Image reading apparatus

Abstract: An image reading apparatus provided with a white reference sheet (416b) which is moveable between the first reading position for the document at which the optical reading unit (21) reading the image information is supplied by the automatic paper feeding mechanism (9) and a second reading position for the document placed on a flat bed (700) and which regulates the absolute white level with respect to the light source (25a), wherein the above-described white reference sheet (416b) is provided at the above-described first reading position on the opposite side to the optical reading unit (21) while sandwiching the document feeding passage therebetween.

Description: The present invention relates to an image reading apparatus such as a facsimile or image scanner and is further directed to the improvement of the components of such an image reading apparatus. A brief explanation will be made first, referring to Fig. 1, of the general configuration of an image reading apparatus (including both the one-side and two-side reading types) in which media having information to be read (below, referred to as documents or paper) are stacked on a hopper and are sequentially taken out'from the lowermost document (bottom take-out type) and the information of the document is optically read (two-side reading type). In the figure, the documents 1 stacked on a document hopper 3 are sequentially taken out from the lowermost document by the coaction of a paper feed roller 5 and a document separation pad elastically pressed against the same. Thereafter, the documents 1 are sent to a paper eject roller 13 via feed rollers 9 and 11 while being guided by paper guides (document stands) 17 and 19 and are ejected from there to the outside and stacked on a stacker 15. During this feeding operation, the information of the document is read by a first optical reading unit 21A and a second optical reading unit 21B. In the illustrated conventional example, the first optical reading unit 21A is arranged beneath a document passage 23 and reads the information (image) on a lower surface of the document, while the second optical reading unit 21B is arranged above the document passage 23 and reads the information (image) on the upper surface of the document. Note that, the first optical reading unit 21A and second optical reading unit 21B are constituted by light source lamps 25a and 25b; first and second reflection mirrors 27a, 29a and 27b, 29b; imaging lenses 31a and 31b; and one-directional image sensors 33a and 33b. Figure 2 shows the general configuration of a single reading unit type image reading apparatus which reads both surfaces of the document by inverting the same. In the figure, parts corresponding to those in Fig. 1 are given the same numerals, and an explanation thereof will be omitted. Note that, in Fig. 2, the document 1 is shown supplied from the left side of the figure reverse to Fig. 1. The document 1 is sent in the right direction in the figure by a feed belt 41, and initially the image of the lower surface is read by the single reading unit 21. Note that, the reading unit 21 is moveable along the document stand 17, which performs a sub-scanning (in a direction orthogonal to a beam scanning direction, that is, the scanning of the document feeding direction). This sub-scanning is exactly the same in the case of Fig. 1 as well. The document whose lower surface has been read is drawn in a direction A of the figure (left direction) by the feed belt 41. Before the rear edge is separated from reversing rollers 43, the feed belt 41 is reversed to pass the document between the reversing rollers 43, draw it in a direction B, and drop it on the reversing stand 45. Thereafter, the reversing rollers 43 are reversed and the document 1 is supplied onto the document stand 17 by coaction with the feed belt 41. At this time, the front and back of the document 1 are inverted from those at the first reading, and accordingly the image of the other surface (initial upper surface) can be read. After the completion of the reading operation, the feed belt 41 is reversed again, and the document 1 is fed rightward in the figure and stacked on the stacker 15. Note that, at this time, the passage switching lever 47 is opened to a position 47'. Although not particularly illustrated, if necessary, the passage switching lever is appropriately provided also at the portion of the reversing rollers 43. US-A-4,907,097 discloses an image reading apparatus according to the preamble of attached claim 1. First and second white reference members are provided in US-A-4,907,097 for defining reference levels with respect to a light source, but there is no disclosure of any cover or protection for the white reference members. According to the present invention there is provided an image reading apparatus comprising an optical reading unit which is moveable between a first reading position for a document supplied by an automatic paper feeding mechanism, and a second reading position for a document disposed on a flat bed, and a white reference sheet which defines an absolute white level with respect to a light source, the white reference sheet being provided at the first reading position on the opposite side to the optical reading unit so that a document feeding passage lies with the optical reading unit at one side thereof'and with the white reference sheet at the opposite side thereof, characterised in that the white reference sheet is sandwiched between a thin plate glass and a thick plate glass, and the periphery is covered by a two-side adhesive