JP2006208440A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that is simple in configuration and low in cost. <P>SOLUTION: A single pattern sensor 18 can detect a belt rotation detection mark TM displayed on an image non-formation part of an intermediate transfer belt 16 and registration marks RM(K), RM(C), RM(M), and RM(Y) displayed on an image formation part of the intermediate transfer belt 16. In this apparatus, after the belt rotation detection mark TM is detected by the pattern sensor 18, the registration marks RM(K), RM(C), RM(M), and RM(Y) are formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that temporarily transfers a toner image formed by an image forming unit to an intermediate transfer belt that circulates and moves in a predetermined direction.

  2. Description of the Related Art Image forming apparatuses such as printers, copiers, and facsimile machines are provided with an image forming station in which a charging unit, an image writing unit, and a developing unit are arranged around a latent image carrier such as a photosensitive drum. In addition, there is a device that primarily transfers a toner image formed at the image forming station onto an intermediate transfer belt and temporarily carries it, and then secondary-transfers the toner image onto a recording medium such as copy paper or transfer paper. In such an image forming apparatus, in order to correct an image shift in the sub-scanning direction due to a temperature change of the circumference of the intermediate transfer belt, a registration mark is formed on the intermediate transfer belt. A so-called registration control is performed in which the formed registration mark is detected, position information of the registration mark is obtained, and image forming means is controlled based on the position information.

  Further, in the image forming apparatus as described above, it is desirable to efficiently perform registration control and shorten the time from the printing operation to the first print output, that is, the first print time. For example, in the image forming apparatus described in Patent Document 1, a temperature fluctuation of a specific part in the apparatus is detected, and registration control is performed when the temperature fluctuation exceeds a predetermined width. In order to efficiently perform image formation, for example, a belt rotation period detection unit as described in Patent Document 2, that is, a belt rotation period detection mark is provided on the intermediate transfer belt and the belt rotation period is provided. A means for detecting the detection mark by the detection means and obtaining the belt rotation period from the detection result may be employed. In other words, efficient image formation is achieved by obtaining the belt rotation cycle based on the detection result of the belt rotation cycle detection mark and performing registration control only when the fluctuation range of the belt rotation cycle exceeds a predetermined width. And the first print time can be shortened.

JP-A-2-304465 (2nd page) JP-A-12-199988 (paragraph 0022)

  However, when the registration control execution timing is controlled based on the rotation cycle fluctuation of the intermediate transfer belt as described above, a plurality of detections of a detection unit that detects a registration mark and a detection unit that detects a belt rotation cycle detection mark. Means are needed. Accordingly, the configuration of the image forming apparatus is complicated, and there is a problem that the cost increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus having a simple configuration and a low cost by integrating a belt rotation period detection unit and a registration mark detection unit. .

In order to achieve the above object, the image forming apparatus according to the present invention has an image forming area where a toner image is formed and an image non-forming area where a belt rotation period detection mark is provided adjacent to each other in the main scanning direction. An intermediate transfer belt that rotates in a sub-scanning direction substantially orthogonal to the main scanning direction, an image forming unit that forms a toner image as a registration mark in the image forming region, and a boundary between the image forming region and the non-image forming region. A detection unit that is arranged so as to straddle and detects a belt rotation period detection mark and a registration mark and outputs a detection signal, and controls the formation of a toner image by the image formation unit based on the detection signal output from the detection unit And a control means.

  In the invention configured as described above, the belt rotation period detection mark and the registration mark are detected by one detection means, so that the configuration of the image forming apparatus can be simplified and the cost can be reduced.

  In addition, the registration mark is formed at a position shifted from the belt rotation period detection mark in the sub-scanning direction, thereby preventing the detection means from detecting the registration mark and the rotation period detection mark at the same time. Of the results, the signal corresponding to the registration mark and the signal corresponding to the belt rotation period detection mark can be separated and discriminated. Based on the signal corresponding to the registration mark thus separated and discriminated, Control can be performed satisfactorily.

