JP4867673B2 - Light quantity measuring device for exposure apparatus and exposure apparatus - Google Patents

Description

  The present invention relates to a light quantity measuring device for measuring the light quantity of an exposure apparatus that performs optical writing.

In image forming apparatuses such as printers and copiers using an electrophotographic system, light emitting elements such as LEDs are arranged in a line as an exposure apparatus that exposes 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.
In such a print head, if there is a variation in the amount of emitted light between the light emitting elements, density unevenness occurs in the image formed on the recording paper, and the formation of a high-quality image is hindered. In particular, when forming a color image, the color reproducibility is deteriorated due to density unevenness of each color image.

  Therefore, conventionally, a light amount measuring device is used to measure the amount of light emitted from each light emitting element of the print head, and a light amount correction value for each light emitting element is obtained based on the measured light amount distribution of each light emitting element. (For example, refer to Patent Document 1). Then, based on the obtained light amount correction value, the light amount of each light emitting element is corrected.

  In that case, the following method is effective in performing light amount correction for each light emitting element with high accuracy. In other words, the lighting pulse width that determines the light amount of each light emitting element is set by first setting a reference pulse width as a reference, and adding an integer value determined based on the light amount correction value for each light emitting element to the reference pulse width. To do. At that time, a decimal point portion (this is referred to as “quantization error”) that is less than one unit of the reference pulse width generated from the light amount correction value is generated. Then, when the sum of them becomes “1” (one unit of the reference pulse width), the unit is added to the lighting pulse width (see, for example, Patent Document 2). By using such a method, it becomes possible to perform light amount correction with high accuracy corresponding to the resolution of the light amount correction value for each region composed of a predetermined number of light emitting elements in which quantization errors are carried forward.

JP 2002-127492 A (page 7-9, FIG. 16) JP 2002-36628 A (Page 7-8, FIG. 6)

Here, in general, it is possible to perform high-precision light amount correction by effectively using the quantization error for each light emitting element generated from the light amount correction value. It is necessary to obtain a highly accurate light amount correction value at the level.
However, since the quantization error is a decimal part that is less than one unit of the reference pulse width, the amount of light due to lighting of the quantization error becomes unstable. Therefore, in order to measure the light amount corresponding to the quantization error in a stable state, it is necessary to emit light as many times as the light amount corresponding to the quantization error is at least one unit of the reference pulse width. Specifically, for example, if the quantization error is 1/128, the light emitting element emits light 128 × N times (N: a positive integer), and the amount of light corresponding to the quantization error is integrated into at least one unit of the reference pulse width. In this state, it is necessary to measure the light amount. As a result, there is a problem that the measurement time per one exposure apparatus becomes long and the productivity is lowered.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to enable high-precision light quantity measurement at high speed.

  For this purpose, the light quantity measuring device of the exposure apparatus of the present invention is arranged in a plurality of lines and faces a light emitting element in which the irradiation light quantity is determined by setting a coefficient for multiplying a predetermined predetermined pulse width. Arranged in a line, and includes a light quantity measuring means for measuring the light quantity of each light emitting element, and a control means for controlling the lighting operation of each light emitting element and controlling the measurement operation of the light quantity measuring means. A plurality of arranged light receiving elements are arranged, and when the number of stages is obtained by multiplying the fractional part of the coefficient set in the light emitting element by a positive integer, the fractional part of the multiplied product is set to 0. The control means is configured to be an integer, and the control means sets the period of the synchronization signal for setting the measurement timing of each stage of the light receiving element of the light quantity measurement means to a positive integer multiple of the period of the synchronization signal for setting the light emission timing of the light emitting element. Set to It is characterized by a door.

Here, the light quantity measurement means has a relative resolution speed S with respect to the light emitting element as S = s / Tc, where s is the measurement resolution of the light quantity measurement means, and Tc is the period of the synchronization signal for setting the measurement timing of each stage of the light receiving element. It can be characterized by being set to. Further, the light amount measuring means sets the above-mentioned predetermined pulse width as BASE, a, b is 0 or an integer, M is a positive integer, and the irradiation light amount of the light emitting element is set as BASE × (a + b / M). In addition, the number of stages of the light receiving elements may be set to M × N, where N is a positive integer. Further, the light quantity measuring means sequentially transfers the light quantity data measured by each of the light receiving elements arranged in a plurality of lines to the light receiving elements located downstream in the movement direction of the light receiving elements, and transfers the transferred light quantity data and the transferred light quantity data. The light quantity data measured by the received light receiving elements can be integrated sequentially.
Further, the control means may output the synchronization signal for setting the measurement timing of each stage of the light receiving element of the light quantity measurement means and the synchronization signal for setting the light emission timing of the light emitting element in synchronization with each other. .

  The light quantity measuring device of the exposure apparatus of the present invention is arranged in a plurality of lines, and is arranged facing a light emitting element whose irradiation light quantity is determined by setting N steps (N is a positive integer) correction amount. A light quantity measuring means for measuring the light quantity of each element, and a control means for controlling the lighting operation of each light emitting element and controlling the measurement operation of the light quantity measuring means, the light quantity measuring means being a plurality of light receiving elements arranged in a line Are arranged in a plurality of stages, and the number of stages is set to an integer multiple of N, and the control means sets the period of the synchronization signal for setting the measurement timing of each stage of the light receiving element of the light quantity measuring means to the light emitting element. The light emission timing is set to a positive integer multiple of the period of the synchronization signal.

  Further, the present invention is regarded as an exposure apparatus, and the exposure apparatus of the present invention includes a plurality of light emitting elements arranged in a line, storage means for storing light amount correction data for correcting the light amount of each light emitting element, and a reference Is set based on the light quantity correction data stored in the storage means, and the light quantity of the light emitting element is corrected by the lighting pulse width multiplied by the coefficient concerning the predetermined pulse width. And a driving circuit that emits light, and the storage means includes a plurality of light receiving elements in which a plurality of light quantity correction data stored in a line are arranged, and the number of stages is a coefficient set by the light emitting element. Is a light quantity measuring means configured to be an integer in which the fractional part of the multiplied product is set to 0, and the measurement timing of each stage of the light receiving element is Set Cycle phases signals, is characterized in that it is generated based on the measured light quantity by the light quantity measuring means is set to an integral multiple of the period of the synchronizing signal for setting the light emission timing of the light emitting element.

  Here, the driving circuit may be characterized in that a decimal part of a coefficient set in the light emitting element is carried over to the light emitting element adjacent to the light emitting element. In particular, the drive circuit may be characterized in that the fractional part of the coefficient is carried over to a light emitting element adjacent to a range in which density unevenness is difficult to be determined by human vision for the light emitting element.

