JP2007098737A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a high-quality image by adjusting a relative positional relationship of write positions of both line latent images in an image forming method in which the writing of the line latent image by forward light beams and writing of the line latent image by return light beams are carried out alternately. <P>SOLUTION: A process for correcting write timing (step S2) is carried out before a write process (steps S3-S9) is carried out. In the correction process (step S2), a sensor reaching time from a time point when a write time passes after the lapse of a return side standby time Tw2 since a first detection signal is outputted while the light beams are scanned back and forth to a time point when a sensor detects the return light beam and outputs a second detection signal is obtained. A forward side standby time Tw1 is changed and corrected to the sensor reaching time Tb. A write starting position of the forward line latent image is adjusted on the basis of the corrected forward side standby time Tw1, whereby a relative positional shift of the line latent image is eliminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming method for forming a latent image in an effective image area by reciprocally scanning a light beam on an effective image area of a latent image carrier with a vibrating deflection mirror surface.

  While the light beam emitted from the light source is deflected by a vibrating mirror such as a galvanometer mirror or a resonance scanner and reciprocally scanned on a latent image carrier such as a photosensitive drum, an outward line latent image is formed by the outward light beam, An apparatus for forming a return line latent image by a return light beam is conventionally known. For example, in the image forming apparatus described in Patent Document 1, a laser diode is used as a light source, and a light beam having a light intensity corresponding to an image signal is emitted from the laser diode. The light beam thus modulated is deflected by the deflecting mirror surface of the galvanometer mirror, and then guided to the photosensitive drum to travel on the photosensitive drum from the forward path side, which is one side in the main scanning direction, to the other side. The outward scan is performed on the return path side. As a result, a forward line latent image corresponding to the image signal is formed on the latent image carrier. On the return side, a return line latent image is formed in the same way as on the forward side.

  A sensor composed of a light receiving element such as a light receiving diode is disposed adjacent to one end of the photosensitive drum to detect the scanning light beam. Then, the writing timing of the forward line latent image by the forward light beam is controlled based on the output of the sensor, and the writing timing of the backward line latent image by the backward light beam is controlled based on the same sensor output. That is, when a detection signal is output from the sensor, the elapsed time from the signal output is counted, and the count value becomes a predetermined first value (corresponding to the “first standby time” of the present invention). At the time, the writing of the forward line latent image (outward writing) is started, and when the count value becomes the second value (corresponding to the “second waiting time” of the present invention), Writing of the line latent image is started. Thereby, reciprocal writing by one sensor is possible.

  Also, a device that arranges sensors adjacent to both ends of the photosensitive drum, detects a scanning light beam at each end, and controls writing timing in forward writing and backward writing based on the output from each sensor Is also known for some time.

Japanese Unexamined Patent Publication No. 2004-230629 (pages 2 and 6, FIGS. 4 to 6)

  However, the vibration characteristics of the vibration mirror vary depending on various factors such as individual differences of the vibration mirror, assembly accuracy, and in-machine temperature. Therefore, in a device that starts writing a line latent image uniformly when a predetermined time has elapsed from the sensor output as in the above-described prior art, the vibration characteristics of the vibrating mirror fluctuate to change the forward path side. In some cases, the line latent image and the line latent image on the backward path are relatively displaced in the main scanning direction, and image quality is deteriorated.

  The present invention has been made in view of the above problems, and in an image forming method in which line latent image writing by an outward light beam and line latent image writing by a backward light beam are alternately performed, writing positions of both line latent images are provided. It is an object of the present invention to form a high-quality image by adjusting the relative positional relationship between the two.

  According to a first aspect of the image forming method of the present invention, the light beam is reciprocated in the main scanning direction in a second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier by the vibrating deflection mirror surface. In an image forming apparatus configured to be capable of scanning, a sensor detects a light beam moving in a position outside the first scanning range on the forward path side, which is one side in the main scanning direction, and obtains a detection signal. An image forming method for writing a latent image on a latent image carrier based on a reciprocating scanning light beam, and moving the latent image carrier in a sub-scanning direction substantially perpendicular to the main scanning direction in order to achieve the above object. However, each time the sensor detects a forward light beam scanned from the forward path to the backward path which is the other side in the main scanning direction and outputs a first detection signal, the following reciprocal writing is performed on the latent image carrier. A two-dimensional latent image is formed on Before performing the writing process and the writing process, the second standby time elapses after the first detection signal is output while reciprocating the light beam, and the sensor returns to the return light beam after the writing time elapses. And a pre-writing correction step of changing the first standby time to the sensor arrival time by obtaining the time from when the sensor is detected and outputting the second detection signal as the sensor arrival time. The reciprocal writing is performed from the output of the first detection signal after the line latent image is written by the outward light beam for a predetermined writing time from the time when the first waiting time has elapsed from the output of the first detection signal. The line latent image is written by a backward light beam scanned from the backward path side to the forward path side for the writing time from the time when the second standby time has elapsed.

  In the invention configured as described above, when the light beam is detected by the sensor and the first detection signal is output, the first writing signal is output for a predetermined writing time from the time when the first standby time has elapsed from the output of the first detection signal. A line latent image is written by the outward light beam to form an outward line latent image. Further, following the formation of the forward line latent image, the line latent image is generated by the backward light beam scanned from the backward path side to the forward path side for the writing time from the time when the second waiting time has elapsed from the output of the first detection signal. Is written. Thus, reciprocal writing is performed by one sensor. Here, what has been a problem in the past is the relative positional deviation between the forward line latent image and the backward line latent image in the main scanning direction. In the present invention, the pre-writing correction is performed before the writing process is executed. The relative positional deviation is eliminated by executing the process. That is, in this pre-writing correction process, the sensor detects the return light beam after the second waiting time has elapsed since the first detection signal was output while reciprocating the light beam, and when the writing time has elapsed. The time until the second detection signal is output is obtained as the sensor arrival time, and the first standby time is changed to the sensor arrival time. By correcting the first waiting time in this way, the writing start position of the forward path line latent image is adjusted, and the relative positional deviation from the backward line latent image is eliminated. As a result, a high quality image is formed.

