JP2609226B2 - Color electrophotographic equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a color electrophotographic apparatus, and more particularly to an improvement thereof.

[Conventional technology]

2. Description of the Related Art In an electrophotographic apparatus, a method is used in which a latent image is formed on a photosensitive drum by a light beam, the phenomenon is formed into a toner image, and then transferred to a recording paper. Accordingly, in color electrophotographic apparatuses, Japanese Patent Application Laid-Open No. 59-46659 and Japanese Patent Publication No.
As described in 3, a method of sequentially transferring toner images corresponding to each color to recording paper using a large number of photosensitive drums,
A method of obtaining a color image by repeating toner image formation and transfer for each color using one drum has been adopted.

[Problems to be solved by the invention]

These conventional apparatuses have disadvantages in that the apparatus becomes large and complicated due to the use of a large number of drums, and the apparatus is complicated because a transfer drum for multiple rotation transfer is used.

An object of the present invention is to solve such a problem of the prior art and to provide a color electrophotographic apparatus having a small size and a simple structure.

[Means for solving the problem]

The above object is achieved by forming a plurality of color toner images on the surface of the same photosensitive drum while performing alignment using digital time control, and transferring the images to recording paper at one time. Can be reached.

[Action]

After all the toner images of a plurality of colors are formed on the surface of one photosensitive drum and then transferred at a time, the apparatus can be made compact and simple in structure.

〔Example〕

FIG. 1 is an overall configuration diagram of a color electrophotographic apparatus showing one embodiment of the present invention. The operation of this apparatus is as follows.

When the photoconductor drum 1 rotates, the previous history is erased by the eraser lamp 18, the photoconductor 1 is uniformly charged by the charger 2, and thereafter, is exposed to the laser beam 3 scanning in the horizontal direction, and the first photoconductor 1 is exposed. Is formed. Here, the laser beam 3 converts the light beam of a semiconductor laser (not shown) into a polygon mirror 4, an fθ lens 5, a mirror 6,
7. Reach the drum 1 via the correction lens 8 and optically scan the drum surface. The polygon mirror 4 is driven by a small motor such as a flat motor. The correction lens 8 corrects a vertical tilt of the beam due to a surface tilt error or vibration of the polygon mirror, and uses a cylindrical lens or a distributed index optical waveguide. The first latent image is first developed by a Y (yellow) developing device 9. At this time, the other developing units 10, 11, 12
Is at rest and does not contact the drum surface. After the development in the developing device 9, the latent image is erased by the eraser lamp 18. There is a developed toner image on the drum 1, and a toner image of the next color is created at the same position on the surface of the photoreceptor where the toner image is present.
Is a pause state until the toner image on the drum 1 is finally transferred to the recording paper. That is, the cleaner 19 and the drum 1 are kept out of contact. Hereinafter, similarly to the formation of the first color toner image, uniform charging, optical image exposure, development, and erase exposure are performed. In this way, M (magenta), C (cyan), and B (blutter) toner images are formed on the surface of the same drum 1 following Y. In this image forming method, the next toner image is formed while the toner image of the previous image forming cycle is present, so at least development in M, C, B may destroy the previously formed toner image. There must not be. for that purpose,
Must be soft touch or non-contact development. B
After the development is completed, the toner images of four colors are simultaneously transferred. That is, the recording paper 15 is fed out of the paper cassette 13 by the paper feed roll 14, comes into contact with the photoreceptor 1, and is transferred with the corona charge of the transfer unit 16 applied thereto. The transfer unit 16 includes a DC corona discharger for transferring a toner image and an AC corona discharger for removing static electricity for facilitating separation of a sheet from the drum 1. After the transfer, the toner image is heated and fixed by the fixing device 17. The residual charge and the toner remaining on the drum 1 after the transfer are respectively erased by the eraser lamp 18,
It is removed by the cleaner 19. Therefore, the cleaner 19 comes into contact with the drum surface in this step. Although a full-color print can be obtained as described above, according to this embodiment, since the toner images of a plurality of colors are simultaneously transferred onto the transfer paper, a complicated transfer drum is not required as in the case of transferring each color. A small and simple color electrophotographic apparatus can be realized.

