JP2005074906A - Image forming apparatus and image quality control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out correction of a quantity of light of an LED device as a light source of an exposing device in an adequate range in an image forming apparatus. <P>SOLUTION: This image forming apparatus 10 has a light quantity correction value calculating section 20. When the quantity of light of an LED 142 forming the exposing device 140 of the image forming apparatus is corrected, the light quantity correction value calculating section 20 compares an output of a first test pattern obtained by using the exposing device 140 with that of a second test pattern obtained by not using the exposing device 140. When the second test pattern has a defective in an image, the light quantity correction value calculating section 20 judges whether or not the defective can be corrected by the correction of the quantity of light of the LED device. When it is judged that the defective can be corrected, only the defective in the image is corrected by the correction of the quantity of light of the LED. The variation of the quantity of light of the LED is corrected by calculating correction data of the first test pattern. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image quality adjustment system for adjusting density unevenness and image quality defect of an output image by correcting light quantity of a light emitting element.

  An image forming apparatus that uses an electrophotographic process includes an exposure device for forming an electrostatic latent image on a photosensitive drum. As this type of exposure apparatus, there is one in which a light source is configured by arranging a plurality of LED (Light Emitting Diode) elements in a straight line or a staggered pattern.

  Generally, since the light emission characteristics of these LED elements vary, a desired exposure result may not be obtained when these elements are driven on the assumption that they have a certain light emission characteristic. Therefore, in this case, it is necessary to correct the light quantity of the LED element.

  As a conventional light amount correction method, for example, as disclosed in Patent Document 1, correction data corresponding to variations in light emission characteristics of each LED is stored in advance in a ROM (Random Access Memory), and based on this correction data. There is a method of making the light quantity of each LED uniform by controlling the drive current. Patent Document 2 discloses a technique for suppressing variations in the amount of light between LED elements by dividing the LED elements into a plurality of groups and performing light amount correction that maintains the total light amount of the groups at a constant value. ing. In this specification, the technique described in Patent Document 1 is referred to as a first conventional technique, and the technique described in Patent Document 2 is referred to as a second conventional technique.

JP-A-62-200966 JP-A-6-143682

  On the other hand, when a plurality of LEDs are disposed as light sources of the exposure apparatus in the image forming apparatus, the distance between the photosensitive drum and each LED element varies depending on the mounting accuracy. In such a state, as in the first and second prior arts described above, even if the drive currents flowing through the LED elements are corrected and the light amounts of all the LED elements are made uniform, the arrangement direction of these LEDs (hereinafter referred to as the LED arrangement direction) , It is unavoidable that uneven exposure occurs in the “main scanning direction”. This exposure unevenness eventually becomes density unevenness in the main scanning direction and an image quality defect in the output image, and becomes a factor that deteriorates the image quality. Accordingly, the correction of the light amount of the LED element must also take into account the factors caused by mounting in the image forming apparatus.

  Such light amount correction is disclosed in Patent Document 3 (referred to as a third prior art). In the third prior art, the test pattern is output by the image forming apparatus and read by the image reading apparatus. The read test pattern is converted into density data, and the light amount correction data of the LED element is changed according to the density data of the test pattern. Therefore, with this technology, it is possible to perform corrections that take into account variations in the amount of LED light that occurs when mounted on an image forming apparatus. Further, even if the light emission characteristics of the LED elements change over time, testing can be performed as needed. By outputting the pattern and converting the correction data, appropriate light quantity correction is always performed.

JP-A-5-42682

  By the way, the cause of density unevenness and image quality defect in the image forming apparatus is not limited to the above-described variation in the light amount of the LED elements. For example, when charging unevenness occurs when the photosensitive drum is charged to a predetermined potential by the charger, density unevenness also occurs in the output image. In addition, when there are scratches or adhered substances on the photosensitive drum, streaky image quality defects may occur in the output image.

However, in the above-described conventional techniques (first to third conventional techniques), even if the density unevenness or image quality defect is not caused by the light quantity variation of the LED element, the light quantity correction of the LED element is performed based on the density unevenness or the image quality defect. In this case, the light amount correction for the LED element is overcorrected, and the final output image quality adjustment is not performed correctly.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an image forming apparatus and an image quality adjustment system capable of correcting the light amount of LED elements within an appropriate range.

In order to solve the above-described problems, an image forming apparatus according to the present invention includes a photoconductive image carrier, charging means for charging the image carrier to a predetermined potential, and a plurality of devices arranged in a predetermined direction. An exposure unit that has a light emitting element, exposes the surface of the image carrier charged to the predetermined potential by the light emitted from the light emitting element, and attaches a developer to the surface of the image carrier, and an image formed by the developer. An image forming means having a developing means for forming the image, an output means for outputting an image formed by the developing means to a predetermined medium, an image processing means for reading the image and converting it into density data, and based on the image data And controlling image formation by the image forming unit, and causing the image forming unit to perform image formation using the exposure device, and to perform image formation without using the exposure device. Control means for performing the second control, and when the first control by the control means is performed and the image output to the medium by the output means is read by the image processing means, the image processing means A light amount correction information generating means for generating light amount correction information for correcting the light amounts of the plurality of light emitting elements based on density data obtained from the light amount, and a light amount for correcting the light amounts of the plurality of light emitting elements based on the light amount correction information. Based on the density data obtained from the image processing means when the second control is performed by the correction means and the control means, and the image output to the medium by the output means is read by the image processing means, A first discriminating unit that discriminates whether or not there is an image quality defect; and when the discriminating unit determines that there is an image quality defect, the image quality defect is And a second discriminating unit that discriminates whether or not the light-emitting element can be repaired by correcting the light amount of the light-emitting element. In this case, the light quantity correction means is controlled so that the light quantity correction of the light emitting element corresponding to the occurrence position of the image quality defect is not performed.
According to such an image forming apparatus, the presence / absence of an image quality defect is determined. As a result, when there is an image quality defect, only the image quality defect determined to be corrected by the LED light amount correction is corrected by the LED light amount correction. Therefore, the light quantity correction of the LED is performed within an appropriate range.