tape. The image reading apparatus may be operable such that at the automatic paper feeding and reading, just before the document is fed to the first reading position, the white reference sheet is read by the optical reading unit. In a preferred embodiment the image reading apparatus has a means operable to read the white reference sheet by a plurality of rasters by slightly relatively moving the optical reading unit and the white reference sheet at the reading of the white reference sheet, and to correct white level defects caused in the reading result by dust or stains. It is possible thereby to correct white level defects caused in the reading result of one of the rasters, by adopting the reading result of another one of the rasters. In a particularly preferred embodiment of the invention, the thick plate glass is a platen glass, and the thin plate glass faces the optical reading unit. For a better understanding of the invention and to show how it may be put into effect, reference will now be made by way of example to the accompanying drawings in which: Fig. 1 is a diagrammatical side view showing one example of a conventional two-side reading construction; Fig. 2 is a view explaining another conventional paper feeding mechanism; Fig. 3 is an illustrative side view showing a paper feeding mechanism which is claimed in parent EPC patent No. 0591593 and which may be attached to an embodiment of the present invention; Fig. 4 is a structural view of the principle of the reading mechanism of a white reference sheet in an image reading apparatus which is in accordance with the present invention; Fig. 5 is a Figure showing one embodiment of the concrete structure of the apparatus shown in Figure 4; and Fig. 6 is a flowchart of the white reference setting processing performed by the embodiment of Figure 5. Note that, in the following explanation, parts corresponding to those in the prior art are indicated by the same numerals for clearer understanding, but this does not always mean that the structures are exactly the same. Figure 3 is a side view showing an automatic paper feeding apparatus, attached to an image reading apparatus which is not in accordance with the present invention. A first roller 5a of the paper feed rollers 5 is arranged at the front edge portion of the hopper 3 on which the documents 1 to be read are stacked. A gate plate 57 is arranged at a part against which the front edge of the document 1 above this first roller 5a abuts. The gate plate 57 is provided with an inclination leftward with respect to the normal of the first roller 5a so that the position is made more eccentric to the feeding direction (leftward in the figure) as the gate plate 57 is at lower position of the document 1. Between that front end 57a and the circumferential surface of the first roller 5a, a slit 58 allowing the passing of 10 to 20 sheets of documents is formed. The gate plate 57 of Fig. 3 is of a fixed construction and is attached by being secured to the frame of the not illustrated apparatus etc. A second roller 5b of the paper feed rollers 5 is arranged on the document feed-out side of the first roller 5a. The front edge portion of the sheet-like separation pad 7, provided with flexibility, is in contact with the upper portion thereof in a manner curling around the same. The first roller 5a and the second roller 5b are synchronously driven by the transmission gear 18. A plurality of sheets of paper passed through the slit 58 are guided to the contact portion between the second roller 5b and the separation pad 7 by the frictional force of the first roller 5a. Only the lowermost sheet of paper is separated and fed out from the front end of.the separation pad 7. On the extension of the front end of the separation pad 7, the contact portion between a drive roller 9a and driven roller 9b of the feed rollers 9 is positioned. The paper 1 passing this contact portion changes in its direction when abutting against a horizontally provided platen glass 101 and is guided to the contact portion between a drive roller 13a and a driven roller 13b of the eject rollers 13. The reading portion "a" of the document is formed on the platen glass 101, and the image information of the document in the reading portion "a" illuminated by the light source lamp 25 is read by the light receiving cell of the CCD 33 through a reflection mirror 27 and an imaging lens 31. A white reference sheet 29 setting the reading level of the CCD 33 is adhered to the upstream side from "a" of the reading portion of the platen glass 101. The paper feed roller 5, feed roller 9, and the eject roller 13 are synchronously driven by a feed motor 51 via transfer gears 4 and 6 indicated by a broken line in the figure. The rotation of the feed motor 51 is transferred via the first transmission gear 4 to the drive roller 9a of the feed rollers, and that rotation is transferred via the second transmission gear 6 and the one-directional clutch 20 to the drive roller 13a of the eject rollers 13. This one-directional clutch is for preventing the rotation of the feed rollers 9 from being transferred to the eject rollers 13 when the feed rollers 9 rotate in reverse. When the drive roller 9a of the feed rollers rotates in the forward direction, that is, in the clockwise direction in Fig. 3, the related one-directional clutch 20 is connected and the eject rollers 13 rotate in the same direction, while when the feed rollers 9 rotate in reverse (in the counterclockwise direction of Fig. 3), the connection of the one-directional clutch is released, and the eject rollers 13 are kept in