JP2007185856A - Optical scanner and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of image expansion/contraction resulting from a variation in scanning speed of a light beam caused by a variation in oscillation amplitude of a deflection mirror. <P>SOLUTION: Time interval TA1 from time T1 when first detection signal Hsync1 is outputted till time T2 when second detection signal Hsync2 is outputted from a sensor 60 following the first detection signal Hsync1 is determined, and then a speed variation is determined from a variation in the time interval (steps S3-S6). From the speed variation thus determined, image information is corrected to create corrected image information (step S7) and a spot is formed on the scanned surface from the corrected image information (step S8). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device used in an image forming apparatus such as a laser printer and a method for controlling the optical scanning device, and more particularly to a technique for scanning a scanning surface with a light beam in a main scanning direction.

  In this type of optical scanning device, a light beam modulated based on image information by a video clock having a predetermined frequency is emitted from a light source. The modulated light beam is deflected by the deflector toward the scanning optical system. As a result, the modulated light beam scans the surface to be scanned in the main scanning direction via the scanning optical system, and the light beam is irradiated in a spot shape at a predetermined position on the surface to be scanned. Hereinafter, when simply referred to as “spot” in the present specification, it represents a light beam irradiated onto the surface to be scanned in a spot shape.

  In order to reduce the size and increase the speed of the deflector, it has been proposed to use the deflecting mirror surface as a deflector by vibrating the surface (see Patent Document 1). That is, in this apparatus, the deflection mirror surface supported by the torsion bar is sine-oscillated, and the light beam emitted from the light source is reflected by the deflection mirror surface and reciprocally scanned in the main scanning direction on the surface to be scanned. .

  In the apparatus described in Patent Document 1, a scanning optical system having an arc-sin characteristic is used to scan the surface to be scanned at a constant speed with the light beam deflected by the deflecting mirror surface oscillating sinusoidally as described above. ing. That is, the angular velocity of the incident angle of the light beam deflected by the sinusoidally oscillating deflecting mirror surface to the scanning optical system becomes slower as the incident angle increases. Therefore, for example, when a scanning optical system that does not have distortion characteristics is used, the scanning speed of the light beam on the surface to be scanned becomes slower as the distance (image height) from the optical axis in the main scanning direction increases. Therefore, in order to compensate for the decrease in scanning speed at a position where the image height is large, a scanning optical system having an arc-sin characteristic that scans the light beam with an exit angle larger than the incident angle as the incident angle increases is used. It has been.

JP 2002-182147 A (page 3, page 5, FIGS. 9 and 10)

  However, by using a scanning optical system having an arc-sin characteristic, the absolute value of the scanning speed may fluctuate for the following reason even when the scanning speed is uniform. That is, the vibration characteristics of the deflecting mirror surface fluctuate due to various factors such as individual differences of the vibrating mirror, assembly accuracy, and changes in the internal environment such as the internal temperature. When the vibration amplitude of the deflecting mirror surface changes due to a change in the in-machine environment, the absolute value of the scanning speed of the light beam on the surface to be scanned changes. As a result, when an image is formed on the surface to be scanned using such an optical scanning device, there has been a problem that the image expands and contracts in the main scanning direction.

  The present invention has been made in view of the above problems, and deflects a light beam by a deflecting mirror surface oscillating sinusoidally, and transmits the light beam to a surface to be scanned at a constant speed via a scanning optical system having arc-sin characteristics. An object of the present invention is to provide a technique for suppressing expansion and contraction of an image in a main scanning direction even when an image is formed on a surface to be scanned by using the optical scanning device in an optical scanning device that performs reciprocating scanning. .

  The control method of the optical scanning device according to the present invention includes a light source that emits a light beam, a scanning optical system having an arc-sin characteristic, and a light beam emitted from the light source is deflected by a deflection mirror surface that sine vibrates. A deflector that reciprocally scans the deflected light beam in the main scanning direction in a second scanning range wider than the first scanning range corresponding to the effective scanning region of the surface to be scanned via the scanning optical system, and deviates from the first scanning range. And a sensor that outputs a detection signal by detecting a light beam that moves in a predetermined position, and a video clock generator that generates a video clock having a predetermined frequency. The light beam is spotted in an effective scanning area of the surface to be scanned. In an optical scanning apparatus capable of forming a spot in the effective scanning region by irradiation, a light beam modulated with reference to a video clock is emitted from a light source, and the modulated light beam is effectively applied to a scanned surface. An optical scanning device control method for causing an optical scanning device to perform an optical scanning operation for scanning an inspection region, and in order to achieve the above object, based on a detection result of a sensor, a scanning speed of a light beam on a surface to be scanned Among the image information indicating whether or not to form a spot for each pixel given to the optical scanning device from the outside of the optical scanning device, and a main scanning Online data indicating that an online image is formed by forming a spot at each of a plurality of pixels adjacent to each other in the direction, and an offline image is formed without forming a spot at each of a plurality of pixels adjacent to each other in the main scanning direction. The result of the speed fluctuation detection process is the extraction process for extracting offline data indicating the number of pixels constituting the online data extracted by the extraction process. A correction step of correcting the image information to generate corrected image information by changing the number of pixels constituting the offline data extracted by the extraction step based on the result of the speed motion detection step And a spot forming step of modulating the light beam based on the corrected image information, scanning the modulated light beam over the effective scanning area of the surface to be scanned, and forming a spot in the effective scanning area.

  The optical scanning device according to the present invention also includes a light source that emits a light beam, a scanning optical system having arc-sin characteristics, and a deflection mirror surface that sinusoidally vibrates the light beam emitted from the light source. A deflector for reciprocally scanning the deflected light beam in the main scanning direction in a second scanning range wider than the first scanning range corresponding to the effective scanning region of the surface to be scanned via the scanning optical system, and deviating from the first scanning range It includes a sensor that detects a light beam that moves and outputs a detection signal, and a video clock generator that generates a video clock of a predetermined frequency, and irradiates the effective scanning area of the surface to be scanned in a spot shape. In addition, a spot can be formed in the effective scanning area, and a light beam modulated on the basis of the video clock is emitted from the light source, and the modulated light beam is applied to the effective scanning area of the scanning surface. In the optical scanning device that performs the optical scanning operation to be examined, based on the detection result of the sensor, a speed fluctuation detecting means for detecting a fluctuation from a predetermined speed of the scanning speed of the light beam on the surface to be scanned, and an outside of the optical scanning apparatus To form an online image by forming spots on a plurality of pixels adjacent to each other in the main scanning direction among the image information indicating whether or not to form a spot for each pixel given to the optical scanning device. And online data extracted by the extraction means, and online data indicating that an offline image is formed without forming a spot on each of a plurality of pixels adjacent to each other in the main scanning direction. Is changed based on the result of the speed fluctuation detecting means, and the off-line extracted by the extracting means is changed. A correction unit that corrects image information by generating the corrected image information by changing the number of pixels constituting the data based on the result of the velocity motion detection unit, and modulates the light beam based on the corrected image information, It further comprises spot forming means for scanning the effective scanning region of the surface to be scanned with the modulated light beam to form spots in the effective scanning region.

