JP2007286357A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately correcting a magnification error in a main scanning direction, caused by the eccentricity of the rotation shaft of each photoreceptor, without decreasing productivity by setting the frequency of a writing clock during image formation. <P>SOLUTION: The image forming apparatus 1 detects the position of the rotation shaft and a change in the radius of each photoreceptor 2 by a corresponding photoreceptor sensor 12. From a table in an EEPROM, in which sets of pieces of information about the amount of eccentricity and corresponding writing clock frequency are written, the apparatus 1 reads information about a frequency corresponding to the result of the detection. Also, based on information about the corresponding writing clock frequency, the apparatus adjusts the frequency of the writing clock, thereby correcting a magnification in the main scanning direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that corrects a main scanning magnification error caused by eccentricity of a rotating shaft of a photosensitive member by adjusting a frequency of a pixel synchronization clock during image formation. is there.

  2. Description of the Related Art Conventionally, as a so-called tandem type image forming apparatus that forms a full-color image by arranging a plurality of electrophotographic writing units and image forming cartridges in parallel, there is a full-color copying machine, for example. Such a full-color copying machine includes an image forming station that forms images of each color of cyan, magenta, yellow, and black. Each color image forming station includes a writing unit and an image forming cartridge. The modulated laser is irradiated from the writing unit to the photosensitive member of the image forming cartridge to form a latent image, and each color image forming cartridge supplies each color toner to the photosensitive member on which the latent image is formed. The toner image is developed. The image forming cartridges for each color sequentially transfer the toner images on the photoconductor onto transfer paper, which is a transfer medium conveyed on the transfer belt, and form a color image by superimposing the toner images of each color on the transfer paper. .

  In this way, in an image forming apparatus having a plurality of image forming stations, the same transfer is performed at each image forming station as compared with an image forming apparatus that forms a color image with only one photoconductor called a one-drum system. Since different toner images are sequentially superimposed on the same surface of the paper to form a color image, if the transfer image position on the transfer paper in each image forming station is shifted, the image interval formed in each image forming station is In the case of a color image, the image quality is deteriorated due to a color difference or color shift.

  As this color misregistration, there is an inclination of the scanning line for each color due to an assembly error inside the writing optical system, an installation error of each unit to the image forming apparatus main body, an attachment error of the photosensitive member to the image forming apparatus main body, etc. There are two types of color misregistration, and parallel color misregistration that occurs when the position of the scanning line deviates in parallel to the reference position and the four color images deviate in the vertical or horizontal direction as a whole.

  Among these color misregistrations, the color misregistration is corrected by finely adjusting the position of the reflecting mirror of the writing device (skew correction), and the parallel color misregistration causes the start timing of writing to be in the main scanning direction or sub-scanning direction. Correction can be performed by adjusting in the scanning direction (registration correction). Further, the length of the image in the main scanning direction can be corrected by changing the frequency of the writing pixel, that is, by adjusting the magnification error (main scanning magnification correction).

  Such color misregistration occurs due to replacement of the image forming cartridge, maintenance of the image forming apparatus, transportation of the image forming apparatus, etc., even if initial adjustment is performed on the image forming apparatus. The error also fluctuates over time due to the temperature expansion of the mechanism after the image is formed.

  On the other hand, in Patent Document 1, in a tandem-type image forming apparatus including a plurality of image forming stations that form black, yellow, magenta, and cyan images, the image forming station has a positional shift of each color image. As a position detection pattern (toner mark) for detecting the position, four lines for measuring a positional deviation in the sub-scanning direction (black, yellow, magenta, cyan) and four lines for measuring a positional deviation in the main scanning direction ( By forming multiple sets of black, yellow, magenta, and cyan) on the transfer belt and measuring the amount of misregistration of each color, performing skew correction, registration correction, and main scanning magnification correction based on the measurement results, A correction method for appropriately correcting color misregistration is disclosed.

  In the correction method, in an image forming apparatus including a plurality of image forming stations, for example, the plurality of image forming stations form toner marks at both ends in the width direction of the transfer belt and are provided on the most downstream side of the transfer belt. The detection means detects the toner marks at both ends, finds the position shift based on the detection results of the toner marks at both ends of the transfer belt, and corrects the image position shift by each image forming station from the result. Yes.

