JP4968241B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

In general, in an image forming apparatus using an electrophotographic method, an electrostatic latent image corresponding to image data (image signal) is formed on a photoconductor, and a toner image obtained by developing the image is transferred onto a sheet. An image is formed on the paper by fixing the toner image on the paper. In this type of image forming apparatus, when the paper is transported toward the transfer position where the toner image is transferred, the time when the paper reaches the transfer position matches the time when the toner image reaches the transfer position. In addition, there is one having a function of notifying the time at which the toner image reaches or near the transfer position by generating a pseudo signal (see Patent Document 1). In addition, in an electrophotographic image forming apparatus, a plurality of photosensitive members and an intermediate transfer member are used to form a multicolor image on a sheet, and the relative positional shift of each color image Some have a function to correct
There is something.

Japanese Patent No. 3632738

  According to the present invention, when the positional deviation correction amount applied when correcting the positional deviation of the image is changed, the simulation is performed at a time suitable for the position of the image to be corrected based on the changed positional deviation correction amount. It is an object to provide a mechanism capable of generating a signal.

According to the first aspect of the present invention, a plurality of photoconductors on which images of different colors are formed, an intermediate transfer member to which images of each color formed on the plurality of photoconductors are transferred, and the intermediate transfer member Transfer means for transferring the transferred image onto the paper at the transfer position, paper conveyance means for conveying the paper toward the transfer position of the transfer means, and start of writing of the electrostatic latent image on the photosensitive member in the sub-scanning direction The reference value is the time from when the image transferred to the intermediate transfer body reaches the transfer position or the vicinity thereof, and the reference value is counted from the start of writing of the electrostatic latent image on the photoconductor in the sub-scanning direction. Computation means for outputting a pseudo signal after completion, paper conveyance control means for controlling paper conveyance of the paper conveyance means based on the pseudo signal output by the arithmetic means , and for each color transferred to the intermediate transfer member Image position Detecting means for detecting a deviation, based on the detection results obtain the position deviation correction amount of the image of the detection means, and image position correction means for correcting the timing of the write start in accordance with the position shift correction amount determined such, When the write start timing after the correction is later than before the correction, the reference value is corrected to be smaller, and when the write start timing after the correction is earlier than the correction, the reference value is corrected. An image forming apparatus comprising: a pseudo signal correcting unit that corrects the reference value so as to increase .

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the misregistration correction amount applied to the correction of the image forming position on the photoconductor is changed in the pseudo signal correcting unit. In this case, the reference value is corrected.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the pseudo signal correcting unit sets the reference value when the change amount of the positional deviation correction amount is equal to or larger than a preset threshold value. It is characterized by correcting.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the pseudo signal correcting unit determines the correction amount of the reference value based on a difference before and after the change of the misalignment correction amount. It is characterized by.

  According to the first aspect of the present invention, when the misregistration correction amount applied when correcting the misregistration of the image is changed, the image to be corrected is corrected based on the changed misregistration correction amount. A pseudo signal can be generated at a time suitable for the position.

  According to the second aspect of the present invention, the reference value can be corrected every time the positional deviation correction amount is changed.

  According to the third aspect of the present invention, the reference value is not corrected when the change amount of the misalignment correction amount is less than the threshold value, and the reference value is corrected when the change amount of the misalignment correction amount is equal to or greater than the threshold value. Can be operated to.

  According to the fourth aspect of the present invention, the reference value can be changed according to the difference before and after the change of the positional deviation correction amount.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. The technical scope of the present invention is not limited to the embodiments described below, and various modifications and improvements have been made within the scope of deriving specific effects obtained by the constituent requirements of the invention and combinations thereof. Also includes form.

  FIG. 1 is a schematic view showing a configuration example of an electrophotographic image forming apparatus to which the present invention is applied. The image forming apparatus 1 is roughly configured to include an image reading device 2, an image forming unit 3, and a paper transport device 4.

  The image reading device 2 optically reads an image of a document. The image forming unit 3 forms an image on a sheet serving as a recording medium based on image data of a document read by the image reading device 2 or image data sent from an external terminal device (for example, a personal computer) ( Printing). The paper transport device 4 transports paper used for image formation. The image reading apparatus 2 is provided on the upper part of the image forming apparatus main body 5. The image forming unit 3 is provided inside the image forming apparatus main body 5. The paper transport device 4 is provided inside the image forming apparatus main body 5 except for a part thereof.

