JP4798460B2 - Exposure apparatus, drive control method thereof, and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus, a drive control method thereof, and an image forming apparatus including the exposure apparatus.

An image forming apparatus such as an electrophotographic system has an exposure device for image formation. In recent years, various attempts have been made to use a light emitting element such as an organic EL element as a light source of the exposure apparatus. In the case of performing exposure using such a light emitting element, since there are variations in the amount of emitted light due to variations in the light emission characteristics of the light emitting elements, various techniques for correcting this have been proposed. Some correction data are stored in a memory, and the emission intensity measured based on the correction data is corrected (for example, see Patent Document 1).
JP-A-11-138890

  However, it is known that the light emitting characteristics of the light emitting element as described above change with the passage of time of use, and the amount of light emitted when the light emitting element emits light changes with the passage of the light emitting time. However, no solution has been made to such a change with time.

  Accordingly, the present invention has been made paying attention to such problems, and an object of the present invention is to provide an exposure apparatus capable of obtaining a stable printed image even if the light emitting characteristics of the light emitting element deteriorate over time, and An object of the present invention is to provide a drive control method and an image forming apparatus.

To achieve the above object, an exposure apparatus according to a first aspect of the present invention is an exposure apparatus that performs exposure by irradiating light corresponding to image data onto a photosensitive drum, and includes a plurality of light emitting elements arranged in the main scanning direction. comprising a light emitting element array in which light-emitting elements of said plurality of divided into a plurality of light emitting element groups having two or more of said light emitting elements adjacent, each provided corresponding to each of the plurality of light emitting element groups a plurality of light receiving elements, one of said light receiving element corresponds to one of said light-emitting element group, you detect light emission amount in accordance with the emission luminance of each light emitting element by the plurality of light receiving elements the light quantity detection circuit Each light emitting element of the light emitting element array sequentially emits light in a predetermined light emitting period, and one of the light quantity detection circuits corresponding to one light emitting element group including the light emitting element emitting light in the light quantity detection circuit . in front And driven corresponding to the light receiving element to the light emitting period, the sequentially drives the respective light receiving elements corresponding to the respective light emitting element groups, based on the value of the detected amount of light emitted by the respective light receiving elements, each A correction control circuit for correcting a value of a drive signal based on the image data supplied to the light emitting element, and each of the plurality of light receiving elements in the light amount detecting circuit receives the incident light. The semiconductor layer is provided in a region along the width of the corresponding one of the light emitting element groups in the main scanning direction, and faces the direction orthogonal to the main scanning direction when the light is received. A channel is formed in the semiconductor layer between the drain and source provided, and a channel width corresponding to a length of the semiconductor layer in the direction along the main scanning direction corresponds to the light receiving element. One said departure Characterized in that it is set in the main width greater than the scanning direction of at least two of the light emitting element of the element group.

  As a preferred mode, for example, in the exposure apparatus according to claim 1, the correction control circuit supplies a selection signal for selecting each of the plurality of light emitting element groups to the light emitting element array. And a control signal for starting detection operation of the light receiving element corresponding to the light emitting element group corresponding to the selection signal is supplied to the light amount detection circuit in synchronization with the supply timing of the selection signal. A control signal supply circuit, and the drive signal may be sequentially supplied to each light emitting element of the selected light emitting element group in synchronization with a supply timing of the selection signal.

  As a preferred aspect, for example, in the exposure apparatus according to claim 2, the selection signal is transmitted to each of the plurality of light emitting element groups at a time interval corresponding to the light emission period. The light quantity detection circuit detects the light emission quantity of each light emitting element at each time interval at a timing corresponding to the supply of the selection signal. In addition, a single AD conversion circuit that sequentially AD-converts the value of the amount of emitted light detected at each time interval and outputs it as a digital value may be provided.

  As a preferred mode, for example, in the exposure apparatus according to claim 3, the time interval is set to a time equal to or longer than a detection time of the light emission amount by the light amount detection circuit. You may be made to do.

  As a preferred aspect, for example, in the exposure apparatus according to claim 1, the correction control circuit further includes the plurality of light receiving elements detected by the plurality of light receiving elements at a first timing. A light amount storage circuit for storing each light emission amount of the light emitting element as a first light amount, and the plurality of light emission detected by the plurality of light receiving elements at a second timing after a predetermined time has elapsed from the first timing. A comparison circuit that compares the first light amount stored in the light amount storage circuit with the second light amount, and a first light amount by the comparison circuit, wherein the light emission amount of each element is a second light amount. And a correction data storage circuit for storing light amount correction data corresponding to the difference between the second light amount and a data correction circuit for correcting the drive signal by adding the light amount correction data to the image data. It may have a.

In order to achieve the above object, an image forming apparatus according to a sixth aspect of the present invention is an image forming apparatus that includes a photosensitive drum, a charger, an exposure device, and a developing device, and performs printing according to image data. The exposure device includes a plurality of light emitting elements arranged in a main scanning direction orthogonal to the moving direction of the photosensitive drum, and the plurality of light emitting elements having two or more light emitting elements adjacent to each other. A light-emitting element array that is divided into groups and irradiates the photosensitive drum with emitted light; and a plurality of light-receiving elements each provided corresponding to each of the plurality of light-emitting element groups. There corresponds to one of the light emitting element group, the light quantity detection circuit by the plurality of light receiving elements that detect the amount of light emission corresponding to the light emission luminance of each light emitting element, said light emitting element array of the light emitting element array Each light emitting element is Are sequentially emitting a light period, the light intensity detecting one of said light receiving element corresponding to the light emitting element group one that contains the light emitting device that emits light in the circuit and driven corresponding to the light emitting period, the respective light emitting element groups And sequentially driving each of the light receiving elements, and correcting the value of the drive signal based on the image data supplied to each of the light emitting elements based on the value of the amount of light detected by each of the light receiving elements. A correction control circuit, and each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, and the semiconductor layer includes the corresponding one of the light emitting element groups. A channel is formed in the semiconductor layer between the drain and source provided in a region along the width in the main scanning direction and facing the direction orthogonal to the main scanning direction when receiving the light , H The direction along the main scanning direction of the semiconductor layer of the channel the channel width corresponding to the length of the main scanning direction of at least two of said light-emitting element of one of the light emitting element groups corresponding to the light receiving element It is characterized by being set to a value larger than the width.

