Development of Control Mechanism for Safety Enhancement in Bilateral Control Robot Applications

Bilateral control facilitates access with haptic feedback to remote environment through master-slave robots. The technique is applicable for remote assist robots working in human spaces where safety is a must. This paper proposes step by step implementation of safe and comfortable operating mechanism to be used with bilateral control robots. It will protect the object touched by the slave robot. In bilateral control, master operator freely applies force on remote objects via interface devices. This force could exceed object safe force limit and could damage it. Therefore, this paper implements master-slave local safety functions when reaction force from the environment exceeds the predefined force limit. Explicit force control is implemented on the slave side and virtual stiffness control is implemented on the master side during safe mode operation. The state transition from bilateral control to local safety functions causes loss of reaction force experience on the master side. This paper explains the procedure to remove loss of reaction force experience on the master side and how to facilitate continues force increasing with virtual stiffness control. Further proposed method uses bilateral control common mode force servoing property to maintain the master slave connection during local safe mode operation. This study uses sensorless sensing techniques of disturbance observer for robust motion control and reaction force observer for reaction force estimation. The effectiveness of the proposed methods is validated through experiments.