Optical Triangulation Range Sensors

The close range manœuvres of an autonomous vehicle such as obstacle avoidance, parking and docking require range sensing which is robust, high bandwidth and accurate at short ranges. Range sensors based on active optical triangulation are currently among the best means of realising these requirements. Although the geometric principle of sensing is simple and proven, it is not obvious, for a given application, what sensor configuration will give the best performance. This is because there are a large number of performance trade-offs to be dealt with which interact over the boundaries of optical, mechanical and electronic sensor design. This chapter is mainly practical in content and is divided into two main parts: The first part (sections 6.2 to 6.4) describes, in general terms, the design choices and trade-offs which must be confronted when developing an optical triangulation range sensor. The design options for optical source, image detector, and means of scene coverage are detailed in the context of the performance requirements of a given application. The second part of the chapter (sections 6.4 to 6.8) is more specific and deals with a short range design (maximum range 2.5m) for close range vehicle manœuvres which has been implemented within the Oxford AGV project. The optical, electronic and mechanical design of the sensor is described and subsequently its performance is characterised using least squares on logarithmic plots to estimate intrinsic sensor parameters. This is necessary both to assess the success of the design and to apply