JP2008278278A - Image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading device updating correction data while suppressing a decrease in read speed. <P>SOLUTION: Through correction data full determination processing (S10), timing (T<SB>5</SB>) for starting reading reflected light from a white tape 21c is put closer to timing (T<SB>10</SB>) for starting reading a document. Even if the quantity of light varies between the start of feeding of a document and the start of reading of a document, therefore, an influence thereof is suppressed extremely small, and a suitable gain value and shading correction data are determined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that can suppress the influence of light amount fluctuation of a light source and determine appropriate correction data.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads an image such as a graphic drawn on a document is known. In such an image reading apparatus, a document to be read is irradiated with light from a light source, and reflected light reflected by the document is converted into a plurality of charge coupled devices (hereinafter referred to as “CCD”) arranged in a line in the main scanning direction. The image of the original is read by converting the voltage value into the digital data according to the intensity of the reflected light.

  At this time, in order to correct unevenness appearing in the main scanning direction due to a difference in the light amount between the central portion and the end portion of the light source in the main scanning direction, a temporal light amount fluctuation of the light source, and a variation in CCD characteristics, Each time the reading unit is read, the reading unit is returned to the home position, the white reference plate is read by the CCD, light quantity distribution data in the main scanning direction is acquired, and based on the light quantity distribution data, main data of the image data when the original is read is read. Shading correction for correcting unevenness in the scanning direction is performed (see, for example, Patent Document 1).

Here, calculation of correction data for shading correction has been conventionally performed in the following procedure. First, the gain adjustment is started by reading the white reference plate almost simultaneously with the start of feeding the document. Then, white level data is acquired by reading the white reference plate, and shading correction data is determined based on the white level data.
JP 2002-330269 A

  However, in the conventional procedure, it takes a long time from when the gain adjustment is completed and the shading correction data is determined until the fed document reaches the reading position and reading is started. Therefore, if a light amount fluctuation occurs during a relatively long standby time after the gain adjustment and shading correction data determination, the light amount greatly differs at the time of actually starting the reading of the document, and the previously determined gain adjustment value, There has been a problem that shading correction data becomes an inappropriate value.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus capable of suppressing the influence of light amount fluctuation of a light source and determining appropriate correction data.

  In order to achieve this object, the image reading apparatus according to claim 1 includes a document conveyance path that connects a document placement portion and a document discharge portion via a reading position, and the reading position via the document conveyance path. A conveying unit that conveys the original document page by page, a reading unit that converts the reflected light irradiated from the light source and reflected by the irradiation target into image data, and corrects the image data output by the reading unit. A correction means; and correction data determination means for determining correction data to be referred to when correction is performed by the correction means, wherein the correction data determination means has a leading end in the transport direction of the document transported by the transport means. The correction data is determined based on image data output by reading reflected light by the reading means after reaching a predetermined position on the conveyance path.

  The image reading apparatus according to claim 2 is characterized in that, in the image reading apparatus according to claim 1, the correction means corrects analog image data or digital image data output from the reading means. To do.

  The image reading apparatus according to claim 3, further comprising: a conversion unit that performs A / D conversion on image data output by the reading unit in the image reading apparatus according to claim 1, wherein the correction unit includes the conversion unit. The digital image data after A / D conversion by the means is corrected.

  An image reading apparatus according to claim 4 is the image reading apparatus according to claim 1 or 2, further comprising a conversion unit that performs A / D conversion on image data output by the reading unit, and the correction unit includes the conversion unit. It is characterized in that the means corrects the relationship between the analog image data and the reference voltage referred to when converting the analog image data into the digital image data.

  5. The image reading apparatus according to claim 1, wherein the correction data determination unit is configured such that a leading end of a document transported by the transport unit is in the document transport path. After the predetermined position is reached, the correction data is determined before the leading end in the transport direction of the document transported by the transport means reaches the reading position.

  An image reading apparatus according to a sixth aspect of the present invention is the image reading apparatus according to any one of the first to fifth aspects, further comprising detection means for detecting a leading end of the document in the conveyance direction, wherein the correction data determination means is determined by the detection means. The correction data is determined based on image data output by the reading unit after the leading edge of the document in the conveyance direction is detected.

  According to a seventh aspect of the present invention, in the image reading apparatus according to the sixth aspect, after the leading end of the document in the conveyance direction is detected by the detection unit, a conveyance determination unit that determines whether the document has been conveyed by a predetermined distance. The correction data determining means determines the correction data based on the image data output by the reading means after the conveyance determining means determines that the document has been conveyed a predetermined distance. Features.

  The image reading apparatus according to claim 8 is set in any one of the mode group including a plurality of modes in which the time required for reading one page of the document is different from each other in the image reading apparatus according to any one of claims 1 to 7. A mode setting unit that changes the timing of correction data determination by the correction data determination unit for each mode set by the mode setting unit.

  According to the image reading apparatus of the first aspect, since the correction data is determined after the leading end of the document in the transport direction reaches a predetermined position on the document transport path, it is assumed that there is a fluctuation in the amount of light during transport of the document by the transport unit. However, there is an effect that the influence can be suppressed and appropriate correction data can be determined.

  According to the image reading apparatus of the second aspect, in addition to the effect produced by the image reading apparatus of the first aspect, it is possible to determine appropriate correction data for correcting analog image data or digital image data. There is an effect.

  According to the image reading apparatus of the third aspect, in addition to the effect produced by the image reading apparatus according to the first or second aspect, it is possible to determine appropriate correction data for correcting the digital image data. There is.

  According to the image reading apparatus of the fourth aspect, in addition to the effect produced by the image reading apparatus of the first or second aspect, appropriate correction data for correcting the relationship between the reference voltage and the analog image data is determined. There is an effect that can be done.

  According to the image reading apparatus of the fifth aspect, in addition to the effect achieved by the image reading apparatus according to any one of the first to fourth aspects, the correction data is corrected before the leading end of the document in the conveyance direction reaches the reading position. Therefore, the reading of the document that has reached the reading position can be started quickly, and the reading can be performed at high speed.

  According to the image reading apparatus of the sixth aspect, in addition to the effect produced by the image reading apparatus according to any one of the first to fifth aspects, the leading end position of the document in the conveyance direction is reliably detected, and the correction data is obtained at an appropriate timing. There is an effect that can be determined.

  According to the image reading apparatus of the seventh aspect, in addition to the effect achieved by the image reading apparatus of the sixth aspect, the leading edge of the document in the conveyance direction is determined reliably and easily, and correction data is determined at an appropriate timing. There is an effect that can be.

  According to the image reading apparatus of the eighth aspect, in addition to the effect produced by the image reading apparatus according to any one of the first to seventh aspects, correction data can be determined at an appropriate timing according to each mode. effective.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an external configuration of an image reading apparatus 1 according to an embodiment of the present invention, and FIG. 2 shows a main internal configuration of the image reading apparatus 1. The image reading apparatus 1 is, for example, a copy apparatus, a facsimile apparatus, a scanner apparatus, a multi-function apparatus (MFD: Multi Function Device) or the like that is integrally provided with a copy function, a facsimile mechanism, a scanner function, and the like. This is realized as an image reading unit for performing the above.
As shown in FIGS. 1 and 2, the image reading apparatus 1 has an auto document feeder (ADF) that is an automatic document feeder mechanism with respect to a document table 2 that functions as an FBS (Flatbed Scanner). A document cover 4 having 3 is attached so as to be openable and closable via a hinge on the back side (back of the paper surface).

