JP6041441B2 - Image reading apparatus and image forming apparatus having the same - Google Patents

Description

  The present invention relates to an image reading apparatus that reads a document. The present invention also relates to an image forming apparatus provided with the image reading apparatus.

  The image reading apparatus includes a light source that irradiates light on a document, an image sensor that receives reflected light from the document and performs photoelectric conversion, and the like, and outputs image data of the document. In the image reading apparatus, when the light source is turned on / off, noise may be propagated to the image sensor and noise may be applied to the analog signal. When noise is applied, the image quality of the image data obtained by scanning deteriorates. Japanese Patent Application Laid-Open No. H10-228707 describes a technique for preventing image quality deterioration of image data caused by switching between turning on and off of the light source.

  Specifically, Patent Document 1 includes a light source and an image sensor that converts electric charges accumulated in the photoelectric conversion element into an electric signal and sequentially outputs the data to an A / D converter, and the light source is turned on and off. An image reading apparatus is described that stops outputting data from an image sensor to an A / D converter at the switching timing. With this configuration, data transfer is stopped and the image quality is improved at the switching timing of turning on / off the light source (see Patent Document 1: Claim 1, paragraphs [0006], [0007), etc.).

JP 2009-200555 A

  In an image sensor such as a CIS (Contact Image Sensor), a light receiving element, a transfer unit (CCD or CMOS) for transferring charges accumulated in the light receiving element, a light source, and the like may be unitized.

  Here, depending on the magnitude of the voltage applied to the transfer unit, the value of the analog signal output from the image sensor may change even if the same amount of charge is accumulated in the light receiving element. In other words, the transfer characteristics (transfer performance) of the transfer unit and the output characteristics of the image sensor may change depending on the magnitude of the voltage applied to the transfer unit. In other words, when the voltage applied to the transfer unit changes depending on the case, the analog output signal value of each pixel includes a deviation, and the image quality of the image data obtained by reading the original document is degraded. For example, the reproducibility of the original document is reduced. For this reason, it is preferable that the voltage applied to the transfer unit that transfers the charge during the transfer of the charge is constant.

  By the way, from the viewpoint of simplification of the circuit configuration, wiring, and reduction of manufacturing cost, it is preferable to supply power from the common power supply unit (common power supply terminal) to the light source and the transfer unit. However, when the light source is turned on, the power supply voltage of the common power supply unit (power supply terminal) may decrease. On the other hand, when the light source is turned off, the power supply voltage is recovered. Therefore, the power supply voltage may change as the light source is turned on / off.

  In an image sensor that supports color reading, light sources of a plurality of colors are provided, and the lighting time width of each light source during reading of one line is adjusted for each color. For example, the lighting time width of each color light source is adjusted so that the analog output value of a pixel with a line sensor when a white reference plate is read becomes a predetermined analog output value. Accordingly, since there is a difference in the characteristics of each color and each light source, the lighting time width of the light source is generally different for each color.

  For discharging and transferring charges from each pixel (light receiving element), after the light source is turned off (after the charge accumulation in the light receiving element in that line is finished), the light source of the next color is turned on. Performed before lighting (while light source lighting is temporarily interrupted). For example, discharge and transfer of charges from each pixel (light receiving element) are performed based on a synchronization signal that changes at a constant period (frequency).

  The power supply voltage is restored by turning off the light source. However, when power is supplied from the common power supply unit (power supply terminal) to the light source or transfer unit in parallel, if the synchronization signal has a constant period, the light source lighting time width varies depending on the color, and the light reception When the transfer of charges from the element (vertical transfer) is started or the magnitude of the power supply voltage during the transfer may be different for each color. For example, in some colors, the power supply voltage is recovered before the start of vertical transfer, but in other colors, vertical transfer may be started before the power supply voltage is fully recovered.

  Due to such a difference in power supply voltage value for each color at the start of vertical transfer, the voltage applied to the transfer unit at the time of vertical transfer differs depending on the color, which may affect transfer characteristics. For example, even if an achromatic color is read, there may be a relatively large difference in pixel values of R, G, and B pixels. In this case, image data including a color different from that of the original or image data in which the color changes with a gradation different from that of the original may be generated. As described above, when power is supplied from the common power supply unit (power supply terminal) to the light source or the transfer unit, there is a problem that the image quality of the image data obtained by reading the document may be deteriorated. Therefore, conventionally, in a CIS image sensor, power is not supplied from a common power supply unit to a light source or a transfer unit.

  Here, the technique described in Patent Document 1 is an invention relating to noise generated when the light source is switched. Patent Document 1 does not mention that the power supply voltage of the common power supply unit changes due to turning on and off of the light source, resulting in deterioration of image quality. Therefore, the above problem cannot be solved. Patent Document 1 describes that supply of a read clock for causing an image sensor to perform data output operation is stopped (Patent Document 1: Paragraph [0008] and the like). However, if some switching is performed, a certain amount of noise is generated, and the technique described in Patent Document 1 has a demerit that another type of noise may be generated.

  In view of the above-described problems of the prior art, the present invention provides a voltage applied to a transfer unit at the start of transfer or during transfer even when power is supplied from a common power supply unit (common power supply terminal) to a light source or transfer unit. An object of the present invention is to improve the image quality of image data obtained by reading a document by eliminating the influence on the operation of the transfer unit caused by turning on and off the light source by setting the size of the image to a constant level regardless of the color.

  In order to achieve the above object, an image reading apparatus according to claim 1 is a unit for irradiating light on a document and reading the document based on reflected light of the document, and a plurality of units for irradiating the document with light. A light source unit that includes a color light source and switches the light source to be turned on in a predetermined order; a line sensor unit in which a plurality of light receiving elements that store an amount of charge according to the level of reflected light from the document are arranged; A reading unit that includes at least a transfer unit that transmits charges stored in each of the light receiving elements, an image processing unit that generates image data based on an analog output value of each pixel output from the reading unit, and at least the reading unit A common power supply unit that supplies power to the light source unit and the transfer unit of the unit, and the transfer unit is after the light source is turned off until the light source of the next color starts to turn on, After restored to a level voltage predetermined for serial common power unit, it was decided to initiate a vertical transfer of charges of the light receiving elements of the line sensor unit.

  According to the present invention, even when power is supplied from a common power supply unit (common power supply terminal) to a light source or a transfer unit, a change in the power supply voltage is suppressed, and the influence on the operation of the transfer unit due to the light source turning on and off is eliminated. be able to. Thereby, the image quality of the image data obtained by reading the document can be improved.

1 is a diagram illustrating a multifunction machine. It is a figure which shows an image reading apparatus. It is a figure which shows a reading unit. FIG. 2 is a diagram illustrating a hardware configuration of a multifunction machine. It is a figure which shows an image reading apparatus. It is a figure for demonstrating reading with a reading unit. It is explanatory drawing which shows the structure of a line sensor part. It is a figure for demonstrating turning on / off of each light source of a reading unit. 6 is a timing chart showing lighting of a light source, charge transfer, and transition of a power supply voltage of a common power supply unit when a document is read in color. It is a timing chart which shows transition of a power supply voltage when electric power is supplied to a light source part and a transfer part from a common power supply part (power supply terminal) in a conventional example. It is a graph which shows the relationship between lighting time width and the analog output from a line sensor.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the following description, a multifunction device 200 (corresponding to an image forming apparatus) including the image reading apparatus 100 will be described as an example. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of MFP 200)
First, the outline of the multifunction peripheral 200 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a multifunction device 200.

  As shown in FIG. 1, an image reading device 100 is provided on the upper part of the multifunction device 200. The image reading apparatus 100 includes a document conveying unit 1 and an image reading unit 2 (details will be described later). The multifunction device 200 of the present embodiment has an operation panel 3 attached to the front surface. The multifunction device 200 includes a paper feeding unit 4a, a conveyance unit 4b, an image forming unit 4c, an intermediate transfer unit 4d, and a fixing unit 4e as the printing unit 4.