The toner mark is formed on the transfer belt with a line parallel to the scanning direction (main scanning direction) of optical writing and a line having a specific angle (for example, 45 degrees) with respect to the main scanning direction. The detecting means includes an issuing element and a light receiving element, and a slit member in which a transmission window corresponding to the shape of the toner mark is formed between the light receiving element and the transfer belt. Therefore, the light receiving element of the detecting means receives the light from the light emitting element that has passed through the transparent transfer belt as it is, and receives the light blocked by the toner mark when the toner mark coincides with the position of the transmission window. The detecting means detects the timing at which the toner mark passes based on the difference in the amount of light received by the light receiving element, and detects the positional deviation in the sub-scanning direction based on the peak time difference between the toner mark lines formed parallel to the main scanning direction. And detecting a positional deviation in the main scanning direction based on a peak time difference of a line having a specific angle with respect to the main scanning direction. In this way, the image forming apparatus calculates the positional deviation based on the detection result of the detection unit and performs the adjustment process.
JP 2001-228672 A

  Incidentally, it is necessary to take into account that the magnification error in the main scanning direction is caused by the eccentricity of the rotation axis of the photosensitive member. This is due to the eccentricity of the rotation axis of the photoconductor, because the rotation axis of the photoconductor is deviated from the center, the surface of the photoconductor moves up and down during rotation, and the optical path length of the laser for optical writing changes. The change causes expansion and contraction in the main scanning direction. The magnification error in the main scanning direction due to the eccentricity of the rotation axis of the photosensitive member is repeated with one rotation of the photosensitive member as a cycle, and the value of the magnification error changes according to the cycle without continuing constant. It has the property. In this case, it is necessary to correct the magnification error corresponding to the change according to the cycle.

  In the correction method disclosed in Patent Document 1, although correction of magnification error in the main scanning direction is supported by changing the clock frequency of the writing pixel, the frequency is set before image formation. Therefore, it is not appropriate when the value of the magnification error changes according to the photosensitive member rotation period.

  Also, when correction operations such as toner mark formation, misregistration amount calculation, and clock frequency setting are performed immediately before image formation, it is necessary to pause normal image formation operations during these operations. The performance will be reduced.

  Therefore, the present invention appropriately corrects the magnification error in the main scanning direction caused by the eccentricity of the rotating shaft of the photosensitive member without reducing the productivity by setting the frequency of the writing clock during image formation. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

  In order to achieve this object, the invention according to claim 1, the image data of each color is modulated to the intensity of the laser beam in synchronism with the write clock, and is irradiated onto the photoconductor corresponding to each color component, thereby electrostatic latent image. Image forming means for forming the electrostatic latent image into a toner image by a developing unit corresponding to each color component and superimposing the toner image on a recording medium or an intermediate transfer member conveyed by a conveying belt. In the image forming apparatus, a pattern generation unit that generates a misregistration detection pattern on the transport belt or the intermediate transfer member, a pattern detection unit that detects a misregistration detection pattern generated by the pattern generation unit, and Deviation amount calculation that calculates the deviation amount from the calculated pattern position predicted from the setting of the write clock based on the detection result by the pattern detection means A correction information holding means for holding correction information for correcting the deviation amount calculated by the deviation amount calculating means, and the frequency of the write clock based on the correction information held by the correction information holding means. Main scanning magnification correction means for adjusting and correcting main scanning magnification error caused by eccentricity of the rotation axis of the photosensitive member, and the main scanning magnification correction means is configured to form the electrostatic latent image during the formation of the electrostatic latent image. The write clock frequency is changed.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus further includes an eccentric amount measuring unit that measures an eccentric amount of the photosensitive member, and the main scanning magnification correction unit includes the eccentric amount. The frequency of the write clock is changed based on the measurement result by the measuring means.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the eccentricity measuring unit measures a change in a rotational axis position of the photoconductor and a radius of the photoconductor, and The scanning magnification correction unit changes the frequency of the writing clock based on the change in the position of the rotation axis of the photoconductor and the radius of the photoconductor measured by the eccentricity measurement unit.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the pattern generating means is a timing at which the radius of the photoconductor becomes maximum during a period in which the photoconductor rotates once. And a misregistration detection pattern is generated at a timing at which the radius is minimized.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the pattern detection unit is a detection unit used for registration correction in the main scanning direction and the sub-scanning direction. It is also used as a combination.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the eccentricity measuring unit is a detecting unit used for resist correction in the main scanning direction and the sub-scanning direction. It is also used in combination.

