Active Prosthesis Research Articles

A Novel Robust Model Reference Adaptive Impedance Control Scheme for an Active Transtibial Prosthesis

SummaryIn this paper, a novel robust model reference adaptive impedance control (RMRAIC) scheme is presented for an active transtibial ankle prosthesis. The controller makes the closed loop dynamics of the prosthesis similar to a reference impedance model and provides asymptotic tracking of the response trajectory of this impedance model. The interactions between human and prosthesis are taken into account by designing a second-order reference impedance model. The proposed controller is robust against parametric uncertainties in the nonlinear dynamic model of the prosthesis. Also, the controller has robustness against bounded uncertainties due to unavailable ground reaction forces and unmeasurable feedbacks of accelerations at the socket place. Moreover, an appropriate Series Elastic Actuator (SEA) mechanism for the prosthetic ankle is included in this work and its effects are discussed. Tracking performance and stability of the closed-loop system are proven via the Lyapunov stability analysis. Using simulations on an overall amputee prosthetic foot system, the effectiveness of the proposed RMRAIC controller is investigated for the task of level ground walking.

Impact Testing of Prosthetic Feet for High-Activity Prosthesis Users: A Pilot Study

ABSTRACT Introduction There is currently no accepted test standard for prosthetic feet to demonstrate durability to impact loading such as that encountered in physically demanding professions (e.g., construction, farming, or military service). The goal of the study was to build a system to pilot test the impact resilience of a selection of prosthetic feet marketed for high-activity prosthesis users. Materials and Methods Three specimens each of nine prosthetic feet (n = 27 total) were selected by prosthetists at the Minneapolis VA Health Care System (with specifications in accordance with an associated human-subjects research study, n = 3). Maximum drop height without failure was used to assess impact resilience. Drop testing was performed using a custom system with an electromagnet to lift and release a weighted frame in increments of 10 cm until failure. The test specimens were organized into three sets, each with one specimen of each foot with the spring category for a particular user mass. Sets A, B, and C were tested with 45.9, 57.8, and 61.5 kg, respectively (101, 127, and 135 lb, respectively) simulating the mass of the user plus an added 22 kg (48 lb) of worn/carried load, then divided by two to represent even load distribution to both legs at impact. Results The feet withstood drop heights without failure ranging from 20 cm to 100 cm. The type of foot was found to significantly affect maximum drop height (P = 0.014). Effect sizes for comparisons of individual feet range from 0.15 to 3.17 with the median effect size being 0.94, which is considered “large.” Conclusions The test system successfully measures impact resilience and is sensitive to foot type. Large effect sizes indicate substantial differences between prosthetic feet marketed for active prosthesis users.

Static and dynamic forces in the incudostapedial joint gap

Dynamic pressure at the tympanic membrane is transformed and subsequently transferred through the ossicular chain in the form of forces and moments. The forces are primarily transferred to the inner ear. They are transferred partly to the stapedial annular ligament which exhibits non-linear behavior and stiffens for larger static forces. In unventilated middle ears, static pressure is additionally transferred to the ossicles. The purpose of this study was to measure the force inside the ossicular chain as a physiological parameter. We determined the forces which act for dynamic sound transmission and for static load on the ossicular chain. The study is the first one which introduces these forces. The static forces have direct impact on clinically relevant questions for middle ear reconstructions with passive or active prosthesis. The dynamic forces have an impact on the development of middle ear sensors. Quasi-static forces in the incudostapedial joint (ISJ) gap were measured with two different sensor types in 17 temporal bones. The sensing elements, a single crystal piezo and a strain gauge element for validation, were bonded to a thin flexible titanium plate and encapsulated in a titanium housing to allow the acquisition of the applied force signal inside the ossicular chain. Dynamic forces were measured in 11 temporal bones with the piezo sensor. We measured a static force of 23 mN in the ISJ after sensor insertion. The mean force for dynamic physiological acoustic excitation from 250 Hz to 6 kHz was 26 μN/Pa. If the tympanic membrane is loaded with a static pressure, the static force in the ISJ increases up to 1 N for a maximum static pressure load scenario of 30 kPa.

