JP5862293B2 - Image reading apparatus, automatic document feeder, and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus, an automatic document feeder, and an image forming apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads image data by irradiating light on a document and taking in light from the document uses a photoelectric conversion element array that is generally called an image sensor and in which photoelectric conversion elements are arranged in one line in the main scanning direction. The document image is read by moving the document relative to the image sensor in the sub-scanning direction or by transporting the document.

  Since the output of the image sensor includes dark output (hereinafter referred to as black level data) that is output from the element itself when no optical signal is incident, the output data of the image sensor. The black correction for subtracting the black level data from is performed.

  Further, in order to correct the influence on the image data by the light source or the reading optical system that illuminates the document, and to determine the reference white level, the reading result of the density reference member having a predetermined white color (hereinafter, this reading result) In general, shading correction using white level data (or white data) is performed (shading correction data generated from white level data is referred to as shading data). From the white level data, it is calculated by averaging a plurality of lines of pixels having the same main scanning pixel position).

  The shading correction is preferably performed every time the image is read because the light amount of the light source decreases with time. However, if the shading correction is performed every time the image is read, it is necessary to provide a shading data generation period. The nature will decline. In particular, when the white reference member reading position and the original data reading position are different in the sub-scanning direction, a process for moving the carriage is added, so that the production efficiency is remarkably reduced.

  As a technique for preventing such a decrease in production efficiency, at the original reading position, the original is read and at the same time the density reference member is read, and the result of reading the density reference member and the result of reading the previous density reference member are compared. A technique is known in which the degree of light reduction (correction coefficient) is obtained based on the comparison, and the time between sheets is shortened by further correcting the shading correction result.

  Further, in Patent Document 1, for the purpose of shortening the shading data generation time between sheets, the variation in the light amount reference value and the light amount fluctuation value acquired from the same portion among the plurality of portions of the facing member on the reading surface is the most. A technique for correcting the amount of light using a small amount is disclosed.

  By the way, in a CCD image sensor used in a reduction optical system scanner, an OPB pixel (optical black pixel), which is a pixel that detects an output in the dark without being reacted to light because the photoelectric conversion element is shielded from light, may be provided. Therefore, it is possible to perform black correction based on the black level data obtained from the OPB pixel every time the line is read.

  However, in an image reading apparatus using a configuration without OPB pixels, for example, a contact image sensor (CIS) in which a plurality of sensor IC chips (sensor chips) are arranged side by side, the reference black data (black level) is turned off once. From the data, it is necessary to generate (black correction data calculated by averaging a plurality of lines of pixels having the same main scanning pixel position). Therefore, when reading an original in an image reading apparatus using an image sensor having no OPB pixel, generally, the light source is once turned off, the reference black data is generated, the light source is turned on again, and the light amount after the light source is turned on. After waiting for the stabilization time, shading data and image data are acquired and black correction and shading correction are performed, resulting in a decrease in production efficiency.

  In order to shorten the time between sheets and increase productivity during continuous reading, it is conceivable to perform black correction with reference black data generated at the start of the job without turning off the light source between sheets. In this case, since the light source is continuously lit until the end of the job, the temperature of the sensor substrate rises due to the heat generated by the light source. For this reason, a difference in the amount of increase in dark current (amount of increase in black level) occurs due to a difference in temperature characteristics between sensor chips, resulting in a step difference for each chip in the final read image.

  When the reference black data is generated every paper interval in order to cope with this problem, the step difference for each chip due to the above black level fluctuation does not occur, but the light source is turned off, the reference black data is generated, the light source is turned on, and the light source is turned on again. It takes time to secure the light amount stabilization time, which takes time. Even in the case of shadingless in which shading data is generated only at the beginning of a job and no shading data is acquired between sheets, a light source relighting time is required before reading a document, and it is difficult to further reduce the sheet interval time. In particular, the light amount stabilization time after the light source is turned on depends on the temperature characteristics of the light source and depends on the immediately preceding light source turn-off time. Specifically, when the light source turn-off time is long, the temperature of the light source decreases and the time required for the light amount stabilization time increases. However, if the light source turn-off time is short, the light source temperature does not decrease, so the light source is turned on. There is a characteristic that the subsequent light quantity stabilization time can be shortened.

