JP2019101194A - Optical scanner and image formation apparatus using the same - Google Patents

Abstract

To improve an image defect caused depending upon an entering/exiting quantity of a deflection surface of a rotary polygon mirror easily at low cost without making an image formation apparatus large-sized.SOLUTION: The present invention relates to an optical scanner which scans a scanned surface, and the optical scanner has a light source, a rotary polygon mirror which comprises a plurality of deflection surfaces reflecting light emitted from the light source to make a deflection scan on the scanned surface, a sensor which detects the light reflected by the rotary polygon mirror, and a control part which controls the light source. The control part acquires a difference in distance between the distance from the center of rotation of the rotary polygon mirror to a first deflection surface and the distance from the center of rotation to a second deflection surface from a time difference between a first time from emission of the light from the light source to the first deflection surface of the rotary polygon mirror to incidence of the light on the sensor from the first deflection surface and a second time from emission of the light from the light source to the second deflection surface of the rotary polygon mirror to incidence of the light on the sensor from the second deflection surface, and controls timing of the emission of the light from the light source based upon the acquired difference in distance.SELECTED DRAWING: Figure 12

Description

  The present invention relates to an optical scanning device for use in an image forming apparatus such as a laser printer, a copying machine, a facsimile machine, etc. having a function of forming an image on a transfer material (recording medium) such as a sheet, and an optical scanning device The present invention relates to an image forming apparatus using the apparatus.

  An optical scanning device used in an image forming apparatus such as a conventional laser printer modulates a laser beam emitted from a light source in accordance with an image signal and converts the light modulated laser beam into, for example, a light deflector having a rotary polygon mirror It is scanning with deflection. The deflected laser beam is guided to the writing position synchronization signal detection means in order to control the timing of the scanning start position on the surface to be scanned. Next, an image is recorded by optically scanning in a spot-like image formed on the photosensitive recording medium surface by a scanning lens such as an imaging optical system having an fθ characteristic. When a signal is detected by the writing position synchronization signal detection means, writing of an image is performed after a predetermined time.

  In recent years, the demand for downsizing of an image forming apparatus and high image quality has been high, and an optical system associated with the demand has been widely adopted in an optical scanning apparatus. With regard to downsizing of the image forming apparatus, for example, in the monochrome image forming apparatus, downsizing of the entire image forming apparatus is achieved by shortening the optical path length from the optical scanning device to the photosensitive member. An optical system which shortens the optical path length by converging the light beam incident on the rotary polygon mirror in the main scanning direction in advance and forming an image in front of the conventional parallel luminous beam as one of the configurations for shortening the optical path length And so on (hereinafter referred to as a converging optical system). Further, in the in-line color machine, in order to miniaturize the apparatus and reduce the number of parts, four light beams of Y, M, C and K are obliquely incident on the same rotary polygon mirror in the sub-scanning direction of the deflection surface. The configuration is known. By making incident obliquely, the light beam after deflection is separated and scanned onto the photosensitive drum surface according to each color, and the optical scanning device and the image forming apparatus are miniaturized (hereinafter referred to as oblique incident optical system). ).

  In addition, an electrical correction means for the printing position has been proposed for improving the image quality. In patent document 1, the signal in the timing of writing start and writing end is detected for every scanning line, and the frequency of the clock which determines the rotation speed of an optical deflector for every scanning line according to the difference from the reference scanning time is changed. A means for correcting the magnification of the image in the main scanning direction has been proposed. Further, in Patent Document 2, the difference with respect to the reference in the main scanning direction of each scanning line is measured at the time of factory shipment or the like, and data regarding the difference is held in the optical scanning device. Then, there has been proposed means for inputting the held data into the image forming apparatus and correcting the magnification in the main scanning direction by the image forming apparatus based on the data.

Japanese Patent Application Publication No. 2007-078876 JP 2007-071918A

In an optical scanning device used in an image forming apparatus, how far the deflection surface of the rotary polygon mirror is located from the rotation center may be expressed as an in / out amount. Then, in the convergent optical system, if the in / out amount of the deflection surface of the deflection surface of the rotary polygon mirror is large, the following problems occur. FIGS. 4 and 5 are diagrams for explaining the jitter (hereinafter referred to as convergence eccentricity jitter) caused by the entrance and exit of the deflection surface of the rotary polygon mirror in the convergence optical system. The term "jitter" refers to the deviation of the scanning position in the main scanning direction. FIG. 4 shows the reflection direction of the light beam when the incident light beam L is deflected by the deflecting surfaces Ma and Mc having the in / out direction. The light beam reflected by the deflection surface Ma is La, and the light beam reflected by the deflection surface Mc is Lc. FIG. 5A is a view showing the irradiation position on the surface of the photosensitive drum 103 in the case where the light beam incident on the rotary polygon mirror is a substantially parallel light beam. As shown in FIG. 5A, even when the reflected light beams are deviated in parallel by the deflection surface, they do not become jitter because they are imaged at the same position on the surface of the photosensitive drum 103 by the scanning lens. FIG. 5B is a view showing the irradiation position on the surface of the photosensitive drum 103 in the case where the light beam incident on the rotary polygon mirror is a convergent light beam. When the incident light beam is a convergent light beam, the light is focused on the front side of the focal length f of the scanning lens, so that the difference between the irradiation positions of La and Lc shown in FIG.
Also in the oblique incidence optical system, as described later, there is a problem that the scanning line is shifted in the sub scanning direction on the photosensitive drum 103 surface and the sub scanning pitch unevenness is generated when the entering / exiting amount of the deflection surface of the rotary polygon mirror is large. is there. Whether in monochrome or color, the entrance and exit of the deflecting surface of the rotary polygon mirror often causes problems in image quality.

As means for solving the above problem cases, it is considered that electric correction means for the printing position as in Patent Document 1 and Patent Document 2 may be used. However, the technology described in Patent Document 1 has the following problems.
In the configuration described in Patent Document 1, first, folding mirrors are installed at respective positions in order to detect a scanning time from the beginning of writing to the end of writing. Next, by guiding the reflected light from each mirror to the same writing position synchronization signal detection means, the scanning time of the scanning line deflected by each deflection surface is detected, and the difference from the reference scanning time is corrected. However, this configuration requires a plurality of folding mirrors, which increases the cost. Further, in a small-sized optical scanning device, there is a problem that the optical path to the writing position synchronization signal detecting means can not be secured, or the optical scanning device becomes large in order to secure.
In the configuration of Patent Document 2, there is a problem that correction can not be performed on the image forming apparatus unless the optical scanning device holds data at the time of factory shipment or the like. In addition, there is a problem that significant cost increase occurs by adding a memory for holding data. In order to solve the above problems, an object of the invention according to the present application is to easily and inexpensively improve image defects caused by the amount of movement of a deflection surface of a rotary polygon mirror without increasing the size of an image forming apparatus. .

