Active Ankle Foot Orthosis Research Articles

A Portable Passive Ankle-Foot Orthosis for Walking Propulsion and Drop-Foot Prevention

Abstract Individuals with a drop-foot generally have issues of foot-slap and toe-drag, and ankle-foot orthoses (AFOs) have been developed for them to address the drop-foot gait. However, the currently available active AFOs usually have heavier mass, larger volume, and additional power sources, and almost all of the passive AFOs can achieve dorsiflexion assistance at the cost of making plantarflexion more difficult, which increases the wearer's metabolic cost of walking. This paper illustrates the development and validation of a passive AFO for walking propulsion and drop-foot prevention of individuals with a drop-foot gait. The AFO is primarily composed of a propulsion module, a drop-foot prevention module, and a support module. The propulsion module can detect the wearer's gait stages, and it can control the energy storage and release of an energy storage spring-A by switching the state of a clutch-A mechanism. The drop-foot prevention module is designed to correct the abnormal gait of individuals with a drop-foot gait during the swing phase. Experiments are conducted to evaluate the performance of the developed AFO. The experimental results demonstrate that during a gait cycle, reductions of 7.74%, 6.72%, and 16.36% of the average muscle activities of the gastrocnemius, soleus, and tibialis anterior are observed, respectively. The significance of this study is the development of a portable passive AFO that has the potential to provide plantarflexion assistance and dorsiflexion assistance for the wearers during the late stance phase and swing phase, respectively.

Development of Ankle-Foot Orthosis Using Servo Motor with On-Off Control System for Drop-Foot

This research addresses the imperative need for a lightweight, compact, and efficient design of an Active Ankle-Foot Orthosis (AFO), with the potential for everyday use and enhancement of gait cycles in individuals with drop-foot. The proposed AFO employs a servo motor to generate ankle moments based on gait phase detection, ensuring low power consumption and a structurally lightweight configuration. The study encompasses a kinematic analysis of the gait mechanism utilizing a graphical method, facilitating the determination of the requisite force for the motor actuator. Additionally, a finite element approach is employed to assess the strength of linkages. The connecting mechanism utilizes Poly (methyl methacrylate) or PMMA board due to its lightweight nature and ease of fabrication. Based on the simulation result, the minimum safety factor of link bars was 1.8. While, based on the kinematic analysis, the minimum required torque that should be provided by the servo motor is 3.838 Nm. The servo motor serves as the active element within the AFO, and an on-off control system, driven by a rotary encoder detecting gait phases, governs the AFO's movement. Ankle joint angle readings obtained through AFO implementation exhibit values within the range of normal individuals. The entire control system operates with remarkably low power consumption, registering at 0.06 W over one running cycle. Based on these analyses, a prototype has been developed for further evaluation in patient trials, underscoring the potential efficacy and practicality of the proposed active AFO design.

Model predictive control of an active ankle-foot orthosis with non-linear actuation constraints

The goal of active ankle-foot orthoses (AAFO) is to assist the user in recreating a nominal gait motion. Previously proposed control systems for AAFOs have been reactive, with controllers based on the current tracking error. However, the optimal AAFO controller must ensure adequate trajectory tracking while minimizing the amount of assistance provided to the user. To this end, a model predictive controller (MPC) can be considered to determine the optimal control sequence for a given trajectory. The MPC minimizes the control effort, thereby determining the minimal assistance required for a user to regain a natural gait. This work outlines the formulation of a non-linear MPC for an AAFO and its combination with an extended state observer (ESO) for tracking of an AAFO.In this work, a MPC controller is proposed for optimal control of an AAFO, a linear plant subject to non-linear actuation constraints. A novel method is expressed to determine the initial control horizon selection in combination with variable step Newton-based optimization to enable real-time implementation. The MPC control effort is then combined with the estimated disturbance from an ESO to accurately track the desired gait.Simulations and experimental results prove the tracking capabilities of the proposed method. Compared to a tuned proportional–derivative controller, the simulated controller reduced the trajectory tracking error by up to 65.1% and 15.3% in an undisturbed and disturbed environment, respectively. The MPC and ESO combination allows the controller to identify the optimal control action for accurate trajectory tracking. Concurrently, the ESO rejects both external and internal disturbances, with superior tracking capabilities in both undisturbed and heavily disturbed systems, making it the optimal choice for AAFO control.

