JP2010072634A - Optical scanning apparatus, image forming apparatus, control method, program and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method capable of detecting the scanning timing of respective stages of multiple-reflection mirrors. <P>SOLUTION: The apparatus includes: a deflection means having a rotation shaft and at least two stages of multiple-reflection mirrors provided on the rotation shaft with a shift in angle in the rotating direction; a split means which splits a light beam from a light source at least into two beams and allows the respective split beams incident on the multiple-reflection mirrors of the different stages; a light receiving means which detects the beams scanned with the deflection means; and a detection means which detects the time at which the respective stages of the multiple-reflection mirrors scan the beams on the basis of the detected interval of the beams with the light receiving means, wherein the deflection means is characterized in that the respective stages of the multiple-reflection mirrors are disposed to be shifted in the angles in the rotating direction so that the detection intervals do not become an equal interval. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning device that scans different scanned surfaces with a beam from a common light source, an image forming apparatus including the optical scanning device, and a predetermined scanned surface with a beam from a common light source. And a computer-readable program for realizing the method, and a recording medium on which the program is recorded.

  In electrophotographic image forming apparatuses used in laser printers, fax machines, digital multi-function peripherals, etc., tandem type apparatuses having a plurality of photosensitive drums have become widespread due to colorization and high speed printing. In this tandem apparatus, since it is necessary to irradiate each of the plurality of photosensitive drums, the number of light sources increases as the number of photosensitive drums increases. This increase in the number of light sources causes an increase in the number of parts, resulting in an increase in cost, and further a color shift due to a wavelength difference between a plurality of light sources. Further, when the number of light sources increases, the failure probability of the writing unit due to deterioration of the semiconductor laser also increases, and the recyclability decreases.

  Therefore, in order to prevent an increase in the number of light sources in a tandem electrophotographic image forming apparatus, an apparatus that divides a beam from a common light source and scans different surfaces to be scanned by the divided beams is proposed. (See Patent Document 1). In this apparatus, the light beam emitted from the light source is split into two by the light beam splitting means, and the two polygon mirrors that are overlapped at different angles are input to the polygon mirrors mounted on the upper and lower stages of the deflecting means for coaxial rotation. Each light beam deflected and scanned by this deflecting means at different timings reaches a separate photoconductor through a first scanning lens, a mirror, and a second scanning lens, which are predetermined optical systems, and performs main scanning. It is configured.

  In this way, by defining the optical arrangement for scanning different scanning surfaces with multiple stages of polygon mirrors, while reducing the number of light sources, high-speed image output is possible and ghost light is generated This makes it possible to output a good image. The reduction in the number of light sources can reduce the number of parts, achieve cost reduction, reduce the failure rate of the entire unit, and improve the recyclability.

  In this apparatus, the angular deviation amount φ in the rotational direction of the polygon mirrors at different stages and the number M of the mirror surfaces of the polygon mirror are calculated so that the deviation angle φ in the rotational direction of the multi-surface reflective mirrors at different stages is π / It is characterized by becoming M. That is, when a four-sided polygon mirror is used, the shift angle φ is π / 4 (45 deg).

  In the conventional apparatus described above, in order to divide a beam from a common light source and scan different surfaces to be scanned by the divided beams, the scanning timing by the polygon mirror and the lighting timing of the light source must be matched. That is, in the apparatus, the polygon mirror is aligned with the surface to be scanned and the mirror surface of the multi-stage polygon mirror is shifted in phase (angle in the rotation direction). The rotation phase must match the data of the scanned surface.

  For detecting the rotational phase of the polygon mirror, a technique is widely known in which a light receiving element arranged outside the image region detects the timing at which the mirror surface reaches a predetermined phase with beam incident light. When detecting with this technique, it is possible to detect the rotation angles of the polygon mirrors in a plurality of stages. However, since the amount of angular deviation in the rotation direction of the polygon mirrors in different stages is uniform, It is impossible to detect the rotational phase. That is, in the configuration in which the polygon mirrors are stacked in two stages, it can be detected that the polygon mirrors stacked in the two stages have reached the predetermined rotation angle, but either the upper stage or the lower stage has reached the predetermined rotation angle. It is impossible to detect whether

  In an image forming apparatus that forms a general color image, electrostatic latent images are formed on four photosensitive drums, and toner images are individually formed with magenta, yellow, cyan, and black toners. For this reason, the four photosensitive drums correspond to the four scanned surfaces. That is, in the configuration in which magenta and yellow are scanned in the upper and lower stages, magenta and upper polygon mirrors, and yellow and lower polygon mirrors correspond to each other. If the correspondence between the photosensitive drum and the polygon mirror is mistaken, a yellow electrostatic latent image is formed on the magenta photosensitive drum, and a magenta electrostatic latent image is formed on the yellow photosensitive drum. There is a problem that the color image output on the transfer paper as an output does not have an appropriate color scheme.

