JP4283649B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus that conveys an original to a reading unit, reads an image of the original while conveying the original, and an image forming apparatus including the apparatus.

  In recent years, an image reading apparatus that conveys a sheet-like document to a reading unit and sequentially reads an image of the document is provided in an image forming apparatus or the like, and efficient image reading and image formation are performed. With the advancement of digital technology in this image reading apparatus, in order to cope with variations in optical characteristics (light intensity and sensitivity of the light receiving section) of optical means that performs photoelectric exchange and changes in performance over time, Read data for a reference image (a uniform brightness image and generally a white reference reflecting member) is used as a reference value so that good reading can be performed even when the amount of light changes. It has a function of performing shading correction that corrects image data at a uniform level (brightness) when the read data of a document image is converted into image data.

As such an image reading apparatus, there is an apparatus in which a reference reflecting member is provided on the image sensor side to read a reference image (see, for example, Patent Document 1). In addition, there is a reference reflection member that is movably provided with respect to a document reading position, and that the reference reflection member is exposed to the document reading position during reference image reading (see, for example, Patent Document 2).
JP-A-3-52377 Japanese Patent Laid-Open No. 3-62778

  By the way, as an optical means used when reading an image of a document while conveying a sheet such as a document as described above, a contact type image sensor that projects and reads an equal-size image of the document on a line sensor; There is a reduction optical system image sensor that projects and reads a reduced image of a document on a line sensor, and a contact image sensor is often used in a small image forming apparatus.

  Each of these optical means has different optical characteristics, and there is a great difference in the depth of focus. That is, the reduction optical system image sensor has a relatively large depth of focus, whereas the contact image sensor has a very small depth of focus. For this reason, in the contact image sensor, the focal point is easily blurred due to the variation in the distance to the object to be read (original and reference reflection member). Therefore, in the contact image sensor, good reading cannot be performed unless the distance from the object to be read is always set to a constant distance.

  For this reason, a reference reflection member must be provided on the surface of the back plate to which the document is conveyed when the reference image is read. However, there is a problem that the reference reflection member is rubbed and soiled by the document to be conveyed. In order to avoid this problem, if a transparent member is provided on the surface of the reference reflecting member, the difference between the distance from the contact image sensor to the document and the distance to the reference reflecting member becomes large, and the reference reflecting member is read when reading the reference image. As a result, the amount of illumination with respect to the light source decreases and unevenness in the amount of light with respect to the reference reflecting member cannot be accurately read. For this reason, improper shading correction by an incorrect reference value is performed.

  Such a problem also occurs due to a difference in the thickness of the document. In other words, the distance from the surface of the document to the contact image sensor varies depending on whether the document is thin or thick. When the focus of the contact image sensor is adjusted to one thickness, the thickness of the other Defocusing occurs when reading an image from a document, and proper shading correction can be performed only for a document of one thickness.

  These problems also occur in the reduction optical system image sensor when the shading correction is strictly performed in order to read the original image more accurately.

  An object of the present invention is to appropriately read an image from both a document and a reference reflecting member by setting the position of the optical means to an appropriate position in accordance with the distance from the optical means to the object to be read. And an image reading apparatus capable of accurately performing shading correction and moving the position of the reading optical system in accordance with the thickness of the document to set it to an appropriate position (a position where the focus is best on the surface of the document). An object of the present invention is to provide an image forming apparatus including the apparatus.

  In order to solve the above problems, the present invention has the following configuration.

(1) An image reading apparatus that reads an image of a document conveyed along a conveyance path with a contact image sensor, and includes a transparent plate member, a shading member, a conveyance member, a moving mechanism, and a control unit. The transparent plate member includes a first surface facing the image sensor and a second surface opposite to the first surface. The shading member is provided on the second surface. The conveying member conveys the document while introducing the document obliquely with respect to the first surface and sliding the document on the first surface between the image sensor and the first surface. The moving mechanism supports the image sensor so as to be movable in a direction approaching / separating from the first surface. The control unit causes the image sensor to read an image of the original when the original conveyed by the conveying member passes the first surface, and the position of the image sensor according to the thickness of the original to be read when reading the original image. Make them different. The control means causes the image sensor to approach the shading member side by a distance substantially equivalent to the distance between the first surface and the second surface by the moving mechanism, and then causes the image sensor to read the shading member and execute shading correction. Features.

