JP4864028B2 - Image reading apparatus and image forming apparatus having the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used for a digital copying machine, an image scanner, and the like, for scanning and reading an original, and an image forming apparatus including the image reading apparatus. The present invention relates to a reading device.

  2. Description of the Related Art Conventionally, in an image reading apparatus mounted on a copying machine using an electrophotographic process, a document is conveyed so that a sheet-like document is sequentially sent to a document placing table and discharged from the document placing table after reading. Some are equipped with devices. In such an image reading apparatus, a sheet-through method in which a document is automatically conveyed and read by a document conveying device while the document press is closed, and the document press is opened and closed each time reading is performed on a document placement table (contact glass). Two types of reading methods are possible: a document fixing method in which one document is replaced one by one. In the former sheet-through method, the optical system in the image reading apparatus is scanned and moved while being held at a predetermined image reading position. On the other hand, in the latter document fixing method, A reading operation is performed while the optical system scans and moves.

  In the case of the above sheet-through method, if foreign matter such as dust or dirt adheres to the contact glass surface immediately above the image reading position, black streaks in the transport direction may occur at positions corresponding to the foreign matter in the read image. there were.

Therefore, a method for preventing the occurrence of black streaks due to the adhesion of foreign matter has been proposed. For example, Patent Document 1 moves the optical system to a position where no foreign matter is attached when image data abnormality is detected at the image reading position. A method for performing reading is disclosed. Patent Document 2 discloses a method of replacing pixel data in which an abnormality is detected with surrounding pixel data when the abnormality of the image data is detected.
Japanese Patent No. 3577477 JP 2002-185725 A

  However, the method of Patent Document 1 has a problem in that it cannot read at high speed because it takes time to move the optical system when a foreign object is detected. Further, in the method of replacing with peripheral pixel data as in Patent Document 2, the size per pixel (pixel) is 42.3 μm when the resolution is 600 dpi, 84.6 μm when the resolution is 300 dpi, and 126.9 μm when the resolution is 200 dpi, As the resolution becomes lower, the pixel data located at a position away from the abnormal pixel is replaced. For this reason, there is a possibility that an abnormal image is generated by replacing the data.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus and an image forming apparatus that can easily suppress the occurrence of black streaks in sheet-through scanning.

  In order to achieve the above object, the present invention provides a document conveying device that sequentially conveys a sheet-like document to an image reading position, a light source that illuminates the document conveyed to the image reading position by the document conveying device, and Scanning means having a mirror for guiding reflected light as image light, a photoelectric conversion element for converting image light guided by the scanning means into an electric signal, and an electric signal output from the photoelectric conversion element as image data Reading means, dividing the pixel row in the main scanning direction of the image data into a plurality of continuous pixel groups, and selecting low-resolution image data by selecting pixel data one by one from each pixel group; The control means detects whether or not the image reading position is abnormal before conveying the document from the document conveying device and detects the abnormality. In this case, pixel position information in the main scanning direction corresponding to the abnormality detection position is stored, and abnormal pixels that match the pixel position information and normal pixels that do not match the pixel position information exist in the pixel group. In this case, image data is created by selecting the normal pixels.

  According to the present invention, in the image reading apparatus configured as described above, the control unit stops the reading operation when the pixel position information continues for more than the number of pixels constituting the pixel group.

  According to the present invention, in the image reading apparatus configured as described above, the control unit stops the reading operation and notifies the abnormality of the image reading position.

  The present invention also provides an image forming apparatus including the image reading apparatus having the above-described configuration.

  According to the first configuration of the present invention, the pixel row in the main scanning direction of the image data is divided into a plurality of continuous pixel groups, and pixel data is selected one by one from each pixel group to obtain low-resolution image data. In the case of creation, when an abnormality is detected at the image reading position before the document is conveyed, pixel position information in the main scanning direction corresponding to the abnormality detection position is stored, and each abnormal pixel that matches the pixel position information is stored. Since image data removed from the pixel group as much as possible can be created, the occurrence of black streaks in the sub-scanning direction can be suppressed.

  According to the second configuration of the present invention, in the image reading apparatus having the first configuration, the reading operation is performed when the pixel position information corresponding to the abnormality detection position continues for the number of pixels constituting the pixel group. By canceling, it is possible to reliably eliminate the incorporation of abnormal pixel data into low-resolution image data. Therefore, even when a large foreign matter adheres to the image reading position, black streaks in the sub-scanning direction can be completely prevented.

