Patent Application
20210117739
The present invention relates to an electrophotographic image forming apparatus.
With regard to a printer being an electrophotographic image forming apparatus, there is generally known a method of exposing a photosensitive drum through use of an exposure head adopting, for example, a light emitting diode (LED) or an organic electro luminescence (EL), to thereby form a latent image on the photosensitive drum. The exposure head includes rows of light emitting elements arranged in a longitudinal direction of the photosensitive drum and a rod lens array configured to cause light beams from the rows of light emitting elements to form an image on the photosensitive drum. A known configuration of the LED or the organic EL has a surface emitting shape, in which a direction of illuminating light from a light emitting surface is matched with a direction of the rod lens array. A length of each of the rows of the light emitting elements is determined by a width of an image region on the photosensitive drum, and intervals between the light emitting elements are determined by a resolution of the printer. For example, in the case of a 1,200 dpi printer, intervals between pixels are 21.16 μm and accordingly the intervals between the light emitting elements have values corresponding to 21.16 μm. A printer using such an exposure head uses fewer components than those used in a laser scanning printer, in which a photosensitive drum is scanned with a laser beam deflected by a rotary polygon mirror. Therefore, it is easier to reduce the size and cost of the apparatus. In addition, in the printer using the exposure head, sound resulting from the rotation of the rotary polygon minor is reduced.
In such a configuration using the exposure head, an image tilt is liable to occur for each toner color due to variations in mounting position of the exposure head with respect to the photosensitive drum. In order to correct this tilt, there is a method of shifting a position of image data in a rotation direction (sub-scanning direction) of the photosensitive drum. Further, as a method for reducing an image defect at misregistration position of the image when the image data is shifted, there is known a method of increasing a resolution in the sub-scanning direction to shift the image data more finely. In Japanese Patent No. 5691330, there is described a proposal for achieving a process of performing image data shift in the sub-scanning direction at a resolution of N times larger than that in a main scanning direction with a simpler configuration.
Further, the exposure head using the LED generally has a configuration in which a plurality of surface emitting element array chips are arranged side by side to allow image formation corresponding to an image width of about 316 mm. However, depending on an accuracy of mounting the surface emitting element array chips, a misregistration of about several microns occurs at a joint portion. This misregistration may disadvantageously cause formation of a black streak image or a white streak image at the joint portion. There is known a technology of correcting a streak formed at the joint portion. For example, in Japanese Patent No. 4344585, there is described a configuration in which a light amount of the light emitting element corresponding to the joint position and a light amount of the surrounding light emitting element are controlled depending on an overlapping degree of the light emitting elements corresponding to the position of the joint portion.
However, although Japanese Patent No. 5691330 has a description about a filtering process (resolution converting process), there is no description about correction of the joint portion. Further, although Japanese Patent No. 4344585 has a description about correction of the joint portion, there is no description about the filtering process (resolution conversion). In the configuration in which the image data is subjected to image processing other than the correction of the joint portion, the timing at which the joint portion is corrected greatly affects an accuracy of the correction. For example, in a case in which an interval between pixels of the image data is converted to have a lower resolution by image processing in accordance with an interval between elements of the exposure head, when the joint correction is performed before the conversion to the lower resolution, the image data may be deteriorated through the resolution decreasing process, thereby causing reduction in positional accuracy of the joint correction. As a result, accurate correction cannot be performed at the joint portion, and hence a black streak image or a white streak image is formed.
The present invention has been made in view of the above-mentioned circumstances, and has an object to achieve high-quality image formation regardless of an accuracy of mounting surface emitting element array chips.
In order to achieve the above-mentioned object, the present invention has the following configuration.
An image forming apparatus includes: (1) a photosensitive member to be driven to rotate; (2) an exposure head including: a chip including a plurality of light emitting elements configured to expose the photosensitive member, the chip including a plurality of chips; and a circuit board on which the plurality of chips are arrayed at positions different from each other in an intersecting direction intersecting with a rotation direction of the photosensitive member, the plurality of chips including odd-numbered chips and even-numbered chips arrayed at positions different from each other in the rotation direction and further including chips arranged adjacent to each other in the intersecting direction so as to have an overlapping portion at end portions thereof, the image forming apparatus being configured to form an image at a first resolution corresponding to an array interval of the plurality of light emitting elements in the intersecting direction; a data generating unit configured to generate, based on input image data, pixel data items respectively corresponding to pixels equivalent to a second resolution higher than the first resolution, in association with positions of the pixels in the intersecting direction; a first correction unit configured to correct a misregistration amount from an interval equivalent to the first resolution at the overlapping portion between a predetermined chip and a chip arranged adjacent to the predetermined chip in the intersecting direction; and a conversion unit configured to convert a plurality of pixel data items equivalent to the second resolution into pixel data items of pixels equivalent to the first resolution corresponding to the positions of the plurality of pixel data items, the first correction unit being configured to correct the misregistration amount at the overlapping portion with respect to pixel data obtained after a resolution thereof is converted by the conversion unit.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Referring to the drawings, an embodiment of the present invention is described below in detail.
[Configuration of Image Forming Apparatus]
The image forming portion 103 includes a series of four image forming stations arranged in the color order of cyan (C), magenta (M), yellow (Y), and black (K) along a direction (counterclockwise direction) of rotation of an endless conveying belt 111. Each of the four image forming stations has the same configuration, and includes a photosensitive drum 102 serving as a photosensitive member configured to rotate in a direction of the arrow (clockwise direction), an exposure head 106, a charging device 107, and a developing device 108. Suffixes “a”, “b”, “c”, and “d” following the reference numerals 102, 106, 107, and 108 of the photosensitive drum 102, the exposure head 106, the charging device 107, and the developing device 108 represent respective configurations corresponding to the black (K), the yellow (Y), the magenta (M), and the cyan (C) associated with the image forming stations. In the following, the suffixes of the reference numerals are omitted except when a specific photosensitive drum or the like is to be specified by the suffix.