In this configuration, the image sensor moves in a direction approaching / separating the first surface via the moving mechanism. Accordingly, the image sensor is focused on a plurality of positions in the direction approaching / separating from the first surface .
In this configuration, at the time of shading correction, the image sensor moves in a direction closer to the shading member side by a distance substantially the same as the thickness of the transparent plate member than at the time of reading a document image. As a result, the distance from the image sensor to the image to be read at the time of document reading and at the time of shading correction is kept substantially constant.
In this configuration, the contact image sensor is moved in a direction approaching / separating from the first surface to read an image. As a result, since the focal depth is very shallow, the focal point of the contact image sensor having a narrow range in which good reading can be performed coincides with the image planes arranged at a plurality of positions in the direction approaching / separating from the first surface. Can be made.
In this configuration, the image sensor moves in a direction approaching / separating from the first surface according to the thickness of the document. Accordingly, even when the thickness of the document changes, the distance from the surface of the document to the image sensor is maintained substantially constant.

(2) the shading member may be a white member having a uniform reflection characteristic which is affixed to the second surface.

( 3 ) Thickness detection means for detecting the thickness of the document is provided, and the control means sets the position of the image sensor in accordance with a detection signal of the thickness detection means.

  In this configuration, the optical means moves in the normal direction of the image plane based on the thickness of the original detected by the thickness detecting means while the original is conveyed to the optical means. Therefore, the optical means moves to the optimum position for reading the image of the document according to the thickness of the document being conveyed.

( 4 ) An operation unit that receives a setting input of a reading condition at the time of reading the document image including a condition related to the thickness of the document is provided, and the control unit responds to a condition regarding the thickness of the document set by the operation unit. The position of the image sensor is set.

  In this configuration, the optical means moves in the normal direction of the image plane based on the information regarding the thickness of the document input from the operation unit. Therefore, the optical means moves to the optimum position for reading the image of the document according to the thickness of the document that the user desires to read the image.

  In this configuration, the contact image sensor that reads an image close to the image surface moves in the normal direction of the image surface. Therefore, the focal point of the contact image sensor having a narrow range that can be read well because the depth of focus is very shallow coincides with the image planes arranged at a plurality of positions in the normal direction of the image plane.

( 5 ) An image forming apparatus comprising the image reading apparatus according to any one of (1) to ( 4 ), wherein image forming processing and shading correction are performed based on image data read by the image reading apparatus. It is characterized by.

  In this configuration, shading correction and image formation processing are performed based on the reference image and the image data of the document image read by the optical means with a constant distance to the image surface. Therefore, image formation is performed faithfully to the original image based on the image data of the original image after shading correction by appropriate correction data.

  According to the present invention, the following effects can be obtained.

(1) Since the optical means can be focused on a plurality of positions in the normal direction of the image plane, images arranged at different positions in the normal direction of the image plane can be read accurately.

(2) Since the distance from the optical means to the image to be read can be made constant even when the image position to be read by the optical means changes between when reading the original image and when reading the reference image, the image surface of the original can be kept constant. Even when the image plane of the reference image and the image plane of the reference image are different from each other in the normal direction of the image plane, both the original image and the reference image can be accurately read, and the reference image is read from the image data read from the original. Therefore, accurate shading correction based on can be performed.

(3) Even when a transparent member is positioned between the original and the reference image, the distance from the optical means to the image to be read can be made constant when reading the original image and when reading the reference image. Even when the reference image is placed at a position different from the document transport position with the transparent member in between to prevent contamination or damage due to contact with the dust or the like, both the document image and the reference image are accurately read Thus, accurate shading correction based on the reference image can be performed on the image data read from the document.

(4) A white member having uniform reflection characteristics at the time of reading a reference image can be read by optical means from a distance substantially equal to the distance to the document image surface at the time of document image reading, and the light source of the image data read from the document can be read It is possible to accurately read shading correction data that corrects the influence of unevenness in the amount of light and sensitivity in the sensor.

(5) Since the distance from the surface of the document to the optical means can be maintained substantially constant even when the thickness of the document changes, it is possible to accurately read images of a plurality of types of documents having different thicknesses. .

