JP2008155458A - Light emitting device and image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control the occurrence of light-amount unevenness even in case an environmental change occurs. <P>SOLUTION: LPH 14 is equipped with a printed circuit board 52 which mounts LED array composed by putting in order 60 pieces of LED chips in which 128 pieces of LED are installed and a rod lens array 54 composed by aligning two or more rod lens in two trains. The luminescence light-amount of each LED is corrected using LED correction data which are established from individual light amount unevenness of LED and the pitch unevenness of rod lens. Considering the positional gap which is generated by the expanding and contracting of the printed circuit board 52 and rod lens array 54 due to a temperature changing, the lens correction data are changed according to the temperature. Concretely, the culling or adding data from or to lens correction standard data are performed according to the temperature, and then the lens correction data are made out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light-emitting device that emits light using a plurality of light-emitting elements.

  2. Description of the Related Art In recent years, in an image forming apparatus employing an electrophotographic method, an LED configured by arranging a large number of LEDs (Light Emitting Diodes) in the main scanning direction as an exposure device that exposes an image carrier such as a photoconductor. A print head (LPH: LED Print Head) has been used. This type of LPH usually includes a rod lens array in which a large number of rod lenses are arranged to form an image of light output from each LED on the surface of the photoreceptor. In order to suppress unevenness in the amount of light irradiated on the image carrier, a technique is known in which light amount correction data of each LED is acquired in advance and light amount correction is performed based on the light amount correction data when used (Patent Literature). 1).

JP-A-11-227254

  The present invention has been made against the background of the above-described technology, and its object is to suppress the occurrence of unevenness in the amount of light even when, for example, an environmental change or the like occurs.

  For this purpose, a light-emitting device to which the present invention is applied includes a light-emitting unit in which a plurality of light-emitting elements are arranged, and a light that is disposed so as to face the light-emitting unit along the light-emitting unit. Using the correction value set for each light-emitting element using the condensing lens unit, the correction unit that corrects the amount of emitted light for each light-emitting element, and correction according to the positional deviation that occurs between the light-emitting unit and the lens unit And a setting unit for setting a value.

  In such a light emitting device, when the correction unit further includes a holding unit that holds the correction value, the setting unit thins out or adds a part of the correction value read from the holding unit when setting the correction value. It can be. In addition, the lens unit can be characterized in that a plurality of lenses are arranged along the light emitting unit. Furthermore, the lens unit can be characterized in that a plurality of gradient index lenses are arranged along the light emitting unit.

  From another point of view, an image forming apparatus to which the present invention is applied includes an image holding body, a light emitting section in which a plurality of light emitting elements are arranged, and a light emitting section and an image holding body along the light emitting section. A lens unit that concentrically arranges light emitted from a plurality of light emitting elements on an image carrier, an element correction value for correcting unevenness in the light amount of each light emitting element in the light emitting unit, and a light amount of each light emitting element in the lens unit A correction unit that corrects the amount of emitted light for each light emitting element using the lens correction value for correcting unevenness, and a lens correction value change unit that changes the lens correction value based on environmental conditions are included.

  In such an image forming apparatus, when the lens correction value changing unit further includes an element correction value holding unit that holds an element correction value and a lens correction value holding unit that holds reference data of the lens correction value, the lens correction value changing unit The lens correction value obtained by thinning out or adding a part of the reference data of the lens correction value read from the correction value holding unit may be output to the correction unit.

According to the first aspect of the present invention, for example, even when an environmental change or the like occurs, it is possible to suppress the occurrence of unevenness in the amount of light due to the positional deviation that occurs between the light emitting unit and the lens unit.
According to the second aspect of the present invention, it is not necessary to have a plurality of correction values in advance, and the memory capacity and the like can be reduced.
According to the third aspect of the invention, even when a plurality of lenses are used as the lens portion, the occurrence of unevenness in the amount of light can be suppressed.
According to the fourth aspect of the present invention, even when a plurality of gradient index lenses are used as the lens portion, the occurrence of unevenness in the amount of light can be suppressed.
According to the fifth aspect of the present invention, for example, even when an environmental change or the like occurs, it is possible to suppress the occurrence of unevenness in the amount of light due to the positional deviation between the light emitting unit and the lens unit.
According to the sixth aspect of the present invention, the lens correction value can be easily created, and the apparatus configuration can be simplified.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) 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 according to the present embodiment, and shows a so-called tandem type digital color copying machine. The image forming apparatus shown in FIG. 1 controls an image process system 10 that forms an image corresponding to gradation data of each color, a sheet conveyance system 30 that conveys recording paper (sheet), and the image process system 10 in the main body 1. The image output control unit 41 is connected to a personal computer, a scanner unit 45, or the like, and includes an image processing unit 42 that performs predetermined image processing on the received image data.

  The image processing system 10 includes four image forming units 11Y and 11M of yellow (Y), magenta (M), cyan (C), and black (K), which are arranged in parallel at regular intervals in the horizontal direction. 11C, 11K, and a transfer unit 20 for transferring the toner images of the respective colors formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, 11K onto the intermediate transfer belt 21. The main body 1 also includes a fixing device 29 that fixes the image on the recording paper (sheet) secondarily transferred by the transfer unit 20 to the recording paper using heat and pressure. Further, the main body 1 is provided with toner cartridges 19Y, 19M, 19C, and 19K for supplying toner of each color to the image forming units 11Y, 11M, 11C, and 11K. A temperature sensor 43 that measures the temperature in the main body 1 as an environmental condition is mounted below the black image forming unit 11K.

  The transfer unit 20 includes a drive roll 22 that drives the intermediate transfer belt 21, a tension roll 23 that applies a constant tension to the intermediate transfer belt 21, and a backup roll that secondarily transfers the superimposed toner images of each color onto a recording sheet. 24, a belt cleaner 25 for removing residual toner and the like existing on the intermediate transfer belt 21 is provided. The intermediate transfer belt 21 is wound around the drive roll 22, the tension roll 23, and the backup roll 24 with a constant tension, and is driven at a predetermined speed by the drive roll 22 that is rotationally driven by a drive motor (not shown). Circulation driven. As the intermediate transfer belt 21, for example, a belt whose resistance is adjusted with a belt material (rubber or resin) that does not cause charge-up is used.

