JP4823922B2 - Optical scanning system - Google Patents

Description

  The present invention belongs to the technical field of image forming apparatuses, and particularly relates to a light irradiation technique for performing exposure by irradiating light on the surface of a photosensitive drum.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a laser beam irradiated from a laser irradiation unit is reflected by each reflecting surface of a rotary polygon mirror to expose the surface of the photosensitive drum, and electrostatically adhere to the surface of the photosensitive drum. Optical scanning devices that form latent images are widely known. Further, in this type of scanning device, a BD sensor that receives a laser beam at a predetermined position is installed, and a technique for setting a light scanning start timing (start position) using an output signal of the BD sensor is disclosed in, for example, the following Patent Document 1 is disclosed.
JP-A-8-72309

  The optical scanning device is configured to be capable of irradiating a plurality of laser beams, and includes a plurality of polygon mirrors that are rotationally driven by different motors, and the irradiation positions of the laser beams are in the main scanning direction and the sub-scanning direction. In some cases, each laser beam is scanned on the surface of the photosensitive drum.

  In the optical scanning device having such a configuration, particularly when the irradiation positions of the respective laser beams are designed to be close to each other, the light receiving surface of the BD sensor is arranged due to an error caused in the operation of the polygon motor or the polygon mirror. The order of passing light rays may change, and when the order of the BD signals changes in this way, a so-called line omission occurs in which a line in which no image is formed is generated at a certain position in the sub-scanning direction.

  For example, it is assumed that the optical scanning device outputs two laser beams, and the BD signal from the laser beam on the side to be incident on the light receiving surface of the BD sensor first determines the timing for starting the beam scanning for image formation. If a laser beam that should be incident later on the light receiving surface of the BD sensor is first incident on the light receiving surface of the BD sensor, the BD signal generated by the laser beam is not recognized. If the BD signal is not recognized, the beam scanning for image formation on the line is not executed, and the above-mentioned line omission occurs at a certain position in the sub-scanning direction.

  Further, in the optical scanning device, when the above-described light beam scanning is executed in the sub-scanning direction, a sub-scanning reference signal that instructs the start of the execution is generated. Here, even if the order of the light beams passing through the light receiving surface of the BD sensor is appropriate, after a part of the laser light beams pass through the light receiving surface of the BD sensor, the remaining laser light beams pass through the light receiving surface of the BD sensor. If the sub-scanning reference signal is output before, the BD signal of the laser beam that has already passed is not recognized, and in this case, the above-described line loss occurs.

The present invention has been made to solve the above problems, to provide an optical run 査Shi stem capable of preventing the occurrence of missing line due to unrecognized of the BD signal as With the goal.

The invention according to claim 1 is a first light source that outputs a first light beam, a second light source that outputs a second light beam, and a reflective surface that reflects the first light beam toward a photoreceptor. And a first rotating polygon mirror that repeatedly scans the first light beam on the surface of the photosensitive member in the main scanning direction by reflecting and rotating the second light beam toward the photosensitive member. A plurality of reflecting surfaces are provided, and the second light beam is predetermined on the surface of the photoconductor in the main scanning direction from the first light beam by being rotated by a driving source different from that of the first rotating polygon mirror. A second rotary polygon mirror that repeatedly scans to be separated by a target distance, and a light beam scanned by the first and second rotary polygon mirrors is received at a predetermined position to perform a photoelectric conversion operation; A BD sensor that outputs a BD signal, and a position of the light beam scanning in the sub-scanning direction; A sub-scanning reference signal for instructing the start of said actual line when going running at different, first output from the BD sensor after the output of the sub-scanning reference signal, based on the second BD signal, Based on the light source control unit for controlling the operation of the light source and the first and second BD signals, a new sub-scanning reference signal for adjusting the start timing of the light beam scanning on the photoconductor is generated. An optical scanning timing adjustment device including a new sub-scanning reference signal generation unit that is used in place of the sub-scanning reference signal by the light source control unit, and the new sub-scanning reference signal generation unit is temporally connected to the BD sensor. A first time from when the first BD signal is output to when the second BD signal is output for the first BD signal and the second BD signal output adjacent to each other, After the BD signal is output, the first When the pair of first and second BD signals to be output continuously through a shorter one of the second times until the D signal is output is a set, the sub-scanning reference When a signal is received, one of the BD signals is already output until the BD signal of the next set of BD signals output immediately after the output timing of the sub-scanning reference signal is output, or at the output timing. The new sub-scanning reference signal is generated until the BD signal of the next set of the set is output.

