JP5651566B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads a document and outputs image data is known, and is mounted on, for example, an image forming apparatus such as a multifunction peripheral (see, for example, Patent Document 1). Such an image reading apparatus includes a mounting table for placing a document, a light source that irradiates light on the document, a line sensor that photoelectrically converts reflected light reflected from the document, and accumulates charges. It is common.

  When reading a document, the document placed on the mounting table is irradiated with light from the light source, and the reflected light reflected by the document is photoelectrically converted for each pixel by the line sensor, and the analog output of the line sensor is digitally converted. To generate image data indicating the pixel value of each pixel. The image data generated by the image reading apparatus is transferred to, for example, a control unit of the image forming apparatus, and printing based on the image data is performed in the image forming apparatus.

  Further, for example, the image reading apparatus may perform scanning for detecting the size of the document placed on the placement table prior to reading the document. For example, when detecting the size of a document in the main scanning direction, reading is performed in a main scanning direction at a predetermined position on the mounting table while the document cover is being lowered. As a result, image data for one or more lines in the main scanning direction is acquired. Then, based on the image data, the control unit of the image reading apparatus specifies a boundary between a bright pixel (a pixel where an original exists) and a dark pixel (a pixel where no original exists). Here, the boundary between a bright pixel (a pixel in which a document exists) and a dark pixel (a pixel in which a document does not exist) varies depending on the size of the document. For this reason, it is possible to detect the size of the document by specifying the boundary between the bright pixel (the pixel where the document exists) and the dark pixel (the pixel where the document does not exist).

JP 2011-71779 A

  As described above, the document size detection is performed while the document cover is being lowered. Therefore, disturbance light may enter the line sensor when the document size is detected. If disturbance light enters the line sensor, accurate document size detection cannot be performed.

  Specifically, in the photoelectric conversion region corresponding to a pixel (hereinafter referred to as a predetermined pixel) in which a document does not exist among the plurality of photoelectric conversion regions of the line sensor, reflected light (light from a light source reflected by the document). ) Is less incident. That is, the predetermined pixel is darker than the pixels other than the predetermined pixel. Therefore, the control unit of the image reading apparatus determines that the predetermined pixel is a pixel in which no document exists. However, when disturbance light enters the photoelectric conversion region corresponding to the predetermined pixel among the plurality of photoelectric conversion regions of the line sensor, the difference in brightness between the predetermined pixel and the pixels other than the predetermined pixel is reduced. For this reason, the control unit of the image reading apparatus may erroneously determine that the predetermined pixel is a pixel in which a document exists. As a result, erroneous detection occurs in document size detection.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus and an image forming apparatus capable of reducing the occurrence of erroneous detection in document size detection.

  In order to achieve the above object, an image reading apparatus according to the present invention photoelectrically converts a placement table on which a document is placed, a light source for irradiating the document with light, and reflected light reflected by the document in line units. A line sensor that accumulates charges for each pixel, a document pressing unit that presses the document placed on the mounting table by being opened and closed with respect to the mounting table, and the document pressing unit is tilted more than a predetermined position. An open / close detection unit for detecting that the image has been detected, and a control unit for processing image data obtained by reading the line sensor. Then, when the open / close detection unit detects that the document pressing unit is lifted from a predetermined position, the line sensor takes a longer time than the photoelectric conversion time during normal image reading, Disturbance light is photoelectrically converted on a line-by-line basis, and charges are accumulated for each pixel to generate disturbance light detection image data. The controller is brightened by the influence of disturbance light based on the disturbance light detection image data. Identifies the pixel.

  Here, as a light source of disturbance light, there is a light source that repeatedly blinks at a constant cycle like a fluorescent lamp. The photoelectric conversion time (charge storage time) of the line sensor during normal image reading is generally shorter than the blinking cycle of the disturbance light source.

  For this reason, in the image data obtained by reading the line sensor when the light source of disturbance light is bright (the light emission level is high), the pixel value of the pixel where the document does not exist is affected by disturbance light. As a result, the pixel value of the pixel in which the document exists is brighter. However, in the image data obtained by the line sensor reading when the disturbance light source is dark (off), the pixel values of the pixels of the entire read line are dark. Therefore, in the ambient light detection image data obtained by reading the line sensor when the ambient light source is dark, the disturbance light is incident because there are pixels in the area where the ambient light is incident and the document. It is difficult for a difference in pixel value from a pixel with a small portion to appear in the image data. That is, highly reliable ambient light detection image data cannot be obtained.

  Therefore, in the image reading apparatus of the present invention, the line sensor accumulates electric charges for each pixel while photoelectrically converting disturbance light in units of lines over a longer time than the photoelectric conversion time during normal image reading. Image data for light detection is generated. As a result, when the disturbance light detection image data is generated, the line sensor is photoelectrically converted when the disturbance light source is darker than when the photoelectric conversion time of the line sensor is the same as the photoelectric conversion time during normal image reading. It is possible to suppress a complete overlap with the period of performing. For this reason, the pixel value of the pixel where the document exists remains dark, and the pixel value of the pixel where the document does not exist is certainly brighter than the pixel value of the pixel where the document exists. This makes it possible to accurately identify pixels that have become brighter due to the influence of disturbance light, so that it is possible to suppress the inconvenience that document size detection becomes inaccurate due to disturbance light.

