JP2016161815A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can eliminate incorrect detection without reducing production efficiency.SOLUTION: An image forming apparatus comprises: an optical sensor 12 that detects a sheet P to be conveyed along a conveyance direction; a background plate 213 that is provided opposite to the optical sensor 12 and has a background image printed thereon; a background color control part 251 that, when the sheet P is conveyed along the conveyance direction, alternately switches background colors of the background image between black and white; and an end specification part 252 that causes the optical sensor 12 to detect an image printed on the sheet P and the background image as the sheet P is conveyed along the conveyance direction to specify the positions of the ends of the sheet P.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus is known as a multi-function peripheral (MFP) having a composite function of a printer, a copier, and the like. Such an image forming apparatus performs printing by forming an image on a photoconductor of an image forming unit based on image data, transferring the formed image onto a sheet conveyed from a paper feed tray, and fixing the image.

  When a sheet is printed through the above-described series of processes, if the sheet is always conveyed at the same position, an image is formed on the sheet based on the same position reference in the image forming unit. can do. However, a slight misalignment may occur in the transport path from the paper feed tray to the photoconductor.

  Therefore, an edge detection sensor that uses reflection of sensor light such as an LED detects the position of the edge in the width direction of the paper, and a slight positional deviation is corrected based on the detection result. However, the amount of reflection from a dark color image is small if the paper has a dark color image printed at the edge in the width direction of the paper. In this case, the end portion in the width direction of the sheet and the periphery thereof are not distinguished, and the position of the end portion in the width direction of the sheet may be erroneously detected. When such an erroneous detection occurs, the image forming apparatus is stopped due to an error or the like, so that the production efficiency is lowered.

  Therefore, when a background plate that can move below the paper is provided, and the position of the edge of the paper is erroneously detected as a reference value or less, the background plate is positioned from black to white, There is a technique in which a density difference is generated at the boundary with the white color of the background plate to detect the edge of the paper (for example, see Patent Document 1).

JP 2012-128268 A

  However, the technique described in Japanese Patent Laid-Open No. 2004-228561 detects the position of the edge of the paper again by changing the background color from black to white by moving the background plate once erroneously detected. Therefore, although the technique described in Patent Document 1 can specify the position of the edge of the sheet after erroneous detection, the image forming apparatus cannot be stopped. Therefore, the technique described in Patent Document 1 cannot eliminate false detection without reducing production efficiency.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can eliminate erroneous detection without deteriorating production efficiency.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an optical sensor that detects a sheet conveyed along a conveyance direction, and a background plate that is provided opposite to the optical sensor and on which a background image is printed. A background color control unit that alternately switches a background color of the background image to one of black and white when the paper is transported along the transport direction, and the paper along the transport direction. And an edge identifying unit that identifies the position of the edge of the sheet by causing the optical sensor to detect the sheet and the background image as the sheet is conveyed.

  According to this image forming apparatus, it is possible to eliminate erroneous detection without reducing production efficiency.

  In the image forming apparatus according to the aspect of the invention, the edge specifying unit may determine the position of the edge of the sheet based on the estimated position of the edge of the sheet estimated according to the sensor output value of the optical sensor. It is preferable to specify.

  According to this image forming apparatus, it is possible to use a highly valid sensor output value of the optical sensor.

  In the image forming apparatus according to the aspect of the invention, it is preferable that the edge specifying unit specifies the most estimated position among the estimated positions as the position of the edge of the sheet.

  According to this image forming apparatus, the position of the edge portion of the sheet specified based on the sensor output value of the optical sensor can be made highly valid.

  In the image forming apparatus according to the present invention, the image forming apparatus further includes a conveyance control unit that continuously conveys the plurality of sheets, and the conveyance control unit has the most estimated position among the estimated positions. It is preferable that the sheet is transported at a first transport speed corresponding to a background color switching speed of the background image until it is specified at the end position.

  According to this image forming apparatus, it is possible to increase the resolution for detecting the position of the edge of the sheet. In addition, since the paper is not wasted, the paper resource can be used effectively.

  In the image forming apparatus according to the present invention, the transport control unit may determine the first transport speed when the most estimated position among the estimated positions is specified as the position of the edge of the sheet. It is preferable that the sheet is transported at a second transport speed that is faster than the second transport speed.

  According to this image forming apparatus, the production efficiency of paper can be improved.

  In the image forming apparatus according to the aspect of the invention, the edge specifying unit may determine the most estimated position among the estimated positions when the sheet is in the first conveyance. It is preferable to specify the position.

  According to this image forming apparatus, erroneous detection of the position of the end of the sheet can be avoided, so that the first sheet after feeding can be effectively discarded without wasting the first sheet.

  In the image forming apparatus according to the present invention, when the number of times that the estimated position is estimated exceeds a preset threshold, the edge specifying unit determines the most estimated position as the edge of the sheet. It is preferable that the position is specified.

  According to this image forming apparatus, even when one sheet is being conveyed, the position of the end of the sheet is specified, and then the sheet is conveyed at the second conveyance speed. Time can be shortened.

  Further, in the image forming apparatus according to the present invention, the end specifying unit corresponds to a first end from the front end of the paper to the optical sensor corresponding to the position of the end of the paper at the first transport speed. It is preferable that the background color at the first distance is stored in association with the sensor output value of the optical sensor at the first distance and the sensor output value at the first distance.

  According to this image forming apparatus, the second and subsequent sheets conveyed at different conveyance speeds can be compared with the first sheet.

  In the image forming apparatus according to the present invention, the first distance extracted based on a preset condition is set as a collation distance, and the background color control unit performs the second conveyance speed. The second distance from the leading edge of the paper to the optical sensor reaches the verification distance as the paper different from the first transport speed is transported along the transport direction. In addition, it is preferable that the background color of the background image at the second transport speed matches the background color when the position of the edge of the paper is specified.

  According to this image forming apparatus, it is possible to determine whether or not the same image is printed on the paper transported at the first transport speed and the paper transported at the second transport speed. .

  Further, in the image forming apparatus according to the present invention, based on a sensor output value of the optical sensor at the second transport speed and a sensor output value of the optical sensor at the first transport speed. A paper determination unit for determining whether or not the same image is printed on the paper conveyed at the conveyance speed and the paper conveyed at the second conveyance speed; Each time the background color of the background image is matched with the background color when the position of the edge of the paper is specified at the second transport speed, the optical at the second transport speed is When the sensor output value of the sensor and the sensor output value of the optical sensor at the first transport speed are the same, the paper transported at the second transport speed and the first transport The said sheet conveyed in degrees, it is preferable the same image is to determined to be printed.

  According to this image forming apparatus, it is possible to determine whether the same image is printed on continuously conveyed paper without lowering the production efficiency.

  The image forming apparatus according to the present invention further includes a time-series determination unit that determines a time-series change pattern of the sensor output value of the optical sensor, and the time-series determination unit is transported at the second transport speed. It is not determined that the same image is printed on the paper that has been transported and the paper that has been transported at the first transport speed, and the sensor output value of the optical sensor at the second transport speed is not When the time-series change pattern matches the time-series change pattern of the sensor output value of the optical sensor at the first conveyance speed, it is determined that the sheet is conveyed while being inclined. Is preferred.

  According to this image forming apparatus, the inclination of the sheet can be determined at low cost.

The image forming apparatus according to the present invention may further include an image correction unit that corrects an image printed on the sheet, and the time-series determination unit determines that the sheet is conveyed while being tilted. Based on a time-series change pattern, the inclination angle of the paper is obtained,
It is preferable that the image correction unit corrects the position of the image printed on the paper based on the inclination angle of the paper obtained by the time series determination unit and the deviation amount of the paper. .

  According to this image forming apparatus, wasteful disposal of paper can be reduced at low cost.

  The image forming apparatus according to the present invention further includes a time-series determination unit that determines a time-series change pattern of the sensor output value of the optical sensor, and the time-series determination unit is transported at the second transport speed. It is not determined that the same image is printed on the paper that has been transported and the paper that has been transported at the first transport speed, and the sensor output value of the optical sensor at the second transport speed is not When the time-series change pattern and the time-series change pattern of the sensor output value of the optical sensor at the first transport speed do not match, it is determined that an image of a different pattern is printed. Is preferred.

  According to this image forming apparatus, it is possible to determine whether or not the continuously conveyed paper is printed with different images without reducing the production efficiency.

