Abstract:
An apparatus and associated method contemplating a goniometer stage having a base, and a roller bearing having a first annular race supported by the base and a concentric second annular race. A rotor plate is configured to support a workpiece, and defines a bearing surface contacting the second annular race throughout a selective movement of the rotor plate with respect to the base along an arc defining an axis of rotation that is spaced apart from the rotor plate.

Description:
SUMMARY 
     Various embodiments of the present technology are generally directed to the construction and use of broad range goniometry. 
     Some embodiments of this disclosure contemplate a goniometer stage having a base, and a roller bearing having a first annular race supported by the base and a concentric second annular race. A rotor plate is configured to support a workpiece, and defines a bearing surface contacting the second annular race throughout a selective movement of the rotor plate with respect to the base along an arc defining an axis of rotation that is spaced apart from the rotor plate. 
     Some embodiments of this disclosure contemplate a positioning apparatus having a base supporting a plurality of discrete roller bearings arranged to collectively form a bearing cradle. A rotor plate is configured to support a workpiece, and is supported by the bearing cradle during selective movement with respect to the base along an arc having an axis of rotation that is spaced apart from the rotor plate. A drive assembly is configured to selectively position the rotor plate at a nominal position and alternatively to rotate the rotor plate more than twenty degrees around the axis of rotation in each of opposing rotational directions from the nominal position. 
     Some embodiments of this disclosure contemplate a method that includes: obtaining a goniometer stage having a moveable rotor plate that is rotatably supported upon a bearing cradle in a stationary base, the rotor plate configured to support and rotate a workpiece around an offset axis of rotation that is separate from boundaries of the goniometer stage; and selectively rotating the workpiece around the offset axis at least twenty degrees in each of opposing rotational directions from a nominal position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially exploded isometric depiction of a goniometer stage that is constructed in accordance with illustrative embodiments of this technology. 
         FIG. 2  diagrammatically depicts a side of the rotor plate supported upon the bearing cradle. 
         FIG. 3  diagrammatically depicts an end of the rotor plate supported upon the bearing cradle. 
         FIG. 4  is an elevational depiction of the goniometer stage of  FIG. 1  with the rotor plate at zero degrees of rotation. 
         FIG. 5  is similar to  FIG. 4  but depicting the rotor plate rotated clockwise more than thirty degrees. 
         FIG. 6  is an enlarged detail view of a spindle bearing forming a portion of the bearing cradle. 
         FIG. 7  is an enlarged detail view of an alternative construction of a bearing forming a portion of the bearing cradle. 
         FIG. 8  is similar to  FIG. 3  but depicting tapered roller bearings in an alternative construction of this technology. 
         FIG. 9  is an isometric depiction of the goniometer of  FIG. 1  with a servo motor and position encoder for selectively moving the rotor plate. 
         FIG. 10  is an elevational depiction of the flexible belt coupling the servo motor to the rotor plate. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to the design and use of positioning goniometer technology. A positioning goniometer, referred to herein as a goniometer stage, is used to selectively position a workpiece for precise measurements. That is, a goniometer stage can be used to precisely position an article being measured, or a goniometer stage can be used to precisely position a measurement device for measuring an article. For purposes of this description and meaning of the appended claims, the term “workpiece” can mean either an article being measured or a measurement device. The workpiece is secured to a rotor platform portion of the goniometer stage that is selectively movable, so that the workpiece and the rotor platform move in unison. A goniometer stage is similar to a linear positioner except that the movement of the rotor plate relative to a stationary base is arcuate instead of linear. That is, the rotor platform is moveable along an arc having a relatively large axis of rotation. The axis of rotation is actually located beyond the physical boundary of the goniometer stage itself. 
     Previously attempted solutions are typically constructed with an integrated cross roller bearing supporting the rotor platform in its movement relative to the stationary base. The cross roller bearing has a number of rolling elements, such as ball bearings, trapped in a cage that is curved to closely mate between the concave base and the convex rotor platform. An inherent limitation of that design is that rotation away from a nominal (zero degrees) position reduces the surface area of bearing support. That means most previously attempted solutions can only provide up to about ten degrees of rotation in a given direction. There is a need for a positioning goniometer that retains the advantage of a large open field of view above the rotor platform yet can significantly increase the range of rotor platform rotation. It is to that solution that the embodiments of this technology are directed. 
       FIG. 1  is a partially exploded isometric depiction of a goniometer stage  100  that is constructed in accordance with illustrative embodiments of the present technology. The goniometer stage  100  generally has a base  102  defining a concave opening  104  in which a plurality of (in these illustrative embodiments four) bearings  106 ,  108 ,  110 ,  112  are arranged to collectively form a bearing cradle  114 . A rotor platform  116  defines a pair of convex, arcuate bearing surfaces  118 ,  120  that roll against the bearings  106 ,  108 ,  110 ,  112  in operably supporting the rotor platform  116  at various selected rotational positions. 
     The rotor platform  116  has a top plate  115  defining an exposed surface  117  that is configured to support the workpiece (not depicted) for selective positioning. To that end, although not depicted it is understood that the surface  117  can be provided with attachment features such as threaded apertures, T-shaped slots, and the like for affixing the workpiece to the rotor platform  116 . 