  Note that, even when the ambient light detection image data is generated by causing the line sensor to perform reading with the photoelectric conversion time during normal image reading, for example, the disturbance light detection image data for a plurality of lines is stored in the memory. By storing and comparing the disturbance light detection image data for a plurality of lines, it is possible to specify the boundary between the pixel where the original does not exist and the pixel where the original exists. However, in this case, it is necessary to secure a memory capacity for simultaneously storing disturbance light detection image data for a plurality of lines, leading to an increase in cost. However, in the image reading apparatus of the present invention, even if the disturbance light detection image data is only for one line, the disturbance light detection image data for one line is highly reliable. It is possible to identify pixels that have become bright under the influence of the above. That is, it is not necessary to increase the memory capacity in order to compare the disturbance light detection image data for a plurality of lines, and the cost increase can be suppressed.

  In the above configuration, preferably, when the open / close detection unit detects that the document pressing unit is tilted from a predetermined position, the control unit turns on the light source and causes the line sensor to perform normal image reading. The document size detection image data is generated by performing the reading with the photoelectric conversion time, and the pixel identified as being brightened by the influence of the ambient light based on the ambient light detection image data is recognized as a dark pixel. Detect the document size. According to this configuration, the influence of ambient light can be accurately removed when the document size is detected based on the document size detection image data.

  In the above configuration, preferably, the line sensor makes the photoelectric conversion time for generating the disturbance light detection image data longer than the blinking period of the disturbance light. With this configuration, when the disturbance light source is a fluorescent lamp or the like, more reliable document size detection can be performed.

  An image forming apparatus of the present invention includes the above-described image reading apparatus. In such an image forming apparatus, it is possible to reduce the occurrence of erroneous detection in document size detection while suppressing an increase in cost.

  As described above, according to the present invention, it is possible to easily obtain an image reading apparatus and an image forming apparatus that can reduce the occurrence of erroneous detection in document size detection.

1 is a schematic diagram of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. Detailed view of the image reading apparatus shown in FIG. The figure when the original conveyance part (original press part) of the image reading apparatus shown in FIG. 1 is opened. FIG. 2 is a diagram in the middle of closing the document conveying section (document pressing section) of the image reading apparatus shown in FIG. The top view of the image reading part of the image reading apparatus shown in FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus including the image reading apparatus illustrated in FIG. 1 is a block diagram showing a hardware configuration of the image reading apparatus shown in FIG. The figure for demonstrating the photoelectric conversion time of the line sensor provided in the image reading part of the image reading apparatus shown in FIG. FIG. 1 is a flowchart for explaining a series of document size detection steps performed by the image reading apparatus shown in FIG.

  Hereinafter, an overall configuration of an image forming apparatus 200 including an image reading apparatus 100 according to an embodiment of the present invention will be described with reference to FIG.

  An image forming apparatus 200 including the image reading apparatus 100 according to the present embodiment is a color multifunction peripheral capable of executing a plurality of types of jobs such as a copy, a printer, a scanner, and a fax machine. The image reading apparatus 100 is disposed above the image forming apparatus 200, and includes an image reading unit 1 and a document conveying unit 2 (document pressing unit). The image reading unit 1 reads a document and generates image data. The document conveying unit 2 conveys the document to the image reading unit 1 or presses the document read by the image reading unit 1. The configuration of each part of the image reading apparatus 100 will be described in detail later.

  The image forming apparatus 200 includes an operation panel 3, a paper feed unit 4A, a conveyance path 4B, an image forming unit 5A, an intermediate transfer unit 5B, a fixing unit 5C, and the like.

  The operation panel 3 is disposed on the front side of the image reading unit 1 (a portion indicated by a broken line in FIG. 1). The operation panel 3 includes a liquid crystal display unit 31 whose display surface is covered with a touch panel. The liquid crystal display unit 31 displays a menu for performing various settings and setting keys (soft keys), and also displays a message indicating the device status and the like. The operation panel 3 also includes a numeric keypad 32 for accepting setting instructions that require numerical input from the user, a start key 33 for accepting instructions for starting execution of various jobs from the user, and the like.

  The paper supply unit 4A stores paper and supplies the stored paper to the transport path 4B. For this reason, the paper feed unit 4A is provided with a pickup roller 41 that pulls out the stored paper one by one and supplies it to the transport path 4B. The conveyance path 4B conveys the sheet supplied from the sheet feeding unit 4A in the order of the intermediate transfer unit 5B and the fixing unit 5C. The conveyance roller pair 42 performs conveyance of the paper in the conveyance path 4B. Further, a registration roller pair 43 is provided in the conveyance path 4B, and the registration roller pair 43 causes the sheet to wait in front of the intermediate transfer unit 5B and sends it to the intermediate transfer unit 5B at the same timing. The sheet conveyed by the conveyance path 4B is finally guided to the discharge tray 44.

