JP4308783B2 - Image forming apparatus - Google Patents

Description

  The present invention uses, for example, a beam light scanning device for simultaneously scanning and exposing a single photosensitive drum with a plurality of laser beam lights to form a single electrostatic latent image on the photosensitive drum. The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer.

  In recent years, for example, various digital copying machines have been developed that perform image formation by scanning exposure using a laser beam and an electrophotographic process.

  Recently, in order to further increase the image forming speed, a multi-beam method, that is, a plurality of laser beam lights is generated, and a plurality of lines are simultaneously scanned by the plurality of laser beam lights. A digital copier has been developed.

  In such a multi-beam type digital copying machine, a plurality of semiconductor laser oscillators that generate laser beam light, each laser beam light output from the plurality of laser oscillators is reflected toward a photosensitive drum, and each laser beam is reflected. It has an optical system unit as a beam light scanning device mainly composed of a multi-surface rotating mirror such as a polygon mirror that scans the photosensitive drum with the beam light, and a collimator lens and an f-θ lens.

  Conventionally, there is a method of accurately controlling the exposure position in the scanning direction (main scanning direction) of the laser beam in such a multi-beam type digital copying machine (for example, Patent Documents 1, 2, 3, 4, and 5).

  Japanese Patent Publication No. 1-343294 as Patent Document 1 is a method of detecting the arrival timing of a plurality of light beams using a single light beam detector, as in the embodiment of the present invention described later. It is unclear which light beam arrives in which order, and in some cases it is not suitable for the configuration of an optical system that may be simultaneous.

  Japanese Patent Publication No. 3-57452 as Patent Document 2 separately prepares a light receiving unit for detecting each of a plurality of light beams, and each light beam is lit on each light receiving unit. The light emission timing for printing (recording or image formation) of each light beam is obtained based on signals from the respective light receiving units.

  However, for example, when a plurality of types of dot pitches (resolutions) to be recorded are required, such as 300 dpi, 400 dpi, 600 dpi, 16 lines / mm, and 15.4 lines / mm, the rotation speed of the polygon mirror and the image clock Need to be changed. In such a case, the phase of the output signal from each light receiving unit with respect to each light beam changes, the timing at which each light beam arrives at the print start position changes, or these timings are in one cycle of the image clock. Problems such as inability to split occur, and it is difficult to align the print start positions of the respective light beams.

  Japanese Patent Publication No. 3-57453 as Patent Document 3 is based on the premise that each beam light is configured to be shifted in the main scanning direction, and has an optical system configuration as shown in the embodiment of the present invention. Is not suitable.

  Japanese Utility Model Publication No. 5-32824 as Patent Document 4 is not suitable for the configuration of the optical system as shown in the embodiment of the present invention for the same reason as the aforementioned Japanese Patent Publication No. 3-57452.

Japanese Patent Laid-Open No. 56-104572 as Patent Document 5 obtains a synchronization signal from one of a plurality of light beams, and based on this synchronization signal, the emission timing of each light beam. Is to control. However, the positional relationship between the plurality of light beams needs to be clear in advance, and is not suitable for the configuration of the optical system as shown in the embodiment of the present invention.
Japanese Patent Publication No. 1-343294 Japanese Patent Publication No. 3-57452 Japanese Examined Patent Publication No. 3-57453 Japanese Utility Model Publication 5-32824 JP-A-56-104572

  Therefore, the present invention can also be applied to an optical system in which the light beam order in the light beam scanning direction (main scanning direction) is unknown (in some cases, at the same time), and the exposure position in the main scanning direction is always accurately controlled. It is an object of the present invention to provide an image forming apparatus that can be used.

  It is another object of the present invention to provide an image forming apparatus that can be applied to a plurality of types of recording pitches (resolutions).

The image forming apparatus of the present invention is an image forming apparatus that forms an image for each scanning line on the image carrier by simultaneously scanning and exposing the image carrier with a plurality of light beams. And a plurality of light beams generated from the plurality of light beam generators are optically combined and then reflected toward the image carrier, respectively. Scanning means for scanning the image carrier, beam light power detecting means for detecting each power of the plurality of light beams that scan the image carrier by the scanning means, and beam light power detecting means Based on each detection result, the beam light power for controlling each of the plurality of beam light generating means so that each power of the plurality of beam lights scanned on the image carrier becomes a predetermined value Control means, first beam light detection means for detecting the leading beams of the plurality of light beams scanned on the image carrier by the scanning means, and a beam light scanning direction from the first beam light detection means. A second light beam detecting means for detecting the plurality of light beams, and a clock generating means (116) for generating a clock synchronized with the output of the first light beam detecting means. A delay clock means (117) for generating a plurality of delayed clocks out of phase with each other by delaying the clock generated by the clock generating means a plurality of times with a delay amount equal to or less than the period of the clock; and printing As a clock for setting an area, a plurality of delay clock selections for selecting one delay clock from the plurality of delay clocks generated by the delay clock means. Means a (118a-d), said plurality of means for obtaining the positional information of the light beam scanning direction on the light beam, said plurality of light beams, the printing area setting means respectively for setting the respective print area (119a~d) And a control means (51), wherein the optical power of the plurality of beams is controlled to be the predetermined value using the optical power control means, and then the optical beam scanning is performed. In the first step, the means for obtaining the positional information of the direction has a predetermined relationship between the position of each light beam scanning direction of each exposure region of a predetermined length exposed by each light beam and the second light beam detecting means. And setting the print area setting means in units of clocks provided from the delay clock selecting means, and as a second step, scanning the exposure areas. The position information is obtained by setting each delay clock selected by each delay clock selection means so that the direction positions coincide with each other, and the control means obtains the position information in the beam light scanning direction. Based on the setting value of the print area setting means obtained as the position information by the obtaining means, the print area setting means assigns each print area of each beam light on the image carrier in units of each delay clock. Control to set.

The image forming apparatus according to the present invention includes a resolution setting unit that sets a resolution for image formation, a scanning speed changing unit that changes a scanning speed of the scanning unit, and a clock that changes the frequency of the clock for image formation. a frequency changing means, depending on the setting of the resolution setting unit, by using the scanning speed changing means and the clock frequency changing means, and a resolution switching control means for changing the clock frequency and the change in the scanning speed It has.

Further, the image forming apparatus of the present invention includes a beam light position detecting unit that detects each passing position of the plurality of light beams scanned on the image carrier by the scanning unit, and each of the beam light position detecting units. A beam light generation control means for controlling the light beam generation means so that the plurality of light beams are not scanned and exposed on the image carrier when each of the light beam passage positions is detected; and And a beam light position control means for controlling the passage positions of the light beams so that the passage positions of the plurality of light beams that scan the image carrier become predetermined positions based on the detection result .

In the image forming apparatus of the present invention, the beam light generating means is arranged so that the beam light is not scanned and exposed on the image carrier when the light power detection means detects the power of each beam light. First controlling means for controlling .

  The image forming apparatus of the present invention can also be applied to an optical system in which the light beam order in the light beam scanning direction (main scanning direction) is unknown (there may be simultaneous), and the exposure position in the main scanning direction is always accurate. Can be controlled.

  The image forming apparatus of the present invention can also be applied to a plurality of types of recording pitches (resolutions).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the configuration of a digital copying machine as an image forming apparatus to which the light beam scanning apparatus according to this embodiment is applied. In other words, this digital copying machine includes, for example, a scanner unit 1 as an image reading unit and a printer unit 2 as an image forming unit. The scanner unit 1 includes a first carriage 3 and a second carriage 4 that can move in the direction of the arrow, an imaging lens 5, a photoelectric conversion element 6, and the like.

  In FIG. 1, a document O is placed downward on a document table 7 made of transparent glass, and the document O is placed on the center right on the front right side of the document table 7 in the short direction. The document O is pressed onto the document table 7 by a document fixing cover 8 provided so as to be freely opened and closed.

  The document O is illuminated by a light source 9, and the reflected light is condensed on the light receiving surface of the photoelectric conversion element 6 via the mirrors 10, 11, 12 and the imaging lens 5. Here, the first carriage 3 on which the light source 9 and the mirror 10 are mounted and the second carriage 4 on which the mirrors 11 and 12 are mounted move at a relative speed of 2: 1 so as to make the optical path length constant. It has become. The first carriage 3 and the second carriage 4 are moved from right to left by a carriage driving motor (not shown) in synchronization with the reading timing signal.

  As described above, the image of the document O placed on the document table 7 is sequentially read line by line by the scanner unit 1, and the read output is 8 indicating the density of the image in the image processing unit (not shown). It is converted into a bit digital image signal.

  The printer unit 2 includes an optical system unit 13 and an image forming unit 14 that combines an electrophotographic system capable of forming an image on a sheet P that is an image forming medium. That is, an image signal read from the original O by the scanner unit 1 is processed by an image processing unit (not shown) and then converted into a laser beam light (hereinafter simply referred to as a beam light) from a semiconductor laser oscillator. . In this embodiment, a multi-beam optical system using a plurality (two or more) of semiconductor laser oscillators is employed.

  The configuration of the optical system unit 13 will be described in detail later. The plurality of semiconductor laser oscillators provided in the unit emit light in accordance with a laser modulation signal output from an image processing unit (not shown) and output from these. The plurality of light beams are reflected by a polygon mirror to become scanning light and output to the outside of the unit.

  A plurality of light beams output from the optical system unit 13 are imaged as spot scanning light having a necessary resolution at the exposure position X on the photosensitive drum 15 as an image carrier, and are subjected to scanning exposure. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 15.

  Around the photosensitive drum 15, a charging charger 16, a developing unit 17, a transfer charger 18, a peeling charger 19, a cleaner 20, and the like are disposed. The photosensitive drum 17 is rotationally driven at a predetermined outer peripheral speed by a drive motor (not shown), and is charged by a charging charger 16 provided facing the surface thereof. A plurality of light beams (scanning light) are spot-imaged at the position of the exposure position X on the charged photosensitive drum 15.

  The electrostatic latent image formed on the photosensitive drum 15 is developed with toner (developer) from the developing unit 17. The photosensitive drum 15 on which the toner image is formed by development is transferred by the transfer charger 18 onto the paper P supplied at a timing of the transfer position by the paper feed system.

  The paper feed system separates and feeds the paper P in the paper feed cassette 21 provided at the bottom by the paper feed roller 22 and the separation roller 23 one by one. Then, it is sent to the registration roller 24 and supplied to the transfer position at a predetermined timing. On the downstream side of the transfer charger 18, a paper transport mechanism 25, a fixing device 26, and a paper discharge roller 27 for discharging the paper P on which an image has been formed are disposed. As a result, the toner image is transferred onto the paper P on which the toner image has been transferred, and is then discharged onto the external paper discharge tray 28 via the paper discharge roller 27.

  In addition, the photosensitive drum 15 whose transfer to the paper P has been completed, the residual toner on the surface thereof is removed by the cleaner 20, the initial state is restored, and a standby state for the next image formation is entered.

  By repeating the above process operation, the image forming operation is continuously performed.

  As described above, the document O placed on the document table 7 is read by the scanner unit 1, and the read information is processed as a toner image on the paper P after being subjected to a series of processing by the printer unit 2. It will be recorded.

  Next, the optical system unit 13 will be described.

  FIG. 2 shows the configuration of the optical system unit 13 and the positional relationship between the photosensitive drum 15. The optical system unit 13 includes, for example, semiconductor laser oscillators 31a, 31b, 31c, and 31d as four beam light generating means, and each laser oscillator 31a to 31d simultaneously forms an image for each scanning line. By doing so, high-speed image formation is possible without extremely increasing the rotational speed of the polygon mirror.

  That is, the laser oscillator 31a is driven by the laser driver 32a, and the output light beam passes through a collimator lens (not shown) and then enters a galvanometer mirror 33a serving as an optical path changing unit. The beam light reflected by the galvanometer mirror 33a passes through the half mirror 34a and the half mirror 34b, and is incident on the polygon mirror 35 as a polyhedral rotating mirror.

  The polygon mirror 35 is rotated at a constant speed by a polygon motor 36 driven by a polygon motor driver 37. Thereby, the reflected light from the polygon mirror 35 is scanned in a fixed direction at an angular velocity determined by the number of rotations of the polygon motor 36. The beam light scanned by the polygon mirror 35 passes through the f-θ characteristic of an f-θ lens (not shown), thereby passing the beam light at a constant speed as beam light detection means and beam light position detection means. The light receiving surface of the detection device 38 and the photosensitive drum 15 are scanned.

  The laser oscillator 31b is driven by the laser driver 32b, and the output beam light passes through a collimator lens (not shown), is reflected by the galvano mirror 33b, and is further reflected by the half mirror 34a. The reflected light from the half mirror 34 a passes through the half mirror 34 b and enters the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillator 31a described above, passes through an f-θ lens (not shown), and scans the light receiving surface of the beam light detector 38 and the photosensitive drum 15 at a constant speed.

  The laser oscillator 31c is driven by the laser driver 32c, and the output beam light passes through a collimator lens (not shown), is reflected by the galvanometer mirror 33c, further passes through the half mirror 34c, and is reflected by the half mirror 34b. Incident on the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillators 31a and 31b described above, passes through an f-θ lens (not shown), and scans the light receiving surface of the beam light detector 38 and the photosensitive drum 15 at a constant speed. To do.

  The laser oscillator 31d is driven by a laser driver 32d, and the output beam light passes through a collimator lens (not shown), is reflected by a galvano mirror 33d, is further reflected by a half mirror 34c, and is reflected by a half mirror 34b. Incident on the polygon mirror 35. The path after the polygon mirror 35 is the same as that of the laser oscillators 31a, 31b, 31c described above, passes through an f-θ lens (not shown), and on the light receiving surface of the light beam detector 38 and the photosensitive drum 15 at a constant speed. Scan.

  Each of the laser drivers 32a to 32d incorporates an auto power control (APC) circuit, and always emits the laser oscillators 31a to 31d at a light emission power level set by a main control unit (CPU) 51 described later. It is supposed to work.

  In this way, the light beams output from the separate laser oscillators 31a, 31b, 31c, and 31d are combined by the half mirrors 34a, 34b, and 34c, and the four light beams travel in the direction of the polygon mirror 35. Become.

  Therefore, the four light beams can simultaneously scan the photosensitive drum 15, and when the rotation speed of the polygon mirror 35 is the same as that of the conventional single beam, an image is recorded at a speed four times higher. It becomes possible to do.

  The galvanometer mirrors 33a, 33b, 33c, and 33d are for adjusting (controlling) the positional relationship between the light beams in the sub-scanning direction. The galvanometer mirror drive circuits 39a, 39b, 39c, and 39d that drive the galvanometer mirrors 33a, 33b, 33c, and 33d It is connected.

  The beam light detection device 38 is for detecting the passage position, passage timing and power of the four light beams, and the photosensitive drum 15 has a light receiving surface equal to the surface of the photosensitive drum 15. It is arrange | positioned in the edge part vicinity. Based on the detection signal from the light beam detector 38, control of the galvanometer mirrors 33a, 33b, 33c, 33d corresponding to each light beam (image forming position control in the sub-scanning direction), laser oscillators 31a, 31b, 31c. , 31d and the light emission timing (image forming position control in the main scanning direction) are controlled (details will be described later). In order to generate a signal for performing these controls, the light beam detector 38 is connected to a light beam detector output processing circuit 40.

  Next, the beam light detector 38 will be described.

  FIG. 3 schematically shows the relationship between the configuration of the beam light detector 38 and the scanning direction of the beam light. The beam lights a to d from the four semiconductor laser oscillators 31a, 31b, 31c, and 31d are scanned from the left to the right by the rotation of the polygon mirror 35, and cross the beam light detector 38.

  The beam light detector 38 includes two vertically long sensor patterns S1 and S2 serving as a first light detector, and second and third lights disposed so as to be sandwiched between the two sensor patterns S1 and S2. Seven sensor patterns SA, SB, SC, SD, SE, SF, and SG as detection units, and these sensor patterns S1, S2, SA, SB, SC, SD, SE, SF, and SG are integrally held. It comprises a holding substrate 38a as a holding member. In addition, sensor pattern S1, S2, SA-SG is comprised by the photodiode, for example.

