JP2018078501A - Sheet end detection device, image formation apparatus and sheet end detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet end detection device which can detect the position of an end of a sheet accurately even with an additional printing sheet.SOLUTION: A sheet end detection device 50 includes: a mode switching unit 61 which switches between the first mode of turning on a first light source unit 52 and turning off a second light source unit 54 and the second mode of turning on the second light source unit 54 and turning off the first light source unit 52; an edge detection unit 62 which detects edge positions in a reflection image imaged by an imaging unit 53 when turning on the first light source unit 52 and a transmission image imaged by the imaging unit 53 when turning on the second light source unit 54; a drawing region detection unit 63 which detects a drawing region corresponding to a drawing portion formed on a sheet from the reflection image and transmission image; and a decision unit 64 which decides the position of the end of the sheet S on the basis of the edge positions on the outer end side with respect to the drawing region in the reflection image and transmission image.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a sheet end detection device, an image forming apparatus, and a sheet end detection method for detecting the position of the end of a sheet being conveyed.

  An electrophotographic image forming apparatus is widely used. A general electrophotographic image forming apparatus includes, as a printing process, a process of attaching toner to an electrostatic latent image on a photoreceptor, a process of primary transfer of the toner image on the photoreceptor to a transfer belt, and a transfer belt A step of secondarily transferring the upper toner image onto the sheet and a step of fixing the toner image on the sheet by the fixing device are executed.

  If the paper is always conveyed to the same position, an image can be formed on the paper according to the same position reference. However, there are cases where a slight lateral shift occurs in the paper due to various slips and paper bending occurring in the transport path. The lateral deviation is a positional deviation in the width direction (that is, the main scanning direction) orthogonal to the sheet conveyance direction. In order to perform high-quality printing on a sheet even when a lateral shift occurs, it is necessary to adjust the image forming position in accordance with the positional shift amount in the width direction of the sheet. Therefore, conventionally, using a photo sensor array arranged in the main scanning direction, an image obtained by reflected light from the paper irradiated with light is acquired, and the edge position in the image is detected as the position of the paper edge. It has been broken.

  By the way, there are papers on which images have already been formed (hereinafter referred to as reprint papers) as papers to be subjected to image formation. If an image is formed over the entire edge of the sheet, the amount of reflected light from the sheet is reduced, and no edge is detected in the image. In this case, the paper edge cannot be detected.

  In view of this, Japanese Unexamined Patent Application Publication No. 2012-128268 (Patent Document 1) discloses a paper end detection unit including an antireflection unit and a reflection unit that are selectively disposed at a detection position on the opposite side of the optical sensor at a position where the paper is sandwiched. Is disclosed. The paper edge detection unit positions the reflection unit at the detection position when an edge is not detected in the image in a state where the reflection preventing unit is positioned at the detection position. The paper edge detection unit detects the edge position in the image in a state where the reflection part is positioned at the detection position as the paper edge position.

JP 2012-128268 A

  However, an image is not always formed on the entire end portion of the paper in the additionally printed paper. In the case of reprinted paper in which an image (for example, a ruled line on the front surface) is formed on a part of the edge of the paper, in the technique disclosed in Japanese Patent Application Laid-Open No. 2012-128268, the antireflection portion is positioned at the detection position. Therefore, there is a problem that an edge that is a boundary between an area on which the image of reprinted paper is formed and an area on which no image is formed is erroneously detected as the paper edge.

  The present disclosure has been made in order to solve the above-described problems, and an object in one aspect is to detect the edge of the paper with high accuracy even if the paper is reprinted paper. To provide a detection device, an image forming apparatus, and a paper edge detection method.

  According to a certain aspect, the sheet edge detection device captures a one-dimensional image along the width direction of the sheet being conveyed, one end of the one-dimensional image is located in the sheet, and the other end of the one-dimensional image is the sheet. An imaging unit disposed so as to be located outside, and a first light source unit that is disposed on the same side as the imaging unit with respect to the paper and that irradiates light on the paper side to cause the reflected light of the paper to enter the imaging unit And a second light source unit that is disposed on the opposite side of the imaging unit with respect to the paper, irradiates light toward the imaging unit, and irradiates light from the first light source unit and does not irradiate light from the second light source unit. A mode switching unit for switching between a first mode and a second mode in which light is emitted from the second light source unit and light is not emitted from the first light source unit, and a one-dimensional image captured by the imaging unit in the first mode. A first image and a one-dimensional image captured by the imaging unit in the second mode. In the second image, an edge detection unit for detecting an edge position where a pixel having a luminance higher than a threshold and a pixel having a luminance lower than the threshold are adjacent to each other, a sheet from among the first image and the second image A drawing area detection unit for detecting a drawing area corresponding to the drawing part formed on the edge of the paper based on an edge position on the other end side of the drawing area in the first image and the second image. And a determining unit for determining the position of.

  According to another aspect, the sheet edge detection device captures a one-dimensional image along the width direction of the sheet being conveyed, one end of the one-dimensional image is located in the sheet, and the other end of the one-dimensional image is the sheet. An imaging unit disposed so as to be located outside the light source, and a light source unit that is disposed on the same side as the imaging unit with respect to the paper, and that causes the reflected light of the paper to enter the imaging unit by irradiating light on the paper side Switching between a reflection mode that is arranged on the opposite side of the imaging unit with respect to the paper and reflects the light from the light source unit toward the imaging unit and a non-reflection mode that does not reflect the light from the light source unit toward the imaging unit A possible reflection switching unit, a first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode, and a second image obtained by the imaging unit when the reflection switching unit is in the reflection mode. , Pixels with brightness greater than the threshold and brightness less than the threshold An edge detection unit for detecting an edge position adjacent to a pixel, and a drawing area detection for detecting a drawing area corresponding to a drawing part formed on the paper from the first image and the second image And a determination unit for determining the position of the end of the paper based on the edge position on the other end side of the drawing area in the first image and the second image.

  Preferably, in the first image, the edge detection unit detects at least one edge position where the luminance is changed from a pixel having a luminance higher than the threshold to a pixel having a luminance lower than the threshold along a direction from one end to the other end. The first edge position is detected. In the second image, the edge detection unit determines at least one edge position that changes from a pixel whose luminance is lower than the threshold value to a pixel whose luminance is higher than the threshold value along the direction from one end to the other end of the second image. Detect as position. When the first edge position closest to the one end and the second edge position closest to the one end are different, the drawing area detection unit has a pixel whose luminance is smaller than the threshold value in both the first image and the second image. This area is detected as a drawing area.

  Preferably, in the first image, the edge detection unit detects at least one edge position where the luminance is changed from a pixel having a luminance lower than the threshold to a pixel having a luminance higher than the threshold along a direction from one end to the other end. It is detected as the third edge position. The determination unit sets the candidate position when the second edge position that is located on the other end side of the drawing region and is closest to the one end is set as a candidate position, and the candidate position does not match any third edge position. Determine the position of the edge of the paper.

  Preferably, when the candidate position matches any of the third edge positions, the determination unit sets the first edge position that is located on the other end side closest to the candidate position and that is closest to the one end to the end of the sheet. Determine as position.

  Preferably, when the drawing area detection unit cannot detect the drawing area, the determination unit determines the first edge position closest to the one end as the position of the end of the sheet.

  Preferably, the paper end detection device further includes an information acquisition unit capable of acquiring information indicating whether the color of the paper is white and information indicating whether an image has already been formed on the paper. When the information acquisition unit acquires information indicating that the color of the paper is white and information indicating that no image is formed on the paper, the determination unit determines the first edge position closest to the one end side. Determine the position of the edge of the paper.

  Preferably, the paper end detection device further includes an information acquisition unit capable of acquiring information indicating whether the thickness of the paper is greater than a predetermined value. When the information acquisition unit acquires information indicating that the thickness of the sheet is greater than the predetermined value, the determination unit determines the second edge position closest to the one end side as the position of the end of the sheet.

  Preferably, the determination unit performs error notification when the edge detection unit cannot detect the edge position in both the first image and the second image.

  According to yet another aspect, the sheet edge detection device captures a one-dimensional image along the width direction of the sheet being conveyed, one end of the one-dimensional image is located in the sheet, and the other end of the one-dimensional image is An imaging unit disposed so as to be located outside the paper, and a light source unit that is disposed on the same side as the imaging unit with respect to the paper and causes the reflected light of the paper to enter the imaging unit by irradiating light on the paper side And a reflection mode in which light from the light source unit is reflected toward the imaging unit and a non-reflection mode in which light from the light source unit is not reflected toward the imaging unit. From the switchable reflection switching unit and the first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode, from the second image obtained by the imaging unit when the reflection switching unit is in the reflection mode Difference image to generate a difference image by subtracting And an edge for detecting at least one edge position in the difference image that changes from a pixel whose luminance is lower than the threshold value to a pixel whose luminance is higher than the threshold value along a direction from one end to the other end. A detection unit, and a determination unit for determining an edge position closest to one end side as the position of the end of the sheet.

  Preferably, the imaging unit captures a one-dimensional image having a length set in advance according to the positional deviation amount in the width direction of the sheet.

  Preferably, the edge detection unit sets a threshold according to the luminance distribution of each pixel of the first image and the second image.

  According to yet another aspect, the image forming apparatus includes an image forming unit for forming an image on the paper, the paper edge detection device, and the position of the paper edge detected by the paper edge detection device. And a control device that adjusts a position at which the image forming unit forms an image on a sheet.