  However, in order to generate the reference black data with a certain degree of accuracy, data for a certain line period is necessary, and it is difficult to shorten the turn-off time. Therefore, there is a problem that it is difficult to reduce the sheet interval time while generating the reference black data in the continuous reading of the image reading apparatus using the image sensor having no OPB pixels.

  The present invention has been made in view of the above, and in continuous reading of an image reading apparatus using an image sensor having no OPB pixels, it reduces the time between sheets while generating reference black data between sheets. It aims to be able to do it.

In order to solve the above-described problems and achieve the object, an image reading apparatus according to the present invention includes a light source that irradiates light on a document, and an image sensor that photoelectrically converts reflected light from the document irradiated with light from the light source. In the image reading apparatus for acquiring image data, a lighting control means for adjusting the lighting period of the light source so as to alternately turn on and off in units of line periods outside the document reading period, and a document reading period If the image data read outside is smaller than a predetermined threshold, it is determined as black level data for generating reference black data used for black correction, and if it is larger than the threshold, it is used for generating shading data used for shading correction. and data discriminating means for discriminating the white level data, the reference black data from the black level data discriminated by the data discrimination means It means for forming, characterized by having a means for generating shading data from the white level data discriminated by the data discrimination means.

  According to the present invention, it is not necessary to secure the light amount stabilization time after the light source is turned on again by repeatedly turning on and off the light source in a predetermined line unit. Time can be reduced.

FIG. 1 is a diagram illustrating a schematic configuration of a copying machine as an image forming apparatus including an automatic document feeder having a function of the image reading apparatus according to the first embodiment. FIG. 2 is a cross-sectional view illustrating a configuration example of a mechanism system of the ADF in the first embodiment. FIG. 3 is a block diagram illustrating a configuration example of the control system of the ADF in the first embodiment. FIG. 4 is a block diagram showing main parts of an electric circuit of the second reading unit and the main body control unit. FIG. 5 is a diagram (timing chart) for explaining a case where lighting and extinguishing of the light source unit are alternately repeated (the number of lines in the lighting period and the extinguishing period is the same). FIG. 6 is a diagram (timing chart) illustrating a case where lighting and extinguishing are repeated alternately (the number of lines in which the lighting period and the extinguishing period are different). FIG. 7 is a diagram illustrating a case where lighting and extinguishing are repeated alternately (the number of lines in which the lighting period and the extinguishing period are different). FIG. 8 is a diagram (timing chart) for explaining a case where a period in which lighting and extinguishing are alternately repeated in units of line cycles is controlled. FIG. 9 is a diagram illustrating a case where a period in which lighting and extinguishing are alternately repeated in units of line cycles is controlled. FIG. 10 is a flowchart illustrating an example of an outline of control when reading a document. FIG. 11 is a flowchart illustrating an example of a control flow during document reading as a reference example. FIG. 12 is a flowchart illustrating an example of a control flow during document reading as a reference example.

  Hereinafter, embodiments of an image reading apparatus and an image forming apparatus will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a schematic configuration of a copying machine as an image forming apparatus provided with an automatic document feeder having a function of an image reading apparatus according to the present embodiment.

  As shown in FIG. 1, the copying machine 1 includes an automatic document feeder (ADF) 100 having a function as an image reading device, a paper feeding unit 200, and an image forming unit 300.

  The paper feeding unit 200 includes paper feeding cassettes 201 and 202 that store recording papers having different paper sizes, and various rollers that transport the recording paper stored in the paper feeding cassettes 201 and 202 to the image forming position of the image forming unit 300. The sheet feeding means 203.

  The image forming unit 300 includes an exposure device 301, a photosensitive drum 302, a developing device 303, a transfer belt 304, and a fixing device 305. The image forming unit 300 exposes the photosensitive drum 302 by the exposure device 301 based on image data of a document read by a reading unit (described later) that reads the document image, and forms a latent image on the photosensitive drum 302. A developing device 303 supplies toner of different colors to the photosensitive drum 302 for development. The image forming unit 300 transfers the image developed on the photosensitive drum 302 by the transfer belt 304 to the recording paper supplied from the paper feeding unit 200, and then transfers the toner image transferred to the recording paper by the fixing device 305. The toner is melted to fix the color image on the recording paper.

