Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-08-07
2004-07-27
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06768245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric drives, to piezoelectric resonators for drives and to the use of piezoelectric drives as well as to piezoelectric resonators.
2. Description of Related Art
Certain, so-called piezoelectric materials may be excited into mechanical oscillation by applying an electrical alternating current. This physical effect is also called the reverse piezoelectrical effect. A known use of this effect is the use of piezoelectric materials as oscillation exciters in resonators. Such piezoelectric resonators may be installed into drives in order to drive rotatably mounted rotors.
The drives that are known in the art and that are based on the piezoelectric effect have severe disadvantages, which until today have prevented a widespread industrial use as drives. A complex actuation of the piezoelectric oscillation elements, a large danger of contamination, very small mechanical tolerances that prevent a trouble-free operation and a poor efficiency are the most severe disadvantages. Furthermore, with the solutions known today only very low rotational speeds with an extremely small torque are possible. A reduction in size of these drives so that they may be used, for example, in micro-technology or medical technology or also in the field of clocks is possible only at a great expense, rendering economical manufacture impossible. The large mechanical abrasion of the known arrangements further demand the use of particularly hard, and therefore expensive, materials that are difficult to machine. Only a small amount of abrasion causes an increase of the play and a contamination of the drive, which inevitably leads to a failure after a short operational duration.
Such piezoelectric drives are, for example, disclosed in the documents EP-0,505,848 (hereinafter referred to as EP'848), EP-0,723,213 (hereinafter referred to as EP'213) and FR-2,277,458 (hereinafter referred to as FR'458) as well as the document equivalent to this DE 25 30 045 (hereinafter referred to as DE'045).
EP'848 and EP'213 show multi-part centrally arranged piezoelectric resonators with two or three resonator wings. The ends of the resonator wings have abutments for abutting rotors, which are arranged annularly on the outside around the resonators. With these piezoelectric drives there is the disadvantage of the abrasion at the abutment surfaces of the resonator wings and at the capture surfaces of the rotors as well as the bearing play of the rotors. The abrasion results in a high wear, which shortens the life duration of the piezoelectric drives and limits its potential field of application.
DE'045 (corresponding to FR'458) describes the most varied of arrangements of electrical motors that are based on piezoelectric elements. These motors have a stator and a rotor, wherein at least one or both has a vibrator that encloses a piezoelement. The stator and the rotor are pressed against one another at a point of the surface that lies on the surface of the vibrator by way of an elastic element in order to transmit a moment. A direction change is effected by way of a reversal means, which functions to the extent that several vibrators are alternately applied. In DE'045 it is mentioned that with these motors with a resonator it is impossible to change the rotational direction. A change of the rotational direction demands two vibrators (for example rotor and stator active). Furthermore, the abutments perpendicular to the contact surface between the rotor and the stator are disadvantageous. It is mentioned that the wear with the motors is very large, in particular with several rotational directions. A reversal of the rotational direction is only achieved at a great expense. On account of the parts, which are very difficult to manufacture, a suitable design is very expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a piezoelectric drive that has a low wear, is inexpensive, and is manufacturable in any size, particularly small and flat. The drive is to be robust in operation, simple in maintenance and large in power. It is to have a large rotational speed range in several rotational directions and, furthermore, permit a simple position determination. This piezoelectric drive is to be compatible with common standards.
Piezoelectric drives are, as a rule, based on resonators that are set into oscillation. These are, in turn, transmitted to a body to be driven. The present invention is based on the recognition that the oscillation behavior of a piezoelectrically excited resonator may be influenced in the longitudinal direction as well as the transverse direction by way of a targeted design and arrangement. A piezoelectrically driven resonator operated in a mix mode by way of the design of the present invention permits a body to be set into motion. According to the shaping of the resonator and the arrangement of one or more resonators to a body, a variety of structural embodiments and uses become possible. By way of the special design, several dominant oscillation forms may be excited. By way of the special design, it is possible to select the. oscillation forms such that the rotational direction amongst other things may be selected dependent on the frequency. An influencing of the rotational speed is advantageously effected by way of the magnitude of the amplitude. Due to the inventive shaping of the resonator, it is further possible to minimize damaging vibrations that cause wear. By way of a directed arrangement it is achieved that abrasion does not have a negative effect and is compensated. The piezoelectric drive may be used for the unidirectional or bi-directional drive of bodies, such as shafts and disks, with only one piezoelement. In contrast to this, the state of the art arrangements as a rule require several oscillation quartzes, which must be exactly coordinated to one another.
In an advantageous solution a longitudinal oscillation component of the piezoelectric resonator serves for driving a body while a transverse oscillation component of the resonator exerts a temporary pressure on the body. By way of the thus created pressure angle large forces may be transmitted onto the body to be driven. The drive, when required, has a great self-locking so that, among other things, the body is held. An additional mounting of the parts to be moved may be avoided in a directed manner.
The piezoelectric drive according to the invention comprises an excitation element and a resonator that is coupled to the excitation element and in interactive connection with a body to be driven. The excitation element is advantageously mounted between two parts of the resonator and acts indirectly on the body to be driven. The movement induced by the excitation element is transformed by the resonator and then transmitted to the body to be driven. The resonator has a mass distribution, which is configured such that, as a result of an excitation oscillation by way of the excitation element, dependent on the frequency of the excitation oscillation, the resonator begins to oscillate asymmetrically in several directions. These oscillations, via an interactive connection, are transmitted onto the body to be driven via the interactive connection so that this is set into a directed movement. The mass inertia of the oscillating elements is exploited in a directed manner in order to produce advantageous oscillation forms, By way of the arrangement and design it is achieved that the excited forms of movement achieve an optimized drive with a minimal of wear and material loading. By way of adjustable elements it is achieved that any occurring incidences of wear are compensated and equalized. The resonators are advantageously excited with a frequency that corresponds to frequency of resonance or of a multiple thereof. A resonator as a rule comprises severally differently and asymmetrically formed arms that, depending on the frequency of excitation, oscillate differently. These are also infl
Mock Elmar
Witteveen Bontko
Creaholic SA
Rankin, Hill Porter & Clark LLP
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