their stopped state. The second roller 5b of the feed rollers 5 is connected to the first transmission gear 4 via the one-directional clutch 22. Due to the fact that the drive roller 9a of the feed rollers is in contact with the paper at the bottom part and the paper feed rollers 5 are in contact with the paper at the top part, the feed rollers 9 and the paper feed rollers 5 are driven in a reverse direction to each other in relationship with respect to that paper. The one-directional clutch 22 interposed between the first transmission gear 4 and the second roller 5b is connected when the feed roller 9 rotates in the reverse direction, that is, in a direction feeding back the paper, to rotate the paper feed roller 5 in a forward direction, that is, in a direction feeding out the paper. When the feed roller 9 rotates in the forward direction, the connection of the related clutch is released, and the paper feed roller 5 is kept in a free rotation state. The second paper feeding detection sensor 103 is attached between the second roller 5b and the feed roller 9 and a paper rear edge detection sensor 105 is attached to the position immediately upstream of the reading portion "a". Note that the first and second clutches 22 and 24 are provided on the rotation shafts of for example the second transmission gear 6 and the second roller 5b, respectively, and that it is assumed that the above-described rollers and gears are connected by gears (not illustrated) having the same diameter as those of the respective rollers. An explanation will be made next of a paper feeding operation of the apparatus of Fig. 3. After the documents are placed on the hopper 3, the feed motor 51 is rotated in a direction of reverse rotation of the feed rollers 9. At this time, the first roller 5a and second roller 5b of the paper feed rollers 5 rotate in synchronization in a direction feeding out the paper. First, the first roller 5a feeds out a plurality of sheets (for example 10 to 20 sheets) of paper primarily separated through the slit 58 between the same and the gate plate 57 to a space between the second roller 5b and the separation pad 7, subsequently the lowermost one sheet of paper separated by the second roller 5b and the separation pad 7 is fed out to the feed rollers 9 in a state where bent slightly downward along the circumferential surface of the second roller 5b. Then, after the front edge of the fed out paper is detected by the second paper feeding detection sensor 103, the feed motor 51 is further rotated exactly by a preliminarily set pulse number, and the front edge of the fed out paper is made to abut against the nip portion of the feed rollers 9, to slightly bend the same between the feed rollers 9 and the front end of the separation pad 7. Then, the feed rollers 9 are rotated forward. The front edge of the paper fed out by this operation is aligned in a direction parallel to the shaft of the feed roller 9, that is, the skew is corrected, and the paper is fed to the reading portion "a" in a state where gripped by the feed rollers 9. At this time, the paper feed rollers 5 are in a free rotation state due to the action of the one-directional clutch 22 interposed between the first transmission gear 4 and the second roller 5b. The two rollers 5a and 5b rotate at a speed according to the movement of the paper fed by the feed rollers 9. When the paper fed into the reading portion "a" is further fed and gripped by the eject rollers 13 and the rear edge of the paper is separated from the feed rollers 9 and reaches the position of the paper rear end detection sensor 105, the rotation of the feed motor 51 is reversed again at this position. By this operation, the next paper on the hopper 3 is fed out toward the feed rollers 9. When the feed rollers 9 are switched to the forward rotation side again, also the eject rollers 13 start rotation in the forward direction again and feed out the previous paper to a stacker. In this way, the sheets of paper stacked on the hopper 3 successively pass through the reading portion "a" in a state with an interval equal to the distance between the feed rollers 9 and the paper rear edge detection sensor 105 is formed and are ejected to the stacker. Figures 4 to 6 show an embodiment applying the present invention to a composite type image reading apparatus in which an optical reading unit is mounted and wherein both automatic paper feeding and reading for reading the document by its movement, and also flat bed reading for performing reading by fixing the document and moving the optical reading unit, are possible. A particular improvement is directed to the method of providing a white reference in the image reading apparatus. In general, in the image reading of the document, the white reference sheet attached to the apparatus is read by the optical reading unit, whereby the absolute white level with respect to the light source is set up. In the automatic paper feeding and reading, the reading of the document is carried out by fixing the optical reading unit, but in the conventional document reading apparatus, the white reference was placed on the flat bed reading portion side, and therefore it was necessary to perform the reading of the white reference by moving the optical reading unit. The optical reading unit moves beneath the white reference sheet before the start of the reading of the documents and reads the white reference, thereafter returns to the reading position (first reading position) of the automatic paper feeding, and continuously reads the image on the surface of the document passing above. Also, at