Abstract:
A non-mechanical gimbal system is presented. The gimbal system includes a gimbal housing, including hemispherical and annular caps, rotatable sphere, and at least two curvilinear actuators. The hemispherical cap is attached to the annular cap in a removable fashion so as to surround the rotatable sphere. The curvilinear actuators are disposed between the rotatable sphere and gimbal housing. Curvilinear actuators rotate the rotatable sphere, via shear induced motion, with respect to the interior surface of the gimbal housing. The present invention has immediate applicability within security devices, games, toys, weapons (including guidance systems and aiming), and communication systems.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims priority under 35 U.S.C. § 119(e) from U.S. Provisional Application No. 60/692,938 filed Jun. 22, 2005, entitled “Solid State Gimbal System”, the contents of which are hereby incorporated in its entirety by reference thereto. 

   FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   The invention disclosed herein was supported, at least in part, by a grant from the Defense Advance Research Projects Agency (DARPA) under DARPA Order No. S039-38 issued by the U.S. Army Aviation and Missile Command under Contract No. W31P4Q-05-C-0180. The Government has certain limited rights to at least one form of the invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a gimbal system. Specifically, the invention is a lightweight, robust gimbal actively controllable via curvilinear piezo-actuators operating in the shear mode which directly contact and rotate a spherical-shaped element within a like-shaped housing. 
   2. Description of the Related Art 
   Games, toys, weapons and communication systems typically couple an acoustic-based device, a light-based device, an imaging device or the like to hardware for the purpose of transmitting, recording, detecting, classifying, and/or tracking. Presently known devices are aimed by a variety of steering methods. 
   Altitude-azimuth steering systems are typically composed of gyroscopes, motors, rings, and bearings. Exemplary systems include a gyroscope and mechanically complicated inner and outer gimbal elements, so as to achieve tilt within a range limited by the size of components within and packaging of the system. As such, altitude-azimuth systems are inherently complex, costly, and heavy. Furthermore, components are susceptible to stiction, fretting, and friction, which limit and frustrate the translation of any device mounted to the gimbal. 
   Waveguide steering includes various approaches. For example, an array of actuators might translate a microlens array along orthogonal lateral directions. Large two-dimensional lenslet arrays are possible wherein pixels are independently controlled. In another example, liquid crystal optical phase arrays (LC-OPAs) steer a beam via a phase change electrically introduced along the array. Steering results when an incident beam sees a varying refractive index as it propagates along the array. While the described approaches accurately steer a beam to within submicron accuracy, both are mechanically and electrically complex, difficult and costly to manufacture, fragile, and unreliable in and/or unsuitable to many applications. 
   Several steering systems based upon piezoelectric actuators are also noteworthy. 
   Nishimura et al., in U.S. Pat. No. 6,734,914, describes and claims an image recording unit permitting 360 degrees of rotation. The device includes four sets of piezoelectric elements, a rotary unit fixing frame, and a spherical rotary unit. Piezoelectric elements operate in the longitudinal mode, whereby each linear rectangular actuator is electrically poled and driven through its thickness, referred to as the d 33  mode, or is electrically poled through its thickness and driven along its length, referred to as the d 31  mode. The spherical rotary unit contacts and presses against the fixing frame. Piezoelectric elements are arranged and electrically activated in a pair-wise fashion so that a traveling wave is formed in the fixing frame around either the Y-axis and/or X-axis. Thereafter, the fixing frame exhibits motion which is communicated to the spherical rotary unit so as to frictionally drive the rotary unit. As such, the piezoelectric elements do not directly drive the spherical rotary unit. 
   Johansson, in U.S. Pat. No. 6,437,485, describes and claims a double bimorph electromechanical element capable of rotating an element via bending motion along the piezoelectric device. 
   Sugaya, in U.S. Pat. No. 5,872,417, describes and claims a device capable of rotating a sphere via a plurality of piezoelectric elements that first vibrate an elastic member which is thereafter communicated into the sphere as rotational motion. 
   Staufenberg, Jr. et al. in U.S. Pat. No. 4,727,278 describes and claims a device capable of rotating a sphere via the electromechanical translation of linear piezoelectric elements which expand and contract in response to electrical signals. 
   The related arts do not provide a gimbal device capable of rapidly rotating a sphere via the direct contact by curvilinear actuators comprised of a piezoelectric material operating in the shear mode, also referred to as d 12 , d 14 , d 15 , or d 16  mode. 
   Therefore, what is required is a lightweight, low-volume, and mechanically simple gimbal device which provides for the direct rotational drive of a spherical element by curvilinear piezoelectric actuators operating in the shear mode. 
   SUMMARY OF INVENTION 
   An object of the present invention is to provide a lightweight, low-volume, and mechanically simple gimbal device which provides for the direct rotational drive of a spherical element by curvilinear piezoelectric actuators operating in the shear mode. 
   In the present invention, a rotatable sphere is accurately rotated and positioned within a gimbal housing by four non-bimorph piezoelectric actuators. Piezoelectric actuators operate in a shear mode (such as d 15 ) rather than a longitudinal mode (d 31  or d 33 ). Shear mode motion includes both linear and bending components within the same piezoelectric material. The shear mode is achieved by a combination of two voltage directions whereby a piezo-ceramic is poled from end to end along the longest length of the actuator and electrically powered via electrodes disposed about the thickness of the same actuator. Shear mode actuators ensure greater electromechanical coupling and as such are capable of directly driving the rotatable sphere. 
   The present invention is a modular solid state gimbal system comprised of a gimbal housing, including hemispherical and annular caps, rotatable sphere, and at least two curvilinear actuators. The hemispherical cap is attached to the annular cap in a removable fashion so as to surround the rotatable sphere. The rotatable sphere has a radius of curvature less than that of the gimbal housing. Curvilinear actuators are disposed between the rotatable sphere and gimbal housing. Curvilinear actuators rotate the rotatable sphere, via shear induced motion, with respect to the interior surface of the gimbal housing. Hemispherical and annular caps are dimensionally sized to compress the curvilinear actuators against the rotatable sphere. An acoustic, light, or optical device may be attached to the rotatable sphere so as to allow precision aiming of the device at a high angular rate over a wide acceptance angle. 
   Several advantages are noteworthy. The present invention is scalable for use within many applications, including MEMS. The present invention requires substantially less power than mechanically actuated gimbals. The present invention has substantially less moving parts than mechanically actuated gimbals, thereby providing higher operational reliability. The present invention is lighter and smaller than mechanically actuated gimbals. The present invention enables a large field of view over a wide acceptance angle with higher angular rotation rates and precision than mechanically actuated gimbals. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               REFERENCE NUMERALS 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                1 
               Gimbal system 
             