  Here, the sensor pattern S1 detects the passage of the beam light and generates a reset signal (integration operation start signal) of an integrator described later, and the sensor pattern S2 similarly detects the passage of the beam light, This is a pattern for generating a conversion start signal of an A / D converter to be described later. Further, as will be described in detail later, the sensor patterns S1 and S2 are patterns serving as a reference for performing various controls in the main scanning direction. The sensor patterns SA to SG are patterns for detecting the passage position of the beam light.

  As shown in FIG. 3, the sensor patterns S <b> 1 and S <b> 2 are arranged with respect to the scanning direction of the light beam so that the light beams a to d scanned by the polygon mirror 35 always cross regardless of the positions of the galvanometer mirrors 33 a to 33 d. It is long in the perpendicular direction. For example, in this example, the widths W1 and W3 in the scanning direction of the light beam are 200 μm, while the length L1 in the direction perpendicular to the scanning direction of the light beam is 2000 μm.

  As shown in FIG. 3, the sensor patterns SA to SG are arranged so as to be stacked between the sensor patterns S1 and S2 in a direction perpendicular to the scanning direction of the beam light. It is the same as the length L1 of S1 and S2. The width W2 in the scanning direction of the beam light of the sensor patterns SA to SG is, for example, 600 μm.

  Further, in order to detect the power of the beam light on the photosensitive drum 15, for example, as indicated by a broken arrow Pa or Pb in FIG. 3, the beam light passes over the sensor pattern SA or SG. The beam light passing position is controlled to take in the output from the sensor pattern SA or SG.

  FIG. 4 is an enlarged view of the pattern shapes of the sensor patterns SA to SG of the beam light detector 38.

  The pattern shape of the sensor patterns SB to SF is, for example, a rectangle of 32.3 μm × 600 μm, and a minute gap G of about 10 μm is formed in a direction perpendicular to the beam light scanning direction. Therefore, the arrangement pitch between the gaps is 42.3 μm. Further, the sensor patterns SA and SB and the gaps between the sensor patterns SF and SG are also arranged to be about 10 μm. Note that the width of the sensor patterns SA and SG in the direction perpendicular to the scanning direction of the beam light is larger than the width of the sensor patterns SB to SF.

  The details of the control using the output of the light beam detector 38 configured as described above will be described later. A gap formed at a pitch of 42.3 μm determines the passage position of the light beams a, b, c, and d. This is a target for controlling the pitch (42.3 μm in this example). That is, the beam light a has a gap G (BC) formed by the sensor patterns SB and SC, the beam light b has a gap G (CD) formed by the sensor patterns SC and SD, and the beam light c has The gap G (DE) formed by the sensor patterns SD and SE, and the gap G (EF) formed by the sensor patterns SE and SF for the beam light d are targets of the passing positions.

  Next, the features of the beam light detection device 38 having such a sensor pattern will be described with reference to FIG.

  As described above, the present beam light detection device 38 is arranged near the end of the photosensitive drum 15 or from the polygon mirror 35 so that the light receiving surface thereof is at the same position as the photosensitive drum 15. It is arrange | positioned in the position which can obtain the optical path length equivalent to the distance to. In order to accurately capture the passage position of the light beam with the light beam detector 38 arranged in this way, the sensor pattern described above is arranged in a direction perpendicular to the light beam passage direction. Ideal. However, in practice, there is a slight inclination in the mounting of the beam light detector 38.

  In contrast to such an attachment position being inclined with respect to an ideal position, in the light beam detection device 38 of this example, the point for detecting the passing position for each light beam is the position of the sensor pattern. By arranging it so as not to deviate with respect to the light passing direction, even if the beam light detector 38 is mounted with a slight inclination, the detection pitch can be minimized.

  Further, as will be described in detail later, an integrator is provided in the output processing circuit for processing the output of the light beam detector 38, so that the light beam can be transmitted regardless of the inclination of the light beam detector 38. The influence on the position detection result can be minimized.

  FIG. 5A shows the relationship between the sensor patterns SA to SG and the scanning positions of the light beams a to d when the light beam detection device 38 of the present example is mounted inclined with respect to the scanning direction of the light beam. Is. However, in the figure, the scanning direction of the light beams a to d is expressed as being inclined with respect to the light beam detector 38. The scanning lines of the beam lights a to d in the figure are those when controlled at an ideal interval (42.3 μm pitch).

  Further, between the sensor patterns SA to SG, control target points (white circles) in the present sensor pattern are shown. As will be described later in detail, this point is in the middle (intermediate) between patterns even when the beam lights a to d are incident obliquely due to the effect of the integrator.

  As is apparent from the figure, the trajectory of the scanning line controlled at an ideal interval (42.3 μm pitch) passes through the approximate center of the control target on the sensor patterns SA to SG. That is, even if the light beam detection device 38 of this example is mounted with a slight inclination, the influence on the detection accuracy is extremely small.

  For example, when the light beam detection device 38 is mounted with an inclination of 5 degrees with respect to the scanning line of the light beam, the scanning position pitch of each light beam to be controlled with a 42.3 μm pitch as a target is originally inclined. Due to the detection error of the light beam detector 38 caused by the above, the pitch is controlled to a target of 42.14 μm. The error at this time is about 0.16 μm (0.03%), and if controlled in this way, the influence on the image quality is very small. This value can be easily obtained using a trigonometric function, but will not be described in detail here.

  As described above, by using the sensor patterns SA to SG of the light beam detection device 38 of this example, it is possible to accurately detect the scanning position of the light beam even if the mounting accuracy with respect to the inclination of the light beam detection device 38 is somewhat poor. It becomes.

  On the other hand, the light beam detection device 80 shown in FIG. 5B is an example of a sensor pattern for realizing the same function as the light beam detection device 38 of the present invention that has been conventionally used.

  When such a sensor pattern is adopted, the light beam passage position cannot be accurately detected if the sensor pattern is attached with a slight inclination with respect to the scanning direction of the light beams a to d. The cause is that a sensor pattern (in this example, S3 *, S4 *, S5 *, S6 *: * indicates a and b) that detects the passing positions of the light beams a to d in the scanning direction of the light beams. It is located at a distance from it. In other words, the longer the distance is in the scanning direction of the light beam, the larger the detection error is even for a slight inclination.

  In FIG. 5 (b), similarly to FIG. 5 (a), it is assumed that the light beam detector 80 is mounted at an inclination, and the scanning line controlled to an ideal interval (42.3 μm pitch) is used. The trajectory is shown. As is apparent from FIG. 5B, it can be seen that the conventional light beam detection device 80 requires much higher mounting accuracy than the light beam detection device 38 of this example shown in FIG.

  For example, similar to the beam light detection device 38 in FIG. 5A, the beam light detection device 80 in FIG. 5B is attached with an inclination of 5 degrees, and the distance between the sensor patterns S3a, S3b and S6a, S6b. Is 900 μm, the control target of the beam light d is shifted by 78.34 μm from the ideal position. This value is an error far exceeding the target control pitch of 42.3 μm in this example, and gives a serious defect to the image quality. Therefore, when such a beam light detector 80 is used, a very high mounting accuracy is required at least with respect to the inclination of the beam light with respect to the scanning direction.

  Conventionally, in order to make up for such a problem, the sensor pattern width W in the scanning direction of the beam light is reduced as much as possible without sacrificing some sensitivity, and the passage position of the beam light with respect to the scanning direction of the beam light. It is necessary to consider that the detection points are not separated. In addition, in order to compensate for the lack of sensitivity, it is essential to increase the power of the laser oscillator and decrease the rotation speed of the polygon motor when detecting the passage position of the beam light.

  Next, the control system will be described.

  FIG. 6 shows a control system mainly for controlling the multi-beam optical system. That is, 51 is a main control unit that controls the entire control, and is composed of, for example, a CPU, which includes a memory 52, a control panel 53, an external communication interface (I / F) 54, and laser drivers 32a, 32b, and 32c. , 32d, polygon mirror motor driver 37, galvanometer mirror drive circuits 39a, 39b, 39c, 39d, beam light detector output processing circuit 40 as signal processing means, synchronization circuit 55, and image data interface (I / F) 56 is connected.

  An image data I / F 56 is connected to the synchronization circuit 55, and an image processing unit 57 and a page memory 58 are connected to the image data I / F 56. The scanner unit 1 is connected to the image processing unit 57, and an external interface (I / F) 59 is connected to the page memory 58.

  Here, the flow of image data when forming an image will be briefly described as follows.

  First, in the case of the copying operation, as described above, the image of the document O set on the document table 7 is read by the scanner unit 1 and sent to the image processing unit 57. The image processing unit 57 performs, for example, known shading correction, various filtering processes, gradation processing, gamma correction and the like on the image signal from the scanner unit 1.

  Image data from the image processing unit 57 is sent to the image data I / F 56. The image data I / F 56 plays a role of distributing the image data to the four laser drivers 32a, 32b, 32c, and 32d.

  The synchronization circuit 55 generates a clock synchronized with the timing of each light beam passing through the light beam detector 38, and in synchronization with this clock, the laser driver 32a, 32b, 32c, 32d from the image data I / F 56. The image data is transmitted as a laser modulation signal.

  In this way, image data is transferred while being synchronized with the scanning of each light beam, so that image formation synchronized with the main scanning direction (to the correct position) is performed.

  Further, the synchronizing circuit 55 forcibly causes each laser oscillator 31a, 31b, 31c, 31d to emit light in the non-image region and controls the power of each beam light, and a beam light described later. A drum for preventing each light beam from exposing the photosensitive drum 15 by forced light emission by the main controller 51 when passing (scanning) position control and light power control between each light beam are executed. The top emission prohibition timer etc. are included.

  The control panel 53 is a man-machine interface for starting a copying operation and setting the number of sheets.

  This digital copying machine is configured not only to perform a copying operation but also to form and output image data input from the outside via an external I / F 59 connected to the page memory 58. The image data input from the external I / F 59 is once stored in the page memory 58 and then sent to the synchronization circuit 55 via the image data I / F 56.

  Further, when the digital copying machine is controlled from the outside via a network or the like, for example, the external communication I / F 54 serves as the control panel 53.

  The galvanometer mirror drive circuits 39a, 39b, 39c, and 39d are circuits that drive the galvanometer mirrors 33a, 33b, 33c, and 33d in accordance with the instruction value from the main control unit 51. Therefore, the main controller 51 can freely control the angles of the galvanometer mirrors 33a, 33b, 33c, and 33d via the galvanometer mirror drive circuits 39a, 39b, 39c, and 39d.

  The polygon motor driver 37 is a driver that drives the polygon motor 36 for rotating the polygon mirror 35 that scans the four light beams described above. The main control unit 51 can start and stop the rotation of the polygon motor driver 37 and change the number of rotations. The rotation speed is switched when the recording pitch (resolution) is changed.

  The laser drivers 32a, 32b, 32c, and 32d emit a laser beam in accordance with a laser modulation signal synchronized with the scanning of the beam light from the synchronization circuit 55 described above, and a forced emission signal from the main control unit 51. The laser oscillators 31a, 31b, 31c and 31d are forced to emit light independently of each other regardless of the image data.

  In addition to confirming the operating state of each laser oscillator 31a, 31b, 31c, 31d, this function executes beam light passage (scanning) position control, which will be described later, and beam light power control between the light beams. At this time, the laser oscillators 31a, 31b, 31c and 31d are forcibly made to emit light so that each light beam scans on the light beam detector 38. However, as described above, it is not possible to prevent the photosensitive drum 15 from being exposed by the on-drum light emission inhibition timer in the synchronization circuit 55.

  Further, the main control unit 51 sets the power at which each laser oscillator 31a, 31b, 31c, 31d emits light for each laser driver 32a, 32b, 32c, 32d. The setting of the light emission power is changed in accordance with a change in process conditions, detection of a light beam passage position, and the like.

  The memory 52 is for storing information necessary for control. For example, the control amount of each galvanometer mirror 33a, 33b, 33c, 33d, circuit characteristics for detecting the passage position of the beam light (amplifier offset value), and print area information corresponding to each beam light are stored. Thus, the optical system unit 13 can be brought into a state in which image formation is possible immediately after the power is turned on.

  Hereinafter, the beam light position control (print area setting) in the main scanning direction will be described in detail.

  FIG. 7 shows the positional relationship between the sensor patterns S1 and S2 of the beam light detector 38 and the photosensitive drum 15, the exposure areas (printing areas) of the beam lights a to d by the sample timer, which will be described later, and the light emission area by the image data. FIG. 6 is a diagram showing the positional relationship of the on-drum light emission inhibition timer output together with the time chart.

  As shown in the figure, the sample timer is reset by the output of the sensor pattern S1 of the beam light detector 38, and starts counting a clock (not shown) from “0”. When the sample timer reaches a predetermined value, the output of the sample timer becomes 'H', and the four laser oscillators 31a to 31d are caused to emit light. As shown in the figure, the value set in the sample timer is usually set so that each beam light a to d passes through the photosensitive drum 15 and before each beam light a to d is scanned by the next polygon mirror surface. The values are such that each of the light beams a to d emits light.

  The scanning of each of the light beams a to d is started by the next polygon mirror surface, and when the first light beam reaches the sensor pattern S1, the sample timer is reset, and the operation described above is repeated. That is, each of the laser oscillators 31a to 31d is forced to emit light for a certain period of time for each line in an area not related to image formation. During this compulsory light emission time, auto power control (APC) for maintaining the light emission power of the laser light at a predetermined value is executed for each of the laser oscillators 31a to 31d.

  Here, the on-drum light emission prohibition timer will be described. In the forced light emission, in addition to the light emission by the output of the sample timer, as described above, there is a forced light emission operation that the main control unit 51 performs directly on each of the laser drivers 32a to 32d. In this forced light emission operation, the main control unit 51 arbitrarily causes each of the laser oscillators 31a to 31d to emit light. In addition to checking the operation state of each of the laser oscillators 31a to 31d, the passage of beam light (described later) This is used when the beam light is scanned on the beam light detector 38 when performing (scanning) position control and beam light power control between the beams.

  However, when the laser oscillators 31a to 31d continuously emit light, the photosensitive drum 15 is exposed, and the following problems occur.

  That is, when the photosensitive drum 15 is stopped, a specific portion of the photosensitive drum 15 is concentrated and exposed, which may cause local deterioration of the photosensitive drum 15. Further, when the photosensitive drum 15 is rotating, a large amount of toner may be attached (consumed) or carrier may be attached.

  The on-drum light emission prohibition timer is for preventing these problems, and when this timer is operated, as shown in the time chart of FIG. The forced light emission by 51 is prohibited. That is, based on the output of the sensor pattern S1 of the light beam detection device 38, the light beam is forced from the timing before passing the light beam detection device 38 and hitting the photosensitive drum 15 (after TOFF1 has elapsed from the output S1). Light emission is prohibited (output from the on-drum light emission prohibition timer: H), and forced light emission prohibition is released (output from the on-drum light emission inhibition timer) at the timing of passing over the photosensitive drum 15 (after TOFF2 has elapsed from the S1 output). : L).

  On the other hand, light emission based on image data (including test image data) is normally performed on the print area of the photosensitive drum 15 as shown in FIG. Although not described in detail here, the positional relationship of the light beams in the main scanning direction is usually not constant in a structure in which a plurality of light beams are combined by a half mirror and scanned as described above.

In this figure, as an example, the case where the beam light a is at the head and is followed by the beam lights b, c, and d is shown. As shown in the figure, with reference to the beam light a, the beam light b is delayed by ΔTab, the beam light c is delayed by ΔTac, and the beam light d is delayed by ΔTad.

  Now, in order to make the exposure areas of the light beams a to d having such a positional (phase) relationship exactly coincide with each other, as shown in the figure, the light emission timing based on the image data is based on the light beam a. It is necessary to shift the beam light b by ΔTab, the beam light c by ΔTac, and the beam light d by ΔTad.

  Normally, the exposure area is generally adjusted in units of one clock (one pixel unit) based on a reference clock. However, in the optical system configuration of this example, there is no guarantee that the positional relationship between the light beams is shifted by one clock unit, and finer adjustment is required.

  FIG. 8 shows a configuration for setting a print area (exposure area) in fine units of one clock or less, and a configuration for avoiding the drum exposure due to the above-described forced exposure. This is shown in FIG. In the block diagram shown, only the portion related to the print area is extracted.

  In FIG. 8, reference numeral 40a denotes a main scanning direction light beam position detection circuit provided in the light beam detector output processing circuit 40, which is constituted by a first counter 111, a second counter 112, a latch circuit 113, and the like. ing.

