JP2020001285A - Optical scanner and image formation apparatus including the same - Google Patents

Abstract

To inexpensively and accurately suppress the color shift in the main-scanning direction of two light beams in an opposite scan type optical scanner for scanning the two light beams reversely and an image formation apparatus including the optical scanner.SOLUTION: An optical scanner 100 includes detection sensors 15a, 15b on the scan start sides of the two light beams. The optical scanner detects one detection time difference of the first detection time difference Tbeing the time from the detection by the first detection sensor 15a to the detection by the second detection sensor 15b of the light beam deflected by the same reflection surfaces 1-5 of a rotary polygon mirror 12 and the second detection time difference Tbeing the time from the detection by the second detection sensor 15b to the detection by the first detection sensor 15a, calculates the change rate of the one detection time difference at each prescribed time, and determines the color shift correction amount for performing the color shift correction in the main-scanning direction on the basis of the calculated change rate.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.

  2. Description of the Related Art Conventionally, there has been known an opposing scanning optical scanning device in which scanning directions of light beams on both sides of a rotary polygon mirror are opposite to each other. The oppositely scanned light beams are applied to image carriers that carry toners of different colors to form electrostatic latent images. If the scanning positions of the two light beams that are opposed to each other are relatively displaced in the main scanning direction, there is a possibility that color misregistration may occur. One of the causes of the positional shift (color shift) between the two light beams in the main scanning direction is thermal deformation of the housing.

  In the optical scanning device disclosed in Patent Literature 1, a temperature sensor is disposed in a housing to suppress color shift due to the thermal deformation, and a writing start position of image data by each light beam is corrected according to a temperature detected by the temperature sensor. I am trying to do it. In this optical scanning device, a BD sensor is provided on each of the writing start sides (scanning start sides) of two light beams that are opposed to each other. The correction of the writing position of the image data is performed by changing the time from the detection of the light beam by each BD sensor to the start of the writing of the image data. The temperature sensor is provided near one of the BD sensors.

JP 2016-153203 A

  By the way, the displacement of the two light beams in the main scanning direction includes thermal deformation of various portions such as thermal deformation of a holding portion for holding the BD sensor and thermal deformation of a holding portion of a reflection mirror for guiding the light beam to the BD sensor. Influences.

  Therefore, in the optical scanning device disclosed in Patent Document 1, since the temperature sensor is provided only in the vicinity of the BD sensor, the effect of thermal deformation of other parts is not taken into consideration, and the accuracy of color misregistration correction is low. is there. In addition, since it is necessary to provide a temperature sensor in order to perform color misregistration correction, there is a problem that the cost is increased.

  The present invention has been made in view of such a point, and an object of the present invention is to provide an opposing scanning type optical scanning device that scans two light beams in opposite directions, and an image forming apparatus including the optical scanning device. Another object of the present invention is to suppress color misregistration of two light beams in the main scanning direction at low cost and with high accuracy.

An optical scanning device according to one aspect of the present invention includes: two light sources that emit light beams; a rotary polygon mirror that deflects light beams emitted from the two light sources to scan in opposite directions; Two scanning lenses through which light beams deflected and scanned by mirrors in opposite directions pass, respectively, and first detection for detecting the light beam on the scanning start side of one light beam deflected and scanned by the rotary polygon mirror A sensor, a second detection sensor for detecting the light beam on the scanning start side of the other light beam deflected and scanned by the rotating polygon mirror, and a first predetermined time elapses from the time of detection by the first detection sensor. Then, the scanning for writing the image data by one light beam is started, and after the scanning is completed, the same as the reflection surface of the rotary polygon mirror that deflects the one light beam. The irradiation of the other light beam is started toward the projection surface, and thereafter, when a second predetermined time has elapsed from the time of detection by the second detection sensor, scanning for writing image data by the other light beam is performed. And a control unit for controlling the two light sources to start.
And a first detection time difference that is a time from a time when the light beam deflected by the same reflection surface of the rotary polygon mirror is detected by the first detection sensor to a time when the light beam is detected by the second detection sensor; A second detection time difference, which is a period of time from the time of detection by the second detection sensor to the time of detection by the first detection sensor, and a change rate of the one detection time difference at predetermined time intervals. And a color misregistration correction amount determining unit that determines a color misregistration correction amount for performing color misregistration correction in the main scanning direction based on the calculated change rate. A color misregistration correction unit that corrects color misregistration in the main scanning direction by correcting at least one of the first predetermined time and the second predetermined time according to the color misregistration correction amount.