             
                 
                2 
               Hemispherical cap 
             
             
                 
                3 
               Rotatable sphere 
             
             
                 
                4 
               Socket 
             
             
                 
                5 
               Spherical profile 
             
             
                 
                6 
               Device 
             
             
                 
                7a-7d 
               Curvilinear actuator 
             
             
                 
                8 
               Field of view 
             
             
                 
                9 
               Electrode 
             
             
                 
               10 
               Piezoelectric layer 
             
             
                 
               11 
               Electrode 
             
             
                 
               12 
               Storage medium 
             
             
                 
               13 
               Programmable logic device 
             
             
                 
               14 
               USB module 
             
             
                 
               15 
               Sensor 
             
             
                 
               16 
               Support cavity 
             
             
                 
               17 
               Central axis 
             
             
                 
               18 
               Protrusion 
             
             
                 
               19 
               Curvilinear actuator 
             
             
                 
               20 
               Annular cap 
             
             
                 
               21 
               Gimbal housing 
             
             
                 
               22 
               Opening 
             
             
                 
               23 
               Opening 
             
             
                 
               24 
               Channel 
             
             
                 
               25 
               Optical tracker 
             
             
                 
               26 
               Joystick 
             
             
                 
               27 
               Controller 
             
             
                 
               28 
               Direct digital synthesizer 
             
             
                 
               29 
               Direct digital synthesizer 
             
             
                 
               30 
               Target 
             
             
                 
               31a-31b 
               Receiver 
             
             
                 
               32 
               Phase detector 
             
             
                 
               33 
               Position controller 
             
             
                 
               34 
               Acoustic tracking system 
             
             
                 
               35 
               Variable gain amplifier 
             
             
                 
               36 
               Amplifier 
             
             
                 
               37 
               Amplifier 
             
             
                 
               38 
               Optical sensor 
             
             
                 
               39a-39d 
               Curvilinear actuator 
             
             
                 
               40a-40c 
               Target 
             
             
                 
               41 
               Image Processor 
             
             
                 
               42 
               Position controller 
             
             
                 
               43 
               Optical tracking system 
             
             
                 
               44 
               Seam 
             
             
                 
                 
             
           
        
       
     
