Intelligent Prosthetic Systems, Llc

ANN ARBOR, MI, United States

Intelligent Prosthetic Systems, Llc

ANN ARBOR, MI, United States
SEARCH FILTERS
Time filter
Source Type

Rebula J.R.,Intelligent Prosthetic Systems, Llc | Ojeda L.V.,University of Michigan | Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
Journal of Biomechanics | Year: 2017

Humans perform a variety of feedback adjustments to maintain balance during walking. These include lateral footfall placement, and center of pressure adjustment under the stance foot, to stabilize lateral balance. A less appreciated possibility would be to steer for balance like a bicycle, whose front wheel may be turned toward the direction of a lean to capture the center of mass. Humans could potentially combine steering with other strategies to distribute balance adjustments across multiple degrees of freedom. We tested whether human balance can theoretically benefit from steering, and experimentally tested for evidence of steering for balance. We first developed a simple dynamic walking model, which shows that bipedal walking may indeed be stabilized through steering-externally rotating the foot about vertical toward the direction of lateral lean for each footfall-governed by linear feedback control. Moreover, least effort (mean-square control torque) is required if steering is combined with lateral foot placement. If humans use such control, footfall variability should show a statistical coupling between external rotation with lateral placement. We therefore examined the spontaneous fluctuations of hundreds of strides of normal overground walking in healthy adults (N=26). We found significant coupling (P=9·10-8), of 0.54. rad of external rotation per meter of lateral foot deviation. Successive footfalls showed a weaker, negative correlation with each other, similar to how a bicycle's steering adjustment made for balance must be followed by gradual corrections to resume the original travel direction. Steering may be one of multiple strategies to stabilize balance during walking. © 2017 Elsevier Ltd.


Zelik K.E.,University of Michigan | Zelik K.E.,IRCCS Santa Lucia Foundation | Huang T.W.P.,University of Michigan | Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
Journal of Theoretical Biology | Year: 2014

The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active work demands on the plantarflexor muscles in series. However, this does not explain why or when this ankle work, whether by muscle or tendon, needs to be performed during gait. We therefore employ a simple bipedal walking model to investigate how ankle work and series elasticity impact economical locomotion. Our model shows that ankle elasticity can use passive dynamics to aid push-off late in single support, redirecting the body's center-of-mass (COM) motion upward. An appropriately timed, elastic push-off helps to reduce dissipative collision losses at contralateral heelstrike, and therefore the positive work needed to offset those losses and power steady walking. Thus, the model demonstrates how elastic ankle work can reduce the total energetic demands of walking, including work required from more proximal knee and hip muscles. We found that the key requirement for using ankle elasticity to achieve economical gait is the proper ratio of ankle stiffness to foot length. Optimal combination of these parameters ensures proper timing of elastic energy release prior to contralateral heelstrike, and sufficient energy storage to redirect the COM velocity. In fact, there exist parameter combinations that theoretically yield collision-free walking, thus requiring zero active work, albeit with relatively high ankle torques. Ankle elasticity also allows the hip to power economical walking by contributing indirectly to push-off. Whether walking is powered by the ankle or hip, ankle elasticity may aid walking economy by reducing collision losses. © 2013 Elsevier Ltd.


Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
IEEE Transactions on Neural Systems and Rehabilitation Engineering | Year: 2015

Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, step time, step length, and joint mechanics. Although these asymmetries result from weak prosthetic-side push-off, there is no proven mechanistic explanation of how that impairment propagates to the rest of the body. We used a simple dynamic walking model to explore possible consequences of a unilateral impairment similar to that of a transtibial amputee. The model compensates for reduced push-off work from one leg by performing more work elsewhere, for example during the middle of stance by either or both legs. The model predicts several gait abnormalities, including slower forward velocity of the body center-of-mass during intact-side stance, greater energy dissipation in the intact side, and more positive work overall. We tested these predictions with data from unilateral transtibial amputees (N = 11) and nonamputee control subjects (N = 10) walking on an instrumented treadmill. We observed several predicted asymmetries, including forward velocity during stance phases and energy dissipation from the two limbs, as well as greater work overall. Secondary adaptations, such as to reduce discomfort, may exacerbate asymmetry, but these simple principles suggest that some asymmetry may be unavoidable in cases of unilateral limb loss. © 2014 IEEE.