  Here, the pre-writing correction step is executed before the writing step is executed, but the in-writing correction step similar to the pre-writing correction step may be executed every time the reciprocal writing is performed. . In other words, in the correction process during writing, in the latter half of the reciprocal writing, after the writing by the return light beam is completed, the return light beam is detected by the sensor and the second detection signal is output, and the sensor arrival time is obtained. . Then, the first waiting time is rewritten to the sensor arrival time. Further, in the reciprocal writing performed immediately after the correction process during writing in this way, the latent image writing is performed by the outward light beam at the writing timing (first waiting time) corrected by the correction process (outbound writing). On the other hand, the latent image writing by the backward light beam is performed at the same writing timing (second waiting time) as the previous time (returning writing). By correcting the first standby time while continuously performing reciprocal writing in this way, even if the vibration characteristics of the deflecting mirror surface fluctuate during execution of the writing process, the return line latent image follows it. The writing start position is adjusted to eliminate the relative positional deviation from the forward line latent image.

  In the above invention, the correction process is executed before the writing process, but the first waiting time and the second waiting time are stored in the memory before the writing process, and the writing process is started. You may comprise so that a correction process in writing may be performed whenever it performs each reciprocal writing. In this case, the first round-trip writing in the writing process is executed based on the first and second standby times stored in the memory, and in the latter half of the round-trip writing, after the writing by the backward light beam is completed. The return light beam is detected by the sensor, a second detection signal is output, and the sensor arrival time is obtained. Then, the first standby time is changed to the sensor arrival time. Further, in the reciprocal writing performed immediately after the correction process during writing in this way, the latent image writing is performed by the outward light beam at the writing timing (first waiting time) corrected by the correction process (outbound writing). On the other hand, the latent image writing by the backward light beam is performed at the same writing timing (second waiting time) as the previous time (returning writing). By correcting the first standby time while continuously performing reciprocal writing in this way, even if the vibration characteristics of the deflecting mirror surface fluctuate during execution of the writing process, the return line latent image follows it. The writing start position is adjusted to eliminate the relative positional deviation from the forward line latent image.

  According to a second aspect of the image forming method of the present invention, in the main scanning direction, the light beam is deflected by the vibrating deflection mirror surface in a second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier. A forward-side sensor that detects a light beam that moves outside the first scanning range on the forward path side, which is one side in the main scanning direction, and outputs a detection signal. An image forming apparatus having a return path sensor that detects a light beam that moves in a position outside the first scanning range on the return path side that is the other side of the direction and outputs a detection signal. An image forming method for writing a latent image on a latent image carrier using a reciprocating scanning light beam based on an output detection signal. In order to achieve the above object, a latent image is written in a sub-scanning direction substantially perpendicular to the main scanning direction. Image carrier The writing process for forming the two-dimensional latent image on the latent image carrier by performing the following reciprocal writing while moving the optical path, and the forward writing while scanning the outgoing light beam before the writing process. The time from when the writing time elapses until the return side sensor detects the forward light beam and outputs the second detection signal is obtained as the sensor arrival time, and the return side standby time is rewritten to the sensor arrival time before writing. And a correction step. The reciprocal writing is performed for a predetermined writing time from the time when the forward side waiting time has elapsed after the forward side sensor detects the forward light beam scanned from the forward side to the backward side and outputs the first detection signal. The backward waiting time elapses after the return path sensor detects the return path light beam scanned from the return path side to the outbound path side and outputs the first detection signal. From this point in time, the return path writing in which the line latent image is written by the return path light beam for a predetermined writing time is alternately performed.

  In the invention configured as described above, sensors are provided on both sides in the main scanning direction, and each sensor can detect a reciprocating light beam. The forward writing and the backward writing are alternately performed. When the write end timing of the forward writing and the write start timing of the backward writing following the forward writing are different from each other, the forward line There is a relative displacement between the latent image and the backward line latent image in the main scanning direction. Therefore, in the above invention, the relative positional deviation is eliminated by executing the pre-writing correction step before the writing step. That is, in the pre-writing correction process, while the forward light beam is scanned, the return side sensor detects the forward light beam and outputs the second detection signal from the time when the write time for the forward writing has elapsed. Time is obtained as the sensor arrival time. Then, the return-side waiting time is rewritten to the sensor arrival time. In this way, by correcting the return-side waiting time, the writing start position of the return-line latent image is adjusted, and the relative displacement from the forward-line latent image is eliminated. As a result, a high quality image is formed.

  In the above invention, the correction process is executed before the writing process. However, the outbound waiting time is stored in the memory before the writing process, and each outbound writing is performed when the writing process is started. You may comprise so that a correction process in writing may be performed whenever it performs. In this case, the first forward writing in the writing process is performed based on the forward waiting time stored in the memory, and after the writing by the forward light beam is completed, the forward light beam is detected by the backward sensor. The second detection signal is output and the sensor arrival time is obtained. Then, the return-side waiting time is changed to the sensor arrival time. Further, in the backward writing performed immediately after performing the correction process during writing in this way, the latent image writing by the backward light beam is performed at the writing timing (return side waiting time) corrected by the correction process (return writing). Included). By correcting the return-side waiting time while continuously performing reciprocal writing in this way, even if the vibration characteristics of the deflecting mirror surface fluctuate during execution of the writing process, the return-line latent image follows it. The writing start position is adjusted to eliminate the relative positional deviation from the forward line latent image.

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

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

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

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

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

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

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

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

  3 is a main scanning sectional view showing the structure of the exposure unit equipped in the image forming apparatus of FIG. 1, FIG. 4 is a view showing the scanning range of the light beam in the exposure unit of FIG. 3, and FIG. FIG. 2 is a diagram illustrating an exposure control unit for controlling the exposure unit and the exposure unit of one image forming apparatus. Hereinafter, the configuration and operation of the exposure unit 6 and the exposure control unit 12 will be described in detail with reference to these drawings. The configuration of the exposure unit 6 and the exposure control unit 12 is the same for all color components, so the configuration relating to yellow will be described here, and the other color components will be denoted by corresponding reference numerals and description thereof will be omitted.

  As shown in FIG. 3, the exposure unit 6 </ b> Y has an exposure housing 61. A single laser light source 62 is fixed to the exposure housing 61, and a light beam can be emitted from the laser light source 62. The laser light source 62 is ON / OFF controlled based on the image signal Sv from the main controller 11, and a light beam modulated in accordance with the image signal Sv is emitted forward from the laser light source 62. That is, in this embodiment, the video clock generator 111 is provided in the main controller 11 and outputs a video clock signal VC having a reference frequency, for example, 68 MHz. Then, the image output unit 112 generates an image signal Sv corresponding to the yellow image data included in the image formation command given to the main controller 11 based on the video clock signal VC. The image signal Sv is output to the laser light source 62 of the exposure unit 6Y, the light beam is modulated according to the image signal Sv, and the modulated light beam is emitted forward from the laser light source 62.

