Condition Monitoring by position encoders

Detecting damages in machinery before they lead to a complete system failure is an important aim in modern machine maintenance and diagnostics. Early and automated detection of damages in gearboxes allows for longer maintenance intervals, less downtime and lower total costs. One mechanism of gear failure is the occurrence of pitting on the flanks of gear teeth. Pitting progress leads to a change in the noise excitation behaviour of the gear mesh. Common condition monitoring devices rely on acceleration measurements on the gearbox housing. Angular position encoders are capable of providing precise data on transmission error, but work preferably at low rotational speeds. Transmission error is widely used to characterize the tooth flank form. It is a challenge for measurement instrumentation to record and process precise encoder signals sufficient for detecting beginning flank damage at high rotational speeds. An FZG spur gear test rig used for gear pitting tests was equipped with angular position encoders and data acquisition units. This sensorial equipment is capable of performing synchronous, high-frequency combined measurements of angular positions of the shafts and acceleration signals on the gear housing. A detailed evaluation shows that an early damage detection with position encoder signals is possible.