  In addition, the timing at which the image forming unit forms the toner image as a registration mark in the image forming region is controlled based on the detection result of the signal corresponding to the belt rotation period detection mark by the detection unit, thereby efficiently. Resist control is possible, and the first print time can be shortened. In other words, the first print time is determined by determining whether or not registration control is necessary based on the detection result of the signal corresponding to the belt rotation period detection mark, performing registration control only when necessary, and not performing unnecessary registration control. Can be shortened. Further, since the number of registration marks to be created is reduced, toner consumption can be suppressed.

  In addition, a plurality of image forming stations, each forming a different color toner image, are arranged along the moving direction of the intermediate transfer belt, and the toner images formed by the plurality of image forming stations are used as registration marks to the intermediate transfer belt. In an image forming apparatus that is formed on the surface so as to be separated in the moving direction and performs color misregistration correction processing based on the detection result of the signal corresponding to the registration mark by the detecting means, the timing for performing the color misregistration correction processing is set. By determining based on the detection result of the signal corresponding to the rotation period detection mark, efficient color misregistration correction can be performed, and the first print time and the toner consumption can be reduced as in the case of the above-described invention. it can. That is, by determining whether color misregistration correction is necessary based on the detection result of the signal corresponding to the belt rotation period detection mark, performing color misregistration correction only when necessary, and not performing unnecessary color misregistration correction, Similar to the invention, the first print time can be shortened and the toner consumption can be reduced.

  The detection means controls the image forming means so as to form a registration mark with a predetermined time difference from when the belt rotation period detection mark is detected, and a detection signal from the first detection means immediately after the registration mark is formed. The control means may be configured to eliminate the above. In such a configuration, since the registration mark is formed with a predetermined time lag from when the detection means detects the belt rotation period detection mark, the registration mark is displaced from the belt rotation period detection mark in the sub-scanning direction. Formed. Therefore, the detecting means does not detect the belt rotation period detection mark and the registration mark at the same time. Further, in the above-described configuration, the control means is configured to exclude the first detection signal immediately after the registration mark is formed. As a result, it is possible to distinguish between the signal corresponding to the registration mark and the signal corresponding to the belt rotation period detection mark from the detection results of the detection means. That is, the first signal detected by the detecting means after the registration mark is formed is a signal corresponding to the belt rotation period detection mark, and the signal corresponding to the registration mark and the belt rotation period detection are detected by eliminating this signal. It becomes possible to distinguish the signal corresponding to the mark. As a result, registration control can be performed satisfactorily based on the signal corresponding to the registration mark that has been divided and discriminated in this way.

  Various materials can be used as the material of the intermediate transfer belt. For example, an elastomer alloy may be used as the material of the intermediate transfer belt. As described above, the intermediate transfer belt based on the thermoplastic elastomer alloy is superior in bending resistance to the intermediate transfer belt based on PC (polycarbonate) resin or PET (polyethylene terephthalate) resin, and the resist mark Since there is little possibility that a detection failure will occur, good resist control is possible. In addition, an intermediate transfer belt based on a thermoplastic elastomer alloy is more sensitive to temperature fluctuations than an intermediate transfer belt based on a PC resin or PET resin. Accordingly, the peripheral length of the intermediate transfer belt made of a thermoplastic elastomer alloy as a base material varies sensitively with respect to temperature fluctuations inside the image forming apparatus, and the belt rotation period also fluctuates accordingly. Therefore, in the image forming apparatus according to any one of claims 1 to 5, by using an intermediate transfer belt that is made of a thermoplastic elastomer alloy as a base material, it is possible to achieve higher accuracy with respect to temperature fluctuations inside the image forming apparatus. Resist control can be performed.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. The apparatus 1 includes a color printing process for forming a full color image by superposing four color toners (developers) of black (K), cyan (C), magenta (M), and yellow (Y), and black (K ) To selectively execute monochromatic printing processing for forming a monochrome image using only toner. In this image forming apparatus 1, when an image forming command (printing command) is given to the main controller 51 from an external device such as a host computer, the engine controller 52 controls each part of the engine unit EG in accordance with the command from the main controller 51. Then, a predetermined image forming operation is executed, and an image corresponding to the image forming command is formed on a sheet (recording material) S such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  In FIG. 1, an image forming apparatus 1 according to the present embodiment includes a housing body 2, a first opening / closing member 3 that is detachably mounted on the front surface of the housing body 2 (right-hand side surface in FIG. 1), And a second opening / closing member 4 (also serving as a paper discharge tray) mounted on the upper surface so as to be freely opened and closed. The first opening / closing member 3 is provided with an opening / closing lid 3 a that can be opened and closed on the front surface of the housing body 2. The opening / closing lid 3a can be opened / closed in conjunction with or independently of the first opening / closing member 3.

