Method for aligning charge coupled device of a scanner

A method for automatically aligning a charge coupled device of a scanner by using a software contained in the scanner instead of physically aligning the charge coupled device is disclosed. The scanner comprises a charge coupled device (CCD) having an array of optic sensors for converting a reflected line image into an analog signal array, an analog-to-digital (A/D) converter for converting the analog signal array into an image data array, and a test region having a positioning mark in it. The method comprises the following steps of: PA0 (1) generating an image data array which comprises the image of the test region in it by using the CCD and the A/D converter; PA0 (2) identifying the positioning mark from the image data array; and PA0 (3) setting an effective scanning range which defines the start and stop positions of valid image data within the image data array according to the identified positioning mark.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a scanner, and more particularly, to a method for
 aligning a charge coupled device (CCD) of a scanner.
 2. Description of the Prior Art
 Scanners are commonly used in office environment for scanning document
 images into computers. A scanner usually comprises a transparent window
 for allowing light reflected from a document to be scanned back to the
 scanner, a charge coupled device (CCD) having a plurality of optic sensors
 for converting a line image reflected from the document into an array of
 analog signals, a set of lenses for conveying light reflected from the
 document to the CCD, an analog-to-digital (A/D) converter for converting
 the analog signal array into an image data array, a control unit for
 controlling operations of the scanner, and a memory for storing the image
 data array. If the scanner is a flat bed scanner, the CCD and the lens set
 are packed inside a housing which is called a scanning module and the
 whole module is movably mounted on a guiding shaft. A step motor is used
 to move the scanning module forward and backward along the shaft for
 scanning a complete document placed above the transparent window of the
 scanner.
 The CCD usually contains more light sensors than what are really needed for
 scanning a document. For example, it may contain 2750 light sensors which
 can generate 2750 analog signals or 2750 image data after A/D conversion
 when converting a line image, but within the 2750 image data only 2550 of
 them are taken by the scanner as valid image data and the rest of them are
 usually ignored. The selected 2550 image data within the overall 2750
 image data are defined as effective scanning range of the CCD.
 The effective scanning range is usually pre-programmed into a scanner by
 prior art methods. When assembling a new scanner, the physical location of
 each CCD within the scanner is precisely aligned in the assembly process
 in order to make sure that the effective scanning range of the CCD can
 match up with a target area within the transparent window for scanning a
 document placed on the window. One problem faced by the prior art methods
 is that even with such a precision alignment step, a scanner may still
 fail to pass a final effective scanning range test after the scanner is
 completely assembled.
 The reason is that throughout the assembly process mechanical tolerances of
 various mechanical parts are continually accumulated between the relative
 position of the CCD and the target area of the transparent window. For
 example, when assembling a flat bed scanner, after the CCD within a
 scanning module is precisely aligned, the relative position between the
 scanning module and the shaft, the location of the transparent window
 within the scanner housing, the location of the shaft within the scanner
 housing, the connection part between the upper and lower scanner housing,
 etc., will all introduce some mechanical variations which may cause a line
 image reflected a document placed within the target area of the
 transparent window failed to be completely received by the CCD within the
 effective scanning range. In this case the scanner must be thoroughly
 checked and aligned again in order to make sure it can pass the effective
 scanning range test. In general, the precision alignment process of the
 CCD is a very time consuming process, and the rework of the scanner for
 passing the effective scanning range test also consumes a lot of time and
 effort.
 SUMMARY OF THE INVENTION
 It is therefore the goal of the present invention, by overcoming the limits
 of the prior art, to devise a new CCD alignment method to solve the above
 mentioned problem.
 Briefly, in a preferred embodiment, the present invention includes a method
 for aligning a scanner, said scanner comprising a charge coupled device
 (CCD) having an array of optic sensors for converting a reflected line
 image into an analog signal array, an analog-to-digital (A/D) converter
 for converting the analog signal array into an image data array, and a
 test region having a positioning mark in it, the method comprising the
 following steps of:
 (1) generating an image data array which comprises the image of the test
 region in it by using the CCD and the A/D converter;
 (2) identifying the positioning mark from the image data array; and
 (3) setting an effective scanning range which defines the start and stop
 positions of valid image data within the image data array according to the
 identified positioning mark.
 The scanner further comprises a memory for storing the image data array,
 and a control unit for controlling operations of the scanner and
 identifying the positioning mark from the image data array wherein the
 control unit generates the effective scanning range after identifying the
 positioning mark from the image data array and stores the effective
 scanning range in the memory.
 It is an advantage of the present invention that since the effective
 scanning range of the CCD is identified by the control unit after the
 scanner is assembled, the tuning process of the CCD can easily be done. An
 assembly worker can roughly align the CCD to make sure that the target
 area of the transparent window is located over the center part of the CCD
 as long as the positioning mark is covered. The scanner itself will
 automatically set the effective scanning range of the CCD.
 These and other objects and the advantages of the present invention will no
 doubt become obvious to those of ordinary skill in the art after having
 read the following detailed description of the preferred embodiment which
 is illustrated in the various figures and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 FIG. 1 is a perspective view of an optic scanner 10 according to the
 present invention. The scanner 10 comprises a housing 12, a transparent
 window 14 and a document 16 to be scanned placed on the window 14. FIG. 2
 is a sectional view of a corner portion of the scanner 10 shown in FIG. 1.
