JPH1073780A - Light beam scanning device and image forming device provided with same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the phases of polygon mirrors coincident with each other even when the positional relation, etc., of a rotating direction between the mirror surfaces of the respective polygon mirrors and an object to be detected (magnetic pole) for detecting a rotating position is varied between the respective polygons. SOLUTION: This device is provided with plural sets of motor drivers 12 (PLL control part) for controlling a polygon motor 10 so that a polygon mirror 9 rotates at a constant speed based on the output signal of each Hall element 11 for detecting the rotating position of the polygon mirror 9 and a reference rotary signal PCLK, a time difference between the output signal DP1 of a laser beam detector 13 corresponding to a reference polygon mirror 9(1) and the output signal DP2 of the laser beam detector 13 corresponding to the remainder polygon mirror 9(2) is calculated and the phase difference of a dummy output signal used for the motor driver 12(2) to the output signal of the Hall element 11 is set based on the time difference.

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 (including a color image forming apparatus) such as a copying machine, a facsimile, a printer, and a printing machine, and a light beam scanning apparatus used in the image forming apparatus. The present invention relates to the control of the rotation phase of each rotating polygon in a light beam scanning device having the rotating polygon mirror.

[0002]

2. Description of the Related Art Conventionally, as a light beam scanning device used for an image forming apparatus such as a copying machine, a facsimile, a printer, a printing machine, etc. A driving unit for driving the rotating polygon mirror, a rotating position detecting unit for detecting a rotating position of the rotating polygon mirror, the rotating polygon mirror based on a rotation reference signal and an output signal of the rotating position detecting unit, and the like. It is known that a plurality of sets of rotation drive control means for controlling the drive means so as to rotate at high speed and a rotation reference signal generation means for generating a rotation reference signal used in each of the rotation drive control means are known.

In the light beam scanning device having the above configuration,
Each drive unit is controlled based on the rotation reference signal generated by the rotation reference signal generation unit and the output signal of each rotation position detection unit so that each rotary polygon mirror rotates at a constant speed. And in the image forming apparatus provided with this light beam scanning device,
A latent image is formed on an image carrier by a light beam deflected and scanned by each rotating polygon mirror, and each image obtained by developing the latent image is superimposed and transferred onto a recording medium. Here, in order to superimpose each image on an accurate position on the recording medium and prevent the occurrence of image shift, the main scanning direction (light beam scanning direction) and the sub-scanning direction of each image on the image carrier are required. The image writing start position in the (moving direction of the image carrier surface) must be set to a predetermined position.

In the main scanning direction, for example, a light beam is detected at a predetermined position on a scanning path, and the writing timing of each scanning line in the main scanning direction of an image is adjusted based on the detection result. When such adjustment is performed, even if the initial mounting angle of each rotary polygon mirror to the image carrier, that is, the surface phase of each rotary polygon mirror does not match each other, it is possible to prevent the occurrence of image shift in the main scanning direction. it can.

On the other hand, in the sub-scanning direction, for example, when a plurality of image carriers are provided corresponding to a plurality of rotating polygon mirrors, the interval (pitch) between the image carriers is an integral multiple of the scanning pitch in the sub-scanning direction. , And the image writing start timing is set in units of time required for one light beam scanning in the main scanning direction, and the rotating polygon mirror is driven to rotate based on the rotation reference signal of the same frequency to write the image. Do.

However, in the light beam scanning apparatus provided with the plurality of rotating polygon mirrors, the surface phases of the respective rotating polygon mirrors may not coincide with each other. In the case where the light beam scanning device in which the surface phases do not coincide with each other is used for the image forming apparatus, even when the writing start timing of the image is set in the time unit required for one light beam scanning in the main scanning direction, There is a problem that an image shift in the sub-scanning direction of one scanning pitch or less (84.67 μm or less when the image resolution is 300 dpi) occurs. This image shift causes a color shift error in the color image forming apparatus.

Heretofore, there has been known an apparatus which controls the rotation phase between the rotating polygon mirrors in order to prevent the image shift in the sub-scanning direction of one scanning pitch or less. For example, Japanese Patent Application Laid-Open
Japanese Patent No. 242909 discloses a common frequency signal generating means (rotation reference signal generation means) for supplying a common reference frequency signal (rotation reference signal) to a plurality of PLL (Phase-Locked Loop) control means for controlling the rotation of each rotary polygon mirror. Means). In the laser beam printer described as an example in the publication, a common frequency signal generating means supplies a common reference frequency signal f0 to a signal input terminal of a PLLIC chip as a PLL control means for each color. In the chip, the reference frequency signal f0 is compared with the frequency signal FG fed back from each Hall IC as the rotational position detecting means, and the phase of the rotation of the scanner motor as the driving means of each rotary polygon mirror is controlled. The surface phases of the rotating polygon mirrors are matched.

[0008]

However, in the light beam scanning device having the above-mentioned structure, the rotation between the mirror surface of the rotary polygon mirror and the detection object on the rotary polygon mirror side detected by the rotation position detecting means. The positional relationship in the direction and the relative positional relationship of the rotation position detecting means with respect to the rotating polygon mirror may vary between the rotating polygon mirrors. in this case,
P described in JP-A-62-242909 is described.
Even if the LL control is performed, the surface phases of the rotating polygon mirrors cannot be matched, and an image shift in the sub-scanning direction that is equal to or less than the one scanning pitch occurs. As described above, the surface phases cannot be matched by the control of the above publication because the mirror surface of the rotating polygon mirror and the object to be detected by the rotation position detecting means (Hall IC), more specifically, the rotating polygon mirror Poles (S-pole, N-pole) attached to a part of the rotating body (rotor)
And the relative positional relationship of the rotational position detecting means (Hall IC) with respect to the rotating polygon mirror is assumed to be the same between the rotating polygon mirrors. .

FIG. 1 shows how the above-mentioned surface phase shift occurs.
This will be specifically described with reference to FIGS. FIGS. 17 and 18 show a rotation reference signal before and after the conventional PLL control (a common reference frequency signal in the example of the above publication) and a Hall element as a rotation position detecting means. An output signal, an output signal (detector pulse) of a magnetic pole and each mirror surface as a detection object of the Hall element passing through a predetermined rotation position, and a light beam sensor as a light beam detecting means for detecting a light beam from a rotating polygon mirror The relationship between signals DP1 and DP2 is illustrated for a case where two light beam scanning units (unit 1 and unit 2) are provided. Here, the coincidence of the surface phases means that the directions of the mirror surfaces of the rotary polygon mirrors are the same, that is, the timings of the detector pulse signals are the same.

