Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-07-20
2001-09-04
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06285113
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to surface acoustic wave actuators, and magnetic disk devices and optical disk devices incorporating surface acoustic wave actuators.
BACKGROUND OF THE INVENTION
Surface acoustic wave actuators have potential for use as small linear actuators due to their advantages of high speed and high thrust driving capabilities with a small size.
Japanese Laid-open Patent No. H10-296186 and an invention introduced on p. 505 of the 10th “Electromagnetic Dynamics” symposium reports disclose means of improving the energy efficiency of conventional surface acoustic wave actuators.
FIG. 9
shows a surface acoustic wave actuator disclosed in Japanese Laid-open Patent No. H10-296186. Waveguide
17
is configured in an orbital circuit, and surface acoustic waves are propagated along this orbital circuit, thus improving the energy efficiency for driving slider
18
.
FIG. 10
shows a surface acoustic wave actuator introduced on p. 505 of the 10th “Electromagnetic Dynamics” Symposium reports. In this surface acoustic wave actuator, four unidirectional interdigital transducers
19
having reflector
100
circulate energy, and two driving electrodes
20
work to replenish only the energy lost by circulation to improve the energy efficiency.
However, the means of improving the energy efficiency in the conventional surface acoustic wave actuators as described above requires a larger area on the vibrator for areas other than the propagating face. The system disclosed in Japanese Laid-open patent No. H10-296186 requires an area equivalent to the propagating face for circulating the surface acoustic waves, and the system disclosed on p. 505 of the 10th “Electromagnetic Dynamics” symposium reports, requires many interdigital transducers, enlarging the area occupied by these electrodes on the vibrator.
The present invention aims to offer a surface acoustic wave actuator with even better energy efficiency while maintaining a small area for that other than the propagating face on the vibrator.
SUMMARY OF THE INVENTION
The surface acoustic wave actuator of the present invention includes a vibrator, a first unidirectional interdigital transducer disposed on the vibrator, a second unidirectional interdigital transducer disposed on the vibrator, and an electrical combiner. One of the unidirectional interdigital transducers is connected to an input port of the electrical combiner, and the other unidirectional interdigital transducer is connected to an output port.
This configuration limits an area other than the propagating face on the vibrator to that occupied by two unidirectional interdigital transducers. Energy of the surface acoustic waves propagated on the propagating face is excited by one of the unidirectional interdigital transducers connected to the output port of the electrical combiner, and then converted to electrical energy by the unidirectional interdigital transducer connected to the input port. The electrical combiner adds this electrical energy and high frequency signal energy input from the external power supply, and then the combined energy is input again to the unidirectional interdigital transducer connected to the output port for exciting the surface acoustic waves. This configuration allows to circulate the energy, and thus energy of the surface acoustic waves is kept constant by just replenishing energy from the external power supply lost during circulation. Accordingly, a surface acoustic wave actuator with good energy efficiency is achievable. The present invention thus reduces the area other than the propagating face on the vibrator, achieving a surface acoustic wave actuator with even better energy efficiency.
Moreover, the surface acoustic wave actuator of the present invention includes the first and second unidirectional interdigital transducers; vibrator on which the unidirectional interdigital transducers are disposed in a way to have the first unidirectional interdigital transducer to electrically convert the surface acoustic wave excited by the second unidirectional interdigital transducer; relative movement member which moves relative to the vibrator; an electrical combiner to which the first unidirectional interdigital transducer and external power supply is connected to its input port and the second unidirectional interdigital transducer is connected to its output port; and means for generating contact pressure between the vibrator and relative movement member. This configuration makes it possible to achieve a surface acoustic wave actuator with a smaller area outside the propagating face and better energy efficiency than the prior art.
The surface acoustic wave actuator of the present invention also includes the first and second unidirectional interdigital transducers; vibrator on which the unidirectional interdigital transducers are disposed in a way to have one unidirectional interdigital transducer to electrically convert the surface acoustic wave excited by the other unidirectional interdigital transducer; a relative movement member which moves relative to the vibrator, a switch for changing the combination of connection of the first and second unidirectional interdigital transducers to the input and output ports of the electrical combiner; an electrical combiner to which the switch is connected and external power supply is also connected to its remaining input port; and means for generating contact pressure between the vibrator and relative movement member. Changing the combination of connections selected by the switch allows it to be driven in both directions, and enables the surface acoustic wave actuator with a smaller area outside the propagating face and further better energy efficiency than the prior art to be achieved.
The surface acoustic wave actuator of the present invention also connects the output and input ports of the electrical combiner by means of the switch when the relative movement member does not move in relative to the vibrator. The actuator may thus be driven, stopped, and its driving direction switched without any adjustment of the external power supply. This configuration allows a surface acoustic wave actuator occupying a smaller area outside the propagating face and better energy efficiency than the prior art to be achieved.
The surface acoustic wave actuator of the present invention is also provided with the electrical combiner which combines energy in a way such that energy input from the unidirectional interdigital transducer is four times or greater than the energy input from the external power supply. A higher combining ratio allows the energy efficiency to be further improved.
The surface acoustic wave actuator of the present invention also has equivalent input admittance at the driving frequency of both first and second unidirectional interdigital transducers. This facilitates the manufacture of the electrical combiner or switch, reducing any loss which may occur by matching.
The surface acoustic wave actuator of the present invention also has a unidirectional interdigital transducer whose input admittance at the driving frequency satisfies a matching condition with characteristic impedance. Easier matching with the electrical combiner or switch reduces matching loss, and thus further improves energy efficiency.
The surface acoustic wave actuator of the present invention also propagates the surface acoustic waves to at least one waveguide provided on the vibrator. This reduces the loss by diffraction of the surface acoustic waves, enabling further improvement of energy efficiency.
The surface acoustic wave actuator of the present invention also has a vibrator whose face propagating the surface acoustic waves is partially made of a different material. Selection of the most suitable material allows good friction driving characteristics and cost reduction to be achieved.
The use of the above surface acoustic wave actuators as an actuator for driving a head in a magnetic disk device allows the magnetic disk device with good access performance to be achieved.
The use of the above surface a
Aoki Shin-ichiro
Asai Katsuhiko
Higuchi Toshiro
Ikeda Junji
Kurosawa Minoru
Addison Karen
Enad Elvin
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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