Modeling and Evaluation of Adaptive Super Twisting Sliding Mode Control in Lower Extremity Exoskeleton

Abstract

In this paper, an integrated human-in-the-loop simulation paradigm for the design and performance analysis of a 6 DOF lower extremity exoskeleton is presented. An adaptive Super Twisting Sliding Mode Controller (ASTSMC) is designed for the trajectory tracking control of the exoskeleton by considering the human motion as reference trajectory. The dynamic model, that include linear and rotational displacement of hip, knee and ankle joints of both the legs is developed using Lagrange energy formulation. The position and angular velocity error of the wearer and the exoskeleton are being considered to establish the control law. Super twisting SMC is a robust control scheme that works effectively in the presence of external disturbances and parameter variations. However, the STSMC introduces chattering in the closed loop because of its high gain, to overcome this drawback, an adaptive STSMC is proposed for the control of exoskeleton against unknown disturbances without chattering. An adaptation scheme using Lyapunov criterion is derived that ensures the stability of the system in closed loop. The performance of the proposed control strategy is verified by implementing on the integrated CAD model of the exoskeleton along with the wearer. The effectiveness of the controller is tested under wind disturbance of varying velocity and direction. The results demonstrate improved tracking performance of the proposed control scheme with least error and less control effort compared to constant gain STSMC in normal and uneven terrain.

Design and analysis of three-dimensional braiding machine with track change interlocking

“…30,31 It has obvious advantages in kinematics and dynamics calculations of complex mechanical design, research and development. [32][33][34] Using the kinematics and dynamics by mechanical software instead of analytical models in various engineering applications, engineers could build complex and multi-body structures. 35,36 The three-dimensional model of track change interlocking mechanism is enforced on ADAMS software, and the connection relationship of fixed pair, the rotating pair and moving pair are set to simulate the movement process of slider.…”

Adaptive Fractional‐Order Super‐Twisting Sliding Mode Controller for Lower Limb Rehabilitation Exoskeleton in Constraint Circumstances Based on the Grey Wolf Optimization Algorithm

“…Te frst controller is an adaptive super-twisting sliding mode controller (ASTSM) developed by [25] which has the following controller formula: where z, Γ 1 , and Γ 2 ∈ R 2 * 2 are the positive diagonal matrices.…”

“…In addition, high-order SMC (HOSM) was adopted to settle the chattering efect efectively [23]. In fact, most of these HOSM controllers require the knowledge of sliding surface derivatives except an effective type which is known as a super-twisting algorithm (ST) [25]. Tanks to its magic performance, the supertwisting algorithm (ST) has been developed to ensure an excellent control performance and eliminate the chattering problem in a simultaneous manner [25,26].…”