JP2020005048A - Image reading device, control device, control method of sensor unit - Google Patents

Abstract

Provided is an image reading apparatus that suppresses the influence of a change in ground voltage and prevents a decrease in image quality of a read document image. An image reading apparatus includes a CIS for reading an image of a document, and a main board for controlling an operation of the CIS. The CIS 116 includes an LED 122 that irradiates the document with light, a line sensor 125 that receives light reflected by the document, and outputs an electric signal corresponding to the received reflected light, and a pseudo load 205. The main board 200 puts the pseudo load 205 into a non-operation state when the CIS 116 turns on the LED 122 to perform the reading operation, and puts the pseudo load 205 into an operation state when the CIS 116 turns off the LED 122 and performs the reading operation. . Thereby, the ground voltage of the CIS 116 when the LED 122 is turned on and when the LED 122 is turned off becomes equal. [Selection] Figure 2

Description

  The present invention relates to an image reading device that reads an image (document image) from a document.

  An image reading device mounted on a copying machine, a facsimile device, or the like reads, using a sensor unit, a document image of a document placed on a platen glass or a document fed from an ADF (Auto Document Feeder). The sensor unit includes a light source that irradiates the document and a line sensor that receives light reflected by the document. The line sensor photoelectrically converts the received reflected light and outputs an electric signal representing a document image.

  The line sensor includes a plurality of light receiving elements for receiving the reflected light. Before reading the document image, the line sensor performs shading correction for correcting variations in the outputs of the light receiving elements. The shading correction includes black shading correction performed by turning off the light source and white shading correction performed by turning on the light source. The black shading correction is a process for correcting variations in the output (dark output) of the light receiving element when the power is turned off. White shading is a process of correcting variations in the output (bright output) of the light receiving element when the power is turned on.

  In addition to the light source and the line sensor, the sensor unit is configured integrally with components such as an AFE (Analog Front End) that performs predetermined processing including AD conversion on an electric signal output from the line sensor. A power supply voltage is supplied to the sensor unit from a main board of the image reading apparatus via a wiring such as a flat cable. When a power supply voltage is supplied to each component of the sensor unit from a common power supply, the power supply voltage value (power supply voltage value) varies between when the light source is turned off and when the light source is turned on, depending on the supply capability of the power supply. Sometimes. That is, when the light source is turned on, the current flowing through the light source increases, so that the power supply voltage value may decrease.

The output characteristics of the line sensor change due to the fluctuation of the supplied power supply voltage. For example, since the power supply voltage value fluctuates between when the light source is turned off and when it is turned on, the output characteristics of the line sensor change when the light source is turned off and when it is turned on. As a result, the output characteristics of the line sensor change between black shading correction and white shading correction, making accurate shading correction difficult. This causes a decrease in the image quality of the read document image.
Patent Literature 1 discloses an image reading apparatus that drives a dummy load (dummy load) when the light source is turned off in order to suppress fluctuations in the power supply voltage when the light source is turned off and when the light source is turned on. In this image reading apparatus, the power supply of the light source and the power supply of the line sensor are common, and by driving the pseudo load when the light source is off, the power supply voltage value is obtained when the light source is off and on. Constant.

JP 2015-106739 A

  A sensor unit to which a power supply voltage is supplied via a flat cable or the like includes a power supply terminal to which a power supply voltage is supplied to a connector and a ground terminal. The ground voltage makes the ground voltage common to the sensor unit and the main board. The ground terminal forms a return path for flowing current (return current) consumed by the line sensor and the light source of the sensor unit to the main board. Flat cables and the like have an impedance component. Due to the return current and the impedance component, the ground voltage of the sensor unit becomes higher than the ground voltage of the main board. Therefore, when the return current fluctuates between when the light source is turned off and when it is turned on, the ground voltage also fluctuates. Therefore, even when the power supply voltage value supplied to the sensor unit is constant, the power supply voltage value varies between when the light source is turned on and when the light source is turned off, based on the ground voltage of the sensor unit. As a result, the image quality of the read document image is reduced.

  SUMMARY OF THE INVENTION In view of the above-described problems, it is a main object of the present invention to provide an image reading apparatus that suppresses the influence of fluctuations in ground voltage and prevents a deterioration in the quality of a read document image.

