JPH04314257A - laser printer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a laser printer.
In particular, it relates to print start position control in the sub-scanning direction.

0002

[Prior Art] A laser printer using electrophotographic technology rotates a photoreceptor such as a photoconductive drum or a photoreceptor belt at a predetermined speed, uniformly charges the surface of the photoreceptor, and Exposure control is performed such that an electrostatic latent image is formed on the surface of the photosensitive drum by intermittent control of a laser beam deflected and scanned in a direction perpendicular to the rotational direction of the photosensitive drum according to video data corresponding to the image to be printed. The electrostatic latent image formed on the surface of the photoreceptor by exposure to light is developed to form a toner image, and the toner image is transferred and fixed onto a sheet of paper.

In such a laser printer, the image printing position is controlled by detecting the timing at which the laser beam passes through the deflection scan start reference position for each deflection scan in the deflection scan (main scan) direction, and by detecting the timing. The video data generation start timing for each deflection scan is controlled in synchronization with the signal, and a home position signal indicating the home position is generated in the rotation (sub-scanning) direction, and the video data generation start timing is controlled in synchronization with the home position signal. This is done by controlling the start timing of data generation control. In such print position control, the print position in the main scanning direction is adjusted in units of one video clock (one dot) or by specifying one video clock with a plurality of video clock signals having a phase difference and selecting one of them. It is possible to perform highly accurate adjustment control as required. However, since the printing position adjustment in the sub-scanning direction must be adjusted in units of one deflection scan (scanning line pitch), highly accurate adjustment control below the scanning line pitch is not possible.

By the way, a laser printer that prints color images generally prints a toner image formed with yellow toner, a toner image formed with magenta toner, and a toner image formed with cyan toner. are polymerized to complete a color image. In printing such color images, in order to obtain high-definition color images,
The amount of printing position deviation of each color toner image needs to be within 1/2 to 1/3 dots or scanning line pitch.

Even in conventional laser printers, printing position deviation in the main scanning direction can be adjusted by controlling the phase of the video clock signal, as described above, but in the sub-scanning direction, it is difficult to adjust the printing position within such a desirable range. Can not do it.

Note that a synchronization control technique in the sub-scanning direction is disclosed in Japanese Patent Laid-Open No. 1-236863.

[0007]

[Problems to be Solved by the Invention] As described above, conventional laser printers cannot finely adjust the printing position in the sub-scanning direction to less than the scanning line pitch, so they overlap multiple toner images to create a color image. When completing an image, there is a problem in that color shift occurs and a high-definition color image cannot be obtained. In monochrome image printing, such a problem appears as misalignment at the seam when a plurality of partial images are combined to complete one image.

An object of the present invention is to provide a laser printer that can adjust the printing position in the sub-scanning direction with high precision and print a high-definition image.

[0009]

[Means for Solving the Problems] The present invention includes a rotating photoreceptor, a deflection device that repeatedly deflects and scans a laser beam at a predetermined period to expose the surface of the photoreceptor, and a start of deflection scanning of the laser beam. Main scanning synchronizing signal generating means for generating a main scanning synchronizing signal indicating a reference position, sub-scanning synchronizing signal generating means generating a sub-scanning synchronizing signal indicating a printing start position in the sub-scanning direction, a device that forms an electrostatic latent image on the surface of the photoreceptor by intermittent application of the laser beam according to video data generated in synchronization with a scanning synchronization signal; and a developer that develops the electrostatic latent image to form a toner image. In the laser printer, the laser beam deflection scanning period by the deflection device is set to 1/1 of the predetermined deflection scanning period. n times, and the main scanning synchronization signal generating means generates a signal by one time in response to the deflection scanning reference position signal and the sub-scanning synchronization signal generated in each deflection cycle.
/n to generate a main scanning synchronizing signal, and more specifically, the main scanning synchronizing signal generating means includes a deflection scanning reference that generates a deflection scanning reference position signal for each deflection period. a position signal generating means, and a position signal generator having a period n times the predetermined deflection period and a phase difference from each of the deflection scanning reference position signals.
means for generating different kinds of deflection scanning start reference signals; and generating and outputting a main scanning synchronization signal by selectively using one of the n kinds of deflection scanning start reference signals in response to the subscanning synchronization signal. A feature is that a selection means is provided.

