Development and Control of Upper-Limb Exoskeleton Robots

Several countries of the world are facing the problem of aged society. The birthrate is decreasing since the fertility rate is declining and the people enjoy longer life since the increasing in life expectancy. Therefore, such society is an aged society (i.e., more percentage of population is aged). In addition, considerable number of injured and/or handicapped population is living in the society. In this society, taking care of physically weak individuals (aged, injured and/or handicapped person) is becoming a major problem. Therefore, assistive robotic technology is supposed to play an important role in power-assist and rehabilitation to make the physically weak individuals’ life easy and comfort. An exoskeleton robot is one of the most effective assistive robot that can assist the motions of the physically weak individuals from the outside of his body. It is an external structural mechanism which can be worn by the human user as an orthotic device. It has joints and links which correspond to those of the human joints and limbs, respectively. The exoskeleton robot transmits torques to the human joints from the actuators through the exoskeletal links. In the context of exoskeleton robots, upper-limb exoskeleton robots become the great interest of the researchers as upper-limb motions are very important to perform daily activities. This thesis addresses the issues related to development and control of upper-limb exoskeleton robots for assisting the upper-limb motions of physically weak individuals. In the design of the exoskeleton robots, biomechanically similar motion generation (biomechnical design) is considered. Issues such as estimation of joint torques using the electromyography signals (EMG) of human muscles, generation of natural motion, and efficient power assist are addressed in the control methods. The research work presented in this thesis is motivated by the increasing need of assistive robots to assist the daily motions of physically weak individuals. At the beginning, the thesis explains a review of exoskeleton robots. It is performed to identify the state of art technologies and the challenges faced. Then, a three degrees of freedom (DOF) wrist and forearm motion assist exoskeleton robot (named W-EXOS) is proposed to assist the motions of forearm supination/pronation, wrist flexion/extension and wrist radial/ulnar deviation of physically weak individuals. The wrist joint of the W-EXOS is designed including the offset of wrist axes. Thereby the W-EXOS can generate biomechanically similar motion as human wrist. Other than the W-EXOS in this thesis, the offset of wrist axes has not been considered in other designs of wrist exoskeletons found in literature. The electromyography signals (EMG) of human muscles can directly reflect the human motion intentions. Therefore, the EMG signals can be used as input information for the control of robotic systems. Although intramuscular EMG signals give better muscle activation pattern than that of the skin surface EMG signals, they are difficult to use practically, since the procedure is invasive. Therefore, the skin surface EMG signals of the upper-limb muscles of the exoskeleton user are used as the primary input to control the exoskeleton robots in this study. The signals of the robot sensors are used as secondary input information to the controller. An EMG-based fuzzy-neuro control method is proposed to control the proposed W-EXOS. Fuzzy IF-THEN control rules are defined to estimate the joint torques of the robot using EMG signals. In the proposed control strategy, multiple fuzzy-neuro controllers are switched moderately according to the angles of motions. Multiple controllers are used to deal with the changes of muscle activation levels according to the angles of motions. The controller is required to adapt according to the changes of EMG signal levels with the person. Adaptation method of the controller is also described.