JP7683301B2 - Reading device - Google Patents

Description

The present invention relates to a reading device.

Conventionally, reading devices that read documents using the FB (Flat Bed) method have been provided.

In an FB type reading device, a reading device extending in the main scanning direction is provided below a document table made of transparent glass so that it can move back and forth in the sub-scanning direction perpendicular to the main scanning direction. The reading device has a built-in light source, light guide, image sensor, etc. Light from the light source is irradiated onto the document through the light guide, and the light reflected from the document passes through a lens and enters the image sensor. Photoelectric conversion is performed in each light receiving element of the image sensor, and an electrical signal is output from each light receiving element. The electrical signal is converted into a pixel value, and the reading device achieves reading of one line in the main scanning direction.

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 control unit detects the home position (reference position) of the reading device. For example, a reference plate is provided in which a white area and a black area are arranged adjacent to each other in the sub-scanning direction, the reference plate is read by the reading device, and the position of the black area that has been read is detected as the home position.

JP 2000-115473 A

Conventionally, no light adjustment or shading correction is performed when detecting the home position. As a result, there is a risk of the home position being erroneously detected due to photo response non-uniformity (PRNU) of the image sensor, fluctuations in illumination depth due to mechanical factors such as warping of the document table, and deterioration of the light source over time.

The object of the present invention is to provide a reading device that can suppress erroneous detection of the home position of the reading device.

In order to achieve the above object, the reading device according to the present invention comprises a document table having a support surface for supporting a document, a reading device provided on the opposite side of the document table from the support surface side so as to be movable back and forth 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 section disposed at a position corresponding to the home position of the reading device, a memory section, and a control section, and when the control section causes the reading device to read a document, the control section causes the reading device to read the reference section before reading the document, and obtains an adjustment value for adjusting the light intensity of the light source using a signal output from the image sensor by this reading, and stores the adjustment value in the memory section. The adjustment value is stored in the memory, and before reading the document, the light source is caused to emit light with an amount of light adjusted using the adjustment value, the reading device is caused to read the reference portion, a correction value for shading correction is obtained using the signal output from the image sensor by this reading, the correction value is stored in the memory, the light source is caused to emit light with an amount of light adjusted using the adjustment value stored in the memory, and the reading device is caused to read while moving the reading device in the sub-scanning direction, shading correction is performed on pixel values indicated by the signal output from the image sensor by this reading using the correction value stored in the memory, and the position where the pixel value after shading correction has changed by straddling a predetermined threshold is detected as the home position.

According to this configuration, when an original is read by a reading device, the reading device reads the reference portion before the reading, and the control unit acquires an adjustment value for adjusting the amount of light from the light source. In addition, after the amount of light from the light source is adjusted using the adjustment value, the reading device reads the reference portion again, and the control unit acquires a correction value for shading correction. The adjustment value and correction value are stored in the memory unit.

When detecting the home position of the reading device, the amount of light from the light source is adjusted using the adjustment value stored in the memory unit, and the reading device reads while moving in the sub-scanning direction. Then, the pixel values indicated by the signal output from the image sensor are shading-corrected using the correction value stored in the memory unit, and the position where the pixel value after shading correction has changed by crossing a predetermined threshold is detected as the home position of the reading device.

This makes it possible to detect the home position of the reading device while eliminating the effects of the image sensor's sensitivity non-uniformity (PRNU), fluctuations in illumination depth due to mechanical factors, and deterioration of the light source over time. As a result, false detection of the home position can be suppressed.

The present invention makes it possible to suppress erroneous detection of the home position of the reading device.

1 is a cross-sectional view diagrammatically showing a configuration of a reading device according to an embodiment of the present invention; 4 is a bottom view of the top panel of the housing of the reading device. FIG. FIG. 2 is a perspective view showing a configuration of a CIS unit. FIG. 2 is a block diagram showing an electrical configuration of the reading device. 13 is a flowchart showing the flow of a reading process. 11 is a diagram showing an example of the relationship between pixel positions and amounts of received light when a black and white reference portion is read; FIG. 13 is a flowchart showing a flow of HP detection processing. 10 is a flowchart showing a flow of a process for calculating a light amount adjustment value for HP detection. 13 is a flowchart showing a flow of HP detection processing according to another embodiment.