  In the image forming apparatus according to the present invention, when it is determined that the image of the different pattern is printed, the transport control unit changes the transport speed of the paper from the second transport speed to the first. It is preferable that the speed is changed to this transport speed.

  According to this image forming apparatus, when an image with a different pattern is printed, it is possible to shift to the process of specifying the position of the edge of the paper again.

  Further, in the image forming apparatus according to the present invention, the edge specifying unit is identical to the sheet conveyed at the second conveyance speed and the sheet conveyed at the first conveyance speed. When it is not determined that an image is printed, it is preferable that the image is returned to the first conveyance speed and the position of the edge of the sheet is specified.

  According to this image forming apparatus, when it is not determined that the same image is printed, it is possible to shift to the process of specifying the position of the edge of the paper again.

  In the image forming apparatus according to the aspect of the invention, it is preferable that the conveyance control unit conveys the leading edge of the sheet to the upstream side to a preset position.

  According to this image forming apparatus, even if an image with a different pattern is printed, the process can be shifted to the process of estimating the position of the edge of the sheet.

  In the image forming apparatus according to the aspect of the invention, it is preferable that the conveyance control unit discharges the sheet to the outside when it is determined that the image of the different pattern is printed.

  According to this image forming apparatus, although wasteful disposal of paper occurs, paper production efficiency can be maintained.

  According to the present invention, it is possible to eliminate erroneous detection without reducing production efficiency.

1 is a configuration diagram schematically illustrating a configuration of an image forming apparatus 1 according to an embodiment. It is a figure explaining the schematic output relation of paper P, optical sensor 12, and background board 213, and the sensor output waveform of optical sensor 12 based on the arrangement relation. It is a figure explaining the detailed output relation of paper P, optical sensor 12, and background board 213, and the sensor output waveform of optical sensor 12 based on the arrangement relation. 2 is a diagram illustrating an example of a functional configuration of an image forming apparatus 1 according to the present embodiment. FIG. It is a figure explaining the detection point of the optical sensor 12 in the 1st conveyance speed, and the detection point of the optical sensor 12 in the 2nd conveyance speed. 4 is a flowchart illustrating an example of control of the image forming apparatus 1 according to the present embodiment. FIG. 6 is a diagram illustrating an example in which the position of the edge of a blank paper P is detected without providing a background plate 213. FIG. 10 is a diagram illustrating an example in which the position of the end portion of a non-white paper sheet P is erroneously detected without providing a background plate 213. It is a figure which shows an example of various parameters when A4 paper is conveyed. When the paper P on which the image of the first black belt pattern is printed is conveyed at the first conveyance speed, the background color of the background image printed on the background plate 213 and the sensor output value Vedge of the optical sensor 12 It is a figure which shows a correspondence. When the paper P on which the image of the first black belt pattern is printed is conveyed at the second conveyance speed, the background color of the background image printed on the background plate 213 and the sensor output value Vedge of the optical sensor 12 It is a figure which shows a correspondence. When the paper P on which the image of the second black belt pattern is printed is conveyed at the second conveyance speed, the background color of the background image printed on the background plate 213 and the sensor output value Vedge of the optical sensor 12 It is a figure which shows a correspondence. When the paper P on which the image of the second black belt pattern is printed is conveyed at the first conveyance speed, the background color of the background image printed on the background plate 213 and the sensor output value Vedge of the optical sensor 12 It is a figure which shows a correspondence.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

  FIG. 1 is a configuration diagram schematically illustrating a configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 forms an image by, for example, an electrophotographic method, and arranges a plurality of photosensitive drums 11Y, 11M, 11C, and 11K in a vertical direction by facing a single intermediate transfer belt 15. This is a so-called tandem color image forming apparatus that forms a full-color image.

  The image forming apparatus 1 mainly includes a document reading device SC, four sets of image forming units 10Y, 10M, 10C, and 10K, a fixing device 30, and a control unit 100, which are housed in a single casing.

  The document reader SC scans and exposes an image of the document with the optical system of the scanning exposure device, reads the reflected light with a line image sensor, and obtains an image signal. The image signal is subjected to processing such as A / D conversion, shading correction, and compression, and then input to the control unit 100 as image data. Note that the image data input to the control unit 100 is not limited to data read by the document reading device SC, for example, data received from a personal computer connected to the image forming device 1, another image forming device, or It may be read from a portable recording medium such as a semiconductor memory.

  The four image forming units 10Y, 10M, 10C, and 10K include an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and a cyan (C) image. The image forming unit 10 </ b> C to be formed and the image forming unit 10 </ b> K that forms a black (K) image are configured. Each of the image forming units 10Y, 10M, 10C, and 10K includes a photosensitive drum 11Y, 11M, 11C, and 11K, a charging unit, an optical writing unit, a developing device, and a drum cleaner arranged around the photosensitive drums 11Y, 11M, 11C, and 11K. .

  The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are uniformly charged by the charging unit, and the latent image is transferred to the photosensitive drums 11Y, 11M, 11C, and 11K by scanning exposure by the optical writing unit. It is formed. The developing device develops the latent images on the photosensitive drums 11Y, 11M, 11C, and 11K by developing with toner. As a result, an image (toner image) of a predetermined color corresponding to any one of yellow, magenta, cyan, and black is formed on the photosensitive drums 11Y, 11M, 11C, and 11K. The images formed on the photosensitive drums 11Y, 11M, 11C, and 11K are sequentially transferred to predetermined positions on the rotating intermediate transfer belt 15 by the primary transfer roller.

  An image composed of each color transferred onto the intermediate transfer belt 15 is transferred onto a sheet P conveyed at a predetermined timing by a sheet conveying unit 20 described later by a secondary transfer roller 16. The secondary transfer roller 16 is disposed in pressure contact with the intermediate transfer belt 15 to form a transfer nip.

  That is, the image forming units 10Y, 10M, 10C, and 10K are formed by charging the photosensitive drums 11Y, 11M, 11C, and 11K and forming electrostatic latent images on the photosensitive drums 11Y, 11M, 11C, and 11K. The toner is attached to the electrostatic latent image, and the image formed by developing the latent images on the photosensitive drums 11Y, 11M, 11C, and 11K is primarily transferred to the intermediate transfer belt 15, and the intermediate transfer belt 15 is transferred. An image to be transferred is formed by a series of processes in which the image primarily transferred above is secondarily transferred to the paper P by the secondary transfer roller 16, and the formed image is transferred to the paper P.

  The paper transport unit 20 transports the paper P fed from the paper feed unit 21 along the transport path. In the paper supply unit 21, the paper P is stacked on a paper tray, and the paper P stacked on the paper tray is taken in by the paper supply unit 22 and sent out to the conveyance path.

  In the transport path, a plurality of paper transport means for transporting the paper P is provided upstream of a transfer position (specifically, a transfer nip) where the image is transferred to the paper P. Each conveying means is constituted by a pair of rollers that are pressed against each other. Each of the conveying means conveys the paper P by a roller being rotated by a driving mechanism mainly composed of an electric motor. In addition, the pair of rollers constituting the individual conveying means is configured so that the state between the rollers can be switched between a pressure contact state and a separated state. In addition to the configuration of the pair of rollers, the conveyance unit can widely employ a configuration including a pair of rotating members, such as a combination of belts or a combination of a belt and a roller.

  A plurality of intermediate transport rollers, a loop roller, and a registration roller 25 are provided as transport means from the upstream side to the downstream side of the transport path of the paper P. Specifically, the paper P fed from the paper feeding unit 22 is sequentially transported by a plurality of intermediate transport rollers and loop rollers, and travels along the transport path. As the leading edge of the paper P approaches the registration roller 25, the plurality of intermediate transport rollers on the upstream side of the loop roller are switched from the pressure contact state to the separated state.

  The paper P is transported only by the loop roller, and the leading end of the paper P abuts against the registration roller 25 in a rotation stopped state. In this state, the loop roller continues to rotate for a predetermined time, whereby a loop is formed on the paper P. By the action of this loop formation, the bending of the paper P is corrected (skew correction).

  Next, when the registration roller 25 starts to rotate at a predetermined timing, the paper P is conveyed forward by the registration roller 25, and the loop roller is switched from the press-contact state to the separated state in the same manner as the intermediate conveyance roller. The registration roller 25 transports the paper P to the transfer nip while transporting the paper P.

