JPH09304995A - Picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a picture image without shear in color even if a pulse motor is used as a photosensitive body drum drive motor which drives a photosensitive body drum in the direction of auxiliary scanning. SOLUTION: Scan time outside of a picture image data region by laser beam is set in advance to be time after time Y elapsed from a scan start signal. It is detected that time T elapsed from the scan start signal, and a picture image data region end signal is set to a photosensitive body drum drive motor control circuit at the time of the detection. It the photosensitive body drum drive motor control circuit,. an excitation pattern is generated by using the picture image data region end signal which is received as a reference pulse of a photosensitive body drum drive motor constituted by a pulse motor. Consequently, the change-over of excitation of the photosensitive body drum drive motor is done outside the picture image data region.

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 more particularly, to an image carrier for carrying an electrostatic latent image, a pulse motor for moving the image carrier in one direction, and the pulse motor. A pulse motor driving means for driving the light beam, an irradiation means for emitting a light beam, a scanning means for scanning the light beam emitted by the irradiation means in a direction perpendicular to the moving direction of the image carrier, and the pulse motor drive And a control unit that controls the unit.

[0002]

2. Description of the Related Art Conventionally, a toner having a plurality of colors is charged and charged one by one by one rotation of a photosensitive drum as an image carrier.
Proposes a color image forming apparatus that performs exposure and development, and repeats this multiple times to form toner images of multiple colors on a photoconductor drum, and transfers the formed toner images of multiple colors to recording paper all at once. Has been done. In this color image forming apparatus, color misregistration occurs when the position of the scanning line for each rotation on the photosensitive drum is deviated by the laser beam,
There is a problem that the color reproducibility is reduced.

In order to solve this problem, a photoelectric conversion element for receiving a laser beam is provided at one end of the photosensitive drum in the axial direction, and the output signal of this element is used as a line synchronization pulse for laser scanning. An image forming apparatus has been proposed that forms a high-quality image without color misregistration by using a reference clock for controlling the rotation speed of a photosensitive drum drive motor configured by a pulse motor (Japanese Patent Laid-Open No. 62-279).
362).

FIG. 12 shows a laser beam scanning unit 80 in such an image forming apparatus. The polygon mirror 82 of the laser beam scanning unit 80 is a polygon mirror drive motor control circuit 92 (see FIGS. 13 and 14) described later.
Is controlled to rotate in the direction of arrow R at a substantially constant angular velocity. The laser beam emitted from the laser output unit 88 and deflected by the polygon mirror 82 is the beam A.
The angle is changed by the reflecting mirror 84 at the position of, and the beam is incident on the beam detector 86. The beam detector 86 detects the incidence of the laser beam and outputs a pulsed scanning start signal to the laser scanning controller 90.

In order for the beam detector 86 to detect the laser beam, it is necessary to emit the laser beam from the laser output section 88 while the laser beam scans the beam detector 86. Therefore, the laser scanning controller 90 outputs a laser output signal to the laser output unit 88 while the laser beam scans the beam detector 86.
A laser beam is emitted by 8.

The laser output section 88 emits a laser beam based on the laser output signal from the laser scanning control device 90 and the image data signal from an image processing device (not shown). Outside the image forming area, a laser beam is output for each scanning by the laser output signal for beam detection, and inside the image forming area, a laser beam based on the image data signal is output.

The laser beam scanning unit 80 having such a configuration
In the image forming apparatus having a polygon mirror drive motor control circuit 92 (FIG. 13, FIG. 13) for rotationally driving the polygon mirror 82 in order to synchronize the scanning of the laser beam (main scanning) and the rotation of the photosensitive drum (sub scanning). (See FIG. 14) and two examples of the configuration of the photoconductor drum drive motor control circuit 94 that rotationally drives the photoconductor drum.

First, as shown in FIG. 13, the polygon mirror drive motor control circuit 92 controls the clock supplied from the clock generator 91 by the frequency divider 92A to control the rotation speed of the polygon mirror drive motor 92C. Divide the frequency so that it becomes the reference clock. The PLL control circuit 92B is
Reference clock from frequency divider 92A and encoder 92D
Based on the signal from, the polygon mirror drive motor 92C is feedback-controlled so as to rotate at a predetermined rotation speed.

On the other hand, the photosensitive drum drive motor control circuit 9
In 4, the clock from the clock generator 91 is frequency-divided by the frequency divider 94A to create a reference pulse for the photoconductor drum drive motor 94D composed of a pulse motor. The pulse motor control circuit 94C includes an excitation pattern generator 94.
Based on the excitation pattern from B, the photosensitive drum drive motor 94D is controlled to rotate at a predetermined angular velocity.

