JP2010166370A - Image reading device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading device and an image forming device which can obtain high-quality image data. <P>SOLUTION: The image reading device, which includes a first image reading means for reading a first surface of an original transferred on an original transfer path, a second image reading means for reading a second surface of the original, and a white reference material arranged at a position facing the second image reading means, comprises a space control means for controlling a distance between the second image reading means and the white reference material by changing the position of the white reference material, an original edge detection means for detecting a main scanning edge of the original from the image data obtained by the second image reading means and detecting a shift amount between the main scanning edge and a reference original edge position, and a resist adjustment means for increasing a distance between the second image reading means and the white reference material more than the usual distance when the original is read by using the space control means in a mode in which the original is read by using only the first image reading means, detecting the shift amount by using the original edge detection means, and correcting a resist position of the image data read by the first image reading means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a first image reading unit for reading a first surface of a document conveyed on a document conveyance path, a second image reading unit for reading a second surface of the document, and the second The present invention relates to an image reading apparatus including a white reference member disposed at a position facing an image reading unit, and an image forming apparatus including the image reading apparatus.

  Conventionally, in an image forming process in a digital copying machine, a facsimile apparatus, and a scanner apparatus, an original is mounted on an original table or an original feeder, the original is irradiated by a light source, and the reflected light is an optical reading element such as a CCD as image information. Read to (input element). Here, the above-described document conveying apparatus is called ADF (Automatic Document Feeder) or DF (Document Feeder), and is hereinafter referred to as ADF.

  The image information of the original is usually taken line by line, and when the original is placed on a fixed original table, the optical path between the light source, the original and the element is moved sequentially, When the document is moved, the document reading operation is performed by moving the document while fixing the optical path between the light source, the document, and the element. That is, the image information in the main scanning direction (document line direction) is determined by the number of input elements, and the number of lines in the sub-scanning direction (direction orthogonal to the main scanning direction) is determined by the reading timing of the elements and document feeding. Is done.

  On the other hand, the input element on the back side of the equal-magnification optical system is fixed in a state where the white reference is opposed to the reading position (position through which the document passes), and the position (reference position) for reading the white reference member is always the same. It is.

  An image reading apparatus using a contact image sensor (CIS) conveys a document in contact with the contact glass, irradiates the conveyed document with light from the light source through the contact glass, and reflects the document reflected by the document. Reflected light including image information is again incident on a photoelectric conversion element (for example, a CCD (Charge Coupled Device)) through the contact glass, and photoelectric conversion is performed by the photoelectric conversion element, thereby reading an image of the document.

  In an image reading apparatus using such a contact image sensor, in order to correct fluctuations in the amount of light of a light source (for example, a rare gas xenon lamp) and sensitivity variations of photosensitive pixels of a photoelectric conversion element such as a CCD, the conventional technique is used. The white reference member is read before reading the document, and the data obtained by reading the white reference member is used as shading data, and shading correction processing is performed on the image data of the document.

  In such an image reading apparatus, it is necessary to perform a regular image reading process at a set position of the original document. However, after assembly of the apparatus, there is a cumulative dimensional error in assembling the parts. It is difficult to perform regular image reading at a predetermined set position. For this reason, registration adjustment (hereinafter referred to as registration adjustment) in the main scanning direction and the sub-scanning direction of the document is performed for each unit when the product is shipped from the factory.

  As such a resist adjustment method, for example, those disclosed in Patent Documents 1 and 2 can be employed.

  However, even if the above registration adjustment is performed in the process, under the actual usage conditions, the position where the user sets the document at the time of image reading may differ from the normal position (document setting failure), or ADF In the transport reading, there is a concern that even if the original set position is the normal position, transport unevenness / skew or the like may occur due to some cause, and registration deviation may occur.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus and an image forming apparatus capable of obtaining high-quality image data.

  The present invention provides a first image reading unit for reading a first surface of a document conveyed on a document conveyance path, a second image reading unit for reading a second surface of the document, and the second In an image reading apparatus having a white reference member disposed at a position facing the image reading means, the position of the white reference member is changed, and the distance between the second image reading means and the white reference member is set. A separation control unit for controlling, a document edge detection unit for detecting a main scanning edge of the document from the image data obtained by the second image reading unit, and detecting a deviation amount from a reference document edge position; In the mode of reading a document using only the image reading unit, the separation control unit is used to separate the distance between the second image reading unit and the white reference member from that during normal document reading, thereby detecting the document edge. Deviation using means It detects, those having a registration adjustment means for correcting the registration position of the image data read by the first image reading means.

