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FAIR-CT95-1188
X-Ray Log Scanner |
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Contract No: | FAIR-CT95-1188 |
| Date Prepared: | June 2000 | |
| Source: | Final Report Abstract |
Introduction
Wood is a biological material with great variability. Every piece of wood is a unique individual. The great challenge in the wood products manufacturing process has always been to select pieces of wood with properties that fulfil the product requirements. Sawmill people have become more and more aware that what is lacking is a tool that can characterise the raw material in order to control the conversion process in an optimal way. There is a large economical potential in better utilisation of the raw-material if the internal and external properties of the logs are taken into consideration.
Today there are several systems for scanning and automatic grading of logs used in sawmills. These systems use either optical scanners or, in a few cases, gamma-ray scanners. The conventional optical scanners used for grading of logs typically measures the log diameter every 10 mm along the log in two or three directions, or (in the case of "3 D- scanners") the "true" cross-section of the log. From these values, new variables such as taper, butt taper and bumpiness are calculated. With the aid of these new secondary variables, statistical classification algorithms can be developed.
The gamma-ray scanners (Tina), also measures density variations along the log and gives some grading possibilities based on this. When sorting into two grades, Tina obtained 75% correct classifications for Scots pine and 65% correct classifications for Norway spruce. The major drawbacks with Tina are the low signal to noise ratio and the radiation hazard from the two radioactive isotopes.
The signals from the optical scanners and Tina are too coarse for very accurate log grading and good control of the sawing process at the single log level. The signals only give information about general properties and large individual defects in the axial direction of the log. For good process control we also have to find the position of individual defects in the radial and tangential direction of the log.
This is very important, as customers increasingly demand sawn products with special properties regarding dimension, moisture content, warp and last, but not least biological or aesthetic features. To be able to fulfil these requirements, the right logs have to be selected for a certain product before the sawing process. This means that an accurate tool that can measure external and internal features in logs will be very much needed in the future.
Objectives
The Main objectives of this European demonstration project were:
To build, install, test and demonstrate an X-ray LogSeanner that can detect type, size and location of different defects in the interior of logs at a feed speed of 3 m/s.
To demonstrate how the sawmills in an optimal way can use the new possibilities the X- ray LogScanner gives: demonstration of economic, technical, quality, environmental, advantages with respect to existing solutions.
To identify specific target groups (extended audience) to whom the technology should be demonstrated and best exploited. To organise workshops and/or information days during which the demonstration projects achievements will be presented to an extended audience.
The project started with a system specification where different foreseen applications, parameters to be measured and new possibilities offered by tile X-ray LogScanner were analysed and described.
The decision regarding the final system specification for the pilot installation have been based on the profitability of the different applications for the host sawmill and on what is possible to achieve from a technical point of view.
The different system components such as x-ray sources, x-ray detectors and control algorithms were after that enhanced and adopted to the requirements stated in the system specification. The development of machine configuration and control algorithms has mainly been carried out with aid of simulation technique and with data from the Swedish pine stem bank and the EC FAIR II financed Norway spruce stem bank.
The basis of the Stem Banks is the CT scanning of about 400 carefully selected stems from sample plots all over Sweden, Finland and France. The stems were chosen from well-documented sample plots.
Finally a X-ray LogSanner prototype has been built, installed, demonstrated and tested at a sawmill.
All features of the X-ray LogScanner have not been tested yet. However, the results of the first industrial test show that the performance of the pilot installation in most cases is on the same level as what could be expected from the simulations. The exception is for separation between pine and spruce due to the fact that the enhanced separation algorithm still is too time-consuming for a real time application.
The Log Scanner has the ability to measure features of a log such as:
Top-diameter under bark measured before debarking 0 Automatic separation of species (pine and spruce)
The prototype installation has been used for log sorting but other foreseen applications for installation of a Log Scanner are:
The Log Scanner will be able to carry out some of these applications in parallel.
The first tests of the industrial X-ray LogScanner have shown that:
The X-ray LogScanner measures diameter under bark before debarking with an standard deviation of 3,2 mm for both pine and spruce
The X-ray LogScanner sorts logs according to species (separation between pine and spruce) with an accuracy of 96%
The X-ray LogScanner sorts spruce logs in two groups according to average year ring width with an accuracy of 89%
When sorting logs according to the expected grade of the sawn products, 85% of both the spruce logs and the pine logs were correctly sorted.
Conclusion
In summary, the work carried out in this project has shown that an X-ray LogScanner with two X-ray sources has a great potential to become a powerful tool for controlling the sawmill process. However, a lot of work remains to be done before the full potential of the scanner can be utilised.
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