   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view showing one embodiment of the solid state gimbal system for the present invention. 
       FIG. 2  is a cross sectional view of the present invention showing the solid state gimbal system including a gimbal housing comprised of a lower hemispherical cap and an upper annular cap mutually attached and surrounding a rotatable sphere with four curvilinear actuators disposed between and compressed by the sphere and housing. 
       FIG. 3  is an exploded section view of the gimbal system embodiment described in  FIGS. 1 and 2 . 
       FIG. 4  is a top view of the gimbal system shown in  FIGS. 1 and 2  without rotatable sphere showing the paired and opposed arrangement of curvilinear actuators along both the X-axis and the Y-axis. 
       FIG. 5  is an enlarged section view of the hemispherical cap showing exemplary curvilinear actuators composed of a piezoelectric layer disposed between a pair of electrodes. 
       FIG. 6  is a side view of an alternate embodiment for the curvilinear actuators having a plurality of protrusions outwardly disposed along and projecting from one electrode. 
       FIG. 7  is a top view of the curvilinear actuator in  FIG. 6  showing a row-column arrangement of protrusions. 
       FIG. 8  shows a side elevation view of the solid state gimbal system having an optical tracker attached to the gimbal housing adjacent to the opening at the back end of the gimbal housing. 
       FIG. 9  is a block diagram for an exemplary embodiment showing data acquisition from a sensor attached to the gimbal system. 
       FIG. 10  is a schematic block diagram for an exemplary application of the present invention within an acoustic tracking system. 
       FIG. 11  is a schematic block diagram for an exemplary application of the present invention within an optical tracking system. 
       FIG. 12  is a block diagram for an exemplary application of the present invention including a joystick used to control the position of the rotatable sphere within the gimbal system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , the gimbal system  1  is shown in a perspective view including a rotatable sphere  3  disposed within a gimbal housing  21 , comprising a hemispherical cap  2  and an annular cap  20 , with at least two curvilinear actuators  7   a ,  7   d  (actuators  7   b  and  7   c  not shown) disposed between the rotatable sphere  3  and gimbal housing  21 . The rotatable sphere  3  and gimbal housing  21  are dimensioned so as to form a press or compression fit with the curvilinear actuators  7   a - 7   d  sufficiently to fix the rotatable sphere  3  in a specific orientation when the curvilinear actuators  7   a - 7   d  are electrically inactive. It is also required for the press or compression fit to allow rotation of the rotatable sphere  3  when the curvilinear actuators  7   a - 7   d  are activated by an electric field. 
   Referring now to  FIGS. 2 and 3 , the gimbal system  1  is shown in more detail comprised of a hemispherical cap  2 , an annular cap  20 , curvilinear actuators  7   a - 7   d , and a rotatable sphere  3 . Hemispherical cap  2 , rotatable sphere  3 , and annular cap  20  are preferred to be composed of dimensionally stable and non-conductive materials, non-limiting examples including polymers and composites. Furthermore, the rotatable sphere  3  may include a dense metal insert to increase its total mass without compromising the non-conductive nature of the element. The gimbal housing  21  may be fabricated via conventional manufacturing methods, including machining, stereo lithography, injection molding, and extrusion. Curvilinear actuators  7   a ,  7   b  (actuators  7   c  and  7   d  not shown) are generally composed of a piezoelectric material, preferably a piezoceramic, one example being PZT, disposed between a pair of electrically conductive elements, preferably composed of a metal. Conventional methods are also applicable to the fabrication, poling, and electroding of curvilinear actuators  7   a - 7   d.    
