The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Size Control of Sawn Timber by Optical Means in Breakdown Saw Machines
Jaakko Vuorilehto
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Forest Products Technology, Helsinki University of Technology for public examination and debate in Auditorium Ko 216 at Helsinki University of Technology (Espoo, Finland) on the 23rd of November, 2001, at 12 noon.
Dissertation in PDF format (ISBN 951-22-5662-2) [2804 KB]
Errata (in PDF)
Dissertation is also available in print (ISBN 951-22-5661-4)
Abstract
The thesis investigates optical measuring and statistical data processing, and presents a method to understand and reduce sawing variation by examination of sawn timber sizes. Continuous timber size control offers improved opportunities for analysing saw machines or even individual sawblades. The thesis is illustrated with seven saw machine case studies that relate to the development of the technique. Log and cant breakdown is examined in single- and double-arbor circular saws and bandsaws. The first analysis of each saw machine is made in normal production, and the second using a controlled benchmarking test. A total of 44350 logs were sawn in the study.
The behaviour of a saw machine is described using such descriptors as total, within-board and between-board standard deviations, and sawblade bend. Based on observations in benchmarking, an equation y=αeβx±R, where α and β are constants, R the process reproducibility, and x a variable that expresses sawing time and saw load, can be established for each of the saw machine descriptors. An example is the total standard deviation descriptor function s=0.21e0.58x±0.11, established for a single-arbor circular saw in a 4-piece saw set-up.
The method will help a sawmill to establish descriptors and equations used to describe the behaviour of their saw machines, to baseline saw machine performance and to compare it to best practices in the industry. The descriptors may be used to establish current, short- or long-term capabilities and characteristics. The method can be used to examine various production conditions and tooling, such as effects of log size, feed speed, and sawing time. Other factors include saw speed, sawblade parameters, operation of setworks and feedworks, and effects of seasons. The results of the study show that sawblade behaviour, feedworks and work piece holding problems, and previous saw machines may be causes of large sawing variation.
Keywords: sawing variation, lumber size control, sawn timber size, optical measurement, saw machines
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© 2001 Helsinki University of Technology
Last update 2011-05-26