Head-medium contact detection using an oscillating electromagnetic force

Patent metadata

Field	Value
Publication number	US-9721603-B2
Application number	US-201615237878-A
Country	US
Kind code	B2
Filing date	Aug 16, 2016
Priority date	Sep 25, 2015
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

An apparatus comprises circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium. The applied AC signal causes an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal. A thermal sensor is configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance. A detector is coupled to the circuitry and the thermal sensor. The detector is configured to detect one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal.

First claim

The invention claimed is:

1. A method, comprising:
applying an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the AC signal causing an oscillation in an electrostatic force between the slider and the medium at the frequency of the AC signal;
causing, by the oscillating electrostatic force, an oscillation in a signal produced by a thermal sensor at the slider, the thermal sensor signal oscillating at the AC signal frequency; and
detecting one or both of head-medium spacing changes and head-medium contact using a change in a phase delay between a phase of a first harmonic of the thermal sensor signal and a phase of the applied AC signal.

2. The method of claim 1 , wherein the AC signal is a sinusoidal waveform or a square waveform.

3. The method of claim 1 , wherein the frequency of the AC signal is defined in relation to a servo sampling rate.

4. The method of claim 1 , wherein the frequency of the AC signal is between 90 Hz and 400 kHz.

5. The method of claim 1 , wherein:
electrical noise is introduced in the recording head in a frequency range that includes a first harmonic of the thermal sensor signal; and
detecting using the amplitude of the second harmonic avoids the noise.

6. The method of claim 1 , wherein:
applying comprises applying the AC signal using a circuit that includes the thermal sensor; and
detecting comprises detecting one or both of head-medium spacing changes and head-medium contact using the circuit.

7. An apparatus, comprising:
circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the applied AC signal causing an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal;
a thermal sensor configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance; and
a detector coupled to the circuitry and the thermal sensor, the detector configured to detect one or both of head-medium spacing changes and head-medium contact using a change in a phase delay between a phase of a first harmonic of the thermal sensor signal and a phase of the applied AC signal.

8. The apparatus of claim 7 , wherein the circuitry comprises the thermal sensor.

9. The apparatus of claim 8 , wherein:
electrical noise is introduced by bond pad sharing between the circuitry and the thermal sensor, the noise falling within a frequency range that includes a first harmonic of the thermal sensor signal; and
detecting one or both of head-medium spacing changes and head-medium contact by the detector avoids the noise.

10. The apparatus of claim 7 , wherein the thermal sensor is separate from the circuitry that applies the AC signal to one of the slider and the medium.

11. The apparatus of claim 10 , wherein:
the slider comprises a plurality of electrical bond pads;
the circuitry is coupled to at least a pair of the bond pads; and
the thermal sensor shares at least one bond pad with the circuitry.

12. The apparatus of claim 7 , wherein the AC signal is a sinusoidal waveform or a square waveform.

13. The apparatus of claim 7 , wherein the frequency of the AC signal is defined in relation to a servo sampling rate.

14. The apparatus of claim 7 , wherein the frequency AC signal is between 90 Hz and 400 kHz.

15. The apparatus of claim 7 , wherein the thermal sensor comprises a dual-ended temperature coefficient of resistance (DETCR) sensor.

16. A method, comprising:
applying an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the AC signal causing an oscillation in an electrostatic force between the slider and the medium at the frequency of the AC signal;
causing, by the oscillating electrostatic force, an oscillation in a signal produced by a thermal sensor at the slider, the thermal sensor signal oscillating at the AC signal frequency; and
detecting one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal;
wherein:
electrical noise is introduced in the recording head in a frequency range that includes a first harmonic of the thermal sensor signal; and
detecting using the amplitude of the second harmonic avoids the noise.

17. An apparatus, comprising:
circuitry configured to apply an AC signal having a frequency to one of a slider of a recording head and a magnetic recording medium, the applied AC signal causing an oscillation in an electrostatic force and clearance between the slider and the medium at the frequency of the AC signal;
a thermal sensor configured to generate a sensor signal at the AC signal frequency in response to sensing changes in temperature resulting from the oscillating clearance, the circuitry comprising the thermal sensor; and
a detector coupled to the circuitry and the thermal sensor, the detector configured to detect one or both of head-medium spacing changes and head-medium contact using a phase of a first harmonic or an amplitude of a second harmonic of the thermal sensor signal;
wherein:
electrical noise is introduced by bond pad sharing between the circuitry and the thermal sensor, the noise falling within a frequency range that includes a first harmonic of the thermal sensor signal; and
detecting one or both of head-medium spacing changes and head-medium contact by the detector avoids the noise.

Assignees

• Seagate Technology Llc

Inventors

• Olson Daniel W
• Macken Declan
• Geer Andrea L

Classifications

• G11B5/6011 Primary

  Control of flying height · CPC title

• G11B5/6035

  using electrostatic forces · CPC title

• G11B5/607

  using thermal means · CPC title

• G11B5/6076 Primary

  Detecting head-disk contact · CPC title