JP2006205615A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device which can adjust deviation in a main scanning direction when a plurality of light sources are employed for light exposure. <P>SOLUTION: The image formation device is comprised of a control section, a computing section, and a pixel clock generating section. The control section controls light emission from the plurality of light sources such that laser beams are emitted from the alternately different light sources to scan surfaces of a polygon mirror, and that each surface of the polygon mirror rotating a plurality of times is scanned by laser beams emitted from the alternately different light sources at every rotation. The computing section obtains a difference between intervals of index signals generated by scanning on each surface of the polygon mirror rotating a plurality of times during calibration operation, calculates a deviation of the interval of the index signals on each surface, averages the deviation of the interval of the index signals for each surface, and further calculates the deviation of the plurality of light sources in the main scanning direction. The pixel clock generating section generates pixel clocks as references for use when image data is supplied to the plurality of light sources, and adjusts at least one of the pixel clocks depending on the deviation in the main scanning direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to a multi-function having a function of writing images for a plurality of lines onto a recording medium such as a photosensitive member by a single scan using laser beams from a plurality of light sources. The present invention relates to a beam type image forming apparatus.

  An image forming apparatus that forms an image of one line in the main scanning direction according to image data, and forms an image for one page by repeating image formation for each line in the main scanning direction in the sub-scanning direction. Are known.

  As an example, an electrophotographic image forming apparatus scans a laser beam modulated in accordance with image data in the main scanning direction, and rotates in the sub-scanning direction in parallel with this. Above, an image is formed by the laser beam. In this case, the laser beam is modulated with image data on the basis of a clock signal (pixel clock) called a dot clock.

  In addition, in order to perform image formation at high speed, a light source such as two or three or more laser diodes (LD) is provided, and laser beams from the plurality of light sources are used in the main scanning direction according to the image data. An image forming apparatus that forms an image for one page by repeating image formation for each line in the sub-scanning direction is known. Such a multi-beam type image forming apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 63-124664.

  In order to achieve high image quality with such a multi-beam type image forming apparatus, it is important to align the start positions of the plurality of laser beams in the main scanning direction, that is, to eliminate the main scanning direction deviation between the laser beams. It becomes.

For solving such a deviation in the main scanning direction, for example, various solutions are described in Patent Documents 1 to 3 below.
Japanese Patent Application Laid-Open No. 11-208023 (first page, FIG. 1) Japanese Patent Laying-Open No. 2001-197271 (first page, FIG. 1) Japanese Unexamined Patent Publication No. 2003-266664 (first page, FIG. 1)

  As a result of intensive studies by the inventors of the present application, it has been found that there is a problem as described below even if the main scanning direction deviation is adjusted by the method described in the above patent document.

  Here, in the case of the image forming apparatus described in Patent Document 1 described above, one of the LDs is determined as a reference LD, and the index signal interval is first measured using only the reference LD, and the index signal interval is calculated using only the comparison target LD. The difference from the measured result is obtained. In this case, there is a problem that the measurement accuracy is not so high.

  Further, in the case of the image forming apparatus described in Patent Document 2, the index signal interval corresponding to one rotation of the polygon mirror is measured only by the first LD, and then switched to the second LD, and the index signal interval corresponding to one rotation of the polygon mirror is performed. Is measured only by the second LD, and the deviation in the main scanning direction is calculated from the difference. As a result, since the calculation for one round unit is repeated, it takes time to measure, and the counter length for holding the measurement result for one round unit is also required for one round, which increases the problem.

  In the case of the image forming apparatus described in Patent Document 3, the first LD detects the index signal in the first main scanning direction image forming line, and the second LD detects the index signal in the next main scanning direction image forming line. The time difference (index signal interval) is measured. This is executed a plurality of times and averaged to calculate the main scanning direction deviation between the plurality of beams. In this case, there is a problem that a jitter component for each surface of the polygon mirror appears as an error.

  Note that it is possible to eliminate the main scanning direction deviation with high accuracy by using a dedicated sensor that can detect each of a plurality of laser beams instead of the index signal generated by the index sensor. This is not a preferable solution from the viewpoint of cost increase.

  The present invention has been made to solve the above-described problems, and detects and adjusts the main scanning direction deviation when using a plurality of laser beams for exposure with high accuracy and a simple configuration without the need for additional components. An object of the present invention is to realize a multi-beam type image forming apparatus capable of performing