  The sheet transport system 30 is supplied from a paper feed tray 31 that loads and supplies recording paper (sheets) on which images are recorded, a feed roll 32 that picks up and feeds recording paper from the paper feed tray 31, and a feed roll 32. A feed roll 33 that separates and conveys the recording sheets one by one, and a conveyance path 34 that conveys the recording sheets separated one by one by the feed roll 33 toward the secondary transfer position are provided. In addition, a registration roll 35 that conveys the recording paper conveyed through the conveyance path 34 toward the secondary transfer position in time, and a backup roll 24 that is provided at the secondary transfer position and is in pressure contact with the recording paper. A secondary transfer roll 36 for secondary transfer of the image onto the recording paper, a discharge paper 37 for discharging the recording paper on which the toner image is fixed by the fixing device 29 to the outside of the main body 1, and a recording paper discharged by the discharge roll 37 are stacked. A discharge tray 38 is provided.

  The scanner unit 45 reads an image of a document placed on the platen glass or an image of the document conveyed on the platen glass by a CCD image sensor or the like (not shown). Here, in the image forming apparatus according to the present embodiment, the scanner unit 45 is disposed on the upper side of the main body 1 to save space. Note that a predetermined gap is formed between the discharge tray 38 and the scanner unit 45 so that the recording paper after image formation discharged to the discharge tray 38 can be easily taken out.

  Next, the image forming units 11Y, 11M, 11C, and 11K in the image process system 10 will be described in detail. FIG. 2 is a diagram for explaining the configuration of the image forming units 11Y, 11M, 11C, and 11K. Here, the yellow (Y) image forming unit 11Y is illustrated. The other image forming units 11M, 11C, and 11K have substantially the same configuration except for the color of toner stored in the developing device 15.

The image forming unit 11Y (11M, 11C, 11K) is charged by a photosensitive drum 12 as an image holding body for holding a toner image, a charger 13 for charging the photosensitive drum 12 using a charging roll, and a charger 13. An LED print head (LPH) 14 that irradiates the photosensitive drum 12 with light to form an electrostatic latent image on the photosensitive drum 12, and the electrostatic formed on the photosensitive drum 12 by the LPH 14. A developing unit 15 that develops a latent image with toner and a photosensitive drum 12 that are provided across the intermediate transfer belt 21 and a toner image developed on the photosensitive drum 12 are transferred onto the intermediate transfer belt 21. A transfer roll 16 and a drum cleaner 17 for removing residual toner remaining on the photosensitive drum 12 after transfer are provided.
Further, the intermediate transfer belt 21 is disposed on the upper side in the vertical direction of the photoconductive drum 12, and the LPH 14 is disposed on the lower side in the vertical direction of the photoconductive drum 12.

  Next, the operation of the image forming apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2. For example, the color material reflected light image of the original read by the scanner unit 45 and the color material image data formed by a personal computer (not shown) are, for example, R (red), G (green), and B (blue). The data is input to the image processing unit 42 as 8-bit reflectance data. In the image processing unit 42, a predetermined image such as shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and the like is applied to the input reflectance data. Processing is performed. The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and each image forming unit 11Y, 11M, It is output to the LPH 14 of 11C and 11K.

  In each of the image forming units 11Y, 11M, 11C, and 11K, the photosensitive drum 12 is charged to a predetermined potential by the charger 13. In addition, the LPH 14 of each of the image forming units 11Y, 11M, 11C, and 11K causes the corresponding LED to emit light according to the color material gradation data input from the image processing unit 42, and via a rod lens array 54 (described later). The photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K are irradiated. On the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K, the charged surface is exposed to form an electrostatic latent image. The formed electrostatic latent image is developed into each color of yellow (Y), magenta (M), cyan (C), and black (K) by the developing unit 15 of each image forming unit 11Y, 11M, 11C, and 11K. Developed as a toner image.

  The toner images formed on the respective photoconductive drums 12 of the image forming units 11Y, 11M, 11C, and 11K are multiple transferred onto the intermediate transfer belt 21. Further, the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K after the transfer are cleaned by the respective drum cleaners 17.

  On the other hand, in the sheet conveyance system 30, the feeding roll 32 rotates in synchronization with the image formation timing, and a recording paper of a predetermined size is supplied from the paper feed tray 31. The recording sheets separated one by one by the feed roll 33 are conveyed to the registration roll 35 through the conveyance path 34 and are temporarily stopped. Thereafter, the registration roll 35 rotates in accordance with the movement timing of the intermediate transfer belt 21 on which the toner image is formed, and the recording paper is conveyed to the secondary transfer position formed by the backup roll 24 and the secondary transfer roll 36. . On the recording sheet conveyed from the lower side to the upper side at the secondary transfer position, the toner images on which the four colors are superimposed are sequentially transferred in the sub-scanning direction using a pressing force and a predetermined electric field. The recording paper on which the toner images of the respective colors are transferred is subjected to a fixing process by heat and pressure by the fixing device 29 and then discharged to a discharge tray 38 provided on the upper portion of the main body 1 by a discharge roll 37. On the other hand, the intermediate transfer belt 21 after the secondary transfer is cleaned by the belt cleaner 25 to prepare for the next process.

Next, the LPH 14 will be described in detail. FIG. 3 shows an enlarged sectional view of the LPH 14 described above.
The LPH 14 includes an LED array 51, a printed board 52, a support member 53, a rod lens array 54, and an LPH housing 55. Here, the LED array 51 as a light emitting unit is configured by staggering LED chips 56 in which a large number of LEDs (light emitting elements) are linearly arranged as will be described later. The printed circuit board 52 is constituted by a so-called glass epoxy substrate having, for example, a glass cloth base material epoxy resin as a base material. The printed circuit board 52 supports the LED array 51 and is attached with a driver IC 64 (described later) for controlling the driving of the LED array 51, and a wiring (not shown) is formed on the surface or inside thereof. The support member 53 is made of, for example, FRP (Fiber Reinforced Plastics), and supports the printed circuit board 52. The rod lens array 54 as a lens unit is provided on the upper side of the LED array 51 and forms an image on the photosensitive drum 12 of the light beam emitted from each LED. The LPH housing 55 is made of, for example, FRP, and holds the support member 53 and the rod lens array 54 to which the printed circuit board 52 is attached.

