JP2015091036A - Image reading device, image reading method, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading device, image reading method, and image forming apparatus that enable a reduction in time for reading a background board in performing level correction when performing intermittent shading.SOLUTION: An image reading device according to the present invention includes: a pixel signal output unit that outputs signals in which part of light-receiving elements, of a predetermined number of light-receiving elements arranged in the main scanning direction, have photoelectrically converted reflected light from a reference member for each pixel, in continuously reading a plurality of documents during a first period from the reading of the previous document until the reading of the subsequent document; an interpolation unit that interpolates the signals output from the part of the light-receiving elements that have photoelectrically converted the reflected light from the reference member for each pixel, to be signals of the predetermined number light-receiving elements; and a shading correction unit that performs shading correction on the basis of the signals of the predetermined number of light-receiving elements interpolated by the interpolation unit.

Description

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

  In an image reading device using a photoelectric conversion element (image sensor), in order to correct the optical system non-uniformity and the output non-uniformity of each pixel of the image sensor, a reference white plate serving as a reference for main scanning is read. A process of shading correction for correcting the main scanning distribution is performed. During flatbed reading (scan reading mode), when the carriage passes through the reference white plate attached to the end of the contact glass, the main white plate distribution as a reference is read, and the read reference white plate data is stored in the storage element. The At the time of sheet-through reading, the carriage moves from the home position directly below the reference white plate every time the document is read, similarly reads the white plate main scanning distribution, and the read reference white plate data is stored in the storage element.

  However, recently, during continuous sheet-through reading, the carriage operation for reading the reference white plate as intermittent shading is omitted once every few minutes of document reading or once every several sheets, and shading correction is performed. Increasing the interval between carriage operations is performed. As a result, the paper interval is shortened to improve productivity during continuous reading. When intermittent shading is performed, the reading level of the document decreases over time due to the short-term light intensity reduction caused by the heat generated by the continuous lighting of the light source, so shading correction is performed using the reference whiteboard data acquired in the initial stage. As a result, there is a problem that a density difference occurs between the first and last scanned originals. In order to solve this problem, the level of the background plate on the reading surface at the carriage home position is monitored every time the document is read, and the background plate reading level attenuation amount (change amount) is obtained as the amount of light quantity fluctuation. Then, a gain adjustment value (hereinafter referred to as a level correction coefficient) for each original is calculated according to the background plate reading level attenuation, and this level correction coefficient is multiplied by the reading level of each pixel subjected to shading correction. Therefore, a control method (hereinafter referred to as level correction) that can obtain an image with an appropriate density is known.

  Normally, in calculating the level correction coefficient, the ratio between the initial background plate level and the time-lapse background plate level is used as the attenuation amount, and the inverse of the ratio is uniformly multiplied by the shading corrected pixels. In general, a main scanning peak value, an area average value, or the like is used. However, in the above method, since all the main scanning pixels are multiplied by a uniform level correction value, if there is a short-term light amount change of the light source, variation in attenuation amount for each light source or local heat generation difference Therefore, it is impossible to cope with the change in the main scanning distribution between the initial stage and the time course, and therefore, the local light quantity fluctuation of the main scanning distribution cannot be corrected in the level correction. In addition, in order to cope with the above-mentioned local light amount fluctuation of the main scanning distribution, all the main scanning pixels of the background plate are read, an average value is obtained for each of a plurality of blocks, and a pixel portion between them is calculated by linear interpolation. A method for calculating a level correction value for all pixels is known.

  Patent Document 1 discloses an image forming apparatus that can correct a local change in level correction in a short-term light amount change of a light source. The image forming apparatus described in Patent Literature 1 reads all the main scanning pixels of the background plate, calculates an average for each of the set plurality of pixel blocks, sets the average value as the block center pixel, and the pixel level up to the next block center pixel Is obtained by interpolation, and level correction values are calculated for all pixels from these values.

  However, in the image forming apparatus described in Patent Document 1, all the main scanning pixels of the background plate are read and processed in the level correction at the time of intermittent shading, so that much processing time is consumed. Therefore, there is a problem that the reading time of the document increases.

  The present invention has been made in view of the above, and provides an image reading apparatus, an image reading method, and an image forming apparatus capable of reducing the reading time of a background plate when performing level correction when intermittent shading is performed. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the image reading apparatus according to the present invention provides a first process from reading a previous document to reading a next document when reading a plurality of documents continuously. A pixel signal output unit that outputs a signal obtained by photoelectrically converting the reflected light from the reference member for each pixel by a part of the predetermined number of light receiving elements arranged in the main scanning direction in the period, and the reflected light from the reference member Based on the predetermined number of signals interpolated by the interpolation unit so that the signal output from a part of the light receiving elements obtained by photoelectric conversion of each pixel is used as the signal of the predetermined number of light receiving elements. And a shading correction unit that performs shading correction.

  According to the present invention, there is an advantageous effect that it is possible to shorten the reading time of the background plate when performing level correction when executing intermittent shading.

FIG. 1 is a diagram illustrating a configuration example of an image reading apparatus according to the present embodiment. FIG. 2 is a block diagram illustrating a functional configuration example of the image reading unit of the image reading apparatus according to the present embodiment. FIG. 3 is a block diagram illustrating a functional configuration example of the photoelectric conversion element. FIG. 4 is a diagram illustrating a functional configuration example of the pixel signal output unit. FIG. 5A is a diagram illustrating the timing of each signal from the pixel signal output unit. FIG. 5B is a diagram illustrating the timing of each signal from the pixel signal output unit. FIG. 6 is a diagram illustrating the distribution generation unit. FIG. 7A is a diagram for explaining generation of distribution data of image signals of all pixels in one line in the main scanning direction of background plate data in the distribution generation unit. FIG. 7B is a diagram illustrating generation of distribution data of image signals of all pixels in one line in the main scanning direction of background plate data in the distribution generation unit. FIG. 8 is a diagram illustrating a functional configuration example of the level correction coefficient calculation unit. FIG. 9 is a diagram for explaining the level correction coefficient when dust or dirt adheres to the background plate. FIG. 10 is a diagram illustrating a functional configuration example of the shading correction unit. FIG. 11 is a flowchart illustrating an example of a document continuous reading process operation of the image reading apparatus. FIG. 12 is a diagram illustrating a configuration example of a mechanism unit of the image forming apparatus according to the present embodiment.

  Hereinafter, embodiments of an image reading apparatus, an image reading method, and an image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, an image reading apparatus using a photoelectric conversion element (image sensor) will be described as an example of an image reading apparatus, but the present invention is not limited to this. Any reading device can be applied.

  The image reading apparatus according to the present embodiment is a scanner apparatus or a single scanner apparatus mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine. The image reading apparatus can read the image data of the document by illuminating the document, which is the subject, with the light emitted from the light source, and processing the reflected light from the document with a photoelectric conversion element.

  FIG. 1 is a diagram illustrating a configuration example of an image reading apparatus. As shown in FIG. 1, the image reading apparatus 1 includes an image reading unit 100 and an automatic document feeder 200. The image reading unit 100 includes a contact glass 101, a first carriage 106 including a light source 102 and a first reflection mirror 103, a second carriage 107 including a second reflection mirror 104 and a third reflection mirror 105, and a lens unit 108. , A photoelectric conversion element 109, a reference member 110, and a sheet-through (continuous) reading slit 111.