That is, the present invention as means for solving the problems is as described below.
(1) The invention according to claim 1 is an image forming apparatus that performs scanning for a plurality of lines in parallel by scanning a plurality of laser beams from a plurality of light sources in the main scanning direction, and according to image data. A plurality of light sources that are driven to emit light, a polygon mirror that performs exposure for a plurality of lines in parallel by scanning a plurality of laser beams from the plurality of light sources in the main scanning direction, and a reference position in the scanning of the laser beams An index sensor that generates an index signal indicating exposure timing, and at the time of calibration operation, one of the plurality of light sources is set as a reference light source and the other is set as a light source to be adjusted, and alternately for each surface of the polygon mirror While scanning the laser beams from the different light sources and rotating the polygon mirror a plurality of times, the polygon mirror is rotated on the same surface for each rotation. A controller for controlling the light emission of the plurality of light sources so as to scan laser beams from the different light sources alternately, and the same surface of the polygon mirror while the polygon mirror rotates a plurality of times during the calibration operation. The index for each surface is determined by the difference between the index signal interval when switching from the reference light source to the adjustment target light source and the index signal interval when switching from the adjustment target light source to the reference light source. A calculation unit that calculates a signal interval shift, further calculates an amount of shift in the main scanning direction of the plurality of light sources by averaging the index signal interval shift for each surface, and each of the image data when supplying image data to the plurality of light sources An image for generating a pixel clock as a reference for the light source and adjusting at least one of the pixel clocks according to the amount of deviation in the main scanning direction. A clock generation unit is an image forming apparatus characterized by having a.

  (2) The image forming apparatus according to claim 2, wherein the calculation unit calculates the difference based on a difference between measurement data before and after one rotation of the polygon mirror. It is.

  (3) The invention according to claim 3 is characterized in that the controller slows down the rotational speed of the polygon mirror within a rotational speed range in which the polygon mirror is stably rotated during the calibration operation. The image forming apparatus described.

  (4) The invention according to claim 4 is characterized in that the calculation unit uses a clock faster than the pixel clock for measuring the amount of deviation in the main scanning direction using the index signal interval. The image forming apparatus according to claim 1.

  (5) The image forming apparatus according to claim 5, wherein an image processing clock which is a clock before being separated into data for a plurality of light sources is used as the high-speed clock. It is.

  (6) In the invention according to claim 6, during the calibration operation, when a writing unit including the plurality of light sources and the polygon mirror is replaced, when a temperature fluctuation of the writing unit exceeds a predetermined value, or 6. The image forming apparatus according to claim 1, wherein the image forming apparatus is executed when the power of the image forming apparatus is turned on.

As described above, according to the present invention, the following effects can be obtained.
(1) In the invention of the image forming apparatus according to claim 1, the calibration operation is performed in the image forming apparatus that scans a plurality of laser beams from a plurality of light sources in the main scanning direction and performs exposure for a plurality of lines in parallel. Sometimes, one of the plurality of light sources is set as a reference light source and the other is set as a light source to be adjusted, and laser beams from different light sources are alternately scanned for each surface of the polygon mirror, and the polygon mirror is moved a plurality of times. Control is performed so as to control light emission of a plurality of light sources so that laser beams from different light sources are alternately scanned at each rotation on the same surface of the polygon mirror during the rotation. Here, during the calibration operation, while the polygon mirror rotates a plurality of times, scanning is performed on the same surface of each polygon mirror, and the index signal interval when the reference light source is switched to the light source to be adjusted and the adjustment. The index signal interval deviation for each surface is calculated based on the difference from the index signal interval when the target light source is switched to the reference light source, and the index signal interval deviation for each surface is averaged to calculate the main difference of the plurality of light sources. The amount of deviation in the scanning direction is calculated. Then, the timing of the pixel clock serving as a reference for each light source is adjusted according to the amount of deviation in the main scanning direction.

  In this case, during the calibration operation, laser beams from different light sources are alternately scanned on each surface of the polygon mirror, and alternately on each rotation of the same surface of the polygon mirror while the polygon mirror rotates a plurality of times. Since the emission of multiple light sources is controlled so that laser beams from different light sources are scanned, the index for each surface is determined by the difference in the index signal interval due to scanning on the same surface of the polygon mirror. It is possible to calculate the signal interval deviation with high accuracy.

  Therefore, it is possible to realize a multi-beam type image forming apparatus that can detect and adjust with high accuracy with a simple configuration without adding any parts to the main scanning direction deviation when using a plurality of laser beams for exposure. .

  (2) In the invention of the image forming apparatus according to the second aspect, in the above (1), the difference between the measurement data before and after one rotation of the polygon mirror is calculated as the difference between the index signal intervals. This makes it less susceptible to the effects of polygon mirror rotation unevenness and eliminates the need for additional parts for the main scanning direction misalignment when using multiple laser beams for exposure. And become possible.

  (3) In the invention of the image forming apparatus according to the third aspect, in the above (1), during the calibration operation, the rotation speed of the polygon mirror is controlled to be slower within the range of the rotation speed at which the polygon mirror rotates stably. As a result, the counting clock at the time of calibration operation is relatively increased, and there is no need to add parts for the deviation in the main scanning direction when using a plurality of laser beams for exposure. Detection and adjustment are possible.

  (4) In the invention of the image forming apparatus according to claim 4, in (1) to (3) above, a clock faster than the pixel clock is used for measuring the amount of deviation in the main scanning direction using the index signal interval. Like to do. As a result, the counting clock at the time of the calibration operation is increased, and the main scanning direction deviation when using a plurality of laser beams for exposure can be detected with a simple configuration and higher accuracy without the need for additional components. Adjustment is possible.