  Further, according to the third configuration of the present invention, in the image reading apparatus having the second configuration, the control unit stops the reading operation and notifies the abnormality of the image reading position, so that the user can quickly detect the abnormality. It is possible to remove foreign matters and the like that have been recognized and adhered to the image reading position.

  In addition, according to the fourth configuration of the present invention, it is possible to effectively generate black streaks in the sub-scanning direction in a low-resolution output image by mounting the image reading device having any one of the first to third configurations. Therefore, the image forming apparatus can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front sectional view showing an internal configuration of an image forming apparatus on which an image reading apparatus of the present invention is mounted.

  As shown in FIG. 1, the image forming apparatus 100 is a so-called in-cylinder discharge type digital copying machine, and mainly includes a main body housing 20 and an image reading device 21 disposed on the main body housing 20. Yes. Various mechanisms, which will be described later, are provided in the image reading device 21 for reading an image of a document as an electrical signal. On the other hand, the main body housing 20 is based on an electrical signal of a document image read by the image reading device 21. Various mechanisms to be described later are provided for transferring the image onto the paper.

  The main body housing 20 includes a lower housing 20a and a connection housing 20b that is positioned along the left side and is connected to the image reading device 21. The lower housing 20a accommodates and feeds paper. A paper feeding unit for forming a toner image on the paper, a fixing unit for fixing the toner image on the paper, and the like. A paper discharge unit for conveying and discharging is provided. Further, an in-cylinder discharge space 22 is formed on the right side of the connecting housing 20b immediately below the image reading device 21 so as to be largely open toward the right side and the front surface. A paper discharge tray 23 for receiving and stacking paper discharged horizontally from the right side surface of the connecting housing 20b is provided.

  On the upper surface of the image reading device 21, a contact glass (document placing table) 25 and an operation panel (not shown) exposed on the front side are arranged. Further, above the image reading device 21, a document holding device 28 equipped with a document conveying device 27 that conveys a sheet-like document to the image reading position R on the contact glass 25 is opened and closed by a hinge portion on the back surface of the image reading device 21. It is supported freely. The document presser 28 can take a closed state in which the document reading operation is performed by closing the contact glass 25 and an open state in which the document presser 28 is opened.

  The document transport device 27 includes a document feed tray 29 provided with a document guide 29 a for aligning and stacking a plurality of documents, and a document feed tray 29 located above the image reading position R on the contact glass 25. And a document discharge tray 31 formed directly on a part of the upper surface of the document presser 28 at the side of the document cover 30, and passes through the document cover 30 from the document feed tray 29. A document conveyance path d reaching the document discharge tray 31 is formed.

  In the document cover 30, document conveyance means including a pickup roller 32, a conveyance roller pair 33, a registration roller pair 34, and a discharge roller pair 35 is provided in order from the upstream side along the document conveyance path d. Among these, the conveyance roller pair 33 is composed of a drive roller 33a and a separation roller 33b. The separation roller 33b rotates in the opposite direction to the drive roller 33a only when the rotational load is lower than a predetermined torque, and the rotational load is reduced. When the torque exceeds a predetermined torque, the drive roller 33a is driven to rotate.

  Between the registration roller pair 34 and the discharge roller pair 35, a white reference plate 36 for shading correction disposed opposite to the image reading position R on the contact glass 25, and a white reference plate above the white reference plate 36. A document pressing portion 36a for pressing the plate 36 toward the image reading position R is provided. The document conveyance path d is curved so as to be reversed between the conveyance roller pair 33 and the image reading position R.

  The document transport path d is provided with a plurality of sensors for detecting whether or not a document exists. For example, a document detection sensor S 1 is provided at the center of the document feed tray 29, a paper feed sensor S 2 is provided downstream of the transport roller pair 33, and a discharge sensor S 3 is provided downstream of the discharge roller pair 35. ing. The documents set on the document feed tray 29 are sequentially conveyed one by one by the document conveying means through the document conveying path d, and are sequentially discharged onto the document discharge tray 31 after passing through the image reading position R. The document discharged on the document discharge tray 31 is taken out by the user's hand.