Statistical analysis of timeseries data reveals changes in 3D segmental coordination of balance in response to prosthetic ankle power on ramps

Active ankle-foot prostheses generate mechanical power during the push-off phase of gait, which can offer advantages over passive prostheses. However, these benefits manifest primarily in joint kinetics (e.g., joint work) and energetics (e.g., metabolic cost) rather than balance (whole-body angular momentum, H), and are typically constrained to push-off. The purpose of this study was to analyze differences between active and passive prostheses and non-amputees in coordination of balance throughout gait on ramps. We used Statistical Parametric Mapping (SPM) to analyze time-series contributions of body segments (arms, legs, trunk) to three-dimensional H on uphill, downhill, and level grades. The trunk and prosthetic-side leg contributions to H at toe-off when using the active prosthesis were more similar to non-amputees compared to using a passive prosthesis. However, using either a passive or active prosthesis was different compared to non-amputees in trunk contributions to sagittal-plane H during mid-stance and transverse-plane H at toe-off. The intact side of the body was unaffected by prosthesis type. In contrast to clinical balance assessments (e.g., single-leg standing, functional reach), our analysis identifies significant changes in the mechanics of segmental coordination of balance during specific portions of the gait cycle, providing valuable biofeedback for targeted gait retraining.

Automatic real-time gait event detection in children using deep neural networks.

Annotation of foot-contact and foot-off events is the initial step in post-processing for most quantitative gait analysis workflows. If clean force plate strikes are present, the events can be automatically detected. Otherwise, annotation of gait events is performed manually, since reliable automatic tools are not available. Automatic annotation methods have been proposed for normal gait, but are usually based on heuristics of the coordinates and velocities of motion capture markers placed on the feet. These heuristics do not generalize to pathological gait due to greater variability in kinematics and anatomy of patients, as well as the presence of assistive devices. In this paper, we use a data-driven approach to predict foot-contact and foot-off events from kinematic and marker time series in children with normal and pathological gait. Through analysis of 9092 gait cycle measurements we build a predictive model using Long Short-Term Memory (LSTM) artificial neural networks. The best-performing model identifies foot-contact and foot-off events with an average error of 10 and 13 milliseconds respectively, outperforming popular heuristic-based approaches. We conclude that the accuracy of our approach is sufficient for most clinical and research applications in the pediatric population. Moreover, the LSTM architecture enables real-time predictions, enabling applications for real-time control of active assistive devices, orthoses, or prostheses. We provide the model, usage examples, and the training code in an open-source package.

A strain gauge based locomotion mode recognition method using convolutional neural network

ABSTRACTLocomotion mode recognition can contribute to precise control of active lower-limb prostheses in different environments. In this paper, we propose a novel locomotion mode recognition method based on convolutional neural network and strain gauge signals. The strain gauge only provides one-dimensional signals and is also used in the control strategy of the robotic prosthesis. The convolutional neural network takes the raw noisy signals as inputs. Three transtibial amputee subjects were recruited in the experiments, and three locomotion modes were recognized. The overall three-class locomotion mode recognition accuracy is in the hold-out test and in the 5-fold cross-validation. The results show that the strain gauge contains information of locomotion modes, and the convolutional neural network has the capacity of extracting features from raw signals.

Adjustable sockets may improve residual limb fluid volume retention in transtibial prosthesis users.

Loss of residual limb volume degrades socket fit and may require accommodation. To examine if either of two accommodation strategies executed during resting, socket release with full socket size return and socket release with partial socket size return, enhanced limb fluid volume retention during subsequent activity. Two repeated-measures experiments were conducted to assess the effects of socket release on limb fluid volume retention. Limb fluid volume was monitored while participants wore a socket with a single adjustable panel. Participants performed eight activity cycles that each included 10 min of sitting and 2 min of walking. The socket's posterior panel and pin lock were released during the fifth cycle while participants were sitting. In one experiment (Full Return), the socket was returned to its pre-release size; in a second experiment (Partial Return), it was returned to 102% of its pre-release size. Short-term and long-term limb fluid volume retention were calculated and compared to a projected, No Intervention condition. Partial Return and Full Return short-term retentions and Partial Return long-term retention were greater than those projected under the control condition ( p < 0.05). Socket release during resting after activity, particularly when the socket is returned to a slightly larger size, may be an effective accommodation strategy to reduce fluid volume loss in transtibial prosthesis users. This study suggests that existing prosthetic technologies' adjustable sockets and locking pin tethers can be used in novel ways to help maintain residual limb fluid volume in active prosthesis users.

Fingers Movements Control System Based on Artificial Neural Network Model

Surface electromyographic (sEMG) signal is used in the various fields of applications where the need exists to measure the activity of body muscles, such as brain-computer interfaces, game industry, medical engineering, and other practical spheres. Even more, the use of sEMG signal in the field of active prosthesis industry has become traditional for many years. However, despite the fact that the question of using it in the field of fingers prostheses is still open, in general, the sEMG signal required multichannel measuring devices or massive, voluminous equipment for precise recognition of hands or fingers movement. That is decreasing the possible portability and convenience of prostheses and as a consequence is increasing their final price. In this paper we propose a method of organizing the controlling and measuring unit of the prosthetic device based on artificial neural network (ANN) model and one-channel microcontroller based sEMG measuring system. The proposed ANN model works with only 4 input time-domain features of sEMG signal and provides an accuracy of 95.52% for classification of 6 different types of finger movements that makes it a good solution for next implementation in the system of prosthetic fingers or wrist devices.