 It shows that the scanner 10 comprises a guiding shaft 18, a scanning
 module 20 movably mounted on the shaft 18 with a charge coupled device
 (CCD) 22 installed in it for scanning the document 16, and a test region
 32 installed under one end of the transparent window 14 for calibrating
 the CCD 22. The scanning module 20 comprises a light source 24 for
 illuminating the document 16 and a lens set which comprises three
 reflective mirrors 26, 28 and 30 for conveying light to the CCD 22.
 FIG. 3 is a function block diagram of the optic scanner 10 shown in FIG. 1
 which is connected to a host computer 34. The scanner 10 comprises a
 scanning module 20, a CCD 22 installed in the scanning module 20 which
 comprises an array of optic sensors (not shown) for converting a reflected
 line image into an analog signal array, an analog-to-digital (A/D)
 converter 36 for converting the analog signal array into an image data
 array, a memory 40 for storing the image data array, a control unit 38 for
 controlling operations of the scanner 10, and a step motor 42 for moving
 the scanning module 20 along the shaft 18 shown in FIG. 2.
 FIG. 4 is a bottom view of portion of the transparent window 14 and the
 scanner housing 12 for illustrating the test region 32 of the scanner 12
 shown in FIG. 2. The test region 32 is installed under one end of the
 transparent window 14 which comprises a white strip 44 and a black strip
 46 for calibrating image data arrays generated from the optic sensors of
 the CCD 22. The scanner housing 12 is made by plastics and the surrounding
 area 48 of the housing 12 is usually presented in light grey color. The
 boundary 50 between the black strip 46 and the surrounding area 48 is used
 as a positioning mark for aligning the effective scanning range of the CCD
 22. The target area of the transparent window 14 which is to be scanned by
 the CCD 22 is located between the boundaries 50 and 51.
 FIG. 5 presents a process 60 executed by the control unit 38 for aligning
 the effective scanning range of the CCD 22. The process 60 comprises the
 following steps:
 step 61 moving the scanning module 20 to a position under the black strip
 46 of the test region 32 by using the step motor 42;
 step 62 scanning the test region 32 and generating an image data array
 which comprises the image of the test region 32 in it by using the CCD 22
 and the A/D converter 36;
 step 63 identifying the positioning mark 50 from the image data array;
 step 64 generating an effective scanning range which defines start and stop
 positions of valid image data within the image data array according to the
 identified positioning mark within the image data array;
 step 65 storing the effective scanning range in the memory 40.
 The process 60 can be executed when powering on the scanner 10 to set the
 effective scanning range of the CCD 22, or it can be executed each time
 before scanning a new document. There are many ways to determine the
 effective scanning range of a CCD by using various positioning marks. In
 FIG. 4, since the width of the target area from points 50 to 51 of the
 transparent window 14 is fixed, once the location of the positioning mark
 50 within the image data array is identified, the effective scanning range
 of the CCD 22 can also be determined. The positioning marks can also be
 placed on both ends (points 50 and 51) of the black strip 46 for
 identifying the effective scanning range. In this way the control unit 38
 must identify both positioning marks in step 63 so that the start and stop
 positions of the effective scanning range can be obtained.
 FIG. 6 is a diagrammatic view which shows both the scanned area and target
 area of the CCD 22 shown in FIG. 3. The CCD 22 comprises an array of optic
 sensors (not shown) positioned between points 76 and 78 for converting a
 line image reflected from the scanned area between points 84 and 86 into
 an analog signal array. And the optic sensors located between points 72
 and 74 are set as the effective scanning range by the control unit 38 for
 scanning the target area between points 80 to 82 of the transparent window
 14 after the process 60 is executed. The lens set which comprises three
 reflect mirrors 26, 28 and 30 shown in FIG. 2 is represented as a block 70
 for conveying light between the transparent window 14 and the CCD 22.
 It can easily be seen that the scanned area (between points 84 and 86) is
 wider than the target area (between points 80 and 82). By using the
 process 60 presented in this invention, the tuning process of the CCD 22
 can easily be done because an assembly worker needs only to make sure that
 the target area is approximately located in the center of the scanned area
 as long as the positioning mark is covered. Mechanical variations added to
 the physical location of the CCD 22 will not cause any problem as long as
 the target area is still located within the scanned area of the CCD 22
 after the scanner 10 is assembled. The process 60 will automatically
 identify the target area and set the effective scanning range of the CCD
 22 accordingly.
 In contrast, the traditional methods mentioned above fix the effective
 scanning range of the CCD 22 first and then have an assembly worker to
 fine tune the CCD 22 to make sure that the target area is closely matched
 up with the effective scanning range of the CCD 22. By using this method
 it can easily be seen that mechanical variations added to the CCD 22 can
 easily cause mismatch between the effective scanning range (between points
 72 and 74) and the target area (between points 80 and 82), and rework of
 the scanner 10 is required if such a mismatch happens.
 Those skilled in the art will readily observe that numerous modifications
 and alterations of the device may be made while retaining the teachings of
 the invention. Accordingly, the above disclosure should be construed as
 limited only by the metes and bounds of the appended claims.