Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2001-02-26
2002-10-29
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06472795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrostatic actuator and a method of driving the same. More specifically, the present invention relates to an electrostatic actuator that does not comprise any structural bearing nor guide and is compact and adapted to support the rotor in a non-contact way and drive it in a desired direction of rotation with a low voltage.
2. Related Background Art
Various electrostatic actuators have been proposed in recent years. The electrostatic actuator provides the following advantages relative to the electromagnetic actuator.
(1) It is highly efficient and does not give rises to any loss in a stationary state.
(2) Since it comprises only electrodes, it is structurally simple and adapted to down-sizing.
FIG. 1
of the accompanying drawings is a schematic perspective view of a floating rotary drive system using an electrostatic actuator that was proposed at page 537 of the released papers for the lectures in the 1998 Spring Meeting of the Japan Society for Precision Engineering. The floating rotary drive system uses an electrostatic actuator comprising a rotor
401
and a stator
402
and is designed to eliminate the frictional force between the rotary
401
and the stator
402
by causing the rotor
401
to acoustically float relative to the stator
402
.
FIG. 2
schematically illustrates the pattern of arrangement of the electrodes on the stator
402
of the electrostatic actuator of FIG.
1
.
Referring to
FIGS. 1 and 2
, the oscillator
404
is driven to operate according to a signal from oscillator driver
405
. With this electrostatic actuator, an acoustic floating force is generated on the surface of the stator
402
as the oscillator
404
is driven to operate and the oscillation of the oscillator
404
is amplified by means of a horn
403
so that the rotor
401
is supported above the surface of the stator
402
in a non-contact way. Thus, the rotor
401
is driven to rotate as a drive voltage is applied to drive electrodes
406
according to the signal from electrostatic drive circuit
407
. The drive voltage output from the electrostatic drive circuit
407
is a 3-phase AC voltage. The rotor is made of glass.
As shown in
FIG. 2
, a large number of circular electrodes
406
are arranged on the stator
402
so that both a torque and a centripetal force arise simultaneously and are applied to the rotor
401
. The drive voltage is 1 kV p-p and the rotor
401
rotates only clockwise.
The above described known electrostatic actuator is, however, accompanied by the following problems. Firstly, the rotor of the electrostatic actuator rotates only clockwise. Secondary, the electrodes of the stator have a circular profile and are separated from adjacent ones by a large distance so that the inductive electric charge generated on the rotor is located remote from the electrodes on the stator to consequently reduce the rotary force that is actually applied to the rotor. In other words, a large drive voltage is required to make the electrostatic actuator operate properly. Then, the overall arrangement will be rather bulky.
SUMMARY OF THE INVENTION
In view of the above identified problems of the prior art, it is therefore the object of the present invention to provide an electrostatic actuator that is compact and adapted to drive the rotor in a desired direction of rotation with a low drive voltage and a method of driving such an electrostatic actuator.
According to the invention, the above object is achieved by providing an electrostatic actuator comprising:
a stator formed by a circular substrate having a surface carrying thereon a plurality of drive electrodes, each of the drive electrodes having an arcuate profile extending from the center of the substrate toward the outer periphery thereof;
a rotor arranged opposite to the surface of the stator carrying thereon the drive electrodes; and
a drive circuit for applying a drive voltage to the drive electrodes of the stator.
According to the invention, there is also provided a rotary stage comprising:
an electrostatic actuator as defined above; and
a sample holding jig arranged on the rotor of the electrostatic actuator.
According to the invention, there is also provided an optical scanning device comprising:
a light source adapted to emit a laser beam;
an electrostatic actuator as defined above; and
a polygon mirror arranged on the rotor of the electrostatic actuator and adapted to deflect the laser beam emitted from the light source.
According to another aspect of the invention, there is also provided a method of driving an electrostatic actuator comprising a stator formed by a circular substrate having a surface carrying thereon a plurality of drive electrodes, each of the drive electrodes having an arcuate profile extending from the center of the substrate toward the outer periphery thereof, a rotor arranged opposite to the surface of the stator carrying thereon the drive electrodes, a drive circuit for applying a drive voltage to the drive electrodes of the stator and an oscillator for generating dynamic pressure between the stator and the rotor, the method comprising the steps of:
generating dynamic pressure between the stator and the rotor by means of the oscillator to float the rotor above the stator; and
applying a multiphase drive voltage to the drive circuit to drive the rotor to rotate.
REFERENCES:
patent: 3143671 (1964-08-01), Gale
patent: 4754185 (1988-06-01), Gabriel et al.
patent: 5955800 (1999-09-01), Shearwood et al.
patent: 6211599 (2001-04-01), Barnes et al.
patent: 6329737 (2001-12-01), Jerman et al.
patent: 6359367 (2002-03-01), Sumanaweera et all
Hirose Futoshi
Yagi Takayuki
Yasuda Susumu
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