Calibration and uncertainty evaluation of double parallel-joint coordinate measuring machine

On the basis of advantages of ScanMax measuring machines at abroad,a double parallel-joint Coordinate Measuring Machine(CMM)with a RRP structure(two rotation movements and a line movement)was developed,and its error model,calibration method and uncertainty evaluation was investigated.Firstly,the mathematical model and error model was established according to the mechanical structure of the double parallel-joint CMM.Then,the calibration scheme was designed based on the total error analysis,and calibration methods of the parameters such as gravity,torque deformation,parallelism,arm length,null were introduced.Finally,based on the national Calibration Specification for CMM,a evaluation method by measurement repeatability and the precision of length measurement to evaluate measurement uncertainty was proposed.The experiments by proposed method show that the measurement uncertainty of double parallel-joints CMM can reach 12μm(k=2)in a measurement range of 1 000 mm×250 mm(diameter×height).It is proved that both doubleparallel-joint coordinate measuring technique and total error analysis technology are feasible.It explores a new way to calibrate non-orthogonal CMM.