JP2017049470A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form good images in a case where an optical constitution not including a lens with fθ characteristics is used, despite variations in positions of tips of surfaces of a deflector and planes.SOLUTION: An image forming apparatus specifies a reflection surface of a deflector to be used for scanning, and emits a laser beam on the basis of profile information corresponding to the specified reflection surface, the profile information indicating the characteristics of modulation of a frequency according a main scanning position.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a technique for performing optical writing using a laser beam in an image forming apparatus using an electrophotographic system.

  An electrophotographic image forming apparatus has an optical scanning unit for exposing a photosensitive member. The optical scanning unit emits laser light based on the image data, reflects the emitted laser light with a rotary polygon mirror (deflector or polygon mirror), and transmits the scanning lens to irradiate and expose the photosensitive member. . A latent image is formed on the photoconductor by scanning the laser beam spot formed on the surface of the photoconductor by rotating the rotary polygon mirror.

  Usually, a lens having a so-called fθ characteristic is used as a scanning lens. Here, the fθ characteristic means that the laser beam is moved on the surface of the photoconductor so that the spot of the laser beam on the surface of the photoconductor moves at a constant speed on the surface of the photoconductor when the rotary polygon mirror rotates at an equal angular velocity. This is an optical characteristic for forming an image. By using a scanning lens having such fθ characteristics, appropriate exposure can be performed. However, the scanning lens having the fθ characteristic is relatively large in size and high in cost. Therefore, for the purpose of downsizing the image forming apparatus, it has been studied to use a scanning lens that does not use the scanning lens itself or that does not have the fθ characteristic.

  When a scanning lens having no fθ characteristic is used, there arises a problem that the laser beam spot on the surface of the photosensitive member does not move on the surface of the photosensitive member at a constant speed.

  Patent Document 1 discloses a technique relating to a case where a laser beam spot on the surface of a photoconductor does not move at a constant speed on the surface of the photoconductor. Japanese Patent Application Laid-Open No. H10-228867 discloses a technique for performing electrical correction so as to change the image clock frequency within one scanning period of the surface of the photoconductor so that dots formed on the surface of the photoconductor have a constant width. It is disclosed.

JP 58-1225064 A

  However, the technique of Patent Document 1 does not consider anything about the variation of the tip position and the plane on each surface of the rotary polygon mirror. If the front end position and the plane variation of each surface of the rotary polygon mirror are not uniform, the effect appears as an image, and it is difficult to obtain a high-quality image. The optical scanning unit reflects the laser beam by the rotating polygon mirror and transmits it through the scanning lens to irradiate and expose the photosensitive member. If it is not corrected accordingly, the effect will appear as an image.

  An image forming apparatus according to the present invention forms a latent image on a photosensitive member by scanning the photosensitive member with a laser beam reflected from the reflecting surface in a deflector having a plurality of reflecting surfaces and rotationally driven. A forming device, a specifying means for specifying a reflecting surface of the deflector used for scanning, and profile information corresponding to the reflecting surface specified by the specifying means, wherein the laser light is reflected by the reflecting surface. And a light emitting means for emitting the laser beam based on profile information indicating a characteristic of a scanning speed according to the main scanning position.

  According to the present invention, it is possible to perform high-quality printing even when there are variations in the tip position and the plane on each surface of the rotary polygon mirror.

1 is a schematic configuration diagram of an image forming apparatus. It is sectional drawing of an optical scanning device, (a) is a main scanning sectional view, (b) is a figure which shows a sub-scanning sectional view. It is a figure which shows the relationship between image height and partial magnification at the time of fitting the scanning position on a to-be-scanned surface with the characteristic of Y = K (theta). It is an electric block diagram which shows an exposure control structure. It is a figure which shows the timing chart of various synchronizing signals and an image signal, and the dot image on a to-be-scanned surface. It is a figure which shows the example of the image to output, and the example of the image output in the optical structure which has the imaging lens which does not have f (theta) characteristic. It is a figure which shows the detail of an image modulation part. It is a timing chart of an image signal, a modulation graph of the frequency of an image clock, and a dot image diagram. It is the image signal timing chart of multiple lines, and the modulation graph of the frequency of an image clock. It is a figure which shows the detail of a general frequency divider type | mold frequency spread clock generator. It is a figure which shows the frequency modulation information of a frequency divider type | mold frequency spread clock generator. It is a figure which shows the modulation graph of the frequency of a frequency divider type | mold frequency spread clock generator. It is a figure which shows the detail of the frequency divider type | mold frequency spread clock generator in a present Example. It is a figure which shows the detail of LowPassFilter inside the frequency divider type | mold frequency spread clock generator in a present Example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not exclusively.

[Example 1]
<Image forming apparatus>
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The laser driving unit 300 in the optical scanning device 400 serving as an optical scanning unit generates scanning light (laser light) 410 based on the image signal output from the image signal generation unit 100 and the control signal output from the control unit 200. Emitted toward the photosensitive drum (photoconductor) 500. Then, the photosensitive drum (photosensitive member) 500 charged by a charging unit (not shown) is scanned with a laser beam 410 to form a latent image on the surface of the photosensitive drum 500. A toner is attached to the latent image formed in this manner by developing means (not shown) to form a toner image corresponding to the latent image. The toner image is transferred to a recording medium such as paper fed from the paper feeding unit 900 and transported to a position where the roller 600 contacts the photosensitive drum 500. The toner image transferred to the recording medium is thermally fixed to the recording medium by the fixing device 700 and is discharged out of the apparatus through the paper discharge roller 800.

<Optical scanning device>
2A and 2B are cross-sectional views of the optical scanning device 400 according to the present embodiment. FIG. 2A shows a main scanning cross section, and FIG. 2B shows a sub-scanning cross section.

  In this embodiment, laser light (light beam) 410 emitted from the light source 401 is shaped into an elliptical shape by the aperture stop 402 and enters the coupling lens 403. The light beam that has passed through the coupling lens 403 is converted into substantially parallel light and enters the anamorphic lens 404. The substantially parallel light includes weakly convergent light and weakly divergent light.

  The anamorphic lens 404 has a positive refractive power in the main scanning section, and converts an incident light beam into convergent light in the main scanning section. The anamorphic lens 404 condenses the light beam in the vicinity of the deflecting surface 405a of the deflector 405 in the sub-scan section, and forms a long line image in the main scanning direction.

  The light beam that has passed through the anamorphic lens 404 is reflected by a deflecting surface (reflecting surface) 405a of a deflector (polygon mirror) 405. The light beam reflected by the reflection surface 405 a passes through the imaging lens 406 as the scanning light 410 and enters the surface of the photosensitive drum 500. The imaging lens 406 is an imaging optical element.

  In this embodiment, the deflector 405 has four polarization planes (405a, 405b, 405c, 405d). In addition, the imaging optical system is composed of only a single imaging optical element (imaging lens 406). The surface of the photosensitive drum 500 on which the light beam that has passed (transmitted) through the imaging lens 406 is incident is a surface to be scanned 407 that is scanned by the light beam.

