Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-06-12
2004-07-20
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000
Reexamination Certificate
active
06765335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a piezoelectric adjusting element in accordance with the preamble of patent claim
1
.
2. Description of the Related Art
Linear piezoelectric motors whose functionality is based on the utilization of travelling waves are part of the state of the art and are, for example, the subject-matter of the printed patent specifications EP 0 475 752 B2 and U.S. Pat. No. 5,596,241.
Motors of this type suffer from the disadvantage that it is impossible to minimize them to any desired dimensions, because the minimum length of their wave guides must be a multiple value of 6&lgr; to 10&lgr; of the wave that expands in them. Moreover, from a technological perspective, they are difficult to manufacture, very complicated in terms of their setup and, therefore, correspondingly expensive.
Also known are piezoelectric motors whose functionality relies on standing acoustic waves. Prior art of this kind is reflected, among others, in U.S. Pat. No. 5,453,653. The motor of this style of execution can be realized small enough and allows, in terms of technology, for the production of major piece numbers. A monolithic piezoelectric oscillator is used as the drive element for this motor; and the oscillator has a long side, a short side as well as a friction element that is arranged on the small surface of the short side. On the first large side, the piezoelectric oscillator is equipped with a first group of electrodes and with a second group of electrodes. A joint electrode is arranged on the second large side. Two areas of a metallized piezo-ceramic surface, which are of equal size and arranged in a rectangular and diagonal manner, cover each first and second group of electrodes. An oscillator supplies electric a.c. voltage to the joint electrode and to the first or to the second group of electrodes. Due to the asymmetrical style of execution of each of the two groups of electrodes in relation to the longitudinal axis of the piezo-plate, an asymmetrical deformation results. This causes the friction element to perform a movement along closed paths either in the one direction or in the other direction, depending on which group of electrodes is supplied with the electric voltage.
The moving friction element sets a pressed-on driven element in motion which, in turn, performs movements in the one direction or in the other direction. The motor is excited with a frequency that is close to the frequency of resonance of the second vibration mode of the bending vibrations of the piezo-plate in its longitudinal direction.
In piezoelectric motors of this construction type, longitudinal vibrations of the oscillator pass the energy, that is stored inside the oscillator, on to the driven element. The parameters of these vibrations determine the size of the supply voltage of the motor, the geometry of the motor and the overall construction of the motor.
The supply voltage of the piezoelectric motor addressed here must be chosen very high by way of the small electro-mechanical coupling coefficient of the bending modes of the oscillator vibrations. Furthermore, in a piezoelectric motor of this construction type, the driven element has a strong dampening effect on the bending oscillator, which further increases the necessary supply voltage. Accordingly, piezoelectric oscillators in motors of known styles of execution in accordance with the state of the art require supply voltages of up to 500 V, resulting is a corresponding need for high voltage protection.
The relationship between the dimensions of the long side of the oscillator plate and the short side is approximately 3.7 in piezoelectric motors that are versions of the state of the art. With its short side, the oscillator plate is arranged parallel in relation to the surface of a driven element, and it bends along its long side during the operation of the motor. This kind of motor construction limits the maximum possible force that is generated by the motor by way of the flexural strength of the oscillator plate.
Since the friction element is located on the short side of the oscillator plate, its dimensions are limited. The width of the friction element may not be larger than one third of the short side of the piezo-element. This way, consequently, the width of the friction contact is limited to approximately 0.3 . . . 0.4 mm in construction types of motors according to the state of the art. The fact that this width of the friction contact is minimal additionally considerably limits the force that is to be generated by the motor. Correspondingly, motors of the construction types that are known in the art, which are comprised of an oscillator, only achieve a maximum force of approximately 10 N. Moreover, the small width of the friction contact also increases wear and tear, thereby resulting in the temporary instability of the operation of the motor. The small width of the friction contact especially reduces the movement stability of the driven element at low rates of motion. Furthermore, the narrow friction contact leads to parameter changes of the motor when the motor is stored over longer periods of time.
A motor construction in accordance with U.S. Pat. No. 5,453,653 envisions only one friction element on the surface of a piezoelectric oscillator. This causes the piezoelectric oscillator to become mechanically unstable, thereby reducing its positioning accuracy and rendering the construction of the oscillator mounting more complicated.
In addition to the above, one friction element limits the maximum possible force that is generated by the motor with a piezoelectric oscillator. If several oscillators are used, which are combined into a package, the positioning accuracy of the driven element deteriorates, and the electronic motor control is, moreover, very complicated in terms of its realization.
SUMMARY OF THE INVENTION
Therefore, it is the subject-matter of the present invention to design a piezoelectric motor on the basis of a monolithic piezoelectric oscillator and that will allow achieving greater force with a smaller excitation voltage, a better operating stability with a longer serviceable life, a more even movement of the driven element at lower rates of motion, a higher parameter stability when the motor is stored for longer periods of time, a mechanically robust oscillator construction, and that allows for a controlling means for tracking the oscillator frequency of resonance and for regulating position and parameters of the driven element.
This object is achieved with a piezoelectric adjusting element, in particular a piezoelectric motor as claimed in patent claim
1
.
The piezoelectric motor according to the invention is comprised of a housing, a driven element, a friction layer, which is located on the housing or on the driven element, and of a drive element, which is electrically connected to an electric exciter source containing at least one friction element that is in friction contact with the friction layer, in the form of at least one monolithic plate-shaped or cylindrical piezoelectric oscillator with first and second main surfaces, first and second side surfaces as well as first electrodes and second groups of electrodes that are arranged on its main surfaces.
In the present context, it is essential that the piezoelectric oscillator referred to above has a resonant length and a resonant height, and the first group of electrodes and the second group of electrodes constitute two generators of acoustic waves. Accordingly, the first generator excites a standing longitudinal acoustic wave that vibrates in the direction of the oscillator resonant length. Analogously, the second generator excites a standing longitudinal acoustic wave that vibrates in the direction of the oscillator resonant height. The oscillator resonant length is equal to an integral multiple of the wave length of the standing acoustic longitudinal wave vibrating in its direction, which is generated by the first generator; and the oscillator resonant height is equal to one half of the wave length of the stan
Budd Mark
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Physik-Instrumente (PI) GmbH & Co. KG
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