JP2006231836A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce the variation in luminescence quantity of light for every LED element generated in connection with the temperature difference due to the luminescence for every LED element of LPH without adding a new sensor. <P>SOLUTION: In a copying machine 1 of this invention, the amount of data of pixel which corresponds respectively for every LED element per predetermined unit time is monitored with the image data which has been input into an LPH-data controlling circuit section 158. The difference obtained from the comparison between the pixel and the amount of data of pixel excluding the former pixel for every pixel corresponding to the LED element is further compared with a predetermined threshold value. According to the comparison result, initial correction data or new correction data for every LED element to which a predetermined correction data portion that makes the variation in quantity of light for every LED element decreased has been added is input into a light-quantity correcting circuit section 160a. Based on the initial correction data or the new correction data, the driving current value for every LED element is corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a lighting control technology for each light emitting diode element in a light emitting diode printer head in which a plurality of light emitting diode elements are arranged.

  An LPH in an image forming apparatus provided with a light emitting diode printer head (hereinafter referred to as LPH [LED Print head]) has a plurality of light emitting diode elements (hereinafter referred to as LED [Light Emitting Diode] elements) arranged in an array. This is a device in which lighting of each LED element is controlled based on image data, and a latent image is written on the surface by LED light irradiated on the photosensitive drum.

  An image forming apparatus including an LPH has a structure in which the LPH includes a plurality of LED elements. Therefore, unevenness in the latent image on the photosensitive drum written based on the image data due to variations in the amount of emitted light for each LED element. This may cause density unevenness in the image of the toner image finally formed on the paper. Therefore, a correction method that suppresses variation in the amount of emitted light for each LED element has been proposed.

  One of the methods is to dynamically control the amount of emitted light by monitoring the amount of emitted light of each LED element (see, for example, Patent Document 1 and Patent Document 2). For example, the amount of light emitted from each LED element is monitored by a photodiode or CCD, and feedback control is performed so that the amount of light emitted from each LED element becomes a predetermined value, thereby correcting variations in the amount of light emitted due to changes over time of the LED elements. LED writing devices that can be used are disclosed and proposed (see, for example, Patent Document 1).

  Further, as an apparatus having a control method different from the above, for example, the number of times of lighting for each light emitting element of the exposure head is accumulated, and additional lighting is performed on the light emitting elements other than the light emitting element having the largest accumulated number of times of lighting. Thus, the deterioration state of all the light emitting elements can be made uniform, and the intensity of light emitted from the exposure head can be detected to control the driving voltage or driving current of the light emitting elements for exposure. There has been disclosed and proposed an exposure head control method and an electrophotographic apparatus equipped with the exposure head capable of always keeping the light amount of the head constant (see, for example, Patent Document 2).

Further, as a correction method for suppressing variations in the amount of emitted light for each general LPH LED element, the amount of emitted light for each LPH LED element is measured at a certain point in time (for example, when the LPH is shipped from the factory). A correction control method for adjusting the drive current and drive time of each LED element based on the data is used.
JP 9-309223 A JP 2003-334990 A

  Certainly, with the LED writing device disclosed in Patent Document 1, since the light emission amount is monitored and dynamically controlled for each LED element of LPH, the variation in the light emission amount for each LED element is suppressed. Is possible.

  In addition, in the case of an electrophotographic apparatus equipped with an exposure head control method and an exposure head disclosed in Patent Document 2, when applied to an image forming apparatus equipped with LPH, the number of times of lighting for each LED element is accumulated. By performing additional lighting on the LED elements other than the LED element having the largest number of times of lighting, and detecting the intensity of light emitted from the LPH and controlling the drive current for each LED element, the LED It is possible to suppress variations in the amount of emitted light for each element.

  Also, an image forming apparatus provided with a conventional LPH, in which the amount of emitted light for each LED element of LPH is measured in advance, and correction control can be performed by adjusting the drive current and drive time of each LED element based on the measurement data. If so, since the control for each LED element is performed based on the measurement data, it is possible to suppress the variation in the amount of emitted light for each LED element.

  However, the LED writing device disclosed in Patent Document 1 requires a separate sensor for monitoring the amount of emitted light for each LED element, which increases the manufacturing cost of the device.