Rebula J.R.,University of Michigan | Rebula J.R.,Intelligent Prosthetic Systems, Llc | Ojeda L.V.,University of Michigan | Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
Gait and Posture | Year: 2013

Gait parameters such as stride length, width, and period, as well as their respective variabilities, are widely used as indicators of mobility and walking function. Foot placement and its variability have thus been applied in areas such as aging, fall risk, spinal cord injury, diabetic neuropathy, and neurological conditions. But a drawback is that these measures are presently best obtained with specialized laboratory equipment such as motion capture systems and instrumented walkways, which may not be available in many clinics and certainly not during daily activities. One alternative is to fix inertial measurement units (IMUs) to the feet or body to gather motion data. However, few existing methods measure foot placement directly, due to drift associated with inertial data. We developed a method to measure stride-to-stride foot placement in unconstrained environments, and tested whether it can accurately quantify gait parameters over long walking distances. The method uses ground contact conditions to correct for drift, and state estimation algorithms to improve estimation of angular orientation. We tested the method with healthy adults walking over-ground, averaging 93 steps per trial, using a mobile motion capture system to provide reference data. We found IMU estimates of mean stride length and duration within 1% of motion capture, and standard deviations of length and width within 4% of motion capture. Step width cannot be directly estimated by IMUs, although lateral stride variability can. Inertial sensors measure walks over arbitrary distances, yielding estimates with good statistical confidence. Gait can thus be measured in a variety of environments, and even applied to long-term monitoring of everyday walking. © 2013.


Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Adamczyk P.G.,University of Michigan | Kuo A.D.,University of Michigan
Journal of Experimental Biology | Year: 2013

During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, p>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM. © 2013. Published by The Company of Biologists Ltd.


Grant
Agency: Department of Health and Human Services | Branch: National Institutes of Health | Program: SBIR | Phase: Phase I | Award Amount: 157.47K | Year: 2015

DESCRIPTION provided by applicant The long term goal of this project is to develop prosthetic foot technology that can function differently for different activities Although current prostheses can be very effective for particular tasks e g walking running or standing an amputee must choose a single prosthesis to achieve reasonably good performance across all daily activities This results in a compromise because the biomechanical demands of walking for example are different from those for standing A prosthetic foot that can modulate its mechanical properties to biomechanically accommodate each activity could be very helpful This prosthesis is intended for use by subjects with amputation of both traumatic and non traumatic origin The proposed biomechanical behavior is to modulate foot stiffness differently for many activities most notably walking and standing During walking the prosthesis needs to provide strong weight support to prevent hard landings on the intact leg This behavior is facilitated by high stiffness During standing different users may desire a stable base of support or a compliant foot with large range of motion The ideal stiffness for each task also depends on the differing demands of dynamic and static stability Based on studies of gait mechanics stiffness should be adjusted for each different task The Specific Aims of this project are to To design and construct a prosthetic foot that modulates its mechanical stiffness under automatic computer control based on the userandapos s activity and test its mechanical characteristics such as stiffness adjustability and fast modulation To perform proof of concept testing of the prototype prosthetic footandapos s effect on walking and standing in amputees PUBLIC HEALTH RELEVANCE The most common mobility issues for lower limb amputees are discomfort stability and fatigue Persons wearing prosthetic feet find it uncomfortable to stand for long periods or to walk more than moderate distances These issues are in part due to the fact that walking and standing and other tasks all have different biomechanical demands which must be addressed by a single prosthetic foot We propose to develop a computer controlled prosthetic foot that can automatically change its mechanical stiffness depending on the userandapos s task The prosthetic foot is intended to improve stability and comfort for standing and reduce impact forces on the leg during walking and to automatically vary its characteristics during daily life Such technology may improve comfort and reduce fatigue for amputees It is intended for use by subjects with amputation of both traumatic and non traumatic etiology