Since the polygon mirror drive motor 92C and the photosensitive drum drive motor 94D are controlled in rotation on the basis of a common clock, their rotations can be synchronized.

In such a relationship, when the rotation period of the photosensitive drum is set to be an integral multiple of the scanning period of the laser beam, the laser beam scans at the same position as the position scanned one revolution before. Thus, the positions of the scanning lines for each color can be adjusted.

On the other hand, as shown in FIG. 14, the polygon mirror drive motor 92C is rotationally controlled based on the clock from the clock generator 91, and the photosensitive drum drive motor control circuit 94 scans by the excitation pattern generator 94B. An excitation pattern is generated based on the start signal, and the pulse motor control circuit 94C controls the photosensitive drum drive motor 94D to rotate at a predetermined angular velocity based on the excitation pattern. That is, since the scanning of the laser beam is synchronized with the rotation speed of the polygon mirror drive motor 92C, the photosensitive drum drive motor 94D whose rotation is controlled by the scan start signal must rotate in synchronization with the polygon mirror drive motor 92C. become.

Therefore, in this case as well, if the rotation period of the photosensitive drum is set to be an integral multiple of the scanning period of the laser beam, the laser beam is exactly the same as the position scanned one revolution before. The position is scanned, and the position of the scanning line for each color can be adjusted.

In the above two examples, the polygon mirror drive motor 92C is a combination of a PLL control DC motor and the photosensitive drum drive motor 94D is a pulse motor, but each motor is a pulse control DC motor. The same control can be performed with a motor.

When a DC motor is used, a method is generally used in which a photo sensor reads an encoder or mark on the photosensitive drum and detects one rotation of the photosensitive drum to align the writing position of each color. ing.

However, in the above method, an encoder, a photosensor, etc. for detecting the position of the photosensitive drum are required, so that it is difficult to reduce the cost and size of the apparatus. That is, it has been considered desirable to use the pulse motor in order to save the cost of the apparatus and reduce the size of the apparatus.

However, when the pulse motor is used as the photosensitive drum drive motor, the following problems may occur.

The pulse motor has a characteristic that the excitation is switched at a predetermined timing according to the reference pulse and the rotation angle changes stepwise to rotate. Therefore, the rotation fluctuation becomes large during the transient response period in which the excitation is switched. Therefore, when a pulse motor is used as the photosensitive drum drive motor, the rotational fluctuation of the photosensitive drum becomes large during the transient response period. This allows
The laser beam cannot scan a predetermined position on the photosensitive drum, but apparently scans the photosensitive drum while undulating.

Particularly, in a device for synchronizing the scanning of the laser beam and the rotation of the photosensitive drum, as shown in FIG. 15, when the excitation switching timing is within the image data area, the swell is mainly generated for each scanning. Since they occur at the same position in the scanning direction, the color misregistration becomes conspicuous, and the image quality is remarkably degraded due to the color misregistration.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems and uses a pulse motor as a photosensitive drum drive motor for driving a photosensitive drum as an image carrier. However, it is an object of the present invention to provide an image forming apparatus capable of forming an image without color misregistration.

[0021]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises an image carrier for carrying an electrostatic latent image and the image carrier. Direction, a pulse motor driving means for driving the pulse motor, an irradiation means for irradiating a light beam based on an image to be formed, and a light beam irradiated by the irradiation means for the image carrier. An image forming apparatus comprising: a scanning unit that scans in a direction perpendicular to a moving direction; and a control unit that controls the pulse motor driving unit, wherein the control unit is configured to generate when the excitation of the pulse motor is switched. At least a part of the transient response period of the pulse motor is included in the period from the rear end of the image data area in one scan by the scanning means to the start of the image data area in the next one scan. Cormorants control, characterized in that.

In the image forming apparatus of the present invention, the image bearing member is moved in one direction by the pulse motor. On the other hand, a light beam based on an image to be formed is emitted by the irradiation means, and the emitted light beam is scanned by the scanning means in a direction perpendicular to the moving direction of the image carrier. As a result, the image carrier is scanned by the light beam based on the image to be formed, and the image is formed on the image carrier.

An image forming apparatus for performing such image formation is provided with pulse motor driving means for driving the pulse motor and control means for controlling the pulse motor driving means. Moreover, the control means is such that at least a part of the transient response period of the pulse motor generated when the excitation of the pulse motor is switched is changed from the rear end of the image data area in one scan by the scanning means to the image data area in the next one scan. It is controlled so that it is included in the period until the start, that is, the period outside the image data area.

