Reading device

Abstract

To provide a reading apparatus with which it is possible to prevent the home position of a reading device from being erroneously detected.SOLUTION: When a document is read by a CIS unit, a light quantity adjustment value for adjusting the light quantity of a light source is acquired before this reading. Also, a shading correction value for correcting shading is acquired. The light quantity adjustment value the shading correction value are stored in a nonvolatile memory. In a HP detection process, the light quantity of the light source is adjusted using the light quantity adjustment value stored in the nonvolatile memory, and the CIS unit is moved in a sub-scan direction and reads the document (S26). Then, shading correction is carried out using the shading correction value stored in the nonvolatile memory (S27). After this shading correction, detection of a position where mutually adjacent pixel values change across a prescribed HP detection threshold is carried out (S28), and when it is detected, the position is made to be the home position of the CIS unit.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a reading device.

Background Art

[0002] Conventionally, a reading device for reading a document by a FB (Flat Bed) method has been provided.

[0003] In a FB method reading device, a reading device extending in the main scanning direction is provided below a document table made of transparent glass so as to be reciprocally movable in a sub-scanning direction orthogonal to the main scanning direction. The reading device incorporates a light source, a light guide, an image sensor, and the like. Light from the light source is irradiated onto the document through the light guide, and the reflected light from the document passes through a lens and enters the image sensor. Photoelectric conversion is performed by each light receiving element of the image sensor, an electrical signal is output from each light receiving element, and by converting the electrical signal into a pixel value, reading of one line in the main scanning direction by the reading device is achieved.

[0004] In order to control the movement of the reading device when reading a document, the control unit needs to know the position of the reading device. To know the position of the reading device, the home position (reference position) of the reading device is detected by the control unit. For example, a reference plate in which a white area and a black area are arranged adjacent to each other in the sub-scanning direction is provided, the reference plate is read by the reading device, and the position of the read black area is detected as the home position.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Conventionally, when detecting the home position, light amount adjustment and shading correction are not performed. Therefore, there is a risk of misdetecting the home position due to non-uniform sensitivity (PRNU: Photo Response Non-Uniformity) of the image sensor, fluctuations in illumination depth due to mechanical factors such as warping of the platen, and aging degradation of the light source.

[0007] An object of the present invention is to provide a reading device capable of suppressing misdetection of the home position of a reading device.

Means for Solving the Problems

[0008] To achieve the above object, a reading device according to the present invention includes a platen having a support surface for supporting a document, and a reading device provided on the side opposite to the support surface side with respect to the platen so as to be reciprocally movable in a sub-scanning direction parallel to the support surface, the reading device having a light source for irradiating light onto a reading target on the support surface and an image sensor for converting reflected light from the reading target into a signal, a reference portion disposed at a position corresponding to the home position of the reading device, a storage portion, and a control portion. The control portion, when causing the reading device to read a document, before reading the document, causes the reading device to read the reference portion, obtains an adjustment value for adjusting the light amount of the light source using the signal output from the image sensor by this reading, stores the adjustment value in the storage portion, before reading the document, causes the light source to emit light with the light amount adjusted using the adjustment value, causes the reading device to read the reference portion, obtains a correction value for shading correction using the signal output from the image sensor by this reading, stores the correction value in the storage portion, causes the light source to emit light with the light amount adjusted using the adjustment value stored in the storage portion, causes the reading device to read while moving the reading device in the sub-scanning direction, and performs shading correction on the pixel value indicated by the signal output from the image sensor by this reading using the correction value stored in the storage portion, and detects the position where the pixel value after shading correction changes across a predetermined threshold value as the home position.

[0009] According to this configuration, when a document is read by a reading device, before the reading, a reference portion is read by the reading device, and an adjustment value for adjusting the light amount of a light source is obtained by a control unit. Further, after the light amount of the light source is adjusted using the adjustment value, the reference portion is read again by the reading device, and a correction value for shading correction is obtained by the control unit. The adjustment value and the correction value are stored in a storage unit.

[0010] When detecting the home position of the reading device, the light amount of the light source is adjusted using the adjustment value stored in the storage unit, and reading by the reading device is performed while the reading device is moved in the sub-scanning direction. Then, the pixel value indicated by the signal output from the image sensor is subjected to shading correction using the correction value stored in the storage unit, and the position where the pixel value after the shading correction changes across a predetermined threshold value is detected as the home position of the reading device.