  An image reading apparatus according to the present invention for solving the above problems includes a sensor unit for reading an image on a document, and a controller for controlling an operation of the sensor unit, and the sensor unit irradiates the document with light. A light source, a sensor that receives the reflected light of the light from the document, and outputs an electric signal corresponding to the received reflected light, and a pseudo load; and the controller turns on the light source to the sensor unit. When performing the reading operation, the pseudo load is deactivated, and when the reading operation is performed by causing the sensor unit to turn off the light source, the ground of the sensor unit when the light source is turned on and when the light source is turned off. Control means for setting the pseudo load to an operating state in order to make the voltages equal.

  According to the present invention, it is possible to prevent the image quality of the read document image from deteriorating by suppressing the fluctuation of the ground voltage of the sensor unit.

FIG. 1 is a configuration diagram of an image reading device. FIG. (A), (b) is explanatory drawing of the ground voltage of CIS116. 9 is a flowchart illustrating a reading process of a document image.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

(overall structure)
FIG. 1 is a configuration diagram of the image reading apparatus of the present embodiment. The image reading apparatus 100 includes an ADF 101 that transports a document, and a reader 102 that reads a document image.

  The ADF 101 includes a document tray 104 on which the document 103 is placed, an ADF motor 105, a transport path for transporting the document 103 to a reading position of the reader 102, and a discharge tray for discharging the document 103 from which a document image has been read. 111. In the transport path, a paper feed roller 106, a separation roller pair 107, a transport roller pair 108, a document edge sensor 109, and a paper discharge roller pair 110 are provided. The ADF 101 includes a white guide plate 112 serving as a reference member for correcting a change in a read image due to a light distribution change of the reader 102.

  The paper feed roller 106 is normally retracted above the home position so as not to hinder the placement of the document 103 on the document tray 104. When the sheet feeding operation is started, the sheet feeding roller 106 descends, comes into contact with the upper surface of the document 103 placed on the document tray 104, and rotates to feed the document 103 to the transport path. The paper feed roller 106 is supported by an arm (not shown), and moves up and down by swinging of the arm.

  The fed document 103 is separated one by one by a separation roller pair 107 and transported along the transport path. The document 103 conveyed by the separation roller pair 107 is conveyed to a reading position by the reader 102 by the conveyance roller pair 108. The document edge sensor 109 is disposed downstream of the transport roller pair 108 in the transport direction of the document 103, and detects the document 103 transported to the reading position by the transport roller pair 108. When the document edge sensor 109 detects the document 103, the reader 102 starts the reading operation of the document 103 at the reading position. The white guide plate 112 is arranged at the reading position so as to face the reader 102. The document 103 whose document image has been read at the reading position is discharged to a discharge tray 111 by a pair of discharge rollers 110. The discharged documents 103 are stacked on a discharge tray 111.

  The reader 102 includes a platen glass 115, a reading glass 113, a contact image sensor (CIS) 116, a CIS holder 117, a timing belt 118, and an optical motor 119. An original 114 can be placed on the original platen glass 115. The moving reading glass 113 is arranged at a reading position of the document 103 conveyed by the ADF 101. The CIS 116 is a sensor unit for reading a document image. The CIS 116 is held by the CIS holder 117. The timing belt 118 is connected to the CIS holder 117. The optical motor 119 is connected to the timing belt 118 via a drive gear 120. The optical motor 119 drives the timing belt 118 via the drive gear 120, so that the CIS 116 can reciprocate in the direction of the arrow in the figure.

  The platen glass 115 is provided with a white reference plate 121. The white reference plate 121 is a reference member used for adjusting the amount of light emitted from the CIS 116 and correcting shading.

  When reading a document image from the document 103 conveyed by the ADF 101, the CIS 116 is located below the flow reading glass 113 and reads the document image of the document 103 conveyed at the reading position. When reading the document image from the document 114 placed on the document glass 115, the CIS 116 reads the document image of the document 114 while moving in the direction of the arrow by the timing belt 118 under the document glass 115. In this case, the CIS 116 performs shading correction using the white reference plate 121.