  An operation panel 5 is provided on the front side of the document table 2. The operation panel 5 includes various operation keys 11 and a liquid crystal display unit 12. The image reading apparatus 1 receives a predetermined input from these operation panels 5 and performs a predetermined operation. The image reading apparatus 1 is operated not only by a command input to the operation panel 5 but also by a command connected to the computer and transmitted from the computer via a printer driver, a scanner driver, or the like.

  As shown in FIG. 2, a platen glass 21 is disposed on the top surface of the document table 2 that faces the document cover 4. An image reading unit 22 is built in the document table 2 so as to face the platen glass 21.

  The platen glass 21 is made of, for example, a transparent glass plate, and when the ADF 3 of the image reading apparatus 1 is used, a reading position 21a where a document is placed, and a reference position where the document is not located at a position different from the reading position 21a. 21b. An opening for exposing the platen glass 21 is formed at the reading position 21 a of the document table 2. The platen glass 21 exposed from the opening is extended in the depth direction of the image reading apparatus 1 corresponding to the length of the image reading unit 22 in the main scanning direction.

  A document retainer 19 is disposed above the reading position 21a of the platen glass 21 so as to face each other. The document retainer 19 always moves downward in FIG. 2 due to its own weight or under the urging force of an elastic member such as a spring. Further, the document holder 19 extends in the depth direction of the image reading apparatus 1 corresponding to the length of the image reading unit 22 in the main scanning direction. Therefore, the document conveyed to the reading position 21a via the document conveyance path 32 described later is pressed to the platen glass 21 side by the document pressing unit 19 to improve the adhesion between the platen glass 21 and the document.

  On the other hand, a white tape 21 c is attached to the upper surface of the reference position 21 b of the platen glass 21. This allows the white tape 21c to function as a white reference plate for gain adjustment and shading correction data creation. The gain adjustment and shading correction will be described later.

  The image reading unit 22 irradiates light upward from the light source through the platen glass 21, collects reflected light from the irradiation target on the light receiving element by the lens, and outputs it as an image signal. The image reading unit 22 is provided so as to be able to reciprocate below the platen glass 21 by a belt driving mechanism that is a scanning mechanism, and reciprocates in parallel with the platen glass 21 under the driving force of the carriage motor.

  In particular, the image reading unit 22 moves below the reading position 21 a when reading a document fed by the ADF 3 below the platen glass 21. As shown in FIG. 2, when the image reading unit 22 is arranged below the reading position 21a, the light emitted from the image reading unit 22 passes through the platen glass 21 and is arranged at the reading position 21a. The original is irradiated.

  FIG. 3 is a diagram illustrating a state in which the image reading unit 22 has moved below the reference position 21b. As shown in FIG. 3, the image reading unit 22 that has moved downward below the reference position 21b irradiates the reference position 221b with light and reads the reflected light from the reference position 21b. The white tape 21c attached to the reference position 21b functions as a white reference plate. Therefore, when determining shading correction data to be described later, a digital obtained by reading reflected light from the white tape 21c is used. Shading correction data is determined using the data. Here, since the white tape 21c is arranged at a position separated from the reading position 21a, it is possible to suppress contamination from a document or the like, and appropriate shading correction data is determined.

  Returning to FIG. 1 and FIG. The document cover 4 includes an ADF 3 that continuously conveys documents from the paper feed tray 30 to the paper discharge tray 31 through the document conveyance path 32. In the conveyance process by the ADF 3, the document passes through the reading position 21 a on the platen glass 21, and the image reading unit 22 waiting under the platen glass 21 reads the image of the document.

  As shown in FIG. 2, in the ADF 3, a paper feed tray 30 and a paper discharge tray 31 are connected to each other via a reading position 21 a on the platen glass 21, and are substantially U-shaped in the horizontal direction in a vertical sectional view. A document conveyance path 32 is formed. The document transport path 32 is continuously formed as a passage having a predetermined width through which a document can pass by members, guide plates, guide ribs, and the like constituting the ADF main body. In this way, the paper feed tray 30 and the paper discharge tray 31 are provided in two upper and lower stages, and a document conveying path 32 that is substantially U-shaped in the horizontal direction in the longitudinal sectional view is formed so as to connect them.

  The document transport path 32 includes a suction roller 33 and a separation roller 34 for feeding a document from the paper feed tray 30 to the document transport path 32, transport rollers 35A, 35B, 35C, and 35D, and a pinch roller that is in pressure contact therewith. 37 is provided. The conveyance rollers 35A, 35B, 35C, and 35D and the pinch roller 37 that is in pressure contact with them correspond to an example of a conveyance unit.

  A switchback path 39 is connected to the connection position 38 of the document transport path 32. When performing double-sided reading, the switchback path 39 reverses the leading edge and the trailing edge of the document whose first surface is read at the reading position 21a, and the document conveying path 32 from the downstream side to the upstream side of the reading position 21a. It is for resending to. The switchback path 39 extends obliquely upward from the connection position 38 toward the upper side of the paper feed tray 30 and intersects the upper portion of the document conveyance path 32. The document that is switched back and conveyed from the intersection position 40 between the upper portion and the switchback path 39 is returned to the document conveyance path 32. A terminal end 41 of the switchback path 39 is opened on the upper surface of the ADF 3.

  A switchback roller 43 is disposed immediately downstream from the crossover position 40 of the switchback path 39 on the end 41 side. The switchback roller 43 is driven to rotate in both forward and reverse directions by receiving driving force from a motor (not shown). A pinch roller 44 is provided at a position facing the switchback roller 43. The pinch roller 44 is pressed against the roller surface of the switchback roller 43 with its shaft elastically biased by a spring, and rotates in accordance with the rotation of the switchback roller 43. The document is pressed against the switchback roller 43 by the pinch roller 44, and the rotational force of the switchback roller 43 is transmitted to the document.

  As shown in FIG. 2, the document transport path 32 is provided with a plurality of sensors for detecting document transport. Specifically, the document transport path 32 is provided with a first front sensor 52 and a second front sensor 53, which is an example of a detection unit, on the upstream side and the downstream side of the separation roller 34, respectively. A rear sensor 54 is disposed immediately upstream of the position 21a. Each of these sensors is a so-called optical sensor that detects the rotation of the detector that appears and disappears in the document conveyance path 32 as on / off of the photo interrupter.

  When a document is placed on the paper feed tray 30, the first front sensor 52 is turned on. Whether the document is placed on the paper feed tray 30 is detected by turning on / off the first front sensor 52. The second front sensor 53 disposed immediately downstream of the separation roller 34 is for detecting the leading edge or trailing edge of the document fed to the document conveying path 32 by turning on / off thereof. For example, the number of rotations of the conveying rollers 35A, 35B, 35C, and 35D after the second front sensor 53 detects the trailing edge of the document is monitored by the number of steps of the encoder or motor, and the like. The position of the front end or the rear end is determined.

The rear sensor 54 disposed immediately upstream of the reading position 21a is for detecting the leading edge and the trailing edge of the document conveyed on the document conveyance path 32 by turning on / off thereof. The transport rollers 35A, 35B, 35C, and 35D after the rear sensor 54 detects the leading edge or trailing edge of the document.
The number of rotations is monitored by the number of steps of the encoder or motor, and it is determined whether or not the leading edge or trailing edge of the document has reached the reading position 21a. Image reading of the image reading unit 22 is controlled based on a signal from the rear sensor 54. Image reading is started when the leading edge of the document reaches the reading position 21a, and image reading is performed when the trailing edge of the document reaches the reading position 21a. Reading is terminated.

