Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-03-30
2001-02-27
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323170
Reexamination Certificate
active
06194811
ABSTRACT:
This application is based on application No. Hei 10-85843 filed in Japan, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a drive apparatus. More particularly, the present invention relates to a drive apparatus using an electromechanical transducer, such as a piezoelectric device, and more specifically relates to a drive apparatus using an electromechanical transducer suited for general drive use for precision machines, such as drive portions for XY drive tables, photographing lenses of cameras, projecting lenses of overhead projectors, lenses of binoculars and the like.
DESCRIPTION OF THE RELATED ART
A drive apparatus using an electric motor have been used conventionally to drive XY drive tables, photographing lenses of cameras and the like. However, such drive apparatus are large in size and problematically generate magnetic fields and noise. To solve these various problems, the applicants of the present application have proposed drive apparatuses using electromechanical transducers. U.S. Pat. Nos. 5,589,723 and 5,786,654 are examples of drive apparatus that use electromechanical transducers.
The exploded perspective view shown in FIG.
1
and the assembled perspective view shown in
FIG. 2
show an example of a drive apparatus using a piezoelectric device as an electromechanical transducer. This drive apparatus
90
comprises a securing member
24
secured to a base (not shown), a piezoelectric device
22
, and a drive shaft
26
supported by the securing member
24
so as to be slidable in the expansion/contraction direction of the piezoelectric device
22
. A drive unit
28
is frictionally coupled to the drive shaft
26
.
More specifically, one end surface of the piezoelectric device
22
in the extension/contraction direction thereof is secured to the securing member
24
, and the other end surface of the piezoelectric device is secured to one end surface of the drive shaft
26
. A driven member (not shown), such as a stage on which parts are mounted, is connected to the drive unit
28
.
The drive unit
28
comprises a main body
28
a
, a pad
28
b
, a leaf spring
28
c
and screws
28
d
. A hole is formed in the main body
28
a
, in which the drive shaft
26
is inserted. Furthermore, a groove is formed at the upper central portion of the main body
28
a
so that the upper half of the drive shaft
26
inserted in the main body
28
a
is exposed. The pad
28
b
is fitted in the groove. The pad
28
b
is pushed down by the leaf spring
28
c
secured to the upper surface of the main body
28
a
with the screws
28
d
so as to make contact with the drive shaft
26
. With this configuration, the drive shaft
26
is frictionally coupled to the drive unit
28
. Moreover, a scale
12
is secured to a side surface of the drive unit
28
in the direction of movement thereof. A sensor
14
is secured to the securing member
24
so as to face the scale
12
, and is used to detect the position of the drive unit
28
.
Next, the operation of the drive apparatus
90
will be described below. When a sawtooth pulse voltage
92
shown in
FIG. 3A
is applied to the piezoelectric device
22
for example, the drive shaft
26
(in particular, its frictional coupling point to the drive unit
28
) is displaced in a triangular shape with respect to the securing member
24
as shown in the model view in FIG.
3
B.
In other words, the piezoelectric device
22
extends gradually in the extension/contraction direction thereof at the gradually rising portion
92
a
of the pulse voltage
92
as shown in FIG.
3
A. As indicated by code
94
a
in
FIG. 3B
, the drive shaft
26
is gradually displaced in the positive direction (the direction indicated by arrow a in
FIGS. 1 and 2
) with a slight time delay with respect to the waveform of the pulse voltage
92
because of the effect of the elastic deformation of the drive shaft
26
and the like. At this time, since a friction force is applied to the friction surface of the drive unit
28
making frictional coupling to the drive shaft
26
in the movement direction of the drive shaft
26
, the drive unit
28
is moved in the positive direction along the drive shaft
26
. When the frequency of the pulse voltage
92
is raised, a relative slip is generated between the drive shaft
26
and the drive unit
28
. Even in this case, the drive unit
28
is moved in the positive direction along the drive shaft
26
.
Next, the piezoelectric device
22
contracts abruptly in the extension/contraction direction thereof at the abruptly falling portion
92
b
of the pulse voltage
92
as shown in FIG.
3
A. As indicated by code
94
b
in
FIG. 3B
, the drive shaft
26
is abruptly displaced in the negative direction (the direction indicated by arrow b in
FIGS. 1 and 2
) with a slight time delay with respect to the waveform of the pulse voltage
92
because of the effect of the elastic deformation of the drive shaft
26
and the like. At this time, a friction force is applied to the friction surface of the drive unit
28
making frictional coupling to the drive shaft
26
in the movement direction of the drive shaft
26
. However, since the application time of the force is short and the inertia force of the drive unit
28
(and the driven member) is present, the drive unit
28
is not moved at all or is hardly moved, and only the drive shaft
26
is moved. In other words, a relative slip is generated between the drive shaft
26
and the drive unit
28
, and the drive shaft
26
returns to its original position. However, the drive unit
28
is hardly moved. Therefore, the drive unit
28
is moved in the positive direction a when the drive shaft
26
is displaced gradually as a whole. This occurs when a pulse voltage comprising a gradually rising portion and an abruptly falling portion is supplied to the piezoelectric device
22
.
On the other hand, a pulse voltage comprising an abruptly rising portion and a gradually falling portion is supplied to the piezoelectric device
22
to drive the drive unit
28
in the negative direction b.
Furthermore, in the drive apparatus
90
, the sensor
14
detects the position of the drive unit
28
, and this detection is used for feedback control in order to move the drive unit
28
to its target position.
Generally, the drive speed of the drive unit
28
is roughly proportional to the movement speed of the drive shaft
26
in the direction wherein the drive unit
26
is moved gradually. Therefore, as indicated by codes
96
to
98
in
FIG. 3C
for example, the movement speed of the drive shaft
26
is changed by changing the voltage amplitude H (see
FIG. 3A
) of the pulse voltage
92
, thereby to control the drive speed of the drive unit
28
. In order to raise the drive speed of the drive unit
28
for example, the voltage amplitude H of the pulse voltage
92
is increased.
As described above, in the conventional drive apparatus
90
, the speed of the drive unit
28
has been controlled by changing the voltage amplitude H of the above-mentioned pulse voltage
92
.
However, if a drive load changes, optimal drive control cannot be attained by the above-mentioned method and apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a drive apparatus using an electromechanical transducer usable for drive control depending on a change in drive load.
In order to solve the above-mentioned problem, the drive apparatus using an electromechanical transducer in accordance with the present invention comprises a drive pulse generation device for generating pulses, an electromechanical transducer which is connected to the drive pulse generation device and extends or contracts depending on the pulses supplied from the drive pulse generation device, a support member secured to one end of the electromechanical transducer in the extension/contraction direction thereof, a first friction member secured to the other end of the electromechanical transducer in the extension/contraction direction thereof, and a second friction member frictionally coupled to the
Nishihara Yasuo
Shinke Satoshi
Burns Doane , Swecker, Mathis LLP
Dougherty Thomas M.
Minolta Co. , Ltd.
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