  The image forming unit 5A includes a plurality of image forming units 51 (an image forming unit 51Bk for black, an image forming unit 51Y for yellow, an image forming unit 51C for cyan, and an image forming unit 51M for magenta) and an exposure device 52. including. Each of the plurality of image forming units 51 includes a photosensitive drum that is rotatably supported, a charging device, a developing device, and a cleaning device that are disposed around the photosensitive drum. Based on the image data, the exposure device 52 scans and exposes a laser beam to the circumferential surface of each photosensitive drum, and forms an electrostatic latent image on the circumferential surface of each photosensitive drum. Each of the plurality of image forming units 51 supplies toner to the electrostatic latent image formed on the peripheral surface of each photosensitive drum. Thereby, a toner image is formed on the peripheral surface of each photosensitive drum.

  The intermediate transfer unit 5B includes a plurality of primary transfer rollers 53 (one primary transfer roller 53Bk for black, one primary transfer roller 53Y for yellow, one primary transfer roller 53C for cyan, and magenta assigned to each color. Primary transfer roller 53M), intermediate transfer belt 54, drive roller 55, driven roller 56, secondary transfer roller 57, belt cleaning device 58, and the like. The plurality of primary transfer rollers 53 sandwich the intermediate transfer belt 54 between the corresponding photosensitive drums. Therefore, when a transfer voltage is applied to the plurality of primary transfer rollers 53, the toner images formed on the peripheral surfaces of the respective photosensitive drums are transferred to the intermediate transfer belt 54.

  The intermediate transfer belt 54 is stretched around a driving roller 55, a driven roller 56, and the like, and rotates around the driving roller 55. The secondary transfer roller 57 sandwiches the intermediate transfer belt 54 between the drive roller 55 and the secondary transfer roller 57. Then, the sheet conveyed to the intermediate transfer unit 5B enters between the secondary transfer roller 57 and the intermediate transfer belt 54. At this time, a transfer voltage is applied to the secondary transfer roller 57, whereby the toner image transferred to the intermediate transfer belt 54 is transferred to the sheet.

  The fixing unit 5C heats and pressurizes the toner image transferred to the paper and fixes it. The fixing unit 5 </ b> C includes a fixing roller 58 having a built-in heat generation source, and a pressure roller 59 pressed against the fixing roller 58. Then, the sheet on which the toner image is transferred passes between the fixing roller 58 and the pressure roller 59, and is heated and pressurized. As a result, the toner image is fixed on the paper and printing is completed. Then, the printed paper is guided to the conveyance path 4B and sent to the discharge tray 44.

  Next, the configuration of the image reading apparatus 100 (the image reading unit 1 and the document conveying unit 2) according to the present embodiment will be described with reference to FIG.

  The document conveying section 2 pulls out the paper set on the document setting tray 21 and discharges it to the document discharge tray 22 via a reading position (above a conveyance reading contact glass 11 described later). Note that, when a plurality of sheets are set on the document set tray 21, the document conveying unit 2 automatically and continuously pulls out the documents one by one from the plurality of documents.

  In the document transport path 23 from the document set tray 21 to the document discharge tray 22, a document supply roller 24, a document transport roller pair 25, and a document discharge roller pair 26 are provided in this order from the upstream side in the document transport direction. The original set on the original setting tray 21 is pulled out by the original supply roller 24 and conveyed by the original conveying roller pair 25. Thereafter, the document is discharged onto the document discharge tray 22 by the document discharge roller pair 26. The document supply roller 24, the document transport roller pair 25, and the document discharge roller pair 26 are rotationally driven by a document transport motor 27 (see FIG. 7).

  The image reading unit 1 has a box-shaped housing. A transparent conveyance reading contact glass 11 is disposed on one end of the upper surface of the casing. Further, a transparent placement reading contact glass 12 (mounting table) is disposed at the center of the upper surface of the housing.

  In the housing, a lamp 13 (light source), a first mirror 14, a second mirror 15, a third mirror 16, a lens 17 and a line sensor 18 are also provided. The lamp 13 irradiates the original with light. Then, the reflected light reflected from the document (light from the lamp 13) is reflected in the order of the first mirror 14, the second mirror 15, and the third mirror 16 and guided to the lens 17. The lens 17 collects the reflected light and makes the collected reflected light enter the line sensor 18. The line sensor 18 includes a CCD having a plurality of photoelectric conversion elements arranged in a line in the main scanning direction (direction perpendicular to the document conveyance direction (direction perpendicular to the paper surface of FIG. 2)), and reflects light ( When the light from the lamp 13 reflected by the original is incident, photoelectric conversion is performed for each pixel in units of lines to accumulate charges, and an analog signal is output according to the accumulated charges.