   The gimbal housing  21  is composed of a two-piece construction, namely, hemispherical cap  2  and annular cap  20 , so as to facilitate assembly of the rotatable sphere  3  and curvilinear actuators  7   a - 7   d  into the interior cavity of the gimbal system  1 . The annular cap  20  may be mechanically or adhesively fastened to the hemispherical cap  2  along a mutually aligned and contacting seam  44  or flange arrangement. While it is preferred for the seam  44  between the hemispherical cap  2  and annular cap  20  to be located along the center of the gimbal housing  21 , the location of the seam  44  must provide an opening of sufficient diameter so as to allow insertion of the rotatable sphere  3  into the gimbal housing  21 . The interior contour of the gimbal housing  21  is preferred to be spherically shaped and dimensionally larger than the diameter of the rotatable sphere  3 . 
   Curvilinear actuators  7   a - 7   d  are generally described as elongated elements disposed in a radial fashion about the central axis  17  and contacting both hemispherical cap  2  and annular cap  20  along a first surface and the rotatable sphere  3  along a second surface. Each curvilinear actuator  7   a - 7   d  contacts the interior of the hemispherical cap  2  beginning at the seam  44  and ending adjacent to opening  22  which resides at the bottom of the hemispherical cap  2 . Likewise, each curvilinear actuator  7   a - 7   d  contacts the interior of the annular cap  20  beginning at the seam  44  and ending adjacent to the opening  23  at the top of the annular cap  20 . While an infinite number of designs are possible for the present invention, it was preferred for each curvilinear actuator  7   a - 7   d  to sufficiently long so as to provide an arc with a total angle from 80 to 90 degrees. In some embodiments, it may be preferred to include a layer of soft material, examples including felt or rubber, between the rotatable sphere  3  and hemispherical cap  2  and annular cap  20  to reduce the damping of the shear mode dynamics within the curvilinear actuators  7   a - 7   d  by the gimbal housing  21 . In other embodiments, it may be preferred to adhesively bond the curvilinear actuators  7   a - 7   d  to the hemispherical cap  2  and/or annular cap  20 . 
   In some embodiments of the invention, it was preferred for the curvilinear actuators  7   a - 7   d  to exhibit both bending mode and shear mode vibrations. The coupling of these two modes was found to be dependent on the length-to-thickness ratio of the curvilinear actuators  7   a - 7   d . While mode coupling is possible over a variety of length-to-thickness ratios, coupled modes were achieved in a traveling wave along the curvilinear actuators  7   a - 7   d  at a ratio equal to 12. 
   The opening  23  within the annular cap  20  and opening  22  within the hemispherical cap  2  are preferred to be circular shaped and symmetrically disposed about the central axis  17 . The diameter of the opening  23  determines the field of view  8  for a device  6  attached to or within the support cavity  16  which is provided within the rotatable sphere  3  adjacent to the opening  23 . It was preferred for the opening  23  to have a total angle of 110 degrees, although other values are possible. 
   The gimbal housing  21  is preferred to include channels  24  which are dimensioned so as to sufficiently accommodate the length and width of the curvilinear actuators  7   a - 7   d , so as to support the curvilinear actuators  7   a - 7   d  in a non-binding fashion. The depth of each channel  24  should be less than the thickness of the curvilinear actuators  7   a - 7   d  so that the curvilinear actuators  7   a - 7   d  extend into the interior cavity of the gimbal housing  21 . 
   The spherical ball  3  is supported within the structure formed by the hemispherical cap  2  and annular cap  20  so as to compress the curvilinear actuators  7   a - 7   d . Compression of the curvilinear actuators  7   a - 7   d  couples shear induced motion within the curvilinear actuators  7   a - 7   d  to rotational motion of the spherical ball  3  about the field of view  8 . Compression is achieved when
 
