Measuring and testing – Vibration – Vibrator
Reexamination Certificate
2000-04-11
2001-12-18
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Vibrator
C073S662000
Reexamination Certificate
active
06330828
ABSTRACT:
FIELD OF THE INVENTION
This application relates to magnetic disc drives and more particularly to a method and apparatus for subjecting a magnetic disc drive or other device to rotational vibration.
BACKGROUND OF THE INVENTION
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
Radial actuators employ a voice coil motor (VCM) to position the heads with respect to the disc surfaces. The actuator VCM includes a coil mounted on the end of the actuator body opposite the head arms so as to be immersed in the magnetic field of a magnetic circuit comprising one or more permanent magnets and magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the heads to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
Minimizing structural vibration within the disc drive is critical to maintaining proper head positioning within a track, as well as to maintaining proper disc drive integrity. It is, therefore, highly desirable to experimentally evaluate the effects structural vibrations have within a disc drive and, further, to test possible solutions for preventing and minimizing anticipated structural vibrations which could arise under normal or predetermined disc drive operating conditions and handling conditions.
Structural vibration testing of disc drives is well known. Conventionally, structural vibration testing occurs though the use of a shaker apparatus, in which the subject disc drive is secured to the shaker apparatus and shaken in a reciprocal linear motion fashion, i.e., shaken back and forth, side to side, or up and down. Linear external energy is inputted into the disc drive to simulate structural vibrations introduced into a disc drive during normal operating conditions by fastening the drive to a shaker table and vibrating or oscillating the table in accordance with a predetermined acceleration profile. A key shortcoming to the use of a conventional “linear” shaker apparatus is that the operating disc drive is sensitive to both linear and rotational energy. In fact, since the late 1980s/early 1990s when a rotational actuator, instead of a linear actuator, was introduced into disc drive unit, the rotational component of structural vibrations is the predominate energy component responsible for disrupting proper head positioning within a disc drive track. Additionally, it is known in the art that rotational vibrations have other disruptive effects on disc drive operation and integrity. However, there has been no direct means of testing drives for these rotary vibrations. Accordingly, there is a need in the disc drive art for a disc drive shaker apparatus which can produce a predominately rotational energy spectrum for subjecting disc drives to rotational accelerations. Such a device can be used in accurately and more realistically testing and characterizing disc drives function under normal and predetermined operating conditions.
SUMMARY OF THE INVENTION
Against this backdrop the present invention has been developed. The present invention is a rotational shaker test apparatus for subjecting a device to be tested to a predetermined regimen of rotary oscillatory accelerations to closely simulate accelerations that may be experienced by a device during normal and anticipated operating conditions. The rotational shaker test apparatus in accordance with the present invention preferably has a base for mounting the apparatus to a stationary surface, such as a table or floor, a rotatable shaft extending substantially normal to the plane of the base and bearing supported by a pair of spaced support plates and a set of three voice coil motors (VCMs) spaced 120 degrees apart around the shaft. The motor armatures are fastened to a flanged hub fixed to the shaft. The VCM coils, as part of the armatures, are oriented so as to each move through a maximum arc of about 60 degrees in either a clockwise or counterclockwise direction about the central axis of the shaft, thus rotating the shaft through an arc of about 120 degrees. The VCM coils are electrically connected in series so that a current through one coil is the same as through the other two coils. This results in a uniform rotational movement and torque being applied to the shaft by each VCM.
The method of vibrational testing in accordance with a preferred embodiment of the present invention includes mounting a disc drive to be tested on the mounting platform fastened to one end of the cylindrical shaft and then driving the VCMS each with a predetermined current profile corresponding to a desired acceleration profile to reciprocally rotate the shaft about its central axis in accordance with the profile.
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Freeman John Jay
Nagl Alan Thomas
Merchant & Gould
Miller Rose M.
Seagate Technology LLC
Wahl John R.
Williams Hezron
LandOfFree
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