According to the first aspect of the present invention, it is possible to perform highly accurate light quantity measurement at high speed.
According to the second aspect of the present invention, the light quantity can be measured without causing overlap in the measurement region, and the measurement time can be further shortened.
Further, according to claim 1 of the present invention enables high-precision light quantity measuring corresponding to the resolution of the light quantity correction data.

According to claim 3 of the present invention, it is possible to measure the integrated value of the light quantity measured in a plurality of stages by one scan of the light quantity measuring means, and to further shorten the measurement time. it can.
According to the fourth aspect of the present invention, the amount of irradiation light at each stage of the light amount measuring means is uniform, and accurate light amount measurement is possible.

According to claim 5 of the present invention, it is possible to perform highly accurate light quantity measurement at high speed.
Further, according to the sixth aspect of the present invention, it is possible to perform exposure with a light amount whose light amount has been corrected with high accuracy.
According to claim 5 of the present invention, in an exposure apparatus that carries out light amount correction by carrying over a quantization error, light amount correction data generated based on the light amount measured at a level equivalent to the quantization error, It becomes possible to perform light amount correction with high accuracy.
Further, according to the fifth aspect of the present invention, it is possible to perform exposure with the light amount corrected for the light amount within a range that is difficult for human vision to discriminate.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a view showing the overall configuration of an image forming apparatus using a print head which is an example of an exposure apparatus of 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. The control unit 30 is connected to an external device such as a personal computer (PC) 2 or an image reading device 3, and includes an image processing unit 40 that performs predetermined image processing on image data received from these devices.

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 holds 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 that exposes the photosensitive drum 12 charged by the developing device 13, a developing device 15 that develops 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 PC 2 or the image reading device 3 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 diagram showing the configuration of an LED print head (LPH) 14 that is an exposure apparatus. In FIG. 2, the LPH 14 is equipped with a housing 61 as a support, a self-scanning LED array (SLED) 63 constituting a light emitting unit, a signal generation circuit 100 for driving the SLED 63 and SLED 63 (see FIG. 3 in the subsequent stage), and the like. The rod lens array 64, which is an optical member for imaging the light from the LED circuit board 62 and SLED 63 on the surface of the photosensitive drum 12, the holder 65 for supporting the rod lens array 64 and shielding the SLED 63 from the outside, and the housing 61 for the rod lens A leaf spring 66 that pressurizes in the direction of the 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 as described above 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, light amount correction data for the SLED 63, and the like. A harness 103 for transmitting and receiving signals between the EEPROM 102 and the image forming apparatus main body is provided.

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 The signal lines 107 (107_1 to 107_58) for transmitting the lighting signals ΦI (ΦI1 to ΦI58) corresponding to the image data from the image processing unit 40 to the respective SLED chips from 100, and further, the respective light emitting points of the respective SLED chips are set. 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 variations in the amount of emitted light for each LED in the SLED 63. 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.
The EEPROM 102 stores light amount correction data Corr_I for each LED, which is measured and calculated by the light profile measuring apparatus 200 described later, and other density unevenness correction data as necessary. When the machine power is turned on, the light amount correction data Corr_I for each LED is downloaded from the EEPROM 102 to the density unevenness correction data unit 112. The density unevenness correction data unit 112 generates density unevenness correction data Corr based on the acquired light quantity correction data Corr_I for each LED, and further, based on the light quantity correction data Corr_I and other data as necessary. , And outputs it to the lighting time control / drive units 118-1 to 118-58.

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, a frequency divider 1 / N144, and a phase comparator. 146 and a voltage controlled oscillator 148, and a lookup table (LUT) 132. 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 clock signal at a frequency based on the control voltage. In the present embodiment, a control voltage corresponding to a frequency that divides the lightable period into 256 is supplied, a clock signal (reference clock signal) of this frequency is generated, and the timing signal generator 114 and all lighting time controls are generated. -It outputs to drive part 118-1-118-58. The voltage controlled oscillator 148 is also connected to the frequency divider 1 / M142, and the 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 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 pixel from the image data development unit 110, and data for reading density unevenness correction data corresponding to each pixel (each LED) from the density unevenness correction data unit 112 A read signal is output to 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, a trigger signal for starting the lighting of the SLED 63 ( TRG) is output.

The lighting time control / drive units 118-1 to 118-58 correct the lighting time of each pixel (each LED) based on the density unevenness correction data Corr, and control signal CKI (=) for lighting each pixel of the SLED 63. A lighting signal ΦI) is generated.
Specifically, the lighting time control / drive units 118-1 to 118-58 are presettable digital one-shot multi, as shown in FIG. 7 (block diagram for explaining the configuration of the lighting time control / drive unit 118). A vibrator (PDOMV) 160, a linearity correction unit 162, an AND circuit 170, and a correction calculation unit 180 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 from the timing signal generation unit 114 is displayed. When (TRG) is output to PDOMV 160 and the image data is 0 (OFF), the trigger signal (TRG) is not output.

The correction calculation unit 180 receives the density unevenness correction data Corr and the image data, and represents the density unevenness correction amount calculated based on the density unevenness correction data Corr and the quantization error carried over from the neighboring pixels (see the subsequent stage). Generate a data signal. The data signal generated by the correction calculation unit 180 is input to the PDOMV 160 (SETDATA terminal).
In the correction calculation unit 180 of this embodiment, the correction accuracy is set to 4 bits (0 to 15), and the correction amount corresponding to the upper 4 bits of the 8-bit density unevenness correction data Corr for each pixel is set. Make corrections. In addition, a correction amount having a resolution higher than the correction resolution, that is, a correction amount for the remaining lower 4 bits (referred to as “quantization error”) is handled as a correction amount carried over to neighboring pixels (see later stage).

  The PDOMV 160 is connected to the AND circuit 170, the correction calculation unit 180, the reference clock generation unit 116, and the linearity correction unit 162, and is synchronized with the trigger signal (TRG) from the AND circuit 170 from the correction calculation unit 180. A lighting pulse signal having the number of clocks corresponding to the output data signal is generated.

  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 delay selection data for each LED in the SLED 63 and lighting signal selection data. . Delay selection data and lighting signal selection data for each LED are measured in advance and stored in the EEPROM 102. The delay selection data and lighting signal selection data stored in the EEPROM 102 are downloaded to the delay selection register 166 when the machine power is turned on. Note that a flash ROM can also be used as the storage means, and in that case, the flash ROM itself can function as the delay selection register 166.