  According to this invention, the first light beam output from the first light source is scanned in the main scanning direction on the photosensitive member by the first rotary polygon mirror, and the second light beam output from the second light source. The light beam is scanned by the second rotating polygon mirror on the photosensitive member so as to be separated from the first light beam by a predetermined target distance in the main scanning direction. Then, normally, the first BD signal by the first light beam and the second BD signal by the second light beam are temporally continuous from the BD sensor (the first and second BD signals are (Via a minute time difference determined by the target distance and scanning speed). When scanning of one line in the main scanning direction is completed, scanning of the next line in the main scanning direction is performed, and the first and second BD signals are continuously output from the BD sensor again by this scanning. .

  In such a configuration, the first time from the output of the first BD signal to the output of the second BD signal and the output of the first BD signal after the output of the second BD signal are output. When the pair of first and second BD signals to be output continuously through the shorter one of the second times until the second time is taken as one set, the sub-scanning reference signal is received. Until the next BD signal of the set of BD signals output immediately after the output timing of the sub-scanning reference signal is output, or one set of BD signals already output at the output timing. Since the new sub-scanning reference signal is generated before the next set of BD signals is output, the order of the light beams passing through the light receiving surface of the BD sensor changes immediately after receiving the sub-scanning reference signal. Or one light beam passes through the light receiving surface of the BD sensor. When the sub-scanning reference signal is output before the other light beam passes through the light receiving surface of the BD sensor later, the first and second BD signals obtained by the first and second light beams whose order has changed, The first and second BD signals obtained by passing through the light receiving surface of the BD sensor before the output timing of the sub-scanning reference signal and the other light beam passing through the light receiving surface of the BD sensor after the output timing are ignored. The BD signal of the next set of those BD signals is recognized by the light source control unit.

  Therefore, it becomes possible to make the light source control unit recognize the first and second BD signals output continuously in time without any loss, and the light source control unit can recognize the first and second BD signals. The operation of the light source is controlled based on the BD signal.

According to a second aspect of the present invention, in the optical scanning system according to the first aspect , the optical scanning timing adjusting device includes a comparison unit that compares the first time and the second time. Upon receiving the sub-scanning reference signal, the new sub-scanning reference signal generation unit selects the first time when the comparison unit determines that the first time is greater than the second time, Half of the first time is calculated as the new sub-scanning reference signal generation timing setting time, and the new sub-scanning signal is output from the output timing of the first BD signal output for the first time after receiving the sub-scanning reference signal. When a new sub-scanning reference signal is generated at the timing when the scanning reference signal generation timing setting time elapses, and the second time is determined to be greater than the first time by the comparison unit The second time is selected, and the half time of the second time is calculated as the new sub-scanning reference signal generation timing setting time, and the second time output only after receiving the sub-scanning reference signal A new sub-scanning reference signal is generated at the timing when the new sub-scanning reference signal generation timing setting time has elapsed from the output timing of the BD signal.

According to the present invention, when the comparison unit determines that the first time is greater than the second time, the first time is selected, and half the first time is the new sub time. It is calculated as the scanning reference signal generation timing setting time, and is the timing when the new sub-scanning reference signal generation timing setting time has elapsed from the output timing of the first BD signal output for the first time after receiving the sub-scanning reference signal. A new sub-scanning reference signal is generated. Further, when the comparison unit determines that the second time is greater than the first time, the second time is selected, and a time that is half the second time is generated. The new sub-scanning reference is calculated at the timing when the new sub-scanning reference signal generation timing setting time has elapsed from the output timing of the second BD signal that is calculated as the timing setting time and is output for the first time after receiving the sub-scanning reference signal. A signal is generated .

  According to the present invention, the first and second BD signals obtained by the first and second light beams whose order has changed, or one of the light beams passes through the light receiving surface of the BD sensor before the output timing of the sub-scanning reference signal. However, the first and second BD signals obtained by passing the other light beam through the light receiving surface of the BD sensor after the output timing are ignored, and the first and second BD signals of the next set of the BD signals are ignored. Since it becomes possible to make the light source control unit recognize without missing any one of them, it is possible to prevent line omission.

  Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a side view schematically showing an internal configuration of a multifunction peripheral as an example of an image forming apparatus according to an embodiment of the present disclosure. The multifunction device 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multi-function device 1 includes a main body 2, a stack tray 3 disposed on the left side of the main body 2, a document reading unit 5 disposed on the top of the main body 2, and an upper side of the document reading unit 5. And a document feeding unit 6 disposed.

  An operation unit 47 is provided at the front part of the multifunction machine 1. The operation unit 47 displays a start key 471 for a user to input a print execution instruction, a ten key 472 for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. A display unit 473 formed of a liquid crystal display or the like having a touch panel function, a reset key 474 for resetting setting contents set in the display unit 473, and a stop key for stopping a printing (image forming) operation being executed 475 and a function switching key 476 for switching between a copy function, a printer function, a scanner function, and a facsimile function.