  With reference to FIG. 4, the configuration of the image reading unit 22 and the outline of the flow of signals output from the image reading unit 22 will be described. FIG. 4A is a diagram illustrating a schematic configuration of the ASIC 66 that processes the image reading unit 22 and data output from the image reading unit 22.

  As shown in FIG. 4, the image reading unit 22, which is an example of a reading unit, includes, for example, a light source 22 a configured by a cold cathode tube and a CCD (Charge) that covers a main scanning range that is at least the long side of the platen glass 21. The image sensor 22b comprised by the coupled device) image sensor and the AFE (analog front end IC) 22c are provided. According to the image reading unit 22, the reflected light obtained by reflecting the irradiation light from the light source 22a by the irradiation target is read by the image sensor 22b. The image sensor 22b photoelectrically converts the reflected light and outputs an image signal to the AFE 22c. This image signal corresponds to an example of “analog image data”. In the AFE 22 c, the image signal is A / D converted into digital data and output to the ASIC 66. This digital data corresponds to an example of “digital image data”. Note that the image sensor 22b may be formed of other types of image sensors such as a contact type CIS (Contact Image Sensor) image sensor. Further, an A / D converter or the like may be used instead of the AFE.

  The digital data output from the image reading unit 22 to the ASIC 66 is first black-corrected by the black correction unit 66a of the ASIC 66. The digital data black-corrected by the black correction unit 66a is then subjected to shading correction by a shading correction unit 66b which is an example of a correction unit. Here, the shading correction is a process of multiplying the digital data for each pixel by the shading correction data set for each pixel in the main scanning direction in order to correct the variation for each pixel in the main scanning direction during white reading. is there. The shading correction data corresponds to an example of correction data according to the present invention.

  FIG. 5 is a graph showing the relationship between the image signal output from the image sensor 22 during white reading and the position in the main scanning direction at the reading position 21a. According to this graph, it can be seen that a high value is obtained at the central portion in the main scanning direction, while a relatively low value is obtained at both ends in the main scanning direction. Furthermore, in addition to variations in the amount of light from the light source 22a, there is also non-uniformity in the sensitivity of the image sensor 22b in the main scanning direction, so that the image signal of each pixel is non-uniform even during white reading. That is, even during white reading, when the image signal output from the image reading unit 22 corresponding to each pixel is digitized without correction, the digital data corresponding to each pixel has a predetermined maximum reference value. (For example, 255). Therefore, the shading correction makes the variation in the main scanning direction uniform.

  Returning to FIG. The data subjected to the shading correction by the shading correction unit 66b is further subjected to various processing such as color conversion and encoding processing, and then stored as image data in the image memory 63f of the RAM 63.

  FIG. 4B is a diagram illustrating a schematic configuration of the AFE 22c. As shown in FIG. 4B, the AFE 22c includes a gain correction unit 22c1 that is an example of a correction unit, and an A / D conversion unit 22c2 that is an example of a conversion unit. The gain correction unit 22c1 amplifies the image signal output from the image sensor 22b according to the gain value, and outputs the amplified signal to the A / D conversion unit 22c. In the gain correction unit 22c, the image sensor 22b is adjusted according to the gain value adjusted so that the value obtained by amplifying the image signal obtained at the time of reading white matches the maximum reference value of the A / D conversion unit 22c2. The image signal output from is amplified and output. The gain value multiplied by the image signal in the gain correction unit 22c1 corresponds to an example of correction data of the present invention.

  The A / D conversion unit 22c2 compares the analog image signal whose gain has been corrected by the gain correction unit 22c with a predetermined reference value, and performs A / D conversion to, for example, digital data of 00h to FFh (hexadecimal number) and outputs it. To do.

  According to the image reading apparatus 1 of the present embodiment, first, the image reading unit 22 is moved below the reference position 21b (see FIG. 3), reads the white tape 21c, and as a result, an image signal output from the image sensor 22b. The gain is adjusted based on the above to determine the gain value. When the gain value is determined, the gain value is set in the gain correction unit 66a, and the image signal from the image sensor 22b is gain-corrected by the gain correction unit 66a and input to the A / D conversion unit 22c2. Converted to digital data.

  Then, based on the digital data output from the image reading unit 22, black correction data and shading correction data are determined and set in the black correction unit 66a and the shading correction unit 66b, respectively. After these settings are made, the image reading unit 22 is moved below the reading position 21a (see FIG. 2) to read the original, and the image signal obtained by reading the original is subjected to gain correction, A / D conversion, black correction, shading correction, and other various image processing are performed and input to the image memory 63e.

  FIG. 6 shows a configuration of the control unit 60 of the image reading apparatus 1. The control unit 60 controls not only the ADF 3 but also the entire operation of the image reading apparatus 1. As shown in the figure, the control unit 60 is configured as a microcomputer including a CPU 61, a ROM 62, a RAM 63, and an EEPROM (Electrically Erasable and Programmable ROM) 64, and an ASIC (Application Specific Integrated Circuit) via a bus 65. 66.

  The ROM 62 stores a program for controlling various operations of the image reading apparatus 1 and the ADF 3.

  The RAM 63 is used as a storage area or a work area for temporarily storing various data used when the CPU 61 executes the program. The RAM 63 includes a correction gain value storage area 63a, a white level data storage area 63b, a shading correction data storage area 63c, a black level data storage area 63d, a black correction data storage area 63e, and a correction A / D data maximum luminance storage area. 63f, an inter-page A / D data maximum luminance storage area 63g, an A / D data maximum luminance change rate storage area 63h, a temporary gain value storage area 63i, a scan page number counter 63j, and an image memory 63k are provided.

  The correction gain value storage area 63a is an area for storing the gain value determined by the gain adjustment immediately before the determination as the correction gain value when determining the shading correction data. The correction gain value stored in the correction gain value storage area 63a is set in the gain correction unit 22c1 (see FIG. 4B). Therefore, the image signal output from the image sensor 22b is gain-corrected using the correction gain value.

  The white level data storage area 63b is digital data obtained by the image reading unit 22 that has been moved below the reference position 21b and obtained from the light source with respect to the full width in the main scanning direction as reflected light applied to the white tape 21c as a white reference plate. This area is stored as white level data. Therefore, based on the white level data stored in the white level data storage area 63b, the white level data can be equalized to the maximum reference value (eg, 255) at the time of white reading for each pixel. The shading correction data to be multiplied by the digital data is determined for each pixel.

  The shading correction data storage area 63c is an area for storing shading correction data determined based on the white level data. The shading correction data stored in the shading correction data storage area 63c is set in the shading correction unit 66b (see FIG. 4A). Therefore, shading correction is performed using this shading correction data.

  The black level data storage area 63d uses, as black level data, digital data acquired using the image sensor 22b provided in the light-shielding area where the reflected light does not enter, among the image reading unit 22 moved below the reference position 21b. This is the memory area. Based on the black level data, black correction data to be subtracted from the digital data output from the image reading unit 22 is determined.

