required for this and the distance L1 traveled during this time can be set to a substantially constant value, whereby the predetermined time T3 can be obtained with high accuracy.
[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 composed of an endless belt joined at a joint is used. However, the intermediate transfer medium of the present invention is not limited to this, for example, an intermediate transfer composed of a seamless endless belt without a joint. A belt or a cylindrical intermediate transfer drum may be used.
[0072]
In the above embodiment, at the time t7 when the intermediate transfer belt 31 is stably driven at the peripheral speed of the second speed S2, the leading end 75 of the primary transfer toner image 74 on the intermediate transfer belt 31 is the primary transfer portion. The deceleration start time t6 of the intermediate transfer belt 31 is set so as to reach 14. However, the present invention is not limited to this, and if it is after the development end time, the deceleration is started at a time earlier than the deceleration start time t6. Also good. Even in this case, it is possible to prevent a situation in which the primary transfer toner image 74 is uneven and the image quality is deteriorated.
[0073]
In the above embodiment, the elapsed time T1 from the vertical synchronization signal Vsync to the output of the image request signal Vreq is a constant value, and the position of the tip 75 of the primary transfer toner image 74 is the same regardless of the transfer paper size. Therefore, the predetermined time T3 is also a constant value regardless of the transfer paper size, but is not limited thereto. For example, in order to make the position of the rear end of the primary transfer toner image 74 (upstream end in the rotational drive direction 71) the same regardless of the transfer paper size, the image request signal Vreq is output from the vertical synchronization signal Vsync for each transfer paper size. It is good also as what changes the elapsed time until it does. In this case, a predetermined time T3 may be obtained for each transfer paper size and stored in the ROM 112 as a control program.
[0074]
In addition, as described in the above embodiment, it is preferable to use a stepping motor as the photoreceptor driving motor 36, but the present invention is not limited to this, and other motors such as a DC brushless motor are adopted. Also good.
[0075]
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.
[0076]
【The invention's effect】
As described above, according to the first and second aspects of the present invention, when the primary transfer toner image re-passes the primary transfer portion after completion of the primary transfer in the primary transfer portion in the low speed mode. When the leading edge of the primary transfer toner image reaches the primary transfer portion, the intermediate transfer medium is driven at the second speed, so that the primary transfer toner image is in the middle of being re-passed through the primary transfer portion. Since the driving speed of the transfer medium does not change, the environmental conditions between the intermediate transfer medium and the photoconductor in the primary transfer portion do not change during the primary transfer toner image. Therefore, it is possible to prevent a situation in which the primary transfer toner image is uneven due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer unit, and the image quality is deteriorated. Can do.
[0078]
Further, the leading edge of the primary transfer toner image is upstream from the primary transfer portion in the rotational drive direction by the distance traveled by the intermediate transfer medium from the start of deceleration from the first speed to the second speed until the time when it stabilizes at the second speed. Since the deceleration from the first speed is started when the position on the intermediate transfer medium is reached, the intermediate transfer medium is reliably transferred to the intermediate transfer medium in synchronism with the time when the intermediate transfer medium is stably driven at the second speed. The leading edge of the primary transfer toner image can reach the primary transfer portion. As a result, the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, so that a decrease in throughput of image formation can be suppressed as much as possible.
[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 timing chart for explaining the operation of each part of the engine unit.
FIG. 4 is a timing chart for explaining the operation of each part of the engine part, showing the continuation of FIG. 3;
FIG. 5 is a diagram illustrating a deceleration start time of the intermediate transfer belt.
[Explanation of symbols]
4 Transfer paper
11 photoconductor
20 Rotary development section (development means)
31 Intermediate transfer belt (intermediate transfer medium)
31A Primary transfer roller (primary transfer means)
35 Secondary transfer roller (secondary transfer means)
40 Fixing unit (fixing means)
71 Rotation drive direction
74 Primary transfer toner image on intermediate transfer belt
75 Tip of primary transfer toner image
110 Engine control unit
111 CPU (conveyance control means, intermediate transfer medium control means)
118 Transfer bias generation circuit (primary transfer means, secondary transfer means)
S1 1st speed
S2 Second speed