  Therefore, it has been desired to provide an apparatus and a method capable of detecting which stage of polygon mirror scans at which timing.

  In order to solve the above-mentioned problems, the present invention provides a light receiving means for detecting a beam scanned by a polygon mirror, which is a multi-stage multi-faced reflecting mirror, and a multi-sided surface of each stage from the detection interval of the beam detected by the light receiving means And a detecting means for detecting the timing of scanning with the reflecting mirror, and the misalignment angle of the polygon mirror is made uneven. Thereby, it is possible to detect which stage of the multi-surface reflecting mirror scans at which timing, and it is possible to form an electrostatic latent image of an appropriate color on the surface to be scanned.

  In addition, while reducing the number of light sources, high-speed image output is possible, and the scanning angle of each mirror surface can be detected without adding new components. As the number of light sources is reduced, the number of parts can be reduced and the cost can be reduced, the failure rate of the entire unit of the optical scanning device can be reduced, and the recyclability can be improved.

  In the configuration including the light receiving means and the detection means, there is no problem when the rotating state of the multi-surface reflecting mirror is stable and operating normally, but since the deviation angle is small, the rotating state becomes slightly unstable. It becomes impossible to detect accurately. For this reason, it is desirable to further include a determination unit that determines from the detection result by the detection unit whether the rotational state of the polygonal reflecting mirror is stable and operating normally.

  Thus, by determining whether the rotation state of the multi-surface reflecting mirror is appropriate, it is possible to realize an appropriate color image output. It is also possible to detect a defect in the components of the optical scanning device.

  Therefore, according to the present invention, at least two beams from the light source and the deflecting means having the rotating shaft and the multi-faced reflecting mirror provided around the rotating shaft in at least two stages and shifted in the rotational direction are arranged. And splitting means for causing the divided beams to enter the multi-stage reflecting mirrors of different stages, and the beams reflected by the multi-stage reflecting mirrors of different stages rotating about the rotation axis are differently covered. An optical scanning device that scans a scanning surface, and detects a timing at which scanning is performed by a multi-surface reflecting mirror at each stage based on a light receiving unit that detects a beam scanned by a deflecting unit and a beam detection interval by the light receiving unit. An optical scanning device is further provided, further comprising detection means. In addition, the optical scanning device can further include a determination unit that determines whether or not the polyhedral reflecting mirror is normally rotated based on a detection result by the detection unit.

  The light source is preferably a surface emitting semiconductor laser array element having a plurality of light emitting portions. This is because the number of parts of the optical scanning device can be reduced.

  The polarizing means is a multi-surface reflecting mirror having four reflecting surfaces, and the lower multi-surface reflecting mirror is disposed on the rotation axis at an angle of 45 ° in the rotational direction with respect to the upper multi-surface reflecting mirror. In this case, the intervals of the detection signals are equal, and scanning by the polyhedral reflectors at each stage is started at a constant interval, and it is difficult to detect which stage of the polyhedral reflector is scanned at which timing. On the other hand, the polarizing means is a multi-surface reflecting mirror having four reflecting surfaces, and the lower multi-surface reflecting mirror is shifted from the upper multi-surface reflecting mirror by 45 ° ± α in the rotation direction and arranged on the rotation axis. In the case of being provided, the intervals of the detection signals are different even with a slight amount of deviation, and it is possible to detect which stage of the multi-surface reflecting mirror is scanning at which timing. Therefore, the deflecting means is characterized in that the multi-surface reflecting mirrors of each stage are arranged at different angles in the rotation direction so that the detection intervals of the beams by the light receiving means are not equal.

  The angle is represented by π / M ± α (M is the number of faces of the multi-faced reflector, and α is the amount of angular deviation), and α is larger than the absolute value of the tolerance that is an allowable range when the multi-faced reflector is assembled. It is characterized by. Tolerance is the difference between the specified value and the actual value, and is the allowance in machining within the range allowed by law. When α is the same as the absolute value of the tolerance, at the actual detection, the intervals of the detection signals are equal, and it is impossible to detect which stage of the polygonal mirror is scanned at which timing. However, by making it larger than the absolute value of the tolerance, the intervals of the detection signals are different as described above, and it is possible to detect which stage of the polygonal mirror is scanned at which timing.

  The detection means can include a measurement means for measuring an interval between detection signals output from the light receiving means. Further, the detecting means compares the interval measured by the measuring means with a previously measured value or a preset fixed value, and determines whether or not the interval is larger than the measured value or the fixed value. A comparison / determination unit may be further included. As the measurement value, the interval measured immediately before can be used. As an example of the fixed value, an interval between detection signals can be measured in advance, and an average value of all measured intervals can be employed.

  The determination means is operating normally when an interval larger than the measured value or fixed value and an interval smaller than the measured value or fixed value are alternately detected from the comparison result determined by the comparison determining means. Otherwise, it is determined that it is not operating normally.