  The document reading unit 5 includes a scanner unit 51 including a CCD (Charge Coupled Device) sensor and an exposure lamp, and a document table 52 and a document reading slit 53 made of a transparent member such as glass. The scanner unit 51 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 52, the scanner unit 51 is moved along the document surface at a position facing the document table 52, and the document image is scanned. Image data acquired while scanning is output to an unillustrated image processing unit. Further, when reading a document fed by the document feeding unit 6, the document is moved to a position facing the document reading slit 53 and synchronized with the document feeding operation by the document feeding unit 6 via the document reading slit 53. The image of the original is acquired and the image data is output to the image processing unit.

  The document feeding unit 6 includes a document placing unit 61 for placing a document, a document discharge unit 62 for discharging a document whose image has been read, and a document placed on the document placing unit 61. A document transport mechanism 63 including a paper feed roller (not shown), a transport roller (not shown) and the like for feeding the paper one by one to a position facing the document reading slit 53 and discharging it to the document discharge section 62 is provided. The document conveyance mechanism 63 further includes a sheet reversing mechanism (not shown) that reverses the document and reversely conveys the document to a position facing the document reading slit 53, and scans both sides of the document through the document reading slit 53. 51 can be read.

  The document feeding unit 6 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 6 upward to open the upper surface of the document table 52, the operator can place a read document, for example, a book in a spread state, on the upper surface of the document table 52. It has become.

  The main body 2 includes a plurality of paper feed cassettes 461, a paper feed roller 462 that feeds the recording paper from the paper feed cassette 461 one by one and transports it to the recording unit 40, and a recording paper transported from the paper feed cassette 461. And a recording unit 40 for forming an image.

  The recording unit 40 outputs a laser or the like based on the image data acquired by the scanner unit 51 or the like and exposes the photosensitive drum 43, and a developing unit 44 that forms a toner image on the photosensitive drum 43. A transfer unit 41 that transfers the toner image on the photosensitive drum 43 to the recording paper, a fixing unit 45 that heats the recording paper to which the toner image has been transferred and fixes the toner image on the recording paper, and a recording unit 40. And transport rollers 463, 464, etc. for transporting the recording paper to the stack tray 3 or the discharge tray 48.

  When forming images on both sides of the recording paper, the recording unit 40 forms an image on one side of the recording paper, and then the recording paper is nipped by the conveyance roller 463 on the discharge tray 48 side. . In this state, the conveyance roller 463 is reversed to switch back the recording paper, and the recording paper is sent to the paper conveyance path L and conveyed again to the upstream area of the recording unit 40, and an image is formed on the other surface by the recording unit 40. Thereafter, the recording paper is discharged to the stack tray 3 or the discharge tray 48.

  FIG. 2 is a configuration diagram of the optical scanning device 49. As shown in FIG. 2, an optical scanning device 49 according to the present invention includes a laser irradiation unit 491, a collimator lens 492, a prism 493, a polygon mirror (rotating polygon mirror) 494, an f-θ lens 495, a polygon motor 496, and a beam detector. A saddle sensor (hereinafter referred to as a BD sensor) 497 is provided.

  The laser irradiation unit 491 includes a laser light source (LD). Laser light output from the laser light source is converted into parallel light by a collimator lens 492, a prism 493, and the like. The parallel light is reflected toward the polygon mirror 494 by a reflection mirror (not shown) and is incident on the polygon mirror 494 that is rotating by driving the polygon motor 496.

  The polygon mirror 494 has a plurality of reflection surfaces that reflect the laser beam output from the laser irradiation unit 491 toward the photosensitive drum 43, and the laser beam emitted from the laser irradiation unit 491 is a different reflection surface of the polygon mirror 494. Is reflected toward the photosensitive drum 43. The laser light reflected toward the photosensitive drum 43 by the polygon mirror 494 is imaged in a spot shape having a predetermined diameter on the surface of the photosensitive drum 43 by the f-θ lens 495. The polygon mirror 494 is rotated at a constant speed by a polygon motor 496 in the direction of an arrow in FIG. 2, for example, so that the laser beam is reflected by each reflecting surface and in the rotation axis direction (main scanning direction) of the photosensitive drum 43. The electric charges on the surface of the photosensitive drum 43 are removed by scanning.

  The optical scanning device 49 of this embodiment includes two sets of the members 491 to 496. If these members are referred to as a first LSU 70 and a second LSU 71, the first and second LSUs 70 and 71 are, for example, the polygon mirror 494. They are arranged side by side in the rotation axis direction (direction perpendicular to the paper surface of FIG. 2). The installation form of the first and second LSUs 70 and 71 is not limited to that described above. FIG. 3 is a diagram schematically illustrating the scanning mode of the first and second LSUs 70 and 71 by developing the surface of the photosensitive drum 43. The first and second LSUs 70 and 71 are illustrated in the main scanning direction (arrow D). The light beam scanning is repeated in the direction indicated by. Further, by the rotation of the photosensitive drum 43, the scanning of the first and second LSUs 70 and 71 is executed at different positions in the sub-scanning direction.

