Fly Height Control Circuit Slew Rate Adjustment
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Solution Overview
Problem
Conventional fly height control mechanisms in hard disk drives face challenges in maintaining precise clearance between read/write heads and the storage disk surface, especially as operating temperatures change, leading to suboptimal data reading and writing performance due to electromagnetic coupling and varying resistance of the resistive heater element.
Innovation Solution
A fly height control circuit that includes an input node for digital control signals, an output node for controlling a resistive heater element, and control circuitry to process these signals, generating slew rate controlled reference currents to adjust the output current, ensuring constant power dissipation and output voltage ramping speed, independent of the heater element's resistance, thereby maintaining precise spacing between the read/write head and the storage disk surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fly height control circuitry is used with resistive heating element, then fly height adjustment is achieved, but electromagnetic coupling between heater element and read/write heads causes performance degradation
Solution Approach 1:
The patent extracts the harmful electromagnetic coupling effect by introducing a slew rate control mechanism that separates the power delivery function from the electromagnetic interference. The control circuitry processes the digital control signal through slew rate control to generate the output control current, effectively removing the electromagnetic coupling path while preserving the thermal expansion function for fly height adjustment.
2Manufacturing precision
If resistive heater element resistance varies with temperature, then thermal expansion for fly height control is achieved, but control precision deteriorates
Solution Approach 1:
The patent implements feedback control by comparing the actual output control current with a reference current that compensates for temperature variations. The control circuitry continuously monitors the heater element's resistance changes and adjusts the control signal accordingly, ensuring precise fly height control despite temperature-induced resistance variations.
Solution Approach 2:
The patent changes the control parameter from direct voltage application to slew rate-controlled current generation. By controlling the rate of change of the output current rather than the absolute voltage, the system becomes less sensitive to resistance variations and maintains stable thermal expansion control across temperature ranges.
3Measurement precision
If high precision fly height control is required for small clearances, then read/write accuracy is improved, but electromagnetic coupling effects become more significant
Solution Approach 1:
The patent extracts the harmful electromagnetic coupling effect by introducing a slew rate control mechanism that separates the power delivery function from the electromagnetic interference. The control circuitry processes the digital control signal through slew rate control to generate the output control current, effectively removing the electromagnetic coupling path while preserving the thermal expansion function for fly height adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively eliminates electromagnetic voltage coupling and maintains accurate fly height control, ensuring optimal read/write performance across varying conditions by controlling the slew rate and power dissipation of the resistive heater element, regardless of its resistance.
Implementation Method 1
a resistive heating element on a slider element is incorporated near an electromagnetic pole tip of the read/write head, and fly height control circuitry is employed to apply power to the heater element sitting on the slider to adjust the fly height of the read/write head such that the spacing between the read/write head and the surface of the storage disk can be electronically controlled via thermal expansion of the electromagnet poles
Data Source
AI summary
A fly height control circuit includes an input node to receive a digital control signal, an output node to output a control current to a resistive heater element to adjust a spacing between a read/write head and a surface of a storage medium, and control circuitry to process the digital control signal and generate the output control current based on the digital control signal. The control circuitry generates a first reference current based at least in part on the control current output from the output node. The control circuitry controls a slew rate of the first reference current to generate a slew rate controlled reference current. The control circuitry generates a second reference current based on a feedback voltage at the output node. The control circuitry compares the slew rate controlled reference current with the second reference current to adjust the control current output from the output node.