  The optical scanning device includes data selection means for selecting data for turning on the light source in correspondence with the multi-surface reflecting mirror of the stage to be scanned based on the detected timing of scanning by the multi-surface reflecting mirror of each stage. Furthermore, it can be provided. Thereby, an electrostatic latent image of a predetermined color can be reliably formed on a predetermined surface to be scanned.

  The present invention can also provide an image forming apparatus including the above optical scanning device and a plurality of image carriers each having a scanned surface that is scanned by the optical scanning device.

  In addition, the present invention can also provide a control method that is executed in order that each beam reflected by the multi-stage reflecting mirrors of different stages rotating around the rotation axis scans different surfaces to be scanned at a predetermined timing. . This method includes a step of detecting a beam scanned by the deflecting unit, and a step of detecting a timing at which scanning is performed by a multi-surface reflecting mirror at each stage based on a beam detection interval by the light receiving unit. The method may further include a step of determining whether or not the polyhedral reflecting mirror is normally rotated based on the detection result detected in the detecting step. Further, this method includes processing steps performed by the measurement unit, the comparison determination unit, and the data selection unit.

  In the present invention, a computer-readable program for realizing the above control method and a recording medium on which the program is recorded can also be provided.

1 is a diagram illustrating a configuration of a tandem color image forming apparatus according to an embodiment. The figure which showed the structure of the optical scanning device of this embodiment. The sub-scanning sectional view of a half mirror prism. The figure which showed the arrangement configuration of a polygon mirror. The figure which showed the place which scans a to-be-scanned surface with a beam. The figure which showed the structure of the control part with which an optical scanning device is provided. The figure which showed another structural example of the control part with which an optical scanning device is provided. The figure which illustrated the control timing at the time of normal of an optical scanning device. The figure which illustrated the control timing at the time of abnormality of an optical scanning device.

  FIG. 1 is a diagram illustrating the configuration of a tandem color image forming apparatus according to the present embodiment. This color image forming apparatus includes four photosensitive drums 10a to 10d, four charging units 11a to 11d, four toner cartridges 12a to 12d as developing units, four transfer rollers 13a to 13d, and a photosensitive member. Four cleaners (not shown) for removing toner on the drums 10a to 10d, an intermediate transfer belt 14, an intermediate transfer roller 15, an intermediate transfer belt cleaning device 16, a transfer device 17, a paper feeding registration sensor 18, and fixing The apparatus 19 includes a paper discharge device 20 and an optical scanning device 21.

  When the start button of the color image forming apparatus is pressed or the print job start signal from the printer host is validated, the optical scanning device 21 exposes the timing-controlled beam onto the photosensitive drums 10a to 10d. . In this optical scanning device 21, a polygon mirror, which is a two-sided multi-surface reflecting mirror, is rotated by a polygon motor, the beam from the light source is scanned, and the beam is written on the scanned surface of each of the photosensitive drums 10a to 10d. An electrostatic latent image is formed.

  The formed electrostatic latent images are developed with the toner supplied from the toner cartridges 12a to 12d, and single color images are formed on the photosensitive drums 10a to 10d. In the embodiment shown in FIG. 1, first, black (K) toner is deposited on the first photosensitive drum 10a to form a black image, which is transferred onto the intermediate transfer belt 14 by the transfer roller 13a. On the next photosensitive drum 10b, cyan (C) toner adheres to form a cyan image, which is transferred onto the intermediate transfer belt 14 by the transfer roller 13b. Since a black image has already been transferred onto the intermediate transfer belt 14, a cyan image is transferred thereon.

  Further, yellow (Y) toner adheres to the next photosensitive drum 10c, and a yellow image is formed, and is transferred onto the intermediate transfer belt 14 by the transfer roller 13c. Since the black image and the cyan image have already been transferred onto the intermediate transfer belt 14, the yellow image is transferred onto them. Magenta (M) toner adheres to the last photosensitive drum 10d and is transferred onto the intermediate transfer belt 14 by the transfer roller 13d. A magenta image is already transferred onto the intermediate transfer belt 14 on the black image, cyan image, and yellow image. The intermediate transfer belt 14 conveys the toner images of each color transferred by rotating the intermediate transfer roller 15 as a driving roller in a predetermined direction. In this manner, the toner images of the respective colors are superimposed on the intermediate transfer belt 14 to form a composite color image. Here, images are formed in the order of black, cyan, yellow, and magenta, but the order of colors to be formed is not limited to this.

  On the other hand, in the color image forming apparatus, when the job start signal is validated, the transfer sheets S are separated one by one from the sheet feeding device, conveyed and fed, and the transfer sheet S is detected by the sheet feeding registration sensor 18. Then, the paper feeding is temporarily stopped. Then, in synchronization with the conveyance of the composite color image on the intermediate transfer belt 14, the registration roller is rotated, and the transfer paper is sent between the intermediate transfer belt 14 and the transfer device 17. The transfer device 17 transfers the composite color image to the transfer paper S, and the fixing device 19 fixes the transfer paper S to which the composite color image to be conveyed is transferred by applying heat and pressure. After fixing, the transfer paper S is discharged by a paper discharge roller attached to the paper discharge device 20 and stacked on a paper discharge tray.