  In the housing main body 2, an electrical component box 5 containing a power circuit board, a main controller 51, and an engine controller 52 is provided. An image forming unit 6, a blower fan 7, a transfer belt unit 9 and a paper feed unit 10 are also disposed in the housing body 2. On the other hand, on the first opening / closing member 3 side, a secondary transfer unit 11, a fixing unit 12 and a sheet conveying mechanism 13 are disposed. In this embodiment, the consumables in the image forming unit 6 and the paper feeding unit 10 are configured to be detachable from the apparatus main body. The consumables and the transfer belt unit 9 can be removed and repaired or exchanged.

  The transfer belt unit 9 is disposed below the housing body 2 and is driven to rotate by a black drive motor described later, and a driven roller 15 disposed obliquely above the drive roller 14. An intermediate transfer belt 16 that is stretched between the rollers 14 and 15 and driven to circulate in the direction of the arrow D16 in the figure, and a belt cleaner 17 that abuts against the surface of the intermediate transfer belt 16. The driven roller 15 is disposed obliquely above the drive roller 14 (upward on the left hand in FIG. 1). For this reason, the intermediate transfer belt 16 rotates and moves in the direction D16 while being inclined. Further, the belt surface 16a in which the belt conveyance direction D16 when the intermediate transfer belt 16 is driven is downward (right downward in FIG. 1) is positioned below. In the present embodiment, the belt surface 16a is a belt tension surface (surface pulled by the drive roller 14) when the belt is driven, and the peripheral speed is lower than the peripheral speed of the photosensitive drum (image carrier) 20 of each color. have. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Driving.

  In this embodiment, the intermediate transfer belt 16 is made of a thermoplastic elastomer alloy mainly composed of a thermoplastic elastomer (hereinafter referred to as “TPE”) as a belt base material. The main reason is bending resistance. That is, the intermediate transfer belt 16 based on TPE alloy is superior in bending resistance compared with the intermediate transfer belts based on PC resin and PET resin, which have been widely used so far. Resist control is possible. In particular, in order to reduce the number of rollers provided to stretch the intermediate transfer belt 16 or to reduce the size of the rollers, it is necessary to increase the degree of curvature of the intermediate transfer belt 16 with the rollers. In that case, bending resistance becomes a big problem. Accordingly, the present inventors have examined the physical characteristics of the intermediate transfer belt 16 such as PC resin and PET resin as well as PI (polyimide) resin, PA (polyamide) resin, and TPE alloy. It was found that the intermediate transfer belt 16 having excellent bending resistance can be obtained by using it as a belt base material. Therefore, in this embodiment, the intermediate transfer belt 16 that employs TPE alloy is used as the belt base material.

The drive roller 14 also serves as a backup roller for the secondary transfer roller 19. A rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 14, and the illustration is omitted by grounding through a metal shaft 2. A conductive path of the secondary transfer bias supplied from the secondary transfer bias generator through the secondary transfer roller 19 is used. Thus, by providing the driving roller 14 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet S enters the secondary transfer portion to be transmitted to the intermediate transfer belt 16, and deterioration of image quality is prevented. can do.

  In the present embodiment, the diameter of the driving roller 14 is smaller than the diameter of the driven roller 15. Thereby, the sheet S after the secondary transfer can be easily peeled by the elastic force of the sheet S itself. The driven roller 15 is also used as a backup roller for the belt cleaner 17. The belt cleaner 17 is provided on the side of the belt surface 16a facing downward in the transport direction, and includes a cleaning blade 17a that removes residual toner and a toner transport member that transports the removed toner, as shown in FIG. Yes. The cleaning blade 17a contacts the intermediate transfer belt 16 at a portion where the intermediate transfer belt 16 is wound around the driven roller 15, and cleans and removes toner remaining on the surface of the intermediate transfer belt 16 after the secondary transfer.