Further, in a preferred embodiment, the predetermined image obtained as a result of the first control is formed by stepwise arranging a plurality of patterns having different gradation area ratios in a direction orthogonal to the arrangement direction of the light emitting elements, The light amount correction by the light amount correction unit is performed for each of the plurality of patterns having different gradation area ratios.
In a preferred embodiment, the light amount correction information generating means manages the light emitting elements as a plurality of light emitting element groups, and based on a deviation from an average value of the density corresponding to each light emitting element in the light emitting element group. First light amount correction information for correcting the light amount of each light emitting element is calculated, and the average value of the density corresponding to each light emitting element in the light emitting element group is further deviated from the average value obtained by averaging all light emitting element groups. Based on the above, second light amount correction information for correcting the light amount of each light emitting element group is calculated.

  In order to solve the above-described problem, an image quality adjustment system according to the present invention includes the image forming unit, the control unit, the light amount correction information generation unit, the light amount correction unit, the first determination unit, and the first determination unit. An image forming apparatus having two determination means; the image processing means; a connection means for electrically connecting the image forming apparatus and the image processing apparatus; and the density data supplied from the image processing means. And an interface unit that delivers the image to the image forming apparatus.

<First Embodiment: Image Forming Apparatus>
FIG. 1 is a schematic diagram of an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 includes an image forming unit 100 and an image processing unit 200.

<1-1: Image Forming Unit 100>
The image forming unit 100 includes four image forming engines 110Y, 110M, 110C, and 110K corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black), respectively. Since the basic configuration of each image forming engine is common, the image forming engine 110Y will be described here.

The image forming engine 110Y includes a charging device 130, an exposure device 140, a developing device 150, and the like arranged around a cylindrical photoconductive drum 120 having photoconductivity.
The charging device 130 is for charging the photosensitive drum 120 that is rotationally driven. In the present embodiment, the charging device 130 is a BCR (Bias Charging Roller) that charges the surface of the photosensitive drum 120 by contacting a roll-shaped member. : Roller type charger) is used. By this charging device 130, the surface potential of the photosensitive drum 120 becomes a predetermined charging potential.
There are various charging modes, such as those using a direct current BCR, an alternating current BCR, or a charging brush, and those using corona discharge, but the effect according to the present embodiment can be obtained by using any charging means. be able to.

  The exposure device 140 is a device that irradiates the photosensitive drum 120 charged to a predetermined charging potential by the charging device 130 with an exposure beam based on the output image. The surface potential of the surface irradiated with the beam on the surface of the photosensitive drum 120 is reduced to a predetermined level due to the photoconductivity of the photosensitive drum 120. Accordingly, an electrostatic latent image based on the output image is formed on the surface of the photosensitive drum 120 exposed by the exposure device 140.

FIG. 2 is a view for explaining the light source arrangement in the exposure apparatus 140. A plurality of LEDs 142 are disposed on the light source substrate 141 in a direction parallel to the rotation axis of the photosensitive drum 120. These LEDs 142 are each driven based on a drive signal supplied from the LED drive circuit 232 of the image processing unit 200.
The LEDs 142 are arranged in a staggered manner on the light source substrate 141 in order to increase the mounting density. In addition, a rod lens array 143 is provided between the light source substrate 141 and the photosensitive drum 120, and beams emitted from the respective LEDs 142 are collected by the rod lens array 143 and connected to the surface of the photosensitive drum 120. Imaged. This rod lens array 143 has its shape, material, arrangement condition, etc. determined so that the beams emitted from the LEDs 142 arranged in a staggered manner are imaged in a straight line on the surface of the photosensitive drum 120. Has been.
FIG. 3 is a layout diagram of the LEDs 142. In this embodiment, 256 LEDs 142 are arranged in a staggered manner for each element group with one element group. The total number of element groups is 58. Therefore, the total number of LEDs 142 is 14848. Further, the array density of image forming points on the surface of the photosensitive drum 120 by the LED 142 is 1200 dpi (dot per inch). In the present embodiment, each element group in which the LEDs 142 are gathered is expressed as “element group Nx (x = 1, 2,..., 58)”.

In FIG. 1, a developing device 150 is a device that visualizes an electrostatic latent image formed on the surface of the photosensitive drum 120. The developing device 150 visualizes the electrostatic latent image by adhering the developer (toner) conveyed on a developing sleeve (not shown) to the electrostatic latent image formed on the surface of the photosensitive drum 120. To do. The toner moves from the developing sleeve to the surface of the photosensitive drum 120 due to a potential difference between the potential generated on the developing sleeve by a predetermined developing bias and the surface potential of the photosensitive drum 120, and adheres. Therefore, the toner adheres only to the portion where the surface potential is reduced by exposure, and the electrostatic latent image becomes a visible image.
The above is the details of the image forming engine 110Y. The other image forming engines 110M, 110C, and 110K have the same configuration except that the toner corresponds to each color. The image forming unit 100 according to the present embodiment has a so-called 4-drum tandem arrangement configuration in which these four image forming engines are arranged in series.

  Below each image forming engine, an intermediate transfer member 160 is provided so that a part of the intermediate transfer member 160 comes into contact with the photosensitive drum 120. The intermediate transfer body 160 is an endless belt, and is wound around the drive roll 161 and the backup roll 162 driven by the drive roll 161 so as to maintain a constant tension. The photosensitive drums 120 of the above-described image forming engines 110Y, 110M, 110C, and 110K are rotationally driven in the same direction with their surfaces in contact with the surface of the intermediate transfer member 160. The intermediate transfer member 160 is driven to circulate in the same direction as the moving direction of the surface of the photosensitive drum 120 by a driving device (not shown) that drives the driving roll 161. At each contact position between the intermediate transfer body 160 and the photosensitive drum 120 corresponding to each color, a primary transfer roll 163 corresponding to each color is disposed so as to sandwich the intermediate transfer body 160. The visible image on each photoconductor drum 120 is pressed against the intermediate transfer member 160 by the primary transfer roll and is multiplex-transferred to the intermediate transfer member 160.

  The secondary transfer roll 173 faces the backup roll 162 with the intermediate transfer member 160 interposed therebetween. The paper 171 held on the paper tray 170 in the image forming unit 100 is sent to a position where the secondary transfer roll 173 and the backup roll 162 face each other by a plurality of transport rolls 172, and a visible image of each color is multiplex-transferred. The intermediate transfer body 160 passes between the secondary transfer roll 173 and the backup roll 162. At that time, the sheet 171 is brought into pressure contact with the intermediate transfer member 160 by the secondary transfer roll 173, and the visible image that has been multiple-transferred onto the intermediate transfer member 160 is transferred to the sheet 171. The visible image transferred onto the paper 171 in this manner is finally subjected to fixing processing such as heating and pressing by the fixing device 180 and then discharged from the discharge unit 181. The details of the image forming unit 100 have been described above.