  Next, a sheet-through type document conveyance operation using the document conveyance unit 27 will be described. In the sheet-through type document conveying operation, first, a plurality of documents set with the image surface facing upward on the document feeding tray 29 is subjected to a predetermined pressure by a lifting plate 37 biased upward by a spring member 37a. Is pressed against the pickup roller 32. Here, when the copy start button on the operation panel is turned on, the pickup roller 32 and the conveyance roller pair 33 are rotationally driven by a primary paper feed driving means (not shown).

  The document set on the document feed tray 29 is normally fed by the pickup roller 32 to the upper pair of transport rollers 33. The plurality of originals sent to the conveyance roller pair 33 are separated by the separation roller 33b and are conveyed toward the registration roller pair 34 after being separated by the separation roller 33b. At that time, after the leading edge of the document is detected by the sheet feeding sensor S2, the document is conveyed by a predetermined distance, and then the driving roller 33a and the pickup roller 32 of the conveying roller pair 33 are stopped by the operation of the primary sheet feeding driving means. Is stopped and the primary paper feeding is completed. The document that has been primarily fed is stopped with its leading end pressed against the nip portion of the registration roller pair 34 and with its leading end being bent.

  Secondary feeding is started after a predetermined time has elapsed since the completion of primary feeding. That is, the registration roller pair 34 is rotationally driven by the operation of the secondary paper feed driving means (not shown). The document is conveyed by the registration roller pair 34 to the discharge roller pair 35 through the image reading position R, and finally discharged onto the document discharge tray 31 by the discharge roller pair 35. At this time, the completion of image reading of one original is detected by detecting the passage of the rear end of the original by the discharge sensor S3.

  Here, the discharge sensor S3 has a counting function that counts the number of documents every time the document feed and conveyance is completed. If the document detection sensor S1 detects a subsequent document, the second and subsequent document conveyance is performed. Will continue as above. When the document passes through the image reading position R, the document is conveyed while being lightly pressed against the contact glass 25 by the white reference plate 36 and the document pressing portion 36a, and the image of the document is read through the image reading position R. It is like that.

  Next, the configuration of the image reading device 21 for reading an image of a document as an electrical signal will be described with reference to FIG. In the image reading device 21, a lamp 1 which is a light source for irradiating light toward the image surface of the document, a reflection plate 2 for efficiently applying light from the lamp 1 to the image surface of the document, and document reflection A first mirror 3 that receives and reflects light directly, a second mirror 4 that receives and reflects light reflected from the first mirror 3, and a third mirror that receives and reflects light reflected from the second mirror 4. A mirror 5, a lens barrel 6 that holds a lens group (not shown) that introduces and collects reflected light from the third mirror 5, and original reflected light collected by the lens group of the lens barrel 6 A photoelectric conversion element (for example, a line type CCD) 7 that receives and converts it into an electric signal is disposed on the base plate 10. The optical path of the original reflected light is indicated by a one-dot chain line.

  Here, the lamp 1, the reflector 2 and the first mirror 3 are integrally fixed on the first carriage 8, and the second mirror 4 and the third mirror 5 are integrally fixed on the second carriage 9. The first carriage 8 and the second carriage 9 are independent of each other, but can reciprocate in cooperation. That is, when the document image reading operation is performed by the sheet through method, the first carriage 8 is moved and held immediately below the image reading position R, and the second carriage 9 is held at a predetermined position. On the other hand, in the original fixing method, the first carriage 8 and the second carriage 9 reciprocate (scan) while maintaining the optical path length of the original reflected light constant.

  Under such a configuration, the document reflected light irradiated from the lamp 1 and reflected by the image surface of the document is reflected by the first mirror 3 to the third mirror 5 and introduced into the lens group in the lens barrel 6. The light is condensed by the lens group and imaged on the photoelectric conversion element 7. The photoelectric conversion element 7 performs a photoelectric conversion process, and the document image is read as an electrical signal.

  Next, the configuration of various mechanisms provided in the main body housing 20 for transferring the image to the sheet based on the electric signal of the read document image will be described below with reference to FIG. First, the sheet feeding unit will be described. Under the lower housing 20a, sheets of various sizes (mainly sheets) are stored, and a sheet feeding cassette 40 that can be taken in and out from the front is disposed. The sheets P stored in the sheet feeding cassette 40 are: The sheets are fed one by one by the feeding roller 40a. Further, an openable and closable manual feed tray 41 that is pulled down as necessary is provided on the left side surface of the lower portion of the lower housing 20a, and a sheet (paper or OHP sheet) P ′ set on the manual feed tray 41 is provided. Are fed one by one by the feeding roller 41a.