  First, the operation panel 3 includes a display unit 31 that displays the state of the multifunction device 200, various messages, and a setting screen. The display unit 31 is provided with a touch panel unit 32 and hard keys 33 for receiving various operations. The operation panel 3 receives a transmission method, settings related to a job such as copying and scanning, and a job execution instruction.

  The printing unit 4 performs printing based on image data obtained by reading an original with the image reading apparatus 100. The paper supply unit 4a stores a plurality of sheets and sends out the sheets during printing. The first transport unit 4b transports the paper supplied from the paper feed unit 4a to the image forming unit 4c. The image forming unit 4c forms a toner image of each color based on the image data to be printed. The intermediate transfer unit 4d receives the primary transfer of the toner image formed by the image forming unit 4c, and secondarily transfers the toner image to the sheet. The fixing unit 4e heats and pressurizes the paper on which the toner image is transferred, and fixes the toner image on the paper. The sheet that has passed through the fixing unit 4e is discharged to a discharge tray.

(Configuration of Image Reading Apparatus 100)
Next, the image reading apparatus 100 according to the embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating the image reading apparatus 100. FIG. 3 is a diagram showing the reading unit 5.

  As shown in FIG. 1, the multifunction device 200 includes an image reading device 100 on the upper side. The image reading apparatus 100 is provided above the image reading unit 2, opens and closes in the vertical direction with respect to the image reading unit 2, and conveys a document toward the conveyance reading contact glass 21. And an image reading unit 2 that emits light toward the upper surface of the contact glass 21 or the placement reading contact glass 22 and reads the original based on the reflected light to generate image data.

  The document conveyance unit 1 automatically and continuously conveys documents to be read one by one to the conveyance reading contact glass 21. The document transport unit 1 includes a document tray 11, a document supply roller 12, a document transport path 13, a plurality of document transport roller pairs 14, a document discharge roller pair 15, and a document discharge tray 16 in order from the upstream side in the document transport direction. Further, the document conveying unit 1 is attached to the image reading unit 2 so as to be able to be opened and closed in the vertical direction with the back side of the paper surface of FIG.

  A white reference plate 17 is provided on the upper surface of the conveyance reading contact glass 21. The white reference plate 17 is a pure white plate-like member for obtaining a white reference. The white reference plate 17 has a main scanning direction of the image reading apparatus 100 (a direction perpendicular to the document conveying direction, a direction perpendicular to the paper surface of FIG. 2) as a longitudinal direction. The document is conveyed while passing between the conveyance reading contact glass 21 and the white reference plate 17. If reading is performed when the document is not conveyed, the white reference plate 17 is read.

  A plurality of documents to be read can be placed on the document tray 11. Then, the document supply roller 12 contacts the uppermost document among the documents placed on the document tray 11. When an input for reading a document is input to the operation panel 3, the document supply roller 12 sends the document to the document transport path 13 one by one.

  The documents sent out from the document tray 11 are guided and conveyed by a plurality of document conveyance roller pairs 14 and guides. Then, the document passes above the conveyance reading contact glass 21 provided on the upper surface of the image reading unit 2. During this passage, the image reading unit 2 performs reading. Then, the read original is discharged from the original discharge roller pair 15 to the original discharge tray 16 (the original conveyance path is indicated by a two-dot chain line). Each of the rotating bodies (the document supply roller 12, the document transport roller pair 14, and the document discharge roller pair 15) rotates using the document transport motor 18 (see FIG. 5) as a drive source.

  Next, the image reading unit 2 in the present embodiment will be described. As shown in FIGS. 1 and 2, the image reading unit 2 has a box-shaped housing. Then, on the left side of the upper surface of the image reading unit 2, a transparent plate-shaped transport reading contact glass 21 is disposed with the main scanning direction (direction perpendicular to the paper surface of FIG. 2) as the longitudinal direction. A transparent plate-like placement reading contact glass 22 is arranged on the upper surface of the image reading unit 2 on the right side of the conveyance reading contact glass 21. When reading a document such as a book one by one, the user places the document on the placement reading contact glass 22 by lifting the document transport unit 1 and with the reading surface facing downward.

  As shown in FIG. 2, the housing of the image reading unit 2 includes a reading unit 5, a wire 23, and a winding drum 24.

  Here, the configuration of the reading unit 5 will be described with reference to FIG. The reading unit 5 of the present embodiment is a CIS type reading unit 5.

  First, the reading unit 5 includes a housing 51 (external frame) having a substantially U-shaped cross section. The casing 51 has a box shape with the vertical direction in FIG. 3 as the longitudinal direction. The longitudinal direction of the housing 51 is the main scanning direction of the reading unit 5.

  A line sensor unit 6 extending in the direction perpendicular to the paper surface (main scanning direction) in FIG. 3 is provided on the lower surface of the casing 51. The image reading apparatus 100 according to the present embodiment is compatible with color reading. Therefore, the line sensor unit 6 includes a line sensor 60. The line sensor 60 has a plurality of light receiving elements 61 (photoelectric conversion elements) arranged in the main scanning direction (details will be described later).

  A rod lens array 53 is provided above the line sensor unit 6. A light guide 54 is provided on the side of the rod lens array 53. As indicated by a broken line in FIG. 3, a light source unit 7 is provided for each light guide 54 at either or both ends of the front side and the back side of the casing 51 in the direction perpendicular to the paper surface ( In FIG. 3, the light source unit 7 on the near side is invisible. For color reading, the light source unit 7 includes a plurality of (a plurality of) light sources 70. For example, the light source 70 is an LED.

  The light guide 54 guides light emitted from the light source unit 7 in the longitudinal direction (main scanning direction) of the reading unit 5. Further, as indicated by a two-dot chain line arrow in FIG. 3, the light guide 54 emits light toward the upper side of the rod lens array 53 (above the glass 52). The light guide 54 emits light so as to obtain a substantially uniform light level at each position in the longitudinal direction (main scanning direction) of the reading unit 5.

  Each rod lens included in the rod lens array 53 condenses the light irradiated on the document and guides it to the line sensor unit 6 (in FIG. 3, the optical path of the collected light is indicated by a two-dotted line with an arrow). . As a result, charges corresponding to the intensity of the reflected light are stored in each light receiving element 61 of the line sensor unit 6, and image data is generated based on the charge stored in each light receiving element 61 (each pixel).

  As shown in FIG. 2, the reading unit 5 is connected to the winding drum 24 by a wire 23. The winding drum 24 is rotated by a winding motor 25 (see FIG. 5) that rotates forward and backward. Accordingly, the reading unit 5 can be freely moved in the horizontal direction (the left-right direction of the multi-function device 200). When reading the document on the placement reading contact glass 22, the reading unit 5 is moved in the horizontal direction by the rotational drive of the winding drum 24, and reading is performed. Further, when reading a document conveyed by the document conveying unit 1, the reading unit 5 is fixed below the conveyance reading contact glass 21.

(Hardware configuration of MFP 200)
Next, a hardware configuration of the multifunction machine 200 according to the embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating a hardware configuration of the multifunction device 200.

  First, the multifunction device 200 is provided with a main control unit 201 that controls the entire multifunction device 200. The main control unit 201 is provided with a CPU 202 as a central processing unit. In addition, a storage device 203 formed of a nonvolatile and volatile memory such as a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), or a flash ROM is provided for the main control unit 201.

  The storage device 203 stores programs, data, and the like for controlling the multifunction device 200. The main control unit 201 uses programs and data in the storage device 203 to control each unit, and to perform various jobs such as scanning, printing, transmission, and storage of image data. In addition, the main control unit 201 is provided with an image data processing unit 204 that performs image processing for printing and transmission based on image data output from the image reading apparatus 100.

  The main control unit 201 is communicably connected to the engine control unit 40. The engine control unit 40 controls the operation of the printing unit 4 based on an instruction from the main control unit 201. The main control unit 201 is connected to the operation panel 3. The main control unit 201 recognizes settings made on the operation panel 3 and job execution instructions. The main control unit 201 causes the image reading apparatus 100 and the printing unit 4 to perform an operation corresponding to the setting made on the operation panel 3. For example, when executing copying or scanning, the main control unit 201 instructs the image reading apparatus 100 to read a document, and causes the image reading apparatus 100 to output image data of the document.

