JP4706285B2 - LED array density correction method and image forming apparatus - Google Patents

Description

  The present invention relates to an LED array in which a plurality of LED elements whose lighting is controlled in accordance with image data are arranged in the main scanning direction, and in particular, a density correction method for an LED array suitable for a self-scanning LED array and the same The present invention relates to an image forming apparatus using the above.

  In a copying machine, a printer, a facsimile, and the like, an image forming apparatus is generally used to form an image. Recently, such an image forming apparatus is required to be further downsized and cost-reduced. . In order to respond to such a demand, instead of a conventional exposure apparatus using a laser diode and a polygon mirror, for example, a so-called element called an LED array has recently been utilized.

  This LED array is formed by arranging a plurality (large number) of LED (light emitting diode) elements in a line in the main scanning direction, and by controlling lighting of each LED element according to image data, Is written to form an electrostatic latent image. However, it is almost impossible to manufacture a plurality of LED elements manufactured on this LED array with uniform characteristics due to manufacturing problems.

  That is, according to the non-uniformity (variation) of the LED elements, the amount of light and the dot diameter of each LED element are different, resulting in non-uniformity (variation) in the drive current for driving each element. Differences in technology result in a difference in the energy of optical writing on the photoconductor, resulting in non-uniform toner density in the formed image.

  Therefore, conventionally, in order to suppress non-uniformity (variation) due to the manufacturing factors of these LED elements, for example, correction values for the individual LED elements are obtained in advance for the individual LED elements. A technique for correcting the amount of light of each LED element by storing the correction value in a storage device such as an EEPROM and installing the correction value is already known.

  However, when the LED array is actually used as an image forming apparatus, in addition to the above, the temperature of the element itself tends to increase depending on how the LED element is used. By the way, as is generally known, an LED element has a temperature characteristic that its light quantity decreases as its temperature increases. For this reason, if the amount of light decreases, the light energy to the photosensitive member decreases, so that the above-described density non-uniformity (variation) also occurs.

  As a solution to this problem, for example, in Patent Document 1 below, the temperature of the LED array is detected by a thermistor, and the detected value is A / D converted and encoded in the memory of the gamma correction unit. A technique for selecting one of a plurality of stored tables, correcting input image data, and outputting a fixed image has already been disclosed. Further, in Patent Document 2 below, correction is performed at a temperature at which the temperature of the LED element becomes the highest, so-called full lighting, thereby reducing non-uniformity (variation) in the amount of light during actual image formation. What to do is disclosed. Further, Patent Document 3 below includes light emission data processing means for generating light emission data of the LED array. The light emission data processing means converts image data into the number of bits matching the LED array. In addition, there has already been disclosed a technique for generating light emission data by converting image data in order to correct the light quantity characteristics of the LED array. Furthermore, in the following Patent Document 4, voltage control means for adjusting the voltage supplied to the LED array according to the temperature measurement result by the temperature sensor that detects the temperature of the LED array is provided. A technique for suppressing a decrease in the amount of light is disclosed.

In addition, Patent Document 5 below grasps the total number of pixels of image data and the current flowing through the LED elements against the movement (skew) of the imaging position caused by the LED array warping due to a temperature rise. A technique for correcting image data for forming an image has been reported.
Japanese Patent Laid-Open No. 11-075037 JP-A-11-254740 JP 2002-036622 A JP 7-214819 A JP 2004-174854 A

  However, in the above-described conventional techniques, particularly the techniques described in Patent Documents 1 to 4, the temperature is detected by providing a temperature sensor in the LED array, and the detection result is compared with the temperature-light quantity characteristic of the LED element ( The amount of light is corrected. Therefore, according to the techniques described in these Patent Documents 1 to 4, since it is necessary to provide a temperature measuring means such as a temperature sensor, the LED array itself becomes expensive, and in addition, in the element For this reason, there is a disadvantage that it is necessary to secure an installation space.

  On the other hand, in the above-mentioned Patent Document 5, unlike the above-described prior art, the image data is corrected without using the temperature measuring means. However, the object is to warp the LED array due to the temperature rise. This is to eliminate the movement (skew) of the imaging position caused by this, and is different from the density correction intended by the present invention described later.

