Image forming apparatus and image forming method

Abstract

To perform control of eliminating unevenness in the conveyance speed of a sheet without printing an image on the sheet with toner.SOLUTION: An image forming apparatus 1 comprises: conveyance rollers 32, 33 that convey a sheet 2; measurement units 18a, 18b that measure the contour of the sheet 2 to be conveyed; and a detection unit that, based on a result of measurement performed by the measurement units 18a, 18b, detects unevenness in the conveyance speed of the sheet 2 conveyed by the conveyance rollers 32, 33.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and an image forming method that eliminates unevenness in the conveying speed of paper on which an image is printed, which changes the conveying speed, and controls the conveying speed to a constant value. [Background technology]

[0002] In general, image forming devices control the paper transport speed to a constant value to eliminate density unevenness in images printed on the paper. Patent Document 1 describes an image forming device that uses this type of technology. This image forming device performs a test print by printing an image on paper and measures the density of the printed image on the paper using a density measurement sensor. Periodically fluctuating density unevenness components are extracted from the density profile in the paper transport direction obtained from this measurement. The extracted density unevenness components for one cycle are matched with the rotational position of the motor that rotates the transport roller that transports the paper, creating a periodic profile of drive pulses to be applied to the motor to cancel out the density unevenness components. The rotational drive of the motor is controlled based on this periodic profile. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-219311 Summary of the Invention [Problem to be solved by the invention]

[0004] The image forming apparatus in Patent Document 1 measures the density of an image printed on paper in advance by test printing to obtain density unevenness, and then controls the rotational drive of the motor that rotates the paper transport roller so as to cancel out this density unevenness. However, to perform this control, a recording medium such as paper and toner for printing an image on this recording medium may be required during the test print. In this case, there is a problem in that the recording medium and toner are wasted.

[0005] The present invention has been made in view of the above circumstances, and has as its object to eliminate unevenness in the conveyance speed of a recording medium in an image forming apparatus and an image forming method without printing an image on the recording medium. [Means for solving the problem]

[0006] That is, the above-mentioned problems of the present invention are solved by the following configuration.

[0007] That is, the above-mentioned problems of the present invention are solved by the following configuration. (1) a conveying roller for conveying a recording medium; a measuring unit that reads the outer shape of the recording medium conveyed by the conveying rollers at predetermined intervals, the outer shape of the recording medium being conveyed by the conveying rollers at each timing when the recording medium enters the conveying rollers, and measures read data at predetermined intervals from the same plane side of the recording medium; From the read data of the recording medium at the predetermined intervals read at each timing of entering the conveying roller, a leading edge side read image is formed for each of the first and second scanning periods, and a read interval length is calculated from a difference between the read timings of the leading edge side read images; The calculated reading Interval length and base a calculation unit that calculates a difference from the sub-interval length; a detection unit that detects unevenness in the conveying speed of the recording medium by the conveying roller based on each deviation value calculated by the difference; An image forming apparatus comprising:

[0008] (2) The image forming apparatus according to (1) above, further comprising a rotation control section that controls the rotation of the transport roller to correct the transport speed unevenness detected by the detection section.

[0009] (3) An image forming apparatus as described in (2) above, wherein the measurement unit is composed of two sensors that measure the passage of the leading or trailing end of the recording medium, and the rotation control unit controls the time it takes for the leading or trailing end of the recording medium to pass between the two sensors to be equal regardless of the angle of the conveying roller.

[0010] (4) An image forming apparatus as described in (2) above, wherein the measurement unit is a line sensor installed in the transport direction of the recording medium, and the rotation control unit controls the speed at which the front or rear end of the recording medium passes through the line sensor to be uniform regardless of the angle of the transport roller.

[0011] (5) An image forming apparatus as described in (2) above, wherein the measurement unit is two line sensors installed at an angle to the transport direction of the recording medium, and the rotation control unit controls the rotation so that the time it takes for the front or rear end of the recording medium to pass through the two line sensors is equal, regardless of the angle of the transport roller, and the speed at which the front or rear end of the recording medium passes through the line sensors is equal.

[0013] ( 6 ) The image forming apparatus according to any one of (2) to (5) above, further comprising an image forming unit that forms an image on the recording medium, and the rotation control unit controls the rotation of the conveying roller so as to correct the unevenness in the conveying speed detected by the detection unit.

[0014] ( 7 ) The image forming apparatus according to any one of (2) to (5) above, further comprising a reading unit that reads the recording medium, and the rotation control unit controls the rotation of the conveying roller so as to correct the unevenness in the conveying speed detected by the detection unit.

[0015] ( 8 2) The image forming apparatus according to (1) or (2) above, wherein the measuring unit is a photosensor that reads the recording medium by irradiating it with a small diameter spot light.

[0016] (9) An image forming method for an image forming apparatus having a conveying roller for conveying a recording medium, comprising: a step in which measurement units are arranged in parallel at predetermined intervals in a conveying direction in which the recording medium is conveyed, read the outer shape of the recording medium conveyed by the conveying rollers at each timing when the recording medium enters the conveying rollers, and measure read data at predetermined intervals from the same plane side of the recording medium; a calculation unit that calculates the predetermined interval from the read data of the recording medium read at each timing of entering the conveyance roller; a leading edge side read image is formed for each of the first and second scanning periods, and a read interval length is calculated from a difference between the read timings of the leading edge side read images; The calculated reading Interval length and base Calculating a difference between the sub-interval length; a detecting unit detecting unevenness in the conveying speed of the recording medium by the conveying roller based on each deviation value calculated by the difference; An image forming method comprising: [Effects of the Invention]

[0017] The present invention provides an image forming apparatus and an image forming method that can eliminate unevenness in the conveyance speed of a recording medium without printing an image on the recording medium. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 3] 2 is a side view showing first and second paper reading units disposed between first and second transport rollers of the image forming apparatus according to the present embodiment, and a paper transported by the first transport rollers. FIG. [Figure 4] FIG. 2 is a plan view of the first and second paper reading units. [Figure 5] 10 is a plan view showing the same read interval length of the first and second front end side read images for each of different timings T1 to T4 when the paper enters the first conveyance roller. FIG. [Figure 6] 10 is a side view showing a state in which the rotation axis of the first conveyor roller is deviated from the center of the roller. FIG. [Figure 7] 10 is a plan view showing different read interval lengths of the first and second front end side read images for each of different timings T1 to T4 at which the paper enters the first transport roller. FIG. [Figure 8] 6 is a flowchart illustrating an operation of eliminating unevenness in the sheet conveying speed by the image forming apparatus according to the present embodiment. [Figure 9] FIG. 10 is a side view showing a sheet being transported by a second transport roller. [Figure 10] 10 is a plan view showing the same read interval length of the first and second rear end side read images for each of different timings T11 to T14 when the paper enters the second conveyance roller. FIG. [Figure 11] 10 is a side view showing a state in which the rotation axis of the second conveyor roller is deviated from the center of the roller. FIG. [Figure 12] 10 is a plan view showing different read interval lengths of the first and second rear end side read images for each of different timings T11 to T14 at which the paper enters the second conveyance roller. FIG. [Figure 13] 10 is a plan view showing different read interval lengths of the first and second front end side read images for each of different timings T1 to T4 at which the paper enters the first transport roller when photosensors are used in the first and second paper reading units. FIG. [Figure 14] 10 is a plan view showing different read interval lengths of the first and second rear end side read images for different timings T11 to T14 at which the paper enters the second transport roller when photosensors are used in the first and second paper reading units. FIG. [Figure 15] 10 is a side view showing one paper reading unit arranged in the conveying direction Y1 in place of the first and second paper reading units. FIG. [Figure 16] FIG. 2 is a plan view showing the arrangement of one paper reading unit. [Figure 17] FIG. 10 is a plan view showing a parallelogram image read by one paper reading unit when a paper is transported by first and second transport rollers at timings T1 to T4. [Figure 18] FIG. 2 is a first plan view for explaining a paper reading process by one paper reading unit. [Figure 19] FIG. 10 is a second plan view for explaining a paper reading process by one paper reading unit. [Figure 20] FIG. 10 is a third plan view for explaining a paper reading process by one paper reading unit. [Figure 21] 10 is a side view showing a state in which a paper is read by one paper reading unit in a configuration in which the rotation axes of the first and second transport rollers are offset from the centers of the rollers. FIG. [Figure 22]22 is a plan view showing a parallelogram image obtained by reading with one paper reading unit when a paper is transported at each of timings T1 to T4 in the configuration of FIG. 21. FIG. [Figure 23] 10 is a side view showing a configuration in which the first and second paper reading units are arranged parallel to each other and at an angle. FIG. [Figure 24] FIG. 10 is a plan view showing a configuration in which first and second paper reading units are arranged parallel to each other and at an angle. [Figure 25] 24 is a plan view showing a front end side image of a parallelogram image obtained by reading at each of timings T1 to T4 in the first and second paper reading units shown in FIG. 23, all of which have the same reading interval length. FIG. [Figure 26] 24 is a side view showing a state in which the rotation axis of the first transport roller is deviated from the center of the roller in the arrangement of the first and second paper reading units shown in FIG. 23. FIG. [Figure 27] 27 is a plan view showing front-end side images of parallelogram images read at timings T1 to T4 by the first and second paper reading units shown in FIG. 26 with different read interval lengths. FIG. [Figure 28] 24 is a side view showing a state in which the rotation axis of the second conveying roller is deviated from the center of the roller in the arrangement of the first and second paper reading units shown in FIG. 23. FIG. [Figure 29] 29 is a plan view showing a rear end side image of a parallelogram image read at timings T1 to T4 by the first and second paper reading units shown in FIG. 28, with different read interval lengths. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in all the drawings in this specification, components having corresponding functions are designated by the same reference numerals, and their description will be omitted as appropriate. <Configuration of the first embodiment> FIG. 1 is a diagram schematically illustrating the overall configuration of an image forming apparatus 1 according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of the hardware configuration of the image forming apparatus 1. The image forming apparatus 1 functions as a sheet conveying device that conveys a sheet. However, in this embodiment, the sheet is assumed to be a sheet of paper 2 shown in FIG. 3. The sheet of paper 2 constitutes a recording medium as claimed.