The delay signal selection unit 165 is connected to the AND circuit 167 and the OR circuit 168, and is one of outputs from the delay circuits 164-0 to 164-7 based on the delay selection data stored in the delay selection register 166. Select one. 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 there is, output a lighting pulse. 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 signal is output to the LPH 16 via the MOSFET 172 as the control signal CKI.

  As shown in FIG. 5, a three-terminal regulator 101 is connected to the LPH 14, and a stable +3.3 V voltage is supplied from the three-terminal regulator 101 to the LPH 14.

Here, the correction calculation unit 180 disposed in the lighting time control / drive units 118-1 to 118-58 of the present embodiment will be described.
As shown in FIG. 8 (a block diagram for explaining the configuration of the correction calculation unit 180), the correction calculation unit 180 of this embodiment includes an AND circuit 181, a quantization error carry-over memory 182, an adder 183, and a buffer 184. It is comprised including. In the following, the bit of the data signal input to each part is indicated by [n: m]. That is, for example, [7: 0] indicates a signal from the 0th bit to the 7th bit.

  In the correction calculation unit 180, the input density unevenness correction data Corr is sent to the AND circuit 181. The input image data is sent to the AND circuit 181 and the buffer 184. The AND circuit 181 performs an AND operation on the input density unevenness correction data Corr (8 bits) and the image data (1 bit), and outputs an 8-bit data signal [7: 0] as a calculation result. That is, when the image data is 1 (ON), the value of the density unevenness correction data Corr is generated as a calculation result, and when the image data is 0 (OFF), “0” is generated as the calculation result. . This data signal [7: 0] is input to the adder 183 at the subsequent stage.

The adder 183 receives the data signal [7: 0] from the AND circuit 181 and the 4-bit quantization error data [3: 0] representing the carried quantization error from the quantization error carry memory 182. Are entered. The adder 183 adds the data signals input from the AND circuit 181 and the quantization error carry-over memory 182 and generates an 8-bit data signal Y0 [7: 0] as a calculation result.
In the adder 183, the 8-bit data signal Y0 [7: 0] is divided into the data signal Y1 [7: 4] which is the upper 4 bits and the data signal Y2 [3: 0] which is the lower 4 bits. Generated. Each of the data signal Y1 [7: 4] and the data signal Y2 [3: 0] includes a signal line for the data signal Y1 [7: 4] and a signal line for the data signal Y2 [3: 0]. It is divided and output. The signal line for the data signal Y1 [7: 4] is merged with the signal line of the data signal representing the image data (1 bit) output at the same timing by the buffer 184, and becomes the data signal Y1 [7: 4]. A data signal Y [8: 4] is generated by combining the image data as the fifth most significant bit. Then, the generated data signal Y [8: 4] is output from the correction calculation unit 180 as new density unevenness correction data Corr_M. That is, the upper 1 bit of the 5-bit data signal Y [8: 4] represents image data, and the lower 4 bits were calculated based on density unevenness correction data and quantization error carried over from neighboring pixels. It represents density unevenness correction data Corr_M.

On the other hand, the signal lines for the lower 4 bits of the data signal Y2 [3: 0] are connected to the quantization error carry-over memory 182 and the data signal Y2 [3: 0], that is, the quantization error is in the vicinity. It is stored in the quantization error carry memory 182 as a carry amount to the pixel.
Here, the carry-over of the data signal Y2 [3: 0] to neighboring pixels can be determined by address control when data is input / output to / from the quantization error carry-over memory 182. That is, when generating the control signal CKI for lighting each pixel (LED) of the SLED 63 of the LPH 14, the correction calculation unit 180 determines the access address of the quantization error carry-over memory 182 (address control). Then, the quantization error carried over to the lighting target pixel (LED) is read from the quantization error carry-over memory 182, and the lighting pulse of the lighting target pixel is read based on the density unevenness correction data Corr and the quantization error. Density unevenness correction data Corr_M (lower 4 bits of Y [8: 4]) for correcting the width is generated.

In this case, since the resolution of the density unevenness correction data Corr (8 bits) is higher than the correction resolution (4 bits) of the correction calculation unit 180, the correction calculation unit 180 cannot complete the correction by correcting the lighting pulse width. The remaining quantization error is stored in the quantization error carry memory 182 as a quantization error carried over to neighboring pixels.
As described above, in the LPH 14 according to the present embodiment, even if the correction resolution (4 bits) of the correction calculation unit 180 is smaller than the resolution (8 bits) of the density unevenness correction data, the amount of correction cannot be corrected. Is carried forward to neighboring pixels, and light quantity correction is performed accordingly. For this reason, it is possible to perform high-precision light amount correction while maintaining the resolution of the density unevenness correction data Corr for each pixel region where the quantization error is carried forward.

In the PDOMV 160, in synchronization with the trigger signal (TRG) from the AND circuit 170, the lighting pulse signal having the number of clocks corrected according to the density unevenness correction data Corr_M generated by the correction calculation unit 180 is generated, Output to the correction unit 162. Then, the linearity correction unit 162 performs offset correction using the delay selection data Offset.
Specifically, in the lighting time control / drive units 118-1 to 118-58 of the present embodiment, as shown in the following equation (1), the lighting pulse width of each LED is set to the density unevenness correction data Corr_M and By setting the lighting pulse width based on the delay 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 is output to the LPH 14.
Lighting pulse width = BASE. (1 + Corr_M / 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. Further, the density unevenness correction data Corr_M of the present embodiment is composed of the upper 4 bits of the density unevenness correction data Corr of 8 bit data (0 to 255). This shows a case where the light amount correction width is set to maximum correction value / minimum correction value = 3.
In this way, by setting the lighting pulse width according to the equation (1), the light quantity characteristic in the lighting pulse width area used in the image forming apparatus substantially matches the target light quantity characteristic. The light quantity of the LED is set to fall within a predetermined range.

On the other hand, the quantization error is temporarily stored in the quantization error carry-over memory 182 but carried over to neighboring pixels as described above.
Here, FIG. 9 is a diagram illustrating an example of a form in which the quantization error is carried over to neighboring pixels. In FIG. 9, the LEDs arranged in the main scanning direction in the SLED chip 63 of the LPH 14 are sequentially supplied from the LED (1), LED (2), LED (3), LED (4),. The correction values for each LED (1), LED (2), LED (3), LED (4),... Determined by the density unevenness correction data Corr are A1, A2, A3, A4,.
In the LPH 14 according to the present embodiment, between four adjacent LEDs, that is, between the LED (1) and the LED (2), between the LED (2) and the LED (3), and between the LED (3) and the LED (4 ) And between LED (4) and LED (1) is addressed to carry forward the quantization error. In this case, first, LED (1) is turned on (image data is 1). At that time, LED (1) is based on the integer part m1 of correction value A1 (corresponding to the upper 4 bits of A1). While the lighting pulse width is corrected by the first term of the above-described equation (1), the decimal part n1 (corresponding to the lower 4 bits of A1) is carried over to the adjacent LED (2) as a quantization error. When the LED (1) is turned on, the LED (2) is turned on. The LED (2) adds the correction value A2 and n1 carried over from the LED (1), and the integer part m2 of the addition result Based on the above, while the lighting pulse width is corrected by the first term of the above-described equation (1), the decimal part n2 of the addition result is carried over to the adjacent LED (3) as a quantization error.

