Design and Analysis of Multifunctional Actuators for Assistive Knee Braces

In this research, a novel magnetorheological (MR) fluids based multifunctional actuator for assistive knee braces is designed. To decrease the dimension of the actuation device while enhancing its perfonnances, a motor and MR fluids are integrated into a single device. With MR fluids, the actuator possesses multiple functions as motor, clutch, and brake while meeting the requirement of nonnal human motion as well. In this thesis, design details and operating principle of the actuator are illustrated, and possible configurations of the motor part and clutch/brake part are discussed. Finite element method is utilized to analyze the magnetic circuits, influence of pennanent magnet on MR fluids, and magnetic flux distribution. Different clutch/brake parts with various inner coils are compared and analyzed, followed by a design optimization to improve the output torque. Prototypes of the multifunctional actuator are fabricated and tested, and characteristics of each function are investigated. As the actuator has multiple functions, modeling is developed for different functions, and system identification is carried out to determine the parameters. Adaptive control is utilized to control the actuator for torque and speed tracking. A smart joint using such a multifunctional actuator is designed, and its prototype is fabricated and tested. Power consumptions of knee brace using the smart joint are investigated during normal walking cycle. The results show that the developed actuator and smart joint are promising to be used in assistive knee braces.