  In addition, since the exposure head control method disclosed in Patent Document 2 and the electrophotographic apparatus equipped with the exposure head are additionally lit for LED elements other than the LED element having the largest number of times of lighting, The deterioration of the LED element is accelerated. In addition, since a sensor for monitoring the amount of light emitted from the LED element is required separately, the manufacturing cost of the apparatus increases.

  Also, an image forming apparatus provided with a conventional LPH, in which the amount of emitted light for each LED element of LPH is measured in advance, and correction control can be performed by adjusting the drive current and drive time of each LED element based on the measurement data. Since there is no means for monitoring the change in the amount of emitted light for each LED element due to the change in LPH over time or the environmental change around the LPH, it is not possible to correct the change in the amount of emitted light for each LED element. Variations in the amount of emitted light for each LED element occur due to changes over time and environmental changes around the LPH.

  In the image forming apparatus having the conventional LPH, the main cause of the variation in the amount of emitted light for each LED element caused by the environmental change around the LPH is due to the temperature change of the LED element.

  In general, it is said that the temperature characteristic of an LED element changes in a direction in which the amount of light decreases by 1% and the emission center wavelength extends by about 0.3 nm with each increase. Further, the density unevenness of the image after printing on the paper can be recognized with the naked eye if there is a difference of about 5 to 6% in the light amount difference. Further, it is known that if the spectral sensitivity characteristics of the photosensitive drum to be used are not flat, the density unevenness of the toner image occurs even when the emission wavelength is shifted by about 5 nm.

  When the temperature of the entire LPH rises due to the light emission of the LED elements, only the light quantity / wavelength change of all the LED elements occurs, and the density unevenness of the image due to the increase in the light quantity / wavelength variation for each LED element occurs. There is little possibility.

  However, when printing is repeated only for a certain pixel, only the LED element used for the printing generates heat, and the temperature of the other LED elements does not rise so much. If such a situation continues, a temperature difference will occur between the LED elements used for printing and the other LED elements, and the variation in the amount of emitted light will be greatly different from the initial state. The image density may become uneven and the image quality may be impaired.

  In view of the above problems, the present invention can reduce the variation in the amount of emitted light for each LED element caused by the temperature difference due to the light emission for each LED element of LPH without adding a new sensor. An object of the present invention is to provide a simple image forming apparatus.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a light emitting diode element array in which a plurality of light emitting diode elements are arranged in an array, and each light emitting diode element based on image data and correction data. A light amount correction unit that corrects the drive current value, supplies a corrected drive current for each light emitting diode element, and controls the drive current so as to maintain the corrected drive current value; and the image data Based on gradation control means for controlling the lighting time for each light emitting diode element, light quantity correction data storage means for storing light quantity measurement data for each light emitting diode element, and light quantity correction data storage means. Correction data processing means for generating correction data for correcting the drive current value for each light emitting diode element based on the measurement data. Adding means for summing up the data amount of the pixel corresponding to each light emitting diode element from one or a plurality of image data at a predetermined time, and the data amount of the pixel summed up by the adding means for each pixel. Total data storage means for storing, peripheral comparison means for comparing and outputting a difference in data amount between a pixel and a predetermined pixel excluding the pixel for the data amount for each pixel stored in the total data storage means, Correction data for comparing the difference in data amount for each pixel with a predetermined threshold value, and generating and outputting the correction data or new correction data obtained by adding predetermined data to the correction data based on the comparison result And a calculation means. With such a configuration, the temperature difference between the light emitting diode elements can be reduced even when image formation is continuously performed on a sheet without adding a new sensor. It is possible to suppress variations in the amount of emitted light every time, and it is possible to obtain an image without density unevenness on the paper.