A Discrete Non-Linear Series Elastic Actuator for Active Ankle-Foot Orthoses

This letter outlines the modelling, design, and experimental validation of a novel power-efficient actuator for an active ankle-foot orthosis (AAFO). The actuator is based on a new principle of discrete non-linear stiffness. Two or more linear springs are discretely compressed at specified displacement intervals to reduce the peak mechanical power required to actuate the AAFO. The actuator uses a crank-rocker configuration. The connecting link is comprised of the discrete non-linear technique, a DC motor powers the crank, and the rocker is connected directly to the ankle joint. Multi-objective optimization is carried out to select the link lengths and spring stiffnesses to reduce input power and size. The actuator design weighs 460 g with bounding box dimensions of 103x45x94 mm. The newly proposed discrete non-linear stiffness configuration reduces the peak mechanical input power by 77.2% with respect to nominal biological ankle joint power. A prototype was developed and tested using static loading and human walking trials to verify the actuator models and simulations. The experimental results confirm the validity of the models by comparing the actual and theoretical ankle and motor torque values in the presence of discrete variable stiffness.

Design of An Active Power Ankle-Foot Orthosis with Myoelectric Control for Drop-Foot Rehabilitation

Drop-foot is an inability to lift the foot when walking due to muscle weakness or paralysis. One of the common rehabilitation aids for stroke sufferers with drop-foot is Ankle Foot Orthosis (AFO). This tool serves as a stabilizer for road pattern balance. However, most of the AFO used is passive, so it doesn't help users run properly. Therefore, an active AFO system has been designed as a rehabilitation aid. This AFO is designed with motor control from myoelectric feedback signal (EMG) and also a semi-dynamic ankle joint so that it is more flexible to help the user when stepping. The AFO movement set of to the foot's position in Dorsi and Plantarflexion conditions based on the EMG parameter received by the control unit. Then, the angle sensor standardizes the user's ankle position so that the foot fits the states that have set. This design uses the fuzzy logic method, which functions to control the rotation of the servo motor. The interface system is for monitoring parameters. In this design, pressure sensors (force), EMG, and angle sensors transmitted wirelessly to a computer are used for data analysis under the needs of real-time statistical data processing.

Design and analysis of a passive ankle foot orthosis by using transient structural method

Foot drop is a condition where individuals are unable to lift the foot through the ankle. It results in slap foot after heel contact and toe drag during the swing phase. Ankle Foot Orthosis (AFO) is a mechanical device that supports both the ankle and foot of the individual and guides the movements of the foot to prevent slap foot and toe drag. There are two types of AFOs:Passive AFO and Active AFO. In this work, design and static analysis of a passive AFO to fit a human foot is presented. The static analysis was carried out for AFO made of two different materials (Polypropylene and High-Density Polyethylene (HDPE)) with two different thicknesses (3mm and 4mm). Based on the results obtained from the static analysis, the design of AFO was optimized for shape and thickness.Further dynamic analysis was carried out on the optimized AFO to know its behaviour in walking condition. The results obtained from the static and dynamic analyses showed that the polypropylene AFO was better compared to that of HDPE AFO by generating less stress, deformation, and factor of safety. The proposed AFO can be fabricated and tested for real-time walking conditions.

Design of active ankle foot orthotics for gait assistance and fall prevention

An active ankle-foot orthosis (AAFO) was developed with the intent of providing propulsive ground reaction force to individuals at risk of experiencing fall. The device makes use of one double-acting cylinder per leg, and a lever arm system to transfer propulsive force to the ground, and potentially assist in fall prevention and rehabilitation. Preliminary tests have been shown to improve ground reaction forces in walking. In this paper, the design and construction of the device is included as well as the control algorithm used and testing procedure. This research may be used to advance the field of gait assistance and fall prevention through use of active foot orthotics.