  Further, a first moving frame 131, a second moving frame 132, a wire 133, and a winding drum 134 are provided in the housing. The first moving frame 131 supports the lamp 13 and the first mirror 14. The second moving frame 132 supports the second mirror 15 and the third mirror 16. One end of a wire 133 is connected to the first moving frame 131 and the second moving frame 132. The other end of the wire 133 is connected (wound) to the winding drum 134. Therefore, when the winding drum 134 rotates, the first moving frame 131 and the second moving frame 132 move in the sub-scanning direction (direction perpendicular to the main scanning direction). That is, the lamp 13, the first mirror 14, the second mirror 15, and the third mirror 16 move in the sub scanning direction. The rotational drive of the winding drum 134 is performed by transmitting the driving force of the winding motor 135 (see FIG. 7) to the winding drum 134.

  When reading a document transported from the document transport unit 2, the take-up drum 134 rotates and the first moving frame 131 and the second moving frame 132 are moved to the reading position (below the transport reading contact glass 11). Move and stop. Thereafter, the document transport unit 2 transports the document. There is a reading position (above the conveyance reading contact glass 11) in the middle of the document conveyance path 23, and the document traveling on the document conveyance path 23 passes through the reading position. At this time, the document is read by the lamp 13 irradiating light to the document passing through the reading position, and the line sensor 18 photoelectrically converts the reflected light reflected by the document.

  On the other hand, when reading a document placed on the placement reading contact glass 12, the take-up drum 134 rotates and the first moving frame 131 and the second moving frame 132 move in the sub-scanning direction. While the first moving frame 131 and the second moving frame 132 are moving in the sub-scanning direction, the lamp 13 irradiates the document placed on the placement reading contact glass 12 with light. The line sensor 18 continuously and repeatedly performs photoelectric conversion of the reflected light reflected from the document. As a result, the document is read.

  The document conveying unit 2 is attached to the image reading unit 1 so as to be opened and closed in the vertical direction. When the document conveying section 2 is closed, the document conveying section 2 and the placement reading contact glass 12 are overlapped, and the placement reading contact glass 12 is completely covered by the document conveying section 2. For this reason, when reading the document placed on the placement reading contact glass 12, the document placed on the placement reading contact glass 12 can be pressed by the document transport unit 2.

  The attachment structure of the document conveying section 2 with respect to the image reading section 1 is as shown in FIGS. Specifically, a rotating shaft 1a is provided on the back side of the main body of the image reading unit 1, and a document conveying unit 2 is attached to the rotating shaft 1a so as to be rotatable. As a result, the document conveying unit 2 rotates with the front side of the main body as a free end and swings the front side of the main body in the up and down direction, with respect to the image reading unit 1 (the upper surface of the placement reading contact glass 12). Take the open / close position.

  An open / close detection unit 140 is provided on the back side of the main body of the image reading unit 1 to detect that the tilt of the document conveying unit 2 has reached a predetermined angle. The open / close detection unit 140 includes a contact piece 141, a sensor 142, a spring 143, and the like.

  The contact piece 141 is made of a rod-like member extending in the vertical direction, and slides in the vertical direction. The upper end 141a of the contact piece 141 protrudes upward from the upper surface of the placement reading contact glass 12 in a state where the document conveying section 2 is opened. Therefore, when the document conveying unit 2 is tilted from the opened state, the upper end 141a of the contact piece 141 is pressed by the document conveying unit 2, and the contact piece 141 is pressed downward. A lower end 141 b of the contact piece 141 is wide and is used for detection by the sensor 142.

  The sensor 142 is disposed below the placement reading contact glass 12. The sensor 142 is, for example, a transmissive optical sensor, and has a light emitting unit and a light receiving unit. When the document conveying unit 2 is opened, the lower end 141 b of the contact piece 141 is positioned above the sensor 142. When the document conveying unit 2 is tilted from the opened state and the lower end 141b of the contact piece 141 is pushed downward, the lower end 141b of the contact piece 141 moves along the optical path of the sensor 142 (between the light emitting unit and the light receiving unit). Start blocking. When the document conveying unit 2 is tilted, the lower end 141b of the contact piece 141 continues to block the optical path of the sensor 142. As a result, it is possible to detect that the document conveying unit 2 is tilted.

  The spring 143 is, for example, a compression coil spring. The spring 143 is disposed below the contact piece 141 and urges the contact piece 141 upward. As a result, when the document conveying unit 2 is opened, the upper end 141 a of the contact piece 141 is held so as to protrude above the upper surface of the placement reading contact glass 12.

  By the way, the position at which it is detected that the document conveying unit 2 is tilted is determined in advance in association with the angle θ of the document conveying unit 2 with respect to the placement reading contact glass 12. The predetermined angle θ is, for example, 20 degrees to 45 degrees. Accordingly, the position of the lower end 141b of the contact piece 141 is adjusted so as to block the optical path of the sensor 142 when the inclination of the document conveying unit 2 reaches a predetermined angle θ. Then, when the sensor 142 detects that the document conveying unit 2 is tilted from a predetermined position (the tilt of the document conveying unit 2 is at an angle θ), the image reading unit 1 detects the document size. Start detection.