In a preferable embodiment, for example, as according to claim 7, wherein, in the image forming apparatus according to claim 6, wherein the control circuit comprises a selection signal for selecting each of the plurality of light emitting element groups of the light emitting element array A selection signal supply circuit for supplying to the light emitting element array, and a control signal for starting the detection operation of the light receiving element corresponding to the light emitting element group corresponding to the selection signal in synchronization with the supply timing of the selection signal. A control signal supply circuit for supplying to the detection circuit, wherein the drive signal is sequentially supplied to each light emitting element of the selected light emitting element group in synchronization with the supply timing of the selection signal. May be.

In a preferable embodiment, for example, as according to claim 8, wherein, in the image forming apparatus according to claim 7, wherein the selection signal, to each of the plurality of light emitting element groups, the time interval corresponding to the light emission period The light quantity detection circuit supplies the light emission quantity of each light emitting element at each time interval at a timing corresponding to the supply of the selection signal. It is also possible to have a single AD conversion circuit that detects and sequentially AD converts the value of the emitted light quantity detected at each time interval and outputs it as a digital value.

As a preferred mode, for example, as in claim 9, in the image forming apparatus according to claim 8 , the time interval is equal to or longer than a detection time of the emitted light quantity by the light quantity detection circuit. It may be set.

As a preferred mode, for example, as in claim 10, in the image forming apparatus according to claim 6 , the correction control circuit is further configured to detect the plurality of light detection elements detected by the plurality of light receiving elements at a first timing. A light quantity storage circuit for storing the light emission quantity of each of the light emitting elements as a first quantity of light, and the plurality of light receiving elements detected by the plurality of light receiving elements at a second timing after a predetermined time has elapsed from the first timing. A comparison circuit that compares the first light amount stored in the light amount storage circuit and the second light amount with the light emission amount of each light emitting element as a second light amount, and the first circuit by the comparison circuit A correction data storage circuit for storing light amount correction data corresponding to a difference between the light amount and the second light amount; and data correction for correcting the drive signal by adding the light amount correction data to the image data And road may be provided with a correction circuit having a.

  According to the present invention, there is an advantage that a stable printed image can be obtained even if the light emission characteristics of the light emitting element are deteriorated with time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

A. Configuration of Embodiment FIG. 1 is a schematic diagram showing an example of the structure of an image forming apparatus (electrophotographic printing apparatus) equipped with an exposure apparatus according to an embodiment of the present invention. The image forming apparatus includes a photosensitive drum 1, a charging roller 2, an exposure head 3, a developing device 4, a conveyor belt 5, a transfer roller 6, a fixing roller 7, an eraser light source 8, and a cleaning device 9. Thus, image formation (printing) is performed. That is, the photosensitive drum 1 is charged by the charging roller 2 and is exposed on the photosensitive drum 1 by the exposure head (exposure device) 3 according to the image data to form a latent image, and the latent image on the photosensitive drum 1 is formed by the developing device 4. The toner is placed, the toner on the photosensitive drum 1 is transferred onto the sheet conveyed in the direction of the arrow by the conveying belt 5 by the transfer roller 6, fixed by the fixing roller 7, and discharged. Further, the photosensitive drum 1 after toner transfer is neutralized by the eraser light source 8 and cleaned by the cleaning device 9.

  In the present embodiment, a light emitting element array in which a plurality of light emitting elements by organic EL are arranged in the main scanning direction is used as the light source of the exposure head 3 in the above-described electrophotographic process printing. 2. Description of the Related Art In recent years, surface light emitting devices having a plurality of pixels having organic EL light emitting elements arranged two-dimensionally and light emitting element arrays in which a plurality of light emitting elements are arranged in a straight line have been actively studied and formed in a lump instead of LEDs. In addition, by adopting a plurality of light emitting elements by organic EL, the number of wire bondings connected to each LED can be reduced, which has the advantage of greatly contributing to cost reduction.

  However, at present, a light emitting element using an organic EL has a problem in that it does not take advantage of the cost reduction because the light amount is reduced due to deterioration with time. In this embodiment, countermeasures are taken for this problem, considering changes in characteristics of organic EL over time, suppressing changes in light intensity over time, and maintaining high image quality over a long period of time. It is.

  FIG. 2 is a block diagram showing a schematic configuration of the exposure apparatus in the present embodiment. In the figure, a plurality of light emitting elements 10 are arranged in the main scanning direction of the photosensitive drum 1 and emit light with a luminance corresponding to the value of the drive current. The light emitting element array 11 has a plurality of light emitting element groups each including two or more adjacent light emitting elements in the plurality of light emitting elements 10. The light emission drive circuit 12 supplies a drive signal corresponding to the image data to each light emitting element of each light emitting element group. The light amount detection circuit 13 detects the light emission amount corresponding to the light emission luminance of each light emitting element 10 by the plurality of light receiving elements 14 provided corresponding to each of the plurality of light emitting element groups.

