The synchronization of loosely coupled motion control systems: Dissertation

The aim of this thesis is to create an easily implemented, effective, dynamically schedulable flow control method, and to show how the methods indroduced can be analysed using fixed priority scheduling. One ofthe most important problems in a distributed system is the delay and variation of it (the jitter) caused by a serial based network, especially when media load is relatively high. This thesis has looked for possibilities to implement a deterministic motion control system which can also operate with high media loads. The problem of end-to-end delay in distributed control systems has been addressed. The most promising ones are based on the two window concept, where critical messages are transmitted in the statically scheduled part of window while other, non-critical messages are transmitted in the remaining part.The concept of the chained link is indroduced and it is shown how the latency time of a certain set of messages can be controlled. It has been shown that the two window concept is possible to implement using a chained link. This thesis has indroduced the detailed characteristics of this easy-to-assemble chain which is simpler than time or sync-message based methods used commercially. One benefit is that only those nodes needing synchronization must support synchronization tasks. Other nodes are exempt from supporting unnecessary functions, making system programming easier. The chain can be scheduled dynamically as one long message. The benefit of the method indroduced is that, in spite of a chain, the system is open i.e. all other nodes (non-chained) can operate as before. The chain can be scheduled using a deadline- or rate-monotonic approach. The concept of a CAN based producer-consumer method, a statical scheduling method which can be used with a bus-master has been indroduced. The benefit of a bus-master is that the entire system (transmitted messages) can be controlled from one place. The drawback of this method is increased media load. The producer-consumer method is possible to implement effectively using the remote-request procedure of the CAN protocol. A hydraulic mobile is used as a practical example for analysing and comparing the indroduced distribution and flow control methods. As the number of distributed nodes and media load increases in the future, the method indroduced can be used to guarantee the deterministic operation of real-time systems so that all timing constraints will be satisfied. This work has shown that a deterministic distributed control system for high media loads can be implemented. This method as indroduced can be used with commercial components and is thus suited for immediate use.