  With reference to FIG. 2, the configuration of the optical scanning device of the present embodiment will be described. 2 includes a coupling lens 31 that converts a beam 30 that is a divergent light beam emitted from a light source (not shown) into a weak convergent light beam, a parallel light beam, or a weak divergent light beam, and a beam that has exited the coupling lens 31. An aperture stop 32 for stabilizing the beam diameter on the surface to be scanned, and a half mirror prism 33 for dividing the beam 30 from the light source into upper and lower stages. When the number of the beams 30 emitted from the light source is one, the beams emitted from the half mirror prism 33 are two beams. The number of beams 30 emitted from the light source is not limited to one and may be two or more.

  Here, the half mirror prism 33 will be described with reference to FIG. FIG. 3 is a sub-scan sectional view of the half mirror prism 33. The half mirror prism 33 includes a half mirror 33a that separates incident light into transmitted light and reflected light at a ratio of 1: 1. Further, the half mirror prism 33 includes a total reflection surface 33b having a function of converting the traveling direction of light.

  The beam exiting the aperture stop 32 is incident on the half mirror prism 33. The beam is separated into the upper and lower stages by the half mirror 33a, the direction is changed by the total reflection surface 33b, and then arranged on the upper and lower stages to be described later. The light is emitted to the polygon mirror.

  Although a half mirror prism is used here, an optical device having the same function can be configured using a single half mirror and a commonly used mirror. Further, the light separation ratio by the half mirror is not limited to the above 1: 1, and can be appropriately set according to the conditions of other optical system devices.

  With reference to FIG. 2 again, the optical scanning device will be described. In addition, the optical scanning device includes cylindrical lenses 34a and 34b, soundproof glass 35, polygon mirrors 36a and 36b, deflection means 36, scanning lenses 37a and 37b, mirror 38, and scanning lenses 39a and 39b.

  The beam that exits the half mirror prism 33 is converted into a latent image that is long in the main scanning direction in the vicinity of the deflection reflection surface by cylindrical lenses 34a and 34b arranged in accordance with the upper and lower stages. The deflecting means 36 is configured such that polygon mirrors 36a and 36b are provided around the rotation axis in two upper and lower stages, and the polygon mirror 36b is displaced from the polygon mirror 36a by an angle φ in the rotation direction. . The polygon mirrors 36a and 36b may be integrally formed or may be assembled separately.

  When the shift angle φ in the rotation direction is uniform, the shift angle φ can be expressed by π / M with respect to the number of mirror surfaces (M) of the polygon mirror. When the number of faces is 4, the deviation angle φ is π / 4, that is, 45 deg. When the deviation angle is 45 deg, scanning is started by the upper polygon mirror 36a, the interval until the scanning is started by the lower polygon mirror 36b, and scanning is started by the lower polygon mirror 36b. The interval until scanning is started by the upper polygon mirror 36a is the same interval, and it is impossible to distinguish which timing beam is reflected at the upper stage and which timing beam is reflected at the lower stage to perform scanning.

  Therefore, the deviation angle φ of the mirror surface is made uneven. Specifically, as shown in FIG. 4 (a), when the lower polygon mirror 36b is viewed from the upper polygon mirror 36a, the deviation angle of the mirror surface is φ1, and as shown in FIG. 4 (c), An angle difference of ± α is provided so that φ1 = π / M + α and φ2 = π / M−α, where φ2 is the deviation angle of the mirror surface when the upper polygon mirror 36a is viewed from the lower polygon mirror 36b. Position the mirror surface. In addition, the figure seen from the side in the case of Fig.4 (a) is FIG.4 (b).

  For example, if there are four mirror surfaces and the angle deviation α is 1 °, φ1 = 46 ° and φ2 = 44 °. In this case, scanning is started by the lower polygon mirror 36b after the scanning is started by the upper polygon mirror 36a, and thereafter the scanning is started by the lower polygon mirror 36b. The interval is longer than the interval until scanning is started, and it can be determined that the longer interval has been scanned by the upper polygon mirror 36a, and that the shorter interval has been scanned by the lower polygon mirror 36b. Therefore, by providing the angle deviation amount α, it is possible to detect which stage the scanning is performed from the interval.

  The range of the angular deviation amount α is a parameter having a large component tolerance in assembling the polygon mirror. This tolerance is the difference between the specified value and the actual value, and is the allowance in machining within the range allowed by law. For example, if the component tolerance is ± 0.25 deg, even if α = 0.25, φ1 = φ2, and the upper and lower stages of the polygon mirror cannot be detected. When α is less than 0.25, the magnitude relationship between φ1 and φ2 is reversed, and the upper and lower stages of the polygon mirror can be detected, but the result is the opposite of the upper and lower stages. For this reason, α must be a value exceeding 0.25.

