JP2008271464A - Image reading device - Google Patents

Abstract

An object of the present invention is to provide an image reading apparatus capable of reducing the apparatus cost.
An optical system for guiding a document image to a line image sensor has traveling means for moving a document image reading position, and a reference white image on a reference white plate provided on a moving path of the reading position is displayed on the line image sensor. In the image reading apparatus that performs shading correction for image reading by reading the image, the reference white plate is provided with a density image having a density different from that of the reference white image continuously to the reference white image, and the reading position is set to the reference white plate. The boundary between the reference white image provided on the reference white plate and the density image is determined based on the signal level output from the line image sensor when moving across the line, and the moving path of the determined boundary The upper coordinate value is set to the origin of the reading position.
[Selection] Figure 3

Description

  The present invention has traveling means for moving a reading position of an original document image of an optical system that guides a document image to a line image sensor, and a reference white image on a reference white plate provided on a moving path of the reading position is used as the line image sensor. The present invention relates to an image reading apparatus that performs shading correction for image reading.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads a document image with a line image sensor, converts image data into a digital signal, and processes the image data is generally a contact glass on which the document is placed, a light source for document exposure, and a first reflecting mirror. A first carriage comprising: a second carriage comprising a second reflecting mirror and a third reflecting mirror; a CCD line image sensor as a photoelectric conversion element; a lens unit for forming an image on the CCD line image sensor; a reading optical system; It is composed of a reference white plate used for shading correction of various waveform distortions due to the above. When scanning a document, the first carriage and the second carriage are moved in the sub-scanning direction by a stepping motor.

  In an image reading apparatus, an analog image signal from a line sensor that has read an image is input to an analog / digital conversion circuit to obtain a digital signal. At this time, in order to fully demonstrate the accuracy of the analog / digital converter, the gain amount in the gain amplifier is set so that the analog image signal changes widely between the upper limit reference value and the lower limit reference value of the analog / digital converter. The offset amount in the offset setting unit needs to be adjusted. Generally, in an image reading apparatus, an output of an analog / digital conversion circuit whose peak is detected is taken into a CPU, and an optimum gain setting value is calculated by comparison with a target value, and the gain of the gain amplifier is calculated based on the gain setting value. The configuration is changed (automatic adjustment of reading level). Here, the above-described reference white plate is used for peak detection.

  By the way, in the scanner, the movement of the carriage on which the reading means is mounted is controlled according to the respective operating conditions at the time of initialization processing (initialization processing is performed when the power is turned on or when returning from the standby mode) and at the time of document reading. . That is, the carriage has a home position sensor effective range (a range in which the detection output of the home position sensor (HPS) that detects the carriage is effective), a reference white plate effective range (a reference white plate is disposed, Forward movement and reverse movement control are performed between each of the range in which the white plate reading signal is valid) and the document reading range. During the initialization process, it is necessary to perform a home position movement operation performed according to the HPS output and an operation for reading the reference white plate (arranged between the HPS effective range and the document reading range of the document).

Patent Document 1 proposes a method for detecting the position of the first carriage without using this HPS. That is, position detection is performed by reading a position detection patch arranged outside the document reading area by a signal from a CCD element outside the document reading area in a CCD line image sensor that reads the document.
JP2003-032446

  However, in the case of this conventional method, not only an extra part such as the above-described position detection patch has to be arranged, but also an extra CCD element is required in the CCD line image sensor in order to read outside the original reading area. For this reason, there are problems such as an increase in cost and an increase in time for outputting one line.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus capable of reducing the cost of the apparatus.

  The present invention has traveling means for moving a reading position of an original document image of an optical system that guides a document image to a line image sensor, and a reference white image on a reference white plate provided on a moving path of the reading position is used as the line image sensor. In the image reading apparatus that performs shading correction for image reading by reading the image, the reference white plate is provided with a density image having a density different from that of the reference white image continuously to the reference white image, and the reading position is set to the reference white plate. The boundary between the reference white image provided on the reference white plate and the density image is determined based on the signal level output from the line image sensor when moving across the line, and the moving path of the determined boundary The upper coordinate value is set to the origin of the reading position.