  The BD (Beam Detect) sensor 497 is configured using a photodiode, and adjusts the timing of performing light beam scanning (hereinafter referred to as image writing operation) for forming an image on the photosensitive drum 43. It is used for. When the laser beam reflected by the polygon mirror 494 rotating in the direction of the arrow shown in FIG. 2 passes through the f-θ lens 495 and enters the BD sensor 497, a detection signal (in this embodiment, L (low ) Signal) is output. The detection signal (BD signal) of the BD sensor 497 is input to the BD signal conversion unit 102 and then input to the image writing timing adjustment unit 104, and the image writing timing of the laser beam scanned on the surface of the photosensitive drum 43. Used for adjustment.

  The light beam output from the first LSU 70 and the light beam output from the second LSU 71 are connected to different positions in the main scanning direction and the sub-scanning direction on the surface of the photosensitive drum 43 and the light receiving surface of the BD sensor 497, respectively. When these light rays are scanned in the main scanning direction, the position of the spot light by the light rays changes relative to the light receiving surface of the BD sensor 497 as shown in FIGS. . 4A shows a state before the light beams output from the first and second LSUs 70 and 71 pass on the light receiving surface of the BD sensor 497, and FIG. 4B shows the state output from the first LSU 70. 4C shows a state in which only the light beam passing through the light receiving surface of the BD sensor 497 is shown, and FIG. 4C shows the state immediately after the light beam output from the first LSU 70 passes through the light receiving surface of the BD sensor 497. FIG. 4D shows a state immediately before the light beam output from the second LSU 71 passes on the light receiving surface of the BD sensor 497. FIG. 4D shows only the light beam output from the second LSU 71 on the light receiving surface of the BD sensor 497. The state that passes is shown.

  In this way, the light beam output from the first LSU 70 and the light beam output from the second LSU 71 pass through the light receiving surface of the BD sensor 497 through a predetermined minute time difference, as shown in FIG. A BD signal (hereinafter referred to as a first BD signal) output from the BD sensor 497 by a light beam output from the first LSU 70, and a BD signal (hereinafter referred to as a BD signal) output from the BD sensor 497 by a light beam output from the second LSU 71. , The second BD signal) is output in a state shifted by the predetermined time (phase) T1. This time T1 is referred to as a first time T1. In the time chart shown in FIG. 6, the L (low) period is a period in which the light beam that generated the BD signal passes through the light receiving surface of the BD sensor 497, and the H (high) period mainly This is a period of passing over the surface of the photosensitive drum 43.

  In the present embodiment, the distance between the spot lights in the main scanning direction is substantially the same as the width W (see FIG. 4A) of the light receiving surface of the BD sensor 497 in the main scanning direction. The first time T1 is determined by the width W in the main scanning direction on the light receiving surface of the BD sensor 497 and the scanning speed of the light beam in the main scanning direction, and the timing at which the first BD signal switches from L (low) to H (high). And the timing at which the second BD signal is switched from H (high) to L (low) at the same time, the separation distance between the two spot lights in the main scanning direction is the width W in the main scanning direction on the light receiving surface of the BD sensor 497. In this case, the first distance may be determined by the separation distance between the two spot lights in the main scanning direction and the scanning speed of the light beam in the main scanning direction. During T1 is determined, the timing is shifted to switch timing and the 2BD signal first 1BD signal switched from L (Low) to H (high) from H (high) to L (low).

  Returning to FIG. 2, the optical scanning device 49 includes a reference oscillator 8 and a control unit 10 having an image writing timing adjustment unit 104. The reference oscillator 8 outputs a reference clock signal, and the control unit 10 takes an operation timing according to the reference clock signal. The control unit 10 adjusts the image writing timing at the operation timing, and drives and controls the laser irradiation unit 491 based on the image signal of the writing target image output from the image memory 9.

  The control unit 10 includes an LD drive unit 101, a BD signal conversion unit 102, a drawing unit 103, and an image writing timing adjustment unit 104. The drawing unit 103 starts driving of the LD driving unit 101 based on the image signal of the writing target image output from the image memory 9. The LD driving unit 101 drives and controls the laser irradiation unit 491 based on an instruction from the drawing unit 103. The BD signal conversion unit 102 outputs the BD signal output from the BD sensor 497 to the image writing timing adjustment unit 104.

  The image writing timing adjustment unit 104 adjusts the image writing timing for scanning the surface of the photosensitive drum 43 based on the BD signal input from the BD signal conversion unit 102, and outputs the image writing timing to the drawing unit 103.