Grant
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 149.56K | Year: 2013

DESCRIPTION (provided by applicant): Robotic Amputee Gait Capacity Assessment System Robotic prostheses can improve mobility for individuals with amputation, but assessment and prescription for each individual is difficult and errors are costly. We propose to determine the feasibility of a product that allows rapid, objective assessment of the functional benefits of various conventional and robotic ankle-foot prostheses in a clinical setting. Our first aim is to demonstrate a system capable of dynamic prosthesis emulation. We have recently developed an experimental robotic test bed with significantly enhanced mechatronic performance. In this project, we will test its suitability for high-level emulation of three classes of prosthesis: conventional (e.g. SACH), dynamic-elastic (e.g. FlexFoot), and robotic (e.g. BiOM), differentiated by the mechanical work absorbed or produced during a step. Our second aim is to develop objective and repeatable measures of the functional benefits to potential users of these devices, specialized for use in coordination with the robotic prosthesis emulator. Finally, we aim to demonstrate that such a system can differentiate between patients who would benefit from advanced robotic prostheses and those who would not. We propose toperform an experiment in which different classes of prosthesis are emulated and functional outcomes are assessed in four amputee subjects with different activity levels and etiologies. These experimental results will help determine which population groupscan be expected to benefit from the mechanical work provided by robotic foot-ankle prostheses, and provide insight into measures that systematically differentiate between potential beneficiaries and non-candidates. This research is the first step toward developing a diagnostic product that Orthotics and Prosthetics clinics can use to assess candidates for advanced robotic prostheses and justify reimbursement from insurance carriers on the basis of objective functional benefits. The eventual integrated product will consist of robotic prosthesis emulator hardware and software, with optional experimental tools. This clinical tool will be priced competitively with single autonomous robotic devices, in te same class as robotic gait trainers. More advanced platforms will eventually enable dynamic optimization of device parameters, such as keel length or stiffness, prior to device construction and purchase, and may even lead to the development of improved autonomous designs. PUBLIC HEALTH RELEVANCE PUBLICHEALTH RELEVANCE: This project comprises the development of a robotic prosthesis emulator for use in clinical settings. This system will allow rapid, objective, prospective assessment of the functional benefits of different conventional and robotic ankle-foot prostheses for individual patients with amputation, allowing the determination of the best choice of prescribed prosthesis. The proposed system will emulate commercial prostheses across the available spectrum, and provide hard data demonstrating howmuch gait improvement (e.g. increased speed or reduced energy cost) an individual subject can expect at each level of prosthesis performance and cost.


Grant
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2012

DESCRIPTION (provided by applicant): The long-term goal of this project is to develop prosthetic foot technology that can function differently for walking and standing tasks. Although current prostheses can be very effective for particular tasks (e.g. walking, running, or standing), an amputee must often choose a single prosthesis to achieve reasonably good performance across all daily activities. This results in a compromise, because the biomechanical demands of walking are different from those for standing. Because walking and standing are two of the most common functional tasks performed daily, a dual function prosthetic foot could switch between two biomechanical modes of behavior. The proposed biomechanical behaviors include different foot bottom shapes and stiffnesses for walking and standing. During walking, the foot effectively rolls over the ground, in a motion that is facilitated by a convex foot bottom shape. During standing, a stable base of support is needed, which is facilitated by a concave foot bottom shape. The ideal stiffness for each task also depends on the differing demands of dynamic and static stability. Based on studies of gait mechanics, both shape and stiffness should be adjusted for the task. The Specific Aims of this project are to: 1.To design and construct a prosthetic foot prototype with separate modes for walking and standing under computer control based on the user's activity, and test its mechanical characteristics such as stiffness, adjustability, and fast mode switching. 2.To perform proof-of-concept testing of the prototype prosthetic foot's effect on walking and standing in amputees. PUBLIC HEALTH RELEVANCE: The two most common mobility issues for lower limb amputees are discomfort and fatigue. Persons wearing prosthetic feet find it uncomfortable to stand for long periods or to walk more than moderate distances. These issues are in part due to the fact that walking and standing have different biomechanical demands, which must be addressed by a single prosthetic foot. We propose to develop a computer-controlled prosthetic foot that can switch between different biomechanical characteristics depending on the user's task. The prosthetic foot is intended to improve stability for standing, and reduce impact forces on theleg during walking, and to automatically switch between characteristics during daily life. Such technology may improve comfort and reduce fatigue for amputees.


