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반궤도식 임내작업차 개발에 관한 연구 (A Study on Development of Half Crawler Type Mini-Forwarder)

Abstract : 

       In this study, a half-crawler type mini-forwarder which is appropriate for the mountainous topography of South Korea was designed and manufactured, its running safety was analyzed by using a dynamic analysis program and the working process and costs in a small-scale transportation work using a half-crawler type mini-forwarder were analyzed. As a result from such a study, the following conclusion could be obtained. 1. In oder to design and manufacture a mini-forwarder appropriate for the topography of South Korea, some general ideas on the current status of the domestic and foreign mini-forwarders were first collected and their specifications were analyzed. As a result from such an analysis, a half-crawler type running method with superior smooth running and hill-climbing ability was adopted and it was designed and manufactured for the purpose of developing a small half-crawler type mini-forwarder which can run on a narrow road for working. Based on the established target specification, a model machine for the half-crawler type mini-forwarder was manufactured and as a result from an on-site test for the model machine. Although such speeds are somewhat slower than those intended when it was developed, it is judged that the development goal was obtained being considered the reduction gear ratio of the hydraulic motor and the test conditions, etc. It is assumed that designing and manufacturing of a half-crawler type mini-forwarder which is appropriate for the mountainous topography of South Korea can contribute to a solution for the lack of forest workforce in South Korea, the diversification of forest machinery, the supply and proliferation of high-performance forest machines. 2. For analyzing the running safety of the half-crawler type mini-forwarder, a 3D modelling for it by using AutoCAD was implemented, the analyses of physical characteristics, sideways overturning, hill-climbing ability and running safety when passing through obstacles were conducted. As a result from the analysis of the physical characteristics of the half-crawler type mini-forwarder, and thus, it is judged that the 3D model of the half-crawler type mini-forwarder can be used for analyzing the running simulation by using a dynamic analysis program. As a result from the computer simulation of stationary sideways overturning, it was found that the critical angels of the stationary sideways overturning when it was empty and loaded were 33°and 30° respectively and in case of running on a road with 25% slope, it can be seen that the right rear wheel crawler part slightly comes off the ground. Therefore, is was found that the half-crawler type mini-forwarder runs with safety on a road with a slope not bigger than 20° regardless whether it is empty or loaded, but in case of a road with a slope bigger than 20°, it is assumed that it is difficult for the car to run with safety due to some dangers. In addition, it was found that the critical slope of its sideways overturning gets much smaller since the location of its gravity center is elevated much higher when it is loaded. As a result from the computer simulation of its hill-climbing ability, it was found that the critical hill-climbing angles when it is empty and loaded were 35° and 34° respectively, but since the running speed is unstable in case of a road with a vertical slope not smaller than 28°, it is assumed that it is safe to drive it on a road with a slope not bigger than 28°. Taking a look at the result from an analysis of the running safety when it passes an obstacle, it was expected that a front tyre comes off the ground when the running speed of the car is 5 and 4 km per hour respectively when it is empty and loaded while the gravity center of the front tyre is watched. When taking a look at the changes in the location of the gravity center of the rear wheel crawler shaft, it was not found that the shaft comes off the ground at the test speeds when it is empty and loaded. It is assumed that the rear wheel crawler whose contact area to the ground is bigger than that of tyre doesn't come off the ground while its track part is running over an obstacle. 3. An analysis of the process and costs of small-scale transportation work by using the developed half-crawler type mini-forwarder at a site collecting the harvested lumbers was conducted. As a result from an analysis of number of working hours for each work element, since the operator was not familiar to the model machine for the half-crawler type mini-forwarder which was newly developed, it was found that the ratio that a timber merchant gets off the car while working is high as 60.2%. Therefore, it is judged that the number of working hours with the half-crawler type mini-forwarder can be reduced by educating and fostering operators in the future. Moreover, it is necessary to construct some efficient forest road network appropriate for the work system since the small-scale transportation work with a half-crawler type mini-forwarder is characterized that it is highly affected by the transportation distance for timber and the slope of a forest road. Since a day's work amount at a forest site where timbers are well arranged is high as a result from an analysis of the process of each working condition with the half-crawler type mini-forwarder, it is judged that the progress of a small-scale transportation work can be accelerated by inducing yarding using a cable yarding machine while refraining from yarding using an excavator. As a result from an analysis of the cost of working with a half-crawler type mini-forwarder, it was found that it is necessary to promote the supply of such half-crawler type mini-forwarders after establishing some efficient working system using such cars and by fostering the operators since risks are high due to the aging of machines and the overloaded cars even though more efficient trucks are currently used in terms of the expenses for small-scale transportation work in South Korea.