Basics for structure integrated measurement und control integrated processing of spatial forces and moments in machine tools

• Applicant: Professor Dr.-Ing. Steffen Ihlenfeldt
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: from 2011 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 202081830

Online force measurement is increasingly required in many production-related applications, like process monitoring or closed loop process control. With the high mobility of modern machine tools, as five axis machines or hexapods, measuring spatial TCP forces and moments in up to 6 DOF is required. Thus far mostly 6 DOF forces plates are used and mounted close to the TCP. Because of harsh environment conditions in this area elaborate protective measures are necessary. Furthermore the workspace will be reduced as well as the machines sturdiness and at least forces plates are disproportionately expensive. With estimating forces from drives currents a satisfying measuring accuracy cannot be achieved for machine tools because of numerous interfering influences like frictions.The integration of single-axis forces sensors in the machine structure presents high potential with regard to the costs. Main objective of the project is to provide a spatial TCP forces and moments measurement and closed loop control system with the use of structure integrated single-axis forces sensors as an economic alternative to forces plates. In the first part of the project the integration of sensors in machine structures, static measurement models and parameter identification as well as the model integration in machine control systems has been evaluated for different measurement configurations. In the second part dynamic measurement and dynamic trajectory based parameter identification was studied as well as a proof of concept for a force control using integrated sensors. For all variants extensive experimental studies were performed.The biggest potential for structure-integrated force measurement has its application in force control, which is the main objective within the continuation of the project. After a basic proof of concept of a force control based on integrated sensors in the second part, the approach for the further project is overcoming the current deficits of asynchronous set points, nonlinear machine stiffness, dimensional accuracy during force control as well as force controlled practical processes, such as milling. Thereby a significant need for research exists, especially relating to structure-integrated sensors.The works include the development of synchronous set point provision for force and position control in one G-Code line, which allows a variation of force and force direction during the process, evaluations concerning modelling and correction of the pose-dependent spatial machine stiffness, which can influence stability in force control as well as evaluations of contact modelling contact search and achieving dimensional accuracy during force control.

• DFG Programme: Research Grants