Many European sawmills
employ remotely controlled log chariots to cut hardwood and softwood
trunks into shape for a variety of end products. Manual control
of such equipment is a demanding occupation, involving careful overall
surveillance and selection of the most appropriate cutting patterns.
Even for experienced operators, it is sometimes
difficult to take full account of the form and quality of a log
in deciding how to achieve the highest yield. Consequently, waste
levels run at an estimated 5% to 10%. As raw materials constitute
50% to 70% of a mill's overall costs, any improvements in this area
can have a dramatic impact on the bottom-line.
Need for automation
In the past, various efforts have been made
to automate the process, using scanners based on light barriers
or cameras to determine the log shape and select a preferred position
for the initial saw-cut. So far, these have met with only limited
Project 5056 was therefore launched in July
1996, with the objective of creating a more effective solution.
The consortium brought together six saw milling SMEs and Ciris Engineering,
a specialist in process design and system installation for primary
and secondary wood processing. EC funding supported a two-year programme,
in which the group explored the use of laser triangulation as the
measuring technique. They also developed and tested new control
software to translate the readings into optimised application-specific
The differing requirements of the partner mills
reflect a broad cross-section of industry needs. Etablissement Darré
from southern France, for example, is mainly active in hardwood
milling - especially as a producer of railway sleepers. These have
a particularly complex shape, and must be cut so that wane defects
are minimised on the rail-bearing face. Spanish company Maderas
Gallastegui, on the other hand, handles pine balks, typically ranging
in diameter from 25 cm to 80 cm, which pose a different set of problems.
In fact, Castellegui had already participated
in an earlier EC project under the CRAFT (Cooperative Research Action
For Technology) programme. It was thus able to bring valuable know-how
related to the treatment of resinous woods.
Consistent high accuracy
Ciris - which has more than twenty years of
timber industry experience spanning Europe, North and South America
- proceeded to develop a prototype laser scanning system. This comprises
a series of laser sensors mounted at 30 cm intervals above the loading
cradle of the chariot.
Initial introduction of a log remains a manual
procedure. The log is then advanced to bring it to the sawing position.
During this process, the sensors take measurements at each centimetre
along the full length of the balk. The resultant readings are downloaded
to a PC, with a total of 30,000 reference points per linear meter
producing much more highly detailed digital images than had previously
Data processing is completed in less than one
second, determining the location of the critical first cut and adjusting
the chariot settings without any delay in throughput. This cut reveals
the so-called 'minimum opening face', which corresponds to the smallest
width considered acceptable as a starting point. In contrast to
traditional practice, each log is treated with the same high degree
of accuracy throughout the working day - so such decisions are not
affected by human fallibility.
The balk then is rotated through 180° and
rescanned to determine the position of the second parallel cut.
The software provides graphical displays of the profile, together
with the measured cross section at various points. In this way,
it is possible to decide how many products of given dimensions can
be produced, indicating the most economical strategy for subsequent
cutting. The log optimiser measures, calculates the best pattern,
displays results on a screen and sends requirements to the carriag
settings thus resulting in the achievement of higher recovery factors
and better productivity.
Advantage for SMEs
The automation system has now completed
2 years of extensive trials in partner mills, and is now being marketed
under the brand-name 'Oscar'. Its fully modular design means that
it is adaptable to retrofit virtually all sawmills where log chariots
are used, without necessitating extensive modification. An important
advantage for European SMEs is that the EC's financial backing of
the development programme will permit commercial introduction at
a significantly lower price that that of competitive tools now emerging
in the USA.