Two books in German language describe bus systems and data communication in road vehicles. The book “Bussysteme in der Fahrzeugtechnik (bus systems in vehicles)” by Vieweg (publisher) comprises 298 pages, 156 figures, and 89 tables (ISBN 978-3-8348-0235-4). The authors, Werner Zimmermann and Ralf Schmidgall, give an overview on in-vehicle network protocols and standards. This includes K-line, CAN, LIN, FlexRay and SAE J1850. The content of the 2^nd issue also covers higher-layer protocols (e.g. ISO TP, SAE J1939) and profile specifications (e.g. KWP 2000, Unified Diagnostic Services, On-board diagnostic). The book, which is available for 39,90 €, describes standards for measuring and calibration purposes (ASAM, Fibex, etc.) as well as for ECU (electronic control unit) software (OSEK/VDX, Autosar, HIS).
It provides a complete overview of in-vehicle networking and ECU programming and testing. The authors stick to the facts of the described standards and specifications. Sometimes they add critical statements and their personal opinions, which is very helpful to get a better understanding. However, in the detail description of the protocols and standards the authors are not always precise. An example: The description of the CAN frame format shows a 7-bit control field, which is specified in the ISO 11898-1 standard as 6 bit. The CAN header (SOF, arbitration field and control field) is described as 37 bit long instead of the 39 bit as defined in the ISO standard. In the book there are many references to the CAN 2.0A/B specification (which does not contain the entire CAN data link layer functionality) instead to the official ISO 11898-1 CAN data link layer standard. Nevertheless, the book is very valuable for those readers, who like to get an overview of in-vehicle networking. In particular, the list of standards and specifications at the end of each chapter is helpful to not get lost in the document jungle.
The book “Datenkommunikation im Automobil (data communication in automobiles)” by Huethig comprises 377 pages (ISBN 978-3-7785-2969-0). The authors, Christoph Marscholik and Peter Subke, also give an overview of all relevant bus systems and the higher-layer protocols for diagnostic services. The paperback book available for 46 € discusses in detail the use of software tools based on the ASAM specifications. It also covers the ODX (open diagnostics data exchange) format in minute detail. In general, the authors provide a lot of details, however, the reader may get lost at times. Missing in the book is the CAN Calibration Protocol. The book often references the CAN 2.0A/B specification instead of the ISO 11898-1/2 specifications. The data flow diagrams simplify the understanding of the quite complex protocols, but readers do not particularly benefit from the product photos.

To summarize: Readers who need to understand bus systems and data communication in vehicles, may require both books. The Vieweg book should be read first in order to understand the basics and get a complete picture of the topic. If you require more details, then you can read the Huethig book. I have not double-checked all details, but sometimes the technical details are different in the two books. This means, if you want to know something very accurately, you have to look into the corresponding standards and specifications.

The SAE (www.sae.org) has published the 434-page book „Multiplexed networks for embedded systems: CAN, LIN, FlexRay, Safe-by-Wire“. Written by Dominique Paret in English language the book provides an introduction to automotive multiplexed network buses, covering the technical principles, components, implementation issues, and applications of numerous systems. The book covers CAN, LIN, TTCAN, FlexRay, X-by-Wire, Fail-Safe-System Basis Chip (SBC), Safe-by-Wire, I2C, and MOST networks. According to the SAE, the book will be a valuable reference for engineers and researchers developing electronics, as well as anyone interested in the application of network technologies.

By Dr. Rolf Schmidt (Sensor-Technik Wiedemann)

Floor space in modern high-rack warehouses is very expensive, and every square foot saved also saves a high amount of investment costs. For this reason, warehouse architects design the aisles as narrow as possible. Much faster forklift movements and less distance to the racks are possible with an automatic guidance system, which takes over the steering in the aisle, than with manual steering. One important aspect of this application is safety for the driver and the vehicle by an automatic self-monitoring of the guidance system.

