JP5441742B2 - Image forming apparatus and light amount correction method thereof - Google Patents

Description

  The present invention relates to an image forming apparatus that controls an exposure amount of a photoconductor according to an exposure position and a light amount correction method thereof in order to correct a density variation of an output image caused by a variation in potential characteristics on the surface of the photoconductor.

  In an electrophotographic image forming apparatus, first, the surface of the photosensitive drum is uniformly charged, and then the photosensitive drum is exposed.

  2. Description of the Related Art In recent years, the performance of electrophotographic image forming apparatuses has been improved, and a technology has been developed that can improve the immediate responsiveness of printing, the printing speed, the printing image quality, and the low cost. In particular, in a laser scanning printer, the number of light beams scanned at a time is increased to 2, 4, etc., the individual laser spots are reduced, and the scanning line interval is reduced to 600 dpi, 1200 dpi, etc. The printing speed and the printing resolution are improved.

  Since the manufacturing accuracy is limited, it is difficult to make the thickness of the photosensitive layer of one photoconductor uniform when manufacturing the photoconductor. If the thickness of the photosensitive layer varies, the charge amount varies for each surface of the photosensitive drum even when charged with the same bias. Even if the photosensitive drum is exposed with the same amount of light, the amount of potential attenuation differs for each exposure position. In other words, even when charged and exposed under the same conditions, the thickness of the photosensitive layer varies, so the potential of the electrostatic latent image does not become uniform at each position on the surface of the photosensitive drum, resulting in uneven density in the output image. End up.

  In response to such a problem, Patent Document 1 discloses the following. The exposure position where the laser beam exposes the photosensitive drum is detected, and the light amount correction data stored in the memory is read according to the detection result. The laser driving unit drives the light emitting element based on the input image data and the correction data. As described above, the variation in the potential characteristic of the photosensitive drum is corrected by adjusting the laser exposure amount by the correction data read from the memory in accordance with the exposure position. As a result, the print image quality is improved, and even if the photosensitive drum has a large variation in thickness, the print image quality can be maintained by adjusting the laser exposure amount, so that the yield of the photosensitive drum can be improved.

JP 2007-187829 A

  However, when the conventional image forming apparatus method is applied to an image forming apparatus that exposes a photosensitive drum with multi-beams, the following problems occur. In the conventional configuration described above, in an image forming apparatus that scans a photosensitive member with a plurality of laser beams in a single scan with laser beams emitted from a plurality of light emitting elements, an exposure position during operation is detected for each light emitting element. Since correction data needs to be read from the memory based on the detection result, a circuit must be provided for each light emitting element. This causes a problem that the circuit scale provided in the image forming apparatus increases.

  Therefore, the present invention increases the circuit scale for reading correction data from the memory when correcting the variation in potential characteristics, even when the photosensitive drum is exposed by light beams emitted from a plurality of light emitting elements. An object of the present invention is to provide an image forming apparatus that can be suppressed and a light amount correction method thereof.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a photoconductor, first and second light-emitting elements that emit light for exposing the photoconductor, and the first light-emitting element. Deflection scanning means for simultaneously deflecting and scanning the light emitted from the element and the second light emitting element, and in one scan by the deflection scanning means, the light emitted from the first light emitting element is the photoreceptor. The first light emitting element is arranged with respect to the second light emitting element so that the exposure position for exposing the light and the exposure position for exposing the light emitted from the second light emitting element to the photosensitive member are different. Exposure means; storage means for storing correction data for correcting the amount of light emitted from the first light emitting element in association with the position of the surface of the photoconductor; and the first light emitting element serving as the photoconductor. Depending on the exposure position to be exposed. Reading the correction data from the means, and having a correction means for correcting the amount of light emitted from the first light emitting element and the second light emitting element based on the correction data.

  According to the image forming apparatus of the first aspect of the present invention, even when the photosensitive member is exposed by the light beams emitted from the plurality of light emitting elements, the correction data is read from the memory when correcting the variation in potential characteristics. Can be suppressed from increasing in circuit scale.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic diagram showing a configuration of an optical scanning device in an image forming apparatus and a photosensitive drum on which an electrostatic latent image is formed by the optical scanning device. 6 is a flowchart illustrating an image forming operation procedure and a photosensitive unevenness correction operation procedure. It is a figure which shows the drum nonuniformity correction state of a certain moment during photosensitive nonuniformity correction. It is a figure which shows the drum nonuniformity correction state after 1 microsecond progress. It is a figure which shows the drum nonuniformity correction state after 2 microsecond progress. It is a figure which shows arrangement | positioning of the correction data at the time of performing the photosensitive nonuniformity correction in 2nd Embodiment. It is a figure which shows the linear interpolation calculation of correction data. It is a figure which shows the drum nonuniformity correction | amendment state when a linear interpolation calculation is performed. It is a figure which shows the profile of the correction data at the time of performing a linear interpolation calculation when it is divided into 8 in the main scanning direction and the sub-scanning direction in the 4 × 4 block. It is a figure which shows the linear interpolation calculation of the photosensitive nonuniformity correction data in case the relationship between a laser writing shift | offset | difference correction amount and the pitch of a linear interpolation unit does not become an integer ratio.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus and a light amount correction method thereof according to the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus according to the first embodiment. The configuration of an electrophotographic image forming apparatus and an image forming process will be described with reference to FIG. The image forming apparatus includes an image reader unit 11 and a printer unit 13 that read an image of a document. The image reader unit 11 includes a document feeding device 12.

