Abstract:
In a method of controlling a gaze direction of a camera, the camera is placed on a top surface of a substrate that is pivotally coupled to a frame, wherein a movement arm depends downwardly from the substrate. The movement arm is moved with two spaced apart amplified piezoelectric ceramic stack actuators that are affixed to the frame and coupled to the movement arm by deforming the amplified piezoelectric ceramic stack actuators as a result of applying a voltage thereto, thereby changing an angular orientation of the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/659,614, filed Jun. 14, 2012, the entirety of which is hereby incorporated herein by reference. 
     
    
     STATEMENT OF GOVERNMENT INTEREST 
       [0002]    This invention was made with government support under agreement No. ECCS-0932208, awarded by National Science Foundation. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to camera positioning systems and, more specifically, to a camera positioning system using antagonistic actuators. 
         [0005]    2. Description of the Related Art 
         [0006]    The human eye enables the brain to perceive large amounts of information quickly, yet not all regions of space are perceived equally. Objects near the gaze direction, or fovea, receive the most attention, a lesser amount of information is gathered about objects in the remainder of the field of view, and some objects are out of the field of view and are not perceived. In this way, the brain is not overwhelmed by information that is not of interest. Because the area of interest may change rapidly, the eye can be reoriented with astounding performance by lightweight recti muscles. The recti muscles are contractile, compliant actuators that are activated in discrete steps by neural impulses. 
         [0007]    The human eyeball, or globe, is oriented by means of antagonistic pairs of recti and oblique muscles. The range of achievable orientations follows Donders&#39; Law and Listing&#39;s law, both for saccadic motion and smooth pursuit. Antagonistic pairs of contractile actuators with insertion points into the globe are an important part of the eye&#39;s kinematics. In actuality, eye muscles consist of a finite number of on-off motor units, or collection of muscle fibers innervated by a particular motor neuron. Cytoskeletal tissue couples the active acto-myosin filaments to the load. It is believed that this property allows muscles to function well in unstructured environments, since the elasticity of the muscle tends to return to a stable equilibrium when perturbed. Muscles are controlled by recruitment, whereby the nervous system increases or decreases the number of motor units active to increase or decrease the amount of actuation. Each individual motor unit can only be on or off and it cannot be proportionally controlled. 
         [0008]    Most camera positioners use heavy traditional servo-motors. One example employs a cable-driven mechanism that is actuated by traditional servomotors. A cable-driven eye may be able to enforce the eye&#39;s kinematics, but rigid servomotors do not actually follow the processes related to the neurological basis for natural eye motion. This is partly because servo-motors tend to introduce velocity saturations and backlash. The resulting movement lacks the bandwidth of an actual eye. 
         [0009]    Therefore, there is a need for a camera positioning system the models natural eye movement. 
       SUMMARY OF THE INVENTION 
       [0010]    The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a camera system that includes a frame that supports a substrate in a pivotal relationship along a first axis. A camera is disposed on the substrate. A first actuator is affixed to a first side the frame and is disposed along a second axis that is transverse to the first axis. A second actuator is affixed to a second side of the frame and is disposed along the second axis. The second side of the frame is opposite the first side of the frame so that the substrate is between the first side of the frame and the second side of the frame. The first actuator and the second actuator are both deformable in response to a signal. When the first actuator deforms away from the first side of the frame, the second actuator deforms toward the second side of the frame and when the first actuator deforms toward from the first side of the frame, the second actuator deforms away from the second side of the frame. A transverse member is disposed along a second axis that is transverse to the first axis. The transverse member mechanically couples the first actuator and the second actuator to the frame. The transverse member imparts deformation of the first actuator and the second actuator to the substrate in response to the signal so as to cause the substrate to pivot in relation to the frame, thereby changing an angular orientation of the camera. 
         [0011]    In another aspect, the invention is a directional device that includes a frame that supports a substrate in a pivotal relationship along a first axis. A first amplified piezoelectric ceramic stack actuator is affixed to a first side the frame and is disposed along a second axis, transverse to the first axis. A second amplified piezoelectric ceramic stack actuator is affixed to a second side of the frame and is disposed along the second axis. The second side of the frame is opposite the first side of the frame so that the substrate is between the first side of the frame and the second side of the frame. The first amplified piezoelectric ceramic stack actuator and the second amplified piezoelectric ceramic stack actuator are both mable in response to a signal. When the first amplified piezoelectric ceramic stack actuator deforms away from the first side of the frame, the second amplified piezoelectric ceramic stack actuator deforms toward the second side of the frame. When the first amplified piezoelectric ceramic stack actuator deforms toward from the first side of the frame, the second amplified piezoelectric ceramic stack actuator deforms away from the second side of the frame. A transverse member is disposed along a second axis that is transverse to the first axis. The transverse member mechanically couples the first amplified piezoelectric ceramic stack actuator and the second amplified piezoelectric ceramic stack actuator to the frame. The transverse member imparts deformation of the first amplified piezoelectric ceramic stack actuator and the second amplified piezoelectric ceramic stack actuator to the substrate in response to the signal so as to cause the substrate to pivot in relation to the frame to a predetermined orientation. 
         [0012]    In yet another aspect, the invention is a method of controlling a gaze direction of a camera, in which the camera is placed on a top surface of a substrate that is pivotally coupled to a frame, wherein a movement arm depends downwardly from the substrate. The movement arm is moved with two spaced apart amplified piezoelectric ceramic stack actuators that are affixed to the frame and coupled to the movement arm by deforming the amplified piezoelectric ceramic stack actuators as a result of applying a voltage thereto, thereby changing an angular orientation of the substrate. 