[0011] Therefore, it is possible to detect the home position of the reading device while eliminating the influences such as the sensitivity non-uniformity (PRNU) of the image sensor, the variation in illumination depth due to mechanical factors, and the secular deterioration of the light source. As a result, it is possible to suppress the misdetection of the home position.

Advantages of the Invention

[0012] According to the present invention, it is possible to suppress the misdetection of the home position of the reading device.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] <Configuration of the Reading Device> The reading device 1 shown in FIG. 1 is a device for reading a document, and includes a housing 2 and a document cover 3. The reading device 1 is configured to be able to read a document by both the FB method and the ADF method. An ADF (Auto Document Feeder) 4 is provided on the document cover 3 of the reading device 1.

[0016] For use in the following description, the front, rear, left, and right of the reading device 1 are defined based on the state of the reading device 1 as viewed from its front side. Also, the up and down are defined in the state where the reading device 1 is installed on a horizontal plane. FIG. 1 shows a cross-section of the reading device 1 cut along a cutting plane line extending in the left-right direction.

[0017] The housing 2 has a substantially rectangular parallelepiped shape. As shown in FIG. 2, a first opening 12 and a second opening 13 are provided on the top plate 11 of the housing 2.

[0018] The first opening 12 has edges extending in the front-rear and left-right directions, and is formed in a rectangular shape that is longer left-right than it is front-rear. An original placement plate 14 is provided so as to cover the first opening 12 from below. The original placement plate 14 is formed in a flat plate shape using a transparent material.

[0019] The second opening 13 has edges extending in the front-rear and left-right directions on the left side of the first opening 12, and is formed in an elongated rectangular shape extending in the front-rear direction. An original passing plate 15 is provided so as to cover the second opening 13 from below. The original passing plate 15 is formed in a flat plate shape using a transparent material.

[0020] 1, a CIS (Contact Image Sensor) unit 21 is provided within the housing 2 so as to be movable in the sub-scanning direction, which is the left-right direction, below the document placement plate 14 (an example of a document table) and the document passing plate 15. The CIS unit 21 (an example of a reading device) includes a light source 22, a light guide 23, a rod lens array 24, and an image sensor 25.

[0021] The light source 22 includes three light emitting diodes (LEDs) of red, green and blue colors. The lighting of the light source 22 is controlled by pulse width modulation.

[0022] The light guide 23 is made of a transparent material and is a member that propagates light from the light source 22. The light guide 23 is disposed in front of the light source 22 and extends in the main scanning direction, which is the front-rear direction perpendicular to the sub-scanning direction.

[0023] The rod lens array 24 is shifted in position in the left-right direction from the light guide 23, and is disposed, for example, on the left side of the light guide 23. As shown in Fig. 3, the rod lens array 24 includes a large number of rod lenses 26 (an example of a lens) aligned in the main scanning direction. The rod lenses 26 are gradient index lenses with a fixed magnification.

[0024] The image sensor 25 includes a predetermined number (for example, 12) of sensor IC chips 27. The sensor IC chips 27 are arranged in a row in the main scanning direction. Each sensor IC chip 27 includes a light receiving element array 28. The light receiving element array 28 is configured by arranging a plurality of light receiving elements 29 in a row at equal pitches in the main scanning direction. Each light receiving element 29 outputs an electric charge corresponding to the amount of received light as an electric signal of one pixel.

[0025] Also, the image sensor 25 is provided with a gain adjustment circuit, an A / D conversion circuit, and the like. The voltage output from each light receiving element 29 is amplified by the gain adjustment circuit and then converted into pixel data (pixel value), which is a digital value, by the A / D conversion circuit. The A / D conversion circuit has a resolution of, for example, 8 bits (0 to 255). Voltages less than the lower reference voltage (lower limit value) are uniformly converted to "0", voltages exceeding the upper reference voltage (upper limit value) are uniformly converted to "255", and voltages in the range from the lower limit value to the upper limit value are converted into pixel data according to the magnitude of the voltage.

[0026] The light from the light source 22 is irradiated onto the object to be read through the light guide 23, and the reflected light from the object to be read passes through the rod lens array 24 and enters the image sensor 25. One rod lens 26 forms a conjugate image on the light receiving surfaces of, for example, about 3.5 light receiving elements 29. Photoelectric conversion is performed by each light receiving element 29, an electric signal is output from each light receiving element 29, and the electric signal is converted into pixel data, thereby achieving the reading of one line in the main scanning direction by the CIS unit 21.