An optical scanning device according to another aspect of the present invention includes: two light sources that emit light beams; a rotary polygon mirror that deflects the light beams emitted from the two light sources to scan in opposite directions; Two scanning lenses through which light beams deflected and scanned by the polygon mirror in opposite directions pass, respectively, and a first sensor for detecting the light beam on the scanning start side of one of the light beams deflected and scanned by the rotary polygon mirror A detection sensor, a second detection sensor for detecting the light beam on the scanning start side of the other light beam deflected and scanned by the rotary polygon mirror, and a first predetermined time from the time of detection by the first detection sensor. At the elapse of time, scanning for writing image data by one light beam is started, and after the scanning is completed, the scanning is performed with the reflecting surface of the rotary polygon mirror that deflects the one light beam. The irradiation of the other light beam is started toward the reflection surface, and after that, when a second predetermined time has elapsed from the time of detection by the second detection sensor, scanning for writing image data by the other light beam is performed. A control unit that controls the two light sources to start.
And a first detection time difference that is a time from a time when the light beam deflected by the same reflecting surface of the rotary polygon mirror is detected by the first detection sensor to a time when the light beam is detected by the second detection sensor; The second detection time difference, which is the time from the detection by the second detection sensor to the detection by the first detection sensor, is detected, and the average value of the absolute values of the two detection time differences is calculated. A parameter obtained by multiplying the sign of one of the detection time differences, a change rate of the parameter is calculated at predetermined time intervals, and color shift correction in the main scanning direction is performed based on the calculated change rate. A color shift correction amount determining unit that determines the color shift correction amount, and at least one of the first predetermined time and the second predetermined time according to the color shift correction amount determined by the color shift correction amount determining unit. By Lord And a color shift correcting unit for correcting the 査 direction color misregistration.

  An image forming apparatus according to the present invention includes the above optical scanning device.

  According to the present invention, in an opposing scanning type optical scanning device that scans two light beams in opposite directions, and in an image forming apparatus equipped with the optical scanning device, color shift in the main scanning direction of the two light beams can be reduced at low cost. In addition, it can be suppressed with high accuracy.

FIG. 1 is a block diagram illustrating a schematic configuration of the image forming apparatus. FIG. 2 is a block diagram illustrating a schematic configuration of the optical scanning device. FIG. 3 is a plan view showing a schematic configuration of the optical scanning device. FIG. 4 is a plan view showing the relationship between the polygon mirror and the laser light. FIG. 5 is a time chart showing the start and end of scanning of the laser beam. FIG. 6 shows detection result data of a parameter (light beam detection time difference) necessary for color shift correction in the main scanning direction. FIG. 7 is a graph illustrating an example of a detection result of a detection time difference of a light beam. FIG. 8 is an example of color shift correction data in which the change rate of the detection time difference of the light beam and the color shift correction amount in the main scanning direction are associated with each other. FIG. 9 is a diagram corresponding to FIG. 6 showing the second embodiment. FIG. 10 is a diagram corresponding to FIG. 6 showing the third embodiment. FIG. 11 is a diagram corresponding to FIG. 7 showing the third embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments.

  FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus 101 including an optical scanning device 100 according to the embodiment. The image forming apparatus 101 is, for example, a laser printer or a multifunction peripheral, and forms an image on a sheet based on image data transmitted from a terminal or the like (not shown) while conveying the sheet. As shown in FIG. 1, the image forming apparatus 101 includes a paper feeding unit 102, an image forming unit 103, a fixing unit 104, and a paper discharging unit 105.