FIG. 4 is a perspective view of the LPH 14.
In the LPH 14, the LPH housing 55 is formed so as to protrude outward from both ends in the main scanning direction of the rod lens array 54. In the LPH housing 55, these protruding portions are referred to as a first protruding portion 55a and a second protruding portion 55b. Here, the 1st protrusion part 55a is set longer than the 2nd protrusion part 55b. Bolts 58a and 58b for positioning the LPH 14 with respect to a frame (not shown) provided on the main body 1 (see FIG. 1) are vertically provided in the projecting portions 55a and 55b. ing. A printed circuit board 52 to which the LED array 51 (see FIG. 3) is attached extends to one end of the LPH 14 in the main scanning direction, specifically, to the first protrusion 55a provided on the LPH housing 55. Has been placed. A driver IC 64 for driving the LED array 51 is attached to the upper surface of the printed board 52 exposed on the first protrusion 55a.

  A power cable 71 for supplying power to the driver IC 64, the LED array 51, and the like is attached to the upper surface of the printed board 52 between the driver IC 64 and the bolt 58a attachment position. Further, the video data (Vdata) sent from the image processing unit 42 (see FIG. 1) and the image output control unit 41 (see FIG. 1) are sent to the upper surface of the printed circuit board 52 outside the mounting position of the bolt 58a. A harness 72 for receiving a clock (clk), a synchronization signal (Lsync), and the like is attached.

5 shows the main part of the LPH 14. FIG. 5 (a) shows a top view of the printed circuit board 52, and FIG. 5 (b) shows a top view of the rod lens array 54 and the LPH housing 55, respectively. is doing.
In the printed circuit board 52, as shown in FIG. 5A, the LED array 51 has LED chips 56 arranged in a staggered pattern in two rows in the sub-scanning direction (y direction) on the printed circuit board 52. In the LED chip 56 configured by arranging LEDs in a row, for example, light emitting points (LEDs) of 128 pixels are arranged in one chip. When all the LED chips 56 are arranged in a straight line, the distance between the LEDs at the connection portion of the adjacent LED chips 56 is set to a pixel interval (for example, 42.2 μm if 600 dpi). The interval between the light emitting portion and the light emitting portion is likely to be defective. Therefore, as shown in FIG. 5A, the LED chips 56 are arranged in a staggered manner to increase the distance between the cut surface of the chip end and the light emitting point, and is necessary in the main scanning direction (x direction). It is effective to arrange pixels. This staggered arrangement of LED chips 56 is advantageous particularly when high-density mounting of 1200 dpi or higher is required.

  The printed circuit board 52 includes a driver IC 64 for driving the LED array 51 and a power cable 71 (on the one end side of the LPH 14 in the main scanning direction and substantially in series with the rod lens array 54 (LED array 51)). A power supply power line connector 65 to which a power supply is attached and a signal line connector 66 for communication to which a harness 72 (see FIG. 4) is attached are arranged.

  Further, as shown in FIG. 5B, the rod lens array 54 is arranged in two rows in the LPH housing 55 so that the rod lenses 57 are staggered. However, “alignment” has periodic unevenness in optical characteristics (light transmittance) due to its structure. Each rod lens 57 has, for example, a cylindrical shape, and is constituted by a refractive index distribution type lens having a refractive index distribution in the radial direction. An example of such a gradient index lens is a SELFOC (trademark of Nippon Sheet Glass Co., Ltd.) lens array. In this embodiment, a rod lens 57 having a diameter of 0.9 mm is used.

  In the following description, the LED chip 56 provided on one end side (side where the driver IC 64 is disposed) of the LED array 51 is referred to as C1, and the LED chip 56 provided adjacent to C1 is referred to as C2. Call it. In the present embodiment, a total of 60 LED chips 56 (C1 to C60) are mounted on the printed circuit board 52. That is, the LED array 51 includes a total of 7680 LEDs. Further, the distance from the outer end portion of C1 to the outer end portion of C60 (the length in the main scanning direction of the LED array 51) is set to 324 mm in order to correspond to the image formation on the recording paper of A3 Nobi. For this reason, the interval between adjacent LEDs is set to about 42.2 μm, and the output resolution of the LPH 14 in the main scanning direction is 600 dpi (dot per inch).

FIG. 6 is a view for explaining attachment of the printed circuit board 52 to the support member 53.
In the present embodiment, the printed circuit board 52 is attached to the support member 53 using two types of adhesives. More specifically, the side of the printed circuit board 52 on which the driver IC 64 is mounted is bonded to the support member 53 by the first adhesive 81 that increases the strength after bonding. On the other hand, the side on which each LED chip 56 is mounted in the printed circuit board 52 is bonded to the support member 53 by the second adhesive 82 whose strength after bonding is weaker than that of the first adhesive 81. Here, as the first adhesive 81, for example, an epoxy-based adhesive can be used, and as the second adhesive 82, for example, a silicone-based adhesive can be used.

  Thereby, in this Embodiment, compared with the one end side (driver IC64 side) of the printed circuit board 52, the adhesive strength of the other end side (LED chip 56 side) becomes low. For this reason, when the printed circuit board 52 expands due to heat generated by light emission of the LED, the printed circuit board 52 extends toward the LED chip 56 (C60).

  FIG. 7 is a diagram illustrating the configuration of the driver IC 64 and the wiring structure formed on the printed circuit board 52. Here, the driver IC 64 includes a signal generation circuit 100, an EEPROM (Electrically Erasable and Programmable ROM) 102, and a level shift circuit 104.