  According to another aspect, a one-dimensional image is taken along the width direction of the paper being conveyed, one end of the one-dimensional image is located in the paper, and the other end of the one-dimensional image is located outside the paper. A first light source unit that is disposed on the same side as the imaging unit with respect to the sheet and that irradiates light on the sheet side to cause the reflected light of the sheet to enter the imaging unit, and the sheet On the other hand, a paper edge detection method in a paper edge detection device that is disposed on the opposite side of the imaging unit and includes a second light source unit that irradiates light toward the imaging unit, irradiates light from the first light source unit, Obtained by the imaging unit in the first mode, a step of switching between a first mode in which light is not emitted from the two light source units and a second mode in which light is emitted from the second light source unit and light is not emitted from the first light source unit. The first image and the first image obtained by the imaging unit in the second mode. A step of detecting an edge position where a pixel having a luminance higher than a threshold and a pixel having a luminance lower than the threshold are adjacent to each other, and a drawing formed on the paper from the first image and the second image A step of detecting a drawing area corresponding to the portion, and a step of determining the position of the edge of the paper based on the edge position on the other end side of the drawing area in the first image and the second image.

  According to another aspect, a one-dimensional image is taken along the width direction of the paper being conveyed, one end of the one-dimensional image is located in the paper, and the other end of the one-dimensional image is located outside the paper. An imaging unit disposed on the same side as the imaging unit with respect to the paper, and a light source unit that causes the reflected light of the paper to enter the imaging unit by irradiating light on the paper side, and the paper A reflection switching unit arranged on the opposite side of the imaging unit and capable of switching between a reflection mode in which light from the light source unit is reflected toward the imaging unit and a non-reflection mode in which light from the light source unit is not reflected toward the imaging unit The paper edge detection method in the paper edge detection apparatus includes a first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode, and an imaging unit when the reflection switching unit is in the reflection mode. In the obtained second image, the luminance is lower than the threshold value. A step of detecting an edge position where a large pixel and a pixel whose luminance is lower than a threshold value are adjacent to each other, and a drawing region corresponding to a drawing portion formed on the paper is detected from the first image and the second image. And a step of determining the position of the edge of the paper based on the edge position on the other end side of the drawing area in the first image and the second image.

  According to another aspect, a one-dimensional image is taken along the width direction of the paper being conveyed, one end of the one-dimensional image is located in the paper, and the other end of the one-dimensional image is located outside the paper. An imaging unit disposed on the same side as the imaging unit with respect to the paper, and a light source unit that causes the reflected light of the paper to enter the imaging unit by irradiating light on the paper side, and the paper A reflection switching unit arranged on the opposite side of the imaging unit and capable of switching between a reflection mode in which light from the light source unit is reflected toward the imaging unit and a non-reflection mode in which light from the light source unit is not reflected toward the imaging unit The paper edge detection method in the paper edge detection apparatus includes the first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode, and the imaging unit when the reflection switching unit is in the reflection mode. Subtract by subtracting from the obtained second image And generating at least one edge position in which the luminance changes from a pixel whose luminance is lower than the threshold value to a pixel whose luminance is higher than the threshold value along a direction from one end to the other end in the difference image. And a step of determining the edge position closest to the one end side as the position of the end of the sheet.

  In one aspect, the position of the edge of the paper can be detected with high accuracy even if the paper is additionally printed.

2 is a diagram illustrating an example of an internal structure of the image forming apparatus according to Embodiment 1. FIG. FIG. 2 is a block diagram illustrating a main hardware configuration of the image forming apparatus illustrated in FIG. 1. 1 is a block diagram illustrating a schematic configuration of a paper edge detection device according to a first embodiment. FIG. 4 is a plan view illustrating a schematic configuration of the sheet edge detection device illustrated in FIG. 3. It is a figure which shows a reflected image and a transmission image in case the normal paper in which the drawing part is not formed is a detection target. It is a figure which shows a reflective image and a permeation | transmission image in case the normal paper which has one drawing part by black toner is a detection target. FIG. 6 is a diagram illustrating a reflected image and a transmitted image when a normal sheet on which a plurality of drawn portions of black toner are formed is a detection target. It is a figure which shows a reflective image and a permeation | transmission image when the thin paper which has one drawing part by black toner is a detection target. It is a figure which shows a reflective image and a permeation | transmission image in case the thin paper in which the drawing part by black toner was formed in multiple numbers is a detection target. It is a figure which shows a reflective image and a permeation | transmission image in case the thin paper which has one drawing part by yellow toner is a detection target. It is a figure which shows the reflection image and transmission image when the thin paper in which a drawing part is not formed is a detection target, and paper dust adheres to CIS. FIG. 4 is a flowchart showing a part of a processing flow in the paper edge detection apparatus shown in FIG. 3. FIG. FIG. 4 is a flowchart showing the remaining part of the flow of determination processing in the paper edge detection device shown in FIG. 3. FIG. FIG. 6 is a block diagram illustrating a configuration of a paper edge detection device according to a second embodiment. It is a figure explaining the change of the optical path by the state of the reflection switching part with which the paper edge detection apparatus shown in FIG. 14 is provided. FIG. 9 is a block diagram illustrating a configuration of a paper edge detection device according to a third embodiment. It is a figure which shows the image when the normal paper which has the drawing part by a black toner in an edge part is a detection target, and paper dust has adhered to CIS. FIG. 10 is a block diagram illustrating a configuration of a detection processing unit included in a paper edge detection device according to Modification 3.

  Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated. Each embodiment and each modified example described below may be selectively combined as appropriate.

<Embodiment 1>
[Internal configuration of image forming apparatus]
With reference to FIG. 1, an image forming apparatus 100 equipped with a paper end detection device 50 will be described. FIG. 1 is a diagram illustrating an example of the internal structure of the image forming apparatus 100.

  FIG. 1 shows an image forming apparatus 100 that is a color printer. Hereinafter, the image forming apparatus 100 that is a color printer will be described. However, the image forming apparatus 100 is not limited to a color printer. For example, the image forming apparatus 100 may be a monochrome printer or a multi-functional peripheral (MFP).

  The image forming apparatus 100 includes image forming units 1Y, 1M, 1C, and 1K, a transfer belt 30, a primary transfer roller 31, a secondary transfer roller 33, a cassette 37, a driven roller 38, a driving roller 39, A pickup roller 41, a transport roller 43, a fixing device 44, and a paper end detection device 50 are provided. Furthermore, although not shown in FIG. 1, the image forming apparatus 100 includes a control device (described later) that controls the operation of the image forming apparatus 100.

  The image forming units 1Y, 1M, 1C, and 1K are arranged in order along the transfer belt 30. The image forming unit 1Y receives toner from the toner bottle 15Y and forms a yellow (Y) toner image. The image forming unit 1M receives the supply of toner from the toner bottle 15M and forms a magenta (M) toner image. The image forming unit 1C receives toner from the toner bottle 15C and forms a cyan (C) toner image. The image forming unit 1K receives toner from the toner bottle 15K and forms a black (BK) toner image.

  The image forming units 1Y, 1M, 1C, and 1K are arranged along the transfer belt 30 in the order of the rotation direction of the transfer belt 30, respectively. Each of the image forming units 1Y, 1M, 1C, and 1K includes a photoconductor 10, a charging device 11, an exposure device 12, a developing device 13, and a cleaning device 17.

  The charging device 11 uniformly charges the surface of the photoconductor 10. The exposure device 12 irradiates the photoconductor 10 with laser light in accordance with a control signal from a control device to be described later, and exposes the surface of the photoconductor 10 in accordance with the input image pattern. Thereby, an electrostatic latent image corresponding to the input image is formed on the photoreceptor 10.

  The developing device 13 applies a developing bias to the developing roller 14 while rotating the developing roller 14, and causes the toner to adhere to the surface of the developing roller 14. As a result, the toner is transferred from the developing roller 14 to the photoreceptor 10, and a toner image corresponding to the electrostatic latent image is developed on the surface of the photoreceptor 10.

  The photoconductor 10 and the transfer belt 30 are in contact with each other at a portion where the primary transfer roller 31 is provided. The primary transfer roller 31 is configured to be rotatable. By applying a transfer voltage having a polarity opposite to that of the toner image to the primary transfer roller 31, the toner image is transferred from the photoreceptor 10 to the transfer belt 30.

  A yellow (Y) toner image, a magenta (M) toner image, a cyan (C) toner image, and a black (BK) toner image are sequentially superimposed and transferred from the photoreceptor 10 to the transfer belt 30. As a result, a color toner image is formed on the transfer belt 30.

  The transfer belt 30 is stretched around a driven roller 38 and a driving roller 39. The drive roller 39 is rotationally driven by, for example, a motor (not shown). The transfer belt 30 and the driven roller 38 rotate in conjunction with the driving roller 39. As a result, the toner image on the transfer belt 30 is conveyed to the secondary transfer roller 33.

  In the cassette 37, a sheet S as a recording medium is set. A plurality of sheets S are separated one by one by the pickup roller 41.

  The single sheet S that has been separated by the pickup roller 41 is sent out to the transport path 40. The transport roller 43 transports the paper S in the transport path 40 to the secondary transfer roller 33.

  Similarly to the primary transfer roller 31, a transfer voltage is applied to the secondary transfer roller 33, and the toner image conveyed by the transfer belt 30 is transferred to the sheet S at the nip portion with the secondary transfer roller 33, and the fixing device 44. Is fixed on the paper S under heat and pressure. The paper S on which the image is formed is discharged onto the paper discharge tray 48.

  The paper edge detection device 50 detects the position (paper edge position) of the edge (paper edge) in the width direction (main scanning direction) of the paper S in the transport path 40. Details of the sheet edge detection device 50 will be described later.

