Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-07-27
2001-04-03
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323010
Reexamination Certificate
active
06211607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an actuator using an electro-mechanical transducer suitable for driving typical precision machinery including an X-Y drive table, a lens for a camera, a projection lens for an overhead projector, a lens for a binocular, and a probe for medical equipment.
DESCRIPTION OF THE RELATED ART
To drive an X-Y drive table, a lens for a camera, and the like, there has conventionally been used an actuator using an electric motor. However, the device has been increased in size and such drawbacks as the occurrence of a magnetic field and noise production have been reported. As means for solving the variety of problems, the present applicant has proposed an actuator using an electro-mechanical transducer, i.e., an actuator wherein a moving member is coupled frictionally to a driving member that has been coupled securely to the electro-mechanical transducer. A drive pulse with a sawtooth waveform is applied to the electro-mechanical transducer to cause displacements at different speeds in the direction of expansion or contraction, thereby causing the driving member to move the moving member frictionally coupled thereto in a specified direction (U.S. Pat. No. 5,589,723).
FIGS. 9 and 10
show an example of the foregoing actuator using the electro-mechanical transducer, of which
FIG. 9
is a perspective view showing the actuator in disassembled state and
FIG. 10
is a perspective view showing the actuator in assembled state.
In
FIGS. 9 and 10
, the actuator
100
is composed of: a holding member
101
; a piezoelectric element
110
which is a type of electro-mechanical transducer; a drive shaft
111
; a slider
112
; and other members.
The holding member
101
is formed as a whole into a generally cylindrical configuration. First and second holes
102
and
103
are formed in the holding member
101
to extend therethrough in the diametrical direction (vertical direction in FIG.
9
). A wall portion
104
located between the holes
102
and
103
is formed with a bearing
104
a
for supporting the drive shaft
111
. On the other hand, the portion of the holding member
101
corresponding to an end face thereof and composing the wall portion
105
of the hole
103
is formed with a bearing
105
a
for supporting the drive shaft
111
. The holding member has a portion
106
as a mounting portion for mounting the actuator to equipment.
The piezoelectric element
110
is disposed in the first hole
102
to have one end secured adhesively to the wall face of the holding member
101
closer to the mounting portion
106
and the other end secured adhesively to the drive shaft
111
. The drive shaft
111
secured adhesively to the piezoelectric element
110
can reciprocate in the axial direction when the piezoelectric element
110
undergoes an expansive or contractive displacement in the direction of thickness, since the drive shaft
111
is supported by the respective bearings
104
a
and
105
a
of the wall portions
104
and
105
.
The slider designated at
112
is disposed in the hole
103
of the holding member
101
to be movable in the direction of the cylindrical axis within the hole
103
, while using the longitudinal inner wall face composing the wall
103
as a detent and guide. The lower portion of the slider
112
is provided with a member to be driven by the actuator
100
, e.g., a mounting portion
112
c
for the mounting of, e.g., a movable lens barrel if in a lens system.
The main body portion of the slider
112
is formed with a hole
112
a
through which the drive shaft
111
extends, while the portion of the slider
112
overlying the drive shaft
111
extending through the hole
112
a
is formed with an opening
112
b
, in which the upper half of the drive shaft
111
is exposed. A pad
113
for abutting on the upper half of the drive shaft
111
is fitted in the opening
112
b
. The upper part of the pad
113
is provided with a projection
113
a
, while the bottom surface thereof is provided with a groove
13
b
for abutting on the upper half of the drive shaft
111
. The groove
113
b
of the pad
113
abuts on the drive shaft
111
with the projection
113
a
of the pad
113
being pressed down by a plate spring
114
, whereby a downward biasing force is applied. Screws for securing the plate spring
114
to the slider
112
are designated at
115
.
With the structure, the drive shaft
111
, the pad
113
, and the slider
112
are frictionally coupled to each other under a proper frictional coupling force. The biasing force F which determines the frictional coupling force can be adjusted by moderating the tightening of the screws
115
.
As described above, the drive shaft
111
is supported by the respective bearings
104
a
and
105
a
of the wall portions
104
and
105
and has an end portion
111
a
on the opposite side of the piezoelectric element
110
slightly protruding from within the hole of the bearing
105
a
.
A plate spring
117
is secured to the outer side of the wall portion
104
with screws
118
to axially press the end portion
111
a
of the drive shaft
111
. The pressing force can be adjusted by moderating the tightening of the screws
118
.
A description will be given next to the operation. When a sawtooth wave drive pulse having a slow rising portion and a rapid falling portion, as shown in
FIG. 11A
, is initially applied to the piezoelectric element
110
, the piezoelectric element
110
is displaced slowly expansively in the direction of thickness with the slow rising portion of the drive pulse. As a result, the drive shaft
111
coupled to the piezoelectric element
110
is also displaced slowly in a positive direction (direction indicated by the arrow a). At this time, the slider
112
frictionally coupled to the drive shaft
111
moves in the positive direction together with the drive shaft
111
under the frictional coupling force.
With the rapid falling portion of the drive pulse, the piezoelectric element
110
is displaced rapidly contractively in the direction of thickness, so that the drive shaft
111
coupled to the piezoelectric element
110
is also displaced rapidly in a negative direction (direction opposite to the direction indicated by the arrow a). At this time, the slider
112
frictionally coupled to the drive shaft
111
inertially overcomes the frictional coupling force so that it stays in place and does not substantially move. By continuously applying the drive pulse to the piezoelectric element
110
, it becomes possible to produce reciprocal vibrations at different speeds in the drive shaft
111
and continuously move the slider
112
frictionally coupled to the drive shaft
111
in the positive direction.
In the terminology used here, “substantially” covers the case where the slider
112
moves after the drive shaft
111
with a slide occurring at a frictional coupling plane between the slider
112
and the drive shaft
111
so that the slider
112
and the drive shaft
111
move as a whole entity in the direction indicated by the arrow a due to different driving times.
The movement of the slider
112
in the direction opposite to the foregoing (direction opposite to the direction indicated by the arrow a) can be achieved by changing the waveform of the sawtooth wave drive pulse applied to the piezoelectric element
110
and applying a drive pulse consisting of a rapid rising portion and a slow falling portion, as shown in FIG.
11
B.
Thus, in the conventional actuator using the electro-mechanical transducer, the piezoelectric element and the electro-mechanical transducer are secured adhesively to the holding member and to the drive shaft, respectively. Consequently, adhesion at the securely coupled portion gradually deteriorates due to vibrations transmitted from the electro-mechanical transducer during driving, which may cause such a problem as the peeling off of the securely coupled portion. To overcome the problem, a plate spring (plate sprint
117
in the conventional embodiment mentioned above) is disposed at the end portion of the drive shaft to bias the drive
Dougherty Thomas M.
McDermott & Will & Emery
Minolta Co. , Ltd.
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