Dielectric Elastomer Actuator Self-Sensing via Capacitance Calculation
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Solution Overview
Problem
Existing self-sensing methods for dielectric elastomer actuators are inaccurate under dynamic conditions and external perturbations, and are not suitable for portable systems, lacking robustness in determining capacitance and state, especially when leakage current and high actuation speeds are involved.
Innovation Solution
A method involving measuring voltage difference, its derivative, and total instantaneous current to calculate capacitance, accounting for leakage current and error terms, using a pulse-width modulated current source with controlled slew rate, and employing a resistor ladder and differentiator circuit for accurate feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing self-sensing methods are used to determine capacitance of DEA, then the system is simple and easy to implement, but the measurement precision is poor under dynamic conditions and external perturbations
Solution Approach 1:
The patent implements a feedback-based self-sensing method where the measured capacitance value is fed back to adjust the control signal to the DEA. The system continuously monitors the capacitance between electrodes and uses this information to determine the actual state of the actuator, enabling closed-loop control that improves measurement accuracy under dynamic conditions while maintaining system simplicity through the use of basic electrical measurement components.
Solution Approach 2:
The DEA structure itself is utilized as the sensing element by measuring the capacitance between its electrodes. The dielectric elastomer membrane and electrode assembly serve dual functions as both the actuating element and the sensing element, eliminating the need for separate sensors and reducing system complexity while providing accurate capacitance measurement for state determination.
2Reliability
If existing self-sensing methods are used for high actuation speeds, then the device complexity remains low, but the reliability of capacitance determination deteriorates due to leakage current and dynamic effects
Solution Approach 1:
The patent applies preliminary compensation for leakage current effects by measuring the capacitance at specific moments in the actuation cycle when the DEA is stationary or at equilibrium positions. By taking measurements at these predetermined timing points before dynamic effects significantly impact the system, the method achieves reliable capacitance determination even during high-speed actuation sequences.
Solution Approach 2:
The system employs periodic measurement cycles where capacitance is measured at regular intervals during the actuation cycle. This periodic sampling approach allows the system to capture accurate capacitance values at multiple points throughout the motion cycle, improving reliability by averaging out dynamic effects and leakage current variations while maintaining a simple measurement architecture.
3Adaptability or versatility
If traditional actuation technologies are used, then the actuator can operate under specific conditions with high performance, but the adaptability to wide ranges of loads and speeds is limited
Solution Approach 1:
The patent implements dynamic control of the DEA by continuously adjusting the control signal based on real-time capacitance measurements. The system adapts its operation to match the actual state of the actuator, allowing it to maintain reliable performance across a wide range of loads and speeds. The dynamic feedback control enables the actuator to optimize its operation for different operating conditions while maintaining performance consistency.
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 accurate and robust feedback on the state and capacitance of dielectric elastomer actuators, enabling precise control and preventing dielectric breakdown, suitable for portable and dynamic applications.
Implementation Method 1
The dielectric elastomer membrane 11 is compressed by electrostatic pressure when a high voltage is applied across the electrodes 12 in the manner of a capacitor
Implementation Method 2
a dielectric elastomer actuator (DEA) generally referenced 10 comprises a dielectric elastomer membrane 11 provided between compliant electrodes 12
Implementation Method 3
Because a DEA is constructed from a material which is resistant to compression, it is possible to relate a change in capacitance to changes in the physical geometry of the DEA
Data Source
AI summary
A system and method is provided for determining the capacitance between electrodes of an artificial muscle or dielectric elastomer actuator (DEA). The method comprises measuring the voltage difference between the electrodes of the DEA, the first derivative of that voltage with respect to time, and the total instantaneous current through the DEA, then calculating the capacitance of the DEA as the difference between the total instantaneous current through the DEA and the product of the voltage between the electrodes and an error term, divided by the first derivative of the voltage between the electrodes with respect to time. The capacitance may then be used to derive estimates of the leakage current, charge upon the DEA, and/or the physical state of the DEA, thereby implementing self-sensing to allow closed-loop feedback control of DEA actuation.