Björn Löfgren
The Forest Research Institute of Sweden
Jan Wikander
Royal Institute of Technology, Sweden
Abstract
The Swedish forestry industry competes on an international market; because raw material is more expensive than in other parts of the world, the chain from the stump to the industry needs to be very effective. One part in this chain is cutting and transporting trees from the forest to the landing area for further transportation with trucks to the paper or saw mill. When cutting and transporting trees, forestry machines equipped with booms are used to handle the trees. If boom handling time can be reduced thereby increasing productivity by 10 percent, the Swedish forestry industry can earn up to 250 million Swedish crowns (US$35 million) per year.
One way to decrease boom handling time is to introduce automatization. This paper describes how to solve the kinematic control of knuckle booms used on forestry machines when automatization is introduced. The objective was to develop a kinematic control strategy for maximum lifting capacity, which is suited for computer-controlled knuckle booms that are redundant. This strategy was analyzed with respect to time consumption when the manipulator tip moves along a predetermined path. The analysis was conducted on a knuckle boom used on a forwarder in a forestry application. The knuckle boom had one redundant degree of freedom. The analysis showed the necessary joint speed requirements and time consumption for certain motion cycles and also what happens when the joints reach their maximum velocity limits.
