Lightweight Exoskeletons With Controllable Actuators
- Created on Friday, 01 October 2004
Resistive or assistive forces and torques would be generated on command.
A proposed class of lightweight exoskeletal electromechanical systems would include electrically controllable actuators that would generate torques and forces that, depending on specific applications, would resist and/or assist wearers’ movements. The proposed systems would be successors to relatively heavy, bulky, and less capable human strength amplifying exoskeletal electromechanical systems that have been subjects of research during the past four decades. The proposed systems could be useful in diverse applications in which there are needs for systems that could be donned or doffed easily, that would exert little effect when idle, and that could be activated on demand: examples of such applications include (1) providing controlled movement and/or resistance to movement for physical exercise and (2) augmenting wearers’ strengths in the performance of military, law-enforcement, and industrial tasks.
An exoskeleton according to the proposal would include adjustable lightweight graphite/epoxy struts and would be attached to the wearer’s body by belts made of hook-and-pile material (see figure). At selected rotary and linear joints, the exoskeleton would be fitted, variously, with lightweight, low power-consumption rotary and linear brakes, clutches, and motors. The exoskeleton would also be equipped with electronic circuitry for monitoring, control, and possibly communication with external electronic circuits that would perform additional monitoring and control functions.
The linear motors could be lightweight actuators that move in the manner of an inchworm. The rotary motor actuators could be fairly conventional rotary motors, possibly equipped with clutches. Each brake or clutch would be, essentially, a rotary or linear dashpot of advanced design, containing an electrorheological fluid. (A typical electrorheological fluid is a dielectric fluid containing suspended microscopic dielectric particles. The viscosity of the fluid increases with applied electric field, with a typical response time of the order of milliseconds.) Within each brake or clutch, electrodes and flow channels would be sized, shaped, and placed so that in the absence of applied voltage, there would be minimal resistance to the affected linear or rotary motion, while at the maximum applied voltage, the actuator would resist the motion with a required force or torque, respectively. Because very little power is consumed in applying an electric field to an electrorheological liquid, a system according to the proposal used only for controlled-resistance exercise would consume little power and, hence, could be powered by a small, lightweight battery.
The electronic circuitry of the exoskeleton would include a Pentium (or equivalent) digital processor, digital-to-analog and analog-to-digital converter circuit boards, motion-control circuits, sensor-interface circuit boards, and a modem circuit card for radio communication with a remote control station. A small display device would present data on required and performed physical activity. Most of this circuitry could be mounted in a backpack.
Miniature position sensors would be placed on the joints of the exoskeleton. Miniature force and touch sensors and myoelectric or myopneumatic sensors would be placed on the wearer’s body to measure flexion and extension of muscles. The sensor and control circuitry would be designed to act together to enable the wearer to act intuitively in controlling the exoskeleton. The software in the microprocessor would (1) take account of all sensor signals to infer the motion of, and the forces and torques exerted by and on, the wearer and (2) generate commands to assist or resist the wearer’s motion as needed. The sensor and control design would be characterized by redundancy and robustness.
This work was done by Yoseph Bar-Cohen, Constantinos Mavrodis, Juan Melli-Huber, and Avi (Alan) Fisch of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Machinery/Automation category. NPO-30558
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