  The black correction data storage area 63e is an area for storing black correction data determined based on black level data. The black correction unit 66a (see FIG. 4A) of the ASIC 66 performs black correction on the digital data output from the image reading unit 22 based on the black correction data stored in the black correction data storage area 63e. As a characteristic of the image sensor 22b, there is a dark output level output even in the absence of light input, and therefore black correction data is subtracted from the output of the image sensor 22b by black correction. The black correction data is newly determined at the same timing as the determination of the shading correction data described above, and the value is updated.

  The corrected A / D data maximum luminance storage area 63f is an area for storing the corrected A / D data maximum luminance. The A / D data maximum luminance at the time of correction is a value corresponding to the maximum luminance among the digital data for one line acquired after the shading correction data is determined.

  In the inter-page A / D data maximum luminance storage area 63g, the rear end in the conveyance direction of one page of the document that has been read passes through the reading position 21a, and the front end of the next page in the conveyance direction is conveyed. The digital data obtained by reading the reflected light from the document holder 19 by the image reading unit 22 below the reading position 21a until reaching the position 21a, that is, between pages where no document is arranged at the reading position 21a. In this area, the value corresponding to the maximum luminance is stored as the inter-page A / D data maximum luminance.

The A / D data maximum luminance change rate storage area 63h is an area for storing the A / D data maximum luminance change rate indicating the amount of change in inter-page A / D data maximum luminance with respect to the corrected A / D data maximum luminance. is there. Specifically, for example, a value calculated by the following formula (1) is calculated as the A / D data maximum luminance change rate and stored in the A / D data maximum luminance change rate storage area 63h.
A / D data maximum luminance change rate = {(A / D data maximum luminance between pages ÷ A / D data maximum luminance during correction) −1} × 100 (1)

  Specifically, the calculated A / D data maximum luminance change rate is compared with the first range stored in advance in the ROM 62, and if the A / D data maximum luminance change rate is outside the first range, It is determined that the amount of change in the amount of light since the determination of the shading correction data is large, the image reading unit 22 is moved below the reference position 21b, the reflected light from the white tape 21c is read, and the shading correction data is newly determined and updated. . The first range is set to, for example, −5% or more and + 5% or less.

  On the other hand, when the A / D data maximum luminance change rate is within the first range, according to the image reading apparatus 1 of the present embodiment, the image reading unit 22 is kept waiting at the reading position 21a. That is, the image reading unit 22 is not returned to the lower side of the reference position 21b, and gain adjustment and shading correction data are not updated. Therefore, when the light amount change amount is small, it is not necessary for the image reading unit 22 to reciprocate between the reading position 21a and the reference position 21b, so that the time required for the reading process can be shortened.

  The temporary gain value storage area 63i is an area for storing a temporary gain value calculated from the correction gain value and the A / D data maximum luminance change rate. As described above, the gain correction unit 22c1 is set with the gain value stored in the correction gain value storage area 63a. The document for five pages after the temporary gain value is determined (claims) For example, the temporary gain value is set in the gain correction unit 22c1 (see FIG. 4B), and an image is obtained using the temporary gain value. The gain of the image signal output from the sensor 22b is corrected.

  In this way, even if there is a light amount variation of the light source 22a, an appropriate temporary gain value corresponding to the light amount variation is determined without moving the image reading unit 22 below the reference position 21a. The image signal can be gain corrected using an appropriate temporary gain value.

  The scan page number counter 63j is a counter that counts the number of pages that have been read.

  The image memory 63k is a memory in which digital data subjected to black correction, shading correction, and other image processing in the ASIC 66 is stored. The digital data stored in the image memory 63k is transferred to an external device connected to the image reading device 1 in accordance with an instruction from the user or preset contents.

  The EEPROM 64 is a storage area for storing various settings, flags, and the like that should be stored even after the power is turned off.

  In addition to the above-described black correction and shading correction, the ASIC 66 further follows the suction roller 33, the separation roller 34, the transport rollers 35A, 35B, 35C, and 35D, the paper discharge roller 36, and the switchback roller (SB) according to a command from the CPU 61. A motor (not shown) for applying a driving force to the roller 43 is controlled.

  Connected to the ASIC 66 is an image reading unit 22 that reads an image of a document conveyed to a reading position by the ADF 3. Based on the control program stored in the ROM 62, the image reading unit 22 reads an image of the document. Although not shown in the figure, a drive mechanism for reciprocating the image reading unit 22 is also operated in response to an output signal from the ASIC 66.

  Next, the single-sided reading process executed in the image reading apparatus 1 configured as described above will be described with reference to the flowcharts of FIGS.

  FIG. 7 is a flowchart of the single-sided reading process executed by the image reading apparatus 1. This single-sided reading process is started when a document is placed on the paper feed tray 30 of the ADF 3 and “start” is input using the operation keys 11. First, the image reading unit 22 is moved below the reference position 21 b. (S2). Next, it waits until the light source 22a of the image reading unit 22 is stabilized (S4). Specifically, it is determined that the light source 22a is stable on the condition that the amount of fluctuation per unit time of the amount of light emitted from the light source 22a is equal to or less than a predetermined value. If a sufficient time has elapsed after the power is turned on, it may be determined that the light source 22a is stable, and the process of S4 may be skipped.

  Next, the value of the scan page number counter 63j is set to “0” (S5), and the supply of the document placed on the paper feed tray 30 of the ADF 3 is started (S6). Then, it is determined whether or not the leading edge of the document is detected by the second front sensor 53 (see FIG. 2) (S7). Then, the process waits while the leading edge of the document conveyance direction is not detected (S7: No).

  When the supply of the document proceeds and the leading end of the document in the conveyance direction is detected by the second front sensor 53 (S7: Yes), it is next determined whether or not the document has been conveyed by a predetermined distance (S8). This determination is made by monitoring the number of rotations of the transport rollers 35A, 35B, 35C, and 35D (see FIGS. 2 and 3) based on the number of encoders and motor steps.

  Then, while the original is not conveyed for a predetermined distance (S8: No), the process waits, but when it is determined that the original has been conveyed and has been conveyed for a predetermined distance (S8: Yes), the correction data full determination process (S10). ). That is, the correction data full determination process (S10) is executed after the leading end of the document in the transport direction reaches a predetermined position on the document transport path 32 (see FIGS. 2 and 3).

  This correction data full determination process (S10) is a process for determining a gain value, black correction data, and shading correction data, and details will be described later with reference to FIG.

  Next, it is determined whether the leading end of the supplied document in the transport direction has reached the reading position 21a (S12). While the leading end of the document in the conveyance direction does not reach the reading position 21a (S12: No), the process is on standby. When the leading end of the document in the conveyance direction reaches the reading position 21a (S12: Yes), the document is scanned (read) (S14).

  When reading of one page of the original is completed in this way, next, “1” is added to the value of the scan page number counter 63j (S16), and whether the value of the scan page number counter 63j becomes “5” or more. Is determined (S18). Initially, since the value of the scan page number counter 63j is less than “5” (S18: No), the process proceeds to S26, and it is determined whether or not the leading end of the next document in the conveyance direction has reached the reading position 21a. (S26). If it is determined that the leading edge of the next page of the document in the conveyance direction does not reach the reading position 21a (S26: No), it is then determined whether the document has been conveyed by a predetermined distance or more (S38). If this determination is negative (S38: No), the process returns to S26.

  If it is determined that the leading edge of the document of the next page has reached the reading position 21a while the processing is repeated in this way (S26: Yes), the process returns to S14 and reading of the next page is started.

