JP5145723B2 - Exposure apparatus and image forming apparatus having the same - Google Patents

Description

  The present invention relates to an exposure apparatus in an electrophotographic image forming apparatus and the like, and an image forming apparatus using the same.

  An electrophotographic image forming apparatus (printer apparatus) has an exposure apparatus 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.

On the other hand, when exposure is performed using such a light emitting element, there are variations in light emission caused by the light emitting element, and various techniques for correcting this have been proposed. For example, in Japanese Patent Laid-Open No. 11-138890, data for light emitting element correction is stored in a memory in advance, and the light emission intensity measured based on the correction data is corrected.
JP-A-11-138890

  By the way, it is known that the light emission characteristics of the light emitting element change with the passage of time, and the brightness when the light emitting element emits light changes with the passage of time. He did not propose any specific solution.

  The present invention has been made paying attention to such problems, and the object of the present invention is to perform exposure capable of obtaining a stable and uniform printed image wp even if the light emitting characteristics of the light emitting element deteriorate with time. An apparatus and an image forming apparatus using the same are provided.

In order to achieve the above object, an invention according to claim 1 of the present invention provides an exposure apparatus that performs exposure by irradiating light corresponding to image data onto a photosensitive drum, corresponding to the image data. A plurality of light emitting elements that emit light according to the driving signal are linearly arranged on one surface, a light emitting element substrate made of a transparent substrate, and on the other surface of the light emitting element substrate, At least one photosensor for receiving a part of the light emitted from each of the plurality of light emitting elements provided corresponding to each of a predetermined number of the two or more light emitting elements; The light sensor with respect to the light emission intensity of each of the plurality of light emitting elements and the light emission intensity of each of the plurality of light emitting elements at a second timing after a predetermined time has elapsed from the first timing. Received light intensity Based on the comparison, the image data by correcting the emission luminance of each light-emitting element, anda control means for maintaining the light emission luminance of each light emitting element at the first timing, each of the light emitting The element has a top emission structure that emits light in the direction of the one surface of the light emitting element substrate, is provided to face the one surface of the light emitting element substrate, and emits the light emitted from each of the light emitting elements. Light guide means for guiding light to the other surface side of the element substrate, and the light guide means emits light emitted from each light emitting element from the other surface of the light emitting element substrate to irradiate the photosensitive drum. It is characterized by comprising means for generating light for the purpose .

  According to a second aspect of the present invention, when the drive signal reaches a maximum value that can be supplied to the light emitting element by correcting the image data at the second timing, The light emission time is controlled, The exposure energy based on the light emission brightness | luminance and light emission time of each said light emitting element is provided, The means to control to maintain to the said exposure energy in a said 1st timing is provided, The means characterized by the above-mentioned. 2. The exposure apparatus according to 1.

  According to a third aspect of the present invention, in the exposure apparatus according to the first aspect, the optical sensor is provided on the other surface of the light emitting element substrate via an adhesive layer.

Invention according to claim 4, in the exposure apparatus according to claim 1, wherein the light guiding means, in that it comprises means for guiding a portion of said emitted from the light emitting element light to the light sensor Features.

According to a fifth aspect of the present invention, in the exposure apparatus according to the fourth aspect, each of the light emitting elements has a light emitting layer that emits light corresponding to the image data, and the light emitted from each of the light emitting elements. means for guiding the optical sensor part of, provided opposite to the light-emitting layer, have a reflective film that reflects light emitted from the light emitting layer on the other surface direction of the light emitting element substrate It is characterized by.

According to a sixth aspect of the present invention, in the exposure apparatus according to the first aspect , each of the light emitting elements has a light emitting layer having a predetermined area that emits light according to the image data, and the light guiding unit. The means for generating light for irradiating the photosensitive drum is provided corresponding to the light emitting layer, and condenses the light emitted from the light emitting layer in an area smaller than the area of the light emitting layer. It has a reflective film that reflects in the direction of the other surface of the light emitting element substrate.

According to a seventh aspect of the present invention, there is provided an image forming apparatus that includes a photosensitive drum, a charger, an exposure device, and a development device, and performs printing according to image data, wherein the exposure device corresponds to the image data. A plurality of light emitting elements that emit light according to a supplied drive signal are linearly arranged on one surface, a light emitting element substrate made of a transparent substrate, and the other surface of the light emitting element substrate. At least one photosensor for receiving a part of light emitted from each of the plurality of light emitting elements provided corresponding to each of a predetermined number of two or more light emitting elements; and at a first timing The light sensor for the light emission intensity of each of the plurality of light emitting elements and the light emission intensity of each of the plurality of light emitting elements at a second timing after a predetermined time has elapsed from the first timing. With the amount of light received at Based on the compare, the image data by correcting the emission luminance of each light-emitting element, anda control means for maintaining the light emission luminance of each light emitting element at the first timing, each of the light emitting The element has a top emission structure that emits light in the direction of the one surface of the light emitting element substrate, is provided to face the one surface of the light emitting element substrate, and emits the light emitted from each of the light emitting elements. Light guide means for guiding light to the other surface side of the element substrate, and the light guide means emits light emitted from each light emitting element from the other surface of the light emitting element substrate to irradiate the photosensitive drum. It is characterized by comprising means for generating light for the purpose .