In order to achieve the above object, the optical scanning device in the present invention is
An optical scanning device for scanning a surface to be scanned, comprising:
Light source,
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
It is characterized by controlling the timing which emits light from the light source based on the acquired difference of the distance.

Further, in order to achieve the above object, the optical scanning device in the present invention is
An optical scanning device for scanning a surface to be scanned, comprising:
Light source,
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
Based on the difference in the distance, in the main scanning direction of the electrostatic latent image, the distance between the adjacent line and the adjacent line is smaller than the density of the other line. And controlling the light source such that the density of the second line wider than a predetermined interval is higher than the density of the other lines.

Further, in order to achieve the above object, the optical scanning device in the present invention is
An optical scanning device for scanning a surface to be scanned, comprising:
A plurality of light sources arranged in the sub scanning direction;
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
Of the plurality of light sources, a sub-scan of a first line formed by deflection scanning by the first deflection surface and a second line formed by deflection scanning of the second deflection surface It is characterized in that an electrostatic latent image is formed on the surface to be scanned by using the light source having a smaller deviation from the reference spacing of the directional spacing.

Furthermore, in order to achieve the above object, the image forming apparatus in the present invention is
An optical scanning device as described above,
At least one image carrier on which light deflected from the optical scanning device is imaged on the surface;
A transfer unit configured to transfer an image formed on the surface of the image carrier onto a recording material;
And the like.

  As described above, according to the present invention, it is possible to easily and inexpensively improve the image failure caused by the in / out amount of the deflection surface of the rotary polygon mirror without increasing the size of the image forming apparatus.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. Principal part cross-sectional view of the optical scanning device according to the first embodiment in the main scanning direction The figure which showed the in and out of the deflection | deviation surface of the rotary polygon mirror which concerns on an Example The figure which demonstrated reflection of the light beam by the rotating polygon mirror which concerns on an Example The figure which demonstrated the jitter which generate | occur | produces in the convergence optical system which concerns on Example 1 The figure which showed the waveform of BD signal concerning Example 1 A diagram showing an example of a BD signal cycle according to the first embodiment The figure which showed the waveform of BD signal concerning Example 1 The figure which showed the waveform of BD signal concerning Example 1 The figure which showed the waveform of BD signal concerning Example 1 A diagram showing an example of a BD signal cycle according to the first embodiment Explanatory drawing of the relationship between the in and out of the deflection | deviation surface of the rotary polygon mirror based on Example 1, and an optical axis. The figure which shows the in-out direction of the deflection | deviation surface of the rotary polygon mirror based on Example 1, and the relationship of a jitter. FIG. 2 is a schematic cross-sectional view of an image forming apparatus according to a second embodiment. The perspective view of the optical scanning device concerning Example 2 Second Embodiment Main Sectional Cross-Sectional View of Optical Scanning Device According to Second Embodiment Second Embodiment Main Sectional Cross-sectional View of Optical Scanning Device According to Second Embodiment Explanatory drawing of the pitch nonuniformity which generate | occur | produces in the oblique incidence optical system which concerns on Example 2. The figure which shows the relationship between the in and out of the deflection | deviation surface of the rotary polygon mirror which concerns on Example 2, and a pitch nonuniformity.

  Hereinafter, with reference to the drawings, modes for carrying out the present invention will be exemplarily described in detail based on examples.

Example 1
An image forming apparatus provided with the optical scanning device according to the first embodiment of the present invention will be described. In the following description, the image forming apparatus according to the first embodiment of the present invention will be illustrated and described first, and then the optical scanning device will be described in detail.
The dimensions, materials, shapes, relative positions, etc. of the components described in the following embodiments are intended to limit the scope of the present invention to only those unless otherwise specified. Absent.

  FIG. 1 is a schematic cross-sectional view of an image forming apparatus D1 according to a first embodiment of the present invention. The image forming apparatus D1 according to the present embodiment includes an optical scanning device S1, and scans an image carrier such as a photosensitive drum by the optical scanning device S1, and an image is formed on a recording material such as recording paper based on the scanned image. It is an image forming apparatus provided with an image forming unit that performs formation. Here, a printer will be described as an example of the image forming apparatus D1. As shown in FIG. 1, the image forming apparatus D1 emits a laser beam flux based on the obtained image information by an optical scanning device S1 as an exposure unit, and a photosensitive member as an image carrier incorporated in the process cartridge 102. It irradiates on the drum 103. A light beam is irradiated onto the photosensitive drum 103 and exposed to light, whereby a latent image is formed on the photosensitive drum 103, and the latent image is visualized as a toner image by the toner as the developer by the process cartridge 102. The process cartridge 102 integrally includes a photosensitive drum 103 and a charging unit and a developing unit as process units acting on the photosensitive drum 103.

On the other hand, the recording materials P stacked on the recording material loading plate 104 are separated while being separated one by one by the feeding roller 105, and then conveyed further downstream by the conveying roller 106. The toner image formed on the photosensitive drum 103 is transferred by the transfer roller 109 onto the conveyed recording material. The recording material P on which the unfixed toner image is formed is conveyed further downstream, and the toner image is fixed to the recording material P by a fixing device 110 having a heating member inside. Thereafter, the recording material P is discharged to the outside of the apparatus by the discharge roller 111.
In this embodiment, the charging unit and the developing unit as process units acting on the photosensitive drum 103 are integrally provided in the process cartridge 102 with the photosensitive drum 103. However, each process unit is separate from the photosensitive drum 103. It may be configured as

  Next, the optical scanning device S1 will be described with reference to FIG. FIG. 2 is a sectional view of an essential part (optical system) in the main scanning direction of an optical scanning device S1 according to a first embodiment of the present invention. In FIG. 2, reference numeral 112 denotes a semiconductor laser (light source) for emitting a laser beam, and reference numeral 113 denotes an anamorphic collimator lens in which a collimator lens and a cylindrical lens are integrally formed. Reference numeral 114 denotes an aperture stop, 115 denotes a rotary polygon mirror, 116 denotes a deflecting device for rotating the rotary polygon mirror, 117 denotes a writing position synchronization signal detection sensor (BD sensor), and 118 denotes an fθ lens (scanning lens).

  In the above configuration, the laser light flux L emitted from the light source 112 is substantially converged light in the main scanning cross section by the compound anamorphic collimator lens 113 and is converged light in the sub scanning cross section. Next, the laser beam L passes through the aperture stop 114, and the beam width is limited, and is imaged as a substantially line image (line image elongated in the main scanning direction) on the deflection surface of the rotating polygon mirror 115. The laser beam L is deflected and scanned by rotating the rotary polygon mirror 115. The laser beam L is reflected by the deflection surface of the rotating polygon mirror 115 and enters the BD sensor 117. At this time, a signal is detected by the BD sensor 117, and this timing is used as a synchronization detection timing of the writing position in the main scanning direction. Next, the laser beam L enters the fθ lens 118. The fθ lens 118 is designed to condense the laser beam L so as to form a spot on the photosensitive drum 103, and to keep the scanning speed of the spot constant. In order to obtain such characteristics of the fθ lens 118, the fθ lens 118 is formed of an aspheric lens. The laser beam L passing through the fθ lens 118 is imaged and scanned on the photosensitive drum 103.

