JP6515868B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus for reading an image of a document.

  In general, light sources (such as LEDs) of three colors corresponding to R (red), G (green), and B (blue) are sequentially turned on, and at that time, R data (original A light source switching method that acquires color image data by reading as image data of the red component of the image, G data (image data of the green component of the image of the original), and B data (image data of the blue component of the image of the original) Image reading devices are known.

  In the light source switching type image reading apparatus, the image data of each color is read while moving the document and the imaging device relatively at a constant speed in the sub scanning direction, so the reading position of each color in the document does not match. Misaligned. As a result, for example, at a color boundary or the like, the color may be different from that of the original.

  In order to suppress the color shift as described above, a plurality of (for example, five) light receiving element rows formed by a plurality of light receiving elements arranged in the main scanning direction are provided, and the light receiving element rows used for imaging There is known a document reading apparatus configured to sequentially switch combinations of the above (see, for example, Patent Document 1).

JP, 2013-131861, A

  However, in the above-described document reading apparatus, since it is necessary to provide a plurality of light receiving element rows formed by a plurality of light receiving elements, for example, when the number of rows is five, the number is five times the usual number. The light receiving element of In addition, in order to be able to switch the combination of the columns of light receiving elements used for imaging, it is necessary to provide the same number of transistors as the number of light receiving elements. Therefore, in the above-described document reading apparatus, the configuration of the light receiving unit becomes complicated.

  An object of the present invention is to provide an image reading apparatus and an image forming apparatus capable of suppressing color misregistration with a simple configuration.

  An image reading apparatus according to one aspect of the present invention includes a light source, an imaging device, a scanning unit, a light shielding unit, and a light shielding control unit. The light source sequentially emits light of different colors to the document. The image pickup element receives reflected light from a linear reading area extending in the main scanning direction of the document, and sequentially outputs image data of each color. The scanning unit moves the reading area of the document in a sub-scanning direction. The light blocking portion can individually block the reflected light which is incident on a plurality of divided areas divided in the sub scanning direction on the light receiving surface of the imaging device. The light shielding control unit switches a light shielding range by the light shielding unit in synchronization with switching of a color of light emitted from the light source.

  An image forming apparatus according to another aspect of the present invention includes the image reading apparatus and an image forming unit. The image forming unit forms an image on a sheet based on the image data of each color output from the imaging device.

  According to the present invention, an image reading apparatus and an image forming apparatus capable of suppressing color misregistration with a simple configuration are provided.

FIG. 1 is a view showing the appearance of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing the system configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a view showing a schematic configuration of an ADF and an image reading unit of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a view showing a configuration of an image sensor unit of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram showing an image reading operation in an image forming apparatus according to a comparative example of the present invention. FIG. 6 is a view showing the configuration of the light shielding portion of the image forming apparatus according to the embodiment of the present invention. FIG. 7 is a view showing a first light shielding state by the light shielding portion in the image forming apparatus according to the embodiment of the present invention. FIG. 8 is a view showing a second light blocking state by the light blocking portion in the image forming apparatus according to the embodiment of the present invention. FIG. 9 is a view showing a third light blocking state by the light blocking portion in the image forming apparatus according to the embodiment of the present invention. FIG. 10 is a diagram showing an image reading operation in the image forming apparatus according to the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following embodiments are merely specific examples of the present invention, and do not limit the technical scope of the present invention.

[Overview of Image Forming Apparatus]
As shown in FIGS. 1 and 2, the image forming apparatus 1 according to the embodiment of the present invention includes an operation display unit 11, an ADF (Auto Document Feeder) 12, an image reading unit 13, an image forming unit 14, and a communication I / I. It comprises F15, a storage unit 16, a control unit 17 and the like. The image forming apparatus 1 is a multifunction peripheral having a printer function, a scanner function, a copy function, a facsimile function, and the like. The image forming apparatus 1 is an example of the image reading apparatus of the present invention. The present invention is applicable to any image reading apparatus capable of reading an image of a document 90, such as a copying machine, a scanner, or a facsimile machine, as well as a multifunction peripheral.

  The operation display unit 11 includes a display unit such as a liquid crystal display that displays information, and an operation unit such as a touch panel that receives a user operation and an operation button.

  The ADF 12 is an automatic document feeder for feeding a document 90 to be read by the image reading unit 13. The ADF 12 is an example of the scanning unit of the present invention. Details of the ADF 12 will be described later.