To realize such an electrophotographic apparatus, it is necessary to form a toner image of each color in a state of being accurately aligned on the same drum, to be able to superimpose a toner image of a previous color without destruction at the time of development, and to use a cleaner for each color toner. When an image is superimposed and created, it is necessary to control so as to be in a resting state and finally in an operating state. Furthermore, any residual toner or toner collected in the cleaner section after cleaning must not remain as a mass on the drum. if,
If the toner is accumulated on the drum of the cleaner unit, when the cleaner is deactivated, a mass of the toner falls into the developing device, causing color smearing. Hereinafter, methods for solving the problems of alignment, drum driving, development, and cleaning will be described in detail. In the above description, a case in which a full-color image is obtained with four colors has been described. However, it is needless to say that the apparatus of FIG. 1 can record a single color, two to four colors, or a juxtaposed image. Absent.

FIG. 2 shows an embodiment of a timing circuit for setting the timing of the operation of each section. First, a mechanism for generating a reference signal BD to be input to this circuit will be described. FIG. 3 shows the mechanism. The drum photosensitive member 1 is scanned by a beam 3 from left to right as shown by an arrow, and this beam is sent to a beam detector 20 fixed at a fixed position by a lens 21. , And the time is used as a reference for the scanning timing. However, since the lens 21 has the beam detector 20 installed at a position ahead of the surface of the drum 1 (the drum 1 cannot be installed on the same surface), a spot shape equivalent to that on the drum can be obtained at this position. Has a role.

FIG. 4 is an explanatory diagram of the horizontal scanning timing of the generation of the recording beam based on the reference signal BD from the beam detector 20. The clock BD is opened by the signal BD to pass the basic clock CLK. , Count the number of pulses to counter 101
In counted to set the time t _1. That is, from the time when the counter 101 has finished counting the number of pulses corresponding to this time, a laser signal LSH for each scanning line is output from the signal source 102, thereby modulating the laser beam 3 and providing necessary information. The latent image,
It is formed regularly on the drum 1.

FIG. 5 is a view for explaining vertical synchronization timing for correctly forming latent images for four colors on the drum 1, developing the latent images, and transferring the images of the respective colors onto the recording paper with high alignment accuracy. It is. Here, one print is obtained, but it is easy to extend the printing to continuously perform a plurality of prints. Here, the unit of control is the signal BD, but this may be the clock signal CLA. However, if the signal BD is used, there is an advantage that if the rotation of the polygon mirror or the optical system becomes abnormal, the signal BD disappears, and it is easy to make the entire system inoperable.

When the print ON signal is input in FIG. 5, the eraser lamp 18 is turned on by a mechanism (not shown), and the cleaner 19 is activated. At the same time, the gate 103 is opened. This Yotsute the pulse motor 107 is started driving starts the photosensitive drum 1 rotation, also be due connexion time t ₂ is counted in counter 104, a start signal when the count termination is output. The time t ₂ becomes the rotation of the drum 1 is constant, the time required for eliminating the influence of Batsukuratsushiyu and drum rotation rise is set to about 0.1 to 0.5 seconds. It is preferable to apply a certain brake to the drum 1 in order to make its rotation accurate. However when the start signal by connexion signal BD to open the gate 105 is input to the counter 106, the counter 106 starts counting, following described time t ₄ ~t ₇ corresponding count during the output signal to the signal source 102 I do. Next, when the rotation of the drum 1 starts, the eraser lamp
Immediately after the drum section just below 18 passes under the charge 2
Applying a high voltage to Chiyajiya 2 after or time t ₈ has elapsed from the start signal. The time t ₈ does not require high precision, the circuit will be omitted. When a high voltage is applied to the charger 2, the drum 1 is uniformly charged, so that exposure with a laser beam is started next. That is, the first optical image (Y color) starts from the time the time from the start signal t ₄ elapsed and exit end connexion sends a signal for one page. The delivery time is a time slightly shorter than the time when the drum makes one round. Hereinafter, the image exposure of each color M, C, B is transmitted after t ₅ , t ₆ , t ₇ after the start signal. Thus t _5, t _6, t ₇ is set to match the position Y to start image exposure to t ₄ at a location on the drum. The drum on which the latent image has been formed by the Y image exposure is developed by the first color developing unit 9. The development is started t ₈ seconds after the reference signal. The development is continued until one page is completed, and after completion, the carry-out of the developer in the developing device 9 is stopped so that the Y developer does not contact the drum. The following colors M, C, developer unit 10 to 12 starts to operate from the time t _9, t _10, t ₁₁ after each start signal B, and stopped after completion operation the development of one page. Although the cleaner 19 is started at the same time operating the printing ON signal, it stops the operation immediately before (after t ₁₂ from the start signal) Y toner image of the first color comes to the cleaner unit, i.e. the cleaner is separated from the photoreceptor surface, waiting period state Becomes Then, the toner images of all colors are superimposed and formed, and the recording paper 15
After being transferred to, the operation state is set again. That again actuated resting between t ₁₂ after t _13, and stops receiving the print OFF signal. The recording paper 15 is supplied such that when the final color B image is superimposed and the leading end of the image on the drum comes directly below the transfer unit 16, the leading end of the paper comes directly below the transfer unit 16. In this way, since the images of the respective colors are aligned and formed on the drum, and are collectively transferred to the recording paper, the structure is simpler and the alignment accuracy is higher than that of the transfer for each color. An image is obtained.