[Hardware configuration of image forming apparatus]
An example of the hardware configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 2 is a block diagram illustrating a main hardware configuration of the image forming apparatus 100.

  As shown in FIG. 2, the image forming apparatus 100 includes a paper end detection device 50, a control device 70, an image forming unit 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, A network interface 104, an operation panel 107, and a storage device 120 are included.

  The image forming unit 101 is configured to form an image on the paper S, and includes the image forming units 1Y, 1M, 1C, and 1K, the secondary transfer roller 33, the fixing device 44, and the like illustrated in FIG.

  The paper edge detection device 50 detects the paper edge position of the paper S and outputs position information indicating the detected paper edge position to the control device 70.

  The control device 70 is configured by at least one integrated circuit, for example. The integrated circuit is configured by, for example, at least one CPU, at least one DSP, at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or a combination thereof.

  The control device 70 controls the operation of the image forming apparatus 100 by executing the control program 122.

  The control device 70 reads the control program 122 from the storage device 120 to the ROM 102 based on receiving the execution instruction of the control program 122. The RAM 103 functions as a working memory and temporarily stores various data necessary for executing the control program 122.

  The control device 70 adjusts the image position formed on the paper S by the image forming unit 101 based on the paper edge position indicated by the position information received from the paper edge detection device 50.

  An antenna (not shown) or the like is connected to the network interface 104. The image forming apparatus 100 exchanges data with an external communication device via an antenna. The external communication device includes, for example, a mobile communication terminal such as a smartphone, a server, and the like. The image forming apparatus 100 may be configured such that the control program 122 can be downloaded from a server via an antenna.

  The operation panel 107 includes a display and a touch panel. The display and the touch panel are overlapped with each other, and the operation panel 107 receives, for example, a printing operation or a scanning operation for the image forming apparatus 100.

  The storage device 120 is a storage medium such as a hard disk or an external storage device. The storage device 120 stores the control program 122 of the image forming apparatus 100 and the like. The storage location of the control program 122 is not limited to the storage device 120, and the control program 122 is stored in a storage area (for example, a cache) of the control device 70, a ROM 102, a RAM 103, an external device (for example, a server), or the like. Also good.

  The control program 122 may be provided by being incorporated in a part of an arbitrary program, not as a single program. In this case, the control process according to the present embodiment is realized in cooperation with an arbitrary program. Even such a program that does not include some modules does not depart from the spirit of the control program 122 according to the present embodiment. Furthermore, some or all of the functions provided by the control program 122 may be realized by dedicated hardware. Furthermore, the image forming apparatus 100 may be configured in the form of a so-called cloud service in which at least one server executes a part of the processing of the control program 122.

[Internal configuration of paper edge detector]
With reference to FIG. 3 and FIG. 4, the configuration of the sheet edge detection device 50 will be described. FIG. 3 is a block diagram illustrating a schematic configuration of the sheet end detection device 50. FIG. 4 is a plan view showing a schematic configuration of the sheet end detection device 50.

  As shown in FIGS. 3 and 4, the sheet end detection device 50 includes a CIS (Contact Image Sensor) 51, a second light source unit 54, and a detection processing unit 55.

  The CIS 51 is an image sensor that reads a one-dimensional image, and has a bar shape extending in a direction perpendicular to the transport direction of the paper S. The CIS 51 includes an imaging unit 53 that extends in a rod shape, and a first light source unit 52 that is a linear light source parallel to the imaging unit 53. The first light source unit 52 includes an LED (Light Emitting Diode) 52a and a light guide 52b that converts light from the LED 52a into a linear light source.

  The imaging unit 53 includes a light receiving element array including a plurality of light receiving elements arranged in a line, and captures a one-dimensional image. Specifically, the imaging unit 53 converts one-dimensional image data composed of an analog voltage signal corresponding to the amount of light received by each light receiving element into one-dimensional image data in digital format, and outputs the converted one-dimensional image data To do. The value of each pixel in the one-dimensional image data indicates luminance.

  The image pickup unit 53 is arranged so as to pick up a one-dimensional image along a direction (paper width direction) perpendicular to the transport direction of the paper S and to pick up the edge of the paper. Specifically, as shown in FIG. 4, when viewed from the normal direction of the paper S, one end in the longitudinal direction of the imaging unit 53 overlaps with the vicinity of the approximate center of the paper S, and the other end is Arranged so as not to overlap the paper S. Accordingly, the imaging unit 53 can capture a one-dimensional image in which one end is located in the paper S and the other end is located outside the paper S. Hereinafter, in the one-dimensional image obtained by the imaging unit 53, one end located in the paper S is referred to as a paper side end, and the other end located outside the paper S is referred to as an external end.

  When there are a plurality of types of paper S used in the image forming apparatus 100, the imaging unit 53 has a length that overlaps all the end portions of the plurality of types of paper S.

  When the sheet S exists in the transport path 40, the light emitted from the first light source unit 52 is reflected by the sheet S and enters the imaging unit 53.

  The second light source unit 54 is a linear light source parallel to the CIS 51 and is disposed at a position facing the imaging unit 53 of the CIS 51 with the paper S interposed therebetween. That is, the second light source unit 54 is arranged on the opposite side of the imaging unit 53 with respect to the surface including the paper S. The second light source unit 54 emits light toward the imaging unit 53.

  Similar to the first light source unit 52, the second light source unit 54 includes an LED as a light emitting element and a light guide that converts light from the LED into a linear light source.

  Based on the one-dimensional image obtained by the imaging unit 53, the detection processing unit 55 performs detection processing for the paper edge position of the paper S. As shown in FIG. 4, the detection processing unit 55 includes a mode switching unit 61, an edge detection unit 62, a drawing area detection unit 63, and a determination unit 64.

  The mode switching unit 61 switches the operation state of the first light source unit 52 and the second light source unit 54 in order from the first mode to the second mode when the sheet S is present at a position facing the sheet end detection device 50. Switch. The first mode is a mode in which the first light source unit 52 is turned on and the second light source unit 54 is turned off. The second mode is a mode in which the first light source unit 52 is turned off and the second light source unit 54 is turned on.

  The mode switching unit 61 acquires a reflection image that is a one-dimensional image captured by the imaging unit 53 in the first mode, and acquires a transmission image that is a one-dimensional image captured by the imaging unit 53 in the second mode.

  The edge detection unit 62 binarizes the reflected image and the transmitted image, and specifies the edge position. Specifically, for each pixel, the edge detection unit 62 sets the value of the pixel to H level when the luminance is equal to or higher than a predetermined threshold, and sets the value of the pixel to L level when the luminance is lower than the threshold. As a result, the image is binarized.

  The edge detection unit 62 detects an edge position where an H level pixel and an L level pixel are adjacent in each of the binarized reflection image and transmission image. Specifically, the edge detection unit 62 detects the following four types of edge positions (1) to (4).

  (1) First edge position: In the reflected image, an edge position that changes from the H level to the L level when viewed from the sheet side end (that is, along the direction from the sheet side end toward the external end).

  (2) Second edge position: In the transparent image, it is an edge position that changes from the L level to the H level when viewed from the sheet side end.

  (3) Third edge position: In the reflected image, the edge position changes from the L level to the H level when viewed from the sheet side end.

  (4) Fourth edge position: In the transparent image, it is an edge position that changes from the H level to the L level when viewed from the sheet side edge.

  Here, in the first mode in which light is emitted from the first light source unit 52, the light emitted from the first light source unit 52 is reflected by the surface of the paper S and the part of the imaging unit 53 facing the paper S. Incident on the light receiving element. On the other hand, in the area where the sheet S does not exist, the light emitted from the first light source unit 52 travels straight, so that the light does not enter the light receiving element of the imaging unit 53 that is not opposed to the sheet S. Therefore, in the reflected image, ideally, the value of the pixel corresponding to the light receiving element facing the paper S is H level, and the value of the pixel corresponding to the light receiving element not facing the paper S is L level.

  Therefore, the edge detection unit 62 detects the first edge position as a position that is highly likely to be a paper edge, and detects the third edge position as a position that is unlikely to be a paper edge.

  In the second mode in which light is emitted from the second light source unit 54, when the light transmittance of the paper S is low, most of the light emitted from the second light source unit 54 does not pass through the paper S. Light does not enter the light receiving element of the imaging unit 53 in the facing part. On the other hand, in the area where the sheet S does not exist, the light emitted from the second light source unit 54 enters the imaging unit 53. Therefore, when the light transmittance of the paper S is low, the value of the pixel corresponding to the light receiving element facing the paper S is L level in the transmission image, and the value of the pixel corresponding to the light receiving element not facing the paper S is H. Become a level.

  Therefore, the edge detection unit 62 detects the second edge position as a position that is highly likely to be a paper edge, and detects the fourth edge position as a position that is unlikely to be a paper edge.

  The drawing area detection unit 63 corresponds to a drawing portion formed on the paper S with a color material having a high light absorption rate (a color material having a light absorption rate equal to or greater than a predetermined value) in each of the reflected image and the transmission image. Detect the drawing area. An example of the color material having a high light absorption rate is black toner. In addition, a combination of a plurality of toners is also included in the color material having a high light absorption rate in order to indicate a dark color (for example, blue or red). Further, not only toner but also color ink having a high light absorption rate is included. In the following description, it is assumed that the color material having a high light absorption rate is black toner, but the present invention is not limited to this.

  A drawing portion formed on the paper S by the black toner absorbs light emitted from the first light source unit 52. For this reason, in the reflected image, the pixels in the region corresponding to the drawing portion are at the L level.