  Next, an image forming unit for forming a toner image on a sheet and a fixing unit for fixing the toner image on the sheet will be described. Above the paper feed cassette 40 in the lower housing 20a, a photosensitive drum 42 constituting a main image forming unit, a charging device 43, a laser exposure unit 44, a developing device 45, A transfer roller 46 and a cleaning device 47 are provided. A fixing device 48 is disposed in the lower housing 20a above the transfer roller 46 and directly below the connecting housing 20b.

  The photosensitive drum 42 is made of positively chargeable amorphous silicon, and rotates clockwise in FIG. 3 at a predetermined peripheral speed when driven. The surface of the photosensitive drum 42 is uniformly charged by corona discharge generated from the charging device 43 to which a high voltage is applied, and then the laser exposure unit 44 based on the electrical signal of the original image from the photoelectric conversion module 7 described above. The electrostatic latent image composed of a predetermined light potential and dark potential portion is formed by the irradiation of the light beam from.

  Further, the electrostatic latent image rotates to the developing position by the rotation of the photosensitive drum 42. The developing roller 45a, which is a constituent element of the developing device 45, is made of stainless steel and has a fixed magnet inside. The developing roller 45a is rotatably supported with a predetermined gap from the photosensitive drum 42, and in the same direction as the photosensitive drum 42 when driven. At a predetermined peripheral speed. The developing device 45 is filled with, for example, a positively charged magnetic toner having a volume average particle diameter of 9 μm (median diameter measured by a Coulter counter), and a toner thin film is formed on the surface of the developing roller 45a by a magnetic blade (not shown). A layer is formed. A predetermined developing bias voltage is applied to the developing roller 45a. The toner that has reached the developing region flies from the surface of the developing roller 45a by the developing bias voltage, and is attracted to the electrostatic latent image on the surface of the photosensitive drum 42, whereby a toner image is formed (developed).

  Here, the sheet P (or P ′) that is fed one by one from the paper feed cassette 40 (or the manual feed tray 41) and reaches the registration roller pair 49 has a toner image on the photosensitive drum 42 approaching the transfer roller 46. In synchronization with this, the registration roller pair 49 feeds the sheet upward while adjusting the conveyance timing, and is conveyed between the photosensitive drum 42 and the transfer roller 46 through the conveyance path T1. Then, most of the toner in the toner image is transferred onto the sheet P when the leading edge of the sheet P and the leading edge of the toner image pass through the transfer roller 46.

  The toner remaining on the surface of the photosensitive drum 42 without being transferred onto the sheet P is removed from the photosensitive drum 42 by the cleaning device 47. On the other hand, the sheet P on which the toner image is transferred is sent to the fixing device 48. The fixing device 48 has a pair of fixing rollers including a heating roller 48a and a pressure roller 48b, and the toner image on the sheet P passing through the nip is heated and pressed by the pair of fixing rollers to be fixed. As a result, a fixed transfer image is formed on the sheet P.

  The sheet P that has passed through the fixing device 48 is conveyed into the connecting housing 20b along the vertical conveyance path T2 that is directed vertically upward. In the connection housing 20b, a conveyance roller pair 50 connected to the vertical conveyance path T2 and a discharge roller pair 51 for discharging the sheet P to the paper discharge tray 23 are disposed. The sheet P sent out from the conveyance roller pair 50 reaches the discharge roller pair 51 through the conveyance path T3 and is discharged from the discharge roller pair 51 to the paper discharge tray 23.

  FIG. 2 is a block diagram illustrating an example of a control path of the image reading apparatus. It should be noted that since various controls of each part of the image forming apparatus 100 are performed when using the image reading apparatus 21, the entire control path becomes complicated. Therefore, here, only a portion of the control path that is necessary for implementing the present invention will be described. The control unit 60 is a CPU (Central Processing Unit), for example, and controls the driving of the first carriage 8 and the second carriage 9 by transmitting a control signal to the carriage drive motor 53 according to a set program. At the same time, the light emission timing of the lamp 1 in the first carriage 8 is controlled. Further, as will be described later, an electrical signal transmitted from the photoelectric conversion element 7 is subjected to resolution processing, scaling processing, or gradation processing as necessary to create image data.

