CA1263925A - Method and apparatus for mounting a ccd array used in a digital imaging system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An apparatus for mounting in close proximity the following elements used in a digital imaging process is disclosed: a charge coupled device (CCD); a condensing lens and a reticle. The mounting apparatus improves the prior art by automatically spacing the combination of a condensing lens and a reticle, the proper optical distance from the CCD array needed for scanning a specimen, thereby eliminating the need to adjust the position of these elements after mounting. The condensing lens is readily attachable and detachable using flexible fingers to hold it into place on top of the reticle, which is automatically located at the proper optical distance from the CCD array once placed in a recess on the mounting apparatus. The CCD array, condensing lens and reticle move in unison during the scanning process.

Description

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METHOD AND APPARATUS FOR MOUNTING A CCD ARRAY
USED IN A DIGITAL IMAGIN~ SYSTEM

Background of the Invention This invention relates generally to a method and apparatus for digital imaging systems capable of converting documents and the like to a digital (binary) representation. Specifically, the present invention relates to a method and apparatus for mounting the charge-coupled device (CCD) array and a condensing lens and reticle used in the scanning and digitiziny phases of the digital imaying process.

Digital imaging is a process whereby a visual object or scene i5 converted to a representation comprising binary bits which control the optical density of the discrete elements (pixels) which represent the image.
Digital~imaging systems like the PIC System of Wang Laboratories, Inc., Lowell, MA 01851 (the assignee of the present invention) are used to digitize pictures charts, graphs and other images. In the imaging process the specimen is scanned for its intensity or transmissivity and converted to a pattern of contrasting light and dark picture elements (pixels).

The pixels are created by comparing the optical density of the areas corresponding to the pixels to a threshold value, which may vary from region to region.
The value of the pixel depends on whether the optical density of the pixel area exceeds the threshold level, or is less than or equal to the threshold level.

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Digital imaging processes usually require a scanner/camera in the digitization process. The specimen is illuminated by a focused light source which may be part oE the scanner configuration. The scanner receives light from the the specimen and focuses it onto a CCD array, which produces analog signals proportional to the optical densities of the scanned areas of the document.

Prior art scanner/cameras require cumbersome adjustments o~ the CCD array and the condensing lens needed for the light source, after these components are mounted in the system, to insure that the CCD array and condensing lenses are positioned relative to each other so that the CCD array is in the correct focal plane of the light reflected from the the specimen.

Summary of the Inv_ntion Accordingly, it is a principal object of this invention to devise a method and apparat~ls for mounting the CCD array and condensing lens used in the scanner/camera of a digital imaging system such that the CCD array and condensing lens are automatically located in the correct optical position.

Another object of this invention is to provide a common mount for a CCD array and a condensing lens with predetermined locations for these components.

Yet another object of this invention is to provide the above mentioned mount with simple fastening means.

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Still another object of this invention is to provide a mount capable of simple attachment of a CCD array, a condensing lens and a reticle used for projectiny optical grid patterns onto a specimen being scanned.

Consistent with the foregoing, it is also an object of this invention to provide a one-piece assembly for the CCD array, condensing lens and reticle which is easily insertable in or removable from the the scanner/camera.

The foregoing and other objects of the present invention are realized by utilizing a special mounting device which includes tabs to snap the CCD array, condensing lens and reticle into predetermined locations on a base or carriage. The mounting device is a one-piece assembly which automatically places the aforementioned components in their proper operating positions. The mounting device is conveniently attachable to the scanner housing assembly.

Descriptlon of the Draw~

The foregoing and other objects and features of the present invention are apparent from the specification, the drawings and the two taken together. The drawings are:

Figure 1 is an isometric drawing of a communication terminal capable of use in a digital imaging process.

Figure 2 is a side view of the scanner.

Figure 3 is a multi-view representation of the mounting device used to mount and position the CCD array, a condensing lens and a reticle.