  Based on the light emitting diode element array in which a plurality of light emitting diode elements are arranged in an array, and image data and correction data, the drive current value is corrected for each light emitting diode element and corrected for each light emitting diode element. A light amount correcting means for supplying a driving current and controlling the driving current so as to maintain the corrected driving current value, and a gradation control means for controlling a lighting time for each light emitting diode element based on the image data And a light amount correction data storage means for storing correction data of the drive current value for each light emitting diode element, and corresponding to each light emitting diode element from a single or a plurality of image data at predetermined time intervals. Summing means for summing up the data amount of the pixel obtained, summing data storage means for storing the data amount of the pixel summed up by the summing means for each pixel, Peripheral comparing means for comparing and outputting the difference in data amount between a pixel and a predetermined pixel excluding the pixel for the data amount for each pixel stored in the aggregate data storage means, and the difference in the data amount for each pixel And a correction data calculation means for generating and outputting the correction data or new correction data obtained by adding predetermined data to the correction data based on the comparison result. It is configured. With such a configuration, the temperature difference between the light emitting diode elements can be reduced even when image formation is continuously performed on a sheet without adding a new sensor. It is possible to suppress variations in the amount of emitted light every time, and it is possible to obtain an image without density unevenness on the paper. Further, since the correction data for the drive current value for each light emitting diode element is stored in advance in the light quantity correction data storage means, the correction data for the drive current value is obtained from the measurement data of the emitted light quantity for each light emitting diode element measured in advance. Since there is no need to newly install a function for generating, manufacturing cost can be reduced.

  As described above, with the image forming apparatus according to the present invention, even if a latent image is formed on the surface of the photosensitive drum by the light emitting diode without adding a new sensor, the temperature difference between the light emitting diode elements is reduced. Since it can be reduced, it is possible to suppress variations in the amount of emitted light for each light emitting diode element.

  Hereinafter, a case where the present invention is applied to a copying machine will be described as an example. FIG. 1 is a block diagram showing the configuration of the main part of a copying machine according to the present invention, and FIG. 2 is a longitudinal sectional view schematically showing the structure of the main part of the copying machine according to the present invention. As shown in both figures, the copier 1 of this embodiment includes a central processing unit 10 (hereinafter referred to as a CPU [Central Processing Unit] 10) that controls the operation of the entire apparatus, and a document transport that automatically transports a document. Unit 11, a document take-in unit 12 that takes in a document transported from document transport unit 11 and generates image data, and an operation display unit 13 that includes operation means (such as a numeric keypad or touch panel) and display means (such as a liquid crystal display). An image forming unit 15 that forms a toner image on a sheet based on the image data, a fixing unit 16 that fixes the toner image obtained by the image forming unit 15 to the sheet, and a paper feed to the image forming unit 15 A sheet feeding unit 14 that performs various control programs, light amount correction data (described later), image data, and various data, and a memory unit 17 that is used as a work area. Comprising a sheet discharge portion 18 comprising a Kamisaki, the.

  In addition to controlling the operation of the entire apparatus, the CPU 10 performs processing related to the entire correction control for suppressing variations in the amount of emitted light for each LED element in the LPH, which will be described in detail later.

  The paper feed unit 14 includes a plurality of (three levels in the present embodiment) paper storage units 141 a to 141 c serving as a paper supply source to the image forming unit 15, and the paper storage units 141 a to 141 c to the image forming unit 15. And a sheet conveying unit 142 serving as a common sheet conveying path.

  The memory unit 17 includes a ROM [Read Only Memory] 171 storing various control programs and the like, a RAM [Random Access Memory] 172 used as a work area, and a non-volatile memory. For example, it includes a light amount correction data storage unit 173 in which measurement data in which the variation in light emission amount for each LED element in the initial state is measured is stored.

  The image forming unit 15 will be described below. FIG. 3 is a diagram showing the main components of the LPH and LPH data control circuit. As shown in FIGS. 2 and 3, the image forming unit 15 has a photosensitive drum 151 as an image end member on which a toner image is formed on the drum surface based on image data, and a predetermined surface on the surface of the photosensitive drum 151. A charger 154 for uniformly charging the potential and a plurality of LED elements, as will be described later, for the width of the photosensitive drum 151 in the main scanning direction (that is, the direction perpendicular to the paper transport direction) (that is, for the printable width). ) Using LED arrays arranged in a row as a light source and irradiating LED light based on image data and correction data to form a latent image on the surface of the photosensitive drum 151, and the surface of the photosensitive drum 151 A developing device 152 that forms a toner image from the electrostatic latent image on the surface of the photosensitive drum 151 and the toner image formed on the surface of the photosensitive drum 151 are electrostatically transferred to the conveyed paper. A transfer roller 157, a cleaning unit 156 that collects toner remaining on the surface of the photosensitive drum 151, a static eliminator 155 that performs static neutralization on the surface of the photosensitive drum 151, and driving of each LED element provided in the LPH 153. Correction data for performing correction processing of current values, and an LPH data control circuit unit 158 for performing image data conversion processing for transfer to the LPH 153 and then transferring to the LPH 153.

