Real-time estimation of temperature distribution in a ball-screw system

A ball screw is usually preloaded for high rigidity and accuracy, thus increasing the frictional resistance. Subsequently its temperatures and positioning error are significantly raised. When it comes to high speed or high precision, this thermal error becomes more serious and dominates the total error. In this paper, two-dimensional temperature distributions of a ball-screw system preloaded in the axial direction are estimated at various moving velocities and stop times by the finite element method (FEM). The thermal behavior of the ball screw was measured for comparison with the data estimated by FEM. The comparison shows that the pattern of temperature increase and the temperature distribution of the ball screw in a steady state are well estimated, whereas the absolute values of the temperature are not well estimated in spite of a long computation time. Therefore a modified lumped method is proposed for the real-time estimation of the temperature distribution for the ball screw. This method, after compensation for heat transfer coefficients, estimates the temperature more exactly than FEM within several milliseconds, which makes practical implementation feasible. (C) 1997 Elsevier Science Ltd.