# US 9,437,234 B1 · Head-medium contact detection using high frequency heater oscillation

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- Number: US 9,437,234 B1
- Document ID: US9437234B1
- Status: Granted
- Kind: B1
- Application number: 14/831,314
- Filed: 2015-08-20
- Granted: 2016-09-06
- Earliest claimed: 2015-08-20
- Assignees: Seagate Technology LLC
- Applicants: Seagate Technology LLC
- Inventors: Shi Jung Kim; Dong Wook Lee; Ju Yong Lee; Won Choul Yang
- Web page: https://patentgrep.com/patent/US9437234B1

## CPC

- G11B 5/6076: {Detecting head-disk contact}
- G11B 5/3136: {for reducing the pole-tip-protrusion at the head transducing surface, e.g. caused by thermal expansion of dissimilar materials}
- G11B 7/1263: Power control during transducing, e.g. by monitoring
- G11B 20/18: Error detection or correction; Testing {, e.g. of drop-outs}
- G11B 5/607: {using thermal means}
- G11B 2005/0021: {Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

An apparatus comprises a read/write head having a heater, wherein a low- or non-modulation interface is defined between the head and a magnetic recording medium. A microactuator is coupled to the head. A main actuator is coupled to the microactuator and the head. A controller is coupled to the main actuator, the microactuator, and the head. The controller is configured to control movement of the main actuator and the microactuator in response to a position error signal. The controller is further configured to induce an oscillation in the heater at a predetermined frequency. A detector is coupled to the controller. The detector is configured to sense a disturbance in the PES supplied to the microactuator resulting from the induced heater oscillation, and detect contact between the head and the medium using the PES disturbance.

## Claims

### Claim 1

A method, comprising:
providing relative movement between a read/write head and a magnetic recording medium wherein a low- or non-modulation interface is defined between the head and medium, the head movable by a microactuator and a main actuator;
inducing an oscillation in a heater of the head, the oscillation being at a predetermined frequency;
sensing a disturbance in a position error signal (PES) supplied to the microactuator resulting from the induced heater oscillation; and
detecting contact between the head and the medium using the PES disturbance.

### Claim 2 (depends on 1)

The method of claim 1, wherein the predetermined frequency is greater than a frequency bandwidth for controlling the main actuator.

### Claim 3 (depends on 1)

The method of claim 1, wherein the heater is oscillated at a frequency greater than about 3 kHz.

### Claim 4 (depends on 1)

The method of claim 1, wherein the sensed disturbance of the PES is indicative of a mechanical response of the microactuator at the predetermined frequency due to contact between the head and the medium.

### Claim 5 (depends on 1)

The method of claim 1, wherein:
the head is induced to oscillate along a z-direction normal to a plane of the medium in response to the heater oscillation; and
the sensed disturbance of the PES is indicative of a mechanical response of the microactuator along an x-direction parallel with the plane of the medium.

### Claim 6 (depends on 1)

The method of claim 1, wherein:
the heater is a heater proximate a reader of the head; and
the method is performed during a read operation.

### Claim 7 (depends on 1)

The method of claim 1, wherein:
the heater is a heater proximate a writer of the head; and
the method is performed during a write operation.

### Claim 8 (depends on 1)

The method of claim 1, further comprising:
detecting contact between the head and the medium using the PES disturbance for inner and outer diameter regions of the medium; and
detecting contact between the head and the medium using a parameter other than the PES disturbance for a middle diameter region of the medium.

### Claim 9 (depends on 8)

The method of claim 8, wherein:
the head comprises a thermal sensor; and
detecting contact between the head and the medium for the middle diameter region of the medium comprises detecting the contact using the thermal sensor.

### Claim 10 (depends on 1)

The method of claim 1, wherein contact between the head and the medium is detected as a change in the PES that exceeds a threshold.

### Claim 11 (depends on 1)

The method of claim 1, wherein the induced heater oscillation is a sinusoidal oscillation.

### Claim 12

An apparatus, comprising:
a read/write head comprising a heater, wherein a low- or non-modulation interface is defined between the head and a magnetic recording medium;
a microactuator coupled to the head;
a main actuator coupled to the microactuator and the head;
a controller coupled to the main actuator, the microactuator, and the head, the controller configured to control movement of the main actuator and the microactuator in response to a position error signal (PES), the controller further configured to induce an oscillation in the heater, the oscillation being at a predetermined frequency; and
a detector coupled to the controller, the detector configured to:
sense a disturbance in the PES supplied to the microactuator resulting from the induced heater oscillation; and
detect contact between the head and the medium using the PES disturbance.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein the predetermined frequency is greater than a frequency bandwidth for controlling the main actuator.

### Claim 14 (depends on 12)

The apparatus of claim 12, wherein heater is oscillated at a frequency greater than about 3 kHz.

### Claim 15 (depends on 12)

The apparatus of claim 12, wherein the sensed disturbance of the PES is indicative of a mechanical response of the microactuator at the predetermined frequency due to contact between the head and the medium.

### Claim 16 (depends on 12)

The apparatus of claim 12, wherein:
the head is induced to oscillate along a z-direction normal to a plane of the medium in response to the heater oscillation; and
the sensed disturbance of the PES is indicative of a mechanical response of the microactuator along an x-direction parallel with the plane of the medium.

### Claim 17 (depends on 12)

The apparatus of claim 12, wherein:
the heater is a heater proximate a reader of the head; and
the detector is configured to perform head-medium detection during a read operation.

### Claim 18 (depends on 12)

The apparatus of claim 12, wherein:
the heater is a heater proximate a writer of the head; and
the detector is configured to perform head-medium detection during a write operation.

### Claim 19 (depends on 12)

The apparatus of claim 12, wherein the detector is configured to:
detect contact between the head and the medium using the PES disturbance for inner and outer diameter regions of the medium; and
detect contact between the head and the medium using a parameter other than the PES disturbance for a middle diameter region of the medium.

### Claim 20 (depends on 19)

The apparatus of claim 19, wherein:
the head comprises a thermal sensor; and
the detector is further configured to detect contact between the head and the medium for the middle diameter region using the thermal sensor.

### Claim 21 (depends on 12)

The apparatus of claim 12, wherein the detector is configured to detect contact between the head and the medium as a change in the PES that exceeds a threshold.

### Claim 22 (depends on 12)

The apparatus of claim 12, wherein the induced heater oscillation is a sinusoidal oscillation.

### Claim 23 (depends on 12)

The apparatus of claim 12, wherein the read/write head is configured for heat-assisted magnetic recording.