JP2003215945A - Apparatus and method for image formation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration of an image quality in the case of providing a low speed mode as transfer paper feeding speed. <P>SOLUTION: Elapsed time from a vertical synchronizing signal needed until the top end 75 of a primary transferred toner image 74 on an intermediate transfer belt 31 reaches the position of an upstream side in a rotating/driving direction 71 from a primary transfer part 14 by a distance L1 by which it is advanced in the total time (T4+T5) of time T4 needed for the belt 31 so as to decelerate from first speed S1 to second speed S2 and time T5 needed so as to stabilize at the second speed S2 is previously calculated, and a value obtained by deducting the known time (T4+T5) from the elapsed time is stored as specified time T3 in a ROM. Thus, the top end 75 of the primary transferred toner image 74 reaches the primary transfer part 14 at the point in time t7 when the intermediate transfer belt 31 is stably driven at the circumferential speed of the second speed S2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming technique for printers, copiers, facsimile machines and the like.

[0002]

2. Description of the Related Art Conventionally, toner is attached to an electrostatic latent image formed on a photoconductor by an exposing means by a developing means to form a toner image, the toner image is transferred onto a transfer paper, and the toner image on the transfer paper is transferred. There is known an electrophotographic image forming apparatus in which a transfer sheet is fixed to the transfer sheet while being conveyed by a fixing unit, and in particular, it is formed on a photoconductor as an apparatus capable of forming a color image. An image forming apparatus is known in which a toner image is primarily transferred onto an intermediate transfer medium, and the primary transfer toner image on the intermediate transfer medium is secondarily transferred onto a transfer paper.

In this image forming apparatus, when forming a color image, toner images of a plurality of colors are sequentially formed on a photosensitive member,
Each time a toner image of each color is formed, primary transfer to the intermediate transfer medium is performed to form a color toner image on which the toner images of a plurality of colors are superposed, and the color toner image is secondarily transferred to a transfer paper. I try to get a color image. In the image forming apparatus thus configured, it is possible to perform a single color printing using a specific color among a plurality of colors, and in many cases, black toner.

On the other hand, conventionally, as a transfer paper, in addition to plain paper, an image forming apparatus capable of using thick paper such as high-quality paper, postcards, envelopes, glossy paper, and high-definition paper that is thicker than plain paper has been put into practical use. ing. However, when the above thick paper is conveyed at the same speed as the plain paper and the fixing unit is operated, sufficient fixing performance cannot be obtained and the image quality is deteriorated. Such a situation can be prevented by improving the fixing performance, for example, by increasing the heat capacity of the fixing unit, but as a result, the size of the apparatus is increased, and conversely, excessive heat is applied during fixing of plain paper to improve the image quality. In such an image forming apparatus, when thick paper is used as the transfer paper, it is sufficient to reduce the paper conveyance speed and increase the fixing time as compared with plain paper. Secures fixing performance.

In this case, at the time of the secondary transfer, it is necessary to set the driving speed of the intermediate transfer medium to a low speed in accordance with the sheet conveying speed. However, processes such as image formation on the photosensitive member and primary transfer to the intermediate transfer medium An apparatus in which the speed is also low, and an apparatus in which the drive speed is low only during the secondary transfer while the process speed is the normal speed can be considered. In the former apparatus, since the image forming process is performed at two types of speeds, it takes twice as much time to obtain a good process set value for the developing condition and the transfer condition as compared with the case of one type. Although there is a problem that it takes time to design the device and check the operation, the latter device does not have the above problem because the image forming process has only one speed.

[0006]

However, when the latter device is adopted, it is necessary to sufficiently consider the deceleration start timing from the normal speed to the low speed. In general, the distance between the primary transfer section and the secondary transfer section is shorter than that of a large-sized transfer sheet in order to downsize the apparatus. Therefore, in the case of the apparatus having such a configuration, the front end of the primary transfer toner image has already passed through the secondary transfer portion at the end of the primary transfer. 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.
The secondary transfer is performed when passing through the secondary transfer portion. Therefore, before the leading edge of the primary transfer toner image next reaches the secondary transfer portion, the speed may be reduced from the normal speed to the low speed.

However, if the deceleration of the intermediate transfer medium is started while the primary transfer toner image is re-passing through the primary transfer portion, a difference occurs in the degree of reverse transfer from the intermediate transfer medium to the photosensitive member. There is a risk that the primary transfer toner image may be uneven and the image quality may be degraded. On the other hand, if the deceleration start timing is too early and the driving time of the intermediate transfer medium at a low speed becomes long, the throughput of image formation will decrease.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus and method capable of preventing deterioration of image quality when a low transfer speed mode is provided. .

Another object of the present invention is to provide an image forming apparatus and method capable of suppressing a decrease in image forming throughput when a low speed mode is provided as a transfer paper conveying speed.