  The present invention has been made in view of the above-described prior art, and it is possible to reduce density unevenness (variation) during image formation caused by temperature characteristics of an LED element in which the amount of light decreases with increasing temperature. However, without using a temperature measuring means such as a temperature sensor as in the above prior art, it is not necessary to add parts that lead to cost increase of the device and expansion of space. It is an object of the present invention to provide an LED array density correction method capable of making the density uniform at low cost, and to provide an image forming apparatus using the method.

  In order to achieve the above object, according to the present invention, first, in an LED array in which a plurality of LED elements that are controlled to be turned on according to image data are arranged in the main scanning direction, the light quantity due to the temperature rise of the LED elements. An LED array density correction method for correcting density fluctuations caused by fluctuations, wherein the light quantity fluctuation due to the temperature rise of the LED elements is previously related as the number of LED elements lit in the sub-scanning direction during image formation. The number of lighting in the sub-scanning direction of each LED element during actual image formation is calculated and stored according to the calculated number of lighting in the sub-scanning direction of each LED element during actual image formation. Based on the relationship stored in the storage means, a correction value for the light amount fluctuation amount of each LED element is obtained, and each LED of the LED array is determined by the correction value. Density correction method of the LED array for controlling the lighting operation of the child is provided.

  Further, in the present invention, in the correction method, the storage means is provided with light amount fluctuations due to a temperature rise of the LED element classified into a plurality of patterns according to different lighting efficiencies of the LED elements. At the time of image formation, it is preferable to select one pattern depending on the lighting efficiency of each LED element, and to obtain a correction value for the light quantity fluctuation amount of each LED element based on the light quantity fluctuation of the selected pattern. Here, the lighting efficiency of the LED element can be a ratio at which the LED element is lit for each image to be formed in a certain print job. Alternatively, the relationship between the light amount fluctuation of the LED element and the lighting number recorded in advance in the storage means is such that the lighting number has a different width so that the light quantity fluctuation of the LED element changes step by step in a predetermined unit. It is preferable that the setting is divided. Further, a correction value for the light amount fluctuation amount of the LED element obtained in the above is stored, and together with the stored correction value, based on the relationship between the lighting number of the LED element stored in the storage means and the light amount fluctuation. The correction value of each LED element can be obtained from the correction value of each LED element obtained in this way.

  Further, according to the present invention, in the correction method, when the series of jobs are completed, the corrected light amount correction value of the LED element is returned to the initial value, or the series of jobs is completed and a predetermined value is obtained. When a new job is started without elapse of the time, it is possible to control the lighting operation of each LED element by estimating the temperature variation of the LED element due to the elapsed time until the start of the new job. It is.

  In addition, in the present invention, in order to achieve the above object, an LED array in which a plurality of LED elements whose lighting is controlled at least according to image data is arranged in the main scanning direction, and is exposed to the LED array. An image forming apparatus including a photosensitive unit that forms an image corresponding to image data, and further, in advance, a light amount variation of the LED element due to a temperature rise, and a lighting number of the LED element in the sub-scanning direction at the time of image formation. Storage means stored as a relationship, means for calculating the number of lighting in the sub-scanning direction of each LED element at the time of actual image formation, and the sub-scanning direction of each LED element at the time of actual image formation calculated above. Means for obtaining a correction value for the light quantity fluctuation amount of each LED element based on the relationship stored in the storage means according to the lighting number of The image forming apparatus is provided and a drive circuit for controlling the lighting operation of the LED elements of the array.

  In the image forming apparatus of the present invention, it is preferable that the drive circuit controls a drive voltage or current to each LED element of the LED array, and further, with respect to the amount of light quantity fluctuation of the obtained LED element. It is preferable to include second storage means for storing the correction value.

  According to the present invention, it is possible to suppress nonuniformity (variation) in density at the time of image formation caused by the temperature characteristics of the LED element, such as a decrease in the amount of light as the temperature increases, and the temperature as in the prior art. Providing a density correction method for an LED array that can be realized at low cost and an image forming apparatus using the same, because it is not necessary to add a component that leads to an increase in cost and an increase in apparatus space, such as preparing a sensor. Demonstrates the excellent effect of being possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an image forming apparatus 100 including an LED array 110 formed by arranging a plurality of LED (light emitting diode) elements 101 in a line in the main scanning direction according to an embodiment of the present invention. According to the LED array 110, each LED element 101 is controlled to be turned on in accordance with image data, so that, for example, on a photosensitive drum 130 such as a copying machine, a printer, or a facsimile machine via a gradient index rod lens 120 or the like. Optical writing is performed to form an electrostatic latent image.

