Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-06-16
2001-05-15
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323020
Reexamination Certificate
active
06232697
ABSTRACT:
This application is based on application No. Hei 10-169474 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving apparatus and equipment comprising the driving apparatus.
The present invention relates to a driving apparatus and equipment for moving a member e.g. the lens of a camera by means of a plurality of electro-mechanical transducer such as piezoelectric elements.
2. Description of the Prior Art
A description will be given to a conventional driving apparatus which performs linear driving by means of piezoelectric elements with reference to
FIG. 11
showing a lens unit for driving a plurality of lenses.
FIG. 11
is a perspective view of the lens unit.
201
,
205
denote lens barrels for holding lenses. Shafts
202
,
203
for slidably guiding the lens barrels
201
,
225
in the direction of an optical axis extend through projections
201
a,
201
c,
225
a,
225
c
formed integrally with the lens barrels
201
,
225
. The shafts
202
,
203
have their respective near-front and near-rear end portions held slidably lengthwise thereof in respective holes formed in the upright portions
213
a,
218
a
of support members
213
,
218
and in respective holes formed in the upright portions
213
c,
218
c
of the support members
213
,
218
.
The projections
201
a,
201
c,
225
a,
225
c
are provided with leaf springs
214
,
219
attached thereto with screws. The leaf springs
214
,
219
are pressed against the shafts
202
,
203
, respectively. When the lens barrels
201
,
225
move, therefore, they slide frictionally along the shafts
202
,
203
. Piezoelectric elements
212
,
217
are attached to the respective rear end portions of the shafts
202
,
203
. The piezoelectric elements
212
,
217
have respective rear end portions secured to the upright portions
213
e,
218
e
of the support members
213
,
218
. The support members
213
,
218
are secured to a common fixed portion.
The principle of operation of a moving mechanism using piezoelectric elements is disclosed in U.S. Pat. No. 5,225,941 or the like, which will be described briefly with reference to the schematic diagram shown in FIG.
2
. As shown in (a) section of
FIG. 2
, a shaft
53
is secured to one end of a piezoelectric element
52
, while a fixed portion
51
is secured to the other end thereof. A moving member
54
to be moved is held on the shaft
53
under a frictional force produced by spring biasing. The mass of the fixed portion
51
is sufficiently large compared with the mass of the moving member
54
.
When a voltage is applied to the piezoelectric element
52
, the inertial force of the fixed portion
51
prevents the piezoelectric element
52
from extending in the direction of the fixed portion
51
, so that the piezoelectric element
52
extends in the direction of the shaft
53
to move the shaft
53
to the left in the drawing. At this time, on a gentle rising edge of the applied voltage as shown in A section of
FIG. 3
, the moving member
54
moves by a distance x along with the shaft
53
, as shown in (b) section of
FIG. 2
, since the frictional force produced between the moving member
54
and the shaft
53
is larger than the inertial force of the moving member
54
.
Next, when the piezoelectric element
52
releases a voltage on a steep falling edge as shown in B section of
FIG. 3
, the inertial force of the moving member
54
becomes larger than the frictional force produced between the moving member
54
and the shaft
53
, so that the moving member
54
remains in place and only the shaft
53
moves by the distance x toward the initial position, as shown in (c) section of FIG.
2
. By applying a sawtooth drive pulse to the piezoelectric element
52
to cause it to repeat this action, the moving member
54
can be moved to a specified position. To move the moving member
54
in the opposite direction, a drive pulse with a steep rising edge and with a gentle falling edge is applied properly.
If the frequency of a waveform as shown in
FIG. 3
is increased to increase a frequency for extending and contracting an electro-mechanical transducer, a transition is made to a state in which a skid occurs between the driving frictional member (shaft) and the moving member which are frictionally combined with each other upon each of the extension and contraction of the electro-mechanical transducer. In this case, since a relative skid occurring between the driving frictional member and the moving member upon the extension of the electro-mechanical transducer is different in direction and magnitude from the skid occurring therebetween upon the contraction of the electro-mechanical transducer, the moving member can be driven in a desired direction relative to the fixed portion.
In the lens driving apparatus having a structure as shown in
FIG. 11
, the piezoelectric elements
212
,
217
extend and contract when a sawtooth drive pulse is applied thereto for a specified period of time, thereby causing the forward and backward movements of the shafts
202
,
204
. The order relationship between the frictional force between the shafts
202
,
203
and the leaf springs
214
,
219
and the inertial force resulting from the masses of the lenses and the lens barrels
201
,
225
vary depending on the moving speeds of the shafts
202
,
203
, so that the lenses are moved to specified positions. It is to be noted that the force applied to the fixed portion upon the extension or contraction of the piezoelectric elements
212
,
217
causes the fixed portion to reciprocate along with the support members
213
,
218
, though it is indistinct because of the relatively large mass of the fixed portion.
In
FIG. 4
, the vertical axis represents the magnitude of a voltage and the horizontal axis represents time. In the case where the drive pulses applied to the two piezoelectric elements
212
,
217
have waveforms G
1
, G
2
shown in
FIG. 4
in which portions with abrupt voltage changes B
1
, B
2
are coincident with each other, the forces are applied simultaneously to the fixed portion so that the respective driving operations interfere with each other.
For example, the fixed portion experiences an increased amount of elastic deformation and an increased amount of travel compared with the case where a single piezoelectric element and a single shaft are provided, so that the shafts
202
,
203
(driving shafts) undergo a lower degree of acceleration.
occasionally, the inertial forces of the lens barrels
201
,
225
(moving members) become smaller than the frictional forces, which deteriorates driving properties. As a result, the speeds of the lens barrels
201
,
225
are lowered or, in some cases, the lens barrels
201
,
225
are not moved at all. This leads to such a problem as an elongated time required to dispose the lenses at desired positions, which degrades the operability of a camera used in conjunction with the lens unit. Similar problems occur when three or more piezoelectric elements are used.
Although the description has thus been given to the case where the common fixed portion is used, interference occurs even when fixed portions are provided for individual piezoelectric elements on a one-by-one basis if the fixed portions are at positions close to each other. That is, if the voltages applied to the piezoelectric elements have the waveforms G
1
, G
2
in which the portions B
1
, B
2
with abrupt voltage changes are coincident with each other, as shown in
FIG. 4
, the forces are applied simultaneously to the fixed portions and therefore the forces are applied simultaneously to the lens unit in which the fixed portions are disposed.
This also deteriorates the driving properties for the lens barrels (moving members), similarly to the foregoing case. If the fixed portions contain elastic bodies such as plastic moldings, in particular, the fixed portions are likely to warp and move, so that the amount of elastic deformation experienced by the fixed portions is increased and
Budd Mark O.
Minolta Co. , Ltd.
Morrison & Foerster / LLP
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