  The fixing device 30 is a device that performs a fixing process on the paper P on which the image is transferred, that is, the paper P conveyed from the transfer nip. The fixing device 30 includes, for example, a pair of fixing rollers that are pressed against each other to form a fixing nip, and a heater that heats one or both of the fixing rollers. The fixing device 30 fixes the transferred image on the paper P through the action of the pressure applied by the pair of fixing rollers and the heat of the fixing roller. The paper P subjected to the fixing process by the fixing device 30 is discharged out of the apparatus by the paper discharge roller 23.

  When image formation is performed also on the back surface of the paper P, the paper P on which image formation on the front surface of the paper P has been completed is conveyed to the refeed conveyance path by the switching gate 24. In the re-feed conveyance route, the rear end of the conveyed paper P is nipped by the reverse roller, and then reversely fed to reverse the front and back of the paper P. The paper P whose front and back are reversed is transported by a plurality of transport rollers, and is joined to a transport path on the upstream side of the transfer position in order to provide image formation on the other surface.

  Further, downstream of the registration roller 25, a leading edge detection sensor 17 and an optical sensor 12 are provided from the upstream side to the downstream side of the conveyance path of the paper P. Specifically, the tip detection sensor 17 and the optical sensor 12 are provided between the registration roller 25 and the secondary transfer roller 16. Details of the optical sensor 12 will be described in detail with reference to FIG.

  The leading edge detection sensor 17 detects the arrival of the leading edge of the paper P. The detection result of the leading edge detection sensor 17 is used to grasp the arrival timing of the leading edge of the paper P to the transfer nip. The leading edge detection sensor 17 is used to detect the leading edge position of the paper P when determining the distance a from the leading edge of the paper P to the detection position of the optical sensor 12, as will be described later.

  The operation panel 45 is a touch panel type input unit capable of inputting information in accordance with information displayed on a display (not shown). The user can set information regarding the paper P, specifically, the density or magnification of the image, a paper tray as a paper supply source, and the like through the operation on the operation panel 45, and the information is acquired by the control unit 100. Is done. The operation panel 45 also functions as a display unit that displays various information to the user via the operation panel 45 by being controlled by the control unit 100.

  The control unit 100 controls the operation of the image forming apparatus 1. As the control unit 100, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used.

  FIG. 2 is a diagram for explaining a schematic arrangement relationship between the paper P, the optical sensor 12, and the background plate 213 and a sensor output waveform of the optical sensor 12 based on the arrangement relationship.

  The optical sensor 12 detects the paper P that is transported along the transport direction. The background plate 213 is provided facing the optical sensor 12 and has a background image printed thereon. The background color of the background image is alternately switched to one of black and white when the paper P is transported along the transport direction. For example, when the background plate 213 is printed with white and black one by one, when the background color of the background image printed on the background plate 213 is switched, the background plate is moved along the transport direction. What is necessary is just to move 213 back and forth one color at a time.

  Specifically, while the optical sensor 12 performs the detection operation for one line along the scanning direction, that is, while the optical sensor 12 detects at the detection position, the background plate 213 holds the first color, for example, black. To do. Next, while the paper P is transported and the optical sensor 12 performs the detection operation for the next one line along the scanning direction, the background plate 213 may hold the second color, for example, white.

  Assuming the control of the background color of the background image printed on the background plate 213 described above, the optical sensor 12 prints on the paper P and the background plate 213 as the paper P is transported along the transport direction. The detected background image is detected. As a result, the position of the end of the paper P is specified. The details of the operation of specifying the position of the end of the paper P will be described later.

  The optical sensor 12 detects the amount of deviation of the paper P based on the edge position of the paper P, and determines the amount of deviation for correcting the image writing start position or the paper position based on the detection result. Used as a sensor.

  The optical sensor 12 will be specifically described. The optical sensor 12 includes LEDs, a lens array, and a CCD line sensor arranged in a line along the paper width direction, that is, the scanning direction, and reads each pixel on a one-to-one basis. The optical sensor 12 irradiates the target by causing the LED to emit light, and the CCD line sensor detects the amount of light reflected from the target. The CCD line sensor changes its current and voltage according to the amount of light received.

  For example, when the target color is black, it is not regressed because the irradiation light is absorbed. On the other hand, when the target color is white, the irradiation light is reflected and is returned. That is, as the target color becomes darker, the degree of regression of irradiation light becomes weaker. Therefore, it is possible to determine the density of the target color, specifically white or black, based on the sensor output value of the CCD line sensor. Here, the leading edge of the paper P is detected by the leading edge detection sensor 17, the sensor output value when the distance a from the leading edge of the paper P to the optical sensor 12 is Vedge, and the final sensor output value of the optical sensor 12 is Vedge. 'And.

  Incidentally, in addition to printing on white paper, the paper P may be additionally printed by printing the already printed paper P again. For example, when the paper P is reprinted from now on, a dark color such as a black belt may already be printed on the edge of the paper P. In this case, in the determination of the edge of the paper P based on the presence or absence of reflected light due to the return of the irradiation light, the edge of the paper P cannot be read and may be erroneously detected. Such a case will be described with reference to FIG.

  FIG. 3 is a diagram for explaining the detailed arrangement relationship of the paper P, the optical sensor 12, and the background plate 213 and the sensor output waveform of the optical sensor 12 based on the arrangement relationship. In FIG. 3, in the case of A, the optical sensor 12, the paper P, and the background plate 213 are viewed from the side. In FIG. 3, in the case of B, only the optical sensor 12 and the paper P are viewed from above. In FIG. 3, in the case of C, only the optical sensor 12 and the background plate 213 are viewed from above. In FIG. 3, in the case of D, the final sensor output value Vedge 'will be described.

  In FIG. 3, the case of A will be specifically described. A sheet P and a background plate 213 are disposed below the optical sensor 12. Among these, the background plate 213 is disposed below the paper P and at a position where a part thereof overlaps a part of the paper P.

  In FIG. 3, the case of B will be specifically described. A black belt is printed on a part of the edge of the paper P. When the optical sensor 12 performs the detection operation at the detection position, the irradiation light does not return at the black belt, so that the sensor output waveform changes from High to Low just before the black belt. Therefore, the sensor output value Vedge is 4500.

  In FIG. 3, the case of C will be specifically described. The background plate 213 is configured to alternately switch the background color of the background image to one of black and white when the paper P is transported along the transport direction. Thereby, from the viewpoint of the optical sensor 12, as the paper P is transported along the transport direction, the background color of the background image periodically changes in black and white at the detection position. Therefore, as described in the case of B, even if the sensor output value Vedge is 4500 due to the black belt at the edge of the paper P, if the background color of the background image of the background plate 213 is white, At the detection position, the optical sensor 12 detects, and the sensor output waveform changes from Low to High. Therefore, the sensor output value Vedge is 4600.

  Next, when the detection operation of the optical sensor 12 is performed at the detection position as it is, the irradiation light is not regressed when the edge of the background plate 213 is exceeded, so the sensor output waveform changes from High to Low. As a result, the sensor output value Vedge becomes FFFFF. Thus, when the sensor output value Vedge is FFFFF, it means the end of the background plate 213. Therefore, when the sensor output value Vedge becomes FFFFF, the sensor output value Vedge may be excluded.

  In FIG. 3, the case of D will be specifically described. The sensor output waveform of the optical sensor 12 changes from High to Low at the black belt of the paper P, and the sensor output value Vedge at this time is 4500. Thereafter, the background color of the background image on the background plate 213 changes from Low to High when the background color is white, and the sensor output value Vedge at this time is 4600. After that, it changes from High to Low at the end of the background plate 213, and the sensor output value Vedge at this time becomes FFFFF. That is, the sensor output value Vedge of the optical sensor 12 changes along the scanning direction as 4500, 4600, and FFFFF.

  Therefore, if the case where the sensor output value Vedge is FFFFF is excluded, it is estimated that the position of the end portion of the paper P is when the sensor output value Vedge before that is 4600. As described above, the optical sensor 12 detects the paper P and the background image printed on the background plate 213 at the detection position, so that the edge of the paper P corresponding to the sensor output value Vedge of the optical sensor 12 is detected. The estimated position is obtained. That is, as the paper P is transported along the transport direction, the background color of the background image is switched to any one of black and white. What kind of pattern and color is the image printed on the paper P? Even if there is, there will be many opportunities to cause a density difference between the density of the image printed on the paper P and the density of the background image. Thereby, the position of the edge part of the paper P can be estimated.