  The image reading device 2 includes a document pressing member 7 on which the automatic document feeder 6 is mounted, and an image reading unit 8. The automatic document feeder 6 conveys a document as a medium to be read one by one through a reading position. The document pressing member 7 presses the document placed on the document table from above, and is provided at the top of the image forming apparatus main body 5 so as to be freely opened and closed. The image reading unit 8 optically reads an image of a document placed on a document table and an image of a document conveyed to a reading position by the automatic document conveying device 6. The image reading unit 8 is configured using, for example, a light source, a mirror, a lens, an image sensor, and the like (not shown).

  The image forming unit 3 includes four photosensitive drums 9, 10, 11, and 12 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K), and the respective photosensitive drums 9. ˜12, four primary transfer rolls 13, 14, 15, 16, an endless intermediate transfer belt 17 serving as an intermediate transfer member, and a transfer unit 18, and a four-tandem machine configuration. Yes.

  Around each of the photosensitive drums 9 to 12, a charger, a latent image forming device, a developing device, a cleaner, and the like are arranged. The charger uniformly charges the surface of the photosensitive drum. The latent image forming apparatus forms an electrostatic latent image on the surface of the photosensitive drum by exposing and scanning the surface of the photosensitive drum charged by the charger with laser light. The developing device develops the electrostatic latent image into a toner image (visible image) by supplying toner contained in the two-component developer to the surface of the photosensitive drum. The cleaner removes unnecessary toner remaining on the photosensitive drum.

  The primary transfer rolls 13 to 16 are arranged in a state of being opposed to each other in the vicinity of the corresponding photosensitive drums 9 to 12 via the intermediate transfer belt 17. The primary transfer roll 13 transfers (primary transfer) the toner image formed on the photosensitive drum 9 to the intermediate transfer belt 17. The primary transfer roll 14 is for transferring (primary transfer) the toner image formed on the photosensitive drum 10 to the intermediate transfer belt 17. The primary transfer roll 15 transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 17 (primary transfer). The primary transfer roll 16 transfers (primary transfer) the toner image formed on the photosensitive drum 12 to the intermediate transfer belt 17.

  The intermediate transfer belt 17 is provided as an intermediate transfer member that holds a toner image. The intermediate transfer belt 17 is supported in a loop shape by a plurality of belt support rolls. A transfer portion 18 is provided in the middle of the loop of the intermediate transfer belt 17. The intermediate transfer belt 17 travels counterclockwise on the travel path of the intermediate transfer belt 17. The transfer unit 18 is a part where an image is transferred from the intermediate transfer belt 17 to a sheet. The transfer unit 18 includes a pair of rolls that sandwich the intermediate transfer belt 17 with one roll as a secondary transfer roll and the other roll as a belt support roll. The secondary transfer roll is for transferring (secondary transfer) the toner image formed on the intermediate transfer belt 17 to a sheet as described above. For this reason, the intermediate transfer belt 17 is sandwiched between the secondary transfer roll and the belt support roll (nip portion) between which the image (toner image) is transferred from the intermediate transfer belt 17 to the sheet. "

  A home sensor 34 and a registration sensor 35 are arranged on the travel path of the intermediate transfer belt 17. The home sensor 34 is disposed on the downstream side of the final photosensitive drum 12 in the traveling direction of the intermediate transfer belt 17 and in the vicinity of the photosensitive drum 12. The home sensor 34 detects the home position of the intermediate transfer belt 17. Specifically, the home sensor 34 optically reads, for example, a mark provided at one place in the circumferential direction of the intermediate transfer belt 17. The home sensor 34 outputs a belt home signal when the mark attached to the intermediate transfer belt 17 is read.

  The registration sensor 35 is disposed upstream of the foremost photosensitive drum 9 in the traveling direction of the intermediate transfer belt 17. The registration sensor 35 is provided to detect a relative positional shift of each color image transferred to the intermediate transfer belt 17 as a “color registration shift”. For example, assuming that a yellow toner image is formed on the photosensitive drum 9 in the foremost stage, the color registration shift is determined based on the position of the image of the reference color using the yellow as a reference color. This is expressed by the relative displacement of the color (magenta, cyan, black) image. When actually detecting a color registration shift, for example, a pattern image for registration shift detection is formed for each color of YMCK on the surface of the intermediate transfer belt 17, and the pattern image is read by the registration sensor 35. Based on this, a positional deviation amount (color registration deviation amount) of an image of another color with respect to the reference color is calculated. Here, yellow has been described as the reference color, but other colors may be used as the reference color.

