Abstract:
A flat surface tilting device including a selectably positionable flat surface element assembly defining a flat surface element having a flat surface and a pivot location portion, the pivot location portion being generally centered with respect to the flat surface, a pivot support element pivotably engaging the pivot location portion, an electromagnet, fixed with respect to the pivot support element and arranged for application of magnetic force in a direction generally perpendicular to the flat surface thereby to pivot the flat surface element about the pivot support element, a sensor for sensing the position of the flat surface element and feedback circuitry operative in response to an output of the sensor to govern operation of the electromagnet.

Description:
FIELD OF THE INVENTION 
   The present invention relates to tilting devices generally, and specifically to three-dimensional positioners. 
   BACKGROUND OF THE INVENTION 
   Tilting devices are employed in various applications. One typical application for a tilting device, although not the only application, is a fast steering mirror employed to quickly change the direction at which laser beams impinging thereon are deflected. 
   SUMMARY OF THE INVENTION 
   The present inventions seeks to provide an improved tilting device. 
   There is thus provided in accordance with an embodiment of the present invention a low-inertia flat surface tilting device having a selectably positionable flat surface element assembly having a flat surface element defining a flat surface and having a pivot location portion, the pivot location portion being generally centered with respect to the flat surface, a pivot support element pivotably engaging the pivot location portion, at least one electromagnet, fixed with respect to the pivot support element and arranged for application of magnetic force in a direction generally perpendicular to the flat surface thereby to pivot the flat surface element about the pivot support element, at least one sensor for sensing the position of the flat surface element and feedback circuitry operative in response to at least one output of the at least one sensor to govern operation of the at least one electromagnet. 
   Embodiments of the invention may include in the alternative one, or more, or none, of the following features: 
   The pivot location portion includes a recess in the flat surface element; 
   The pivot support element includes a shaft having a pivot point; 
   The pivot point has a generally spherical configuration. 
   The device includes a rotationally retaining magnet mounted onto an underside of the flat surface element which is magnetized in a manner which acts against rotation of the flat surface element about the pivot point. The rotationally retaining magnet includes, for example, a ring-shaped magnet; 
   The device includes at least one compression spring mounted onto the shaft and anchored to the flat surface element. The at least one compression spring is operative to prevent the flat surface element from rotating about the pivot point. 
   The pivot support element includes a first pair of spheres arranged along a first axis extending perpendicularly to the direction. The first pair of spheres may be in mutual touching, or non-touching arrangement. 
   The pivot location portion includes a second pair of spheres mounted onto an underside of the flat surface element, the second pair of spheres pivotably engaging the first pair of spheres and being arranged along a second axis extending generally perpendicular to the first axis and to the direction. The second pair of may be are in mutual touching arrangement, or non-touching arrangement. 
   At least one of the first pair of spheres and the second pair of spheres is formed of tungsten carbide. 
   The device also includes a retaining magnet, for example an annular magnet, which is operative to retain the flat surface element in pivotable engagement with the pivot support element. 
   The at least one electromagnet includes a plurality of electromagnets symmetrically distributed with respect to the pivot location portion. 
   The device includes at least one spring located opposite the at least one electromagnet with respect to the pivot location portion. 
   The at least one sensor includes a capacitive sensor. 
   Feedback circuitry controls tilting of the flat surface element about a single axis, thereby effecting a two-dimensional position of the flat surface element. Additionally or alternatively, the feedback circuitry controls tilting of the flat surface element about at least two axes, thereby effecting a three-dimensional position of the flat surface element. 
   The feedback circuitry includes first control circuitry operative to control positioning of the flat surface element about a first positioning axis, and second control circuitry operative to control positioning of the flat surface element about a second positioning axis which extends perpendicular to the first positioning axis. 
   The flat surface element includes a base for a mirror element. 