  As shown in FIG. 3, the LPH 153 is an LED array in which LED elements each having one LED element corresponding to each pixel in the 1st to nth pixels for one line in the main scanning direction of image data are arranged in a line. 159 is electrically connected to each LED element of the LED array 159, and further corrects the drive current value S1 of the LED element input from the CPU 10 based on the drive current value correction data and image data for each LED element. And an LED drive IC [Integrated Circuit] 160 that controls the lighting of each LED element of the LED array 159 while supplying a corrected drive current for each LED element.

  As shown in FIG. 3, the LED drive IC 160 is based on correction data of the drive current value of each LED element input from the LPH data control circuit unit 158 and image data converted for input to the LED drive IC 160. Then, the drive current value S1 of the LED element input from the CPU 10 is corrected to supply the corrected drive current for each LED element, and the drive current for each LED element maintains the corrected drive current value. And a gradation correction circuit unit 160b for controlling the lighting time of each LED element of the LED array 159 based on image data converted for input to the LED drive IC 160. Have. The LED driving IC 160 is supplied with electric power from a power source (not shown) in order to light each LED element.

  As shown in FIG. 3, the LPH data control circuit unit 158 is a measurement data in which a variation in the amount of emitted light for each LED element at a certain point in time (for example, an initial state) in the LPH 153 from the light amount data correction data storage unit 173 is measured. Is input by the CPU 10 during a predetermined unit time, and a correction data processing circuit unit 158a that converts the correction data into correction data (hereinafter referred to as initial correction data) for correcting the drive current value for each LED element. For each line from the head in the main scanning direction, the data amount of the first pixel to the n-th pixel corresponding to each LED element is totaled for each pixel, and the data amount is corresponding to each pixel. Unit time addition circuit unit 158b that converts the data into the lighting time data, and sequentially adds and sums up all the image data, and unit time addition circuit unit 158b. There is a total data storage memory unit 158c for storing the lighting time data of the LED elements corresponding to each of the aggregated pixels, and the lighting time data of the LED elements corresponding to each pixel stored in the total data storage memory unit 158c. The peripheral data comparison circuit unit 158d and the peripheral data comparison circuit unit 158d output the difference in lighting time of the LED element corresponding to each pixel by comparing the lighting time data of the LED element corresponding to the pixel and the neighboring pixel. Based on a comparison between the lighting time difference of the LED element corresponding to each pixel and a predetermined threshold, the pixel is obtained by adding predetermined correction data for reducing variation in the amount of emitted light for each LED element to the initial correction data. A correction data calculation circuit unit 158e that newly generates correction data (hereinafter referred to as new correction data) of the LED element corresponding to each LED, A correction data transfer circuit unit 158f that converts initial correction data or new correction data to be input to the driving IC 160 and inputs the converted correction data to the LED driving IC 160, and image data input by the CPU 10 is input to the LED driving IC unit 160. Image data transfer circuit unit 158g that converts (for example, converts the LED element to be lit corresponding to each pixel of the image data and data of the lighting time for each LED element to be lit) and transfers the data to the LED drive IC unit 160 And comprising.

  Next, an example of a document copying operation in the copying machine 1 configured as described above will be described. In the document copying operation in the copying machine 1 of the present embodiment, first, a document is transported from the document transport unit 11 to the document fetching unit 12, and after the document image is captured by the document fetching unit 12, the image data is stored. Generated. The generated image data is temporarily stored in the RAM 172 by the CPU 10, read again, and sent to the image forming unit 15.