  The invention according to claim 7 is the image forming apparatus according to any one of claims 1 to 6, further comprising in-apparatus temperature measuring means for measuring the temperature in the image forming apparatus, wherein the main scanning is performed. The magnification correction means changes the frequency of the write clock based on the measurement result by the internal temperature measurement means.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, whether or not to correct a main scanning magnification error by the main scanning magnification correcting means can be arbitrarily selected. It has a correction selection means.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus further includes an eccentricity amount information holding unit that holds information on the eccentricity amount of the photoconductor measured in advance, and the main scanning magnification correction unit. Is characterized in that the frequency of the write clock is changed based on the information of the eccentricity held by the eccentricity information holding means.

  According to the present invention, by setting the frequency of the writing clock during image formation, the magnification error in the main scanning direction due to the eccentricity of the rotating shaft of the photosensitive member is appropriately corrected without reducing the productivity. An image forming apparatus that can be used is realized.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of the image forming apparatus according to the present exemplary embodiment. The image forming apparatus 1 includes a photosensitive member 2, a conveyance belt 3, a reading sensor 4, an optical scanning device 5, a developing device 6, a fixing device 7, a paper feeding unit 8, a vertical conveyance unit 9, a paper discharge unit 10, a finisher 11, and It is composed of a photoreceptor sensor 12.

  The photoreceptor 2 carries an electrostatic latent image written on the surface by the laser beam from the optical scanning device 5. The vertical conveyance unit 3 is provided to face the photoconductor 3 and conveys the recording medium on which the toner image is transferred to the fixing device 7. The reading sensor 4 reads a position detection pattern formed on the conveyance belt 3. The optical scanning device 5 exposes and scans the photosensitive member 2 with laser light, and performs line unit recording. The developing device 6 develops the electrostatic latent image carried on the photoreceptor 2 with toner. The fixing device 7 heat-fixes the toner image transferred onto the recording medium.

  The paper supply unit 8 sends the recording medium to the vertical conveyance unit 9 and supplies it to an image forming process such as the photosensitive member 2 and the conveyance belt 3. The vertical conveyance unit 9 conveys the recording medium sent from the paper supply unit 8 to the image forming process. The paper discharge unit 10 discharges the recording medium heated and fixed by the fixing device 7 to the finisher 11. The finisher 11 performs post-processing according to a predetermined command. The photoconductor sensor 12 measures the amount of eccentricity of the photoconductor 2, that is, changes in the position and radius of the rotation axis of the photoconductor 2.

  The reading sensor 4 may also be used as a resist correction sensor (not shown), and the photoconductor sensor 12 may also be used as a resist correction sensor.

  An image forming processing operation in the image forming apparatus of this embodiment will be described. First, the recording medium loaded on the paper feeding tray 8 is fed by a paper feeding device and conveyed to a position where it abuts on the photoreceptor 2 by a vertical conveying unit 9. On the other hand, image data read by a reading device (not shown) or image data sent from a PC is written on the photoconductor 2 by laser light from the optical scanning device 5 and electrostatic latent image is formed on the photoconductor 2. An image is formed. The electrostatic latent image is developed by passing through the developing device 6, and a toner image is formed on the photoreceptor 2.

  Next, the recording medium transported from the vertical transport unit 9 is transported by the transport belt 3 having the same speed as the rotational speed of the photoconductor 2, and at this time, the toner image formed on the photoconductor 2 is transferred onto the recording medium. Transcribed. Thereafter, the toner image transferred onto the recording medium is heat-fixed on the recording medium on which the toner image is transferred by the conveying belt 3 and transferred onto the recording medium. The paper discharge unit 10 discharges the recording medium to the finisher 11 that is a post-processing device. The finisher 11 guides the recording medium ejected from the paper ejection unit 10 to a normal paper ejection tray for simply sorting the recording media, or a stapling table for stapling the collected recording media.