0010

[Operation] When the laser beam deflection scanning period by the deflection device is set to 1/n times the predetermined deflection scanning period, the deflection scanning reference position signal generated from the deflection scanning reference position signal generating means is the main beam used for deflection scanning. The period is 1/n of the scanning synchronization signal, and the main scanning synchronization reference signal generating means generates n types of deflection scanning start reference signals having a period n times the predetermined deflection period and different phases, and the sub-scanning synchronization When the signal is generated, one of the n types of deflection scan start reference signals is selectively used to output a main scan synchronization signal of a predetermined period.

Therefore, by selecting the deflection scanning start reference signal, the period of the main scanning synchronization signal is 1/n (1/n of the scanning line pitch).
The printing position in the sub-scanning direction can be adjusted in units of n).

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a cross section of a main part of a laser printer 200 connected to the information processing apparatus 100. The printing unit of this laser printer 200 includes a belt-shaped photoreceptor 211 that is wrapped around a rotating wheel so as to rotate at a constant speed in the direction of the arrow, and a charging unit that uniformly charges the surface of the photoreceptor 211. a scanning exposure device 213 that exposes the uniformly charged surface of the photoreceptor to form an electrostatic latent image on the surface;
Three developing devices 214, 215, 216 develop the electrostatic latent image to form a toner image, a cleaner 217 removes the toner remaining on the surface of the photoreceptor after the toner image is transferred, and a cleaner 217 removes the charge remaining on the surface of the photoreceptor. Erase lamp 218 to be removed
Equipped with

The scanning exposure device 213 focuses a laser beam output from a semiconductor laser 213a according to video data into a parallel laser beam using a condensing lens 213b, and a polygon mirror 213d rotated at a constant speed by a mirror motor 213c. The laser beam is reflected repeatedly to form a deflected beam, and the deflected beam is irradiated onto the surface of the photoreceptor through the projection lens 213e and the folding mirror 213f to form a beam spot, and by scanning the beam spot, the photoreceptor is This structure exposes the surface. Further, as shown in FIG. 4, the scanning exposure device 213 includes a beam detector 213g for detecting the timing at which the beam spot passes through the deflection scan start reference position in each deflection scan, and The signal is amplified by an amplifier 213h and outputted as a deflection scan start reference detection signal BDT1.

A developing device 214 uses yellow toner as a developer, a developing device 215 uses magenta toner as a developer, and a developing device 216 uses cyan toner as a developer. The developing function is imparted or eliminated by controlling the bias voltage of each developing device. The bias voltage is controlled by a designation signal from the information processing device 100 so that the developing device corresponding to the designated color of the video data used to form the electrostatic latent image functions effectively.

The transfer drum 221 is used to complete one color toner image by polymerizing a plurality of toner images formed on the surface of the photoreceptor, and to transfer the color toner image to paper. The transfer drum 221 is driven to rotate in the direction of the arrow at a speed synchronized with the surface of the photoreceptor while in contact with the surface of the photoreceptor, and the area inside the transfer drum in contact with the surface of the photoreceptor is filled with the photoreceptor. A transfer device 222 is installed to transfer the toner image on the body surface onto the transfer drum surface. In addition, a cleaner 223 that can be controlled to come into contact with and separate from the surface of the transfer drum 221 to remove toner remaining on the surface of the transfer drum 221 and a sub-scanning direction reference position detection signal HPS are generated to superimpose a plurality of toner images with high precision. A home position sensor 224 is combined for this purpose. The home position sensor 224 is a reflective photosensor that reads a writing reference position mark formed on the outer peripheral surface of the transfer drum 221.

A cassette 231 stores paper 232, and a paper feed roller 233 extracts the paper 232 and supplies it to a registration roller 234. The registration roller 234 holds down the leading edge of the paper 232 fed by the paper feed roller 233 to stop the advance of the paper 232, and adjusts paper alignment and paper feeding timing.

The transfer device 241 applies a transfer charge to the back surface of the paper 232 conveyed from the registration roller 234 in a region where the paper 232 contacts the transfer drum 221, and transfers the toner image on the surface of the transfer drum to the paper 232. do.

The fixing device 251 is configured to weld (fix) the toner image onto the paper 232 by passing the paper 232 onto which the toner image has been transferred between a heating roller and a pressure roller.