  Further, the document edge detecting means includes a binarizing means for binarizing the output of the photoelectric conversion means constituting the second image reading means, and the background of the reference document obtained by the first image reading means. Threshold voltage calculating means for calculating the threshold voltage of the binarizing means from the ratio between the output level and the background output level of the read document, and control means for switching the threshold voltage obtained by the threshold voltage calculating means. Is.

  Further, the spectral sensitivity characteristics of the photoelectric conversion means constituting the first image reading means, the total spectral characteristics determined by the spectral intensity of the illumination means, and the spectral sensitivity of the photoelectric conversion means constituting the second image reading means. The characteristic and the total spectral characteristic determined by the spectral intensity of the illumination means are the same or close characteristics.

  In addition, the image forming apparatus includes a switching unit that allows a user interface to set whether or not to perform registration adjustment using the second reading unit.

  An image forming apparatus comprising the image reading apparatus according to claim 1.

  Therefore, according to the present invention, only in the mode in which the original is read using only the first image reading means, the misregistration amount of the registration position of the original is detected using the second image reading means that is originally unused. In addition, by correcting the registration position of the image data read by the first image reading unit, it is possible to provide high-quality image data.

1 is a schematic configuration diagram illustrating a configuration example of an image reading apparatus according to an embodiment of the present invention. Sectional drawing which showed schematic structure of this apparatus. The block diagram which showed an example of the structure of a control system. The block diagram which showed the circuit structural example of the 1st reading part. The schematic block diagram which showed the structural example of the 2nd reading part and the 2nd reading roller. Schematic showing a CIS configuration example. The circuit diagram showing the example of the generation circuit of a CIS_LED signal. The block diagram which showed the circuit structural example of the 2nd reading part. FIG. 3 is a block diagram showing an example of a document edge detection configuration. FIG. 6 is a timing chart for explaining an operation example when executing edge detection in the document main scanning direction. FIG. 3 is a block diagram showing a part of the image processing circuit 307 in detail. FIG. 3 is an explanatory diagram simply showing a main scanning timing signal for correcting an edge of a document when a document main scanning direction shift occurs. The flowchart which showed an example of the control flow. Schematic for demonstrating the detection location of a background part. FIG. 4 is a first diagram for explaining document leading edge detection. FIG. 6 is a second diagram for explaining document leading edge detection. The graph for demonstrating the spectral reflectance of a recording medium, the spectral-intensity characteristic of an illumination means, the spectral sensitivity characteristic of CIS301, and the spectral characteristic which synthesize | combined them. Schematic which showed an example of UI displayed on an operation part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a configuration example of an image reading apparatus according to an embodiment of the present invention.
In the figure, the image reading apparatus includes a contact glass 701 on which a document 705 is mounted, a reference white plate 703 for white level adjustment and shading data generation, a light source 707 for irradiating the document, and a first carriage 709 on which a first mirror 708 is mounted. The second mirror 710, the second carriage 712 on which the third mirror 711 is mounted, the lens unit 713 for reducing and forming an image on the CCD image sensor 714, the image reading circuit 715 on which the CCD image sensor 714 is mounted, the image processing circuit 716, Although not shown in the drawing, it includes a scanner drive motor for driving the first and second carriages, a home position sensor, a document detection sensor, and the like.

  In the above configuration, when the document 705 is mounted on the contact glass 701, the light source 707 is turned on, and the first carriage 709 and the second carriage 712 are moved and scanned to the right by the scanner motor to read the document 705. Then, with the first carriage 709 and the second carriage 712 stopped, the light source 707 is turned on, and the document 706 conveyed by the ADF (document conveying device) 704 is irradiated through the sheet-through reading contact glass 702. The reading method can be selected.

  When reading a document by scanning the carriage, the reference white plate data is acquired prior to reading the document, shading correction data is generated and stored in the memory, and the image data of the document 705 is normalized using the shading correction data. As a result, the light amount distribution unevenness and CCD sensitivity unevenness in the apparatus are corrected, and the image information of the original is read with high quality. In the case of sheet-through reading in which the original 706 is conveyed and the original image data is read while the carriage is stopped, the shading correction data is first moved under the reference white plate 703 before reading the original 706. Is generated and returned to the sheet-through reading position, the conveyance of the original is started, and the original reading operation is started.

