JP2007118194A - Method and unit for adjusting amount of lighting of print head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the accuracy of the adjustment of the amount of lighting of each lighting element which constitutes a print head. <P>SOLUTION: In an LPH, SLED chips (Chips 1-58), in which a plurality of LEDs are arranged in a main scanning direction, are arranged in a zigzag pattern in the main scanning direction. When the quantity of light from each LED is corrected, firstly, the LPH singly and directly measures the quantity of the light emitted from each LED, and a first light-quantity correction value A of each LED, which is acquired on the basis of the result of this measurement, is written in an EEPROM 102. Next, the LPH is mounted on a digital color printer; the quantity of the light emitted from each LED is indirectly measured on the basis of the result of reading of a test chart which is acquired by an image forming operation; and a second light-quantity correction value B of each LED is determined on the basis of the result of this measurement. A third final light-quantity correction value C, which is acquired by performing correction while referring to the value B on the basis of the value A, is written in the EEPROM 102. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a print head lighting amount adjustment method and the like for adjusting a lighting amount of each lighting element in a print head that records an image or the like by a plurality of lighting elements arranged in a main scanning direction.

In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, first, for example, the surface of a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged by a charging device. The charged photosensitive drum is exposed by an exposure device controlled based on the image data, and an electrostatic latent image is formed on the surface thereof. Subsequently, the electrostatic latent image formed on the photosensitive drum is converted into a visible image (toner image) by the developing device. Thereafter, the toner image is transported to the transfer unit as the photosensitive drum rotates, and is electrostatically transferred onto the recording paper. The toner image carried on the recording paper is subjected to a fixing process to become a permanent image.
As an exposure apparatus used in such an image forming apparatus, conventionally, an optical scanning method in which a laser diode and a polygon mirror are combined to scan and expose laser light in the main scanning direction has been used. However, in recent years, exposure using an LED print head (LPH: LED Print Head) configured by arranging a large number of LEDs (Light Emitting Diodes) in the main scanning direction due to demands for downsizing of the apparatus. Many devices are also used.

  The LPH generally has an LED array in which a plurality of LED chips in which a large number of LEDs are arranged in a line are arranged, and a large number of rods for imaging light output from the LEDs on the surface of the photosensitive member (photosensitive drum). And a rod lens array in which lenses are arranged. In the image forming apparatus, each LED of the LPH is driven based on input image data, light is output toward the photosensitive member, and light is imaged on the surface of the photosensitive member by the rod lens. An electrostatic latent image is formed in the sub-scanning direction by relatively moving the photoconductor and LPH.

Since LPH has a structure in which a plurality of LEDs and rod lenses, which are light emitting elements, are arranged in the main scanning direction, variation in each light emitting point has a great influence on image quality. In particular, when there is a variation in the amount of light emitted from the light emitting points or when the lens characteristics vary, streaks and density unevenness in the sub-scanning direction occur, and image quality defects are likely to occur.
Therefore, a technique for attaching a LPH to the image forming apparatus, outputting a correction chart including a halftone image, etc., reading the output correction chart with a scanner or the like, and correcting the light quantity of each LED based on the reading result of the correction chart. (See Patent Documents 1 and 2).

JP 2001-146038 A (page 5-7, FIG. 2) Japanese Patent Laying-Open No. 2005-254491 (page 5-6, FIG. 4)

  By the way, when the light amount correction is performed by the above-described method, in the correction chart to be output, in addition to the density unevenness caused by the light amount unevenness of each LED constituting the LPH, the density unevenness caused by other factors is also superimposed. The As another factor, for example, there is a case where a difference in charging characteristics occurs due to a difference in film thickness distribution of the photosensitive layer on the photosensitive drum in the main scanning direction. In addition, for example, development unevenness may occur due to a difference in developer distribution in the developing device in the main scanning direction. Therefore, when the light amount correction of each LED is performed based on the reading result of the correction chart, the variation due to these other factors is also corrected by the light amount of each LED. Then, when the developer distribution in the developing device changes over time or the photosensitive drum is replaced, density unevenness is caused by the light amount correction of each LED.

With respect to such a problem, in Patent Document 2 described above, density unevenness due to other factors is corrected by extracting density unevenness (streak) specific to the LPH when reading the correction chart. Propose not to do.
However, in Patent Document 2, the procedure for extracting the concentration unevenness specific to LPH is very complicated, and it is difficult to improve the accuracy of detecting the concentration unevenness specific to LPH.

  The present invention has been made to solve such technical problems, and an object of the present invention is to improve the accuracy of adjusting the lighting amount of each lighting element constituting the print head.

For this purpose, the present invention is a method for adjusting a lighting amount of a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction. A step of directly measuring the lighting amount of the element, a step of obtaining a first correction value of the lighting amount for a plurality of lighting elements based on a result of directly measuring the lighting amount, and a lighting amount including the first correction value The step of measuring the lighting amount of the plurality of lighting elements indirectly based on the reading result of the output correction chart, and the lighting amount was indirectly measured Based on the result, the step of obtaining the second correction value of the lighting amount for the plurality of lighting elements, and the correction value for each lighting element is determined based on the difference between the first correction value and the second correction value, Using the determined correction value And a step of modifying the first correction value, the step of modifying the first correction value, so that the first correction value is not changed more than a certain, is characterized by determining a correction value.
Here, in the step of correcting the first correction value, if the difference exceeds a predetermined threshold value, the threshold value can be set as the correction value.

From another point of view, the present invention is a method for adjusting the lighting amount of a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction, Taking into account the step of directly measuring the lighting amount of the plurality of lighting elements, the step of obtaining the first correction value of the lighting amount for the plurality of lighting elements based on the result of directly measuring the lighting amount, and the first correction value A step of lighting a plurality of lighting elements at a lighting amount and performing image formation, and indirectly measuring a lighting amount of the plurality of lighting elements based on a read result of the output correction chart;
Based on the result of indirectly measuring the lighting amount, obtaining a second correction value of the lighting amount for the plurality of lighting elements, and correcting in the step of indirectly measuring the lighting amount of the plurality of lighting elements It is characterized in that density unevenness having a period different from the length of the lighting element chip in the main scanning direction is removed from the density data obtained by reading the chart.
Here, in the step of indirectly measuring the lighting amounts of the plurality of lighting elements, from the density data obtained by reading the correction chart, density unevenness with a period equal to or less than half the length of the lighting element chip in the main scanning direction, and Further, it is possible to remove density unevenness having a period of 5 times or more the length of the lighting element chip in the main scanning direction.