   There is also provided in accordance with another embodiment of the present invention a low-inertia flat surface tilting device including a selectably positionable flat surface element assembly including a flat surface element having a flat surface and a pivot location element including a first pair of spheres arranged along a first axis which extends parallel to the flat surface, the first pair of spheres being generally centered with respect to the flat surface, a pivot support element formed of a second pair of spheres arranged along a second axis which extends perpendicular to the first axis, the second pair of spheres pivotably engaging the first pair of spheres, at least one electromagnet, fixed with respect to the pivot support element and arranged for application of magnetic force to the flat surface thereby to pivot the flat surface element about the pivot support element, at least one sensor for sensing the position of the flat surface element and feedback circuitry operative in response to at least one output of the at least one sensor for governing operation of the at least one electromagnet. 
   This embodiment of the invention includes, alternatively and additionally, one or more or none of the features detailed hereinabove. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
       FIG. 1  is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with an embodiment of the present invention; 
       FIGS. 2A ,  2 B and  2 C are respective side view illustrations of the tilting device of  FIG. 1  in respective intermediate orientation, first extreme orientation and second extreme orientation; 
       FIG. 3  is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with another embodiment of the present invention; 
       FIGS. 4A ,  4 B and  4 C are respective side view illustrations of the tilting device of  FIG. 3  in respective intermediate orientation, first extreme orientation and second extreme orientation; 
       FIG. 5  is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with yet another embodiment of the present invention; 
       FIGS. 6A ,  6 B and  6 C are respective side view illustrations of the tilting device of  FIG. 5  in respective intermediate orientation, first extreme orientation and second extreme orientation; 
       FIG. 7  is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with still another embodiment of the present invention; 
       FIG. 8  is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with a further embodiment of the present invention; and 
       FIG. 9  is a simplified block diagram of the tilting devices of  FIGS. 1-8  and of control circuitry used therein. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   Reference is now made to  FIG. 1 , which is a simplified, partially cut-away pictorial illustration of a low-inertia tilting device constructed and operative in accordance with an embodiment of the present invention and to  FIGS. 2A ,  2 B and  2 C which are respective side view illustrations of the tilting device of  FIG. 1  in respective intermediate orientation, first extreme orientation and second extreme orientation. 
     FIGS. 1-2C  illustrate a tilting device, such as a three-dimensional positioner, typically comprising a base  10  onto which is mounted a central shaft  12  having a support point  14 , which has a generally spherical configuration having a diameter of about 1.5 mm. An annular magnet  16  is mounted onto central shaft  12  and is positioned thereon such that a top surface  18  thereof is spaced vertically below the extreme end of support point  14 . Magnet  16  is operative to apply an attractive magnetic force on an object to be positioned, such as a flat plate  20 , which is suitably formed at least partially of a ferromagnetic material. 
   An additional magnet  22  which is typically mounted onto an underside of flat plate  20  and which in an embodiment of the invention is a ring-shaped magnet, is operative, when appropriately magnetized, to prevent the flat plate  20  from rotating about a longitudinal axis of shaft  12 . Flat plate  20  suitably functions as a base for a mirror  24  and is formed with a central recess  26  for receiving support point  14  of shaft  12 . Alternatively, flat plate  20  may have any other suitable function and may be part of an actuator or a positioner. 
   Spaced radially outwardly from support shaft  12  are a plurality of displacers, suitably electromagnets, which when actuated, attract flat plate  20 . In the illustrated embodiment four such displacers  28 ,  30 ,  32  and  34  are provided and are generally uniformly spaced from each other, it being appreciated that a greater or lesser number and any suitable configuration of the displacers may alternatively be employed depending on the application. It is appreciated that a first axis  35  extends between displacers  30  and  34 , and a second axis  36 , which is not parallel and suitably perpendicular to the first axis  35 , extends between displacers  28  and  32 . 
   As seen most clearly from a consideration of  FIGS. 2A-2C , the top surfaces of displacers  28 ,  30 ,  32  and  34  are spaced vertically below the support point  14  and thus below the bottom of plate  20 , when it is in a generally horizontal orientation, as shown in  FIG. 2A . The operation of displacers  28 ,  30 ,  32  and  34  is governed by control circuitry, which is designated by reference numerals  37  and  38  in  FIG. 9  and is described in greater detail hereinbelow with reference to  FIG. 9 . 
