Abstract:
A goniometer comprising a rotor and a support base having therebetween three or four balls or rollers constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the balls being constrained to be spaced apart in at least two dimensions to ensure a three point spaced contact with the rotor and the support base.

Description:
This is a Continuation-in-Part of International Application No. PCT/US02/02648 filed Jan. 30, 2002 which designates the United States of America and which claims priority from U.S. patent application Ser. No. 60/267274 filed Feb. 8, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to goniometers, namely a rotational positioner whose center of rotation is located outside the physical boundaries of the device. It is used for partial rotation of parts too large for the thru hole of a full rotational stage. 
     BACKGROUND OF THE INVENTION 
     Linear micropositioners are known e.g. from U.S. Pat. No. 3,046,006 and arcuate rolling bearings in which balls, controlled by cages, roll in opposed arcuate gothic arch shaped tracks allegedly providing a four-point contact surface are known e.g. from U.S. Pat. No. H539. Goniometers are also known with current designs typically comprising stages, mounted for limited rotation, controlled by i.e. arcuate dovetail mating grooves or arcuate cross-roller arrangements with cooperating V-grooves. These arrangements do not provide negligible eccentricity coupled with smooth sensitive action as is required i.e. for fiber optic alignment. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide a number of designs of goniometers which overcome shortcomings of current designs. 
     SUMMARY OF THE INVENTION 
     The design is an improvement over the current designs where shorter rotational travels (minor adjustments, 3-20°) and smooth sensitive and repeatable action are required, but exact long range eccentricity and load capacity are not, such as in fiberoptic alignment. The present invention provides goniometers which are considerably cheaper, and possibly better than using precision roller ways. It employs three or four bearing balls, two riding in counter-v-grooves at least one of which is a V-groove opposed to a non-constraining flat surface, to give complete kinematic stability in every aspect except rotation. 
     The design with the three ball bearings is the simplest and this affords a three-point contact for low load requirements. 
     The four-ball version allows perfect four-point contact, which is not achievable in the linear stage as patented (see U.S. Pat. No. 3,046,006). This is because the rotor is free to rotate on its axis normal to the axis of rotation of the device until all four points are touched simultaneously. 
     The invention provides a goniometer comprising a rotor and a support base having therebetween four balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the four balls being constrained to be spaced apart in at least two dimensions with at least one ball thereof being supported to adjust its position to ensure a four point spaced apart support contact between the rotor and the support base. 
     The invention also provides a goniometer comprising a rotor and a support base having therebetween three balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the three balls being constrained to be spaced apart in at least two dimensions to ensure a three point spaced contact with the rotor and the support base. 
     A possible further version employs pre-fabricated bearing races, cut into sections for partial rotation, as separate parts attached to receiving areas in the goniometer body, rather than machining them right in. This allows the design to eliminate the third groove pair, while the second groove pair manages its former operation by having the attributes of both groove pairs built into one. 
     Another embodiment, using the four ball system, is one in which the cylinder pair is “very long as compared to the diameter, and also in 2 sections. This would allow a very lightweight off-axis tilt table. 
     According to the invention there is provided a goniometer comprising a rotor and a support base having therebetween at least three balls constrained to at least two arcuate paths to allow rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the balls being constrained to be spaced apart in at least two dimensions arranged in said arcuate paths to ensure at least a three point spaced contact of the rotor with the support base. 
     Preferably there are two parallel spaced apart said arcuate grooves, at least one said arcuate groove being formed by facing cooperating V-grooves, one defined by the rotor and the other defined by the support base, retaining two said balls in spaced apart relationship in laterally constrained contact with said V-grooves. 