 r   is   +d   c   −t   ca   &lt;r   rs  
 
where r is  is the radius of the interior surface of the gimbal housing  21 , d c  is the depth of the channel  24 , t ca  is the thickness of the curvilinear actuator  7   a - 7   b , and r rs  is the radius of the rotatable sphere  3 .
 
   Referring again to  FIGS. 2 and 3 , the hemispherical cap  2  is shown with a socket  4  therein; although, other generally symmetrical shapes about a central axis  17  are likewise possible. Curvilinear actuators  7   a - 7   d  are attached to the interior surface of the hemispherical cap  2  within the socket  4 , preferably in a symmetrically disposed fashion. Each curvilinear actuator  7   a - 7   d  extends beyond the seam  44  so as to ensure continued contact between the rotatable sphere  3  and both hemispherical cap  2  and annular cap  20 . Curvilinear actuators  7   a ,  7   b  are required to be shear-type devices. The annular cap  20  is identical or nearly identical to the hemispherical cap  2  in size and cross section. The opening  23  is provided to ensure an unobstructed field of view  8  for the device  6  attached to or within the support cavity  16 . The support cavity  16  should be sufficiently shaped so as to allow fixed and precise attachment of the device  6  to the rotatable sphere  3  via methods understood in the art. 
   The spherical ball  3  is preferred to have a spherical profile  5 . The spherical profile  5  should match or nearly match the contour of the curvilinear actuators  7   a - 7   d  so as to ensure complete, yet slidable contact between the curvilinear actuators  7   a - 7   d  and rotatable sphere  3 . 
   Referring now to  FIG. 4 , the hemispherical cap  2  is shown with two pair-wise arrangements of curvilinear actuators  7   a - 7   b  and  7   c - 7   d  within the socket  4 , although other arrangements are possible. Two curvilinear actuators  7   a ,  7   b  are disposed along the X-axis in a symmetric fashion. Likewise, two curvilinear actuators  7   c  and  7   d  are disposed along the Y-axis in a symmetrical fashion. It is preferred for the curvilinear actuators  7   a - 7   d  to be unidirectional and functionally paired, as represented by the arrows in  FIG. 4 , so as to enable rotation about the Z-axis. For example, curvilinear actuators  7   a  and  7   d  are shown functionally aligned to induce clockwise rotation of the rotatable sphere  3 ; whereas, curvilinear actuators  7   b  and  7   c  are arranged to induce counter-clockwise rotation of the same. Furthermore, compound rotations are possible where X-axis and Y-axis actuators are electrically activated simultaneously or in sequence. Other functional arrangements and applications of the curvilinear actuators  7   a - 7   d  are possible, including but not limited to a single bi-directional and unidirectional actuator disposed along the X-axis and Y-axis. 
   Referring now to  FIG. 5 , exemplary curvilinear actuators  7   a ,  7   b  are shown comprised of a pair of electrodes  9 ,  11  disposed about and attached to a piezoelectric layer  10 . The piezoelectric layer  10  may be composed of one or more plates of PZT material or the like. 
   Curvilinear actuators  7   a - 7   d  function as an ultrasonic motor when energized so as to couple vibrational energy directly into the rotatable sphere  3 , thereby causing it to rotate in a preferred direction. The length-to-thickness ratio of the piezoelectric layer  10  is tailored to optimize electromechanical coupling, so as to maximize a shear mode (such as d 15 ) rather than the longitudinal modes (d 31  or d 33 ). The resultant shear vibration mode produces a corresponding bending mode thereby causing a traveling wave along the piezoelectric plate. 
   Curvilinear actuators  7   a - 7   d  are arc-shaped segments with a total length to achieve the desired angular coverage. In one embodiment of the invention, curvilinear actuators  7   a - 7   d  were fabricated having an inner radius of 29.21 mm, an outer radius of 30.23 mm, a thickness of 1.10 mm, and a total angle of 80 degrees. 
   Curvilinear actuators  7   a - 7   d  were fabricated from unfired green tape composed of hard PZT and an organic binder. The tape was cut into strips, layered, and shaped to form a green body. Dimensions of the green body were oversized based on the densification properties of the green material to account for shrinkage during sintering, which could be as large as 16%. The green body was placed onto a mold composed of zirconia having a profile which replicated the desired arc shape of the actuator. The ends of the green body were constrained so as to avoid curling during the sintering process. After sintering, the ceramic body was machined and polished to ensure the required dimensional properties. 
   Next, the curved ceramic actuator bodies were poled to enhance their piezoelectric properties. The shear mode material response desired in the present invention required the poling orientation to be along the arc length of each ceramic body. As such, a conductive paint comprised of silver palladium (AgPd) was applied to both ends of each ceramic body and then cured at 850° C. for 15 minutes. The poling voltage was generally material dependent. For example, hard PZT electro-ceramics are normally poled at 1 kV for each millimeter of length. Thus, a 45 kV voltage was applied to a ceramic body having an arc length of 45 mm. It was preferred to secure the ceramic actuator body to a non-conductive planar fixture during the poling process. The planar fixture included a pair of metal pins so as to contact the electrodes at the ends of the ceramic actuator body and to support the ceramic actuator body. A non-conductive pin was also disposed along the jig and centrally located so as to contact and support the ceramic actuator body at its midpoint. A thin piece of polytetrafluoroethylene was employed to wedge the ceramic actuator body tightly against the non-conductive pin. Thereafter, the fixture with ceramic actuator body was submersed in a bath of silicon oil at a temperature of 150° C. and a voltage applied thereto. The temperature of the bath enhanced poling; whereas, the bath provided a dielectric medium to avoid breakdown. 