By such control, a part or the whole of the transient response period of the pulse motor is included in the period outside the image data area, and the unstable movement operation of the image carrier accompanying the switching of the excitation of the pulse motor. It is possible to suppress the color misregistration of the image due to (for example, the rotational fluctuation of the rotating photosensitive drum).

As described above, in the present invention, when a part of the transient response period of the pulse motor is included in the period outside the image data area, conversely, a part of the transient response period is included in the image data area. It also includes cases where it takes time. As described above, even if a part of the transient response period extends over the period within the image data area, in the image data area, the vicinity of the trailing edge of the image data area and the vicinity of the leading edge of the image data area in the next one scan are normally blank areas. Therefore, the image quality of the formed image is not significantly affected.

However, as in the second aspect of the invention, the transient response period of the pulse motor is from the rear end of the image data area in one scan by the scanning means to the start of the image data area in the next one scan. It is desirable to control so as to be included in the period. By controlling in this way, the color shift of the image caused by the unstable movement of the image carrier (for example, the fluctuation of the rotation of the rotating photosensitive drum) accompanying the switching of the excitation of the pulse motor is completely prevented. be able to.

The timing for switching the excitation of the pulse motor may be determined based on the detection output by detecting a part of the deflected light beam by the beam detecting means, as in the third aspect of the invention. it can. For example, when the scanning start position in the deflected light beam is detected by the beam detecting means and a predetermined image data area time has elapsed from the scanning start time, that is, the image data area within one scan is completed. At this time, the excitation of the pulse motor may be switched. In this way, by switching the excitation of the pulse motor based on the detection output of the beam detection means, even if the device has a short period outside the image data area or a device that performs high-speed scanning of the light beam, the pulse motor The transient response period can be outside the image data area.

By the way, at least a part of the transient response period of the pulse motor generated when the excitation of the pulse motor is switched as in the first aspect of the present invention is as follows from the rear end of the image data area within one scan by the scanning means. In order to perform control so as to be included in a period until the image data region within one scan starts, that is, a period outside the image data region, the control means, as in the invention described in claim 4, controls the excitation of the pulse motor. The switching may be controlled to be performed from the time when the image data area within one scan by the scanning means is completed.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings.

First, the configuration of the image forming apparatus 10 in the first embodiment will be described with reference to FIG. As shown in FIG. 1, the image forming apparatus 10 is provided with an exposure device 12 for irradiating a laser beam based on an image to be formed, which will be described later, and a cylindrical photosensitive drum 16.

The photoconductor drum 16 is rotated in the direction of arrow Q1 by a photoconductor drum drive motor 24 composed of a pulse motor, and in the vicinity of the side surface of the photoconductor drum 16,
A charging device 14 that charges the surface of the photoconductor drum 16 along the rotation direction, and four developing devices 18A and 18B that respectively attach toners of yellow, magenta, cyan, and black to the surface of the photoconductor drum 16 respectively. , 18C, 18D
A transfer device 20 for transferring the toner from the surface of the photoconductor drum 16 to the recording paper P, a destaticizing device 21 for removing charges from the surface of the photoconductor drum 16, and a cleaning for removing toner from the surface of the photoconductor drum 16. The device 23 is installed in order.

The photoconductor drum 16 charged by the charging device 14 has a characteristic that, when it receives light, the potential of the light receiving portion is lowered. The image forming apparatus 10 utilizes this characteristic and corresponds to each color component of yellow, magenta, cyan, and black of the image to be formed on the surface of the photosensitive drum 16 that is charged by the charging device 14 and rotates in the direction of arrow Q1. A laser beam is sequentially irradiated from the exposure device 12 to reduce the potential of the light receiving portion of the photoconductor drum 16,
An electrostatic latent image corresponding to each color component of the image is formed on the surface of 6. This electrostatic latent image is developed by a developing device corresponding to each color component, and toner of each color is attached. This allows
The toner images of the four colors are formed on the photosensitive drum 16 in an overlapping manner, and the image to be formed is formed.

On the other hand, the recording paper P is sent out by the paper feed roll 32 to the transport path W indicated by the dotted line in FIG. 1, and is transported along the transport path W by the transport roll 38. Transport path W
A registration roll 30 is installed in the middle of, and the registration roll 30 is stopped when a predetermined time has elapsed from the start of the conveyance, whereby the conveyance of the recording paper P is stopped.

