JP4577661B2 - 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 the 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 in a main scanning direction. A light emitting element array having a plurality of light emitting element groups composed of two or more adjacent light emitting elements in a plurality of light emitting elements, and a light emission of each light emitting element provided corresponding to each of the plurality of light emitting element groups A light amount detection circuit having a plurality of light receiving elements for detecting a light emission amount according to luminance and each light emitting element of each light emitting element group of the light emitting element array has a light emitting period between at least two light emitting element groups. Light is emitted sequentially in parallel at overlapping light emission timings, the light receiving elements of the light amount detection circuit are driven in synchronization with the light emission timings of the light emitting elements, and light emission detected by the light receiving elements is detected. On the basis of the value of the light amount is supplied to each light emitting element, have a, a correction control circuit for correcting the value of the drive signal based on the image data, the correction control circuit further wherein at a first timing A light amount storage circuit for storing a light emission amount of each of the plurality of light emitting elements detected by the light amount detection circuit as a first light amount, and the light amount at a second timing after a predetermined time has elapsed from the first timing. The amount of light emitted from each of the plurality of light emitting elements at the second timing detected by the detection circuit is set as a second amount of light, and the first amount of light stored in the light amount storage circuit and the second amount of light are stored. A comparison circuit for comparing the light amount, a correction data storage circuit for storing light amount correction data according to a difference between the first light amount and the second light amount by the comparison circuit, and the light amount correction data as the image data. Characterized by comprising the data correction circuit for correcting the driving signal in addition to data, the.

  As a preferred aspect, for example, in the exposure apparatus according to claim 1, the correction control circuit supplies a selection signal for selecting each light emitting element group at a predetermined time interval. A selection signal supply circuit for sequentially supplying to the light source, 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 in synchronization with the supply timing of the selection signal And a control signal supply circuit that supplies the control signal.

  As a preferred aspect, for example, in the exposure apparatus according to claim 2, the drive signal is selected from the light emitting element groups selected in synchronization with the supply timing of the selection signal. You may make it supply to each light emitting element.

  As a preferred aspect, for example, in the exposure apparatus according to claim 2, the light amount detection circuit includes the light-emitting elements at the predetermined time intervals according to the supply timing of the selection signal. A single AD conversion circuit that detects the light emission amount of each light emitting element of the group and sequentially AD-converts the value of the light emission amount detected at each predetermined time interval and outputs it as a digital value is provided. Also good.

Further, as a preferred aspect, for example, as in claim 5, in the exposure apparatus according to claim 1, each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, The semiconductor layer may be provided along the main scanning direction, and the channel width of the semiconductor layer may be set to a value corresponding to the width of the light emitting element group corresponding to the light receiving element.

In order to achieve the above object, a drive control method for an exposure apparatus according to the invention described in claim 6 is a drive control method for an exposure apparatus that performs exposure by irradiating a photosensitive drum with light according to image data. A light emitting element array having a plurality of light emitting elements in the main scanning direction and having a plurality of light emitting element groups composed of two or more adjacent light emitting elements in the plurality of light emitting elements, and corresponding to each of the plurality of light emitting element groups to prepare a plurality of light receiving elements, an exposure apparatus that have a for detecting the light emission amount in accordance with the emission luminance of the respective light emitting elements provided, the respective light emitting elements of the respective light emitting element groups, at least two The light emitting elements sequentially emit light in parallel at a light emission timing having an overlapping period, and the light receiving elements are driven in synchronization with the light emission timings of the light emitting elements. Detects the amount, on the basis of the value of the quantity of detected light by the light receiving element, said supplied to each light emitting element includes an act of correcting the value of the drive signal based on the image data, detects the light emission amount The operation is to detect the amount of emitted light by each of the light receiving elements at a first timing, store the detected amount of emitted light as a first amount of light in a light amount storage circuit, and elapse of a predetermined time from the first timing. The operation of correcting the value of the drive signal includes the operation of detecting the amount of emitted light by each of the light receiving elements at the second timing after that, and setting the detected amount of emitted light as the second amount of light. The first light amount stored in the light amount storage circuit is compared with the second light amount, and light amount correction data corresponding to a difference between the second light amount and the first light amount is added to the image signal. Said Characterized in that it comprises an operation for correcting the motion signal.

