PRECISION LOCATING ROTARY STAGE

Abstract

A rotary stage assembly includes a platform and a rotary drive defining an axis of rotation. The platform is mounted on a spindle for receiving rotary movement from the rotary drive. A cylindrical wall is attached to the platform receiving rotary movement from the rotary drive and is coaxial with the axis of rotation defined by the rotary drive. The cylindrical wall defines an inner surface including reference patterns. An imaging assembly images the reference patterns on the inner surface of the cylindrical wall. The imaging assembly detects angular orientation and tilt of the platform from an axis of rotation of the platform from imaging the reference patterns on the inner surface of the cylindrical wall. A controller calculates angular orientation and tilt of the platform from the location of said reference patterns signaled from the imaging assembly.

Claims

1. A rotary stage assembly; comprising: a platform and a rotary drive defining an axis of rotation with a spindle, said platform being mounted on said spindle for receiving rotary movement from said rotary drive; a cylindrical wall fixedly attached to said platform receiving rotary movement with said platform from said rotary drive and being coaxial with said axis of rotation defined by said rotary drive; said cylindrical wall defining an inner surface including reference patterns; an imaging assembly for imaging said reference patterns disposed upon said inner surface of said cylindrical wall; said imaging assembly for detecting angular orientation and tilt of said platform from an axis of rotation of said platform from imaging said reference patterns disposed upon said inner surface of said cylindrical wall; and a controller for calculating angular orientation and tilt of said platform from said axis of rotation from the location of said reference patterns signaled from said imaging assembly to said controller.

2. The assembly set forth in claim 1, wherein said platform supports a payload apparatus including one of a laser projector, photogrammetric measurement system, or inspection system.

3. The assembly set forth in claim 2, wherein said controller is interconnected with said payload apparatus, said rotary drive and said imaging assembly for determining an axial and angular orientation of said platform and signaling said payload apparatus the axial and angular orientation of said platform.

4. The assembly set forth in claim 1, wherein said imaging assembly includes a plurality of cameras for generating images of said reference pattern at spaced locations.

5. The assembly set forth in claim 4, wherein said imaging assembly includes at least three cameras.

6. The assembly set forth in claim 1, wherein said imaging assembly includes an illumination device for illuminating said reference pattern.

7. The assembly set forth in claim 1, wherein said rotary drive and said imaging assembly are affixed to a support structure.

8. The assembly set forth in claim 1, wherein said reference pattern includes random marking.

9. The assembly set forth in claim 1, wherein said reference pattern includes vertical and horizontal identifiers.

10. The assembly set forth in claim 1, wherein said controller determines three dimensional orientation of said platform from images of said reference pattern by said imaging assembly.

11. The assembly set forth in claim 1, wherein said rotary drive includes a brake for stopping or holding said rotary drive in a fixed angular orientation.

12. A method of identifying an orientation of a platform used to support a payload in a three dimensional coordinate system, comprising the steps of: providing a platform for supporting a payload being fixedly attached to said platform; providing a rotary drive defining an axis of rotation including a spindle for translating angular movement to said platform around said axis defined by said rotary drive; applying a reference pattern to said platform being movable with said platform around said axis of rotation defined by said spindle; said rotary drive rotating said platform in a direction of a predetermined angular orientation and stopping said rotary drive at a proximate angular orientation to said predetermined angular orientation; generating an image of said reference pattern with an imaging assembly after said rotary drive has stopped at the proximate angular orientation; transmitting the image of the reference pattern to a controllers; and said controller calculating an angular orientation and tilt of said platform relative to said axis of rotation for determining an orientation of said payload.

13. The method set forth in claim 12, wherein said step of providing a platform for supporting a payload is further defined by providing said payload comprising at least one of a laser projector, photogrammetric measurement system, and inspection system.

14. The method set forth in claim 12, further including the step of said payload being in electronic communication with said controller.

15. The method set forth in claim 14, further including the step of said controller identifying an orientation of said payload in a three dimensional coordinate system by generating an image of said reference pattern with said imaging assembly.

16. The method set forth in claim 14, wherein said step of providing an imaging system is further defined by providing a plurality of cameras for generating a plurality of images of said reference pattern.

17. The method set forth in claim 16, wherein said step of generating a plurality of images of said reference pattern is further defined by generating a plurality of images at spaced locations.

18. The method set forth in claim 16, wherein said step of providing a plurality of cameras is further defined by providing at least three cameras.

19. The method set forth in claim 12, wherein said step of applying a reference pattern to said platform is further defined by applying an arbitrary pattern to said platform.

20. The method set forth in claim 12, further including the step of adjusting said payload based upon said controller calculating an angular orientation and tilt of said platform relative to said axis of rotation.

