JP6307806B2 - Image forming apparatus and light amount correction method - Google Patents

Description

The present invention relates to an image forming apparatus and the light quantity correction how.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that exposes a photosensitive member using an optical writing head in which a plurality of light emitting units such as LEDs (light emitting diodes) are arranged in the main scanning direction is known. . In this type of image forming apparatus, if there is a variation in the amount of light among the plurality of light emitting units of the optical writing head, the image appears as vertical stripe-like density unevenness (streaks along the sub-scanning direction, which is the paper transport direction). Density unevenness). For this reason, the light quantity of the light emitting part of the optical writing head is corrected using correction data for correcting the light quantity variation.

  Further, not only correction data for correcting the light quantity variation of the optical writing head, but also correction of light quantity using correction data for correcting uneven charging of the photoconductor or correction data for correcting toner thin layer unevenness of the developing device. Is also known (see, for example, Patent Document 1). According to this technology, it is possible to effectively suppress the density unevenness of the image caused by the photoreceptor and the developing device.

  However, even when the technique described in Patent Document 1 is used, vertical stripe-like density unevenness may occur in the image. The cause of this is, for example, that the size of the beam spot irradiated on the photoconductor is between the light emitting units due to a lens creation error inside the optical writing head, a scratch on the lens, an alignment error, etc. In other words, even if the exposure energy on the photoconductor is uniform, the density unevenness is generated in the image due to the variation in the size of the beam spot.

The present invention has been made in view of the above, and an image forming apparatus and a light amount correction capable of effectively suppressing vertical stripe-like density unevenness occurring in an image and performing high-quality image formation. an object of the present invention is to provide an mETHODS.

In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention includes an optical writing head in which a plurality of light emitting units that emit light according to image data are arranged in the main scanning direction; An image forming unit having a photoconductor exposed by writing light from the optical writing head, developing a latent image by exposure of the photoconductor to form an image according to the image data; A first acquisition unit configured to acquire first correction data for correcting light amounts of a plurality of light emitting units of the optical writing head so as to correct density unevenness of an image caused by the writing head; A second acquisition unit that acquires second correction data for correcting the light amounts of the plurality of light emitting units of the optical writing head so as to cancel out the density unevenness of the image due to the first correction data; the first correction data; The third correction data is generated by combining the second correction data. A generating unit, based on the third correction data, a correction unit that corrects a plurality of light intensity of the light emitting portion of the optical write head, an image forming apparatus wherein the first correction data, the First lightness data representing the lightness distribution in the main scanning direction of the first image obtained by mounting the optical writing head at a reference position of another image forming apparatus different from the image forming apparatus and forming an image of the test pattern. A main image scanning direction of a second image obtained by mounting the optical writing head at a position shifted by a predetermined distance in the main scanning direction from the reference position of the other image forming apparatus. Correction data calculated based on a difference from the second lightness data representing the lightness distribution .

  According to the present invention, there is an effect that high-quality image formation can be performed by more effectively suppressing vertical stripe-like density unevenness generated in an image.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating the internal structure of the optical writing head. FIG. 3 is a functional block diagram illustrating functions of the control unit related to light amount correction. FIG. 4 is a flowchart illustrating a processing procedure of light amount correction executed in the image forming apparatus according to the embodiment. FIG. 5 is a diagram showing a specific example of a position adjusting mechanism for adjusting the mounting position of the optical writing head in the image forming apparatus in the factory. FIG. 6 is an enlarged view showing the vicinity of the left end portion of the optical writing head shown in FIG. FIG. 7 is a diagram illustrating an example of a gray image obtained by forming an image of a test pattern. FIG. 8 is a diagram illustrating a specific example of a method for generating the first correction data and the second correction data. FIG. 9 is a diagram illustrating the relationship between the brightness of an image and the amount of exposure light. FIG. 10 is a diagram illustrating a method for generating first correction data and second correction data using three images.

With reference to the accompanying drawings, an embodiment of an image forming apparatus and the light quantity correction how according to the present invention in detail.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 according to the present embodiment forms an image by an electrophotographic method. As shown in FIG. 1, an optical writing head 10, an image forming unit 20, a paper feeding device 30, And a fixing device 40. In addition, the image forming apparatus 1 according to the present embodiment includes a head driving unit 50 that drives the optical writing head 10 according to image data, a control unit 60 that controls the operation of the entire image forming apparatus 1, and various types of information. And a non-volatile memory 70 for storage.

  FIG. 1 assumes an image forming apparatus 1 configured as a monochrome printer, and shows only one optical writing head 10 and one image forming unit 20. When the image forming apparatus 1 is configured as a color printer, the optical writing head 10 and the image forming unit 20 are provided corresponding to each color.

  The optical writing head 10 is driven by the head driving unit 50 and outputs writing light corresponding to the image data.

