US Patent 7412905 Paddle sensor

A rotary paddle sensor for detecting a substance. A paddle or paddles are mounted on a rotating shaft coupled to a motion of the shaft by a slip clutch mechanism. The sensor detects movement of the paddle. If a substance impedes the movement of the paddle, the sensor detects this occurrence. The sensor can be used for many different applications, such as to detect the level of material in a bin, to determine the distance to a wall, to determine the height from the ground, to detect the boundary between two surfaces such as mowed or unmowed vegetation, or to detect the vegetation in a row.