JP2000019896A - Image forming device and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve image quality while making the device small in size and low in cost. SOLUTION: A carrying control system CPU 70 controls the driving of an intermediate transfer body, and an image forming control system CPU 72 controls the formation of an electrostatic latent image and a toner image. A switch 82 selects an intermediate transfer body driving pulse 70a or a beam detecting pulse BD outputted from a scanner unit 20 and applies it to a reference signal generation circuit 84. An HP/RS sensor 38 detects the specified rotating position of the intermediate transfer body. The circuit 84 is started from a flag detecting pulse from the sensor 38 and generates an ETOP signal according to the pulse 70a or the pulse BD. The generated ETOP signal is applied to the CPU 70, the CPU 72 and a TOP generation circuit 76 and used to decide image forming start timing on the intermediate transfer body 36 and timing that the leading edge of an image is transferred to recording paper 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and method, and more particularly, to an image forming apparatus and method for forming an image in which a plurality of colors are superimposed, such as a full-color printer and a full-color copying machine. .

[0002]

2. Description of the Related Art In a full-color image forming apparatus such as a full-color printer or a full-color copying machine, the accuracy with which a plurality of developing materials are overlaid on one image unit greatly affects the image quality of an image to be formed.

In particular, in a full-color laser beam printer, in order to synchronize the image formation in the main scanning direction and the image formation in the sub-scanning direction, the main scanning direction and the sub-scanning direction must be driven by mutually synchronized drive signals. No.
Further, in the case of full color, color misregistration occurs if the formed image does not correspond to each color.

In the main scanning direction, the rotation of the regular polygon polygon mirror of the laser scanner unit forms an image of an integral number of lines per rotation. An image forming object (here, an intermediate transfer body is taken as an example) is driven so as to move by one line in one line of image formation in the main scanning direction in synchronization with image formation in the main scanning direction. Needless to say, in order for a plurality of developers forming one pixel to be positioned at the same position with high accuracy, the image formation start position must also match for each color.

On the other hand, in order to reduce the cost, a multi-CPU configuration in which a transport control system CPU and an image formation control system CPU are generally provided. In this case, at the time of image formation, the transport control system CPU for controlling the driving of the intermediate transfer body and the image formation control system CPU for controlling the image formation need to proceed in synchronization with each other. In particular, during image formation,
Since the drive control of the intermediate transfer member and the rotation of the polygon mirror must be completely synchronized, the transport control system CPU and the image formation control system CPU send a signal that determines the image formation start timing to the transport control system CPU and the image formation control. The signals are applied to the system CPUs, and both CPUs are synchronized with each other based on this signal.

[0006]

By the way, depending on the type of transfer material, it may be necessary to convey it at a speed different from the normal speed during fixing. This relates to the control of the type and color tone of the developer. For example, OHT paper generally has poor fixability and needs to be transported at the time of fixing at a speed different from that of ordinary paper.

On the other hand, the recording paper cannot be conveyed at different speeds for fixing and transfer on the conveyance path for reasons such as downsizing and cost reduction of the image forming apparatus. The speed of the fixing depends on the conveyance speed of the fixing.

In order to cope with different fixing speeds of special recording paper while maintaining low cost and miniaturization, in the conventional example, the synchronization of the drive signals in the main scanning direction and the sub-scanning direction is somewhat abandoned. Therefore, the conventional color image forming apparatus has a problem in output accuracy when a special transfer material is used.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus and a method which overcome such problems.

[0010]

An image forming apparatus according to the present invention is an electrophotographic image forming apparatus for forming an image of a plurality of colors by stacking a plurality of developing materials on an intermediate transfer member, A conveyance control system CPU for controlling the driving of the intermediate transfer body and an image formation control system CP for controlling image formation
U, selecting means for selecting an intermediate transfer member drive signal and a synchronizing signal in image formation in the main scanning direction, and a signal indicating the leading edge timing of image data output electrically generated in accordance with the signal selected by the selecting means Means for synchronizing the transport control system CPU and the image forming control system CPU with the leading edge timing signal.