  The image forming unit 3 includes a fixing unit 19. The fixing unit 19 fixes the toner image transferred to the paper by the transfer unit 18. For example, the fixing unit 19 includes a pair of rolls in which one roll is a heating roll with a built-in heater and the other roll is a pressure roll.

  The paper transport device 4 includes four paper storage units 21, 22, 23, and 24 that are arranged in multiple stages in the top and bottom, a paper supply unit 25 that feeds paper from each of the paper storage units 21 to 24, and a paper supply unit 25, and a registration unit that feeds the sheet conveyed by the vertical conveyance unit 26 to the transfer unit 18 (transfer position) in accordance with the transfer time. 27, a vacuum transport unit 28 for feeding the paper that has passed through the transfer unit 18 to the fixing unit 19, a reverse transport unit 29 for reversing the paper sent from the fixing unit 19 by switchback, and a reverse transport unit 29 Re-feed transport unit 30 for transporting the paper again, discharge unit 31 for discharging the paper after single-sided printing or double-sided printing, and discharge for storing the paper discharged by discharge unit 31 in a stacked state Housing part 3 When, and a manual-feed device 33 for feeding the paper to be used for printing images in the manual feed. Among these, the resist part 27 is comprised using a pair of resist roll, and the discharge part 31 is comprised using a pair of discharge roll. The reverse conveyance unit 29 and the refeed conveyance unit 30 are provided as a duplex printing conveyance unit.

  Next, a basic operation of the image forming apparatus 1 having the above configuration will be described.

  First, when an image of a document is read by the image reading device 2, a toner image is formed by the image forming unit 3 based on the image data obtained thereby. In the image forming unit 3, while rotating the four photosensitive drums 9 to 12, yellow, magenta, and cyan are formed on the surfaces of the photosensitive drums 9 to 12 by corresponding chargers, latent image forming devices, and developing units. A black toner image is formed. The toner images of the respective colors formed in this manner are sequentially transferred onto the intermediate transfer belt 17 by the primary transfer rolls 13 to 16. As a result, a multicolor (full color) toner image is formed on the intermediate transfer belt 17 by superimposing four color toners. The toner image formed on the intermediate transfer belt 17 in this way is held by the intermediate transfer belt 17 and sent to the transfer unit 18. Here, the case of color printing is assumed, but in the case of monochrome printing, only the black toner image is transferred to the intermediate transfer belt 17.

  On the other hand, the paper selected by the user using the operation panel of the image forming apparatus 1, the paper selected by the automatic selection function, or the paper supplied from the manual feed device 33 is transferred at a preset transfer time. In order to reach the transfer unit 18, it is fed from the resist unit 27 to the transfer unit 18 in accordance with the transfer time. For example, if the sheet selected by the user is a sheet stored in the uppermost sheet storage unit 21, the sheet is fed from the sheet storage unit 21 by the sheet feeding unit 25 and the sheet is fed. The sheet is fed into the registration unit 27 via the vertical conveyance unit 26.

  The registration unit 27 is disposed upstream of the transfer unit 18 in the sheet conveyance direction. In the registration unit 27, for example, the leading end of the sheet is abutted against the contact portion (nip part) of the registration roll which is in a rotation stopped state, and the sheet is conveyed by a predetermined amount by the vertical conveyance unit 26 in this abutting state. Then, the paper is bent in a loop shape by temporarily stopping the conveyance of the paper. Thereby, the skew of the sheet is corrected so that the leading edge of the sheet is parallel to the rotation axis of the registration roll. Thereafter, the sheet is fed from the registration unit 27 to the transfer unit 18 by starting the rotation of the registration roll in accordance with the transfer time.

  On the other hand, the toner images transferred to the intermediate transfer belt 17 by the respective primary transfer rolls 13 to 16 are sent to the transfer unit 18 according to the rotation of the intermediate transfer belt 17. At this time, the toner image held on the intermediate transfer belt 17 is transferred (secondary transfer) onto the paper by the transfer unit 18. Thereafter, the sheet is sent to the fixing unit 19 by the vacuum conveyance unit 28, where the toner image is fixed. Subsequent operations differ depending on whether the image forming mode is the single-sided printing mode or the double-sided printing mode.

  The single-sided printing mode is an image forming mode applied when printing an image on one side of a sheet. The duplex printing mode is an image forming mode that is applied when printing an image on both sides of a sheet. When operating in the single-sided printing mode, the sheet on which the toner image has been fixed by the fixing unit 19 as described above is discharged from the discharge unit 31 to the discharge storage unit 32.