<1-2: Image Processing Unit 200>
The image processing unit 200 is an apparatus that converts an externally input image into image data and supplies the image data to the image forming unit 100. The image processing unit 200 includes a scanner interface 210, an image processing circuit 220, and an LED control unit 230. Hereinafter, the image processing unit 200 will be described with reference to FIG.

The scanner interface 210 reads an image and supplies it to the image processing circuit 220 as image data, and has the following configuration.
The document table 211 is a glass table on which a document to be scanned is placed. The document placed on the document table 211 is irradiated with light emitted from the light source 212. The light collector 213 reflects the light emitted from the light source 212 to the direction other than the original and condenses the light on the original. The light irradiated on the original in this way is reflected by the original surface, and further, the traveling direction thereof is appropriately changed by the reflecting mirror 214 and enters the lens 215. The lens 215 collects the reflected light and forms an image on a CCD (Charge Coupled Diode) 216.

The CCD 216 converts the reflected light from the document into image data representing the brightness of each color of R (red), G (green), and B (blue). In the CCD 216 according to this embodiment, a charge coupled device as a reading device reads a document with a resolution of 600 dpi. The CCD mode is, for example, a one-line sensor system that obtains a resolution of 600 dpi by allowing reflected light to pass through a color filter that is repeatedly arranged in the order of R, G, and B and inputting the reflected light to a CCD that is arranged at 1800 dpi. Alternatively, a three-line sensor system may be employed in which reflected light that has passed through the R, G, and B color filters is input to a CCD that is arranged in three rows at a resolution of 600 dpi. Further, the resolution is not limited to this.
Here, the light source 212 and the light collector 213 are mounted on a first carriage (not shown), and the reflection mirror 214 is mounted on a second carriage (not shown). These carriages are sequentially driven by a drive circuit (not shown) in a direction perpendicular to the electrical scanning direction of the CCD 216, that is, in the sub-scanning direction, so that the image data of the entire original is output from the CCD 216. It has become.

  Image data corresponding to RGB colors obtained by the CCD 216 (hereinafter referred to as “RGB image data”) is converted into digital data by the A / D conversion circuit 217 and then supplied to the image processing circuit 220. The RGB image data is converted by the image processing circuit 220 into density data corresponding to each color of YMCK (hereinafter referred to as “YMCK density data”), and then supplied to the LED control unit 230. The LED control unit 230 newly generates a drive signal waveform for driving the LED 142 based on the YMCK density data and the light amount correction data of the LED 142 supplied from the light amount correction value calculation unit 20 described later. Is driven. Hereinafter, the image processing circuit 220 and the LED control unit 230 will be described in more detail.

FIG. 4 is a block diagram of signal processing in the image processing unit 200.
The image processing circuit 220 includes an input side image processing circuit 221 and an output side image processing circuit 222. The A / D converted RGB image data output from the CCD 216 is first supplied to the input side image processing circuit 221. The input-side image processing circuit 221 performs shading correction processing by the shading correction circuit 221a and input gradation correction processing by the input gradation correction circuit 221b on the RGB image data, and an error from the original image caused by the characteristics of the CCD 216 Correct. The output data of the input side image processing circuit 221 is output to the output side image processing circuit 222 as RGB image data that faithfully reproduces the original image.

  The output side image processing circuit 222 generates YMCK density data based on the RGB image data supplied from the input side image processing circuit 221, and supplies the YMCK density data to the LED control unit 230. Specifically, first, image data in which RGB image data is represented in the L * a * b * color system by the first color conversion processing circuit 222a (hereinafter referred to as “L * a * b * image data”). )). The L * a * b * color system is a color space represented by planar chromaticity coordinates and luminance coordinates that are orthogonal thereto. Next, the L * a * b * image data thus obtained is converted into YMCK density data by the second color conversion processing circuit 222b. The YMCK density data is corrected for definition and gradation by the definition processing circuit 222c and the output gradation correction circuit 222d, and then supplied to the LED control unit 230 as output data of the image processing circuit 220. The

  The LED control unit 230 includes a light amount correction circuit 231, an LED drive circuit 232, and the like. The light amount correction circuit 231 includes light amount correction data FIXE obtained by abutting the light amount correction data LEDE determined for each LED element and the light amount correction data IITE for each LED element group Nx, and a halftone processing circuit. Based on the YMCK density data supplied from the output-side image processing circuit 222 that has been subjected to halftone processing by H.233, drive data for the LED 142 is generated and supplied to the LED drive circuit 232. The LED drive circuit 232 generates a drive signal pulse for driving the LED 142 in each image forming engine based on the given drive data, and supplies the drive pulse to the LED 142. In the image processing unit 200, such an operation is performed.

  When light amount correction described later is performed, RGB image data output from the input side image processing circuit 221 is supplied to the light amount correction value calculation unit 20. The light amount correction value calculation unit 20 is a circuit that calculates light amount correction data IOTE for each LED element group Nx, and includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM, and the like. The CPU 21 converts the supplied RGB image data into YMCK density data, calculates light quantity correction data IOTE for correcting the light quantity of the LED element group Nx based on the density data, and corrects the correction data RAM 22. Write to. Further, by this light amount correction process, LEDE which is the light amount correction data of the single LED element is also updated and similarly written in the correction data RAM 22. The previous light amount correction circuit 231 generates drive data for the LED 142 based on the two correction data supplied from the light amount correction value calculation unit 20.

  The light amount correction value calculation unit 20 has a density profile RAM 23 different from the correction data RAM 22, and density profiles PRFa and PRFb are stored in the density profile RAM 23. The CPU 21 appropriately updates the light amount correction data LEDE and the light amount correction data IOTE by updating and referring to the density profile. Details of the light amount correction of the LED 142 including the density profiles PRFa and PRFb will be described later.