  The imaging lens 406 forms an image of a light beam on the surface to be scanned 407 to form a predetermined spot-like image (spot). When the deflector 405 is driven to rotate at a constant angular velocity in the direction of arrow A by a driving unit (not shown), the spot moves on the scanned surface 407 in the main scanning direction, and electrostatically acts on the scanned surface 407 on the photosensitive member. A latent image is formed. By rotating at a constant angular velocity in the direction of arrow A, an electrostatic latent image is formed on the scanning surface 407 in the order of polarization plane 405a → 405b → 405c → 405d → 405a. In this embodiment, the light beam scans the surface to be scanned 407 for one scan by scanning using one polarization plane.

  The main scanning direction is a direction parallel to the surface of the photosensitive drum 500 and orthogonal to the moving direction of the surface of the photosensitive drum 500. The sub-scanning direction is a direction orthogonal to the main scanning direction and the optical axis of the light beam.

  A beam detect (hereinafter referred to as BD) sensor 409 and a BD lens 408 are a synchronization optical system that determines the timing for writing an electrostatic latent image on the scanned surface 407. The light beam that has passed through the BD lens 408 enters the BD sensor 409 including a photodiode and is detected. Based on the timing at which the light beam is detected by the BD sensor 409, the writing timing is controlled.

  The light source 401 is a semiconductor laser chip. The light source 401 of this embodiment has a configuration including one light emitting unit 342 (see FIG. 4). However, the light source 401 may include a plurality of light emitting units that can independently control light emission. Even when a plurality of light emitting units are provided, a plurality of light beams generated therefrom reach the scanned surface 407 via the coupling lens 403, the anamorphic lens 404, the deflector 405, and the imaging lens 406, respectively. On the surface to be scanned 407, spots corresponding to the respective light beams are formed at positions shifted in the sub-scanning direction.

  Note that various optical members such as the light source 401, the coupling lens 403, the anamorphic lens 404, the imaging lens 406, and the deflector 405 described above are housed in a housing (optical box).

<Imaging lens>
As shown in FIG. 2, the imaging lens 406 has two optical surfaces (lens surfaces), an incident surface (first surface) 406a and an exit surface (second surface) 406b. The imaging lens 406 has a configuration in which the light beam deflected by the deflection surface 405a scans the scanned surface 407 with desired scanning characteristics in the main scanning section.

  Further, the imaging lens 406 has a configuration in which the spot of the laser beam 410 on the scanned surface 407 has a desired shape. In addition, the imaging lens 406 has a conjugate relationship between the vicinity of the deflection surface 405a and the vicinity of the surface to be scanned 407 in the sub-scan section. Thus, the surface tilt is compensated (scanning position deviation in the sub-scanning direction on the surface to be scanned 407 when the deflection surface 405a tilts is reduced).

  The imaging lens 406 according to the present embodiment is a plastic mold lens formed by injection molding, but a glass mold lens may be adopted as the imaging lens 406. Since the molded lens can be easily molded into an aspherical shape and is suitable for mass production, the productivity and optical performance can be improved by adopting the molded lens as the imaging lens 406.

  The imaging lens 406 does not have a so-called fθ characteristic. That is, when the deflector 405 is rotating at an equal angular velocity, it does not have a scanning characteristic that moves the spot of the light beam passing through the imaging lens 406 at a constant velocity on the scanned surface 407. As described above, by using the imaging lens 406 having no fθ characteristic, the imaging lens 406 can be disposed close to the deflector 405 (at a position where the distance D1 is small).

  In addition, the imaging lens 406 not having the fθ characteristic can be made smaller in the main scanning direction (width LW) and the optical axis direction (thickness LT) than the imaging lens having the fθ characteristic. Therefore, the housing of the optical scanning device 400 can be reduced in size.

  In addition, in the case of a lens having an fθ characteristic, there may be a sharp change in the shape of the entrance surface and exit surface of the lens when viewed in the main scanning section. You may not get On the other hand, in the imaging lens 406 having no fθ characteristics, since there are few steep changes in the shape of the entrance surface and exit surface of the lens when viewed in the main scanning section, good imaging performance can be obtained. Can do.

  The scanning characteristic of the imaging lens 406 that does not have such an fθ characteristic is expressed by the following equation (1).

  In Expression (1), the scanning angle (scanning field angle) by the deflector 405 is θ, the light beam condensing position (image height) on the scanned surface 407 is Y [mm], and the axial image height. The image formation coefficient at is K [mm], and the coefficient (scanning characteristic coefficient) for determining the scanning characteristic of the imaging lens 406 is B. In this embodiment, the on-axis image height indicates the image height on the optical axis (Y = 0 = Ymin), and corresponds to the scanning angle θ = 0. The off-axis image height indicates the image height (Y ≠ 0) outside the central optical axis (when the scanning angle θ = 0), and corresponds to the scanning angle θ ≠ 0. Further, the most off-axis image height refers to the image height (Y = + Ymax, −Ymax) when the scanning angle θ is maximum (maximum scanning field angle). The scanning width W, which is the width in the main scanning direction of a predetermined region (scanning region) where a latent image can be formed on the scanned surface 407, is expressed as W = | + Ymax | + | −Ymax |. The center of the predetermined area is the on-axis image height and the end is the most off-axis image height.

  Here, the imaging coefficient K is a coefficient corresponding to f at the scanning characteristic (fθ characteristic) Y = fθ when parallel light enters the imaging lens 406. In other words, the imaging coefficient K is a coefficient for making the condensing position Y and the scanning angle θ proportional to each other in the same manner as the fθ characteristic when a light beam other than parallel light enters the imaging lens 406.

  Supplementing the scanning characteristic coefficient, since equation (1) when B = 0 is Y = Kθ, it corresponds to the scanning characteristic Y = fθ of the imaging lens having the fθ characteristic used in the conventional optical scanning device. . In addition, since the equation (1) when B = 1 is Y = K tan θ, it corresponds to the projection characteristic Y = f tan θ of a lens used in an imaging device (camera) or the like. That is, by setting the scanning characteristic coefficient B in the range of 0 ≦ B ≦ 1 in the expression (1), a scanning characteristic between the projection characteristic Y = ftan θ and the fθ characteristic Y = fθ can be obtained.

  Here, when the equation (1) is differentiated by the scanning angle θ, the scanning speed of the light beam on the scanned surface 407 with respect to the scanning angle θ is obtained as shown in the following equation (2).

  Further, when the equation (2) is divided by the velocity dY / dθ = K at the on-axis image height, the following equation (3) is obtained.

  Expression (3) expresses a deviation amount (partial magnification) of the scanning speed of each off-axis image height with respect to the scanning speed of the on-axis image height. In the optical scanning device 400 according to the present embodiment, the scanning speed of the light beam is different between the on-axis image height and the off-axis image height except when B = 0.

  FIG. 3 shows the relationship between the image height and the partial magnification when the scanning position on the scanned surface 407 is fitted with the characteristic of Y = Kθ. In the present embodiment, the scanning characteristic shown in Expression (1) is given to the imaging lens 406, and as shown in FIG. 3, the partial magnification increases from the on-axis image height to the off-axis image height. It has become. This is because the scanning speed gradually increases from the on-axis image height to the off-axis image height. The partial magnification of 30% means that the irradiation length in the main scanning direction on the surface to be scanned 407 is 1.3 times when light is irradiated for a unit time. Accordingly, if the pixel width in the main scanning direction is determined at a constant time interval determined by the clock cycle for image output, the pixel density differs between the on-axis image height and the off-axis image height. Details will be described later.

