Image reading device

Abstract

To improve the image quality of an image while outputting an image without color shift.SOLUTION: An image reading device comprises: luminous elements 72; a plurality of line sensors 76 being line-shaped photoelectric conversion elements that receive light emitted from the luminous elements 72 and reflected on a document to be read, and output electric signals corresponding to wavelength regions different from each other; and light emission control means 70 that controls the lighting start time, the lighting period, and the amount of energization of the luminous elements 72. The line sensors 76 are arranged at a predetermined interval in a sub-scanning direction. The light emission control means 70 changes the amount of energization according to the number of luminous elements 72 that are simultaneously turned on.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image reading device that is applicable to an image scanner or copying machine and that is equipped with an image sensor for reading an image of a document. [Background technology]

[0002] As an image sensor used in a conventional image reading device, a contact image sensor (CIS) is used, which is placed close to an original document and reads the original document at the same magnification as the original document.

[0003] A CIS requires a substrate on which an image sensor chip is mounted, an LED as a light source, a light guide to direct the LED light to the document surface, and a housing to hold all of these components. The CIS is then incorporated into an image reading device as a CIS unit.

[0004] The LEDs in the CIS unit are light-emitting elements of three colors: red, green, and blue (RGB), each of which can be turned on and off independently.The image sensor chip has three line sensors (photoelectric conversion elements) arranged in parallel at equal intervals in the sub-scanning direction, and has peak sensitivity to the three colors: red, green, and blue (RGB).

[0005] To read an image of an original using a CIS, the CIS unit and the original are moved relative to each other. However, because the RGB line sensors are misaligned in the sub-scanning direction, there is a problem in that when a single-line image is generated from images simultaneously acquired by the RGB line sensors, the image itself will be misaligned by the amount of the misalignment.

[0006] To address the above problem, Patent Document 1 provides a method for generating a one-line image from delayed RGB line images acquired using a line memory when the amount of misalignment of the line sensor in the sub-scanning direction is equal to an integer multiple of the pixel spacing of the reading resolution.

[0007] Furthermore, Patent Document 2 provides a method for controlling the lighting timing of each RGB LED relative to the accumulation period of each line sensor so that, when the amount by which the line sensor is shifted in the sub-scanning direction is not an integer multiple of the pixel spacing of the reading resolution, each RGB line sensor can acquire an image at a position that is shifted by approximately an integer number of lines relative to the line sensor in the sub-scanning direction.

[0008] Furthermore, Patent Document 3 provides a method for controlling the timing and duration of lighting of each RGB LED according to the arrangement position of each RGB line sensor and the relative moving speed of the CIS unit and the document. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 1-109966 [Patent Document 2] Patent No. 4141981 [Patent Document 3] Patent No. 3990437 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the method of Patent Document 1 works well when the amount of shift of the line sensor in the sub-scanning direction is equal to an integer multiple of the pixel spacing of the reading resolution, but if it is not an integer multiple, the pixels are artificially interpolated, which causes the generated image to be blurred and reduces image quality.

[0011] The method of Patent Document 2 controls the lighting start time within the scanning time of one line to match the deviation in the sub-scanning direction of each line sensor, controlling the deviation to approximately an integer number of lines, thereby solving the problem of the generated image being blurred and the image quality being reduced.However, the lighting time is reduced by the amount of the delay in the lighting start time within one line, and the reduced light intensity can result in the image quality being reduced.

[0012] Patent Document 3 proposes a circuit configuration that independently changes the light intensity of each LED, in addition to a method for controlling the lighting start time and lighting duration within one line scanning time, making it easy to adjust the color balance while keeping the lighting duration constant. However, increasing the LED light intensity too much can lead to a rise in temperature, which could exceed the rated temperature of the CIS unit. Continuing to use the unit above the rated temperature can lead to a decrease in light intensity due to LED degradation, resulting in a deterioration in the quality of the generated image. [Means for solving the problem]

[0013] In view of the above, an image reading device according to the present invention comprises: A light-emitting element; a plurality of line sensors, each of which is a linear photoelectric conversion element that receives light emitted from the light emitting element and reflected by a document to be read, and outputs an electrical signal corresponding to a different wavelength range; a light emission control means for controlling the lighting start time, lighting period, and amount of current of the light emitting element; Equipped with The line sensors are arranged at predetermined intervals in the sub-scanning direction, The light emission control means changes the amount of current flowing in accordance with the number of light emitting elements that are to be simultaneously lit. [Effects of the Invention]

[0014] According to the present invention, it is possible to improve the image quality while preventing color shift in the image. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically showing the configuration of an image reading apparatus according to a first embodiment. [Figure 2] FIG. 1 is a block diagram showing the configuration of an image reading apparatus according to a first embodiment. [Figure 3] FIG. 2 is a simplified schematic diagram of the internal configuration of an image reading sensor. [Figure 4] Block diagram of the LED driver. [Figure 5]The spectral transmittance of the color filter of an image reading sensor. [Figure 6] FIG. [Figure 7] 5 is a sequence chart showing LED lighting control when reading an image of 300 dpi in the image reading device according to the first embodiment. [Figure 8] FIG. 4 is an explanatory diagram showing the relationship between a light receiving unit and a sheet. [Figure 9] 5 is a sequence chart showing LED lighting control when reading an image of 300 dpi in the image reading device according to the first embodiment. [Figure 10] 10 is a sequence chart showing LED lighting control when an image of 300 dpi is read in an image reading apparatus according to a second embodiment. [Figure 11] 10 is a sequence chart showing LED lighting control when an image of 300 dpi is read in an image reading apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the present invention.

