CAN Newsletter magazine
Process stages in the agricultural- and construction-machinery industry are becoming more and more optimized and assisted. Technical implementation requires the use of the most advanced electronics.
Machinery manufacturers are working together with Gigatronik to develop new hardware and software concepts. The intention is to implement the latest and future functions by using a unified electrical/electronic (E/E) platform strategy to ensure future-proofing through flexibility and modularity.
One real challenge for manufacturers of industrial machinery is the small number of vehicles sold per year. This means that development costs are spread over relatively few control units. For this reason, a key requirement of the project is to develop an electronics concept that is suitable for cost-sensitive machines yet at the same time can be modularly extended for use in complex machines. A single control unit cannot meet these requirements, which is why Gigatronik has developed a concept for extending E/E architecture on the basis of a motherboard. The E/E architecture can be scaled according to the equipment configuration and machine type.
The concept involves a motherboard and an add-on module (Figure 1). The motherboard covers the basic functions of a machine, providing a cost-optimized control unit. For more complex machines, add-on modules that are output- or input-optimized can be used. For very complex machines, more control units can be connected via the CAN network to extend the inputs and outputs for hydraulic functions, for example. This concept also has the side effect of creating potential for the optimization of the cable harness.
To meet the requirements for scalability, a control unit was developed that provides the required number of inputs and outputs for small, cost-sensitive machines. This control unit acts as a central master control unit that always has to be present in the architecture and provides the gateway for Isobus (Figure 2).
Larger machines require more inputs and outputs. These can be connected via I/O-extenders on the central master control unit. A special feature here is the presence of the two redundant extension CAN networks: “I/O Master 1 Left” and “I/O Master 1 Right” (Figure 3). While the hydraulics for important system features can be directly connected to the central control unit, the low priority functions can be swapped out to the left and right I/O networks. In this case, even if the network is severely damaged, it is still possible to work with the main features.
The means of extending the E/E architecture described above provides scalability in terms of inputs and outputs. The architecture can also be extended in terms of application performance, and this is done by extending the application bus. This allows application elements to be distributed across the master control units at will (Figure 4). Extensive simulations have been performed to assure the maximum bus load. In these, the bus utilization is measured for a given number of I/O extenders and cyclical update rates for process data. These data are stored in a CAN database. Gigatronik has developed a tool that generates the CAN interface layer as C source code from the CAN databases. This ensures synchronization between simulation and reality.
The V-Model is a structured development method for tasks of this complexity. It is widely used in joint development projects. It uses tried-and-tested development methods, and these are applied by Gigatronik: requirements engineering, model-based software development, Autosar-layered basic software, a generic hardware design with a motherboard and add-on module, UDS-on-CAN diagnostics, assurance by testing (MIL, SIL, and HIL).
Automotive Open System Architecture (Autosar) is the de-facto standard for software architecture in the automotive sector. In it, the application layer is always separated from the basic software layer by middleware. This creates three software layers:
The runtime environment as an interface between application and basic software. With this technology, the basic software modules can be developed once and used over and over again, saving on development costs. Depending on the E/E architecture chosen, the software components can be applied across various control units. This allows the number of control units required to be varied in a cost-effective way.
However, for some customers in the agricultural- and construction-machinery field, the usually high level of complexity of this architecture is not necessary. This is why the company offers an own implementation of the basic software layer. The accesses to the hardware and the layer model are similar to Autosar but for example the communication layer is simplified. This results in a simple structure that can be configured even without expensive software tools.
The implementation of new features is particularly complex in the world of agricultural engineering, often requiring expertise in hydraulics, control technology, electronics and programming. A model-based development process lowers the hurdle for implementing a new feature in an electronic system. It allows control-technology experts to implement functions in Matlab/Simulink without having to get a deeper understanding of hardware or software characteristics. New functions can be tested as prototypes on a computer or HIL test bench. The source code is generated from the model and automatically integrated into the existing basic software. By using the latest development methods, OEMs in agricultural machineries are now able to use an E/E architecture tailored to the equipment configuration.
This article originally appeared in the March issue of the CAN Newsletter magazine 2016.
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