  The storage unit 61 includes an image memory 70, a ROM (Read Only Memory) 71, and a RAM (Random Access Memory) 72. The image memory 70 converts the image data created in the control unit 60 into a digital signal and stores it. To do. The ROM 71 and RAM 72 store basic programs used in the control unit 70, processing contents, and the like, and if foreign matter adhesion is detected during pre-scanning described later, the pixel position in the main scanning direction corresponding to the abnormality detection position is stored in the RAM 72. Information is stored.

  The image reading apparatus 21 of the present invention can read at a high resolution (for example, 600 dpi) and a low resolution (for example, 300 dpi or 200 dpi). When a character document is read, reading is performed at a low resolution.

  Here, since the resolution in the main scanning direction (direction orthogonal to the document conveying direction) is determined by the number of pixels of the photoelectric conversion element 7, when reading at low resolution, the image data read at high resolution is temporarily compressed. It is necessary to create low-resolution image data. As a compression method of this image data, the image data is divided into a plurality of pixel groups in the main scanning direction, the pixels in each group are averaged to be one pixel, and one of the pixels in each group. A thinning method for selecting pixels is common.

  For example, when creating 300 dpi image data from 600 dpi image data, it is necessary to compress the image data by half. Therefore, in the averaging method, as shown in FIG. 3, two pixels in the main scanning direction are consecutive. Each pixel group (pixel 1, 2, pixel 3, 4,...) Is divided, and the data for one pixel is created by averaging the data for two pixels in each group. On the other hand, in the thinning-out method, as shown in FIG. 4, pixel data at a predetermined position (here, pixel 1, pixel 3, pixel 5...) Is selected from the data for two pixels in each group, and the rest. The data for one pixel is created by erasing the data.

  However, when reading is performed by the sheet-through method, if a foreign matter is attached to the image reading position R (see FIG. 1), the pixel corresponding to the position where the foreign matter is attached (hereinafter referred to as an abnormal pixel) in the averaging method shown in FIG. Data) is also averaged, so that image data containing black stripes in the sub-scanning direction (original transport direction) is created.

  Also in the thinning method shown in FIG. 4, pixel data at predetermined positions (pixel 1, pixel 3, pixel 5...) Are selected. For example, as shown in FIG. In the case of pixels (displayed by hatching), the pixel data of the pixels 3 and 5 are selected, and the generation of black stripes cannot be removed. Further, when creating 200 dpi image data from 600 dpi image data, as shown in FIG. 6, a pixel group of three pixels (pixels 1 to 3, pixels 4 to 6,...) Having consecutive pixels in the main scanning direction. The pixel data at a predetermined position (here, pixel 1, pixel 4, pixel 7...) Is selected from the data for three pixels in each group. For example, pixels 2 to 5 are abnormal pixels. In this case, the pixel data of the abnormal pixel (pixel 4) is selected as in FIG.

  Therefore, in the present invention, when pixel data is selected one by one from each pixel group of image data read at high resolution by the thinning method and low resolution image data is created, an abnormality at the image reading position R is previously detected. If an abnormality is detected at the image reading position R due to the detection of foreign matter or the like, pixel position information in the main scanning direction corresponding to the abnormality detection position is stored. Then, the position information in the main scanning direction of each pixel group is compared with the stored pixel position information, and there are abnormal pixels that match the pixel position information and normal pixels that do not match the pixel position information in each group. In some cases, control is performed to select a normal pixel.

  For example, when creating 300 dpi image data from 600 dpi image data, as shown in FIG. 7, a pixel group (pixels 1, 2, 3, 4,...) That includes two consecutive pixels in the main scanning direction. And check whether there is an abnormal pixel in each group. In FIG. 7, since the pixels 2, 3, and 5 are abnormal pixels, the pixel data of the pixel 1 is selected from the group of the pixels 1 and 2. Similarly, pixel data of the pixel 4 is selected from the group of the pixels 3 and 4, and pixel data of the pixel 6 is selected from the group of the pixels 5 and 6. Since there is no abnormal pixel in the group of pixels 7 and 8, arbitrary pixel data (here, pixel 7) is selected.

