JP5187286B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms a color image by superimposing and transferring toner images of respective colors formed on a transfer belt on transfer paper.

  In this type of image forming apparatus, color misregistration occurs in superposition of toner images of different colors due to various factors. For this reason, it is necessary to correct this color shift. However, when the color misregistration is corrected by a dedicated sequence that interrupts the image forming job, the productivity of the image forming apparatus is lowered.

  Therefore, a technique called “inter-sheet color registration correction” for correcting color misregistration without reducing the productivity of the image forming apparatus is known (see, for example, Patent Document 1). In the technique described in Patent Document 1, a color misregistration detection mark is formed as a toner image at a position on a transfer belt corresponding to a space between transfer sheets, and the color misregistration detection mark formed between the transfer sheets is detected by a sensor. By calculating the color misregistration amount based on the color misregistration detection mark detected by the sensor, it is possible to correct the color misregistration during the sheet passing without interrupting the image forming job.

JP-A-8-85234

  By the way, the speed of the transfer belt varies depending on its driving cycle, and this speed variation affects the color misregistration amount of the color misregistration detection mark. For this reason, in the dedicated sequence in which the image forming job is interrupted, the influence of the speed unevenness is canceled by transferring the color misregistration detection mark to a predetermined position. However, in the technique described in Patent Document 1, since the color misregistration detection mark can be formed only at the position between the transfer papers on the transfer belt, the speed unevenness due to the driving cycle cannot be canceled, and accurate color misregistration correction is difficult. End up.

  The present invention has been made in view of the above problems, and its object is to improve the accuracy of color misregistration correction when forming a color misregistration detection mark at a position between transfer sheets on a transfer belt. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that forms a color image by transferring onto a toner image transfer paper of each color formed on an endless transfer belt. Mark forming means for forming a color misregistration detection mark for each color between transfer papers on the belt, and each of the color misregistration detection marks formed by the mark forming means for the transfer corresponding to the detection mark forming position. A belt phase detecting means for detecting the phase of the belt, a mark detecting means for detecting a color misregistration detection mark for each color formed by the mark forming means, and a color misregistration amount is calculated based on the detection by the mark detecting means. Color misregistration amount calculating means, information on the color misregistration amount of each color misregistration detection mark calculated by the color misregistration amount calculating means, and the belt phase Storage means for storing the phase information of the transfer belt detected by the output means in association with each color misregistration detection mark, and the phase of the transfer belt is mutually determined from the phase information stored in the storage means. An average color misregistration amount calculating unit that extracts a color misregistration detection mark that is shifted by about 180 degrees and calculates an average value of the color misregistration amounts of the extracted color misregistration detection mark, and the average color misregistration amount calculation unit Correction execution means for correcting the control of the mark forming means based on the amount of color misregistration.

  According to this image forming apparatus, for each formed color misregistration detection mark, the phase on the transfer belt corresponding to the formation position of the detection mark is detected, and the color misregistration amount of the formed color misregistration detection mark Is calculated. Then, the information on the color misregistration amount and the phase information are stored in association with each color misregistration detection mark. Further, color misregistration detection marks whose phases of the transfer belt are shifted from each other by about 180 degrees are extracted from the stored phase information, and an average value of the color misregistration amounts of the extracted color misregistration detection marks is calculated. Here, the transfer belt has a speed variation due to a driving cycle, and the color misregistration amount tends to fluctuate. For this reason, by extracting the color misregistration detection marks formed with phases shifted by about 180 degrees from each other, the color misregistration detection marks are extracted so as to cancel the influence of the speed unevenness. Then, by calculating the average value of the color misregistration amounts of the extracted color misregistration detection marks, it is possible to cancel the influence of speed unevenness and improve the accuracy of color misregistration correction.

  In the image forming apparatus, the storage unit divides a moving distance until the transfer belt makes one turn into a plurality of regions, stores in which region the color misregistration detection mark is located, and stores the average color It is preferable that the deviation amount calculation means extracts color misregistration detection marks that exist in regions having a positional relationship that are substantially 180 degrees apart from each other.

  According to this image forming apparatus, the movement distance until the transfer belt makes one turn is divided into a plurality of areas, the areas where the color misregistration detection marks are located are stored, and the positional relationship is shifted by approximately 180 degrees from each other. The color misregistration detection mark existing in the area is extracted. Here, it is rare that the phase of the color misregistration detection marks is strictly shifted by approximately 180 degrees, and extracting such a color misregistration detection mark misses the opportunity of color misregistration correction. For this reason, the movement distance until the transfer belt makes one turn is divided into a plurality of areas, and the color misregistration correction marks are extracted by extracting the color misregistration detection marks existing in the positional relation areas that are deviated from each other by approximately 180 degrees. Opportunities can be made difficult to miss.

  In the image forming apparatus, the image forming apparatus further includes: a photosensitive drum that carries a toner image transferred to the transfer belt; and a drum phase detecting unit that detects a phase of the photosensitive drum, and the storage unit includes the drum phase. The phase information of the photosensitive drum detected by the detecting unit, the information of the color misregistration amount of each color misregistration detection mark calculated by the color misregistration amount calculating unit, and the transfer belt detected by the belt phase detecting unit. The average color misregistration amount calculating means stores the phase of the transfer belt at 180 degrees from the phase information of the transfer belt stored in the storage means. A color misregistration detection mark is formed by extracting from the phase information of the photoconductive drum that is formed with a shift and the phase of the photoconductive drum being shifted by 180 degrees and extracting the mark. It is preferable to calculate the average value of the color shift amount of the color shift detection mark.

