JP5158123B2 - Image reading device - Google Patents

Description

  The present invention relates to an image reading apparatus that reads an image of an original, and more specifically, a first image that reads an image on one side of an original conveyed along a conveyance path and outputs an analog read signal corresponding to the image. The present invention relates to an image reading apparatus including a reading unit and a second image reading unit that reads an image on the other side of the document conveyed along the conveyance path and outputs an analog read signal corresponding to the image.

  2. Description of the Related Art Conventionally, an image reading device that reads an image of a document is applied to devices such as a scanner, a copying machine, and a facsimile machine. As a configuration for reading images on both sides of a document with this type of image reading apparatus, a configuration has been proposed in which a single image reading unit reads images on both the front and back sides by reversing the document by devising the conveyance path of the document. In recent years, however, a configuration has been proposed in which two image reading units simultaneously read both front and back images.

  For example, a first image reading unit that reads an image on one side of a document conveyed along a conveyance path and outputs an analog read signal corresponding to the image, and the document conveyed along the conveyance path In an image reading apparatus comprising a second image reading unit that reads an image on the other side of the image and outputs an analog read signal corresponding to the image, the image reading operation on the one side by the first image reading unit And the image reading operation on the other side by the second image reading unit can be executed in parallel, and the reading speed can be improved. In this type of image reading apparatus, the first image reading unit and the second image reading unit are connected to separate analog front ends (AFE), and the analog read signals output from the image reading units are individually received. It is converted into a digital signal (see, for example, Patent Document 1).

JP 2007-281718 A

  However, in the image reading apparatus described in Patent Document 1, since the first image reading unit and the second image reading unit are connected to separate AFEs, the manufacturing cost of the apparatus increases. Accordingly, the present invention provides a first image reading unit that reads an image on one side of a document conveyed along a conveyance path and outputs an analog read signal corresponding to the image, and conveys the image along the conveyance path. And a second image reading unit that reads an image on the other side of the original and outputs an analog read signal corresponding to the image. It was made for the purpose of making it possible to reduce the manufacturing cost of the apparatus by reducing the number of analog front end parts that can be D-converted.

  In order to achieve the above object, an image reading apparatus according to the present invention includes an analog front-end unit capable of A / D converting analog read signals from a plurality of channels, and one of originals conveyed along a conveyance path. A first image reading unit that reads an image of a surface and outputs an analog read signal corresponding to the image from one channel; and the analog front end unit has the same number of channels as the number of channels that can be A / D converted. A second image reading unit that reads an image of the other side of the document conveyed along the conveyance path for each channel and outputs an analog read signal corresponding to the image; and a second image reading unit Switch between the first channel as one of a plurality of channels and one channel of the first image reading unit and connect to the analog front end unit Each of the plurality of channels of the second image reading unit excluding the first channel is connected to the analog front end unit, and the first channel is further connected to the first switching unit. Control for connecting to the analog front end unit via the first switching unit and instructing the second image reading unit to output the reading signal, and switching the channel of the first image reading unit to the first switching unit. A first control unit that is connected to the analog front end unit via a unit and that alternately executes control for instructing the first image reading unit to output the read signal. Yes.

  In the image reading apparatus of the present invention configured as described above, the first image reading unit reads an image on one side of the document conveyed along the conveyance path and outputs an analog read signal corresponding to the image as 1. Output from one channel. The second image reading unit reads an image on the other side of the document conveyed along the conveyance path and outputs an analog read signal corresponding to the image. Here, the second image reading unit has the same number of channels as the number of channels that can be A / D converted by the analog front end unit, and outputs the reading signal for each channel. Of the plurality of channels of the second image reading unit, each channel except the first channel is connected to the analog front end unit, and the read signal from each channel is A / D converted by the analog front end unit. The

  The first channel and one channel of the first image reading unit are switched by a first switching unit and connected to the analog front end unit. Therefore, the first control unit connects the first channel to the analog front end unit via the first switching unit, and controls the second image reading unit to output the reading signal (hereinafter referred to as “reading signal”). Control A), the channel of the first image reading unit is connected to the analog front end unit via the first switching unit, and the first image reading unit is instructed to output the reading signal. Control to be performed (hereinafter also referred to as control B) is executed alternately.

