Patent Application: US-83947910-A

Abstract:
system for establishing a surface shape . the system includes a compliant substrate including the surface and having a reverse side , and a plurality of discrete actuators engaging the reverse side and arranged in a selected pattern to control the surface shape as individual discrete activators are activated . it is preferred that the actuators have multiple discrete stable states of elongation . a particularly preferred embodiment uses actuators that are binary with two stable states of elongation .

Description:
throughout the specification , whenever the term “ mirror ” is used it is noted that other elements such as photovoltaic collectors or thermal solar concentrator elements are intended as well . a mirror is usually mounted on a supporting structure that might contain hinges and elastic elements . also contained in or mounted to the structure are actuators that can assume a multiplicity of stable positions of elongation . power is not necessary to maintain each actuator in its stable positions . in a preferred embodiment these actuators are binary , but multi - stable configurations with larger numbers of states are also contemplated . one implementation of an embodiment of the invention is shown in fig2 . the discrete actuators 10 may be based on simple binary dielectric elastic actuators [ 12 ], lead screws , pneumatic or hydraulic cylinders , electromagnetic solenoids or other devices . in one of the implementations of the invention , the binary actuators 10 may be mounted to mechanisms with relatively rigid elements . in this case , the mechanisms become a discrete positioning system . one instance is a tracking structure in which a base drive has a number of discrete stable positions so that the system is able to track a target , such as the sun , in a finite number of small steps . in another application the bi - stable actuators 10 might be attached to a large structure with members having some significant elasticity . in this case , very simple actuators can apply known displacements or rotations to various points on the structure depending on whether linear or rotational actuators are used , respectively . the structure would then naturally deform , based on its design , to mediate the imposed displacements . the structural members must be of sufficient compliance so that the actuators can apply enough force to switch their state and result in motions large enough to compensate for any undesired distortions . an example system comprising segmented mirrors 12 , binary actuators 10 , and elastic elements 14 is shown in fig3 . assuming small actuator displacements , compared to the size of the structure to which the actuator is attached , the output displacements of the mirror segments can be calculated easily in the form of a linear matrix equation given by y = ad wherein y is a vector of structure displacements and d is a vector of ones and zeros defining which actuators are extended ( 1 ), and which actuators are contracted ( 0 ). this formulation can be used to determine which actuators need to be “ switched ” between their discrete positions to achieve a given structure shape . ideally , the shape would compensate for errors in the structure due to manufacturing imperfections and disturbances described earlier . also , limited - tracking motions can be achieved by this means to supplement the tracking function discussed above . the approach of using discrete actuators according to the invention has many advantages . binary actuators are simple , inexpensive and lightweight . binary actuated systems are also robust due to their redundancy . failure of individual binary actuators would result in a graceful degradation of performance . in addition , since the actuator output is discrete , low - level actuator sensors are not necessary , and computations for figure control can be performed offline . the control for the actuators themselves is very simple compared to conventional systems that require proportional control amplifiers . in contrast , with the present invention , in order to toggle the position , one would need only to switch the polarity of the signal to the actuators . further , binary actuators are energy efficient as power is required only to change their states . in this way , very reliable , simple , low cost mirror correction systems are developed . the mirror shape control technology system disclosed herein has been implemented in a small experimental system as shown in fig4 . in this implementation , the binary actuated mirror 12 comprises 19 hexagonal mirror panels mounted on a compliant plate . a cross section of the experimental system is shown in fig5 . a rigid plate 16 is supported by 13 vertical actuators 10 , and 30 vertical compliant struts 18 , as shown in fig6 . because of force output limitations of current dielectric elastic actuators , micro - linear actuators were used in a binary fashion in the experiments conducted by the inventors . in this demonstration system , the range and rotational workspace of the center mirror has been evaluated . in order to measure the workspace in an automated fashion , a vision - based measurement system was implemented . in this system , a laser beam is reflected off a center mirror onto a focal plane . a ccd camera captures images of the reflected ray in the focal plane . these images are processed to determine the position of the reflected ray and the angular deflection of the center mirror . the workspace of the center mirror was queried for different actuator configurations . with 13 actuators , the system has 8192 ( 2 13 ) different configurations . using varying stiffness elastic elements distributed throughout the system the workspace of the center mirror is evenly distributed . an example workspace is shown in fig7 . through proper design of the supporting structure the mirror workspace can be distributed as desired . the kinematics of the surface control system of the invention and other details may be found in [ 13 , 14 ]. it is recognized that modifications and variations of the present invention will be apparent to those of ordinary skill in the art , and it is intended that all such modifications and variations be included within the scope of the appended claims . 1 . gardner , j . p ., mather , j . c ., clampin , m ., doyon , r ., greenhouse , m . a ., hammel , h . b ., hutchings , j . b ., jakobsen , p ., lilly , s . j ., long , k . s ., lunine , j . i ., mccaughrean , m . j ., mountain , m ., nella , j ., rieke , g . h ., rieke , m . j ., rix , h ., smith , e . p ., sonneborn , g ., stiavelli , m ., stockman , h . s ., windhorst , r . a ., and wright , g . s ., 2006 , “ the james webb space telescope .” space science reviews , 123 ( 4 ), pp . 485 - 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