Powered Ankle-Foot Prosthesis for the Improvement of Amputee Ambulation

Abstract

This paper presents the mechanical design, control scheme, and clinical evaluation of a novel, motorized ankle-foot prosthesis, called MIT Powered Ankle-Foot Prosthesis. Unlike a conventional passive-elastic ankle-foot prosthesis, this prosthesis can provide active mechanical power during the stance period of walking. The basic architecture of the prosthesis is a unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. With this architecture, the anklefoot prosthesis matches the size and weight of the human ankle, and is also capable of delivering high mechanical power and torque observed in normal human walking. We also propose a biomimetic control scheme that allows the prosthesis to mimic the normal human ankle behavior during walking. To evaluate the performance of the prosthesis, we measured the rate of oxygen consumption of three unilateral transtibial amputees walking at self-selected speeds to estimate the metabolic walking economy. We find that the powered prosthesis improves amputee metabolic economy from 7% to 20% compared to the conventional passive-elastic prostheses (Flex-Foot Ceterus and Freedom Innovations Sierra), even though the powered system is twofold heavier than the conventional devices. This result highlights the benefit of performing net positive work at the ankle joint to amputee ambulation and also suggests a new direction for further advancement of an ankle-foot prosthesis.

Performance Evaluation Methods for Assistive Robotic Technology

“…The performance measures include joint angle, joint torque, and power consumption. However, several research institutions have conducted end-user evaluations, including RIC [67,57], Northwestern University [67,57], Massachusetts Institute of Technology [4,5], and Hong Kong Polytechnic University [58].…”

Design and Qualitative Testing of a Prosthetic Foot With Rotational Ankle and Metatarsal Joints to Mimic Physiological Roll-Over Shape

“…Typical loading is often assumed in measuring the roll-over shape of prosthetic feet through mechanical testing [5,9,24]. Also, powered prostheses designed to reproduce the ankle angle versus moment curve as measured during typical walking have been shown to lower the metabolic cost of walking relative to passive prostheses [6]. For these reasons, the authors believe that using typical, unimpaired gait data in calculating the roll-over shapes of this prototype is the best option.…”

“…At the end of stance phase, the muscles around the ankle provide a power input to aid in push-off. Powered prosthetic ankle/feet have successfully lowered the metabolic cost of walking compared to passive prosthetic feet by replicating this power input with onboard actuators, sensors, and batteries [6]. However, these robotic prostheses are expensive and would not withstand the sand, mud and water in which prosthetic feet are commonly used in developing countries.…”

Engineered embodiment: Comment on “The embodiment of assistive devices—from wheelchair to exoskeleton” by M. Pazzaglia and M. Molinari

“…In part for these reasons and in part due to technological limitations, commercially available prostheses are to this day largely restricted to passive devices that rely on spring or damping mechanisms offering little adaptability and increasing the amputees' energy expenditure [6]. Only recently have active, powered lower limb prostheses become commercially available [7,8]. While the most common control strategy for these prostheses are finite state machines based on abstracted gait cycles, the availability of microcontrollers has already brought forth biomimetic control strategies incorporating neuromuscular models [9].…”