   In accordance with an embodiment of the present invention, a plurality of propinquity sensors, suitably four capacitive sensors  40 , are mounted on a support  42  which is parallel to base  10 , vertically below flat plate  20  and radially outward with respect to the support point  14 . Propinquity sensors  40  together provide an output indication of the three-dimensional orientation of plate  20  to the control circuitry, which serves as a feedback indication which assists the control circuitry in governing the operation of displacers  28 ,  30 ,  32  and  34 . It is appreciated that the propinquity sensors  40  are azimuthally offset by approximately 45 degrees with respect to displacers  28 ,  30 ,  32  and  34 . This offset is taken into account by the control circuitry when determining the three-dimensional positioning of flat plate  20 . 
     FIGS. 2A ,  2 B and  2 C are respective side view illustrations of the tilting device of  FIG. 1  in respective intermediate, first extreme orientation and second extreme orientation. It is appreciated that the apparatus of  FIGS. 1-2C  is capable of positioning plate  20  at any three-dimensional position within the limits illustrated in  FIGS. 2A-2C . 
   Reference is now made to  FIG. 3 , which is a simplified, partially cut-away pictorial illustration of a tilting device constructed and operative in accordance with another embodiment of the present invention and to  FIGS. 4A ,  4 B and  4 C which are respective side view illustrations of the tilting device of  FIG. 3  in respective intermediate orientation, first extreme orientation and second extreme orientation. 
     FIGS. 3-4C  illustrate a tilting device, such as a three-dimensional positioner, typically comprising a base  110  onto which is mounted a central shaft  112  having support point  114 , suitably having a generally spherical configuration having a diameter of about 1.5 mm. 
   An object to be positioned, such as a flat plate  120 , is suitably formed at least partially of a ferromagnetic material, functions as a base for a mirror  124  and is typically formed with a central recess  126  for receiving support point  114  of shaft  112 . Alternatively flat plate  120  may have any other suitable function and may be part of an actuator or a positioner. 
   Spaced radially outwardly from support shaft  112  are a plurality of displacers including a pair of active displacers  128  and  130 , which when actuated, attract plate  120 , and a pair of passive displacers  132  and  134 , which typically include springs. In the illustrated embodiment, the displacers are generally uniformly spaced from each other. It is appreciated that a greater or lesser number of passive and active displacers may be employed depending on the application. 
   Active displacers  128  and  130  comprise electromagnets, and passive displacers  132  and  134  are located respectively opposite displacers  128  and  130 . Passive displacers  132  and  134  each include a tension coil spring  136  having a first end anchored, via an anchoring structure, to base  110  and a second end fixed, via an attachment disk  137 , to an underside of plate  120 . Passive displacers  132  and  134  provide a force which is directed oppositely to the force applied to flat plate  120  by the electromagnets  128  and  130 . It is appreciated that a first axis  138  extends between displacers  130  and  134 , and a second axis  139 , which is not parallel and suitably perpendicular to first axis  138 , extends between displacers  128  and  130   
   As seen most clearly from a consideration of  FIGS. 4A-4C , the top surfaces of displacers  128  and  130  are spaced vertically below the support point  114  and thus below the bottom of plate  120 , when it is in a generally horizontal orientation, as shown in  FIG. 4A . The operation of electromagnets  128  and  130  is governed by control circuitry which is designated by reference numerals  37  and  38  in  FIG. 9  and is described in greater detail hereinbelow with reference to  FIG. 9 . 
   In accordance with an embodiment of the present invention, a plurality of propinquity sensors, suitably four capacitive sensors  140 , are mounted on a support  142  which is parallel to base  110 , vertically below flat plate  120  and radially outward with respect to the support point  114 . Propinquity sensors  140  together provide an output indication of the three-dimensional orientation of plate  120  to the control circuitry, which serves as a feedback indication which assists the control circuitry in governing the operation of displacers  128  and  130 . It is appreciated that the propinquity sensors  140  are azimuthally offset by approximately 45 degrees with respect to displacers  128 ,  130 ,  132  and  134 . This offset is taken into account by the control circuitry when determining the three-dimensional positioning of flat plate  120 . 
     FIGS. 4A ,  4 B and  4 C are respective side view illustrations of the tilting device of  FIG. 3  in respective intermediate, first extreme orientation and second extreme orientation which is the equilibrium orientation. 