  Such an estimation operation is repeated as the paper P is transported along the transport direction and the background image is alternately switched to one of black and white. As a result, a plurality of estimated positions are obtained.

  In addition, although the case where the background plate 213 is below the paper P has been described, the background plate 213 may be provided so as to face the optical sensor 12. Specifically, any arrangement configuration may be used as long as the paper P is transported between the optical sensor 12 and the background plate 213 and the optical sensor 12 detects the paper P and the background plate 213 at the detection position.

  Next, details of a configuration for specifying the position of the end portion of the paper P based on a plurality of estimated positions will be described with reference to FIGS.

  FIG. 4 is a diagram illustrating an example of a functional configuration of the image forming apparatus 1 according to the present embodiment. FIG. 5 is a diagram illustrating detection points of the optical sensor 12 at the first conveyance speed and detection points of the optical sensor 12 at the second conveyance speed.

  As shown in FIG. 4, as a functional configuration of the image forming apparatus 1, a background color control unit 251 and an end specifying unit 252 are provided. The background color control unit 251 switches the background color of the background image printed on the background plate 213 alternately to one of black and white when the paper P is transported along the transport direction.

  For example, as shown in FIG. 5, the background color of the background image printed on the background plate 213 is alternately black or white at both the first transport speed and the second transport speed. It has been switched. Here, the first transport speed corresponds to the background color switching speed of the background image printed on the background plate 213. On the other hand, the second transport speed is faster than the first transport speed.

  The edge identifying unit 252 in FIG. 4 causes the optical sensor 12 to detect the paper P and the background image printed on the background plate 213 as the paper P is transported along the transport direction. The position of the part is specified. The edge identifying unit 252 identifies the position of the edge of the paper P based on the estimated position of the edge of the paper P estimated according to the sensor output value Vedge of the optical sensor 12.

  Specifically, the edge specifying unit 252 specifies the most estimated position among the estimated positions as the position of the edge of the paper P. The edge identifying unit 252 identifies the most estimated position among the estimated positions as the position of the edge of the sheet P when the sheet P is in the first conveyance. Further, the edge identifying unit 252 may identify the most estimated position as the position of the edge of the paper P when the estimated number of times exceeds a preset threshold.

  For example, as shown in FIG. The different points from 1 to 20 are detection points, and the sensor output value Vedge is either 4500, 4600, or FFFFF. Here, the detection No. Nos. 1 to 20 correspond to the first distance a from the leading edge of the paper P to the optical sensor 12, and the detection Nos. As the value of becomes larger, the correspondence is made such that the first distance a increases.

  That is, each detection point of the first distance a corresponds to the estimated position. Since the most estimated position among the plurality of estimated positions is specified as the position of the end of the paper P, here, the position corresponding to the sensor output value Vedge of 4600 when the number of detection points is the largest is shown. The position of the end portion of the paper P may be specified.

  The edge specifying unit 252 in FIG. 4 performs optical measurement from the leading edge of the paper P corresponding to the position of the edge of the paper P at the first transport speed corresponding to the background color switching speed of the background image of the background plate 213. The background color at the first distance a is stored in association with the first distance a to the sensor 12 and the sensor output value Vedge of the optical sensor 12 at the first distance a. These parameters may be stored in the storage unit 261.

  For example, as shown in FIG. 5, when the sensor output value Vedge is 4600, it corresponds to the position of the edge of the paper P. The sensor output value Vedge of the optical sensor 12 corresponding to 1, 4 to 7, 11 to 14 and the background color may be stored in association with each other.

  As shown in FIG. 4, a conveyance control unit 253 is provided as a functional configuration of the image forming apparatus 1. The conveyance control unit 253 conveys a plurality of sheets P continuously. The conveyance control unit 253 responds to the background color switching speed of the background image printed on the background board 213 until the most estimated position among the estimated positions is specified as the end position of the paper P. The paper P is transported at the first transport speed. The conveyance control unit 253 conveys the sheet P at the second conveyance speed that is faster than the first conveyance speed when the most estimated position among the estimated positions is specified as the position of the end of the sheet P. To do.

  For example, as shown in FIG. 5, the background color of the background image on the background plate 213 is periodically switched between white and black at the first conveyance speed, and the background of the background plate 213 at the second conveyance speed. Although the background color of the image is alternately switched between white and black, the paper P is conveyed in a state where the number of switching is reduced.

  Here, the background color switching operation at the second conveyance speed will be specifically described. First, a first distance a extracted based on a preset condition is set as a collation distance a ′. As the paper P different from the first transport speed is transported along the transport direction at the second transport speed, the background color control unit 251 performs the first control from the leading edge of the paper P to the optical sensor 12. When the distance b of 2 reaches the collation distance a ′, the background color of the background image printed on the background plate 213 at the second transport speed is specified as the position of the edge of the paper P. To match the background color.

  For example, as shown in FIG. The sensor output value Vedge is 4600 at each of 1, 6 and 11. Therefore, the detection No. In each of 1, 6 and 11, the background color at the first transport speed and the background color at the second transport speed are matched.

  That is, the sensor output value Vedge of the optical sensor 12 at the [a] -th, [b] -th, and [c] -th, that is, the detection result of the optical sensor 12 corresponds to the position of the edge of the paper P. Therefore, it is used as collation data at the second transport speed. On the other hand, the detection result of the optical sensor 12 at the [d] -th time does not correspond to the position of the end portion of the paper P, and therefore is not used as collation data at the second transport speed. Although the [a] to [d] -th first distances a are selected at regular intervals, they need not be at regular intervals.

  Next, a configuration for determining whether or not the same image is printed on the sheet P conveyed at the first conveyance speed and the sheet P conveyed at the second conveyance speed. Will be described. As illustrated in FIG. 4, a sheet determination unit 254 is provided as a functional configuration of the image forming apparatus 1. The paper determination unit 254 is transported at the first transport speed based on the sensor output value Vedge of the optical sensor 12 at the second transport speed and the sensor output value Vedge of the optical sensor 12 at the first transport speed. It is determined whether or not the same image is printed on the paper P and the paper P being conveyed at the second conveyance speed.

  Specifically, the paper determination unit 254 in FIG. 4 uses the background color of the background image printed on the background plate 213 as the background when the edge position of the paper P is specified at the second transport speed. When the sensor output value Vedge of the optical sensor 12 at the second transport speed is the same as the sensor output value Vedge of the optical sensor 12 at the first transport speed every time the color is matched, the second transport is performed. It is determined that the same image is printed on the sheet P conveyed at the speed and the sheet P conveyed at the first conveyance speed.

  For example, as shown in FIG. In each of 1, 6 and 11, the sensor output value Vedge at the first transport speed and the sensor output value Vedge at the second transport speed are the same. In this case, it is determined that the same image is printed on the sheet P conveyed at the second conveyance speed and the sheet P conveyed at the first conveyance speed.

  Note that the initial adjustment mode may be used when the paper P is conveyed at the first conveyance speed, and the normal printing mode or the collation mode may be used when the paper P is conveyed at the second conveyance speed.

  Next, a description will be given of a configuration for determining whether or not the factor that determines that the same image has not been printed is due to the fact that the paper P is being conveyed while being inclined. As shown in FIG. 4, the image forming apparatus 1 includes a time series determination unit 255.

  The time-series determination unit 255 in FIG. 4 does not determine that the same image is printed on the paper P conveyed at the second conveyance speed and the paper P conveyed at the first conveyance speed. When the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the second transport speed matches the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the first transport speed, It is determined that the paper P is conveyed while being inclined.

  As described above, even if the paper P is transported at an inclination, when the same image is printed on the paper P, the pattern that changes as the paper P is transported is the same. It is possible to determine whether or not the same image has been printed.

  4 determines that the same image is printed on the paper P transported at the second transport speed and the paper P transported at the first transport speed. The time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the second transport speed does not match the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the first transport speed. In this case, it is determined that an image having a different pattern is printed.