  According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, at the second timing, when the drive signal reaches a maximum value that can be supplied to the light emitting element by correcting the image data. And a means for controlling the light emission time of each light emitting element so as to maintain the exposure energy based on the light emission luminance and the light emission time of each light emitting element at the exposure energy at the first timing. It is characterized by.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the optical sensor is provided on the other surface of the light emitting element substrate via an adhesive layer.

According to a tenth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the light guide means includes means for guiding a part of the light emitted from each of the light emitting elements to the optical sensor. It is characterized by.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, each of the light emitting elements has a light emitting layer that emits light corresponding to the image data, and is emitted from each of the light emitting elements. means for guiding the part of light to the light sensor is disposed to face the light-emitting layer has a reflective film that reflects light emitted from the light emitting layer on the other surface direction of the light emitting element substrate It is characterized by that.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the seventh aspect , each of the light emitting elements includes a light emitting layer having a predetermined area for emitting light according to the image data, and the light guide. The means for generating light for irradiating the photosensitive drum in the means is provided corresponding to the light emitting layer, and condenses the light emitted from the light emitting layer in an area smaller than the area of the light emitting layer. It has a reflective film reflecting in the direction of the other surface of the light emitting element substrate.

According to the present invention, in the exposure apparatus, light is emitted from each light emitting element corresponding to each of a predetermined number of two or more light emitting elements on the other surface side of the light emitting element substrate in which a plurality of light emitting elements are arranged on one surface. An optical sensor is provided for receiving a part of the emitted light, and the received light quantity with respect to the emission luminance of each light emitting element at the first timing and the emission luminance of each light emitting element at the second timing by the optical sensor. Based on the comparison with the amount of received light, the image data is corrected so that the light emission luminance of each light emitting element is maintained at the light emission luminance of each light emitting element at the first timing. Even if the characteristics deteriorate over time, a stable and uniform printed image can be obtained. In addition, since the optical sensor for receiving the light emitted from each light emitting element is provided for every two or more light emitting elements, the number of necessary optical sensors can be reduced, and the cost of the exposure apparatus can be reduced. Reduction can be achieved.

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

(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of an electrophotographic image forming apparatus (printer apparatus) to which the present invention is applied. The image forming apparatus 200 includes a photosensitive drum 201, a charger 202, an exposure device (exposure device) 203, a developing device 204, a transfer device 206, a fixing device 207, a static eliminator 208, and a cleaner 209. It has. After the photosensitive drum 201 is uniformly charged by the charger 202, an electrostatic latent image is formed by light irradiation according to the gradation value of the image data from the light emitting elements of the light emitting element array provided in the exposure device 203. It is formed. Next, in order to embody the electrostatic latent image, toner is adhered by the developing device 204. The toner image is transferred onto the sheet 205 between the transfer unit 206 and the photosensitive drum 201. The paper 205 to which the toner is attached is thermally fixed by the fixing device 207 and then discharged.

  A small amount of transfer leakage toner on the photosensitive drum 201 is removed by a cleaner 209, and the surface of the photosensitive drum 201 is uniformly discharged by a charge eliminator 208.

  Here, the light emitting element described above includes a light emitting element array including a plurality of light emitting elements arranged in a line in the main scanning direction of the recording scan (the width direction of the photosensitive drum 201, that is, the width direction of the paper). Each light emitting element is made of organic EL, for example. For example, in the case of a printer device that can print at a print density of 1200 dpi (dots / inch) to the full width using A4 size paper in the horizontal direction, this light emitting element array has approximately 15400 light emitting elements. I have. A pulse voltage (drive signal) according to print information (image data) output from the host device is applied to these individual light-emitting elements, and each individual light-emitting element is individually controlled according to the drive current supplied according to the pulse voltage. The light emitting element is selectively controlled to emit light. In recent years, light-emitting devices using organic EL have been actively studied. By adopting organic EL instead of LEDs as the light source of the electrophotographic process, the number of wire bondings connected to each LED can be reduced and the cost can be reduced.

  Next, the structure of the light emitting element provided in the exposure unit 203 will be described. FIG. 2 is a view showing a cross-sectional structure in the optical waveguide direction of the light emitting elements in the light emitting element array provided in the exposure device 3 described in FIG. FIG. 3 is a cross-sectional view when the cross-sectional structure shown in FIG. 2 is cut along D-D ′. FIG. 4 is a diagram showing a lower surface of the cross-sectional structure shown in FIG. In this structure, a plurality of planar light emitting portions such as a top emission type organic EL light emitting layer 7 are arranged in an array on the upper surface side of the transparent light emitting element substrate 1 and individually opposed to each of the light emitting portions. It is a structure provided with the waveguide formation part 16 which has the optical waveguide space 14 which has an inclined surface and is provided with the reflective mirror 15 which consists of a light reflection metal film on the inner surface. With this structure, the light emitted from the organic EL light emitting layer 7 is reflected and collected from the left side to the right side in FIG. 1 by the reflecting mirror made of the light reflecting metal film 15 provided in the optical waveguide space 14, and then the light reflecting metal film 15. Thus, the light is guided in the direction of the lower surface of the light emitting element substrate 1 and emitted through the condensing opening 18.