  Further, if the component tolerance is ± 0.5 deg, even if α = 0.5, φ1 = φ2, and the upper and lower stages of the polygon mirror cannot be detected. For this reason, the value must exceed α = 0.5. For example, α can be set to 0.5005, but this 0.5005 is only about 0.0005 larger than 0.5, but since the count is performed by the high-speed clock, the interval of the detection signal Since there is a difference of several hundred or more, the upper and lower stages can be sufficiently detected.

  Therefore, when the component tolerance is ± 0.25 deg, the minimum value of the angle deviation amount α can be a value exceeding the absolute value of the tolerance 0.25 deg, for example, 0.2505 deg. Further, when the component tolerance is ± 0.5 deg, α can be a value exceeding the absolute value of the tolerance 0.5 deg, for example, 0.5005 deg. On the other hand, the maximum value of the angle shift amount α is such that when α is increased, the deflection angle corresponding to the effective writing width that can scan the photosensitive drum with the mirror surface with a short detection signal interval decreases, and the main scanning width is scanned. For this reason, it is necessary to significantly increase the speed of the control clock. Therefore, about 0.9 to 1.35 °, which is about 2 to 3% with respect to 45 °, is preferable.

  In this optical scanning device, it is possible to detect which stage the scanning is performed by including the deflecting unit 36 provided with the angle deviation amount α. In this optical scanning device, when the deflection means 36 with an angle deviation α of 0 is attached, the upper and lower stages cannot be detected, but it is detected that the interval is constant and constant, and that there is no angular difference. can do. For this reason, even when it is manufactured in such a way that there is no angle difference, it is possible to detect that an angle difference has occurred at the manufacturing stage if the detection signal intervals detected in this way are different. it can.

  The actual scanning will be described. As shown in FIG. 5A, when the upper beam B1 from the common light source is scanning the photosensitive drum (scanned surface), the lower beam B2 is scanned. The light shielding member 40 blocks light so that the beam does not reach the top.

  Further, when the lower stage beam B2 from the common light source scans the surface to be scanned, as shown in FIG. 5B, the upper stage beam B1 prevents the beam from reaching the surface to be scanned. The light is shielded by 40.

  With reference to FIG. 6, the configuration of the control unit included in the optical scanning device and the scanning control performed by the control unit will be described in detail.

  This control unit includes a light source control unit 50, a data selection unit 51, and a deflection scanning stage detection unit 52. The deflection scanning stage detection unit 52 includes a synchronization detection measurement unit 52a and a comparison determination unit 52b.

  The light source control unit 50 outputs a modulation signal to each light source in order to control each beam emitted from the two light sources to the polygon mirror 36a and the polygon mirror 36b. The beams emitted from the respective light sources are incident on the mirror surface of the upper polygon mirror 36a and the mirror surface of the lower polygon mirror 36b. As the polygon mirrors 36a and 36b rotate, the beam scans in the main scanning direction, and scans the photosensitive drums 10a to 10d via the scanning lens 38 and the mirror 39 shown in FIG. The rotational positions of the polygon mirrors 36a and 36b are detected as synchronization detection signals indicating the main scanning start position by the light receiving elements 53a and 53b arranged at the scanning tip position. Here, since the light is detected simultaneously by the light receiving elements 53a and 53b, the synchronization detection signal is used.

  The synchronization detection signals detected by the light receiving elements 53a and 53b are input to the deflection scanning stage detection unit 52, and the synchronization detection measurement unit 52a of the deflection scanning stage detection unit 52 measures the interval of the synchronization detection signals. The result measured by the synchronization detection measurement unit 52a is output to the comparison determination unit 52b, and the comparison determination unit 52b compares it with a predetermined value. This predetermined value can be a limit value for determining the upper and lower stages of the polygon mirrors 36a, 36b, a fixed value, or a value immediately before being measured by the synchronization detection measuring unit 52a.

  In the case of a fixed value, the beam reflected by the lower polygon mirror 36b is detected after receiving the synchronization detection signal output from the light receiving elements 53a and 53b that have detected the beam reflected by the upper polygon mirror 36a. The interval Ta until the synchronization detection signal output from the light receiving elements 53a and 53b is received, and the synchronization detection signal output from the light receiving elements 53a and 53b that detect the beam reflected by the lower polygon mirror 36b, and then the upper stage. The average value (Ta + Tb) / 2 with respect to the interval Tb can be obtained until the synchronous detection signal output from the light receiving elements 53a and 53b that detect the beam reflected by the polygon mirror 36a is received.