[0010]

In order to achieve the above object, the invention according to claim 1 is a developing means for forming a toner image by adhering toner to an electrostatic latent image formed on a photoreceptor. An intermediate transfer medium that rotates to circulate through the primary transfer section and the secondary transfer section; a primary transfer unit that primarily transfers the toner image onto the intermediate transfer medium at the primary transfer section; Secondary transfer means for secondarily transferring the primary transfer toner image on the intermediate transfer medium to the transfer paper at the secondary transfer portion;
In an image forming apparatus including a fixing unit configured to fix the secondary transfer toner image on the transfer sheet to the transfer sheet while conveying the transfer sheet, a normal mode for conveying the transfer sheet at a first speed and a transfer mode At least from the secondary transfer portion to the end of fixing, a transport control unit having a low speed mode of transporting at a second speed lower than the first speed, and 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 toner image formation by the developing unit is completed, and the drive speed of the intermediate transfer medium is decreased at least 2 after the toner image formation is completed. An intermediate transfer medium control means for controlling the intermediate transfer medium to be driven at the second speed until the end of the next transfer, and the primary transfer section in the low speed mode. After the completion of the primary transfer, after the primary transfer toner image re-passes the primary transfer toner image, the secondary transfer portion immediately after the primary transfer toner image does not perform the secondary transfer of the primary transfer toner image. And a transfer control unit for performing the secondary transfer of the primary transfer toner image at the secondary transfer unit that passes next, and the intermediate transfer medium control unit, when in the low speed mode, the primary transfer unit. When the primary transfer toner image again passes through the primary transfer portion after the completion of the primary transfer in, the intermediate transfer medium is moved when the front end of the primary transfer toner image reaches the primary transfer portion. It is characterized in that it is driven at the second speed.

According to this structure, there are 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 the second speed lower than the first speed from at least the secondary transfer portion to the end of fixing. Then, 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 the toner image formation by the developing unit is completed, and the toner image formation is completed. After that, the driving speed of the intermediate transfer 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. Also, in the low speed mode, the 1
After the completion of the next transfer, the secondary transfer portion immediately after passing the secondary transfer does not perform the secondary transfer of the primary transfer toner image. Secondary transfer of the primary transfer toner image is performed in the transfer section.

Then, in the low speed mode, the intermediate transfer medium control means controls the primary transfer when the primary transfer toner image again passes through the primary transfer section after the primary transfer in the primary transfer section is completed. When the front end of the toner image reaches the primary transfer portion, the intermediate transfer medium is being driven at the second speed.

Therefore, since the driving speed of the intermediate transfer medium does not change while the primary transfer toner image re-passes through the first transfer portion,
Since 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,
It is possible to prevent a situation in which unevenness in the primary transfer toner image due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer portion, resulting in deterioration of image quality is prevented. Become.

Further, the intermediate transfer medium control means controls the intermediate transfer medium to be stably driven at the second speed when the front end of the primary transfer toner image reaches the first transfer portion. In addition, it is also possible to control the start point of deceleration from the first speed to the second speed (claim 2).

With this structure, the intermediate transfer medium is stably driven at the second speed when the front end of the primary transfer toner image reaches the first transfer portion, so that the intermediate transfer medium can be driven at a speed. Since the first speed is maintained as much as possible, the decrease in the throughput of image formation is suppressed as much as possible.

Further, the intermediate transfer medium control unit controls the intermediate transfer from the time point when the leading edge of the primary transfer toner image starts decelerating from the first speed to the second speed to the time point when the leading edge of the primary transfer toner image stabilizes at the second speed. The deceleration from the first speed may be started at the time when the medium reaches the position on the upstream side in the rotational driving direction from the first transfer portion by the distance traveled by the medium (claim 3).

According to this structure, the front end of the primary transfer toner image is moved from the first speed to the second speed to the second speed from the start point of deceleration.
When the speed reaches the position on the upstream side in the rotational driving direction from the first transfer portion by the distance traveled by the intermediate transfer medium by the time of stabilizing at the speed, deceleration from the first speed is started,
The leading end of the primary transfer toner image on the intermediate transfer medium will surely reach the primary transfer portion in synchronization with the time when the intermediate transfer medium is stably driven at the second speed. In addition, since the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, the decrease in the throughput of image formation is suppressed as much as possible.