  The correction control circuit 15 sequentially applies a drive signal corresponding to the image data to each light emitting element of the plurality of light emitting element groups by the light emission driving circuit 12 to emit light, and corresponds to each light emitting element group including the light emitting elements that emit light. The light receiving element 14 is driven, a correction value corresponding to the amount of fluctuation of the light emission amount of each light emitting element 10 is acquired based on the comparison between the light amount value detected by each light receiving element 14 and the reference value, and the light emission drive circuit 12. The drive signal to be supplied to is corrected with a correction value.

  FIG. 3 is a conceptual diagram for explaining a drive control system of the exposure apparatus when printing is performed by an image forming apparatus equipped with the exposure apparatus of the present embodiment. In FIG. 3A, for the sake of simplicity, the plurality of light emitting elements 10 are composed of a plurality of light emitting element groups of a block to h block, and each block includes a1 to a6, b1 to b6, c1 to c1. Suppose that it has six light emitting elements like c6, ..., h1-h6. The light receiving elements A, B, C,..., H are arranged so as to cover a plurality of light emitting element groups of corresponding a block to h block.

  At the time of printing by the image forming apparatus (electrophotographic printing apparatus) using the exposure apparatus according to the present embodiment, a plurality of light emitting element groups of a block to h block are in units of blocks as shown in FIG. It is designed to light up sequentially. First, the a block light emitting elements a1 to a6 are caused to emit light, and then the b block light emitting elements b1 to b6, the c block light emitting elements c1 to c6,..., The h block light emitting elements h1 to h6 are emitted.

  FIG. 4 is a conceptual diagram for explaining a drive control method when correcting the light emission quantity of the light emitting element in the exposure apparatus of the present embodiment. In the figure, when correcting the amount of light emitted from the light emitting elements of the exposure apparatus, the light emitting elements a1 to a6, b1 to b6, c1 to c6, d1 to d6,. Drive control is performed so that light is emitted in order. Further, the light receiving elements A to H corresponding to the a block to the h block are driven in synchronization with the light emitting periods of the light emitting elements a1 to a6, b1 to b6, c1 to c6, d1 to d6,. At the end of each light receiving period, a light emission amount (output) corresponding to the light emission luminance of each light emitting element a1 to a6, b1 to b6, c1 to c6, d1 to d6,.

  Here, as shown in FIG. 4, the detection start timing of the light emission amount of each light emitting element is a timing corresponding to the light emission start of each light emitting element a <b> 1 to h <b> 6 of the light emitting element array 11. The amount of light emitted from the light emitting element is detected. As shown in FIGS. 5 and 8 to be described later, the detected light emission amount value is finally AD-converted and supplied to the head controller 20 as a digital value. In this embodiment, Since the detection of the amount of light emitted by each light emitting element is performed not at the same time but at regular time intervals, only one AD conversion circuit for performing AD conversion can be provided, and each detected light emission There is no need to provide a storage circuit for temporarily storing the value of the light emission amount of the element. As a result, the circuit scale involved in detecting the amount of light emitted from each light emitting element can be reduced.

  In this way, the light emission elements a1 to a6, b1 to b6, c1 to c6, d1 to d6,..., H1 to h6 are sequentially emitted to emit only one light emitting element at a time. Therefore, light from other light emitting elements does not enter, and noise can be reduced.

  FIG. 5 is a block configuration diagram showing an example of a specific configuration of the exposure apparatus in the present embodiment. In FIG. 5, the exposure head 3 includes a head controller 20, a data driver 21, a select driver (selection signal supply circuit) 22, a sensor driver (control signal supply circuit) 23, and an organic EL panel 24. The head controller 20 receives control signals such as HSYNC (horizontal control signal) and VSYNC (vertical control signal) according to image data, paper size, and conveyance speed from a raster image processor unit (not shown) of the image forming apparatus. The data driver 21, select driver 22 and sensor driver 23 are driven in accordance with these control signals.

  The data driver 21 corresponds to the light emission drive circuit 12 described above, generates gradation signals (drive signals) Vdata1 to Vdata6 corresponding to the gradation values of the image data for each light emitting element of the organic EL panel 24, and generates the organic EL panel. 24 is supplied to each of the light emitting elements of a plurality of a blocks to h blocks. The organic EL panel 24 is formed with a light emitting element array in which a plurality of light emitting elements of organic EL are arranged, for example, in a line in the main scanning direction, and light for detecting the amount of light emitted from each of the plurality of light emitting elements. A sensor circuit (corresponding to the light amount detection circuit 13 described above) is formed. The plurality of light emitting elements of the organic EL panel 24 are grouped into a plurality of blocks (light emitting element groups) each having a predetermined number of light emitting elements. In addition, the optical sensor circuit is provided corresponding to each block.

  The select driver 22 generates block selection signals Vsel1 to Vsel8 for selecting a block to emit light from among a plurality of blocks constituting the organic EL panel 24, and each of the plurality of blocks constituting the organic EL panel 24. To supply. The sensor driver 23 generates a start signal SCG for starting light amount detection in the optical sensor circuit of each block of the organic EL panel 24, and a refresh signal RFSH for refreshing the optical sensor circuit of each block of the organic EL panel 24, While supplying to the plurality of blocks constituting the organic EL panel 24, the sensor currents Sout1 to Sout8 corresponding to the detected light amount detected by the optical sensor circuit of the organic EL panel 24 are sequentially converted into voltages, and the head controller is used as the sensor voltage Psout. 20 is supplied.

  The organic EL panel 24 has a structure that is substantially the same as that in which all vertical pixel arrays are arranged in a horizontal direction with respect to a surface light emitting device in which pixels having light emitting elements are two-dimensionally arranged. The organic EL panel 24 is divided into a plurality of blocks (eight in the example shown, a to h), and one block includes a lighting circuit 40 (described later) for lighting a plurality of light emitting elements, and 1 An optical sensor circuit 41 (described later) for detecting the amount of light emitted from each of the plurality of light emitting elements in the block by one optical sensor is provided.

