Scanning lumber for defects and increased profits.

Wood-scanning technology can be used to identify the defects in lumber, and can help optimize cutting strategies to get the most value from lumber.

AFTER YEARS OF ANXIOUS anticipation wood scanners are actually being used successfully in manufacturing facilities. This is very good news. However, this does not mean that anyone has developed a scanner that can identify all of the things that people Would like to know about a board -- far from it. At the same time, you can now find out more about a board than you might think you can at production speeds.

Illustration 1 shows the top and bottom view of a board from the scanner's perspective. It is easy to see that the board looks completely different on the reverse side, so both sides must be scanned.

[ILLUSTRATION 1 OMITTED]

Also the edges of the boards need to be scanned for wane (wane is a defect in the edge or corner of lumber characterized by the presence of bark or the lack of wood). When material greater than 3 inches thick is scanned, all four sides should be scanned in order to detect edge defects.

The top of the board in Illustration 1 has a few small knots and a strip of wane on the lower edge. The bottom of the board has larger knots, but the face is free of wane. The difference in the defects detected on the two sides will have an effect in the decision-making process of the system when determining how best to cut the board. For example, depending on the manufacturer's grading and cutting requirements, some of the defects may be allowed to stay in the finished product. This is one of the key benefits scanners have over human operators because the scanner can determine which is the best side of the board and make cutting decisions much quicker and more consistently than an operator.

How Wood Scanners Work

The images displayed in this article were not obtained using cameras, but with special detectors that actually analyze the cell structure of the wood. Knots, stain, rot, mineral and twisted grain all have different cell structures that can be detected individually.

Also, several different cell structures may be present in one defect. For instance, consider how many different categories of knots there are: live, dead, loose, cracked, tight, face, spike and pin knots, to name a few.

The amount of information flowing from the scanner to the computer is huge, but it is all necessary. Otherwise, it would be impossible to differentiate between cutting strategies. As the board passes through the scanner, it is divided into thousands (sometimes millions) of small rectangles, each providing specific information for the scanner to analyze. The size of these small rectangles determines how precisely the board data will be picked up and stored. The speed of the board through the scanner, the speed or ability of the scanner and the speed of the computers all influence the precision of the scan.

Currently, scanners are being produced that operate fast enough to keep up with available high-production optimization equipment. However, as the speeds of computerized optimizers increases, scanners will also need to become faster.

The next step in the process is categorizing the defects. Before scanning, the user will have programmed the specifications for acceptable and unacceptable defects as they apply to different grades. What is acceptable in a particular grade may vary depending on location, quantity, and whether or not the defects are on both sides of the board. There can be dozens of choices that pertain to knot size alone. The list of choices may be extensive; however, after a grade is initially defined and named, it can simply be recalled by that name.

Illustration 2A shows the signal data from the scanner. In this illustration, the boxes represent unacceptable knots (with want, excluded) based on the company's cutting specifications.

[ILLUSTRATION 2 OMITTED]

Illustration 2B shows the same board, only this time, distorted grain around the knots has been added to the definition of the knot. Obviously, the rectangle's defining knots are larger and more numerous in Illustration 2B. The signal for wane would be shown in a separate graphic. Again, each company's part specifications will define whether the amount of wane is a defect; and, if so, whether it is a defect in all parts.

Making Softer Cutting Decisions

After setting up the system to cut according to a set of in-house rules or grades, the final key element concerns the assignment of part values. Unfortunately, part values are often difficult to determine. For instance, if you cut a 26-inch by 3-inch Grade 10 part and you also cut a 26-inch by 3-inch Grade 1 part (defined as clear two sides, no defects), what is the value of the Grade 10 part versus the Grade 1 part? Grade 1 is clearly worth more, but how much more?

Also, is a 25-inch Grade 10 part worth more than a 20-inch Grade 1 part? If so, leave in more defects and cut the 25-inch Grade 10 part. There are hundreds of ways to cut up some boards. Finding the best way will result in the greatest profit.

The Advantages of Scanning

So far, the industry has really just scratched the surface of lumber scanning. Within a few years, scanners will become more commonplace in the woodworking industry. But what are the real benefits of this new technology? More often than not, the justification for purchasing a scanner is the appeal of reduced labor costs.

The real answer, however, is in the information we can obtain from scanning. Today's optimizing systems are capable of processing enormous amounts of material using fewer man-hours of labor than manual systems. But their ability to produce the overall highest yield and value is still limited by the information they receive concerning the lumber being processed. Lumber defect scanning gives manufacturers the ability to supply the optimizing system with much more information, so that the material can be optimized more effectively. This information can also be used for tracking lumber usage, production run simulations, purchasing decisions, quality control, etc.

Lumber defect scanning is one of the most exciting prospects for improving yield and value. How quickly will you be using defect scanning in your operation? Some people are doing it now. In some applications, it will be several years before it, becomes a reality.

RELATED ARTICLE: Companies who after lumber defect scanning systems:

BARR-MULLIN INC. Raleigh, NC [phone] Circle #140 on Reader Service Card

GRECON DIMTER INC. Hickory, NC (704) 397-400 Circle #141 on Reader Service Card

GROUP SEVEN SYSTEMS INC. Hudson, NC [phone] Circle #142 on Reader Service Card

KOCH LTD. MACHINERY & SYSTEMS Atlanta, GA [phone] Circle #143 on Reader Service Card

LUCIDYNE TECHNOLOGIES Corvallis, OR [phone] Circle #144 on Reader Service Card

Sandy Mullin is president of Barr-Mullin Inc., manufacturers of rough mill equipment and Cell Scan, an automatic lumber defect recognition system. Mullin can be reached at [phone].