  The multifunction device 200 includes a communication unit 205 as a communication interface with the outside. The communication unit 205 is communicably connected to the computer 300 (for example, a personal computer or a server) or the FAX apparatus 400 via a network, a cable, or a public line. The communication unit can transmit image data based on document reading by the image reading apparatus 100 to the computer 300 or the FAX apparatus 400 (scanning and transmission function).

(Hardware configuration of image reading apparatus 100)
Next, a hardware configuration of the image reading apparatus 100 according to the embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating the image reading apparatus 100.

  First, the document conveying unit 1 will be described. When reading a document for a copy job or a transmission job, the document conveying unit 1 automatically and continuously feeds the document placed on the document tray 11 toward the conveyance reading contact glass 21 one by one. Transport. The document feeder 1 may be called an ADF (Auto Document Feeder).

  The document transport unit 1 is provided with a document transport control unit 10 that controls the operation of the document transport unit 1. The document conveyance control unit 10 is communicably connected to the main control unit 201 and the reading control unit 20. For example, the document conveyance control unit 10 is a substrate including a CPU as a central processing unit, a ROM and a RAM for storing control programs and data. The document conveyance control unit 10 receives an instruction to start document conveyance from the main control unit 201 or the reading control unit 20 and controls the operation of the document conveyance unit 1.

  The document transport unit 1 is provided with a document detection sensor 19 for detecting whether or not there is a sheet in the document tray 11. When there is a document reading instruction from the main control unit 201, the document conveyance control unit 10 confirms the output of the document detection sensor 19 and detects whether or not there is a sheet on the document tray 11. When a document is present on the document tray 11, the document conveyance control unit 10 drives the document conveyance motor 18 to rotate the document supply roller 12 and the document conveyance roller pair 14 to convey the document toward the reading position. .

  Next, the image reading unit 2 will be described. First, the image reading unit 2 is provided with a reading control unit 20 that controls the operation of the image reading unit 2. The reading control unit 20 receives an instruction and signal from the main control unit 201 and reads a document. The reading control unit 20 is a substrate including a CPU, an integrated circuit, and the like as a processing device.

  The reading control unit 20 includes operations of a lighting control circuit 20 a that controls turning on and off of each light source 70 (light source unit 7) and a transfer unit 9 that transfers charges accumulated in each pixel of the line sensor unit 6. A transfer control unit 20b to be controlled, and a synchronization signal generation unit 20c that generates a synchronization signal S1 used for reading a document and supplies the synchronization signal S1 to the line sensor unit 6, the lighting control circuit 20a, and a transfer control unit 20b described later are included. It is.

  The reading control unit 20 is communicably connected to the storage unit 26. The storage unit 26 includes a ROM and a RAM that store programs and data necessary for controlling the image reading apparatus 100. The reading control unit 20 controls the operation of each unit included in the image reading unit 2 based on the program and data in the storage unit 26.

  When the operation panel 3 is operated and a document is read for a copy job or a transmission job (when scanning is started), the main control unit 201 gives a document reading instruction to the reading control unit 20. Upon receiving this instruction, the reading control unit 20 performs operation control of each member in the image reading unit 2 and transmission control of image data obtained by reading to the main control unit 201.

  The reading control unit 20 is connected to the winding motor 25. Thereby, the rotation of the winding motor 25 is controlled, the winding drum 24 is rotated, and the reading unit 5 is moved in the horizontal direction. For example, the winding motor 25 is a pulse motor. Then, the reading control unit 20 inputs a pulse for moving each reading unit 5 to the winding motor 25. The take-up motor 25 rotates in accordance with the input pulse and moves the reading unit 5 as necessary for reading. In other words, the reading control unit 20 controls the rotation of the take-up motor 25 to control the movement of each reading unit 5 in the sub-scanning direction.

  The reading control unit 20 moves the reading unit 5 according to the magnification set on the operation panel 3. For example, when reading a document on the placement reading contact glass 22 at the same magnification, the reading control unit 20 determines the width per line (for example, 42 for 600 dpi) during a predetermined reading time for one line. .3 μm), the take-up motor 25 is rotated so that the reading unit 5 moves.

  The reading control unit 20 is communicably connected to the reading unit 5 and controls the operation of members included in the reading unit 5 (details will be described later). The reading control unit 20 is connected to the image processing unit 8 including the A / D conversion unit 81 and the correction processing unit 82, and in accordance with an instruction from the main control unit 201, signals and data obtained by reading the original are read. Let the process do.

  The reading control unit 20 is connected to the home position sensor 27. The home position sensor 27 is a sensor that detects that the reading unit 5 has reached the home position. The reading control unit 20 controls the take-up motor 25 and returns the reading unit 5 to the home position when the job is completed. The home position can be arbitrarily determined. For example, the home position is set below the placement reading contact glass 22 and the conveyance reading contact glass 21.

  Further, for example, how far the range moved from the home position is the reading position of the document passing over the conveyance reading contact glass 21 (the reading line 8 of the line sensor 60 is on the conveyance reading contact glass 21). Information indicating the range in which the image is located is stored in the storage unit 2616. When reading a document passing through the conveyance reading contact glass 21, the reading control unit 20 reads data in the storage unit 26, moves the reading unit 5 below the conveyance reading contact glass 21, and fixes it during reading. . On the other hand, when reading the document placed on the placement reading contact glass 22, the reading control unit 20 operates the winding motor 25 to move the reading unit 5 from the home position to the placement reading contact glass 22. Move from the left end to the right.

  The A / D converter 81 receives the analog output of each pixel (each light receiving element 61) output from the reading unit 5 (line sensor unit 6), performs quantization, and converts it into a digital signal. As a result, image data is generated. Thereby, a pixel value indicating the density is assigned to each pixel. For example, the A / D conversion unit 81 performs quantization on 8 to 10 bits for each of R, G, B, and Bk.

  The correction processing unit 82 receives the image data output from the A / D conversion unit 81 and performs image processing. In the present embodiment, an example in which the correction processing unit 82 is provided in the image reading unit 2 and the image data processing unit 204 is provided in the main control unit 201 will be described. However, only one image processing portion is provided on the main body side, and only one image processing portion (circuit) is provided in the image processing unit 8 and the image data processing unit 204 in this description. You may make it perform the process of.

  The correction processing unit 82 includes a work memory that is a work area for processing image data and a circuit for image processing. The correction processing unit 82 corrects distortion caused by the characteristics of the light source 70 and the line sensor 60 such as gamma correction on the image data. Further, the correction processing unit 82 is provided with a shading correction unit 83. The shading correction unit 83 performs shading correction on the image data. Details of the shading correction will be described later.

  The image data processed by the correction processing unit 82 is stored in the image memory 28. Then, the image data is transferred from the image memory 28 to the storage device 203 (for example, RAM) or the main control unit 201 of the main body. Further, when printing is performed, the image data processing unit 204 transmits image data after image processing in accordance with the setting to the image forming unit 4c. The image forming unit 4c performs printing (toner image formation) based on the image data. Further, when performing a transmission job, the image data processing unit 204 causes the communication unit 205 to transmit image data after image processing in accordance with the setting to the computer 300 or the like.

(Transfer unit 9 and line sensor unit 6)
Next, the line sensor unit 6 and the transfer unit 9 included in the reading unit 5 of the present embodiment will be described with reference to FIGS. FIG. 6 is a diagram for explaining reading by the reading unit 5. FIG. 7 is an explanatory diagram showing the configuration of the line sensor unit 6.

  As shown in FIG. 6, the reading unit 5 of the present embodiment includes a line sensor unit 6, a transfer control unit 20 b, and a transfer unit 9. The line sensor unit 6 includes a line sensor 60 in which a plurality of light receiving elements are arranged. In the reading unit 5 of the present embodiment, since the light source unit 7 is a color light source, the line sensor 60 is one (one line). The transfer control unit 20 b controls the operation of the transfer unit 9 that transfers charges accumulated in each pixel of the line sensor unit 6.