  The synchronization circuit 55 includes four crystal oscillators 114a to 114d, a selector 115 that selects the crystal oscillators 114a to 114d, a clock synchronization circuit 116, a delay line 117, four delay clock selectors 118a to 118d, and four image transfer clock generation units ( (Print area setting section) 119a to 119d, sample timer 120, OR gate circuit 121, and on-drum light emission prohibition timer 122, and the like.

  Hereinafter, FIG. 8 will be described in more detail.

  First, a configuration for avoiding drum exposure due to forced light emission will be described. As shown in the figure, the main controller 51 can forcibly cause the laser oscillators 31a to 31d to emit light by individually sending forced light emission signals to the laser drivers 32a to 32d, respectively.

  However, the laser drivers 32 a to 32 d are configured such that the forced light emission signal from the main control unit 51 loses its effectiveness while the on-drum light emission inhibition signal is output from the on-drum light emission inhibition timer 122. As a result, even if a forced light emission signal is output from the main control unit 51, the laser oscillators 31a to 31d are prevented from emitting light.

  The operation of the on-drum light emission prohibition timer 122 is controlled by a start / stop signal from the main control unit 51. That is, when the stop signal is output from the main control unit 51 to the on-drum light emission prohibition timer 122, the timer operation is stopped and the drum light emission prohibition signal is not output to the laser drivers 32a to 32d. Therefore, the main control unit 51 stops the on-drum light emission prohibition timer 122 by a stop signal and outputs a forced light emission signal to the laser drivers 32a to 32d, thereby continuously causing the laser oscillators 31a to 31d to emit light. be able to.

  On the other hand, when the main control unit 51 activates the on-drum emission prohibition timer 122 by the activation signal, even if the main control unit 51 outputs a forced emission signal to the laser drivers 32a to 32d, the laser driver 32a. While the on-drum emission prohibition signal 122 is output from the on-drum emission inhibition timer 122 to .about.32d, the laser oscillators 31a to 31d do not perform the emission operation.

  The operation timing of the on-drum light emission prohibition timer 122 is as described above with reference to FIG. That is, when the beam light is scanned by the polygon mirror 35, the on-drum light emission prohibition timer 122 scans the sensor pattern S1 of the beam light detection device 38, based on the pulse signal output from the sensor pattern S1. Operate.

  That is, when a pulse signal is output from the sensor pattern S1, the on-drum forced emission prohibition signal becomes “H” (high) before the light beam reaches the photosensitive drum 15 after the time TOFF1 has elapsed, and the main control unit The forced light emission operation by 51 stops. When the pulse signal is output from the sensor pattern S1 and the time TOFF2 has passed and the light beam passes over the photosensitive drum 15, the on-drum forced light emission signal becomes 'L' (low), and the main control unit 51 Forced flash operation is enabled.

  As described above, the main control unit 51 outputs a forced light emission signal to the laser drivers 32a to 32d and outputs an activation signal to the on-drum light emission inhibition timer 122, thereby being aware of the movement of the beam light. In addition, the light beam detector 38 can be exposed with an arbitrary light beam without exposing the photosensitive drum 15.

  The passage (scanning) position control of the light beam and the light power control between the light beams will be described in detail later. Unless otherwise specified, the on-drum light emission prohibition timer 122 is activated and the photosensitive member is activated. The description will be made assuming that the drum 15 is not exposed.

  Next, a configuration for setting a print area (exposure area) in fine units of one clock or less will be described. As described above, the sensor pattern S1 of the light beam detection device 38 depends on one of the light beams a, b, c, and d forcedly emitted by the sample timer 120 (in some cases, 2 The signal level is changed from “L” (low) to “H” (high) (see FIG. 9). As described above, this signal is input to the sample timer 120, and the forced light emission of each of the laser oscillators 31a to 31d is released.

Therefore, the beam lights a, b, c, and d disappear, and the output of the sensor pattern S1 becomes a pulse output. (When the response of the sample timer 120 is slow, it may become a pulse signal due to the passage of the head beam light.)
The output of the sensor pattern S1 is also input to the clock synchronization circuit 116 in the synchronization circuit 55. The operation of the clock synchronization circuit 116 is to output a clock having the same frequency as the output clock of the crystal oscillator synchronized with the output of the sensor pattern S1, as shown in FIG. As shown in the figure, the output synchronous clock is a clock that rises with a delay of ΔTSYNC from the trailing edge of the sensor pattern S1 output.

  Next, this synchronous clock is input to the delay line 117. The delay line 117 has a function of delaying an input signal for a certain time. The delay line 117 shown in the figure has 10 taps as an output. That is, the delay clock D1 output from the first stage tap is delayed by Δtd with respect to the input synchronous clock, and the delay clock D2 output from the second stage tap is further delayed by Δtd. Become.

  The delay clock D10 output from the final stage (10th stage) tap is a clock delayed by 10Δtd with respect to the input synchronous clock. In this example, 1/10 of one synchronization of the synchronization clock is substantially equal to Δtd. That is, the delay clock D10 is substantially in phase with the input synchronous clock and is shifted by one clock.

  In this example, the delay amount of the delay line 117 is set to 1/10 of one clock. However, if more precise print area setting accuracy is required, the delay amount per tap is further reduced. Just increase the number of taps.

  The outputs from the delay line 117, that is, the delay clocks D1 to D10 are input to the delay clock selectors 118a to 118d corresponding to the beam lights a to d. The functions of the delay clock selectors 118a to 118d are output to the next-stage image transfer clock generation units (print area setting units) 119a to 119d based on the delay clock selection signal output from the main control unit 51 to each selector. The clock to be selected is to be selected. In other words, the main control unit 51 can freely select a clock for setting the print area from the delay clocks D1 to D10 for each of the light beams a to d.

Next, the image transfer clock generation units (print area setting units) 119a to 119d will be described. The main control unit 51 sets a print area for each beam light a to d in units of one clock (one pixel unit) using a print area setting signal. That is, it is possible to set the output timing and the number of outputs of the image transfer clock. At the time of normal image formation, as described above, the light emission area of each of the light beams a to d is set at a predetermined position on the photosensitive drum 15. The predetermined position here changes depending on the paper size used, the binding margin setting, and the like.

  The image transfer clock (printing area signal) obtained in this way is sent to the image data I / F 56, and the image data (laser modulation signals) corresponding to the respective beam lights a to d are transferred to the image data. Output in synchronization with the clock (print area signal). The laser drivers 32a to 32d modulate the laser oscillators 31a to 31d with this image data (laser modulation signal).

  In this way, the main control unit 51 sets the print area in units of one clock (in units of one pixel) for the image transfer clock generation units (print area setting units) 119a to 119d by the print area setting signal. Furthermore, the print area is set in units of 1/10 clock (1/10 pixel unit) independently for each of the light beams a to d by the delay clock selection signal for each of the delay clock selectors 118a to 118d. it can.

  Next, the main controller 51 sets the print area in units of 1 clock (1 pixel) and 1/10 clock (1/10 pixel). The principle of the beam position information acquisition method will be described with reference to FIG.

  FIG. 10 shows a case where an extremely small value is set in the image transfer clock generation unit (print area setting unit) 119a described above as compared with the normal image formation. As shown in the figure, for example, the main control unit 51 selects the delay clock D1 for the light beam a, sets the print area to “1 to 5”, and outputs a test print command to the image data I / F 56. When solid black (laser emission in the printing area) is instructed, the beam light a exposes the printing area “1 to 5”.

  As described above, when the setting of the print area is a small value, the beam light does not reach the area of the photosensitive drum 15 and the beam light detecting device 38 is exposed. In this state, if the output of the sensor pattern S2 located downstream of the sensor pattern S1 is monitored, the main control unit 51 knows how much print area the sensor pattern S2 will respond to. Can do. In the example of FIG. 10, it can be seen that when the print area is set to “6 to 10”, the sensor pattern S2 starts to respond.

  In this way, the main control unit 51 can detect the relative positional relationship of the light beam a with respect to the output of the sensor pattern S1 in increments of 1 clock (1 pixel).

  Next, a method for detecting the relative positional relationship of the light beam a with respect to the output of the sensor pattern S1 in units of one clock (one pixel) or less will be described with reference to FIG. As described with reference to FIG. 10, when the delay light D1 is selected for the light beam a, the sensor pattern S2 responds when the print area is set to “6-10”. Therefore, the main control unit 51 reduces the setting of the print area to “5-9” and changes the selection of the delay clock.

  As shown in FIG. 11, as the selection of the delay clock is changed from D1 to D2 to D3, the print area moves to the right in units of 1/10 clock (1/10 pixel). In this example, when the delay clock D5 is selected, the sensor pattern S2 starts to respond.

  Therefore, when the light beam a is set to 5 pixels on the basis of the output of the sensor pattern S1, the main control unit 51 prints when the delay clock D5 is selected with the setting of the area “5 to 9”. It can be detected that the right end of the area exposes the sensor pattern S2.

  Depending on the positional relationship with the head beam, the sensor pattern S1 may be exposed again depending on the print area and the second pulse may be output, but only the first pulse output is valid. This problem can be avoided by providing the circuit as follows (details are not described here).

  If such a detection operation is also performed for the light beams b, c, and d, it is possible to determine the positional relationship of each light beam with respect to the output of the sensor pattern S1 by the head light beam. If the main control unit 51 selects a delay clock and sets a print area for each of the light beams a to d based on this positional relationship during an actual printing operation, the main control unit 51 can obtain 1/10 clock (1/10 pixel). The print area can be adjusted with accuracy.

  The main control unit 51 stores in the memory 52 information regarding the respective light beams a to d obtained in this way. By storing these pieces of information in the memory 52, for example, even when the power of the apparatus is turned off, it is possible to immediately return to the original state after the power is turned on again.

  Even when the print area is set again in the main scanning direction, if these pieces of information are stored in the memory 52, it is possible to perform only fine adjustments, and no extra time is required for control. There is an advantage.

  Next, the operation of the light beam position detection circuit 40a in the main scanning direction in the light beam detector output processing circuit 40 will be described.

  As described above, the main control unit 51 monitors the output of the sensor pattern S2 while changing the selection of the delay clock and changing the print area for each of the light beams a to d, and thereby the beam in the main scanning direction. Although it becomes possible to detect the light position, here, how to output the output of the sensor pattern S2 to the main control unit 51 will be described.

  FIG. 12 is a timing chart showing the operation when the beam light a to d is not exposed at all for the sensor pattern S2. As described above, since the laser oscillators 31a to 31d are forced to emit light by the sample timer 120 as described above, the head beam light always exposes the sensor pattern S1 once per scan. , Output a pulse-like signal.

  The first counter 111 is a counter that counts the pulse signal from the sensor pattern S1, for example, counts “0 to 7” endlessly, and in the second half of the count value “7”, as shown in FIG. A carry signal is output. The second counter is a counter that counts the output of the sensor pattern S2.

  The second counter 112 is cleared (reset) by a signal obtained by delaying the carry signal of the first counter 111 described above. Therefore, the count value of the second counter 112 becomes “0” every 8 scans.

  The latch circuit 113 latches (holds) the output value of the second counter 112. The latch timing of the latch circuit 113 is the leading edge of the carry signal of the first counter 111. Therefore, the latch circuit 113 can hold the value before the second counter 112 is reset.

  The value latched by the latch circuit 113 is updated when the first counter 111 outputs the next carry signal. The count value of the second counter 112 immediately before (latest) is always stored in the latch circuit 113. Will be held. The main control unit 51 can obtain the latest information by reading the value (main scanning direction beam position information) held in the latch circuit 113.

  In the case of FIG. 12, since the sensor pattern S2 does not detect any light beam, the value of the second counter 112 is always “0”, and the value held in the latch circuit 113 is also “0”. Therefore, the main control unit 51 can know from the latched value “0” that the sensor pattern S2 does not detect the light beam.

  FIG. 13 is a timing chart showing the operation when the sensor pattern S2 always detects the light beam. This figure is a timing chart showing the operation when the sensor pattern S2 always detects the light beam.

  As shown in FIG. 13, the second counter 112 that counts the output of the sensor pattern S2 counts “0 to 8” according to the output of the sensor pattern S2. Briefly describing this operation, the second counter 112 is cleared to 0 (reset) by the carry output delay signal of the counter, but the output of the sensor pattern S2 is immediately input and the count value becomes “1”. .

  Thereafter, the count is incremented by the output of the sensor pattern S2 for each scan, the count value becomes “8” in the eighth scan, and the value 8 is held in the latch at the timing when the first counter 111 outputs a carry signal. It will be. After the value “” 8 is held in the latch circuit 113, the second counter 112 is cleared to 0 (reset) again and starts counting from “1”.

  Thus, in a state where the sensor pattern S2 always detects the light beam, the value held in the latch circuit 113 is “8”. Accordingly, when the value of the latch circuit 113 is “8”, the main control unit 51 can determine that the sensor pattern S2 is always detecting the light beam.

  FIG. 14 is a timing chart in a case where the sensor pattern S2 does not detect the beam light or is delicate. Since the sensor pattern S2 does not detect the light beam, the count value of the second counter 112 increases in a certain scan and does not increase in a certain scan. In this example, since the sensor pattern S2 outputs a signal every other scan, the value held in the latch circuit 113 is “4”. Therefore, the main control unit 51 can determine that the edge of the print area and the signal of the sensor pattern S2 have a delicate positional relationship by reading the value “4” held in the latch circuit 113.

In this way, the merit of counting the output of the sensor pattern S2 multiple times is:
1) As described above, the delicate positional relationship between the print area and the sensor pattern S2 can be grasped.

  2) The main controller 51 only needs to read information in units of 8 scans, and the load is lighter than when reading for each scan.

Such points are given.

  In addition, it is preferable that the information acquisition unit is a multiple of the number of polygon mirror surfaces in consideration of surface accuracy for each polygon mirror surface. In this example, since the number of polygon mirror surfaces is “8”, the first counter 111 outputs a carry signal every eight scans.

  Next, the relationship between the beam light power and the print area setting accuracy will be described.

  FIG. 15 schematically shows an exposure area when the same delay clock is selected, the number of set clocks in the print area is the same, and the beam light power is different. This figure shows that the light beam power is the strongest in the case of A, and the light beam power becomes weaker in the order of B and C below.

  As shown in the figure, when considering a region exposed at a certain energy or higher, the region becomes larger as the beam light power is stronger. Here, considering the response of the sensor pattern S2, it can be seen that there is a difference in the response of the sensor pattern S2 even in the case of the same print area setting.

  As shown in the figure, when the edge of the exposure area of the light beam is at the same position as the edge of the sensor pattern S2, it is recognized whether the sensor pattern S2 responds or not depending on the light beam power. In the example of the figure, when the light beam power is A and B, the outputs a and b of the sensor pattern S2 reach the threshold level TH, and the second counter 112 described above counts this, but the light beam power is C. In this case, the output c of the sensor pattern S2 does not reach the threshold level TH, and the second counter 112 cannot count this output.

  Therefore, in order to align a plurality of light beam print areas with high accuracy, the power of the light beams must be the same before the print area is controlled.

  Next, beam light passage (scanning) position control will be described in detail.

  FIG. 16 is a diagram for explaining the light beam passage position control when the light beam detector 38 of FIG. 3 is used, focusing on the light beam passage position control in the block diagram of FIG. The part relevant to control is extracted and shown in detail.

  As described above, a pulse signal indicating that the light beam has passed is output from the sensor patterns S1 and S2 of the light beam detector 38. In addition, independent signals are output from the plurality of sensor patterns SA to SG according to the passage positions of the light beams.

  Among the plurality of sensor patterns SA to SG, output signals of the sensor patterns SA and SG are respectively input to amplifiers 61 and 62 (hereinafter also referred to as amplifiers A and G). The amplification factors of the amplifiers 61 and 62 are set by the main control unit 51 including a CPU.

  Further, as described above, the galvano mirrors 33a to 33d are controlled so that the light beam passing position is on the sensor pattern SA or SG, and the output of the sensor pattern SA or SG is monitored, whereby the photosensitive drum 15 The relative light beam power at the top is detected.