   In the orientation shown in  FIG. 4A , the attractive force applied by the electromagnets  128  and  130  is equal to the force applied by springs  136 , thereby maintaining the flat plate  120  in a horizontal, intermediate orientation, wherein the flat plate  120  is generally parallel to base  110 . 
   In a first extreme orientation shown in  FIG. 4B , the attractive force applied by the electromagnets  128  and  130  is greater than the force applied by springs  136 , thereby causing springs  136  to extend, and tilting the flat plate  120  in a first direction with respect to base  110 . It is appreciated that when the electromagnets  128  and  130  are not actuated, the springs  136  compress to their relaxed state, thereby causing flat plate  120  to be in its equilibrium orientation, shown in  FIG. 4C . 
   It is appreciated that the apparatus of  FIGS. 3-4C  is capable of positioning plate  120  at any three dimensional position within the limits illustrated in  FIGS. 4A-4C . 
   Reference is now made to  FIG. 5 , which is a simplified, partially cut-away pictorial illustration of a low-inertia tilting device constructed and operative in accordance with yet another embodiment of the present invention and to  FIGS. 6A ,  6 B and  6 C which are respective side view illustrations of the tilting device of  FIG. 5  in respective intermediate orientation, first extreme orientation and second extreme orientation. 
     FIGS. 5-6C  illustrate a tilting device, such as a three-dimensional positioner, typically comprising a base  150  onto which is mounted a central shaft  152  having a support point  154 . In the embodiment seen in  FIGS. 5-6C , support point  154  has a generally spherical configuration having a diameter of about 1.5 mm, although this need not be the case. A compression spring  156  is mounted around shaft  152 , a bottom end of spring  156  being anchored to shaft  152  and a top end of spring  156  being anchored to an attachment disk  158 . Attachment disk  158  is anchored to an underside of an object to be positioned, such as a flat plate  160 , which is suitably formed of an at least partially of a ferromagnetic material. The anchoring of attachment disk  158  to flat plate  160  is operative to hold flat plate  160  in pivotal contact with shaft  152  and to prevent flat plate  160  from rotating about a longitudinal axis of shaft  152 . 
   Flat plate  160  suitably functions as a base for a mirror  164  and is typically formed with a central recess  166  for receiving support point  154  of shaft  152 . Central recess suitably is generally pyramidal in shape. Alternatively flat plate  160  may have any other suitable function and may be part of an actuator or a positioner. 
   Spaced radially outwardly from support shaft  152  are a plurality of displacers, suitably electromagnets, which when actuated, attract flat plate  160 . In the illustrated embodiment four such displacers  168 ,  170 ,  172  and  174  are provided and are generally uniformly spaced from each other, it being appreciated that a greater or lesser number and any suitable configuration of the displacers may alternatively be employed depending on the application. It is appreciated that a first axis  175  extends between displacers  170  and  174 , and a second axis  176 , which is suitably not parallel and generally perpendicular to the first axis  175 , extends between displacers  168  and  172 . 
   As seen most clearly from a consideration of  FIGS. 6A-6C , the top surfaces of displacers  168 ,  170 ,  172  and  174  are spaced vertically below the support point  154  and thus below the bottom of plate  160 , when it is in a generally horizontal orientation, as shown in  FIG. 6A . The operation of displacers  168 ,  170 ,  172  and  174  is governed by control circuitry, which is designated by reference numerals  37  and  38  in  FIG. 9  and is described in greater detail hereinbelow with reference to  FIG. 9 . 
   In accordance with an embodiment of the present invention, a plurality of propinquity sensors, suitably four capacitive sensors  180 , are mounted on a support  182  which is parallel to base  150 , vertically below flat plate  160  and radially outward with respect to the support point  154 . Propinquity sensors  180  together provide an output indication of the three-dimensional orientation of plate  160  to the control circuitry, which serves as a feedback indication which assists the control circuitry in governing the operation of displacers  168 ,  170 ,  172  and  174 . It is appreciated that the propinquity sensors  180  are azimuthally offset by approximately 45 degrees with respect to displacers  168 ,  170 ,  172  and  174 . This offset is taken into account by the control circuitry when determining the three-dimensional positioning of flat plate  160 . 