     Four balls may be provided, between the rotor and the support base, constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions with at least one ball thereof being supported to allow self adjustment of its position to ensure a four point spaced apart support contact between the rotor and the support base; preferably there are first, second and third said arcuate paths, the first and second said arcuate paths being spaced apart and each defined by an arcuate V-groove defined one of the rotor and the support base and an arcuate flat surface defined by the other of the rotor and support base and the third arcuate path being defined by facing cooperating arcuate V-grooves located adjacent said first arcuate path, two said balls being disposed and constrained in spaced relationship in the second said arcuate path in contact with the rotor and the support base, a third said ball being disposed and constrained in said first arcuate path in contact with the rotor and support base and the fourth said ball being disposed in said third arcuate path wherein the said fourth ball is free to move along said third arcuate path to allow said self adjustment to a position to ensure said four point spaced apart support contact. 
     In another embodiment, four balls between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths each defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, two said balls being disposed in spaced relationship in each arcuate path in contact with the rotor and the support base arranged to ensure a four point spaced apart support contact between the rotor and the support base. 
     In another embodiment, four balls, between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths, the first said arcuate path being defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, two said balls being disposed in spaced relationship in each arcuate path in contact with the rotor and the support base with the two balls disposed in the second arcuate path being constrained by opposed V-grooves forming the second arcuate path, thereby to ensure a four point spaced apart support contact between the rotor and the support base. Longitudinal movement of the rotor on the support base parallel to axis of rotation may be controlled by a lateral support arrangement. 
     In another embodiment, a rotor and a support base have therebetween three balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the three balls being constrained to be spaced apart in at least two dimensions to ensure a three point spaced contact with the rotor and the support base. 
     In a preferred three ball embodiment, three balls, between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the three balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths, the first said arcuate path being defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, one said ball being disposed in the first said arcuate path in contact with the rotor and the support base and two balls being disposed spaced apart in the second arcuate path constrained by opposed V-grooves forming the second arcuate path, thereby to ensure a three point spaced apart support contact between the rotor and the support base. 
     In yet another four ball embodiment the goniometer has a rotor and support base each defining a single arcuate surface which are complimentary and together define an arcuate space with four balls therein, the four balls being constrained to at least two arcuate paths by a cage common to all four balls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic top view of a first embodiment of a four ball goniometer according to the present invention; 
     FIG. 2 is a perspective view of the embodiment of FIG. 1; 
     FIG. 3 is a diagrammatic side elevation of the embodiment of FIG. 1; 
     FIG. 4 is a cross-section taken on section line  4 — 4  of FIG. 3; 
     FIG. 5 is a diagrammatic end elevation of the embodiment of FIG. 1; 
     FIG. 6 is a diagrammatic side elevation of a second embodiment of a four-ball goniometer according to the present invention; 
     FIG.  7 ( a ) is an illustrative cross-section of the arcuate groove arrangement of the embodiment of FIG. 6; 
     FIG.  7 ( b ) is a diagrammatic end elevation of the second embodiment of FIG. 6; 
     FIG. 8 is an illustrative inverted perspective view showing the arcuate grooves and four balls of the embodiment of FIG. 6; 
     FIG. 9 is a diagrammatic top view of a third embodiment of a four ball goniometer according to the present invention; 
     FIG. 10 is a diagrammatic side elevation of the embodiment of FIG. 9; 
     FIGS. 11-14 are illustrative cross-sections of various arcuate groove arrangements referred to with respect to FIGS. 9 and 10 and FIGS. 19 and 20; 
     FIG. 15 is a diagrammatic top view of a first embodiment of a three ball goniometer according to the present invention; 
     FIG. 16 is a perspective view of the embodiment of FIG. 15; 
     FIG. 17 is a diagrammatic side elevation of the embodiment of FIG. 15; 
     FIG. 18 is a cross-section taken on section line  18 — 18  of FIG. 17; 
     FIG. 19 is a diagrammatic top view of a second embodiment of a three ball goniometer according to the present invention; 
     FIG. 20 is a diagrammatic side elevation of the embodiment of FIG. 19; 
     FIG. 21 is a diagrammatic top view of a four ball grooveless and trackless goniometer; and 
     FIG. 22 is a diagrammatic side elevation of the goniometer of FIG.  21 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-5 a rotor  1  is supported for limited rotation by a base  2 . Through holes  3  are provided in the rotor  1  to allow access to base mounting holes  4  by which screws may mount the base  2  to a support structure. In this embodiment three parallel arcuate tracks  5 ,  6  and  7  engage four balls  8  with tracks  5  and  6  having opposed arcuate surfaces as shown in FIG.  12  and track  7  having an arcuate surface as shown in FIG.  13 . In this arrangement the tracks  5  and  6  comprise a arcuate V-groove  9  in base  2  laterally locating the associated balls  8  and in engagement with a flat matching arcuate surface  10  defined by rotor  1  and track  7  has opposed arcuate V-grooves  11  laterally locating the associated ball  8  and in engagement with each other freedom of movement along these grooves as hereinafter described. Three of the balls  8  are arranged with two spaced apart in track  5  and one in track  6  all three being located by cages  15  while the fourth ball  8  is located in track  7  and is free to move along track  7  to find a position in which all four balls touch and support the rotor  1  on the base  2 . By this means a smooth sensitive stable high load non-eccentric stage with a movement range typically of about 10° about the axis of rotation of the rotor is provided. 
