Acoustic Extension Sensing for Piezo Actuators
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Solution Overview
Problem
Piezo ceramic actuators face challenges in accurate extension measurement due to high hysteresis and nonlinearity, as well as complications from fringing fields and stray capacitances in conventional capacitor sensors, which affect the reliability of position measurements.
Innovation Solution
The method involves using acoustic signals to determine the length of the actuator by analyzing the delay between input and return signals, leveraging the change in sound velocity as the actuator extends, which is measurable and not predicted by conventional finite element simulations or analytical approaches. This method can be implemented using integrated transmitters and receivers within the actuator layers or attached separately, and can be used in conjunction with signal processors to calculate the actuator length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitor sensor is used to measure actuator extension, then position measurement capability is provided, but measurement precision deteriorates due to fringing fields and stray capacitances
Solution Approach 1:
The patent replaces the electrical capacitor sensing system with an acoustic wave-based measurement system. Acoustic waves are transmitted through the actuator material, and the time-of-flight or velocity changes of these acoustic waves are used to determine actuator extension, eliminating the harmful electrical field effects of capacitor sensors.
Solution Approach 2:
The patent measures changes in acoustic wave velocity through the actuator material as the actuator extends. The velocity of sound in the piezoelectric material changes with applied voltage and strain, providing a measurable parameter that directly correlates with actuator extension without suffering from hysteresis or capacitance issues.
2Reliability
If conventional capacitor sensing is used, then position measurement is possible, but reliability worsens due to hysteresis and nonlinearity in piezo actuators
Solution Approach 1:
The patent substitutes acoustic wave propagation measurement for electrical capacitor-based measurement. The acoustic velocity through the piezoelectric material provides a more reliable measurement that is less susceptible to the hysteresis and nonlinearity problems inherent in piezoelectric actuation and capacitor sensing.
3Measurement precision
If acoustic signals are used to measure actuator length, then measurement precision improves, but device complexity increases due to integrated transmitters and receivers
Solution Approach 1:
The patent integrates the acoustic transmitter and receiver functions directly into the actuator structure itself. The piezoelectric layers that constitute the actuator are also configured to generate and detect acoustic waves, merging the actuation and sensing functions into a single integrated device, thereby reducing overall system complexity.
Solution Approach 2:
The piezoelectric actuator structure serves dual functions: it acts as both the actuation element (converting electrical voltage to mechanical extension) and the sensing element (transmitting and detecting acoustic waves to measure its own extension). This multi-functionality eliminates the need for separate sensing components.
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 provides a simple and effective means to accurately quantify actuator extension by measuring changes in acoustic signal transit time or resonant frequency, reducing errors associated with hysteresis and nonlinearity, and is applicable to various solid-state actuators including piezo ceramic and electrostrictive types.
Implementation Method 1
A piezo electric actuator is extended by application of a voltage across the actuator
Implementation Method 2
for piezo actuators sound travels faster as the actuator is extended. This effect is measurable and allows the amount by which the actuator is extended to be quantified
Data Source
AI summary
A device comprising a solid-state actuator (100), means for inputting an acoustic signal to the actuator (104) and means for measuring the resultant signal (104). The measured acoustic signal can be used to determine the extension of the solid-state actuator.