  (5) In the invention of the image forming apparatus according to claim 5, in the above (4), an image processing clock which is a clock before being separated into data for a plurality of light sources is used as a clock faster than the pixel clock. Therefore, it is not necessary to prepare a dedicated counting clock, no additional components are required, and detection and adjustment can be performed with high accuracy with a simple configuration.

  (6) In the image forming apparatus according to the sixth aspect, in the above (1) to (5), when the writing unit is replaced, when the temperature fluctuation of the writing unit exceeds a predetermined value, or image formation is performed. The above calibration operation (adjustment of the pixel clock timing based on the amount of deviation in the main scanning direction) is executed at any time when the apparatus is powered on. As a result, it is possible to use the image forming apparatus while performing detection and adjustment with higher accuracy with a simple configuration without adding any parts to the main scanning direction deviation when using a plurality of laser beams for exposure. It becomes possible.

  The best mode (embodiment) for carrying out the present invention will be described below in detail with reference to the drawings. The image forming apparatus to which this embodiment is applied is a multi-beam image forming apparatus that scans a plurality of laser beams from a plurality of light sources in the main scanning direction and performs exposure for a plurality of lines in parallel.

  Hereinafter, the electrical configuration of the first embodiment of the multi-beam image forming apparatus 100 of the present embodiment will be described in detail with reference to FIG. In this embodiment, description will be made mainly on the configuration requirements necessary for performing a calibration operation for calibrating a deviation in the main scanning direction when a plurality of laser beams are used for exposure. Therefore, it is common for an image forming apparatus, and well-known constituent elements are omitted.

  A control unit 101 is configured by a CPU or the like to control each unit of the image forming apparatus 100. In addition to the normal image forming operation, the control unit 101 uses any one of the plurality of light sources as a reference light source during a calibration operation for calibrating a main scanning direction deviation when using a plurality of laser beams for exposure. Others are determined as light sources to be adjusted, and together with an index search control unit to be described later, a laser beam from a different light source is alternately scanned for each surface of the polygon mirror, and the polygon mirror is rotated while the polygon mirror rotates a plurality of times. On the same surface, the light emission of a plurality of light sources is controlled so that laser beams from different light sources are alternately scanned at each rotation.

  In addition, the control unit 101 scans on the same surface of the polygon mirror while the polygon mirror rotates a plurality of times during the calibration operation, and the index signal when the reference light source is switched to the light source to be adjusted. The index signal interval deviation for each surface is calculated based on the difference between the interval and the index signal interval when the light source to be adjusted is switched to the reference light source, and the index signal interval deviation for each surface is averaged to obtain a plurality. The calculation part which calculates the amount of main scanning direction shift | offset | difference of this light source is comprised.

  Reference numeral 103 denotes a pixel having a function of generating a pixel clock serving as a reference for each light source when supplying image data to the light source and adjusting at least one of the pixel clocks in accordance with the amount of deviation in the main scanning direction. The clock generation unit includes an oscillator 104 that generates a reference clock that serves as a reference for the pixel clock, and a delay circuit 105 that adjusts the reference clock so as to eliminate the deviation in the main scanning direction.

  Reference numeral 107 denotes an oscillator that generates a count clock. This count clock is used for measuring the index signal interval, calculating the difference between the index signal intervals, calculating the index signal interval deviation, and calculating the amount of deviation in the main scanning direction. The oscillator 107 generates a clock that is faster than the pixel clock.

Reference numeral 108 denotes an oscillator that generates an image processing clock. This image processing clock is used for various types of image processing in the image processing unit.
Note that the above-described image processing clock that is a clock before being separated into data for a plurality of light sources can be used as a clock faster than the pixel clock generated by the oscillator 107. When such an image processing clock is used, it is not necessary to prepare a dedicated counting clock, no additional components are required, and a simple configuration can be achieved.

  The index signal detection unit 109 is an index sensor that detects the exposure timing of the reference position in the scanning of the laser beam, and generates an index signal indicating the timing.

  An image processing unit 110 performs various types of image processing necessary for image formation on image data. In this embodiment, the image processing unit operates according to an image processing clock, and outputs image data to a frequency conversion unit 115 described later. To do.

  Reference numeral 115 denotes a frequency conversion unit having a FIFO memory, which writes image data output from the image processing unit 110 to the FIFO memory based on the image processing clock, and a plurality of light sources (in this embodiment, LD # in this embodiment). 1 and LD # 2) are read from the FIFO memory. The frequency converter 115 reads the image data for LD # 1 from the FIFO memory in accordance with the pixel clock from the oscillator 104, and the image data for LD # 2 in accordance with the pixel clock that has passed through the delay circuit 105. Read from FIFO memory. That is, in this embodiment, the frequency converter 115 performs image data for LD # 1 on the odd-numbered line in order to perform simultaneous exposure with a plurality of light sources (in this embodiment, LD # 1 and LD # 2). The image data for LD # 2 on the even line is output in parallel.

  120 is an LD control unit that receives image data (parallel data) from the frequency conversion unit 115 and converts the image data into a PWM signal for LD driving. The LD control unit 121 for LD # 1 and the LD control unit for LD # 2 And an LD control unit 122.