  In the printer unit 13, the photosensitive drum 130, which is an image carrier uniformly charged by the charging device 112, is emitted from the semiconductor laser 113 in the optical scanning device 100 based on the input image data ( Light beam). The photosensitive drum 130 rotates at a constant speed, and the photosensitive surface of the photosensitive drum 130 moves in the sub-scanning direction (rotating direction) with respect to the light beam. In this way, an electrostatic latent image based on the image data is formed on the photosensitive drum 130. The electrostatic latent image is developed with toner which is a developer held in the developing device 114. Thereafter, a bias is applied to the transfer roller 116 serving as a transfer device. As a result, in the transfer portion formed by the transfer roller 116 and the photosensitive drum 130, the toner image carried on the photosensitive drum 130 is transferred from the cassette 118, 119 or the like via the registration roller 117 (recording material). Material).

  Then, the transfer material carrying the toner image is conveyed to the fixing device 132, and the toner image on the transfer material is fixed by heating or the like. In this way, a transfer material on which an image is formed is obtained.

  FIG. 2 is a schematic diagram showing a configuration of an optical scanning device in the image forming apparatus and a photosensitive drum on which an electrostatic latent image is formed by the optical scanning device. This image forming apparatus is an electrophotographic printer that employs a writing system that simultaneously scans one photosensitive drum with four laser beams. The exposure apparatus in FIG. 2 includes a multi-beam laser light writing unit (optical scanning device) 100, a system control unit 140, an image data processing unit 150, a photosensitive drum 130, and the like.

  The system control unit 140 controls the entire apparatus, and includes a CPU, a ROM, a RAM, a user interface (not shown) for controlling devices, and the like. The image data processing unit 150 is configured by an ASIC, and operates while performing information communication with each other by register access from the CPU in the system control unit 140.

  The multi-beam laser beam writing unit 100 forms a latent image by irradiating the surface of the photosensitive drum 130 with a laser beam, and functions as an exposure unit. The multi-beam laser beam writing unit 100 is provided with a 4-beam multi-laser semiconductor chip 101, a collimator lens 102, a polygon mirror 103, an fθ lens 104, a laser current driving unit 106, and a polygon mirror motor driving unit (polygon motor) 103a. ing.

  The 4-beam multi-laser semiconductor chip 101 has a plurality of light emitting elements (including a first light emitting element and a second light emitting element) that emit laser light for exposing the photosensitive drum 130. In the first light emitting element, the exposure position where the laser light emitted from the first light emitting element exposes the photosensitive drum 130 is emitted from the second light emitting element in the scanning direction of the laser light. The laser beam is arranged with respect to the second light emitting element so as to precede the exposure position for exposing the photosensitive drum 130.

  The polygon mirror motor drive unit (polygon motor) 103a drives the polygon mirror 103 that simultaneously deflects and scans the laser beams emitted from a plurality of light emitting elements (first light emitting element and second light emitting element).

  The image forming apparatus according to the present exemplary embodiment is provided with a DC brushless motor (drum motor) 136 that rotates the photosensitive drum 130. A BD 134 (Beam Detector) that generates a BD signal for determining a scanning start position in the direction in which the laser beam is scanned (main scanning direction) is provided on the side of the photosensitive drum 130. From the BD 134, a BD signal which is a synchronization signal is generated. The BD signal is input to the system control unit 140. The CPU in the system control unit 140 outputs an enable signal that permits emission of laser light to the laser current driving unit 106 in response to the input of the BD signal. The laser current driving unit 106 transmits a control signal to the light source so as to emit laser light when a PWM (Pulse Width modulation) signal based on image data is input from the PWM modulator 155 during the period when the enable signal is input. To do.

  A rotation reference position sensor 120 that reads a rotation position mark 121 provided on the side surface of the photosensitive drum 130 and outputs a rotation reference position signal 122 is provided on the circumference of the photosensitive drum 130. When the photosensitive drum 130 rotates, a detection signal (rotation reference signal) is generated by the rotation reference position sensor 120 in response to the rotation position mark 121 passing through the detection surface of the rotation reference position sensor 120. This detection signal is input to the system control unit 140.

  The image data processing unit 150 includes a line buffer control unit 152, a photosensitive drum unevenness correction image processing unit (multiplication unit) 154, a laser PWM modulator 155, a delay holding unit 164, a table memory (nonvolatile memory) 160, and a photosensitive unevenness. A correction unit 161 is provided. The line buffer control unit 152 is provided with a line buffer 153 for inputting image data.

  The delay holding unit 164 (correction data holding means) is provided with a ring buffer address counter 182, a ring buffer address decoding unit 184, ring buffers A0 to A4, and a ring buffer read selector 178. The operation of each of these units will be described later.

