Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-07-23
2001-05-15
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S317000
Reexamination Certificate
active
06232700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an actuator using an electromechanical transducer, particularly to an actuator using an electromechanical transducer suitable for finely positioning an optical system of a lens or the like.
The present invention also relates to an apparatus such as an optical system which employs such actuator.
2. Prior Art
There have been proposed actuators using an electromechanical transducer having a piezoelectric element for driving component parts in a camera and other precision equipment. Such actuators are disclosed in U.S. Pat. No. 5,589,723 and Japanese Laid Open Patent Publication No. 10-39359.
Here, an explanation will be given of a basic construction of such an actuator.
FIG. 12
is a perspective view showing an actuator by disassembling it into constituent members,
FIG. 13
is a perspective view showing a state where the actuator is assembled and
FIG. 14
is a sectional view showing the structure of a portion where a drive shaft, a slider block and a pad are frictionally coupled. An actuator
100
is constituted by a frame
111
, support blocks
113
,
113
a
and
114
, a drive shaft
116
, a piezoelectric element
115
, a slider block
112
, and a pad
118
. The drive shaft
116
is supported by the support block
113
a
and the support block
114
movably in the axial direction. One end of the piezoelectric element
115
is fixedly adhered to the support block
113
and other end thereof is fixedly adhered to one end of the drive shaft
116
. The drive shaft
116
is supported such that it can be displaced in the axial direction (arrow mark “a” direction and direction opposed thereto) when a displacement is caused in the thickness direction of the piezoelectric element
115
.
The drive shaft
116
penetrates the slider block
112
in the horizontal direction, an opening portion
112
a
is formed at an upper portion of the slider block
112
which the drive shaft
116
penetrates and an upper half of the drive shaft
116
is exposed. Further, a pad
118
which is brought into contact with the upper half of the drive shaft is fittedly inserted into the opening portion
112
a
, a projection
118
a
is installed at an upper portion of the pad
118
, the projection
118
a
of the pad
118
is pushed down by a leaf spring
119
and downward urging force F for bringing the pad
118
in contact with the drive shaft
116
is applied on the pad
118
. Incidentally, numeral
121
designates screws for fixing the leaf spring
119
to the slider block
112
. The structure of the portion where the drive shaft
116
, the slider block
112
and the pad
118
are brought into contact with each other is shown by FIG.
14
.
By such a structure, the drive shaft
116
, the pad
118
and the slider block
112
are frictionally coupled by pertinent frictional coupling force. Adjustment of the urging force F for determining the frictional coupling force can be controlled by a degree of fastening the screws
121
.
Next, an explanation will be given of the operation. First, when a sawtooth wave drive pulse having a gradual rise portion and a steep fall portion as shown by FIG.
15
(
a
) is applied to the piezoelectric element
115
, at the gradual rise portion of the drive pulse, the piezoelectric element
115
is gradually displaced to elongate in the thickness direction and the drive shaft
116
coupled to the piezoelectric element
115
is also displaced gradually in the positive direction (arrow mark “a” direction). At this moment, the slider block
112
frictionally coupled to the drive shaft
116
is moved in the positive direction along with the drive shaft
116
by the frictional coupling force and accordingly, a driven member not illustrated which is coupled to the slider block, for example, a frame for holding a correcting lens in the case of a correcting lens drive mechanism can be moved.
At the steep fall portion of the drive pulse, the piezoelectric element
115
is rapidly displaced to contract in the thickness direction and the drive shaft
116
coupled to the piezoelectric element
115
is also displaced rapidly in the negative direction (direction opposed to arrow mark “a”). At this moment, the slider block
112
frictionally coupled to the drive shaft
116
remains unmoved substantially at the position by overcoming the frictional coupling force by inertia force. By continuously applying the drive pulses to the piezoelectric element
115
, reciprocating oscillation having different speeds is caused in the drive shaft
116
and the slider block
112
frictionally coupled to the drive shaft
116
can be moved continuously in the positive direction.
Incidentally, “substantially” mentioned here includes a case where the slider block
112
follows the drive shaft
116
while causing a slip on faces where the slider block
112
and the drive shaft
116
are frictionally coupled in either of the positive direction and the direction opposed thereto and the slider block
112
is moved as a whole in the arrow mark “a” direction by a difference in drive time periods.
In moving the slider block
112
in a direction opposed to the previous direction (direction opposed to arrow mark “a”), the movement can be achieved by changing the waveform of the sawtooth wave drive pulse applied on the piezoelectric element
115
and applying a drive pulse comprising a steep rise portion and a gradual fall portion as shown by FIG.
15
(
b
).
According to the actuator using a piezoelectric element mentioned above, it has become apparent by experiments that the elongation displacement characteristic and the contraction displacement characteristic of the piezoelectric element in respect of the same applied voltage differ from each other and accordingly, the drive speeds differ from each other between a case where the sawtooth wave drive pulse having the gradual rise portion and the steep fall portion as shown by, for example, FIG.
15
(
a
) and a case where the drive pulse comprising the steep rise portion and the gradual fall portion as shown by FIG.
15
(
b
) having a waveform where the previous drive pulse is reverted.
Therefore, in order to provide the same drive speed in either of the directions of both in the case of moving the slider block in the positive direction (arrow mark “a” direction) by utilizing the gradual elongation displacement of the piezoelectric element (hereinafter, referred to as elongation displacement drive) and in the case of moving the slider block in the negative direction (direction opposed to arrow mark “a”) by utilizing the gradual contraction displacement of the piezoelectric element (hereinafter, referred to as contraction displacement drive), the piezoelectric element may be driven by generating drive pulses respectively having different waveforms in accordance with the elongation displacement drive and the contraction displacement drive.
However, generation of the drive pulses respectively having different waveforms in accordance with the elongation displacement drive and the contraction displacement drive gives rise to inconvenience where not only the structure of a drive pulse generating circuit or a control circuit becomes complicated but also number of parts is increased and the manufacturing cost is increased.
Further, depending on an apparatus to which the above-described actuator is applied, the drive speed of the actuator is changed by a direction of the gravitational force exerted on the apparatus. For example, when the above-described actuator is applied in driving a correcting lens for correcting a shift in holding a camera, load applied on the actuator is varied and the speed for driving the correcting lens is changed in either of a case where the correcting lens is moved in the up and down direction, that is, in the direction of the gravitational force when the optical axis of the photographing lens of the camera is substantially at the horizontal position and in the case where it is moved against the gravitational force.
In this way, depending on an apparatus to which the actua
Kanbara Tetsuro
Kosaka Akira
Dougherty Thomas M.
Minolta Co. , Ltd.
Sidley & Austin
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