21. The method set forth in claim 12, wherein said step of applying a reference pattern to said platform is further defined by applying a referent pattern to cylindrical surface being coaxial with said axis define by said spindle.

22. The method set forth in claim 12, wherein said step of stopping said rotary drive at a proximate angular orientation to said predetermined angular orientation is further defined by holding said rotary drive at a proximate angular orientation to said predetermined angular orientation while generating an image of said reference pattern with said imaging assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0010] FIG. 1 shows a plan view of a rotary stage assembly of the present invention;

[0011] FIG. 2 shows a side schematic view of the rotary stage assembly of the present invention though line 2-2 of FIG. 1;

[0012] FIG. 3 shows a top sectional view of the imaging assembly and frame through line 3-3 of FIG. 2; and

[0013] FIG. 4 shows an image of the reference patter disposed upon an inner surface of a cylindrical wall.

DETAILED DESCRIPTION

[0014] Referring to FIGS. 1 and 2, a rotary stage assembly is generally shown at 10. A rotary drive 12 transfers an axis a of rotation with a spindle 14. The rotary drive 12 takes the form of a servo motor or any low cost electric motor capable of transferring rotational movement to the spindle 14. The rotary drive 12 need not translate rotational movement to the spindle 14 in a highly accurate manner. The rotary drive 12 need merely transfer rotational movement proximate a desired angular orientation as will be explained further herein below. The rotary drive 12 is contemplated to be any drive that is capable of transferring rotational movement to an approximate angular orientation and then stop in a fixed position. In one embodiment, the rotary drive 12 is a direct drive motor with a high gear ratio such that the position of the drive is disposed in a fixed position when not operating. In another embodiment, the rotary drive 12 takes the form of a servo-motor with a brake 13 that will stop and hold the rotary drive 12 in a fixed position when the rotary drive 12 is not operating. The brake 13 prevents dithering or oscillation around a desired stopping angular orientation as is typical of even high cost drives that make use of complex encoders. In a still further embodiment, the rotary drive 12 is depowered or deactivated once the rotary drive 12 has reached an approximate, desired angular orientation. The brake 13 can take any form of a device that will stop or secure the rotary drive 12 at the desired stopping angular orientation. As used within the present application, angular orientation is relative to the axis a of rotation of the rotary drive 12

[0015] A platform 16, in one embodiment, is supported on the spindle 14 and receives rotational movement around axis a as shown by arrow 18 (FIG. 2) from the rotary drive 12. As used herein, the spindle 14 includes any element that transfers rotational movement to the platform 16, whether or not including substantially vertical orientation. A payload 20 is secured to the platform 16 by a plurality of fasteners 22 so that the payload 20 is fixedly secured relative to the platform 16. In one embodiment, at least 3 fasteners 22 are received by pre-existing apertures (not shown) disposed in the platform 16. However, it should be understood that additional fasteners 22 may be used to secure the payload 20 to the platform 16.

[0016] The rotary drive 12 is secured to a support structure 24. The support structure 24 includes a base 26 supported by legs 28. The legs 28 orient the base substantially horizontally. However, the base 26 need not be precisely horizontal to achieve a high degree of accuracy as will be explained further herein below.

[0017] A cylindrical wall 30 is located beneath the platform 16 proximate the periphery of the platform 16. The cylindrical wall 30 defines an inner surface 32 onto which a reference pattern 34 is disposed. The reference pattern 34, in one embodiment, is an arbitrary pattern. Any pattern providing distinguishing and unique characteristics in both the axial direction and an angular direction around the axis a is suitable. In one embodiment, a dark anodized coating having circular portions 36 removed to expose the inner surface 32 is believed suitable. Different size and shaped oval portions 36 offer identifiable features that are useful in determining an orientation of the platform 16. However, other distinguishing elements of a reference pattern 34, including decals, arbitrary lines, or any pattern that is distinguishable and presents uniqueness at different locations will suffice.

[0018] An imaging assembly 38 is mounted on the base 26 beneath the platform 16. The imaging assembly 38 includes a plurality of cameras 40 that generate an image of the reference pattern 34 disposed upon the inner surface 32 of the cylindrical wall 30. In one embodiment, the imaging assembly 38 includes three cameras 40. However, more or less cameras 40 are included within the scope of this invention. It is believed three or more cameras 40 provide a higher degree of accuracy than one or two cameras and that the number of cameras 40 selected may be based upon a desired level accuracy.