  The table memory 160 (storage means) holds (stores) correction data (table data) for photosensitive drum unevenness (photosensitive unevenness) prepared in advance in accordance with the photosensitive drum provided in the image forming apparatus. That is, the table memory 160 holds correction data in accordance with the main scanning position of the photosensitive drum for correcting the photosensitive unevenness generated on the photosensitive drum 130. The photosensitive unevenness correction unit (memory controller) 161 includes an address calculation unit 170 that calculates an address of correction data held in the table memory 160, and the correction data to match the data multiplied by the image data. The matching processing unit 163 is provided. Further, the photosensitive unevenness correction unit 161 is provided with a counter memory (not shown), a hardware counter (not shown) that measures the clock of the crystal oscillator, and the like.

  Further, the image forming apparatus is provided with a DC brushless motor (drum motor) 136 that rotates the photosensitive drum 130. Further, a BD sensor 134 that generates a BD signal indicating a scanning start position is provided on the side of the photosensitive drum 130. A rotation reference position sensor 120 that reads a rotation position mark 121 provided on the side surface of the photosensitive drum 130 and outputs a rotation reference position signal 122 is provided on the shaft periphery of the photosensitive drum 130.

  FIG. 3 is a flowchart showing an image forming operation procedure and a photosensitive unevenness correcting operation procedure. FIG. 4A shows the operation of the CPU in the system control unit 140. FIG. 4B shows the operation of the image data processing unit 150 (ASIC). In the drawing, information transmission by input / output signals of each device is indicated by a broken line.

  The operation of the image forming apparatus will be described with reference to FIGS. As an initial state, the system control unit 140 sets the image forming apparatus in a state where the image formation is stopped and the drum is stopped, and stands by (step S101). On the other hand, as an initial state, the image data processing unit 150 is in a state where the drum is stopped and the unevenness correction processing is also invalid, that is, the state in which unevenness correction is not performed.

  The system control unit 140 waits for an instruction to start image formation (step S102). When instructed to start image formation, the system control unit 140 instructs activation of the drum drive unit 136 and the polygon motor 103a, and starts an image formation preparation operation (step S103). In this image formation preparation operation, the drum driving unit 136 starts driving the photosensitive drum 130 in accordance with the rotation instruction signal 141 to the drum driving unit. At the same time, the polygon mirror motor driving unit (polygon motor) 103a starts driving to rotate the polygon mirror 103 at a constant speed in accordance with the rotation instruction signal 142 for scanning the laser beam from the system control unit 140.

  The system control unit 140 waits for a predetermined waiting time from the start of each motor (step S104), and when the predetermined waiting time elapses, the photosensitive drum 130 reaches a stable constant speed necessary for image formation.

  The system control unit 140 confirms the input of the drum reference signal (step S105). In the driving state in which the drum starts to rotate, every time the rotation position mark 121 passes through the position on the photosensitive drum facing the detection surface of the rotation reference position sensor 120 provided in the vicinity, the rotation reference position sensor 120 rotates the rotation reference position. A position signal 122 is generated.

  After the photosensitive drum 130 reaches a driving state at a stable speed, the rotation speed of the polygon mirror 103 is stabilized, and from the timing when the rotation reference position signal 122 is input to the system control unit 140, the system control unit 140 A photosensitive unevenness correction instruction is issued (step S106). As a result, a register access instruction 143 for photosensitive unevenness correction is generated, and the image data processing unit 150 enters a state of unevenness correction processing.

  The system control unit 140 performs an image forming operation (step S107). During this image forming operation, the image data processing unit 150 starts image data processing in response to an image forming register access instruction 143 from the system control unit 140.

  When image data 151 is input from an external personal computer (not shown), it is sent to the line buffer control unit 152 and stored as data in the line buffer 153 for the number of multiple lasers. The accumulated data is simultaneously read out from the line buffer 153 as data corresponding to the number of multiple lasers at the timing of the BD signal 135 and sent to the multiplier 154.

  Here, the flow of photosensitive drum unevenness correction image processing will be described. The photosensitive unevenness correction unit 161 in the image data processing unit 150 includes an address calculation unit 170 and an adaptation processing unit 163 for selecting correction data for photosensitive drum unevenness. The photosensitive unevenness correction unit 161 reads correction data from a table memory (nonvolatile memory) 160 that holds correction data for photosensitive drum unevenness.

  The read correction data is processed by a matching processing unit 163 for matching data to be multiplied with image data via a data bus 171, and multiplied by a data bus 177 via a delay holding unit 164. Is transmitted to the unit 154.

  Specifically, after the photosensitive drum reaches a stable speed state, the image data processing unit 150 performs address calculation from the timing at which the rotation reference position signal 122 is input by the photosensitive unevenness correction unit 161 (step S201). ). This address calculation is performed based on the BD signal 135 of the scanning start position generated by the laser beam incident on the laser beam sensor for controlling the beam exposure start position in laser scanning and the time measurement by the crystal oscillator clock. As a result of this address calculation, an appropriate address for extracting correction data is selected.

  The image data processing unit 150 selects and sequentially reads the photosensitive drum unevenness correction data from the non-volatile memory (table memory) 160 that holds the photosensitive drum unevenness correction data in the photosensitive unevenness correcting unit 161 (step S202). The process of step S202 is an example of a reading step.