  The basic configuration, operation, and action of the ADF 704 will be described below with reference to FIG. 2 that is a cross-sectional view of this apparatus and FIG. 3 that is a control block diagram.

  A document setting unit A for setting a read document bundle, a separation feeding unit B for separating and feeding originals one by one from the set document bundle, a function for primary abutting alignment of fed documents, and after alignment The resist part C, which serves to pull out and convey the original, the turn part D which turns the conveyed original and conveys the original surface toward the reading side (downward), reads the surface image of the original from below the contact glass A first reading / conveying unit E for performing reading, a second reading / conveying unit F for reading a back side image of a document after reading, a paper discharge unit G for discharging a document whose front and back have been read out of the apparatus, and a document after reading The stacking unit H is configured to be loaded and held, driving units 101 to 105 that drive these transport operations, and a controller 100 that controls a series of operations.

  The original bundle 1 to be read is set on the original table 2 including the movable original table 3 with the original surface facing upward. Further, the width direction of the document bundle 1 is positioned in a direction perpendicular to the conveyance direction by a side guide (not shown). The document set is detected by the set filler 4 and the set sensor 5 and transmitted to the main body control unit 111 by the I / F 107.

  Further, the document length detection sensor 30 or 31 provided on the document table surface (a reflection type sensor or an actuator type sensor capable of detecting even one document is used) can be used to approximate the length of the document in the conveyance direction. It is determined (a sensor arrangement capable of determining at least whether the document size is vertical or horizontal is necessary).

  The movable document table 3 can be moved up and down in the directions a and b shown in the figure by a bottom plate raising motor 105. When the set filler 4 and the set sensor 5 detect that a document is set, the bottom plate raising motor 105 is moved. Is moved forward so that the movable document table 3 is raised so that the uppermost surface of the document bundle contacts the pickup roller 7.

  The pickup roller 7 is operated by the pickup motor 101 in the c and d directions shown in the figure by the cam mechanism, and the movable table 3 is lifted and pushed by the upper surface of the document on the movable table 3 to be raised in the c direction. The upper limit can be detected by the sensor 8.

  When a copy or scan key is pressed from the main body operation unit 108 and a document feed signal is transmitted from the main body control unit 111 to the ADF control unit 100 via the I / F 107, the pickup roller 7 rotates the feed motor 102 in the normal direction. As a result, the roller is rotated to pick up several (ideally, one) originals on the original table 2. The rotation direction is a direction in which the uppermost document is conveyed to the sheet feeding port.

  The paper feed belt 9 is driven in the paper feed direction by the normal rotation of the paper feed motor 102, and the reverse roller 10 is driven to rotate in the reverse direction to the paper feed by the normal rotation of the paper 102 to separate the uppermost document from the document under it. Thus, only the uppermost document can be fed.

  More specifically, the reverse roller 10 is in contact with the paper feeding belt 9 at a predetermined pressure, and when the paper is in direct contact with the paper feeding belt 9 or through a single document, the reverse roller 10 rotates. Therefore, when two or more originals enter between the paper feeding belt 9 and the reverse roller 10, the revolving force is set to be lower than the torque of the torque limiter. The roller 10 rotates in the clockwise direction, which is the original driving direction, and pushes back an excess original, thereby preventing double feeding.

  The original separated by the action of the paper feeding belt 9 and the reverse roller 10 is further fed by the paper feeding belt 9, and the leading edge is detected by the abutting sensor 11 and further abuts against the pull-out roller 12 stopped. Thereafter, the sheet feeding motor 102 is stopped in a state in which it is fed by a predetermined amount from the detection of the abutting sensor 11 and is pressed against the pull-out roller 12 with a predetermined amount of deflection. As a result, the driving of the paper feed belt 9 is stopped.

  At this time, by rotating the pickup motor 101, the pickup roller is retracted from the upper surface of the document and the document is fed only by the conveying force of the paper feed belt, whereby the leading edge of the document enters the nip of the pair of upper and lower rollers of the pull-out roller 12, Tip alignment (skew correction) is performed.