  The signal generation circuit 100 includes a lighting signal generation unit 101 that outputs a lighting signal ΦI (ΦI1 to ΦI60) to each LED chip 56 (C1 to C60). Further, the signal generation circuit 100 divides each LED chip 56 (C1 to C60) into six sets (every 10 chips), and the transfer signal CK1 (CK1_1 to CK1_6) and the transfer signal CK2 (CK2_1 to CK2_6) for each set. ) Is output. The signal generation circuit 100 receives a line synchronization signal Lsync, video data Vdata, a clock signal clk, and a temperature detection signal Temp. The signal generation circuit 100 also receives LED correction data U, lens correction reference data V, and correction table Ta from the EEPROM 102. These LED correction data U, lens correction reference data V, and correction table Ta are determined in advance before shipment of the image forming apparatus, and are stored in the EEPROM 102. In the present embodiment, the EEPROM 102 functions as a holding unit, an element correction value holding unit, and a lens correction value holding unit. Details of the LED correction data U, the lens correction reference data V, and the correction table Ta will be described later.

  The printed circuit board 52 is provided with a power supply line 105 of Vcc = + 3.3 V for supplying power to the LED chips 56 (C1 to C60) and a power supply line 106 that is grounded (GND). Further, lighting signal lines 107 (107_1 to 107_60) for transmitting lighting signals ΦI (ΦI1 to ΦI60) from the lighting signal generation unit 101 of the signal generation circuit 100 to the LED chips 56 are also provided. Furthermore, the first transfer signal line 108 (108_1 to 108_6) for transmitting the first transfer signal CK1 (CK1_1 to 1_6) from the transfer signal generator 103 of the signal generation circuit 100, and the second transfer signal CK2 (CK2_1). ˜2_6) is also provided. Second transfer signal lines 109 (109_1 to 109_6) are also provided.

  A corresponding lighting signal ΦI (ΦI1 to ΦI60) is input to each LED chip 56 (C1 to C60) via the lighting signal line 107. In addition, each LED chip 56 has a corresponding first transfer signal CK1 (CK1_1 to 1_6) via the first transfer signal line 108 and a corresponding second transfer signal line 109 via the second transfer signal line 109. Transfer signals CK2 (CK2_1 to 2_6) are respectively input.

  FIG. 8 is a diagram illustrating the configuration of the LED chip 56, the signal generation circuit 100, and the level shift circuit 104. However, in FIG. 8, only C1 is shown among the several LED chips 56 which comprise the LED array 51. FIG. The other LED chips 56, C2 to C60, also have the same configuration as C1.

  The LED chip 56 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 C1A are connected in parallel, and a resistor R2B and a capacitor C2A are connected in parallel. Each one end is connected to the input terminal of the LED chip 56, and the other end is connected to the output terminal of the signal generation circuit 100. In the level shift circuit 104, the first transfer signal CK1 is based on the transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C output from the signal generation circuit 100 (specifically, the transfer signal generation unit 103 illustrated in FIG. 7). (In the case of the LED chip 56 (C1), CK1_1, and so on) and the second transfer signal CK2 (CK2_1) are output to the LED chip 56 (C1). The LED chip 56 is connected to the signal generation circuit 100 via a drive current setting resistor RID. Then, the signal generation circuit 100 (specifically, the lighting signal generation unit 101 shown in FIG. 7) outputs the driving signal ID, and outputs the lighting signal ΦI (ΦI1) via the driving current setting resistor RID to the LED chip. 56 (C1). Note that the signal generation circuit 100 generates and outputs transfer signals CK1R and CK1C, transfer signals CK2R and CK2C, and a drive signal ID based on various input signals.

  As shown in FIG. 8, the LED chip 56 includes 128 thyristors S1 to S128 and 128 LEDs L1 to L128. The LED chip 56 has an excess current in the 128 diodes D1 to D128, the 128 resistors R1 to R128, the first transfer signal line 108 (108_1), and the second transfer signal line 109 (109_1). Transfer current limiting resistors R1A and R2A are provided to prevent flow.

In the LED chip 56, anode terminals (input terminals) A 1 to A 128 of the thyristors S 1 to S 128 are connected to the power supply line 105. A power supply voltage Vcc (= + 3.3 V) is supplied to the power supply line 105.
The cathode terminals K1, K3,..., K125, K127 of the odd-numbered thyristors S1, S3,..., S125, S127 are transferred from the signal generating circuit 100 to the level shift circuit 104, the first transfer signal line 108 (108_1), The first transfer signal CK1 (CK1_1) is transmitted through the current limiting resistor R1A. The cathode terminals K2, K4,..., K126, K128 of the even-numbered thyristors S2, S4,..., S126, S128 are connected to the level shift circuit 104 and the second transfer signal line 109 (109_1) from the signal generation circuit 100. And the second transfer signal CK2 (CK2_1) is transmitted through the transfer current limiting resistor R2A.

On the other hand, the gate 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 anode terminals of the next-stage diodes D2 to D128 are connected to the gate terminals G1 to G127 of the thyristors S1 to S127, respectively. That is, the diodes D1 to D128 are connected in series with the gate terminals G1 to G127 interposed therebetween.
Furthermore, the anode terminal of the diode D1 is connected to the signal generation circuit 100 via the transfer current limiting resistor R2A, the second transfer signal line 109 (109_1), and the level shift circuit 104. For this reason, the second transfer signal CK2 (CK2_1) is transmitted to the diode D1. The cathode terminals of the LEDs L1 to L128 are connected to the signal generation circuit 100 via the lighting signal line 107 (107_1) and the drive current setting resistor RID, and the lighting signal ΦI (ΦI1) is transmitted.

  The LED chip 56 is provided with a light shielding mask (not shown) so as to cover the thyristors S1 to S128 and the diodes D1 to D128. During the image forming operation, the light shielding mask blocks light emission from the thyristors S1 to S128 when the current is flowing and the diodes D1 to D128 when the current is flowing, and unnecessary light is generated. Exposure of the photosensitive drum 12 (see FIG. 2) is suppressed.

Next, signals for driving the LED array 51 (each LED chip 56) output from the signal generation circuit 100 and the level shift circuit 104 will be described.
FIG. 9 is a timing chart for explaining the signals output from the signal generation circuit 100 and the level shift circuit 104 and the light emission operation of each LED. In the timing chart shown in FIG. 9, the case where all the LEDs L1 to L128 perform optical writing (light emission) in each LED chip 56 is described.