The rotation of the registration roll 30 is restarted in synchronism with the rotational position of the toner image formed on the photosensitive drum 16, and the recording paper P is conveyed at a constant and stable speed. The recording paper P is guided between the photoconductor drum 16 and the transfer device 20, and the toner image on the photoconductor drum 16 is electrostatically transferred from the surface of the photoconductor drum 16 to the recording paper P by the transfer device 20. To be done.

The recording paper P transferred here is removed by a charge eliminating needle (not shown) arranged on the downstream side of the transfer device 20.
The back surface of the photosensitive drum 16 is destaticized and peeled off from the surface of the photosensitive drum 16. The recording paper P that has been peeled off is conveyed by the paper conveyance belt 26.
Is conveyed in the direction of arrow G and is conveyed to the fixing device 28 installed on the downstream side in the conveying direction.

In the fixing device 28, a heat roll 40 for heating the recording paper P and a pressure roll 42 for pressing the recording paper P against the heat roll 40 are in sliding contact with each other in a predetermined width in the direction perpendicular to the paper surface in FIG. Has been installed,
The recording paper P is conveyed between the heat roll 40 and the pressure roll 42. At this time, the side of the recording paper P on which the toner image is transferred (the upper side in FIG. 1) is the heat roll 40 side, and the pressure roll 42 presses the recording paper P against the heat roll 40 to enable efficient heat transfer. . The heat roll 40 and the pressure roll 42 are maintained at a high constant temperature. In this state, the toner image on the recording paper P is thermally fixed on the paper surface.
The recording sheet P thermally fixed by the fixing device 28 is discharged to the outside of the image forming apparatus 10.

On the other hand, the electric charge remaining on the surface of the photosensitive drum 16 is removed by the static eliminator 21, and the photosensitive drum 1
The toner remaining on the surface of 6 is removed by a cleaning device 23 including a brush or the like.

Next, the schematic structure of the exposure apparatus 12 will be described with reference to FIG. As shown in FIG.
A laser output unit 56 configured by a semiconductor laser or the like that modulates and outputs a laser beam according to image data is installed, and a laser beam from the laser output unit 56 is provided near the emission side of the laser output unit 56. A collimator lens 152 for converting the diffused rays into parallel rays is arranged.

The laser beam, which has been converted into parallel rays by the collimator lens 152, is passed through the cylindrical lens 154, and the reflecting surface 34 provided on the side surface of the polygon mirror 34.
Focus on C. The cylindrical lens 154 has a role of correcting the surface tilt of each reflecting surface 34C.

The polygon mirror 34 has eight reflecting surfaces 34C on its side surface, and an arrow Q2 around the axis 158.
It rotates in the same direction at a constant angular velocity, and has a role of continuously changing and deflecting the incident angle of the laser beam on each reflecting surface 34C. That is, the polygon mirror 34 deflects the laser beam and scans it along the main scanning direction indicated by the arrow K.

In the traveling direction of the laser beam deflected by the polygon mirror 34, an fθ lens 160 for moving the image forming point of the laser beam on the photosensitive drum 16 in the main scanning direction indicated by arrow K at a constant speed is provided. It is arranged.
The laser beam that has passed through the fθ lens 160 forms an image on the surface of the photoconductor drum 16 via the cylindrical lens 162.

On the other hand, the cylindrical photosensitive drum 16 is driven by the driving force of a photosensitive drum driving motor 64D described later.
It rotates about the axis V in the direction of arrow Q1. That is,
The side surface 16A of the photosensitive drum 16 is scrolled from top to bottom (in the sub-scanning direction) in FIG.

Therefore, by the action of the fθ lens 160, the image forming point on the photosensitive drum 16 is moved at a constant speed along the main scanning direction, and the photosensitive drum 16 is scrolled in the sub scanning direction. The side surface 16A of the drum 16 is scanned by the laser beam.

A mirror 54 is arranged at the end of the laser beam in the main scanning direction that does not affect the exposure of the image on the photosensitive drum 16, and the main scanning is performed in the laser beam reflection direction by the mirror 54. A beam detector 52 is arranged to detect the start timing of the. When the laser beam reflected by the mirror 54 is detected, the beam detector 52 outputs a scanning start signal for notifying the scanning start timing to the laser scanning control device 50 that controls the laser beam emission operation by the laser output unit 56. And the image data area detection device 66.

The laser scanning control device 50 includes a microcomputer (not shown), and the laser scanning control device 50 is provided with a 8000-ary counter 72, a laser output section 56, and a signal based on image data to be formed. An image processing device 68 for sending to the laser output unit 56 is connected.

