Model-based study of the energy efficiency of two different types of harvester cranes

Abstract: In today’s forest industry two mechanized methods are used, the Tree Length (TL) method and the Cut To Length (CTL) method. With the Tree Length method, trees are harvested and extracted from the forest as a whole tree to be further processed whereas with the Cut To Length method trees are harvested, branches are removed and the tree is cut to desired length to be extracted by a forwarder. The Cut To Length method is now a day 100 percent mechanized and more and more emphasis is put on efficiency in both harvesting and forwarding the trees. Efficiency can be measured in trees harvested per hour but also in fuel consumption. As an effect, the performance of the machines is in higher demand. Ponsse Plc is a finnish forestry machine company with production in Vieremä where both harvesters and forwarders are manufactured. Cranes and loaders are also made by Ponsse to match their harvesters and forwarders. Ponsse manufactures two designs of harvester cranes; a sliding boom crane and a parallel crane. The different types of cranes have the same reach but with different geometries and weights, which also leads to different momentum of inertia. The purpose of this master thesis is to investigate, from an energy efficiency point of view, the difference in performance between a sliding boom crane, C2, and a parallel crane, C22 by measuring the hydraulic pump’s flow and the rotational energy of the cranes. This has been done by modelling the cranes’ hydraulic circuits and by using 3D-CAD models with mass and inertias in Simulink. More specific, only the crane tips of the cranes have moved along a set trajectory, equal for both crane types. Different range and loads have been simulated. The energy needed for rotating the cranes have been calculated for different crane tip positions and compared. Simulink simulations gave beneficial results for the parallel crane when unloaded and acting at a shorter reach. For longer reach, the sliding boom crane was more efficient. The calculations of the cranes rotational energies showed that the parallel crane C22 yielded higher values than the C2 at shorter distance from the axis of revolution. The C2 crane had however slightly higher values than the C22 crane at longer reach, but it should be noted that differences were small. From this analysis, it is concluded that the C2 crane has an overall lower need of rotational energy and is therefore deemed the better crane. Keywords: Forest machines, hydraulics, efficiency