  According to this image forming apparatus, the phase of the transfer belt is formed with a phase shift of approximately 180 degrees from the phase information of the transfer belt, and the phase of the photoconductive drum is shifted with respect to the phase of the photoconductive drum by approximately 180 degrees. The color misregistration detection marks formed in this way are extracted, and the average value of the color misregistration amounts of the extracted color misregistration detection marks is calculated. For this reason, the color misregistration detection mark is extracted and the average value of the color misregistration amounts is calculated so as to cancel not only the periodic variation of the transfer belt but also the periodic variation of the photosensitive drum. The accuracy of color misregistration correction can be improved.

  In the image forming apparatus, the storage unit divides a rotation distance until the photosensitive drum makes one turn into a plurality of regions, stores in which region the color misregistration detection mark is located, and stores the average It is preferable that the color misregistration amount calculating means extracts color misregistration detection marks that exist in regions of positional relationship that are deviated from each other by approximately 180 degrees.

  According to this image forming apparatus, the rotation distance until the photosensitive drum makes one turn is divided into a plurality of areas, the areas where the color misregistration detection marks are located are stored, and the positions are shifted by approximately 180 degrees from each other. Color misregistration detection marks existing in the related area are extracted. Here, it is rare that the phase of the color misregistration detection marks is strictly shifted by approximately 180 degrees, and extracting such a color misregistration detection mark misses the opportunity of color misregistration correction. For this reason, the color shift correction is performed by dividing the rotation distance until the photosensitive drum makes one turn into a plurality of areas and extracting the color shift detection marks existing in the positional relation areas that are shifted from each other by approximately 180 degrees. Can make it difficult to miss the opportunity.

  In the image forming apparatus, it is preferable that the average color misregistration amount calculation unit calculates a re-average value obtained by further averaging the calculated average values of the plurality of color misregistration amounts.

  According to this image forming apparatus, in order to calculate a re-average value obtained by further averaging the calculated average values of the plurality of color misregistration amounts, the average value of the plurality of color misregistration amounts is further averaged to further correct the color misregistration. Accuracy can be improved.

  The image forming apparatus preferably further includes a rotary encoder that detects rotational displacement of the transfer belt.

  The image forming apparatus preferably further includes a rotary encoder that detects a rotational displacement of the photosensitive drum.

  According to the present invention, the accuracy of color misregistration correction can be improved.

1 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a block diagram showing a photosensitive drum and a driving mechanism of a belt driving roller. FIG. 6 is a diagram illustrating an example of a time change of an image forming operation in an exposure portion portion of each photosensitive drum and a color registration sensor portion of a transfer belt. FIG. 6 is a diagram illustrating a position for forming a color misregistration detection mark according to a conventional dedicated sequence and a position for forming a color misregistration detection mark according to the present embodiment. It is a conceptual diagram which shows the memory content in a memory | storage means. It is a figure which shows the average value calculated by the average color shift amount calculation means. It is a figure which shows the re-average value calculated by the average color shift amount calculation means. 6 is a flowchart illustrating an operation performed by the image forming apparatus according to the present exemplary embodiment. 4A and 4B are diagrams illustrating phases of a transfer belt and a photosensitive drum, where FIG. 5A illustrates a phase of the transfer belt, FIG. 5B illustrates a phase of the photosensitive drum, and FIG. 5C illustrates a phase obtained by adding both phases. ing. It is a block diagram which shows the drive mechanism etc. of a photoconductive drum and a belt drive roller in 2nd Embodiment. It is a conceptual diagram which shows the memory content in the memory | storage means concerning 2nd Embodiment. 12 is a flowchart illustrating an operation performed by the image forming apparatus according to the second embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same parts are denoted by the same reference numerals and description thereof is omitted.

  FIG. 1 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 12 according to the embodiment of the present invention forms a full-color image in which a plurality of photosensitive drums 31Y, 31M, 31C, and 31K face a transfer belt 41 functioning as an intermediate transfer member and are arranged in a vertical direction. This is called a tandem type color image forming apparatus.

  The image forming apparatus 12 includes an automatic document feeder ADF at the top thereof. The documents D placed on the document placement table 103 of the automatic document feeder ADF are separated one by one, sent out to the document conveyance path, and conveyed by the conveyance drum 102.

  The document reading unit 101 reads an image of the document D being conveyed at the document image reading position RP. The first conveyance guide G1 and the document discharge roller 105 discharge the document D that has been read to the document discharge tray 107.

  The image forming apparatus 12 includes the document reading unit 101, the exposure units 2Y, 2M, 2C, and 2K, the image forming units 3Y, 3M, 3C, and 3K, the intermediate transfer unit 104, the fixing unit 115, the paper discharge reversing unit 106, The sheet feeding unit 117, the sheet feeding unit 108, the control unit 27, and the like are configured in a single casing.

  The document reading unit 101 irradiates the image of the document D with the lamp L at the document image reading position RP, guides the reflected light by the first mirror unit 111, the second mirror unit 112, and the lens 113, and captures the image sensor CCD. An image is formed on the light receiving surface. The imaging device CCD photoelectrically converts incident light and outputs a predetermined image signal. The image reading control unit 114 performs processing such as A / D conversion, shading correction, and compression on the image signal, and stores it as image data in the storage unit of the control unit 27. The image data stored in the storage means is subjected to appropriate image processing according to conditions set by the user, and output image data is generated.

  The exposure units 2Y, 2M, 2C, and 2K include a laser light source, a polygon mirror, and a plurality of lenses that are not shown, and generate a laser beam. The exposure units 2Y, 2M, 2C, and 2K correspond to output information that is output based on the output image data sent from the control unit 27, and are photoconductors that are constituent elements of the image forming units 3Y, 3M, 3C, and 3K. The surfaces of the drums 31Y, 31M, 31C, and 31K are scanned and exposed with a laser beam. By scanning the laser beam in a direction (main scanning direction) parallel to the rotation axis of the rotating photosensitive drums 31Y, 31M, 31C, and 31K, latent images are formed on the photosensitive drums 31Y, 31M, 31C, and 31K. The

  The image forming unit 3Y includes a photosensitive drum 31Y, and a main charging unit 32Y, a developing unit 33Y, a first transfer roller 34Y, and a cleaning unit 35Y, which are arranged around the photosensitive drum 31Y. The other image forming units 3M, 3C, and 3K have the same configuration as that of the image forming unit 3Y. The main charging units 32M, 32C, and 32C are arranged around the photosensitive drums 31M, 31C, and 31K, respectively. 32K, developing units 33M, 33C, and 33K, first transfer rollers 34M, 34C, and 34K, and cleaning units 35M, 35C, and 35K are arranged.