  Further, as the image height Y moves away from the on-axis image height and approaches the most off-axis image height (as the absolute value of the image height Y increases), the scanning speed gradually increases. As a result, the unit length is scanned when the image height is near the most off-axis image height, rather than the time taken to scan the unit length when the image height on the scanned surface 407 is near the on-axis image height. It takes less time to do. This is because, when the light emission luminance of the light source 401 is constant, the unit length when the image height is near the off-axis image height is larger than the total exposure amount around the unit length when the image height is near the on-axis image height. This means that the total exposure amount around is smaller.

  Thus, in the case of having an optical configuration that employs an imaging lens that does not have fθ characteristics, the variation in partial magnification in the main scanning direction and the total exposure amount per unit length is required to maintain good image quality. It may not be appropriate. Therefore, in order to obtain good image quality even in an optical configuration that employs an imaging lens that does not have fθ characteristics, partial magnification correction and total exposure amount correction (luminance correction) per unit length are performed. In the embodiments described below, an example relating to partial magnification correction will be described.

  Note that, as the optical path length from the deflector 405 to the photosensitive drum 500 becomes shorter, the angle of view becomes larger, so that the difference in scanning speed between the above-described on-axis image height and the most off-axis image height increases. In general, an optical configuration in which the change rate of the scanning speed is 20% or more such that the scanning speed at the most off-axis image height is 120% or more of the scanning speed at the on-axis image height is conceivable. In the case of such an optical configuration, it is difficult to maintain good image quality due to the influence of variations in partial magnification in the main scanning direction and the total exposure amount around the unit length.

  The change rate C (%) of the scanning speed is a value represented by C = ((Vmax−Vmin) / Vmin) * 100, where Vmin is the slowest scanning speed and Vmax is the fastest scanning speed. In the optical configuration of the present embodiment, the slowest scanning speed is obtained at the on-axis image height (center portion in the scanning region), and the fastest scanning speed is obtained at the most off-axis image height (end portion in the scanning region).

  It is known that the change rate of the scanning speed is 35% or more in the case of an optical configuration with an angle of view of 52 ° or more. The conditions for the angle of view to be 52 ° or more are as follows. For example, in the case of an optical configuration that forms a latent image having a short side width of an A4 sheet in the main scanning direction, the optical path from the deflection surface 405a to the scanned surface 407 when the scanning width W = 214 mm and the scanning field angle is 0 °. Length D2 (see FIG. 2) = 125 mm or less. In the case of an optical configuration that forms a latent image having a short side width of the A3 sheet in the main scanning direction, the optical path length D2 from the deflection surface 405a to the scanned surface 407 when the scanning width W = 300 mm and the scanning field angle is 0 °. (See FIG. 2) = 247 mm or less. In an image forming apparatus having such an optical configuration, it is possible to obtain good image quality even when an imaging lens having no fθ characteristic is used by using the configuration of the present embodiment described below. It becomes. The above is an example, and the present invention is not limited to this.

<Exposure control configuration>
FIG. 4 is an electric block diagram showing an exposure control configuration in the image forming apparatus of this embodiment.

  The image signal generation unit 100 includes an image modulation unit 101, a CPU 102, and a bus 103. The image signal generation unit 100 is configured to perform various operations under the control of the CPU 102, and the CPU 102 and the image modulation unit 101 are connected by a bus 103. The image signal generation unit 100 receives print information from a host computer (not shown) and generates a VDO signal (image signal) 110 corresponding to the image data. The image signal generation unit 100 also has a function as a pixel width correction unit.

  The control unit 200 performs control of the image forming apparatus and light amount control of the light source 401 in FIG. 2 as a luminance correction unit. The laser driving unit 300 causes the light source 401 to emit light by supplying current to the light source 401 based on the VDO signal 110.

  When the image signal generation unit 100 is ready to output an image signal for image formation, the image signal generation unit 100 instructs the control unit 200 to start printing through the serial communication 113. When preparation for printing is completed, the control unit 200 transmits a TOP signal 112, which is a sub-scanning synchronization signal that is a signal for notifying position information of the leading end of the sheet, and a main scanning synchronization signal for notifying position information of the left end of the sheet. Is output to the image signal generation unit 100. When receiving the synchronization signal, the image signal generation unit 100 outputs a VDO signal 110 that is an image signal to the laser driving unit 300 at a predetermined timing. In this embodiment, when the VDO signal 110 is output by the image signal generation unit 100, processing using an image output clock corresponding to the main scanning position (image height) is performed. Details will be described later.

  Next, brightness correction for improving an image will be briefly described here.

  The control unit 200 in FIG. 4 includes an IC 202 having a CPU 201, an 8-bit DA converter 203, and a regulator 204, and constitutes a luminance correction unit together with the laser driving unit 300. The laser driving unit 300 includes a memory 320, a VI conversion circuit 330 that converts voltage into current, and a laser driver IC 310, and supplies driving current to the light emitting unit 342 that is a laser diode of the light source 401. In the memory 320, partial magnification characteristic information corresponding to the optical configuration of the image forming apparatus as shown in FIG. 3 is stored, and information on the correction current supplied to the light emitting unit 342 is stored for each reflection surface. Has been. This correction current information is generated in correspondence with the partial magnification characteristic information, and the laser beam driving current for an image height with a relatively large partial magnification is used as the laser beam drive current for a relatively small image magnification. It is information used to make it larger than the drive current. In order to explain the reason for using the information on the correction current, it is assumed that the drive current having the same value is used for the exposure for the image height having a relatively large partial magnification and the exposure for the image height having a small partial magnification. In this case, since the scanning speed of the laser beam at the former image height is larger than the latter image height, the exposure amount per unit area at the former image height becomes smaller than the image height at the latter. As a result, when the latent image formed at the former image height is developed, the density of the toner image becomes lower than the density of the toner image developed at the latter image height, resulting in uneven density. End up. In order to suppress such density non-uniformity, correction current information is used. That is, the partial magnification (scanning speed) at the main scanning position where the laser light is exposed (scanned) is set so that the exposure amount per unit area of the laser light to the outside of the axial image height is equal to that for the axial image height. Based on this, the current value used for laser light emission is corrected. This is the purpose of luminance correction. This luminance correction (correction of light emission intensity) is performed for each reflection surface based on information on the correction current corresponding to the reflection surface that reflects the laser light.

  The partial magnification characteristic information is partial magnification information corresponding to a plurality of image heights in the main scanning direction. The partial magnification characteristic information may be information indicating the characteristics of the scanning speed on the surface to be scanned. The partial magnification characteristic information may be measured and stored in individual apparatuses after the optical scanning apparatus 400 is assembled. If there is little variation between the individual apparatuses, the characteristic characteristics are not measured individually. May be stored. In consideration of the fact that the partial magnification characteristic information of the optical scanning device 400 changes with the passage of time, it may be periodically measured again in the device. In addition, when accuracy is more important, remeasurement may be performed for each job. Information indicating the scanning characteristics (scanning speed) of the laser beam at each main scanning position is referred to as profile information.