the flat bed reading, the document is placed on the flat bed, the optical reading unit first reads the white reference beneath the white reference sheet, and thereafter proceeds beneath the flat bed (second reading position) and reads the document on the flat bed while moving. Therefore, in the embodiment shown in Figs. 4 to 6, in the composite type image reading apparatus of automatic paper feeding and reading and flat bed reading, to shorten the time required for the white reference reading at the automatic paper feeding and reading and to improve the through-put, a white reference is provided on the side opposite to the optical reading unit. Before the document is fed to the reading position, the reading of the white reference by the optical reading unit is made possible. Figure 4 is a structural diagram of the principle thereof and shows only a principal part of the image reading apparatus of the two-side document reading type. Parts corresponding to those in the mechanisms already illustrated and described are indicated by the same numerals, and an overlapping explanation will be omitted. "a 1 " and "a 2 " are reading positions for reading the front surface and back surface of the document, respectively. Reference numerals 101a and 101b are platen glasses for reading the front surface and back surface of the document. Reference numerals 416a and 416b are white reference sheets for use in reading the back surface and front surface respectively of the document and are adhered to the platen glasses 101a and 101b. The document is fed between the platen glasses 101a and 101b by the feed rollers 9 and ejected by the eject rollers 13. This document feeding passage 23 is indicated by an arrow. When the document is not fed, the optical reading unit 21 can read the white reference sheet 416b adhered to the platen glass 101b through the opposite platen glass 101a at the reading position "a 1 ", and similarly the optical reading unit for the back surface reading, the illustration of which is omitted, can read the white reference sheet 416a adhered to the platen glass 101a at the reading position "a 2 ". Next, when the document is fed to the reading positions "a 1 " and "a 2 ", the white reference sheet is hidden behind the document. For example, the optical reading unit 21 operates so as to read the front surface of the passing document. In Fig. 4, during the automatic paper feeding and reading, the optical reading unit 21 can sequentially read the white reference sheet 416b and then the front surface of the document while being fixed at the illustrated position. During flat bed reading, after reading the white reference sheet 416b at the illustrated position, the optical reading unit 21 moves beneath a flat bed 700 (Fig. 5) on the right, the illustration of which is omitted from Fig.4, and performs the reading of the document on the flat bed. Note that, the flat bed is used when reading a document which cannot be stacked on the hopper 3, for example, a book. In the conventional example, the white reference sheet was arranged at a position separate from the automatic paper feeding and reading position, but in the invention of the present application, it is provided at the automatic paper feeding and reading position, and therefore a large movement of the optical reading unit for reading the white reference is not required. Therefore, the time for the reading operation of the document can be shortened. Figure 5 shows the structure of a concrete embodiment of Fig. 4. In Fig. 5, a2 is a reading position of the back surface of the document; 419a and 419b are thin plate glasses for covering the reference sheets 416a and 416b; 421a and 421b are two-surface adhesion tapes; 25a and 25b are lamps for illuminating the document; 27 is a mirror; 31 is a lens; 33 is a CCD; 428 is a plate spring; and 429 is a projection. The white reference sheets 416a and 416b are held between the platen glasses 101a and 101b and the thin plate glasses 419a and 419b respectively in a sandwiched state and retain , and the platen glasses and the thin plate glasses are stuck together by the two-surface adhesion tapes 421a and 421b, respectively. When there is no document at the reading position, the white reference sheets 416a and 416b are illuminated by the lamps 25a and 25b, respectively, and the reflection light is read by the CCD 33 inside the optical reading unit 21. The platen glass 101a is constituted so that it can move slightly leftward (about 2 to 3 mm) and is usually pressed rightward by the plate spring 428. At the reading of the front surface of the document, the optical reading unit 21 is moved slightly (2 to 3 mm) rightward from the illustrated position. During this movement, the white reference sheet 416b is read by a plurality of rasters. The signal is sent to a white level follower circuit (usually provided in the image reading apparatus). Any disturbance of the white reference level due to dust or stain deposited on the platen glass is removed to set the white reference. At the reading of the back surface of the document, the optical reading unit 21 is moved leftward and the platen glass 101a is moved leftward (by 2 to 3 mm) against the force of the plate spring 428 by the projection 429. During this movement, the white reference sheet 416a is read by a plurality of rasters by the CCD for reading the back surface (the illustration is omitted). In the same way as that mentioned before, the influence of dust or stains on the white reference level is eliminated to set up the white reference. A detailed explanation of the processing