  FIG. 2 is a diagram illustrating a schematic configuration of an optical scanning device of the image forming apparatus of the present embodiment.

  The optical scanning device according to this embodiment includes a laser diode (LD) unit 21, a collimator lens 22, a first mirror 23, a polygon mirror 24, an fθ lens 25, a second mirror 26, a third mirror 27, and a synchronization detection sensor 28. Composed. The above-described units are provided for each color component of black (K), cyan (C), yellow (Y), and magenta (M) except for the polygon mirror 24, and each unit corresponding to each color component is provided. It is shown with an alphabet.

  The LD unit 21 has a semiconductor laser serving as a light source, and emits laser light toward the collimator lens 22 by the semiconductor laser. The collimator lens 22 is an imaging lens system, and converts the laser light beam emitted from the LD unit 21 into parallel light. The polygon mirror 24 is rotated by a polygon motor (not shown) and deflects the light beam of the laser beam that has been made parallel by the collimator lens 22. The fθ lens 25 is a scanning lens system, and forms an image of the light beam of the laser beam deflected by the polygon mirror 24 on a photoconductor as a scanning medium. The first mirror 23 reflects the laser beam to the polygon mirror 24, the second mirror 26 reflects the laser beam onto the photosensitive member, and the third mirror 27 reflects the synchronization detection sensor 28. The synchronization detection sensor 28 detects the laser beam reflected by the third mirror 27 in order to synchronize the write clock.

  The optical scanning operation of the optical scanning device in this embodiment will be described. First, the laser light emitted from the LD unit 21K is collected by the collimator lens 22K, reaches the first mirror 23K, and is reflected in the direction of the polygon mirror 24 by the first mirror 23K. Then, the laser beam reflected by the polygon mirror 24 that is driven to rotate passes through the fθ lens 25KC (shared with C (cyan)), is reflected by the second mirror 26K, and is directed toward the photoconductor.

  The laser beam is reflected by a third mirror 27KC (shared with C (cyan)) disposed at a position away from the second mirror 26K and is incident on the synchronization detection sensor 28KC (shared with C (cyan)). A signal detected and output by the synchronization detection sensor 28KC is used as a synchronization signal serving as a reference for the writing start timing in the main scanning direction in the image forming operation of the black color component. The laser beam is scanned in the main scanning direction by the rotation of the polygon motor, and an electrostatic latent image corresponding to the black component image is formed on the photoconductor.

  The optical scanning operation described above relates to the black color component, but the operation is the same for the other color components.

  In the optical scanning device according to the present embodiment, the color misregistration caused by the arrangement accuracy of each component corresponding to each color component and the lens formation accuracy, that is, each color constituting the color image formed on the transfer belt and superimposed. There is a relative shift in the image forming position of the components. Therefore, for color misregistration caused by the arrangement and formation accuracy of each component corresponding to each color component, skew correction that changes the reflection angle of the mirror and registration correction that controls the image writing start timing are performed. Adjustment in the main scanning direction is performed, and magnification correction for controlling the write clock frequency is performed for expansion and contraction of the image in the main scanning direction.

  FIG. 3 is a diagram illustrating a system configuration of the image forming apparatus according to the present exemplary embodiment.

  The image forming apparatus 31 of this embodiment includes a CPU (Central Processing Unit) 32, a ROM (Read Only Memory) 33, a RAM (Random Access Memory) 34, an EEPROM (Electrically Erasable Programmable ROM) 35, a timer 36, and an operation display unit 37. , NCU (Network Control Unit) 38, communication control unit 39, LAN (Local Area Network) communication control unit 40, image processing unit 41, image forming unit 42, image reading unit 43, and system bus 44.

  The CPU 32 controls each part of the apparatus and performs various data processing based on a control program written in the ROM 33 while using the RAM 34 as a work area. The ROM 33 stores various data necessary for control of the control program for the CPU 32 to control each part of the apparatus and font data corresponding to each character code. The RAM 34 is a memory used as a work area for the CPU 32. The EEPROM 35 is a read-only memory that can be electrically rewritten, stores various information necessary for the operation of the apparatus, and retains the stored contents even when the apparatus is turned off.

