Optical tilt sensor

An optical tilt measurement apparatus for use in measuring a tilt angle of a flat reflective surface around a pivot axis, the optical tilt measurement apparatus comprising:

• an optical tilt sensor for use in sensing a tilt angle of a flat reflective surface around a pivot axis, the optical tilt sensor comprising:
• an optical emitter arrangement for emitting at least three beams of light so that each emitted beam of light is incident on, and reflected from, the flat reflective surface to form a corresponding reflected beam of light;
• and
• an image sensor having a sensor area for detecting an intensity distribution of each of the reflected beams of light and outputting one or more signals representative of the detected intensity distribution of each of the reflected beams of light,
• wherein the at least three emitted beams of light are emitted along at least three corresponding different emission paths, each emission path extending from a corresponding emission point along a corresponding different emission direction,
• wherein each emission direction has a different known orientation relative to an orientation of the sensor area of the image sensor,
• wherein each emission point has a known spatial relationship relative to each of the other emission points, and points,
• wherein the optical tilt sensor is arranged relative to the flat reflective surface so that each emission direction defines a corresponding known angle relative to the pivot axis, and
• wherein the optical tilt measurement apparatus further comprises a processing resource configured to:
• receive the one or more output signals from the image sensor;
• determine, from the one or more received output signals, a position of each of at least three intensity peaks on the sensor area of the image sensor, each intensity peak corresponding to the peak intensity of a corresponding one of the reflected beams of light when incident on the sensor area of the image sensor;
• determine a spacing of a first pair of the at least three intensity peaks on the sensor area of the image sensor;
• determine a spacing of a second pair of the at least three intensity peaks on the sensor area of the image sensor;
• and
• determine the tilt angle of the flat reflective surface around the pivot axis based at least in part on the different known orientations of the different emission directions relative to the orientation of the sensor area of the image sensor, the known relative spatial relationship between the emission points, the different known angle of each emission direction relative to the pivot axis, and the determined spacing of the first pair of intensity peaks and the determined spacing of the second pair of intensity peaks.