[0027] As shown in FIG. 1, the ADF 4 is provided with a supply tray 31 and a discharge tray 32. The supply tray 31 and the discharge tray 32 are provided in a state where they are vertically spaced apart and overlap each other. Inside the ADF 4, a conveyance path 33 is formed. One end of the conveyance path 33 is open on one end of the supply tray 31 in the sub-scanning direction, is bent while curving in a U shape, passes over the document passing surface 17, and the other end is open between the supply tray 31 and the discharge tray 32. Further, inside the ADF 4, a supply roller 34, a separation roller 35, a conveyance roller 36, a reverse roller 37, and a discharge roller 38 are provided in this order from the supply tray 31 side along the conveyance path 33.

[0028] The document cover 3 is provided so as to be openable and closable between an open position and a closed position. In a state where the document cover 3 is in the closed position, the entire upper surface of the housing 2 is covered by the document cover 3. The document cover 3 is displaced to the open position by lifting the front side from the closed position. In a state where the document cover 3 is in the open position, the entire upper surface of the housing 2 is exposed.

[0029] When reading a document by the FB method, the document cover 3 is opened to the open position, and the document is placed on the upper surface (an example of a support surface) of the document placement plate 14. At this time, the document is arranged in a state where the left edge abuts against the left edge of the first opening 12 from the right side, and the rear edge abuts against the rear edge of the first opening 12 from the front side. Then, the document cover 3 is closed to the closed position, and the document is covered from above by the document cover 3. Then, in response to a command to execute scanning, the CIS unit 21 is moved to a position corresponding to the reading start position at the head of the reading range, and while moving in the sub-scanning direction from that position, the CIS unit 21 reads the document on the document placement plate 14 one line at a time in the sub-scanning direction in order, thereby achieving reading of the document.

[0030] On one hand, when reading a document by the ADF method, the document is placed on the supply tray 31 of the ADF 4. Also, the CIS unit 21 is stopped at a position facing the document passing plate 15 from below. Then, in response to a command to execute scanning, the conveyance of the document by the supply roller 34 is started. The document is separated one by one by the separation roller 35 and conveyed through the conveyance path 33 by the conveyance roller 36 and the reverse roller 37. While the document passes over the document passing plate 15, the CIS unit 21 reads the document line by line in order, thereby achieving the reading of the document.

[0031] On the left side of the document passing plate 15, as shown in FIG. 2, a black-and-white reference portion 41 (an example of a reference portion) is provided. The black-and-white reference portion 41 is formed as a rectangular tape and is adhered to the back surface (the surface facing downward) of the top plate 11 of the housing 2 so as to extend in the front-rear direction that coincides with the main scanning direction on the left side of the document passing plate 15. In the black-and-white reference portion 41, rectangular regions at the front right and rear right corners are black regions 42, and the remaining regions are white regions 43. Thereby, in the region along the right edge of the black-and-white reference portion 41, the white region 43 is sandwiched between two black regions 42, and each black region 42 and the white region 43 are continuous. In the region along the front edge and the region along the rear edge, the white region 43 is adjacent to the left side of the black region 42, and the black region 42 and the white region 43 are continuous.

[0032] Also, as shown in FIG. 4, the reading device 1 includes a CPU (Central Processing Unit) 51, a non-volatile memory 52 (an example of a storage unit) capable of rewriting data such as a flash memory and an E2PROM, and a volatile memory 53 such as an SDRAM. The CPU 51, the non-volatile memory 52, and the volatile memory 53 are connected to a bus 54 for data communication.

[0033] The CPU 51 (an example of a control unit) controls each part of the reading device 1 by executing programs for various processes, such as the ADF 4, the CIS unit 21, and the CIS unit moving mechanism 55 that moves the CIS unit 21 in the sub-scanning direction. The non-volatile memory 52 stores programs executed by the CPU 51, various data, and the like. The volatile memory 53 is used as a work area when the CPU 51 executes programs.

[0034] The CIS unit moving mechanism 55 includes a carriage that carries the CIS unit 21, a stepping motor that can rotate forward and backward, a drive pulley that is rotationally driven by the stepping motor, a driven pulley that pairs with the drive pulley, and a belt wound around the drive pulley and the driven pulley. The drive pulley and the driven pulley are spaced apart from each other in the left-right direction, and their rotation axes are arranged so as to extend in the front-rear direction. The middle part of the belt is fixed to the carriage. When the drive pulley rotates, the belt runs, and as the belt runs, the carriage carrying the CIS unit 21 moves in the sub-scanning direction that coincides with the left-right direction.