The image forming apparatus according to the present invention is also an electrophotographic image forming apparatus for forming an image of a plurality of colors by superposing a plurality of developing materials on an intermediate transfer member. A signal generating means for generating a signal indicating the leading edge timing of the image data output, and two or more control CPUs using the leading edge timing signal as a synchronization means.

An image forming method according to the present invention is an electrophotographic image forming method for forming an image composed of a plurality of colors by superposing a plurality of developing materials on an intermediate transfer member. A signal generating step of generating a signal indicating a leading edge timing of image data output, and a step of two or more control CPUs controlling a predetermined operation in synchronization with the leading edge timing signal are provided.

In these arrangements, a phase for forming an image on the intermediate transfer member and a phase for fixing and fixing the paper are separated.
By switching the intermediate transfer member drive signal between the main scanning direction control signal and the fixing conveyance speed drive signal at a timing corresponding to the phase switching, it is possible to achieve an improvement in printing accuracy while maintaining compactness at low cost.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram of an embodiment of the present invention, and FIG. 2 is a schematic side view of a mechanical portion of the embodiment.

First, the structure and operation of the mechanism shown in FIG. 2 will be described. The drum unit 10 includes an image carrier (photosensitive drum) 12 integrated with a cleaning container 14 for holding unnecessary toner on the image carrier 12 apart from the image carrier 12. Drum unit 10
Is detachably supported with respect to the printer main body, and is replaced in accordance with the life of the image carrier 12. The image carrier 12 is
An organic photoconductor layer is applied to the outside of an aluminum cylinder having a diameter t, and is rotatably supported by the cleaning container 14.

The driving force of a driving motor (not shown) causes the image carrier 12 to rotate counterclockwise in accordance with the image forming operation. A cleaner blade 1 is provided around the image carrier 12.
6 and a primary charging roller 18 are provided. The cleaner blade 16 separates unnecessary toner remaining on the image carrier 12 from the image carrier 12. The waste toner separated from the image carrier 12 is held in the cleaning container 14.
The amount of waste toner stored in the container 14 does not fill the container 14 earlier than the life of the image carrier 12. Therefore, the cleaning container 14 is simultaneously replaced when the life of the image carrier 12 is replaced. The primary charging roller 18 is in contact with the image carrier 12 and uniformly charges the surface of the image carrier 12 when a predetermined voltage is applied.

The image carrier 12 is irradiated with a laser beam from a laser scanner unit 20. That is, a laser diode (not shown) outputs a laser beam having an intensity corresponding to the applied image signal, and the laser beam is reflected by the polygon mirror 22 which rotates continuously at a high speed, and is horizontally (main scanning direction). Is scanned. Polygon mirror 22
The laser light reflected by the light source selectively exposes the photosensitive layer of the image carrier 12 rotating at a constant speed by the imaging lens 24 and the reflection mirror 26. Thereby, the image carrier 12
An electrostatic latent image is formed thereon.

A black developing unit 28B and a color developing unit 30 are arranged around the image carrier 12 behind the laser beam irradiation position of the scanner unit 20 in the rotation direction. The black developing device 28B and the color developing device 30 are individually detachable. The black developing device 28B develops black.
The color developing device 30 includes yellow, magenta, and cyan developing devices 30Y, 30M, and 30C, and develops each color of yellow, magenta, and yellow.

The black developing device 28B has a sleeve 28BS
Are arranged at a position facing the image carrier 12 with a slight space therebetween.

The black developing device 21B is applied to the outer periphery of the clockwise rotating sleeve 28BS by a coating blade 28BB pressed against the outer periphery of the sleeve 28BS.
The black toner in B is applied in a thin layer, and at the same time,
Electric charge is applied to the black toner by frictional charging. By applying a developing bias voltage to the sleeve 28BS, a toner image is formed on the image carrier 12 according to the latent image.