  The driving roller 14 and the driven roller 15 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, a primary transfer roller 21 is provided on the back surface of the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 so as to face the photosensitive drum 20 of each image forming station Y, M, C, K described later. . These four primary transfer rollers 21 are rotatably supported with respect to the support frame, and are electrically connected to the primary transfer bias generator 525. From the primary transfer bias generator 525 at an appropriate timing. A primary transfer bias is applied.

  The support frame is rotatable with respect to the housing main body 2 in the arrow direction D21 with the drive roller 14 as a rotation center. Then, by actuating an actuator (not shown), the support frame is rotated to face the photosensitive drums 20 of the yellow (Y), magenta (M), and cyan (C) image forming stations Y, M, and C. The primary transfer roller 21 arranged in this manner approaches the photosensitive drum 20 and moves away from the photosensitive drum 20. For this reason, when the primary transfer rollers 21 for yellow, magenta, and cyan are moved closer to the photosensitive drum 20, they are brought into contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween (solid line in FIG. 1). This contact position is the primary transfer position, and the toner image is transferred to the intermediate transfer belt 16 at the primary transfer position. Conversely, when the primary transfer rollers 21 for yellow, magenta, and cyan move away from the photosensitive drum 20, the photosensitive drum 20 and the intermediate transfer belt 16 of the image forming stations Y, M, and C are separated from each other (FIG. Dashed line in 1). On the other hand, the primary transfer roller 21 disposed facing the photosensitive drum 20 of the black (K) image forming station K rotates while being in contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween. Is configured to do. Therefore, as shown by the solid line in FIG. 1, the color printing process can be executed by positioning all the primary transfer rollers 21 on the photosensitive drum 20 side. On the other hand, as shown by a broken line in FIG. 5, the intermediate transfer belt is executed while only the monochrome printing process is performed by leaving the primary transfer roller 21 for black and separating the other primary transfer roller 21 from the photosensitive drum 20. 16 is separated from the image forming stations Y, M, and C, and yellow, magenta, and cyan colors can be set to a non-printing state. Note that the primary transfer roller 21 for black may also be configured to move away from the photosensitive drum 20 as necessary.

  FIG. 3 is a diagram showing a sensor disposed in the vicinity of the drive roller. In this embodiment, a pattern sensor 18 is installed on the support frame of the transfer belt unit 9 in the vicinity of the drive roller 14. The pattern sensor 18 corresponds to the “detecting means” of the present invention, and is disposed across the boundary between the image forming area and the non-image forming area of the intermediate transfer belt 16. The pattern sensor 18 is a so-called reflection type optical sensor, and is a surface region 181 that exists across the boundary between the image forming region (maximum region where an image is formed) of the intermediate transfer belt 16 and the image non-forming region. A light projecting portion (not shown) that emits light toward the surface, a registration mark RM formed on the surface of the intermediate transfer belt 16 and the image forming area, and a belt rotation period detecting mark TM provided on the non-image forming area. A light receiving unit (not shown) for receiving the reflected light is provided. Light is emitted from the light projecting unit to the registration mark RM and the belt rotation period detection mark TM on the intermediate transfer belt 16, while the light from the registration mark RM and the belt rotation period detection mark TM is received by the light receiving unit. A signal corresponding to the amount of light received by the light receiving unit is output from the pattern sensor 18 as shown in FIG. Then, each color toner image on the intermediate transfer belt 16 is positioned based on an output signal from the pattern sensor 18 to correct a color shift of each color image.

  In this embodiment, as described above, the belt rotation period detection mark TM can be detected by the sensor 18. Therefore, when no registration mark is formed in the image forming area, every time the belt rotation period detection mark TM of the intermediate transfer belt 16 passes the pattern sensor 18, a signal (belt) corresponding to the belt rotation detection mark TM is detected. Only the rotation period detection signal) is output. In this embodiment, since one belt rotation period detection mark TM is provided in the non-image forming area, the belt rotation period detection signal is detected once every time the intermediate transfer belt 16 makes one rotation. It becomes. Therefore, as shown in FIG. 5, the rotation period T (T1, T2,...) Of the intermediate transfer belt 16 can be obtained by measuring the interval of the belt rotation period detection signal.