  FIG. 2 shows a circuit configuration including the LED array 110 shown in FIG. 1 and its control unit. In the figure, an LED printer head (LPH) 200 is configured by arranging a plurality (N in this example) of LED chips 103 formed by arranging a plurality of LED elements 101 in a line in the main scanning direction. In each LED chip 103, the LED element 101 is driven and controlled by the driver IC 210. Here, a so-called self-scanning LED (SLED) chip is used as the LED chip 103 composed of the plurality of LED elements 101. However, the present invention is not limited to this, and a plurality of ordinary LEDs may be arranged.

  On the other hand, the image signal from the image forming unit 300 is supplied to the LPH 200 described above. The image forming unit 300 is connected to, for example, an image pattern generation circuit 310 that generates an image to be formed as an electrostatic latent image on a photoconductor as an electric signal (image pattern), as shown in FIG. The storage device 320 further includes a CPU 330 connected to the circuit via a bus line 305, and a memory unit 340 such as a ROM, a RAM, and an NVM. In addition, a reference numeral 400 in the drawing indicates a power supply control circuit. The power supply control circuit 400 supplies a power supply voltage to the LPH 200 and is also connected to the above-described units via the bus line 305.

  That is, according to the LPH 200 configured as described above, a plurality of LED (light emitting diode) elements 101 arranged in a line in the main scanning direction are respectively controlled by the power supply control circuit 400 and supplied with a power supply voltage. The lighting / non-lighting is controlled based on the image pattern from the image pattern generation circuit 310.

  Next, in the self-scanning LED described above, the characteristics (“LED temperature-light quantity characteristics”) obtained when the LED elements are driven continuously with the driving conditions (voltage, current) constant are shown in FIG. Shown in That is, as is clear from the characteristic curve shown in the figure, the LED element has a temperature at which the number of lighting (number of times) increases with the lapse of time (horizontal axis) and the amount of light decreases as the temperature increases. Show properties. This means that an LED element that is frequently turned on corresponds to an input image pattern (image data), and the element temperature increases as the number of times of lighting increases.

  However, in an image forming apparatus, when the temperature of an LED element increases with an increase in the number of times the LED element is turned on, and the amount of light of the element decreases, the density of an image obtained at the corresponding location decreases. In the case of continuous print output, the density differs between the first and 100th print outputs. Such a phenomenon may be recognized relatively easily even in an actual copying machine, printer, facsimile, or the like, that is, the print quality is deteriorated. Therefore, a density correction method related to the number of lighting times of the LED element is necessary.

  Further, FIG. 4 shows “lighting number-light quantity characteristic” of one pixel (LED element) based on the “LED temperature-light quantity characteristic” shown in FIG. Here, on the horizontal axis, the number of lighting of a certain pixel (LED element) during a series of operations is shown in units of mega dots (Mdot).

Here, the calculation is made assuming a self-scanning LED employed in a 35 ppm (pages / min) class model with a resolution of 1,200 dpi × 1,200 dpi, and in this case, the sub-scanning direction (the above main scanning direction) The number of lighting in the vertical direction of the sub-scanning direction and in the vertical direction of the paper is, for example, the following for one minute when printing on black on A4 horizontal size paper (297 × 210 mm). It becomes like this.
Number of lights in the sub-scanning direction on one sheet = 1,200 dpi x 1/24 x 210 mm = 9,921 dots
The number of lighting at 35 ppm (pages / min) = 9,921 dots × 35 = 347,235 dots / min Further, for example, in 5 minutes, the following occurs.
347,235dot / min × 5 = 1,736,175dot ≒ 1.7Mdot
As described above, according to the “lighting number-light quantity characteristic” shown in FIG. 4, it is possible to grasp the tendency of the temperature increase due to the total lighting number of a certain pixel (LED element).