  Here, the line sensor 60 will be described with reference to FIG. As shown in FIG. 7, the line sensor 60 sets the main scanning direction (the front-rear direction of the multifunction device 200 and the direction perpendicular to the document conveyance direction) as the longitudinal direction. Each of the line sensors 60 includes a plurality of light receiving elements 61 (photoelectric conversion elements, pixels) arranged in a row. Each light receiving element 61 generates a charge according to the intensity of light hitting the imaging surface (light receiving surface) and accumulates the charge.

  When reading in monochrome (monochrome mode), the original is read using the line sensor 60 while the lamps for one color or a plurality of colors are turned on. In other words, when reading in black and white, image data is generated based on the output of the line sensor 60.

  At the time of monochrome reading, the synchronization signal generation unit 20c generates a signal indicating a cycle of one line (a signal having a frequency that changes with the cycle of one line) as the synchronization signal S1, and inputs the generated signal to the line sensor 60 and the transfer control unit 20b. To do.

  On the other hand, when reading in color (color mode), the original is read using the line sensor 60 while the lamps of the respective colors are turned on once in one line. Then, when reading in color, R, G, and B image data are generated based on the output of the line sensor 60. Note that the image processing unit 8 and the image data processing unit 204 can generate luminance information (information indicating black and white) from R, G, and B image data. May be read using the line sensor 60 so that is lit (three colors are read in one line).

  Further, at the time of color reading, the synchronization signal generation unit 20c generates a signal (a signal that changes at a reading period for one color) indicating a period for one color (time allocated to one color) in one line. The synchronization signal S1 is generated and input to the line sensor 60, the transfer control unit 20b, and the lighting control circuit 20a.

  A transfer unit 9 is provided for the line sensor 60. The transfer unit 9 includes a vertical transfer unit 91 and a horizontal transfer unit 92.

  The charges stored in the respective light receiving elements 61 are transferred from the respective light receiving elements 61 to the vertical transfer unit 91 all at once. In other words, the vertical transfer unit 91 receives charges from each light receiving element 61. Then, the vertical transfer unit 91 transfers the charge of each pixel to the horizontal transfer unit 92. The transfer control unit 20b controls charge transfer. The transfer control unit 20b supplies a transfer clock signal CL1 to the vertical transfer unit 91. The vertical transfer unit 91 transfers the charge of each pixel to the horizontal transfer unit 92 in accordance with the clock signal CL1 from the transfer control unit 20b.

  Then, the horizontal transfer unit 92 outputs the charges output from the light receiving elements 61 (each pixel) to the differential amplifier circuit 55 in order for each pixel. Note that the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) of the present embodiment has a ground level of each light receiving element 61 for noise countermeasures in addition to the electric charge (analog signal) stored in each light receiving element 61. A signal indicating (for example, the output level and reference level of each light receiving element 61 after discharging the charge) is also transferred.

  The reading unit 5 includes a differential amplifier circuit 55. The differential amplifier circuit 55 amplifies the difference between the charge (analog signal) stored in each pixel (each light receiving element 61) sequentially output from the horizontal transfer unit 92 and the reference level. The gain of the differential amplifier circuit 55 can be set as appropriate, but the gain is set to “1” if there is no need to increase the amplitude.

  Then, the analog output voltage after amplification (after current-voltage conversion) of each pixel from the differential amplifier circuit 55 is input to the A / D conversion unit 81 of the image processing unit 8. The A / D conversion unit 81 A / D converts the analog output voltage of each pixel into a value corresponding to the magnitude of the analog output voltage (A / D conversion to about 8 to 10 bits). Thereby, image data is generated.

(Control of turning on / off the light source 70)
Next, turning on / off control of the light source 70 will be described with reference to FIG. FIG. 8 is a diagram for explaining turning on / off of each light source 70 of the reading unit 5.

  As shown in FIG. 8, the light source unit 7 of the reading unit 5 includes light sources 70 of a plurality of colors. In the image reading apparatus 100 of the present embodiment, an LED is provided as the light source 70. The light source 70 includes a blue light source 70B (blue LED in the present embodiment), a green light source 70G (green LED in the present embodiment), and a red light source 70R (red LED in the present embodiment).

  Each light source 70 is connected in parallel to the light source driving circuit 56. The light source driving circuit 56 is provided in the reading unit 5. Electric power is supplied to the light source driving circuit 56 from the common power supply unit 57 (power supply terminal 57a). The light source drive circuit 56 includes a switch circuit 56a. The switch circuit 56a passes a current so that the light source 70 of the color to be turned on emits light, and does not emit light (the light source 70 to be turned off) does not emit light (is not made conductive or does not emit light). ).

  A lighting control circuit 20 a of the reading control unit 20 is connected to the light source driving circuit 56. The lighting control circuit 20a sets the level of the signal line of the lighting control signal S2 corresponding to the light source 70 to emit light to High (three signal lines are B, G, and R). Then, the light source driving circuit 56 turns on the light source 70 of a color whose signal from the lighting control circuit 20a is at a high level. At the time of reading, the lighting control circuit 20a turns on the light sources 70 of the respective colors in order in a predetermined order during the reading of one line (switches the light sources 70 to be turned on in order). For example, when the color reading is in the order of reading in blue, the lighting control circuit 20a sets the level of the signal line of the lighting control signal S2 corresponding to the blue light source 70B to High. The light source driving circuit 56 turns on the blue light source 70B (blue LED) based on the lighting control signal S2.

  Further, the lighting control circuit 20a receives the synchronization signal S1 generated by the synchronization signal generator 20c (see FIG. 5). When a predetermined time (time required for vertical transfer) elapses after the synchronization signal S1 changes, the lighting control circuit 20a sets the lighting control signal S2 corresponding to the next color to be turned on to a high level. The driving circuit 56 starts lighting the light source 70. The lighting control circuit 20a turns on when a predetermined lighting time (lighting time width) elapses during the reading of one line for each color from the start of lighting (after the lighting control signal S2 is set to High level). The control signal S2 is set to the low level, and the light source driving circuit 56 turns off the light source 70. The details of the lighting time width of the light source 70 will be described later.

(Power supply in the reading unit 5)
Next, power supply to the light source unit 7, the line sensor unit 6, the vertical transfer unit 91, and the horizontal transfer unit 92 in the reading unit 5 will be described with reference to FIG.

  A power supply device is provided inside the image reading apparatus 100 or the multifunction device 200 of the present embodiment. The power supply device is connected to a commercial power supply and performs rectification, step-down, and the like. The power supply device generates a voltage for rotating the motor (for example, DC 24 V) and a voltage (for example, DC 12 V or DC 5 V) to be supplied to a circuit or element such as the reading unit 5.

  The voltage generated by the power supply device is supplied to the reading unit 5. For example, power is supplied to the reading unit 5 by connecting a bundle of signal lines including a power cord to a connector provided in the reading unit 5.

  The common power supply unit 57 (common power supply terminal 57a) of the reading unit 5 includes a light source unit 7 (light source driving circuit 56 and each light source 70), a horizontal transfer unit 92 for each color, and a vertical transfer unit 91 for each color. The line sensor unit 6 (line sensor 60) is connected in parallel. In other words, power is supplied to the light source unit 7 (light source drive circuit 56), the horizontal transfer unit 92, the vertical transfer unit 91, and the line sensor 60 from the common power supply unit 57 (power supply terminal 57a) of the reading unit 5. Is done. That is, the power supply unit 57 functions as a common power supply unit (the power supply terminal 57a used jointly by these members) for the light source unit 7, the horizontal transfer unit 92, the vertical transfer unit 91, and the line sensor unit 6.

(Lighting of light source 70 and transfer of charge during reading)
Next, the lighting of each light source 70 and the transfer of electric charges when reading a document will be described with reference to FIG. FIG. 9 is a timing chart showing the lighting of the light source 70 and the transfer of charges and the transition of the power supply voltage of the common power supply unit 57 when reading an original in color.

  Of the timing chart of FIG. 9, the uppermost chart shows the synchronization signal S1 generated by the synchronization signal generation unit 20c. As shown in FIG. 9, a period from when the synchronization signal S1 falls to when it falls three times corresponds to one line reading time (time allocated to reading one line).

