Development of a Sensitive Two-Axis Micro-Angle Sensor

This paper presents a two-axis micro-angle sensor for measurement of surface profiles and error motions. The sensor, which is based on the principle of laser autocollimation, employs a laser diode as the light source. The reflected beam from the target surface is received by an autocollimation unit consisting of an objective lens and a quadrant photodiode (QPD) located at the focal position of the lens. It is verified that the sensor sensitivity does not depend on the focal length of the objective lens, which is important for reduction of the sensor size. It is also confirmed that applying an offset to the QPD position along the optical axis is effective for avoiding the influence of the gaps between the PD cells. A prototype micro-angle sensor with a dimensional of 26 mm (W)×22 mm (L)×12 mm (H) is designed and constructed. Experimental results have shown that the sensor has a resolution of 0.05 arc-seconds.