<1-3: Light amount correction processing>
Next, an outline of the light amount correction processing of the LED 142 will be described.
The CPU 21 of the light amount correction value calculation unit 20 in the present embodiment calculates light amount correction data IOTE based on the test pattern output result. Here, the test pattern includes a first test pattern and a second test pattern. The former is obtained by a normal image forming process using the exposure apparatus 140, and the latter is an image formation not using the exposure apparatus 140. Obtained by the process.

  The CPU 21 refers to the output result of the second test pattern, so that the density unevenness or the image quality defect that appears in the first test pattern is caused by the light amount unevenness of the LED 142 or occurs in another image forming process. If it is determined that the density unevenness or the image quality defect is present, it is further determined whether the light can be adjusted by correcting the light amount of the LED 142, and the density unevenness that can be corrected by correcting the light amount of the LED 142. Alternatively, if it is determined that the image quality is defective, image quality adjustment is performed by correcting the light amount of the LED 142.

  FIG. 5 is a flowchart of the light amount correction processing of the LED 142. The light amount correction process described here is a light amount correction process that is first performed in the image forming apparatus 10.

  When the power of the image forming apparatus 10 is turned on, the light amount correction process is started, and the first test pattern is output first (step S501). The pattern data of the first test pattern is stored in advance in the ROM 24 of the light quantity correction value calculation unit 20, and the CPU 21 reads this pattern data and supplies it to the light quantity correction circuit 231 in step S501. Further, the CPU 21 reads the light amount correction data LEDE from the ROM 24 and writes it in the correction data RAM 22. Here, the light amount correction data LEDE read from the ROM 24 is an initial value of the light amount correction data LEDE, and is data measured before the LED is mounted on the image forming unit 100. The light quantity correction circuit 231 calculates drive data for driving the LED 142 based on the given pattern data and the light quantity correction data LEDE stored in the correction data RAM 22 and supplies the drive data to the LED drive circuit 232. In the image forming unit 100, each unit is controlled by a control device (not shown), and the exposure device 140 is driven. In the image forming unit 100, the LED drive circuit 232 supplies a drive pulse to the LED 142 based on the drive data supplied from the light amount correction circuit 231, causes the LED 142 to emit light, and outputs a first test pattern.

  FIG. 6 is a schematic diagram of the first test pattern. In FIG. 6, the output paper and the LED element group Nx in the image forming unit 100 are displayed in correspondence with each other in order to facilitate the description of the first test pattern.

The LED arrays 400Y, 400M, 400C, and 400K represent aggregates of LED element groups Nx mounted on the image forming engines 110Y, 110M, 110C, and 110K of YMCK. In each LED array, the LED element groups N _{1 to} N ₅₈ are arranged in a staggered manner as described above. On the other hand, as described above, in this LED element group Nx, the individual LEDs 142 are arranged at a density of 1200 dpi, and the total number of LEDs 142 is 14848 per LED array. The total length in the direction (LED arrangement direction) is about 314 mm. On the other hand, the paper used in the image forming apparatus 10 is A4 size (297 mm (main scanning direction) × 210 mm (sub-scanning direction)). Therefore, the total length of the LED array is slightly longer than the paper width. Has been.

When outputting the first test pattern, first, a pair of left and right is formed, and a cross-shaped skew correction pattern 401 common to each color is output. The cross-shaped skew correction pattern 401 is used for skew correction described later.
The element group pitch confirmation pattern 402Y is a pattern for giving the CPU 21 the reference position information of the LED element group Nx. This element group pitch confirmation pattern 402Y is a staggered pattern having the same arrangement form as the element group Nx, and the CPU 21 turns on the LED element groups Nx alternately in the sub-scanning direction, that is, in the first scan. Only LEDs belonging to the element group N _2x-1 (x = 1, 2,..., 29) are changed to the element group N _2x (x = 1, 2,..., 29) in the second scan. It is obtained by controlling the LED drive circuit 232 so that only the LED to which it belongs is lit. The reason why such a staggered pattern is used is that when all the LED element groups Nx are turned on in one scan, the pattern obtained is a straight line dotted at 1200 dpi, and the boundary between the element groups Nx is This is because it becomes unclear and the CPU 21 cannot obtain the correct position information of the LED element group Nx.
With these two patterns, the skew correction pattern 401, and the element group pitch confirmation pattern 402Y, the CPU 21 can accurately grasp the position of each LED element group Nx on the screen pattern to be described, and correct light quantity correction. Can be implemented.

  When the element group pitch confirmation pattern 402Y is output, a plurality of screen patterns 410Y, 420Y, and 430Y having different gradations are output. Note that “Y” at the end of each symbol indicates a pattern obtained by light emission of the LED array 400Y.

  Generally, the gradation expression method expresses the density of each pixel by density data of a plurality of bits, and gives a density gradation method for each pixel, and a plurality of pixels having a density of 1 bit. Thus, there is an area gray scale method in which a matrix which is a gray scale unit is formed, and the matrix is expressed as a single pixel, and the latter is used in this embodiment. In this method, the number of gradations that can be expressed differs depending on the number of pixels constituting the matrix. For example, if one matrix is composed of 6 pixels × 6 pixels, that is, 36 pixels, the number of gradations that can be represented by this matrix is “36”.

  When the area gradation method is used, since one pixel is substantially constituted by a plurality of pixels, the resolution is deteriorated as compared with the density gradation method, but each pixel may be controlled with 1-bit density information. The processing burden on the arithmetic unit is reduced. In the present embodiment, one matrix is composed of 16 pixels × 16 pixels, and density representation of 256 gradations is possible. Accordingly, by outputting an image of 16 lines in the sub-scanning direction, 928 matrices are completed in the main scanning direction.

  FIG. 7 shows an example of the screen pattern. A screen pattern is a pattern expressed as a collection of the above-described matrices. For example, if 4 × 4 pixels in one matrix, that is, every 16 pixels, are staggered, a pattern represented by (c) in the figure is obtained. This pattern is a screen pattern with a gradation area ratio of 50% because the number of dot pixels in one matrix is 128. On the other hand, when expressing the type of screen pattern, the expression “number of lines” may be used. This shows how many lines are formed per one inch of diagonal of the matrix described above by the pixels that have been dotted, and the pattern in FIG. This is a 212-line screen pattern. A screen pattern having a number of lines near 200 lines has high reading accuracy when reading an image with a scanner or the like, and is therefore suitable for use in LED light amount correction as in this embodiment.