  By the way, in a light emitting element using organic EL, deterioration with the lapse of time occurs in which the light emission characteristics deteriorate according to the history of the light emitting time of the light emitting element and the value of the applied voltage. When this is applied to an image forming apparatus due to a decrease or variation in light emission characteristics of each light emitting element in the light emitting element array, a stable and uniform printed image cannot be obtained. On the other hand, in the present invention, the brightness of light emitted from the organic EL light emitting layer 7 is detected by a method described later, and the light emission brightness and exposure energy with respect to the gradation value of the image data are maintained close to a constant value. Thus, a configuration for performing correction control is provided. For this purpose, a small sensor opening 19 is provided separately from the condensing opening 18. The sensor opening 19 is provided on the lower side in the vicinity of the end of the organic EL light emitting layer 7, and one end of the light reflecting metal film 15 is provided above the sensor opening 19. At this time, the left side of the reflection mirror 15 is not greatly involved in the light collection due to the directionality of the reflection light collection amplification, so that it is possible to provide a minute opening such as the sensor opening 19. The light from the organic EL light emitting layer 7 is guided to the lower surface side of the light emitting element substrate 1 from the sensor opening 19, and the luminance is detected by a photosensor (PD: photodiode, for example) 20.

  Note that the optical sensors 20 do not have to be provided on the sensor openings 19 and can be provided in an arbitrary number at arbitrary positions. For example, as shown in FIG. 4, it can be provided across two sensor openings 19, or one can be provided for every 960 pixels in each group shown in FIG. In this case, even if the luminance by light emission of each organic EL light emitting layer 7 is the same, the amount of light received by the optical sensor 20 changes according to the distance from the organic EL light emitting layer 7. However, as will be described later, since the luminance correction control in the present embodiment is performed based on detecting a relative change from the initial value, the correction is performed regardless of the distance from the organic EL light emitting layer 7. Control can be performed.

  The optical sensor 20 is composed of, for example, a general-purpose photodiode. The optical sensor 20 is bonded to the lower surface side of the light emitting element substrate 1 via, for example, an optically permeable adhesive layer 21. As the adhesive layer 21, it is preferable to use an adhesive capable of adjusting the refractive index, for example, a UV curable epoxy-based optical path coupling adhesive so as to match the refractive index with the light emitting element substrate 1. The light emitting element substrate 1 is provided with switching elements such as TFTs and TFDs for constituting a drive circuit as necessary. That is, the optical sensor 20 in the present embodiment is not integrally formed with the light emitting element substrate 1, but a general-purpose photodiode or the like separately formed is used and attached to the lower surface side of the light emitting element substrate 1. For example, by integrally forming the light sensor on the light emitting element substrate, the structure becomes complicated, and the yield may be reduced or the reliability may be reduced. Absent.

  The upper part of the light emitting element is a waveguide forming part 16 made of a waveguide forming resin. A groove is provided in the waveguide forming portion 16, and the light reflecting metal film 15 is formed on the inner surface of the groove by vapor deposition or the like. The optical waveguide space 14 constituted by the groove and the light reflecting metal film 15 is formed on a one-to-one basis at a position facing the organic EL light emitting layer 7 in the form of an array. The waveguide structure is formed by various molding methods such as nanoimprint, injection molding, and photolithography. In the present embodiment, the sealing substrate 17 and the waveguide forming portion 16 have a two-layer structure made of different materials, but may be configured of a single material.

  FIG. 5 shows a schematic configuration of the pixel drive circuit 30 and the optical sensor 20 according to an embodiment of the present invention. The pixel driving circuit 30 here has a two-transistor configuration, for example, a light emitting element 38 made of an organic EL element, a source electrode connected to the light emitting element 38, a drain electrode connected to the power supply voltage Vsource, A current control thin film transistor 36 for controlling the drive current supplied to the light emitting element 38 to control the light emission, a signal holding capacitor 37 connected to the gate electrode of the current control thin film transistor 36, and a drain electrode Is supplied with a drive signal Vdata corresponding to the gradation value of the image data, the source electrode is connected to the gate electrode of the current control thin film transistor 36, the selection signal Vselect is applied to the gate electrode, the pixel is selected, and the capacitor And a switching thin film transistor 35 which is turned on when data is written to 37. The photosensor 20 includes a photodiode (PD) 31, a reset transistor 32 to which a reset signal Vrst is applied to the gate electrode, an amplification transistor 33, and a read selection transistor 34 to which the sensor selection signal Psel is applied to the gate electrode. Consists of

  The optical sensor 20 includes a photodiode (PD) 31, a reset transistor 32, an amplification transistor 33, and a read selection transistor 34.