  The image data processing unit 150 is a process for adapting the photosensitive drum unevenness correction data transmitted via the data bus 171 to the data to be multiplied by the image data in the adaptation processing unit 163 in the photosensitive unevenness correcting unit 161. Are sequentially performed (step S203). Further, the image data processing unit 150 temporarily holds the correction data from the adaptation processing unit 163 after being delayed by the delay holding unit 164 (step S204). Then, the image data processing unit 150 takes out the correction data delayed and held by the delay holding unit 164 and sequentially transmits the correction data to the multiplication unit 154, and the multiplication unit 154 multiplies the correction data by the image data (step S205). The process in step S205 is an example of a correction step.

  Thus, the image data processing unit 150 delays the time corresponding to the preceding amount of the exposure position of the laser light emitted from the second light emitting element with respect to the exposure position of the laser light emitted from the first light emitting element. The correction data held in the delay holding unit 164 is read out. Then, the image data processing unit 150 corrects the amount of laser light emitted from the second light emitting element based on the correction data.

  Thereafter, the image data processing unit 150 ends this operation. Note that the processing in steps S202 to S205 is performed as a pipeline operation in parallel in the sequential circuit in the ASIC.

  As described above, after the photosensitive drum reaches a stable speed, from the timing when the rotation reference position signal 122 is input, it is appropriate to take out correction data based on the time measured by the BD signal 135 at the scanning start position and the crystal oscillator clock. Address is selected. That is, an appropriate address is selected in order to select and read out the photosensitive drum unevenness correction data in accordance with the laser exposure position of the photosensitive drum. Thereafter, the photosensitive unevenness correction unit 161 is in a state of performing photosensitive unevenness correction.

  When the image forming time corresponding to the predetermined image size has elapsed, the system control unit 140 determines whether or not the image forming operation has ended (step S108). If the image forming operation has not ended, the system control unit 140 returns to the process of step S107. On the other hand, when the image forming operation is finished, the system control unit 140 outputs a rotation instruction signal 141 for decelerating the photosensitive drum (step S109) and waits until it is confirmed that the photosensitive drum is stopped (step S110). When the stop is confirmed, that is, when the deceleration is finished, the system control unit 140 finishes this operation.

  By performing such an operation, the image forming apparatus performs a latent image drawing subjected to appropriate photosensitive drum unevenness correction and appropriate laser writing deviation correction.

  Here, the delay holding unit 164 is configured to hold the correction data subjected to the adaptation processing by the adaptation processing unit 163 by using the ring buffer for the time and the number of laser writing deviation amounts. Then, the delay holding unit 164 outputs the corrected and delayed correction data after the adaptation process.

  The multiplication unit 154 calculates (multiplies) the image data and the correction data from the line buffer 153, and the exposure data subjected to the photosensitive unevenness correction process is transmitted to the laser PWM modulator 155. The laser PWM modulator 155 performs blinking driving of the four-beam multi-laser semiconductor chip 101 via the laser current driving unit 106. The laser light is collected by the collimator lens 102, reflected and scanned by the polygon mirror 103, and transmitted through the fθ lens 104. Further, the laser beam follows the laser beam path 105 from the polygon mirror 103 to the photosensitive drum 130, and rotates on the photosensitive drum 130 as indicated by the scanning line 133 of the exposure spot 131 by the four-beam multi-laser by the rotation of the polygon mirror. Scanned. An electrostatic latent image is formed on the charged photosensitive drum. After the electrostatic latent image is formed, the image forming apparatus performs subsequent toner development, transfer to a paper medium, and heating and pressure fixing to the paper medium to form an image.

  The adaptation processing unit 163 has constant multiplication and addition / subtraction offset calculation functions. The adaptation process has two roles. One of them is the role of suppressing the amount of correction data while maintaining the ability to finely adjust the photosensitive drum unevenness. The variation in the photosensitive drum unevenness is actually about 10% of the entire potential. The 256-tone (8-bit) photosensitive drum unevenness correction data is designed to correspond to a modulation range of 95% to 105% of the drum surface potential. Then, the 8-bit table memory is designed so that exposure data having a resolution equivalent to 2560 gradations of 10 bits or more is obtained by multiplying the correction data obtained by adding the offset of 95% with the actual laser light quantity.

  The other is the role of correcting the correction data so as to follow the characteristic variation of the laser chip and the photosensitive drum in a timely manner. In the operation at the initial stage of image formation, fluctuations in temperature characteristics of the laser chip and the photosensitive drum appear. The coefficient for correcting this is used when feedback is performed as light amount adjustment of the entire laser chip. Further, this coefficient is used when feedback compensation is performed as a light amount adjustment of the entire laser chip using a variation amount in which the light amount variation of the photosensitive drum or the laser chip has occurred due to deterioration over time.

