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Circular Saw Inspection System and Sawing Accuracy

The goal with this work, which extend over a period of 3 years, is to create a tool/tools that can help sawdoctors perform better. This thesis covers the first five months and was made year 1999 at Forest Research Institute, Rotorua New Zeeland. It contains of a Literature review, what features to measure and how this affect a sawblades performance, building and evaluating of the first prototypes. The thesis also include a test of a statistical method in order to measure every sawblades individual performance.

Two prototypes were constructed which measure five features:

  • A video inspection system that measures every tooth individual side clearence angle and tip width.
  • A system for measuring a sawblades individual topography
  • Two systems for measuring sawblades tension (light gap and naturalfrequency).

The video inspections system have a precision in measuring the side clearance angle of 0.56 degree average standard deviation and tip width precision of 0.14 mm average standard deviation. Better precision in measuring side clearance must be made and can be achived with higher resolution in camera and bigger monitor.

First prototype aimed to measure a sawblades individual topography and tension at the same time. As a result the blade was mounted on a hub horizontally. Unfortunately result showed that sawblades topography became inconsistent. The sawblade has to be mounted vertically to prevent effects from gravity. A new prototype was constructed but could not be evaluated due to an accident when transporting the prototype to the mill.

The tension was measured in two ways: by light gap method and measuring a blades natural frequency. Measuring the tension by its natural frequency was more of a test in order to determine if this could be an adequate method. An accelerometer was used to create a pulse into the blade. The evaluation showed that it was hard to tune in the right frequency which is crucial for a consistent result. One way to get around this problem would be to send a number a frequency in to the blade (pink noise) and record all naturalfrequencies.

To eliminate effects of lumps the light gap method was performed on new sawblades. Each blade was mounted horizontally on a hub and fixed at a point in the rim. A bending force was performed on the opposite side of the fixed point and the light gap was measured on a 90 degree angle from the fixed point and the bending force. The result showed inconsistent readings. Up to 1.92mm difference in light gap on the same sawblade was measured. Next step is to perform the test again but now redesign the prototype so that the blade is being mounted vertically.

A Mathematical method was created and tested which aimed to calculate sawblades individual performance by knowing the boards position in the saw and by measuring the boards thickness (variance) in a number of points. Result show negative variance on a number of sawblades which is mathematically impossible. The conclusion is therefore that this mathematical method for measuring the blades performance can not be made. 

  • Dan Olofsson
  • Luleå University of Technology Department of Engineering Sciences and Mathematics
  • Originalspråk: En

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