The setting of the Figure 5 time t ₈ ~t ₁₃ an alien one which does not require a special high precision, can be easily set in but not shown appropriate counter or the like. In particular, what needs to be time-controlled with high accuracy are the driving of the Y, C, M, and B signal sources 102 and the driving of the photosensitive drum 1, and these are described in the circuit of FIG. Is executed by In other words, it is preferable that the pulse motor 107 for driving the drum be provided independently of the motor for feeding and discharging paper and the fixing device.

Next, FIG. 6 shows an embodiment of a small developing device for forming a plurality of color toner images on the same photosensitive member. The features of this developing device are that the toner concentration detecting toner supply mechanism is eliminated, and the mechanism for stopping the developer conveyance when the developing operation is stopped is simplified. In FIG. 6, a developer 26 is magnetically attracted onto a rotating sleeve roll 24 having a fixed magnet roll 23 therein, and a magnetic brush having a constant thickness is regulated by a regulating plate 25 as the sleeve roll 24 rotates. And develops the latent image in the vicinity of the upper photosensitive drum 1. The surplus developer scraped off by the regulating plate 25 moves or is divided right and left by the stirring fin 27 and falls and circulates. After the development, the developer is peeled off from the sleeve roll 24 by the scraper 35, and is shifted or distributed to the left and right by the stirring fin 34, whereby the toner concentration in the developer is made uniform. Thereafter, it is attracted to the sleeve roll 24 again by the magnetic force and rotates. On the other hand, since the toner in the developer is consumed as the printing progresses, it must be replenished. Conventionally, a complicated method of detecting and replenishing the toner concentration has been adopted for this purpose, and therefore, there has been a disadvantage that the developing machine is large and expensive. In the developing machine of the embodiment of the present invention, this is abolished, and the toner is automatically replenished at any time by the self-adsorption ability of the developer. That is, the toner roll 30 is provided below the sleeve roll 24 to which the developer has been adsorbed. A magnetic bar 33 is provided inside the toner roll 30.
Aspirate 31. The replenishment toner 29 is charged by electrostatic friction with the carrier 31 and the toner roll 30, and is applied to the surface of the toner roll 30 by suction. The toner is attracted to the toner roll 30 not only by electrostatic but also by physical mechanical coating. The stopper 32 prevents the carrier 31 from being transported along with the roll when the toner roll 30 rotates, and only the toner is applied to the roll. When the toner on the toner roll 30 contacts or approaches the developer on the sleeve roll, if the toner concentration in the developer is low, the toner is taken into the developer. If the toner concentration is high, the toner is not taken in and is returned to the toner tank storing the toner 29 again. The supply of the replenishment toner 29 to the toner tank is performed from the toner input port 28. Toner roll
The toner taken into the developer from 30 is a sleeve roll
At 24, the toner is uniformly stirred and charged when it is rotated and circulated on the circumference of the roll, and is subjected to development.

A concave portion is provided in the magnetic poles N ₁ and S ₂ in front of the regulation plate of the magnet roll 23. In this case, the magnetic brush spikes in this portion are large and the movement of the developer becomes intense.
The stirring action is promoted and the excess toner is separated, which has the effect of suppressing toner density fluctuation in the developing section. Incidentally, the magnet roll 23 may be a combination of block magnets, in which case,
The magnetic pole provided with the concave portion can have the same effect by bringing two magnets of the same polarity close to each other. It is preferable to provide a large number of magnetic poles after the regulating plate 25 with a small interval. By doing so, the thin film developer layer can be formed on the sleeve, and the uniformity of the image can be improved. The bias power supplies 36 and 37 are for adjusting the developing characteristics and taking in the toner into the developer, respectively, and may be omitted. The bias power supply may be DC, AC or a combination thereof. Carriers in the developer 26 preferable for the present development system include an average particle diameter of 15%.
Small-grain type ferrite of about 70 μφ is preferred. This is because, in the case of a small-particle carrier, the allowable range of toner concentration fluctuation is wide, and a ferrite carrier can form a soft magnetic brush and have a long carrier life.