  In FIG. 5, as an example, the data driver 21 applies one Vdata to the eight light emitting elements in each block, and the supply line to the organic EL panel 24 is set to six gradation signals Vdata1 to Vdata6. This is not the case. The same applies to the selection signals Vsel1 to Vsel8 from the select driver 22 to the organic EL panel 24. In this embodiment, the organic EL panel 24 is formed with 6 * 8 = 48 light emitting elements in a row in the horizontal direction, but the actual organic EL exposure head substrate has a paper size in one row or several rows. The number of minute light-emitting elements is formed, and this is not restrictive.

  FIG. 6 is a circuit diagram showing an equivalent circuit diagram of a main part of the organic EL panel 24 of the exposure apparatus according to the present embodiment. In the figure, the organic EL panel 24 includes a selection TFT 31 that functions as a switch for selecting each light emitting element 34 in each block, a driving TFT 33 for driving the light emitting element 34, a holding capacitor 32, and the light emitting element 34. A lighting circuit 40 is provided. Here, in the following, for the sake of convenience, one light emitting element 34, and the corresponding selection TFT 31, driving TFT 33, and holding capacitor 32 are referred to as one pixel.

  In the selection state, that is, in the selection period, the selection TFT 31 is turned on, and the gradation signals Vdata1 to Vdata6 are supplied from the data driver 21 to the holding capacitor 32, and the gradation signals Vdata1 to Vdata6 are supplied to the block selection signals Vsel1 to Vsel8. A corresponding signal charge is written, and a current corresponding to the signal charge is supplied from the driving TFT 33 to the light emitting element 34, and the light emitting element 34 is turned on. In the non-selection period, the signal charge written in the holding capacitor 32 is held, and the supply of the current corresponding to the signal charge from the driving TFT 33 to the light emitting element 34 is maintained, and the luminance at the luminance corresponding to the previous current value is maintained. The lighting of the light emitting element 34 is maintained.

  The organic EL panel 24 is a photosensor circuit including a photosensor TFT 35, a charge TFT 36, a readout TFT 38, and a dark current holding capacitor 37, which are formed in the same process as each pixel lighting TFT in each block. 41. Further, the optical sensor circuit 41 is formed with one circuit for a plurality of pixels in one block. In the example shown in the figure, for convenience, one circuit is formed for three pixels, but actually, for example, the circuit is formed on a scale of one circuit for several thousand pixels.

  In the example shown in FIG. 6, only three pixels extracted partially are shown, but the channel width of the photosensor TFT 35 is formed to be about the width in the main scanning direction in which the pixels to capture light emission are arranged. The pixel is disposed immediately below the sub-scanning direction. As will be described later, since the correction is performed by comparing the light emission amount (first light amount) at the initial stage (first timing) with the light emission amount (second light amount) after the lapse of a predetermined time (second timing), If the light of the pixel portion can be sufficiently sensed, the optical sensor circuit 41 does not need to be provided for each pixel. If the optical sensor circuit 41 is arranged in the vicinity of the pixel as in this embodiment, the corresponding block is provided. It is possible to sufficiently capture the amount of light emitted from the light emitting element. Further, since the TFTs for photosensor circuits (the photosensor TFT 35, the charge TFT 36, and the readout TFT 38) are formed in the same process as the lighting circuit TFTs (selection TFT 31, drive TFT 33), the number of processes is not increased.

  Next, FIG. 7 is a timing chart for explaining a lighting operation when printing is performed by the exposure apparatus according to the present embodiment. When selecting each block, that is, in the Vsel1 selection period in which the block selection signals Vsel1 to 8 are asserted, the grayscale signals Vdata1 to 6 are supplied from the data driver 21, and the holding capacitors 32 are supplied with the grayscale signals Vdata1 to 6. The corresponding signal charge is written, and a current corresponding to the signal charge is supplied from the driving TFT 33 to the light emitting element 34. In the Vsel1 non-selection period, the signal charge written in the holding capacitor 32 is held, and the supply of current according to this signal charge from the driving TFT 33 to the light emitting element 34 is maintained. In both the Vsel1 selection period and the Vsel1 non-selection period, The light emitting element 34 is turned on at the previous current value.

  The horizontal control signal / HSYNC is a synchronization signal in the main scanning direction of the image forming apparatus and has a dot formation processing time 1LineTime in which an active to active period is allowed for one line. For example, if the printing density is 1200 dpi × 1200 dpi, 40 ppm, and the sheet-to-paper size is 50 mm and the light source unit is A4 horizontal size, then ((25.4 mm / 1200 dpi) / (210 mm × 40 sheets + 50 mm × 40 sheets)) / 60≈122 μsec. Since the output of the data driver 21 is valid only during the Vsel1 selection period, the block selection signals Vsel1-8 are sequentially asserted so that the / HSYNC is active to active, that is, 1LineTime. Accordingly, a plurality of pixels can be turned on with one output of the data driver 21.

  As shown in FIG. 5, if eight block selection signals Vsel1 to 8 are connected to the entire pixel, each block selection signal Vsel1 to 8 is 122/8 μsec = 15. The signal is shifted by 25 μsec. That is, during the period of the block selection signal Vsel1, a current corresponding to the lighting gradation data is output from the data driver 21 to the a1, b1, c1, d1, e1, and f1 pixel circuits, and the signal charge corresponding to the display luminance of the pixel. Is written in the holding capacitor 32, lighting starts, and even when the block selection signal Vsel1 is negated, it is held, and the current corresponding to this signal charge is supplied from the driving transistor to the pixel display element, so that the lighting is performed even during the non-selection period. To do.