According to a fourth aspect of the invention, the toner image formed by adhering toner to the electrostatic latent image formed on the photoconductor by the developing means is transferred to the rotating intermediate transfer medium at the primary transfer portion. Primary transfer is performed, and the primary transfer toner image on the intermediate transfer medium is secondarily transferred to the transfer paper at the secondary transfer section.
In the image forming method in which the secondary transfer toner image on the transfer paper is fixed on the transfer paper while the transfer paper is being transported, a normal mode in which the transfer paper is transported at a first speed and at least the secondary transfer paper From the transfer unit to the end of fixing, the first
Has a low speed mode of conveying at a second speed lower than the speed,
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 the toner image formation by the developing unit is completed. An intermediate transfer medium control step of reducing the drive speed of the intermediate transfer medium after the toner image formation is completed, and controlling the intermediate transfer medium to be driven at the second speed until at least the secondary transfer is completed; When the secondary transfer portion passing immediately after the completion of the primary transfer in the primary transfer portion is
After the primary transfer toner image passes through the primary transfer portion again without performing the secondary transfer of the secondary transfer toner image, the secondary transfer portion of the primary transfer toner image passes through the secondary transfer portion of the primary transfer toner image. A transfer control step for performing transfer, and in the intermediate transfer medium control step, when the low speed mode is set,
After the completion of the primary transfer in the secondary transfer portion, when the front end 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 is performed. It is characterized in that the transfer medium is driven at the second speed.

According to this structure, there are 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 the second speed lower than the first speed from at least the secondary transfer portion to the end of fixing. Then, 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 the toner image formation by the developing unit is completed, and the toner image formation is completed. After that, the driving speed of the intermediate transfer 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. Also, in the low speed mode, the 1
After the completion of the next transfer, the secondary transfer portion immediately after passing the secondary transfer does not perform the secondary transfer of the primary transfer toner image. Secondary transfer of the primary transfer toner image is performed in the transfer section.

Then, in the low speed mode, when the primary transfer toner image is re-passed through the primary transfer portion after the primary transfer is completed, the intermediate transfer medium control means controls the primary transfer. When the front end of the toner image reaches the primary transfer portion, the intermediate transfer medium is being driven at the second speed.

Therefore, since the driving speed of the intermediate transfer medium does not change while the primary transfer toner image re-passes through the first transfer portion,
Since 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,
It is possible to prevent a situation in which unevenness in the primary transfer toner image due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer portion, resulting in deterioration of image quality is prevented. Become.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the configuration of a printer which 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.

This printer forms a full-color image by superposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K), for example, only black (K) toner. Is used to form a monochrome image. 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 unit of the engine unit 1 to respond to the control signal from the main control unit 100. Is controlled to print out an image corresponding to the image signal on the transfer paper 4 conveyed from the paper feed cassette 3 arranged below the apparatus main body 2.

As the transfer paper 4, in addition to plain paper, fine paper, postcards, envelopes, glossy paper, high-definition paper (for example, white PET)
A thick paper thicker than plain paper such as a sheet) or a transparent sheet for OHP can be used. And with this printer,
In the case of plain paper or a transparent sheet for OHP, it is conveyed at a normal first speed, and as described later, in the case of thick paper, it is conveyed at a second speed lower than the first speed.

The engine unit 1 includes the photoconductor unit 1
0, 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, and the rotary developing unit 20 includes
Yellow developing unit 2 containing yellow toner
Y, magenta developing unit 2M containing magenta toner, cyan developing unit 2 containing cyan toner
C, a black developing unit 2K containing black toner, and the like. The intermediate transfer unit 30 includes an intermediate transfer belt 31, a vertical synchronization sensor 32, a belt cleaner 33,
A gate roller pair 34, a secondary transfer roller 35, a photoconductor driving motor 36, and the like are provided. Above 7 units 1
Each of 0, 2Y, 2M, 2C, 2K, 30, and 40 is configured to be detachable from the apparatus body 2.

The photoconductor 11 of the photoconductor unit 10 includes the seven units 10, 2Y, 2M, 2C, 2K, 30,
In the state in which 40 is attached to the apparatus main body 2, it is rotated in the direction of arrow 5 by the photoconductor driving motor 36. Around the photoconductor 11 along the rotation direction 5, the charging unit 1
2. A rotary developing unit 20 and a cleaning unit 13 are arranged.

The charging unit 12 is provided with a wire electrode to which a high voltage of a predetermined level is applied, and uniformly charges the outer peripheral surface of the photoconductor 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 photoconductor 11 is cleaned by scraping off the existing toner.

The exposure unit 50 includes a laser light source 51 formed of, for example, a semiconductor laser, a polygon mirror 52 that reflects the laser light from the laser light source 51, a scanner motor 53 that drives the polygon mirror 52 to rotate at high speed, and a polygon mirror 52. A lens unit 54 for focusing the reflected laser light, a plurality of reflection mirrors 55, a horizontal synchronization sensor 5
6 and so on. The laser beam 57 reflected by the polygon mirror 52 and emitted through the lens unit 54 and the reflection mirror 55 scans the surface of the photoconductor 11 in the main scanning direction (direction perpendicular to the paper surface of FIG. 1). ,
An electrostatic latent image corresponding to the image signal is formed on the surface of the photoconductor 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.

