A Review on the Control of the Mechanical Properties of Ankle Foot Orthosis for Gait Assistance

Abstract

In the past decade, advanced technologies in robotics have been explored to enhance the rehabilitation of post-stroke patients. Previous works have shown that gait assistance for post-stroke patients can be provided through the use of robotics technology in ancillary equipment, such as Ankle Foot Orthosis (AFO). An AFO is usually used to assist patients with spasticity or foot drop problems. There are several types of AFOs, depending on the flexibility of the joint, such as rigid, flexible rigid, and articulated AFOs. A rigid AFO has a fixed joint, and a flexible rigid AFO has a more flexible joint, while the articulated AFO has a freely rotating ankle joint, where the mechanical properties of the AFO are more controllable compared to the other two types of AFOs. This paper reviews the control of the mechanical properties of existing AFOs for gait assistance in post-stroke patients. Several aspects that affect the control of the mechanical properties of an AFO, such as the controller input, number of gait phases, controller output reference, and controller performance evaluation are discussed and compared. Thus, this paper will be of interest to AFO researchers or developers who would like to design their own AFOs with the most suitable mechanical properties based on their application. The controller input and the number of gait phases are discussed first. Then, the discussion moves forward to the methods of estimating the controller output reference, which is the main focus of this study. Based on the estimation method, the gait control strategies can be classified into subject-oriented estimations and phase-oriented estimations. Finally, suggestions for future studies are addressed, one of which is the application of the adaptive controller output reference to maximize the benefits of the AFO to users.

Effects of Wearable Ankle Robotics for Stair and Over-ground Training on Sub-acute Stroke: A Randomized Controlled Trial

“…Our ndings showed chronic stroke subjects had signi cant improvement in gait independency and enhanced gait con dence at heel strike after 20-session gait training wearing this robot for stair and over-ground gait training [18]. Similar ankle rehabilitation robotics have also shown their potential to be an alternative gait rehabilitation for stroke [19][20][21][22][23], examples are Anklebot [8] and ReStore (ReWalk Robotics, USA) [24]. Nevertheless, few existing researches investigated into the potential of ankle robotics in facilitating stair training.…”

Control Reference Parameter for Stance Assistance Using a Passive Controlled Ankle Foot Orthosis—A Preliminary Study

“…The goal of this preliminary study was to identify whether ankle angular velocity or ankle torque is the better control reference parameter for implementation of stance assistance using MR brake in PICAFO. The control reference parameter must adapt to different subjects and walking situations to maximize the benefit of using PICAFO [11]. Here, different subjects were represented by BMI, while the walking situations were represented by walking speed.…”

“…For instance, sufficient work replacement by actuator will reduce muscle activity [9,10]. Different types of joints, such as rigid joint, flexible joint, and articulated joint, have different joint stiffnesses [11]. Rigid AFO has the highest possible joint stiffness, as the joint is fix and cannot rotate all.…”

“…Lastly, the articulated AFO allows maximum ROM as compared with the other two. It has electronic actuators (passive or active) and gait controller to control not only the joint stiffness but also ankle joint movement [11]. Therefore, an articulated AFO offers greater flexibility compared to rigid and flexible AFOs, and is capable of normal walking replication for intensive training purposes [16].…”

“…Controlling the walking gait at the stance phase is not limited to the joint stiffness only. Other mechanical properties that can serve as the control reference parameter is also presented, such as motion parameter and assistive torque [11]. These mechanical properties are possible to be controlled using active actuators such as tracking and generation of the ankle motion path using electric motors [22][23][24][25], and assistive torque generation using pneumatics muscle [26][27][28] for balancing the body [29].…”