The color developing device 30 is also basically a black developing device 2
8, a toner image of each color is formed on the image carrier 12. However, in the color developing device 30, the developing device 30 of each color is used.
Y, 30M, and 30C are sequentially opposed to the image carrier 12.

The three developing units 30Y, 30M, and 30C are:
The developing rotary 34 that rotates about the shaft 32 is detachably held. At the time of image formation, each of the developing units 30Y, 30M, and 30C is rotated around the shaft 32 while being held by the developing rotary 34, and the developing units 30Y, 30M, and 30C are rotated.
30M and 30C sequentially stop at the position facing the image carrier 12. Further, after the developing sleeves of the developing units 30Y, 30M, and 30C for the respective colors are positioned so as to face the image carrier 12 at a small interval, a toner image of a color corresponding to the image carrier 12 is formed.

In the state shown in FIG. 2, the yellow developing device 3
0Y is positioned at a position facing the image carrier 12,
It is stationary. In the developing device 30Y, the toner in the container is supplied to the application roller 30YR by a feed mechanism. A coating roller 30YR that rotates clockwise and a sleeve 30Y
The toner is thinly applied to the outer circumference of the sleeve 30YS that rotates clockwise by the blade 30YB pressed against the outer circumference of S, and charge is applied to the toner by frictional charging.
By applying a predetermined developing bias voltage between the image carrier 12 on which the latent image is formed and the sleeve 30YS opposed thereto, a toner image corresponding to the latent image is formed on the image carrier 12. . In the magenta developing device 30M and the cyan developing device 30C, toner images are formed on the image carrier 12 by the same mechanism.

Each sleeve of each of the developing units 30Y, 30M, 30C is connected to a high-voltage power source for each color provided in the printer body when each of the developing units 30Y, 30M, 30C is located at the developing position. Thereby, a high voltage is sequentially and selectively applied for each color development.

The toner image on the image carrier 12 is transferred to the intermediate transfer body 36 for each color. That is, the developing rotary 34 rotates 120 degrees for each rotation of the intermediate transfer member 36, and the yellow developing device 30Y, the magenta developing device 30M, and the cyan developing device 3
Each development by O.C, and then development by the black developing device 28B is performed, and the intermediate transfer member 36 is rotated four times to complete a full-color toner image of yellow, magenta, cyan, and black toner on the intermediate transfer member 36. I do.

The intermediate transfer member 36 of this embodiment has a structure in which the outer surface of an aluminum cylinder 36a is covered with an elastic layer 36b such as a medium resistance sponge or medium resistance rubber. A large number of protrusions (flags) 36c are added to the surface of the intermediate transfer body 36 at regular intervals, and the HP / RS sensor 38 adjacent to the intermediate transfer body 36 detects the flag 36c, thereby detecting the intermediate transfer body 36. 36 rotation positions are detected. H
The output of the P / RS sensor 38 is
Is used to determine the laser scanning start timing and the recording paper supply timing. The intermediate transfer member 36
Is driven clockwise by a gear (not shown).

The recording paper 40 is stored in a cassette 42. The recording paper 40 in the cassette 42 is
The paper is taken out of the cassette 42 by the rotation of the paper feed roller 44 under frictional contact with the feed roller 46 and fed between the feed roller 46 and the retard roller 48 for preventing double feed. The recording paper 40 that has exited between the feed roller 46 and the retard roller 48 for preventing double feed is turned by a guide plate 50, passes through a conveyance roller 52 and a registration roller 54, and is transferred onto the surface of the intermediate transfer body 36. The sheet is conveyed toward the intermediate transfer member 36 so as to be in contact therewith. During the image forming operation, the registration roller 54 temporarily stops the recording paper 40 in a standby state to adjust the transfer timing of the toner image from the intermediate transfer body 36 to the recording paper 40. After the transfer timing, the recording paper 40 is continuously rotated to send the recording paper 40 toward the intermediate transfer body 36.