  In this way, when creating 300 dpi image data, it is possible to erase up to two abnormal pixels across each pixel group. Here, since the size of one pixel is 42.3 μm at a resolution of 600 dpi, it is possible to eliminate the influence of a foreign matter having a maximum of 84.6 μm that causes black stripes.

  200 dpi image data can be created in exactly the same procedure. That is, as shown in FIG. 8, the pixels in the main scanning direction are divided into consecutive pixel groups of three pixels (pixels 1 to 3, pixels 4 to 6...), And abnormal pixels exist in each group. Check whether or not. In FIG. 8, since the pixels 2 to 5 are abnormal pixels, the pixel data of the pixel 1 is selected from the group of the pixels 1 to 3. Similarly, pixel data of the pixel 6 is selected from the group of the pixels 4 to 6. Since there is no abnormal pixel in the group of pixels 7 to 9, arbitrary pixel data (here, pixel 8) is selected. When creating 200 dpi image data, it is possible to erase up to four abnormal pixels across each pixel group, so that it is possible to eliminate the influence of foreign matter up to 169.2 μm.

  Abnormalities such as adhesion of foreign matter at the image reading position R are caused by moving the first carriage 8 directly below the image reading position R and moving the second carriage 9 to a predetermined position, and then conveying the document by the document conveying device 27. This can be detected by reading (pre-scanning) without a document. In a normal pre-scan, the light emitted from the lamp 1 passes through the contact glass 25 and is reflected by the white reference plate 36, and photoelectrically passes through the first to third mirrors 3 to 5 and the lens group in the lens barrel 6. An image is formed on the conversion element 7. And it outputs as an electrical signal of a predetermined level by photoelectric conversion processing.

  If there is a place where foreign matter is attached to the contact glass 25 on the image reading position R, the light emitted from the lamp 1 is not transmitted, so that the output level of the electric signal is lower than usual. The pixel position (address) in the main scanning direction on the photoelectric conversion element 7 corresponding to the portion where the output level is reduced is stored in the RAM 72 as an abnormal pixel address, and is read out at the time of actual document reading and read in each pixel group. The presence / absence of an abnormal pixel is determined by comparison with the pixel address.

  The compression method of the image data in the main scanning direction at the time of reading at low resolution has been described above. However, in order to read at the low resolution, it is necessary to create low resolution data also in the sub scanning direction. Therefore, for example, when reading at a resolution of 300 dpi, after reading at 600 dpi as in the main scanning direction, every other pixel row parallel to the main scanning direction is thinned out and the image data in the sub-scanning direction is compressed to ½. It ’s fine. In the case of reading at a resolution of 200 dpi, the image data in the sub-scanning direction may be compressed to 1/3 by thinning out all the pixel columns so that every other column remains.

  As another method, for example, when reading at a resolution of 300 dpi, the scanning time (reading time) of the photoelectric conversion element 7 is set to the same time as 600 dpi, and the document conveyance speed is doubled (200 dpi is tripled). Alternatively, the scanning time of the photoelectric conversion element 7 is set to 2 times 600 dpi (3 times at 200 dpi) without changing the document conveyance speed, and the reading is performed over 2 times 600 dpi (3 times at 200 dpi). It is done. When the scanning time of the photoelectric conversion element 7 is doubled (or tripled), the amount of light received by the photoelectric conversion element 7 is also doubled (or tripled). Alternatively, the light receiving amount of the photoelectric conversion element 7 needs to be equal to that at the time of reading at 600 dpi.

  FIG. 9 is a flowchart showing an example of document reading control at a low resolution by the sheet-through method. The creation of low-resolution (300 dpi) image data by the image reading apparatus will be described in detail along the steps of FIG. 9 with reference to FIGS. 1 to 8 as necessary. First, when document reading is started by a user input operation (step S1), a control signal is transmitted from the control unit 60 to the carriage drive motor 53 to move the first carriage 8 and the second carriage 9 to predetermined positions. . In this state, the lamp 1 is caused to emit light and a pre-scan is executed (step S2), and the adhesion of foreign matter on the image reading position R is detected. If there is a portion where the output level of the electric signal is reduced due to the adhesion of foreign matter, the pixel position in the main scanning direction on the photoelectric conversion element 7 corresponding to the portion is stored in the RAM 72 as an abnormal pixel address.

