Biomechatronics
Enhancing 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

    Hugh Herr, Elliott Rouse and Luke Mooney
    Using biologically inspired design principles, a biomimetic robotic knee prosthesis is proposed that uses a clutchable series-elastic actuator. In this design, a clutch is placed in parallel to a combined motor and spring. This architecture permits the mechanism to provide biomimetic walking dynamics while requiring minimal electromechanical energy from the prosthesis. The overarching goal for this project is to design a new generation of robotic knee prostheses capable of generating significant energy during level-ground walking, that can be stored in a battery and used to power a robotic ankle prosthesis and other net-positive locomotion modes (e.g., stair ascent).

  • 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.

  • Dancing Control System for Bionic Ankle Prosthesis

    Hugh Herr, Bevin Lin, Elliott Rouse, Nathan Villagaray-Carski and Robert Emerson

    Professional ballroom dancer Adrianne Haslet-Davis lost her natural ability to dance when her left leg was amputated below the knee following the Boston Marathon bombings in April 2013. Hugh Herr was introduced to Adrianne while meeting with bombing survivors at Boston's Spaulding Rehabilitation Hospital. For Professor Herr, this meeting generated a research challenge: build Adrianne a bionic ankle prosthesis, and restore her ability to dance. The research team for this project spent some 200 days studying the biomechanics of dancing and designing the bionic technology based on their investigations. The control system for Adrianne was implemented on a customized BiOM bionic ankle prosthesis.

  • 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.

  • FitSocket: Measurement for Attaching Objects to People

    Arthur Petron, Hugh Herr and Neri Oxman

    A better understanding of the biomechanics of human tissue allows for better attachment of load-bearing objects to people. Think of shoes, ski boots, car seats, orthotics, and more. We are focusing on prosthetic sockets, the cup-shaped devices that attach an amputated limb to a lower-limb prosthesis, which currently are made through unscientific, artisanal methods that do not have repeatable quality and comfort from one individual to the next. The FitSocket project aims to identify the correlation between leg tissue properties and the design of a comfortable socket. The FitSocket is a robotic socket measurement device that directly measures tissue properties. With these data, we can rapid-prototype test sockets and socket molds in order to make rigid, spatially variable stiffness, and spatially/temporally variable stiffness sockets.

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  • FlexSEA: Flexible, Scalable Electronics Architecture for Wearable Robotics Applications

    Hugh Herr and Jean-Francois Duval

    This project aims to enable fast prototyping of a multi-axis and multi-joint active prosthesis by developing a new modular electronics system. This system provides the required hardware and software to do precise motion control, data acquisition, and networking. Scalability is achieved through the use of a fast industrial communication protocol between the modules, and by a standardization of the peripherals' interfaces: it is possible to add functionalities to the system simply by plugging in additional cards. Hardware and software encapsulation are used to provide high-performance, real-time control of the actuators, while keeping the high-level algorithmic development and prototyping simple, fast, and easy.

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

    Hugh Herr, Matthew Furtney and Stanford Research Institute
    We are studying the mechanical behavior of leg muscles and tendons during human walking in order to motivate the design of power-efficient robotic legs. The Endo-Herr walking model uses only three actuators (leg muscles) to power locomotion. It uses springs and clutches in place of other essential tendons and muscles to store energy and transfer energy from one joint to another during walking. Since mechanical clutches require much less energy than electric motors, this model can be used to design highly efficient robotic legs and exoskeletons. Current work includes analysis of the model at variable walking speeds and informing design specifications for a collaborative "SuperFlex" exosuit project.

  • 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.

  • Neural Interface Technology for Advanced Prosthetic Limbs

    Edward Boyden, Hugh Herr, Ron Riso and Katherine Song

    Recent advances in artificial limbs have resulted in the provision of powered ankle and knee function for lower extremity amputees and powered elbow, wrist, and finger joints for upper extremity prostheses. Researchers still struggle, however, with how to provide prosthesis users with full volitional and simultaneous control of the powered joints. This project seeks to develop means to allow amputees to control their powered prostheses by activating the peripheral nerves present in their residual limb. Such neural control can be more natural than currently used myoelectric control, since the same functions previously served by particular motor fascicles can be directed to the corresponding prosthesis actuators for simultaneous joint control, as in normal limbs. Future plans include the capability to electrically activate the sensory components of residual limb nerves to provide amputees with tactile feedback and an awareness of joint position from their prostheses.

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  • Powered Ankle-Foot Prosthesis

    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 are also conducting a clinical evaluation of the proposed prosthesis on different amputee participants.

  • 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 can successfully navigate by using command signals taken from the intact and residual limbs of an amputee. By combining these command 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.

  • Terrain-Adaptive Lower Limb Prosthesis

    Hugh Herr and Roman Stolyarov

    Although there have been great advances in the control of lower extremity prostheses, transitioning between terrains such as ramps or stairs remains a major challenge for the field. The mobility of leg amputees is thus limited, impacting their quality of life and independence. This projects aims to solve this problem by designing, implementing, and integrating a combined terrain-adaptive and volitional controller for powered lower limb prostheses. The controller will be able to predict terrain changes using data from both intrinsic sensors and electromyography (EMG) signals from the user; adapt the ankle position before footfall in a biologically accurate manner; and provide a torque profile consistent with biological ankle kinetics during stance. The result will allow amputees to traverse and transition among flat ground, stairs, and slopes of varying grade with lower energy and pain, greater balance, and without manually changing the walking mode of their prosthesis.

  • Tethered Robotic System for Understanding Human Movements

    Hugh Herr and Jiun-Yih Kuan

    The goal of this project is to build a powerful system as a scientific tool for bridging the gap in the literature by determining the dynamic biomechanics of the lower-limb joints and metabolic effects of physical interventions during natural locomotion. This system is meant for use in applying forces to the human body and measuring the force, displacement, and other physiological properties simultaneously, helping investigate controllability and efficacy of mechanical devices physically interacting with a human subject.

  • Variable-Impedance Prosthetic (VIPr) Socket Design

    Hugh Herr, Arthur J Petron, Bryan Ranger 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.

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  • Volitional Control of a Powered Ankle-Foot Prosthesis

    Hugh Herr and Oliver Kannape

    This project focuses on giving transtibial amputees volitional control over their prostheses by combining electromyographic (EMG) activity from the amputees' residual limb muscles with intrinsic controllers on the prosthesis. The aim is to generalize biomimetic behavior of the prosthesis, making it independent of walking terrains and transitions.