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

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

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

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

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

  Then, the light beam deflected by the deflecting mirror surface 651 of the deflector 65 is deflected toward the scanning lens 66. In this embodiment, the scanning lens 66 is configured so that the F values are substantially the same over the entire effective image area EIR on the surface of the photoreceptor 2. Accordingly, the light beam deflected toward the scanning lens 66 is focused on the effective image area EIR on the surface of the photoreceptor 2Y through the scanning lens 66 with substantially the same spot diameter. As a result, a light beam is scanned in parallel with the main scanning direction X, and a line-like latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2. In this embodiment, the scanning range (the “second scanning range” of the present invention) SR2 that can be scanned by the deflector 65 is for scanning the light beam on the effective image area EIR as shown in FIG. The scanning range (the “first scanning range” in the present invention) is set wider than SR1. Further, the first scanning range SR1 is located substantially at the center of the second scanning range SR2, and is substantially symmetric with respect to the optical axis. Further, the symbol θir in the figure indicates the amplitude angle of the deflection mirror surface 651 corresponding to the end of the effective image area EIR, and the symbol θs indicates the amplitude angle of the deflection mirror surface 651 corresponding to the light detection sensor described below. Show.

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

  In the specification, one side (+ X) in the main scanning direction X is referred to as “forward path side”, and the other side (−X) is referred to as “return path side”. A light beam scanned from the forward path side (+ X) to the backward path side (−X) is referred to as an “outward path light beam”, and the operation and position of writing a line latent image on the photosensitive member 2 by scanning the forward path light beam are “ This is referred to as “outward writing”. Conversely, a light beam scanned from the return path side (−X) to the forward path side (+ X) is referred to as a “return path light beam”, and the operation and position for writing a line latent image on the photosensitive member 2 by scanning of the return path light beam This is called “return writing”.

  In this embodiment, since the light detection sensor 60 is disposed at the end of the second scanning range SR2 on the forward path side, the light beam passes through the light detection sensor 60 and is detected at the initial scanning stage of the forward light beam. The signal Hsync is output, and the light beam passes through the light detection sensor 60 and the detection signal Hsync is output at the end of scanning of the return light beam. Thus, the detection signal Hsync is output twice for each reciprocating scan of the light beam. Therefore, in order to distinguish these signals, in this specification, the detection signal Hsync corresponding to the detection of the outward light beam is referred to as “first detection signal Hsync1”, and conversely, the detection signal Hsync corresponding to the detection of the return light beam is referred to as “detection signal Hsync”. The second detection signal Hsync2 is assumed. Further, when explaining without distinguishing these, they are simply referred to as “detection signal Hsync”.

  The signal Hsync detected in this way is given to the write timing adjustment unit 102 of the engine controller 10. The write timing adjusting unit 102 is supplied with a clock signal for timing from the count clock generating unit 103 of the engine controller 10, and based on this clock signal for timing, the write timing adjusting unit 102 has elapsed from the detection signal Hsync. Time is measured and a video request signal is output to the image output unit 112 at a timing as will be described later. Upon receiving this signal, the image output unit 112 outputs the image signal Sv with reference to the video clock signal VC. In this way, the writing timing adjusting unit 102 adjusts the output timing of the video request signal, thereby adjusting the writing position of the latent image on the photosensitive member 2. In this embodiment, the frequency of the clock signal for timing is set to a value larger than that of the video clock signal VC, for example, four times the frequency of the video clock signal VC. As a result, the video request signal can be controlled with high resolution, and the writing start position of the latent image can be accurately controlled.

  The detection signal Hsync of the scanning light beam from the light detection sensor 60 is also transmitted to the measurement unit 123 of the exposure control unit 12Y, and the measurement unit 123 scans the first scanning range SR1 with the light beam and the driving cycle. The driving information related to is calculated. The actual measurement information calculated by the measurement unit 123 is transmitted to the frequency control unit 122, and the frequency control unit 122 adjusts the resonance frequency of the deflector 65.

  FIG. 6 is a flowchart showing the operation of the image forming apparatus of FIG. 1, and shows the first embodiment of the present invention. In the apparatus configured as described above, when an image formation command is given in a state where the deflector 65 is in a vibration stopped state, the start-up process (step S1) is executed before the start of image formation. After executing the writing timing correction process (step S2) corresponding to the “pre-insertion correction process”, the writing process (steps S3 to S9) is performed while moving the photosensitive member 2 in the sub-scanning direction Y, and the two-dimensional latent Form an image.

  FIG. 7 is a flowchart showing a startup process executed by the image forming apparatus of FIG. FIG. 8 is a diagram showing the operation of the activation process. When this activation process (step S1) is started, the drive control amount for operating the deflector 65 is set to an initial value stored in advance in a memory (not shown) in step S11. More specifically, the electrical characteristic values (frequency, voltage and current) of the mirror drive signal and the signal applied to the resonance frequency adjustment unit 653 are read from the memory and set. Further, the count value N indicating the number of outputs of the detection signal Hsync is reset to zero (step S12).

  Thus, when the initial setting is completed, mirror driving is started with the above-described initial value (step S13). At this time, the amplitude of the deflector 65 gradually increases from zero as shown in FIG. Then, the detection signal Hsync is output from the light detection sensor 60 at a timing when the amplitude reaches the sensor position (Hsync equivalent angle θs), that is, the scanning light beam passes through the light detection sensor 60. Thereby, the emission of the light beam from the laser light source 62 is confirmed, and the write timing correction process (step S2) based on the detection signal Hsync from the light detection sensor 60 is possible.