  The conveyance control unit 253 in FIG. 4 changes the conveyance speed of the paper P from the second conveyance speed to the first conveyance speed when it is determined that an image with a different pattern is printed. The conveyance control unit 253 conveys the leading edge of the paper P to the upstream side to a preset position at the first conveyance speed.

  As described above, when it is determined that images of different patterns are printed on the paper P transported at the first transport speed and the paper P transported at the second transport speed, The transport speed is changed to the first transport speed, and the leading edge of the paper P is transported upstream. Thereby, since it can transfer to the operation | movement which switches the background color of the background image of the background board 213 periodically, it can transfer to the process which specifies the position of the edge part of the paper P again.

  For example, when it is not determined that the same image is printed on the paper P being conveyed at the second conveyance speed and the paper P being conveyed at the first conveyance speed, The position of the end of the paper P is specified by returning to the first transport speed.

  The conveyance control unit 253 may discharge the paper P to the outside when it is determined that an image with a different pattern is printed.

  Next, a description will be given of a configuration for correcting an image in accordance with the inclination when the paper P is conveyed while being inclined. As illustrated in FIG. 4, the image forming apparatus 1 includes an image correction unit 256.

  The image correcting unit 256 in FIG. 4 corrects an image printed on the paper P. First, the time-series determination unit 255 obtains the inclination angle of the paper P based on the time-series change pattern when it is determined that the paper P is being conveyed while being inclined. Next, the image correction unit 256 corrects the position of the image printed on the paper P based on the inclination angle of the paper P obtained by the time series determination unit 255 and the offset amount of the paper P. .

  From the above description, the image forming apparatus 1 can detect the edge of the paper P including the black belt. Next, a specific operation example will be described with reference to FIG. FIG. 6 is a flowchart illustrating a control example of the image forming apparatus 1 according to the present embodiment.

  In step S11, the paper P is transported at the first transport speed. In step S12, it is determined whether or not the sampling period T1 has arrived. When the sampling period T1 has arrived, the process proceeds to step S13. In step S13, the sensor output values Vedge_a1 to Vedge_aN, the background color, and the distance a from the leading edge of the paper P to the optical sensor 12 are stored. In step S14, the background color is switched.

  In step S15, it is determined whether or not the trailing edge of the paper P is detected. When the trailing edge of the paper P is detected, the process proceeds to step S16. In step S16, the position of the edge of the first sheet P is specified. In step S17, the sampling period T2 for the second and subsequent sheets is determined. In step S18, the sheet P is conveyed at the second conveyance speed. The

  In step S19, the background color stored in step S13 is switched to before the sampling period T2. In step S20, it is determined whether or not the sampling period T2 has come. If the sampling period T2 has come, the sensor output value Vedge_bN is detected in step S21.

  In step S22, it is determined whether or not the sensor output value Vedge_bN matches the sensor output value Vedge_aN. When the sensor output value Vedge_bN matches the sensor output value Vedge_aN, the process proceeds to step S23, and the sensor output When the value Vedge_bN does not match the sensor output value Vedge_aN, the process returns to step S11.

  In step S23, it is determined whether or not the trailing edge of the sheet P has been detected. When the trailing edge of the sheet P is detected, the process proceeds to step S24. When the trailing edge of the sheet P is not detected, the process of step S19 is performed. Return to. In step S24, it is determined whether or not the next sheet P is conveyed. When the next sheet P is conveyed, the process returns to step S19, and when the next sheet P is not conveyed, the process ends. To do.

  Next, the reason why the background plate 213 is provided will be specifically described with reference to FIGS. FIG. 7 is a diagram illustrating an example in which the position of the edge of the blank paper P is detected without providing the background plate 213. FIG. 8 is a diagram illustrating an example in which the background plate 213 is not provided and the position of the end portion of the non-white paper P is erroneously detected.

  As shown in FIG. 7, as the paper P is transported along the transport direction, the optical sensor 12 detects the paper P at the detection position. For example, when the distance from the leading edge of the paper P to the detection position of the optical sensor 12 is the first distance a, the sensor output waveform of the optical sensor 12 changes from Low to High at the start of scanning, and the edge of the paper P Changes from High to Low. As a result, the sensor output value Vedge of the optical sensor 12 is 4600, which matches the position of the edge of the paper P. For this reason, if the paper P is a white paper, the position of the edge part of the paper P can be specified only by the optical sensor 12.

  On the other hand, as shown in FIG. 8, when the paper P is not a white paper and a dark color image such as a black belt is printed on the edge of the paper P, the edge of the paper P is correctly detected only by the optical sensor 12. The position of is not specified. Specifically, when the distance from the leading edge of the paper P to the detection position of the optical sensor 12 is the first distance a, the sensor output waveform of the optical sensor 12 changes from Low to High at the start of scanning, and the paper P It changes from High to Low in the black belt on the near side of the end of the. As a result, the sensor output value Vedge of the optical sensor 12 is 4500 and does not coincide with the position of the edge of the paper P. For this reason, when the paper P is not a white paper, depending on the pattern of the printed image, there is a possibility that the position of the end of the paper P cannot be specified only by the optical sensor 12.

  Therefore, as described above, the background plate 213 facing the optical sensor 12 is provided. The background plate 213 is configured such that the background color of the background image is alternately switched between black and white corresponding to the detection position of the optical sensor 12 as the paper P is conveyed. As a result, the position of the edge of the paper P is specified without depending on the pattern and color of the image printed on the paper P.

  Next, the reason why the conveyance speed of the paper P is lowered to the switching speed of the background plate 213 will be described with reference to FIG. FIG. 9 is a diagram illustrating an example of various parameters when A4 paper is conveyed. In FIG. 9, it is assumed that the paper P is A4 size. The process linear velocity is set to 460 mm / s, the length of A4 is set to 210 mm, the sheet passing time is set to 0.4565217 seconds, the background monochrome switching period is set to 0.05 seconds, and the sheet edge detection point is set to 9 points. In this case, there is a risk of detection omission before and after detection.

  In other words, if the background color of the background image printed on the background plate 213 is switched at the minimum detection cycle of the leading edge detection sensor 17, the edge of the paper P can be accurately detected even if the position of the black belt changes. can do. However, in actuality, the configuration for switching between black and white is mechanical and is slower than the sheet passing speed. For this reason, the number of times of detection decreases, and the detection accuracy becomes rough, so that the position of the end portion of the paper P may be erroneously detected. Therefore, in order to specify the position of the edge of the paper P, it is necessary to reduce the transport speed of the paper P to the switching speed of the background color of the background image on the background plate 213.

  Next, the case where the collation distance a ′ is not a constant interval but an indefinite interval as described above will be described with reference to FIGS.

  FIG. 10 shows the background color of the background image printed on the background plate 213 and the sensor output of the optical sensor 12 when the paper P on which the first black belt pattern image is printed is conveyed at the first conveyance speed. It is a figure which shows the correspondence with value Vedge.

  As shown in FIG. 10, an image of the first black belt pattern is printed on the first sheet P. Therefore, the transport speed of the paper P is lowered to the first transport speed that is the same as the background color switching speed of the background image of the background plate 213, and the image printed on the paper P and the background image are detected. As a result, since the sensor output value Vedge is the largest at 4600, the position corresponding to the sensor output value Vedge of 4600 is specified as the end position of the paper P.

  FIG. 11 shows the background color of the background image printed on the background plate 213 and the sensor output of the optical sensor 12 when the paper P on which the first black belt pattern image is printed is conveyed at the second conveyance speed. It is a figure which shows the correspondence with value Vedge.

  As shown in FIG. 11, an image of the first black belt pattern is printed on the second sheet P. That is, the same image is printed on the first sheet P and the second sheet P. In this case, every time the second distance b from the leading edge of the paper P to the optical sensor 12 reaches the collation distance a ′ as the paper P is transported along the transport direction at the second transport speed. In addition, the background color at the second conveyance speed is made to match the background color when the position of the end portion of the paper P is specified. At this time, if the sensor output value Vedge of the optical sensor 12 at the second transport speed and the sensor output value Vedge of the optical sensor 12 at the first transport speed are the same, the same image is printed. Determined.

  As shown in FIG. 11, the sensor output value Vedge matches when the collation distance a ′. This also confirms that the same image is printed on the first sheet P and the second sheet P.

  Next, a case where the image printed on the paper P conveyed on the third sheet is different from the image printed on the paper P conveyed on the first and second sheets will be described.