  Further, among the plurality of sensor patterns SA to SG, the output signals of the sensor patterns SB to SF are differential amplifiers 63 to 66 (hereinafter referred to as differential) that amplify the difference between adjacent output signals of the sensor patterns SB to SF. Amplifiers BC, CD, DE, and EF). The differential amplifier 63 amplifies the difference between the output signals of the sensor patterns SB and SC, the differential amplifier 64 amplifies the difference between the output signals of the sensor patterns SC and SD, and the differential amplifier 65 The difference between the output signals of the sensor patterns SD and SE is amplified, and the differential amplifier 66 amplifies the difference between the output signals of the sensor patterns SE and SF.

  The output signals of the amplifiers 61 to 66 are input to the selection circuit (analog switch) 41, respectively. The selection circuit 41 selects a signal to be input to the integrator 42 based on a sensor selection signal from the main control unit (CPU) 51. The output signal of the amplifier selected by the selection circuit 41 is input to the integrator 42 and integrated.

  On the other hand, a pulsed signal output from the sensor pattern S1 is also input to the integrator 42. The pulse signal from the sensor pattern S1 is used as a reset signal (integration operation start signal) for resetting the integrator 42 and simultaneously starting a new integration operation. The role of the integrator 42 is to remove noise and to remove the influence of the inclination of the light beam detector 38, which will be described in detail later.

  The output of the integrator 42 is input to the A / D converter 43. A pulse signal output from the sensor pattern S 2 is also input to the A / D converter 43. The A / D conversion operation of the A / D converter 43 is started when a signal from the sensor pattern S2 is applied as a conversion start signal. That is, A / D conversion is started at the timing when the light beam passes through the sensor pattern S2.

  In this way, the pulse signal from the sensor pattern S1 resets the integrator 42 immediately before the beam light passes through the sensor patterns SA to SG, and simultaneously starts the integration operation, so that the beam light passes over the sensor patterns SA to SG. During this time, the integrator 42 integrates a signal indicating the passage position of the beam light.

  Immediately after the beam light has passed through the sensor patterns SA to SG, the A / D converter 43 performs A / D conversion on the result of integration by the integrator 42 using the pulse signal from the sensor pattern S2 as a trigger. As a result, for the detection of the light beam passage position, the detection signal from which the influence of the inclination of the light beam detection device 38 is removed can be converted into a digital signal.

  The A / D converter 43 that has completed the A / D conversion outputs an interrupt signal INT indicating that the processing has been completed to the main control unit 51.

  Here, the amplifiers 61 to 66, the selection circuit 41, the integrator 42, and the A / D converter 43 constitute a beam light detector output processing circuit 40.

  In this way, the light beam power detection signal and the light beam position detection signal from the light beam detection device 38 converted into a digital signal are used as relative light beam power information or beam light position information on the photosensitive drum 15. To the main control unit 51, and the light power of each light beam on the photosensitive drum 15 and the passage position of the light beam are determined.

  Based on the relative light beam power detection signal and the light beam position detection signal obtained on the photosensitive drum 15 thus obtained, the main control unit 51 determines the light emission power for each of the laser oscillators 31a to 31d. Settings and control amounts of the galvanometer mirrors 33a to 33d are calculated. The calculation results are stored in the memory 52 as necessary. The main control unit 51 sends out the calculation results to the laser drivers 32a to 32d and the galvanometer mirror drive circuits 39a to 39d.

  As shown in FIG. 8, the galvanometer mirror drive circuits 39a to 39d are provided with latches 44a to 44d for holding data of the calculation results. Once the main control unit 51 writes the data, This value is held until the next data update.

  The data held in the latches 44a to 44d are converted into analog signals (voltages) by the D / A converters 45a to 45d, and input to the drivers 46a to 46d for driving the galvanometer mirrors 33a to 33d. The drivers 46a to 46d drive and control the galvanometer mirrors 33a to 33d according to the analog signals (voltages) input from the D / A converters 45a to 45d.

  In this example, since the amplified output signals of the sensor patterns SA to SG are selected and integrated by the selection circuit 41 and integrated and A / D converted, the sensor patterns SA to SG at a time are selected. Cannot be input to the main control unit 51.

  Therefore, when detecting the power of the beam light, the beam light passing position is moved onto the sensor pattern SA or SG, and an output signal from the corresponding sensor pattern is input to the main control unit 51. The selection circuit 41 needs to be switched.

  Further, in a state where it is not known where the light beam passes, the selection circuit 41 is sequentially switched, and output signals from all the sensor patterns SA to SG are input to the main control unit 51, and the light beam is transmitted. It is necessary to determine the passing position.

  However, once it can be recognized where the light beam passes, unless the galvanometer mirrors 33a to 34d are moved extremely, the position where the light beam passes can be almost predicted, and the output signals of all sensor patterns are always output. Is not required to be input to the main control unit 51. Detailed processing will be described later.

  Hereinafter, the relationship between the light beam passage position and the output of the light beam detector 38, the outputs of the differential amplifiers 63 to 66, and the output of the integrator 42 in the circuit operation of FIG. 16 will be described with reference to FIG.

  FIG. 17A shows a case where the light beam passes through the middle of the sensor patterns SB and SC, and FIG. 17B shows the sensor light beam more than in the case of FIG. The case where the pattern SB side is passed is shown. FIG. 17C shows a case where the light beam detection device 38 is attached to be inclined with respect to the light beam passage direction.

  Hereinafter, the output of the beam light detector 38, the output of the differential amplifier 63, and the output of the integrator 42 in each case will be described.

Circuit Operation in the Case of FIG. 17A First, the beam light crosses the sensor pattern S1, and a pulse signal is output from the sensor pattern S1. This pulse-like signal resets the integrator 42 and makes its output “0” as shown in the figure. Therefore, when the light beam crosses the sensor pattern S1, the previous detection result is reset and the new detection result is integrated.

  When the light beam passes through the middle of the sensor patterns SB and SC, the output magnitudes of the sensor patterns SB and SC are equal as shown in FIG. However, since the output of the sensor pattern is very small, some noise components may be superimposed as shown in FIG.

  Such a signal is input to the differential amplifier 63, and the difference is amplified. The outputs of the sensor patterns SB and SC are substantially equal. In this case, the output of the differential amplifier 63 is substantially “0” as shown in FIG. 17A, but some noise components may be superimposed. . The differential amplification result thus obtained is input to the integrator 42 through the selection circuit 41.

  Here, it is the offset of the differential amplifier 63 that requires attention. Here, the offset is a phenomenon in which the output is shifted to either plus or minus even when an equal value is inputted to the differential amplifier 63, for example. Such a phenomenon is present in any differential amplifier more or less. In the case of this example, this offset appears as a beam light passing position detection error, which hinders correct beam light passing position control. Therefore, it is necessary to remove this offset by some method (details will be described later). Hereinafter, this offset will be ignored and described.

  The integrator 42 integrates the output of the differential amplifier 63 and outputs the result to the next A / D converter 43. The output of the integrator 42 is noise as shown in FIG. The signal is the component removed. This is because the high frequency component noise superimposed on the differential amplification result is removed by integration. In this way, simultaneously with the passage of the beam light, the output difference between the sensor patterns SB and SC is amplified, further integrated, and input to the A / D converter 43.

  On the other hand, the output of the sensor pattern S2 is input to the A / D converter 43, and at the timing when the light beam has passed through the sensor patterns SB and SC, a pulse shape as shown in FIG. Is output from the sensor pattern S2 to the A / D converter 43. The A / D converter 43 starts A / D conversion of the output of the integrator 42 with this pulse signal as a trigger. Therefore, the A / D converter 43 can convert analog beam passage position information with a good S / N ratio from which noise components are removed into a digital signal in a timely manner.

Circuit Operation in the Case of FIG. 17B The basic operation is the same as in FIG. 17A, but the output of the sensor pattern SB is increased by the amount that the light beam passage position is closer to the sensor pattern SB side. The output of the sensor pattern SC is reduced. Therefore, the output of the differential amplifier 63 becomes positive by the difference.

  As in the case of FIG. 17A, the integrator 42 is reset at the timing when the light beam passes through the sensor pattern S1, and thereafter, such a differential amplification result is input to the integrator 42. Is done. The integrator 42 gradually increases its output to the plus side while the input (output of the differential amplifier 63) is on the plus side. When the input returns to “0”, the value is maintained. Therefore, the output of the integrator 42 shows the degree of deviation of the light beam passage position.

  As in the case of FIG. 17A, the integration result is A / D converted by the A / D converter 43 at the timing when the sensor pattern S2 of the light beam passes, so that the accurate beam passing position is time-resolved. Is converted into digital information.

Circuit Operation in the Case of FIG. 17 (c) The basic operation is the same as in FIGS. 17 (a) and 17 (b), except that the light beam passes through the light beam detector 38 at an angle. The outputs of the patterns SB and SC, the output of the differential amplifier 63, and the output of the integrator 42 are characteristic.

  As shown in FIG. 17 (c), after the light beam has passed through the sensor pattern S1, the sensor patterns SB and SC are incident obliquely from the sensor pattern SC side and pass through almost the center of the sensor patterns SB and SC. After that, the sensor pattern SB side is obliquely passed. When the light beam passes in this way, the output of the sensor pattern SB is small immediately after the light beam is incident and increases with the passage of the light beam, as shown in FIG. On the other hand, the output of the sensor pattern SC is large immediately after the light beam is incident, and gradually decreases as the light beam passes.

  As shown in FIG. 17C, the output of the differential amplifier 63 to which the outputs of the sensor patterns SB and SC are inputted is large on the minus side immediately after the incidence of the beam light, and thereafter the output is gradually reduced. Thus, when the light beam passes between the sensor patterns SB and SC, it becomes almost “0”. After that, it gradually increases to the plus side, and reaches the maximum value on the plus side immediately before the beam light finishes passing.

  The output of the integrator 42 to which the output of the differential amplifier 63 is input increases toward the minus side immediately after the incident light beam. The negative value increases until the output of the differential amplifier 63 becomes almost “0”. Thereafter, when the output of the differential amplifier 63 turns to the positive side, the negative value gradually decreases, and becomes almost “0” at the point where the beam finishes passing.

  This is because although the light beam crosses the light beam detector 38 obliquely, on the average, it passes through the middle of the sensor patterns SB and SC. Therefore, the A / D conversion operation of the A / D converter 43 is started when the light beam passes through the sensor pattern S2. In this case, the integrated value is “0”, and the beam passing position is The digital information shown is also processed as “0”, that is, the beam light passes through the middle of the sensor patterns SB and SC.

  The beam light passing position, the output of the sensor patterns S1, S2, SB, and SC, the output of the differential amplifier 63, the output of the integrator 42, and the operation of the A / D converter 43 have been described above. Since the operations of the sensor patterns SC, SD, SE, SF and the differential amplifiers 64, 65, 66 are basically the same as the operations of the sensor patterns SB, SC and the differential amplifier 63, the description of each operation is omitted. .

  Next, the relationship between the light beam passage position and the output of the A / D converter 43 will be described with reference to FIG.

  The vertical axis of the graph of FIG. 18 indicates the magnitude of the output of the A / D converter (12 bits) 43, and the horizontal axis indicates the passage position of the beam light. The beam light passing position on the horizontal axis indicates that the beam light passes the sensor pattern SG side as it goes to the left, and that the beam light passes the sensor pattern SA side as it goes to the right. .

  There is a possibility that the output of the differential amplifier (63, 64, 65, 66) is output in both positive and negative directions, and the output of the A / D converter 43 at that time is as follows. That is, when the output of the differential amplifier (63, 64, 65, 66) is on the plus side, the output (A / D conversion value) of the A / D converter 43 is 000H (as the output of the differential amplifier increases). The value of 7FFH (maximum value) is output from the minimum value.

  On the other hand, when the output of the differential amplifier (63, 64, 65, 66) is negative, the output (A / D conversion value) of the A / D converter 43 is from 800H (minimum value) to FFFH (maximum value). The value of is output. In this case, the one where the absolute value of the output of the differential amplifier is larger corresponds to the 800H (minimum value) side, and the one where the output of the differential amplifier is closer to “0” corresponds to the FFFH (maximum value) side.

  Here, the case where the outputs of the differential amplifiers 63 of the sensor patterns SB and SC are A / D converted by the A / D converter 43 will be specifically described.

  The output of the sensor pattern SB is connected to the plus terminal of the differential amplifier 63, and the output of the sensor pattern SC is connected to the minus terminal of the differential amplifier 63. Therefore, as shown in FIG. 18, the output of the differential amplifier 63 becomes the largest when the light beam passes near the center of the sensor pattern SB, and the A / D conversion value in the A / D converter 43 is 7FFH. It becomes. This is because the output of the sensor pattern SB is the largest in this vicinity.

  Further, even if the light beam is shifted from this position to the sensor pattern SA side or to the sensor pattern SC side, the A / D conversion value (the output of the differential amplifier 63) becomes small.

  Further, considering the case where the light beam passage position is shifted to the sensor pattern SA side, neither the sensor pattern SB nor SC can detect the passage of the light beam, and the A / D conversion value (the output of the differential amplifier 63) is almost equal. It becomes “0”.

  On the other hand, when the passage position of the beam light is shifted to the sensor pattern SC side, the A / D conversion value (output of the differential amplifier 63) is gradually decreased, and the beam light is reduced to the sensor patterns SB and SC. The value becomes “0” when passing just between. This is because the outputs of the sensor patterns SB and SC are equal. In this example, this point becomes the passage target point of the beam light a.

  When the light beam passing point is shifted to the sensor pattern SC side, the output of the differential amplifier 63 becomes a negative output, the A / D conversion value changes from 000H to FFFH, and then the A / D conversion value gradually increases. To decrease. Further, when the light beam passage position is near the center of the sensor pattern SC, the output of the differential amplifier 63 becomes a negative maximum, and the A / D conversion value at this time is 800H.

  When detecting the power of the beam light on the photosensitive drum 15, the output of the amplifier 61 or 62 in the area A or G in FIG. 18 is used. In the graph of FIG. 18, the output of the A / D converter 43 is 7FFH when the light beam passes on the sensor pattern SA or SG, but when detecting the power of the light beam, As described above, the optical power can be detected by lowering the setting of the amplification factor for the amplifier 61 or 62. That is, the output value of the A / D converter 43 changes depending on the intensity of the light beam.

  Further, when the light beam passage position is shifted to the sensor pattern SD side, the negative value of the output of the differential amplifier 63 decreases this time, and the A / D conversion value increases from 800H. It changes from FFFH to 000H. This is because the passage position of the beam light is too shifted to the sensor pattern SD (SE) side, and neither of the sensor patterns SB and SC can detect the passage of the beam light, and both outputs become “0”. This is because the difference disappears.

  Next, control characteristics of the galvanometer mirror 33 will be described.

  19 and 20 show the relationship between the data given to the galvanometer mirror drive circuits 39a to 39d and the beam light passage position on the beam light detector 38 (that is, on the photosensitive drum 15). As shown in FIG. 16, the inputs of the D / A converters 45a to 45d of the galvano mirror drive circuits 39a to 39d are 16 bits.

  FIG. 19 shows how the beam light passing position changes with respect to the upper 8 bits of the 16-bit data. As shown in the figure, the passing position of the beam light moves 2000 μm (2 mm) with respect to the data 00H to FFH. In addition, for the input near 00H and near FFH, the response range of the galvanometer mirror is exceeded, and the beam light passage position does not change.

  However, when the input is in the range of approximately 18H to E8H, the light beam passage position changes substantially linearly with respect to the input, and the ratio corresponds to a distance of approximately 10 μm per LSB.

  FIG. 20 shows how the beam light passing position changes with respect to the lower 8 bits input of the D / A converters 45a to 45d of the galvanometer mirror drive circuits 39a to 39d. However, FIG. 20 shows the change in the passage position of the light beam with respect to the input of the lower 8 bits when the above-described range value in which the passage position of the light beam linearly changes is input as the upper 8 bits. Represents. As is apparent from the figure, for the lower 8 bits, the beam light passage position changes from 00H to FFH, and changes by 0.04 μm per 1LSB.

  In this way, the main control unit 51 gives 16-bit data to the galvanometer mirror drive circuits 39a to 39d, so that the beam light passing position on the beam light detector 38, that is, on the photosensitive drum 15. Can be moved within a range of about 2000 μm (2 mm) with a resolution of about 0.04 μm.

  Next, a schematic operation when the printer unit 2 is turned on will be described with reference to a flowchart shown in FIG. The operation of the scanner unit 1 is omitted.

  When the power of the copying machine is turned on, the main controller 51 rotates the fixing roller in the fixing device 26 and starts heating control of the fixing device 26 (S311 and S312). Next, a light beam power control routine is executed to control the power of each light beam on the photosensitive drum 15 to be the same (S313).