  For this reason, when the control A is executed, all the channels of the second image reading unit are connected to the analog front end unit, and the second image reading unit is instructed to output the reading signal. All the read signals from the image reading unit are A / D converted. In addition, when the control B is executed, the channel of the first image reading unit is connected to the analog front end unit, and the first image reading unit is instructed to output the reading signal to the first image reading unit. All the read signals from the unit are A / D converted. In the present invention, since such control A and control B are executed alternately, it is possible to read the images on both sides of the document with a small number of analog front end units and A / D convert the read signals. Manufacturing cost can be reduced satisfactorily.

  In the present invention, it is possible to set a single-sided reading mode for reading only the image on the other side of the original. When the single-sided reading mode is set, the first control unit switches the first channel to the first switching unit. The control may be repeatedly performed by connecting to the analog front end unit via the control unit and instructing the second image reading unit to output the read signal.

  In this case, when setting the single-sided reading mode for reading only the image on the other side of the document, the first control unit connects the first channel to the analog front end unit via the first switching unit, In addition, the control for instructing the second image reading unit to output the read signal (that is, the control A) is repeatedly executed. For this reason, the process which reads only the image of the said other surface via the said 2nd image reading part can be performed favorably.

  The image reading apparatus of the present invention, which has been made to achieve the above object, includes an analog front-end unit capable of A / D converting analog read signals from a plurality of channels, and a document conveyed along a conveyance path. A first image reading unit that reads an image of one surface and outputs an analog read signal corresponding to the image from one channel, and the same number of channels as the number of channels that the analog front end unit can perform A / D conversion. A second image reading unit that reads an image on the other side of the document conveyed along the conveyance path for each channel and outputs an analog read signal corresponding to the image; and the second image reading A second switching unit that switches between the first channel and the second channel as two of the plurality of channels and connects to the analog front end unit One channel of the first image reading unit and a plurality of channels other than the first channel and the second channel among the plurality of channels of the second image reading unit are connected to the analog front end unit. And a control for connecting the first channel to the analog front end unit via the second switching unit and instructing the second image reading unit to output the reading signal; and The second image reading is performed by alternately executing control for connecting the channel to the analog front end unit via the second switching unit and instructing the second image reading unit to output the reading signal. A second control unit for instructing the first image reading unit to output the reading signal once between the two reading signal output instructions to the first image reading unit; For the read signal output instruction of the two, for the channels that the read signal has been twice the A / D conversion by the analog front-end unit, it may be configured to discard one of the conversion result.

  In the image reading apparatus of the present invention configured as described above, the first image reading unit reads an image on one side of the document conveyed along the conveyance path and outputs an analog read signal corresponding to the image as 1. Output from one channel. The second image reading unit reads an image on the other side of the document conveyed along the conveyance path and outputs an analog read signal corresponding to the image. Here, the second image reading unit has the same number of channels as the number of channels that can be A / D converted by the analog front end unit, and outputs the reading signal for each channel. Of the plurality of channels of the second image reading unit, each channel except the first channel and the second channel and one channel of the first image reading unit are connected to the analog front end unit, and The read signal from the channel is A / D converted by the analog front end unit.

  The first channel and the second channel are switched by a second switching unit and connected to the analog front end unit. Therefore, the second control unit controls the first channel to be connected to the analog front end unit via the second switching unit, and instructs the second image reading unit to output the reading signal (hereinafter referred to as “reading signal”). Control C), the second channel is connected to the analog front end unit via the second switching unit, and the second image reading unit is instructed to output the reading signal (hereinafter referred to as control). D) are alternately executed, and the first image reading unit is instructed to output the reading signal once during the two reading signal output instructions to the second image reading unit. .

  Therefore, when the control C is executed, one channel of the first image reading unit and each channel of the second image reading unit excluding the second channel are connected to the analog front end unit, and When the two-image reading unit is instructed to output the reading signal, the reading signals of the channels other than the second channel among the channels of the second image reading unit are A / D converted. When executing the control D, one channel of the first image reading unit and each channel of the second image reading unit excluding the first channel are connected to the analog front end unit, and the second When the image reading unit is instructed to output the reading signal, the reading signals of the channels other than the first channel among the channels of the second image reading unit are A / D converted.