The paper discharge roller 261 discharges the paper 232 on which the toner image has been fixed to the outside of the machine.

The control device 270 is the upper information processing device 10
0 to exchange control information and print data (video data) with the information processing device, and the laser printer 20
Printing control is executed by controlling internal configuration means.

FIG. 5 is a block diagram detailing the internal configuration of the control device 270. The control device 270 includes a CPU 27
A ROM that is configured around 1 and stores programs.
272, R for storing error information, maintenance information, etc.
AM273, a laser control circuit 274 that controls the blinking of the semiconductor laser 213a, a laser power monitor circuit 275 that detects the intensity of the laser beam, the deflection scan start reference detection signal BDT1 and the sub-scanning direction reference position detection signal HPS are input. A detection signal processing circuit 276 for processing, and a main scanning synchronization reference signal generation circuit 277 for generating a main scanning synchronization reference signal.
, an oscillator 278, and a peripheral device control drive circuit 279 for controlling the constituent means inside the laser printer. As the internal configuration means of the printer, FIG. 5 shows a polygon mirror 213.
the mirror motor 213c that drives the transfer drum 221 and the main motor 281 that drives the transfer drum 221 and the paper conveyance system;
A photoreceptor motor 282 that rotates the photoreceptor 211 and a high voltage power supply circuit 283 that energizes the developing devices 214, 215, 216, the transfer device 222, etc. are shown.

As shown in FIG. 1, the detection signal processing circuit 276 includes a binary counter 276a, a D-type flip-flop 276b, a NOT circuit element 276c, AND circuit elements 276d and 276e, and an OR circuit element 276f. The binary counter 276a inputs the deflection scan start reference detection signal BDT1 to the clock terminal CK1, and uses the divided output obtained from the output terminal Q1 as the deflection scan start normal reference signal BDT2 to input the D of the D type flip-flop 276b.
Terminal, NOT circuit element 276c, and AND circuit element 276
d. The D-type flip-flop 276b further inputs the sub-scanning direction reference position detection signal HPS to the clock terminal CK2, and provides an output signal obtained from the output terminal Q2 to the AND circuit element 276e.
It is connected to provide an inverted output signal obtained from the inverted output terminal Q3 to the AND circuit element 276d. The NOT circuit element 276c uses its output as a deflection scan start sub-reference signal B.
DT3 is connected to the input terminal of AND circuit element 276e, and both AND circuit elements 276d, 276
The output terminals of e are respectively connected to the input terminals of the OR circuit element 276f. Then, the OR circuit element 276f outputs the main scanning synchronization reference signal BDT4.

Therefore, as shown in FIG. 2, the operation of the detection signal processing circuit 276 is such that the binary counter 276a divides the deflection scan start reference detection signal BDT1 into 1/2 and outputs the divided signal, so that the AND circuit element 276d A deflection scan start normal reference signal BDT2 having the same phase as the frequency-divided output is input to one input terminal of the AND circuit element 276e, and a deflection scan start sub-reference signal BDT2 having the opposite phase to the frequency-divided output is input to one input terminal of the AND circuit element 276e. Signal BDT
3 will be input. When the sub-scanning direction reference position detection signal HPS is generated in such a state, when the deflection scan start normal reference signal BDT2 is at a high level, the output terminal Q2 of the D type flip-flop 276b is at a high level, and the output terminal is at a high level. Q3 becomes low level. As a result, the deflection scan start sub-reference signal BDT3 becomes AND
It passes through circuit element 276e and becomes an effective deflection scan start reference signal BDT3', which is output from OR circuit element 276f as main scan synchronization reference signal BDT4.

On the other hand, the sub-scanning direction reference position detection signal HPS
The generation timing is the deflection scan start sub-reference signal BDT.
2 is high level, D type flip-flop 2
The output terminal Q2 of 76b becomes low level, and the output terminal Q3 becomes high level. As a result, the deflection scanning start normal reference signal B
DT2 passes through AND circuit element 276d to become an effective deflection scan start reference signal BDT2', which is output from OR circuit element 276f as main scan synchronization reference signal BDT4.

Furthermore, the main scanning synchronization signal generation circuit 277
The main scanning synchronization reference signal BDT4 and an oscillation output signal of an oscillator 278 which oscillates at a frequency eight times that of the video clock signal are inputted, and a main scanning synchronization reference signal BDT5 is outputted at a phase obtained by the AND of both signals.