[0017] [First embodiment] First, an image reading apparatus according to the first embodiment will be described.

[0018] <Image reading device 200> FIG. 1 is a partial cross-sectional view showing the schematic configuration of an image reading device equipped with a document feeding device.

[0019] In FIG. 1, the image reading device 200 includes a sheet loading device 101. A plurality of sheets (documents) are loaded (placed) on a sheet loading tray (document tray) 1, which is configured to be freely raised and lowered. A loading tray drive motor (not shown) raises and lowers the sheet loading tray 1. A sheet detection sensor 3 detects that the sheets loaded on the sheet loading tray 1 are at the sheet loading position. If the sheets loaded on the sheet loading tray 1 are not at the sheet loading position, the loading tray drive motor is driven to move the sheet loading tray 1 so that the top surface of the sheets is at the loading position. A sheet loading detection sensor 12 detects that a sheet is loaded on the sheet loading surface 1a of the sheet loading tray 1.

[0020] A pickup roller 4 (taking-in means) takes in a sheet on the sheet stacking table 1 and sends it to a feed roller 6. A pickup motor (not shown) rotates the pickup roller 4. In FIG. 1, the upper surface of the sheet is at the sheet taking-in position, and when the pickup roller 4 is rotated, the sheet taking-in begins.

[0021] The feed roller 6 is provided downstream of the pickup roller 4 and is driven by a feed motor 8 to rotate in a direction that feeds the sheet downstream in the conveyance direction. The feed roller 6 is connected to the feed motor 8 via a one-way clutch (not shown), and the drive force of the feed motor 8 is transmitted in only one direction. When a sheet is fed by the feed motor 8, the drive force is transmitted to the feed roller 6, but when the sheet is transported by registration rollers 17, 18 or the like at a speed faster than that of the feed motor 8, the rotation of the feed motor 8 is not transmitted by the one-way clutch, and the feed roller 6 rotates in response to the sheet transport. The separation roller 7, which is provided opposite the feed roller 6 across the conveyance path, constantly receives a rotational force from the separation motor 9 via a torque limiter (slip clutch) (not shown) that rotates in a direction that pushes the sheet back upstream in the conveyance direction. When there is one sheet between the feed roller 6 and the separation roller 7, the frictional force between the sheet being sent downstream by the feed roller 6 and the separation roller 7 causes the rotational force in the direction in which the sheet is fed downstream to exceed the upper limit of the rotational force in the direction in which the separation roller 7 pushes the sheet back upstream, as transmitted by the torque limiter, and the separation roller 7 rotates following the feed roller 6 (rotates together).

[0022] On the other hand, when there are multiple sheets between the feeding roller 6 and the separation roller 7, the separation roller 7 receives rotation from the roller shaft in a direction to push the sheets back upstream, so that sheets other than the topmost one are not conveyed downstream.

[0023] In this way, due to the action of the feed roller 6 to feed sheets downstream and the action of the separation roller 7 to prevent sheets from being transported downstream, when overlapping sheets are fed into the nip portion between the feed roller 6 and the separation roller 7, only the topmost sheet is fed downstream and the other sheets are prevented from being transported downstream, so that the overlapping sheets are separated and fed. Thus, the feed roller 6 and the separation roller 7 constitute a pair of separation rollers 42. The separation roller pair 42 functions as an example of a sheet separation section that separates and transports multiple sheets to be transported one by one.

[0024] The sheet separation force of the separation roller 7 can be changed. The sheets can be separated simply by holding the separation motor 9 without rotating it. An even stronger separation force can be obtained by driving the separation motor 9 so that the separation roller 7 rotates in the direction returning the sheets to the upstream side.

[0025] In this embodiment, the separation roller pair 42 is used, but a separation belt roller pair in which either the separation roller or the feed roller is a belt may be used instead of the separation roller pair 42. Also, the separation roller may be replaced with a separation pad that comes into contact with the sheet to prevent multiple sheets from being transported downstream.

[0026] Furthermore, by providing a double feed detection sensor 30 at a position where the separated sheets pass, it is possible to detect whether the sheets have been separated one by one by the sheet separating unit. In this embodiment, a detection device using an ultrasonic transmitter / receiver is used as the double feed detection sensor 30, and double feed can be detected by the amount of ultrasonic wave attenuation between the transmitter / receivers across the conveyance path.

[0027] The transport motor 10 drives the registration roller 18 and transport rollers 21 and 23 to transport the separated sheet to an image reading position where the image on the sheet (document) is read by image reading sensors 14 and 15 (image reading unit), and then to a discharge position. The driving of each roller drives the opposing rollers (registration roller 17 and transport rollers 20 and 22) that make up a roller pair, thereby transporting the sheet to the discharge position. The transport motor 10 also drives each roller so that the sheet transport speed can be changed according to settings such as the optimal speed for sheet reading and the sheet resolution. A registration clutch (not shown) transmits or blocks the rotational drive force of the transport motor 10 to the registration roller 18 (document transport unit), thereby driving or stopping the drive of the registration roller 18.

