Enhancing Signal Quality of Capacitive Displacement Measurements in Machine Tool Environments？

Capacitive displacement sensors are a valuable choice for high accuracy geometric spindle measurements. Although these sensors show the specified performance in electromagnetic friendly environments, the performance may degrade drastically in machine tool environments due to electromagnetic disturbances. An in-situ testing procedure based on a cap test setup is proposed, which enables a simplified error diagnosis and verification of sensor performance. The functionality of the device and the application to different practical cases are presented. The results of these tests suggest that a decisive part of disturbances may couple into the measurement system via electrical conduction at interfaces between the machine tool and measurement device parts. Disturbances originate in the power electronics of the machine tool and are passed on to the safety ground of the machine tool, which is connected to all structural components of the machine tool. The proposed counter measure targets a complete galvanic separation of the measurement system from machine tool parts. The effectiveness of this counter measure was verified in different tests on two different machine tools. It is shown that the application of the galvanic separation leads to a comparable sensor performance in machine tool environments as achieved by the manufacturer under calibration conditions. View Full-Tex