Shape memory alloy actuated ankle foot orthosis for reduction of locomotion force

peer reviewedHumans can be considered inefficient at walking because they are unable to achieve the theoretically ideal 'zero energy cost' of steady-state locomotion that is possible for bipeds who have elastic tissues. This inefficiency is mainly due to part of the energy that is generated by the body to complete a single step being dissipated instead of being stored for use in the proceeding step. This suggests that we can improve locomotion efficiency and reduce the metabolic energy cost of walking by manipulating the elasticity of the lower limbs using exoskeletal devices [1]. However, most traditional designs use springs made from regular material that have a constant stiffness. These devices exert a linear force pattern that is not biocompatible because they do not mimic the forces of the muscles or the tendons of the human body. This paper presents an interdisciplinary study of the design of a passive-dynamic ankle foot orthosis mechanism that reduces the biological muscle force requirements during locomotion, thus reducing the metabolic energy cost of walking while maintaining biocompatibility. Shape memory alloy is used as a smart material for an actuator owing to its super-elasticity. This super-elasticity provides a nonlinear stiffness pattern that generates forces comparable to those of healthy muscles

Design, Control, and Perception of Bionic Legs and Exoskeletons

Bionic systems---wearable robots designed to replace, augment, or interact with the human body---have the potential to meaningfully impact quality of life; in particular, lower-limb prostheses and exoskeletons can help people walk faster, better, and safer. From a technical standpoint, there is a high barrier-to-entry to conduct research with bionic systems, limiting the quantity of research done; additionally, the constraints introduced by bionic systems often prohibit accurate measurement of the robot's output dynamics, limiting the quality of research done. From a scientific standpoint, we have begun to understand how people regulate lower-limb joint impedance (stiffness and damping), but not how they sense and perceive changes in joint impedance. To address these issues, I first present an open-source bionic leg prosthesis; I describe the design and testing process, and demonstrate patients meeting clinical ambulation goals in a rehabilitation hospital. Second, I develop tools to characterize open-loop impedance control systems and show how to achieve accurate impedance control without a torque feedback signal; additionally, I evaluate the efficiency of multiple bionic systems. Finally, I investigate how well people can perceive changes in the damping properties of a robot, similar to an exoskeleton. With this dissertation, I provide technical and scientific advances aimed at accelerating the field of bionics, with the ultimate goal of enabling meaningful impact with bionic systems.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163108/1/afazocar_1.pd