Development and evaluation of a straightforward method to identify the elastic structure of a lightweight robot

Lightweight serial robots are highly suitable for tasks with human interaction. The low mass contributes to inherent safety properties due to lower inertial forces and torques. However, the slender structure makes such robots more compliant, which leads to higher deflections under load. This work introduces a straightforward method to identify the elastic parameters of a lightweight robot. The virtual joint method was used for elastostatic modelling of the robot. For the parameter identification process a set of robot poses was defined by a combination of two different angular positions for each of the seven joints. At each pose the robot was deformed by using a constant load and the resulting deflection was measured using an optical 3D localizer. Based on this data the unknown parameters of the elastostatic model were calculated. Finally, the accuracy of the elastostatic model was evaluated by implementing a compliance error compensation algorithm. Experimental evaluation with a loaded robot in a set of application oriented poses show an average improvement of the static position accuracy of about 65 %. The largest uncompensated deflection was 9.4 mm at a load of 20 N which could be compensated to 0.9 mm.