  The configuration example of the ADF 100 shown in FIG. 2 relates to an automatic document conveying device having a function of an image reading device that conveys a document to be read to a fixed reading device unit and reads an image while conveying the document at a predetermined speed. In the following, the basic configuration, operation and action will be described based on FIG. 2 which is a cross-sectional view of the present apparatus and FIG. 3 which is a block diagram showing a configuration example of a control system.

  As shown in FIG. 2, the ADF 100 includes a document setting unit A that sets a read document bundle, a separation feeding unit B that separates and feeds documents one by one from the set document bundle, and a fed document. Registration section C, which performs primary abutting alignment and pulls out and conveys the original after alignment, turns the original to be conveyed and turns the original surface toward the reading side (downward), A first reading / conveying unit E for reading the front image from below the contact glass, a second reading / conveying unit F for reading the back side image of the original after reading, and a discharge for discharging the original on which the front / back reading has been completed to the outside. As shown in FIG. 3, various units of motors 141 to 145 as driving units for driving these conveying operations, and a series of units, each unit of the paper unit G and the stack unit H that stacks and holds the document after reading is completed. Control And a to the controller 140..

  The original bundle 101 to be read is set on the original table 102 including the movable original table 103 with the original surface facing upward. Further, the document bundle 101 is positioned in a direction orthogonal to the conveyance direction by a side guide (not shown). The setting of the document bundle 101 is detected by the set filler 104 and the set sensor 105, and the detection result is notified to the main body control unit 160 via the I / F 147.

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

  The movable document table 103 can be moved up and down in the a and b directions shown in FIG. 2 by a bottom plate raising motor 145. When the set filler 104 and the set sensor 105 detect that the document bundle 101 is set, the controller Under the control of 140, the bottom plate raising motor 145 is rotated forward to raise the movable document table 103 so that the uppermost surface of the document bundle 101 comes into contact with the pickup roller 107. The pickup roller 107 is operated by the pickup motor 141 in the c and d directions shown in FIG. 2 by the cam mechanism, and the movable document table 103 is raised and pushed by the upper surface of the document bundle 101 on the movable document table 103 in the c direction. The upper limit can be detected by the proper sheet feeding position sensor 108. The position of the movable document table 103 is detected by the bottom plate HP sensor 106.

  When the user presses the print key on the operation unit 170 and a document feed signal is transmitted from the main body control unit 160 to the controller 140 which is the control unit of the ADF 100 via the I / F 147, the pickup roller 107 is moved to the feed motor. The roller is rotated by the forward rotation of 142, and several (ideally one) originals on the original table 102 are picked up. The rotation direction of the paper feed motor 142 is a direction in which the uppermost document is conveyed to the paper feed port.

  The paper feeding belt 109 is driven in the paper feeding direction by the normal rotation of the paper feeding motor 142, and the reverse roller 110 is rotationally driven in the reverse direction to the paper feeding by the normal rotation of the paper feeding motor 142, and the uppermost document from the document bundle 101 is driven. And the document under it, and only the top document can be fed. More specifically, the reverse roller 110 is in contact with the paper feeding belt 109 at a predetermined pressure, and when the paper is in direct contact with the paper feeding belt 109 or in contact with a single document, the reverse roller 110 rotates the paper feeding belt 109. Therefore, when two or more documents are moved counterclockwise and entered between the paper feeding belt 109 and the reverse roller 110, the rotation force is set to be lower than the torque of the torque limiter. The reverse roller 110 rotates in the clockwise direction, which is the original driving direction, to push back an excess original, thereby preventing double feeding.

  The document separated into one sheet by the action of the paper feeding belt 109 and the reverse roller 110 is further fed by the paper feeding belt 109, the leading edge of the original is detected by the abutting sensor 111, and the pull-out roller which is further stopped. It hits 112. Thereafter, the paper feeding motor 142 is stopped in a state where the predetermined distance is sent from the detection of the abutting sensor 111 and as a result is pressed against the pull-out roller 112 with a predetermined amount of bending. As a result, the driving of the paper feeding belt 109 is stopped. At this time, by rotating the pickup motor 141, the pickup roller 107 is retracted from the upper surface of the document, and the document is fed only by the conveying force of the paper feed belt 109, so that the leading edge of the document is in the nip between the pair of upper and lower rollers of the pull-out roller 112. Enter and align the tip (skew correction).