The intermediate transfer body 36 sandwiches the recording paper 40 fed from the registration roller 54 with the transfer roller 56 to which a predetermined voltage is applied, and sends it out. During,
The color toner image on the intermediate transfer body 36 is integrally transferred to the recording paper 40. The transfer roller 56 has a structure in which a metal shaft is wound with a medium-resistance foam elastic body, and can occupy two positions, a position in contact with the intermediate transfer member 36 and a position separated from the intermediate transfer member 36. 4
Until the color toner image is transferred from the image carrier 12 to the intermediate transfer member 36, the transfer roller 56 is separated from the intermediate transfer member 36, and when the four color toner images have been transferred onto the intermediate transfer member 36, The transfer roller 56 is pressed against the intermediate transfer body 36 with a predetermined pressure while the recording paper 40 is held therebetween.
At this time, a predetermined bias voltage is applied to the transfer roller 56 at the same time, and the toner image on the intermediate transfer body 36 is transferred to the recording paper 4.
Transferred to 0. The intermediate transfer member 36 and the transfer roller 56 are driven separately. Intermediate transfer body 36 and transfer roller 56
The recording paper 40 on which the toner image has been transferred is sent out toward the fixing device 58.

The fixing device 58 makes the toner image adhered to the recording paper 40 firmly adhere to the recording paper 40. The fixing device 58
The recording paper from the intermediate transfer body 36 is sandwiched between the fixing roller 60 and the pressure roller 62. The fixing roller 60 and the pressure roller 62 are both hollow, and each has a heater 6 inside.
4,66. That is, the toner image is firmly fixed on the recording paper 40 by heating and pressing.

The fixed recording paper 40 is discharged to a discharge section 68 on the upper surface of the apparatus via a guide mechanism.

Next, the configuration and operation of control of image formation and paper transport in the present embodiment will be described with reference to FIG. In this embodiment, the transport control system CPU 70 and the image forming control system C
The PU 72 cooperates to print an image on the recording paper 40. The controller 74 creates image data to be printed, selects an image forming mode, selects a recording medium, and the like. Usually, the controller 74 operates according to a request from an external host computer. For example, when an instruction to print a document is issued from the host computer, the controller 74 expands the character string specified by the host computer into bitmap image data. The controller 74 instructs the image forming control system CPU 72 to select a recording medium (such as plain paper and OHT paper) and to switch the number of printed pages. The controller 74 also operates as a TOP
The image data to be printed is supplied to the image data conversion circuit 78 at a timing according to the TOP signal from the generation circuit 76.

The image data conversion circuit 78 converts the image data supplied from the controller 74 into an image formation control system CP.
The data is converted in the mode specified by U72, and the converted data is supplied to the scanner unit 20 in synchronization with the control of the scanner unit 20 by the scanner control circuit 80. The scanner control circuit 80 controls the activation of the scanner unit 20 and also controls the scanner unit 20.
Is controlled to rotate at a predetermined constant speed.

The image forming control system CPU 72 instructs the scanner control circuit 80 to start the scanner unit 20.
It is confirmed that the polygon mirror 22 of the scanner unit 20 is rotating at a constant speed. The confirmation result is transferred from the scanner control circuit 80 to the image forming control system CPU 72. Each time the polygon mirror 22 rotates by one line in the main scanning direction, the scanner unit 20
One pulse (beam detection pulse BD) is generated and supplied to the image data conversion circuit 78 and the scanner control circuit 80. This pulse BD is used to generate a TOP signal and
By using the synchronization of 0 and 72, image formation without color shift can be realized.

The conveyance control system CPU 70 controls members related to paper conveyance and driving of the intermediate transfer drum, such as a motor and a clutch for driving each unit.
A pulse signal (intermediate transfer member driving pulse) 70a for rotationally driving is output. The intermediate transfer body 36 is moved in the sub-scanning direction by the unit of the intermediate transfer body drive pulse 70a.
That is, the intermediate transfer body 36 rotates by one line in the sub-scanning direction for each one pulse.