The rotary developing section 20 adheres the toner of each color to the electrostatic latent image and develops it. 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 rotatably provided around the axis, and these developing units 2Y, 2M, 2C and 2K are predetermined. It is movably arranged at the plurality of positions, and is selectively arranged at the contact position and the separated position with respect to the photoconductor 11. Then, a developing bias in which a direct current component or a direct current component and an alternating current component are superimposed is applied, and the toner of the color is attached to the surface of the photoconductor 11 from the developing unit in the contact position with respect to the photoconductor 11. This rotary development unit 2
0 corresponds to the developing means.

Intermediate transfer belt 3 of intermediate transfer unit 30
1 is wound around a plurality of rollers including a primary transfer roller 31A, and is rotationally driven together with the photoconductor 11 by a photoconductor driving motor 36. A predetermined primary transfer bias is applied to the primary transfer roller 31A, and the toner image on the photoconductor 11 is primarily transferred to the intermediate transfer belt 31 by this primary transfer bias. The photoconductor 11 is in contact with the intermediate transfer belt 31 immediately downstream of the primary transfer roller 31A in the rotational driving direction 71 (see FIG. 5) of the intermediate transfer belt 31, and the contact position is the primary transfer portion 14. It is set.

The intermediate transfer belt 31 is 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) in the rotation axis direction 72 orthogonal to the rotation driving direction 71.

The vertical synchronization sensor 32 is composed of, for example, a photo interrupter having a light emitting portion and a light receiving portion which are arranged to face each other, is arranged on one end side in the rotation axis direction 72 of the rotating intermediate transfer belt 31, and passes through the protruding portion 73. Is detected, and 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 the cleaner connecting / disconnecting clutch 3.
The contact state (solid line in FIG. 1) and the separated state (broken line in FIG. 1) of the intermediate transfer belt 31 are switchably arranged by means of 7, and remain on the intermediate transfer belt 31 in the contact state. Scrape off the toner. The gate roller pair 34 is rotationally driven by the driving force of the transport system driving motor 60 being transmitted when the gate clutch is turned on.

The secondary transfer roller 35 is switched between a contact state (solid line in FIG. 1) and a separated state (broken line in FIG. 1) with respect to the intermediate transfer belt 31 by the secondary transfer roller separation / contact clutch 38. The secondary transfer roller 35 is applied with a predetermined secondary transfer bias while being in contact with the intermediate transfer belt 31, and conveys the transfer paper 4 while the intermediate transfer belt 31 is being conveyed.
The upper toner image is secondarily transferred to the transfer paper 4, and the contact position is set in the secondary transfer portion 39.

The intermediate transfer belt 31 corresponds to the intermediate transfer medium, the primary transfer roller 31A and the transfer bias generating circuit 118 (described later) correspond to the primary transfer means, and the secondary transfer roller 35 and the transfer bias generating circuit 118. It corresponds to the secondary transfer means.

The fixing unit 40 is provided with a heating roller 41 and a pressure roller 42, and conveys the transfer paper 4 by a heat roller fixing method while transferring the toner image on the transfer paper 4 to the transfer paper 4.
It will be established in. The fixing unit 40 corresponds to a fixing unit.

A half-moon-shaped pickup roller 61 extends upward from the front end (right end in FIG. 1) of the paper feed cassette 3.
The feed roller pair 62 is disposed, and the gate roller pair 3
4, the secondary transfer roller 35 and the fixing unit 40 are sandwiched, and a conveyance roller pair 63 and a discharge roller pair 64 are further provided, and a conveyance path for the transfer paper 4 (a chain line in FIG. 1) is formed by these. ing.

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 conveyance roller pair 63, and the discharge roller pair 64 are the same conveyance system drive motor via the drive force transmission mechanism. It is connected to 60. When the feed clutch is turned on, the feed roller pair 62 is rotationally driven by transmitting the driving force of the transport system driving motor 60. The rotation speed of the transport system drive motor 60 is the same as that of the transfer paper 4
The normal first speed S for transporting plain paper as the transport speed of
1 and a second speed S2 (<S1) for transporting thick paper can be switched.

Feed roller pair 62, gate roller pair 3
4, the conveyance roller pair 63, and the discharge roller pair 64 are the transfer paper 4
Constituting the transport means.

In FIG. 2, the main controller 100 is a CPU
101, an interface 102 for exchanging control signals with an external device such as a host computer, and an image memory 103 for storing an image signal given via the interface 102. CP
Upon receiving a print command signal including an image signal from an external device via the interface 102, the U 101 converts the job data into a job data in a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110.

The engine control unit 110 includes a CPU 111,
The ROM 112 and the RAM 113 are provided. ROM
Reference numeral 112 stores a control program of the CPU 111, and the RAM 113 temporarily stores control data of the engine unit 1, a calculation result by the CPU 111, and the like.