  The developing units 33Y, 33M, 33C, and 33K are developed on the photosensitive drums 31Y, 31M, 31C, and 31K by developing with yellow (Y), magenta (M), cyan (C), and black (BK) toners. Visualize the image. As a result, yellow (Y), magenta (M), cyan (C), and black (BK) toner images are formed on the photosensitive drums 31Y, 31M, 31C, and 31K.

  The first transfer rollers 34Y, 34M, 34C, and 34K of the intermediate transfer unit 104 sequentially transfer the toner images formed on the photosensitive drums 31Y, 31M, 31C, and 31K to predetermined positions on the transfer belt 41. The cleaning units 35Y, 35M, 35C, and 35K remove the toner remaining on the surfaces of the photosensitive drums 31Y, 31M, 31C, and 31K after the transfer of the toner images.

  On the other hand, the second transfer roller 42 transports the toner image transferred onto the transfer belt 41 from the trays PG1, PG2, and PG3 of the paper supply unit 108, and is transferred by the paper supply roller 81 at a timing. Transfer to paper P. The belt cleaning unit 43 cleans the surface of the transfer belt 41 that has finished transferring the toner image onto the transfer paper P, and the cleaned transfer belt 41 is used for the next image transfer.

  The transfer paper P carrying the toner image is sent to the fixing unit 115, and the fixing unit 115 pressurizes and heats the transfer paper P to fix the toner image to the transfer paper P.

  Further, the exposure units 2Y, 2M, 2C, and 2K and the image forming units 3Y, 3M, 3C, and 3K according to the present embodiment function as a mark forming unit. That is, each of the above portions forms a color misregistration detection mark on the transfer belt 41 as a toner image in order to perform color misregistration correction. The marks are sequentially formed at positions on the transfer belt 41 corresponding to the space between the transfer sheets P fed by the sheet feeding unit 108.

  The paper discharge reversing unit 106 conveys the transfer paper P that has undergone the fixing process by the fixing unit 115 and discharges the transfer paper P to the paper discharge tray 61. When the transfer paper P is reversed and discharged, the paper discharge guide 62 temporarily guides the transfer paper P downward, holds the rear end of the transfer paper P between the discharge reverse roller 63, and then reversely conveys the transfer paper P. Then, the paper discharge guide 62 guides the transfer paper P to the paper discharge roller 64 and discharges it.

  When image formation is also performed on the back surface of the transfer paper P, the paper discharge guide 62 conveys the transfer paper P that has been subjected to the fixing process of the toner image on the front surface to the re-feeding unit 117 below, and re-feeds the transfer paper P. After the rear end is nipped by the reversing roller 71, the transfer paper P is reversed by reverse feeding and sent to the refeed conveyance path 72 for image formation on the back surface.

  In the image forming apparatus 12, the photosensitive drums 31Y, 31M, 31C, and 31K rotate in the direction indicated by the arrows in FIG. The endless transfer belt 41 moves while rotating in the direction indicated by the arrow in FIG. 1 by the driving force of the belt driving roller 44. A color registration sensor 49 that functions as a mark detection unit is disposed on the transfer belt 41 between the photosensitive drum 31K and the second transfer roller. The color registration sensor 49 detects a color misregistration detection mark formed to correct the color misregistration.

  FIG. 2 is a configuration diagram showing the photosensitive drums 31Y, 31M, 31C, 31K, the driving mechanism of the belt driving roller 44, and the like. Although only the photosensitive drum 31Y is shown in FIG. 2, the other photosensitive drums 31M, 31C, and 31K are also provided with a similar drive mechanism.

  As shown in FIG. 2, a rod-shaped rotating shaft 39Y is fixed to the photosensitive drum 31Y so as to penetrate the central axis. The rotation shaft 39Y is mechanically connected to the drum drive motor 38Y via the drive gear 37Y, and the rotation drive force of the drum drive motor 38Y is transmitted to the photosensitive drum 31Y via the drive gear 37Y and the rotation shaft 39Y. .

  A rotary encoder 36Y including a rotary plate and a sensor unit is installed on the rotary shaft 39Y. The rotating plate is fixed together with the drive gear 37Y on the rotating shaft 39Y. Marks are formed at equal intervals on the circumferential side of the rotating plate. The sensor unit is provided to read this mark and count the number of times. The encoder 36Y can obtain the rotational speed of the rotary shaft 39Y from the number of times the mark is read per unit time by previously obtaining the total number of marks formed on the rotating plate.

  The encoder 36Y is an example for detecting the rotational speed of the photosensitive drum 31Y, and means for detecting the rotational speed of the photosensitive drum 31Y is not limited to this. Therefore, the means for detecting the rotational speed of the photosensitive drum 31Y may be a device that measures the rotational speed of the photosensitive drum 31Y or a device that measures the rotational speed of the outer peripheral surface of the photosensitive drum 31Y. Alternatively, the rotation speed of the drum drive motor 38Y or the drive gear 37Y may be measured and converted into the rotation speed of the photosensitive drum 31Y. That is, the means for detecting the rotational speed of the photosensitive drum 31Y includes a device that detects the rotational speed of the photosensitive drum 31Y directly or indirectly.