[0028] The nip gap adjustment motor 11 adjusts the gap between the feed roller 6 and the separation roller 7, or the pressure force with which the feed roller 6 presses against the separation roller 7 via the sheet. This adjusts the gap or pressure force to suit the thickness of the sheet, allowing the sheet to be separated.

[0029] 1 convey the sheet to the discharge stacking section 44. The upper guide plate 40 and the lower guide plate 41 guide the sheet conveyed by the separation roller pair, the registration roller pair, each conveyance roller pair, and the downstream roller pair.

[0030] The image reading device 200 includes a control board 45 that controls the operation of the entire device, and is responsible for driving each actuator and controlling the image reading sensors 14 and 15.

[0031] <Signal system and operation> 2, the signal system and operation of the control board 45 and the image reading sensors 14 and 15 will be described. First, the control board 45 will be described.

[0032] A control unit 46 (CPU) in the control board 45 controls the settings and operations of each unit, controls the image reading sensors 14 and 15, and performs various calculations.

[0033] The control unit 46 outputs a sensor clock signal to the image reading sensors 14 and 15 through a sensor clock generating unit 63 .

[0034] The control unit 46 sets the cycle for reading one line of image, and outputs a line synchronization signal, which is the reference timing for reading one line, to the image reading sensors 14 and 15 through the line synchronization signal generation unit 64. The control unit 46 performs various settings related to image reading for the image reading sensors 14 and 15.

[0035] The image processing unit 66 also performs various image processing operations on the digital image data obtained by the image reading sensors 14 and 15 .

[0036] Next, we will explain the image reading sensors 14 and 15. The image reading sensors 14 and 15 are controlled by a sensor control unit 70. The sensor control unit 70 operates in synchronization with the sensor clock output by a sensor clock generation unit 63, and outputs various timing signals for reading one line in synchronization with the line synchronization signal output by a line synchronization signal generation unit 64.

[0037] The sensor control unit 70 outputs a control signal at a preset timing every time a line synchronization signal is input.

[0038] The sensor control unit 70 drives the LED 72 through the LED drive unit 71 in response to a control signal for reading one line, that is, functions as a light emission control unit.

[0039] The LED driving unit 71 drives and lights the LEDs 72, which are light sources, by passing a current at a current value set for each LED 72 at a lighting timing (lighting start time, lighting period) according to a timing signal from the sensor control unit .

[0040] The LED driving unit 71 stops the current to the LED 72, which is the light source, at the light-off timing according to the timing signal from the sensor control unit 70, and drives the LED 72 to turn off the light.

[0041] The sensor control unit 70 also controls the current value (amount of current) that drives the LED 72 through the LED drive unit 71.

[0042] The LED 72 has three color LED light sources, with the LED (R) 73 emitting red light, the LED (G) 74 emitting green light, and the LED (B) 75 emitting blue light, each independently emitting light of each color.

[0043] The light receiving unit 76 has three lines of light receiving elements (line sensors) corresponding to the three color LED light sources. The three lines of light receiving elements are a light receiving unit (R) 77 corresponding to the LED (R) 73, a light receiving unit (G) 78 corresponding to the LED (G) 74, and a light receiving unit (B) 79 corresponding to the LED (B) 75. Color filters with different spectral transmittances are formed on the surface of the light receiving unit 76, and each line has spectral sensitivity corresponding to a different wavelength range of RGB.

[0044] 5 shows the spectral transmittance of the color filters formed on the surface of the light receiving section 76. Reference numeral 501 denotes the spectral transmittance of the color filter (R), 502 denotes the spectral transmittance of the color filter (G), and 503 denotes the spectral transmittance of the color filter (B).

[0045] The light receiving element of the light receiving unit 76 outputs an electrical signal corresponding to the amount of light incident from outside. This electrical signal is received by the sensor control unit 70, converted into a digital signal by an internal AD converter, and output to the image processing unit 66 mounted on the control board 45.

[0046] FIG. 3 is a schematic diagram showing a simplified internal configuration of the image reading sensors 14 and 15. As shown in FIG.

[0047] The sensor control unit 70 mounted on the sensor board 83 outputs a control signal to the LED driving unit 71, and the LED 72 is driven to emit light at a timing according to the timing signal output from the LED driving unit 71.

[0048] The light emitted from the LED 72 passes through the inside of the light guide 80 and is emitted as linear light toward the surface facing the image reading sensors 14 and 15. The emitted light passes through the reading glass 81 of the reading sensors 14 and 15 and illuminates the sheet F to be read. Furthermore, the light reflected by the sheet F passes through the reading glass 81 again, passes through the lens array 82, and is collected on the light receiving unit 76 mounted on the sensor board 83.

[0049] 3 shows a lead-type element in which LED(R) 73, LED(G) 74, and LED(B) 75 are sealed in the same package, but this is not necessarily limited to this, and a configuration in which a surface-mounted LED is mounted on the sensor substrate 83 and a light guide is attached that can emit the LED as linear light is also possible. Also, in FIG. 3, a so-called double-illuminated image reading sensor in which LEDs 72 are arranged on both sides of the lens array 82 has been described, but this is not limiting and the present invention can also be applied to a single-illuminated image reading sensor in which only one of the LEDs 72 is provided.

[0050] The light receiving unit 76 outputs an electrical signal corresponding to the amount of light imaged by the lens array 82. The sensor control unit 70 receives the electrical signal from the light receiving unit 76, converts it into a digital signal in an internal AD conversion unit, and outputs it as digital image data to the control board 45 via an interface unit (not shown) provided on the sensor board 83.