  Furthermore, from another viewpoint, the present invention is a lighting amount adjustment device for a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction, The read data of the correction chart output by the image forming operation performed by lighting a plurality of lighting elements with the lighting amount taking into account the first correction value stored in advance in the memory corresponds to the plurality of lighting elements. A density conversion unit for converting to density data, a frequency filter unit for filtering density data output from the density conversion unit to remove density unevenness having a period different from the length in the main scanning direction of the lighting element chip, and density unevenness Is output from the correction value calculation unit that calculates the second correction value of the lighting amount for the plurality of lighting elements, and the first correction value and the correction value calculation unit based on the density data from which the light is removed. A correction value for each lighting element is determined based on the difference between the correction value and the correction value setting unit that corrects the first correction value using the determined correction value; And a correction value writing unit for writing the third correction value obtained by correcting the correction value with the correction value to the memory.

  Here, the first correction value can be characterized in that it is set based on a result of directly measuring the lighting amounts of a plurality of lighting elements constituting the print head. In addition, the frequency filter unit may remove density unevenness with a period of half or less of the length of the lighting element chip in the main scanning direction and density unevenness with a period of 5 times or more of the length of the lighting element chip in the main scanning direction. it can. Furthermore, the correction value setting unit can determine the correction value so that the first correction value does not change beyond a certain level. In this case, the correction value setting unit can set the threshold value as the correction value when the difference exceeds a predetermined threshold value. A plurality of lighting element chips constituting the print head to be adjusted can be arranged in a staggered manner.

  ADVANTAGE OF THE INVENTION According to this invention, the precision of the lighting amount adjustment of each lighting element which comprises a print head can be improved.

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 an LED print head to be measured in the present embodiment. The image forming apparatus shown in FIG. 1 is a so-called tandem type digital color printer 1. The digital color printer 1 includes an image forming process unit 10 that forms an image corresponding to image data of each color, and a control unit 30 that controls the image forming process unit 10. The digital color printer 1 is connected to, for example, a personal computer (PC) 2 or an image reading device (IIT) 3, and an image processing unit (IPS: IPS) that performs predetermined image processing on image data received from these. Image Processing System) 40 is provided.

The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K that are arranged in parallel at a predetermined interval. The image forming units 11Y, 11M, 11C, and 11K include a photosensitive drum 12, a charger 13, an LED print head (LPH) 14, a developing device 15, and a cleaner 16. Here, the photosensitive drum 12 forms an electrostatic latent image and carries a toner image. The charger 13 uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. The LPH 14 exposes the photosensitive drum 12 charged by the charger 13. The developing device 15 develops the electrostatic latent image obtained by the LPH 14. The cleaner 16 cleans the surface of the photosensitive drum 12 after transfer. Here, the image forming units 11Y, 11M, 11C, and 11K are configured in substantially the same manner except for the toner stored in the developing unit 15. The image forming units 11Y, 11M, 11C, and 11K respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images.
Further, the image forming process unit 10 includes an intermediate transfer belt 21, a primary transfer roll 22, a secondary transfer roll 23, and a fixing device 25. To the intermediate transfer belt 21, the toner images of the respective colors formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K are transferred in a multiple manner. The primary transfer roll 22 sequentially transfers (primary transfer) the color toner images of the image forming units 11Y, 11M, 11C, and 11K to the intermediate transfer belt 21. The secondary transfer roll 23 collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 21 onto the paper P as a recording material. The fixing device 25 fixes the secondary transferred image on the paper P.

  Now, an image forming operation in the digital color printer 1 will be described. In the digital color printer 1, 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 IIT 3 is subjected to image processing by the image processing unit 40 and supplied to each of the image forming units 11Y, 11M, 11C, and 11K via the interface. For example, in the yellow image forming unit 11 </ b> Y, the surface of the photosensitive drum 12 uniformly charged to 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. The electrostatic latent image formed on the photosensitive drum 12 is developed by the developing device 15 to form a yellow toner image. Similarly, magenta, cyan, and black toner images are formed in the other image forming units 11M, 11C, and 11K.

The color toner images formed by the image forming units 11Y, 11M, 11C, and 11K are sequentially electrostatically attracted by the primary transfer roll 22 onto the intermediate transfer belt 21 that rotates in the direction of arrow A in FIG. A toner image superimposed on the belt 21 is formed. The formed superimposed toner image is conveyed to an area (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 the LED print head (LPH) 14. In FIG. 2, the LPH 14 includes a housing 61 and a self-scanning LED array (SLED) 63. The LPH 14 is an LED circuit board 62 on which an SLED 63 and a drive circuit (signal generation circuit) 100 (see FIG. 3 below) for driving the SLED 63 are mounted, and a rod that forms an image of light from the SLED 63 on the surface of the photosensitive drum 12. A lens array 64 is provided. Further, the LPH 14 includes a holder 65 that supports the rod lens array 64 and shields the SLED 63 from the outside, and a leaf spring 66 that biases the housing 61 toward the rod lens array 64.

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. Therefore, it is possible to prevent dust from adhering to the SLED 63 from the outside. On the other hand, the leaf spring 66 urges the LED circuit board 62 toward 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 adjusting 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 SLEDs 63 made up of, for example, 58 lighting element chips (Chip 1 to Chip 58). They are arranged in a row with high precision so as to be parallel to the axial direction. In this case, as shown in FIG. 4 (a diagram for explaining a connecting portion of each SLED chip), each LED array is connected to each other at the end boundary of the LED array arranged in each SLED chip (Chip 1 to Chip 58). The SLED chips are alternately arranged in a staggered manner so as to be continuously arranged at the connecting portions. In addition, in FIG. 4, the connection part of Chip1, Chip2, and Chip3 is shown as an example.
The LED circuit board 62 includes a signal generation circuit 100, a level shift circuit 104, a three-terminal regulator 101 for stabilizing the output voltage, an EEPROM 102 for storing light amount correction value data in the SLED 63, the digital color printer 1 main body, and the like. Is provided with a harness 103 for transmitting and receiving signals.