  Note that FIG. 4 shows the “number of lighting-light quantity characteristics” when the LED elements are continuously lit. However, in actuality, however, the image data continuously lights the LED elements. It is rare to be. Therefore, it is necessary to correct the light amount correction value according to the lighting ratio. By the way, the reduction in the amount of light when the LED elements are continuously lit is experimentally determined. The light amount reduction graph at that time is taken as 100%, and the lighting efficiency of the LED elements is further 80%, 60%, 40 FIG. 5 shows the decrease (%) in the amount of light when sequentially decreasing to% and 20%. These lighting number-light quantity characteristics are obtained in advance and stored in the storage device 320 connected to the image pattern generation circuit 310.

  The lighting efficiency of each LED element is based on the image pattern (image data) from the image pattern generation circuit 310, that is, by using a signal for controlling lighting / non-lighting of the LED element, It is requested in this way.

Now, for example, let X be the number of pixels to be lit in the sub-scanning direction per sheet of A4 paper (lighting number), and the total number of pixels (lighting number) Xtotal and the average number of pixels (lighting number) when the print output is m sheets. Number) Xave is as follows.
Xtotal = X1 + X2 + X3 ... Xm-1 + Xm
Xave = (X1 + X2 + X3... Xm-1 + Xm)) / m

  Next, a simple example of the process until the light amount correction value in each LED element is determined using the total pixel number (lighting number) Xtotal and the average pixel number (lighting number) Xave described above will be described. Now, for example, with a resolution of 1,200 dpi × 1,200 dpi, the total number of pixels (9,921 dots) in the sub-scanning direction (paper vertical direction) is 100%. On the other hand, from the image pattern (image data), Xave = 1,500 dots and Xtotal = 300,000 dots are obtained, 1,500 / 9,921 × 100 = about 15% is calculated as the lighting efficiency of the LED element. In this case, the lighting efficiency = 15% lighting number-light quantity characteristic can also be obtained by the interpolation method, but here, the lighting efficiency = 20%, which is closest to 15% from the lighting number-light quantity characteristic of FIG. Select a characteristic curve. The light quantity at the lighting number = 300,000 dots (0.3 Mdot on the horizontal axis in FIG. 5) on the 20% characteristic curve is the reduced light quantity obtained when the total number of pixels (lighting number) Xtotal = 300,000 dots. . Therefore, it is understood that a desired light amount can be obtained from the LED element regardless of the temperature change by setting a light amount correction value based on the reduced light amount and correcting it by the control means. .

  Next, the details of the light amount correction based on the number of lighting-light amount characteristics, that is, the LED array density correction method, whose principle has been described above, will be described below. By the way, as described above, in order to reduce non-uniformity in the amount of light between the LED elements due to the non-uniformity (variation) of the LED elements themselves and the mounting state, voltage control and current control are usually performed on the LED elements. Control means for correcting the amount of light, such as lighting time control, is provided. Also in the above-described embodiment of the present invention, for example, the driver IC 210 in FIG. 2 includes the control unit described above, and the light amount is adjusted based on the correction value corrected thereby.

  In the present invention, in addition, as described above, the LED element is controlled based on the characteristic that the amount of light decreases with the number of lighting of the LED element (the graph of FIG. 4 above). Therefore, when correcting each LED element in real time, the circuit configuration of the control means becomes complicated, which leads to an increase in the scale of the circuit and the like, which is not preferable. Therefore, in the present invention, by using the total number of pixels (the number of lighting) Xtotal and the average number of pixels (the number of lighting) Xave, the amount of light increases as the temperature rises without using temperature measuring means such as a temperature sensor. An image forming apparatus that suppresses non-uniform density during image formation caused by the temperature characteristics of the LED element that decreases, and that can be realized at low cost without increasing the cost of the apparatus or adding parts. I will provide a.

  6A and 6B are flowcharts illustrating details of density correction (LED element light amount correction) executed by the image forming apparatus of the present invention. This is sequentially executed, for example, at a predetermined timing by the CPU 330 and the memory unit 340 shown in FIG.