  In the timing chart of FIG. 9, the second chart from the top indicates that the blue light source 70 </ b> B is turned on / off, High indicates a lighting state, and Low indicates a lighting state. Further, the third chart from the top shows that the green light source 70G is turned on / off, High indicates a lighting state, and Low indicates a lighting state. The fourth chart from the top indicates that the red light source 70R is turned on / off, High indicates a lighting state, and Low indicates a lighting state.

  As shown in FIG. 9, in the color reading of the image reading apparatus 100 of the present embodiment, the light source 70 (LED) is lit in the order of blue → green → red during reading of one line. Since reading is performed continuously, lighting is performed in the order of blue → green → red, and when reading of the current line is completed, lighting in the order of blue → green → red is performed again on the next line. Is called. The sequential lighting of the light source 70 is repeated from reading the first line to the last line. During the reading of one line, the lighting control circuit 20a turns on the light source 70 of any color from the time when the synchronization signal S1 falls until the time when the synchronization signal S1 falls next time. In other words, reading is performed in the color of the light source 70 to be lit within one cycle of the synchronization signal S1, and charges are accumulated in each light receiving element 61 of the line sensor 60.

  In the image reading apparatus 100 according to the present embodiment, after the synchronization signal S1 falls, the charge stored for the color of the light source that was turned on immediately before is read out from the line sensor 60 and transferred (vertical transfer). In other words, when the synchronization signal S1 falls, the vertical transfer unit 91 performs vertical transfer of charges stored for the color of the light source that has been turned on immediately before.

  Therefore, as shown in FIGS. 5 and 6, the synchronization signal S1 generated by the synchronization signal generation unit 20c is input to the transfer control unit 20b. In color reading, the transfer control unit 20b operates the vertical transfer unit 91 based on the falling edge of the synchronization signal S1, and vertically transfers the charge stored for the color of the light source 70 that has been turned on immediately before.

  In FIG. 9, the vertical transfer time of electric charges (stored when the red light source 70R is turned on) when read in red is indicated by time T1. Further, in FIG. 9, the vertical transfer time of electric charges (stored when the blue light source 70B is turned on) when read in blue is indicated by time T2. Further, in FIG. 9, the vertical transfer time of electric charges when read in green (stored when the green light source 70G is turned on) is indicated by time T3. Since the number of pixels of the line sensor 60 (the number of light receiving elements 61) is the same and the frequency of the readout clock may be the same for each color, the time lengths (time widths) of the times T1 to T3 are the same.

  In color reading, when the vertical transfer of charges by the vertical transfer unit 91 is completed, the lighting control circuit 20a (light source driving circuit 56) turns on the light source 70 of the color to be lit in the cycle (section) of the synchronization signal S1. Let Since the time required for the vertical transfer is determined in advance, the lighting control circuit 20a starts lighting the light sources 70 in the order of lighting when the time required for the vertical transfer elapses from the fall of the synchronization signal S1. . Specifically, the lighting control circuit 20a sets the lighting control signal S2 of the light source 70 of the color in the turn-on order to High with the elapse of time required for vertical transfer.

  Here, the lighting time width of each color light source 70 in one cycle of the synchronization signal S1 is determined in advance. The lighting time width of the light source 70 is shorter than the time obtained by subtracting the time required for charge transfer by the vertical transfer unit 91 (time T1 to T3) from one period (time from the falling to the falling) of the synchronization signal S1. The lighting time width of the light source 70 is the average value of the pixel values of the pixels with the line sensor 60, the analog output values, or the pixel values of a plurality of pixels in the line sensor 60 when the white reference plate 17 is read. And the average value of the analog output values is determined to be a predetermined target value. If the pixel value when the white reference plate 17 is read does not become the target value even when the lighting time width is set to the upper limit, the differential amplifier circuit is set so that the pixel value corresponding to the target value or the analog output value is obtained. The gain of 55 is adjusted. Details of the upper limit of the lighting time width will be described later.

  Thus, the lighting time width of the light source 70 of each color is determined in consideration of the sensitivity of the line sensor 60 and the light amount of the light source 70. In the example of FIG. 9, in reading one color line, the lighting time width of the blue light source 70B is the longest, then the lighting time width of the red light source 70R is long, and the lighting time width of the green light source 70G is the shortest. Thus, the lighting time widths of the light sources 70 of the respective colors are not the same.

(Instability of power supply voltage)
Next, instability of the power supply voltage when power is supplied from the common power supply unit (power supply terminal 57a) to the light source unit 7 and the transfer unit 9 will be described with reference to FIG. FIG. 10 is a timing chart showing the transition of the power supply voltage when power is supplied from the common power supply section (power supply terminal 57a) to the light source section 7 and the transfer section 9 in the conventional example.

  When power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source unit 7 or the transfer unit 9, when the light source 70 is turned on due to problems such as current supply capability, the power supply voltage of the common power supply unit 57 drops. There is. When the light source 70 is turned off, the power supply voltage of the common power supply unit 57 is restored.

    After the light source 70 is turned off, the line sensor 60 performs vertical transfer of charges of the color of the light source 70 that has been turned on (turned off) immediately before. And the lighting time width | variety of the light source 70 changes with each color. For this reason, after the light source 70 having a long lighting time width is turned on, the vertical transfer may be started before the power supply voltage level is completely recovered. In other words, as shown in FIG. 10, when the frequency (cycle) and waveform of the synchronization signal S1 are constant, the level of the power supply voltage becomes a predetermined level after the light source 70 having a long lighting time width is turned on. Before recovery, the vertical transfer unit 91 may start vertical transfer.

  FIG. 10 shows an example in which the vertical transfer of the stored charge is started when the blue light source 70B is turned on before the power supply voltage is fully recovered because the lighting time width of the blue light source 70B is long. For this reason, in the example of FIG. 10, when the vertical transfer of the charge stored when the green light source 70G is turned on or the charge stored when the red light source 70R is turned on, the blue light source 70B is turned on. The magnitude of the power supply voltage is different from that in the vertical transfer of the stored charge.

  If there is a difference in the voltage applied to the vertical transfer unit 91 at the start of the vertical transfer and during the vertical transfer, the image quality of the image data read in color may deteriorate. In this case, the gradation of the image data obtained by reading becomes unnatural, or colors that are not in the document appear in the image data.

  There are various reasons for the deterioration in image quality, but if the power supply voltage level is different, the analog output value of the reference level transferred by the vertical transfer unit 91 is affected (the reference level changes depending on the power supply voltage). ) And charge transfer characteristics (transfer efficiency) may change. Therefore, if the power supply voltage level is different, the analog output value output from the differential amplifier circuit 55 and the pixel value after A / D conversion differ even if the same amount of charge is stored in the light receiving element 61. There is a case. Further, if the power supply voltage level is different, the pixel value of each pixel obtained by reading the white reference plate 17 may change. For this reason, when performing vertical transfer of charges, it is desirable to equalize the voltage applied to the vertical transfer unit 91 regardless of the color.

  However, conventionally, since there is a difference in the lighting time width of the light source 70 of each color, the level (magnitude) of the voltage applied to the vertical transfer unit 91 at the start of vertical transfer or during vertical transfer is the same for all colors. I couldn't match the level. For this reason, when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source unit 7 and the transfer unit 9, there is a problem in that image quality deteriorates.

(Stabilization of power supply voltage during charge transfer)
Next, the stabilization of the power supply voltage during charge transfer when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source unit 7 and the transfer unit 9 will be described with reference to FIG.

  First, in the image reading apparatus 100 of the present embodiment, the vertical transfer unit 91, when the power supply voltage recovers to a predetermined level after the light source 70 is turned off, each light receiving element 61 in which charges are stored (turns off immediately before). The vertical transfer of the color charges of the light source 70 is started.