  The contact glass 101 is a transparent member on which a document is placed in the scan reading mode. In the scan reading mode, a first carriage 106 and a second carriage 107 (to be described later) are moved in the direction indicated by an arrow A (sub-scanning direction) shown in FIG. 1 with respect to a document placed on the contact glass 101. In this mode, an image on the lower surface of the original is read.

  The first carriage 106 includes a light source 102 for document exposure and a first reflecting mirror 103, and is movable in the direction of arrow A, which is the sub-scanning direction of image reading. The light source 102 is lit before starting the reading operation in any reading mode.

  The second carriage 107 has a second reflecting mirror 104 and a third reflecting mirror 105, and is at a speed that is half the moving speed of the first carriage 106 in the direction of arrow A, which is also the sub-scanning direction of image reading. It is movable. Accordingly, the optical path length from the light source 102 to the photoelectric conversion element 109 is always kept constant while the first carriage 106 and the second carriage 107 are moving.

  The lens unit 108 and the photoelectric conversion element 109 for forming an image on the photoelectric conversion element 109 together with the first carriage 106 and the second carriage 107 described above constitute a reading optical system. Details of the photoelectric conversion element 109 will be described later.

  The reference member 110 corrects various distortions caused by the reading optical system or the like. The reference member 110 is, for example, a reference member (white plate) that is read before reading image data of a document in order to obtain shading data for shading correction. Like the background plate 112 described later, main scanning for image reading is performed. The lower surface provided along the direction is a white, elongated plate-like member. That is, in order to perform shading correction for correcting the light amount fluctuation of the light source 102, the reference member (white plate) 110 is read in advance by the photoelectric conversion element 109, and white reference data serving as a density reference of the image data is acquired. The reference member 110 that acquires the white reference data corresponds to a “white reference member” in the claims. Hereinafter, the reference member 110 may be referred to as a “white plate 110”. Also, the white reference data may be written as “white plate data”. In the present embodiment, in the level correction when the intermittent shading is executed, the operation for reading the white plate 110 is omitted once every several minutes of reading the document or once every several sheets. Run. In the present embodiment, the reference member 110 is described as being divided into the white plate 110 and the background plate 112. However, the present invention is not limited to this, and the reference member 110 may be either the white plate 110 or the background plate 112. Only one can be used. Further, only one reference member 110 may be provided.

  The sheet-through reading slit 111 is a window for reading a document continuously and sequentially conveyed by an automatic document feeder 200 described later in the sheet-through reading mode. It is provided along the scanning direction. The sheet-through reading mode includes a light source while conveying a document fed by an automatic document feeder 200 that conveys documents one by one from a document table to a reading position in the sub-scanning direction (arrow A direction). In this mode, the reading optical system and the photoelectric conversion element read the image. In the sheet-through reading mode, the reading optical system does not move from a predetermined reading position. The main scanning direction is a direction that intersects the direction in which the original is conveyed by the automatic document feeder 200, and the sub-scanning direction indicates the same direction as the direction in which the original is conveyed.

  The automatic document feeder 200 is an automatic document feeder that continuously conveys a document. The automatic document feeder 200 corresponds to a “document transport unit”. Hereinafter, the automatic document feeder 200 is referred to as an ADF (Auto Document Feeder) 200. The ADF 200 is mounted on the upper part of the image reading unit 100 and is connected via a hinge or the like (not shown) so that the ADF 200 can be opened and closed with respect to the contact glass 101.

  The ADF 200 includes a document tray 201 and a feeding roller 202. The document tray 201 is a document placing table on which a document bundle composed of a plurality of documents can be placed. The feeding roller 202 is included in a separation / feeding unit (not shown) that separates documents one by one from a bundle of documents placed on the document tray 201 and automatically feeds them toward the sheet-through reading slit 111. It is. Hereinafter, the surface of the feeding roller 202 that faces the light source 102 is referred to as a “background plate 112”. The background plate 112 corresponds to a “reference member” in the claims.

  Next, the document reading operation of the image reading apparatus 1 will be described. In the image reading apparatus 1 configured as described above, in the scan reading mode in which the image surface of the document is scanned (scanned) to read the image of the document, the first carriage 106 and the second carriage 107 are moved by a stepping motor (not shown). The document is scanned in the arrow A direction (sub-scanning direction). At this time, the second carriage 107 moves at a speed half that of the first carriage 106 in order to keep the optical path length from the contact glass 101 to the photoelectric conversion element 109 constant. At the same time, the image surface which is the lower surface of the document set on the contact glass 101 is illuminated (exposed) by the light source 102 of the first carriage 106. The reflected light image from the image plane is passed through the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and then to the photoelectric conversion element 109 via the lens unit 108. Images are sent sequentially. A signal is output by photoelectric conversion of the photoelectric conversion element 109 and converted into a digital signal by a signal processing unit (not shown) in the subsequent stage. As a result, the image of the original is read and digital image data is obtained.

  On the other hand, in the sheet-through reading mode in which the document is automatically fed and the image of the document is read, the first carriage 106 and the second carriage 107 move below the sheet-through reading slit 111. Thereafter, the document placed on the document tray 201 is automatically fed in the arrow B direction (sub-scanning direction) by the feeding roller 202, and the document is scanned at the position of the sheet through reading slit 111. At this time, the lower surface (image surface) of the automatically fed document is illuminated by the light source 102 of the first carriage 106. The reflected light image from the image plane is passed through the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and then to the photoelectric conversion element 109 via the lens unit 108. Images are sent sequentially. It is converted into a digital signal by photoelectric conversion of the photoelectric conversion element 109 and outputted, and is converted into a digital signal by an image processing unit (not shown) in the subsequent stage. As a result, the image of the original is read and digital image data is obtained.

  The document whose image has been read as described above is discharged to a discharge port (not shown). Note that the reflected light from the white plate 110 is converted into a digital signal by the photoelectric conversion element 109 by illumination by the light source 102 started before the image reading in the scan reading mode or the sheet through reading mode. As a result, the white plate 110 is read, and shading correction at the time of image reading of the document is performed based on the reading result (white reference data). It should be noted that in the level correction when executing intermittent shading, the operation for reading the white plate 110 is omitted once every few minutes of reading the document, or once every several sheets.

  Next, a functional configuration example of the image reading unit 100 will be described. FIG. 2 is a block diagram illustrating a functional configuration example of the image reading unit of the image reading apparatus according to the present embodiment.

  The image reading unit 100 includes a light source 102, a photoelectric conversion element 109, a distribution generation unit 11, a level correction coefficient calculation unit 12, a shading correction unit 13, and a document detection sensor 14.