Next, the print control processing executed by the CPU 271 will be explained with reference to FIGS. 6 to 9. The information processing device 100 and the laser printer 200 have control programs configured to form toner images in the order of yellow, magenta, and cyan.

When the information processing device 100 generates a print request signal, the CPU 271 in the control device 270 of the laser printer 200 responds to the print request signal, and the ROM 27
Print control processing according to the control program stored in 2 is started.

First, in process 401, the mirror motor 213c
, the main motor 281 and the photoreceptor motor 282 are rotated, and then in process 402 the erase lamp 218 is turned on,
In process 403, the charger 212 is brought into operation state, and in process 404
The transfer device 222 is brought into operation.

In process 405, it is checked whether the video data provided from the information processing device 100 corresponds to a yellow toner image. If the image corresponds to a yellow toner image, the developing device 2
controlling the peripheral device control drive circuit 279 to generate a developing bias voltage for enabling the developing function of No. 14;
The process moves to print processing 407.

In the printing process 407, as detailed in FIG. 7, the sub-scanning direction reference position detection signal HPS is
When the transfer drum 221 rotates to the writing reference position and the sub-scanning direction reference position detection signal HPS is generated, the process moves to process 407b.

In process 407b, time management is performed such that a print permission signal Vsync in the sub-scanning direction is generated t1 time after the sub-scanning direction reference position signal HPS is generated, and when the time t1 has elapsed, the process proceeds to process 407c. Then, the sub-scanning direction print permission signal Vsync is generated (the signal line for transmitting the sub-scanning direction print permission signal Vsync to the information processing apparatus 100 is set to low level). This time management is performed by counting the main scanning synchronization reference signal BDT5, but as mentioned above, the main scanning synchronization reference signal BDT5 is the deflection scan start reference detection signal that first occurs immediately after the sub-scanning direction reference position detection signal HPS. Since it is created using the signal BDT1 as a trigger, it has a matching accuracy of 1/2 the scanning line pitch. The length t2 of the generation period of this sub-scanning direction print permission signal Vsync corresponds to the time it takes to convey the length of the paper 232 in the conveyance direction.

Then, the sub-scanning direction print permission signal Vsy
Within the nc generation period, first, in process 407d, from the generation timing of the main scanning synchronization reference signal BDT5 to t3.
Time management is performed such that the main scanning direction print permission signal Hsync is generated after the time t3, and when the time t3 elapses, processing 4 is performed.
07e, the main scanning direction printing permission signal Hsync is generated (the signal line for transmitting the main scanning direction printing permission signal Hsync to the information processing apparatus 100 is set to low level). Length t of the generation period of the main scanning direction print permission signal Hsync
4 corresponds to the time required to scan the widthwise dimension area of the paper 232.

Thereafter, the process moves to process 407f, in which the information processing apparatus 100 is activated in synchronization with the sub-scanning direction print permission signal Vsync.
The video data Vdata transmitted from is received and transmitted to the laser control circuit 274, and the semiconductor laser 213a
Control flashing. Incidentally, like the oscillator 278, the information processing device 100 uses an oscillator output signal that oscillates at a cycle eight times as long as the video clock signal as the sub-scanning direction print permission signal Vs.
A signal whose frequency is divided by 1/8 at the falling phase of ync is used as a video clock signal. By controlling the semiconductor laser blinking, an electrostatic latent image for one scanning line is formed on the surface of the photoreceptor 211. Further, the information processing device 100
The predetermined margin areas (tv) at the front and rear ends of 32 and the predetermined margin areas (th) at the left and right ends of the video data Vdat are printed in white.
generate a.

When the reception of video data Vdata for one scanning line and the semiconductor laser blinking control are completed, processing 407g
Moving on to the sub-scanning direction print permission signal Vsync generation period t
Check whether it is within 2 and set the sub-scanning direction print permission signal Vsy.
If it is within the nc generation period t2, the process moves to process 407h to monitor the generation of the next main scanning synchronization reference signal BDT5, and when the next main scanning synchronization reference signal BDT5 occurs, the process returns to process 407d. When the sub-scanning direction print permission signal Vsync generation period t2 ends, the process moves to process 407j, returns the sub-scanning direction print permission signal Vsync to high level, and ends the exposure of the yellow toner image, and then in process 407k. The developing bias voltage is controlled so that the developing function of the developing device 214 disappears after the development of the electrostatic latent image formed by the exposure is completed.

