JP2008093835A - Print head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly precisely correct the amount of light on a print head. <P>SOLUTION: The print head comprises an LPH (LED print head) 14 having a plurality of LED arranged in a line and exposing a photo-conductor drum with an outgoing light from the LED to form an electrostatic latent image, an EEPROM 102 for storing a first light amount correcting data for correcting fluctuation of the amount of the outgoing light existing inherently among the LED each other of the LPH 14, and an EEPROM_A301 for storing a second light amount correcting data for correcting fluctuation of electric potential generated in the electrostatic latent image caused by factors except light exposure by the LPH 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a print head used for a print head of an image forming apparatus such as a copying machine or a printer.

In an image forming apparatus such as a printer or a copying machine using an electrophotographic system, light emitting elements such as LEDs are arranged in a line as an exposure unit for exposing an image carrier such as a photosensitive drum in response to a request for downsizing the apparatus. There has been proposed a print head using a light emitting element array and a lens array that forms an image of light output from each light emitting element on the surface of an image holding member.
If there is a variation in the amount of emitted light in such a print head, density unevenness occurs in the image formed on the recording paper, thereby hindering the formation of a high-quality image. In particular, when forming a color image, the color reproducibility is deteriorated due to density unevenness of each color image.

Therefore, in an image forming apparatus equipped with such a print head, the amount of light emitted from each light emitting element is corrected (light amount correction) so that the exposure amount on the image carrier is substantially uniform. At that time, it is necessary to perform light amount correction in consideration of fluctuations in image forming conditions such as a change in photosensitive characteristics of the image carrier over time.
For this reason, in such a print head, the light amount correction is generally performed using the density value of the image actually formed during the running of the apparatus. That is, for example, a predetermined test pattern image is formed for every predetermined number of running sheets, and this is read by an image reading device such as an image scanner to obtain density data. And the light quantity correction of each light emitting element is performed based on the obtained density data (see, for example, Patent Document 1).

JP 2001-146038 A (page 4-5)

  Here, in general, an image reading apparatus that reads an image density value of a test pattern image has a reading error in the arrangement direction of light emitting elements of a print head, for example. For this reason, if the light amount correction based on the image density value of the test pattern image is repeated many times, the reading error of the image reading apparatus is accumulated in the print head, and the accuracy of the light amount correction gradually decreases. As a result, there has been a problem that unevenness in image density becomes obvious and image quality is deteriorated.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to accurately perform light amount correction in the print head.

  For this purpose, the print head of the present invention is a print head that exposes a photoreceptor to form an electrostatic latent image, and includes a plurality of light emitting elements arranged in a line and the exposure energy of each light emitting element. A light amount setting unit that adjusts the amount of light, and the light amount setting unit includes first light amount correction data for correcting variations in the emitted light amount inherent between the light emitting elements, and variations in the emitted light amount between the light emitting elements. The exposure energy amount is adjusted based on the second light amount correction data for correcting the potential unevenness generated in the electrostatic latent image due to factors other than the above.

  Here, the light amount setting means sets a lighting pulse width for driving each light emitting element based on the light amount correction data generated by adding the first light amount correction data and the second light amount correction data. The exposure energy amount may be adjusted. The light quantity setting means corrects potential unevenness generated in the electrostatic latent image due to variations in the first light quantity correction data, the second light quantity correction data, and the axial photosensitive characteristic inherent to the photosensitive member. The exposure energy amount can be adjusted by setting a lighting pulse width for driving each light emitting element based on the light amount correction data. Further, the light amount setting means can adjust the exposure energy amount using the second light amount correction data updated at a predetermined timing or at an arbitrary timing. In addition, the first light quantity correction data is stored in a first storage unit that is provided integrally with the print head, and the second light quantity correction data is provided on the image forming apparatus side on which the print head is mounted. It can be characterized by being stored in the second storage means.

  Furthermore, the present invention is regarded as an image forming apparatus, and the image forming apparatus of the present invention includes a photosensitive member and a plurality of light emitting elements arranged in a line, and exposes the photosensitive member by light emitted from the light emitting elements. A print head for forming an electrostatic latent image; first storage means for storing first light amount correction data for correcting variations in the emitted light amount inherent between the light emitting elements of the print head; and exposure by the print head. And second storage means for storing second light amount correction data for correcting potential unevenness generated in the electrostatic latent image due to factors other than the above.

  Here, it further includes a control unit that generates light amount correction data for correcting the emitted light amount of the print head, and transmits the generated light amount correction data to the print head. The control unit stores the first storage unit stored in the first storage unit. The light amount correction data can be generated based on the light amount correction data and the second light amount correction data stored in the second storage unit. Furthermore, the control unit further includes third storage means for storing third light quantity correction data for correcting potential unevenness generated in the electrostatic latent image due to variations in photosensitive characteristics in the axial direction inherent to the photosensitive member. Based on the first light amount correction data stored in the first storage unit, the second light amount correction data stored in the second storage unit, and the third light amount correction data stored in the third storage unit, the light amount correction data Is generated. In particular, the third storage means may be provided integrally with the photoconductor.

  An image forming unit that forms a toner image on a medium based on an electrostatic latent image formed on a photosensitive member by a print head; and a second light amount that generates second light amount correction data stored in a second storage unit. A correction data generation unit, and the second light amount correction data generation unit is a predetermined test pattern image formed on the basis of an electrostatic latent image by a print head whose light amount is corrected by the first light amount correction data. The second light quantity correction data may be generated based on the image density. In particular, the second light quantity correction data generation unit has a predetermined degree of density unevenness of the toner image formed by the image forming unit at the initial installation of the image forming device, every time when the predetermined number of running sheets has passed. The second light quantity correction data can be generated at any one or a plurality of timings when the level falls below the level. In addition, the first storage unit may be provided integrally with the print head, and the second storage unit may be provided on the image forming apparatus main body side.

According to the first aspect of the present invention, it is possible to accurately correct the light amount in the print head.
According to the second aspect of the present invention, the light amount correction of the print head can always be performed with high accuracy while the image forming apparatus is in operation.
According to the third aspect of the present invention, it is possible to perform light quantity correction corresponding to the variation in the photosensitive characteristic of the photosensitive drum in the axial direction.

According to the fourth aspect of the present invention, it is possible to perform light amount correction corresponding to a change with time of image forming conditions.
According to the fifth aspect of the present invention, the first light quantity correction data can be easily exchanged simultaneously with the exchange of the print head, and the second light quantity correction based on the factor on the image forming apparatus side is facilitated. The data can also be applied to a print head that is exchanged as it is.

According to the sixth aspect of the present invention, it is possible to perform light amount correction in the print head with high accuracy.
According to the seventh aspect of the present invention, the light amount correction of the print head can always be performed with high accuracy while the image forming apparatus is in operation.
According to the eighth aspect of the present invention, it is possible to perform light quantity correction corresponding to the variation in the photosensitive characteristic of the photosensitive drum in the axial direction.
According to the ninth aspect of the present invention, the third light quantity correction data can be easily exchanged simultaneously with the exchange of the photosensitive member.