  The invention configured as described above guides the light beam deflected by the sinusoidally oscillating deflecting mirror surface to the surface to be scanned through the scanning optical system having the arc-sin characteristic, so that the light beam is directed in the main scanning direction. The following optical scanning operation is performed. That is, a light beam modulated by a video clock having a predetermined frequency is emitted from a light source, and the modulated light beam is scanned over an effective scanning area of a surface to be scanned. A spot is formed by irradiating a predetermined position of the effective scanning region with a light beam in a spot shape. Here, what has become a problem from the past is the fluctuation of the absolute value of the scanning speed of the light beam on the surface to be scanned due to the fluctuation of the vibration amplitude of the deflection mirror surface. That is, since the light beam deflected by the sine-vibrating deflection mirror surface is scanned through the scanning optical system having the arc-sin characteristic, the constant scanning speed on the surface to be scanned is realized. However, as will be described in detail later in the section “Analysis of Cause of Image Expansion / Reduction”, when the vibration amplitude of the deflecting mirror fluctuates, the absolute value of the scanning speed fluctuates even if constant velocity is achieved. Therefore, when an image is formed on the surface to be scanned, there has been a problem that the image expands and contracts in the main scanning direction.

  On the other hand, in the present invention, the fluctuation of the scanning speed of the light beam on the scanning surface from the predetermined speed is detected based on the detection result of the sensor, and applied to the optical scanning apparatus from the outside of the optical scanning apparatus. Online data indicating that an online image is formed by forming a spot on each of a plurality of pixels adjacent to each other in the main scanning direction, and main scanning among the image information indicating whether or not a spot is formed for each pixel. Offline data indicating that an offline image is formed without forming a spot at each of a plurality of pixels adjacent to each other in the direction is extracted. The number of pixels constituting the extracted online data is changed based on the detected speed fluctuation, and the number of pixels constituting the extracted offline data is changed based on the detected speed fluctuation. The corrected image information is generated by correcting the image information. Then, the light beam is modulated based on the corrected image information, and the modulated light beam is scanned over the effective scanning area of the surface to be scanned to form spots in the effective scanning area. Therefore, it is possible to suppress expansion and contraction of the image formed on the scanned surface in the main scanning direction.

  In addition, the optical scanning device is configured to detect a light beam that moves in a position outside the first scanning range with a single sensor, and the speed variation detection step is scanned in a direction away from the first scanning range. The first time when the first light detection signal is output by the sensor and the second detection signal is output when the light beam scanned in the direction approaching the first scanning range is detected by the sensor. You may comprise so that the fluctuation | variation of a scanning speed may be calculated | required based on 2 time. More specifically, for example, the speed fluctuation detection step is performed from the first time when the first detection signal is output from the sensor to the second time when the second detection signal is output from the sensor following the first detection signal. It is also possible to obtain the interval time, and to obtain the fluctuation of the scanning speed from the fluctuation of the interval time during the execution of the optical scanning operation. In other words, in the optical scanning device configured as described above, the interval time fluctuates when the scanning speed fluctuates. Therefore, the fluctuation of the scanning speed can be detected by a single sensor using the fluctuation of the interval time. it can. Therefore, since it is possible to detect a change in scanning speed without providing a plurality of sensors, the apparatus configuration can be simplified, which is preferable.

  Contrary to the above, the speed variation detection step is performed from the second time when the second detection signal is output from the sensor to the first time when the first detection signal is output from the sensor following the second detection signal. It is also possible to obtain the interval time, and to obtain the fluctuation of the scanning speed from the fluctuation of the interval time during the execution of the optical scanning operation. Even in such a configuration, it is possible to detect a change in scanning speed with a single sensor from a change in interval time. Therefore, since it is possible to detect a change in scanning speed without providing a plurality of sensors, the apparatus configuration can be simplified, which is preferable.

  The present invention relates to an optical scanning device for forming a latent image in an effective scanning region by scanning a light beam from a light source on an effective scanning region of a latent image carrier as a surface to be scanned by a vibrating deflecting mirror surface. It relates to a control method. Therefore, in the following, a schematic configuration of an optical scanning apparatus to which the present invention can be applied and an image forming apparatus using the optical scanning apparatus will be described, and thereafter, analysis of the cause of image expansion / contraction, basic concept of the invention, and specific examples The embodiment will be described in detail.

<Basic configuration of the device>
FIG. 1 is a view showing an image forming apparatus using one embodiment of an optical scanning device according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is a so-called tandem type color printer, and yellow (Y), magenta (M), cyan (C), and black (K) four-color photoconductors 2Y, 2M, and 2C as latent image carriers. 2K are arranged in the apparatus main body 5 side by side. The apparatus forms a full-color image by superimposing the toner images on the photoreceptors 2Y, 2M, 2C, and 2K, or forms a monochrome image using only the black (K) toner image. That is, in this image forming apparatus, when an image forming command is given from an external device such as a host computer to the main controller 11 having a CPU, a memory and the like in response to a user's image forming request, an image corresponding to the image forming command is displayed. Signals, control signals, and the like are given from the main controller 11 to the engine controller 10. Then, the CPU of the engine controller 10 controls each part of the engine unit EG to form an image corresponding to the image formation command on the sheet S such as copy paper, transfer paper, paper, and OHP transparent sheet.

  In the engine unit EG, a charging unit, a developing unit, an exposure unit, and a cleaning unit are provided for each of the four photoconductors 2Y, 2M, 2C, and 2K. As described above, for each toner color, an image forming unit is provided that includes a photoreceptor, a charging unit, a developing unit, an exposure unit, and a cleaning unit, and forms a toner image of the toner color. The configuration of these image forming means (photosensitive member, charging unit, developing unit, exposure unit, and cleaning unit) is the same for all color components. Therefore, the configuration relating to yellow will be described here, and the other color components will be described. Are denoted by corresponding reference numerals, and description thereof is omitted.