(6) The optical means can be moved to an optimum position for reading an image of a document according to the thickness of the document being conveyed, and images of a plurality of types of documents having different thicknesses can be read accurately.

(7) The optical means can be moved to the optimum position for reading the original image according to the thickness of the original that the user wants to read the image, and the images of multiple types of originals with different thicknesses can be accurately Can be read.

(8) Since the depth of focus is very shallow, the focus of the contact image sensor with a narrow range that can be read well can be made to coincide with the image planes arranged at a plurality of positions in the normal direction of the image plane. By using the contact image sensor, it is possible to accurately read images of plural types of documents having different thicknesses.

(9) Based on the image data of the original image after the shading correction by the appropriate correction data, the original image can be formed faithfully, and the original image can be reproduced faithfully.

  FIG. 8 is a diagram showing a schematic configuration of a digital multi-function peripheral 100 which is an image forming apparatus provided with the image reading apparatus according to the embodiment of the present invention. The digital multi-function peripheral 100 reads an image of a document in a reading unit (configured by an image reading device according to an embodiment of the present invention) 110. The document image read by the reading unit 110 is subjected to predetermined image processing in an image processing unit included in the control unit 228, and then temporarily stored as image data in a memory. The laser writing unit 227 is an optical writing device 210.

  The laser writing unit 227 includes a semiconductor laser light source that emits laser light in accordance with image data, a polygon mirror that deflects the laser light at a uniform angular velocity, and a laser beam deflected at a uniform angular velocity on the photosensitive drum 222. It includes an f-θ lens that deflects at an angular velocity. Instead of the laser writing unit 227, a solid scanning optical writing device using a light emitting element array such as an LED or an EL as a light source may be used.

  The image forming unit 210 is configured by arranging a charger 223, a developing unit 224, a transfer unit 225, a cleaner 226, and a static eliminator 229 around a photosensitive drum 222 that is rotationally driven in the direction of an arrow. The charger 223 charges the surface of the photosensitive drum 222 to a predetermined potential. The developing unit 224 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 222 with the laser light emitted from the laser writing unit 227 on the toner cartridge. The transfer unit 225 transfers the toner image formed on the surface of the photosensitive drum 222 to a sheet. The cleaner 226 collects toner remaining on the surface of the photosensitive drum 222 after the transfer process. The static eliminator 229 removes charges remaining on the surface of the photosensitive drum 222 after the transfer process.

  Below the image forming unit 210, a paper feeding unit 250 is located. The sheet feeding unit 250 includes a manual feed tray 254, a duplex unit 255 and a sheet tray 251 provided in the image forming apparatus 100, and sheet feeding trays 252 and 253 provided in the multistage sheet feeding unit 270. Inside the image forming apparatus 100, a sheet conveyance path that conveys the sheets stored in the trays 251 to 254 to the fixing roller 217 via the photosensitive drum 222 and the transfer device 225 of the image forming unit 210. Is formed. The fixing roller 217 heats and pressurizes the sheet on which the image is transferred by the image forming unit 210 to fix the toner image on the sheet.

  A discharge roller 219 is disposed on the discharge side of the fixing roller 217. The paper discharge roller 219 guides the sheet that has passed through the fixing roller 217 to the post-processing device 260 that is mounted on one side surface of the image forming apparatus 100. The post-processing device 260 stores the sheet discharged from the image forming apparatus 100 in the lifting tray 261 after selectively performing a stapling process or a punching process.

  Further, a switchback conveying path 221 that reverses the front and rear in the sheet conveying direction is selectively continuous on the discharge side of the fixing roller 217. The duplex unit 255 also communicates with the switchback conveyance path 221 and stores a sheet that has passed through the switchback conveyance path 221 when image formation is performed on both sides of the sheet. The duplex unit 255 is replaced with a normal paper cassette. Further, the image forming apparatus 100 can be equipped with a large capacity sheet feeding tray.

  FIG. 7 is a plan view showing a configuration of an operation unit provided in the image forming apparatus. The operation unit 46 is provided on the upper surface of the image reading apparatus 1 and includes a display P realized by a liquid crystal touch panel or the like at the center. On the right side of the display P, a numeric key K1, a start key K5, a clear key K3, an interrupt key K2 and a full release key K4 are arranged. On the left side of the display P is a fax key which is a mode key for switching the operation mode. K6, printer key K7 and copy key K8 are arranged.