  Further, as a preferred aspect, for example, as in claim 8, in the drive control method for an exposure apparatus according to claim 7, the operation of detecting the amount of emitted light of each light emitting element is performed by each precursor of each light emitting element group. An operation of detecting the amount of emitted light of the light emitting element at a predetermined time interval, and AD-converting the value of the amount of emitted light detected at each predetermined time interval through a single AD conversion circuit and outputting it as a digital value May be included.

To achieve the above object, an image forming apparatus according to an eighth 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 unit includes a plurality of light emitting elements in the main scanning direction orthogonal to the moving direction of the photosensitive drum, and includes a plurality of light emitting element groups including two or more adjacent light emitting elements in the plurality of light emitting elements. A plurality of light emitting element arrays that irradiate the photosensitive drum with the emitted light and a plurality of light emitting element groups that detect light emission amounts corresponding to the light emission luminances of the light emitting elements. A light amount detection circuit having a light receiving element; and each light emitting element of each light emitting element group of the light emitting element array sequentially emits light in parallel at an emission timing at which a light emission period partially overlaps between at least two light emitting element groups light The image data, wherein each light receiving element of the detection circuit is driven in synchronization with the light emission timing of each light emitting element, and is supplied to each light emitting element based on the value of the amount of emitted light detected by each light receiving element. the value of the drive signal based on have a, a correction control circuit for correcting the said correction control circuit is further detected by the light quantity detection circuit at a first timing, the light emission amount of each of the plurality of light emitting elements And a plurality of light emission at the second timing detected by the light amount detection circuit 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 of the elements as a second light amount, and the first circuit by the comparison circuit Comprising a correction data storage circuit that stores the light quantity correction data corresponding to the difference between the amount and the second light quantity, and a data correction circuit for correcting the driving signal to the light quantity correction data in addition to the image data, the It is characterized by that.

As a preferred mode, for example, as in claim 9, in the image forming apparatus according to claim 8 , the correction control circuit sends a selection signal for selecting each light emitting element group at a predetermined time interval. A selection signal supply circuit for sequentially supplying the 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 in synchronization with the supply timing of the selection signal. And a control signal supply circuit that supplies the circuit.

As a preferred aspect, for example, as in claim 10, in the image forming apparatus according to claim 9 , the drive signal is selected from the light emitting element groups selected in synchronization with the supply timing of the selection signal. You may make it supply to each said light emitting element.

As a preferred aspect, for example, as in claim 11, in the image forming apparatus according to claim 9 , the light quantity detection circuit emits each of the light emission at the predetermined time interval according to a supply timing of the selection signal. A single AD conversion circuit that detects the light emission amount of each light emitting element of the element group, sequentially AD converts the value of the light emission amount detected at each predetermined time interval, and outputs it as a digital value is provided. May be.

Further, as a preferable aspect, for example, as in claim 12, in the image forming apparatus according to claim 8 , each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light. The semiconductor layer may be provided along the main scanning direction, and the channel width of the semiconductor layer may be set to a value corresponding to the width of the light emitting element group corresponding to the light receiving element.

  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, exposed on the photosensitive drum 1 by the exposure head 3 in accordance with the image data to form a latent image, and a toner is put on the latent image on the photosensitive drum 1 by the developing device 4, The transfer roller 6 transfers the toner on the photosensitive drum 1 onto the sheet conveyed in the direction of the arrow by the conveyance belt 5, and the toner is 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 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 because it does not take advantage of the cost reduction because the amount of emitted light is reduced due to deterioration over time. In the present embodiment, countermeasures are taken for this problem. Considering the change in characteristics of the organic EL with time, the change in the amount of emitted light with time is suppressed, and high image quality is maintained over a long period of time. 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 a line with respect to the main scanning direction of the photosensitive drum, and emit light with luminance corresponding to the value of the drive current. The light emitting element array 11 includes a plurality of light emitting element groups 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 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 causes each light receiving element 14 of the light amount detection circuit 13 to emit light. The 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 is performed. The drive signal supplied to the drive circuit 12 is corrected by the 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 emission is partially performed in parallel. 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,.

  In this way, by controlling the light emission of the light emitting elements a1 to a6, b1 to b6, c1 to c6, d1 to d6,. The light emission periods of the light emitting elements a1 to a6, b1 to b6, c1 to c6, d1 to d6,..., H1 to h6 while suppressing an increase in the entire detection period (a1 light emission light reception period to h6 light emission light reception period). (= The light receiving period of the photosensor) can be made relatively long.