Before the PLL control shown in FIG. 17, a common rotation reference signal is input to each of the PLL control units of the units 1 and 2 and when the polygon motor is rotated, the magnetic poles (S pole, S pole, The corresponding output signals are output from the respective Hall elements corresponding to the (N pole), and the respective mirror surfaces of the rotary polygon mirror corresponding to the output signals are as illustrated. The relationship between the output signal of the Hall element and each mirror surface is determined by removing the mirror member for forming the mirror surface of the rotating polygon mirror, or by changing the mirror surface of the rotating polygon mirror and the magnetic poles (S pole, This does not change unless the positional relationship with the (N pole) is changed.

When each of the PLL control units performs PLL control for matching the phases of the rotation reference signal and the output signal from the Hall element as shown by the arrow in FIG. 17, each rotating polygon mirror is rotated stably. However, as shown by the reference numeral E in FIG. 18, the mirror surfaces of the unit 1 and the unit 2 do not have the same orientation, and the surface phases do not match. Will happen. The discrepancy between the surface phases is caused by the fact that the magnitude of the displacement in the rotation direction of the magnetic poles (S-pole, N-pole) as the object to be detected on the rotor with respect to the mirror surface of the rotating polygon mirror is different between the units 1 and It is different. When the surface phases do not match, the phase of the output signal (detector pulse signal) of the light beam sensor also does not match, as indicated by reference numeral D in FIG.

It is to be noted that the inconsistency of the surface phases is solved by adjusting the magnitude of the positional deviation of the object to be detected attached to the rotor with respect to the mirror surface of the rotary polygon mirror between the rotary polygon mirrors. It is considered possible, but if such alignment is performed between units, the cost of the apparatus will increase.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a first object of the present invention is to provide a method of detecting a position of a mirror surface of each rotary polygonal mirror and an object to be detected on the rotary polygonal mirror side which is detected by a rotational position detecting means. An object of the present invention is to provide a light beam scanning device that can make the surface phases of the rotating polygon mirrors coincide with each other even when the positional relationship in the rotating direction between the polygon mirrors varies among the rotating polygon mirrors. A second object of the present invention is to provide an image forming apparatus capable of preventing an image shift in the sub-scanning direction of one scanning pitch or less by using a light beam scanning device capable of making the surface phases of the rotary polygon mirrors coincide with each other. To provide.

[0014]

In order to achieve the above object, the present invention is directed to a rotary polygon mirror for deflecting and scanning a light beam generated by a light beam generating means on an image carrier, and the rotary polygon mirror. Driving means for driving the rotating polygon mirror, a rotating position detecting means for detecting the rotating position of the rotating polygon mirror, and a rotating reference signal and an output signal of the rotating position detecting means so that the rotating polygon mirror rotates at a constant speed. In a light beam scanning apparatus comprising a plurality of sets of rotation drive control means for controlling the driving means, so as to eliminate the surface phase difference of the remaining rotation polygon mirrors with respect to the reference rotation polygon mirror among the plurality of rotation polygon mirrors,
A signal having a phase difference with respect to an output signal of the rotation position detection means is used for the rotation drive control means.

According to a second aspect of the present invention, in the light beam scanning device of the first aspect, a plurality of light beam detecting means for detecting a light beam scanned and deflected by each rotating polygonal mirror at a predetermined position on a scanning path; A time difference calculating means for calculating a time difference between an output signal of the light beam detecting means corresponding to the reference rotating polygonal mirror and an output signal of the light beam detecting means corresponding to each of the remaining rotating polygonal mirrors among the plurality of rotating polygonal mirrors; Phase difference setting means for setting the phase difference based on the time difference.

According to a third aspect of the present invention, in the light beam scanning device of the second aspect, storage means for storing phase information of the signal used for the time difference or the rotation drive control means is provided. It is.

According to a fourth aspect of the present invention, in the light beam scanning device of the second aspect, the setting of the phase difference based on the time difference is performed each time the power is turned on.

According to a fifth aspect of the present invention, in the light beam scanning device of the second aspect, the setting of the phase difference based on the time difference is repeatedly performed at a predetermined timing during standby for image writing.

According to a sixth aspect of the present invention, in the light beam scanning device of the fifth aspect, the setting of the phase difference based on the time difference is performed when the time difference becomes equal to or greater than a specified value. is there.

According to a seventh aspect of the present invention, in the light beam scanning device of the sixth aspect, a prescribed value input means for inputting the prescribed value from outside is provided.

According to an eighth aspect of the present invention, in the light beam scanning device of the sixth aspect, there is provided an image shift amount input means for inputting an image shift amount from outside, and a data converter for converting the image shift amount to the specified value. Means are provided.

According to a ninth aspect of the present invention, in the light beam scanning device according to any one of the second to fifth aspects, data for externally inputting data for determining whether or not to set the phase difference based on the time difference is provided. An input means is provided.

According to a tenth aspect of the present invention, in the light beam scanning device of the ninth aspect, display means for displaying the time difference is provided.

According to an eleventh aspect of the present invention, in the light beam scanning device according to the ninth aspect, a data conversion means for converting the time difference into an image shift amount and a display means for displaying the image shift amount are provided. It is assumed that.

According to a twelfth aspect of the present invention, there is provided a light beam scanning device according to any one of the first to eleventh aspects, an image carrier on which a latent image is formed using the light beam scanning device, and an image carrier on the image carrier. A developing device for developing a latent image, and a transfer device for transferring a superimposed image on the image carrier formed by development by the developing device onto a medium to be transferred. It is. A plurality of sets of the image carrier, the developing device, and the transfer device may be provided corresponding to a plurality of rotary polygon mirrors of the light beam scanning device, but one set is provided so as to be commonly used for each rotary polygon mirror. Is also good. The transfer medium may be a transfer material such as paper to be finally output, or an intermediate transfer member interposed before transfer to the transfer material.

In the light beam scanning device of the first aspect, the rotational position of the rotary polygon mirror is detected by the rotational position detecting means, and based on the output signal of the rotational position detecting means and the rotation reference signal,
The rotation drive control means controls the driving means of each rotary polygon mirror so that the frequency and phase of the output signal match the frequency and phase of the rotation reference signal. A signal having a phase difference with respect to an output signal of the rotation position detecting means is rotated by the rotation drive so as to eliminate a surface phase difference of each of the remaining rotation polygons with respect to a reference rotation polygon among the plurality of rotation polygons. The use of the control means makes the surface phases of the respective polygons coincide with each other when the respective polygons rotate at a constant speed.

