Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1996-01-31
1997-07-15
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
H01L 4108
Patent
active
056486960
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The subject of the present invention is a traveling-wave piezoelectric motor comprising a stator, consisting of an annular elastic body, two groups of piezoelectric elements dispersed around the stator, in permanent contact with the stator and excited by an alternating current with a 90.degree. phase shift between the groups so as to produce, at the surface of the stator, a traveling wavelike deformation, and a rotor in the form of a disk held elastically in contact with the stator for the rotational driving thereof by the traveling wave produced on the stator.
PRIOR ART
The principle of the construction and operation of such a motor is described in detail in the U.S. Pat. No. 4,562,374. So as to produce a traveling wave on the stator, the two groups of piezoelectric elements are supplied with a voltage of like frequency but phase-shifted in time by an angle .pi./2 and the groups are arranged on the stator in such a way that the standing waves generated by each of the groups are shifted in space by .lambda./4, .lambda. being the wavelength of the standing waves. The groups of piezoelectric elements can be separated from one another or nested, the piezoelectric elements of the two groups then being intercalated so that there is alternately a piezoelectric element from each group. The motors described in U.S. Pat. No. 4,562,374 are made with ceramic wafers, in the shape of a segment of an annulus, these wafers being adhesively bonded to the stator thereby forming a complete annulus or portions of an annulus, depending on whether the groups are or are not nested.
Motors of like design are described in the U.S. Pat. No. 4,562,373. So as to increase the effectiveness of such motors, two rings of nested piezoelectric elements are superposed and supplied with an appropriate phase shift.
The U.S. Pat. No. 4,513,219 describes motors of electrostrictive type in which the electrostrictive elements likewise consist of wafers pressed against a stator.
It is therefore noted that in general piezoelectric elements have been used in the form of thin wafers so as to adapt to the undulation of the stator. These wafers function in 3.1 mode, that is to say they expand and contract in a direction perpendicular to the applied electric field. The amplitude of the deformation in the 3.1 mode is relatively small and this is precisely why it was proposed in the U.S. Pat. No. 4,562,373 to superpose two systems of wafers so as to increase the effectiveness of the motor. Furthermore, the ceramics used are fragile parts with complex shapes, and they require elaborate tooling for manufacture, polarization and handling which moreover are often specific to each ceramic. They are therefore expensive to implement and poorly suited to mass production.
SUMMARY OF THE INVENTION
The purpose of the present invention is to propose a traveling-wave piezoelectric motor which is robust, effective and of advantageous manufacturing cost.
For this purpose, the piezoelectric motor according to the invention is such that the piezoelectric elements are mutually independent polarized ceramic bars arranged perpendicularly to the stator and each connected to the stator by an articulation.
The use of bars functioning perpendicularly to the stator, makes it possible to function in 3.3 mode, at their natural resonant frequency, and this makes it possible to benefit from a high electromechanical coupling factor and hence to obtain at constant electric field, deformations around three times greater than the levels obtained in motors according to the prior art. High axial mechanical rigidity is moreover obtained.
Ceramic bars are relatively tough elements and therefore do not require special precautions for their implementation. The ceramic bars may be standard commercial parts, such as the ceramic bars of gas and cigarette lighters produced cheaply in very large quantity.
The bars make it possible furthermore to more easily make nested systems in which the piezoelectric elements of each group are dispersed around the entire circumfere
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Claeyssen Frank
Gonnard Paul
Guillemot-Amadei Marie-Madeleine
Le Letty Ronan
Lebrun Laurent
Budd Mark O.
Figest B.V.
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