In the present embodiment, a plurality of screen patterns having different gradation area ratios are used as the first test pattern. If the variation in the light amount of the LED element group Nx is constant regardless of the gradation area ratio, the light amount correction based on a pattern of a certain gradation area ratio may be performed. However, in actuality, since there is a variation in the light amount of each LED 142 constituting the element group, there is a difference in the light amount variation of the element group depending on the gradation area ratio of the screen pattern, and the required light amount correction value is also It may vary accordingly. For this reason, in this embodiment, correction values based on a plurality of gradation area ratios, that is, three patterns of 50% (410Y), 40% (420Y), and 30% (430Y) are determined. It has become.
Each of these screen patterns is output with a width of about 1 cm in the sub-scanning direction. Since the pitch between the elements of the LED 142 arranged at 1200 dpi is about 21 μm, about 470 lines are arranged in this width. As already described, since one matrix is composed of 16 lines in this embodiment, each screen pattern is calculated to include about 30 matrices in the sub-scanning direction.

When the output of the first test pattern is completed, the skew correction pattern 401, the element group pitch confirmation pattern 402Y, and the screen patterns 410Y, 420Y, and 430Y are sequentially formed on the output sheet.
Here, only the pattern formed by the LED array 400Y has been described, but actually, the element group pitch confirmation pattern 402M, the screen patterns 410M, 420M, and 430M corresponding to the LED array 400M are subsequently formed. Then, an element group pitch confirmation pattern 402C and screen patterns 410C, 420C, and 430C corresponding to the LED array 400C are formed. Finally, an element group pitch confirmation pattern 402K and screen patterns 410K and 420K corresponding to the LED array 400K are formed. 430K is formed, and the output of the first test pattern shown in FIG. 6 is completed.

  The gradation area ratio of the pattern and the number of patterns are not limited to this. It may be a pattern with a gradation area ratio of 50% or more, or a pattern with a gradation area ratio of 30% or less. Of course, the number of lines of the screen pattern is not limited to that exemplified in this embodiment. Further, the accuracy of light amount correction may be increased by increasing the number of screen patterns used for light amount correction, or light amount correction may be performed only with a single gradation area ratio. In this case, as already described, there is a possibility that overcorrection or undercorrection may occur other than the gradation area ratio subjected to light amount correction, but the effect according to the present invention is not hindered.

  When the output of the first test pattern is completed, the second test pattern is output on a sheet different from the output sheet of the same pattern (step S502). FIG. 8 is a schematic diagram of the second test pattern. In the figure, as in the case of the first test pattern, the output paper and the LED arrays 400Y, 400M, 400C, and 400K in the image forming unit 100 are displayed in correspondence with each other.

  The CPU 21 of the light quantity correction value calculation unit 20 requests the control device (not shown) that controls the image forming unit 100 to output the second test pattern. Based on this request, the control device controls each image forming engine of the image forming unit 100 and outputs a second test pattern using each device except the exposure device 140. At this time, similarly to the first test pattern, the skew correction pattern 401 and the element group pitch confirmation pattern 402Y are output, and then the pattern 440Y is output. Similarly to the first test pattern, the second test pattern also outputs patterns 402M, 440M, 402C, 440C, 402K, and 440K corresponding to the respective colors following the pattern 440Y.

  Here, the image formation of the second test pattern will be described. In a normal image forming process, the photosensitive drum 120 is uniformly charged by the charging device 130 and then exposed by the exposure device 140. The photosensitive drum 120 has a mechanism in which an electrostatic latent image is carried by reducing the surface potential of only the exposed portion. However, in the formation of the second test pattern, the exposure device 140 is not used, and an electrostatic latent image is not formed on the photosensitive drum 120. Therefore, the output image formed on the surface of the photosensitive drum 120 is merely a uniform monochromatic pattern. When the toner is attached to the photosensitive drum 120, the charging potential of the photosensitive drum 120 by the charging device 130 is lower than that of the normal image forming process, that is, the charging potential of the photosensitive drum 120 is set in the normal image forming process. The toner is adhered with a potential difference from the developing bias while suppressing the surface potential after exposure. For this reason, the toner adheres to the surface of the photosensitive drum 120 substantially uniformly.

When the output of the first and second test patterns is completed, the output sheet of the first test pattern and the output sheet of the second test pattern are discharged to the discharge unit 181 of the image forming unit 100. In this state, first, the output paper of the first test pattern is set on the document table 211, and the image is read by the scanner interface 210 (step S503). As a result, image data obtained as reflectance data for each color of RGB is input to the input side image processing circuit 221.
When the reading of the first test pattern is completed, the output paper of the second test pattern is subsequently set on the document table 211, and the image is read by the scanner interface 210 (step S504). The image data obtained as a result is also input to the input side image processing circuit 221. These image data are supplied to the light amount correction value calculation unit 20 after being subjected to the above-described correction processing by the input side image processing circuit 221.

  When the image data of the first and second test patterns is supplied, the CPU 21 of the light quantity correction value calculation unit 20 performs a skew correction process (step S505). This skew correction processing is first performed for the first test pattern and then for the second test pattern.

FIG. 9 is a diagram for explaining the skew correction processing. Skew correction is a process for correcting the tilt of an input image. The skew correction pattern 401 described above is used for this skew correction. When outputting the skew correction pattern 401, the CPU 21 stores the coordinates of the center position in the pair of left and right patterns. This coordinate plane is composed of an x-axis extending in the main scanning direction and a y-axis extending in the sub-scanning direction. That is, the coordinate points on this coordinate plane indicate the individual LEDs 142 constituting the LED array 400Y.
For example, assume that the center coordinates of the left pattern are (x, y) = (5, 5) and the center coordinates of the right pattern are (x, y) = (14840, 5). The CPU 21 corrects the inclination by associating data corresponding to the skew correction pattern in the image data supplied from the input-side image processing circuit 221 with the coordinate point. By this skew correction processing, even if the reading by the scanner interface 210 is performed in a state where the sheet is inclined, the inclination can be corrected.

  When the skew correction processing is completed, the light amount correction data calculation processing of each LED 142 constituting the LED array is started for each color of YMCK. Since this light amount correction data calculation processing is the same processing for each color of YMCK, only the LED element group Nx of the LED array 400Y will be described here.

