Design And Application Of Control System For Wood Drying Contraction Stress Based On S7-200smartPLC

Drying contraction stress is an external force and internal stress caused by the decrease in size of water loss during drying.The study found that the drying contraction stress during wood drying was the main factor leading to wood cracking and deformation.Therefore,the detection and control of drying contraction stress are crucial for wood drying.If a control system can be designed and an appropriate evaluation system can be established for the drying contraction stress in the process of wood drying.The use of this control system to achieve accurate control of the size of the wood drying contraction stress can greatly avoid wood cracking,deformation and other defects,which is of great significance to the development of the wood drying industry.This paper takes S7-200 smart PLC as the controller,and combines MCGS configuration software,touch screen,sensors and actuators to design a control system that can control the drying process of wood based on the drying contraction stress.The detection device of wood drying contraction stress,PLC controller and actuator are the main bodies of the control system.Firstly,the three-dimensional model of the control system and detection device for drying contraction stress is drawn by the three-dimensional modeling software Sketch Up.Secondly,according to the process requirements and system design principles for hardware selection,circuit design,programming and touch screen configuration,completed the overall design of the control system.Finally,the stable operation of the control system for drying contraction stress was realized through system wiring,debugging and performance testing.In order to apply the control system for wood drying contraction stress to production practice as soon as possible,and verify the actual control effect of the system,In this study,45 mm thick elm saw timber was used as the research object,under the condition of 120°C high temperature,the maximal value of drying contraction stress for elm before cracking was detected by the detection device of wood drying contraction stress;before the drying contraction stress of elm reached the maximal value,the drying contraction stress of elm in the drying process was alleviated by boiling conditioning for a certain time;by determining the maximal value of drying contraction stress and boiling conditioning time before cracking of elm,the high temperature drying schedule of drying contraction stress for 45 mm thick elm was preliminarily established.The control system of wood drying contraction stress was used to dry elm specimens according to 45 mm thick elm high temperature drying schedule of drying contraction stress and three-stage drying schedule.It was found that the average drying speed of the specimen with high temperature drying schedule of drying contraction stress as the drying schedule was 11 times higher than that of the three-stage drying schedule under the condition of high initial moisture content,and the drying effect was good without obvious drying defects.Through the above research,including the design of control system for wood drying contraction stress and the establishment of high temperature drying schedule of drying contraction stress for 45 mm thick elm,the preliminary application of wood drying contraction stress control system is realized,and the stability and efficiency of the system are verified by experiments.