  The CIS 116 includes an LED (Light Emitting Diode) 122 as a light source, a light guide 123, a lens array 124, and a line sensor 125. The LED 122 is configured by an LED that emits light in R (red), G (green), and B (blue). The light guide 123 uniformly scatters the light emitted from the LED 122 in the main scanning direction and irradiates the original with a linear shape. The irradiated light is reflected by the document. Light reflected by the document is guided to a line sensor 125 via a lens array 124. The line sensor 125 receives the reflected light, performs photoelectric conversion, and sequentially outputs image data representing a document image for each pixel.

(controller)
FIG. 2 is an explanatory diagram of a controller for controlling the operation of the image reading device 100. In FIG. 2, the configuration of the main board 200 and the CIS 116 constituting the controller will be described, and the description of the configuration for controlling the operation of the ADF 101 by the controller will be omitted.

  The main board 200 and the CIS 116 are connected by a flat cable (FFC: Flexible Flat Cable) 201. The FFC 201 transmits a power supply voltage and a control signal from the main board 200 to each component on the CIS 116, and transmits image data from the CIS 116 to the main board 200. The FFC 201 forms a return path for flowing the current (return current) consumed by the CIS 116 to the main board 200.

  The CIS 116 includes an LED driver 202, an AFE 203, a switching circuit 204, and a pseudo load 205 in addition to the LED 122 and the line sensor 125. The LED driver 202 drives the LED 122 according to a control signal obtained from the main board 200. Lighting and extinguishing of the LED 122 are controlled by the LED driver 202. The AFE 203 performs analog processing such as sample hold, offset processing, and gain processing on an analog electric signal corresponding to a document image output from the line sensor 125, and converts the analog electric signal into digital signal image data. The AFE 203 transmits the image data to the main board 200. The switching circuit 204 controls supply of a power supply voltage from the main board 200 to the dummy load 205 according to a control signal obtained from the main board 200. As a result, the switching circuit 204 switches between the operation state and the non-operation state of the pseudo load 205. The pseudo load 205 becomes a load equivalent to the LED 122 during operation.

  The grounds of the LED driver 202, the line sensor 125, the AFE 203, and the pseudo load 205 are connected in a common ground pattern in the CIS 116, and are connected to the ground pattern of the main board 200 via the FFC 201. Therefore, the ground pattern of the LED driver 202, the line sensor 125, the AFE 203, and the pseudo load 205 and the ground pattern of the main board 200 are common.

  The main board 200 includes an LED driver power supply 206, a sensor / AFE power supply 207, a timing generation unit 208, an image processing unit 209, and a CPU (Central Processing Unit) 210.

The LED driver power supply 206 supplies a power supply voltage for operating the LED driver 202. The sensor / AFE power supply 207 supplies a power supply voltage for operating the line sensor 125 and the AFE 203. That is, the LED driver 202 and the line sensor 125 are driven by different power supply voltages.
The timing generation unit 208 generates a timing signal that is a control signal for operating the LED driver 202, a clock signal and a sampling timing signal of the AFE 203, and a timing signal that is a control signal for operating the switching circuit 204. The timing generation unit 208 transmits the generated timing signals to the corresponding units of the CIS 116. The image processing unit 209 performs image processing such as shading correction on image data acquired from the CIS 116. The CPU 210 controls the operation of the entire image reading apparatus 100 by executing a predetermined control program.

(Power supply voltage of sensor / AFE power supply)
FIG. 3 is an explanatory diagram of the ground voltage of the CIS 116 when the LED 122 is turned on and when the LED 122 is turned off. Here, the ground voltage on the main board 200 side is 0 [V], and the power supply voltage value (sensor / AFE power supply voltage) supplied from the sensor / AFE power supply 207 to the CIS 116 is 3.3 [V].

  FIG. 3A shows the ground voltage of the CIS 116 when the dummy load 205 is not operated. The ground voltage of the CIS 116 varies according to the lighting state of the LED 122.

  When the reading operation is performed with the LED 122 turned off, that is, when the black shading correction is performed, the line sensor 125 and the AFE 203 operate and the LED driver 202 does not operate. The current consumed by the line sensor 125 and the AFE 203 flows as a return current to the ground of the main substrate 200 via the FFC 201. Therefore, the ground voltage of the CIS 116 rises by the multiplication of the return current and the impedance component of the FFC 201 (a0V).

