Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-06-02
2003-04-08
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06545389
ABSTRACT:
This application is based on application No. Hei 9-143993 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 control circuit and a control method of a driving apparatus using a transducer.
2. Description of the Related Art
Conventionally, a variety of driving apparatuses using a piezoelectric element have been proposed.
FIG. 1
is an exploded perspective view of a prior art linear movement type driving apparatus, while
FIG. 2
is an overall perspective view of the driving apparatus shown in
FIG. 1. A
driving apparatus
10
a
is provided with a fixed member
24
, a piezoelectric element
22
, a driving shaft
26
slidably supported in its axial direction by the fixed member
24
and a driving unit
28
to be connected to a stage (not shown) which moves with a driven member of, for example, a component placed on it. The piezoelectric element
22
is a sort of electromechanical transducer, the length of which is varied by voltage application. The piezoelectric element
22
has one end surface
22
a
affixed to the fixed member
24
in the direction in which it extends or contracts and has the other end surface
22
b
affixed to one axial end surface
26
a
of the driving shaft
26
in the direction in which it extends or contracts. The driving unit
28
is provided with a leaf spring
28
a,
and the driving unit
28
is frictionally coupled with the driving shaft
26
by the urging force of this leaf spring
28
a.
In this driving apparatus
10
a,
the driving unit
28
is moved in a specified direction along the driving shaft
26
when the driving shaft
26
is vibrated in a reciprocating manner in the axial direction by applying to the piezoelectric element
22
a periodic pulse voltage having a sawtooth waveform, for example.
For the purpose of applying a sawtooth-shaped pulse voltage to an electromechanical transducer, or to the piezoelectric element
22
of this driving apparatus
10
a,
a driving circuit
50
shown in
FIG. 3
is used. This driving circuit
50
is constructed by combining a low-speed charging circuit, a high-speed discharging circuit, a low-speed discharging circuit and a high-speed charging circuit, and it has the advantage that its circuit can be compacted as compared with a driving circuit of a type which forms a sawtooth-shaped pulse by means of a digital circuit and further amplifies this pulse.
The driving circuit
50
has a first circuit
52
for driving in a first direction and a second circuit
54
for driving in a second direction opposite the first direction.
The first circuit
52
is constructed of switches C and D and a constant-current section
56
. One terminal of the switch C is connected to a power source for supplying a constant voltage Vs, and the other terminal of the switch C is connected to one terminal of the constant-current section
56
. The other terminal of the constant-current section
56
is connected to one terminal of the switch D and to one terminal of the piezoelectric element
22
, and the other terminal of the switch D and the other terminal of the piezoelectric element
22
are connected to the ground.
The second circuit
54
is constructed of switches A and C and a constant-current section
56
. One terminal of the switch A is connected to the power source for supplying the constant voltage Vs, and the other terminal of the switch A is connected to one terminal of the switch B and to one terminal of the piezoelectric element
22
. The other terminal of the switch B is connected to one terminal of the constant-current section
56
, and the other terminal of the constant-current section
56
is connected to the ground.
This driving circuit
50
applies a periodic sawtooth-shaped pulse voltage to the piezoelectric element
22
as shown in
FIG. 4
when driving the driving apparatus in the first direction. This voltage waveform is generated by forming a low-speed charging circuit by closing the switch C, thereafter opening the switch C and then closing the switch D thus forming a high-speed discharging circuit.
In this case, as shown in
FIG. 4
, the driving speed can be varied by changing the duration of only low-speed charging duration t
1
, t
2
, t
3
during which time the switch C is closed and making constant at all times a duration t
4
starting from the start of the low-speed charging to the start of high-speed discharging at which point the switch D is closed. That is, if the low-speed charging duration is reduced in the order of t
1
→t
2
→t
3
as indicated by waveforms {circle around (
1
)}, {circle around (
2
)} and {circle around (
3
)} of the piezoelectric element voltage in
FIG. 4
, then a voltage VH to be supplied to the piezoelectric element
22
is reduced, so that the driving speed becomes low, or slow.
However, according to this control method, as shown in the voltage-to-speed characteristic of
FIG. 5
, the inclination of the characteristic line becomes steep. Furthermore, a voltage VB of the piezoelectric element
22
when the driving apparatus starts driving becomes high. Therefore, the resolution of the driving speed cannot be made excessively high. Furthermore, the speed stability during low-speed driving is bad.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a driving control apparatus and driving control method whose resolution of driving speed and speed stability at low speed are improved.
Specifically, the driving control apparatus of the present invention is a driving control apparatus for use in a driving apparatus comprising an electromechanical transducer which extends and contracts in a specified direction, either a fixed body or a moving body connected to one end in a direction in which the electromechanical transducer extends or contracts; a driving frictional member connected to the other end in the extension/contraction direction of the electromechanical transducer; and the other one of either the fixed body or the moving body frictionally coupled with the driving frictional member.
The driving control apparatus of the present invention comprises a driving pulse generating means including a high-speed electrifying circuit and a low-speed electrifying circuit connected to the electromechanical transducer; and a controller which sets a low-speed electrification time to a first specified time, sets a time from a low-speed electrification start time to a high-speed electrification start time to a second specified time, makes the low-speed charging duration shorter than the first specified time during low-speed driving and makes a time period from a low-speed charging start time to a high-speed discharging start time shorter than the second specified time, thereby controlling the electrification timing. An approximately sawtooth-shaped pulse voltage formed by low-speed electrification by means of the low-speed electrifying circuit of the driving pulse generating means and the high-speed electrification by means of the high-speed electrifying circuit of the driving pulse generating means is applied to the electromechanical transducer to extend or contract the same, thereby driving the moving body in a specified direction with respect to the fixed body.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.
REFERENCES:
patent: 4284996 (1981-08-01), Greve
patent: 4507762 (1985-03-01), Meyer et al.
patent: 4639735 (1987-01-01), Yamamoto et al.
patent: 4743789 (1988-05-01), Puskas
patent: 5204576 (1993-04-01), Mitsuyasu
patent: 5225941 (1993-07-01), Saito et al.
patent: 5589723 (1996-12-01), Yoshida et al.
patent: 5786654 (1998-07-01), Yoshida et al.
patent: 5907212 (1999-05-01), Odada
patent: 5917267 (1999-06-01), Miyazawa et al.
Dougherty Thomas M.
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
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