  The pull-out roller 12 has the skew correction function and is a roller for conveying the skew-corrected document after separation to the intermediate roller 14 and is driven by the reverse rotation of the paper feed motor 102.

  At this time (at the time of reverse rotation of the paper feed motor 102), the pull-out roller 12 and the intermediate roller 14 are driven, but the pickup roller 7 and the paper feed belt 9 are not driven. A plurality of document width sensors 13 are arranged in the depth direction and detect the size in the width direction perpendicular to the conveyance direction of the document conveyed by the pull-out roller 12.

  Further, the length of the document in the conveyance direction is detected from the motor pulse by reading the leading and trailing edges of the document with the abutment sensor 11. When the document is transported from the resist section C to the turn section D by driving the pull-out roller 12 and the intermediate roller 14, the transport speed at the resist section C is set to be higher than the transport speed at the reading transport section E. The processing time for sending the document to the reading unit is shortened.

  When the leading edge of the document is detected by the reading entrance sensor 15, before the leading edge of the document enters the nip between the upper and lower roller pairs of the reading entrance roller 16, deceleration is started to make the document transportation speed the same as the scanning transportation speed. Then, the reading motor 103 is driven forward to drive the reading inlet roller 16, the reading outlet roller 23, and the CIS outlet roller 27. When the registration sensor 17 detects the leading edge of the document, it decelerates over a predetermined conveyance distance, temporarily stops before the reading position 20, and transmits a registration stop signal to the main body control unit 111 via the I / F 107. .

  Subsequently, when a reading start signal is received from the main body control unit 111, the document whose registration has been stopped is transported at an increased speed so as to rise to a predetermined transport speed before the leading end of the document reaches the scanning position. At the timing when the leading edge of the document detected by the pulse count of the reading motor reaches the reading unit, a gate signal indicating an effective image area in the sub-scanning direction on the first surface is sent to the main body control unit 111 after the first reading unit Sent until the edge is removed.

  In the case of single-sided document reading, the document that has passed through the reading conveyance unit E is conveyed to the paper discharge unit G through the second reading unit. At this time, when the leading edge of the original is detected by the paper discharge sensor 24, the paper discharge motor 104 is driven to rotate forward to rotate the paper discharge roller 28 counterclockwise. In addition, the discharge motor pulse count from the detection of the leading edge of the document by the discharge sensor 24 reduces the discharge motor drive speed immediately before the trailing edge of the document comes out of the nip of the pair of upper and lower rollers of the discharge roller 28 to discharge the document. Control is performed so that the document discharged onto the tray 29 does not jump out.

  In the case of double-sided document reading, DF is read from the second reading unit 25 at the timing when the document leading edge reaches the second reading unit 25 by the pulse count of the reading motor 103 after the paper discharge sensor 24 detects the document leading end. A gate signal indicating an effective image area in the sub-scanning direction is transmitted from the control unit 100 until the trailing edge of the original passes through the reading unit.

  FIG. 4 shows a circuit configuration example of the first reading unit according to the embodiment of the present invention.

  First, the CCD 801 photoelectrically converts the reflected light from the document and outputs an analog image signal.

  The analog signal processing circuit 806 includes a sample hold circuit 802, a black level correction circuit 803, an amplification circuit 804, and an AD conversion circuit 805.

  The analog image signal from the CCD 801 is sampled by a sample hold circuit 802 by a sample pulse from a timing generator (not shown) and held at an input level to be a continuous analog image signal.

  Thereafter, the black level correction circuit 803 corrects the variation in the dark output level of the CCD 801, and the amplifier circuit 804 amplifies the signal with a gain such that the reference white plate level becomes a predetermined constant level. It is converted into a digital image signal.

  The digital image signal thus obtained is output to the shading correction circuit 807.

  In the shading correction circuit 807, the image processing circuit 808 performs various types of image processing on the image data in which the sensitivity variation of the CCD 801 and the light distribution unevenness of the illumination optical system are corrected using the reference white plate data and the image data.

  FIG. 5 shows a configuration example of the second reading unit and the second reading roller according to the embodiment of the present invention.

  A white reference member 201 that can move up and down and a guide member 202 that can move in the transport direction are connected to the opposing portion of the second reading unit 25 by a link member 210 so as to be rotatable. The white reference member 201 is configured to be movable along the white reference member guide 203 in the vertical direction along the white reference member guide 203 by rotating a cam 205 by rotation of a stepping motor (not shown).