  The paper feeding unit 102 is a cassette paper feeding unit that supplies paper to the image forming unit 103 or a manual tray. The image forming unit 103 includes four photosensitive drums 106a to 106d corresponding to toners of four colors (black, magenta, yellow, and cyan). Although not shown, the image forming unit 103 includes an intermediate transfer belt extending in the direction in which the photosensitive drums 106a to 106d are arranged, a charger, a developing device, and a transfer device arranged around each of the photosensitive drums 106a to 106d. It has rollers and the like. The image forming unit 103 further includes an optical scanning device 100 that emits a laser beam to each of the photosensitive drums 106a to 106d to form an electrostatic latent image. The image forming unit 103 develops the electrostatic latent images on the photoconductor drums 106a to 106d with toner of each color supplied from a developing device to form a toner image. Then, the image forming unit 103 forms a color toner image by superimposing and transferring the toner images of each color on the intermediate transfer belt, and transfers the formed color toner image to a sheet supplied from the sheet feeding unit 102. Has become. Note that the image forming unit 103 may employ a direct transfer method in which the toner images of the respective colors are sequentially superimposed on a sheet and transferred without using an intermediate transfer belt.

  Although not shown, the fixing unit 104 includes a fixing roller and a pressure roller that rotate while being pressed against each other. The fixing unit 104 fixes the toner image transferred onto the sheet by the image forming unit 103 to the sheet by heating and pressing. The paper discharge unit 105 has a paper discharge tray (not shown) to which paper on which an image is formed from the fixing unit 104 is supplied.

<Optical scanning device>
In the present embodiment, as described above, the four photosensitive drums 106a to 106d are provided corresponding to the four color (black, magenta, yellow, and cyan) toners. The optical scanning device 100 has two optical scanning systems having the same configuration. One scanning system emits laser beams to the black and magenta photosensitive drums 106a and 106b, and the other scanning optical system. Irradiates laser light to the yellow and cyan photosensitive drums 106c and 106d. Hereinafter, a light scanning system that emits laser light to two photosensitive drums 106a and 106b corresponding to black (BK) and magenta (Magenta) will be described as a representative.

  As shown in FIGS. 2 and 3, the optical scanning system of the optical scanning device 100 includes two light sources 11a, 11b, one polygon mirror 12, two scanning lenses 13a, 13b, and two BD sensors 15a, 15b (Beam detect sensor) and a light source control unit 20. The light sources 11a and 11b, the polygon mirror 12, and the scanning lenses 13a and 13b are housed in a resin housing (not shown).

  The first light source 11a and the first scanning lens 13a correspond to the black first photosensitive drum 106a. The second light source 11b and the second scanning lens 13b correspond to the magenta second photosensitive drum 106b.

  Each of the light sources 11a and 11b emits a laser beam (light beam). The polygon mirror 12 is a regular pentagonal rotating polygon mirror. The radially outer surfaces of the polygon mirror 12 constitute reflection surfaces 1 to 5 for reflecting a light beam. The polygon mirror 12 may be a regular triangle, a square, or a polygon having a regular hexagon or more. The polygon mirror 12 deflects each laser beam emitted from the light sources 11a and 11b and scans them in opposite directions.

  Specifically, the laser light from the first light source 11a is deflected by the polygon mirror 12, passes through the first scanning lens 13a, and is emitted to the first photosensitive drum 106a. After being deflected by the polygon mirror 12, the laser light of the second light source 11b passes through the second scanning lens 13b and is emitted to the second photosensitive drum 106b. The scanning directions of the laser light of the first light source 11a and the laser light of the second light source 11b are opposite to each other. That is, the laser light of the first light source 11a is scanned upward in FIG. 3, and the laser light of the second light source 11b is scanned downward in FIG. Although not shown, a collimator lens and a cylinder lens are arranged between the light sources 11a and 11b and the polygon mirror 12 in this order from the light sources 11a and 11b, and a laser beam passes through each of them.

  The first BD sensor 15a is provided on the scanning start side of the laser light of the first light source 11a that has been deflected and scanned by the polygon mirror 12. A turning mirror 14a is provided on the optical path on the scanning start side of the laser light of the first light source 11a that has been deflected and scanned by the polygon mirror 12, and the laser light is reflected by the turning mirror 14a and is transmitted to the first BD sensor 15a. By being incident, a BD signal is output from the first BD sensor 15a. The BD signal is transmitted to a light source control unit 20 described later and used as a reference signal for starting writing of image data by the laser light.

