Measurement of Surface-Normal Using a Range Sensor with a Pair of Wedge-Prisms

We propose a method of measuring not only distance but also surface-normal of an object at several meters away with a single light source. Basically, one light beam source is enough to measure the distance, since the light beam is scanned toward wide area mechanically, however we use a pair of wedge-prisms for the purpose of collecting three distance data within a small surface of the object. That is, we make the light shift a little bit from the original laser beam axis by attaching a driving mechanism to rotate the pair of the wedge-prisms. There is no need to use optical lenses and mirrors for the light shift. This is beneficial to construct a simple device. Firstly we describe the measurement principle of the surface normal by using laser sensor with optical hood for beam shift. Then, we show the usefulness of the method by showing experimental data. It is applied to environmental recognition which is useful to mobile robots, e.g. a wall inclination or a stair layout