  Similarly, when the LED (2) is turned on, the LED (3) is turned on. The LED (3) adds the correction value A3 and n2 carried over from the LED (2), and the integer part of the addition result On the basis of m3, while the lighting pulse width is corrected by the first term of the above-described equation (1), the decimal part n3 of the addition result is carried over to the adjacent LED (4) as a quantization error. When the lighting of the LED (3) is finished, the next LED (4) adds the correction value A4 and n3 carried over from the LED (3), and based on the integer part m4 of the addition result (1 While the lighting pulse width is corrected by the first term of the equation (1), the fractional part n4 of the addition result is the next time the next LED (1) is turned on as a quantization error, that is, the LED ( Carry over when 1) lights up.

  The lighting pulse width is corrected while carrying forward the quantization error between the four pixels, for example, LED (1) to LED (4) adjacent to each other in the main scanning direction, and each SLED chip (CHIP1 to CHIP58) of the SLED 63 has one line. When the lighting of each LED is finished and the formation of an image for one line is finished, the lighting of each LED for forming the image of the next line is started. In the next line, the LED (1) is first turned on. In the LED (1), the correction value A1 and n4 carried over from the LED (4) when the previous line is turned on are added, and the integer part m5 of the addition result is obtained. Based on the above, the lighting pulse width is corrected by the first term of the above-described equation (1). On the other hand, the decimal part n5 of the addition result is carried over to the adjacent LED (2) as a quantization error. When the lighting of the LED (1) is finished, the LED (2) is turned on, and the LED (2) adds the correction value A2 and n5 carried over from the LED (1), and based on the integer part m6 of the addition result. Thus, while the lighting pulse width is corrected by the first term of the above equation (1), the decimal part n6 of the addition result is carried over to the adjacent LED (3) as a quantization error.

  When the image data is 0 (OFF) in the next LED (3), the correction value A3 is not input, and the integer part does not appear only by the decimal part n6 carried over from the LED (2). Therefore, the LED (3) is not turned on, and this fractional part n6 is carried over to the adjacent LED (4) as it is. That is, when an LED is not turned on, the quantization error (here, fractional part n6) carried over to the LED at this point (here, LED (3)) is the adjacent LED (here, fractional part n6). , LED (4)) is carried over. Therefore, it is possible to prevent occurrence of correction errors. The next LED (4) has the image data 1 (ON) and is lit. At that time, the LED (4) uses the correction value A4 and n6 carried forward from the LED (3) as it is. Based on the integer part m7 of the addition result, the lighting pulse width is corrected by the first term of the above equation (1). On the other hand, the decimal part n7 of the addition result is carried over to the time of lighting of the next line of LED (1) as a quantization error.

  Although FIG. 9 shows an example in which the quantization error is carried over between four pixels adjacent in the main scanning direction, neighboring pixels carrying over the quantization error are within a predetermined range from the carry-over source pixel (for example, Any pixel can be used as long as it is below the pitch at which output unevenness can be visually discerned, and can be carried over with various carry-over patterns such as carrying over quantization error between two pixels adjacent in the main scanning direction.

Next, a method for measuring and calculating the light quantity correction data Corr_I of the LPH 14 stored in the EEPROM 102 will be described. As described above, the light amount correction data Corr_I is data for correcting variations in the amount of light generated for each LED in the SLED 63 during image formation, and the density unevenness correction data unit 112 generates the density unevenness correction data Corr. This data is used when
First, an optical profile measuring apparatus 200 as a light quantity measuring apparatus for measuring the exposure energy distribution (optical profile) of the LPH 14 will be described. FIG. 10 is a diagram showing a configuration of the optical profile measuring apparatus 200. As shown in FIG. 10, the optical profile measuring apparatus 200 is provided as an example of a light quantity measurement sensor, the 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. A TDI-CCD (Time Delay Integration-CCD) 261 arranged in multiple stages, and a CCD board 270 that includes the TDI-CCD 261 and measures the light quantity distribution from the LPH 14 using the output from the TDI-CCD 261 The optical system 260 includes a magnifying optical system 260 that forms an image by enlarging the light from the light emitting portion (SLED 63) of the LPH 14 onto the surface of the TDI-CCD 261.

Further, the optical profile measuring 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 IF board 264 that outputs various operation signals and lights each SLED 63 is provided.
Processing of the obtained data signal, movement control of the moving stage 262, operation control of the LPH driver IF board 264, and the like are executed by a personal computer (PC) 266 that is a processing unit. That is, the PC 266 controls the frame grabber board 265 for taking in the light amount data signal, the X, Y, Z motor controller 267 for controlling the drive of the stage driver 263, the CCD board 270, and the LPH driver IF board 264.
The moving stage 262 has, for example, a non-contact structure using an air bearing and a linear motor. The X, Y, Z motor controller 267 performs PLL control by feedback from a linear encoder, and the like of the CCD board 270. Realizes fast movement control.
Then, the optical profile measuring apparatus 200 converts the measured light quantity data into a digital value via the frame grabber board 265 while moving the CCD board 270 having the TDI-CCD 261 at a constant speed in the main scanning direction, and sends it to the PC 266. It is taken in.

The magnifying optical system 260 is composed of an optical system (both telecentric optical system or afocal optical system) that is telecentric on both sides with respect to the wavelength (780 nm) of light emitted from the SLED 63 of the LPH 14.
FIG. 11 is a diagram illustrating the configuration of the magnifying optical system 260. As shown in FIG. 11, the enlarging optical system 260 at the barrel K, the object-side lens Len1 focal length _{f 1,} and the image side lens Len2 focal length _{f 2,} along the optical axis, The image-side focal point F ₁ ′ of the object-side lens Len1 and the object-side focal point F ₂ of the image-side lens Len2 are arranged so as to coincide with each other. The first diaphragm S1 is disposed at a position where the image side focal point F ₁ ′ of the object side lens Len1 and the object side focal point F ₂ of the image side lens Len2 coincide.
The object-side focal point F1 of the object-side lens Len1 is disposed so as to coincide with the focal plane Q1 (focal length f) of the rod lens array 64 of the LPH ₁₄ . A second diaphragm S2 is disposed at the object-side focal point F ₁ (focal plane Q1 of the rod lens array 64) of the object-side lens Len1.
Furthermore, the sensor surface of the TDI-CCD 261 is disposed so as to coincide with a surface orthogonal to the optical axis at the position of the image side focal point F ₂ ′ of the image side lens Len2. Note that the surface orthogonal to the optical axis at the position of the image side focal point F ₂ ′ of the image side lens Len2 is the focal plane Q2 of the magnifying optical system 260.