  Thus, by executing the controls C and D, all the read signals from the second image reading unit are A / D converted. Of the channels of the second image reading unit, the reading signals of the channels other than the first channel and the second channel are output from the analog front end according to the two reading signal output instructions to the second image reading unit. A / D conversion is performed twice, but one of the conversion results is discarded.

  As described above, since the one channel of the first image reading unit is always connected to the analog front end unit, the second control unit performs the second image reading by the controls C and D. Instructing the first image reading unit to output the read signal once while instructing the output of the read signal to the unit twice. For this reason, also in the present invention, it is possible to read the images on both sides of the document with a small number of analog front end parts and A / D convert the read signals, and to reduce the manufacturing cost of the apparatus satisfactorily. In this case, while the first image reading unit is instructed to output the reading signal once, the second image reading unit is instructed to output the reading signal twice. However, in many cases, the second image reading unit having a large number of channels can instruct the output of the read signal at short intervals, and in this case, the reading speed as a whole is not reduced.

  In this case, a first switching unit that switches between the first channel and one channel of the first image reading unit and connects to the analog front end unit is further provided, and the image on the other side of the document is provided. A single-sided reading mode for reading only the single-sided reading mode can be set, and when the single-sided reading mode is set, the second control unit connects the first channel to the analog front end unit via the first switching unit, and Control for connecting the second channel to the analog front end unit via the second switching unit and instructing the second image reading unit to output the reading signal may be repeatedly executed.

  In this case, if the first channel is connected to the analog front end unit via the first switching unit, and the second channel is connected to the analog front end unit via the second switching unit, All channels of the second image reading unit are connected to the analog front end unit. Therefore, when setting the single-sided reading mode for reading only the image on the other side of the document, the second control unit performs such a connection and performs control for instructing the second image reading unit to output the reading signal. By repeating, the process of reading only the image on the other side through the second image reading unit can be executed satisfactorily.

  In the present invention, the second image reading unit includes a light source for irradiating the original with light in order to read the image on the other side, and the second control unit is configured to output the two reading signal output instructions. Among them, the light source is irradiated with light for outputting the read signal corresponding to the read signal output instruction immediately before the previous read signal output instruction, and the next read signal output is output immediately after the previous read signal output instruction. The light source may be irradiated with light for outputting the read signal in response to an instruction.

  As described above, in the present invention, all the read signals from the second image reading unit are A / D converted by instructing the output of the read signal twice by the controls C and D. It is desirable that the lines on the document read by the above are the same line or very close lines in order to accurately read the image on the other side. When the light irradiation by the light source is controlled as described above, the light irradiation for the previous reading signal output and the light irradiation for the next reading signal output sandwich the previous reading signal output instruction. Since they are arranged close to each other, the lines on the original corresponding to each read signal are close to each other, and the image on the other surface can be read more accurately.

  In this case, the light sources are provided corresponding to a plurality of colors, and the second control unit controls the light sources corresponding to the same color to emit light in response to the two reading signal output instructions. May be sequentially executed for each color. In this case, since the reading of the image corresponding to the same color is performed on the adjacent lines on the document, the image on the other side of the document having a plurality of colors can be read more accurately.

1 is a cross-sectional view schematically illustrating a configuration of an image reading apparatus to which the present invention is applied. It is a block diagram showing the structure of the control system of the image reading apparatus. FIG. 2 is a block diagram (A) showing in detail the configuration of the AFE of the control system, and an explanatory diagram (B) showing its operation. FIG. 4 is a schematic diagram (A) showing the configuration of one CIS of the control system, an explanatory diagram (B) showing its operation, and an explanatory diagram (C) showing a digital signal corresponding to the operation. It is a time chart showing the process of the double-sided reading mode by the control system. It is a time chart showing the other form of the double-sided reading mode. It is a time chart showing the further another form of the double-sided reading mode.

[Entire configuration of image reading apparatus]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the configuration of an image reading apparatus 10 to which the present invention is applied. The image reading apparatus 10 is provided on an upper portion of a base body 20 of a multifunction machine having an image forming unit (not shown), and a document cover 30 is provided on the upper surface of the base body 20 so as to be opened and closed.