In calculating the LED light amount correction data, the CPU 21 first performs a pitch confirmation process for the LED element group Nx (step S506). This pitch confirmation process is performed using the element group pitch confirmation pattern 402Y. Since the element group pitch confirmation pattern 402Y is the arrangement pattern itself of the LED element group Nx of the LED array 400Y as described above, data corresponding to the element group pitch confirmation pattern 402Y is read from the supplied image data. Thus, the CPU 21 can correctly grasp the position of the LED element group Nx. Note that this pitch confirmation process is similarly performed for the second test pattern.
From then on, the skew correction process and the pitch confirmation process allow the CPU 21 to accurately match the density data of the first and second test patterns with the position of the element group Nx, and perform an appropriate light amount correction. Can be implemented.
The element group pitch confirmation pattern 402Y is a staggered pattern in the present embodiment, similar to the array pattern of the LED element group Nx, but may be any pattern that allows the CPU 21 to recognize the boundary of the element group Nx. anything is fine.

  When the pitch confirmation processing for the LED element group Nx is completed, the CPU 21 starts parallel calculation processing for each of the first test pattern and the second test pattern in order to calculate LED light amount correction data. In the following, in order to prevent the explanation from becoming complicated, the calculation process related to the first test pattern will be described first, and then the calculation process related to the second test pattern will be described. As described above, three patterns of the first test pattern are formed for each gradation area ratio. However, since the processing performed by the CPU 21 is the same in any pattern, the gradation area ratio is 50% here. Only processing related to the pattern 410Y will be described.

  The CPU 21 converts the image data of the pattern 410Y out of the image data of the first test pattern supplied from the input side image processing circuit 221 into density data (step S507). Since the resolution of the CCD 216 in the main scanning direction is 600 dpi, this density data is calculated with two LED elements as one unit. Accordingly, 128 density data per element group, and a total of 7424 density data are obtained. The density data conversion is performed for the number of lines in the sub-scanning direction of the pattern 410Y, that is, about 470 lines. The density data thus obtained is temporarily stored in the internal RAM of the CPU 21. Note that the density data calculation unit may not be every two LEDs. The density data of 64 pieces per element group may be acquired by taking 4 pieces as a set, or other than that.

Next, the density data stored in the internal RAM is averaged for a plurality of lines in the sub-scanning direction (step S508). Actually, out of about 470 lines in the sub-scanning direction, 32 lines near the center, that is, lines for two matrices are extracted and this averaging process is performed. By this averaging process, the density variation in the sub-scanning direction is absorbed, and a density curve in which 7424 density data are arranged in the main scanning direction is obtained. In the present embodiment, this density curve is referred to as a “density profile”. FIG. 10 is a schematic diagram of this density profile.
Since the CPU 21 has already acquired the position information of the element group Nx by the pitch confirmation process, this density profile can be divided corresponding to the 58 element groups. This divided concentration profile for each element group is referred to as an “element group concentration profile”. That is, the density profile is a concatenation of 58 element group density profiles.

  Next, the CPU 21 averages the element group concentration profile (step S509). FIG. 11 is a schematic diagram of this averaging. Since the pattern 410Y is a pattern with a gradation area ratio of 50%, all the 128 density data in the main scanning direction are ideally equal and become one straight line, but actually shown in FIG. There are street variations. By averaging this variation, a straight line is obtained. This straight line represents the average density of each element group Nx.

  The density corresponding to each LED element 142 constituting the element group Nx has a difference with respect to the averaged density. In step S509, along with the averaging, a correction light amount of the LED 142 for correcting this difference is calculated. Since this correction light quantity is a correction value based on the light quantity characteristic of the LED 142 alone, it is equivalent to the light quantity correction data LEDE. Therefore, the CPU 21 writes the newly obtained light amount correction data LEDE in the correction data RAM 22 and updates the light amount correction data LEDE.

When the averaging process is completed for each element group Nx, the CPU 21 connects the averaged element group concentration profiles for all the element groups to obtain new density profiles (step S510). This density profile is stored in the density profile RAM 23 as “density profile PRFa”.
FIG. 12 is a schematic diagram of the concentration profile PRFa. With this density profile PRFA, the CPU 21 can obtain difference information between the density average value of all element groups obtained by further averaging the average density of each element group and the density average value of each element group.

When the density profile PRFa is obtained, the CPU 21 refers to the density profile PRFa and calculates the light amount correction data IOTE necessary for each LED element group Nx (step S511).
FIG. 13 is a schematic diagram of light amount correction data IOTE calculation. Since the CPU 21 acquires the density difference information for each element group Nx, the CPU 21 can calculate the light amount correction amount corresponding to the density difference information. The light amount correction data IOTE for each LED element group Nx thus obtained is stored in the light amount correction RAM 22 (step S512), and the light amount correction processing according to the present embodiment is completed.
Thereafter, when image formation is performed, the light amount correction data LEDE for each LED element and the light amount correction data IOTE for each LED element group, which are stored in the correction data RAM 22, are abutted and finally processed. The light amount correction data FIXE that is the light amount correction data is supplied to the LED light amount correction circuit 231.

  By the way, when the light amount correction data of the LED element group Nx is calculated based only on the density profile PRFa, as already described in the problem, the density variation caused by the factor in the image forming unit 100 is also corrected by the light amount of the LED element group. This can cause problems. Therefore, in the present embodiment, this problem is solved by isolating the cause of the density variation based on the output result of the second test pattern and correcting only the density variation that can be corrected by the light amount correction of the LED. In the following, a calculation process related to the second test pattern will be described.

  The CPU 21 converts the image data of the second test pattern supplied from the input side image processing circuit 221 into density data (step S601). Subsequently, as in the case of the first test pattern, this density data is averaged for a plurality of lines in the sub-scanning direction (step S602). Actually, the averaging process for 32 lines is performed as in the first test pattern. By this averaging process, the density variation in the sub-scanning direction is absorbed, and the density profile PRFb of the second test pattern is obtained (step S603). FIG. 14 is a schematic diagram of the concentration profile PRFb. This density profile PRFb is stored in the density profile RAM 23.

  When the density profile PRFb is obtained, the CPU 21 determines whether there is an image quality defect (step S604). The presence / absence determination of the image quality defect is performed by determining a location where a density difference of a certain value or more is generated from the density of an adjacent area. When it is determined that there is no image quality defect (No in step S604), the CPU 21 shifts the process to the above-described step S511, and the light amount correction data IOTE of the LED element group is calculated.