  Similarly, as shown in FIG. 7, the block selection signal Vsel2 is a2, b2, c2, d2, e2, f2, the block selection signal Vsel3 is a3, b3, c3, d3, e3, f3, and the block selection signal Vsel4 is In the same manner as a4, b4, c4, d4, e4, f4, and so on, the current corresponding to the lighting gradation data is output from the data driver 21 to the pixel up to the block selection signal Vsel8, and the corresponding pixel is turned on. , All pixels can be turned on for one line.

  Next, FIG. 8 is a block diagram showing the configuration of the sensor driver 23 of the exposure apparatus according to the present embodiment. In the figure, the sensor driver 23 includes an IV converter 51, a selector 53, an AD converter 52, and an SCG / RFSH generator 54. The IV conversions 51 are provided in the number corresponding to the number of outputs of the optical sensor circuit, and the sensor currents Sout1 to Sout8 corresponding to the luminance of the optical element from the optical sensor circuit (readout TFT 38) are converted into sensor voltages CSout1 to CSout8 to be selected by the selector 53. To supply.

  The selector 53 sequentially outputs sensor voltages Sout1 to Sout8 to the AD converter 52 in accordance with a select timing signal PreVsel described later. The AD converter 52 converts the sensor voltages Sout1 to Sout8 sequentially supplied from the selector 53 into a sensor voltage Psout that is a digital value, and supplies the sensor voltage Psout to the head controller 20. The SCG / RFSH generator 54 generates a start signal SCG and a refresh signal RFSH for starting the measurement of the amount of emitted light by the optical sensor circuit 41 from the PreVsel supplied from the head controller 20. It supplies to the optical sensor circuit 41 in a block.

  FIG. 9 is a block diagram showing the configuration of the head controller 20 of the exposure apparatus according to the present embodiment. In the figure, the head controller 20 includes an arbitration control unit 71, a sensor driver timing generation unit 72, a selector driver timing generation unit 73, a data driver data transmission unit (data correction circuit) 74, a light amount storage unit (light amount storage circuit) 75, a light amount. A comparison unit (comparison circuit) 76 and a correction data storage unit (correction data storage circuit) 78 are included. The light amount storage unit 75 stores the sensor voltage Psout, which is a light amount measurement result by the sensor driver 23 at the time of initial printer startup (first timing), as emission light amount data (first light amount). The light amount comparison unit 76 is stored in the light amount storage unit 75 and the sensor voltage Psout, which is the light emission amount data for each dot, which is a light amount measurement result by the sensor driver 23 at a time other than the initial startup of the printer (second timing). And the difference between the two is supplied to the correction data storage unit 78.

  The correction data storage unit 78 stores light amount correction data corresponding to the post-comparison difference created in advance, and outputs light amount correction data corresponding to the difference supplied from the light amount comparison unit 76. The data driver data sending unit 74 adds the light amount correction data output from the correction data storage unit 78 to the image data, and sends it to the data driver 21 as a gradation signal Vdata.

  The arbitration control unit 71 receives / HSYNC (horizontal synchronization signal), / VSYNC (vertical synchronization signal) and each printer control signal from a control unit that controls the entire printer (not shown), and a sensor driver timing generation unit 72, the select driver timing generator 73 and the data driver data transmitter 74 are monitored and controlled to perform timing arbitration.

  Next, the select driver timing generator 73 generates a timing signal PreVsel when the select driver 22 generates the block selection signals Vsel1 to Vsel8 under the control of the arbitration controller 71, and supplies the timing signal PreVsel to the select driver 22. The sensor driver timing generation unit 72 generates a timing signal PreRFSH signal when the sensor driver 23 generates the refresh signal RFSH and the start signal SCG under the control of the arbitration control unit 71, and supplies the timing signal PreRFSH signal to the sensor driver 23.

  FIG. 10 is a timing chart for explaining the basic operation of the optical sensor circuit 41. The photosensor TFT 35, the charge TFT 36, and the readout TFT 38 are turned on by asserting the start signal SCG and the refresh signal RFSH, and the dark current holding capacitor 37 is discharged. Next, by negating the refresh signal RFSH, the photosensor TFT 35 is turned off, and as shown in FIG. 10, the start signal SCG is asserted sufficiently longer than the refresh signal RFSH to charge the holding capacitor 37. To do. In this state, the photosensor TFT 35 is in an off state, the readout TFT 38 is turned on in accordance with the charge charged in the dark current holding capacitor 37, and the current Is is observed.

  In this state, when light from any one of the light emitting elements 34 is irradiated to the gate portion of the photosensor TFT 35, a drain-source channel of the photosensor TFT 35 is formed according to the amount of emitted light, and current flows out. Since the dark current holding capacitor 37 starts discharging, the drain current Is of the readout TFT 38 decreases. This ΔIs is a current corresponding to the amount of light emitted from the light emitting element 34. 10 is an observation waveform that is IV-converted by the IV conversion circuit 51 shown in FIG. 8, and corresponds to the change in the current Is. The start signal SCG is asserted, and the potential after the elapse of a predetermined detection time A is converted into a digital value having an arbitrary number of bits by the AD conversion circuit 52 and delivered to the head controller 20.

  In the present embodiment, the above-described light amount observation cycle is sequentially performed for every dot, one by one. However, among the plurality of photosensor circuits 41, the output of the photosensor TFT 35 located at the dot site is selected and delivered to the head controller 20. Thus, the selector 53 in the sensor driver 23 is selected. The measurement timing is performed in a state in which printing is not performed. Therefore, the light emission time, that is, the non-selection period is arbitrary, and the light emission time is not dependent on the print timing shown in FIG. What is necessary is just to measure the optical sensor output after the same non-selection period elapses.

