Studies on the development of a new yarder which is exclusively used for Iw.U.S. in standing skyline system of cable logging

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This yarder is characterized by the installation of a new special equipment of DRK (Differentialreibungskupplung), which enables the speed of the two operating lines (main and endless line) to be simply balanced, when it is applied to the Iw.U.S.. The fundamental principle of DRK is based on differential friction clutch, but unlike traditional interlocking in America, DRK functions not between every drive gear and driven drum, but direct between two drums (main and endless-drum) each other. Therefore any special design as a complicated, expensive or great and heavy yarder of interlocking is thoroughly avoidable.This yarder can be also widely used for the other cable logging systems in general if DRK is merely kept to be free. The friction inside DRK causes the losses of power but it is sufficiently small to practical use and serves favorably as a brake for running of carriage caused by the gravity of load in the case of down-hill yarding, so that the control of another brake may not be necessary.During inhaul the operator can control DRK with its lever very easily and almost stationarily. The trial product of the yarder with a power of 48 PS was developed in 1985 and then its expected properties were realized through the logging operations performed in the experimental forest of Iwate University. The main contributions of this method were : A. Continuous lifting the load above ground could be guaranteed under every skidding conditions. B. The operational efficiency of skidding could be greater than that when using of the brake on the endless-drum. C. From the ergonomical point of view the strain of the operator during control DRK was very slight (rather in relaxation), which was proved by the pulse measurment (heart checker) of the operator.