[0020] A feature of the first embodiment is that, in the image forming apparatus 1, as shown in Fig. 3, measuring units 18a and 18b disposed at a distance between the first and second conveyance rollers 32 and 33 detect the planar shape of the paper 2 conveyed in the conveyance direction (arrow Y1) by the first conveyance roller 32, and detect unevenness in the conveyance speed. To eliminate the detected unevenness in the conveyance speed, the rotation of a motor 32m (Fig. 2) that rotates the first conveyance roller 32 is variably controlled. Note that the conveyance direction Y1 is a sub-scanning direction that is perpendicular to the main scanning direction in which the printed image on the paper 2 is read and scanned in the image forming apparatus 1.

[0021] First, the standard configuration of the image forming apparatus 1 will be described. The image forming apparatus 1 shown in FIG. 1 employs an intermediate transfer method that utilizes electrophotographic process technology. The image forming apparatus 1 primarily transfers toner images of each color, Y (yellow), M (magenta), C (cyan), and K (black), formed on photosensitive drums 23Y, 23M, 23C, and 23K, onto an intermediate transfer belt 26. The image forming apparatus 1 forms a toner image by superimposing the four color toner images on the intermediate transfer belt 26 and then secondary transferring the images onto a sheet.

[0022] As shown in FIG. 2, the image forming apparatus 1 mainly includes a control unit 10, an image reading unit 11, an operation display unit 12, an image processing unit 13, an image forming unit 14, a conveying unit 15, and the like.

[0023] The control unit 10 includes a CPU (Central Processing Unit) 10a, a ROM (Read Only Memory) 10b, and a RAM (Random Access Memory) 10c. The CPU 10a reads a program corresponding to the processing content from the ROM 10b, loads it into the RAM 10c, and controls each component of the image forming apparatus 1 in cooperation with the loaded program. At this time, various data stored in a storage unit 16 is referenced. The storage unit 16 is configured, for example, with a non-volatile semiconductor memory (such as a flash memory) or a hard disk drive.

[0024] The control unit 10 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 17. The control unit 10 receives, for example, image data transmitted from an external device, and forms a toner image on a sheet based on this image data (input image data). The communication unit 17 is configured, for example, by a communication control card such as a LAN card.

[0025] The image forming section 14 includes an intermediate transfer unit 19 and a fixing device 5. The intermediate transfer unit 19 forms a toner image on the intermediate transfer belt 26 shown in FIG. 1 and transfers the formed toner image onto a sheet. The fixing device 5 fixes the toner image onto the sheet by applying heat and pressure to the sheet onto which the toner image has been secondarily transferred, at a fixing nip.

[0026] The conveying section 15 includes all rollers such as the conveying rollers 32 and 33 shown in FIG. The control unit 10 controls the conveyance of the sheet along a conveyance path 43 in a conveyance direction Y1 shown in Figure 1 by driving the conveyance unit 15. The control unit 10 controls each component included in the image forming apparatus 1.

[0027] The image reading unit 11 includes an ADF (Auto Document Feeder) device and a scanner device. The ADF device transports one or more documents placed on a document tray using a transport mechanism and sends them to the scanner device. The scanner device optically scans the documents transported from the ADF device onto a contact glass or documents placed on the contact glass. The scanner device focuses reflected light from the documents onto the light receiving surface of a CCD (Charge Coupled Device) sensor to read the document image. The image reading unit 11 generates input image data based on the reading results by the scanner device. The image processing unit 13 performs predetermined image processing on this input image data.

[0028] The operation display unit 12 is configured, for example, with a liquid crystal display (LCD) with a touch panel, and includes a display unit 121 and an operation unit 122. The display unit 121 displays various operation screens, image status displays, operation statuses of various functions, etc. under the control of the control unit 10. The operation unit 122 includes various operation keys such as a numeric keypad and a start key. The operation unit 122 accepts various input operations by the user and outputs operation signals to the control unit 10.

[0029] The image processing unit 13 performs digital image processing according to initial settings or user settings on the input image data from the image reading unit 11. The image forming unit 14 is controlled based on the image data that has been subjected to digital image processing.

[0030] 1, transfer units 20Y, 20M, 20C, and 20K, intermediate transfer unit 19 (FIG. 2), and fixing device 5 constitute image forming section 14 (FIG. 2). Transfer units 20Y, 20M, 20C, and 20K transfer Y, M, C, and K components of toner based on input image data. Since transfer units 20Y to 20K have the same configuration, transfer unit 20Y for Y component will be described as a representative.

[0031] The transfer unit 20Y includes an exposure device 21Y, a developing device 22Y, a photosensitive drum 23Y, a charging device 24Y, and a drum cleaning device 25Y. The transfer unit 20Y forms a Y component toner image on the intermediate transfer belt .

[0032] The photosensitive drum 23Y is a negatively charged organic photoconductor (OPC) in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the circumferential surface of a conductive cylinder made of aluminum (e.g., an aluminum tube).

[0033] The control unit 10 supplies a driving current to a driving motor (not shown) of the photosensitive drum 23Y, thereby rotating the photosensitive drum 23Y at a constant peripheral speed.

[0034] The charging device 24Y uniformly charges the photoconductive surface of the photoreceptor drum 23Y to a negative polarity. The exposure device 21Y is configured, for example, with a semiconductor laser, and irradiates the photoreceptor drum 23Y with laser light corresponding to an image of each color component. Positive charges are generated in the charge generation layer of the photoreceptor drum 23Y and transported to the surface of the charge transport layer, thereby neutralizing the surface charge (negative charge) of the photoreceptor drum 23Y. An electrostatic latent image of each color component is formed on the surface of the photoreceptor drum 23Y due to the potential difference with the surrounding area.

[0035] The developing device 22Y is, for example, a two-component developing device. The developing device 22Y forms a toner image by depositing toner of each color component on the surface of the photosensitive drum 23Y. The toner image is formed by visualizing the electrostatic latent image.

[0036] The drum cleaning device 25Y has a drum cleaning blade or the like as a cleaning member that is in sliding contact with the surface of the photosensitive drum 23Y. The drum cleaning device 25Y removes toner remaining on the surface of the photosensitive drum 23Y after the primary transfer using the drum cleaning blade.

[0037] The intermediate transfer belt 26, primary transfer rollers 231Y, 231M, 231C, and 231K, backup roller 27, multiple support rollers 29, drive roller 28, secondary transfer roller 34, and belt cleaning device 261 constitute an intermediate transfer unit 19 (see FIG. 2).

[0038] The intermediate transfer belt 26 is an endless belt that is looped and stretched around multiple support rollers 29, a backup roller 27, a drive roller 28, and primary transfer rollers 231Y, 231M, 231C, and 231K. The multiple support rollers 29 are driven rollers. As the drive roller 28 rotates, the intermediate transfer belt 26 runs at a constant speed in the clockwise direction in the drawing.

[0039] The primary transfer roller 231Y faces the photosensitive drum 23Y and is disposed on the inner circumferential surface side of the intermediate transfer belt 26. The primary transfer roller 231Y is pressed against the photosensitive drum 23Y to form a primary transfer nip, which transfers the toner image from the photosensitive drum 23Y to the intermediate transfer belt 26. The primary transfer rollers 231M, 231C, and 231K similarly transfer the toner images of the respective color components to the intermediate transfer belt 26.

[0040] The secondary transfer roller 34 is disposed on the outer peripheral surface side of the intermediate transfer belt 26, facing the backup roller 27. The backup roller 27 is disposed downstream of the drive roller 28 in the belt running direction. The secondary transfer roller 34 and the backup roller 27 sandwich the intermediate transfer belt 26, and a secondary transfer nip is formed when the two are pressed against each other. The secondary transfer nip transfers a toner image from the intermediate transfer belt 26 to a sheet.

