Diameter sensors for tree-length harvesting systems
Most cut-to-length (CTL) harvesters provide sensors for measuring diameter of trees as they are cut and processed. Among other uses, this capability provides a data collection tool for marketing of logs in real time. Logs can be sorted and stacked based on up-to-date market information, then transportation systems optimized to route wood to proper destinations at lowest cost. This capability does not currently exist in tree-length logging systems common in the US South, but that deficiency may soon have to change as wood and fibre companies in the regon adopt technology in order to reduce delivered wood costs. CTL logging systems may become more common in the region as this change occurs, but tree-length will remain an important mode of harvest for many years. In order to take advantage of logistical technology to lower costs, as well as other potential benefits of 'precision forestry', tree hameter sensor systems for feller-buncher-type harvesting equipment d be needed. This paper presents some preliminary results comparing the performance of two alternative approaches to measuring tree diameter as a tree is being cut using a feller-buncher equipped with a rotating disk saw. One approach used a set of lasers to time the passage of a tree through the saw blade and into the head, then inferred diameter from this information. The other system resembled a class of yield monitors used on cereal grain combines, measuring the mass of chips being ejected from the saw head as an indicator of tree dameter. Both systems were implemented in a laboratory setting, with the laser system further deployed and tested on a feller-buncher. Both systems showed potential, with the laser device having advantages in apparent accuracy and suurvivabihty in harsh operating conditions.