  For example, referring to FIG. 5, the user who executes the scan job faces the document so that the document reading surface faces downward and the corner of the document matches the reference point P at the upper left corner of the placement reading contact glass 12. It mounts on the contact glass 12 for mounting reading. In FIG. 5, the document is indicated by a two-dot chain line.

  Then, the document size detection in the main scanning direction is performed by reading the left end portion of the document when the sensor 142 detects that the document transport unit 2 is tilted from a predetermined position. The document size detection in the main scanning direction will be described in detail later. On the other hand, the document size detection in the sub-scanning direction is performed based on output values of a plurality of document detection units (for example, a reflection type optical sensor) 150 arranged in the sub-scanning direction.

  Next, an example of a hardware configuration of the image forming apparatus 200 including the image reading apparatus 100 will be described with reference to FIG.

  The image forming apparatus 200 includes a main body control unit 210. The main body control unit 210 includes a CPU 211 that is a central processing unit, a storage unit 212, an image processing unit 213, and the like. The storage unit 212 includes a ROM, a RAM, an HDD, and the like. For example, various programs and data are stored in the ROM and expanded in the RAM. The image processing unit 213 includes an ASIC dedicated to image processing, a memory, and the like, and performs various types of image processing such as enlargement / reduction, density conversion, and data format conversion on the image data.

  The main body control unit 210 is connected to the operation panel 3, the paper feeding unit 4A, the conveyance path 4B, the image forming unit 5A, the intermediate transfer unit 5B, and the fixing unit 5C. Then, the main body control unit 210 performs control and calculation of each unit based on various programs and data stored in the storage unit 212.

  Next, an example of the hardware configuration of the image reading apparatus 100 will be described with reference to FIG.

  The image reading apparatus 100 is provided with a reading control unit 110 (control unit) that controls the operation of the image reading unit 1 and a document conveyance control unit 120 that controls the operation of the document conveyance unit 2.

  The document conveyance control unit 120 is connected to the main body control unit 210. The document conveyance control unit 120 includes a CPU 121 and a storage unit 122 (ROM or RAM). For example, a program and data relating to document conveyance are stored in the ROM, and the program and data are expanded in the RAM. The document conveyance control unit 120 is connected to the document conveyance motor 27. The document conveyance control unit 120 receives an instruction from the main body control unit 210, controls the driving of the document conveyance motor 27, and appropriately operates the document supply roller 24, the document conveyance roller pair 25, and the document discharge roller pair 26.

  The reading control unit 110 is connected to the main body control unit 210. The reading control unit 110 includes a CPU 111 and a storage unit 112 (ROM or RAM). For example, a program and data relating to document reading are stored in the ROM, and the program and data are expanded in the RAM. The reading control unit 110 is connected to the inverter 19 for causing the lamp 13 to emit light, the line sensor 18, the take-up motor 135, the open / close detection unit 140, etc., and receives these instructions from the main body control unit 210. Control.

  Further, the reading control unit 110 is connected to the A / D conversion unit 113 and the image memory 114, and controls these operations in response to instructions from the main body control unit 210. The A / D converter 113 converts the analog signal output from the line sensor 18 into digital image data. The image memory 114 temporarily stores the image data output from the A / D conversion unit 113 and transfers the image data to the main body control unit 210.

  Further, the reading control unit 110 performs scanning for detecting the document size in the main scanning direction before reading the document. Specifically, when the open / close detection unit 140 detects that the document transport unit 2 is tilted from a predetermined position in a state where the document is placed on the placement reading contact glass 12, the reading control unit 140 Reference numeral 110 causes each unit of the image reading unit 1 to scan for document size detection.

  At this time, the take-up motor 135 moves the first moving frame 131 and the second moving frame 132 so that the portion located at the left end of the placement reading contact glass 12 in the original can be read. Fix it.

  In this state, the lamp 13 irradiates the original with light. The line sensor 18 photoelectrically converts the reflected light reflected from the document, and accumulates the charge of each pixel for one line. Note that the photoelectric conversion time (charge accumulation time) of the line sensor 18 at this time is the same as the photoelectric conversion time during normal image reading, for example. The A / D conversion unit 113 digitizes an analog signal from the line sensor 18 that has received the reflected light (light from the lamp 13 reflected by the document), and the pixel value (density value) of each pixel for one line. Document size detection image data indicating () is generated. The image memory 114 receives the transfer of the document size detection image data from the A / D conversion unit 113 and accumulates the document size detection image data.

