The disclosed device provides key elements to enabling compact exercise machines that overcome many of the disadvantages of the current spacesuit, as well as medical prosthetics and exoskeletons. The mechanism is based on switchable, curved, leaf, and torsion spring mechanisms that support the user joints and at the contact with the ground to enable high-speed, low-loss locomotion. The springs are primed with an actuator to counteract losses and recycle the user’s elastic energy in the locomotion. The mechanism is designed to be switchable and to allow for removing the springs from the structure for fine control. Adjustable hard-stops are embedded into each joint to prevent overextension and optimize the performance at each gait. The spring mechanisms are made from carbon fiber composites to reduce the weight of the system. The components of this mechanism can be structurally connected to each other via a mechanical clutch to form a symmetric lower-extremity system with a passive spring mechanism to reduce the requirement of the joints to dampen the impact forces and recycle some of the energy of walking and running.

Adjustable stiffness link element with active and passive joints.
The disclosed mechanism allows for recycling elastic power, and employs a flexure spring structure to assist the movement of such body joints as the ankle, knee, and/or hip. Generally, the use of spring systems in prosthetics has been widely shown to allow a disabled user to run at levels of performance that match an able user, or better, with reduced metabolic rates. Springs are used as lightweight energy-storing devices that allow for more functional gait, and reduce the level of exertion in users of prosthetic devices. Generally, storing and releasing energy in elastic mechanisms to assist in ambulation is not new. Most commercial prosthetic feet consist of carbon fiber leaf springs that store energy at the heel strike stage, and it is released during late stance.

These springs are incorporated into the suit and structurally connected to each other by engaging a mechanism as a clutch at each joint to rigidize it to the related flexure. This configuration forms a symmetric lower-extremity suit with a passive spring mechanism.

This structure is used to reduce the requirement of the joints to dampen the impact forces and recycle some of the energy of walking and running. In addition, gearless ultrasonic motors can assist the spring displacement under extension and compression in order to augment the motion of the suit structure. The extensions and rotation of the springs are set to avoid possibility of overextension of a joint by using adjustable hard-stops. In addition, the connected flexures are designed to have adjustable stiffness by controlling the attachment points and the number of flexures that are optimal for different user actions.

These spring flexures are made controllable to adjust to the torque requirements, range of motion, and length of the adjacent links of each joint and the initial angular displacement. This spring-based mechanism enables a system that will mimic the power, energy, motion, and weight of the human hips, knees, and ankles. This mechanism allows tuning of the spring performance to minimize the peak motor requirements, thus producing a much lighter device. This approach of storing and releasing energy during the gait cycle supports the various motion possibilities related to walking, jogging, jumping, walking up and down slopes, and ascending and descending stairs.

The disclosed invention would support future human exploration in space where astronauts can be assisted in their ambulation by reducing the metabolism that is required, and thus help them address potential difficulties if they encounter significant loss of bones and muscles prior to their arrival to the specific planetary body.

This work was done by Mircea Badescu, Stewart Sherrit, and Yoseph Bar-Cohen of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48462


This Brief includes a Technical Support Package (TSP).
Mobility Augmentation System Using Switchable Spring Mechanisms

(reference NPO48462) is currently available for download from the TSP library.

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This article first appeared in the November, 2014 issue of NASA Tech Briefs Magazine.

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