“…In particular, approaches such as PD/PID control, robust/adaptive control, adaptive neural networks, and combined solutions with the concept of energy passivity have been considered to solve this problem. Early but still pioneering and valuable works using an observer-controller scheme, passive decomposition, a force symmetry bilateral control strategy and, an impedance identifier are presented in [1][2][3][4][5][6][7][8][9]. [1] presented experimental results for master-slave synchronization of two robotic manipulators based on the observer-controller scheme.…”