JP3452166B2 - Light beam scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used for an image forming apparatus (including a color image forming apparatus) such as a copying machine, a facsimile, a printer, a printing machine,
More specifically, the present invention relates to the control of the rotational phase between the rotary polygon mirrors in a light beam scanning device having a plurality of rotary polygon mirrors.

[0002]

2. Description of the Related Art Conventionally, as a light beam scanning device used in an image forming apparatus such as a copying machine, a facsimile machine, a printer, a printing machine or the like, a light beam generating means and a light beam generated by the light beam generating means are used as an image carrier. Based on a rotary polygonal mirror for deflection scanning, a driving unit for rotationally driving the rotary polygonal mirror, a rotary position detecting unit for detecting a rotary position of the rotary polygonal mirror, a rotation reference signal and an output signal of the rotary position detecting unit. And a plurality of sets of rotation drive control means for controlling the drive means so that the rotary polygon mirror rotates at a constant speed, and a rotation reference signal generator for generating the rotation reference signal corresponding to each rotary polygon mirror. Those equipped with means are known.

In the light beam scanning device having the above structure,
Based on each rotation reference signal generated by the rotation reference signal generation means and the output signal of each rotation position detection means, each drive means is controlled so that each rotary polygon mirror rotates at a constant speed. And
In an image forming apparatus equipped with this light beam scanning device, an independent latent image is formed on each corresponding image carrier by the light beam deflected and scanned by each rotary polygon mirror, and each latent image is developed. Are superposed on the recording medium and transferred. Here, in order to superimpose each image on the accurate position on the recording medium, the main scanning direction (light beam scanning direction) and the sub-scanning direction (movement direction of the image carrier surface) of each image on the image carrier The image formation start position in () must be adjusted accurately.

In the main scanning direction, for example, a light beam is detected at a predetermined position on the scanning path, and the writing timing of each scanning line of the image is adjusted based on the detection result, so that each light beam scanning device Even if the initial mounting angles of the rotary polygon mirrors with respect to the image carrier, that is, the surface phases of the rotary polygon mirrors do not completely match each other, it is possible to prevent the occurrence of image shift in the main scanning direction.

On the other hand, in the sub-scanning direction, when a plurality of image carriers are provided corresponding to, for example, a plurality of rotary polygon mirrors, the interval (pitch) between the image carriers is set to an integral multiple of the scanning pitch. Then, the timing of starting writing the image is adjusted by the time unit required for one light beam scanning, and the rotary polygon mirror is rotationally driven based on the rotation reference signal of the same frequency to write the image. It is possible to prevent the occurrence of image shift in the sub-scanning direction that is larger than one scanning pitch.

However, even when the image writing start timing is adjusted in the time unit required for the one-time light beam scanning, if the surface phases of the respective rotary polygon mirrors do not completely match each other, 1 Scanning pitch or less (image resolution 3
In the case of 00 dpi, there is a problem that an image shift of 84.67 μm or less in the sub-scanning direction occurs. This image shift causes a problem of color shift when a color image is formed.

Therefore, conventionally, in order to prevent the image shift in the sub-scanning direction of 1 scanning pitch or less, there is known one in which the rotational phase between the rotary polygon mirrors is controlled as follows.

For example, in Japanese Unexamined Patent Publication No. 64-73369, as the rotation reference signal generating means for generating a reference frequency signal as the rotation reference signal for each of the PLL control means as the rotation drive control means. And a horizontal synchronization signal output timing output from each synchronization sensor remaining in synchronism with the output of the horizontal synchronization signal as the output signal output from the reference frequency signal generation means and one synchronization sensor as the light beam detection means. Timing measuring means for measuring the difference based on the reference frequency signal, and adjusting the phase of the reference frequency signal supplied to the PLL control means on the basis of the horizontal synchronization signal output timing difference measured by the timing measuring means. An apparatus including a phase adjusting means is disclosed.

According to this apparatus, one P based on the reference frequency signal generated from the reference frequency signal generating means.
The LL control means starts the rotation speed control of the rotating polyhedron (rotating polygonal mirror). When the synchronization sensor generates a horizontal synchronization signal by receiving a laser beam deflected by a rotating polyhedron rotating at a constant speed, the timing measuring means remains in synchronization with the output of the horizontal synchronization signal output from one synchronization sensor. The horizontal sync signal output timing difference output from each sync sensor is measured based on the reference frequency signal. And
The phase adjusting means adjusts the phase of the reference frequency signal supplied to the PLL controlling means based on the measured difference in the output timing of each horizontal synchronizing signal. As a result, the phase shift can be finely adjusted within the pixel unit distance, and the top scan line shift of the laser beam on each photosensitive drum (image carrier) can be set to the minimum.

Further, for example, in Japanese Unexamined Patent Publication No. 2-170110, a detecting means for receiving each light beam deflected by each rotating polygonal mirror and detecting the phase difference between the beams, and this detecting means are used. On the basis of the phase difference, the rotational phase angle of the driving means for rotating each rotary polygon mirror at a constant speed so as to cancel the phase angle difference between at least one rotary polygon mirror and the remaining rotary polygon mirrors. There is disclosed a light beam scanning device including a phase control unit that is controlled independently of a mirror.

According to this apparatus, when each rotary polygon mirror is started by each drive means and reaches a constant speed rotation, the detection means receives each light beam deflected by each rotary polygon mirror and receives each light beam. Of the phase difference is detected, and the phase difference information is sent to the phase control means. The phase control means individually adjusts the rotational phase angles of the respective driving means so that the phase difference between the at least one rotary polygon mirror and the remaining rotary polygon mirrors is canceled based on the detected phase difference, and one rotary polygon surface. It is possible to make the writing positions of the respective light beams deflected and scanned from the respective rotating polygon mirrors on the image carrier coincide with each other by controlling the light beams so as to be subordinate to the mirrors.

