A study of compensation of thermal displacement of the ball screw in NC machine tools.

Thermal displacement of the ball screw in semi-closed loop type NC machine tools directly introduces position error in the machine tool. In this paper, the thermal displacement of the ball screw is estimated by using FEM. In the estimation, data for the driving conditions of the machine tool, i.e. feed rate, slider position, and armature current of the servo motor are used as inputs. The estimated displacements of the ball screw are given to the NC in the form of pitch error compensation data. The thermal behaviour of a vertical type machining center was measured to examine the effectiveness of this compensating method. The results showed that thermal displacement of the ball screw were decreased to 15-20% while using this compensation.