  A rod-like rotating shaft 48 is fixed to the belt driving roller 44 so as to penetrate the central shaft. The rotation shaft 48 is mechanically connected to the belt drive motor 47 via the drive gear 46, and the rotation drive force of the belt drive motor 47 is transmitted to the belt drive roller 44 via the drive gear 46 and the rotation shaft 48. .

  A rotary encoder 45 including a rotary plate and a sensor unit is installed on the rotary shaft 48. The rotating plate is fixed together with the drive gear 46 on the rotating shaft 48. Marks are formed at equal intervals on the circumferential side of the rotating plate. The sensor unit is provided to read this mark and count the number of times. The encoder 45 can directly determine the rotational speed of the rotary shaft 48 from the number of times of reading the mark by previously obtaining the total number of marks formed on the rotating plate. Then, the moving speed of the transfer belt 41 can be obtained from the diameter of the belt driving roller 44 and the rotating speed of the rotating shaft 48.

  As with the encoder 36Y, the encoder 45 directly measures the rotational speed of the transfer belt 41 and the rotational speed of the outer peripheral surface of the belt drive roller 44, or measures the rotational speed of the belt drive roller 44 itself. A device that converts the rotation speed of the transfer belt 41, a device that measures the rotation speed of the belt drive motor 47 and the drive gear 46, and converts this to the rotation speed of the transfer belt 41, directly or indirectly. A device for detecting the rotational speed of 41 is included.

  The rotational speed signals detected by the encoders 36Y and 36 are input to the control unit 27. The control unit 27 outputs a signal indicating a control command to the drum drive motor 38Y and the belt drive motor 47, and the rotation drive force of the drum drive motor 38Y and the belt drive motor 47, and further the rotation speed of the photosensitive drum 31Y, and the like. The moving speed of the transfer belt 41 is controlled.

  FIG. 3 is a diagram illustrating an example of a time change of an image forming operation in the exposure portions 2Y, 2M, 2C, and 2K portions of the photosensitive drums 31Y, 31M, 31C, and 31K and the color registration sensor 49 portion of the transfer belt 41. It is. First, the exposure unit 2Y of the photosensitive drum 31Y exposes the photosensitive drum 31Y to form a yellow image latent image, and the developing unit 33Y forms a yellow image toner image. After a predetermined time from the yellow image, the photosensitive drum 31M is exposed and developed to form a magenta toner image. Thereafter, similarly, cyan and black toner images are formed on the photosensitive drum 31C and the photosensitive drum 31K.

  The toner images on the photosensitive drums 31Y, 31M, 31C, and 31K are sequentially transferred to predetermined positions on the transfer belt 41 by the first transfer rollers 34Y, 34M, 34C, and 34K. By shifting the exposure timing of the toner images on the photosensitive drums 31Y, 31M, 31C, and 31K, the toner images of the respective colors are superimposed and transferred on the transfer belt 41. For this reason, a color image made up of superimposed toner images of each color is formed at a location where the color registration sensor 49 is installed.

  If the positions where the toner images of the respective colors are superimposed are shifted, color shift occurs in the color image and the image quality is degraded. Therefore, the image forming apparatus 12 according to the embodiment of the present invention provides a color misregistration detection mark for detecting the magnitude of the color misregistration (hereinafter referred to as “color misregistration amount”) to each of the photosensitive drums 31Y and 31M. , 31C and 31K, and the color registration sensor 49 detects the color misregistration detection marks sequentially transferred on the transfer belt 41.

  FIG. 3 shows a case where the image forming apparatus 12 is executing an image forming job for continuously forming color images on a plurality of transfer sheets P. In this case, since each transfer paper P is conveyed through the image forming apparatus 12 with a predetermined interval, each color toner image and color image are formed with a predetermined interval. Therefore, the image forming apparatus 12 forms “inter-sheet mark” at a position corresponding to between the transfer sheets P as an example of the color misregistration detection mark. Accordingly, it is possible to form and detect a color misregistration detection mark while the paper is passing without interrupting an image forming job for continuously forming a color image on a plurality of transfer papers P.

  In the period TdY indicated by the arrow in FIG. 3 from the exposure of the yellow inter-paper mark on each photoconductor drum 31Y to the transfer to the transfer belt 41, the yellow inter-paper mark moves on the rotating photoconductor drum 31Y. Moving. The yellow inter-paper mark moves on the transfer belt 41 during a period TvY indicated by an arrow in FIG. 3 from when the yellow inter-paper mark is transferred to the transfer belt 41 until the color registration sensor 49 detects it.

  The control unit 27 integrates the rotational speed of the photosensitive drum 31Y detected by the encoder 36Y in the period TdY and integrates the moving speed of the transfer belt 41 detected by the encoder 45 in the period TvY. Then, the control unit 27 can calculate the formation position of the yellow inter-paper mark by adding the two integral values. The control unit 27 calculates the formation position of the inter-sheet mark in the same manner for the other colors. Then, the control unit 27 calculates the color misregistration amount from the formation position of the inter-sheet mark for each color.

  Reference is now made to FIG. FIG. 4 is a diagram showing a position for forming a color misregistration detection mark according to a conventional dedicated sequence and a position for forming a color misregistration detection mark according to this embodiment. In FIG. 4, the vertical axis represents the color misregistration amount (pixel), and the horizontal axis represents the moving distance (mm) of the transfer belt 41. Further, in the example shown in FIG. 4, it is assumed that the transfer belt 41 has a circumference of 1200 mm.

  As shown in FIG. 4, the transfer belt 41 undergoes color misregistration due to uneven speed during one round. As shown in FIG. 4, the color shift is a sine wave, and one cycle of the sine wave corresponds to one turn of the transfer belt 41. As described above, the color misregistration amount varies like a sine wave by one rotation of the transfer belt 41. Therefore, as shown by the square marks in FIG. 4, in the conventional dedicated sequence, for example, the color shift at the position on the transfer belt 41 where the amplitude of the sine wave becomes the largest is canceled so as to cancel the fluctuation of the color shift amount due to the speed unevenness. By forming a detection mark and taking an average value of these, a color misregistration amount in which the speed unevenness due to the driving cycle is canceled is calculated. According to this method, the average value of color misregistration amounts to about 0.3 pixels.

