Abstract:
A pizoelectric actuator assembly for actuating industrial control valves or clamps provides a compact actuator including a single piece main structure with integrated hinge, mechanical lever, and spring in a shape such that in response to electrical activation, the piezoelectric device transfers mechanical energy from a predetermined axis into the force transfer member operably positioned for driving at least one pivotable arm portion in rotational movement with a loss of motion of less than 40%.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation-In-Part application of U.S. patent application Ser. No. 09/771,533 filed Jan. 29, 2001, published as Publication No. U.S. Pat. No. 2001/0030306 A1, on Oct. 18, 2001, and U.S. patent application Ser. No. 10/067,762, filed Feb. 6, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an actuator assembly, and more specifically relates to moving folded-back arms having a pair of opposing surfaces in response to electrical activation. 
     BACKGROUND OF THE INVENTION 
     Actuators are required in a wide variety of modern applications. For example, valves and relays are used throughout industry, transportation, architecture, etc. Presently, electromagnetic solenoids are used in a wide variety of clamping and valving applications. However, electro-magnetic solenoids have many shortcomings. In general, solenoids are relatively large and heavy. Solenoids consume relatively high amounts of power to remain energized. When supplied with only a reduced amount of power, solenoids operate unpredictably. It is difficult to maintain a solenoid in a partially open or partially closed position. Solenoids have relatively slow cycle times, provide weak opening and closing forces, and generate EMF (electromotive force). Differential pressure is required to operate most solenoids. When designed as a valve, most solenoids are gravity sensitive and include a fixed inlet valve port and a fixed outlet valve port requiring a predetermined installation orientation. Recently, piezoelectric bimorphs have also been used in some valve applications. Piezoelectric bimorph valves have several advantages including low power consumption, small size, light weight, and fast cycle times. Piezoelectric bimorph valves can be operated in a partially open or partially closed valve position. However, such valves produce relatively weak valve sealing forces resulting in substantial potential for fluid leakage. 
     Various types of piezoelectric devices are known to those skilled in the art. Many of these devices include complex configurations and are very expensive to manufacture. Other devices include simpler configurations, but are extremely limited in the corresponding maximum range of movement or the corresponding maximum application of force. 
     In such known devices, when the piezoelectric actuator is electrically activated, the rectangular prism geometry of the device expands predominantly along a predetermined axis. When the piezoelectric device is deactivated, the geometry of the device contracts predominantly along the predetermined axis. This expansion open and close a clamp or valve. An apparatus for clamping or valving typically includes a support having two members spaced with respect to each other. The piezoelectric device is transversely disposed between the two spaced members. As the piezoelectric device expands in a linear direction, the members are driven or pivoted along a curvilinear path, The pivoting of the members along a curvilinear path results in an inefficient transfer of force from the piezoelectric device to the support. The piezoelectric actuator in most known configurations is positioned parallel to the desired motion providing little opportunity to select different hinge axis locations and/or structural configurations to optimize performance. 
     SUMMARY OF THE INVENTION 
     The present invention improves the prior art by providing additional options to structural configurations, and performance optimizations never possible before. The present invention provides an apparatus for moving at least one folded-back arm having a surface in response to an electrical activation. Preferably, a pair of folded-back arms having a pair of opposing surfaces are moved relative to one another in response to an electrical activation. The apparatus includes a support having a rigid non-flexing portion, first and second arm portions extending rearward from the rigid portion, a pair of opposing surfaces with one opposing surface on each pivotable arm portion for movement relative to one another, and a force transfer member operably positioned between the first and second pivotable arm portions. An actuator is operably engaged between the rigid non-flexing portion and the force transfer member to drive the force transfer member in movement along a fixed path causing at least one of the first and second pivotable arm portions to pivot in response to an electrical activation of the actuator. The support, pivotable arms, and force transfer of the structure are designed to be rigid, non-flexing portions of a monolithic structure interconnected by flexible hinge portions allowing the rigid portions to move relative to one another. Any unplanned flexing can reduce the effective life of the mechanism, and reduces the amount of force transferred through the hinge axis to the pivot arms. The reduction in force limits the displacement and force of the pivoting arms. The selection of the hinge axis location and corresponding structural configuration allows substantial capability to optimize the performance and size of the apparatus for the particular application. 
     The piezoelectric actuator can be preloaded with force when installed in the support element. For example, the piezoelectric actuator can be clamped within the support structure with an adjustable screw supporting one end allowing the optimal force preloading. An adjustable screw configuration is easy to use and allows a large degree of adjustability. Preloading the piezoelectric actuator in any suitable fashion contributes to the maximum efficiency of the force transfer during actuation, and allows fine-tuning of the initial position of the apparatus prior to actuation of the piezoelectric element. Preloading can also ensure that the piezoelectric actuator maintains contact with the apparatus at opposite ends throughout the range of expansion and contraction. The use of a threaded adjustment screw for preloading enables assembly without requiring adhesives or other means of securely connecting the piezoelectric actuator at opposite ends to the apparatus, and avoids the possibility of damaging tension or torsional moments on the piezoelectric actuator. The threaded adjustment screw allows simple compensation for dimensional variations in the piezoelectric actuator during assembly to the support. 
