Fuzzy Logic based Cycle-to-Cycle Control of FES- induced Swinging Motion B.S. K. K. Ibrahim Dept of Mechatronics and Robotics, Faculty of Electrical & Electronic Engineering University Tun Hussein Onn Batu Pahat, Johor, Malaysia babul@uthm.edu.my M.O. Tokhi, M.S. Huq and S.C. Gharooni Department of Automatic Control and System Engineering, University of Sheffield, Sheffield, United Kingdom. Abstract— FES induced movement control is a significantly challenging area due to complexity and non-linearity of musculo- skeletal system. The goal of this study is to design a cycle-to-cycle control of FES-induced swinging motion. In this approach only the quadriceps muscle is stimulated by controlling the amount of stimulation pulsewidth. This time dependent behaviour is successfully compensated for using a cycle-to cycle fuzzy controller, which computes the amount of knee extension stimulation on the basis of the achieved flexion angle in previous cycles.The capability of fuzzy control in automatic generation of stimulation burst duration is assessed in computer simulations using a musculo-skeletal model. This paper presents the development of a fuzzy logic control scheme based on discrete- time cycle to cycle control strategies without predefined trajectory. The results show the effectiveness of the approach in controlling FES-induced swinging motion Keywords- Functional electrical stimulation, fuzzy logic, genetic algorithm, swinging motion, quadriceps, paraplegic. I. INTRODUCTION Many researchers have developed electrically stimulated muscle control ranging in levels of sophistication from simple to complex. Primarily due to the complexity of the system (nonlinearities, time- variation) practical FES systems are predominantly open-loop where the controller receives no information about the actual state of the system [1]. In its basic form, these systems require continuous user input. Practical success of this open-loop control strategy is still, however, seriously limited due to the fixed nature of the associated parameters. Accurate control of FES-induced movement can be ensured with a suitable closed-loop adaptive control mechanism. Such approach has several advantages over open-loop schemes, including better tracking performance and smaller sensitivity to modeling errors, parameter variations, and external disturbances. Although conventional PID control is still the most widely adopted method in industry for various control applications due to its simple structure, ease of design, and low implementation cost, it might not perform satisfactorily if the system to be controlled is of highly nonlinear and/or uncertain nature [2]. Classical closed-loop control algorithms have failed to provide satisfactory performance and are not able to guarantee stability, a desired property of the controlled system [3]. Jezernik et al. (2004) used sliding mode FES control to regulate knee joint angle. The controller was tested on six neurologically intact subjects and two untrained paraplegic subjects. Good tracking of a desired knee joint trajectory was achieved, but this could only be applied to mathematical model based plant. The overall model of the plant being considered is a multi-input-multi-output (MIMO) nonlinear model consisting of nonlinear lumped parameters comprising passive joint viscoelasticity and active joint properties and segmental dynamics. On the other hand, fuzzy logic control (FLC) has long been known for its ability to handle nonlinearities and uncertainties without the need for mathematical model of the plant. Thus FLC is the preferred option in the current work. In controlling cyclical movement, one can try to follow pre-set joint angle trajectories. In the swing phase of gait, following exact trajectories is unimportant and inefficient, leading to fatigue due to the large forces that must be exerted to precisely control the high inertia body segments (Crago et al., 1996). Therefore, the cycle-to- cycle control method is expected to be an alternative to the trajectory based closed-loop FES control. The cycle-to-cycle control delivers the electrical stimulation in the form of the open-loop control in each cycle without reference trajectory but it is still closed-loop control. In this control strategy, movement parameters at the end of each cycle were compared to the desired set point, and the stimulation for the next cycle was adjusted on the basis of the error in the preceding cycle. This paper presents the development of strategies for swinging motion control by controlling the amount of stimulation pulsewidth to the quadriceps muscle of the knee joints. Capability of the controller to control knee joint movements is assessed in computer simulations using a musculoskeletal knee joint model.The knee joint model developed in Matlab/Simulink, as described in [4], is used to develop an FLC-based cycle-to-cycle control strategy for the knee joint movement. The FLC output is the controlled FES stimulation pulsewidth signal which stimulates the knee extensors providing torque to the knee joint. The swinging movement is performed by only controlling stimulation pulsewidth to the knee extensors to extent the knee and then the knee is left freely to flex in the flexion period. II. MATERIALS AND METHOD The role of simulation was to design, test, and optimize the control strategies, thus reducing time-consuming trial and error adjustments during human experiments. International Conference on Electrical, Control and Computer Engineering Pahang, Malaysia, June 21-22, 2011 978-1-61284-230-1/11/$26.00 ©2011 IEEE 60