  Specifically, as shown in FIG. 9, after the light source 70 (the blue light source 70B in the example of FIG. 9) having the longest lighting time width among the three color light sources 70 is turned on, the power supply voltage is set at a predetermined level. When the blue light source 70B is turned on, the vertical transfer unit 91 starts the vertical transfer (time t1 in FIG. 9) in order to read out the electric charge stored when the blue light source 70B is turned on. The predetermined level (size) can be determined as appropriate. In the image reading apparatus 100 according to the present embodiment, the predetermined level is the rated voltage of the common power supply unit 57.

  In the example shown in FIG. 9, in order to transmit the delay of the start of the vertical transfer to the vertical transfer unit 91 and the light source unit 7, the time until the fall of the synchronization signal S1 is delayed from the normal synchronization signal S1. In other words, in the example of FIG. 9, in order to perform vertical transfer after the power supply voltage has been recovered to a predetermined level, the synchronization signal generation unit 20c generates a synchronization signal S1 that falls at the start of vertical transfer. Generate. Then, the transfer control unit 20b generates a transfer clock in response to the fall (change) of the synchronization signal S1, and causes the vertical transfer unit 91 to start vertical transfer. The lighting control circuit 20a starts lighting the green light source 70G after the time required for vertical transfer has elapsed since the falling edge of the synchronization signal S1.

  The lighting time width of the light source 70 is determined in advance, and it is possible to measure in advance the time from when the synchronization signal S1 rises periodically until the power supply voltage of the common power supply unit 57 recovers to a predetermined level. it can. Therefore, the time from the predetermined starting point such as the rising edge of the synchronization signal S1 or the falling edge of the previous synchronization signal S1 to the start of the vertical transfer of the vertical transfer unit 91 of each color or the start of lighting of each light source 70. The time is determined in advance and stored in the storage unit 26. Then, based on the data stored in the storage unit 26, the synchronization signal generation unit 20c measures the time from the rise of the synchronization signal S1 or the fall of the previous synchronization signal S1, and sets the synchronization signal S1 to rise. When the time to be lowered is reached (when the time at which vertical transfer can be started by recovery of the power supply voltage level is reached), the synchronization signal S1 falls.

  As described above, in the image reading apparatus 100 according to the present embodiment, the synchronization signal generation unit 20c generates and outputs the synchronization signal S1 that rises at a constant cycle in order to start the vertical transfer with respect to document reading. Then, the vertical transfer unit 91 starts vertical transfer of charges of the respective light receiving elements 61 of the line sensor 60 in accordance with a predetermined change (falling) of the synchronization signal S1. In addition, the synchronization signal generation unit 20c moves the time of the fall to the time when the voltage of the common power supply unit 57 (power supply terminal 57a) recovers to a predetermined level in accordance with the lighting time width of the light source 70 of each color. .

  In addition, instead of increasing or decreasing the time until the falling, the synchronization signal generation unit 20c generates the synchronization signal S1 having a periodic constant waveform regardless of whether or not to wait for recovery of the power supply voltage. It may be. In this case, the time when the vertical transfer unit 91 of each color starts vertical transfer and the time when the light source 70 of each color starts lighting is stored in the storage unit 26 in advance from the rise or fall of the synchronization signal S1. Let me. Then, the transfer control unit 20b waits for a predetermined waiting time from the rising or falling edge of the previous synchronization signal S1 based on the data in the storage unit 26 for the color for which the vertical transfer is started (when the waiting time is zero). (In accordance with the change of the synchronization signal S1), the vertical transfer unit 91 starts vertical transfer. Further, the lighting control circuit 20a waits for a predetermined time from the rising or falling of the synchronization signal S1 to the start of lighting of the light source 70 based on the data in the storage unit 26 (after waiting for the time required for vertical transfer). You may make it light the light source 70 of the color to light next.

  Since the start of the vertical transfer is waited until the power supply voltage recovers to a predetermined level, the time from the start of the vertical transfer to the rise of the next synchronization signal S1 is shorter than when the power supply voltage is not recovered. Become. Therefore, when the vertical transfer is started after waiting until the power supply voltage recovers to a predetermined level, the time during which the light source 70 of the next color can be turned on becomes shorter than the case where the power supply voltage is not waited (lighting time during which the light can be turned on). The width becomes narrower). On the other hand, the light source 70 must be turned on and off in a predetermined lighting time width until the next synchronization signal S1 rises.

  Therefore, in the image reading apparatus 100 according to the present embodiment, the order in which the light source 70 is turned on during color reading is devised. Specifically, in the image reading apparatus 100 of this embodiment, the lighting order of the light source 70 is the color with the shortest lighting time width (the narrowest) next to the color with the longest lighting time width (the widest), and the third color. (Last) is the color with the second longest (or short) lighting duration.

  Specifically, in the example of FIG. 9, during color reading, during reading of one line, the blue light source 70B having the longest lighting time width is turned on first, and then the green light source 70G having the shortest lighting time width is turned on. Finally, the red light source 70R having the second longest (short) lighting time width is turned on. As described above, in the color reading, the lighting order of the light source 70 during reading of one line corresponds to the lighting time width of the light source 70 of each color according to the length in the order of first → third → second. It may be determined so that

  Conventionally, when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the transfer unit 9 and the light source unit 7, the lighting time widths of the light sources 70 of the respective colors are different. The voltage applied to the transfer unit 91 may be different for each color. In addition, due to the difference in voltage applied to the vertical transfer unit 91 during vertical transfer, the image quality may be deteriorated due to the influence on the output after differential amplification based on the change in the reference level and the change in transfer characteristics. . For example, when a white achromatic color is read, the R, G, and B pixel values in the same pixel should be substantially the same color, but may be shifted due to a difference in power supply voltage. In some cases, the gradation is different from that of the original.

  On the other hand, in the image reading apparatus 100 of the present embodiment, the voltage applied to the vertical transfer unit 91 at the start of vertical transfer or during vertical transfer is substantially constant regardless of the lighting time width of the light source 70. In other words, when the charge is read from the line sensor 60 and vertical transfer is performed, the magnitude of the voltage applied to each vertical transfer unit 91 is almost the same for any color. Therefore, even if power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source unit 7 and the transfer unit 9, it is possible to suppress a decrease in image quality in the obtained image data.

(Lighting as long as linearity is maintained)
Next, the setting of the lighting time width will be described with reference to FIG. FIG. 11 is a graph showing the relationship between the lighting time width and the analog output from the line sensor 60.

  FIG. 11 will be described. The horizontal axis of the graph of FIG. 11 indicates the lighting time width of the light source 70, and the vertical axis indicates an analog output voltage value after amplification of a certain pixel of the line sensor 60 (an output value of a certain pixel from the reading unit 5), or The average value of analog output values after amplification of a plurality of pixels included in the line sensor 60 (average value of outputs from the reading unit 5) is shown (hereinafter referred to as “reference output value”).

  Each pixel of the line sensor 60 of the present embodiment accumulates electric charge according to the amount of received light. In other words, the longer the light receiving time, the larger the analog output value (analog output voltage after differential amplification) from the reading unit 5 based on the output of each pixel (each light receiving element 61) of the line sensor 60. Thus, a proportional relationship is recognized for the reference output value with respect to the lighting time width of the light source 70 (linearity).

  For example, in FIG. 11, the ratio of the reference output value B to the lighting time width b and the ratio of the reference output value C to the lighting time width c are (almost) the same.

  However, as shown in FIG. 11, when the lighting time becomes long (when the lighting time width becomes wide), linearity breaks down due to saturation of accumulated charges, change in conversion efficiency of light to charges, and the like. . If the lighting time width of the light source 70 is in a range where the linearity is broken, the linearity is lost, and thus an abnormal pixel value (density significantly different from that of the original document) may occur. In the example of FIG. 11, the ratio (slope) of the reference output value D to the lighting time width d is clearly larger than that in the lighting time widths b and c.

  Therefore, in the image reading apparatus 100 of the present embodiment, the lighting time width of each light source 70 is set so that the ratio of the reference output value to the lighting time width is within a range in which linearity is maintained (a range in which the inclination is substantially the same). The In addition, the upper limit of the lighting time width is set to the longest lighting time width in a range where the linearity is maintained.