As shown in FIG. 4, the image data area detecting device 66 is provided with a predetermined clock (hereinafter, referred to as a clock for image formation).
A clock generator 66 for generating an image clock)
A C, a counter 66B, a comparator 66A, and an image data area end signal generator 66D are provided. Counter 6
The 6B counts the image clock from the clock generator 66C and sends the count value CT to the comparator 66A.
However, the counter 66B resets the count value CT each time the scanning start signal is input.

On the other hand, the relative position of the image data area with respect to the scanning start signal is predetermined, and in the example of the time chart of FIG. 3, the image data area ends when the time T has elapsed from the scanning start signal, It is known in advance that the laser beam scans outside the image data area. Comparator 6
A value HT corresponding to the time T is preset in 6A, and the comparator 66A determines that the image data area end signal generator 66 when the value HT and the count value CT match.
A predetermined coincidence signal is sent to D, and the image data area end signal generator 66D sends an image data area end signal to the photosensitive drum drive motor control circuit 64.

The photoconductor drum drive motor control circuit 64 includes a photoconductor drum drive motor 64D composed of a pulse motor, a pulse motor control circuit 64C for controlling the operation of the photoconductor drum drive motor 64D, and a photoconductor drum drive motor 64D. An excitation pattern generator 64B for generating the excitation pattern is provided. Here, the excitation pattern generator 64B uses the image data area end signal from the image data area end signal generator 66D as a reference pulse of the pulse motor to generate an excitation pattern, thereby switching the excitation outside the image data area. Is configured to do.

Further, in the image forming apparatus 10, the above-mentioned 4
In order to align the color toner images, the rotation period of the photoconductor drum 16 is configured to be an integral multiple of the reference pulse period of the photoconductor drum drive motor 64D as a pulse motor. The 64D reference pulse is counted to accurately detect one rotation of the photosensitive drum 16, and the image writing start timing is determined. Further, since the scanning cycle of the laser beam and the cycle of the reference pulse of the photosensitive drum driving motor 64D are made to coincide with each other, the positions of the scanning lines for each color are completely coincident with each other.

Specifically, as an example, the photosensitive drum 16
Has a diameter of 107.8 mm and an outer circumference of 338.664 mm
, The resolution is 600 dpi, and one line is set to 42.333 μm. That is,
There are 8000 lines per revolution of the photosensitive drum 16.

The photoconductor drum drive motor 64D has eight gear teeth, and the photoconductor drum 16 has 16 gear teeth.
It is set to 0, and the photosensitive drum drive motor 64D is 2
The photosensitive drum 16 is configured to rotate once when it is rotated 0 times. The photosensitive drum drive motor 64D
Is driven by a 1-2 phase excitation method, and is configured to make one rotation in 400 steps. That is, the photosensitive drum 16 makes one rotation in 8000 steps.

On the other hand, FIG. 5 shows a block diagram of a configuration relating to alignment in the sub-scanning direction. In FIG. 5, 8
The 000-ary counter 72 counts the reference pulse of the photoconductor drum drive motor 64D received from the photoconductor drum drive motor control circuit 64, and outputs an overflow signal every 8000 counts, that is, every one rotation of the photoconductor drum 16 by the laser scanning control device. Output to 50.

When the laser scanning controller 50 receives the image writing start signal from the image processor 68,
A reset signal is output to the 0-ary counter 72, and then a sub-scanning direction synchronization signal for the first color is output to the image processing device 68. The image processing device 68 outputs a signal based on the image data of the first color to the laser output unit 56 based on the synchronization signal in the sub-scanning direction, and the laser output unit 56 emits a laser beam based on the image data of the first color. .

When the photosensitive drum 16 makes one rotation thereafter, an overflow signal is output from the 8000-ary counter 72 to the laser scanning control device 50, and the laser scanning control device 50 outputs a sub-scanning direction synchronization signal for the second color.

By repeating the above procedure up to the fourth color, the image processing device 68 sequentially outputs the signals based on the image data for four colors to the laser output section 56 based on the sub-scanning direction synchronizing signal, and the laser output section 56. Laser beams based on the image data of four colors are sequentially emitted, and a toner image with no positional deviation is formed on the photosensitive drum 16.

Next, the operation of the first embodiment will be described.
In the image data area detection device 66 shown in FIG. 4, the counter 66B counts the image clock from the clock generator 66C and sends the count value CT to the comparator 66A. The comparator 66A compares the count value CT with the value HT corresponding to the time T from the scanning start signal to the scanning outside the image data area.