  The image reading unit 13 can read an image of the document 90 and output it as image data. Details of the image reading unit 13 will be described later.

  The image forming unit 14 can execute print processing based on image data by an electrophotographic method or an inkjet method, and forms an image on a sheet based on the image data. For example, when the image forming unit 14 is an electrophotographic image forming unit, the image forming unit 14 includes a photosensitive drum, a charger, an exposure device, a developing device, a transfer device, a fixing device, and the like.

  The communication I / F 15 executes communication processing in accordance with a predetermined communication protocol with an external facsimile apparatus or an information processing apparatus such as a personal computer via a communication line such as a telephone line, the Internet, or a LAN. Is a possible communication interface.

  The storage unit 16 is a non-volatile storage unit such as a hard disk or an EEPROM (registered trademark). The storage unit 16 stores control programs, data, and the like for executing various processes executed by the control unit 17.

  The control unit 17 includes control devices such as a CPU, a ROM, and a RAM. The CPU is a processor that executes various arithmetic processing. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile or non-volatile storage unit used as a temporary storage memory (work area) when the CPU executes various processes.

  More specifically, the control unit 17 includes a scan control unit 171, a light emission control unit 172, and a light blocking control unit 173. The control unit 17 functions as each processing unit by executing various processes according to the control program. In addition, the control unit 17 may include an electronic circuit that realizes part or a plurality of processing functions of each of the processing units. Details of the scan control unit 171, the light emission control unit 172, and the light blocking control unit 173 will be described later.

[Configuration of ADF and Image Reading Unit]
Next, the configurations of the ADF 12 and the image reading unit 13 will be described with reference to FIGS. 3 and 4.

  As shown in FIG. 3, the image reading unit 13 includes a transparent document platen 131, an image sensor unit 132, a scanning mechanism 133, and the like.

  A document 90, which is an object to be read of an image, is placed on the document table 131. Above the image reading unit 13, a document platen cover in which the ADF 12 is incorporated is provided. The document platen cover is rotatably supported by the housing of the image forming apparatus 1 between a closed position covering the document platen 131 and an open position opening the document platen 131.

  As shown in FIG. 4, the image sensor unit 132 includes a light emitting unit 21, a lens 22, a light shielding unit 23, an image sensor 24 (an example of an imaging device of the present invention), and the like. The image sensor unit 132 is, for example, a CIS (Contact Image Sensor) unit. The light emitting unit 21, the lens 22, the light shielding unit 23, and the image sensor 24 are arranged in the main scanning direction from one end to the other end in the main scanning direction of the document table 131 (direction perpendicular to the paper in FIGS. It is formed in the shape which extended along.

  The light emitting unit 21 includes a red light emitting unit 21R, a green light emitting unit 21G, and a blue light emitting unit 21B. The red light emitting unit 21R, the green light emitting unit 21G, and the blue light emitting unit 21B sequentially emit light of different colors toward the document 90. The light emission control unit 172 controls the light emission timing of each of the red light emission unit 21R, the green light emission unit 21G, and the blue light emission unit 21B. The red light emitting unit 21R, the green light emitting unit 21G, and the blue light emitting unit 21B are, for example, an LED array including a plurality of light emitting diodes arranged along the main scanning direction. The light emitting unit 21 is an example of the light source of the present invention.

  The lens 22 condenses the reflected light from the document 90 on the light receiving portion of the image sensor 24. The lens 22 is, for example, a rod lens array.

  The light shielding portion 23 can individually block reflected light from the document 90 that is incident on a plurality of divided regions (for example, divided regions A1 to A4 shown in FIG. 6) divided in the sub scanning direction on the light receiving surface of the image sensor 24 It is. Details of the light shielding portion 23 will be described later.

  The image sensor 24 is a linear image sensor including a plurality of photoelectric conversion elements aligned along the main scanning direction. The image sensor 24 is, for example, a CMOS image sensor. Reflected light from a partial area (a linear area extending in the main scanning direction) on the document 90 is incident on the image sensor 24. Hereinafter, this area is referred to as a reading area. As described later, by moving the image sensor unit 132 at a constant speed along the sub scanning direction (horizontal direction in FIGS. 2 and 3) by the scanning mechanism 133, the reading area also has a constant speed in the sub scanning direction. It will move by. The image sensor 24 receives the reflected light from the reading area of the document 90 and sequentially outputs the image data of each color.

