Assessment of industrial robots accuracy in relation to accuracy improvement in machining processes

Using standard 6 DOF industrial robots for machining applications represents a significant market potential. Industrial robots have become a tool for various machining processes due to its universality - an ability to perform any type of movement in space - and low price compared to CNC milling machines. However, there are still limitations concerned with a much lower absolute accuracy, in comparison with CNC machines, caused mainly by a low static stiffness of the whole serial kinematic chain of a 6 DOF robot. Using the robots for machining is rather limited to applications with lower geometrical accuracy. To expand a possible scope of applications into milling operations, a new methodology is proposed to address the problem of lower absolute accuracy and concerned with KUKA robots. First, an experimental investigation of sources of main errors, having the impact on the product accuracy and surface quality, is presented. In this paper, we also focused on a comparison of internal robots states (actual robot positions) with measurements obtained from external systems such as Ballbar and Laser Tracker systems. Based on this investigation focused on KUKA robots, an online method for compensating the main source of errors - backlash errors resulting from the drive reversion - is proposed.