  When operating in the double-sided printing mode, after the sheet on which single-sided printing has been completed is sent to the reverse conveyance unit 29, the sheet is again fed to the registration unit 27 via the refeed conveyance unit 30. Therefore, the reverse conveyance unit 29 and the refeed conveyance unit 30 are conveyance units for printing images on both sides of the sheet. Thereafter, the toner image is transferred and fixed on the paper in the same procedure as in single-sided printing, and then the paper is discharged. In addition, when the paper sent out from the fixing unit 19 is reversed and discharged, the paper is sent from the fixing unit 19 to the discharge unit 31 via the reverse conveyance unit 29.

  FIG. 2 is a schematic diagram showing a configuration example of the latent image forming apparatus. The illustrated latent image forming device 36 is provided for each of the colors Y, M, C, and K in a form corresponding to each of the photosensitive drums 5, 6, 7, and 8. FIG. 2 shows one of them. The latent image forming apparatus 36 includes a laser emitter 101 made of a semiconductor laser or the like, a collimator lens 102, a polygon mirror (rotating polygon mirror) 103, a lens system 104 made of an fθ lens, and a beam detect sensor (hereinafter referred to as “ BD sensor ") 105.

  The laser beam generated by the laser emitter 101 is irradiated onto one surface of the polygon mirror 103 that rotates at a constant speed in the B direction in the drawing after the beam shape is shaped by the collimator lens 102. At this time, the laser beam is reflected by one surface of the polygon mirror 103, and the reflected laser beam is deflected according to the rotation of the polygon mirror 103. As a result, the laser light reflected by one surface of the polygon mirror 103 is scanned in the direction A in the drawing on the surface of the photosensitive drum (5, 6, 7, 8) via the lens system 104. The lens system 104 plays a role of deflecting the laser light so that the laser light deflected by the polygon mirror 103 moves linearly at a constant speed on the photosensitive drum (5, 6, 7, 8).

  The BD sensor 105 is positioned in front (end) of the electrostatic latent image writing start position P1 by the latent image forming device 36 in the main scanning direction along the axial direction of the photosensitive drum (5, 6, 7, 8). It is arranged at P0, and outputs a reference signal when it senses the reception of laser light there. The reference signal output from the BD sensor 105 is a reference for determining the electrostatic latent image writing start position P1 in the main scanning direction when an electrostatic latent image is written on the photosensitive drum by laser beam line scanning. The synchronization signal (hereinafter referred to as “main scanning synchronization signal”). Further, when forming an electrostatic latent image by the latent image forming device 36, a synchronization signal (hereinafter referred to as a reference) for determining the writing start position of the electrostatic latent image in the sub-scanning direction (the rotation direction of the photosensitive drum). The “sub-scanning synchronization signal”) is output by an image formation controller described later.

  In the latent image forming apparatus 36 configured as described above, the laser light emitted from the laser emitter 101 through the collimator lens 102 to the polygon mirror 103 is rotated by the rotation of the polygon mirror 103 so that the photosensitive drums (5, 6, 7, 8) Line scanning is performed in the axial direction (main scanning direction). By repeating this line scanning for each line by the rotation of the polygon mirror 103 and the rotation of the photosensitive drum, a two-dimensional electrostatic latent image is formed on the surface of the photosensitive drum (5, 6, 7, 8). .

  At this time, if an area where an electrostatic latent image writing operation is actually performed on the drum surface by scanning with a laser beam in the axial direction of the photosensitive drum (5, 6, 7, 8) is defined as an effective area, this effective area Is defined between the writing start position P1 and the writing end position P2 of the electrostatic latent image by the latent image forming device 36. On the other hand, the image writing operation by the laser beam is not performed on the photosensitive drum between the position P0 where the BD sensor 105 senses the laser beam and the electrostatic latent image writing start position P1. For this reason, the area between P0 and P1 is substantially an invalid area. When the effective area (between P1 and P2) of the photosensitive drum is exposed and scanned with laser light, the laser light is modulated (flashing) in accordance with the image signal decomposed for each color of K, Y, M, and C. Is done.

  FIG. 3 is a block diagram showing a configuration example of a control system of the image forming apparatus according to the embodiment of the present invention. In FIG. 3, the system control unit 41 controls the overall processing operation of the image forming apparatus 1. The image input control unit 42 controls a document image reading operation by the image reading device 2. The image processing unit 43 performs preset image processing (for example, color conversion, color correction, gradation correction, enlargement / reduction, image processing) on an image signal obtained when the image reading apparatus 2 reads an image of a document. Processing such as rotation and screen generation). The operation panel 44 serves as an interface for a user who uses the image forming apparatus 1 to input various information and display various information to the user. The operation panel 44 includes, for example, an input unit having various buttons, switches, keys, and the like, and a display unit including a liquid crystal display with a touch panel. The communication control unit 45 controls communication with an external device such as a personal computer.