The signal used for the rotation drive control means may be a signal obtained by shifting the phase of the output signal itself of the rotation position detection means by the phase difference. A signal having a phase shifted by the phase difference with respect to the output signal may be newly generated, and the generated signal may be used.

According to a second aspect of the present invention, in the light beam scanning apparatus according to the first aspect, the output signal of the light beam detecting means corresponding to the remaining rotary polygon mirror other than the reference rotary polygon mirror and the reference rotary polygon mirror. Is calculated by the time difference calculating means. This time difference is caused by the rotation direction positional relationship between the mirror surface of each rotary polygon mirror and the object to be detected on the rotary polygon mirror side detected by the rotary position detecting means, etc., varied between the rotary polygon mirrors. It corresponds to the surface phase difference between polygon mirrors. Therefore, based on the time difference calculated by the time difference calculating means,
By setting the phase difference of the signal used for the rotation drive control means by the phase difference setting means so that the time difference disappears, the rotation of each rotation polygon mirror when each rotation polygon mirror starts rotating at a constant speed. Make the surface phases coincide with each other.

The output signal of the rotational position detecting means is used as it is for control of the driving means of each rotary polygon mirror prior to detecting the output signal of the light beam detecting means and calculating the time difference between the output signals. Alternatively, a signal whose phase is shifted by a predetermined phase difference from the output signal may be used.

According to a third aspect of the present invention, in the light beam scanning apparatus according to the second aspect, the time difference or phase information of the signal used for the rotation drive control means is stored in a storage means. The time difference or phase information stored in the storage means is retained even when the power is turned off. When the power supply is turned on again, the phase difference set based on the time difference stored in the storage means, or the phase difference set based on the phase information stored in the storage means, is applied to the output signal of the rotational position output means. The signal having the data is used for the rotation drive control means.

According to a fourth aspect of the present invention, in the light beam scanning apparatus according to the second aspect, the setting of the phase difference based on the time difference is performed at every power-on.
After each power supply is turned on, the surface phases of the respective rotating polygon mirrors when the respective rotating polygon mirrors rotate at a constant speed are made to coincide with each other.

According to a fifth aspect of the present invention, in the light beam scanning device according to the second aspect, the setting of the phase difference based on the time difference is repeatedly performed at a predetermined timing at the time of waiting for the image writing, whereby the image writing standby is performed. Inside, when the respective rotating polygon mirrors rotate at a constant speed, the surface phases of the respective rotating polygon mirrors are made to coincide with each other.

According to a sixth aspect of the present invention, in the light beam scanning apparatus according to the fifth aspect, the upper limit of the time difference at which an unacceptable image shift in the sub-scanning direction of one scanning pitch or less starts to occur is set as a predetermined value in advance. In addition, the setting of the phase difference based on the time difference is performed at a timing when the time difference becomes equal to or more than the specified value.

According to a seventh aspect of the present invention, in the light beam scanning apparatus according to the sixth aspect, it is determined whether or not a user sets the phase difference based on the time difference using a specified value input means. Is input from outside.

In the light beam scanning device according to claim 8, in the light beam scanning device according to claim 6, a user inputs an image shift amount from outside using an image shift amount input unit, and the input image is input by a data conversion unit. The shift amount is converted to the specified value used for determining whether to set the phase difference.

According to a ninth aspect of the present invention, in the light beam scanning apparatus according to any one of the second to fifth aspects, the user sets the phase difference based on the time difference using data input means. Input data to determine whether or not to do so from outside.

According to a tenth aspect of the present invention, in the light beam scanning device of the ninth aspect, the time difference is displayed by a display means. The user looks at the displayed time difference and determines whether to set the phase difference based on the time difference.

In the light beam scanning device according to the eleventh aspect, in the light beam scanning device according to the ninth aspect, the calculated time difference is converted into an image shift amount by a data conversion unit, and the converted image shift amount is displayed by a display unit. I do. The user looks at the displayed image shift amount and determines whether or not to set the phase difference based on the time difference.

According to a twelfth aspect of the present invention, a latent image is formed on an image carrier by using the light beam scanning device according to any one of the first to eleventh aspects, wherein the surface phases of the rotary polygon mirrors are matched with each other. Then, the latent image is developed by a developing device and superimposed on a transfer medium by a transfer device.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a light beam scanning device used in a four-drum type color laser beam printer (hereinafter referred to as a "color printer") as an image forming apparatus will be described below.

[Embodiment 1] FIG. 1 is a perspective view showing a schematic configuration of a color printer according to the present embodiment. This color printer includes four sets of image forming units and the like for forming a color image in which images of four colors (yellow, magenta, cyan, and black) are superimposed. Each image forming unit is
A photosensitive drum 1 as an image carrier, a charging charger 2,
A light beam scanning unit 3, a developing unit 4, and a transfer charger 5 are provided.
Exposure, development, and transfer processes are performed, and the first color image is transferred onto the recording paper 7 conveyed in the direction of arrow A by the transfer belt 6, and then the second color, third color, and fourth color images are transferred in that order. Accordingly, a color image in which the four color images are superimposed can be formed on the recording paper 7.

FIG. 2 shows the laser beam scanning unit 3
FIG. 3 is a block diagram of a control system of the light beam scanning device. Here, the numerical values in parentheses of the reference numerals in FIG. 3 indicate the number of sets of laser scanning units to which the constituent elements belong. Although the color printer according to the present embodiment includes four laser beam scanning units, the configuration and control of the two laser beam scanning units will be described below for the sake of convenience.

Each laser scanning unit 3 of the light beam scanning device of the present color printer includes a laser light source (LD) 8 as a light beam generating means, and a rotation for deflecting and scanning the laser beam from the laser light source 8 to the photosensitive drum 1. A polygon mirror 9 as a polygon mirror, a polygon motor 10 as driving means for driving the polygon mirror 9 to rotate in the direction of arrow B,
The Hall element 11 as a rotation position detecting means for detecting the rotation position of the polygon mirror 9, and the polygon mirror 9 rotates at a constant speed based on a rotation reference signal generated by a rotation reference signal generating means described later and an output signal of the Hall element 11. A motor driver (PLL control unit) 12 as a rotation drive control unit that controls the polygon motor 10 so as to perform the operation, and a laser beam as a light beam detection unit that detects a laser beam scanned and deflected by the polygon mirror 9 at a scanning start position. A detector 13 and a controller 14 or the like as light beam generation control means for controlling the laser light source 8 based on an output signal of the laser beam detector 13 are provided.