  The timer 36 always counts the current date and time, and the CPU 32 can know the current date and time by reading the timer 36 via the system bus 44. The operation display unit 37 is provided with various keys for accepting operation inputs from the user, and includes a display device such as a liquid crystal display device, and displays an operation state of the device and various messages to be notified to the user.

  The NCU 38 is connected to a PSTN (Public Switched Telephone Network) (not shown), and closes the line and detects a call signal. The communication control unit 39 is connected to the PSTN via the NCU 38 and controls communication with the other communication terminal, controls the NCU 38, detects a ringing voltage pulse detected by the NCU 38, and performs DTMF (Dial Tone Multi Frequency). ) Signal detection, tone signal detection, and outgoing call. The LAN communication control unit 40 is a so-called NIC (Network Interface Card), and is connected to a LAN (not shown) so that various kinds of information can be exchanged via the LAN.

  The image processing unit 41 encodes and compresses the raw image data and encodes and decodes the encoded compressed data, and performs binarization, scaling, reduction / enlargement, image correction, and addition Various image processing related to image data handled in the image forming apparatus 31 such as information addition processing is performed. The image forming unit 42 forms and outputs color or monochrome image data on a recording medium by electrophotography as image forming means. The image reading unit 43 reads a set original and acquires color or monochrome document image data.

  The system bus 44 is a signal line including a data bus, an address bus, a control bus, an interrupt signal line, and the like for the above-described units to exchange data.

  FIG. 4 is a diagram showing the contents stored in the EEPROM of the image forming apparatus of the present embodiment.

  In the EEPROM 35, a pattern deviation amount / write clock frequency information correspondence table 351 and an eccentricity / write clock frequency information correspondence table 352 are stored in advance.

  The pattern deviation amount / write clock frequency information correspondence table 351 includes information on the pattern position deviation amount and information on the write clock frequency adjusted at the time of correction. The information of the write clock frequency for correcting to is stored in correspondence with the information of the positional deviation amount. For example, the frequency for correcting the positional shift when the pattern shift amount information (1) is the write clock frequency information (1).

  Further, the eccentricity / writing clock frequency information correspondence table 352 includes information on the amount of eccentricity of the photosensitive member and information on the writing clock frequency used for correction, and color misregistration due to eccentricity of the rotating shaft of each photosensitive member. Is stored in correspondence with the information on the amount of eccentricity. For example, the frequency for correcting misalignment when the amount of eccentricity information (II) is write clock frequency information (II).

  FIG. 5 is a diagram showing an image in which the image length varies depending on the upper and lower surfaces of the photosensitive member due to the eccentricity of the rotational axis of the photosensitive member, the left diagram shows the case where the rotational radius is maximum, and the right diagram shows the smallest rotational radius. Represents the case. FIG. 6 is a diagram showing an image of expansion and contraction due to the eccentricity of the photoconductor.

  As shown in FIG. 5, the image length A is obtained when the rotation radius of the photoconductor is the maximum, and the image length A ′ is obtained when the rotation radius of the photoconductor is the minimum. The image length increases as the rotation radius decreases. . As described above, when the laser beam is irradiated onto the photosensitive member surface by the LD unit and the polygon mirror, the photosensitive member surface moves up and down with respect to the rotating shaft due to the eccentricity of the rotating shaft of the photosensitive member, and the optical path of the laser light is changed. Due to the change, the image written on the photoreceptor surface expands and contracts. Further, as shown in FIG. 6, the image expands and contracts with the rotation cycle of the photoconductor.

  The above-described image expansion / contraction correction is performed by changing the frequency of the writing clock in the optical writing operation by the LD unit in accordance with the rotation of the photosensitive member. Specifically, a change in the position and radius of the rotation axis of the photoconductor is detected by the photoconductor sensor, and frequency information corresponding to the detection result is read from the eccentricity / write clock frequency information correspondence table in the EEPROM. The magnification correction in the main scanning direction is performed by adjusting the frequency of the write clock based on the write clock frequency information.

  FIG. 7 is a diagram for explaining the detection operation of the position detection pattern in the image forming apparatus of the present embodiment.