  The image reading unit 100 illuminates a subject (original, white plate 110, background plate 112, etc.) with light emitted from the light source 102, and photoelectrically converts the reflected light from the subject into an electrical signal by the photoelectric conversion element 109. Output as a signal. Background plate data obtained by reading the background plate 112 in the digital signal output from the photoelectric conversion element 109 is transmitted to the distribution generation unit 11, the level correction coefficient calculation unit 12, and the shading correction unit 13. Each process is performed by a circuit that forms the correction coefficient calculation unit 12 and the shading correction unit 13. Also, the original data read from the original and the white reference (white plate) data read from the white plate 110 in the digital signal output from the photoelectric conversion element 109 are transmitted to the shading correction unit 13 to form the shading correction unit 13. Each process is performed by a circuit that performs the processing. The document data finally subjected to the shading correction by the shading correction unit 13 is then transmitted to a subsequent processing unit (not shown). The post-processing unit performs various corrections such as dot correction and color correction, and other image processing such as scaling, but the detailed description is omitted because it is the same as general processing.

  Although not shown in FIG. 1, the document detection sensor 14 is inside the ADF 200, and detects the leading edge and the trailing edge of the document when the document is conveyed to the sheet-through reading slit 111, thereby detecting the document. The signal F_de is output.

  As described above, the light source 102 irradiates the subject reading surface with light for subject exposure.

  Next, the photoelectric conversion element will be described. FIG. 3 is a block diagram illustrating a functional configuration example of the photoelectric conversion element. As shown in FIG. 3, the photoelectric conversion element 109 includes a predetermined number (plurality) of light receiving elements 20 arranged in the main scanning direction, a timing generation unit 21, and a pixel signal output unit 22. The predetermined number is arbitrary. The photoelectric conversion element 109 irradiates a subject (for example, a document, a white plate 110, a background plate 112, etc.) from the light source 102, photoelectrically converts reflected light from the subject, and reads image data of the subject. The photoelectric conversion element 109 is configured by an image sensor such as a CMOS (Complementary MOS), for example, in which a plurality of light receiving elements 20 are arranged in the main scanning direction. The light receiving element 20 is a semiconductor diode that functions as a photodetector. A plurality of light receiving elements 20 are arranged in the photoelectric conversion element 109 by the number of main scanning pixels (0 pixels to n pixels). The light receiving element 20 corresponding to each pixel converts reflected light of the light emitted from the light source 102 onto the subject into an electric signal (photoelectric conversion), and accumulates electric charges. Thereafter, the accumulated charge is transmitted to the pixel signal output unit 22 as a digital signal through processing by an amplifier, an A / D converter, or the like (not shown). As the light receiving element 20, for example, a photodiode or the like can be used. In addition, as a solid-state imaging device that is a semiconductor image sensor, a CMOS image sensor, a CCD (Charge Coupled Device) image sensor, or the like that uses a photodiode that detects light and generates charges as a photoelectric conversion element can be used. . In the CMOS image sensor, the charge converted for each photodiode is amplified and output.

  The timing generation unit 21 generates a signal transmission timing control signal. Slsync is a synchronization clock for one main scanning line, mclk is a synchronization clock for one pixel, sw is a paper interval (between originals) between the original and the next original, and an original reading period. It is a gate signal for switching between. Note that the sw signal is generated in synchronization with the output signal F_de of the document detection sensor 14. The timing generation unit 21 generates a synchronization signal slsync that determines a cycle for outputting a signal for each pixel of image data.

  In addition, the timing generation unit 21 is configured such that a part of the light receiving elements 20 emits reflected light from the background plate 112 in a first period from when a pixel signal output unit 22 described later reads a previous document until the next document is read. When outputting a signal photoelectrically converted for each pixel, a period in which a part of the light receiving elements 20 selected from a predetermined number of light receiving elements 20 outputs a signal obtained by photoelectrically converting reflected light from the background plate 112 for each pixel, In the second period, a synchronization signal is generated that is set shorter than a period in which a predetermined number of light receiving elements 20 output all the signals photoelectrically converted for each pixel. That is, a period in which some pixel signals are output from the background plate data in the first period from reading the previous document to reading the next document, and all pixel signals from the document data in the second period for reading the document. A synchronization signal set shorter than the output cycle is generated. As a result, only a part of the pixel signals is output without outputting all the pixel signals from the background plate data, so that the time can be shortened.

  In addition, the timing generation unit 21 is a period in which a part of the light receiving elements 20 selected from the predetermined number of light receiving elements 20 in the first period outputs a signal obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel. The first period setting and the second period setting, which is a period for outputting all signals photoelectrically converted for each pixel by the predetermined number of light receiving elements 20 in the second period, are held. The first period setting and the second period setting are switched by a pixel signal output unit 22 described later. The first period setting and the second period setting are arbitrarily set in advance.

  In the pixel signal output unit 22, an arbitrary pixel to be read (an arbitrary pixel signal to be output) is set, and data that is image data is output. A detailed description of the pixel signal output unit 22 will be described later.

  By performing one line of image data for a document line a plurality of times by the above processing, two-dimensional read data can be acquired by a one-dimensional line sensor (for example, a CMOS image sensor).

  Next, the pixel signal output unit 22 will be described. The pixel signal output unit 22 is a part of a predetermined number of light receiving elements arranged in the main scanning direction in a first period from reading a previous document to reading a next document when continuously reading a plurality of documents. The light receiving element outputs a signal obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel. And the signal for every pixel is output with the period according to the signal number of the pixel to output. That is, the first period corresponds to the case where the background plate 112 is read. In the case where the background plate 112 is read, the pixel signal output unit 22 detects the reflected light from the background plate 112 for each pixel. Output the converted signal.

  In addition, the pixel signal output unit 22 outputs all signals photoelectrically converted for each pixel by a predetermined number of light receiving elements arranged in the main scanning direction in the second period other than the first period. And the signal for every pixel is output with the period according to the signal number of the pixel to output. That is, the second period corresponds to the case of reading an original, and the pixel signal output unit 22 outputs all signals photoelectrically converted for each pixel by a predetermined number of light receiving elements arranged in the main scanning direction when the original is read. .

  Note that some of the light receiving elements 20 selected from the predetermined number of light receiving elements 20 are selected at arbitrary intervals in the main scanning direction. Here, the arbitrary interval means that the interval between the light receiving elements 20 in the central portion in the main scanning direction is rough and the interval between the light receiving elements 20 at both end portions in the main scanning direction is close, or with respect to the main scanning direction. Or even intervals. However, the present invention is not limited to this, and the intervals of the selected light receiving elements 20 can be arbitrarily set.

  Further, when reading a plurality of documents continuously, the pixel signal output unit 22 causes some of the light receiving elements 20 from the background plate 112 during the first period from reading the previous document to reading the next document. It is selected to output a signal obtained by photoelectrically converting the reflected light for each pixel. In addition, when reading a document in the second period, the pixel signal output unit 22 selects that a predetermined number of light receiving elements arranged in the main scanning direction output all signals photoelectrically converted for each pixel.

  The pixel signal output unit 22 outputs a signal obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel by a part of the light receiving elements 20 selected from the predetermined number of light receiving elements 20 in the first period. The signal output setting and the second signal output setting for outputting all signals photoelectrically converted for each pixel by the predetermined number of light receiving elements 20 in the second period are held. The pixel signal output unit 22 changes the first signal output setting and the first cycle with respect to the first cycle setting and the second cycle setting held by the timing generation unit 21 when changing each setting. The setting is changed at the same time, and the second signal output setting and the second cycle setting are changed at the same time.

