Disk Drive Track Map Servo Compensation
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Solution Overview
Problem
Existing removable data cartridge systems face challenges in accurately calculating microjog values due to manufacturing tolerances and mechanical variations, leading to positioning inaccuracies and reduced storage capacities when using dual-element read/write heads like MR and GMR heads.
Innovation Solution
A track map is generated and stored on the disk, measuring the average width of every servo half track to adjust scale factors for precise positioning, compensating for varying servo track widths and microjog distances, ensuring accurate alignment of read and write elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If dual-element read/write heads (MR/GMR) are used to increase storage density, then storage capacity is improved, but positioning accuracy deteriorates due to radial offset variations from manufacturing tolerances and mechanical variations
Solution Approach 1:
The system performs preliminary measurement of actual servo track widths during cartridge initialization or factory calibration, storing these measurements in a lookup table. This preliminary action captures the actual dimensional variations before normal operation, allowing the system to compensate for manufacturing tolerances and mechanical variations without requiring real-time complex calculations during data operations.
Solution Approach 2:
The system dynamically adjusts the microjog offset parameter based on measured servo track width variations. By changing the microjog parameter according to actual track conditions rather than using a fixed value, the system compensates for radial offset variations caused by manufacturing tolerances and mechanical variations, maintaining positioning accuracy while using high-density dual-element heads.
2Device complexity
If fixed microjog values are used to simplify positioning calculations, then device complexity is reduced, but positioning accuracy deteriorates due to varying servo track widths from manufacturing tolerances
Solution Approach 1:
The system pre-measures and stores servo track width variations in a lookup table during initialization. This preliminary measurement phase separates the complex measurement and calculation work from normal operation, allowing simple table lookups during data access while maintaining high positioning accuracy through the stored calibration data.
Solution Approach 2:
The system creates a digital copy or model of the actual servo track geometry through measurement and storage in a lookup table. This copied geometric information is then used to adjust positioning calculations without requiring complex real-time measurements, simplifying the operational complexity while maintaining accuracy through the stored geometric model.
3Device complexity
If servo track width variations are not compensated, then device complexity is reduced, but data reliability deteriorates due to data encroachment from positioning inaccuracies
Solution Approach 1:
The system performs preliminary measurement and calibration of servo track widths, storing correction factors in advance. This preliminary action prevents data encroachment by establishing accurate positioning parameters before normal operation begins, ensuring data reliability without adding complex real-time compensation mechanisms during data access.
Solution Approach 2:
The system uses measured servo track width information as feedback to adjust positioning calculations. By incorporating this feedback from actual track measurements, the system compensates for width variations and maintains accurate head positioning, preventing data encroachment and improving data reliability through continuous adaptation to actual geometric conditions.
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
The track map effectively corrects positioning errors, preventing data encroachment and improving data throughput by accurately positioning the read and write elements, even with varying servo track widths and mechanical variations, thus enhancing storage density and reliability.
Implementation Method 1
one result is that new types of heads have come into common use, examples of which include the magneto-resistive (MR) head, and the giant magneto-resistive (GMR) head
Implementation Method 2
Current magnetic recording devices use an inductive-write and GMR-read dual element head
Data Source
AI summary
A track map of a disk drive is generated to compensate for various conditions. A track map is a stored measurement of every “half” servo track width on a disk. Every servo half track width is measured in the factory on a disk and then the data is stored on the disk for use during drive operations. When an individual track is accessed, the appropriate servo half track width data is pulled from memory and is used to adjust a scale factor for that local half track width. The track map may be used to compensate for various conditions including varying servo track width, microjog distance, and data track spacing.