  The guide member 202 and the white reference member 201 are driven by a single stepping motor by the link member 210. Further, the position of the guide member 202 and the white reference member 201 is controlled by the link member 210 only by the number of driving steps of the stepping motor.

  The rotating shaft of the cam 205 is provided with a filler 208 provided for controlling the position of the cam 205, and a cam position detection sensor 209 for detecting the filler 208 is provided separately. The cam position detection sensor 209 is provided so as to detect the filler 208 in a state where the guide member 202 is located at the opposite portion of the second reading unit 25.

  A controller (not shown) moves the cam 205 to a position where the guide member 202 is retracted from the second reading unit 25 and the white reference member 201 is brought close to the second reading unit 25 at the time of document reading (scanning) by the second reading unit. (FIG. 5A), shading data is acquired.

  When the document edge is detected, first, after performing the shading operation at the above-mentioned proximity position, the white reference member 201 is moved by a predetermined amount from the position of the white reference member 201 at the time of shading data acquisition (the stepping motor is driven by a predetermined number of steps: FIG. 5). (B)) Document edge detection is executed.

  A CIS configuration example of the second reading unit will be described with reference to FIG.

  The CIS 301 is roughly divided into a light receiving element part, a shift register part, and a light source part (LED). The amount of LED light is adjusted by driving the CIS_LED signal by an external LED current control circuit 308.

  As for the LED current control circuit 308, the internal circuit configuration varies depending on the LED driving method. For example, in PWM control, the LED_PWM signal from the CIS control circuit 305 is supplied with a pulse signal having an arbitrary period, and drives the CIS_LED signal by switching the transistor.

  The light amount can be adjusted by changing the duty of the LED_PWM signal. In the constant current control, for example, the CIS_LED signal is driven with a direct current by a circuit as shown in FIG. The light amount adjustment can be performed by changing the duty of the pulse signal because the LED_PWM signal, which is a pulse signal, is converted into a DC voltage by an integration circuit.

  An analog signal from the CIS 301 is converted into a binary digital signal by the comparator 302. In this conversion process, if the CIS output signal level is small, it is likely to be affected by noise or the like due to a decrease in gradation, so that the LED light quantity is adjusted so that the CIS output signal level when a specific document is read becomes a certain level. Adjustments are made.

  FIG. 8 shows a circuit configuration example of the second reading unit according to the embodiment of the present invention.

  The circuit configuration is basically the same as that of the first reading unit (see FIG. 4).

  Reflected light from the document is photoelectrically converted by the CIS 301 and an analog image signal is output. Similar to FIG. 4, the analog signal processing circuit 901 includes a sample hold circuit, a black level correction circuit, an amplifier circuit, an AD conversion circuit, and the like (the detailed block is omitted because it is a well-known configuration).

  A digital image signal output from the analog signal processing circuit 901 is input to the shading correction circuit 902, and shading correction processing is performed using the shading correction data obtained by reading the reference white member (= second reading roller 26). Is executed and output to the image processing circuit 307.

  An example of document edge detection will be described with reference to FIG.

  The CIS control circuit 305 is controlled by the controller 100. The CIS 301 is supplied with the CIS_CLK signal of the system clock and the CIS_SH signal for determining the charge accumulation time, and the CIS_CLK and CIS_SH signals are also supplied to the document edge detection circuit 303. The CIS_CLK signal is used for system clock and CIS data latch clock of the document edge detection circuit 303, and the CIS_SH signal is used for resetting the internal counter.

  A COMP_PWM signal is supplied to a threshold adjustment circuit (hereinafter, TH adjustment circuit) 306. The TH adjustment circuit 306 includes an integration circuit therein, generates a DC voltage from the COMP_PWM signal, and supplies a reference TH voltage to the comparator 302. Therefore, the TH voltage can be adjusted by changing the duty of the COMP_PWM signal.

  Further, the LED_PWM signal is supplied to the LED current control circuit 308. The operation based on the LED_PWM signal is as described above.

  An analog signal from the CIS 301 is converted into a binary digital signal by the comparator 302. The document edge detection circuit 303 generates a gate signal indicating the document edge from the binarized digital signal, and the controller 304 generates a difference between the gate signal position and the reference position as a count value to generate an image (not shown). By setting the count value in the processing unit, the image processing unit can correct the main scanning registration position of the document.