     FIGS. 6A ,  6 B and  6 C are respective side view illustrations of the tilting device of  FIG. 5  in respective intermediate, first extreme orientation and second extreme orientation. It is appreciated that the apparatus of  FIGS. 5-6C  is capable of positioning plate  160  at any three-dimensional position within the limits illustrated in  FIGS. 6A-6C . 
   Reference is now made to  FIG. 7 , which illustrates a tilting device, such as a three-dimensional positioner, typically comprising a base  210 , which is typically in a horizontal plane, onto which is mounted a central shaft  212 . Mounted onto a top surface of central shaft  212  is a pivot support assembly  214 , which in the embodiment seen, comprises a pair of spheres  215 , suitably formed of tungsten carbide, which are arranged along a first axis  216  which is parallel to base  210 . Spheres  215  are arranged in mutual touching arrangement, although this need not be the case. 
   An annular magnet  217  is mounted onto central shaft  212 . Magnet  217  is operative to apply an attractive magnetic force on an object to be positioned, such as a flat plate  220 , suitably formed at least partially of a ferromagnetic material. Mounted onto an underside surface of flat plate  220  is a pivot location assembly  221 , which in the embodiment seen, comprises a pair of spheres  222 , suitably formed of tungsten carbide, which are arranged along a second axis  223 . Spheres  223  are arranged in mutual touching arrangement, although this need not be the case. Second axis  223  is perpendicular to first axis  216  and is parallel to the plane of plate  220 . 
   The arrangement of spheres  215  and  222  along respective axes  216  and  223  tends to prevent the flat plate  220  from rotating about a longitudinal axis of shaft  212 , which extends perpendicular to base  210 . Flat plate  220  suitably functions as a base for a mirror  224 . Alternatively flat plate  220  may have any other suitable function and may be part of an actuator or a positioner. 
   Spaced radially outwardly from support shaft  212  are a plurality of displacers, suitably electromagnets, which when actuated, attract flat plate  220 . In the illustrated embodiment, four such displacers  228 ,  230 ,  232  and  234  are provided and are generally uniformally spaced from each other, it being appreciated that a greater or lesser number and alternative configurations may alternatively be employed depending on the application. It is appreciated that a first axis  236  extends between displacers  230  and  134 , and a second axis  238 , which is not parallel and suitably perpendicular to the first axis  236 , extends between displacers  228  and  232 . It is appreciated that axes  236  and  238  need not necessarily be related to axes  216  and  223 . 
   Similarly to that shown and described hereinabove with reference to  FIGS. 2A-2C , the top surfaces of displacers  228 ,  230 ,  232  and  234  are spaced vertically below the plate  220 , when it is in a generally horizontal orientation. The operation of displacers  228 ,  230 ,  232  and  234  is governed by control circuitry similar to the control circuitry similar to the control circuitry designated by reference numerals  37  and  38  in  FIG. 9  and is described in greater detail hereinbelow with reference to  FIG. 9 . 
   In accordance with an embodiment of the present invention, a plurality of propinquity sensors, suitably four capacitive sensors  240 , are mounted on a support  242  which is parallel to base  210 , vertically below flat plate  220  and radially outward with respect to support shaft  212 . Propinquity sensors  240  together provide an output indication of the three-dimensional orientation of plate  220  to the control circuitry, which serves as a feedback indication which assists the control circuitry in governing the operation of displacers  228 ,  230 ,  232  and  234 . It is appreciated that the propinquity sensors  240  are azimuthally offset by approximately 45 degrees with respect to displacers  228 ,  230 ,  232  and  234 . This offset is taken into account by the control circuitry when determining the three-dimensional positioning of flat plate  220 . 
   It is appreciated that the apparatus of  FIG. 7  is capable of positioning plate  220  at any three dimensional position within predetermined limits which are defined at least partially by the heights and positioning of displacers  228 ,  230 ,  232  and  234 . 
