Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-02-22
2003-01-28
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316020, C310S323020
Reexamination Certificate
active
06512321
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims the priority of Japanese Patent Application No. 00-5 0081544, filed on Mar. 23, 2000 in Japan, the entire contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE APPLICATION
1. Field of the Invention
The present invention relates to a driving apparatus, and more particularly to a driving apparatus appropriate for the driving of a movable XY stage, the photo-taking lens of a camera, the projecting lens of an overhead projector, or the lenses of binoculars, and the like.
2. Description of the Related Art
One driving apparatus known in the conventional art comprises an impact-type piezoelectric actuator wherein an engaging member to which a photo-taking lens is mounted is caused to engage with a cylindrical drive member such that a prescribed friction force occurs, and a piezoelectric element is attached to one end of the drive member. For example,
FIG. 18
shows the basic construction of a driving apparatus for. adjusting the position of the photo-taking lens of a camera.
The driving apparatus
100
in this drawing comprises a piezoelectric element
101
that comprises an electromechanical conversion element, a cylindrical drive member
102
that is driven by the piezoelectric element
101
, an engaging member
103
that engages with the drive member
102
through a prescribed friction force, and a drive circuit
104
that applies a drive voltage to the piezoelectric element
101
.
The piezoelectric element
101
expands and contracts in response to the drive voltage applied by the drive circuit
104
. One end of the piezoelectric element
101
is fixed to a support member
105
in the direction of expansion or contraction, while the other end is attached to one end of the drive member
102
along the axial direction. The photo-taking lens L comprising the driven object is mounted to the engaging member
103
at a prescribed location, and can move along the drive member
102
in the axial direction.
The drive circuit
104
comprises a waveform generating unit
107
and a power amp
108
, as shown in FIG.
19
. It inputs to the power amp
108
a drive voltage having a 0-5V sawtooth-type waveform obtained from the waveform generating unit
107
, and outputs from the power amp
108
a drive voltage having a 0-10V sawtooth-type waveform.
In the driving apparatus
100
constructed as described above, when a drive voltage having the waveform shown in FIG.
20
(
a
) that has gentle rising edges and steep falling edges (a so-called outward waveform) is repeatedly applied to the piezoelectric element
101
from the drive circuit
104
, the engaging member
103
moves in the direction of the arrow (a), which is the outward direction (the direction away from the piezoelectric element
101
) due to the expansion and contraction of the piezoelectric element
101
. In other words, because the piezoelectric element
101
expands gradually during the gentle rising edge of the drive voltage, the engaging member
103
moves in the outward direction together with the drive member
102
, and because the piezoelectric element
101
contracts suddenly during the steep falling edge, even though the drive member
102
moves in the return direction, the engaging member
103
slips relative to the drive member
102
and remains in essentially the same position. As a result, when a drive voltage having the waveform shown in FIG.
20
(
a
) is repeatedly applied to the piezoelectric element
101
, the engaging member
103
moves intermittently in the direction of the arrow (a).
When a drive voltage having the waveform shown in FIG.
20
(
b
) that has steep rising edges and gentle falling edges (a so-called return waveform) is repeatedly applied to the piezoelectric element
101
from the drive circuit
104
, the engaging member
103
moves in the return direction (the direction toward the piezoelectric element
101
) opposite the direction of the arrow (a) due to the expansion and contraction of the piezoelectric element
101
. In other words, because the piezoelectric element
101
expands suddenly during the steep rising edge of the drive voltage, even though the drive member
102
moves in the outward direction, the engaging member
103
slips relative to the drive member
102
and remains in essentially the same position, and because the piezoelectric element
101
contracts gradually during the gentle falling edge, the engaging member
103
moves in the return direction together with the drive member
102
. As a result, when a drive voltage having the waveform shown in FIG.
26
(
b
) is repeatedly applied to the piezoelectric element
101
, the engaging member
103
moves intermittently in the direction opposite the direction of the arrow (a). By applying a drive voltage having the waveform shown in either FIG.
20
(
a
) or
20
(
b
) to the piezoelectric element
101
in this way, the photo-taking lens L can be moved in the outward direction or the return direction.
The drive circuit
104
may have the construction shown in
FIG. 21
, for example. The drive circuit
104
shown in the drawing comprises a first drive circuit
109
consisting of a slow-charging circuit and a rapid-charging circuit, and a second drive circuit
110
consisting of a rapid-charging circuit and a slow-charging circuit, and carries out the drive control of the drive circuits
109
and
110
through prescribed 0-5V control signals generated by a digital circuit.
In other words, the first drive circuit
109
has a construction in which two switches
111
and
112
are serially connected with a constant-current source
113
such that the constant-current source
113
comes between the switches
111
and
112
with respect to the power supply voltage Vs, while the second drive circuit
110
has a construction in which two switches
114
and
115
are serially connected with a constant-current source
116
such that the constant-current source
116
comes between the switches
114
and
115
with respect to the power supply voltage Vs. The piezoelectric element
101
is connected to both ends of the switch element
112
in the first drive circuit
109
and to both ends of the serial circuit connecting the switch element
115
and the constant-current source
116
in the second drive circuit
110
.
In the drive circuit
104
shown in
FIG. 21
, a slow-charging circuit is formed through the closing of the switch
111
of the first drive circuit
109
, and a rapid-charging circuit is formed through the subsequent opening of the switch
111
and the closing of the switch
112
. By repeatedly carrying out these switch operations through control signals, a drive voltage having the outward waveform shown in FIG.
20
(
a
) is repeatedly applied to the piezoelectric element
101
.
Similarly, a rapid-charging circuit is formed through the closing of the switch
114
of the second drive circuit
110
, and a slow-charging circuit is formed through the subsequent opening of the switch
114
and the closing of the switch
115
. By repeatedly carrying out these switch operations through control signals, a drive voltage having the return waveform shown in FIG.
20
(
b
) is repeatedly applied to the piezoelectric element
101
. In this way, the photo-taking lens L can be moved in both the outward and return directions as a result of the movement of the engaging member
103
in the outward and return directions as described above.
When a driving apparatus comprising an impact-type piezoelectric actuator is applied as the drive source for an optical system such as a camera photo-taking lens, it is preferred that the driving apparatus be as inexpensive and compact as possible. However, with the conventional driving apparatus
100
, where the drive circuit
104
shown in
FIG. 19
is used, the circuit to generate signals having a sawtooth-type waveform is complex, and therefore the problem arises that the goals of low cost and compactness become difficult to achieve. This problem also arises with the drive circuit
104
shown in
FIG. 21
as well, because th
Okada Hiroyuki
Okamoto Yasuhiro
Yoshida Ryuichi
Budd Mark O.
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
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