  The laser beam L is deflected and scanned by the rotation of the rotary polygon mirror 115, and the main scan with the laser beam L is performed on the photosensitive drum 103, and the photosensitive drum 103 is rotated around the axis of the cylinder to perform sub scanning. It will be. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum 103.

  Next, with reference to FIG. 3, the amount of movement of the deflection surface of the rotary polygon mirror will be described. FIG. 3 is a schematic view of the rotary polygon mirror as viewed from the rotation axis direction, and illustrates the entrance and exit of the deflection surface of the rotary polygon mirror 115. Usually, the rotary polygon mirror 115 is positioned by fitting the fitting hole 120 provided at the center thereof with the rotary shaft 119 of the deflecting device 116, and is fixed by a spring or adhesive for pressing the rotary polygon mirror 115. In most cases, the center 122 of the fitting hole 120 of the rotating polygon mirror 115 is with respect to the center 121 of the rotating shaft 119 because the fitting hole 120 of the rotating polygon mirror 115 and the rotation shaft 119 have a clearance for insertion. It is fixed in a state where it is close to one side. The centers 121 and 122 of the rotation shaft 119 and the fitting hole 120 are shifted and fixed, so that they enter and leave the deflection surfaces Ma, Mb, Mc and Md, that is, something like the rotation center 121 and other deflection surfaces. A difference occurs in the distance from the reference point. FIG. 3 shows an example in which the fitting hole 120 of the rotating polygon mirror 115 is biased to the rotating shaft 119 and fixed. The inner diameter of the fitting hole 120 on the deflection surface Mb side and the deflection surface Mc side is in contact with the rotating shaft 119. In this state, the deflection surface Ma and the deflection surface Md move away from the rotation center 121 (face up) and the deflection surface Mb and the deflection surface Mc come close to the rotation center 121 (surface entry) with respect to the position of the ideal surface. Hereinafter, the fact that the deflection surface is away from the reference point is referred to as "outside", and the fact that the deflection surface is closer to the rotation center 121 than the reference point is referred to as "surface entry".

  First, in the present embodiment, in order to briefly describe the amount of entry and exit, when all the distances from the fitting hole 120 of the rotary polygon mirror 115 to the respective deflection surfaces are the same, that is, entry and exit of facing deflection surfaces of the rotary polygon mirror 115 alone. The case where the sum of the quantities is 0 will be described.

  FIG. 4 is a view showing how a light beam is reflected when the deflection surface Ma and the deflection surface Mc are in the same phase. FIG. 4A shows a state in which the light beam deflected by the deflection surface reaches the approximate writing start position of the photosensitive drum 103, and FIG. 4B shows the light beam after the approximate writing end of the photosensitive drum 103. It shows the state when reaching the position. The rotating polygon mirror 115 rotates with the deflection surface Ma facing out and the deflection surface Mc entering with the rotation center 121 as a reference, and the light flux emitted from the light source 112 is deflected and scanned. In this case, with respect to the light flux La reflected by the deflection surface Ma, the light flux Lc reflected by the deflection surface Mc when the rotary polygon mirror 115 rotates 180 ° and has the same deflection angle has the same reflection angle but deviates in parallel. Is reflected. Therefore, in order for the light beams La and Lc reflected by the deflection surfaces Ma and Mc to be incident on the same BD sensor 117, the deflection surface Ma, which is an out-of-plane surface, is advanced after the phase shown in FIG. .

  The rotating polygon mirror 115 is rotated at an equal angular velocity by the deflecting device 116. Therefore, the light beam scanned on the deflection surface Ma is scanned behind the light beam scanned on the deflection surface Mc, and the timing of incidence on the BD sensor 117 is delayed, that is, the timing of the BD signal is delayed. Here, a BD lens may be disposed on the optical path between the rotary polygon mirror 115 and the BD sensor 117 in order to substantially form an image of the light flux incident on the BD sensor 117. In that case, as described above, the light beams reflected in parallel and reflected are refracted by the BD lens, and the amount of deviation becomes small on the BD sensor 117. Even when there is a BD lens, although the shift can be detected, it is preferable not to dispose the BD lens (optical element) because the timing shift amount becomes more remarkable by not arranging the BD lens.

FIG. 5 is a main scanning cross-sectional view of the main part of the optical scanning device, which describes the jitter generated by the entrance and exit of the deflection surface in the focusing optical system. FIG. 5A is a view showing the irradiation position on the surface of the photosensitive drum 103 in the case where the light beam incident on the rotary polygon mirror is a substantially parallel light beam. As shown in FIG. 5A, even when the reflected light beams are shifted in parallel due to the entrance and exit of the deflecting surface, they do not become jitter because they are imaged at the same position on the photosensitive drum 103 surface by the scanning lens 118.
On the other hand, FIG. 5B is a view showing the irradiation position on the surface of the photosensitive drum 103 in the case where the light beam incident on the rotary polygon mirror is a convergent light beam. When the incident light flux is a convergent light flux, when the light flux is deviated and incident on the scanning lens in parallel, the light is imaged in front of the focal distance f of the scanning lens, so the irradiation positions of La and Lc shown in FIG. Deviation occurs. As shown in FIG. 4, the amount of deviation is larger at the end of writing than the amount of deviation when entering the BD sensor 117. That is, even though the writing position for each scanning line can be roughly adjusted by the light flux incident on the BD sensor 117, jitter appears more notably on the writing end side.

  FIG. 6 is a diagram showing a waveform of a signal output from the BD sensor 117 when the light flux deflected by the deflection planes Ma, Mb, Mc and Md enters the BD sensor 117. As shown in FIG. Since the light beam reflected by the deflection surface Ma is incident on the BD sensor 117 at a later timing than when reflected by the ideal surface, the signal is delayed, while the light beam reflected by the deflection surface Mc is BD earlier than when reflected by the ideal surface. The light is incident on the sensor 117. Similarly, the light flux reflected by the deflection surface Mb is incident on the BD sensor 117 at a timing earlier than when reflected by the ideal surface, and the light flux reflected by the deflection surface Md is delayed later than when reflected by the ideal surface. The light is incident on the sensor 117. Therefore, the time interval (time difference) of each BD signal (hereinafter referred to as BD period) has a relationship of Tab <Tbc <Tda <Tcd. In Tab, a light flux is emitted from the light source 112 to the deflection surface Ma, and a time from the deflection surface Ma to the light flux entering the BD sensor 117 and a light flux from the light source 112 are emitted to the deflection surface Mb. Represents the difference from the time it takes for the luminous flux to enter the BD sensor 117. Similarly, Tbc represents the time difference between the deflection surfaces Mb and Mc, Tcd represents the time difference between the deflection surfaces Mc and Md, and Tda represents the time difference between the deflection surfaces Md and Ma. .