  When the power of the light beams on the photosensitive drum 15 is controlled to be the same, an offset correction routine is executed to detect the offset value of the beam light detector output processing circuit 40 and perform the correction process. (S314). Next, a beam light passing position control routine is executed (S315).

  Next, a main scanning direction beam light position control routine is executed (S316). Next, process-related initialization, such as rotating the photosensitive drum 15 and making conditions such as the surface of the photosensitive drum 15 constant, is executed (S317).

  Thus, after executing a series of initializations, the fixing roller continues to rotate until the temperature of the fixing device 26 rises to a predetermined temperature, and enters a standby state (S318). When the temperature of the fixing device 26 rises to a predetermined temperature, the rotation of the fixing roller is stopped (S319), and a copy command wait state is entered (S320).

  When a copy command is not received from the control panel 53 while waiting for a copy command (S320), for example, when 30 minutes have passed after execution of the beam light passing position control routine (S321), the beam light is automatically generated. A power control routine is executed (S322), an offset correction routine is automatically executed (S323), and then a beam light passing position control routine and a main scanning direction beam light position control routine are executed again (S324, S325). ). When this is completed, the process returns to step S3220, and again enters the copy command wait state.

  When a copy command is received from the control panel 53 while waiting for a copy command (S320), it is checked whether there is a resolution change command (S326). If there is a resolution change command as a result of this check, the number of revolutions of the polygon motor 36 is switched to a value suitable for the commanded resolution (S327).

  Next, the crystal oscillators 114a to 114d that are suitable for the resolution are selected (S328). Further, a light beam power control routine is executed (S329), then an offset correction routine is executed (S330), a light beam passage position control routine is executed (S331), and then the light beam position control in the main scanning direction. A routine is executed (S332), and a copying operation is executed (S333).

  On the other hand, if there is no resolution change command as a result of the check in step S326, there is no change in the rotation speed of the polygon motor 36, the crystal oscillator, etc., so the beam light power control routine is executed (S329), and the offset correction routine is executed. Execute (S330), execute a beam light passing position control routine (S331), execute a main scanning direction beam light position control routine (S332), and execute a copying operation (S333).

  When the copying operation is completed, the process returns to step S320 and the operation is repeated.

  In this manner, the light beam power control routine, the light beam passage position control routine, and the main scanning direction beam light position control routine are executed between copying operations, and are always in an optimum state for a large amount of continuous copying. To form an image.

  Next, the schematic operation of the light beam passage position control routine in steps S315, S324, and S331 of FIG. 21 will be described using the flowchart shown in FIG.

  First, the main controller 51 turns on the polygon motor 36 and rotates the polygon mirror 35 at a predetermined rotational speed (S20). Next, the main control unit 51 reads the latest drive values of the galvanometer mirrors 33a to 33d from the memory 52, and drives the galvanometer mirrors 33a to 33d based on the values (S21).

  Next, the main control unit 51 controls the passing position of the beam light a (S22). The control content here is to detect the passing position of the beam light a, check whether the passing position is within the specified value, and if not, change the angle of the galvano mirror 33a. If it is within the specified value, the flag is set to indicate that the passing position of the beam light a is within the specified value.

  Subsequently, the main control unit 51 also detects the passing positions of the light beams b, c, and d for the light beams b, c, and d as in the case of the light beam a. It is checked whether the position is within the specified value. If the position is not within the specified value, the angle of each of the galvanometer mirrors 33b to 33d is changed. A flag indicating that the passing position is within the specified value is set (S23, S24, S25).

  In this way, after performing the passing position control of each of the light beams a, b, c, d, the main control unit 51 checks each flag and determines whether or not to end the light beam passing position control. Determine (S26). That is, if all the flags are set, the light beam passing position control is terminated, and if any one of the flags is not set, the process returns to step S22 to control the passing position of each light beam.

  Here, the behavior of the galvanometer mirrors 33a to 33d in such a control flow will be briefly described.

  As described above, the galvanometer mirrors 33a to 33d change the angle according to the control value from the main control unit 51 and change the passing position of the scanned light beam. It is not always possible to respond immediately to an instruction. That is, control data is output from the main control unit 51, the data is latched by the latches 44a to 44d, D / A converted by the D / A converters 45a to 45d, and a drive signal proportional to the magnitude thereof. Is output on the order of “ns” or “μs”, whereas, for example, the response time of the galvanometer mirrors 33a to 33d used in this example is 4 to There is a problem that the order is 5 ms.

  The response time here refers to the time when the angle change of the galvano mirrors 33a to 33d starts with respect to a new drive signal, moves (vibrates) for a certain period of time, and then the movement (vibration) stops and settles to a new angle. Of time. Therefore, the main control unit 51 sends the new control data to the galvanometer mirrors 33a to 33d and then checks the control result. It is necessary to confirm.

  As is apparent from FIG. 22, in this example, the effect of controlling a certain galvano mirror is confirmed after performing another beam light position detection operation or galvano mirror control operation. The effect is confirmed after the time required for the response of the galvanometer mirror has elapsed.

  For example, in steps S21, S22, S23, and S24, the time required to acquire the output of at least one amplifier or differential amplifier by the number of faces of the polygon mirror 35 (for example, eight faces) is required for one scan. When the time is 330 μs, it becomes 2.64 ms.

  Therefore, after controlling a certain galvanometer mirror, after detecting the passing position of the other three light beams, to confirm the effect, there is a time interval of at least 7.92 ms, and the movement (vibration) of the galvanometer mirror is Thus, it is possible to confirm the beam light passing position in a state where it has already been accommodated.

  The reason why the output of the amplifier or differential amplifier is obtained by the number of faces of the polygon mirror 35 is to remove the surface tilt component of the polygon mirror 35.

  23 and 24 are flowcharts for explaining in detail the operation of the beam light a passing position control in step S22 of FIG. As described above, the relationship between the passage position of the light beam and the output of the A / D converter 43 is as shown in FIG. 18, and will be described with reference to FIG.

  First, the main control unit 51 causes the laser oscillator 31a to emit light forcibly (S31). As a result, the beam light a periodically scans the beam light detector 38 as the polygon mirror 35 rotates.

  Next, in accordance with the interrupt signal INT output from the A / D converter 43, the main control unit 51 reads values obtained by A / D converting the outputs of the amplifiers and the differential amplifier. Usually, the scanning position of the beam light is often slightly different for each surface due to the surface tilt component of the polygon mirror 35, and in order to remove the influence, the number of times equal to the number of surfaces of the polygon mirror 35, or It is desirable to read a value that has been A / D converted continuously in an integral number of times. In that case, the main control unit 51 averages the output values of the A / D converters 43 corresponding to the respective amplifiers and differential amplifiers, and uses the result as the outputs of the respective amplifiers and differential amplifiers (S32).

  Therefore, for the amplifiers 61 and 62 (amplifiers A and G) and the differential amplifiers 63 to 66 (amplifiers BC, CD, DE, and EF), the number of faces of the polygon mirror 35 (eight), respectively. If the value of the A / D converter 43 is read the same number of times, it is necessary to scan the light beam 48 times.

  First, the main control unit 51 compares the output (A / D conversion value) of the amplifier 61 (A) obtained in this way with the determination reference value 100H stored in advance in the memory 52 to thereby obtain the amplifier 61. Is determined to be greater than the determination reference value 100H (S33).

  If the result of this determination is that the output of the amplifier 61 is greater than 100H, it indicates that the passing position of the beam light a is on the sensor pattern SA or in the vicinity of the sensor pattern SA. Yes. That is, the light beam a passes through the area A in FIG. Since the target passage position of the beam light a is intermediate between the sensor patterns SB and SC, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SG side (S34).

  At this time, the control amount (the amount of movement of the light beam) is about 120 μm. The control amount is set to 120 μm, as described in the sensor patterns of FIGS. 3 and 4, the sensor patterns SA and SG have large patterns on both sides from the control target point area. This is because it is necessary to change the passage position of the beam light relatively large in order to quickly bring the passage position of the beam light closer to the target point.

  However, even when the output of the amplifier 61 is larger than 100H, if the light beam a passes through a range close to the sensor pattern SB, the beam light passing position may be changed excessively. There is also. However, considering the total efficiency, this amount of movement is necessary.

  If it is determined in step S33 that the output of the amplifier 61 is not greater than 100H, the output (A / D conversion value) of the amplifier 62 (G) is set to the determination reference value 100H stored in the memory 52 in advance. By comparing, it is determined whether the output of the amplifier 62 is larger than the determination reference value 100H (S35).

  As a result of this determination, if the output of the amplifier 62 is greater than 100H, it indicates that the passing position of the beam light a is on the sensor pattern SG or in the vicinity of the sensor pattern SG. Yes. That is, the beam light a passes through the area G in FIG.

  Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S36). ). Note that the control amount at this time requires a control amount (movement amount) of about 120 μm, as in step S34.

  If it is determined in step S35 that the output of the amplifier 62 is not greater than 100H, the output (A / D conversion value) of the differential amplifier 66 (EF) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 66 is equal to or higher than the determination reference value 800H (S37).

  As a result of this determination, when the output of the differential amplifier 66 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SF. That is, the light beam a passes through the area F in FIG.

  Accordingly, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S38). ). Note that the control amount at this time needs a control amount (movement amount) of about 120 μm in consideration of the distance between the target point and the area F.

  If it is determined in step S37 that the output of the differential amplifier 66 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 65 (DE) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 65 is equal to or higher than the determination reference value 800H (S39).

  As a result of this determination, if the output of the differential amplifier 65 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SE. That is, the light beam a passes through the area E in FIG.

  Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S40). ). Note that the control amount at this time needs a control amount (movement amount) of about 80 μm in consideration of the distance between the target point and the area E.

  If it is determined in step S39 that the output of the differential amplifier 65 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 64 (CD) is stored in the memory 52 in advance. By comparing with the reference value 800H, it is determined whether the output of the differential amplifier 64 is equal to or higher than the determination reference value 800H (S41).

  As a result of this determination, when the output of the differential amplifier 64 is 800H or more, it indicates that the passing position of the beam light a is in the vicinity of the sensor pattern SD. That is, the beam light a passes through the area D in FIG.

  Accordingly, in such a case, the galvano mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle of the sensor patterns SB and SC, which are target points for the beam light a (S42). . The control amount at this time needs a control amount (movement amount) of about 40 μm in consideration of the distance between the target point and the area D.

  If it is determined in step S41 that the output of the differential amplifier 64 is not 800H or higher, the output (A / D conversion value) of the differential amplifier 63 (BC) is stored in the memory 52 in advance. By comparing with the reference values 400H and 7FFH, it is determined whether the output of the differential amplifier 63 is greater than the determination reference value 400H and less than or equal to 7FFH (S43).

  As a result of this determination, if the output of the differential amplifier 63 is greater than 400H and less than or equal to 7FFH, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are passage target points. Although it is present, it indicates that it is slightly closer to the sensor pattern SB. That is, the light beam a passes through the area BA of the area B in FIG.

  Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SG side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S44). ). The control amount at this time needs a control amount (movement amount) of about 10 μm in consideration of the distance between the target point and the area D.

  If it is determined in step S43 that the output of the differential amplifier 63 is greater than 400H and not less than 7FFH, the output of the differential amplifier 63 is stored as determination reference values 60H and 400H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is greater than the determination reference value 60H and equal to or less than 400H (S45).

  If the result of this determination is that the output of the differential amplifier 63 is greater than 60H and less than or equal to 400H, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC which are passage target points. Although it is present, it indicates that it is slightly closer to the sensor pattern SB. That is, the light beam a passes through the area BC of the area B in FIG.

  Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SG side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S46). ). The control amount at this time needs a control amount (movement amount) of about 0.5 μm in consideration of the distance between the target point and the area D.

  If it is determined in step S45 that the output of the differential amplifier 63 is greater than 60H and not less than 400H, the output of the differential amplifier 63 is determined as the determination reference values 800H and A00H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is equal to or higher than the determination reference value 800H and smaller than A00H (S47).

  As a result of this determination, when the output of the differential amplifier 63 is 800H or more and smaller than A00H, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are passage target points. Although it exists, it represents that it is slightly close to the sensor pattern SC. That is, the light beam a passes through the area CD of the area C in FIG.

  Therefore, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes through the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the passage target points of the beam light a (S48). ). The control amount at this time requires a control amount (movement amount) of about 10 μm in consideration of the distance between the target point and the area CD.

  If it is determined in step S47 that the output of the differential amplifier 63 is equal to or higher than 800H and not smaller than A00H, the output of the differential amplifier 63 is determined as determination reference values A00H and FA0H stored in the memory 52 in advance. By comparing, it is determined whether the output of the differential amplifier 63 is equal to or greater than the determination reference value A00H and smaller than FA0H (S49).

  If the output of the differential amplifier 63 is equal to or greater than A00H and smaller than FA0H as a result of this determination, the passage position of the beam light a is in the vicinity of the middle between the sensor patterns SB and SC that are the passage target points. Although it exists, it represents that it is slightly close to the sensor pattern SC. That is, the light beam a passes through the area CB of the area C in FIG.

  Accordingly, in such a case, the galvanometer mirror 33a is controlled so that the beam light a passes the sensor pattern SA side in order to approach the middle between the sensor patterns SB and SC, which are the target passage points of the beam light a (S50). ). Note that the control amount at this time needs a control amount (movement amount) of about 0.5 μm in consideration of the distance between the target point and the area CB.

  If it is determined in step S49 that the output of the differential amplifier 63 is not less than A00H and not less than FA0H, the passing position of the beam light a is within a predetermined range (a range of ± 1 μm of the target point). Therefore, the control end flag A of the galvanometer mirror 33a is set (S51).

  In this way, when the light beam a does not pass within the range of ± 1 μm from the ideal passing point (S34, S36, S38, S40, S42, S44, S46, S48, S50), the galvano The mirror 33a is controlled by a predetermined amount, and the value at that time is written in the memory 52 (S52).

  As described above, the main control unit 51 sets the control end flag A of the galvanometer mirror 33a when the light beam a passes through the range of ± 1 μm from the ideal passing point, and passes outside this range. If it is, the galvano mirror control amount is adjusted according to the passing position (area), and the value is written in the memory 52.

  Finally, the main control unit 51 cancels the forced light emission of the laser oscillator 31a, and finishes the series of passage position control of the light beam a (S53).

  As already described with reference to FIG. 22, when the control end flag A of the galvano mirror 33a is not set, the beam light a passing position control routine is executed again. That is, this routine is repeatedly executed until the beam light a passes within the range of ± 1 μm with respect to the ideal passing point.

  The above explanation is the control for the beam light a, but the control for the beam lights b, c, d is basically the same as the case of the beam light a, and the respective laser oscillators 31b to 31d. Are forcibly emitted, and the outputs of the amplifiers 61 and 62 and the differential amplifiers 63 to 66 are determined. If the outputs pass within the range of ± 1 μm from the ideal control point, the respective galvanometer mirrors The control end flags B to D of 33b to 33d are set. In addition, when it does not pass through this range, after determining which area each of the light beams b to d passes, the control corresponding to the passing area is performed on the galvanometer mirrors 33b to 33d. The control value is written in the memory 52.

  Here, the influence given by the power variation of each light beam in the light beam passage position control described above will be described.

  FIG. 25 shows the beam light passage position when the light beam power changes on the photosensitive drum 15 (beam light detection device 38), the output of the differential amplifier (the value obtained by integrating and A / D conversion), and FIG. This shows the relationship.

  In the graph of FIG. 25, the curve B shows the same output characteristics of the amplifiers 63, 64, 65, 66 shown in FIG. 18, and the beam light moves away from the target passing point, and from 000H to 7FFH, Alternatively, it gradually changes from FFFH to 800H, and further changes gradually from 7FFH to 000H or from 800H to FFFH when moving away from the target point. This characteristic is convenient in terms of control because the correspondence between the light beam passage position and the output of the differential amplifier can be easily obtained.

  On the other hand, for example, in the case of the characteristic of curve C when the power of the light beam is large, the output of the differential amplifier changes greatly only when the light beam passage position slightly deviates from the target point. Therefore, if the beam passage position deviates more than a certain value, the output of the differential amplifier is fixed to 7FFH or 800H. Further, the output value of the differential amplifier does not change unless the beam light passing position changes significantly.