The following describes in detail an embodiment of the present invention with reference to the attached drawings.

<Configuration of the reading device>
1 is a device for reading an original document, and includes a housing 2 and an original cover 3. The reading device 1 is configured to be capable of reading an original document by both the FB method and the ADF method. The reading device 1 includes an ADF (Auto Document Feeder) 4 provided on the original cover 3.

For the purposes of the following explanation, the front, back, left and right of the reading device 1 are defined based on the state in which the reading device 1 is viewed from the front side. The top and bottom are defined when the reading device 1 is installed on a horizontal surface. Figure 1 shows a cross section of the reading device 1 cut along a cutting line extending in the left-right direction.

The housing 2 has a generally rectangular parallelepiped shape. As shown in FIG. 2, a first opening 12 and a second opening 13 are provided on the top panel 11 of the housing 2.

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-to-back. An original placement plate 14 is provided to cover the first opening 12 from below. The original placement plate 14 is formed in a flat plate shape using a transparent material.

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

As shown in FIG. 1, within the housing 2, a CIS (Contact Image Sensor) unit 21 is provided below the document placement plate 14 (an example of a document table) and the document passing plate 15, and is movable in the sub-scanning direction, which is the left-right direction. 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.

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

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

The rod lens array 24 is offset from the light guide 23 in the left-right direction, 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.

The image sensor 25 has 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 has a light receiving element array 28. The light receiving element array 28 is composed of a plurality of light receiving elements 29 arranged in a row at equal pitch in the main scanning direction. Each light receiving element 29 outputs a charge according to the amount of light received as an electrical signal for one pixel.

The image sensor 25 is also equipped with a gain adjustment circuit and an A/D conversion circuit. The voltage output from each light receiving element 29 is amplified by the gain adjustment circuit, and then converted by the A/D conversion circuit into digital pixel data (pixel value). The A/D conversion circuit has a resolution of, for example, 8 bits (0 to 255), and uniformly converts voltages below the lower limit reference voltage (lower limit value) to "0", converts voltages above the upper limit reference voltage (upper limit value) to "255", and converts voltages in the range from the lower limit value to the upper limit value into pixel data according to the magnitude of the voltage.

Light from the light source 22 is irradiated onto the object to be read through the light guide 23, and the light reflected 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 magnified image on the light receiving surface of, for example, approximately 3.5 light receiving elements 29. Photoelectric conversion is performed in each light receiving element 29, and an electrical signal is output from each light receiving element 29. The electrical signal is converted into pixel data, thereby achieving reading of one line in the main scanning direction by the CIS unit 21.

As shown in FIG. 1, the ADF 4 has a supply tray 31 and a discharge tray 32. The supply tray 31 and the discharge tray 32 are arranged in a vertically overlapping state with a gap between them. A transport path 33 is formed within the ADF 4. One end of the transport path 33 opens on one end of the supply tray 31 in the sub-scanning direction, curves in a U-shape and folds back, passes over the document passing surface 17, and the other end opens between the supply tray 31 and the discharge tray 32. Also, within the ADF 4, a supply roller 34, a separation roller 35, a transport roller 36, a reversing roller 37, and a discharge roller 38 are provided in this order from the supply tray 31 side along the transport path 33.

The manuscript cover 3 is provided so as to be able to open and close between an open position and a closed position. When the manuscript cover 3 is in the closed position, the manuscript cover 3 covers the entire top surface of the housing 2. The manuscript cover 3 is displaced to the open position by lifting the front side from the closed position. When the manuscript cover 3 is in the open position, the entire top surface of the housing 2 is exposed.

When reading an original using the FB method, the original cover 3 is opened to the open position, and the original is placed on the upper surface (an example of a support surface) of the original placement plate 14. At this time, the original is positioned with its left edge abutting the left edge of the first opening 12 from the right side, and its rear edge abutting the rear edge of the first opening 12 from the front side. The original cover 3 is then closed to the closed position, and the original is covered from above by the original 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 beginning of the reading range, and while moving from that position in the sub-scanning direction, the CIS unit 21 reads the original on the original placement plate 14 line by line in the sub-scanning direction, thereby completing the reading of the original.