  As shown in FIG. 1, a glass platen 21 on which a document (not shown) is placed when the image reading apparatus 10 is used as a flatbed scanner is provided on the upper end surface of the base 20. . The document cover 30 is attached to be freely opened and closed so as to cover the document placed on the document table 21 by being closed on the surface of the document table 21.

  The document cover 30 is configured as a document cover having an ADF (Auto Document Feeder), and conveys a document placed on the paper feed tray 110 along a conveyance path, and functions as an ADF. A first reading device 210 and a second reading device 230 capable of reading an image in parallel on the front surface and the back surface of the document conveyed along the path are provided.

  The transport unit 100 includes transport rollers 121 to 129 that transport a document placed on the paper feed tray 110 to the paper discharge tray 130 along a transport path (dotted line in FIG. 1). In addition, an upstream side reading position and a downstream side reading position are provided in the transport path, and a first reading device 210 (first image) for reading an image on the back side (corresponding to one side) of the document. An example of a reading unit) is provided corresponding to the upstream reading position, and further, a back side document presser 220 that presses the document passing through the upstream reading position against the reading surface of the first reading device 210 is provided. Yes. A second reading device 230 (an example of a second image reading unit) provided on the document table 21 for reading an image on the surface of the document (corresponding to the other surface) is located at a position corresponding to the downstream reading position. A front-surface document holder 240 that is configured to be movable and that presses the document passing through the downstream-side reading position against the reading surface of the second reading device 230 is provided.

  Further, an F sensor 310, an RB sensor 320, and an R sensor 330 are provided as document sensors for detecting the presence or absence of a document being conveyed at a corresponding position on the conveyance path. The second reading device 230 is fixed to an endless belt 357 provided between a driving pulley 353 and a driven pulley 355 that are rotationally driven by a motor 351, and the second reading device 230 is arranged on the platen 21 according to the rotation of the motor 351. The lower part can be moved in the sub-scanning direction (left-right direction).

[Configuration of control system of image reading apparatus]
Next, FIG. 2 is a block diagram showing the configuration of the control system of the image reading apparatus 10. As shown in FIG. 2, the first reading device 210 includes a back surface light source unit 211 (a back surface CIS light source unit) that irradiates light on the back surface of the document that passes through the upstream reading position, and the light on the back surface. A back surface CIS 212 that receives the reflected light. Similarly, the second reading device 230 includes a surface light source unit 231 (surface CIS light source unit) that irradiates light on the surface of the document passing through the downstream reading position, and a reflection in which the light is reflected on the surface. And CIS 232 for the surface that receives light.

  When the front surface SP signal (SP_FS) is input, the front surface CIS 232 is synchronized with the front surface CLK signal (CLK_FS), and analog read signals AO1_FS and AO2_FS corresponding to the image for one line in the main scanning direction. This is a 3-channel CIS that outputs AO3_FS from three terminals AO1, AO2 (an example of the second channel) and AO3 (an example of the first channel). On the other hand, the back surface CIS 212 receives an analog read signal AO_BS corresponding to an image for one line in the main scanning direction in synchronization with the back surface CLK signal (CLK_BS) when the back surface SP signal (SP_BS) is input. This is a 1-channel CIS output from one terminal AO. The configuration of the surface CIS 232 will be described in detail later.

  The read signal AO_BS output from the back surface CIS 212 is input to the analog switch (analog SW) 387 as an example of the first switching unit together with the read signal AO3_FS output from the front surface CIS 232. The read signal AO3_FS is also input to the analog switch 389 as an example of the second switching unit together with the read signal AO2_FS output from the front surface CIS 232. Further, the read signal AO1_FS output from the front surface CIS 232 is input to the terminal AI1 of the AFE 390 (an example of an analog front end unit).

Analog switch 387 inputs either one of the input read signal AO_BS or AO3_FS the terminal AI3 of AFE390, analog switches 389, one of AFE390 any one of the read signal AO2_FS or AO 3 _fs input Input to terminal AI2. The AFE 390 is configured as follows, and sequentially converts the three-channel read signals input to the terminals AI1, AI2, and AI3 into a digital signal DO and outputs the digital signal DO.