  Further, 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 start of light emission of the light emitting elements of the respective blocks a to h of the light emitting element array 11, and at a certain time interval. The amount of emitted light 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.

  The light receiving period corresponds to the sensitivity of the light receiving elements A to H, and the longer the light receiving period is, the higher the sensitivity can be detected. Therefore, in this embodiment, the amount of emitted light can be detected with relatively high accuracy. However, since the light emitting elements emit light in parallel between the a block to the h block, there is a fear that the light receiving element receives light from adjacent blocks. Therefore, in the present embodiment, although not particularly illustrated, a light blocking structure may be provided so that light does not enter from adjacent blocks across the blocks.

  FIG. 5 is a block diagram showing a configuration of the exposure head 3 of the image forming apparatus equipped with the exposure apparatus according to the present embodiment. In FIG. 5, the exposure head 3 includes a head controller 20, a data driver 21, a select sensor driver (selection signal supply circuit, control signal supply circuit) 22, and an organic EL panel 23. 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 and the select sensor driver 22 are driven according to 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 23, and generates the organic EL panel. The light is supplied to each of the light emitting elements of a plurality of a blocks to h blocks that constitute 23. The organic EL panel 23 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 23 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 sensor driver 22 refreshes the block selection signals Vsel1 to Vsel8 for selecting a block to emit light among a plurality of blocks constituting the organic EL panel 23, and refreshes the optical sensor circuit of each block of the organic EL panel 23. The signals Rfsh1 to Rfsh8 are generated and supplied to a plurality of blocks constituting the organic EL panel 23, and the sensor currents Sout1 to Sout8 corresponding to the detected light amounts detected by the optical sensor circuit of the organic EL panel 23 are sequentially converted into voltages. And supplied to the head controller 20 as the sensor voltage Psout.

  The organic EL panel 23 has a structure equivalent to 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 23 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 eight pixels of each block, and uses six gradation signals Vdata1 to Vdata6 as supply lines to the organic EL panel 23. This is not the case. The selection signal from the select sensor driver 22 to the organic EL panel 23 is also the block selection signals Vsel1 to Vsel8, which is the same. In the present embodiment, the organic EL panel 23 is formed with 6 * 8 = 48 pixels 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. However, this is not the case.

  FIG. 6 is a circuit diagram showing an equivalent circuit diagram of a main part of the organic EL panel 23 of the exposure apparatus according to the present embodiment. In the figure, the organic EL panel 23 includes a selection TFT 31 that functions as a switch for selecting the light emitting element 34 for each pixel, a driving TFT 33 for driving the light emitting element 34, a holding capacitor 32, and a light emitting element 34 in each block. The lighting circuit 40 consisting of 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 of the block selection signals Vsel1 to Vsel8, that is, in the selection period, the selection TFT 31 is turned on, the gradation signals Vdata1 to Vdata6 are supplied from the data driver 21, and the storage capacitors 32 are supplied with the gradation signals Vdata1 to Vdata6. 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 23 is formed in the same process as the pixel lighting TFT in each block, and is a photosensor circuit 41 including a photosensor TFT 35, a charge TFT 36, a readout TFT 38, and a dark current holding capacitor 37. Have Further, the optical sensor circuit 41 is formed as one circuit for a plurality of pixels. 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.

  The charge TFT 36 and the read TFT 38 are turned on when the block selection signal Vsel is asserted, and the dark current holding capacitor 37 is charged. At the same time, the refresh signal Rfsh is asserted, whereby the dark current holding capacitor 37 is discharged. Next, when the refresh signal Rfsh is negated, the photosensor TFT 35 is turned off, and the dark current holding capacitor 37 is charged to make the charge charge the same every time. The block selection signal Vsel is asserted sufficiently longer than the refresh signal Rfsh. 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.

  Next, FIG. 7 is a timing chart for explaining a lighting operation when printing is performed by the image forming 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 print density is 1200 dpi × 1200 dpi, 40 ppm, the paper 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 whole pixel, each block selection signal Vsel1 to 8 is 122/8 μsec = 15. The signal is shifted by 25 μsec. That is, 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 in the period of the block selection signal Vsel1, and a signal charge corresponding to the display luminance of the pixel is generated. It is written in the holding capacitor 32, starts lighting, is held even when the block selection signal Vsel1 is negated, and the current corresponding to this signal charge is supplied from the driving transistor to the pixel display element, so that it also lights during the non-selection period. .