  As shown in FIG. 7, on the conveyor belt 72, position detection patterns 73 and 74 are formed at three positions, the left end, the center, and the right end in the main scanning direction (direction perpendicular to the conveying direction (sub-scanning direction)). Then, the pattern is detected by a reading sensor 75 provided in the downstream portion of the conveyor belt 72, and the information of the magnification deviation is acquired by measuring the time difference.

  The pattern is a four-band pattern corresponding to each color component of black, cyan, yellow, and magenta. The pattern includes two types of patterns: a position detection pattern 73 formed parallel to the main scanning direction and a position detection pattern 74 formed at a certain angle with respect to the main scanning direction. It is formed in three places. In FIG. 7, the position detection pattern 74 formed at the right end of the transport belt 72 is omitted.

  By reading the position detection pattern 73 with the reading sensor 75, the color misregistration amount in the sub-scanning direction to be corrected is determined based on the deviation between the theoretical mutual distance and the actual mutual distance formed by the pattern on the photoconductor 71. Information can be obtained. For the position detection pattern 74, information about the color misregistration amount in the main scanning direction to be corrected can be acquired from the deviation between the theoretical mutual distance and the actual mutual distance.

  Regarding the timing for forming (imaging) the position detection patterns 73 and 74, the radius between the rotation periods of the photosensitive member is the maximum, that is, the portion where the imaging magnification in the main scanning direction is the minimum, and the radius is the minimum. That is, an optimal measurement result can be obtained by forming the pattern at a portion where the image forming magnification in the main scanning direction is maximized.

  Further, since the circumferential length of the photosensitive drum increases as the temperature rises, it is necessary to measure the expansion and contraction of the image again according to the rising temperature. For this reason, for example, when the ΔT ° C. temperature has changed since the previous measurement, the above-described measurement of the eccentricity, the formation of the position detection pattern, and the pattern reading are performed again. Also good. With such a configuration, setting with respect to a change with time due to a change in temperature is appropriately performed, and the accuracy of deviation amount correction in the main scanning direction is improved.

  Further, the re-measurement of the image expansion and contraction with respect to the temperature change takes time to form and read the pattern image when the measurement is repeated many times, and may reduce the printing efficiency. Therefore, when it is desired to maintain a certain efficiency without reducing the printing efficiency, a configuration having a function of arbitrarily selecting so as not to perform these correction operations may be employed. In this case, the correction time can be shortened by not performing the correction when the main scanning magnification correction is not necessary.

  In addition, the change in the radius of the drum during the rotation period of one rotation of the photosensitive drum is measured using a dedicated jig, and the measurement result is held in advance in, for example, a memory provided in the photosensitive unit and mounted on the actual machine. The measurement result may be read by a CPU in the main body of the image forming apparatus, and the write clock frequency may be changed so as to correct image expansion and contraction based on the value. In this case, by measuring the change in the radius of the photosensitive drum in advance, there is no need to make adjustments after assembling to the machine, and it is possible to measure the main scanning magnification change caused by the eccentricity of the rotation axis of the photosensitive member. It can be performed with high accuracy.

