CAN Newsletter June 2005

Isobus is on the move - in mobile CAN networks

CAN protocol networks have been in place for many years, but we should not be complacent about that. It is always good to be aware of our competition as well as our strengths. Other protocols have claimed that CAN-based systems are too slow or are not as useful or deterministic (even TTCAN) as a pure Time Triggered network. We have our own opinion on that and this article will demonstrate the strength behind several areas of CAN, how they are alive and well and what various industries/standards are behind them. For those who will be impacted by mobile vehicle communication CAN networks, this article should have some interesting information regarding its developments in the last several years. It will also show how seemingly unrelated industry standards agencies have been working together in this same area.

To start with, a new term to introduce is the identifier called “Isobus” as used in mobile CAN networks. It is a market term that has grown in visibility via machine production and farm shows. The present area of most activity is in agriculture, but can certainly spread into construction and forestry as desired. Since most people have a vested interest in food, we like to know that we’re making things better in this area of interest. As you would expect, one big area of industry interest has been how all of the tractor and other vehicles of the world will interface with all of the electronic implements of the world. Another large area of interest regards the existing virtual terminal systems and the upcoming task controllers, file servers and GPS applications. Since these networks are open systems, there is no system engineer hovering over and controlling every possible combination. This means there has to be some amount of agreed-upon standardization and game rules in order for this system to work well for the operator.

For those who love to dive into the depths of the details, these RPs (recommended practices) and standards are large in size, yes, but manageable. If you count up the SAE J1939 and ISO 11783 standards pages and include the NMEA 2000 documents, they amount to a combined total of over a thousand pages of specifications. That is not as scary as it sounds though, once you understand the top level view.

CANopen sensors in the world’s largest truck

The world’s largest truck, the T282B from Liebherr Mining Equipment uses three MicroControl uCAN.4.ti-IP65 thermocouple modules on the vehicle’s CAN bus. The CAN modules measure critical temperatures in the wheel motors on the truck. The temperature measuring devices must be able to withstand the harsh environment and still provide crucial data. Liebherr chose the unit based on quality, support and price, in that order. The units are living up to the high standards required for CANopen devices on our T282B truck. The device is easy to work with, a manual that is easy to follow, a simple set up of the device through the Object Dictionary and, most importantly, a great support structure when needed. Delivery of the product is dependable.
The module has four channels and allows LME to use two thermocouples per wheel motor. The module must meet the  standard and also be IP65 or greater to survive the environment the units are subjected to. Two units are located in the rear axle box to measure temperatures in the Liebherr developed wheel motors (an electric motor and gear set). One unit measures the gear oil temperature from the large and expensive wheel motors. Both wheel units use Type K thermocouples and we use two thermocouples/gear set for redundancy. If the temperature rises above a low limit the device sends data to trigger an alarm while, if the temp exceeds the high level limit, the device sends data to trigger a high level alarm. The second unit, also located in the axle box, is used to measure the stator temperatures of the two 2000 HP electric motors. This requires LME to monitor PT100 thermocouples embedded in the high voltage electric motor. The goal is to prevent damage from excessive temperatures to the windings of the motor. Again preventing expensive repairs and down time is the main concern. Therefore, the reliability of the monitoring devices is crucial. The T282B is a diesel electric vehicle and uses a diesel to rotate an alternator. The third unit is used to measure the stator windings of the alternator with PT100s and also the bearing temperatures. Again, the goal is to prevent damage to a major component of the drive train on the T282B to prevent expensive repairs and down time. The sensors are used to monitor the health of major components on the Super Haul Class Truck. This prevents costly replacement of major components and keeps the truck in operation.

CANopen on-board PCs in construction equipment

In March 2005, John Deere presented a system concept for the control of construction equipment. The system targets integration of advanced positioning functionality and general, CAN-based machine control features. Work quality and efficiency can be boosted by applying high precision positioning systems, so called ‘autoblade’ systems, in construction equipment such as dozers and motor graders. The systems consist of a GPS receiver, laser detectors, an ‘autoblade’ micro-controller and an on-board computer that runs the application for geographical data. This on-board computer typically runs on Windows CE, Windows XP, or Windows XP Embedded. Autoblade systems can be fitted to basically any machine type as a commodity add-on system. The system is partly integrated with the machine control system so that the blade of the machine can be controlled automatically. This means that the driver can focus on handling the vehicle while the autoblade system ensures that the soil, gravel or shingle is shaped correctly.
John Deere’s TMC (Total Machine Control) system focuses on integration and takes autoblade functionality to the next level; the on-board PC and electro-hydraulic subsystem is supplied as a component in the machine control system from the factory. This means that the PC can be used for a bundle of features:

• Machine diagnostics via CAN network number 1 (J1939),
• Display of meters and gauges via CAN network number 1,
• Video, display of rear-view camera image, and
• Autoblade functionality via CAN network number 2 or RS-232.
  

By utilizing the on-board PC in this way, the company has simplified the machine control significantly; they don’t use any analog gauges and meters, only one display/monitor in the cabin etc. Furthermore, the general on-board PC makes it possible to run autoblade applications from different manufacturers, i.e. it is possible for the end user to use their preferred autoblade system. When running a number of applications on the PC it is important that the operator can swap easily between them; the operator task is to control the entire machine, they should not be absorbed by operating the PC. John Deere has solved this by controlling the different applications via CAN; the CAN joystick is used for swapping between the PC applications. The on-board PC the company employs is developed by the Swedish company CC Systems. In addition to the two CAN buses the PC is equipped with USB, COM, Ethernet and Video-In interfaces. The 8.4-inch size graphical color display has a touch screen, which simplifies the operator’s task to interact with the system. The CPU performance is scalable from Intel Pentium 300 MHz to 700 MHz. A special feature is that an ECU/ I/O-board can be packaged inside the PC-enclosure, communicating with the PC via CAN internally. In the John Deere TMC system the ECU for detectors and gauges is packaged inside the PC in this way. Construction equipment applications place high requirements on robustness of the electronics. This is why the on-board PC has a non-rotating hard disc, fan-less cooling and IP65 protection.