  Next, the operation of the laser driving unit 300 will be described. Under the control of the CPU 201, information on the correction current for each reflecting surface stored in the memory 320 is notified to the IC 202 by the serial communication 321. Based on the correction current information for the light emitting unit 342 stored in the memory 320, the IC 202 adjusts and outputs the voltage 205 (VrefH) output from the regulator 204. The voltage 205 is a reference voltage for the DA converter 203. Next, the IC 202 sets the input data of the DA converter 203 and outputs a luminance correction analog voltage 332 that increases and decreases in synchronization with the profile information of the reflecting surface in the main scan in synchronization with the BD signal 111. Then, it is converted to a current value Id 331 by the subsequent VI conversion circuit 330 and output to the laser driver IC 310. Although an example in which the IC 202 mounted on the control unit 200 outputs the brightness correction analog voltage 332 has been shown, a DA converter is mounted on the laser driving unit 300 to generate the brightness correction analog voltage 332 in the vicinity of the laser driver IC 310. You may do it.

  The laser driver IC 310 controls ON / OFF of the light emission of the light source 401 by switching the switching circuit 311 between the current IL flowing through the light emitting unit 342 or the dummy resistor 341 in accordance with the VDO signal 110. A laser current value IL (third current) supplied to the light emitting unit 342 is a current Id (second current) output from the VI conversion circuit 330 from a current Ia (first current) having a constant current value set by the constant current circuit 312. Current) minus current. The current Ia flowing through the constant current circuit 312 is feedback-controlled by a circuit inside the laser driver IC 310 so that the luminance detected by the photodetector 343 provided in the light source 401 for monitoring the light amount of the light emitting unit 342 becomes a desired luminance P. To adjust automatically. This automatic adjustment is so-called APC (Auto Power Control). The automatic adjustment of the luminance of the light emitting unit 342 is performed while the light emitting unit 342 emits light in order to detect the BD signal outside the print region for each main scan of the laser light emission amount 316. The variable resistor 344 is adjusted in value so as to be input to the laser driver IC 310 as a desired voltage when the light emitting unit 342 emits light with a predetermined luminance at the time of factory assembly. The above is the outline of the luminance correction processing for improving the image in the optical configuration having no fθ characteristic.

  Next, timings of various synchronization signals and image signals output from the image signal generation unit 100 when performing an image forming operation will be described.

  FIG. 5A is a timing chart of various synchronization signals and image signals when the image signal generation unit 100 performs an image forming operation corresponding to one page of the recording medium. Time elapses from left to right in the figure. “HIGH” of the TOP signal 112 which is a sub-scanning synchronization signal is a signal indicating that the leading edge of the recording medium has reached a predetermined position. When the image signal generation unit 100 receives “HIGH” of the TOP signal 112, the image signal generation unit 100 outputs the VDO signal 110, which is an image signal, to the laser driving unit 300 in synchronization with the BD signal 111, which is the main scanning synchronization signal. Then, the laser driving unit 300 emits the light source 401 based on the VDO signal 110 and a latent image is formed on the photosensitive drum 500. In FIG. 5A, for simplicity of illustration, the VDO signal 110 is described as being continuously output across a plurality of BD signals 111. However, actually, the VDO signal 110 is output in a predetermined period of time from when the BD signal 111 is output until the next BD signal 111 is output.

<Partial magnification correction method>
Next, a partial magnification correction method as a main focus in the present embodiment will be described. Prior to the description, the factors of the partial magnification and the correction principle will be described with reference to FIG. FIG. 5B is a diagram illustrating the timing of the BD signal 111 and the VDO signal 110 and a dot image formed by a toner image corresponding to the latent image on the surface to be scanned 407. Time elapses from left to right in the figure.

  When the image signal generator 100 receives the rising edge of the BD signal 111, it outputs a VDO signal 110 after a predetermined timing so that a latent image can be formed at a desired distance from the left end of the photosensitive drum 4. The light source 401 emits light based on the VDO signal 110, and a latent image corresponding to the VDO signal 110 is formed on the scanned surface 407.

  First, based on the VDO signal 110, a dot-shaped latent image is formed by causing the light source 401 to emit light for the same period (that is, using the same clock as an image output clock) at the on-axis image height and the most off-axis image height. The case will be described. The size of this dot corresponds to one dot of 600 dpi (width of 42.3 μm in the main scanning direction). As described above, the optical scanning device 400 has an optical configuration in which the scanning speed of the end portion (most off-axis image height) is higher than the central portion (axial image height) on the surface to be scanned 407.

  As shown in the latent image (toner image) A, the latent image dot1 having the most off-axis image height is enlarged in the main scanning direction as compared with the latent image dot2 having the on-axis image height. As described above, since the scanning speed of the end portion (the most off-axis image height) is high, when the light source 401 emits light during the same period, the end portion (the most off-axis image height) is more in the main scanning direction. This is because the exposed area is enlarged. For this reason, in this embodiment, the frequency of the image output clock for outputting the VDO signal 110 is modulated, and the period and time width of the VDO signal 110 are corrected according to the position in the main scanning direction. That is, as shown in the latent image (toner image) B, the light emission period is controlled so that the latent image dot3 having the most off-axis image height is not enlarged in the main scanning direction as compared with the latent image dot4 having the on-axis image height. .

  By such correction, the substantial period of each pixel is relatively shorter than the center of the main scan at both ends of the main scan in the main scanning direction, and the substantial period of each pixel is at both ends of the main scan at the center of the main scan. Make it relatively longer. As a result, an image can be formed without degrading the image even with a scanning lens having no fθ characteristics.

  However, there is a possibility that the effect of the correction may not be correctly reflected simply by modulating the frequency of the image output clock according to the position in the main scanning direction. Hereinafter, a description will be given with reference to FIG.

  FIG. 6 is a diagram illustrating an example of an image desired to be output and an image output in an optical configuration having an imaging lens that does not have fθ characteristics.

  FIG. 6A shows an image to be output on a sheet. FIG. 6A shows that an image in which a large alphabetic capital letter A is drawn on a sheet is an output target image. On the other hand, FIG. 6B shows an example in which the image of FIG. 6A is output on paper. FIG. 6B shows an image output clock of the image signal generation unit using an optical scanning device having a lens that has no variation in the reflecting surfaces of the deflector (polygon mirror) 405 and does not have fθ characteristics. This is an image output at a constant frequency. As described above, in FIG. 6B, an image in which both ends (edges in the main scanning direction) of the sheet are widened is output. At this time, if there is a variation in each reflecting surface of the deflector, as shown in FIG. 6C, the influence of the variation appears in the image, and an image that appears jagged as it spreads from the center of the paper toward both ends. Will be output. That is, if there is variation between a certain surface A and another surface B among the reflecting surfaces of the deflector, even if the same VDO signal is output, the surface to be scanned and the surface B using the surface A A different latent image is formed with respect to the surface to be scanned using. Accordingly, the frequency of the clock for image output is modulated according to the position in the main scanning direction so that the image on the sheet as shown in FIG. 6B is output like the image in FIG. Even if it is controlled, the jagged portion as shown in FIG. 6C remains uncorrected. In the present embodiment, control is performed so that an image as shown in FIG. 6C is not output by performing processing that further considers the characteristics of each reflecting surface of the deflector. Details will be described below.

