Trepel (Germany) uses in its Challenger 700 tractors CAN connectable panel PCs by Janz Tec (Germany). These vehicles are able to handle pushback, maintenance towing and repositioning of any commercial aircraft, up to the Airbus A380, and almost every military airplane. The panel PC substitutes the usual controls and instruments. It is the main controller and the display of all relevant data.
TWO PROGRAMMABLE MOBILE CONTROLLERS ARE installed at different places. One is located in the driver´s cabin, the other in the middle of the tractor next to the main hydraulic system. Six CANopen devices are used to get the information from the binary switches and the analog sensors. They also drive the hydraulic valves, which are spread all over the machine. Some programmable µPLC´s are working with CAN layer-2 (they are used for add-ons) communication system.
The diesel-engine and the transmission use for data exchange a CAN network running the SAE J1939 protocol. As you can imagine it is not easy to recover a huge vehicle with a weight up to 70 t. Therefore, the system has been designed this way to ensure the utmost reliability.
The devices are connected to six different CAN networks in order of their function and because of the different protocols used. Another reason is to maximize the immunity of the system against failures. Even if one CAN network breaks down, all the others keep on working and the tractor can be operated with a minimum of limitations. This, and the fact that there are some sorts of other emergency strategies, is very important for a highly reliable machine.
One CAN network is reserved just for customer devices such as fleet management solutions etc. Here almost every customer´s requirement can be fulfilled, no matter if it is CANopen, SAE J1939 or CAN layer-2 protocols. Different bit-rates are possible as well. Another CAN segment is used to build the ‘backbone’ for data exchange between all single devices. Every PLC, and of course the panel PC is connected to this backbone network. Each device transmits its set of data over a CAN layer-2 protocol. Needless to say it has access to all messages from the others.
One job of the two main PLC´s is to work as a CAN bridge/gateway. They receive the SAE J1939 messages from the power train CAN (engine and transmission) and make all necessary information accessible via the CAN ‘backbone’ network.
(The full article “A panel PC instead of controls and instruments” by Joachim Nakat (Janz Tec) and Stephan Mark (Trepel) has been published in CAN Newsletter 1/2012)