  By the way, conventionally, when the light beam scanning for image formation is executed at different positions in the sub-scanning direction, a sub-scanning reference signal for instructing the start of the execution is generated, and image writing in the sub-scanning direction is performed. The operation was started based on the BD signal output immediately after receiving the sub-scanning reference signal and receiving the signal.

  In addition, with respect to the BD signal, it has been determined in advance which of the first BD signal and the second BD signal the image writing operation starts. For example, when the first BD signal is set as a reference signal for starting the image writing operation, the image writing operation is started with the first BD signal output from the first LSU 70 as a reference only after the sub-scanning reference signal is output. When the second BD signal is set as a reference signal for starting the image writing operation, the image writing operation is started based on the second BD signal output from the second LSU 71 for the first time after the sub-scanning reference signal is output. The FIG. 15 shows a case where the first BD signal passes on the light receiving surface of the BD sensor 497 earlier than the second BD signal. In this case, the first BD signal is set as the reference signal.

  Focusing on the time difference (phase difference) between the output timings of the first and second BD signals, as shown in FIG. 15A, the time from the timing at which the first BD signal is output to the timing at which the second BD signal is output ( (First time) T1 and time (second time) T2 from the timing when the second BD signal is output to the timing when the first BD signal is output.

  For example, as shown in FIG. 15A, when the first BD signal is set as the reference signal, the longer one of the first and second times T1 and T2 (here, the second time T2). The sub-scanning reference signal is output during the period corresponding to), and the light beams of the first and second LSUs 70 and 71 reach the light receiving surface of the BD sensor 497 in the positional relationship as designed. In response to the first BD signal output for the first time after the output, the image writing operation is executed in order. That is, as shown in FIGS. 15A and 15B, the image writing operation (1) is started with the first BD signal “BD1” as a trigger, and then the image is output based on the second BD signal “BD2”. The writing operation (2) is executed, then the image writing operation (3) is executed based on the first BD signal “BD3”, and then the image writing operation (4) is executed based on the second BD signal “BD4”. ) Is executed. Note that “(1)” to “(4)” in FIG. 15A correspond to “(1)” to “(4)” in FIG. 15B, respectively, and FIG. ) Indicates that an image writing operation has been performed on the surface of the photosensitive drum 43 in the main scanning direction.

  However, the light beams of the first and second LSUs 70 and 71 do not reach the light receiving surface of the BD sensor 497 in the positional relationship as designed, and the positional relationship of the spot light on the light receiving surface of the BD sensor 497 by each light beam changes. As shown by the arrow Z1 in FIG. 16A, when the output order of the first BD signal and the second BD signal changes, the signal is output between the output timing of the sub-scanning reference signal and the output of the first BD signal. The second BD signal BD2 ′ is not recognized as a signal for executing the image writing operation because the first BD signal is set as the reference signal. As a result, as shown in FIGS. 16A and 16B, the image writing operation (2) to be performed based on the BD signal is not performed, and as a result, the image to be formed is not formed. Line missing occurs at a certain position in the direction.

  Furthermore, instead of predetermining a reference BD signal for starting an image writing operation (predetermining whether the reference signal is the first BD signal or the second BD signal), the previously output BD Even when the signal is set to be a reference signal for starting the image writing operation, as shown by an arrow Z2 in FIG. 17, the time in the shorter direction of the first and second times T1 and T2 ( In FIG. 17, when the sub-scanning reference signal is output during a period corresponding to the first time T1), the first BD signal output immediately before the output of the sub-scanning reference signal performs an image writing operation. Is not recognized as a signal. As a result, as shown in FIGS. 17A and 17B, the image writing operation to be performed based on the BD signal is not performed, and as a result, the image to be formed is not formed. Line missing occurs at a certain position in the scanning direction.

  In the present embodiment, in order to eliminate such a problem, the configuration of the image writing timing adjustment unit 104 is configured as shown in FIG. FIG. 5 is a diagram illustrating an electrical configuration of the image writing timing adjustment unit 104. As shown in FIG. 5, the image writing timing adjustment unit 104 includes a first counter 1041, a second counter 1042, a comparison unit 1043, a sub-scanning reference signal generation unit 1044, and a new sub-scanning reference signal generation unit 1045. Is provided.

  The first counter 1041 has first and second BD signals whose output timings are continuous in time, that is, first and second BD signals (hereinafter referred to as the first and second BD signals) that are adjacent to each other with a shorter time difference between the first and second times T1 and T2. The first and second BD signals are expressed as one set), and the first time T1 from the output timing of the first BD signal to the output timing of the second BD signal is measured. The second counter 1042 measures in advance the second time T2 from the output timing of the second BD signal to the output timing of the first BD signal for the first and second BD signals whose output timings are temporally adjacent.