The yellow toner image thus formed is transferred to the surface of the transfer drum 221 when it comes into contact with the transfer drum 221, and is held on the surface.

Next, in process 408, the information processing device 100
Check whether the next video data given by corresponds to a magenta toner image. If the toner image corresponds to a magenta color toner image, in step 409, the peripheral device control drive circuit 279 is controlled to generate a developing bias voltage to enable the developing function of the developing device 215, and the printing process is performed. Moving on to 410. The printing process 410 is also performed in the same manner as the printing process 407, and the magenta toner image is also transferred and held onto the yellow toner image on the surface of the transfer drum 221 so as to be superimposed thereon.

Next, in process 411, the information processing device 100
Check whether the next video data given by is of a cyan toner image. If it is a cyan toner image, in the next process 412, the peripheral device control drive circuit 279 is controlled to generate a developing bias voltage to enable the developing function of the developing device 216, and then in the printing process 413. Move. The printing process 413 is also performed in the same manner as the printing process 407, and the magenta toner image is also transferred and held so as to be superimposed on the yellow toner image and the magenta toner image on the surface of the transfer drum 221. . In this embodiment, since cyan toner image formation is not performed, processing 411
Then, the process moves to process 414.

In process 414, in order to transfer the toner image thus formed on the surface of the transfer drum 221 to the paper 232, the paper feed roller 233 is rotated to transfer the toner image formed on the surface of the transfer drum 221 to the paper 232.
2 is extracted, and in process 415, the rotation is continued for t5 hours to supply the paper 232 to the registration roller 234, and process 4
At step 16, the rotation of the paper feed roller 233 is stopped. Then,
In step 417, the paper feeding timing is adjusted so that the paper 232 comes into contact with the transfer drum 221 in alignment with the toner image, and the rotation of the registration roller 234 is started.

In process 418, the timing at which the leading edge of the paper 232 conveyed by the rotation of the registration rollers 234 comes into contact with the transfer drum 221 is found, and the transfer device 241 is energized to remove the toner image on the surface of the transfer drum 221. is electrostatically transferred onto the paper 232.

By doing this, the color toner image is transferred to the paper 232, and while the paper 232 with the toner image transferred passes through the fixing device 251, the toner image is fixed on the paper 232 and is ejected. The paper is discharged outside the machine by the paper roller 261.

In process 419, the rotation of the registration roller 234 that has finished conveying the paper is stopped, in process 420, the power supply to the transfer device 222 that has completed the transfer is stopped, and in process 421, the power supply to the transfer device 241 that has finished the transfer is stopped. and process 422
Then, the cleaner 223 is energized to start removing the toner remaining on the surface of the transfer drum 221 after the transfer, and the process 42 is started.
In step 3, the power supply to the charger 212 that has finished charging is stopped, and in step 424, the erase lamp 21 that has finished erasing the residual charge is stopped.
In step 425, the cleaner 223 which has finished removing the residual toner is turned off, and in step 426, various motors are stopped.

[0043]

As described above, the present invention allows the laser beam deflection scanning period by the deflection device to be set to 1/1 of the predetermined deflection scanning period.
The deflection scanning reference position signal generated from the deflection scanning reference position signal generating means is set to n times the period of 1/n of the main scanning synchronization signal used for deflection scanning, and the period is set to 1/n of the main scanning synchronization signal used for deflection scanning. n types of deflection scan start reference signals having different phases are generated at n times the predetermined deflection period, and when a sub-scan synchronization signal is generated, one type of the n types of deflection scan start reference signals is selectively used. A main scanning synchronization signal with a predetermined period is generated.

Therefore, by selecting the deflection scanning start reference signal, the period of 1/n of the main scanning synchronizing signal (1/n of the scanning line pitch) can be adjusted.
The printing position in the sub-scanning direction can be adjusted in units of n), making it possible to print high-definition images.

[Brief explanation of the drawing]

FIG. 1 is a detection signal processing circuit diagram according to the present invention.

FIG. 2 is a signal processing timing chart of the detection signal processing circuit shown in FIG. 1;

FIG. 3 is a sectional view of a main part of a laser printer according to the present invention.

