A simultaneous calibration technique of the extrinsic and turntable for structured-light-sensor-integrated CNC system

Abstract

The center of the mandrel-target is unique and does not get affected by the extrinsic angle of the projector. On this basis, a mandrel-target-based method is described to simultaneously calibrate the extrinsic parameters and the turntable of a multi-axis, structured-light-sensor-integrated, three-dimensional (3-D) scanning system. Besides, a cross-section-arc algorithm is developed to identify the conjugate pair. By computing the mandrel-center in the light plane, some collinear scanning points are generated along with the spindle scanning. Further, these calibration points are employed to the tip-tilt self-calibration of the turntable. In the two-scanning strategy, three sets of non-colinear points are derived simultaneously by relatively moving the sensor at distinct world coordinates. These generated points are fulfilled to calibrate the extrinsic parameters with the relative motion model. By determining the direction vectors, the skewed sensor coordinates are converted into the Cartesian world coordinates. The effectiveness of the proposed method is verified using a set of experiments. The accuracy of the proposed model is justified by comparing it with the measurements of a CMM trigger probe. The absolute measurement accuracy for a mandrel-target (about 7.4827 mm in radius and 16 mm in depth) is 0.002 mm. The target is cost-effective and simple in shape. The calibration procedure is easy to carry out and highly accurate.