  FIG. 3A is a block diagram illustrating the configuration of the AFE 390 in detail. As shown in FIG. 3A, the AFE 390 includes three sample hold circuits (S / H) 391, a programmable gain amplifier (PGA) 393, and terminals AI1 to AI3. A multiplexer (MUX) 395, an AD converter (ADC) 397, and an output control unit 399 are provided in common for the AI3.

  The read signals input to the terminals AI1 to AI3 are delayed with a constant time constant as exemplified by AI1-3 in FIG. 3B due to the influence of amplification by amplifiers incorporated in the CISs 212 and 232, and the like. Presents a wavy waveform. Therefore, the three sample hold circuits 391 are synchronized with the sample timing signal VSMP (see FIG. 2) that is output at a timing at which a value that best represents the amount of light received from each pixel can be obtained near the top of the waveform. The values (analog values) of the read signals input to the terminals AI1 to AI3 are individually acquired. The analog values obtained in this way are input to the multiplexer 395 via the programmable gain amplifier 393 and sequentially input to the AD converter 397. Then, the AD converter 397 converts each analog value acquired according to the input from each of the terminals AI1 to AI3 into a digital value in synchronization with the AD conversion main clock MCLK, and the digital value is output via the output control unit 399. Output as signal DO.

  Therefore, as illustrated in FIG. 3B, even if the read signal is input to each of the terminals AI1 to AI3 at the same timing and the analog value is acquired simultaneously by the common sample timing signal VSMP, the digital signal DO For example, digital values corresponding to inputs to the terminals AI1, AI2, and AI3 are sequentially output in synchronization with the AD conversion main clock MCLK.

  Further, as schematically shown in FIG. 4A, the front surface CIS 232 divides the number of light receiving elements corresponding to pixels for one line (for example, 5120 pixels) into three channels including channels ch1 to ch3. Have. Then, each light receiving element accumulates charges corresponding to the reflected light from the original received while the surface light source unit 231 emits light, and when the surface SP signal (SP_FS) is inputted, the accumulation is performed. The charged charges are dropped into a known shift register (not shown).

  Then, as shown in FIG. 4B, the shift register sequentially outputs charges corresponding to each pixel, and the charges are read as signals AO1_FS, AO2_FS, and AO3_FS for each of the channels ch1, ch2, and ch3 through an amplifier or the like. Is output. Therefore, for example, the read signal AO1_FS corresponding to the first to first 1600 pixels is sequentially output from the signal corresponding to the first pixel, and for example, the read signal AO2_FS corresponding to the 1601 to 3392 pixels is a signal corresponding to the 1601st pixel. For example, the read signal AO3_FS corresponding to the 3393th to 5120th pixels is sequentially output from the signal corresponding to the 3393th pixel.

  If the analog switch 389 is switched to the read signal AO2_FS side and the analog switch 387 is switched to the read signal AO3_FS side, the read signals AO1_FS, AO2_FS, and AO3_FS are respectively connected to the terminals AI1, AI2, and AI3. The digital signal DO as illustrated in FIG. 4C is output from the AFE 390. In FIG. 4C, the numbers in the frames represent pixel positions corresponding to the data.

  Returning to FIG. 2, the digital signal DO output from the AFE 390 is input to the back surface digital signal processing unit 401 and the front surface digital signal processing unit 403 provided in the ASIC 400. The ASIC 400 includes a timing generation circuit 405 as an example of a first control unit and a second control unit that output the front surface SP signal, the front surface CLK signal, the back surface SP signal, and the back surface CLK signal. . The timing generation circuit 405 includes an analog SW switching signal SEL1 for switching a reading signal input to the AFE 390 via the analog switch 387, and an analog SW switching for switching a reading signal input to the AFE 390 via the analog switch 389. The signal SEL2, the sample timing signal VSMP, and the AD conversion main clock MCLK are also output.

  The digital signal processing unit 401 for the back side processes the signals related to the back side of the document in the digital signal DO by inputting the output state of each signal of the timing generation circuit 405 from the timing generation circuit 405. Similarly, the front surface digital signal processing unit 403 inputs the output state of each signal of the timing generation circuit 405 from the timing generation circuit 405, and thereby processes a signal related to the surface of the original document from the digital signal DO. . Further, the timing generation circuit 405 transmits the front LED control signal to the front light source control circuit 430 that controls the front light source unit 231, and the rear LED control signal to the rear light source control circuit 410 that controls the rear light source unit 211. Are output respectively.