  Also, immediately after the power is turned on or immediately after the operation is reset, the reading position origin setting process is performed.

  Further, the origin set by the process for setting the origin of the reading position is set as the operation standby position.

  Therefore, according to the present invention, since the origin position of the reading position is detected using the CCD line image sensor, there is an effect that an extra sensor such as a home position sensor becomes unnecessary.

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

  FIG. 1 shows a schematic configuration of an image reading apparatus 1 according to an embodiment of the present invention. The image reading apparatus 1 includes an automatic document conveyance unit 1a that separates read documents from the document table 2 one by one and conveys them to the reading position RL, and an image reading unit that scans document images in the sub-scanning direction and reads line by line. 1b.

  Further, the automatic document conveying unit 1a is rotatably supported by one side of the image reading unit 1b and is in a state in which the automatic document conveying unit 1a is positioned so as to cover the document reading unit 1b. The state in which the automatic document conveyance unit 1a is closed is referred to as “the automatic document conveyance unit 1a is open” when the automatic document conveyance unit 1a releases the contact glass (described later) of the document reading unit 1b. The image reading unit 1b has two document reading functions, a sheet scan type document reading function and a book scan type document reading function.

  In the automatic document feeder unit 1 a, the read document PP placed on the document table 2 is taken out by the pickup roller 3 at the uppermost position and sent to the separation unit 4. They are separated one by one and delivered to the delivery roller 5. The delivery roller 5 sends out one read original in the transport direction through the guide member GG.

  As a result, the read original PP is sandwiched between the transport roller 6 and the transport drum 7, transported in close contact with the surface of the transport drum 7, passes through the reading position RL, and is transported to the discharge roller 8. The paper is discharged onto the paper discharge tray 9 by the discharge roller 8.

  In the document reading unit 1b, a sheet scanning contact glass 10 is disposed corresponding to the reading position RL. The dimension of the contact glass 10 in the sub-scanning direction is about 4 (mm).

  Further, a contact glass 11 for book scanning is disposed on the right side of the contact glass 10. The reference white board WW is used to construct a white reference image for shading correction, and a blackboard WL (density image) for detecting the origin position in the sub-scanning direction of image reading is in the forward direction (described later). It is closely attached.

  During the so-called sheet reading operation (sheet reading mode) using the automatic document feeder unit 1a, the lamp 12 illuminates the document surface of the reading document PP at the reading position RL, and the reflected light from the reading position RL is: The first mirror 13, the second mirror 14, and the third mirror 15 are sequentially reflected, guided to the lens 18, focused by the lens 18, and irradiated to the CCD line image sensor 20 provided on the substrate 19. .

  The lamp 12 and the first mirror 13 are mounted on the first carriage 16 and reciprocated in the sub-scanning direction SS, and the second mirror 14 and the third mirror 15 are mounted on the second carriage 17 and connected to the sub-scanning direction SS. Reciprocates in the scanning direction SS. Further, in order to maintain the optical path length from the contact glass 10 to the CCD line image sensor 20, the second carriage 17 is moved at a speed half that of the first carriage 16.

  The scanner motor 21 is for driving the first carriage 16 and the second carriage 17. The document sensor SS1 is for detecting that a document is placed on the contact glass 11. The open / close sensor SS2 indicates that the automatic document transport unit 1a is opened / closed with respect to the image reading unit 1b. It is for detecting.

  FIG. 2 shows an example of a control system of the image reading apparatus shown in FIG.