  The photoreceptor 2Y is rotatably provided in the arrow direction (sub-scanning direction) in FIG. Further, a charging unit 3Y, a developing unit 4Y, and a cleaning unit (not shown) are arranged around the photoreceptor 2Y along the rotation direction. The charging unit 3Y is composed of, for example, a scorotron charger, and uniformly charges the outer peripheral surface of the photoreceptor 2Y to a predetermined surface potential by applying a charging bias. Then, a scanning light beam Ly is emitted from the exposure unit 6Y onto the surface of the photoreceptor 2Y in a spot shape toward the outer peripheral surface (scanned surface) of the photoreceptor 2Y charged by the charging unit 3Y. As a result, a spot corresponding to yellow image data (image information) included in the image formation command is formed on the surface of the photoreceptor 2Y, and an electrostatic latent image is formed on the spot. The configuration and operation of the exposure unit 6 (6Y, 6M, 6C, 6K) will be described in detail later.

  The electrostatic latent image formed in this way is developed with toner by the developing unit 4Y. The developing unit 4Y contains yellow toner. When a developing bias is applied to the developing roller 41Y, the toner carried on the developing roller 41Y partially adheres to each surface portion of the photoreceptor 2Y according to the surface potential. As a result, the electrostatic latent image on the photoreceptor 2Y is visualized as a yellow toner image.

  The yellow toner image developed by the developing unit 4Y is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TRy1. The color components other than yellow are also configured in exactly the same way as yellow, and a magenta toner image, a cyan toner image, and a black toner image are formed on the photoreceptors 2M, 2C, and 2K, respectively, and a primary transfer region. Primary transfer is performed on the intermediate transfer belt 71 by TRm1, TRc1, and TRk1, respectively.

  The transfer unit 7 includes an intermediate transfer belt 71 stretched between two rollers 72 and 73, and a belt driving unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction R2 by driving the roller 72 to rotate. ). Further, a secondary transfer roller 74 is provided at a position facing the roller 73 with the intermediate transfer belt 71 interposed therebetween, and is configured to be able to contact and separate with respect to the surface of the belt 71 by an electromagnetic clutch (not shown). Yes. When transferring a color image to the sheet S, the primary transfer timing is controlled to superimpose the toner images to form a color image on the intermediate transfer belt 71, and the color image is taken out from the cassette 8 and transferred to the intermediate transfer belt 71. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 between the belt 71 and the secondary transfer roller 74. On the other hand, when a monochrome image is transferred to the sheet S, only the black toner image is formed on the photoreceptor 2K, and the monochrome image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2. In addition, the sheet S that has received the secondary transfer of the image in this way is conveyed toward the discharge tray portion provided on the upper surface portion of the apparatus main body via the fixing unit 9.

  The surface potential of each of the photoreceptors 2Y, 2M, 2C, and 2K after the toner image is primarily transferred to the intermediate transfer belt 71 is reset by a neutralizing unit (not shown), and the toner remaining on the surface is cleaned. Then, the next charging is performed by the charging units 3Y, 3M, 3C, and 3K.

  A transfer belt cleaner 75 and a density sensor are disposed in the vicinity of the roller 72. Among these, the cleaner 75 can be moved toward and away from the roller 72 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 75 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 72 while moving to the roller 72 side, and the toner that remains on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove.

  3 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 1, and FIG. 4 is a view showing a scanning range of a light beam in the exposure unit of FIG. 5 is a view showing an exposure unit of the image forming apparatus of FIG. 1 and an exposure control unit for controlling the exposure unit. Hereinafter, the configuration and operation of the exposure unit 6 and the exposure control unit 12 will be described in detail with reference to these drawings. The configuration of the exposure unit 6 and the exposure control unit 12 is the same for all color components, so the configuration relating to yellow will be described here, and the other color components will be denoted by corresponding reference numerals and description thereof will be omitted.

  As shown in FIG. 3, the exposure unit 6 </ b> Y has an exposure housing 61. A single laser light source 62 (light source) is fixed to the exposure housing 61 so that a light beam can be emitted from the laser light source 62. The laser light source 62 is ON / OFF controlled based on the image signal Sv from the main controller 11, and a light beam modulated in accordance with the image signal Sv is emitted forward from the laser light source 62. . That is, in this embodiment, the main controller 11 includes a video clock generator 111 and an image output unit 112 that generate a video clock VC having a predetermined frequency, for example, 68 MHz. Further, the image output unit 112 includes an image processing unit 1121 and a pulse modulation unit 1122. As will be described in detail later, the image processing unit 1121 corrects the image information DV0 indicating whether or not to form a spot for each pixel, and similarly indicates whether or not to form a spot for each pixel. The corrected image information DV1 is generated, and the corrected image information DV1 is output to the pulse modulation unit 1122. Then, the pulse modulation unit 1122 creates an image signal Sv corresponding to the corrected image information DV1 with the video clock VC as a reference, and outputs the image signal Sv to the laser light source 62 of the exposure unit 6Y. That is, the image signal Sv is output to the laser light source 62 in synchronization with the video clock VC. Then, the light beam is modulated in accordance with the image signal Sv, and the modulated light beam is emitted forward from the laser light source 62.

  Further, in the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a mirror 64, and a deflector 65 are used to scan and expose the light beam from the laser light source 62 onto the surface (not shown) of the photoreceptor 2. A scanning lens 66 (scanning optical system) and a mirror 68 are provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651 of the deflector 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62. In this embodiment, a mirror 64 is provided between the beam shaping system 63 and the deflecting mirror surface 651 of the deflector 65 to constitute a so-called oblique incident structure. That is, the light beam from the laser light source 62 is shaped by the beam shaping system 63 and then folded back by the mirror 64 so that the oscillation axis of the deflection mirror surface 651 of the deflector 65 (an axis perpendicular to the paper surface of FIG. ) Is incident on the deflecting mirror surface 651 so as to form an acute angle with respect to a reference plane (surface parallel to the paper surface) orthogonal to ().

  The deflector 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique, and includes a vibrating mirror that resonates and oscillates. That is, in the deflector 65, the light beam can be deflected in the main scanning direction X by the deflecting mirror surface 651 that resonates and vibrates. More specifically, the deflection mirror surface 651 is pivotally supported around a swing shaft (torsion spring) that is substantially orthogonal to the main scanning direction X, and swings in accordance with an external force applied from the operating portion 652. Swing around the axis. The operation unit 652 applies an electrostatic, electromagnetic, or mechanical external force to the deflection mirror surface 651 based on the mirror drive signal from the mirror drive unit 121 of the yellow exposure control unit 12Y to cause the deflection mirror surface 651 to move. Oscillates at the frequency of the mirror drive signal. Note that any driving method such as electrostatic attraction, electromagnetic force, or mechanical force may be employed as the driving method by the operating unit 652, and since these driving methods are well known, description thereof is omitted here.