Further, Japanese Patent Laid-Open No. 2-170110 discloses the following two-beam system embodiment. The rotation phase synchronization control device that also serves as the detection means and the phase control means is the first as the light beam detection means.
A first beam detect pulse signal, which is an output signal from the laser beam detector, and a second signal, which is an output signal from a second laser beam detector that also serves as a light beam detecting means.
When the beam detect pulse signal of is transmitted with a phase difference, the phase difference is measured by a timing means such as an internal counter circuit, and a plurality of reference signal generators serving as the rotation reference signal generating means output the phase difference. Of the reference signals, a second phase synchronization control unit as a rotation drive control unit that controls the rotation drive of the second rotary polygon mirror by selecting a reference signal that generates a phase close to the measured phase difference with a selection switch. Send to. As a result, the first and second motors as the driving means use the reference signal for generating the measured phase difference, the second phase synchronization controller and the first phase synchronization controller.
Phase synchronization control is performed by the first phase synchronization control unit that controls the rotational drive of the rotating polygon mirror, and the subsequent first and second beam detect pulse signals have substantially the same phase.
And the beam reflecting surfaces of the second rotating polygon mirror have the same phase.
Therefore, the image writing positions by the respective light beams deflected and scanned from the first and second rotary polygon mirrors onto the photosensitive drum as the image carrier become coincident.

Further, for example, in Japanese Unexamined Patent Publication No. 5-227383, a reference writing position detection signal from a scanner motor, which is a driving means of a rotating polygon mirror serving as a reference, and a writing position detection signal from the scanner motor of the remaining rotating polygon mirrors. , Is taken into a microprocessor as a determination means, to determine the time shift of the other write position detection signal with respect to the reference write position detection signal, based on the determination result, to the remaining rotary polygon mirror scanner motor, It is disclosed that a phase control signal for increasing or decreasing the rotation speed of the motor is supplied. With this configuration, the writing position by the remaining rotary polygon mirror is made to coincide with the writing position by the rotary polygon mirror serving as the reference, and the positional deviation in the sub-scanning direction is corrected.

[0014]

However, the rotary polygon mirror used in the conventional apparatus for controlling the phase of rotation of each of the rotary polygon mirrors causes a slight rotation unevenness due to the drive unevenness of the driving means. is doing. This uneven rotation tends to increase due to temperature rise and deterioration over time in the drive unit and the rotation drive control unit that controls the drive unit. Further, the length in the rotation direction of the light reflecting surface formed on the rotary polygon mirror also varies slightly. When there is such uneven rotation of the rotating polygon mirror or variation in the length of the light reflecting surface, the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror and the light beam detecting means of the remaining rotating polygon mirrors are detected. It is considered that the time difference from the output signal also varies.

Further, in the phase control of the conventional device, the image writing position by each of the remaining rotary polygon mirrors is controlled based on the light beam detection signal corresponding to the reference rotary polygon mirror among the plurality of rotary polygon mirrors. By controlling the light beam generating means in this manner, the phase is controlled so that the image writing position by the rotary polygon mirror as the reference coincides with the image writing position by each of the remaining rotary polygon mirrors. For example, when the output signals from the light beam detection signals corresponding to the reference rotating polygon mirror are detected a predetermined number of times, the light beam generating means is controlled so as to start the image writing by the remaining rotating polygon mirror. Therefore, when the time difference between the output signals of the light beam detecting means is varied as described above during the phase control such as the image writing operation period, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is changed. The time until the output signal of the light beam detecting means corresponding to the remaining rotary polygon mirror after receiving is suddenly changed by the time close to the cycle of this output signal, and the image in the sub-scanning direction close to one scanning pitch is obtained. Misalignment may occur suddenly.

This image shift in the sub-scanning direction is shown in FIG.
A specific example of the time chart of the output signal of the light beam detecting means before and after the phase control shown in (a) and (b) will be described. In this specific example, two sets of laser scanning units including a laser as a light beam generating means and a rotating polygon mirror are provided. When the laser is turned on and the rotating polygon mirror rotates at a constant speed, FIG. As described above, the output signals from the light beam detecting means corresponding to the respective rotary polygon mirrors (in the above-mentioned conventional example, referred to as a write start position detection signal, a horizontal synchronizing signal or a detector pulse signal) DP1, D.
P2 is output. Here, the output signal DP1 is used as a reference and the time difference (timing difference) of the other output signal DP2 with respect to it is measured.
Assuming that the time difference of the other output signal DP2 with respect to 1 fluctuates by twice as much as T4 as shown by the chain line in the figure, the measured time difference is T1 as shown in FIG. When the conventional phase control based on the time difference T1 is performed under such conditions, the time chart of each output signal is as shown in FIG. After this phase control, the time difference of the other output signal DP2 with respect to the reference output signal DP1 changes by twice as much as T4. Therefore, if the output signal DP2 is at the position of b, for example, two sets of laser scanning are performed. The direction (plane phase) of the light reflecting surface of the rotary polygon mirror of the unit is matched, and an image without image shift can be obtained. When the output signal DP2 changes to the position c, another output signal D with respect to the reference output signal DP1 is output.
The time difference of P2 is shifted by T4, and the image shift is caused by that amount. When the output signal DP2 fluctuates to the position of a, the direction (plane phase) of the light reflecting surface of the rotary polygon mirror is shifted by T4 as in the case of shifting to the position of c, but the output The change occurs only for a time close to the signal cycle, and an image shift close to one scanning pitch (color shift when a color image is formed) suddenly occurs. To be more precise,
Image shift (color shift) occurs for (1 line writing time-T4).

The present invention has been made in view of the above problems, and an object thereof is a light beam scanning device which performs phase control for adjusting rotational phases of respective rotary polygon mirrors so as to substantially match each other at a predetermined timing. The image shift amount due to the rotation phase difference of each rotary polygon mirror is reduced as much as possible, and the image shift in the sub-scanning direction suddenly occurs due to uneven rotation of the rotary polygon mirror during the period in which the phase control is not performed. It is an object of the present invention to provide a light beam scanning device capable of preventing the above.

[0018]

In order to achieve the above-mentioned object, the invention of claim 1 provides a light beam generating means and a rotary polygonal surface for deflecting and scanning the light beam generated by the light beam generating means onto an image carrier. A mirror, a driving means for rotationally driving the rotary polygonal mirror, a rotary position detecting means for detecting a rotary position of the rotary polygonal mirror, and the rotary polygonal mirror based on a rotation reference signal and an output signal of the rotary position detecting means. A plurality of sets of rotation drive control means for controlling the drive means so that they rotate at a constant speed, and light beam detection means for detecting the light beam deflected and scanned by the rotary polygon mirror at a predetermined position on the scanning path,
Rotation reference signal generating means for generating the rotation reference signal corresponding to each of the rotating polygon mirrors, output signals of light beam detecting means corresponding to the reference rotating polygon mirror among the plurality of rotating polygon mirrors, and the remaining The time difference between the output signal of the light beam detecting means corresponding to the rotating polygon mirror is calculated, and based on the time difference, the rotational phases of the remaining rotating polygon mirrors substantially match the reference rotating polygon mirror. Phase control means for controlling the rotation reference signal generating means, and start the light beam scanning in each main scanning direction based on the output signal of each light beam detection means, and the light corresponding to the reference rotating polygon mirror. Based on the output signal of the beam detection means, the light beam generation means is controlled so as to start the image writing in the sub-scanning direction by the light beam deflectively scanned by each of the remaining rotary polygon mirrors. In the light beam scanning device including the light beam generation control means, the light beam detection means corresponding to each of the remaining rotary polygon mirrors responds to the output signal of the light beam detection means corresponding to the reference rotary polygon mirror. The rotation reference signal generating means is controlled so that the output signal is always output first.

