As shown in the figures, a roller pin 46, or other flexural connection such as a hinge or flexure, is provided between the pivot end plates 16, 26, of the inner and outer frames 12, 22. If a loose rolling mechanism such as a pin is employed, the pin is inherently held between the end plates by the compressive stress of the frames, which pinch against the pin. At the pivot end plates 16, 26, of the outer and inner frames, each of the stacks 32, 34, are preferably provided with a rolling contact mechanism such as a cylindrical endcap 44, or other suitable rolling contact mechanism such as a spherical endcap or other conventional rolling contact mechanism. Each rolling contact can be provided as, e.g., a cylindrical or spherical endcap that abuts the corresponding pivot end member. For many applications, spherical endcaps are preferred because they constrain the stacks to be axially loaded, and thus minimize compliance losses due to eccentric loading of the stacks.
It is found, however, that the slight Hertzian losses are overshadowed by the large reduction in compliance achieved with the contacts. The selected piezoelectric or electrostrictive material preferably has a high energy density, e.g., an energy density level like that associated with the ceramic lead-zirconate-titonate (PZT). Whatever active materials are candidate for a given application of the actuator, it is preferred that considerations of energy density, supported strain, bandwidth, longevity, actuation linearity, thermal sensitivity, cost, technical maturity, and other suitable factors be evaluated in selecting an active material for the application. In other aspects, the invention provides that the actuator be employed for controlling a deflectable trailing edge flap of an airfoil. With this specification, it is found that a piezoelectric or electrostrictive stack is particularly well-suited for the actuator of the invention in that such a stack provides the high bandwidth and low weight required of many applications, and the large stroke amplification enabled by the actuator frame compensates for the relatively small expansion stroke characteristic of such a stack.
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As a result, a stroke amplification mechanism is generally required of an actuator incorporating such a structure. However, the maximum achievable voltage across a wafer in a conventional active stack element formed of a stack of wafers is typically limited, whereby additional stack wafers can be required to produce the given electric field at a selected actuator size. The distal end of the first frame can be adapted to provide an elongated actuator stroke track having two separated side members between which the distal end member of the second frame can operate. The flexural support of the actuator is preferably a centrifugal support having a first support member connected to the first frame, a second support member connected to the second frame, a mounting member, and a flexible strut connected between the mounting plate and each of the first and second support members through corresponding first and second flexural links for distributing centrifugal force equally between the first and second frames.
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The diameter of the pin is selected to maintain the selected angle, θnom, between each stack and the corresponding inner or outer frame. In practice, such scaling implicitly assumes that the applied voltages and corresponding electric fields applied to a given scaled stack length are also scaled to maintain a given electric field strength in the stacks.
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The flexure can further be provided as a flexural support having a first support member connected to the first frame pivot end member, a second support member connected to the second frame pivot end member, a mounting plate, and a flexible strut connected between the mounting plate and each of the first and second support members through corresponding first and second flexural links. A first longitudinal span member is disposed between the distal end member of the second frame and the pivot end member of the first frame, and a second longitudinal span member is disposed between the distal end member of the first frame and the pivot end member of the second frame. A flexure is disposed between an end of the pivot end member of the first frame and an end of the pivot end member of the second frame. A flexural support is connected to each of the first and second frame pivot points and mounted to the airfoil, with the first and second frames located within the airfoil.
- Cistitis intersticial o síndrome de la vejiga dolorosa
- El aviso de Harvard sobre los dientes y el cáncer de estómago
- Tippy: té con una proporción elevada de puntas blancas o doradas
- Tratamientos con fármacos hepatoprotectores
- Retorno a todas las actividades
- Static pressure – 10 s. Static pressure on the starboard side of the Oscillating wing
- Remos invertidos
The pivot mechanism between the pivot ends of the frames is located at a cross member of a truss geometry formed by the actuator; this is a low-force leg of the actuator load-bearing stroke path relative to the expansive elements’ stroke paths. Intell. Syst., pp. Dolor de espalda baja como aliviar . 407-418, 1993. In the Stahlhuth design, two active element stacks are positioned such that their longitudinal reaction creates an amplified perpendicular displacement of saggital linkages connected at ends of the stacks. Expansion of the stack causes the fulcrum to rotate about the hinge away from the stack, in turn extending the lever, thereby translating the longitudinal stack expansion to a correspondingly amplified lever extension. 26-34, 1996, have proposed an actuator, for helicopter rotor blade control, that employs an active monolithic piezoelectric ceramic bimorph structure cantilevered from a blade spar. Turning now to materials considerations, the actuator of the invention can be configured using any actuation element that is capable of producing expansion and contraction along a longitudinal axis of the element.
