WO1990013963A1

WO1990013963A1 - Flatbed document scanning system

Info

Publication number: WO1990013963A1
Application number: PCT/US1990/002479
Authority: WO
Inventors: Gary W. Schneider
Original assignee: Intergraph Corporation
Priority date: 1989-05-05
Filing date: 1990-05-04
Publication date: 1990-11-15

Abstract

The invention provides a scanner system that in one embodiment is of the flatbed type and employs first and second cameras that have first and second areas of view respectively of each scan line, such areas being proximate to one another in a common boundary region of each scan line. The cameras are designed so that in forming first and second images respectively of their corresponding areas of view, the center of each image is displaced from the camera's central axis in such a direction that the angle formed at the document between equivalent optical paths from a point in the common boundary region to each of the images is substantially less than the angle resulting in the absence of such displacement. This design permits relatively good alignment of the two camera images in a desktop scanner notwithstanding some variation in height of the document above the platen. Other embodiments provide improvements in lid design, and isolation from vibration and torsional forces.

Description

FLATBED DOCUMENT SCANNING SYSTEM

DESCRIPTION

Technical Field The present invention relates to document scanners, that is, devices for scanning documents on which graphic information is present and for producing an electrical output related to the intensity of information at identifiable locations along each of a series of successive parallel scan lines.

Background Art Document scanners are well-known in the art- A flatbed document scanner using multiple cameras is disclosed in European patent application 84200083.8, published as number 0115366 on August 8, 1984.

Disclosure of Invention The invention provides a scanner system that in one embodiment is of the flatbed type and employs first and second cameras that have first and second areas of view respectively of each scan line, such areas being proximate to one another in a common boundary region of each scan line. The cameras are designed so that in forming first and second images respectively of their corresponding areas of view, the center of each image is displaced from the camera's central axis in such a direction that the angle formed at the document between equivalent optical paths from a point in the common boundary region to each of the images is substantially less than the angle resulting in the absence of such displacement. This design permits relatively good alignment of the two camera images in a desktop scanner notwithstanding some variation in height of the document above the platen. Other embodiments provide improvements in lid design, and isolation from vibration and torsional forces. Brief Description of the Drawings These and other features of the invention will be more readily understood by consideration of the following detailed description taken with the accompanying drawings, in which:

Figs. 1 and 2 are perspective renderings of a preferred embodiment of the invention from which the platen and side covers have been removed;

Fig. 3 is a cross section of the embodiment of Figs. 1 and 2, which is viewed from the left, showing the isolation mounting and the lid attachment;

Fig. 4 is a similar cross section, showing the camera assembly and its mounting;

Pig. 5 shows a section of the camera assembly of the above embodiment as viewed from the front of the embodiment; Fig. 6 is a similar section, showing a portion of the camera assembly but translated to the left;

Fig. 7 illustrates the optical paths in the embodiment in a generalized top view of the camera assembly; and Fig. 8A presents a bottom view of the lid of the embodiment and Fig. 8B is an exaggerated cross section of the lid taken through the plane BB of Fig. 8A.

Detailed Description of Specific Embodiments Turning now to Figs. 1 and 2, there are shown perspective views of a preferred embodiment of the invention from which the platen and side covers have been removed. (Items described herein have like numbers throughout the figures.) The platen normally is mounted between the upper edge of front wall 152 and rear wall 154, and extends from the upper edge of right wall 153 (on which it also rests) to the vicinity of left wall 151. An assembly containing, among other things, cameras 101 and 102, lamps 16, and trailing mirror assemblies 111 and 112, is slidably mounted on rail support 15 by means of a single rail 14 and carriage 41 (the carriage 41 is shown in Fig. 4) . The lamps are desirably halogen reflector lamps with cold mirrors, with the reflectors providing only a piecewise approximation to an ellipse rather than being smooth, such as type BAB sold by General Electric, to provide more uniform illumination. The rail and carriage system is desirably a precision system similar to the Star ball rail system, 1600 series, available from Deutsche Star Gmbh, Postfach 1164,