  The image forming control unit 46 controls the image forming operation using the image forming unit 3 and the paper transport device 4 via the photoconductor control unit 47, the belt control unit 48, the writing control unit 49, and the paper transport control unit 50. To do. The photoconductor control unit 47 controls the rotation operation of the photoconductor drums 9 to 12. The belt controller 48 controls the rotation operation of the intermediate transfer belt 17. The writing control unit 49 controls the electrostatic latent image writing operation by the latent image forming device 36. The paper transport control unit 50 controls the paper transport operation by the paper transport device 4.

  The image forming control unit 46 receives the belt home signal output from the home sensor 34 and a pattern image reading signal (hereinafter, “registration error detection pattern reading signal”) output from the registration sensor 35. , Each is input. Further, the image formation control unit 46 includes a calculation unit 51, a registration error correction unit 52, and a pseudo signal correction unit 53.

  The calculation unit 51 calculates the time at which the image transferred to the intermediate transfer belt 17 reaches the transfer position or the vicinity thereof, and notifies the sheet conveyance control unit 50 of the calculated time by generation of a pseudo signal. is there. The calculation unit 51 does not directly detect the time when the leading edge of the toner image on the intermediate transfer belt 17 reaches or near the transfer position by using a sensor or the like. By electrically generating a pseudo signal corresponding to the time at which it will reach the vicinity, the time is notified to the paper transport control unit 30.

  The registration error correction unit 52 obtains a positional deviation correction amount in the main scanning direction and the sub-scanning direction of the image based on the registration deviation detection pattern reading signal output from the registration sensor 35, and according to the obtained positional deviation correction amount. Thus, the image forming position on the photosensitive drum (9 to 12) is corrected.

  The pseudo signal correcting unit 53 corrects a reference value (details will be described later) that defines the generation time of the pseudo signal in accordance with the positional deviation correction amount in the sub-scanning direction obtained by the registration error correcting unit 52.

  Here, how to calculate the image arrival time in the calculation unit 51 will be described. First, the time to be notified by the generation of the pseudo signal is the time when the leading edge of the toner image transferred from each of the photosensitive drums 9 to 12 to the intermediate transfer belt 17 reaches or near the transfer position. Here, as an example, the time at which the leading edge of the toner image reaches the vicinity of the transfer position is notified by generation of a pseudo signal. The leading edge of the toner image refers to an image edge on the downstream side in the traveling direction of the intermediate transfer belt 17 (hereinafter referred to as “belt traveling direction”). Further, the vicinity of the transfer position refers to a position set in advance on the downstream side in the belt traveling direction with respect to the last photosensitive drum 12 and on the upstream side in the belt traveling direction with respect to the transfer position.

  The computing unit 51 has a counter for generating a pseudo signal. This counter is provided for each color of YMCK. FIG. 4 is an explanatory diagram showing an outline of the counter. The counter 54 operates in synchronization with a reference clock signal having a fixed period. The counter 64 is configured to start counting the reference clock signal from the timing at which the count start trigger signal is output, and output a pseudo signal as a count-up output when the count value reaches a preset specified value. ing. For this reason, the generation time of the pseudo signal is defined by the reference value. As a trigger signal for starting counting, a sub-scanning writing start signal (described later in detail) applied when writing an electrostatic latent image on one of the four photosensitive drums, for example, the last photosensitive drum 12 is used. May be used. The count value in the counter 54 is reset every time a pseudo signal is output (count-up output).

  The reference value that defines the output timing of the pseudo signal is set as follows based on the rotational speed of the photosensitive drum and the moving speed of the intermediate transfer belt 17. That is, after the latent image forming device 36 starts writing the electrostatic latent image on the photosensitive drum based on the sub-scanning synchronization signal, the toner image obtained by developing the electrostatic latent image is transferred from the photosensitive drum. The reference value is set so as to be a value corresponding to the time required to reach the vicinity of the transfer position after being transferred to the intermediate transfer belt 17. Here, the pseudo signal is output in accordance with the time when the leading edge of the toner image reaches the vicinity of the transfer position. However, the present invention is not limited to this, and the pseudo signal is output in synchronization with the time when the leading edge of the toner image reaches the transfer position. A signal may be output.

