Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
1999-08-23
2001-11-13
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S254100
Reexamination Certificate
active
06316894
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a driving device for a three-phase brushless motor used to rotate a head in, for example, a portable MD (MiniDisk) apparatus or a VCR (videocassette recorder).
BACKGROUND ART
In a conventional driving device for a three-phase brushless motor, the back electromotive forces V
U
, V
V
, and V
W
appearing in the coils of the motor are individually compared with the common-terminal voltage V
N
of the coils by a comparator to obtain three-phase square-wave signals P
U
, P
V
, and P
W
, which are then directly synthesized together to produce a speed signal (hereafter referred to as an “FG (frequency generator) signal”) and drive signals D
UU
, D
UL
, D
VU
, D
VL
, D
WU
, and D
WL
.
The FG signal is then subjected to
30
-degree phase shifting performed by a phase shifting circuit so as to be converted into a phase signal FGP. In accordance with this phase signal FGP and the above-mentioned drive signals D
UU
, D
UL
, D
VU
, D
VL
, D
WU
, and D
WL
, drive currents are supplied from a current supply circuit such as a power transistor circuit to the three-phase brushless motor.
However, in this conventional driving device, as long as the motor is rotating stably, the square-wave signals P
U
, P
V
, and P
W
exhibit stable waveforms as shown in
FIG. 6
; however, as shown in
FIG. 7
, when irregular variations occur in the back electromotive forces V
U
, V
V
, and V
W
as a result of polarity inversion caused by braking applied as in the period T, or by noise appearing as indicated by reference numerals
40
and
41
, or by other factors, the square-wave signals P
U
, P
V
, and P
W
exhibit irregular variations accordingly.
Thus, the FG signal and the drive signals D
UU
, D
UL
, D
VU
, D
VL
, D
WU
, and D
WL
, which are produced from the square-wave signals P
U
, P
V
, and P
W
, are also affected such that the FG signal is no longer usable if left intact and that the drive signals D
UU
, D
UL
, D
VU
, D
VL
, D
WU
, and D
WL
cause unstable rotation of the motor, making it impossible to obtain stable rotation characteristics. Note that, in
FIGS. 6 and 7
, only the drive signals D
UU
, and D
UL
, are shown, and the other drive signals D
VU
, D
VL
, D
UU
, and D
VL
are omitted.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a driving device for a three-phase brushless motor that offers stable rotation characteristics by preventing an FG signal and drive signals from being affected by polarity inversion resulting from braking applied, noise appearing, or other factors arising during rotation of the motor.
To achieve the above object, according to one aspect of the present invention, in a three-phase brushless motor driving device for supplying a three-phase brushless motor with three-phase drive currents that differ in phase by 120 degrees from one another, passage control means is provided that compares the back electromotive forces appearing in three coils provided one for each phase in the three-phase brushless motor individually with the common-terminal voltage of the three coils and that controls the resulting comparison outputs individually in such a way that each of the comparison outputs is, in a predetermined period including a level-shift point thereof, permitted to pass through intact and is, in a period between one such predetermined period and a next such predetermined period, kept at a level at which it is set after the level-shift point, and the drive currents are produced by current supply means in accordance with the signals resulting from passage control.
According to this configuration, in the predetermined period, the driving device, by means of gate circuits or the like, allows passage of the comparison outputs obtained by comparison of the back electromotive forces with the common-terminal voltage so that the level-shift points of the individual comparison outputs are detected. In the period between this predetermined period and the next such predetermined period, the passage control means keeps the comparison outputs at their levels at which they are set after the level-shift points. In accordance with the signals resulting from such passage control, the driving device supplies three-phase drive currents from the current supply means, employing power transistors or the like, to the three-phase brushless motor. As a result, a rotating magnetic field appears in each coil provided in the three-phase brushless motor, and thus the rotor of the motor rotates.
According to another aspect of the present invention, a three-phase brushless motor driving device for supplying a three-phase brushless motor with drive currents is provided with: a comparator circuit for comparing the back electromotive forces appearing in three coils provided one for each phase in the three-phase brushless motor individually with the common-terminal voltage of the three coils to produce square-wave signals; gate circuits for controlling passage of the square-wave signals individually; a drive waveform synthesizing circuit for synthesizing together the outputs of the gate circuits to produce drive signals; an FG circuit for producing a speed signal from the outputs of the gate circuits; a phase shifting circuit for producing from the speed signal a phase signal having a phase shifted by 30 degrees relative to the speed signal; a current supply circuit for supplying the drive currents to the three-phase brushless motor in accordance with the drive signals and the phase signal; and a selector circuit for feeding a select signal back to the gate circuits in accordance with the drive signals and the phase signal. Here, the gate circuits allow passage of the square-wave signals individually only in a predetermined period.
According to this configuration, the driving device, by means of the comparator circuit, compares the back electromotive forces appearing in the motor coils with the common-terminal voltage to produce square-wave signals, and then synthesizes the square-wave signals together to produce drive signals and a phase signal. In accordance with the drive signals and the phase signal, drive currents are supplied from the current supply circuit to the three-phase brushless motor to drive it.
Moreover, in accordance with the drive signals and the phase signal, the selector circuit produces a select signal, and feeds it back to the gate circuits inserted in the stage subsequent to the comparator circuit. This makes it possible to perform masking in the periods other than the periods in which the rotor position of the motor is detected. In this way, it is possible to prevent the drive signals and the phase signal from being affected by irregular variations in the back electromotive forces resulting from braking or noise.
REFERENCES:
patent: 5221881 (1993-06-01), Cameron
patent: 5306988 (1994-04-01), Carobolante et al.
patent: 5451832 (1995-09-01), Cameron et al.
patent: 5517095 (1996-05-01), Carobolante et al.
patent: 5616996 (1997-04-01), Tang et al.
patent: 5866998 (1999-02-01), Menegoli
patent: 6-62593 (1994-03-01), None
patent: 8-33382 (1996-02-01), None
patent: 8-182379 (1996-07-01), None
patent: 8-251978 (1996-09-01), None
Arent Fox Kintner & Plotkin & Kahn, PLLC
Ro Bentsu
Rohm & Co., Ltd.
LandOfFree
Driving device for three-phase brushless motor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Driving device for three-phase brushless motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Driving device for three-phase brushless motor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2585249