Biomechatronics
How technology can be used to enhance human physical capability.
We know from early Roman mosaics that physical rehabilitation and amplification technologies have been used during much of recorded history. Although the goal of constructing such technologies is not new, great scientific and technological hurdles still remain. Even today, permanent assistive devices are viewed by the physically challenged as separate, lifeless mechanisms and not intimate extensions of the human body—structurally, neurologically, and dynamically. The Biomechatronics group seeks to advance technologies that promise to accelerate the merging of body and machine, including device architectures that resemble the body's own musculoskeletal design, actuator technologies that behave like muscle, and control methodologies that exploit principles of biological movement.

Research Projects

  • Artificial Gastrocnemius

    Hugh Herr and Ken Endo
    Human walking neuromechanical models show how each muscle works during normal, level-ground walking. They are mainly modeled with clutches and linear springs, and are able to capture dominant normal walking behavior. This suggests to us to use a series-elastic clutch at the knee joint for below-knee amputees. We have developed the powered ankle prosthesis, which generates enough force to enable a user to walk "normally." However, amputees still have problems at the knee joint due to the lack of gastrocnemius, which works as an ankle-knee flexor and a plantar flexor. We hypothesize that metabolic cost and EMG patterns of an amputee with our powered ankle and virtual gastrocnemius will dramatically improve.

  • Biomimetic Active Prosthesis for Above-Knee Amputees

    Ernesto C. Martinez-Villalpando and Hugh Herr
    We propose a novel biomimetic active prosthesis for above-knee amputees. The clinical impact of this technology focuses on improving an amputee’s gait symmetry, walking speed, and metabolic energy consumption on variant terrain conditions. The electromechanical design of this robotic device mimics the body's own musculoskeletal design, using actuator technologies that have muscle-like behaviors and can integrate control methodologies that exploit the principles of human locomotion. This work seeks to advance the field of biomechatronics by contributing to the development of intelligent assistive technologies that adapt to the needs of the physically challenged.

  • Command of Powered Ankle Angle using Electromyography

    Hugh Herr and Matthew Robert Williams

    While the current powered ankle under development can readily adapt to constant surfaces while walking (including slopes and stairs), it is unable to predict slope transitions; particularly when the walking surface changes from a positive to a negative slope (or vice versa) within one step. This project explores to effect of using voluntary electromyography (EMG) signal from muscles in the residual limb to adjust ankle angle for better accommodation of slope transitions. Unilateral, trans-femoral amputees will walk across a course consisting of a series of changing slopes while using either a conventional prosthesis or the powered ankle with EMG commanded ankle position. It is thought that by giving the user a simple, effective, and rapid means of adjusting ankle angle, the safety and comfort of gait during rapid slope transitions can be improved.

  • Control of Muscle-Actuated Systems via Electrical Stimulation

    Waleed Farahat and Hugh Herr
    Motivated by applications in rehabilitation and robotics, we are developing methodologies to control muscle-actuated systems via electrical stimulation. As a demonstration of such potential, we are developing centimeter-scale robotic systems that utilize muscle for actuation and glucose as a primary source of fuel. This is an interesting control problem because muscles: a) are mechanical state-dependent actuators; b) exhibit strong nonlinearities; and c) have slow time-varying properties due to fatigue-recuperation, growth-atrophy, and damage-healing cycles. We are investigating a variety of adaptive and robust control techniques to enable us to achieve trajectory tracking, as well as mechanical power-output control under sustained oscillatory conditions. To implement and test our algorithms, we developed an experimental capability that allows us to characterize and control muscle in real time, while imposing a wide variety of dynamical boundary conditions.

  • Effect of a Powered Ankle on Shock Absorption and Interfacial Pressure

    Hugh Herr and David Hill

    Lower-extremity amputees face a series of potentially serious post-operative complications. Among these are increased risk of further amputations, excessive stress on the unaffected and residual limbs, and discomfort at the human-prosthesis interface. Currently, conventional, passive prostheses have made strides towards alleviating the risk of experiencing complications, but we believe that the limit of “dumb” elastic prostheses has been reached; in order to make further strides we must integrate “smart” technology in the form of sensors and actuators into lower-limb prostheses. This project compares the elements of shock absorption and socket pressure between passive and active ankle-foot prostheses. It is an attempt to quantitatively evaluate the patient’s comfort.

  • Human Walking Model Predicts Joint Mechanics, Electromyography, and Mechanical Economy

    Hugh Herr and Ken Endo
    We are studying the mechanical behavior of leg muscles and tendons during human walking in order to motivate the design of economical robotic legs. We hypothesize that quasi-passive, series-elastic clutch units spanning the knee joint in a musculoskeletal arrangement can capture the dominant mechanical behaviors of the human knee in level-ground walking. Biarticular elements necessarily need to transfer energy from the knee joint to hip and/or ankle joints, and this mechanism would reduce the necessary muscle work and improve the mechanical economy of a human-like walking robot.