     As shown in the elevational depiction of  FIG. 2 , the arcuate bearing surface  118  simultaneously contacts both bearings  106 ,  108  throughout the selective movement of the rotor platform  116 , and likewise (although not depicted in  FIG. 2 ) the bearing surface  120  simultaneously contacts both bearings  110 ,  112 . The end depiction of  FIG. 3  shows opposing bearings  106 ,  110  are canted, forming a concave angular relationship Ø therebetween, in order to cradle the bearing surfaces  118 ,  120  against the bearings  106 ,  110 . Although not depicted in  FIG. 3 , the other opposing bearings  108 ,  112  are likewise canted in these illustrative embodiments. 
     A roller  119  is positioned inside the rotor plate  116  and rolls in a frictional engagement against an internal surface  121  throughout the movement of the rotor plate  116 . The roller  119  is supported by a shaft  123  sized to pass through a slot  125  provided in the rotor plate  116 . The shaft  123  is biased in the direction of arrow  127  (downward as depicted) to urge the roller  119  against the surface  121  which, in turn, biases the bearing surfaces  118 ,  120  by a selected preload force against the bearings  106 ,  108 ,  110 ,  112 . The force in direction  127  can be provided by a mechanical spring mechanism, or a mechanical actuator, and the like. 
       FIG. 4  is an elevational depiction of the rotor platform  116  as it is operably supported on the bearing cradle  114  in the base  102 . The rotor platform  116  is depicted at a nominal, in this case horizontal, position referenced as a position of zero degrees of rotation. The rotor platform  116  is selectively moveable in both clockwise and counterclockwise rotational directions along an arc depicted by the arrow  122  that has an axis of rotation  124  spaced apart and separate from the boundaries of the goniometer stage  100 .  FIG. 5  is similar to  FIG. 4  but depicting the rotor platform  116  having been rotated more than thirty degrees in the clockwise direction  122  for using the workpiece (not depicted) at that selected orientation. The rotor platform  116  is likewise selectively moveable to the mirror position in the counterclockwise rotational direction. Thus, the illustrative embodiments of this technology are capable of a total range of more than sixty degrees of rotation. 
     The illustrative embodiments so far have four bearings  106 ,  108 ,  110 ,  112  making up the bearing cradle  114 , although the contemplated embodiments are not so limited. In alternative embodiments more or fewer bearings can be employed. In fact, the skilled artisan understands that the bearing surfaces  118 ,  120  and the bearing  106 ,  108 ,  110 ,  112  positioning are necessarily very precise (low tolerances) in order to make four-point rolling contact on the bearing cradle  114  described. Three point contact can also be employed by having two bearings support one of the bearing surfaces  118 ,  120  and only one bearing support the other bearing surface  118 ,  120 . In that case the two bearings on the same bearing surface are spaced apart and the one bearing on the other bearing surface is positioned between them to form a triangular three-point bearing cradle. 
       FIG. 6  is an enlarged detail depiction of one of the bearings  106  in illustrative embodiments constructed as a spindle bearing. In these embodiments the bearing  106  has a stationary spindle  126  with a proximal end thereof that is attached to the base  102 . A distal end of the spindle  126  forms an inner race  128  around which a concentric outer race  130  is journalled in rotation. The outer race  130  rotates around an axis  132  that remains fixed with respect to the base  102  in support of the rotor plate  116  throughout its selective movements. Note that this arrangement provides the same four-point bearing support of the bearing cradle  114  at the nominal position depicted in  FIG. 4 , at the extent of clockwise rotation depicted in  FIG. 5 , and at all rotational positions therebetween. 
       FIG. 7  depicts alternative embodiments similar to  FIG. 6  but wherein a protuberant securement member  134  is either attached to or as depicted is formed as a portion of the base  102 ′. A roller bearing  106 ′ has an inner race  136  attached to the securement member  134 , around which a concentric outer race  138  is journalled in rotation to support the rotor plate  116  during the selective movements. 
       FIG. 8  is similar to  FIG. 3  but depicting alternative embodiments in which tapered roller bearings  106 ′,  110 ′ are mounted parallel to each other rather than the canted arrangement previously described. The tapered bearings  106 ′,  110 ′ cradle the bearing surfaces  118 ,  120  in the same way as the canted bearings. 
     The goniometer stage  100  described so far is well suited for manually positioning the rotor plate  116  at a selected rotational position. A latch or a frictional crowder and the like can be employed to retain the rotor plate  116  at the selected position.  FIG. 9  is an isometric depiction of alternative embodiments that employ a servo motor  140  with a positional encoder  142  for processor-controlled movement of the rotor plate  116  and retaining it at a selected position. The encoder  142  is positioned to read indicia  144 , such as optical or magnetic data, that is affixed to the arcuate surface of the rotor plate  116 . 
     The servo motor  140  drives a pulley  146  according to a control system that responds to a call to move the rotor plate  116  to a selected position, with actual position feedback data provided by the encoder  142 .  FIG. 10  depicts a flexible belt  148  has a medial portion that is trained around the pulley  146  so that rotation of the pulley  146  transfers corresponding forces to the belt  148 . Both ends  150 ,  152  of the flexible belt  148  are clamped in place by an attachment of the top plate  115 . A pair of idler rollers  154 ,  156  impart tension to the belt  148  to prevent slippage between it and the pulley  146 . With this arrangement, programmed actuation of the servo motor  148  rotates the pulley  146  that, in turn, creates tension in the belt  148  to rotate the rotor platform  116  to a selected position. Positional feedback from the encoder  142  is utilized with predefined velocity profiles and positional error compensation to control the movement of the rotor platform  116 . After the desired position is obtained, a dwell load on the servo motor  140  retains the rotor platform  116  at the desired position. 
     It is to be understood that even though numerous characteristics of various embodiments of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.