On the other hand, when reading an original using the ADF method, the original is placed on the supply tray 31 of the ADF 4. The CIS unit 21 is stopped at a position facing the original passing plate 15 from below. Thereafter, in response to a command to execute scanning, the original begins to be transported by the supply rollers 34. The original is separated into individual sheets by the separation rollers 35, and is transported along the transport path 33 by the transport rollers 36 and the reversal rollers 37. As the original passes over the original passing plate 15, the CIS unit 21 reads the original line by line in sequence, thereby completing the reading of the original.

2, a black-and-white reference section 41 (an example of a reference section) is provided on the left side of the document passing plate 15. The black-and-white reference section 41 is formed as a rectangular tape and is attached to the back surface (the surface facing downward) of the top panel 11 of the housing 2 so as to extend in the front-to-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 section 41, rectangular areas at each corner of the front right side and the rear right side are black areas 42, and the remaining area is white area 43. As a result, in the area along the right edge of the black-and-white reference section 41, the white area 43 is sandwiched between two black areas 42, and each black area 42 and the white area 43 are continuous, and in the area along the front edge and the area along the rear edge, the white area 43 is adjacent to the left side of the black area 42, and the black area 42 and the white area 43 are continuous.

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) such as a flash memory or E2PROM that is rewritable, 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.

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

The CIS unit movement mechanism 55 comprises a carriage carrying the CIS unit 21, a stepping motor capable of forward and reverse rotation, a drive pulley that is driven and rotated 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 in the left-right direction and are arranged so that their rotation axes extend in the front-rear direction. A midpoint of the belt is fixed to the carriage. The belt runs as the drive pulley rotates, 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.

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

<Reading process>
When an instruction to read an original is input to the reading device 1, the CPU 51 starts the reading process shown in Fig. 5. The instruction to read an original is input, for example, from the operation panel by the user operating the operation panel 56. When inputting the reading instruction, the user sets the reading resolution of the original by operating the operation panel 56. There are three levels of reading resolution: 300 dpi, 600 dpi, and 1200 dpi.

The following is an example where the document reading instruction is to read using the FB method.

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

Then, the CPU 51 performs light intensity adjustment (S12). In the light intensity adjustment, the CPU 51 controls the CIS unit 21 and the CIS unit movement mechanism 55 to have the CIS unit 21 read the white area 43 of the black and white reference portion 41. The CPU 51 then adjusts the current value supplied to the light source 22 of the CIS unit 21 and the duty ratio of the light source 22's illumination time so that the maximum pixel value of each pixel for one line obtained by the reading becomes a predetermined value (for example, 254). The CPU 51 stores the current value and duty ratio set by the light intensity adjustment in the non-volatile memory 52 as the light intensity adjustment value (S13). The light intensity adjustment value stored in the non-volatile memory 52 is updated by overwriting each time the light intensity adjustment is performed.

After adjusting the amount of light, the CPU 51 acquires a shading correction value (S14). That is, the CPU 51 supplies current to the light source 22 at the current value and 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. The CPU 51 then obtains a white level correction value that corrects the non-uniformity of the white level from the pixel values of one line obtained by this reading, and stores the white level correction value in the volatile memory 53 as a shading correction value.

The CPU 51 also divides the shading correction values into blocks of a certain number of pixels (for example, 550 pixels) as shown in FIG. 6. The CPU 51 then calculates an average value of the shading correction values for each block, and stores the calculated block-based shading correction average value in the non-volatile memory 52 in association with block identification information that identifies the block (S15). The block identification information may be a unique number assigned to each block, or may be a range of pixel numbers included in each block. The block-based shading correction average value stored in the non-volatile memory 52 is updated by overwriting each time a block-based shading correction average value is calculated.

Then, the CPU 51 reads the 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 a standby position set to the left of the left end of the document loading plate 14 to the right, and causes the CIS unit 21 to read the document on the document loading plate 14.

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

Then, the CPU 51 judges whether the reading position of the CIS unit 21 has reached the final reading line of the 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 according to the document size, the CPU 51 judges that the reading position of the CIS unit 21 has not reached the final reading line of the document (S18: NO) and continues reading the document. Then, when the count value of the CIS operation line number counter reaches a predetermined value according to the document size, the CPU 51 judges that the reading position of the CIS unit 21 has reached the final reading line of the document (S18: YES), ends reading of the document, and ends the reading process.