  However, in the image forming apparatus 12 according to the present embodiment, a color misregistration detection mark is formed at a position on the transfer belt 41 corresponding to the space between the transfer sheets P. For this reason, as shown by the circles in FIG. 4, the color misregistration detection mark cannot be formed only at the position where the variation in the color misregistration amount due to the speed unevenness is canceled. When the average value of the color misregistration amounts indicated by the circles in FIG. 4 is calculated, the value is about 0.5 pixels, which is far from the original value.

  Therefore, the image forming apparatus 12 according to the present embodiment includes the following configuration in the control unit 27. Reference is again made to FIG. As illustrated in FIG. 2, the control unit 27 includes a belt phase detection unit 84, a color misregistration amount calculation unit 85, a storage unit 86, an average color misregistration amount calculation unit 87, and a correction execution unit 88. The belt phase detection unit 84 detects the phase of the transfer belt 41 for each of the inter-sheet marks sequentially formed on the transfer belt 41. Here, as described with reference to FIG. 4, the phase corresponds to the moving distance of the transfer belt 41, and when the transfer belt 41 makes one turn, the sine wave makes one cycle. The belt phase detection means 84 detects the relative belt position from a certain point in time by counting the pulses of the speed detection encoder of the belt drive shaft, and detects the phase corresponding to this belt position.

  The color misregistration amount calculation unit 85 calculates the color misregistration amount from the position of the inter-sheet mark detected by the color registration sensor 49. At this time, the color misregistration amount calculation means 85 calculates the misregistration amount of each color with reference to the black color.

  The storage unit 86 stores the information on the color misregistration amount of each inter-sheet mark detected by the color misregistration amount calculation unit 85 and the information on the phase of the transfer belt 41 detected by the belt phase detection unit 84 for each inter-paper mark. This is stored in association with each other. At this time, the storage unit 86 divides the moving distance until the transfer belt 41 makes one turn into a plurality of areas, and stores in which area the inter-paper mark is located.

  More specifically, as shown in FIG. 4, in this embodiment, a distance of 1200 mm in one circumference of the transfer belt 41 is divided into 12 regions A to F and a to f. The storage means 86 stores the areas A to F and a to f as information on the phase of the inter-sheet mark. FIG. 5 is a conceptual diagram showing the contents stored in the storage means 86. Each data shown in FIG. 5 corresponds to each point (1) to (8) on the belt cycle shown in FIG. As shown in FIG. 5, the storage means 86 stores information indicating that the belt position is in the region A as a phase and the color misregistration amount at that time is 0.5 pixel, and the belt position is in the region D as a phase. Information on the existence and the color misregistration amount at that time is 1.7 pixels. Similarly, the storage means 84 is -0.6 pixel for the region b, -0.7 pixel for the region e, 1.2 pixel for the region B, 1.4 pixel for the region E, and 0.2 pixel for the region a. Such information is stored.

  The average color misregistration amount calculation unit 87 extracts a paper interval mark whose phase is shifted by about 180 degrees from the phase information stored in the storage unit 86, and calculates an average value of the color misregistration amount of the extracted paper interval mark. It is. This will be specifically described. First, as shown in FIGS. 4 and 5, the phase between the inter-paper mark located in the area A in the first measurement and the inter-paper mark located in the area a in the seventh measurement are shifted by approximately 180 degrees. It is in a positional relationship. For this reason, the average color misregistration amount calculation means 87 calculates the average value of 0.5 pixels and 0.2 pixels, which is the color misregistration amount of these inter-sheet marks. That is, the average value of color misregistration amounts is 0.35 pixels. This value is close to the color misregistration amount calculated by the conventional dedicated sequence, and is a value obtained by canceling the speed unevenness due to the driving cycle.

  The correction execution unit 88 executes color misregistration correction processing based on the average value of the color misregistration amounts calculated by the average color misregistration amount calculation unit 87. At this time, the correction execution unit 88 corrects the color misregistration of each color by correcting the image formation timing of each color such as the exposure timing.

  In the present embodiment, the average color misregistration amount calculation unit 87 calculates a plurality of average values of the color misregistration amounts, and calculates a re-average value obtained by further averaging the calculated average values of the plurality of color misregistration amounts. desirable. This will be specifically described. FIG. 6 is a diagram showing an average value calculated by the average color misregistration amount calculation means 87, and FIG. 7 is a diagram showing a re-average value calculated by the average color misregistration amount calculation means 87.

  As shown in FIG. 6, the average color misregistration amount calculation unit 87 calculates an average value of a plurality of color misregistration amounts. Specifically, the first average value is the average value of the color misregistration amounts between the sheet interval mark located in the area A in the first measurement and the sheet interval mark located in the area a in the seventh measurement. There are 0.35 pixels. The second average value is an average value of the color misregistration amounts between the sheet interval mark located in the area b in the third measurement and the sheet interval mark located in the area B in the fifth measurement, The pixel is 0.30. Also, as shown in FIG. 6, the average color misregistration amount calculation means 87 obtains a value of 0.20 pixels as the third average value and a value of 0.35 pixels as the fourth average value. Yes.

  The average color misregistration amount calculation means 87 averages these four average values to obtain a re-average value. FIG. 7 is a diagram showing the re-average value. As shown in FIG. 7, the average color misregistration amount calculation means 87 averages four average values to obtain a value of 0.30 pixels. As a result, the correction execution unit 88 executes the color misregistration correction process based on the re-average value calculated by the average color misregistration amount calculation unit 87.

  In the example shown in FIGS. 6 and 7, four average values are averaged. However, the average value is not limited to four, and may be two or three, or may be five or more.