According to claim 10 of the present invention, the second light quantity correction data can be generated with high accuracy.
According to the eleventh aspect of the present invention, it is possible to perform light amount correction corresponding to a change with time of image forming conditions.
According to the twelfth aspect of the present invention, it is easy to exchange the first light quantity correction data simultaneously with the exchange of the print head, and the second light quantity correction based on the factor on the image forming apparatus side. The data can also be applied to a print head that is exchanged as it is.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus using a print head according to the present embodiment. The image forming apparatus shown in FIG. 1 is a so-called tandem digital color printer, and controls the operation of the image forming process unit 10 as an image forming unit that forms an image corresponding to image data of each color, and the operation of the image forming apparatus. An image processing unit 40 is connected to the control unit 30 and the image reading device 3 and an external device such as a personal computer (PC) 2 and performs predetermined image processing on image data received therefrom.

The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (hereinafter collectively referred to simply as “image forming unit 11”) that are arranged in parallel at a predetermined interval. Yes. Each image forming unit 11 includes a photosensitive drum 12 as an image carrier that forms an electrostatic latent image and carries a toner image, a charger 13 that uniformly charges the surface of the photosensitive drum 12 at a predetermined potential, An LED print head (LPH) 14 as an exposure device for exposing the photosensitive drum 12 charged by the device 13, a developing device 15 for developing the electrostatic latent image obtained by the LPH 14, and the surface of the photosensitive drum 12 after transfer. A cleaner 16 for cleaning is provided.
Here, each image forming unit 11 is configured in substantially the same manner except for the toner stored in the developing device 15. Each image forming unit 11 forms yellow (Y), magenta (M), cyan (C), and black (K) toner images.

  The image forming process unit 10 also intermediate-transfers each color toner image of each image forming unit 11 and the intermediate transfer belt 21 onto which the toner images of each color formed on the photosensitive drum 12 of each image forming unit 11 are transferred in a multiple manner. A primary transfer roll 22 that sequentially transfers (primary transfer) to the belt 21, and a secondary transfer that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 21 onto a sheet P that is a recording material (recording paper). A roll 23 and a fixing device 25 for fixing the secondary transferred image on the paper P are provided.

  In the image forming apparatus of the present embodiment, the image forming process unit 10 performs an image forming operation based on a control signal such as a synchronization signal supplied from the control unit 30. At that time, the image data input from the image reading device 3 or the PC 2 is subjected to image processing by the image processing unit 40 and supplied to each image forming unit 11 via the interface. In the yellow image forming unit 11Y, for example, the surface of the photosensitive drum 12 uniformly charged at a predetermined potential by the charger 13 is exposed by the LPH 14 that emits light based on the image data obtained from the image processing unit 40. Thus, an electrostatic latent image is formed on the photosensitive drum 12. The formed electrostatic latent image is developed by the developing device 15, and a yellow toner image is formed on the photosensitive drum 12. Similarly, magenta, cyan, and black toner images are formed in the image forming units 11M, 11C, and 11K.

Each color toner image formed by each image forming unit 11 is sequentially electrostatically attracted by the primary transfer roll 22 onto the intermediate transfer belt 21 rotating in the direction of arrow A in FIG. A toner image is formed. The superimposed toner image is conveyed to a region (secondary transfer portion) where the secondary transfer roll 23 is disposed as the intermediate transfer belt 21 moves. When the superimposed toner image is conveyed to the secondary transfer unit, the paper P is supplied to the secondary transfer unit in accordance with the timing at which the toner image is conveyed to the secondary transfer unit. Then, the superimposed toner images are collectively electrostatically transferred onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 23 in the secondary transfer portion.
Thereafter, the sheet P on which the superimposed toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 21 and conveyed to the fixing device 25 by the conveying belt 24. The unfixed toner image on the paper P conveyed to the fixing device 25 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 25. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion (not shown) provided in the discharge portion of the image forming apparatus.

  FIG. 2 is a view showing a configuration of an LED print head (LPH) 14 that is an exposure unit. 2, the LPH 14 includes a housing 61 as a support, a self-scanning LED array (SLED) 63 that constitutes a light emitting unit, and a signal generation circuit 100 as drive signal generation means for driving the SLED 63 and SLED 63 (see FIG. 3 in the subsequent stage). And the like, and a holder 65 for supporting the rod lens array 64, which is an optical member for imaging light from the SLED 63 on the surface of the photosensitive drum 12, and for shielding the SLED 63 from the outside. A leaf spring 66 that pressurizes the housing 61 in the direction of the rod lens array 64 is provided.

The housing 61 is formed of a block or sheet metal such as aluminum or SUS, and supports the LED circuit board 62. The holder 65 supports the housing 61 and the rod lens array 64, and is set so that the light emitting point of the SLED 63 and the focal point of the rod lens array 64 coincide. Furthermore, the holder 65 is configured to seal the SLED 63. This prevents dust from adhering to the SLED 63 from the outside. On the other hand, the leaf spring 66 presses the LED circuit board 62 in the direction of the rod lens array 64 via the housing 61 so as to maintain the positional relationship between the SLED 63 and the rod lens array 64.
The LPH 14 configured in this way is configured to be movable in the optical axis direction of the rod lens array 64 by an adjustment screw (not shown), and the imaging position (focal plane) of the rod lens array 64 is the surface of the photosensitive drum 12. It is adjusted so that it is located above.

As shown in FIG. 3 (plan view of the LED circuit board 62), the LED circuit board 62 includes, for example, SLEDs 63 composed of 58 SLED chips (CHIP1 to CHIP58) in parallel with the axial direction of the photosensitive drum 12. It is arranged in a line with high accuracy. In this case, each LED array is arranged continuously at the connection portion between the SLED chips at the end boundary of the arrangement (LED array) of the light emitting elements (LEDs) arranged in each SLED chip (CHIP1 to CHIP58). In addition, the SLED chips are alternately arranged in a staggered pattern.
Further, the LED circuit board 62 stores a signal generation circuit 100 and a level shift circuit 104 that output a signal (drive signal) for driving the SLED 63, a three-terminal regulator 101 that outputs a power supply voltage, initial light amount correction data of the SLED 63, and the like. And a harness 103 that transmits and receives signals to and from the image forming apparatus main body.