[0051] The image processing unit 66 performs various image processing on the digital image data to obtain an output image as the image reading device 200 .

[0052] Figure 4 is a block diagram of the LED driver 71. The LED driver 71 is driven by 3.3V supplied from the VDD terminal. To light the LEDs, a power supply exceeding the LED's forward voltage is required, so the power supply booster 90 is incorporated, which boosts the 3.3V supplied to VDD to 6.6V and connects it to the anode terminals of LED (R) 73, LED (G) 74, and LED (B) 75. Note that some configurations do not require the power supply booster 90, depending on the circuit configuration and LED characteristics.

[0053] The control signal output from the sensor control unit 70 is input to a control signal input unit 91 of the LED drive unit 71. This input signal allows the LED(R) 73, LED(G) 74, and LED(B) 75 to be individually turned on.

[0054] In response to the input signal from the control signal input unit 91, the switch circuit of the lighting control unit (R) 92 is turned on to control the lighting of the LED (R) 73. In response to the input signal from the control signal input unit 91, the switch circuit of the lighting control unit (G) 93 is turned on to control the lighting of the LED (G) 74. In response to the input signal from the control signal input unit 91, the switch circuit of the lighting control unit (B) 94 is turned on to control the lighting of the LED (B) 75.

[0055] The control signal output from the sensor control unit 70 is input to the current setting input unit 95 of the LED driving unit 71. The control signal input to the current setting input unit 95 is connected to the current setting unit 96, and the current setting unit 96 can individually set the current flowing when lighting the LED (R) 73, the LED (G) 74, and the LED (B) 75. The current setting unit 96 is controlled by the current source (R) 97 to control the current flowing when lighting the LED (R) 73. The current setting unit 96 is controlled by the current source (G) 98 to control the current flowing when lighting the LED (G) 74. The current setting unit 96 is controlled by the current source (B) 99 to control the current flowing when lighting the LED (B) 75.

[0056] FIG. 6 is an external view of the sensor substrate 83 in the present embodiment, showing that the light receiving portions 76 are mounted in a line. When the light receiving portion 76 is enlarged, three lines of the light receiving portion (R) 77, the light receiving portion (G) 78, and the light receiving portion (B) 79 are arranged at regular intervals.

[0057] The interval between the light receiving elements in the main scanning direction is X. In this embodiment, for an image reading sensor corresponding to reading at a resolution of 600 dpi, X is 42.27 μm. The interval in the sub-scanning direction, that is, the interval between the light receiving portion (R) 77 and the light receiving portion (G) 78, and the interval between the light receiving portion (G) 78 and the light receiving portion (B) 79 is Y, which is also 42.27 μm as in the main scanning direction.

[0058] <LED Lighting Control> FIG. 7 is a sequence chart showing the lighting control of the LED 72, which is a three-color light-emitting element, when an image is read at a resolution equal to the pixel spacing of the light-receiving elements in the main scanning direction and sub-scanning direction, that is, using an image reading sensor with a resolution of 600 dpi, where the pixel spacing is 42.27 μm.

[0059] The SP signal 701 is a line synchronization signal output from the line synchronization signal generator 64, and is a signal that controls the operation cycle of the light receiving unit 76 to synchronize the image in the sub-scanning direction. That is, it is a Start Pulse signal (SP) that starts capturing one line of image. The reading period T_SP is the time from one SP to the next SP, and indicates the reading period (reading interval) of one line.

[0060] The LED on (R) signal 702 controls the on / off of the LED (R) 73, and lights the LED (R) 73 during the period T_RED. The light from the LED (R) 73 is reflected by the sheet F and accumulated in the light receiving unit (R) 77, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (R) as the image data (R) signal 705. The output of the image data (R) signal 705 increases by increasing the current flowing through the LED (R) 73 or by lengthening the period during which the LED (R) 73 is lit.

[0061] The LED lighting (G) signal 703 controls the lighting and extinguishing of the LED (G) 74, lighting the LED (G) 74 during the period T_GREEN. The light from the LED (G) 74 is reflected by the sheet F and accumulated in the light receiving unit (G) 78, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (G) as the image data (G) signal 706. The output of the image data (G) signal 706 increases by increasing the current flowing through the LED (G) 74 or by lengthening the period during which the LED (G) 74 is lit.

[0062] The LED lighting (B) signal 704 controls the lighting and extinguishing of the LED (B) 75, and lights the LED (B) 75 during the period T_BLUE. The light from the LED (B) 75 is reflected by the sheet F and accumulated in the light receiving unit (B) 79, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (B) as the image data (B) signal 707. The output of the image data (B) signal 707 increases by increasing the current flowing through the LED (B) 75 or by lengthening the period during which the LED (B) 75 is lit.

[0063] If the outputs of the image data (R) 705, image data (G) 706, and image data (B) 707 are small, the signal levels will be artificially increased by a signal amplifier circuit (not shown) inside the sensor control unit 70 or by the image processing unit 66, but this will also amplify noise signals contained in the image data, resulting in a decrease in image quality, so other methods are preferable: namely, extending the LED lighting period or increasing the amount of current flowing through the LED.

