Kalman filtering applied to Profibus-DP systems. Multirate control systems with delayed signals

In networked control systems several devices (controllers, sensors and actuators) share a common communication resource. This feature can introduce variable and even random delays when those devices try to transmit information through the shared medium. The limited bandwidth capabilities of the transmission medium also can restrict the freedom to set the sampling periods in the control loop. An attempt to reduce the significance of the signal delays and save to some bandwidth can be based on high values of sampling periods. Usually this solution has remarkable effects in the system performance because with higher sampling periods closed loop response capabilities are decreased. This paper presents a proposal for solving certain type of these problems applying multi-rate techniques on Kalman filters to reduce the data transmission requirements. The overall objective is building a system as close as possible to a single rate conventional system used as starting point and system reference. In this work, an original multi-rate modeling methodology has been considered, achieving successful experimental results on a Profibus-DP based environment and a crane 3D platform. Several experiments have been developed to test control techniques. Some of these experiments have been developed using the Crane under direct control, without the Profibus network in order to avoid some signal delays and skews. The final experiments have been developed with the entire hardware platform, Crane and Profibus network having delays and signal skews present.