Here, FIG. 4 is a diagram showing a part of the wiring formed on the LED circuit board 62. As shown in FIG. 4, on the LED circuit board 62, a + 3.3V power line 105 that supplies power to each SLED chip from the three-terminal regulator 101, a grounded (GND) power line 106, and a signal generation circuit 100 to signal lines 107 (107_1 to 107_58) for transmitting lighting signals ΦI (ΦI1 to ΦI58) corresponding to the image data from the image processing unit 40 to each SLED chip, and further, each light emitting point of each SLED chip. A signal line 108 (108_1 to 108_6) and a signal line 109 (109_1 to 109_6) for transmitting the transfer signal CK1 (CK1_1 to 1_6) and the transfer signal CK2 (CK2_1 to 2_6), which are sequentially shifted to the lighting enabled state, are wired. .
And the lighting signal (PHI) I with respect to CHIP1-CHIP58 is input into each SLED chip (CHIP1-CHIP58) via the signal line 107. FIG. Further, the transfer signal CK1 (CK1_1 to 1_6) is input to the CHIP1 to CHIP58 via the signal line 108, and the transfer signal CK2 (CK2_1 to 2_6) is input to the CHIP1 to CHIP58 via the signal line 109, respectively.

Next, the signal generation circuit 100 provided on the LED circuit board 62 will be described.
FIG. 5 is a block diagram showing a configuration of the signal generation circuit 100. The signal generation circuit 100 includes an image data development unit 110, a density unevenness correction data unit 112, a timing signal generation unit 114, a reference clock generation unit 116, and lighting time control / corresponding to each SLED chip (CHIP1 to CHIP58). The driving unit 118-1 to 118-58 constitutes a main part.
Image data is serially transmitted from the image processing unit (IPS) 40 to the image data development unit 110. The image data development unit 110 divides the transmitted image data into image data for each SLED chip (CHIP1 to CHIP58) and 1st to 128th dot, 129 to 256th dot,..., 7297 to 7424th dot. The image data developing unit 110 is connected to the lighting time control / drive units 118-1 to 118-58, and outputs the divided image data to the corresponding lighting time control / drive units 118-1 to 118-58.

  The density unevenness correction data unit 112 stores density unevenness correction data Corr for correcting image density unevenness at the time of image formation due to variations in the amount of emitted light for each LED in the SLED 63 and changes with time in image forming conditions. ing. Then, in synchronization with the data read signal from the timing signal generator 114, the density unevenness correction data Corr is output to the lighting time control / drive units 118-1 to 118-58. The density unevenness correction data Corr is data set for each LED, and is formed as 8-bit (0 to 255) data in the present embodiment.

  In an EEPROM (first memory, first storage means) 102, light emission points that exist inherently to each light emission point (light emitting element) of the LPH 14 set based on the measured value of the emitted light quantity of the LPH 14 at the time of factory shipment. The light amount correction data for each LED for correcting the variation in the emitted light amount between them, that is, initial light amount correction data (first light amount correction data) Corr_1 is stored. On the other hand, the control unit 30 of the main body is provided with an EEPROM_A (second memory, second storage means) 301, which is caused by a process (process) other than the exposure by the LPH 14 of the image forming apparatus (machine). Due to the change in image forming conditions over time, such as the potential unevenness of the electrostatic latent image on the photosensitive drum 12 and the change in the photosensitive characteristics of the photosensitive drum 12 over time as the machine runs. Light amount correction data for each LED for correcting potential unevenness of the generated electrostatic latent image, that is, process light amount correction data (second light amount correction data) Corr_2 is stored.

When the machine power is turned on, the initial light amount correction data Corr_1 for each LED is downloaded from the EEPROM 102 to the control unit 30. The control unit 30 adds the initial light amount correction data Corr_1 from the EEPROM 102 and the process light amount correction data Corr_2 stored in the EEPROM_A 301 by the adder 302 to generate light amount correction data Corr corresponding to the running time of the machine. Then, the control unit 30 sends the generated light amount correction data Corr to the density unevenness correction data unit 112. Accordingly, the light amount correction data Corr is stored in the density unevenness correction data unit 112 as the density unevenness correction data Corr.
The initial light amount correction data Corr_1 stored in the EEPROM 102 and the process light amount correction data Corr_2 stored in the EEPROM_A301 will be described in detail later.

The reference clock generation unit 116 is connected to the control unit 30, the timing signal generation unit 114, and the lighting time control / drive units 118-1 to 118-58 of the main body.
As shown in FIG. 6 (a block diagram illustrating the configuration of the reference clock generation unit 116), the reference clock generation unit 116 includes a crystal oscillator 140, a frequency divider 1 / M142 that is a second frequency divider, a first frequency divider, and a first frequency divider. A PLL circuit 134 including a frequency divider 1 / N 144, a phase comparator 146, and a voltage controlled oscillator 148 as an oscillator, and a look-up table (LUT) 132 as a memory. Yes.

  The LUT 132 stores a table for determining the frequency division ratios M and N based on the light amount adjustment data from the control unit 30. The crystal oscillator 140 is connected to the frequency divider 1 / N144, oscillates at a predetermined frequency, and outputs the oscillated signal to the frequency divider 1 / N144. The frequency divider 1 / N 144 is connected to the LUT 132 and the phase comparator 146, and divides the signal oscillated by the crystal oscillator 140 based on the frequency division ratio N determined by the light amount adjustment data from the LUT 132. The phase comparator 146 is connected to the frequency divider 1 / M142, the frequency divider 1 / N144, and the voltage controlled oscillator 148, and the output signal from the frequency divider 1 / M142 and the frequency divider 1 / N144. Is compared with the output signal. The control voltage supplied to the voltage controlled oscillator 148 is controlled according to the comparison result (phase difference) by the phase comparator 146. The voltage controlled oscillator 148 outputs a reference clock signal at a frequency based on the control voltage. In the present embodiment, a control voltage corresponding to a frequency that divides the possible lighting period into 256 is supplied, and a reference clock signal having this frequency is generated, and all lighting time control / drive units 118-1 to 118-58 are generated. Output to. The voltage controlled oscillator 148 is also connected to the frequency divider 1 / M142, and the reference clock signal output from the voltage controlled oscillator 148 is also branched and input to the frequency divider 1 / M142. The frequency divider 1 / M 142 divides the reference clock signal fed back from the voltage controlled oscillator 148 based on the frequency division ratio M determined by the light amount adjustment data from the LUT 132.

The timing signal generation unit 114 is connected to the control unit 30 and the reference clock generation unit 116, and is synchronized with the horizontal synchronization signal (HSYNC) from the control unit 30 based on the reference clock signal from the reference clock generation unit 116. Thus, transfer signals CK1R and CK1C and transfer signals CK2R and CK2C are generated. The transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C are transferred to the LPH 14 as the transfer signal CK1 and the transfer signal CK2 via the level shift circuit 104.
The timing signal generation unit 114 is connected to the density unevenness correction data unit 112 and the image data development unit 110 and is synchronized with the HSYNC signal from the control unit 30 based on the reference clock signal from the reference clock generation unit 116. Then, a data read signal for reading image data corresponding to each LED that is a light emitting point from the image data development unit 110, and data for reading density unevenness correction data corresponding to each LED from the density unevenness correction data unit 112 A read signal is output for each. Further, the timing signal generation unit 114 is also connected to the lighting time control / drive units 118-1 to 118-58, and based on the reference clock signal from the reference clock generation unit 116, the timing signal generation unit 114 is connected to the HSYNC signal from the control unit 30. In synchronization, a trigger signal (TRG) for starting lighting of the SLED 63 is output.