The intermediate transfer member driving pulse 70a is
It is also used to generate a reference signal ETOP which is a signal for synchronizing 0 and 72 with each other. That is, the switch 82 selects the intermediate transfer member drive pulse 70 a or the beam detection pulse BD output from the scanner unit 20 and applies the selected pulse to the reference signal generation circuit 84. A flag detection pulse from the HP / RS sensor 38 is applied to the reference signal generation circuit 84, and the reference signal generation circuit 8
4 starts from a flag detection pulse from the HP / RS sensor 38 and generates an ETOP signal in accordance with the intermediate transfer member drive pulse 70a or the beam detection pulse BD. The generated ETOP signal is applied to the conveyance control system CPU 70, the image formation control system CPU 72, and the TOP generation circuit 76, and determines the timing of starting image formation on the intermediate transfer body 36 and the timing of transferring the leading edge of the image to the recording paper 40. Used to do.

Transport control system CPU 70 and image forming control system C
The PUs 72 synchronize with each other by the ETOP signal during image formation. For example, the controller 74 issues an instruction to switch the number of simultaneously formed pages (one or two pages) in the next image formation during image formation.
2, the image forming control system CPU 72
The timing to output the command to switch the number of pages to be formed to the transport control CPU 70 is determined based on the TOP signal, and the transport control CPU 100 controls the number of sheets fed according to the instruction from the image formation control CPU 72.

The TOP generating circuit 76 generates a TOP signal for notifying the controller 74 of an image writing timing in accordance with the ETOP signal from the reference signal generating circuit 84. The controller 74 receives the T from the TOP generation circuit 76.
It knows the timing to start writing an image from the OP signal and supplies the image data to the image data conversion circuit.

The ETOP signal will be described in more detail. FIG. 3 shows a flag detection pulse output from the HP / RS sensor 38, an intermediate transfer member drive pulse 70a, and ETOP.
6 is a timing chart showing a timing relationship between a signal and a TOP signal. The reference signal generation circuit 84
When the flag detection pulse signal is input from the RS sensor 38, the ETOP signal starts to be generated.

The ETOP signal falls to a low level when a flag detection pulse is input. This timing is called HP1. When a predetermined number of intermediate transfer member driving pulses 70a are input from HP1, the ETOP signal rises to a high level. This timing is called RS2 *. Then, after another predetermined number of intermediate transfer member drive pulses 70a are input, the level again falls to a low level. This timing is H
Called P2. Further, a predetermined number of intermediate transfer member driving pulses 70
After a is entered, it goes up to a high level. This timing is called RS1. Further, a predetermined number of intermediate transfer member driving pulses 7
At the input of 0a, the ETOP signal falls to a low level, and at this point, the intermediate transfer body 36 has just completed one round from HP1. This timing is called HP1 '. Further, when the same number of intermediate transfer member drive pulses 70a as between HP1 and RS2 * are input, the ETOP signal goes high again. This is called RS2.

The ETOP signal is an intermediate transfer member drive pulse 7
The waveform between HP1 and HP1 ′ is periodically repeated using the number of pulses of 0a as a scale.

The image forming start timing and the sheet feeding start timing are HP1 and RS1, HP2 and RS1, respectively.
2 corresponds. That is, when an image starts to be formed at the timing of HP1, the registration roller 5 is driven at the timing of RS1.
4 is set so as to transfer the toner image to the recording paper sent from the printer. The same applies to HP2 and RS2. Where H
P2 and RS2 correspond to the second page when two pages of images are simultaneously formed on the intermediate transfer member 36. When only one page is formed on the intermediate transfer body 36, the TOP generation circuit 7 is controlled by an instruction from the image forming control system CPU 72.
6 does not output a TOP signal corresponding to HP2. That is, when forming one page, the TOP generation circuit 76 sets ET.
The TOP signal is generated according to the OP signal HP1, and the TOP signal is generated according to the ETOP signals HP1 and HP2 when two pages are formed.