  • Load-Bearing Exoskeleton for Augmentation of Human Running

    Hugh Herr, Grant Elliott, and Andrew Marecki
    Augmentation of human locomotion has proved an elusive goal. Natural human walking is extremely efficient and the complex articulation of the human leg poses significant engineering difficulties. We present a wearable exoskeleton designed to reduce the metabolic cost of jogging. The exoskeleton places a stiff fiberglass spring in parallel with the complete leg during stance phase, then removes it so that the knee may bend during leg swing. The result is a bouncing gait with reduced reliance on the musculature of the knee and ankle.

  • Metabolic and Biomechanical Effects of Using a Powered Prosthetic Knee

    Hugh Herr and Matthew Robert Williams

    Gait research on trans-femoral prosthesis users has shown that the metabolic costs for these individuals are significantly higher than those of able-bodied individuals for level-ground walking. Additionally, trans-femoral amputees exhibit a much higher degree of gait asymmetry between the affected and non-affected sides, leading to reduced walking speeds and increased hip and back pain compared to non-amputees. This project consists of a clinical study of five to ten unilateral trans-femoral amputees using either a conventional or a powered knee prosthesis and height-weight matched able-bodied individuals. This work will compare the metabolic cost of transport and biomechanics of conventional standard of care prosthetic knees with a novel powered knee. Amputee performance with each prosthesis will also be compared to the performance of able-bodied individuals. It is hypothesized by using a powered prosthetic knee both the metabolic and biomechanical aspects of amputee gait can be improved.

  • Powered Ankle-Foot Prosthesis

    Samuel Au and Hugh Herr
    The human ankle provides a significant amount of net positive work during the stance period of walking, especially at moderate to fast walking speeds. Conversely, conventional ankle-foot prostheses are completely passive during stance, and consequently, cannot provide net positive work. Clinical studies indicate that transtibial amputees using conventional prostheses experience many problems during locomotion, including a high gait metabolism, a low gait speed, and gait asymmetry. Researchers believe the main cause for the observed locomotion is due to the inability of conventional prostheses to provide net positive work during stance. The objective of this project is to develop a powered ankle-foot prosthesis that is capable of providing net positive work during the stance period of walking. To this end, we are investigating the mechanical design and control system architectures for the prosthesis. We also conduct a clinical evaluation of the proposed prosthesis on different amputee participants.

  • Robotic Lower-Limb Sockets

    Hugh Herr and Arthur Petron

    How can socket materials selection and actuation change the way a prosthesis interacts with its user? Can a lower-limb prosthetic be made to be comfortable throughout a normal day? What about during extended periods of high activity? Current prostheses provide little in the way of adjustment to the wearer as their residual limb changes over time. Further, the most comfortable prostheses rely on custom fitting for each user. An active prosthesis can provide increased comfort to the user. Through the use of new and exciting measurement and fabrication techniques we can leverage new types of active and passive materials to make the world's most comfortable sockets.

  • Sensor-Fusions for an EMG Controlled Robotic Prosthesis

    Matthew Todd Farrell and Hugh Herr

    Current unmotorized prostheses do not provide adequate energy return during late stance to improve level-ground locomotion. Robotic prostheses can provide power during late-stance to improve metabolic economy in an amputee during level-ground walking. This project seeks to improve the types of terrain a robotic ankle and successfully navigate by using command signals taken from the intact and residual limbs of an amputee. By combining these commands signals with sensors attached to the robotic ankle it might be possible to further understand the role of physiological signals in the terrain adaptation of robotic ankles.

  • Variable Impedance Prosthetic (VIPr) Socket Design

    Hugh Herr and David Sengeh

    Today, 100 percent of amputees experience some form of prosthetic socket discomfort. This project involves the design and production of a comfortable, variable impedance prosthetic (VIPr) socket using digital anatomical data for a transtibial amputee using computer-aided design and manufacturing (CAD/CAM). The VIPr socket uses multiple materials to achieve compliance, thereby increasing socket comfort for amputees, while maintaining structural integrity. The compliant features are seamlessly integrated into the 3D printed socket to achieve lower interface peak pressures over bony protuberances and other anatomical points in comparison to a conventional socket. This lower peak pressure is achieved through a design that uses anthropomorphic data acquired through surface scan and Magnetic Resonance Imaging techniques. A mathematical transformation maps the quantitative measurements of the human residual limb to the corresponding socket shape and impedance characteristics, spatially.