The lighting time control / drive units 118-1 to 118-58 are an example of a light amount setting unit, which corrects the lighting time of each LED based on density unevenness correction data and delay selection data, and lights each LED of the SLED 63. Control signals (lighting signals) [Phi] I1 to [Phi] I58 are generated.
Specifically, the lighting time control / drive units 118-1 to 118-58 are examples of the reference signal generation unit, as shown in FIG. 7 (block diagram illustrating the configuration of the lighting time control / drive unit 118). A presettable digital one-shot multivibrator (PDOMV) 160, a linearity correction unit 162, and an AND circuit 170 are included.
The AND circuit 170 is connected to the image data development unit 110 and the timing signal generation unit 114. When the image data from the image data development unit 110 is 1 (ON), the trigger signal (TRG) from the timing signal generation unit 114 is displayed. ) Is output to the PDOMV 160, and when the image data is 0 (OFF), the trigger signal is set not to be output. The PDOMV 160 is connected to the AND circuit 170, the OR circuit 168, the density unevenness correction data unit 112, and the reference clock generation unit 116, and a clock corresponding to the density unevenness correction data Corr in synchronization with the trigger signal from the AND circuit 170. Generate a number of lighting pulses.

The linearity correction unit 162 corrects and outputs the lighting pulse signal from the PDOMV 160 in order to correct the variation in the light emission start time of each LED in the SLED 63. Specifically, the linearity correction unit 162 includes a plurality of delay circuits 164 (eight in this embodiment, 164-0 to 164-7), a delay selection register 166, a delay signal selection unit 165, and an AND circuit 167. , An OR circuit 168, and a lighting signal selection unit 169.
The delay circuits 164-0 to 164-7 are connected to the PDOMV 160, and different times for delaying the lighting pulse signal from the PDOMV 160 are set. The delay selection register 166 is connected to the delay signal selection unit 165 and the lighting signal selection unit 169, and the delay selection register 166 stores the delay selection data Offset for each LED in the SLED 63 and the lighting signal selection data. Yes. Delay selection data Offset and lighting signal selection data for each LED are measured in advance and stored in the EEPROM 102. The delay selection data Offset and lighting signal selection data stored in the EEPROM 102 are downloaded to the delay selection register 166 via the density unevenness correction data unit 112 when the machine power is turned on. Note that a flash ROM can also be used as storage means for storing the delay selection data Offset and the lighting signal selection data. In this case, the flash ROM itself can function as the delay selection register 166.

Here, the delay selection data Offset stored in the EEPROM 102 will be described. FIG. 8 is a diagram showing the relationship between the lighting pulse width of the lighting signal ΦI for lighting the LED and the light quantity of the LED. In FIG. 8A, the solid line is emitted from the LED via the rod lens array 64 (see FIG. 2) when the lighting pulse width of the lighting signal ΦI is changed for any one LED in the SLED 63. This is the measured value of the light intensity. A broken line is a target light quantity characteristic (target light quantity characteristic) required when the LED is actually driven.
As shown in FIG. 8A, when light is actually emitted from the LED, the light emission start time is delayed because the output waveform of the lighting signal ΦI does not become a complete rectangle. The delay time usually has a variation of about 3 to 15 nsec. Therefore, in the LPH 14 of this embodiment, the linearity correction unit 162 causes the lighting signal so that the light quantity characteristic of the light from the LED substantially matches the target light quantity characteristic in the lighting pulse width region used in the image forming apparatus. The lighting pulse width of ΦI is offset.
FIG. 8B shows the light quantity characteristic (solid line) of the LED when offset correction is performed on the lighting pulse width of the lighting signal ΦI to the LED. In FIG. 8B, the offset amount is determined so that the LED light amount matches the target light amount at the lower limit lighting pulse width (offset correction position) of the used lighting pulse width region. Then, the offset amount is measured for each LED by such a method, and is stored in the EEPROM 102 as the delay selection data Offset.

The delay signal selection unit 165 is connected to the AND circuit 167 and the OR circuit 168, and based on the delay selection data Offset stored in the delay selection register 166, any of the outputs from the delay circuits 164-0 to 164-7. Select one of them. The AND circuit 167 is a logical product of the lighting pulse signal from the PDOMV 160 and the delayed lighting pulse signal selected by the delay signal selection unit 165, that is, both the lighting pulse signal before the delay and the lighting pulse signal after the delay are in the lighting state. If so, a lighting pulse is output. The OR circuit 168 is a logical sum of the lighting pulse signal from the PDOMV 160 and the delayed lighting pulse signal selected by the delay signal selection unit 165, that is, at least one of the lighting pulse signal before the delay and the lighting pulse signal after the delay is in the lighting state. If so, a lighting pulse is output.
The lighting signal selection unit 169 selects one of the outputs from the AND circuit 167 or the OR circuit 168 based on the lighting selection data stored in the delay selection register 166. Then, the selected lighting pulse is output to the LPH 14 via the MOSFET 172 as the lighting signal ΦI.

  By the way, as described above, the PDOMV 160 generates a lighting pulse of the number of clocks corresponding to the density unevenness correction data Corr in synchronization with the trigger signal from the AND circuit 170 and outputs it to the AND circuit 167 and the OR circuit 168. Therefore, the lighting pulse input to the linearity correction unit 162 has already been corrected by the density unevenness correction data Corr in the PDOMV 160. As described above, the PDOMV 160 also has a function as a signal generation unit that generates a lighting pulse whose gain is corrected. That is, the lighting pulse output to the LPH 14 via the MOSFET 172 is output in a state where density unevenness correction (gain correction) and offset correction are performed.

FIG. 9 is a diagram showing the light quantity characteristics of the LED subjected to gain correction and offset correction. FIG. 9 shows, as an example, a case where gain correction is performed with reference to the center position (gain correction position) of the lighting pulse width region used in the image forming apparatus.
As described above, in the lighting time control / drive units 118-1 to 118-58 of the present embodiment, the lighting pulse width of each LED is set to the density unevenness correction data Corr and the delay as shown in the following equation (1). By correcting based on the selection data Offset, the light quantity characteristic in the lighting pulse width region used in the image forming apparatus is substantially matched with the target light quantity characteristic and outputted to the LPH 14.

Lighting pulse width = BASE. (1 + Corr / 128) + Offset (1)
In the expression (1), “BASE” is a reference pulse width that is a reference for setting the light quantity of the LED. In addition, since the density unevenness correction data Corr of the present embodiment is 8-bit data (0 to 255), the light amount correction width related to density unevenness correction (gain correction) is expressed by the maximum correction value / minimum correction in the equation (1). The case where value = 3 is set is shown.
In this way, by setting the lighting pulse width by the expression (1), as shown in FIG. 9, the light amount characteristic in the lighting pulse width region used in the image forming apparatus substantially matches the target light amount characteristic. Therefore, the light quantity of the LED in the use pulse width region is set to be within a predetermined range.

