1999 albuquerque

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Robotics and Electronics Research Aid in Building "Smart"

Prostheses

The next generation of prosthetic limbs will incorporate technology that provides a more natural gait and greater comfort and

efficiency, and may restore certain sensory functions.

By William Loob

Copyright 2001 Medical Device & Diagnostic Industry

A complicated assemblage of pneumatic tubes and metal rods hangs in the BioRobotics Lab at the University of Washington(Seattle). It vaguely resembles a human arm that has been stripped of its skin to reveal the underlying musculature and

skeletal structure. And that is exactly how it should look, according to the team of research engineers and scientists who built

the contraption. A fully functioning version of the machine is the goal of the lab's Anthroform Arm Projectone of two current

research efforts aimed at developing robotic components that are capable of imitating biological systems.

The Anthroform Biorobotic Arm uses McKibben artificial muscles, bundles of

pneumatic actuators that exhibit many properties found in human muscles.

Although the original intent of the project was not to improve on existing prosthetics technology, the effort could someday

lead to development of an artificial arm that enables an amputee to regain the full range of motion offered by a natural arm.

The lab's director, Blake Hannaford, PhD, states that, in this case, creating a more effective robotic system required the

engineers to learn from other technical fields. One practical benefit of such an interdisciplinary approach might well be a

more efficient prosthesis design.

Increased efforts to address the problems associated with unexploded land mines in some parts of the world have focused

attention on the field of prosthetics and orthotics. Greater consciousness about amputee quality of life has also promoted

research efforts to develop a new generation of products. Some of the technology being explored for use in advanced

prosthesis designs is being drawn from disciplines outside of conventional orthotics and prosthetics development.

The complexity of human limb movements has posed difficult challenges to prosthetic-limb designers. Restoring the

functions of a natural arm or leg has been difficult, and most designs for artificial limbs are generally able to perform only the

simplest functions of the missing extremities. The technologies now in development are expected to address such limitations

in conventional systems. In addition, specialized prosthesis designs are emerging to meet the needs of amputees who are

involved in a range of physical activities.

One of the persistent problems of prosthetics development is designing a suitable method for attaching the prosthesis to the

remaining stump. The goal is to maximize comfort yet retain firm and stable contact for controlling the limb. Use of rigid

materials means that the fit of a prosthesis will vary over the course of the day as the stump tissues swell or shrink. The


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result is often discomfort and reductions in controllability. Sores can also become a problem and may limit the length of time

an amputee can wear the prosthesis.

Prosthesis designs can have a significant effect on an amputee's normal gait and the physical responses to prosthetic limbs.

Researchers analyzing the gait of patients using prosthetic legs have found that amputees often compensate for the loss of

their natural walking gait with unnatural body movements to accommodate the prosthesis. Tailoring a design to restore more-natural movements for the amputee not only would increase comfort, but also could actually reduce fatigue.

USING SMARTER MATERIALS AND COMPONENTS

Prostheses can be fabricated from materials selected to provide characteristics suited to the specific mechanical

requirements of a given activity. An amputee often needs to switch between different prostheses, however, to engage in

different activities. Some firms are incorporating "smart" materials and components into prosthesis designs in an effort to

expand the range of environments in which a prosthetic device will perform most efficiently.

A prosthetic leg developed for above-knee amputees by Biedermann Motech (Schwennigen, Germany) uses an array of

sensors in the artificial knee component to detect force and moment exerted on the prosthesis and the angular position of the

knee joint. The mechanism also includes a damping device filled with a magnetorheological fluid that can adjust rapidly to

changes in external forces. Input from the sensors and software algorithms control the damping qualities of the device. The

fluid, which was developed by Lord Corp. (Cary, NC), is designed to change consistencyfrom a fluid to a near-solid state

in response to the strength of a magnetic field applied to it. According to the company, the time required to react to changing

forces is 20 times faster than systems that use passive fluids. Such results more closely match human neural response times

than hydraulic mechanisms with motor-controlled valve systems, according to the firm.

