Calibration analysis of a direct drive robot

A software-based calibration method is developed to decrease the positioning errors of a SCARA assembly robot caused by static deflection of the robot arm under force and moment load. A robot stiffness model is constructed and used to calculate differential joint angle corrections which are then applied to the inverse kinematic solution of the ideal robot model to compensate for the static deflection errors. Least squares polynomial approximation and a neural network are used for storing the joint correction values and for interpolation. A computer simulation of the calibration method demonstrated a decrease in the average positioning error from 0.43 mm to 0.03 mm and in the range of error from +or-0.35 mm to +or-0.10 mm in the calibrated area. >