  In the figure, a system control unit 31 is for controlling the operation of each unit of the image reading apparatus, and a system memory 32 is referred to by each control program executed by the system control unit 31 and those programs. The parameter memory 33 is for storing information unique to the image reading apparatus (for example, apparatus model number information and manufacturing serial number), and the operation display unit 34 is The image reading device is for user operation and includes various operation keys and a display device (liquid crystal display device, LED, etc.). The external interface circuit 35 connects the image reading apparatus to an external apparatus (for example, a personal computer apparatus) and exchanges various data with the connected external apparatus.

  The ADF motor driving unit 35 is for driving an ADF motor 37 that is a power source of the automatic document conveyance unit 1 a, and the scanner motor driving unit 38 is for driving the scanner motor 21.

  The image processing unit 39 is for applying various processes to the read image data output from the image reading unit 40 including the CCD line image sensor 20 and its peripheral circuits. Here, the image processing unit 39 also performs detection processing such as a level change of a read signal of the CCD line image sensor 20 described later.

  Further, detection signals from the document sensor SS1, the open / close sensor SS2, and other sensors (for example, a cover sensor) SS3 are applied to the system control unit 31.

  Next, the movement of the first carriage 16 and the second carriage 17 in the sub-scanning direction SS will be described with reference to FIGS. 3 (a) and 3 (b). The reference white board WW and the blackboard WL are made of long members corresponding to the dimensions in the sub-scanning direction, as shown in FIG.

  Here, when the first carriage 16 and the second carriage 17 are reciprocated in the sub-scanning direction SS, the sub-scanning reading position of the original image incident on the CCD line image sensor 20 is moved. The position is defined as the sub-scanning position. Further, the forward direction of the sub-scanning direction SS is called “forward direction”, and the reverse direction of the sub-scanning direction SS is called “reverse direction”.

  As the sub-scanning position, a movement limit position (sub-scanning position movement limit) PK on the upstream side in the sub-scanning direction SS is mechanically determined. Accordingly, the first carriage 16 cannot move further upstream in the sub-scanning direction SS.

  Further, in the forward direction from the movement limit position PK, the reading position RL, the movement start position PP of the first carriage 16 in the book reading mode, and the boundary point GP between the reference white board WW and the blackboard WL are sequentially located, and reading A document (not shown) is placed with its end abutting against the right end of the blackboard WL.

  With the above configuration, in the case of the present embodiment, in the process immediately after the power is turned on or immediately after the operation is reset, the moving distance L2 at the time of detecting the origin is moved in the forward direction while monitoring the reading signal of the CCD line image sensor 20. A sub-scanning position where the level of the read signal has changed from the white level to the black level is detected, the detected sub-scanning position is determined as the boundary point GP, and the coordinate value of the boundary point GP is set as the origin position in the sub-scanning direction. Set.

  Here, the dimension of the movement distance L2 at the time of detecting the origin is such that the first carriage 16 moves from the movement limit position PK, gets over the reference white plate WW and the blackboard WL, and further in the sub-scanning direction combining the reference white plate WW and the blackboard WL. A value corresponding to the distance when moving the distance L1 is set.

  Thereby, for example, at the time of processing for setting the origin position in the sub-scanning direction (described later), the boundary point GP can be detected regardless of the position at which the first carriage 16 is stopped.

  When the origin position is set, the first carriage 16 is moved to the reference white plate effective range of the reference white plate WW, and shading reference data sampling and reading level automatic adjustment processing of the image reading unit 40 are performed.

  Thereafter, when the book reading operation mode is instructed by the user, the first carriage 16 is moved to the movement start position PP, and the operation is put on standby. When the reading start is instructed, the first carriage 16 is moved in the forward direction from the movement start position PP, and the speed when the first carriage 16 reaches the document reading range is increased to a predetermined speed. In the reading range, the first carriage 16 is moved at a constant speed.

  Further, when the first carriage 16 is moved and the reading operation of the image reading unit 40 is started and the document reading range is being scanned, the read image data is output line by line.