  Reference numeral 130 denotes a logic circuit unit that transmits light emission data for causing the selected light source to emit light at the timing of the index search signal during the index search time, and allows image data from the frequency conversion unit 115 to pass during other periods.

  Reference numeral 140 denotes an LD drive unit that drives the LD to emit light from image data at the time of image formation or light emission data at the time of calibration operation. The LD drive unit 141 that drives the LD of LD # 1 to emit light and the LD of LD # 2 drives to emit light. And an LD driving unit 142.

  A light source unit 150 generates a plurality of laser beams for performing exposure by scanning the photosensitive member in the main scanning direction. Here, 2 is taken as a specific example as a plurality of examples, and has LD 151 as LD # 1 and LD152 as LD # 2.

  A polygon driving unit 160 generates a polygon driving signal for driving the polygon mirror to rotate at a predetermined rotation number. A polygon motor 163 receives a polygon driving signal from the polygon driving unit 160 and rotates the polygon mirror 165 at a predetermined number of rotations. Reference numeral 165 denotes a polygon mirror as a rotary polygon mirror that rotates at a predetermined rotation speed, and scans a plurality of laser beams from the LD 151 and LD 152 on the photosensitive drum in the main scanning direction. The laser beams emitted from the LD 151 and the LD 152 scan the photosensitive drum after passing through various optical members such as a cylindrical lens, a collimator lens, and an f-θ lens. Since it is a common image forming apparatus, it is omitted.

  In 170, an electrostatic latent image corresponding to image data is formed by exposure of a laser beam scanned in the main scanning direction and a rotation operation in the sub-scanning direction, and the electrostatic latent image is developed to form a toner image. This is a photosensitive drum as an image carrier. The charging for forming the electrostatic latent image, the toner image formation by developing the electrostatic latent image, the transfer of the toner image onto the recording paper, the fixing of the toner image on the recording paper, etc. are generally used as an image forming apparatus. Therefore, the description is omitted.

  Reference numeral 180 denotes an index search control unit for forcibly causing the LD # 1 or LD # 2 to emit light immediately before the light incident timing to the index sensor, detecting the scanning beam, and controlling the emission of the LD so as to generate an index signal. To do. In the calibration operation, the index search control unit 180 scans laser beams from different light sources alternately for each surface of the polygon mirror, and the same surface of the polygon mirror while the polygon mirror rotates a plurality of times. Then, the light emission of the plurality of light sources is controlled so that the laser beams from the different light sources are alternately scanned at each rotation. Further, the index search control unit 180 includes an index search counter unit 181 and an index search LD selection unit 182. That is, the index search control unit 180 and the control unit 101 constitute a control unit in the claims.

  Reference numeral 190 denotes an LD pitch measurement data capturing unit that holds index signal intervals by scanning on the same surface of the polygon mirror 165 while the polygon mirror 165 rotates a plurality of times during the calibration operation. As shown in FIG. 2, the LD pitch measurement data capturing unit 190 includes a counting circuit unit 191 that counts the index signal interval with a counting clock, a bus switching unit 192 that switches data input and output, and a counting result. And a counting memory unit 193 for storing the index signal interval Tmn.

  Note that the control unit 101 constituting the calculation unit reads data necessary for calculating the amount of deviation in the main scanning direction from the LD pitch measurement data acquisition unit 190, and the amount of deviation in the main scanning direction between LD # 1 and LD # 2. Is calculated.

  Hereinafter, the operation of the image forming apparatus 100 of the present embodiment will be described with reference to the flowcharts of FIGS. 2 and 3 and the time charts of FIGS. 4 and 5. In this example, a polygon mirror 165 having six surfaces is taken as a specific example, and the case where two LDs are used as a plurality of light sources is used as a specific example in the description.

  Either when the power of the image forming apparatus 100 is turned on, when a writing unit including a plurality of light sources and a polygon mirror is replaced, or when the temperature fluctuation of the writing unit exceeds a predetermined value, The control unit 101 performs the following control as a calibration operation. First, the control unit 101 initializes each unit and activates the polygon motor 163 to rotate at a predetermined rotational speed via the polygon driving unit 160 (S31 in FIG. 3).

  The control unit 101 refers to a rotation speed feedback signal (not shown) from the polygon motor 163 or the polygon driving unit 160 and waits until the rotation of the polygon motor 163 is stabilized (S32 in FIG. 3).

  When it is determined that the rotation of the polygon motor 163 is stable (Y in S32 in FIG. 3), the control unit 101 first designates LD # 1 as the initial lighting LD by the LD lighting designation signal MOD. Upon receiving the LD lighting designation signal MOD, the index search LD selection unit 182 designates LD # 1 as the LD selection signal SEL_LD (FIG. 5 (c) (1)), and turns on the LD151 (LD # 1) ( FIG. 3S33). In the calibration operation, the control unit 101 determines any one of a plurality of light sources as a reference light source and the other as a light source to be adjusted. Here, LD # 1 is a reference light source, and LD # 2 is a light source to be adjusted.

  Then, the control unit 101 sets the memory bus right selection signal MEM_SEL for selecting the bus right to the counting memory unit 193 to 0, thereby setting the input from the counting circuit unit 191 (S34 in FIG. 3).