  When the document for five pages is read while the processing is repeated, it is determined that the value of the scan page number counter 63j is “5” or more (S18: Yes). Next, the maximum luminance of the A / D data is determined. A change rate calculation process (S20) is executed. In this A / D data maximum luminance change rate calculation process, the trailing end of the one-page original in the conveyance direction passes through the reading position 21a, and the leading end of the next page in the conveyance direction reaches the reading position 21a. In this process, the A / D data maximum luminance change rate indicating the amount of light quantity change of the light source 22a from the previous determination of the shading correction data to the present time is calculated. For details, refer to FIG. It will be described later.

  Next, it is determined whether or not the calculated A / D data maximum luminance change rate is outside a second range (for example, not less than −2% and not more than + 2%) stored in advance in the ROM 62 (S22). For example, when the calculated A / D data maximum luminance change rate is less than −2% or greater than + 2%, it is determined that the A / D data maximum luminance change rate is out of the second range (S22: Yes). Then, it is determined whether the A / D data maximum luminance change rate is out of the first range (for example, -5% or more and + 5% or less) stored in the ROM 62 (S28).

  Here, for example, when the maximum luminance change rate of the A / D data is less than −5% or greater than + 5%, it is determined that it is outside the first range (S28: Yes), and the previous shading correction data is determined. It can be determined that the light amount change amount of the light source 22a from the time to the present time is large. Accordingly, in order to determine and update the shading correction data again, the image reading unit 22 is moved below the reference position 21b (S32).

  Then, it is determined whether or not the leading end in the document transport direction is detected by the second front sensor 53 (see FIG. 2) (S33). If the leading end of the document in the transport direction is not detected (S33: No), it is determined whether the document has been transported over a predetermined distance (S35). If the transport beyond the predetermined distance is not performed (S35: No), the process of S33 is performed. Return.

  On the other hand, when the supply of the document proceeds and the leading edge of the document in the conveyance direction is detected by the second front sensor 53 (S33: Yes), it is next determined whether or not the document has been conveyed by a predetermined distance (S34). This determination is made by monitoring the number of rotations of the transport rollers 35A, 35B, 35C, and 35D (see FIGS. 2 and 3) based on the number of encoders and motor steps.

  Then, while the original is not conveyed for a predetermined distance (S34: No), the process waits, but when it is determined that the original has been conveyed and has been conveyed for a predetermined distance (S34: Yes), the correction data full determination process (S36). ). That is, the correction data full determination process (S36) is executed after the leading end of the document in the transport direction reaches a predetermined position on the document transport path 32 (see FIGS. 2 and 3).

  The correction data full determination process (S36) is the same as the correction data full determination process (S10) described above, and will be described in detail with reference to FIG. 9, but the correction data full determination process (S36). Thus, the gain value, black correction data, and shading correction data are determined, and the correction gain value storage area 63a, the shading correction data 63c, and the black correction data storage area 63e are updated with the determined values or correction data. Next, the value of the scan page number counter is set to “0” (S25), and reading of the next document is started.

  On the other hand, when the leading edge of the next document is not detected by the second front sensor 53 (S34: No), and the original document is transported more than a predetermined distance (S35: Yes), the next page document is fed. Since it can be determined that it is not on the tray 30, the process proceeds to S40, and the rotation of the transport rollers 35A, 35B, 35C, and 35D is stopped (S40).

  Returning to S22, description will be made. When the calculated A / D data maximum luminance change rate is determined to be outside the second range (S22: Yes), and the A / D data maximum luminance change rate is determined to be within the first range ( S28: No), the light quantity variation is seen, but since it can be determined that the shading correction data is not updated, the temporary gain value is determined, and the determined temporary gain value is set in the gain correction unit 22c1. The correction data simple determination process (S30) to be executed is executed. When the temporary gain value is determined by this correction data simple determination process (S30), the value of the scan page counter 63j is then set to "0" (S25), and reading of the next page document is started.

  In this way, after the temporary gain value is determined, the image signal from the image sensor 22b is gain-corrected using the temporary gain value when reading the original for five pages. Therefore, even if there is a change in the amount of light from the time of execution of the previous correction data full determination process (S10, S36) to the present time, appropriate gain correction can be performed using the temporary gain value corresponding to the change in the amount of light. .

  Returning to S22, description will be given. When it is determined that the calculated maximum A / D data luminance change rate is within the second range (S22: No), the correction gain value stored in the correction gain value storage area 63a is input to the gain correction unit 22c1. In step S24, the scan page number counter 63j is set to "0" (S25), and the document on the next page is read. That is, when it is determined that the light amount fluctuation from the execution time of the previous correction data full determination process (S10, S36) to the current time is small, the previous correction data full is read when reading 5 pages of originals to be read thereafter. The gain value, black correction data, and shading correction data determined in the determination process (S10, S36) are used.

  If it is determined that the leading edge of the next original does not reach the reading position 21a while the processing is repeated in this way (S26) and it is determined that the conveyance of a predetermined distance or more has been performed (S38: Yes). Since it can be determined that there is no document on the next page, the conveyance by the conveyance rollers 35A, 35B, 35C, and 35D is stopped (S40), the image reading unit 22 is moved below the reference position 21b, and the single-sided reading process is performed. Exit.

  According to the single-sided reading process, when the A / D data maximum luminance change rate is outside the predetermined first range, it is determined that the light amount change amount from the previous correction data full determination process (S10, S36) is large, A correction data full determination process (S36) is executed. When the amount of change in light quantity from the previous execution of the correction data full determination process (S10, S36) is not so large, the correction data full determination process (S36) is not executed, so the image reading unit 22 has the reference position 21b. There is no need to move down. Therefore, reading of the next page can be started quickly, the time required for the reading process can be shortened, correction data can be updated at an appropriate timing, and gain correction and shading correction are preferably performed. Can be executed.

  With reference to FIG. 8, the A / D data maximum luminance change rate calculation process (S20) will be described. FIG. 8 is a flowchart of the A / D data maximum luminance change rate calculation process (S20).

  Prior to the description of the flowchart, the light amount change determination gain value used for determining the maximum luminance between pages of A / D data in this A / D data maximum luminance change rate calculation process (S20) will be described.

  As described above, in order to determine the maximum luminance of inter-page A / D data, the document holding unit 19 is read by one line in the image reading unit 22, and the read image signal is amplified by amplification for gain correction. The amplified image signal is A / D converted by the A / D converter 22c2, thereby obtaining digital data.

  Here, when the image signal is amplified using the gain value determined in the previous correction data full determination process (S10, S36) and input to the A / D converter 22c2, the previous correction data full determination process ( S10, S36) If the amount of light suddenly increases from the time of execution to the present time, the image signal after gain correction is the maximum that can be converted by the A / D converter 22c2 (see FIG. 4B). The brightness is saturated and a significant value cannot be obtained for evaluating the amount of change in light quantity.

  Therefore, according to the image reading apparatus 1 of the present embodiment, in order to suppress the saturation of the image signal obtained by reading the document pressing unit 19 to the maximum luminance that can be converted by the A / D conversion unit 22c2, the document pressing unit. At the time of reading 19, the predetermined light amount determination gain value is set in the gain correction unit 22c1, and the document retainer 19 is read.