  In this way, by configuring the magnifying optical system 260 as a double-sided telecentric optical system, when the light emitted from the SLED 63 of the LPH 14 is collected by the rod lens array 64, it enters the focal plane Q1 at an incident angle θ. Light is incident on the focal plane Q2 of the magnifying optical system 260, that is, the sensor plane of the TDI-CCD 261 at an incident angle αθ (= θ ′: α is a constant), regardless of the image height h at the focal plane Q1. To do. That is, a unique relationship of θ ′ = αθ can be formed between the incident angle θ on the focal plane Q1 and the incident angle θ ′ on the sensor surface of the TDI-CCD 261. Here, the incident angle refers to an angle formed by the light beam and the optical axis (the same applies hereinafter).

By the way, FIG. 12 is a diagram illustrating the optical paths of the light B1 and the light B2 emitted from different light emitting points (LEDs) of the SLED 63, respectively. As shown in FIG. 12, the rod lens array 64 has a refractive index distribution around its central axis even for the two lights B1 and B2 irradiated perpendicularly from the light emitting point toward the rod lens array 64. Thus, the optical path follows a different path depending on which part of the incident surface of the rod lens array 64 is incident. Therefore, the light B1 and the light B2 have different incident angles when entering the focal plane Q1 of the rod lens array 64. For example, in the example shown in FIG. 12, the light B1 enters perpendicularly to the focal plane Q1, while the light B2 enters the focal plane Q1 at an incident angle γ.
Note that the light emitted from the light emitting point (LED) of the SLED 63 is actually emitted with a spread as shown by the dotted line in FIG. 12, and forms an image on the focal plane Q1 through a plurality of rod lenses. . However, in FIG. 12, for the sake of easy understanding, the portion with the strongest light intensity (solid line) is described to clarify the difference in the optical path. Therefore, the actual condensed light on the focal plane Q1 has a light amount distribution such that the solid line portion has the highest light intensity and becomes weaker along the periphery.

  On the other hand, in the photosensitive drum 12 provided in the image forming unit 11 (see FIG. 1) and the TDI-CCD 261, the sensitivity to light (hereinafter also simply referred to as “sensitivity”) depends on the incident angle of incident light. It has a sensitivity characteristic of changing (incident light angle dependency). Therefore, even if the light set to the same light amount is irradiated on the photosensitive drum 12 and the TDI-CCD 261, if the incident angle of the irradiated light is different, the photosensitive drum 12 and the TDI-CCD 261 are irradiated. Will have different sensitivities.

For this reason, the optical profile measurement apparatus 200 of the present embodiment uses the magnifying optical system 260 configured with a double-side telecentric optical system. As described above, the light incident on the focal plane Q1 of the rod lens array 64 does not depend on the image height h at the focal plane Q1, and is uniform on the sensor plane of the TDI-CCD 261 for any incident angle θ. It is converted into an incident angle αθ (= θ ′) compressed at a predetermined magnification α (constant). Therefore, the incident angle θ of light incident on the photosensitive drum 12 and the incident angle θ ′ of light incident on the sensor surface of the TDI-CCD 261 can be uniquely associated.
Therefore, as can be easily understood from FIG. 13 showing the relationship between the sensitivity of the photosensitive member and the sensitivity of the TDI-CCD 261 and the incident angle of the light incident on each of them, the magnifying optical system 260 is incident on the focal plane Q1. The magnification α is set so that light having an incident angle θ (−M ° ≦ θ ≦ M °) is converted to an incident angle θ ′ (−m ° ≦ θ ≦ m °) on the sensor surface of the TDI-CCD 261. For example, the sensitivity of the photosensitive drum (photosensitive member) 12 and the sensitivity of the TDI-CCD (sensor) 261 can be substantially matched with respect to light in the incident angle range −M ° ≦ θ ≦ M °.

Specifically, the light incident on the photosensitive drum 12 at M ° is incident on the sensor surface of the TDI-CCD 261 at m ° by the magnifying optical system 260. Therefore, the sensitivity at the incident angle | θ | = M ° at the photosensitive drum 12 and the sensitivity at the incident angle | θ ′ | = m ° at the line CCD 261 are both equal to q from FIG.
Even in the range of the incident angle −M ° <θ <M °, since there is a linear relationship of θ ′ = αθ, the sensitivity of the photosensitive drum 12 and the sensitivity of the TDI-CCD 261 are substantially the same.
Therefore, in this case, α = m / M, that is, α = 1 / β and β is β = f ₂ / f ₁ as described above, so that f ₂ / f ₁ = M / m. have a relationship as, the object-side lens Len1 focal length f _1, a double telecentric magnifying optical system 260 with the image-side lens Len2 focal length f _2, the incident angle -M ° ≦ θ ≦ M in ° With respect to the light in the range, the sensitivity characteristic (incident light angle dependency) of the photosensitive drum (photosensitive member) 12 and the sensitivity characteristic of the TDI-CCD (sensor) 261 can be substantially matched.
In the actual image forming apparatus, since the maximum value θ _MAX of the incident angle θ of the light incident on the photosensitive drum 12 is θ _MAX = 23 °, it is preferable to set M = 23 °.

As a result, the light profile measuring apparatus 200 of the present embodiment can generate light amount correction data Corr_I corresponding to the sensitivity characteristic of the photosensitive drum 12. In particular, even in the LPH 14 in which the SLED chips (CHIP1 to CHIP58) are alternately arranged in a staggered manner, the light amount correction data Corr_I corresponding to the sensitivity characteristic of the photosensitive drum 12 can be generated.
Therefore, when the light quantity of the LPH 14 is corrected by the light quantity correction data Corr_I, when the photosensitive drum 12 is exposed by the LPH 14 and an electrostatic latent image is formed in an actual image forming apparatus, a predetermined latent image potential is set. Therefore, it is possible to make the light quantity assumed to obtain the light quantity substantially coincide with the light quantity actually emitted from the LPH 14. As a result, it is possible to obtain a desired latent image potential with respect to a predetermined amount of light, and to realize an appropriate image density and image gradation.

