Hysteresis curve model of precision reducers in robots and its application in lost motion evaluation

A precision reducer is the core component in an industrial robot and its performance largely determines the performance of the whole robot. Lost motion is the key index to characterize the performance of precision reducers and its measurement and evaluation are the basis for improving the performance of precision reducers. However, some problems in the lost motion measurement still remain to be solved, such as the large error introduced by curve fitting. In this paper, aiming at the disadvantages of traditional measurement scheme, the measurement scheme of lost motion is optimized. A closed hysteresis curve can be obtained by single loading-unloading cycle. The hysteresis curve model of a precision reducer is established based on the consideration of the coupling effect of nonlinear stiffness and friction. Based on the established hysteresis curve model, the evaluation method of lost motion is proposed and named median curve method. Compared with the traditional evaluation method, this method essentially reflects the change rule of hysteresis curve and can improve the measurement accuracy. Taking the RV reducer as an example, the measurement experiment was carried out. The measured results were consistent with the sample index, verifying the applicability of the measurement scheme and evaluation method.