  This gain change determination gain value is set sufficiently smaller than the gain value determined by the correction data full determination process (S10, S36) or the temporary gain value determined by the correction data simple determination process (S30). For example, a value corresponding to an amplification factor of 1 is used. By performing gain correction using the light amount change determination gain value set sufficiently small in this way, the value of the image signal after gain correction is saturated to the maximum luminance that can be converted by the A / D conversion unit 22c2. Is suppressed. As a result, even if the amount of light suddenly increases from the previous correction data full determination process (S10, S36) to the present time, a significant maximum inter-page A / D data maximum luminance is determined in order to evaluate the amount of change in the amount of light. It can be done.

  This will be described in more detail with reference to the flowchart shown in FIG. In the A / D data maximum luminance change rate calculation process (S20), first, a light amount change determination gain value is set in the gain correction unit 22c1 (S202). Then, the reflected light from the document holder 19 is read for one line (S204).

  Next, the digital signal for 16 pixels is extracted from the digital data for one line obtained by gain correction of the image signal for one line in the AEF 22c and A / D conversion. (S205). The digital data extracted here is data that has not undergone black correction and shading correction. Then, the average value of the extracted digital data for 16 pixels is calculated as the inter-page A / D data maximum luminance and stored in the inter-page A / D data maximum luminance storage area 63g (S206).

  Next, based on the corrected A / D data maximum luminance stored in the corrected A / D data maximum luminance storage area 63f and the inter-page A / D data maximum luminance, the A / D data maximum luminance change rate is calculated. Calculate (S208).

  Using the A / D data maximum luminance change rate calculated in this way, in the above-described single-sided reading process (see FIG. 7), the light amount change amount from the previous correction data full determination process (S10, S36) is determined. To do.

  According to the A / D data maximum luminance change rate calculation process (S20), the A / D data maximum luminance change rate for determining the amount of change in the light amount can be obtained without moving the image reading unit 22 below the reference position 21b. That is, the calculation can be performed while the image reading unit 22 is kept waiting below the reading position 21a. Therefore, the image reading unit 22 does not need to reciprocate between the reference position 21b and the reading position 21a after reading the previous page and before reading the next page, and can quickly start reading the next page of the document. it can.

  The A / D data maximum luminance change rate calculation process (S20) is executed after the previous page has passed through the reading position until the next page passes through the reading position, so that the time until the next page is reached is effective. The time required for the reading process can be suppressed.

  The correction data full determination process (S10, S36) will be described with reference to FIG. FIG. 9 is a flowchart showing the correction data full determination process (S10, S36). At the start of this correction data full determination process (S10, S36), the image reading unit 22 is moved below the reference position 21b.

  First, the white tape 21c is read by the image sensor 22b of the image reading unit 22 below the reference position 21b, and the maximum luminance of the image signal matches the predetermined reference value input to the A / D conversion unit 22c2. The gain is adjusted to determine the gain value. The determined gain value is stored in the correction gain value storage area 63a as a correction gain value (S102).

  Next, the determined gain value at the time of correction is set in the gain correction unit (S104), and the area for 16 lines is read while moving the image reading unit 22 by 16 lines below the reference position 21b, and the digital data is read. Obtain (S106). The digital data acquired here is read by the white level data read by the image sensor 22b provided at the position where the reflected light from the white tape 21c enters and the image sensor 22b provided in the light shielding area. Black level data. The acquired white level data is stored in the white level data storage area 63b, and the black level data is stored in the black level data storage area 63d (S108).

  Next, black correction data is determined based on the acquired black level data, stored in the black correction data storage area 63e (see FIG. 6), and stored in the black correction unit 66a of the ASIC 66 (see FIG. 4A). Set (S110).

  Next, shading correction data is determined based on the acquired white level data, stored in the shading correction data storage area 63c (see FIG. 6), and stored in the shading correction unit 66b (see FIG. 4A) of the ASIC 66. Set (S112).

  Then, the image reading unit 22 is moved from below the reference position 21b to below the reading position 21a (S114). Thereby, the irradiation object of the light source 22a, that is, the reading object by the image reading unit 22 is switched from the reference position 21b to the reading position 21a.

  Next, the gain change determination gain value is set in the gain correction unit 22c1 (S116). This is for calculating the maximum brightness of the corrected A / D data in the subsequent steps. That is, as described above, the A / D data maximum luminance change rate indicating the light amount change amount is calculated from the corrected A / D data maximum luminance and the inter-page A / D data maximum luminance. A / D data maximum brightness at the time of correction by using a gain value for light amount change determination which is the same value as the gain value used for calculating the maximum brightness of inter-page A / D data so that it can be accurately determined Is determined.

  Next, the document holding unit 19 is read for one line by the image reading unit 22 moved below the reading position 21a, and digital data for one line is acquired (S118). The image signal for one line read here is subjected to gain correction using the light amount change determination gain value set in the processing of S116.

  Next, the digital signal for 16 pixels is extracted from the digital data for one line obtained by gain correction of the image signal for one line in the AEF 22c and A / D conversion. (S119). Then, the average value of the extracted digital data for 16 pixels is calculated as the corrected A / D data maximum luminance and stored in the corrected A / D data maximum luminance storage area 63f (S120).

  Then, the correction gain value is set in the gain correction unit 22c1 (S122), and the correction data full determination process (S10, S36) is terminated. According to the correction data full determination process, the gain value and the shading correction data are determined according to the light amount from the light source 22a at the present time. Then, when reading five pages of documents from the next page, the newly determined gain value and shading correction data are used to perform various corrections. Therefore, it is possible to perform appropriate correction according to the amount of light from.

  The correction data simple determination process (S30) will be described with reference to FIG. FIG. 10 is a flowchart showing the simple correction data determination process (S30).

In the correction data simple determination process (S30), first, a temporary gain value is determined based on the A / D data maximum luminance change rate and the correction gain value, and stored in the temporary gain value storage area 63i (see FIG. 6). (S302). The temporary gain value is determined by, for example, calculation shown in the following formula (2).
Temporary gain value = Gain value during correction × 100 / (100 + A / D data maximum luminance change rate) (2)
That is, instead of adjusting and determining the gain value based on the reflected light from the white tape 21c, the correction gain value determined in the previous correction data full determination process (S10, S36) is changed to the current value. By reflecting the A / D data maximum luminance change rate indicating the light amount change amount, an appropriate gain value corresponding to the light amount variation is determined.

  Then, the determined temporary gain value is set in the gain correction unit 22c1 (S304), and the correction data simple determination process (S30) is terminated. According to this correction data simple determination process (S30), the gain value (temporary gain value) corresponding to the light amount change amount can be determined without returning the image reading unit 22 to the reference position 21b. Then, when reading five pages of the original after the temporary gain value is determined, the temporary gain value is used to appropriately correct the gain of the image signal.

  Further, according to this simple correction data determination process (S30), it is not necessary to return the image reading unit 22 to the reference position 21b for the calculation of the temporary gain value, so that the reading of the next page can be started quickly. it can.

FIG. 11 is a timing chart showing a process flow from the start of the single-sided reading process to S14. As shown in FIG. 11A, first, the first front sensor 52 detects that there is an original on the paper feed tray 30 (T ₁ ). When a scan start instruction is input from the operation panel 5 by the user (T ₂ ), a rotation instruction is given to a motor (not shown) that rotationally drives the suction roller 33 and the separation roller 34 (see FIGS. 2 and 3). Then, paper feeding is started (T ₃ ). Then, the paper feed proceeds, and the leading end of the document in the conveyance direction is detected by the second front sensor 53 (T ₄ ).