[0041] The toner images on the photosensitive drums 23Y, 23M, 23C, and 23K of each color are sequentially superimposed and primarily transferred onto the intermediate transfer belt 26. Thereafter, when the sheet passes through the secondary transfer nip, the toner images on the intermediate transfer belt 26 are secondarily transferred onto the sheet. The sheet onto which the toner images have been transferred is transported toward the fixing device 5. A belt cleaning device 261 removes residual toner remaining on the surface of the intermediate transfer belt 26 after the secondary transfer.

[0042] The fixing device 5 is disposed downstream of the secondary transfer nip and holds and transports the sheet. The fixing device 5 heats and presses the sheet onto which the toner image has been secondarily transferred at the fixing nip, thereby fixing the toner image to the sheet. The fixing device 5 is also provided with an air separation unit (not shown) that blows air to separate the sheet from the fixing surface side member.

[0043] The transport section 15 includes a paper feed section, a paper discharge section, and a transport path 43. The transport path 43 includes a pair of transport rollers 32, 33, a roller 38, and a paper discharge roller 35, which are multiple transport rollers.

[0044] Paper feed tray unit 31 constituting the paper feed section stores paper sheets 2 (e.g., A4 paper sheets) that are sheets identified based on basis weight, size, etc. The paper sheets 2 stored in paper feed tray units 31a to 31c are sent out one by one from the top, transported to fixing device 5 via transport path 43, and discharged from the discharge port of the paper discharge section by paper discharge rollers 35, as shown by arrow Y2.

[0045] <Characteristic configuration of the first embodiment> Next, the characteristic configuration of the image forming apparatus 1 of the first embodiment will be described. 2, the image forming apparatus 1 includes measuring units 18a and 18b, motors 32m and 33m, a reading interval calculation unit 10e, a conveying speed unevenness detection unit 10f, and a rotation control unit 10g, which are configured in the control unit 10. The reading interval calculation unit 10e is also referred to as the calculation unit 10e, and the conveying speed unevenness detection unit 10f is also referred to as the detection unit 10f.

[0046] The measurement units 18a and 18b are configured using a line sensor such as a CIS (Contact Image Sensor) or a CCD, and are disposed between conveyance rollers 32 and 33 of the same diameter, as shown in FIG. 1 or 3. The conveyance roller 32 is driven to rotate by a motor 32m, and the conveyance roller 33 is driven to rotate by a motor 33m, and conveys the paper 2 horizontally in the conveyance direction Y1. The rotational drive is controlled by a rotation control unit 10g. These motors 32m and 33m are stepping motors that can detect their current angles. By knowing the current angles of the motors 32m and 33m, the angles of the conveyance rollers 32 and 33 can be determined.

[0047] Note that measurement unit 18a is also referred to as first measurement unit 18a, and measurement unit 18b is also referred to as second measurement unit 18b. Motor 32m is also referred to as first motor 32m, and motor 33m is also referred to as second motor 33m. Conveyor roller 32 is also referred to as first conveyor roller 32, and conveyor roller 33 is also referred to as second conveyor roller 33.

[0048] As shown in the side view of FIG. 3, the first and second measurement units 18a, 18b have an elongated pillar shape (see FIG. 4) and are arranged parallel to each other and spaced apart by a distance L1 in the conveyance direction Y1 above the first and second conveyance rollers 32, 33. As shown in the plan view of FIG. 4, each measurement unit 18a, 18b is arranged so that the longitudinal direction of the pillar shape is perpendicular to the conveyance direction Y1. Furthermore, each measurement unit 18a, 18b is arranged parallel to the conveyed paper 2 at a fixed interval above and below (see FIG. 3), with the reading light irradiation surface facing the paper 2. This arrangement allows the reading light of each measurement unit 18a, 18b to be irradiated perpendicularly to the plane of the paper 2.

[0049] By detecting the angle of the motor 32m, the control unit 10 can know which of the outer peripheries 321 to 324 of the transport roller 32 is transporting the paper 2. When the center of the transport roller 32 coincides with the rotation axis as shown in Figure 3, rotation unevenness does not occur. However, when the center of the transport roller 32 is misaligned with the rotation axis and is eccentric as shown in Figure 6 described below, rotation unevenness according to the angle of the transport roller 32 occurs, as shown in Figure 7.

[0050] 6, the speed of the sheet 2 is slower than the reference speed when conveyed by the outer periphery 324 of the eccentric conveying roller 32, and is faster than the reference speed when conveyed by the outer periphery 322. There is a difference of approximately half a rotation of the roller between the timing when the sheet 2 enters the conveying roller 32 and the timing when the leading edge of the sheet 2 reaches the first and second measurement units 18a and 18b.

[0051] Furthermore, when the leading edge of the paper 2 enters the outer periphery 324 of the transport roller 32, the paper is transported slower than the reference speed. When the leading edge of the paper 2 approaches the first and second measurement units 18a, 18b, the transport roller 32 has rotated approximately half a revolution (the position of the outer periphery 322). At this time, the paper 2 is transported on the outer periphery 322, so it is transported faster than the reference speed. This is because the midpoint between the first and second measurement units 18a, 18b is located at a position (the position of the outer periphery 322) that is rotated half a revolution of the roller from the position where the paper 2 is sandwiched between the transport rollers 32 and transported.

[0052] 3, the distance L1 between the measuring units 18a and 18b in the conveying direction is equal to a length L2 that is ¼ of the outer periphery of the conveying roller 32. However, the distance L1 may be a length other than L2.

[0053] The first and second measurement units 18a and 18b read the leading edge side shape including the leading edge of the paper 2 transported in the transport direction Y1 by the rotation of the first transport roller 32 and the angle of the transport roller 32 when the leading edge passes, and output the leading edge side read data obtained by this reading to the reading interval calculation unit 10e shown in Fig. 2. However, the leading edge side read data read by the first measurement unit 18a is also referred to as first leading edge side read data, and the leading edge side read data read by the second measurement unit 18b is also referred to as second leading edge side read data.

[0054] FIG. 5 is a plan view showing the same read interval length of the first and second leading edge side read images for each of different timings T1 to T4 at which the paper enters the first conveyor roller 32. In FIG. The reading interval calculation unit 10e first forms first and second leading edge side read images 2a and 2b shown in FIG. 5, in which the outline of the paper 2 can be detected for each of the first and second leading edge side read data. Each leading edge side read image 2a and 2b includes the leading edge of the paper 2. The first and second leading edge side read images 2a and 2b indicated by arrow T1 in FIG. 5 are shown in reading order along the time axis (arrow t). That is, the first leading edge side read image 2a from the first read is shown overlapped by the second leading edge side read image 2b from the second read. The first leading edge side read image 2a has an image of the leading edge 2a1 of the paper 2. The second leading edge side read image 2b has an image of the leading edge 2b1 of the paper 2. The calculation unit 10e also detects the outline of the paper 2 from the first and second leading edge side read images 2a and 2b to calculate the size of the paper 2.

[0055] Arrows T1, T2, T3, and T4 shown in Fig. 5 indicate the timing when the paper 2 enters the first conveyance roller 32. That is, arrow T1 indicates the first leading edge side read image 2a and the second leading edge side read image 2b at timing T1 when the paper 2 enters the outer periphery 321. Arrow T2 indicates the first leading edge side read image 2a and the second leading edge side read image 2b at timing T2 when the paper 2 enters the outer periphery 322. Arrow T3 indicates the first leading edge side read image 2a and the second leading edge side read image 2b at timing T3 when the paper 2 enters the outer periphery 323. Arrow T4 indicates the first leading edge side read image 2a and the second leading edge side read image 2b at timing T4 when the paper 2 enters the outer periphery 324.

[0056] Furthermore, the leading edge side scanned images 2a, 2b at each of the timings T1 to T4 are expressed in the same shape, and the symbols for the leading edge side scanned images 2a, 2b at timing T1 are shown as representative. In this case, it is assumed that the first conveyor roller 32 (FIG. 3) rotates at a constant speed, and the first and second leading edge side scanned images 2a, 2b are in the same state regardless of the timing T1 to T4 at which the paper 2 enters. However, it is assumed that the rotation speed of the first conveyor roller 32 is a predetermined reference speed.

[0057] Therefore, the first and second measuring units 18a and 18b shown in FIG. 2 output the leading end side read data at each of the different timings T1 to T4 to the read interval calculation unit 10e.

[0058] Next, the calculation unit 10e calculates the length of the reading interval (also called the reading interval length G) G1 from the difference between the reading timing of the front end 2a1 of the first front end side reading image 2a and the reading timing of the front end 2b1 of the second front end side reading image 2b for each of the timings T1 to T4.

[0059] Furthermore, the calculation unit 10e calculates the difference between each of the read interval lengths G1 for each of the timings T1 to T4 and the reference interval length G1, and stores and saves each deviation amount (also called deviation value) resulting from this difference in a storage unit (not shown). In the example of Fig. 5, the read interval lengths G1 for the first and second front-end side read images 2a and 2b for each of the timings T1 to T4 are the same as the reference read interval G1, so the deviation value is "0 mm." However, the reference interval length G1 is the average value of the read interval lengths G for all of the timings T1 to T4.