  FIG. 4 is a diagram illustrating a functional configuration example of the pixel signal output unit. As shown in FIG. 4, the pixel signal output unit 22 includes a register 31 and a selector 32. The register 31 is a storage element that stores in advance settings of a pixel (signal to be output) to be read out from all the pixel signals transmitted to the pixel signal output unit 22. In the following, “output signal setting” when the light receiving element 20 outputs a photoelectrically converted signal for each pixel is also referred to as “read pixel setting”.

  As shown in FIG. 4, for example, (1) setting for reading all the pixels 0 to n in the main scanning direction for normal reading, as shown in FIG. The predetermined number of light receiving elements 20 arranged in the main scanning direction is set to output all signals photoelectrically converted for each pixel. Also, for example, (2) for reading background plate data as a reference member (background plate 112), a setting for reading only an arbitrary pixel among pixels 0 to n in the main scanning direction, that is, a predetermined number of pixels A part of the light receiving elements 20 selected from the light receiving elements 20 is set to output a signal obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel. The above two types of settings are shown as an example.

  In addition to the settings of the pixels to be read, slsync, which is a line synchronization signal, stores in advance the settings of the line synchronization signal (slsync) associated with the above settings (1) and (2). Here, the line synchronization signal indicates a synchronization signal that determines a cycle for outputting a signal photoelectrically converted for each pixel in accordance with the number of signals to be output. Note that the setting of the pixel to be read and each setting of the associated line synchronization signal can be arbitrarily set.

  The selector 32 switches the setting of the pixel to be read (setting of the signal to be output) stored in the register 31. The selector 32 switches the setting of the pixel to be read out when the sw signal output from the timing generation unit 21 is input. The selector 32 can switch the setting of the pixel to be read out at a high speed by inputting the sw signal. Since the sw signal is generated in synchronization with the output signal F_de of the document detection sensor 14 described above, for example, when the document is conveyed to the sheet-through reading slit 111, the leading edge and the trailing edge of the document. The sw signal is generated in synchronization with the output signal F_de that has detected Thereby, for example, when the leading edge of the document is detected, the setting for reading all of the pixels 0 to n in the main scanning direction is selected for the above-described (1) normal reading mode which is a mode for reading the document. Further, for example, when the rear end portion of the document is detected, the background which is the above-described (2) reference member (background plate 112) is a mode in which the background plate 112 is read between sheets between the document and the next document. For reading plate data, a setting is selected to read only an arbitrary pixel among pixels 0 to n in the main scanning direction.

  Through the above processing, the pixel signal output unit 22 outputs the slsync signal that is a line cycle signal and the data that is image data according to the setting that is switched and selected by the input of the sw signal.

  As described above, the pixel signal output unit 22 converts the reflected light of the light emitted to the subject by the plurality of light receiving elements 20 arranged in the number corresponding to the number of pixels in the main scanning direction into an electric signal, which is transmitted as a digital signal. Output the pixel signal. In the case of outputting a pixel signal, the setting of the readout pixel (setting of the output signal) stored in advance in the register 31 is selected by the selector 32, and only the set readout pixel (output pixel signal) is read out.

  Next, specific timing examples of pixel readout in the above-described readout pixel settings (1) and (2) will be described. 5A and 5B are diagrams illustrating the timing of each signal from the pixel signal output unit.

  First, the sw signal is sw = L in synchronism with the output signal F_de of the document detection sensor 14 in a normal time (hereinafter, “when reading a document”). As shown in FIG. 5A, the setting when sw = L is (1) a setting for reading all of the pixels 0 to n in the main scanning direction. That is, this is a setting for reading a document and acquiring image data of the document. The setting of slsync when sw = L is synchronized with a period (optical signal accumulation time) in which all 0 pixels to n pixels of the data 1 line are read (during a normal reading operation shown in FIG. 5A).

  Next, after reading the set number of lines of pixels in the main scanning direction, that is, after reading the image data of one original, sw = in synchronization with the output signal F_de of the original detection sensor 14. From L to sw = H, it becomes a reading period between sheets which is between the original and the next original (between originals). In this case, the setting when sw = H is a setting for reading only an arbitrary pixel among the above-described (2) pixels 0 to n in the main scanning direction. That is, it is a setting for reading the background plate 112 and acquiring the background plate data over time between the sheets. In the example shown in FIG. 5B, as an example of the setting of (2) above, only pixels 0, 2, 4,... That is, the number of pixels to be read is halved compared to reading all the numbers of pixels at the time of document reading. At the same time, the setting of slsync when sw = H is ½ of the period (optical signal accumulation time) in which only even-numbered pixels are read from 0 to n pixels of the data 1 line compared to the setting of (1) above. Is the period. In this way, when sw = H is set, the cycle for reading an arbitrary pixel can be shortened to ½ (at the time of reading the background plate shown in FIG. 5B).

  The example of FIG. 5B is an example in the case of reading out even-numbered pixels (intervals of every other pixel). For example, in the case of reading out at intervals of every two pixels, the line cycle slsync is compared with the setting of (1) above. Thus, the period can be shortened to 1/3. In addition, for example, when reading is performed at intervals of every three pixels, slsync can be shortened to ¼ period compared to the setting of (1) above. Similarly, in the case of reading at intervals of every 4 to n pixels, it can be shortened to a period of 1/4 to 1 / n.

  In addition, since the readout pixels can be arbitrarily set by setting the register 31, the intervals may be determined by adding a portion of the pixels in the main scanning direction instead of the regular intervals as described above. For example, when reading an image having a uniform density, the image data obtained by reading the image data in the main scanning direction has the reading levels at both ends in the main scanning direction from the center in the main scanning direction due to the characteristics of the lens and the light source. Tend to be lower. For this reason, in light sources using LEDs, there are cases where, for example, LED chips are arranged more closely at both ends than at the center. The variation in the light amount distribution over time in the main scanning direction at the time of continuous reading is due to the large decrease in the light amount due to heat generation.For example, according to the above LED light source configuration, both ends are more This means that the light quantity distribution variation is large. In that case, the read pixels of the background plate data should also be densely arranged according to the change in the amount of light so that both ends with large fluctuations are correspondingly dense and the central part with little fluctuations is coarse. Thus, the correction accuracy can be improved.

  As described above, in the case of continuously reading a document, there is an advantageous effect that the productivity time can be greatly shortened by reading only an arbitrary pixel by shortening the line cycle during the background plate reading operation. be able to.

  Next, the distribution generation unit 11 will be described. FIG. 6 is a diagram illustrating the distribution generation unit. As shown in FIG. 6, the distribution generation unit 11 includes an interpolation circuit 41. The interpolation circuit 41 corresponds to an “interpolation unit” in the claims. Of the data (image data) output from the pixel signal output unit 22, the image data of the background plate 112 is input to the interpolation circuit 41 of the distribution generation unit 11. Although not shown in FIG. 2, the pixel signal output unit 22 performs switching by the selector 32 based on the sw signal, and outputs the image data of the background plate 112 to the distribution generation unit 11 in the data.

