Virtual Sensor for Calibration of Thermal Models of Machine Tools

Alexander Dementjev,Klaus Kabitzsch,Steffen Schroeder,Burkhard Hensel,Bernd Kauschinger

doi:10.1155/2014/347062

Alexander Dementjev, Klaus Kabitzsch + Show 3 more

Open Access

https://doi.org/10.1155/2014/347062

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Abstract

Machine tools are important parts of high-complex industrial manufacturing. Thus, the end product quality strictly depends on the accuracy of these machines, but they are prone to deformation caused by their own heat. The deformation needs to be compensated in order to assure accurate production. So an adequate model of the high-dimensional thermal deformation process must be created and parameters of this model must be evaluated. Unfortunately, such parameters are often unknown and cannot be calculated a priori. Parameter identification during real experiments is not an option for these models because of its high engineering and machine time effort. The installation of additional sensors to measure these parameters directly is uneconomical. Instead, an effective calibration of thermal models can be reached by combining real and virtual measurements on a machine tool during its real operation, without additional sensors installation. In this paper, a new approach for thermal model calibration is presented. The expected results are very promising and can be recommended as an effective solution for this class of problems.

Highlights

In high-complex industrial manufacturing processes the endproduct quality depends strictly on the accuracy of relevant machine tools.When a machine tool operates, heat is produced by motors, points of friction like gears and bearings, and so forth
The heat spreads through the other parts of the machine and leads to deformation of the machine tool
A similar definition is given by Fortuna: virtual sensors “focus on the process of estimation of any system variable or product quality by using mathematical models, substituting some physical sensors and using data acquired from some variables” [6]

Summary

Introduction

In high-complex industrial manufacturing processes the endproduct quality depends strictly on the accuracy of relevant machine tools. A comparative study of empirical-based models for thermal error compensation on CNC machine tools is given in [4] In these articles, the different model structures were considered and very promising results are presented. In the described solutions only temperatures as model inputs were considered, but it could be very helpful to measure additional machine parameters like spindle speed or motor moments to improve the prediction accuracy, on the one hand, and, on the other hand, to improve the generalization ability of the model. In the collaborative research project “Transregio 96” (founded by the German Research Foundation DFG), the use of different simplified deformation models is investigated Such models should be able to deal with real machine tool control systems in online mode. Our proposal is to use the simplest possible virtual sensors (VS) for the estimation of the unknown parameters for simplified FEM based models, as this allows both the most economic and practically realizable solutions

Virtual Sensors in Industrial Applications

New VS Based Calibration Approach

Results and Discussion

The Vision

Conclusions