In the image forming portion 103, the photosensitive drum 102 is driven to rotate and charged by the charging device 107. The exposure head 106 serving as an exposure unit causes an LED array, in which LEDs are arranged, to emit light based on image data, and causes a rod lens array to focus emitted light from chip surfaces of the LED array onto the photosensitive drum 102 (onto the photosensitive member) to form an electrostatic latent image. The developing device 108 develops the electrostatic latent image formed on the photosensitive drum 102 with a toner. Then, the developed toner image is transferred onto recording paper on the conveying belt 111 configured to convey the recording paper. Such a sequential electrophotographic process is performed in each of the image forming stations. During image formation, after a lapse of a predetermined time period from the initiation of the image formation in the cyan (C) image forming station, respective image forming operations are performed in succession in the magenta (M), yellow (Y), and black (K) image forming stations.
The image forming apparatus illustrated in
On a downstream side of the black (K) image forming station in a direction of conveyance of the recording paper, an optical sensor 113 serving as a sensing unit is disposed at a position facing the conveying belt 111. The optical sensor 113 detects a position of a test image formed on the conveying belt 111 to determine a color misregistration amount between the toner images from the individual image forming stations. The color misregistration amount determined by the optical sensor 113 is reported to a control substrate 415 (see
As an example of the electrophotographic image forming apparatus, the image forming apparatus of the type configured to transfer the toner images formed on the photosensitive drums 102 in the individual image forming stations directly onto the recording paper on the conveying belt 111 has been described above. However, the present invention is not limited to such a printer of the type configured to transfer the toner images on the photosensitive drums 102 directly onto the recording paper. The present invention is also applicable to an image forming apparatus including, for example, a primary transfer portion configured to transfer the toner images on the photosensitive drums 102 onto an intermediate transfer belt and a secondary transfer portion configured to transfer the toner images on the intermediate transfer belt onto the recording paper.
[Configuration of Exposure Head]
Next, each of the exposure heads 106 configured to perform exposure on the corresponding photosensitive drum 102 is described with reference to
As illustrated in
[Configuration of Surface Emitting Element Array Element Group]
As illustrated in
Further, as illustrated in
[Control Configuration of Circuit Board and Exposure Head]
[Control Circuit Board]
In the control circuit board 415, the CPU 400 performs processing of the image data. The control circuit board 415 includes functional blocks including an image data generating portion 401, a line data shift portion 402, a chip data converting portion 403, a chip data shift portion 404, a data transmitting portion 405, and a sync signal generating portion 406. In the following, processing in each of the functional blocks in the order is described in which the image data is processed in the control circuit board 415.
(Image Data Generating Portion)
The image data generating portion 401 serving as a data generating unit performs, on input image data received from the scanner portion 100 or from an external computer connected to the image forming apparatus, a dithering process at a resolution specified by the CPU 400 to generate the image data for print-out. In this embodiment, it is assumed that the image data generating portion 401 performs the dithering process at a resolution of 2,400 dpi equivalent to a second resolution. In other words, the image data generated by the image data generating portion 401 is pixel data equivalent to 2,400 dpi. The pixel data equivalent to 2,400 dpi in this embodiment is assumed to be one-bit data, but it is also possible to represent one pixel in a plurality of bits. The pixel data generated by the image data generating portion 401 is line data corresponding to a line equivalent to 2,400 dpi in the sub-scanning direction. The image data generating portion 401 generates, based on the input image data, the pixel data corresponding to each of pixels equivalent to 2,400 dpi in association with a position of the pixel in the intersecting direction.
(Line Data Shift Portion)
The CPU 400 determines respective amounts of image shift in the main scanning direction (longitudinal direction of the exposure head 106) and the sub-scanning direction (rotation direction of the photosensitive drum 102 and also direction of conveyance of the recording paper) in units of 2,400 dpi based on the color misregistration amounts sensed by the optical sensor 113. The amounts of image shift are determined by the CPU 400 based on, for example, relative amounts of color misregistration from one color to another, which are calculated based on the result of the sensing of a color misregistration detection pattern image by the optical sensor 113. Then, the CPU 400 specifies an amount of image shift to the line data shift portion 402 serving as a second correction unit. The line data shift portion 402 performs, on the entire image region in one page of the recording paper, a shifting process on the image data input from the image data generating portion 401 in units of 2,400 dpi based on the amount of image shift specified by the CPU 400. The line data shift portion 402 may also divide the image region in one page of the recording paper into a plurality of image regions and perform the shifting process on each of the plurality of image regions resulting from the division.
(Sync Signal Generating Portion)
The sync signal generating portion 406 generates a cycle time signal (hereinafter referred to as “line sync signal”), which is synchronous with a rotating speed of the photosensitive drum 102 and corresponds to one line in the direction of rotation of the photosensitive drum 102. The CPU 400 specifies, to the sync signal generating portion 406, the cycle time of the line sync signal, that is, a time period required by the surface of the photosensitive drum 102 to move by a pixel size (about 10.5 μm) at 2,400 dpi in the direction of rotation of the photosensitive drum 102 (in the sub-scanning direction) at the rotating speed of the photosensitive drum 102 determined in advance. For example, when printing is performed at a speed of 200 mm/second in the sub-scanning direction, the CPU 400 determines that the cycle time (cycle time corresponding to one line in the sub-scanning direction) of the line sync signal is about 52.9 μs (≈(25.4 mm/2,400 dots)/200 mm) and specifies the cycle time to the sync signal generating portion 406. When the image forming apparatus has a sensing portion (for example, an encoder placed on a rotary shaft of the photosensitive drum) configured to sense the rotating speed of the photosensitive drum, the CPU 400 calculates the rotating speed of the photosensitive drum 102 in the sub-scanning direction based on a result of sensing (a generation cycle time of a signal output from the encoder) by the sensing portion. Then, the CPU 400 determines the cycle time of the line sync signal based on the result of the calculation. Meanwhile, when the image forming apparatus does not have a sensing portion configured to sense the rotating speed of the photosensitive drum, the CPU 400 determines the cycle time of the line sync signal based on information on the type of paper such as a sheet basis weight (g/cm2) or a sheet size input by a user via an operating portion.
