Simultaneous measurement method of six-degree-of-freedom absolute position and attitude based on light spots

Abstract

This article presents a novel method to simultaneously measure the six-degree-of-freedom (6-DOF) absolute position and attitude based on light spots. The proposed system consists of a measurement unit and a moving target: the measurement unit contains a laser, three cube corner retroreflectors (CCR), three CMOSs, and some beam splitters; the target is a cube with three CCRs installed on each of its three orthogonal planes. In the measurement unit, the laser is split into three reference lights as well as three measured lights which are detected by three CMOSs after returning from six CCRs. Based on the vector analysis of the optical path, the relationship between 6-DOF position and attitude of the moving target and the output coordinates of three CMOSs is established. This method is capable of simultaneously measuring translational motions along as well as rotational motions around three orthogonal axes and achieving the absolute positioning of the target, which has overcome the shortage that the measurement systems based on laser interference can not measure absolute position and attitude. The accuracy of this method has been verified by Monte Carlo stochastic simulation and sinusoidal trajectory simulation in the range of the target's motion. The simulation results show that the errors of position are less than 0.5 μm and the errors of attitude are less than 2.3 ″, which indicates the algorithm error is no more than the minimum pixel size of CMOS. This 6-DOF absolute pose simultaneous measurement method with simplicity and high precision has great potential for application in various precision machining fields.