Abstract
A major hindrance to dynamics and control of flexible robot manipulators is the deficiency of its inherent damping. Damping enhancement, therefore, should result in lower vibration amplitudes, shorter settling times, and improvement of system stability. Since the bulk of robot vibrations is attributed to joint compliance, it is a prudent strategy to design joints with sufficient inherent damping. In this article, a method is proposed to estimate critical damping at each joint and identify the joint that should be targeted for design with sufficient built-in damping. The target joint identification process requires that a n-joint robot system is divided into n-subsystems. Subsystem i includes the compliance of joint i and the inertia of the succeeding links, joint mechanisms, and payload. An equivalent single degree of freedom torsional model is devised and the natural frequency and critical damping is evaluated for each subsystem. The estimated critical damping at the joints are used to determine the elastodynamic response of the entire robot system from a model that includes joint compliance, shear deformation, rotary inertia, and geometric stiffness. The response revealed the following conclusion: The joint of the manipulator that would result in lower amplitudes of vibrations and shorter settling times when designed with sufficient built-in damping is the one that renders a subsystem whose natural frequency is the lowest of all subsystems comprising the robot.
Dynamic Effects Associated with Joint Compliance in Cartesian-Frame Manipulators