Method and apparatus for ensuring precise angular orientation of an optical sensing unit on a housing of an optical imaging device

A testing frame supports a test lens unit below a test image piece. A housing of an imaging device is secured to the frame below the lens unit such that an aperture in the housing is registered with the lens unit along an optical axis. An optical sensing unit is loosely mounted on the housing, is adjustable relative to the aperture along transverse axes of a sensing plane, and is rotatable relative to the housing about a rotary axis that is generally aligned with the optical axis. Upon operation, the sensing unit generates image signals corresponding to a captured image of the image piece. The image signals are processed so as to determine a skew angle of the captured image. The angular orientation of the sensing unit relative to the housing is then corrected in accordance with the skew angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the following description of the preferred embodiment, the optical imaging device is a camera having a housing that includes front and rear housing parts and that contains control circuitry therein, an optical lens unit mounted threadedly in a lens-mounting aperture at a front side of the front housing part, and an optical sensing unit mounted on a rear side of the front housing part. Like the method and apparatus of the aforesaid co-pending U.S. patent application, a correcting database is established in the present invention before the optical sensing unit is mounted securely on the front housing part of the optical imaging device. FIG. 1 illustrates a setup for establishing the correcting database. As illustrated, a testing frame 2 has a downwardly facing test image piece 24 at an upper portion thereof, and supports a test lens unit 22 below the test image piece 22 . A test sensing unit 23 is mounted on an adjustable support 21 at a lower portion of the testing frame 2 below the test lens unit 22 . By operating the support 21 , the test sensing unit 23 can be adjusted relative to the test lens unit 22 along two transverse axes (hereinafter referred to as X and Y axes) of a sensing plane that is transverse to an optical axis (Z′) of the test lens unit 22 . Optical measuring devices (not shown) are employed to detect the position of the test sensing unit 23 relative to the test lens unit 22 . With further reference to FIG. 2 , the test image piece 24 has an image thereon. The image includes two intersecting axes 240 of a rectangular or Cartesian coordinate that form four quadrants, each of which is provided with a pattern 241 in the form of a polygon. One of the quadrants is further provided with a position marker 242 . The position marker 242 can be dispensed with if the patterns 241 have directional properties. The test sensing unit 23 is moved repeatedly relative to the test lens unit 22 along the X and Y axes. Each time the test sensing unit 23 is moved to a new position relative to the test lens unit 22 , the image signals generated by the test sensing unit 23 and corresponding to a captured test image of the test image piece 24 that was received by the test sensing unit 23 via the test lens unit 22 are detected, and the position information for the test sensing unit 23 generated by the optical measuring devices are recorded to form an entry of the correcting database. Particularly, for each new position of the test sensing unit 23 , the boundary information of the patterns 241 in the image captured by the test sensing unit 23 are recorded in the correcting database. Because screw threads can be formed on the front housing part and the optical lens unit with a high degree of precision, the optical lens unit can be mounted precisely on the front housing part of the optical imaging device. Unlike the adjustable support of the aforesaid co-sending U.S. patent application, the entire disclosure of which is incorporated herein by reference, the adjustable support 21 of this invention includes an upper platform 211 , a lower platform 213 and a rotary seat 212 disposed between and coupling rotatably the upper and lower platforms 211 , 213 . The lower platform 213 is operable to align a rotary axis (Z) of the rotary seat 212 with the optical axis (Z′) of the test lens unit 22 . The upper platform 211 has the test sensing unit 23 disposed thereon and is adjustable to move the test sensing unit 23 relative to the test lens unit 22 along the X and Y axes. The rotary seat 212 is operable so as to rotate the test sensing unit 23 relative to the test lens unit 22 . In the method of this invention, the test sensing unit 23 is moved repeatedly relative to the test lens unit 22 along the X and Y axes while maintaining an angular position of the test sensing unit 23 relative to the test lens unit 22 . The angular position of the test sensing unit 23 is hereinafter referred to as a base angle, and the entries of the correcting database are thus generated for the same base angle of the test sensing unit 23 . It should be apparent to one skilled in the art that, in actual practice, if the size of the correcting database and the amount of time required for skew angle detection during the subsequent mounting operation can be neglected, the correcting database can include sets of entries, each of which is generated for a corresponding base angle of the test sensing unit 23 . One of the base angles is then selected as the reference base angle during the subsequent mounting operation. FIG. 3 illustrates how the optical sensing unit 34 is mounted on the front housing part 300 in accordance with the method of this invention. Unlike the setup of FIG. 1 , the front housing part 300 is secured to the testing frame 20 below the test lens unit 