     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view of one embodiment of an apparatus for moving at least one folded-back arm having at least one surface of a pair of opposing surfaces moveable in response to an electrical activation, the apparatus having a support and actuator in accordance with the present invention; 
     FIG. 2 is a side view of the apparatus of FIG. 1 with the actuator deactivated; 
     FIG. 3 is an exaggerated side view of the apparatus of FIG. 1 with the actuator fully activated; and 
     FIG. 4 is a side view of the apparatus illustrating mechanically fastened pivotable arm portions to the rigid portion of the support outwardly from the location of the living hinges. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a perspective view of one embodiment of an apparatus  10  having a support  12  and an actuator  14  in accordance with the present invention. The support  12  includes a rigid, non-flexible portion  16 , at cast one pivotable arm portion, such as first and second pivotable arm portions  18 ,  20  extending rearward from the rigid portion  16 , a pair of opposing surfaces  22 ,  24  with opposing surfaces  22 ,  24  on each pivotable arm portion  18 ,  20  for movement relative to one another, and a force transfer member  26  operably positioned between the first and second pivotable arm portions  18 ,  20 . Preferably, the support  12  is a unitary, integral, single-piece monolithic body. The actuator  14  is operably engaged between the rigid, non-flexable portion  16  and the force transfer member  26  to drive the force transfer member  26  in learn motion away from the rigid, non-flexible portion  16 . The rigid non-flexible potion  16  receives an adjustable support  54  with an adjustable seat  52  having a complementary surface to the end  42  of the actuator  14 . The complementary surface of the adjustable seat  52  can be flat or shaped in any manner to support the actuator  14  in a position suitable for driving the force transfer member  26  in response to an electrical actuation of the actuator  14 . Movement of the force transfer member  26  pivots at least one pivotable arm portion  18 ,  20  about at least one living hinge  36 ,  38  with a loss of motion of less than 40%. At least one living hinge  36 ,  38  extends between each rigid arm portion and a pivotal base portion  46 ,  48  of each corresponding pivotable arm portion, and at least one living hinge  32 ,  34  extends between the corresponding base portion  46 ,  48  of the pivotable arm portions and the force transfer member  26 . A controller  28  can be provided to operate the apparatus  10 . The controller can provide a charging voltage across the piezoelectric device to produce spatial displacement along a predetermined axis. The amount of electrical charge stored by the piezoelectric device is generally proportional to the amount of voltage applied across the piezoelectric device. Thus, varying the amount of voltage applied across the piezoelectric device can control the amount of spatial displacement along one predetermined axis. This spatial displacement is transferred and amplified via the living integral hinge  36 ,  38  into at least one pivotable arm  18 ,  20  causing the corresponding one of the opposing surfaces  22 ,  24  to move in a curvilinear path with respect to the other. 
     In FIG. 2, the actuator  14  is deactivated. The opposing surfaces  22 ,  24  are furthest from each other when the actuator  14  is deactivated. This type of configuration is commonly referred to as a normally open design. When the actuator  14  is electrically activated, the set end  42  of actuator  14  is held fixed by the rigid portion  16 , the driving end  44  of the actuator  14  drives the force transfer member  26  away or apart from the rigid web  30 , and pivotable arms portions  18 ,  20  are pivoted about living hinges  36 ,  38 . In this manner, the space or distance between the opposing surfaces  22 ,  24  is decreased. The distance between the opposing surfaces can be increased or decreased by adjusting the voltage across the piezoelectric device. FIG. 3, illustrates the planar driving end  44  of the actuator  14  in operable contact with the planar seat surface  40  of the force transfer member  26  when the actuator  14  is fully activated and is exaggerated to show a larger closing between the opposing surfaces  22 ,  24 . 
     In the embodiment illustrated in FIGS. 1-3, these components have been machined from a single monolithic piece of metallic material for example stainless steel. Other suitable materials can include powdered metal, metallic alloys, composite materials, or a combination of metallic and composite materials. Although these materials given as examples provide excellent performance, depending on the requirements of a particular application, use of other materials for the support can be appropriate. Some components like the pivotable arm portions can be manufactured separate from the rigid non-flexing generally C-shaped or generally U-shaped structure and joined later to define the generally W-shaped or generally M-shaped combined structure as illustrated in FIG.  4 . 
     In the embodiment illustrated in FIG. 4, the apparatus  10   a  is made with four discrete components. The first component includes the support  12   a  including a rigid web  30   a  connecting rigid arm portions to define a generally C-shaped or generally U-shaped portion of the apparatus  10   a . At least one living hinge  36   a ,  38   a  extends between each rigid arm portion and a pivotal base portion  46   a ,  48   a  of each corresponding pivotable arm portion, and at least one living hinge  32   a ,  34   a  extends between the corresponding base portion  46   a ,  48   a  of the pivotable arm portions and the force transfer member  26   a . The second and third components are the separable and pivotable arm portions  18   a ,  20   a  attached to the corresponding bases  46   a ,  48   a  of the support  12   a  using fasteners  50 . The fourth component is the actuator  14   a  operably engaged between the rigid web  30   a  and the force transfer member  26   a . An adjustable support  54   a  can be provided with an adjustable seat  52   a  having a complementary surface to an end  42   a  of the actuator  14   a . The complementary surface of the adjustable seat  52   a  can be flat or shaped in any manner to support the actuator  14   a  in a position suitable for driving the force transfer member  26   a  in response to electrical actuation of the actuator  14   a.    
     In the embodiments illustrated in FIGS. 1-4, a basic apparatus  10 ,  10   a  is illustrated and described. The present invention can be used in other applications besides the valves, clamps, and relays previously described. These applications can include a broad range of devices using oscillatory motion. By way of example and not limitation, some possible configurations of devices can include a sander, a toothbrush, a shaver, an engraving tool, optical systems, and motors. The efficiency of the apparatus is enhanced for oscillatory motions by operating the structure in mechanical resonance. At a mechanical non-resonant frequency and an input voltage of one, the mechanical output for the structure would be one. At a mechanical resonant frequency and an input voltage of one, the mechanical output for the structure can be as great as four hundred. This property can be used in several ways. The mechanical resonant property can be used to increase the mechanical output for the same electrical input, or the electrical input can be reduced to obtain the same mechanical output. It should be recognized that a balance between the desired input and output can be obtained depending on the particular application. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.