The laser beam from each of the laser light sources 8 is turned on / off by a laser driver (not shown) operating based on the color-separated image information.
Polygon mirror 9 rotated and driven by polygon motor 10
And irradiates the surface of the photosensitive drum 1 through a lens. Further, a beam detecting mirror 13a is provided at an end (scanning start position) of a scanning range of the laser beam from the laser light source 8 (LD scanning range in FIG. 2), and the laser beam reflected by the mirror 13a is provided. The detector pulse signal D detected by the laser beam detector 13
The signals are output to the controller 14 as P1 and DP2.

The Hall element 11 for detecting the rotational position of the polygon mirror 9 is provided with a magnetic pole (S pole / N pole) as a detected part provided on a part of a rotating body (rotor) 9a which rotates together with the polygon mirror 9. ) Is detected, and when the polygon mirror 9 and the rotor 9a rotate, the magnetic field strength detected by the Hall element 11 changes, and an output signal corresponding to the change in the magnetic field strength is output by the Hall element. 11 to the controller 14. From the controller 14, the output signal of the Hall element 11 itself,
Alternatively, a signal having a phase difference with respect to the output signal (hereinafter, referred to as “dummy output signal”) is output to the motor driver (PLL control unit) 12. These output signals and dummy output signals are repetitive pulse signals that are turned ON / OFF at a frequency corresponding to the rotation speed of the polygon mirror 9.

The light beam scanning device according to the present embodiment
A rotation reference signal PC commonly used for a motor driver (PLL control unit) 12 that drives each polygon mirror 9 to rotate.
A rotation reference signal generator 15 for generating LK is provided, and the controller 14 is used as control means of the rotation reference signal generator 15. In addition to controlling the laser light source 8, the controller 14 is also used for calculating a time difference between detector pulse signals, which will be described later, and setting a phase difference based on the time difference when generating the dummy output signal. .

When a color image is formed by a color printer equipped with the light beam scanning device having the above-described configuration, images formed independently for each color of yellow, magenta, cyan, and black are superimposed on exact positions on recording paper. Need to match. In order to superimpose the image of each color on the accurate position on the recording paper, the writing start position in the main scanning direction and the sub-scanning direction by the laser beam corresponding to each color on the photosensitive drum 1 must be accurately adjusted. . As for the adjustment in the main scanning direction, the laser beam detector 13 always detects the scanning start position of the laser beam, and adjusts the writing timing of the recording image data for each color so that the light beam scanning device in the printer and the light beam scanning device can be adjusted. Even if the relative positional relationship with the body drum 1 does not completely match for each color, color misregistration does not occur when images of each color are superimposed. On the other hand, in the adjustment in the sub-scanning direction, the photoconductor pitch (L in FIG. 1) is maintained at an integral multiple of the scanning pitch, the laser scanning start position is always detected by the laser beam detector 13, and the recording image data is written. By controlling the timing by the controller 14, each polygon mirror is driven based on the rotation reference signal of the same scanning frequency to form an image of each color, and no color shift occurs when the images of each color are superimposed. Like that.

However, if the rotation reference signals having the same phase are used for the rotation driving of each polygon mirror 9 in controlling the laser beam scanning, the rotation reference signals are not more than one scanning pitch in the sub-scanning direction (84 when the image resolution is 300 dpi). .67μ
m or less). Therefore, in the light beam scanning device of the present embodiment, the rotation phases of the polygon motors 10 that rotate the respective polygon mirrors 9 are controlled as described below so that the surface phases of the respective polygon mirrors 9 match each other. The color shift is corrected.

FIG. 4 is a flowchart of the rotation phase control of the polygon motor in this embodiment. In FIG. 4, when the power of the color printer is turned on, the rotation reference signal PCLK is output from the rotation reference signal generator 15 and supplied to the motor drivers 12 (1) and (2) (step 1). In the rotation reference signal generator 15, the controller 14 can change the frequency and the like of the rotation reference signal. When the motor ON signal is output from the controller 14 to the motor drivers 12 (1) and (2) and the polygon motors 10 (1) and (2) rotate, the output signal from the Hall element 11 (1) of the laser beam scanning unit 1 is output. H1
CLK, Hall element 11 of laser beam scanning unit 2
The output signal H2CLK is output from (2) and input to the controller 14 (steps 2 to 4).

FIG. 5 shows the state immediately after the rotation of the motor (before PLL control).
3 shows the timing of each signal. Also, in FIG.
The positional relationship between the magnetic poles of the rotor 9a and the mirror surface of the polygon mirror 9 is also shown. In this embodiment, since six polygon mirrors 9 are used, reference numerals 1 to 6 in the drawing indicate mirror surfaces. Since the rotor 9a has two poles, an S pole and an N pole, one cycle of the output signal output from the Hall element 11 corresponds to one rotation of the polygon motor 9.

Next, in the controller 14, the output signal H1CLK is sent to the motor driver 12 (1), and the output signal H2CLK is sent to the motor driver 12 (2). Each motor driver 12 (1), (2) sends a PLL. Control is performed, the polygon motors 10 (1) and (2) rotate at a constant speed, and a motor lock signal is detected (steps 5 and 5).
6). Then, the laser light source 8 is turned on to emit a laser beam. In this case, only when the laser beam reflected by the polygon mirror 9 passes through the beam detector mirror 13a shown in FIG. The laser light source 8 may be turned on. By turning on the laser light source 8,
Detector pulse signals DP1 and DP2 are output from laser beam detectors 13 (1) and 13 (2) (step 7,
8). Here, since the laser beam scanning unit 1 is used as a reference, the DP with respect to the detector pulse signal DP1
2 is calculated, and the time difference is stored. In particular, in the present embodiment, the time difference is repeatedly calculated a predetermined number of times, stored, and the average value A is calculated (steps 9 to 12). Then, the controller 14 generates a dummy output signal H2CLKA in which the output signal H2CLK is shifted in time (shifted in phase) by the time difference A (step 13).

FIG. 6 shows the timing of each signal after the PLL control. From FIG. 6, the Hall element 11
The output signal H1CLK1 of (1) and the Hall element 11 (1)
Output signal H2CLK1 is in phase. The time difference between the output signals DP1 and DP2 of the laser beam detectors 13 (1) and 13 (2) is A, and the mirror surfaces of the unit 1 and the unit 2 are shifted by that amount.
FIG. 7 shows the timing of various signals before the rotation phase control for matching the mirror surfaces between the polygon mirrors 9 and the directions of the mirror surfaces of the units 1 and 2.