  The reference position is set at the time of registration adjustment performed for each product at the time of product shipment from the factory, and is stored in a storage unit such as a register in the image processing circuit.

  Here, an example of operation when performing edge detection in the document main scanning direction using the document edge detection circuit 303 will be described with reference to FIG.

  FIG. 10 is a timing chart showing the operation of the document edge detection circuit 303 when detecting the edge of the document in the main scanning direction. FIG. 10 shows that the edge of the recording medium is recognized when cis_din (binary CIS image data becomes “H” output when there is a recording medium) becomes “H” level for four consecutive pixels as dust removal. Then, the P_EDGE signal is set to the “L” level (in this embodiment, the “L” level is set as the output level when the recording medium is detected). In FIG. 10, as an example, it is expressed that P_EDGE = “L” level is not achieved with three consecutive pixels but P_EDGE = “L” level is achieved with four consecutive pixels. The P_EDGE signal is reset when CIS_SH = "H" level.

  As the reference number of pixels from CIS_SH to P_EDGE = “L” level, a value determined in advance during system adjustment is stored in a memory (not shown).

  In contrast, the controller 100 detects the number of pixels from CIS_SH to P_EDGE = “L” level for each recording medium, and calculates a difference with respect to the reference number of pixels.

  Further, the controller 100 calculates an average value of the number of pixels from CIS_SH for a plurality of lines to P_EDGE = “L” level for the purpose of noise removal, and calculates a final document edge portion.

  Next, the TH voltage generation procedure will be described with reference to FIG.

The image data after the above-described shading correction is also output to the TH voltage calculation circuit 810. The TH voltage calculation circuit 810 receives a TH voltage calculation command from the comparator from the controller 100 and calculates the TH voltage. The TH voltage is a reference document background output level held in advance in the reference document background output level holding unit 809 and image data obtained by an image reading command from the controller 304 (hereinafter referred to as “document background output level”). And is calculated by the following calculation formula (I).
TH voltage = (original background output level) / (reference original background output level) × (reference original background TH voltage−black level) + black level (I)
The black level in the calculation formula (I) is a reference offset output level in the light shielding state of the CIS 101.

  In the calculation formula (I), the TH voltage corresponding to the document set by the user is calculated from the ratio with respect to the reference recording medium. Therefore, the TH voltage is optimum for the read document, and the CIS output is equal to or lower than the comparator TH voltage. Can be prevented. Further, since the optimum TH voltage is used, the end detection error of the recording medium can be reduced.

  The TH voltage calculated by the TH voltage calculation circuit 810 is held by a TH voltage holding circuit 811. The TH voltage holding circuit 1213 transmits TH voltage information to the CIS control circuit 305, and the CIS control circuit 305 adjusts the TH voltage of the comparator 102 for each document by switching the duty of the COMP_PWM signal.

  FIG. 11 is a block diagram showing a part of the image processing circuit 307 in detail, and FIG. 12 is a diagram simply showing a main scanning timing signal for document edge correction when a document main scanning direction shift occurs. A specific image processing method for document edge correction will be described with reference to FIGS.

  Normally, when reading a double-sided document, image data is transferred from both the first reading unit and the second reading unit to the image processing circuit 307. The image data transferred in parallel is temporarily stored in the memory 1802, serialized and read out at a double speed by the image processing unit 1803, and transferred to the subsequent processing block.

  In this embodiment, registration position information detected by the document edge detection processing circuit 303 is transmitted to a registration correction unit 1801 in the image processing circuit. The registration correction unit 1801 detects a difference between the reference position information stored in the register 1804 and the registration position information, that is, a registration correction amount, and transmits the difference amount to the image processing unit.

  The reference position information is set at the time of registration adjustment performed for each product when the product is shipped from the factory, and is stored in a storage unit such as a register in the image processing circuit.

  In FIG. 12, a signal LSYNC is a synchronization signal in the main scanning direction of the CCD 801 of the first reading unit, and there is data for the number of pixels of the CCD within this synchronization signal period (including empty transfer units and OPB pixels). ). The signal LGATE is a main scanning range signal (effective range) indicating an image range in the CCD main scanning direction.

