Curvature Identification in a Prismatic Joint of a Robot Using Gyroscopes Based Dual Quaternions Processing

Abstract. This paper shows a solution to measure the curvature of a rail-guide in which a robot manipulator moves. Such robot, denominated Roboturb, is destined to welding tasks in rotors of high power hydraulic turbines damaged by cavitation effect. This robot has as mainly characteristics the fact of presenting small load (total mass of 20kg), high mobility level due to its seven degrees of freedom and, it has one of the joints in the form of a curvilinear rail with undefined geometry. The influence that this rail curvature impose on paths executed by the robot is analyzed. Tthis is decisive to Roboturb operate because without rail coordinates knowledge is impossible any precision movement. The principles of solution includes a way to obtain 1-axis angular displacement from angular rate gyroscope information; a formulation to derive complete 3-axis angular orientation from two gyroscopes only; and a algorithm to represent the rail profile using dual quaternions. At the end some practical results are show. The implementation was developed in Labview software, and has used two technological kinds of gyroscopes: FOG (fiber optics gyros) and crystal micromachined gyroscopes. With a laser pointer installed on the robot hand and fixed in a target, the robot runs along rail. So, with the profile information (acquired with the measurement system proposed) was possible minimize the orientation error to 40 arc-seconds maximum value.