  On the contrary, when the power of the light beam is small, the characteristic of the curve A is obtained, the change in the output of the differential amplifier is small with respect to the change in the light beam passage position, and the S / N ratio is poor.

  As described above, when the power of the beam light passing on the photosensitive drum 15 changes, the relationship between the beam light passing position and the output of the differential amplifier changes.

  Therefore, when the light beam passage position is controlled in such a state that the power of each light beam varies, the light beam passage position is controlled within a certain standard when the light beam power is small. Even if it is intended, if the accuracy is insufficient and the power of the light beam is large, the change in the output of the differential amplifier relative to the change in the light beam passing position may be too large or not change. The control operation may become unstable.

  Therefore, when performing the light beam passing position control, it is necessary that the power of each light beam is at least equal. Further, ideally, the power of the light beam having the characteristics as shown by the curve B in FIG. 25 is desirable, but for the graph shown in FIG. 25, for example, the amplification factor of the differential amplifier is set to an appropriate value. Thus, the characteristic of the curve A can be changed to the characteristic of the curve B, or the characteristic of the curve C can be changed to the characteristic of the curve B.

  Next, the beam light detection device 38 corresponding to a plurality of (for example, two types) resolutions will be described.

  FIG. 26 schematically shows the relationship between the configuration of the beam light detection device 38 corresponding to two kinds of resolutions and the scanning direction of the beam light. The difference from the beam light detection device 38 in FIG. Sensor patterns SB to SF for detecting the passage positions of the light beams are provided corresponding to two types of resolutions, respectively, and a sensor pattern SH (details will be described later) for detecting the power of the beam light is provided. The other points are the same as those of the beam light detection device 38 of FIG.

  That is, the sensor patterns SB1 to SF1 are beam light passage position detection sensor patterns for the first resolution (for example, 600 dpi), and as shown in FIG. 27, they have the same shape (the same area), and approximately 42 By controlling the passing position so that the beam lights a to d pass through the middle (gap G) between the adjacent sensor patterns, which are arranged at intervals of .3 μm (25.4 mm ÷ 600), 42.3 μm. Are scanned at intervals of.

That is,
Beam light a: Control is performed between sensor patterns SB1 and SC1 Beam light b: Control is performed between sensor patterns SC1 and SD1 Beam light c: Control is performed between sensor patterns SD1 and SE1 Beam Light d: Control is performed halfway between the sensor patterns SE1 and SF1. Since the light beam passage position control has already been described, the description thereof is omitted here.

  Further, the sensor patterns SB2 to SF2 are beam light passing position detection sensor patterns for the second resolution (for example, 400 dpi), and as shown in FIG. 27, they have the same shape (the same area), and approximately 63 By controlling the passing position so that the beam lights a to d pass through the middle (gap G) of the adjacent sensor patterns, which are arranged at intervals of .5 μm (25.4 mm ÷ 400), 63.5 μm Scanning is performed at intervals.

That is,
Beam light a: Control is performed between the sensor patterns SB2 and SC2. Beam light b: Control is performed between the sensor patterns SC2 and SD2. Beam light c: Control is performed between the sensor patterns SD2 and SE2. Light d: Control is performed between the sensor patterns SE2 and SF2. Note that the basic operation of the light beam passage position control is the same as that in the case of 600 dpi, and thus the description thereof is omitted here.

  FIG. 28 shows the relationship between the sensor patterns SB1 to SF1 and SB2 to SF2 and the scanning positions of the beam lights a to d when the beam light detection device 38 of this example is mounted inclined with respect to the beam light scanning direction. FIG. 28A shows the case of the first resolution (600 dpi), and FIG. 28B shows the case of the second resolution (400 dpi). In the drawing, the scanning direction of the light beams a to d is expressed with respect to the light beam detector 38.

For example, assuming that the relative inclination between the sensor pattern and the beam light is 5 degrees, the interval between the beam light a and the beam light d is as shown in Table 1 below in the case of the first resolution, and is about The 0.5 μm interval is only narrowed. In the case of the second resolution, as shown in Table 2 below, the interval of about 0.7 μm is only narrowed.

  FIG. 29 is a diagram for explaining beam light passage position control when the beam light detector 38 of FIG. 26 is used. The difference from FIG. 8 is the configuration of the beam light detector output processing circuit 40. In FIG. 4, a differential amplifier is provided corresponding to the sensor patterns SB1 to SF1 and SB2 to SF2, and a resolution switching signal is added to the sensor selection signal. Since this is the same as FIG.

  That is, the differential amplifier 631 amplifies the difference between the output signals of the sensor patterns SB1 and SC1, the differential amplifier 641 amplifies the difference between the output signals of the sensor patterns SC1 and SD1, and the differential amplifier 651 The difference between the output signals of the sensor patterns SD1 and SE1 is amplified, and the differential amplifier 661 amplifies the difference between the output signals of the sensor patterns SE1 and SF1. The differential amplifier 632 amplifies the difference between the output signals of the sensor patterns SB2 and SC2, the differential amplifier 642 amplifies the difference between the output signals of the sensor patterns SC2 and SD2, and the differential amplifier 652 The difference between the output signals of the sensor patterns SD2 and SE2 is amplified, and the differential amplifier 662 amplifies the difference between the output signals of the sensor patterns SE2 and SF2.

  The output signals of the amplifiers 631 to 661 and 632 to 662 are input to the selection circuit (analog switch) 41, respectively. The selection circuit 41 selects a signal to be input to the integrator 42 based on a sensor selection signal from the main control unit (CPU) 51.

  That is, when the light beam passage position control is performed at the first resolution (600 dpi), the selection circuit 41 selects the following differential amplifier and performs the corresponding beam light passage position control.

Differential amplifier 631: Beam light a
Differential amplifier 641: Beam light b
Differential amplifier 651: beam light c
Differential amplifier 661: beam light d
Similarly, when the light beam passage position control is performed at the second resolution (400 dpi), the following differential amplifier is selected by the selection circuit 41, and the corresponding light beam passage position control is performed.

Differential amplifier 632: beam light a
Differential amplifier 642: beam light b
Differential amplifier 652: beam light c
Differential amplifier 662: beam light d
Next, a first example of the light beam power control routine in steps S313, S322, and S329 of FIG. 21 will be described using the flowcharts shown in FIGS.

  First, the main control unit 51 sets the amplification factor of the amplifier 61 (A) to a predetermined value (S231). The predetermined value here means that the output of the amplifier 61 (A) is integrated by the integrator 42 and A / D converted by the A / D converter 43 when each light beam passes on the sensor pattern SA. In this case, the gain value is a value that does not saturate and changes in proportion to the power of the light beam.

  Next, the main control unit 51 turns on the polygon motor 36 and rotates the polygon mirror 35 at a predetermined rotational speed (S232). Next, the main controller 51 forcibly causes the laser oscillator 31a to emit light at a predetermined value stored in the memory 52 (S233). By this operation, the beam light a starts to be scanned by the polygon mirror 35. Here, the predetermined value is a value suitable for image formation at that time.

  In general, in an image forming apparatus using an electrophotographic process, it is necessary to change the power of beam light depending on the environment in which the image forming apparatus is placed and the usage situation (change over time). The memory 52 stores power information of appropriate beam light under such conditions.

  Next, the main control unit 51 controls the galvanometer mirror 33a so that the beam light a passes on the sensor pattern SA (S234). Here, it is necessary that the light beam a sufficiently passes through the center of the sensor pattern SA so as not to protrude from the sensor pattern SA. If the sensor pattern SA protrudes from the sensor pattern SA, the detected power value becomes small.

  However, the sensor pattern SA (or SG) used for power control of the light beam has a sufficient size (a size close to 900 μm in the sub-scanning direction) as described above (in FIG. 3). Usually, such a problem cannot occur.

  When the light beam a passes through the sensor pattern SA in this way, a value proportional to the power of the light beam a is input from the A / D converter 43 to the main controller 51. become. The main control unit 51 stores this value (ideally, an average value of integral multiples of the number of faces of the polygon mirror 35) in the memory 52 as the optical power Pa of the beam light a on the photosensitive drum 15 ( In step S235, the laser oscillator 31a is turned off (S236).

  Next, the main control unit 51 forcibly causes the laser oscillator 31b to emit light (S237), and controls the galvano mirror 33b in the same manner as in the case of the beam light a, thereby controlling the beam pattern b on the sensor pattern SA. Is passed (S238).

  As a result, a value proportional to the light power of the light beam b on the photosensitive drum 15 is input from the A / D converter 43 to the main control unit 51, and this value is set as the light power Pb first. The light beam a stored in the memory 52 is compared with the optical power Pa on the photosensitive drum 15 (S239). In the case of this light beam b, ideally, it is desirable that the output value of the A / D converter 43 is taken as an integral multiple of the number of faces of the polygon mirror 35, and the averaged value is Pb. .

  As a result of comparing the light powers Pa and Pb of the light beam a and the light beam b on the photosensitive drum 15 in this way, the difference is equal to or less than a certain value (ΔP) (ideally “0”). If so, there is no problem in image quality. However, if there is a difference greater than that, it becomes a problem in image quality, and correction is necessary.

  For example, as a result of comparing the optical powers Pb and Pa, when Pb is larger than Pa and the difference is larger than ΔP (S240, S241), the beam power is reduced by lowering the light emission power setting value to the laser driver 32b. It is possible to reduce the optical power of the light b on the photosensitive drum 15 (S242).

  Conversely, as a result of comparing the optical powers Pb and Pa, if Pa is larger than Pb and the difference is larger than ΔP (S240, S241), by increasing the emission power setting value to the laser driver 32b, It is possible to increase the optical power of the beam b on the photosensitive drum 15 (S243).

  When the light power of the light beam b on the photosensitive drum 15 is corrected in this way, the light emission power setting value at this time is stored in the memory 52 as the value of the laser oscillator 31b (S244), and the process returns to step S239. Returning again, the optical power of the light beam b on the photosensitive drum 15 is detected, compared with Pa, and correction is repeated until the difference becomes ΔP or less.

  In this way, the difference between the power of the beam light a and the power of the beam light b can be made equal to or less than a predetermined value (ΔP).

  Thereafter, the same operation is performed for the beam light c and the beam light d in steps S245 to S264, so that the optical power difference between the beam light a, the beam light b, the beam light c, and the beam light d on the photosensitive drum 15 is determined. Can be set to a predetermined value (ΔP) or less.

  In the above example, the light beam a is used as a reference, but it is also possible to control the light beam b, the light beam c, or the light beam d as a reference. Further, the predetermined value (ΔP) here is desirably 1% or less of the reference (value of Pa).

  In the above description, the method of moving the passage position of each light beam onto the sensor pattern SA (or SG) has not been described in particular. However, as described with reference to FIGS. The approximate characteristics of the mirror are grasped, and as described above, the sensor pattern SA (or SG) has a size of about 900 μm in the sub-scanning direction, and has a light beam passage position near the center. It is easy to come.

  However, as a precaution, confirm that the output value from the sensor pattern does not change from the value corresponding to the power of the beam light even if the passage position of 20 to 30 μm is changed after the passage position of the beam light is determined. Is possible.

  Next, a second example of the light beam power control routine in steps S313, S322, and S329 in FIG. 21 will be described with reference to the flowcharts shown in FIGS.

  The difference of the second example of the light beam power control routine from the first example described above is the difference in the method of taking a reference when controlling the power of the light beam, and the other points are the same as in the first example. . In the first example, the light beam power control reference is the beam light a. Therefore, as a result, the relative optical powers between the light beams are made to coincide. On the other hand, in the second example, power control of each light beam is performed based on a predetermined reference value Pref. Therefore, if the sensitivity correction of the sensor pattern SA (or SG) is performed in advance, the power of each light beam can be controlled based on an absolute reference.

  For example, when a beam light having an optical power equivalent to 100 μW at a predetermined scanning speed passes over the sensor pattern SA, the value output from the amplifier 61 (A) is 100H and the beam light having an optical power equivalent to 200 μW. On the other hand, the sensor pattern SA is used as a kind of measuring device if it has been adjusted (calibrated) in advance so as to produce a value such as 300H for a beam light having an optical power equivalent to 200H and 300 μW. be able to. With such a configuration, it is possible to control the light beam power on the image plane without variations between the airframes.

  Next, the main scanning direction beam light position control routine in steps S316, S325, and S332 of FIG. 21 will be described with reference to the flowchart shown in FIG.

  First, the main control unit 51 obtains light beam position information in the main scanning direction of the light beam a (S341). Here, the light beam position information in the main scanning direction is an image transfer clock generation unit in which the pattern S2 of the light beam detection device 38 is just the edge of the exposure area (printing area) as described above. (Print area setting section) The setting values for 119a to 119d and the selection information for the delay clock selector are obtained. A method for acquiring this information will be described later in detail.

  Similarly, the beam light position information in the main scanning direction is acquired for the beam light b, the beam light c, and the beam light d (S342 to S344).

  After obtaining the main scanning direction beam light position information of each of the light beams a to d in this way, the main control unit 51 sets a print area necessary for actual image formation (copying and printing) ( S345). The setting of the print area necessary for actual image formation (copying and printing) includes the beam light position information in the main scanning direction of each of the light beams a to d, the paper size used for image formation (copying and printing), and the binding margin setting. Is set according to

For example, it is assumed that information shown in Table 3 below is obtained as beam light position information in the main scanning direction of the light beams a to d.

  Assuming that the paper size used for actual image formation is, for example, the A4 horizontal direction and there is no setting for the binding margin or the like, in the case of 600 dpi resolution, the print area is 7015 (≈297 × 600 ÷ 25.4) pixels.

If the distance between the sensor pattern S2 of the light beam detector 38 and the left end of the actual print area is 100 pixels, the print area settings for each light beam are as shown in Table 4 below. Should be set.

  After setting in this way, the delay clock for each of the light beams a to d is D5 for the light beam a, D8 for the light beam b, D2 for the light beam c, and the light beam d. In contrast, if D7 is selected, the print areas of the light beams a to d coincide with each other with a precision of 1/10 pixel even on the paper used for image formation.

  FIG. 35, FIG. 36, and FIG. 37 are flowcharts for explaining a routine for obtaining main-scanning-direction light beam position information of the light beam a in step S341 of FIG. Here, the beam light a will be described, but the same applies to the beam lights b to d.

  First, the main control unit 51 prepares, for example, printing start “7400”, printing in image transfer clock generation units (printing area setting units) 119b to 119d for other light beams as preparation for obtaining information on the light beam a. The end “7401” is set (S351). This step S351 is a step for moving the print (exposure) area other than the beam light a away from the beam light detector 38 and moving it to a place where the photosensitive drum 15 is not exposed. This step S351 is a step necessary to avoid interference between the beam lights a to d.

  That is, in the case of this step S351, by setting the printing (exposure) areas of the beam lights b to d to “7400 to 7401”, the beam lights b to d expose the sensor pattern S2 of the beam light detector 38. There is no. Therefore, accurate information regarding only the beam light a can be acquired.

  Next, as the initial setting, the main control unit 51 sets the delay clock selector 118a to use the delay clock D1 for image formation (S352). Next, the main control unit 51 sets “1” as the print start position and “5” as the print end position in the image transfer clock generation unit (print area setting unit) 119a (S353).

  Next, the main control unit 51 sets the solid black test data in the image data I / F 56, causes the laser oscillator 31a to emit light based on the solid black test data, and cancels the reset signal for the first counter 111 (S354). Thereby, the first counter 111 starts operation. As described above, by this operation, the print areas 1 to 5 (areas for five dots) of the beam light a are exposed on the basis of the sensor pattern S1 of the beam light detector 38.

  Next, the main control unit 51 takes in the data held in the latch circuit 113 by an interrupt signal (carry) from the first counter 111 (S355), and determines whether or not the value is “8”. (Check 1, S356).

  If the acquired data is not “8” as a result of this determination, the sensor pattern S2 of the light beam detection device 38 is not exposed, so that the image transfer clock generation unit (print area setting unit) 119a After “1” is added to the set value (print start and end) and the print area (exposure area) is shifted by one pixel, the reset of the first counter 111 is canceled (S357), and the first counter again. Wait for an interrupt signal from 111.

  On the other hand, if the acquired data is “8” as a result of the determination in step S356, this indicates that the sensor pattern S2 of the beam light detector 38 is exposed. After adding “1” to the set value (printing start and end) of the generation unit (printing area setting unit) 119a and shifting the printing area (exposure area) by one pixel, the reset of the first counter 111 is released. (S358).

