Dynamic Measurement of Spindle Errors of CNC Machine Tools by Capacitive Sensors During Aircraft Parts Machining

The work presents characteristics and practical application of Spindle Error Analyzer, an innovative bespoke diagnostic system, designed for precision measurement of spindles used in high-precision Computerized Numerical Control - CNC machining centres, dedicated to aircraft parts machining. Ultra-precise and high-speed spindles constitute one of the most expensive elements of the CNC machine tool. Their control, diagnostics and proper use should be the matter of utmost importance at any production plant. Dynamic diagnostics of spindles is possible partly due to spindle error analyzers. Static measurements, conducted at low or zero speed, have become inadequate for the determination of the tilt of the spindle, which behaves considerably different in dynamic conditions, when the rotational speed amount to considerable values. The synchronous and asynchronous error motions and radial runout measured at high RPM enables, indirectly, evaluation of bearings condition, backlash, insufficient stiffness or unbalance. Literature analysis indicates that, however important, geometric accuracy of the machining tool alone does not ensure high precision of aircraft parts machining, as spindle error motion is of great significance.