<HP detection process>
When the power supply of the reading device 1 is turned on, or when reading of the document is completed, the CPU 51 executes the HP detection process shown in Fig. 7. In the reading device 1, the CPU 51 grasps the position of the CIS unit 21 in the sub-scanning direction, so that the home position (HP) of the CIS unit 21 is detected by the HP detection process.

The reading resolution, light amount adjustment value, and block-based shading correction average value stored in the non-volatile memory 52 are updated by overwriting each time they are acquired, so the reading resolution, light amount adjustment value, and block-based shading correction average value acquired in the last reading process are stored in the non-volatile memory 52. Hereinafter, the reading resolution, light amount adjustment value, and block-based shading correction average value acquired in the last reading process are referred to as the "final reading resolution," the "light amount adjustment value," and the "final block-based shading correction average value," respectively.

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).

If 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 HP detection light amount adjustment value.

On the other hand, if the final reading resolution is not 300 dpi (S22: NO), that is, if the final reading resolution is 600 dpi or 1200 dpi, the CPU 51 performs a process of calculating the light intensity adjustment value for HP detection (S24).

The flow of the HP detection light amount adjustment value calculation process is shown in FIG. 8. In the HP detection light amount adjustment value calculation process, 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 judges whether the final reading resolution is 1200 dpi or not (S242). If the final reading resolution is 1200 dpi (S242: YES), the CPU 51 sets the duty ratio included in the final light amount adjustment value to 1/4 (= minimum resolution / final reading resolution) as the HP detection light amount adjustment value (duty) (S243), and ends the HP detection light amount adjustment value calculation process. Furthermore, if the final reading resolution is not 1200 dpi (S242: NO) but is 600 dpi, the CPU 51 sets the duty ratio included in the final light amount adjustment value to 1/2 (= minimum resolution/final reading resolution) as the light amount adjustment value for HP detection (duty) (S243), and ends the process of calculating the light amount adjustment value for HP detection. After the process of calculating the light amount adjustment value for HP detection ends, the process returns to the HP detection process shown in FIG. 7.

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

Then, the CPU 51 controls the CIS unit movement mechanism 55 to move the CIS unit 21 from a position spaced to the right of the black and white reference portion 41 (see FIG. 2) toward the black and white reference portion 41 at a movement speed corresponding to the reading resolution of 300 dpi. Meanwhile, the CPU 51 adjusts the light amount of the light source 22 by supplying current to the light source 22 at the current value included in the final light amount adjustment value and the HP detection light amount adjustment value (duty), and causes the CIS unit 21 (image sensor 25) to read one line at a resolution of 300 dpi at a cycle corresponding to 300 dpi (S26).

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

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

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

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

If the CPU 51 does not detect a position where adjacent pixel values change across the specified HP detection threshold (S28: NO), it repeats the process of detecting a position where adjacent pixel values change across the specified HP detection threshold 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. If the CPU 51 detects a position where adjacent pixel values change across the specified HP detection threshold (S28: YES), it detects that position as the home position of the CIS unit 21 and ends the HP detection process.

<Action and effect>
As described above, when the original is read by the CIS unit 21, the black and white reference portion 41 is read by the CIS unit 21 before the reading, and the CPU 51 acquires a light amount adjustment value for adjusting the light amount of the light source 22. After the light amount of the light source 22 is adjusted using the light amount adjustment value, the black and white reference portion 41 is read again by the CIS unit 21, and the CPU 51 acquires a shading correction value for shading correction. The shading correction value is divided into blocks for each fixed number of pixels, and a block-based shading correction average value, which is the average value of the shading correction values, is calculated for each block. The light amount adjustment value and the block-based shading correction average value are stored in the non-volatile memory 52 as the final light amount adjustment value and the final block-based shading correction average value, respectively.