Next, the switching timing of the switch 82 during image formation will be described. FIG. 4 shows a timing chart for plain paper, and FIG. 5 shows a timing chart for special paper that requires low-speed fixing such as OHT. In any case, (1) is an intermediate transfer member drive pulse, and (2)
Indicates an ETOP signal, (3) indicates a TOP signal, and (4) indicates an image signal. 4 and 5 show the case of full-color image formation using four color developers, only the timing chart portion from the last color is shown. That is,
In fact, similar timing charts for three colors exist before the illustrated timing chart.

The case of plain paper shown in FIG. 4 will be described. In the case of plain paper, the reference signal generation circuit 84 always generates an ETOP signal according to the beam detection pulse BD. That is, the switch 82 is always connected to the beam detection pulse side.
The intermediate transfer member drive pulse and the beam detection pulse BD output by the transport control system CPU 70 are signals having exactly the same period, although there is a phase difference. This is the transport control system CP
This is realized by making the operation clock of U70 and the clock supplied to the scanner control circuit 80 the same.
An ETOP signal is generated by the beam detection pulse BD,
By generating the TOP signal according to the TOP signal, it is possible to realize image formation without color shift.

In the case of plain paper, the output of image data is started at the timing of HP1, and the feeding is started at the timing of RS1. Since the rotation speed of the intermediate transfer body 36 and the conveyance speed of the fixing at the time of image formation may be the same, there is no need to change the speed, partially or as a whole, even with timing adjustment.

In the case of OHT, since the fixing speed must be reduced to half that of plain paper, the rotation speed of the intermediate transfer body 36 is also reduced to half in advance. Therefore, the rotation of the intermediate transfer body 36 is provided with one idle rotation after the transfer of the toner image onto the intermediate transfer body 36, and during that time, the speed of the intermediate transfer body 36 is reduced to half. At this time, the image forming control system CPU
The switch 72 switches the switch 82 to the intermediate transfer member drive pulse side at the timing of RS1, and generates an ETOP signal in accordance with the intermediate transfer member drive pulse. Whether or not to switch the switch 82 is previously instructed by the child control roller 74. Actual sheet feeding is started at the position shown in FIG. Thereafter, when the fixing is completed and the intermediate transfer member drive pulse returns to the normal speed, the switch 82 is returned to the beam detection pulse BD side.

A sensor for detecting the type of recording paper, for example,
An OHT sensor for detecting whether or not OHT is provided immediately before the registration roller 54, and the detection result is transmitted to the image forming control system C.
You may make it supply to PU72. The image forming control system CPU 72 switches the switch 82 from the beam detection pulse BD to the intermediate transfer member driving pulse when notified by the OHT sensor that the sheet requires low-speed fixing. As described above, the controller 74 instructs the image forming control system CPU 72 for a recording sheet requiring low-speed fixing, which cannot be determined by the OHT sensor.

[0048]

As can be easily understood from the above description, according to the present invention, it is possible to form a color image with no color shift even on a recording sheet requiring low-speed fixing.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a circuit section according to an embodiment of the present invention.

FIG. 2 is a side structural view of a mechanism portion of the embodiment.

FIG. 3 is a timing chart of ETOP generation.

FIG. 4 is a timing chart of image formation on plain paper.

FIG. 5 is a timing chart of image formation on OHT paper.

