"A cut above the rest"The benefits of continuous dimension control in sawmillsThe traditional control of saw set-ups at most sawmills today is done by manual measurements: when these seem to be "about right", sawing is begun! However, very few sawmills have the time or the interest to take sufficient measurements of the sawn timber, let alone the incentive to analyse the few manual measurements that are done in any way other than just by assessing the order of magnitude of the cut dimensions. In this article, a new way of control measurement is described and the benefits it offers to sawmills are discussed. Introduction In a sawmill, after a change
of blade or saw set-up production must be recommenced as soon as possible.
A thorough manual measurement of a batch of core timber - for example
50 measurements evenly distributed over each plank - could take two
people half an hour or more, delaying the production process. For this
reason, manual measurements are usually only taken at three places: the
top, middle and root of the planks. However, the dimensions of timber can
vary widely: Figure 1 shows the dimensional variations of two core pieces
that have a green (fresh wood) dimension of 45.8mm. If measurements are
only taken at three points on the timber, these variations are not apparent,
and so it is not possible to analyse the sawing process in any useful manner.
 The Seecon system, which measures
the thickness dimensions of sawn wood in real time and on-line (Figure
2), was developed jointly by a forward-looking Swedish sawmill, Vanern
Timber, and the Finnish inX Systems, as part of an ESPRIT High Performance
Computing and Networking (HPCN) programme of the European Commission.
  Fig. 3 Sawn pieces as viewed by the Seecon system. Figure 3 shows the Seecon image of the sawn wood. Here each image is derived from a set of 400 measurements over the length of each plank, the thickness of the sawn wood being measured at every centimetre. (Neither horizontal nor vertical movements of the planks have any effect on the accuracy of the system.) These measurements are then grouped into ten sets (modules), the Seecon computer automatically calculating the averages for each module. Fig. 4 presents the real time results of Seecon for the same planks as shown in Fig. 1.  Accuracy of the new profile saw line What made a sawmill in Billingsfors, Sweden, on the west coast of lake Vanern near the Norwegian border, want to investigate the possibilities and then develop a method of continuous process control? At the end of 1997 the sawmill,
Vanern Timber, acquired a new German profile saw line with two axle saws.
(Almost the whole of the 60m-long sound-insulated production line can be
seen in Figure 5.) The planned production capacity of the saw line was
200,000m3. The installation and trial production were completed during
the Spring of 1998, and performance tests were started in August.
 After the supplier had tuned
the new equipment, an independent sawmill consultant took some manual test
measurements of some of the typical sawn products. Vanern Timber felt the
results were unsatisfactory, and after some adjustments and further tuning,
the control measurements were repeated the following day with green timber
measuring 5 x 45.8mm. Table 1 shows the results.
The adjustments and further tuning had reduced both the standard deviation and maximum spread, but all the cut pieces were now too thick and the maximum spread was still nearly a millimetre. It was not only the dimensional variations that concerned Vanern Timber, however, but also the time it took to set-up the saw blades. It was these problems that Vanern Timber was seeking to resolve. The sawmill wanted a system that could be used to perform set-ups rapidly without manual measurements. It also wanted:
During the development of the system for Vanern Timber, discussions were conducted with numerous Finnish and Swedish sawmills, and their wishes were also taken into account in the development work. Most of these concerned quality and production control, usability, maintenance requirements, and reporting for own and customer purposes. Improved control of the cutting process The prototype that was delivered to Metsä Timber Vilppula sawmill was the starting point for the machine vision instrument and software development. Modifications of the software and equipment were completed in October 1998, and the system was installed at the Vanern Timber sawmill in November. On the saw line there were a number of positions where the system could have been installed. The logical choice, however, was to measure the core timber since that is the most valuable part of Vanern Timber production and, moreover, all previous cuttings affect its dimensions. The installation of the system
was quite easy and the first dimensions were measured on the same day.
One problem was the considerable accumulation of sawdust and wood strips
in the measuring area (as Figure 6 shows), despite the efforts to reduce
them. However, the measurement system functioned well and the results were
consistently correct because the system software can differentiate sawdust
and wood strips from planks as long as the view is not too obscured. Even
so, it is accepted that the removal of sawdust and wood strips must be
improved in order to facilitate reliable long-term measurements.