   After poling, the fixture and ceramic actuator body were removed and the piezoelectric coefficient (d 33 ) was measured to determine the degree of poling. A 10 mm arc length was cut from the ceramic actuator body so that its length was short enough compared to its radius to approximate a linear segment. A d 33  value of 284 pm/V was measured which is slightly higher than 90% of the theoretical d 33  value (315 pm/V) for the hard PZT composition. Thereafter, the end electrodes were removed. 
   Next, electrodes were applied to the top and bottom surfaces of the ceramic actuator body perpendicular to the poling direction to effect shear mode behavior within the actuator. The electroding method was performed at low temperature to avoid depoling of the ceramic actuator body. 
   Ceramic actuator bodies were electroded with nickel plating via a four step process. First, the poled ceramic actuators bodies were etched in a flouroboric bath to roughen the exterior surface of the bodies and to enhance adhesion between electrodes and the ceramic. Next, the ceramic actuator bodies were immersed within a room temperature bath of SnCl dissolved in HCl to deposit a Sn layer onto the ceramic. Thereafter, the ceramic actuator bodies were immersed within a bath containing PdCl, thus depositing a Pd layer onto the Sn layer. Finally, the ceramic actuator bodies were immersed within a bath of Ni at a temperature of 70° C., thus depositing a Ni layer onto the Pd layer. Excess Ni was removed from non-electrode surfaces via a dry polished step. The resultant curvilinear actuators  7   a - 7   d  demonstrated a resonant frequency from 470 kHz to 475 kHz. 
   Referring now to  FIGS. 6-7 , an alternate curvilinear actuator  19  is shown including a piezoelectric layer  10  disposed between a pair of electrodes  9 ,  11 ; however, a plurality of protrusions  18  are disposed along the outer surface of one electrode  9 . Protrusions  18  contact the rotatable sphere  3  so as to enhance coupling of the vibration amplitude along the electrode  9  into the rotatable sphere  3 . Protrusions  18  may include a variety of shapes including, but not limited to, squares, rectangles, circles, and hexagons. Likewise, the protrusions  18  may be implemented in an ordered arrangement consisting of two or more rows and two or more columns or a random arrangement of arbitrary shaped protrusions  18 . Protrusions  18  are fabricated via methods understood in the art, including machining and etching. In the present invention, a curvilinear actuator  7   a - 7   d  with protrusions  18  is capable of a unidirectional drive speed of approximately 100 mm/sec when driven at a frequency of 340 kHz. 
   One or more devices  6  may be attached to the rotatable sphere  3  so as to point or otherwise project from the gimbal system  1 , as represented in  FIGS. 2 and 3 . Devices  6  may include, but are not limited to, microphones, lasers, and cameras. A variety of commercially available acoustic, light, and optical devices are adaptable to the present invention. Optical digital micro-camera technology is one example of devices applicable to the above described gimbal system  1 . Micro-cameras are superior to conventional digital cameras in that they offer higher image quality via mega pixel resolution, true optical zoom performance, and autofocus capability. Such devices are likewise adaptable to infrared imaging. 
   Precision aiming of the device  6  is dependent on the accurate tracking of the rotatable sphere  3  within the gimbal housing  21 . The orientation of the rotatable sphere  3  with respect to the gimbal housing  21  may be determined via tracking devices and techniques for track balls. For example, the track ball optical system, model no. HDNS-2000 sold by Agilent, Inc., includes a light-emitting diode that reflects light from a textured surface, a camera that records the reflections, and a navigation engine that processes reflections to resolve the orientation of the ball or sphere.  FIG. 8  shows one possible embodiment of the present invention, wherein a fully-integrated optical tracker  25  is mechanically fastened to the gimbal housing  21  immediately adjacent to the opening  22 . The optical tracker  25  is arranged to project above the opening  22  as to allow the projection of a light onto the rotatable sphere  3  and recording of the projection there from. 
   Referring now to  FIG. 9 , an exemplary block diagram is provided for acquisition and processing of data from a micro-camera or other sensor  15 . Data from the sensor  15  is communicated to a programmable logic device  13 , one example being the CoolRunner™ Series of programmable logic ICs sold by Xilinx, Inc. The programmable logic device  13  facilitates operation of a multi-spectral digital camera within a compact chip via modifiable software to control logic gates and storage elements therein. The programmable logic device  13  communicates with a storage medium  12  to save image data. The programmable logic device  13  may also communicate image data from the sensor  15  to a USB module  14 , one example being a UZBEE Stinger unit sold by QorTek, Inc., for communication to a host. 
   Referring now to  FIG. 10 , an actively controllable acoustic tracking system  34 , in its simplest form, is composed of a pair of acoustic receivers  31   a ,  31   b  electrically coupled to a phase detector  32  which is coupled to a position controller  33 , thereafter coupled to a gimbal system  1 , the latter shown and described above. Receivers  31   a ,  31   b  are commercially available devices capable of detecting sounds generated by a moving or movable target  30 , examples including but not limited to persons, animals, vehicles, objects, projectiles, and the like. TABLE 1 identifies exemplary commercial components suited to this application of the gimbal system  1 . While two receivers  31   a ,  31   b  are shown, three or more such devices may be advantageous in some applications. 
   Receivers  31   a ,  31   b  acquire acoustic emissions which are thereafter processed by the phase detector  32 , also a commercially available device. Processed emissions are then analyzed via known methods to triangulate the position of the acoustic source relative to the gimbal system  1 . Positional data is communicated to the position controller  33  which then directs the gimbal system  1  to spatially locate the device  6  attached to the rotatable sphere  3 , also described in  FIGS. 2 and 3 . Sampling and correction rates of the described system are application dependent. 
   