  Specifically, when the red light is emitted from the light emitting unit 21 toward the document 90, the image sensor 24 receives the red reflected light from the reading area at that time, and the plurality of photoelectric The light quantity of the red reflected light is detected by the conversion element. As a result, one-dimensional image data (hereinafter referred to as R data) indicating the red component of the image of the reading area is generated and output by the image sensor 24.

  Similarly, when green light is emitted from the light emitting unit 21 toward the document 90, the image sensor 24 receives the green reflected light from the reading area at that time, and the plurality of photoelectric conversion elements The light amount of the reflected green light is detected by As a result, one-dimensional image data (hereinafter referred to as G data) indicating the green component of the image of the reading area is generated and output by the image sensor 24.

  Similarly, when blue light is emitted from the light emitting unit 21 toward the document 90, the image sensor 24 receives the blue reflected light from the reading area at that time, and the plurality of photoelectric conversion elements The light amount of the blue reflected light is detected by As a result, one-dimensional image data (hereinafter referred to as B data) indicating the blue component of the image of the reading area is generated and output by the image sensor 24.

  The scanning mechanism 133 is a mechanism that supports the image sensor unit 132 and moves the image sensor unit 132 at a constant speed along the sub scanning direction (the left and right direction in FIGS. 2 and 3). As a result, the linear reading area of the document 90 moves in the sub-scanning direction. The scanning mechanism 133 also includes a drive unit (not shown) such as a stepping motor. The scanning mechanism 133 is an example of the scanning unit of the present invention.

  The ADF 12 conveys the document 90 set on the document tray 121 to the document discharge tray 124 along the document conveyance path 123 by the plurality of rotating conveyance rollers 122.

  The scanning mechanism 133 can stop the image sensor unit 132 at a predetermined first reading position 81 in the document conveyance path 123 of the ADF 12. In a state where the image sensor unit 132 is positioned at the first reading position 81, the light emitting unit 21 emits light to the first surface of the document 90 conveyed by the ADF 12. Then, the image sensor 24 receives reflected light from a linear reading area extending in the main scanning direction on the first surface of the document 90 conveyed by the ADF 12 and sequentially outputs image data of each color. That is, when the ADF 12 conveys the document 90, the linear reading area on the first surface of the document 90 moves in the sub-scanning direction.

  The image reading unit 13 includes another image sensor unit 125 attached to the second reading position 82 in the document conveyance path 123 of the ADF 12. The image sensor unit 125 has the same structure as the image sensor unit 132. The image sensor unit 125 can read an image of the second side of the document 90 being conveyed by the ADF 12. That is, using the image sensor unit 125 and the image sensor unit 132, it is possible to read in parallel the images on both sides of the document 90 being conveyed by the ADF 12.

  As described above, the red light emitting unit 21R, the green light emitting unit 21G, and the blue light emitting unit 21B are sequentially moved while the document 90 and the image sensor unit 132 are relatively moved at a constant speed in the sub scanning direction by the scanning mechanism 133 or the ADF 12. By lighting the light, image data (R data, G data, B data) of each color can be read by the image sensor 24 to obtain color image data. However, in this case, the reading positions of the respective colors in the document 90 do not match, and are shifted in the sub-scanning direction. As a result, for example, at a color boundary or the like, the color may be different from that of the original 90. Hereinafter, the reason for the occurrence of such color misregistration will be described with reference to FIG.

  FIG. 5 is a diagram showing an image reading operation in an image forming apparatus according to a comparative example of the present invention. Unlike the image forming apparatus 1 according to the present embodiment, the light shielding portion 23 is not provided in the image forming apparatus according to the comparative example.

  In FIG. 5, positions P0 to P8 indicate the positions of the document 90 in the sub-scanning direction. The image sensor 24 moves at a constant speed in the sub-scanning direction with respect to the document 90. At this time, light of each color of R (red), G (green), and B (blue) is emitted from the light emitting unit 21 to the document 90 at a constant cycle. Specifically, light of R (red) is irradiated during a period of time T0 to T1, light of G (green) is irradiated during a period of time T1 to T2, and B (blue) during a period of time T2 to T3. Light is emitted, and R (red) light is emitted again during the period from time T3 to T4.