The CPU 111 receives the vertical synchronization signal Vsy from the vertical synchronization sensor 32 as an input signal from the engine unit 1.
nc is received and the horizontal sync signal H is sent from the horizontal sync sensor 56.
Receive sync etc. Then, the CPU 111 controls the operation of each unit of the engine unit 1 based on these input signals and the control program.

That is, the CPU 111 sends a control signal to the motor drive circuit 114 for driving the photoconductor drive motor 36 to synchronously rotate the photoconductor 11 and the intermediate transfer belt 31. In this embodiment, for example, a stepping motor is used as the photoconductor driving motor 36, and the rotational driving speed of the photoconductor driving motor 36 is controlled by the input control pulse signal.

Further, the CPU 111 sends a control signal to the motor drive circuit 115 which drives the transport system drive motor 60 to control the transport 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 set at a first speed S1 set in advance.
In addition, the peripheral speeds of the photoconductor 11 and the intermediate transfer belt 31 are controlled so as to match the first speed S1.

On the other hand, when the transfer paper 4 is the above-mentioned thick paper, the thick paper (transfer paper) 4 is set to the preset second speed S2 (<S1).
To transport. This increases the passage time of the transfer paper 4 in the fixing unit 40, thereby compensating for the lack of the fixing capacity that occurs when the transfer paper 4 is thick paper. Here, the CPU 111 controls the peripheral speed of the photoconductor 11 and the intermediate transfer belt 31 so as to match the first speed S1 when the photoconductor 11 is being developed. The deceleration is started at a preset time point, and the peripheral speed is set to the second speed S2 so that the secondary transfer to the transfer paper 4 is performed. The start point of deceleration will be described later.

Further, the CPU 111 sends a control signal to the separation / contact clutch drive circuit 116 for driving the cleaner separation / contact clutch 37, and controls separation and contact of the belt cleaner 33 with respect to the intermediate transfer belt 31. Also, CPU
Reference numeral 111 sends a control signal to a separation / engagement clutch drive circuit 117 that drives the separation / connection clutch 38 for the secondary transfer roller, and controls separation and contact of the secondary transfer roller 35 with respect to the intermediate transfer belt 31.

Further, the CPU 111 sends a control signal to the transfer bias generation circuit 118 which generates a transfer bias, applies the primary transfer bias (for example, several hundreds of V) to the primary transfer roller 31A, and applies it to the secondary transfer roller 35. The application of the secondary transfer bias (for example, several kV) is controlled.

The CPU 111 is, for example, the apparatus main body 2
It receives the operation content of the operation keys of the operation display panel 8 arranged on the surface of the display panel and controls the display content of the display section. The CPU 111 corresponds to a conveyance control unit and an intermediate transfer medium control unit.

Next, referring to FIGS. 3 to 5, the transfer paper 4 will be described.
The operation when is the above thick paper will be described. Figure 3,
FIG. 4 is a timing chart for explaining the operation of each part of the engine unit 1, and FIG. 5 is a diagram for explaining the deceleration start time of the intermediate transfer belt 31.

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 unit of the engine unit 1 to respond to the control signal from the main control unit 100. Start operation. 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 replacement of the paper feed cassette is displayed on the operation display panel 8. To do. In addition, in FIG.
Although the printer is provided with one sheet feeding cassette 3, the present invention is not limited to this and may be a printer having a plurality of sheet feeding cassettes.

Transfer paper 4 loaded in paper feed cassette 3
When the size of the laser beam is equal to the size instructed by the print command signal, the laser light 5 from the exposure unit 50 is applied to the surface of the photoconductor 11 uniformly charged by the charging unit 12.
7 forms an electrostatic latent image according to the image signal, and the electrostatic latent image is developed by the rotary developing unit 20 to form a toner image. The toner image is formed in the primary transfer unit 14 by the intermediate transfer belt 31. Primary transfer is performed on top.

That is, in FIG. 3, the photoconductor driving motor 36 is driven at the first speed S1 to drive the intermediate transfer belt 3
1 rotates, and the vertical synchronization signal Vsync is output at times t1, t2, t3, and t4, respectively. Vertical sync signal Vsync
Image request signal Vreq after a predetermined time T1 from the trailing edge of
Is output, and in synchronization with the fall of the image request signal Vreq, formation of an electrostatic latent image corresponding to the image signal is started and the developing bias is turned on.

Then, the developing units of the rotary developing section 20 are switched at times t1, t2, t3, and t4 so that toner images of respective colors are formed on the photoconductor 11 and sequentially primary-transferred onto the intermediate transfer belt 31. It 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 superposed on the intermediate transfer belt 31. The developing bias is at time t1, t2, t
It is turned off after a predetermined time T2 which is predetermined by the transfer paper size from the time point of falling of each vertical synchronizing signal Vsync of 3 and t4.

