Voice Coil Motor Offset Compensation for Supply Voltage Drift
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Solution Overview
Problem
Existing hard disk drive (HDD) systems face challenges in maintaining accurate head positioning due to variations in supply voltage, which cause offset variations in the transconductance loop, leading to errors during track following operations.
Innovation Solution
A method for dynamic compensation of the transconductance amplifier offset by measuring the supply voltage and calculating a relationship between offset values and supply voltage, using multiple calibration conditions to adjust the offset compensation signal based on actual voltage values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single offset calibration is performed before VCM usage, then the calibration process is simple and quick, but the offset accuracy deteriorates when supply voltage varies during normal operations
Solution Approach 1:
The patent performs offset calibration at multiple predetermined supply voltage values before VCM usage, storing multiple offset values in advance. This preliminary multi-condition calibration ensures that accurate offset compensation is available for various voltage scenarios without requiring complex real-time adjustments during operation.
Solution Approach 2:
The patent changes the supply voltage parameter during calibration to multiple predetermined values, measuring offset at each voltage level. By calibrating across a range of voltage conditions rather than a single value, the system captures offset variations due to voltage changes, improving accuracy while maintaining calibration simplicity through automated multi-point measurement.
2Measurement precision
If offset calibration is performed at multiple supply voltage values, then offset calibration accuracy improves across different operating conditions, but the calibration process complexity increases
Solution Approach 1:
The patent performs all multi-voltage offset calibration measurements in advance during manufacturing or initialization, storing the results in a lookup table. This preliminary action eliminates the need for complex real-time voltage measurement and calculation during VCM operation, reducing operational complexity while maintaining high calibration accuracy across varying supply voltages.
Solution Approach 2:
The patent creates a lookup table that stores pre-calculated offset values for multiple supply voltage conditions. During normal operation, the system simply copies the appropriate offset value from the lookup table based on the current voltage range, avoiding complex real-time calculations and reducing operational complexity while maintaining accuracy.
3Ease of operation
If the transconductance loop offset is not compensated for supply voltage variations, then the system operation is simple, but head positioning precision deteriorates during track following
Solution Approach 1:
The patent implements a feedback mechanism where the supply voltage is monitored and used to select the appropriate pre-calibrated offset value from a lookup table. This feedback loop ensures that the correct offset compensation is applied based on actual operating conditions, maintaining head positioning precision without requiring complex real-time offset calculation during VCM operation.
Solution Approach 2:
The patent uses a lookup table that stores pre-calculated offset values for different supply voltage ranges. During operation, the system copies the appropriate offset value from the table based on current voltage conditions and applies it to the transconductance loop, maintaining positioning precision while keeping the operational process simple and efficient.
Data Source
AI summary
Embodiments provide a method of operating a voice coil motor via a transconductance loop. The method includes detecting an actual value of a supply voltage of the transconductance loop. An offset compensation signal of the transconductance loop is produced as a function of the detected actual value of the supply voltage based on a relationship between offset values and the supply voltage of the transconductance loop. The offset compensation signal is applied to a loop control signal of the transconductance loop. A drive current is applied to the voice coil motor. The drive current is related to a target drive current that is based on the loop control signal.