In this research, we attempted to clarify the effective machine control technique and working method of an expert worker by analyzing the motion of a grapple loader used in log loading work. In particularly, we focused on the locus of the grapple attachment, and thus installed sensors on each actuator of the knuckle boom for calculating the three-dimensional coordinates of the attachment. The average positioning error was 34.5 mm and the maximum error was 80.2 mm, both of which were considered adequately precise values for our analysis. We then investigated the task of loading 3.49 m^3 of logs on a forwarder carrier, as performed by two operators with different skill levels. As a result, we found that the productivity of work done by the expert was about two times higher than that by the beginner. A close examination of the operations clarified the expert's characteristic technique that contributed to high productivity as follows: 1) the work space was compact, and there was no unnecessary movement; 2) multiple actuators were operated simultaneously, and the attachment was maintained along the most efficient path; 3) the logs were handled stably by being gripped at their center of gravity; and 4) the machine's power was used effectively and continuously during the work. An apparent difference in the operating skills between the beginner and expert has been suggested, and that difference could cause the difference in productivity.

View full abstract

This study aimed to develop an operational system for thinning using a medium-range tower yarder introduced from Europe. To that end, the productivity of thinning operations was researched, and the uphill-lateral yarding operation was analyzed in this report. The uphill-lateral yarding time did not have a clear relationship with the loading volume, and had a high correlation with the lateral yarding distance, thus a prediction relation of the productivity for uphill lateral yarding was able to derive. On the mean yarding distance of 156.6 m, the mean lateral yarding distance of 25.7 and the mean loading volume of 0.66 m3 in this research area, the whole productivity of uphill-lateral yarding was 6.2 m3/hour, which was predicted 1.8 times higher than the existing similar tower yarder. It is clear that this newly-introduced tower yarder could be expected to get the higher productivity in the forest condition in Japan.

View full abstract