Improving the dynamics of industrial robots by adaptive pretensioning of joint gears

• Applicants: Professorin Dr.-Ing. Nejila Parspour; Professor Dr.-Ing. Alexander Verl
• Subject Area: Production Automation and Assembly Technology ; Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 451271315

Industrial robots (IR) offer significant advantages over traditional machine tools in terms of a wider working area, greater flexibility and lower costs. However, the lower path accuracy of IR compared to conventional machine tools limits the application possibilities. Particularly in machining tasks, where path accuracy is a decisive factor for the quality of the manufacturing process, the accuracy of IR is worse than the accuracy of conventional machine tools by a factor of 100 to 1000. This circumstance prevents the widespread use of IR for many machining processes. The reasons for the path errors are to be found in the non-linear dynamics of the robot joints. The non-linearity manifests in a hysteresis of the gear transmission behavior, which results from the complex interaction of elasticities, frictional forces and the loads acting on the gear. This hysteresis behavior is subject to backlash as well as a loss of stiffness during load changes and thus leads to unfavorable system dynamics for machining. IR machining has been experimentally investigated at the Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW) for several years. The Institute for Electrical Energy Conversion (IEW) at the University of Stuttgart has now developed and patented a new type of drive concept that integrates additional actuators in the gear elements. This concept offers the potential to significantly improve the accuracy and dynamic properties by shifting the hysteresis behaviour to a more desirable operating point by adaptive preloading. The extent, to which this novel concept allows an improvement in the dynamics of IR and the level of accuracy for machining tasks, is to be investigated within the scope of this research project by building a prototype. This should also provide fundamental knowledge about how the required preloading can be realized in terms of control technology. For the development and construction of the prototype as well as for the design of the control system, interdisciplinary expertise in the fields of drive technology, control and machining with IR is necessary. Therefore, the research project will be carried out by IEW and ISW in close cooperation.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Armin Lechler