  Subsequently, on the surface of the photosensitive drum 151 uniformly charged to a predetermined potential by the charger 154, the driving for each LED element is performed as described later based on the image data and the driving current value correction data for each LED element. A latent image is created by the LPH 153 whose current value has been corrected, and a toner image is formed from the latent image on the surface of the photosensitive drum 151 by the developing device 152. The toner image formed on the surface of the photosensitive drum 151 is transferred to the paper conveyed from the paper supply unit 14 by the transfer roller 157.

  Thereafter, the sheet carrying the unfixed toner image is sent to the fixing unit 16, heated and pressurized by the fixing unit 16, and the toner image is fixed on the sheet, and then discharged to the paper discharge unit 18. .

  In the copying machine 1 of the present embodiment, the plurality of LED elements arranged in an array on the LPH 153 suppresses the variation in the amount of light emitted from each LED element caused by a temperature difference between the LED elements. , By monitoring the lighting time of each LED element from a single or a plurality of image data every predetermined unit time, predict the change in the amount of light emitted from each LED element, and based on that, correct the drive current value for each LED element Is characterized by correction control performed sequentially.

  Therefore, in the following, each LED element is monitored by monitoring the lighting time of each LED element from one or a plurality of image data for each predetermined unit time in the copying machine 1 of the present embodiment with reference to the flowchart of FIG. A detailed description will be given of the characteristics of the correction control in which the change in the amount of emitted light is predicted and the correction process is sequentially performed on the drive current value for each LED element.

  In the copying machine 1 of this embodiment, in step S4-1, as shown in FIGS. 3 and 4, the image data generated by the document take-in unit 12 is input by the CPU 10 to the unit time addition circuit unit 158b. . Then, the unit time addition circuit unit 158b aggregates the data amount of the first pixel to the n-th pixel corresponding to each LED element from the image data for each line from the head in the main scanning direction. The data is converted into the lighting time data of the LED element corresponding to each pixel, and sequentially added up and summed up over all the image data. For example, if the first pixel of the image data is 5 / 16-value data, the lighting time of the LED element corresponding to the first pixel is converted to 5 μsec, added, and totaled.

  Subsequently, in step S4-2, when image data is input by the unit time addition circuit unit 158b within a predetermined unit time from the start of counting the lighting time data of the LED elements corresponding to each pixel. (S4-2 YES), if the time within the predetermined unit time has elapsed from the start of the counting, the temperature of each LED element that is input and lit by the image data being input to the LPH 153 does not decrease, so the process returns to step S4-1. As described above, the lighting time data of the LED element corresponding to each pixel is added and totaled from the image data.

  In step S4-2, when the unit time addition circuit unit 158b does not input image data within a predetermined unit time from the start of counting the lighting time data of the LED elements corresponding to each pixel (S4). -2NO), since the temperature of the LED element that is turned on without image data being input decreases, the lighting time of the LED element corresponding to each pixel that is counted in the unit time addition circuit unit 158b in step S4-3. Data is transferred to and stored in the aggregate data storage memory unit 158c for each pixel.

  The predetermined unit time is controlled by a sub-scanning direction synchronization signal generated every time the image forming unit 15 completes the formation of the toner image on the paper or a signal generated in a predetermined number of lines in the sub-scanning direction. This is the time that is input to the unit time addition circuit unit 158b from the timing generation unit (not shown) and controlled by the unit time addition circuit unit 176b. The sub-scanning direction is the paper transport direction.

  Subsequently, in step S4-4, the lighting time data of the LED element corresponding to each pixel stored in the total data storage memory unit 158c is read by the peripheral data comparison circuit unit 158d. Then, for each pixel corresponding to the LED element, the lighting time data of the LED element corresponding to a pixel and a pixel in the vicinity of the pixel (for example, a pixel adjacent to the pixel or both adjacent pixels) is compared, A difference in lighting time of the LED element corresponding to each pixel is output and input to the correction data arithmetic circuit unit 158e. In addition, the pixel compared with a certain pixel for every pixel corresponding to a LED element is not limited to the vicinity of a certain pixel, What is necessary is just a predetermined pixel except a certain pixel and the pixel.

