HASEL

Electro-Hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control

Anonymous — Mon, 02 May 2022 15:09:15 +0000

Electro-Hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control Anonymous (not verified) Mon, 05/02/2022 - 09:09

Locomotion through rolling is attractive compared to other forms of locomotion thanks to uniform designs, high degree of mobility, dynamic stability, and self-recovery from collision. Despite previous efforts to design rolling soft systems, pneumatic and other soft actuators are often limited in terms of high-speed dynamics, system integration, and/or functionalities. Furthermore, mathematical description of the rolling dynamics for this type of robot and how the models can be used for speed control are often not mentioned. This article introduces a cylindrical-shaped shell-bulging rolling soft wheel that employs an array of 16 folded-HASEL actuators as a mean for improved rolling performance. The actuators represent the soft components with discrete forces that propel the wheel, whereas the wheel's frame is rigid but allows for smooth, continuous change in position and speed. We discuss the interplay between the electrical and mechanical design choices, the modeling of the wheel's hybrid (continuous and discrete) dynamic behavior, and the implementation of a model predictive controller (MPC) for the robot's speed. With the balance of several design factors, we show the wheel's ability to carry integrated hardware with a maximum rolling speed at 0.7 m/s (or 2.2 body lengths per second), despite its total weight of 979 g, allowing the wheel to outperform the existing rolling soft wheels with comparable weights and sizes. We also show that the MPC enables the wheel to accelerate and leverage its inherent braking capability to reach desired speeds—a critical function that did not exist in previous rolling soft systems.

Reference

Ly, Khoi, Jatin V. Mayekar, Sarah Aguasvivas, Christoph Keplinger, Mark E. Rentschler, and Nikolaus Correll. "Electro-Hydraulic Rolling Soft Wheel: Design, Hybrid Dynamic Modeling, and Model Predictive Control." IEEE Transactions on Robotics (2022).

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Toward smart composites: small-scale, untethered prediction and control for soft sensor/actuator systems

Anonymous — Mon, 02 May 2022 12:46:34 +0000

Toward smart composites: small-scale, untethered prediction and control for soft sensor/actuator systems Anonymous (not verified) Mon, 05/02/2022 - 06:46

We present a suite of algorithms and tools for model-predictive control of sensor/actuator systems with embedded microcontroller units (MCU). These MCUs can be colocated with sensors and actuators, thereby enabling a new class of smart composites capable of autonomous behavior that does not require an external computer. In this approach, kinematics are learned using a neural network model from offline data and compiled into MCU code using nn4mc, an open-source tool. Online Newton-Raphson optimization solves for the control input. Shallow neural network models applied to 1D sensor signals allow for reduced model sizes and increased control loop frequencies. We validate this approach on a simulated mass-spring-damper system and two experimental setups with different sensing, actuation, and computational hardware: a tendon-based platform with embedded optical lace sensors and a HASEL-based platform with magnetic sensors. Experimental results indicate effective high-bandwidth tracking of reference paths (120 Hz and higher) with a small memory footprint (less than or equal to 6.4% of available flash). The measured path-following error does not exceed 2 mm in the tendon-based platform, and the predicted path following error does not exceed 1 mm in the HASEL-based platform. This controller code's mean power consumption in an ARM Cortex-M4 computer is 45.4 mW. This control approach is also compatible with Tensorflow Lite models and equivalent compilers. Embedded intelligence in composite materials enables a new class of composites that infuse intelligence into structures and systems, making them capable of responding to environmental stimuli using their proprioception.

Reference

Manzano, Sarah Aguasvivas, Vani Sundaram, Artemis Xu, Khoi Ly, Mark Rentschler, Robert Shepherd, and Nikolaus Correll. "Toward smart composites: small-scale, untethered prediction and control for soft sensor/actuator systems." Submitted to Journal of Composite Materials (2022). [PDF]

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Miniaturized circuitry for capacitive self-sensing and closed-loop control of soft electrostatic transducers

Anonymous — Wed, 01 Dec 2021 07:00:00 +0000

Miniaturized circuitry for capacitive self-sensing and closed-loop control of soft electrostatic transducers Anonymous (not verified) Wed, 12/01/2021 - 00:00

Soft robotics is a field of robotic system design characterized by materials and structures that exhibit large-scale deformation, high compliance, and rich multifunctionality. The incorporation of soft and deformable structures endows soft robotic systems with the compliance and resiliency that makes them well-adapted for unstructured and dynamic environments. While actuation mechanisms for soft robots vary widely, soft electrostatic transducers such as dielectric elastomer actuators (DEAs) and hydraulically amplified self-healing electrostatic (HASEL) actuators have demonstrated promise due to their muscle-like performance and capacitive selfsensing capabilities. Despite previous efforts to implement self-sensing in electrostatic transducers by overlaying sinusoidal low-voltage signals, these designs still require sensing high-voltage signals, requiring bulky components that prevent integration with miniature, untethered soft robots. We present a circuit design that eliminates the need for any high-voltage sensing components, thereby facilitating the design of simple, low cost circuits using off-the-shelf components. Using this circuit, we perform simultaneous sensing and actuation for a range of electrostatic transducers including circular DEAs and HASEL actuators and demonstrate accurate estimated displacements with errors under 4%. We further develop this circuit into a compact and portable system that couples HV actuation, sensing, and computation as a prototype towards untethered, multifunctional soft robotic systems. Finally, we demonstrate the capabilities of our self-sensing design through feedback-control of a robotic arm powered by Peano-HASEL actuators.

Reference

Ly, K., Kellaris, N., McMorris, D., Johnson, B.K., Acome, E., Sundaram, V., Naris, M., Humbert, J.S., Rentschler, M.E., Keplinger, C. and Correll, N., 2021. Miniaturized circuitry for capacitive self-sensing and closed-loop control of soft electrostatic transducers. Soft Robotics, 8(6), pp.673-686. [PDF]

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