The scope of applications for industrial robots is limited in cases with strong forces at the end effector and high positioning and path accuracies required. Thus, their use in machining applications as a cost-saving, flexible alternative for machining tools is restricted due to mechanical compliance. A model-based off-line concept is presented to analyze, predict, and compensate the resulting path deviation of the robot under process force in milling applications. For this purpose a rigid multi-body dynamics model of the robot extended with additional joint elasticities and tilting effects is coupled with a material removal simulation providing the process forces. After systematically adjusting model parameters, an efficient simulation-based path correction strategy shows significant improvements of path accuracy. The general framework is applicable to any tree structured robots and allows for sensitivity analysis with respect to arbitrary model parameters.
I. MOTIVATIONMajor fields of machining applications for industrial robots are automated pre-machining, deburring and fettling of cast parts or trimming of carbon fiber reinforced laminate. Due to a kinematic structure with usually six axes industrial robots can cover a large working space and are able to reach difficult work piece positions, so that they can be applied to perform complex machining operations. Therefore, compared to standard machine tools, industrial robots on the one hand offer an economic machining while they do only reach a limited absolute and repeat accuracy on the other hand; e.g. the repeat accuracy of the industrial robot used for the research presented in this paper is ±0.06 mm [11].Under high process load, as appears in milling operations, an additional deviation of the tool center point (TCP) occurs. Measured deflections of 0.25 mm under loads of 100 N in earlier tests [2] confirmed the expected compliance, which is resulting from the low structural stiffness of the serial robot kinematics.In milling applications, the effective process forces lead to significant trajectory deviations that are resulting in a variation of the cutting condition at the cutter. Thus, milling with industrial robots is characterized by the strong interaction of the cutting process and the mechanical robot structure. It is observed, that deviations mainly consist of a static offset