Design and Physical Modelling Series Elastic Actuator for Ankle-Foot Orthosis

This paper describes the development of Physical Modelling of Series Elastic Actuator for Active Ankle-Foot Orthosis by using Simscape Multibody Link. Active Ankle-Foot Orthosis is essential that can be used for the rehabilitation process to the patient. It is useful in medicine to help a patient who loses their walking ability, due to ankle weakness, to regain the walking ability. This project focuses on the design, simulate and physical modelling for Ankle-Foot Orthosis. This project was used Solidworks as a platform to design the Active Ankle-Foot Orthosis and using MatLab/Simulink for simulation by using Simscape Multibody Link tools. The Active Ankle-Foot Orthosis moves in 2 basic movement of ankle that is dorsiflexion and plantar flexion for rehabilitation. So, this project focuses on the physical modelling for the Series Elastic Actuator that drives the ankle movement mimicking the normal gait cycle.

Recent advances on ankle foot orthosis for gait rehabilitation: a review

Since the early 1980s, hydraulic and pneumatic device are used to explore methods of orthotic devices for lower limb. Over the past decades, significant development has been made by researchers in rehabilitation robotics associating assistive orthotic device for the lower limb extremities. The aim in writing this review article is to present a detailed insight towards the development of the controlled ankle foot orthosis (AFO) device for enhancing the functionality of people disabled by injury to the lower limb or by neuromuscular disorders such as multiple sclerosis, spinal muscular atrophy, etc. Different types of approaches towards design, actuation and control strategies of passive and active AFOs are analysed in this article considering gait rehabilitation. In currently available commercialised ankle foot orthotic devices for lower limb, to overcome the weakness and instability produced by drop foot and to follow natural gait is still a challenge. This paper also focuses the impact of active control of AFO device mainly to enhance the functionality of lower limb reducing the deformities. Researchers have put in huge amount of efforts in terms of modelling, simulating and controlling of such devices mainly for gait rehabilitation with kinematic and dynamics analysis.

Recent advances on ankle foot orthosis for gait rehabilitation: a review

Since the early 1980s, hydraulic and pneumatic device are used to explore methods of orthotic devices for lower limb. Over the past decades, significant development has been made by researchers in rehabilitation robotics associating assistive orthotic device for the lower limb extremities. The aim in writing this review article is to present a detailed insight towards the development of the controlled ankle foot orthosis (AFO) device for enhancing the functionality of people disabled by injury to the lower limb or by neuromuscular disorders such as multiple sclerosis, spinal muscular atrophy, etc. Different types of approaches towards design, actuation and control strategies of passive and active AFOs are analysed in this article considering gait rehabilitation. In currently available commercialised ankle foot orthotic devices for lower limb, to overcome the weakness and instability produced by drop foot and to follow natural gait is still a challenge. This paper also focuses the impact of active control of AFO device mainly to enhance the functionality of lower limb reducing the deformities. Researchers have put in huge amount of efforts in terms of modelling, simulating and controlling of such devices mainly for gait rehabilitation with kinematic and dynamics analysis.

Adaptive control of an actuated ankle foot orthosis for paretic patients

This paper deals with the control of an active ankle foot orthosis (AAFO) to assist the gait of paretic patients. The AAFO system is driven by both, the residual human torque delivered by the muscles spanning the ankle joint and the AAFO’s actuator’s torque. A model reference adaptive control is proposed to assist dorsiflexion and plantar-flexion movements of the ankle joint during level walking. Unlike most classical model-based controllers, the proposed one does not require any prior estimation of the system’s (AAFO-wearer) parameters. The ankle reference trajectory is updated online based on the main gait cycle events and is adapted with respect to the self-selected speed of the wearer. The adaptive desired ankle trajectory is estimated using cubic spline interpolations between the different key events of the gait cycle. The closed-loop input-to-state stability of the AAFO-wearer system with respect to a bounded human muscular torque is proved by a Lyapunov analysis. Experimental results obtained from three healthy subjects and one paretic patient, show satisfactory results in terms of tracking performance and ankle assistance throughout the full gait cycle. The experiments also show good performance at different walking speeds and with different gait sub-phase duration proportions.

