Electricity: motive power systems – Motor-reversing
Reexamination Certificate
1999-09-22
2001-06-26
Ip, Paul (Department: 2837)
Electricity: motive power systems
Motor-reversing
C318S561000, C360S100100
Reexamination Certificate
active
06252364
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to the field of disc drive storage devices, and more particularly to a method and apparatus for unlatching an actuator from a latch.
BACKGROUND OF THE INVENTION
In a disc drive system, an actuator is used to position a read/write head over data storage areas, the actuator being driven by a voice coil motor (VCM). A latch is sometimes used for holding the actuator at a latched position when, for example, the disc drive is not in operation.
To unlatch the actuator from the latch, the conventional method is to apply steps of current progressively to the VCM in the direction opposite to the latching force, until the actuator breaks away from the latch. Once it is unlatched, the actuator would tend to move to the other extremity of its range of travel, and may even crash into an outer crash stop. This is undesirable as it introduces shocks and risks damage to the read/write head and the data storage areas.
One method of restraining the motion of the actuator is described in the U.S. Pat. No. 5,600,219 to Kevin A. Gomez granted Feb. 4, 1997 for “Sensorless Closed-Loop Actuator Unlatch”. Through monitoring the slope of the back EMF (electromagnetic force) of the VCM, the actuator unlatch controller is able to determine when the actuator has broken free of the latch, at which point the actuator latch controller would cause the current signal to the voice coil motor to be cut off.
As the requirement for shock-resistance is pushed higher, it has resulted in an increase in the latching force with which the actuator is held at the latched position. Accordingly, the current to the VCM has to increase to a higher and higher level in order to unlatch the actuator. However, the problem of the actuator accelerating beyond control upon release is aggravated as the current to the VCM is increased. Cutting off the current to the VCM once the actuator is unlatched does not provide an adequate solution to the problem. It follows that there is a need for an improved method of unlatching the actuator.
The present invention not only provides an improved method and apparatus for unlatching the actuator suitable for use with disc drive systems with large latching forces, it also provides a faster method of unlatching the actuator. It will be evident from the following description that the present invention offers other advantages over the prior art.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided an apparatus for releasing an actuator from a latched position. The apparatus comprises a voice coil motor operably coupled to an actuator, a latch for holding the actuator at a latched position, and an unlatching mechanism which is configured to energize the voice coil motor with a first current signal of increasing magnitude alternating with a second current signal.
According to another aspect of the invention, there is provided a method of releasing an actuator from a latched position. The method comprises steps of energizing the voice coil motor with a first current signal of increasing magnitude alternating with a second current signal that is out of phase to the first current signal. The first current signal causes the voice coil motor to urge the actuator away from the latched position, and the second current signal causes the voice coil motor to urge the actuator towards the latched position. In the preferred embodiment, the phase difference is 180 degrees.
It is found that not only does the present invention requires much less current, and the time required to unlatch the actuator is also significantly less, as compared with the prior art.
In a preferred embodiment, the magnitude and frequency of the first current signal and of the second current signal may be varied to obtain a release of the actuator from the latch in as short a time as possible, using as little current as possible, for different actuator systems which have different mechanical resonance characteristics. Furthermore, the second current signal may be clipped to minimise the current used.
Preferably, the first current is cut off from the VCM when it is determined that the actuator has been released from the latched position. The present invention is applicable in systems where that is determined from the back EMF of the VCM as well as in systems where that is determined from the Gray code.
REFERENCES:
patent: 5363261 (1994-11-01), Eckberg et al.
patent: 5600219 (1997-02-01), Gomez
patent: 5650891 (1997-07-01), Thayne et al.
patent: 5694271 (1997-12-01), Stefansky
patent: 5805384 (1998-09-01), Bronshvatch et al.
patent: 5825575 (1999-10-01), Lee
Chiang Wing Kong
Lim Choon Kiat
Ooi Kian Keong
Teng Jack Ming
Yeo Ricky Wei Watt
Berger Derek J.
Dempster Shawn B.
Duda Rina I.
Ip Paul
Olson Jonathan E.
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