Measurement of mirror inclination angle and distance using LED light sources and PSD

This paper proposes measurements of a two-dimensional inclination angle of a mirror, and its distance to the mirror, using four infrared LEDs that are located around a position sensitive detector (PSD). The light of each LED is reflected by a mirror and focused on the two-dimensional PSD through a lens. This method has many advantages. The mirror´s inclination angle is able to be measured by two LEDs at opposed positions without having to depend on information about the distance to the mirror. Since the LEDs act as point sources of light, it is unnecessary to have to adjust the axis of light. This device has a simple structure, and the light itself is safe since the source is an LED, not a laser light. It was confirmed that the measurement accuracy of the inclination angle was less than 0.5 degrees in a wide range of -10 to 10 degrees and the result was sufficiently satisfied. This equipment can also measure the distance between the sensor and the mirror with an accuracy of 5 percent.