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 the CIS unit 21 reads while moving in the sub-scanning direction. The pixel values read by the CIS unit 21 are divided into blocks corresponding to the final block-unit shading correction average values, 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, the position where the adjacent pixel values change across a predetermined HP detection threshold is detected. If the position where the adjacent pixel values change across a predetermined HP detection threshold is not detected, the next line of read data read by the CIS unit 21 is subjected to shading correction using the final block-unit shading correction average value, and then the position where the adjacent pixel values change across a predetermined HP detection threshold is detected. This process is repeated until a position is detected where adjacent pixel values change across a predetermined HP detection threshold, and that position is determined to be the home position of the CIS unit 21.

Therefore, the home position of the CIS unit 21 can be detected while eliminating the effects of the sensitivity non-uniformity (PRNU) of the image sensor 25, fluctuations in illumination depth due to mechanical factors, and deterioration over time of the light source 22. As a result, false detection of the home position can be suppressed.

In the non-volatile memory 52, the reading resolution at which the final light amount adjustment value and the final block-unit shading correction average value were obtained is stored as the final reading resolution. The reading by the CIS unit 21 in the HP detection process is performed at a reading resolution lower than the final reading resolution. In other words, if 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 (= minimum resolution), and if the final reading resolution is a higher resolution than the minimum resolution, the reading by the CIS unit 21 in the HP detection process is performed at the lowest resolution. This makes it possible to reduce the time required for reading when the final reading resolution is high, compared to when reading by the CIS unit 21 in the HP detection process is performed at the final reading resolution.

In addition, when the final reading resolution is higher than the minimum resolution and reading by the CIS unit 21 in the HP detection process is performed at the minimum resolution, the amount of light from the light source 22 is adjusted using the final light amount adjustment value and the value obtained by dividing the minimum resolution by the final reading resolution. This allows the amount of light from the light source 22 to be adjusted to a value that corresponds to the minimum resolution, allowing good reading by the CIS unit 21 in the HP detection process.

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, so even if the power supply 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 are not lost from the non-volatile memory 52. Therefore, the home position of the CIS unit 21 can be detected even in the HP detection process that is executed in response to the power supply of the reading device 1 being turned on.

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

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

While an original is being read, for example, the number of steps when the CIS unit 21 is located at the home position is set to 0, and the number of steps of the stepping motor is counted by incrementing (+1) each time the stepping motor of the CIS unit movement mechanism 55 rotates one step in the forward direction and decrementing (-1) each time the stepping motor rotates one step in the reverse direction. The number of steps at the time the last reading process is completed is then written to the non-volatile memory 52 as the number of CIS operating lines. In other words, the number of lines from the home position to the position of the CIS unit 21 at the time the last reading process is completed is stored in the non-volatile memory 52 as the number of CIS operating lines.

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

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

If the number of read lines L is equal to or greater than the predetermined value A (S33: YES), the CPU 51 controls the CIS unit movement mechanism 55 to move the CIS unit 21 back one line toward the home position at the movement 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 the CIS unit 21 may perform reading, or the light source 22 may not be turned on and the CIS unit 21 may not perform reading. The CPU 51 then 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 (L-A) obtained by subtracting the predetermined value A from the number of read lines L (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), it controls the CIS unit movement mechanism 55 to move the CIS unit 21 back another line toward the home position (S34) and again determines whether the total number of lines moved back by the CIS unit 21 is greater than the value (L-A) (S35).

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 by which the CIS unit 21 has been moved back is greater than the value (L-A) (S35: YES), it controls the CIS unit movement mechanism 55 to move the CIS unit 21 at a movement speed according to the final reading resolution. Meanwhile, the CPU 51 reads the final light amount adjustment value from the non-volatile memory 52 and adjusts the light amount of the light source 22 by supplying 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), thereby causing the CIS unit 21 (image sensor 25) to read one line at the final reading resolution (S36).

If the CPU 51 determines that the final reading resolution is 300 dpi (S32: NO), or that the number of read lines L is not equal to or greater than the predetermined value A (S33: NO), it controls the CIS unit movement mechanism 55 to move the CIS unit 55 at a speed corresponding to the final reading resolution. Meanwhile, the CPU 51 reads the final light adjustment value from the non-volatile memory 52, and supplies current to the light source 22 at the current value included in the final light adjustment value and the HP detection light adjustment value (duty), causing the CIS unit 21 (image sensor 25) to read one line at the final reading resolution (S36).