According to a second aspect of the present invention, in the light beam scanning device according to the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon faces immediately after that is output. Calculating the time difference until the output signal of the light beam detecting means corresponding to the mirror is output a plurality of times, and controlling the rotation reference signal generating means based on the maximum time difference which is the maximum value of the plurality of time differences. It is characterized by.

According to a third aspect of the present invention, in the light beam scanning device according to the second aspect, the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output immediately after the output signal is output during the image writing standby. The time difference until the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors is calculated in a certain cycle, and when the time difference becomes larger than a predetermined time difference, the time difference at that time It is characterized in that the phase control is performed based on the maximum value of.

According to a fourth aspect of the present invention, in the light beam scanning device according to the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon surfaces immediately after that. The time difference until the output signal of the light beam detection means corresponding to the mirror is output is calculated a plurality of times, the fluctuation range is obtained from the plurality of time differences, and the fluctuation range is added to any one of the plurality of time differences. The rotation reference signal generating means is controlled based on the added value.

According to a fifth aspect of the present invention, in the light beam scanning device according to the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon faces immediately after that. The time difference until the output signal of the light beam detection means corresponding to the mirror is output is calculated, and based on the added value obtained by adding the fluctuation range of the time difference previously measured and stored to the time difference, the rotation reference It is characterized by controlling the signal generating means.

According to a sixth aspect of the present invention, in the light beam scanning apparatus according to the fourth or fifth aspect, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output during the image writing standby, Immediately after calculating the time difference until the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirror at a certain cycle a plurality of times, from any one of the plurality of time differences or a plurality of time differences thereof. The fluctuation range obtained is
When it becomes larger than a predetermined time difference or a fluctuation range used for the previous phase control, the phase control is performed based on the time difference or fluctuation range at that time.

According to a seventh aspect of the present invention, in the light beam scanning device according to the fourth or fifth aspect, wherein the time difference is calculated a plurality of times, the minimum value of the plurality of time differences is used as the time difference used for the phase control. To do.

According to an eighth aspect of the present invention, in the light beam scanning device according to the first aspect, the phase control based on the time difference is not performed during the image writing operation, and the phase control based on the time difference is performed. During the period, the image writing operation is prohibited and the image writing standby state is set. (Hereafter, margin)

In the first to eighth aspects of the present invention, the light beams generated by the respective light beam generating means are deflected and scanned on the corresponding image carriers by the respective rotary polygon mirrors which are rotationally driven by the respective driving means. Also, by each rotational position detection means,
Detecting the rotational position of each of the rotary polygon mirrors, by the rotation drive control means, based on the rotation reference signal generated by the rotation reference signal generating means and the output signal of each rotation position detecting means,
The driving means are controlled so that the frequency and phase of the output signal match the frequency and phase of the rotation reference signal so that the rotary polygon mirrors rotate at a constant speed. Further, each light beam detection means detects the light beam scanned and deflected by each rotating polygon mirror at a predetermined position on each scanning path, and the light beam generation control means controls the light beam generation means to control each light beam. The light beam scanning in each main scanning direction is started based on the output signal of the beam detection means, and the remaining rotary polygon mirrors are deflected based on the output signal of the light beam detection means corresponding to the reference rotary polygon mirror. By starting the image writing in the sub-scanning direction by the scanning light beam, the writing start position of the image in the main scanning direction is adjusted to a predetermined position, and the writing start position of the image in the sub-scanning direction is performed with an accuracy of one scanning pitch. Align it in place. Further, the phase control means controls the rotation reference signal generation means to correspond to the output signals of the light beam detection means corresponding to the reference rotation polygon among the plurality of rotation polygons and the remaining rotation polygons. By calculating the time difference between the output signal of the light beam detecting means, and based on the time difference, the rotational phase of each of the remaining rotary polygon mirrors is substantially matched with the reference rotary polygon mirror, thereby performing sub-scanning. The writing start position of the image in the direction is adjusted to a predetermined position with an accuracy of one scanning pitch or less.

Then, by controlling the rotation reference signal generating means, in response to the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, the light beam detecting means corresponding to each of the remaining rotating polygon mirrors. By making the output signal always output first, immediately after the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors is output within the period until the next phase control. The time difference until the output signal of the light beam detection means corresponding to the reference rotating polygon mirror is output, that is, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is the output signal. Do not suddenly lengthen for a period close to one cycle.

According to a second aspect of the invention, in the light beam scanning device of the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon surfaces immediately after that. The time difference until the output signal of the light beam detection means corresponding to the mirror is output is calculated a plurality of times, and based on the maximum time difference which is the maximum value of the time difference, the rotation reference in the direction to make the maximum time difference zero. By controlling the signal generating means, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is prevented from suddenly becoming longer by a time period close to one cycle of the output signal.

According to a third aspect of the present invention, in the light beam scanning apparatus according to the second aspect, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output immediately after the output signal is output during the image writing standby. The time difference until the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors is calculated in a certain cycle, and when the time difference becomes larger than a predetermined time difference, the time difference at that time By performing the phase control based on the maximum value of, even when the time difference is not only a normal fluctuation, but also changes over time,
The time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is prevented from suddenly increasing by a time period close to one cycle of the output signal.

According to a fourth aspect of the invention, in the light beam scanning device according to the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon surfaces immediately after that. The time difference until the output signal of the light beam detection means corresponding to the mirror is output is calculated a plurality of times, the fluctuation range is obtained from the plurality of time differences, and the fluctuation range is added to any one of the plurality of time differences. Based on the added value,
By controlling the rotation reference signal generating means so as to make the added value zero, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is 1 cycle of the output signal. Try not to suddenly lengthen for a time close to.