  Further, as shown in FIG. 7, a three-terminal regulator 101 is connected to the LPH 14, and a stable + 3.3V voltage is supplied from the three-terminal regulator 101 to the LPH 14.

By the way, as described above, the density unevenness correction data Corr output from the density unevenness correction data unit 112 is an adder of the initial light amount correction data Corr_1 stored in the EEPROM 102 and the process light amount correction data Corr_2 stored in the EEPROM_A301. This is generated by adding in 302. That is, the density unevenness correction data Corr is expressed by the following equation (2).
Corr = Corr_1 + Corr_2 (2)

Here, first, a method for measuring and calculating the initial light amount correction data Corr_1 stored in the EEPROM 102 will be described.
FIG. 10 is a diagram showing a configuration of an optical profile measuring apparatus 200 as a characteristic measuring apparatus that measures the exposure energy distribution (light quantity distribution) of the LPH 14. As shown in FIG. 10, the optical profile measuring apparatus 200 has a line CCD 261 in which a light receiving surface is provided to face the light emitting portion (SLED 63) of the LPH 14, and a plurality of CCDs (Charge Coupled Devices) are arranged in a line. The line CCD 261 is installed and the CCD board 270 for measuring the light quantity distribution from the LPH 14 using the output from the line CCD 261, and the magnification from which the light from the light emitting portion (SLED 63) of the LPH 14 is enlarged and formed on the surface of the line CCD 261. An optical system 260 is provided.
Furthermore, the optical profile measurement apparatus 200 uses the moving stage 262 that moves the CCD board 270 with the direction (main scanning direction) in which the SLEDs 63 of the LPH 14 are arranged as the moving direction, the stage driver 263 that moves the moving stage 262 at a constant speed, and the LPH 14. On the other hand, an LPH driver 264 that outputs a drive signal to light up each SLED 63 and a CCD interface 280 that processes a data signal transferred from the CCD board 270 are provided.

Processing of the obtained data signal, movement control of the moving stage 262, control of the LPH driver 264, and the like are executed by a personal computer (PC) 266 that is a processing unit. The PC 266 includes a frame grabber 267 for capturing image data, a digital I / O 268 that controls the input of status signals and data signals, the output of control signals, and the like, a motor controller 269 that controls the drive of the stage driver 263, and the like. Yes. The moving stage 262 has, for example, a non-contact structure using an air bearing and a linear motor. The motor controller 269 performs PLL control by feedback from the linear encoder, and performs constant speed movement control of the CCD board 270. Realized.
The optical profile measuring apparatus 200 converts the data into a digital value and takes it into the PC 266 while moving the CCD board 270 having the line CCD 261 at a constant speed in the main scanning direction.

  Next, FIG. 11 is a flowchart showing a flow of processing when the initial light quantity correction data Corr_1 is generated by the optical profile measuring apparatus 200. Note that when performing the process of generating the initial light amount correction data Corr_1, the LPH 14 is held in advance by the holder member (not shown) with respect to the optical profile measuring apparatus 200 and set at a predetermined position.

First, the PC 266 outputs a control signal instructing the LPH driver 264 to turn on the LPH 14 with 4 on 4 off from the digital I / O 268. Thereby, the LPH driver 264 turns on the LPH 14 with 4 on 4 off (S101).
Here, 4on4off lighting means that, as shown in FIG. 12, in the LED array arranged in the SLED 63 of the LPH 14, four adjacent LEDs are turned on, and further, the four adjacent LEDs are turned off. A lighting form. Thus, the reason why the LPH 14 is turned on 4 on 4 off is that when all the lights are turned on, the total light quantity becomes too large, and it is difficult to accurately measure the peak and valley coordinate points of the light quantity by each LED. In addition, as long as each LED is turned on / off alternately, it is possible to use 2on2off lighting in addition to 4on4off lighting.

Next, the PC 266 outputs a control signal for moving the moving stage 262 to the stage driver 263 via the motor controller 269, and moves the CCD board 270 and the magnifying optical system 260 in the arrangement direction of the SLED 63 (main scanning). Direction) (S102).
Further, the PC 266 outputs a control signal instructing measurement of the light amount distribution of the LPH 14 from the digital I / O 268 to the CCD board 270 via the CCD interface 280. Then, the CCD board 270 measures the light quantity distribution of the LPH 14 using the line CCD 261 (S103).

Next, the PC 266 acquires the light amount distribution data measured in step 103 from the CCD board 270 via the CCD interface 280. Then, as shown in FIG. 13, with respect to the light amount distribution data, an integrated value in the sub-scanning direction (y) at each coordinate position (x) in the main scanning direction is calculated, and the light amount distribution (light profile) in the main scanning direction. Is obtained (S104).
At that time, black level correction and shading correction are performed. Here, the black level correction value and the shading correction value for the line CCD 261 are obtained in advance. When obtaining the black level correction value and the shading correction value, light is incident on the magnifying optical system 260 from the integrating sphere and measured. In this case, as the light source used for the integrating sphere, the same LED (wavelength 780 nm) as the LED of the SLED 63 disposed in the LPH 14 is used. In addition, the maximum value of the incident angle of light incident on the magnifying optical system 260 from the integrating sphere is 23 ° which is the maximum value of the incident angle incident on the magnifying optical system 260 from the LPH 14 in the actual optical profile measurement apparatus 200. Is set to be

Subsequently, the PC 266 detects the peak position and valley position in the main scanning direction (x) for the light profile calculated in step 104. Then, the light amount from the valley to the valley in the light profile is integrated, and the integrated value is divided by the distance from the valley to the valley, thereby calculating the light amount (exposure energy) density in the region between the valleys. The exposure energy density of each area thus obtained is set as a correction characteristic value (%) of each light emitting point (LED) (see FIG. 14) (S105).
Further, the PC 266 increases or decreases the amount of light according to the error from the target value so that the correction characteristic value matches the predetermined target value, so that the correction characteristic value (%) in all regions is flat. To be. By such flattening processing, a light amount correction value for each region, that is, a light amount correction value for each LED is calculated (S106).
Then, the PC 266 stores light amount correction data for each LED that is turned on with 4on4off lighting in the memory (S107).