  On the display P, various screens including operation guidance and warnings are switched and displayed. In each screen, keys for accepting setting inputs for various conditions are displayed. By pressing the upper surface of the display position of each key on the display P, the conditions defined for each key are set. On the initial screen of the display P, a thick document processing key K9 is displayed. When performing an image forming process for copying an image of a thick original on a sheet, the upper surface of the display position of the thick original processing key K9 on the display P is pressed. Thereby, it is detected that the document to be fed by the ADF 3 is a thick document.

  FIG. 1 is a cross-sectional view showing an image reading apparatus constituting a reading unit in the image forming apparatus. The image reading apparatus 1 generally includes an optical system 2 and an ADF 3 disposed above the optical system 2. The optical system 2 includes a CCD (Charge Coupled Device) reading unit 11, and an image of a document placed on the first document table 12 and supported in a planar state via a light source unit 13 and a mirror unit 14. Reading is performed by forming an image on the CCD reading unit 11 fixed at a fixed position. The CCD reading unit 11 includes an imaging lens 11a and a CCD image sensor 11b.

  The light source unit 13 includes a light source 13a that emits reading light, a reflector 13b that condenses the reading light emitted from the light source 13a on the image surface of the document on the document table 12, and only reflected light of the reading light on the image surface of the document. A slit 13c to be passed and a mirror 13d to change the optical path of the light passing through the slit 13c by 90 ° are provided. The mirror unit 14 includes a pair of mirrors 14 a and 14 b that change the optical path of light from the light source unit 13 by 180 ° and guide it to the CCD reading unit 11.

  The light source unit 13 and the mirror unit 14 reciprocate in the sub-scanning direction indicated by the arrow 15 in parallel with the document table 12 below the document table 12, and sequentially image the entire surface of the document placed on the document table 12. Guide to the reading unit 11. At this time, the mirror unit 14 moves at half the speed of the light source unit 13. Thus, the optical path length from the image surface to the CCD reading unit 11 via the mirrors 13b, 14a, and 14b is made constant over the entire surface of the document.

  In the CCD reading unit 11, a CCD image sensor, an imaging lens, and a light source are mounted on a single unit that moves parallel to the document table 12, and the light source unit 13 and the mirror unit 14 can be omitted.

  The optical system 2 is provided with a second document table 16, which is a transparent member of the present invention, spaced from the document table 12 in the sub-scanning direction. The light source unit 13 reads an image on the lower surface (hereinafter referred to as the front surface) of the document conveyed on the document table 16 by the ADF 3 while being displaced to the lower side of the document table 16 and standing still.

  The ADF 3 is provided with a contact image sensor (hereinafter referred to as CIS (Contact Image Sensor)) 21 which is an optical means of the present invention, and the originals stacked on the original tray 22 one by one. 16 is conveyed to the paper discharge tray 17 via 16. During this time, the image on the upper surface (hereinafter referred to as the back surface) of the document is read by the CIS 21. Therefore, the ADF 3 includes various rollers R1 to R10, detectors S1 to S6, a curved conveyance path 23 (conveying means of the present invention), and a registration / skew correction region 24. The CIS 21 includes, for example, an array-shaped image sensor that is a sensor of the present invention, an array-shaped light guide (lens array such as a Selfoc lens), a light source (LED array light source or fluorescent lamp), and the like.

  The document tray 22 is an electric tray. When the optical document detector S1 including the actuator S1a and the sensor body S1b detects that a document is set, the start key K5 in the scanning unit 46 of the image forming apparatus 100 is turned on. It will be in a standby state. Further, the document tray 22 starts to rise at a predetermined timing, and the uppermost surface of the stacked documents pushes up the incoming roller R1 supported by the arm 25 so as to be movable up and down. When the incoming roller position detector S2 detects the incoming roller R1 that has been raised to a predetermined position, the raising of the original tray 22 is temporarily stopped, and in this state, the apparatus waits to maintain the height of the original tray 22.

  In the state where the drawing roller R1 is raised to a predetermined position, it waits for the input of a feed start signal instructing the start of the reading operation. When the feed roller R1 is left without being input for a predetermined time, In order to prevent the drawing roller R1 from being deformed, the document tray 22 is lowered to a predetermined lower position and stands by.