According to a fifth aspect of the present invention, in the light beam scanning device according to the first aspect, after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, each of the remaining rotary polygon faces immediately after that is output. Calculating the time difference until the output signal of the light beam detecting means corresponding to the mirror is output, based on the added value obtained by adding the fluctuation range of the time difference previously measured and stored to the time difference, the added value By controlling the rotation reference signal generating means in the direction of zero, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is close to one cycle of the output signal. Don't let it suddenly get longer.

According to a sixth aspect of the present invention, in the light beam scanning apparatus according to the fourth or fifth aspect, the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output during the image writing standby, Immediately after calculating the time difference until the output signal of the light beam detecting means corresponding to each of the remaining rotary polygon mirror at a certain cycle a plurality of times, from any one of the plurality of time differences or a plurality of time differences thereof. When the obtained fluctuation width becomes larger than the predetermined time difference or the fluctuation width used in the previous phase control, by performing the phase control based on the time difference or fluctuation width at that time, the time difference is a normal fluctuation. Not only when it is going to change over time, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is 1 cycle of the output signal. To avoid sudden longer by the close time period.

According to a seventh aspect of the invention, in the light beam scanning device according to the fourth or fifth aspect, the time difference is calculated a plurality of times.
Based on the added value obtained by adding the fluctuation range to the minimum value of the plurality of time differences, by controlling the rotation reference signal generating means in the direction of making the added value zero, the time difference corresponding to the image deviation amount is obtained. Make it shorter.

According to an eighth aspect of the invention, in the light beam scanning device of the first aspect, the phase control based on the time difference is not performed during the image writing operation, and the phase control based on the time difference is performed. By setting the image writing standby state in which the image writing operation is prohibited during the period, the time difference corresponding to the image shift amount does not suddenly change during the image writing operation.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a light beam scanning device used in a 4-drum type color laser beam printer (hereinafter referred to as "color printer") as an image forming apparatus will be described below. [First Embodiment] FIG. 1 is a perspective view showing a schematic configuration of a color printer according to the present embodiment. This color printer is provided with four sets of image forming units and the like for forming a color image in which images of four colors (yellow, magenta, cyan, black) are superimposed. Each image forming unit includes a photosensitive drum 1 serving as an image carrier, a charging charger 2, a light beam scanning unit 3, a developing unit 4, and a transfer charger 5, and the charging, exposing, developing, and the usual electrophotographic processes are performed.
By performing the transfer process, the image of the first color is transferred to the recording paper 7 conveyed in the direction of the arrow A by the transfer belt 6, and then the images of the second color, the third color, and the fourth color are transferred in order.
A color image in which images of four colors are superposed can be formed on the recording paper 7.

FIG. 2 is an explanatory diagram of an optical system of the laser beam scanning unit 3, and FIG. 3 is a block diagram of a control system of a light beam scanning device having four sets of the laser beam scanning unit 3. Here, the numeral in parentheses in FIG. 3 indicates the number of sets of laser scanning units to which the constituent element belongs. Each laser scanning unit 3 of the light beam scanning device of the present color printer is a laser light source (LD) 8 as a light beam generating means, and a rotary polygon mirror for deflecting and scanning the laser beam from the laser light source 8 onto the photosensitive drum 1. Polygon mirror 9 and a polygon motor 10 as driving means for rotating the polygon mirror 9 in the direction of arrow B.
And the hall element 11 as a rotational position detecting means for detecting the rotational position of the polygon mirror 9, and the polygon mirror 9 based on the rotation reference signal generated by the rotation reference signal generating means and the output signal of the hall element 11 described later. A motor driver (PLL controller) 12 as a rotation drive control means for controlling the polygon motor 10 so as to rotate at high speed, and a light beam detection means for detecting the laser beam scan-deflected by the polygon mirror 9 at the scan start position. A laser beam detector 13 and a controller 14 as a light beam generation control means for controlling the laser light source 8 based on the output signal of the laser beam detector 13 are provided.

The laser beam from each of the laser light sources 8 is ON / OFF controlled by a laser driver (not shown) that operates based on the color-separated image information.
Polygon mirror 9 rotated by polygon motor 10
It is deflected and scanned by, and is irradiated onto the surface of the photosensitive drum 1 through the lens. A beam detection mirror 13a is provided at the end (scanning start position) of the scanning range (LD scanning range in FIG. 2) of the laser beam from the laser light source 8, and the laser beam reflected by the mirror 13a is It is detected by the laser beam detector 13 and output to the controller 14 as a beam detect pulse signal. Further, from the hall element 11, a repetitive pulse signal which is turned on / off at a frequency according to the rotation of the polygon mirror 9 is output to the motor driver (PLL controller) 12.

Further, the light beam scanning device is provided with a rotation reference signal generating means for generating a plurality of rotation reference signals corresponding to the polygon mirrors 9 (1) to 9 (4) and a control means thereof. As shown in FIG. 3, the rotation reference signal generating means includes a reference signal generator 15, four sets of rotation reference signal generators 16 (1) to 16 (4), and three sets of selectors 17 (2).
.About.17 (3), and the controller 14 is used as the phase control means. The controller 14 is used not only for controlling the laser light source 8 and the selector 17, but also for checking the constant speed rotation of the polygon motor 10 and measuring the time difference between detector pulse signals which will be described later.

By the way, when a color image is formed by the color printer having the light beam scanning device having the above-mentioned structure, the images independently prepared for each color of yellow, magenta, cyan and black are superposed on the recording paper at the correct positions. 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 adjusted accurately. . Regarding the adjustment in the main scanning direction, the laser beam detector 13 always detects the scanning start position of the laser beam, and the writing timing of the recorded image data is adjusted for each color, so that the light beam scanning device in the printer and the photosensitive element 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 superposed. On the other hand, regarding the adjustment in the sub-scanning direction, the photosensitive member pitch (L in FIG. 1) is maintained at an integral multiple of the scanning pitch, and the laser scanning start position is always detected by the laser beam detector 13 to write the recording image data. By controlling the timing with 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 color misregistration does not occur when images of each color are superposed. I am trying.

However, if a rotation reference signal having the same phase is used to drive the rotation of each polygon mirror 9 when the above laser beam scanning is controlled, it is less than 1 scanning pitch in the sub-scanning direction (84 when the image resolution is 300 dpi). .67μ
Therefore, in the light beam scanning device of the present embodiment, the rotational phase of the polygon motor 10 that rotationally drives each polygon mirror 9 is controlled,
The above-mentioned color misregistration is corrected by matching the surface phases of the polygon mirrors 9.