  The second BD sensor 15b is provided on the scanning start side of the laser light of the second light source 11b that has been deflected and scanned by the polygon mirror 12. A return mirror 14b is provided in the optical path on the scanning start side of the laser light of the second light source 11b deflected and scanned by the polygon mirror 12, and the laser light is reflected by the return mirror 14b and transmitted to the second BD sensor 15b. By being incident, a BD signal is output from the second BD sensor 15b. This BD signal is transmitted to the light source control unit 20 and used as a reference signal for starting writing of image data by the laser light.

The light source control unit 20 controls the irradiation timing of the laser light from each of the light sources 11a and 11b. The light source control unit 20 is configured by a microcomputer having a CPU 21, a ROM 22, and a RAM 33.
The light source control unit 20 starts writing image data using the laser light when a first predetermined time ta has elapsed since the first BD sensor 15a detected the laser light of the first light source 11a. Further, the light source control unit 20 uses the same reflection surfaces 1 to 5 as the reflection surfaces 1 to 5 of the polygon mirror 12 that deflects the laser light of the first light source 11a at the time of detection by the first BD sensor 15a. The laser light irradiation operation of the second light source 11b is controlled so that scanning is started by deflecting the laser light of the light source 11b. When the second BD sensor 15b detects the laser light of the second light source 11b deflected by the same reflection surfaces 1 to 5 as described above, the light source control unit 20 performs a second predetermined time tb from the detection. The writing of the image data is started after elapses.

  Specifically, the control operation of the light source control unit 20 will be described with reference to FIGS. As shown in FIG. 4A, after the laser light (the laser light on the left side in FIG. 4) emitted from the first light source 11a is deflected by the reflection surface 1 of the polygon mirror 12 and passes through the scanning lens 13a. , And enters the first BD sensor 15a. Thereby, the scanning start position of the laser light of the first light source 11a is detected, and the detection signal is sent to the light source control unit 20. Then, as shown in FIG. 5A, when the first predetermined time ta has elapsed from the detection of the BD sensor 15a, the scanning of writing the image data on the first photosensitive drum 106a by the laser light of the first light source 11a. Starts. Thus, the writing of the black (BK) image data is performed. Then, the laser beam scans the first photosensitive drum 106a in a certain direction as the reflecting surface 1 rotates. As a result, an electrostatic latent image for black color is drawn on the first photosensitive drum 106a.

  Subsequently, as shown in FIG. 5B, when a predetermined time elapses from the detection of the first BD sensor 15a, the reflection surface 1 rotates and moves to a position where a magenta color (Magenta) is drawn. Then, as shown in FIG. 4B, the laser light (the laser light on the right side in FIG. 4) emitted from the second light source 11b is deflected by the reflection surface 1 and passes through the scanning lens 13b. The light enters the second BD sensor 15b. Thus, the scanning start position of the laser light of the second light source 11b is detected, and the detection signal is sent to the light source control unit 20. Then, as shown in FIG. 5B, after a second predetermined time tb has elapsed from the detection of the second BD sensor 15b, an image is formed on the second photosensitive drum 106b by the laser light of the second light source 11b. Data writing scanning starts. In this manner, the writing of the magenta (M) image data is performed. Then, the laser light scans the second photosensitive drum 106b in a certain direction as the reflecting surface 1 rotates. As a result, an electrostatic latent image for magenta is drawn on the second photosensitive drum 106b.

−Initial setting process−
The first predetermined time ta and the second predetermined time tb are initially set by a correction process called color registration performed by the light source control unit 20 when the power of the image forming apparatus 101 is turned on. In this correction process, a toner patch image of each color is formed on an intermediate transfer belt provided in the image forming unit 103, and the amount of color misregistration of another color with respect to a reference color (for example, black) in the main scanning direction using a density sensor or the like. Is detected. The light source control unit 20 sets the first predetermined time ta and the second predetermined time tb so that the color shift amount in the main scanning direction becomes zero, and stores the first predetermined time ta and the second predetermined time tb in the RAM 22. This initial set value is deleted when the power of the image forming apparatus 101 is turned off.