In this developing device, it is necessary to prevent the developer from being conveyed when the development is stopped. The state at that time is shown in FIG. In this figure, the magnetic roll 23 is rotated and moved by an angle α as shown by an arrow while the sleeve roll 24 is being rotated. The angle α does not need to be large, and may be 1 / to の of the _two magnetic poles N ₂ and S ₂ sandwiching the regulating plate 25. From the center of the magnetic pole N ₂ and S ₂ as restricting plate 25 is Figure 6, the developer comes into N ₂ side as shown in FIG. 7 is not conveyed cause slips. The rotation of the sleeve roll 24 is stopped at the place where the conveyance is stopped. By doing so, the developer does not come out of the regulating plate 25 to the photosensitive drum 1 side, and the development can be stopped. The toner roll 30 rotates together with the sleeve roll 24,
You only need to stop it. In order to return the developing device to the operating state, the position of the magnet roll 23 is returned to the original position, and the sleeve roll 24 and the toner roll 30 are rotated.

In the embodiment of FIG. 1, the developer for the first color may be in contact with the developer and the photoreceptor, but must be in a non-contact state when not in operation. In this case, the transport of the developer must be stopped by the method described in FIG. on the other hand,
Development for the second and subsequent colors must be lift contact or non-contact development that does not remove the previous color toner image.
In the case of non-contact development, the developing function can be stopped by changing the developing bias voltage without using the method shown in FIG. However, at this time, it can be surely performed as shown in FIG.

FIG. 8 shows an embodiment of the cleaner 19, in which a magnetic brush similar to that for development is used as a cleaning brush. Sleeve roll with fixed magnet roll 38 inside
The magnetic pole carrier 45 is attracted to 39, and the magnetic brush formed by the carrier 45 is slid on the photosensitive member with the rotation of the sleeve roll. Thus, the toner remaining on the photoconductor 1 is cleaned. The thickness of the magnetic brush is made constant by the regulating plate 25. The toner taken into the carrier is electrostatically attracted to and removed from the electrode roll 40 under the application of a bias power supply 43, so that the carrier can be used repeatedly. The toner adsorbed on the electrode roll is scraped off by a blade 41 and discharged and collected by a discharge screw 42 to the outside. The carrier magnetically adsorbed on the sleeve 39 is stripped off by the scraper 35 and used again. This prevents biased use of the carrier. A bias power supply 44 is connected between the sleeve roll 39 and the base of the photosensitive drum 1. This facilitates removal of the toner from the photoconductor. The bias electrodes 43 and 44 may be DC, AC, or a combination of DC and AC. The cleaner operation must be paused while forming a multicolor toner image on the drum, as described in FIG. That is, the magnetic brush must not contact the photoconductor. Therefore, it is extremely difficult to move the entire cleaner 19. Then, as shown in FIG. 9, the magnet roll 38 is rotated by the angle β, and the conveyance of the carrier is stopped. This operation is the same as in the case of the developing device described with reference to FIG.

As described above, by using the cleaner of the present invention, the operation of the cleaner can be quickly switched while the entire cleaner is fixed, and there is no possibility of defective cleaning or residual toner remaining on the drum.