  FIG. 5 is a diagram showing the configuration of the signal generation circuit 100 as a driver and the wiring configuration of the LED circuit board 62. As shown in FIG. 5, the signal generation circuit 100 includes a lighting signal generation unit 110 that outputs a lighting signal ΦI (Φ1 to ΦI58) to each LED chip (Chip1 to Chip58). Further, the signal generation circuit 100 divides each LED chip (Chip1 to Chip58) into six sets, and outputs a transfer signal CK1 (CK1_1 to CK1_6) and a transfer signal CK2 (CK2_1 to CK2_6) to each set. A generator 130 is provided.

On the LED circuit board 62, a + 3.3V power supply line 105 for supplying power to each SLED chip (Chip1 to Chip58) and a grounded (GND) power supply line 106 are provided. Further, signal lines 107 (107_1 to 107_58) for transmitting lighting signals ΦI (ΦI1 to ΦI58) from the signal generation circuit 100 to the respective SLED chips (Chip1 to Chip58) are also provided. Further, signal lines 108 (108_1 to 108_6) for transmitting the transfer signal CK1 (CK1_1 to 1_6) are also provided. Furthermore, signal lines 109 (109_1 to 109_6) for transmitting the transfer signal CK2 (CK2_1 to 2_6) are also provided.
The lighting signals ΦI (ΦI1 to ΦI58) for the Chip1 to Chip58 are input to the SLED chips (Chip1 to Chip58) via the signal line 107. 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 Chip58 via the signal line 109, respectively.

Next, the circuit configuration of the SLED 63 will be described.
FIG. 6 is a diagram for explaining the circuit configuration of the SLED 63. The SLED 63 of this embodiment is connected to the signal generation circuit 100 via the level shift circuit 104. The level shift circuit 104 has a configuration in which a resistor R1B and a capacitor C1, and a resistor R2B and a capacitor C2 are arranged in parallel, one end of which is connected to the input terminal of the SLED 63, and the other end of the signal generating circuit 100 ( It is connected to the output terminal of the transfer signal generator 130). Based on the transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C output from the signal generation circuit 100 (transfer signal generation unit 130), the transfer signal CK1 and the transfer signal CK2 are output to the SLED 63. .
In addition, although 58 SLED chips are arranged in series in the SLED 63 of the present embodiment, only one SLED chip is shown in FIG. In the following description, the SLED chip is referred to as SLED 63 for convenience.

As shown in FIG. 6, the SLED 63 includes 128 thyristors S1 to S128 as switching elements, 128 LEDs L1 to L128 as lighting elements, 128 diodes D1 to D128, and 128 resistors R1 to R128. In addition, the transfer current limiting resistors R1A and R2A are configured to prevent an excessive current from flowing through the signal line.
Here, a part mainly composed of thyristors S1 to S128 and diodes D1 to D128 for controlling supply of current to the LEDs L1 to L128 is referred to as a transfer unit.

In the SLED 63 of the present embodiment, the anode terminals (input terminals) A1 to A128 of the thyristors S1 to S128 are connected to the power supply line 105. A power supply voltage Vcc (Vcc = + 3.3 V) is supplied to the power supply line 105.
A transfer signal CK1 is transmitted from the signal generation circuit 100 via the level shift circuit 104 and the transfer current limiting resistor R1A to the cathode terminals (output terminals) K1, K3,... K127 of the odd-numbered thyristors S1, S3,. Is done.
Further, the cathode signals (output terminals) K2, K4,..., K128 of the even-numbered thyristors S2, S4,..., S128 are transferred from the signal generation circuit 100 through the level shift circuit 104 and the transfer current limiting resistor R2A. CK2 is transmitted.

On the other hand, gate terminals (control terminals) G1 to G128 of the thyristors S1 to S128 are respectively connected to the power supply line 106 via resistors R1 to R128 provided corresponding to the thyristors S1 to S128. The power supply line 106 is grounded (GND).
The gate terminals G1 to G128 of the thyristors S1 to S128 are connected to the gate terminals of the LEDs L1 to L128 provided corresponding to the thyristors S1 to S128, respectively.
Furthermore, the cathode terminals of the diodes D1 to D128 are connected to the gate terminals G1 to G128 of the thyristors S1 to S128. The gate terminals G1 to G127 of the thyristors S1 to S127 are connected to the anode terminals of the next-stage diodes D2 to D128, respectively. That is, the diodes D1 to D128 are connected in series with the gate terminals G1 to G127 interposed therebetween.
The anode terminal of the diode D1 is connected to the signal generation circuit 100 via the transfer current limiting resistor R2A and the level shift circuit 104, and the transfer signal CK2 is transmitted. Further, the cathode terminals of the LEDs L1 to L128 are connected to the signal generation circuit 100 (lighting signal generator 110) via the drive current setting resistor RID, and the lighting signal ΦI is transmitted.

  Further, the light shielding mask 50 is disposed in the SLED 63 so as to cover the thyristors S1 to S128 and the diodes D1 to D128 in the transfer unit. This is because during the image forming operation, light emission from the thyristors S1 to S128 in the on state and current is flowing, and from the diodes D1 to D128 in the current flow state is blocked, and unnecessary light is removed from the photoconductor. It is provided to suppress exposure of the drum 12.

Next, a signal (drive signal) for driving the SLED 63 output from the signal generation circuit 100 and the level shift circuit 104 will be described.
FIG. 7 is a timing chart showing drive signals output from the signal generation circuit 100 and the level shift circuit 104. Note that the timing chart shown in FIG. 7 shows a case where all LEDs perform optical writing (light emission).
(1) First, when a reset signal (RST) is input from the image forming apparatus to the signal generation circuit 100, the signal generation circuit 100 transfers the transfer signal CK1C to a high level (hereinafter referred to as “H”) and transfer. The signal CK1R is set to “H”, the transfer signal CK1 is set to “H”, the transfer signal CK2C is set to low level (hereinafter referred to as “L”), the transfer signal CK2R is set to “L”, and the transfer signal CK2 is set. Is set to a low level (“L”), and all thyristors S1 to S128 are set to an off state (FIG. 7A).
(2) Following the reset signal (RST), the line synchronization signal Lsync output from the signal generation circuit 100 becomes “H” (FIG. 7A), and the operation of the SLED 63 is started. Then, in synchronization with the line synchronization signal Lsync, as shown in FIGS. 7E, 7F, and 7G, the transfer signal CK2C and the transfer signal CK2R are set to “H”, and the transfer signal CK2 is set to “H”. (FIG. 7B).
(3) Next, as shown in FIG. 7C, the transfer signal CK1R is set to “L” (FIG. 7C).