−Color misregistration correction processing−
By the way, after the driving of the optical scanning device 100 is started, the holding portions of the folding mirrors 14a and 14b and the holding portions of the BD sensors 15a and 15b in the housing are thermally deformed due to heat generation of the motor for driving the polygon mirror 12. Then, the installation attitude of the folding mirrors 14a and 14b and the BD sensors 15a and 15b changes, and the detection timing of the laser beam by the BD sensors 15a and 15b changes. Since this change is different between the left optical path and the right optical path in FIG. 3, a color shift in the main scanning direction may occur. In the present embodiment, the color shift correction control is executed in the light source control unit 20 in order to correct the color shift in the main scanning direction caused by the thermal deformation of the housing.

In the color misregistration correction control, a difference between detection times of the light beams deflected by the same reflection surfaces 1 to 5 of the polygon mirror 12 by the two BD sensors 15a and 15b is used.
Referring to FIG. 5, focusing on, for example, the reflection surface 1 of the polygon mirror 12, the difference between the detection times of the light beams deflected by the reflection surface 1 by the two BD sensors 15a and 15b is _TBD1-2 or _{TBD in} the figure. _It is represented by _BD2-1 . _TBD1-2 is the time from when the light beam deflected by the reflecting surface 1 of the polygon mirror 12 is detected by the first BD sensor 15a to when it is detected by the second BD sensor 15b, and _TBD2-1 Is the time from when the light beam deflected by the reflection surface 1 of the polygon mirror 12 is detected by the second BD sensor 15b to when it is detected by the first BD sensor 15a. In the present embodiment, the color misregistration correction may be performed using the former detection time difference _TBD1-2 of the two.

FIG. 6 is a table showing an example of detection result data of the detection time difference _TBD1-2 after the start of driving the polygon mirror 12. In this detection result data, symbols d1, d2, d3,... Are used instead of disclosing specific numerical values of the detection time difference. As shown in the detection result data, after the driving of the polygon mirror 12 starts, the light source control unit 20 detects (measures) the detection time difference _TBD1-2 corresponding to each of the reflection surfaces 1 to 5 of the polygon mirror 12. The light source control unit 20 stores the detection result data in the RAM 22 while updating the data as needed.

  FIG. 7 is an example in which the detection result data of FIG. 6 is represented in a graph format. This graph is for explaining the content of the color misregistration correction control described below in a visually easy-to-understand manner, and it is not always necessary for the light source control unit 20 to create graph data.

The light source control unit 20 calculates the change rate A of the detection time difference _{TBD1-2 every} predetermined time Δt based on the detection result data. The change rate A can be obtained as A = ΔT _BD1-2 / Δt, as shown in FIG. In the present embodiment, the predetermined time Δt is set in advance to, for example, a time during which the polygon mirror 12 makes one rotation. It should be noted that Δt can be, for example, a time during which one reflection surface of the polygon mirror 12 passes (in this embodiment, a time during which the polygon mirror 12 rotates by 2π / 5).

  Then, the light source control unit 20 calculates a color shift correction amount K for correcting a color shift in the main scanning direction (a position shift of the black and magenta light beams in the main scanning direction) based on the calculated change rate A. (decide. The color misregistration correction amount K is calculated based on the correction data stored in the ROM 23 in advance and the calculated change rate A. Then, the light source control unit 20 functions as a color misregistration correction amount determination unit, and the ROM 23 functions as a storage unit that stores correction data.

FIG. 8 shows an example of this correction data. The correction data is data in which the change rate A of the detection time difference _TBD1-2 and the color shift correction amount K are associated with each other on a one-to-one basis, and is calculated in advance by an experiment or the like. The correction data shows an example in which the color misregistration correction amount K changes linearly with the change rate A of the detection time difference _TBD1-2 . In this correction data, when the change rate A is 0, the color misregistration correction amount K becomes 0, and in a region where the change rate A> 0, the color misregistration correction amount K increases along with the increase of the change rate A, In a region where the change rate A <0, the color shift correction amount K increases to the minus side as the change rate A decreases. Note that, when the amount of color misregistration correction is plus and minus, the relative misregistration direction (color misregistration direction) of one light beam relative to the other light beam is opposite.

