Gallring med vinkelkran : en jämförande studie av skördarkran med och utan horisontellt ledad vipparm
Abstract: One of the most important components of a harvester is the crane. Most harvester cranes are only possible to pivot (or horizontally rotate) at the crane pillar. Cranab in Vindeln, Sweden, has developed a new type of harvester crane which has an extra pivot point on the outer boom. This makes it possible to reach around residual trees, easing thinning work in dense stands. The aim of the study was to analyze if the use of a pivoting outer boom (POB) crane gave an increase in thinning production and if there were any differences in time consumption between the work elements for the POB crane and a conventional crane. A Valmet 911.3 equipped with a POB crane was used in the study. The use of a conventional crane was simulated with the same machine, but by not using the outer boom's pivoting function. 16 treatment units were created within a pine-dominated stand with a density ranging from 1113 to 3100 trees per hectares. The operator's stem choice was restricted to pre-marked trees. For the POB crane, the pivoting function was used on between 28 and 36% of the cut trees. The number of machine movements in both forward and backward directions was lower for the POB crane compared to the conventional crane. The use of the POB crane reduced the number of backwards movements by 70%. Due to the POB function and fewer machine movements 24.8% more trees could be cut per machine position. The POB function resulted in a 9% reduction in time consumption in thinning when compared to work with the conventional crane (given a mean stem volume of 0.045 m³). The POB crane's mean time consumption per harvested tree was lower for all work elements, but the differences were statistically significant only for crane in, reversing and waiting. The relative time savings decreased with increased mean stem volume. With mean stem volumes of 0.024 and 0.075 m³ the time savings were 11.0% and 7.1%, respectively.
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