  When a document feed start signal is input, if the document tray 22 is in the lower position, the document tray 22 is raised until the calling roller R1 is detected by the calling roller position detector S2, and then the call is started. The insertion roller R1 is driven to rotate and is fed sequentially from the topmost document on the document tray 22. A separation roller R2 is disposed on the downstream side of the drawing roller R1. The attracting roller R1 is supported by the arm 25, and the arm 25 is rotatably supported on the rotation shaft of the separation roller R2. The attracting roller R1 contacts the upper surface of the document by its own weight or urging force.

  The range in which the incoming roller R1 can be lowered by a stopper (not shown) is limited, and does not fall more than necessary. A convex portion is formed on the arm 25, and the height of the attracting roller R1 is changed depending on whether or not the attracting roller position detector S2 constituted by an optical sensor or the like detects the convex portion. Detect from the corner. Alternatively, the incoming roller position detector S2 may be provided at a position away from the arm 25, and the height of the arm 25 may be detected using a movable connecting means.

  A roller R2a (which may be a friction pad) provided with a trilimiter is opposed to the separation roller R2. The roller R2a is driven by the rotation of the separation roller R2 in a state where a load is applied when one document passes, and stops rotating when a load is applied when two or more documents pass. As a result, when two or more originals are sent between the separation roller R2 and the roller R2a, only the uppermost original is passed between the separation roller R2 and the roller R2a and conveyed. The Whether or not the original is reliably separated and supplied by the separation roller R2 and the roller R2a is detected by a paper feed detector S3 including an actuator S3a and a sensor body S3b. Thereafter, the document is guided to the downstream curved conveyance path 23 at a predetermined timing.

  In the curved conveyance path 23, the document is conveyed by the conveyance rollers R3 to R7. A paper feed detector S4 including an actuator S4a and a sensor body S4b detects whether or not a document is discharged from the curved conveyance path 23. The curved conveyance path 23 has a curvature that can smoothly convey the thickest original among the readable originals, that is, the furthest original, in order to ensure stable supply of many types of originals.

  The document discharged from the curved conveyance path 23 is conveyed to the registration / skew correction region 24. In the registration / skew correction region 24, the registration rollers R8 and R9 stop rotating until a predetermined time elapses after the paper feed detector S5 including the actuator S5a and the sensor body S5b detects the front end of the original. Yes. During this time, the front end of the document abuts against the registration rollers R8 and R9 by the conveying force from the upstream side, so that registration (positioning in the feeding direction) and skew correction are performed.

  In order to ensure that the registration and skew correction of the document can be reliably performed, the document is substantially flat between the last conveyance rollers R6 and R7 and the registration rollers R8 and R9 in the curved conveyance path 23, and the conveyance path The upper and lower guide surfaces constituting the surface are hardly contacted. The distance between the rollers R6 and R7 and the rollers R8 and R9 is set to be equal to or longer than the minimum document length in the readable document. However, the smaller the trailing edge of the document remaining in the curved conveyance path 23, the smoother the registration and skew correction of the document.

  When a predetermined time elapses from when the paper feed detector S5 detects the front edge of the document, the registration rollers R8 and R9 start to rotate, and the document has a first reading position Pos1 where the light source unit 13 faces the front surface and the back surface. Pass sequentially through the second reading position Pos2 facing the CIS21.

  Then, the document from which the images on both the front surface and the front and back surfaces are read is discharged onto the paper discharge tray 17 by the discharge rollers R10 and R11 (the discharge roller R11 is provided on the optical system 2 side). The confirmation of the document discharge operation is detected by a sheet discharge detector S6 including an actuator S6a and a sensor body S6b. The above operation is repeated for all the originals set on the original tray 22.

  Each time the document is fed sequentially, the position of the top surface of the document in the document tray 22 is lowered, but the document tray 22 is raised by the amount of the lowering of the drawing roller R1, and the top surface of the document in the document tray 22 is The drawing roller R1 is always kept in a predetermined contact state. For this reason, the document tray 22 is swingable around a fulcrum 22a, and a rib 22b is provided at the end opposite to the fulcrum 22a. An elevating plate 31 that is rotatable about a plate support shaft 32 is in contact with the rib 22b from below. The plate support shaft 32 is rotationally driven by an elevating motor 33 via an elevating mechanism unit 34 composed of a transmission member (gear train). With this configuration, the document tray 22 is moved up and down by the rotation of the lift motor 33.