Next, when a motor (not shown) that rotationally drives the transport rollers 35A, 35B, 35C, and 35D rotates a predetermined number of steps (T ₅ ), a correction data full determination process (S10) is executed. Specifically, the gain adjustment by the gain correction unit 22c1 is started (T _5), the gain value is determined. Next, black level data and white level data are acquired while moving the image reading unit 22 below the reference position 21b (T ₆ ). When completing the acquisition of the black level data and the white level data, then moves toward the image reading unit 22 to the reading position 21a (T _7), and reaches the reading position 21a, and stops its movement (T ₉ ). The CPU 61 determines black correction data based on the acquired black level data, and determines shading correction data based on the white level data.

On the other hand, the correction data full determination process are parallel document is conveyed execution (S10), the transport approaches to the reading position 21a progresses, the tip is detected by the rear sensor 54 (T _8). Then, from the detection of the leading edge of the document has the rear sensor 54 and reaches the feed rollers 35A, 35B, 35C, the motor for rotating the 35D is rotated a predetermined number of steps _{(T 10),} the conveying direction leading end the reading position 21a of the original So that reading starts.

In this way, the timing (T ₅ ) for starting the reading of the reflected light from the white tape 21c and the timing for starting the reading of the document (T ₁₀ ) can be made closer to each other by the correction data full determination process (S10). it can. Therefore, even if there is a change in the amount of light between the start of document feeding and the start of document reading, the influence can be suppressed to an extremely small level, and an appropriate gain value and shading correction data can be determined. it can.

Further, after the gain adjustment is started, black level data and white level data are acquired, and then the image reading unit 22 is moved from the reference position 21b to the reading position 21a, and the image reading unit 22 reaches the reading position 21a. time T _H until from the conveying direction leading end of the document has reached the predetermined position, so as to be shorter than the time T _G to reach the tip of the reading position, the predetermined position is predetermined ing. In this way, after the original reaches the reading position 21a, it is possible to start reading the original immediately, and the processing is not delayed.

  Similarly, in the correction data full determination process (S36) executed after the previous page is read and before the start of reading the next page, the leading end of the next page in the document transport direction is similarly set to a predetermined position on the document transport path 32. When the time interval until the next page reaches the reading position 21a is long after reading the previous page, for example, during the reading of the previous page or after reading the previous page, the next page Is inserted into the paper feed tray 30, the correction data full determination process (S36) is awaited until the next page reaches the vicinity of the reading position. The value, black correction data, and shading correction data can be determined. As a result, it is possible to determine an appropriate correction value that is hardly affected by the light amount fluctuation that may occur after reading the previous page and before starting reading the next page.

  Here, referring back to FIGS. 2 and 3, the document conveyance order when the image reading apparatus 1 reads both sides of the document will be described. The image reading apparatus 1 alternately reads the front surface and the back surface of the document placed on the paper feed tray 30 in the order of reading the front surface and then reading the back surface.

  First, the document placed on the paper feed tray 30 is transported to the reading position 21 a through the document transport path 32 in the direction in which the surface is read by the image reading unit 22. That is, at the reading position 21 a, the document is transported with the surface of the document facing the platen glass 21. This conveyance is hereinafter referred to as first-pass conveyance.

  Next, the original whose surface has been read and passed through the reading position 21a is guided to the switchback path 39, and the leading edge and the trailing edge are reversed in the switchback path 39 so that the reading position 21a is downstream to the upstream side. The document is returned to the original document conveyance path 32 and conveyed to the reading position 21 a in a direction in which the back surface is read by the image reading unit 22. That is, the document is conveyed with the back side of the document facing the platen glass 21. This conveyance is hereinafter referred to as the second-pass conveyance.

  Next, the original (both sides read) that has been scanned on the back side and passed through the reading position 21a is guided to the switchback path 39. In the switchback path 39, the leading edge and the trailing edge are reversed to read the reading position 21a. The document is returned from the downstream side to the upstream document conveyance path 32, and the document conveyed through the document conveyance path 32 is discharged to the discharge tray 31 through the reading position 21a. This conveyance is hereinafter referred to as the third-pass conveyance.

  That is, for a single document, the first pass is first carried in order to read the surface. Then, the document whose front side is read is reversed by the switchback path 39, and then the second pass is carried for reading the back side. Further, the document whose back side is read is reversed by the switchback path 39 and conveyed in the document conveyance path 32 for the third pass. In the third pass, the document passes through the reading position 21a, but reading by the image reading unit 22 is not executed. However, by carrying this third pass, the documents discharged to the discharge tray 31 are stacked from the bottom in the reading order with the front side facing down. The order of the originals when placed on the paper discharge tray 31 is also maintained as it is. Therefore, it is not necessary for the user to manually rearrange the page order of the documents discharged to the discharge tray 31.

  Next, a double-sided reading process executed in the image reading apparatus 1 will be described with reference to the flowchart of FIG.

  FIG. 12 is a flowchart of double-sided reading processing executed by the image reading apparatus 1. This double-sided reading process is started when a document is placed on the paper feed tray 30 of the ADF 3, double-sided scanning is selected using the operation keys 11, and “START” is input. In this double-sided reading process, the same steps as those in the single-sided reading process described with reference to FIG.

  In this double-sided reading process, first, the processes of S2 and S4 are executed as in the single-sided reading process (see FIG. 7). Next, one page of the original placed on the paper feed tray 30 of the ADF 3 is fed, and conveyance of the first pass is started (S60). As described above, the document placed on the paper feed tray 30 is conveyed to the reading position 21a through the document conveyance path 32 in the direction in which the surface is read by the image reading unit 22 by the first-pass conveyance. .

  Then, similarly to the single-sided reading process (see FIG. 7), it is determined whether or not the leading edge in the document transport direction is detected by the second front sensor 53 (see FIG. 2) (S7). 2 When detected by the front sensor 53 (S7: Yes), it is next determined whether or not the document is conveyed by a predetermined distance (S8).

  Then, while the original is not conveyed for a predetermined distance (S8: No), the process waits, but when it is determined that the original has been conveyed and has been conveyed for a predetermined distance (S8: Yes), the correction data full determination process (S10). ). That is, similar to the single-sided reading process (see FIG. 7), the correction data full determination process (S10) is executed after the leading end in the document transport direction reaches a predetermined position on the document transport path 32 (see FIGS. 2 and 3). It is done.

  Next, it is determined whether or not the leading end of the supplied document in the transport direction has reached the reading position 21a (S120). While the leading end of the document in the conveyance direction does not reach the reading position 21a (S120: No), the process is on standby. When the leading end of the document in the conveyance direction reaches the reading position 21a (S120: Yes), one side of the document is scanned (read) (S140).

  When the reading of one side of the document is completed in this way, it is next determined whether the read side is the front side or the back side (an example of the second side) (S180). When it is determined that the read surface is the front surface (S180: Yes), the second pass of the document is started (S200). Then, the process returns to S12. Thereby, in the subsequent steps, the back side of the original is read.

  On the other hand, when it is determined that the read surface is the back surface (S180: No), the image reading unit 22 is moved to the reference position 21b (S220). This is because in the subsequent correction data determination process (S10), the reflected light from the white tape 21c is read, and gain adjustment, determination of shading correction data, and the like are performed.

  Next, the third pass conveyance is started (S240). By carrying the third pass, the document is discharged to the discharge tray 31 through the reading position 21a.

