Passive control of a Dual-Arm cooperative robot

Some operations such as transferring a heavy object require a Dual-Arm robot instead of a Single-Arm robot. Impedance control is good for controlling a robot interacting with the environment. Passivity is an important requirement for the safety of the people, environment and robots themselves. If the system does not satisfy passivity, high amount of energy has a chance of flowing from the robot to the environment. To prevent such accident, we control the coefficient of the desired velocity field according to the total energy of the system. We also limit the contact force between the object and the environment. In this paper, we propose a new passive control method for object transfer by Dual-Arm robot. Our new method assumes the following four conditions: (a) the system has two manipulators; (b) the controller is based on impedance control; (c) the system keeps passivity; (d) the trajectory of the object is designed with velocity field. Simulations of two robots with 3 D.O.F. holding an object interacting with an unknown stiff wall show that the system controlled with our new method satisfies passivity. Moreover, when the system is kept in a steady-state, we can obtain the relation equation between the energy of the system and the contact force. Computer simulations also validated the correctness of the relationship.