  In this way, by setting the memory bus right selection signal MEM_SEL = 0, in the bus switching unit 192, the address signal ADR to the counting memory unit 193 becomes ADR_A from the counting circuit unit 191 and data input / output of the counting memory unit 193 is performed. DATAI for inputting data from the counting circuit unit 191 is set.

  Furthermore, the control unit 101 sets 1 indicating enable (detection permission) as the index signal detection permission signal DTCT_EN ((L → H) in FIGS. 5A and 5) and permits the counting circuit unit 191 to detect. Notification is made (S35 in FIG. 3).

  The counting circuit unit 191 provided with such an index signal detection permission signal DTCT_EN uses an index signal from the index signal detection unit 109 as a trigger to set an interval from one index signal to the next index signal (index signal interval). Counting is started by the count clock from the oscillator 107 and measurement is started (S36 in FIG. 3).

  In this measurement, laser beams from different light sources (LD # 1 and LD # 2) are alternately scanned for each surface of the polygon mirror 165, and the polygon mirror 165 rotates while the polygon mirror 165 rotates a plurality of times. On the same surface of the polygon mirror 165, the light emission of a plurality of light sources is controlled so that laser beams from different light sources (LD # 1 and LD # 2) are alternately scanned for each rotation.

  Such light emission LD switching control is performed by the LD lighting designation signal MOD from the control unit 101, the count value in the index search counter unit 181 that receives the index signal, and the index search LD selection unit 182 that receives the index signal. This is realized by the LD selection signal SEL_LD output by.

  That is, as shown in FIG. 5 (b), the index signal detection permission signal DTCT_EN = 1 is set, and the first index signal (FIG. 5 (c) (3)) after the detection permission is set is LD # 1. Since it is obtained by performing an index search (FIG. 5 (c) (1)), the next index signal (FIG. 5 (b) (5)) is detected by performing an index search with LD # 2. (FIG. 5 (c) (4), where the surface of the polygon mirror 165 responsible for this portion is the first surface).

  The index signal interval is determined as Tmn when the m-th surface of the polygon mirror 165 is rotated n times, and the index signal interval at this portion is the first surface of the polygon mirror 165. Since it is a one-time rotation, it is treated as T11.

  Similarly, after the index signal (FIGS. 5B and 5) is detected by LD # 2, the next index signal (FIGS. 5B and 7), the surface of the polygon mirror 165 responsible for this part is displayed. 2 side) is detected by performing an index search with LD # 1 (FIGS. 5C and 6).

In this manner, control is performed so that the laser beams from the different light sources (LD # 1 and LD # 2) are alternately scanned for each surface of the polygon mirror 165.
While the polygon mirror 165 rotates a plurality of times of two or more rotations, the same surface (the first surface and the first surface, the second surface and the second surface,...) Of the polygon mirror 165 alternate every rotation. In order to perform index search with laser beams from different light sources (LD # 1 and LD # 2), light emission of a plurality of light sources is controlled.

  That is, after the first index signal (FIGS. 5C and 3) until the next index signal (FIGS. 5B and 5) is detected (during the first rotation of the first surface of the polygon mirror 165). LD # 2 is turned on (FIG. 5 (c) (4)), so the index signal (FIG. 5 (c) (15)) on the sixth surface of the polygon mirror is followed by the next index signal (FIG. 5). 5 (b) (17)) Until the detection (during the second rotation of the first surface of the polygon mirror 165), the LD # 1 is turned on (FIGS. 5C and 16).

  Since the index signal interval T11 is the index signal interval of LD # 1 to LD # 2, the index signal interval T12 is set to be the index signal interval of LD # 2 to LD # 1. Therefore, the period from the index signal (FIGS. 5B and 13) on the fifth surface of the polygon mirror to the detection of the next index signal (FIGS. 5B and 15) (polygon mirror sixth surface) is Then, an index search is continuously performed with LD # 2 (FIGS. 5C, 14 and 16). Although exceeding the range shown in the figure, the fifth and sixth surfaces of the polygon mirror at the time of the next second rotation light up LD # 1 continuously. As described above, since the front and rear surfaces of the sixth surface are caused by lighting of the same LD, the index signal interval T0 that does not include the main scanning direction deviation amount G can be employed.

As described above, the index signal interval and the main scanning direction deviation when the LDs to be driven to emit light are alternated will be described with reference to the time chart of FIG.
Here, as shown in FIG. 6A, the index signal interval of LD # 1 to LD # 1 or the index signal interval of LD # 2 to LD # 2 is T0, and the deviation amount in the main scanning direction is G. .

  FIG. 6B shows an index signal interval T11 (index signal interval of LD # 1 to LD # 2 during the first rotation of the polygon mirror first surface) and an index signal interval T12 (polygon mirror first surface interval). LD # 2 to LD # 1 index signal interval during the second rotation) and index signal interval T13 (index signal interval of LD # 1 to LD # 2 during the third rotation of the polygon mirror first surface) and It is a typical time chart which shows and side by side.

  Actually, index signal intervals T12 to T15 and index signal intervals T22 to T25 exist between T11, T12, and T13, but are omitted here for the sake of simplicity. It has become.

