Session 7: Control-integrated correction of thermal displacements

Thermal issues in machine tools for worldwide utilization
Ö. S. Ganiyusufoglu
Shenyang Machine Tool (Group) Co., Ltd.

Structure model based correction of machine tools
X. Thiem, B. Kauschinger, S. Ihlenfeldt
Institute of Machine Tools and Control Engineering, TU Dresden

The structure model based correction approach utilizes physically based models (e.g. finite element models) for online compensation of thermo‐elastic errors at machine tools. This approach requires only a few additional sensors because it uses control internal data. In this paper the structure model based correction
approach is investigated on the basis of a machine tool with a serial kinematic and a complex structure. Methods for online parameter identification are adapted and integrated in the correction approach to improve the robustness and the accuracy of the correction model.

Optimal temperature probe location for the compensation of transient thermal errors
G. Aguirre, J. Cilla, J. Otaegi, H. Urreta
IK4-IDEKO, Spain

Thermal error compensation is a cost-effective means of improving machine tool accuracy. The effectiveness and robustness of the method depends greatly on the location of the thermal probes, mainly when transient behaviour is relevant, such as in milling machines, where spindle speed and position in workspace are changing frequently and the machine never reaches thermal equilibrium. The influence of temperature probe location on the error compensation of a heavy duty milling machine and the relevance of finding optimal locations will be discussed, looking at both experimental and simulation data.

Adaptive learning control for thermal error compensation on 5-axis machine tools with sudden boundary condition changes
P. Blaser (a), J. Mayr (b), F. Pavlicek (a), P. Hernández-Becerro (b), K. Wegener (a)
(a)    Institute of Machine Tools and Manufacturing, ETH Zurich
(b)    Inspire AG, Zurich

A system of differential equations is used to compute a thermal error prediction model based on temperature and machine states as well as on-machine measurements. The model can predict thermal displacements of the tool center point based on changes in the environmental temperature, load-dependent changes and boundary condition changes and states, like machining with or without cutting fluid. The information gained by the process-intermittent probing is used to adaptively update the model parameters, so that the model learns how to predict thermal position and orientation errors and to maintain a small residual error of the thermally induced errors of the rotary axis over a long time.

Hybrid correction of thermal errors using temperature and deformation sensors
C. Naumann (a), C. Brecher (d), C. Baum (d), F. Tzanetos (b), S. Ihlenfeldt (c), M. Putz (a)
(a)    Fraunhofer Institute for Machine Tools and Forming Technology IWU, Chemnitz
(b)    Fraunhofer Institute for Production Technology IPT, Aachen
(c)    Institute of Machine Tools and Control Engineering, TU Dresden
(d)    Chair of Machine Tools, Laboratory for Machine Tools and Production Engineering, RWTH Aachen University

Thermo-elastic deformations are one of the most significant sources of production inaccuracies in cutting machine tools today. There are numerous methods to model, monitor and correct or compensate these thermal errors in machine tools. Among the indirect correction methods count the characteristic diagram based correction and the correction based on integral deformation sensors (IDS). Both are briefly described and their strengths and weaknesses are discussed. Following this, ways of combining both methods to overcome their respective weaknesses are discussed. A hybrid correction method is proposed which uses characteristic diagrams to derive a relationship between online IDS measurements and the actual tool-center-point (TCP) displacement. Experiments carried out on a 3-axis machine tool demonstrate the effectiveness of both correction methods