Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1999-10-28
2001-04-17
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C310S156030
Reexamination Certificate
active
06218794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spindle motor startup method, and more particularly to a startup method for spindle motors prone to torque balance conditions, such as where the ratio of the number of rotor magnetic poles to the number of stator slots is 4:3.
2. Background Art
Conventional 3.5″ hard disk drives (HDD) having rotational speeds of at least 7200 rpm are typically equipped with a spindle motor such as an eight-pole twelve-slot spindle motor having a rotor magnetic pole to stator slot ratio of 2:3 for optimum startup characteristics. Alternatively, such disk drives may have a spindle motor like an eight-pole nine-slot spindle motor that has a construction to break a torque balance. Startup malfunctions caused by a magnetic balance between a rotor and a stator seldom occur in these types of motors. Recently, three-phase spindle motors such as a twelve-pole nine-slot spindle motor have started to be commonly used in disk drives. In these drives the ratio of the number of rotor magnetic poles to stator slots is 4:3.
Spindle motors with a 4:3 ratio of rotor magnetic poles to stator slots, like the twelve-pole nine-slot spindle motor described above, are prone to startup problems because the initial starting-torque capacity may not be adequate to overcome a magnetic balance that is created in certain startup positions of the rotor and stator. Such startup malfunctions result in long startup times for the motors, which is a critical parameter in applications such as disk drives.
FIGS. 5A through 5G
show the rotor position in a four-pole three-slot spindle motor as a function of time in a startup malfunction.
FIG. 5A
shows the initial rotor position, and
FIGS. 5B-5G
sequentially show the motor at subsequent times. The four-pole three-slot spindle motor
51
comprises a cylindrical rotor
52
comprising four poles composed of pairs of the north and south poles, and a stator
53
composed of three slots, that is, U, V, and W phases. Furthermore, as shown in
FIGS. 5A through 5G
, a driver not shown switches current for starting the motor in the order of the U phase to the V phase, the U to the W, the V to the U, the W to the U, and the W to the V. At this time, the startup malfunction is shown as a state of not being able to normally start the rotation of the motor with sequentially repeating reverse rotation and normal rotation as shown in
FIGS. 5A through 5G
. This is because rotor
52
and stator
53
are magnetically balanced due to relative positions of rotor
52
and stator
53
at the time the motor stopped as shown in
FIG. 5A
, and the magnetic circuit cannot generate sufficient initial starting-torque to break the balance.
An object of the present invention is to provide a spindle motor apparatus and a startup method that can provide excellent startup performance even in spindle motor configurations that are prone to startup malfunctions, such as where the ratio of rotor magnetic poles to stator slots is 4:3.
SUMMARY OF THE INVENTION
The present invention provides a spindle motor start up method wherein a torque balance between the stator and rotor is broken so as to avoid startup malfunctions, and thereby improve motor startup time. In a preferred embodiment the present invention is implemented in spindle motor configurations prone to startup malfunctions, such as those having a 4:3 ratio of the number of rotor magnetic poles to the number of stator slots. Startup time is a critical performance parameter for spindle motors in data storage devices, such as disk drives. Processes for breaking a torque balance according to the present invention include:
(1) gradually decreasing an initial commutation (switching of each phase) frequency at the startup timing from a frequency higher than a commutation frequency in a conventional startup;
(2) gradually decreasing an initial commutation frequency at the startup timing from a frequency higher than a commutation frequency in a conventional startup to a low frequency, and next, gradually increasing the initial frequency from the low frequency;
(3) changing a drive current of the spindle motor so as to break a torque balance between the spindle motor stator and rotor;
(4) monitoring a back electromotive force detection signal while commutating, and restarting commutation when the back electromotive force detection signal is not detected;
(5) resetting the commutation at a time in a commutation sequence after an initial commutation from a first phase to a second phase, and restarting the commutation from the first phase to the second phase; and
(6) monitoring a back electromotive force detection signal while commutating, resetting the commutation at a time in a commutation sequence after an initial commutation from a first phase to a second phase, and restarting the commutation from the first phase to the second phase.
REFERENCES:
patent: 4673849 (1987-06-01), Sears et al.
patent: 5107159 (1992-04-01), Kordik
patent: 5783917 (1998-07-01), Takekawa
patent: 5801500 (1998-09-01), Jensen et al.
patent: 5814957 (1998-09-01), Yoshida
Kagami Naoyuki
Ohyama Akihiro
Shimizu Yasuhito
Tokizono Akira
International Business Machines - Corporation
Leykin Rita
Martin Robert B.
Nappi Robert E.
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