The present invention relates to a method for implementing log cutting in a way which optimises veneer yield, in which method, a log is measured by a measuring apparatus and measuring data are transferred to a computer to determine the contour of the log and to determine the cutting points of blocks such that it is possible to cut the log into blocks having one or more different lengths. When using one cutting measurement, the method enables to optimally cut bad bits out of the log.

Recent devices used for log measuring typically optimise log cutting based only on the lengths of blocks to be cut. Alternatively, they optimise the largest cylinder of the block based on provided yield. That is, they do not take random-sized pieces into account.

The object of the invention is to provide an arrangement which enables optimising both the total veneer yield obtainable in lathing and, simultaneously, a suitable distribution of blocks which provides an adequate number of blocks for all lathes at the plywood factory. This should also consider the numbers of blocks having been ordered.

To achieve this object, the method according to the invention is characterised by, in the method, after having determined the contour of the log, fitting by means of a computer programmatically blocks of different sizes inside the log in a different order such that the total veneer yield of the log can be calculated and optimised considering obtainable full sheets and incomplete sheets of different grades and the demand of blocks of different lengths at the production facility. Different production facilities utilise e.g. the following combinations of block lengths: 2,600 mm and 1,300 mm; 1,600 mm and 1,300 mm; 2,600 mm, 1,600 mm and 1,300 mm; 2,000 mm and 1,000 mm. The optimal yield of a single cut block can be determined e.g. by a method described in specification FI20031390 which takes into account both full sheets and joint veneer.

The invention will next be described in more detail by referring to the accompanying drawings where:

Fig. 1 schematically shows optimising the cutting of a log into blocks based on the volumes of complete cylinders, Fig. 2 schematically shows a block having an extension and

Fig. 3 schematically shows the result of a virtual lathing example.

In Fig. 1, a log is referred with number 9 and blocks obtainable from it with numbers 2-8. Reference number 1 designates surplus wastage. In this schematic example, the optimisation was done based on the volumes of complete cylinders utilising two different block lengths, e.g. blocks of 2,600 mm and 1,300 mm. Fig. 2 schematically shows the veneer yield of one block. Reference number 11 designates a complete cylinder which determines full sheets obtainable in lathing. Reference number 12 refers to incomplete sheets i.e. joint veneers obtainable from the block in lathing. In this step, the block includes one or more extensions. The quantitative and qualitative veneer yield obtainable from the block is determinable by programmatic simulation by outlining veneer being lathed inside the block or by performing virtual lathing into a veneer ribbon. The simulation result can also be shown on a display, whereby particularly the result of virtual lathing gives an illustrative picture of the end result of the actual lathing to be realised. Fig. 3 illustrates a description of sheet cutting in virtual lathing. Reference numbers designate: 21 = full joint veneer, 22 = lower-grade (heartwood) veneer, 23 = lower-grade/high-grade veneer, 24 = high-grade veneer, 25 = joint veneer, split in the middle of the web, 26 = waste. The structure of the fragmented section at the beginning determines the number of usable parts obtainable from it by cutting, which parts can be given their own values. When also the complete section is given its own value, the result is the value yield obtainable in lathing based on these.

In the method according to the invention, the log is first measured and then all block cutting combinations are tested by virtual lathing and such combination is chosen which provides the best total veneer value of the blocks to be cut, considering also incomplete sheets in addition to full sheets. It is also possible to consider the price of sheets of different grades. For example, a full sheet obtained from the surface is often more valuable than one obtained from inside and the value of a random piece is smaller than that of a full sheet. It is possible to keep the length distribution of blocks such which corresponds the distribution required in the production lines. The required distribution can be automatically measured from the lathe lines. The logs can be measured e.g. by a laser profile scanner and measurement data are transferred to the computer. If required, the consumption of different block measurements is collected in the lathe lines. Data on desired block lengths and distribution are entered on the computer and the computer makes the cutting combination and calculates veneer value for each combination by lathing the blocks virtually. It is also possible to measure the logs by a measuring apparatus based e.g. on ultrasound or x-rays. In practice, the measurement can be implemented in many different ways, e.g. by conveying the log through or past the measuring apparatus or by using a moving measuring apparatus which can perform the measurement as the log stays in its place.

The invention also relates to a cutting apparatus implementing the method, which apparatus includes a measuring gate e.g. with laser profile sensors and a computer which calculates and visualises the cutting alternatives with their yields. The computer either offers the selection option to an operator or controls the cutting automatically.