March 2010

COMPENSATION OF MACHINE TOOL THERMAL ERRORS BASED ON TRANSFER FUNCTIONS

MM (Modern Machinery) Science Journal, March 2010
O. Horejs, M. Mares, P. Kohut, P. Barta, J. Hornych
Research Center of Manufacturing Technology
CTU in Prague, Czech Republic
Abstract

This paper reports on a new method for compensation of machine tool thermal errors that is based on system of thermal transfer functions. Due to their relative simplicity they enable real-time calculations which make them suitable for compensation algorithms of thermal displacements at tool centre point. The applicability and robustness of the thermal transfer function compensation model have been experimentally verified on a real machine tool. Tested compensation algorithms proved its ability to significantly reduce thermal errors. The thermal error minimization of more than 85 % of the standard compensation technique based on linear regression model was achieved in particular machine tool coordinate direction.

Keywords: Thermal errors, Compensation, Ultra precision, Accuracy, Transfer function
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PREDICTION OF MACHINE TOOL SPINDLE’S DYNAMICS BASED ON A THERMO-MECHANICAL MODEL

MM (Modern Machinery) Science Journal, March 2010
P. Kolar, T. Holkup
Research Center for Manufacturing Technology,
Faculty of Mechanical Engineering, CTU in Prague, Czech Republic
Abstract

This paper presents a thermo-mechanical model of spindles with rolling bearings. The heat generated in the bearings and the motor is transferred to the ambient air, the motor coolant and the spindle head structure. It warms the spindle up and causes thermal deformations of spindle parts. Thermal deformation affects significantly properties (internal loads, stiffness) of rolling bearings and need to be considered in predictive models of spindles’ dynamics. The structure of the transient model contains thermo-mechanical loops which update the model with respect to the instantaneous condition of the spindle. The changes of the bearings’ internal condition and stiffness are calculated using the Jones’ nonlinear theory. The thermo-mechanical spindle model predicts temperature distribution, thermal growth of spindle parts, and transient changes in bearing stiffness and contact loads under specified operating conditions. The predicted bearing properties are then used to estimate the variation of natural frequencies and dynamic stiffness of the spindle.

Keywords: Spindle, Rolling bearing, FEM modeling, Spindle dynamics, Thermal expansion
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OPTIMIZATION OF ENERGY BY ROBOT MOVEMENT

MM (Modern Machinery) Science Journal, March 2010
Anna Smetanová
Faculty of Mechanical Engineering, Institute of Production Machines, Systems and Robotics, Brno, Czech Republic
Abstract

This paper is describing the influences of movement parameters on energy consumption during robot operation. The experimental verification of mathematical models was performed in the laboratory of the Institute of Production Machines, Systems and Robotics at Brno University of Technology. The measure results are arranged in tables and diagrams from which final evaluation for praxis follow. One of them is the outline of movement parameters setting from the side of robot users before the program is put in manufacture. Another one is recommendation for robot producers to append new items to driving system menu referring to energy consumption calculator for off-hand programming as well as energy consumption meter.

Keywords: Robot, Motion, Energy Consumption, Measuring, Velocity, Acceleration
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COMBINED LOADING OF THE SPECIMENS AND REALIZED EXPERIMENT

MM (Modern Machinery) Science Journal, March 2010
Fr. Fojtík, J. Fuxa
Department of Mechanics of Materials
VSB-Technical University of Ostrava, Czech Republic
Abstract

The article describes experimental results under combined loading of specimens manufactured from common construction steel 11523. Specimens were gradually loaded by amplitude of the torque and then by combination tension prestress. For evaluation of the results the Fuxa’s criterion was applied. The performed experiments and their results embody a good agreement with bellow mentioned conjugated strength criterion. The experiments were performed on reconstructed testing machine Shenck. The reconstruction and experiment will be described in the following article.

Keywords: Combined loading, High-cycle Fatigue, Experiment, Multi-axial fatigue, Mean stress effect
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POSSIBILITIES OF FEM APPLIED IN THE VERIFICATION OF X-RAY MEASUREMENT

MM (Modern Machinery) Science Journal, March 2010
K. Frydrysek
Department of Mechanics of Materials,
Faculty of Mechanical Engineering, VSB-TU Ostrava
Abstract

Residual stress diffraction measurements in a thin surface layer are completely nondestructive. For subsurface stress profiling, the destructive X-ray analysis can be performed by sequentially removing surface layers by using electrolytic or chemical polishing. When stressed layers are removed, the measured stress values in depths beneath the surface are in general affected by the relaxation created due to the layer removal. Therefore a correction should be involved in the depth profiling procedure. Accepted procedures used till now presume the removal of the whole surface of the investigated laboratory samples. The aim of the contribution is to present the possibilities of FEM for evaluation of the credibility of X-ray stress-strain states measurements. An estimation of changes of depth distribution due to the stress relaxation created by the removed layers was simulated by FEM in the case of a small electrolytically polished area 12 mm in diameter in the middle of cylindrical samples of the height of 7 mm.

Keywords: Residual stress, X-ray diffraction, Layers´ removal, Stress redistribution, FEM
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