As a result, the color image in which the toner images Y, C, M and K are superposed is primarily transferred to a predetermined area on the intermediate transfer belt 31.

Subsequently, in FIG. 4, when the development of the final electrostatic latent image (formation of the toner image K) is completed, at time t6, which is a predetermined time T3 after time t5 (falling point of the vertical synchronizing signal Vsync), The deceleration of the photoconductor driving motor 36 is started. The 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 and the intermediate transfer belt 31 are shown.
The position of the upper primary transfer toner image 74 and the primary transfer portion 14
The positions of and are shown in correspondence with each other.

As shown in FIG. 5, the photoconductor driving motor 36, which is a stepping motor, has a first speed S1 to a second speed S2 when it starts deceleration at the deceleration start time t6.
The time T4 required to decrease to the second speed S2 and the time T5 required to stabilize at the second speed S2 are substantially constant values, and the distance L1 traveled during this time is also a substantially constant value. These values are determined as known values when the motor is determined.

Therefore, the front end (downstream end in the rotational driving direction 71) 75 of the primary transfer toner image 74 on the intermediate transfer belt 31.
However, the rotational driving direction 71 is the distance L1 from the primary transfer portion 14.
The elapsed time T0 from the time t5 required to reach the position on the upstream side of is obtained in advance, and the value obtained by subtracting the known time (T4 + T5) from the elapsed time T0 is stored in the ROM 112 as the predetermined time T3. .

As a result, the primary transfer toner image 7 on the intermediate transfer belt 31 is surely synchronized with 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 No. 4 reaches the primary transfer portion 14.

In this operation, deceleration start time t
6, the rear end of the primary transfer toner image 74 (rotational drive direction 7
The condition is that the upstream end 76 of 1) has already passed through the primary transfer portion 14 and the primary transfer at the first speed S1 is completed. Therefore, the total length L of the intermediate transfer belt 31 needs to be set to L> (L1 + L2 + L3). Here, as shown in FIG. 5, L2 is the dimension of the primary transfer toner image 74 in the rotational driving direction, and L3 is the dimension of the primary transfer portion 14 in the rotational driving direction.

On the other hand, the uppermost transfer paper 4 of the transfer paper stack loaded in the paper feed cassette 3 is taken out by the pickup roller 61, conveyed by the feed roller pair 62 at the second speed S2, and is transferred to the gate roller pair 34. Be nipped.
Then, the primary transfer toner image 74 on the intermediate transfer belt 31.
The gate clutch is turned on in time with
The transfer paper 4 is conveyed from the pair of gate rollers 34 toward the secondary transfer portion 39 at the second speed S2.

Then, in FIG. 4, at the time t8, which is a predetermined time after the time t5, the separation clutch 38 for the secondary transfer roller is provided.
Is turned on, and the secondary transfer roller 35 contacts the intermediate transfer belt 31. Next, at a time t9, which is a predetermined time after the time t5, the application of the secondary transfer bias from the transfer bias generation circuit 118 to the secondary transfer roller 35 is turned on.

As a result, the primary transfer toner image of color in which the toner images Y, C, M, and K on the intermediate transfer belt 31 are superimposed is secondarily transferred to the transfer paper 4.

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. At the time when the set application time T6 of the secondary transfer bias has elapsed, the application of the secondary transfer bias is turned off, the separation clutch 38 for the secondary transfer roller is turned on, and the secondary transfer roller 35 is turned on. Separate from the intermediate transfer belt 31.

Then, in the fixing unit 40, the secondary transfer toner image is fixed on the transfer paper 4 while the transfer paper 4 is being 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 sheet 4 is further conveyed by the pair of conveying rollers 63, and is ejected by the pair of ejecting rollers 64 to the sheet ejecting section 7 provided in the upper portion of the apparatus main body 2.

On the other hand, time t1 which is a predetermined time after time t5
At 0, the cleaner separation / engagement clutch 37 is turned on, and cleaning of the residual toner on the intermediate transfer belt 31 is started.
Then, at time t12, which is a predetermined time after the time t11 when the vertical synchronizing signal Vsync falls next, the cleaner connecting / disconnecting clutch 37 is turned on again, and the belt cleaner 33 is turned on.
Separate from the intermediate transfer belt 31.

When the next print command signal is input from the external device through the main controller 100 by time t11, the photoconductor drive motor 36 is accelerated at time t13, which is a predetermined time after time t11. After returning from the second speed S2 to the first speed S1, the next image forming control is performed with reference to the time t14 which is the falling time of the next vertical synchronization signal Vsync.

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 the fixing unit 40 has a sufficient fixing time. As a result, the toner image can be satisfactorily fixed on the transfer paper 4, which is a thick paper.