  In FIG. 6, when processing is started, first, the light amount correction value of each LED element is set (step S1). Here, the initial value of the light amount correction value is set, or the correction value set in the immediately preceding job, that is, the correction value calculated in step S19 described later is set. Subsequently, the counter is initialized before the image forming apparatus starts print output (step S2). Here, “m” indicates the number of output sheets and “n” indicates the number of lines.

  Subsequently, the image forming apparatus starts image formation (step S3), performs image processing necessary for image data in the main scanning direction, and prepares main scanning image data (step S4). Thereafter, according to the image data obtained in the above step S4, that is, according to the obtained image data, lighting / extinguishing of each LED element is determined, and thereby the number of lighting for each LED element is counted ( Step S5). Thereafter, it is determined whether or not the output to one sheet is completed (step S6). As a result, if it is determined that the output has been performed ("Yes"), the process proceeds to the process described below. If it is determined that it is not output ("No"), the number of lines "n" is incremented by "1" (step S7), that is, the count of LED elements to be lit is increased by one, The process returns to step S4, and the above process is repeated again.

  On the other hand, if it is determined in step S6 that the output to one sheet has been completed, “Yes”, the process proceeds to step S8. That is, in this step S8, the total number of pixels (lighting number) Xtotal of each LED element is calculated. Subsequently, in step S9, the average number of pixels (lighting number) that is the number of lighting of the LED elements per sheet. Xave is calculated. In step S10, more specifically, the lighting efficiency is obtained from the calculated average number of pixels (lighting number) Xave from the result of step S9. Thus, the closest characteristic curve is selected from the plurality of characteristic curves shown in FIG. Thereafter, in step S10, a necessary light amount correction value is derived from the selected characteristic curve and the total number of pixels (lighting number) Xtotal, and in step S12, the light amount correction unit applies each LED element to each LED element. Correction based on the derived correction value is performed.

  Thereafter, in step S13, it is determined whether or not the job of the image forming apparatus has been completed. If the job has not been completed ("No"), the process returns to step S3 again. Yes "), the process proceeds to the process described below. That is, the above light amount correction is performed for each output sheet, and an optimum correction value is always obtained and held at an appropriate light amount.

  After the above, first, in step S15, it is determined whether or not the light amount correction has been performed in the job executed above. As a result, if the correction is not performed (“No”), the process is terminated as it is. On the other hand, if the correction is performed (“Yes”), whether or not a certain time has passed. Is determined (step S16). That is, it is determined whether the LED element has completely returned to the initial temperature after a certain period of time. As a result, if the LED element is cooled (“Yes”), it is not necessary to perform light amount correction in the next process, so the light amount correction value is returned to the initial value in step S17, and the series of processes is terminated.

  On the other hand, as a result of the determination in step S16, when the image forming apparatus is to be operated, that is, when the next new print job is performed even though the predetermined time has not elapsed ("No"), the LED The temperature state of the element is obtained from the elapsed time, and the correction value is calculated (step S18). Further, the calculated value is recorded as the correction value in the next job (step S19), and the series of processes is completed. . At this time, the calculated correction value is stored in a location (or a different recording device) different from the number of lighting-light quantity characteristics in FIG. According to this, the use of the LED element stored in the storage means is used, and the correction value is set appropriately in the next job even when the LED element has not completely returned to the initial temperature. Can be performed.

  In the calculation of the light amount correction value from the elapsed time here, similarly to the above, the temperature of the LED element calculated by the total pixel number (lighting number) Xtotal and the average pixel number (lighting) for each sheet of paper. From the result of Xave, the characteristic curve in FIG. 5 is selected to determine the temperature state of the LED element, and the light amount correction value is determined.

  In step S10, the light quantity correction value is determined by selecting and setting a suitable characteristic curve from the plurality of characteristic curves based on the lighting efficiency (%) calculated from the average number of pixels (lighting number) Xave. In that case, in the example of FIG. 5, the example classified into five stages of 80%, 60%, 40%, and 20% including 100% is shown. However, the light quantity is more subdivided. Needless to say, the correction value can be set more accurately. However, the degree of fine classification is appropriately set depending on the required accuracy of light amount correction.

  In addition, when determining a necessary correction value based on the selected / set suitable characteristic curve, as shown in FIG. It is preferable that the correction value to be changed changes in a step-like manner. This is indicated by corrections (1) to (7) in FIG.