   Reference is now made to  FIG. 8 , which illustrates a tilting device, such as a three-dimensional positioner, typically comprising a base  310 , which is typically in a horizontal plane, onto which is suitably mounted a central shaft  312 . Suitably mounted onto a top surface of central shaft  312  is a pivot support assembly  314 , suitably comprising a pair of spheres  315 , suitably formed of tungsten carbide, which are arranged along a first axis  316  which is parallel to base  310 , suitably, but not necessarily, in mutual touching arrangement. 
   An object to be positioned, such as a flat plate  320 , is formed at least partially of a ferromagnetic material and has mounted onto an underside surface thereof a pivot location assembly  321 , suitably comprising a pair of spheres  322 . Spheres  322  are suitably formed of tungsten carbide and are arranged along a second axis  323 , suitably, but not necessarily, in mutual touching arrangement. Second axis  323  is perpendicular to first axis  316  and parallel to the plane of plate  320 . 
   The arrangement of spheres  315  and  322  along respective axes  316  and  323  tends to prevent the flat plate  320  from rotating about a longitudinal axis of shaft  312 , which extends perpendicular to base  310 . Flat plate  320  suitably functions as a base for a mirror  324 . Alternatively flat plate  320  may have any other suitable function and may be part of an actuator or a positioner. 
   Spaced radially outwardly from support shaft  312  are a plurality of displacers including a pair of active displacers  328  and  330 , which when actuated, attract plate  320 , and a pair of passive displacers  332  and  334 , which typically include springs. In the illustrated embodiment, the displacers are generally uniformly spaced from each other, it being appreciated that alternative configurations and a greater or lesser number of active and passive displacers may alternatively be employed depending on the application. 
   Active displacers  328  and  330  comprise electromagnets, and passive displacers  332  and  334  are located respectively opposite displacers  328  and  330 . Passive displacers  332  and  334  suitably include tension coil springs  336  having a first end anchored, via an anchoring structure, to base  310  and a second end fixed, via an attachment disk  337 , to an underside of flat plate  320 . Passive displacers  332  and  334  provide a force which is directed oppositely to the force applied to flat plate  320  by the electromagnets  328  and  330 . It is appreciated that a first axis  338  extends between displacers  328  and  332 , and a second axis  339 , which is not parallel and suitably perpendicular to the first axis  338 , extends between displacers  330  and  334 . It is appreciated that axes  338  and  339  need not necessarily be related to axes  316  and  323 . 
   Similarly to that shown and described hereinabove with reference to  FIGS. 4A-4C , the top surfaces of displacers  328  and  330  are spaced vertically below the bottom of flat plate  320 , when it is in a generally horizontal orientation. The operation of electromagnets  328  and  330  is governed by control circuitry similar to the control circuitry designated by reference numerals  37  and  38  in  FIG. 9  and is described in greater detail hereinbelow with reference to  FIG. 9 . 
   In accordance with an embodiment of the present invention, a plurality of propinquity sensors, suitably four capacitive sensors  340 , are mounted on a support  342  which is parallel to base  310 , vertically below flat plate  320  and radially outward with respect to shaft  312 . Propinquity sensors  340  together provide an output indication of the three-dimensional orientation of plate  320  to the control circuitry, which serves as a feedback indication which assists the control circuitry in governing the operation of displacers  328  and  330 . It is appreciated that the propinquity sensors  340  are azimuthally offset by approximately 45 degrees with respect to displacers  328 ,  330 ,  332  and  334 . This offset is taken into account by the control circuitry when determining the three-dimensional location of flat plate  320 . 
   It is appreciated that the apparatus of  FIG. 8  is capable of positioning plate  320  at any three dimensional position within predetermined limits which are defined at least partially by the heights and positioning of displacers  328 ,  330 ,  332  and  334 . 
   Reference is now made to  FIG. 9 , which is a simplified block diagram of the tilting devices of  FIGS. 1-8  and of control circuitry used therein, such as the control circuitry shown in  FIGS. 1-8 , which is operative to control the operation of the tilting device of  FIGS. 1-8 . 