(Chip Data Converting Portion)
The chip data converting portion 403 reads out, in synchronization with the line sync signal, line data for each one line of an output image at the resolution in the sub-scanning direction (rotation direction) of the photosensitive drum 102 from the line data shift portion 402 on a line-by-line basis. Then, the chip data converting portion 403 performs data processing in which the read line data is divided into line data items corresponding to the individual chips.
When the line sync signal is input to the counter 530, the counter 530 resets a count value to 0 and then increments the count value in synchronization with the pulse number of the clock (CLK) signal (see
Subsequently, the writing of the line data read out from the line data shift portion 402 into the memories 501 to 529 and the outputting of the image data written into the memories 501 to 529 which are performed by the chip data converting portion 403 are described.
Further, “INPUT DATA TO MEMORY 501” of
“OUTPUT DATA FROM MEMORY 501” of
In this embodiment, from the line memory 500, the line data items each corresponding to one line in the main scanning direction are sequentially read out, and the line data item is first written into the memory 501 for storing the line data item corresponding to the surface emitting element array chip 1. Then, the line data item is written into the memory 502 for storing the image data item corresponding to the surface emitting element array chip 2, and subsequently, the line data items are continuously written sequentially into the memories 503 to 529 for storing the image data items corresponding to the surface emitting element array chips 3 to 29. In the chip data shift portion 404 in a stage subsequent to that of the chip data converting portion 403, a data shifting process in the sub-scanning direction is performed individually for each of the surface emitting element array chips. Accordingly, it is assumed that, in the memories 501 to 529, the line data items corresponding to ten lines in the sub-scanning direction are stored.
Further, the line data item is stored in each of the memories 501 to 529 together with, in addition to the line data item for one chip corresponding to each of the surface emitting element array chips, pixel data items obtained by copying pixel data items at end portions of adjacent surface emitting element array chips. For example, the following pixel data item is stored in the memory 502. That is, the pixel data item at the outermost end portion of the surface emitting element array chip 1 on the surface emitting element array chip 2 side and the pixel data item at the outermost end portion of the surface emitting element array chip 3 on the surface emitting element array chip 2 side are respectively added to both ends of the line data item corresponding to the surface emitting element array chip 2, and the obtained data is stored in the memory 502.
Meanwhile, part (b) of
The memory 501 stores the line data corresponding to the surface emitting element array chip 1 with the pixel data of the outermost end portion of the surface emitting element array chip 2 on the surface emitting element array chip 1 side being added to the end portion thereof. Further, the memory 529 stores the line data corresponding to the surface emitting element array chip 29 with the pixel data of the outermost end portion of the surface emitting element array chip 28 on the surface emitting element array chip 29 side being added to the end portion thereof.
As described above, in this embodiment, the pixel data items at the end portions of adjacent surface emitting element array chips are added to both ends of the line data of the corresponding surface emitting element array chip for each of the surface emitting element array chips, and the obtained data is stored in each of the memories 501 to 529. With the above-mentioned operation of the chip data converting portion 403, the line data corresponding to one line in the main scanning direction is stored in each of the memories 501 to 529 provided to correspond to the surface emitting element array chips 1 to 29, respectively, together with the pixel data items of the end portions of the adjacent surface emitting element array chips. The pixel data items of the end portions of the adjacent surface emitting element array chips are used in a filtering processing portion 408 described later.
(Chip Data Shift Portion)
The chip data shift portion 404 serving as a second correction unit performs the following control. Specifically, based on data (in units of 2,400 dpi) related to an amount of image shift in the sub-scanning direction for each of the surface emitting element array chips, which is specified in advance by the CPU 400, relative timing to read out the line data item from each of the memories 501 to 529 is controlled. In the following, an image shifting process in the sub-scanning direction, which is performed by the chip data shift portion 404, is specifically described.
It is desired that, in the longitudinal direction of the exposure head, there be no shift of the position at which each of the even-numbered surface emitting element array chips is mounted. Likewise, it is also desired that, in the longitudinal direction of the exposure head, there be no shift of the position at which each of the odd-numbered surface emitting element array chips is mounted. It is also preferred in terms of design that, in the sub-scanning direction, the position at which each of the even-numbered surface emitting element array chips is mounted and the position at which each of the odd-numbered surface emitting element array chips is mounted be shifted from each other by a predetermined number of pixels (for example, eight pixels) at 2,400 dpi. It is also preferred that a position at which a row of the light emitting elements is disposed in the sub-scanning direction be not allowed to vary from one surface emitting element array chip to another and be fixed in each of the surface emitting element array chips. However, the positions at which the surface emitting element array chips are mounted and the position at which the row of the light emitting elements is disposed include errors, and such errors may possibly degrade the image quality of an output image.
A memory 420 (ROM) illustrated in
(Data Transmitting Portion)
The data transmitting portion 405 transmits, to the drive circuit board 202 of the exposure head 106, the line data obtained after the above-mentioned series of data processing steps are performed on the line data. Referring back to
The data transmitting portion 405 transmits the line data items processed by the chip data shift portion 404 to the drive circuit board 202. The counter 530 includes, instead of an oscillating device, a frequency modulation circuit configured to modulate the line sync signal input thereto to generate a CLK signal at a frequency higher than that of the line sync signal. The counter 530 may also include, instead of the frequency modulation circuit, an embedded oscillating device configured to generate a clock (CLK) signal at a frequency higher than that of the line sync signal. In this embodiment, the frequency of the clock signal (CLK in
Meanwhile, data is read out from the memories 501 to 529 such that, from the 29 memories 501 to 529, the image data items each corresponding to one line in the main scanning direction and corresponding to the individual surface emitting element array chips are output in parallel in one cycle time of the line sync signal. Accordingly, the image data items may also be read out from the memories 501 to 529 at a speed lower than a speed at which the image data items are written into the memories. For example, in this embodiment, it is assumed that the image data items are read out from the memories 501 to 529 in a cycle time that is 58 times longer than the number of pulses at the time when the image data items are written into the memories 501 to 529.