[0035] The reading device 1 is also provided with an operation panel 56. The operation panel 56 includes an operation part that is operated for various settings and a display part for displaying information. The operation part and the display part may be provided separately, or may be in the form of a touch panel configured by overlapping an operation part such as a pressure-sensitive or capacitive transparent film switch on a display part such as a liquid crystal display.

[0036] <Reading process> When a reading instruction for the original document is input to the reading device 1, the CPU 51 starts the reading process shown in FIG. 5. The reading instruction for the original document is input from the operation panel, for example, when the user operates the operation panel 56. When inputting the reading instruction, the user sets the reading resolution of the original document by operating the operation panel 56. Three levels of reading resolution are provided: 300 dpi, 600 dpi, and 1200 dpi.

[0037] Hereinafter, the case where the reading instruction of the manuscript is an instruction for reading by the FB method will be taken as an example.

[0038] In the reading process, the CPU 51 causes the non-volatile memory 52 to store the reading resolution set by the user (S11). The reading resolution stored in the non-volatile memory 52 is updated by overwriting each time the reading process is performed.

[0039] Then, the CPU 51 performs light amount adjustment (S12). In the light amount adjustment, the CPU 51 controls the CIS unit 21 and the CIS unit moving mechanism 55 to cause the CIS unit 21 to read the white area 43 of the black-and-white reference portion 41. Then, the CPU 51 adjusts the current value supplied to the light source 22 of the CIS unit 21 and the duty ratio of the lighting time of the light source 22 so that the maximum value of the pixel values of each pixel for one line obtained by the reading becomes a predetermined value (for example, 254). The CPU 51 causes the non-volatile memory 52 to store the current value and the duty ratio set by the light amount adjustment as the light amount adjustment value (S13). The light amount adjustment value stored in the non-volatile memory 52 is updated by overwriting each time the light amount adjustment is performed.

[0040] After the light amount adjustment, the CPU 51 acquires the shading correction value (S14). That is, the CPU 51 supplies current to the light source 22 at the current value and the duty ratio set by the light amount adjustment, and causes the CIS unit 21 to read the white area 43 of the black-and-white reference portion 41. Then, the CPU 51 obtains a white level correction value for correcting the non-uniformity of the white level from the pixel values for one line obtained by the reading, and causes the volatile memory 53 to store the white level correction value as the shading correction value.

[0041] Further, as shown in FIG. 6, the CPU 51 divides the shading correction values into blocks for every certain number of pixels (for example, 550 pixels). Then, the CPU 51 calculates the average value of the shading correction values for each block, and stores the calculated shading correction average value per block in the non-volatile memory 52 in association with block identification information for identifying the block (S15). The block identification information may be a unique number assigned to each block or the range of pixel numbers included in each block. The shading correction average value per block stored in the non-volatile memory 52 is updated by overwriting each time the calculation of the shading correction average value per block is performed.

[0042] Thereafter, the CPU 51 reads the original document (actual reading) (S16). The CPU 51 controls the CIS unit 21 and the CIS unit moving mechanism 55 to move the CIS unit 21 from the standby position set to the left of the left end of the original document placing plate 14 to the right while causing the CIS unit 21 to read the original document on the original document placing plate 14.

[0043] Each time the CIS unit 21 reads one line of the original document, the CPU 51 increments (+1 count up) the count value of the CIS operation line number storage counter set in the volatile memory 53 (S17).

[0044] Thereafter, the CPU 51 determines whether the reading position of the CIS unit 21 has reached the final reading line of the original document from the count value of the CIS operation line number counter (S18). That is, while the count value of the CIS operation line number counter has not reached a predetermined value corresponding to the original document size, the CPU 51 determines that the reading position of the CIS unit 21 has not reached the final reading line of the original document (S18: NO) and continues reading the original document. When the count value of the CIS operation line number counter reaches a predetermined value corresponding to the original document size, the CPU 51 determines that the reading position of the CIS unit 21 has reached the final reading line of the original document (S18: YES), ends the reading of the original document, and ends the reading process.

[0045] <HP Detection Process> In response to the power of the reading device 1 being turned on and also in response to the completion of reading of the document, the CPU 51 executes the HP detection process shown in FIG. 7. In the reading device 1, in order for the CPU 51 to grasp the position of the CIS unit 21 in the sub-scanning direction, the home position (HP) of the CIS unit 21 is detected by the HP detection process.