  In this embodiment, a mirror drive control unit 101 is provided in the engine controller 10 for ON / OFF control of the vibration operation of the deflector 65, and the CPU of the engine controller 10 has the function of the mirror drive control unit 101. ing. That is, the mirror drive control unit 101 gives the drive signal Sd having a drive frequency (for example, 5 KHz) that matches the operating frequency of the deflector 65 to the mirror drive unit 121 at an appropriate timing to vibrate the deflector 65.

  Further, the deflector 65 driven in this way is provided with a resonance frequency adjusting unit 653 as described in, for example, Japanese Patent Laid-Open No. 9-197334, and changes the resonance frequency of the deflector 65. Is possible. That is, in the resonance frequency adjusting unit 653, an electric resistance element is formed on a torsion spring (not shown) of the deflector 65, and the electric resistance element is electrically connected to the frequency control unit 122 of the exposure control unit 12Y. Yes. Then, the temperature of the torsion spring is changed by the energization control of the electric resistance element by the frequency control unit 122. Thereby, the spring constant of the torsion spring is changed, and the resonance frequency of the deflector 65 can be changed. Therefore, in this embodiment, as will be described later, when the resonance frequency does not match the frequency of the mirror drive signal (drive signal Sd), that is, the drive frequency, the resonance frequency of the deflector 65 is changed by the resonance frequency adjustment unit 653. Thus, the drive frequency is substantially matched (resonance frequency control). Note that the specific configuration for changing the resonance frequency of the deflector 65 is not limited to this, and a conventionally known configuration can be adopted.

  Further, the mirror driving unit 121 is configured to be able to change and set the driving conditions such as the voltage and current of the mirror driving signal. Therefore, the voltage of the mirror drive signal can be changed and set as necessary, and the amplitude value of the deflector 65 can be adjusted by changing the voltage.

  The light beam deflected by the deflecting mirror surface 651 of the deflector 65 is deflected toward the scanning lens 66 (scanning optical system). In this embodiment, the scanning lens 66 has a so-called arc-sin characteristic. Therefore, the light beam deflected by the deflecting mirror surface 651 vibrating as described above is scanned at a constant speed in the main scanning direction X on the surface (scanned surface) of the photosensitive member 2Y via the scanning lens. Further, the scanning lens 66 is configured so that the F values are substantially the same over the entire effective scanning region ESR on the surface of the photoreceptor 2. Accordingly, the light beam deflected toward the scanning lens 66 is imaged in a spot shape with substantially the same diameter on the effective scanning region ESR of the surface (scanned surface) of the photoreceptor 2Y via the scanning lens 66 ( Optical scanning operation). As a result, a line-shaped latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2 by scanning the light beam in parallel with the main scanning direction X. In this embodiment, the scan range (the “second scan range” of the present invention) SR2 that can be scanned by the deflector 65 is for scanning the light beam on the effective scan region ESR, as shown in FIG. The scanning range (the “first scanning range” in the present invention) is set wider than SR1. Further, the first scanning range SR1 is located substantially at the center of the second scanning range SR2, and is substantially symmetric with respect to the optical axis. Further, the symbol θsr in the figure indicates the amplitude angle of the deflection mirror surface 651 corresponding to the end of the effective scanning region ESR, and the symbol θhs indicates the amplitude angle of the deflection mirror surface 651 corresponding to the light detection sensor described below. Show.

  In this embodiment, as shown in FIGS. 3 and 4, one end of the scanning path of the scanning light beam is guided to the light detection sensor 60 by the folding mirror 69. The folding mirror 69 is disposed at one end of the second scanning range SR2, and the scanning light beam that moves on the one side (+ X) in the main scanning direction X outside the first scanning range SR1 is applied to the light detection sensor 60. Light guide. A signal (detection signal) is output from the light detection sensor 60 at a timing when the scanning light beam is received by the light detection sensor 60 and passes through the sensor position (Hsync equivalent angle θhs). As described above, in this embodiment, the light beam scanned in the main scanning direction X by the light detection sensor 60 can be detected in a region outside the first scanning range SR1 on one side (+ X) in the main scanning direction X. This light detection sensor 60 corresponds to the “sensor” of the present invention.

  In this embodiment, since the light detection sensor 60 is disposed at one end of the second scanning range SR2, a light beam scanned in a direction away from the first scanning range SR1 passes through the light detection sensor 60. Then, the detection signal Hsync is output, and the light beam scanned in the direction approaching the first scanning range SR1 passes through the light detection sensor 60 and the detection signal Hsync is output. Thus, the detection signal Hsync is output twice for each reciprocating scan of the light beam. Therefore, in order to distinguish these signals, in this specification, the detection signal Hsync corresponding to the detection of the light beam scanned in the direction away from the first scanning range SR1 is referred to as “first detection signal Hsync1”, and conversely The detection signal Hsync corresponding to the detection of the light beam scanned in the direction approaching the one scanning range SR1 is referred to as “second detection signal Hsync2”. Further, when explaining without distinguishing these, they are simply referred to as “detection signal Hsync”.

  The signal Hsync detected in this way is given to the speed fluctuation detecting unit 104 of the engine controller 10. The speed fluctuation detection unit 104 is supplied with a clock signal for time measurement from the count clock generation unit 103 of the engine controller 10, and measures, for example, a time interval between adjacent detection signals Hsync based on the clock signal for time measurement. It is configured to be possible. In this embodiment, the frequency of the clock signal for timing is set to a value larger than that of the video clock VC. Thereby, the time interval and the like can be measured with high accuracy.

  Further, the detection signal Hsync of the scanning light beam by the light detection sensor 60 is also transmitted to the measurement unit 123 of the exposure control unit 12Y, and the measurement unit 123 calculates drive information related to the drive cycle and the like. The actual measurement information calculated by the measurement unit 123 is transmitted to the frequency control unit 122, and the frequency control unit 122 adjusts the resonance frequency of the deflector 65.

