A novel reconstruction method for on-machine measurement of parallel profiles with a four-probe scanning system

We present a four-probe scanning system to reconstruct a pair of parallel profiles which are the foundation of the straightness and parallelism measurement. The system, which is placed between two profiles to be measured and mainly used for on-machine measurement, consists of four displacement sensors. As the scanning stage moves along the profiles, the sensors collect measurement data of both profiles simultaneously. The reconstruction result is obtained by a double differential and a double integral, and the data processing eliminates the influence of the stage motion errors during the scanning. It is known that the zero-adjustment error of three sensors placed abreast in the system causes a parabolic reconstruction error, which can be removed by rotating the device 180 degrees for a second scanning. Using the measurement data of the two scannings, straightness error and yaw error of the scanning motion, as well as the zero-adjustment error can be removed, and the reconstruction result can be utilized to evaluate straightness. In addition, the relative position of two measured profiles can also be calculated, which means the reconstruction result can be used to evaluate the parallelism of them. The new method possesses these following advantages: (i) reconstruction result is affected by neither motion error of the scanning stage nor the zero-adjustment error of sensors, (ii) reconstruction result can be utilized to evaluate both straightness and parallelism of the measured profiles, (iii) zero calibration of sensors is not required. The effectiveness and advantages of this method are demonstrated by theoretical analyses and simulations. And an experimental system was constructed to confirm its ability to eliminate errors.