  Thereafter, the reading control unit 110 refers to the document size detection image data stored in the image memory 114 and specifies the boundary between the bright pixel (the pixel where the document exists) and the dark pixel (the pixel where the document does not exist). By doing this, the document size in the main scanning direction is detected. Here, among the plurality of photoelectric conversion elements of the line sensor 18, a large amount of reflected light is received by the photoelectric conversion element corresponding to the pixel where the document exists, but the reflected light is reflected by the photoelectric conversion element corresponding to the pixel where the document does not exist. Is not received (the amount of received light is small even if received). Therefore, a difference occurs between the pixel value of the pixel where the document exists and the pixel value of the pixel where the document does not exist. Accordingly, the reading control unit 110 determines, for example, whether or not the pixel value of each pixel exceeds the threshold value with reference to a preset threshold value, whereby a bright pixel (a pixel in which an original exists) and a dark pixel ( A pixel where no document exists). Then, based on the identification result, the reading control unit 110 specifies a boundary between a bright pixel (a pixel where an original exists) and a dark pixel (a pixel where no original exists).

  Note that the threshold value that the reading control unit 110 uses as a reference when determining whether or not a document exists is stored in the storage unit 112. For example, the threshold value is obtained by actually measuring the output value of the line sensor 18 when a document is placed on the placement reading contact glass 12 and the output value of the line sensor 18 when a document is not placed. If so, it can be calculated from the measurement result.

  Then, the reading control unit 110 performs document size detection in the main scanning direction after specifying a boundary between a bright pixel (a pixel where an original exists) and a dark pixel (a pixel where no original exists). For example, the reading control unit 110 obtains the length in the main scanning direction of the document by identifying the number of pixels counted from the reference point P (see FIG. 5) and the main boundary of the document. Based on a table that defines the document size with respect to the length in the scanning direction, the document size in the main scanning direction is detected. A table that defines the document size with respect to the length of the document in the main scanning direction is stored in the storage unit 112, for example.

  Incidentally, if the document size detection is performed by the image reading unit 1 before the document conveying unit 2 is completely closed, disturbance light may enter the line sensor 18 and an accurate detection result may not be obtained. For this reason, in order to perform accurate document size detection, it is necessary to remove the influence of disturbance light from document size detection image data used for document size detection. Therefore, the reading control unit 110 generates disturbance light detection image data for removing the influence of disturbance light.

  Specifically, in a state in which the document is placed on the placement and reading contact glass 12, the reading control unit 110 performs a period during which the document transport unit 2 is lifted from a predetermined position (the document transport unit 2). In a period in which the open / close detection unit 140 does not detect that the sensor has been tilted from a predetermined position), that is, in a period in which disturbance light is likely to enter the line sensor 18, the line sensor is not turned on. 18 is caused to perform photoelectric conversion of disturbance light. Subsequently, the reading control unit 110 causes the A / D conversion unit 113 to digitize the analog output of the line sensor 18 that has received disturbance light, thereby indicating the pixel value (density value) of each pixel for one line. Image data is generated, and the image data is stored in the image memory 114. Note that the image data stored in the image memory 114 at this time is ambient light detection image data.

  Then, the reading control unit 110 identifies bright pixels (pixels where a document exists) and dark pixels (pixels where a document does not exist) based on ambient light detection image data stored in the image memory 114. Here, among the plurality of photoelectric conversion elements of the line sensor 18, the photoelectric conversion element corresponding to the pixel where the document exists does not receive disturbance light (the amount of received light is small even if it is received), but the pixel where there is no document exists. The corresponding photoelectric conversion element has a high possibility of receiving disturbance light. That is, a difference occurs between the pixel value of the pixel where the document exists and the pixel value of the pixel where the document does not exist. Accordingly, the reading control unit 110 determines, for example, whether or not the pixel value of each pixel exceeds the threshold value with reference to a preset threshold value, whereby a bright pixel (a pixel in which an original exists) and a dark pixel ( A pixel where no document exists). The identification result is stored in the storage unit 112.

  Thereafter, when the document size is detected based on the document size detection image data, the reading control unit 110 refers to the ambient light detection image data and identifies pixels that are brightened by the influence of the ambient light. Specifically, during a period in which the document conveying unit 2 is lifted from a predetermined position (a period in which the light from the lamp 13 is not irradiated on the document), among the plurality of photoelectric conversion elements of the line sensor 18, A photoelectric conversion element corresponding to a pixel in which an original is present is unlikely to receive disturbance light, but a photoelectric conversion element corresponding to a pixel in which no original is present may receive disturbance light.

  On the other hand, ideally, the plurality of photoelectric conversion elements of the line sensor 18 are in a period in which the document conveying unit 2 is tilted from a predetermined position (a period in which the light from the lamp 13 is irradiated on the document). Among them, the photoelectric conversion elements corresponding to the pixels in which the document is present receive the reflected light, but the photoelectric conversion elements corresponding to the pixels in which the document is not present do not receive the reflected light. However, when disturbance light is incident on the line sensor 18 during a period in which the document conveying unit 2 is tilted from a predetermined position, the pixel corresponding to a pixel in which no document is present among the plurality of photoelectric conversion elements of the line sensor 18. There is a possibility that the photoelectric conversion element receives disturbance light and a pixel that is determined to have a document even though there is no document is generated.

