Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-03-21
2002-11-26
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S224000
Reexamination Certificate
active
06486660
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data storage systems and, more particularly, to a transfer curve tester for testing magnetic recording heads used in data storage systems.
BACKGROUND OF THE INVENTION
Many data storage systems use magnetic or magneo-optical recording heads for writing information to and reading information from a magnetic: medium. For example, disc drives of the “Winchester” type have one or more rigid discs, which are coated with a magnetizable medium for storing digital. information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head suspension assemblies. Head suspension assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head suspension assemblies from track-to-track across the surfaces of the discs under control of electronic circuitry. “Floppy-type” disc drives use flexible discs, which also have circular, concentric data tracks. For a tape drive, the information is stored along linear tracks on the tape surface.
In these applications, several different types of transducers have been used that rely on magnetic properties for writing to and/or reading from the magnetic medium. For an inductive-type transducer, the direction of current through the transducer is controlled during a write operation to encode magnetic flux reversals on the surface of the medium within the selected data track. When retrieving data from the medium, the inductive transducer is positioned over the data track to sense the flux reversals stored in the data track and generate a read signal based on those flux reversals. In a magnetoresistive type of transducing head, the flux reversals cause a change in the resistance of the head, which is sensed by a detector circuit. Typically, a reference current is passed through the magneto-resistive head and the change in resistance is sensed by measuring changes in the voltage across the head. Other types of detecting circuits can also be used.
In order to understand the basic physics of a magnetic transducing head during development and manufacturing, it is common to test the response of the head to an applied magnetic field. For example, one series of tests is known as “Transfer Curve Testing”. To generate a transfer curve for a particular transducing head, the head is placed in a magnetic field (steady state or time varying) and the output signal from the transducing head is measured. The transfer curve is simply a plot of the output signal versus the applied magnetic field, where the field is varied from some negative value to some positive value., which is usually the same magnitude as the negative value. For a magneto-resistive type of head, the output signal consists of a steady state voltage. which is a function of the bias current applied to the head, the bulk resistance of the head and the applied magnetic field. Typical characteristics that can be measured from the transfer curve data include read signal amplitude at maximum field, noise with zero field, noise with applied field, linearity over some range of field, and symmetry. Symmetry is a comparison of the read signal amplitude with a maximum positive field and the read signal amplitude with a maximum negative field.
Transfer curve testing can be done at the slider level, the head/gimbal assembly (HGA) level or the drive level. A typical transfer curve tester performed at the slider level operates at ambient temperature. Thus, the head characteristics are not measured over the same temperature range that can occur during normal operation at the drive level. A given head can generate noise or have other functional problems at temperatures that are higher or lower than the ambient temperature at which the head was tested. Such functional problems can interfere with the head's ability to reliably read or write data.
In the past, large environmental chambers have been used during transfer curve testing to cycle the temperature at which the head is operated over a predetermined temperature range. However, this typically involved testing the heads at the HDA level or the drive level, which are significantly downstream along a disc drive's assembly process. If a problem is detected, this limits the available solutions to the problem and increases the cost of the solution. Also, these environmental chambers are fairly large in size, are costly to operate and have relatively slow temperature cycle times.
Thus, a transfer curve tester having an improved structure for cycling the operating temperature of the head being tested is desired.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to a head testing apparatus for testing a data recording head. The apparatus includes a test volume, a magnetic field source, a holder and a thermoelectric source. The test volume is adapted to receive the head, and the magnetic, field source is positioned to generate a magnetic field within the test volume. The holder is adapted to hold the head and position the head within the test volume. The thermoelectric source is positioned to contact the head when the head is positioned within the test volume by the holder.
Another aspect of the present invention is directed to a data recording head test fixture having a nest for holding a data recording head. A thermoelectric source is positioned relative to the nest such that the thermoelectric source contacts the data recording head when the data recording head is held within the nest.
Another aspect of the present invention is directed to a method of testing a magnetic data recording head. According to the method, the data recording head is positioned relative to a magnetic field. A response of the data recording head to the magnetic field is then measured while a localized temperature change is induced in the data recording head.
Yet another aspect of the present invention is directed to a head testing apparatus, wherein the apparatus includes a magnetic field source and an apparatus for holding a data recording head relative to the magnetic field source and inducing a. localized temperature change in the data recording head.
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patent: 5015950 (1991-05-01), Rose et al.
patent: 5440233 (1995-08-01), Hodgson et al.
patent: 5517111 (1996-05-01), Shelor
patent: 5696445 (1997-12-01), Inbar
patent: 6194896 (2001-02-01), Takahashi et al.
patent: 6317280 (2001-11-01), Nakajima et al.
Luse Todd A.
Peterson James R.
Tu Thien T.
Kinder Darrell
Lefkowitz Edward
Seagate Technology LLC
Westman Champlin & Kelly
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