Electricity: motive power systems – Braking
Reexamination Certificate
2002-12-03
2004-12-14
Martin, David (Department: 2837)
Electricity: motive power systems
Braking
C318S364000, C318S372000, C318S373000, C318S375000, C318S430000, C318S432000, C318S434000, C318S254100
Reexamination Certificate
active
06831432
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a motor driving device and a motor driving method capable of applying a short brake and a reverse brake to a motor.
A motor can be stopped by decelerating the motor with a short brake or with a reverse brake. A conventional motor driving device has a short brake mode in which a short brake is applied to the motor and a reverse brake mode in which a reverse brake is applied to the motor, one of which is selected for deceleration and stopping of the motor.
In the short brake mode, the motor is decelerated by forming a short circuit between the terminals of motor windings of three phases. In the reverse brake mode, the motor is decelerated by applying a reverse current through motor windings of a plurality of phases to excite the motor windings in the reverse direction.
FIG. 9
is a diagram illustrating a configuration of a conventional motor driving device
1
E.
Referring to
FIG. 9
, the motor driving device
1
E includes position detection means
10
, energization switching signal production means
20
, rotation control means
30
, brake command generation means
40
, brake mode switching means
50
D, reverse rotation detection means
60
, energization control signal production means
70
D, and power transistors Q
1
to Q
6
. A motor M
1
provided outside the motor driving device
1
E includes a rotor r
1
, and motor windings L
1
to L
3
for rotating a disk d
1
via the rotor r
1
.
The operation of the conventional motor driving device
1
E will now be described below in detail.
FIG. 10
is a diagram illustrating an internal configuration of the brake mode switching means
50
D illustrated in FIG.
9
.
During normal rotation of the motor M
1
, torque command generation means
41
provided in the brake command generation means
40
outputs a torque command signal S
2
based on a rotation control signal S
1
from the rotation control means
30
. The energization switching signal production means
20
receives the torque command signal S
2
and outputs, to the energization control signal production means
70
D, an energization switching signal S
4
having a level according to that of the torque command signal S
2
for energizing the motor windings of a plurality of phases with an energization angle that is determined based on a position signal S
3
from the position detection means
10
. The energization control signal production means
70
D successively energizes the power transistors Q
1
to Q
6
based on the energization switching signal S
4
. The rotation control means
30
may be a microcomputer, for example. As the position signal S
3
is received from the position detection means
10
, the microcomputer counts the number of cycles of the received position signal S
3
to obtain count data, and compares the obtained count data with reference data stored therein that corresponds to the number of revolutions per unit time, so as to output the rotation control signal S
1
according to the comparison result. The torque command generation means
41
, which may be a smoothing circuit, outputs a DC voltage, which is obtained by smoothing the rotation control signal S
1
, as the torque command signal S
2
.
The brake command generation means
40
outputs a brake command signal S
5
based on the rotation control signal S
1
from the rotation control means
30
. Then, the brake mode switching means
50
D, which includes logic circuits
511
d
and
512
d
as illustrated in
FIG. 10
, receives the brake command signal S
5
and a brake mode switching signal S
111
, and selects one of the short brake mode and the reverse brake mode.
In a case where the short brake mode is selected, the brake mode switching means
50
D selectively outputs a short brake signal /S
7
based on the brake mode switching signal S
11
. The energization control signal production means
70
D receives the energization switching signal S
4
from the energization switching signal production means
20
and the short brake signal /S
7
to output an energization control signal S
8
to the power transistors Q
1
to Q
6
. Based on the energization control signal S
8
, the power transistors Q
1
, Q
3
and Q
5
may be all turned ON, with the power transistors Q
2
, Q
4
and Q
6
being all turned OFF. Alternatively, the power transistors Q
2
, Q
4
and Q
6
may be all turned ON, with the power transistors Q
1
, Q
3
and Q
5
being all turned OFF, to form a short circuit between the terminals of the motor windings L
1
, L
2
and L
3
of three phases so that a counter electromotive voltage is consumed in the motor windings L
1
, L
2
and L
3
, thereby decelerating and stopping the motor M
1
.
In a case where the reverse brake mode is selected, the brake mode switching means
50
D selectively outputs a reverse brake signal S
7
based on the brake mode switching signal S
11
. The energization control signal production means
70
D receives the energization switching signal S
4
from the energization switching signal production means
20
and the reverse brake signal S
7
to output the energization control signal S
8
of the reverse polarity to the power transistors Q
1
to Q
6
. The power transistors Q
1
to Q
6
apply the energization control signal S
8
of the reverse polarity to the motor windings L
1
, L
2
and L
3
of the three phases so as to excite the motor windings L
1
, L
2
and L
3
in the reverse direction, thereby braking the rotor r
1
.
In such a case, the reverse rotation detection means
60
detects a reverse rotation by, for example, detecting the cycle of the output signal from the position detection means
10
using a timer, or the like. Specifically, the reverse rotation detection means
60
determines that the motor is standing when detecting that the cycle of the position signal S
3
from the position detection means
10
is equal to or greater than a predetermined value, and outputs a reverse rotation signal S
9
assuming that the motor is about to start rotating in the reverse direction. When receiving the reverse rotation signal S
9
, the energization control signal production means
70
D stops supplying the energization control signal S
8
to all the motor windings L
1
, L
2
and L
3
. Then, the motor M
1
comes to a complete stop after continuing to rotate with the force of inertia.
As described above, the conventional motor driving device brakes the motor M
1
by selecting either one of the short brake mode and the reverse brake mode. The short brake mode is advantageous in that the motor M
1
makes substantially no braking noise, and is effective during high-speed rotation because the braking force in this mode is dependent on the counter electromotive voltage. However, the braking force decreases as the number of revolutions decreases, thereby taking a long time for the motor to come to a complete stop.
On the other hand, the reverse brake mode provides a large braking force because the motor windings L
1
to L
3
are excited in the reverse direction while decelerating the motor. However, during high-speed rotation, the motor makes substantial noise due to a phase shift. Moreover, it is difficult to detect a reverse rotation with a high precision, and if the control fails to stop the energization control signal S
8
of the reverse polarity at an appropriate timing, the reverse excitation continues for a while even after the motor M
1
stops, whereby the motor M
1
starts rotating in the reverse direction. Although the energization control signal production means
70
D thereafter stops energizing the motor windings L
1
to L
3
of the three phases, the motor M
1
will continue to rotate for a while with the force of inertia. Therefore, it takes a long time for the motor to come to a complete stop, and causes an error in the position at which the motor M
1
stops.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a motor driving device and a motor driving method capable of stopping a motor while reducing the braking noise and the stopping time.
Specifically, a motor driving device of the present invention includes:
Martin David
McDermott Will & Emery LLP
Smith Tyrone
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