Computers and electronics in agriculture vol:49 issue:2 pages:233-245
Some recent commercial combine harvesters are equipped with a Controller Area Network (CAN) system. This is a serial communications protocol which efficiently supports distributed real-time control with a very high level of security [Bosch, R., 1991. CAN Specification Version 2.0. Robert Bosch GmbH, Stuttgart, 70 pp.]. A new software platform ‘CANbus Control Design Interface’ was developed and evaluated for control design for combine automation. This tool offers new possibilities for experimental design and provides a real-time graphical interface for the control engineer. The software module permits the exchange of the desired sensor and actuator signals between the CANbus network and a measurement computer at a sample rate of 5 Hz. Several control design experiments have already been integrated in the CANbus Control Design Interface environment. The synergy between two programming languages, Visual C++® and Matlab®, characterizes the developed software module.
A standard Windows environment was used as the operating system. The timing of the different measurement and control tasks was performed by two timing protocols, the Windows and the Multimedia timer. This study addresses the question of whether a standard operating system like Windows can be used for control experiments within the combine automation framework.
Experiments have shown that it is possible to use Windows as an operating system for soft real-time applications under certain conditions. The control environment of a combine harvester can be considered as a soft real-time environment because the occurrence of time jitter or the failure of an event will never lead to the failure of the whole control system. By making use of a standard Windows NT-XP environment, a robust and accurate 5 Hz timing performance was achieved.