  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 select sensor driver 22 of the image forming apparatus according to the present embodiment. In the figure, the select sensor driver 22 includes an IV converter 51, a selector 53, an AD converter 52, a Vsel generator 54, a select timing generator 55, and an AND circuit 56.

  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 CSout1 to CSout8 to the AD converter 52 in accordance with a select timing signal from a select timing generator 55 described later. The AD converter 52 converts the sensor voltages CSout1 to CSout8 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 Vsel generator 54 generates block selection signals Vsel1 to Vsel8 for selecting a block from PreVsel supplied from the head controller 20, and selects the selector timing generator 56, one input terminal of the AND circuit 56, and the organic EL panel It supplies to each block of 23. The select timing generator 55 generates a selector timing signal for the selector 53 that sequentially selects the sensor voltages CSout 1 to CSout 8 from the block selection signals Vsel 1 to Vsel 8 supplied from the Vsel generator 54, and supplies the selector timing signal to the selector 53. The AND circuit 56 takes the logical product of PreRfsh supplied from the head controller 20 and block selection signals Vsel1 to Vsel8 supplied from the Vsel generator 54, thereby generating refresh signals Rfsh1 to Rfsh8, and the organic EL panel 23. To each block.

  Next, FIG. 9 is a block diagram showing the configuration of the head controller 20 of the image forming apparatus equipped with the exposure apparatus according to the present embodiment. In the figure, the head controller 20 includes an arbitration control unit 71, an Rfsh timing generation unit 72, a Vsel timing generation unit 73, a data driver data transmission unit (data correction circuit) 74, a light amount storage unit (light amount storage circuit) 75, and a light amount comparison unit. (Comparator circuit) 76 and a correction data storage unit (correction data storage circuit) 78. The light amount storage unit 75 stores the sensor voltage Psout, which is a light amount measurement result by the select sensor driver 22 at the initial startup of the printer (first timing), as emission light amount data (first light amount). The light quantity comparison unit 76 is a sensor voltage Psout that is light emission quantity data for each dot, which is a light quantity measurement result by the select sensor driver 22 except when the printer is initially activated, and emission light quantity data stored in the light quantity storage unit 75. 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 receives an Rfsh timing generation unit 72. The Vsel timing generator 73 and the data driver data transmitter 74 are monitored and controlled to perform timing arbitration.

  Next, the Vsel timing generation unit 73 generates a timing signal PreVsel when the selection sensor driver 22 generates the block selection signals Vsel1 to Vsel8 under the control of the arbitration control unit 71, and supplies the timing signal PreVsel to the selection sensor driver 22. . The Rfsh timing generation unit 72 generates a timing signal PreRfsh signal when the select sensor driver 22 generates the refresh signal Rfsh under the control of the arbitration control unit 71 and supplies the timing signal PreRfsh signal to the select sensor driver 22.

  Next, FIG. 10 is a timing chart for explaining operations of the head controller 20 and the select sensor driver 22 of the image forming apparatus equipped with the exposure apparatus according to the present embodiment. By the way, if the measurement target is the size of the exposure pixel of the electrophotography, for example, 1200 dpi, the light emission of the organic EL element of □ 20 μm is observed, and the amount of light irradiated to the photosensor TFT 35 becomes very small. The longer the irradiation time by light emission, that is, the longer the detection time of the amount of emitted light, the larger the obtained current value and the higher the measurement accuracy.

  However, since the original print job should not be disturbed by measuring the amount of light emitted from the pixels, it is preferable to shorten the time required for detecting the amount of light emitted from each light emitting element as much as possible. Therefore, in the present invention, the light emission amount measurement of the light emitting elements of the pixels in each block is partially performed in parallel, and the measured observation values are continuously read, so that the light emitting elements of all the pixels of the light emitting element array are read. While suppressing an increase in the time required for measuring the amount of emitted light, the detection time used for measuring the amount of emitted light of each light emitting element is made relatively long so that the amount of emitted light can be measured with relatively high accuracy.

