In a production plant for complex assembled products there could be up to several hundred of robots used for handling and joining operations. Thus, improvement in robot motions can have a huge impact on equipment utilization and energy consumption. These are two of the most important aspects of sustainability in a production system. Therefore, this paper presents an algorithm for generating efficient and collision free motion of industrial robots using path planning and direct transcription methods for numerical optimal control. As a measure of efficiency for moving between configurations we use a combination of the energy norm of the applied actuator torques and the cycle time. Velocity and torque limits are handled and modeled as hard constraints. However, more general problems can be solved by the same approach. Our novel algorithm solves the problem in three steps; (i) first a path planning algorithm calculates an initial collision free path, (ii) a convex optimal control problem is then formulated to follow this path, and finally (iii) a nonlinear optimal control problem is solved to iteratively improve the trajectory. The resulting trajectory is guaranteed to be collision free by restrictions in the configuration space based on a local sensitivity analysis. The algorithm has been successfully applied to several industrial cases demonstrating that the proposed method can be used effectively in practical applications.
This work was carried out at the Wingquist Laboratory VINN Excellence Centre, and is part of the Sustainable Production Initiative and the Production Area of Advance at Chalmers University of Technology. It was supported by the Swedish Governmental Agency for Innovation Systems.
Authors and Affiliations
- S. Bjorkenstam, Fraunhofer-Chalmers Centre
- D. Gleeson, Fraunhofer-Chalmers Centre
- R. Bohlin, Fraunhofer-Chalmers Centre
- J. S. Carlson, Fraunhofer-Chalmers Centre
- B. Lennartson, Automation Research Group, Department of Signals and Systems, Chalmers University of Technology