  The pull-out roller 112 has a skew correction function as described above, and is a roller for conveying the skew-corrected document to the intermediate roller 114 as described above, and is driven by the reverse rotation of the paper feed motor 142. Note that when the paper feed motor 142 rotates in reverse, the pull-out roller 112 and the intermediate roller 114 are driven, but the pickup roller 107 and the paper feed belt 109 are not driven.

  A plurality of document width sensors 113 are arranged in the depth direction and detect the size in the width direction orthogonal to the transport direction of the document transported by the pull-out roller 112. Further, the length of the document in the conveyance direction is detected from the motor pulse detected by the abutting sensor 111 against the leading edge and the trailing edge of the document.

  When the document is transported from the resist section C to the turn section D by driving the pull-out roller 112 and the intermediate roller 114, the transport speed at the resist section C is set higher than the transport speed at the first reading transport section E. By doing so, the processing time for sending the document to the first reading unit 120 is shortened. When the leading edge of the document is detected by the reading entrance sensor 115, before the leading edge of the document enters the nip between the pair of upper and lower rollers of the reading entrance roller 116, deceleration is started in order to make the document transportation speed the same as the scanning transportation speed. At the same time, the reading motor 143 is normally driven to drive the reading inlet roller 116, the reading outlet roller 123, and the CIS outlet roller 127. When the registration sensor 117 detects the leading edge of the document, the registration sensor 117 decelerates over a predetermined conveyance distance, temporarily stops before the first reading unit 120, and sends a registration stop signal to the main body control unit 160 via the I / F 147. Send.

  Subsequently, when the controller 140 receives a reading start signal from the main body control unit 160, the document whose registration has been stopped is increased by the control so that it rises to a predetermined conveyance speed until the leading end of the document reaches the reading position. It is transported at high speed. At the timing when the leading edge of the document detected by the pulse count of the reading motor 143 reaches the first reading unit 120, a gate signal indicating an effective image area in the sub-scanning direction on the first surface is sent from the controller 140 to the first reading unit 120. The first reading unit 120 is transmitted until the trailing edge of the document is removed. In accordance with the gate signal, the first reading unit 120 reads a document from below the contact glass 132. The document image data read by the first reading unit 120 is subjected to predetermined image processing by the image processing unit 151 of the digital signal processing unit 150 and then transmitted to the main body control unit 160. The first reading roller 119 suppresses the floating of the document in the first reading unit 120.

  In the case of single-sided document reading, the document that has passed through the first reading conveyance unit E is conveyed to the paper discharge unit G through the second reading unit 125. At this time, when the leading edge of the document is detected by the paper discharge sensor 124, the paper discharge motor 144 is driven to rotate forward to rotate the paper discharge roller 128 counterclockwise. In addition, the discharge motor pulse count from the detection of the leading edge of the document by the discharge sensor 124 reduces the discharge motor drive speed immediately before the trailing edge of the document comes out of the nip between the pair of upper and lower rollers of the discharge roller 128 to discharge the sheet. Control is performed so that the document discharged onto the tray 129 does not jump out.

  In the case of double-sided document reading, the controller 140 detects the leading edge of the document after the paper discharge sensor 124 detects that the leading edge of the document reaches the second reading unit 125 by the pulse count of the reading motor 143. On the other hand, a gate signal indicating an effective image area in the sub-scanning direction is transmitted from the controller 140 through the first reading unit 120 until the trailing edge of the document is removed. In accordance with the gate signal, the second reading unit 125 reads the back side of the document surface read by the first reading unit 120. The original image data read by the second reading unit 125 is subjected to predetermined image processing (described later) by the image processing unit 151 of the digital signal processing unit 150 and then transmitted to the main body control unit 160. The second reading roller 126 serves as a reference white part for acquiring shading data in the second reading unit 125 as well as suppressing the floating of the document in the second reading unit 125.

  Next, main parts of an electric circuit related to image reading of the second reading unit 125 and the main body control unit 160 in the ADF (automatic document feeder) 100 will be described. FIG. 4 is a block diagram showing the main parts of the electric circuit of the second reading unit 125 and the main body control unit 160.