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

  FIG. 9 is a flowchart showing a write timing correction process executed in the image forming apparatus of FIG. FIG. 10 is a diagram showing the operation of the write timing correction process. Further, FIG. 11 is a diagram showing operations of the reciprocal writing operation and the write timing correction processing. Here, before describing the write timing correction process, the reciprocal write operation will be briefly described. In this embodiment, forward writing and backward writing are executed with reference to the first detection signal Hsync1. More specifically, when the first detection signal Hsync1 is output, a line latent image is generated by the forward light beam for a predetermined writing time Tv from the time when the forward side (first) waiting time Tw1 has elapsed from the output of the signal. Following the writing (outward writing), the line latent image is written by the return light beam for the writing time Tv from the time when the return side (second) waiting time Tw2 has elapsed from the output of the first detection signal Hsync1 (return writing). Included). In the ideal state, as shown in FIG. 11 (a), when the forward side and return side standby times Tw1 and Tw2 are set to preset times Ta and Tw2i, respectively, the position corresponding to the light detection sensor 60 in the photosensitive member 2 is set. The distance Ka from the (sensor position) to the forward writing end of the forward writing and the distance Kb from the forward writing end of the backward writing to the sensor position are substantially the same. Therefore, a relative positional shift in the main scanning direction X does not occur between forward writing and backward writing, and a good image can be formed. However, when the vibration characteristics of the deflector 65 fluctuate due to various factors and deviate from the ideal state, the forward writing and the backward writing are relatively displaced in the main scanning direction X as shown in FIG. End up. In order to solve this problem, a write timing correction process (step S2) is executed.

  This write timing correction process (step S2) is executed by the write timing adjustment unit 102, and corrects the forward-side waiting time Tw1 based on the detection signal Hsync and outputs a video request signal related to the forward write. Adjust. In this embodiment, the initial value (= Tw2i) used for the return side waiting time Tw2 is used as it is, and the timing for outputting the video request signal related to the return pass writing is fixed.

  First, in step S201, the interval time Thi and the sensor arrival time Tb are reset to zero. Here, the “interval time Thi” indicates a time interval between two detection signals Hsync that are continuously output from the light detection sensor 60, and the “sensor arrival time Tb” is the end point of the return path writing. The time from when the return light beam reaches the light detection sensor 60 until the second detection signal Hsync2 is output is shown.

  Then, when the first detection signal Hsync in the write timing correction processing is given to the write timing adjustment unit 102 (determined as YES in step S202), the interval time is based on the clock signal for counting from the count clock generation unit 103. The count-up of Thi is started (step S203). This count-up is executed until it is determined that the next detection signal Hsync is input to the write timing adjustment unit 102 (YES is determined in step S204), whereby the time interval between the two detection signals Hsync is obtained. .

  In the next step S205, the types of detection signals detected in steps S202 and S204 are determined based on the interval time Thi. That is, as shown in FIG. 10, whether the output mode of the detected signal is “second detection signal Hsync2 → first detection signal Hsync1” or “first detection signal Hsync1 → second detection signal Hsync2”. Therefore, the interval time Thi differs greatly. Therefore, in this embodiment, the signal output mode is determined based on whether the interval time Thi is longer or shorter than a predetermined value, and whether the detection signal detected in step S204 is the first detection signal Hsync or the second detection signal Hsync. Judgment.

  When it is determined in step S205 that “first detection signal Hsync1 → second detection signal Hsync2” and the detection signal detected in step S204 is the second detection signal Hsync2, the first detection signal Hsync1 is further determined. After waiting for detection (step S206), the process proceeds to step S207. On the other hand, if it is determined in step S205 that “the second detection signal Hsync2 → the first detection signal Hsync1” and the detection signal detected in step S204 is the first detection signal Hsync1, the process directly proceeds to step S207.

  In step S207, the elapsed time from the output of the first detection signal Hsync1 is measured based on the clock signal for time measurement from the count clock generator 103. When the elapsed time reaches (Tw2i + Tv), the sensor arrival time Tb is measured (steps S209 to S210). That is, the sensor arrival time Tb starts to be counted up based on the clock signal for time measurement from the count clock generator 103 from the time point determined as YES in step S208 (step S209). This count-up is executed until the output of the second detection signal Hsync2 is confirmed (YES is determined in step S210), and thus the sensor arrival time Tb is obtained.

  Therefore, the forward path side waiting time Tw1 is changed to the sensor arrival time Tb (step S211). The reason will be described with reference to FIGS. 11B and 11C. When reciprocal writing is performed in a state deviating from the ideal state, the relative positional deviation amount Kc between the forward writing and the backward writing is equivalent to (Tb−Ta). Therefore, by setting the forward path side waiting time Tw1 as the sensor arrival time Tb, the shift amount Kc can be eliminated and a good image can be formed.

  When the forward waiting time Tw1 is corrected in this way and the write timing correction process is completed, the reciprocal writing (steps S3 to S8) is repeated each time the first detection signal Hsync1 is output (writing process). That is, as shown in FIG. 6, when the first detection signal Hsync1 is output in step S3, measurement of the elapsed time from the output of the first detection signal Hsync1 is started (step S4). Then, when the elapsed time reaches the forward waiting time Tw1 corresponding to the “first waiting time” of the present invention (step S5), a video request signal is output from the writing timing adjusting unit 102 to the image output unit 112. In response to this, the image output unit 112 outputs the image signal Sv with reference to the video clock signal VC and executes the forward writing (step S6).

  Further, when the elapsed time reaches the return path side waiting time Tw2 corresponding to the “second waiting time” of the present invention (step S7), a video request signal is output from the writing timing adjusting unit 102 to the image output unit 112. In response to this, the image output unit 112 outputs the image signal Sv with reference to the video clock signal VC and executes the backward writing (step S8). The series of reciprocal writing (steps S3 to S8) is repeatedly executed until it is determined in step S9 that the writing is finished, and writing of the two-dimensional latent image on the photosensitive member 2 (writing process). Is executed.

  As described above, according to this embodiment, since the write timing correction process is executed before the write process (steps S3 to S9), the forward-side waiting time Tw1 corrected by the correction process is used. The forward writing is performed, and the relative positional deviation between the forward writing and the backward writing in the main scanning direction X is eliminated. As a result, a high quality image is formed.