  Next, the configuration of the light emitting unit for driving and controlling the above light emitting element array will be described. FIG. 6 is a diagram illustrating a configuration of the light emitting unit 100, and FIG. 7 is a timing chart of drive control when performing a normal printing operation. The light emitting unit 100 includes a system controller 41 that controls the overall operation, a Vdata driver 45, a Vselect driver 42, a Vsource driver 43, and a light emitting element array 44. The Vselect driver 42 and the Vsource driver 43 are configured to include a shift register that shifts each signal within one line time, for example.

  The light emitting element array 44 is formed by arranging a plurality of light emitting elements 38 in the main scanning direction of the paper. As an example, if a light source unit of 1200 dpi x 1200 dpi, 40 ppm, 50 mm between papers and an A4 horizontal size (A4 horizontal = 297 mm or more, for example, 325 mm in this case) is used, it has approximately 15400 light emitting elements 38, each of which drives a pixel. A pixel including the circuit 30 is configured. Here, 960 pixels are regarded as one unit block, and pixels for 16 blocks of 1 to 16, that is, pixels of 960 × 16 = 15360 dots are arranged in the main scanning direction to form the light emitting element array 44. Suppose you are. In this case, the time allowed for the formation of one line in the main scanning direction and the one line time are ((25.4 mm / 1200 dpi) / (210 mm × 40 sheets + 50 mm × 40 sheets)) / 60≈122 μsec.

  The Vdata driver 45 outputs 960 drive signals from Vdata1 to Vdata960, distributes the 960 drive signals in parallel to 16 blocks corresponding to each block of the light emitting element array 44, and emits the light emitting element array 44. Connected to each pixel of 15360 dots. The Vselect driver 42 outputs 16 selection signals Vselect1 to Vselect16. Each selection signal is connected to each of the 16 blocks of the light emitting element array 44 and is connected to 960 pixels constituting each block. ing. The Vsource driver 43 outputs 16 power signals from Vsource1 to Vsource16, and each power signal is connected to each of the 16 blocks of the light emitting element array 44, and is connected to 960 pixels constituting each block. .

  In the above configuration, when performing a normal printing operation, as shown in FIG. 7, first, a selection signal (Vselect1) is applied from the Vselect driver to the first pixel block, and the first pixel from the Vsource driver 43. At the same time as the power supply signal (Vsource1) is applied to the block, the Vdata driver 45 supplies the drive signals of Vdata1 to Vdata960 corresponding to the gradation values of the image data to the 960 pixels of the first pixel block. As a result, in the pixel block, the switching transistor 35 in each pixel is turned on, and charges corresponding to the drive signals Vdata1 to Vdata960 are held in the signal holding capacitor 37. As a result, when the current control transistor 36 is turned on, a current corresponding to the gradation value of the image data flows from the Vsource 1 to the light emitting element 38, and each light emitting element 38 in the first pixel block emits light. The light emission intensity of the light emitting element 38 is determined by the current flowing in the current control transistor 36 that is stored in the signal holding capacitor 37 and is controlled by the voltage according to the drive signals Vdata1 to Vdata960. In FIG. 7, a period Tse in which each of the selection signals Vselect1 to Vselect16 is applied is a selection period in which each pixel is selected. As shown in FIG. 7, even after the selection period ends and each selection signal (Vselect1 to Vselect16) is set to the low level and shifts to the non-selection period, the power supply signals (Vsource1 to Vsource16) remain at the high level for a predetermined period. Is maintained. As a result, light emission is maintained while the power supply signal is at a high level. This operation is sequentially performed on the 16 blocks, and the light emission of all the pixels of the light emitting element array 44 is controlled.