Impact of friction and gait parameters on the optimization of series elastic actuators for gait assistance

Elastic actuators feature increased energy efficiency and improved human-robot interaction compared to directly driven concepts for active orthoses and prostheses. Structure and parameters of the elastic actuation system are often designed via a model-based minimization of energy consumption based on gait data gained from healthy individuals. However, natural motion exhibits variability among individuals and may not consider requirements of persons using assistive devices. A parametric study is performed examining the impact of varying gait characteristics on the energy consumption and constraints of an optimized (clutchable) series elastic actuator of the knee joint. Furthermore, friction parameters are varied to analyze the impact on actuator constraints. Results of the parametric study indicate increased energy consumption for a slower cadence compared to the healthy gait data for both systems. The clutchable series elastic actuator is less impacted by constraints than the series elastic actuator. The utilized models are evaluated experimentally at a test bench, indicating good accordance to the measured energy consumption. The results highlight the interrelation of friction and gait parameters with energy consumption and actuator constraints and indicate that the optimization procedure for the actuator design requires detailed models of component efficiency as well as subject-specific gait characteristics.

Decoding motor neuron activity from epimysial thin-film electrode recordings following targeted muscle reinnervation

Objective. Surface electromyography (EMG) is currently used as a control signal for active prostheses in amputees who underwent targeted muscle reinnervation (TMR) surgery. Recent research has shown that it is possible to access the spiking activity of spinal motor neurons from multi-channel surface EMG. In this study, we propose the use of multi-channel epimysial EMG electrodes as an interface for decoding motor neurons activity following TMR. Approach. We tested multi-channel epimysial electrodes (48 detection sites) built with thin-film technology in an animal model of TMR. Eight animals were tested 12 weeks after reinnervation of the biceps brachii lateral head by the ulnar nerve. We identified the position of the innervation zone and the muscle fiber conduction velocity of motor units decoded from the multi-channel epimysial recordings. Moreover, we characterized the pick-up volume by the distribution of the motor unit action potential amplitude over the epimysium surface. Main results. The electrodes provided high quality signals with average signal-to-noise ratio >30 dB across 95 identified motor units. The motor unit action potential amplitude decreased with increasing distance of the electrode from the muscle fibers (P 0.001). The decrease was more pronounced for bipolar compared to monopolar derivations. The average muscle fiber conduction velocity was 2.46 ± 0.83 m s−1. Most of the neuromuscular junctions were close to the region where the nerve was neurotized, as observed from the EMG recordings and imaging data. Significance. These results show that epimysial electrodes can be used for selective recordings of motor unit activities with a pick-up volume that included the entire muscle in the rat hindlimb. Epimysial electrodes can thus be used for detecting motor unit activity in muscles with specific fascicular territories associated to different functions following TMR surgery.

The Challenges and Achievements of Experimental Implementation of an Active Transfemoral Prosthesis Based on Biological Quasi-Stiffness: The CYBERLEGs Beta-Prosthesis.

The CYBERLEGs Beta-Prosthesis is an active transfemoral prosthesis that can provide the full torque required for reproducing average level ground walking at both the knee and ankle in the sagittal plane. The prosthesis attempts to produce a natural level ground walking gait that approximates the joint torques and kinematics of a non-amputee while maintaining passively compliant joints, the stiffnesses of which were derived from biological quasi-stiffness measurements. The ankle of the prosthesis consists of a series elastic actuator with a parallel spring and the knee is composed of three different systems that must compliment each other to generate the correct joint behavior: a series elastic actuator, a lockable parallel spring and an energy transfer mechanism. Bench testing of this new prosthesis was completed and demonstrated that the device was able to create the expected torque-angle characteristics for a normal walker under ideal conditions. The experimental trials with four amputees walking on a treadmill to validate the behavior of the prosthesis proved that although the prosthesis could be controlled in a way that allowed all subjects to walk, the accurate timing and kinematic requirements of the output of the device limited the efficacy of using springs with quasi-static stiffnesses. Modification of the control and stiffness of the series springs could provide better performance in future work.