  Next, the main control unit 51 takes in data held in the latch circuit 113 by an interrupt signal (carry) from the first counter 111 (S359), and determines whether or not the value is “8”. (Check 2, S360).

  As a result of this determination, if the fetched data is not “8”, “1” is set as the set value (printing start and end) of the image transfer clock generation unit (printing area setting unit) 119a as in the previous process. In addition, the print area (exposure area) is shifted by one pixel, the reset of the first counter 111 is released (S357), and the first check (check 1) is performed again.

  On the other hand, if the acquired data is “8” as a result of the determination in step S360, “2” is subtracted from the set value (print start and end) of the image transfer clock generation unit (print area setting unit) 119a, The image transfer clock generation unit (print area setting unit) 119a is set (S361). The value at this time is stored in the memory 52 as main-scanning direction light beam position information in units of one pixel with respect to the light beam a (S362).

  With the above operation, the main control unit 51 shifts the printing area (exposure area) for 5 pixels by one pixel, and when the number of pixels is shifted, the printing area (exposure area) becomes the beam light detector 38. Whether or not the sensor pattern S2 is reached can be recognized, and the value immediately before that can be stored in the memory 52.

  In this example, the print area (exposure area) is further shifted by one pixel even though the print area (exposure area) has reached the sensor pattern S2 of the light beam detector 38 (check 1 is passed). The reason for confirming that the sensor pattern S2 is exposed (execution of check 2) is that the sensor pattern S2 of the beam light detector 38 has responded to unnecessary stray light that may occur in the optical unit. This is because it is necessary to make it possible to recognize this and perform correct control.

  Usually, the light energy of the stray light is very small with respect to the original main beam light, and the sensor pattern S2 of the beam light detector 38 does not respond. However, in rare cases, the sensor pattern S2 may respond for some reason. In order to exclude such an erroneous response, as shown in this example, even if the print area (exposure area) is shifted by an extra number of pixels after the sensor pattern S2 starts to respond, the sensor pattern S2 What is necessary is just to confirm that it responds reliably (detects light).

  In this example, in order to simplify the description, the print area (exposure area) is set to 5 pixels and the shift amount for the above confirmation is set to only 1 pixel. However, the value is limited to this value. Instead, the size of the print area (exposure area) and the number of confirmations may be determined in consideration of the relationship with the size of the sensor pattern S2 of the light beam detector 38.

  When the main scanning direction beam light position information of the beam light a in units of one pixel is obtained in this way, the main control unit 51 next moves the main scanning direction beam light in units of 1/10 pixels. An operation for obtaining position information is performed.

  At present, with the delay clock D1 selected, the print area (exposure area) is set one step before the sensor pattern S2 of the beam light detector 38 responds by setting the print area (exposure area) in units of one pixel. Is set. From this state, the main control unit 51 switches the delay clock from D1 to D2 (shifts the clock position by 1/10 clock), releases the reset of the first counter 111, and waits for an interrupt signal (S363).

  When detecting the interrupt signal from the first counter 111, the main control unit 51 takes in the value of the latch circuit 113 of the main scanning beam position detection circuit in the beam light position detection output circuit 40 and resets it to the first counter 111. (S364).

  Next, the main control unit 51 determines whether or not the value of the latch circuit 113 is “8” (S365), and determines whether or not the print area (exposure area) has reached the sensor pattern S2 of the beam light detector 38. To check.

  As a result of this check, if the value of the latch is not “8”, this means that the print area (exposure area) has not yet reached the sensor pattern S2, so the process returns to step S363, and further, the 1/10 clock phase. The shifted delay clock is selected and the same determination operation as described above is performed.

  If the value of the latch is “8” as a result of the check in step S365, it means that the print area (exposure area) has reached the sensor pattern S2, and the delay clock at this time is used for image formation (copying, The selected delay clock is used and stored in the memory 52 (S366).

  As described above, the main control unit 51 can move the print area (exposure area) in units of about 1/10 pixel by setting the print area (exposure area) and selecting the delay clock. By looking at the response of the sensor pattern S2 of the beam light detector 38 at this time, it is possible to obtain the beam light position information of the beam light a in the main scanning direction with an accuracy of about 1/10 pixel.

  In the present embodiment, the printing area (exposure area) is sequentially shifted to the downstream side in the beam light scanning direction, and the operation of finding the point to which the sensor pattern S2 of the beam light detection device 38 responds is shown. The present invention is not limited to this method.

  For example, the printing area (exposure area) is further shifted sequentially downstream in the beam light scanning direction to find a point where the sensor pattern S2 of the beam light detection device 38 stops responding, and this is the main point of each of the light beams a to d. Scanning direction beam light position information may be used.

  Further, for example, the printing area (exposure area) is set in advance in the downstream side in the beam light scanning direction, and the points to which the sensor pattern S2 of the beam light detector 38 responds are shifted in order to the upstream side. You may look for points that you find or stop responding.

  In the above description, in the light beam detection device 38, the light beam power is also detected by the sensor pattern SA (or SG) for detecting the light beam passage position. For example, as shown in FIG. As described above, a dedicated sensor pattern SH for detecting the power of the light beam may be added to the adjacent portion (right adjacent to the drawing) of the sensor pattern S1. As is apparent from the figure, the sensor pattern SH has a sufficiently large size in the sub-scanning direction (the size in the direction perpendicular to the scanning direction of the light beam) as well as the length L1 of the sensor patterns S1 and S2. When the light beam passes through the light beam detector 38, the light beam always passes over the sensor pattern SH.

  Therefore, the laser oscillator of the light beam to be measured is forced to emit light, the light beam detector 38 is scanned at a predetermined speed by the polygon mirror, and the electrical signal output from the sensor pattern SH is as shown in FIG. , Amplified by the amplifier 99 (H), integrated by the integrator 42 based on the timing of the pulse signals output from the sensor patterns S1, S2, A / D converted by the A / D converter 43, and main main control By taking in the unit 5151, the power of the beam light on the photosensitive drum 15 can be detected as in the above example.

  The merit of using such a light beam detection device 38 is that the galvano mirror is operated as in the case of using the light beam detection device 38 in FIG. 3 because the sensor pattern SH is assigned exclusively for light power detection. It is not necessary. Therefore, it is possible to omit extra operations as much as it is unnecessary to operate the galvanometer mirror.

  Next, detection and correction of the offset value in the light beam detector output processing circuit 40 will be described.

  FIG. 40 shows a detailed configuration example up to the integrator 42 for the sensor patterns SB and SC in the light beam detector output processing circuit 40. In FIG. 40, currents flowing through the sensor patterns (photodiodes) SB and SC are converted into currents and voltages by resistors PR1, RL1, RP2 and RL2, respectively, and then amplified by operational amplifiers A1 and A2 as voltage follower circuits, respectively. It is sent to the differential amplifier 63. The differential amplifier 63 includes resistors R1 to R4 and an operational amplifier A3.

  The output of the differential amplifier 63 is sent to the integrator 42 via the analog switch SW1 constituting the selection circuit 41. The integrator 42 includes an operational amplifier A4, an integration resistor R5, an integration capacitor C, an integrator reset analog switch SW7, and a protection resistor R6. The output of the integrator 42 is sent to the A / D converter 43 and converted from an analog value to a digital value. When the A / D conversion is completed, the A / D converter 43 transmits a conversion end signal to the main control unit 51. When receiving the conversion end signal, the main control unit 51 reads the light beam position information converted into a digital value.

  Note that the configuration example up to the integrator 42 for the sensor patterns SD, SE, SF is basically the same as the configuration example up to the integrator 42 for the sensor patterns SB, SC, and thus the description thereof is omitted. To do.

  Here, the offset voltage (offset value) of the operational amplifier will be described with reference to FIG.

  In FIG. 41A, if the operational amplifier is ideal, the output is 0 (zero) if the voltage difference between the non-inverting input and the inverting input is 0 (zero). However, in reality, an output voltage of Vout is generated at the output terminal even though the non-inverting input and the inverting input are connected to the ground potential (GND) and the voltage difference between the inputs is set to “0”.

  In FIG. 41B, the voltage Vos between the input terminals is applied so that the output voltage Vout becomes 0 [V]. This voltage value is called an input offset voltage Vos. This is mainly due to variations in the characteristics of the differential input transistors of the operational amplifier. The input offset voltage of a general operational amplifier is several mV at room temperature. Also, the input offset voltage changes with temperature.

  Next, the influence and problems of the offset voltage of the operational amplifier on the beam light passage position detection will be described with reference to FIG.

  For example, when the passage position of the beam light a is at the center position between the sensor patterns SB and SC, the outputs of the sensor patterns SB and SC are equal (V1 = V2).

  Consider the case where the offset voltage of the operational amplifier constituting the light beam detector output processing circuit 40 is as follows.

Offset voltage of operational amplifier A1: −Vos [V]
Offset voltage of operational amplifier A2: + Vos [V]
Offset voltage of operational amplifier A3: + Vos [V]
Offset voltage of operational amplifier A4: + Vos [V]
Considering the above offset voltage, the output of each operational amplifier is as follows.

Operational amplifier A1 output: V1-Vos [V]
Operational amplifier A2 output: V2 + Vos [V]
Output of operational amplifier A3: (+ 2Vos + Vos) × R3 / R1
= +3 Vos x R3 / R1 [V]
Output of operational amplifier A4:-(+ 3Vos × R3 / R1 + Vos)
/ R5 / C x t [V]
However, V1 = V2
R1 = R2, R3 = R4
R5: integration resistor, C: integration capacitor
t: Integration time Since the outputs of the sensor patterns SB and SC are equal (V1 = V2), the output of the operational amplifier A4 (integrator) is ideally 0 [V]. However, as described above, the output of the operational amplifier A4 does not become “0” due to the influence of the offset voltage of each operational amplifier. In other words, the output of the beam light detector output processing circuit 40 outputs erroneous information that the position of the beam light is deviated even though the beam light passing position is an ideal position. .

For example, if each constant is
Vos = 5 [mV]
R2 / R1 = R4 / R5 = 3
R5 = 220 [Ω]
C = 150 [pF]
t = 406 [ns]
The integrated output is about 0.615 [V]. When this is converted into beam light position information, it is about 1.23 μm.

  Hereinafter, offset detection / correction will be described.

  First, the outline will be described. As described above, in the passing position detection control for detecting the passing position of the light beam on the light beam detecting device 38, the sensor when the light beam passes on the light beam detecting device 38 is used. The difference in pattern output is taken and the result is integrated and A / D converted for detection.

  As already described, the integration start / end timing of the integrator 42 is the timing at which the sensor patterns S1 and S2 output signals. That is, when the beam light is scanned by the polygon mirror 35 and passes over the sensor pattern S1, the integrator 42 is reset, and integration is started simultaneously with the end of the reset. Further, the integration is completed when the light beam passes over the sensor pattern S2, and A / D conversion is started at the same time.

  The offset value of the beam light detector output processing circuit 40 is constantly generated as long as the power of the circuit is turned on. The offset value becomes an error factor of the light beam position information in the light beam passage position detection control during the integration time from the start to the end of the integration operation. Therefore, if the offset value in the integration time can be measured, the beam light passage position control considering the offset value (correcting the offset) can be performed.

  Therefore, in this example, the output signals of the sensor patterns S1 and S2 are used in order to make the integration start / end timing of the integrator 42 equivalent to the beam passage position control. However, if the light beam is detected by the sensor patterns SB, SC, SD, SE, and SF, the light beam information is superimposed and an accurate offset value cannot be detected.

  Therefore, the offset value can be detected (measured) without changing the integration start / end timing by shifting the light beam to a region not detected by the sensor patterns SB, SC, SD, SE, and SF.

  FIG. 43 is a diagram showing how the offset value is detected by shifting the position of the light beam onto the sensor pattern SA. As described above, the offset value is detected by performing integration in a state where the sensor patterns SB to SF are not irradiated with the beam light. The beam light passing position may be equal to the position at the time of execution of the beam light power control routine described above.

  Next, the offset correction routine will be described with reference to the flowcharts shown in FIGS.

  First, the main control unit 51 turns on the polygon motor 36 and rotates the polygon mirror 35 at a predetermined rotational speed (S61). Next, the latest drive values of the galvanometer mirrors 33a to 33d are read from the main controller 51 and the memory 52, and the respective galvanometer mirrors 33a to 33d are driven based on the read values (S62).

  Next, the main control unit 51 controls the galvanometer mirror 33a to move the beam light a to the non-detection region of the beam position detection pattern (S63). The control content here is to grasp the current beam light passing position and to control the galvanometer mirror 33a so as to move the beam light a to a region not detected by the sensor patterns SB, SC, SD, SE, SF.

  Subsequently, the main control unit 51 detects the offset value of the beam light passage position detection unit of the beam light a in the beam light detector output processing circuit 40 (offset detection, S64, S65). Then, offset correction is executed based on the detected offset value (offset correction, S66).

  Thereafter, the same (moving light beam to the non-detection region) → (offset detection) → (offset correction) is also performed on the light beams b, c, and d by sequentially executing steps S67 to S78.

  Next, the routine operation for moving the light beam a in step S63 of FIG. 44 to the non-detection region of the light beam position detection pattern will be described with reference to the flowcharts shown in FIGS.

  First, the main control unit 51 causes the laser oscillator 31a to emit light forcibly (S81). As a result, the beam light a periodically scans the beam light detector 38 as the polygon mirror 35 rotates.

  Next, in accordance with the interrupt signal INT output from the A / D converter 43, the main control unit 51 reads values obtained by A / D converting the outputs of the amplifiers and the differential amplifier. Normally, the scanning position of the beam light is slightly different for each surface depending on the surface tilt component of the polygon mirror 35, and in order to remove the influence, the number of times equal to the number of surfaces of the polygon mirror 35, or It is desirable to read a value that has been continuously A / D converted a plurality of times. In that case, the main control unit 51 averages the output values of the A / D converters 43 corresponding to the respective amplifiers and differential amplifiers, and uses the result as the outputs of the respective amplifiers and differential amplifiers (S82).

  Next, the main control unit 51 compares the output of the amplifier and the differential amplifier thus obtained with the determination reference value, and based on the result, sets the galvanometer mirror so as to move the beam light to the non-detection region. Control.

  Here, an example will be described in which the non-detection region is set near the center of the sensor pattern SA and the sensor pattern SG. As described above, the sensor pattern SA and the sensor pattern SG have a length of 800 μm. If the length of the sensor pattern SA and the sensor pattern SG is in the vicinity of 400 μm at the center, the light beam has a formation of about 100 × 100 μm (or more). However, there is little possibility of being detected by the sensor patterns SB, SC, SD, SE, and SF.

  The main control unit 51 first determines the output of the amplifier 61 by comparing the output (A / D conversion value) of the amplifier 61 (A) with the determination reference value 100H stored in the memory 52 in advance. It is determined whether the reference value is 100H or more (S83).

  As a result of this determination, if the output of the amplifier 61 is 100H or more, it is determined that the passing position of the beam light a is on the sensor pattern SA side or on the sensor pattern SA from the center of the sensor pattern SB. It represents. Accordingly, in this case, the galvanometer mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SA about 450 μm (S84).

  After moving the beam light a in this way, the output of the sensor pattern SA is read again, and the output before and after the movement is compared (S85). Here, if the output after movement is equal to or greater than that before movement (output after movement ≧ output before movement), at least the beam light a is on the sensor pattern SA and the center of the sensor pattern SA. Therefore, the movement to the non-detection area is completed.

  On the other hand, when the output after the movement is smaller than the output before the movement, the passage position of the beam light a is in a state where a part of the beam light is applied on the upper side of the drawing on the sensor pattern SA, or completely the sensor pattern SA. This is the case when it is off the top. This means that the passage position of the beam light a has been in the non-detection region before the movement. Therefore, in this case, the galvanometer mirror 33a is controlled so that the position of the beam light a is moved to the side of the sensor pattern SG by about 450 μm (S86).

  If it is determined in step S83 that the output of the amplifier 61 is not 100H or higher, the output (A / D conversion value) of the amplifier 62 (G) is compared with the determination reference value 100H stored in the memory 52 in advance. Thus, it is determined whether the output of the amplifier 62 has a determination reference value of 100H or more (S87).