  Subsequently, in step S4-5, the correction data calculation circuit unit 158e compares the difference in lighting time of the LED elements corresponding to neighboring pixels for each pixel with a predetermined threshold (for example, 500 μsec). . When the correction data calculation circuit unit 158e determines that the difference in lighting time of the LED elements corresponding to neighboring pixels for each pixel is equal to or greater than a predetermined threshold (YES in S4-5), step S4- 6, since the temperature difference between the LED elements is large and the variation in the amount of emitted light is predicted to be large, the correction data processing circuit unit 158 a causes the light amount correction data storage unit 173 to return at a certain time (for example, the initial state). After the measurement data in which the variation in the amount of emitted light for each LED element is measured in advance is read and converted into initial correction data, a predetermined amount of correction data for reducing the variation in the amount of emitted light for each LED element is added to the initial correction data. New correction data of the drive current value for each LED element (for example, new correction data is correction data obtained by adding 1% of the initial correction data to the initial correction data. Data) is output and input into the correction data transfer circuit unit 158f.

  As described above, the correction data calculation circuit unit 158e adds a predetermined correction amount to the initial correction data based on the difference in lighting time of the LED elements corresponding to the neighboring pixels for each pixel, and the pixel In this configuration, new correction data of the LED element corresponding to each pixel is output, but the correction data calculation circuit unit 158e uses a predetermined function to make a difference between the lighting times of the LED elements corresponding to the neighboring pixels of each pixel and the initial correction. New correction data may be generated by inputting data. For example, the correction data calculation circuit unit 158e may generate new correction data using the function “new correction data = initial correction data × (1+ (lighting time difference / coefficient))”.

  Subsequently, in step S4-7, the new correction data is input to the light quantity correction circuit unit 160a after the new correction data is converted by the correction data transfer circuit unit 158f for input to the LPH 153. Then, the light amount correction circuit unit 160a corrects the drive current value S1 of the LED element input from the CPU 10 based on the new correction data for each LED element.

  Subsequently, in step S4-8, the image data input from the CPU 10 to the image data transfer circuit unit 158g is converted by the image data transfer circuit unit 158g and input to the LED driving IC 160. Then, based on the input converted image data and the corrected drive current value for each LED element, the drive current is set to each LED so as to keep the drive current value corrected for each LED element by the light amount correction circuit unit 160a. It is supplied to the element and controlled, and the lighting time of each LED element is controlled by the gradation correction circuit unit 160a. As a result, each LED element is lit without variation in the amount of emitted light.

  In step S4-5, when the correction data calculation circuit unit 158e determines that the difference in lighting time of the LED elements corresponding to neighboring pixels for each pixel is smaller than a predetermined threshold (for example, 500 μsec). (S4-5NO), in step S4-9, since the temperature difference between the LED elements is small and the variation in the amount of emitted light is small, the correction data processing circuit unit 158a reads the light amount correction data storage unit 173 at a certain time (for example, In the initial state, after the measurement data in which the variation in the amount of emitted light for each LED element is measured in advance is read and converted into the initial correction data, the initial correction data is input to the correction data transfer circuit unit 158f.

  Subsequently, in step S4-10, the initial correction data is converted to the LPH 153 by the correction data transfer circuit unit 158f and then input to the light amount correction circuit unit 160a. Then, the light amount correction circuit unit 160a corrects the drive current value S1 of the LED element input from the CPU 10 based on the initial correction data for each LED element.

  Subsequently, in step S4-11, the image data input from the CPU 10 to the image data transfer circuit unit 158g is converted by the image data transfer circuit unit 158g and input to the LED driving IC 160. Then, based on the input converted image data and the corrected drive current value for each LED element, the drive current is set to each LED so as to keep the drive current value corrected for each LED element by the light amount correction circuit unit 160a. It is supplied to the element and controlled, and the lighting time of each LED element is controlled by the gradation correction circuit unit 160a. As a result, each LED element is lit without variation in the amount of emitted light.

