Electrical generator or motor structure – Dynamoelectric – Linear
Patent
1990-11-14
1992-09-08
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Linear
310 20, 360105, H02K 4102, G11B 555
Patent
active
051461226
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to actuator mechanisms of the voice coil motor variety.
BACKGROUND OF THE INVENTION
Voice coil motor actuators are commonly used in magnetic disk file apparatus. The voice coil is attached to a carriage assembly and is located in an air gap defined in a magnet assembly. A number of magnetic read/write heads are mounted on the carriage. A signal, in the form of a current, is supplied to the coil and interacts with the magnetic field set up by the magnet assembly, causing motion of the carriage and therefore of the heads across the surface of disk or disks within the disk file.
The motive force on the carriage results in an equal and opposite reaction force on the magnet assembly, which can excite unwanted resonances in the disk file e.g. in the spindle of the disk motor. This reaction can therefore lead to relative motion between the disk and the read/write heads and to instability in a closed loop head positioning servo system.
The principle of absorbing the reaction force in voice coil motor actuators is well known; IBM Technical Disclosure Bulletin Vol. 19 no. 9 pp 3561-3562 describes an actuator in which the effects of the reaction force are reduced by floating the voice coil motor magnet structure. The magnet structure is supported at both ends by ring flexure assemblies in which a layer of damping material is laminated between two metal sheets. The flexures are mounted onto rigid connector bars which are in turn mounted on the disk file baseplate. In this way, the magnet assembly is effectively isolated from the magnetic disks. U.S. Pat. No. 3 699 555 describes a similar system.
In the design of voice coil motor actuators, it is also common practice to employ a shorted turn, made from a non-magnetic conductive material, to improve the current rise time in the voice coil. European patent application 0 222 139 describes a shorted turn in the form of a copper sleeve which is in contact with the magnet assembly and located in an air gap defined by the magnet assembly. The shorted turn abuts against two rubber rings used as end stops to prevent overtravel of the carriage. U.S. Pat. No. 4 661 729 also describes a cylindrical shorted turn which, in this case, is located on the cylindrical surfaces of two shoulders at the front and rear of the magnet assembly, the shorted turn abutting against one of these shoulders. A seal is formed between the shorted turn and the shoulders by `O` rings located in two grooves in the shoulders.
DISCLOSURE OF THE INVENTION
While the prior art undoubtedly achieves reduction of the adverse effects of the reaction force by isolating the whole magnet assembly from the rest of the disk file, one drawback with this approach is the consequential increase in size of the disk file. The design of a compact actuator for use in small disk files (e.g. 5.25 inch ) requires a much more compact damping technique.
Accordingly, the invention provides an actuator of the voice coil motor type comprising a coil, a magnet assembly defining an air gap in which the coil is movable on application of a current thereto, a shorted turn, and mounting means for locating the shorted turn in the air gap, characterised in that the shorted turn is located in the air gap clear of the magnet assembly, and is resiliently mounted for movement in a direction parallel to the movement cf the coil.
The principle behind the idea of resiliently mounting the shorted turn to compensate for the carriage reaction is much like the idea used on guns to reduce recoil. Since the shorted turn acts like the secondary of a transformer, any change in current in the voice coil is reflected in the shorted turn but in the opposite direction. The shorted turn being in the same magnetic field thus experiences an equal and opposite force to the carriage. If the shorted turn is fixed in the magnet assembly, the reaction force appears as a stress between the two parts. However, on initiation of coil movement, a resiliently mounted shorted turn moves in the opposite direction t
REFERENCES:
patent: 3643242 (1972-02-01), Bryer
patent: 4144466 (1979-03-01), Hatch
patent: 4305105 (1981-12-01), Ho et al.
patent: 4602175 (1986-07-01), Castagna
patent: 4661729 (1987-04-01), Hames et al.
patent: 4743995 (1988-05-01), Castle et al.
patent: 4827162 (1989-05-01), Morris et al.
patent: 4967296 (1990-10-01), Wiens et al.
Commander Robert D.
Hearn Anthony R.
Haszko Dennis R.
International Business Machines - Corporation
Lahtinen Robert W.
Stephan Steven L.
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