Preload Control of Spindle Bearings by Means of Shape Memory Alloys

Commercial, motor-driven spindles for applications in machine tools are generally developed for specific machining operations. Spindles can be distinguished between spindles for HPC (High Performance Cutting) and spindles for HSC (High Speed Cutting). HPC and HSC require opposing specifications concerning motor configuration and the preload of the spindle bearings. To realize a universal machine tool spindle, changeable motor configuration and preload of the spindle bearings are necessary. In this paper, a new approach for an adaptive preload element is presented to control the preload of a spindle bearing arrangement. The adaptive preload element consists of actuators based on shape memory alloys in combination with Peltier elements. By controlling the current through the Peltier elements the temperature of shape memory alloys bending springs is controlled. Thus, the preload force of the bending springs can be variated. Experimental tests reveal the properties of the preload element and its suitability for preload modification. Within these tests, the adaptive preload element enables a preload modification of about 850 N.