  When the predetermined value is a value immediately before being measured by the synchronization detection measurement unit 52a, in an optical system device having a longer interval Tb compared to the interval Ta, the results measured by the synchronization detection measurement unit 52a are alternately spaced. Since the long and short are repeated, the previous measurement result is compared with the current measurement result, and if the current measurement result is larger, it is determined that the lower stage is scanned, and if the current measurement result is smaller, the upper stage is scanned. Can do. From this determination result, a deflection scanning stage signal for discriminating between the upper stage and the lower stage of scanning of the mirror surface is output from the comparison / determination unit 52b to the data selection unit 51.

  The data selection unit 51 synthesizes the image data from the image processing unit 54 based on the deflection scanning stage signal from the comparison determination unit 52b. The image processing unit 54 inputs four color image data of black (K), cyan (C), yellow (Y), and magenta (M) to the data selection unit 51. The toner color to be imaged by each light source is determined by the arrangement of the optical scanning device and the photosensitive drum. Here, assuming that black and cyan are formed by one light source and yellow and magenta are formed by another light source, the data selection unit 51 sets black and cyan to 1 based on the deflection scanning stage signal from the comparison determination unit 52b. The image data for one light source are combined, and the image data for yellow and magenta are combined for the other light source and output to the light source control unit 50. The light source control unit 50 outputs a modulation signal to each light source, and each light source emits each beam based on this to form a desired electrostatic latent image.

  In the present invention, two color images are formed by one light source. In the embodiment shown in FIG. 6, a total of four color images are formed by two light sources, but the number of light sources is two. For example, in order to perform image formation at high speed, two light sources that form two-color images can be used, and four-color images can be formed using a total of four light sources. . The light source is not only a semiconductor laser having a single light emitting point with a single light source element, but also a semiconductor laser diode array having a plurality of light emitting points and a surface emitting semiconductor laser in which light emitting points are two-dimensionally arranged. Can also be used. Since the number of light emitting points can be reduced by employing the configuration of the present invention, the surface emitting semiconductor laser having a large number of light emitting points can reduce the number of parts in the entire image forming apparatus. It is valid.

  FIG. 7 is a diagram illustrating another configuration example of the control unit included in the optical scanning device. In this embodiment, the control unit further includes a deflection operation determination unit 55.

  In this embodiment, the synchronization detection signals detected by the light receiving elements 53 a and 53 b are input to the deflection scanning stage detection unit 52 and the deflection operation determination unit 55. Further, a deflection scanning stage signal for discriminating the upper stage and the lower stage of scanning of the mirror surface is output from the comparison determination unit 52 b to the data selection unit 51 and the deflection operation determination unit 55.

  To the deflection operation determination unit 55, the synchronization detection signal detected by the light receiving elements 53a and 53b and the deflection scanning stage signal generated by the deflection scanning stage detection unit 52 are input. The light receiving elements 53a and 53b alternately detect the upper and lower synchronization detection signals in accordance with the rotation of the polygon motor. In one light source, the synchronization detection signal is detected once in the upper scanning and once in the lower scanning. Therefore, when the deviation angles of the polygon mirror 36a and the polygon mirror 36b are uneven, the interval between the synchronization detection signals is The deflection scanning stage signals are alternately shown in magnitude, and the deflection scanning stage signal becomes a signal indicating the upper stage and the lower stage alternately. Accordingly, when the polygon motor rotates normally and the polygon mirrors 36a and 36b rotate normally, the deflection scanning stage signal alternately represents the upper stage and the lower stage.

  On the other hand, if the polygon motor does not rotate normally and the polygon mirrors 36a and 36b do not rotate normally, the deviation angle between the mirrors is only about 2 to 3% as described above. Even in a minute rotational unstable state, the intervals of the synchronization detection signals as described above are not alternately formed. For this reason, the deflection scanning stage signal also does not represent the upper stage and the lower stage alternately. In this case, when the data selection unit 51 determines the color of the image data based on the deflection scanning stage signal, an incorrect color is selected, and an abnormality occurs in the final output image.

  Based on this deflection scanning stage signal, the deflection operation determining unit 55 determines whether the rotation of the polygon motor is stable and operating normally. If it is determined that the polygon motor is operating normally, the deflection operation determining unit 55 executes the image forming operation. If it is determined that the operation is not normal, the image processing unit 54 is notified and the image forming operation can be stopped.

  FIG. 8 is a diagram showing the control timing of the optical scanning device when the rotation of the polygon motor is stable and operating normally. DETP_N shown in FIG. 8 is a synchronization detection signal output by the light receiving element 53 shown in FIG. 6 or FIG. When there is one polygon mirror and one mirror surface, one synchronization detection signal is detected. However, when there are two polygon mirrors and two mirror surfaces, two synchronization signals are detected. A detection signal is detected. The synchronization detection measurement unit 52a of the deflection scanning stage detection unit 52 includes a counter that measures the interval of the DETP_N signals. Since the control clock of this counter is a clock for controlling the light source in units of one pixel, the low-end device operates at a frequency of about 10 MHz, and the high-end device operates at a frequency of about 200 MHz.

