Multiple-sense thermo-resistive sensor for contact detection of read-write heads
Techniques of the present invention include detecting a touchdown between a read/write head of a disk drive and a surface of a magnetic disk using multiple touchdown sensors located at an air-bearing surface (ABS). The multiple sensors increase the likelihood that a touchdown event—i.e., a portion of the ABS of the head contacting the underlying magnetic disk surface—will be detected. During touchdown, the portion of the head contacting the magnetic disk generates frictional heat which changes a characteristic (e.g., the electrical resistance) of at least one of the sensors located at the ABS. When the sensors are connected to a detection circuit, the changing characteristic may be monitored to identify a touchdown event. The touchdown sensors may be, for example, electrically connected in either series or parallel to the detection circuit. Thus, as long as the electrical resistance of one of the sensors is changed, a touchdown event may be detected.
1. A disk drive comprising:
a head comprising:
a fly-height actuator disposed within the head;
a first touchdown sensor; and
a second touchdown sensor, wherein both the first and second touchdown sensors are located at an air bearing surface (ABS) of the head; and
a touchdown sensing circuit configured to detect contact between a portion of the head at the ABS and a magnetic medium by measuring a voltage across, or a current through, a combined resistance of the first and second touchdown sensors, wherein a surface of the head is recessed from the ABS forming a recess between the first touchdown sensor and the second touchdown sensor, wherein at least one of the first touchdown sensor and the second touchdown sensor borders the recess.
2. The disk drive of claim 1 , wherein the first and second touchdown sensors are electrically connected at least one of in series and in parallel to the touchdown sensing circuit.
3. The disk drive of claim 1 , wherein the touchdown sensing circuit is configured to detect contact between a portion of the head at the ABS and the magnetic medium only if an electrical resistance of both the first and second touchdown sensors changes.
4. A disk drive comprising:
a head comprising:
a first touchdown sensor; and
a second touchdown sensor, wherein both the first and second touchdown sensors are located at an air bearing surface (ABS) of the head;
a touchdown sensing circuit configured to detect contact between a portion of the head at the ABS and a magnetic medium by measuring a voltage across, or a current through, a combined resistance of the first and second touchdown sensors;
a write pole for writing data to the medium; and
a return pole for writing data to the medium, wherein portions of both the write and write poles are located at the ABS, and wherein the first and second touchdown sensors are both located between the write and return poles.
5. A disk drive comprising:
a head comprising:
a first touchdown sensor; and
a second touchdown sensor, wherein both the first and second touchdown sensors are located at an air bearing surface (ABS) of the head;
a touchdown sensing circuit configured to detect contact between a portion of the head at the ABS and a magnetic medium by measuring a voltage across, or a current through, a combined resistance of the first and second touchdown sensors;
a write pole for writing data to the medium; and
a read pole for reading data from the medium, wherein portions of both the read and write poles are located at the ABS, wherein the first and second touchdown sensors are both located between the read and write poles.
6. A disk drive comprising:
a head comprising:
a first touchdown sensor; and
a second touchdown sensor, wherein both the first and second touchdown sensors are located at an air bearing surface (ABS) of the head;
a touchdown sensing circuit configured to detect contact between a portion of the head at the ABS and a magnetic medium by measuring a voltage across, or a current through, a combined resistance of the first and second touchdown sensors;
a write pole for writing data to the medium; and
a read pole for reading data from the medium, wherein portions of both the read and write poles are located at the ABS, wherein the first touchdown sensor is closer to the portion of the write pole located at the ABS than the second touchdown sensor, and wherein the second touchdown sensor is closer to the portion of the read pole located at the ABS than the first touchdown sensor.
7. The disk drive of claim 6 , wherein a portion of the first touchdown sensor is located not more than 0.25 microns from the portion of the write pole located at the ABS.
8. The disk drive of claim 7 , further comprising a return pole located between the write pole and the read pole, wherein the second touchdown sensor is located between the return pole and the write pole.
9. The disk drive of claim 8 , wherein a portion of the second touchdown sensor is located not more than 0.25 microns from a portion of the return pole located at the ABS.
10. The disk drive of claim 5 , wherein a portion of the second touchdown sensor is located not more than 0.25 microns from the portion of the read pole.
11. A method of detecting contact between a head of a disk drive and a medium, comprising:
determining whether a portion of the head at an air bearing surface (ABS) is contacting the medium by measuring a voltage across, or a current through, a combined resistance of a first touchdown sensor and a second touchdown sensor, wherein both the first and second touchdown sensors are located at the ABS of the head, wherein a surface of the head is recessed from the ABS forming a recess between the first touchdown sensor and the second touchdown sensor, wherein at least one of the first touchdown sensor and the second touchdown sensor borders the recess, and wherein the head includes a fly-height actuator disposed within the head; and
upon determining that the portion of the head at the ABS contacted the medium, transmitting a signal indicating that a touchdown event occurred.
12. A method of detecting contact between a head of a disk drive and a medium, comprising:
determining whether a portion of the head at an air bearing surface (ABS) is contacting the medium by measuring a voltage across, or a current through, a combined resistance of a first touchdown sensor and a second touchdown sensor, wherein both the first and second touchdown sensors are located at the ABS of the head, and wherein the first and second touchdown sensors are both located between a read pole and a write pole of the head; and
upon determining that the portion of the head at the ABS contacted the medium, transmitting a signal indicating that a touchdown event occurred.
13. A method of detecting contact between a head of a disk drive and a medium, comprising:
determining whether a portion of the head at an air bearing surface (ABS) is contacting the medium by measuring a voltage across, or a current through, a combined resistance of a first touchdown sensor and a second touchdown sensor, wherein both the first and second touchdown sensors are located at the ABS of the head, and wherein the first touchdown sensor is closer to a portion of the write pole located at the ABS than the second touchdown sensor, and wherein the second touchdown sensor is closer to a portion of the read pole located at the ABS than the first touchdown sensor; and
upon determining that the portion of the head at the ABS contacted the medium, transmitting a signal indicating that a touchdown event occurred.
14. The method of claim 12 , wherein a portion of the first touchdown sensor is located not more than 0.25 microns from the portion of the write pole located at the ABS.
15. The method of claim 12 , wherein a return pole is located between the write pole and the read pole, and wherein the second touchdown sensor is located between the return pole and the write pole.
16. The method of claim 12 , wherein a portion of the second touchdown sensor is located not more than 0.25 microns from a portion of the read pole located at the ABS.
17. A method of detecting contact between a head of a disk drive and a medium, comprising:
determining whether a portion of the head at an air bearing surface (ABS) is contacting the medium by measuring a voltage across, or a current through, a combined resistance of a first touchdown sensor and a second touchdown sensor, wherein both the first and second touchdown sensors are located at the ABS of the head, and wherein the signal indicating that the touchdown occurred is transmitted only if the electrical resistance of both the first and second sensors changes; and
upon determining that the portion of the head at the ABS contacted the medium, transmitting a signal indicating that a touchdown event occurred.
18. The method of claim 11 , wherein the first and second touchdown sensors are electrically connected in series to a touchdown sensing circuit.
19. The method of claim 11 , wherein the first and second touchdown sensors are electrically connected in parallel to a touchdown sensing circuit.
20. The method of claim 11 , wherein an electrical resistance of the first and second sensors changes when a portion of the ABS contacts the medium.