  FIG. 6 is a graph showing the rotation cycle of the intermediate transfer belt according to temperature. This figure shows how the rotation period T of the intermediate transfer belt 16 using PC resin, PET resin, and TPE alloy as a belt base material varies with temperature changes. As can be seen from the figure, when a belt using TPE alloy as a belt substrate is used as the intermediate transfer belt 16, the rotation period T becomes longer as the temperature rises. This is because the thermal expansion coefficient of TPE is relatively large compared to the thermal expansion coefficient of PC resin and PET resin conventionally used as a belt base material, and expands and contracts relatively depending on the temperature inside the image forming apparatus. Due to As described above, in particular, when TPE alloy is used as the belt base material, the rotation cycle of the intermediate transfer belt 16 greatly varies with the temperature variation in the image forming apparatus. By detecting and performing resist control based on this detection, it is possible to perform resist control with higher accuracy against temperature fluctuations.

  Returning to FIG. 1, the description of the apparatus configuration will be continued. The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. Each of the image forming stations Y, M, C, and K corresponds to an “image forming unit” of the present invention, and a photosensitive drum 20 is provided in each of these image forming stations. A charging unit 22, an image writing unit 23, a developing unit 24, and a photoconductor cleaner 25 are disposed around each photoconductor drum 20. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. In FIG. 1, since the image forming stations of the image forming unit 6 have the same configuration, for convenience of illustration, only some of the image forming stations are denoted by reference numerals, and the other image forming stations are omitted. . Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

  The photosensitive drums 20 of the image forming stations Y, M, C, and K are disposed so as to be in contact with the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 at the primary transfer position TR1. Each of these photosensitive drums 20 is connected to a dedicated drive motor and is driven to rotate at a predetermined peripheral speed in the conveyance direction of the intermediate transfer belt 16 as indicated by an arrow D20 in the figure.

  The charging unit 22 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to be driven to rotate in contact with the surface of the photosensitive drum 20 at a charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 20 as the photosensitive drum 20 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown), and receives the charging bias from the charging bias generator to charge the surface of the photosensitive drum 20 at the charging position.

  The image writing unit 23 is an array writing in which elements such as a liquid crystal shutter including a light emitting diode and a backlight are arranged in a line in the axial direction of the photosensitive drum 20 (direction perpendicular to the paper surface of FIG. 1). The head is used and is spaced from the photosensitive drum 20. The array-like writing head has a shorter optical path length and is more compact than the laser scanning optical system. Therefore, it can be disposed close to the photosensitive drum 20 and has the advantage that the entire apparatus can be downsized.

  In this embodiment, the photoconductive drum 20, the charging unit 22, the developing unit 24, and the photoconductive cleaner 25 of each of the image forming stations Y, M, C, and K are replaced with replacement cartridges 6Y, 6M, 6C, and 6K (FIG. 2). ) As a unit. Each replacement cartridge 6Y, 6M, 6C, 6K is provided with non-volatile memories 91-94 for storing information relating to the replacement cartridge. The transmission / reception units 53Y, 53M, 53C, and 53K provided in each replacement cartridge and the transmission / reception units 522Y, 522M, 522C, and 522K provided on the main body side are arranged close to each other, and the CPU 521 and the memory of the engine controller 52 are arranged. Wireless communication is performed with 91-94. In this way, information regarding each replacement cartridge is transmitted to the CPU 521, and information in each of the memories 91 to 94 is updated and stored.

  Next, details of the developing unit 24 will be described on behalf of the image forming station K. The developing unit 24 includes a toner storage container 26 for storing toner, two toner agitation supply members 28 and 29 disposed in the toner storage container 26, and a partition member disposed in proximity to the toner agitation supply member 29. 30, a toner supply roller 31 disposed above the partition member 30, a developing roller 33 that contacts the toner supply roller 31 and the photosensitive drum 20 and rotates in a direction indicated by an arrow at a predetermined peripheral speed, and a developing roller And a regulating blade 34 abutting on the bearing 33.