  The light quantity correction data storage unit 173 stores the measurement data in which the variation in the emitted light quantity for each LED element at a certain point in time (for example, the initial state) in the LPH 153 is stored in advance. Instead of the measurement data, correction data that suppresses the variation in the amount of emitted light for each LED element obtained from the measurement data is stored in the light amount correction data storage unit 173, and the correction data is read by the correction data processing circuit 158a. After the correction data is input to the correction data calculation circuit 158e or directly read from the light amount correction data storage unit 173 into the correction data calculation circuit 158e, as described above, the drive current value for each LED element is calculated. Corrected and input converted image data and corrected driving current for each LED element The drive current is supplied to each LED element so as to maintain the drive current value corrected for each LED element by the light quantity correction circuit unit 160a, and the gradation correction circuit unit 160a controls each LED element. The lighting time may be controlled. As a result, each LED element is lit without variation in the amount of emitted light. Further, when the correction data is directly read from the light amount correction data storage unit 173 into the correction data calculation circuit 158e, the LPH data control circuit unit 158 can be simplified, and thus the manufacturing cost can be reduced. .

  It should be noted that the peripheral comparison data comparison circuit 158d makes a determination in consideration of the influence of the LED element heat generation around a certain LED element, or the structure of the LPH 153 has a poor heat dissipation or is likely to generate heat. If the cumulative lighting time per unit time of a specific LED element and the rate of change in temperature change are different because the member is in the vicinity of the LED element, considering it in advance, the LED element corresponding to each pixel Processing for comparing the lighting time differences of the LED elements with different set values may be performed.

  As described above, the copying machine 1 of the present embodiment monitors the data amount of pixels corresponding to each LED element per predetermined unit time from the image data input to the LPH data control circuit unit 158. The data amount is converted into the lighting time for each LED element, and for each pixel, the difference between the lighting time of the LED element of the pixel and the pixel excluding the pixel is compared with a predetermined threshold value, and the comparison result Accordingly, the new correction data for each LED element is obtained by adding the initial correction data corresponding to each LED element or the initial correction data corresponding to each LED element to a predetermined correction data for reducing the variation in the amount of light for each LED element. The drive current value is corrected for each LED element based on the initial correction data or the new correction data, and is input to the light amount correction circuit unit 160a, and the input converted data Based on the image data and the corrected drive current value for each LED element, control is performed by supplying the drive current to each LED element so as to keep the drive current value corrected for each LED element by the light amount correction circuit unit 160a. Therefore, the temperature difference between the LED elements can be reduced even when image formation is continuously performed on a sheet without adding a new sensor. Variations can be suppressed. Therefore, an image having no density unevenness can be obtained on the paper.

  As described above, the unit time addition circuit unit 157b in the copying machine 1 according to the present embodiment uses the first pixel to the first pixel corresponding to each LED element from the image data for each line from the head in the main scanning direction. The data amount of the nth pixel is totaled, and the data amount is further converted into the lighting time data of the LED element corresponding to each pixel, and is sequentially added and summed over all the image data, and then the peripheral data The comparison circuit 158b is configured to compare the lighting time data of the LED element between the pixel for each pixel and the neighboring pixels, but the amount of data collected by the unit time addition circuit unit 157b is the lighting of the LED element. Since it corresponds to the time data, after the data amount for each pixel is aggregated by the unit time addition circuit unit 157b, the peripheral data comparison circuit 158b For each pixel corresponding to each child, the difference in data amount for each pixel corresponding to each LED element obtained by comparing the data amount between a certain pixel and its neighboring pixels is used to correct as described above. The data calculation circuit unit 158e may perform comparison with a predetermined threshold value (for example, a data amount corresponding to the lighting time of the LED element of 500 μsec) to obtain initial correction data or new correction data. Thus, similar to the configuration described above, the temperature difference between the LED elements can be reduced even when image formation is continuously performed on a sheet without adding a new sensor. The variation in the amount of emitted light can be suppressed, and an image having no density unevenness can be obtained on the paper.

  In addition, as described above, the copying machine 1 according to the present embodiment is configured so that the LPH data control circuit unit 158 receives the initial correction data for the drive current value for each LED element and the correction data for suppressing the variation in the amount of emitted light for each LED element. Although any of the new correction data is input to the light amount correction circuit unit 160a, the correction data is input from the correction data transfer circuit unit 158f of the LPH data control circuit unit 158 to the gradation correction circuit unit 160b. The lighting time for each LED element by the gradation correction circuit unit 160b may be corrected based on the correction data and the image data to reduce the variation in the amount of emitted light for each LED element.