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

If the CPU 51 does not detect a position where adjacent pixel values change across the specified HP detection threshold (S38: NO), it repeats the process of detecting a position where adjacent pixel values change across the specified HP detection threshold 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. If the CPU 51 detects a position where adjacent pixel values change across the specified HP detection threshold (S38: YES), it detects that position as the home position of the CIS unit 21 and ends the HP detection process.

As described above, when the final reading resolution is the lowest resolution, reading by the CIS unit 21 in the HP detection process is performed at the final reading resolution (= lowest resolution). On the other hand, when the final reading resolution is a higher resolution than the minimum resolution, the CIS unit 21 is returned at a speed according to the minimum resolution until the total number of lines by which the CIS unit 21 is returned toward the home position becomes greater than the value (L-A), and after the total number of lines returned becomes greater than the value (L-A), in other words, after the CIS unit 21 returns to a position a predetermined number of lines A short of the home position, reading is performed by the CIS unit 21 at the final reading resolution. Therefore, when the final reading resolution is high, the time required for reading by the CIS unit 21 in the HP detection process can be shortened compared to when reading is performed at the final reading resolution from start to finish by the CIS unit 21.

<Modification>
Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms.

For example, in the above-described embodiment, the shading correction value obtained in the reading process is divided into blocks of a fixed 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-based shading correction average value, and the final block-based shading correction average value is used in the shading correction in the HP detection process. However, the shading correction value obtained in the reading process may be stored directly in the non-volatile memory 52, and the shading correction value may be used for the shading correction in the HP detection process.

In addition, although the CPU 51 is described as executing each process, multiple CPUs may be provided in the reading device 1, and the multiple CPUs may cooperate to execute each process.

In addition, various design modifications can be made to the above-mentioned configuration within the scope of the claims.

1: Reading device 14: Document placement plate 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 (3)

a document table having a support surface for supporting a document;
a reading device provided on the opposite side of the support surface side of the document table so as to be movable back and forth in a sub-scanning direction parallel to the support surface, the reading device having a light source that irradiates light onto a reading target on the support surface and an image sensor that converts reflected light from the reading target into a signal;
a reference portion disposed at a position corresponding to a home position of the reading device;
A storage unit;
A control unit,
The image sensor includes a plurality of light receiving elements arranged in a main scanning direction,
The control unit is
The reading device may be configured to read at a plurality of reading resolutions;
When the document is read by the reading device, before reading the document, the reading device is caused to read the reference portion, and an adjustment value for adjusting the amount of light of the light source is obtained using a signal output from the image sensor by this reading, and the adjustment value is stored in the storage unit;
prior to reading the document, making the light source emit light with an amount of light adjusted using the adjustment value, making the reading device read the reference portion, using a signal output from the image sensor by this reading to obtain a white level correction value for correcting non-uniformity in the white level from pixel values output from each of the light receiving elements, dividing the white level correction value into a plurality of blocks, obtaining an average value of the white level correction values for each of the blocks as a correction value for shading correction, and storing the correction value in the storage unit in association with the block ;
storing the reading resolution at the time when the adjustment value and the correction value are obtained in the storage unit;
causing the light source to emit light with an amount of light adjusted using the adjustment value stored in the storage unit, and 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 signals 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 the shading correction has changed across a predetermined threshold as the home position;
In the reading for detecting the home position,
when the reading resolution at the time of acquiring the adjustment value and the correction value stored in the storage unit is the lowest resolution, the reading device is caused to perform reading for detecting the home position at the lowest resolution;
when the reading resolution at which the adjustment value and the correction value stored in the storage unit were obtained is a high resolution higher than the minimum resolution, an amount of light of the light source is adjusted using the adjustment value stored in the storage unit and a value obtained by dividing the minimum resolution by the high resolution, and the reading device is caused to perform reading at the minimum resolution;
In the shading correction when detecting the home position, the pixel value output by the light receiving element is corrected for each of the blocks by using the correction value associated with the block . 2. The reading device according to claim 1 ,
A reading device, wherein the adjustment value is a duty ratio when lighting of the light source is controlled by pulse width modulation. 3. The reading device according to claim 1 ,
A reading device, wherein the storage unit is a non-volatile memory.

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