Developing an autonomous tractor
In 2000 we started to develop an autonomous tractor that would allow us to be able to test and develop the knowledge of what is needed to make a tractor truly autonomous.
We started with a 27 HP Hakotrac 3000 tractor from Hako Germany as it was (relatively) small had continuously variable transmission (CVT) many of the control functions were already configured for electronic interfacing.
An electronic control unit (ECU) was fitted that could interface to most of the subsystems on the tractor so that we could control the basic tractor functions.
We added a Parallel power steering valve block from Sauer Danfoss that could interface to the ECU.
Both the CVT linkage and throttle cable were modified to accept linear actuators that could be controlled from the ECU
A remote handset was used to retain manual control of the steering, engine speed and CVT ratio.
Another CPU was added to synchronise the safety and usage logic along with a mode switch. The basic modes are: Off, Manual, Start, Neutral, Remote and Automatic.
Many of the subsystems can be seen on the left.
Safety is always an important concern! Apart from the many BRBs (Big Red Buttons) we used a radio link to a 'dead man's handle'. A safety officer held a radio transmitter with a normally-off button that was held on. If he let go then all the tractor systems would stop.
Finally a GT2000 controller from GEOTEC was fitted and interfaced to the ECU by a CAN (Control Area Network) bus.
The whole tractor is deterministic at this stage. Deterministic means that we can determine all the actions of the tractor before it even starts. As most actions can be spatially determined, we used a very accurate RTK GPS from Trimble that would give us accuracy of +/- 2cm while driving around.
The instructions to the tractor are given in the form of a route plan. This can be determined before hand by using a special program written by GEOTEC that integrates with AutoCad.
The route plan is developed by starting with the outline of the field. Then identify the working width of the implement and the direction of travel. As we know the turning circle of the tractor and working width of the implement we can then estimate the number of working widths needed for turning on the headlands.
The program then gives a set of guidelines that can be used to define the tractor route. These guidelines can then be selected and a complete route is prepared. Certain locations can be identified when the linkage should rise or fall and when the PTO should start or stop.
This route plan is then loaded onto a memory stick and transferred to the GT2000
The tractor is run in a straight line for a few meters to calibrate the Kalman filter before being positioned at a known starting point.
The tractor mode is switched to automatic and the tractor does its best to follow the waypoints.
Note that the RTK GPS lost fix for a few seconds in the middle of the run.
The latest version: The cabriolet autonomous tractor!
Simon Blackmore, Henning Nielsen, Jesper Resting-Jeppesen, Henrik Have, Hans Werner Griepentrog, Michael Nørremark
Blackmore, B. S., Have, H., and Fountas, S. (2001). A specification of behavioural requirements for an autonomous tractor. 6th International Symposium on Fruit, Nut and Vegetable Production Engineering conference. eds. M. Zude, B. Herold, and M. Guyer. Potsdam - Bornim, Germany, Institute für Agrartechnik Bornim e.V. pp.25-36.
Blackmore, B. S., Have, H., and Fountas, S. (2002). A proposed system architecture to enable behavioural control of an autonomous tractor. Automation Technology for Off-Road Equipment. ed. Q. Zhang. 2950 Niles Road, St. Joseph, MI 49085-9659, USA, ASAE. pp.13-23.
Blackmore, B. S., Griepentrog, H. W., Nielsen, H., Nørremark, M., and Resting-Jeppersen, J. (2004). Development of a deterministic autonomous tractor. CIGR International conference Beijing.
Blackmore, B. S., Fountas, S., Vougioukas, S., Tang, L., Sørensen, C. G., and Jørgensen, R. (2004). A method to define agricultural robot behaviours. Mechatronics & Robotics Conference (MECHROB) 2004. pp.1197-1200.
Page updated August 2007