  Here, if the index signal interval of LD # 1 to LD # 1 or LD # 2 to LD # 2 is T0 and the amount of deviation in the main scanning direction is G, as shown in FIG. 6B, T11 is T0 + G, T12 is T0-G and T13 is T0 + G. That is, the main scanning direction deviation of LD # 1 to LD # 2 is added and the main scanning direction deviation of LD # 2 to LD # 1 is subtracted alternately every rotation.

  Accordingly, by calculating G = ((T11−T12) / 2) rather than calculating the amount of deviation G in the main scanning direction at a single index signal interval as G = T11−T0 or G = T0−T12, LD # Since G in the two states 1 to LD # 2 and LD # 2 to LD # 1 is averaged, various errors are canceled out, and the main scanning direction deviation amount G can be calculated with high accuracy.

  As described above, the measurement is performed by rotating the polygon mirror 165 a plurality of times. It should be noted that the multiple times are preferably measured at least twice, preferably for the period of rotation of an integral multiple of 2 (4, 6, 8,...) For further averaging (S37 in FIG. 3). The specific example of FIG. 1 shows a state where index signal intervals T11 to T68 are stored in the count memory unit 193 when the six-sided polygon mirror 165 is rotated eight times.

  The index signal interval Tmn including the main scanning direction deviation amount G is stored in the counting memory unit 193 in accordance with the above-described ADR_A and DATAI. In this embodiment, since data is handled at every index signal interval Tmn, the buffer length and the register length of each unit need only be equivalent to Tmn.

  When the measurement of the index signal interval Tmn including the main scanning direction deviation amount G and the storage in the counting memory unit 193 are completed (Y in S37 in FIG. 3), the stored Tmn is read and the main scanning direction deviation amount is read out. Data processing for calculating G is executed (S38 in FIG. 3).

  This data processing will be described in detail with reference to FIG. First, the control unit 101 sets the output to the control unit 101 by setting the memory bus right selection signal MEM_SEL for selecting the bus right to the counting memory unit 193 to 1 (S41 in FIG. 4).

  By setting the memory bus right selection signal MEM_SEL = 1 in this way, in the bus switching unit 192, the address signal ADR to the counting memory unit 193 becomes ADR_B from the control unit 101, and data input / output of the counting memory unit 193 is controlled. DATAO for outputting data to the unit 101 is set.

  Here, the control unit 101 reads the index signal interval Tmn stored in the count memory unit 193 by designating ADR_B in order (S42 in FIG. 4). In the specific example of FIG. 2, the control unit 101 reads T11 to T68 stored in the counting memory unit 193 as DATAO via the bus switching unit 192.

  First, the control unit 101 averages the index signal intervals T61, T62, T63, T64, T65, T66, T67, and T68 for the sixth surface of the polygon mirror, and the index signal interval T0 does not include the main scanning direction deviation amount G. , T0 = (T61 + T62 + T63 + T64 + T65 + T66 + T67 + T68) / 8 (FIG. 4S43). In this case, since the index signal interval of LD # 1 to LD # 1 and the index signal interval of LD # 2 to LD # 2 are averaged, various errors are canceled and T0 is calculated with high accuracy. Can do.

  Then, the control unit 101 averages the index signal intervals T11, T12, T13, T14, T15, and T16 for the first surface of the polygon mirror, and G1 = the main scanning direction deviation amount G1 for the first surface of the polygon mirror. ((T11-T12) / 2 + (T13-T14) / 2 + (T15-T16) / 2) + (T17-T18) / 2)) / 4 (S44 in FIG. 4). In this case, the index signal interval in the state in which the main scanning direction deviation amount G of LD # 1 to LD # 2 is added and the index signal in the state in which the main scanning direction deviation amount G of LD # 2 to LD # 1 is subtracted. Since the difference from the interval is obtained and further averaged, various errors are canceled out and G1 can be calculated with high accuracy.

  Here, as T11-T12, T13-T14,..., The difference in the index signal interval is calculated from the difference between the measurement data before and after one rotation of the polygon mirror. The situation is not easily affected.

  Then, the control unit 101 averages the index signal intervals T21, T22, T23, T24, T25, and T26 for the second surface of the polygon mirror, and for the main scanning direction deviation amount G1 for the first surface of the polygon mirror, G2 = ((T21-T22) / 2 + (T23-T24) / 2 + (T25-T26) / 2) + (T27-T28) / 2)) / 4 (S45 in FIG. 4). In this case, the index signal interval in the state in which the main scanning direction deviation amount G of LD # 1 to LD # 2 is added and the index signal in the state in which the main scanning direction deviation amount G of LD # 2 to LD # 1 is subtracted. Since the difference from the interval is obtained and further averaged, various errors are canceled out and G2 can be calculated with high accuracy.

  Here, as T21-T22, T23-T24,..., The difference in the index signal interval is calculated by the difference between the measurement data before and after one rotation of the polygon mirror. The situation is not easily affected.