Next, a control operation for detecting the light emission luminance of each light emitting element 38 performed when the correction control in the present embodiment is performed will be described. FIG. 8 is a timing chart for explaining the timing of the control operation when performing the correction control. When the correction control is performed, as shown in FIG. 8, first, the reset signal Vrst in the corresponding optical sensor 20 is set to the high level at the timing before the selection signal (Vselect1) is applied, and the reset transistor 32 is set. Is turned on, a current is supplied from the power supply VDD to charge the photosensor PD31 with the initial charge. Next, the drive signals Vdata1 to Vdata960 are supplied simultaneously with the selection signal (Vselect1) and the power supply signal (Vsource1) being applied. At this time, for example, only Vdata1 is set to the highest gradation voltage and the other Vdata2 to Vdata960 are set to 0 V, so that only the light emitting element 38 of the first pixel of the first pixel block emits light. A part of the light emitted from the light emitting element 38 is irradiated to the corresponding optical sensor (PD) 31 through the sensor opening 19, whereby the dark current increases and a part of the initial charge is discharged. The At this time, the potential at the point A changes according to the emission intensity, and becomes a voltage according to the emission luminance of the light emitting element 38. The amplification transistor 33 amplifies this potential. Next, when the sensor selection signal Psel is set to a high level, the read selection transistor 34 is turned on, and the output voltage corresponding to the light emission luminance of the light emitting element 38 amplified by the amplification transistor 33 is read from the output terminal Pout. Thus, the light emission luminance of the light emitting element 38 is detected (measured). The acquired data is transferred to the system controller 41 and stored in a memory or the like (not shown). Next, at the same time as the selection signal (Vselect1) and the power supply signal (Vsource1) are applied, the drive signals Vdata1 to Vdata960 in which only Vdata2 is set to the highest gradation voltage and the others are set to 0V are supplied. Thereby, only the light emitting element 38 of the second pixel of the first pixel block is caused to emit light. A part of the light emitted from the light emitting element 38 is irradiated to the corresponding optical sensor 31, and the sensor selection signal Psel is set to a high level to detect the light emission luminance and store it in the system controller 41. The above operation is performed for all the pixels in the first pixel block, and the light emission intensity of the light emitting element 38 of each pixel is detected and stored in the system controller 41. Since the optical sensor 20 is provided for each of the plurality of light emitting elements 38 as described above, the optical sensor 20 to be used is controlled to be switched appropriately according to the light emitting element 38 that emits light.

  Next, as shown in FIG. 8, a selection signal (Vselect2) and a power supply signal (Vsource2) are applied to the second pixel block, and at the same time, predetermined drive signals Vdata1 to Vdata960 are supplied, and the same as described above. The light emitting elements 38 of each pixel in the second pixel block are caused to emit light sequentially, and the light emission luminance of the light emitting elements 38 of all the pixels is detected and stored in the system controller 41. Thereafter, the same operation is performed on all the pixel blocks, and the light emission luminances of the light emitting elements 38 of all the pixels of the light emitting element array 44 are detected and stored in the system controller 41.

  Next, an operation procedure when performing correction control according to the present embodiment will be described. In the present embodiment, as correction control, when correcting the light emission luminance of each light emitting element 38, in the initial state (first timing), each light emitting element 38 of the light emitting element array 44 detected by the photosensor 20 is used. The light emission luminance value at a predetermined gradation (for example, the highest gradation) is compared with the light emission luminance value detected by the optical sensor 20 at a time point (second timing) after a predetermined time has elapsed. The light emission luminance of each light emitting element 38 is controlled so that the difference between them approaches 0. In this case, by using a correction table in which the light emission luminance of the light emitting element 38 is associated with the value of the drive current supplied to the light emitting element 38, the light emission luminance at a predetermined gradation is brought close to the light emission luminance in the initial state. Controls the value of the drive current. Further, as the correction control, in the case of controlling the exposure energy irradiated to the photosensitive drum 201, the light emission time of each light emitting element 38 is controlled to control the exposure energy to be close to the value in the initial state. Is done.

  FIG. 9 is a flowchart showing the procedure of the correction control described above. FIG. 10 is a block diagram showing a configuration of the system controller 41 for realizing luminance correction. As shown in FIG. 10, the system controller 41 includes a control unit 411 that controls each unit, a sensor output comparator 412 that compares the output of the optical sensor 20 with a predetermined value, and a correction unit that generates correction image data. The image data generation unit 413, the Vdata correction table 414 used when correcting the value of the drive signal Vdata, the Vsource drive time calculation unit 415 that calculates the time for applying the power supply voltage Vsource, and the light emitting elements 38 of each pixel. An initial value memory 416 that stores an initial value of light emission luminance, a time-varying value memory 417 that stores a value of light emission luminance of the light emitting element 38 of each pixel after a predetermined time has elapsed, and luminance correction was performed. And a correction value memory 418 for storing the value of the later light emission luminance. Here, it is assumed that the Vdata correction value table 414 and the initial value memory 416 are configured by a flash ROM or the like that retains setting values even when the power is turned off and can be rewritten in the system.

  As shown in FIG. 9, when performing correction control, first, an operation of acquiring the following initial value a is performed at a timing (first timing) before printing at the first system startup. That is, after the power of the apparatus is turned on (step S1), it is determined whether or not the system is activated for the first time (step S2). When it is the first time, each of the light emitting elements 38 of all the pixels of the light emitting element array 44 is determined. On the other hand, according to the drive timing shown in FIG. 8 described above, for example, an initial value of the highest gradation voltage is sequentially supplied as the drive signal Vdata to sequentially emit light, and the light emission luminance of the light emitting elements 38 of all the pixels is detected by the optical sensor 20. The measurement is sequentially performed (step S3). Then, the measured value at this time is acquired as the initial value a, and stored in the nonvolatile initial value memory 416 of the system controller 41 (step S4). Then, the drive signal Vdata = image data is set (step S5), and the process ends without performing correction control. Thereafter, when the correction control is performed next, the printing operation is performed with the drive signal Vdata = image data without performing the correction control. The initial value a is not a value for one pixel but a value for all pixels, and each pixel has a different value. In addition, since the light emitting element 38 made of organic EL has a tendency that the light emission luminance gradually decreases due to deterioration with time, the drive signal Vdata supplied to the light emitting element 38 is usually restored to the initial state by luminance correction thereafter. The correction is made in the direction of increasing gradually. For this reason, the value of the maximum output voltage (Vmax) of the Vdata driver 45 may be set to a value higher than the maximum gradation voltage when performing this step S3.