  FIG. 4 is a diagram showing a drum unevenness correction state at a certain moment during photosensitive unevenness correction. The x-axis direction in FIG. 4A indicates the writing position in the longitudinal direction of the photosensitive drum 130. Since the laser light is spot light that is scanned at a constant speed by the fθ lens 104, the x-axis direction also corresponds to the elapsed time t from the BD sensor 134 that is a scanning writing position sensor. Here, the scanning speed by the rotation of the polygon mirror 103 is 1 mm / μsec.

  Further, the y-axis direction in FIG. 5A indicates the writing position in the circumferential direction of the rotating photosensitive drum. The upper spot in the figure is the exposure point of the preceding laser. Assuming that the lasers LA, LB, LC, and LD are the lasers from the foremost laser to the last laser, the exposure spots of these lasers LA, LB, LC, and LD correspond to the exposure spot 131 in FIG. The image forming apparatus has a resolution of 600 dpi for main scanning and 600 dpi for sub-scanning. The four-beam laser chip is adjusted so as to be mounted and fixed at a position inclined so as to have an interval of 600 dpi in the drum circumferential direction, as indicated by a spot in the drawing. Each spot is separated by about 1 mm at equal intervals in the main scanning direction by rotation of the polygon mirror.

  In image formation, input image data 151 is read from the line buffer 153 at a timing shifted for each laser by the line buffer control unit 152 with reference to the BD signal 135, and the image is drawn. In addition, the latent image writing timing is corrected on the photosensitive drum so as not to shift in the main scanning direction.

  In the photosensitive drum unevenness correction, correction data is extracted and processed by the multiplier 154 and the photosensitive unevenness correction unit 161 in accordance with the first laser that precedes scanning in accordance with each spot position on the photosensitive drum.

  In FIG. 4, correction data n1, n2,... For sub-scanning 600 dpi scanning lines corresponding to the drum unevenness surface defined by the rotation time in the circumferential direction from the rotation reference position signal 122 is a table memory (non-volatile). The case where the information is sequentially registered in the (memory) 160 is shown. Here, the photosensitive drum unevenness data (correction data) in the table memory 160 is designed for each 1 mm corresponding to the multi-laser interval (predetermined distance interval) and held in the table memory 160.

  At the timing of FIG. 4, correction data for one laser is read from the table memory 160 via the data bus 171. The correction data is calculated and adjusted by the adaptation processing unit 163 and then held by the delay holding unit 164. In the figure, f (n) represents calculation / adjustment in the adaptation processing unit.

  Next, the multiplication unit 154 multiplies the four input image data and the four correction data from the delay holding unit 164 to generate exposure data. Based on the generated exposure data, the lasers are driven in parallel. At this time, the correction data selected from the table memory 160 is correction data n6 corresponding to the preceding laser. Then, as a result of the processing by the adaptation processing unit 163 and the delay holding unit 164, corrected and adjusted correction data y6, y5, y4, and y3 corresponding to the correction data n6, n5, n4, and n3 are output from the delay holding unit 164. The

  In the present embodiment, the ring buffers A0, A1, A2, A3, and A4 in the delay holding unit 164 are composed of five stages having a value 1 greater than the number of lasers. The read operation of the ring buffer is performed according to the address. Of course, the number of lasers may be other than 4.

  The write address is generated as follows. An enable signal 181 is output in synchronization with the reading of the table memory (data memory) 160 by the address calculation unit 170. The ring buffer address counter 182 counts up by the enable signal 181. The ring buffer address decoding unit 184 alternatively generates a write enable signal for the ring buffers A0 to A4 based on the count signal 183 from the ring buffer address counter 182.

  Simultaneously with the generation of the write enable signal, the ring buffer read selector 178 generates read enable for the ring buffers A0 to A4 in the delay holding unit 164 by the count signal 183.

  Since the scanning speed is 1 mm / μsec, the scanning proceeds exactly 1 mm after the elapse of 1 μsec. FIG. 5 is a diagram showing a drum unevenness correction state after the elapse of 1 μsec. The selected correction data obtained via the data bus 171 is correction data n7, n6, n5, n4 in order from the preceding laser. As a result of the processing by the adaptation processing unit 163 and the delay holding unit 164, correction data y7, y6, y5, and y4 corresponding to the correction data n7, n6, n5, and n4 are output from the delay holding unit 164.

  Further, after 1 μsec has elapsed, the scanning further proceeds by 1 mm. FIG. 6 is a diagram showing a drum unevenness correction state after the elapse of 2 μsec. The selected correction data obtained via the data bus 171 is correction data n8, n7, n6, n5 in order from the preceding laser. As a result of processing by the adaptation processing unit 163 and the delay holding unit 164, correction data y8, y7, y6, and y5 corresponding to the correction data n8, n7, n6, and n5 are obtained.

  As described above, in the unevenness correction in steps S202 to S205, the correction data of the laser LA is read from the table memory 160, held in the ring buffer after the adaptation process, and then read immediately. The subsequent correction data of the laser LB is already read from the table memory 160 and stored in the ring buffer, and the correction data used for the previous laser LA is used. Further, in the subsequent correction data of the laser LC and LD, similarly, correction data that has already been read and used for the laser LA before is used.