<Analysis of causes of image expansion and contraction>
FIG. 6 is a diagram showing the relationship between the amplitude fluctuation of the deflection mirror surface and the fluctuation of the scanning speed. The upper part of the figure shows the time change of the amplitude of the deflection mirror surface. That is, the horizontal axis represents time, and the vertical axis represents the vibration amplitude of the deflecting mirror. The lower part of the figure shows a surface to be scanned of a light beam scanned by a vibrating deflection mirror surface 651 via a scanning lens 66 (scanning optical system) having arc-sin characteristics (in this embodiment, “photosensitive member 2”). The time variation of the scanning position in the main scanning direction X is shown. That is, the horizontal axis represents time, and the vertical axis represents the position in the main scanning direction. A region sandwiched by two two-dot chain lines on the upper and lower sides corresponds to the effective scanning region ESR (first scanning range SR1). The solid line in the figure corresponds to the case where the deflection mirror surface vibrates with a predetermined vibration amplitude. Also, the broken line in the figure corresponds to the case where the vibration amplitude of the deflecting mirror surface varies from a predetermined vibration amplitude due to variations in individual deflectors 65, changes in the surrounding environment, and the like. As indicated by the solid line and the broken line in the lower part of the figure, since the scanning speed is constant on the surface to be scanned, the temporal change in the scanning position of the light beam is linear. However, when the amplitude of the deflection mirror surface 651 fluctuates in the direction of increasing from the solid line in the upper part of the figure to the broken line, the temporal change in the scanning position of the light beam on the surface to be scanned fluctuates from the solid line in the lower part of the figure to the broken line. To do. In the lower part of the figure, since the horizontal axis represents time and the vertical axis represents the position in the main scanning direction, the slope of the straight line is the scanning speed in the main scanning direction X. Therefore, it can be seen from the lower part of the figure that the scanning speed of the light beam is increased by increasing the vibration amplitude of the deflecting mirror surface 651. Here, the slope of the solid line at the bottom of the figure is V0 and the slope of the broken line is V1.

  FIG. 7 is a diagram showing fluctuations in the image formed on the scanned surface (the surface of the photoreceptor 2) when the scanning speed fluctuates. Here, for example, consider a case where an optical scanning operation is performed based on the image information shown in FIG. Note that one square in FIG. 7 corresponds to one pixel, and the number in the square indicates whether or not a spot is formed in the corresponding pixel. That is, when the number in the square is “1”, it indicates that a spot is formed on the corresponding pixel, and when the number in the square is “0”, it indicates that no spot is formed on the corresponding pixel. That is, the image information in FIG. 7 includes online data indicating that a spot is formed on each of N pixels adjacent to each other in the main scanning direction X to form an online image, and the online scanning direction X following the online data. Off-line data indicating that an off-line image is formed without forming a spot on each of the N pixels adjacent to each other, and a spot on each of the N pixels adjacent to each other in the main scanning direction X following the off-line data. And online data indicating that an online image is formed. Thus, for ease of explanation, in FIG. 7, the number of pixels constituting the online data and the offline data is all N pixels.

  Then, when the optical scanning operation is executed at the scanning speeds V0 and V1 based on the image information, an online image and an offline image as shown in FIG. 7 are formed on the surface to be scanned (the surface of the photoreceptor 2). Here, the hatched circles in FIG. 7 indicate the approximate center positions of the spots constituting the online image. Also, the white circles in FIG. 7 indicate the approximate center position of the spot when a spot is temporarily formed at a position where no spot is formed in order to form an offline image. When the optical scanning operation is executed at a predetermined scanning speed V0 corresponding to the case where the deflection mirror surface 651 vibrates with a predetermined amplitude, the lengths of the online image and the offline image in the main scanning direction X are both It becomes a predetermined length L0. However, as described above, since the frequency of the video clock VC is constant in the present invention, the following situation occurs when the oscillation amplitude of the deflecting mirror surface 651 varies and the scanning speed varies from the speed V0 to the speed V1. Occurs. That is, the distance between the hatched circles and the white circles adjacent to each other in the main scanning direction X in FIG. As a result, the lengths of the online image and the offline image in the main scanning direction X vary from L0 to L1. As a result, an image formed by collecting such online images and offline images also expands and contracts in the main scanning direction X. Thus, it can be seen that when an image is formed on the surface to be scanned using the optical scanning device having the above-described configuration, the image may expand or contract in the main scanning direction.

<Basic concept of invention>
8 and 9 are diagrams showing the vibration characteristics of the deflection mirror surface used in the present invention. When the vibration characteristic of the deflector 65 configured as described above was verified, it was found that there was a vibration characteristic as shown in FIG. In the deflector 65, even if the amplitude changes, the maximum amplitude time Tmax at which the amplitude becomes the maximum value and the amplitude zero time T0 at which the amplitude becomes zero do not change. Also, as shown in FIG. 9, each timing T1 to T4 is
T1... Timing when the light beam scanned through the light detection sensor 60 in the direction away from the effective scanning region ESR (first scanning range SR1) passes and the first detection signal Hsync1 is output from the sensor 60;
T2... The timing at which the light beam scanned in the direction approaching the effective scanning region ESR (first scanning range SR2) passes through the light detection sensor 60 and the second detection signal Hsync2 is output from the sensor 60;
T3: Timing at which a light beam scanned in a direction away from the effective scanning region ESR (first scanning range SR1) passes through a position (virtual sensor position) symmetrical to the sensor 60 with respect to the optical axis OA,
T4: Timing at which a light beam scanned in a direction approaching the effective scanning region ESR (first scanning range SR1) passes through a position (virtual sensor position) symmetrical to the sensor 60 with respect to the optical axis OA,
The following relational expression is established. That is, the interval time TA (= T2-T1)
And the scanning time TB (= T3−T2) is a value α that is uniquely determined by the driving frequency of the deflector 65. Further, the interval times TA and TC are equal. That means
TA + TB = α (1)
TA = TC (2)
Is established.

  As described in the section “Analysis of Cause of Image Expansion / Reduction”, when the optical scanning operation is performed using the deflecting mirror surface 651 that vibrates as described above, the scanning speed is changed by the fluctuation of the vibration amplitude of the deflecting mirror surface 651. Fluctuates and image expansion / contraction occurs. Therefore, the present inventors have made various studies in order to suppress image expansion and contraction due to amplitude fluctuations. As a result, the time (first time) when the first detection signal Hsync1 when the light beam scanned in the direction away from the effective scanning region ESR (first scanning range SR1) is detected by the sensor 60 is output (first time), and the effective scanning region. A fluctuation in scanning speed can be detected based on the time (second time) when the second detection signal Hsync2 is output when the light beam scanned in the direction approaching ESR (first scanning range SR1) is detected by the sensor 60. I got the knowledge. More specifically, the interval time TA from the first time at which the first detection signal Hsync1 is output from the sensor 60 to the second time at which the second detection signal is output from the sensor 60 following the first detection signal. And the knowledge that the fluctuation of the scanning speed can be detected based on the interval time TA was obtained.