[0060] If the deviation values ​​of the read interval length G1 for each of the stored timings T1 to T4 are the same, in other words, if they are the same as the reference interval length G1, the detection unit 10f detects that there is no unevenness in the conveyance speed of the paper 2. The case where the deviation values ​​are different will be described later.

[0061] When the detection unit 10f detects that there is no unevenness in the conveying speed, the rotation control unit 10g continues to control the reference speed of the first conveying roller 32.

[0062] 6, suppose that the rotation axis 32j of the first conveyor roller 32 is misaligned from the center of the circular first conveyor roller 32. In this case, unevenness occurs in the speed at which the paper 2 is conveyed by the first conveyor roller 32. Therefore, depending on the timings T1 to T4 at which the paper 2 enters the first conveyor roller 32, the reading interval length G related to the timing at which the paper is read by the first and second measurement units 18a and 18b differs, as shown in FIG.

[0063] 7, at times T1 and T3, the reading interval G1 is the same as the reference interval G1 as described above. On the other hand, at time T2, the reading interval G2 is shorter than the reference interval G1; in other words, it is shorter than the reading interval G1 at time T1. This is because, due to eccentricity of the first conveying roller 32, the conveying speed when the paper 2 is conveyed on the outer periphery 322 is faster than the reference speed; in other words, it is faster at time T2 than at time T1. In this case, the difference between the reading timing of the leading edge 2a1 of the first leading edge side read image 2a at time T2 and the reading timing of the leading edge 2b1 of the second leading edge side read image 2b is shorter than the difference at time T1.

[0064] Conversely, at timing T4, the reading interval G3 is longer than the reference interval G1, in other words, longer than the reading interval G1 at timing T1. This is because, due to eccentricity of the first conveying roller 32, the conveying speed when conveying the paper 2 on the outer periphery 324 is slower than the reference speed, in other words, slower at timing T4 than at timing T1. In this case, the difference at timing T4 is longer than the difference at timing T1.

[0065] Under these conditions, the first and second measurement units 18a, 18b read the shape of the leading edge of the paper 2 being transported by the first transport roller 32 at each of the timings T1 to T4, and output the first and second leading edge read data at each of the timings T1 to T4 to the calculation unit 10e.

[0066] The calculation unit 10e forms first and second leading edge side read images 2a and 2b shown at each of the timings T1 to T4 in FIG. 7 from the first and second leading edge side read data at each of the timings T1 to T4, from which the contour of the paper 2 can be detected.

[0067] Next, the calculation unit 10e calculates the reading interval lengths G1, G2, G1, and G3 (see Figure 7) from the difference between the reading timing of the front end 2a1 of the first front end side reading image 2a and the reading timing of the front end 2b1 of the second front end side reading image 2b for each of the timings T1 to T4.

[0068] The calculation unit 10e calculates the difference between each of the read interval lengths G1, G2, G1, and G3 for each of the timings T1 to T4 and the reference interval length G1, and stores the deviation amounts (also called deviation values) due to these differences in a storage unit (not shown).The stored deviation values ​​of the read interval lengths G1, G2, G1, and G3 for each of the timings T1 to T4 are output to the detection unit 10f and the rotation control unit 10g.

[0069] However, if the reading interval length G1 at timing T1 is the same as the reference interval length G1, the deviation value will be "0 mm." If the reading interval length G2 at timing T2 is different from the reference interval length G1, and G2 is, for example, 1 mm shorter than G1, the deviation value will be "-1 mm." If the reading interval length G1 at timing T3 is the same as the reference interval length G1, the deviation value will be "0 mm." If the reading interval length G3 at timing T4 is different from the reference interval length G1, and G3 is, for example, 1 mm longer than G1, the deviation value will be "+1 mm." A negative deviation value from the reference interval length G1 indicates that the conveying speed of the paper 2 by the first conveying roller 32 is faster than the reference speed, and a positive value indicates that it is slower than the reference speed.

[0070] If the deviation values ​​of the reading interval lengths G1, G2, G1, and G3 stored for each of the timings T1 to T4 are different (or not zero), the detection unit 10f detects that the conveying speed of the paper 2 by the first conveying roller 32 is not constant and that there is unevenness in the conveying speed of the paper 2, and outputs this to the rotation control unit 10g. In this example, the detection unit 10f detects that the deviation values ​​are the same (or zero) at timings T1 and T3, but different (or not zero) at timings T2 and T4, and therefore detects that there is unevenness in the conveying speed.

[0071] However, if the deviation value for the timing T1 is "0 mm" and the deviation value for the timing T2 is "-1 mm," then the timing at which the paper 2 next enters the first conveyor roller 32 is the intermediate timing between the timings T1 and T2. In this case, the calculation unit 10e divides the difference between the deviation value for the timing T1 of "0 mm" and the deviation value for the timing T2 of "-1 mm" by 2, and performs an interpolation calculation to set the resulting "-0.5 mm" as the deviation value for the intermediate timing.

[0072] When data indicating conveyance speed unevenness is input, the rotation control unit 10g variably controls the rotation speed of the motor 32m that rotates the first conveyor roller 32 so that the deviation values ​​of the reading interval lengths G1, G2, G3, and G4 for the stored timings T1 to T4 become "0 mm." For example, if the deviation value for timing T2 is "-1 mm," the rotation speed of the first conveyor roller 32 is faster than the reference speed by an amount corresponding to the deviation value "-1 mm." Therefore, the rotation control unit 10g controls the rotation speed of the motor 32m so that the rotation speed of the first conveyor roller 32 becomes slower by an amount corresponding to the deviation value "+1 mm" that is required to change the deviation value "-1 mm" to "0 mm." This control causes the rotation speed of the first conveyor roller 32 to become the reference speed, so that the deviation value for timing T2 becomes "0 mm" (see FIG. 5).

[0073] Similarly, when the deviation value for timing T4 is "+1 mm," rotation control unit 10g controls the rotation speed of motor 32m so that the rotation speed of first conveyor roller 32 is increased by an amount corresponding to the deviation value "-1 mm" required to change the deviation value "+1 mm" to "0 mm." This control causes the conveyance speed of paper 2 by first conveyor roller 32 to become the reference speed, so the deviation value for timing T4 becomes "0 mm" (see FIG. 5). In other words, rotation control unit 10g controls conveyor roller 32 so that the time it takes for the leading edge or trailing edge of paper 2 to pass between two measurement units 18a, 18b is equal, regardless of the angle of conveyor roller 32.

[0074] <Operation of the first embodiment> Next, an operation for eliminating unevenness in the conveying speed of the paper 2 by the image forming apparatus 1 according to this embodiment will be described with reference to the flowchart shown in FIG.

[0075] As a prerequisite, it is assumed that the rotation axis 32j of the first conveyor roller 32 is offset from the center of the first conveyor roller 32, as shown in FIG.

[0076] 8, the paper 2 is conveyed by being thrust into the first conveying rollers 32 at each of the times T1 to T4, and the shape of the leading edge of the paper 2 conveyed at each of the times T1 to T4 is read by the first and second measuring units 18a and 18b. The first and second leading edge read data obtained by this reading at each of the times T1 to T4 are output to the reading interval calculation unit 10e.

[0077] In step S2, the calculation unit 10e forms the first and second leading edge side read images 2a and 2b shown in FIG. 7 from the first and second leading edge side read data at each of the timings T1 to T4.

[0078] In step S3, the calculation unit 10e calculates the reading interval lengths G1, G2, G1, and G3 from the difference between the reading timing of the leading edge 2a1 of the first leading edge side read image 2a and the reading timing of the leading edge 2b1 of the second leading edge side read image 2b for each of the timings T1 to T4, as shown in Fig. 7. In this case, the reading interval lengths G1 and G1 for the timings T1 and T3 are the same as the reference interval length G1. The reading interval length G2 for the timing T2 is shorter than the reference interval length G1. The reading interval length G3 for the timing T4 is longer than the reference interval length G1.

[0079] Next, in step S4, the calculation unit 10e calculates the difference between each of the read interval lengths G1, G2, G3, and G4 for each of the timings T1 to T4 and the reference interval length G1, and stores the deviation values ​​resulting from these differences in a storage unit (not shown). For example, the deviation values ​​for timings T1 and T3 are assumed to be "0 mm," the deviation value for timing T2 is assumed to be "-1 mm," and the deviation value for timing T4 is assumed to be "+1 mm." The detection unit 10f then determines whether the stored deviation values ​​are the same.

[0080] If the detection unit 10f determines that the stored deviation values ​​are the same (Yes), then in step S5 the detection unit 10f detects that there is no unevenness in the conveying speed of the paper 2 conveyed by the first conveying rollers 32. On the other hand, if the detection unit 10f determines that the deviation values ​​are different (No), then in step S6 the detection unit 10f detects that there is unevenness in the conveying speed of the paper 2 conveyed by the first conveying rollers 32, and outputs this to the rotation control unit 10g.

[0081] In step S7, the calculation unit 10e outputs deviation values ​​due to the differences between the reading interval lengths G1, G2, G1, and G3 for the timings T1 to T4 and the reference interval length G1 to the detection unit 10f. In step S8, the detection unit 10f outputs data with conveying speed unevenness and the deviation values ​​for each of the timings T1 to T4 to the rotation control unit 10g.