  The image sensor 24 outputs the image data (image data R1) of the first line corresponding to red based on the light received during the period from time T0 to T1. Furthermore, the image sensor 24 outputs the image data (image data G1) of the first line corresponding to green based on the light received during the period from time T1 to T2. Furthermore, the image sensor 24 outputs the image data (image data B1) of the first line corresponding to blue based on the light received during the period from time T2 to T3. Furthermore, the image sensor 24 outputs the image data (image data R2) of the second line corresponding to red based on the light received during the period from time T3 to T4.

  Here, the reading area of the image sensor 24 at time T0 is an area of positions P0 to P2. That is, at time T0, the reflected light from the area of positions P0 to P2 is received by the image sensor 24. Since the image sensor 24 moves at a constant speed in the sub scanning direction with respect to the document 90, the reading area of the image sensor 24 at time T1 is an area of positions P1 to P3. That is, at time T1, the reflected light from the area of the positions P1 to P3 is received by the image sensor 24. The image data R1 is generated based on the light received by the image sensor 24 in a period from time T0 to T1. That is, the reading range corresponding to the image data R1 output from the image sensor 24 is an area of positions P0 to P3. Similarly, the reading range corresponding to the image data G1 is the area of the positions P1 to P4. The reading range corresponding to the image data B1 is an area of positions P2 to P5. The reading range corresponding to the image data R2 is an area of positions P3 to P6.

  Here, in the original 90, assuming that positions P0 to P3 are white regions and positions P3 to P6 are black regions, the entire reading range corresponding to the image data R1 is a white region, so the pixels of the image data R1 are The value is close to the maximum value (for example, 250). On the other hand, since a black area is slightly included in the reading range corresponding to the image data G1, the pixel value of the image data G1 is a value (for example, 165) lower than the maximum value. Further, since many black regions are included in the reading range corresponding to the image data B1, the pixel value of the image data B1 is a value (for example, 80) lower than the maximum value. As a result, the color image data of the first line obtained by combining the image data R1, the image data G1, and the image data B1 becomes reddish.

  Similarly, the color image data of the second line obtained by combining the image data R2, the image data G2 and the image data B2 has a bluish color. As described above, the reading result of the boundary portion between the white area and the black area in the document 90 is reddish or bluish.

  In order to suppress the color shift as described above, a plurality of (for example, five) light receiving element rows formed by a plurality of light receiving elements arranged in the main scanning direction are provided, and the light receiving element rows used for imaging There is known a document reading apparatus configured to sequentially switch combinations of However, in such a document reading apparatus, since it is necessary to provide a plurality of light receiving element rows composed of a plurality of light receiving elements, for example, when the number of rows is five, five times the normal A number of light receiving elements are required. In addition, in order to be able to switch the combination of the columns of light receiving elements used for imaging, it is necessary to provide the same number of transistors as the number of light receiving elements. Therefore, in such a document reading apparatus, the configuration of the light receiving unit becomes complicated.

  On the other hand, in the image forming apparatus 1 according to the present embodiment, by controlling the light shielding portion 23 provided in the image sensor unit 132, it is possible to suppress color misregistration with a simple configuration.

[Arrangement of light shield and control method thereof]
Hereinafter, the configuration of the light shielding portion 23 and the control method thereof will be described with reference to FIGS. 6 to 9.

  As shown in FIG. 6, the light shielding portion 23 is provided, for example, on the light receiving surface of the image sensor 24. The light shielding portion 23 is configured to be capable of individually shielding reflected light which enters the four divided areas A1 to A4 divided in the sub scanning direction on the light receiving surface of the image sensor 24. For example, a liquid crystal shutter can be used as the light shielding unit 23. The light shielding portion 23 is not limited to the liquid crystal shutter, and, for example, between the open position where the light shielding portion 23 is parallel to the traveling direction of the reflected light and the closed position where the shielding portion 23 is perpendicular to the traveling direction of the reflected light. Alternatively, the light may be partially blocked by a plurality of plate members rotatable around a predetermined rotation axis.

  The light shielding unit 23 is controlled by the light shielding control unit 173 of the control unit 17. The light blocking control by the light blocking control unit 173 is performed in conjunction with the scan control by the scan control unit 171 and the light emission control by the light emission control unit 172.

  The scan control unit 171 controls the scanning mechanism 133 or the ADF 12 to move the image sensor unit 132 relative to the document 90 at a constant speed in the sub-scanning direction.

  The light emission control unit 172 causes the red light emission unit 21R, the green light emission unit 21G, and the blue light emission unit 21B to emit light periodically in a predetermined order to obtain, for example, R (red (red) ) → G (green) → B (blue) in order.