  Then, the light source control unit 20 corrects the first predetermined time ta and the second predetermined time tb based on the color misregistration correction amount K calculated based on FIG. For example, when the correction amount of the first predetermined time ta corresponding to black is Δt1 and the correction amount of the second predetermined time tb corresponding to magenta is Δt2, the first predetermined time ta is set to ta + Δt1 and the second predetermined time tb Are corrected to tb + Δt2, respectively. Correlation data between the correction amounts Δt1 and Δt2 and the color misregistration correction amount K are calculated in advance by experiments or the like and stored in the ROM 23. Thus, the light source control unit 20 functions as a color shift correction unit.

As described above, in the first embodiment, the light source control unit 20 controls the polygon mirror 12 to perform the second detection from the time when the first BD sensor 15a detects the light beam deflected by the same reflection surfaces 1 to 5. The detection time difference _TBD1-2 , which is the time until the detection by the sensor 15b, is detected, the change rate A is calculated every predetermined time Δt, and the color shift correction amount K is determined based on the calculated change rate A. It is configured to

  According to this configuration, since the existing BD sensors 15a and 15b can be used to determine the color shift correction amount K, there is no need to separately provide a temperature sensor. Therefore, product cost can be reduced.

In addition, the detection time difference _TBD1-2 reflects the influence of thermal deformation of various parts such as thermal deformation of the holding parts holding the BD sensors 15a and 15b and thermal deformation of the holding parts of the folding mirrors 14a and 14b. . Therefore, the color shift correction accuracy can be improved as compared with the case where color shift correction is performed based on a local temperature change of the housing detected by the temperature sensor.

  In the first embodiment, the first predetermined time ta is corrected to ta + Δt1, and the second predetermined time tb is corrected to tb + Δt2. However, only one of the times ta and tb may be corrected. Good. That is, the second predetermined time tb may be corrected to tb + Δt1 + Δt2 without correcting the first predetermined time ta, and the first predetermined time ta is corrected to ta + Δt1 + Δt2 without correcting the second predetermined time tb. You may do so. With this correction method, although the color shift is suppressed, the drawing position on the photosensitive drums 6a and 6b is shifted in the main scanning direction from the drawing position at the time of the initial setting. However, the shift amount of the drawing position in the usage environment of the image forming apparatus 101 is an amount that cannot be recognized by human eyes, and therefore does not cause any particular problem in using the image forming apparatus 101.

<< Embodiment 2 >>
FIG. 9 is a diagram (detection result data) corresponding to FIG. 6 showing the second embodiment of the present invention. In this embodiment, the method of determining the color shift correction amount K by the light source control unit 20 is different from that of the first embodiment. The details of the control other than the method of determining the color misregistration correction amount K are the same as those in the first embodiment, and thus detailed description thereof will be omitted.

In the present embodiment, the light source control unit 20 determines a detection time difference T _BD1-2 (hereinafter, _{referred to} as a first detection time difference) which is a time from the time of detection by the first BD sensor 15a to the time of detection by the second BD sensor 15b. And color shift correction based on a parameter P calculated from a time T _BD2-1 (hereinafter, _{referred to} as a second detection time difference) from the time of detection by the second BD sensor 15b to the time of detection by the first BD sensor 15a. Determine the quantity K.

The parameter P is an average value of the absolute value of the first detection time difference _{TBD1-2 and} the absolute value of the second detection time difference _TBD2-1 (= ｛| _TBD1-2 | + | _TBD2-1 |｝ / 2). , One of the detection time differences (in the present embodiment, for example, the first detection time difference _TBD1-2 ) is multiplied by a code, which is obtained as, for example, _TBD1-2 / | _TBD1-2 |. Can be.

  Then, the light source control unit 20 calculates the change rate A of the parameter P at predetermined time intervals, and based on the calculated change rate A of the parameter P, performs color shift for correcting color shift in the main scanning direction. The correction amount K is determined, and the color shift correction is executed based on the determined color shift correction amount K.