     
       
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Component 
               Exemplary Commercial Item 
             
             
                 
             
           
           
             
               Optical 
                 
             
             
               IR cooled 
               Rockwell TCM2250 HgCdTe FPA, 
             
             
                 
               compact infrared camera 
             
             
               IR uncooled 
               BAE PMC300, miniaturized 
             
             
                 
               infrared camera 
             
             
               Visual color 
               Shenzhen DTC DV-4400CHDN, 
             
             
                 
               micro-camera 
             
             
               Visual B&amp;W 
               C-Pro Electronics PCAM- 
             
             
                 
               BW/PCAM-CR, micro-camera 
             
             
               Infrared data interconnection 
               Agilent HSDL-1001 
             
             
               (IrDA) 
             
             
               Acoustic 
             
             
               Swivel motion 
               Shure KSM44, microphone 
             
             
               Sound activated directional pointing 
               AKG C4000B, dual-diaphragm 
             
             
                 
               electret 
             
             
                 
             
           
        
       
     
   
   Referring now to  FIG. 11 , an actively controllable optical tracking system  43 , in its simplest form, is composed of an optically-based device  6  coupled to a gimbal system  1 , as shown and described above, which is electrically coupled to an image processor  41 , and thereafter coupled to a position controller  42  which is then electrically connected to the gimbal system  1 . TABLE 1 identifies several exemplary commercial components suited to this application of the gimbal system  1 . 
   The optically-based device  6  first acquires a target  40   a  which is digitally mapped and recorded by the image processor  41  for tracking purposes. Subsequent images of the target  40   b  and  40   c  are likewise communicated to the image processor  41  for comparison to determine the new spatial location of the target  40   a - 40   c  relative to the optically-based device  6  housed within the gimbal system  1 . Positional data is communicated to the position controller  42  which then directs the gimbal system  1  to spatially position the device  6  attached to the rotatable sphere  3  to optimize the field of view about the target  40   a - 40   c . Sampling and correction rates of the described system are application dependent. 
   Referring now to  FIG. 12 , an exemplary block diagram is shown for a joystick  26  controlled embodiment of the present invention. Elements of the device include a controller  27 , a pair of direct digital synthesizers  28 ,  29 , a variable gain amplifier  35 , a pair of amplifiers  36 ,  37 , four curvilinear actuators  39   a - 39   d , and an optical sensor  38 , electrically coupled as shown in  FIG. 12 . Curvilinear actuators  39   a - 39   d  are described in detail above. TABLE 2 identifies exemplary commercial components suited to this application of the gimbal system  1 . 
   
     
       
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
               Component 
               Exemplary Commercial Item 
             
             
                 
             
           
           
             
               Joystick (26) 
               Two axis, single joystick 
             
             
               Controller (27) 
               MSP430, ultra-low power 16-bit 
             
             
                 
               RISC mixed signal processor, 0.1 uA 
             
             
                 
               RAM retention, 0.8 uA real-time 
             
             
                 
               clock mode, 250 uA/MIPS active 
             
             
               Direct digital synthesizer (28, 29) 
               Analog Devices (AD9831) DDS 
             
             
                 
               DC-12.5 Mhz 
             
             
               Variable gain amplifier (35) 
               Analog Devices (AD600) 0 to 40 dB 
             
             
                 
               Variable Gain Amplifier 
             
             
               Amplifier (36, 37) 
               Linear Technologies (LT1210) 1.1A 
             
             
                 
               35 Mhz Peizo Amplifier/Driver 
             
             
               Optical sensor (38) 
               Agilent Technologies ADNS-2051 
             
             
                 
             
           
        
       
     
   