  The interpolation circuit 41 calculates (interpolates) the remaining pixel signals that have not been read out using a part of the pixel signals read out from the pixel signal output unit 22, and performs one line in the main scanning direction of the background plate data. All pixel signals are generated. As a method of calculating (interpolating) the remaining pixel signals that have not been read, for example, the remaining pixel signals can be calculated (interpolated) by linear interpolation using the preceding and following read pixel signals. Further, as a pixel signal interpolation method, for example, a generally used method such as a cubic method can be applied.

  Further, the interpolation method may be changed depending on the reading mode, for example, when the document data is text or the document data is a photograph. Note that a general interpolation method can be used for pixel signal interpolation, but linear interpolation is preferable because it requires a small amount of calculation and can form an approximate distribution.

  When a part of the light receiving elements 20 outputs a signal obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel in the first period, the interpolation circuit 41 photoelectrically converts the reflected light from the background plate 112 for each pixel. The signals output from some of the light receiving elements 20 are interpolated so as to be signals of a predetermined number of light receiving elements, that is, pixel signals of one line in the main scanning direction.

  Further, the interpolation circuit 41 is not selected by linear interpolation using a signal output by photoelectric conversion of the reflected light from the background plate 112 for each pixel by some of the light receiving elements 20 selected in the first period. The signals of the remaining light receiving elements 20 are calculated, and distribution data of signals of all lines in the main scanning direction, which is a predetermined number, is generated.

  As a result, since it is not necessary to output all the signals photoelectrically converted for each pixel in the background plate data, the cycle of outputting (reading) an arbitrary pixel signal from all the pixel signals of one line in the main scanning direction is halved. The following can be shortened.

  FIG. 7A and FIG. 7B are diagrams for explaining generation of distribution data of pixel signals of all one line in the main scanning direction of background plate data in the distribution generation unit. As shown in FIGS. 7A and 7B, the distribution generation unit 11 calculates the remaining pixel signals that have not been read (not output) in the main scanning direction of the background plate data by linear interpolation and Distribution data of pixel signals of all one line is generated. In the example of FIGS. 7A and 7B, an initial background plate level (pixel signal level) and a time-dependent background plate level (pixel signal level decreased with time) are shown. 7A and 7B, the horizontal axis represents main scanning pixels (pix) in the main scanning direction, and the vertical axis represents pixel signal levels (digit / 8 bits) in the main scanning direction.

  The example of FIG. 7A is an example in which only even-numbered pixels in the main scanning direction of the background plate data are read to generate pixel signal distribution data for all the lines in the main scanning direction. The distribution generation unit 11 reads out some pixels (only even-numbered pixels) from all the pixel signals of one line in the main scanning direction of the background plate data, and the remaining pixel signals that have not been read (in this example, odd-numbered pixels) And the distribution data of the pixel signals of all the lines in the main scanning direction of the background plate data are generated. In this example, linear interpolation is used for pixel signal interpolation. In the example of FIG. 7A, when the pixel signal level of the first pixel is X1, and the read pixel signal levels adjacent to X1 are X0 and X2, the value of X1 is calculated by the following equation (1).

X1 = (X0 + X2) × 1/2 (1)
Similarly, the pixel signal levels X3 and X5 of the third pixel and the fifth pixel are
X3 = (X2 + X4) × 1/2
X5 = (X4 + X6) × 1/2
Is calculated by

  As described above, the remaining pixel signals that have not been read out are calculated (interpolated) using a part of the pixel signals that have been read out, and the pixel signals of all the lines in the main scanning direction of the background plate data are calculated. Generate distribution data.

  In the example of FIG. 7B, in accordance with the light amount distribution variation of the light source described above, the distribution data of all the pixel signals of one line in the main scanning direction is generated by adding and reading out the read pixels in the main scanning direction of the background plate data. It is an example. The distribution generation unit 11 reads out pixels from all the pixel signals of one line in the main scanning direction of the background plate data, roughly reading the pixels in the central portion in the main scanning direction and densely in the both end portions in the main scanning direction. Interpolation of the remaining pixel signals (in this example, the first pixel to the (m-1) th pixel) (not output) is performed to generate distribution data of pixel signals for all the lines in the main scanning direction of the background plate data. . In this example, linear interpolation is used for pixel signal interpolation. In the example of FIG. 7B, pixel signals to be interpolated are the first pixel to the (m−1) th pixel. In the example of FIG. 7B, when the pixel signal level of the first pixel is X1, the read pixel signal level adjacent immediately before X1 is X0, and the pixel signal level of the m-th pixel is Xm, the value of X1 is expressed by the following equation: Calculated in (2).

X1 = (Xm−X0) × 1 / m + X0 (2)
Similarly, the pixel signal levels X2 and X3 of the second pixel and the third pixel are
X2 = (Xm−X0) × 2 / m + X0
X3 = (Xm−X0) × 3 / m + X0
Is calculated by

  As described above, the linear interpolation for calculating the remaining pixel signals that have not been read out is represented by the following general formula (3).

Xl = {(Xm−Xk) / (m−k)} × (l−k) + Xk (3)
(Where k <l <m, l: pixel signal level of the pixel to be interpolated, k, m: adjacent readout pixels)

  Note that the fluctuation of the light intensity distribution over time of the light source generally does not cause the reading level of the background plate data to change suddenly in several pixels, and the distribution data of the pixel signal in the main scanning direction changes gradually over time. To do. Therefore, correction can be performed with sufficient accuracy by setting the interval between read pixels to several pixels to several tens of pixels.

  As described above, in the image data of the background plate 112, it is not necessary to read out all the pixel signals of one line in the main scanning direction, and the remaining unread pixels are read using a part of the read pixel signals. Since the pixel signal is calculated and the distribution data of all the pixel signals in the main scanning direction of the background plate data is generated, the distribution data of all the pixel signals in the main scanning direction of the background plate data can be obtained. . As a result, in the background plate data, the period for reading (outputting) an arbitrary pixel signal from all the pixel signals in one line in the main scanning direction can be shortened to ½ or less, thereby shortening the background plate reading time. can do.

  Next, the level correction coefficient calculation unit 12 will be described. The level correction coefficient calculation unit 12 includes all signals (initial background plate data) obtained by photoelectrically converting the reflected light from the background plate 112 for each pixel before the first original reading, and 1 in the main scanning direction generated by the interpolation circuit 41. A level correction coefficient for correcting image data of a document is calculated using distribution data (time-lapse background plate data) of all lines.

  If the calculated level correction coefficient is not within the set threshold range, the level correction coefficient calculation unit 12 does not use the calculated level correction coefficient, but calculates the level correction coefficient immediately before being within the threshold range. Use.