[Control in the control system]
In the image reading apparatus 10 configured as described above, when the image of only the surface of the document is read via the second reading device 230 while the document is conveyed by the conveying unit 100, or the second reading device 230 is moved by the motor 351. When reading an image on one side of a document while moving in the sub-scanning direction, the following control is performed. Such a so-called single-sided reading mode is set based on an operation panel (not shown) and a detection state of the F sensor 310. In this case, as described above, the timing generation circuit 405 switches the analog SW switching signal SEL2 to the L level and SEL1 to the H level, thereby setting the analog switch 389 to the read signal AO2_FS side and the analog switch 387 to the read signal. Switch to the AO3_FS side.

  Then, as described above, all the read signals AO1_FS, AO2_FS, and AO3_FS from the second reading device 230 are constantly input to the AFE 390. In this state, every time output of the read signals AO1_FS, AO2_FS, and AO3_FS is completed, the timing generation circuit 405 outputs the front SP signal, and the second read device 230 repeats the output of the read signals AO1_FS, AO2_FS, and AO3_FS. As a result, the image of the original placed on the front side of the conveyed original or on the original table 21 can be read quickly.

  On the other hand, in the double-sided reading mode in which images on both sides of the original are read via the first reading device 210 and the second reading device 230 while the original is being conveyed by the conveying unit 100, the timing generation circuit 405 executes the following control. To do. That is, the analog SW switching signal SEL2 is always switched to the L level. As a result, the analog switch 389 is switched to the read signal AO2_FS side, and the read signals AO1_FS and AO2_FS from the second reading device 230 are always input to the AFE 390. In this state, the timing generation circuit 405 switches the analog SW switching signal SEL1 to the H level as shown in FIG. 5 and outputs the surface SP signal. Then, as in the single-sided reading mode, all the reading signals AO1_FS, AO2_FS, and AO3_FS from the second reading device 230 are input to the AFE 390.

  Subsequently, when the output of the read signals AO1_FS, AO2_FS, and AO3_FS is completed, the timing generation circuit 405 switches the analog SW switching signal SEL1 to the L level and outputs the back surface SP signal. Then, the analog switch 387 is switched to the read signal AO_BS side, and the read signal AO_BS output from the first reading device 210 in accordance with the back surface SP signal is input to the AFE 390. After the output of the read signal AO_BS is completed, the timing generation circuit 405 outputs the surface SP signal by switching the analog SW switching signal SEL1 to the H level as described above, and thereafter repeatedly executes this processing. With this control, in the present embodiment, the images on both sides of the document can be read and the corresponding read signals AO1_FS, AO2_FS, AO3_FS, and AO_BS can be A / D converted by one AFE 390, and the manufacturing cost of the apparatus can be improved. Can be reduced.

[Modified example of the above control]
The control in the double-sided reading mode may be the following control. The image reading apparatus 10 may selectively execute the control of the modification described below and the above-described control, or may execute only one of them.

  In this control, the timing generation circuit 405 always switches the analog SW switching signal SEL1 to the L level. As a result, the analog switch 387 is switched to the read signal AO_BS side, and the read signal AO_BS from the first reading device 210 is always input to the AFE 390. In this state, the timing generation circuit 405 switches the analog SW switching signal SEL2 to the L level as shown in FIG. 6 and simultaneously outputs the front surface SP signal and the rear surface SP signal. Then, the analog switch 389 is switched to the reading signal AO2_FS side, and among the signals output from the second reading device 230 according to the front surface SP signal, the first signals according to the reading signals AO1_FS and AO2_FS and the back surface SP signal. AO_BS output from the reading device 210 is input to the AFE 390.

  Subsequently, when the output of the read signals AO1_FS and AO2_FS is completed, the timing generation circuit 405 switches the analog SW switching signal SEL2 to the H level and outputs only the front surface SP signal. Then, the analog switch 389 is switched to the reading signal AO3_FS side, and the reading signals AO1_FS and AO3_FS among the signals output from the second reading device 230 in accordance with the surface SP signal are input to the AFE 390. Since the back surface CIS 212 outputs a read signal corresponding to the same number of pixels as the front surface CIS 232 from one channel, the output of the read signal AO_BS is not completed at this time.