  However, the sheet conveyance control unit 50 variably controls the timing at which the leading edge of the sheet reaches the transfer position based on the pseudo signal output from the calculation unit 51 of the image formation control unit 46. Specifically, the paper conveyance control unit 50 recognizes the timing at which a certain time has elapsed from the output timing of the pseudo signal as the time when the leading edge of the toner image reaches the transfer position, and the paper conveyance device 4 according to this arrival time. The paper transport operation (for example, the paper transport speed, acceleration timing, deceleration timing, etc. by the registration unit 27) is controlled. Therefore, the calculation unit 51 outputs the pseudo signal before the time when the leading edge of the toner image reaches the transfer position when notifying the time when the toner image reaches the transfer position or its vicinity by the generation of the pseudo signal. It will be.

  Next, a method for correcting color registration (image alignment of each color) by the registration error correction unit 52 will be described. First, in the image forming apparatus 1, color registration correction is performed at a preset timing. Specifically, for example, it is performed at the following timing. That is, the color registration correction is performed when the image forming unit 3 forms a predetermined number of images (for example, several hundreds). The color registration correction is performed when the installation environment (for example, temperature, humidity, etc.) of the image forming apparatus 1 changes beyond a specified range. Color registration correction is performed when the image forming apparatus 1 is turned on. The color registration correction is performed when the image forming apparatus 1 is regularly checked. Further, the color registration correction is performed when a component part (for example, a consumable part or a defective part) of the image forming apparatus 1 is replaced.

  In the color registration correction, a pattern image is formed with each color toner on each photoconductive drum 9-12 based on a preset pattern signal, and the pattern image is transferred from each photoconductive drum 9-12. The images are sequentially transferred to the intermediate transfer belt 17. The pattern image transferred to the intermediate transfer belt 17 in this manner is optically read by the registration sensor 35, and the reading result (registration deviation detection pattern reading signal) is taken into the image formation control unit 46.

  Then, the registration error correction unit 52 obtains the positional deviation amount of the pattern image based on the detection result of the registration sensor 35. The amount of misregistration is that the color of the image formed using the photosensitive drum 9 in the foremost stage is a reference color, and the pattern image of another color is compared with the pattern image of the reference color in the main scanning direction and the sub-scanning direction. In the scanning direction, it indicates how much each is deviated from the normal position. After obtaining this positional deviation amount, the registration deviation correction unit 52 obtains a positional deviation correction amount for setting the corresponding positional deviation amount to zero for images of colors other than the reference color. Then, the image forming positions on the photosensitive drums 10, 11, and 12 are corrected according to the obtained positional deviation correction amount. Specifically, the main scanning direction is corrected by changing the time from when the main scanning synchronization signal is output until the latent image forming apparatus 2 starts writing the electrostatic latent image on the photosensitive drum. . Further, the sub-scanning direction is corrected by changing the time from when the sub-scanning synchronization signal is output until the latent image forming apparatus 2 starts writing the electrostatic latent image on the photosensitive drum.

  Next, a reference value correction method by the pseudo signal correction unit 53 will be described. First, as shown in FIG. 5, when the color registration correction is performed in the pseudo signal correction unit 53 (step ST <b> 1), among the image positional deviation correction amounts obtained by the registration deviation correction unit 52, in particular, It is determined whether or not the positional deviation correction amount of the image in the sub-scanning direction has been changed (step ST2). If the positional deviation correction amount is changed, it is determined whether or not the changed amount is equal to or greater than a preset threshold value (step ST3). If the change amount of the positional deviation correction amount is equal to or greater than the threshold value, the reference value is corrected (step ST4). Further, when the positional deviation correction amount is not changed or when the change amount is less than the threshold value, the process ends without correcting the reference value.

  When the registration error correction unit 52 corrects the toner image formation position in the sub-scanning direction, the latent image forming apparatus 2 writes the electrostatic latent image on the photosensitive drum after the sub-scanning synchronization signal is output as described above. Is changed (hereinafter referred to as “sub-scan writing start time”). For example, the sub-scan writing start time (fixed value) applied when forming the toner image of the reference color on the photosensitive drum 9 is set as the “reference writing start time”, and the registration error correction is performed for any color other than the reference color. Assuming that the correction time (variable control value) corresponding to the positional deviation correction amount of the image in the sub-scanning direction obtained by the unit 52 is “registration deviation correction time”, the registration deviation correction unit 52 performs sub-scan writing of the arbitrary color The start time is changed (corrected) to “reference writing start time + registration deviation correction time”. In this case, if the registration error correction time is a positive value, the sub-scan writing start time of any color is corrected in a direction that is longer than the reference writing start time. If the registration deviation correction time is a negative value, the sub-scan writing start time for any color is corrected in a direction that is shorter than the reference writing start time.

