When evaluating the performance of a scanner system, several methods and criteria can be used. One of the most important, but also not so well known indicator, is the Value yield.
The value of a board is usually calculated from price (in $/€/£/..) per m³, or directly as an item price for each product (dimension / length / grade). When calculating the board value, the price of waste products (chip, sawdust) must also be considered. The goal of the sorting process is to achieve as high value of the produced items as possible. Is it better to make a short high grade solution, or a longer lower grade solution? The value optimization will make the decision.
Value yield is a number given in %. It describes the actual value you get from your production, compared to the theoretical maximum value. In a perfect world the value yield would be 100%; in real life it will be lower. The goal of the sorting process is to get as close to 100% as possible. The importance of the value yield as an indicator of the process performance, can easily be understood. The higher the value yield is, the higher the profit for the sawmill will be.
There are many reasons why the actual value yield will not be 100%. One reason, which usually doesn’t come first into mind, is that there may be disagreements between people what 100% actually is! One person says that a board is grade A, another grade B, or one person measures a knot to be 25 mm, the other 2 mm bigger. Who is right? Everyone, who has made precision measurements of board defects knows how difficult and arbitrary that can be.
When evaluating the value yield of a sorting process (manual or automatic), the process would typically be as follows:
The value yield can now be calculated. It will be the sum of the values of the produced boards (ProdSum), divided by the sum of the maximum values for each board (MaxSum):
Many studies have been done about what levels of yield are achieved in manual sorting, and they indicate that they typically would be 80-85%*. With automatic sorting the goal can be set much higher, reaching levels of 96-99%*.
The BoardMaster system is always maximizing the value yield, and therefore also the profits of the sawmill.
*Comparison between automatic and manual quality grading of sawn softwood, https://www.diva-portal.org/smash/get/diva2:977660/FULLTEXT01.pdf