  FIG. 8 is a flowchart showing an operation by the control unit 27 of the image forming apparatus 12 according to the present embodiment. First, it is assumed that the user gives an image formation instruction for continuously forming color images on a plurality of transfer sheets P. Thereby, the process shown in FIG. 8 is executed.

  In the flowchart shown in FIG. 8, first, the exposure units 2Y, 2M, 2C, and 2K and the image forming units 3Y, 3M, 3C, and 3K that function as the mark forming unit correspond to the space between the transfer sheets P on the transfer belt 41. A sheet interval mark is formed at the position (S1).

  Next, the belt phase detector 84 detects the phase of the transfer belt 41 (S2). At this time, the belt position detection unit 84 detects the phase of the transfer belt 41 by calculating the position where the inter-paper mark is formed on the transfer belt 41 based on the information of the encoders 36Y and 45.

  Thereafter, the color misregistration amount calculation means 85 calculates the color misregistration amount based on the inter-sheet mark (S3). At this time, the color misregistration amount calculation means 85 calculates the color misregistration amount based on the signal from the color registration sensor 49. The storage unit 86 stores the phase information detected in step S2 and the color misregistration amount information calculated in step S3 in association with each interval mark. At this time, the phase information is stored as region information as described with reference to FIG.

  Next, the average color misregistration amount calculation unit 87 determines whether or not there is an inter-sheet mark whose phase of the transfer belt 41 is deviated by about 180 degrees (S5). If it is determined that there is no inter-paper mark shifted by approximately 180 degrees (S5: NO), the process proceeds to step S1, and the inter-paper mark is formed between the transfer papers P again. On the other hand, when it is determined that there is an inter-paper mark that is shifted by approximately 180 degrees (S5: YES), the average color misregistration amount calculation means 87 calculates an average value of the color misregistration amounts (S6). After that, the average color misregistration amount calculation unit 87 determines whether or not the color misregistration amount average value calculation processing has been performed a predetermined number of times (S7).

  If it is determined that the predetermined number of times has not been performed (S7: NO), the process proceeds to step S1. When it is determined that the predetermined number of times has been performed (S7: YES), the average color misregistration amount calculating means 87 averages the average value of the color misregistration amounts for the predetermined number of times and calculates a re-average value (S8). After calculating the re-average value, the correction execution means 88 performs color misregistration correction (S9), and then the processing shown in FIG. 8 ends.

  In this way, according to the image forming apparatus 12 according to the present embodiment, for each of the formed color misregistration detection marks, the phase on the transfer belt 41 corresponding to the formation position of the detection mark is detected and formed. The color misregistration amount of the detected color misregistration detection mark is calculated. Then, the information on the color misregistration amount and the phase information are stored in association with each color misregistration detection mark. Further, color misregistration detection marks whose phases of the transfer belt are shifted from each other by about 180 degrees are extracted from the stored phase information, and an average value of the color misregistration amounts of the extracted color misregistration detection marks is calculated. Here, the transfer belt 41 tends to vary in speed due to uneven speed due to the driving cycle. For this reason, by extracting the color misregistration detection marks formed with phases shifted by about 180 degrees from each other, the color misregistration detection marks are extracted so as to cancel the influence of the speed unevenness. Then, by calculating the average value of the color misregistration amounts of the extracted color misregistration detection marks, it is possible to cancel the influence of speed unevenness and improve the accuracy of color misregistration correction.

  Further, the movement distance until the transfer belt 41 makes one turn is divided into a plurality of regions, the region where the inter-sheet mark is located is stored, and the inter-sheet region existing in the positional relationship that is shifted by approximately 180 degrees from each other. Extract marks. Here, it is rare that the phase of the inter-paper mark is strictly shifted by about 180 degrees, and extracting such an inter-paper mark misses the opportunity of color misregistration correction. For this reason, the movement distance until the transfer belt 41 makes one turn is divided into a plurality of areas, and the inter-sheet marks existing in the positional relation areas that are shifted from each other by approximately 180 degrees are extracted, thereby providing an opportunity for color misregistration correction. Can be difficult to miss.

  In addition, in order to calculate a re-average value obtained by further averaging the calculated average values of the plurality of color misregistration amounts, the average value of the plurality of color misregistration amounts can be further averaged to further improve the accuracy of color misregistration correction. Can do.

  Next, a second embodiment of the present invention will be described. The image forming apparatus 12 according to the second embodiment is the same as that of the first embodiment, but part of the processing content is different. Only differences from the first embodiment will be described below.

  Although the image forming apparatus 12 according to the first embodiment cancels the speed unevenness due to the driving cycle of the transfer belt 41, the image forming apparatus 12 according to the second embodiment has the speed unevenness due to the driving cycle of the transfer belt 41. In addition, the influence of the driving cycle of the photosensitive drums 31Y, 31M, 31C is also canceled.

  9A and 9B are diagrams showing the phases of the transfer belt 41 and the photosensitive drums 31Y, 31M, and 31C. FIG. 9A shows the phase of the transfer belt 41, and FIG. 9B shows the phases of the photosensitive drums 31Y, 31M, and 31C. (C) shows a phase obtained by adding both phases.

  As shown in FIG. 9A, the transfer belt 41 has a phase that makes one cycle per rotation. In addition, the photosensitive drums 31Y, 31M, and 31C also exhibit a phase that makes one cycle per cycle. For this reason, the sum of these phases is as shown in FIG. 9C, and it is possible that the calculation accuracy of the color misregistration amount is not sufficient by simply canceling the speed unevenness due to the driving cycle of the transfer belt 41.

  Therefore, in the second embodiment, the control unit 27 has the following configuration. FIG. 10 is a configuration diagram showing the photosensitive drums 31Y, 31M, 31C, 31K, the driving mechanism of the belt driving roller 44, and the like in the second embodiment.