  The second reading unit 125 includes a light source unit 1251 including an LED, a fluorescent lamp, a cold cathode tube, or the like. In addition, a plurality of sensor chips 1252 arranged in the main scanning direction (direction corresponding to the document width direction) as an image sensor, a plurality of amplifier circuits 1253 individually connected to each sensor chip 1252, and each amplifier circuit 1253 individually. A plurality of A / D converters 1254 connected to each other.

  The main body control unit 160 has a black correction unit 1602 that removes black level offsets other than signal components in the output signal of the A / D converter 1254 of the second reading unit 125. Further, shading correction for removing the influence on the image data due to unevenness of the light source unit 1251 and non-uniform sensitivity of the sensor chip 1252 is generally performed on the output signal after the black correction. The shading correction unit ( (SH correction unit) 1603. In addition, an image processing unit 208 that performs predetermined image processing is also provided.

  Further, as a characteristic configuration in the present embodiment, the main body control unit 160 has a data determination unit 1601 for determining whether the output signal of the A / D converter 1254 is black level data or white level data. The second reading unit 125 is a kind of sensor mounted in the ADF 100, and it is desirable that the second reading unit 125 be as small and light as possible. Therefore, the second reading unit 125 includes only a circuit necessary for obtaining image data. The above-described circuit such as image processing is mounted on the main body control unit 160.

  The sensor chip 1252 includes a photoelectric conversion element called a 1 × contact image sensor and a condenser lens. Prior to a document (not shown) entering the reading position by the second reading unit 125, a lighting ON signal XLAMP is sent from the controller 140 to the lighting control unit 1255. While the lighting ON signal XLAMP is sent, the lighting control unit 1255 continuously lights up the light source unit 1251 during the document reading period, and irradiates the light toward a document (not shown). Further, the lighting control unit 1255 performs control to alternately turn on and off the light source unit 1251 outside the document reading period.

  The reflected light reflected from the document is condensed on the photoelectric conversion element by the condensing lens and read as image information in the plurality of sensor chips 1252. Image information read by each sensor chip 1252 is amplified by an amplifier circuit 1253 and then converted to digital image information by an A / D converter 1254.

  This digital image information is input to the data determination unit 1601 of the main body control unit 160. During the document reading period, the data determination unit 1601 determines the input digital image information as document image data, the offset correction component is removed by the black correction unit 1602, the shading correction is performed by the shading correction unit 1603, and image processing is performed. The image data is input to the unit 1604 and image processing such as interline correction is performed.

  On the other hand, outside the document reading period, it is determined whether the input digital image information is black level data or white level data, and is output to the black correction unit 1602 or the shading correction unit 1603 according to the determination result (for details of the determination method). Will be described later).

  It should be noted that a timing signal (XSSCAN) for notifying the timing at which the leading edge of the document reaches the reading position by the second reading unit 125 (image data after that timing is treated as valid data) or lighting of the light source from the controller 140. A signal (XLAMP) is output and power is supplied.

  FIG. 5 shows a timing chart in the case where the light source unit 1251 is turned on and off alternately (the lighting period and the lighting period are the same number of lines).

  In the timing chart of FIG. 5, as an example, an LED is used as a light source, and its lighting duty is 100%. The lighting period and the extinguishing period are the same number of lines (one line in FIG. 5).

  In FIG. 5, XLSYNC is a synchronization signal for one line, and is a signal that is “L” for a period corresponding to several pixels at the head of the line. XSCAN is a signal indicating the effective image area in the sub-scanning direction, and the “L” period indicates the effective image area. XLAMP is a light source lighting signal notified from the controller to the lighting control unit 1255, and represents a light source period at "L". The LED of the light source unit 1251 is turned on when the LED ON / OFF signal is “H” and turned off when the signal is “L”. When XLAMP is “H”, the LED is not lit, but is lit during “L” (or alternately turned on and off repeatedly).

  Next, reference black data generation outside the document reading period and generation of shading data for shading correction will be described with reference to a flowchart illustrating an example of a control outline during document reading shown in FIG.