  FIG. 2 is a diagram for explaining the internal structure of the optical writing head 10 and shows a part of the optical writing head 10 in an enlarged manner. As shown in FIG. 2, the optical writing head 10 includes a plurality of light emitting units 11 arranged along the main scanning direction indicated by an arrow A in the drawing, and a plurality of lenses 12 corresponding to each light emitting unit 11. .

  For example, an LED is used as the light emitting unit 11 of the optical writing head 10. When the light emitting unit 11 is turned on, light from the light emitting unit 11 is collected by a lens 12 provided corresponding to the light emitting unit 11 to form a beam spot on a photoreceptor 21 described later of the image forming unit 20. This beam spot is applied to the photoconductor 21 as writing light corresponding to one pixel of the image, and the photoconductor 21 is exposed.

  The size of the beam spot applied to the photosensitive member 21 is determined by the error in creating the lens 12 provided corresponding to each light emitting unit 11 of the optical writing head 10, scratches generated in the lens 12, the light emitting unit 11 and the lens 12. May be different for each of the plurality of light emitting units 11 due to an alignment error. When the size of the beam spot irradiated to the photoconductor 21 is different for each light emitting unit 11, even if the light intensity of each light emitting unit 11 is corrected and the exposure energy on the photoconductor 21 is made uniform, the image has a vertical stripe shape. Density unevenness may occur.

  Therefore, in the image forming apparatus 1 according to the present embodiment, not only the image density unevenness due to the variation in the amount of light between the plurality of light emitting units 11 of the optical writing head 10, but also the beam spot when each light emitting unit 11 is turned on. The light quantity of each light emitting unit 11 of the optical writing head 10 is corrected so that all density unevenness due to the optical writing head 10 such as image density unevenness due to the difference in size is corrected. Details of the light amount correction of the optical writing head 10 will be described later.

  The optical writing head 10 is replaceably attached to the main body of the image forming apparatus 1. When a defect such as deterioration with time occurs in the optical writing head 10, the optical writing head 10 in which the defect has occurred is replaced with a new optical writing head 10.

  When the optical writing head 10 is replaced, correction data (first correction data) corresponding to the newly mounted optical writing head 10 is acquired by the control unit 60, and each light emitting unit 11 of the optical writing head 10 is acquired. Correction data (third correction data) for correcting the amount of light is updated. The optical writing head 10 can be replaced by, for example, providing a mechanical switch at a position where the optical writing head 10 of the apparatus main body is mounted, or mounting the optical writing head 10 by an optical or electrical detector. It can be detected by a technique such as detecting the presence or absence.

  The image forming unit 20 is a unit obtained by unitizing an electrophotographic image forming process, and includes a drum-shaped photoreceptor 21, a charging device 22, a developing device 23, and a cleaning device 24.

  The photoconductor 21 is rotated in the direction of arrow B in the drawing at a constant peripheral speed by a motor (not shown). The surface of the photoreceptor 21 is uniformly charged to a specific polarity by the charging device 22. Then, the surface of the charged photoconductor 21 is irradiated with writing light from the optical writing head 10 to expose the photoconductor 21, and an electrostatic latent image corresponding to image data is formed on the photoconductor 21. .

  The electrostatic latent image on the photoreceptor 21 is developed by the developing device 23 and becomes a toner image corresponding to the image data. The toner image on the photoreceptor 21 is transferred onto the paper P. Residual toner on the photoreceptor 21 that has not been transferred to the paper P is removed by the cleaning device 24.

  The sheets P are taken out from the sheet feeding device 30 one by one and conveyed along a predetermined conveyance path by a conveyance device such as a pair of conveyance rollers (not shown). Then, when the paper P passes between the transfer device 35 charged to the opposite polarity to the toner and the photoconductor 21, the toner image formed on the photoconductor 21 is transferred to the paper P.

  The sheet P on which the toner image has been transferred is conveyed to the fixing device 40 and passes through between the heat roller 41 controlled to be heated to a constant temperature and the pressure roller 42 that is in pressure contact with the heat roller 41. The toner image transferred to P is fixed on paper P. The paper P on which the toner image is fixed is discharged to the outside of the image forming apparatus 1.

  In the image forming apparatus 1 illustrated in FIG. 1, the toner image formed on the photoconductor 21 of the image forming unit 20 is directly transferred onto the paper P, but the toner image formed on the photoconductor 21 is used. May be transferred onto the paper P after being transferred to the intermediate transfer member.

  The image forming unit 20 has unique characteristics such as uneven charging of the photosensitive member 21 and uneven development of the developing unit 23. Even if the light quantity of each light emitting section 11 of the optical writing head 10 is corrected so that all density unevenness due to the optical writing head 10 is corrected by the characteristic unique to the image forming unit 20, In some cases, vertical stripe-like density unevenness occurs in an image.

  Therefore, in the image forming apparatus 1 according to the present embodiment, in addition to correcting the density unevenness caused by the optical writing head 10, the image density unevenness caused by the image forming unit 20 is further offset. In addition, the light quantity of each light emitting unit 11 of the optical writing head 10 is corrected.