Next, in the controller 14, a dummy output signal H2CL generated based on the time difference A corresponding to the surface phase difference of each polygon mirror and the output signal H2CLK.
KA is output to the motor driver 12 (2), and PL is again output.
L control is performed (step 14). Then, the motor lock signal is detected, the polygon motors 10 (1) and (2) rotate at a constant speed, and the rotation phase control ends (step 1).
5).

FIG. 8 shows the timing of various signals after the rotation phase control and the directions of the mirror surfaces of the units 1 and 2. By performing the PLL control again with the dummy output signal H2CLKA, it can be seen that the orientation of the mirror surface is the same. Naturally, laser beam detector 1
3, the time difference between the output signals DP1 and DP2 has disappeared. However, since the polygon motors 10 (1) and (2) also have slight rotation unevenness and it is considered that there are variations in the six mirror surfaces, they do not completely match.

As described above, according to the present embodiment, based on the time difference between the output signals DP1 and DP2 of the laser beam detectors 13 (1) and (2), the reference polygon mirror 9 (1) is set so that the time difference disappears. Polygon mirror 9 (2) other than)
The phase difference when the dummy output signal H2CLKA used for the PLL control is generated is set, and the PLL control is performed using the dummy output signal. Therefore, when the positional relationship in the rotational direction between the mirror surface of each polygon mirror 9 and the corresponding Hall element 11 and the magnetic poles (S-pole, N-pole) as the detected part thereof is different among the polygon mirrors 9. However, it is possible to make the surface phases of the polygon mirrors 9 coincide with each other, and to prevent the occurrence of color shift in the sub-scanning direction of one scanning pitch or less.

Further, according to the present embodiment, the setting of the phase difference based on the time difference between the output signals DP1 and DP2 of the laser beam detectors 13 (1) and (2) is performed every time the power is turned on. Even when the surface phase between the polygon mirrors 9 changes with time each time the power is turned on, the surface phases can be matched with each other to prevent the occurrence of the color shift.

In this embodiment, the detect pulse signal DP1 of another polygon mirror 9 (2) is compared with the detect pulse signal DP1 of the reference polygon mirror 9 (1).
Although only the calculation of the time difference of 2 and the rotation phase control have been described, the same applies to the detect pulse signals DP3 and DP4 of the other polygon mirrors 9 (3) and (4). Further, it is preferable that the number of times n for capturing the time difference between the detect pulse signals is as large as possible. Alternatively, the dummy output signal may be generated based on the center value of a plurality of detect pulse signals instead of the average value A of the time difference. If the time difference does not change much, the dummy output signal is measured only once. The set time difference may be used.

In this embodiment, the unit 1
However, an arbitrary unit may be used as a reference, and the reference unit may be changed using a switch, an operation panel, or the like. Although not specifically described in the present embodiment, it is preferable that the image writing operation is not performed during the rotation phase control and the image writing is in a standby state.

[Embodiment 2] Next, another embodiment of the present invention will be described. The difference from the control of the first embodiment is that, after the power is turned on, the replacement or movement of the laser beam detector 13, the hall element 11, and the polygon motor 9 is checked, and the dummy output signal H2CLKA generated from the time difference A is used. The controller 14 is provided with a memory (not shown) as storage means for storing the above information. The optical system and the control system according to the present embodiment are the same as the optical system (FIG. 2) and the control system (FIG. 3) according to the first embodiment, respectively. The direction shown in FIGS. 5 to 8 is applied as in the first embodiment.

FIG. 9 shows a flowchart of the rotation phase control of the polygon motor in this embodiment. Power supply O
After N, the replacement or movement of the laser beam detector 13, the Hall element 11, and the polygon motor 9 is checked (step 1). The replacement or movement of the laser beam detector 13 or the like can be checked by using a sensor or the like when the laser beam detector 13 or the like is removed or attached, or by an external input device ( Input the presence or absence of replacement from the operation panel.

Here, if at least one of the laser beam detector 13, the Hall element 11 and the polygon motor 9 has been replaced or moved, the control flow is almost the same as that of the first embodiment (steps 2 to 17). However, after generating the dummy output signal H2CLKA, the controller 14
The time difference A used to generate the dummy output signal H2CLKA or the dummy output signal H2CLKA
The control step 15 for storing the phase information is added.

On the other hand, if none of the laser beam detector 13, the hall element 11 and the polygon motor 9 have been replaced or moved, the above-described operation is performed until the output signal is output from each hall element 11 to the controller 14. This is the same as mode 1 (steps 18 to 21). Controller 14 receiving output signal from each Hall element 11
When a signal is output to the motor drivers 12 (1) and (2), the Hall element 11 is provided to the motor driver 12 (1).
The output signal H1CLK from (1) is output as it is, and a dummy output signal H2CLKA is output to the motor driver 12 (2) based on the phase information such as the time difference A or the phase difference stored in the memory (step 22). . afterwards,
The motor lock signal is detected, and the rotation phase control ends (step 23).

In particular, according to the present embodiment, the power supply is turned off.
Thereafter, when the power is turned on again, the dummy output signal H2CLKA is generated based on the time difference A or the phase information stored in the memory of the controller 14, so that the time difference A is not calculated. Can be shortened.

In particular, according to the present embodiment, when the laser beam detector 13, the Hall element 11, the polygon mirror 9, etc. are not moved or replaced, the time difference A or the phase information stored in the memory of the controller 14 is not used. Can be used to generate the dummy output signal H2CLKA.
It is possible to simplify the control for matching the surface phases between the two.

[Embodiment 3] Next, still another embodiment of the present invention will be described. The optical system and the control system according to the present embodiment are respectively the optical system according to the first embodiment (FIG. 2).
3 and the timing of various signals and the direction of the mirror surface of the polygon mirror are the same as those shown in FIGS. First
FIG. 0 shows a control flow. In the control flow according to the present embodiment, the same rotation phase control as the control flow shown in FIG.
This embodiment is different from the first embodiment in that the rotation phase control is continuously performed in the same manner during the image writing standby after the rotation phase control.