  The control unit 101 averages the index signal intervals T31, T32, T33, T34, T35, and T36 for the third surface of the polygon mirror, and G3 = the main scanning direction deviation amount G1 for the first surface of the polygon mirror. ((T31-T32) / 2 + (T33-T34) / 2 + (T35-T36) / 2) + (T37-T38) / 2)) / 4 (FIG. 4S46). In this case, the index signal interval in the state in which the main scanning direction deviation amount G of LD # 1 to LD # 2 is added and the index signal in the state in which the main scanning direction deviation amount G of LD # 2 to LD # 1 is subtracted. Since the difference from the interval is obtained and further averaged, various errors are canceled out and G3 can be calculated with high accuracy.

  Here, as T31-T32, T33-T34,..., The difference between the measurement data before and after one rotation of the polygon mirror is calculated as the difference between the index signal intervals. The situation is not easily affected.

  The control unit 101 averages the index signal intervals T41, T42, T43, T44, T45, and T46 for the fourth surface of the polygon mirror, and G4 = the main scanning direction deviation amount G1 for the first surface of the polygon mirror. ((T41−T42) / 2 + (T43−T44) / 2 + (T45−T46) / 2) + (T47−T48) / 2)) / 4 (FIG. 4S47). In this case, the index signal interval in the state in which the main scanning direction deviation amount G of LD # 1 to LD # 2 is added and the index signal in the state in which the main scanning direction deviation amount G of LD # 2 to LD # 1 is subtracted. Since the difference from the interval is obtained and further averaged, various errors are canceled out and G4 can be calculated with high accuracy.

  Here, as T41-T42, T43-T44,..., The difference in the index signal interval is calculated by the difference between the measurement data before and after one rotation of the polygon mirror. The situation is not easily affected.

  Then, the control unit 101 averages the index signal intervals T51, T52, T53, T54, T55, and T56 for the polygon mirror fifth surface, and G5 = the main scanning direction deviation amount G1 for the polygon mirror first surface. ((T51-T52) / 2 + (T53-T54) / 2 + (T55-T56) / 2) + (T57-T58) / 2)) / 4 (S48 in FIG. 4). In this case, the index signal interval in the state in which the main scanning direction deviation amount G of LD # 1 to LD # 2 is added and the index signal in the state in which the main scanning direction deviation amount G of LD # 2 to LD # 1 is subtracted. Since the difference from the interval is obtained and further averaged, various errors are canceled out and G5 can be calculated with high accuracy.

  Here, as T51-T52, T53-T54,..., The difference in the index signal interval is calculated from the difference in the measurement data before and after one rotation of the polygon mirror. The situation is not easily affected.

  Further, the control unit 101 includes a main scanning direction deviation amount G1 on the first surface of the polygon mirror, a main scanning direction deviation amount G2 on the second surface of the polygon mirror, a main scanning direction deviation amount G3 on the third surface of the polygon mirror, and a polygon. The main scanning direction displacement amount G4 on the fourth mirror surface and the main scanning direction displacement amount G5 on the fifth surface of the polygon mirror are averaged as G = (G1 + G2 + G3 + G4 + G5) / 5 to calculate the main scanning direction displacement amount G ( FIG. 4S49).

  In this case, the difference in the index signal interval between LD # 1 to LD # 2 and LD # 2 to LD # 1, that is, scanning on the same surface of the polygon mirror while the polygon mirror rotates a plurality of times. The difference between the index signal intervals when the reference light source (here, LD # 1) is switched to the adjustment target light source (here, LD # 2) and the adjustment target light source (here, LD # 2) to the reference light source The difference between the index signal intervals when switching to (here, LD # 1) is obtained and then averaged to calculate the main scanning direction deviation amount Gm for each surface, and further, the main scanning direction deviation amount Gm for each surface. Therefore, it is possible to calculate G with high accuracy in a state where various errors and errors for each surface are offset.

  The control unit 101 that has executed the data processing (S38 in FIG. 3 (S41 to S49 in FIG. 4)) as described above uses the calculated main scanning direction deviation amount G to either one of the pixels of LD # 1 or LD # 2. A delay is provided to the clock using the delay circuit 105 (S39 in FIG. 3). In this embodiment, LD # 1 is used as a reference light source and LD # 2 is used as a light source to be adjusted. Therefore, a delay may be given to the pixel clock on the LD # 2 side. Alternatively, a delay may be given to the pixel clocks of both LDs. That is, the timing of the pixel clock supplied to each of the plurality of light sources is adjusted according to the main scanning direction deviation amount G and its direction.

  In the calibration operation described above, the count clock during the calibration operation is relatively increased by controlling the rotation speed of the polygon mirror 165 as slow as possible within the range of the rotation speed at which it stably rotates. The main scanning direction deviation when using a plurality of laser beams for exposure does not require any additional parts, and can be detected and adjusted with higher accuracy with a simple configuration.

  Further, in the above embodiment, a clock (counting clock) faster than the pixel clock is used for measuring the amount of deviation G in the main scanning direction using the index signal interval. As a result, it is possible to detect and adjust the displacement in the main scanning direction when a plurality of laser beams are used for exposure with a simple configuration and with higher accuracy without adding parts.

