On-Command Force and Torque Impeding Devices (OC-FTID) Using ERF
- Sunday, 01 December 2013
- NASA’s Jet Propulsion Laboratory, Pasadena, California
This technology is applicable as a rehabilitation or exercise device.
Various machines have been developed to address the need for countermeasures of bone and muscle deterioration when humans operate over extended time in space. Even though these machines are in use, each of them has many limitations that need to be addressed in an effort to prepare for human missions to distant bodies in the solar system.
An exercise exoskeleton was conceived that performs on-demand resistivity by inducing force and torque impedance via ElectroRheological Fluid (ERF). The resistive elements consist of pistons that are moving inside ERF-filled cylinders or a donut-shaped cavity, and the fluid flows through the piston when the piston is moved. Tests of the operation of ERF against load showed the feasibility of this approach.
The inside of the piston consists of parallel electrodes with alternating polarity that increase the ERF viscosity when activated. This increase leads to the formation of a virtual valve inside the piston creating impeding force to the piston motion. The cross-sectional area of the piston is mostly hollow to allow low piston resistance to the motion when the electrodes are not activated, and produce high impedance when the electrodes are activated. A balanced volume is created on the two sides of the piston so that pushing it will only involve fluid flow against the effect of the increased viscosity in the gaps between the electrodes.
The elements are shaped as a cylinder or donut with a piston that is moved inside the internal cavity containing ERF. The elements have a piston inside the cavity with shafts on its two sides. The piston is pushed or pulled inside the chambers and consists of parallel electrodes with opposing polarity wired through one of the shafts. When the electrodes are subjected to electric field, they form a virtual valve causing increased viscosity and impeded flow. Using ERF offers the ability to proportionally (as a function of the voltage) increase the viscosity of the fluid with a very fast reaction time on the order of milliseconds. The feasibility of this approach is straightforward from the nature of ERF materials and preliminary tests made in the lab.
ERF properties of high yield stress, low current density, and fast response (less than one millisecond) offer essential characteristics for the construction of the exoskeleton. ERFs can apply very high electrically controlled resistive forces or torque while their size (weight and geometric parameters) can be very small. Their long life and ability to function in a wide temperature range (from –40 to 200 ºC) allows for their use in extreme environments. ERFs are also non-abrasive, non-toxic, and nonpolluting (meet health and safety regulations).
The technology is applicable as a compact exercise machine for astronauts’ countermeasure of microgravity, an exercise machine for sport, or as a device for rehabilitation of patients with limb issues.
This work was done by Yoseph Bar-Cohen, Mircea Badescu, and Stewart Sherrit of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48393