  Document reading is started (step S101) (the LED is lit at this time), and when it is outside the document reading period (XSSCAN is “H”) (Yes in step S102), the LED is turned off for each line during this period. H ”and lighting“ L ”are alternately repeated (steps S104 and S106). At this time, the sensor chip 1252 outputs the black level data when the LED is turned off and the white level data obtained by reading the white reference member when the LED is turned on via the amplifier circuit 1253 and the A / D converter 1254. The output black level data or white level data is input to the data determination unit 1601 of the main body control unit 160, and the data determination unit 1601 determines whether it is black level data or white level data.

  As a discrimination method at this time, as described below, if the output level D of the data to be discriminated input to the data discriminating unit 1601 is smaller than a predetermined threshold T, it is discriminated as black level data. If so, it is determined as white level data.

(Discriminant)
D <T: Black level data D ≧ T: White level data

  It may be determined that D ≦ T: black level data and D> T: white level data. Further, since it is only necessary to discriminate between black level data and white level data for each line, D may be data of the top pixel in the main scanning direction, or the data discrimination unit 1601 may have an averaging circuit (not shown). The average value of the main scanning top several pixels to several tens of pixels obtained by the averaging circuit may be used.

  Here, when the data D to be discriminated is an average value, the influence of dust and the like can be removed, so that the discrimination can be performed with higher accuracy (the white level data may be reduced in output due to dust. If it is determined only by pixels, it may be erroneously determined as black level data). Further, specifically, the threshold T is set to the maximum black level value + 1 or the like. This is because the black level variation range is determined for each sensor chip, so that the maximum black level that can be generated is assumed as the maximum value of the black level data. Thus, the black level can be reliably determined by setting the maximum black level value + 1 as a threshold value.

  Next, when the determination result is black level data, it is input to the black correction unit 1602 and black level data is acquired (step S105). On the other hand, in the case of white level data, it is input to the shading correction unit 1603 and white level data is acquired (step S103).

  In the black correction unit 1602 and the shading correction unit 1603, during the control period in which the LEDs are turned on and off alternately, a value is added in the sub-scanning direction (for a plurality of lines) at each pixel in the main scanning direction, and the lighting and turning off are repeated alternately. After the end of the control period, the added data is divided by the number of added lines, the sub-scanning average value is calculated for each pixel, and reference black data and shading data are generated (step S107).

  Thereafter, as in the conventional method, the original reading with black correction and shading correction is performed (step S108). If there is a next original (Yes in step S109), the process returns to step S101 to read the original for the next original. Start and perform subsequent control. If there is no next original (No in step S109), the original reading is terminated (step S110).

  Note that the timing when the light source is turned on / off and the white level detection and the black level detection are repeated in the inter-paper period is according to the timing described later. Further, in the example of the control outline of FIG. 10, it is assumed that XSSCAN = “H” in the step S101.

  As described above, in the present embodiment, the LED can be repeatedly turned on and off outside the document reading period, and the black level data and the white level data can be monitored and discriminated, whereby each data can be acquired in line units. Further, since the reference black data and the shading data are generated in this way, the amount of temperature decrease of the light source can be reduced, and the light quantity stabilization time when the light source is turned on can be shortened. As a result, the time between sheets can be shortened.

  In this example, the case where the image reading sensor is a contact image sensor has been described. However, a CCD image sensor that does not have OPB pixels (even if a CCD image sensor is used, an OPB is used for a cheaper configuration). Some of them have no pixel).

  FIG. 6 shows a timing chart in the case where lighting and extinguishing are repeated alternately (the number of lines in which the lighting period and the extinguishing period are different).

  In FIG. 6, in a period in which lighting and extinguishing are repeated alternately, the extinguishing period is two lines, the lighting period is one line, and the reference black data generation period is the latter half of the extinguishing period. Thereby, measures, such as afterglow of LED, are possible. However, when there is afterglow, the black level data becomes higher than the original value, so it is difficult to determine the black level data.

  Therefore, in the data discriminating unit 1601, the white level data line detected after the black level data is detected for the first time is set as the first line, and the white level data → black level data is periodically generated for each line from that line. → If it is determined as white level data (for example, lighting control is performed at a cycle of 1 lighting line and 2 lighting lines, and black level data is data for one line in the latter half of 2 lines), afterglow Even if there is a black level data, it can be determined. In addition, what is necessary is just to preset the LED extinction period and the lighting period according to the afterglow characteristic of LED.