  Similar to the optical writing head 10, the image forming unit 20 is replaceably attached to the apparatus main body of the image forming apparatus 1. When a defect such as deterioration with time occurs in the image forming unit 20, the image forming unit 20 in which the defect has occurred is replaced with a new image forming unit 20.

  When the image forming unit 20 is replaced, correction data (second correction data) corresponding to the newly mounted image forming unit 20 is acquired by the control unit 60, and the light amount of each light emitting unit 11 of the optical writing head 10. Correction data (third correction data) for correcting is updated. The replacement of the image forming unit 20 can be detected by a method similar to the method of detecting the replacement of the optical writing head 10.

  The head drive unit 50 drives the optical writing head 10 according to the image data. Specifically, the head driving unit 50 switches on / off the plurality of light emitting units 11 of the optical writing head 10 according to the image data. At this time, the head driving unit 50 adjusts the value of the energization current to the light emitting unit 11 to be lit based on the output correction signal from the control unit 60. Thereby, the light quantity of each light emission part 11 of the optical writing head 10 is correct | amended.

  The control unit 60 is configured as, for example, a one-chip microcomputer including a CPU, a ROM, a RAM, and the like, and the CPU executes the program stored in the ROM using the RAM as a work area, whereby the operation of the entire image forming apparatus 1 is performed. Control. In particular, as a characteristic function in the image forming apparatus 1 according to the present embodiment, the control unit 60 realizes a function of correcting the light amount of each light emitting unit 11 of the optical writing head 10.

  FIG. 3 is a functional block diagram illustrating functions of the control unit 60 related to light amount correction. As illustrated in FIG. 3, the control unit 60 includes a first acquisition unit 61, a second acquisition unit 62, a generation unit 63, and a correction unit 64 as functions related to light amount correction.

  The first acquisition unit 61 uses first correction data D1 for correcting the light amounts of the plurality of light emitting units 11 of the optical writing head 10 so as to correct the density unevenness of the image caused by the optical writing head 10. Obtained and stored in the nonvolatile memory 70. For example, the first acquisition unit 61 is called when the control unit 60 detects the replacement of the optical writing head 10, and the first correction data corresponding to the optical writing head 10 newly attached to the apparatus main body by the replacement. D1 is acquired.

  Specifically, the optical writing head 10 is provided with a storage device 10a in which the first correction data D1 corresponding to the optical writing head 10 is stored. When the optical writing head 10 is replaced, the first acquisition unit 61 accesses the storage device 10a provided in the optical writing head 10 newly attached to the apparatus main body, and from the storage device 10a to the first The correction data D1 is acquired and stored in the nonvolatile memory 70. Therefore, the nonvolatile memory 70 stores the first correction data D1 corresponding to the optical writing head 10 currently mounted on the apparatus main body.

  The second acquisition unit 62 acquires second correction data D2 for correcting the light amounts of the plurality of light emitting units 11 of the optical writing head 10 so as to cancel out the density unevenness of the image caused by the image forming unit 20. And stored in the nonvolatile memory 70. For example, the second acquisition unit 62 is called when the control unit 60 detects the replacement of the image forming unit 20, and receives the second correction data D2 corresponding to the image forming unit 20 newly attached to the apparatus main body by the replacement. get.

  Specifically, the image forming unit 20 is provided with a storage device 20a in which the second correction data D2 corresponding to the image forming unit 20 is stored. When the image forming unit 20 is replaced, the second acquisition unit 62 accesses the storage device 20a provided in the image forming unit 20 newly attached to the apparatus main body, and receives the second correction data from the storage device 20a. D2 is acquired and stored in the nonvolatile memory 70. Therefore, the non-volatile memory 70 stores the second correction data D2 corresponding to the image forming unit 20 currently attached to the apparatus main body.

  The generating unit 63 combines the first correction data D1 stored in the non-volatile memory 70 and the second correction data D2 stored in the non-volatile memory 70 to generate the third correction data D3. Stored in the memory 70. The combination of the first correction data D1 and the second correction data D2 is, for example, the correction amount represented by the first correction data D1 for each light emitting unit 11 of the optical writing head 10 corresponding to the pixel of the image. And the correction amount represented by the second correction data D2.

  The generation unit 63 is called, for example, when the control unit 60 detects replacement of the optical writing head 10 or replacement of the image forming unit 20. When the optical writing head 10 is replaced, the generation unit 63 includes the first correction data D1 corresponding to the new optical writing head 10 stored in the nonvolatile memory 70 by the first acquisition unit 61, and the nonvolatile The second correction data D2 stored in the memory 70 is synthesized to generate new third correction data D3. In addition, when the image forming unit 20 is replaced, the generating unit 63 includes the second correction data D2 corresponding to the new image forming unit 20 stored in the nonvolatile memory 70 by the second acquiring unit 62, and the nonvolatile memory. The first correction data D1 stored in 70 is combined to generate new third correction data D3.