  Next, when the power is turned on for the second time or after, or when the energized state continues, the determination in step S2 becomes NO when there is no print state after the elapse of an arbitrary time (second timing). At this time, the light emitting elements 38 of all the pixels are sequentially made to emit light at the initial value of the maximum gradation voltage with respect to all the pixels in the same manner as in step S3 described above, and the light emission luminance at this time is measured by the optical sensor 20. (Step S6), this measured value is stored in the time-varying value memory 417 as a time-varying value b (Step S7). Next, the initial value a and the temporal change value b are read from the initial value memory 416 and the temporal change value memory 417, and are compared for each corresponding pixel (step S8). In step S8, it is determined whether or not the temporal change value b is within the allowable range α with respect to the initial value a in each pixel. If it is determined in step S8 that the time-dependent change value b is within the allowable range (a−α ≦ b ≦ a + α, step S8: Yes), the light emission characteristics are not deteriorated or are small, and correction control is performed. Since the drive signal Vdata is equal to the image data (step S8), the process is terminated without correction. That is, thereafter, until the next correction control is performed, the printing operation is performed with the drive signal Vdata = image data without performing the correction control.

  On the other hand, if it is determined in step S8 that the time-dependent change value b is not within the allowable range in at least one pixel (b <a−α or b> a + α, step S8: No), In the target pixel), it is determined that the light emission efficiency of the light emitting element 38 is reduced (deteriorated with time). At this time, the Vdata correction table 414 for correcting the drive signal Vdata is created and rewritten as follows. In the creation / rewriting process of the Vdata correction table 414, first, correction data for correcting the drive signal Vdata is set to a preset correction amount d1 (step S10). Then, the drive signal Vdata is corrected to a value (image data + correction data) obtained by adding the correction data to the image data (step S11). Next, as in the case of step S3 described above, the light emitting element 38 of the target pixel is caused to emit light at the initial value of the maximum gradation voltage, and the light emission luminance at this time is measured by the optical sensor 20 (step S3). S12), this measured value is stored in the correction value memory 418 as a correction value c (step S13). Next, the initial value a of the target pixel is read from the initial value memory 416, and the correction value c of the target pixel is read from the correction value memory 418 and compared for each corresponding pixel (step S14). In step S14, it is determined whether or not the correction value c is within an allowable range with respect to the initial value a in each pixel. If it is determined that the correction value c is within the allowable range, (a−α). ≦ c ≦ a + α, Step S14: Yes) Using the drive signal Vdata and the correction data at this time, the Vdata correction table 414 is created and rewritten (Step S15), and the drive signal Vdata is added to the image data and the correction data. The corrected value (image data + correction data) is corrected (step S16), and the process ends. Thereafter, until the next correction control, based on the rewritten Vdata correction table 414, the drive signal Vdata is corrected to the sum of the image data and the correction data, and the printing operation is performed.

  On the other hand, when it is determined that the correction value c is not within the allowable range (c <a−α or c> a + α, Step S14: No), it is determined that the value of the correction data is still insufficient. A predetermined increment d2 is added to the correction data (step S18). Then, returning to step S11 again, the drive signal Vdata is corrected to a value obtained by adding the correction data to the image data, and thereafter, the same processing (steps S12, S13, S14) is performed until the correction value c falls within the allowable range. )repeat. If it is determined that the correction value c is within the allowable range, the Vdata correction table 414 is created and rewritten using the drive signal Vdata and the correction data at this time (step S15), as described above, and the drive signal Vdata. Is corrected to the sum of the image data and the correction data (step S16), the process is terminated, and thereafter, the drive signal Vdata is based on the rewritten Vdata correction table 414 until the next correction control is performed. Is corrected to the sum of the image data and the correction data, and the printing operation is performed.

