Modeling the Dynamics of Two Cooperating Robots

The paper presents a description of the dynamics of two mobile robots cooperating in the transport of a bulky load in the form of a beam. The purpose of modeling such a system was to obtain a mathematical model in an appropriate form. Lagrange equations of the second type were used to describe the dynamics, followed by the projection method, which allowed for the elimination of Lagrange multipliers. Thanks to this approach, the unknown dry friction forces at the contact points of the robots’ wheels with the ground were eliminated from the description, and the dynamics in the controllable coordinates were obtained. The resulting model has structural properties that enable its use in the synthesis of a control system based on a mathematical model.

Real-time stiffness compensation and force control of cooperating robots in robot-based double sided incremental sheet forming

In robot-based incremental sheet forming, the forming robot is displaced due to the forming forces and the comparable low stiffness. As the forming forces can not be predicted precisely, the stiffness needs to be compensated based on the measurement of a force torque sensor. While previous approaches used precalculated lookup tables, this publication presents a multi body system robot model that can calculate the displacement of the tool center point in real-time. In incremental sheet forming, the supporting robot is typically force controlled to bring superimposed stress into the forming zone. Unfortunately, this could lead to oscillations in the stiffness compensation. The presented force control approach takes the stiffness compensation into account to ensure a smooth movement of the forming robot. In a series of 30 forming experiments the effectiveness of the developed stiffness compensation and force control is validated.