Machining, Measurement, and Control Laboratory

Measurement of Spindle Stiffness for the Monitoring System of Cutting Forces
Atsushi Matsubara, Tomoya Fujita, Iwao Yamaji, Soichi Ibaraki

This paper presents a measurement scheme of the stiffness of rotating spindle in radial directions. The measurement purpose is to characterize the spindle stiffness that is needed for the monitoring of the cutting forces in a sensor-integrated spindle. The spindle has been developed for an intelligent machining center, having four eddy current sensors that detect the radial displacements of the spindle in X and Y directions. The sensor signals are interpreted as the forces applied on the tool-holder-spindle system by using the force-displacement relationship (spindle stiffness) obtained from the calibration tests. In order to measure the stiffness of the rotating spindle, a loading unit is fabricated. Several loading tests are carried out and the force-displacement relationship is investigated under different running conditions. It is found that the force-displacement relationship with the rotating spindle has nonlinear characteristic.