  The comparison unit 1043 compares the first and second times T1 and T2 previously measured by the first and second counters 1041 and 1042, and uses the first BD signal as a reference signal for starting the image writing operation. Or a second BD signal. That is, the comparison unit 1043 sets the second BD signal as the reference signal when the second time T2 is greater than the first time T1, while the first time T1 is greater than the second time T2. If it is larger, the first BD signal is set as the reference signal. The comparison unit 1043 outputs a signal indicating the setting contents to the new sub-scanning reference signal generation unit 1045.

  The sub-scanning reference signal generation unit 1044 generates a sub-scanning reference signal for instructing the start of execution when the light beam for image formation is executed at different positions in the sub-scanning direction. The reference signal is output to the new sub-scanning reference signal generation unit 1045.

  When a sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044, the new sub-scanning reference signal generation unit 1045 generates a new sub-scanning reference signal (hereinafter referred to as a new sub-scanning reference signal (hereinafter referred to as a new sub-scanning reference signal). Scanning reference signal).

  That is, when the first BD signal is set as a reference signal for starting the image writing operation by the comparison unit 1043, in other words, the new sub-scanning reference signal generation unit 1045, as shown in FIG. When the two-hour T2 is larger than the first time T1, as shown in FIG. 7, when the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044, the sub-scanning reference signal is output. A new sub-scanning reference signal is generated at a timing (a timing indicated by an arrow Q1) when a half time T2 / 2 of the second time T2 has elapsed from the output timing of the second BD signal output for the first time.

  As described above, the new sub-scanning reference signal generation unit 1045 generates the new sub-scanning reference signal at the timing and outputs it to the drawing unit 103, whereby the first BD signal output from the first LSU 70 is output from the second LSU 71. Although it should be output before the 2BD signal, the first BD signal output from the first LSU 70 is output after the second BD signal output from the second LSU 71, as indicated by the arrow X1 in FIG. Even if the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044 before the second BD signal, no line omission occurs.

  That is, as shown in FIG. 8, after the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044, the second BD signal and the first BD signal that are continuously output in time are output in this order. In this case, a pair of first and second BD signals (a pair of first and second BD signals whose output order is switched) indicated by an arrow X1 in FIG. 8 immediately after the output of the sub-scanning reference signal is ignored, and the next set The first and second BD signals (first and second BD signals indicated by the arrow Y1 in FIG. 8) are recognized by the drawing unit 103.

  In addition to this, as shown in FIG. 9, when the sub-scanning reference signal is generated between the output timing of the first BD signal by the first LSU 70 and the output timing of the second BD signal by the second LSU 71 (certain Even when the sub-scanning reference signal is generated during the output period of the pair of BD signals), a time T2 that is half the second time T2 from the output timing of the second BD signal that is output for the first time after the output of the sub-scanning reference signal. A new sub-scanning reference signal is generated at the timing when / 2 has elapsed. Therefore, the first and second BD signals (first and second BD signals indicated by the arrow X2 in FIG. 9) in which the generation timing and the output timing of the sub-scanning reference signal overlap are ignored, and the next arrow in FIG. 9 is set. The first and second BD signals indicated by Y2 are recognized by the drawing unit 103, and both the first and second BD signals output continuously in time are recognized by the drawing unit 103.

  On the other hand, when the second BD signal is set as a reference signal for starting the image writing operation by the comparison unit 1043, the new sub-scanning reference signal generation unit 1045, as shown in FIG. When the one-time T1 is larger than the second time T2, as shown in FIG. 11, when the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044, the sub-scanning reference signal is output. A new sub-scanning reference signal is generated at a timing (a timing indicated by an arrow Q2) when a half time T1 / 2 of the first time T1 has elapsed from an output timing of the first BD signal output for the first time.

  As described above, the new sub-scanning reference signal generation unit 1045 generates the new sub-scanning reference signal at the timing and outputs it to the drawing unit 103, so that the first BD signal should be output after the second BD signal. Nevertheless, as indicated by an arrow X3 in FIG. 12, the second BD signal is output after the first BD signal, and the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044 before the first BD signal. Even in such a case, line omission (a line where no image is formed) does not occur.

  That is, as shown in FIG. 12, after the sub-scanning reference signal is output from the sub-scanning reference signal generation unit 1044, the first BD signal and the second BD signal that are continuously output in time are output in this order. In this case, a pair of first and second BD signals (a pair of first and second BD signals whose output order is switched) indicated by an arrow X3 in FIG. 12 immediately after the output of the sub-scanning reference signal is ignored, and the next set The first and second BD signals (the next BD signals of the first and second LSUs 70 and 71 indicated by the arrow Y3 in FIG. 12) are recognized by the drawing unit 103.