(1) First, when the reset signal RST is input to the signal generation circuit 100, the signal generation circuit 100 (transfer signal generation unit 103) sets the transfer signal CK1R to “H” and the transfer signal CK1C to “H”. To "". In response to this, the level shift circuit 104 outputs the first transfer signal CK1 as “H”. On the other hand, the transfer signal generation unit 103 sets the transfer signal CK2R to “L” and the transfer signal CK2C to “L”. In response to this, the level transfer circuit 104 outputs the second transfer signal CK2 as “L”. As a result, in the LED chip 56, all the thyristors S1 to S128 are turned off (FIG. 9A).
In this state, since the video data Vdata is not input to the signal generation circuit 100 (lighting signal generation unit 101), the lighting signal ΦI is set to “H” (FIG. 9 (H)).

  (2) Following the reset signal RST, the line synchronization signal Lsync input to the signal generation circuit 100 is set to “H” only for a predetermined period (FIG. 9A). Thereby, the operation of the LED chip 56 is started. Then, in synchronization with the line synchronization signal Lsync, the transfer signal generator 103 sets the transfer signal CK2C and the transfer signal CK2R to “H” as shown in FIGS. 9E and 9F. In response to this, the level shift circuit 104 sets the second transfer signal CK2 to “H” as shown in FIG. 9G (FIG. 9B).

  (3) Next, as shown in FIG. 9C, the transfer signal generator 103 sets the transfer signal CK1R to “L” (FIG. 9C). In response to this, in the level shift circuit 104, the charge accumulated in the capacitor C1A flows in the direction toward the resistor R1B, and eventually the potential of the first transfer signal CK1 becomes GND as shown in FIG. 9D. Become. Here, since the potential of the transfer signal CK1C is set to + 3.3V, the potential across the capacitor C1A is + 3.3V (= Vcc).

(4) Subsequently, as shown in FIG. 9B, the transfer signal generator 103 sets the transfer signal CK1C to “L” (FIG. 9D).
In this state, the gate current starts to flow through the thyristor S1. At that time, a tri-state buffer (not shown) corresponding to the resistor R1B is set to high impedance (Hiz) to prevent current backflow.
Thereafter, the thyristor S1 starts to be turned on by the gate current flowing through the thyristor S1, and the gate current gradually increases. At the same time, as a current flows into the capacitor C1A of the level shift circuit 104, the potential of the first transfer signal CK1 gradually increases.

(5) After the elapse of a predetermined time (the time when the potential of the first transfer signal CK1 becomes near GND), the transfer signal generation unit 103 sets the transfer signal CK1R to “L” (FIG. 9E). Then, the potential of the first transfer signal CK1 rises due to the rise of the potential of the gate terminal G1, and accordingly, a current starts to flow to the resistor R1B side of the level shift circuit 104. On the other hand, as the potential of the first transfer signal CK1 increases, the current flowing into the capacitor C1A of the level shift circuit 104 gradually decreases.
When the thyristor S1 is completely turned on and enters 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 C1A. When the transfer signal CK1R is set to “L”, a tristate buffer (not shown) corresponding to the capacitor C1A is set to high impedance (HiZ) as shown in FIG. e)).

  (6) With the thyristor S1 completely turned on, the lighting signal ΦI created by the lighting signal generator 101 is set to “L” based on the video data Vdata as shown in FIG. FIG. 9 (f)). At this time, since the potential of the gate terminal G1> the potential of the gate terminal G2, the LED L1 is turned on earlier and is lit. Since the potential of the lighting signal line 107 increases as the LED L1 is turned on, the LEDs L2 to L128 are not turned on. That is, only the LED L1 having the highest gate voltage is turned on (lit).

(7) Next, as shown in FIG. 9 (F), when the transfer signal generator 103 sets the transfer signal CK2R to “L” (FIG. 9 (g)), the current is the same as in FIG. 9 (c). And a voltage is generated across the capacitor C2A of the level shift circuit 104.
(8) As shown in FIG. 9E, in this state, the transfer signal generator 103 sets the transfer signal CK2C to “L” (FIG. 9H). Accordingly, thyristor S2 is turned on.
(9) Then, as shown in FIGS. 9B and 9C, when the transfer signal generation unit 103 simultaneously sets the transfer signals CK1C and CK1R to H (FIG. 9I), the first transfer signal CK1 is “H”. When the first transfer signal CK1 becomes “H”, the thyristor S1 is turned off and discharged through the resistor R1, so that the potential of the gate terminal G1 gradually decreases. At that time, the thyristor S2 is completely turned on by the rise of the potential of the gate terminal G2.

(10) In the state where the thyristor S2 is completely turned on, as shown in FIG. 9H, both the lighting signals ΦI are set to “L”. Thereby, LED L2 lights up. Further, the LED L2 can be turned off by setting the lighting signal ΦI to “H”. In this case, since the potential of the gate terminal G1 is already lower than the potential of the gate terminal G2, the LED L1 is not turned on.
(11) Then, as shown in FIG. 9C, the transfer signal generator 103 sets the transfer signal CK1R to L (FIG. 9 (j)). In response to this, in the level shift circuit 104, the electric charge accumulated in the capacitor C1A flows in the direction toward the resistor R1B, and eventually the potential of the first transfer signal CK1 becomes GND as shown in FIG. 9D. Become.

(12) Thereafter, the above-described operations are sequentially performed, and the other LEDs L3 to L128 are sequentially turned on.
After the terminal LED L128 in the LED chip 56 is turned off, the transfer signals CK1C and CK1R are set to “H”, the first transfer signal CK1 is set to “H”, and the transfer signals CK2C and CK2R are set to “H”. By setting the second transfer signal CK2 to “H”, both the first transfer signal CK1 and the second transfer signal CK2 are kept in the “H” state for a predetermined time. 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 in the off state (not lit).