  On the other hand, when the sheet reading operation mode is instructed by the user, the first carriage 16 is moved to the reading position RL to wait for operation. When the start of reading is instructed, the automatic document conveying unit 1a conveys the read original PP one by one and starts the reading operation of the image reading 40, with the read original PP crossing the reading position RL. The read image data is output line by line.

  4 and 5 show an example of processing executed immediately after turning on the power or immediately after resetting the operation.

  First, the reading operation of the image reading unit 40 is started, and the detection of the boundary point GP is started by the image processing unit 39 (processing 101). As a result, the level change of the read signal of the CCD line image sensor 20 output from the image reading unit 40 is detected by the image reading unit 40.

  Then, the first carriage 16 is moved in the forward direction by a distance corresponding to the movement distance L2 at the time of detecting the origin (processing 102), and it is checked whether the image reading unit 40 detects the boundary point GP during the movement (step 102). Decision 103).

  When the result of determination 103 is YES, the first carriage 16 is moved in the reverse direction by a distance corresponding to the dimension L1 (process 104), and the image reading unit 40 detects the boundary point GP during the movement. A check is made (decision 105).

  When the result of determination 105 is YES, since the boundary point GP is being detected except for the boundary point GP between the reference white board WW and the blackboard WL, the detection operation of the boundary point GP is in error, and the initial operation is not performed. An error detection process or the like is performed (process 106), and the operation at this time ends with an error.

  When the result of determination 105 is NO, since the boundary point GP between the reference white board WW and the blackboard WL has been detected, setting processing is performed using the detected coordinate value in the sub-scanning direction as the origin (processing 107). ).

  Next, using the origin set at that time as a reference, the first carriage 16 is moved to the reference white plate effective range of the reference white plate WW (processing 108), a predetermined reading level automatic adjustment processing (processing 109) is performed, and the scanner standby is performed. The state is shifted (process 110). Here, in the process 109, an optimum gain setting value is calculated by comparing the peak detection value of the reading level of the image reading unit 40 and the target value, and a gain amplifier (not shown) of the image reading unit 40 is calculated based on this gain setting value. ) Is used to change the gain setting.

  If the boundary point GP cannot be detected when the first carriage 16 is moved for the first time and the result of determination 103 is NO, whether or not the boundary point has been detected while moving the first carriage 16 in a slight reverse direction. This determination process is repeated until the movement exceeds an allowable range determined as a process error (NO loop of process 111 and determinations 112 and 113). If the boundary point GP cannot be detected even if it moves beyond the allowable range and the result of determination 112 is YES, error detection processing of the initial operation is performed (processing 114), and the operation at this time is terminated with an error.

  If the boundary point GP is detected before moving within the allowable range and the result of determination 113 is YES, setting processing is performed with the detected coordinate value in the sub-scanning direction as the origin (processing 115). The first carriage 16 is moved to the reference white plate effective range of the reference white plate WW with reference to the origin set at that time (step 116), and the process proceeds to step 109, and the subsequent processing is executed.

  FIG. 6 shows an example of processing in the book reading mode.

  When the open / close sensor SS2 detects opening / closing of the automatic document transport unit 1a (process 201), it is checked whether the document sensor SS1 has detected a document (determination 202). When the result of determination 202 is YES, the first carriage 16 is moved to the movement start position PP (process 202), the reading operation is sequentially completed, and waiting for a user operation (process 204). .

  If the result of determination 202 is NO, the process 203 is not executed and the process proceeds to process 204.

  FIG. 7 shows an example of processing in the sheet reading operation mode.

  First, since it stops at the boundary point GP, the first carriage 16 is moved in the reverse direction, and shading data is generated while reading the image of the reference white board WW (processing 301). Then, the first carriage 16 is stopped at the reading position RL, and the above-described document image reading operation is performed (processing 302).