The line data shift portion 402, the chip data converting portion 403, the chip data shift portion 404, the data transmitting portion 405, and the sync signal generating portion 406 form an integrated circuit 402A different from the integrated circuit 401A. Further, the CPU 400 is an integrated circuit different from the integrated circuit 401A and the integrated circuit 402A.
[Drive Portion of Exposure Head]
(Data Receiving Portion)
Next, a process to be performed in the drive portion 303a of the exposure head 106 is described. The drive portion 303a includes functional blocks of a data receiving portion 407, the filtering processing portion 408, an LUT 410, a PWM signal generating portion 411, a timing controller 412, a control signal generating portion 413, and a drive voltage generating portion 414. In the following, processes to be performed in the individual functional blocks are described in the order in which the image data is processed in the drive portion 303a. As described above, the chip data converting portion 403 obtains an image data array for each of the 29 surface emitting element array chips. The following processing blocks are configured to process in parallel the image data items stored in the 29 chips. It is assumed that the drive portion 303a includes a circuit capable of receiving the image data items corresponding to the surface emitting element array chips 1 to 15 to allow parallel processing for the surface emitting element array chips.
(Data Receiving Portion)
The data receiving portion 407 receives a signal transmitted from the data transmitting portion 405 of the control circuit board 415. It is assumed that the data receiving portion 407 and the data transmitting portion 405 receive and transmit the image data in units of line in the sub-scanning direction in synchronization with the line sync signal.
(Filtering Processing Portion)
The filtering processing portion 408 subjects the image data of each of the surface emitting element array chips to an interpolating process by the filtering process in the main scanning direction, to thereby convert the resolution in the main scanning direction from 2,400 dpi to 1,200 dpi.
Dn′=D(2×n−1)×K2+D(2×n)×K1+D(2×n+1)×K2 (Expression 1)
In Expression 1, “n” corresponds to 516 which is the number of light emitting elements in each of the surface emitting element array chips and, based on the order in which the light emitting elements are turned on, an arithmetic operation of the image data for each of the light emitting elements is sequentially performed in the order of n=1 to 516. K1 serving as a first coefficient represents a weight coefficient for input data at the same coordinate position in the main scanning direction as that of output data, and K2 serving as a second coefficient represents a weight coefficient for input data at a coordinate shifted by half a pixel in the main scanning direction with respect to the output data. In this embodiment, an interpolation arithmetic operation (filtering process) is performed assuming that K1 and K2 have respective values of 0.5 and 0.25, but it is also possible to use weight coefficients different from those values used in this embodiment. In this embodiment, the weight coefficient K2 is set to a value larger than zero so that the information on the image data generated at a resolution (2,400 dpi) higher than the resolution (1,200 dpi) of the output data can be reflected on the output data. Specifically, a process from the image data generating portion 401 of the control circuit board 415 to the data receiving portion 407 of the exposure head 106 is performed with the image position being moved in the main scanning direction at 2,400 dpi, and in the subsequent-stage filtering processing portion 408, the resolution of the image data is converted into 1,200 dpi. In this manner, an image of 1,200 dpi can be generated under a state in which the image movement accuracy in units of 2,400 dpi is maintained.
For example, the density value of the pixel 1′ in the row (m+3) of
Further, while the filtering process is performed, in a case in which the process is performed on the pixel at the end portion of the surface emitting element array chip, when the pixel data of the adjacent surface emitting element array chip is absent, image lack and an image defect are caused. Accordingly, as described above, the chip data converting portion 403 of the control circuit board 415 obtains in advance an image data array in which the pixel data on the end portion side of the adjacent surface emitting element array chip is added. In this manner, the filtering process without image lack can be performed.
(LUT)
Subsequently, the LUT 410 performs data conversion of an image data value (density data value) for each of the pixels corresponding to the light emitting elements in the surface emitting element array chip with reference to a look-up table. The LUT 410 converts the data value for each of the pixels based on a response characteristic of a light emission time of each of the surface emitting element array chips such that an accumulated light amount at the time when pulsed light emission is performed has a predetermined value. For example, when a response of the light emission time of each of the surface emitting element array chips is slow and the accumulated light amount is smaller than a target value, the LUT 410 performs the data conversion so as to increase the data value. In this embodiment, it is assumed that the CPU 400 sets, before the image formation is started, values in a conversion table set in the look-up table to predetermined values that are based on experimentally-obtained response characteristics of each of the light emitting element arrays.