  The signal LGATE is asserted at a timing delayed by a specified amount (counted by the number of CCD pixels) from the assertion timing of the signal LSYNC. The assert timing is equivalent to the registration correction amount obtained by the document edge detection process described above. By changing the assert timing (there may be either advancing or delaying the timing) and reading the first reading unit image data stored in the memory 1802, the image data that has undergone registration correction is passed to the subsequent processing.

  FIG. 13 shows an example of a control flow for explaining the operation of the present embodiment when the above-described functional blocks are used.

  When a document is set on the ADF 704 and reading is started by the first reading unit from the user interface (S1001), although not shown in the flow, after the shading data is acquired, the second reading roller (reference white member) ) Are separated from the second reading unit (S1002), and the conveyance of the document is started (S1003).

  First, normal image reading is performed on the document conveyed by the first reading unit, and the background portion is detected from the image data obtained at this time (S1004). As the background portion, for example, a method of detecting a margin portion of a document as shown in FIG.

  Based on the document background output level detected from the document background area, the TH voltage calculation circuit and the TH voltage holding circuit calculate and hold the optimum TH voltage (S1005). The TH voltage holding circuit 1213 transmits a TH voltage information code to the CIS control circuit 305, and the CIS control circuit 305 adjusts the TH voltage of the comparator (102) for each document by switching the duty of the COMP_PWM signal.

  A document edge is detected and executed by the document edge detection circuit 303 (S1008), and if edge detection is possible in S1009, the document edge information is immediately transmitted to the image processing circuit (307) via the controller 100. Then, the document edge correction as described above is performed in the image processing circuit (S1010).

  After completion of the document edge correction, the presence / absence of the next document is confirmed (S1012). If there is a document, the process returns to S1001 to execute the above series of operations. If there is no next original, the operation ends.

  If the document edge cannot be detected in S1009, the document edge correction is not performed (S1011), and the process proceeds to S1012.

  By the way, as a cause of the variation in the CIS output signal level, an initial variation in the light amount of the light source, a short-term variation in the light amount, a light amount life, a variation in CIS sensor sensitivity, and the like can be considered. The background level of the document is not always the same, and even a white document that is generally used frequently has a different density depending on the type, so that the CIS output level varies. In addition, a document with a colored background may be read, and the CIS output level varies depending on the emission wavelength of the light source and the spectral reflectance characteristics of the document background.

  For example, when the light source of the CIS 301 is an LED and the light emission wavelength center is a yellow-green light source having a light emission wavelength center of 570 [nm], the output level of the CIS 301 of a document having a blue background and a red background is lower than that of a document having a green background. End up.

  In the system in which the analog signal from the CIS 301 is converted into a binary digital signal by the comparator and the document edge position is detected, when the output signal level of the CIS 310 is small as described above, the threshold voltage of the comparator is not reached. There is a possibility that the document edge cannot be detected (FIG. 15).

  As shown in FIG. 16, with a fixed TH voltage, the pixel position that reaches the TH voltage differs between when a colored document is read and when a white document is read, resulting in a detection error. There is a possibility of being invited.

  In order to cope with the above problems, in the system that detects the document edge position by converting the analog signal from the CIS 301 into a binary digital signal by a comparator, according to the document type as in the above-described embodiment. By setting an optimum TH voltage value, the above problem can be solved.

  The magnitude of the output of the CIS 301 is mainly determined by the spectral reflectance of the recording medium, the spectral intensity characteristic of the illumination means, and the spectral sensitivity characteristic of the CIS 301. The integrated value of the total spectral characteristic obtained by multiplying each spectral characteristic for each wavelength. It corresponds to. FIG. 17 shows an example of the above contents.

  Since the spectral reflectances D (λ) of the originals are equal, G (λ determined from the spectral sensitivity characteristic P (λ) of the photoelectric conversion means constituting the first image processing means and the spectral intensity characteristic G (λ) of the illumination means. ) P (λ), and ΣG (λ) P (λ) determined from the spectral sensitivity characteristic P (λ) of the photoelectric conversion means constituting the first image reading means and the spectral intensity characteristic G (λ) of the illumination means. It is desirable to select an optimum means from the evaluation results at the design stage so that the characteristics match or are close to each other.

  Now, according to the above-described embodiment, it is possible to correct the misregistration for each read original, but depending on the system, until the original background level is detected by the first reading unit and the optimum TH voltage is set. It may take time to reduce the document conveyance speed, and as a result, productivity (scan / min) may decrease when reading multiple documents continuously. Conceivable.