FIG. 10 shows the structure of the charger 2 suitable for the present invention.
The corona wire 48 is stretched inside the shield electrode 47, and a high-voltage power supply 46 is applied between the shield electrode 47 and the corona wire 48. A screen electrode 49 is arranged on the surface facing the photoconductor,
A high-voltage Zener diode 50 is connected to this. According to such a charger, the photosensitive member charging pressure can be controlled to a value substantially close to the Zener voltage, and the toner image in the previous image forming cycle is less likely to be disturbed by charging. The screen electrode 49 has a thin line similar to the corona wire 48 or a thin plate provided with a slit by an etching technique. The Zener diode 50 is the one that repeats the steps of charging, image exposure and erase lamp exposure as described in the embodiment of FIG.
When forming toner images of two or more colors by the following process, two or more toner images may be provided, and if the process is changed over, the photosensitive member may be overcharged or may be formed in the previous image forming process. Less disturbs the toner image. This color image forming step uses the apparatus having the configuration shown in FIG. 1 and performs first charging → first exposure → first development → second charging → second exposure → second development...
It is time to take an image forming process in which the afterimage erasing step with the erase lamp 18 is omitted. In such a process, the image is less disturbed when the setting of the second charging is set lower than that of the first charging. Therefore, in FIG. 10, the Zener diode 50 is switched to H on the high voltage side during the first charging, and to L on the low voltage side after the second charging. More specifically, the first
Charged in the Z ₁ to charge the photosensitive member at about 700V with a Zener of 700V, for reversal development of the latent image at the first image exposure. Next, the second charging is performed using a zener of Z ₂ = 500 V. Then, when forming the first color image, the exposed portion is about 500 V, and the area where the exposure is not performed is about 60 V due to the dark decay of the potential in the pre-imaging step.
It is 0V. In this state, the second image exposure is applied to a portion not overlapping with the first image, and the second development is reversely developed as in the first development. The images formed in this way are simultaneously transferred to recording paper to obtain two-color images. In such a process, a two-color image free from image disturbance and color mixture can be obtained by using the charger shown in FIG.

As described in the above embodiment, according to the present invention, 2
A color image of a color or more can be obtained without being positioned and with a simplified device. The color image may be obtained by successively superimposing the toner images and by juxtaposition of color toners, and the developing method may be the normal development method, the reversal development method, or the combination thereof. The invention is applicable. Of course, as can be seen from the configuration of FIG. 1, it is also possible to appropriately select between monochrome recording and color recording.

FIG. 11 shows another embodiment of the color electrophotographic apparatus of the present invention, in which developing units 9 to 12 are mounted above the photosensitive drum 1 and a cleaner 19 is mounted below, and an LED array as a light source. 1 in that a light source 52 (which may be a laser beam optical system) is used. In this embodiment, the photosensitive drum 1 is rotated in the rotation direction of the arrow, and is uniformly charged by the charger 2, and then the LED array light source 52 in which a large number of LEDs are arranged in the axial direction of the drum 1 by a recording signal. Is formed on the drum surface by the lens array 53 and is exposed.
The charge latent image formed by the exposure is developed by selecting one of the developing units 9 to 12. The residual charge is erased by the eraser lamp 18. In this way, one color is recorded. Hereinafter, a toner image of the required number of colors is formed at the same position on the drum to obtain a color image. In this embodiment, the method described with reference to FIGS. 2 to 5 can be applied to the alignment of each color recording. However, in this case the beam detector is not required and the pulse of a constant period corresponding to a horizontal recording density made from clock signal, based on the pulse, the signal to be recorded after a predetermined time t ₁ with respect to one one of the LED What is necessary is just to transmit. In the vertical alignment, a pulse having a constant period for the above-described horizontal synchronization may be used as the signal BD in FIG. Further, in this embodiment, since the cleaner 19 is provided at the lower part of the drum,
There is no inconvenience that the toner after cleaning falls into the developer when the drum is replaced.

FIG. 12 shows a developing device suitable for the embodiment of FIG. A multi-pole magnet bar 33 is fixedly incorporated in the sleeve roll 30. A developer in which the carrier 31 and the toner 29 are mixed is adsorbed to the magnetic pole, and only the toner is electrostatically and physically applied to the surface of the sleeve as the sleeve roll 30 rotates. The carrier stopper 32 is for preventing the carrier 31 from being conveyed with the rotation of the sleeve roll 30. The sleeve roll 30 is kept close to the surface of the photosensitive drum 1 by a gap of 0.1 to 0.5 mm with a gap. The toner applied on the sleeve roll 30 flies to the charge latent image and is developed. A bias power supply 56 is connected between the sleeve roll 30 and the drum base to adjust the development characteristics. It is preferable that the bias power supply is obtained by superimposing AC and DC. To stop the developing operation (when developing other colors), the switch 58 switches the bias power supply. The bias 57 at this time is to prevent the toner applied to the sleeve roll 30 from flying on the drum and to prevent the toner image on the drum developed by another developing device from being reversely transferred to the sleeve. Appropriate size is around 200V with opposite polarity. The unused toner coated on the sleeve roll 30 is returned to the toner tank storing the toner 29 again.On the return side, the magnetic body 55 is opposed to one magnetic pole of the magnet bar 33, and the carrier 31 is Is adsorbed.
This has a sealing function to prevent leakage of the toner 29.