It is to be recognized that this relationship does not account for eccentric loading of the stacks, which condition can exacerbate buckling tendency. The one or both of the longitudinal span members that are expansive elements can be, e.g., a magnetostrictive element, an electrostrictive element, or a piezoelectric element, in the form, e.g., of a stack of piezoelectric ceramic wafers.
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Piezoelectric and electrostrictive elements provided in the form of stacks of ceramic wafers are conversely relatively light, and thus for many applications are the preferred active element. Beyond the rotor blade flap control application described above, the actuator of the invention is particularly well-suited to a wide range of applications. Generally, actuators are included in such applications to generate force and effect displacement, for example, to open or close valves, to deflect transmission linkages, to position components, or to enable another such system function. 2B, the representational actuator truss 25 can be deconstructed into its components, namely, an upper triangle 27 formed of one stack, one frame, and the cross member, and a lower triangle 29 formed of the other stack and frame and the same cross member.
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Ideally, an amplification stroke mechanism acts as nearly as possible like a true mechanism, i.e., it amplifies motion without resistance due to friction in hinges or other effects that impede mechanism motion, and it does not add compliance in series with the active element longitudinal expansion and contraction stroke path. In other embodiments, a displacement sensor is connected along a path of the second frame distal end extension for sensing displacement of a load connected along the path. In preferred embodiments, the first longitudinal span member abuts the pivot end member of the first frame with a rolling contact, and the second longitudinal span member abuts the pivot end member of the second frame with a rolling contact. 2C, it is specified that the point of intersection of the cross member, of height hnom, and the stack member is vertex A, and the intersection of the cross member and the frame is vertex B. Under free-loading conditions, the frame member is unloaded and thus remains at a constant frame length, lf, as the stack element contracts and expands in response to electrical stimulation.
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In addition, the cantilevered monolithic bimorph structure, in which piezoelectric actuation is transverse to the applied electrical stimulus, is found to be characterized by an energy density that is considerably lower than that of a piezoelectric ceramic stack structure, in which piezoelectric actuation is parallel to the applied electrical stimulus. BACKGROUND OF THE INVENTION This invention relates to electromechanical actuators, and more particularly relates to actuator configurations for enabling efficient, large stroke actuation. Dolor parte alta de espalda . With this configuration, actuation of the stroke mechanism of the actuator is enabled by retaining the mounting end plate 14 of the outer frame 12 fixed to a stationary reference frame (not shown) by, e.g., a mounting rod 48 connected between, e.g., a hole 50 in the mounting end plate and a fixed structure. Discrete actuators employed for such functions typically are designed to provide a desired actuation stroke over which a desired force is delivered to a given load.
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In a conventional piezoelectric or electrostrictive wafer stack, each ceramic wafer is separated by a bond layer that extends across the wafer surface and to which electrical connection is made to produce an electric field across the thickness of each wafer to enable actuation along the longitudinal axis of the stack. These example actuator designs point out that actuator compliance is a predominant limitation conventionally associated with discrete actuator design inefficiency, due either to bending of a mechanism in the active element load path or to a hinge mechanism, such as a flexure, provided for accommodating rotational degrees of freedom in the active element load path. Based on this energy relationship, the mass efficiency of a discrete actuator is directly related to the characteristic stiffness of the actuator, reflecting the fact that a stiff actuator load-bearing stroke mechanism is generally more efficient than a relatively more compliant stroke mechanism. As a result, the practical design of relatively larger actuators requires a tradeoff between desired voltage scaling and stack stiffness as it relates to actuator efficiency.
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In addition to hard geometric limits imposed by the actuator stroke mechanism, the design of the actuator also preferably provides consideration for the degree of active stack element end support necessary to prohibit buckling along the length of the stack between the frame end plates. Indeed, in theory, there is no minimum or maximum limit to the size of the actuator under a constraint of geometric scaling. As the stack length changes, the stack and frame are forced to rotate about points A and B, respectively, until a geometric equilibrium is reached. C, and lsΔ is the elongated stack length.