   The embodiment in  FIG. 12  controls orientation of the rotatable sphere  3  within the gimbal system  1  by varying the drive voltage to the appropriate curvilinear actuators  39   a - 39   d . Operation of the controller  27  is dictated primarily by input signals from the joystick  26 . As such, the joystick  26  controls the orientation of the rotatable sphere  3  so as to properly align any device  6  mounted thereto. First, the controller  27  sets the initial output frequency by commanding the direct digital synthesizers  28 ,  29  over the I 2 C bus. Next, the controller  27  outputs a fixed and calculated DC gain voltage, which is directly dependant on the position of the joystick  26 , to the variable gain amplifier  35 . The variable gain amplifier  35  uses the DC gain voltage to either amplify or attenuate the AC signal from the direct digital synthesizers  28 ,  29 . The output of the variable gain amplifier  35  is communicated to one or both final stage amplifiers  36 ,  37  which amplifies the signal voltage by a fixed value. Depending on the input direction control, the amplifiers  36 ,  37  electrically activate the appropriate curvilinear actuators  39   a - 39   d . For example, curvilinear actuators  39   a - 39   d  may be arranged in a pair-wise arrangement so that curvilinear actuators  39   a  and  39   c  rotate the rotatable sphere  3  in a clockwise direction about the X-axis and Y-axis, respectively, and curvilinear actuators  39   b  and  39   d  rotate the rotatable sphere  3  in a counter-clockwise direction, respectively. Both Ch1 (X-axis) and Ch2 (Y-axis) from the variable gain amplifier  35  are identical in operation. 
   Proper function of the joystick  26  interface requires position information there from to be communicated to the controller  27  in a usable form. Position was determined by configuring the potentiometers within the joystick  26  as voltage dividers. An on-chip analog-to-digital converter (ADC) sampled the voltage across the potentiometers to determine absolute positions. However, movement of the potentiometer&#39;s wiper was logarithmic causing the scale to become very sensitive at the high end and very insensitive at the low end. As such, an RC charge network was employed to determine orientation of the joystick  26 . 
   A commercially available dual 555 timer (556), in mono-stable, single-shot mode was configured to discharge the capacitor and to provide input to the controller  27 . In this approach, the controller  27  communicates a “reset/trigger” signal to the 556 timer which discharges a capacitor with a defined capacitance. Once the capacitor voltage rises to the set threshold voltage of the 556 timer (typically, ⅔ V dd ), the output from the 556 timer toggles to a logic high. The time span from capacitor discharge output to the capacitor re-charge set output is directly proportional to the orientation of the joystick  26 . The exponential charge rate of the capacitor minimizes the effect of the logarithmic potentiometers within the joystick  26 . This alleviated would-be overhead in processor calculations to linearize the signal. The circuit was calibrated to ensure limit and center positions were correctly sensed and interpreted via methods understood in the art. 
   To enable closed-loop operation, an optical sensor  38  was employed for position correction and control by tracking movement of the rotatable sphere  3  in both the X-direction and Y-direction. The optical sensor  38  first illuminates the surface of the rotatable sphere  3  with a light emitting diode (LED) and then captures a 16×16 pixel 6-bit gray-scale image. Changes in the gray-scale image are indicative of relative movement, not unlike the centroid method used for wavefront error correction in adaptive optical systems. Data from the optical sensor  38  was available in both serial (modified I 2 C) and quadrature formats, simultaneously. A serial interface was preferred to take advantage of sensor features and to eliminate the need for four additional timed inputs as required with the quadrature format, thus freeing processor resources. 
   Control circuitry for the joystick  26 , controller  27 , and direct digital synthesizers  28 ,  29 , and position feedback connections were incorporated onto a single circuit board. Variable gain amplifier  35  and final amplifiers  36 ,  37  were incorporated onto a second circuit board to reduce noise coupling over board traces and power planes. Control circuitry was designed to compliment the drive specifications of the curvilinear actuators  39   a - 39   d , which included 60V rms  and 3-4 A at 300-500 kHz. The AC signal to the direct digital synthesizers  28 ,  29  and variable gain amplifier  35  was communicated via a miniature coax cable; whereas, a ribbon cable was used for direction control and current sensing. The amplifier board also incorporated current feedback sensors for each of four channels. 
   Because the current curvilinear actuators  39   a - 39   d  are “polarized”, actuators were arranged in an opposed fashion so as to achieve clockwise and counter-clockwise motion about the X-axis and Y-axis. In some embodiments, it may be advantageous to include four rather than two amplifiers  36 ,  37  and related feedback circuits; however, control circuitry only requires two direct digital synthesizers  28 ,  29  and one two-channel variable gain amplifier  35 . It was preferred for one amplifier to be active at any time in this alternate embodiment. Control circuitry was capable of driving the curvilinear actuators  39   a - 39   d  at 0.2-10 Vpk-pk in frequency steps of 0.1 Hz to a max frequency of 12.5 MHz. Final drive output current was limited to 1.1 A on each channel and a bandwidth of 1.2 MHz was achieved. 
   The description above indicates that a great degree of flexibility is offered in terms of the present invention. Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.