FIG. 13 shows the structure of a cleaner 19 suitable for the embodiment of FIG. This cleaner is a magnetic brush cleaner using a magnetic carrier. A magnetic brush is formed by adsorbing a magnetic carrier on a rotating sleeve 39 having a fixed magnet roll 38 therein, and is conveyed. The magnetic brush is made to have a constant thickness by the regulating plate 25. The magnetic brush contacts the photoreceptor 1 and removes toner remaining on the drum by electrostatic and mechanical sliding forces.
The carrier containing the toner is peeled off from the sleeve 39 by the scraper 35 and is adsorbed again. This is to make the mixing of the toner into the carrier uniform and to make the cleaning action uniform. The toner removed from the photosensitive drum 1 is electrostatically attracted and separated by the roll electrode 40. Between the rotating sleeve 39 and the drum substrate and the rotating sleeve 39
A bias power source 69, 68 is connected between the power supply and the electrode roll 40, respectively.
It promotes toner adsorption to 40. AC, D for bias
C and their combination are applicable. The toner adsorbed on the roll electrode 40 is scraped off by the blade 41. With such a configuration, the toner remaining on the drum can be efficiently removed, and the lump of the toner after cleaning such as blade cleaning does not remain. When the cleaner is in the rest state, the carrier can be stopped from being conveyed to the drum surface by rotating the magnet roll 38 as described in FIG.

In the above-described embodiments of FIGS. 1 and 11, a drum is used as the photosensitive member, but it is apparent that the present invention can be applied to a photosensitive member having another shape, for example, a belt.

〔The invention's effect〕

As described above, in the present invention, the photosensitive member is driven at a constant speed, and the exposure of each color is performed so as to be located at the same position on the photosensitive member by the digital clock control unit having the base unit clock or horizontal scanning time as a basic unit. Control, whereby each color toner image is formed on the same portion of the photoreceptor and is simultaneously transferred onto the final recording body, so that a color print without misalignment can be obtained by a simplified apparatus configuration. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, FIGS. 2 to 5 are explanatory views of a timing control method for aligning toner images of respective colors, and FIGS. 6 and 7 are FIG. FIG. 8 is a structural diagram of the developing device in the embodiment of FIG. 1 and an explanatory diagram when the operation is stopped, and FIGS. 8 and 9 are a structural diagram of the cleaner in the embodiment of FIG. 1 and an explanatory diagram when the operation is stopped. FIG. 10 is a view showing the structure of a charger, FIG. 11 is a view showing another embodiment of the present invention, and FIGS. 12 and 13 are views showing the structure of a developing device and a cleaner in the embodiment of FIG. FIG. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charger, 3 ... Polygon mirror, 4 ... Laser beam, 9-12 ... Developing device, 15 ... Recording paper,
16… Transfer unit, 18… Eraser lamp, 19… Cleaner, 20…
Beam detector, 100, 103, 105 ... gate, 101, 104, 106 ... counter, 107 ... pulse motor.

Claims (1)

(57) [Claims] 1. A color electrophotographic apparatus for forming a toner image of two or more colors by repeating a step of corona charging, image exposure, and development on a photoreceptor at least twice or more, and transferring the toner image on recording paper. An exposure unit that scans the photoconductor with a light beam modulated by a signal to form a latent image on the photoconductor; and a clock signal using a signal indicating a start time of each line of scanning by the exposure unit as a reference signal. Horizontal scanning synchronization means for determining the modulation start timing of each scanning line based on the image signal by counting; and when the print signal is input, the reference signal or a clock signal synchronized with the reference signal is supplied as a control pulse and the photoconductor is supplied. A pulse motor that digitally drives the photoconductor, and outputs a start signal when the time required for the photoconductor drive by the pulse motor to reach a stable state has elapsed. Timer means, and a latent image based on an image signal for each color is formed on the photoconductor in a time serial manner by starting operation by a start signal of the timer means and counting the reference signal or the clock signal; and Vertical synchronization means for determining the start timing of the latent image formation of each color so that the latent images of each color are correctly aligned;
Developing means for developing a latent image of each color formed on the photoconductor to generate a toner image of a corresponding color, which is provided for each color, and a developing means for selecting and operating each color on the photoconductor by the developing means; And a transfer means for transferring the formed toner image onto the recording paper at a time after all of the toner images have been formed.