  The stand-by position of the document tray 22 is maintained by controlling the operation of the elevating motor 33 of the elevating mechanism 34 by a control unit described later based on the operation signal of the incoming roller position detector S2. It can be arbitrarily set from the operation unit described later according to the number of frequently set sheets, and is set in advance by a service person or a user.

  Further, the document tray 22 has a height between the entrance side and the exit side of the curved conveyance path 23 inevitably formed by the curved conveyance path 23 set so as to guarantee stable document conveyance as described above. You can move up and down within the range. When the document tray 22 is displaced within this range, a large amount of documents can be placed, and the uppermost surface of the large amount of documents placed on the document tray 22 is fed to the entrance of the curved conveyance path 23. Raise to a possible state.

  The document tray 22 is provided with a document restriction plate 30 for aligning the sides of the document. By detecting the position of the document restricting plate 30 by the document size detector S0, the size of the set document is detected.

  The ADF 3 rotates so that the upper surface of the document table 12 can be opened and closed about a hinge (not shown) on the back side of the image reading apparatus 1. By rotating the ADF 3 so that the front side of the ADF 3 moves upward to open the upper surface of the document table 12, it is possible to manually set a document or the like of a book that cannot be conveyed by the ADF 3 on the document table 12. A document set manually on the document table 12 is pressed against the upper surface of the document table 12 via a flexible document mat 35 attached to the lower surface of the ADF 3. The open / closed state of the ADF 3 is monitored by an ADF open / close detector (not shown) provided in the optical system 2.

  The image reading apparatus 1 configured as described above can perform three reading operations: a stationary reading mode, a traveling reading mode, and a duplex reading mode. In the static reading mode, a document placed on the document table 12 such as a book is read by the CCD reading unit 11 while scanning the light source unit 13 and the mirror unit 14. The traveling reading mode and the duplex reading mode are modes in which the document set on the document tray 22 is read while automatically feeding one sheet at a time by the ADF 3. In the traveling reading mode, only the CCD reading unit 11 performs the duplex reading mode. Then, reading is performed using both the CCD reading unit 11 and the CIS 21. The maximum number of documents that can be set on the document tray 22 is, for example, 200.

  FIG. 2 is a block diagram illustrating the configuration of the control unit of the image reading apparatus. A control unit 70 (a control unit of the present invention) realized by a microcomputer or the like is used based on the detection result of the document size detector S9 that detects the size of the document set on the document tray 22. Switches control of paper and timing.

  In the stationary reading mode, the control unit 70 drives the light source unit 13 and the mirror unit 14 by the stepping motor 42 and controls the exposure lamp 13a and the CCD 11b according to the position of the light source unit 13 detected by the light source unit detector S8. Drives and reads the original image.

  In the traveling reading mode and the double-sided reading mode, the control unit 70 drives the lifting motor 33 in response to the output of the incoming roller position detector S2 to keep the height of the upper surface of the document bundle set on the document tray 22 constant. In response to the detection results of the detectors S3 to S6, the document motor S1, the clutch 44 of the drawing roller R1, The CCD 11b and / or the CIS 21 is driven to read the document image while controlling the clutch 45 of the registration rollers R8 and R9 to carry it.

  Further, the control unit 70 creates display data to be displayed on the display P and outputs it to the operation unit 46, and receives operation signals such as keys K <b> 1 to K <b> 9 from the operation unit 46.

  FIG. 3 is a diagram showing the configuration of the CIS in the image reading apparatus. The CIS 21 includes an arrayed light source 21b, an arrayed light guide 21c, an arrayed photoelectric conversion element 21a, and a sensor unit 40. The CIS 21 irradiates the back surface of the document conveyed on the second document table 16 with the light of the array-shaped light source 21b, and reflects the reflected light on the back surface of the document through the array-shaped light guide means 21c. An image is formed at equal magnification on the light receiving surface of the photoelectric conversion element 21a.