  A means for detecting the amount of movement of the deflecting surface of the rotary polygon mirror 115 from the BD cycle which can be detected by the image forming apparatus D1 by understanding this relationship will be described. FIG. 7 is a graph showing an example of the BD cycle that can be detected by the image forming apparatus D1. The vertical axis in FIG. 7 represents the difference between each BD cycle and the average BD cycle. Tab is the shortest as compared with the average BD cycle, and is -10 [nsec]. Then, since Tbc is next shorter than the average BD period and is -2 [nsec], "the deflection surface Ma surface is out" or "the deflection surface Mb surface is in" or "the deflection surface Ma surface It is understood that the surface is a surface and the deflection surface Mb is a surface.

However, when there is a surface that basically enters and leaves the deflection surface, the opposing surface has the same absolute value. Therefore, as shown in FIG. 8 when “the deflection surface Ma is a surface”. It is contradictory because it should be Tab = Tbc. Further, in the case of “deflection surface Mb surface is in-plane”, as shown in FIG. That is, in the case of the BD cycle shown in FIG. 7, it is understood that the relationship shown in FIG. 10 is that “the deflection surface Ma surface is out of the plane and the deflection surface Mb surface is the surface”. Let Ta, Tb, Tc, and Td be deviations with respect to the average BD period of the BD signal due to light beams deflected by the deflection surfaces Ma, Mb, Mc, and Md. The formula holds.
Ta-Tb = -10 [nsec]
Tb-Tc = -2 [nsec]
Tc-Td = 10 [nsec]
Td-Ta = 2 [nsec]

Also, since | Tab | = | Tcd | and | Tbc | = | Tda |, the absolute value of the amount of in and out of the opposite surface is equal, and | Ta | = | Tc | The following equation holds because
Ta = -Tc
Tb = -Td

The following values can be derived by solving the above-described simultaneous equations.
Ta = + 6 [nsec]
Tb = -4 [nsec]
Tc = -6 [nsec]
Td = + 4 [nsec]
This corresponds to the deviation amount of the BD signal from the rotation center 121 to each deflection surface with respect to the case where the deflection surface is at the ideal position, and therefore the in / out amount calculated therefrom becomes an absolute amount with respect to the ideal surface.

  Next, the case where the amount of movement of the deflection surface of the rotary polygon mirror 115 alone is relatively large compared to that described above, and is added to the movement of the deflection surface caused by assembly will be described. In the above description, for the sake of simplicity, the case has been described where the sum of the in / out amounts of the facing deflection surfaces of the rotary polygon mirror 115 alone is zero. However, according to the processing method of the rotary polygon mirror 115, for example, when manufacturing the rotary polygon mirror 115 by an inexpensive processing method, it is difficult to make the fitting hole and the rotary shaft into an accurate circular shape, and the rotary polyhedron The amount of movement of the deflection surface of the mirror 115 alone increases. Therefore, FIG. 11 shows an example of the BD cycle in the case where the entrance and exit of the deflecting surface caused by the assembly and the entrance and exit of the deflecting surface of the rotary polygon mirror 115 alone are added.

It can be seen that Tab and Tda have a short period with respect to the average, and Tbc and Tcd have a long period with respect to the average. It is difficult to determine if there is any. However, the relative difference can be determined. The means will be described. From FIG. 11, the following equation holds.
Ta-Tb = -30 [nsec]
Tb-Tc = 19 [nsec]
Tc-Td = 38 [nsec]
Td-Ta = -27 [nsec]
Here, with reference to the deflection surface Ma,
Ta = 0
Tb = 30
Td = -27
And from this Tc = 11
Can lead

  From these values and the relationship between the arrangement of the BD sensor 117 and the deflection point, the amount of movement of the deflection surface, ie, the other deflection surface (second deflection surface) based on the deflection surface Ma (first deflection surface) The difference in distance is calculated as to how far the distance is shifted. If it deviates from the rotation center 121, the surface appears. If it deviates from the rotation center 121, the surface enters. FIG. 12 is a view schematically showing the positional relationship between the incident light axis N from the light source 112 to the rotary polygon mirror 115, the deflection point of the rotary polygon mirror 115, and the BD sensor 117. As shown in FIG. For the purpose of easy understanding, the drawings exaggerately represent the size of the rotary polygon mirror and the amount of movement of the deflection surface. The optical axis A represents the optical axis when the light flux La reflected by the deflection surface Ma is incident on the BD sensor 117. That is, it means a straight line connecting the BD sensor 117 and the deflection point P. The deflection point P mentioned here means a reflection point when reflecting an incident light beam on the deflection surface Ma as a reference toward the BD sensor 117.

The light source 112 emits light to the deflection surface Ma, and the time (first time) Ta from the deflection surface Ma to the light beam entering the BD sensor 117 and the light source 112 emits the light to the deflection surface Md. The time (second time) Td until the luminous flux is incident on Since Td = −27 [nsec] based on Ta, the deflection surface Md is exposed by 27 [nsec] with respect to the deflection surface Ma, that is, the deflection surface Md has its center of rotation than the deflection surface Ma. It is located away from. Therefore, as shown by the dotted line in FIG. 12, when the angle of the deflection surface Md to the incident light axis N is the same as the angle of the deflection surface Ma to the incident light axis N, the reflection angles become the same as described above. It is reflected off in parallel. In order for the light beam Ld reflected by the deflection surface Md to enter the BD sensor 117, the light beam La reflected by the deflection surface Ma is rotated by a predetermined angle δ after the angle when it enters the BD sensor 117 It will be done. Therefore, the light beam Ld reflected by the deflection surface Md has not reached the BD sensor 117 yet. Assuming that the rotation number of the rotating polygon mirror 115 is 30,000 [rpm], the rotation angle (angular velocity) per unit time of the rotating polygon mirror 115 is 0.18 [° / μsec]. The luminous flux Ld reaches the BD sensor 117 after the deflection surface Md is inclined by an angle δ from the state parallel to the deflection surface Ma, so that the luminous flux La reflected by the deflection surface Ma is BD 27 n seconds after reaching the sensor 117. This time difference is converted into an angle α shown in FIG. 12 using the rotation angle δ of the rotating polygon mirror 115. The angle α is the angle between the two sides when the light axis of the light flux deflected by the perpendicular x and the deflection surface Ma is incident on the BD sensor 117 is two angles, and the angle x is deflected by the perpendicular x and the deflection surface Md The angle difference between the two sides when the optical axis of the light beam incident on 117 is the two sides is pointed out. In determining the angle α, the rotation angle of the reflected light beam is twice the rotation angle of the rotary polygon mirror, so 0.18 [° / μsec] × 2 × 27 [nsec] = 9.72 × 10 ⁻³ [° ]. Since the angle α shown in FIG. 12 is 9.72 × 10 ⁻³ [°], the axis obtained by rotating the optical axis A clockwise by 9.72 × 10 ⁻³ [°] centering on the BD sensor 117 is This is the optical axis D when the light beam Ld reflected by the deflection surface Md enters the BD sensor 117. The distance y from the intersection point Q between the optical axis D and the incident optical axis N to the deflection point P is an approximate amount of movement of the deflection surface Md relative to the deflection surface Ma.