Next, the PC 266 outputs a control signal instructing the LPH driver 264 to turn on the LPH 14 with 4off4on from the digital I / O 268. Thereby, the LPH driver 264 turns on the LPH 14 with 4off4on (S109). That is, the setting is changed to the lighting mode in which the LED that was turned on in step 101 is turned off and the LED that was turned off in step 101 is turned on.
Then, Step 102 to Step 107 are performed in the same manner, and the PC 266 stores the light amount correction data for each LED that is turned on by 4off4on lighting in the memory (S107).
After the measurement in the 4off4on lighting mode is completed (S108), the PC 266 stores the stored light amount correction data for each LED lit by 4on4off lighting and the light amount correction data for each LED lit by 4off4on lighting. Then, rearrangement is performed in accordance with the arrangement order of the LEDs in the LPH 14 to synthesize the light amount correction data for all the LEDs in the LPH 14. And this is memorize | stored in a memory as light quantity correction data of LPH14 (S110).
In this way, the initial light amount correction data Corr_1 of the LPH 14 (SLED 63) is generated. The generated initial light quantity correction data Corr_1 is stored from the PC 266 into the EEPROM 102 provided on the LED circuit board 62 (see FIGS. 2 and 3).

Subsequently, a method for measuring and calculating the process light amount correction data Corr_2 stored in the EEPROM_A301 will be described.
FIG. 15 is a block diagram illustrating a functional configuration of a process light amount correction data generation circuit 400 as an example of a second light amount correction data generation unit that generates process light amount correction data Corr_2 configured in the control unit 30. The process light amount correction data generation circuit 400 illustrated in FIG. 15 includes an image data calculation unit 410, a density unevenness calculation unit 420, and a correction data calculation unit 430.
The image data calculation unit 410 places the read image density data from the image reading device 3 on which the paper P on which the test pattern image is formed is placed and reads the image density data of the test pattern image from the placed paper P. Acquire and perform a predetermined calculation on the acquired image density data.
The density unevenness calculation unit 420 obtains density unevenness data for each LED, which is a density distribution in the main scanning direction generated on the image density data, from the image density data calculated by the image data calculation unit 410.
Based on the density unevenness data for each LED calculated by the density unevenness calculation unit 420, the correction data calculation unit 430 obtains correction data for each LED (process light amount correction data Corr_2) for suppressing the density unevenness. calculate.

Next, FIG. 16 is a flowchart showing a flow of processing when the process light amount correction data generation circuit 400 generates the process light amount correction data Corr_2.
First, the control unit 30 downloads the initial light amount correction data Corr_1 from the EEPROM 102. Then, the downloaded initial light amount correction data Corr_1 is sent to the density unevenness correction data unit 112 of the signal generation circuit 100. Thereby, the light amount of each LED of the LPH 14 is set to be corrected by the initial light amount correction data Corr_1 (S201). That is, here, the density unevenness correction data Corr in the equation (1) for setting the lighting pulse width of each LED is set as the following equation (3).
Corr = Corr_1 (3)

Then, the control unit 30 instructs each image forming unit 11 to form a predetermined test pattern image. At the same time, each image forming unit 11 instructs the image processing unit 40 to transmit an image signal for forming a predetermined test pattern image for each color. Accordingly, the image forming process unit 10 forms a test pattern image for each color on the paper P (S202).
Here, FIG. 17 is a diagram illustrating an example of a test pattern image. The test pattern image shown in FIG. 17 includes a yellow (Y) density detection pattern 51Y, a magenta (M) density detection pattern 51M, a cyan (C) density detection pattern 51C, and a black (K) density. A detection pattern 51K is formed.
Each color used when correcting the inclination of the test pattern image when the paper P on which the test pattern image is formed is placed on the paper P on which the test pattern image is formed. Each position information detection pattern (marker) is also formed at the same time. That is, as shown in FIG. 17, yellow (Y) position information detection pattern 52Y, magenta (M) position information detection pattern 52M, cyan (C) position information detection pattern 52C, black (K). A position information detecting pattern 52K is formed.

  Subsequently, the generated test pattern image is placed on the image reading device 3. Then, the image reading device 3 reads the test pattern image of each color formed on the paper P in Step 202 and measures the image density of each color test pattern image. Thereby, image density data of each color test pattern image is generated over the arrangement direction (main scanning direction) of the LEDs of the LPH 14. Further, the image reading device 3 simultaneously generates position information data for each color marker (S203).

Each color image density data generated by the image reading device 3 and position information data of each color marker are sent to the image data calculation unit 410 of the process light quantity correction data generation circuit 400. Then, the image data calculation unit 410 receives each color image density data and position coordinate data of each color marker.
The image data calculation unit 410 associates each color image density data with each LED with high accuracy so that the paper P is placed in an inclined state on the image reading device 3 or the paper P is inclined during image formation. The tilt correction is performed when the test pattern image is tilted on the paper P in the image forming apparatus. That is, the image data calculation unit 410 calculates the tilt error amount of the test pattern image read by the image reading device 3 based on the position coordinate data of each color marker read by the image reading device 3. Then, the inclination of each color image density data is corrected based on the calculated inclination error amount (S204).
Then, the image data calculation unit 410 sends the color image density data subjected to the inclination correction to the density unevenness calculation unit 420.

The density unevenness calculation unit 420 obtains density unevenness data by averaging the color image density data subjected to the inclination correction received from the image data calculation unit 410 in the sub-scanning direction. Furthermore, magnification correction is performed by performing a scaling process (reduction or enlargement) in a one-dimensional manner in the main scanning direction so that the number of pixels in the density unevenness data matches the number of LEDs on which the test pattern image is formed. The data is associated with the position of each LED (S205).
Thereby, density unevenness data, which is a density distribution in the main scanning direction, generated on an image formed by the image forming apparatus is generated in association with the position of each LED (S206). Then, the density unevenness calculation unit 420 sends the density unevenness data to the correction data calculation unit 430.

The correction data calculation unit 430 calculates correction data for making the density distribution in the main scanning direction substantially flat, that is, process light amount correction data Corr_2, based on the density unevenness data received from the density unevenness calculation unit 420 (S207). . For example, an average value of image density in the main scanning direction is calculated, and a difference between the image density and the image density average value at the position of each LED in the main scanning direction is obtained. Then, a light amount correction value that sets the difference between the image density and the average image density value to 0 for each LED position is set as the process light amount correction data Corr_2. That is, the process light amount correction data Corr_2 uses the potential of the electrostatic latent image formed on the photosensitive drum 12 to be uniform so that the density of each pixel of the image formed by each LED of the LPH 14 is uniform. It is a correction value for correcting the light emission intensity in each LED for forming.
Then, the process light amount correction data Corr_2 calculated by the correction data calculation unit 430 is stored in the EEPROM_A301 (S208).

  In the above processing flow, a test pattern image is formed on the paper P, and the process light amount correction data Corr_2 is generated based on the image density. Thus, instead of using the image density of the test pattern image formed on the paper P, for example, the image density of the test pattern image (toner image) formed on the intermediate transfer belt 21 of the image forming process unit 10 is changed. The process light amount correction data Corr_2 can be generated based on the image density read on the intermediate transfer belt 21.