for setting the white reference (controller) will be made by Fig. 6. Step S1: Control for moving the optical reading unit from the initial position of Fig. 5 is started. In the case of the front surface reading, it is moved rightward, while in the case of the back surface reading, it is moved leftward. The number of rasters of the white reference read during the movement is made b. Also, the variable n is defined as: 1 ≤ n ≤ b. S2: The CCD output V m0 at the point of time of starting the movement is read for each bit position X m and is recorded. S3: Movement of one raster is performed (n < n + 1). The CCD output V mn at that time is read. S4: The previous CCD output V m(n-1) and the present CCD output V mn are compared at each bit position X m . When the former is larger, step S5 is executed, while when the latter is larger, step S6 is executed. S5: When the previous value is larger than the present value, the present value is corrected to the previous value (V mn = V m(n-1) ). S6: When the present value is larger than the previous value, the previous value is increased exactly by a value obtained by multiplying the difference between the previous value and the present value (V mn - V m(n-1) ) by a constant a (0 < a < 1). V mn = V m(n-1) x {1 + (V mn - V m(n-1) ) x a} S7: The processing from S3 to S7 is repeated until n becomes equal to the defined raster number b, and the operation proceeds to step S8 when n becomes equal to b. S8: The optical reading unit is restored to the initial position shown in Fig. 5. S9: The feeding of document is started and the image is read. In the processing of steps of S4, S5, and S6 mentioned above, at the white reference reading of the continuous rasters, when the present value is smaller than the previous value, the present value is abandoned and the previous value is held, while when the present value is larger than the previous value, the white level is corrected to the larger one by the method of performing a correction only with a constant proportion of the increased amount. Accordingly, as exemplified by [1], [2], and [3] at the right bottom of Fig. 6, even if the CCD output is reduced due to dust in the raster of [1] and the disturbance of the white level occurs, if the normal white reference reading is carried out by the subsequent raster, it is possible to gradually obtain a proper white level as in [2] and [3]. The embodiment explained above is for two-side reading, and therefore white reference sheets were adhered to the front surface and back surface platen glasses, respectively, but in the case of a one-side reading apparatus etc., it is also possible to adhere the white reference sheet to an appropriate member such as a back abutment member in the vicinity of the reading position or the like. According to this embodiment, it is not necessary to excessively increase the dimensions of the apparatus for the attachment of the white reference sheets, and an increase of the through-put can be achieved without the problem of degrading the attachment strength of the frame plate. Further, it becomes possible to effectively cope with the disturbance of the white reference due to stains of the white reference sheet surface, and therefore the quality of the reading image can be improved.

Claims: An image reading apparatus comprising an optical reading unit (21) which is moveable between a first reading position (a1) for a document supplied by an automatic paper feeding mechanism, and a second reading position for a document disposed on a flat bed (700), and a white reference sheet (416b) which defines an absolute white level with respect to a light source (25a), said white reference sheet (416b) being provided at the first reading position (a1) on the opposite side to the optical reading unit (21) so that a document feeding passage lies with the optical reading unit (21) at one side thereof and with the white reference sheet (416b) at the opposite side thereof, characterised in that said white reference sheet (416b) is sandwiched between a thin plate glass (419b) and a thick plate glass (101b), and the periphery is covered by a two-sided adhesive tape (421b). An image reading apparatus as set forth in claim 1, which is operable such that at the automatic paper feeding and reading, just before the document is fed to the first reading position (a1), the white reference sheet (416b) is read by the optical reading unit (21). An image reading apparatus as set forth in claim 1 or 2, wherein it has a means operable to read the white reference sheet (416b) by a plurality of rasters by slightly relatively moving the optical reading unit (21) and the white reference sheet (416b) at the reading of the white reference sheet (416b), and to correct white level defects caused in the reading result by dust or stains. An image reading apparatus as set forth in claim 3, wherein said means is operable to correct said white level defects caused in the reading result of one of said rasters, by adopting the reading result of another one of said rasters. An image reading apparatus as set forth in any one of the preceding claims, wherein said thick plate glass (101b) is a platen glass, and said thin plate glass (419b) faces the optical reading unit (21).

Inventors: FUTATSUKA MASAHIKO, ISHIDA SATOSHI, MASUDA MINORU, MIYAUCHI YASUNORI, MORIKAWA SHUICHI, TAKAGAWA MAKOTO, FUTATSUKA, MASAHIKO, ISHIDA, SATOSHI, MASUDA, MINORU, MIYAUCHI, YASUNORI, MORIKAWA,SHUICHI, TAKAGAWA, MAKOTO
Applicants: FUJITSU LTD, PFU LTD, FUJITSU LIMITED, PFU LIMITED
Application year: 1993
Main classification: H04N1
IPC codes: H04N1