In the case of the configuration shown in this embodiment, in FIG. 12, the incident optical axis from the light source 112 to the deflection point P on the deflection surface Ma is one side, and the perpendicular x drawn from the BD sensor 117, the incident optical axis N, A first right triangle having three sides on the optical axis A from the deflection point P to the BD sensor 117 is assumed. Also, the incident optical axis from the light source 112 to the deflection point Q on the deflection surface Md is perpendicular x drawn from the BD sensor 117, the incident optical axis N, and the optical axis D from the deflection point Q to the BD sensor 117 with three sides Assuming the second right triangle to be, the above-mentioned distance y can be determined from the following equation. That is, y is acquired by inputting each numerical value to y = x × tan β−x × tan (β−α). For example, assuming that x = 15 [mm] and angle β = 70 [°], y = 15 [mm] × tan (70) [°] −15 [mm] × tan (70−9.72 × 10 ⁻³ ) [°] = 21.7 [μm]. Therefore, it is possible to calculate that the deflection surface Md is a surface of about 21.7 [μm] with respect to the deflection surface Ma. The deflection surface Mb and the deflection surface Mc can be calculated by the same calculation method. That is, with reference to the deflection surface Ma, a difference in distance indicating how far the deflection surfaces Mb and Mc are away from the center of rotation or how close the center is to the center of rotation is determined as described above. Strictly speaking, the deflection point of the deflection surface Md is slightly shifted due to rotation, so the amount is calculated according to the distance from the rotation axis, and it is included in the calculation to calculate and acquire the more accurate amount of deflection surface movement. be able to. The above-mentioned calculation method is a method for calculating simply and is not limited to this in order to calculate in more detail, that is, the advance of another deflection surface with respect to the reference surface determined from the BD cycle It is characterized in that the amount of movement of the deflection surface is calculated by the angle. The calculation of the amount of movement of the deflection surface may be performed by a controller (control unit) or the like that is an arithmetic unit provided in the image forming apparatus D1.

Next, correction of jitter will be described.
FIG. 13 is a graph showing the amount of jitter in the main scanning direction at each image height due to the entrance and exit of the deflection surface in the converging optical system. Indicates the shift amount of the scanning position (printing position) in the main scanning direction with respect to the reference surface in the case of so-called surface intrusion where another surface approaches the reference surface by 10 μm due to the entry and exit of the deflection surface. . In the case of a 20 μm surface, the deviation is doubled, and in the case of a 10 μm surface, the sign of the deviation shown on the vertical axis of the graph is reversed. The amount of deviation differs depending on the optical system, mainly on the degree of convergence of the incident light beam. The jitter at each image height according to the amount of movement of the deflection surface of the rotary polygon mirror 115 is known in advance by the optical system. Therefore, by controlling the light source 112 by the control unit and electrically correcting the scanning line scanned by each deflection plane according to the in / out amount of the deflection plane determined from the BD cycle, the scanning line scanned by the reference plane Match. That is, of the (scanning line) lines in the main scanning direction of the electrostatic latent image, the writing position of the second line formed by the deflection scanning with the second deflection surface is the first deflection surface. It is made to correspond with the writing position of the 1st line formed by being deflected and scanned by. Furthermore, the length of the second line may be made to match the length of the first line.

As the electrical correction means, the following methods may be mentioned. First, the inside of each main scanning line is divided into a predetermined number, the image clock is modulated for each divided section, and the light source 112 is changed so as to change the pixel interval at the position where the image clock of the second line is modulated. Control, etc. Specifically, first, the deviation amount (jitter amount) of the scanning position in the main scanning direction with respect to the reference surface can be determined by obtaining the in / out amount of the deflection surface by the method described above. If a deviation occurs in the scanning position in the main scanning direction, it may occur that pixels of each color can not be accurately disposed at a desired position. For example, when it is desired to output black at an appropriate density in this embodiment, the toner may be scanned on the photosensitive drum at an appropriate ratio. However, if it is not possible to arrange the pixel at the desired position accurately, positional deviation between the pixels occurs, and as a result, black having a density different from the originally required color is output. Therefore, a correction value is determined from the amount of jitter corresponding to the amount of movement of the deflection surface, and the image clock is modulated for each section of each main scan line divided into a predetermined number according to the correction value. As an example, when the image clock is modulated by 1/16 image clock of the image clock before modulation (the frequency is higher) according to the correction value, the size of one pixel is 15/16 in size compared to that before modulation. Become. Each part of a pixel obtained by dividing one pixel into a predetermined number is referred to as a pixel piece. Here, 1 pixel is divided into 16
The number of divisions is arbitrarily set according to the resolution. Then, if the image clock is modulated as short as 1/16 image clock before modulation in the same way as in the previous case in six pixels in a row, the write width can be shortened by a total of 6/16 pixels for a total of six pixels. . That is, by modulating the image clock, the size of one pixel is shortened by 1/16 (pixel fragment), and as a result, the distance between the pixels is changed compared to before the modulation of the image clock. It will be done. As described above, when the correction value is +, the image clock is extended (the frequency is decreased), and when the correction value is-the image clock is decreased (the frequency is increased), and the light scanning timing from the light source to the main scanning line Changes the pixel spacing of the second line. As a result, it is possible to correct the pixels so as to be evenly arranged.