  Output value when reading the white reference member: The white level (shading data-reference black data) is proportional to the amount of light. That is, the variation in the white level represents the variation in the amount of light. The shading correction unit 1603 has an arithmetic circuit and an averaging circuit (not shown) and calculates a white level (shading data-reference black data). Here, as for the white level (shading data-reference black data), if the output value of one pixel with main scanning is observed, if there is dust, the original output may not be obtained due to the influence of dust. The average value of the entire area in the main scanning direction or the average value of each sensor chip 1252 is calculated.

  FIG. 7 shows a look-up table (right diagram) of the white level variation with respect to time (left diagram) and the lighting / extinguishing period with respect to each threshold of the white level. The left diagram of FIG. 7 shows the white level fluctuation between one job. The detected white level is greatly decreased immediately after the LED lighting is started (t0 → t1), but as the time passes after the lighting starts (t1 → t2). It shows how white level fluctuations converge. The LED extinguishing period and lighting period are changed according to the white level fluctuation.

  In the example shown in FIG. 7, the initial values are the lighting period 3 lines and the lighting period 2 lines. However, when the white level is observed and falls below the threshold value y1, the lighting period and the lighting period corresponding to the white level are defined. With reference to the lookup table, the lighting period is 2 lines and the lighting period is 2 lines. When the white level is lower than the threshold value y2, the lighting period is 1 line and the lighting period is 2 lines. As a result, in the early stage of a job with a large amount of light fluctuation, the white level fluctuation increases, so increasing the lighting period (shortening the extinguishing period) increases the white level data acquisition period, and averages the acquired white level data. As a result, the fluctuation amount is removed, and shading data can be generated with high accuracy. On the other hand, after the fluctuation of the amount of light is stabilized, accurate shading data can be generated even with a short number of lines. As a result, the gap between the sheets can be shortened. Note that the same effect can be obtained by changing the LED extinguishing period and the lighting period in accordance with a predetermined number of scanned sheets (number of scanned sheets).

  FIG. 8 shows a timing chart in the case of controlling a period in which lighting and extinguishing are repeated alternately.

  XBKGATE is an area indicating a period in which the LED is turned on and off alternately. During the XBKGATE period of the XSSCAN negation period, lighting and extinction are alternately repeated, shading data for shading correction is generated during the lighting period, and reference black data for black correction is generated during the period when the LED is off. Then, shading data for shading correction is generated outside the XBKGATE period of the XSSCAN negation period. As a result, it is possible to keep the reference black data generation area to the minimum necessary, and to increase the number of lines spent on shading data generation, and to reduce the influence of dust in a configuration in which shading data is acquired from a white roller. Can do.

  FIG. 9 shows an example of a look-up table (right diagram) of white level variation with respect to time (left diagram) and the number of white level acquisition lines for each threshold of white level.

  The left diagram of FIG. 9 shows the white level fluctuation between jobs, and the detected white level is greatly decreased immediately after the start of LED lighting (t0 → t1), but time passes after the start of lighting (t1 → t2). This shows how the white level fluctuations converge.

  Immediately after the start of LED lighting, the white level data acquisition line is set to 200, and when the white level falls below the threshold value y1, the white level data acquisition line is set to 180 lines with reference to the lookup table, and the white level is the threshold value y2. If the value is less than, the white level data acquisition line is set to 160 lines.

  As a result, in the early stage of a job with large white level fluctuation, the amount of fluctuation is eliminated by increasing the white level data acquisition period and averaging the acquired white level data, making it possible to generate highly accurate shading data. . On the other hand, after the fluctuation of the amount of light is stabilized, accurate shading data can be generated even with a short number of lines. Accordingly, it is possible to shorten the gap between sheets while generating highly accurate shading data. The same effect can be obtained even if the white level data acquisition period is changed according to the predetermined number of scans.

  In the above embodiment, a copying machine has been described as an example of an image forming apparatus having a function as an image reading apparatus. However, there are at least two functions among a copy function, a printer function, a scanner function, and a facsimile function. The present invention can also be applied to an image forming apparatus such as a multifunction device having a function, a scanner device, or a facsimile device.