(PWM Signal Generating Portion, Timing Controller, Control Signal Generating Portion, and Drive Voltage Generating Portion)
Subsequently, the PWM signal generating portion 411 generates a pulse width signal (hereinafter referred to as “PWM signal”) corresponding to the light emission time during which each of the surface emitting element array chips emits light in one pixel interval based on the data value for each of the pixels. The timing to output the PWM signal is controlled by the timing controller 412. The timing controller 412 generates a sync signal corresponding to the pixel interval of each of the pixels from the line sync signal generated from the sync signal generating portion 406 of the control circuit board 415 and outputs the sync signal to the PWM signal generating portion 411. The drive voltage generating portion 414 generates a drive voltage for driving each of the surface emitting element array chips in synchronization with the PWM signal. The drive voltage generating portion 414 has a configuration that allows the CPU 400 to adjust a voltage level of the output signal to around 5 V so as to achieve a predetermined light amount. In this embodiment, each of the surface emitting element array chips is configured to be able to simultaneously and independently drive the four light emitting elements. The drive voltage generating portion 414 supplies drive signals to four lines for each of the surface emitting element array chips, specifically, supplies the drive signals to 1 line (15 chips)×4=60 lines in the staggered configuration in the entire exposure head 106. It is assumed that the respective drive signals supplied to the individual surface emitting element array chips are represented by ΦW1 to ΦW4 (see
[Description of SLED Circuit]
[Operation of SLED Circuit]
Next, the operation of the SLED circuit illustrated in
Further, with regard to the shift thyristors connected to the transfer line Φ1, the threshold value voltage of the shift thyristor Tn+1 having the lowest threshold value voltage is 3.2 V (=1.7 V+1.5 V). Further, the threshold value voltage of the shift thyristor Tn+3 having the second lowest threshold value voltage (not shown in
[Light Emitting Operation of Light Emitting Thyristor]
Next, a light emitting operation of the light emitting thyristor is described. When only the shift thyristor Tn is turned on, the gates of the four light emitting thyristors of from L4n−3 to L4n are connected in common to the common gate Gn of the shift thyristor Tn. Accordingly, the gate potentials of the light emitting thyristors L4n−3 to L4n are equal to that of the common gate Gn, that is, 0.2 V. Thus, the threshold value of each of the light emitting thyristors is 1.7 V (=0.2 V+1.5 V), and the light emitting thyristors L4n−3 to L4n can be turned on when a voltage of 1.7 V or more is input thereto from the lighting signal lines ΦW1 to ΦW4 for the light emitting thyristors. Thus, when the shift thyristor Tn is turned on, lighting signals are input to the lighting signal lines ΦW1 to ΦW4 so that the four light emitting thyristors L4n−3 to L4n in any combination can be selectively caused to emit light. At this time, the potential of the common gate Gn+1 of the shift thyristor Tn+1 adjacent to the shift thyristor Tn is 1.7 V, and the threshold value voltages of the light emitting thyristors L4n+1 to L4n+4 gate-connected to the common gate Gn+1 are 3.2 V (=1.7 V+1.5 V). The lighting signals input from the lighting signal lines ΦW1 to ΦW4 are 5 V, and hence also the light emitting thyristors L4n+1 to L4n+4 seem to be turned on by the same lighting pattern as the lighting pattern of the light emitting thyristors L4n−3 to L4n. However, the light emitting thyristors L4n−3 to L4n have lower threshold value voltages, and are thus turned on earlier than the light emitting thyristors L4n+1 to L4n+4 when the lighting signals are input from the lighting signal lines ΦW1 to ΦW4. Once the light emitting thyristors L4n−3 to L4n are turned on, the connected lighting signal lines ΦW1 to ΦW4 are drawn to about 1.5 V (diffusion potential). Accordingly, the potentials of the lighting signal lines ΦW1 to ΦW4 become lower than the threshold value voltages of the light emitting thyristors L4n+1 to L4n+4, and hence the light emitting thyristors L4n+1 to L4n+4 cannot be turned on. As described above, when a plurality of light emitting thyristors L are connected to one shift thyristor T, the plurality of light emitting thyristors L can be simultaneously turned on.
The gate line VGK is always supplied with a voltage of 5 V. Further, the clock signal Φ1 for the odd-numbered shift thyristors and the clock signal Φ2 for the even-numbered shift thyristors are input at the same cycle time Tc, and the start pulse line supplies the signal Φs of 5 V. Slightly before the clock signal Φ1 for the odd-numbered shift thyristors first becomes 5 V, the signal Φs of the start pulse line is dropped to 0 V in order to provide a potential difference to the gate line VGK. In this manner, the gate potential of the first shift thyristor Tn−1 is drawn from 5 V to 1.7 V, and the threshold value voltage becomes 3.2 V so that the shift thyristor Tn−1 can be turned on by the signal from the transfer line Φ1. Slightly after a voltage of 5 V is applied to the transfer line Φ1 and the first shift thyristor Tn−1 transitions to the ON state, a voltage of 5 V is supplied to the start pulse line Φs. A voltage of 5 V is thereafter continuously supplied to the start pulse line Φs.
The transfer line Φ1 and the transfer line Φ2 are configured to have a time period Tov of the overlapped ON state (in this case, 5 V) and have a substantially complementary relationship. A signal is transmitted to each of the lighting signal lines ΦW1 to ΦW4 for turning on the light emitting thyristor at a cycle time that is half of the cycle time of the transfer lines Φ1 and Φ2, and the light emitting thyristor is turned on when a voltage of 5 V is applied when the corresponding shift thyristor is in the ON state. For example, in a period “a”, all of the four light emitting thyristors connected to the same shift thyristor are in the ON state, and in a period “b”, three light emitting thyristors are simultaneously in the ON state. Further, in a period “c”, all of the light emitting thyristor are in the OFF state, and in a period “d”, two light emitting thyristors are simultaneously in the ON state. In a period “e”, only one light emitting thyristor is in the ON state.
In this embodiment, the number of light emitting thyristors connected to one shift thyristor is 4, but the present invention is not limited thereto. The number may be smaller or larger than 4 depending on applications. The circuit described above is a circuit having a common cathode for the thyristors, but even a circuit having a common anode is applicable by inverting the polarities as appropriate.
[Structure of Surface Emitting Thyristor]
Further, the surface emitting elements of the mesa structure type use a current confinement mechanism to prevent a current from flowing to side surfaces of the mesa structures 922, thereby improving the light emitting efficiency. Now, the current confinement mechanism in this embodiment is described. As illustrated in
In the exposure head 106 in this embodiment, the density of the luminous points (interval between the light emitting elements) is determined based on a resolution. The individual light emitting elements inside the surface emitting element array chip are separated by the element isolation grooves 924 to have the mesa structures 922. For example, when image formation is performed at a resolution of 1,200 dpi, the light emitting elements are arrayed so that an interval between element centers of adjacent light emitting elements (luminous points) is 21.16 μm.
