Design of a New High Bandwidth Network for Agricultural Machines

Ethernet is by now the most adopted bus for fast digital communications in many environments, from household entertainment to PLC robotics in industrial assembly lines. Even in automotive industry, the interest in this technology is increasingly growing, pushed forward by research and by the need of high throughput that high dynamics distributed control demands. Although 100base-TX physical layer (PHY) does not seem to meet EMC requirements for vehicular and heavy-duty environments, OPEN Alliance BroadR Reach (soon becoming IEEE standard as IEEE 802.3bw) technology is the most promising and already adopted Ethernet-compatible PHY, reaching 100Mbps over an unshielded twisted pair. An agricultural machine is usually a system including tractor and one or more implements attached to it, to the back or to the front. Nowadays, a specific CAN-based distributed control network support treatments and applications, namely ISOBUS, defined by ISO 11783. This work deals with architectural and technological aspects of advanced Ethernet networks in order to provide a high-throughput deterministic network for in-vehicle distributed control for agricultural machinery. Two main paths of investigation will be presented: one concerning the prioritization of standard Ethernet taking advantage of standard ways of prioritization in well-established technologies; the other changing the channel access method of Ethernet using an industrial fieldbus, chosen after careful investigation. The prioritization of standard Ethernet is performed at two, non-mutual exclusive layers of the ISO OSI stack: one at L3, using the diffserv (former TOS) Ip field; one at L2, using the priorities defined in IEEE 802.1p, used in IEEE 802.1q (VLAN). These choices have several implications in the specific field of application of the agricultural machines. The change of the access method, instead, focused on the adoption of a specific fieldbus, in order to grant deterministic access to the medium and reliability of communications for safety-relevant applications. After a survey, that will be reported, the Powerlink fieldbus was chosen and some modifications will be discussed in order to suit the scope of the research

Nuove architetture di controllo distribuito per automazione di macchine da lavoro e agricole

The topics described in this thesis are inherent to safety-relevant systems architectures for heavy-duty machines and new communication protocols between ECUs for agricultural machines. The first topic is about the study, design and implementation of a new communication protocol for agricultural machines capable of high throughput, reliability and dynamicity to realize advanced automation functionalities for precision farming, keeping compatibility for current communication standards. The study starts from the analysis of the current standard for communication (ISO 11783) and on its limits in terms of feasible functionalities, due to the physical layer, the CAN Bus. Migration to different physical layers is mandatory and it has been done in automotive, industrial and aeronautics world, using Ethernet Fieldbuses. Several solutions based on CAN and Ethernet are analyzed, which made the adoption of TCP/IP Stack preferable due to its flexibility and customization capabilities for different purposes. Some tests are performed, in order to evaluate TCP/IP Stack behavior with typical traffic between ECUs on agricultural machines. The results confirm the feasibility of using TCP/IP Stack with Ethernet as a valid solution for superseding CAN. Later, the TCP/IP stack has been improved to fulfil ISO 11783 requirements. A proof-of-concept has been realized, made of a hybrid network with the new high throughput protocol based on Ethernet on one side, and the older one based on CAN on the other. The second theme is about the design and validation of a system architecture for safety-relevant applications on heavy-duty machines. The approach is based on designing an architecture made of hardware and software components, which is general purpose for different application. This approach is in contrast with the one proposed by the safety standards (ISO 13849, ISO 25119, IEC 61508), but can achieve the same goals, increasing the re-use of validated architectures