Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-01-18
2002-12-17
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C310SDIG006
Reexamination Certificate
active
06495938
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a brushless motor that may be used as a capstan motor for a video player or the like, an operation method therefor and a manufacturing method therefor. More particularly, the present invention relates to a direct pulse width modulation (PWM) brushless motor, an operation method therefor and a manufacturing method therefor.
A typical brushless motor may be used as a capstan motor for a video player or the like that is a main apparatus for the brushless motor. As shown in
FIG. 1
, the brushless motor is generally composed of a motor main body
11
mounted on a metal substrate
40
and a motor drive circuit (not shown) that drives the motor main body
11
. The motor main body
11
has a bearing
20
, a rotor shaft
10
rotatably supported by he bearing
20
, a rotor
5
capable of rotating with the rotor shaft
10
in one piece, an a stator
30
having cores
32
with driving coils
31
wound around the cores
32
. If the motor drive circuit is not provided on the metal rate
40
but is provided on a separate control circuit substrate in the main apparatus (i.e., the video player or the like), the motor main body
11
and the motor drive circuit may need to be connected to each other by wirings. Accordingly, a connector
8
may be mounted on the metal substrate
40
for connecting the motor main body
11
to the motor drive circuit.
FIG. 8
shows an electrical connection structure in the brushless motor
1
in which the motor main body
11
is electrically connected to the motor drive circuit through the connector
8
.
Referring to
FIG. 8
, a motor drive circuit
6
that is equipped with a driver IC
60
is formed with other control circuits for the main apparatus at a location other than the metal substrate
40
, such as, for example, in a circuit substrate of the main apparatus. The driver IC
60
has built-in power transistors (i.e., switching elements) Q
1
-Q
4
, for example. The motor drive circuit
6
is supplied with a motor power source potential VM, a motor ground potential M.GND, an IC power source potential Vcc and an IC grand potential S.GND. Also, the motor drive circuit
6
and the motor main body
11
are electrically connected to each other through the connector
8
in the following manner. The connector
8
has twelve connector pins
801
through
812
. Among the twelve pins, the connector pins
801
through
803
are used for power supply to three driving coils
31
of the motor. The connector pins
804
and
812
are used for supplying the IC power source potential Vcc and the IC grand potential S.GND to three Hall elements H and a sensor FG that is used for speed control of the motor. The connector pins
805
through
811
are used for outputting signals from the Hall elements H or the sensor FG.
In the brushless motor thus structured, the power transistors built in the driver IC
60
are directly turned on and off. Furthermore, the brushless motor uses a direct PWM control system in which the switching pulse width applied to the switching elements is modulated to control current that is conducted through the driving coils.
By the direct PWM control system, the power consumption, which may be wasted through heat generation of the driver IC, is substantially reduced. Therefore, the direct PWM control system is greatly effective in reducing the energy consumption for driving the motor. In addition, the direct PWM control system is effective in reducing the cost because it-can be implemented with almost no additional parts.
A typical direct PWM control system is described with reference to FIGS.
2
(A),
2
(B),
3
and
4
. FIG.
2
(A) shows a state of the driver IC
60
of the brushless motor with a direct PWM control system in which power is supplied from a motor power supply source to the driving coils
31
. FIG.
2
(B) shows a state in which regeneration current flows by a back electromotive force that is generated in the driving coils
31
when the power supply from the motor power supply source to the driving coils
31
is stopped.
FIG. 3
shows waveforms of voltage and current that are applied to the driving coils
31
for one phase when the controls shown in FIGS.
2
(A) and
2
(B) are conducted.
FIG. 4
shows waveforms in period a shown in
FIG. 3
, which includes periods b when voltage is applied to the driving coils
31
and periods c when the voltage supply to the driving coils
31
is stopped. More specifically,
FIG. 4
shows a voltage waveform and a current waveform during periods b when a voltage is applied to the driving coils
31
and during periods c when the voltage supply to the driving coils
31
is stopped.
As shown in FIG.
2
(A) and
FIG. 3
, when the power transistor Q
4
is in an ON state and the power transistor Q
1
is turned ON, the motor power supply potential VM is applied to the driving coils
31
from a motor power supply source
66
, such that current flows through the driving coils
31
. The current flows through the power transistor Q
4
to the motor ground potential M.GND of the motor power supply source
66
(during periods b shown in FIG.
4
). As shown in
FIG. 4
, the current gradually increases in accordance with a time constant of the driving coils
31
.
On the other hand, as shown in FIG.
2
(B) and
FIG. 3
, when the power transistor Q
4
is in an ON state and the power transistor Q
1
is turned OFF, the application of the motor power supply potential VM to the driving coils
31
from the motor power supply source
66
is stopped. At this moment, electromotive forces E
1
and E
2
are generated in the respective driving coils
31
. The electromotive forces E
1
and E
2
cause regeneration current that flows in the driving coils
31
through a diode
61
. The regeneration current gradually decreases in accordance with the time constant of the driving coils
31
. However, before the regeneration current completely disappears, the power transistor Q
1
is turned ON, and the motor power supply source
66
starts power supply.
In this manner, in the brushless motor using the direct PWM control system, a part of the motor current is supplied by the regeneration current, such that the current (power) to be externally supplied can be cut down. Also, since the power transistors through which the motor current flows are always in a saturated state, the power that may be consumed in the driver IC
60
is reduced to a minimum required level.
However, in the brushless motor using the direct PWM control system, the voltage that is applied to the driving coils
31
shifts between the motor power supply potential VM and the motor ground potential M.GND in a short period of time. As a result, the voltage applied to the wiring that extends from the driver IC
60
to the driving coils
31
or the wiring pattern of the metal substrate
40
as well as the voltage applied to the driving coils
31
continuously repeat rapid shifts, which generates electromagnetic noises. The electromagnetic noises cause a variety of adverse effects on the operation of the main apparatus that uses the brushless motor. Moreover, portions of the metal substrate
40
where the wiring patterns are formed over dielectric layers form capacitive coupling with respect to the driving coils
31
and the wirings, which results in the diffusion of the electromagnetic noises.
SUMMARY OF THE INVENTION
In view of the problems described above, it is an object of the present invention to provide a brushless motor using a direct PWM control system, which has a motor driving circuit provided on a circuit substrate that is independent of a motor main body, and which has a structure that can suppress the diffusion of electromagnetic noises.
In accordance with one embodiment of the present invention, a direct PWM brushless motor may have a motor main body mounted on a metal substrate and a motor drive circuit formed on a circuit substrate that is separated from the metal substrate. The motor main body may have a baring, a rotor shaft rotatably supported by the bearing, a rotor capable of rota
Komatsu Izumi
Naito Hayato
Tanimura Satohi
Hogan & Hartson LLP
Mullins Burton S.
Sankyo Seiki Mfg. Co. Ltd.
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