  The photoelectric conversion element 21 a outputs an electrical signal corresponding to the amount of received light to the sensor unit 40. The sensor unit 40 converts the input electric signal into digital data and inputs the digital data to the image processing unit 4 as image data. The image processing unit 4 outputs the image data after performing image processing on the image data by the shading correction unit 41, the MTF correction unit 42, and the γ correction unit 43. The image processing unit 4 is controlled by the control unit 70.

  FIG. 4 is a diagram showing the configuration of the moving mechanism of the present invention provided in the image reading apparatus. The moving mechanism 60 includes an eccentric cam 47, a spring 48, a moving support member 49, and a position detector 50. The CIS 21 is opposed to the upper surface of the document table 16 with the glass guide member 55 that constitutes the document conveyance path together with the guide plate 56 in the ADF 3. The CIS 21 is supported by the moving mechanism 60 so as to be movable in the vertical direction, which is the normal direction of the image plane.

  That is, the upper end portion of the CIS 21 is fixed to the movement support member 49, and the circumferential surface of the eccentric cam 47 is in contact with the movement support member 49 from the upper side. The moving support member 49 is biased upward by the elastic force of the spring 48. The position of the moving support member 49 is detected by a position detector 50 fixed to the main body frame 51. The eccentric cam 47 is fixed to the rotating shaft of a moving motor 47a which is a stepping motor.

  A reference reflecting member 21d, which is a reference image for shading correction, is attached to the lower surface of the document table 16 on which the document is conveyed on the upper surface. Accordingly, the position in the normal direction of the image surface between the back surface of the document read by the CIS 21 when reading the document image and the reference reflecting member 21d read when reading the reference image differs by the sum of the thickness of the document and the thickness of the document table 16. .

  In general, the CIS 21 that is an equal magnification optical system has a shallow depth of focus and a very narrow range of focus. For this reason, if the position of the image plane to be read by the CIS 21 changes between when reading the original image and when reading the reference image, the focus of the CIS 21 cannot be made coincident with the image plane during at least one reading.

  Further, when the document image is read, if the thickness of the document is changed, the position of the image surface to be read by the CIS 21 is changed. For this reason, the focus of the CIS 21 may not coincide with the image plane in at least one of reading a document image of a thick document and reading a document image of a thin document.

  Therefore, in the image reading apparatus according to the present invention, the CIS 21 is displayed on the image plane via the moving mechanism 51 when the original image is read and when the reference image is read, and when the original image of a thick original is read and when the original image of a thin original is read. The focus of the CIS 21 is accurately adjusted to the image plane both when reading the original image and when reading the reference image, and when reading the original image of a thick original and when reading the original image of a thin original. To match.

  The positioning of the CIS 21 is performed by rotating the moving motor 47a by a predetermined number of steps (the number of steps at the reading position and the number of steps at the shading position) while detecting the position of the moving support member 49 by the position detector 50. 70 does. Accordingly, the CIS 21 moves up and down in the normal direction of the image plane together with the moving support member 49 according to the rotational position of the eccentric cam 47.

  The shading correction based on the read data of the reference reflecting member 21d by the CIS 21 is performed as a preparatory operation when the image reading apparatus is energized, and is also performed under a predetermined condition set in advance. For example, when the image reading apparatus returns from a mode in which power consumption is reduced, such as the energy saving mode, when the image reading operation is continuously performed a predetermined number of times, when the standby state continues for a predetermined time, the document transport jam The shading correction is performed when returning from a trouble such as when the exterior cover is closed. Further, the shading correction may be performed every time immediately before reading the document.

  At the time of reading the reference image, the reference reflector 21d is read once or a plurality of times, and the read data of the CIS 21 is stored as shading correction data. However, with respect to a portion where an abnormal value such as a value that is too large or too small is obtained, A process of replacing with reference data and a process of averaging a plurality of reading results are performed.

FIGS. 5A and 5B are diagrams showing the state of the moving mechanism during document image reading and reference image reading. The thickness of the document table 16 is “a”, the distance from the upper surface of the document table 16 to the CIS 21 at the time of document image reading is “b”, the distance from the upper surface of the document table 16 to the CIS 21 at the time of reference image reading is “c”, and the thickness of the document. d
a + c = b-d
Thus, the CIS 21 is displaced in the normal direction of the image plane when the document image is read and when the reference image is read. Accordingly, when reading the reference image, the CIS 21 is positioned lower by the sum of the thickness a of the document table 16 and the thickness d of the document than when reading the document image.