     FIGS. 6-8 refer to an alternative two track  17  arrangement which may be substituted for the three track arrangement of FIGS. 1-5. In FIGS. 6-8 one track is as illustrated in FIG. 13 while the other track is as illustrated in FIG.  12 . The arcuate flat surface  10  on one side of one of tracks permits the required rotation of the rotor about an axis normal to the axis or rotation  12  to achieve the necessary four point contact of the balls with the rotor  1  and base  2 . An actuating mechanism  18  (motorized or manual) is operatively connected to rotor  1  to control movement about the axis  12 . A spring  14  engages the rotor  1  and base  2  to bias these together in engagement with the balls  8 . 
     This embodiment provides no adjustment along axis  12 . 
     This four ball  8  arrangement is an example of the track configuration which may be utilized in the four ball embodiment of FIGS. 9 and 10 which illustrates a preferred four ball embodiment allowing an angular travel of the rotor  1  about the axis of rotation  12  typically of about 10° total under the spring  14  biased control of micrometer  13  or other actuator and, optionally, linear travel under the spring  19  biased control of micrometer  16  or other actuator. The spring  25  located in base  2  engages a pin  20  fast with the rotor  1  and moveable in an opening  21  against the bias of spring  25  by micrometer  13  to pivot the rotor  1 , relative to the base, about axis  12 . The spring  19  engages rotor  1  and a support  22  for micrometer  16  to allow linear movement of the rotor  1  relative to the base  2  along axis  12  against the bias of the spring  19  by operation of the micrometer  16 . In the preferred form the arcuate grooves are either or both grooves shown in FIGS. 11 and 14. 
     To restrain longitudinal movement, a stop/micrometer support  22  may be placed at any convenient point against which the rotor may be pre-loaded. This “stop” may also be a ball placed up against a plate attached to the base, and free to rotate with the rotor Longitudinal movement may even be locked by having one of the balls captivated between  2  transaxial V-grooves, one in the rotor and one in the base  2 . 
     FIGS. 11-14 illustrate four groove configurations of which those of FIG. 12 and 13 have already been described above. In addition FIG. 11 illustrates a captivation ( 1 ) in which two flat opposed arcuate surfaces  10  having surface defining side walls oppose one another with a ball  8  between the surfaces and FIG. 14 illustrates a captivation ( 4 ) comprising two flat arcuate opposed surfaces  10  without surface defining side walls. 
     Possible configurations are 
     1) One ball with captivation  3  (FIG.  13 ), and three balls  8  with captivation  1 ,  2  or  4  (FIGS. 11,  12  or  14 ); 
     2) No longitudinal adjustment, with an external stop. Here four balls are used with any combination of captivations  1  and  4  (FIGS.  11  and  14 ); and 
     3) Longitudinal adjustment is provided by micrometer or motor screw with four balls with any combination of captivations  1  and  4  (FIGS.  11  and  14 ). 