  FIG. 12 shows the background color of the background image printed on the background plate 213 and the sensor output of the optical sensor 12 when the paper P on which the image of the second black belt pattern is printed is conveyed at the second conveyance speed. It is a figure which shows the correspondence with value Vedge.

  As shown in FIG. 12, an image of the second black belt pattern is printed on the third sheet P. That is, the same image is not printed on the first and second sheets P and the third sheet P. In this case, as described above, as the paper P is transported along the transport direction at the second transport speed, the second distance b from the leading edge of the paper P to the optical sensor 12 is the collation distance a. Each time 'is reached, the background color at the second conveyance speed is made to match the background color when the position of the edge of the paper P is specified. At this time, if the sensor output value Vedge of the optical sensor 12 at the second transport speed and the sensor output value Vedge of the optical sensor 12 at the first transport speed are not the same, it is determined that the same image is printed. Not.

  As shown in FIG. 12, the sensor output value Vedge does not coincide with the collation distance a ′. Also from this, it cannot be confirmed that the same image is printed on the first and second sheets P and P.

  Therefore, the transport speed of the paper P is lowered to the first transport speed that is the same as the background color switching speed of the background image printed on the background plate 213, and the paper P and the background image are detected.

  FIG. 13 shows the background color of the background image printed on the background plate 213 and the sensor output of the optical sensor 12 when the paper P on which the second black belt pattern image is printed is conveyed at the first conveyance speed. It is a figure which shows the correspondence with value Vedge. In this case, since the sensor output value Vedge is the largest at 4600, the position corresponding to the sensor output value Vedge of 4600 is specified as the position of the end of the paper P.

  As described above, when the conveyed paper P is not printed with the same image, the process moves to the process of specifying the position of the edge of the paper P again, whereby the position of the edge of the paper P is determined. Can be specified.

  From the above description, the image forming apparatus 1 causes the optical sensor 12 to detect the paper P and the background image printed on the background plate 213 as the paper P is transported along the transport direction, whereby the paper P The position of the end of the is specified.

  Specifically, when the paper P is transported along the transport direction, the background color of the background image printed on the background plate 213 is alternately switched to one of black and white. Thus, when the optical sensor 12 detects the paper P and the background plate 213, the combination of the edge of the paper P and the background image of the white background color, and the combination of the edge of the paper P and the background image of the black background color However, it occurs frequently.

  As a result, even if the color of the image printed on the edge of the paper P is black in the same scanning direction, that is, in the same detection position, the background color of the background plate 213 adjacent to the edge of the paper P May be white. In other words, by switching the background color of the background image printed on the background board 213 alternately between black and white, what is the pattern and color of the image printed on the edge of the paper P. Even so, there are many opportunities to generate a density difference between the density of the image printed on the edge of the paper P and the density of the background image. As a result, the resolution for specifying the position of the edge of the paper P is increased. Therefore, the validity of the detection result of the optical sensor 12 is improved. Thereby, erroneous detection of the position of the end of the paper P can be eliminated.

  Further, since the position of the end portion of the paper P is specified as the paper P is transported along the transport direction, it is not necessary to stop the transport of the paper P halfway. Therefore, it is not necessary to stop the operation halfway in a series of steps of printing the paper P by forming an image on the paper P, transferring the formed image to the paper P, and fixing the image. Thereby, the production efficiency of the paper P is not reduced.

  In other words, the image forming apparatus 1 switches the paper P and the background plate 213 with the optical sensor 12 while alternately switching the background color of the background image printed on the background plate 213 to one of black and white. By detecting, the validity of the detection result of the optical sensor 12 can be improved, so that erroneous detection can be eliminated without reducing production efficiency.

  Further, the estimated position of the edge of the paper P is estimated according to the sensor output value Vedge of the optical sensor 12, and the position of the edge of the paper P is specified based on the estimated position. Therefore, the first stage in which the position of the edge of the paper P corresponding to the sensor output value Vedge of the optical sensor 12 is estimated, and the position of the edge of the paper P is specified based on the estimated position estimated. By the second stage, the position of the edge of the paper P is specified. Thereby, it is possible to utilize a highly valid one of the sensor output values Vedge of the optical sensor 12.

  Further, among the estimated positions of the edge of the paper P, the most estimated position is specified as the position of the edge of the paper P. Therefore, an invalid value can be excluded from the sensor output value Vedge of the optical sensor 12. Thereby, the position of the edge part of the paper P specified based on the sensor output value Vedge of the optical sensor 12 can be made highly valid.

  Further, the first estimated position corresponding to the background color switching speed of the background image printed on the background plate 213 is determined until the most estimated position among the estimated positions is specified as the position of the edge of the paper P. The paper P is transported at the transport speed. Therefore, when detecting the background image printed on the background plate 213, the optical sensor 12 can alternately detect the paper P and the white background color image and the paper P and the black background color background image. .

  That is, from the viewpoint of the optical sensor 12, the background color of the background image printed on the background plate 213 is controlled so as to periodically change to black and white. As a result, the resolution of detecting the position of the edge of the paper P can be increased. Since the first transport speed is a speed corresponding to the background color switching speed of the background image, the first transport speed is slower than normal printing, but the position of the edge of the paper P may be erroneously detected. Therefore, the paper P is not wasted. Thereby, the resource of the paper P can be used effectively.

  Further, when the most estimated position among the estimated positions is specified as the position of the end of the paper P, the paper P is transported at a second transport speed that is faster than the first transport speed. Therefore, it is not necessary to reduce the time required for printing the paper P in accordance with the background color switching speed of the background image. Thereby, the production efficiency of the paper P can be improved.

  Further, when the paper P is in the first transport, the most estimated position among the estimated positions is specified as the position of the end of the paper P. Therefore, in the first sheet after feeding, while the sheet P is conveyed, the position of the end of the sheet P is detected from the leading end of the sheet P to a predetermined position while switching the background color a plurality of times. Become. Accordingly, it is possible to avoid erroneous detection of the position of the end portion of the sheet P, so that the first sheet P after the sheet feeding is not wasted and resources can be effectively utilized.

  Further, when the estimated number of estimated positions exceeds a preset threshold value, the most estimated position is specified as the position of the edge of the paper P. When the position of the edge of the paper P is specified, the paper P is transported at a second transport speed that is faster than the first transport speed. Therefore, even when one sheet P is being conveyed, the position of the end of the sheet P is specified, and thereafter the sheet P is conveyed at the second conveyance speed. Thereby, the production time of the paper P can be shortened.

  At the first transport speed, the sensor output value of the optical sensor 12 at the first distance a corresponding to the position of the edge of the paper P and the optical sensor 12 from the leading edge of the paper P and the first distance a. A background color at the first distance a is associated and stored together with Vedge. Therefore, since the first distance a, the sensor output value Vedge, and the background color corresponding to the position of the end portion of the sheet P conveyed at the first conveyance speed are associated, the first conveyance speed. It is possible to compare the paper P transported at the time of the paper and the paper P transported at the second transport speed. As a result, the second and subsequent sheets P conveyed at different conveyance speeds can be compared with the first sheet P.

  Further, the first distance a extracted based on a preset condition is set as a collation distance a ′. At the second transport speed, as the paper P different from the first transport speed is transported along the transport direction, the second distance b from the front end of the paper P to the optical sensor 12 is verified. Each time the distance a ′ is reached, the background color of the background image printed on the background plate 213 at the second transport speed is made to match the background color when the position of the edge of the paper P is specified. .

  Therefore, since the background color at the collation distance a ′ at the first transport speed matches the background color at the second distance b at the second transport speed, the images printed on the paper P are the same. If so, the same sensor output value Vedge is obtained. Thereby, it is possible to determine whether or not the same image is printed on the paper P transported at the first transport speed and the paper P transported at the second transport speed.

  In addition, whenever the background color of the background image printed on the background board 213 is matched with the background color when the position of the edge of the paper P is specified at the second transport speed, the second transport is performed. When the sensor output value Vedge of the optical sensor 12 at the speed and the sensor output value Vedge of the optical sensor 12 at the first transport speed are the same, the sheet P transported at the second transport speed and the first It is determined that the same image is printed on the paper P transported at the transport speed. Therefore, whether or not the same image is printed on the first sheet P and the second and subsequent sheets P can be determined at different transport speeds. Thereby, it is possible to determine whether the same image is printed on the continuously conveyed paper without lowering the production efficiency.