  When the LED 122 is turned on to perform a reading operation, that is, when performing white shading correction and reading a document image, the line sensor 125, the AFE 203, and the LED driver 202 are in an operating state. The return current increases by an amount corresponding to the lighting of the LED 122 as compared with the case where the black shading correction is performed. The ground voltage of the CIS 116 is higher (b0 V) than the case where the LED 122 is turned off, by the amount that the LED 122 is turned on.

  The sensor / AFE power supply 207 supplies a constant voltage of 3.3 [V] as a power supply voltage. However, when the ground voltage of the CIS 116 is used as a reference, the power supply voltage (b1V) when the LED 122 is on is lower than the power supply voltage (a1V) when the LED 122 is off. That is, the potential difference between the power supply voltage output from the sensor / AFE power supply 207 and the ground voltage of the CIS 116 fluctuates according to the lighting state of the LED 122.

  FIG. 3B shows the ground voltage of the CIS 116 when the dummy load 205 is operated. Due to the operation of the dummy load 205, the fluctuation of the ground voltage of the CIS 116 according to the lighting state of the LED 122 is suppressed.

  The dummy load 205 operates only when the LED 122 is turned off. When the dummy load 205 operates when the LED 122 is turned off, the ground voltage when the LED 122 is turned off is raised by a2V and becomes the same level as the ground voltage when the LED 122 is turned on. When the ground voltage becomes the same level, the difference in power supply voltage supplied from the sensor / AFE power supply 207 between when the LED 122 is turned off and when it is turned on is suppressed when the ground voltage of the CIS 116 is used as a reference. Therefore, the power supply voltage supplied from the sensor / AFE power supply 207 based on the ground voltage of the CIS 116 becomes the same value (b1V) when the LED 122 is turned off and when the LED 122 is turned on. The amount of return current that increases when the dummy load 205 operates is the same as the amount of return current that increases when the LED 122 is turned on.

(Original image reading process)
FIG. 4 is a flowchart illustrating a document image reading process performed by the image reading apparatus 100 having the above-described configuration. This processing is executed, for example, when the user presses a reading start button (not shown) and inputs a reading start instruction.

  Upon acquiring the reading start instruction, the CPU 210 first starts black shading correction (S401). The CPU 210 transmits an instruction (timing signal) for turning off the LED 122 to the LED driver 202 by the timing generation unit 208. This turns off the LED 122 (S402). During this time, the power supply 206 for the LED driver keeps supplying the power supply voltage.

  The CPU 210 that has turned off the LED 122 transmits an instruction (timing signal) for operating the pseudo load 205 to the switching circuit 204 by the timing generation unit 208. As a result, the pseudo load 205 enters the operating state (S403).

  The image processing unit 209 acquires image data (black data) corresponding to the reading result of the line sensor 125 from the AFE 203 with the LED 122 turned off and the pseudo load 205 operated (S404). The black data includes a read luminance value of each pixel in the main scanning direction. The image processing unit 209 calculates a black shading correction value according to the acquired black data (S405). The image processing unit 209 calculates a black shading correction value for each pixel such that the read luminance value of each pixel in the main scanning direction included in the black data becomes a predetermined luminance value. CPU 210 stores the generated black shading correction value in a predetermined memory. Thus, the black shading correction is completed.

  After the black shading correction, the CPU 210 starts the white shading correction (S406). The CPU 210 transmits an instruction (timing signal) for turning on the LED 122 to the LED driver 202 by the timing generation unit 208. Thereby, the LED 122 is turned on (S407). During this time, the power supply 206 for the LED driver keeps supplying the power supply voltage.

  The CPU 210 that has turned on the LED 122 transmits an instruction (timing signal) for disabling the pseudo load 205 to the switching circuit 204 by the timing generation unit 208. As a result, the pseudo load 205 enters the non-operation state (S408).

  The image processing unit 209 acquires image data (white data) according to the reading result of the line sensor 125 from the AFE 203 in a state where the LED 122 is turned on and the pseudo load 205 is inactive (S409). At this time, the CPU 210 moves the CIS 116 below the white reference plate 121, and reads the white reference plate 121. Therefore, the white data is a result of reading the white reference plate 121. The white data includes a read luminance value of each pixel in the main scanning direction. The image processing unit 209 calculates a white shading correction value according to the acquired white data (S410). The image processing unit 209 calculates a white shading correction value for each pixel such that the read luminance value of each pixel in the main scanning direction included in the white data becomes a predetermined luminance value. CPU 210 stores the generated white shading correction value in a predetermined memory.

