Control of twin-double pendulum lower extremity exoskeleton system with fuzzy logic control method

Abstract

In this article, a two degree of freedom lower-limb exoskeleton (LLE) design control is developed to reduce the fatigue level of healthy people and increase their load-carrying capacity. The LLE robot system is designed by comparing it to the twin-double pendulum system. One of the twin pendulums models is the human leg (with a knee and hip joint), and the other twin pendulum model is the exoskeleton robot. The movement of the human knee and hip joints in a walking pattern is recreated with a joint angle generator and applied to the joints with the help of a linear motor. The exoskeleton robot is provided to follow the movements of the leg with the help of a fuzzy controller. The control simulation with the mathematical model of the twin-double pendulum system and the fuzzy logic method was made using the MATLAB/Simulink program. The system response was analyzed and graphed for two different limb sizes (45 cm and 50 cm) and three different load conditions (no load, 25 Nm and 75 Nm). The maximum tracking errors are 3.2105° and 3.4730° for the hip and knee joint, respectively, with a 75 Nm load disturbance condition. These tracking error values can be interpreted as very low with high tracking success. The FL controller is robust to load changing and limb size-changing factors, and for this reason, it was suitable for use in LLEs.