 The measurement of core timber Seecon measures core timber from an overhead position using special optics which make the light beams from the object parallel. The benefit of this is that the height of the planks has no effect on the accuracy of the measurements and so blocks of wood can be any height. Since Seecon takes measurements at every centimetre along the length of each plank, depending on its length the plank can be measured 300-500 times. Obviously it would not be feasible to take the same quantity of manual measurements. As a result of the large number of measurements, information received can be used not only to adjust saw blade set-ups but also:
The Seecon system also has the advantage that a saw operator can view the measurements of all sawn planks on a monitor close to him in real time. In addition the monitor uses a graph to show how the dimensions have changed on a long run. Reliability and comparability of the measurements Test measurements were conducted when Seecon had been in operation at Vanern Timber for two months. The aim of these tests was to check the sawing accuracy of the profile saw line and to compare manual measurements with the Seecon measurements. New measurements similar to the ones in Figures 1 and 4 were taken, and the results indicated that the comparability was very good and that the saw accuracy had been stable. Vanern Timber had already reached this conclusion and, based on Seecon measurement data, had instigated set-up changes. The next question was whether the Seecon measurements were repeatable. This was tested by passing a set of three planks with a green dimension of 42.6 mm several times through the measurement instrument and comparing the results. Figure 7 shows the results.
During these measurements the planks were divided into four modules. The
curve of one set of plank measurements matches with the other curves so
well that only four curves can be seen in the figure. For module 2 the
standard deviation of the Seecon measurements was only 0.04mm; for the
other modules it was 0.11mm. During the tests the biggest single standard
deviation was 0.19mm. The standard deviation of all repeated measurement
averages was 0.12mm.
 In our study the technical values of the process, as well as log and timber sales prices, relate to the situation at Vanern Timber at the end of 1998. Previously the set-ups at Vanern Timber were made in a converging sequence of set-up changes and trial cuttings. These cycles were repeated until the set-up was right and production could be started. When Seecon was introduced, the set-up was done "in-flight", in real time, and actual processing time increased significantly. Table 2 summarises the increase
in productivity. The presumption is, of course, that the increased production
time can be utilised: the time saved in doing the set-up offers the sawmill
an opportunity to earn more money. Even when based on average values, the
faster set-up times are of value to Vanern Timber and indicate significant
additional earnings for the sawmill. It should be noted that in the following
net earning calculation, we did not take into consideration the fact that
the value of chips for pulp also increases the profitability somewhat.
The possibility of earning an extra half a million Euros should be an attractive incentive for any sawmill! However, this new measurement technology also improves the sawmill's yield and economy in other ways for instance:
An interesting study at Vanern Timber involved the question of how many "uncontrolled" and therefore rejected planks are sawn during the set-ups when manual measurements are used, and what the value of these planks is. At Vanern Timber it took on average 20 minutes to carry out all the adjustments for a new set-up using manual measurements. During this process approximately 30 (20-50) logs were sawn. Each log typically produced three core planks, which gives a total of 90 planks per set-up. The sawmill is operated in two shifts with four new set-ups per shift. The quantity of uncontrolled planks per day was therefore 8 x 90 planks - 720 planks. Over a year this totalled around 165,000 planks. The sawmill estimated that about half of this quantity was more or less unusable - in other words, a total of 82,000 planks with a sales value of over 0.3 million Euros were unsaleable. If these reject planks are perhaps inadvertently sold to a customer who complains, the sawmill has to reduce the price of the whole batch f.ex. by 30% and the losses can even be greater, not to mention the fact that at the same time the supplier-customer relationship suffers. An extra million Euros! As the raw material and transportation
costs are practically the same for all sawmills, a sawmill can only compete
on the basis of its production technology and practices. By using its Seecon
measurement and reporting system effectively, Vanern Timber can now tolerate
an increase of 10% in raw material prices or a drop of 5% in sales prices
without any effect on its profitability. More importantly, if the market
situation remains the same, Vanern Timber can earn an extra profit of one
million Euros with its improved production practices.
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