ROBOTICS BASED ON BIOLOGICAL MODELS

Development of systems that emulate biological models promises to yield significant advances in prosthetics technology.

Efforts to mimic human anatomy with mechanical systems at the BioRobotics Lab have focused on the use of actuators

bundled into what is called the McKibben artificial muscle. The pneumatically operated actuators provide a high force-to-

weight ratio, the researchers indicate. In addition to the arm project, the lab is engaged in developing a prototype of a lower-

limb prosthesis that is also powered by these actuators.

"We started with the robotic arm development project, and prosthetics is a natural application for such an arm," Hannaford

says. "We wanted to see how far we could go with this idea." The early work on the project, which was focused more on

robotics, led the lab's team to seek out medical researchers working with prostheses. The lab is also collaborating with the

Veterans Administration Medical Center in Seattle to develop potential applications of the system for below-knee amputees.

Researchers at the BioRobotics Lab became intrigued by the physical energy requirements of conventional prostheses. "We

learned that for an amputee with a conventional prosthetic, the rest of the body is compensating with energy: The amputee is

working harder to walk at the same pace as a normal person." A power-assist system capable of replicating the function of

natural muscle seemed to be a logical solution to the problem, Hannaford explains. "We thought that the gait of a prosthesis

wearer would be more natural if we could replace some of the power of the lower-leg muscles." The team is still building a

functional prototype of the powered prosthetic leg, but the main design effort is complete.


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After the working prototype is finished, Hannaford says, the project team will move on to the next phase. They will assess

how well an amputee adjusts to using this type of device and whether it can save energy for the prosthetic wearer. "We still

need to take measurements and ask: 'What does an amputee's gait look like using an active limb replacement, versus how

he or she uses a passive prosthetic?' and 'How much energy is the amputee using?'"

The development of a workable power-assist system would be a significant advance in the state of limb-prosthesistechnology. The artificial muscle is easy to make, Hannaford says. The amount of strength per unit of weight and area is

within a range to make the mechanism practical in this application. "It is actually a little stronger than human muscle, and the

weight is comparable to the natural muscle mass." The bundle of actuators is capable of equaling the power supplied by the

natural muscles that move the foot at the ankle joint. Hannaford admits, however, that the actuator bundle must also

compensate for the weight of the compressed-air source. Also, the artificial muscle has a shorter range of motion than

human muscle.

CYBERNETIC SYSTEMS

Researchers at Sandia National Laboratories (Albuquerque, NM), working in collaboration with engineers at the Russian

nuclear weapons lab at Chelyabinsk-70 and the Seattle Orthopedic Group (Poulsbo, WA), are taking a more inclusive

approach to addressing the most common problems for amputees. The international research team began a project this year

to develop a prosthetic leg capable of adjusting itself to an amputee's gait, and of adapting to changes in the stump shape

caused by tissue swelling.

Sandia's synthetic lower limbs are expected to provide the foundation for the next generation ofprostheses.

Sandia is developing the set of sensors and microprocessing chips that will provide information to the "smart leg," then

calculate the optimum movement of its components to support the walker's gait. The system will be capable of altering the

wearer's gait in response to changes in terrain.

Like Hannaford's group, the Smart Integrated Lower Limb Project will focus on reducing the energy an amputee will need to

exert to walk with a prosthesis. The smart leg will be designed to simulate the human gaits used on uphill and downhill

slopes, or on less-predictable and irregular terrain.

One set of sensors placed along critical points in the prosthesis components will feed data to microprocessor-based Controls

used to govern hydraulic joints and piezoelectric motors that power the ankle- and knee-joint mechanisms. A second group

of sensors in the leg socket will enable the device to compensate for any changes that occur in the diameter of the stump

over the course of a day. Designing the prosthesis with a self-adjusting socket for attachment to the stump is a major goal

that researchers believe will enhance overall efficiency. Not only are pressure sores a nuisance associated with lower-limb

prostheses, discomfort can affect the wearer's physical posture and gait. Researchers expect the complement of

improvements in performance to extend the effective time of use for leg prostheses.