  However, the electric jitter correction means is not limited to this, and for example, the dot position is shifted in the main scanning direction by inserting and removing minute pixel pieces before and after the dots on the photosensitive drum which is an image carrier. , May be corrected. Specifically, due to the deviation of the size of each deflection surface of the rotary polygon mirror, the length of the scanning line in the main scanning direction deviates from the reference value which is the length of the ideal scanning line. The controller generates a pulse width modulation signal (PWM signal) that modulates the light from the light source 112 based on the deviation amount with respect to the reference value and the image data to be formed, and each deflection plane is based on that signal. Scan. In this PWM control, the width of one pixel in the main scanning direction is divided into a predetermined number to improve the resolution in the main scanning direction. Each portion obtained by dividing one pixel in this manner is a pixel piece. The pulse of the PWM signal having a width corresponding to the pixel piece is called a minimum width pulse. Here, a case is considered in which the resolution in the main scanning direction is 600 DPI, the number of facets of the rotating polygon mirror is four, and the bit width of PWM control is four bits, that is, one pixel is divided into 15 pixel pieces. Then, assuming that the size of the recording material is A4, the minimum width pulse is 1 inch = 25.4 mm, so it becomes a pulse with a width of 25.4 / (600 * 15) ≒ 0.0028 mm. Furthermore, when scanning using the deflection surfaces Ma and Mb of the rotating polygon mirror 115, the scanning line becomes shorter by 0.0105 mm than the reference value, and when scanning using the deflection surfaces Mc and Md, the scanning line becomes the reference It shall be 0.0105 mm longer than the value. Then, 0.0105 mm corresponds to about 3.7 periods of the minimum width pulse. This value is rounded off to determine the minimum number of pulses of width to be inserted as an integer. That is, when scanning using the deflection planes Ma and Mb, the control unit inserts a pulse signal having a width corresponding to four minimum width pulses into the PWM signal corresponding to the image data. On the other hand, when scanning using the deflection planes Mc and Md, the control unit extracts a pulse signal having a width corresponding to four minimum width pulses from the PWM signal corresponding to the image data. In this way, the scanning line is corrected so as to approach the reference value, that is, the ideal length. In this embodiment, for example, in order to make the length of the above-mentioned second line coincide with the length of the first line, the light source 112 is controlled so as to insert and remove the pixel piece in the second line.

  In this case, after the amount of movement (difference in distance) of the deflection surface of the rotary polygon mirror is calculated once, the correction value is determined from the relationship of the amount of jitter corresponding to the amount of movement of the deflection surface. However, the jitter can be corrected more accurately by determining the jitter amount correction value directly from the difference (time difference) of the BD cycle. In this case, since the jitter correction amount corresponding to the difference of the BD cycle can be determined by design, the correction value may be used.

Also, the amount of deviation of the reflected light beam due to the entry and exit of the deflecting surface is the writing end side shown in FIG. 4B where the deflecting surface to be scanned is inclined away from the light source with respect to the writing start side shown in FIG. growing. Therefore, in the optical system in which the rotation direction of the rotating polygon mirror shown in this embodiment is opposite (counterclockwise) to the rotation direction in FIG. 4 and the scanning starts from the far side from the light source, Deploy. Specifically, in FIG. 2, the BD sensor 117 is disposed on the immediate right side (light source side) of the light source 112, but this is opposite to the light source 112 across the rotary polygon mirror, and the light source is on the lower side in the figure. Position away from 112. By doing so, as shown in FIG. 4A, it is possible to reflect the light flux from the deflecting surface to the BD sensor 117 in a state in which the amount of deviation of the reflected light due to the entering and leaving of the deflecting surface is small. It is possible to calculate the amount of coming and going of the surface.
According to the above-described method and calculation means, it is possible to estimate the in / out amount of the deflection surface of the rotary polygon mirror without increasing the number of parts etc. by utilizing the existing elements generally used for the optical scanning device. In addition, it is possible to easily improve the image defect which is a problem of the image forming apparatus by using the calculated amount of movement of the deflection surface.

(Example 2)
Next, another application will be described in which the amount of movement of the deflection surface of the rotary polygon mirror 115 is known from the BD cycle. FIG. 14 is a main sectional view of an inline color image forming apparatus D2 equipped with an optical scanning device. In the image forming apparatus D2 of this embodiment, the optical scanning device S2 emits the light beams Ly, Lm, Lc, and Lk based on the image information. The luminous fluxes Ly to Lk irradiate the surfaces of the photosensitive drums 202y, 202m, 202c and 202k uniformly charged by the primary chargers 201y, 201m, 201c and 201k, thereby forming electrostatic latent images. The electrostatic latent images thus formed are visualized as toner images of yellow, magenta, cyan and black by the developing devices 203y, 203m, 203c and 203k.
On the other hand, the transfer material P placed on the feed tray is fed by the feed rollers 204a and 204b, conveyed to the nip portion between the transfer belt 205 and the photosensitive drums 202y to 202k, and the toner images of the respective colors are overlapped. Transcribed. The transfer material P to which the toner image has been transferred is heated and pressurized by the fixing device 206 to fix the toner image, and is discharged out of the apparatus by the discharge roller 207.

  FIG. 15 is a top perspective view of the optical scanning device S2 according to the present embodiment as viewed from the back of the sheet of FIG. FIG. 16 is a cross-sectional view of a main part (optical system) in the main scanning direction of the optical scanning device S2 according to the present embodiment. FIG. 17 is a cross-sectional view of an essential part (optical system) in the sub scanning direction of the optical scanning device S2 according to the present embodiment. As shown to FIGS. 15-17, optical scanning device S2 is being fixed to the frame of the image forming apparatus D2 by fixing | fixed part 211, 212, 213. As shown in FIG. The optical scanning device S2 is provided with the deflecting device 116 substantially at the center of the substantially square housing member 214, the first scanning optical system on the left side and the second scanning optical system on the right side with respect to the rotation axis 119 of the deflecting device 116. Have. The first scanning optical system has a yellow Y station and a magenta M station. The second scanning optical system has a cyan C station and a black K station. The Y station and the K station are arranged substantially symmetrically with respect to the rotary polygon mirror 115, and so are the M station and the C station.

  In the Y station, the light beam Ly emitted from the light source 215y is collimated by the collimator lens 216y, passes through the cylindrical lens 217, and is deflected by the deflecting device 116 having the rotary polygon mirror 115. The deflected light flux Ly passes through the first scanning lens 218ym and the second scanning lens 219y, and is then guided to the photosensitive drum 202y by the folding mirror 220y1 of the plane mirror to draw a scanning line. Similarly, also in the M to K stations, scanning lines are drawn on the photosensitive drums 202m to 202k of the light beams Ly to Lk emitted from the light sources 215m to 215k, respectively, through the following configuration. The configuration refers to the collimator lenses 216m to 216k, the cylindrical lens 217, the deflector 116, the first scanning lenses 218ym and 218ck, the second scanning lenses 219m to 219k, and the folding mirrors 220m1 to 220k1.

