Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-09-12
2003-05-20
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06566790
ABSTRACT:
This application is based on patent application Hei.11-259165 filed in Japan, the contents of which are hereby incorporated by references.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a driving apparatus and a driving method of an impact type piezoelectric actuator.
2. Description of the Related Art
In an impact type piezoelectric actuator, a driven member is movably connected to a rod shaped driving member in an axial direction thereof and a piezoelectric device is connected on an end of the driving member in a manner so that the polarization of the piezoelectric device coincides with the axial direction. For example, Publication Gazette of Japanese Patent Application Hei.7-298656 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.
14
. 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 force larger than the friction force is applied to the driven member
102
, it can be moved in an axial direction of 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 electrode
103
b
is grounded and the other electrode
103
a
is connected to the driving circuit
104
.
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 circuit
106
.
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
respect 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 potential to the piezoelectric device
103
in the opposite direction to the polarization or discharging the electric charge in the piezoelectric device
103
by grounding the electrode
103
a
for contracting the piezoelectric device
103
.
The slow charger
105
a
is configured by a constant current circuit for controlling the charging speed by restricting the charging current. The slow charger
106
b
is configured by a constant current circuit for controlling the discharging speed by restricting the discharging current.
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 friction force acting between the driving member
101
and the driven member
102
becomes smaller when the driving member
101
moves quickly, and it becomes larger when the driving member
101
moves slowly. Thus, the driven member
102
moves with the driving member
101
only when the driving member
101
moves slowly. Consequently, the driven member
102
moves forward relative to the driving member
101
in the forward driving operation, and the driven member
102
moves backward relative to the driving member
101
in the backward driving operation.
The impact type piezoelectric actuator is generally used for driving an optical system of a portable equipment such as a taking lens of a camera and a lens of a binoculars. It is preferable to make the driving circuit of the actuator compact and simple with regard to the downsizing and the lightening of the equipment. Since the electric power supply of the portable equipment is a dry battery, it is preferable to drive the driving circuit of the actuator by a voltage of the battery.
The voltage of the battery, however, is relatively lower, so that the quantity of the expansion and contraction of the piezoelectric device
103
becomes smaller when the piezoelectric device
103
is charged and discharged between the voltage Vp of the battery and the grounded voltage (0V). Consequently, the moving speed of the driven member
102
becomes slower. When the moving distance of the driven member
102
is relatively longer, the driving time period of the piezoelectric device
103
becomes longer, and the exhaustion of the battery becomes larger. Furthermore, when the voltage of the battery is dropped due to the exhaustion of the battery or the variation of the ambient temperature, the moving speed of the driven member
102
becomes much slower or the driven member
102
becomes immovable.
For solving the above-mentioned problem, it is proposed to apply a technique for increasing amplitude of output signals virtually double by using the BTL (Bridged Tied Load) connection into the driving circuit
104
of the piezoelectric actuator. The BTL connection is generally used in a car audio system for increasing output power of speaker. By applying the technique into the driving circuit
104
of the piezoelectric actuator, the voltages +Vp and −Vp are alternately applied to the piezoelectric device
103
. The piezoelectric device
103
is repeatedly charged and discharged between the voltage +Vp and −Vp, so that the voltage of the driving signal of the piezoelectric device
103
becomes substantially double. The voltage of the electric power supply, however, is applied to the piezoelectric device
103
in the discharging time period in the opposite direction, so that the electric power consumption of the piezoelectric actuator becomes larger than the conventional driving method. When the battery is used as the electric power supply, the exhaustion of the battery becomes faster.
SUMMARY OF THE INVENTION
An object of this invention is to provide a driving apparatus for the piezoelectric actuator which can effectively be driven by a battery and can save the electric power consumption without causing the upsizing of the circuit and the reduction of the driving efficiency.
A driving apparatus of impact type piezoelectric actuator in accordance with an aspect of this invention comprises a controller for switching a first driving mode and a second driving mode of the piezoelectric actuator corresponding to a condition with respect to a moving speed of a driven member driven by the piezoelectric actuator.
When the moving spe
Addison Karen
Minolta Co. , Ltd.
Ramirez Nestor
Sidley Austin Brown & Wood LLP
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