[0019] The imaging assembly 38 also identifies an angular orientation of the platform 16 in the direction of arrow 18 by generating an image of the reference pattern 34. The reference pattern 34 provides unique features at different locations of the inner surface 32 of the cylindrical wall 30. Therefore, the imaging assembly 38 is capable of accurately detecting the angular orientation of the platform 16 by imaging unique features defined by the reference patter 34. In addition, the reference pattern provides unique features in the direction of the axis a defined by the spindle 14. Therefore, the imaging assembly 38 also identifies tilt of the platform 16 relative to the axis a of rotation of the spindle 14 by imaging unique features in the axial direction.

[0020] As set forth above, a payload 20 is secured to the platform 16. In one embodiment, the payload 20 includes a laser projector 42. As known to those skilled in the art, the laser projector 42 projects a laser beam (not shown), the direction of which is established by mirrors 44 controlled as part of a galvanometer 46. Additionally, lenses (not shown) and other apparatus required to project a laser beam are included within the scope of this invention but not explained further herein. In alternative embodiments, the payload 20 also includes a photogrammetric measurement system and an inspection system or combination of the laser projector 42, photogrammetric measurement system and inspection system. For simplicity, the photogrammetric measurement system and the inspection system are all represented by element number 42. It is within the scope of this invention that the payload 20 includes any device required to either generate a photographic image or project a laser image at a wide angle.

[0021] The payload 20, the imaging assembly 38 and the rotary drive 12 are electronically connected to a controller 48. The controller 48 determines a three-dimensional orientation of the platform 16 from images generated by the imaging assembly 38 of the reference pattern 34. Unlike prior art assemblies that require an encoder to direct a high cost motor to move to a specific location, the controller 48 merely signals the rotary drive 12 to rotate to a general or proximate angular orientation not requiring a high degree of precision. Once moved to a proximate angular orientation, the rotary drive 12 may be stopped by the brake 13 and deactivated by the controller 48. As set forth above, any combination of braking or deactivation may be used to hold the rotary drive 12 in a fixed position. Subsequent to deactivating or terminating movement of the rotary drive 12, the controller 48 receives an image generated by the imaging assembly 38 of the reference pattern 34. From the image generated of the reference pattern 34, the controller 48 determines a precise angular orientation and tilt of the platform 16 from the axis of rotation of the platform 16. Once the angular orientation and tilt of the platform 16 is determined by the controller 48, the controller signals the payload 20 the tilt and angular orientation so that the payload 20 can precisely either project a laser image or generate photogrammetric measurement of an object. As set forth above, the accurate method of measuring angular orientation and tilt of the platform 16 eliminates the need for a high accuracy, cost prohibitive motor and encoder combination to move a platform.

[0022] The controller 48, in one embodiment, is included with the payload 20. In an alternative embodiment, the controller 48 is affixed to the support structure 24. In a still further embodiment, the controller 48 is disposed at a remote location and is wirelessly connected to the payload 20, the imaging assembly 38 and the rotary drive 12.

[0023] To achieve high precision measurement, it is desirable to calibrate the imaging assembly 38 relative to the reference pattern 34 and the payload 20. As such, the assembly 10 is calibrated on a fixture capable of identifying an unique features of the reference pattern 34 relative to the payload 20 at different locations of the reference pattern 34. The accurate location of the reference pattern 34 is stored by the controller and is referenced when performing a high precision measurement of the tilt and angular orientation of the platform 16 and the payload 20. Once calibrated, the payload 20 is capable of projecting a laser image at a wide angle in a precise manner, even up to 0.5 millimeters tolerance. In addition, the payload 20 is capable of performing a photogrammetric measurement or inspection of an object within a similar tolerance as explained above, which was previously not achievable.

[0024] Additional accuracy is achieved by including the plurality of cameras 40 in the imaging assembly 38. With a plurality of cameras 40, images are generated of the reference pattern 34 at spaced location. It is believed that generating images at spaced locations enables the imaging assembly 38 to more accurately generate useful data for the controller 48 to calculate both the angular orientation and the tilt relative to the axis a of the platform 16. A further enhancement to the imaging assembly 38 includes a light source 50 to illuminate the reference pattern 34 to allow the cameras 40 to more clearly generate an image of the reference pattern 34.

[0025] Once the angular orientation and tilt of the platform 16 is established by the controller 48, the controller 48 determines the proper orientation of the payload to achieve the desired degree of accuracy. When the proper orientation of the payload 20 is determined, the payload 20 is signaled by the controller 48 the make the necessary adjustment to project or scan the object.

[0026] The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the specification, the reference numerals are merely for convenience, and are not to be in any way limiting, the invention may be practiced otherwise than is specifically described. The invention can be practiced otherwise than as specifically described within the scope of the appended claims.