FIG. 4 is a flow chart of the rotation phase control of the polygon motor, and FIGS. 5A and 5B are time charts of the rotation reference signals and the output signals of the laser beam detectors 13 before the phase control, respectively. And FIG.
(A) And (b) is a time chart of each rotation reference signal and the output signal of each laser beam detector 13 after phase control, respectively. When the power switch of the color printer is turned on, electric power is supplied to the polygon motor 10 and the rotation reference signal / PCLK1 (see FIG. 5A) of a predetermined frequency output from the rotation reference signal generator 16 (1) is supplied to the motor driver. (PLL control unit) 12 (1) and the rotation reference signal / PCLK1 from the rotation reference signal generation unit 16 (1)
The selectors 17 (2) to 17 (4) are controlled by the controller 14 so as to select the rotation reference signal / PCLK1 to the rotation reference signals / PCLK2 to / PCLK4 (see FIG. 5 (a).
3, / PCLK4 is the same as / PCLK2 although not shown. )
Each remaining motor driver (PLL controller) 12
(2) to 12 (4) are supplied (step 1). Then, when an ON signal is sent from the controller 14 to each motor driver (PLL control unit) 12 (1) to 12 (4), each polygon motor 10 (1) to 10 (4) rotates and the polygon motor 10 When is rotated at a constant speed, a motor lock signal is sent from each motor driver (PLL control unit) 12 (1) to 12 (4) to the controller 14 (steps 2 to 4).

Next, when each polygon motor 10 rotates at a constant speed, each laser light source 8 is turned on (step 5).
In this case, each laser light source 8 may be turned on only when the laser beam passes through the beam detection mirror 13a of FIG. When the laser light source 8 is turned on, the beam detect pulse signals DP1 to DP4 are sent from the laser beam detectors 13 (1) to 13 (4) to the controller 14 (step 6). For example, as shown in FIG. 5B, the signal DP1 from the laser beam detector 13 (1),
A signal DP2 is output from the laser beam detector 13 (2). Hereinafter, the remaining beam detect pulse signal DP
Since 3 and DP4 can be considered in the same manner as DP2, they are omitted. Further, it is assumed that the time difference of DP2 with respect to the beam detect pulse signal DP1 varies within the width of T5.

In this embodiment, the polygon mirror 9 (1)
Since the phase control is performed with reference to the polygon motor 10 (1), the controller 14 detects the rising edge of the pulse of each of the beam detect pulse signals DP1 and DP2, and detects the remaining signal DP2 from the rising edge of the pulse of the signal DP1. The time difference T1 until the pulse rise is calculated and the calculated time difference is stored (step 7,
8). Detection of such beam detect pulse signal,
Calculation and storage of the time difference are repeated a certain number of times (n times) (steps 6 to 9). Then, the maximum value of the plurality of stored time differences is selected (step 1
0). In the example of FIG. 5B, the time difference T3 is selected. Then, the pulse width T6 of the signal DP2 is added to the selected time difference T3, and the added value is converted into data for input to the rotation reference signal generator 16 (2) (steps 11, 1).
2) The data converted from the time difference T2 is input to the rotation reference signal generator 16 (2) (step 13).

In the rotation reference signal generator 16 (2), based on the data sent from the controller 14 and the reference signal sent from the reference signal generator 15, as shown in FIG. 6 (a). A new rotation reference signal / PCLK2 whose phase is shifted by the sum T3 + T6 of the selected time difference and pulse width is output (step 14). This rotation reference signal / PCLK2 is sent to the selector 17 (2), and the rotation reference signal is switched from the signal / PCLK1 to the signal / PCLK2 in the selector 17 (2) by the switching signal from the controller 14, and the motor driver (PLL control unit ) 12 (2) (steps 15 and 16).

Motor driver (PLL controller)
12 (1), the rotation position detection signal and the rotation reference signal generation unit 16 output from the hall element 11 for detecting the rotation position
PLL control is performed based on the rotation reference signal / PCLK2 output from (2), and phase control of the polygon motor is performed so that each polygon motor 10 (2) rotates again at a constant speed. When the polygon motor 10 (2) rotates at a constant speed, a motor lock signal is detected (step 17).

FIG. 6 (b) shows the detect pulse signals DP1 and DP2 after the above phase control. It can be seen that, before the phase control shown in FIG. 5B, the maximum shift (T2 + T5) shifts from the maximum shift (T2 + T5). In the above phase control, the case where the rotational phase of the polygon mirror 9 (2) is controlled based on the time difference of DP2 with respect to the detect pulse signal DP1 has been described, but the remaining polygon mirrors 9 (3) and 9 (4) are controlled. As for the rotation phase, D with respect to the detect pulse signal DP1
The same control can be performed based on the time difference between P3 and P4. Further, it is preferable that the number of times of detecting the detect pulse signal and calculating the time difference thereof is as large as possible.

FIG. 7 is a flow chart of image writing control using the light beam scanning device. This image writing control is performed after the phase control of FIG. 4 is completed. In this embodiment, the reference polygon mirror 9 is used.
Beam detect pulse signal DP1 corresponding to (1)
Is used as an image writing start signal by each laser scanning unit 3. In FIG. 7, when an image writing start command signal is sent from the operation unit of the color printer or the external control unit (host), the controller 14 starts counting the reference beam detect pulse signal DP1 (step 1). . Then, when the input of the signal DP1 is started, the writing of the image of the first color is started, and the signal DP1 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 2 and 3). When the signal DP1 is counted by the specified number of lines (the number of writing lines), the writing of the image of the first color is completed on that line (step 4,
5).

Here, the first color laser scanning unit and the second color
The photosensitive member pitch L between the color laser scanning unit is m times the scanning pitch (m is an integer), and the photosensitive member pitch L between the first color laser scanning unit and the third color laser scanning unit is the scanning pitch. It is assumed that the photoconductor pitch L between the laser scanning unit for the first color and the laser scanning unit for the fourth color is 2 m times and the scanning pitch is 3 m times the scanning pitch.

The above-mentioned reference beam detect pulse signal D
When the count number of P1 reaches m, counting of the beam detect pulse signal DP2 of the second color is started (steps 6 and 7). Then, when the input of the signal DP2 is started, the writing of the image of the second color is started, and the signal DP2 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 8 and 9). Then, the signal DP2
When the number of specified lines has been counted (the number of writing lines), the counting of the signal DP2 is finished, and the writing of the image of the second color is finished at that line (steps 10 to 12).