  Next, FIG. 11 is a timing chart for explaining operations of the head controller 20 and the select sensor driver 22 of the exposure apparatus when detecting the amount of light emitted from each light emitting element 38 in the present embodiment. First, the block selection signal Vsel1 is supplied from the select driver 22 to the leftmost block a in FIG. 5 at regular time intervals, and the grayscale signals Vdata1 to Vdata6 are output from the data driver 21 in synchronization with the supply timing of the block selection signal Vsel1. Is supplied. Thereby, each light emitting element of the a block sequentially emits light in the order of a1 to a2, a3, a4, a5, and a6. Since the optical sensor circuit 41 is arranged for each block of the organic EL panel 24, there are eight sensor outputs in the present embodiment for the number of blocks.

  In synchronization with the supply timing of the block selection signal Vsel1, the start signal SCG and the refresh signal RFSH are supplied from the sensor driver 23 to each optical sensor circuit 41, and the measurement operation of the emitted light quantity is started. Similarly to FIG. 10, the value of the sensor output Sout1 after the predetermined detection time A has elapsed is converted into a digital value by the AD conversion circuit 52, and the amount of light emitted at that time is measured. Next, the light emitting elements of the second b block from the left end are similarly caused to emit light sequentially as b1, b2, and b3, and the amount of emitted light is measured from the corresponding sensor output Sout2. Similarly, light is measured by emitting light to the rightmost h-block light-emitting elements h1 to h6. These operations are first performed at the initial startup of the printer (first timing) for comparison with the initial light amount, and then performed after an arbitrary time has elapsed, or when the power is turned on (second timing).

  Here, the timing for measuring the amount of light emitted from each light emitting element is set to a timing for every fixed time interval shifted by the detection time A from the supply timing of the block selection signals Vsel1 to Vsel8. The detected light emission quantity value is AD converted by the AD conversion circuit 52 and supplied to the head controller 20 as a digital value. However, detection of the light emission quantity of each light emitting element is not performed at the same time, but at regular time intervals. Therefore, it is not necessary to temporarily store the detected value of the emitted light amount of each light emitting element, and only one AD conversion circuit 52 can be used. As a result, the circuit scale involved in detecting the amount of light emitted from each light emitting element can be reduced.

  FIG. 12 is a schematic view of the mounting arrangement of the exposure apparatus according to the present embodiment on the image forming apparatus. The organic EL panel (substrate) 24 is formed with a plurality of light emitting elements 24-1 arranged in the main scanning direction, and an optical sensor unit 24-2 that measures the amount of light emitted from the plurality of light emitting elements 24-1. ing. Further, the select driver 22, the sensor driver 23, and the head controller 20 are mounted on the head controller board 86. Further, the printer controller interface 86-1 may be mounted on the head controller board 86.

  The organic EL panel 24 and the head controller board 86 include a COF (Chip On Film) 83 on which the data driver 21 is mounted, an FPC (Flexible) on which signals from the head controller 20, the select driver 22, and the sensor driver 22 are arranged and mounted. Printed Circuit) 85. The optical sensor unit 24-2 has a channel width corresponding to about pixels measured by the optical sensor TFT 35 shown in FIG. 5 in the main scanning direction.

  Next, FIG. 13 is a partial schematic view seen from the top surface of the pixel portion and the photosensor circuit portion for one circuit in the exposure apparatus according to the present embodiment. FIG. 14 is a cross-sectional view taken along C-C ′ in FIG. 13. First, the portion of the lighting circuit 40 including the metal thin film (gate electrode and light shielding) 91, the light emitting element portion 92, the transparent electrode (organic EL anode) 93, the metal thin film (drain electrode) 94, and the gate drain electrode contact 95 is provided for each pixel. Formed in the main scanning direction.

  The gate 35-1, the source 35-2, and the drain 35-3 are the optical sensor TFT 35 shown in FIG. The gate 36-1, the source 36-2, and the drain 36-3 are the charging TFTs 36. The gate 38-1, the source 38-2, and the drain 38-3 are the readout TFT 38 shown in FIG. A dark current holding capacitor 37 is formed in the vicinity of the photosensor TFT 35.

  The gate 35-1 of the photosensor TFT 35 is connected to the supply line of the refresh signal RFSH (m), and the source 35-2 is connected to the ground GND. The drain 35-3 of the photosensor TFT 35 is connected to the gate of the readout TFT 38 and to the source 36-2 of the charging TFT 36.

  The source 38-2 of the readout TFT 38 is connected to the ground GND. The drain 38-3 of the readout TFT 38 is connected to the output line of Sout (m). The gate 36-1 of the charging TFT 36 is connected to the SCG (m) supply line, and the drain 36-3 is connected to the supply line of the power supply voltage VDD.

  As shown in FIG. 14, the light from the light emitting element portion 92 is emitted in the direction of arrow A through the slit of the metal thin film (gate electrode and light shielding) 91 and is refracted and reflected within the organic EL panel substrate 24. Then, it propagates and is applied to the gate 35-1 of the photosensor TFT 35.

  Next, FIG. 15 is a flowchart for explaining the operation of the present embodiment. First, when the power is turned on, it is determined whether or not it is the first system activation (step S10). If it is the first system activation, the lighting circuit 40 is supplied with arbitrary data for all pixels. Then, the light emitting element 34 is caused to emit light, the light emission amount value is measured (step S12), and the measurement value is stored in the light amount storage unit 75. Next, the luminance signal Vdata is sent as it is to the data driver 21 as pixel data (step S16), and the process is terminated.