  As described above, in the image forming apparatus according to the first embodiment, a large-scale circuit including the table memory 160, the address calculation unit 170, and the matching processing unit 163 is used for only one laser equivalent to the correction of photosensitive unevenness of a single laser. Consists of. Further, the image forming apparatus further includes a delay holding unit 164 having a ring buffer for the number of lasers. As a result, it is possible to draw a latent image that has been subjected to appropriate multi-beam multi-beam photosensitive drum unevenness correction and proper laser writing deviation correction while realizing an inexpensive and small circuit configuration. The effect of suppressing the increase in circuit scale is greater as the number of multi-beam lasers is increased. Therefore, even in a configuration having a plurality of lasers, an increase in the circuit scale of the photosensitive unevenness correction unit can be suppressed.

  In the first embodiment, as shown in FIG. 4, strictly speaking, the four lasers are arranged with a shift of 42 μm in the sub-scanning direction, which is the rotation direction of the photosensitive drum. Therefore, the laser LA and the laser LD have a maximum positional deviation of 126 μm. However, this deviation is sufficiently small as compared with the 3 mm deviation, which is a problem in the photosensitive drum unevenness correction, and can be ignored. Therefore, in the present embodiment, the four lasers are processed as being at the same position on the photosensitive drum in the sub-scanning direction. In addition, in the multi-beam scanning optical system with the optical design as in this embodiment, the adjustment of the attachment of the laser chip and the lens is performed with the resolution in the sub-scanning direction being increased, so there is almost no problem. is there.

  In the first embodiment, the multi-beam photosensitive drum unevenness correction is applied to the two-dimensional drum surface in the longitudinal direction of the drum and the circumferential direction of the rotation. However, the one-dimensional drum surface in the longitudinal direction of the drum is shown. It can also be applied to. That is, the present invention is applicable even when the correction data is constant at the position in the longitudinal direction regardless of the rotation in the circumferential direction. In this case, although one-dimensional correction is performed, the above-described problem of positional deviation of 126 μm in the sub-scanning direction does not occur.

  As described above, in the image forming apparatus according to the first embodiment, even if there are four lasers, a readout circuit and an arithmetic processing circuit equivalent to the configuration in which only one laser is used are necessary. In addition, a delay holding unit that delays data by the number of lasers is provided. Therefore, the increase in the scale of the reading circuit from the table memory and the arithmetic processing circuit can be suppressed, and the cost can be reduced. Further, by providing a ring buffer in accordance with the write laser misalignment amount of a plurality of lasers, more accurate photosensitive drum unevenness correction can be applied to all lasers.

[Second Embodiment]
In the first embodiment, the multi-beam photosensitive drum unevenness correction is applied to the two-dimensional drum surface in the longitudinal direction of the drum and the circumferential direction of the rotation. In general, in the case of correction data on the surface of a photoreceptor having a density of 600 dpi, the amount of data is very large. For this reason, since it is necessary to make data processing capacity high, cost starts.

  For example, in the case of an A4 size having 8 bits of data per point, the amount of data needs to be 278 Mbits as shown in Equation (1).

8bit x 297mm x 210mm / (25.4mm / 600) ^ 2 = 278Mbit (1)
On the other hand, in actual photosensitive drum unevenness correction, unevenness correction with a low spatial frequency, such as 1 mm to 20 mm, is performed, and therefore a method has been proposed in which an actual correction profile is completed with a relatively small amount of data (Patent Document 2). . However, since a large variation in the correction amount may cause a partial density step and cause image quality degradation, it is desirable that the correction profile be realized by one-dimensional or two-dimensional linear interpolation.

  FIG. 7 is a diagram showing an arrangement of correction data when performing the photosensitive unevenness correction in the second embodiment. The correction data is composed of lattice points at intervals of about 10 mm when the surface of the photoreceptor is a flat surface. FIG. 8 is a diagram showing linear interpolation calculation of correction data. FIG. 8 shows linear interpolation calculation in the case where the block surrounded by the correction data A, B, D, and C is divided into eight in the main scanning direction and the sub-scanning direction.

  FIG. 9 is a diagram illustrating a drum unevenness correction state when linear interpolation calculation is performed. As shown in FIG. 9, in the second embodiment, a profile linear interpolation unit 163a (correction data generation means) is added to the matching processing unit 163 in the photosensitive unevenness correction unit 161. In the figure, p (n) represents a linear interpolation operation in the profile linear interpolation unit 163a. F (n) represents calculation / adjustment in the adaptation processing unit. Other configurations are the same as those of the first embodiment.

  The correction data in the table memory 160 corresponds to lattice points at intervals of 10 mm in the sub-scanning direction on the drum unevenness surface defined by the elapsed time of rotation in the circumferential direction from the drum rotation reference signal, and correction data n1 in the main scanning direction. n2,... are registered in order. Further, the correction data m1, m2,... Are correction data of the next m columns shifted by 10 mm in the sub-scanning direction with respect to the n columns.

  Here, the 10 mm interval of the correction data and the interval of the multilasers do not correspond one to one. At the timing shown in FIG. 9, when correction data for one laser is read from the table memory 160 via the data bus 171, linear interpolation calculation (p (n)) is performed by the profile linear interpolation unit 163a, and linear interpolation is performed. Corrected data is generated. The linearly interpolated correction data becomes correction data calculated and adjusted (f (n)) by the adaptation processing unit 163 and then held by the delay holding unit 164.