[0064] The current and duration of illumination for LED (R) 73, LED (G) 74, and LED (B) 75 may be appropriately determined during light intensity adjustment before scanning sheet F or continuously scanning a stack of sheets. The duration of illumination for each LED is adjusted within the T_SP scanning period. However, because only image information is obtained during the illumination period, shortening the illumination period results in loss of image information. Therefore, it is recommended to start adjusting the current for each LED from a low setting and adjust it so that the illumination is as long as possible without exceeding the T_SP scanning period. If the target light intensity is not achieved even when the LED is illuminated within the T_SP scanning period at a low current, the LED current is increased by a certain amount and the LED is illuminated again within the T_SP scanning period, adjusting the LED to achieve the target light intensity.

[0065] If Figure 7 shows the timing for image reading at 600 dpi, the SP signal is controlled to be issued when sheet F moves 42.27 μm. Figure 8 shows the relationship between the light receiving unit mounted on sensor board 83 and the position of point A, which is artificially marked on sheet F. In Figure 8(a), point A is at the position of light receiving unit (R) 77, and the SP signal is issued at this point. Figure 8(b) shows the state when sheet F has moved 42.27 μm from there, where point A is at the position of light receiving unit (G) 78, and the next SP signal is issued at this point. Then, in Figure 8(c), sheet F has moved another 42.27 μm, where point A is at the position of light receiving unit (B) 79, and the next SP signal is issued at this point.

[0066] With this timing, as shown in Figure 7, by combining image data 705-1 from the light receiving unit (R) in the section where the first SP signal was issued, image data 706-2 from the light receiving unit (G) in the section where the next SP signal was issued, and image data 707-3 from the light receiving unit (B) in the section where the next SP signal was issued, it is possible to generate 600 dpi color image data at point A without color shift.

[0067] Increasing the current flowing through the LEDs can increase the amount of light, but this not only increases the amount of light emitted by the LEDs but also their temperature in proportion to the current. In the 600 dpi example described here, LED (R) 73, LED (G) 74, and LED (B) 75 are lit simultaneously, so the current is intentionally limited to prevent the LED temperature from exceeding the rated temperature. The amount of current flowing through the LEDs at this time is referred to as the first amount of current (see Figure 7).

[0068] Next, the timing for reading a 300 dpi image in the image processing device according to the first embodiment will be described with reference to Fig. 9. Fig. 9 is a sequence chart showing the lighting control of the LEDs 72, which are three-color light-emitting elements, when reading an image at a resolution of 300 dpi, which is twice the pixel spacing, using an image reading sensor that supports a resolution of 600 dpi, where the pixel spacing of the light-receiving elements in the main scanning direction and sub-scanning direction is 42.27 μm.

[0069] At a resolution of 300 dpi, the lighting of the LED 72 is controlled by dividing the time T_SP from one SP to the next SP into a reading period T_SP1 in the first half and a reading period T_SP2 in the second half of T_SP.

[0070] The LED on (R) signal 702 controls the on / off of the LED (R) 73, and turns on the LED (R) 73 during the period T_RED-1 included in T_SP1. The light emitted by the LED (R) 73 during the period T_RED-1 is reflected by the sheet F and accumulated in the light receiving unit (R) 77, and the next SP signal is used as a trigger to output image data (R) as an image data (R) signal 705-1 depending on the accumulated amount. The light emitted by the LED (R) 73 during the period T_RED-2 of the next SP signal is reflected by the sheet F and accumulated in the light receiving unit (R) 77, and the next SP signal is used as a trigger to output image data (R) as an image data (R) signal 705-2 depending on the accumulated amount.

[0071] The LED lighting (G) signal 703 controls the lighting and extinguishing of the LED (G) 74, and lights the LED (G) 74 during the period T_GREEN-1 included in T_SP2. The light emitted by the LED (G) 74 during the period T_GREEN-1 is reflected by the sheet F and accumulated in the light receiving unit (G) 78, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (G) as an image data (G) signal 706-1. The light emitted by the LED (G) 74 during the period T_GREEN-2 of the next SP signal is reflected by the sheet F and accumulated in the light receiving unit (G) 78, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (G) as an image data (G) signal 706-2.

[0072] The LED lighting (B) signal 704 controls the lighting and extinguishing of the LED (B) 75, and lights the LED (B) 75 during the period T_BLUE-1 included in T_SP1. The light emitted by the LED (B) 75 during the period T_BLUE-1 is reflected by the sheet F and accumulated in the light receiving unit (B) 79, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (B) as an image data (B) signal 707-1. The light emitted by the LED (B) 75 during the period T_BLUE-2 of the next SP signal is reflected by the sheet F and accumulated in the light receiving unit (B) 79, and depending on the accumulated amount, the next SP signal is used as a trigger to output image data (B) as an image data (B) signal 707-2.

[0073] The 300 dpi image data can be used to generate a color image without color shift by using image data (R) obtained by turning on T_RED-1, image data (G) obtained by turning on T_GREEN-1, and image data (B) obtained by turning on T_BLUE-2. That is, one line of color image data is generated from an image data (R) signal 705-1 and an image data (G) signal 706-1 acquired in the first and second halves of the same SP, respectively, and an image data (B) signal 707-2 acquired in the first half of the next SP. Similarly, one line of color image data is generated from an image data (R) signal 705-2 and an image data (G) signal 706-2 acquired in the first and second halves of the same SP, respectively, and an image data (B) signal 707-3 acquired in the first half of the next SP. By repeating this process sequentially, a color image for one surface of the sheet is generated.

