The controlling requirements and control objectives of an exoskeleton robot differ considerably from the conventional industrial and field robots. This is mainly due to the reason that human operator is not only the commander of the control system but also a component in the control system. The human operator mainly makes the decisions and the exoskeleton implements the tasks. However, feedback information received by the human operator and the exoskeleton robot keeps interchanging between each other. Therefore, intelligence of the exoskeleton system is enhanced while the power of the human operator is also improved. The principle criterion to control the exoskeleton robot, especially power assist exoskeleton robot is to work according to the user motion intention. This becomes much more important for a physically weak person, who is not capable of generating daily motions properly.
An exoskeleton robot consists of two types of controllers: robot controller and human brain. Those controllers are working parallel to each other. The controller of exoskeleton robot especially power assist exoskeleton robot aims at controlling the robot based on the human motion intention most of the time. However, identifying the exact human motion intention is still under at research level [24]. Therefore, understanding and optimizing the best control method is difficult. Control methods of upper-limb exoskeleton robots can be classified in several ways: based on input information to the controller, controller architecture and output of the controller [171]. Based on input information to the controller, the control methods can be categorized as human biological signal based control methods, non-biological signal based control methods and platform independent control methods. The categorization is shown in Fig. 10. We identified that the categorization based on input signals is more important, since the input signals are essential to identify the human motion. EMG signals have successfully employed in some of upper-limb exoskeleton robots [15] and [100]. In [15] muscle-model oriented EMG based control method is proposed to control 7DOF upper-limb exoskeleton robot. Since the method is adaptable for the user it can be used for most upper-limb disable persons. Most of the EMG based control methods used with upper-limb exoskeleton robots are of binary (on–off) nature [100]. Some elderly persons whose motor ability is deteriorated, the environment perception ability may also be deteriorated. In order to cater this problem, the power-assist robot with the perception-assist, which assists not only the user’s motion but also the user’s interaction with an environment, has been proposed in [172] by Kiguchi et al.