Voice Coil Resistance Update for Disk Drive Velocity Control
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Solution Overview
Problem
Existing disk drive technologies face challenges in controlling the velocity of the actuator arm when servo sector information is unavailable, leading to potential head damage or unload operation failures due to inaccurate estimation of voice coil resistance, especially during ramp loading/unloading and servo sector synchronization issues.
Innovation Solution
The implementation of a VCM control loop with an IR voltage detector that updates the resistance estimation by measuring delta voltages generated during controlled current pulses in both directions, and using a microprocessor to adjust the IR voltage detector, ensuring accurate velocity control even when servo sectors are inaccessible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistance estimation is performed prior to load operation using calibration technique, then initial resistance estimate is obtained, but the estimate becomes unreliable during unload operation due to temperature changes
Solution Approach 1:
The system performs preliminary resistance calibration before load operation to establish an initial resistance estimate, then updates this estimate during operation by detecting back EMF voltage changes. This preliminary action combined with continuous updating resolves the contradiction by ensuring accurate initial measurement while maintaining reliability over time through dynamic adjustment.
Solution Approach 2:
The system uses feedback from back EMF voltage detection to continuously update the resistance estimate. The controller detects changes in back EMF voltage during motor operation and uses this feedback to adjust the resistance estimate, thereby maintaining measurement precision and reliability throughout the operation cycle despite temperature fluctuations.
2Ease of operation
If velocity control loop uses detected back EMF voltage as feedback, then velocity control is achieved without servo sector information, but head damage may occur due to excessive unload velocity from resistance estimation error
Solution Approach 1:
The system implements a velocity control loop that uses feedback from back EMF voltage detection to continuously adjust the resistance estimate. This feedback mechanism ensures that velocity control remains accurate even when servo sector information is unavailable, preventing head damage by maintaining correct velocity limits during unload operations.
Solution Approach 2:
The system dynamically changes the resistance parameter based on detected back EMF voltage variations during operation. By updating the resistance estimate in real-time, the system maintains accurate velocity control calculations, preventing excessive unload velocity and associated head damage risks while operating without servo sector information.
3Measurement precision
If resistance estimate is updated by detecting delta back EMF voltage during current pulses, then accurate resistance estimation is maintained despite temperature fluctuations, but additional control loop complexity is introduced
Solution Approach 1:
The system performs periodic resistance calibration by applying current pulses at specific intervals and detecting the resulting back EMF voltage changes. This periodic action allows the system to maintain accurate resistance estimation without continuous complex measurements, balancing precision requirements with acceptable control loop complexity.
Solution Approach 2:
The system uses the motor's own back EMF voltage during normal operation to update the resistance estimate, rather than requiring separate dedicated measurement circuits. This self-service approach maintains measurement precision while minimizing additional hardware and control complexity by utilizing existing operational signals.
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 provides reliable velocity control of the actuator arm, preventing head damage and ensuring successful unload operations by accurately accounting for changes in voice coil resistance and external factors like flex bias and temperature fluctuations.
Implementation Method 1
the detected back EMF voltage generated by the VCM as the feedback
Implementation Method 2
The voltage across the voice coil (the voice coil voltage) comprises a component due to the inductance L of the VCM, a component due to the resistance R of the VCM
Implementation Method 3
a voice coil motor (VCM) to position the head radially over the disk
Data Source
AI summary
A disk drive is disclosed comprising a disk and a head actuated over the disk by a voice coil motor (VCM) comprising a voice coil, wherein the VCM is controlled by a VCM control loop comprising an IR voltage detector. The IR voltage detector is updated by measuring a first back EMF voltage of the voice coil, and after measuring the first back EMF voltage, applying a first control current to the voice coil for a first interval and applying a second control current to the voice coil for a second interval. After the second interval, a second back EMF voltage is measured, and a delta voltage is computed relative to a difference between the first back EMF voltage and the second back EMF voltage. The IR voltage detector is adjusted in response to the delta voltage and at least one of the first and second control currents.