  The light shielding control unit 173 switches the light shielding range by the light shielding unit 23 in synchronization with the switching of the color of the light emitted from the light emitting unit 21. The light shielding control unit 173 switches the light shielding range by the light shielding unit 23 based on, for example, a timing signal (a signal indicating the switching timing of the light color) supplied to the light emission control unit 172.

  Specifically, when the color of the light emitted from the light emitting unit 21 is R (red), the light blocking control unit 173 sets the original 90 of the four divided areas A1 to A4 as shown in FIG. Light reflected on the divided area A4 (an example of the fourth divided area of the present invention) positioned at the rear end in the relative movement direction of the image sensor 24 with respect to the light, and the divided area A4 of the four divided areas A1 to A4 The light shielding portion 23 is controlled such that the reflected light incident on the divided area A3 (an example of the third divided area of the present invention) adjacent to the light shielding section 23 is shielded. Hereinafter, the light blocking state by the light blocking portion 23 shown in FIG. 7 will be referred to as a first light blocking state.

  In addition, when the color of light emitted from the light emitting unit 21 is G (green), the light shielding control unit 173 controls the image sensor for the document 90 in the four divided areas A1 to A4 as shown in FIG. The light is blocked so that the reflected light incident on the divided area A1 (an example of the first divided area of the present invention) positioned at the front end in the relative movement direction of 24 and the reflected light incident on the divided area A4 are blocked Control unit 23; Hereinafter, the light blocking state by the light blocking portion 23 shown in FIG. 8 will be referred to as a second light blocking state.

  In addition, when the color of the light emitted from the light emitting unit 21 is B (blue), the light shielding control unit 173, as shown in FIG. 9, reflects light that is incident on the divided region A1 and four divided regions A1. The light shielding unit 23 is controlled such that the reflected light that is incident on the divided area A2 (an example of the second divided area of the present invention) adjacent to the divided area A1 among ~ A4 is blocked. Hereinafter, the light blocking state by the light blocking portion 23 shown in FIG. 9 is referred to as a third light blocking state.

  The light shielding control unit 173 synchronizes the switching of the color of the light emitted from the light emitting unit 21 and sets the light shielding state by the light shielding unit 23 in the order of the first light shielding state → the second light shielding state → the third light shielding state. Switch periodically with. As a result, the exposure range on the light receiving surface of the image sensor 24 (that is, the area other than the light blocking range by the light blocking portion 23) sequentially shifts in the same direction as the moving direction (relative moving direction) of the document 90 with respect to the image sensor 24. .

  Hereinafter, the image reading operation in the image forming apparatus 1 according to the present embodiment will be specifically described with reference to FIG. FIG. 10 is a diagram showing an image reading operation in the image forming apparatus 1 according to the present embodiment.

  In FIG. 10, positions P0 to P8 indicate the positions of the document 90 in the sub-scanning direction. The light shielding portion 23 and the image sensor 24 move relative to the document 90 at a constant speed in the sub scanning direction. At this time, light of each color of R (red), G (green), and B (blue) is emitted from the light emitting unit 21 to the document 90 at a constant cycle. Specifically, light of R (red) is irradiated during a period of time T0 to T1, light of G (green) is irradiated during a period of time T1 to T2, and B (blue) during a period of time T2 to T3. Light is emitted, and R (red) light is emitted again during the period from time T3 to T4.

  The image sensor 24 outputs the image data (image data R1) of the first line corresponding to red based on the light received during the period from time T0 to T1. Furthermore, the image sensor 24 outputs the image data (image data G1) of the first line corresponding to green based on the light received during the period from time T1 to T2. Furthermore, the image sensor 24 outputs the image data (image data B1) of the first line corresponding to blue based on the light received during the period from time T2 to T3. Furthermore, the image sensor 24 outputs the image data (image data R2) of the second line corresponding to red based on the light received during the period from time T3 to T4.

  Here, in the period from time T0 to T1, the light blocking state by the light blocking portion 23 is the first light blocking state as shown in FIG. Therefore, the reflected light that enters the divided area A3 and the divided area A4 is blocked by the light shielding unit 23, and only the reflected light that enters the divided area A1 and the divided area A2 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T0 to time T1 is reflected light from the area of the positions P0 to P3 as shown in FIG. That is, the reading range corresponding to the image data R1 output from the image sensor 24 is an area of positions P0 to P3.