When the reference beam detect pulse signal DP1 counts to 2 m, counting of the beam detect pulse signal DP3 for the third color is started (steps 13 and 14). Then, when the input of the signal DP3 is started, the writing of the image of the third color is started, and the signal D
P3 is written on the photosensitive drum 1 line by line as a line synchronization signal (steps 15 and 16). Then, when the signal DP4 is counted by the prescribed number of lines (the number of writing lines), the counting of the signal DP4 is finished, and the writing of the image of the fourth color is finished at that line (step 17).
~ 19).

When the count number of the reference beam detect pulse signal DP1 reaches 3 m, counting of the beam detect pulse signal DP4 of the fourth color is started (steps 20 and 21). Then, when the input of the signal DP4 is started, the writing of the image of the fourth color is started, and the signal D
P4 is written as a line synchronization signal line by line on the photosensitive drum 1 (steps 22 and 23). Then, when the signal DP3 is counted by the specified number of lines (the number of writing lines), the counting of the signal DP3 is finished, and the writing of the image of the third color is finished at that line (step 24).
~ 26).

As described above, in this embodiment, the beam detect pulse signals DP2, DP3 detected after the beam detect pulse signal DP1 corresponding to the reference first color image is detected a predetermined number of times (m, 2m, 3m), respectively. , D
By starting the image writing of the second to fourth colors by P4, the images are superimposed in the sub-scanning direction in units of one scanning pitch so that the color shift of each image does not occur.

Since the start of the image writing is controlled, the remaining signals DP2, DP3, DP4 are always detected immediately after the beam detect pulse signal DP1, and the entire image is scanned by one scanning pitch unit. Although the images are superposed on each other, in the present embodiment, each polygon mirror 9 is controlled by the phase control described above.
Even if the time difference between the remaining signals DP2, DP3, DP4 with respect to the signal DP1 varies due to uneven rotation of the above, the signals DP2, DP3, DP4 are always output to the DP1 simultaneously or always first. It is possible to prevent a color shift close to one scanning pitch from suddenly occurring during the image writing operation.

Further, due to the above-mentioned phase control, the color shift of less than one scanning pitch is caused by the beam detect pulse signal D.
The signal DP2, DP3, DP4 with respect to P1 is generated only by an amount corresponding to the fluctuation width T5 + T6 of the time lag. (Hereafter, margin)

[Embodiment 2] Next, another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to the present embodiment have the same configurations as those shown in FIGS. FIG. 8 is a flowchart of the rotational phase control of the polygon motor according to this embodiment. The difference from the phase control in the first embodiment is that the time difference is calculated from the detect pulse signal even after the first phase control after the power is turned on and the motor lock signal is detected, and the value is specified in advance. The point is that the phase control is performed based on the result of comparison with the time difference.

The control flow after detecting the motor lock signal after the first phase control will be described below. 1
When the motor lock signal is detected in the second phase control (step 17), the image writing is possible (READY), but after that, the detection of the detect pulse signals DP1 to DP4 and the time difference (T1 and T2 in FIG. 5B). , T3, etc.) is repeated n times, and the maximum value T3 of the plurality of time differences is selected (steps 18 to 22). Then, when the time difference data (maximum value) becomes larger than the predetermined time difference data, if image writing is not in progress, the operation after the data conversion described in the first embodiment is performed, and the same phase Control is performed (steps 23 to 31). Then, the above operation is repeated. Here, when the newly calculated time difference data (maximum value) is less than or equal to the predetermined time difference data, or when the image writing operation is in progress, detection of the detect pulse signals DP1 to 4 and calculation of the time difference are repeated. It will be.

In the flowchart of FIG. 8, DP2, DP3, DP4 for the detect pulse signal DP1
Polygon mirrors 9 (2) -9 (4) based on the time difference of
Although it is shown that the phase control of 1 is performed simultaneously, they are all processed in parallel. Therefore, when only one of the maximum values of the time difference between the detect pulse signal DP1 and the remaining signals DP2, DP3, DP4 becomes larger than the predetermined time difference data, the other time differences continue to be calculated, The phase will be controlled only when it becomes large. The specified value of the time difference data is determined based on the allowable color shift amount, may be stored in advance, and may be changed from the outside.

According to the phase control according to the present embodiment, not only when the power is turned on, but also after that, the above time difference is continuously calculated and the phase control is executed as necessary. The increase can be prevented.

[Third Embodiment] Next, still another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to this embodiment have the same configurations as those shown in FIGS. FIG. 9 is a flowchart of the rotational phase control of the polygon mirror according to this embodiment. The difference from the phase control in the first embodiment is not the maximum time difference but n
The fluctuation range for the captured data is calculated, and the phase control is performed based on the added value obtained by adding the fluctuation width together with the pulse width to an arbitrary time difference (step 1 in the figure).
0 and 11).

FIGS. 10 to 12 show the Borgon mirrors 9 (1) and 9 (2) after the phase control in the third embodiment, respectively.
Rotation reference signal and detect pulse signal D after phase control
P1 and 2 are shown. The relationship between DP1 and DP2 before phase control is as shown in FIG. 5B, and the fluctuation range of the time difference of DP2 with respect to DP1 is T5. here,
If the time difference is T2, the rotation reference signal / P
CLK2 is T from reference / PCLK1 as shown in Fig. 10 (a).
The phase is advanced by 2 + T5 + T6, and as a result, as shown in FIG. 10B, the minimum T6 and the maximum T5 + T6.
And the color shift occurs accordingly (No. 1). Further, if the time difference is T1, the rotation reference signal / PCLK2 becomes the reference as shown in FIG.
/ PCLK1 leads the phase by T1 + T5 + T6, and as a result, as shown in FIG. 11 (b), the minimum T4 + T
6, the maximum time difference is T4 + T5 + T6, and the color shift occurs by that amount (No. 2). Also, if the time difference is T
If it is 3, the rotation reference signal / PCLK2 is shown in FIG.
As shown in FIG. 12, the phase is advanced from the reference / PCLK1 by T3 + T5 + T6, and as a result, as shown in FIG. Part 3). Above 3
Although the above examples have been given, it can be seen that although there is a difference in the amount of color misregistration, color misregistration close to one line does not occur in any case.