  Next, the pickup roller 32 and the conveyance roller pair 33 are rotationally driven by a control signal from the control unit 60, and conveyance of the document is started (step S3). When the original passes through the image reading position R with the lamp 1 turned on, the reflected light from the original forms an image on the photoelectric conversion element 7 and is read with a resolution of 600 dpi (step S4). The read document image is converted into a digital signal by photoelectric conversion processing and stored in the image memory 70.

  Next, the control unit 60 divides the image row (resolution 600 dpi) in the main scanning direction in the image memory 70 into two consecutive pixel groups, and the pixel addresses in each group are abnormal pixel addresses stored in the RAM 72. (Step S5). Then, it is determined whether only one of the two pixels is an abnormal pixel (step S6). If only one pixel is an abnormal pixel, the abnormal pixel data is erased and normal pixel data is selected ( Step S7). On the other hand, if the two pixels in the group are both normal pixels or both are abnormal pixels in step S6, the data of any one pixel is deleted and the remaining pixel data is selected (step S8).

  Further, every other pixel row parallel to the main scanning direction is subjected to thinning processing (low resolution processing in the sub-scanning direction) to create image data with a resolution of 300 dpi (step S9). In place of the low-resolution processing in the sub-scanning direction in step S9, the document scanning speed in step S3 is doubled, or the scanning time of the photoelectric conversion element 7 in step S4 is doubled, thereby sub-scanning. For the direction, a method of directly reading as 300 dpi image data may be used.

  Thereafter, it is determined whether or not the reading has been completed (step S10). When a plurality of documents are continuously read, the process returns to step S3, a new document is conveyed from the document conveying device 27, and the same processing is performed. (Steps S3 to S9). By performing the above-described control, it is possible to create image data from which abnormal pixels are selectively removed when performing high-speed reading at a low resolution, so that black streaks in the sub-scanning direction can be suppressed.

  FIG. 10 is a flowchart showing another example of document reading control at a low resolution by the sheet-through method. In the control example of FIG. 10, pre-scanning is executed (step S2), and when abnormal pixel addresses are two or more consecutive pixels (YES in steps S3 and S4), reading of the document is stopped (step S13), and the operation is performed. An error is displayed on the panel or the like (step S14). The other steps are the same as those in FIG.

  In the control example shown in FIG. 9, for example, when the abnormality detection position (abnormal pixel address) is continuous for 3 pixels (126.9 μm) or more in the main scanning direction, or for 2 pixels (84.6 μm) If the addresses coincide with the address of the same pixel group, a pixel group in which two pixels in the group are both abnormal pixels occurs, and there is a possibility that abnormal pixel data is captured in 300 dpi image data. Therefore, when a large foreign matter adheres to the image reading position R, the influence of the foreign matter cannot be completely removed.

  On the other hand, in the control example of FIG. 10, since reading is stopped when two or more abnormal pixel addresses are consecutive, it is possible to reliably prevent abnormal pixel data from being captured in 300 dpi image data. Can do. In addition, since the error display is performed when the reading is stopped, the user can quickly recognize the abnormality and remove the foreign matter attached to the image reading position R.

  9 and 10, the case where image data with a resolution of 300 dpi is created has been described. However, the case where image data with a resolution of 200 dpi is created can be described in exactly the same manner. In the control example of FIG. 9, the pixel row in the main scanning direction is divided into continuous pixel groups of three pixels, and when there are abnormal pixels and normal pixels in each group, the abnormal pixel data is erased and normal pixels 1 are deleted. What is necessary is just to select data for pixels. Further, in the control example of FIG. 10, when the abnormal pixel address is continuous for three or more pixels, the reading may be stopped.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the dedicated control unit 60 for reading the electrical signal output from the photoelectric conversion element 7 as image data is provided, but it can also be used as the control unit of the image forming apparatus main body.

  In addition, as an image forming apparatus on which the image reading apparatus of the present invention is mounted, only a digital multifunction peripheral is shown here, but the present invention is an image forming apparatus of another type such as an analog type copying machine or a color copying machine. Of course, the present invention can also be applied to an image scanner separate from the image forming apparatus.