  In addition, in order to suppress variations in the amount of emitted light for each LED element, either the initial correction data or the new correction data of the drive current value for each LED element from the LPH data control circuit unit 158 is sent to the light amount correction circuit unit 160a. The correction data described above from the LPH data control circuit unit 158 is input to the gradation correction circuit unit 160b and controlled by the light amount correction circuit unit 160a and the gradation correction circuit unit 160b based on the correction data and the image data. May be performed to reduce the variation in the amount of emitted light for each LED element.

  The present invention can be widely applied to image forming apparatuses such as printers and facsimiles in addition to copying machines, and is useful for reducing image density unevenness in an image forming apparatus provided with a light emitting diode print head. It is.

FIG. 2 is a block diagram showing a main configuration of a copier according to the present invention. These are the longitudinal cross-sectional views which show typically the principal part structure of the copying machine which concerns on this invention. These are figures which show the principal part structure part of LPH and a LPH data control circuit. These are the flowcharts which show the operation | movement of correction | amendment control of the drive current value for every LED element in the copying machine 1 of this embodiment.

Explanation of symbols

1 Copier 10 Central processing unit (CPU)
DESCRIPTION OF SYMBOLS 11 Document conveyance part 12 Document take-in part 13 Operation display part 14 Paper feed part 141a-141c Paper storage part 142 Paper conveyance part 15 Image formation part 151 Photosensitive drum 152 Developer 153 Light emitting diode print head (LPH)
154 Charger 155 Charger 156 Cleaning unit 157 Transfer roller 158 LPH data control circuit unit 158a Correction data processing circuit unit 158b Unit time addition circuit unit 158c Total data storage memory unit 158d Peripheral data comparison circuit unit 158e Correction data calculation circuit unit 158f Correction Data transfer circuit unit 158g Image data transfer circuit unit 159 Light emitting diode array (LED array)
160 LED drive IC
160a Light amount correction circuit unit 160b Gradation correction circuit unit 16 Fixing unit 17 Memory unit 18 Paper discharge unit

Claims (2)

Based on the light emitting diode element array in which a plurality of light emitting diode elements are arranged in an array, and image data and correction data, the drive current value is corrected for each light emitting diode element and corrected for each light emitting diode element. A light amount correcting means for supplying a driving current and controlling the driving current so as to maintain the corrected driving current value, and a gradation control means for controlling a lighting time for each light emitting diode element based on the image data And a light amount correction data storage means for storing light amount measurement data for each light emitting diode element, and a drive current value for each light emitting diode element based on the measurement data stored in the light quantity correction data storage means Correction data processing means for generating correction data for correcting the image, and an image forming apparatus comprising:
Summing data for storing the data amount for each pixel summed by the summing means and summing means for summing the data amount for each pixel corresponding to each light emitting diode element from a single or a plurality of image data at a predetermined time Storage means, peripheral comparison means for comparing and outputting a difference in data amount between a pixel and a predetermined pixel excluding the pixel, with respect to the data amount for each pixel stored in the total data storage means, and for each pixel A correction data calculation means for comparing the difference in data amount with a predetermined threshold, and generating and outputting the correction data or new correction data obtained by adding predetermined data to the correction data based on the comparison result; An image forming apparatus comprising: Based on the light emitting diode element array in which a plurality of light emitting diode elements are arranged in an array, and image data and correction data, the drive current value is corrected for each light emitting diode element and corrected for each light emitting diode element. A light amount correcting means for supplying a driving current and controlling the driving current so as to maintain the corrected driving current value, and a gradation control means for controlling a lighting time for each light emitting diode element based on the image data And a light quantity correction data storage means for storing correction data of the drive current value for each light emitting diode element,
An adding means for summing up the data amount of the pixel corresponding to each light emitting diode element from one or a plurality of image data at a predetermined time, and storing the data amount of the pixel summed up by the adding means for each pixel. Total data storage means, peripheral comparison means for comparing and outputting a difference in data amount between a pixel and a predetermined pixel excluding the pixel, with respect to the data amount for each pixel stored in the total data storage means, and the pixel Correction data calculation means for comparing the difference between the data amounts for each and a predetermined threshold value, and generating and outputting the correction data or new correction data obtained by adding predetermined data to the correction data based on the comparison result And an image forming apparatus.

Images