When the value HT and the count value CT match,
Since it can be determined that scanning is being performed outside the image data area, the comparator 66A sends a predetermined coincidence signal to the image data area end signal generator 66D, and the image data area end signal generator 66D controls the photosensitive drum drive motor. An image data area end signal is sent to the circuit 64.

In the photoconductor drum drive motor control circuit 64 which receives the image data area end signal, the excitation pattern generator 64B generates an excitation pattern using the image data area end signal as the reference pulse of the pulse motor, and the pulse motor control circuit 64C. Thus, the excitation of the photosensitive drum drive motor 64D is switched based on the excitation pattern.

As a result, the excitation of the photoconductor drum drive motor 64D is switched while scanning outside the image data area.

That is, as shown in the timing chart of FIG. 3, after a lapse of time T from the scanning start signal, the image data area end signal is output from the image data area detection device 66 to the photosensitive drum drive motor control circuit 64, and the photosensitive drum drive motor control circuit 64 is exposed. Since the body drum drive motor control circuit 64 outputs the excitation pattern using the image data area end signal as a reference pulse of the pulse motor, the transient response period of the excitation switching that causes a large rotation fluctuation becomes the scanning period outside the image data area, It is possible to eliminate the influence of rotational fluctuation on the exposure of the image on the photosensitive drum 16.

On the other hand, the process relating to the alignment in the sub-scanning direction will be described with reference to FIGS. 6 and 7. In the image forming apparatus 10, the control routine of FIG. 6 is executed by the laser scanning control device 50 as a process related to the alignment in the sub-scanning direction.

In step 202, it is judged whether or not an image writing start signal is input from the image processing device 68. Here, as shown by an arrow U1 in FIG. 7, when an image writing start signal is input, the process proceeds to step 204, and a reset signal is output to the 8000-ary counter 72 (arrow U2 part in FIG. 7).

The 8000-ary counter 72 counts the reference pulse of the photoconductor drum drive motor 64D received from the photoconductor drum drive motor control circuit 64. When the reset signal is received, the count value is reset and Count from 0 "again.

At the next step 206, the counter N for counting the number of development times of the toner images of the respective colors is reset to "1", and at the next step 208, first, the sub-scanning direction synchronizing signal of the first color (for example, yellow) is sent. Image processing device 6
8 (arrow U3 portion in FIG. 7). Image processing device 68
Outputs the first color yellow image data to the laser output unit 56 based on the sub-scanning direction synchronization signal, and causes the laser output unit 56 to emit a laser beam based on the first color yellow image data. Thereby, the photosensitive drum 1
A toner image based on the image data of yellow is developed on the image surface 6 (arrow U4 in FIG. 7).

In the next step 210, it is judged whether or not the counter N is equal to "4", that is, whether or not the development of the toner images of four colors is completed. Since the counter N is "1" at the beginning, a negative decision is made and the routine proceeds to step 212 where the input of an overflow signal from the 8000-ary counter 72 is awaited.

Thereafter, when the development of the toner image based on the yellow image data is completed and the photosensitive drum 16 makes one rotation, an overflow signal is output from the 8000-ary counter 72 to the laser scanning controller 50 (arrow in FIG. 7). U5
Part). As a result, an affirmative decision is made in step 212, the routine proceeds to step 214, and the counter N is incremented by one.

Then, the process returns to step 208 to output the sub-scanning direction synchronizing signal of the second color (for example, magenta) to the image processing device 68 (arrow U6 portion in FIG. 7). Image processing device 6
Reference numeral 8 outputs magenta image data for the second color to the laser output section 56 based on the sub-scanning direction synchronization signal, and causes the laser output section 56 to emit a laser beam based on the magenta image data for the second color. As a result, a toner image based on magenta image data is developed on the photosensitive drum 16 (arrow U7 portion in FIG. 7). At this time, the photosensitive drum 1
As for the position on 6, the 8000 decimal counter 72 accurately counts 8000 steps, so that the position is the same as the toner image based on the previous yellow image data, and color misregistration is prevented. There is.

Thereafter, by repeating the processing of steps 208 to 214, toner images of four colors in total including yellow, magenta, cyan and black are developed on the photosensitive drum 16 at the same position on the photosensitive drum 16. A color image with no color shift is formed. Since the counter N is "4" at this time, an affirmative decision is made in step 210 and the operation proceeds to step 216. In step 216, it is determined whether or not development has been completed for all pages to be formed. If not completed, the process returns to step 202, and the development process for each color in steps 202 to 214 is executed for the next page. To do.