  FIG. 7 shows details of the image modulation unit 101 included in the image signal generation unit 100 of FIG.

  The crystal oscillator 701 is a crystal oscillator that oscillates a clock having a specific frequency, and generates an original oscillation clock for image output.

  The frequency divider 702 generates REFrence CLocK (REFCLK) which is a reference clock for SSCG (Spread Spectrum Clock Generator).

  The SSCG 703 is a spread spectrum clock generator. The SSCG 703 outputs VCLK (VideoCLocK) which is an output clock for outputting an image signal.

  Hereinafter, a specific number will be described. If the frequency of the clock oscillated by the crystal oscillator 701 is 24 MHz and the frequency division ratio of the frequency divider 702 is N = 24, REFCLK is 1 MHz. In the SSCG of this embodiment, when the nRST signal that is a reset signal becomes “True”, the SSCG returns to the frequency at which the oscillation first started. The reset signal nRST is output from the image output unit 705 in synchronization with the BD signal 111. As described above, the BD signal 111 is output in response to detection of reflected light on one reflecting surface of the deflector, and is output as a main scanning synchronization signal. Therefore, the SSCG returns to the frequency at which oscillation first started for each reflecting surface of the deflector. That is, the SSCG returns VCLK to the image output frequency required at both ends of the sheet according to the reset signal nRST for each scan.

  A register 704 is a parameter storage register for determining the modulation frequency, SweepRate, and the like of the SSCG 703. The SSCG 703 performs control according to the main scanning position and the characteristics of each reflecting surface of the deflector using the parameters stored in the register. Details will be described later.

  The image output unit 705 outputs a VDO signal that is an image signal. If VCLK (VideoCLocK), which is a video clock for outputting an image signal, has a constant frequency, the VDO signal 110, which is an image signal, is output at a constant speed corresponding thereto. If the frequency of VCLK (VideoCLocK) is modulated, the VDO signal 110 that is an image signal is output at a speed corresponding to the modulation.

  The per-surface profile storage unit 707 stores profile information for each reflection surface of the deflector 405 notified by the serial communication 113 with the control unit 200. The per-surface profile storage unit 707 stores this profile information in association with each reflecting surface of the deflector. That is, profile information that takes into account the characteristics of the reflecting surface of the deflector is stored for each reflecting surface. As will be described later, profile information common to a plurality of reflecting surfaces may be stored without storing profile information for each surface.

  The register set value calculator 706 calculates parameters for determining the SSCG modulation frequency, SweepRate, and the like based on the profile information for each reflecting surface of the deflector 405. This parameter is information for each reflecting surface as shown in FIG. Then, the register setting value calculation unit 706 writes the calculated parameters in the register 704 so that the setting value matches the profile of the current surface reflecting the laser beam. Thereby, the modulation of the frequency of VCLK (VideoCLocK) is finely adjusted for each surface in accordance with the profile information for each reflecting surface of the deflector 405, and the VDO signal 110, which is an image signal, is output at a speed corresponding to the modulation. .

  FIG. 8 shows a BD signal (Beam Detect) that is a main scanning synchronization signal, an nRST signal (nReSeT), a VDO signal (ViDeO) that is an image signal, a frequency transition diagram of a VCLK that is a video clock for image output, and an image dot Describe the image.

  FIG. 8A shows a 1-BD section of main scanning. The 1BD section is a section from the detection of the rising edge of the BD signal to the detection of the rising edge of the next BD signal. FIG. 8B shows a reset signal for returning the SSCG frequency to the frequency at which oscillation was first started. Assume that a reset pulse of the nRST signal is generated every time the BD signal 111 rises. FIG. 8C shows an output section of an image signal output in one BD section.

  FIG. 8D shows that the frequency of VCLK is modulated (changed) in one BD interval in synchronization with the BD signal 111. A straight line 801 in FIG. 8D indicates frequency characteristics when frequency modulation is not performed. That is, when frequency modulation is not performed, VCLK outputs a constant frequency. On the other hand, a solid line 802 and a dotted line 803 in FIG. 8D indicate the frequency characteristics of VCLK subjected to frequency modulation described in this embodiment. In the example of FIG. 8, the number of reflection surfaces of the deflector 405 is four (surfaces 405a, 405b, 405c, and 405d), and the surfaces 405a, 405b, and 405c have substantially the same characteristics (described by a solid line 802). This is the case. Then, 405d shows a case of a unique characteristic (described by a dotted line 803) as compared with other surfaces. Such characteristics (profile information) can be obtained by measuring each optical device after assembling the optical scanning device 400, similarly to the partial magnification characteristic information described above. In addition, when there is little variation between individual devices, representative characteristics may be obtained without performing individual measurement. In consideration of the fact that the partial magnification characteristic information of the optical scanning device 400 changes with the passage of time, it may be periodically measured again in the device. In addition, when accuracy is more important, remeasurement may be performed for each job.

  As a characteristic of VCLK indicated by a solid line 802 and a dotted line 803 in FIG. 8D, when a reset pulse of the nRST signal is generated, oscillation starts from a high frequency and the frequency gradually decreases. In the case of VCLK on the surfaces 405a, 405b, and 405c indicated by the solid line 802, the frequency is lowest in the middle of one main scanning synchronization period, that is, around the center of the paper, and gradually increases toward the edge of the paper. Come. On the other hand, in the case of VCLK on the surface 405d indicated by the dotted line 803, the frequency becomes the lowest slightly before the middle of one main scanning synchronization period, that is, slightly to the left of the center of the paper, and gradually toward the edge of the paper. The frequency goes up. In the example of FIG. 8, the reset by the nRST signal is particularly useful when the reflection surface profile is changed, such as when the surface 405c is changed to the surface 405d and when the surface 405d is changed to 405a. Here, the center and the edge of the sheet have been described, but more precisely, the area of the photoconductor corresponding to the center and the edge of the sheet.

  FIG. 8E shows the width of 1 dot output in the 1BD section, and shows the width according to the frequency characteristic of VCLK shown in FIG. The width of 1 dot here is not the actual width exposed on the surface to be scanned 407 but the time when VDO corresponding to 1 dot is output. As indicated by a straight line 801 in FIG. 8D, when the frequency is not modulated, the frequency of VCLK is always constant, so the width of 1 dot is always constant. On the other hand, when the frequency modulation shown by the solid line 802 and the dotted line 803 in FIG. 8D is performed, the frequency of VCLK is modulated, and the frequency at both ends becomes higher than that at the center. For this reason, the time required for 1 dot is shorter at both ends than at the center. Therefore, as shown in FIG. 8E, the width of 1 dot at both end portions is shortened. As described above, when an imaging lens having no fθ characteristic is used, a partial magnification relationship as shown in FIG. 3 is generated, so that an image as shown in FIGS. 6B and 6C is obtained. Here, when image output is performed using an image output clock having frequency characteristics as shown in FIG. 8D, a desired image as shown in FIG. 6A is output.

  In the frequency characteristics shown in FIG. 8D, the frequency at the end in the main scanning direction is higher than that at the center. In this embodiment, the frequency relationship between the end portion in the main scanning direction and the center is merely a relative relationship. For example, even when processing is performed such that the value of REFCLK in FIG. 6 is set to a high value and the value of VCLK is modulated to a frequency at which both ends and the center are low, the main value of VCLK is set. The frequency relationship between the end in the scanning direction and the center is the same as in FIG. Therefore, the case where such frequency modulation is used is also included in the present embodiment.