[0046] Since the reading resolution, the light amount adjustment value, and the block unit shading correction average value stored in the non-volatile memory 52 are updated by overwriting each time they are acquired, the non-volatile memory 52 stores the reading resolution, the light amount adjustment value, and the block unit shading correction average value acquired in the last performed reading process. Hereinafter, the reading resolution, the light amount adjustment value, and the block unit shading correction average value acquired in the last performed reading process are referred to as the "final reading resolution", the "light amount adjustment value", and the "final block unit shading correction average value", respectively.

[0047] In the HP detection process, the CPU 51 reads the final reading resolution from the non-volatile memory 52 (S21). Then, the CPU 51 determines whether the final reading resolution is 300 dpi (S22).

[0048] When the final reading resolution is 300 dpi (S22: YES), the CPU 51 reads the final light amount adjustment value from the non-volatile memory 52 (S23). Then, the CPU 51 sets the read final light amount adjustment value as the light amount adjustment value for HP detection.

[0049] On the other hand, when the final reading resolution is not 300 dpi (S22: NO), that is, when the final reading resolution is 600 dpi or 1200 dpi, the CPU 51 performs the light amount adjustment value calculation process for HP detection (S24).

[0050] The flow of the light amount adjustment value calculation process for HP detection is shown in FIG. 8. In the light amount adjustment value calculation process for HP detection, the CPU 51 reads the final reading resolution and the final light amount adjustment value from the non-volatile memory 52 (S241). Then, the CPU 51 determines whether the final reading resolution is 1200 dpi (S242). If the final reading resolution is 1200 dpi (S242: YES), the CPU 51 sets the value obtained by dividing the duty ratio included in the final light amount adjustment value by 1 / 4 (= lowest resolution / final reading resolution) as the light amount adjustment value for HP detection (duty) (S243), and ends the light amount adjustment value calculation process for HP detection. Also, if the final reading resolution is not 1200 dpi (S242: NO) and the final reading resolution is 600 dpi, the CPU 51 sets the value obtained by dividing the duty ratio included in the final light amount adjustment value by 1 / 2 (= lowest resolution / final reading resolution) as the light amount adjustment value for HP detection (duty) (S243), and ends the light amount adjustment value calculation process for HP detection. After the end of the light amount adjustment value calculation process for HP detection, the process returns to the HP detection process shown in FIG. 7.

[0051] After setting the light amount adjustment value for HP detection, the CPU 51 reads the final block unit shading correction average value from the non-volatile memory 52 (S25). Then, the CPU 51 sets the read final block unit shading correction average value as the block unit shading correction average value for HP detection.

[0052] Then, the CPU 51 controls the CIS unit moving mechanism 55 to move the CIS unit 21 from a position separated to the right of the black-and-white reference part 41 (see FIG. 2) toward the black-and-white reference part 41 at a moving speed corresponding to a reading resolution of 300 dpi. On the other hand, the CPU 51 supplies current to the light source 22 with the current value included in the final light amount adjustment value and the light amount adjustment value for HP detection (duty) to adjust the light amount of the light source 22, and causes the CIS unit 21 (image sensor 25) to perform one-line reading at a resolution of 300 dpi at a cycle corresponding to 300 dpi (S26).

[0053] The CPU 51 performs shading correction (S27) on the one-line read data read by the CIS unit 21 using the shading correction average value for each final block unit. That is, the CPU 51 divides the pixel values read by the CIS unit 21 into blocks corresponding to the shading correction average value for each final block unit, and for each block, corrects each pixel value included in that block using the shading correction average value for the final block unit.

[0054] When the final read resolution read from the non-volatile memory 52 is 1200 dpi, the CPU 51 adds the pixel values of four consecutive pixels in one line of the read data after shading correction to obtain the pixel value of one pixel. Then, starting from one side in the main scanning direction in order for each pixel value after the pixel addition, the CPU 51 detects the position where the adjacent pixel values change across a predetermined HP detection threshold value (S28: black and white detection).

[0055] When the final read resolution read from the non-volatile memory 52 is 600 dpi, the CPU 51 adds the pixel values of two consecutive pixels in one line of the read data after shading correction to obtain the pixel value of one pixel. Then, starting from one side in the main scanning direction in order for each pixel value after the pixel addition, the CPU 51 detects the position where the adjacent pixel values change across a predetermined HP detection threshold value (S28: black and white detection).

