Mechanically Induced Path Deviations in an Industrial Parallelogram Robot

The influence of the mechanical structure of an industrial parallelogram robot (the GMF S215 robot) on its path accuracy is studied. A computer program has been developed to analyze the dynamic behavior of the manipulator in a vertical plane considering mechanical compliance and damping as well as motor torque limitation. The compliance sources are assumed to be located in three joints in the form of unidirectional translational and rotational springs introducing three additional DOFs; for each of these DOFs, Lagrange equations of motion are derived using MACSYMA and solved using an advanced continuous simulation program (ACSL). Experiments have been performed in order to measure the tip trajectory of the robot as well as displacements of the transmission elements. When the trajectory generation errors were also simulated, an excellent correlation between these tests and the computer simulation results was obtained. This allows to identify the influence of various factors on the overall path inaccuracy.