����������� �������� ������ �������������� �������� �����

Purpose Develop a technology of manufacturing silicone sockets for functional hand prosthesis. Methods The technology of fabricating sockets for functional hand prosthesis made of high temperature vulcanization (HTV) silicone was developed and tested for the first time in the practice of domestic prosthetics, including the traditional stages of molding, positive reproduction, and manufacturing of sockets. However, there are technological peculiarities in each of the stages that enable to manufacture a comfortable individual full-contact socket for hand prosthesis made of silicone that was successfully used in active and functional prostheses and prostheses with external power in patients with congenital and amputation hand defects. Results The technology has a number of advantages over traditional ones, as it provides comfortable conditions for full contact and partial loading of the residual segment of a clubshaped hand stump in the liner socket of the prosthesis. These properties of the liner socket allow the production of the most skeletonized carrying socket made of composite material for reliable attachment of the components of functional hand prostheses to it. Conclusion Successful trials of the liner sockets of the hand prosthesis made from HTV silicone created the conditions for a wider application of this silicone brand in the manufacture of a new generation of sockets for upper and lower limb prosthesis.

A Systematic Design Selection Methodology for System-Optimal Compliant Actuation

SummaryThis work presents a systematic design selection methodology that utilizes a co-design strategy for system-level optimization of compliantly actuated robots that are known for their advantages over robotic systems driven by rigid actuators. The introduced methodology facilitates a decision-making strategy that is instrumental in making selections among system-optimal robot designs actuated by various degrees of variable or fixed compliance. While the simultaneous co-design method that is utilized throughout guarantees systems performing at their full potential, a homotopy technique is used to maintain integrity via generation of a continuum of robot designs actuated with varying degrees of variable and fixed compliance. Fairness of the selection methodology is ensured via utilization of common underlying (variable) compliant actuation principle and dynamical task requirements throughout the generated system designs. The direct consequence of the developed methodology is that it allows robot designers make informed selections among a variety of systems which are guaranteed to perform at their best. Applicability of the introduced methodology has been validated using a case study for system-optimal design of an active knee prosthesis that is driven by a mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA) under a periodic/real-life dynamical task.

Volitional control of an active prosthetic ankle: a survey

In this work, state of the art in the field of intent recognition, its application to prostheses and subsequent volitional control algorithms are reviewed. In this paper, competitive landscape is also studied with the aim to learn from the successes and failures of the researchers who have been working in this area. This research hopes to further advance the technology for volitional control of prostheses/wearable robots that will enable much integrated human robot collaboration/interaction specifically focused on passive and active prostheses. The overarching aim of this work is to develop a prosthetic ankle that is as close to a human ankle as possible.

Is Lower Extremity Transplantation a Superior Alternative to Prostheses? No—At Least Not Yet

This paper reviews previously attempted cases of lower extremity vascularized composite allotransplantation (VCA), critically assesses the challenges associated with this procedure, and highlights alternative approaches to restore function for patients with lower limb loss. Despite progress in the field of upper extremity transplantation, attempts at lower extremity transplantation have resulted in zero successes. Major hurdles that must be overcome prior to future attempts include, but are not limited to, large motor nerve regeneration and immunosuppression-related complications. For those patients unable to achieve satisfactory function with traditional prostheses, alternative strategies involving osseointegration, active prostheses, and advanced human-machine interfaces provide improved function with a more favorable risk/benefit profile. Given the uncertain functional outcomes and considerable surgical and immunosuppression related risks, lower extremity VCA is far from being a superior alternative to advanced or even traditional prostheses. We believe the transplant community should focus on upper extremity transplantation and revisit this topic as further advances in the field are made.

Spectral-Distance-Based Detection of EMG Activity From Capacitive Measurements

Electromyographic (EMG) activity is often used as a diagnostic tool in hospitals. In addition, in the last decade, EMG signals are used for the control of assistive devices such as active exoskeletons and prostheses. Conventional surface electrodes used for the acquisition of EMG signals can cause irritation, discomfort, skin allergy, and inflammation. To cope with these issues capacitive contactless EMG electrodes have been developed. The method proposed in this paper is based on the use of short time Fourier transform and spectral distance computation to detect muscle activation from signals recorded using capacitive sensors. The method has been experimentally tested on five young healthy subjects. To assess the reliability of our method, we quantified the latency between the output of the detection algorithm and results of a gold standard protocol created by an expert bioengineer. The results show reliable off-line EMG detection. In the future, we plan to test whether the method could be used for online EMG detection.

