Development and Evaluation of a Felling Head for a Light Forest Crawler

Abstract

With motor-manual wood harvesting (by a forest worker with a chainsaw) fatal accidents happen every year when the tree is felled or when parts of the crown fall down. The alternative is to fell trees mechanically using a timber harvester head, which, however, must be brought up to the trees in the forest by means of its crane. With the usual crane reach of 10 m, the harvester needs a system of parallel strip roads with a spacing of 20 m. Furthermore, the harvester needs a dead weight of around 20 tons that compacts the soil. Both consequences increasingly evoke critics. The requirement to fell trees mechanically and to enlarge the distance between the strip roads calls for a solution to fell trees with a small, light machine that can apply its felling tool to the tree in close proximity. Together Pfanzelt Maschinenbau GmbH and the Professorship for Forest Technology of Technische Universität Dresden have run a project for developing a compact, new type of felling head, which is attached to the existing forest crawler »Moritz FR70/75« by means of a short manipulation arm. This head imitates the felling technique, which is applied by a forest worker, in a mechanical way with a high grade of automatization. Even though this machine works with higher system costs, it is significantly faster and more precise than the motor-manual version. The functional principle of the felling head was developed, patented, conceptualized and optimized with the help of prototypes and individual tests at the TU Dresden, Professorship for Forest Technology. After that, it was completely designed, manufactured and automated in terms of control technology by the Pfanzelt company. More than 100 conifers with a felling diameter of up to 50 cm were felled safely and without any problems with the prototype. The possible integration into harvesting processes as well as the effects on the use in the forest stands were analyzed in detail. The project has shown that it is possible to fell trees in a fully mechanized way without danger for the forest worker with a machine that weights roughly a tenth of the dead weight of a conventional harvester.