  On the other hand, when the system is not activated for the first time, for example, after an arbitrary time has elapsed since the first activation, or at a timing after printing a predetermined number of sheets (second timing), the lighting circuit 40 is supplied with arbitrary data for all pixels. The light emitting element 34 is caused to emit light and the light emission light amount value (second light amount) is measured (step S18), and the light amount comparison unit 76 has a measurement value within an allowable range with respect to the initial light amount value (first light amount). Whether or not (step S20). When the measured value is within the allowable range with respect to the initial light amount value, there is little deterioration and no correction is required. Therefore, the data driver does not send correction data from the correction data storage unit 78 to the data driver transmission unit 74. The image data is sent from the sending unit 74 as it is as the luminance signal Vdata to the data driver 21 (step S22), and the processing is finished.

  On the other hand, when the measured value is outside the allowable range with respect to the initial light amount value, it is determined that the deterioration is relatively large and correction is necessary, and the difference is sent to the correction data storage unit 78. The correction data corresponding to the difference is sent to the data driver sending unit 74, the correction data is added to the image data from the data driver sending unit 74, and the result is sent to the data driver 21 as the luminance signal Vdata (step S24), and the processing ends. To do.

  According to the above-described embodiment, even in an electrophotographic exposure head employing an organic EL, the initial light amount of the light emitting element by the organic EL is measured, and the initial light amount is compared with the light emission amount with time, By performing the correction according to the difference between the two, even when the deterioration is caused with time, the shortage of light quantity can be compensated, and the quality of the print image of the printer can be ensured.

  Moreover, according to the present embodiment, the cost can be reduced by adopting the organic EL element in the exposure head of the electrophotographic process.

  In addition, according to the present embodiment, the active drive organic EL elements formed in a line on one substrate are used as the light source, so that the optical sensor circuit 41 is placed in the organic EL substrate during the organic EL element formation process. In addition to being able to be formed at the same time, it is possible to eliminate the need for driving wire bonding to each light emitting element, thereby reducing the work load in the manufacturing process and reducing the circuit scale.

1 is a schematic diagram showing an example of the structure of an image forming apparatus equipped with an exposure apparatus according to the present invention. It is a block diagram which shows the structure outline | summary of the exposure apparatus in this embodiment. It is a conceptual diagram for explaining a drive control method of the exposure apparatus when printing is performed by an image forming apparatus equipped with the exposure apparatus of the present embodiment. In the exposure apparatus of this embodiment, it is a conceptual diagram for demonstrating the drive control system at the time of correct | amending the emitted light amount of a light emitting element. 1 is a block diagram showing a configuration of an exposure head 3 of an image forming apparatus (electrophotographic printing apparatus) equipped with an exposure apparatus according to an embodiment. It is a circuit diagram which shows a part of equivalent circuit diagram of the organic electroluminescent panel 24 of the exposure apparatus by this embodiment. It is a timing chart for demonstrating the lighting operation at the time of printing by the exposure apparatus by this embodiment. It is a block diagram which shows the structure of the sensor driver 23 of the exposure apparatus by this embodiment. It is a block diagram which shows the structure of the head controller 20 of the exposure apparatus by this embodiment. 3 is a timing chart for explaining the basic operation of the optical sensor circuit 41. 6 is a timing chart for explaining operations of a head controller 20 and a select sensor driver 22 of the exposure apparatus according to the present embodiment. 1 is a schematic view of a mounting arrangement of an image forming apparatus according to an embodiment. It is the partial schematic diagram seen from the upper surface of the pixel part in the exposure apparatus by this embodiment, and the optical sensor circuit part for one circuit. It is sectional drawing in C-C 'of a pixel part and the optical sensor circuit part for one circuit. It is a flowchart for demonstrating operation | movement of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Exposure head 10 Light emitting element 11 Light emitting element array 12 Light emission drive circuit 13 Light quantity detection circuit 14 Light receiving element 15 Correction control circuit 20 Head controller 21 Data driver 22 Select driver 23 Sensor driver 24 Organic EL panel 31 Selection TFT
32 holding capacitor 33 driving TFT
34 Light Emitting Element 35 Optical Sensor TFT
36 Charging TFT
38 Read TFT
37 dark current holding capacitor 40 lighting circuit 41 optical sensor circuit 51 IV converter 52 selector 53 AD converter 54 Vsel generator 55 select timing generator 56 AND circuit 71 arbitration controller 72 Rfsh timing generator 73 Vsel timing generator 74 data Driver data sending section 75 Light quantity storage section 76 Light quantity comparison section 78 Correction data storage section

Claims (10)