Further, according to the present embodiment, when the primary transfer toner image 74 on the intermediate transfer belt 31 re-passes the primary transfer portion 14, the driving speed does not change during the passage and the driving speed does not change. Since it is re-passed at the (second speed S2), the environmental conditions between the intermediate transfer belt 31 and the photoconductor 11 in the primary transfer portion 14 do not change in the middle of the primary transfer toner image 74. Therefore, it is possible to prevent the situation where the primary transfer toner image 74 becomes 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. .

Further, according to this embodiment, at the time t7 when the intermediate transfer belt 31 is stably driven at the peripheral speed of the second speed S2, the primary transfer toner image 74 on the intermediate transfer belt 31 is obtained.
Since the deceleration start time t6 of the intermediate transfer belt 31 is set so that the leading end 75 of the intermediate transfer belt 31 reaches the primary transfer portion 14,
The drive speed of the intermediate transfer belt 31 is set to the first speed S as much as possible.
Since it is maintained at 1, it is possible to suppress the decrease in the throughput of image formation as much as possible.

Further, according to the present embodiment, since the stepping motor is used as the photoconductor driving motor 36, the time T4 and the second speed S2 required to decrease from the first speed S1 to the second speed S2 are used. The time T5 required for stabilization and the distance L1 traveled during this time can be set to a substantially constant value, and thus the predetermined time T3 can be accurately obtained.

The present invention is not limited to the above embodiment, and various changes can be made to the above without departing from the spirit of the present invention.

For example, in the above-described embodiment, the intermediate transfer belt 31 which is an endless belt spliced at seams is used, but the intermediate transfer medium of the present invention is not limited to this.
For example, an intermediate transfer belt composed of a seamless seamless endless belt or a cylindrical intermediate transfer drum may be used.

In the above embodiment, the time t at which the intermediate transfer belt 31 is stably driven at the peripheral speed of the second speed S2.
In FIG. 7, the deceleration start time t6 of the intermediate transfer belt 31 is set so that the front end 75 of the primary transfer toner image 74 on the intermediate transfer belt 31 reaches the primary transfer portion 14, but the invention is not limited to this. After the end of development, deceleration start time t
The deceleration may be started at a time earlier than 6. Even in this case, it is possible to prevent the situation in which the primary transfer toner image 74 becomes uneven and the image quality is deteriorated.

In the above embodiment, the vertical synchronizing signal V
The elapsed time T1 from sync to the output of the image request signal Vreq is a constant value, and the front end 75 of the primary transfer toner image 74 is
Since the position of is the same regardless of the transfer paper size, the predetermined time T3 is also a constant value regardless of the transfer paper size, but is not limited to this. 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. The elapsed time up to may be different. In this case, the predetermined time T3 is obtained for each transfer paper size, and the ROM 11 is used as a control program.
You can store it in 2.

Further, as described in the above embodiment, it is preferable to use a stepping motor as the photoconductor driving motor 36, but the present invention is not limited to this, and another motor such as a DC brushless motor may be used. May be adopted.

In the above embodiment, a printer for printing an image provided from an external device such as a host computer on a transfer paper is used for description, but the present invention is not limited to this, and a copying machine or a facsimile device is used. It can be applied to a general electrophotographic image forming apparatus including the above.

[0076]

As described above, according to the inventions of claims 1 and 4, in the low speed mode, after the primary transfer in the primary transfer portion is completed, the primary transfer toner image is transferred to the primary transfer portion. At the time of re-passing, the intermediate transfer medium is driven at the second speed when the front end of the primary transfer toner image reaches the primary transfer portion. Since the drive speed of the intermediate transfer medium does not change during re-passing, the environmental conditions between the intermediate transfer medium and the photoconductor in the primary transfer portion do not change in the middle of the primary transfer toner image. Therefore, it is possible to prevent the situation in which the primary transfer toner image becomes uneven and the image quality is deteriorated due to a change in the level of reverse transfer from the intermediate transfer medium to the photoconductor in the primary transfer portion. You can

According to the second aspect of the invention, when the front end of the primary transfer toner image reaches the first transfer portion, the intermediate transfer medium is stably driven at the second speed. Since the start point of deceleration from the first speed to the second speed is controlled, the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, so that the decrease in the throughput of image formation is suppressed as much as possible. be able to.

According to the third aspect of the invention, the intermediate transfer medium advances from the time when the leading edge of the primary transfer toner image starts decelerating from the first speed to the second speed to the time when it stabilizes at the second speed. The intermediate transfer medium is stably driven at the second speed because the deceleration from the first speed is started when the position reaches the position on the upstream side in the rotational driving direction from the first transfer unit by a distance. The leading edge of the primary transfer toner image on the intermediate transfer medium can be surely reached to the primary transfer portion in synchronization with the time point. As a result, the driving speed of the intermediate transfer medium is maintained at the first speed as much as possible, so that the reduction in the throughput of image formation can be suppressed as much as possible.

[Brief description of drawings]

FIG. 1 is a diagram showing 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 showing an electrical configuration of the printer.