  In addition to this, as shown in FIG. 13, when the sub-scanning reference signal is generated between the output timing of the second BD signal by the second LSU 71 and the output timing of the first BD signal by the first LSU 70 (certain Even when the sub-scanning reference signal is generated during the output period of the pair of BD signals), the time T1 which is half the first time T1 from the output timing of the first BD signal output for the first time after the output of the sub-scanning reference signal A new sub-scanning reference signal is generated at the timing when / 2 has elapsed. Therefore, the first and second BD signals (first and second BD signals indicated by arrow X4 in FIG. 13) in which the generation timing and output timing of the sub-scanning reference signal overlap are ignored, and the next arrow in FIG. 13 is set. The first and second BD signals indicated by Y4 are recognized by the drawing unit 103.

  According to these processes, the timing of starting the light beam scanning for image formation is delayed by one line or two lines, and as a result, the image formation position on the recording paper is shifted by one line or two lines. When the positional relationship of the spot light on the light receiving surface of the BD sensor 497 by each light beam changes, or during the period corresponding to the shorter time of the first and second times T1 and T2, the sub-scanning reference Even if a signal is output, the first and second BD signals that are continuous in time are recognized by the drawing unit 103 as a pair without being lost, and line omission occurs in the middle of the sub-scanning direction. It can be prevented from occurring. It should be noted that since the amount of displacement of the image formation position is very small, there is almost no problem.

  The drawing unit 103 illustrated in FIGS. 2 and 5 includes a new sub-scanning reference signal generated by the sub-scanning reference signal update unit 1045 and first and second BDs output after the output of the new sub-scanning reference signal. Based on the signal, the driving of the LD driving unit 101 is started based on the image signal of the image to be written output from the image memory 9.

  FIG. 14 is a flowchart showing image write timing adjustment processing by the control unit 10.

  As shown in FIG. 14, the control unit 10 includes a first time T1 from the output timing of the first BD signal to the output timing of the second BD signal for the first and second BD signals whose output timings are temporally continuous, The second time T2 from the output timing of the 2BD signal to the output timing of the first BD signal is compared (step # 1), and when the first time T1 is equal to or greater than the second time T2 (YES in step # 1); In the case of the mode shown in FIG. 10, when the sub-scanning reference signal and the first BD signal are output (YES in steps # 2 and # 3), a time T1 that is half the first time T1 from the output timing of the first BD signal. After a lapse of / 2, a new sub-scanning reference signal is generated (step # 4), and the operation of the laser irradiation unit 491 is controlled based on this new sub-scanning reference signal (step # 5).

  On the other hand, when the first time T1 is smaller than the second time T2 (NO in step # 1; in the case shown in FIG. 6), the control unit 10 outputs the sub-scanning reference signal and the second BD signal (step S1). # 6, YES at step # 7), a new sub-scanning reference signal is generated after a time T2 / 2 half the second time T2 has elapsed from the output timing of the second BD signal (step # 8). Based on the above, the operation of the laser irradiation unit 491 is controlled (step # 5).

  As described above, for the first and second BD signals whose output timings are continuous in time, the first time T1 from the output timing of the first BD signal to the output timing of the second BD signal and the output timing of the second BD signal When the first time T1 is equal to or greater than the second time T2, the first BD signal is output when the sub-scanning reference signal and the first BD signal are output. A new sub-scanning reference signal is generated after the time T1 / 2, which is half of the first time T1, has elapsed from the output timing, and when the first time T1 is smaller than the second time T2, the sub-scanning reference signal and the second BD signal are output. Then, the new sub-scanning reference signal is generated after the time T2 / 2, which is half of the second time T2, from the output timing of the second BD signal. The sub-scanning reference signal is output when the positional relationship of the spot light on the light receiving surface of the BD sensor 497 changes or during a period corresponding to the shorter time of the first and second times T1 and T2. Even in such a case, the drawing unit 103 can recognize the first and second BD signals that are temporally continuous without missing one, and it is possible to prevent occurrence of line omission in the sub-scanning direction. it can.

  In addition, this case includes the following forms instead of or in addition to the above embodiments.

  (1) In the above-described embodiment, the generation timing of the new sub-scanning reference signal is set to the timing at which half the first time T1 or the second time T2 has elapsed from the output timing of the first BD signal or the second BD signal. For example, the generation timing of the new sub-scanning reference signal is 2/3 of the first time T1 or the second time T2 from the output timing of the first BD signal or the second BD signal. The generation timing of the new sub-scanning reference signal may be a parameter such as the scanning speed of the light beam or the length of the photosensitive drum 43 in the rotation axis direction. It is good to decide according to.

  (2) The LD drive control unit 101 and the image writing timing adjustment unit 104 (the first and second counters 1041 and 1042, the comparison unit 1043, the new sub-scanning reference signal generation unit 1045, and the drawing unit 103) Aside from the reference signal generation unit 1044, an ASIC (Application Specific IC) may be configured.

