Knee-ankle Orthosis Research Articles

Development and Dynamic State Estimation for Robotic Knee–Ankle Orthosis With Shape Memory Alloy Actuators

Abstract The development of rehabilitation robots has long been an issue of increasing interest in a wide range of fields. An important aspect of the ongoing research field is applying flexible components to rehabilitation equipment to enhance human−machine interaction. Another major challenge is to accurately estimate the individual’s intention to achieve safe operation and efficient training. In this article, a robotic knee−ankle orthosis (KAO) with shape memory alloy (SMA) actuators is developed, and the estimation method is proposed to determine the joint torque. First, based on the analysis of human lower limb structure and walking patterns, the mechanical design of the KAO that can achieve various rehabilitation training modes is detailed. Next, the dynamic model of the hybrid-driven KAO is established using the thermodynamic constitutive equation and Lagrange formalism. In addition, the joint torque estimation is realized by the nonlinear Kalman filter method. Finally, the prototype and human subject experiments are conducted, and the experimental results demonstrate that the KAO can assist lower limb movements. In the three experimental scenarios, reductions of 59.1%, 16.5%, and 73% of the torque estimation error during the knee joint movement are observed, respectively.

Design, Modeling, and Evaluation of a Hybrid Driven Knee-Ankle Orthosis With Shape Memory Alloy Actuators

Abstract This paper demonstrates the mechanical design, analysis, and evaluation of a knee-ankle orthosis (KAO) for lower limb rehabilitation, including shape memory alloy (SMA) actuators and DC brushless motor actuators. First, the mechanical structure of the KAO is detailed, including the actuator system, transmission mechanism, monitoring device, and processing method of SMA actuators. Next, the dynamic model of SMA spring actuators in the phase transition process is established based on the thermal constitutive model of SMA. In addition, the dynamic output response of the knee joint under three working states is analyzed, and the rotation angle of SMA soft actuator during bending is described by pseudo rigid body model. Finally, the output of SMA actuator is preliminarily evaluated through experiments. The experimental results show that the maximum displacement of SMA spring actuator is 54.36 mm, the maximum restoring force during phase transformation is 4.14 N, and the maximum rotation angle of SMA soft actuator is 43.18 deg. The experimental results are consistent with the theoretical model.

Optimal Linear Quadratic Control for Knee-Ankle Orthosis System

The control technique for an exoskeleton system for lower limb rehabilitation is complicated, and numerous internal and external elements must be taken into account, in addition to the uncertainties in the system model. In this paper, through the analysis of the lower extremity exoskeleton is utilized to obtain the corresponding equation and its linearized form. The nonlinear differential equations have been linearized by using Jacobean’s method in order to facilitate the controller design. Considering the interior and external factors of the connecting rod, the uncertain elements are introduced and therefore the optimal control technique is applied to regulate the system. An optimal state feedback control strategy of Linear Quadratic Regulator (LQR), and LQR-Servo have been implemented in this work. Finally, the physical parameters of the Knee-Ankle Orthosis (KAO) exoskeleton are used, and the simulation results show the advantage and applicability of the proposed controller’s design of the Knee-Ankle orthosis system. Index Terms— Rehabilitation, Knee-Ankle orthosis (KAO), Optimal control, LQR-Servo controller.

Design, Modeling and Evaluation of a Hybrid Driven Knee-Ankle Orthosis with Sma Actuators

Design, Modeling and Evaluation of a Hybrid Driven Knee-Ankle Orthosis with Sma Actuators

Design and Validation of a Torque Dense, Highly Backdrivable Powered Knee-Ankle Orthosis.

This paper presents the mechatronic design and experimental validation of a novel powered knee-ankle orthosis for testing torque-driven rehabilitation control strategies. The modular actuator of the orthosis is designed with a torque dense motor and a custom low-ratio transmission (24:1) to provide mechanical transparency to the user, allowing them to actively contribute to their joint kinematics during gait training. The 4.88 kg orthosis utilizes frameless components and light materials, such as aluminum alloy and carbon fiber, to reduce its mass. A human subject experiment demonstrates accurate torque control with high output torque during stance and low backdrive torque during swing at fast walking speeds. This work shows that backdrivability, precise torque control, high torque output, and light weight can be achieved in a powered orthosis without the high cost and complexity of variable transmissions, clutches, and/or series elastic components.

