Design and analysis of 3-DOF cylindrical-coordinate-based manipulator

Abstract

Abstract The joint-type six-degrees-of-freedom (6-DOF) manipulator fulfills many complex motion and industrial operations, but does not need so much freedom in many practical situations. For example, the mechanical arm operations of stamped work-piece feeding and the automatic process of picking and placing work-pieces on the conveyor belt only require three translational degrees of freedom. In this study, the principle of the cylindrical coordinate mechanism is used to design a mechanical arm with one revolute pair and two prismatic pairs, meeting the low-cost, small volume, and specificity requirements of practical applications. This article analyzes the size-synthesis problem of the 3-DOF mechanism and optimum design of the cylindrical coordinate mechanism according to various constraint conditions. The direct and inverse kinematics equations of the manipulator are established, and the dynamic equations of the manipulator are derived using Lagrangian methods. Using the minimum weight principle of mechanical design, this paper discusses a modular design method and the optimum structural design of the manipulator, and applies a design scheme for an elastic spherical pair to compensate for the displacement and deflection errors between the motor driving shaft and the slider motion along the guide. The structural strength and stiffness are calculated using the finite element method. Through the application of a planar machine-vision system, the profile of the work-piece can be identified and positional coordinates located synchronously during the robot manipulations. The kinematic calibration method of the manipulator system is studied using a genetic algorithm, and the mathematical calibration equations are established. Experimental studies on the mechanical reliability, positional accuracy, and calibration application of a mechanical arm prototype are carried out. The experimental results show that the selected stepper motor has sufficient driving ability in the process of manipulating the work-piece, and the repeated positioning errors after the calibration satisfy the design requirements of the manipulator.