  As shown in FIG. 10, in the second embodiment, the control unit 27 includes a drum phase detection unit 89. The drum phase detector 89 functions as a drum phase detector that detects the phases of the photosensitive drums 31Y, 31M, and 31C. Here, the photosensitive drums 31Y, 31M, and 31C shown in FIG. 9B show a phase of one cycle in one round. For this reason, the drum phase detector 89 detects the position of the photosensitive drum 31Y from the rotational speed detected based on the signal from the encoder 36Y, and detects the detected position as the phase of the photosensitive drum 31Y. The same applies to the other photosensitive drums 31M and 31C.

  Furthermore, in the second embodiment, the storage unit 86 stores the phase information of the photosensitive drums 31Y, 31M, and 31C detected by the drum phase detection unit 89. At this time, the storage unit 86 stores the phase information of the photoconductive drums 31Y, 31M, and 31C together with the color misregistration amount of the inter-sheet mark and the phase information of the transfer belt 41 in association with each inter-sheet mark. The storage unit 86 divides the moving distance until each photosensitive drum 31Y, 31M, 31C makes one round into a plurality of areas, and stores in which area the inter-paper mark is located.

  More specifically, in the present embodiment, one circumference of each of the photosensitive drums 31Y, 31M, and 31C is divided into 12 regions A to F and a to f. The storage means 86 stores the areas A to F and a to f as information on the phase of the inter-sheet mark. FIG. 11 is a conceptual diagram showing the contents stored in the storage means 86 according to the second embodiment. Each data shown in FIG. 11 corresponds to each point shown in FIG. As shown in FIG. 11, the storage means 86 uses the belt position in the region A as the belt phase and the color misregistration amount at that time is 1.5 pixels, as well as the phase of the photosensitive drum 31Y. Information indicating that the rotational position is the region A, the rotational position is the region B as the phase of the photosensitive drum 31M, and the rotational position is the region C as the phase of the photosensitive drum 31C is stored. Similarly, for each point shown in FIG. 11, the belt phase, the phase of the photosensitive drum 31Y, the phase of the photosensitive drum 31M, the phase of the photosensitive drum 31C, and the amount of color misregistration are stored.

  Further, the average color misregistration amount calculating means 87 is formed with a phase shift of about 180 degrees from the phase information of the transfer belt 41 stored in the storage means 86, and from the phase information of the photosensitive drums 31Y, 31M, 31C. Then, an inter-paper mark formed with a shift of about 180 degrees from each other is extracted, and an average value of the color misregistration amounts of the extracted inter-paper marks is calculated. In other words, the inter-paper mark in the third measurement shown in FIG. 11 and the inter-paper mark in the eleventh measurement have a positional relationship in which the belt phase and the phases of the photosensitive drums 31Y, 31M, and 31C are shifted from each other by approximately 180 degrees. It is in. For this reason, the average color misregistration amount calculation means 87 calculates the average value of −0.5 pixel and 0.3 pixel, which is the color misregistration amount of these inter-sheet marks. That is, the average value of the color misregistration amount is −0.10 pixel.

  In the second embodiment, the average color misregistration amount calculation unit 87 may calculate a re-average value obtained by further averaging a plurality of average values.

  FIG. 12 is a flowchart showing the operation of the image forming apparatus 12 according to the second embodiment. First, it is assumed that the user gives an image formation instruction for continuously forming color images on a plurality of transfer sheets P. Thereby, the process shown in FIG. 12 is performed.

  First, the transfer paper of the transfer belt 41 is formed by the exposure units 2Y, 2M, 2C, and 2K, the image forming units 3Y, 3M, 3C, and 3K, and the first transfer rollers 34Y, 34M, 34C, and 34K that function as mark forming units. An inter-paper mark is formed at a position corresponding to P (S11).

  Next, the drum phase detector 89 detects the phases of the photosensitive drums 31Y, 31M, and 31C (S12). At this time, the drum phase detector 89 detects the phase of each of the photosensitive drums 31Y, 31M, and 31C based on information from the encoder 36Y and the like. Thereafter, the color misregistration amount calculating means 85 calculates the color misregistration amount of the inter-sheet mark (S14), and the storage means 86 stores the information detected in steps S12 to S14 in association with each inter-paper mark ( S15). At this time, the phase information is stored as region information as described with reference to FIG.

  Next, in step S16, the same processing as in step S5 shown in FIG. 8 is executed, and then it is determined whether or not there is an inter-sheet mark in which the phases of the photosensitive drums 31Y, 31M, and 31C are shifted by approximately 180 degrees. (S17). If it is determined that there is no inter-paper mark shifted by approximately 180 degrees (S17: NO), the process proceeds to step S11, and the inter-paper mark is formed again between the transfer sheets P. On the other hand, when it is determined that there is an inter-paper mark that is shifted by approximately 180 degrees (S17: YES), the same processing as that shown in steps S6 to S9 shown in FIG. 8 is executed in steps S18 to S21, and step S21 is executed. After execution of the process, the process shown in FIG. 12 ends.

  In this way, according to the image forming apparatus 12 according to the second embodiment, the same effect as in the first embodiment can be obtained.

  Furthermore, according to the second embodiment, the phase information of the transfer belt 41 is formed with a shift of about 180 degrees from each other, and the phase information of the photosensitive drums 31Y, 31M, and 31C is formed with a shift of about 180 degrees with respect to each other. The inter-paper mark is extracted, and the average value of the color misregistration amounts of the extracted inter-paper mark is calculated. For this reason, not only the periodic variation of the transfer belt 41 but also the periodic variations of the photosensitive drums 31Y, 31M, and 31C are cancelled, and the inter-sheet mark is extracted to calculate the average value of the color misregistration amounts. As a result, the accuracy of color misregistration correction can be further improved.