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"The majority of lower-limb prosthetic devices are based upon passive technologies," says Dave Kozlowski, a Sandia

robotics specialist. Without powered systems to operate moving parts, passive prostheses rely on inertia to open the knee

joint as the thigh moves forward so that the shin can then swing forward. The amputee must generally wait for the assembly

to lock into its new position before the prosthesis can support the body as it moves forward.

This series of functions does not allow for a natural gait, Kozlowski explains. Without powered components, prosthetic legs"require far more energy for amputees to cover the same distance as nonamputees." Achieving proper limb motion will ease

the physical effort of using an artificial legrather than draining energy from the wearer, he says.

One of the more difficult challenges of the project is developing a power source that is light enough to be practical, yet

adequately robust to operate all of the required systems, according to the group. The Sandia researchers estimate that a

marketable version of the system may be developed within about two years.

IMPROVING COMMUNICATION WITH PROSTHESES

The user's ability to control a prosthetic limb has been a particularly difficult problem to overcome with upper-limb

prostheses. The range of motion required for arms, hands, and fingers involves the use of a complex set of variables that

must be addressed by prosthetic mechanisms, and a correspondingly complex control interface to communicate with the

device and direct its movements.

Animated Prosthetics (Greensboro, NC), a company specializing in prosthetic-control circuits, has developed systems to

allow amputees to exert myoelectric control of hand and wrist movements in the prosthesis. The firm's Animation Control

Systems circuits are based on use of different algorithms to respond to myoelectric signals from a patient's stump. The circuit

response depends on the strength of the signal that is received. Gaining conscious control over the minute electrical signals

generated by the muscles can be a difficult task for amputees to learn. To facilitate learning, the company designs its circuitsto opt for a simpler operational algorithm to control the prosthesis when the signal is weak, as it is when the patient is still

learning to regulate the signals sent to the device. Under those conditions, for instance, the circuit controls the grasping

function of the hand with a simple, open-and-immediately-close operation. As the amputee learns to control the signals

better, the algorithm adapts to keep the grasping appendages open until it receives a close command.

The Edinburgh Arm System uses self-contained modular actuators.

Researchers are working on more advanced interfaces, however, which will be capable of returning full control to the patient.

A number of research groups are exploring development of direct neural interfaces that will link the thought of an action with

a signal that can be directly interpreted by a robotic device. One such project currently being conducted at the Georgia

Institute of Technology's Biomedical Interactive Technology Center (Atlanta) is investigating whether signals recorded from

micromachined electrodes implanted in the motor cortex can be reproduced to instruct robotic systems to prompt the

movements associated with a conscious thought of the corresponding actions.


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Neural signals associated with defined arm and hand movements are processed using pattern recognition techniques to

determine the intended movement of an individual's arm. The same signals are then used to instruct a robotic arm to move

according to control parameters derived from the neural data. Researchers at Emory University (Atlanta), who are

collaborating in the project, have tested the system on a group of rhesus monkeys. Project funding from the NIH Neural

Prosthesis Program is supporting the research and the development of similar technologies.

RESTORING SENSATION ARTIFICIALLY

An intriguing application of sensor technology is being used to feed information back to the amputee. Two systems invented

by John Sabolich at his lab, Sabolich Research and Development (Oklahoma City), are designed to restore an amputee's

temperature sensitivity through a prosthetic arm and pressure sensitivity through a prosthetic foot. The Sense of Feel

Sensory System connects a pair of pressure transducers in the sole of an artificial foot to a circuit that conveys a signal to

electrodes in the leg socket where it contacts the skin of the stump.