  When the generation unit 63 generates new third correction data D3, the generation unit 63 stores the generated new third correction data D3 in the nonvolatile memory 70. At this time, if the third correction data D3 generated in the past is stored in the nonvolatile memory 70, the third correction data D3 is updated with the newly generated third correction data D3. As a result, the latest third correction data D3 is stored in the nonvolatile memory 70.

  The correcting unit 64 corrects the light amounts of the plurality of light emitting units 11 of the optical writing head 10 based on the third correction data D3 stored in the nonvolatile memory 70. For example, the correction unit 64 is called when image data is input to the head driving unit 50 and the optical writing head 10 is driven according to the image data input by the head driving unit 50. Then, the correction unit 64 reads out the third correction data D3 from the nonvolatile memory 70, and outputs an output correction signal for correcting the light amount of each light emitting unit 11 of the optical writing head 10 according to the third correction data D3. It is generated and supplied to the head driving unit 50. As described above, the head drive unit 50 adjusts the value of the energization current to the light emitting unit 11 that is turned on according to the image data, based on the output correction signal from the control unit 60. Thereby, the light quantity of each light emission part 11 of the optical writing head 10 is correct | amended.

  FIG. 4 is a flowchart showing a processing procedure of light amount correction executed in the image forming apparatus 1 according to the present embodiment. The light amount correction shown in the flowchart of FIG. 4 is repeatedly executed by the control unit 60 at a predetermined cycle while the image forming apparatus 1 is activated, for example.

  First, the control unit 60 determines whether or not the optical writing head 10 has been replaced (step S101). When the optical writing head 10 is replaced (step S101: Yes), the first acquisition unit 61 obtains the first correction data D1 corresponding to the optical writing head 10 newly attached to the apparatus main body by replacement. Obtained (step S102), the obtained first correction data D1 is stored in the nonvolatile memory 70 (step S103), and the process proceeds to step S104. On the other hand, when the optical writing head 10 has not been replaced (step S101: No), the process proceeds to step S104 without performing the processes of steps S102 and S103.

  Next, the control unit 60 determines whether or not the image forming unit 20 has been replaced (step S104). When the image forming unit 20 is replaced (step S104: Yes), the second acquisition unit 62 acquires the second correction data D2 corresponding to the image forming unit 20 newly attached to the apparatus main body by replacement. (Step S105), the acquired second correction data D2 is stored in the nonvolatile memory 70 (Step S106), and the process proceeds to Step S107. On the other hand, if the image forming unit 20 has not been exchanged (step S104: No), the process proceeds to step S107 without performing the processes of steps S105 and S106.

  Next, the control unit 60 determines whether or not the optical writing head 10 has been replaced or the image forming unit 20 has been replaced (step S107). If the optical writing head 10 or the image forming unit 20 is replaced (step S107: Yes), the generation unit 63 uses the first correction data D1 and the second correction data stored in the nonvolatile memory 70. The third correction data D3 is generated by combining with the data D2 (step S108), the generated third correction data D3 is stored in the nonvolatile memory 70 (step S109), and the process proceeds to step S110. On the other hand, if neither the optical writing head 10 nor the image forming unit 20 has been replaced (step S107: No), the process proceeds to step S110 without performing the processes of steps S108 and S109.

  Next, the control unit 60 determines whether image data is input to the head driving unit 50 (step S110). When the image data is input to the head driving unit 50 (step S110: Yes), the correction unit 64 generates an output correction signal corresponding to the third correction data D3 stored in the nonvolatile memory 70, The head drive unit 50 is supplied (step S111). Thereby, the optical writing head 10 is driven according to the image data in a state where the light amount of each light emitting unit 11 of the optical writing head 10 is corrected based on the third correction data D3. On the other hand, if no image data is input to the head drive unit 50 (step S110: No), the process returns to step S101 and the subsequent processing is repeated.

  Hereinafter, an example of a specific method for generating the first correction data D1 unique to the optical writing head 10 and the second correction data D2 unique to the image forming unit 20 will be described. As described above, the first correction data D1 unique to the optical writing head 10 is stored in advance in the storage device 10a provided in the optical writing head 10, for example. Further, as described above, the second correction data D2 unique to the image forming unit 20 is stored in advance in the storage device 20a provided in the image forming unit 20, for example. The first correction data D1 and the second correction data D2 are generated in advance in a factory that manufactures the optical writing head 10 and the image forming unit 20, and are stored in the storage device 10a and the storage device 20a.

  The first correction data D1 and the second correction data D2 are stored in, for example, the optical writing head 10 and the image forming apparatus installed in the factory (an image forming apparatus different from the image forming apparatus 1 according to the present embodiment). The image forming unit 20 is mounted, and this image forming apparatus generates the test pattern in an image formation state without performing the light amount correction of the optical writing head 10. The test pattern is a pattern that becomes a gray image having a uniform density, and the light emitting units 11 of the optical writing heads 10 arranged in the main scanning direction are always lit at a rate of, for example, about 25% of all the lines in the sub scanning direction. It is a pattern.