  FIG. 8 is a diagram illustrating a functional configuration example of the level correction coefficient calculation unit. As shown in FIG. 8, the level correction coefficient calculation unit 12 includes a register 51, a divider 52, and a comparator 53. The register 51 stores initial background plate data hdata0 of the background plate 112 read in advance before reading the first original. Further, the register 51 stores a threshold value h_lim of a level correction coefficient that is arbitrarily set in advance, which will be described later. The divider 52 uses the initial background plate data hdata0 and the time-lapse background plate data hdata of the background plate 112 read over time, and is a reciprocal of the decay rate of the reading value (pixel signal level) over time. A level correction value (hereinafter referred to as a level correction coefficient) h_co of the distribution data of the pixel signal in the direction is calculated by the following equation (4).

h_co = hdata0 / hdata (4)
(However, when reading the first sheet, hdata = hdata0)

  The comparator 53 is used for dust detection described later. The comparator 53 compares the level correction coefficient threshold value h_lim arbitrarily set and stored in advance in the register 51 with the level correction coefficient h_co calculated from each pixel using the above equation (4). The comparator 53 compares the level correction coefficient h_co calculated by the divider 52 with the threshold value h_lim previously stored in the register 51. If the level correction coefficient h_co is within the threshold value range, the level from the comparator 53 is compared. If the correction coefficient h_co is output and the level correction coefficient h_co is outside the threshold range, the level correction coefficient h_co from the comparator 53 outputs the level correction coefficient h_co calculated immediately before being within the threshold range.

  FIG. 9 is a diagram for explaining the level correction coefficient when dust or dirt adheres to the background plate 112. In the example of FIG. 9, the initial background plate level (pixel signal level) and the time-lapse background plate level (pixel signal level decreased with time) are shown. In FIG. 9, the horizontal axis represents main scanning pixels (pix) in the main scanning direction, and the vertical axis represents pixel signal levels (digit / 8 bits) in the main scanning direction.

  Since the background plate 112 is in the document conveyance path, dust and dirt may adhere to the background plate 112 during document conveyance. As shown in the upper side of FIG. 9, the initial background plate level of the background plate 112 read in advance before reading the first document is a state in which dust and dirt are not attached. When dust or dirt adheres to the background plate 112 while the document is being conveyed over time, as shown in the lower side of FIG. The signal level is low. When the level correction coefficient h_co is calculated using the above equation (4) in the state of the background plate level over time shown in FIG. 9, the pixel signal level of the dust mixed portion of the background plate 112 is higher than the pixel signal levels before and after that. Since the level correction coefficient has a high value, the background plate 112 dust mixed portion appears as a vertical stripe in the output image after correction. Note that an arrow ↑ shown in the blowing portion in FIG. 9 represents the level correction coefficient value in each pixel.

  Therefore, in order to detect dust and dirt, a threshold value is set in advance for the level correction coefficient, and there is a level correction coefficient value that falls outside the range of the predetermined threshold value. In this case, without using the level correction coefficient value outside the threshold range, the level correction coefficient of the pixel immediately before going out of the threshold range, that is, the previous level correction coefficient value within the threshold range is used. Incorrect correction due to dust and dirt can be prevented.

  Therefore, by including the configuration of the comparator 53 in the level correction coefficient calculation unit 12, dust and dirt can be detected without increasing the memory and the like, so that erroneous level correction can be prevented.

  Next, the shading correction unit 13 will be described. The shading correction unit 13 performs shading correction based on a predetermined number of signals interpolated by the interpolation circuit 41. Further, the shading correction unit 13 photoelectrically converts all the reflected light from the white plate 110 for each pixel (white reference data) before reading the first document, and the level correction coefficient calculated by the level correction coefficient calculation unit 12. Is used to perform shading correction on the image data of the document.

  In addition, when the level correction coefficient calculated by the level correction coefficient calculation unit 12 is not within a predetermined threshold range, the shading correction unit 13 does not use the calculated level correction coefficient and uses the threshold correction coefficient. The immediately preceding level correction coefficient within the range is used.

  FIG. 10 is a diagram illustrating a functional configuration example of the shading correction unit. As shown in FIG. 10, the shading correction unit 13 includes a register 61, a divider 62, a multiplier 63, and a register 64. The register 61 stores white reference (white plate) data wdata read in advance before reading the first original. The divider 62 performs normalization for each pixel using the document data data and the white reference (white plate) data wdata. The multiplier 63 multiplies the original data normalized by the divider 62 by the level correction coefficient h_co output from the level correction coefficient calculation unit 12 and the quantization level number stored in advance in the register 64. The final output image data odata is calculated. The register 64 stores a preset number of quantization levels as described above.

The final document data can be calculated by the following equation (5).
odata = (data / wdata) × 1023 × h_co (5)
(Note that 1023 is the number of quantization levels in 10 bits)

  2, the level correction coefficient calculation unit 12 illustrated in FIG. 8 and the shading correction unit 13 illustrated in FIG. 10 are separated from each other. However, the level correction coefficient calculation unit 12 is included in the shading correction unit 13. Can be configured.

  Next, an operation example of the image reading apparatus 1 according to the present embodiment will be described. FIG. 11 is a flowchart illustrating an example of a document continuous reading process operation of the image reading apparatus. In the following example, an example of a document continuous reading process operation when level correction is performed when intermittent shading is performed will be described. As shown in FIG. 11, in the sheet-through reading mode, the image reading apparatus 1 sets the pixel setting read by the register 31 of the pixel signal output unit 22 as an initial setting as shown in FIG. (Step S11).

  Next, it is determined whether or not the original scan is the first original reading (step S12). If the read original is the first page (step S12: Yes), the image reading apparatus 1 moves the first carriage 106 to below the white plate (white reference member) 110 (step S13). The image reading apparatus 1 reads the white plate 110 to acquire white reference data, and holds it in the register 61 of the shading correction unit 13 (step S14). Thereafter, the carriage 106 is moved to the home position (step S15).

  Next, the background plate 112 is read, initial background plate data is acquired, and held in the register 51 of the level correction coefficient calculation unit 12 (step S16). Next, in the image reading apparatus 1, the level correction coefficient calculation unit 12 calculates the level correction coefficient using the initial background plate data and the time-lapse background plate data (step S17). Here, at the time of reading the first sheet, the level correction coefficient is “1” as described in FIG.

  Next, continuous reading of the document starts, the document is detected by the document detection sensor 14 in the ADF 200 described above (step S18), and sw is generated in synchronization with the output signal F_de. The image reading apparatus 1 sets the pixel to be read from the register 31 of the pixel signal output unit 22 by the sw signal for (1) normal reading shown in FIG. 4 (step S19). Here, at the time of reading the first sheet, the setting is the same as the initial setting. Next, the original is read (step S20).

  Next, in the image reading apparatus 1, the shading correction unit 13 performs shading correction on the read document data using the white reference data and the calculated level correction coefficient value (step S21). Next, the image reading apparatus 1 determines whether there is a next document (step S22). If there is no next original (step S22: No), the process is terminated. If there is a next document (step S22: Yes), the process proceeds to step S12 and the process is continued.

  Returning to step S12, when the read original is not the first page (step S12: No), the image reading apparatus 1 shows the pixel settings read by the register 31 of the pixel signal output unit 22 in FIG. 4 (2). Switching to background plate reading is set (step S23). Next, the image reading apparatus 1 reads the background plate 112 and obtains background plate data over time (step S24). Next, the image reading device 1 has not been read by using the partial background signal data read from the pixel signal output unit 22 by the distribution generation unit 11 using the acquired background plate data over time. The remaining pixel signals are calculated (interpolated) to generate distribution data of pixel signals of all the lines in the main scanning direction of the background plate data (step S25).

