Piezoelectric actuator with low stress electrodes

Details Piezoelectric actuator with low stress electrodes Piezoelectric actuator with low stress electrodes

1999-04-08

2001-02-20

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S366000

Reexamination Certificate

active

06191522

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a piezoelectric torque actuator with low stress electrodes which is particularly used to produce tilting motions in high-frequency ranges.
Piezoelectric driving and adjusting elements are already known. The driving and adjusting elements, respectively, underlying the present invention, are of the kind employing piezoelectric stack drives as actuating elements. Such drives and their advantages are described in detail, for example, in Vol. 104, F&M Feinwerktechnik, Mikrotechnik, MeBtechnik, (Carl Hanser Publishing House Munich 1996), pg. 68ff. Such a drive is also described in DE 44 45 642 A1, in which narrowly adjacent piezoelectric double 15 stacks are employed and which can be used to realize many different drive operations. A general disadvantage of all known stack drives lies in the fact that the external electric stack contacts required (refer to, for example, DE 42 24 284 A1) are subject to considerable mechanical load both, in statical and in dynamical operation. The stacks are formed of a plurality of superimposed piezoelectric foils which are connected to one another. Each of the foils are provided with flat contacts on both faces of each foil. The external contact for the individual foils with each other is effected by having an electrode pass through, in particular a solder layer, on the respective opposing longitudinal sides of the stacks. Such electrodes, but also the field-free interactive insulation ranges, are subject to the most extreme mechanical and electric stress during the expansions and contractions of the stacks. When these stacks are operated by pulsed currents in the ampere range and at frequencies in the kHz-range, conventional stacks undergo expansions of 1-2% which distinctly limits the stress cycles to less than 109.
A further disadvantage of the known drives is the considerable mechanical expenditures which are required to convert the pure translatory motions produced by the stacks into tilting motions (refer to, for example, DE 44 45 642 A1 or EP 0 574 945 A1).
Furthermore, the prior art discloses designs for other applications. So, for example, DE 196 05 214 A1 describes an ultra-sonic drive element which typically operates at frequencies of greater than (>) 20 kHz. In this mode of operation only very small lifting motions occur and therefore there are low mechanical expansions of the external contacts as a result there is no need for any special description as to the arrangement of the electrodes in the referred to disclosure.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a piezoelectric driving or adjusting element of laminated structure operated in the d
33
−mode. The required electric connection contacts of the structure is subject to a substantially reduced mechanical stress and, in particular, results in direct tilting motions without any further means for motion transformation.
The object of the invention is realized by the features described herein.
The essential feature of the invention resides in a stack of a laminated structure formed of a first range and a second range, both made of piezoelectric active, in particular, piezoceramic material with an in-between third range, the latter includes areas which are not covered by an electric field originating from the voltage applied across the flat laminate contacts; the external electrode connections of the two piezoelectrically active ranges are substantially displaced in direction of the mentioned field-free areas, wherein the third range is at least in positive fit, preferably in material fit, illustrates to the first and second range.


REFERENCES:
patent: 4639630 (1987-01-01), Rodloff et al.
patent: 5233260 (1993-08-01), Harada et al.
patent: 5237239 (1993-08-01), Inoue et al.
patent: 5245734 (1993-09-01), Issartel
patent: 5834879 (1998-11-01), Watanabe et al.
patent: 5912526 (1999-06-01), Okawa et al.

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