Adaptive Proxy-Based Controller of an Active Ankle Foot Orthosis to Assist Lower Limb Movements of Paretic Patients

SummaryThis paper deals with the control of an active ankle foot orthosis (AAFO) for paretic patients. State of the art methods using an AAFO try to track a predefined trajectory of the ankle joint while guaranteeing the wearer’s safety in the presence of a large tracking error. Combining the wearer’s safety and tracking accuracy is generally difficult to achieve at the same time, hence a trade-off should be found. Proxy-based sliding mode control (PSMC) offers great performances in both position tracking and safety guarantee. However, its tracking performance is subject to the influences of parameter uncertainties and external disturbances that generally occur during walking. This paper introduces an adaptation interaction method to the basic PSMC with an online adaptation of the proportional, integral and derivative parameters. At the same time, a gait phase-based ankle reference generation algorithm was proposed to adjust the joint reference trajectory in real time. The experiments using the AAFO show better tracking results with respect to basic PSMC while guaranteeing the safety.

Adaptive control of an actuated-ankle-foot-orthosis.

This paper deals with the control of an active ankle foot orthosis (AAFO) to assist the gait of paretic patients. The AAFO system is driven by both, the residual human torque delivered by the muscles spanning the ankle joint and the AAFO's actuator's torque. A projection-based model reference adaptive control is proposed to assist dorsiflexion and plantar-flexion of the ankle joint during daily living walking activities. Unlike most classical model-based controllers, the proposed one does not require any prior estimation of the system's (foot-AAFO) parameters. The ankle reference trajectory was extracted from healthy subjects gait activities in a clinical environment. The input-to-state stability of the foot-AAFO system with respect to a bounded human muscular torque is proved in closed-loop based on a Lyapunov analysis. Preliminary experimental results with a healthy subject walking on a treadmill, show satisfactory results in terms of tracking performance and ankle assistance throughout the gait cycle.

Boosting the traditional physiotherapist approach for stroke spasticity using a sensorized ankle foot orthosis: a pilot study

Background: Spasticity is a motor disorder that is commonly treated manually by a physical therapist (PhT) stretching the muscles. Recent data on learning have demonstrated the importance of human-to-human interaction in improving rehabilitation: cooperative motor behavior engages specific areas of the motor system compared with execution of a task alone.Objectives: We hypothesize that PhT-guided therapy that involves active collaboration with the patient (Pt) through shared biomechanical visual biofeedback (vBFB) positively impacts learning and performance by the Pt during ankle spasticity treatment. A sensorized ankle foot orthosis (AFO) was developed to provide online quantitative data of joint range of motion (ROM), angular velocity, and electromyographic activity to the PhT and Pt during the treatment of ankle spasticity.Methods: Randomized controlled clinical trial. Ten subacute stroke inpatients, randomized into experimental (EXP) and control (CTRL) groups, underwent six weeks of daily treatment. The EXP group was treated with an active AFO, and the CTRL group was given an inactive AFO. Spasticity, ankle ROM, ankle active and passive joint speed, and coactivation index (CI) were assessed at enrollment and after 15–30 sessions.Results: Spasticity and CI (p < 0.005) decreased significantly after training only in the EXP group, in association with a significant rise in active joint speed and active ROM (p < 0.05). Improvements in spasticity (p < 0.05), active joint speed (p < 0.001), and CI (p < 0.001) after treatment differed between the EXP and CTRL groups.Conclusions: PhT–Pt sharing of exercise information, provided by joint sensorization and vBFB, improved the efficacy of the conventional approach for treating ankle spasticity in subacute stroke Pts.

Robotic AFO to enhance walking capacity: initial development

The development of an active ankle foot orthosis (AFO) to enhance the walking capacity is presented. The proposed device consists of a linear actuator mechanism with supportive brace and is controlled by measuring user's interaction force. Initial experimental characterisation of performance of the control system and system usability tested on healthy individuals are reported. Results indicate a decrease in muscle activation, by a factor of 29 and 26% for plantar flexion and dorsiflexion motion while walking with assistance from the developed AFO. The developed system has potential application in the field of assistive technology for geriatrics or for patient with mobility impairments, muscle weakness or as a performance enhancer.