Claims (2)

Developing means for forming a toner image by attaching toner to the electrostatic latent image formed on the photosensitive member, an intermediate transfer medium that rotates and cyclically passes through the primary transfer portion and the secondary transfer portion; A primary transfer unit that primarily transfers the toner image to the intermediate transfer medium in a secondary transfer unit, and a secondary that secondary-transfers the primary transfer toner image on the intermediate transfer medium to transfer paper in the secondary transfer unit. In an image forming apparatus comprising transfer means and fixing means for fixing a secondary transfer toner image on the transfer paper to the transfer paper while conveying the transfer paper,
A transport control unit having a normal mode for transporting the transfer paper at a first speed and a low speed mode for transporting the transfer paper at least at a second speed lower than the first speed from the secondary transfer unit to the end of fixing;
In the normal mode, the intermediate transfer medium is driven at the first speed. In the low speed mode, the intermediate transfer medium is driven at the first speed at least until the end of toner image formation by the developing unit. Intermediate transfer medium control means for controlling to drive the intermediate transfer medium at the second speed at least until the end of the secondary transfer, by decreasing the driving speed of the intermediate transfer medium after completion of toner image formation;
In the low speed mode, the primary transfer toner image is not transferred in the secondary transfer portion that passes immediately after the primary transfer in the primary transfer portion is completed, and the primary transfer toner is not transferred. Transfer control means for performing secondary transfer of the primary transfer toner image in the secondary transfer portion that passes next after the image has re-passed the primary transfer portion;
When the intermediate transfer medium control means is in the low speed mode, the end of the primary transfer toner image is decelerated from the first speed to the second speed after completion of the primary transfer in the primary transfer portion. From the primary transfer portion to the upstream position in the rotational driving direction by the distance traveled by the intermediate transfer medium from when the second transfer speed becomes stable to the second speed, the deceleration from the first speed is started. Thus, when the leading edge of the primary transfer toner image reaches the primary transfer portion when the primary transfer toner image passes through the primary transfer portion again, the intermediate transfer medium is driven at the second speed. An image forming apparatus. A toner image formed by adhering toner to the electrostatic latent image formed on the photosensitive member by a developing unit is primarily transferred to a rotating intermediate transfer medium at a primary transfer unit, and the primary image on the intermediate transfer medium is transferred. In the image forming method in which the transfer toner image is secondarily transferred to the transfer paper in the secondary transfer unit, and the secondary transfer toner image on the transfer paper is fixed to the transfer paper while transporting the transfer paper.
A normal mode in which the transfer paper is conveyed at a first speed, and a low speed mode in which the transfer paper is conveyed at a second speed lower than the first speed from the secondary transfer unit to the end of fixing,
In the normal mode, the intermediate transfer medium is driven at the first speed. In the low speed mode, the intermediate transfer medium is driven at the first speed at least until the end of toner image formation by the developing unit. An intermediate transfer medium control step of controlling the intermediate transfer medium to be driven at the second speed at least until the end of the secondary transfer, by decreasing the driving speed of the intermediate transfer medium after completion of toner image formation;
In the low speed mode, the primary transfer toner image is not transferred in the secondary transfer portion that passes immediately after the primary transfer in the primary transfer portion is completed, and the primary transfer toner is not transferred. A transfer control step of performing secondary transfer of the primary transfer toner image in the secondary transfer portion that passes next after the image has re-passed the primary transfer portion;
In the intermediate transfer medium control step, in the low speed mode, after the completion of the primary transfer in the primary transfer portion, the leading edge of the primary transfer toner image starts decelerating from the first speed to the second speed. From the primary transfer portion to the upstream position in the rotational driving direction by the distance traveled by the intermediate transfer medium from when the second transfer speed becomes stable to the second speed, the deceleration from the first speed is started. Thus, when the leading edge of the primary transfer toner image reaches the primary transfer portion when the primary transfer toner image passes through the primary transfer portion again, the intermediate transfer medium is driven at the second speed. An image forming method.

Images