Grant
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 856.20K | Year: 2010

DESCRIPTION (provided by applicant): Health management of older adults can be improved through convenient and objective assessment of their gait. Although a number of quantitative measures of walking, such as the variability of steps taken, have been shown to predict the risk of falls, these measurements are difficult to obtain outside the laboratory. It would be helpful to obtain accurate and objective measures in the clinic or even in the home during normal activities of daily living. Long-term monitoring could even be used to track compliance to a rehabilitation program or to determine when the dosage of medicines should be adjusted, all without requiring frequent visits to the clinic. Unfortunately, current devices for long-term monitoring are limited to simplistic data such as step count, and there is no convenient means to accurately measure the gait variables most indicative of mobility, balance, and fall risk. Miniature sensors are rapidly improving in accuracy and power economy, offering great potential for field-based activity assessment. Simple accelerometer-based devices have been miniaturized, and wireless systems can provide rough estimates of running speed and distance accurate enough for casual use, while remaining unobtrusive enough to wear conveniently for long durations. New microchip technologies make it feasible for highly accurate, inertial sensor systems to be packaged similarly for daily use. A major barrier for gait measurements is the need to eliminate drift errors that occur with these devices when estimating stride length and other quantities related to mobility. This project seeks to develop sensor fusion algorithms for this purpose, and integrate them with wearable inertial measurement sensors. The Specific Aims of this project are to: 1. Implement drift reduction algorithms and software for integrating inertial sensor data to accurately estimate gait parameters. 2. Develop wireless sensor and receiver unit hardware for field-based gait monitoring, with miniature packages suitable for long-term use. 3. Perform accuracy and usability testing on younger and older adults, to characterize device specifications in realistic environments. PUBLIC HEALTH RELEVANCE: Falling and related injuries greatly limit mobility in older adults, and their risk can be reduced substantially with exercise, rehabilitation, and other interventions. It is currently difficult, however, to monitor mobility in the home and for long durations, either to assess compliance to an intervention or to determine dosage of medicine. This proposal seeks to develop new technology to enable accurate, long-term measurements of gait and mobility in the home.


Ojeda L.,University of Michigan | Rebula J.R.,University of Michigan | Adamczyk P.G.,Intelligent Prosthetic Systems, Llc | Kuo A.D.,University of Michigan
Journal of Biomechanics | Year: 2013

Motion capture is usually performed on only a few steps of over-ground locomotion, limited by the finite sensing volume of most capture systems. This makes it difficult to evaluate walking over longer distances, or in a natural environment outside the laboratory. Here we show that motion capture may be performed relative to a mobile platform, such as a wheeled cart that is moved with the walking subject. To determine the person's absolute displacement in space, the cart's own motion must be localized. We present three localization methods and evaluate their performance. The first detects cart motion solely from the relative motion of the subject's feet during walking. The others use sensed motion of the cart's wheels to perform odometry, with and without an additional gyroscope to enhance sensitivity to turning about the vertical axis. We show that such methods are practical to implement, and with present-day sensors can yield accuracy of better than 1% over arbitrary distances. © 2013.

Loading Intelligent Prosthetic Systems, Llc collaborators
Loading Intelligent Prosthetic Systems, Llc collaborators