  According to the above-described embodiment, it is possible to correct the main scanning magnification error caused by the eccentricity of the rotation axis of the photosensitive drum. In addition, it is possible to improve the accuracy of correction of the shift amount in the main scanning direction. It is also possible to reduce the amount of deviation in the main scanning direction. In addition, it is possible to measure the expansion and contraction of the image at an optimum interval with respect to the eccentricity of the rotation axis of the photosensitive drum. Further, by reducing the number of sensors, the system can be simplified and the cost can be reduced. When it is not necessary to perform main scanning magnification correction, the correction time can be shortened by not performing the magnification correction. Further, by measuring in advance, it is not necessary to make adjustments after being assembled in the machine, and it is possible to measure the change in main scanning magnification with higher accuracy.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of an optical scanning device of an image forming apparatus according to an embodiment of the present invention. 1 is a system configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing storage contents of an EEPROM of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram illustrating an image in which an image length varies depending on the upper and lower surfaces of a photoconductor surface due to the eccentricity of the rotation axis of the photoconductor. FIG. 6 is a diagram illustrating an image expansion / contraction image caused by the eccentricity of the rotation axis of the photoconductor. FIG. 6 is a diagram for explaining a position detection pattern detection operation in the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31 Image forming apparatus 2,71 Photoconductor 3 Conveyor belt 4,75 Reading sensor 5 Optical scanning device 6 Developing device 7 Fixing device 8 Paper feed unit 9 Vertical conveyance unit 10 Paper discharge unit 11 Finisher 12 Photoconductor sensor 21 Laser diode (LD) unit 22 collimator lens 23 first mirror 24 polygon mirror 25 fθ lens 26 second mirror 27 third mirror 27
28 Synchronization detection sensor 32 CPU
33 ROM
34 RAM
35 EEPROM
36 Timer 37 Operation display section 38 NCU
39 Communication Control Unit 40 LAN Communication Control Unit 41 Image Processing Unit 42 Image Forming Unit 43 Image Reading Unit 44 System Bus 72 Conveyance Belts 73 and 74 Pattern Detection Sensor for Position Detection 351 Pattern Deviation / Write Clock Frequency Information Correspondence Table 352 Eccentricity / Write clock frequency information correspondence table

Claims (9)

The image data of each color is modulated to the intensity of the laser beam in synchronization with the write clock, and is irradiated onto the photoconductor corresponding to each color component to form an electrostatic latent image, and the electrostatic latent image is developed by a developer corresponding to each color component. In an image forming apparatus comprising an image forming unit that forms an image into a toner image and superimposes and forms the toner image on a recording medium or an intermediate transfer member that is conveyed by a conveying belt.
Pattern generating means for generating a misregistration detection pattern on the conveying belt or the intermediate transfer member;
Pattern detection means for detecting a misregistration detection pattern generated by the pattern generation means;
A deviation amount calculating means for calculating a deviation amount from a calculated pattern position predicted from the setting of the write clock based on a detection result by the pattern detection means;
Correction information holding means for holding correction information for correcting the deviation amount calculated by the deviation amount calculating means;
Main scanning magnification correction means that adjusts the frequency of the writing clock based on the correction information held by the correction information holding means and corrects the main scanning magnification error caused by the eccentricity of the rotation axis of the photosensitive member. And
The image forming apparatus according to claim 1, wherein the main scanning magnification correction unit changes a frequency of the writing clock during the formation of the electrostatic latent image. Further comprising an eccentricity measuring means for measuring the eccentricity of the photoconductor,
The image forming apparatus according to claim 1, wherein the main scanning magnification correction unit changes a frequency of the writing clock based on a measurement result by the eccentricity measurement unit. The eccentricity measuring means measures the change in the position of the rotating shaft of the photoconductor and the radius of the photoconductor,
The main scanning magnification correction unit changes the frequency of the writing clock based on a change in a position of a rotation axis of the photoconductor and a radius of the photoconductor measured by the eccentricity measurement unit. Item 3. The image forming apparatus according to Item 2.   The pattern generation means generates a misregistration detection pattern at a timing at which the radius of the photoconductor becomes maximum and at a timing at which the radius becomes minimum during a period in which the photoconductor rotates once. The image forming apparatus according to claim 3.   5. The image forming apparatus according to claim 1, wherein the pattern detection unit is also used as a detection unit used for registration correction in the main scanning direction and the sub-scanning direction. 6.   The image forming apparatus according to claim 2, wherein the eccentricity measuring unit is also used as a detecting unit used for registration correction in the main scanning direction and the sub-scanning direction. The apparatus further includes an apparatus temperature measuring means for measuring the temperature in the image forming apparatus,
The image forming apparatus according to claim 1, wherein the main scanning magnification correction unit changes a frequency of the writing clock based on a measurement result by the temperature measuring unit in the apparatus.   The image forming apparatus according to claim 1, further comprising a correction selection unit that can arbitrarily select whether or not to correct a main scanning magnification error by the main scanning magnification correction unit. Eccentric amount information holding means for holding information on the eccentric amount of the photoreceptor measured in advance,
The image forming apparatus according to claim 1, wherein the main scanning magnification correction unit changes the frequency of the writing clock based on the information on the amount of eccentricity held by the amount of eccentricity information holding unit.

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