  A gray image obtained by image-forming a test pattern without performing light amount correction of the optical writing head 10 by the image forming apparatus in the factory to which the optical writing head 10 and the image forming unit 20 are mounted is, The density unevenness caused by the optical writing head 10 and the density unevenness caused by the image forming unit 20 are mixed and generated. Therefore, a gray image (hereinafter referred to as a first image) obtained by mounting the optical writing head 10 at the reference position of the image forming apparatus in the factory and forming an image of the test pattern, and the main scanning direction from the reference position. The optical writing head 10 is mounted at a position shifted by a predetermined distance X and a gray image (hereinafter referred to as a second image) obtained by forming a test pattern image is used. Density unevenness caused by the image forming unit 20 is separated.

  FIG. 5 is a diagram showing a specific example of a position adjusting mechanism for adjusting the mounting position of the optical writing head 10 in the image forming apparatus in the factory, and FIG. 6 is a diagram of the optical writing head 10 shown in FIG. It is a figure which expands and shows the left end part vicinity.

  As shown in FIG. 5, the optical writing head 10 is attached to a head support member 100 included in an image forming apparatus in a factory via a position adjustment member 110. As shown in FIG. 6, the position adjusting member 110 is provided with a long hole 111 that is long in the main scanning direction. Then, the fixing bracket 112 provided in the optical writing head 10 is inserted into the long hole 111 of the position adjusting member 110. The length of the long hole 111 corresponds to the predetermined distance X described above.

  The first image and the second image are acquired as follows. First, as shown in FIG. 6A, the shaft of the fixing bracket 112 provided in the optical writing head 10 is abutted against one end of the long hole 111, and the fixing bracket 112 is tightened. As a result, the optical writing head 10 is mounted at the reference position of the image forming apparatus in the factory. In this state, the first image is obtained by performing the above-described test pattern image formation.

  Next, as shown in FIG. 6B, the shaft of the fixing bracket 112 provided in the optical writing head 10 is abutted against the other end of the long hole 111 to tighten the fixing bracket 112. As a result, the optical writing head 10 is mounted at a position shifted by a predetermined distance X from the reference position of the image forming apparatus in the factory. In this state, the second image is obtained by performing the above-described test pattern image formation.

  FIG. 7 is a diagram illustrating an example of a gray image obtained by forming an image of a test pattern. FIG. 7A illustrates an example of the first image, and FIG. 7B illustrates an example of the second image. ing. The direction indicated by arrow A in the figure is the main scanning direction.

  In the first image shown in FIG. 7 (a) and the second image shown in FIG. 7 (b), vertical stripe-shaped density irregularities indicated by L1, L2, and L3 in the figure respectively appear. When the positions of the density unevenness of L1, L2, and L3 in the main scanning direction are compared between the first image and the second image, the positions of the density unevenness of L1 and L3 in the second image are the positions of L1 and L3 in the first image. The position is a predetermined distance X away from the density unevenness position. On the other hand, the position of L2 density unevenness in the second image is the same as the position of L2 density unevenness in the first image.

  Therefore, L1 and L3 are vertical stripe-like density unevenness caused by the optical writing head 10, and L2 is vertical stripe-like density unevenness caused by the image forming unit 20. It turns out that it is. As described above, by using the first image and the second image, it is possible to separate the density unevenness caused by the optical writing head 10 and the density unevenness caused by the image forming unit 20. And from these 1st image and 2nd image, the 1st correction data D1 for correct | amending the light quantity of each light emission part 11 of the optical writing head 10 so that the density nonuniformity resulting from the optical writing head 10 may be eliminated, Second correction data D2 for correcting the light amount of each light emitting unit 11 of the optical writing head 10 so as to eliminate density unevenness due to the image forming unit 20 is generated.

  The value of the predetermined distance X is preferably 1 mm or more. According to visual evaluation or the like, the width of the most noticeable vertical stripe-shaped density unevenness is 0.5 to 1 mm. This is because, when the value of the predetermined distance X is less than 1 mm, among the density unevenness caused by the optical writing head 10, the most noticeable density unevenness having a width of 1 mm or less cannot be separated from the density unevenness caused by the image forming unit 20. .

  FIG. 8 is a diagram illustrating a specific example of a method for generating the first correction data D1 and the second correction data D2. In order to generate the first correction data D1 and the second correction data D2, first, the first image and the second image are optically read by a scanner or the like, and first brightness data as shown in FIG. And second brightness data as shown in FIG.

  The first lightness data is data representing the lightness distribution in the main scanning direction of the first image. For example, the lightness of a plurality of pixels arranged in the sub-scanning direction at the same position in the main scanning direction of the first image is averaged. Can be obtained. The second lightness data is data representing the lightness distribution in the main scanning direction of the second image. For example, the lightness distribution of a plurality of pixels arranged in the subscanning direction at the same position in the main scanning direction of the second image is averaged. Can be obtained. The first lightness data and the second lightness data are data reflecting vertical stripe-like density unevenness appearing in the first image and the second image, respectively.