  Next, the process proceeds to step S17, and the processing after step S17 is continued. That is, in the image reading apparatus 1, the level correction coefficient calculation unit 12 calculates the level correction coefficient using the initial background board data and the time-lapse background board data (step S17). Next, continuous reading of the document starts, the document is detected by the document detection sensor 14 in the ADF 200 described above (step S18), and sw is generated in synchronization with the output signal F_de. The image reading apparatus 1 sets the pixel to be read by the register 31 of the pixel signal output unit 22 in accordance with the sw signal by switching to (1) normal reading shown in FIG. 4 (step S19). In other words, when the second original is read, the setting of the pixel read by the register 31 of the pixel signal output unit 22 is switched from (2) background plate reading to (1) normal reading in step S19.

  Next, the original is read (step S20). Next, in the image reading apparatus 1, the shading correction unit 13 performs shading correction on the read document data using the white reference data and the calculated level correction coefficient value (step S21). Next, the image reading apparatus 1 determines whether there is a next document (step S22).

  Note that the setting of the pixel to be read by the register 31 of the pixel signal output unit 22 is switched between the output signal F_de output by the document detection sensor 14 detecting the trailing edge of the document when reading of the document is completed in step S20. Based on the sw signal generated in synchronization, it can be determined that the sheet interval is between the original and the next original, and (2) it can be switched and set for background plate reading. In this case, between the step S20 and the step S21, the above-described (2) processing for switching to background plate reading is performed, and the processing of the step S23 subsequent to the step S12 (No) is unnecessary, and the processing after the step S24 is performed. Processing is performed.

  By causing the image reading apparatus 1 to execute the above processing, the background plate is calculated (interpolated) by calculating (interpolating) the remaining pixel signals that have not been read using a part of the pixel signals of the background plate data when performing level correction. Since the distribution data of the pixel signals of all the lines in the main scanning direction of the data is generated, there is an advantageous effect that the reading time of the background plate 112 can be greatly shortened.

  Next, an image forming apparatus 300 equipped with the image reading apparatus 1 of the present embodiment will be described. FIG. 12 is a diagram illustrating a configuration example of a mechanism unit of the image forming apparatus according to the present embodiment. As shown in FIG. 12, the image forming apparatus 300 will be described by taking, for example, a digital copying machine equipped with the image reading apparatus 1 shown in FIG. In the example of FIG. 12, the image reading apparatus 1 includes the image reading unit 100 and the ADF 400. In the image forming apparatus 300, an ADF 400 is provided on an upper part of a contact glass 101 on which a document is placed, and the ADF 400 is connected to the contact glass 101 via a hinge or the like (not shown) so that the ADF 400 can be opened and closed. The ADF 400 is the same as the ADF 200 shown in FIG.

  The ADF 400 includes a document tray 401 as a document placement table on which a document bundle composed of a plurality of documents can be placed. In addition, when a print key on an operation unit (not shown) is pressed, the originals are separated one by one from the original bundle placed on the original tray 401 with the image surface facing upward, and automatically fed to the sheet through reading slit 111. Alternatively, separation / feeding means including a feeding roller 402 and a conveying belt 403 that are conveyed toward the contact glass 101 is also provided. The document fed by the feeding roller 402 or the conveying belt 403 is read out as described with reference to FIG. 1 and then discharged onto the upper surface of the ADF 400 by the conveying belt 403 and the discharging roller 404.

  The image reading unit 100 includes a contact glass 101, a first carriage 106 including a light source 102 and a first reflection mirror 103, a second carriage 107 including a second reflection mirror 104 and a third reflection mirror 105, and a lens unit 108. , A photoelectric conversion element 109, a reference member 110, and a sheet-through (continuous) reading slit 111.

  Here, the operation of the controller (not shown) and the ADF 400 when the document is conveyed to the reading position of the contact glass 101 by the ADF 400 will be described. The feed motor of the ADF 400 is driven by an output signal from the controller. When the feed start signal generated by pressing the print key on the operation unit is input, the controller corrects the feed motor.・ Reverse drive. When the feeding motor is driven to rotate forward, the feeding roller 402 rotates clockwise to automatically feed the document located at the highest position from the bundle of documents toward the sheet through reading slit 111 or the contact glass 101. Be transported. When the leading edge of the document is detected by the document detection sensor 405, the controller drives the feed motor in the reverse direction based on the output signal from the document detection sensor 405. This prevents subsequent documents from entering and prevents separation.

  When the document detection sensor 405 detects the trailing edge of the document, the controller counts a rotation pulse of a conveyance belt motor (not shown) from this detection time point, and drives the conveyance belt 403 when the rotation pulse reaches a predetermined value. Is stopped and the conveying belt 403 is stopped, whereby the document is stopped at the reading position on the contact glass 101. Further, when the trailing edge of the document is detected by the document detection sensor 405, the feeding motor is driven again, and the subsequent document is separated and automatically fed as described above. Then, the sheet is conveyed toward the contact glass 101, and when the pulse of the feeding motor from the time when the document is detected by the document detection sensor 405 reaches a predetermined pulse, the feeding motor is stopped and the next document is stopped. First wait.

  When the document stops at the reading position on the contact glass 101, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveyance belt motor in the normal direction by this signal, and the document is discharged from the contact glass 101 by the conveyance belt 403 to the discharge roller. Unload to 404.

  As described above, the document bundle placed on the document tray 401 in the ADF 400 with the image surface of the document facing up is automatically fed from the top document by pressing the print key, for example, a reading position on the contact glass 101. It is conveyed to. The document which has been conveyed to the reading position and stopped is discharged from the discharge port by the conveying belt 403 or the like after reading the image. Further, when it is detected that there is a next document on the document tray 401, the next document is automatically fed and conveyed onto the contact glass 101 like the previous document.

  The transfer sheets (paper sheets) stacked on the first tray 301, the second tray 302, and the third tray 303, which are sheet feeding trays, are a first sheet feeding unit 311, a second sheet feeding unit 312, and a third sheet feeding unit, respectively. The sheet is fed by 313 and conveyed by the vertical conveyance unit 314 to a position where it abuts on a drum-shaped photosensitive member (photosensitive drum) 315 as an image carrier. Actually, any one of the trays 301 to 303 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

  On the other hand, the image data read by the image reading unit 100 is written onto the surface of the photoreceptor 315 that is pre-charged by a charging unit (not shown) by a laser beam from a writing unit 350 in the printer, which is an image forming unit. When the surface is exposed), the portion passes through the developing unit 327, and a toner image is formed there. The developing unit 327 that performs the image formation, the charging unit, and the like constitute image forming means.

  The transfer paper fed from the selected paper feed trays 301 to 303 is transferred by the transfer belt 316 at the same speed as the rotation of the photoconductor 315, and the toner image on the photoconductor 315 is transferred. Further, the toner image is fixed by the fixing unit 317, and is discharged by a paper discharge unit 318 to a paper discharge tray 319 outside the apparatus. At this time, for example, in order to reverse the transfer paper on which the toner image is formed on one side in order to discharge face-down (the image surface faces downward in order to align the transfer paper in the page order), the transfer paper is discharged. The paper is conveyed to the double-sided paper conveyance path 320 by the unit 318, switched reverse by the reversing unit 321, and then discharged to the paper discharge tray 319 through the reverse paper conveyance path 322.