  In each developing unit 24, the toner stirred and carried by the toner stirring supply member 29 is supplied to the toner supply roller 31 along the upper surface of the partition member 30. The toner thus supplied is supplied to the surface of the developing roller 33 via the supply roller 31. The toner supplied to the developing roller 33 is regulated to a predetermined layer thickness by the regulating blade 34 and is conveyed to the photosensitive drum 20. The charged toner is developed at a developing position where the developing roller 33 and the photosensitive drum 20 come into contact with each other by a developing bias applied to the developing roller 33 from a developing bias generator (not shown) electrically connected to the developing roller 33. Moves from the developing roller 33 to the photosensitive drum 20, and the electrostatic latent image formed by the image writing unit 23 is visualized.

  In this embodiment, a photoreceptor cleaner 25 is provided in contact with the surface of the photoreceptor drum 20 on the downstream side of the primary transfer position TR1 in the rotation direction D20 of the photoreceptor drum 20. The photoconductor cleaner 25 is in contact with the surface of the photoconductor drum 20 to remove the toner remaining on the surface of the photoconductor drum 20 after the primary transfer.

  The sheet feeding unit 10 includes a sheet feeding unit including a sheet feeding cassette 35 in which sheets S are stacked and held, and a pickup roller 36 that feeds the sheets S from the sheet feeding cassette 35 one by one. In the first opening / closing member 3, a registration roller pair 37 that defines the timing of feeding the sheet S to the secondary transfer region TR 2, and a secondary transfer unit that is pressed against the drive roller 14 and the intermediate transfer belt 16. A secondary transfer roller 19, a fixing unit 12, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  The secondary transfer roller 19 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, and a pressure roller 46 that presses and biases the heating roller 45. The image secondarily transferred to the sheet S is fixed to the sheet S at a predetermined temperature at a nip formed by the heating roller 45 and the pressure roller 46. In the present embodiment, the fixing unit 12 can be disposed in a space formed obliquely above the intermediate transfer belt 16, in other words, in a space opposite to the image forming unit 6 with respect to the intermediate transfer belt 16. Thus, heat transfer to the electrical component box 5, the image forming unit 6, and the intermediate transfer belt 16 can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced.

  Further, the sheet S thus subjected to the fixing process is conveyed to a second opening / closing member (discharge tray) 4 provided on the upper surface portion of the housing body 2 via the discharge roller pair 39. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position behind the pair of discharge rollers 39. The rotation direction of the discharge roller pair 39 is reversed, whereby the sheet S is conveyed along the duplex printing conveyance path 40. Then, it is put on the conveyance path again before the registration roller pair 37. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 16 in the secondary transfer region TR2 is transferred first. It is the opposite side of the surface that was made. In this way, images can be formed on both sides of the sheet S.

  In addition, as shown in FIG. 2, the apparatus 1 includes a display unit 54 that is controlled by the CPU 511 of the main controller 51. The display unit 54 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 511, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, and the like. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 513 denotes an image memory provided in the main controller 51 for storing an image given from an external device such as a host computer via the interface 512. Reference numeral 523 denotes a ROM for storing a calculation program executed by the CPU 521, control data for controlling the engine unit EG, and the like. Reference numeral 524 denotes a RAM for temporarily storing calculation results in the CPU 521 and other data. is there.

  FIG. 7 is a view showing the operation of the image forming apparatus of FIG. In this apparatus, as shown in the figure, the rotation cycle of the intermediate transfer belt 16 is detected by the pattern sensor 18, and the execution timing of the color misregistration correction process is controlled based on the detection result. More specifically, the CPU 521 of the engine controller 52 controls each part of the apparatus as follows according to a program relating to color misregistration correction stored in the ROM 523 to adjust the execution timing of the color misregistration correction processing.

  When the belt rotation cycle detection signal is output twice from the pattern sensor 18 in step S1, an internal timer (not shown) counts the time from the output of the first belt rotation cycle detection signal to the output of the next signal. The time for which the transfer belt 16 makes one turn, that is, the rotation period T is calculated (step S2). The rotation period T is stored in the RAM 524 as the reference period Tr (step S3).