Second Embodiment
FIG. 12 is a flowchart showing a second embodiment of the image forming method according to the present invention. This embodiment differs greatly from the first embodiment in that a correction process (step S22) similar to the write timing correction process (step S2) is executed every time reciprocal writing (steps S3 to S8) is performed. It is a point. That is, when an image formation command is given, a start-up process (step S1) is executed before image formation is started, and a write timing correction process (step S2) is further executed. Then, reciprocal writing (steps S3 to S8) is repeated while moving the photosensitive member 2 in the sub-scanning direction Y to form a two-dimensional latent image. For this first round-trip write, the forward write timing is adjusted based on the forward waiting time Tw1 corrected by the write timing correction process to prevent a relative positional shift between the forward write and the return write. In addition, the backward write is performed following the forward write. When the backward write is completed, the write timing corresponding to the “writing correction process” of the present invention is performed prior to the next reciprocal write. A correction process (step S22) is executed to correct the outward waiting time Tw1. That is, in the second half of the reciprocal writing, after completion of writing by the return light beam, the sensor arrival time Tb is cleared to zero (step S221), and then the sensor arrival time based on the clock signal for counting from the count clock generation unit 103 is reached. The count up of Tb is started (step S222). This count-up is executed until the output of the second detection signal Hsync2 is confirmed (YES is determined in step S223), and thus the sensor arrival time Tb is obtained. Then, the outward waiting time Tw1 is rewritten to the sensor arrival time Tb (step S224).

  When the correction of the outbound side waiting time Tw1 is thus completed, the process proceeds to step S9 to determine whether or not the writing is finished, and the process returns to step S3 until the writing process is finished. Thereby, when the next first detection signal Hsync1 is output, the reciprocal writing is repeated. However, in the second and subsequent round-trip writing, the forward writing is corrected by the immediately preceding write timing correction process (step S22). On the other hand, the return write is performed at the same write timing (return side waiting time Tw2) as the first time. By correcting the forward path (first) standby time Tw1 while continuously performing the reciprocal writing as described above, even if the vibration characteristic of the deflector 65 fluctuates during execution of the writing process, the follow-up is followed. Thus, the start position of forward writing is adjusted, and the relative positional deviation from the backward writing is eliminated. Therefore, according to this embodiment, it is possible to form a higher quality image.

<Third Embodiment>
FIG. 13 is a flowchart showing a third embodiment of the image forming method according to the present invention. This embodiment differs greatly from the second embodiment in that, instead of the write timing correction process (step S2), the forward path side (first) waiting time Tw1 and the return path side (second) before the write process in advance. The waiting time Tw2 is stored in the memory, and the writing process is started after the waiting times Tw1 and Tw2 are read from the memory before the writing process (step S200). Therefore, in this embodiment, for the first reciprocal writing, the write timing is adjusted based on the waiting times Tw1 and Tw2 stored in the memory to prevent the relative positional deviation between the forward writing and the backward writing. When the backward writing is completed, the writing timing correction process (step S22) is executed prior to the next reciprocal writing to correct the outward waiting time Tw1. For this reason, basically the same effect as in the second embodiment, that is, even if the vibration characteristic of the deflector 65 fluctuates during the execution of the writing process, the start position of the forward writing is adjusted accordingly. Higher quality image formation is possible.

<Fourth embodiment>
FIG. 14 is a main scanning sectional view showing the structure of an exposure unit provided in an image forming apparatus to which the fourth embodiment of the image forming method according to the present invention is applicable. This exposure unit is greatly different from the exposure unit shown in FIG. 3 in that two light detection sensors are provided. Since other configurations are basically the same as those of the first embodiment, the same configurations are denoted by the same reference numerals, description thereof will be omitted, and differences in configuration and operations will be mainly described.

  In this embodiment, as shown in FIG. 14, one end of the scanning path of the scanning light beam is guided to the light detection sensor 60A by the folding mirror 69a. The folding mirror 69a is disposed at one end of the second scanning range SR2, and a scanning light beam that moves on the forward path side (+ X) in the main scanning direction X and moves outside the first scanning range SR1 is applied to the light detection sensor 60A. Light guide. The signal HsyncA is output from the light detection sensor 60A at a timing when the scanning light beam is received by the light detection sensor 60A and passes the sensor position (Hsync equivalent angle θs). As described above, in this embodiment, the light beam scanned in the main scanning direction X by the light detection sensor 60 can be detected in a region outside the first scanning range SR1 on the forward path side (+ X) in the main scanning direction X. The light detection sensor 60A corresponds to the “outward path sensor” of the present invention. Further, one end of the scanning path of the scanning light beam is guided to the light detection sensor 60B by a folding mirror 69b. This folding mirror 69b is disposed at the other end of the second scanning range SR2, and a scanning light beam that moves on the return path side (-X) in the main scanning direction X away from the first scanning range SR1 is detected by the light detection sensor 60B. To guide the light. The signal HsyncB is output from the light detection sensor 60B at a timing when the scanning light beam is received by the light detection sensor 60B and passes through the sensor position (Hsync equivalent angle θs). In order to distinguish these signals, in this specification, the detection signals Hsync corresponding to the detection of the outward light beam by the light detection sensors 60A and 60B are referred to as “first detection signal HsyncA1” and “second detection signal HsyncB2”, respectively. Conversely, the detection signals Hsync corresponding to the detection of the return light beam by the light detection sensors 60A and 60B are referred to as “second detection signal HsyncA2” and “first detection signal HsyncB1”, respectively. Further, when explaining without distinguishing these, they are simply referred to as “detection signal Hsync”.

  As described above, in this embodiment, the light beam scanned in the main scanning direction X by the light detection sensor 60 is detected in the region outside the first scanning range SR1 on the return path side (−X) in the main scanning direction X. The light detection sensor 60B corresponds to the “return path sensor” of the present invention. In this embodiment, the folding mirrors 69a and 69b are disposed substantially symmetrically with respect to the optical axis L0 when the light beam scans the substantial center of the first scanning region SR1. Therefore, the light detection sensors 60A and 60B can be considered to be equivalent to being arranged substantially symmetrically with respect to the optical axis L0.

  The signal Hsync detected in this way is given to the write timing adjustment unit 102 of the engine controller 10. The write timing adjusting unit 102 is supplied with a clock signal for timing from the count clock generating unit 103 of the engine controller 10, and based on this clock signal for timing, the write timing adjusting unit 102 has elapsed from the detection signal Hsync. Time is measured, and a video request signal is output to the image output unit 112 at the timing described below. Upon receiving this signal, the image output unit 112 outputs the image signal Sv with reference to the video clock signal VC. In this way, the writing timing adjusting unit 102 adjusts the output timing of the video request signal, thereby adjusting the writing position of the latent image on the photosensitive member 2.

  FIG. 15 is a flowchart showing the operation of the image forming apparatus shown in FIG. 14, and shows a fourth embodiment of the present invention. In the apparatus configured as described above, when an image formation command is given in a state where the deflector 65 is in a vibration stopped state, the start-up process (step S1) is executed before the start of image formation. After performing the write timing correction process (step S2) corresponding to the “in-process correction process”, the write process (steps S3 to S6, S71 to S73, S8, S9) is performed to form a two-dimensional latent image.