Next, the TDI-CCD 261 used in the optical profile measuring apparatus 200 of the present embodiment will be described. FIG. 14A is a plan view for explaining the structure of the TDI-CCD 261, and FIG. 14B is a view for explaining the operation during light quantity measurement.
As shown in FIG. 14A, the TDI-CCD 261 includes a sensor unit and a horizontal register unit. The sensor unit includes, for example, a CCD chip of 1024 pixels in the longitudinal direction and 128 pixels in the lateral direction. Has a planar structure. Then, according to the movement of the moving stage 262 of the light profile measuring apparatus 200, the light profile of each light emitting point (LED) of the LPH 14 is measured while the short side direction moves toward the main scanning direction of the LPH 14.

  Therefore, in the TDI-CCD 261, the CCDs in the sub-scanning direction 1024 pixels arranged in the main scanning direction of the LPH 14 measure the light profile of each light emitting point (LED). At this time, as shown in FIG. 14B, the TDI-CCD 261 (1) first receives the light from the LPH 14 by each of the first-stage 1024 pixel CCDs and measures the light quantity in the region R. (2) The light amount data measured by the first stage CCD is transferred to the second stage CCD. (3) Each 1024 pixel CCD in the second stage again measures the amount of light in the region R measured by the first CCD. Accordingly, the second-stage CCD generates light-quantity data obtained by adding the light-quantity data measured by the second-stage CCD to the light-quantity data measured by the first-stage CCD.

Subsequently, (4) the light quantity data obtained by integrating the first-stage light quantity data and the second-stage light quantity data is transferred to the third-stage CCD. Further, (5) each of the third-stage 1024 pixel CCDs measures the light quantity in the region R again. Therefore, the light quantity data measured by the third stage CCD is added to the light quantity data obtained by integrating the first stage light quantity data and the second stage light quantity data in the third stage CCD. Light quantity data is generated. (6) The light quantity data obtained by integrating the first to third stage light quantity data is transferred to the fourth stage CCD.
In this way, the light amount data obtained by integrating the 128-step light amount data is generated for each 1024 pixels arranged in the sub-scanning direction of the 128th step. Then, the 128-stage integrated light quantity data in each of the 1024 pixels in the sub-scanning direction is sent to the horizontal register unit, and is sequentially transmitted from the horizontal register unit to the CCD board 270.

  As described above, the TDI-CCD 261 of the present embodiment has the number of stages (128 stages in this case) formed in the main scanning direction for each area in the main scanning direction (for example, the area R in FIG. 14B). The amount of light is measured as many times as the number of times. Accordingly, as in the present embodiment, the lighting time control / drive unit 118 carries forward the correction amount (decimal part) that cannot be corrected by the above-described equation (1) to the neighboring pixels as a quantization error. By measuring the light quantity of each LED at high speed with the same accuracy as the resolution of the density unevenness correction data Corr, the LPH 14 that enables high-precision light quantity correction while maintaining the resolution of the density unevenness correction data Corr by the light quantity correction by Is possible. Hereinafter, this point will be described.

In the light profile measuring apparatus 200, when the light amount correction data Corr_I is set, for example, the light amount when the lighting pulse width (lighting pulse width at measurement) shown in the following equation (2) is set to the LED is measured. Is done.
Measurement pulse width = BASE · (1 + Corr_I / 128) (2)
Here, it is assumed that, for example, light amount correction data Corr_I = 120 is set. Then, equation (2) becomes the following equation (2 ′).
Measurement pulse width = BASE · (1 + 120/128) (2 ')
In the equation (2 ′), (1 + 120/128) = 1.9375, so that the lighting of the fractional part (0.9375 part) less than one unit of BASE (reference pulse width) is unstable. Therefore, it is difficult to accurately measure the amount of light with a lighting pulse width of 1.9375 × BASE with one lighting.
However, if this is measured, for example, by lighting it 128 times,
BASE · (1 + 120/128) × 128 = BASE · (128 + 120)
Thus, the amount of light at the lighting pulse width that is an integral multiple of BASE is measured. Therefore, stable lighting can be realized, and an accurate light amount with the light amount correction data Corr_I = 120 can be measured.

Generally, when the LED is lit 128 times with the measurement lighting pulse width according to equation (2), the measured light quantity is set to the lighting pulse width BASE · (128 + Corr_I) for the set light quantity correction data Corr_I. It becomes the light quantity by the LED which is done. Here, since 128 · BASE is constant, the light amount obtained by subtracting the light amount corresponding to the lighting pulse width 128 · BASE from the measured light amount, that is, the light amount corresponding to the lighting pulse width BASE · Corr_I is easily obtained. Therefore, by turning on the LED only 128 times, it is possible to perform light quantity measurement with the resolution of the light quantity correction data Corr_I.
As described above, in order to measure the light amount with the resolution of the light amount correction data Corr_I, the number of times that the fractional part (quantization error) less than one unit of BASE (reference pulse width) does not occur, that is, the quantization error It is necessary to measure the amount of light in a state where the amount of the minute light is integrated to at least one unit of the reference pulse width.
In the LPH 14 of the present embodiment, if a value of 0 to 255 (8 bits) is set as the light amount correction data Corr_I, 128 × N (N: positive integer) in which (1 + Corr_I / 128) is always an integer. By performing lighting once, it is possible to measure the light amount with a resolution of 8 bits.

As described above, in order to perform highly accurate light amount measurement with the same level of resolution as the light amount correction data Corr_I, when the lighting pulse width is defined by the equation (2), as described above, 128 × N Therefore, it is necessary to measure the amount of light that has just been turned on. However, if it is assumed that a normal line CCD sensor in which only one CCD is arranged as the light quantity measurement sensor, each LED of the SLED 63 of the LPH 14 is provided for each light receiving surface of the line CCD sensor having one CCD. Needs to be lit 128 × N times. In this case, assuming that the chip size of one CCD is L, and the period of the horizontal synchronization signal (HSYNC) when the SLED 63 in the LPH 14 is turned on is T and N = 1, the moving speed of the line CCD sensor is (3 )
Moving speed of line CCD sensor = L / (T × 128) (3)

On the other hand, if the TDI-CCD 261 of this embodiment is used, each LED of the SLED 63 of the LPH 14 may be lighted 128 × N times for each light receiving surface of the TDI-CCD 261 having 128 stages of CCD. In this case, the chip size of the TDI-CCD 261 is 128L. For this reason, the moving speed of the TDI-CCD 261 of the present embodiment is expressed by the following equation (4).
Movement speed of TDI-CCD 261 = 128L / (T × 128) (4)
Therefore, from the equations (3) and (4),
Movement speed of TDI-CCD 261 / movement speed of line CCD sensor = 128
Thus, by using the TDI-CCD 261, the light quantity can be measured at a high speed with 128 times the normal line CCD sensor, that is, the number of LED stages arranged in the main scanning direction of the TDI-CCD 261.
Specifically, assuming that L = 13 μm and T = 50 μsec, the moving speed of the TDI-CCD 261 is 26 mm / sec from equation (4). Accordingly, it takes 12.3 seconds to measure the A3 size LPH 14 (320 mm in length).
As described above, by using the TDI-CCD 261, highly accurate light amount measurement with a resolution equivalent to the light amount correction data Corr_I can be performed at a very high speed.