  In the present embodiment, as shown in FIG. 10, first, block selection signals Vsel1 to Vsel8 are supplied from the select sensor driver 22 to each block a to h at a time interval consisting of a certain shift time, and block selection is performed. The grayscale signal Vdata1 is supplied from the data driver 21 in synchronization with the supply timing of the signals Vsel1 to Vsel8. As shown in FIG. 5, Vdata1 is supplied to the light emitting elements a1, b1, c1, d1, e1, f1, g1, and h1 at the left end of each block. Thereby, the light emitting elements a1 to h1 at the left end of each block sequentially emit light. At this time, the light emitting elements a1 to h1 of each block are set so that the light emission start timings are shifted from each other by the shift time in parallel, and the light emission periods are partially overlapped between the blocks.

  In addition, the refresh signals Rfsh1 to Rfsh8 are supplied from the select sensor driver 22 to the photosensor circuit 41 of each block in synchronization with the supply timing of the block selection signals Vsel1 to Vsel8, and the light emitting elements a1 to h1 of each block emit light. The light quantity measurement operation is started. That is, the timing for starting the measurement of the light emission amount of the light emitting elements a1 to h1 in each block is the timing for each shift time.

  Next, after the block selection signal Vsel8 is supplied to the h block, the supply of the block selection signals Vsel1 to Vsel8 to the respective blocks a to h is started again, and in synchronization with this, the gradation signal Vdata2 is output from the data driver 21. Then, the second light emitting elements a2 to h2 from the left end of each block sequentially emit light, and the refresh signals Rfsh1 to Rfsh8 are synchronized with the supply timing of the block selection signals Vsel1 to Vsel8. The operation of measuring the amount of light emitted from the light emitting elements a2 to h2 of each block is started every shift time. The above operation is repeated until the measurement of the light emission quantity of all the light emitting elements in each block is performed.

  As described above, in FIG. 6, the sensor current Sout (m) terminal through which the drain current Is of the readout TFT 38 flows is connected to the input of the IV conversion circuit 51 shown in FIG. The sensor voltages CSout to CSout8 output from the IV conversion circuit 51 have waveforms as shown in FIG. 10, and the output signals immediately before the block selection signals Vsel1 to Vsel8 are asserted and the same block selection signal Vsel is asserted next time. The value of Sout is a value corresponding to the light emission amount of each light emitting element. Therefore, the output of the IV conversion circuit 51 with respect to the amount of light emitted from each light emitting element of the light emitting element array is made every shift time.

  Therefore, the sensor voltages CSout1 to CSout8 are selected one by one by the selector 53 for each shift time and converted to an arbitrary number of bits by the AD conversion circuit 52, whereby the data driver 21 is converted from the output signal Psout. The light emission quantity of the pixels in each block connected to the same output can be read out continuously. The sensor voltage Psout is supplied to the head controller 20. In other words, in the present embodiment, the timing for detecting the amount of light emitted from the light emitting element of each pixel is set not to be the same, but to be detected at a certain time interval shifted by the shift time. It is not necessary to temporarily store the value of the detected light emission amount, and the sensor voltages CSout1 to CSout8 can be sequentially AD converted by only one AD conversion circuit 52. As a result, the circuit scale related to the detection of the amount of emitted light can be reduced.

  FIG. 11 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) 23 is formed with a plurality of light emitting elements 23-1 arranged in the main scanning direction and an optical sensor unit 23-2 that measures the amount of light emitted from the plurality of light emitting elements 23-1. ing. Further, the select sensor driver 22 and the head controller 20 are mounted on the head controller board 86.

  The organic EL panel 23 and the head controller board 86 include a data driver COF 83 on which the data driver 21 is mounted, and a sensor select FPC (flexible printing FPC) on which signals from the head controller 20 and the select sensor driver 22 are arranged and mounted. Circuit) 85. The optical sensor unit 23-2 has a channel width corresponding to about the pixel that the optical sensor TFT 35 shown in FIG. 6 measures in the main scanning direction.

  Next, FIG. 12 is a partial schematic view of the pixel portion and the optical sensor circuit portion for one circuit in the image forming apparatus according to the present embodiment as viewed from above. FIG. 13 is a cross-sectional view taken along C-C ′ in FIG. 12. First, the portion of the lighting circuit 40 including the metal thin film (gate electrode and light shielding) 91, the light emitting pixel 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 supply line of the block selection signal Vsel (m), and the drain 36-3 is connected to the supply line of the power supply voltage VDD.

  As shown in FIG. 13, the light from the light emitting pixel unit 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 23. Then, it propagates and is applied to the gate 35-1 of the photosensor TFT 35.