  The registration error correction time corresponding to the image positional error correction amount is obtained by the registration error correction unit 52 every time color registration correction is performed. For example, if the registration error correction time obtained in the current color registration correction is different from the registration error correction time applied to the image forming operation immediately before the current color registration correction is performed, The registration error correction time is updated so that the registration error correction time obtained by the color registration correction is applied to the image forming operation after the current color registration correction.

  In contrast, the pseudo signal correction unit 53 changes the registration error correction amount (registration error correction time) for the registration error correction unit 52 to correct the toner image formation position in the sub-scanning direction as described above. In addition, the reference value that defines the generation time of the pseudo signal is corrected based on the post-change positional deviation correction amount. Further, when actually changing the reference value, the pseudo signal correction unit 53 determines the correction amount of the reference value based on the difference before and after the change of the positional deviation correction amount. For example, if the misregistration correction amount applied to the image forming operation before the change and the misregistration correction amount applied to the image forming operation after the change are expressed by positive and negative values, respectively, the pseudo signal correction The part 53 calculates | requires the difference of both by adding them. Then, the obtained difference in the amount of misalignment correction is reflected in the correction of the reference value. Specifically, the processing may be performed as follows.

  First, when a reference color toner image is formed, the image formation control unit 46 outputs an electrostatic latent image writing start signal (in the sub-scanning direction) when the reference writing start time has elapsed since the output of the sub-scanning synchronization signal. Hereinafter, “sub-scan writing start signal”) is output. Then, after outputting the write start signal, the counter 54 counts up and outputs the pseudo signal. At this time, if the reference value input to the counter 54 is increased, the generation time of the pseudo signal is corrected in the direction of being delayed, and if the reference value is decreased, the generation time of the pseudo signal is corrected in the direction of being advanced. For this reason, the pseudo signal correction unit 53 determines that the pseudo signal correction unit 53 has a pseudo signal when the registration deviation correction amount is changed in a direction in which the sub-scan writing start time becomes longer (in other words, a direction in which the output timing of the sub-scan writing start signal is delayed). The reference value is corrected in the direction in which the occurrence time of becomes earlier. In addition, the pseudo signal correction unit 53 changes the pseudo signal when the registration deviation correction amount is changed in a direction in which the sub-scan writing start time is shortened (in other words, the output timing of the sub-scan writing start signal is earlier). The reference value is corrected in the direction in which the generation time is delayed.

  The above contents are schematically shown in FIG. In the upper diagram, the vertical axis represents the position in the sub-scanning direction, and the horizontal axis represents time. In the drawing, P10k represents an ideal exposure start position, P11 represents a detection position of the registration sensor 35, and P12 represents a position in the vicinity of the transfer position.

  First, in the first state, the sub-scanning write start signal S2 is output at the time when the time T1 (reference write start time in the case of the reference color) elapses after the sub-scan synchronization signal S1 is output. In this case, in the sub-scanning direction, the actual exposure start position (electrostatic latent image writing start position) P10a is shifted by Δd1 from the ideal exposure start position P10k. Accordingly, the registration sensor 35 outputs the toner image detection signal S3 at a timing earlier by Δt1 than the target timing. On the other hand, the pseudo signal S4 is generated when the time T2 elapses after the sub-scan writing start signal S2 is output. “Ideal” described here assumes a situation in which the components of the image forming apparatus 1 are attached as designed without error.

  In the second state, the time T1 + Δt1 (in the example shown, Δt1 takes a positive value) has elapsed since the sub-scanning synchronization signal S1 was output in order to correct the above-described image misalignment in the sub-scanning direction. At this point, the sub-scan writing start signal S2 is output. Δt1 is a correction time for correcting the image position shift (Δd1) in the sub-scanning direction. Therefore, the registration sensor 35 outputs a toner image detection signal S3 at a target timing. On the other hand, the pseudo signal S4 is generated when the time T2 elapses after the sub-scan writing start signal S2 is output as described above. For this reason, the generation timing of the pseudo signal S4 is shifted between the first state and the second state.

