Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-04-24
2004-06-08
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06747391
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems for driving piezoelectric actuators and piezoelectric motors and more particularly to the electronic circuitry of such drivers.
BACKGROUND OF THE INVENTION
Piezoelectric materials are characterized in that when they are subjected to electrical fields they can be made to deflect; i.e., produce mechanical motion. Also when mechanical stress is applied to piezoelectric elements so hat they undergo displacement they generate electrical signals. These characteristics are the reason that piezoelectric materials are useful in applications ranging from sensors to mechanical motors. Examples of piezoelectric elements being used as motors is shown for example in U.S. Pat. Nos. 5,714,833 and 5,777,423; which patents are assigned to the assignee of the invention of this application. Piezoelectric motors are characterized by their mechanical simplicity. They have very few parts, no separate moving parts, and there are no critical mechanical components such as gears, shafts, bearings etc. Consequently, piezoelectric motors are relatively inexpensive and highly reliable.
A piezoelectric element represents an electrical reactive load (mainly capacative) that requires an AC signal of substantial voltage amplitude to cause the mechanical displacement. The required voltage amplitude is generally in the range of a few hundred volts (RMS). For effectively operating the piezoelectric element as a motor or actuator a drive circuit applies voltage thereto of a specific frequency with low harmonic distortion. For the best results, i.e. maximum displacement, the specific frequency should equal the mechanical resonant frequency of the piezoelectric element. A simplified circuit that could be used to drive a piezoelectric motor is shown in
FIG. 1A
, while such a motor is illustrated in FIG.
1
B. This method required two sources and two matching (high-Q) resonant circuits (not shown).
A preferred manner of actuating bidirectional operation of the piezoelectric element provides one side of the element with a pair of electrodes that are connected to a voltage source, such as a switch mode inverter. An opposite side of the piezoelectric element has a single common electrode. The common electrode is grounded or connected to ground by passive or active elements so that current from each of the pair of electrodes flows in opposite directions to cause bidirectional displacement of the piezoelectric element.
The drive circuits for piezoelectric motors basically provide AC voltages to the electrodes according to the directional movement required or desired. Typical prior art drive circuits for actuating the piezoelectric elements to provide movement in a selected direction or selected directions comprise separate inverter circuits coupled to the piezoelectric element through resonant circuitry attached to each of the elements high side electrodes. The prior art utilizes such multiple inverters to cause directional motion of the piezoelectric motors without any separate switching units. Other prior art devices utilize a single high voltage source and switching circuitry to switch the source between different electrodes. This methodology requires high voltage capable switching circuitry.
A major disadvantage of the prior art drivers is the complexity of the circuitry that is used. For example, a commonly used driver comprises a bridge type inverter circuit (see
FIG. 2
) that requires six power switches, and two high Q resonant circuits. Other prior art drivers require only one high Q resonant circuit The reduction in the number of high Q resonant circuits is accomplished by placing the high Q resonant circuit in series with the common electrode. However, six power switches are still used in that prior art device (see EP 0712 170 A1), which application is assigned to the assignee of this application. In
FIG. 7
of that device, four switches are used for displacement directional control with two switches for each of the selectable directions. The high Q resonant circuits are sensitive to the accuracy of the circuit component and to the frequency of the applied voltage. As a practical solution for overcoming this sensitively, in the prior art the Q of the drivers was often lowered and the input voltage from the prior art drivers was raised Extra DC/DC converters were required to enable operation with lower input voltages. Consequently, in the prior art, while the piezoelectric motors are simple the driver circuitry has until now been complex, especially when driving piezoelectric motors in two directions.
SUMMARY OF THE INVENTION
Accordingly, it is an object of some preferred embodiments of the present invention to provide drivers for piezoelectric elements that are reliable, simple and of low cost.
It is an object of some preferred embodiments of the present invention is to provide drivers for piezoelectric elements that operate the piezoelectric elements as actuators or motors bi-directionally with a minimum of components.
It is an object of some preferred embodiments of the invention to provide bi-directional drivers for piezoelectric motors or actuators in which a single high voltage unswitched drive circuit is used for both direction of motion.
It is an object of some preferred embodiments of the present invention to provide bi-directional drivers for piezoelectric motors or actuators in which the direction of motion is changed by switching circuitry located at a low voltage connection of the control circuitry.
It is an object of some preferred embodiments of the present invention to provide drivers for piezoelectric elements that utilize soft switching so as to minimize switching losses and increase the overall efficiency of the piezoelectric driver unit and to improve electromagnetic compatability.
It is an object of some preferred embodiments of the present invention to provide a piezoelectric driver operated from a low DC voltage source without additional complexity.
It is an object of some preferred embodiments of the present invention to provide a discrete bidirectional switching circuit used in conjunction with an AC voltage provided for operating a piezoelectric motor or other AC load.
Some prior art driver circuits for driving piezoelectric motor firm a DC voltage source, integrally, combined switching and inverter circuitry. That is the inverters did the switching of the inverter output to the piezoelectric element's electrodes without any discrete switching circuitry. The present invention separates the inverter and switching portions of the driver circuitry by providing discrete switching circuitry. Surprisingly, the result is a circuit for driving the piezoelectric element bidirectionally of decreased complexity using fewer components and operating more reliably.
In accordance with one aspect of the invention, a driver circuit for driving a piezoelectric type motor comprises an inverter circuit for providing an oscillating voltage to cause a mechanical displacement of a piezoelectric element and a separate switching arrangement for selecting the direction of said displacement. The driver circuit in the invention of this application delivers the driving voltages to the piezoelectric element at the mechanical resonant frequency of said piezoelectric element.
In a preferred embodiment of the invention a discrete switch arrangement includes high frequency switches for selectively applying voltages across said piezoelectric element to cause mechanical displacement of the piezoelectric element in a selected direction or selected directions. In preferred embodiments of the invention, the switches are on a low voltage side of the connection to the piezoelectric element.
There is thus provided, in accordance with a preferred embodiment of the invention, a micromotor comprising:
a piezoelectric element including a common electrode and a plurality of other electrodes formed thereon and including at least a first and a second electrode group, each group including at least one electrode, where the piezoelectric element causes motion in a fir
Addison Karen
Dougherty Thomas M.
Fenster & Company
Nanomotion Ltd.
LandOfFree
Driver for piezoelectric motors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Driver for piezoelectric motors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Driver for piezoelectric motors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3334808