  Hereinafter, the first lightness data illustrated in FIG. 8A is represented as data a, and the second lightness data illustrated in FIG. 8B is represented as data b. When the data a and the data b are compared, the position of the L4 waveform in the main scanning direction is shifted by a predetermined distance X, and the other waveforms match. From this, it can be seen that the waveform of L4 is a waveform reflecting density unevenness due to the optical writing head 10, and the other waveforms are waveforms reflecting density unevenness due to the image forming unit 20.

  Next, the data b is subtracted from the data a to obtain data c from which the influence of density unevenness caused by the image forming unit 20 is eliminated, as shown in FIG. When obtaining the data c, data corresponding to a predetermined distance X at both ends in the main scanning direction of the data a and data corresponding to a predetermined distance X at both ends in the main scanning direction of the data b are deleted, and these data are deleted. Data c is obtained by subtracting data b from a. In this data c, the same waveform as the waveform L4 appears at the same position as the waveform L4 in the data a, and a waveform obtained by inverting the waveform L4 appears at the same position as the waveform L4 in the data b.

  Next, by shifting the data c by −X in the main scanning direction (shifting the data c by a predetermined distance X in the left direction in the figure), data d as shown in FIG. 8D is created. Then, the data e shown in FIG. 8E is obtained by subtracting the data d from the data c and multiplying by 1/2. This data e is data representing the vertical stripe-like density unevenness caused by the optical writing head 10. Further, by subtracting data e from data a, data f shown in FIG. 8F is obtained. This data f is data representing the vertical stripe-like density unevenness caused by the image forming unit 20.

  It should be noted that the data e representing the vertical stripe-shaped density unevenness caused by the optical writing head 10 is inverted at half of the waveform at both ends of the waveform corresponding to the vertical stripe-shaped density unevenness. Waveforms L5 and L6 appear. These waveforms L5 and L6 are waveforms that occur as a side effect when data representing vertical stripe-like density unevenness due to the optical writing head 10 is obtained by the above-described method, but are waveforms with small peaks, and are used for light amount correction. The effect is small and can be ignored.

  The data e and data f obtained as described above are data corresponding to the brightness of the image, but since there is a linear correlation between the brightness of the image and the amount of exposure light, a coefficient K representing the relationship is obtained. Is multiplied by the data e and the data f, respectively, so that the data e and the data f can be converted into data representing the light quantity.

  FIG. 9 is a diagram illustrating the relationship between the brightness of an image and the amount of exposure light. The slope of the graph shown in FIG. For example, if the left end value of the graph in FIG. 9 is lightness 30 and the exposure light amount is 1 mW, the right end value is lightness 60 and the exposure light amount is 0.3 mW, the slope (coefficient K) of the graph is 0.01 ( = (1-0.7) / (60-30)).

  As described above, the vertical stripe-like density unevenness caused by the optical writing head 10 is exposed by multiplying the data e representing the vertical stripe-like density unevenness caused by the optical writing head 10 by the coefficient K described above. Data converted to light intensity is obtained. Then, the data obtained by inverting the data corrects the light quantity of the plurality of light emitting units 11 of the optical writing head 10 so that the vertical stripe-shaped density unevenness caused by the optical writing head 10 is corrected. 1 correction data D1. The first correction data D1 obtained in this way is stored in the storage device 10a of the optical writing head 10. The optical writing head 10 is shipped from the factory with the first correction data D1 stored in the storage device 10a.

  Further, the data f representing the vertical stripe-like density unevenness caused by the image forming unit 20 is multiplied by the coefficient K described above, thereby converting the vertical stripe-like density unevenness caused by the image forming unit 20 into the exposure light amount. Is obtained. Then, a second correction for correcting the light amounts of the plurality of light emitting units 11 of the optical writing head 10 so that the data obtained by inverting this data cancels the vertical stripe-shaped density unevenness caused by the image forming unit 20. Data D2. The second correction data D2 obtained in this way is stored in the storage device 20a of the image forming unit 20. The image forming unit 20 is shipped from the factory with the second correction data D2 stored in the storage device 20a.

  In the example described above, the first image obtained by mounting the optical writing head 10 at the reference position of the image forming apparatus in the factory and the first image obtained by mounting at a position shifted by a predetermined distance X from the reference position. The first correction data D1 and the second correction data D2 are generated using the two images. However, three or more images may be acquired with three or more mounting positions of the optical writing head 10 and the first correction data D1 and the second correction data D2 may be generated using these three or more images. .

  FIG. 10 is a diagram illustrating a method for generating the first correction data D1 and the second correction data D2 using three images. In this case, the first image is acquired by mounting the optical writing head 10 at the reference position, the second image is acquired by mounting the optical writing head 10 at a position shifted by a predetermined distance X1 from the reference position, The writing head 10 is mounted at a position shifted by a predetermined distance X2 from the reference position, and a third image is acquired.