   As seen in  FIG. 9 , tilting of a positionable element  400 , such as flat plates  20 ,  120 ,  220  and  320  ( FIGS. 1-8 ), about a first axis, such as axis  36  ( FIG. 1 ) which joins displacers  28  and  32  ( FIG. 1 ), is controlled by a first control system  37 , such as an X-axis control system, and tilting of the element  400  about a second axis, such as axis  35  ( FIG. 1 ) which joins displacers  30  and  34  ( FIG. 1 ), is controlled by a second control system  38 , such as a Y-axis control system. 
   Control system  37  receives a command signal, for example and error signal, indicating a required orientation change of element  400  along the first axis. The command signal for the X-axis is provided by summation circuitry  408  which compares the X-axis portion of a desired orientation signal, provided by an external control system (not shown), with a sensed X-axis position of element  400 , and calculates the difference between the sensed X-axis position of the element  400  and the desired X-axis position of the element to thereby indicate the required orientation change of element  400  along the first axis. 
   A first control filter  410  receives the command signal which it processes, for example by amplification, so that suitably small incremental changes in position of element  400  can be effected. The output of control filter  410  is provided as an input to first pre-driver control circuitry  412 . The pre-driver control circuitry  412  calculates the power required by X-axis displacers  418  and  420 , such as displacers  30  and  34  shown in  FIG. 1 , to effect a desired displacement of positionable element  400  along the X-axis. Pre-driver control circuitry  412  outputs signals to drivers  414  and  416  respectively indicating the respective power requirements required by X-axis displacers  418  and  420 , and drivers  414  and  416  provide suitably amplified signals to these displacers to effect X-axis positioning of element  400 . 
   In a similar manner, control system  38  receives a command signal, for example an error signal, indicating a required orientation change of element  400  along the second axis. The command signal command signal for the Y-axis is provided by summation circuitry  428  which compares the Y-axis portion of a desired orientation signal, provided by an external control system (not shown), with a sensed Y-axis position of element  400 , and calculates the difference between the sensed Y-axis position of the element  400  and the desired Y-axis position of the element to thereby indicate the required orientation change of element  400  along the second axis. 
   A second control filter  430  receives the command signal which it processes, for example by amplification, so that suitably small incremental changes in position of element  400  can be effected. The output of control filter  430  is provided as an input to second pre-driver control circuitry  432 . The pre-driver control circuitry  432  calculates the power required by Y-axis displacers  438  and  440 , such as displacers  28  and  32  shown in  FIG. 1 , to effect a desired displacement of positionable element  400  along the Y-axis. Pre-driver control circuitry  432  outputs signals to drivers  434  and  436  respectively indicating the respective power requirements required by Y-axis displacers  438  and  440 , and drivers  434  and  436  provide suitably amplified signals to these displacers to effect Y-axis positioning of element  400   
   At selected time intervals the position of element  400  is sensed by X-axis sensors  423  and  424 , and by Y-axis sensors  443  and  444 , for example by sensors  40  ( FIG. 1-2C ) and fed back to control circuitry  37  and  38 . Outputs from these sensors are provided to a sensor processor  450  which calculates the respective X-axis and Y-axis orientation of element  400 , taking into account a rotational orientation of sensors  423 ,  424 ,  443  and  444  with respect to their respective axes, as defined by corresponding displacers  418  and  420 ,  438  and  440 . Sensor processor  450  outputs an X-axis orientation signal to first summation circuitry  408  which is used by control circuitry  37 , and a Y-axis orientation signal to second summation circuitry  428  which is used by control circuitry  38 . A control loop is thus closed for both X and Y axes. 
   It is appreciated that in the embodiments shown in  FIG. 1-8 , by position sensing and displacing element  400 , such as flat plate  20 ,  120 ,  160 ,  220  and  320  in  FIGS. 1-8 , along two orthogonal axes, a multitude of orientations in three dimensional space may be effected. Furthermore, it is appreciated that in the embodiments shown in  FIGS. 3-4C  and  8 , the control circuitry  38  only controls a single displacer, such as displacer  130  ( FIG. 3 ), but receives feedback from a pair of sensors. 
   It will be apparent to persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of features described and shown hereinabove as well as variations thereof which would occur to persons skilled in the art upon seeing the foregoing description and drawings and which are not in the prior art.