In this embodiment described above, dithering at 2,400 dpi is performed with respect to the light emitting element interval of 1,200 dpi, and the image data is shifted depending on a color misregistration amount or a mounting misregistration amount. In this manner, image position control at a higher resolution is allowed, and high-quality image formation with less misregistration is allowed with respect to the color misregistration or the mounting misregistration of the surface emitting element array chip. Further, when the chip data converting portion 403 of the control circuit board 415 obtains the image data array for each of the surface emitting element array chips, the image data of the adjacent chip is added to the image data, and the obtained data is transmitted to the subsequent-stage filtering processing portion 408. In this manner, when the filtering processing portion 408 performs the resolution conversion, high-quality image formation without image lack between the surface emitting element array chips is allowed. In this embodiment, the example in which the surface emitting element array chips are arranged in two rows in a staggered configuration is described, but similar processing is allowed also in a configuration in which the surface emitting element array chips are arrayed in one row, thereby being capable of obtaining similar effects as those in the case in which the surface emitting element array chips are arrayed in two rows. Further, even in the case of an exposure head in which the surface light emitting elements have a pitch of 600 dpi, the resolution of the dithering process and the image shifting process may be increased (for example, to 1,200 dpi or 2,400 dpi) so that position control is allowed at a resolution equal to or larger than the pitch of the light emitting elements.
In such a resolution conversion method in which the data of adjacent pixels is interpolated by the filtering process, the positional accuracy of a dot (image) to be formed is improved. On the other hand, a latent image at an edge portion is liable to become unstable due to a large amount of multi-value halftone data being generated at an edge portion in the main scanning direction of the dot (image). Accordingly, a phenomenon that the sharpness of an image to be formed is reduced may occur depending on image forming conditions (for example, charging amount of the photosensitive drum 102). In view of the above, description is given of an image forming apparatus which is configured to perform resolution conversion and has a configuration in which a sharpness priority mode can be selected in accordance with an image type or an instruction from a user. In this embodiment, it is assumed that an image controller selects the sharpness priority mode based on the image type. Further, it is assumed that the image forming apparatus of this embodiment includes an operation portion (not shown), and that a user can set the sharpness priority mode through the operation portion.
In this embodiment, as described later, the filtering processing portion 408 of the drive portion 303a of the exposure head 106 is notified of changes of the filter coefficients K1 and K2 from the CPU 400 of the control circuit board 415. Accordingly, in this embodiment, in the drive portion 303a of
In this embodiment, when the sharpness priority mode corresponding to a second process is selected, the values of the filter coefficients K1 and K2 to be used in the filtering arithmetic operation (Expression 1) performed by the filtering processing portion 408 are switched to K1=1.0 and K2=0. Switching of the values of the filter coefficients K1 and K2 is performed by rewriting the settings of K1 and K2 in the filtering processing portion 408 in response to an instruction from the CPU 400 of the control circuit board 415. As a result of the filter coefficient K2 corresponding to the adjacent pixel becoming 0, Expression 1 for calculating image data of each pixel becomes Expression 2 given below, and the input data at the same main scanning position as that of the output data is calculated as it is as the output data.
Dn′=D(2×n) (Expression 2)
In Expression 2, “n” corresponds to 516 which is the number of light emitting elements in each of the surface emitting element array chips, and, based on the order in which the light emitting elements are turned on, an arithmetic operation of the image data for each of the light emitting elements is sequentially performed in the order of n=1 to 516. In the case of Expression 2, the odd-numbered input data items D1, D3, D5, D7, and D9 of
In the sharpness priority mode, the density data after the filtering process is binary (black or white), and hence a sharp latent image can be formed particularly at the edge portion of the image. Meanwhile, with regard to the movement accuracy of the image centroid, the image data is only moved in units of 1,200 dpi, and hence the movement accuracy of the image position is decreased. Thus, the CPU 400 performs the switching of the filtering process described above depending on the image characteristic, in accordance with the image type input to the control circuit board 415. For example, in a case in which a text or a line image is input, the CPU 400 switches to the sharpness priority mode to form a sharp image. Meanwhile, in a case in which a color image is input, the CPU 400 switches to an image position priority mode to form an image with a reduced color misregistration. In this case, it is assumed that, in the image position priority mode, the filter coefficients K1=0.5 and K2=0.25 described above are used.
Further, the above-mentioned switching of the filtering process may be switching in accordance with a change in the image forming conditions other than the image type. It is known that, in a case of an electrophotographic printer, the triboelectricity (electric charge amount) of toner decreases under a high-temperature, high-humidity environment, and as a result, developing performance and transferring performance are reduced to cause toner scattering at image edge portions. As a countermeasure against such a decrease in the triboelectricity, there is available a method of performing control for keeping the image density constant by lowering the charging amount to the photosensitive drum and the output light amount of the exposure head. The image position priority mode is selected before the triboelectricity of the toner decreases, and the sharpness priority mode is selected after the triboelectricity decreases. In this manner, a deterioration in the sharpness of the image edge portions can be moderated.
In this embodiment, the method of switching the filter coefficients between the image position priority mode (K1=0.5 and K2=0.25) and the sharpness priority mode (K1=1 and K2=0) is described, but it is not necessarily required to use the above-mentioned values as the coefficient values of the coefficients K1 and K2. Coefficient values satisfying Expression 3 and Expression 4 given below may be used.
(K1 value of sharpness priority mode)>(K1 value of image position priority mode) (Expression 3)
(K2 value of sharpness priority mode)>(K2 value of image position priority mode) (Expression 4)
As described above, in this embodiment, through switching of the settings of the image data generating portion 401 and the filtering processing portion 408, selection of the sharpness priority mode and the image position priority mode is allowed by a simple method. As a result, output of an optimal image is allowed through switching in accordance with the image type and the image forming conditions of the image forming apparatus.