  If the amount of eccentricity of the eccentric cam 47 is set to the sum of the thickness a of the document table 16 and the thickness d of the document, the top dead center and the bottom dead center of the eccentric cam are respectively the position at the time of document image reading and the reference The position can be set at the time of image reading. Further, by making the eccentric amount of the eccentric cam 47 larger than the sum of the thickness a of the document table 16 and the thickness d of the document, it is possible to correct dimensional errors and assembly errors of each component constituting the apparatus. Therefore, it is possible to cope with reading a document image of a thick document.

FIGS. 6A and 6B are diagrams showing the state of the moving mechanism when reading a document image of a thick document and reading a document image of a thin document. The distance from the top surface of the document table 16 to the CIS 21 when reading a document image of a thick document is b, the distance from the top surface of the document table 16 to the CIS 21 when reading a document image of a thin document is b ', and the thickness of a thick document is d. , Where d 'is the thickness of a thin document,
b−d = b′−d ′
Thus, the CIS 21 is displaced in the normal direction of the image plane when reading a document image of a thick document and reading a document image of a thin document. Therefore, when reading a document image of a thick document, the CIS 21 is positioned above the difference between the thickness d of the thick document and the thickness d ′ of the thin document as compared to reading the document image of a thin document.

  Whether the document to be read is a thick document or a thin document is determined based on whether or not the document processing key K9 is operated as a proposal in the operation unit 46.

  Further, the operation of the moving mechanism 60 can be controlled based on the detection result of the thickness detecting means provided in the curved conveyance path 23 of the ADF 3. As shown in FIG. 1, the thickness detector 26, which is a thickness detecting means of the present invention, is constituted by a spring 26a, a photo sensor 26b, and a document thickness detecting actuator 26c, and is based on the displacement of the document thickness detecting actuator 26c. The thickness of the document is determined from the strength of the detected waist. Further, the thickness of the document may be directly detected from the displacement amount of the conveying member.

1 is a diagram illustrating a configuration of an image reading apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the control part of the said image reading apparatus. It is a figure which shows the structure of CIS applied to the said image reading apparatus. It is a figure which shows the structure of the moving mechanism applied to the said image reading apparatus. It is a figure which shows the state of the moving mechanism at the time of the original image reading in the said image reading apparatus, and a reference | standard image reading. FIG. 4 is a diagram illustrating an invitation of a moving mechanism when reading a document image of a thick document and reading a document image of a thin document in the image reading apparatus. 2 is a plan view of an operation unit 46 of an image forming apparatus provided with the image reading apparatus. FIG. FIG. 2 is a diagram illustrating a schematic configuration of a digital multi-function peripheral that is the image forming apparatus.

Claims (5)

An image reading device that reads an image of a document conveyed along a conveyance path with a contact image sensor,
A transparent plate member comprising a first surface facing the image sensor and a second surface opposite to the first surface;
A shading member provided on the second surface;
A conveying member that introduces a document obliquely with respect to the first surface and conveys the document while sliding on the first surface between the image sensor and the first surface;
A moving mechanism that supports the image sensor so as to be movable in a direction approaching / separating from the first surface;
When the document transported by the transport member passes the first surface, the image sensor reads the image of the document, and the image sensor reads the image according to the thickness of the document to be scanned when the document image is read. Control means for different positions ;
With
The control means causes the image sensor to read the shading member after the moving mechanism causes the image sensor to approach the shading member side by a distance substantially corresponding to the distance between the first surface and the second surface. To perform shading correction,
Image reading device. The shading member is a white member having a uniform reflection characteristic attached to the second surface.
The image reading apparatus according to claim 1. A thickness detecting means for detecting the thickness of the document;
The control means sets the position of the image sensor in accordance with a detection signal of the thickness detection means;
The image reading apparatus according to claim 1. An operation unit that receives an input of setting of a reading condition at the time of reading the original image including a condition related to the thickness of the original, and the control unit includes the image according to the condition related to the thickness of the original set by the operating unit. Set the sensor position,
The image reading apparatus according to claim 1 . An image reading apparatus according to any one of claims 1 to 4, comprising image forming processing and shading correction based on image data read by the image reading apparatus.
Image forming apparatus.

Images