Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
1998-06-17
2001-04-10
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S430000, C318S702000
Reexamination Certificate
active
06215266
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of this invention relate generally to spindle motors of disk drives of the type generally used for storing digital data, and in particular embodiments to methods for generating low acoustic noise spindle motor commutation, and disk drive systems incorporating the same.
2. Description of Related Art
Modem computers require media in which digital data can be quickly stored and retrieved. Magnetizable (hard) layers on disks have proven to be a reliable media for fast and accurate data storage and retrieval. Disk drives that read data from and write data to hard disks have thus become popular components of computer systems. To access memory locations on a hard disk, a read/write head is positioned over the hard disk, and the hard disk rotates at an essentially constant velocity. By moving the read/write head radially over the rotating hard disk, all memory locations on the hard disk can be accessed.
A spindle motor coupled to a spindle and the hard disk is often used to rotate the hard disk at an essentially constant velocity. Spindle motors are often brushless DC motors, which develop torque by the interaction of radial magnetic fields produced by permanent magnets on the rotor and rotating radial magnetic fields produced by sequencing alternating currents in the multi-phase windings of the stator. Rotation of the rotor occurs as the rotor's magnetic fields, and hence its permanent magnets, “follow” the rotating magnetic fields of the stator.
A plurality of spindle motor drivers repetitively source and sink current through the stator windings to produce the alternating currents in the windings, with each winding's alternating current maintaining a fixed phase relationship with respect to the alternating currents in the other windings. This phasing of alternating current in the windings of a motor is known as commutation. Because each winding acts essentially as an inductor, as the current in each winding changes direction at the switching frequency of its corresponding spindle motor driver, the reduction of current flowing through the winding causes its magnetic field to collapse, producing a back electromotive force (EMF) across the winding. The back EMF causes a surge voltage and a corresponding surge current to appear at the spindle motor driver at the switching frequency of the spindle motor driver. The repetitive switching of current in the winding results in a fluctuating magnetic field, creating a voice-coil effect with small forces of attraction and repulsion between the winding and the adjacent housing causing slight vibrations and acoustic noise at the switching frequency.
Snubber circuits are often coupled between each winding and ground to reduce the surge voltages and currents caused by the back EMF. An example of a snubber circuit is disclosed in U.S. Pat. No. 4,334,254, incorporated herein by reference. Capacitive snubber circuits suppress voltage transients by supplying a discharge path between the inductive winding and ground, but require high charging currents when the spindle motor drivers are sourcing current into the windings. High charging current is undesirable because it increases the power dissipation of transistors in the spindle motor drivers, requiring more expensive larger-geometry transistors.
To minimize these charging currents, a resistance is often included in series with the snubber capacitance. The resistance provides a resistive charging path for the capacitor, slowing down the charging rate of the capacitor and decreasing the instantaneous current sourcing requirements of the spindle motor drivers. The reduced charging current rate is also beneficial because many spindle motor driver circuits rely on a specific current ramp profile during the initial application of power to the spindle motor to determine the start phase of commutation, and without the resistance the high charging currents would distort the current ramp profile and introduce commutation start-up errors.
However, the resistance also creates drawbacks. The resistance impedes the flow of current through the capacitance to ground during spindle motor commutation, reducing the ability of the capacitance to suppress voltage transients, surge currents, and acoustic noise.
SUMMARY OF THE DISCLOSURE
Therefore, it is an object of embodiments of the invention to provide a system and method for reducing the voltage transients, surge currents, and acoustic noise generated during spindle motor commutation by decreasing the resistance and increasing the capacitance of discharge paths between the windings and a reference voltage.
It is a further object of preferred embodiments of the invention to provide a system and method for reducing the acoustic noise generated during spindle motor commutation by decreasing the resistance and increasing the capacitance of discharge paths between the windings and a reference voltage, while causing minimal disturbance to the start-up current ramp profile and ensuring the proper start-up of commutation by increasing the resistance and decreasing the capacitance of the discharge paths during the initial application of power to the spindle motor.
These and other objects are accomplished according to a system for low acoustic noise spindle motor commutation. The system contains a control device that generates commutation control signals which cause spindle motor drivers to source or sink current through windings of a spindle motor. The windings create electromagnetic fields which induce rotational movement in a spindle motor rotor. Low acoustic noise snubber devices are coupled to each winding and are dynamically configurable by the control device to provide low spindle motor driver charging current upon initial application of power to the spindle motor, and reduced acoustic noise and back EMF-generated current and voltage surges at the spindle motor driver during spindle motor commutation.
These and other objects, features, and advantages of embodiments of the invention will be apparent to those skilled in the art from the following detailed description of embodiments of the invention, when read with the drawings and appended claims.
REFERENCES:
patent: 4334254 (1982-06-01), Baker et al.
patent: 5260607 (1993-11-01), Kinbara
patent: 5449988 (1995-09-01), Gurstein et al.
patent: 5874826 (1999-02-01), Chen et al.
Chang James Lai Kein
Gan Kah Liang
Goh Nan Ling
Kan Utt Heng
Tham Yam Pheng
Merchant & Gould P.C.
Ro Bentsu
Seagate Technology LLC
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