Schweinfurt 1 D-8720, West Germany. The camera assembly is translated along the rail by means of motor drive pulley assembly 19 and toothed belt 17, which is supported at the opposite end of the scanner by idler pulley 17. A finger (not shown) protrudes down from the camera assembly and grabs the belt 17. The rail support 15 is suspended between the left wall 151 and right wall 153, and the rail 14 is attached to the rail support 15 by insertion of a series of bolts in the holes 141. It will be appreciated, that although the camera assembly is relatively light, it will cause some amount of sag in the rail support 15 (and consequently in the rail 14) , particularly when the camera assembly is near the midpoint along the length of the rail support. The sag can alter the vertical distance between the camera assembly and the platen and thus affect imaging by the cameras and ultimately the precision and resolution of the scanner. In accordance with the invention, this distance may be adjusted by the insertion of shims of suitable thickness at desirable locations along the rail 14; the shims are placed between the rail 14 and the rail support 15. It is equivalently possible in the alternative to adjust the height of front and rear walls 152 and 154 respectively, causing the height of the platen to change in the areas of adjustment, although shimming of the rail 14 may be more convenient.

As can be seen by reference to Fig. 3, the entire opto¬ mechanical assembly, including the camera assembly and the rail and rail support, is isolated by means of a three-point isolation mount. Specifically, there can be seen in Fig. 3 a rigid frame 12 of square cross section that is disposed around the outside of rear wall 154 and front wall 152 at the base of each; it is similarly disposed at the base of right wall 153 and left wall 151. The frame 12 is secured to a lower plate 18. The walls 151-154 do not rest on the lower plate 18, however, but instead are mounted with shock- absorbing bushings to the frame at three locations, two of which are shown in Fig. 3, namely near the left edges of front and rear walls 152 and 154, where the bushings are shown as items 11 and 301 respectively. The third location is at the midpoint along the length of right wall 153; for symmetry, at the third location the mounting utilizes two adjacent bushings, with each mounting being otherwise configured exactly as shown for busings 11 and 301. The mounting arrangement described reduces the transmission of vibration and distortion experienced by the lower plate 18 and frame 12 to the opto-mechanical assembly.

Importantl , it will be seen that the lid 13, which rests on the document being scanned, forms a part of the opto-mechanical assembly that is isolated from the frame 12. The lid 13 is attached via a piano hinge 33 to member 311 that is permitted to travel vertically with the lid 12 to an extent depending on thickness of the document. The member 311 is mounted to the rear wall 154 by means of a pair of spaced apart screws 14 that are disposed in slots permitting vertical travel of the member 311. A bearing 315 of Teflon or other suitable material is disposed between the member 311 and the wall 154. The member 311 is urged downwardly by springs 310 at the left and right ends of the member 311 disposed between screws 312 on the wall and 313 on the member. To balance the forces on the document created by the springs 310 at the rear of the lid 13, a metal weight 34 is disposed toward the front of the lid along its width. To support the lid in the open position, a pair of gas springs 131 are mounted on each side of the lid. On the left side the lower end of the spring 131 is mounted to bracket 155 running between front and rear wall, and on the right side the lower end of the spring 131 is mounted to the right wall 153.

Fig. 4 shows further details of the camera assembly, which is mounted on carriage 41 that rides on rail 14; the rail 14 is mounted on rail support 15. The camera assembly includes trailing mirror assemblies 112 and 111; mirror assembly 111 has been removed here to show beyond it the camera 101; a similar camera 102 lies beyond mirror assembly 112. Locations for the lamps 16 are also shown. Fig. 5 shows the optical path associated with camera 101. Light from the document strikes the leading mirror 54 and is reflected to trailing mirror assembly 111 that includes lower mirror 51 and upper mirror 52. Light is reflected from the lower mirror 51 to the upper mirror 52 and from the upper mirror 52 to the camera 101. Alignment of the optical path into the camera is achieved by displacement of the mirror assembly 111. The displacement is achieved by a pair of opposing adjustment screws 531 and 532 mounted in the frame of the camera assembly that grab a deformable nib 533 affixed to the mirror assembly 111. The screw-nib combination achieves an adjustment in a manner analogous to the camera adjustment described in United States patent 4,686,581, column 5, lines 36-48, for a scanner system of which I am a co-inventor, which patent is hereby incorporated herein by reference. A similar adjustment utilizing a pair of screws and a nib is disposed on the far side of mirror assembly 111.