  Next, it is determined whether there is a next original on the paper feed tray 30 of the ADF 3 (S280). If it is determined that there is a next document on the paper feed tray 30 (S280: Yes), whether or not the rear end of the document transported in the document transport path 32 in the transport direction has passed the rear sensor 54. Is determined (S300). While the rear end of the document in the conveyance direction does not pass the rear sensor 54 (S30: No), the process waits and the conveyance of the third pass is advanced.

  If it is determined that the three-pass conveyance has progressed in this way and the rear end in the conveyance direction of the document conveyed in the third pass has passed the rear sensor 54 (S300: Yes), then the process of S60 Returning to FIG. 1, one page of the original placed on the paper feed tray 30 is fed, and the conveyance of the first pass is started (S60). Then, it is determined whether or not the leading end of the document in the transport direction is detected by the second front sensor 53 (see FIG. 2) (S7). If the leading end of the document in the transport direction is detected by the second front sensor 53 (S7: Next, it is determined whether or not the document has been conveyed by a predetermined distance (S8).

  Then, while the original is not conveyed for a predetermined distance (S8: No), the process waits, but when it is determined that the original has been conveyed and has been conveyed for a predetermined distance (S8: Yes), the correction data full determination process (S10). ).

  Here, when executing the correction data determination process (S10), it is necessary to read the reflected light from the white tape 21c by the image reading unit 22, but according to the double-sided reading process of this embodiment, After the back side reading (S18: No), since the image reading unit 22 is moved below the reference position 21b (S22), the execution of the correction data determination process (S10) can be started quickly, and the reading speed can be increased. There is no reduction.

  As described above, in the image reading apparatus 1 of the present embodiment, the correction data determination process (S10) is not executed after the front side reading, while the correction data determination process (S10) is executed after the back side reading. .

  If it is determined that there is no next original on the paper feed tray 30 while the processing is repeated in this manner (S280: No), then the conveyance by the conveyance roller 35 is stopped (S40), and the image is displayed. The reading unit 22 is moved below the reference position 21b (S42), and the double-sided reading process is terminated.

Also in the double-sided reading process, similar to the above-described single-sided reading process (see FIG. 7), the timing (T ₅ ) at which reading of the reflected light from the white tape 21c is started by the correction data full determination process (S10), and the document The reading start timing (T ₁₀ ) can be made closer. Therefore, even if there is a change in the amount of light between the start of document feeding and the start of document reading, the influence can be suppressed to an extremely small level, and an appropriate gain value and shading correction data can be determined. it can.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

  For example, when the correction data full determination process (S10, S36) is executed after scanning the surface of the double-sided reading described with reference to FIG. 12, after the document is reversed by the switchback path 39, a predetermined distance is conveyed. The correction data full determination process (S10, S36) may be started.

  When the image reading device 1 is an image reading unit of a multifunction peripheral device functioning as, for example, a facsimile device, a copy device, or a scanner device, the user can operate the facsimile mode from the operation panel 5 which is an example of mode setting means. The copy mode and the scanner mode can be set.

  In this case, in the process of S4 of the single-sided reading process (see FIG. 7) and the double-sided reading process (see FIG. 12), the waiting time until the light source stabilizes differs for each mode. For example, a relatively short standby time is provided in the copy mode and the facsimile mode, whereas a relatively long standby time is provided in the scanner mode. In this case, for example, the light source 22a is sufficiently stable during execution of single-sided reading processing and double-sided reading processing in the scanner mode. Therefore, even if the correction data full determination process (S10) is executed relatively early, appropriate correction data can be obtained.

  Therefore, before the step S8 of the single-sided reading process (see FIG. 7) and the double-sided reading process (see FIG. 12), a step of setting a predetermined distance according to the mode is provided (an example of changing means), and the step of S8 The predetermined distance amount determined in step 1 may be changed for each mode, and the correction data determination timing may be changed for each mode.

1 is a perspective view showing an external configuration of an image reading apparatus according to an embodiment of the present invention. It is sectional drawing which shows the internal structure of an image reading apparatus. It is a figure which shows the state which the image reading unit moved below the reference position. (A) is a figure which shows schematic structure of ASIC which processes the data output from an image reading unit and an image reading unit, (b) is a figure which shows schematic structure of AFE. It is a graph which shows the relationship between the image signal read with an image sensor at the time of white reading, and the main scanning direction position in a reading position. It is a block diagram which shows the structure of a control part. It is a flowchart of the single-sided reading process performed with an image reading apparatus. It is a flowchart of A / D data maximum luminance change rate calculation processing. It is a flowchart which shows a correction data full determination process. It is a flowchart which shows a correction data simple determination process. It is a timing chart which shows the flow of a process from the start of a single-sided reading process to S14. 6 is a flowchart of double-sided reading processing executed by the image reading device.

Explanation of symbols

1 Image reading device 22 Image reading unit (reading means)
22a Light source 22c1 Gain correction unit (correction means)
22c2 A / D converter (conversion means)
30 Paper feed tray (document placement section)
31 Paper output tray (original output)
32 Document conveying path 35A, 35B, 35C, 35D Conveying roller (conveying means)
53 Second front sensor (detection means)
66 ASIC (correction means)
S8, S34 Transport determination means S10, S36 Correction data determination means S112 Correction data determination means, correction data update means

Claims (8)

A document conveying path that connects the document placing portion and the document discharge portion via the reading position;
Conveying means for conveying the document one page at a time to the reading position via the document conveying path;
Reading means for reading the reflected light reflected from the irradiation target by the irradiation light from the light source, converting it into image data, and outputting it,
Correction means for correcting the image data output by the reading means;
Correction data determination means for determining correction data to be referred to in the correction by the correction means,
The correction data determining unit is configured to read the reflected light by the reading unit and output the image data after the leading end of the document conveyed by the conveying unit reaches a predetermined position on the document conveying path. An image reading apparatus for determining correction data.   2. The image reading apparatus according to claim 1, wherein the correction unit corrects analog image data or digital image data output from the reading unit. Conversion means for A / D converting the image data output by the reading means;
The image reading apparatus according to claim 1, wherein the correction unit corrects digital image data after A / D conversion by the conversion unit. Conversion means for A / D converting the image data output by the reading means;
The correction means corrects a relationship between a reference voltage and analog image data that are referred to when the conversion means converts analog image data into digital image data. The image reading apparatus according to 1 or 2.   The correction data determining unit is configured to allow the leading end of the document transported by the transporting unit to reach the reading position after the leading end of the document transported by the transporting unit has reached a predetermined position on the document transporting path. 5. The image reading apparatus according to claim 1, wherein the correction data is determined before the correction. A detecting means for detecting the leading end of the document in the conveyance direction;
The correction data determination unit determines the correction data based on image data output by the reading unit after the leading end of the document is detected by the detection unit. The image reading apparatus according to any one of 1 to 5. A conveyance determining means for determining whether or not the document has been conveyed a predetermined distance after the detection means detects the leading edge of the document in the conveyance direction;
The correction data determining means determines the correction data based on image data output from the reading means after the conveyance determining means determines that the document has been conveyed by a predetermined distance. The image reading apparatus according to claim 6. Comprising mode setting means for setting one of a plurality of modes including a plurality of modes in which the time required for reading one page of the document is different;
8. The image reading apparatus according to claim 1, further comprising: a changing unit that changes a correction data determination timing by the correction data determining unit for each mode set by the mode setting unit. 9. .

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