Accurate extrinsic calibration method of line structured-light sensor based on standard ball

Abstract

In order to implement 3D measurement in different measurement systems with line structured-light sensor, the extrinsic matrix for transforming the position between the structured-light sensor and the measurement platform must be calibrated. An extrinsic calibration method, achieved by measuring the fixed point (the center of a standard ball) of the measuring system with the sensor on the different positions, was proposed. After collecting the images of the line structured-light stripe on the ball, the information of the slices can be extracted by direction template. The coordinate of the ball center in the laser plane frame can be calculated more accurately though image filtration and slice denoising. The extrinsic matrix can be solved by the conjugate pairs, which include the coordinates of both the ball center in the laser plane frame and the sensor in the measuring system. Experimental study was carried out on a four-axis CMM with a ball supplied by CIMCORE, of which the diameter was 25.40145 mm. 203 conjugate pairs were extracted and the extrinsic parameters were calculated. The ball was fitted with the calibrated parameters and the measured point cloud on the ball surface. The average error of the radius calculated was 0.0052mm. This method is simple; it can also be used in non-orthogonal measurement system.