  If the output of the amplifier 62 is 100H or more as a result of this determination, it is determined that the passage position of the beam light a is on the sensor pattern SG side or on the sensor pattern SG from the center of the sensor pattern SF. It represents. Therefore, in this case, the galvanometer mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SG (lower side in the drawing) about 450 μm (S88).

  After moving the beam light a in this way, the output of the sensor pattern SG is read again, and the output before and after the movement is compared (S89). Here, if the output after movement is equal to or larger than that before movement (output after movement ≧ output before movement), at least the beam light a is on the sensor pattern SG and the center of the sensor pattern SG. Therefore, the movement to the non-detection area ends.

  On the other hand, when the output after the movement is smaller than the output before the movement, the passage position of the beam light a is in a state where a part of the beam light is applied to the lower side of the drawing on the sensor pattern SG or completely. This is the case when it is off the SG. This means that the passage position of the beam light a has been in the non-detection region before the movement. Accordingly, in this case, the galvanometer mirror 33a is controlled so as to move the position of the beam light a to the sensor pattern SA side (S90).

  If it is determined in step S83 that the output of the amplifier 62 is not equal to or greater than 100H, the output (A / D conversion value) of the differential amplifier 66 (EF) is stored in the memory 52 in advance. By comparing with the values 800H and A00H, it is determined whether the output of the differential amplifier 66 is not less than 800H and not more than A00H (S91).

  As a result of this determination, when the output of the differential amplifier 66 is 800H or more and A00H or less, the passing position of the beam light a is a position closer to the sensor pattern SF side than the target passing position of the beam light d. It represents that. Therefore, in this case, the galvanometer mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SG about 450 μm (S92).

  If it is determined in step S91 that the output of the differential amplifier 66 is 800H or more and not A00H or less, the output (A / D conversion value) of the differential amplifier 65 (DE) is stored in the memory 52 in advance. By comparing with the stored determination reference values 800H and A00H, it is determined whether the output of the differential amplifier 65 is the determination reference value of 800H or more and A00H or less (S93).

  As a result of this determination, when the output of the differential amplifier 65 is 800H or more and A00H or less, the passage position of the beam light a is closer to the sensor pattern SE side than the target passage position of the beam light c. It represents that. Therefore, in this case, the galvanometer mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SG about 500 μm (S94).

  If it is determined in step S93 that the output of the differential amplifier 65 is 800H or higher and not A00H or lower, the output (A / D conversion value) of the differential amplifier 64 (CD) is stored in the memory 52 in advance. By comparing with the stored determination reference values 800H and A00H, it is determined whether the output of the differential amplifier 64 has a determination reference value of 800H or more and A00H or less (S95).

  As a result of this determination, when the output of the differential amplifier 64 is 800H or more and A00H or less, the passage position of the beam light a is closer to the sensor pattern SD side than the target passage position of the beam light b. It represents that. Therefore, in this case, the galvanomirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SG about 540 μm (S96).

  If it is determined in step S95 that the output of the differential amplifier 64 is 800H or higher and not A00H or lower, the output (A / D conversion value) of the differential amplifier 63 (BC) is stored in the memory 52 in advance. By comparing with the stored determination reference values 800H and A00H, it is determined whether the output of the differential amplifier 63 is the determination reference value of 800H or more and A00H or less (S97).

  As a result of this determination, when the output of the differential amplifier 63 is 800H or more and A00H or less, the passage position of the beam light a is closer to the sensor pattern SC side than the target passage position of the beam light a. It represents that. Therefore, in this case, the galvano mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SA by about 520 μm (S98).

  In cases other than the above, the passage position of the beam light a represents a position closer to the sensor pattern SC side than the center of the sensor pattern SB. Accordingly, in this case, the galvanometer mirror 33a is controlled so that the beam light a moves to the side of the sensor pattern SA about 450 μm (S99).

  Note that the above control is intended to move the light beam a to the non-detection region, so high-precision light beam position control (for example, control of 1 μm or less) is not necessarily required, and rough control is sufficient. It is.

  By performing the same control to move the light beam b, the light beam c, and the light beam d to the non-detection regions in steps S67, S71, and S75 of FIGS. 44 and 45, all the light beams a to d are obtained. It is moved to the non-detection area of the beam light position detection pattern.

  Next, the routine operation for detecting (measuring) the offset value of the light beam passage position detecting unit for the light beam a in step S64 of FIG. 44 will be described with reference to the flowchart shown in FIG.

  First, the main control unit 51 selects a beam light passage position detection unit for the beam light a in the beam light detector output processing circuit 40 (S101). This is because when the analog switch SW1 is turned on, the output terminal of the differential amplifier 63 for calculating the difference between the outputs of the sensor patterns SB and SC for detecting the passing position of the light beam a is connected to the input terminal of the integrator 42. To do.

  Next, the main control unit 51 causes the laser oscillator 31a to emit light forcibly (S102). As a result, the light beam a periodically scans the light beam detector 38. Then, as the light beam a passes over the light beam detector 38, the signal of the sensor pattern S1 is output, the integrator 42 is reset by the output signal of the sensor pattern S1, and integration is started at the same time ( S103).

  However, since the beam light a is moved to the non-detection region, it is not detected by the sensor patterns SB and SC that control the passing position of the beam light a, and only the offset component is integrated. That is, if the operational amplifier is ideal, since the beam light a does not strike the sensor patterns SB and SC, the outputs of the operational amplifiers A1 and A2 are 0 [V], and the output of the operational amplifier A3 is also 0 [V]. ]. Since the output of the operational amplifier A4 is also 0 [V], the value that is A / D converted and read into the main controller 51 is also 000H.

  However, since an offset voltage exists in the operational amplifier constituting the light beam passage position detection unit, the value read by the main control unit 51 is not 000H, and a certain value is read. That is, this is an offset value.

  Then, the integration operation ends with the output of the sensor pattern S2, and A / D conversion is performed simultaneously (S104). When the A / D conversion is completed, the A / D converter 43 outputs an A / D conversion end signal (S105). Upon receiving the A / D conversion signal end signal, the main control unit 51 receives the laser oscillator 31a. Is released (S106), and the A / D converted value is read (S107).

  Next, the main control unit 51 stores the read offset value in the memory 52 (S108). Finally, the selection of the light beam passage position detection unit for the light beam a is canceled (S109). That is, the main control unit 51 turns off the analog switch SW1.

  Similar control is performed to detect the offsets of the light beams b, c, and d in steps S68, S72, and S76 of FIGS. 44 and 45, so that the light beam passage positions of all the light beams a to d are detected. The offset value of the detection unit, that is, the light beam detector output processing circuit 40 is detected.

  Next, the operation of the routine for correcting the offset value in steps S66, S70, S74, and S78 in FIG. 44 will be described with reference to the flowchart shown in FIG.

  First, the main control unit 51 determines the polarity of the detected offset value (S111). The polarity of the offset value varies depending on the operational amplifier. Further, the beam light detector output processing circuit 40 is composed of a plurality of operational amplifiers, and the polarity thereof differs depending on the image forming apparatus to be used. Therefore, it is necessary to determine the polarity.

  The main control unit 51 determines the polarity of the read offset value, and if it is positive (plus), the main control unit 51 is offset with respect to the determination reference (Vref) in the beam light passage position control routine of FIGS. The absolute value (| + Vos |) of the value is subtracted (S112). On the other hand, if the read offset value is negative (minus), the absolute value (| + Vos |) of the offset value is added from the determination reference value (S113).

  If normal beam light passing position control is executed after performing the offset value detection and offset value correction processes described above, the offset value is taken into account in the light beam passing position control determination reference value. A control error of the beam light passing position does not occur.

  As described above, according to the above-described embodiment, in the image forming apparatus such as a digital copying machine, for example, when a multi-beam optical system is used, the print area is set as a clock unit for image formation for each light beam. It is possible to set in the following, and by selecting the optimum setting value while checking the actual beam light position with a sensor, the exposure position in the beam light scanning direction (main scanning direction) can always be controlled accurately, It is possible to realize exposure position control in the beam light scanning direction (main scanning direction) that can support a plurality of types of recording pitches (resolutions).

  In the above embodiment, the case where the present invention is applied to a digital copying machine using a multi-beam optical system has been described. However, the present invention is not limited to this, and image formation other than the digital copying machine such as a high-speed printer is possible. The same applies to the device.

1 is a configuration diagram schematically showing a configuration of a digital copying machine according to an embodiment of the present invention. The figure which shows the structure of an optical system unit, and the positional relationship of a photosensitive drum. The block diagram which shows schematically the structure of a beam light detection apparatus. The block diagram which shows schematically the principal part structure of a beam light detection apparatus. The figure for demonstrating the inclination of a beam light detection apparatus and the scanning direction of beam light. FIG. 2 is a block diagram showing a control system that mainly controls an optical system. The figure which showed the positional relationship of a beam light detection apparatus and a photosensitive drum, the exposure area (printing area) of each beam light by a sample timer, and the positional relationship of the light emission area by image data with the time chart. The block diagram which shows the structure for setting a printing area (exposure area) in a fine unit of 1 clock or less. FIG. 6 illustrates an operation of a clock synchronization circuit. The figure explaining the principle of the acquisition method of the main scanning direction beam position information about each beam light. The figure explaining the method to detect the relative positional relationship of the beam light with respect to the output of the beam light detection apparatus. The figure for demonstrating operation | movement of the main scanning direction beam light position detection circuit. The figure for demonstrating operation | movement of the main scanning direction beam light position detection circuit. The figure for demonstrating operation | movement of the main scanning direction beam light position detection circuit. The figure which represented the exposure area in case beam light powers differed in simulation. FIG. 5 is a block diagram for explaining beam light passage position control and offset detection / correction processing. The figure which shows the relationship between the passage position of a beam light, the output of the light reception pattern of a beam light detection apparatus, the output of a differential amplifier, and the output of an integrator. The graph which shows the relationship between the passage position of a beam light, and the output of an A / D converter. The graph explaining the operation | movement resolution of a galvanometer mirror. The graph explaining the operation | movement resolution of a galvanometer mirror. 6 is a flowchart for explaining a schematic operation when a printer unit is powered on. The flowchart explaining a beam light passage position control routine. The flowchart explaining one light beam passage position control routine. The flowchart explaining one light beam passage position control routine. The figure for demonstrating the influence which the dispersion | variation in the power of each beam light gives in beam light passage position control. The schematic block diagram which shows typically the structure of the beam light detection apparatus corresponding to two types of resolutions. The block diagram which shows schematically the principal part structure of the beam light detection apparatus of FIG. The figure for demonstrating the inclination with the scanning direction of the beam light detection apparatus of FIG. 26 and a beam light. The block diagram for demonstrating passage position control of the beam light using the beam light detection apparatus of FIG. 6 is a flowchart for explaining a first example of a beam light power control routine. 6 is a flowchart for explaining a first example of a beam light power control routine. 9 is a flowchart for explaining a second example of a beam light power control routine. 9 is a flowchart for explaining a second example of a beam light power control routine. The flowchart explaining the main scanning direction beam light position control routine. 7 is a flowchart for explaining a main scanning direction beam light position information acquisition routine of the beam light. 7 is a flowchart for explaining a main scanning direction beam light position information acquisition routine of the beam light. 7 is a flowchart for explaining a main scanning direction beam light position information acquisition routine of the beam light. The block diagram which shows schematically the modification of a beam light detection apparatus. The block diagram for demonstrating the passage position control of a beam light at the time of using a beam light detection apparatus, and an offset detection and correction process. The block diagram which shows the specific circuit example of a beam light detector output processing circuit. The figure for demonstrating the offset voltage of an operational amplifier. The figure for demonstrating the influence and problem which the offset voltage of an operational amplifier has on beam light passage position detection. The figure showing a mode that the position of beam light is shifted to a non-detection area | region, and an offset value is detected. The flowchart explaining the routine which correct | amends an offset value. The flowchart explaining the routine which correct | amends an offset value. The flowchart explaining the routine which moves a beam light to a non-detection area | region. The flowchart explaining the routine which moves a beam light to a non-detection area | region. The flowchart explaining the routine which detects an offset value. The flowchart explaining the routine which correct | amends an offset value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Scanner part, 2 ... Printer part, 13 ... Optical system unit, 14 ... Image formation part, 15 ... Photosensitive drum (image carrier), 31a-31d ... Semiconductor laser oscillator (beam light generation) Means), 35... Polygon mirror (polyhedral rotating mirror), 38... Beam light detection device (beam light detection means, beam light power detection means), 38 a... Holding substrate (holding member), 40. Device output processing circuit, 40a... Main scanning direction beam light position detection circuit, 55... Synchronization circuit, S1 to S4... Sensor pattern (light detection unit, beam light detection means), SH. , Beam light power detection means), SA to SG... Sensor pattern (light detection section, beam light detection means), 51... Main control section (control means), 52... Memory (storage means), 111. 1 Counter 112 112 Second counter 113 Latch circuit 114 a to 114 d Crystal oscillator 116 Clock synchronization circuit 117 Delay line 118 a 118 d Delay clock selector 119 a 119 d ... Image transfer clock generation unit (print area setting unit), 120... Sample timer, 122.

Claims (4)

An image forming apparatus for forming an image of one scanning line on the image carrier by simultaneously scanning and exposing the image carrier with a plurality of light beams,
A plurality of beam light generating means for generating beam light;
Scanning means for optically synthesizing the plurality of light beams generated from the plurality of light beam generation means and then reflecting the light beams toward the image carrier and scanning the image carrier with the plurality of light beams; ,
Beam light power detecting means for detecting each power of the plurality of light beams scanned on the image carrier by the scanning means;
Beam light power control means for controlling each of the plurality of light beam generating means so that each power of the plurality of light beams scanned on the image carrier becomes a predetermined value based on each detection result of the light beam power detection means. When,
First beam light detection means for detecting a leading beam of the plurality of light beams scanned on the image carrier by the scanning means;
A second beam light detection unit disposed downstream of the first beam light detection unit with respect to the beam light scanning direction and detecting the plurality of beam lights;
Clock generation means (116) for generating a clock synchronized with the output of the first beam light detection means;
A delay clock means (117) for generating a plurality of delayed clocks out of phase with each other by delaying the clock generated by the clock generating means a plurality of times with a delay amount equal to or less than the period of the clock;
A plurality of delay clock selection means (118a-d) for selecting one delay clock from the plurality of delay clocks generated by the delay clock means as clocks for setting a print area;
Means for obtaining position information in the beam light scanning direction for the plurality of light beams;
Print area setting means (119a-d) for setting the print areas for the plurality of light beams, respectively ;
An image forming apparatus comprising: a control unit (51);
Means for obtaining position information in the scanning direction of the light beam after controlling the light power of the plurality of beams to be the predetermined value using the light beam power control means includes, as a first step, each light beam In each clock unit provided by each delay clock selection unit, each beam light scanning direction position of each exposure region of a predetermined length exposed by the above has a predetermined relationship with the second beam light detection unit. The position information is set by setting the print area setting means and setting the delay clocks selected by the delay clock selection means so that the scanning direction positions of the exposure areas coincide with each other as a second step. Is what you get
Wherein the control means, the means for obtaining the positional information of the light beam scanning direction, based on the set value of the printing area setting means to be obtained as the position information, the printing area setting means, wherein on said image bearing member Control to set each print area of each light beam in each delay clock unit,
An image forming apparatus. Resolution setting means for setting the resolution of image formation;
Scanning speed changing means for changing the scanning speed of the scanning means;
Clock frequency changing means for changing the frequency of the clock for image formation;
Resolution switching control means for changing the scanning speed and changing the clock frequency using the scanning speed changing means and the clock frequency changing means according to the setting contents of the resolution setting means. The image forming apparatus according to claim 1, wherein: Beam light position detecting means for detecting each passing position of the plurality of light beams scanned on the image carrier by the scanning means;
Beam light generation control means for controlling the light beam generation means so that the plurality of light beams do not scan and expose the image carrier when the light beam position detection means detects the passage positions of the respective light beams; ,
Beam light position control means for controlling the passage positions of the respective light beams so that the passage positions of the plurality of light beams that scan on the image carrier become a predetermined position based on the detection result of the light beam position detection means; The image forming apparatus according to claim 1, further comprising:   A first control unit that controls the beam light generation unit so that the beam light is not scanned and exposed on the image carrier when the beam light power detection unit detects the power of each beam light; The image forming apparatus according to claim 1, further comprising:

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