     Captivation modules may be externally added rather than machined into the base  2  and rotor  1 , to provide one or more of the grooves. 
     Additionally, external bearing housing segments may be transplanted into receivers to form captivation style  3  (FIG.  13 ), with three of those segments being longitudinally free to find seating for the bearings, then i.e. bonded into those seating places as found. 
     Any combinations of these arrangements may be used. 
     Referring now to the three ball embodiments, reference is first made to FIGS. 15-18 in which a rotor  1  is supported for limited rotation by a base  2 . Through holes  3  are provided in the rotor  1  to allow access to base mounting holes  4  by which screws may mount the base  2  to a support structure. In this embodiment two parallel arcuate tracks  5  and  6  engage three balls  8  with tracks  5  and  6  having opposed arcuate surfaces as shown in FIGS. 12 and 13 respectively. The balls  8  two spaced apart in track  5  (FIG. 13) and one located centrally in track  6  (FIG. 12) are located by cages ( 15 ). By this means a smooth sensitive stable non-eccentric stage with a movement range typically of about 10° about the axis of rotation  12  of the rotor  1  is provided. 
     Now referring to FIGS. 19 and 20 a preferred  3  ball embodiment allowing an angular travel of the rotor  1  about the axis of rotation  12  typically of about 10° total under the spring  14  biased control of micrometer  13  or other actuator. The spring  14  located in base  2  engages a pin  20  fast with the rotor  1  and moveable in an opening  21  against the bias of spring  14  by micrometer  13  to pivot the rotor  1 , relative to the base, about axis  12 . 
     The goniometer of FIGS. 19 and 20 may be embodied in the same arrangements as described with reference to FIGS. 11-14 above. 
     It will be appreciated that in tracks having an arcuate V-groove opposing flat arcuate surface the arcuate V-groove may be located in either the base  2  and the arcuate flat surface on or in the rotor  1  or vise-versa. 
     Except where freedom of movement of a ball  8  along its associated arcuate groove is required the balls  8  are located by retaining cages (i.e. cage  15  in FIG.  19 ). Such retaining cages will be well known to those in the bearing arts. 
     The goniometer of FIGS. 21 and 22 has four balls  8  unconstrained by grooves or tracks. The balls  8  are retained by a cage  15 , common to all four balls  8 , to maintain ball pairs separated at desired spacings. As with the above described embodiments, this embodiment has a rotor  1  supported for limited rotation, about axis  12 , on a base  2 . As with FIGS. 19 and 20 a stop pin  20 , in an opening  21 , maybe provided to facilitate manual or motorized actuation. A stop  22  (ball, roller or friction slide) supported by a stop support  23  is provided and a spring  24  is positioned to urge the rotor  1  against the stop support  23  by way of the stop  22 . A possible variation permits the use of the track shown in FIG.  11 . It will be appreciated that the embodiment of FIGS. 21 and 22 is quite similar to the arrangement suggested by FIG. 14 which illustrates a captivation comprising two opposed flat arcuate surfaces without surface defining side walls. 
     To restrain longitudinal movement, a stop may be placed at any convenient point against the rotor. This “stop” may be a ball placed up against a plate attached to the base, and free to rotate with the rotor. 
     As used in this application “balls” shall be construed to include “rollers” in cases where the arcuate flat surfaces as shown in FIGS. 11 and 14 are used. 
     REFERENCE NUMBERS 
       1  rotor 
       2  base 
       3  through holes 
       4  base mounting holes 
       5  arcuate track 
       6  arcuate track 
       7  arcuate track 
       8  balls 
       9  arcuate V-groove 
       10  arcuate flat surface 
       11  arcuate V-grooves 
       12  axis of motion 
       13  micrometer 
       14  spring 
       15  cages 
       16  micrometer 
       17  two tracks 
       18  actuating mechanism 
       19  spring 
       20  pin 
       21  opening 
       22  stop 
       23  stop support 
       24  spring 
       25  spring