Employing wave variables for coordinated control of robots with distributed control architecture

By controlling complex robotic systems one often has to cope with the situation that different sub-systems are interfaced and controlled by different computers. In this paper the problem of coordinated control of such a system with distributed control structure is addressed. In particular one must handle the transmission delays in the communication between the different computers, which can be considered small but not negligible, since also small delays in the transmission of power variables violate the passivity and therefore may lead to instability. In this paper the wave variables concept is applied to handle the delays and is used in combination with a virtual inertia for designing a Cartesian compliance controller. Therefore, in particular the steady state properties of the wave variable based communication is of interest and leads for the case of small delays to the analogy with a flexible joint robot. In a second step the virtual inertia is eliminated in order to approximate the desired closed loop behavior better. Finally, some simple planar simulations are presented which validate the proposed approach.