[Fourth Embodiment] FIG. 13 is a flowchart of phase control according to still another embodiment. This phase control is basically the same as the control flow shown in FIG. 9 of the third embodiment, but the fluctuation width of the time difference between the signals DP2, DP3, DP4 with respect to the detect pulse signal DP1 is measured in advance and stored, The difference is that the stored value is used for control. In this case, as shown in steps 7 and 8 of the control flow of FIG. 13, only the time difference is calculated, the data of the fluctuation width stored in advance is added to the value, and the phase is controlled using the added value. It will be. According to the phase control according to the present embodiment, the function for calculating the fluctuation range is unnecessary, so that the configuration of the controller 14 can be simplified.

[Fifth Embodiment] Next, still another embodiment of the present invention will be described. The optical system and the control system of the light beam scanning device according to this embodiment have the same configurations as those shown in FIGS. FIG. 14 is a flowchart of the rotational phase control of the polygon mirror according to this embodiment. The phase control of the present embodiment is basically the same as the control of the third embodiment, except that the fluctuation range of the time difference calculated from the detect pulse signal is stored (step 11 in the figure). Even after the first phase control after the power is turned on and the motor lock signal is detected, the fluctuation range of the time difference calculated from the plurality of detect pulse signals, the selected arbitrary time difference value and the previous fluctuation range are defined in advance. This is different from the third embodiment in that the phase difference is compared with the time difference and the phase control is performed based on the comparison result.

In FIG. 14, after the power is turned on, the first phase control is performed and the motor lock signal is detected, the state becomes the image writable (READY) state (steps 1 to 18). Even after entering the READY state, the detect pulse signals DP1 to DP4 are detected, the fluctuation width for n times is calculated, and an arbitrary time difference is selected from a plurality of time differences (steps 19 to 23). . When the fluctuation range or the selected time difference becomes larger than the stored fluctuation range or a predetermined time difference, if the image writing is not in progress, the new fluctuation range is stored, and the pulse width is added to the time difference. And the phase control is performed based on the added value obtained by adding the fluctuation range (steps 24 to 33). If the fluctuation width is less than the stored value, the time difference is less than the specified value, or during the image writing operation, the detect pulse signal DP
Processing from detection of 1 to 4 to comparison of data is performed. When the phase control is completed, the processes from detection of the detect pulse signals DP1 to DP4 to data comparison are performed again.

In the flowchart of FIG. 14, DP2, DP3, DP for the detect pulse signal DP1
The polygon mirrors 9 (2) -9 based on the time difference of 4
Although the phase control of (4) is shown to be performed at the same time, they are all processed in parallel. Therefore, the detect pulse signal DP1 and the remaining signals DP2, DP3, D
If only one of the time difference from P4 or the fluctuation range is different from the previously defined time difference or the stored fluctuation range,
In other cases, the calculation of the time difference or the fluctuation range is continued, and the phase control is performed only at different points. The specified value of the time difference may be determined in advance from the allowable color shift amount, may be stored in advance, and may be changeable from the outside.

According to the phase control according to the present embodiment, not only when the power is turned on, but also after that, the above time difference is continuously calculated and the phase control is executed as necessary. The increase can be prevented.

[Sixth Embodiment] FIG. 15 is a flowchart of phase control according to still another embodiment. This phase control is basically the same as the control flow shown in FIG. 14 of the fifth embodiment, except that the minimum time difference is selected from the detected plurality of time differences and used for control. Figure 5
In the example of the detect pulse signal of (b), T2 is the minimum time difference. According to the phase control according to the present embodiment, the amount of color misregistration can be further reduced as compared with the case of the fifth embodiment.

[Seventh Embodiment] FIG. 16 is a flowchart of phase control according to still another embodiment. This phase control is basically the same as the control flow of FIG. 8 of the second embodiment, except that the phase control is not performed during the image writing operation, and the image writing is prohibited during the phase control. The difference is that it is in the image writing standby state. In FIG. 16, after the power is turned on, when the motor lock signal is detected by performing the first phase control, the image writing (READY) state is set (steps 1 to 17). After entering the READY state, the image writing control section is notified that the image writing is possible (step 18). Further maximum value T3
Is selected and the phase control is performed, the image writing disabled state is similarly notified to the image writing control unit, the image writing standby state is set, and the writing start signal is waited for (steps 19 to 26). ). Then, after the phase control, when a motor lock signal is detected, image writing is started (steps 27 to 34). According to the phase control according to the present embodiment, it is possible to prevent image distortion due to image writing during the phase control.

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

Further, 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 is shown. However, the present invention is an optical device used in other image forming apparatuses such as a copying machine and a facsimile. It can also be applied to a beam scanning device.

[0070]

According to the present invention, the output signals of the light beam detecting means corresponding to the respective remaining rotary polygon mirrors are output within the period until the next phase control, and Immediately after that, the time difference until the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, that is, the time difference corresponding to the image shift amount is shortened as much as possible, and the time difference corresponding to the image shift amount is the output signal. I try not to suddenly lengthen it by a time close to one cycle. Therefore, the image shift amount due to the rotational phase difference of each rotary polygon mirror is reduced as much as possible, and the image shift in the sub-scanning direction suddenly occurs due to the uneven rotation of the rotary polygon mirror while the phase control is not performed. The effect is that it can be prevented.

In particular, according to the invention of claim 3 or 6, even when the time difference is not only a normal fluctuation but also changes with time, the time difference corresponding to the image shift amount is shortened as much as possible, and Since the time difference corresponding to the image shift amount is prevented from suddenly increasing for a time period close to one cycle of the output signal, it is possible to prevent the image shift due to a change over time.

Further, in particular, according to the invention of claim 5, the time difference between the output signals of the light beam detecting means corresponding to the reference rotary polygon mirror and the output signals of the light beam detecting means corresponding to each of the remaining rotary polygon mirrors. On the basis of the added value to which the fluctuation width of the time difference previously measured and stored is added, the rotation reference signal generating means is controlled, so the time difference is calculated a plurality of times, and the time difference is calculated from the plurality of time differences. There is an effect that the configuration of the phase control means can be simplified by the amount of the function of calculating the fluctuation range, as compared with the case of further calculating the fluctuation range.

Further, according to the invention of claim 7, in the light beam scanning device of claim 4 or 5, wherein the time difference is calculated a plurality of times, an added value obtained by adding the fluctuation range to the minimum value of the plurality of time differences. Based on, by controlling the rotation reference signal generating means in the direction of making the added value zero,
Since the time difference corresponding to the image shift amount becomes shorter,
Further, there is an effect that the image shift amount can be reduced.