  Further, the rotation distance until the photosensitive drums 31Y, 31M, and 31C make one turn is divided into a plurality of areas, the areas where the inter-sheet marks are located are stored, and the areas of the positional relationship shifted by approximately 180 degrees from each other. Is extracted. Here, it is rare that the phase of the inter-paper mark is strictly shifted by about 180 degrees, and extracting such an inter-paper mark misses the opportunity of color misregistration correction. For this reason, by dividing the rotation distance until the photosensitive drums 31Y, 31M, and 31C make one rotation into a plurality of areas, and extracting the inter-sheet marks that exist in the positional relationship areas that are shifted from each other by approximately 180 degrees, It is possible to make it difficult to miss the opportunity for color misregistration correction.

  The image forming apparatus according to the present invention has been described above based on the embodiment. However, the present invention is not limited to this, and modifications may be made without departing from the spirit of the present invention.

  For example, in the above embodiment, a copying machine has been described as an example of the image forming apparatus 12, but the present invention is not limited to this, and other image forming apparatuses such as a printer may be used. In the second embodiment, the phases of the three photosensitive drums 31Y, 31M, and 31C excluding the black photosensitive drum 31K are detected, and the inter-paper marks whose phases are shifted by 180 degrees are extracted. However, the present invention is not limited to this, and phase detection or the like may be performed including the black photosensitive drum 31K, or any one or two of the three photosensitive drums 31Y, 31M, and 31C may be detected. Etc. may be performed. Further, color misregistration correction may be performed using a color other than black as a reference.

2Y, 2M, 2C, 2K Exposure unit 3Y, 3M, 3C, 3K Image forming unit 12 Image forming apparatus 27 Control unit 31Y, 31M, 31C, 31K Photosensitive drum 32Y, 32M, 32C, 32K Main charging unit 33Y, 33M, 33C, 33K Developing unit 34Y, 34M, 34C, 34K First transfer roller 35Y, 35M, 35C, 35K Cleaning unit 36Y Encoder 37Y, 46 Drive gear 38Y Drum drive motor 39Y, 48 Rotating shaft 41 Transfer belt 42 Second transfer roller 43 Belt cleaning unit 44 Belt drive roller 45 Encoder 47 Belt drive motor 49 Color registration sensor 61 Paper discharge tray 62 Paper discharge guide 63 Paper discharge reversing roller 64 Paper discharge roller 71 Refeed reverse roller 72 Refeed conveyance path 81 Paper feed roller 84 Belt phase detector Stage 85 Color misregistration detection unit 86 Storage unit 87 Average color misregistration amount calculation unit 88 Correction execution unit 89 Drum phase detection unit 101 Document reading unit 102 Conveying drum 103 Document placing table 104 Intermediate transfer unit 105 Document discharge roller 106 Paper discharge reversing unit 107 Document discharge tray 108 Paper feed unit 111 First mirror unit 112 Second mirror unit 113 Lens 114 Image reading control unit 115 Fixing unit 117 Refeed unit

Claims (7)

An image forming apparatus for forming a color image by transferring onto a toner image transfer paper of each color formed on an endless transfer belt,
Mark forming means for forming a color misregistration detection mark for each color between the transfer sheets of the transfer belt;
Belt phase detection means for detecting the phase of the transfer belt corresponding to the formation position of the detection mark for each color misregistration detection mark formed by the mark forming means;
Mark detection means for detecting a color misregistration detection mark for each color formed by the mark forming means;
Color misregistration amount calculating means for calculating a color misregistration amount based on detection by the mark detection means;
Corresponding color misregistration amount information of each color misregistration detection mark calculated by the color misregistration amount calculation unit and phase information of the transfer belt detected by the belt phase detection unit for each color misregistration detection mark. Storage means for storing information;
From the phase information stored in the storage means, color misregistration detection marks whose phases of the transfer belt are deviated from each other by approximately 180 degrees are extracted, and an average value of the color misregistration amounts of the extracted color misregistration detection marks is calculated. An average color shift amount calculating means;
Correction execution means for correcting the control of the mark forming means based on the color misregistration amount calculated by the average color misregistration amount calculating means;
An image forming apparatus comprising: The storage means divides the moving distance until the transfer belt makes one turn into a plurality of regions, stores in which region the color misregistration detection mark is located,
The image forming apparatus according to claim 1, wherein the average color misregistration amount calculation unit extracts a color misregistration detection mark that exists in a region having a positional relationship that is deviated approximately 180 degrees from each other. A photosensitive drum carrying a toner image transferred to the transfer belt;
Drum phase detection means for detecting the phase of the photosensitive drum,
The storage means includes phase information of the photosensitive drum detected by the drum phase detection means, information on the color misregistration amount of each color misregistration detection mark calculated by the color misregistration amount calculation means, and the belt phase detection. The phase information of the transfer belt detected by the means is stored in association with each color misregistration detection mark,
The average color misregistration amount calculating means is formed by shifting the phase of the transfer belt by 180 degrees from the phase information of the transfer belt stored in the storage means, and from the phase information of the photosensitive drum. The color misregistration detection mark formed by shifting the phase of the body drum by 180 degrees is extracted, and an average value of the color misregistration amounts of the extracted color misregistration detection marks is calculated. The image forming apparatus according to any one of 2. The storage means divides a rotation distance until the photosensitive drum makes one turn into a plurality of regions, stores in which region the color misregistration detection mark is located,
The image forming apparatus according to claim 3, wherein the average color misregistration amount calculating unit extracts a color misregistration detection mark that exists in a region having a positional relationship shifted by 180 degrees. 5. The average color misregistration amount calculation unit calculates a re-average value obtained by further averaging the average values of the plurality of calculated color misregistration amounts. 6. Image forming apparatus. The image forming apparatus according to claim 1, further comprising a rotary encoder that detects rotational displacement of the transfer belt. The image forming apparatus according to claim 1, further comprising a rotary encoder that detects a rotational displacement of the photosensitive drum.

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