  The multiplying unit 154 multiplies the four input image data and the four correction data input from the delay holding unit 164 to generate exposure data. Each laser is driven in parallel based on the generated exposure data.

  At this time, the correction data selected from the table memory 160 is four data including correction data n5, n6, m5, and m6 for the preceding laser. As a result of the arithmetic processing, the correction data y6 is output from the delay holding unit 164. Further, the correction data y5, y4, and y3 are output from the delay holding unit 164 as a result of the arithmetic processing.

  When image data 151 from an external personal computer (not shown) is input, it is sent to the line buffer control unit 152 and stored in the line buffer 153 for the number of multilasers. The image data stored in the line buffer 153 is read out in parallel as data corresponding to the number of multiple lasers from the line buffer 153 at the timing of the BD signal 135 and sent to the multiplier 154.

  Here, the photosensitive unevenness correction unit 161 reads the correction data from the table memory 160 and inputs the correction data to the adaptation processing unit 163 via the data bus 171. The correction data processed by the adaptation processing unit 163 is held by the delay holding unit 164 for the number of lasers and then transmitted to the multiplication unit 154.

  As described above, in the second embodiment, the table memory 160 stores the two-dimensional lattice profile. The address for reading the correction data from the table memory 160 is specified from the rotation reference position signal 122 and the BD signal 135. For example, when obtaining the correction data of the point G in the area shown in FIG. 8, the correction data A, C, B, and D are read from the table memory 160.

  In the adaptation processing unit 163, a two-dimensional linear interpolation calculation is performed prior to the calculation described in the first embodiment. A variable x shown in FIG. 8 indicates a ratio in the main scanning direction corresponding to the point G between AB. Similarly, the variable y indicates the ratio in the sub-scanning direction corresponding to the G point between AC. The correction data G for point G is calculated according to equation (2) indicating a linear interpolation algorithm.

G = (1-x) (1-y) A + x (1-y) B + (1-x) yC + xyD (2)
FIG. 10 is a diagram showing a profile of correction data when linear interpolation calculation is performed when a 4 × 4 block is divided into eight in the main scanning direction and the sub-scanning direction. In the figure, the X and Y axes correspond to 4 × 4 blocks on the surface of the photoreceptor. The Z axis corresponds to the correction data amount (relative amount) and is the basis of the laser light amount adjustment data.

  Here, in the calculation step of the linear interpolation operation, multiplication is performed in a divided manner. The correction data G for point G is calculated according to equation (3), which is a modification of equation (2) indicating the linear interpolation algorithm.

G = {(1-y) A + yC} (1-x) + {(1-y) B + yD} x
= (1-x) E + xF (3)
Actually, during the correction operation, the exposure point of the laser LA moves in the main scanning direction from the point G, so that the sub-scanning linear interpolation calculation of the variables E and F is performed at any stage when the boundary of the block is reached. Further, main scanning linear interpolation calculation from point E to point F is performed, and variables x, E, and F are calculated.

  Next, when the exposure point of the laser LA reaches the point F, linear interpolation based on the four points B, H, D, and I is performed. In this case, the correction data of the points H and I are read from the table memory 160, only the calculation of the point J is performed, and the previous calculation result is used as it is as the data of the point F.

  Further, by configuring the linear interpolation unit to be a multiple of 2, division as a decimal multiplication of x and y can be performed by bit shift. As a result, it is only necessary to have a computing capability capable of performing parallel processing of reading out two pieces of data in units of data blocks in reading from the table memory and the linear interpolation calculation step. Therefore, the calculation load is reduced.

  The data obtained as a result of the linear interpolation thus calculated is one data for the drum position of the laser LA, and is calculated by the matching processing unit and then held in the delay holding unit.

  As described above, the image forming apparatus according to the second embodiment is designed so that the pitch of the linear interpolation unit matches the laser writing deviation amount. Therefore, the exposure points of the lasers LB, LC, and LD coincide with the squares of the linear interpolation. For example, in FIG. 8, the exposure point of the laser LD coincides with the F point. The correction data of each laser after 1 μsec corresponds to the exact position on the photosensitive drum in the main scanning direction by shifting the data of the delay holding unit by one. In addition, the adaptation processing unit including the linear interpolation unit is configured by one without depending on the number of lasers. In addition, the performance of the correction data readout circuit that is the source of linear interpolation is also independent of the number of lasers. Further, it is not necessary to store correction data with high density in the table memory, and the amount of data held in the table memory can be reduced.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable.

  For example, since the present invention does not depend on the light amount modulation method of the light emitting element, the PWM method as in the above embodiment or the current modulation method as in Patent Document 4 may be used. Is also applicable.

  Further, the relationship between the laser writing deviation correction amount and the pitch of the linear interpolation unit is an integer ratio even when the linear interpolation unit is finer, even if it is one-to-one as in the second embodiment. The following effects can be obtained. That is, when the laser writing deviation correction amount (distance interval which is the difference between exposure points) is an integral multiple of the pitch of the linear interpolation unit, linearly interpolated correction corresponding to the exact position of the photosensitive drum in the main scanning direction Data can be easily realized at low cost by the delay holding unit.