[0056] When the final read resolution read from the non-volatile memory 52 is 300 dpi, the CPU 51 does not perform pixel addition on the one-line read data after shading correction. Then, starting from one side in the main scanning direction in order for each pixel value after the pixel addition, the CPU 51 detects the position where the adjacent pixel values change across a predetermined HP detection threshold value (S28: black and white detection).

[0057] Then, when the CPU 51 does not detect a position where pixel values adjacent to each other change across a predetermined HP detection threshold value (S28: NO), for the next line of read data read by the CIS unit 21, after shading correction using the final block unit shading correction average value, the process of detecting a position where pixel values adjacent to each other change across a predetermined HP detection threshold value is repeated. When the CPU 51 detects a position where pixel values adjacent to each other change across a predetermined HP detection threshold value (S28: YES), it detects that position as the home position of the CIS unit 21 and ends the HP detection process.

[0058] <Effect> As described above, when the original document is read by the CIS unit 21, before the reading, the black-and-white reference portion 41 is read by the CIS unit 21, and the CPU 51 obtains a light quantity adjustment value for adjusting the light quantity of the light source 22. Also, after the light quantity of the light source 22 is adjusted using the light quantity adjustment value, the black-and-white reference portion 41 is read again by the CIS unit 21, and the CPU 51 obtains a shading correction value for shading correction. The shading correction values are divided into blocks for every certain number of pixels, and for each block, a block unit shading correction average value, which is the average value of the shading correction values, is calculated. The light quantity adjustment value and the block unit shading correction average value are stored in the non-volatile memory 52 as the final light quantity adjustment value and the final block unit shading correction average value, respectively.

[0059] In the HP detection process for detecting the home position of the CIS unit 21, the light amount of the light source 22 is adjusted using the final light amount adjustment value stored in the non-volatile memory 52, and reading is performed by the CIS unit 21 while the CIS unit 21 is moved in the sub-scanning direction. Then, the pixel values read by the CIS unit 21 are divided into blocks corresponding to each final block unit shading correction average value, and for each block, each pixel value included in the block is shading-corrected using the final block unit shading correction average value. After this shading correction, detection is performed on the position where adjacent pixel values change across a predetermined HP detection threshold value. If the position where adjacent pixel values change across a predetermined HP detection threshold value is not detected, for the next one-line read data read by the CIS unit 21, after shading correction using the final block unit shading correction average value, detection is performed on the position where adjacent pixel values change across a predetermined HP detection threshold value. This is repeated, and when the position where adjacent pixel values change across a predetermined HP detection threshold value is detected, that position is regarded as the home position of the CIS unit 21.

[0060] Therefore, it is possible to detect the home position of the CIS unit 21 by eliminating the influences such as the sensitivity non-uniformity (PRNU) of the image sensor 25, the variation in illumination depth due to mechanical factors, and the secular deterioration of the light source 22. As a result, false detection of the home position can be suppressed.

[0061] In the non-volatile memory 52, together with the final light amount adjustment value and the final block unit shading correction average value, the reading resolution at the time when they are acquired is stored as the final reading resolution. And the reading by the CIS unit 21 in the HP detection process is performed at a reading resolution equal to or lower than the final reading resolution. That is, when the final reading resolution is the lowest resolution, the reading by the CIS unit 21 in the HP detection process is performed at the final reading resolution (= the lowest resolution), and when the final reading resolution is a high resolution higher than the lowest resolution, the reading by the CIS unit 21 in the HP detection process is performed at the lowest resolution. Thereby, when the final reading resolution is high, compared with the case where the reading by the CIS unit 21 in the HP detection process is performed at the final reading resolution, the time required for the reading can be shortened.

[0062] Also, when the final reading resolution is higher than the lowest resolution and the reading by the CIS unit 21 in the HP detection process is performed at the lowest resolution, the light amount of the light source 22 is adjusted using the final light amount adjustment value and the value obtained by dividing the lowest resolution by the final reading resolution. Thereby, the light amount of the light source 22 can be adjusted to the light amount corresponding to the lowest resolution, and the reading by the CIS unit 21 in the HP detection process can be performed favorably.

[0063] Since the final reading resolution, the final light amount adjustment value, and the final block unit shading correction average value are stored in the non-volatile memory 52, even when the power of the reading device 1 is turned off, the final reading resolution, the final light amount adjustment value, and the final block unit shading correction average value do not disappear from the non-volatile memory 52. Therefore, even in the HP detection process executed in response to the power-on of the reading device 1, the home position of the CIS unit 21 can be detected.

