Communications jitter influences on Control loops using Protocols for Distributed Real-Time Sys- tems on CAN bus

The paper focuses on the behaviour of distributed control loops affected by the jitter derived from the communication latencies of CAN. The work proposes a hy- brid communication protocol between a pure TTP (Time Triggered Protocol) and ETP (Event Triggered Protocol) as possible solution in distributed real-time systems as a reactive mobile robot. The proposed hybrid protocol shares the time-slots to reduce the jitter effects. This guarantees fixed transmissions latencies for periodic messages, al- lowing also sporadic messages transmission, as is the case of alarms as well as in long data blocks, by means of using shared TTP slots. The protocol assigns private time slots for real-time messages, and shared time slots for non real-time messages. Also, the protocol uses only a simple and static table. The implementation is validated by means of a quantitative comparison, using the data obtained from a simulation of a typical distributed control system consisting of an industrial process and a remote con- troller forming a closed control loop that uses CAN as its communication channel. In the simulation, the effect of the jitter introduced into the control loop is measured for the above mentioned communication protocols, and the obtained results from this simulation are also discussed.