FIG. 3 is a timing chart illustrating the operation of each unit 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.

FIG. 5 is a diagram illustrating a time point at which deceleration of the intermediate transfer belt is started.

[Explanation of symbols]

4 Transfer Paper 11 Photoreceptor 20 Rotary Developing Section (Developing 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) 71) rotational driving direction 74 primary transfer toner image on the intermediate transfer belt 75 front end of primary transfer toner image 110 engine control unit 111 CPU (conveyance control unit, intermediate transfer medium control unit) 118 transfer bias generation circuit (primary) Transfer means, secondary transfer means) S1 first speed S2 second speed

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H027 DA38 DC02 EB04 ED16 ED24                       EE02 EE03 EE04 EE07 EE08                       EF09 FA28 FA35                 2H072 AA36 AB07 BA12 CA01 CA02                       CB09                 2H200 GA04 GA23 GA47 GB25 GB43                       GB44 HA02 HB12 HB22 JA02                       JA29 JB06 JB49 JC03 JC19                       PA10 PA11 PA26

Claims (4)

[Claims] 1. A developing unit for forming a toner image by adhering toner to an electrostatic latent image formed on a photoconductor, and rotating the developing unit.
An intermediate transfer medium that circulates through the secondary transfer unit and the secondary transfer unit; a primary transfer unit that primarily transfers the toner image onto the intermediate transfer medium at the primary transfer unit; and a secondary transfer unit at the secondary transfer unit. Secondary transfer means for secondarily transferring the primary transfer toner image on the intermediate transfer medium to a transfer paper, and fixing means for fixing the secondary transfer toner image on the transfer paper to the transfer paper while conveying the transfer paper. And a low speed mode in which the transfer sheet is conveyed at a second speed lower than the first speed from at least the secondary transfer unit to the end of fixing in the image forming apparatus including And a conveyance control unit that drives the intermediate transfer medium at the first speed in the normal mode, and drives the intermediate transfer medium in the low speed mode at least until the toner image formation by the developing unit is completed. The intermediate transfer in which the intermediate transfer medium is driven at the first speed, the driving speed of the intermediate transfer medium is reduced after the toner image formation is completed, and the intermediate transfer medium is driven at the second speed until at least the secondary transfer is completed. In the medium control unit, in the low speed mode, after the primary transfer in the primary transfer unit is finished, the secondary transfer unit passing immediately after does not perform the secondary transfer of the primary transfer toner image, Transfer control means for performing secondary transfer of the primary transfer toner image at the secondary transfer portion that next passes after the primary transfer toner image passes through the primary transfer portion again, In the low speed mode, the transfer medium control means is configured to perform the first transfer after completion of the primary transfer in the primary transfer section.
When the leading edge of the primary transfer toner image reaches the primary transfer portion when the secondary transfer toner image passes through the primary transfer portion again, the intermediate transfer medium is driven at the second speed. An image forming apparatus characterized by. 2. The intermediate transfer medium control means controls the intermediate transfer medium to be stably driven at the second speed when the front end of the primary transfer toner image reaches the first transfer portion. The image forming apparatus according to claim 1, wherein the image forming apparatus controls a deceleration start point from the first speed to the second speed. 3. The intermediate transfer medium control unit controls the intermediate transfer from the time when the leading edge of the primary transfer toner image starts decelerating from the first speed to the second speed to the time when the leading edge of the primary transfer toner image stabilizes at the second speed. 2. The image according to claim 1, wherein deceleration from the first speed is started at a point of time when a position on the upstream side in the rotational driving direction from the first transfer portion is reached by a distance traveled by the medium. Forming equipment. 4. A toner image formed by adhering toner to an electrostatic latent image formed on a photoconductor by developing means is primarily transferred to a rotating intermediate transfer medium at a primary transfer portion, and the intermediate transfer is performed. An image forming method in which a primary transfer toner image on a medium is secondarily transferred to a transfer paper at a secondary transfer portion, and the secondary transfer toner image on the transfer paper is fixed to the transfer paper while the transfer paper is being conveyed. In 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 at least the secondary transfer unit to the end of fixing. In the case of, 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 the toner image formation by the developing device is completed, An intermediate transfer medium control step of controlling the intermediate transfer medium to be driven at the second speed at least until the secondary transfer is completed by reducing the driving speed of the intermediate transfer medium after completion, and in the low speed mode, After the completion of the primary transfer in the primary transfer section, the secondary transfer section passing immediately after the primary transfer does not perform the secondary transfer of the primary transfer toner image, and the primary transfer toner image is transferred to the primary transfer section. And a transfer control step of performing a secondary transfer of the primary transfer toner image in the secondary transfer portion that next passes through, in the intermediate transfer medium control step, in the low speed mode, After the completion of the primary transfer in the primary transfer section,
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 characterized by the following.