  Here, in the above processing flow, when the test pattern image is formed (step 202 in FIG. 16), the initial light amount correction is always performed as the density unevenness correction data Corr in the equation (1) for setting the lighting pulse width of each LED. Data Corr_1 is used (step 201 in FIG. 16). As a result, unevenness in the potential of the electrostatic latent image on the photosensitive drum 12 caused by a process (process) other than the exposure by the LPH 14 of the image forming apparatus (machine), and the lapse of machine operation (running) time. It is possible to generate process light amount correction data Corr_2 for correcting the potential unevenness of the electrostatic latent image caused by the change with time of the image forming condition such as the change with time of the photosensitive characteristic of the photosensitive drum 12. That is, by correcting the light amount of the LPH 14 only by the initial light amount correction data Corr_1, the light amount emitted from the LPH 14 can be set substantially uniformly in the main scanning direction. Therefore, if density unevenness occurs in the formed test pattern image, it is caused by a factor other than LPH14, that is, caused by a process other than exposure by LPH14, or a photosensitive drum as the machine running time elapses. This is due to a change in image forming conditions over time, such as a change in the photosensitive characteristics of 12 over time. Therefore, the generated process light amount correction data Corr_2 uniformly forms the potential of the electrostatic latent image formed on the photosensitive drum 12 with respect to the potential unevenness of the electrostatic latent image caused by factors other than the LPH 14. It means the correction value for

In addition, the process light amount correction data Corr_2 can be generated with high accuracy by using the initial light amount correction data Corr_1 when forming the test pattern image.
That is, in the conventional light quantity correction, when the process light quantity correction data Corr_2 is first generated based on the test pattern image formed using the initial light quantity correction data Corr_1, the initial light quantity correction data Corr_1 is generated. It was rewritten with the correction data Corr_2. Therefore, when the next process light amount correction data Corr_2 is generated, new process light amount correction data Corr_2 is generated based on the test pattern image formed using the previously rewritten process light amount correction data Corr_2. For this reason, the light amount correction by the LPH 14 is performed by the process light amount correction data Corr_2 newly generated sequentially. That is, the density unevenness correction data Corr in the equation (1) for setting the lighting pulse width of each LED is set as the following equation (4).
Corr = Corr_2 (4)

  However, for example, the image reading device 3 has an image density reading error in the main scanning direction. An error also occurs when the density unevenness data and the position of each LED are associated in step 205 of the processing flow of FIG. Therefore, in the newly generated process light amount correction data Corr_2, for example, the reading error of the image reading device 3 or the correspondence error with the LED position, etc. that occurred in the process light amount correction data Corr_2 when it was generated last time is again displayed. Will be stacked. For this reason, the process light amount correction data Corr_2 is newly generated many times during the running of the image forming apparatus, and the contents of the memory are sequentially rewritten. Errors and the like are gradually accumulated. As a result, the process light amount correction data Corr_2 has a tendency to gradually decrease in accuracy.

  On the other hand, in the image forming apparatus according to the present embodiment, when the test pattern image is formed (step 202 in FIG. 16), the initial light quantity correction data Corr_1 is always used (step 201 in FIG. 16). For this reason, the process light amount correction data Corr_2 generated does not accumulate the reading error of the image reading device 3, the association error with the LED position, and the like. Therefore, even if the process light amount correction data Corr_2 is newly generated any number of times during the running of the image forming apparatus, a decrease in accuracy of the generated process light amount correction data Corr_2 is suppressed.

As described above, in the image forming apparatus according to the present embodiment, the potential of the electrostatic latent image caused by a process other than the exposure by the LPH 14 or the change with time of the image forming condition with the lapse of the running time of the machine is caused. The process light amount correction data Corr_2 for correcting the potential unevenness of the electrostatic latent image generated in this way can be generated.
Further, the initial light quantity correction data Corr_1 generated based on the inherent configuration factor of the LPH 14 itself is stored in the EEPROM 102, and the process light quantity correction data Corr_2 is stored in the EEPROM_A301, whereby the initial light quantity correction data Corr_1 and the process light quantity are stored. The correction data Corr_2 is held separately. As a result, by downloading the initial light amount correction data Corr_1 from the EEPROM 102, the process light amount correction data Corr_2 can be generated with high accuracy at any time without accumulating the reading error of the image reading device 3 or the error associated with the LED position. can do. Therefore, in the image forming apparatus according to the present embodiment, the light amount correction of the LPH 14 can always be performed with high accuracy.
For example, even when the LPH 14 is replaced with a new one, the process light amount correction data Corr_2 stored in the EEPROM_A 301 and the initial setting regarding the newly installed LPH 14 are not generated again. The light amount correction can be performed with high accuracy by using the light amount correction data Corr_1.

  In addition, for example, as a characteristic unique to each photosensitive drum 12, there may be a variation in the longitudinal direction (axial direction) in the photosensitive characteristic of the photosensitive drum 12. In that case, at the time of shipment from the factory, such a variation in the photosensitive drum 12 is measured, and the corresponding light amount correction data, that is, the photosensitive member light amount correction data (third light amount correction data) Corr_3 is obtained. . For example, an EEPROM (not shown: third memory) may be disposed in a photosensitive drum unit (not shown) that holds the photosensitive drum 12, and the photoreceptor light quantity correction data Corr_3 may be stored in the EEPROM.

When the machine power is turned on, the photoreceptor light quantity correction data Corr_3 is downloaded from the EEPROM of the photoreceptor drum unit to the control unit 30. Similarly, the control unit 30 adds the initial light amount correction data Corr_1 from the EEPROM 102 downloaded, the process light amount correction data Corr_2 stored in the EEPROM_A301, and the photoreceptor light amount correction data Corr_3 by the adder 302. Light amount correction data Corr corresponding to the running time is generated. Then, the control unit 30 sends the generated light amount correction data Corr to the density unevenness correction data unit 112. Accordingly, the light amount correction data Corr is stored in the density unevenness correction data unit 112 as the density unevenness correction data Corr.
Therefore, in this case, the density unevenness correction data Corr is expressed by the following equation (5).
Corr = Corr_1 + Corr_2 + Corr_3 (5)
With this configuration, it is possible to perform light amount correction corresponding to variations in the photosensitive characteristic of the photosensitive drum 12 in the axial direction.

  By the way, since the initial light quantity correction data Corr_1 is light quantity correction data based on a unique configuration factor of the LPH 14 itself, the EEPROM 102 that stores the initial light quantity correction data Corr_1 is preferably disposed integrally with the LPH 14. Further, the process light amount correction data Corr_2 is a light amount for correcting a potential non-uniformity of the electrostatic latent image caused by a process other than the exposure by the LPH 14 and a change in image forming conditions with the passage of the running time of the machine. Since it is correction data, it is preferable that the EEPROM_A 301 that stores the process light amount correction data Corr_2 is disposed on the main body side, for example, the control unit 30.