  In FIG. 9, the period from when the first transfer signal CK1 becomes “L” to when the second transfer signal becomes “L”, and the second transfer signal CK2 becomes “L”. A period from when the first transfer signal CK1 becomes “L” to when the first transfer signal CK1 becomes “L”. A period from when the line synchronization signal Lsync becomes “L” to when the next line synchronization signal Lsync becomes “L” is referred to as one line transfer cycle.

  Next, the configuration of the lighting signal generation unit 101 in the signal generation circuit 100 will be described in detail with reference to FIG. The lighting signal generation unit 101 includes a staggered array correction unit 111, a lighting time calculation unit 112, a serial / parallel conversion unit 113, and pulse generation units 114 (114_1 to 114_60). Further, the lighting time calculation unit 112 includes a correction data determination unit 121 that functions as a setting unit or a lens correction value change unit, and a calculation unit 122 that functions as a correction unit.

  Video data Vdata is input from the image processing unit 42 to the staggered array correction unit 111. Then, the staggered array correction unit 111 divides the video data Vdata input from the image processing unit 42 for each LED chip 56 (data group for each 128 dots). Then, the staggered array correction unit 111 includes a data group corresponding to the odd-numbered LED chips 56 (C1, C3,..., C59) and a data group corresponding to the even-numbered LED chips 56 (C2, C4,..., C60). Are output to the lighting time calculator 112 at different output timings. Specifically, the light emission timing of the even-numbered LED chips 56 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 LED chips 56 arranged on the upstream side in the sub-scanning direction. Set to. Thereby, the position of the electrostatic latent image formed on the photosensitive drum 12 by the odd-numbered LED chips 56 and the position of the electrostatic latent image formed on the photosensitive drum 12 by the even-numbered LED chips 56 in the sub-scanning direction. Can be combined.

  In the lighting time calculation unit 112, the correction data determination unit 121 includes a temperature detection signal Temp sent from the temperature sensor 43, LED correction data U sent from the EEPROM 102, lens correction reference data V, and a correction table Ta. Entered. The correction data determination unit 121 creates lens correction data W based on the temperature detection signal Temp, the correction table Ta, and the lens correction reference data V, and outputs the lens correction data W together with the LED correction data U to the calculation unit 122.

  Further, in the lighting time calculation unit 112, the calculation unit 122 is supplied with the line synchronization signal Lsync sent from the image output control unit 41, and the video data that has been subjected to the staggered array correction by the staggered array correction unit 111 (hereinafter, staggered correction). Vdata, and LED correction data U and lens correction data W sent from the correction data determination unit 121 are input. The calculation unit 122 uses the LED correction data U and the lens correction data W for the staggered correction video data Vdata while synchronizing with the line synchronization signal Lsync, and each lighting time (the number of lighting clocks) for each of 7680 LEDs. ). More specifically, the lighting time calculation unit 112 lights in proportion to the magnitude of the light amount correction value by adding the light amount correction value based on the LED correction data U and the lens correction data W to the staggered correction video data Vdata. The number of lighting clocks of the corresponding LED is calculated so that the time becomes longer.

  The serial / parallel converter 113 converts the number of lighting clocks for each LED calculated by the lighting time calculator 112 into parallel data. Further, the pulse generator 114 (114_1 to 114_60) generates the lighting signals ΦI1 to ΦI60 by changing the amount of light by pulse width modulation for each signal converted in parallel by the serial / parallel converter 113. Then, the pulse generator 114 (114_1 to 114_60) outputs the generated lighting signals ΦI1 to ΦI60 to the LED chips 56 (C1 to C60) of the LPH 14, respectively. Thereby, in each LED chip 56 of LPH14, LED used as lighting object will light for the set lighting time, respectively.

  FIG. 11 is a diagram for explaining the LED correction data U as the element correction value held in the EEPROM 102 and the lens correction reference data V as the reference data of the lens correction value. Of these, the LED correction data U is for correcting unevenness in the amount of light of each LED alone. The LED correction data U has 7680 (U1 to U7680) light quantity correction values corresponding to the number of LEDs. On the other hand, the lens correction reference data V is used to correct structural unevenness in the amount of light accompanying the arrangement of the rod lenses 57 constituting the rod lens array 54. Unlike the LED correction data U, the lens correction reference data V has 7682 (V1 to V7682) light quantity correction values that are larger than the number of LEDs. However, as will be described later, the lens correction data W as the lens correction value obtained based on the lens correction reference data V is composed of 7680 light quantity correction values corresponding to the number of LEDs. In the present embodiment, the LED correction data U and the lens correction data W correspond to correction values.

  FIG. 12 shows an example of the LED correction data U and the lens correction reference data V. In FIG. 12, LED correction data U and lens correction reference data V corresponding to LEDs L1 to L256 mounted on pixel numbers 1 to 256, that is, LED chip 56 (C1) and LED chip 56 (C2) are shown. Yes. From the figure, the LED correction data U has a correction value corresponding to each LED, and the lens correction reference data V is 21.3 pixels for the lens pitch of the rod lens 57 (0.9 mm, 600 dpi). It is understood that the period fluctuates in a period corresponding to

FIG. 13 is a diagram for explaining the correction table Ta held in the EEPROM 102. The correction table Ta includes pixel numbers that are thinned from the temperature detection signal Temp and the lens correction reference data V by the temperature sensor 43 or added to the lens correction reference data V (referred to as a thinning target pixel number and an additional target pixel number, respectively). Are associated. For example, when the temperature detection signal Temp is 0 ° C. or higher and lower than 10 ° C., the thinning target pixel number “none” and the additional target pixel number “7000” are selected. Further, when the temperature detection signal Temp is 10 ° C. or higher and lower than 30 ° C., the thinning target pixel number “none” and the additional target pixel number “none” are selected. Further, when the temperature detection signal Temp is 30 ° C. or higher and lower than 35 ° C., the thinning target pixel number “7000” and the additional target pixel number “None” are selected. Furthermore, when the temperature detection signal Temp is 35 ° C. or higher and lower than 40 ° C., the thinning target pixel number “6000” and the additional target pixel number “none” are selected. When the temperature detection signal Temp is 40 ° C. or higher and lower than 45 ° C., the thinning target pixel number “4500, 6500” and the additional target pixel number “none” are selected. Further, when the temperature detection signal Temp is 45 ° C. or higher and lower than 50 ° C., the thinning target pixel number “2000, 5000” and the additional target pixel number “none” are selected.
The reason why the pixel to be thinned out and the pixel to be added in the temperature region below 0 ° C. and 50 ° C. or higher are not set because it is outside the assumed use environment of this image forming apparatus.