Specifically, the upper limit of the lighting time width is predetermined based on the following (Formula 1) and (Formula 2), and the lighting time width of the light source 70 of each color is based on (Formula 1) and (Formula 2). It is set in a range where linearity is maintained. In other words, (Expression 1) satisfying (Expression 2) L = ((EA) / e) / ((FA) / f)
(Formula 2) -L1 ≦ L ≦ + L2
However, L: A value indicating linearity.
A: Reference output value when the light source 70 is turned off.
e: A lighting time width of a certain length (arbitrary) (first lighting time width).
E: Reference output value when the light source 70 is turned on in the first lighting time width.
f: A lighting time width of a certain length (arbitrary) (second lighting time width).
E: Reference output value when the light source 70 is lit in the second lighting time width.
-L1: Allowable lower limit value of L (for example, 0.98)
L2: Allowable upper limit value of L (for example, 1.04)
At least one of e and f belongs to a range in which linearity is maintained.
The allowable lower limit value and the allowable upper limit value are appropriately set to values that do not cause an abnormality in image quality based on experiments and the like.
If linearity is maintained (if the inclination is the same), the value (first value) and the value ((FA) / f) of ((E−A) / e) in Equation 1 The ratio of (second value) is substantially “1”.

  Even if the power supply voltage of the common power supply unit 57 at the start of vertical transfer or during vertical transfer differs for each color, the vertical transfer is started without waiting for the recovery of the power supply voltage within the allowable range of linearity. May be. On the other hand, if the image quality is to be pursued, the lighting time width is stopped to the upper limit and the start of the vertical transfer is waited until the power supply voltage is recovered before starting.

(Shading correction)
Next, shading correction will be described with reference to FIG.

  In the image reading apparatus 100 of the present embodiment, the image processing unit 8 performs shading correction as one of corrections for image data obtained by reading a document. A shading correction unit 83 is provided in the correction unit of the image processing unit 8 for shading correction.

  In the image reading apparatus 100 according to the present embodiment, the shading correction is performed using the white reference value and the black reference value. The white reference value is a pixel value (digital value after A / D conversion) of each pixel obtained by reading the white reference plate 17. For example, the shading correction unit 83 obtains the average value of the pixel values of each pixel based on the reading result of the white reference plate 17 a plurality of times, and performs the shading using the obtained average value of each pixel as the white reference value of each pixel. The data is stored in the reference value storage unit 84 in the correction unit 83 (see FIG. 5). The white reference value is acquired for each color. For example, the white reference value for blue is stored in the reference value storage unit 84 based on the pixel value after A / D conversion of the charge obtained from each light receiving element 61 that has read the white reference plate 17 by turning on the blue light source 70B. Memorized (same for green, red, white / black).

  The black reference value is a pixel value (digital value after A / D conversion) of each pixel when the light source 70 is turned off. For example, the shading correction unit 83 obtains an average value of the pixel values of each pixel when the light source 70 is turned off a plurality of times, and stores the obtained average value of each pixel in the reference value storage unit 84 as the black reference value of each pixel. (See FIG. 5). For example, based on the pixel value after A / D conversion of each light receiving element 61 when the light source 70 is turned off, the black reference value of each light receiving element 61 (each pixel) of the line sensor 60 is stored in the reference value storage unit 84 ( Common to blue, green, red and white / black).

  Conventionally, when power is supplied from the common power supply unit 57 to the light source unit 7 and the transfer unit 9, the power supply voltage at the time of reading each color or vertical transfer may be different as the light source 70 is turned on and off. Since the white reference value is acquired by turning on the light source 70 and the black reference value is acquired by turning off the light source 70, conventionally, at the time of reading and charge transfer for acquiring the white reference value, the black reference value is obtained. At the time of reading and charge transfer for acquisition, the power supply voltage applied to the transfer unit 9 (vertical transfer unit 91) may be different. Therefore, conventionally, when the power is supplied from the common power supply unit 57 to the light source unit 7 and the transfer unit 9, the charge of the transfer unit 9 at the time of reading for obtaining the white reference value and at the time of reading for the black reference value Due to differences in transfer characteristics, it is difficult to appropriately acquire the white reference value and the black reference value, and it may be difficult to appropriately perform shading correction.

  However, in the image reading apparatus 100 of the present embodiment, the power supply voltage of the common power supply unit 57 (power supply terminal 57a) is such that the power supply voltage is recovered in the vertical transfer even if the light source 70 is turned on / off. Starts from. Accordingly, even when the power is supplied from the common power supply unit 57 to the light source unit 7 and the transfer unit 9, the charge of the transfer unit 9 is transferred at the time of reading for obtaining the white reference value and at the time of reading for the black reference value. Since there is no difference in characteristics and an appropriate white reference value and black reference value can be acquired, appropriate shading correction can be performed.

An example of calculation for shading correction is shown below.
(Formula) X = (IB) × {Y / (WB)}
“X” is a pixel value after correction of the correction target pixel.
“Y” is the maximum density value (for example, “255” for 8 bits).
“I” is a pixel value before correction of the correction target pixel.
“B” is a black reference value corresponding to the correction target pixel.
“W” is a white reference value corresponding to the correction target pixel.

  The image reading apparatus 100 according to the present embodiment includes a reading unit 5, an image processing unit 8, and a common power supply unit 57. The reading unit 5 is a unit for irradiating the original with light and reading the original based on the reflected light of the original, and a light source 70 (blue light source 70B, green light source 70G, red light source 70R) for irradiating the original with light. ), A line sensor unit in which a light source unit 7 that switches a light source 70 to be turned on in a predetermined order and a plurality of light receiving elements 61 that store an amount of electric charge according to the level of reflected light from the document are arranged. 6 and a transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) for sending the charge stored in each light receiving element 61. The image processing unit 8 generates image data based on the analog output value of each pixel output from the reading unit 5. Power is supplied to at least the light source unit 7 and the transfer unit 9 of the reading unit 5 from the common power supply unit 57 (power supply terminal 57a). The transfer unit 9 waits until the light source 70 of the next color starts to turn on after the light source 70 is turned off, and after the voltage of the common power supply unit 57 is restored to a predetermined level, the line 9 The vertical transfer of the charge of each light receiving element 61 of the sensor unit 6 (line sensor 60) is started.

  As a result, the power supply voltage at the start of charge transfer (vertical transfer) by the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) becomes a constant level (recovered to a constant level) during reading of the document. Will start at the time). Therefore, it is possible to discharge and transfer charges of each color in the same voltage applied to the transfer unit 9. For this reason, it is possible to eliminate the difference between the transfer characteristics (transfer performance) of the transfer unit 9 based on the difference in the power supply voltage and the output characteristics of the analog signal from the reading unit 5 between the colors. As described above, when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9, the transfer unit 9 caused by the difference in the lighting time width of the light source 70 of each color, which has occurred in the past. Further, it is possible to prevent the influence on the analog signal output from the reading unit 5 (degradation of image quality such as gradation variation and color abnormality with respect to the original). In addition, since power is supplied from the common power supply unit 57 to the light source 70 and the transfer unit 9, it is possible to simplify the circuit configuration and wiring of the image reading apparatus 100, reduce the number of power supply lines, and reduce manufacturing costs. it can.

  The longer the lighting time of the light source 70 is, the longer it takes for the power supply voltage to recover to a predetermined level. Therefore, once the light sources 70 (blue light source 70B, green light source 70G, red light source 70R) of each color are lit, they continue to be lit with a predetermined lighting time width for each color. The color with the shortest lighting time width is set next to the color with the longest lighting time width, and the light source unit 7 turns on when the vertical transfer of the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) is completed. The lighting of the light source 70 in the order to be started is started.

