Jeff Weber

Powered Ankle--Foot Prosthesis Improves Walking Metabolic Economy

At moderate to fast walking speeds, the human ankle provides net positive work at high-mechanical-power output to propel the body upward and forward during the stance period. On the contrary, conventional ankle-foot prostheses exhibit a passive-elastic response during stance, and consequently, cannot provide net work. Clinical studies indicate that transtibial amputees using conventional prostheses have higher gait metabolic rates than normal. Researchers believe that the main cause for these higher rates is due to the inability of conventional prostheses to provide sufficient positive power at terminal stance in the trailing leg to limit heel strike losses of the adjacent leading leg. In this investigation, we evaluate the hypothesis that a powered ankle-foot prosthesis, capable of providing human-like ankle work and power during stance, can decrease the metabolic cost of transport (COT) compared to a conventional passive-elastic prosthesis. To test the hypothesis, a powered prosthesis is built that comprises a unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. The prosthesis is shown to deliver the high mechanical power and net positive work observed in normal human walking. The rate of oxygen consumption and carbon dioxide production is measured as a determinant of metabolic rate on three unilateral transtibial amputees walking at self-selected speeds. We find that the powered prosthesis decreases the amputees metabolic COT on average by 14% compared to the conventional passive-elastic prostheses evaluated (Flex-Foot Ceterusreg and Freedom Innovations Sierra), even though the powered system is over twofold heavier than the conventional devices. These results highlight the clinical importance of prosthetic interventions that closely mimic the mass distribution, kinetics, and kinematics of the missing limb.

Powered Ankle-Foot Prosthesis for the Improvement of Amputee Ambulation

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 ankle-foot 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.

SENSING AND MANIPULATING BUILT-FOR-HUMAN ENVIRONMENTS

We report on a dynamically balancing robot with a dexterous arm designed to operate in built-for-human environments. Our initial target task was for the robot to navigate, identify doors, open them, and proceed through them.

Biomechanical Design of a Powered Ankle-Foot Prosthesis

Although the potential benefits of a powered ankle-foot prosthesis have been well documented, no one has successfully developed and verified that such a prosthesis can improve amputee gait compared to a conventional passive-elastic prosthesis. One of the main hurdles that hinder such a development is the challenge of building an ankle-foot prosthesis that matches the size and weight of the intact ankle, but still provides a sufficiently large instantaneous power output and torque to propel an amputee. In this paper, we present a novel, powered ankle-foot prosthesis that overcomes these design challenges. The prosthesis comprises an unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. With this architecture, the ankle-foot prosthesis matches the size and weight of the human ankle, and is shown to be satisfying the restrictive design specifications dictated by normal human ankle walking biomechanics.

Domo: a force sensing humanoid robot for manipulation research

Humanoid robots found in research and commercial use today typically lack the ability to operate in unstructured and unknown environments. Force sensing and compliance at each robot joint can allow the robot to safely act in these environments. However, these features can be difficult to incorporate into robot designs. We present a new force sensing and compliant humanoid under development in the humanoid robotics group at MIT CSAIL. The robot, named Domo, is to be a research platform for exploring issues in general dexterous manipulation, visual perception, and learning. In this paper we describe aspects of the design, detail proposed research directions for the robot, and illustrate how the design of humanoid robots can be informed by the desired research goals.

Design of an agonist-antagonist active knee prosthesis

The majority of commercial prosthetic knees are passive in nature and therefore cannot replicate the positive mechanical work exhibited by the natural human knee in early and late stance. In contrast to traditional purely dissipative prosthetic knees, we propose a biomimetic active agonist-antagonist structure designed to reproduce both positive and negative work phases of the natural joint while using series elasticity to minimize net energy consumption. We present the design and physical implementation of the active knee prosthesis prototype.

MERTZ: a quest for a robust and scalable active vision humanoid head robot

We present the design and construction of MERTZ, an active-vision humanoid head robot, with the immediate goal of having the robot runs continuously for many hours a day without supervision at various locations. We address how the lack of robustness and reliability lead to limitations and scalability issues in research robotic platforms. We propose to attend to these issues in parallel with the course of robot development. Drawing from lessons learned from our previous robots, we incorporated various fault prevention strategies into the electromechanical design. We have implemented a preliminary system, integrating sensorimotor, vision, and audio in order to test the full range of all degrees of freedom and enable the robot to engage in simple visual and verbal interaction with people. We conducted a series of experiment where the robot ran for

Biomimetic Prosthetic Knee Using Antagonistic Muscle-Like Activation

2 hours within 9 days at different public spaces. The robot interacted with a large number of passersby and collected at least 100,000 face images of at least 600 individuals within 4 days. We learned various lessons involving the robustness of current design and identified a set of failure modes. Lastly, we present the long term research direction for the robot.

Powered artificial knee with agonist-antagonist actuation

The majority of commercial prosthetic knees are passive in nature and therefore cannot replicate the positive mechanical work exhibited by the natural human knee in early and late stance. In contrast to traditional purely dissipative prosthetic knees, we propose a biomimetic active agonist-antagonist structure designed to reproduce both positive and negative work phases of the natural joint while using series elasticity to minimize net energy consumption. We present the design and implementation of the active knee prosthesis prototype.Copyright