Safety functions of automated mobile work machines

In the near future workers, manually driven mobile work machines and automated mobile machines may be working at the same time in large worksites. It is difficult to arrange adequate safety for workers while the production interruptions need to be minimised. This paper presents an idea of a toolbox, which helps the designer to create a safety system by applying suitable safety functions dynamically according to the existing risk. Typical safety functions are presented including stopping functions, reduced speed, movement towards safe direction, restricted area and dynamically changing safety distance. The user can invent other safety functions too, but then also the corresponding safety requirements need to be determined. The main goal is to keep the distance between persons and moving mobile work machines all the time longer than the stopping distance.
Another aspect is how the safety system can apply uncertain information received from sensors. Current sensors, which have adequate detection range, are not reliable enough and therefore additional measures are required to compensate the uncertainty of information. Several sensors and methods for detecting the position of a person are needed and all uncertainty or disparity in information increase the safety distance between a person and the machine. Complete stopping of the machine is tried to be avoided even under malfunction of the system. For example manual limping mode offers limited performance, but it is adequate to drive the machine out of a dangerous place.
When there is both manual and automated driving in the production site, it is essential to consider the responsibility of each party. Basically, automation is responsible for safety in automated drive and humans in manual drive. However, automation has always the major responsibility when it is applied. The automation and the safety system may be considered to be responsible for accidents caused by malfunction of machines or even foreseeable human mistakes.