  After the output of the read signals AO3_FS and AO_BS, the timing generation circuit 405 outputs the front SP signal and the back SP signal by switching the analog SW switching signal SEL2 to the L level as described above, and this process is repeated thereafter. Run. With this control, in the present embodiment, the images on both sides of the document can be read and the corresponding read signals AO1_FS, AO2_FS, AO3_FS, and AO_BS can be A / D converted by one AFE 390, and the manufacturing cost of the apparatus can be improved. Can be reduced.

  In this control, while the read signals AO2_FS, AO3_FS, and AO_BS are input once to the AFE 390, the read signal AO1_FS is input twice to the AFE 390. Of these, the input of one time (for example, at a later time) is AFE 390. Are discarded in the output control or processing in the digital signal processing unit 403 for the surface. Further, as described above, since the output of the three-channel read signals AO1_FS, AO2_FS, and AO3_FS may be completed in a shorter time than the output of the one-channel read signal AO_BS, this control further improves the reading speed. There are cases where it is possible.

  In this control, valid AO1_FS, AO2_FS, and AO3_FS among the read signals corresponding to the surface image of the document are output according to different front surface SP signals. For this reason, three 1 cycle periods in which the output of the SP signal for the front surface and the output of the SP signal for the back surface are performed twice are combined into one line cycle, and light of a different color for each cycle cycle. In the case of so-called color reading that irradiates a document, the light irradiation timing may be set as follows.

FIG. 7 shows lighting timings (LE D R, LED G, LED B) of LEDs of R (red), G (green), and B (blue) colors that the surface light source unit 231 has in the case of color reading. It is explanatory drawing which illustrates the output of the read signal AO1_FS, AO2_FS, AO3_FS. As illustrated in FIG. 7, in the case of color reading, for the convenience of control, so-called full lighting in which LEDs of each color are continuously lit from the surface SP signal to the next surface SP signal is often not performed. Therefore, as shown in FIG. 7, the lighting timing may be arranged immediately before and after the first SP signal for the first surface in one cycle period.

  In the example of FIG. 7, the timing immediately before the surface SP signal that is output to acquire the read signal AO1_FS (hereinafter referred to as AO1R: the same applies to other signals) corresponding to red (R) reflected light and AO2R. Further, a lighting timing LED R for accumulating charges corresponding to the red reflected light in the front surface CIS 232 is disposed. The lighting timing LED R is also arranged immediately after the front surface SP signal, and the charge accumulated in the front surface CIS 232 during the lighting timing acquires the read signal AO3R in synchronization with the next front surface SP signal. To be output. As described above, the read signal AO1R is also input to the AFE 390 at this time, but the signal is discarded as described above. The timing generation circuit 405 controls the surface light source unit 231 via the surface light source control circuit 430, and similarly performs such LED lighting control for green (G) and blue (B). The process is repeated for each color.

  As a result, the lines on the original where the reflected light for the same color is read by the CIS 232 for the front surface of the three channels are the same lines for ch1 and ch2 (see FIG. 4), but the ch3 line is also very close to the line. An image with little misalignment can be read. Such control may be executed in the same way even in the case of monochrome reading. For example, if the lighting period of the surface light source unit 231 is shortened and lighting timings are arranged immediately before and immediately after the first surface SP signal in one line cycle, the ch1 and ch2 reading lines and the ch3 reading line Can be read close to each other.

  In addition, this invention is not limited to the said embodiment at all, It can implement with a various form in the range which does not deviate from the summary of this invention. For example, the number of channels of the second image reading unit may be four or more. In that case, a plurality of channels of the second image reading unit may be directly connected to the analog front end unit. Further, the present invention can be similarly applied to an image reading apparatus that does not perform so-called FB reading that reads an image of a document placed on a document table while moving the second image reading unit in the sub-scanning direction.