An Ankle–Foot Prosthesis Emulator With Control of Plantarflexion and Inversion–Eversion Torque

Ankle inversion–eversion compliance is an important feature of conventional prosthetic feet, and control of inversion, or roll, in active prostheses could improve balance for people with amputation. We designed a tethered ankle–foot prosthesis with two independently actuated toes that are coordinated to provide plantar-flexion and inversion–eversion torques. A Bowden cable tether provides series elasticity. The prosthesis is simple and lightweight, with a mass of 0.72 kg. Strain gauges on the toes measure torque with less than 1% root mean squared (RMS) error. Benchtop tests demonstrated a step response rise time of less than 33 ms, peak torques of 250 N $\cdot$ m in plantarflexion and $\pm$ 30 N $\cdot$ m in inversion–eversion, and peak power above 3 kW. The phase-limited closed-loop torque bandwidth is 20 Hz with a chirp from 10 to 90 N $\cdot$ m in plantarflexion, and 24 Hz with a chirp from $-$ 20 to 20 N $\cdot$ m in inversion. The system has low sensitivity to toe position disturbances at frequencies of up to 18 Hz. Walking trials with an amputee subject demonstrated RMS torque tracking errors of less than 5.1 N $\cdot$ m in plantarflexion and less than 1.5 N $\cdot$ m in inversion–eversion. These properties make the platform suitable for testing inversion-related prosthesis features and controllers in experiments with humans.

Prosthetic Limb Options for Below and Above Knee Amputations: Making the Correct Choice for the Right Patient

This review focuses on the options that are available for people who have had below and above knee amputations. Prosthetic limbs have evolved, with substantial technological advancements in the past two decades. However, the most sophisticated device is not the most appropriate for everyone. Osseointegration appears to have become an established treatment option for a selected group of patients with limb amputation. However, there is sufficient evidence to fully inform patients as to the possible risks and complications compared with the benefits. The active prostheses clinical research is limited to prototypes and low number of subjects, although test results show the potential to restore the functional performance of an amputee. This review article highlights the prosthetic options that are available for people who have had below and above knee amputations. The development of osseointegration and active prostheses is a challenging task and thus should remain subject to future research including extended clinical evaluations.

Ten guidelines for the design of non-assembly mechanisms: The case of 3D-printed prosthetic hands.

In developing countries, prosthetic workshops are limited, difficult to reach, or even non-existent. Especially, fabrication of active, multi-articulated, and personalized hand prosthetic devices is often seen as a time-consuming and demanding process. An active prosthetic hand made through the fused deposition modelling technology and fully assembled right after the end of the 3D printing process will increase accessibility of prosthetic devices by reducing or bypassing the current manufacturing and post-processing steps. In this study, an approach for producing active hand prosthesis that could be fabricated fully assembled by fused deposition modelling technology is developed. By presenting a successful case of non-assembly 3D printing, this article defines a list of design considerations that should be followed in order to achieve fully functional non-assembly devices. Ten design considerations for additive manufacturing of non-assembly mechanisms have been proposed and a design case has been successfully addressed resulting in a fully functional prosthetic hand. The hand prosthesis can be 3D printed with an inexpensive fused deposition modelling machine and is capable of performing different types of grasping. The activation force required to start a pinch grasp, the energy required for closing, and the overall mass are significantly lower than body-powered commercial prosthetic hands. The results suggest that this non-assembly design may be a good alternative for amputees in developing countries.

A simple movement based control approach to ease the control of a myoelectric elbow prosthetics in transhumeral amputees

Common myoelectric control strategy remains complex to use and produce unnatural gestures since it does not allow simultaneous movements of several joints. This is especially an issue for the transhumeral amputees who can use an active elbow in addition to active prosthetic wrist and hand. Since most transhumeral amputees have a mobile residual limb, an interesting approach aims at utilizing this mobility to control the elbow. We thus developed a simple electronic device relying on an inertial measurement unit, that can be interfaced with existing commercial myoelectric elbows and which convert chosen displacements of the residual limb into control signals, offering an intuitive way of controlling an active elbow prosthesis whilst allowing a simultaneous myoelectric control of the wrist and hand. We performed an experiment with one transhumeral amputee wearing his myoelectric prosthetic (active elbow, wrist and hand) who was asked to grasp and transfer different objects several times while being recorded with a motion capture system. Theses task were performed twice: with a conventional full myoelectric control and with the proposed movement based control. Several metrics (position error, time, smoothness, along with body compensatory strategies) were used to quantify the performances obtained with these two modes. Analyses showed that the participant was able to perform the tasks in both condition, but that the movement based control approach allowed a reduction in task time and in exhibited body compensatory strategies, by offering an easier access to adjustments of the elbow posture compared to the full myoelectric control approach. This work illustrates the potential of using residual limb mobility in the control of prosthetics, to make it more natural and intuitive, and how this can have an indirect but positive impact on the whole body compensatory strategies exhibited by amputated subjects.