This article describes an optical method for measurement of three-axis angles (roll angle ΔθX, pitch angle ΔθY, yaw angle ΔθZ). The laser autocollimation method is improved from two-axis angle measurement to three-axis angle measurement by employing a diffraction grating instead of a plane mirror as the target reflector. The three-axis angle components can be calculated by three methods of using different diffraction light spots reflected from the diffraction grating. Method 1 uses three beams, which are the 0th-order and the ±1st-order diffraction light spots. Both Method 2 and Method 3 use two light spots. The former uses the ±1st-order diffraction light spots and the latter combines the 0th-order with the +1st-order or the -1st-order diffraction light spots. A prototype three-axis angle sensor is also designed and fabricated to compare the characteristics of the three methods from the viewpoints of sensitivity, linearity and resolution of the sensor output.
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