Underactuated Potential Energy Shaping with Contact Constraints: Application to a Powered Knee-Ankle Orthosis.

Body-weight support (i.e., gravity compensation) is an effective clinical tool for gait rehabilitation after neurological impairment. Body-weight supported training systems have been developed to help patients regain mobility and confidence during walking, but conventional systems constrain the patient's treatment in clinical environments. We propose that this challenge could be addressed by virtually providing patients with bodyweight support through the actuators of a powered orthosis (or exoskeleton) utilizing potential energy shaping control. However, the changing contact conditions and degrees of underactuation encountered during human walking present significant challenges to consistently matching a desired potential energy for the human in closed loop. We therefore derive a generalized matching condition for shaping Lagrangian systems with holonomic contact constraints. By satisfying this matching condition for four phases of gait, we derive passivity-based control laws to achieve virtual body-weight support through a powered knee-ankle orthosis. We demonstrate beneficial effects of virtual body-weight support in simulations of a human-like biped model, indicating the potential clinical value of this proposed control approach.

Orthotic Body-Weight Support Through Underactuated Potential Energy Shaping with Contact Constraints.

Body-weight support is an effective clinical tool for gait rehabilitation after neurological impairment. Body-weight supported training systems have been developed to help patients regain mobility and confidence during walking, but conventional systems constrain the patient's treatment in clinical environments. We propose that this challenge could be addressed by virtually providing patients with body-weight support through the actuators of a powered orthosis (or exoskeleton) utilizing potential energy shaping control. However, the changing contact conditions and degrees of underactuation encountered during human walking present significant challenges to consistently matching a desired potential energy for the human in closed loop. We therefore introduce a generalized matching condition for shaping Lagrangian systems with holonomic contact constraints. By satisfying this matching condition for four phases of gait, we derive control laws to achieve virtual body-weight support through a powered knee-ankle orthosis. We demonstrate beneficial effects of virtual body-weight support in simulations of a human-like biped model, indicating the potential clinical value of this proposed control approach.

Orthotic design from the New England Regional Spinal Cord Injury Center. Suggestion from the field.

Long-leg bracing affords ambulatory potential and helps reduce the incidence of deformity in patients with paralysis or weakness caused by lesions of the spinal cord. The conventional long-leg brace or knee-ankle orthosis (KAO) consists of double metal uprights, drop locks or bail locks at the knee, double action ankle joints with anterior and posterior pin stops, metal stirrup, and steel shank extending to the metatarsal heads. Uprights are fastened to the leg with various combinations of thigh and shank bands.1 In the Craig-Scott Orthosis (CSO), Scott refined this design by minimizing the number of leg bands so that three-point knee stabilization comes from a rigid anterior closure below the knee coupled with a thigh band superiorly and a heel counter inferiorly.2 In addition, the knee joints are displaced 0.75 to 0.73 in* posterior to the transverse axis of the knee and behind the weight-bearing line.…

Use of gait simulation in the evaluation of a spring-loaded knee joint orthosis for Duchenne muscular dystrophy patients

Conventional knee-ankle orthoses are still widely used in the management of lower-extremities instabilities. Often, these supporting devices maintain the leg in extension during gait and contribute to an increase in postural lumbar lordosis and thoracic kyphosis. This paper presents a new dynamic knee-ankle orthosis equipped with a spring-loaded knee mechanism which provides a more natural and comfortable gait by allowing knee flexion while insuring knee stability during stance. A mathematical model of the dynamic joint is proposed and a nonlinear optimisation technique is used to determine its parameters. A simulation of the dynamic joint behaviour over a gait cycle is presented and its main characteristics are clinically verified in a prototype fitted bilaterally to a Duchenne muscular dystrophy patient.