  In addition, the drawing portion absorbs light emitted from the second light source unit 54 even if the light transmittance of the paper S is high. Therefore, also in the transparent image, the pixels in the area corresponding to the drawing portion are at the L level.

  Therefore, the drawing area detection unit 63 detects a pixel area having an L level value as a drawing area in both the reflected image and the transmitted image.

  The determination unit 64 determines the edge position (paper edge position) of the paper S based on the drawing area detected by the drawing area detection unit 63 and the edge position detected by the edge detection unit 62. Specifically, when the drawing area detection unit 63 detects the drawing area, the determination unit 64 determines the sheet end position based on the edge position on the outer end side of the drawing area.

  The determination unit 64 outputs position information indicating the determined sheet edge position to the control device 70. However, the determination unit 64 outputs an error notification to the control device 70 when the paper edge position cannot be determined. Upon receiving the error notification, the control device 70 displays a paper S transport error on the operation panel 107 (see FIG. 2).

[Paper edge position determination method]
A specific method for determining the sheet edge position in the determination unit 64 will be described with reference to FIGS.

(In the case of regular paper with no drawing part)
FIG. 5 is a diagram illustrating a reflection image and a transmission image when a normal paper Sa on which a drawing portion is not formed is a detection target. Here, the normal paper Sa is a white paper whose light transmittance is lower than a predetermined value and does not transmit most of the light from the second light source unit 54.

  In the example illustrated in FIG. 5, the edge detection unit 62 detects the position P1 as an edge position. The position P1 is a first edge position in the reflected image that changes from the H level to the L level when viewed from the sheet side end. The position P1 is also a second edge position that changes from the L level to the H level when viewed from the sheet side edge in the transmission image.

  As described above, both the first edge position and the second edge position are detected as positions that are highly likely to be the sheet edge. Therefore, the determination unit 64 may determine the position P1 that is the first edge position and the second edge position as the sheet end position.

(In the case of regular paper (reprinted paper) on which one drawing part (black toner) is formed)
FIG. 6 is a diagram showing a reflection image and a transmission image when the normal paper Sa having one drawing portion D1 made of black toner at the end is a detection target.

  Black toner has a high light absorption rate. Therefore, most of the light emitted from the first light source unit 52 to the drawing portion D <b> 1 is not reflected in the direction of the imaging unit 53.

  In the example illustrated in FIG. 6, the edge detection unit 62 detects the positions P2 and P3 as edge positions.

  The position P2 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  The position P3 is a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  A region R between the position P2 and the position P3 is a drawing region corresponding to the drawing portion D1 formed on the paper (normal paper Sa in FIG. 6) with black toner. Therefore, the determination unit 64 may determine the sheet end position based on the edge position that exists on the outer end side of the region R.

  In the region R, both the reflected image and the transmitted image are at the L level. Therefore, the drawing area detection unit 63 can detect an area of a pixel that is at the L level in both the reflection image and the transmission image as a drawing area.

  In the example illustrated in FIG. 6, a position P3 exists as an edge position that exists on the outer end side of the region R. The position P3 is a second edge position that is detected as a position that is likely to be the edge of the sheet as described above. Therefore, the determination unit 64 may determine the position P3 as the paper end position.

(In the case of regular paper (reprinted paper) with multiple drawing parts (black toner))
FIG. 7 is a diagram showing a reflection image and a transmission image when the normal paper Sa on which a plurality of drawing portions D1 with black toner are formed is a detection target.

  In the example illustrated in FIG. 7, the edge detection unit 62 detects positions P4, P5, P6, P7, and P8 as edge positions.

  The position P4 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  The position P5 is a third edge position in the reflected image that changes from the L level to the H level when viewed from the sheet side end.

  The position P6 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  The position P7 is a third edge position in the reflected image that changes from the L level to the H level when viewed from the sheet side end.

  The position P8 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end. The position P8 is also a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  A region R1 between the position P4 and the position P5 and a region R2 between the position P6 and the position P7 correspond to the drawing portion D1 formed on the paper (normal paper Sa in FIG. 7) by the black toner. This is a drawing area. For this reason, the determination unit 64 may determine the paper end position based on the edge position that is present on the outer end side with respect to the drawing region (region R2 in FIG. 7) located on the outermost end side.

  In the region R1 and the region R2, both the reflected image and the transmitted image are at the L level. Therefore, the drawing area detection unit 63 can detect an L level area in both the reflection image and the transmission image as the drawing area.

  In the example shown in FIG. 7, there are a position P7 and a position P8 as edge positions existing on the outer end side with respect to the region R2.

  The position P7 closest to the paper edge side is the third edge position detected as a position that is unlikely to be the paper edge. Therefore, the determination unit 64 determines that the position P7 is not the paper end position.

  Next, a position P8 close to the paper edge side is a first edge position detected as a position that is highly likely to be the paper edge, and a second edge position that is detected as a position that is highly likely to be the paper edge. But there is. Therefore, the determination unit 64 may determine the position P8 as the paper end position.

(In the case of thin paper (reprinted paper) on which one drawing part (black toner) is formed)
FIG. 8 is a diagram showing a reflection image and a transmission image when the thin paper Sb having one drawing portion D1 made of black toner is a detection target.

  Here, the thin paper Sb is a white paper having a light transmittance higher than a predetermined value and transmitting most of the light from the second light source unit 54. Therefore, even in the second mode in which light is emitted from the second light source unit 54, the imaging unit 53 receives light in a region facing the thin paper Sb. However, black toner has a high light absorption rate. Therefore, most of the light emitted from the second light source unit 54 to the drawing portion D1 is blocked by the drawing portion D1 and is not transmitted in the direction of the imaging unit 53.

  In the example illustrated in FIG. 8, the edge detection unit 62 detects the positions P9 and P10 as edge positions.

  The position P9 is a third edge position in the reflected image that changes from the L level to the H level when viewed from the sheet side end. The position P8 is also a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  The position P10 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  A region R between the paper side edge and the position P9 is a drawing region corresponding to a drawing portion D1 formed on the paper (thin paper Sb in FIG. 8) with black toner. Therefore, the determination unit 64 may determine the sheet end position based on the edge position that exists on the outer end side of the region R.

  In the example shown in FIG. 8, there are a position P9 and a position P10 as edge positions existing on the outer end side from the region R.

  The position P9 closest to the sheet edge side is a second edge position that is detected as a position that is highly likely to be the sheet edge in the transmission image, but is detected as a position that is unlikely to be the sheet edge in the reflected image. It is also the third edge position. Therefore, the determination unit 64 determines that the position P9 is not the paper end position.

  Next, the position P10 close to the sheet end side is a first edge position that is not detected as an edge position in the transmission image but is detected as a position that is likely to be the sheet end in the reflection image. Therefore, the determination unit 64 may determine the position P10 as the paper end position.

(In the case of thin paper (reprinted paper) with multiple drawing parts (black toner))
FIG. 9 is a diagram showing a reflection image and a transmission image when the thin paper Sb on which a plurality of drawing portions D1 with black toner are formed is a detection target.

  In the example shown in FIG. 9, the edge detection unit 62 detects positions P11, P12, P13, P14, and P15 as edge positions.

  The position P11 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end. The position P11 is also a fourth edge position that changes from the H level to the L level when viewed from the sheet side edge in the transmission image.

  The position P12 is a third edge position where the reflected image changes from the L level to the H level when viewed from the sheet side end. The position P12 is also a second edge position that changes from the L level to the H level when viewed from the sheet side edge in the transmission image.

  The position P13 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end. The position P13 is also a fourth edge position that changes from the H level to the L level when viewed from the sheet side edge in the transparent image.

  The position P14 is a third edge position in the reflected image that changes from the L level to the H level when viewed from the sheet side end. Further, the position P14 is a second edge position that changes from the L level to the H level when viewed from the sheet side end in the transmission image.

  The position P15 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  An area R1 between the position P11 and the position P12 and an area R2 between the position P13 and the position P14 are drawn corresponding to the drawing portion D1 formed on the paper (thin paper Sb in FIG. 9) with black toner. It is an area. Therefore, the determination unit 64 may determine the sheet end position based on the edge position that exists on the outer end side with respect to the drawing area (region R2 in FIG. 9) positioned on the outermost end side.

  In the region R1 and the region R2, both the reflected image and the transmitted image are at the L level. Therefore, the drawing area detection unit 63 can detect an area of a pixel that is at the L level in both the reflection image and the transmission image as a drawing area.

  In the example shown in FIG. 9, there are a position P14 and a position P15 as edge positions existing on the outer end side of the region R2.

  The position P14 closest to the sheet edge side is a second edge position that is detected as a position that is highly likely to be the sheet edge in the transmission image, but is detected as a position that is unlikely to be the sheet edge in the reflected image. It is also the third edge position. Therefore, the determination unit 64 determines that the position P14 is not the sheet edge.

  Next, the position P15 close to the sheet end side is a first edge position that is not detected as an edge position in the transmission image but is detected as a position that is likely to be the sheet end in the reflection image. Therefore, the determination unit 64 may determine the position P15 as the paper end position.

(In the case of thin paper (reprinted paper) on which one drawing part (yellow toner) is formed)
FIG. 10 is a diagram illustrating a reflection image and a transmission image when the thin paper Sb having one drawing portion D2 made of yellow toner is a detection target.

  Yellow toner has a low light absorptivity and reflects most of the irradiated light. Therefore, in the first mode, most of the light emitted from the first light source unit 52 to the drawing portion D2 is reflected in the direction of the imaging unit 53. On the other hand, in the second mode, most of the light emitted from the second light source unit 54 to the drawing portion D2 is reflected by the drawing portion D2 and does not pass in the direction of the imaging unit 53 even though it passes through the thin paper Sb.