(4) Subsequently, as shown in FIG. 7B, the transfer signal CK1C is set to “L” (FIG. 7D).
In this state, the gate current of the thyristor S1 starts to flow. At that time, the tri-state buffer B1R of the signal generation circuit 100 is set to high impedance (Hiz), thereby preventing current backflow.
Thereafter, the thyristor S1 starts to be turned on by the gate current of the thyristor S1, and the gate current gradually increases. At the same time, when a current flows into the capacitor C1 of the level shift circuit 104, the potential of the transfer signal CK1 also gradually increases.

(5) After the elapse of a predetermined time (the time when the transfer signal CK1 potential becomes close to GND), the tristate buffer B1R of the signal generation circuit 100 is set to “L” (FIG. 7E). As a result, the potential of the signal line Φ1 and the potential of the transfer signal CK1 rise due to the rise of the gate G1 potential, and accordingly, a current starts to flow to the resistor R1B side of the level shift circuit 104. On the other hand, the current flowing into the capacitor C1 of the level shift circuit 104 gradually decreases as the potential of the transfer signal CK1 increases.
When the thyristor S1 is completely turned on and becomes a steady state, a current for maintaining the on state of the thyristor S1 flows to the resistor R1B of the level shift circuit 104, but does not flow to the capacitor C1.
At this time, as shown in FIG. 7B, the tri-state buffer B1C of the signal generation circuit 100 is set to high impedance (Hiz) (FIG. 7E).

  (6) With the thyristor S1 completely turned on, the lighting signal ΦI is set to “L” as shown in FIG. 7 (H) (FIG. 7 (f)). At this time, since the potential of the gate G1> the potential of the gate G2, the LED L1 having a thyristor structure is turned on earlier and lights up. As the LED L1 is turned on, the potential of the signal line Φ1 rises, so that the LEDs after the LED L2 are not turned on. That is, as for the LEDs L1, L2, L3, L4,..., Only the LED L1 having the highest gate voltage is turned on (lit).

(7) Next, as shown in FIG. 7 (F), when the transfer signal CK2R is set to “L” (FIG. 7 (g)), a current flows in the same manner as in FIG. A voltage is generated across the capacitor C2 104.
(8) As shown in FIG. 7E, when the transfer signal CK2C is set to “L” in this state (FIG. 7H), the thyristor switch S2 is turned on.
(9) Then, as shown in FIGS. 7B and 7C, when the transfer signals CK1C and CK1R are simultaneously set to “H” (FIG. 7 (i)), the thyristor switch S1 is turned off and passes through the resistor R1. As a result, the potential of the gate G1 gradually decreases. At that time, the thyristor switch S2 is completely turned on. Therefore, by turning on / off the lighting signal ΦI corresponding to the image data from the lighting signal terminal ID, the LED L2 can be turned on / off. In this case, since the potential of the gate G1 is already lower than the potential of the gate G2, the LED L1 is not turned on.

(10) The above-described operations are sequentially performed to turn on the LEDs L1 to L128 sequentially.
Then, after the “transfer operation period” in FIG. 7 in which the terminal LED L128 is extinguished, the transfer signals CK1C and CK1R are set to “H”, the transfer signal CK1 is set to “H”, and the transfer signals CK2C and CK2R are set to “H”. The transfer signal CK2 is set to “H” as “H”, and both the transfer signal CK1 and the transfer signal CK2 are kept in the “H” state for a predetermined time (“transfer thyristor is turned off” in FIG. 7). As a result, all thyristors S1 to S128 are turned off. Therefore, in this state, no current flows through all the thyristors S1 to S128, so that the thyristors S1 to S128 are held off (not lit).

(11) Further, after the transfer signals CK1 and CK2 are both kept at "H" for a predetermined time, the transfer signals CK2C and CK2R are set to "L" and the transfer signal CK2 is set to "L" (in FIG. 7, “Period during which no current flows through the transfer unit”). Thereby, since no current flows through the diodes D1 to D128, all the diodes D1 to D128 are also kept in the non-lighted state.
Accordingly, after the lighting signal ΦI is output and the image formation is completed, during the unsteady operation including the state where the photosensitive drum 12 (see FIG. 1) stops rotating, the transfer unit of the SLED 63 is operated. No current is applied. For this reason, in a state where the photoconductor 12 is stopped from rotating, current does not flow through the thyristors S1 to S128 and the diodes D1 to D128 arranged in the transfer unit together with the LEDs L1 to L128, and the thyristors S1 to S128 and Since no light is emitted from the diodes D1 to D128, unnecessary exposure of the photosensitive drum 12 is suppressed.

  Next, the configuration of the lighting signal generation unit 110 in the signal generation circuit 100 shown in FIG. 6 will be described in detail with reference to FIG. The lighting signal generator 110 supplies the lighting signals ΦI1 to ΦI58 to the SLEDs 63 (Chip1 to Chip58) constituting the LPH 14. The lighting signal generator 110 also has a function of correcting the lighting timing of the SLEDs 63 arranged in a staggered pattern. Further, the lighting signal generator 110 also has a function of correcting the unevenness in the amount of light of each LED constituting each SLED 63 when supplying a lighting signal to each SLED 63. In the present embodiment, the lighting signal generation unit 110 adjusts the lighting time length (number of lighting clocks) of each LED based on the light amount correction value data read from the EEPROM 102, and thereby the light amount unevenness in each LED. Correction is performed.

  The lighting signal generation unit 110 receives the image data sent from the image processing unit (IPS) 40 and the line synchronization signal Lsync sent from the control unit 30. In addition, light amount correction value data corresponding to each LED is also input to the lighting signal generation unit 110 from the EEPROM 102. On the other hand, the lighting signal generator 110 outputs the lighting signals ΦI1 to ΦI58 to 58 SLED chips constituting the LPH 14.

