A method for determining the Effective Ground Pressure (EGP) of tracked or wheeled logging machines that can be directly and unambiguously related to their impact on soils is described. When several machines operate together in a logging system, the methodology allows their individual EGP's to be combined to derive a System Effective Ground Pressure (SEGP), which measures the impact of the system as a whole. The methodology has been applied to determine the relative impact of logging systems and influence the choice of machine running gear. Given also the temporal variability in the bearing capacity of soils, it has also been applied to forecasting the minimum level of disruption to operations on flat ground arising from limitations placed on soil disturbance. These applications have led to increased efficiency of operations through a reduction in wood stockpiling during wet weather. The method is sufficiently simplistic at the core, that contractors with the aid of appropriate charts have evaluated the relative impact of machines and systems on soils themselves.
Whole-body vibration data from recent tests on several log skidders are presented. Weighted RMS (root mean square) and RMQ (root mean quad) values are compared to FERIC results of 1987. The PSD (power spectral density) of the vertical motion of the seat base is compared with the PSDs currently defined in ISO and SAE Standards for the evaluation of seat suspensions on earthmoving equipment and agricultural tractors.
This paper suggests the adoption of a seat performance test such as those contained in ISO 7096/ SAE J1385 for earthmoving equipment, or in ISO 5007/SAE J1386 for agricultural tractors. Seat suspensions capable of meeting the requirements of such a test will attenuate the vibration at the frequencies most prevalent on skidders, and should significantly improve the ride on these machines.
Anthropometric dimensions critical to the design of operator workspaces and cab access in grapple skidders were collected from a sample of Southern United States loggers. The data were then compared to existing SAE and ILO anthropometric recommendations and data. Results indicated that southern grapple skidder operators are generally taller in stature, sitting height and seated eye height than the worldwide population measured to determine the SAE and ILO guides. Southern operators are also heavier than subjects measured for the SAE recommendations.
A production study of a single-grip harvester and forwarder was conducted in a second-growth thinning operation in western Oregon, USA. Production levels for the harvester exceeded 30 m3/ PMH (productive machine hour, delay-free). There was no significant difference in harvester production between stands marked prior to logging and those in which the trees were selected by the operator. Production levels for the forwarder ranged from 10.2 m3 to 14.5 m3/PMH. When landing space was limited, a two-pass forwarding technique (separate loads of sawlogs and pulpwood) was more productive than a single-pass technique (products mixed on each load and sorted at the landing). Regression equations were developed to predict harvester production per PMH on the basis of tree dbh and to predict forwarder production per PMH on the basis of product type, volume per load, and travel distance. Thinning cost for this cut-to-length system wasUS$12.49/m3 [US$35.37/c unit],excluding hauling and a profit-and-risk allowance.
The development and experimental verification of a numerical model for the dynamic behavior of a cable logging system skyline is discussed. The model is intended to simulate the skyline behavior after a turn of logs breaks out of a "hang-up" on the ground. Output from the model may be used as a forcing function for a dynamic load on the tailspar or other component of the cable logging system.
The numerical model uses finite difference and Runge-Kutta techniques. Output from the model consists of time-histories of the fluctuations in skyline tensions. From this output the frequencies of the skyline vibrations may be determined. The model was verified by experimental data collected while operating a small cable logging system in Oregon State University's McDonald Research Forest.