Note that the process light amount correction data Corr_2 is, for example, at the initial installation of the image forming apparatus, and every time a predetermined number of running sheets elapses, the density unevenness of the formed image (for example, a streak shape extending in the sub-scanning direction). Can be generated, for example, when the degree of density unevenness is lower than a predetermined level.
In addition, the means for correcting the light quantity of each LED of the LPH 14 is not limited to the one that controls the lighting pulse width described above. For example, the light quantity of each LED of the LPH 14 can be corrected by adjusting the current value while keeping the lighting pulse width constant. Further, the light quantity of each LED of the LPH 14 can be corrected by adjusting both the lighting pulse width and the current value.

  As described above, in the LPH 14 according to the present embodiment, the initial light amount correction data Corr_1 based on the inherent components of the LPH 14 itself is stored in the EEPROM 102, and the processes other than the exposure by the LPH 14 and the running time of the machine are accompanied. By storing the process light amount correction data Corr_2 for correcting the potential unevenness of the electrostatic latent image caused by the change in the image forming condition with time in the EEPROM_A301, the initial light amount correction data Corr_1 and the process light amount correction data Corr_2 are stored. Are held separately. Thereby, the process light amount correction data Corr_2 can be generated without degrading the accuracy. Therefore, in the image forming apparatus according to the present embodiment, the light quantity correction of the LPH 14 can always be performed with high accuracy even if the running is repeated.

1 is a diagram illustrating an overall configuration of an image forming apparatus using an LED print head according to an embodiment. It is the figure which showed the structure of the LED print head (LPH). It is a top view of a LED circuit board. It is the figure which showed a part of wiring currently formed on the LED circuit board. It is a block diagram which shows the structure of a signal generation circuit. It is a block diagram explaining the structure of a reference clock generation part. It is a block diagram explaining the structure of lighting time control and a drive part. It is the figure which showed the relationship between the lighting pulse width of lighting signal (PHI) which lights LED, and the light quantity of LED. It is the figure which showed the light quantity characteristic of LED in which gain correction and offset correction were performed. It is the figure which showed the structure of the optical profile measuring device. It is a flowchart which shows the flow of a process at the time of producing | generating initial light quantity correction data Corr_1. It is a figure explaining 4on4off lighting. It is a figure explaining calculation of the integral value of the subscanning direction (y) in each coordinate position (x) of the main scanning direction of light quantity distribution data. It is a figure explaining the correction characteristic value of each light emission point (LED). It is a block diagram which shows the function structure of a process light quantity correction data generation circuit. It is a flowchart which shows the flow of a process at the time of process light quantity correction data Corr_2 being produced | generated. It is the figure which showed an example of the test pattern image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Image reading apparatus, 10 ... Image formation process part, 11 (11Y, 11M, 11C, 11K) ... Image formation unit, 12 ... Photosensitive drum, 14 ... LED print head (LPH), 30 ... Control part, 40 ... Image processing unit 63 ... Self-scanning LED array (SLED) 100 ... Signal generation circuit 102 ... EEPROM 110 ... Image data development unit 112 ... Density unevenness correction data unit 114 ... Timing signal generation unit 116 ... Reference Clock generation unit, 118-1 to 118-58, lighting time control / drive unit, 200, optical profile measurement device, 301, EEPROM_A, 400, process light amount correction data generation circuit, 410, image data calculation unit, 420, density unevenness Calculation unit, 430 ... correction data calculation unit

Claims (12)

A print head that exposes a photoreceptor to form an electrostatic latent image;
A plurality of light emitting elements arranged in a line;
A light amount setting means for adjusting an exposure energy amount of each of the light emitting elements,
The light amount setting means is configured to cause the electrostatic latent image to be generated by factors other than the first light amount correction data for correcting the variation in the emitted light amount inherent between the light emitting elements and the variation in the emitted light amount between the light emitting elements. A print head, wherein the exposure energy amount is adjusted based on second light amount correction data for correcting potential unevenness generated in an image.   The light amount setting means sets a lighting pulse width for driving each of the light emitting elements based on the light amount correction data generated by adding the first light amount correction data and the second light amount correction data. 2. The print head according to claim 1, wherein the exposure energy amount is adjusted.   The light amount setting means corrects potential unevenness generated in the electrostatic latent image due to variations in the first light amount correction data, the second light amount correction data, and the axial photosensitive characteristic inherent in the photoconductor. The print head according to claim 1, wherein the exposure energy amount is adjusted by setting a lighting pulse width for driving each of the light emitting elements based on the third light quantity correction data.   2. The print head according to claim 1, wherein the light amount setting unit adjusts the exposure energy amount using the second light amount correction data updated at a predetermined timing or an arbitrary timing.   The first light quantity correction data is stored in a first storage unit integrally provided with the print head, and the second light quantity correction data is provided on the image forming apparatus side on which the print head is mounted. 2. A print head according to claim 1, wherein said print head is stored in said second storage means. A photoreceptor,
A print head having a plurality of light emitting elements arranged in a line, and exposing the photosensitive member with light emitted from the light emitting elements to form an electrostatic latent image;
First storage means for storing first light amount correction data for correcting variations in the emitted light amount inherent between the light emitting elements of the print head;
An image forming apparatus comprising: a second storage unit that stores second light amount correction data for correcting potential unevenness generated in the electrostatic latent image due to a factor other than exposure by the print head. Further comprising: a control unit that generates light amount correction data for correcting the emitted light amount of the print head, and transmits the generated light amount correction data to the print head;
The controller generates the light amount correction data based on the first light amount correction data stored in the first storage unit and the second light amount correction data stored in the second storage unit. The image forming apparatus according to claim 6. And further comprising third storage means for storing third light amount correction data for correcting potential unevenness generated in the electrostatic latent image due to variations in axial photosensitive characteristics inherent to the photoconductor.
The control unit includes the first light amount correction data stored in the first storage unit, the second light amount correction data stored in the second storage unit, and the first light amount correction data stored in the third storage unit. 8. The image forming apparatus according to claim 7, wherein the light amount correction data is generated based on the three light amount correction data.   The image forming apparatus according to claim 8, wherein the third storage unit is disposed integrally with the photosensitive member. An image forming unit that forms a toner image on a medium based on an electrostatic latent image formed on the photosensitive member by the print head;
A second light amount correction data generation unit that generates the second light amount correction data stored in the second storage unit;
The second light amount correction data generation unit is based on an image density of a predetermined test pattern image formed on the basis of an electrostatic latent image by the print head whose light amount is corrected by the image forming unit by the first light amount correction data. The image forming apparatus according to claim 6, wherein the second light quantity correction data is generated.   The second light amount correction data generation unit is configured to detect density unevenness of the toner image formed in the image forming unit when the image forming device is initially installed, and every time the image forming device has passed a predetermined running number. The image forming apparatus according to claim 10, wherein the second light amount correction data is generated at any one or a plurality of timings when the degree is lower than a predetermined level.   The image forming apparatus according to claim 6, wherein the first storage unit is disposed integrally with the print head, and the second storage unit is disposed on the image forming apparatus main body side.

Images