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.

Description:
PRIOR APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 62/343,910 filed on Jun. 1, 2016, the contents of which are included herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally toward a rotary stage for supporting a payload. More specifically, the present invention relates to a simplified rotary stage providing precise identification of angular orientation and tilt of the payload. 
       BACKGROUND 
       [0003]    Rotary stages and platforms have been used to provide a wider angle of view to, for example, imaging devices including cameras for some time. Cameras or other technical devices are installed as part of a payload on a rotary stage or platform. It is generally desirable to identify the angle of rotation of which the technical device is oriented. Efforts to identify the angular orientation require the use of complex encoders in combination with expensive, high accuracy rotary drives. It has been customary to signal the rotary drive in intended angular orientation to rotate the stage to the angular orientation without performing any remedial measurement to determine the angular orientation of the stage or platform. To achieve some degree of accuracy, the drive typically includes a stepper motor that is particularly costly when working in combination with an encoder to direct the motor to the desired orientation. Achieving a high degree of accuracy has still proven elusive, particularly at a reasonable cost. To achieve a high degree of accuracy, the prior art rotary drives are known to dither or oscillate around a target angular orientation while attempting to establish desired accuracy. Even high cost rotary drives can only achieve a degree of accuracy that makes it difficult to use the payload for high precision operations such as, for example, template laser projection, photographic measurement, and inspection systems performed on large objects, such as, for example, an airplane fuselage that requires a wide angle of view not achievable by a stationary system. 
         [0004]    In addition, rotary platforms or stages have not included provisions to determine tilt of a platform or stage from away from a vertical axis or axis of rotation. Therefore, the platforms or stages must be secured in highly accurate horizontal orientation. Alternatively, tilt is simply ignored reducing accuracy of the imaging device located on the platform or stage. 
         [0005]    Alternatively, to perform these functions on a large object, the payload is moved a long distance from the object further resulting in reduction in accuracy. A low cost system to overcome these problems has not yet been found. Therefore, it would be desirable to provide a rotary stage or platform capable of working in unison with the highly technical payload such as, for example, a laser projector, the photogrammetric measurement system, or an inspection system that is low cost, and simple to maintain that is capable of providing a high degree of accuracy. 
       SUMMARY 
       [0006]    A rotary stage assembly includes a platform and a rotary drive. The rotary drive defines an axis of rotation including a spindle. The platform is mounted on the spindle for receiving rotary movement from the rotary drive. A cylindrical wall is fixably attached to the platform receiving rotary movement with the platform from the rotary drive. The cylindrical wall is co-axial 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 disposed on the inner surface of the cylindrical wall. The imaging assembly detects angular orientation and tilt of the platform an axis of rotation of the platform from imaging the reference patterns disposed upon the inner surface of the cylindrical wall. A controller calculates angular orientation and tilt of the platform from the axis of rotation of the platform from a location of the reference patterns signaled from the imaging assembly to the controller. 
         [0007]    The rotary stage assembly of the present application works in an opposite manner of high cost rotary stage assembly of the prior art. Unlike prior art rotary stage assemblies with highly expensive and technical rotary drives that are directed by an encoder to move to a predetermined location, the low cost rotary drive of the present invention merely moves to a proximate a desired angular orientation. The imaging assembly identifies precise angular orientation of the platform by imaging the reference patterns disposed on an inner surface of the cylindrical wall after the platform has been moved to a proximate angular orientation. The angular orientation need not be precise as required of prior art devices because the imaging assembly identifies the precise location after the platform has been rotated to an approximate angular orientation. When the precise location of the platform is identified, the controller signals the payload to make responsive adjustments to achieve a high degree of projection or imaging accuracy. 
         [0008]    In addition, prior art rotary stage assemblies are incapable of determining the tilt of the platform away from a an axis of rotation as defined by a spindle of a rotary drive. Many spindles of rotary drives experience wobble from low cost bearings or other technical inaccuracies, such as, for example a spindle that is not perfectly straight. The imaging assembly of the present invention is capable of identifying an amount of tilt from an axis of rotation resulting from any of these, and other technical inaccuracies of the rotary drive. By measuring an accurate orientation of the platform the reliance on high cost, precision mechanical drives is eliminated. After calibration, the rotary stage assembly of the present invention is capable of directing the payload including laser projector, photogrammetric measurement system, or inspection system in a highly precise manner achieving tolerances of 0.5 millimeters or less even when the payload has not been moved in a precise manner. 
     
    
     
       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.