  In the third state, as in the second state, the sub-scan writing start signal S2 is output when T1 + Δt1 time elapses after the sub-scan synchronization signal S1 is output. Therefore, the registration sensor 35 outputs a toner image detection signal S3 at a target timing. On the other hand, the pseudo signal S4 is generated when time T2 + Δt2 (in the example, Δt2 takes a negative value) has elapsed since the sub-scanning writing start signal S2 was output. In this case, Δt1 corresponds to an image displacement correction amount, and Δt2 corresponds to a reference value correction amount. In addition, Δt1 and Δt2 have different positive and negative values, but the absolute values of both may be the same value.

  In the fourth state, the sub-scan writing start signal S2 is output at the time when T1 + Δt3 (in the example, Δt3 takes a negative value) has elapsed since the sub-scan synchronization signal S1 was output. In this case, in the sub-scanning direction, the actual exposure start position (electrostatic latent image writing start position) P10b is shifted by Δd2 from the ideal exposure start position P10k. Δt3 is a correction time for correcting the image position shift (Δd2) in the sub-scanning direction. Therefore, the registration sensor 35 outputs a toner image detection signal S3 at a target timing. On the other hand, the pseudo signal S4 is generated when time T2 + Δt4 (in the example, Δt4 takes a positive value) has elapsed since the sub-scanning writing start signal S2 was output. In this case, Δt3 corresponds to an image displacement correction amount, and Δt4 corresponds to a reference value correction amount. In addition, Δt3 and Δt4 have different values of positive and negative, but the absolute values of both may be the same value.

  Among the first to fourth states, the third state and the fourth state are obtained by the image forming apparatus 1 according to the embodiment of the present invention. When the image displacement correction amount is changed from Δt1 (third state) to Δt3 (fourth state), for example, based on the difference before and after the change (Δt1−Δt3), The reference value correction amount Δt4 is determined with the same value.

1 is a schematic diagram illustrating a configuration example of an electrophotographic image forming apparatus to which the present invention is applied. It is the schematic which shows the structural example of a latent-image formation apparatus. 3 is a block diagram illustrating a configuration example of a control system of the image forming apparatus according to the embodiment of the present invention. FIG. It is explanatory drawing which shows the outline | summary of a counter. It is a flowchart which shows an example of the process sequence which concerns on embodiment of this invention. It is a schematic diagram which concerns on correction | amendment of a reference value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Image forming part, 4 ... Paper conveying apparatus, 9-12 ... Photoconductor drum, 17 ... Intermediate transfer belt, 18 ... Transfer part, 36 ... Latent image forming apparatus, 35 ... Registration sensor, 46 ... Image forming control unit 50... Paper conveyance control unit 51. Calculation unit 52. Registration misregistration correction unit 53 53 Pseudo signal correction unit

Claims (4)

A plurality of photoreceptors on which images of different colors are formed;
An intermediate transfer member to which images of respective colors formed on the plurality of photosensitive members are transferred;
Transfer means for transferring the image transferred to the intermediate transfer member to a sheet at a transfer position;
A paper transporting means for transporting the paper toward the transfer position of the transfer means;
The time from the start of writing of the electrostatic latent image on the photoconductor in the sub-scanning direction until the image transferred to the intermediate transfer body reaches the transfer position or the vicinity thereof is used as a reference value, and the static image on the photoconductor is determined. A calculation means for outputting a pseudo signal after counting of the reference value from the start of writing of the electrostatic latent image in the sub scanning direction ;
Paper transport control means for controlling paper transport of the paper transport means based on the pseudo signal output by the computing means;
Detecting means for detecting a positional shift of each color image transferred to the intermediate transfer member;
An image position correction unit that obtains an image misregistration correction amount based on the detection result of the detection unit, and that corrects the writing start timing according to the obtained misregistration correction amount;
When the write start timing after the correction is later than before the correction, the reference value is corrected to be smaller, and when the write start timing after the correction is earlier than the correction, the reference value is corrected. An image forming apparatus comprising: a pseudo signal correcting unit that corrects the reference value so as to increase . The said pseudo signal correction means correct | amends the said reference value, when the said positional offset correction amount applied to correction | amendment of the image formation position on the said photoreceptor is changed. Image forming apparatus. The image forming apparatus according to claim 2, wherein the pseudo signal correcting unit corrects the reference value when a change amount of the misalignment correction amount is equal to or greater than a preset threshold value. The image forming apparatus according to claim 3, wherein the pseudo signal correcting unit determines the correction amount of the reference value based on a difference between before and after the change of the positional deviation correction amount.

Images