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Detailed Desc~ ~_on Figure 1 shows a digital imaging system 10 supported on table 16. Its major components are a monitor 11, scanner 12, printer 13, keyboard 14, and console 15.
During use, the operation is controlled by the user by operation of the keyboard 14. The user gives instructions to the console 15, whlch contains a microprocessor for controlling the system. The monitor 11 has a screen 18, which the user views while communicating with the system. A further description of system 10 is given in U.S. patent No. 4,587,633 which issued on May 6, 1986.
The imaging process is begun by placing specimen 20 under the scanner 12. Scanner is comprised of a camera 21 and a lamp 22. The lamp 22 places light onto the specimen 20 which is reflected back to camera 21. Camera 21 takes a succession of p1ctures of specimen 20, one line at a time. The number of lines and the~number o~ pixels is generally related to the resolution of the image that can be displayed on the screen 18 and or printed on printer 13.
The image is digitized by the microprocessor by assign-., ing a binary number for each pixel. In the preferred embodiment a binary digit "1" signifies that the pixel is placed in the "ON"
state, wh1le "0" signifies that the pixel is placed in the "OFF"
state. The digitized image can be stored in a memory 36 of CPU
or console 15.

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Once the imaging process is complete and the image stored, the user may "edit" the image by giving the system a series of commands from keyboard 14. The image may be displayed on screen 18, or printed on printer 13.

Referring now to Figure 2, the scanner 12 will be described. Scanner carriage assembly 21 accounts for most of the components of scanner 12, and performs many oE the important operations during the scanning process, and hence is illustrated in Figure 2. Light source or lamp 22, connected to a power source, provides the necessary illumination for the scanning process. ~ight from light source 22 propagates through a first condensing lens 25, which refracts the light to form a more concentrated beam of lightO Condensing lens 25 is easily attached to the walls of the scanner carriage assembly 21, as shown.

After passing through the upper condensing lens 25, light from light source 22 passes through a second condensing lens 30, used to further refract the light to decrease the focal length. The lower condensing lens 30 is mounted on array mount or base 35, which will be later described in more detail. Thereafter the light passes through lens column 85, connected to focusing means 90.
Before leaving the scanner 12, focusing lens 95, which focuses the light upon the specimen 20 for purposes of illumination.

In the preferred embodiment the light impacting on specimen 20 is reflected back through the focusing means 90 and the lens column 85. Some of the reflected light contacts the CCD array 37 (to be described in detail later). The Iight contacting CCD array 37 is directly proportional to the optical densities of the pixels . .

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representing one scan line of the specimen. The analog signals from the CCD array representing the pixel optical densities is relayed by contact pins 100 to circuit 105, which begins the digitizing process.

During the digitizing process the CCD array is moved to scan the specimen on a line-by-line basis. This is accomplished by connecting the array mount 35 to a nut 110. Nut 110 is rotably mounted on a threaded column 115. When the threaded column 115 is turned by the motor 120, the nut moves axially and thereby causes axial movement of the array mount 35. In this manner the entire specimen is scanned on a line-by-line basis.

The CCD array mount 35 is further illustrated in Figure 3. The CCD array 37 is adjacently placed with an infrared filter 39 into a slot 41. Tabs 43 and 45 form a filter nest for nesting the infrared filter 39 into slot 41. The CCD array 37 is then placed over the infrared filter 39 into slot 41. The array and filter combination are met ak one edge by catch or fixed tab 47 which prevents opposing lateral motion of the combination, while fastening one end of the combination into the slot 41.

The array retainer 49 is slidably mounted in a slot 51. Once the CCD array and infrared filter are in place the array retainer 49 is pushed towards the combination until its finger extends over the edge of the CCD array, and it is flush with the combination. The CCD array is now fastened securely to mount 35. A centering tab 53 fit6 inside of a notch on the array filter 39 to help place the CCD array in the proper longitudinal position.
The array is easily removed by sliding and disengaging the etainer 49.