  In addition, it is not determined that the same image is printed on the paper P transported at the second transport speed and the paper P transported at the first transport speed, and the optical at the second transport speed is not determined. When the time-series change pattern of the sensor output value Vedge of the sensor 12 matches the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the first transport speed, the sheet P is transported in an inclined manner. It is determined that Thereby, the inclination of the paper P can be determined at low cost.

  Further, the position of the image printed on the paper P is corrected based on the inclination angle of the paper P obtained based on the time-series change pattern and the offset amount of the paper P. Thereby, wasteful disposal of the paper P can be reduced at a low cost.

  In addition, it is not determined that the same image is printed on the paper P transported at the second transport speed and the paper P transported at the first transport speed, and the optical at the second transport speed is not determined. If the time-series change pattern of the sensor output value Vedge of the sensor 12 and the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the first transport speed do not match, an image of a different pattern is printed. It is determined that Accordingly, whether or not images of different patterns are printed on the first sheet P and the second and subsequent sheets P at different transport speeds, more specifically than the first sheet P. The second sheet P can be determined at a higher transport speed. Thereby, it is possible to determine whether or not the continuously conveyed paper is printed with different images without reducing the production efficiency.

  If it is determined that an image with a different pattern is printed, the transport speed of the paper P is changed from the second transport speed to the first transport speed. Therefore, the conveyance speed is changed according to the switching speed of the background color of the background image printed on the background plate 213. Thereby, when an image of a different pattern is printed, the process can be shifted to the process of specifying the position of the edge of the paper P again.

  If it is not determined that the same image is printed on the paper P being transported at the second transport speed and the paper P transported at the first transport speed, the process returns to the first transport speed. Then, the position of the edge of the paper P is specified. Therefore, even if it is not determined that the same image is printed, the position of the edge of the sheet P is estimated again at the first conveyance speed, and the most estimated position among the estimated positions is the sheet P. It is specified at the end position. Thereby, when it is not determined that the same image is printed, it is possible to shift to the process of specifying the position of the end portion of the paper P again.

  Further, when the image is changed to the first transport speed due to the printing of a different pattern image, the leading edge of the paper P is transported upstream to a preset position. Therefore, the process for estimating the position of the edge of the paper P can be performed again. Thereby, even if an image of a different pattern is printed, the process can be shifted to the process of estimating the position of the edge of the paper P.

  If it is determined that an image having a different pattern is printed, the paper P is discharged to the outside. Thereby, although wasteful disposal of the paper P occurs, the production efficiency of the paper P can be maintained.

  As described above, according to the image forming apparatus 1 according to the present embodiment, the optical sensor 12 that detects the paper P that is transported along the transport direction and the optical sensor 12 are provided so as to face the background image. When the paper P is transported along the transport direction, the background color control unit 251 that switches the background color of the background image alternately to one of black and white, and the transport direction As the paper P is conveyed, the optical sensor 12 detects the paper P and the background image, and an end specifying unit 252 that specifies the position of the end of the paper P is provided. As a result, erroneous detection can be eliminated without reducing production efficiency.

  Further, the edge specifying unit 252 specifies the position of the edge of the paper P based on the estimated position of the edge of the paper P estimated according to the sensor output value Vedge of the optical sensor 12. Thereby, it is possible to utilize a highly valid one of the sensor output values Vedge of the optical sensor 12.

  Further, the edge specifying unit 252 specifies the most estimated position among the estimated positions as the position of the edge of the paper P. Thereby, the position of the edge part of the paper P specified based on the sensor output value Vedge of the optical sensor 12 can be made highly valid.

  The conveyance control unit 253 further conveys a plurality of sheets of paper P continuously. The conveyance control unit 253 specifies the most estimated position among the estimated positions as the end position of the sheet P. Up to this point, the paper P is transported at the first transport speed corresponding to the background color switching speed of the background image. As a result, the resolution of detection of the position of the edge of the paper P is increased and the paper P is not discarded wastefully, so that the resource of the paper P can be used effectively. be able to.

  Further, when the most estimated position among the estimated positions is specified as the end position of the paper P, the transport control unit 253 sets the paper P at the second transport speed that is faster than the first transport speed. Are to be transported. Thereby, the production efficiency of the paper P can be improved.

  Further, the edge specifying unit 252 specifies the most estimated position among the estimated positions as the position of the edge of the paper P when the paper P is in the first transport. Accordingly, it is possible to avoid erroneous detection of the position of the end portion of the sheet P, so that the first sheet P after the sheet feeding is not wasted and resources can be effectively utilized.

  Further, the edge specifying unit 252 specifies the most estimated position as the position of the edge of the paper P when the number of times the estimated position is estimated exceeds a preset threshold value. As a result, the position of the end portion of the sheet P is specified even while the sheet P is being conveyed, and thereafter the sheet P is conveyed at the second conveyance speed. It can be shortened.

  The edge specifying unit 252 also corresponds to the first distance a from the leading edge of the paper P to the optical sensor 12 and the first distance a corresponding to the position of the edge of the paper P at the first transport speed. In addition to the sensor output value Vedge of the optical sensor 12 at the time, the background color at the first distance a is associated and stored. As a result, the second and subsequent sheets P conveyed at different conveyance speeds can be compared with the first sheet P.

  Further, the first distance a extracted based on a preset condition is set as a collation distance a ′, and the background color control unit 251 performs the first operation along the transport direction at the second transport speed. As the paper P different from that at the first transport speed is transported, every time the second distance b from the leading edge of the paper P to the optical sensor 12 reaches the collation distance a ′, the second transport speed is increased. The background color of the background image at that time is made to coincide with the background color when the position of the edge of the paper P is specified. Thereby, it is possible to determine whether or not the same image is printed on the paper P transported at the first transport speed and the paper P transported at the second transport speed.

  Further, based on the sensor output value Vedge of the optical sensor 12 at the second transport speed and the sensor output value Vedge of the optical sensor 12 at the first transport speed, the paper P transported at the first transport speed, The paper determination unit 254 further determines whether or not the same image is printed on the paper P being conveyed at the second conveyance speed. The sensor output value Vedge of the optical sensor 12 at the second transport speed and the first transport speed each time the background color of the background image matches the background color when the position of the edge of the paper P is specified. When the sensor output value Vedge of the optical sensor 12 is the same, the paper P transported at the second transport speed and the paper P transported at the first transport speed are the same. Image is one which determined to be printed. Thereby, it is possible to determine whether the same image is printed on the continuously conveyed paper without lowering the production efficiency.

  The optical sensor 12 further includes a time-series determination unit 255 that determines a time-series change pattern of the sensor output value Vedge of the optical sensor 12, and the time-series determination unit 255 includes the paper P being conveyed at the second conveyance speed, and the first It is not determined that the same image is printed on the paper P conveyed at the first conveyance speed, and the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the second conveyance speed and the first When the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the same transport speed matches, it is determined that the paper P is being transported in an inclined manner. Thereby, the inclination of the paper P can be determined at low cost.

  Further, the image correction unit 256 for correcting an image printed on the paper P is further provided. When the time-series determination unit 255 determines that the paper P is conveyed while being tilted, based on the time-series change pattern, The image correction unit 256 obtains the inclination angle of the paper P, and the image correction unit 256 prints the image printed on the paper P based on the inclination angle of the paper P obtained by the time series determination unit 255 and the deviation amount of the paper P. This corrects the position of. Thereby, wasteful disposal of the paper P can be reduced at a low cost.

  The optical sensor 12 further includes a time-series determination unit 255 that determines a time-series change pattern of the sensor output value Vedge of the optical sensor 12, and the time-series determination unit 255 includes the paper P being conveyed at the second conveyance speed, and the first It is not determined that the same image is printed on the paper P conveyed at the first conveyance speed, and the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at the second conveyance speed and the first If the time-series change pattern of the sensor output value Vedge of the optical sensor 12 at this transport speed does not match, it is determined that an image of a different pattern is printed. Thereby, it is possible to determine whether or not the continuously conveyed paper is printed with different images without reducing the production efficiency.

  Also, the conveyance control unit 253 changes the conveyance speed of the paper P from the second conveyance speed to the first conveyance speed when it is determined that an image of a different pattern is printed. Thereby, when an image of a different pattern is printed, the process can be shifted to the process of specifying the position of the edge of the paper P again.