As described above, in the second embodiment, the average value of the absolute value of the first detection time difference _{TBD1-2 and} the absolute value of the second detection time difference _TBD2-1 is used as the parameter P used for color misregistration correction. In addition, the correction of the color misregistration is executed with high accuracy by minimizing the influence of the rotational vibration of the motor driving the polygon mirror 12. That is, assuming that there is no rotational fluctuation of the motor, the relationship of _TBD1-2 + _TBD2-1 = 0 is established. However, this relationship does not hold if the motor has rotational runout. For example, in the example of FIG. 9, if d1 is a positive value, D1 should be −d1, but if there is a rotational fluctuation of the motor, even if d1 is a positive value, D1 will be 0, for example. There is. In this case, when the first detection time difference _TBD1-2 is focused on as in the first embodiment, the color shift correction is "necessary", but when the second detection time difference _TBD2-1 is focused on, the color shift correction is "unnecessary". That is, the result greatly differs depending on which parameter is used, and the correction accuracy is reduced. In the present embodiment, the sign of the parameter P used for color misregistration correction adopts the sign of one of the detection time differences _TBD1-2 , and the absolute value of the parameter P is changed to the two detection time differences _TBD1-2 , _TBD2-1. By using the average value of the absolute values of, the color misregistration correction can be executed with high accuracy even if there is a rotational fluctuation of the motor.
<< Embodiment 3 >>

  FIGS. 10 and 11 are equivalent to FIGS. 6 and 7 showing the third embodiment of the present invention. In this embodiment, the method of determining the color shift correction amount K by the light source control unit 20 is different from that of the first embodiment. The details of the control other than the method of determining the color misregistration correction amount K are the same as those in the first embodiment, and thus detailed description thereof will be omitted.

That is, the light source control unit 20 detects the detection time difference _TBD1-2 only for the light beam deflected by one predetermined reflection surface (the reflection surface 5 in the present embodiment) of the polygon mirror 12, and detects the detection time difference _TBD1-2 for a predetermined time. The change rate A of the detection time difference _TBD1-2 is calculated _every Δt, and the color shift correction amount K is determined based on the change rate A. In the present embodiment, the predetermined time Δt is, for example, a time during which the polygon mirror 12 makes one rotation (see FIG. 11).

According to this configuration, it is possible to accurately correct the color shift by the light source control unit 20 by excluding the influence of the surface accuracy (surface inclination or the like) of each of the reflection surfaces 1 to 5 of the polygon mirror 12. Also, unlike the first embodiment, it is not necessary to detect (measure) the detection time difference _TBD1-2 in small increments, so that the load on the CPU 21 of the light source control unit 20 can be reduced.

<< Other embodiments >>
In the first and third embodiments, the detection time difference _TBD1-2 (first detection time difference) is used as a parameter used for color misregistration correction in the light source control unit 20, but the present invention is not limited to this. _TBD2-1 (second detection time difference) may be used. Also in the second embodiment, the sign of the second detection time difference _TBD2-1 may be adopted as the sign of the parameter P.

  Further, the present invention is not limited to the first to third embodiments, and the present invention includes a configuration in which the first to third embodiments are appropriately combined. That is, for example, by combining the second embodiment and the third embodiment, the detection of the parameter P in the second embodiment may be performed only on one predetermined reflection surface.

  As described above, the present invention is useful for an optical scanning device and an image forming apparatus including the optical scanning device.

A: Change rate K: Color shift correction amount P: Parameter _TBD1-2 : First detection time difference (detection time difference)
T _BD2-1 : Second detection time difference (detection time difference)
ta: first predetermined time tb: second predetermined time 1: reflection surface 2: reflection surface 3: reflection surface 4: reflection surface 5: reflection surface 11a: first light source 11b: second light source 12: polygon mirror (rotation) Polygon mirror)
13a: first scanning lens 13b: second scanning lens 15a: first BD sensor (first detection sensor)
15b: 2nd BD sensor (2nd detection sensor)
20: light source control unit (color shift correction unit, color shift correction amount determination unit)
100: Optical scanning device 101: Image forming device

Claims (6)