FIG. 14 is a flowchart for explaining the flow of processing executed by the lighting time calculation unit 112 (specifically, the correction data determination unit 121 and the calculation unit 122) of the lighting signal generation unit 101.
First, the correction data determination unit 121 acquires LED correction data U and lens correction reference data V from the EEPROM 102 (step 101). Next, the correction data determination unit 121 acquires a temperature detection signal Temp as a temperature detection result from the temperature sensor 43 (step 102). Further, the correction data determination unit 121 acquires a corresponding correction table Ta based on the acquired temperature detection result (step 103). Then, the correction data determination unit 121 corrects the lens correction reference data V using the correction table Ta, and creates lens correction data W (step 104). Thereafter, the correction data determination unit 121 outputs the LED correction data U acquired in step 101 and the lens correction data W created in step 104 to the calculation unit 122 (step 105).

  Next, the calculation unit 122 receives an input of the staggered corrected video data Vdata from the staggered array correcting unit 111 (step 106). Then, the calculation unit 122 corrects the staggered correction video data Vdata using the LED correction data U and the lens correction data W acquired from the correction data determination unit 121, and outputs them to the serial / parallel conversion unit 113 (step 107). . Thus, a series of processing is completed.

Now, explanation will be given with specific examples.
FIG. 15 shows the relationship between the pixel number, LED correction data U, and lens correction data W set when 10 ° C. ≦ Temp <30 ° C. In this case, the thinning target pixel number “none” and the addition target pixel number “none” are selected as the correction table Ta. Therefore, for pixel numbers 1 to 7680, U1 to U7680 are set as LED correction data U, and V1 to V7680 are set as lens correction data W, respectively.

  FIG. 16 shows the relationship between the pixel number, LED correction data U, and lens correction data W set when 30 ° C. ≦ Temp <35 ° C. In this case, the thinning target pixel number “7000” and the additional target pixel number “none” are selected as the correction table Ta. Therefore, U1 to U7680 are set as the LED correction data U for the pixel numbers 1 to 7680. On the other hand, in the lens correction data W, the lens correction reference data V7000 corresponding to the pixel number 7000 is thinned out. As a result, as lens correction data W, V1 to V6999 are set for pixel numbers 1 to 6999, and V7001 to V7681 are set for pixel numbers 7000 to 7680, respectively.

  Further, FIG. 17 shows the relationship between the pixel number, LED correction data U, and lens correction data W set when 40 ° C. ≦ Temp <45 ° C. In this case, the thinning target pixel number “4500, 6500” and the additional target pixel number “none” are selected as the correction table Ta. Therefore, U1 to U7680 are set as the LED correction data U for the pixel numbers 1 to 7680. On the other hand, in the lens correction data W, the lens correction reference data V4500 corresponding to the pixel number 4500 and the lens correction reference data V6000 corresponding to the pixel number 6000 are thinned out. As a result, as the lens correction data W, V1 to V4499 for pixel numbers 1 to 4499, V4501 to V6500 for pixel numbers 4500 to 6499, and V6502 to V7682 for pixel numbers 6500 to 7680, Each is set.

  On the other hand, FIG. 18 shows the relationship between the pixel number, the LED correction data U, and the lens correction data W set when 0 ° C. ≦ Temp <10 ° C. In this case, the thinning target pixel number “none” and the addition target pixel number “7000” are selected as the correction table Ta. Therefore, U1 to U7680 are set as the LED correction data U for the pixel numbers 1 to 7680. On the other hand, in the lens correction data W, lens correction data V6999 corresponding to the pixel number 6999 is added. As a result, as lens correction data W, V1 to V6999 are set for pixel numbers 1 to 6999, and V6999 to V7679 are set for pixel numbers 7000 to 7680, respectively.

  In the present embodiment, the materials of the printed circuit board 52 on which the LED array 51 composed of 60 LED chips 56 is mounted and the LPH housing 55 that supports the rod lens array 54 composed of a plurality of rod lenses 57 are different. For this reason, there is a difference in the degree of thermal expansion accompanying the temperature change in the image forming apparatus. For example, in the present embodiment, the glass epoxy material constituting the printed circuit board 52 is more easily stretched by heat than the FRP constituting the LPH housing 55.

  When the rod lens array 54 is used, unevenness in the amount of light due to the lens pitch occurs as shown in FIG. For this reason, in the present embodiment, light amount correction is performed in consideration of unevenness of the LED itself and unevenness of the rod lens array 54. However, when the printed circuit board 52 and the LPH housing 55 expand and contract in accordance with a change in ambient temperature, a slight shift occurs in the positional relationship between the LEDs constituting the LED array 51 and the rod lenses 57 constituting the rod lens array 54. In this example, a positional deviation of about 100 μm at maximum occurs with a temperature change. When the output resolution of the LPH 14 is 600 dpi, 100 μm corresponds to a shift of about 2.36 pixels.

When such a positional shift occurs, a positional relationship between the LED and the rod lens 57 is shifted, and as a result, it becomes impossible to correct unevenness in the amount of light caused by the lens pitch.
Here, FIG. 19A is a diagram for explaining the relationship between the positional deviation generated between the LED array 51 and the rod lens array 54 and the unevenness in the amount of light caused by the positional deviation, and FIG. Is an enlarged view of the main part. In FIGS. 19A and 19B, the horizontal axis indicates the position in the main scanning direction, and the vertical axis indicates the light amount ratio when the initial state in which the light amount unevenness correction is performed is 100%.

