Estimation of Joint Stiffness Using Instantaneous Loads via an Electromyogram and Application to a Master–Slave System with an Artificial Muscle Manipulator

Abstract

Master–slave systems and human-assisted systems in which robots can work together with humans have been widely developed. Such systems are necessary to communicate human intentions to a robot. Therefore, it is important for these systems to be able to estimate human joint characteristics such as torque, position and stiffness. In this context, we focus on the myoelectric (ME) potential. In many previous studies, an electric motor has been used as an actuator, and the torque and position are estimated from the ME potential. However, the joint stiffness of humans has not been studied extensively. In this study, we propose a method to estimate the stiffness of the human elbow by using antagonistic muscles when an instantaneous load is applied. Furthermore, we apply our method to a 1-d.o.f. manipulator with an artificial muscle. In the case of eccentric contraction, it has been shown that the stiffness of a joint can be estimated solely by an electromyogram of the triceps. Then, the stiffness and angle control of the artificial muscle manipulator that used it as the slave side is proposed. Furthermore, the estimated joint stiffness is set as a desired value for joint stiffness control of the artificial muscle manipulator. Experimental results of stiffness control indicate that the angle and the stiffness of the 1-d.o.f. artificial muscle manipulator can be adequately controlled for a master–slave system. Safer remote control systems can be developed by using this system.