  In such a method, for example, the correction value of the light amount changes in increments of 1%. Therefore, in the worst case, there is a possibility that the correction is -1% with respect to the initial value. Obviously, if you need to: Alternatively, various methods are conceivable such that the setting of the width of the number of times of lighting for each step is within ± 0.5% by appropriately moving on the horizontal axis.

  According to the above processing flow, each LED element whose light intensity decreases due to temperature rise due to lighting can be individually corrected at low cost without increasing the cost of the apparatus or adding parts. It becomes.

  Subsequently, a print output obtained by the image forming apparatus (LED array density correction method) of the present invention described in detail above, and a print output obtained when the density correction method is not performed as a comparative example, This will be described with reference to FIGS. 8 (a) and 8 (b), the LED elements provided in the image forming apparatus continuously perform image formation in both cases. In the example of the present invention shown in FIG. As described above, correction is performed due to a decrease in the amount of light due to temperature. On the other hand, the comparative example in FIG. 8B shows a case where the amount of light correction is not performed as in the present invention.

  When there is an image in which a certain LED element is continuously lit in the sub-scanning direction as shown in the figure, the temperature rise of the LED element has not started yet for the first and second sheets of print output. For this reason, there is no decrease in the amount of light and the density appears dark. However, in the case of continuous output, when the temperature rises in a certain LED element of the LED array and the light quantity decreases, as shown in FIG. Arise. Furthermore, if a strip-shaped black image is formed in the main scanning direction on the 100th sheet, the light and darkness that is obtained appears clearly, especially for LEDs with reduced light intensity and LEDs that have not decreased. It will end up. On the other hand, as shown in FIG. 8 (a), the print output obtained by the LED array density correction method of the present invention is shaded between the first and 99th sheets regardless of the position of the LED array. Therefore, even in the 100th sheet, the striped black image in the main scanning direction has the same shade as the striped black portion in the vertical direction (the lower portions of FIGS. 8A and 8B). Comparison).

  As described above in detail, according to the density correction method of the LED array according to the present invention, the amount of light decreases as the temperature rises. Can be suppressed. Further, it is not necessary to add a component that leads to cost increase and apparatus space expansion, such as preparing a temperature sensor as in the prior art, and therefore, an image forming apparatus capable of making the density uniform at low cost is provided. Can do.

  The present invention relates to an LED array in which a plurality of LED elements whose lighting is controlled in accordance with image data are arranged in the main scanning direction, and in particular, a density correction method for an LED array suitable for a self-scanning LED array and the same And is industrially applicable.

1 is a configuration diagram for schematically illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a circuit diagram illustrating an example of a circuit configuration including a control unit of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the LED temperature-light quantity characteristic for demonstrating the principle in the density correction method of the LED array of this invention. It is a figure which shows the lighting number-light quantity characteristic of the LED element used in the density | concentration correction method of the LED array of this invention. FIG. 5 is a diagram showing lighting number-light quantity characteristics obtained by classifying the lighting number-light quantity characteristics of FIG. 4 according to the lighting efficiency of LED elements. (A), (b) is a flowchart explaining the detail of the density | concentration correction method of the LED array by the lighting number-light quantity characteristic of this invention. In the density correction method of this invention, it is a figure which shows an example of the setting method of the lighting number-light quantity characteristic for obtaining the step-shaped correction value of a fixed step. (A), (b) is a figure which compares the state of the print output obtained by the density correction method of the LED array of this invention with the case where this density correction method is not performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 LED (light emitting diode) element 103 LED chip 110 LED array 120 Rod lens 130 Photosensitive drum 200 LED printer head (LPH)
210 Driver IC
DESCRIPTION OF SYMBOLS 300 Image formation part 305 Bus line 310 Image pattern generation circuit 320 Memory | storage device 330 CPU
340 Memory unit 400 Power supply control circuit

Claims (7)