FIG. 10 shows a part of the control flow in the present embodiment, which is a control flow after the motor lock signal is detected by executing the control flow in FIG. 4 of the first embodiment. When the phase control is completed and the motor lock signal is detected, a ready state, that is, an image writing standby state is set (steps 15 and 16). During this image writing standby, the laser beam is
The laser light source (LD) 8 is turned on when passing the portion a, the detect pulse signals DP1 and DP2 are detected, and the average value B of the time difference is calculated in the same manner as in the first embodiment (steps 17 to 21). . If the image is being written, the control flow of steps 17 to 21 is repeated. If the image is not being written, the dummy output signal H2C
The LKA further generates a dummy output signal H2CLKAB whose time is shifted (shifted in phase) by the calculated time difference B, and outputs the generated dummy output signal H2CLKAB from the controller 14 to the motor driver 12 (2) (step 23). , 24). When the motor lock signal is detected and the PLL control using the dummy output signal H2CLKAB ends, the detect pulse signals DP1, DP2
Is detected, and the control flow of steps 16 to 25 is repeated.

In particular, according to this embodiment, the setting of the phase difference at the time of generating the dummy output signal based on the time difference B between the output signals DP1 and DP2 of the laser beam detectors 13 (1) and (2) is performed by setting the image writing standby. By repeating the process at a predetermined timing, even when the surface phase between the polygon mirrors 9 changes due to aging, temperature rise, or the like during image writing standby, the surface phases are matched with each other, and the surface phase is not more than one scanning pitch. Color misregistration in the sub-scanning direction can be reduced.

[Embodiment 4] Next, still another embodiment of the present invention will be described. The optical system and the control system in the present embodiment are respectively the optical system of the first embodiment (FIG.
3) and the control system (FIG. 4), and the timings of various signals and the orientation of the mirror surface of the polygon mirror shown in FIGS. 5 to 8 are applied as in the first embodiment. In the control flow according to the present embodiment, after the power lock is detected and the motor lock signal is detected by performing the same phase control as the control flow shown in FIG.
As shown in (1), the average value B of the time difference between the detect pulse signals DP1 and DP2 is calculated during the image writing standby (steps 16 to 21). Then, the calculated average value B is compared with a preset specified value. If the average value B is equal to or larger than the specified value, the rotation phase control is performed in the same manner as in the third embodiment (steps 24 to 26). When the value B is smaller than the specified value, the detection of the detect pulse signals DP1 and DP2 and the calculation of the average value of the time difference are repeated again.

In particular, according to the present embodiment, the phase difference at the time of generating the dummy output signal based on the average value B is set at the timing when the average value B of the time difference becomes equal to or greater than a predetermined value. Accordingly, unnecessary control need not be performed as much as unnecessary setting of the phase difference is not performed.

[Fifth Embodiment] Next, still another embodiment of the present invention will be described. FIG. 12 is a block diagram of a control system in the present embodiment. The control system of the first embodiment is different from the control system of the first embodiment in that an operation panel 16 as a specified value input means is provided so that a user can set the specified value of the fourth embodiment. The optical system according to the present embodiment is the same as the optical system according to the first embodiment.
The optical system (FIG. 2) is the same as that described above, and the timings of various signals and the orientation of the mirror surface of the polygon mirror are the same as those shown in FIGS.

FIG. 13 is a flowchart of the rotation phase control of the polygon motor in this embodiment. The difference from the control flow shown in FIG. 11 of the fourth embodiment is that the user can input a specified value to be compared with the average value B of the time difference from the operation panel 16 and can always change the setting of the specified value (step). 16, 28). The setting of the specified value may be changed at any time from the end of a series of rotation phase controls to the start of the next rotation phase control.

In particular, according to the present embodiment, the user uses the operation panel 16 to determine whether or not to set the phase difference at the time of generating the dummy output signal based on the average value B of the time differences. Since the specified value can be input from the outside, the specified value can be easily changed by the user according to the required image quality.

The above-mentioned specified value may be set based on the amount of color misregistration of the image which is easy for the user to understand. For example, an image is actually output, and the user inputs an allowable color shift amount from the operation panel 16 while viewing the image. Then, the controller 14 converts the color shift amount into a specified value to be compared with the time difference. Data conversion to the specified value can be easily performed based on the image writing density, the linear speed of the photosensitive drum 1, the number of rotations of the polygon motor 9, and the like.

[Embodiment 6] Next, still another embodiment of the present invention will be described. The optical system and the control system according to the present embodiment are respectively the optical system according to the first embodiment (FIG. 2).
And the same as the control system of the fifth embodiment (FIG. 12).
The timings of various signals and the orientation of the mirror surface of the polygon mirror are the same as those shown in FIGS. The control flow in this embodiment performs the same rotation phase control as the control flow shown in FIG. 10 of the third embodiment, but does or does not perform the rotation phase control of the polygon motor 10 for correcting the amount of color misregistration. The difference is that you can choose.

FIG. 14 is a control flow after the motor lock signal is detected after the rotation phase control shown in the control flow of FIG. 4 of the first embodiment. In the control flow of FIG. 14, after the motor lock signal is detected and the READY state is entered, the operation panel 16 selects whether or not to control the rotation phase of the polygon motor 10 for color misregistration correction (step 15). To 17). If the user selects not to perform color misregistration correction, the printer remains in the READY state and waits until printing starts (step 16). on the other hand,
If the color shift correction method is selected, detect pulse signals DP1 and DP2 are detected, and PLL control using the dummy output signal H2CLKAB is performed as in the third embodiment (steps 18 to 25). Then, the PLL control is completed, the motor lock signal is detected, the state becomes READY, and it is possible to select again whether or not to perform color misregistration correction (steps 26, 16, 17).

In particular, according to the present embodiment, it is possible for the user to determine whether or not to set the phase difference at the time of generating the dummy output signal based on the time difference, if necessary, without performing useless control. It has the effect of saving.

[Seventh Embodiment] Next, still another embodiment of the present invention will be described. The optical system and the control system according to the present embodiment are respectively the optical system according to the first embodiment (FIG. 2).
And the same as the control system of the fifth embodiment (FIG. 12).
The timings of various signals and the orientation of the mirror surface of the polygon mirror are the same as those shown in FIGS. The control flow in the present embodiment performs the same rotation phase control as the control flow shown in FIG. 14 of the sixth embodiment, but calculates the time difference B between the detect pulse signals when performing the rotation phase control of the polygon motor 10. The difference is that the value is displayed on the operation panel 16 as a display means, and whether the color misregistration correction is performed or not is selected after checking the value.