  In the example illustrated in FIG. 10, the edge detection unit 62 detects the positions P16 and P17 as edge positions.

  The position P16 is a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  The position P17 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  As shown in FIG. 10, in the reflected image, the region where the paper (here, the thin paper Sb) is at the H level regardless of the presence or absence of the drawing portion D2.

  In the example shown in FIG. 10, the second edge position (position P16) detected as a position that is highly likely to be the paper edge in the transmission image, and the first position that is detected as a position that is highly likely to be the paper edge in the reflection image. One edge position (position P17) does not match.

  The case where the second edge position matches the sheet edge position is limited to when the sheet transmittance is lower than a predetermined value. Therefore, in the case of the thin paper Sb, the second edge position detected as a position that is highly likely to be the paper edge in the transmission image is shifted from the paper edge position.

  Therefore, the determination unit 64 detects the second edge position (position P16) detected as a position that is highly likely to be the paper edge in the transmission image and the position that is highly likely to be the paper edge in the reflected image. If the one edge position (position P17) does not match, the first edge position (position P17) may be determined as the paper edge position.

(Thin paper on which the drawing part is not formed is the detection target, and paper dust adheres to the CIS)
FIG. 11 is a diagram illustrating a reflection image and a transmission image when the thin paper Sb on which a drawing portion is not formed is a detection target and paper dust adheres to the CIS 51.

  When paper dust adheres to the CIS 51, the light receiving element of the imaging unit 53 in the portion where the paper dust adheres receives reflected light from the paper dust in the first mode. On the other hand, in the second mode, since the light from the second light source unit 54 is blocked by the paper dust, the light receiving element of the imaging unit 53 in the portion where the paper dust is attached does not receive light.

  In the example shown in FIG. 11, the edge detection unit 62 detects positions P18, P19, P20, P21, and P22 as edge positions.

  The position P18 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end.

  The position P19 is a third edge position where the reflected image changes from the L level to the H level when viewed from the sheet side end. The position P19 is also a fourth edge position where the transparent image changes from the H level to the L level when viewed from the sheet side end.

  The position P20 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end. Further, the position P20 is also a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  The position P21 is a third edge position in the reflected image that changes from the L level to the H level when viewed from the sheet side end. The position P21 is also a fourth edge position where the transparent image changes from the H level to the L level when viewed from the sheet side end.

  The position P22 is a first edge position where the reflected image changes from the H level to the L level when viewed from the sheet side end. Further, the position P22 is also a second edge position where the transparent image changes from the L level to the H level when viewed from the sheet side end.

  In this way, three positions P18, P20, and P22 are detected as edge positions (first edge position or second edge position) that are detected as positions that are likely to be paper edges. The position P18 is the first edge position, and the positions P20 and P22 are the first edge position and the second edge position.

  In the example illustrated in FIG. 11, the drawing portion D1 is not formed on the thin paper Sb, and there is no drawing region that is at the L level in both the reflected image and the transmitted image.

  When the drawing area does not exist, the determination unit 64 may determine an edge position closest to the paper side edge as the paper edge position among edge positions detected as positions that are likely to be the paper edge. However, as described above, the second edge position detected as a position that is likely to be the paper edge in the transmission image is shifted from the paper edge position when the paper is the thin paper Sb.

  Therefore, the determination unit 64 may determine the first edge position closest to the sheet side edge as the sheet edge position among the first edge positions detected as the position that is likely to be the sheet edge in the reflected image. In the example illustrated in FIG. 11, the determination unit 64 determines the position P18 as the paper end position.

[Paper edge position determination process]
Next, referring to FIGS. 12 and 13, the flow of processing in the sheet edge detection device 50 for realizing the above-described specific sheet edge position determination method will be described. FIG. 12 is a flowchart showing a part of the processing flow in the sheet edge detection device 50. FIG. 13 is a flowchart showing the remaining part of the flow of determination processing in the sheet edge detection device 50.

  First, when the sheet S is conveyed to the position of the sheet end detection device 50, the mode switching unit 61 switches the operation state of the first light source unit 52 and the second light source unit 54 to the first mode. That is, the mode switching unit 61 turns on the first light source unit 52 and turns off the second light source unit 54 (step S1).

  The mode switching unit 61 acquires a reflection image obtained by imaging by the imaging unit 53 in the first mode (step S2).

  Next, the mode switching unit 61 switches the operation state of the first light source unit 52 and the second light source unit 54 to the second mode. That is, the mode switching unit 61 turns off the first light source unit 52 and turns on the second light source unit 54 (step S3).

  The mode switching unit 61 acquires a transmission image obtained by imaging by the imaging unit 53 in the second mode (step S4).

  Next, the edge detection unit 62 detects the edge position from the reflected image and the transmitted image (step S5). The edge positions that can be detected in step S5 include the first to fourth edge positions.

  The determination unit 64 determines whether or not at least one first edge position is detected (step S6).

  When at least one first edge position is not detected (NO in step S6), the determination unit 64 determines whether or not at least one second edge position is detected (step S7).

  If at least one second edge position is not detected (NO in step S7), the determination unit 64 determines that the sheet edge position cannot be determined, and outputs an error notification to the control device 70 (step S8). Case A is a case where an error is notified in step S8.

  When at least one second edge position is detected (YES in step S7), the determination unit 64 determines the second edge position closest to the sheet side edge as the sheet end position (step S9). Case B is when the paper edge position is determined in step S8. Note that the edge position closest to the sheet end side is indicated as “the innermost edge position” in the drawing. The same applies to the subsequent steps.

  When at least one first edge position is detected (YES in step S6), the determination unit 64 determines whether or not at least one second edge position is detected (step S10).

  When at least one second edge position is not detected (NO in step S10), the determination unit 64 determines the first edge position closest to the sheet side edge as the sheet end position (step S11). Case C is when the paper edge position is determined in step S11.

  When at least one second edge position is detected (YES in step S10), the determination unit 64 specifies the first edge position closest to the sheet side edge as the first candidate position (step S12).

  Next, as illustrated in FIG. 13, the determination unit 64 determines whether the identified first candidate position matches any second edge position (step S <b> 13).

  If the first candidate position matches any second edge position (YES in step S13), the determination unit 64 determines the first candidate position as the paper edge position (step S14). Case D is when the paper edge position is determined in step S14.

  When the first candidate position does not coincide with any second edge position (NO in step S13), the drawing region detection unit 63 starts from the first candidate position and continues toward the external end side, and the reflected image and the transmission image. It is determined whether there is a pixel (drawing pixel) having an L level value in both images (step S15).

  If there is no drawing pixel (NO in step S15), the determination unit 64 determines the first candidate position as the paper edge position (step S16). Case E is when the paper edge position is determined in step S16.

  If there is a drawing pixel (YES in step S15), the drawing area detection unit 63 detects an area including the drawing pixel as a drawing area (step S17).

  Next, the determination unit 64 specifies the second edge position closest to the paper edge side from the second edge positions existing on the outer edge side of the drawing area as the second candidate position (step S18). The determination unit 64 determines whether the identified second candidate position matches any third edge position (step S19).

  If the second candidate position does not coincide with any third edge position (NO in step S19), the determination unit 64 determines the second candidate position as the paper edge position (step S20). Case F is determined when the paper edge position is determined in step S20.

  If the second candidate position matches any third edge position (YES in step S19), the determination unit 64 is located closest to the paper edge from among the first edge positions on the outer edge side of the second candidate position. The near first edge position is specified as the third candidate position (step S21). The determination unit 64 determines whether the identified third candidate position matches any fourth edge position (step S22).

  If the third candidate position does not coincide with any fourth edge position (NO in step S22), the determination unit 64 determines the third candidate position as the paper edge position (step S23). Case G is when the paper edge position is determined in step S23.

  When the third candidate position matches any of the fourth edge positions (YES in step S22), the determination unit 64 starts from the third candidate position and continues toward the external end side, and the reflected image and the transmitted image. In both cases, a pixel region having an L level value is specified as a new drawing region (step S24). Thereafter, the paper edge position determination process returns to the process of step S18. That is, a new second candidate position is set based on the new drawing area specified in step S24.

  According to the above paper edge position determination method, the example shown in FIG. 5 is classified as case D, and the position P1 which is the first edge position and the second edge position is determined as the paper edge position. The

  The example shown in FIG. 6 is classified as case F, is located at the outer edge side of the drawing area R, is the second edge position closest to the paper side edge, and is at the third edge position. No position P3 is determined as the sheet edge position.

  The example shown in FIG. 7 is also classified as case F, is located on the outer edge side of the drawing area R1, is the second edge position closest to the paper side edge, and is the third edge position. No position P8 is determined as the sheet edge position.

  In the example shown in FIG. 7, there are a region R1 and a region R2 as drawing regions. In step S17, the region R1 is detected as a drawing region, and in step S18, a position P8, which is the second edge position closest to the paper side end and closer to the outer end side than the region R1, is specified as the second candidate position. The Since the position P8 does not coincide with the third edge position, NO is determined in step S19, and the position P8 is determined as the paper end position in step S20. Therefore, the drawing area detection unit 63 may not detect the area R2 as a drawing area.

  The example shown in FIG. 8 is classified as case E, and the position P10 that is the first edge position closest to the sheet side edge and not the second edge position is determined as the sheet edge position.

