NI LabVIEW and PXI Optimize Plywood Sorting Process

Author(s):
Rob Taylor - LightWave Computing

Industry:
Industrial Controls/ Devices/ Systems, Process Industries

Products:
LabVIEW, Vision, PXI/CompactPCI,

The Challenge:
Sorting green veneer plywood panels according to moisture content on a high-speed conveyor line.

The Solution:
Measuring moisture content through a high-performance image acquisition and analysis system based on National Instruments LabVIEW software and PXI hardware.

Plywood veneer moisture content can be very high if the wood is cut from a tree’s outer sapwood layer instead of its inner heartwood core. To maintain a good glue bond between plywood veneers and maximize veneer strength, plant operators must dry each sheet within a tightly controlled moisture range. A wet section of veneer in an otherwise dry heartwood sheet can make the sheet blow out inside the steam press, causing delamination of the plywood and resulting in lost production and increased costs.

Overdrying the veneer can make it brittle and cause it to lose its strength properties. Depending on the moisture profile, plant operators may either place wet veneers in ambient air to equilibrate or send them through a series of kilns at precisely controlled temperatures. The moisture sort system also uses feedback from the kilns to optimize the sort process, making it a key component in a plywood mill’s ability to maximize productivity and quality.

Identifying the Right Technology Solution

Plant operators have attempted to measure the moisture content and sort the green veneer panels accordingly, but they have lacked the ability to measure both peak and average moisture contents with the necessary precision (current RF-based sensors measure only averages and are not very accurate).

These plant operators have considered alternatives, but they have found that most vendors provide only canned image acquisition solutions that do not have the flexibility or performance needed for the job. Other vendors offer the performance and flexibility, but their systems require intimate knowledge of complex real-time operating systems and text-based programming languages that make development cost-prohibitive.

Because of this, Westmill Machine Automation collaborated with National Instruments Alliance Partner LightWave Computing to develop the software for a patented, vision-based moisture sensing system. In this system, a high-powered, tightly pulsed LED linear light source penetrates the veneer on the conveyor. A highly sensitive line-scan CCD camera picks up the intensity of the light that passes through each sheet and sends it to a frame grabber on an NI PXI-8187 Controller.

Depending on the veneer species and thickness, plant operators can use the NI LabVIEW Real-Time Module to adjust the LED brightness on the fly and get the maximum dynamic range from the CCD camera. The image intensity captured correlates closely with the localized veneer moisture content. The system analyzes each panel for peak and average moisture content and uses an NI digital I/O module to signal to downstream PLCs which panels to put in certain bins.

The real-time chassis communicates over an Ethernet interface to a Windows-based user interface application. With this feature, plant operators can select sort criteria based on peak moisture, average moisture, veneer thickness, and wood species while the real-time system sends sort statistics to help plant operators verify that the system is running properly. The system also displays the panel images with coded captions via the PXI controller’s video-out port.

The LabVIEW graphical development environment and IMAQ vision software have a wide variety of analysis tools. Plant operators can use the flexible triggering capabilities of the Camera Link interface to easily integrate the camera into the system.

The LabVIEW Advantage

This project required the development of two programs – a real-time application running on a PXI chassis and a Windows-based application running on an industrial PC. With new LabVIEW 8 shared variables, plant operators can improve their productivity by easily sharing data between the real-time and Windows systems. In addition, LabVIEW 8 provides the ability to debug both the real-time software and the user interface software at the same time while both systems are running. This eliminates switching between target systems when making changes, which further improves plant operator productivity using the LabVIEW graphical development environment.

The tight integration of the LabVIEW environment and IMAQ vision tools provided both the performance and ease of use lacking in other solutions. We were able to build a reliable system that performs the required analysis in the tight time window available to signal downstream equipment. As a result, plywood mills using Westmill’s patented LightSORT Green Veneer Moisture Measuring Technology can expect to see a significant improvement in their bottom lines.

For more information, contact:

Rob Taylor

LightWave Computing

Tel: (604) 522-1786

Fax: (604) 522-1726

E-mail: rob.taylor@lightwavecomputing.com

 

 

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