  In this example, a positional deviation of one pixel occurs from the main scanning direction position of 10000 μm, and a positional deviation of two pixels occurs from the main scanning direction position of 30000 μm. In the main scanning direction position of 5000 μm to 10000 μm, no positional deviation of one pixel or more has occurred, so that the occurrence of unevenness in light amount is suppressed by light amount correction. On the other hand, in the region of 10000 μm to 30000 μm, the lens correction data is not matched due to the positional deviation of one pixel, and the light amount unevenness corresponding to the lens pitch (0.9 mm) is generated. Furthermore, in a region exceeding 30000 μm, the lens correction data is not further matched due to the positional deviation of two pixels, and the amount of unevenness in the amount of light according to the lens pitch becomes larger.

  On the other hand, in the present embodiment, the lens correction data W is created by thinning out or adding data at a specific position from the lens correction reference data V according to such a temperature change. This specific position is set to a pixel corresponding to a part where the light amount fluctuation due to the positional deviation starts to occur, such as 10000 μm and 30000 μm shown in FIG. That is, the correction table Ta shown in FIG. 13 is set in advance based on the results of such an experiment. By performing the light amount correction using the lens correction data W created from the lens correction reference data V based on such settings, it is possible to suppress the occurrence of uneven light amount in the LPH 14 regardless of the expansion and contraction of the LPH 14 due to a temperature change. It becomes possible.

  In the present embodiment, the correction table Ta is selected based on the temperature detection signal Temp by the temperature sensor 43, but the present invention is not limited to this. More specifically, since the printed circuit board 52 and the LPH housing 55 may contract due to other environmental conditions such as humidity, the correction table Ta may be selected in a state where the humidity detection signal is also taken into account. .

  In this embodiment, the lens correction data W is generated by thinning out or adding data at a specific position from the lens correction reference data V based on the temperature detection signal Temp. However, the present invention is not limited to this. is not. For example, a plurality of lens correction data for each temperature region can be held, and corresponding lens correction data can be read according to the temperature detection signal Temp.

  Furthermore, in the present embodiment, the LED correction data U and the lens correction data W are set separately for each pixel. However, the present invention is not limited to this, and the correction data may be combined into one correction data. In this case, a plurality of correction data for each temperature region may be held, and corresponding lens correction data may be read according to the temperature detection signal Temp.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a figure for demonstrating the structure of an image forming unit. It is an expanded sectional view of LPH (LED Print Head). It is a perspective view of LPH. (A) is a top view of a printed circuit board, (b) is a top view of a rod lens array and an LPH housing. It is a figure for demonstrating attachment of the printed circuit board with respect to a supporting member. It is a figure which shows the structure of driver IC, and the wiring structure formed in a printed circuit board. It is a figure for demonstrating the structure of a LED chip, a signal generation circuit, and a level shift circuit. It is a timing chart for demonstrating lighting operation of LED. It is a figure for demonstrating the structure of a lighting signal generation part. It is a figure for demonstrating LED correction data and lens correction reference data. It is a figure which shows an example of LED correction data and lens correction reference data. It is a figure for demonstrating a correction table. It is a flowchart for demonstrating the flow of the process performed in the lighting time calculation part of a lighting signal generation part. It is a figure which shows the relationship between a pixel number, LED correction data, and lens correction data set in the case of 10 degreeC <= Temp <30 degreeC. It is a figure which shows the relationship between a pixel number, LED correction data, and lens correction data set in the case of 30 degreeC <= Temp <35 degreeC. It is a figure which shows the relationship between a pixel number, LED correction data, and lens correction data set in the case of 40 degreeC <= Temp <45 degreeC. It is a figure which shows the relationship between a pixel number, LED correction data, and lens correction data set in the case of 0 degreeC <= Temp <10 degreeC. (A) is a figure for demonstrating the relationship between the position shift which arose between LED array and a rod lens array, and the light quantity nonuniformity which arises by position shift, (b) is the principal part enlarged view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 14 ... LED print head (LPH) 41 ... Image output control part 42 ... Image processing part 43 ... Temperature sensor 51 ... LED array 52 ... Printed circuit board 53 ... Support member 54 ... Rod lens array 55 ... LPH housing, 56 (C1 to C60) ... LED chip, 57 ... rod lens, 64 ... driver IC, 100 ... signal generation circuit, 101 ... lighting signal generation unit, 102 ... EEPROM, 103 ... transfer signal generation unit, 104 ... level Shift circuit 111 ... Staggered array correction unit 112 ... Lighting time calculation unit 113 113 Serial to parallel conversion unit 114 (114_1 to 114_60) ... Pulse generation unit 121 ... Correction data determination unit 122 ... Calculation unit

Claims (6)

A light emitting section in which a plurality of light emitting elements are arranged;
A lens unit that is disposed to face the light emitting unit along the light emitting unit and collects light emitted by the plurality of light emitting elements;
Using a correction value set for each light emitting element, a correction unit that corrects the amount of light emitted for each light emitting element,
A light-emitting device including a setting unit that sets the correction value according to a positional shift that occurs between the light-emitting unit and the lens unit. A holding unit for holding the correction value;
The light-emitting device according to claim 1, wherein the setting unit thins out or adds a part of the correction value read from the holding unit when setting the correction value.   The light emitting device according to claim 1, wherein the lens unit includes a plurality of lenses arranged along the light emitting unit.   The light emitting device according to claim 1, wherein the lens unit includes a plurality of gradient index lenses arranged along the light emitting unit. An image carrier,
A light emitting section in which a plurality of light emitting elements are arranged;
A lens unit that is disposed to face the light emitting unit and the image carrier along the light emitting unit, and collects light emitted from the plurality of light emitting elements on the image carrier,
Light emission for each light emitting element using an element correction value for correcting light amount unevenness for each light emitting element in the light emitting unit and a lens correction value for correcting light amount unevenness for each light emitting element in the lens unit. A correction unit for correcting the amount of light;
An image forming apparatus including a lens correction value changing unit that changes the lens correction value based on an environmental condition. An element correction value holding unit for holding the element correction value;
A lens correction value holding unit that holds reference data of the lens correction value,
The lens correction value changing unit outputs the lens correction value obtained by thinning out or adding a part of the reference data of the lens correction value read from the lens correction value holding unit to the correction unit. The image forming apparatus according to claim 5.

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