The Application
Weyerhaeuser’s Princeton, British Columbia facility processes raw logs into interior dimensional lumber. This particular application systematically separates the raw logs and places them on various conveyor belts through linear actuators under servo control (commonly referred to as Quandrant feeders). The initial processing step is debarking. In this step the log is scanned to determine its diameter (using an algorithm developed by Weyerhaeuser) and stripped of its bark. The algorithm takes into account the diameter of the log, tool speed, force applied on material and the amount of overlap of the knives removing the bark. Through this sophisticated algorithm, optimal performance of the process is achieved.

Secondly, a log length image is generated from photoelectric sensors on the feed conveyers. The log then passes through a hybrid scanner and a 3D surface profile is developed. The surface profile determines the log’s length, curve, and taper information which is then transferred to a programmable controller. The controller uses this information to position saws – through servo actuators – for the maximum recovery of the log.

Finally, the logs are sorted into bins and sent for additional processing into interior dimensional lumber.

This facility had been using Modicon 984 controllers and a limited number of Modicon Quantum controllers. All the controllers were programmed using 984 ladder logic.

“The use of Modicon Quantum controllers and Concept 2.0 software with IEC 1131-3 program-ming languages achieved Weyerhaeuser’s objective of reducing develop-ment and commis-sioning time. “

The Problem
Weyerhaeuser found that the sophistication of this application required a simpler and less time consuming programming language than 984 ladder logic. Their objective was to increase productivity by reducing PLC programming time and difficulty.

The Solution
The decision was made to standardize the project with Quantum controllers and Concept 2.0 software. The high speed sampling capabilities of the Quantum controllers and the reusable code functionality of Concept software provided the perfect solution.

Four IEC 1131-3 programming languages were utilized on this project. Parts of the system were supervised through Sequential Function Chart (SFC). SFC gave the engineers quick graphical feedback as to the state of the system. Function Block Diagram (FBD) was used for process control and Ladder Diagram (LD) was used for the motor control and other simple combination logic. Structured Text (ST) was incorporated primarily in the Derived Function Blocks (DFBs) for analytical processes and communications to the linear positioning modules. DFBs allowed the engineers to standardize on a set of functions that could be used throughout the application. The use of DFBs allowed quick trouble shooting of problems and kept complicated code invisible to the facility maintenance personnel.

For some of the high speed sampling required, the Quantum controllers were programmed using Interrupt Timer processing developed using 984 ladder logic. The consistent timed interrupt allowed for accurate sampling of pulses coming in from field devices measuring the position of logs on the conveyor system.

In addition to the standard Quantum hardware, MMC 120 linear positioning modules (Modconnect partner - Delta Computer System Inc.) were employed throughout the facility for positioning saws and feeders using hydraulic cylinders and magnetostrictive position feedback transducers. Standard DFBs were developed to simplify the configuration of these modules.

The entire system was developed using Distrib-uted I/O (DIO) on Modbus Plus. DIO provided sufficient speed for the high speed updates of the field devices. Traditionally, Remote I/O would have been used for this step. Finally, the control of the variable frequency drives for feed conveyor speeds was handled through Modbus Plus.

Results
The use of Modicon Quantum controllers and Concept 2.0 software with IEC 1131-3 program-ming languages achieved Weyerhaeuser’s reduction of development time and commissioning goals. The consultant on the project believes that future applications with Concept 2.0 will become increasingly shorter as compared to traditional methods