Triaxial loading device for reliability tests of three-axis machine tools

This paper presents a triaxial loading device (TLD), which can apply a triaxial force on the spindle of a three-axis machine tool that is executing a 3-degree-of-freedon feeding motion, aiming at simulating cutting forces applied on the spindle in a machining process. A prototype was fabricated and its kinematics and dynamics were analyzed. An explicit force control system was designed based on a fuzzy proportional-integral (PI) controller, integrating a force and a position feedforward. The effectiveness of the control system was evaluated; results illustrate that the fuzzy PI controller reduces the rising time and overshoots, and the force and the position feedforward eliminate the hysteresis and following errors caused by unknown feeding motions, respectively. Loading experiments were conducted to test the dynamic loading capacity of the TLD. The experimental results illustrate that the device is capable to add a triaxial force, which tracks a reference force with acceptable errors, on a spatially-moving spindle with random trajectories in real time. The TLD can simulate the cutting forces that the spindle encounters in real machining process and provides an efficient and economical loading approach that avoids a costly long-term cutting for the reliability tests of three-axis machine tools.