Geometric Model Identification of a Serial Robot

Robots find their applications in various fields and are used to perform repetitive and adaptive tasks very accurately. This requires exact kinematic parameters of the robot. Generally, for a serial robot, these parameters are represented using the Denavit-Hartenberg (DH) parameters, whose nominal values are provided by the robot manufacturers. In this paper, a technique is proposed to determine the exact DH parameters of a serial robot. For this, each joint of the robot is rotated while the others are locked. Hence, the end-effector moves in a circle, which can be measured using external measurement devices, say a theodolite, a vision system or a laser scanner. From these measurements, the axis and center of the circles traced by the points are determined. If the joint axes are represented using dual vectors, the exact DH parameters can be extracted with the help of Dual Vector Algebra proposed here. The proposed technique has an advantage that it does not require any calibration of base frame of the robot with the measurement frame. Since, the technique allows one to determine the exact DH parameters at the site of installed robot, the robot need not to be taken to a separate calibration section. The proposed measurement methodology is simulated in a CAD software environment using the CAD model of a KUKA KR5 robot.