The circuit delivers a "tingling" sensation to the skin, which varies in amplitude corresponding to the force detected by the

transducers. The ability to sense the difference in signal strength between the front of the foot and heel enables the patient to

learn to interpret whether body weight is balanced over the foot. In the system developed for artificial hands, temperature

sensors deliver signals corresponding to a hot or a cold sensation as interpreted by an onboard microprocessor. Both

systems are being tested currently on amputees. Sabolich states that new patients are generally able to begin interpreting

the signals as the proper sensations after only a few minutes of use.

CONCLUSION

Only a few years ago futurists and science fiction writers speculated about the potential of smart prosthetic devices to

improve the quality of life for amputees. They visulaized the promise of creating prosthetic mechanisms capable of more

naturally emulating the appearance and function of human limbs. Today, the development of advanced prostheses is

benefitting from increased collaboration between old competitors, and by the use of new materials technology, as well as

emerging processing and mechanical concepts.

FORMER COLD WAR OPPONENTS COLLABORATE ON ARTIFICAL

KNEE DEVELOPMENT

Efforts to develop advanced prosthetic systems are clearly benefitting from the rapid changes occuring in the materials and

computing sciences. The end of the Cold War and the refocusing of the nation's technological capabilities away from

weapons research and toward helping the victims of war has become a significant factor in the development of prosthesis

technologies.

In 1999, a unique collaboration was initiated between nuclear laboratories in the United States and Russia. The arrangement

between Sandia National Laboratory and the Russian laboratory known as Chelyabinsk-70 called for the two former

adversaries to work together on the joint development of advanced prostheses.


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One of the driving factors behind the collaborative effort was to provide advanced treatment options for victims of land mines.

"Someone in this world loses a limb to a land mine explosion every 20 minutes. Our work, though only remedial, will help

land mine survivors and other amputees," said Sandia chemist and project leader Mort Lieberman when the project was

announced. He added that, "We will have created the world's biggest research center for lower-limb prostheses in a Russian

laboratory." Lieberman also serves on the executive board of the International Institute for the Prosthetic Rehabilitation of

Landmine Survivors.

The first collaboration, aimed at development of an artificial foot, resulted in significant improvements in motion over currently

marketed prosthetic feet. A subsequent project, a mechanical polycentric knee, was based upon Sandia's electronic

expertise and Russian materials knowledge. The partners' efforts were focused on creating, respectively, the brains and

shape of the knee. "The work is a good fit with the capabilities of both labs," according to Lieberman. "It involves stress

analysis, mechanical testing, reliability testing, microprocessor control, and materials analysis."

Sandia Laboratory's mechanical polycentric knee weighs 1.37 lb and is 4.12 in. tall.

Under the collaborative agreement, the Ohio Willow Wood lab (Columbus, OH) was responsible for defining the requirements

for parts and for performed final laboratory and clinical testing. The Russian lab designed the titanium housing, and Sandia's

robotics researchers designed the knee's internal workings and electronics. The project received approximately $1.4 million

in initial research and development funding.

The researchers emphasize that a knee must offer a variable speed of response. It must also lock to keep the wearer from

falling when standing. They explain that the knee is more than a simple hinge. It must offer adequate control and stability to

the wearer.

The ongoing U.S./Russian project is also expected to help the prosthetics industry as a whole. The industry has typically

been dominated by small companies, which have relatively limited support. Most often, they lack the necessary resources to

perform the type of testing that is possible at the nuclear laboratories.

The current research project, development of the "smart" leg microprocessor-controlled prosthetic to help lower-limb

amputees obtain a more natural gait, is only one of the proposals that have been submitted by the Sandia and Chelyabinsk-

70 researchers to various funding organizations. Other proposals deal with the creation of sockets capable of adjusting to the

swelling and shrinkage of an amputee's stump during the course of the day and knees that can help prevent falling when awearer stumbles.


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1999 albuquerque

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