Repeatability analysis of a SCARA robot with planetary gearbox

Repeatability is one of the most important features of an industrial robot. It is a key feature stated by commercial robot manufacturers. Details of repeatability calculation method for industrial robots is presented by ISO 9283. However, the well-known robot manufactures do not state how they calculate their repeatability. In this paper, the industrial FUM SCARA robot, designed by the Ferdowsi University of Mashhad in Iran, is used and its repeatability is measured according to the ISO 9283 method. Planetary reducers are applied as a part of the power transmission system. Although planetary reducers have pre-defined backlash, experimental results show satisfactory repeatability for the FUM SCARA. An ideal and intelligible mathematical model of backlash is developed to show the low effect of backlash in the repeatability calculation. Consequently, it is shown that the result of ideal backlash model corresponds with the experimental result.