  Therefore, for example, as shown in FIG. 18, it is possible to change the setting to a user interface such as the operation unit 108 so that the user can arbitrarily select whether to give priority to the image quality or the productivity. Thus, it is possible to improve user convenience / convenience.

  As described above, in this embodiment, the registration position deviation of the original is shifted using the second image reading unit that is originally unused only in the mode of reading the original using only the first image reading unit. By detecting the amount and correcting the registration position of the image data read by the first image reading means, it is possible to provide high-quality image data.

  In a system in which an analog signal from the CIS is converted into a binary digital signal by a comparator and a document edge position is detected, the document edge detection is performed by setting an optimum TH voltage value according to the document type. An error can be suppressed.

  Also, the total spectral characteristic determined by the spectral sensitivity characteristic of the first photoelectric conversion means and the spectral intensity of the illumination means, and the total spectral characteristic determined by the spectral sensitivity characteristic of the second photoelectric conversion means and the spectral intensity of the illumination means By making the characteristics coincide with or close to each other, it is possible to avoid a malfunction of detection of the recording medium edge and to detect the edge of the recording medium with a small detection error.

  In addition, it is possible to correct the registration error for each read original, but depending on the system, it may be considered that productivity (scan / min) is lowered when a plurality of originals are continuously read. Therefore, user-friendliness can be improved by enabling the user to change settings in the user interface such as the operation unit so that the user can arbitrarily select whether to give priority to image quality or productivity. It becomes possible.

  In addition, by incorporating the document reading apparatus according to the above-described embodiment into an image forming apparatus such as a copying machine or a multifunction peripheral, an image with good reading accuracy can be formed.

  In the above-described embodiments, the present invention is applied to a so-called stand-alone type image reading apparatus or image forming apparatus. However, the image reading apparatus and the image are connected to a network and capable of data communication with other apparatuses. The present invention can be similarly applied to a forming apparatus.

25 Second Reading Unit 100 Controller 108 Operation Unit 201 White Reference Member 202 Guide Member 203 White Reference Member Guide 205 Cam 208 Filler 209 Cam Position Detection Sensor 210 Link Member 301 CIS
302 Comparator 303 Document Edge Detection Circuit 305 CIS Control Circuit 306 TH Adjustment Circuit 704 ADF (Document Feeder)
714, 801 CCD image sensor 813 TH voltage holding circuit

JP 2004-147078 A JP 2005-012782 A

Claims (5)

A first image reading unit for reading a first surface of a document conveyed on the document conveyance path, a second image reading unit for reading a second surface of the document, and the second image reading unit. In an image reading apparatus provided with a white reference member disposed at an opposed position,
A separation control means for controlling the distance between the second image reading means and the white reference member by changing the position of the white reference member;
Document edge detection means for detecting a main scanning edge of a document from image data obtained by the second image reading means and detecting a deviation amount from a reference document edge position;
In a mode of reading a document using only the first image reading unit, the distance control unit is used to separate the distance between the second image reading unit and the white reference member from that during normal document reading, and An image reading apparatus comprising: a registration adjusting unit that detects a deviation amount using a document edge detecting unit and corrects a registration position of image data read by the first image reading unit.   The document edge detecting means includes a binarizing means for binarizing the output of the photoelectric conversion means constituting the second image reading means, and a background output level of the reference document obtained by the first image reading means. And a threshold voltage calculating means for calculating a threshold voltage of the binarizing means from a ratio with the background output level of the read document, and a control means for switching the threshold voltage obtained by the threshold voltage calculating means. The image reading apparatus according to claim 1, wherein:   The spectral sensitivity characteristics of the photoelectric conversion means constituting the first image reading means, and the overall spectral characteristics determined by the spectral intensity of the illumination means, and the spectral sensitivity characteristics of the photoelectric conversion means constituting the second image reading means, The image reading apparatus according to claim 1, wherein the total spectral characteristic determined by the spectral intensity of the illumination unit coincides with or is close to the characteristic.   4. The image reading apparatus according to claim 1, further comprising: a switching unit that allows a user interface to set whether or not to perform registration adjustment using the second reading unit. 5. .   An image forming apparatus comprising the image reading apparatus according to claim 1.