DESCRIPTION OF SYMBOLS 10 ... Image reading apparatus 20 ... Base | substrate 21 ... Document stand 30 ... Document cover 100 ... Conveyance part 210 ... 1st reading device 211 ... Back surface light source part 212 ... Back surface CIS 230 ... 2nd reading device 231 ... Front surface light source part 232 ... CIS 387, 389 for front side: Analog switch 390 ... AFE 400 ... ASIC 401 ... Digital signal processing unit 403 for back side: Digital signal processing unit 405 for front side: Timing generation circuit 410 ... Light source control circuit for back side 430 ... Light source control for front side circuit

Claims (6)

An analog front end capable of A / D converting analog read signals from a plurality of channels;
A first image reading unit that reads an image on one side of a document conveyed along a conveyance path and outputs an analog read signal corresponding to the image from one channel;
The analog front end unit has the same number of channels as the number of channels that can be A / D converted, and reads an image on the other side of the document conveyed along the conveyance path for each channel and corresponds to the image. A second image reading unit for outputting an analog reading signal;
A first switching unit that switches between a first channel as one of a plurality of channels of the second image reading unit and one channel of the first image reading unit and connects to the analog front end unit;
With
Of the plurality of channels of the second image reading unit, each channel except the first channel is connected to the analog front end unit,
Furthermore,
A control for connecting the first channel to the analog front end unit via the first switching unit and instructing the second image reading unit to output the reading signal; and the first image reading unit A first control unit that connects a channel to the analog front end unit via the first switching unit and that alternately performs control to instruct the first image reading unit to output the read signal;
An image reading apparatus comprising: A single-sided reading mode that reads only the image on the other side of the document can be set,
At the time of setting the single-sided reading mode, the first control unit connects the first channel to the analog front end unit via the first switching unit, and sends the reading signal to the second image reading unit. The image reading apparatus according to claim 1, wherein control for instructing output is repeatedly executed. An analog front end capable of A / D converting analog read signals from a plurality of channels;
A first image reading unit that reads an image on one side of a document conveyed along a conveyance path and outputs an analog read signal corresponding to the image from one channel;
The analog front end unit has the same number of channels as the number of channels that can be A / D converted, and reads an image on the other side of the document conveyed along the conveyance path for each channel and corresponds to the image. A second image reading unit for outputting an analog reading signal;
A second switching unit that switches between the first channel and the second channel as two of the plurality of channels of the second image reading unit and connects to the analog front end unit;
With
One channel of the first image reading unit and each channel except the first channel and the second channel among the plurality of channels of the second image reading unit are connected to the analog front end unit,
Furthermore,
Control for connecting the first channel to the analog front end unit via the second switching unit and instructing the second image reading unit to output the read signal; and controlling the second channel to the second channel. Control that connects to the analog front end unit via the switching unit and instructs the second image reading unit to output the reading signal is alternately executed, and the second image reading unit is controlled twice. A second control unit that instructs the first image reading unit to output the reading signal once during the reading signal output instruction of
Prepared,
In response to the second read signal output instruction to the second image reading unit, one of the conversion results is discarded for a channel in which the read signal is A / D converted twice by the analog front end unit. A characteristic image reading apparatus. A first switching unit that switches between the first channel and one channel of the first image reading unit and connects to the analog front end unit;
In addition,
A single-sided reading mode that reads only the image on the other side of the document can be set,
At the time of setting the single-sided reading mode, the second control unit connects the first channel to the analog front end unit via the first switching unit, and connects the second channel to the second switching unit. 4. The image reading apparatus according to claim 3 , wherein the image reading apparatus is connected repeatedly to the analog front end unit, and repeatedly executes control to instruct the second image reading unit to output the read signal. The second image reading unit includes a light source that irradiates light on the document in order to read the image on the other side,
The second control unit emits light to the light source for the read signal output according to the read signal output instruction immediately before the previous read signal output instruction among the two read signal output instructions, 5. The image reading apparatus according to claim 3, wherein the light source is irradiated with light for outputting the read signal corresponding to the next read signal output instruction immediately after the previous read signal output instruction. The light sources are provided corresponding to a plurality of colors, respectively.
6. The image according to claim 5, wherein the second control unit sequentially executes control for irradiating light to the light source corresponding to the same color for each of the colors in response to the two reading signal output instructions. Reader.