For example, consider the case where the scanning speed increases as the amplitude of the deflecting mirror surface 651 increases as described above with reference to FIG. Then, it is assumed that the interval time has changed from TA to TA = TA + ΔTA with the fluctuation of the amplitude. At this time, since the sum of TA and TB is constant according to the equation (1), the scanning time TB changes to TB−ΔTA. Then, the scanning speed is increased by the shortening of the scanning time. Therefore, if the scanning speed changes from the speed V0 to the speed V1, between the speed V0 and the speed V1,
V1 = V0 × TB / (TB−ΔTA) (3)
Is established. From the equations (3) and (1), V1 / V0 = (α−TA) / (α− (TA + ΔTA)) (4)
Can be derived. Here, the value α is a value that is uniquely determined by the driving frequency of the deflection mirror and is known. Therefore, the scanning speed fluctuation V1 / V0 can be detected by measuring the interval time.

As described in the column “Analysis of Causes of Image Expansion / Reduction” with reference to FIG. 7, when the scanning speed changes from the speed V0 to the speed V1 while the frequency of the video clock VC remains constant, the surface to be scanned (on the photosensitive member 2). The image formed on the front surface expands and contracts in the main scanning direction X. In other words, in the example of FIG. 7, for example, the length of the online data and the offline data in the main scanning direction varies from L0 to L1 as the scanning speed varies from V0 to V1. At this time, if the frequency of the video clock VC is fvc,
L0 = N × V0 / fvc (6)
L1 = N × V1 / fvc (7)
Is established. Therefore, the inventors of the present application generate corrected image information by changing the number of pixels constituting the online data and offline data of the image information so that the length in the main scanning direction does not change even if the scanning speed varies. It was decided to. Then, when the number of pixels of the corrected online data and offline data is changed from N to N1, N1 = N × V0 / V1 (8)
Got. The equation (8) is obtained by requesting the equations (6) and (7) to satisfy L0 = L1. That is, first, the scanning speed fluctuation V1 / V0 is detected based on the interval time as described above. Next, online data and offline data are extracted from the image information, the number of pixels constituting the extracted online data is changed from N pixels to (N × V0 / V1) pixels, and the extracted offline data is The corrected image information is generated by changing the number of pixels to be configured from N pixels to (N × V0 / V1) pixels. Then, by executing an optical scanning operation on the surface to be scanned based on the corrected image information, the online image and the offline image formed on the surface to be scanned can be obtained even when the scanning speed changes to V1. The length in the main scanning direction is approximately L0. Thereby, even when the scanning speed fluctuates, the length of the image formed on the surface to be scanned in the main scanning direction X can be kept constant. Hereinafter, specific embodiments will be exemplified and described in detail.

<Embodiment>
FIG. 10 is a flowchart showing an embodiment of the control method of the optical scanning device according to the present invention. In the apparatus configured as described above, when an optical scanning operation execution command is given in a state where the deflector 65 is stopped from oscillating, the startup process (step S1) is executed before the optical scanning operation. FIG. 11 is a flowchart showing a startup process executed by the optical scanning device of FIG. FIG. 12 is a diagram showing the operation of the activation process. When this activation process (step S1) is started, the drive control amount for operating the deflector 65 is set to an initial value stored in advance in a memory (not shown) in step S11. More specifically, the electrical characteristic values (frequency, voltage and current) of the mirror drive signal and the signal applied to the resonance frequency adjustment unit 653 are read from the memory and set. Further, the count value N indicating the number of outputs of the detection signal Hsync is reset to zero (step S12).

  Thus, when the initial setting is completed, mirror driving is started with the above-described initial value (step S13). At this time, the amplitude of the deflector 65 gradually increases from zero as shown in FIG. Then, the detection signal Hsync is output from the light detection sensor 60 at a timing when the amplitude reaches the sensor position (Hsync equivalent angle θs), that is, the scanning light beam passes through the light detection sensor 60. Thereby, the emission of the light beam from the laser light source 62 is confirmed, and an optical scanning operation based on the detection signal Hsync from the light detection sensor 60 is enabled.

  Therefore, in this embodiment, in order to confirm that the amplitude of the light beam is substantially constant and the vibration operation is stabilized, waiting for the detection signal Hsync to be output four times or more (steps S14 to S16), End the startup process. The number of detection signals Hsync, that is, the count value N is not limited to “4”, and can be set to a value of “1” or more. Further, instead of the number of detection signals Hsync, a time required for stabilization may be obtained in advance, and the start-up process may be terminated after the time has elapsed since the start of mirror driving.

  When the activation process is completed, the optical scanning operation is performed next. In such an optical scanning operation, a light beam modulated with the video clock VC generated by the video clock generator 111 as a reference is emitted from the laser light source 62, and the deflected light beam is emitted from the surface (scanned surface) of the photosensitive member 2. The effective scanning area ESR is scanned. As a result, the modulated light beam is irradiated onto the surface of the photoconductor 2 in a spot shape, and an electrostatic latent image is formed on the surface of the photoconductor 2. And in this embodiment, the process to step S2-S10 in the flowchart of FIG. 10 is started with the start of the said optical scanning operation | movement.

  When the optical scanning operation is started, first, the sensor 60 detects a light beam scanned in a direction away from the first scanning range SR1, and outputs a first detection signal Hsync1 to the speed fluctuation detection unit 104 (step S2). . Then, the time T1 (first time) at which the first detection signal Hsync1 is output is stored in a memory (not shown) provided in the speed fluctuation detection unit 104 (step S3). Next, the sensor 60 detects the light beam scanned in the direction approaching the first scanning range SR2, and outputs the second detection signal Hsync2 to the speed fluctuation detection unit 104 (step S4). Then, the time T2 (second time) at which the second detection signal Hsync2 is output is stored in a memory provided in the speed fluctuation detection unit 104 (step S5). Further, the speed fluctuation detecting unit 104 obtains an interval time TA1 (= T2−T1) from the times T1 and T2. Then, the reference interval time TA0 is substituted for TA in equation (4), and the interval time TA1 (= T2-T1) is substituted for (TA + ΔTA) in equation (4). The reference interval time TA0 is an interval time when the vibration amplitude of the deflecting mirror surface 651 is a predetermined amplitude and the scanning speed is a predetermined speed V0. Thereby, the speed fluctuation V1 / V0 from the predetermined scanning speed V0 is obtained (step S6). The speed fluctuation detecting unit 104 functions as “speed fluctuation detecting means” in the present invention.