  Next, FIG. 14 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.

  Even in the above-described electrophotographic exposure head employing the organic EL, the initial light amount of the light emitting element by the organic EL is measured, the initial light amount is compared with the light emission amount with time, and correction according to the difference between the two is performed. As a result, even when it deteriorates over time, the shortage of light quantity can be compensated for and the quality of the print image of the printer can be ensured.

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

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

  Since the selection signal to the selection TFT 31 is used as a shift signal, the light emission amount of the light emitting element 34 is measured at the same timing as the light emitting elements 34 connected to the same driver output emit light while sequentially shifting. The light emission amount values measured by the plurality of optical sensor circuits 41 can be read continuously, and only one AD conversion circuit for the light emission amount value is required, so that the circuit scale relating to the detection of the light emission amount can be reduced.

  Further, since the selection signal Vsel (m) of the selection TFT 31 for pixel emission is used as the gate signal to the charging TFT 36 of the photosensor circuit 41, the circuit scale can be reduced.

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 23 of the exposure apparatus by this embodiment. 6 is a timing chart for explaining a lighting operation when printing is performed by the image forming apparatus according to the embodiment. 2 is a block diagram illustrating a configuration of a select sensor driver 22 of the image forming apparatus according to the present embodiment. FIG. 2 is a block diagram illustrating a configuration of a head controller 20 of the image forming apparatus according to the present embodiment. FIG. 4 is a timing chart for explaining operations of a head controller 20 and a select sensor driver 22 of the image forming apparatus according to the present embodiment. 1 is a schematic view of a mounting arrangement of an image forming apparatus according to an embodiment. FIG. 3 is a partial schematic view of a pixel portion and an optical sensor circuit portion for one circuit in the image forming apparatus according to the present embodiment as viewed from above. 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 sensor driver 23 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 (12)