  FIG. 16 is a flowchart showing a write timing correction process executed in the image forming apparatus of FIG. FIG. 17 shows the operation of the write timing correction process. Further, FIG. 18 is a diagram showing operations of the reciprocal writing operation and the write timing correction processing. Here, before describing the write timing correction process, the reciprocal write operation in the fourth embodiment will be briefly described. In this embodiment, the forward writing is executed with reference to the first detection signal HsyncA1, while the backward writing is executed with reference to the first detection signal HsyncB1. More specifically, as shown in FIG. 15, when the first detection signal HsyncA1 is output (step S3), the forward side (first) waiting time Tw1 has elapsed from the signal output (step S5). A line latent image is written by a forward light beam for a predetermined writing time Tv (step S6; forward writing). After this, when the first detection signal HsyncB1 is output (step S71), the return light beam for a predetermined writing time Tv from the time when the return side (second) waiting time Tw2 has elapsed from the signal output (step S73). To write the line latent image (step S8; return path writing). In the ideal state, as shown in FIG. 18 (a), when the forward side and return side standby times Tw1 and Tw2 are set to preset times Ta1 and Ta2, respectively, the position corresponding to the light detection sensor 60A in the photosensitive member 2 is set. The distance Ka1 from the (sensor position) to the forward writing end of the forward writing and the distance Kb2 from the forward writing end of the backward writing to the sensor position are substantially the same. Further, the distance Kb1 from the position corresponding to the light detection sensor 60B (sensor position) on the photosensitive member 2 to the return side writing end for forward writing, and from the return side writing end to the sensor position for backward writing. Is substantially the same as the distance Ka2. Therefore, a relative positional shift in the main scanning direction X does not occur between forward writing and backward writing, and a good image can be formed. However, when the vibration characteristics of the deflector 65 fluctuate due to various factors and deviate from the ideal state, the forward writing and the backward writing are relatively displaced in the main scanning direction X as shown in FIG. End up. In order to solve this problem, a write timing correction process (step S2) is executed.

  This write timing correction process (step S2) is executed by the write timing adjustment unit 102, and corrects the return-side waiting time Tw2 based on the detection signal Hsync and outputs a video request signal related to return-path writing. Adjust. Note that in this embodiment, the initial value (= Ta1) used for the forward path side waiting time Tw1 is used as it is, and the timing for outputting the video request signal related to the forward path writing is fixed.

  First, in the first step S231, the interval time Thi and the sensor arrival time Tb1 are reset to zero. Here, the “sensor arrival time Tb1” indicates the time from the end of the forward writing until the outgoing light beam reaches the backward light detection sensor 60B and the second detection signal Hsync2B is output. Then, when the first detection signal HsyncA is given to the write timing adjustment unit 102 from the forward path side light detection sensor 60A in the write timing correction processing (determined as YES in step S232), the time count from the count clock generation unit 103 is measured. The count-up of the interval time Thi is started based on the clock signal for use (step S233). This count-up is executed until it is determined that the next detection signal HsyncA has been input to the write timing adjustment unit 102 (YES in step S234), whereby the time interval between the two detection signals HsyncA is obtained. .

  In the next step S235, the type of detection signal detected in steps S232 and S234 is determined based on the interval time Thi. That is, as shown in FIG. 17, whether the output mode of the detected signal is “second detection signal HsyncA2 → first detection signal HsyncA1” or “first detection signal HsyncA1 → second detection signal HsyncA2”. Therefore, the interval time Thi differs greatly. Therefore, in this embodiment, the signal output mode is determined based on whether the interval time Thi is longer or shorter than the predetermined value, and whether the detection signal detected in step S234 is the first detection signal HsyncA1 or the second detection signal HsyncA2 is determined. Judgment.

  When it is determined in step S235 that “first detection signal HsyncA1 → second detection signal HsyncA2” and the detection signal detected in step S234 is the second detection signal HsyncA2, the first detection signal HsyncA1 is further determined. After waiting for detection (step S236), the process proceeds to step S237. On the other hand, if it is determined in step S235 that “the second detection signal HsyncA2 → the first detection signal HsyncA1” and the detection signal detected in step S234 is the first detection signal HsyncA1, the process proceeds to step S237 as it is.

  In this step S237, the elapsed time from the output of the first detection signal HsyncA1 is measured based on the clock signal for timing from the count clock generator 103. When the elapsed time reaches the writing time Tv, the sensor arrival time Tb1 is measured (steps S239 to S240). That is, counting up of the sensor arrival time Tb1 based on the clock signal for counting from the count clock generation unit 103 is started from the time point determined as YES in Step S238 (Step S239). This count-up is executed until the output of the second detection signal HsyncB2 from the return path side light detection sensor 60B is confirmed (YES is determined in Step S240), and thus the sensor arrival time Tb1 is obtained.

  Therefore, the return side waiting time Tw2 is changed to the sensor arrival time Tb1 (step S241). The reason will be described with reference to FIGS. 18B and 18C. When reciprocal writing is performed in a state deviating from the ideal state, the relative positional deviation amount Kc between forward writing and backward writing corresponds to (Ta2−Tb1). Therefore, by setting the return-side waiting time Tw2 as the sensor arrival time Tb1, the shift amount Kc can be eliminated and a good image can be formed.

  When the return-side waiting time Tw2 is corrected in this way and the write timing correction processing is completed, the forward-pass writing corresponding to the output of the first detection signal HsyncA1 from the forward-side light detection sensor 60A and the return-side light detection sensor 60B are thereafter performed. To forward writing corresponding to the output of the first detection signal HsyncB1 are alternately repeated (round-trip writing). Such reciprocal writing is repeatedly executed until it is determined in step S9 that the writing has been completed, and writing of the two-dimensional latent image on the photosensitive member 2 (writing process) is executed.

  As described above, in the fourth embodiment as well, as in the first embodiment, the write timing correction process is performed before the write process is executed, so the return-side waiting time corrected by the correction process. The backward writing is performed at Tw2, and the relative positional deviation in the main scanning direction X between the forward writing and the backward writing is eliminated. As a result, a high quality image is formed. In the fourth embodiment, since the light detection sensors 60A and 60B are provided on both sides of the first scanning range SR1, the (+ X) side in the main scanning direction X is defined as the return path side, and the (−X) side is defined as the outbound path. The present invention can also be applied to the image forming apparatus on the side. In this regard, the same applies to a fifth embodiment described later.