As shown in FIG. 8, the lighting signal generation unit 110 includes a staggered array correction unit 111, a lighting time calculation unit 112, a serial / parallel conversion unit 113, and a pulse generator 114 (114_1 to 114_58).
Image data is input to the staggered array correction unit 111 from the image processing unit (IPS) 40. The staggered array correction unit 111 divides the image data input from the image processing unit (IPS) 40 into units of SLED chips (data group of 128 dots). Then, the staggered array correcting unit 111 outputs the data group corresponding to the odd-numbered SLED 63 and the data group corresponding to the even-numbered SLED 63 to the lighting time calculating unit 112 with different output timings. Specifically, the setting is performed such that the light emission timing of the even-numbered SLEDs 63 arranged on the downstream side in the sub-scanning direction is delayed by a predetermined time from the light emission timing of the odd-numbered SLEDs 63 arranged on the upstream side in the sub-scanning direction. . Accordingly, the positions of the electrostatic latent image formed by the odd-numbered SLEDs 63 arranged on the upstream side in the sub-scanning direction and the electrostatic latent image formed by the even-numbered SLEDs 63 arranged on the downstream side in the sub-scanning direction are determined. It becomes possible to match.

  The lighting time calculation unit 112 receives the line synchronization signal Lsync sent from the control unit 30 and the light amount correction value data sent from the EEPROM 102. Further, the staggered array correction unit 111 also receives the staggered array corrected image data from the lighting time calculation unit 112. This light quantity correction value data is set corresponding to 7424 LEDs constituting the LPH 14. The lighting time calculation unit 112 uses the image data that has undergone the staggered array correction sent from the staggered array correction unit 111 and the light amount correction value of each LED read from the EEPROM 102 while synchronizing with the line synchronization signal Lsync. Then, the lighting time (number of lighting clocks) of each LED is calculated. More specifically, the lighting time calculation unit 112 adds the light amount correction value to the zigzag corrected image data, so that the lighting time of the corresponding LED becomes longer in proportion to the magnitude of the light amount correction value. Calculate the number of lighting clocks.

  The serial / parallel converter 113 converts the number of lighting clocks for each LED calculated by the lighting time calculator 112 into parallel data. The pulse generator 114 (114_1 to 114_58) generates the lighting signals ΦI1 to ΦI58 by changing the light amount by pulse width modulation with respect to the signals converted in parallel by the serial / parallel converter 113. Then, the pulse generator 114 (114_1 to 114_58) outputs the generated lighting signals ΦI1 to ΦI58 to the SLEDs 63 (Chip1 to Chip58) of the LPH 14, respectively. Thereby, in each SLED63 of LPH14, LED used as lighting object will light for the set lighting time.

  Next, the setting of the light amount correction value of each LED in the LPH 14 will be described. In the present embodiment, first, the light emission amount of each LED is directly measured by the LPH 14 alone, and the light amount correction value of each LED (referred to as the first light amount correction value A in the following description) based on this measurement result. Set up. Next, the LPH 14 is mounted on the digital color printer 1 shown in FIG. 1, and the light emission amount of each LED is indirectly measured based on the reading result of the test chart obtained by the image forming operation, and based on the measurement result. A light amount correction value (referred to as a second light amount correction value B in the following description) of each LED is obtained. Then, correction is performed with reference to the second light quantity correction value B based on the first light quantity correction value A to obtain a final light quantity correction value (referred to as a third light quantity correction value C in the following description). . In the following description, the former light amount correction of the LPH 14 alone is referred to as direct light amount correction, and the latter light amount correction using the digital color printer 1 is referred to as indirect light amount correction.

FIG. 9 is a diagram showing a light amount correction device 70 used for direct light amount correction. The light amount correction device 70 is arranged so as to be opposed to the LPH 14 along the main scanning direction of the LPH 14, and is slidably arranged on the moving stage 71 in the direction of the arrow, and receives the light emitted from the LPH 14. It has. Here, the sensor 72 is configured to slide on the moving stage 71 by a driving mechanism (not shown). In the initial state before the slide operation is started, the light receiving surface 72a of the sensor 72 is placed at a position facing the first dot LED (mounted on the Chip 1) as indicated by a solid line in the figure. On the other hand, in the final state after the end of the sliding operation, the sensor 72 is placed at a position where the light receiving surface 72a of the sensor 72 faces the 7424 dot LED (mounted on the Chip 58) as indicated by a broken line in the figure. That is, in this light quantity correction device 70, the sensor 72 can receive light from all the LEDs (1st to 7424th dots) as it moves on the moving stage 71. Here, the sensor 72 can be configured by a PD (Photo Detector) or a CCD (Charge Coupled Device).
The light quantity correction device 70 includes a correction value calculation unit 73 that calculates a first light quantity correction value A (first correction value) corresponding to each LED based on the light reception result of the sensor 72. further. The light amount correction device 70 includes a correction value writing unit 74 that writes the first light amount correction value A obtained by the correction value calculation unit 73 to the EEPROM 102 provided in the LPH 14.

  On the other hand, FIG. 10 is a diagram showing a measurement system (scanner correction measurement system) used in indirect light amount correction. This scanner correction measurement system includes a scanner 160 that reads a test pattern (correction chart) output using the digital color printer 1 on which the LPH 14 that has been subjected to direct light amount correction is mounted. Further, the scanner correction measurement system corrects the first light quantity correction value A using the second light quantity correction value B obtained based on the image data read by the scanner 160, and the EEPROM 102 provided in the LPH 14. A correction value correction unit 170 that writes as a third light quantity correction value C is provided (see FIG. 3). As the scanner 160, the IIT3 shown in FIG. 1 may be used as it is, or another scanner may be used. As the correction value correction unit 170, for example, a personal computer (PC) can be used.

Further, FIG. 11 shows a functional block of the correction value correcting unit 170 as the lighting amount adjusting device. The correction value correction unit 170 includes a density conversion unit 171, a frequency filter 172, a correction value calculation unit 173, a correction value setting unit 174, and a correction value writing unit 175.
The density conversion unit 171 converts read data obtained by reading the correction chart with the scanner 160 into density data corresponding to each LED. The frequency filter 172 performs a filtering process on the density data corresponding to each LED. Here, a band pass filter is used as the frequency filter 172. Thereby, the frequency filter 172 removes density unevenness shorter than the length in the main scanning direction of the SLED 63 (see FIG. 9) and density unevenness included in the density unevenness included in the density data. This reason and details thereof will be described later. The correction value calculation unit 173 calculates a second light amount correction value B (second correction value) of each LED based on the density data subjected to the filtering process. The correction value setting unit 174 compares the second light amount correction value B sent from the correction value calculation unit 174 with the first light amount correction value A read from the EEPROM 102 for each LED. Then, the correction value setting unit 174 sets a correction value for the first light amount correction value A of each LED based on the obtained comparison result, and uses the correction value to set a third light amount correction value for each LED. C (third correction value) is determined. The correction value writing unit 175 writes the third light amount correction value C of each LED sent from the correction value determination unit 174 to the EEPROM 102 as a memory provided in the LPH 14.

