Using near-infrared hyperspectral images on subalpine fir board. Part 2: Density and basic specific gravity estimation

Abstract

Wood density (ρ_MC) and basic specific gravity (BSG) are important properties in several forest products manufacturing processes. In this study, near-infrared hyperspectral images were tested to produce two-dimensional (2D) ρ_MC and BSG images of subalpine fir (Abies lasiocarpa Hook) board. A total of 107 cubic samples with the size of 4 cm were prepared from 14 boards. All samples were dried to various moisture contents (MCs) during several steps until being completely dried. The resulting MCs ranged from 1% to 137% (dry basis). After the last drying step, the samples were soaked in water to determine BSG. Hyperspectral images and weight measurements were acquired over each sample at each drying step. ρ_MC was also estimated at each MC level. Partial least squares (PLS) models were developed for estimating both ρ_MC and BSG from the near-infrared hyperspectral imaging (NIR-HSI) system absorbance spectra acquired over all the samples during each drying step. The ρ_MC model provides a reasonable accuracy with the validation data-set (R² = 0.81, RMSE = 39 kg/m³, and RPD = 2.3). For BSG, only models built with samples having MC of less than 12% are significant. The calibration data-set provides similar accuracy as the ρ_MC model (RMSE = 0.004, R² = 0.82, and RPD = 2.28), but the accuracy is lower with the validation data-set (RMSE = 0.007, R² = 0.53, and RPD = 1.39). Our data-set has BSG values varying only from 0.326 to 0.374, and further work is needed to apply these methods to a data-set that includes a more extended range of BSG variations for improving estimation accuracy.     

Combined effect of wood moisture content,drill bit rotational speed and feed rate on drilling resistance measurements in Norway spruce (Picea abies (L.) Karst.)

ABSTRACT

An IML-RESI PD 400 drilling tool and a standard spade drill bit (IML System GmbH, Wiesloch, Germany) were used to study the combined effect of wood moisture content (MC), drill bit rotational speed and feed rate on drilling resistance (DR) and feeding force (FF). Tests were made with Norway spruce (Picea abies (L.) Karst.) conditioned in a normal climate (20°C/65% RH), at 20°C/95% RH, vacuum-pressure impregnated in water, and oven-dried. Rotational speeds and feed rates had an impact on feed rate per cutting edge for the major cutting edge of the drill bit which was used for correlation with DR and FF for various MC. Impact of MC on DR and FF depended on rotational speeds and feed rates of the drill bit. For feed rates per cutting edge less than 0.09?mm, DR was higher for water saturated (WS) specimens. Negligible differences between DR for various MC were found for feed rates per cutting edge between 0.09 and 0.15?mm. DR was higher at low MC for feed rates per cutting edge which were higher than 0.15?mm. FF extremely increased in conditioned (20°C/95% RH) and WS specimens at feed rates per cutting edge less than 0.1?mm.