Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-07-07
2002-05-07
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000, C271S264000
Reexamination Certificate
active
06384514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to piezoelectric positioning devices and in particular to piezoelectric positioning devices with reversible action of both rotational and linear reciprocal types. More specifically, the positioning device of the invention contains one or more actuators having a linear contact with the corresponding rotor or the slider. The positioning device of the invention can be used generally as a high performance replacement for small conventional electric drivers used in computer equipment, robotics, manufacturing equipment, aerospace, automobiles, toys, etc. The positioning device of the present invention can be used particularly effectively in various turntable and disk drive devices such as for magnetic and optical data storage equipment, especially when small size and weight are required for compactness and when precision positioning of a magnetic or optical reading head is needed for accurate and reliable performance.
2. Description of the Prior Art
Linear and rotational piezoelectric positioning devices with reversible action are generally well known and widely used in various applications. All of these known devices incorporate a basic piezoelectric drive arrangement in which a piezoelectric actuator is placed in contact with a movable element such as a slider or a rotor made typically of a hard to compress material. A frictional contact surface is therefore intermittently present between the actuator and that movable element which transmits the driving force or torque from the piezoelectric actuator to the movable element. Limitations of such arrangement are described in detail in the parent patent applications. Briefly, these devices have limited number of operating hours due to the wear and ultimately mechanical failure of the surface of the movable element. Once the surface is damaged, the contact between the actuator and the movable element is no longer optimal and the driving force transmission is no longer present. One negative consequence of that is reduced accuracy of positioning as well as reduced operational life. Another limitation of these devices is in the relatively high clamping force between the actuator and the movable element in an attempt to partially compensate for the wear of the surface contact. That high clamping force reduces the efficiency of the force transmission and overall efficiency of the device.
We have proposed and described in details in our previous applications the piezoelectric drive device with linear contact between the actuator and the movable element. Briefly stated, the actuator equipped with a hard surface insert engages with the compressible surface of the movable element to compress it within the elastic limits thereof without any slippage and to form a temporary microgroove on that surface. Upon disengagement, the surface of the movable element restores its initial shape until the next compression cycle. These devices demonstrate higher energy transmission efficiency and longer operating life. However, reversible devices with such linear contact, both linear and rotational were not known before in the prior art.
One particularly advantageous application of a reversible device of this type is for data storage devices. Those skilled in the art of making and using data processing and storage equipment are familiar with magnetic data storage arrangements when a transducer is positioned adjacent a moving magnetic recording surface. Such a device will record magnetic bits as data from the disk surface and recover this information by processing the signal from a transducer adjacent a particular “recording track” along the surface.
This invention relates in part to a piezoelectric positioning device for establishing and maintaining the placement of such a transducer with respect to such recording tracks; it is particularly adapted for recording on magnetic tape, drum, and disk media, especially for high density, high TPI recording as well as for recording on various optical disks and other optical devices. In such recording, a fast, non-magnetic, miniaturized, solid state translation means is particularly desired—especially where translation distances are relatively small, on the order of a few dozen micro inches or more, typically over a total excursion of only a few mils.
Limitations in present-day transducer positioning apparatus, such as the typical voice coil actuator systems, or the like are well known. In addition to their mechanical inefficiency due to a large number of moving parts, such systems are undesirably large, slow and inflexible in their design approach. They are particularly unsatisfactory for “centering” a transducer relative to a narrow recording track, where positioning is critical. Such systems are also troublesome in that they use solenoid magnets or other magnetic actuator means, creating stray magnetic fields that can interfere with the magnetic recording apparatus. The present invention is adapted to improve these shortcomings with a solid state, piezo-electric flexure arrangement for mounting and positioning magnetic heads.
Various reversible piezoelectric positioning devices were proposed in the prior art for use in this disk drive application. Examples of such devices can be found in U.S. Pat. Nos. 4,188,645 by Ragle; 4,764,828 by Gollbach; 5,189,578 by Mori; 5,400,192 by Mizoshita; 5,438,469 by Rudi; 5,521,778 by Boutaghou and others. As was indicated above, all of these devices suffer from the limitations arising from the surface contact between the piezoelectric actuator and the movable element, a rotor or a swinging arm in this case. A smaller and more efficient positioning device with extended operational life is therefore needed for these disk drives.
Various reversible piezoelectric devices were proposed by Zumeris of Nanomotion and described in the following U.S. Patents which are incorporated herein by reference: Nos. 5,616,980; 5,682,076; 5,696,421; 5,714,833; and 5,777,423. The design of a piezoelectric plate is of particular interest for this invention. Generally speaking, the piezoelectric plate is described as having a rectangular shape. Four electrodes are plated or otherwise attached to the top face of the plate in a checkerboard alternating arrangement. A larger single electrode is placed on the opposite bottom face of the plate. By exciting the top and the bottom electrodes in alternate sequence, one can achieve certain vibrations of the plate in either one of the opposite directions. These vibrations can then be used to reversibly drive a movable element. Although the design of the piezoelectric plate has certain advantages such as simplicity of operation, these devices have similar limitations to those of the other patents of the prior art. The most important limitation is limited operational life and low efficiency of energy transmission due to the wear and eventual slippage of the contact surface of the movable element made of a hard to compress material. That leads to reduced accuracy and lower efficiency of operation. Piezoelectric reversible positioning device is therefore needed to overcome these limitations.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome these and other drawbacks of the prior art by providing a novel reversible piezoelectric positioning device of both rotational and linear type with linear contact between the actuator and the movable element with improved operational life.
Another object of the invention is to provide a reversible piezoelectric positioning device for moving the arm containing a reading head of a disk drive for data storage devices such as optical, CD-ROM, hard drive, floppy drive, and other similar magnetic and optical disks and tapes; such positioning device being more accurate in positioning, smaller in size, lower in weight, and requiring less energy for its operation.
Yet another object of the present invention is to provide a reversible piezoelectric positioning device with superior start-stop characteristics an
Slutcky Alexandr I.
Slutskiy Imanuil A.
Leschinsky Boris
Sircus Brian
Technology Commercialization Corp.
Zarroli Michael C.
LandOfFree
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