  Next, FIG. 9 shows the transition of the frequency of VCLK for several lines. FIG. 9A shows a TOP signal that is a sub-scanning synchronization signal. The TOP signal is issued when printing is started and the leading edge of the sheet is conveyed to a specific position. Another application of the TOP signal can be used to indicate which surface the deflector 405 is scanning. For example, the control unit 200 always controls the TOP signal so as to start from the surface 405a among the four reflecting surfaces of the deflector 405. As an example, a predetermined mark is attached to the reflecting surface of the deflector 405, and the timing at which the TOP signal is output and the timing at which the surface 405a becomes the reflecting surface are synchronized. Thereby, the image modulation unit 101 starts processing from processing using the profile information corresponding to the surface 405a, and performs processing by sequentially changing the profile information according to the BD signal.

  FIG. 9B shows that a BD signal, which is a main scanning synchronization signal, is issued for each line. FIG. 9C shows that the VDO signal that is an image signal is output in each BD section. FIG. 9D shows that the frequency of VCLK is a set value based on the profile information of each reflecting surface of the deflector 405 and the frequency is modulated in each BD section.

  In the present embodiment, an example in which the optical scanning device 400 outputs laser light for one scan in synchronization with the BD signal will be described. However, the optical scanning device 400 includes a plurality of light emitting units and is provided for a plurality of scans in synchronization with the BD signal. It may be configured to output laser light.

  Next, a frequency divider type SSCG (spread spectrum clock generator) will be described. For convenience of explanation, a general SSCG will be described first. Thereafter, the SSCG used in this embodiment will be described.

  FIG. 10 describes a detailed view of a common frequency divider type SSCG. For specific explanation, the frequency is defined as follows. The reference clock REFCLK = 1 MHz and the video clock VCLK output from the SSCG is modulated in a range from a maximum of 945 MHz to a minimum of 720 MHz in the 1BD section. In this embodiment, the 1BD section is divided into a plurality of small sections, and VCLK for each small section is set so as to approximate the frequency characteristics shown in FIG. In the present embodiment, the frequency modulation information (see FIG. 11) calculated by the register setting value calculation unit 706 includes the number of small sections (the number of Tables in FIG. 11) and the VCLK set in each small section (see FIG. 11). Information (M value in FIG. 11) indicating the frequency). In the present embodiment, the number of small sections is 32, and VCLK set for each small section increases stepwise (frequency increases) as the position of the small section goes from the center of the 1BD section to both ends. ing.

  If REFCLK is 2 MHz and M changes by 1 with respect to the division ratio M, the voltage controlled oscillator VCO (Voltage Control Oscillator) increases or decreases by 2 MHz. Originally, SSCG is a technology that applies PLL (Phase Locked Loop).

  The frequency phase comparator 1001 compares the reference clock REFCLK and the feedback clock FBCLK (Feed Back CLocK), and issues an error modulation pulse. The error modulation pulse passes through a low pass filter LPF 1002 (Low Pass Filter). The LPF 1002 removes unnecessary noise components and converts the error modulation pulse into a DC voltage. The LPF 1002 is generated by a resistor and a capacitor. Also, it should be noted that the correct frequency cannot be generated unless the resistance value and the capacitor value that generate the LPF 1002 are optimized by the frequency to be generated. Passing through the LPF 1002, the error modulation pulse is converted into a DC voltage and input to a VCO 1003 (Voltage Control Oscillator) which is a voltage controlled oscillator. Whether to increase or decrease the frequency is determined by the DC voltage value input to the VCO 1003.

  Here, assuming that the frequency division ratio M of the frequency divider 1004 is constant, the VCO 1003 itself has a function of increasing the frequency if it is left as it is. However, the error modulation pulse issued by the frequency phase comparator 1001 becomes a DC voltage value that attempts to lower the frequency to the LPF 1002, and this time the VCO 1003 starts to lower the frequency. That is, when the feedback FBCLK decreases with respect to the reference REFCLK, the frequency phase comparator 1001 issues an error modulation pulse for increasing the frequency. When FBCLK rises with respect to REFCLK, the frequency phase comparator 1001 issues an error modulation pulse for lowering the frequency. This repetition is a state where the PLL is locked, and the frequency is kept constant.

  By changing the value of M, which is the frequency division ratio of the frequency divider 1004, the SSCG function becomes effective. The frequency is changed little by little by changing the value of the frequency division ratio M in a fixed time unit. The basic principle and outline of a general PLL and frequency division type SSCG have been described above. Such a frequency division type SSCG is used as a programmable oscillator by determining the value of the frequency division ratio M to an arbitrary fixed value.

  FIG. 11 shows frequency modulation information of the frequency divider type SSCG, and shows the relationship between the Table, the M value, the setting value of the LPF 1302 described later, and the frequency of VCLK to be output. The frequency modulation information as shown in FIG. 11 is calculated by the register setting value calculation unit 706 based on the profile information stored in the per-surface profile storage unit 707 and set in the register 704. The frequency modulation information of the reflection surface is calculated from the characteristics of the scanning speed of one scan on the surface to be scanned 704 of the laser beam reflected by the reflection surface, for controlling the emission of the laser beam for each reflection surface. It can be said that it is control information. In the present embodiment, different profile information is stored in the profile storage unit 707 for each of the surfaces 405a, 405b, 405c, and 405d, but the profile information for the surfaces 405a, 405b, and 405c is the same. Will be described. Therefore, the frequency modulation information written to the register 704 for each surface is the same for the surfaces 405a, 405b, and 405c as shown in FIG. 11, but only for the surface 405d. What is important here is that the frequency modulation information of each surface has a small difference in the scanning width (exposure width, latent image width) of laser light per dot at each main scanning position on the surface to be scanned 407 for all reflecting surfaces. It is calculated so that.

  In this embodiment, since REFCLK is set to 1 MHz, the value of M becomes the frequency of VCLK as it is. In the case of FIG. 11, the frequency is gradually decreased from the maximum frequency of 945 MHz, and the frequency is gradually increased after the minimum frequency of 720 MHz. The frequency gradually changes near the center of the paper, and the frequency rapidly increases and decreases at both ends of the paper. The table changes from 1 to 1 in a fixed time unit, and the frequency of the VCO 1003 is determined based on the M value corresponding to the table. That is, Table is a parameter indicating the position (image height) in the main scanning direction. One Table corresponds to one small section obtained by dividing the 1BD section described above into a plurality of sections. The value of M increases around the center of the paper and the frequency increases. The value indicating the LPF 1002 is changed where the frequency exceeds 800 MHz. Processing associated with this change will be described later.

  FIG. 12 is a diagram showing a state of SSCG frequency modulation according to the frequency modulation information of FIG. FIG. 12A shows a setting example corresponding to the reflecting surfaces 405a, 405b, and 405c of the deflector 405, and FIG. 12B shows a setting example corresponding to the reflecting surface 405d.

