By Yvon Hubert, Comact Equipment Inc.
There isn’t an industry around that doesn’t have to keep getting better. Manufacturers have enormous competitive pressures to improve yields, quality, throughput, and labor costs. Much of that pressure lands squarely on the shoulders of machine builders serving those manufacturers.
That’s how it is for Comact Equipment, Boisbriand, Quebec, a well-known developer of sawmill technology and equipment for the lumber industry. Our company offers a line of products from basic conveyors to complete, automated production lines.
To help our customers optimize yields in a highly competitive lumber industry, Comact uses machine vision as a key performance sensor. The company has used a camera/laser setup for geometric reading since the ‘80s, and its use of color vision technologies began about five years ago.
Scan and Optimize
In machinery used for the linear transport of tree trunks, machine vision precisely identifies each tree trunk’s shape to optimize cutting operations. “A triangulation method and an optimizer lets us determine how to cut a given trunk to get the maximum amount of usable wood,” says Guy Morissette, development engineer at Comact.
Figure 1: Snap-Scan uses many lasers and cameras to build a complete 3-D shape of a moving or stationary log with a single “exposure,” with a laser line every 4 inches.
The log first goes through a rotation scanner, which builds a 3-D shape, which is used by the optimizer to find the rotation required for proper orientation. The optimizer sends the rotation solution to the PLC before the log arrives at the log turner. The PLC controls the rolls that rotate the log. During the rotation, another scanner—the correction scanner—examines the log to do any needed rotation correction. If the real rotation of the log is not precisely what it was supposed to be because of knots or butts on the log or hydraulic pressure variation, the optimizer provides feedback to the PLC to rotate the log a bit more or less. Once the log is rotated, it goes through the infeed of the machine. This uses another scanner to align the log in the canter heads. Most OLI machines will have saws to cut side boards after the canter heads. The side boards will fall at the outfeed in a conveyor, and the cant (the log with two plane faces on each side) goes to the next cutting machine.
Electric drives and motors power the saws and canter. Hydraulic-powered servo positioning is used for saws and canter positioning.
To perform the optimizer analysis, two to 25 area cameras are used and up to 80 Lasiris laser scanners perform the triangulation calculations.
We were using Pulnix TM-7, TM-200 or TM-250 area cameras, and to efficiently capture the large number of images required, our company chose a Dalsa imaging board with four asynchronous acquisition channels.
"Because we can connect up to four asynchronous cameras to this board, we were able to eliminate the synchronization circuits Comact needed with other boards,” explains Dalsa’s vice president of sales and marketing, Philip Colet. “The high-speed imaging board performs simultaneous acquisition at up to 40 MHz digitization per channel from up to four camera channels.”
Each channel, says Colet, features an A/D converter, synchronization circuitry, anti-aliasing filter, input lookup tables and the ability to respond to four independent trigger events. Buffer image data can be stored in local memory during heavy PCI bus traffic, helping to increase acquisition speed and host availability for processing.
So today instead of using the coaxial camera and a grabber card, we’re using Dalsa’s Ethernet Genie camera.
Dalsa worked with us to develop a new dedicated protocol for this application to compress the digital video signal. This type of camera allows us to scan at speeds of 120 Hz and is being used successfully in almost all of the geometry scanner system replacing coaxial cable technologies. “Ethernet eliminates the need for frame-grabber boards, which lowers the cost, and is more flexible because no specific backplane with PCI slots is needed” says Morissette. Most of the configurations that needed switching with the coaxial camera are now all software programmable.
Comact used JAI, Panasonic and IVP cameras before, but now standardizes on Dalsa for homemade scanners.
“We use Hermary and LMI products, if required by the customer,” says Morissette.
Images are transferred to a PC for processing and optimization analysis. “The image analyzer detects the laser slices on the trunk and builds a 3-D shape. Then the optimizer determines what products can be cut from each shape,” says Morissette.
Our Snap-Scan (Figure 1) uses many lasers and cameras because it builds a complete 3-D shape of a log with a single “exposure.” There is one laser line every 4 inches for a 4-in-scanning density. Scanning is done with the log in motion or stationary.
“By comparison, our C2 builds the complete 3-D shape with only two lasers and cameras,” says Morissette. "The scanning is synchronized to the movement of the log along the conveyor using a shaft encoder. The log must be moving to build the shape. All the scanners are geometric only. They use laser/camera triangulation to build the shape.”