Precision force control of an underactuated stance leg exoskeleton for human performance augmentation

Abstract

Lower limb exoskeleton which augments the human performance is a wearable human–machine integrated system used to assist people carrying heavy loads. Recently, underactuated lower limb exoskeleton systems with some passive joints become more and more attractive due to the advantages of smaller weight, lower system energy consumption and lower cost. However, because of the less of control inputs, the existed control methods of fully actuated exoskeletons cannot be extended to underactuated systems, which makes the robust controller design of underactuated lower limb exoskeletons becomes more challenged. This article focuses on the high-performance human–machine interaction force control design of underactuated lower limb exoskeletons with passive ankle joint. In order to solve the reduction of control inputs, the holonomic constraint from the wearer is considered, which help transform the dynamics of 3-degree-of-freedom underactuated exoskeleton in joint space into a 2-degree-of-freedom fully actuated system in Cartesian space. A two-level interaction force controller using adaptive robust control algorithm is proposed to effectively address the negative effect of various model uncertainties and external disturbances. In order to facilitate the control parameter selection, a gain tuning method is also presented. Comparative simulations are carried out, which indicate that the proposed two-level interaction force controller achieves smaller interaction force and better robust performance to various modeling errors and disturbances.

Development of a hierarchical control strategy for a soft knee exoskeleton based on wearable multi-sensor system

“…Traditionally, most of the existing exoskeletons apply auxiliary torque to the biological joint through rigid structure. [5][6][7] Because of rigid frame, the exoskeleton can apply large moment to the biological joint. Typically, these systems run in parallel with the biological limb and provide a load path to ground to support external payload.…”

Comparison of dynamic models for the lower limb exoskeleton based on absolute and relative coordinates

“…With the development of robot technology and computer computing power, people can design many devices to enhance human strength. Among them, the lower limb exoskeleton has obvious advantages in improving the ability and efficiency of workers and soldiers [1][2][3]. At the same time, exoskeleton is also often used for nerve rehabilitation training and walking aid [4][5][6].…”