The optical scanning device S2 has a non-effective area sandwiched between an optical path of an incident light beam on a deflecting surface and an optical path of a scanning light beam (actual scanning light beam) deflected and scanned on the deflecting surface and incident on a scan surface. The BD sensor 117 is provided. The BD sensor 117 detects the deflection-scanned light flux, and controls the writing timing of a plurality of light fluxes emitted from the four light sources 215y to 215k. The above-described optical component is housed in a housing member 214 formed of glass reinforced resin or the like.
In the sub-scanning cross section shown in FIG. 17, light beams Ly and Lm (light beams Lc and Lk) are obliquely incident on the rotating polygon mirror 115 so as to be oblique to a plane perpendicular to the rotation axis 119 of the deflecting device 116. And intersect in the sub-scanning direction on the substantially deflection surface. Hereinafter, such an optical system obliquely incident on the rotating polygon mirror 115 is referred to as an oblique incident optical system.

(Problems in grazing incidence optical system)
FIG. 18 is a view showing a problem due to the entrance and exit of the deflection surface of the rotary polygon mirror in the optical scanning device using the oblique incidence optical system. In order to explain briefly, the folding mirror is omitted and the scanning lens is expressed by one sheet. This is common to all Y to K stations. Ma and Mb are deflection surfaces of the rotating polygon mirror 115, respectively. La and Lb are the optical axes of the light beams reflected by the respective deflection surfaces. As shown in FIG. 18, the light flux obliquely incident in the sub-scanning direction with respect to the deflection surface is reflected by a given deflection surface Ma and reflected by a deflection surface Mb which is a surface exit with respect to the deflection surface Ma. It is reflected off parallel to. The light beam Lb reflected in a shifted manner is incident at different positions in the sub scanning direction of the scanning lens, and is also irradiated on the photosensitive drum 202 at different positions in the sub scanning direction. Since the light beam to be originally irradiated to the same position in the sub scanning direction is irradiated to different positions, in the image, the portion where the printing becomes dense and the portion where the printing becomes sparse are repeated in the sub scanning direction, and adjacent scanning lines (lines There is variation in the distance (interval) in the sub-scanning direction between the As a result, unevenness in density (sub scanning pitch unevenness) occurs. As described above, in the case of an oblique incidence optical system which is incident at an angle in the sub-scanning direction with respect to the rotary polygon mirror 115, the entrance and exit of the deflection surface of the rotary polygon mirror 115 becomes a major issue.

  Also in the oblique incidence optical system, since the writing start timing is controlled by the BD sensor 117 as in the first embodiment, the in / out amount of the deflection surface can be specified by the same method. That is, first, the amount of deviation of the BD cycle, which is the timing of the light flux incident on the BD sensor 117 from each deflection surface, is determined in the same manner as in the first embodiment. Next, when considering the deflection surfaces Ma and Mb, the deflection surface Mb, which is the other deflection surface, is based on the deflection surface Ma as in the first embodiment, from the deviation amount of the BD cycle determined. Find out if there is a shift in distance (the amount of in and out). Then, similarly to the first embodiment, the rotation angle of the rotating polygon mirror 115 is calculated from the deviation amount of the BD cycle, and the optical axis D and the incident optical axis N with which the reflected light flux from the deflection surface Mb enters the BD sensor 117 The distance y to the deflection point P may be obtained from the intersection point Q of FIG. 19 is a view showing the relationship between the amount of in and out of the deflection surface of the rotary polygon mirror 115 and the sub scanning pitch unevenness in the oblique incidence optical system. The amount of movement in and out of the deflection surface and the amount of unevenness in sub-scanning pitch vary depending on the incident angle to the deflection surface and the magnification of the optical system, but can be calculated by design. Strictly speaking, although the "tilt" that the irradiation position in the sub-scanning direction changes depending on the image height occurs, the amount of tilt can also be calculated from the design for the tilt, so the calculated amount of tilt can be given as a correction value. Just do it.

  As described with reference to FIG. 18, in the present embodiment, when the surface is projected from or brought into contact with the reference deflection surface, a shift occurs in the sub-scanning direction. In the case where the deflection surface is exposed to a certain surface, the scanning line is shifted in the downstream direction of the photosensitive drum 202 in the direction of rotation of the photosensitive drum 202 on the photosensitive drum 202, so that the deviation direction of the scanning line is opposite to the paper tip direction. On the other hand, in the case where the deflecting surface is in contact with the surface, the photosensitive drum 202 is shifted upstream in the rotational direction of the photosensitive drum 202, so that the scanning line as an image is shifted toward the trailing edge of the paper. Also, when the incident angles to the deflection surface are opposite, they are all opposite. From this principle, the irradiation position on the surface of the photosensitive drum 202 is estimated according to the amount of movement of the deflection surface specified by the above-mentioned method. Then, by controlling the light source 112 so as to electrically correct the irradiation position according to the correction value obtained from the design, it is possible to improve the sub-scanning pitch unevenness due to the entrance and exit of the deflection surface. Incidentally, also for the correction of the sub-scanning pitch unevenness, the sub-scanning pitch unevenness and the inclination can be corrected more accurately by determining the correction value directly without obtaining the difference of the distance between the deflection surfaces from the BD cycle (time difference). . In this case, since the sub-scanning pitch unevenness correction amount and the inclination correction amount can be obtained by design according to the difference of the BD cycle, the correction value may be used.

Further, in the present embodiment, a light beam obliquely incident in the sub-scanning direction with respect to the deflection surface is reflected in parallel in a case of being reflected by a given deflection surface Ma and a case of being reflected by a deflection surface Mb. . Since the light flux reflected in a shifted manner is incident on different positions in the sub-scanning direction of the scanning lens, it is also irradiated on the photosensitive drum 202 at different positions in the sub-scanning direction. That is, since the light flux to be originally irradiated to the same position is irradiated to different positions, the portion where the printing becomes dense as the image and the portion where the printing becomes sparse are repeated. As a result, the color appears dark in the dense area and light in the sparse area, resulting in unevenness in density (sub scanning pitch unevenness). Then, the following method is mentioned as an electric correction | amendment means of subscanning pitch nonuniformity. First, the density of the main scanning line in the portion where the pitch is narrowed is reduced, and the density of the main scanning line in the portion where the pitch is widened is increased. In other words, first, the line interval (predetermined interval) in the ideal main scanning direction is determined as the reference interval without deviation. Then, the light source 112 is controlled to make the density of the line smaller than a predetermined interval smaller than the predetermined interval among the lines in the main scanning direction of the electrostatic latent image, specifically, to make the line thinner. . Then, there is a method of thickening the density of a line in which the distance between adjacent lines is wider than a predetermined distance, specifically, a method of thickening the line. As described above, by making the line thinner in the portion where the line spacing in the main scanning direction is smaller and making the line thicker in the portion where the line spacing is smaller, the pitch unevenness can be seen to be alleviated. That is, for example, a method may be used in which on / off of the light source 112 is controlled by a PWM signal according to image information and the light amount is changed for each scanning line to make the sub-scanning pitch unevenness less noticeable visually.