FIG. 12 is a flowchart for explaining the procedure of direct light quantity correction in the light quantity correction apparatus 70 shown in FIG. In the initial state, it is assumed that the sensor 72 is placed directly under the LED of the first dot.
In the direct light amount correction, first, the number of the LED to be measured, that is, the dot number N is set to 1 (step 101), and in this state, the LED of the Nth dot (first dot) is turned on. Is called. At this time, the target LED is supplied with a lighting signal in a state in which no correction is performed, that is, only a reference clock number (for example, 256). The sensor 72 measures the amount of light emitted from the Nth LED (step 102). Next, based on the light quantity measurement result of the Nth LED, the correction value calculator 73 calculates a light quantity correction value A corresponding to the Nth LED (step 103). At this time, the correction value calculation unit 73 compares a predetermined reference light amount with a light amount measured by the sensor 72. Based on this comparison result, as the first light quantity correction value A, a correction clock number selected from a range of, for example, 6 bits (0 to 63) with respect to the reference clock number 256 is determined. Next, the first light amount correction value A corresponding to the obtained LED of the Nth dot is written into the EEPROM 102 of the LPH 14 by the correction value writing unit 74 (step 104). Thereafter, the dot number N is set to N + 1 (step 105), and the sensor 72 is moved to a position immediately below the next adjacent LED. Then, it is determined whether the dot number N is 7425 (step 106). If the dot number N has not reached 7425, the process returns to step 102, and the calculation of the first light quantity correction value A corresponding to the Nth LED and the writing to the EEPROM 102 are continued. On the other hand, if the dot number N becomes 7425 in step 106, that is, if the sensor 72 has finished measuring the light quantity of the 7424th (last) LED, this process is terminated. As described above, the first light amount correction value A corresponding to the LEDs from the first dot to the 7424th dot is stored in the EEPROM 102.

FIG. 13 is a flowchart for explaining the procedure of indirect light amount correction in the scanner correction measurement system shown in FIG. In the initial state, it is assumed that the LPH 14 in which the first light amount correction value A is stored in the EEPROM 102 is attached to the digital color printer 1.
In the indirect light amount correction, first, the correction chart is output by performing the exposure operation by the LPH 14 using the first light amount correction value A (step 201). This will be specifically described with reference to FIG. 1. First, charging, exposure, development, and primary transfer are performed on the intermediate transfer belt 21 in each of the image forming units 11Y, 11M, 11C, and 11K. A toner image of each color is formed. These toner images of each color are halftone images having a constant density formed over the entire main scanning direction. The toner image formed on the intermediate transfer belt 21 is secondarily transferred onto the paper P, and the toner image is fixed by the fixing device 25 and output as a correction chart.

  At this time, image data instructing the formation of a halftone image having a constant density is sent from the image processing unit (IPS) 40 to the entire area in the main scanning direction to the lighting signal generation unit 110 (see FIG. 8) of each LPH 14. . In addition, the lighting time calculation unit 112 of the lighting signal generation unit 110 uses the first light amount correction value A read from the EEPROM 102 for the halftone image data that has been zigzag corrected by the zigzag array correction unit 111. The amount of light is corrected for each LED. Then, the lighting signals ΦI1 to ΦI58 are output to the SLEDs 63 (Chip1 to Chip58) via the serial / parallel conversion unit 113 and the pulse generators 114 (114_1 to 114_58), respectively. Therefore, each LED constituting the LPH 14 is turned on at the number of lighting clocks obtained by adding the number of correction clocks set for each LED to the number of reference clocks, and the photosensitive drum 12 is exposed.

Next, the output correction chart is set in the scanner 160, and the scanner 160 reads the correction chart (step 202). Data read by the scanner 160 is output to the correction value correction unit 170.
In the correction value correction unit 170, the density conversion unit 171 converts the read data input from the scanner 160 into density data (step 203). Next, the frequency filter 172 performs a filtering process on the density data input from the density converter 171 (step 204). Further, the correction value calculation unit 173 calculates a second light amount correction value B corresponding to each LED based on the density data subjected to the filtering process (step 205). Next, the correction value setting unit 174 reads the first light quantity correction value A stored in the EEPROM 102 of the LPH 14 (step 206). Further, the correction value setting unit 174 calculates the difference between the second light amount correction value B obtained in step 205 and the first light amount correction value A read in step 206 for each LED (step 207). . Then, based on the difference in the light amount correction value for each LED obtained in step 207, a correction value for the first light amount correction value A is calculated for each LED (step 208). Then, with respect to the first light quantity correction value A, a third light quantity correction value C is calculated by adding the correction value obtained in step 208 for each LED (step 209). Thereafter, the obtained third light quantity correction value C is written into the EEPROM 102 of the LPH 14 by the correction value writing unit 74 (step 210). The third light quantity correction value C is written in the EEPROM 102 in the form of overwriting the first light quantity correction value A.

Here, the reason why the direct light amount correction and the indirect light amount correction are combined in determining the light amount correction value of each LED constituting the LPH 14 will be described.
FIG. 14 is a diagram showing a state of direct light amount correction in the light amount correction apparatus 70 shown in FIG. In the present embodiment, the SLEDs 63 constituting the LPH 14 are arranged in a staggered manner. For this reason, the light receiving surface 72a of the sensor 72 has a shape facing both so as to receive both the light emitted from the SLEDs 63 arranged on the upstream side in the sub-scanning direction and the downstream side in the sub-scanning direction.

  However, the sensitivity (sensitivity to light) of the light receiving surface 72a of the sensor 72 is not always constant in the entire region. That is, as shown on the right side in the figure, the region facing the SLED 63 disposed upstream in the sub-scanning direction has a relatively high sensitivity, while the region facing the SLED 63 disposed downstream in the sub-scanning direction. It can happen that it has a relatively low sensitivity. In this case, it is determined that each LED constituting the SLED 63 arranged downstream in the sub-scanning direction has a small amount of emitted light as compared with each LED constituting the SLED 63 arranged upstream in the sub-scanning direction. . Then, in the correction value calculation unit 73, each LED constituting the SLED 63 arranged downstream in the sub-scanning direction with respect to the first light amount correction value A of each LED constituting the SLED 63 arranged upstream in the sub-scanning direction. The first light quantity correction value A is set uniformly large.

