Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-06-22
2001-10-02
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S369000
Reexamination Certificate
active
06297576
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and method to precisely control the relative position of two surfaces. More particularly, this invention relates to piezoelectric or magnetostrictive actuators.
BACKGROUND OF THE INVENTION
Piezoelectric materials and magnetostrictive materials (collectively referred to below as “piezoelectric materials”) deform when an electric field or magnetic field is applied. Thus, piezoelectric materials, when used as an actuator, are capable of controlling the relative position of two surfaces.
One of the most used piezoelectric materials is quartz. Other piezoelectric materials include certain ceramic materials and certain polymer materials. Since they are capable of controlling the relative position of two surfaces, piezoelectric materials have been used in the past as valve actuators and positional controls for microscopes. Piezoelectric materials, especially those of the ceramic type, are capable of generating a large amount of force. However, they are only capable of generating a small displacement when a large voltage is applied. In the case of piezoelectric ceramics, this displacement can be a maximum of 0.1% of the length of the material. Thus, piezoelectric materials have been used as valve actuators and positional controls for applications requiring small displacements.
Two methods of generating more displacement per unit of applied voltage include bimorph assemblies and stack assemblies. Bimorph assemblies have two piezoelectric ceramic materials bonded together and constrained by a rim at their edges, such that when a voltage is applied, one of the piezoelectric materials shrinks and the other piezoelectric material expands. The resulting stress causes the materials to form a dome. The displacement at the center of the dome is larger than the shrinkage or expansion of the individual materials. However, constraining the rim of the bimorph assembly decreases the amount of available displacement. Moreover, the force generated by a bimorph assembly is significantly lower than the force that is generated by the shrinkage or expansion of the individual materials.
Stack assemblies contain multiple layers of piezoelectric materials interlaced with electrodes that are connected together. A voltage across the electrodes causes the stack to expand or contract. The displacement of the stack is equal to the sum of the displacements of the individual materials. Thus, to achieve reasonable displacement distances, a very high voltage or many layers are required. However, convention stack actuators lose positional control due to the thermal expansion of the piezoelectric material and the material(s) on which the stack is mounted.
Due to the high strength, or stiffness, of piezoelectric material, it is capable of opening and closing against high forces, such as the force generated by a high pressure acting on a large surface area. Thus, the high strength of the piezoelectric material allows for the use of a large valve opening, which reduces the displacement or actuation necessary to open or close the valve.
The typical actuation distance requirement for liquid and gas (collectively referred to below as “fluid”) valves is small, generally less than 5 um. However, most are sealed by the compression of an elastomeric seal. In practice, it is the formation of a seal caused by the required compression of the elastomeric seal that consumes a large portion of the 5 um actuation distance.
SUMMARY OF THE INVENTION
The present invention is directed to an piezoelectric actuator assembly. Moreover, the present invention is directed to one and two dimensional arrays of piezoelectric actuator assemblies.
It has been determined by the inventors that a good seal can be formed by forcing two clean flat surfaces together. It is, therefore, not necessary to have an elastomeric seal as long as the two mating surfaces are clean and flat, and as long as the force is sufficient to maintain the surfaces in contact with one another.
Thus, the present invention utilizes the high force generated by piezoelectric materials to provide a force sufficient to precisely control the relative position of two flat surfaces with respect to one another. Moreover, the present invention overcomes the minimal actuation distance available from piezoelectric materials by not requiring elastomeric seals and by effectively doubling the actuation distance available from piezoelectric materials by means of a unique structure.
The actuator assembly in accordance with the teachings herein has a first and a second stack of piezoelectric materials with electrode layers connecting the stacks to a voltage source. A cavity is defined within said first stack and is adapted to receive a first end of the second stack. A first opening and a second opening are defined within the stack wherein each is in fluid communication with the cavity and wherein the first opening has a flat surface within the cavity. A flat face opposite the first opening forms a contact seal with the flat surface. The contact seal of the present invention is formed by forcing together two clean flat surfaces to create a barrier to fluid flow. The first and second stacks are adapted to unseal the face from the surface in response to a voltage.
REFERENCES:
patent: 4510412 (1985-04-01), Suda et al.
patent: 4765140 (1988-08-01), Imoto et al.
patent: 5214342 (1993-05-01), Yang
patent: 5332942 (1994-07-01), Rennex
patent: 6025671 (2000-02-01), Boecking
patent: 6140742 (2000-10-01), Kahn
Law Clayton E.
Wang Tak K.
Agilent Technologie,s Inc.
Budd Mark O.
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