22 ′ .The optical sensing unit 34 , such as a charge-coupled device, is mounted loosely on the front housing part 300 at a rear side of the lens-mounting aperture with the use of fasteners, and the optical sensing unit 34 is clamped to an adjustable support 210 . The support 210 includes an upper platform 2101 , a lower platform 2102 and a rotary seat 2103 disposed between and coupling rotatably the upper and lower platforms 2101 , 2102 . The lower platform 2102 is operable so as to alien a rotary axis of the rotary seat 2103 with the optical axis of the test lens unit 22 ′ .The upper platform 2 l 0 has the optical sensing unit 34 disposed thereon and is operable so as to move the optical sensing unit 34 relative to the front housing part 300 along the X and Y axes. Because the fastener holes in the optical sensing unit 34 are slightly larger than the fasteners, the optical sensing unit 34 is adjustable relative to the lens-mounting aperture in the front housing part 300 along the X and Y axes. The rotary seat 2103 is operable so as to rotate the optical sensing unit 34 relative to the front housing part 300 . When mounting the optical sensing unit 34 on the front housing part 300 , a captured image of the test image piece 24 ′ is provided to the optical sensing unit 34 via the test lens unit 22 ′. Upon operation, the optical sensing unit 34 generates image signals corresponding to the captured image and processed by a control device 28 ′, such as a personal computer. Subsequently, the optical sensing unit 34 is adjusted relative to the front housing part 300 along the optical axis so that the captured image has optimum contrast. An appropriate number of washers may be installed by the operator between the optical sensing unit 34 and the front housing part 300 to retain the optical sensing unit 34 at a position for optimum contrast with respect to the optical axis. Since the adjustment of the optical sensing unit 34 along the optical axis proceeds in a manner similar to that described in the aforesaid co-pending U.S. patent application, a detailed description of the same will be dispensed with herein for the sake of brevity. Thereafter, while viewing the image captured by the optical sensing unit 34 and shown on the control device 28 ′, the operator operates the adjustable support 210 such that the rotary axis is generally aligned with the optical axis. Then, with reference to the contents of the correcting database, the control device 28 ′ determines a skew angle of the image captured by the optical sensing unit 34 . With further reference to FIG. 4 , when determining the skew angle, the control device 28 ′ processes the image signals generated by the optical sensing unit 34 to find the intersecting axes in the captured image and to find an intersection point (A) of the intersecting axes. Since many methods for finding the intersection point of ruled lines from a plurality of point information are known to those skilled in the art, a description of the same is omitted herein for the sake of brevity. Upon determination of the intersection point (A), a sampling region of the captured image is defined by a circular boundary having a predetermined diameter and centered at the intersection point (A). Because the sampling region is located at a central part of the captured, the adverse effects of edge distortion attributed to the test lens unit 22 ′ can be minimized. Thereafter, using well-known skew angle determination algorithms, and with reference to the image data associated with the selected reference base angle as stored in the correcting database, pixel points in the sampling region are evaluated by the control device 28 ′ so as to determine the relative skew angle. The adjustable support 210 is then operated via manual or automatic means to correct the angular orientation of the optical sensing unit 34 with respect to the front housing part 300 in accordance with the skew angle determined by the control device 28 ′. After correcting the skew angle of the optical sensing unit 34 , the boundary information of the patterns in the image captured by the optical sensing unit 34 , with respect to the previously found intersecting axes of the captured image, are determined by the control device 28 ′ in a manner similar to that described in the aforesaid co-pending U.S. patent application. The boundary information are then compared with the contents of the correcting database in order to determine an actual position of the optical sensing unit 34 along the X and Y axes. Adjustment of the optical sensing unit 34 from the actual position to an optimum position on the X and Y axes as determined from the contents of the correcting database is subsequently performed via manual or automatic means so as to ensure precise alignment with the aperture in the front housing part 300 . Upon adjustment of the optical sensing unit 34 to the optimum position relative to the aperture, the fasteners are tightened by the operator to mount the optical sensing unit 34 securely on the front housing part 300 . Thereafter, the rear housing part is assembled onto the front housing part 300 , and the optical lens unit is mounted threadedly and securely in the aperture at the front side of the front housing part 300 in the manner described beforehand to complete assembly of the optical imaging device. It has thus been shown that the method and apparatus of this invention can ensure both precise angular orientation of the optical sensing unit on the housing of the optical imaging device and precise alignment between the optical lens unit and the optical sensing unit, and can be applied to the mass production of optical imaging devices having uniform quality. While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.