  When the value to be compared by the comparison determination unit 52b is a fixed value, the measured value of the counter of the synchronization detection signal (DETP_N) input timing is compared with the fixed value (MRLIMIT_R). ) To low and mirrorside to high if less than a fixed value. Specifically, it is set to 0 representing low if it is greater than or equal to a fixed value, and set to 1 representing high if less than a fixed value. In FIG. 8, since the interval between the DETP_N signals of (I) and (II) is less than the fixed value (MRLIMIT_R), mirrorside is set to high after receiving the DETP_N signal of (II).

  Further, when the value compared by the comparison determination unit 52b is a result immediately before measurement by the synchronization detection measurement unit 52a, the previous value a1 is compared with the current value b1, and when the current value is large, the mirrorside Set to low. When the immediately preceding value is b1 and the current value is a2, and the current value a2 is smaller than the immediately preceding value b1, mirrorside is set to high.

  Although not shown in FIG. 8, when the value to be compared by the comparison determination unit 52b is a fixed value (MRLIMIT_R), the fixed value is a value set in the storage unit included in the control unit. For example, a value capable of determining the upper and lower stages of the polygon mirror from the interval of the synchronization detection signal can be set in advance. When the interval of the synchronization detection signal changes, such as when the rotational speed of the photosensitive drum included in the image forming apparatus is changed, an arbitrary value is set so that the determination limit value can be changed according to the change width. Is possible.

  In FIG. 8, the mirrorside is switched between high and low for each input of the synchronization detection signal (DETP_N), and when the configuration shown in FIG. 7 is adopted, the deflection operation determination unit 55 stabilizes the rotation of the polygon motor, Judge that it is operating normally. From this result, the error signal “mirror_error” is kept low, and the image forming operation is executed. In the image forming operation, data of a plurality of colors is synthesized by the data selection unit 51 based on mirrorside. When combining black and cyan images, it is assumed that black is a color scanned by the upper stage of the polygon mirror and cyan is scanned by the lower stage. When mirrorside is low, black data (k) is selected, and when mirrorside is high, cyan data (c) is selected and combined as a modulation signal for driving one light source. The same applies to the remaining yellow and magenta.

  FIG. 9 is a diagram showing the control timing of the optical scanning device when the rotation of the polygon motor is unstable and not operating normally. In FIG. 9, the mirrorside is alternately switched between high and low during the DETP_N period of (I) to (IV). However, although it is normal that the detection interval of the DETP_N period of (V) is larger than the fixed value MRLIMIT_R, the rotation of the polygon motor is disturbed and the interval is smaller than the fixed value. For this reason, when the configuration shown in FIG. 7 is adopted in which the deflection operation stage signal is not alternately switched between high and low every time the synchronization detection signal is input, the deflection operation determination unit 55 detects that it is in an error state, It is determined that the operation is not normal. As a result, the deflection operation determination unit 55 sets the error signal “mirror_error” to high, and performs a notification process for causing the image processing unit 54 to stop the image forming operation.

  Although the present invention has been described with the embodiments, the present invention is not limited to the above-described embodiments, and other embodiments, additions, changes, deletions, and the like may occur to those skilled in the art. It can be changed within the range that can be done, and any embodiment is included in the scope of the present invention as long as the effects of the present invention are exhibited. The processing by the control unit can be configured as a program and can be executed by the optical scanning device. This program can be provided by being stored on any computer-readable medium, and can be provided by being stored on a flexible disk, MD disk, SD card, CD-ROM, DVD-ROM or the like. .

10a to 10d ... photosensitive drum, 11a to 11d ... charging unit, 12a to 12d ... toner cartridge, 13a to 13d ... transfer roller, 14 ... intermediate transfer belt, 15 ... intermediate transfer roller, 16 ... intermediate transfer belt cleaning device, 17 DESCRIPTION OF SYMBOLS ... Transfer device, 18 ... Paper feed registration sensor, 19 ... Fixing device, 20 ... Paper discharge device, 21 ... Optical scanning device, 30 ... Semiconductor laser, 31 ... Coupling lens, 32 ... Aperture stop, 33 ... Half mirror prism, 33a ... Half mirror, 33b ... Total reflection surface, 34a, 34b ... Cylindrical lens, 35 ... Soundproof glass, 36 ... Deflection means, 36a, 36b ... Polygon mirror, 37a, 37b ... Scanning lens, 38 ... Mirror, 39a, 39b ... Scanning lens, 40 ... light shielding member, 50 ... light source control unit, 51 ... data selection unit, 52 ... deflection査段 detection unit, 52a ... synchronization detection measurement unit, 52 b ... comparison section, 53 ... light-receiving element, 54 ... image processing unit, 55 ... deflection operation determination unit

