Capacitive Sensing Enables High-Frequency Control of Electrohydraulic Soft Actuators

Core Concepts

A new HASEL actuator design and compact sensing circuitry enable accurate displacement estimation during high-frequency actuation and external loading using miniaturized components.

Abstract

The paper introduces the F-HASEL actuator, which features an additional electrode pair used exclusively for capacitive sensing, separating sensing from actuation. Two compact sensing circuit designs using low-cost off-the-shelf components are proposed to estimate the F-HASEL's displacement. The experiments demonstrate the capability of the circuits to accurately estimate the displacement during high-frequency actuation up to 20 Hz and external loading using a miniature high-voltage power supply. The sensing methods are also shown to be agnostic to the driving voltage polarity, enabling the mitigation of charge retention effects. Furthermore, a circuitry is proposed to enable quasi-simultaneous displacement estimation of multiple F-HASELs, which is demonstrated in a wearable virtual reality application that tracks the knee and hip joint rotations of a user in real-time. The key highlights include: Introduction of the F-HASEL actuator design with dedicated sensing electrodes Two compact sensing circuit designs using low-cost off-the-shelf components Accurate displacement estimation during high-frequency actuation up to 20 Hz Displacement estimation under external loading using miniature power supplies Polarity-agnostic sensing enabling mitigation of charge retention effects Quasi-simultaneous displacement estimation of multiple F-HASELs Demonstration of a wearable VR application tracking joint rotations in real-time

Stats

The experiments show a reduction in noise magnitude of around 17 times on the voltage measurement across the F-HASEL's sensing electrodes compared to previous methods. The voltage-based sensing method achieves a normalized root mean squared error (NRMSE) of 0.0302 at 1 Hz and 0.0524 at 5 Hz actuation, a significant improvement over the previous state-of-the-art. At 8 Hz actuation, the voltage-based method has an NRMSE of 0.0638, while the impedance-based method has an NRMSE of 0.0589.

Quotes

"The reduction in noise across the LV sensing electrodes, compared to the resistors (RK) and (RC), means that any sensing method based on measuring changes in the voltage (VH) will have a notably higher signal-to-noise ratio than methods measuring changes across measuring resistors (RC) or (RK), assuming the same LV signal is applied." "Compared to the work of Ly et al. [5], which this paper considers the state-of-art in capacitive sensing of Peano-HASEL actuators, we see at 1 Hz a reduction from an NRMSE of approx. 0.1000 to 0.0302, and at 5 Hz a reduction from an NRMSE of approx. 0.8000 to 0.0524."

Key Insights Distilled From

High-Frequency Capacitive Sensing for Electrohydraulic Soft Actuators

by Michel R. Vo... at arxiv.org 04-08-2024

https://arxiv.org/pdf/2404.04071.pdf

Deeper Inquiries

How can the sensing electrode geometry, size, and positioning on the F-HASEL be further optimized to maximize sensing performance?

To optimize the sensing performance of the F-HASEL actuators, several factors related to the sensing electrode geometry, size, and positioning can be considered: Geometry Optimization: The shape of the sensing electrodes can be optimized to enhance the capacitance changes during actuation. This could involve exploring different electrode shapes such as interdigitated electrodes or fractal patterns to increase the sensitivity to displacement. Size Adjustment: The size of the sensing electrodes can impact the resolution and accuracy of the displacement estimation. By adjusting the size of the electrodes, it may be possible to achieve a balance between sensitivity and noise reduction. Positioning Refinement: The precise positioning of the sensing electrodes on the F-HASEL actuator is crucial for accurate displacement estimation. Fine-tuning the placement to maximize the change in capacitance during actuation while minimizing interference from external factors can improve overall performance. Multiple Electrode Configurations: Exploring different configurations of sensing electrodes, such as varying the distance between electrodes or adding additional electrode pairs, could provide insights into optimizing the sensing setup for enhanced performance. By systematically analyzing and experimenting with these parameters, it is possible to further optimize the sensing electrode geometry, size, and positioning on the F-HASEL actuators to maximize sensing performance.

How can the sensing electrode geometry, size, and positioning on the F-HASEL be further optimized to maximize sensing performance?

To optimize the sensing performance of the F-HASEL actuators, several factors related to the sensing electrode geometry, size, and positioning can be considered: Geometry Optimization: The shape of the sensing electrodes can be optimized to enhance the capacitance changes during actuation. This could involve exploring different electrode shapes such as interdigitated electrodes or fractal patterns to increase the sensitivity to displacement. Size Adjustment: The size of the sensing electrodes can impact the resolution and accuracy of the displacement estimation. By adjusting the size of the electrodes, it may be possible to achieve a balance between sensitivity and noise reduction. Positioning Refinement: The precise positioning of the sensing electrodes on the F-HASEL actuator is crucial for accurate displacement estimation. Fine-tuning the placement to maximize the change in capacitance during actuation while minimizing interference from external factors can improve overall performance. Multiple Electrode Configurations: Exploring different configurations of sensing electrodes, such as varying the distance between electrodes or adding additional electrode pairs, could provide insights into optimizing the sensing setup for enhanced performance. By systematically analyzing and experimenting with these parameters, it is possible to further optimize the sensing electrode geometry, size, and positioning on the F-HASEL actuators to maximize sensing performance.

How can the sensing electrode geometry, size, and positioning on the F-HASEL be further optimized to maximize sensing performance?

To optimize the sensing performance of the F-HASEL actuators, several factors related to the sensing electrode geometry, size, and positioning can be considered: Geometry Optimization: The shape of the sensing electrodes can be optimized to enhance the capacitance changes during actuation. This could involve exploring different electrode shapes such as interdigitated electrodes or fractal patterns to increase the sensitivity to displacement. Size Adjustment: The size of the sensing electrodes can impact the resolution and accuracy of the displacement estimation. By adjusting the size of the electrodes, it may be possible to achieve a balance between sensitivity and noise reduction. Positioning Refinement: The precise positioning of the sensing electrodes on the F-HASEL actuator is crucial for accurate displacement estimation. Fine-tuning the placement to maximize the change in capacitance during actuation while minimizing interference from external factors can improve overall performance. Multiple Electrode Configurations: Exploring different configurations of sensing electrodes, such as varying the distance between electrodes or adding additional electrode pairs, could provide insights into optimizing the sensing setup for enhanced performance. By systematically analyzing and experimenting with these parameters, it is possible to further optimize the sensing electrode geometry, size, and positioning on the F-HASEL actuators to maximize sensing performance.