Flying height control for read-to-write and write-to-read transitions

Abstract

Various embodiments of the present invention are directed to substantially eliminating transient changes in a flying height of a head during read-to-write and write-to-read transitions. In various embodiments, flying height transient compensation is provided to substantially maintain a desired flying height during one or both of read-to-write and write-to-read transitions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating an example of a normalized spacing change versus time for thermal distortion growth due to FHA, a normalized spacing change versus time for thermal distortion decay of WPTP, and a normalized spacing change versus time for a difference between thermal distortion decay of WPTP and thermal distortion growth due to FHA;

FIG. 2 illustrates a disk drive in accordance with an embodiment of the present invention;

FIG. 3 illustrates an actuator arm assembly and a disk stack in accordance with an embodiment of the present invention;

FIG. 4 illustrates a block diagram of a host device, circuitry, and a head disk assembly (HDA) in accordance with an embodiment of the present invention;

FIG. 5 illustrates a side view of a portion of a HDA in accordance with an embodiment of the present invention;

FIG. 6A illustrates an embodiment of a heating element in accordance with an embodiment of the present invention;

FIG. 6B illustrates an embodiment of a heating element in accordance with an embodiment of the present invention;

FIG. 6C illustrates an embodiment of a heating element in accordance with an embodiment of the present invention;

FIG. 6D illustrates an embodiment of a heating element in accordance with an embodiment of the present invention;

FIG. 7A illustrates a system in accordance with an embodiment of the present invention;

FIG. 7B illustrates a system in accordance with an embodiment of the present invention;

FIG. 7C illustrates a system in accordance with an embodiment of the present invention;

FIG. 8 illustrates a flowchart of a method in accordance with an embodiment of the present invention;

FIG. 9 illustrates a graph with example measured values of a displacement of an air bearing surface of a head at multiple time points and an exponential function fit of the measured values;

FIG. 10 illustrates an example of a simulation model in accordance with an embodiment of the present invention;

FIG. 11 illustrates sample output results of a simulation using a simulation model with a first order equalizer in accordance with an embodiment of the present invention;

FIG. 12 illustrates sample output results of a simulation using a simulation model with a third order equalizer in accordance with an embodiment of the present invention;

FIG. 13A illustrates a fly height controller in accordance with an embodiment of the present invention;

FIG. 13B illustrates a fly height controller in accordance with an embodiment of the present invention; and

FIG. 14 illustrates a flowchart of a method in accordance with an embodiment of the present invention.

Claims

1. A circuit, comprising: a head heater controller that substantially destructively cancels a transient fly height change resulting from a transition between a write operation and a read operation.

2. The circuit of claim 1, wherein the head heater controller provides a signal component calculated to offset the transient fly height change.

3. The circuit of claim 1, wherein the read operation precedes the write operation.

4. The circuit of claim 3, wherein the head heater controller is configured to control a heating element during the transition from the read operation to the write operation such that thermal distortion decay of a head due to reduced heat from the heating element substantially matches thermal distortion growth of the head due to increased heat from a write structure.

5. The circuit of claim 1, wherein the write operation precedes the read operation.

6. The circuit of claim 5, wherein the head heater controller is configured to control a heating element during the transition from the write operation to the read operation such that thermal distortion growth of a head due to increased heat from the heating element substantially matches thermal distortion decay of the head due to reduced heat from a write structure.

7. The circuit of claim 6, wherein the head heater controller comprises a digital signal processor configured to implement one or more transfer functions determined based on a simulation to compensate for the thermal distortion decay of the head due to reduced heat from the write structure; andwherein the one or more transfer functions implemented in the digital signal processor enable an attenuation of an amplitude of the transient fly height change by more than 60% of an amplitude of an uncompensated transient fly height change.

8. The circuit of claim 1, wherein the head heater controller is configured to adjust a power applied to a heating element in a time dependent manner in accordance with a function that has been determined to compensate for transient fly height changes.

9. The circuit of claim 1, wherein the head heater controller is configured to adjust, in a case where a write current provided to a write structure during the write operation varies, an amount of heat provided by a heating element during the write operation so as to maintain a substantially constant flying height of the head away from a recording medium during the write operation.

10. A system, comprising: circuitry for controlling a heating element, the heating element allowing for providing heat to a head, the head allowing for performing read operations and write operations;wherein the circuitry is configured to control the heating element during a transition from a read operation to a write operation such that thermal distortion decay of the head due to reduced heat from the heating element substantially matches thermal distortion growth of the head due to increased heat from a write structure.

11. The system of claim 10, wherein the circuitry is configured to control the heating element during transitions from write operations to read operations such that thermal distortion growth of the head due to increased heat from the heating element substantially matches thermal distortion decay of the head due to reduced heat from the write structure.

12. The system of claim 10, wherein the circuitry is configured to adjust, during the transition from the read operation to the write operation, a power applied to the heating element in a time dependent manner in accordance with a function that has been determined to compensate for thermal distortion growth of the head due to increased heat from the write structure.

13. The system of claim 10, wherein the circuitry comprises an equalizing network for equalizing a power applied to the heating element based on a write pole tip protrusion response due to power dissipated by the write structure.

14. The system of claim 10, wherein the circuitry is tunable to implement different equalization transfer functions, such that a desired equalization transfer function is able to be implemented based on a result of a simulation using values related to actual measurements of thermal distortion growth of the head due to increased heat from the write structure.

15. A method, comprising: controlling a heating element when a head transitions from performing a write operation to performing a read operation such that thermal distortion growth of the head due to increased heat from the heating element substantially matches thermal distortion decay of the head due to reduced heat from a write structure.

16. The method of claim 15, further comprising: controlling the heating element when the head transitions from performing read operations to performing write operations such that thermal distortion decay of the head due to reduced heat from the heating element substantially matches thermal distortion growth of the head due to increased heat from the write structure.

17. The method of claim 15, wherein said controlling, comprises: adjusting a power applied to the heating element in a time dependent manner in accordance with a function that has been determined to compensate for thermal distortion decay of the head due to reduced heat from the write structure.

18. The method of claim 15, further comprising: measuring values related to thermal distortion decay of the head due to reduced heat from the write structure; anddetermining one or more time constants related to thermal distortion decay of the head based on the measured values.

19. The method of claim 18, further comprising: performing a simulation using the one or more time constants to determine an equalization transfer function that allows for substantially compensating for transient changes in a flying height of the head.

20. The method of claim 19, wherein said controlling, comprises: controlling the heating element using the equalization transfer function when the head transitions from performing the write operation to performing the read operation such that thermal distortion growth of the head due to increased heat from the heating element substantially matches thermal distortion decay of the head due to reduced heat from the write structure.