JP 2006-284822 A

Claims (19)

A deflecting means having a rotating shaft and a multi-faceted reflecting mirror provided at least in two stages on the rotating shaft and shifted in the rotational direction, and a beam from the light source are divided into at least two parts, Splitting means for causing the beams to be incident on the multi-surface reflecting mirrors of different stages, and each beam reflected by the multi-surface reflecting mirrors of the different stages rotating about the rotation axis scans different surfaces to be scanned. An optical scanning device,
A light receiving means for detecting the beam scanned by the deflection means;
Detecting means for detecting the timing of scanning by the multi-surface reflecting mirror at each stage based on the detection interval of the beam by the light receiving means;
The optical scanning device characterized in that the deflecting means is arranged such that the multi-surface reflecting mirrors of each stage are shifted in the rotation direction so that the detection intervals of the beams by the light receiving means are not equal. .   The optical scanning device according to claim 1, further comprising: a determination unit that determines whether or not the polyhedral reflecting mirror is normally rotated based on a detection result by the detection unit.   The optical scanning device according to claim 1, wherein the light source is a surface-emitting type semiconductor laser array element having a plurality of light emitting units.   The angle is represented by π / M ± α (M is the number of faces of the multi-faced reflecting mirror, α is the amount of angular deviation), and α is an absolute value of a tolerance that is an allowable range when the multi-faced reflecting mirror is assembled. The optical scanning device according to claim 1, wherein the optical scanning device is large.   5. The optical scanning device according to claim 1, wherein the detection unit includes a measurement unit that measures an interval between detection signals output from the light receiving unit.   The detection unit compares the interval measured by the measurement unit with a previously measured value or a preset fixed value, and determines whether the interval is greater than the measured value or the fixed value. The optical scanning device according to claim 5, further comprising a comparison determination unit for determining.   The determination unit operates normally when an interval larger than the measurement value or the fixed value and an interval smaller than the measurement value or the fixed value are alternately detected from the comparison result determined by the comparison determination unit. The optical scanning device according to claim 6, wherein the optical scanning device is determined to be operating.   Further comprising data selection means for selecting data for turning on the light source in correspondence with the multi-surface reflecting mirror of the stage to be scanned based on the detected timing of the multi-surface reflecting mirror of each stage. The optical scanning device according to claim 1.   An image forming apparatus comprising: the optical scanning device according to claim 1; and a plurality of image carriers each having a scanned surface that is scanned by the optical scanning device. A deflecting means having a rotating shaft and a multi-faceted reflecting mirror provided at least in two stages on the rotating shaft and shifted in the rotational direction, and a beam from the light source are divided into at least two parts, Splitting means for causing the beams to be incident on the multi-surface reflecting mirrors at different stages, and each beam reflected by the multi-surface reflecting mirrors at the different stages rotating about the rotation axis is scanned differently. A control method executed to scan a surface at a predetermined timing,
Detecting the beam scanned by the deflection means;
Detecting the timing of scanning by the multi-surface reflecting mirrors of each stage based on the detection interval of the beam by the light receiving means,
The control method according to claim 1, wherein the deflecting means is arranged such that the multi-surface reflecting mirrors of each stage are shifted in the rotation direction so that the detection intervals of the beams by the light receiving means are not equal.   The control method according to claim 10, further comprising a step of determining whether or not the polyhedral reflecting mirror is normally rotated based on a detection result detected in the detecting step.   The control method according to claim 10, wherein the light source is a surface-emitting type semiconductor laser array element having a plurality of light emitting units.   The angle is represented by π / M ± α (M is the number of faces of the multi-faced reflecting mirror, α is the amount of angular deviation), and α is an absolute value of a tolerance that is an allowable range when the multi-faced reflecting mirror is assembled. The control method according to claim 10, wherein the control method is large.   The control method according to any one of claims 10 to 13, wherein the step of detecting the timing includes a step of measuring an interval between detection signals output from the light receiving means.   The step of detecting the timing compares the interval measured in the measuring step with a previously measured value or a preset fixed value, and the interval is greater than the measured value or the fixed value. The control method according to claim 14, further comprising a step of determining whether or not.   The step of determining whether or not the polygonal mirror is normally rotated is based on the comparison value determined in the step of determining whether or not the measurement value or the fixed value is larger than the measurement value or the fixed value. The control method according to claim 15, wherein when the larger interval and the interval smaller than the measurement value or the fixed value are alternately detected, it is determined that the operation is normally performed.   Based on the timing of scanning by each of the multi-surface reflecting mirrors detected in the step of detecting the timing, data for turning on the light source is selected corresponding to the multi-surface reflecting mirror of the step to be scanned. The control method according to claim 10, further comprising a step.   The computer-readable program for implement | achieving the control method of any one of Claims 10-17.   A recording medium on which the program according to claim 18 is recorded.

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