The automatic grading with machine vision systems is efficient when both green and dry boards are graded with similar automatic systems. Typically, those are different lines,
Automatic systems
The benefits of automatic grading systems are:
- Increased value yield In the manual grading the value yield is maximum of 80-85%. In the automatic grading a value yield of 96% can be guaranteed. That has a very significant role in the overall financial result of the sawmill.
- The management of customer requirements and grading rules Automatic grading system allows the sorting for different market areas and customers. The system can easily grade to e.g. European, American and Japanese customers. There can be unlimited number of customer specific grading rules.
- Optimization of the production Machine vision system optimizes continuously the production and gives feedback to different process areas. For example, the amount of cracks in the boards is valuable information to the drying process. The exact data from the sawn goods are also available for the purchasing organization of the logs. The system can easily report the blue stain or decay of the boards.
- Low operation costs The automatic grading system has very few moving parts. The electronics is reliable and the cameras, as well as LED-light units, have a long-life time. In addition to regular daily cleaning only a few hours yearly maintenance is needed.
- Reliability of grading The machine vision system grades always in the same way. The grading results are available for all users and all the key measuring data can be stored for later use. The customer reclamations are thus easy and fast to handle.
- Constant quality in customer deliveries The quality of deliveries from the sawmill can be kept constant. If the company has several sawmills the quality data is easy to compare. The shipments can be arranged from any mill in the corporation and the production in the whole corporation can be optimized.
- High capacity utilisation rate With manual quality grading, the speed is max. of 30 boards/minute and even in the simplest manual grading process the speed is max. 60 boards/minute. With automatic grading, the grading speed can be increased to over 200 boards/minute.
Calibration of the measuring systems
The cameras and light units in the machine vision system are tuned with a metallic calibration beam. The system adapts automatically in the production conditions.
Recalibration is needed only with major technical changes like exchange of cameras in the system.
The suppliers of the grading systems
There are roughly ten suppliers of machine vision systems for the sawmill industry.
In Finland only FinScan Oy and Lisker Oy have supplied systems for the transversal grading lines in the sawmills. Both companies have been established in the 1980´s and they have long experience of grading systems. The oldest systems were based on black and white linescan cameras. Later on matrix colour cameras and special LED-lights have been utilized. The old systems needed board turning devices, but the new systems can analyse boards from top and bottom side without any board turning. The grading speeds have been increased from about 100 to over 200 boards/minute.
The other suppliers of grading systems are Microtec, RemaSawco, Comact, USNR and VAB Solutions (owned by Timber Automation). Weinig, Lucidyne and Woodeye are delivering systems only for lengthwise measurement and normally for remanufacturing plants. Microtec owns nowadays FinScan and Wood-Eye companies having the widest portfolio of grading scanners in Europe.
