Calibration of an Eye-to-Hand System Using a Laser Pointer on Hand and Planar Constraints

Abstract

This work proposes a technique for calibration of an eye-to-hand system. The target of the hand-eye calibration is to estimate the geometric transformation between the hand and the eye. This calibration method further considers camera intrinsic parameters and geometric relations of a working plane in space at the same time. A laser pointer casually mounted on the hand is utilized. By manipulating the robot and projecting the laser beam on a plane of unknown orientations, a batch of related image positions of light-spots are extracted from images of the camera. Since the laser is rigidly mounted and the plane is fixed at each orientation, the geometric parameters and measurement data must obey a certain nonlinear constraints and the solutions of parameters can be estimated accordingly. A close-form solution is developed by decoupling the nonlinear equations into linear forms to compute all of the initial values. As a result, the calibration method does not need any manual initial guess of the unknown parameters. To achieve a higher accuracy, a nonlinear optimization method is implemented to refine the estimation. The advantage of using laser pointer is that this technique can be used for the case when the eye does not see the hand. Experimental results of simulations and real data are presented to show the validity and the simple requirements of the proposed algorithm.