In this way, the color image development processing is executed for each page, and when the development is completed for all pages, an affirmative decision is made in step 216 and the control routine of FIG. 6 is terminated.

The registration roll 30 is rotationally driven in synchronization with the rotational position of the toner image corresponding to the color image of each page formed on the photosensitive drum 16 as described above. As a result, the recording paper P is guided at a constant speed between the photoconductor drum 16 and the transfer device 20, and a toner image corresponding to the color image of each page on the photoconductor drum 16 is transferred to the photoconductor by the transfer device 20. Each page is transferred from the surface of the drum 16 to the recording paper P.

The rear surface of the recording paper P transferred here is neutralized by a neutralization needle (not shown), and the recording paper P is separated from the surface of the photosensitive drum 16. The peeled recording paper P is
The sheet is conveyed in the direction of arrow G by the sheet conveying belt 26, and is conveyed between the heat roll 40 and the pressure roll 42 in the fixing device 28. At this time, the side of the recording paper P on which the toner image is transferred faces the heat roll 40 side, and the toner image on the recording paper P pressed against the heat roll 40 by the pressure roll 42 is thermally fixed on the paper surface. . The recording paper P thermally fixed by the fixing device 28 in this manner is discharged to the outside of the image forming apparatus 10.

The charges remaining on the surface of the photoconductor drum 16 are removed by the static eliminator 21, and the toner remaining on the surface of the photoconductor drum 16 is removed by the cleaning device 23. It is reused for the image forming process.

As is apparent from the above description, according to the first embodiment, in the photosensitive drum drive motor constituted by the pulse motor, the transient response period of the excitation switching in which the rotation fluctuation is large is outside the image data area. Therefore, it is possible to eliminate the influence of rotation fluctuation on the exposure of the image on the photosensitive drum 16. Also, yellow,
The toner image of each color of magenta, cyan and black is 80
By accurately detecting 8000 steps, that is, one rotation of the photosensitive drum 16, the development is performed at the same position on the photosensitive drum 16, so that a color image having no color shift can be formed. .

In this way, the photosensitive drum drive motor 64D
Since the influence of the fluctuation in rotation due to the excitation switching is removed and the color shift is prevented, it is possible to form a high-quality color image.

[Second Embodiment] Next, a second embodiment according to the present invention will be described.
An embodiment will be described. In the second embodiment, an embodiment will be described in which the excitation of the photosensitive drum drive motor 64D is switched based on the laser output signal sent from the laser scanning control device 50 to the laser output section 56 to output the scanning start signal. To do.

8 to 10 show the configuration of the second embodiment. Note that, in FIGS. 8 to 10, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted here. Since the configuration related to the alignment in the sub-scanning direction shown in FIG. 5 is the same as that of the first embodiment,
The description is omitted.

As shown in FIGS. 8 and 9, the image forming apparatus 10 in the second embodiment is not provided with the image data area detecting device 66, and the laser output signal is sent from the laser scanning control device 50 to the photosensitive member. Drum drive motor control circuit 64
Sent to

The laser scanning controller 50 detects the laser beam by the beam detector 52 every time the beam detector 52 scans the laser beam, so that the laser beam scans the beam detector 52 (that is, outside the image forming area). Then, the laser output signal is output to the laser output unit 56, and the laser output unit 56 forces the laser beam to be emitted.

In the second embodiment, as shown in FIG. 10, the laser output signal is also sent to the excitation pattern generator 64B. In the photoconductor drum drive motor control circuit 64 that receives the laser output signal, the excitation pattern generator 64B generates an excitation pattern using the laser output signal as the reference pulse of the pulse motor, and the pulse motor control circuit 64C generates the excitation pattern based on the excitation pattern. Photoconductor drum drive motor 6
4D excitation is switched.

As a result, the excitation of the photosensitive drum drive motor 64D is switched while scanning outside the image data area.

That is, as shown in the timing chart of FIG. 11, the laser output signal rises (that is, from the laser scanning control device 50 to the photosensitive drum drive motor control circuit 6).
Immediately after (outputting to 4), the photosensitive drum drive motor control circuit 64 outputs an excitation pattern using the laser output signal as a reference pulse of the pulse motor. As a result, similarly to the above-described first embodiment, the transient response period of the excitation switching in which the rotation fluctuation becomes large is outside the image data area, and it is possible to eliminate the influence of the rotation fluctuation on the exposure of the image on the photosensitive drum 16. .