  Thus, after the light source 70 of the color with the longest lighting time width is turned off, the lighting time width of the light source 70 of the next color is short. Therefore, after the light source 70 with the longest lighting time width is turned off, Even when waiting for recovery to a predetermined level, both vertical transfer and lighting of the light source 70 of the next color can be performed within the reading time for one line assigned to one color. Therefore, even if the recovery time of the power supply voltage is taken, reading can be performed without failure. In addition, the voltage applied to the transfer unit 9 (vertical transfer unit 91 and horizontal transfer unit 92) at the start of vertical transfer of each color or during transfer can be made substantially the same by taking the recovery time of the power supply voltage. . Even if power is supplied to the light source 70 and the transfer unit 9 from the common power supply unit 57 (power supply terminal 57a), the transfer characteristic (transfer performance) of the transfer unit 9 and the output characteristic of the analog signal from the reading unit 5 are large. The charge of each color and each pixel (each light receiving element 61) can be read out without causing a difference. Furthermore, since the lighting order is the lighting order in which the power supply voltage recovery time can be maximized in the lighting order (lighting pattern) of the light sources 70 of the respective colors, a predetermined level can be set to as large a voltage value as possible.

  In addition, the light source 70 (blue light source 70B, green light source 70G, red light source 70R) is a reference output value that is an average value of a lighting time width of the light source 70 and an analog output value of a certain pixel or an analog output value of a plurality of pixels. The upper limit of the lighting time width of the light source 70 is the longest lighting time width in the lighting time width of the range maintaining the linearity.

  Thus, when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92), the analog output of each pixel is proportional to the lighting time width. The lighting time width of the light source 70 of each color can be determined in such a range that becomes large. Accordingly, the lighting time width of the light source 70 is not set to such a length that the linearity is lost, and the image quality is not deteriorated (gradation variation or color abnormality with respect to the original document).

  The light source 70 (blue light source 70B, green light source 70G, red light source 70R) is obtained by subtracting the reference output value when the light source 70 is not lit from the reference output value when the light source 70 is lit for the first lighting time width. Is subtracted by the first lighting time width and the reference output value when the light source 70 is not lit is subtracted from the reference output value when the second lighting time width is different from the first lighting time width. Lights up with a time width such that the ratio of the calculated value to the second value obtained by dividing the value by the second lighting time width falls within a predetermined allowable upper limit and allowable lower limit range. Thereby, the light source 70 can be appropriately turned on in a range in which the ratio of the analog output value of each pixel to the lighting time width is kept substantially constant and no image quality abnormality occurs.

  The black reference value is acquired with the light source 70 turned off. On the other hand, the white reference value is acquired with the light source 70 turned on. Therefore, when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92), reading for black reference acquisition and white reference acquisition are performed. Therefore, it may be difficult to perform proper shading correction because the power supply voltage of the common power supply unit 57 (power supply terminal 57a) is different. When power is supplied from the common power source 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92), reading for black reference acquisition and white reference acquisition are performed. In order to make the power supply voltage of the common power supply unit 57 (power supply terminal 57a) in reading for the same value, it is possible to turn on the light source 70 and read the black reference plate to obtain the black reference value. Providing the reference plate increases the manufacturing cost of the image reading apparatus 100.

  Therefore, the image reading apparatus 100 according to the present embodiment includes a white reference plate 17 for obtaining a white reference in shading correction. When the image processing unit 8 of the image reading apparatus 100 performs reading with the white reference value of each pixel based on the image data when the white reference plate 17 is read and all the light source units 7 turned off. The black reference value of each pixel based on the image data is stored, and shading correction is performed based on the white reference value and the black reference value. Thus, even when power is supplied from the common power supply unit 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92), the power supply voltage at the time of obtaining the white reference value and the black reference The power supply voltage at the time of value acquisition is set to the same level. Accordingly, it is possible to acquire appropriate white reference values and black reference values, and perform suitable shading correction on the image data. Further, since it is not necessary to provide a black reference plate, the manufacturing cost of the image reading apparatus 100 is not increased.

  The image reading apparatus 100 according to the present embodiment includes a synchronization signal generation unit 20c that generates a synchronization signal S1 related to document reading. Then, the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) starts vertical transfer from each light receiving element 61 of the line sensor unit 6 (line sensor 60) in accordance with the predetermined change of the synchronization signal S1, The synchronization signal generation unit 20c moves the time point of the predetermined change to the time point when the voltage of the common power supply unit 57 (power supply terminal 57a) recovers to a predetermined level in accordance with the lighting time width of the light source 70. As a result, the voltage applied to the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92) can be set to any color at the start of vertical transfer or during vertical transfer simply by adjusting the change timing of the synchronization signal S1. But it can be the same size.

  Further, the image forming apparatus (multifunction device 200) of the present embodiment may supply power from the common power supply unit 57 (power supply terminal 57a) to the light source 70 and the transfer unit 9 (vertical transfer unit 91, horizontal transfer unit 92). The image reading apparatus 100 is provided that has no degradation in image quality (grayscale variation or color abnormality with respect to the original) and reduced manufacturing costs. As a result, an image forming apparatus with high image quality and reduced manufacturing costs can be provided.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to the image reading apparatus 100 and an image forming apparatus including the same.

DESCRIPTION OF SYMBOLS 100 Image reader 17 White reference board 2 Image reading part 20c Synchronization signal generation part 5 Reading unit 57 Common power supply part 57a Power supply terminal (common power supply part) 6 Line sensor part 60 Line sensor 61 Light receiving element 7 Light source part 70 Light source 70B Blue light source (Light source) 70G Green light source (Light source)
70R Red light source (light source) 8 Image processing unit 9 Transfer unit 91 Vertical transfer unit (transfer unit)
92 Horizontal transfer unit (transfer unit) 200 MFP (image forming apparatus)
S1 Sync signal

Claims (7)

A unit for irradiating a document with light and reading the document based on reflected light of the document, including a plurality of color light sources for irradiating the document with light, and switching the light sources to be turned on in a predetermined order At least a light source unit, a line sensor unit in which a plurality of light receiving elements that store an amount of charge according to the level of reflected light from the document are arranged, and a transfer unit that sends the charges stored in each of the light receiving elements A reading unit;
An image processing unit that generates image data based on an analog output value of each pixel output by the reading unit;
A common power supply unit that supplies power to at least the light source unit and the transfer unit of the reading unit,
The transfer unit is a period from when the light source is turned off until a light source of the next color starts to be turned on, and after the voltage of the common power supply unit is restored to a predetermined level, the line sensor unit An image reading apparatus which starts vertical transfer of charges of each light receiving element. Once the light source of each color is lit, it continues to light for a predetermined lighting time width for each color, and the lighting order of the light source is the lighting time width next to the color with the longest lighting time width. A short color is set,
The image reading apparatus according to claim 1, wherein the light source unit starts turning on the light sources in the turn-on order when the vertical transfer of the transfer unit is completed. The light source is lit in a range in which the ratio of the lighting time width of the light source and the analog output value of a certain pixel or the reference output value that is the average value of the analog output values of a plurality of pixels maintains linearity,
3. The image reading apparatus according to claim 1, wherein an upper limit of a lighting time width of the light source is a longest lighting time width in a lighting time width within a range in which the linearity is maintained.   The light source has a first value obtained by dividing a value obtained by subtracting the reference output value when the light source is not lit by a first lighting time width from the reference output value when the light source is lit for the first lighting time width. A value obtained by subtracting the reference output value when the light source is not turned on from the reference output value when the light is turned on with a second lighting time width different from the first lighting time width is divided by the second lighting time width. The image reading apparatus according to claim 3, wherein the image reading apparatus is lit with a time width such that a ratio between the second value and the second value falls within a predetermined allowable upper limit and allowable lower limit range. A white reference plate for obtaining a white reference for shading correction is further provided.
The image processing unit includes a white reference value of each pixel based on image data when the white reference plate is read and each pixel based on image data when reading is performed with all the light source units turned off. 5. The image reading apparatus according to claim 1, wherein a black reference value is stored, and shading correction is performed based on the white reference value and the black reference value. 6. A synchronization signal generation unit that generates a synchronization signal related to document reading;
In accordance with the predetermined change of the synchronization signal, the transfer unit starts vertical transfer of charges of each light receiving element of the line sensor unit,
The synchronization signal generation unit moves the predetermined change point to a point in time when the voltage of the common power supply unit is restored to a predetermined level in accordance with a lighting time width of the light source. Item 6. The image reading apparatus according to any one of Items 1 to 5.   An image forming apparatus comprising the image reading apparatus according to claim 1.

Images