Piezoelectric actuator

Details Piezoelectric actuator Piezoelectric actuator

2000-09-27

2002-08-13

Budd, Mark O. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S316030

Reexamination Certificate

active

06433459

ABSTRACT:

This application is based on patent application Hei. 11-280180 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a piezoelectric actuator suitable for moving a driven member such as a two-dimensional moving table, a taking lens of a camera, a projection lens of an over-head projector, a lens of a binocular, and so on.
2. Description of the Related Art
In an impact type piezoelectric actuator, a driven member is movably coupled with a rod shaped driving member in an axial direction thereof. An end of the driving member is fixed on an end of a piezoelectric device in a manner so that the polarization of the piezoelectric device coincides with the axial direction of the driving member. For example, U.S. Pat. No. 5,589,723 shows a conventional impact type piezoelectric actuator used for moving a taking lens of a camera.
A basic configuration of the conventional impact type piezoelectric actuator is shown in FIG.
20
. The piezoelectric actuator
100
comprises a rod shaped driving member
101
, a driven member
102
, a lamination type piezoelectric device
103
and a driving circuit
104
. The driven member
102
is coupled with the driving member
101
by a predetermined friction force. When a dynamic force larger than the friction force is applied to the driven member
102
, it can be moved in an axial direction relative to the driving member
101
. An object to be moved such as a taking lens is connected to the driven member
102
. The piezoelectric device
103
is connected on a base end
101
b
of the driving member
101
in a manner so that the polarization of the piezoelectric device
103
coincides with the axial direction of the driving member
101
. A pair of electrodes
103
a
and
103
b
are provided on both ends of the piezoelectric device
103
. The first electrode
103
a
is connected to the driving circuit
104
and the second electrode
103
b
is grounded.
The driving circuit
104
is configured by a forward driving circuit
105
for moving the driven member
102
toward a top end
101
a
of the driving member
101
(hereinafter, this direction is called “forward”), a backward driving circuit
106
for moving the driven member
102
toward the base end
101
b
of the driving member
101
(hereinafter, this direction is called “backward”) and a controller
107
for controlling the forward driving circuit
105
and the backward driving controller
106
, alternatively.
The piezoelectric actuator
100
moves the driven member
102
relative to the driving member
101
by utilizing a difference of friction forces acting between the driving member
101
and the driven member
102
corresponding to the moving speed of the driving member
101
. When the driving member
101
moves quickly, the friction force becomes smaller. Alternatively, when the driving member
101
moves slowly, the friction force becomes larger. For moving the driven member
102
forward, the driving member is slowly moved forward and quickly moved backward (forward driving). For moving the driven member
102
backward, the driving member is quickly moved forward and slowly moved backward (backward driving).
The forward driving circuit
105
is configured by a slow charger
105
a
and a quick discharger
105
b
. The backward driving circuit
106
is configured by a quick charger
106
a
and a slow discharger
106
b
. The slow charger
105
a
and the quick charger
106
a
respectively apply a driving voltage Vp to the piezoelectric device
103
in the polarization direction (or charge the piezoelectric device
103
in the polarization direction) for expanding the piezoelectric device
103
in the polarization direction (or in the axial direction of the driving device
101
). The quick discharger
105
b
and the slow discharger
106
b
respectively apply a voltage to the piezoelectric device
103
in the opposite direction to the polarization (or discharges the electric charge in the piezoelectric device
103
by grounding the electrode
103
a
) for contracting the piezoelectric device
103
.
A configuration of the slow charger
105
a
is shown in FIG.
21
. As can be seen from
FIG. 21
, the slow charger
105
a
is configured by a constant current charging circuit, in which a zener diode ZD is connected in parallel with a fixed biasing circuit of a pnp type transistor Tr
1
. Resistors r
1
and r
2
serve as biasing resistors of the transistor Tr
1
. The zener diode ZD is connected in parallel with the resistor r
2
. Since the zener diode ZD restricts the base current of the transistor Tr
1
at a predetermined constant value, voltage drop owing to the resistor r
1
can be maintained at a predetermined value. The collector current of the transistor Tr
1
can be restricted to be constant. As a result, the charging current for charging the piezoelectric device
103
is restricted, so that the forward moving speed of the driving member
101
is restricted.
Alternatively, another configuration shown in
FIG. 22
is used as the slow charger
105
a
. As can be seen from
FIG. 22
, an npn transistor Tr
2
is used instead of the parallel circuit of the resistor r
2
and the zener diode ZD. The collector and the base of the transistor Tr
2
are respectively connected to the emitter and the base of the transistor Tr
1
. The emitter of the transistor Tr
2
is connected to an electric power supply and the driving voltage Vp is applied thereto. Since the voltage at the base of the transistor Tr
1
is maintained at a constant value by the transistor Tr
2
, voltage drop owing to the resistor r
1
can be maintained at a predetermined value. The collector current of the transistor Tr
1
can be restricted to be constant.
The quick discharger
105
b
and the slow discharger
106
b
apply a voltage to the piezoelectric device
103
in a direction opposite to the polarization of the piezoelectric device
103
, so that the electric charge stored in the piezoelectric device
103
is discharged. Thus, the expanded piezoelectric device
103
is contracted. In
FIG. 20
, the electric charge in the piezoelectric device
103
is discharged by grounding the electrode
103
a.
A configuration of the slow discharger
106
b
is shown in FIG.
23
. As can be seen from
FIG. 23
, the slow discharger
106
b
is configured by a constant current discharging circuit, in which a zener diode ZD is connected between the base of an npn type transistor Tr
3
and the ground. A resistor r
4
restricts the discharging current. Since the zener diode ZD restricts the base voltage of the transistor Tr
3
at a predetermined constant value, voltage drop owing to the resistor r
4
can be maintained at a predetermined value. The emitter current corresponding to the discharging current flowing in the resistor r
4
can be restricted to be a predetermined value. As a result, the discharging current for discharging the piezoelectric device
103
is restricted, so that the backward moving speed of the driving member
101
is restricted.
The controller
107
alternately switches the slow charger
105
a
and the quick discharger
105
b
in the forward driving operation. The controller
107
alternately switches the quick charger
106
a
and the slow discharger
106
b
in the backward driving operation.
When the slow charger
105
a
and the quick discharger
105
b
are alternately driven in the forward driving operation, the piezoelectric device
103
repeats the slow expansion and the quick contraction, alternately. By such operation, the driving member
101
repeats the forward slow movement and the backward quick movement. When the quick charger
106
a
and the slow discharger
106
b
are alternately driven in the backward driving operation, the piezoelectric device
103
repeats the quick expansion and the slow contraction, alternately. By such operation, the driving member
101
repeats the forward quick movement and the backward slow movement.
The impact type piezoelectric actuator is generally used for driving an optical system of a portable equipment

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