[0074] Thus, in this embodiment, when generating a 300 dpi output image, in order to eliminate color shift, the reading period T_SP is divided into a first half T_SP1 and a second half T_SP2, and lighting control is performed on the LEDs 72. In other words, when reading a one-line image at 600 dpi, one color of the LEDs 72 can be lit for a time close to T_SP, but when reading at 300 dpi, which does not cause color shift, the time during which one color of the LEDs 72 with the longest lighting time is lit is shortened to half of T_SP.

[0075] Since the lighting time of the LED 72 is shortened, the outputs of the image data (R) signal 705, the image data (G) signal 706, and the image data (B) signal 707 become smaller. Therefore, if the signal level is artificially increased in a signal amplifier circuit (not shown) inside the sensor control unit 70 or in the image processing unit 66, the image quality will deteriorate.

[0076] On the other hand, if the current flowing through the LED 72 remains unchanged, the temperature rise of the LED 72 when reading an image at 300 dpi is reduced by half compared to when reading an image at 600 dpi due to the shorter lighting time of the LED 72.

[0077] Therefore, in this embodiment, if the amount of current applied to the LEDs when reading at 600 dpi is set to a first amount of current, the amount of current applied when reading at 300 dpi is set to a second amount of current, which is greater than the first amount of light. Specifically, the current setting input unit 95 changes the setting value of the current setting unit 96 so that, when reading at 600 dpi, a current of 20 mA is applied to each of the LEDs (R) 73, LED (G) 74, and LED (B) 75 as the first amount of current, and when reading at 300 dpi, a current of 40 mA is applied to each of the LEDs (R) 73, LED (G) 74, and LED (B) 75 as the second amount of current. Note that this change in the amount of current is just one example. As shown in FIG. 4, the current setting unit 96 can change the amount of current applied in eight steps, from which an appropriate setting value can be selected.

[0078] However, in reality, even if the same current is passed through the LED(R) 73, LED(G) 74, and LED(B) 75, the amount of light varies due to differences in their characteristics, so the current passed through the LED(R) 73, LED(G) 74, and LED(B) may not be the same and may be adjusted as appropriate. For example, at 600 dpi, a first current amount of 18 mA is passed through the LED(R) 73, 16 mA is passed through the LED(G) 74, and 24 mA is passed through the LED(B) 75, and at 300 dpi, a second current amount of 36 mA is passed through the LED(R) 73, 32 mA is passed through the LED(G) 74, and 48 mA is passed through the LED(B) 75, thereby equalizing the output of the image data (R) 705, image data (G) 706, and image data (B) 707. It is preferable that the difference between these adjusted amounts of current flow is set in advance by a separate light intensity adjustment, i.e., an adjustment that makes the output values ​​of the image data (R) signal 705, the image data (G) signal 706, and the image data (B) signal 707 uniform when current is applied at a reference current.

[0079] Here, an example is shown in which the second current flow rate is twice the first current flow rate, but it may be adjusted as appropriate by setting a limit depending on the temperature rise of the LED 72 and the rated current of the LED 72.

[0080] Alternatively, the LED that is lit for the longest duration as a result of the light intensity adjustment may be lit in only one color during the latter period, T_SP2. In this case, if the same magnification is applied to both LEDs as the second power level, and the current setting unit 96 exceeds the upper limit of the current it can supply when attempting to achieve the desired light intensity (second light intensity) by applying the same magnification to the two colors lit during the first period, T_SP1, the lighting times of the two colors can be adjusted to achieve the desired light intensity (second light intensity) with a power level greater than the first power level but less than the second power level. In other words, the desired light intensity (second light intensity) can be achieved with the second power level for the LEDs lit in only one color, while the desired light intensity (second light intensity) can be achieved by adjusting the second power level and the lighting time for the LEDs lit in two colors. The lighting time for the LEDs lit in two colors may also be shortened while still using the second power level. This is particularly effective when it is necessary to suppress the temperature rise of the LEDs.

[0081] [Second embodiment] Next, an image reading apparatus according to a second embodiment will be described. Note that a description of parts common to the first embodiment will be omitted, and differences from the first embodiment will be mainly described.

[0082] The timing for reading a 300 dpi image in the image processing device according to the second embodiment will be described with reference to Fig. 10. That is, the lighting control of the LEDs 72, which are three-color light-emitting elements, when reading an image at a resolution of 300 dpi, which is twice the pixel spacing, using an image reading sensor with a resolution of 600 dpi, where the pixel spacing of the light-receiving elements in the main scanning direction and sub-scanning direction is 42.27 µm.

[0083] As described in the first embodiment, at a resolution of 300 dpi, the reading period T_SP, which is the time from SP to the next SP, is divided into T_SP1, which is the first half of the reading period, and T_SP2, which is the second half of the reading period T_SP, and the lighting control of the LED 72 is performed.

[0084] The 300 dpi image data can generate a color image without color shift by using image data (R) obtained by turning on T_RED-1, image data (G) obtained by turning on T_GREEN-1, and image data (B) obtained by turning on T_BLUE-2. That is, one line of color image data is generated from image data (R) signal 705-1, image data (G) signal 706-1, and the image data (B) signal 707-2 of the next SP. Similarly, one line of color image data is generated from image data (R) signal 705-2, image data (G) signal 706-2, and the image data (B) signal 707-3 of the next SP. By sequentially repeating this process, a color image for one surface of the sheet is generated.