3~32!5i A reticle 67 is shaped to the contours of the recess 61 and placed in the recess, which is large enough to receive the projected area oE the lens~ The lower condensing lens 30 is mounted in the array mount 35 on top oE the reticle 67. The recess 61 is bordered by a retaining walls 63 and 65. The reticle contains a pattern of grids for positioning the specimen for the digitizing process. Usually before the scanning is begun the user shines the pattern of grids resulting from the travel of light through the reticle via the underlying passage or hole in base 35 upon the specimen so that the scanner may be aligned with the specimen.

The lower condensing lens 30 is ground on one of its edges as shown in Figures 2 and 3, so that a flat portion is formed. When the lower condensing lens 30 is mounted, its flat edge touches the retainer wall 63. The purpose of this flat portion is to locate the lens the correct horizontal distance from the CCD array 37 centerline.
This is to assure that the light rays passing through the lens 30 always touches the centerline of the CCD array at its focal points.

The lower condensing lens 30 is fastened by a pair of flexible fingers 69. The lens is mounted by placing it on top of the reticle 67 and sliding it between the flexible fingers 69 and the reticle until the flat edge of the lens is flush with the retaining wall 63. The lens 30 snaps into the proper position when the edge located opposite to its flat edge touches the retaining wall 65.
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The CCD array mount 35 has two bezels lor arms~ 71, which are attached to the nut 110 in Figure 2. The nut fits into notches of the bezels 71. During scanning the motor 120 turns the shaft 115, which in turn moves the nut 110. Since the nut 110 is attached to the arms 71 of the array mount 35, the mount is moved when the nut moves, allowing the specimen to be scanned.

The second condensing lens 30 and the CCD array 37 are automatically located the proper horizontal distance from each other once mounted, obviating the need to adjust their positions after mountin~ as in prior art scanners.
The novel array mount 35 also allows the CCD array and the lower condensing lens to be inserted in and removed rom the scanner carriage assembly 21 simultaneously, thereby further reducing mounting complications associatecl with prior art scanners.

Various modifications and variations of the foregoing described invention are obvious to those skilled in the art. Such modifications and variations are intended to be within the scope of the present invention. The embodiment described is representative of a multitude of variations without changing the essence of the system operation. For example, the specimen may be transparent, such as a microfiche, and a means for reflecting light transmitted through the specimen can be added.

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Claims (6)

We claim:

1. A mounting device for mounting a charge-coupled device (CCD) array used in a digital imaging process comprising:

a generally planar base having a slot in which said CCD
array is placed on an infrared filter, said base having a fixed tab extending into the slot for protruding over the edge of said CCD array at one of its ends to prevent lateral motion of that end of said CCD array and infrared filter, and said fixed tab preventing said CCD array and infrared filter from moving perpendicular to the plane of said base; and said base having a recess spaced from said slot for retaining a reticle and a condensing lens mounted thereon with a ground edge on the condensing lens mating with an alignment surface of the recess to align the lens and reticle relative to the CCD array, said recess including a passage through the base to permit projection of an image of the reticle onto a target.

2. The mounting device in claim 1 further comprising:

at least one flexible finger coupled to the base for fastening said condensing lens and reticle together when the two are placed into the recess.

3. The mounting device in claim 2 further comprising:

a slidably mounted array retainer at the end of said slot opposite said fixed tab for selectively fastening and unfastening an end of said CCD array and infrared filter, in conjunction with said fixed tab, preventing lateral and perpendicular motion relative to the plane of said base.

4. The mounting device in claim 3 further comprising:

bezel means for coupling to drive means for moving the CCD
array during the scanning of a specimen in a digital imaging process and for positioning the reticle and lens at a location in the optical path employed during scanning to assist in the alignment of the specimen to the optical path.

5. The mounting device in claim 4 wherein said base further includes.

a nesting means in the slot for nesting said infrared filter.

6. The mounting device in claim 5 wherein said base further includes:

a centering tab for longitudinally centering said CCD
array which extends into the slot and resiliently contacts said CCD array.