  In step S7, corrected image information is generated from the speed fluctuation V1 / V0 obtained as described above. FIG. 13 is a flowchart illustrating generation of corrected image information executed in the present embodiment. First, in the extraction step of step S71, online data and offline data are extracted from the image information DV0 input to the image processing unit 1121 of the image output unit 112. Then, in the correction process of step S72, as described in detail in the section "Basic concept of invention", the number of pixels constituting each of the extracted online data and offline data is determined by the speed fluctuation V1 // The corrected image information DV1 is generated based on V0. That is, the corrected image information DV1 is generated by using the number of pixels obtained by multiplying the number of pixels constituting each of the extracted online data and offline data by V0 / V1 as the number of pixels of the online data and offline data. Then, the image processing unit 1121 outputs the corrected image information DV1 toward the pulse modulation unit 1122. As described above, in this embodiment, the image processing unit functions as the “extraction unit” and the “correction unit” of the present invention.

  Next, the pulse modulation unit 1122 generates an image signal Sv with reference to the video clock VC based on the corrected image information DV1, and outputs the image signal Sv toward the laser light source 62. As a result, a light beam modulated based on the corrected image information DV1 is emitted from the laser light source 62 toward the deflecting mirror surface 651 that vibrates, and the surface of the photosensitive member 2 (scanned surface) via the scanning lens 66. ). Then, a spot is formed in the effective scanning region ESR on the surface (scanned surface) of the photosensitive member 2 (step S8). Thus, in the present embodiment, step S8 corresponds to the “spot forming step” of the present invention, and the pulse modulator 1122, the laser light source 62, the deflection mirror surface 651, and the scanning lens 66 are “spot forming means” of the present invention. Is functioning. Then, when the sensor 60 detects the light beam scanned in the direction away from the first scanning range SR1 again and outputs the first detection signal Hsync1 to the speed fluctuation detection unit 104 (step S9), the optical scanning operation is performed. It is determined whether or not to end (step S10). If the optical scanning operation is not terminated, the process returns to step S3, and the time T1 at which the first detection signal Hsync1 is output in step S9 is stored in a memory provided inside the speed fluctuation detection unit 104. If it is determined that the optical scanning operation is to be terminated, the optical scanning operation is terminated as it is. Thus, in the present embodiment, steps S2 to S6 or steps S9, S10, and S3 to S6 correspond to the “speed fluctuation detecting step” of the present invention.

  As described above, in the present embodiment, the variation in the scanning speed of the light beam caused by the variation in the vibration amplitude of the deflecting mirror surface 651 is detected, and the online data and the offline data are extracted from the image information DV0. Further, the corrected image information DV1 is generated by changing the number of pixels constituting each of the extracted online data and offline data based on the result of the detected speed fluctuation. Then, the light beam is modulated based on the corrected image information DV1, and the modulated light beam is scanned to the effective scanning region ESR on the surface (scanned surface) of the photosensitive member 2. Therefore, it is possible to suppress expansion and contraction of the image formed on the surface (scanned surface) of the photosensitive member 2 in the main scanning direction X regardless of the vibration amplitude fluctuation of the deflection mirror surface 651.

  In the present embodiment, the fluctuation in the scanning speed is detected based on the knowledge that the fluctuation in the scanning speed can be obtained by obtaining the fluctuation in the interval time TA. Therefore, since a single sensor 60 can detect a change in scanning speed without providing a plurality of sensors, the apparatus configuration is simplified, which is preferable.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the time T2 when the second detection signal Hsync2 is output from the sensor 60 following the first detection signal Hsync1 from the time T1 (first time) when the first detection signal Hsync1 is output from the sensor 60. The interval time TA until (second time) is obtained, and the speed fluctuation is obtained from the fluctuation of the interval time. However, the interval time from the time (second time) when the second detection signal is output from the sensor 60 to the time (first time) when the first detection signal Hsync1 is output from the sensor 60 following the second detection signal. And the speed fluctuation may be obtained from the fluctuation of the interval time. FIG. 14 is a diagram showing the principle of detecting the speed fluctuation in another embodiment. That is, from time T2 (second time) when the second detection signal is output from the sensor 60 to time T5 (first time) when the first detection signal Hsync1 is output from the sensor 60 following the second detection signal. The sum of the interval time TE and the interval time TA is 2α which is a constant value. Therefore, the fluctuation of the interval time TA can be obtained indirectly by obtaining the fluctuation of the interval time TE. Then, based on the fluctuation of the interval time TA obtained indirectly as described above, it is possible to detect the speed fluctuation using the knowledge described in the section “Basic Concept of Invention”.

  Further, in the above embodiment, the time T2 (first time) when the second detection signal is output from the sensor 60 following the first detection signal from the time T1 (first time) when the first detection signal Hsync1 is output from the sensor 60. 2), an interval time TA is obtained, and a speed fluctuation is obtained from the fluctuation of the interval time. However, from the time (first time) when the first detection signal Hsync1 is output from the sensor 60 to the time (second time) when the second detection signal for the second time after the first detection signal is output from the sensor 60. It is also possible to obtain a change in speed of the interval time from the change in the interval time. FIG. 15 is a diagram illustrating the principle of detecting a speed variation in still another embodiment. That is, from time T1 (first time) when the first detection signal Hsync1 is output from the sensor 60, time T6 (second time) when the second detection signal for the second time after the first detection signal is output from the sensor 60. ) Is a time obtained by adding a constant value 2α to the interval time TA. Therefore, the fluctuation of the interval time TA can be obtained indirectly by obtaining the fluctuation of the interval time TF. Then, it is possible to detect the speed fluctuation by using the knowledge described in the “basic principle of the invention” based on the fluctuation of the interval time TA obtained indirectly as described above.

  In the above-described embodiment, the present invention is applied to a color image forming apparatus. However, the application target of the present invention is not limited to this, and it is also applicable to a monochrome image forming apparatus that forms a so-called monochromatic image. The present invention can be applied.

  Furthermore, in the above-described embodiment, the deflector 65 formed by using micromachining technology is employed as the vibration mirror. However, the light beam is deflected by using the vibration mirror that resonates and oscillates on the latent image carrier. The present invention can be applied to any image forming apparatus that scans a beam.