Illumination of the document is achieved by utilizing light from each lamp 16 shown in Figs. 1-4. Associated with each lamp 16 is a fiber optic bundle. One end of the bundle is disposed proximate to the lamp to receive light energy therefrom. The other end of the bundle is disposed in a linear array parallel to the direction of scan. Fibers from the two bundles associated with the two lamps on the camera assembly that are closer to the front of the scanner are intermingled in the array somewhat, in order to enhance uniformity of the light output along the array. A similar disposition of the fibers from the two bundles associated with the two lamps that are closer to the rear of the scanner is also utilized, and the entire array is shown in Fig. 5 as item 570 proximate to cylindrical lens 57. The cylindrical lens focuses the light from the output of the array onto the portion of the document being scanned, and illuminates the entire width of scan.

Fig. 6 shows a portion of the camera assembly of Fig. 5 displaced to the left of the position it occupies shown in Fig. 5. Also shown in this Figure is the plate 61, which may be of glass.

Fig. 7 illustrates in further detail the optical paths that are utilized by the embodiment herein discussed. Camera 101 employs a CCD array 701 and camera 102 employs a CCD array 702. It will be seen that the midpoint of each CCD array does not coincide with the central axis Cl of camera 101 or C2 of camera 102, but in each case one CCD array is displaced toward the other CCD array. It will be apparent on viewing Fig. 7, that item 73 is the plane of the camera lens, item 72 is the plane of the trailing mirror assemblies 111 and 112, and item 74 is the plane of the leading mirror. Although the leading mirror 74 reflects the rays upward toward the document, the rays are shown continuing in the same direction, for purposes of clarity of illustration of the document plane 75. The paths of light rays through the center of the camera lens of the extrema of each CCD array are shown in this figure. Of particular interest are the pairs of rays 711 and 712 which relate to viewing by each camera of a region in the document plane 75 near the center of scan, where the views of each camera either overlap or are contiguous. In the absence of displacement (described above) of the CCDs away from the central axes, the angle formed between the rays 711 and 712 would be considerable, for example, in the case as here of a desktop scanner with a 75 mm lens in the camera, the .angle might be of the order of 20 or 30 degrees. If the document is not precisely in the plane 75 at the point where it is being imaged, the extent of the document seen by each camera can change by an objectionable amount, causing undesirable overlap of images. Although overlap of the images can be treated in the manner described generally in the previously mentioned patent, the techniques disclosed therein are not intended to deal with the problems of overlap caused by unpredictable lack of document flatness. Displacement of the CCD array in the manner shown herein and appropriate imaging as shown herein has reduced the angle between rays 712 and 711 to approximately 7 degrees in typical desktop applications, thereby dramatically reducing the problem, since the rays are very nearly parallel.

Figs. 8A and 8B illustrate further detail of the lid. As seen from the underside, shown in Fig. 8A the lid includes a rigid frame 82 around the periphery. Area 81 lies along the midpoint of scan for each scan line along the length of the document. This area is least likely to have the document flat against the platen and, for the reasons described above, is most in need of document flatness. Fig. 8B is a section of the lid taken through plane BB of Fig. 8A. In the drawing, the thickness of the lid is greatly exaggerated for purposes of illustration, and the items therein are not drawn to scale. In order to encourage document flatness in the region 81, a plate 810 is disposed in the lid, and is suspended from the lid case 87 by resilient cushioning members 86, which may, for example, be adhesive-backed foam used for weather stripping and other applications. The plate 810 should be very flat, and may be satisfactorily embodied by a glass plate. The suspending members 86 are designed so that the weight of the plate 810 bears through layer 85 on the document. In the region 83 of Fig. 8A, adjacent to the area 81 occupied by the plate 810 _r is disposed an adhesive backed foam or similar material 84, which also bears against the document through layer 85. Layer 85 is a vinyl coated-foam. The vinyl coating is colored a uniform white that permits scanning of transparencies without adding a carrier between the document and the lid and also permits ready calibration of the scanner intensity outputs.

