UBC Theses and Dissertations

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UBC Theses and Dissertations

An analysis of an interlock mechanism for small running skyline yarders Pendlebury, Ian


This thesis proposes a new interlock mechanism for a running skyline yarder which utilizes an automotive-type bevel gear differential. It proposes to place this differential inside the haulback drum, which also acts as a gear box/oil bath. A hydrostatic transmission is used to control the speed ratio across the differential. The resulting interlock permits the relative drum speeds to be continuously varied to compensate for the effects of changing drum wrap-radii as line is spooled on and off the drums. It also provides an efficient pathway for the circulation of power between the drums. A gear force analysis was used to determine the torque-speed relationships of the differential. The resulting relationships were used to construct a mathematical model of the power flows in the simplified cable system, interlocked winch set and hydrostatic control circuit. A computer program, written for the Hewlett Packard 9 845A desktop computer, in BASIC language, was used to combine a parabolic cable mechanics model, for the determination of line tensions, and the power flow model; to model the yarding of logs with the interlocked winch set. An examination of the torque loading imposed on the differential, when modelling the yarding of thinnings/ smallwood-sized materials, indicates that a large truck differential unit would have sufficient torque capacity to handle this loading.

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