In this project, optimal control methods are applied to combined navigation system. With the help of these methods, required level of accuracy is achieved also with modern large scale towed implements. Optimal control methods are applicable also when there are not just tractor steering wheels to control but also the speed and implement’s own steering mechanism. Within the project, solutions for other challenges of the navigation system are also developed and presented:
- Semi-automatic parameter tuning procedure to ease farmers’ work.
- Obstacle detection and collision avoidance methods incorporated with the combined navigation system to reduce risk of accidents.
- Local positioning system based on laser scanner and method to merge all measurements to enable navigation during GPS blackouts.
- Headland driving line generation and simplified path planning method to complete autonomous navigation in field.
- Connecting the towed implement automatically.
In agriculture, there is a growing demand to increase the efficiency of machinery. This has led to increasingly larger machines and an increasing usage of automation. Therefore GPS-based guidance and automatic navigation systems are becoming common in modern tractors. More accurate driving lines are achieved and the workload of the driver is reduced. However, because of their size, implements are more commonly towed these days. The navigation system should also take into account the towed implement. In most commercial products, only the tractor is considered. The challenge is that in combined navigation system where both the tractor and the implement are commanded, the control problem is multivariate and therefore traditional solutions are ineffective. Another challenge is that there are numerous different combinations of tractors and implements and they all have to work together. The ISO 11783 standard is a widely accepted standard for realizing an information exchange between the tractors and implements.
The results of the field tests show that the goals were met. The accuracy of the navigation system is within the given limits. The system is also able to complete the field work without human intervention, including making headland turnings and avoiding electricity poles. The required information on combined navigation has been illustrated based on the case studies. It is possible to build a combined navigation system based on the ISO 11783 standard and distribute the sensors and actuators.
In the project, it is demonstrated that new features including collision avoidance and implement connecting are clearly exploitable features and would bring added value to commercial navigation systems. Valtra looks forward to opportunities to develop these features further into commercial products.
Juha Backman, Aalto University
Valtra Oy Ab, Aalto University, Junkkari Oy