  If it is determined in step S14 that the correction value c is not within the allowable range, the degree of deterioration with time of the light emission efficiency of the light emitting element 38 is relatively large, and the corrected drive signal Vdata at this time is the Vdata driver 45. If the maximum output value (Vmax) has been reached, the drive signal Vdata cannot be corrected any higher to increase the light emission luminance. Therefore, before performing the process of adding the increment d2 to the correction data in step S18, it is determined whether or not the drive signal Vdata has reached the maximum output value (Vmax) of the Vdata driver 45 (step S17). If it is determined in step S17 that the drive signal Vdata has reached the maximum output value (Vmax) of the Vdata driver 45 (Vdata = Vmax, step S17: No), the light emission time is lengthened and the exposure energy (photosensitive drum 201) is determined. The amount of irradiation is controlled to increase. For this purpose, control is performed to increase the application time of the power supply signal Vsource. In order to perform this control, the Vsource application time calculation unit 415 calculates an insufficient exposure energy relative to the exposure energy in the initial state based on the output value of the optical sensor 20 and the current Vsource application time. Based on the result, the extension time of the Vsource application time is calculated to correct the Vsource application time (step S19). Thereafter, the process returns to step S11 again to correct the drive signal Vdata to a value obtained by adding the correction data to the image data, and thereafter the same processing (steps S12, S13, and so on) until the correction value c falls within the allowable range. S14) is repeated. If it is determined that the correction value c is within the allowable range, the Vdata correction table 414 is created and rewritten using the drive signal Vdata and the correction data at this time (step S15), as described above, and the drive signal Vdata. Is corrected to the sum of the image data and the correction data (step S16), the Vsource application time is corrected and the process is terminated. Thereafter, the drive signal Vdata is rewritten until the next correction control is performed. Based on the Vdata correction table 414, the image data and the correction data are corrected to a total value, and a printing operation is performed using the corrected Vsource application time.

  Even when the light emission characteristics of the light emitting elements 38 of each pixel of the light emitting element array 44 deteriorate due to these correction control operations, the light emission luminance or the exposure energy with respect to the gradation value of the image data is a constant value. It is possible to perform correction control so as to keep it close to.

  As described above, according to the above-described embodiment, the light-emitting element array 44 applied to the exposure device 203 of the image forming apparatus 200 includes the optical sensor 20 that detects the light emission luminance of each light-emitting element 38, and is activated. In addition, the light emission luminance of each light emitting element 38 is measured by the optical sensor 20 at a timing other than during printing after an arbitrary time has elapsed, and is compared with the initial value, so that appropriate correction control according to the deterioration with time of each light emitting element 38 is performed. Thus, it is possible to always obtain a stable and uniform printed image by performing correction control so that the light emission luminance with respect to the gradation value of the image data of each light emitting element 38 is maintained close to a constant value. Furthermore, in addition to the light emission brightness correction control, the light emission time is corrected and the correction control is performed so that the exposure energy approaches a constant value. And a stable and uniform printed image can be obtained.

  In the present embodiment, the optical sensor 20 is configured to perform correction control based on the relative change in the amount of received light when the optical sensor 20 detects an initial state and an arbitrary time. There is no need to provide each light-emitting element 38 of the array 44, and only one light sensor 20 needs to be provided for a plurality of light-emitting elements, and the number of necessary light sensors 20 can be reduced to reduce the cost. . Further, since a general-purpose photodiode or the like separately formed can be used as the optical sensor 20 and can be attached to the lower surface side of the light emitting element substrate 1, the optical sensor is integrally formed on the light emitting element substrate. Thus, problems such as a decrease in yield and a decrease in reliability due to the complicated structure can be prevented.

  Further, by providing an opening 19 for the light amount sensor for receiving light by the optical sensor 20 on the one end side of the organic EL light emitting layer 7, light emission is hardly effected on the brightness of the condensed light for exposure. Luminance can be detected.

FIG. 1 is a diagram showing a schematic configuration of an electrophotographic image forming apparatus (printer apparatus) to which the present invention is applied. FIG. 2 is a view showing a cross-sectional structure of the light emitting element provided in the exposure device 3 described in FIG. FIG. 3 is a cross-sectional view when the cross-sectional structure shown in FIG. 1 is cut along D-D ′. FIG. 4 is a diagram showing a lower surface of the cross-sectional structure shown in FIG. FIG. 5 is a diagram illustrating a schematic configuration of a pixel driving circuit and an optical sensor including an organic EL light emitting unit according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a configuration of the light emitting unit. FIG. 7 is a timing chart of drive control when a normal printing operation is performed. FIG. 8 is a timing chart for explaining the timing of the control operation when performing the correction control. FIG. 9 is a flowchart showing a correction control procedure. FIG. 10 is a block diagram showing a configuration of a system controller for realizing correction control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element substrate 7 Organic electroluminescent light emitting layer 15 Light reflection metal film (reflection mirror)
18 Condensing aperture 19 Sensor aperture 20 Optical sensor (PD)
30 pixel drive circuit 38 light emitting element 41 system controller 42 Vselect driver 43 Vsource driver 411 control unit 412 sensor output comparator 413 correction image data generation unit 414 Vdata correction table 415 Vsource drive time calculation unit

Claims (12)