  When the reading operation for one page is completed, the next original is detected, and when the result of determination 303 is YES, the first carriage 16 is moved to the reference white plate WW (processing 304), and shading data is generated (processing). Next, the first carriage 16 is moved to the reading position RL (process 306), and the reading operation at the reading position RL is repeated (process 307).

  When the document is finished and the result of determination 303 is NO, the reading operation is finished.

  By the way, in the reading level automatic adjustment process 109, the peak detection value of the reading level of the image reading unit 40 and the target value are compared to calculate an optimum gain setting value, and the gain setting value of the image reading unit 40 is calculated. An algorithm that changes the gain setting of a gain amplifier (not shown) is applied.

  However, using this algorithm requires a certain amount of adjustment time and takes time. Therefore, the detection value used in the detection of the boundary point GP is stored, and the ratio between the detection value at the previous detection of the boundary point GP and the detection value at the detection of the current boundary point GP is set to the previously set gain. The gain can be quickly adjusted by multiplying by.

  FIGS. 8 and 9 show an example of processing executed immediately after power-on or operation reset in this case.

  First, the reading operation of the image reading unit 40 is started, and the detection of the boundary point GP is started by the image processing unit 39 (processing 401). As a result, the level change of the read signal of the CCD line image sensor 20 output from the image reading unit 40 is detected by the image reading unit 40.

  Then, the first carriage 16 is moved in the forward direction by a distance corresponding to the movement distance L2 at the time of detecting the origin (processing 402), and it is checked whether the image reading unit 40 detects the boundary point GP during the movement (step 402). Decision 403).

  When the result of determination 403 is YES, the first carriage 16 is moved in the reverse direction by a distance corresponding to the dimension L1 (process 404), and the image reading unit 40 detects the boundary point GP during the movement. A check is made (decision 405).

  When the result of determination 405 is YES, since the boundary point GP is being detected except for the boundary point GP between the reference white board WW and the blackboard WL, the detection operation of the boundary point GP has an error, and the initial operation is not performed. An error detection process or the like is performed (process 406), and the operation at this time ends with an error.

  Further, when the result of determination 405 is NO, the boundary point GP between the reference white board WW and the blackboard WL has been detected, so a setting process is performed with the detected coordinate value in the sub-scanning direction as the origin (process 407). ).

  Next, using the origin set at that time as a reference, the first carriage 16 is moved to the reference white plate effective range of the reference white plate WW (processing 408), a predetermined reading level automatic adjustment processing (processing 409) is performed, and scanner standby is performed. The state is shifted (process 410). In this reading level automatic adjustment processing, the previously set gain is multiplied by the ratio of the detection value at the previous detection of the boundary point GP and the detection value at the detection of the current boundary point GP.

  If the boundary point GP cannot be detected when the first carriage 16 is moved for the first time and the result of determination 103 is NO, whether or not the boundary point has been detected while moving the first carriage 16 in a slight reverse direction. This determination process is repeated until the movement exceeds an allowable range determined as a process error (NO loop of process 411, determinations 412 and 413). If the boundary point GP cannot be detected even if it moves beyond the allowable range and the result of determination 412 is YES, error detection processing of the initial operation is performed (processing 414), and the operation at this time is terminated with an error.

  If the boundary point GP is detected before moving within the allowable range and the result of determination 413 is YES, a setting process is performed with the detected coordinate value in the sub-scanning direction as the origin (process 415). Then, the first carriage 16 is moved to the reference white plate effective range of the reference white plate WW with reference to the origin set at that time (step 416), and the processing shifts to step 409 to execute the subsequent processing.

  As described above, in this embodiment, since no special sensor is used to detect the origin of the first carriage 16, the cost of the apparatus can be reduced.