1 is a side view schematically showing an internal configuration of a multifunction peripheral as an example of an image forming apparatus according to an embodiment of the present disclosure. It is a block diagram of an optical scanning device. FIG. 5 is a diagram illustrating a scanning mode of the first and second LSUs by developing the surface of the photosensitive drum. It is a figure which shows the relationship between the position of the spot light by each light beam output from 1st, 2nd LSU, and the position of the light-receiving surface of a BD sensor, and its change. It is a figure which shows the electrical structure of an image writing timing adjustment part. It is a figure which shows an example of the signal waveform of the BD signal output from a BD sensor by the light ray output from 1st, 2nd LSU. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal, and is a figure which shows the output waveform of a BD signal when the output order of a 1st, 2nd BD signal changes especially. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal, and especially when a subscanning reference signal is produced | generated between the output timing of the 1st BD signal, and the output timing of the 2nd BD signal. It is a figure which shows the output waveform of no BD signal. It is a figure which shows an example of the signal waveform of the BD signal output from a BD sensor by the light ray output from 1st, 2nd LSU. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal, and is a figure which shows the output waveform of a BD signal when the output order of a 1st, 2nd BD signal changes especially. It is a figure which shows the output waveform of a subscanning reference signal, a new subscanning reference signal, and a BD signal, and especially when a subscanning reference signal is produced | generated between the output timing of a 2nd BD signal, and the output timing of a 1st BD signal. It is a figure which shows the output waveform of no BD signal. It is a flowchart which shows an image writing timing adjustment process. It is a figure which shows an example of the signal waveform of the BD signal in the normal case. It is a figure for demonstrating a problem. It is a figure for demonstrating a problem.

10 control unit 49 optical scanning device 70, 71 first and second LSU
DESCRIPTION OF SYMBOLS 101 LD drive part 102 BD signal conversion part 103 Drawing part 104 Image writing timing adjustment part 491 Laser irradiation part 496 Polygon motor 497 BD sensor 1041,1042 1st, 2nd counter 1043 Comparison part 1044 Subscanning reference signal generation part 1045 New sub Scanning reference signal generator

Claims (2)

A first light source that outputs a first light beam;
A second light source that outputs a second light beam;
A first rotating polygon mirror that includes a plurality of reflecting surfaces that reflect the first light beam toward the photoconductor, and that repeatedly rotates the first light beam on the surface of the photoconductor in the main scanning direction by performing a rotation operation. When,
A plurality of reflecting surfaces for reflecting the second light beam toward the photoconductor, and receiving a rotational drive by a driving source different from the first rotary polygon mirror, the second light beam on the surface of the photoconductor, A second rotary polygon mirror that repeatedly scans the main scanning direction so as to be separated from the first light beam by a predetermined target distance;
A BD sensor that receives a light beam scanned by the first and second rotary polygon mirrors at a predetermined position, performs a photoelectric conversion operation, and outputs a BD signal;
When the light beam scanning is executed with different positions in the sub-scanning direction, a sub-scanning reference signal for instructing the start of the execution, and a first and a first output from the BD sensor after the output of the sub-scanning reference signal A light source control unit for controlling the operation of the light source based on the second BD signal ;
Based on the first and second BD signals, a new sub-scanning reference signal for adjusting the light scanning start timing on the photoconductor is generated, and the light source control unit generates the sub-scanning reference signal. An optical scanning timing adjustment device including a new sub-scanning reference signal generation unit to be used instead,
The new sub-scanning reference signal generator is
The first BD signal and the second BD signal that are output side by side from the BD sensor in the first period from when the first BD signal is output until the second BD signal is output. A pair of first signals to be output continuously over a shorter time of the first time and the second time from when the second BD signal is output until the first BD signal is output. When the sub-scanning reference signal is received when the second BD signal is one set, the next set of BD signals output immediately after the sub-scanning reference signal output timing is output. by, or said the one of the BD signal at the output timing is one that already produces a sub scanning reference signal said new until the next set of set of BD signal being output is output an optical scanning system. The optical scanning timing adjustment device includes a comparison unit that compares the first time and the second time.
The new sub-scanning reference signal generator is
When the sub-scanning reference signal is received, the first time is selected when the comparison unit determines that the first time is greater than the second time, and the half time of the first time is selected. The new sub-scanning reference signal generation timing setting time is calculated and only the new sub-scanning reference signal generation timing setting time from the output timing of the first BD signal output for the first time after receiving the sub-scanning reference signal. A new sub-scanning reference signal is generated at the elapsed time,
When the comparison unit determines that the second time is greater than the first time, the second time is selected, and half the second time is set as the new sub-scanning reference signal generation timing setting. And a new sub-scanning reference at the timing when the new sub-scanning reference signal generation timing setting time has elapsed from the output timing of the second BD signal output for the first time after receiving the sub-scanning reference signal. The optical scanning system according to claim 1, which generates a signal.

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