  An image reading apparatus according to the present invention includes a document conveying device that sequentially conveys a sheet-like document to an image reading position, a light source that illuminates the document conveyed to the image reading position by the document conveying device, and reflected light from the document as an image. Scanning means having a mirror that guides as light, a photoelectric conversion element that converts image light guided by the scanning means into an electrical signal, an electrical signal output from the photoelectric conversion element as image data, and an image Control means capable of dividing a pixel row in the main scanning direction of data into a plurality of continuous pixel groups, selecting pixel data from each pixel group one by one, and creating low-resolution image data; Before the document is transported from the document transport device, it is detected whether there is an abnormality in the image reading position, and if an abnormality is detected, pixel position information in the main scanning direction corresponding to the abnormality detection position is obtained.憶; then, create and abnormal pixels that match the pixel position information, the image data by selecting the normal pixels when the the normal pixel which does not coincide with the pixel position information exists in the pixel group.

  Accordingly, it is possible to provide an image reading apparatus capable of selectively removing abnormal pixels when performing high-speed reading at a low resolution and creating image data in which black lines in the sub-scanning direction are suppressed.

  In addition, if the pixel position information corresponding to the abnormality detection position continues for more than the number of pixels constituting the pixel group, the reading operation is stopped, so that even if a large foreign matter adheres to the image reading position, An image reading apparatus that can completely prevent the occurrence of black stripes in the scanning direction is obtained. Further, if the user is notified of the abnormality when the reading operation is stopped and the user can immediately recognize the abnormality, the reading operation can be resumed quickly.

1 is a front sectional view showing an internal configuration of an image forming apparatus on which a document conveying device of the present invention is mounted. FIG. 3 is a block diagram illustrating an example of a control path of the image reading apparatus. These are schematic diagrams showing a state in which a pixel column in the main scanning direction is compressed from 600 dpi to 300 dpi by a conventional method (averaging method). These are schematic diagrams showing how a pixel row in the main scanning direction is compressed from 600 dpi to 300 dpi by a conventional method (thinning-out method). These are schematic diagrams showing how a pixel row in the main scanning direction including abnormal pixels is compressed from 600 dpi to 300 dpi by a conventional method (thinning-out method). These are schematic diagrams showing how a pixel row in the main scanning direction including abnormal pixels is compressed from 600 dpi to 200 dpi by a conventional method (thinning-out method). FIG. 4 is a schematic diagram illustrating a state in which a pixel row in the main scanning direction including abnormal pixels is compressed from 600 dpi to 300 dpi by the image reading apparatus of the present invention. These are the schematic diagrams which show a mode that the pixel row | line of the main scanning direction containing an abnormal pixel is compressed from 600 dpi to 200 dpi by the image reading apparatus of this invention. These are flowcharts showing an example of document reading control at a low resolution by the sheet through method. These are flowcharts showing another example of document reading control at a low resolution by the sheet-through method.

Explanation of symbols

1 lamp (light source)
3 to 5 mirror 7 photoelectric conversion element 8 first carriage (scanning means)
9 Second carriage (scanning means)
21 Image Reading Device 27 Document Conveying Device 53 Carriage Drive Motor 60 Control Unit (Control Unit)
61 Memory 70 Image memory 71 ROM
72 RAM
100 Image forming apparatus R Image reading position d Document transport path

Claims (4)

A document conveying device that sequentially conveys a sheet-shaped document to an image reading position;
Scanning means comprising a light source for illuminating the document conveyed to the image reading position by the document conveying device and a mirror for guiding reflected light from the document as image light;
A photoelectric conversion element that converts image light guided by the scanning means into an electrical signal;
The electrical signal output from the photoelectric conversion element is read as image data, the pixel row in the main scanning direction of the image data is divided into a plurality of continuous pixel groups, and pixel data is selected one by one from each pixel group. Control means capable of creating low-resolution image data,
In an image reading apparatus comprising:
The control means detects whether or not the image reading position is abnormal before conveying the document from the document conveying device, and if abnormality is detected, pixel position information in the main scanning direction corresponding to the abnormality detection position. If there are abnormal pixels that match the pixel position information and normal pixels that do not match the pixel position information in the pixel group, the normal pixel is selected to generate low-resolution image data An image reading apparatus.   The image reading apparatus according to claim 1, wherein the control unit stops the reading operation when the pixel position information continues for more than the number of pixels constituting the pixel group.   The image reading apparatus according to claim 2, wherein the control unit stops the reading operation and notifies the abnormality of the image reading position.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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