  Further, when it is not determined that the same image is printed on the paper P being transported at the second transport speed and the paper P transported at the first transport speed, the edge identifying unit 252 The position of the end of the paper P is specified by returning to the first transport speed. Thereby, when it is not determined that the same image is printed, it is possible to shift to the process of specifying the position of the end portion of the paper P again.

  The conveyance control unit 253 conveys the leading edge of the paper P to the upstream side to a preset position. Thereby, even if an image of a different pattern is printed, the process can be shifted to the process of estimating the position of the edge of the paper P.

The conveyance control unit 253 discharges the paper P to the outside when it is determined that an image with a different pattern is printed. Thereby, although wasteful disposal of the paper P occurs, the production efficiency of the paper P can be maintained.

  As described above, the image forming apparatus 1 according to the present invention has been described based on the embodiment. However, the present invention is not limited thereto, and modifications may be made without departing from the spirit of the present invention.

  For example, although an example in which a black belt is printed on the end of the paper P has been described, the present invention is not limited thereto, and a black pattern may be printed on the end of the paper P.

  In addition, in the present embodiment, the background color switching speed of the background image of the background plate 213 is reduced during the second conveyance speed, but this is not limiting, and the background color at the second conveyance speed is not limited. When the second distance b matches the collation distance a ′ by making the switching speed the same as the background color switching speed at the first transport speed and further increasing the second transport speed, the second speed The background color at the transport speed of may be matched with the background color at the first transport speed.

  Moreover, when switching the background color of the background image printed on the background plate 213, an example in which the background plate 213 is moved back and forth one color at a time along the transport direction has been described. The background color of the printed background image may be switched.

  For example, the background plate 213 is larger than the size from the leading edge to the trailing edge of the paper P, and white and black are alternately printed so that the background color is switched in units of detection positions of the optical sensor 12. Also good. In this case, the background plate 213 may be moved in one direction as the paper P is transported along the transport direction.

  Further, for example, the background plate 213 has a cylindrical shape, and white and black may be alternately printed on the surface of the cylindrical shape so that the background color is switched in units of detection positions of the optical sensor 12. . In this case, the background plate 213 may be rotated as the paper P is transported along the transport direction.

  Further, although an example in which a black image is printed on the edge of the paper P has been described, the present invention is not limited thereto, and a dark image may be printed on the edge of the paper P.

  Further, although an example in which the background color is alternately switched to white and black has been described, the present invention is not limited thereto, and the background color may be switched to white and dark colors alternately.

  In addition, although an example in which a CCD line sensor is used as a CIS line sensor has been described as the optical sensor 12, the present invention is not limited to this, and a different one, for example, a CMOS line sensor may be used.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y, 10M, 10C, 10K Image forming part 11Y, 11M, 11C, 11K Photosensitive drum 12 Optical sensor 15 Intermediate transfer belt 16 Secondary transfer roller 17 Front end detection sensor 20 Paper conveyance part 21 Paper feed unit 22 Paper Paper feeding unit 23 Paper discharge roller 24 Switching gate 25 Registration roller 30 Fixing device 45 Operation panel 100 Control unit 213 Background plate 251 Background color control unit 252 Edge specifying unit 253 Transport control unit 254 Paper determination unit 255 Time series determination unit 256 Image Correction unit 261 Storage unit SC Document reading device P Paper a First distance a ′ Collation distance b Second distance

Claims (17)

An optical sensor for detecting paper conveyed along the conveyance direction;
A background plate provided facing the optical sensor and having a background image printed thereon;
A background color control unit that alternately switches a background color of the background image to one of black and white when the paper is transported along the transport direction;
As the paper is transported along the transport direction, the optical sensor detects the paper and the background image, and an edge identifying unit that identifies the position of the edge of the paper;
An image forming apparatus comprising:   The edge identifying unit is configured to identify a position of an edge of the sheet based on an estimated position of the edge of the sheet estimated according to a sensor output value of the optical sensor. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 2, wherein the end specifying unit specifies a position estimated most among the estimated positions as a position of an end of the sheet. A transport control unit for transporting a plurality of sheets of the paper continuously;
The conveyance control unit is configured to determine a first conveyance speed according to a background color switching speed of the background image until the most estimated position among the estimated positions is specified as the position of the edge of the sheet. The image forming apparatus according to claim 3, wherein the sheet is conveyed.   When the most estimated position among the estimated positions is specified as the position of the edge of the sheet, the conveyance control unit is configured to perform the sheet at a second conveyance speed that is faster than the first conveyance speed. The image forming apparatus according to claim 4, wherein the image forming apparatus conveys the image.   The edge identifying unit is configured to identify the most estimated position among the estimated positions as the position of the edge of the sheet when the sheet is in the first conveyance. The image forming apparatus according to claim 5.   The edge identifying unit is configured to identify the most estimated position as the position of the edge of the sheet when the number of times the estimated position is estimated exceeds a preset threshold value. The image forming apparatus according to claim 5.   The edge identifying unit corresponds to a position of an edge of the sheet at the first conveyance speed, and corresponds to a first distance from the leading edge of the sheet to the optical sensor and the first distance. The image forming apparatus according to claim 5, wherein a background color at the first distance is associated and stored together with a sensor output value of the optical sensor. Among the first distance, the one extracted based on a preset condition is set as a collation distance,
The background color control unit detects the optical sensor from the leading edge of the paper as the paper different from that at the first transport speed is transported along the transport direction at the second transport speed. The background color of the background image at the second conveyance speed is changed to the background color when the position of the edge of the paper is specified every time the second distance up to the collation distance is reached. The image forming apparatus according to claim 8, wherein the image forming apparatuses match each other. The paper transported at the first transport speed based on the sensor output value of the optical sensor at the second transport speed and the sensor output value of the optical sensor at the first transport speed; A paper determination unit for determining whether or not the same image is printed on the paper transported at the second transport speed;
The paper determination unit performs the second transport every time the background color of the background image matches the background color when the position of the edge of the paper is specified at the second transport speed. When the sensor output value of the optical sensor at the speed and the sensor output value of the optical sensor at the first transport speed are the same, the paper transported at the second transport speed; The image forming apparatus according to claim 9, wherein the image forming apparatus determines that the same image is printed on the sheet conveyed at a conveyance speed of one. A time-series determining unit that determines a time-series change pattern of the sensor output value of the optical sensor;
The time-series determination unit is not determined that the same image is printed on the paper transported at the second transport speed and the paper transported at the first transport speed, When the time-series change pattern of the sensor output value of the optical sensor at the second transport speed matches the time-series change pattern of the sensor output value of the optical sensor at the first transport speed, The image forming apparatus according to claim 10, wherein the image forming apparatus determines that the sheet is conveyed while being inclined. An image correction unit for correcting an image printed on the paper;
The time-series determination unit obtains the inclination angle of the paper based on the change pattern of the time series when it is determined that the paper is being conveyed while being inclined,
The image correction unit corrects the position of an image printed on the paper based on the inclination angle of the paper obtained by the time-series determination unit and a deviation amount of the paper. The image forming apparatus according to claim 11. A time-series determining unit that determines a time-series change pattern of the sensor output value of the optical sensor;
The time-series determination unit is not determined that the same image is printed on the paper transported at the second transport speed and the paper transported at the first transport speed, If the time-series change pattern of the sensor output value of the optical sensor at the second transport speed and the time-series change pattern of the sensor output value of the optical sensor at the first transport speed do not match, they are different. The image forming apparatus according to claim 10, wherein the image forming apparatus determines that a pattern image is printed.   The conveyance control unit changes the conveyance speed of the paper from the second conveyance speed to the first conveyance speed when it is determined that the image of the different pattern is printed. The image forming apparatus according to claim 13.   When the edge specifying unit does not determine that the same image is printed on the paper transported at the second transport speed and the paper transported at the first transport speed, The image forming apparatus according to claim 10, wherein the position is returned to the first conveyance speed and the position of the end of the sheet is specified.   The image forming apparatus according to claim 14, wherein the conveyance control unit conveys the leading edge of the sheet to the upstream side to a preset position.   The image forming apparatus according to claim 13, wherein the conveyance control unit discharges the sheet to the outside when it is determined that the image of the different pattern is printed.

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