In the first and second embodiments described above, as shown in the time charts of FIGS. 3 and 11, the case where the transient response period of excitation switching is shorter than the period outside the image data area has been exemplified. For example, in a device having a short period outside the image data region, a device performing high-speed scanning of a light beam, or the like, the transient response period may be longer than the period outside the image data region. Even in such an apparatus, the end of the image data area is detected based on the image data area end signal as in the first embodiment or the laser output signal as in the second embodiment, and the excitation is performed immediately after that. By switching between the two, most of the transient response period can be outside the image data area, and the color misregistration of the image due to the rotation fluctuation due to the switching of the excitation can be suppressed. actually,
Even if a part of the transient response period is in the image data area, in the image data area, the vicinity of the rear end of the image data area and the vicinity of the leading edge of the image data area in the next one scan are usually blank areas. It does not significantly affect the quality of the image formed.

[0083]

According to the present invention, at least a part of the transient response period of the pulse motor is included in the period outside the image data area, and the unstable movement of the image carrier due to the switching of the excitation of the pulse motor. It is possible to obtain the effect that the color misregistration of the image due to the operation (for example, the rotation fluctuation of the rotating photosensitive drum) can be suppressed.

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram of an exposure device in the image forming apparatus of the first embodiment.

FIG. 3 is a timing chart when switching the excitation of the motor based on an image data area end signal.

FIG. 4 is a block diagram showing a configuration related to scanning of a laser beam in the image forming apparatus of the first embodiment.

FIG. 5 is a block diagram showing a configuration relating to alignment in the sub-scanning direction in the image forming apparatuses of the first and second embodiments.

FIG. 6 is a flow chart showing a control routine of position adjustment processing in the sub-scanning direction according to the configuration of FIG.

FIG. 7 is a timing chart relating to alignment in the sub-scanning direction.

FIG. 8 is a schematic overall configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 9 is a schematic configuration diagram of an exposure device in the image forming apparatus of the second embodiment.

FIG. 10 is a block diagram showing a configuration related to scanning with a laser beam in the image forming apparatus of the second embodiment.

FIG. 11 is a timing chart when switching the excitation of the motor based on the laser output signal.

FIG. 12 is a diagram showing a configuration related to laser beam scanning in a conventional image forming apparatus and a signal output timing in one scanning.

FIG. 13 is a block diagram showing a configuration example of a conventional image forming apparatus that aligns a scanning line on a drum of a laser beam for each rotation.

FIG. 14 is a block diagram showing another example of the configuration of a conventional image forming apparatus that aligns a scanning line on a drum with a laser beam for each rotation.

FIG. 15 is a timing chart when color misregistration occurs.

[Explanation of symbols]

 10 image forming apparatus 16 photoconductor drum (image carrier) 24 photoconductor drum drive motor (pulse motor) 34 polygon mirror 50 laser scanning control device 52 beam detector 56 laser output unit (irradiation means) 64 photoconductor drum drive motor control Circuit 66 Image data area detection device

Claims (4)

[Claims] 1. An image carrier that carries an electrostatic latent image, a pulse motor that moves the image carrier in one direction, a pulse motor drive unit that drives the pulse motor, and light based on an image to be formed. An irradiation unit that emits a beam; a scanning unit that scans the light beam emitted by the irradiation unit in a direction perpendicular to the moving direction of the image carrier; and a control unit that controls the pulse motor driving unit. In the image forming apparatus, at least a part of a transient response period of the pulse motor generated when the excitation of the pulse motor is switched is changed from a trailing end of an image data area in one scan by the scanning unit. An image forming apparatus, wherein the image data area in one scan is controlled to be included in a period until the start. 2. The transient response period of the pulse motor, which occurs when the excitation of the pulse motor is switched, starts from the rear end of the image data area in one scan by the scanning means to the image data area in the next one scan. The image forming apparatus according to claim 1, wherein the image forming apparatus is included in the period up to. 3. A beam detecting means for detecting a part of the light beam deflected by the scanning means, wherein the control means switches excitation of the pulse motor based on a detection output of the beam detecting means. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to perform the following. 4. An image carrier that carries an electrostatic latent image, a pulse motor that moves the image carrier in one direction, a pulse motor drive unit that drives the pulse motor, and light based on an image to be formed. An irradiation unit that emits a beam; a scanning unit that scans the light beam emitted by the irradiation unit in a direction perpendicular to the moving direction of the image carrier; and a control unit that controls the pulse motor driving unit. The image forming apparatus is an image forming apparatus, wherein the control unit controls switching of excitation of the pulse motor to be performed from a time point when an image data area in one scan by the scanning unit is completed.