The effects of ankle foot orthoses and stance width in people with diabetic peripheral neuropthy

This paper deals with the control of an active ankle foot orthosis (AAFO) to assist the gait of paretic patients. The AAFO system is driven by both, the residual human torque delivered by the muscles spanning the ankle joint and the AAFO’s actuator’s torque. A model reference adaptive control is proposed to assist dorsiflexion and plantar-flexion movements of the ankle joint during level walking. Unlike most classical model-based controllers, the proposed one does not require any prior estimation of the system’s (AAFO-wearer) parameters. The ankle reference trajectory is updated online based on the main gait cycle events and is adapted with respect to the self-selected speed of the wearer. The adaptive desired ankle trajectory is estimated using cubic spline interpolations between the different key events of the gait cycle. The closed-loop input-to-state stability of the AAFO-wearer system with respect to a bounded human muscular torque is proved by a Lyapunov analysis. Experimental results obtained from three healthy subjects and one paretic patient, show satisfactory results in terms of tracking performance and ankle assistance throughout the full gait cycle. The experiments also show good performance at different walking speeds and with different gait sub-phase duration proportions.

Characterization of a Pneumatic Artificial Muscle for its application in an Active Ankle-Foot Orthosis

The training of lower limbs with robotic exoskeletons or active orthoses has proven to be an effective tool to help patients with various types of neurological movement disorders, to recover their functional ambulation capacity. A key component to achieve this purpose is the type of active element used to compensate for muscle weakness, typically observed in such locomotor disorders. Based on these considerations, this paper presents the results of an experimental test developed for calibration, tuning and behavioral identification of a commercial pneumatic artificial muscle Festo®, with view to its application as active element of an active ankle – foot orthosis prototype for human gait rehabilitation. It is expected that such prototype would enable to recover the ankle joint function in patients with Myelomeningocele. The actuator performance analysis from the achieved tests, as well as the study of gait patterns in persons with Myelomeningocele, evidence the potentiality of this actuator as an active element of a robotic exoskeleton applied to human gait rehabilitation.

Electrical Resistivity-Based Study of Self-Sensing Properties for Shape Memory Alloy-Actuated Artificial Muscle

Shape memory alloy (SMA) has great potential to develop light and compact artificial muscle (AM) due to its muscle-like high power-to-weight ratio, flexibility and silent operation properties. In this paper, SMA self-sensing properties are explored and modeled in depth to imitate the integrated muscle-like functions of actuating and self-sensing for SMA-AM based on the investigation of SMA electrical resistivity (ER). Firstly, an ER transformation kinetics model is proposed based on the simulation of SMA differential scanning calorimetry (DSC) curves. Then a series of thermal-electrical-mechanical experiments are carried out to verify the validity of the ER model, whereby the SMA-AM self-sensing function is well established under different stress conditions. Finally the self-sensing capability is further demonstrated by its application to a novel SMA-AM-actuated active ankle-foot orthosis (AAFO).

Sigmoid-based hysteresis modeling and high-speed tracking control of SMA-artificial muscle

This paper presents a novel compact shape memory alloy (SMA) based artificial muscle (AM) with self-sensing, silent operation and high force-to-weight ratio functions. The AM has great potential to develop light and compact active ankle–foot orthosis (AAFO) for ankle–foot rehabilitation. However, its performance is severely limited by SMA's slow-speed response and hysteresis properties. Firstly, an effective forced vessel cooling method is introduced to improve the AM response speed without compromising its compactness. Then SMA hysteresis properties are deeply explored and modeled under different stress and driving frequency conditions, whereby the hysteresis is well compensated when the hysteresis model based feedforward controller is proposed to the AM. Finally, a newly AM actuated AAFO is proposed to demonstrate the actuating capability of the AM. Experimental results show that the AM response speed and accuracy are greatly improved with tracking frequency increased from 0.08 to 1Hz, RMS tracking errors reduced by up to 82%, which basically satisfies the initial ankle–foot rehabilitation application.

Development of an active ankle foot orthosis to prevent foot drop and toe drag in hemiplegic patients

We developed an active ankle-foot orthosis AAFO that controls dorsiflexion/plantarflexion of the ankle joint to prevent foot drop and toe drag during hemiplegic walking. To prevent foot slap after ...