[Explanation of symbols]

 10: Drum unit 12: Image carrier (photosensitive drum) 14: Cleaning container 16: Cleaner blade 18: Primary charging roller 20: Laser scanner unit 22: Polygon mirror 24: Imaging lens 26: Reflection mirror 28B : Black developing device 30: Color developing device 28BS: Sleeve 28BB: Coating blade 30Y, 30M, 30C: Developing device 30YR: Coating roller 30YS: Sleeve 30YB: Blade 32: Shaft 34: Development rotary 36: Intermediate transfer body 36a: Aluminum Cylinder 36b: Elastic layer 36c: Projection (flag) 38: HP / RS sensor 40: Recording paper 42: Cassette 44: Feed roller 46: Feed roller 48: Double feed prevention retard roller 50: Guide plate 52: Transport Roller 54: Registration roller 56: Transfer Roller 58: Fixing unit 60: Fixing roller 62: Pressure roller 64, 66: Heater 68: Discharge unit 70: Transport control system CPU 70a: Intermediate transfer member drive pulse 72: Image formation control system CPU 74: Controller 76: TOP Generation circuit 78: Image data conversion circuit 80: Scanner control circuit 82: Switch 84: Reference signal generation circuit

Claims (13)

[Claims] 1. An electrophotographic image forming apparatus for forming an image of a plurality of colors by superposing a plurality of developing materials on an intermediate transfer member, comprising: a transport control system CPU for controlling driving of the intermediate transfer member. An image forming control system CPU for controlling image formation; a selecting means for selecting an intermediate transfer member driving signal and a synchronizing signal in image forming in the main scanning direction; and electrically generating the signal in accordance with the signal selected by the selecting means. Means for generating a signal indicating the leading edge timing of the output image data, wherein the transport control system CPU and the image forming control system CPU are operated in synchronization by the leading edge timing signal. 2. An electrophotographic image forming apparatus for forming an image of a plurality of colors by superposing a plurality of developing materials on an intermediate transfer member, wherein the timing of the leading end of the electrically generated image data output is controlled. Signal generating means for generating a signal to be indicated, and using the tip timing signal as a means for synchronizing 2
An image forming apparatus, comprising: at least one control CPU. 3. The image forming apparatus according to claim 2, further comprising switching means for selecting and switching from a plurality of reference signals for generating said leading edge timing signal. 4. The image forming apparatus according to claim 3, wherein a driving signal for the intermediate transfer member is used as one of the reference signals for generating the leading edge timing signal. 5. The image forming apparatus according to claim 3, wherein a synchronization signal used for image formation in a main scanning direction is used as one of the reference signals for generating the leading edge timing signal. 6. The front end timing signal according to claim 4, wherein the conveying speed of the fixing device and the driving speed of the intermediate transfer member are linked, and when the fixing device is conveyed at a predetermined low speed, the leading end timing signal is switched. Image forming device. 7. A fixing device, wherein the conveying speed of the fixing device and the driving speed of the intermediate transfer member are linked to each other, and a means for knowing that the developing material needs to be conveyed at a low speed is provided. The image forming apparatus according to claim 4, wherein a timing signal is switched. 8. An electrophotographic image forming method for forming an image of a plurality of colors by superposing a plurality of developing materials on an intermediate transfer member, wherein a timing of a leading edge of an electrically generated image data output is determined. An image forming method, comprising: a signal generating step of generating a signal to be indicated; and a step of controlling a predetermined operation by two or more control CPUs in synchronization with the front end timing signal. 9. The image forming method according to claim 8, further comprising a switching step of selecting and switching from a plurality of reference signals for generating the front end timing signal. 10. The image forming method according to claim 9, wherein a driving signal for an intermediate transfer member is used as one of the reference signals for generating the leading edge timing signal. 11. The image forming method according to claim 9, wherein a synchronization signal used for image formation in a main scanning direction is used as one of the reference signals for generating the leading edge timing signal. 12. The image forming apparatus according to claim 10, wherein the conveying speed of the fixing device and the driving speed of the intermediate transfer member are linked, and when the fixing device is conveyed at a predetermined low speed, the leading edge timing signal is switched. Image forming method. 13. The method according to claim 13, further comprising the step of knowing that the transport speed of the fixing device and the driving speed of the intermediate transfer body are linked, and that the developing material needs to be transported at a low speed to the fixing device. 11. The timing signal is switched.
Or the image forming method according to 11.