  If the first light quantity correction value A is set in this way, the following problem occurs when, for example, a halftone image having a constant density is formed using the LPH 14. That is, since the level of the first light amount correction value A is different between the SLED 63 arranged upstream in the sub-scanning direction and the SLED 63 arranged downstream in the sub-scanning direction, as shown in FIG. In the electrostatic latent image (toner image), light and shade having a period in the main scanning direction length X of the LED array of each SLED 63 occurs.

  In addition, even in the case where the emission wavelength of the LED is different for each SLED 63, light and shade having a period in the main scanning direction length of the LED array of each SLED 63 may occur. This is because the sensitivity of the sensor 72 has wavelength dependency of light. The SLED 63 is obtained by being formed on a semiconductor wafer and then cut out from the semiconductor wafer. At this time, if each SLED 63 constituting the LPH 14 contains a sample taken from a different lot, the emission wavelength of the LED (in this embodiment) due to a subtle difference in the semiconductor layer thickness or the like. In the form, 780 nm) is slightly shifted. Even if the LPH 14 is configured using the SLED 63 collected from the same lot, if the sampling position from the semiconductor wafer is different, the emission wavelength of the LED is slightly different for each SLED 63 due to a slight difference in the thickness of the semiconductor layer. It may shift to. This problem can also occur when the SLEDs 63 are not arranged in a staggered manner but are arranged in a line in the main scanning direction.

  As described above, in the direct light amount correction, the first light amount correction value A may increase or decrease in units of SLED 63 (128 LEDs), and density unevenness may not be completely excluded. For this reason, in this embodiment, after performing the direct light amount correction, the indirect light amount correction is further performed to eliminate such density unevenness in units of the SLED 63. However, in the indirect light amount correction, in addition to density unevenness caused by the LPH 14, density unevenness caused by the photosensitive drum 12, the charger 13, and the developing device 15 shown in FIG. 1, and density caused by primary transfer and secondary transfer. A correction chart can be obtained in a state including unevenness (hereinafter collectively referred to as density unevenness during image formation).

  Therefore, in the indirect light amount correction, density unevenness caused by the arrangement of the SLEDs 63 is extracted by filtering the density data of each LED obtained by reading the correction chart using the frequency filter 172 (FIG. 13 (see steps 202 to 204 shown in FIG. 13). In other words, density unevenness at the time of image formation is removed by performing filtering processing on the density data of each LED obtained by reading the correction chart.

  In the present embodiment, the length of each SLED 63 in the main scanning direction is 5.4 mm. For this reason, the density unevenness caused by the arrangement of the SLEDs 63 appears with a period of about 5 mm. From the opposite point of view, the density unevenness appearing in a cycle shorter than 5 mm and the density unevenness appearing in a cycle longer than 5 mm are the density unevenness caused by other than the SLED 63, that is, the density unevenness at the time of image formation. It is thoughtful. Therefore, in the frequency filter 172, density irregularities appearing at a period of 2 mm or less (less than half of the length of the SLED 63 in the main scanning direction) and density irregularities appearing at a period of 30 mm or more (more than 5 times the length of the SLED 63 in the main scanning direction). The parameter is set so that it is excluded. Here, the density unevenness appearing at a period of 30 mm or more is considered to be caused by the film thickness distribution unevenness of the photosensitive layer provided on the photosensitive drum 12.

FIG. 15A is a graph showing the LED dot number as the horizontal axis and the density data before and after the filtering process by the frequency filter 172 as the vertical axis. FIG. 15A shows the range of LED dot numbers 3840 to 5120 (corresponding to 10 chips of SLED 63). As described above, it is understood that the increase / decrease of the light amount (density) for each SLED 63 is extracted by performing the bandpass filtering process on the density data.
In the present embodiment, the second light quantity correction value B is calculated based on the density data subjected to the filtering process (see step 205 shown in FIG. 13). As a result, the second light quantity correction value B can be obtained in a state where density unevenness due to the arrangement of the SLEDs 63 is also taken into consideration.

  However, it is difficult to completely remove the influence of density unevenness at the time of image formation only by performing filtering processing on density data. Further, the reading accuracy of the scanner 160 and the density conversion accuracy in the density conversion unit 171 are limited. For this reason, the second light quantity correction value B may contain an error due to these. Therefore, in indirect light amount correction, first, a difference between the obtained second light amount correction value B and the first light amount correction value A obtained by direct light amount correction is calculated for each LED (for each dot number). (See step 207 shown in FIG. 13). And when calculating | requiring the correction value for every LED with respect to the 1st light quantity correction value A based on the obtained difference, the value of a difference is made into the correction value as it is about the site | part whose difference is below a threshold value. On the other hand, the threshold value is set as a correction value for a portion where the difference is larger than the threshold value (see step 208 shown in FIG. 13). This is based on the premise that the direct light amount correction in which the light amount of each LED is directly measured is less likely to introduce an error than the indirect light amount correction in which the light amount of each LED is indirectly measured through the toner image. Is.

  FIG. 15B is a graph with the LED dot number as the horizontal axis and the difference (correction value) before and after the correction value setting in the correction value setting unit 174 as the vertical axis. 15B shows the range of LED dot numbers 3840 to 5120 (corresponding to 10 chips of SLED 63), as in FIG. 15A. In this example, the threshold is set to 3, and when the difference exceeds +3, the correction value is set to 3, and when the difference exceeds -3, the correction value is set to -3. .

  Then, the correction value obtained for the first light quantity correction value A is taken into account for each LED, the third light quantity correction value C is calculated (see step 209 shown in FIG. 13), and the obtained third light quantity is obtained. The correction value C is stored in the EEPROM 102 (see step 210 shown in FIG. 13). As a result, when the image is actually formed, the light amount correction based on the third light amount correction value C is performed, the light amount unevenness of each LED is sufficiently corrected, and the light amount unevenness of the SLED 63 unit is also included. The lighting operation in the LPH 14 can be performed in the corrected state.

  In the present embodiment, the case where an LED is used as a lighting element has been described, but the present invention is not limited to this. For example, the present invention can be similarly applied to a print head composed of an assembly of point light sources, such as a print head using a liquid crystal shutter and a print head using an organic EL element.