  During the period from time T1 to T2, the light shielding state by the light shielding portion 23 is the second light shielding state as shown in FIG. Therefore, the reflected light that enters the divided area A1 and the divided area A4 is blocked by the light shielding unit 23, and only the reflected light that enters the divided area A2 and the divided area A3 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T1 to T2 is reflected light from the area of the positions P0 to P3 as shown in FIG. That is, the reading range corresponding to the image data G1 output from the image sensor 24 is the area of the positions P0 to P3.

  During the period from time T2 to time T3, the light shielding state by the light shielding portion 23 is the third light shielding state as shown in FIG. Therefore, the reflected light which enters the divided area A1 and the divided area A2 is blocked by the light shielding portion 23, and only the reflected light which enters the divided area A3 and the divided area A4 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T2 to time T3 is reflected light from the area of the positions P0 to P3 as shown in FIG. That is, the reading range corresponding to the image data B1 output from the image sensor 24 is the area of the positions P0 to P3.

  As described above, the reading ranges corresponding to the image data R1, the image data G1, and the image data B1 are all regions of positions P0 to P3. Here, in the original 90, assuming that positions P0 to P3 are white regions and positions P3 to P6 are black regions, the entire reading range corresponding to the image data R1 is a white region, so the pixels of the image data R1 are The value is close to the maximum value (for example, 250). The same applies to the image data G1 and the image data B1. Therefore, the color image data of the first line obtained by combining the image data R1, the image data G1, and the image data B1 is white.

  In the period from time T3 to T4, the light blocking state by the light blocking portion 23 is the first light blocking state as shown in FIG. Therefore, the reflected light that enters the divided area A3 and the divided area A4 is blocked by the light shielding unit 23, and only the reflected light that enters the divided area A1 and the divided area A2 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T3 to time T4 is reflected light from the area of the positions P3 to P6 as shown in FIG. That is, the reading range corresponding to the image data R2 output from the image sensor 24 is the area of the positions P3 to P6.

  During the period from time T4 to T5, the light shielding state by the light shielding portion 23 is the second light shielding state as shown in FIG. Therefore, the reflected light that enters the divided area A1 and the divided area A4 is blocked by the light shielding unit 23, and only the reflected light that enters the divided area A2 and the divided area A3 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T4 to T5 is reflected light from the area of the positions P3 to P6 as shown in FIG. That is, the reading range corresponding to the image data G2 output from the image sensor 24 is an area of positions P3 to P6.

  During the period from time T5 to T6, the light shielding state by the light shielding portion 23 is the third light shielding state as shown in FIG. Therefore, the reflected light which enters the divided area A1 and the divided area A2 is blocked by the light shielding portion 23, and only the reflected light which enters the divided area A3 and the divided area A4 enters the image sensor 24. Therefore, what is received by the image sensor 24 in the period from time T5 to T6 is reflected light from the area of the positions P3 to P6 as shown in FIG. That is, the reading range corresponding to the image data B2 output from the image sensor 24 is the area of the positions P3 to P6.

  As described above, the reading ranges corresponding to the image data R2, the image data G2, and the image data B2 are all regions of the positions P3 to P6. Here, since the entire reading range corresponding to the image data R2 is a black area, the pixel value of the image data R2 is a value (for example, 10) close to the minimum value. The same applies to the image data G2 and the image data B2. Therefore, the color image data of the second line obtained by combining the image data R2, the image data G2 and the image data B2 is black.

  As described above, in the image forming apparatus 1 according to the present embodiment, the light blocking state by the light blocking portion 23 corresponds to the first light blocking state → the second in synchronization with the switching of the color of the light emitted from the light emitting portion 21. It switches periodically in the order of the light blocking state → the third light blocking state. Therefore, the reading position of each color in each line of color image data matches without shifting in the sub-scanning direction. Therefore, according to the image forming apparatus 1 according to the present embodiment, it is possible to suppress color misregistration with a simple configuration.

[Modification]
In the present embodiment, the light shielding portion 23 is configured to be capable of individually shielding reflected light incident on four divided areas divided in the sub scanning direction on the light receiving surface of the image sensor 24. It is not limited to this. In another embodiment, the light shielding unit 23 can individually block reflected light incident on five or more divided regions (for example, eight divided regions) divided in the sub scanning direction on the light receiving surface of the image sensor 24. May be configured.