<Fifth Embodiment>
FIG. 19 is a flowchart showing the fifth embodiment of the image forming method according to the present invention. This embodiment is greatly different from the fourth embodiment in the following two points. First, in place of the write timing correction process (step S2), the first point stores the forward path side (first) standby time Tw1 and the return path side (second) standby time Tw2 in the memory before the write process. In addition, the writing process is started after the standby times Tw1 and Tw2 are read from the memory before the writing process (step S200). The second point is that a correction process (step S25) similar to the write timing correction process (step S2) is performed every time the forward writing (step S6) is performed. That is, when an image formation command is given, a start-up process (step S1) is executed before starting image formation, and forward writing is performed based on the forward waiting time Tw1 read from the memory. When the forward writing is completed, a correction process (step S25) similar to the write timing correction process (step S22) of the fourth embodiment is executed prior to the next backward writing, and the backward waiting time Tw2 is executed. Correct. That is, after the writing by the forward light beam is completed (step S6), the sensor arrival time Tb1 is cleared to zero (step S251), and then the sensor arrival time Tb1 based on the clock signal for timing from the count clock generator 103 is set. Counting up is started (step S252). This count-up is executed until the output of the second detection signal HsyncB2 from the return path side light detection sensor 60B is confirmed (YES is determined in step S253), and thus the sensor arrival time Tb1 is obtained. Then, the return path side waiting time Tw2 is rewritten to the sensor arrival time Tb1 (step S254).

  When the correction of the return path side waiting time Tw2 is thus completed, the process proceeds to step S71 to wait for the output of the first detection signal HsyncB1 from the return path side light detection sensor 60B. When the first detection signal HsyncB1 is output, the line latent image is generated by the return light beam for a predetermined writing time Tv from the time when the return side (second) waiting time Tw2 has elapsed from the output of the signal (step S73). Writing (step S8; return path writing). As described above, in the forward write, the write timing is adjusted based on the standby time Tw1 read from the memory, while in the backward write, the write timing is adjusted based on the standby time Tw2 corrected by the write timing correction process (step S25). Reciprocal writing is continuously performed while adjusting. This reciprocal writing is repeatedly executed until it is determined in step S9 that the writing is finished, and writing of the two-dimensional latent image on the photosensitive member 2 (writing process) is executed.

  As described above, according to the fifth embodiment, the return side (second) waiting time Tw2 is corrected after the forward pass write and before the return pass write. Therefore, even if the vibration characteristics of the deflector 65 change during the execution of the writing process, the start position of the backward writing is adjusted following the change and the relative positional deviation from the forward writing is eliminated. Therefore, according to this embodiment, it is possible to form a higher quality image.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the sensor arrival times Tb and Tb1 are obtained once and the standby time is corrected in the above embodiment, but the sensor arrival time is obtained several times and the standby time is corrected based on these multiple values. You may comprise.

  In the fourth and fifth embodiments, the light detection sensors 60A and 60B are arranged corresponding to both ends of the second scanning range SR2, but the number and arrangement of the sensors are not limited thereto. Is not to be done. For example, as shown in FIG. 20, the scanning light beam may be detected by one light detection sensor 60C and folding mirrors 69c to 69e. In this case, the mirror 69c and the light detection sensor 60C constitute the “outward path side sensor” of the present invention, while the mirrors 69d and 69e and the light detection sensor 60C constitute the “return path side sensor” of the present invention.

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

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

1 is a diagram illustrating an image forming apparatus to which an image forming method according to the present invention is applicable. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a main scanning sectional view showing a configuration of an exposure unit of the image forming apparatus of FIG. 1. The figure which shows the scanning range of the light beam in the exposure unit of FIG. FIG. 2 is a view showing an exposure unit and an exposure control unit of the image forming apparatus in FIG. 1. 1 is a flowchart showing a first embodiment of an image forming method according to the present invention. 3 is a flowchart showing start-up processing executed by the image forming apparatus in FIG. 1. The figure which shows operation | movement of a starting process. 6 is a flowchart showing a write timing correction process executed in the image forming apparatus. The figure which shows operation | movement of a write timing correction process. The figure which shows operation | movement of a reciprocal writing operation | movement and a write timing correction process. 9 is a flowchart showing a second embodiment of the image forming method according to the invention. 9 is a flowchart showing a third embodiment of the image forming method according to the invention. FIG. 10 is a main scanning sectional view showing a configuration of an exposure unit equipped in an image forming apparatus to which a fourth embodiment of an image forming method according to the present invention can be applied. 9 is a flowchart showing a fourth embodiment of the image forming method according to the invention. The flowchart which shows the write-timing correction process in 4th Embodiment. The figure which shows the operation | movement of the write-timing correction process in 4th Embodiment. The figure which shows operation | movement of a reciprocal writing operation | movement and a write timing correction process. 10 is a flowchart showing write timing correction processing in the fifth embodiment. FIG. 6 is a diagram illustrating another configuration of an image forming apparatus to which the present invention is applicable.

Explanation of symbols

  2, 2Y, 2M, 2C, 2K ... photosensitive member (latent image carrier), 60 ... light detection sensor, 651 ... deflection mirror surface, EIR ... effective image area, Hsync ... detection signal, Hsync1, HsyncA1, HsyncB1 ... first Detection signal, Hsync2, HsyncA2, HsyncB2 ... second detection signal, Tb, Tb1 ... sensor arrival time, Tv ... writing time, Tw1 ... forward path side standby time (first standby time), Tw2 ... return path side standby time (second) (Standby time), X ... main scanning direction, (+ X) ... forward path side (in main scanning direction), (-X) ... return path side (in main scanning direction), Y ... sub-scanning direction

Claims (6)