  Therefore, when the document size is detected based on the document size detection image data, the reading control unit 110 refers to the ambient light detection image data and identifies pixels that have become bright due to the influence of the ambient light. Then, the reading control unit 110 recognizes a pixel that has become bright under the influence of ambient light as a dark pixel (a pixel in which no document exists).

  By the way, when the light source of disturbance light is a fluorescent lamp, the disturbance light blinks at a constant cycle (for example, 100 times / second in the 50 Hz region and 120 times / second in the 60 Hz region). For this reason, at the time of generating disturbance light detection image data for identifying pixels that have become bright due to the influence of disturbance light, the line sensor 18 is photoelectrically operated during a period when the light source of disturbance light is dark, as shown in FIG. There is a case where the period for conversion completely overlaps (see period T1 in FIG. 8). In this case, since the photoelectric conversion of disturbance light is not performed in the photoelectric conversion element (photoelectric conversion element corresponding to a pixel on which no document exists) that originally performs disturbance light photoelectric conversion, an accurate disturbance light detection image is obtained. Data cannot be obtained.

  In order to eliminate such inconvenience, disturbance light detection image data for a plurality of lines may be generated and stored in the image memory 114, and the disturbance light detection image data for the plurality of lines may be compared. However, in order to compare disturbance light detection image data for a plurality of lines, it is necessary to store disturbance light detection image data for a plurality of lines in the image memory 114, so the memory capacity must be increased. , Leading to increased costs.

  Therefore, in the present embodiment, as shown in FIG. 8, when generating disturbance light detection image data for identifying a pixel that has become bright due to the influence of disturbance light, the photoelectric conversion time of the line sensor 18 is normally set. Longer than the photoelectric conversion time during image reading (photoelectric conversion time during document size detection). More specifically, the photoelectric conversion time of the line sensor 18 is set longer than the blinking cycle of the fluorescent lamp (see period T2 in FIG. 8). As a result, if the light source of disturbance light is a fluorescent lamp, disturbance light is always incident on the photoelectric conversion element corresponding to the pixel on which no document exists at the time of generation of disturbance light detection image data. Is done). Therefore, in the present embodiment, pixels that have become brighter due to the influence of disturbance light can be accurately identified with only one line of disturbance light detection image data.

  Next, a sequence of document size detection performed by the image reading apparatus 100 will be described with reference to the flow of FIG.

  First, it is assumed that the user who intends to execute a scanner job has opened the document transport unit 2 at the start of the flow of FIG. Then, when the user places a document on the placement reading contact glass 12, the flow of FIG. 9 starts. Note that there is a difference in the output value from the A / D converter 113 (the output value from the line sensor 18) between when the document is placed on the placement reading contact glass 12 and when the document is not placed. Arise. Therefore, it is possible to determine whether or not a document is placed on the placement reading contact glass 12 based on an output value from the A / D conversion unit 113, for example.

  In step S1, the reading control unit 110 sets the photoelectric conversion time of the line sensor 18 to be longer than the photoelectric conversion time during normal image reading. For example, the reading control unit 110 sets the photoelectric conversion time of the line sensor 18 to be longer than the blinking cycle of the ambient light source (fluorescent lamp).

  In step S <b> 2, the reading control unit 110 reads one line without turning on the lamp 13 in a state where the document conveying unit 2 is opened (a state where disturbance light may enter the line memory 18). The image data for detecting ambient light is acquired by causing each unit of the image reading unit 1 to perform the above. Specifically, at this time, the line sensor 18 photoelectrically converts disturbance light over a longer time than the photoelectric conversion time at the time of normal image reading in a state where the lamp 13 does not irradiate the document with light. Then, the charge of each pixel for one line is accumulated. The A / D conversion unit 113 digitizes the analog output of the line sensor 18 that has received disturbance light, and generates disturbance light detection image data indicating the pixel value of each pixel. The image memory 114 stores disturbance light detection image data.

  In step S <b> 3, the reading control unit 110 refers to the ambient light detection image data, identifies bright pixels (pixels where a document exists) and dark pixels (pixels where a document does not exist), and stores them in the storage unit 112. .

  In step S <b> 4, the reading control unit 110 determines whether or not the document conveying unit 2 is tilted from a predetermined position. If the document transport unit 2 is tilted from a predetermined position, the process proceeds to step S5. If the document transport unit 2 is not tilted from a predetermined position, the operation of step S4 is repeated. .

  In step S5, the reading control unit 110 turns on the lamp 13 and causes each unit of the image reading unit 1 to read one line before the document conveying unit 2 is completely closed, thereby making the document size. Obtain image data for detection. Specifically, at this time, the line sensor 18 photoelectrically converts the reflected light reflected by the document, and accumulates the charge of each pixel for one line. Further, the A / D conversion unit 113 digitizes the analog output of the line sensor 18 that has received the reflected light, and generates document size detection image data indicating the pixel value of each pixel. The image memory 114 stores document size detection image data.