  The counting clock is preferably faster than the pixel clock. As a more specific example, it is possible to use an image processing clock, which is a clock before being separated into data for a plurality of light sources, as a high-speed clock. By doing so, it is not necessary to prepare a dedicated counting clock, and the configuration can be simplified.

  In the above embodiment, during the calibration operation, when a writing unit including a plurality of light sources and a polygon mirror is replaced, when the temperature fluctuation of the writing unit exceeds a predetermined value, or when the power of the image forming apparatus is turned on. It is desirable to be performed at any time. By executing the calibration operation of the amount of deviation in the main scanning direction at such timing, it becomes possible to maintain a constant image quality.

<Other embodiment (1)>
In the above embodiment, LD # 1 and LD # 2 are used as a plurality of LDs as specific examples. However, this can also be applied to a multi-beam type image forming apparatus using three or more LDs. is there.

  In this case, LD # 1 is a reference light source, and LD # 2 and LD # 3 are light sources to be adjusted. Then, the difference between the index signal intervals is obtained between LD # 1 and LD # 2 (LD # 1 to LD # 2 and LD # 2 to LD # 1) in the same manner as in the above embodiment, and Performs a calibration operation for deviation in the main scanning direction. Further, the difference between the index signal intervals between LD # 1 and LD # 3 (LD # 1 to LD # 3 and LD # 3 to LD # 1) is obtained in the same manner as in the above embodiment, and LD # 3 is obtained. Performs a calibration operation for deviation in the main scanning direction. In this way, by adjusting the delay of the LD # 2 to the pixel clock and the delay of the LD # 3 to the pixel clock, the multi-beam type image forming apparatus using three or more LDs is adjusted. The embodiment of the present invention can be applied.

<Other embodiment (2)>
In the above embodiment, an electrophotographic image forming apparatus using a laser beam has been described. However, the present invention is not limited to this. For example, each embodiment of the present invention can be applied to various image forming apparatuses such as a laser imager that exposes photographic paper using a laser beam, and good results can be obtained.

1 is a block diagram illustrating an electrical configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of a main part of an image forming apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating an overall operation state of a calibration operation of the image forming apparatus according to the embodiment of the present invention. 5 is a flowchart for explaining an operation state of a main part of a calibration operation of the image forming apparatus according to the embodiment of the present invention. 6 is a time chart for explaining an overall operation state of a calibration operation of the image forming apparatus according to the embodiment of the present invention. 6 is a time chart for explaining an operation state of a main part of a calibration operation of the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

100 Image forming apparatus 101 CPU
109 Index signal detection unit 110 Image processing unit 115 Frequency conversion unit 120 LD control unit 130 Logic circuit 140 LD drive unit 150 Light source (LD)
160 Polygon drive unit 165 Polygon mirror 170 Photosensitive drum 180 Index search control unit 190 LD pitch measurement data capturing unit

Claims (6)

An image forming apparatus that performs exposure for a plurality of lines in parallel by scanning a plurality of laser beams from a plurality of light sources in a main scanning direction,
A plurality of light sources driven to emit light according to image data;
A polygon mirror that performs exposure for a plurality of lines in parallel by scanning a plurality of laser beams from a plurality of light sources in the main scanning direction;
An index sensor that generates an index signal indicating an exposure timing of a reference position in the scanning of the laser beam;
During the calibration operation, one of the plurality of light sources is used as a reference light source and the other is set as a light source to be adjusted, and each surface of the polygon mirror is alternately scanned with a laser beam from the different light sources, and A controller that controls the light emission of the plurality of light sources so that the laser beams from the different light sources are alternately scanned at each rotation on the same surface of the polygon mirror while the polygon mirror rotates a plurality of times;
During the calibration operation, while the polygon mirror rotates a plurality of times, scanning is performed on the same surface of the polygon mirror, and the index signal interval when the reference light source is switched to the adjustment target light source, and the adjustment target The index signal interval deviation for each surface is calculated based on the difference from the index signal interval when the light source is switched to the reference light source, and the index signal interval deviation for each surface is averaged to calculate the main scanning direction of a plurality of light sources. An arithmetic unit for calculating a deviation amount;
A pixel clock that generates a reference pixel clock for each light source when supplying image data to the plurality of light sources, and adjusts at least one of the pixel clocks according to the amount of deviation in the main scanning direction A generator,
An image forming apparatus comprising: The calculation unit calculates the difference as a difference between measurement data before and after one rotation of the polygon mirror.
The image forming apparatus according to claim 1. The controller slows down the rotational speed of the polygon mirror within a range of rotational speed at which it stably rotates during the calibration operation.
The image forming apparatus according to claim 1. The arithmetic unit uses a clock that is faster than the pixel clock for measuring the amount of deviation in the main scanning direction using the index signal interval.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. As the high-speed clock, an image processing clock that is a clock before being separated into data for a plurality of light sources is used.
The image forming apparatus according to claim 4. During the calibration operation, either when the writing unit including the plurality of light sources and the polygon mirror is replaced, when the temperature fluctuation of the writing unit exceeds a predetermined value, or when the image forming apparatus is turned on. To be executed,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.