Seeing is believing: Vision system advances wood inspection

Tuesday October 16, 2007
Written by Philip Colet
It takes vision to achieve success. Literally. Comact Optimization Inc., a Boisbriand, Que.-based developer of sawmill technology and equipment–which ranges from basic conveyors to complete, automated production lines–helps its customers optimize yields in the highly competitive lumber industry with machine vision. For example, in machinery used for the linear transport of tree trunks, machine vision provides precise identification of each trunk's shape to optimize cutting operations. "Using a triangulation method and an optimizer, we can determine how we should cut a given trunk to get the maximum amount of usable wood from it," says Guy Morissette, a development engineer at Comact. Between two and 25 Pulnix TM-7, TM-200 or TM-250 cameras snap images of each tree trunk, and from two to 80 Lasiris lasers perform the triangulation calculations. To efficiently capture the large number of images required, Comact chose a Dalsa imaging board with four asynchronous acquisition channels. "Because we can use up to four asynchronous cameras with this board, we were able to eliminate the synchronization circuits we needed for other boards," explains Morissette. The high-speed Dalsa imaging board performs simultaneous acquisition of up to 40 MHz digitization per channel from up to four camera channels. Each channel 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. Images are transferred from the image acquisition board to a PC for processing and optimization. The image analyser detects the slices of the laser on the trunk and builds a 3D shape. Then, the optimizer determines what products can be cut from each shape. The resulting solution is transmitted to a programmable robot system, which controls the mechanical equipment that cuts each piece of wood accordingly. Making the gradeComact and its customers are also reaping the rewards of machine vision on the GradExpert grader. Using a 3D scanner reading and a colour machine vision system to detect such defects as rot, knots and cracks, GradExpert automatically determines the quality grade of each piece of cut timber (2x4s and other boards). Using machine vision dramatically increases throughput and provides more reliable inspections and more accurate grading than human operators. High-frequency fluorescent tubes light each piece of wood. Eight Basler L301BC line scan cameras and eight image capture boards from Dalsa acquire images of the wood at speeds of up to 160 MB/second in search of any defects that would affect the grade of each piece. The Viper-Digital is a single-slot video acquisition and pre-processing board for the PCI bus that features high-speed, highquality image acquisition up to 160 MB/second. This board can handle a variety of data formats, including eight, 16, 24 or 32 bits/ pixel. Hardware speed is crucial to the success of the application, which demands real-time image acquisition and processing. "The fact that our architecture is based on a PC helps us achieve our performance goals," comments Morissette. "In addition, programming is simpler and we can benefit from the flexibility offered by the PC." And since the frame grabber features a driver to Baslerís L301BC line scan camera, Comact saved the time and money involved in developing a driver from scratch. Another reason that Comact chose image acquisition boards from Dalsa for both applications is the ability to connect the boards to the QNX real-time operating system used in Comact's equipment via a simple serial interface. Comact develops all of its software in-house, from drivers to the user interface, using QNX technology. According to Morissette, both Comact and its customers are pleased with the reliability and performance of Dalsa's boards in these two applications. So pleased, in fact, that Comact is also using Dalsa's Genie-M640 Ethernet camera, which can scan at speeds of 120 Hz. The company is using the camera in its geometry scanner system, replacing coaxial cable technologies. Indeed, vision continues to bring the company success. Philip Colet is the vice-president of sales and marketing at Dalsa.

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