[0082] In step S9, the rotation control unit 10g variably controls the rotation speed of the motor 32m that rotates the first conveyor roller 32 so that the deviation value for each of the timings T1 to T4 becomes "0 mm." That is, based on the deviation value "-1 mm" for timing T2, the rotation control unit 10g controls the rotation speed of the motor 32m so that the rotation speed of the first conveyor roller 32 becomes slower by an amount corresponding to the deviation value "+1 mm." Through this control, the rotation speed of the first conveyor roller 32 becomes the reference speed, and the deviation value for timing T2 becomes "0 mm."

[0083] Furthermore, based on the deviation value "+1 mm" for timing T4, the rotation control unit 10g controls the rotation speed of the motor 32m so that the rotation speed of the first conveyor roller 32 becomes faster by an amount corresponding to the deviation value "-1 mm." Through this control, the conveyance speed of the paper 2 by the first conveyor roller 32 becomes the reference speed, and the deviation value for timing T4 becomes "0 mm."

[0084] According to the image forming apparatus 1 of the first embodiment described above, it is possible to read the shape of the leading edge side of the paper 2 and detect the existence of unevenness in the conveying speed of the paper 2 conveyed by the first conveying roller 32, which is the speed at which the paper 2 is conveyed deviating from the reference speed. Furthermore, it is possible to variably control the rotation speed of the first conveying roller 32 so as to eliminate unevenness in the conveying speed. In other words, it is possible to perform control to eliminate unevenness in the conveying speed of the paper 2 without printing an image on the paper 2.

[0085] <Characteristic configuration of the second embodiment> Next, a characteristic configuration of the image forming apparatus 1 according to the second embodiment will be described.

[0086] 9, in the image forming apparatus 1, first and second measuring units 18a and 18b between the first and second conveying rollers 32 and 33 detect the planar shape of the sheet 2 conveyed in the conveying direction Y1 by the second conveying roller 33, and detect unevenness in the conveying speed. To eliminate the detected unevenness in the conveying speed, the rotation of the motor 33m (FIG. 2) that rotates the second conveying roller 33 is variably controlled.

[0087] The characteristic configuration of the second embodiment, like the first embodiment, includes measurement units 18a and 18b shown in FIG. 2, motors 32m and 33m, a reading interval calculation unit 10e configured in the control unit 10, a conveying speed unevenness detection unit 10f, and a rotation control unit 10g.

[0088] The first and second measurement units 18a and 18b read the shape of the rear end side, including the rear end, of the paper 2 being transported in the transport direction Y1 by the rotation of the first transport roller 32, and output the rear end side read data obtained by this reading to the calculation unit 10e shown in Fig. 2. However, the rear end side read data read by the first measurement unit 18a is also referred to as first rear end side read data, and the rear end side read data read by the second measurement unit 18b is also referred to as second rear end side read data.

[0089] The calculation unit 10e first forms first and second rear end side read images 2c and 2d shown in FIG. 10, which enable detection of the contour of the paper 2 for each of the first and second rear end side read data. Each of the rear end side read images 2c and 2d includes the rear end side of the paper 2. The first and second rear end side read images 2c and 2d indicated by arrow T11 in FIG. 10 are shown in the order of reading along the time axis (arrow t). That is, the first rear end side read image 2c obtained by the first read hides the second rear end side read image 2d obtained by the next read, excluding its rear end side. The first rear end side read image 2c has an image of the rear end 2c2 of the paper 2. The second rear end side read image 2d has an image of the rear end 2d2 of the paper 2.

[0090] 10 indicate the timing when the paper 2 enters the second conveyance roller 33. That is, arrow T11 indicates the first rear edge side read image 2c and the second rear edge side read image 2d at timing T11 when the paper 2 enters the outer periphery 331. Arrow T12 indicates the first rear edge side read image 2c and the second rear edge side read image 2d at timing T2 when the paper 2 enters the outer periphery 332. Arrow T13 indicates the first rear edge side read image 2c and the second rear edge side read image 2d at timing T13 when the paper 2 enters the outer periphery 333. Arrow T14 indicates the first rear edge side read image 2c and the second rear edge side read image 2d at timing T14 when the paper 2 enters the outer periphery 334.

[0091] Furthermore, the rear end side scanned images 2c and 2d at each of the timings T11 to T14 are expressed in the same shape, and the symbols for the rear end side scanned images 2c and 2d at timing T11 are shown as representative. In this case, it is assumed that the second conveyor roller 33 (FIG. 9) rotates at a constant speed, and the first and second rear end side scanned images 2c and 2d are in the same state regardless of the timing T11 to T14 at which the paper 2 enters. However, the constant rotation speed of the second conveyor roller 33 is assumed to be a predetermined reference speed.

[0092] Therefore, the first and second measuring units 18a and 18b shown in FIG. 2 output the rear end side read data at each of the different timings T11 to T14 to the read interval calculation unit 10e.

[0093] Next, the calculation unit 10e calculates the length of the reading interval (also called the reading interval length G) G11 from the difference between the reading timing of the rear end 2c2 of the first rear end side reading image 2c and the reading timing of the rear end 2d2 of the second rear end side reading image 2d for each of the timings T11 to T14.

[0094] Furthermore, the calculation unit 10e calculates the difference between each of the read interval lengths G11 for each of the timings T11 to T14 and the reference interval length G11, and stores and saves each deviation amount (deviation value) resulting from this difference in a storage unit (not shown). In the example of Fig. 10, the read interval lengths G11 for the first and second rear end side read images 2c and 2d for each of the timings T11 to T14 are the same as the reference read interval G11, so the deviation value is "0 mm." However, the reference interval length G11 is the average value of the read interval lengths G for all of the timings T11 to T14.

[0095] If the deviation values ​​of the read interval length G11 for each of the stored timings T11 to T14 are the same, in other words, if they are the same as the reference interval length G11, the detection unit 10f detects that there is no unevenness in the conveyance speed of the paper 2. The case where the deviation values ​​are different will be described later.

[0096] When the detection unit 10f detects that there is no unevenness in the conveying speed, the rotation control unit 10g continues to control the reference speed of the second conveying roller 33.

[0097] 11, suppose that the rotation axis 33j of the second conveyor roller 33 is misaligned from the center of the circular second conveyor roller 33. In this case, unevenness occurs in the speed at which the paper 2 is conveyed by the second conveyor roller 33. Therefore, depending on the timing T11 to T14 at which the paper 2 enters the second conveyor roller 33, the reading interval length G related to the timing at which the paper is read by the first and second measurement units 18a and 18b differs, as shown in FIG.

[0098] 12, at times T11 and T13, the reading interval G11 is the same as the reference interval G11 as described above. On the other hand, at time T12, the reading interval G12 is shorter than the reference interval G11; in other words, it is shorter than the reading interval G11 at time T11. This is because, due to eccentricity of the second conveying roller 33, the conveying speed when the paper 2 is conveyed on the outer periphery 332 (see FIG. 11) is faster than the reference speed; in other words, it is faster at time T12 than at time T11. In this case, the difference between the reading timing of the trailing edge 2c2 of the first trailing edge side read image 2c at time T12 and the reading timing of the trailing edge 2d2 of the second trailing edge side read image 2d at time T12 is shorter than the difference at time T11.

[0099] Conversely, at timing T14, the reading interval G13 is longer than the reference interval G11, in other words, it is longer than the reading interval G11 at timing T11. This is because, due to eccentricity of the second conveying roller 33, the conveying speed when conveying the paper 2 on the outer periphery 324 is slower than the reference speed, in other words, it is slower at timing T14 than at timing T11. In this case, the difference at timing T14 is longer than the difference at timing T11.

[0100] Under these conditions, the first and second measurement units 18a, 18b read the overall shape of the paper 2 being transported by the second transport roller 33 at each timing T11 to T14, and output the first and second rear end side reading data at each timing T11 to T14 to the calculation unit 10e.

[0101] The calculation unit 10e forms first and second rear end side read images 2c and 2d shown at times T11 to T14 in FIG. 12 from the first and second rear end side read data at times T11 to T14, in which the contour of the paper 2 can be detected.

[0102] Next, the calculation unit 10e calculates the read interval lengths G11, G12, G11, and G13 from the difference between the read timing of the rear end 2c2 of the first rear end side read image 2c and the read timing of the rear end 2d2 of the second rear end side read image 2d for each of the timings T11 to T14.

[0103] The calculation unit 10e calculates the difference between each of the read interval lengths G11, G12, G11, and G13 for each of the timings T11 to T14 and the reference interval length G11, and stores the deviation amount (deviation value) due to this difference in a storage unit (not shown).The saved deviation values ​​of the read interval lengths G11, G12, G11, and G13 for each of the timings T11 to T14 are output to the detection unit 10f and the rotation control unit 10g.