FIG. 15 is a control flow after the motor lock signal is detected after the rotation phase control shown in the control flow of FIG. 4 of the first embodiment. In the control flow of FIG. 15, after the motor lock signal is detected and the state becomes the READY state, detection of the detect pulse signals DP1 and DP2 and calculation of the time difference B are performed.
(Steps 15 to 22). If the image is being written, the detection of the detect pulse signals DP1 and DP2 and the calculation of the time difference B are performed again, and the time difference B is displayed (steps 17 to 22). If the image is not being written, the operation panel 16 selects whether or not to control the rotation phase of the polygon motor 10 for color misregistration correction based on the displayed time difference B (step 24). Here, if the user does not select the color shift correction, the state becomes READY,
The control flow of steps 16 to 23 is repeated again. On the other hand, when the color shift correction is selected, the dummy output signal H2CLKA is further shifted by the calculated time difference B (phase is shifted) to generate a dummy output signal H2CLKAB, and the motor driver 12 (2 )
To perform PLL control (steps 25 and 26).
The motor lock signal is detected and the dummy output signal H2CL
When the PLL control using the KAB is completed, the detection pulse signals DP1 and DP2 are detected again, and the control flow of steps 16 to 26 is repeated.

In particular, according to the present embodiment, the operation panel 1
6 The displayed time difference B can be used for determining whether or not the user sets the phase difference when generating the dummy output signal.

In this embodiment, instead of displaying the time difference on the operation panel 16, the time difference may be converted into a color misregistration amount of an image which is easy for the user to display. The conversion of the data into the color shift amount can be easily performed based on the image writing density, the linear speed of the photosensitive drum 1, the rotation speed of the polygon motor 9, and the like.

[Embodiment 8] Next, still another embodiment of the present invention will be described. The optical system and the control system according to the present embodiment are respectively the optical system according to the first embodiment (FIG. 2).
3 and the timing of various signals and the direction of the mirror surface of the polygon mirror are the same as those shown in FIGS.

FIG. 16 is a control flow after the motor lock signal is detected after the rotation phase control shown in the control flow of FIG. 4 of the first embodiment. In the control flow of FIG. 16, when a motor lock signal is detected, a READY state (image writing standby state) is set. In this READY state, detection of the detect pulse signals DP1 and DP2 and calculation of the time difference B are performed (step S1). 17-21). If the image is being written, the detection of the detect pulse signals DP1 and DP2 and the calculation of the time difference B are performed again (steps 17 to 21). On the other hand, if the image is not being written, the controller 14 outputs the dummy output signal H2CLKA to the motor driver 12 (2).
The signal to be output to (2) is changed from the dummy output signal H2CLKA to the output signal H2CLK of the Hall element 11 and the PLL
Control is performed (steps 23 and 24). When the motor lock signal is detected, the detection of the detect pulse signals DP1 and DP2 and the calculation of the time difference are repeated n times, and the average value C of the time difference is calculated. The dummy output signal H2 whose output signal H2CLK of the Hall element 11 (2) is shifted (shifted in phase) by the average value C of the calculated time difference.
CLKC is generated (steps 25 to 30). And
The generated dummy output signal H2CLKC is output from the controller 14 to the motor driver 12 (2), and PLL control is performed using the dummy output signal H2CLKC (step 31). Motor lock signal is detected and READ
The state becomes Y, and the control flow of steps 16 to 32 is repeated again.

In each of the above embodiments, an example is shown in which the light beam scanning apparatus according to the present invention is applied to a four-drum type color printer having four sets of laser scanning units and photosensitive drums. Is applicable not only to the 4-drum system but also to the 2-drum, 3-drum, or 5-drum system. Further, the present invention is also applicable to a photosensitive drum 1 having a plurality of laser scanning units.

In each of the above embodiments, an example in which the light beam scanning device according to the present invention is applied to a color printer has been described. However, the present invention relates to a light beam scanning device used in other image forming apparatuses such as a copying machine and a facsimile. The present invention can also be applied to a beam scanning device.

[0085]

According to any one of the first to eleventh aspects of the present invention, a signal having a phase difference with respect to the output signal of the rotational position detecting means is used for the rotational drive control means, so that a plurality of rotary polygon mirrors Since the surface phase difference of each of the remaining rotating polygons with respect to the reference rotating polygon is eliminated, the rotation direction between the mirror surface of each rotating polygon mirror and the detected object on the rotating polygon mirror side detected by the rotation position detecting means is determined. Even when the positional relationship and the like vary among the rotating polygon mirrors, there is an effect that the surface phases between the rotating polygon mirrors when the rotating polygon mirrors rotate at a constant speed can be matched with each other. .

In particular, according to the second aspect of the present invention, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is used by utilizing the output signal of the light beam detecting means normally used for controlling the light beam in the main scanning direction. Based on the calculated value of the time difference between the signal and the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors, it is possible to set the phase difference of the signal used for the rotation drive control means. is there.

In particular, according to the invention of claim 3, the power supply OF
F, when the power is turned on again, a signal having a phase difference set based on the time difference stored in the storage means or a signal having a phase difference set based on the phase information stored in the storage means is transmitted to the rotation drive control. By using the means, it is possible to shorten the time from power-on to the standby state for image writing as compared to a case where the setting of the phase difference is changed based on the time difference every time the power is turned on. effective. Also, when the light beam detecting means, the rotational position detecting means, the rotating polygon mirror, etc. are not moved or exchanged, the surface phase between the rotating polygon mirrors is unlikely to be shifted, but in such a case, the information is stored in the storage means. Since the signal having a phase set using the time difference or the phase information can be used for the rotation drive control unit, only the amount of the detection of the output signal of the light beam detection unit and the calculation of the time difference are not performed. There is an effect that control for making the surface phases of the rotary polygon mirrors coincide with each other can be simplified.

In particular, according to the fourth aspect of the invention, the phase difference is set based on the time difference every time the power is turned on, so that the surface phase difference between the rotary polygon mirrors becomes longer as the power is turned on. Also has the effect that the surface phases can be matched with each other.

In particular, according to the fifth aspect of the present invention, the setting of the phase difference based on the time difference is repeatedly performed at a predetermined timing at the time of standby for writing the image, so that the surface between the rotating polygon mirrors is standby during the writing of the image. Even when the phase changes due to aging, temperature rise, or the like, there is an effect that the surface phases can be matched with each other.

In particular, according to the invention of claim 6, at the timing when the time difference becomes equal to or more than a predetermined value set as an upper limit time difference at which an image shift in the sub-scanning direction below an unacceptable one scanning pitch starts to occur. By setting the phase difference based on the time difference, there is an effect that unnecessary control is not performed as much as unnecessary phase difference is not set.

