Planning of Energy-Efficient Trajectories with Utilization of Energy Storage and Energy Interchange between Electrical Drives

• Applicant: Professor Dr.-Ing. Tobias Johannes Ortmaier
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 170398655

In German production plants about 2/3 of electrical energy are consumed by electrical drives. Here, energy losses mainly result from inefficient operating points and braking energy dissipation by conversion to thermal energy. The internal DC buses of modern servo inverters can be electrically coupled (e.g. in multi-axis systems). Hence, a continuous exchange of electrical energy between motor and generator drives is possible. During the first and completed project period path planning methods were established that reduce the energy demand of positioning tasks of miscellaneous, mechanically decoupled multi-axis systems. Therefore, model based optimization algorithms were applied. On the one hand, operating point-dependent energy losses of the drive components are considered in the model and consequently reduced where possible. On the other hand, the possibility of electrical energy exchange using the DC bus is systematically amplified. Also the energy storage capacity of the DC bus capacitors as well as kinetic and potential energy storage of the mechanical axes are utilized. In consequence, a significantly bigger amount of the recuperable mechanical energy can be used for the supply of other electrical drives or the initiation of subsequent movements. Finally, the total energy demand is decreased.During the second period of the project, as already outlined in the initial proposal, the developed methods are transmitted to mechanically coupled multi-axis kinematics (e.g. serial robots). Therefore, the developed model equations of the first project period must be extended and the additional model parameters must be identified. To improve the transferability of the approaches to other robotic systems and kinematics, the efforts for modeling and parameter identification must be reduced. Therefore, valid model reductions will be determined using a sensitivity analysis of the model parameters. Simultaneously, the risk of collisions must be regarded during the path planning procedure using appropriate algorithms. Generally, the energy storage capacities of the existing system components are limited and usually not sufficient for a given application. Hence, the multi-axis system is extended by electrical and mechanical energy storage equipment and appropriate control strategies. In complex production lines, usually numerous different single- and multi-axis systems are utilized simultaneously. To further reduce the consumption of electrical grid energy, all systems are connected via an extended DC bus. Furthermore, new operation techniques for efficient process coordination are essential to amplify the exchange of electrical energy between different (e.g. multiple robotic) systems. Finally, the approaches are assigned to a real-time control procedure for the development of a new online trajectory optimization method. Hereby, the exchange of electrical energy reduces the demand of e.g. an exemplary camera controlled Pick&Place applications.

• DFG Programme: Research Grants