In an exposure apparatus that performs exposure by irradiating light corresponding to image data to a photosensitive drum,
A light emitting element array comprising a plurality of light emitting elements arranged in the main scanning direction, the light emitting elements being divided into a plurality of light emitting element groups each having two or more light emitting elements adjacent to each other;
Each has a plurality of light receiving elements provided corresponding to each of the plurality of light emitting element groups , and one light receiving element corresponds to one light emitting element group, and each of the light emitting elements by the plurality of light receiving elements. a light amount detection circuit that detect the amount of light emission corresponding to the light emission luminance of the device,
The causes the respective light emitting elements of the light emitting element array sequentially emit light at a predetermined light emission period, one of the reception of the light quantity detection circuit corresponding to the light emitting element group one that contains the light emitting element that emits in the light quantity detection circuit The elements are driven corresponding to the light emission periods, the light receiving elements are sequentially driven corresponding to the light emitting element groups, and the light emission amounts are determined based on the light emission amount detected by the light receiving elements. A correction control circuit for correcting the value of the drive signal based on the image data supplied to the element;
Have
Each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, and the semiconductor layer is a region along the width of the corresponding one of the light emitting element groups in the main scanning direction. A channel is formed in the semiconductor layer between the drain and source provided opposite to a direction orthogonal to the main scanning direction when receiving the light, and the main scanning of the semiconductor layer of the channel The channel width corresponding to the length in the direction along the direction is set to a value larger than the width in the main scanning direction of at least two light emitting elements of one light emitting element group corresponding to the light receiving element. An exposure apparatus characterized by that. The correction control circuit corresponds to the selection signal in synchronization with a selection signal supply circuit that supplies a selection signal for selecting each of the plurality of light emitting element groups to the light emitting element array, and a supply timing of the selection signal. A control signal supply circuit that supplies a control signal for starting a detection operation of the light receiving element corresponding to the light emitting element group to the light amount detection circuit,
2. The exposure apparatus according to claim 1, wherein the drive signal is sequentially supplied to each light emitting element of the selected light emitting element group in synchronization with a supply timing of the selection signal. The selection signal is supplied to each of the plurality of light emitting element groups a number of times corresponding to the number of the light emitting elements included in the light emitting element group at a time interval corresponding to the light emitting period.
The light amount detection circuit detects the light emission amount of each light emitting element at each time interval at a timing corresponding to the supply of the selection signal, and sequentially sets the value of the light emission amount detected at each time interval. 3. An exposure apparatus according to claim 2, further comprising a single AD conversion circuit for converting and outputting as a digital value.   4. The exposure apparatus according to claim 3, wherein the time interval is set to a time equal to or longer than a detection time of the emitted light amount by the light amount detection circuit. The correction control circuit further includes:
A light amount storage circuit that stores, as a first light amount, a light emission amount of each of the plurality of light emitting elements detected by the plurality of light receiving elements at a first timing;
The light emission amount of each of the plurality of light emitting elements detected by the plurality of light receiving elements at a second timing after a predetermined time has elapsed from the first timing is set as a second light amount and stored in the light amount storage circuit. A comparison circuit that compares the first light quantity and the second light quantity;
A correction data storage circuit that stores light amount correction data according to a difference between the first light amount and the second light amount by the comparison circuit;
A data correction circuit for correcting the drive signal by adding the light amount correction data to the image data;
The exposure apparatus according to claim 1, further comprising: An image forming apparatus that includes a photosensitive drum, a charger, an exposure device, and a developing device, and performs printing according to image data,
The exposure device
A plurality of light emitting elements arranged in a main scanning direction orthogonal to the moving direction of the photosensitive drum;
A light emitting element array in which the plurality of light emitting elements are divided into a plurality of light emitting element groups having two or more adjacent light emitting elements, and the emitted light is irradiated to the photosensitive drum;
Each has a plurality of light receiving elements provided corresponding to each of the plurality of light emitting element groups , and one light receiving element corresponds to one light emitting element group, and each of the light emitting elements by the plurality of light receiving elements. a light amount detection circuit that detect the amount of light emission corresponding to the light emission luminance of the device,
The causes the respective light emitting elements of the light emitting element array of the light emitting element array sequentially emit light at a predetermined light emission period, one of the light receiving corresponding to one of the light emitting element group includes the light-emitting element that emits in the light quantity detection circuit Each light emitting element is driven based on the value of the amount of light detected by each light receiving element by driving the element corresponding to the light emitting period, sequentially driving each light receiving element corresponding to each light emitting element group A correction control circuit for correcting the value of the drive signal based on the image data,
Have
Each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, and the semiconductor layer is a region along the width of the corresponding one of the light emitting element groups in the main scanning direction. A channel is formed in the semiconductor layer between the drain and source provided opposite to a direction orthogonal to the main scanning direction when receiving the light, and the main scanning of the semiconductor layer of the channel The channel width corresponding to the length in the direction along the direction is set to a value larger than the width in the main scanning direction of at least two light emitting elements of one light emitting element group corresponding to the light receiving element. An image forming apparatus. The control circuit includes a selection signal supply circuit that supplies a selection signal for selecting each of the plurality of light emitting element groups of the light emitting element array to the light emitting element array, and the selection signal is synchronized with the supply timing of the selection signal. A control signal supply circuit for supplying a control signal for starting a detection operation of the light receiving element corresponding to the light emitting element group corresponding to a signal to the light amount detection circuit,
The image forming apparatus according to claim 6, wherein the driving signal is sequentially supplied to the light emitting elements of the selected light emitting element group in synchronization with a supply timing of the selection signal. The selection signal is supplied to each of the plurality of light emitting element groups a number of times corresponding to the number of the light emitting elements included in the light emitting element group at a time interval corresponding to the light emitting period.
The light amount detection circuit detects the light emission amount of each light emitting element at each time interval at a timing corresponding to the supply of the selection signal, and sequentially sets the value of the light emission amount detected at each time interval. 8. The image forming apparatus according to claim 7, further comprising a single AD conversion circuit for converting and outputting as a digital value.   The image forming apparatus according to claim 8, wherein the time interval is set to be equal to or longer than a detection time of the light emission amount by the light amount detection circuit. The correction control circuit further includes:
A light amount storage circuit that stores, as a first light amount, a light emission amount of each of the plurality of light emitting elements detected by the plurality of light receiving elements at a first timing;
The light emission amount of each of the plurality of light emitting elements detected by the plurality of light receiving elements at a second timing after a predetermined time has elapsed from the first timing is set as a second light amount and stored in the light amount storage circuit. A comparison circuit that compares the first light quantity and the second light quantity;
A correction data storage circuit that stores light amount correction data according to a difference between the first light amount and the second light amount by the comparison circuit;
A data correction circuit for correcting the drive signal by adding the light amount correction data to the image data;
The image forming apparatus according to claim 6, further comprising: a correction circuit including a correction circuit.

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