  The CPU 210 performs shading correction according to the black shading correction value and the white shading correction value, and reads a document image (S411). The CPU 210 can control the light emission amount of each pixel of the LED 122 and correct the image data according to the black shading correction value and the white shading correction value, thereby reading a document image while suppressing a decrease in image quality. .

  As described above, the image reading apparatus 100 according to the present embodiment includes the pseudo load 205 in the CIS 116 according to the return current amount that changes when the LED 122 is turned on. As a result, even when the LED 122 is turned off, the CIS 116 can supply the same amount of return current as the return current when the LED 122 is turned on by the current flowing through the pseudo load 205. In the CIS 116, the pseudo load 205 operates during the black shading correction, and does not operate during the white shading correction, so that the ground voltage of the CIS 116 can be set to the same value. Therefore, the power supply voltage value based on the ground voltage of the CIS 116 can be made constant. Therefore, accurate shading correction can be performed.

Claims (8)

A sensor unit for reading an image of a document, and a controller for controlling the operation of the sensor unit,
The sensor unit includes:
A light source for irradiating the document with light,
A sensor that receives reflected light of the light from the document and outputs an electric signal according to the received reflected light;
And a dummy load,
The controller is
When the reading operation is performed by turning on the light source in the sensor unit, the pseudo load is deactivated, and when the reading operation is performed by turning off the light source in the sensor unit, the light source is turned on. Control means for setting the pseudo load to an operating state in order to make the ground voltage of the sensor unit equal when the light is turned off,
Image reading device. The apparatus further includes a cable that connects the sensor unit and the controller and forms a return path for flowing current consumed by the sensor unit to the controller.
The sensor unit is characterized in that the amount of current flowing through the return path is the same when the light source is turned on and when the light source is turned off, when the pseudo load is in an operating state when the light source is turned off. And
The image reading device according to claim 1. The cable connects a ground pattern of the sensor unit and a ground pattern of the controller in common.
The image reading device according to claim 2. The sensor unit further includes a driver for driving the light source,
The controller is
A first power supply for supplying a first power supply voltage to the driver;
A second power supply that supplies a second power supply voltage to the sensor and the pseudo load.
By setting the pseudo load to the operating state when the light source is turned off, the potential difference between the second power supply voltage and the ground voltage of the sensor unit is made the same between when the light source is turned on and when the light source is turned off. Characterized by
The image reading device according to claim 1. The sensor unit further includes a switching unit configured to control supply of the second power supply voltage to the pseudo load according to a control signal obtained from the controller, thereby switching a pseudo load between an operation state and a non-operation state. Characterized by having
The image reading device according to claim 4. It further includes a reference member used for shading correction,
The control means causes the sensor unit to turn on the light source and deactivate the pseudo load to read the reference member, perform white shading correction according to the read result, turn off the light source, and Setting the pseudo load to an operating state to read the reference member, and performing black shading according to the read result.
The image reading device according to claim 1. A light source that irradiates the original with light, a sensor that receives reflected light of the light from the original, and outputs an electric signal corresponding to the received reflected light, and a pseudo load, and is connected to a sensor unit including:
When the reading operation is performed by turning on the light source in the sensor unit, the pseudo load is set to the non-operation state, and when the reading operation is performed by turning off the light source in the sensor unit, the light source is turned on. In order to equalize the ground voltage of the sensor unit when the light is turned off, the sensor unit includes a control unit that sets the pseudo load to an operation state.
Control device. A controller connected to a sensor unit comprising: a light source for irradiating a document with light; a sensor for receiving reflected light of the light from the document and outputting an electric signal corresponding to the received reflected light; and a pseudo load The method performed by
The controller is
When the reading operation is performed by lighting the light source in the sensor unit, the pseudo load is set to a non-operation state,
In the case where the reading operation is performed by turning off the light source to the sensor unit, the pseudo load is set to an operating state in order to equalize the ground voltage of the sensor unit when the light source is turned on and when the light source is turned off. Features,
How to control the sensor unit.

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