  The example shown in FIG. 9 is classified as case G, is the first edge position that is closer to the outer edge side than the area R2 that is the drawing area, is closest to the paper side edge, and is the fourth edge position. No position P15 is determined as the sheet edge position.

  Specifically, in the example shown in FIG. 9, the region R1 is detected as a drawing region in step S17, and in step S18, the second edge that is closer to the outer end side than the region R1 and closest to the paper side end. A position P12 that is a position is specified as the second candidate position. Since the position P12 coincides with the third edge position, YES is determined in the step S19. Furthermore, since the position P13 is specified as the third candidate position in step S21, and the position P13 is also the fourth edge position, Yes in step S22. Therefore, in step S24, the region R2 is detected as a new drawing region.

  Thereafter, in step S18, the position P14 that is the second edge position that is closer to the outer end side than the region R2 and closest to the sheet side end is specified as the second candidate position. Since the position P14 coincides with the third edge position, YES is determined in the step S19. In step S21, the position P15 is specified as the third candidate position. Since the position P15 is not the fourth edge position, No is determined in step S22, and the position P15 is determined as the sheet end position in step S23.

  The example shown in FIG. 10 is classified as case E, and the position P17 that is the first edge position closest to the sheet side edge and is not the second edge position is determined as the sheet edge position.

  The example shown in FIG. 11 is also classified as case E, and the position P18 that is the first edge position closest to the sheet side edge and not the second edge position is determined as the sheet edge position.

[advantage]
As described above, the sheet edge detection device 50 according to the first embodiment emits light from the first light source unit 52 and does not emit light from the second light source unit 54, and light from the second light source unit 54. And a mode switching unit 61 for switching between the second mode in which light is not emitted from the first light source unit 52.

  The sheet edge detection device 50 includes a reflection image (first image) that is a one-dimensional image captured by the imaging unit 53 in the first mode, and a transmission image (first image) that is a one-dimensional image captured by the imaging unit 53 in the second mode. 2), an edge detection unit 62 is provided for detecting an edge position where a pixel having a luminance higher than the threshold and a pixel having a luminance lower than the threshold are adjacent to each other.

  The paper edge detection device 50 includes a drawing area detection unit 63 for detecting a drawing area corresponding to a drawing portion formed on the paper from the reflection image and the transmission image.

  The paper edge detection device 50 includes a determination unit 64 for determining the position of the edge of the paper S based on the edge position on the outer edge side of the drawing area in the reflection image and the transmission image.

  Accordingly, it is possible to prevent the drawing area from being erroneously detected as the paper edge in the paper S on which the drawing area is formed, that is, the overprinting paper. As a result, the position of the sheet edge can be detected with high accuracy.

  Specifically, the edge detection unit 62 detects a first edge position that changes from the H level to the L level when viewed from the sheet side edge in the reflected image. Further, the edge detection unit 62 detects a second edge position that changes from the H level to the L level when viewed from the sheet side edge in the transmission image. When there is no drawing area on the paper S, the first edge position closest to the paper side edge and the second edge position usually coincide. However, if a drawing area exists on the sheet S, the first edge position and the second edge position closest to the sheet side edge are different positions. Light is absorbed in a color drawing region having a high light absorption rate.

  Therefore, when the first edge position closest to the sheet side edge and the second edge position are different, the drawing area detection unit 63 detects an L-level pixel area as a drawing area in both the reflection image and the transmission image. . Thereby, the drawing area can be easily detected.

  The drawing area corresponds to a drawing portion formed on the paper. Therefore, the determination unit 64 sets a second edge position that is present on the outer edge side of the drawing area and closest to the paper side edge as the second candidate position. The determination unit 64 determines the second candidate position as the paper end position when the second candidate position is different from the third edge position that is present on the outer edge side of the drawing area and closest to the paper side edge. To do. In addition, when the second candidate position matches any of the third edge positions, the determination unit 64 exists on the outer end side of the second candidate position and is closest to the paper side end. Is determined as the paper edge position.

  When a plurality of drawing areas are detected, the determination unit 64 determines the second edge position that is located on the outer end side closest to the drawing area on the outermost end side and is closest to the paper side end as the second candidate. It may be the position.

  The second candidate position can be either the paper edge position or the boundary between the drawing region and the paper margin when the paper transmittance is high. When the second candidate position is the boundary between the drawing area and the margin portion of the paper, the imaging unit 53 receives the reflected light from the margin portion of the paper S, so the second candidate position matches the third edge position.

  Therefore, the determination unit 64 determines the second candidate position as the paper edge position when the second candidate position does not match any third edge position. In addition, when the second candidate position matches any of the third edge positions, the determination unit 64 exists on the outer end side of the second candidate position and is closest to the paper side end. Is determined as the paper edge position. Thereby, the paper edge can be detected with high accuracy.

  When the drawing area is not detected, the determination unit 64 determines the first edge position closest to the paper side edge as the paper edge position. When there is no drawing portion on the paper S, the light emitted from the first light source unit 52 is reflected in an area where the paper S is present. Therefore, by determining the first edge region closest to the paper side edge as the paper edge position, the paper edge can be detected with high accuracy.

<Embodiment 2>
The paper edge detection device according to the second embodiment of the present disclosure is a modification of the paper edge detection device 50 according to the first embodiment.

  With reference to FIGS. 14 and 15, the configuration of the sheet edge detection device 50 </ b> A according to the second embodiment will be described. FIG. 14 is a block diagram illustrating a configuration of a sheet end detection device 50A according to the second embodiment.

  As illustrated in FIG. 14, the sheet edge detection device 50 </ b> A includes the reflection switching unit 56 instead of the second light source unit 54, and includes a detection processing unit 55 a instead of the detection processing unit 55. This is different from the sheet edge detection device 50. The detection processing unit 55a is different from the detection processing unit 55 according to the first embodiment in that a mode switching unit 61a is provided instead of the mode switching unit 61. Since other points are the same as the configuration of the sheet end detection device 50 according to the first embodiment, the description thereof will not be repeated below.

  The reflection switching unit 56 is disposed at a position facing the CIS 51 with the paper S interposed therebetween, a reflection mode for reflecting light emitted from the first light source unit 52 included in the CIS 51 in the direction of the CIS 51, and the first light source unit 52. This is an optical component that can be switched between a non-reflective mode that does not reflect the light emitted from the CIS 51 in the direction.

  The reflection switching unit 56 includes, for example, a reflection surface that reflects most of the incident light and a non-reflection surface that absorbs most of the incident light, and the surface facing the CIS 51 is a reflection surface and non-reflection. By switching to one of the surfaces, the reflection mode and the non-reflection mode are switched.

  Alternatively, the reflection switching unit 56 may be an optical component that can be switched between a mirror state and a transparent state by an applied voltage. Thereby, the reflection switching part 56 will be in reflection mode by becoming a mirror state, and will be in non-reflection mode by becoming transparent state.

  The mode switching unit 61a sequentially switches the state of the reflection switching unit 56 between the reflection mode and the non-reflection mode when the sheet S is present at a position facing the sheet end detection device 50A. The mode switching unit 61a always turns on the first light source unit 52.

  FIG. 15 is a diagram for explaining a change in the optical path depending on the state of the reflection switching unit 56. FIG. 15A shows an optical path when the reflection switching unit 56 is in the reflection mode, and FIG. 15B shows an optical path when the reflection switching unit 56 is in the non-reflection mode.

  As shown in FIG. 15A, when the reflection switching unit 56 is in the reflection mode, the light emitted from the first light source unit 52 is reflected by the reflection switching unit 56 in an area where the paper S does not exist, The light enters the imaging unit 53.

  As shown in FIG. 15B, when the reflection switching unit 56 is in the non-reflection mode, the light emitted from the first light source unit 52 is absorbed by the reflection switching unit 56 in the area where the paper S does not exist, It does not enter the imaging unit 53.

  In the area where the paper S exists, regardless of the state of the reflection switching unit 56, the light emitted from the first light source unit 52 is reflected by the paper S (excluding the drawing portion by the black toner) and enters the imaging unit 53. To do.

  When the reflection switching unit 56 is in the non-reflection mode, the optical path of the light emitted from the first light source unit 52 turns on the first light source unit 52 and turns off the second light source unit 54 in the first embodiment. The first mode is substantially the same state.

  In the case where the reflection switching unit 56 is in the reflection mode, the light travels from the opposite side of the imaging unit 53 to the imaging unit 53 with respect to the surface including the paper S in an area where the paper S does not exist. 1 is common to the second mode in which the first light source unit 52 is turned off and the second light source unit 54 is turned on.

  Therefore, the mode switching unit 61a acquires a one-dimensional image captured by the imaging unit 53 when the reflection switching unit 56 is in the non-reflection mode as a reflection image, and the imaging unit when the reflection switching unit 56 is in the reflection mode. The one-dimensional image imaged by 53 is acquired as a transmission image.

  Also in the second embodiment, the region of the pixel that is at the L level in both the reflected image and the transmitted image corresponds to a drawing portion formed by the black toner formed on the paper S. Therefore, the drawing area detection unit 63 can detect the drawing area as in the first embodiment. In addition, the edge detection unit 62 and the determination unit 64 may perform the same processing as in the first embodiment. Thereby, also in the second embodiment, as in the first embodiment, the position of the edge of the paper S can be detected with high accuracy.

<Embodiment 3>
The paper edge detection device according to the third embodiment of the present disclosure is a modification of the paper edge detection device 50A according to the second embodiment.

  With reference to FIGS. 16 and 17, the configuration of the sheet edge detection device 50 </ b> B according to Embodiment 3 will be described. FIG. 16 is a block diagram illustrating a configuration of a sheet end detection device 50B according to the third embodiment.