[0085] In this embodiment, when the amount of current flowing through the LEDs during 600 dpi reading is set to a first current flowing amount, LED(R) 73 and LED(B) 75 are illuminated at a second current flowing amount during T_SP1 in the first half of 300 dpi, and LED(G) 74 is illuminated at a third current flowing amount (>second current flowing amount) during T_SP2 in the second half of 300 dpi. The third current flowing amount, which illuminates LED(G) 74 in one color, can be made larger than the second current flowing amount, which illuminates LED(R) 73 and LED(B) 75 simultaneously.

[0086] Specifically, the setting of the current setting unit 96 is changed from the current setting input unit 95, and at 600 dpi, a current of 20 mA is passed to each of the LED(R) 73, LED(G) 74, and LED(B) 75 as the first current amount, and at 300 dpi, a current of 30 mA is passed to each of the LED(R) 73 and LED(B) 75 as the second current amount, and 60 mA is passed to the LED(G) 74 as the third current amount.

[0087] Here, the second current is set to 1.5 times the first current, and the third current is set to twice the first current. However, these currents may be adjusted appropriately based on the temperature rise of the LEDs 72 and the rated current of the LEDs 72. The second current and the third current are set to 1.5 and 2 times the first current, respectively, but the ratios are not limited to these. Furthermore, because a difference in the ratio between the second current and the third current may result in a deviation from the light intensity adjustment result at the first current, it is preferable to adjust the light intensity again. If this results in the current duration for the LEDs at the third current exceeding T_SP2, it is preferable to readjust the second and third currents by reducing them by the same ratio so as not to exceed T_SP2, or to set the current duration for the LEDs at the third current to the maximum allowable time equal to or less than T_SP2. This allows the third current to be set to the maximum light duration and maximum current.

[0088] [Third embodiment] Next, an image reading apparatus according to a third embodiment will be described. Note that a description of parts common to the first and second embodiments will be omitted, and differences from the first embodiment will be mainly described.

[0089] The timing for reading a 300 dpi image in the image processing device according to the third embodiment will be described with reference to Fig. 11. That is, the lighting control of the LEDs 72, which are three-color light-emitting elements, when reading an image at a resolution of 300 dpi, which is twice the pixel spacing, using an image reading sensor with a resolution of 600 dpi, where the pixel spacing of the light-receiving elements in the main scanning direction and sub-scanning direction is 42.27 µm.

[0090] In this embodiment, when an image is read at a resolution of 300 dpi, the main scanning direction is read at 300 dpi, but the sub-scanning direction is read at 600 dpi, and then every other line is thinned out and output at 300 dpi.

[0091] The 300 dpi image data can be generated as a color image without color shift by using an image data (R) signal 705-1 obtained by issuing an SP signal to light up T_RED-1, an image data (G) signal 706-2 obtained by issuing another SP signal to light up T_GREEN-2, and an image data (B) signal 707-3 obtained by issuing yet another SP signal to light up T_BLUE-3. No output is performed on the next line, and on the next line, color image data for one line is generated from the image data (R) signal 705-3, an image data (G) signal 706-4 (not shown), and an image data (B) signal 706-5. By repeating this process sequentially, a color image for one surface of the sheet is generated.

[0092] In this embodiment, when the LED current amount during 600 dpi reading (first reading control) is set to a first current amount, the 300 dpi LED(R) 73 and LED(B) 75 (corresponding to the two lines at both ends in the sub-scanning direction) are lit at a second current amount (second reading control), and the 300 dpi LED(G) 74 (corresponding to the central line in the sub-scanning direction) is lit at a third current amount (third reading control). The third current amount, which lights up LED(G) 74 in one color, can be made larger than the second current amount, which lights up LED(R) 73 and LED(B) 75 simultaneously.

[0093] Specifically, the setting of the current setting unit 96 is changed from the current setting input unit 95, and at 600 dpi, a current of 20 mA is passed to each of the LED(R) 73, LED(G) 74, and LED(B) 75 as the first current amount, and at 300 dpi, a current of 30 mA is passed to each of the LED(R) 73 and LED(B) 75 as the second current amount, and 60 mA is passed to the LED(G) 74 as the third current amount.

[0094] Here, an example is shown in which the second current flow rate is 1.5 times the first current flow rate, and the third current flow rate is twice the first current flow rate, but limitations may be set and adjusted as appropriate depending on the temperature rise of the LEDs 72 and the rated current of the LEDs 72. Also, although the relationship between the second current flow rate and the third current flow rate is set to be twice the first current flow rate here, it is not limited to this.

[0095] As described above, the present invention can improve the image quality while suppressing the occurrence of color shift by changing the energization amount according to the number of LEDs 72 (light emitting elements) that are lit simultaneously. In particular, in the case of having three light sources of RGB, when performing light amount adjustment by adjusting the lighting period, it is preferable to repeat the control of lighting the color with the longest lighting period alone and lighting the remaining two colors simultaneously. Further, it is possible to multiply the energization amount by m times (1 < m) without changing the lighting period of the color with the longest lighting period, and multiply the remaining two colors by n times (1 < n < m). In that case, the lighting period of the remaining two colors can be made m / n times, and as the light amount, it becomes n × (m / n) = m times, and it can be made equivalent to the light amount ratio of each color whose light amount has been adjusted in advance, and it is not necessary to re-adjust the light amount. Actually, the light amount adjustment may be redone with the changed current value, and the current value and the lighting period may be adjusted again as necessary.

