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".
A measurement method of two-dimensional small-angle is proposed in this paper. This method is based on laser diodes,
dual-axis charge coupled devices (CCD) camera, and a series of reflections between two first-surface mirrors.
Measurement accuracy is improved as the laser beam is reflected back and forth several times between the mirrors.
Analytic ray tracing is used to model the reflected light ray so as to determine the system equations implicitly in terms of
the measured angles. A 2-dimensional high-precision tunable plane mirror is used to simulate the deflection angle. The
real-time position changes of the laser spot on the tunable plane mirror are recorded by means of CCD camera; and the
position coordinates of all laser spots in pictures are obtained by digital image processing methods and sub-pixel
weighted centroid algorithm. According to the centroid coordinate changes of laser spot, the deflection angle of the
measured object is obtained. To validate the system, a prototype is built. Calibration and stability experiments are
performed. Experimental results show that the resolution, accuracy, and measurement range are, respectively, 0.02, 0.1,
and 720 arc sec.
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