Here, in the optical profile measuring apparatus 200 of the present embodiment, in order to enable the above-described high-precision and high-speed light amount measurement, the following conditions must be satisfied. That is,
(I) The number of LED stages arranged in the main scanning direction of the TDI-CCD 261 is made to coincide with the number of lighting times that does not cause a quantization error in the lighting pulse width set for the LED. Specifically, in the LPH 14 of the present embodiment, the number of times of lighting is set to 128 × N (N: positive integer) where (1 + Corr_I / 128) is always an integer. As a result, when measuring the light quantity of each LED, the TDI-CCD 261 is moved and always 128 × N times for each area of the light profile of each LED (for example, the area R in FIG. 14B). Since the amount of light for lighting is measured, the amount of light for 128 × N times of lighting can be measured for each LED.
(Ii) The period of the horizontal synchronization signal of the TDI-CCD 261 is set to N times (N: a positive integer) the period of the horizontal synchronization signal of the SLED 63 of the LHP 14. As a result, when the light quantity is measured at each stage of the TDI-CCD 261, the LED is always turned on N times, so that the irradiation light quantity at each stage is uniform and accurate light quantity measurement is possible.
In this case, the horizontal synchronizing signal of the TDI-CCD 261 and the horizontal synchronizing signal of the SLED 63 of the LHP 14 are synchronized.

  Further, if each stage of the TDI-CCD 261 is set so as to move by one stage relative to the position of the LED during one period of the horizontal synchronization signal of the TDI-CCD 261, the light profile of each LED overlaps. It can measure without. Thereby, the measurement time can be further shortened. Therefore, the relative moving speed S between the LPH 14 and the TDI-CCD 261 is preferably set to S = s / Tc, where s is the measurement resolution of the TDI-CCD 261 and Tc is the period of the horizontal synchronization signal of the TDI-CCD 261.

  Subsequently, a process when the light amount correction data Corr_I is generated by the light profile measuring apparatus 200 of the present embodiment will be described. FIG. 15 is a flowchart showing the overall flow of processing when the light amount correction data Corr_I is generated. When performing the light amount correction data generation process, the LPH 14 used for the image forming apparatus is held in advance in the optical profile measuring apparatus 200 by a holder member (not shown) and set at a predetermined position.

  As shown in FIG. 15, first, in the optical profile measuring apparatus 200, shading correction relating to the TDI-CCD 261 is performed (S101). In this shading correction, an integrating sphere is used. That is, with the integrating sphere turned off, the output value of the TDI-CCD 261 is measured, and the black level correction value is calculated from the measured value to obtain the black level correction value. Next, light is incident on the magnifying optical system 260 from the integrating sphere. Then, the output value of the TDI-CCD 261 is measured, and shading correction is calculated from the measured value to obtain the shading correction. As the light source used for the integrating sphere in this case, the same LED (wavelength 780 nm) as that 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

Next, light amount correction data Corr_I1 in a state where the LPH 14 is turned on at 4 on 4 off is generated (S102).
Here, 4on4off lighting means that, as shown in FIG. 16, 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.
When generating the light amount correction data Corr_I1 in step 102, 128 is used as the light amount correction data Corr_I set in the equation (2). That is, the measurement lighting pulse width is set to 2 · BASE (lighting pulse width twice as large as the reference pulse width), and each LED is lit.

Subsequently, the light amount correction data Corr_I2 is generated using the light amount correction data Corr_I1 generated in step 102 in a state where the light is again turned on at 4 on 4 off (S103). This means that the light amount correction data Corr_I1 obtained only at one time in step 102 may not be able to be accurately corrected, and thus has the meaning of finely adjusting the light amount correction data Corr_I1 generated in step 102. It is a step.
Therefore, the measurement lighting pulse width set by the equation (2) is expressed by the following equation (5).
Measurement pulse width = BASE · (1 + Corr_I 1/128) (5)
In this case, as described above, since the lighting of the decimal part (a decimal part of Corr_I1 / 128) that is less than one unit of BASE is unstable, for example, (1 + Corr_I1 / The integrated light quantity is measured in a state where 128 × N (N: positive integer) lighting is always performed with 128) being an integer. Here, the lighting is performed 128 times.
As described above, even when the light amount is measured while lighting 128 times, the light amount can be measured at high speed by using the TDI-CCD 261 as described above.

Next, light amount correction data Corr_I3 in a state where the LPH 14 is turned on with 4off4on is generated (S104).
Further, for the same purpose as in step 103, the light amount correction data Corr_I4 is generated using the light amount correction data Corr_I3 generated in step 104 in a state where the light is again turned on at 4off4on (S105).
Then, the light amount correction data Corr_I2 generated in step 103 and the light amount correction data Corr_I4 generated in step 105 are rearranged in accordance with the arrangement order of the LEDs in the LPH 14, and the light amounts of all the LEDs of the LPH 14 The correction data Corr_I is combined. And this is memorize | stored in memory (EEPROM102) as the light quantity correction data Corr_I of LPH14 (S106).

Subsequently, the generation processing of the light amount correction data Corr_I in each of steps 102 to 105 will be described. FIG. 17 is a flowchart showing a flow of processing when generating the light amount correction data Corr_I2 in step 103 as an example.
The PC 266 outputs a control signal instructing the LPH driver IF board 264 to light the LPH 14 with 4 on 4 off. Thereby, the LPH driver IF board 264 turns on the LPH 14 with 4 on 4 off (S201).
Here, the LPH driver IF board 264 sends the light amount correction data Corr_I1 generated in step 102 as the light amount correction data. Further, a reference clock signal for generating the reference pulse width BASE and a horizontal synchronization signal (HSYNC) for controlling the lighting timing of the LPH 14 are transmitted.