[0096] The present invention is not limited to the above-described embodiments, and various changes can be made without changing the gist of the present invention.

[0097] For example, although the example of dividing T_SP into two periods of the first half and the second half and continuously lighting with the start timing of the period as the lighting start timing has been described, it is not limited to this, and it may be divided and lit so that the total lighting time within the period becomes a predetermined time.

Explanation of Reference Numerals

[0098] F: Sheet 1: Sheet Loading Table 1a: Sheet Loading Surface 2: Loading Table Drive Motor 3: Sheet Detection Sensor 4: Pickup Roller 6: Feed Roller 7: Separation Roller 8: Feed Motor 9: Separation Motor 10: Conveyor Motor 11: Nip Gap Adjustment Motor 12: Sheet stacking detection sensor 13: Home position detection sensor 14, 15: Image reading sensor 17,18: Registration roller 19: Resist Clutch 20-23: Conveyor rollers 30: Double feed detection sensor 40: Upper guide plate 41: Lower guide plate 42: Separation roller pair (sheet separation section) 44: Discharge and loading section 45: Control board 46: Control unit (CPU) 63: Sensor clock generation unit 64: Line synchronization signal generator 66: Image processing unit 70: Sensor control unit 71: LED driver 72: LED 73: LED(R) 74: LED (G) 75: LED (B) 76: Light receiving part 77: Light receiving part (R) 78: Light receiving part (G) 79: Light receiving part (B) 80: Light guide 81: Reading glass 82: Lens array 83: Sensor board 90: Power supply booster 91: Control signal input section 92: Lighting control unit (R) 93: Lighting control unit (G) 94: Lighting control unit (B) 95: Current setting input section 96: Current setting section 97: Current source (R) 98: Current source (G) 99: Current source (B) 101: Sheet intake device 200: Image reader 501: Color filter (R) 502: Color filter (G) 503: Color filter (B) 701:SP 702: LED light (R) 703: LED light (G) 704: LED lit (B) 705, 705-1, 705-2, 705-3: Image data (R) 706, 706-1, 706-2, 706-3: Image data (G) 707, 707-1, 707-2, 707-3: Image data (B)

Claims

1. A light-emitting element; a plurality of line sensors, each of which is a linear photoelectric conversion element that receives light emitted from the light emitting element and reflected by a document to be read, and outputs an electrical signal corresponding to a different wavelength range; a light emission control means for controlling the lighting start time, lighting period, and amount of current of the light emitting element; Equipped with The line sensors are arranged at predetermined intervals in the sub-scanning direction, The image reading device is characterized in that the light emission control means changes the amount of current flowing in accordance with the number of light emitting elements that are simultaneously turned on.

2. 2. The image reading device according to claim 1, wherein the light-emitting elements are three light-emitting elements corresponding to the RGB wavelength ranges, and the line sensors are three line sensors that output electrical signals corresponding to the RGB wavelength ranges.

3. The light emission control means during a first period of one line of image reading in which the image is read at a resolution equal to a pixel interval in the sub-scanning direction of the line sensor, the three light-emitting elements are controlled to emit light with a first current amount that is specified in advance; a second period for reading an image of one line at a resolution twice the pixel interval in the sub-scanning direction of the line sensor is divided into a first lighting period in which two of the light-emitting elements are turned on and a second lighting period in which the remaining light-emitting element is turned on; 3. The image reading device according to claim 2, wherein the light emitting element is controlled to emit light with a second amount of current that is greater than the first amount of current.

4. The light emission control means during a first period of one line of image reading in which the image is read at a resolution equal to a pixel interval in the sub-scanning direction of the line sensor, the three light-emitting elements are controlled to emit light with a first current amount that is specified in advance; a first period for reading an image of one line at a resolution twice the pixel interval in the sub-scanning direction of the line sensor is divided into a first lighting period during which one of the light-emitting elements is turned on and a second lighting period during which the remaining two of the light-emitting elements are turned on; 3. The image reading device according to claim 2, wherein during the first lighting period, light emission is controlled with a second current amount greater than the first current amount, and during the second lighting period, light emission of the light-emitting element is controlled with a third current amount greater than the second current amount.

5. a first read control for reading one line of an image by controlling the three light-emitting elements to emit light with a predetermined first current amount during a first period of one line of image reading in which the image is read at a resolution equal to a pixel interval in the sub-scanning direction of the line sensor; a second read control for reading an image of one line by controlling the two light-emitting elements corresponding to two lines at both ends in the sub-scanning direction of the line sensor to emit light with a second current amount greater than the first current amount during a second period of image reading of one line in which the image is read at a resolution twice the pixel interval in the sub-scanning direction of the line sensor; a third read control for reading an image of one line by controlling two of the light-emitting elements corresponding to one line at the center in the sub-scanning direction of the line sensor to emit light with a third current amount equal to or greater than the second current amount during the second period; is executable, The image reading device according to claim 2, characterized in that the second reading control and the third reading control are repeated for each line at a timing corresponding to the pixel spacing in the sub-scanning direction of the line sensor, thereby generating an image with a resolution twice the pixel spacing in the sub-scanning direction of the line sensor.

6. 6. The image reading device according to claim 5, wherein the light emission control means controls the amount of light emitted by the two light emitting elements that emit light with the second amount of current by controlling the time for which the two light emitting elements are turned on during the second reading control.

Images