Control of the static and dynamic stiffness of feed drive axes by using an external force sensor

To increase the dynamic and static stiffness of machine tools, hardware-based approaches are common. In recent years, several force sensors have been developed that are capable to measure process forces at the tool center point. They give not only deep insights in the process, but they also offer the ability to improve the effective stiffness of a compliant machine structure. This publication extends existing approaches for stiffness control by using a current feedforward control for the conventionally used nested control loops of feed drives that is able to reduce deflections of a compliant machine structure due to external forces. The control loop is validated exemplarily at a feed drive axis test bench. To increase also the dynamic stiffness, a further approach is analyzed on its potential if the forces are known or unknown in advance.