Automatic detection of gear backlash in servo mechanisms.

Abstract

Machine and product condition monitoring is important to product quality control, especially for unmanned manufacturing. This dissertation proposes a technique for the detection of clearance in mechanical systems under dynamic conditions with specific application to detecting backlash in gear systems of servomechanisms. The technique is based on a momentum transfer analysis that shows that the change in the speed (defined as the bounce) of the primary gear due to impact with the secondary gear is related to the magnitude of the backlash. The bounce can be retrieved by an algorithm developed in the dissertation, and called standard bounce. It is proposed that the standard bounce, determined by the standard deviation of the demodulated envelope of the speed of the primary gear, is a good measure of the bounce when the system is excited harmonically. The algorithm is verified through computer simulation and experimental validation of an open loop DC servosystem. An approximately linear relationship between the mean bounce and the backlash magnitude is observed. This holds for backlash values exceeding recommended tolerances by $\pm$100 percent. The technique appears promising for the automated detection of gear backlash.