University of Twente Student Theses


Increasing deterministic behavior of mobile robots by adding a safety layer

Bruijn, M.N. (2019) Increasing deterministic behavior of mobile robots by adding a safety layer.

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Abstract:Tele-operated mobile robots have a potentially high value for emergency services. Mobile robots can aid in observations and act in place of humans in dealing with unsafe situations. However, mobile robots can currently show non-deterministic behavior after onboard failures, resulting in mission failure or unsafe situations. Non-deterministic behavior of a mobile robot implies that the robot expresses random behavior that does not match the operator’s expected response. Operators require the mobile robots to behave deterministically at all times, even after onboard failures. If this requirement is met, overall support for using mobile robots will increase, fewer emergency operations will fail and dangerous consequences will be prevented. In this thesis, I will research how to increase deterministic behavior of mobile robots by implementing a safety layer. The safety layer is modeled analogous to safety layers used in critical chemical processes, in which a safety layer is added that shuts down the process after detecting failures. This gives the operator time to eliminate dangerous behavior and mitigate failures. Inspired by this principle, the safety layer detects onboardcomputer failures using a watchdog onboard the mobile robot. Once the failures are detected, the safety layer is responsible for taking over the robot’s controls, stopping all movement, and eliminating non-deterministic behavior using its GPS sensor and compass. Emergency services utilize different types of mobile robots. Therefore, the safety layer is designed to be generic so that it can be implemented on any mobile robot. After implementing and testing the functionalities, the effect of the safety layer on a mobile robot is determined. This is done by estimating the probabilities of negative consequences and yields the safety layer’s effect on the deterministic behavior of the mobile robot. By implementing a safety layer, the deterministic behavior of a mobile robot is increased. The safety layer mitigates onboard failures. This includes onboard-computer failures, to which protection is currently complex. The safety layer is tested for 25 continuous hours, in which a failure was introduced every 30 minutes. The safety layer caught all failures and resolved them without false positive or false negatives. The estimation shows that the safety layer increases the deterministic behavior by 23.6% for the mobile robot at the University of Twente.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Embedded Systems MSc (60331)
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