Use of a Structural Model in Compensating for Robot Deflections

Summary A robot with six revolute axes and DC drives was investigated. Using impact excitation a spring, sass, dashpot model was established comprising nine concentrated flexibilities and four masses. Most of the flexibilities are found in mechanical transmissions of the drives. Two of the drives (shoulder and elbow) include these flexibilities within the position loop; the corresponding deflections are completely eliminated after a transient of about 2 sec. The lowest structural natural frequencies are about 10 Hz and one of the modes is very lowly damped, ζ = 0.014. This low damping is the main obstacle to increasing the gain of the servos. The transient errors are, however, not considered serious for most applications. A scheme is designed to compensate for static deflections in routing sheet metal aircraft parts.