Calibrators can effectively improve the calibration accuracy of articulated coordinate measuring machine (AACMM). However, the traditional calibration method of a calibrator is usually cumbersome. To study the influence of sampling strategies of various calibration methods on the calibration effect of AACMM, we design a new multifunctional calibrator for AACMM kinematics parameters, and propose three calibration methods with high accuracy and high efficiency. In the multifunctional calibrator, 84 different calibration points are provided by changing the rotation angle of calibration bar and the inclination angle of calibration plate. Compared with previous calibrators, the calibrator can obtain more positions and directions. The length calibration, multi-point calibration and virtual center distance calibration methods are proposed to calibrate kinematic parameter of AACMM. In addition, the sampling strategy for the three calibration methods is explored. Finally, the consistency of single-axis coordinate measurement is verified based on the three calibration methods. The results show that the three calibration methods can effectively improve the measurement accuracy of AACMM. Especially, the length calibration method has the highest accuracy of the three methods. The multi-point calibration method can significantly improve the calibration efficiency.

An articulated arm coordinate measuring machine (AACMM) is a kind of instrument used to test workpieces in the industrial field, and its measurement uncertainty depends on the on-site environmental factors to a certain extent. If there is a problem with the AACMM during on-site testing, it needs to be re-calibrated to ensure the measurement uncertainty. In this work, a fast on-site calibration method of the AACMM is proposed using a high-precision CNC machine tool. The AACMM is fixed on the machine tool table. A calibration artifact is clamped on the machine tool spindle. This calibration artifact could move to any point in the global space of the AACMM along with the operation of the spindle. Then, a virtual calibration artifact with calibration points is achieved using the CNC machine tool. The positions of these points are calculated by the improved Hammersley sequence. The calibration method using a high-precision CNC machine tool is experimentally verified through the single-point articulation performance test of ASME B89.4.22-2004 and the length measurement test of ISO 10360-12. The calibration method proposed in this work only uses an on-site high-precision CNC machine tool, one of the common machines in many industrial fields, as the calibration instrument for the AACMM calibration. No extra equipment is required, which is convenient and beneficial to calibrate the AACMM. And the CNC machine tool could construct different kinds of virtual structures for the AACMM calibration, such as virtual rods, virtual circles, virtual balls, and even non-uniform three-dimensional artifacts with complex curved surfaces. This may arouse many novel calibration methods and further improve the calibration accuracy.

Articulated Arm Coordinate Measuring Machines (AACMM) are usually used to measure mechanical parts of different sizes in practical applications. When the size of parts is smaller than that of the AACMM, a redundant measurement space of the measuring machine is generated, resulting in reduced measurement accuracy of the AACMM. Moreover, due to the series structure of the AACMM, the joint errors would be propagated with the increasing length of the bar, which could amplify the measurement error. Therefore, on the premise of ensuring the measurement space required by the measured parts, this work proposes a new method based on variable measurement space, i.e., locking some movable joints of the AACMM, to improve the measurement accuracy of the AACMM for small mechanical parts. The measurement accuracy of the AACMM is examined under various measurement spaces. Firstly, the Monte Carlo method is used to simulate the measurement space of the AACMM with one or more joints locked. Then, the spatial error of the AACMM and the multipoint calibration with joint locked are simulated and discussed in detail. Finally, the feasibility and effectiveness of the proposed variable-measurement-space method are verified by the standard single-point cone experiments. The results show that the measurement accuracy of the AACMM is substantially improved under three kinds of strategies, i.e., locking joint 1, joint 2, and joint 3, respectively.