Control strategies for active lower extremity prosthetics and orthotics: a review

Abstract

Technological advancements have led to the development of numerous wearable robotic devices for the physical assistance and restoration of human locomotion. While many challenges remain with respect to the mechanical design of such devices, it is at least equally challenging and important to develop strategies to control them in concert with the intentions of the user.This work reviews the state-of-the-art techniques for controlling portable active lower limb prosthetic and orthotic (P/O) devices in the context of locomotive activities of daily living (ADL), and considers how these can be interfaced with the user’s sensory-motor control system. This review underscores the practical challenges and opportunities associated with P/O control, which can be used to accelerate future developments in this field. Furthermore, this work provides a classification scheme for the comparison of the various control strategies.As a novel contribution, a general framework for the control of portable gait-assistance devices is proposed. This framework accounts for the physical and informatic interactions between the controller, the user, the environment, and the mechanical device itself. Such a treatment of P/Os – not as independent devices, but as actors within an ecosystem – is suggested to be necessary to structure the next generation of intelligent and multifunctional controllers.Each element of the proposed framework is discussed with respect to the role that it plays in the assistance of locomotion, along with how its states can be sensed as inputs to the controller. The reviewed controllers are shown to fit within different levels of a hierarchical scheme, which loosely resembles the structure and functionality of the nominal human central nervous system (CNS). Active and passive safety mechanisms are considered to be central aspects underlying all of P/O design and control, and are shown to be critical for regulatory approval of such devices for real-world use.The works discussed herein provide evidence that, while we are getting ever closer, significant challenges still exist for the development of controllers for portable powered P/O devices that can seamlessly integrate with the user’s neuromusculoskeletal system and are practical for use in locomotive ADL.

Transfemoral Prostheses Control in a Frame of Intellectual-Synergetic Concept

“…In such biotechnical systems as Transfemoral Prostheses (TFP), the most popular are three-level hierarchical systems, including subsystems of higher (HLC), middle (MLC) and lower (LLC) control levels [6]. In most known control systems at the MLC level, the problem of coordinating the movements of TFP elements is solved, as a multi-links system with excessive number degrees of freedom.…”

Towards Intelligent Lower Limb Prostheses with Activity Recognition

“…A combination of temporal information, user or device states which are used to identify the gait phases/events, is the main difference between middle level and high level control [14]. The gait cycle (GC) is generally divided into two main phases: stance and swing phases.…”

“…The generalized control scheme for the lower limb prostheses consists of three level hierarchy as shown in Figure 1 adapted from [14]. The high level deals with the perception of user's intent based on the signals from prosthesis, environment and the user.…”

An adaptive and robust online method to predict gait events

“…For these applications, it is common that a constant estimate of stride duration -derived by averaging the stride duration over a period of steadystate walking [4], [5] -is used as a reference to control intervention timing. This is based on the rather constant stride duration of human walking at fixed speeds [6], and works well when strides are in fact consistent [7].…”