Steps towards a protection system for machine tool main spindles against crash-caused damages

High productivity and availability of machining centers can only be achieved by avoiding unplanned machine downtimes. Machine failures induced by wear can be coped with by implementing preventive and conditionbased maintenance strategies so that downtimes are as short as possible. In contrast, machine damages caused by collisions cannot be avoided by these strategies, but only fixed afterwards by reactive maintenance, leading to high repair costs and long machine downtimes. This article presents a new approach for the avoidance of damages to the main spindle unit caused by collisions in machining centers. The mechanical components of this protection system enable the controlled reversible decoupling of the main spindle from the machine structure in case of exceedance of an adjustable force limit. Decoupling leads to a reduction of the whole machine stiffness, resulting in the decrease of the acting collision force. Consequently, all machine components in the collision’s force flux are protected against overload and damage. Once a collision occurred, a general method is shown, where the spindle and its collision objects are separated automatically by the machine’s numerical control. Due to the reversible decoupling mechanism of the protection system, the described retreat strategy eases the handling after a collision for the machine operator