[Relationship Between Position of Joint Portion and Streak]
As described above with reference to
A joint portion A between the surface emitting element array chip 1 and the surface emitting element array chip 2 corresponds to a case of an interval smaller than the desired surface emitting element interval “c” (c>a). When a surface emitting element interval “a” at the joint portion A satisfies a condition of c>a, misregistration occurs such that the surface emitting elements at the end portions overlap each other. Thus, the light amount at the time when the surface emitting elements are caused to emit light at the position of the joint portion A is increased as compared to that in the case of the ideal surface emitting element interval “c”, and an image having a high density is formed. That is, a part of an exposure range (one pixel) of the surface emitting element positioned on the rightmost side of the surface emitting element array chip 1 overlaps with a part of an exposure range (one pixel) of the surface emitting element positioned on the leftmost side of the surface emitting element array chip 2. Accordingly, an exposure amount of a part exposed in an overlapping manner is increased as compared to that in the case in which the surface emitting element array chips are ideally mounted on the printed circuit board. Thus, the image at the joint is formed at a density higher than the desired density. As a result, as illustrated in
Further, a joint portion B between the surface emitting element array chip 2 and the surface emitting element array chip 2 corresponds to a case of an interval larger than the desired surface emitting element interval “c” (c<b). When a surface emitting element interval “b” at the joint portion B satisfies a condition of c<b, misregistration occurs such that the surface emitting elements at the end portions separate from each other. Thus, the light amount at the time when the surface emitting elements are caused to emit light at the position of the joint portion B is decreased as compared to that in the case of the ideal surface emitting element interval “c”, and an image having a low density is formed. That is, the center-to-center distance between the surface emitting element positioned on the rightmost side of the center surface emitting element array chip 2 and the surface emitting element positioned on the leftmost side of the surface emitting element array chip 2 is larger than the nominal value. Accordingly, an exposure amount of the above-mentioned part is decreased as compared to that in the case in which the surface emitting element array chips are ideally mounted on the printed circuit board. Thus, the image at the joint is formed at a density lower than the desired density. As a result, as illustrated in
As described above, an image is formed as a streak when the surface emitting element interval deviates from an ideal interval. Accordingly, a process of correcting the misregistration at the joint portion between the surface emitting element array chips is required. Now, how to perform, with respect to the image data, correction of the misregistration at the joint portion between the surface emitting element array chips is described. The correction of the misregistration at the joint portion between the surface emitting element array chips performed with respect to the image data is referred to as “joint correction.”
[Correction of Misregistration at Joint Portion]
The joint positions are measured in a step of inspecting the exposure head 106. Further, the filter coefficients between the individual surface emitting element array chips are calculated based on the joint positions measured in the step of inspecting the exposure head 106. The measurement values of the measured joint positions and the calculated filter coefficients are stored in the memory 1703 via the CPU 400. The filter coefficients are calculated based on the measured mounting information (above-mentioned positions) onto the drive circuit board 202 in the main scanning direction (longitudinal direction) between the surface emitting element array chips. The method of calculating the filter coefficient is described later.
[Joint Correcting Portion]
As described above, the resolution converting portion 1701 of the filtering processing portion 408 performs the filtering process for converting the resolution from 2,400 dpi to 1,200 dpi. The filtering process has been already described, and hence description thereof is omitted (conversion from part (i) to part (ii) of
[Front End Portion Filtering Process]
In the following, the position of the joint is represented by “n”. The joint correcting portion 1702 performs the filtering process with respect to the pixel data (in this case, D3′) of the pixel positioned at the joint with reference to the position n=D3′ of the joint stored in the memory 1703. The filtering process is started from D3′, transitions to the next pixel (that is, incremented by 1) every time the correcting process ends for each pixel, and is performed until the process ends for the pixels in the predetermined range (X). In this embodiment, the predetermined range is set to X=3. The value of X is set by the instruction from the CPU 400.
It is assumed that, for example, under a condition of c>a at the joint portion A illustrated in
C00(0): 0.5, C01(0): 0.5, C02(0): 0
Further, the joint correcting portion 1702 calculates the filter coefficients to be used for other pixels as follows based on C00(0), C01(0), and C02(0) stored in the memory 1703.
The size of one pixel at 1,200 dpi is 21.16 μm. Accordingly, in order to correct the mounting distance of 10.5 μm in the main scanning direction between the surface emitting element array chips, the position is required to be shifted by 0.5 pixels (about half a pixel). The mounting distance of 10.5 μm is also a correction amount in which correction is required. As illustrated in part (iii) of
The filter coefficient C01(0) of the pixel of interest (for example, pixel D3′) is obtained as follows.
1−[(Correction amount (10.5 μm))/(Size of one pixel (21.16 μm))]
C02(0) is not used, and hence is 0.
In the filtering process of the front end portion of the surface emitting element array chip N, the filter coefficients are computed inside such that the correction amount is gradually reduced within the predetermined range (D3′ to D3′+X).
For example, in
C00(1)=0.33, C01(1)=0.67, C02(1)=0
C00(2)=0.17, C01(2)=0.83, C02(2)=0
The arithmetic operation of the filter coefficients computed by the joint correcting portion 1702 can be expressed by the following general expressions.
C00(i)=C00(0)/X×(X−i) (Expression 5-1)
C01(i)=C01(0)+i×(C00(0)/X+C02(0)/X) (Expression 5-2)
C02(i)=C02(0)/X×(X−i) (Expression 5-3)
In this case, “i” represents a value to be incremented every time the filtering process is performed from the joint position, and 0≤i<X is satisfied. In the case of X=3, “i” is 0, 1, and 2. Specifically, in the case of D3′, i=0 is set, and, in the case of D4′, i=1 is set. Further, in the case of D5′, i=2 is set. When X=0 is set for the predetermined range, the arithmetic operation of the filter coefficient and the filtering process are not performed.
The joint correcting portion 1702 performs the arithmetic operation of the filtering process based on Expression 6 given below.
