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A new grey box approach for friction modelling of machine tool drives

Rüppel Adrian Karl, Meurer Markus, Bergs Thomas

Journal of Machine Engineering

2024

Vol. 24, No. 1

5--16

Measurement of the process force in milling is usually conducted by using piezo-electric dynamometers which are costly and reduce the stiffness of the system. A less invasive alternative is an indirect estimation of cutting forces based on the power of the servo drives. However, a correction of frictional effects from the transmission system is necessary to achieve accurate results. Most machine tools are equipped with ball-screw drives whose friction behavior is highly nonlinear due to dependency on both velocity and position. This study provides a novel approach to consider all frictional and inertial effects in transmission behavior of ball-screw drives by utilizing the well-established generalized MAXWELL slip (GMS) model and combines it with a data-based approach, namely support vector regression (SVR). The approach acquires the internal states of the GMS model and uses them as an additionnal input for the SVR. The model is validated on different experiments conducted on a five-axis machining center and compared to established friction models, as well as a sole SVR. The results show the model to have errors between 7% and 12% over the full working range of the x- and y-axes, respectively, outperforming the benchmark models significantly.

Accuracy in force estimation applied on a piezoelectric fine positioning system for machine tools

Uhlmann Eckart, Polte Mitchel, Triebel Florian, Overbeck Rasmus, Thom Simon

Journal of Machine Engineering

2021

Vol. 21, No. 2

24--34

In order to improve the accuracy of machine tools, the use of additional active modules meeting the requirements of the “Plug & Produce” approach is focused. In this context one approach is the installation of a high precision positioning table for online compensation of machine tool deflections. For the model-based determination of the deflection, the knowledge of the effecting process force is crucial. This article examines the use of displacement sensors for force estimation in a piezoelectric system. The method is implemented on a high precision positioning table applicable in milling machine tools. In order to compensate nonlinear effects of piezoelectric actuators, a hysteresis operator is implemented. Experimental investigations are carried out to quantify the influence of preload stiffness, preload force and workpiece weight. Finally, a resolution d ≤ 78 N could be achieved and further improvements to meet the requirements for online compensation of machine tool deflection are discussed.