  If there is any defect in the image forming unit 100, for example, if dust adheres to the surface of the photosensitive drum 120 or if charging failure occurs on the photosensitive drum, the second test pattern is displayed on the second test pattern. Therefore, image quality defects such as so-called “white spots” and “image stripes” appear. The image quality defect also appears in the density profile PRFb.

  FIG. 15 is a schematic diagram of the density profile PRFb when there is an image quality defect in this way. In this case, it is determined in step S604 that four image quality defects as shown in (a) to (d) have occurred on the second test pattern. Among them, the image quality defects of (a) and (d) are large in scale, in which there is no toner attached at all and a solid solid state. Also, (c) and (d) are relatively small image quality defects.

  As described above, when it is determined that there is an image quality defect (Yes in Step S604), the CPU 21 determines whether or not the image quality defect can be corrected by correcting the light amount of the LED element (Step S605). The discrimination criterion for this discrimination process is given to the CPU 21 in advance.

  FIG. 16 is a diagram showing the relationship between the correction density and the pulse width for causing the LED element to emit light. In the present embodiment, the light quantity correction of the LED is realized by changing the pulse width of the drive pulse for causing the LED element to emit light according to the correction density. In general, the density is saturated with respect to the drive pulse width at a certain point. Therefore, there is a limit to the density that can be corrected by controlling the pulse width. In this embodiment, the area designated by the dotted line in the figure is defined as the correctable range, including a certain margin. The CPU 21 performs light amount correction only for the light amount for correcting the target image quality defect within the correctable range. In FIG. 15, it is assumed that image quality defects (a) and (d) are image quality defects that cannot be corrected by the light amount correction of the LED.

  If it is determined that the image quality defect is not within the correctable range (step S605 is negative), for example, if there is an image quality defect corresponding to (a) or (d) in FIG. It is determined that the correction is caused by the defect of the image forming unit 100 and cannot be corrected by the light amount correction of the LED, and information notifying the abnormality of the image forming unit 100 is supplied to the outside (step S606). When step S606 is executed, the light amount correction processing of the image forming engine is forcibly ended. In this case, after the image forming apparatus 10 is appropriately repaired and adjusted, the light amount correction process is executed again.

On the other hand, when it is determined that the image quality defect is within the correctable range (step S605 is positive), for example, the image quality defect that currently occurs is an image quality defect corresponding to (b) or (c) in FIG. In the case where it is detected, the CPU 21 shifts the processing to step S511. However, since the first test pattern output as a result of using the exposure apparatus 140 is also output using the image forming unit 100, if there is an image quality defect, Of course, the image quality defect should be reflected in the density profile PRFa, and it is not necessary to refer to the density profile PRFb during the processing in step S511.
FIG. 17 is a schematic diagram of a new density profile obtained by this LED light quantity correction processing. It can be seen that the density variation is clearly corrected as compared with FIG.

  In the present embodiment, only the light amount correction based on the pattern 410Y having the gradation area ratio of 50% in the LED array 400Y mounted on the image forming engine 110Y has been described. The light amount correction process is similarly performed for the pattern and the LED arrays of other image forming engines.

  The image forming apparatus 10 according to the present embodiment has such an image quality adjustment function. Therefore, a situation in which image quality defects that cannot be corrected by LED light amount correction, which has been a problem in the past, is not corrected by LED light amount correction. Accordingly, the light amount correction of the LED is performed within a very appropriate range, and a high-quality image can be provided.

  In the present embodiment, density averaging processing is performed in the sub-scanning direction, but this sub-scanning direction averaging processing is not necessarily required. In particular, with respect to the second test pattern, image quality defects caused by the image forming unit 100 such as white spots and image streaks occur uniformly in the sub-scanning direction, and this pattern originally uses the exposure apparatus 140. Therefore, the density change in the sub-scanning direction does not occur so much.

  In the present embodiment, the element group is defined as a correction unit for the LED light amount. By calculating the light amount correction value with this element group as a unit, the processing load on the CPU 21 is reduced. However, even if the light quantity correction of the LED is performed on an element basis, the effect according to the present invention is not hindered.

The above description has been made on the premise of the light amount correction processing performed first in the image forming apparatus 10. This corresponds to, for example, a light amount correction process performed at the factory when the image forming apparatus 10 is shipped. However, of course, the user may perform the light amount correction process under each use environment.
Further, in this embodiment, when there is an image quality defect that is determined to be uncorrectable by the light amount correction of the LED 142, the CPU 21 stops the light amount correction process at that time. For example, the CPU 21 corresponds to the image quality defect. The light quantity correction may be performed for the other LED element groups Nx without performing only the correction of the element group Nx. In that case, after adjustment of the image forming unit 100, the light amount correction may be performed only for the element group that has not been corrected.

<Second Embodiment: Image Quality Adjustment System>
In the above-described embodiment, the image forming apparatus 10 in which the image forming unit 100 and the image processing unit 200 are integrated has been described. However, even in an image forming apparatus that does not have an image input function typified by a single printer or the like, the necessity of correcting the amount of light of the LED can occur in the same manner. Here, the second embodiment that can provide the same effects as those of the first embodiment described above will be described.

  FIG. 18 is a schematic diagram of an image quality adjustment system 30 according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the location which overlaps with the above-mentioned 1st Embodiment in the same figure, and the description is abbreviate | omitted.

  The image forming apparatus 31 is an apparatus in which the image forming unit 100, the image processing circuit 220, the LED control unit 230, and the light amount correction value calculation unit 20 are integrated. The image forming apparatus 31 is equipped with an IO interface 32. The IO interface 32 is a control board for transmitting image information from the outside to a control device (not shown) in the image forming apparatus 31 according to a connection standard such as SCSI or USB. A computer 34 is connected to the IO interface 32 via a cable 33. A scanner 35 is connected to the computer 34.

  The scanner 35 is an implementation of the scanner interface 210 in the above-described embodiment, and a document placed on the document table 211 is converted into image data by the CCD 216 and supplied to the computer 34. The computer 34 supplies the supplied image data to the image forming apparatus 31. In the image forming apparatus 31, the light amount correction value calculation unit 20 calculates the light amount correction data of the LED based on the supplied image data, and the light amount. Make corrections. According to such an image quality adjustment system, it is possible to perform LED light amount correction within an appropriate range even if an apparatus for reading the first and second test patterns is not provided.