D(n−2)″=D(n−1)′×C00(m)+D(n)′×C01(m)+D(n+1)′×C02(m) (Expression 6)
The ranges of “n” and “m” are set as 3≤n<3+X, 0≤m<X, and 1≤X<11. For example, in the case of the predetermined range of X=3, “n” is 3, 4, and 5, and “m” is 0, 1, and 2. That is, “n” corresponds to the pixel numbers of D3′, D4′, and D5′ corresponding to the luminous points positioned at the front end in the surface emitting element array chip N. Further, “m” is a numerical value in parentheses of the filter coefficient.
Expression 6 can be specifically expressed as follows with reference to parts (ii) to (iv) of
D1″=D2′×C00(0)+D3′×C01(0)+D4′×C02(0)
Further, D2″ of n=4 and m=1 and D3″ of n=5 and m=2 are expressed as follows.
D2″=D3′×C00(1)+D4′×C01(1)+D5′×C02(1)
D3″=D4′×C00(2)+D5′×C01(2)+D6′×C02(2)
As described above, through the filtering process performed by the joint correcting portion 1702, the value of the pixel data at the joint between the surface emitting element array chips is increased or decreased. As a result, the centroid of the image data can be moved by an amount attenuated from 10.5 μm with respect to the pixels within the predetermined range from the joint position, and thus smooth joint correction is allowed. For example, at the joint portion A of
[Rear End Portion Filtering Process]
The joint correcting portion 1702 performs the filtering process with respect to the pixel data (in this case of X=3, D516′) of the pixel positioned at the joint with reference to the position n=D519′−X of the joint stored in the memory 1703. The filtering process is started from D519′−X, transitions to the next pixel (that is, incremented by 1) every time the correcting process ends for each pixel, and is performed until the process ends for the pixels in the predetermined range (D518′). In this embodiment, the predetermined range is set to X=3. The value of X is set by the instruction from the CPU 400.
For example, also with regard to the joint portion B illustrated in
C10(0): 0, C11(0): 0.5, C12(0): 0.5
Further, the joint correcting portion 1702 calculates the filter coefficients used for other pixels based on C10(0), C11(0), and C12(0) stored in the memory 1703. The calculation method is omitted because the method is similar to the method described in the filtering process at the front end portion, and differs only in pixels adjacent to the pixel of interest in the direction in which correction is required.
In the filtering process of the rear end portion of the surface emitting element array chip N, the filter coefficients are computed inside such that the correction amount is gradually increased within the predetermined range (D519′ to D518′).
For example, in
C10(1)=0,C11(1)=0.67,C12(1)=0.33
C10(2)=0,C11(2)=0.83,C12(2)=0.17
The arithmetic operation of the filter coefficients computed by the joint correcting portion 1702 can be expressed by the following general expressions.
C10(i)=C10(0)/X×(X−i) (Expression 7-1)
C11(i)=C11(0)+i×(C10(0)/X+C12(0)/X) (Expression 7-2)
C12(i)=C12(0)/X×(X−i) (Expression 7-3)
In this case, “i” represents a value to be incremented every time the filtering process is performed from the joint position, and 0≤i<X is satisfied. In the case of X=3, “i” is 0, 1, and 2. When X=0 is set for the predetermined range, the arithmetic operation of the filter coefficient and the filtering process are not performed.
The joint correcting portion 1702 performs the arithmetic operation of the filtering process based on Expression 6 given above. The ranges of “n” and “m” are set as 519−X≤n<519, 0≤m<X, and 1≤X<11. For example, in the case of the predetermined range of X=3, “n” is 516, 517, and 518, and “m” is 0, 1, and 2. That is, “n” corresponds to the pixel numbers of D516′, D517′, and D518′ corresponding to the luminous points positioned at the front end in the surface emitting element array chip N. Further, “m” is a numerical value in parentheses of the filter coefficient, and is in the order of 2, 1, and 0 which is opposite to that in the case of the front end.
Expression 6 can be specifically expressed as follows with reference to parts (ii) to (iv) of
D514″=D515′×C10(2)+D516′×C11(2)+D517′×C12(2)
Further, D515″ of n=517 and m=1 and D516″ of n=518 and m=0 are expressed as follows.
D515″=D516′×C10(1)+D517′×C11(1)+D518′×C12(1)
D516″=D517′×C10(0)+D518′×C11(0)+D519′×C12(0)
As described above, through the filtering process performed by the joint correcting portion 1702, the value of the pixel data at the joint between the surface emitting element array chips is increased or decreased. As a result, the centroid of the image data can be moved by an amount attenuated from 10.5 μm with respect to the pixels within the predetermined range from the joint position, and thus smooth joint correction is allowed.
With the above-mentioned arithmetic operation, correction of the misregistration at the position of the joint at each of the front end and the rear end is performed with respect to a predetermined surface emitting element array chip. In
As described above, in this embodiment, the image data at 2,400 dpi is converted by the resolution converting portion 1701 to have a lower resolution, and then the joint correction is performed by the joint correcting portion 1702. Accordingly, the reduction in accuracy at the joint correction position due to the image deterioration caused by the resolution converting process can be prevented. Further, in this embodiment, with the resolution converting process, the image data is converted into multi-value data at 1,200 dpi which appears to have an accuracy at 2,400 dpi. This multi-value data is subjected to the joint correcting process, and hence high-accuracy joint correction with less image deterioration is allowed.
In
[Modification Examples of
As Modification Example 1 of
As Modification Example 2 of
[Other Embodiment]
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
As described above, the present invention enables high-quality image formation regardless of an accuracy of mounting the surface emitting element array chips.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-121820 | Jun 2018 | JP | national |
This application is a Continuation of International Patent Application No. PCT/JP2019/025416, filed Jun. 26, 2019, which claims the benefit of Japanese Patent Application No. 2018-121820, filed Jun. 27, 2018, both of which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2019/025416 | Jun 2019 | US |
| Child | 17132968 | US |
