Guaranteeing Functional Safety: Design for Provability and Computer-Aided Verification
In Autonomous Robots, Springer, volume 32, number 3, pages 303-331, Apr/2012.
When autonomous robots begin to share the human living and working spaces, safety becomes paramount.
It is legally required that the safety of such systems is ensured, e.g. by certification according to relevant standards
such as IEC61508. However, such safety considerations are usually not addressed in academic robotics. In this paper
we report on one such successful endeavour, which is concerned with designing, implementing, and certifying a
collision avoidance safety function for autonomous vehicles and static obstacles. The safety function calculates a safety zone
for the vehicle, depending on its current motion, which is as large as required but as small as feasible, thus ensuring
safety against collision with static obstacles. We outline the algorithm which was specifically designed with safety
in mind, and present our verification methodology which is based on formal proof and verification using the
theorem prover Isabelle. The implementation and our methodology have been certified for use in applications up to SIL3
of IEC61508 by a certification authority (TÜV Süd Rail GmbH, Germany). Throughout, issues we recognised as
being important for a successful application of formal methods in robotics are highlighted. Moreover, we argue that formal
analysis deepens the understanding of the algorithm, and hence is valuable even outside the safety context.
Collision Detection; Functional Safety; Formal Verification; Certification; IEC 61508; Braking Model; Mathematical Proof