  First, using the first image and the second image, data e1 representing the vertical streak-like density unevenness caused by the optical writing head 10 in the same procedure as described above (see FIG. 10A). Get. Subsequently, using the first image and the third image, the data e2 representing the vertical stripe-shaped density unevenness caused by the optical writing head 10 in the same procedure as described above (see FIG. 10B). Get. And the data e3 shown in FIG.10 (c) is obtained by taking the average of the data e1 and the data e2. The data e3 shown in FIG. 10C is used as final data representing the vertical stripe-shaped density unevenness caused by the optical writing head 10, and the data e3 multiplied by the coefficient K is inverted. 1 correction data D1.

  Further, by subtracting the data e3 shown in FIG. 10C from the first brightness data (data a shown in FIG. 8A) obtained from the first image, the data f shown in FIG. can get. This data f is data representing the vertical stripe-like density unevenness caused by the image forming unit 20. The data f multiplied by a coefficient K and inverted is referred to as second correction data D2.

  In the data e3 representing the vertical stripe-shaped density unevenness caused by the optical writing head 10, four waveforms appearing as side effects described above appear. However, these waveforms can be ignored because their peaks are sufficiently small as 1/4 of the waveform corresponding to the vertical stripe-shaped density unevenness, and the influence on the light amount correction is smaller than the above-described example.

  The above is an example in which the first correction data D1 and the second correction data D2 are generated using three images. By using more images, it is possible to further reduce the influence of the side effect waveform described above. Therefore, it is possible to generate the first correction data D1 and the second correction data D2 with higher accuracy.

  As described above in detail with reference to specific examples, in the image forming apparatus 1 according to the present embodiment, the first acquisition unit 61 is configured to display an image caused by the optical writing head 10 attached to the apparatus main body. First correction data D1 for correcting the light amounts of the plurality of light emitting units 11 of the optical writing head 10 so as to correct density unevenness is acquired. In addition, the second acquisition unit 62 corrects the light amounts of the plurality of light emitting units 11 of the optical writing head 10 so as to cancel out the density unevenness of the image caused by the image forming unit 20 mounted on the apparatus main body. Second correction data D2 is acquired. Then, the generation unit 63 generates the third correction data D3 by combining the first correction data D1 and the second correction data D2, and the correction unit 64 uses the optical write head based on the third correction data D3. The light amount of each of the ten light emitting units 11 is corrected. Therefore, according to the image forming apparatus 1 according to the present embodiment, high-quality image formation can be performed by more effectively suppressing the vertical stripe-like density unevenness generated in the image.

  Further, according to the image forming apparatus 1 according to the present embodiment, when the optical writing head 10 is replaced, the first correction data corresponding to the optical writing head 10 to which the first acquisition unit 61 is newly attached is provided. When D1 is acquired and the image forming unit 20 is replaced, the second acquisition unit 62 acquires second correction data D2 corresponding to the newly mounted image forming unit 20. Then, when the first correction data D1 and the second correction data D2 are newly acquired, the generation unit 63 generates new third correction data D3. Therefore, when the optical writing head 10 or the image forming unit 20 is replaced, it is not necessary to generate light amount correction data by actually forming an image of a test pattern in the image forming apparatus 1. Light amount correction can be performed efficiently.

  For example, the CPU of the control unit 60 uses the RAM as a work area to execute a program provided by being incorporated in advance in the ROM in the process related to the light amount correction in the image forming apparatus 1 according to the present embodiment. Can be realized. The program executed by the CPU of the control unit 60 is an installable or executable file and can be read by a computer such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). You may comprise so that it may record and provide on a recording medium.

  The program executed by the CPU of the control unit 60 may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. Further, the program executed by the CPU of the control unit 60 may be provided or distributed via a network such as the Internet.

  The program executed by the CPU of the control unit 60 has a module configuration including the first acquisition unit 61, the second acquisition unit 62, the generation unit 63, and the correction unit 64 described above. As actual hardware, for example, When the CPU reads the program from the ROM and executes it, the above-described units are loaded onto the RAM, and the above-described units are generated on the RAM.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied with various modifications and changes in the implementation stage without departing from the scope of the invention. For example, in the above-described embodiment, when the optical writing head 10 or the image forming unit 20 is replaced, the generation unit 63 generates new third correction data D3 and stores it in the nonvolatile memory 70. When performing image formation according to image data, the correction unit 64 performs light amount correction of the optical writing head 10 based on the third correction data D3 stored in the nonvolatile memory 70. However, only the first correction data D1 and the second correction data D2 are stored in the non-volatile memory 70, and the generation unit 63 performs the first correction data D1 and the second correction data D2 each time image formation corresponding to the image data is performed. The third correction data D3 may be generated by combining the correction data D2, and the correction unit 64 may perform light amount correction based on the generated third correction data.