Next, the PC 266 outputs a control signal for moving the moving stage 262 to the stage driver 263 via the X, Y, Z motor controller 267, and the CCD board 270 and the magnifying optical system 260 are connected to the SLED 63. It is moved at a constant speed in the arrangement direction (main scanning direction) (S202).
Further, the PC 266 outputs a control signal that instructs the CCD board 270 to measure the light amount distribution of the LPH 14. Then, the CCD board 270 measures the light quantity distribution of the LPH 14 by the TDI-CCD 261 (S203). At that time, the TDI-CCD 261 simultaneously receives a horizontal synchronization signal (HSYNC) transmitted from the LPH driver IF board 264 to the LPH 14 and synchronizes the measurement timing of the TDI-CCD 261 with the lighting timing of the LPH 14. That is, here, the condition (ii), N = 1, is set.

  Next, the PC 266 acquires the light amount distribution data measured in step 203 from the CCD board 270. Then, as shown in FIG. 18, 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 (in the main scanning direction (x)) An optical profile is obtained (S204).

Subsequently, the PC 266 detects the peak position and valley position in the main scanning direction (x) for the light profile calculated in step 204. 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 the correction characteristic value (%) of each light emitting point (LED) (see FIG. 19) (S205).
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 (S206).
Then, the PC 266 generates the calculated light amount correction value for each LED as the light amount correction data Corr_I (S207).

  As described above, in the optical profile measurement apparatus 200 of the present embodiment, the TDI-CCD 261 is used as the light quantity measurement sensor, and the number of LED stages arranged in the main scanning direction of the TDI-CCD 261 does not cause a quantization error. It matches the lighting count. The period of the horizontal synchronization signal of the TDI-CCD 261 is set to N times (N: a positive integer) the period of the horizontal synchronization signal of the SLED 63 of the LHP 14. Thereby, the light quantity of each LED can be measured at high speed with the same accuracy as the resolution of the density unevenness correction data Corr.

1 is a diagram showing an overall configuration of an image forming apparatus using an exposure apparatus (print head) to be measured in the present 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 a block diagram explaining the structure of a correction | amendment calculating part. It is the figure which showed an example of the form by which a quantization error is carried over to the nearby pixel. It is the figure which showed the structure of the optical profile measuring device. It is a figure explaining the structure of an expansion optical system. It is the figure which each represented the optical path of light B1 and light B2 which were radiate | emitted from LED from which SLED differs. It is the figure which showed the relationship between the sensitivity of a photoreceptor and the sensitivity of TDI-CCD, and the incident angle of the light which injects into each. (A) It is a top view explaining the structure of TDI-CCD, (b) It is a figure explaining operation | movement at the time of light quantity measurement. It is a flowchart which shows the flow of the whole process at the time of producing | generating light quantity correction data Corr_I. It is a figure explaining the lighting form of 4on4off. It is a flowchart which shows the flow of a process at the time of producing | generating light quantity correction data Corr_I. It is a figure explaining the direction of integration of light quantity distribution data. It is a figure explaining a correction characteristic value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 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 part, 62 ... LED circuit board, 63 ... Self-scanning LED array (SLED), 64 ... Rod lens array, 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 180: Correction calculation unit 182: Quantization error carry-over memory 200: Optical profile measurement device 260: Expansion Optical system, 261 ... TDI-CCD

Claims (6)

A plurality of lines are arranged and arranged so as to face the light emitting elements determined by correcting the irradiation light quantity at 1 / M steps (M is a positive integer) of the reference pulse width which is a reference of the irradiation light quantity , A light amount measuring means for measuring the light amount of each of the light emitting elements;
Control means for controlling the lighting of each of the light emitting elements, and for controlling the measuring operation of the light quantity measuring means,
The light amount measuring means includes a plurality of light receiving elements arranged in a line, and the reference pulse width is set to BASE, a and b are set to 0 or an integer, and the irradiation light amount of the light emitting element is set to BASE × (a + b / M), the number of stages of the light receiving element is set to M × n, where n is a positive integer ,
The control means sets the cycle of the synchronization signal that sets the measurement timing of each stage of the light receiving element of the light quantity measurement means to a positive integer multiple of the cycle of the synchronization signal that sets the light emission timing of the light emitting element. A light quantity measuring device characterized by The light quantity measuring means has a relative resolution speed S with respect to the light emitting element, where s is a measurement resolution of the light quantity measuring means, and Tc is a period of a synchronization signal for setting a measurement timing of each stage of the light receiving element.
S = s / Tc
The light quantity measuring device according to claim 1, wherein   The light quantity measuring means sequentially transfers the light quantity data measured by each of the light receiving elements arranged in a plurality of lines to a light receiving element located downstream in the movement direction of the light receiving element, and the transferred light quantity data and 2. The light quantity measuring device according to claim 1, wherein the transferred light quantity data measured by the light receiving element are sequentially integrated.   The control means synchronizes and outputs a synchronization signal for setting the measurement timing of each stage of the light receiving element of the light quantity measuring means and a synchronization signal for setting the light emission timing of the light emitting element. Item 4. The light quantity measuring device according to Item 1. A light quantity measuring means that is arranged in a plurality of lines and is arranged opposite to a light emitting element in which the amount of irradiation light is determined by setting N-stage (N is a positive integer) correction amount, and measures the light quantity of each light emitting element. When,
Control means for controlling the lighting of each of the light emitting elements, and for controlling the measuring operation of the light quantity measuring means,
The light quantity measuring means is configured such that a plurality of light receiving elements arranged in a line are arranged in a plurality of stages, and the number of stages is set to an integral multiple of the N,
The control means sets the cycle of the synchronization signal that sets the measurement timing of each stage of the light receiving element of the light quantity measurement means to a positive integer multiple of the cycle of the synchronization signal that sets the light emission timing of the light emitting element. A light quantity measuring device characterized by A plurality of light emitting elements that are arranged in a line and whose irradiation light quantity is determined by setting correction amounts in N stages (N is a positive integer) ;
Storage means for storing light amount correction data for correcting the light amount of each of the light emitting elements;
A drive circuit that sets the correction amount based on the light amount correction data stored in the storage unit, corrects the light amount of each light emitting element by the correction amount, and causes each light emitting element to emit light ;
The storage means is configured such that the stored light quantity correction data includes a plurality of stages of light receiving elements arranged in a line, and the number of stages of the light receiving elements is set to an integer multiple of N. The light quantity measurement means, which is a light quantity measurement means, and the period of the synchronization signal that sets the measurement timing of each stage of the light receiving element is set to an integral multiple of the period of the synchronization signal that sets the light emission timing of the light emitting element. An exposure apparatus generated based on a light amount measured by a means.

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