For a long time, the assessment of veneer drying quality has relied on traditional methods involving manual, random spot-checks of moisture content on the veneer surface, with the overall quality being evaluated based on empirical judgment. Furthermore, traditional equipment is gradually being phased out by the market due to issues such as high energy consumption, frequent malfunctions, and low control precision. To address these challenges, we have independently developed an online veneer moisture content detector and established an automated control system for veneer drying that incorporates online moisture monitoring. This control system utilizes the OMRON C200Hα Programmable Logic Controller (PLC) as its central processing unit. By continuously monitoring the temperature and humidity conditions at the moisture exhaust vents, the system regulates the discharge of humid air during the drying process-transforming chaotic, unregulated venting into a systematic, controlled process-thereby achieving significant energy savings and cost reductions in veneer drying. Additionally, by continuously monitoring the final moisture content of the veneer, the system dynamically adjusts the conveyor belt speed of the dryer; this not only enhances the quality of the dried veneer but also contributes, to a certain extent, to an increase in overall product yield.
In terms of system architecture, we have designed and implemented an automated veneer drying control system based on a "PLC + Industrial PC + Touchscreen" configuration, guided by the principles of distributed control. This architecture enables a management paradigm characterized by centralized oversight combined with distributed control within the plywood production environment. Through the touchscreen interface, a user-friendly Human-Machine Interface (HMI) has been established, facilitating functions such as real-time production monitoring, dynamic data visualization, fault alarms, and production reporting. Currently, with the widespread adoption of sensor technology and the Internet of Things (IoT), the equipment is capable of real-time temperature and humidity monitoring, remote operation and maintenance, and data traceability, thereby reducing the costs associated with manual intervention. Our roller-type veneer dryers offer a range of control options-including manual control systems, stepless variable speed control systems, and fully automated computer-controlled systems-which can be selected according to specific client requirements.