[0064] <Another example of HP detection process> Instead of the HP detection process shown in FIG. 7, the HP detection process shown in FIG. 9 may be performed.

[0065] In the HP detection process shown in FIG. 9, the CPU 51 reads the number of CIS operation lines and the final reading resolution from the non-volatile memory 52 (S31).

[0066] While the original document is being read, for example, with the number of steps when the CIS unit 21 is at the home position set to 0, the step number of the stepping motor of the CIS unit moving mechanism 55 is incremented (+1) when the stepping motor rotates one step in the forward direction, and decremented (-1) when the stepping motor rotates one step in the reverse direction, so that the step number of the stepping motor is counted. Then, the step number at the time when the last performed reading process ends is written into the non-volatile memory 52 as the number of CIS operation lines. That is, in the non-volatile memory 52, the number of lines from the home position to the position of the CIS unit 21 at the time when the last performed reading process ends is stored as the number of CIS operation lines.

[0067] The CPU 51 determines whether the final reading resolution is 300 dpi (S32).

[0068] If the final reading resolution is not 300 dpi (S32: NO), the CPU 51 determines whether the number of CIS operation lines read from the non-volatile memory 52 (hereinafter referred to as "read line number L") is equal to or greater than a predetermined value A (S33).

[0069] When the number of read lines L is equal to or greater than a predetermined value A (S33: YES), the CPU 51 controls the CIS unit moving mechanism 55 to move the CIS unit 21 back one line toward the home position at the moving speed of the CIS unit 21 when the reading resolution is 300 dpi (S34). At this time, the light source 22 of the CIS unit 21 may be turned on and reading by the CIS unit 21 may be performed, or the light source 22 may not be turned on and reading by the CIS unit 21 may not be performed. Thereafter, the CPU 51 determines whether the total number of lines by which the CIS unit 21 has been moved back toward the home position is greater than the value obtained by subtracting the predetermined value A from the number of read lines L (L - A) (S35). If the total number of lines moved back is equal to or less than the value (L - A) and the CPU 51 determines that the total number of lines moved back is not greater than the value (L - A) (S35: NO), the CPU 51 controls the CIS unit moving mechanism 55 to move the CIS unit 21 back one more line toward the home position (S34) and again determines whether the total number of lines by which the CIS unit 21 has been moved back is greater than the value (L - A) (S35).

[0070] When the total number of lines by which the CIS unit 21 has been moved back becomes greater than the value (L - A) and the CPU 51 determines that the total number of lines moved back is greater than the value (L - A) (S35: YES), the CPU 51 controls the CIS unit moving mechanism 55 to move it at a moving speed corresponding to the final reading resolution. On the other hand, the CPU 51 reads the final light amount adjustment value from the nonvolatile memory 52 and supplies a current to the light source 22 with the current value and the light amount adjustment value (duty) for HP detection included in the final light amount adjustment value, thereby adjusting the light amount of the light source 22 and causing the CIS unit 21 (image sensor 25) to perform reading of one line at the final reading resolution (S36).

[0071] Also, when the CPU 51 determines that the final reading resolution is 300 dpi (S32: NO), or when it determines that the number of read lines L is not greater than or equal to the predetermined value A (S33: NO), it controls the CIS unit moving mechanism 55 to move at a moving speed according to the final reading resolution. On the other hand, the CPU 51 reads the final light amount adjustment value from the non-volatile memory 52, supplies current to the light source 22 with the current value included in the final light amount adjustment value and the light amount adjustment value (duty) for HP detection, and causes the CIS unit 21 (image sensor 25) to perform one-line reading at the final reading resolution (S36).

[0072] Then, the CPU 51 performs shading correction on the one-line read data read by the CIS unit 21 using the average shading correction value for each final block unit (S37). After that, for the one-line read data after shading correction, the CPU 51 sequentially focuses on each pixel value after pixel addition from one side in the main scanning direction and detects the position where the adjacent pixel values change across a predetermined HP detection threshold value (S38: black-and-white detection).

[0073] When the CPU 51 does not detect the position where the adjacent pixel values change across a predetermined HP detection threshold value (S38: NO), it repeats the process of performing shading correction using the average shading correction value for each final block unit on the next one-line read data read by the CIS unit 21 and then detecting the position where the adjacent pixel values change across a predetermined HP detection threshold value. When the CPU 51 detects the position where the adjacent pixel values change across a predetermined HP detection threshold value (S38: YES), it detects that position as the home position of the CIS unit 21 and ends the HP detection process.

