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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.

Modelling of a thermoelectric self-cooling system based on thermal resistance networks for linear direct drives in machine tools

Uhlmann Eckart, Salein Sebastian, Polte Mitchel, Triebel Florian

Journal of Machine Engineering

2020

Vol. 20, No. 1

43--57

The use of direct drives in linear and rotary axes as well as increased power density of main drives offer the potential to raise feet rate, acceleration and thus allow higher productivity of machine tools. The induced heat flow rates of these drives could lead to thermo-elastic deformations of precision related machine tool components. In order to reduce thermally caused displacements of the tool-center-point and to prevent a negative impact on the achievable accuracy, the induced heat flow rates of main drives must be dissipated by effective cooling systems. These systems account for a major share of the machine tool’s total energy consumption.With the intention to overcome the area of conflict regarding productivity and energy efficiency, a so called thermoelectric self-cooling system has been developed. To convert a proportion of thermal losses into electrical energy, thermoelectric generators are placed in the heat flow between the primary part of a linear direct drive and the cooling system. The harvested energy is directly supplied to a pump of the water cooling circuit, which operates a decentralised cooling system with reasonable coolant flow rates. For predicting the thermoelectric system behaviour and to enable a model-based design of thermoelectric self-cooling systems, a thermal resistance network as a system simulation in MATLAB/Simulink is presented. The model is applied to a feed unit with a linear direct drive and allows the calculation of harvested energy as well as the simulation of steady and transient states of the cooling system. The comparison of simulative and experimental determined data indicates a predominantly high model prediction accuracy with short simulation times. At an early stage of development the model turns out to be a powerful tool for design and analysis of water flow thermoelectric self-cooling systems.