Three-dimensional angular measurement based on moiré fringe

The conventional angular measurement method based on moiré fringe is only competent to measure one-dimensional angle. The grating is replaced by combined horizontal and vertical gratings, therefore the yaw and pitch angles can be measured at the same time by figuring out the displacement of the vertical and horizontal moiré fringe. Moreover, when the main grating is adhered to the mirror which is rigidly attached to the measurement target, the roll angle can be measured by obtaining the width change of the moiré fringe. To validate this improved method, an experimental verification system is set up. The moiré fringe images are captured by a CCD detector, and then the width change and displacement of moiré fringe are obtained using image processing technology. Experimental results indicate that in a view field of ±30' the yaw and pitch angles measurement precision reaches 0.5" and the roll angle measurement precision reaches 1.5".