  By the way, in the above-described embodiment, one boundary point GP between the reference white board WW and the blackboard WL (density image) is provided. By providing a plurality of boundary points GP, the boundary point GP (= first boundary point, ie, Misdetection of the origin) can be suppressed. For example, as shown in FIGS. 10A and 10B, when a black and white density image WL ′ that is long in the sub-scanning direction is provided and two density boundary points TN1 and TN2 are provided, this density boundary is provided. Are formed at three boundary points GP, TN1, and TN2, and by detecting the boundary point GP after confirming that the boundary points GP, TN1, and TN2 are detected, the detection accuracy of the boundary point GP is improved. Can be improved.

  Further, the standby position of the first carriage 16 immediately after the power is turned on or immediately after the operation is reset can be set to an arbitrary position. For example, when waiting at the boundary point GP, it is possible to reduce the moving distance when generating shading data, so that the activation time can be shortened. Further, the reading position RL can be set as a standby position.

  In the above-described embodiment, the boundary point GP between the reference white board WW and the blackboard WL is detected. However, the boundary point GP is detected by detecting the edge of the reference white board WW without using the blackboard WL. It can also be detected. In that case, since the read signal level of the CCD line image sensor 20 changes based on the difference between the reflectance of the reference white plate WW and the reflectance of the contact glass 11, it is possible to detect the boundary by detecting the change in the signal level. The point GP can be detected. Alternatively, when there is a difference between the reflectance of the reference white plate WW and the reflectance at the edge portion of the reference white plate WW, the change in the read signal level of the CCD line image sensor 20 based on the difference in reflectance is used. Can do.

  In the above-described embodiment, the first carriage 16 is moved in the forward direction in order to detect the boundary point GP. However, the detection operation of the boundary point GP is performed by moving the first carriage 16 in the reverse direction. You can also. In this case, for example, the moving direction when the boundary point GP is detected may be determined depending on where the return position of the first carriage 16 at the end of the reading operation of the image reading unit 1b is determined.

  In each of the above-described embodiments, the case where the present invention is applied to a single image reading apparatus has been described. However, the present invention is similarly applied to an image processing apparatus having an image reading function such as a copying machine or a multifunction peripheral. Can be applied.

1 is a schematic configuration diagram of an image reading apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of a control system of the image reading apparatus illustrated in FIG. 1. FIG. 4 is a schematic diagram for explaining movement of the first carriage 16 and the second carriage 17 in the sub-scanning direction SS. 6 is a flowchart showing an example of processing executed immediately after power-on or immediately after operation reset (continuing to FIG. 5). The flowchart which showed an example of the process performed immediately after power activation or immediately after operation reset (continuation of FIG. 4). The flowchart which showed an example of the process at the time of book reading mode. 6 is a flowchart illustrating an example of processing in a sheet reading operation mode. 10 is a flowchart showing another example of processing executed immediately after power-on or immediately after operation reset (continuing to FIG. 9). The flowchart which showed the other example of the process performed immediately after power-on or operation reset (continuation of FIG. 8). Schematic for demonstrating the other example of the reference | standard white board WW and a density image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Automatic document conveyance unit 1b Document reading unit 16 1st carriage 20 CCD line image sensor 31 System control part 39 Image processing part 40 Image reading part WW Reference white board WL, WL 'Blackboard (density image)

Claims (3)

A traveling unit that moves the reading position of the original image of the optical system that guides the original image to the line image sensor, and reads the reference white image of the reference white plate provided on the moving path of the reading position by the line image sensor. In an image reading apparatus that performs shading correction of reading,
On the reference white plate, a density image having a density different from that of the reference white image is provided continuously to the reference white image,
Based on the signal level output from the line image sensor when the reading position is moved across the reference white plate, the boundary between the reference white image provided on the reference white plate and the density image is determined, An image reading apparatus, wherein a coordinate value of the determined boundary on the moving path is set as an origin of the reading position.   2. The image reading apparatus according to claim 1, wherein the reading position origin is set immediately after the power is turned on or immediately after the operation is reset.   The image reading apparatus according to claim 1, wherein the origin set by the setting process of the origin of the reading position is set as an operation standby position.