[0074] As described above, when the final reading resolution is the lowest resolution, the reading by the CIS unit 21 in the HP detection process is performed at the final reading resolution (= the lowest resolution). On the other hand, when the final reading resolution is a high resolution higher than the lowest resolution, the CIS unit 21 is returned at a speed corresponding to the lowest resolution until the total number of lines returned with the CIS unit 21 facing the home position becomes larger than the value (L - A). After the total number of lines returned becomes larger than the value (L - A), in other words, after the CIS unit 21 returns from the home position to a position A lines before the predetermined number of lines, the reading by the CIS unit 21 is performed at the final reading resolution. Therefore, when the final reading resolution is high, the time required for the reading can be shortened compared to the case where the reading by the CIS unit 21 in the HP detection process is always performed at the final reading resolution.

[0075] <Modification Example> As described above, the embodiments of the present invention have been described, but the present invention can also be implemented in other forms.

[0076] For example, in the above-described embodiment, the shading correction values obtained in the reading process are divided into blocks of a certain number of pixels, the average value of the shading correction values is calculated for each block, and the calculated average value is stored in the non-volatile memory 52 as the final block unit shading correction average value. In the shading correction in the HP detection process, the final block unit shading correction average value is used. However, this is not the only case. The shading correction values obtained in the reading process may be directly stored in the non-volatile memory 52 and used for the shading correction in the HP detection process.

[0077] Also, although the CPU 51 is assumed to execute each process, a plurality of CPUs may be provided in the reading device 1, and the plurality of CPUs may cooperate to execute each process.

[0078] In addition, various design changes can be made to the above-described configuration within the scope of the matters described in the claims.

Explanation of Reference Numerals

[0079] 1: Reading device 14: Original document placement board 21: CIS unit 22: Light source 25: Image sensor 29: Light receiving element 41: Black-and-white reference section 51: CPU 52: Non-volatile memory

Claims

【Claim 1】 A document table having a support surface for supporting a document, A reading device provided on the side opposite to the support surface side with respect to the document table so as to be reciprocally movable in a sub-scanning direction parallel to the support surface, the reading device having a light source for irradiating light onto a reading target on the support surface and an image sensor for converting reflected light from the reading target into a signal, A reference portion disposed at a position corresponding to the home position of the reading device, A storage unit, A control unit, and The image sensor includes a plurality of light receiving elements arranged in a main scanning direction, The control unit, Is capable of causing the reading device to perform reading at a plurality of reading resolutions, When causing the reading device to read the document, before reading the document, causing the reading device to read the reference portion, and using a signal output from the image sensor by this reading to obtain an adjustment value for adjusting the light amount of the light source, and storing the adjustment value in the storage unit, Before reading the document, causing the light source to emit light with a light amount adjusted using the adjustment value, causing the reading device to read the reference portion, and using a signal output from the image sensor by this reading to obtain a white level correction value for correcting non-uniformity of the white level from pixel values output by each of the light receiving elements, dividing the white level correction value into a plurality of blocks, and for each block, obtaining an average value of the white level correction value as a correction value for shading correction, and storing the correction value in the storage unit in association with the block, Storing in the storage unit the reading resolution at which the adjustment value and the correction value are obtained, Causing the light source to emit light with a light amount adjusted using the adjustment value stored in the storage unit, causing the reading device to perform reading while moving the reading device in the sub-scanning direction, and performing shading correction on pixel values indicated by the signal output from the image sensor by this reading using the correction value stored in the storage unit, Detecting a position where the pixel value after shading correction changes across a predetermined threshold value as the home position, In the reading for detecting the home position, When the reading resolution at which the adjustment value and the correction value stored in the storage unit are obtained is the lowest resolution, causing the reading device to perform reading for detecting the home position at the lowest resolution, When the reading resolution when acquiring the adjustment value and the correction value stored in the memory unit is a high resolution higher than the lowest resolution, the light amount of the light source is adjusted using the adjustment value stored in the memory unit and a value obtained by dividing the lowest resolution by the high resolution, and the reading device is caused to perform reading at the lowest resolution. A reading device that corrects a pixel value output by the light receiving element for each block using the correction value associated with the block in shading correction during detection of the home position. **Claim 2** A reading device according to claim 1, wherein the adjustment value is a duty ratio when controlling lighting of the light source by pulse width modulation. **Claim 3** A reading device according to claim 1 or 2, wherein the memory unit is a non-volatile memory.

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