  Each time image formation is performed according to the image data, the first acquisition unit 61 and the second acquisition unit 62 acquire the first correction data D1 and the second correction data D2, and the generation unit 63 performs the first correction. The data D1 and the second correction data D2 may be combined to generate the third correction data D3, and the correction unit 64 may perform light amount correction based on the third correction data.

  In the above-described embodiment, the first acquisition unit 61 acquires the first correction data D1 from the storage device 10a provided in the optical writing head 10. The structure which acquires the 1st correction data D1 which the operator input manually at the time of replacement | exchange of the insertion head 10 may be sufficient. In the above-described embodiment, the second acquisition unit 62 acquires the second correction data D2 from the storage device 20a provided in the image forming unit 20. However, the second acquisition unit 62 is configured to acquire the second correction data D2. The structure which acquires the 2nd correction data D2 which the operator input manually at the time of replacement | exchange of 20 may be sufficient.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Optical writing head 10a Memory | storage device 11 Light emission part 20 Image forming unit 20a Memory | storage device 21 Photoconductor 50 Head drive part 60 Control part 61 1st acquisition part 62 2nd acquisition part 63 Generation part 64 Correction | amendment part D1 1st 1 correction data D2 2nd correction data D3 3rd correction data

JP 2004-351721 A

Claims (7)

An optical writing head in which a plurality of light emitting sections that emit light according to image data are arranged in the main scanning direction;
An image forming unit that has a photoconductor exposed by writing light from the optical writing head, develops a latent image by exposure of the photoconductor, and forms an image according to the image data;
A first acquisition unit that acquires first correction data for correcting light amounts of a plurality of light emitting units of the optical writing head so as to correct density unevenness of an image caused by the optical writing head;
A second acquisition unit that acquires second correction data for correcting light amounts of a plurality of light emitting units of the optical writing head so as to cancel out density unevenness of an image caused by the image forming unit;
A generating unit that combines the first correction data and the second correction data to generate third correction data;
An image forming apparatus comprising: a correction unit that corrects light amounts of a plurality of light emitting units of the optical writing head based on the third correction data;
The first correction data is obtained by mounting the optical writing head at a reference position of another image forming apparatus different from the image forming apparatus and forming a test pattern in the main scanning direction of the first image. First brightness data representing a brightness distribution and the optical writing head mounted at a position shifted from the reference position of the other image forming apparatus by a predetermined distance in the main scanning direction to obtain the test pattern. An image forming apparatus comprising: correction data calculated based on a difference from second brightness data representing a brightness distribution in a main scanning direction of the second image.   The image forming apparatus according to claim 1, wherein the second correction data is correction data calculated based on a difference between the first brightness data and the first correction data.   The image density unevenness caused by the optical writing head includes image density unevenness due to a difference in size of a beam spot on the photosensitive member when each light emitting portion of the optical writing head is turned on. The image forming apparatus according to claim 1 or 2. The optical writing head and the image forming unit are mounted to be exchangeable with respect to the apparatus main body,
The first acquisition unit acquires the first correction data corresponding to the newly mounted optical writing head when the optical writing head is replaced;
The said 2nd acquisition part acquires the said 2nd correction data corresponding to the said newly installed image forming unit, when the said image forming unit is replaced | exchanged, The Claim 1 thru | or 3 characterized by the above-mentioned. The image forming apparatus according to claim 1. The first correction data is stored in a storage device provided in the optical writing head,
The first acquisition unit acquires the first correction data from the storage device provided in the newly installed optical writing head when the optical writing head is replaced. The image forming apparatus according to any one of claims 1 to 4. The second correction data is stored in a storage device provided in the image forming unit,
The second acquisition unit, when the imaging unit is replaced, acquires the second correction data from the storage device provided in the newly installed imaging unit. Item 6. The image forming apparatus according to any one of Items 1 to 5. An optical writing head in which a plurality of light emitting sections that emit light according to image data are arranged in the main scanning direction;
An image forming unit that has a photoconductor exposed by writing light from the optical writing head and develops a latent image generated by exposure of the photoconductor to form an image according to the image data. A light amount correction method executed in an image forming apparatus,
Obtaining first correction data for correcting light amounts of a plurality of light emitting portions of the optical writing head so as to correct density unevenness of an image caused by the optical writing head;
Obtaining second correction data for correcting light amounts of a plurality of light emitting units of the optical writing head so as to cancel out density unevenness of an image caused by the image forming unit;
Combining the first correction data and the second correction data to generate third correction data;
Correcting the light amounts of a plurality of light emitting units of the optical writing head based on the third correction data,
The first correction data is obtained by mounting the optical writing head at a reference position of another image forming apparatus different from the image forming apparatus and forming a test pattern in the main scanning direction of the first image. First brightness data representing a brightness distribution and the optical writing head mounted at a position shifted from the reference position of the other image forming apparatus by a predetermined distance in the main scanning direction to obtain the test pattern. A light amount correction method, characterized in that the correction data is correction data calculated based on a difference from the second lightness data representing the lightness distribution in the main scanning direction of the second image.