  When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318 and is switched back by the reverse unit 321. After that, it is sent to the duplex conveying unit 323.

  The transfer paper sent to the double-sided conveyance unit 323 is fed again from the double-sided conveyance unit 323 to transfer the toner image formed on the photoconductor 315 again, and is again applied to the photoconductor 315 by the vertical conveyance unit 314. It is transported to the contact position. Then, after the toner image is transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photoconductor 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and the driving power of the main motor is transmitted to each paper feed unit 311 to 313 by a paper feed clutch. To be driven. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, and a mirror 353. Inside the laser output unit 351, a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) that scans the laser light. Or it has a vibrating mirror. The laser light emitted from the laser output unit 351 is deflected by a polygon mirror or a vibrating mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photoreceptor 315.

  As described above, according to the image forming apparatus (digital copying machine) 300 of the present embodiment, the image reading apparatus 1 of the present embodiment is provided, and the local light amount fluctuation of the light source in the level correction at the time of continuous multiple sheet copying. In addition, the reading speed can be improved and an image can be formed.

  As mentioned above, although embodiment of this invention was described, each above-mentioned embodiment was shown as an example and is not intending limiting the range of invention. The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, the above embodiments and modifications can be arbitrarily combined.

  The control program executed by the image reading device 1 of each of the above-described embodiments is a file in an installable format or an executable format, and is a CD-ROM, flexible disk (FD), CD-R, DVD (Digital Versatile). It may be configured to be recorded on a computer-readable recording medium such as Disk).

  Furthermore, the control program for executing the image reading device 1 of each of the above-described embodiments may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. . The control program for executing the image reading apparatus 1 of each of the above-described embodiments may be provided or distributed via a network such as the Internet.

DESCRIPTION OF SYMBOLS 1 Image reader 11 Distribution generation part 12 Level correction coefficient calculation part 13 Shading correction part 14 Document detection sensor 20 Light receiving element 21 Timing generation part 22 Pixel signal output part 31 Register 32 Selector 41 Interpolation circuit 51 Register 52 Divider 53 Comparator 61 Register 62 Divider 63 Multiplier 64 Register 100 Image reading unit 101 Contact glass 102 Light source 103 First reflecting mirror 104 Second reflecting mirror 105 Third reflecting mirror 106 First carriage 107 Second carriage 108 Lens unit 109 Photoelectric conversion element 110 Reference Material (white board)
111 Sheet Through Reading Slit 112 Background Plate 200 Automatic Document Feeder (ADF)
201 Document tray 202 Feed roller 300 Image forming apparatus 301 First tray 302 Second tray 303 Third tray 311 First paper feed unit 312 Second paper feed unit 313 Third paper feed unit 314 Vertical transport unit 315 Photosensitive drum 316 Conveying belt 317 Fixing unit 318 Discharging unit 319 Discharging tray 320 Double-sided paper conveying path 321 Reverse unit 322 Reversed paper conveying path 323 Double-sided conveying unit 327 Developing unit 350 Writing unit 351 Laser output unit 352 Imaging lens 353 Mirror 400 ADF
401 Document tray 402 Feed roller 403 Conveying belt 404 Discharge roller 405 Document detection sensor

JP 2008-022195 A

Claims (11)

When reading a plurality of documents continuously, some of the light receiving elements of a predetermined number of light receiving elements arranged in the main scanning direction from the reference member in the first period from reading the previous document to reading the next document. A pixel signal output unit that outputs a signal obtained by photoelectrically converting the reflected light of each pixel,
An interpolation unit that interpolates the signal output from a part of the light receiving elements obtained by photoelectrically converting the reflected light from the reference member for each pixel as a signal of the predetermined number of light receiving elements;
A shading correction unit that performs shading correction based on the predetermined number of signals interpolated by the interpolation unit;
An image reading apparatus comprising:   2. The pixel signal output unit outputs all signals photoelectrically converted for each pixel by the predetermined number of light receiving elements arranged in the main scanning direction in a second period other than the first period. The image reading apparatus described in 1. A timing generation unit that generates a synchronization signal for determining a period for outputting a signal photoelectrically converted for each pixel according to the number of signals to be output;
When the pixel signal output unit outputs a signal obtained by photoelectrically converting the reflected light from the reference member for each pixel in the first period, the timing generation unit includes a part of the light receiving element. Generating a synchronization signal in which the period in which the signal from the reference member is output is set shorter than the period in which the predetermined number of light receiving elements output all the signals in the second period,
The image reading apparatus according to claim 1 or 2. Some of the light receiving elements are selected at arbitrary intervals with respect to the main scanning direction,
The interpolation unit uses a signal output by photoelectrically converting reflected light from a reference member for each pixel by a part of the light receiving elements selected in the first period, and the remaining unselected by linear interpolation Calculating a signal of a light receiving element, and generating distribution data of signals of all the one line in the main scanning direction which is the predetermined number;
The image reading apparatus according to claim 1. The arbitrary interval is such that the interval between the light receiving elements in the center portion in the main scanning direction is coarse, and the interval between the light receiving elements at both end portions in the main scanning direction is close,
The image reading apparatus according to claim 4.   Before reading the first document, all signals obtained by photoelectrically converting the reflected light from the reference member for each pixel and the distribution data of all signals in one line in the main scanning direction generated by the interpolation unit are used. The image reading apparatus according to claim 4, further comprising a level correction coefficient calculation unit that calculates a level correction coefficient for correcting the image data. The shading correction unit performs shading correction on the image data of the document using all the signals obtained by photoelectrically converting the reflected light from the white reference member for each pixel before the first document reading and the level correction coefficient. What to do,
The image reading apparatus according to claim 6. If the level correction coefficient calculated by the level correction coefficient calculation unit is not within the set threshold range, the shading correction unit does not use the calculated level correction coefficient, but falls within the threshold range. Using a previous level correction factor,
The image reading apparatus according to claim 7. The pixel signal output unit includes a first signal output setting in which some of the light receiving elements output the signal from the reference member in the first period, and the predetermined number of light receiving elements output the signal in the second period. Hold the second signal output setting to output all,
The timing generator includes a first period setting in which a part of the light receiving elements outputs the signal from the reference member in the first period, and the predetermined number of light receiving elements outputs the signal in the second period. Holds the second cycle setting, which is the cycle for all output,
When changing each setting, the pixel signal output unit changes the first signal output setting and the first cycle setting at the same time, and simultaneously changes the second signal output setting and the second cycle setting. Changing,
The image reading apparatus according to claim 1, wherein: When reading a plurality of documents continuously, some of the light receiving elements of a predetermined number of light receiving elements arranged in the main scanning direction from the reference member in the first period from reading the previous document to reading the next document. A pixel signal output step for outputting a signal obtained by photoelectrically converting the reflected light of each pixel,
An interpolation step for interpolating the signals output from some of the light receiving elements obtained by photoelectrically converting the reflected light from the reference member for each pixel to be signals of the predetermined number of light receiving elements;
A shading correction step for performing shading correction based on the predetermined number of signals interpolated in the interpolation step;
An image reading method comprising:   An image forming apparatus comprising the image reading apparatus according to claim 1.

Images