A novel, miniature, low-mass vehicle has been created that is driven by piezoelectric stacks and a resonance structure. Preliminary tests on similar mechanisms that are used to transmit electrical power across the wall showed efficiencies of the order of 90%. The transmitted mechanical power, and signals through metallic walls using the direct and indirect piezoelectric effects in similar motors, is of the order of 50%. The transmitted power is generated inside the vehicle body, and the mechanism is applicable to any robotic system that may require an ambulation of locomotion mechanism such as a rover, a miniature vehicle, a crawler, or a flying device.

Cross-sectional view of the axis actuators and a wheel.
For this purpose, a piezoelectric stack, with a backing and stress bolt, generates ultrasonic vibrations that are transmitted through the vehicle walls. The stress wave excites a resonant structure that produces micro-motion at high frequency to create a rotary or linear actuation for the ambulation of the vehicle. This design avoids the need to use gears or bearings, as well as avoiding shafts or cabling through the wall. In addition to driving the actuators that move the wheels or robot legs, the transferred power can be used to activate sensors and other mechanisms. The elastic waves transmit mechanical power and signals through walls, and allow the performance of multiple electromechanical tasks. Tests have demonstrated using such vibrations to generate high torques at speeds as high as 900 RPM without the need for gears, bearings, or shafts. The motors are non-back-drivable, i.e., provide self-braking.

This innovation allows the driving of wheels or legs through the vehicle wall without perforating the structure. This can be critical in terrains that have harsh environments, such as Venus with its high temperature and pressure. Also, this design method can be used to drive a submarine in Titan’s lakes without concern for extremely low-temperature seals.

This work was done by Yoseph Bar-Cohen, Stewart Sherrit, and Mircea Badescu of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49101

Topics:
Automation Bearings Cables Electric power Gears Mechanical Components Off-board energy sources Parts Robotics Sensors and actuators Wheels
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Miniature, Multi-Functional, Self-Braking Vehicle

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NASA Tech Briefs Magazine

This article first appeared in the January, 2016 issue of NASA Tech Briefs Magazine (Vol. 40 No. 1).

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Overview

The document presents a technical disclosure of a novel miniature, multi-functional, self-braking vehicle developed by the Jet Propulsion Laboratory (JPL) at the California Institute of Technology, under NASA's sponsorship. This vehicle is actuated by piezoelectric stacks that utilize ultrasonic vibrations to create rotary or linear motion, enabling ambulation without the need for traditional mechanical components such as gears, bearings, or shafts.

The primary innovation lies in the vehicle's ability to transfer mechanical power through its walls using acoustic mechanical feed-throughs. This design enhances reliability by minimizing the number of components, which is particularly advantageous in extreme environments and harsh terrain conditions, such as those encountered in military applications or planetary exploration. The vehicle can operate effectively in challenging conditions, including high temperatures and wet environments, where conventional electromagnetic motors may fail due to their complexity and numerous potential failure points.

The piezoelectric actuators generate high torque at speeds up to 900 RPM, and the system is non-back-drivable, meaning it provides self-braking capabilities. This feature is crucial for applications requiring precise control and stability. The mechanical energy generated inside the vehicle can also be used to power sensors and other mechanisms, allowing for multiple electromechanical tasks to be performed simultaneously.

Preliminary tests have demonstrated efficiencies of around 90% for transmitting electrical power across the vehicle walls, with mechanical power transmission efficiencies of approximately 50%. The vehicle's design is applicable to various robotic systems, including rovers, miniature vehicles, crawlers, and flying devices, making it a versatile solution for future technological applications.

Overall, this document outlines a significant advancement in actuator technology, emphasizing the potential for enhanced performance and reliability in miniature vehicles designed for diverse applications. The research highlights the importance of developing systems that can operate effectively in extreme conditions while minimizing mechanical complexity, paving the way for future innovations in robotics and automation.