Volume 13, numéro 1, january 2002

EN :

A method and functions are introduced for estimating the dry mass of logging residues for the most common Scandinavian tree species. Functions were formulated for single trees using different combinations of independent variables that can be measured by standard measuring equipment on harvesters. Cross-validation was used to test the functions and to assess their validity. According to the cross-validation, the total dry mass of logging residues in a clear-cut area could be estimated with a relative standard error of 9.4 - 11.2%. For individual trees, however, the relative standard error for estimating the dry mass of logging residues was as high as 21.5 - 27.6%, depending on the tree species and on the independent variables used in the functions. The models introduced were however more accurate than the generally applied method of estimation, which is based on the average ratio of the dry mass of logging residues to the volume of merchantable wood.

EN :

Shovel logging, a ground-based, non-tractive yarding method that uses an excavator fixed with a grapple instead of a bucket, offers the potential to yard felled wood with less impact to forest soils than conventional rubber-tired skidding methods. The results of this study, carried out in Apalachian hardwoods, indicated that, although neither conventional nor shovel logging methods can be recommended over the other based solely on short-term impacts to soil bulk density, shovel logging resulted in significantly less surface soil disturbance. In addition, shovel logging eliminated the need for primary skid trail construction, identified as a potential source of particulate matter that may contribute to nonpoint source pollution.

EN :

Quantified, performance indicators for dynamic mode Differential GPS (DGPS) were collected at 31 sites established under 3 canopy classes (none, pre-first thinning and mature) of Sitka spruce stands in Ireland with varying altitude (100-500 m) and aspect. Canopy cover was quantified using total obstruction, size of largest opening and fragmentation of sky view. At sites with no canopy above 2 m, a mean precision of 1.5 m was recorded. Where canopy was present, precision ranged between 2.6 m and 2.8 m. The results indicated that in dynamic mode, differences in DGPS performance between canopy cover types were limited to a presence/absence effect. oss of 3-dimensional operation (i.e. only 3 satellites in view) occurred more frequently than loss of differential correction signal and thus had a greater impact on recorded precision over the duration of the experiment. It was concluded from the data collected that the most versatile approach when using dynamic DGPS is to collect more (potentially poorer quality) data, rather than to apply a filter at the signal acquisition stage. The observations made, and the conclusions drawn in this paper are relevant to the forest industry in the selection and operation of DGPS equipment for dynamic tasks where ~ 2 m precision is required.

EN :

The cutting function is an essential part of a harvester's work in the cut-to-length method. The quality of cutting is the most significant feature of a cut. Trees should be cut without causing damage to logs produced. Nowadays end checks of logs are the main problem in the cutting process. It has been observed that end checks are found in as many as 70% of the logs produced by harvesters. Cutting damage reduces the amount of useful material and causes considerable economical loss to the sawmill and veneer industries.

This study presents a theoretical background for the boom-lowering function, which is one solution to avoid cutting damage during the timber cutting process. The purpose is to momentarily counterbalance the gravitational force of the log in horizontal timber cutting. The study discusses the feasibility of controlling the boom tip in the vertical plane during the cut. In this study the boom tip motion trajectory along the g-vector is modelled for both one and two linear actuators. On the basis of this theoretical study, it seems that acceleration of one g is possible to realise with certain improvements in hydraulics. However, experimental measurements are required to verify these theoretical results. This will include the more detailed study of the effects of deceleration limits on boom stability.

EN :

This paper describes an investigation of the differences in service lives between three steel wire rope constructions — one standard and two compacted — tested on varying sheave diameters. Test results indicate the following: 1) The differences in service life between standard and compacted ropes decreased on larger sheaves. This can be explained by mechanical treatment process used in the manufacture of compacted ropes. 2) The compacted Filler construction tested had a service life approximately 50% longer than a compacted Warrington Seale construction. Both had a diameter of 12.7 mm. 3) Service life increased up to 10 times when the sheave diameter was increased by 50%.