  Further, in the present embodiment, the image reading unit 13 includes the image sensor unit 132 in which the light emitting unit 21 and the image sensor 24 are integrated, but the present invention is not limited to this. In another embodiment, the image reading unit 13 includes a light emitting unit 21 moved by the scanning mechanism 133 and an image sensor 24 (for example, a CCD linear image sensor) provided at a fixed position. The light reflected by the light source may be configured to be incident on the image sensor 24 through a plurality of mirrors and an optical lens. In this case, the light shielding unit 23 is provided, for example, on the light receiving surface of the image sensor 24.

  Moreover, although the light shielding part 23 is provided on the light-receiving surface of the image sensor 24 in this embodiment, the present invention is not limited to this. For example, the light shielding unit 23 may be provided at a position away from the image sensor 24. That is, the light shielding portion 23 may be provided at an arbitrary position on the path of the reflected light from the document 90 to the image sensor 24. For example, the light shielding portion 23 may be provided on the lower surface of the document table 131 or the like at the first reading position 81 (see FIG. 3) shown in FIG. However, since it is preferable that the light shielding portion 23 be provided at a position where the reflected light from the document 90 is in focus as much as possible, for example, when the present invention is applied to an image reading device of a reduction optical system, Preferably, the light shielding portion 23 is provided on the light receiving surface of the light emitting diode.

1 Image Forming Apparatus 11 Operation Display Unit 12 ADF
121 document tray 122 conveyance roller 123 document conveyance path 124 document discharge tray 13 image reading unit 131 transparent document table 132 image sensor unit 133 scanning mechanism 14 image forming unit 21 light emitting unit 21R red light emitting unit 21G green light emitting unit 21B blue light emitting unit 22 Lens 23 Light shield 24 Image sensor 81 First reading position 82 Second reading position 90 Original

Claims (5)

A light source for sequentially irradiating the document with light of different colors;
An imaging element that receives reflected light from a linear reading area extending in a main scanning direction of the original and sequentially outputs image data of each color;
A scanning unit that moves the reading area of the document in a sub-scanning direction;
A light shielding portion capable of individually shielding the reflected light incident on a plurality of divided regions divided in the sub scanning direction on the light receiving surface of the image sensor;
A light shielding control unit that switches a light shielding range by the light shielding unit in synchronization with switching of a color of light emitted from the light source;
Equipped with
The light shielding control unit sequentially switches a light shielding range by the light shielding unit such that an exposure range on a light receiving surface of the imaging device is sequentially shifted in the same direction as a moving direction of the document with respect to the imaging device. A light source for sequentially irradiating the document with light of different colors;
An imaging element that receives reflected light from a linear reading area extending in a main scanning direction of the original and sequentially outputs image data of each color;
A scanning unit that moves the reading area of the document in a sub-scanning direction;
A light shielding portion capable of individually shielding the reflected light incident on a plurality of divided regions divided in the sub scanning direction on the light receiving surface of the image sensor;
A light shielding control unit that switches a light shielding range by the light shielding unit in synchronization with switching of a color of light emitted from the light source;
Equipped with
The light source sequentially emits three colors of light to the document,
The light shielding portion is configured to be capable of individually shielding the reflected light which enters the four divided areas divided in the sub scanning direction on the light receiving surface of the imaging device.
The light shielding control unit is configured to control a light shielding state by the light shielding unit.
The reflected light incident on the fourth divided area positioned at the rear end in the relative moving direction of the image pickup device with respect to the document among the four divided areas, and the fourth divided area of the four divided areas A first light blocking state in which the reflected light incident on the third divided area adjacent to the area is blocked;
The reflected light incident on the first divided area positioned at the front end in the relative moving direction of the imaging device with respect to the document among the four divided areas, and the reflected light incident on the fourth divided area A second light shielding state in which the light is shielded,
A third light shielding state in which the reflected light incident on the first divided area and the reflected light incident on a second divided area adjacent to the first divided area among the four divided areas are shielded;
Periodically toggle its images reader between. The light shielding unit includes a liquid crystal shutter,
The image reading apparatus according to claim 1 or 2. The light shielding unit is provided on a light receiving surface of the imaging device.
The image reading apparatus according to any one of claims 1 to 3 . An image reading apparatus according to any one of claims 1 to 4 .
An image forming unit that forms an image on a sheet based on the image data of each color output from the imaging device;
An image forming apparatus comprising:

Images