Measuring robot repeatability an application of ISO and ANSI standards

Abstract

The paper presents the results of a study in which warm-up and repeatability characteristics of an industrial robot were measured. To facilitate the study, two commonly available draft standards aimed at evaluating the performance of robots were employed as case studies; in particular, ISO 9283 and ANSI/RIA R15.05. As a result, a comparison of the standards is made and areas that need improvement are revealed. In order to implement the proposals, two measuring systems capable of recording robot repeatability with varying degrees of accuracy are introduced. As they do not specify the type of measuring system to be used, the consequence of implementing the two systems will reveal significant differences in the results obtained. Here, simulation results, along with experimental results, will demonstrate how the calculated value of repeatability varies as a function of measurement error. Also, the required number of cycles to capture long-term repeatability is investigated. Here, it is found that as many as 250 cycles may be required. Finally, the effect of varying the ambient temperature during testing is examined. Results show that changes of as little as 2°C can significantly affect robot end-effector positioning characteristics.