Rearch On Networked Control Systems Based On CAN Bus

Network scheduling plays an important role on the performance of Networked Control Systems (NCS). A reasonable scheduling algorithm can improve the network utilization and the performance of the control system. This paper proposes a kind of closed-loop scheduling algorithm, which adjusts the basic sampling period of node according to network condition and implements the closed-loop control to the network utilization.Rate Monotonic (RM) algorithm distributes the priority according to the period of the tasks. Earliest Deadline First (EDF) algorithm dynamically distributes the priority according to the deadline. Mixed Traffic Scheduling (MTS) algorithm makes full use of both. Because the MTS algorithm distributes the priority through the signs, it can not solve the problem of the excessive delay when many messages are sent at the same time. In this paper, an improved MTS algorithm is proposed.The closed-loop scheduling algorithm combines the feedback control theory with the scheduling algorithm. It analyses and builds the scheduling model of networked control systems with the control theory and maintains optimal performance through adjusting the regulator continuously. A closed-loop scheduling model is designed in this paper. It supposes that the network is the controlled variable, and the basic sampling period is the control variable, which controls the quantity of the messages through the network by adjusting the basic sampling period of task. The TMS320F2812 of TI's DSP chip brings with an enhanced CAN controller, which has the fixed time mail delivery function and the overtime function. This paper makes some experiment on the DSP to run closed-loop scheduling algorithms. The network condition can be detected by the fixed time mail function. Overtime function can be used to improve the MTS algorithm. Experimental results show that the design of the closed-loop scheduling algorithm can be realized.