Claims

What is claimed is:

1. A system for scanning a document on which is recorded graphic information, the system comprising: document holder means, for holding the document; camera means, for receiving light over an optical path from the document along a scan line and for producing an electrical output related to the intensity of information at identifiable locations along the scan line, the camera means being translatably mounted with respect to the document holder means so as to permit motion of the scan line on the document in a direction transverse to the direction of scan; wherein the camera means includes first and second cameras (i) having first and second areas of view respectively of each scan line, such areas being proximate to one another in a common boundary region proximate to the center of each scan line, (ii) being mounted with respect to the first and second areas of view such that the optical paths from the first camera to the first area of view do not cross the optical paths from the second camera to the second area of view except where such areas of view may overlap, (iii) having first and second central axes respectively, (iv) forming first and second images respectively of their corresponding areas of view, the center of each image being displaced from its corresponding central axis in such a direction that the angle formed at the document between equivalent optical paths from a point in the common boundary region to each of the images is substantially less than the angle resulting in the absence of such displacement.

2. A system according to claim 1, further comprising: a mirror in the optical path; and mounting means, for adjustably mounting the mirror to a frame, including (i) a pair of opposing adjustment screws, each screw having a tip and threadably movable within a first member and (ii) a deformable nib, disposed between the tips and affixed to a second member, wherein one of the first and second members is affixed to the mirror.

3. A system according to claim l, further including: document holder means, for holding the document, including a lid and a transparent substantially flat document platen, such that the lid when closed tends to urge the document against the platen; wherein the lid includes a substantially flat plate having a length not substantially shorter than that of the effective translation of the camera means but a width substantially less that the length of the scan line, such plate providing a flattening force of the document against the platen when the lid is closed; and wherein the plate is disposed over the common boundary region when the lid is closed such as to provide a greater flattening force over such region.

4. A system according to claim 3, wherein the lid includes a flexible sheet of material disposed across substantially the entire surface thereof that is in contact with the document when the lid is closed, whereby force gradients near boundaries of the plate are reduced.

5. A system according to claim 4, wherein the lid further includes resilient material disposed in areas thereof not occupied by the plate.

6. A system for scanning a document on which is recorded graphic information, the system comprising: document holder means, for holding the document; camera means, for viewing the document along a scan line and for producing an electrical output related to the intensity of information at identifiable locations along the scan line, the camera means being translatably mounted with respect to the document holder means so as to permit motion of the scan line on the document in direction transverse to the direction of scan; the document holder means and the camera means being included in an opto-mechanical assembly that is mounted on a substantially rigid subframe; a frame that is subject to vibration and distortion; drive means, for translating the camera means relative to the document so as to cause motion of the scan line on the document in a direction transverse to the direction of the scan; isolation means for shock-mounting the opto-mechanical assembly to the frame at only first, second, and third spaced-apart locations, so that the opto-mechanical assembly tends to be isolated from the vibration of the frame and from torsional forces that might otherwise result from distortion of the frame; wherein the document holder means includes a lid that is attached hingedly only to the opto-mechanical assembly.

7. A system according to claim 6, wherein the document holder means further includes a transparent platen mounted only on the opto-mechanical assembly.

8. An illumination system for a document scanner for illuminating a document along a scan line, the system comprising: a light source; a fiber optic bundle having a first end disposed to receive light from the light source and a second end disposed to form a linear array; and a cylindrical condensing lens for focussing light along the scan line in optical communication with the second end.