  Thick lines shown in FIGS. 12A and 12B indicate the frequency of the clock (VCLK) modulated by SSCG according to the frequency modulation information of FIG. Note that the dotted line indicates the frequency characteristic of FIG. In SSCG, the frequency of VCLK is gradually reduced by changing the M value at a constant interval. The same frequency is continuously output in a fixed time unit, and when the fixed time passes, it shifts to the next frequency.

  FIG. 13 is a detailed view of the frequency divider type SSCG in the present embodiment. The frequency phase comparator 1001, VCO 1003, and frequency divider 1004 are the same as those shown in FIG. The LPF 1302 is a low-pass filter, and switches the internal circuit depending on the frequency band as will be described later. The LPF 1302 (LowPassFilter) is generated by a resistor and a capacitor, but it is necessary to determine a resistance value and a capacitance according to the frequency characteristics generated by the VCO 1003. As a characteristic of the imaging lens in this embodiment, it is necessary to change the frequency by about 30%. In that case, since the frequency range is too wide, there is a possibility that constant resistance and capacitor values cannot always be selected. Accordingly, it may be necessary to dynamically change the value of the LPF 1302 during frequency modulation.

  The M value & LPF table 1305 is a table for loading the frequency division value M from the register 704 to the frequency divider and selecting the value of the LPF 1302. In the register 704, frequency modulation information (FIG. 11) corresponding to the current reflecting surface is set by the register set value calculation unit 706. The LPF 1302 and the frequency divider 1004 are configured to be able to select a value with a selector. For the LPF 1302, two values can be selected with one selector signal, and for the frequency divider 1004, 10 values are selected. It is assumed that 1024 values can be selected by the selector signal. When the nRST signal is applied, M returns to the initial value, that is, the value corresponding to Teable1 in FIG. That is, the M value and the LPF selection value return to the values corresponding to Table1.

  The load time determiner 1306 is a load time determiner for determining a time interval when shifting the M value of the M value & LPF table 1305 and the selection value of the LPF. Based on the set value, signals are generated at regular intervals, and the M value and the LPF value are determined based on this signal.

  In the example of FIG. 13, the M value & LPF table 1305 and the load time determiner 1306 are included in the SSCG. The values stored in the M value & LPF table are calculated by the register setting value calculation unit 706 based on the profile information stored in the per-surface profile storage unit 707 shown in FIG. 7, and the parameters (frequency modulation) stored in the register 704 are calculated. Information). Alternatively, the M value & LPF table 1305 itself may be configured as the per-surface profile storage unit 707, the register setting value calculation unit 706, and the register 704 in place of the SSCG. Further, without providing the per-surface profile storage unit 707 and the register set value calculation unit 706, the following may be performed. That is, a storage unit for storing frequency modulation information for each reflection surface calculated in advance based on profile information for each reflection surface at the time of factory shipment, and frequency modulation information corresponding to the current reflection surface are selected from the storage unit. Thus, a setting unit for setting in the register 704 may be provided.

  FIG. 14A shows a detailed view of the LPF 1302 which is a LowPassFilter inside the frequency divider type SSCG representing the present embodiment.

  The LPF 1302 of this embodiment includes two types of LowPassFilter composed of a resistor and a capacitor, and a selector that selects one of the two types of LowPassFilter. In FIG. 14A, C and D are the LowPassFilters, but the values of the resistors and capacitors are different. This selects a LowPassFilter according to the frequency band characteristics. The value of each LowPassFilter is determined according to the required frequency. For example, LowPassFilterC is a value suitable for 600 to 800 MHz. LowPassFilterD is a value suitable for 800 to 1000 MHz. In this way, the value of the LPF is switched according to the value stored in the M value & LPF table 1305 according to the required frequency.

  FIG. 14B shows an example of the LPF frequency range and the VCLK frequency range that are possible in this embodiment. LowPassFilterC is a value suitable for 600 to 800 MHz, and LowPassFilterD is a value suitable for 800 to 1000 MHz. When frequency modulation is performed in the frequency range from 945 MHz to 720 MHz as in this embodiment, the VCLK frequency is stabilized by changing the LPF value of the M value & LPF table 1305 from C to D at 800 MHz as a boundary. It becomes possible to supply to.

  By such a method, for example, the frequency as shown in FIG. 12 can be modulated without a sine curve, and for example, it is possible to finely adjust the frequency of VCLK even for a slight fluctuation of the deflector. .

  In the above description, an example in which two types of profiles are used as the profile for each surface with respect to four reflecting surfaces of the deflector 405 has been described. At this time, which profile is to be used for which surface may be notified from the control unit 200 to the image signal generation unit 100, or the CPU 102 of the image signal generation unit 100 may approximate the four types of profiles to two types. You may judge. Of course, four types of settings may be made according to the four types of profiles. However, if approximation is possible, the circuit scale can be reduced and control can be afforded.

  As described above, according to the present embodiment, the image output clock is controlled in consideration of the profile for each reflecting surface of the deflector, so that an imaging lens having no fθ characteristic is used. Can also form a good image.

[Example 2]
In the first embodiment, the control unit 200 detects which surface the deflector 405 is scanning, and the control unit 200 controls the TOP signal so as to always start from the surface 405a. Thus, an example has been described in which the CPU 102 of the image signal generation unit 100 knows which surface the deflector 405 is scanning. As another method, the image signal generation unit 100 side can be configured to count the period of the BD signal and determine which surface the deflector 405 is scanning from the difference in the period.

<Other examples>
In the above embodiment, frequency modulation information indicating the frequency of VCLK when emitting laser light is obtained based on the profile information of each reflecting surface, and the emission time of laser light for each reflecting surface is determined according to that information. It was something to modulate. Then, the exposure width (VDO output period) per dot (one pixel) in the image data of the laser beam that scans the scanned surface 407 by this frequency modulation is controlled for each reflecting surface. However, the present invention is not limited to the control method of the width of 1 dot (VDO output period per pixel. Exposure width) by such frequency modulation, and any method capable of adjusting the width of 1 dot for each main scanning position. That's fine. For example, instead of modulating the frequency of VCLK, using a clock having a frequency higher than VCLK (for example, 32 times VCLK) (referred to as 32 VCLK), the data of one pixel is shortened by a minute time based on the main scanning position. There is a method of outputting as VDO. Specifically, the 1BD section is divided into a plurality of small sections (for example, 32 small sections) as in the above embodiment. Then, for each small section, based on the profile information and the main scanning position of the small section, it is determined how long the data for one pixel is output as VDO.

  For example, since the small section near the on-axis image height is a small section of the standard scanning speed according to the profile information, the data for one pixel for each pixel is only 32 cycles of 32 VCLK (that is, a period equal to the above VCLK). Output as VDO. On the other hand, the small section at the most off-axis image height is a small section whose scanning speed is 1.3 times faster than the reference according to the profile information. Therefore, if data for one pixel is output as VDO for 32 cycles of 32 VCLK for each pixel, as described above, the exposure width of each pixel included in the small section is compared with that near the axial image height. 1.3 times longer. Therefore, it is desirable to shorten the VDO output period based on the data of each pixel in a small section at the most off-axis image height by about 1 / 1.3≈0.77 times. For example, in the small section, data for one pixel is output as VDO for 24 cycles of 32 VCLK (that is, 0.77 times the above VCLK). Also for other small sections, based on the profile information, how much the scanning speed in the small section is faster than the reference is calculated, and how much the VDO output period should be shortened is calculated. For example, according to the profile information shown in FIG. 3, since the scanning speed is 1.1 times the reference in the small section near the middle of the most off-axis image height and the on-axis image height, the data for one pixel is equivalent to 29 cycles of 32 VCLK. Only (= 32 × 1 / 1.1) may be output as VDO. This corresponds to the frequency modulation information calculation process based on the profile information in the first and second embodiments.