  In step S <b> 6, the reading control unit 110 identifies pixels that have become bright under the influence of disturbance light based on the disturbance light detection image data. Subsequently, in step S7, the reading control unit 110 regards the pixels that have become brighter due to the influence of ambient light as dark pixels (pixels where no document exists), and bright pixels (pixels where the document exists) and dark pixels. A boundary with a pixel (a pixel in which no document exists) is specified. In step S8, the reading control unit 110 determines the length of the document in the main scanning direction based on the specified boundary.

  In the present embodiment, as described above, the line sensor 18 accumulates charges for each pixel while photoelectrically converting disturbance light in units of lines over a longer time than the photoelectric conversion time during normal image reading. Image data for detecting ambient light is generated. As a result, when the disturbance light detection image data is generated, the light source of the disturbance light source is darker than the case where the photoelectric conversion time of the line sensor 18 is the same as the photoelectric conversion time at the time of normal image reading. It is possible to suppress a complete overlap with the conversion period. For this reason, the pixel value of the pixel where the document exists remains dark, and the pixel value of the pixel where the document does not exist is certainly brighter than the pixel value of the pixel where the document exists. This makes it possible to accurately identify pixels that have become brighter due to the influence of disturbance light, so that it is possible to suppress the inconvenience that document size detection becomes inaccurate due to disturbance light.

  Even when the disturbance light detection image data is generated by causing the line sensor 18 to perform reading with the photoelectric conversion time at the time of normal image reading, for example, the disturbance light detection image data for a plurality of lines is stored in the memory. When the disturbance light detection image data for a plurality of lines is compared, the boundary between the pixel where the document does not exist and the pixel where the document exists can be specified. However, in this case, it is necessary to secure a memory capacity for simultaneously storing disturbance light detection image data for a plurality of lines, leading to an increase in cost. However, in this embodiment, even if the disturbance light detection image data is only for one line, the disturbance light detection image data for one line is highly reliable. Pixels that have been brightened upon reception can be identified. That is, it is not necessary to increase the memory capacity in order to compare the disturbance light detection image data for a plurality of lines, and the cost increase can be suppressed.

  In the present embodiment, as described above, when the open / close detection unit 140 detects that the document transport unit 2 (document pressing unit) is tilted from a predetermined position, the reading control unit 110 (control unit). ) Turns on the lamp 13 (light source) and causes the line sensor 18 to perform reading in the photoelectric conversion time at the time of normal image reading to generate document size detection image data. Based on the ambient light detection image data A pixel identified as having become bright under the influence of ambient light is recognized as a dark pixel, and the document size is detected. According to this configuration, the influence of ambient light can be accurately removed when the document size is detected based on the document size detection image data.

  In the present embodiment, as described above, the line sensor 18 makes the photoelectric conversion time for generating disturbance light detection image data longer than the disturbance light blinking cycle. With this configuration, when the disturbance light source is a fluorescent lamp or the like, more reliable document size detection can be performed.

  In the configuration of the above-described embodiment, a change in setting of the photoelectric conversion time when generating disturbance light detection image data may be received from the user. With this configuration, when the installation environment of the image forming apparatus 100 changes, the user can reset the photoelectric conversion time according to the change. Alternatively, the reading control unit 110 may automatically change the setting of the photoelectric conversion time.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the description of the above-described embodiment but by the scope of claims for patent, and further includes meanings equivalent to the scope of claims for patent and all modifications within the scope.

1 Image reading unit 2 Document conveying unit (document holding unit)
12 Contact glass for mounting reading (mounting table)
13 Lamp (light source)
18 Line sensor 100 Image reading device 110 Reading control unit (control unit)
140 Open / close detection unit 200 Image forming apparatus

Claims (2)

A table on which the document is placed;
A light source for irradiating the document with light;
A line sensor that photoelectrically converts the reflected light reflected by the original in units of lines and accumulates charges for each pixel;
An openable and closable with respect to the mounting table, and a document holder to obtain the original placed on the mounting table by closed pressing of,
An open / close detection unit for detecting that the document pressing unit is tilted more than a predetermined position when the document pressing unit is tilted from the opened state ;
A control unit that processes image data obtained by reading the line sensor,
When said document holder is brought down than a predetermined position is the open-close detecting unit does not detect,
The line sensor generates disturbance light detection image data by accumulating charges for each pixel while photoelectrically converting disturbance light in units of lines over a time longer than the photoelectric conversion time during normal image reading, And the photoelectric conversion time when generating the disturbance light detection image data is longer than the blinking period of the disturbance light,
The control unit identifies pixels that have become bright under the influence of the ambient light based on the ambient light detection image data ,
When the open / close detection unit detects that the document pressing unit is tilted from the opened state and the document pressing unit is tilted more than a predetermined position,
The control unit turns on the light source and causes the line sensor to read the photoelectric conversion time at the time of the normal image reading to generate document size detection image data, and the disturbance light detection image data An image reading apparatus that detects a document size by recognizing a pixel identified as having become bright under the influence of ambient light as a dark pixel . An image forming apparatus comprising the image reading apparatus according to claim 1 .

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