Automatic detection of clearance in mechanical systems: Experimental validation

The performance of servosystems with gears (e.g. machine tool drive systems) depends on the clearance or backlash between the gear teeth. Too little and the gears cannot accommodate lubrication and manufacturing errors. Too much and the system accuracy and stability degrade. Therefore, to ensure that a machine system with gears is operating within specifications, the backlash magnitude should be checked frequently. A technique to estimate the backlash automatically is required. The objective of this paper is to evaluate experimentally a clearance detection technique, previously published by the authors, to detect backlash in a servosystem with gears. The technique estimates the backlash by computing the speed variations induced into the primary gear speed by the gear tooth impacts caused by exciting the system sinusoidally. It is shown that a low-cost conventional tachometer is sufficient to measure the induced speed variations. The estimates are shown to represent accurately the actual backlash for ranges +/- 100% of the recommended backlash setting. In addition, by exciting the system with a sinusoid having a DC offset, it is shown that, in a simple one step automatic procedure, the backlash can be averaged over all the gear tooth combinations or computed for individual gear tooth pairs. The results, along with the previously developed theory, indicate that this clearance detection can be inexpensively applied to many machine systems. (C) 1996 Academic Press Limited