Two light sources for emitting light beams, a rotating polygon mirror for deflecting the light beams emitted from the two light sources and scanning in opposite directions, and a light beam deflected and scanned in opposite directions by the rotating polygon mirror , Two scanning lenses respectively passing therethrough, a first detection sensor for detecting the light beam on the scanning start side of one of the light beams deflected and scanned by the rotating polygon mirror, and a deflection scanning performed by the rotating polygon mirror. A second detection sensor for detecting the light beam on the scanning start side of the other light beam, and writing of image data by one of the light beams when a first predetermined time has elapsed since the detection by the first detection sensor. Scan, and after the end of the scan, the one light beam is deflected and the other light beam is directed toward the same reflection surface as the reflection surface of the rotating polygon mirror. And then, when a second predetermined time has elapsed from the time of detection by the second detection sensor, the two light sources are controlled so as to start scanning for writing image data with the other light beam. An optical scanning device comprising a control unit and
A first detection time difference that is a time from a time when the light beam deflected by the same reflection surface of the rotary polygon mirror is detected by the first detection sensor to a time when the light beam is detected by the second detection sensor; and Of the second detection time difference, which is the time from the detection by the first detection sensor to the detection by the first detection sensor, and, at predetermined time intervals, the rate of change of the one detection time difference. Calculating a color shift correction amount for determining a color shift correction amount for performing color shift correction in the main scanning direction based on the calculated change rate;
A color shift correction unit that corrects a color shift in the main scanning direction by correcting at least one of the first predetermined time and the second predetermined time according to the color shift correction amount determined by the color shift correction amount determination unit. An optical scanning device comprising: Two light sources for emitting light beams, a rotating polygon mirror for deflecting the light beams emitted from the two light sources and scanning in opposite directions, and a light beam deflected and scanned in opposite directions by the rotating polygon mirror , Two scanning lenses respectively passing therethrough, a first detection sensor for detecting the light beam on the scanning start side of one of the light beams deflected and scanned by the rotating polygon mirror, and a deflection scanning performed by the rotating polygon mirror. A second detection sensor for detecting the light beam on the scanning start side of the other light beam, and writing of image data by one of the light beams when a first predetermined time has elapsed since the detection by the first detection sensor. Scan, and after the end of the scan, the one light beam is deflected and the other light beam is directed toward the same reflection surface as the reflection surface of the rotating polygon mirror. And then, when a second predetermined time has elapsed from the time of detection by the second detection sensor, the two light sources are controlled so as to start scanning for writing image data with the other light beam. A control unit, comprising:
A first detection time difference that is a time from a time when the light beam deflected by the same reflection surface of the rotary polygon mirror is detected by the first detection sensor to a time when the light beam is detected by the second detection sensor; and A second detection time difference, which is the time from the detection by the detection sensor to the detection by the first detection sensor, is detected, and the average value of the absolute values of the two detection time differences is calculated. A parameter obtained by multiplying the sign of the detection time difference is obtained, a change rate of the parameter is calculated at predetermined time intervals, and a color shift for correcting color shift in the main scanning direction is calculated based on the calculated change rate. A color misregistration correction amount determining unit for determining a correction amount;
A color shift correction unit that corrects a color shift in the main scanning direction by correcting at least one of the first predetermined time and the second predetermined time according to the color shift correction amount determined by the color shift correction amount determination unit. An optical scanning device comprising: The optical scanning device according to claim 1,
The optical scanning device, wherein the color misregistration correction amount determination unit is configured to detect the one detection time difference only for a light beam deflected by one predetermined reflecting surface of the rotary polygon mirror. The optical scanning device according to claim 2,
The color misregistration correction amount determining unit is configured to detect the difference between the two detection times only for the light beam deflected by one predetermined reflection surface of the rotary polygon mirror when obtaining the parameter. , Optical scanning device. The optical scanning device according to any one of claims 1 to 4,
A storage unit that stores in advance color shift correction data in which the change rate and the color shift correction amount in the main scanning direction are associated with each other;
The color misregistration correction amount determining unit is configured to determine the color misregistration correction amount in the main scanning direction based on the color misregistration correction data stored in the storage unit and the change rate. Optical scanning device. An image forming apparatus comprising the optical scanning device according to claim 1.

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