  The VDO output period may be relatively controlled according to the main scanning position. That is, as described above, the VDO output period may not only be shortened based on the profile information, but conversely may be lengthened. That is, when the scanning speed at the most off-axis image height is taken as a reference, it is desirable that the VDO output period for outputting data for one pixel is lengthened based on the profile information toward the on-axis image height. Such control of the number of clock cycles may be performed for each reflecting surface based on profile information of each reflecting surface.

  In any case, what is important in the present invention is to perform various corrections corresponding to the profile information for each reflecting surface (in other words, information relating to the scanning speed of the laser beam). The various types of correction include adjustment of the exposure width (VDO output period per dot) on the surface to be scanned 407 corresponding to each reflective surface, and exposure amount correction (the above-described luminance correction). ) And other image corrections.

  Another image correction is adjustment of the VDO output timing. That is, the laser beam reflected by the reflecting surface having a relatively high scanning speed near the most off-axis image height is reflected by the reflecting surface having a relatively small scanning speed near the most off-axis image height. Rather, it is considered that the scanning position of the image edge portion is advanced to the axial image height side. For example, the image output unit 705 determines the output timing of the image signal (VDO) when forming the image through the former reflecting surface, and the image output clock has elapsed from the detection of the BD signal 111 by the number of first cycles. It is time. Further, the image output unit 705 determines the output timing of the image signal (VDO) when forming the image through the latter reflecting surface, and the image output clock from the detection of the BD signal 111 is less than the first cycle number. When two cycles have elapsed. This output timing relationship is determined according to the profile information of each reflecting surface. Alternatively, when the number of cycles on the former reflecting surface (first cycle number) is used as a reference, based on the profile information on the former reflecting surface and the latter reflecting surface, how many cycles from the first cycle number. To increase (or decrease). Then, the second cycle number is obtained by adding (or subtracting) the obtained cycle number to the first cycle number.

  In the above embodiment, the image forming apparatus to which the optical scanning device using the imaging lens having no fθ characteristic is applied has been described as an example. However, the example described above may be applied to an image forming apparatus to which an optical scanning device using an imaging lens having fθ characteristics is applied. That is, in the case where variations occur in each reflecting surface of the deflector, a better image can be obtained by applying the above-described processing even when an imaging lens having θ characteristics is used. Can do.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Claims (18)

An image forming apparatus that forms a latent image on the photosensitive member by scanning the photosensitive member with a laser beam reflected from the reflecting surface of a deflector that has a plurality of reflecting surfaces and is driven to rotate.
A specifying means for specifying a reflecting surface of the deflector used for scanning;
Based on profile information corresponding to the reflecting surface specified by the specifying means, the profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface, the laser light is A light emitting means for emitting light;
An image forming apparatus comprising: Storage means for storing profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected from the reflecting surface in the deflector, in association with each reflecting surface;
The profile information stored corresponding to the first reflecting surface of the deflector and the profile information stored corresponding to the second reflecting surface of the deflector have different scanning speed characteristics. The image forming apparatus according to claim 1, wherein:   The light emitting means is profile information corresponding to the reflecting surface specified by the specifying means, and is based on profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface. The image forming apparatus according to claim 1, wherein a period during which the laser beam is emitted is controlled.   The light emitting means is profile information corresponding to the reflecting surface specified by the specifying means, and is based on profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface. 4. The image forming apparatus according to claim 1, wherein the intensity of the laser light emission is controlled. 5. A first receiving means for receiving the sub-scanning synchronization signal;
5. The image forming apparatus according to claim 1, wherein the specifying unit specifies a reflection surface used for the scanning based on a received sub-scanning synchronization signal. 6. A second receiving means for receiving a main scanning synchronization signal;
5. The image forming apparatus according to claim 1, wherein the specifying unit specifies a reflection surface used for the scanning by counting the number of received main scanning synchronization signals. 6.   The light emitting means is profile information corresponding to the reflecting surface specified by the specifying means, and is based on profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface. The image according to any one of claims 1 to 6, wherein the laser beam is emitted by controlling a frequency of an output clock of an image signal per pixel for emitting the laser beam. Forming equipment.   The light emitting means is profile information corresponding to the reflecting surface specified by the specifying means, and is based on profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface. The laser light is emitted by controlling the number of output clock cycles of an image signal per pixel for emitting the laser light. Image forming apparatus.   The light emitting means is configured to switch the profile information to be used when the reflecting surface specified by the specifying means is switched from the first reflecting surface to a second reflecting surface different from the first reflecting surface. The image forming apparatus according to claim 1, wherein the image forming apparatus switches to profile information corresponding to the reflective surface.   The image forming apparatus according to claim 9, wherein the light emitting unit determines that the reflection surface is switched every time a main scanning synchronization signal is received.   The light emitting means switches the profile information to be used when the reflecting surface specified by the specifying means is switched from the first reflecting surface to a second reflecting surface having a characteristic different from that of the first reflecting surface. The image forming apparatus according to claim 1, wherein the image forming apparatus switches to profile information corresponding to the second reflecting surface.   The image forming apparatus according to claim 1, wherein the light emitting unit uses profile information common to at least two of the plurality of reflecting surfaces.   13. The image formation according to claim 1, wherein the light emitting unit uses common profile information on a reflective surface having similar characteristics of the reflective surface among the plurality of reflective surfaces. apparatus.   The image forming apparatus according to claim 1, wherein the light emitting unit uses different profile information on each of the plurality of reflecting surfaces.   The profile information includes at least one pixel in a region including an on-axis image height, rather than one pixel in a region including the most off-axis image height, during the light emission period of the laser light emitted by the light emitting unit. 15. The image forming apparatus according to claim 1, further comprising information for making the length relatively longer.   The image forming apparatus includes an imaging lens having no fθ characteristics, and the laser beam reflected by the deflector scans the photosensitive member through the imaging lens. The image forming apparatus according to any one of 15. An image forming apparatus that forms a latent image on the photosensitive member by scanning the photosensitive member with a laser beam reflected from the reflecting surface of a deflector that has a plurality of reflecting surfaces and is driven to rotate.
A specifying means for specifying a reflecting surface of the deflector used for scanning;
Control means for controlling the emission of the laser light based on control information obtained according to the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface specified by the specifying means;
An image forming apparatus comprising: A control method in an image forming apparatus for forming a latent image on the photosensitive member by scanning the photosensitive member with a laser beam reflected from the reflecting surface in a deflector having a plurality of reflecting surfaces and rotationally driven,
A specifying means for specifying a reflecting surface of the deflector used for scanning;
Based on profile information corresponding to the reflecting surface specified by the specifying means, the profile information indicating the characteristics of the scanning speed according to the main scanning position of the laser light reflected by the reflecting surface, the laser light is A light emitting means for emitting light;
An image forming apparatus comprising: