| 摘要 |
The invention relates to a crane-supported pivotal tree felling unit of the type at which gripping arms press the tree stem against a thrust on the unit whereafter the steam is cut by a cross cut member disposed below the gripping arms. In the final phase of the cross cutting operation the jib is lifted so that the breaking of the stem is facilitated by lever action, whereby the force-actuated end of the lever corresponds to the suspension point of the unit on the jib. According to the invention said suspension point is so movably connected with the unit by a linkage that at said lifting of the jib a spring means retaining the linkage is overcome and the suspension point is moved rearwards from the tree, thereby increasing the effective length of the lever and, thus, increasing correspondingly the breaking moment acting on the tree. |