1 is a diagram illustrating an overall configuration of an image forming apparatus equipped with an LED print head (LPH) to be measured in the present embodiment. It is the figure which showed the structure of LPH. It is a top view of a LED circuit board. It is a figure explaining the connection part of each SLED chip. It is the figure which showed the wiring diagram currently formed on the LED circuit board. It is a circuit diagram for demonstrating the structure of a SLED chip (SLED). 6 is a timing chart for explaining LPH driving (lighting operation) in an image forming operation. It is a figure explaining the structure of a lighting signal generation part. It is a figure which shows the light quantity correction apparatus used for the direct light quantity correction of LPH. It is a figure which shows the scanner correction | amendment measurement system used by the indirect light quantity correction | amendment of LPH. It is a functional block diagram which shows the structure of a correction value correction part. It is a flowchart explaining the procedure of the light quantity correction value setting by direct light quantity correction. It is a flowchart explaining the procedure of light quantity correction value correction by indirect light quantity correction. It is a figure for demonstrating the cause which density | concentration nonuniformity which makes the main scanning direction length of SLED a period occurs. (a) is a graph in which the horizontal axis represents the LED dot number and the vertical axis represents density data before and after filtering processing in indirect light amount correction, and (b) represents the correction value setting unit with the horizontal axis representing the LED dot number. 6 is a graph with the vertical axis representing the difference (correction value) before and after setting the correction value in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Digital color printer, 10 ... Image formation process part, 11Y, 11M, 11C, 11K ... Image formation unit, 12 ... Photosensitive drum, 13 ... Charger, 14 ... LPH, 15 ... Developing device, 30 ... Control part, DESCRIPTION OF SYMBOLS 40 ... Image processing part (IPS), 62 ... LED circuit board, 63 ... SLED, 64 ... Rod lens array, 70 ... Light quantity correction device, 71 ... Moving stage, 72 ... Sensor, 72a ... Light-receiving surface, 73 ... Correction value calculation , 74 ... correction value writing unit, 100 ... signal generation circuit, 102 ... EEPROM, 110 ... lighting signal generation unit, 111 ... staggered array correction unit, 112 ... lighting time calculation unit, 160 ... scanner, 170 ... correction value correction unit , 171 ... Density conversion unit, 172 ... Frequency filter, 173 ... Correction value calculation unit, 174 ... Correction value setting unit, 175 ... Correction value writing unit

Claims (10)

A lighting amount adjustment method for a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction,
Directly measuring the lighting amount of the plurality of lighting elements;
Based on the result of directly measuring the lighting amount, obtaining a first correction value of the lighting amount for a plurality of the lighting elements;
The plurality of lighting elements are turned on with the lighting amount in consideration of the first correction value to form an image, and the lighting amounts of the plurality of lighting elements are indirectly determined based on the read result of the output correction chart. Measuring step;
Based on the result of indirectly measuring the lighting amount, obtaining a second correction value of the lighting amount for the plurality of lighting elements;
Determining a correction value for each of the lighting elements based on a difference between the first correction value and the second correction value, and correcting the first correction value using the determined correction value; Including
In the step of correcting the first correction value, the correction value is determined so that the first correction value does not change beyond a certain level.   The print head lighting amount adjustment according to claim 1, wherein, in the step of correcting the first correction value, when the difference exceeds a predetermined threshold value, the threshold value is set as the correction value. Method. A lighting amount adjustment method for a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction,
Directly measuring the lighting amount of the plurality of lighting elements;
Based on the result of directly measuring the lighting amount, obtaining a first correction value of the lighting amount for a plurality of the lighting elements;
The plurality of lighting elements are turned on with the lighting amount in consideration of the first correction value to form an image, and the lighting amounts of the plurality of lighting elements are indirectly determined based on the read result of the output correction chart. Measuring step;
Obtaining a second correction value of the lighting amount for a plurality of the lighting elements based on the result of indirectly measuring the lighting amount,
In the step of indirectly measuring the lighting amounts of the plurality of lighting elements, density unevenness having a period different from the length of the lighting element chip in the main scanning direction is removed from the density data obtained by reading the correction chart. A method for adjusting the lighting amount of the print head.   In the step of indirectly measuring the lighting amount of the plurality of lighting elements, from the density data obtained by reading the correction chart, density unevenness with a period equal to or less than half of the length in the main scanning direction of the lighting element chip, and 4. A method for adjusting a lighting amount of a print head according to claim 3, wherein density unevenness having a period of 5 times or more the length of the lighting element chip in the main scanning direction is removed. A lighting amount adjustment device for a print head in which a plurality of lighting element chips in which a plurality of lighting elements are arranged in the main scanning direction are arranged in the main scanning direction,
Reading data of a correction chart output by an image forming operation performed by lighting a plurality of the lighting elements with a lighting amount in consideration of a first correction value stored in advance in a memory is supplied to the plurality of lighting elements. A density converter for converting into corresponding density data;
Applying a filtering process to the density data output from the density converter, a frequency filter unit that removes density unevenness having a period different from the main scanning direction length of the lighting element chip;
A correction value calculation unit that calculates a second correction value of the lighting amount for the plurality of lighting elements, based on the density data from which the density unevenness has been removed;
A correction value for each lighting element is determined based on a difference between the first correction value and the second correction value output from the correction value calculation unit, and the first correction value is determined using the determined correction value. A correction value setting unit for correcting one correction value;
A print head lighting amount adjusting device including: a correction value writing unit that writes a third correction value obtained by correcting the first correction value with the correction value in the correction value setting unit.   The print head lighting amount adjustment according to claim 5, wherein the first correction value is set based on a result of directly measuring the lighting amounts of the plurality of lighting elements constituting the print head. apparatus.   The frequency filter section removes density unevenness with a period of half or less of the length of the lighting element chip in the main scanning direction and density unevenness with a period of 5 times or more of the length of the lighting element chip in the main scanning direction. The lighting amount adjustment device for a print head according to claim 5.   6. The print head lighting amount adjustment apparatus according to claim 5, wherein the correction value setting unit determines the correction value so that the first correction value does not change beyond a certain level.   9. The print head lighting amount adjustment apparatus according to claim 8, wherein when the difference exceeds a predetermined threshold, the correction value setting unit sets the threshold as the correction value.   6. The lighting amount adjustment device for a print head according to claim 5, wherein the plurality of lighting element chips constituting the print head to be adjusted are arranged in a staggered manner.

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