In an exposure apparatus that performs exposure by irradiating light corresponding to image data to a photosensitive drum,
A plurality of light emitting elements that emit light according to a drive signal supplied corresponding to the image data, and are formed in a linear arrangement on one surface, a light emitting element substrate made of a transparent substrate;
On the other surface of the light emitting element substrate, at least one light received from each of the plurality of light emitting elements provided corresponding to each of a predetermined number of two or more light emitting elements is received. An optical sensor;
The amount of light received by the photosensor with respect to the light emission luminance of each of the plurality of light emitting elements at a first timing and the light emission of each of the plurality of light emitting elements at a second timing after a predetermined time has elapsed from the first timing. The image data is corrected based on the comparison of the received light amount of the light sensor with respect to the brightness, and the light emission brightness of each light emitting element is maintained at the light emission brightness of each light emitting element at the first timing. Control means;
Equipped with,
Each light emitting element has a top emission structure that emits light in the direction of the one surface of the light emitting element substrate,
A light guide means provided to face the one surface of the light emitting element substrate and guides the light emitted from each light emitting element to the other surface side of the light emitting element substrate;
The light guide means includes means for generating light for emitting light emitted from the light emitting elements from the other surface of the light emitting element substrate to irradiate the photosensitive drum.
An exposure apparatus characterized by that.   The control means controls the light emission time of each of the light emitting elements when the drive signal reaches a maximum value that can be supplied to the light emitting elements by correcting the image data at the second timing. 2. The exposure apparatus according to claim 1, further comprising means for controlling the exposure energy based on the light emission luminance and the light emission time of the light emitting element to maintain the exposure energy at the first timing.   The exposure apparatus according to claim 1, wherein the optical sensor is provided on the other surface of the light emitting element substrate via an adhesive layer. 2. The exposure apparatus according to claim 1, wherein the light guide means includes means for guiding a part of light emitted from the light emitting elements to the optical sensor. Each of the light emitting elements has a light emitting layer that emits light according to the image data,
Said means for guiding said light sensor a portion of the light emitted from the light emitting element is provided opposite to the light-emitting layer, the other surface of the light emitting element substrate of the light emitted from the light emitting layer 5. The exposure apparatus according to claim 4, further comprising a reflective film that reflects in a direction. Each light emitting element has a light emitting layer having a predetermined area for emitting light according to the image data,
The means for generating light for irradiating the photosensitive drum in the light guide means is provided corresponding to the light emitting layer, and collects the light emitted from the light emitting layer in an area smaller than the area of the light emitting layer. The exposure apparatus according to claim 1 , further comprising a reflective film that reflects light toward the other surface of the light emitting element substrate. In 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 that emit light according to a drive signal supplied corresponding to the image data, and are formed in a linear arrangement on one surface, a light emitting element substrate made of a transparent substrate;
On the other surface of the light emitting element substrate, at least one light received from each of the plurality of light emitting elements provided corresponding to each of a predetermined number of two or more light emitting elements is received. An optical sensor;
The amount of light received by the photosensor with respect to the light emission luminance of each of the plurality of light emitting elements at a first timing and the light emission of each of the plurality of light emitting elements at a second timing after a predetermined time has elapsed from the first timing. The image data is corrected based on the comparison of the received light amount of the light sensor with respect to the brightness, and the light emission brightness of each light emitting element is maintained at the light emission brightness of each light emitting element at the first timing. Control means;
Equipped with,
Each light emitting element has a top emission structure that emits light in the direction of the one surface of the light emitting element substrate,
A light guide means provided to face the one surface of the light emitting element substrate and guides the light emitted from each light emitting element to the other surface side of the light emitting element substrate;
The light guide means includes means for generating light for emitting light emitted from the light emitting elements from the other surface of the light emitting element substrate to irradiate the photosensitive drum.
An image forming apparatus.   The control means controls the light emission time of each of the light emitting elements when the drive signal reaches a maximum value that can be supplied to the light emitting elements by correcting the image data at the second timing. 8. The image forming apparatus according to claim 7, further comprising means for controlling exposure energy based on light emission luminance and light emission time of the light emitting element so as to maintain the exposure energy at the first timing.   The image forming apparatus according to claim 7, wherein the optical sensor is provided on the other surface of the light emitting element substrate via an adhesive layer. It said guiding means, the image forming apparatus according to a portion of the emitted from the light emitting element light in claim 7, characterized in that it comprises means for guiding the light sensor. Each of the light emitting elements has a light emitting layer that emits light according to the image data,
Said means for guiding said light sensor a portion of the light emitted from the light emitting element is provided opposite to the light-emitting layer, the other surface of the light emitting element substrate of the light emitted from the light emitting layer The image forming apparatus according to claim 10, further comprising a reflective film that reflects in a direction. Each light emitting element has a light emitting layer having a predetermined area for emitting light according to the image data,
The means for generating light for irradiating the photosensitive drum in the light guide means is provided corresponding to the light emitting layer, and collects the light emitted from the light emitting layer in an area smaller than the area of the light emitting layer. The image forming apparatus according to claim 7 , further comprising a reflective film that reflects light toward the other surface of the light emitting element substrate.

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