  Here, for reference, an example (reference example) of control at the time of document reading described in the column of the problem to be solved by the invention is shown in FIG. 11 and FIG. FIG. 11 shows an example in which the reference black data is generated for each paper interval, and FIG. 12 shows an example in the case of shadingless in which shading data is generated only at the head of a job and no shading data is acquired between papers. is there. In the example of FIG. 11 (step S201 to step S209) and the example of FIG. 12 (step S301 to step S314), at the time of document reading, the light source is once turned off to generate reference black data, and then the light source is turned on. Then, after waiting for the light amount stabilization time after the light source is turned on, control for obtaining shading data and image data and performing black correction and shading correction is performed.

  As described above, in the example of FIG. 11, it takes time to secure the light amount stabilization time after the light source is turned off, the reference black data is generated, the light source is turned on, and the light source is turned on again. Further, as shown in the example of FIG. 12, even when shading data is generated only at the head of a job and shading data is not acquired between sheets, a light source relighting time is required before reading a document, and additional paper is required. There is a problem that it is difficult to shorten the time.

1 Copier 100 Automatic document feeder (ADF)
125 Second reading unit 140 Controller 152 Frame memory 153 Output control circuit 154 I / F circuit 160 Main body control unit 170 Operation unit 1251 Light source unit 1252 Sensor chip 1253 A / D converter 1255 Lighting control unit 1601 Data determination unit 1602 Black Correction unit 1603 SH correction unit (shading correction unit)
1604 Image processing unit

JP 2006-13852 A

Claims (11)

In an image reading apparatus that acquires image data by a light source that irradiates light on a document and an image sensor that photoelectrically converts reflected light from the document irradiated with light from the light source,
A lighting control means for adjusting the lighting period of the light source so as to alternately turn on and off in units of line periods outside the document reading period;
If the image data read outside the document reading period is smaller than a predetermined threshold, it is determined as black level data for generating reference black data used for black correction. If the image data is larger than the threshold, the shading data used for shading correction is determined. Data discriminating means for discriminating from white level data for generation;
Means for generating reference black data from the black level data determined by the data determination means;
An image reading apparatus comprising: means for generating shading data from white level data determined by the data determination means.   The image reading apparatus according to claim 1, wherein the image sensor includes a plurality of sensor chips that perform photoelectric conversion. The threshold value T as the threshold value of the data discriminating means is a value equal to or greater than the maximum value of the black level data + 1 when each data is represented by digital data consisting of a plurality of bits , and image data input outside the document reading period is , is less than the threshold value T, and determines that the black level data, image according to claim 1 or claim 2, characterized in that to determine said threshold value T or value, if the white level data reader.   4. The lighting device according to claim 1, wherein the lighting control unit periodically turns on and off a predetermined number of lines outside a document reading period. 5. Image reading device.   5. The image according to claim 1, wherein the lighting control unit changes the lighting period and the extinguishing period of the light source in units of lines according to the number of read sheets. 6. Reader.   The lighting control means refers to the light-on period and the light-off period with reference to a lookup table that defines a light-on period and a light-off period according to the white level at that time according to the light amount fluctuation of the light source. The image reading apparatus according to claim 1, wherein the period and the turn-off period are changed in units of lines.   7. The lighting control unit according to claim 1, wherein the lighting control unit arbitrarily changes a period in which the light source is turned on and off in a line unit outside a document reading period. 8. Image reading device.   8. The lighting control unit according to claim 1, wherein the lighting control unit changes a period in which the light source is repeatedly turned on and off outside the original reading period in units of lines according to the number of readings. The image reading apparatus described in 1.   The lighting control means defines a number of lines to be used for generating shading data corresponding to the white level at the time when the light source is turned on and off, outside the original reading period, according to the light amount fluctuation of the light source. The image reading apparatus according to claim 1, wherein the image reading apparatus is changed in units of lines with reference to the up table. An automatic document feeder comprising: the image reading device according to any one of claims 1 to 9 ; and an automatic document feeder that conveys a document read by the image reading device. An image forming apparatus comprising: the image reading device according to any one of claims 1 to 9 ; and an image forming unit that forms an image on a sheet based on image data output from the image reading device. .

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