Image formation comprising: an LED array in which a plurality of LED elements that are controlled to be turned on according to image data are arranged in the main scanning direction; and a photosensitive means that is exposed by the LED array to form an image corresponding to the image data In the apparatus, a density correction method of the LED array for correcting density fluctuation caused by light quantity fluctuation due to temperature rise of the LED element,
In advance, the light quantity fluctuation due to the temperature rise of the LED element is stored in the storage means as a relationship with the number of lighting of the LED element in the sub-scanning direction at the time of image formation,
Calculate the number of lighting in the sub-scanning direction of each LED element during actual image formation,
Based on the relationship stored in the storage unit, the correction value for the light amount fluctuation amount of each LED element is obtained based on the number of lighting in the sub-scanning direction of each LED element at the time of the actual image formation calculated.
The lighting operation of each LED element of the LED array is controlled by the correction value,
In the storage means, one LED element at the time of actual image formation with respect to the number of pixels that one LED element can record in the sub-scanning direction per sheet of paper at a predetermined resolution, due to the temperature rise of the LED element. Is the ratio of the average number of pixels per sheet of the number of lights lit at a predetermined resolution, and is the ratio of the calculated number of lights in the sub-scanning direction to the number of pixels in the sub-scanning direction Depending on the efficiency , a graph showing the relationship between the total number of pixels and the amount of light in a predetermined number of sheets of a single LED element lit at a predetermined resolution during actual image formation is prepared by being classified into a plurality of characteristic curves. At the time of the actual image formation, a single characteristic curve is selected according to the lighting efficiency of each LED element, and based on the light quantity fluctuation of the selected characteristic curve, A density correction method for an LED array, characterized in that a correction value for a light quantity fluctuation amount of each LED element is obtained.   2. The density correction method according to claim 1, wherein the relationship between the light amount fluctuation of the LED element recorded in advance in the storage means and the lighting number is such that the light quantity fluctuation of the LED element changes stepwise in a predetermined unit. A density correction method for an LED array, wherein the number of lighting is divided and set with different widths. 2. A density correction method for an LED array according to claim 1, wherein when the fixed time has elapsed after a series of jobs are completed, the corrected light quantity correction value of the LED element is returned to an initial value. .   2. The density correction method according to claim 1, wherein when a series of jobs are completed and a new job is started without lapse of a predetermined time, an LED element according to an elapsed time until the start of the new job. A method for correcting the density of an LED array, which estimates a temperature fluctuation of the LED array and controls the lighting operation of each LED element. An image comprising: an LED array in which a plurality of LED elements whose lighting is controlled at least in accordance with image data are arranged in the main scanning direction; and a photosensitive means that is exposed by the LED array to form an image corresponding to the image data A forming device,
Storage means for storing in advance the light amount fluctuation due to the temperature rise of the LED element as a relationship with the number of lighting of the LED element in the sub-scanning direction at the time of image formation;
Means for calculating the number of lighting in the sub-scanning direction of each LED element during actual image formation;
Means for obtaining a correction value for the light amount fluctuation amount of each LED element based on the relationship stored in the storage means by the number of lighting in the sub-scanning direction of each LED element at the time of actual image formation calculated above;
A drive circuit for controlling the lighting operation of each LED element of the LED array by the correction value,
In the storage means, one LED element at the time of actual image formation with respect to the number of pixels that one LED element can record in the sub-scanning direction per sheet of paper at a predetermined resolution, due to the temperature rise of the LED element. Is the ratio of the average number of pixels per sheet of the number of lights lit at a predetermined resolution, and is the ratio of the calculated number of lights in the sub-scanning direction to the number of pixels in the sub-scanning direction Depending on the efficiency , a graph showing the relationship between the total number of pixels and the amount of light in a predetermined number of sheets of a single LED element lit at a predetermined resolution during actual image formation is prepared by being classified into a plurality of characteristic curves. At the time of the actual image formation, a single characteristic curve is selected according to the lighting efficiency of each LED element, and based on the light quantity fluctuation of the selected characteristic curve, An image forming apparatus characterized in that a correction value for a light quantity fluctuation amount of each LED element is obtained. 6. The image forming apparatus according to claim 5 , wherein the drive circuit controls a drive voltage or a current to each LED element of the LED array. 6. The image forming apparatus according to claim 5 , further comprising a second storage unit for storing a correction value for the light amount fluctuation amount of the LED element obtained as described above. .

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