         [0013]    These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
         [0014]      FIG. 1A  is a plan view schematic diagram of one embodiment of a camera system. 
           [0015]      FIG. 1B  is a cross-sectional schematic view of the embodiment shown in  FIG. 1A , taken along line  1 B- 1 B. 
           [0016]      FIG. 2  is a cross-sectional schematic view of the embodiment shown in  FIG. 1A  showing a result of deformation of the actuators. 
           [0017]      FIG. 3A  is a schematic diagram of a single cell of an amplified piezoelectric ceramic stack actuator unit in a non-deformed state. 
           [0018]      FIG. 3B  is a schematic diagram of a single cell of an amplified piezoelectric ceramic stack actuator unit in a deformed state. 
           [0019]      FIG. 4A  is a schematic diagram of an actuator with three levels of amplification in a non-deformed state. 
           [0020]      FIG. 4B  is a schematic diagram of an actuator with three levels of amplification in a deformed state. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” 
         [0022]    As shown in  FIGS. 1A-1B , one embodiment of a camera positioning system  100  employs a frame  110  on which is mounted a substrate  120 . A pivot rod  124  pivotally couples the substrate  120  to the frame  110  along a first axis  10 . A camera  122  may be mounted on the substrate  120 . (It should be recognized that other embodiments may be employed to position objects other than cameras.) A movement arm  128  depends downwardly from the substrate  120 . A first actuator  112  is mounted to a first side of the frame  110  and a second actuator  114  is mounted to a second, opposite, side of the frame  110 . A transverse member  126  is disposed along a second axis  12  that is transverse to the first axis  10  and that mechanically couples the first actuator  112  and the second actuator  114  to the substrate  120 . The transverse member  126  imparts the deformation of the first actuator  112  and the second actuator  114  to the substrate  120  in response to the signal so as to cause the substrate  120  to pivot in relation to the frame  110 , which changes the angular orientation of the camera. 
         [0023]    The first actuator  112  and the second actuator  114  are both deformable in response to a signal (such as a voltage signal). As shown in  FIG. 2 , when the first actuator deforms  112  away from the first side of the frame  110 , the second actuator  114  deforms toward the second side of the frame  110 , which causes the transverse member  126  to move toward the second side of the frame  110 . As a result, the movement arm  128  is displaced along with the transverse member  126 , which causes the substrate  120  to rotate in a counter-clockwise direction. Similarly, when a signal of opposite polarity is applied to the first actuator  112  and to the second actuator  114 , the first actuator  112  deforms toward from the first side of the frame  110  and the second actuator  114  deforms away from the second side of the frame  110 , which causes the transverse member  126  to move toward the first side of the frame  110 , thereby causing clockwise rotation of the substrate  110 . 
         [0024]    In one embodiment, the actuators  112  and  114  include amplified piezoelectric ceramic stack actuators, such as an actuator employing a lead zirconate titanate (PZT) ceramic (which is contractile along one axis when a voltage is applied thereto). One method of making and using amplified piezoelectric ceramic stack actuators is disclosed in “Strain Amplification Devices and Methods,” U.S. Patent Application Publication No. 2009/0115292 A1, published on May 7, 2009 and filed by Ueda et al. on Oct. 24, 2008, the entirety of which is incorporated herein by reference for the purpose of disclosing amplified piezoelectric ceramic stack actuators and methods of making, using and controlling the same. 
         [0025]    As shown in  FIGS. 3A and 3B , a simple piezoelectric ceramic stack actuator  200  employs a piezoelectric element  202  that deforms in at least one direction when a voltage  211  is applied thereto. The piezoelectric element  202  is surrounded by a flexible loop  210 , which includes two first opposite surfaces  212  and two second opposite surfaces  214  that are disposed transversely to the two first opposite surfaces  212 . One of the second opposite surfaces  214  is affixed to a fixed surface  22  (such as a frame). The flexible loop  210  can be made of a flexible material such as a metal strip or a plastic and can take the form of a non-regular octagon (it should be understood that many other shapes, such as an oval, could also be used). When the voltage  211  is applied to the piezoelectric element  202 , as shown in  FIG. 3B , the piezoelectric element expands and forces the two first opposite surfaces  212  apart, which forces two second opposite surfaces  214  closer together. Because of the angular differences of the sides of the flexible loop  210 , the somewhat limited expansion of the piezoelectric element  202  is amplified to substantially more movement between the two second opposite surfaces  214 . 
         [0026]    As shown in  FIGS. 4A and 4B , this amplification can be exaggerated by nesting piezoelectric ceramic stack actuators  200  in flexible loops to make an amplified actuator  300 . In this embodiment, several piezoelectric ceramic actuators  200  are stacked adjacently to each other, with a peripheral flexible loop  312  surrounding the stack thereby forming an amplified actuator unit  310 . Several actuator units  310  can then be stacked and an outer flexible loop  320  can be placed around them to form a complex actuator  300 . Because of the angular relationships of the sides of loops  312  and  320 , a substantial amount of displacement between the sides of the complex actuator  300  can be achieved with relatively little displacement of the piezoelectric elements in the ceramic actuators  200 . Also, by applying a voltage to only selected ones of the ceramic actuators  200 , the amount of displacement the complex actuator  300  can be controlled with a relatively high level of precision. This mimics the way contraction of muscle fibers control movement of such things as eyeballs. 
         [0027]    While above embodiment shows a single degree of freedom positioning system, this system could employ gimbals to achieve multiple degrees of freedom 
         [0028]    The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.