  Each time the belt rotation cycle detection signal is output (step S4), the internal timer counts the elapsed time from the previous rotation cycle detection signal and the rotation cycle T is calculated (step S5). Further, the absolute value | T−Tr | of the difference between the rotation period T and the reference period Tr is compared with a preset allowable value Ta (step S6). That is, the absolute value | T−Tr | indicates the amount of change in the belt rotation period. There are various factors that cause the belt rotation period to vary. For example, when the temperature inside the image forming apparatus fluctuates more than a certain level, TPE alloy is used as the material of the intermediate transfer belt 16 in the present embodiment. The circumferential length of the transfer belt 16 changes, and the belt rotation cycle changes. Therefore, when the temperature fluctuation inside the image forming apparatus is small and the fluctuation amount of the belt rotation cycle is small, “NO” is determined in Step 6 and the process returns to Step S4 to detect the next belt rotation cycle detection signal and the belt rotation cycle. Repeat the calculation of T. On the other hand, if the temperature fluctuation inside the image forming apparatus is large and the fluctuation amount of the belt rotation period fluctuates beyond the allowable value Ta, “YES” is determined in the step 6, and the color misregistration correction process is executed (step S7). ).

  In this color misregistration correction process, the image forming stations Y, M, C, and K use, for example, an image area of the intermediate transfer belt 16 in the main scanning direction X orthogonal to the conveyance direction D16 of the intermediate transfer belt 16 as shown in FIG. The strip-shaped registration marks RM extending in parallel (for example, 0.5 mm in width) are spaced apart from each other by a predetermined interval (for example, 0.5 mm) in the transport direction (sub-scanning direction) D16 in the order of K, C, M, and Y. It is formed. In the figure, a yellow registration mark RM (Y), a black registration mark RM (K), a cyan registration mark RM (C), a magenta registration mark RM (M), and a yellow registration mark RM (Y ) Only is shown, but a plurality of lines are formed for each color. The registration marks RM (K), RM (C), RM (M), and RM (Y) formed on the intermediate transfer belt 16 as described above move in the transport direction D16 along with the movement of the intermediate transfer belt 16. Passes the detection area 181 of the sensor 18. At this time, the voltage level of the signal output from the pattern sensor 18 changes according to the amount of received light. Therefore, by measuring the voltage level, the timing at which each registration mark RM passes through the pattern sensor 18 can be measured, and the position information of the registration mark RM can be acquired. When position information is obtained for all registration marks RM, color misregistration correction is performed based on the position information. Hereinafter, specific color misregistration correction processing in the present embodiment will be described.

  FIG. 8 shows the operation of the color misregistration correction process. Prior to the formation of the registration mark RM, first, the pattern sensor 18 detects the rotation period detection mark TM (step S71). Next, as shown in the middle of FIG. 9, each image forming station Y, M, C, and so on forms the registration mark RM at a timing shifted by a predetermined time ΔT after detecting the belt rotation period detection mark TM. K (image forming means) is controlled (step S72). As a result, as shown in the lower part of FIG. 9, registration marks RM are formed on the intermediate transfer belt 16 from positions shifted from the belt rotation period detection mark TM by a distance ΔR in the sub-scanning direction. Here, the distance ΔR is the distance that the intermediate transfer belt 16 has moved during the time ΔT. Next, the detection signal of the pattern sensor 18 immediately after forming the registration mark RM in step S72 is excluded as a belt rotation period detection signal (step S73). Thereby, only the signal corresponding to the registration mark RM among the detection signals of the pattern sensor 18 can be separated and discriminated. That is, after the registration mark RM is formed, the signal first detected by the pattern sensor 18 is a belt rotation period detection signal. Therefore, this signal is excluded, and is detected by the pattern sensor 18 after the belt rotation period detection signal. The signal is detected as a signal corresponding to the registration mark RM. Thus, the signal (resist pattern) corresponding to the registration mark RM is detected by the pattern sensor 18 (step S74), and color misregistration correction is performed based on the detection result (step S75).

  In this way, in parallel with or after completion of the color misregistration correction process, the reference cycle Tr stored in the RAM 524 is rewritten to the rotation cycle T calculated in step S5 (step S8), and then the process returns to step S4 to return to the above series. Are repeated (steps S4 to S8).

  As described above, according to this embodiment, since the belt rotation period detection mark TM and the registration mark RM are detected by the single pattern sensor (detection means) 18, the configuration of the image forming apparatus can be simplified and the cost can be reduced. Can be reduced. Further, since only the signal corresponding to the registration mark RM among the detection signals of the pattern sensor 18 can be discriminated and discriminated, the resist control is favorably performed based on the signal corresponding to the discriminating and discriminating RM. Can do.

