Microactuator Crack Detection via Resonant Frequency Excitation
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Solution Overview
Problem
As data track density increases in disk drives, existing technologies face challenges in effectively testing and identifying defective microactuators, which can lead to performance degradation and potential data corruption, especially when using microactuators like piezoelectric actuators in combination with voice coil motors.
Innovation Solution
The proposed solution involves disabling the servo loop to accentuate cracks in microactuators by exciting them with a test frequency different from the resonant frequency of the load beam, evaluating position error signals, and using control circuitry to determine performance degradation by comparing pre- and post-excitation measurements, thereby identifying defective microactuators and minimizing the risk of head-disk interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the servo loop is enabled during microactuator testing, then the head positioning accuracy is maintained, but cracks in the microactuator are not accentuated and cannot be detected
Solution Approach 1:
The system dynamically switches the servo loop state based on the testing phase: disabled during crack detection testing to accentuate vibrations from cracks, and enabled during normal operation to maintain positioning accuracy. This dynamic configuration allows the system to optimize for different functional requirements at different times.
Solution Approach 2:
The microactuator is tested for cracks before normal operation by exciting it at its resonant frequency. This preliminary testing action identifies defective microactuators before they are deployed, preventing potential head-disk interactions and ensuring reliable operation.
2Ease of manufacture
If the microactuator is excited at resonant frequency of the load beam, then vibrations are amplified, but it becomes difficult to distinguish microactuator cracks from load beam vibrations
Solution Approach 1:
The testing method changes the excitation frequency parameter from the load beam's resonant frequency to the microactuator's resonant frequency. This parameter change allows vibrations to be amplified specifically from the microactuator, making crack-induced vibrations distinguishable from load beam vibrations.
Solution Approach 2:
The system uses mechanical vibration at the microactuator's resonant frequency to amplify vibrations caused by cracks. By targeting the specific resonant frequency of the microactuator rather than the load beam, the system can detect crack-induced vibrations with high sensitivity while avoiding interference from load beam vibrations.
3Reliability
If extensive microactuator testing is performed, then defective microactuators are identified, but testing time and complexity increase
Solution Approach 1:
The microactuator undergoes preliminary resonant frequency identification during manufacturing or initialization, followed by a single comprehensive crack detection test using that identified frequency. This preliminary action eliminates the need for repeated frequency sweeps during actual testing, significantly reducing testing time while maintaining high reliability.
Solution Approach 2:
The system replaces complex, time-consuming mechanical testing procedures with a streamlined electrical excitation and signal analysis method. By using electrical signals to excite the microactuator and analyzing the resulting vibrations through signal processing, the system achieves comprehensive defect identification much faster than traditional mechanical testing methods.
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 the accurate identification and potential replacement of defective microactuators, ensuring continued reliable operation and reducing the risk of data corruption by minimizing vibrations and wear during the testing process.
Implementation Method 1
exciting them with a test frequency different from the resonant frequency of the load beam
Implementation Method 2
exciting them with a test frequency different from the resonant frequency of the load beam
Implementation Method 3
microactuators like piezoelectric actuators
Data Source
AI summary
A disk drive is disclosed comprising a disk media, a head stack assembly (HSA) having a head coupled to its distal end, a microactuator used to provide fine position of the head and a voice coil motor (VCM) configured to actuate the HSA over the disk media, and control circuitry. The control circuitry may be configured to move the HSA in an alternating manner across the disk media while actuating the microactuator. One or more performance characteristics of the microactuator may be measured before and after the actuation of the microactuator, and failure may be detected based on the absolute or relative change of the one or more performance characteristics.