Further, in particular, according to the invention of claim 8, the image writing is such that the phase control is not performed during the image writing operation, and the image writing operation is prohibited while the phase control is being performed. Since the time difference corresponding to the image shift amount does not suddenly change during the image writing operation by setting the input standby state, it is possible to prevent the image from being disturbed due to the image writing during the phase control. The effect is that you can do it.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a color printer according to an embodiment of the invention.

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

FIG. 3 is a block diagram of a control system of a light beam scanning device of the color printer.

FIG. 4 is a flowchart of rotational phase control in the light beam scanning device.

5A and 5B are time charts of a rotation reference signal before phase control and an output signal of each laser beam detector, respectively.

6A and 6B are time charts of a rotation reference signal after phase control and an output signal of each laser beam detector.

FIG. 7 is a flowchart of image writing control by the light beam scanning device.

FIG. 8 is a flowchart of rotational phase control according to another embodiment.

FIG. 9 is a flowchart of rotation phase control according to still another embodiment.

10A and 10B are time charts showing an example of a rotation reference signal after phase control in the same rotation phase control and an output signal of a laser beam detector.

11A and 11B are time charts showing another example of the rotation reference signal after phase control and the output signal of the laser beam detector in the same rotation phase control.

12A and 12B are time charts showing still another example of the rotation reference signal after the phase control and the output signal of the laser beam detector in the same rotation phase control, respectively.

FIG. 13 is a flowchart of rotational phase control according to still another embodiment.

FIG. 14 is a flowchart of rotation phase control according to still another embodiment.

FIG. 15 is a flowchart of rotational phase control according to still another embodiment.

FIG. 16 is a flowchart of rotational phase control according to still another embodiment.

17A and 17B are time charts of output signals of the laser beam detector before and after the rotational phase control according to the conventional example, respectively.

[Explanation of symbols]

1 photoconductor drum 3 Light beam scanning unit 8 laser light source 9 polygon mirror 10 polygon motor 11 Hall element 12 Motor driver 13 Laser beam detector 14 Controller 15 Reference signal generator 16 Rotation reference signal generator 17 Selector

Claims (8)

(57) [Claims] 1. A light beam generating means, a rotary polygonal mirror for deflecting and scanning the light beam generated by the light beam generating means onto an image carrier, a driving means for rotationally driving the rotary polygonal mirror, and the rotary polygonal mirror. A rotation position detecting means for detecting the rotation position of the, and a rotation drive control means for controlling the driving means so that the rotary polygon mirror rotates at a constant speed based on a rotation reference signal and an output signal of the rotation position detecting means, A plurality of sets of light beam detection means for detecting a light beam deflected and scanned by the rotary polygon mirror at a predetermined position on a scanning path, and a rotation reference signal for generating the rotation reference signal corresponding to each of the rotary polygon mirrors. A time difference between the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror among the plurality of rotating polygon mirrors and the output signal of the light beam detecting means corresponding to each of the remaining rotating polygon mirrors. Based on the time difference, phase control means for controlling the rotation reference signal generating means so that the rotation phase of each of the remaining rotary polygon mirrors substantially coincides with the reference rotary polygon mirror; Start the light beam scanning in each main scanning direction based on the output signal of the light beam detecting means, and based on the output signal of the light beam detecting means corresponding to the reference rotating polygon mirror, in each of the remaining rotating polygon mirrors. A light beam scanning device comprising a light beam generation control means for controlling the light beam generation means so as to start image writing in the sub-scanning direction by a light beam deflectively scanned, which corresponds to the reference rotary polygon mirror. With respect to the output signal of the light beam detection means, the output signal of the light beam detection means corresponding to each of the remaining rotary polygon mirrors is always output first,
A light beam scanning device for controlling the rotation reference signal generating means. 2. The light beam scanning device according to claim 1, wherein after the output signal of the light beam detecting means corresponding to the reference rotary polygon mirror is output, the light corresponding to each of the remaining rotary polygon mirrors immediately after that is output. A light characterized by calculating a plurality of times until the output signal of the beam detecting means is output, and controlling the rotation reference signal generating means based on the maximum time difference which is the maximum value of the plurality of time differences. Beam scanning device. 3. The light beam scanning device according to claim 2, wherein each of the remaining rotations immediately after the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output during image writing standby. Calculate the time difference until the output signal of the light beam detecting means corresponding to the polygon is output at a certain period,
A light beam scanning device, wherein when the time difference becomes larger than a predetermined time difference, phase control is performed based on the maximum value of the time difference at that time. 4. The light beam scanning device according to claim 1, wherein the output signals of the light beam detection means corresponding to the reference rotary polygon mirror are output, and the light beams corresponding to the remaining rotary polygon mirrors immediately after that are output. Calculate the time difference until the output signal of the beam detection means is output a plurality of times, obtain the fluctuation range from the plurality of time differences, and based on the added value obtained by adding the fluctuation range to any one of the plurality of time differences. A light beam scanning device characterized by controlling the rotation reference signal generating means. 5. The light beam scanning device according to claim 1, wherein after the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output, the light corresponding to each of the remaining rotary polygon mirrors immediately after that is output. The time difference until the output signal of the beam detection means is output is calculated, and the rotation reference signal generation means is controlled based on the added value obtained by adding the fluctuation width of the time difference previously measured and stored to the time difference. A light beam scanning device characterized by: 6. The light beam scanning device according to claim 4, wherein the output signal of the light beam detection means corresponding to the reference rotary polygon mirror is output during the image writing standby, and the remaining portion immediately after the output signal is output. The time difference until the output signal of the light beam detection means corresponding to each rotary polygon mirror is calculated a plurality of times at a certain cycle, and the fluctuation width obtained from any one of the plurality of time differences or the plurality of time differences is A light beam scanning device, characterized in that, when it becomes larger than a predetermined time difference or a fluctuation width used for the previous phase control, phase control is performed based on the time difference or fluctuation width at that time. 7. The light beam scanning device according to claim 4, wherein the time difference is calculated a plurality of times, wherein a minimum value of the plurality of time differences is used as the time difference used for the phase control. . 8. The light beam scanning device according to claim 1, wherein phase control based on the time difference is not performed during the image writing operation, and image writing is performed during phase control based on the time difference. A light beam scanning device which is placed in an image writing standby state in which operation is prohibited.