  In addition, according to this embodiment, since a thermoplastic elastomer alloy is used as the material of the intermediate transfer belt 16, it has superior bending resistance compared to an intermediate transfer belt based on PC resin or PET resin, Good resist control is possible. In addition, the intermediate transfer belt 16 based on a thermoplastic elastomer alloy is more sensitive to temperature fluctuations than an intermediate transfer belt based on PC resin or PET resin. Accordingly, the peripheral length of the intermediate transfer belt 16 made of a thermoplastic elastomer alloy as a base material changes sensitively to temperature fluctuations in the image forming apparatus, and the belt rotation period also fluctuates accordingly. Therefore, as in this embodiment, an apparatus using a thermoplastic elastomer alloy as a base material as the intermediate transfer belt 16 tends to have a large rotational cycle fluctuation accompanying a temperature fluctuation. However, the execution timing of the resist control is appropriately controlled based on the signal detected by the pattern sensor 18. As a result, it is possible to perform resist control with higher accuracy against temperature fluctuations inside the image forming apparatus.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the present invention is applied to a so-called tandem image forming apparatus. However, the scope of the present invention is not limited to this, and a toner image formed by image forming means is predetermined. The present invention can be applied to all image forming apparatuses that transfer to an intermediate transfer belt that circulates in a direction and temporarily holds the toner image.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The enlarged view of pattern sensor vicinity. The figure which shows an example of the output signal of a pattern sensor. The figure which shows a belt rotation period detection signal. FIG. 4 is a diagram illustrating a rotation cycle of an intermediate transfer belt according to temperature. FIG. 2 is a diagram illustrating an operation of the image forming apparatus in FIG. 1. The figure which showed operation | movement of the color shift correction process. FIG. 4 is a diagram illustrating an operation of an image forming station when color misregistration correction is executed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 9 ... Transfer belt unit, 16 ... Intermediate transfer belt, 18 ... Pattern sensor (detection means), 52 ... Engine controller (control means), 521 ... CPU (control means), RM, RM (K) , RM (C), RM (M), RM (Y) ... registration mark, TM ... belt rotation period detection mark, T1, T2, T3 ... rotation period, Y, M, C, K ... image forming station (image Forming means)

Claims (6)

An image forming area in which a toner image is formed and an image non-forming area in which a belt rotation period detection mark is provided are provided adjacent to each other in the main scanning direction, and rotate and move in the sub-scanning direction substantially orthogonal to the main scanning direction. Intermediate transfer belt,
Image forming means for forming a toner image as a registration mark in the image forming area;
A detecting unit arranged to straddle a boundary between the image forming region and the image non-forming region, detecting the belt rotation period detection mark and the registration mark, and outputting a detection signal;
An image forming apparatus comprising: a control unit that controls toner image formation by the image forming unit based on a detection signal output from the detection unit.   The image forming apparatus according to claim 1, wherein the registration mark is formed at a position shifted from the belt rotation period detection mark in the sub-scanning direction.   The control unit determines timing for forming the registration mark in the image forming area by the image forming unit based on a detection result of a signal corresponding to the belt rotation period detection mark by the detection unit. Image forming apparatus. As the image forming means, a plurality of image forming stations each forming a toner image of a different color are arranged along the moving direction of the intermediate transfer belt, and the toner images formed by the plurality of image forming stations are arranged. The image according to claim 2, wherein the registration mark is formed on the surface of the intermediate transfer belt so as to be separated in the moving direction, and color misregistration correction processing is performed based on a detection result of a signal corresponding to the registration mark by the detection unit. A forming device,
The image forming apparatus determines the timing for performing the color misregistration correction processing based on a detection result of a signal corresponding to the rotation period detection mark.   The control unit controls the image forming unit to form the registration mark with a predetermined time difference from when the detection unit detects the belt rotation period detection mark, and immediately after the registration mark is formed. 5. The image forming apparatus according to claim 2, wherein a detection signal from the first detection means is excluded.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt uses a thermoplastic elastomer alloy mainly composed of a thermoplastic elastomer as a belt base material.

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