[0104] However, if the reading interval length G11 at timing T11 is the same as the reference interval length G11, the deviation value will be "0 mm." If the reading interval length G12 at timing T12 is different from the reference interval length G11, and G12 is, for example, 1 mm shorter than G11, the deviation value will be "-1 mm." If the reading interval length G11 at timing T13 is the same as the reference interval length G11, the deviation value will be "0 mm." If the reading interval length G13 at timing T14 is different from the reference interval length G11, and G13 is, for example, 1 mm longer than G11, the deviation value will be "+1 mm." A negative deviation value from the reference interval length G11 indicates that the conveying speed of the paper 2 by the second conveying roller 33 is faster than the reference speed, and a positive value indicates that it is slower than the reference speed.

[0105] If the deviation values ​​of the reading interval lengths G11, G12, G11, and G13 for the stored timings T11 to T14 are different (or not 0), the detection unit 10f detects that the conveying speed of the paper 2 by the second conveying roller 33 is not constant and there is unevenness in the conveying speed of the paper 2, and outputs this to the rotation control unit 10g. In this example, the detection unit 10f detects that the timings T11 and T13 are the same (or 0), but the deviation values ​​are different (or not 0) for the timings T12 and T14, so there is unevenness in the conveying speed.

[0106] However, if the deviation value for the timing T11 is "0 mm" and the deviation value for the timing T12 is "-1 mm," and the next timing at which the paper 2 enters the second conveyor roller 33 is the intermediate timing between the timings T11 and T12, the calculation unit 10e divides the difference between the deviation value for the timing T11 of "0 mm" and the deviation value for the timing T12 of "-1 mm" by 2, and performs an interpolation calculation to set the resulting "-0.5 mm" as the deviation value for the intermediate timing.

[0107] When data indicating conveyance speed unevenness is input, the rotation control unit 10g variably controls the rotation speed of the motor 33m that rotates the second conveyance roller 33 so that the deviation values ​​of the reading interval lengths G11, G12, G13, and G14 for the stored timings T11 to T14 become "0 mm." For example, if the deviation value for timing T12 is "-1 mm," the rotation speed of the second conveyance roller 33 is faster than the reference speed by an amount corresponding to the deviation value "-1 mm." Therefore, the rotation control unit 10g controls the rotation speed of the motor 33m so that the rotation speed of the second conveyance roller 33 becomes slower by an amount corresponding to the deviation value "+1 mm" that changes the deviation value "-1 mm" to "0 mm." This control causes the rotation speed of the second conveyance roller 33 to become the reference speed, so that the deviation value for timing T12 becomes "0 mm" (see FIG. 10).

[0108] Similarly, when the deviation value for timing T14 is "+1 mm," rotation control unit 10g controls the rotation speed of motor 33m so that the rotation speed of second conveyor roller 33 becomes faster by an amount corresponding to the deviation value "-1 mm" required to change the deviation value "+1 mm" to "0 mm." This control causes the conveyance speed of paper 2 by second conveyor roller 33 to become the reference speed, so the deviation value for timing T14 becomes "0 mm" (see FIG. 10).

[0109] According to the image forming apparatus 1 of the second embodiment described above, it is possible to read the shape of the rear end side of the paper 2 and detect unevenness in the conveying speed of the paper 2 by the second conveying roller 33, which is the speed at which the paper 2 is conveyed deviating from the reference speed. In addition, it is possible to variably control the rotation speed of the second conveying roller 33 so as to eliminate unevenness in the conveying speed. In other words, it is possible to perform control to eliminate unevenness in the conveying speed of the paper 2 without printing an image on the paper 2.

[0110] <Modification 1 of the First and Second Embodiments> Next, a first modification of the first and second embodiments will be described.

[0111] The difference between the first and second embodiments of the present invention is that a photosensor is used for the measurement units 18a and 18b shown in Fig. 6 or 11. In the first embodiment, the first and second measurement units 18a and 18b are referred to as the first and second photosensors 18a and 18b. The first and second photosensors 18a and 18b read the paper 2 by irradiating it with a small-diameter spot light.

[0112] In the first modification of the first embodiment, for example, as shown in Fig. 6, when the rotation axis 32j of the first conveyor roller 32 is misaligned from the center of the first conveyor roller 32, the first and second photosensors 18a, 18b read the conveyed paper 2 at the above-mentioned timings T1 to T4. In this case, as shown at timings T1 to T4 in Fig. 13, the calculation unit 10e (Fig. 2) obtains first and second leading edge side read images 2e, 2f whose width W1 in the direction (main operation direction) perpendicular to the conveyance direction Y1 (see Fig. 6) is narrowed.

[0113] That is, the width W1 of the first and second front end side read images 2e, 2f is narrower than the width in the main scanning direction of the first and second front end side read images 2a, 2b (Figure 7) when read by the first and second measurement units 18a, 18b using CIS or CCD in the first embodiment.

[0114] Even when such first and second leading-end side scanned images 2e and 2f are obtained, the calculation unit 10e calculates the scanning interval lengths G1, G2, G1, and G3 from the difference between the scanning timing of the leading end 2e1 of the first leading-end side scanned image 2e and the scanning timing of the leading end 2f1 of the second leading-end side scanned image 2f for each of the timings T1 to T4. Furthermore, the calculation unit 10e calculates the difference between each of the scanning interval lengths G1, G2, G1, and G3 for each of the timings T1 to T4 and the reference interval length G1, and stores the deviation values ​​resulting from these differences in a storage unit (not shown).

[0115] Therefore, in the detection unit 10f, if the deviation values ​​of the reading interval lengths G1, G2, G1, G3 for each of the stored timings T1 to T4 are different (or are not 0), it can detect that the conveying speed of the paper 2 by the first conveying roller 32 is not constant and that there is unevenness in the conveying speed of the paper 2.

[0116] When data indicating that there is unevenness in the conveying speed is input, the rotation control unit 10g can variably control the rotation speed of the motor 32m that rotates the first conveying roller 32 so that the deviation values ​​of the reading interval lengths G1, G2, G1, and G3 for each of the stored timings T1 to T4 become "0 mm."

[0117] Similarly, in variant 1 of the second embodiment, unevenness in the conveying speed can be detected, and the rotational speed of the motor 33m that rotates the second conveying roller 33 (see Figure 11) can be variably controlled so that each deviation value becomes "0 mm."

[0118] 11, suppose that the first and second photosensors 18a, 18b read the conveyed paper 2 at the timings T11 to T14 described above when the rotation shaft 33j of the second conveyor roller 33 is misaligned from the center of the second conveyor roller 33. In this case, as shown at the timings T11 to T14 in FIG. 14, the calculation unit 10e obtains first and second trailing edge side read images 2g, 2h whose width W1 in the direction perpendicular to the conveyance direction Y1 (see FIG. 6) is narrowed.

[0119] In this case, the calculation unit 10e calculates the reading interval lengths G1, G2, G1, and G3 from the difference between the reading timing of the rear end 2h1 of the first rear end side read image 2g and the reading timing of the rear end 2h1 of the second rear end side read image 2h for each of the timings T11 to T14. Furthermore, the calculation unit 10e calculates the difference between each of the reading interval lengths G1, G2, G1, and G3 for each of the timings T1 to T4 and the reference interval length G1, and stores the deviation values ​​resulting from these differences in the storage unit.

[0120] Therefore, when the deviation values ​​of the reading interval lengths G1, G2, G1, G3 for each of the stored timings T1 to T4 are different (or are not 0), the detection unit 10f can detect that the conveying speed of the paper 2 by the second conveying roller 33 is not constant and that there is unevenness in the conveying speed of the paper 2.

[0121] When data indicating that there is unevenness in the conveying speed is input, the rotation control unit 10g can variably control the rotation speed of the motor 33m that rotates the second conveying roller 33 so that the deviation values ​​of the reading interval lengths G1, G2, G1, and G3 for each of the stored timings T1 to T4 become "0 mm."

[0122] <Modification 2 of the First and Second Embodiments> Next, a second modification of the first and second embodiments will be described.

[0123] The difference between the second modified example and the first and second embodiments is that the two Measuring partThe difference is that instead of 18a and 18b, one measurement unit 18c shown in Fig. 15 is used. Measurement unit 18c is a line sensor such as a CIS or CCD, and is disposed parallel to and above the paper 2 along the conveyance direction Y1, and is disposed in the center of the width of the paper 2 in the direction perpendicular to the conveyance direction Y1, with the irradiation surface facing the paper 2, as shown in Fig. 16. Note that measurement unit 18c constitutes one measurement unit recited in the claims.

[0124] Assume that the measurement unit 18c reads the paper conveyed by both the first and second conveyance rollers 32, 33, which rotate at a constant rate, at each of the above-mentioned timings T1 to T4. In this case, the calculation unit 10e (FIG. 2) obtains a parallelogram-shaped read image (also called a parallelogram image) 2i as shown in FIG. 17. The parallelogram image 2i has both sides at the front end 2i1 and the rear end 2i2 that are parallel to each other.