1 is a diagram showing an image forming apparatus using an embodiment of an optical scanning device of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a main scanning sectional view of an exposure unit (optical scanning device) of the image forming apparatus of FIG. 1. The figure which shows the scanning range of the light beam in the exposure unit (optical scanning device) of FIG. FIG. 2 is a view showing an exposure unit and an exposure control unit of the image forming apparatus in FIG. 1. The figure which shows the relationship between the amplitude fluctuation | variation of a deflection | deviation mirror surface, and the fluctuation | variation of a scanning speed. The figure which shows the fluctuation | variation of the image formed in the to-be-scanned surface when inspection speed fluctuates. The figure which shows the vibration characteristic of the deflection | deviation mirror surface used by this invention. The figure which shows the vibration characteristic of the deflection | deviation mirror surface used by this invention. 3 is a flowchart showing an embodiment of a method for controlling an optical scanning device according to the present invention. FIG. 4 is a flowchart showing start-up processing executed by the optical scanning device of FIG. 3. The figure which shows operation | movement of a starting process. 6 is a flowchart showing generation of corrected image information executed in the present invention. The figure which shows the speed fluctuation | variation detection principle in another embodiment. The figure which shows the speed fluctuation | variation detection principle in another embodiment.

Explanation of symbols

  2Y, 2M, 2C, 2K ... photosensitive member, 104 ... speed fluctuation detecting section (speed fluctuation detecting means), 111 ... video clock generating section, 112 ... image output unit, 1121 ... image processing section (extracting means, correcting means), DESCRIPTION OF SYMBOLS 1122 ... Pulse modulation part, 60 ... Light detection sensor, 62 ... Laser light source (light source) 651 ... Deflection mirror surface, 66 ... Scanning lens (scanning optical system), ESR ... Effective scanning area, Hsync ... Detection signal, Hsync1 ... First Detection signal, Hsync2 ... second detection signal, SR1 ... first scanning range, SR2 ... second scanning range, VC ... video clock, DV0 ... image information, DV1 ... corrected image information, Sv ... image signal, TA, TE, TF ... interval time, X ... main scanning direction, Y ... sub-scanning direction

Claims (5)

A light source for emitting a light beam, a scanning optical system having an arc-sin characteristic, and deflecting the light beam emitted from the light source by a deflecting mirror surface that sine vibrates through the scanning optical system. A deflector that reciprocates in the main scanning direction in a second scanning range that is wider than the first scanning range corresponding to the effective scanning area of the surface to be scanned, and a light beam that moves in a position outside the first scanning range. And a sensor for outputting a detection signal and a video clock generator for generating a video clock having a predetermined frequency, and the effective scanning region of the scanned surface is irradiated with the light beam in the form of a spot. In the optical scanning device capable of forming a spot in an area, a light beam modulated with reference to the video clock is emitted from the light source, and the modulated light beam is provided on the surface to be scanned. The control method of the optical scanning apparatus for performing optical scanning operation for scanning the scanning area to the optical scanning device,
A speed fluctuation detecting step of detecting a fluctuation from a predetermined speed of the scanning speed of the light beam on the scanned surface based on a detection result of the sensor;
Of the image information indicating whether or not to form the spot for each pixel given to the optical scanning device from the outside of the optical scanning device, the spot is applied to each of a plurality of pixels adjacent to each other in the main scanning direction. To extract online data indicating that an online image is formed by forming an image and offline data indicating that an offline image is formed without forming the spot at each of a plurality of pixels adjacent to each other in the main scanning direction. Process,
The number of pixels constituting the online data extracted by the extraction step is changed based on the result of the speed variation detection step, and the number of pixels constituting the offline data extracted by the extraction step is changed to the speed A correction step of generating corrected image information by correcting the image information by changing based on a result of the motion detection step;
And a spot forming step of modulating the light beam based on the corrected image information and scanning the modulated light beam over the effective scanning area of the surface to be scanned to form a spot in the effective scanning area. A method for controlling an optical scanning device. The method of controlling an optical scanning device according to claim 1, wherein the optical scanning device includes a single sensor as the sensor and detects a light beam moving at a position outside the first scanning range by the sensor. And
The speed fluctuation detecting step includes a first time when a light beam scanned in a direction away from the first scanning range is detected by the sensor and a first detection signal is output, and a direction approaching the first scanning range. A method for controlling an optical scanning device, wherein a variation in the scanning speed is obtained based on a second time when a scanned light beam is detected by the sensor and a second detection signal is output.   The speed variation detection step includes an interval time from a first time when the first detection signal is output from the sensor to a second time when the second detection signal is output from the sensor following the first detection signal. 3. The method of controlling an optical scanning device according to claim 2, wherein the fluctuation of the scanning speed is obtained from the fluctuation of the interval time during execution of the optical scanning operation.   The speed variation detection step includes an interval time from a second time when the second detection signal is output from the sensor to a first time when the first detection signal is output from the sensor following the second detection signal. 3. The method of controlling an optical scanning device according to claim 2, wherein the fluctuation of the scanning speed is obtained from the fluctuation of the interval time during execution of the optical scanning operation. A light source for emitting a light beam, a scanning optical system having an arc-sin characteristic, and deflecting the light beam emitted from the light source by a deflecting mirror surface that sine vibrates through the scanning optical system. A deflector that reciprocates in the main scanning direction in a second scanning range that is wider than the first scanning range corresponding to the effective scanning area of the surface to be scanned, and a light beam that moves in a position outside the first scanning range. And a sensor for outputting a detection signal and a video clock generator for generating a video clock having a predetermined frequency, and the effective scanning region of the scanned surface is irradiated with the light beam in the form of a spot. A spot can be formed in a region, and a light beam modulated with reference to the video clock is emitted from the light source, and the modulated light beam is scanned on the surface to be scanned. The optical scanning apparatus for performing optical scanning operation for scanning the frequency band,
A speed fluctuation detecting means for detecting a fluctuation from a predetermined speed of the scanning speed of the light beam on the surface to be scanned based on a detection result of the sensor;
Of the image information indicating whether or not to form the spot for each pixel given to the optical scanning device from the outside of the optical scanning device, the spot is applied to each of a plurality of pixels adjacent to each other in the main scanning direction. To extract online data indicating that an online image is formed by forming an image and offline data indicating that an offline image is formed without forming the spot at each of a plurality of pixels adjacent to each other in the main scanning direction. Means,
The number of pixels constituting the online data extracted by the extracting means is changed based on the result of the speed fluctuation detecting means, and the number of pixels constituting the offline data extracted by the extracting means is changed to the speed Correction means for correcting the image information by changing based on the result of the motion detection means to generate corrected image information;
Spot light forming means for modulating the light beam based on the corrected image information and scanning the modulated light beam over the effective scanning area of the surface to be scanned to form a spot in the effective scanning area. An optical scanning device.

Images