Inductive guidance system

Part of an inductive guidance system is the inlaid floor guidance wire, which carries current with a defined amperage and frequency. An antenna measures the magnetic field around the wire. Through the signal strength and direction of the magnetic field the system can determine its position in relation to the guidance wire. A steering controller then calculates set-points for the steering system. A simultaneous supervision of the vehicle deviation from the guidance wire allows an emergency stop.
An inductive guidance system has advantages in harsh and blind surroundings compared to optical solutions. An accurate inlaid guidance wire allows interference-free operations, regardless of dust, dirt, snow, ice, uneven or steep flooring. With a resolution of down to ±1mm, the inductive guidance system is the ideal high accuracy solution for forklifts operating within narrow aisles. Unlike systems with selective guide information, the continuous signal logging of an inductive solution carries all the necessary information. This allows real-time distance measurement, directional correcting, and emergency stopping, if needed. With antennas on the front and on the rear, the vehicles can be guided in both directions.
The driver can control vehicles with an aided steering system during normal operations. Only in the narrow aisles the automatic guidance system takes over control of the vehicle. The transition from manual to automatic control, called feed-in process, is especially interesting. The transition time and required space for entering the aisle should be as small as possible to minimize working time and floor space.

Enhanced system

STW, as a premier manufacturer of mobile electronics and measurement technologies for off-highway and on-highway vehicles, in collaboration with Still Wagner, developed a new state-of-the-art inductive guidance system. This guidance system allows the following improvements:

• Detection distance greater than 500 mm between antenna and guidance wire (guidance wire current of 100 mA) by way of digital and DSP (digital signal processor) technology
• Vehicle feed-in angles of up to 70° through the arrangement of the antenna-coils
• Adjustable feed-in curves to be flexible for local conditions
• Feed-in speed of up to 2,5 km/h

STW developed an antenna with four coils to detect the vertical and horizontal parts of the magnetic field of the guidance wire, processed with a DSP.
The coil signals are filtered with an adjustable frequency and examined. After the feed-in process is finished, the guidance wire current can be controlled. The distance information is available on the integrated CAN network and as an analog voltage signal.
The electronics, including a second DSP for redundancy, and the coils are placed in a compact enclosure of 30 mm x 40 mm x 200 mm.
The steering controller calculates set-points for the steering angle from antenna signals and vehicle parameters, and sends the data via a second CAN interface over the vehicle CAN network to the steering system. During the feed-in process the steering controller calculates the optimal feed-in curve using the distance information to the guidance wire, the steering angle and the odometer information. The feed-in control starts with guidance wire signal detection at the front antenna. After receiving the signal on the rear antenna, the vehicle is controlled by both antennas. The feed-in curve is adaptable to the specific application. After reaching the minimum feed-in distance to the guide wire, the feed-in process is finished and the velocity of the vehicle is no longer limited by the inductive guidance system. The steering controller acts as a CANopen slave in the vehicle CAN network. Additional inputs and outputs might be used for auxiliary functionalities of the steering controller.

Safety demands

Due to the high demands on safety for automatic steering, the system is completely redundant and provides features for self-supervision. The four-coil design of the antenna allows detection of interference in the magnetic field. It is also possible to adjust the system to a distorted magnetic field. The signal processing in the antenna uses two DSPs, forming a completely redundant system. For additional safety, the data transfer from both DSPs is redundant by using two channels: via CAN and an analogue signal. The CAN signals are sent with dedicated techniques for data integrity.
The antenna signals are constantly checked in the steering controller before the steering set-point is processed. Additionally, a second processor monitors the antenna signals and set-points for the steering angle. The vehicle is equipped with an emergency-stop line. It provides a safe second path to stop the vehicle. This line can be shut off both by the steering processor and the supervising processor.
The demand for more functionality and safety is increasing steadily. The automatic inductive guidance system developed by STW shows an innovative and reliable solution, even in a harsh environment.

The Zoomlion PuYuan Crane company uses a CAN-based control system for their “600 tons” crane that was designed by the Shanghai-based Pal-Fin Automatic Control Technology. The system uses several control units by Epec, a Finnland-based expert in CAN technology. The CAN-based control system is used to control e.g. driving and engine functions.
Epec Oy in cooperation with two Chinese partners supply Chinese customers e.g. Sany, XCMG, Zoomlion, etc. with CAN solutions for off-highway and off-road vehicles. Epec is a manufacturer of embedded CAN control systems for the industrial vehicle market. Their business partners import the Epec controllers into China and provide system design for Chinese machine manufacturers. For this they use CAN-based embedded control systems.
Tomi Kohtanen, Director of Sales & Marketing Epec says: “According to our experiences, many Chinese manufacturers have accepted new technologies very well. They have done so to increase their competitiveness and to add new features to their machines. In some cases, they are accepting these new ideas even faster than in some western countries.”