  As shown in FIG. 16, the sheet edge detection device 50B is different from the sheet edge detection device 50A according to the second embodiment in that it includes a detection processing unit 55b instead of the detection processing unit 55a. The detection processing unit 55b includes a difference image generation unit 65, an edge detection unit 62b instead of the edge detection unit 62, and a determination unit 64b instead of the drawing area detection unit 63 and the determination unit 64. This is different from the detection processing unit 55a according to the second embodiment. Since other points are the same as the configuration of the sheet end detection device 50A according to the second embodiment, the description thereof will not be repeated below.

  As described above, in the area where the paper S exists, the light emitted from the first light source unit 52 is reflected by the paper S (except for the drawing portion by the black toner) regardless of the state of the reflection switching unit 56. The light enters the imaging unit 53. Therefore, the one-dimensional image captured when the reflection switching unit 56 is in the non-reflection mode and the one-dimensional image captured when the reflection switching unit 56 is in the reflection mode are images of an area corresponding to the paper S. Match.

  The difference image generation unit 65 subtracts the difference image obtained by subtracting the one-dimensional image captured when the reflection switching unit 56 is in the non-reflection mode from the one-dimensional image captured when the reflection switching unit 56 is in the reflection mode. Generate.

  The edge detection unit 62b binarizes the difference image and specifies the edge position. Specifically, for each pixel of the difference image, the edge detection unit 62b sets the value of the pixel to H level when the luminance is equal to or higher than a predetermined threshold, and sets the value of the pixel to L when the luminance is lower than the threshold. Level.

  The edge detection unit 62b detects a fifth edge position that changes from the L level to the H level when viewed from the sheet side edge in the difference image.

  The determination unit 64b specifies the fifth edge position closest to the paper side edge among the fifth edge positions detected by the edge detection unit 62b, and determines the specified fifth edge position as the paper edge position.

  FIG. 17 is a diagram showing an image when the normal paper Sa having the drawing portion D1 of black toner at the end is the detection target and the paper dust adheres to the CIS 51. In FIG. 17, the one-dimensional image captured when the reflection switching unit 56 is in the reflection mode is shown in the upper stage, and the one-dimensional image captured when the reflection switching unit 56 is in the non-reflection mode is shown in the middle stage. The image is shown in the bottom row.

  In the example illustrated in FIG. 17, the edge detection unit 62b detects positions P23, P24, and P25 as fifth edge positions.

  As shown in FIG. 17, the fifth edge position is detected only from the boundary between the area where the paper (normal paper Sa in FIG. 17) exists and the area where the paper does not exist, and the area where the paper does not exist, and the paper exists. It is not detected from the area to be.

  Therefore, the determination unit 64b may determine the position P23, which is the fifth edge position closest to the sheet side edge, as the sheet end position.

  According to the third embodiment, by using the difference image, it is possible to easily detect the sheet edge position without using a complicated algorithm.

<Modification>
[Modification 1]
In each of the above embodiments, the length of the one-dimensional image generated by the imaging unit 53 may be set in advance according to the amount of positional deviation in the width direction of the paper S.

  In general, the maximum value of the positional deviation amount in the width direction of the paper S generated in the transport path is defined by the specifications of the image forming apparatus 100. Therefore, the imaging unit 53 may capture a one-dimensional image having a length twice as large as the maximum value of the positional deviation amount with the ideal position of the edge of the paper S in the transport path as the center. As a result, the processing of the detection processing units 55, 55a, and 55b can be speeded up, and the resource can be optimized.

  For example, when the maximum value of the positional deviation amount is 1 mm and the resolution of the one-dimensional image obtained by imaging by the imaging unit 53 is 600 dpi, the maximum value of the positional deviation amount is expressed by 1 / (25. 4/600) ≈24 pixels. For this reason, the imaging unit 53 may capture a one-dimensional image having a length of ± 24 pixels with the ideal position of the edge of the paper S as the center.

  Further, when the paper S having a different size is transported in the transport path, the imaging unit 53 acquires size information indicating the size of the paper S being transported from the control device 70, and performs image capturing according to the acquired size information. Switch the range.

  Specifically, the imaging unit 53 stores in advance a table in which the size information, the reference position of the edge of the paper S, and the length of the one-dimensional image are associated, and sets the imaging range according to the table. .

  As a result, even if the size of the paper S is changed, it is possible to speed up the processing of the detection processing units 55, 55a, and 55b and to optimize resources.

[Modification 2]
As described above, the first light source unit 52 included in the imaging unit 53 includes the LED 52a as a light emitting element. Similarly, the second light source unit 54 includes LEDs. When the LED deteriorates with age, it is conceivable that the light emission amount gradually decreases. When the amount of light emitted from the first light source unit 52 and the second light source unit 54 decreases, the edge detectors 62 and 62b may regard the pixel that should originally be at the H level as an L level pixel. As a result, the edge position detection accuracy decreases.

  Therefore, the edge detectors 62 and 62b may set a threshold used when binarizing the one-dimensional image according to the luminance distribution of each pixel in the one-dimensional image.

  The edge detection units 62 and 62b set a threshold every time the image forming apparatus 100 prints a predetermined number of sheets (for example, 1000 sheets). Alternatively, the edge detectors 62 and 62b may set a threshold value every predetermined period (for example, one month).

  The edge detection units 62 and 62b may store the one-dimensional images for the most recent predetermined number of times acquired from the imaging unit 53, and determine a threshold based on the luminance distribution in the stored one-dimensional image.

  The method for determining the threshold based on the luminance distribution in the one-dimensional image is not particularly limited. For example, the edge detectors 62 and 62b may set the median value between the maximum value and the minimum value of the luminance in the accumulated one-dimensional image as the threshold value. Alternatively, the edge detectors 62 and 62b may set a value that is ½ of the maximum luminance value in the accumulated one-dimensional image as the threshold value. Alternatively, the edge detectors 62 and 62b may set an average value of luminance in the accumulated one-dimensional image as a threshold value.

  Thereby, even if LED deteriorates, the edge detection parts 62 and 62b can detect an edge position accurately.

[Modification 3]
A paper edge detection device according to Modification 3 is a modification of the paper edge detection device 50 according to Embodiment 1 described above. Note that Modification 3 can also be applied to the sheet end detection device 50A of the second embodiment.

  FIG. 18 is a block diagram illustrating a configuration of a detection processing unit 55c included in the paper edge detection device according to the third modification. The paper edge detection device according to the modification 3 is different from the paper edge detection device 50 only in that a detection processing unit 55c is provided instead of the detection processing unit 55.

  As illustrated in FIG. 18, the detection processing unit 55 c includes an information acquisition unit 66 and is different from the detection processing unit 55 only in that a determination unit 64 c is provided instead of the determination unit 64.

  The information acquisition unit 66 acquires from the control device 70 (see FIG. 2) type information indicating the type of the paper S that is transported in the transport path 40. The control device 70 displays on the operation panel 107 (see FIG. 2) a screen that prompts the user to input the type of paper S to be printed, and receives type information from the user. The information acquisition unit 66 acquires the type information received by the control device 70.

  The type information includes information indicating whether the color of the paper S is white, information indicating whether an image is formed on the paper S, and information indicating whether the thickness of the paper S is greater than a predetermined value. included.

  The determination unit 64c has the same function as the determination unit 64 of the first embodiment. However, when the information acquisition unit 66 acquires information indicating that the color of the paper S is white and no image is formed on the paper S, and indicates that the thickness of the paper S is greater than a predetermined value. When the information acquisition unit 66 acquires information, the following processing is performed.

  When the information acquisition unit 66 acquires information indicating that the color of the paper S is white and no image is formed on the paper S, the determination unit 64c determines the first edge closest to the paper side edge. The position is determined as the paper edge position.

  When the color of the paper S is white and no image is formed on the paper S, the area where the paper S exists in the reflected image is at the H level. In the area where the paper S does not exist, it is basically at the L level, but can be at the H level when paper dust is attached. In this case, the determination unit 64c determines the first edge position closest to the sheet side edge as the sheet end position when YES is obtained in S6 shown in FIG. Thereby, it is possible to easily detect the sheet edge.

  When the information acquisition unit 66 acquires information indicating that the thickness of the sheet S is greater than the predetermined value, the determination unit 64c determines the second edge position closest to the sheet side edge as the sheet end position. .

  When the thickness of the paper S is larger than a predetermined value, the area where the paper S exists in the transmission image is at the L level. In the area where the paper S does not exist, basically, it is at the H level, but can be at the L level when paper dust is attached. Therefore, in this case, the determination unit 64c determines the second edge position closest to the sheet side end as the sheet end position when YES in S7 or S10 shown in FIG. Thereby, it is possible to easily detect the sheet edge.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1C, 1K, 1M, 1Y Image forming unit, 10 photoconductor, 11 charging device, 12 exposure device, 13 developing device, 14 developing roller, 15C, 15K, 15M, 15Y toner bottle, 17 cleaning device, 30 transfer belt, 31 Primary transfer roller, 33 Secondary transfer roller, 37 Cassette, 38 Driven roller, 39 Drive roller, 40 Transport path, 41 Pickup roller, 43 Transport roller, 44 Fixing device, 48 Paper discharge tray, 50, 50A, 50B Paper edge detection Apparatus, 51 CIS, 52 first light source unit, 53 imaging unit, 52a LED, 52b light guide, 54 second light source unit, 55, 55a to 55c detection processing unit, 56 reflection switching unit, 61, 61a mode switching unit, 62, 62b Edge detection unit, 63 Drawing area detection unit, 64, 6 b, 64c determination unit, 65 difference image generation unit, 66 information acquisition unit, 70 control device, 100 image forming device, 101 image forming unit, 102 ROM, 103 RAM, 104 network interface, 107 operation panel, 120 storage device, S Paper, Sa normal paper, Sb thin paper.