[0125] The process of reading this parallelogram image 2i will now be described. It is assumed, however, that the measurement unit 18c is a CIS. As shown in FIG. 18, if the paper 2 conveyed in the conveying direction Y1 comes very close to the measurement unit 18c, the leading edge of the paper 2 will be positioned in a very small part of the irradiation area of ​​the measurement unit 18c. In this case, the read image will be such that the leading edge 2i1 of the parallelogram image 2i (FIG. 17) is slightly visible.

[0126] 19, if the paper 2 is transported to a position about halfway between the measuring unit 18c and the measuring unit 18c, the paper 2 will be positioned in half of the irradiation area of ​​the measuring unit 18c. In this case, the image area of ​​the front end 2i1 of the parallelogram image 2i increases in the read image.

[0127] 20, if the paper 2 is transported to a position that encompasses the entire measurement unit 18c, the paper 2 is placed in the entire irradiation area of ​​the measurement unit 18c. In this case, the entire irradiation area reads the paper 2, so the read image spreads from the front end 2i1 to the rear end 2i2 of the parallelogram image 2i.

[0128] 15, when the paper 2 is conveyed from the first conveyor rollers 32 to the second conveyor rollers 33 as indicated by the solid line to the dashed line, the expansion of the parallelogram image 2i shown in FIG. 17 progresses toward the rear end 2i2, and finally, when the paper 2 passes through the measurement unit 18c as a result of being conveyed by the second conveyor rollers 33, the rear end 2i2 of the parallelogram image 2i is obtained. That is, the parallelogram image 2i is obtained by the calculation unit 10e.

[0129] 21, it is assumed that the rotation axes 32j, 33j of the first and second transport rollers 32, 33 are offset from the centers of the first and second transport rollers 32, 33. In this case, the rotation speed of the first and second transport rollers 32, 33 is no longer constant, causing unevenness in the transport speed of the paper 2. In this case, depending on the timing T1 to T4 at which the paper 2 enters the first and second transport rollers 32, 33, the shape of the front and rear ends of the parallelogram image 2i will be distorted, as shown at timings T2 and T4 in FIG. 22, for example. This distorted shape is also obtained by the calculation unit 10e.

[0130] In other words, when the measurement unit 18c reads a sheet of paper being transported when the first and second transport rollers 32, 33 are not rotating at a constant rate, the calculation unit 10e forms an image in which the front end 2i1 and rear end 2i2 of the parallelogram image 2i are deformed.

[0131] At the timing T2, the front end 2i1 and the rear end 2i2 are roughly S-shaped (simply referred to as S-shaped). This S-shape has a recess 2i1a recessed toward the rear end at the front end 2i1, and a recess 2i2a recessed toward the front end at the rear end 2i2.

[0132] At timing T4, the front end 2i1 and the rear end 2i2 also form an S-shape. This S-shape has a protruding portion 2i1b that rises forward from the front end 2i1, and a protruding portion 2i2b that rises rearward from the rear end 2i2.

[0133] The calculation unit 10e calculates the depth of the recess or the height of the protrusion at each of timings T1 to T4. At timing T2, the deviation value (amount of deviation) corresponding to the depth from the front end 2i1 to the bottom of the recess 2i1a is calculated as, for example, "-1 mm," and the deviation value corresponding to the depth from the rear end 2i2 to the bottom of the recess 2i2a is calculated as, for example, "-1 mm." These calculated deviation values ​​are stored in a storage unit (not shown) of the calculation unit 10e. The same applies below.

[0134] At timing T4, the deviation value corresponding to the height from the leading end 2i1 to the apex of the convex portion 2i1b is calculated as, for example, "+1 mm," and the deviation value corresponding to the height from the trailing end 2i2 to the apex of the convex portion 2i2b is calculated as, for example, "+1 mm." A negative deviation value indicates that the conveying speed of the paper 2 by the first and second conveying rollers 32, 33 is faster than the above-mentioned reference speed, and a positive deviation value indicates that it is slower than the reference speed.

[0135] At times T1 and T3, there are no irregularities at the front end 2i1 and the rear end 2i2, so the deviation value is 0.

[0136] If the deviation value for each of the stored timings T1 to T4 is 0, the detection unit 10f detects that there is no unevenness in the conveying speed of the paper 2. On the other hand, if any of the deviation values ​​is other than 0, the detection unit 10f detects that the conveying speed of the paper 2 by the first and second conveying rollers 32, 33 is not constant and that there is unevenness in the conveying speed of the paper 2, and outputs this to the rotation control unit 10g. In this example, since the deviation value is 0 at timings T1 and T3, it is detected that there is no unevenness in the conveying speed, and since the deviation value is other than 0 at timings T2 and T4, it is detected that there is unevenness in the conveying speed, and this is output to the rotation control unit 10g.

[0137] In other words, the detection unit 10f detects that there is unevenness in the conveying speed when the calculation unit 10e forms an image in which the front end 2i1 and the rear end 2i2 of the parallelogram image 2i are deformed.

[0138] When data indicating unevenness in the conveyance speed is input, the rotation control unit 10g variably controls the rotation speeds of the motors 32m and 33m that rotate the first and second conveyance rollers 32 and 33 so that the deviation value for each of the stored timings T1 to T4 becomes "0 mm." In other words, when the calculation unit 10e forms an image in which the leading end 2i1 and the trailing end 2i2 of the parallelogram image 2i are deformed, the rotation control unit 10g variably controls the rotation speeds of the first and second conveyance rollers 32 and 33 so that the deformation disappears and the leading end 2i1 and the trailing end 2i2 become parallel and inclined. In other words, the rotation control unit 10g controls the speed at which the leading end or the trailing end of the paper 2 passes through the measurement unit 18c, which serves as a line sensor, so that it is uniform, regardless of the angle of the conveyance rollers 32 and 33.

[0139] By this control, unevenness in the conveying speed of each of the conveying rollers 32 and 33 is eliminated, and the read image obtained by the calculation unit 10e becomes the parallelogram image 2i shown in Fig. 17. To perform this control, only one measurement unit 18c is required as a means for reading the paper 2.

[0140] <Modification 3 of the First and Second Embodiments> Next, a third modification of the first and second embodiments will be described.

[0141] Modification 3 differs from the first and second embodiments in that, instead of the two measurement units 18a and 18b shown in Figures 3 and 4, first and second measurement units 18e and 18d are used, which are arranged parallel to each other and at an angle, as shown in Figures 23 and 24. In other words, the first and second measurement units 18e and 18d are the two measurement units 18a and 18b shown in Figures 3 and 4 arranged parallel to each other and at an angle.

[0142] When the first and second measurement units 18e and 18d read the paper 2 being transported by the second transport roller 33, the calculation unit 10e (FIG. 2) obtains the leading edge side images 2j and 2k of the first and second parallelogram images as shown in FIG. 25. The leading edge side images 2j and 2k are shown in the order in which they were read along the time axis t. That is, the second leading edge side image 2k obtained by the next read is shown overlapping the first leading edge side image 2j obtained by the first read.

[0143] The calculation unit 10e (FIG. 2) calculates the reading interval length G31 from the difference between the reading timing of the front end 2j1 of the first front end side image 2j and the reading timing of the front end 2k1 of the second front end side image 2k for each of the above-mentioned timings T1 to T4.

[0144] Furthermore, the calculation unit 10e calculates the difference between each of the read interval lengths G31 for each of the timings T1 to T4 and a reference interval length G31, which will be described later, and stores each deviation value resulting from this difference in the storage unit. In the example of Fig. 25, the deviation value is "0 mm." However, the reference interval length G31 is the average value of the read interval lengths G31 for all of the timings T1 to T4.

[0145] If the deviation values ​​of the reading interval length G31 for each of the stored timings T1 to T4 are the same, in other words, the same as the reference interval length G1, the detection unit 10f detects that the rotation speed of the first conveying roller 32 is constant and there is no unevenness in the conveying speed of the paper 2.

[0146] 26, it is assumed that the rotation axis 32j of the first conveyor roller 32 is misaligned from the center of the first conveyor roller 32, the rotation speed is not constant, and there is variation in the conveyance speed of the paper 2. In this case, depending on the timing T1 to T4 at which the paper 2 enters the first conveyor roller 32, the reading interval length G related to the timing at which the paper is read by the first and second measuring units 18e and 18d will differ as shown in FIG.

[0147] At timings T1 and T3 shown in Figure 27, the reading interval G31 is the same as the reference interval G31 as described above. On the other hand, at timing T2, the reading interval G32 is shorter than the reference interval G31. This indicates that the speed at which the first conveyor roller 32 conveys the paper 2 is faster than the reference speed. Conversely, at timing T4, the reading interval G33 is longer than the reference interval G31. This indicates that the speed at which the first conveyor roller 32 conveys the paper 2 is slower than the reference speed.

[0148] At the same time, at times T2 and T4, the shape of the leading ends of the leading end-side images 2j and 2k is distorted. In other words, when the first and second measurement units 18e and 18d read a sheet of paper conveyed when the first conveyance roller 32 is not rotating at a constant speed, the calculation unit 10e forms an image in which the leading ends 2j1 and 2k1 of the leading end-side images 2j and 2k are deformed.