  Note that the aspect of the image quality adjustment system is not limited to that of the present embodiment. For example, in the present embodiment, the scanner 35 and the image forming apparatus 31 may be directly connected. In addition, the image forming apparatus 31 may not have the light amount correction value calculation unit 20, and the calculation process to be performed by the light amount correction value calculation unit 20 may be performed by the computer 34.

1 is a schematic diagram of an image forming apparatus 10 according to a first embodiment of the present invention. The light source arrangement | positioning figure of the exposure apparatus 140 in the same apparatus. The schematic diagram of LED element group Nx in the exposure apparatus 140. FIG. The block diagram of the signal processing of the image process part 200 in the apparatus. 5 is a flowchart of LED light amount correction processing in the image forming apparatus 10; The schematic diagram of the 1st test pattern which concerns on the same light quantity correction process. FIG. 6 is an exemplary diagram of a screen pattern related to the same light amount correction process. The schematic diagram of the 2nd test pattern which concerns on the same light quantity correction process. Explanatory drawing of the skew correction process which concerns on the same light quantity correction process. The schematic diagram of the density profile which concerns on the same light quantity correction process. The schematic diagram of the density profile average process in an element group which concerns on the same light quantity correction process. The schematic diagram of density profile PRFa which concerns on the same light quantity correction process. The schematic diagram of light quantity correction data IOTE calculation which concerns on the same light quantity correction process. The schematic diagram of density profile PRFb which concerns on the same light quantity correction process. FIG. 6 is an exemplary diagram of a density profile PRFb when there is an image quality defect. FIG. 6 is a relationship diagram between a correction density related to the same light amount correction process and an LED drive pulse width. The schematic diagram of the density profile after the same light quantity correction process. The schematic diagram of the image quality adjustment system 30 which concerns on 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 20 ... Light quantity correction value calculating part, 21 ... CPU, 22 ... Correction data RAM, 23 ... Density profile RAM, 24 ... ROM, 30 ... Image quality adjustment system, 31 ... Image forming apparatus, 32 ... IO interface, 33 ... cable, 34 ... computer, 35 ... scanner, 100 ... image forming unit, 110 ... image forming engine, 120 ... photosensitive drum, 130 ... charging device, 140 ... exposure device, 150 ... developing device, 160 ... Intermediate transfer member 161... Drive roll 162 162 backup roll 163 primary transfer roll 170 paper tray 171 paper 172 transport roll 173 secondary transfer roll 180 fixing device
181: Discharge unit, 200: Image processing unit, 210: Scanner interface, 211 ... Document table, 212 ... Light source, 213 ... Light collecting plate, 214 ... Reflection mirror, 215 ... Lens, 216 ... CCD, 217 ... A / D conversion circuit , 220 ... Image processing circuit, 221 ... Input side image processing circuit, 221a ... Shading correction circuit, 221b ... Input tone correction circuit, 222 ... Output side image processing circuit, 222a ... First color conversion processing circuit, 222b ... Second Color conversion processing circuit, 222c ... definition processing circuit, 222d ... output gradation correction circuit, 230 ... LED control unit, 231 ... light quantity correction circuit, 232 ... LED drive circuit, 233 ... halftone processing circuit, 400 ... LED array, 401 ... Skew correction pattern, 402 ... Element group pitch confirmation pattern, 410, 420, 430 ... Screen pattern, 40 ... the second test pattern.

Claims (4)

An image carrier having photoconductivity, a charging unit that charges the image carrier to a predetermined potential, and a plurality of light emitting elements arranged in a predetermined direction, and the predetermined light is emitted from the light emitting elements. An exposure means for exposing the surface of the image carrier charged to a potential of, a development means for attaching a developer to the surface of the image carrier and forming an image with the developer, and an image formed by the development means. Image forming means having output means for outputting to the medium;
Image processing means for reading an image and converting it into density data;
First control for controlling image formation by the image forming unit based on image data, and causing the image forming unit to perform image formation using the exposure device, and without using the exposure device. Control means for performing second control for causing image formation;
When the first control by the control means is performed and the image output to the medium by the output means is read by the image processing means, the plurality of light emission based on the density data obtained from the image processing means A light amount correction information generating means for generating light amount correction information for correcting the light amount of the element;
A light amount correction means for correcting light amounts of the plurality of light emitting elements based on the light amount correction information;
When the second control by the control means is performed and the image output to the medium by the output means is read by the image processing means, the presence or absence of image quality defects based on the density data obtained from the image processing means First discriminating means for discriminating;
A second discriminating unit for discriminating whether the image quality defect can be repaired by the light amount correction of the light emitting element by the light amount correcting unit when the discriminating unit determines that there is an image quality defect;
When the second determination unit determines that there is an image quality defect that cannot be repaired by the light amount correction, the control unit does not perform the light amount correction of the light emitting element corresponding to the occurrence position of the image quality defect. An image forming apparatus that controls the light amount correction unit. The predetermined image obtained as a result of the first control is formed by stepwise arranging a plurality of patterns having different gradation area ratios in a direction orthogonal to the arrangement direction of the light emitting elements,
The image forming apparatus according to claim 1, wherein the light amount correction by the light amount correction unit is performed for each of the plurality of patterns having different gradation area ratios. The light quantity correction information generating means
A first light quantity for managing the light emitting elements as a plurality of light emitting element groups and correcting the light quantity of each light emitting element based on a deviation from the average value of the density corresponding to each light emitting element in the light emitting element group Calculate correction information,
Second light amount correction for correcting the light amount of each light emitting element group based on a deviation from the average value of the density corresponding to each light emitting element in the light emitting element group further averaged for all light emitting element groups The image forming apparatus according to claim 1, wherein the information is calculated. An image forming apparatus comprising the image forming unit, the control unit, the light amount correction information generating unit, the light amount correcting unit, the first determining unit, and the second determining unit;
The image processing means;
Connection means for electrically connecting the image forming apparatus and the image processing apparatus;
An image quality adjustment system comprising: an interface unit that delivers the density data supplied from the image processing unit to the image forming apparatus.

Images