Autocollimator, Electro Optical, Basic
Wednesday, August 30, 2006
An Electro-Optical Autocollimator provides a continuous output voltage, whose sign (direction) and amplitude (distance from null or any chosen position) is directly proportional to the angular displacement of a target mirror.
An Electro Optical Autocollimator projects an image of a small point light source focused at infinity and reflected of a target mirror onto a photodetector instead of a human eye, as in a Visual Autocollimator. Greater angular resolution, accuracy and repeatability can be obtained with amplified electronic readouts and automatic data processing, than with the human eye.
An Electro-Optical Autocollimator can use a high-power IR LED to generate a light beam. The light beam is emitted through a beam-splitter and collimated by the Autocollimator lens. The collimated light beam reflects off a target mirror and returns through the collimating lens back to the beamsplitter and photodetector. The photodetector can measure the position of the focused light beam spot by an electrical measurement output to determine the angular position change of the target mirror. The focal length of the Autocollimator lens determines the sensitivity and angle of coverage, in combination with the photodetector characteristics. A filter is used to reduce (minimize) the influence of ambient light.
An Electro-Optical Autocollimator can use a two-axis photodetector for continuous simultaneous two-axis angular positioning. The two-axis photodetector acts as a pair of light-controlled variable resistors for measuring the position of a light spot on its X and Y coordinate axes. The Autocollimator angular coverage can be as small 0.025 radians with a resolution of 5 μ radians. A quadrant photodetector can be used for centering or nulling applications with an achievable resolution of better that 1 μ radian.
Source: Sensors, December 1988
Reference:
1) “Optical Alignment”, by Thomas H. Thurston, SPIE Proceedings, Volume 251, 1980;
2) Ian K. Edwards, United Detector Technology, Orlando, FL
Industrial Products
posted by JD52 @ 8:11 PM,