[0149] That is, at timing T2, the front ends 2j1, 2k1 have an S-shape. This S-shape has a recess 2j1a recessed toward the rear end at the front end 2j1, and a recess 2k1a recessed toward the rear end at the other front end 2k1. At timing T4, a protrusion 2j1b protruding forward from the front end 2j1, and a protrusion 2k1b protruding forward from the other rear end 2k2, are formed.

[0150] If any of the deviation values ​​of the reading interval lengths G31, G32, G31, and G33 stored for each of the timings T1 to T4 is not 0, the detection unit 10f detects that the conveying speed of the paper 2 by the first conveying roller 32 is not constant and that there is unevenness in the conveying speed of the paper 2, and outputs this to the rotation control unit 10g. At the same time, the detection unit 10f detects that there is unevenness in the conveying speed when the calculation unit 10e forms an image in which the shapes of the leading ends 2j1 and 2k1 of the leading end side images 2j and 2k are deformed into an S-shape.

[0151] When data indicating the presence of conveyance speed unevenness is input, rotation control unit 10g variably controls (first control) the rotation speed of motor 32m that rotates first conveyance roller 32 so that the deviation values ​​of reading interval lengths G31, G32, G31, and G33 for each of the stored timings T1 to T4 become zero. At the same time, since the calculation unit 10e forms an image in which the leading end 2j1 of leading end side image 2j is deformed into a recess 2j1a and the leading end 2k1 of leading end side image 2k is deformed into a recess 2k1a, rotation control unit 10g variably controls (second control) the rotation speed of first conveyance roller 32 so that this deformation is eliminated. By these first and second controls, conveyance speed unevenness can be corrected more appropriately.

[0152] Next, as shown in FIG. 28, it is assumed that the rotation axis 33j of the second conveyor roller 33 is misaligned from the center of the second conveyor roller 33, so that the rotation speed is not constant and the conveyance speed of the paper 2 is uneven.

[0153] When the first and second measurement units 18e and 18d read the paper 2 being transported by the second transport roller 33, the calculation unit 10e (FIG. 2) obtains the trailing end side images 2m and 2n of the first and second parallelogram images as shown in FIG. 29. The trailing end side images 2m and 2n are shown in the order they were read along the time axis t. That is, the trailing end portion of the second trailing end side image 2n read next is visible below the first trailing end side image 2m read first.

[0154] The calculation unit 10e calculates the reading interval lengths G41, G42, G41, and G43 from the difference between the reading timing of the rear end 2m2 of the first rear end side image 2m and the reading timing of the rear end 2n2 of the second rear end side image 2n for each of the above-mentioned timings T11 to T14. These reading interval lengths G41, G42, G41, and G43 are assumed to differ as follows:

[0155] At timings T11 and T13, the reading interval G41 is the same as the reference interval G41. On the other hand, at timing T12, the reading interval G42 is shorter than the reference interval G41. This indicates that the speed at which the second conveyor rollers 33 convey the paper 2 is faster than the reference speed. Conversely, at timing T14, the reading interval G43 is longer than the reference interval G41. This indicates that the speed at which the second conveyor rollers 33 convey the paper 2 is slower than the reference speed.

[0156] At the same time, at times T12 and T14, the shape of the rear ends of the rear end side images 2m and 2n is distorted. In other words, when the first and second measurement units 18e and 18d read the paper 2 being conveyed when the second conveying roller 33 is not rotating at a constant rate, the calculation unit 10e forms images in which the rear ends 2m2 and 2n2 of the rear end side images 2m and 2n are deformed as follows:

[0157] That is, at timing T12, the shape of the rear ends 2m2, 2n2 becomes S-shaped. This S-shape has a protruding portion 2m2a that protrudes toward the front end at the rear end 2m2, and a protruding portion 2n2a that protrudes toward the front end at the other rear end 2n2. At timing T14, a protruding portion 2m2b that protrudes toward the rear end from the rear end 2m2, and a protruding portion 2n2b that protrudes toward the rear end at the other rear end 2n2.

[0158] If any of the deviation values ​​of the reading interval lengths G41, G42, G41, and G43 for each of the timings T11 to T14 stored above is not 0, the detection unit 10f detects that the conveying speed of the paper 2 by the second conveying roller 33 is not constant and that there is unevenness in the conveying speed of the paper 2, and outputs this to the rotation control unit 10g. At the same time, the detection unit 10f detects that there is unevenness in the conveying speed when the calculation unit 10e forms an image in which the shapes of the rear ends 2m2 and 2n2 of the rear end side images 2m and 2n are deformed into an S-shape.

[0159] When data indicating the existence of conveyance speed unevenness is input, the rotation control unit 10g variably controls (first control) the rotation speed of the motor 33m that rotates the second conveyance roller 33 so that the deviation values ​​of the read interval lengths G41, G42, G41, and G43 for the stored timings T1 to T4 become zero. At the same time, the rotation control unit 10g variably controls (second control) the rotation speed of the second conveyance roller 33 so as to eliminate the deformations formed by the calculation unit 10e, in which the rear end 2m2 of the trailing edge image 2m is deformed into a convex portion 2m2a and the rear end 2n2 of the trailing edge image 2n is deformed into a convex portion 2n2a. These first and second controls enable more appropriate correction of conveyance speed unevenness. The above-described invention allows the size of the paper 2 in the sub-scanning direction to be accurately calculated, preventing density unevenness in the sub-scanning direction of the output image and further preventing density unevenness in the sub-scanning direction of the read image.

[0160] Although the configuration according to this embodiment has been described above, the present invention is not limited to this, and can be modified as appropriate within the scope of the gist of the present invention. [Explanation of symbols]

[0161] 1. Image forming device 18a,18b,18c,18d,18e Measuring part 10e Reading interval calculation unit (calculation unit) 10f Conveyance speed unevenness detection unit (detection unit) 10g Rotation control section 11 Image reading unit (reading unit) 14 Image forming unit 32, 33 Conveying rollers (first and second conveying rollers) 32m, 33m motor

Claims

1. a conveying roller for conveying the recording medium; a measuring unit that reads the outer shape of the recording medium conveyed by the conveying rollers at predetermined intervals, the outer shape of the recording medium being arranged in parallel in a conveying direction in which the recording medium is conveyed, and measures read data at predetermined intervals from the same plane side of the recording medium; a calculation unit that forms a front end side read image at each predetermined interval from read data of the recording medium read at each timing at which the recording medium enters the conveying roller, calculates a read interval length from a difference between each read timing of the front end side read image, and calculates a difference between the calculated read interval length and a reference interval length; a detection unit that detects unevenness in the conveying speed of the recording medium by the conveying roller based on each deviation value calculated by the difference; An image forming apparatus comprising:

2. a rotation control unit that controls the rotation of the transport roller to correct the transport speed unevenness detected by the detection unit; The image forming apparatus according to claim 1 .

3. the measuring unit is composed of two sensors that measure the passage of the leading edge or the trailing edge of the recording medium; the rotation control unit controls the recording medium so that the time it takes for the leading edge or the trailing edge to pass between the two sensors is equal, regardless of the angle of the conveyance roller. The image forming apparatus according to claim 2 .

4. the measuring unit is a line sensor installed in a conveying direction of the recording medium, the rotation control unit controls the speed at which the leading edge or the trailing edge of the recording medium passes the line sensor to be uniform regardless of the angle of the conveying roller; The image forming apparatus according to claim 2 .

5. the measuring unit is two line sensors installed obliquely with respect to the conveying direction of the recording medium, the rotation control unit controls the recording medium so that the time it takes for the leading edge or the trailing edge of the recording medium to pass the two line sensors is equal, and the speed at which the leading edge or the trailing edge of the recording medium passes the line sensors is equal, regardless of the angle of the conveying roller. The image forming apparatus according to claim 2 .

6. further comprising an image forming unit that forms an image on the recording medium; the rotation control unit controls the rotation of the conveying roller so as to correct the unevenness in the conveying speed detected by the detection unit. The image forming apparatus according to any one of claims 2 to 5.

7. further comprising a reading unit that reads the recording medium, the rotation control unit controls the rotation of the conveying roller so as to correct the unevenness in the conveying speed detected by the detection unit. The image forming apparatus according to any one of claims 2 to 5.

8. The measuring unit is a photosensor that irradiates a small diameter spot light to read the recording medium.

3. The image forming apparatus according to claim 1.

9. 1. An image forming method for an image forming apparatus having a conveying roller for conveying a recording medium, comprising: a step in which measurement units are arranged in parallel at predetermined intervals in a conveying direction in which the recording medium is conveyed, read the outer shape of the recording medium conveyed by the conveying rollers at each timing when the recording medium enters the conveying rollers, and measure read data at predetermined intervals from the same plane side of the recording medium; a calculation unit forming a front end side read image at each predetermined interval from read data of the recording medium read at each timing of entering the conveyance roller, calculating a read interval length from a difference between each read timing of the front end side read image, and calculating a difference between the calculated read interval length and a reference interval length; a detecting unit detecting unevenness in the conveying speed of the recording medium by the conveying roller based on each deviation value calculated by the difference; An image forming method comprising:

Images