In particular, according to the invention of claim 7, the user can externally input the specified value used for determining whether or not to set the phase difference based on the time difference, using the specified value input means. Therefore, there is an effect that the specified value can be easily changed according to the image quality required by the user.

In particular, according to the invention of claim 8, there is an effect that the user can input an image shift amount which is easy for the user to understand in order to set the specified value.

In particular, according to the ninth aspect of the present invention, it is possible to determine whether or not the user sets the phase difference based on the time difference as necessary, so that unnecessary control is not performed. There is.

In particular, according to the tenth aspect, there is an effect that the time difference displayed on the display means can be used for determining whether or not the user sets the phase difference.

In particular, according to the eleventh aspect of the invention, there is an effect that an image shift amount that is easy for the user to understand can be used as a criterion for determining whether or not to set the phase difference.

According to the twelfth aspect of the present invention, the positional relationship in the rotating direction between the mirror surface of each rotating polygon mirror and the object to be detected on the rotating polygon mirror side detected by the rotating position detecting means is determined by each rotating polygon mirror. Even if there is a variation between them, a latent image is formed on the image carrier using a light beam scanning device in which the surface phases of the rotating polygon mirrors are made to coincide with each other, and the latent image is developed by a developing device to transfer the latent image. This makes it possible to superimpose images on the transfer medium, and to prevent the occurrence of image shift in the sub-scanning direction of one scanning pitch or less between images.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a color printer including a laser beam scanning unit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an optical system of the laser beam scanning unit.

FIG. 3 is a block diagram of a control system of the laser beam scanning device.

FIG. 4 is a flowchart of rotation phase control in the laser beam scanning device.

FIG. 5 is a time chart showing a temporal relationship between a rotation reference signal PCLK immediately after polygon motor rotation and an output signal of each Hall element in the control system.

FIG. 6 is a time chart showing a temporal relationship between a rotation reference signal PCLK after PLL control and an output signal of each Hall element in the control system.

FIG. 7 is a rotation reference signal P before phase control in the control system.
6 is a time chart showing a temporal relationship among CLK, a detect pulse signal, and an output signal of each Hall element.

FIG. 8 is a rotation reference signal P after phase control in the control system.
6 is a time chart showing a temporal relationship among CLK, a detect pulse signal, and an output signal of each Hall element.

FIG. 9 is a flowchart of rotation phase control in a light beam scanning device according to another embodiment.

FIG. 10 is a flowchart of rotational phase control in a light beam scanning device according to still another embodiment.

FIG. 11 is a flowchart of rotation phase control in a light beam scanning device according to still another embodiment.

FIG. 12 is a block diagram of a control system of a light beam scanning device according to still another embodiment.

FIG. 13 is a flowchart of rotation phase control in the light beam scanning device.

FIG. 14 is a flowchart of rotation phase control in a light beam scanning device according to still another embodiment.

FIG. 15 is a flowchart of rotation phase control in a light beam scanning device according to still another embodiment.

FIG. 16 is a flowchart of rotation phase control in a light beam scanning device according to still another embodiment.

FIG. 17 shows a rotation reference signal P before phase control in a conventional example.
6 is a time chart showing a temporal relationship among CLK, a detect pulse signal, and an output signal of each Hall element.

FIG. 18 shows a rotation reference signal P after phase control in a conventional example.
6 is a time chart showing a temporal relationship among CLK, a detect pulse signal, and an output signal of each Hall element.

[Description of Signs] 1 Photoconductor drum 3 Light beam scanning unit 8 Laser light source 9 Polygon mirror 9a Rotor 10 Polygon motor 11 Hall element 12 Motor driver 13 Laser beam detector 14 Controller 15 Rotation reference signal generator 16 Operation panel

Claims (12)

[Claims] A rotating polygon mirror for deflecting and scanning a light beam generated by a light beam generating means on an image carrier; a driving means for rotating the rotating polygon mirror; and a rotation detecting a rotation position of the rotating polygon mirror. Light beam scanning comprising a plurality of sets of position detecting means and a plurality of sets of rotational drive control means for controlling the driving means such that the rotary polygon mirror rotates at a constant speed based on a rotation reference signal and an output signal of the rotational position detecting means. In the apparatus, a signal having a phase difference with respect to an output signal of the rotation position detecting means may be rotated so as to eliminate a surface phase difference of each of the remaining rotation polygons with respect to a reference rotation polygon among the plurality of rotation polygons. A light beam scanning device characterized by being used for drive control means. 2. The light beam scanning device according to claim 1, wherein a plurality of light beam detecting means for detecting a light beam scanned and deflected by each rotating polygon mirror at a predetermined position on a scanning path, and said plurality of rotating polygon mirrors. Time difference calculating means for calculating a time difference between the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror and the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors, based on the time difference And a phase difference setting means for setting the phase difference. 3. The light beam scanning device according to claim 2, further comprising storage means for storing phase information of said signal used for said time difference or said rotation drive control means. 4. The light beam scanning device according to claim 2, wherein the setting of the phase difference based on the time difference is performed each time the power is turned on. 5. The light beam scanning device according to claim 2, wherein the setting of the phase difference based on the time difference is repeated at a predetermined timing during standby for image writing. 6. The light beam scanning device according to claim 5, wherein the setting of the phase difference based on the time difference is performed when the time difference becomes a specified value or more. 7. The light beam scanning device according to claim 6, further comprising a specified value input means for externally inputting said specified value. 8. The light beam scanning device according to claim 6, further comprising: an image shift amount input means for inputting an image shift amount from outside; and a data converting means for converting the image shift amount to the specified value. A light beam scanning device characterized by the above-mentioned. 9. The light beam scanning device according to claim 2, further comprising: data input means for externally inputting data for determining whether to set the phase difference based on the time difference. A light beam scanning device characterized by the above-mentioned. 10. The light beam scanning device according to claim 9, further comprising display means for displaying the time difference. 11. The light beam scanning device according to claim 9, further comprising: data conversion means for converting the time difference into an image shift amount; and display means for displaying the image shift amount. apparatus. 12. A light beam scanning device according to claim 1, an image carrier on which a latent image is formed using said light beam scanning device, and a latent image on said image carrier is developed. An image forming apparatus comprising: a developing device; and a transfer device configured to transfer a superimposed image on the image carrier formed by development by the developing device onto a medium to be transferred.