Development and investigation of an indirect dynamic force measurement system based on voltage and current signals for cutting technology

• Applicant: Professor Dr.-Ing. Thomas Bergs
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497676155

Tool load is crucial in the cutting process including milling, and monitoring the process force provides valuable information about the tool condition as well as the machining process itself regarding surface integrity. It enables us to understand/optimize the process toward the enhancement of productivity and quality control. In terms of the investment costs of a dynamometer, the indirect force measurement is desirable for an industrial application. Although many existing methods that use the motor-drive information, e.g., motor current, can monitor the slow (static) change of the process force, they cannot acquire the rapid (dynamic) change. Therefore, a monitoring solution of the process force with a wide measurement frequency-bandwidth is desired especially for the dynamic milling process, on which this project focuses. For this purpose, this project utilizes the voltage and current signals of the motor drive since these signals can be measured with a high sampling speed. In order to indirectly-measure the dynamic force, two characteristics that limit the measurement bandwidth of the existing methods must be considered: the nonlinear friction and the high-order transfer behavior from the process force at the tooltip to the motor current. These characteristics depend on the mechanical structure of the motor drives (direct-driven and ball-screw-driven axes), and this project solves these two difficulties of both types of drive mechanisms to indirectly-measure each process torque/force acting on the spindle/feed axes. Here, each drive axis is supposed to have its own measurement accuracy and bandwidth. This project then fuses the torque and forces based on the online identification of the coefficients of a mechanistic force model that is a function of the current cutting (engagement) conditions so that the overall measurement performance is enhanced. In this project, not only the establishment of the monitoring methodology but also an investigation of the measurement accuracy under different cutting conditions are to be handled.

• DFG Programme: Research Grants