Claims (16)

A one-dimensional image is taken along the width direction of the paper being conveyed, and is arranged so that one end of the one-dimensional image is located in the paper and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A first light source unit that is disposed on the same side as the imaging unit with respect to the paper and that irradiates light on the paper side to cause reflected light of the paper to enter the imaging unit;
A second light source unit disposed on the opposite side of the imaging unit with respect to the paper and irradiating light toward the imaging unit;
A first mode in which light is emitted from the first light source unit and light is not emitted from the second light source unit, and a second mode in which light is emitted from the second light source unit and light is not emitted from the first light source unit A mode switching unit for switching between and
Pixels whose luminance is greater than a threshold in a first image that is a one-dimensional image captured by the imaging unit in the first mode and a second image that is a one-dimensional image captured by the imaging unit in the second mode And an edge detection unit for detecting an edge position adjacent to a pixel whose luminance is smaller than the threshold value;
A drawing area detecting unit for detecting a drawing area corresponding to a drawing part formed on the paper from the first image and the second image;
A paper end detection device comprising: a determination unit configured to determine a position of an end of the paper based on the edge position on the other end side of the drawing area in the first image and the second image; . A one-dimensional image is taken along the width direction of the paper being conveyed, and is arranged so that one end of the one-dimensional image is located in the paper and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A light source unit that is disposed on the same side as the imaging unit with respect to the paper, and irradiates light on the paper side, thereby causing reflected light of the paper to enter the imaging unit;
A reflection mode that is disposed on the opposite side of the image pickup unit with respect to the paper and reflects light from the light source unit toward the image pickup unit, and non-reflection of light from the light source unit toward the image pickup unit. A reflection switching unit capable of switching between reflection modes;
In the first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode and the second image obtained by the imaging unit when the reflection switching unit is in the reflection mode, An edge detection unit for detecting an edge position where a pixel having a luminance higher than a threshold and a pixel having a luminance lower than the threshold are adjacent to each other;
A drawing area detecting unit for detecting a drawing area corresponding to a drawing part formed on the paper from the first image and the second image;
A paper end detection device comprising: a determination unit configured to determine a position of an end of the paper based on the edge position on the other end side of the drawing area in the first image and the second image; . In the first image, the edge detection unit includes at least one pixel that changes from a pixel having a luminance higher than the threshold value to a pixel having a luminance lower than the threshold value along a direction from the one end toward the other end. Detecting the edge position as a first edge position;
In the second image, the edge detection unit is configured to change at least one pixel that changes from a pixel having a luminance smaller than the threshold value to a pixel having a luminance larger than the threshold value along a direction from the one end toward the other end. Detecting the edge position as a second edge position;
The drawing area detection unit is configured to detect the first edge position closest to the one end and the second edge position closest to the one end in both the first image and the second image. The paper edge detection apparatus according to claim 1, wherein an area of a pixel having a luminance smaller than a threshold is detected as the drawing area. In the first image, the edge detection unit includes at least one pixel that changes from a pixel having a luminance smaller than the threshold value to a pixel having a luminance larger than the threshold value along a direction from the one end toward the other end. Detecting the edge position as a third edge position;
The determination unit sets the second edge position that is present on the other end side of the drawing area and closest to the one end as a candidate position, and the candidate position does not match any of the third edge positions. The paper edge detection device according to claim 3, wherein the candidate position is determined as a position of an edge of the paper.   When the candidate position matches any of the third edge positions, the determination unit determines the first edge position that is present on the other end side than the candidate position and is closest to the one end. The paper edge detection device according to claim 4, wherein the paper edge detection device is determined as a position of an edge of the paper.   The determination unit determines the first edge position closest to the one end as the position of the end of the paper when the drawing region detection unit cannot detect the drawing region. The sheet end detection device according to claim 1. An information acquisition unit capable of acquiring information indicating whether the color of the paper is white and information indicating whether an image has already been formed on the paper;
When the information acquisition unit acquires information indicating that the color of the paper is white and information indicating that no image is formed on the paper, the determination unit is closest to the one end side. The paper edge detection device according to any one of claims 3 to 6, wherein the first edge position is determined as a position of an edge of the paper. An information acquisition unit capable of acquiring information indicating whether the thickness of the paper is greater than a predetermined value;
The determination unit determines the second edge position closest to the one end side as the end position of the sheet when the information acquisition unit acquires information indicating that the thickness of the sheet is larger than a predetermined value. The paper edge detecting device according to any one of claims 3 to 6.   The paper edge according to any one of claims 1 to 8, wherein the determination unit issues an error notification when the edge detection unit cannot detect an edge position in both the first image and the second image. Detection device. A one-dimensional image is taken along the width direction of the paper being conveyed, and is arranged so that one end of the one-dimensional image is located in the paper and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A light source unit that is disposed on the same side as the imaging unit with respect to the paper, and irradiates light on the paper side, thereby causing reflected light of the paper to enter the imaging unit;
A reflection mode that is disposed on the opposite side of the image pickup unit with respect to the paper and reflects light from the light source unit toward the image pickup unit, and non-reflection of light from the light source unit toward the image pickup unit. A reflection switching unit capable of switching between reflection modes;
The first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode is subtracted from the second image obtained by the imaging unit when the reflection switching unit is in the reflection mode. A difference image generation unit for generating a difference image by:
In the difference image, an edge for detecting at least one edge position that changes from a pixel having a luminance lower than a threshold value to a pixel having a luminance higher than the threshold value along a direction from the one end to the other end. A detection unit;
A paper end detection device comprising: a determination unit configured to determine the edge position closest to the one end side as the position of the end of the paper.   The sheet edge detection device according to claim 1, wherein the imaging unit captures a one-dimensional image having a length set in advance according to a positional deviation amount in the width direction of the sheet.   The paper edge detection device according to any one of claims 1 to 11, wherein the edge detection unit sets the threshold according to a luminance distribution of each pixel of the first image and the second image. A transport unit for transporting the paper;
An image forming unit for forming an image on the paper;
A paper edge detection device according to any one of claims 1 to 12,
An image forming apparatus comprising: a control device that adjusts a position at which the image forming unit forms an image on the paper according to a position of an edge of the paper detected by the paper edge detecting device. A one-dimensional image is taken along the width direction of the paper being transported, and one end of the one-dimensional image is located in the paper, and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A first light source unit that is disposed on the same side as the imaging unit with respect to the paper and that irradiates light on the paper side to cause reflected light of the paper to enter the imaging unit;
A paper edge detection method in a paper edge detection device comprising a second light source part that is disposed on the opposite side of the imaging unit with respect to the paper and irradiates light toward the imaging part,
A first mode in which light is emitted from the first light source unit and light is not emitted from the second light source unit, and a second mode in which light is emitted from the second light source unit and light is not emitted from the first light source unit A process of switching between and
In the first image obtained by the imaging unit in the first mode and the second image obtained by the imaging unit in the second mode, a pixel having a luminance greater than a threshold, and a luminance greater than the threshold Detecting edge positions adjacent to small pixels;
Detecting a drawing area corresponding to a drawing portion formed on the paper from the first image and the second image;
And determining a position of the end of the sheet based on the edge position on the other end side of the drawing area in the first image and the second image. A one-dimensional image is taken along the width direction of the paper being conveyed, and is arranged so that one end of the one-dimensional image is located in the paper and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A light source unit that is disposed on the same side as the imaging unit with respect to the paper, and irradiates light on the paper side, thereby causing reflected light of the paper to enter the imaging unit;
A reflection mode that is disposed on the opposite side of the image pickup unit with respect to the paper and reflects light from the light source unit toward the image pickup unit, and non-reflection of light from the light source unit toward the image pickup unit. A paper edge detection method in a paper edge detection device comprising a reflection switching unit capable of switching between reflection modes,
In the first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode and the second image obtained by the imaging unit when the reflection switching unit is in the reflection mode, Detecting an edge position where a pixel having a luminance greater than a threshold and a pixel having a luminance smaller than the threshold are adjacent to each other;
Detecting a drawing area corresponding to a drawing portion formed on the paper from the first image and the second image;
And determining a position of the end of the sheet based on the edge position on the other end side of the drawing area in the first image and the second image. A one-dimensional image is taken along the width direction of the paper being conveyed, and is arranged so that one end of the one-dimensional image is located in the paper and the other end of the one-dimensional image is located outside the paper. An imaging unit;
A light source unit that is disposed on the same side as the imaging unit with respect to the paper, and irradiates light on the paper side, thereby causing reflected light of the paper to enter the imaging unit;
A reflection mode that is disposed on the opposite side of the image pickup unit with respect to the paper and reflects light from the light source unit toward the image pickup unit, and non-reflection of light from the light source unit toward the image pickup unit. A paper edge detection method in a paper edge detection device comprising a reflection switching unit capable of switching between reflection modes,
The first image obtained by the imaging unit when the reflection switching unit is in the non-reflection mode is subtracted from the second image obtained by the imaging unit when the reflection switching unit is in the reflection mode. A step of generating a difference image by:
Detecting, in the difference image, at least one edge position where a luminance is changed from a pixel having a luminance smaller than a threshold value to a pixel having a luminance larger than the threshold value along a direction from the one end to the other end;
And determining the edge position closest to the one end side as the position of the edge of the sheet.

Images