Also, as another means, another multi-beam light source is prepared and arranged in multiples in the sub-scanning direction, and the multi-beam light source having a smaller deviation from the reference spacing of the line spacing in the sub-scanning direction is selected. May be configured to be used. A specific example of this multi-beam light source is a VCSEL (Vertical Cavity Surface Emitting LASER), which has a configuration in which a plurality of laser light emitting points are arranged in the sub-scanning direction. For example, in the case where the deviation of the scanning line (line) spacing from the reference scanning line (line) spacing deviates upward from the ideal position, it is emitted from the lower multi-beam light source (light emitting point) Selectively use a laser (light flux). If the gap between the scanning lines (lines) deviates from the reference scanning line (line) from the ideal position, the light beam is emitted from the upper multi-beam light source (light emitting point). Select the laser (light flux). That is, by selecting a light emitting point shifted by the same distance in the opposite direction with respect to the direction in which the scanning line (line) deviates from the ideal position, the position of the scanning line (line) approaches the ideal position. It may be corrected to However, another means may be used as the electrical correction means, and the invention is not limited to this.
As described above, the image quality in the image forming apparatus can be improved by specifying the in / out amount of the deflection surface of the rotary polygon mirror from the BD cycle.

112: light source, 103: photosensitive drum, 115: rotating polygon mirror, 117: BD sensor, La, Lb, Lc, Ld: luminous flux, Ma, Mb, Mc, Md: deflection surface, 202: photosensitive drum

Claims (13)

An optical scanning device for scanning a surface to be scanned, comprising:
Light source,
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
An optical scanning device characterized by controlling a timing at which light is emitted from the light source based on the acquired difference in the distance. The difference of the distance is
A time difference between the first time and the second time;
Based on the angular velocity per unit time of the rotating polygon mirror,
The perpendicular drawn from the sensor to the incident optical axis of the light emitted from the light source to the first deflection surface, and the optical axis of the light deflected by the first deflection surface and incident on the sensor have two sides The angle between the two sides when
The perpendicular drawn from the sensor to the incident optical axis of the light emitted from the light source to the second deflection surface, and the optical axis of the light deflected by the second deflection surface and incident on the sensor have two sides Get the difference of the angle from the angle between the time of
The optical scanning device according to claim 1, wherein the optical scanning device is acquired from a difference of the acquired angles. The incident optical axis of the light emitted from the first deflection surface to the sensor is one side, and a perpendicular line is drawn from the sensor to the incident optical axis of the light emitted from the light source to the first deflection surface. The first right triangle, and
The incident optical axis of the light emitted from the second deflection surface to the sensor is one side, and a perpendicular line is drawn from the sensor to the incident optical axis of the light emitted from the light source to the second deflection surface. A second right triangle, and
When assuming
An angle formed between the incident optical axis of light emitted from the first deflection surface to the sensor and the perpendicular is represented by β, and an incident optical axis of light emitted from the second deflection surface to the sensor and the perpendicular Of the difference between the angle
The optical scanning device according to claim 1, wherein y can be obtained by the following equation, where x is a length of the perpendicular and y is a difference in the distance.
y = x × tan β-x × tan (β-α) Jitter correction is
Among the lines in the main scanning direction of the electrostatic latent image on the surface to be scanned, the control unit is configured to
In order to make the length of the second line formed by the deflection scanning by the second deflection surface coincide with the length of the first line formed by the deflection scanning by the first deflection surface,
The optical scanning device according to any one of claims 1 to 3, wherein the light source is controlled to change a distance between pixels of the second line. Jitter correction is
Among the lines in the main scanning direction of the electrostatic latent image on the surface to be scanned, the control unit is configured to
In order to make the length of the second line formed by the deflection scanning by the second deflection surface coincide with the length of the first line formed by the deflection scanning by the first deflection surface,
The optical scanning device according to any one of claims 1 to 3, wherein the light source is controlled to insert and remove a pixel piece in the second line.   The control unit is configured to, based on the difference in the distance, set the density of the first line in which the distance between the adjacent line among the lines in the main scanning direction of the electrostatic latent image is smaller than a predetermined distance. 6. The light source according to claim 1, wherein the light source is controlled so as to be thinner than the concentration of the second line and to make the concentration of the second line wider than a predetermined interval greater than the density of the other line. Optical scanning device. The plurality of light sources are arranged in the sub scanning direction,
The control unit is configured to perform a first line formed by deflection scanning with the first deflection surface among a plurality of the light sources and a second line formed by deflection scanning with the second deflection surface. 6. An electrostatic latent image is formed on the surface to be scanned by using the light source having a smaller deviation from the reference spacing of the spacing in the sub-scanning direction of and. An optical scanning device according to any one of the preceding claims. An optical scanning device for scanning a surface to be scanned, comprising:
Light source,
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
Based on the difference in the distance, in the main scanning direction of the electrostatic latent image, the distance between the adjacent line and the adjacent line is smaller than the density of the other line. An optical scanning device controlling the light source such that the density of a second line wider than a predetermined interval is higher than the density of the other lines. An optical scanning device for scanning a surface to be scanned, comprising:
A plurality of light sources arranged in the sub scanning direction;
A rotary polygon mirror provided with a plurality of deflection surfaces for deflecting and scanning the surface to be scanned by reflecting the light emitted from the light source;
A sensor that detects light reflected by the rotating polygon mirror;
A control unit that controls the light source;
Have
The control unit
A light is emitted from the light source to a first deflection surface of the rotary polygon mirror, and a first time from when the light enters the sensor from the first deflection surface, and a second deflection surface of the rotary polygon mirror from the light source Light from the second deflection surface and the second time for light to enter the sensor from the second deflection surface,
Obtaining a difference between a distance from the rotation center of the polygon mirror to the first deflection surface and a distance from the rotation center to the second deflection surface;
Of the plurality of light sources, a sub-scan of a first line formed by deflection scanning by the first deflection surface and a second line formed by deflection scanning of the second deflection surface An optical scanning device characterized in that an electrostatic latent image is formed on the surface to be scanned by using the light source having a smaller deviation from a reference spacing of the directional spacing. Said first time,
Said second time,
Compare time to get a difference,
From the acquired time difference, without acquiring the difference of the distance,
The optical scanning device according to any one of claims 1 to 9, wherein the light source is controlled based on the acquired time difference.   The sensor is disposed on the opposite side of the light source across the rotating polygon mirror when the rotating polygon mirror rotates counterclockwise and starts scanning from the side of the deflecting surface far from the light source. The optical scanning device according to any one of claims 1 to 10, wherein   The optical scanning device according to any one of claims 1 to 11, wherein no optical element is provided on an optical path along which light is emitted from the polygon mirror to the sensor. An optical scanning device according to any one of claims 1 to 12.
At least one image carrier on which light deflected from the optical scanning device is imaged on the surface;
A transfer unit configured to transfer an image formed on the surface of the image carrier onto a recording material;
An image forming apparatus comprising: