JP2014175710A - Image reading device and image formation device including the image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of image quality due to heat generation in turning on a light emission part.SOLUTION: An image reading device includes: a light emission part for emitting light in order to irradiate a manuscript with the light; a light guide part for guiding the light to be radiated over the whole range of the main scan direction of the manuscript; a photoelectric conversion part for receiving reflection light from the manuscript over the whole range of the main scan direction of the manuscript and outputting an electric signal corresponding to the amount of the light; a lens arranged over the whole range of the main scan direction of the manuscript and adjusting the light collection state of the light in an optical path where the light radiated from the light emission part is made incident to the photoelectric conversion part; and a manuscript transportation part for transporting the manuscript in a state where one side surface of the manuscript is set to a reference set position predetermined in the main scan direction. The light emission part is arranged only at an end part positioned relatively apart from the reference set position between the two end parts of the light guide part in the main scan direction.

Description

  The present invention relates to an image reading apparatus and an image forming apparatus including the image reading apparatus, and more particularly to a technique for suppressing deterioration in image quality caused by heat generated from a light source unit provided in the image reading apparatus.

  In recent years, information digitization has been promoted, and image reading apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image reading apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, and a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Such an image reading apparatus is equipped with a light source that irradiates light on a document and an image sensor that reads reflected light from the document. Results can be affected. For example, the amount of light decreases as the lighting time of the light source becomes longer. Therefore, it is necessary to eliminate the deterioration in image quality due to the decrease in the amount of light.

  On the other hand, in order to correct the influence on the image data by the light source or the reading optical system, white correction using a reading result of a reference density member having a predetermined white color (hereinafter referred to as “white shading data”) is generally used. Has been done. However, as described above, since the light amount of the light source decreases with time, it is desirable to perform the white shading data every time the image is read.

  However, when white correction is performed for each page, it is necessary to provide a shading data generation period in the non-document reading period (hereinafter referred to as a sheet interval), and there is a problem that productivity is reduced by that amount. . In particular, when the reference density member reading position and the document data reading position are different in the sub-scanning direction, a control for moving the carriage back and forth is added, so that the productivity is significantly reduced.

  Therefore, using the light quantity reference value and the light quantity fluctuation value at the place where the ratio between the light quantity reference values at the plurality of positions of the opposing member and the light quantity fluctuation value at each place is closest to 1, the image data after white correction is obtained. On the other hand, it has been proposed to further correct the amount of light (see Patent Document 1). As a result, the paper interval is shortened as compared with the case where white shading data is generated for each page, and correction for a decrease in light quantity with time is also performed.

  Furthermore, as time elapses after the light source is turned on, heat generated from the light source causes thermal expansion of components in the reader, particularly the lens array and the light receiving element array. At this time, there is a difference in thermal expansion between the lens array and the light receiving element array, which may cause a variation in the amount of received light in the light receiving element array. To solve this problem, the first lens array includes a first lens array in which a plurality of columnar lenses are arranged in the main scanning direction, and a second lens array in which a plurality of columnar lenses are arrayed in the main scanning direction. Are arranged in the sub-scanning direction so that the columnar lenses of the first lens and the columnar lenses of the second lens are staggered in the main scanning direction. Then, by arranging the image sensor along the boundary portion between the first lens array and the second lens array, the variation in the amount of light received in the light receiving element array due to the difference in thermal expansion between the lens array and the light receiving element. It has been proposed to suppress (see Patent Document 2).

  According to the above-mentioned patent document 1, it is possible to eliminate the deterioration in image quality due to the decrease in the amount of light accompanying the elapsed time from the lighting of the light source, and to improve the productivity of the image. However, the influence of the elapsed time since the lighting of the light source is not limited to the reduction of the light amount, and the influence of the heat generated from the light source cannot be ignored. That is, the reading unit includes a lens array in which lenses for collecting the reflected light are arranged along a direction (referred to as a main scanning direction) intersecting the conveyance direction of the reading object, and the collected light. And a sensor array in which photoelectric conversion elements for photoelectric conversion are arranged along the main scanning direction. When the reading unit having such a configuration is used, there is a case where at least one of the plurality of image sensors and the plurality of lenses is thermally expanded due to heat of the light source and the like, thereby causing a shift in the relative positional relationship between them. As a result, the peak position of the intensity of the reflected light condensed on the photoelectric conversion element side by each of the plurality of lenses shifts with time. Such a shift in the peak position is a factor causing black stripes, white stripes, and the like in the read image.

  Furthermore, in order to eliminate the influence of dark current accumulated in the photoelectric conversion element, black shading data is generated using the output of the photoelectric conversion element when the light source is turned off, and the offset correction of the image is performed using this. Yes. Here, the photoelectric conversion element has a characteristic that dark current is easily accumulated as the temperature is higher. Therefore, if the elapsed time from the lighting of the light source becomes long, there arises a problem that sufficient offset correction cannot be performed with the black shading data generated before the start of reading.

  However, Patent Document 1 solves a problem caused by thermal expansion due to heat generated by the light source, for example, a problem of suppressing a shift in peak position due to thermal expansion and a deterioration in image quality due to a change in the accumulated amount of dark current. It has not been. Further, in Patent Document 2, there is a problem that positioning is troublesome when the lens array and the light receiving element array are arranged.

  The present invention has been made in consideration of the above-described problems, and an object of the present invention is to reduce labor required for manufacturing while suppressing deterioration in image quality caused by heat generation due to lighting of a light source.

  In order to solve the above problems, one embodiment of the present invention includes a light emitting unit that emits light for irradiating a document, and light emitted from the light emitting unit so as to be irradiated over the entire main scanning direction of the document. A light guide unit for guiding light, a photoelectric conversion unit that receives reflected light from the document over the entire range in the main scanning direction of the document and outputs an electric signal according to the amount of light, and an entire range in the main scanning direction of the document A reference set in which the lens for adjusting the light condensing state in the optical path where the light emitted from the light emitting unit enters the photoelectric conversion unit and one side surface of the document are defined in the main scanning direction A light-emitting portion that is relatively separated from the reference set position among two ends of the light guide portion along the main scanning direction. At the end of the position Characterized in that it is seen disposed.

  According to another aspect of the present invention, there is provided an image forming apparatus including the image reading apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the effort which manufacture requires can be reduced, suppressing the fall of the image quality which the heat_generation | fever by light source lighting causes.

1 is a block diagram showing a hardware configuration of an image forming apparatus according to the present embodiment. 1 is a block diagram showing a functional configuration of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. The figure which shows the structure of an image reading apparatus Block diagram showing the configuration of the control system of the image reading apparatus The figure which shows the principal part of the electric circuit of a 2nd reading part. The figure which shows the component of a 2nd reading part. The figure which shows the arrangement position of LED contained in a 2nd reading part. The figure explaining the main scanning distribution fluctuation of white shading data by thermal expansion The figure explaining the relationship between the thermal expansion amount (shift amount) of the lens array and the document size The figure which shows the temperature characteristic of the output level of the image sensor when the light emitting part is turned off A diagram for explaining the relationship between the black offset level variation and the document size A flowchart showing an example of an operation flow of the image forming apparatus according to the present embodiment. 10 is a flowchart showing another example of the operation flow of the image forming apparatus according to the present embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an image forming apparatus as an MFP (Multi Function Peripheral) will be described as an example. The image forming apparatus according to the present embodiment is an electrophotographic image forming apparatus, and includes an image reading apparatus that reads a document to be imaged.

  FIG. 1 is a block diagram illustrating a hardware configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an engine that executes image formation in addition to the same configuration as an information processing terminal such as a general server or a PC (Personal Computer). That is, the image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (ReA / D Only Memory) 12, an engine 13, an HDD (Hard Disk Drive) 14, and the like. The I / F 15 is connected via the bus 18. Further, an LCD (Liquid Crystal Display) 16 and an operation unit 17 are connected to the I / F 15.

  The CPU 10 is a calculation unit and controls the operation of the entire image forming apparatus 1. The RAM 11 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The engine 13 is a mechanism that actually executes image formation in the image forming apparatus 1.

  The HDD 14 is a nonvolatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 15 connects and controls the bus 18 and various hardware and networks. The LCD 16 is a visual user interface for the user to check the state of the image forming apparatus 1. The operation unit 17 is a user interface such as a keyboard and a mouse for the user to input information to the image forming apparatus 1.

  In such a hardware configuration, a program stored in a recording medium such as the ROM 12, the HDD 14, or an optical disk (not shown) is read into the RAM 11 and operates according to the control of the CPU 10, thereby configuring a software control unit. A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the functional configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes a controller 20, an ADF (Auto Document Feeder) 21, a scanner unit 22, a paper discharge tray 23, a display panel 24, and a paper feed table. 25, a print engine 26, a paper discharge tray 27, and a network I / F 28. The ADF 21, the scanner unit 22, and the paper discharge tray 23 are collectively referred to as an image reading apparatus 100.

  The controller 20 includes a main control unit 30, an engine control unit 31, an input / output control unit 32, an image processing unit 33, and an operation display control unit 34. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment is configured as a multifunction machine having a scanner unit 22 and a print engine 26. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of paper is indicated by broken arrows.

  The display panel 24 is an output interface that visually displays the state of the image forming apparatus 1 and is an input when the user directly operates the image forming apparatus 1 or inputs information to the image forming apparatus 1 as a touch panel. It is also an interface (operation unit). The network I / F 28 is an interface for the image forming apparatus 1 to communicate with other devices via the network, and an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface is used.

  The controller 20 is configured by a combination of software and hardware. Specifically, a control program such as firmware stored in a nonvolatile recording medium such as the ROM 12 and the nonvolatile memory and the HDD 14 and the optical disk is loaded into a volatile memory (hereinafter referred to as a memory) such as the RAM 11 to control the CPU 10. The controller 20 is configured by a software control unit configured according to the above and hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire image forming apparatus 1.

  The main control unit 30 plays a role of controlling each unit included in the controller 20 and gives a command to each unit of the controller 20. The engine control unit 31 serves as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like.

  The input / output control unit 32 inputs a signal or a command input via the network I / F 28 to the main control unit 30. The main control unit 30 controls the input / output control unit 32 and accesses other devices via the network I / F 28.

  The image processing unit 33 generates drawing information based on the print information included in the input print job under the control of the main control unit 30. The drawing information is information for drawing an image to be formed in the image forming operation by the print engine 26 as an image forming unit. The print information included in the print job is image information converted into a format that can be recognized by the image forming apparatus 1 by a printer driver installed in an information processing apparatus such as a PC. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

  When the image forming apparatus 1 operates as a printer, first, the input / output control unit 32 receives a print job via the network I / F 28. The input / output control unit 32 transfers the received print job to the main control unit 30. When receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

  When drawing information is generated by the image processing unit 33, the engine control unit 31 performs image formation on the paper conveyed from the paper feed table 25 based on the generated drawing information. That is, the print engine 26 functions as an image forming unit. A document on which an image has been formed by the print engine 26 is discharged to a discharge tray 27.

  When the image forming apparatus 1 operates as a scanner, the operation display control unit 34 or the input / output unit is operated in accordance with a user operation on the display panel 24 or a scan execution instruction input from an external PC or the like via the network I / F 28. The control unit 32 transfers a scan execution signal to the main control unit 30. The main control unit 30 controls the engine control unit 31 based on the received scan execution signal.

  The engine control unit 31 drives the ADF 21 and conveys an imaging target document (hereinafter abbreviated as “original”) set on the ADF 21 to the scanner unit 22. Further, the engine control unit 31 drives the scanner unit 22 and images a document conveyed from the ADF 21. If no original is set on the ADF 21 and the original is directly set on the scanner unit 22, the scanner unit 22 takes an image of the set original under the control of the engine control unit 31. That is, the scanner unit 22 operates as a document reading unit.

  In the imaging operation, the imaging element included in the scanner unit 22 optically scans the document, and imaging information generated based on the optical information is generated. The engine control unit 31 transfers the imaging information generated by the scanner unit 22 to the image processing unit 33. The image processing unit 33 generates image information based on the imaging information received from the engine control unit 31 according to the control of the main control unit 30.

  The image information generated by the image processing unit 33 is stored in the HDD 14 or the like as it is according to a user instruction or transmitted to an external device via the input / output control unit 32 and the network I / F 28.

  Further, when the image forming apparatus 1 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. To do. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

  Next, a schematic configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating a schematic configuration of the image forming apparatus according to the present embodiment.

  As shown in FIG. 3, the image forming apparatus 1 includes an image reading device 100, a paper feeding unit 200, and an image forming unit 300.

  The paper feeding unit 200 includes paper feeding cassettes 221 and 222 that store recording papers having different paper sizes, and various rollers that transport the recording papers stored in the paper feeding cassettes 221 and 222 to the image forming position of the image forming unit 300. The sheet feeding means 223.

  The image forming unit 300 includes an exposure device 331, a photosensitive drum 332, a developing device 333, a transfer belt 334, and a fixing device 335. The image forming unit 300 exposes the photosensitive drum 332 by the exposure device 331 to form a latent image on the photosensitive drum 332 based on the image data of the original read by the reading unit inside the image reading device 100, and develops it. A device 333 supplies toner of different colors to the photosensitive drum 332 for development. The image forming unit 300 transfers the image developed on the photosensitive drum 332 by the transfer belt 334 to the recording paper supplied from the paper feeding unit 200, and then transfers the toner image transferred to the recording paper by the fixing device 335. The toner is melted to fix the color image on the recording paper.

  The image reading apparatus 100 is an apparatus that reads an image while conveying a document to be read to a fixed reading device unit and conveying the document at a predetermined speed. The basic configuration and function will be described with reference to FIGS. FIG. 4 is a diagram illustrating a configuration of the image reading apparatus. FIG. 5 is a block diagram showing the configuration of the control system of the image reading apparatus.

  As shown in FIGS. 4 and 5, the image reading apparatus 100 generally includes an original setting unit A for setting a read original bundle, and a separate feed for separating and feeding originals one by one from the set original bundle. Part B, registration part C for primary abutting alignment of the fed document and for pulling out and transporting the aligned document, turning the conveyed document, and directing the document surface to the reading side (downward) The turn section D that conveys the image, the first reading conveyance section E that reads an image on one side (hereinafter referred to as “front surface”) of the document from below the contact glass, and the other surface of the document (hereinafter referred to as “back surface”). ), The second reading and conveying unit F for reading the image, the paper discharge unit G for discharging the document whose front and back scanning has been completed to the outside of the apparatus, the stack unit H for stacking and holding the document after reading, and driving these conveying operations. Drive unit 190 and a controller for controlling a series of operations Configured to include a roller 180. The separation feeding unit B, the first reading conveyance unit E, the second reading conveyance unit F, and the paper discharge unit G correspond to the document conveyance unit.

  As shown in FIG. 5, the drive unit 190 includes a pickup motor 191, a paper feed motor 192, a reading motor 193, a paper discharge motor 194, and a bottom plate raising motor 195. In addition, an RTC (Real Time Clock) 105 is connected to the controller 180. The RTC 105 is used for measuring an elapsed time from the start of lighting of a light source included in the second reading unit 125 described later. That is, the RTC 105 corresponds to a time measuring unit.

  The bundle of the originals 101 to be read is set on the original table 102 including the movable original table 103 with the surface of the original 101 facing upward. Further, the width direction of the original 101 is positioned in a direction coinciding with the conveyance direction by a side guide (not shown). The setting of the document 101 is detected by a set filler 104 and a set sensor (not shown) and transmitted to the main control unit 30 via the engine control unit 31. When the controller 180 of the image reading apparatus 100 has a function of controlling the image reading apparatus 100, the detection signal may be output to the controller 180 instead of the main control unit 30.

  Further, the length of the document in the conveying direction is roughly determined by a document length detection sensor 130 or 131 (a reflective sensor or an actuator type sensor that can detect even one document) provided on the document table surface. Is determined. Instead of the document length detection sensor, a sensor that can determine whether the document size is vertical or horizontal may be provided.

  The movable document table 103 can be moved up and down in the directions a and b shown in FIG. 4 by a bottom plate raising motor 195. When the set filler 104 and the set sensor detect that the original is set, the bottom plate raising motor 195 is rotated forward to raise the movable original table 103 so that the uppermost surface of the original bundle contacts the pickup roller 107. . The pickup roller 107 has a cam mechanism, and operates in the c and d directions shown in FIG. At the same time, the movable document table 103 is raised, pushed by the upper surface of the document on the movable document table 103 and raised in the direction c, and the upper limit can be detected by the table feed proper position sensor 108.

  When the print key is pressed from the operation unit 17 and a document feed signal is transmitted from the main control unit 30 to the image reading apparatus 100 via the engine control unit 31, the pickup roller 107 is rotated by the forward rotation of the feed motor 192. Is rotated to pick up several (ideally one) originals on the original table 102. The rotation direction is a direction in which the uppermost document is conveyed to the sheet feeding port.

  The paper feeding belt 109 is driven in the paper feeding direction by the normal rotation of the paper feeding motor 192, and the reverse roller 110 is rotationally driven in the reverse direction to the paper feeding by the normal rotation of the paper feeding motor 192, and the uppermost document and its lower side. The original is separated, and only the uppermost original can be fed. More specifically, the reverse roller 110 is in contact with the paper feeding belt 109 at a predetermined pressure, and in a state where it is in direct contact with the paper feeding belt 109 or through a single document, the reverse roller 110 rotates. Therefore, if two or more originals enter between the paper feeding belt 109 and the reverse roller 110, the turning force is set to be lower than the torque limiter torque, The roller 110 rotates in the clockwise direction, which is the original driving direction, and pushes back an excess original, thereby preventing double feeding.

  The original 101 separated by the action of the paper feed belt 109 and the reverse roller 110 is further fed by the paper feed belt 109, detected by the abutting sensor 111, further advanced to the pull-out roller 112 stopped. After that, the sheet feeding motor 192 is stopped in a state where the sheet is fed by a predetermined amount from the detection of the above-described abutting sensor 111 and as a result is pressed against the pull-out roller 112 with a predetermined amount of bending. As a result, the driving of the paper feeding belt 109 is stopped. At this time, the pickup motor 191 is rotated to retract the pickup roller 107 from the upper surface of the original, and the original 101 is fed only by the conveying force of the paper feeding belt 109, so that the front end of the original is a nip between the upper and lower rollers of the pull-out roller 112. And the tip is aligned (skew correction).

  The pull-out roller 112 has the skew correction function and is a roller for transporting the skew-corrected original document to the intermediate roller 114 after separation, and is driven by the reverse rotation of the paper feed motor 192. At this time (at the time of reverse rotation of the paper feed motor 192), the pull-out roller 112 and the intermediate roller 114 are driven, but the pickup roller 107 and the paper feed belt 109 are not driven.

  A plurality of document width sensors 113 are arranged in the main scanning direction and detect the size (document width size) of the document conveyed by the pull-out roller 112 in the main scanning direction. The length of the document in the conveyance direction is detected from the motor pulse by reading the leading and trailing edges of the document with the butting sensor 111.

  When the document is transported from the resist section C to the turn section D by driving the pull-out roller 112 and the intermediate roller 114, the transport speed at the resist section C is set higher than the transport speed at the reading transport section E. The processing time for sending the document to the reading unit is shortened. When the leading edge of the document is detected by the reading entrance sensor 115, before the leading edge of the document enters the nip between the upper and lower roller pairs of the reading entrance roller 116, deceleration is started to make the document transportation speed the same as the scanning transportation speed. Then, the reading motor 193 is driven to rotate forward to drive the reading entrance roller 116, the reading exit roller 123, and the exit roller 127. When the leading edge of the document 101 is detected by the registration sensor 117, the document is decelerated over a predetermined conveyance distance, temporarily stopped in front of the first reading unit 120, and stopped at the main control unit 30 via the engine control unit 31. Send a signal.

  Subsequently, when a reading start signal is received from the main control unit 30, the temporarily stopped document 101 is accelerated so as to rise to a predetermined conveyance speed before the leading edge of the document reaches the reading position of the first reading unit 120. Are transported. At the timing when the leading edge of the document detected by the pulse count of the reading motor 193 reaches the reading unit, a gate signal indicating an effective image area in the sub-scanning direction on the first surface is sent to the first reading unit 120 by the main control unit 30. Sent until the trailing edge of the document is removed.

  In the case of single-sided document reading, the document that has passed through the reading conveyance unit E is conveyed to the paper discharge unit G through the second reading unit 125. At this time, when the leading edge of the document is detected by the paper discharge sensor 124, the paper discharge motor 194 is driven to rotate forward to rotate the paper discharge roller 128 counterclockwise. In addition, the discharge motor pulse count from the detection of the leading edge of the document by the discharge sensor 124 reduces the discharge motor drive speed immediately before the trailing edge of the document comes out of the nip between the upper and lower roller pairs of the discharge roller 128, thereby discharging the sheet. Control is performed so that the document discharged onto the tray 23 does not jump out.

  In the case of double-sided document reading, the main document is read from the second reading unit 125 at the timing when the document leading edge reaches the second reading unit 125 by the pulse count of the reading motor 193 after the discharge sensor 124 detects the document leading end. A gate signal indicating an effective image area in the sub-scanning direction is transmitted from the control unit 30 through the second reading unit 125 until the trailing edge of the document is removed. The second reading roller 126 serves as a white reference member 170 for obtaining shading data in the second reading unit 125 as well as suppressing the floating of the document in the second reading unit 125. This white reference member 170 serves as a density reference.

  Next, the configuration of the second reading unit 125 will be described with reference to FIGS. FIG. 6 is a diagram illustrating a main part of an electric circuit of the second reading unit. FIG. 7 is a diagram illustrating components of the second reading unit. FIG. 8 is a diagram illustrating an arrangement position of LEDs included in the second reading unit.

  As illustrated in FIG. 6, the second reading unit 125 includes a light source unit 250, an image sensor 251, an amplifier circuit 252, an analog-digital converter (hereinafter referred to as “A / D converter”) 253, a black correction unit 254, and a white correction unit 255. An image processing unit 256, a frame memory 257, an output control circuit 258, and an interface circuit (hereinafter referred to as “I / F circuit”) 259.

  The light source unit 250 includes an LED 2501 as a point light source and a light guide unit 2502 (see FIG. 7). The LED 2501 corresponds to a light emitting unit. Details will be described later.

  The image sensor 251 is configured as a line sensor in which sensor chips 2511 including photoelectric conversion elements are arranged along the main scanning direction. The sensor chip 2511 includes a photoelectric conversion element called a contact image sensor (CIS: Contact Image Sensor) and a condenser lens. The photoelectric conversion element may be a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The photoelectric conversion elements arranged side by side on the line sensor receive reflected light from the document and the density reference member over the entire range of the document and density reference member in the main scanning direction, and output an electrical signal corresponding to the amount of light. is there. Therefore, the photoelectric conversion element corresponds to a photoelectric conversion unit. The condensing lens adjusts the light condensing state in the optical path where the light emitted from the LED 2501 enters the photoelectric conversion unit. The same number of amplifier circuits 252 and A / D converters 253 as the sensor chips 2511 are provided, and the sensor chips 2511, the amplifier circuits 252 and the A / D converters 253 are connected in series in this order. An analog signal output from the sensor chip 2511 is amplified by the amplifier circuit 252 and converted into a digital signal by the A / D converter 253.

  The signal output from the A / D converter 253 has a black offset level in addition to the signal component. The black correction unit 254 generates black shading data for correcting the black offset level based on the output from the image sensor 251 when the light source unit 250 is turned off, and the image sensor 251 uses the black shading data to generate black shading data. Correction (hereinafter referred to as “black correction”) for removing a signal corresponding to the black offset level is performed on the output obtained by reading the document. That is, the illuminance when the light source unit 250 is turned off is a density reference for offset correction.

  The white correction unit 255 removes the influence on the image data due to unevenness in the main scanning direction of the light source unit 250 and nonuniform sensitivity of the image sensor 251, so that the white reference member 170 (the second reading roller 126 uses the white reference member). White shading data is generated on the basis of the output obtained by reading the image, and white correction is performed on the output after black correction using the white shading data.

  The controller 180 outputs a lighting signal to the light source unit 250 and simultaneously outputs a timing start signal to the RTC 105. The RTC 105 measures the elapsed time from the start of lighting, and outputs the result to the black correction unit 254 and the white correction unit 255. The black correction unit 254 and the white correction unit 255 compare the acquired elapsed time with the allowable time set to determine whether black shading data and white shading data need to be regenerated, and if necessary, Black shading data and white shading data are regenerated. Of the permissible time, a threshold that is determined as to whether black shading data needs to be regenerated is referred to as black correction permissible time, and a threshold that is determined as to whether white shading data needs to be regenerated is referred to as white correction permissible time. The allowable time may be changed according to the document width size. In this case, the black correction unit 254 and the white correction unit 255 obtain the detection result of the document width sensor 113 via the controller 180, and based on the detection result, the black correction allowable time and the white correction allowable time according to the document width. Time may be determined.

  After black correction, white correction, and the like, a signal that has been subjected to various other image processing in the image processing unit 256 is temporarily stored in the frame memory 257 as image data. Thereafter, the image data stored in the frame memory 257 is converted into a data format that can be received by the main control unit 30 by the output control circuit 258, and then via the engine control unit 31 via the I / F circuit 259. It is output to the main control unit 30.

  The operation of the second reading unit 125 described above is comprehensively controlled by the controller 180. For example, the controller 180 may detect a timing signal for notifying the timing at which the leading edge of the document 101 reaches the reading position by the second reading unit 125 (image data after that timing is treated as valid data), and each of the image sensors 251. A timing signal for driving the sensor chip 2511, a lighting signal of the light source unit 250, and the like are output, and the operation of the second reading unit 125 is controlled. The power supply to the second reading unit 125 is performed under the control of the controller 180.

  As shown in FIG. 7, the light source unit 250 included in the second reading unit 125 includes an LED 2501 serving as a light emitting unit and a light guide unit 2502 that guides light emitted from the LED 2501 in the irradiation direction. . In the present embodiment, the light emitting element is used as the light emitting unit, but the light emitting element is not limited to the light emitting element as long as it emits visible light. The light guide unit 2502 is configured using a long optical member that receives light from the end surface, diffuses the received light over the entire range in the main scanning direction, and emits light from the output surface. The axial direction of the light guide unit 2502 coincides with the main scanning direction. The light guide section 2502 here may have any function as long as it has a function of diffusing and irradiating light emitted from the LED 2501 over the entire range in the main scanning direction as described above. For example, the light is refracted like a prism. It is also possible to emit light to the original 101 or to irradiate the original 101 by reflecting light like a mirror. In the present embodiment, the LED 2501 is disposed only at the end of the light guide unit 2502 in the main scanning direction. This configuration is the gist of the invention.

  In this embodiment, the CIS is used as the image sensor 251, a lens array 2511 a in which a plurality of equal-magnification lenses are arranged over the entire range of the document in the main scanning direction, a photoelectric conversion element 2511 b stacked on the sensor substrate 2511 c, including. Then, the light emitted from the LED 2501 is applied to the document or the white reference member via the light guide unit 2502. Then, the reflected light from the original or the white reference member enters the photoelectric conversion element 2511b through the lens array 2511a.

  As shown in FIG. 8, in the image reading apparatus 100, at the start of the document reading operation, the document 101 is set with one side surface of the document table abutting on the leading portion of the document table 102 in the main scanning direction. Thus, positioning in the main scanning direction is performed. The position of the one side surface of the document 101 in the main scanning direction in this positioned state is referred to as a reference set position. On the document conveyance path, the one side surface of the document 101 is conveyed while maintaining the state of being arranged at the reference set position in the main scanning direction. The document width is determined by an output signal from the document width sensor 113 installed upstream of the conveyance path after passing the document. The document width sensor 113 forms a document width detection unit. The LED 2501 of the second reading unit 125 is disposed at the end of the light guide unit 2502 in the main scanning direction opposite to the head position in the main scanning direction (hereinafter referred to as “main scanning direction rear end”). This arrangement position is also one of the features of the present invention.

  By arranging the LEDs 2501 in this way, when the document width is small, among the photoelectric conversion elements 2511b arranged in the main scanning direction, the photoelectric conversion element 2511b that actually performs the image reading operation is the front end in the main scanning direction. Only the photoelectric conversion element 2511b within the distance from the document width. Therefore, by disposing the LED 2501 at the rear end portion in the main scanning direction, the distance between the LED 2501 and the sensor chip 2511 that performs the reading operation can be increased as compared with the case where the LED 2501 is disposed at the front end portion in the main scanning direction. Thereby, the heat transfer from LED2501 to the photoelectric conversion element 2511b can be delayed.

  The heat generated from the LED 2501 causes thermal expansion of the lens array 2511a, the photoelectric conversion element 2511b, and the sensor substrate 2511c. This thermal expansion becomes a cause of occurrence of vertical stripes in the image. Hereinafter, based on FIG. 9, the influence by this thermal expansion is demonstrated. FIG. 9 is a diagram for explaining a main scanning distribution variation of white shading data due to thermal expansion. FIG. 9 shows the concept that the lens array is deformed (expanded) and the shading data output distribution changes after a predetermined time X has elapsed since the generation of the shading data.

  In FIG. 9, the CIS included in the second reading unit 125 will be described as an example of processing in which the white reference member 170 is read to generate shading data. However, the adverse effect of thermal expansion is that the reading target is the white reference member 170. This occurs in the same way not only for a manuscript.

  The CIS condenses the reflected light from the white reference member 170 on the image sensor 251 through each of the equal magnification lenses 2511a1 and 2511a2 included in the lens array 2511a. Therefore, light is easily collected near the center of each of the equal magnification lenses 2511a1 and 2511a2, and a high sensor output is obtained. However, the sensor output is reduced at each end of the equal magnification lenses 2511a1 and 2511a2. For this reason, high output positions and low output positions are periodically generated in the arrangement cycle of the equal magnification lenses 2511a1 and 2511a2.

  A graph 900 in FIG. 9 shows an output level corresponding to the main scanning position. In the graph 900, a main scanning distribution (illustrated by a solid line) obtained by reading the white reference member 170 at the time of shading data generation (hereinafter referred to as “0 minute”), and a main scanning distribution after X minutes from the 0 minute time (shown by a solid line). (Illustrated by a one-dot chain line). As shown in the graph 900, the heat generated by the continuous lighting of the LED 2501 causes a decrease in the amount of light, and a phenomenon in which the high output position and the low output position slightly shift with time. Hereinafter, the high output position and the low output position are collectively referred to as a peak position. In this example, since the LED 2501 that is a heat source is disposed at the rear end portion in the main scanning direction, the photoelectric conversion element 2511b becomes higher in temperature as it approaches the rear end portion in the main scanning direction, and the shift amount ( The position change of the equal magnification lenses 2511a1 and 2511a2 at the time when the shading data is generated and after X minutes increases.

  The reason for shifting the main scanning distribution is that each of the lens array 2511a, the photoelectric conversion element 2511b, and the sensor substrate 2511c extends in the main scanning direction due to thermal expansion. At this time, the respective thermal expansion coefficients are different. There is a difference in the amount of elongation. As a result, the relative positional relationship between the lens array 2511a and the photoelectric conversion element 2511b is shifted.

  As shown in the graph 900 of FIG. 9, in a situation where the light collection rate changes for each main scanning position over time, the pixel whose light collection rate after X minutes is higher than the light collection rate at the start of the job. If the shading correction is performed using the shading data acquired at 0 minutes, the output is further increased compared to the surrounding positions. As a result, white stripes are generated. On the other hand, if the shading correction is performed using the shading data acquired at 0 minutes for pixel data that has a lower light collection rate after X minutes than the light collection rate at the start of the job, it is compared with the surrounding positions. As a result, the output is lowered, resulting in black streaks.

  For the above reasons, the lens array 2511a and the photoelectric conversion element 2511b are thermally expanded, so that their relative positions are shifted and vertical stripes are generated in the image. The amount of displacement increases as the distance from the LED 2501 serving as a heat source is closer. Here, as described above with reference to FIG. 8, the document is conveyed with its end aligned with the document set reference. Therefore, if the size of the document in the main scanning direction is different, there may be a document size in which a vertical streak caused by a positional deviation occurs and a size in which it does not occur under similar printing conditions. This phenomenon will be described with reference to FIG. Here, FIG. 10 is a diagram for explaining the relationship between the thermal expansion amount (shift amount) of the lens array and the document size.

  A graph 1000 in FIG. 10 shows a change characteristic of the thermal expansion amount (shift amount) Z of the lens array along the main scanning direction after X minutes. In the graph 1000, the change characteristic after X1 minutes is indicated by a solid line, and the change characteristic after X2 minutes is indicated by a dotted line. As is apparent from FIG. 10, when the LED 2501 serving as a heat source is disposed at the rear end portion in the main scanning direction, the shift amount Z increases toward the rear end portion in the main scanning direction, and the elapsed time from the start of lighting. The longer the shift amount Z is, the longer it is.

  The white correction unit 255 compares the predetermined allowable shift amount with the current shift amount Z, and if the relationship of shift amount Z> allowable shift amount is satisfied, the image quality based on the above-described white stripe or black stripe is obtained. Assuming that the deterioration is not allowed, white shading data is regenerated. An example of this determination is shown below.

When the document width is A4 (vertical) document,
X1 minutes later ... shift amount Z> allowable shift amount X2 minutes later ... shift amount Z <allowable shift amount. Therefore, it is desirable to generate and update shading data again between papers using X2 minutes as a guide. Therefore, when the document width is A4 portrait, X2 is the white correction allowable time.

When the document width is A3 document,
After X1 minutes: Since shift amount Z> allowable shift amount, it is desirable to generate and update shading data again between papers using X1 minutes as a guide. Therefore, when the document width is A3, the white correction allowable time is X1 minutes.

  It should be noted that the elapsed time until it corresponds to the allowable shift amount varies depending on the configuration of the second reading unit 125 and its peripheral component configuration, and therefore it is desirable to determine the elapsed time based on the evaluation result in the system at the development stage. Note that the shift amount may vary depending on the temperature of the place where the image forming apparatus 1 is installed (referred to as the outside air temperature) even at the same elapsed time. That is, if the outside air temperature is relatively low, thermal expansion of the lens array 2511a, the photoelectric conversion element 2511b, and the sensor substrate 2511c is less likely to occur even when the LED 2501 is turned on for the same time compared to when the outside air temperature is relatively high. The shift amount Z becomes relatively small. Therefore, a temperature sensor that measures the outside air temperature and a table that defines the white correction allowable time according to the outside air temperature and the document size may be provided. Then, a white correction allowable time according to the outside air temperature may be set. Thereby, the generation interval of white shading data can be adjusted in consideration of not only the document size but also the outside air temperature. In this alternative embodiment, the temperature of the image sensor 251 such as the surface temperature of the lens array 2511a may be measured instead of the outside air temperature.

  Next, black correction will be described with reference to FIGS. FIG. 11 is a diagram illustrating temperature characteristics of the output level of the image sensor when the light emitting unit is turned off. FIG. 12 is a diagram for explaining the relationship between the black offset level fluctuation amount and the document size.

  The black correction unit 254 generates black shading data based on the output from the image sensor 251 outside the original reading period, that is, between papers, in the light-emitting unit off state, and stores it in a memory (not shown). That is, when the black shading data is acquired, the light emitting part is turned off as a density reference. The black shading data is stored in the memory as an average value of a plurality of lines for each pixel in consideration of the offset level difference for each pixel and the influence of random noise. Then, the black correction unit 254 performs a correction process of subtracting the black shading data from the white reference member 170 and the original reading data when the light source unit 250 is turned on.

  The output of the image sensor when the light emitting unit is turned off has temperature characteristics. As shown in FIG. 11, this temperature characteristic generally has a characteristic that its output level increases as the temperature increases. For this reason, it is desirable to update the black shading data between sheets of paper, but this case is not preferable because it hinders productivity improvement.

  Therefore, as in the case of white shading data, the minimum interval for black shading data generation is determined from the relationship between temperature characteristics and black shading data, and black shading data is regenerated accordingly to improve productivity while maintaining image quality. Can be achieved. A graph 1200 in FIG. 12 shows a change characteristic of the fluctuation amount Z of the black offset level when the light emitting unit is turned off along the main scanning direction after X minutes. In the graph 1200, the change characteristic after X1 minutes is indicated by a solid line, and the change characteristic after X2 minutes is indicated by a dotted line. As is clear from FIG. 12, the variation amount Z increases as it goes toward the rear end in the main scanning direction, and the variation amount Z increases as the elapsed time from the start of lighting increases.

  The black correction unit 254 compares the predetermined allowable variation amount with the current variation amount Z, and regenerates black shading data when the relationship of variation amount Z> allowable variation amount is satisfied. Therefore, the allowable variation amount corresponds to a threshold value used for determining whether to regenerate black shading data. An example of this determination is shown below.

When the document is an A4 (vertical) document X1 minute later ... Fluctuation amount Z> Allowable fluctuation amount X2 minutes later ... Fluctuation amount Z <Allowable fluctuation amount It is desirable to create and update. In this case, the black correction allowable time is X2.

When the original is an A3 original, after X1 minutes. Since the fluctuation amount Z> the allowable fluctuation amount, the black shading data is generated and updated again between the papers with X1 minutes as a guide. In this case, the black correction allowable time is X1.

  It should be noted that the elapsed time until the amount corresponding to the permissible fluctuation amount varies depending on the configuration of the second reading unit 125 and the configuration of its peripheral components, and is therefore preferably determined based on the evaluation result in the system at the development stage.

  Next, based on FIG. 13, as an example of the operation of the image forming apparatus according to the present embodiment, a flow of an operation of changing the white shading data regeneration interval based on the document size and the elapsed time since the light emitting unit is turned on. Will be described. FIG. 13 is a flowchart illustrating an example of the operation flow of the image forming apparatus according to the present embodiment.

  When the user sets a document on the paper feed tray of the image reading apparatus, the main scanning width of the document is detected (step S1301). In this example, the size relationship with the predetermined document size width W1 is determined. If it is greater than W1 (step S1302 / Yes), T1 is set to limit_time which is the white correction allowable time (step S1302). The white correction allowable time is a time during which it can be determined that it is not necessary to regenerate white shading data. If W1 or less (step S1302 / No), T2 is set in limit_time (step S1303). Since the larger the main scanning width of the document, the more easily affected by thermal expansion, the relationship of T1 <T2 is established. Although there are only two types in this example, since there are a wide variety of original sizes used, it is possible to subdivide T3, T4, etc. in addition to T1, T2, etc. It is not limited to two ways.

  Next, before starting image reading, the light emitting unit in the light source unit is turned off (step S1304), and black shading data is generated (step S1305). Thereafter, the light emitting unit in the light source unit is turned on (step S1306).

  It is determined whether or not the first document is read (step S1307). If the document is not the first one (step S1307 / No), sh_time, which is the elapsed time since the light emitting unit is turned on, is compared with the white correction allowable time limit_time (step S1308).

  When sh_time is equal to or less than limit_time (step S1308 / Yes), and when the first document is read (step S1307 / Yes), sh_time is reset to 0 and measurement of sh_time is started (step S1309), and white shading data is set. Is generated (step S1310).

  After step S1310 and when sh_time is larger than limit_time (step S1308 / No), the document reading operation is started. Here, offset correction (black shading correction) using the black shading data generated in step S1305 is performed on the read image, and white shading correction generated in step S1310 is performed on the image after the offset correction ( Step S1311). If there is a next original after the original reading operation is completed (step S1312 / Yes), the process returns to step S1304 to start reading the next original. If there is no next original (step S1312 / No), the process is terminated.

  Thus, the white shading data generation interval can be intermittently changed in accordance with the document width size and the elapsed time from lighting of the light emitting unit. As a result, it is possible to improve reading productivity by reducing the processing time required to regenerate white shading data while suppressing the occurrence of vertical stripes and improving image quality.

  Next, as an example of the operation of the image forming apparatus according to the present embodiment, based on FIG. 14, the white shading data and black shading data regeneration intervals are changed based on the document size and the elapsed time since the light emitting unit is turned on. A flow of operations to be performed will be described. FIG. 14 is a flowchart illustrating another example of the operation of the image forming apparatus according to the present embodiment. Detailed description of the same processing as in FIG. 13 is omitted.

  In steps S1401 to S1403, similarly to steps S1301 to S1303, T1 and T2 which are limit_time corresponding to the document size are set (steps S1401 to S1403). The limit_time set here is one of the white correction allowable time and the black correction allowable time. Which one is to be used is determined from the evaluation result at the development stage, which of white shading data and black shading data has a greater effect on image quality. Then, T1 and T2 are set using the allowable time used for determining the regeneration interval of either one (data having a greater influence on the image quality). In this example, the white correction allowable time and the black correction allowable time are not set separately, but the white correction allowable time is used as a common allowable time, and the sh_time is compared with the common allowable time (white correction allowable time). Is executed once, and white shading data and black shading data are regenerated based on the comparison result.

  If the document is the second or subsequent document (S1404 / No), a comparison process between sh_time and limit_time is performed (S1405). If sh_time is greater than limit_time (long time) (step S1405 / Yes), and if the first document (S1404 / Yes), sh_time is reset to 0 and measurement of sh_time is started (step S1406). ). Then, the light emitting unit is turned off (step S1407), and black shading data is generated (step S1408).

  Next, the light emitting unit is turned on (step S1409), and white shading data is generated (step S1410).

  White shading data is generated (step S1410), or when sh_time is equal to or less than limit_time (step S1405 / No), a document reading operation is started (step S1411). If there is a next original (step S1412 / Yes), the process returns to step S1404 to start reading the next original. Here, black shading correction and white shading correction are also executed. If there is no next original (step S1412 / No), the process is terminated.

  As described above, in this flow, while managing time, black shading data generation is also performed intermittently in addition to white shading data generation, while suppressing deterioration in image quality due to changes in black shading data due to heat generation. Therefore, it is possible to improve the reading productivity.

  In the above operation example, as the time threshold setting method, the allowable times T1 and T2 that are adapted to regenerate data that affects the image quality of white shading data and black shading data, and the elapsed time from lighting of the light emitting unit And the generation intervals of the white shading data and the black shading data were changed in a unified manner. However, as another embodiment, a white correction permissible time and a black correction permissible time are respectively set, and when one of the white correction permissible time and the black correction permissible time exceeds the permissible time after the light source is turned on. Alternatively, only the generation of shading data corresponding to the exceeding one may be performed.

  In the operation examples of FIGS. 13 and 14, the generation interval of the black shading data and the white shading data is changed according to both the document size and the lighting of the light emitting unit, but the light emitting unit is considered without considering the document size. The generation interval may be changed according to only the elapsed time from lighting. In this case, steps S1301 to S1303 in FIG. 13 and steps S1401 to S1403 in FIG. 14 can be omitted. Further, although the generation interval of white shading data is managed in FIG. 13 and the generation interval of white shading data and black shading data is managed in FIG. 14, only the generation interval of black shading data may be managed. This operation can be achieved by replacing step S1310 in FIG. 13 with black shading data generation.

  In the present embodiment, the time between sheets can be shortened by not regenerating the white shading data and the black shading data within the time when the image quality is not deteriorated due to thermal expansion, and the reading productivity is improved. Can do. Furthermore, when the document width is small, the time during which image quality deterioration due to thermal expansion of the lens array, the sensor substrate, and the like can be tolerated increases. Therefore, the reading productivity can be further improved by changing the length of the allowable time according to the document width. In addition, since the light emitting unit is provided on the side opposite to the reference set position, a heat source is disposed at a position relatively close to a lens or sensor that is not on the optical path of the reflected light from the document when the document width is relatively large. On the other hand, since the heat source is frequently placed at a position relatively far from the actual lens or sensor for reading the document, it is possible to more effectively suppress the deterioration of the image quality due to thermal expansion. As a configuration for that purpose, it is only necessary to provide the position of the light emitting portion on the side opposite to the reference set position, so that the manufacturing process can be prevented from becoming complicated.

1 Image forming apparatus 10 CPU
11 RAM
12 ROM
13 Engine 14 HDD
15 I / F
16 LCD
17 Operation unit 18 Bus 20 Controller 21 ADF
22 Scanner unit 23 Paper discharge tray 24 Display panel 26 Print engine 25 Paper feed table 27 Paper discharge tray 28 Network I / F
30 Main control unit 31 Engine control unit 32 Input / output control unit 33 Image processing unit 34 Operation display control unit 100 Image reading apparatus 101 Document 102 Document table 103 Movable document table 104 Set filler 105 RTC
107 Pickup roller 108 Table feed appropriate position sensor 109 Paper feed belt 110 Reverse roller 111 Abutting sensor sensor 112 Pull-out roller 113 Document width sensor 114 Intermediate roller 115 Reading entrance sensor 116 Reading entrance roller 117 Registration sensor 120 First reading section 123 Reading Exit roller 124 Paper discharge sensor 125 Second reading unit 126 Second reading roller 127 Exit roller 128 Paper discharge rollers 130 and 131 Document length detection sensor 136 Side guide 170 White reference member 180 Controller 190 Drive unit 191 Pickup motor 192 Paper feed motor 193 Reading motor 194 Paper discharge motor 195 Bottom plate raising motor 200 Paper feed unit 221 Paper feed cassette 223 Paper feed unit 250 Light source unit 2501 LED
2502 Light guide unit 251 Image sensor 2511 Sensor chip 2511a Lens array 2511a1, 2511a2 1x lens 2511b Photoelectric conversion element 2511c Sensor substrate 252 Amplifier circuit 253 A / D converter 254 Black correction unit 255 White correction unit 256 Image processing unit 257 Frame memory 258 Output control circuit 259 I / F circuit 300 Image forming unit 331 Exposure device 332 Photosensitive drum 333 Development device 334 Transfer belt 355 Fixing device 900, 1000, 1200 Graph

JP 2006-13852 A JP 2011-205214 A

Claims (6)

A light emitting unit that emits light for irradiating the document;
A light guide unit that guides light emitted from the light emitting unit so as to be irradiated over the entire range of the document in the main scanning direction;
A photoelectric conversion unit that receives reflected light from the document over the entire range of the document in the main scanning direction and outputs an electrical signal corresponding to the amount of light;
A lens that is arranged over the entire range of the document in the main scanning direction, and that adjusts the light condensing state in an optical path in which light emitted from the light emitting unit is incident on the photoelectric conversion unit;
A document conveying section that conveys one side of the document in a state in which the document is aligned with a reference set position defined in the main scanning direction;
Including
The light emitting unit is disposed only at an end portion at a position relatively distant from the reference set position among two end portions of the light guide unit along the main scanning direction. Reader. A time measuring unit for measuring an elapsed time from the start of lighting of the light emitting unit;
A correction that generates shading data based on the output obtained by the photoelectric conversion unit reading the density reference, and uses the shading data to perform shading correction on the image obtained by the photoelectric conversion unit reading the document. And further comprising,
The image reading apparatus according to claim 1, wherein the correction unit regenerates the shading data when the elapsed time exceeds a predetermined allowable time. A document width detector for detecting the width of the document in the main scanning direction;
The image reading apparatus according to claim 2, wherein the correction unit changes the length of the allowable time in accordance with the document width detected by the document width detection unit.   The correction unit generates white shading data based on an output obtained by the photoelectric conversion unit reading a white reference member as the density reference, and the photoelectric conversion unit uses the white shading data to generate the white shading data. The image reading apparatus according to claim 2, wherein white shading correction of an image obtained by reading is performed.   The correction unit generates black shading data for correcting an offset level based on the output of the photoelectric conversion unit when the light emitting unit is turned off, and the photoelectric conversion unit uses the black shading data to generate the shading data. 5. The image reading apparatus according to claim 2, wherein black shading correction is performed on an image obtained by reading a document.   An image forming apparatus comprising the image reading apparatus according to claim 1.