In the image forming apparatus configured to be capable of reciprocating scanning in the main scanning direction in the second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier by the oscillating deflection mirror surface, A light beam moving at a position outside the first scanning range on one side in the scanning direction is detected by a sensor to obtain a detection signal, and the latent image is supported by a reciprocating scanning light beam based on the detection signal. An image forming method for writing a latent image on a body,
While the latent image carrier is moved in the sub-scanning direction substantially perpendicular to the main scanning direction, the sensor detects a forward light beam that is scanned from the forward path to the backward path that is the other side of the main scanning direction. A writing step of performing the following reciprocal writing each time the first detection signal is output to form a two-dimensional latent image on the latent image carrier;
Before performing the writing step, the second standby time elapses after the first detection signal is output while reciprocating the light beam, and the sensor returns to the return path after the writing time elapses. A pre-writing correction step of obtaining a sensor arrival time as a sensor arrival time after detecting the light beam and outputting a second detection signal, and changing the first standby time to the sensor arrival time. Image forming method.
The reciprocal writing is performed from the output of the first detection signal after the line latent image is written by the forward light beam for a predetermined writing time from the time when the first standby time has elapsed from the output of the first detection signal. A line latent image is written by a return light beam scanned from the return path side to the forward path side for the writing time from the time when the second standby time has elapsed. In each round-trip writing, the following correction process during writing is executed, and in the round-trip writing performed immediately after the correction process during writing, the writing corrected by the correction process during writing is performed. 2. The image forming method according to claim 1, wherein the latent image is written by the forward light beam at the timing, and the latent image is written by the backward light beam at the same writing timing as the previous time.
In the writing correction step, the second standby time elapses after the first detection signal is output, and the sensor detects the return light beam from the time when the writing time elapses. In this step, the time until the detection signal is output is obtained as the sensor arrival time, and the first waiting time is rewritten to the sensor arrival time. In the image forming apparatus configured to be capable of reciprocating scanning in the main scanning direction in the second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier by the oscillating deflection mirror surface, A light beam moving at a position outside the first scanning range on one side in the scanning direction is detected by a sensor to obtain a detection signal, and the latent image is supported by a reciprocating scanning light beam based on the detection signal. An image forming method for writing a latent image on a body,
While the latent image carrier is moved in the sub-scanning direction substantially perpendicular to the main scanning direction, the sensor detects a forward light beam that is scanned from the forward path to the backward path that is the other side of the main scanning direction. A writing step of performing the following reciprocal writing each time the first detection signal is output to form a two-dimensional latent image on the latent image carrier;
A storage step of storing a first waiting time and a second waiting time in a memory before the writing step;
Whenever each reciprocal writing is performed, the second standby time elapses after the first detection signal is output, and the sensor detects the return light beam from the time when the writing time elapses. 2. An image forming method comprising: a correction process during writing in which a time until the two detection signals are output is obtained as a sensor arrival time, and the first standby time is rewritten to the sensor arrival time.
The reciprocal writing is performed from the output of the first detection signal after the line latent image is written by the forward light beam for a predetermined writing time from the time when the first standby time has elapsed from the output of the first detection signal. A line latent image is written by a return light beam scanned from the return path side to the forward path side for the writing time from the time when the second standby time has elapsed. The oscillating deflection mirror surface is configured so that the light beam can be reciprocally scanned in the main scanning direction in a second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier, and in the main scanning direction The forward path sensor that detects a light beam that moves in a position outside the first scanning range on the forward path side that is one side and outputs a detection signal; and the first path path that is the other side in the main scanning direction. A reciprocating scan based on a detection signal output from the forward path sensor and the backward path sensor in an image forming apparatus having a backward path sensor that detects a light beam that moves outside a scanning range and outputs a detection signal An image forming method for performing latent image writing on the latent image carrier by a light beam,
A writing step of forming a two-dimensional latent image on the latent image carrier by performing the following reciprocal writing while moving the latent image carrier in a sub-scanning direction substantially perpendicular to the main scanning direction;
Before performing the writing step, while scanning the forward light beam, the return side sensor detects the forward light beam from the time when the writing time of the forward writing has elapsed, and outputs a second detection signal. An image forming method comprising: a pre-writing correction step of obtaining a time until output as a sensor arrival time and rewriting the return path side waiting time to the sensor arrival time.
The reciprocal writing is a predetermined writing from the time when the forward side waiting time has elapsed after the forward side sensor detects the forward light beam scanned from the forward side to the backward side and outputs the first detection signal. After the forward writing for writing the line latent image with the forward light beam for the set time, and the return light beam scanned from the backward side to the forward side is detected by the return side sensor and the first detection signal is output. The return path writing for writing the line latent image by the return path light beam is alternately performed for a predetermined writing time from the time when the return path side waiting time has elapsed. The following correction process during writing is performed every time each forward writing is performed, and the write timing corrected by the correction process during writing is performed in the backward writing performed immediately after performing the correction process during writing. 5. The image forming method according to claim 4, wherein latent image writing is performed by the backward light beam.
In the writing correction process, the time from when the write time of the forward writing has elapsed until the return side sensor detects the forward light beam and outputs the second detection signal is defined as a sensor arrival time. This is a step of rewriting the return path side waiting time to the sensor arrival time. The oscillating deflection mirror surface is configured so that the light beam can be reciprocally scanned in the main scanning direction in a second scanning range wider than the first scanning range corresponding to the effective image area of the latent image carrier, and in the main scanning direction The forward path sensor that detects a light beam that moves in a position outside the first scanning range on the forward path side that is one side and outputs a detection signal; and the first path path that is the other side in the main scanning direction. A reciprocating scan based on a detection signal output from the forward path sensor and the backward path sensor in an image forming apparatus having a backward path sensor that detects a light beam that moves outside a scanning range and outputs a detection signal An image forming method for performing latent image writing on the latent image carrier by a light beam,
A writing step of forming a two-dimensional latent image on the latent image carrier by performing the following reciprocal writing while moving the latent image carrier in a sub-scanning direction substantially perpendicular to the main scanning direction;
A storage step of storing a first waiting time in a memory before the writing step;
The time from when the write time for the forward writing elapses for each forward writing until the return side sensor detects the forward light beam and outputs the second detection signal is defined as the sensor arrival time. An image forming method comprising: an in-writing correction step having a return-side rewriting step of obtaining and returning the return-side waiting time to the sensor arrival time.
The reciprocal writing is a predetermined writing from the time when the forward side waiting time has elapsed after the forward side sensor detects the forward light beam scanned from the forward side to the backward side and outputs the first detection signal. After the forward writing for writing the line latent image with the forward light beam for the set time, and the return light beam scanned from the backward side to the forward side is detected by the return side sensor and the first detection signal is output. The return path writing for writing the line latent image by the return path light beam is alternately performed for a predetermined writing time from the time when the return path side waiting time has elapsed.

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