In an exposure apparatus that performs exposure by irradiating light corresponding to image data to a photosensitive drum,
A light emitting element array having a plurality of light emitting elements in the main scanning direction, the light emitting element array having a plurality of light emitting element groups composed of two or more adjacent light emitting elements in the plurality of light emitting elements;
A light amount detection circuit having a plurality of light receiving elements provided corresponding to each of the plurality of light emitting element groups and detecting a light emission amount according to the light emission luminance of each of the light emitting elements;
Each light emitting element of each light emitting element group of the light emitting element array sequentially emits light in parallel at a light emission timing at which a light emission period partially overlaps between at least two light emitting element groups, and each light receiving element of the light amount detection circuit Is driven in synchronism with the light emission timing of each light emitting element, and the value of the drive signal based on the image data is supplied to each light emitting element based on the value of the amount of emitted light detected by each light receiving element. A correction control circuit to correct,
I have a,
The correction control circuit further includes:
A light amount storage circuit for storing the light emission amount of each of the plurality of light emitting elements detected by the light amount detection circuit at a first timing as a first light amount;
The amount of light emitted from each of the plurality of light emitting elements at the second timing detected by the light amount detection circuit at a second timing after a predetermined time has elapsed from the first timing is defined as a second light amount, A comparison circuit for comparing the first light amount stored in the light amount storage circuit with the second light amount;
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;
An exposure apparatus comprising:   The correction control circuit sequentially supplies a selection signal for selecting each light emitting element group to the light emitting element array at a predetermined time interval, and the selection signal is synchronized with the selection signal supply timing. The exposure apparatus according to claim 1, further comprising: 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 corresponding to the light amount detection circuit.   3. The exposure apparatus according to claim 2, wherein the driving signal is supplied to each light emitting element of each light emitting element group selected in synchronization with a supply timing of the selection signal.   The light amount detection circuit detects the light emission amount of each light emitting element of each light emitting element group at the predetermined time interval according to the supply timing of the selection signal, and detects the light amount at each predetermined time interval. 3. The exposure apparatus according to claim 2, further comprising a single AD conversion circuit that sequentially AD converts the value of the amount of emitted light and outputs the digital value.   Each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, the semiconductor layer is provided along the main scanning direction, and a channel width of the semiconductor layer is determined by the light receiving element. The exposure apparatus according to claim 1, wherein the exposure apparatus is set to a value corresponding to a width of the light emitting element group corresponding to. An exposure apparatus drive control method for performing exposure by irradiating light corresponding to image data to a photosensitive drum,
A light emitting element array having a plurality of light emitting elements in the main scanning direction and having a plurality of light emitting element groups composed of two or more adjacent light emitting elements in the plurality of light emitting elements, and corresponding to each of the plurality of light emitting element groups prepare a plurality of light receiving elements, an exposure apparatus that have a for detecting the light emission amount in accordance with the emission luminance of each light-emitting element provided with,
Each light emitting element of each light emitting element group is caused to emit light sequentially in parallel at a light emission timing having an overlapping period between at least two light emitting element groups,
Driving each light receiving element in synchronization with the light emission timing of each light emitting element to detect the amount of light emitted from each light emitting element;
An operation of correcting a value of a drive signal based on the image data supplied to each light emitting element based on a value of a light amount detected by each light receiving element;
The operation of detecting the amount of emitted light includes detecting the amount of emitted light by each of the light receiving elements at a first timing, storing the detected amount of emitted light as a first amount of light in a light amount storage circuit, and An operation of detecting the amount of emitted light by each of the light receiving elements at a second timing after a predetermined time has elapsed from the timing of, and setting the detected amount of emitted light as a second amount of light,
The operation of correcting the value of the drive signal compares the first light amount and the second light amount stored in the light amount storage circuit, and calculates a difference between the second light amount and the first light amount. A drive control method for an exposure apparatus, comprising an operation of adding the corresponding light amount correction data to the image signal to correct the drive signal . The operation of detecting the amount of emitted light of each light emitting element is performed by detecting the amount of emitted light of each of the precursor light emitting elements of each light emitting element group at a predetermined time interval, and detecting the light emission detected at each predetermined time interval. 7. The exposure apparatus drive control method according to claim 6 , further comprising an operation of AD-converting a light amount value through a single AD conversion circuit and outputting the digital value as a digital value. 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 are provided in a main scanning direction orthogonal to the moving direction of the photosensitive drum, and the light emitting element includes a plurality of light emitting element groups including two or more adjacent light emitting elements in the plurality of light emitting elements. A light emitting element array for irradiating the photosensitive drum;
A light amount detection circuit having a plurality of light receiving elements provided corresponding to each of the plurality of light emitting element groups and detecting a light emission amount according to the light emission luminance of each of the light emitting elements;
Each light emitting element of each light emitting element group of the light emitting element array is sequentially caused to emit light in parallel at a light emission timing at which a light emission period partially overlaps between at least two light emitting element groups, and each light receiving element of the light amount detection circuit is Drives in synchronization with the light emission timing of each light emitting element, and corrects the value of the drive signal based on the image data supplied to each light emitting element based on the value of the light emission amount detected by each light receiving element A correction control circuit to
I have a,
The correction control circuit further includes:
A light amount storage circuit for storing the light emission amount of each of the plurality of light emitting elements detected by the light amount detection circuit at a first timing as a first light amount;
The amount of light emitted from each of the plurality of light emitting elements at the second timing detected by the light amount detection circuit at a second timing after a predetermined time has elapsed from the first timing is defined as a second light amount, A comparison circuit for comparing the first light amount stored in the light amount storage circuit with the second light amount;
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;
An image forming apparatus comprising: The correction control circuit sequentially supplies a selection signal for selecting each light emitting element group to the light emitting element array at a predetermined time interval, and the selection signal is synchronized with the selection signal supply timing. The image forming apparatus according to claim 8 , further comprising: 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 corresponding to the light amount detection circuit to the light amount detection circuit. . The image forming apparatus according to claim 9 , wherein the drive signal is supplied to the light emitting elements of the selected light emitting element groups in synchronization with a supply timing of the selection signal. The light amount detection circuit detects the light emission amount of each light emitting element of each light emitting element group at the predetermined time interval according to the supply timing of the selection signal, and detects the light amount at each predetermined time interval. The image forming apparatus according to claim 9, further comprising a single AD conversion circuit that sequentially AD-converts the value of the amount of emitted light and outputs the digital value. Each of the plurality of light receiving elements in the light amount detection circuit includes a semiconductor layer that receives incident light, the semiconductor layer is provided along the main scanning direction, and a channel width of the semiconductor layer is determined by the light receiving element. The image forming apparatus according to claim 8 , wherein the image forming apparatus is set to a value corresponding to a width of the light emitting element group corresponding to.

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