Fly Height Control via Laser Pre-bias Thermal Protrusion
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Solution Overview
Problem
Existing data storage devices face challenges in accurately determining partial thermal protrusion of write elements during short write operations, which is crucial for precise and safe implementation of self-servo writing, as existing methods require comparison with long write operations and are not capable of handling the fast and precise calibration needed for short write operations.
Innovation Solution
The implementation of control circuitry that iteratively performs spiral write operations at various values of laser pre-bias current, write backoff, and start disk phase, detects pattern signal amplitudes, and determines the relation of write backoff to laser pre-bias current, enabling accurate calibration and control of fly height during short write operations without requiring comparison with normal, long write operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional methods are used to determine thermal protrusion by comparing long write operations, then measurement accuracy can be achieved, but the process is too slow and cannot handle fast calibration needed for short write operations
Solution Approach 1:
The patent applies preliminary action by performing pre-lasing of the laser unit before the actual short write operation. This pre-lasing causes partial thermal protrusion that can be measured and used to calibrate the fly height control element. By performing the thermal preparation in advance, the system can accurately determine thermal protrusion effects without requiring long write operations, thus achieving both fast calibration and measurement accuracy.
Solution Approach 2:
The patent uses partial action by applying only a portion of the full laser power (pre-bias current) during the pre-lasing phase. This partial lasing creates a controlled, measurable thermal protrusion that is sufficient for calibration purposes but does not require the full energy of a complete write operation. The partial thermal protrusion is then used to determine the relationship between write backoff and laser pre-bias current, enabling accurate fast calibration.
2Productivity
If short write operations are performed without accurate thermal protrusion determination, then productivity increases, but reliability decreases due to unsafe operations
Solution Approach 1:
The patent implements feedback by measuring the pattern signal amplitude during short write operations and using this information to determine the relationship between write backoff and laser pre-bias current. This measured feedback is then used to accurately determine thermal protrusion and adjust the fly height control element accordingly. The closed-loop feedback ensures that short write operations are both fast and safe, as the system continuously monitors and adjusts based on actual thermal effects.
Solution Approach 2:
The system performs self-calibration by automatically determining its own thermal protrusion characteristics during the write process. The fly height control element uses the determined relationship between write backoff and laser pre-bias current to self-adjust the head position, eliminating the need for external calibration procedures. This self-service capability enables both high productivity and reliability through automated safety adjustments.
3Manufacturing precision
If conventional fly height control is used without accounting for partial thermal protrusion, then device complexity is reduced, but manufacturing precision deteriorates
Solution Approach 1:
The patent applies universality by making the fly height control element serve multiple functions: it not only controls the basic head position but also compensates for thermal protrusion effects during short write operations. The same control element is used to adjust for both mechanical positioning and thermal deformation, eliminating the need for separate compensation mechanisms. This multi-functionality achieves high manufacturing precision without significantly increasing device complexity.
Solution Approach 2:
The system achieves precise fly height control by dynamically changing parameters - specifically, it adjusts the write backoff distance based on the determined relationship with laser pre-bias current. By varying the write backoff parameter in response to measured thermal effects, the system compensates for thermal protrusion and maintains accurate fly height control during short write operations, achieving high precision through parameter optimization rather than complex structural changes.
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 approach allows for precise and safe implementation of very short write operations, enabling faster and more precise self-servo writing, and accurately determines the thermal protrusion of write elements, even for each head individually, thereby improving the reliability and accuracy of data storage devices.
Implementation Method 1
The pre-biasing of the laser may cause partial thermal protrusion of the head write element
Implementation Method 2
characterize thermal deformation and laser current threshold of a disk drive read/write head during transient pre-lasing
Data Source
AI summary
Various illustrative aspects are directed to a data storage device, comprising: one or more disks; an actuator assembly comprising a head, and configured to position the head over a corresponding disk surface; and one or more processing devices, the head comprising: a write element; a laser unit; and a fly height control element, and wherein the one or more processing devices are configured to: iteratively perform spiral write operations of spiral patterns comprising a plurality of sync marks with the head on the corresponding disk surface, wherein the spiral write operations are performed at: a plurality of values of laser pre-bias current, write backoff, and/or start disk phase; detect pattern signal amplitudes of the spiral patterns on the corresponding disk surface; and determine a relation of write backoff to laser pre-bias current for the head, based on the pattern signal amplitudes of the spiral patterns.