FIG. 4 is a diagram showing the arrangement of beam detectors for detecting the timing at which a beam spot passes through a deflection scan start reference position.

FIG. 5 is a block diagram detailing the internal configuration of the control device according to the present invention.

FIG. 6 is a flowchart of print control processing executed by the CPU of the control device according to the present invention.

FIG. 7 is a detailed flowchart of printing processing in the printing control processing flowchart shown in FIG. 6;

FIG. 8 is a print control time chart by the control device according to the present invention.

FIG. 9 is an explanatory diagram of print start position control by the control device according to the present invention.

[Explanation of symbols]

100... Information processing device, 200... Laser printer, 21
1...Photoreceptor, 213...Scanning exposure device, 214-216...
Developing device, 213a... Semiconductor laser, 213d... Polygon mirror, 213g... Beam detector, 221... Transfer drum, 222... Transfer device, 224... Home position sensor, 270... Control device, 271... CPU, 274... Laser control circuit, 276 ...Detection signal processing circuit, 276a...
Binary counter, 276b...D type flip-flop,
277... Main scanning synchronization reference signal generation circuit, 279... Peripheral device control drive circuit.

Claims (3)

[Claims] 1. A rotating photoreceptor, a deflection device that repeatedly deflects and scans a laser beam at a predetermined period to expose the surface of the photoreceptor, and a main scanning synchronization signal that indicates a reference position to start deflection scanning of the laser beam. a main scanning synchronizing signal generating means for generating a sub-scanning synchronizing signal that indicates a printing start position in the sub-scanning direction; a device for forming an electrostatic latent image on the surface of the photoconductor by intermittent application of the laser beam according to video data; a developing device for developing the electrostatic latent image to form a toner image; In the laser printer, the laser beam deflection period by the deflection device is set to 1/n times the predetermined deflection scanning period, and the main scanning A laser printer characterized in that the synchronization signal generating means divides the frequency of the deflection scanning reference position signal and the sub-scanning synchronization signal generated in each deflection cycle into 1/n to generate the main-scanning synchronization signal. 2. A rotating photoreceptor, a deflection device that repeatedly deflects and scans a laser beam at a predetermined period to expose the surface of the photoreceptor, and a main scanning synchronization signal that indicates a reference position for starting deflection scanning of the laser beam. a main scanning synchronizing signal generating means for generating a sub-scanning synchronizing signal that indicates a printing start position in the sub-scanning direction; a device for forming an electrostatic latent image on the surface of the photoconductor by intermittent application of the laser beam according to video data; a developing device for developing the electrostatic latent image to form a toner image; In the laser printer, the laser beam deflection period by the deflection device is set to 1/n times the predetermined deflection scanning period, and the main scanning The synchronizing signal generating means includes a deflection scanning reference position signal generating means that generates a deflection scanning reference position signal for each deflection cycle, and n types of deflection scanning reference position signals whose cycles are n times the deflection cycle and whose phases are different from each other. a deflection scan start reference signal generation means for generating a deflection scan start reference signal; and a main scan synchronization signal by selectively using one of the n types of deflection scan start reference signals in response to the subscan synchronization signal. A laser printer characterized by comprising a selection means for generating and outputting. 3. A rotating photoreceptor, a deflection device that repeatedly deflects and scans a laser beam at a predetermined period to expose the surface of the photoreceptor, and a main scanning synchronization signal that indicates a reference position for starting deflection scanning of the laser beam. a main scanning synchronizing signal generating means for generating a sub-scanning synchronizing signal that indicates a printing start position in the sub-scanning direction; a device for forming an electrostatic latent image on the surface of the photoconductor by intermittent application of the laser beam according to video data; In a laser printer including a plurality of developing devices that form toner images, a device that transfers the toner images onto paper, and a device that fixes the toner images on the paper, the laser beam deflection period by the deflection device is set to the predetermined period. 1 of the deflection scanning period of
/n times, and the main scanning synchronizing signal generating means includes a deflection scanning reference position signal generating means for generating a deflection scanning reference position signal for each deflection period, and a deflection scanning reference position signal generating means that generates a deflection scanning reference position signal for each deflection period, and means for generating n types of deflection scan start reference signals having n times the period and different phases; A laser printer characterized by comprising a selection means for generating and outputting a scanning synchronization signal.