  Further, even when the relationship between the laser writing deviation correction amount and the pitch of the linear interpolation unit does not become an integer ratio, linear interpolation calculation of correction data is possible. FIG. 11 is a diagram showing linear interpolation calculation of photosensitive unevenness correction data when the relationship between the laser writing deviation correction amount and the pitch of the linear interpolation unit does not become an integer ratio. As shown in FIG. 11, even when the relationship between the laser write deviation correction amount and the pitch of the linear interpolation unit does not become an integer ratio due to insufficient arithmetic processing capability or variable modulation of the scanning speed, the following configuration is selected. Is possible. (A) Control to refer to correction data obtained by linear interpolation corresponding to the position on the photosensitive drum as appropriate as possible from the delay holding unit, or (b) 2 less than the number of lasers in accordance with the multi-laser pitch. There is a configuration option in which correction data is calculated by two or more photosensitive unevenness correction units. Accordingly, it is possible to configure so as to maximize the simplification of the circuit while minimizing the image quality deterioration due to the deviation of the correction data in the laser writing deviation amount.

  In addition to the original printing apparatus, the present invention may be a facsimile machine having a printing function, a multifunction machine (MFP) having a printing function, a copy function, a scanner function, or the like as an image forming apparatus. is there. The electrophotographic image forming apparatus may be applied to either a monochrome image forming apparatus or a color image forming apparatus.

130 Photosensitive drum 140 System control unit 150 Image data processing unit 154 Photosensitive drum unevenness correction image processing unit (multiplication unit)
160 Table memory (non-volatile memory)
161 Photosensitive unevenness correction unit 164 Delay holding unit 170 Address calculation unit

Claims (6)

A photoreceptor,
First and second light emitting elements that emit light for exposing the photosensitive member, and deflection scanning that simultaneously deflects and scans the light emitted from the first and second light emitting elements. An exposure position where the light emitted from the first light emitting element exposes the photosensitive member and the light emitted from the second light emitting element is the photosensitive in one scan by the deflection scanning means. Exposure means in which the first light emitting element is arranged with respect to the second light emitting element so that an exposure position for exposing the body is different;
Storage means for storing correction data for correcting the amount of light emitted from the first light emitting element in association with the position of the surface of the photosensitive member;
The first light emitting element reads the correction data from the storage unit according to an exposure position at which the photosensitive member is exposed, and is emitted from the first light emitting element and the second light emitting element based on the correction data. An image forming apparatus comprising: a correction unit that corrects the amount of light. Correction data holding means for temporarily holding correction data read from the storage means according to the exposure position of the light emitted from the first light emitting element;
The first light emitting element emits from the second light emitting element an exposure position at which the light emitted from the first light emitting element exposes the photoreceptor in the direction in which the light is scanned in the one scan. Disposed with respect to the second light emitting element so that the light preceding the exposure position for exposing the photoconductor,
The correction means delays the exposure position of the light emitted from the first light emitting element by a time corresponding to the preceding amount of the exposure position of the light emitted from the second light emitting element from the correction data holding means. 2. The image forming apparatus according to claim 1, wherein the correction data held in the correction data holding unit is read, and the amount of light emitted from the second light emitting element is corrected based on the correction data. . Correction data generating means for generating correction data at exposure positions between the plurality of exposure positions based on the plurality of correction data read out according to each of the plurality of exposure positions from the storage means;
The correction means is an amount of light emitted from the first light emitting element and the second light emitting element based on correction data generated by the correction data generating means at an exposure position between the plurality of exposure positions. The image forming apparatus according to claim 1, wherein:   When performing the linear interpolation calculation, an exposure position where light emitted from the first light emitting element exposes the photoconductor, and an exposure position where light emitted from the second light emitting element exposes the photoconductor 4. The image forming apparatus according to claim 3, wherein the interval is an integer multiple of the pitch of the linear interpolation unit.   The image forming apparatus according to claim 1, wherein the storage unit stores two-dimensional correction data corresponding to the position of the surface of the photoconductor. Simultaneously deflecting the light emitted from the photoconductor, the first light emitting element and the second light emitting element that emit light for exposing the photoconductor, and the first light emitting element and the second light emitting element Deflection scanning means for scanning, and in one scan by the deflection scanning means, light emitted from the first light emitting element is emitted from an exposure position for exposing the photosensitive member and the second light emitting element. Exposure means in which the first light emitting element is disposed with respect to the second light emitting element so that light is exposed at an exposure position at which the photoconductor is exposed; and light emitted from the first light emitting element. A light amount correction method for an image forming apparatus, comprising: storage means for storing correction data for correcting the light amount in association with the position of the surface of the photosensitive member;
A reading step of reading out the correction data from the storage unit in accordance with an exposure position at which the first light emitting element exposes the photoconductor;
A light amount correction method for an image forming apparatus, comprising: a correction step of correcting light amounts of light emitted from the first light emitting element and the second light emitting element based on the correction data.

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