Piezoelectric Element Crack Detection via Transfer Function
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Solution Overview
Problem
Current methods fail to reliably detect micro cracks in piezoelectric elements used in hard disk drives, as cracks are difficult to identify visually or through electric characteristics, and existing frequency and phase comparison methods are not effective for practical application.
Innovation Solution
A method and apparatus that apply voltage to a first piezoelectric element of a pair to cause deformation, generating voltage in a second element, and calculating a transfer function based on applied and generated voltages to detect cracks, using objective values from the transfer function to determine the presence of cracks regardless of their size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visual inspection using stereoscopic microscope is performed, then appearance quality is improved, but micro cracks remain undetectable due to surface hardening from electrode plating
Solution Approach 1:
The patent replaces visual inspection (optical/mechanical system) with electrical characteristic measurement. By measuring capacitance and impedance of the piezoelectric element, the system detects internal micro cracks that are invisible to visual inspection, overcoming the limitation of surface hardening from electrode plating.
Solution Approach 2:
The patent introduces electrical characteristics (capacitance, impedance) as an intermediary parameter to indirectly detect cracks. Instead of directly observing the crack, the system measures the electrical properties that change in response to the presence of a crack, providing a detectable signal without requiring visual access to the crack itself.
2Productivity
If electrical characteristic measurement (capacitance measurement) is performed, then production efficiency is improved, but micro cracks are not detected because capacitance remains unchanged
Solution Approach 1:
The patent expands the measurement parameters from solely capacitance to include impedance and phase characteristics. By measuring multiple electrical parameters, particularly impedance at different frequencies and phase angles, the system detects micro cracks that do not affect capacitance, thereby improving crack detection accuracy while maintaining production efficiency.
Solution Approach 2:
The patent adds new measurement dimensions beyond traditional capacitance measurement. By introducing impedance magnitude and phase angle as additional parameters, the system creates a multi-dimensional electrical characteristic space where cracks become detectable through patterns that would be invisible in single-parameter capacitance measurement alone.
3Measurement precision
If frequency characteristic comparison methods are used, then crack detection is attempted, but the methods are not effective for practical application
Solution Approach 1:
The patent employs the piezoelectric element's own electrical characteristics (impedance, phase) as the detection signal. The element itself generates the measurement data through its inherent piezoelectric response to electrical excitation, eliminating the need for complex external sensing systems and making the method practically applicable.
Solution Approach 2:
The patent creates a universal detection method that works for all piezoelectric elements regardless of size or application. By measuring fundamental electrical characteristics (impedance, phase) that are inherent to the element's operation, the system provides a universally applicable crack detection approach that can be integrated into existing manufacturing processes.
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 reliable detection of micro cracks in piezoelectric elements, even if they do not affect electric characteristics, ensuring the long-term reliability of piezoelectric actuators by identifying fine micro cracks that would otherwise be overlooked.
Implementation Method 1
piezoelectric elements being arranged at an intermediate portion between a base plate and a load beam or at a head portion and being deformable according to voltage applied thereto
Data Source
AI summary
The present invention provides a method of surely detecting a crack in piezoelectric elements regardless of size of the crack. The method includes applying voltage to a first piezoelectric element of a pair of piezoelectric elements to cause deformation in the first piezoelectric element, forcibly deforming a second piezoelectric element of the pair of the piezoelectric elements to generate voltage from the second piezoelectric element according to the deformation of the first piezoelectric element, finding a transfer function of the pair of the piezoelectric elements based on values of the applied voltage and the generated voltage, and detecting presence or absence of a crack in the pair of the piezoelectric elements based on an objective value obtained from the found transfer function.