| Formaldehyde has been identified as a high carcinogen by the international agency for research on cancer,over 0.08 mg/m3 of the formaldehyde concentration can cause the unwell reaction of the human body.More than 90%of wood-based panels using urea-formaldehyde adhesive containing formaldehyde are made in our country,and the formaldehyde emitted from its products is a long process within a period of 3?15 years.This issue is aroused great concern all over the world.The formaldehyde emission limits in wood-based panels and its products are restricted by laws and mandatory standards,which are made by various countries and areas in the world.Meanwhile,the concentration limits of the formaldehyde indoor the building that is requested by the active national standards in Chain,which "GB 50325-2010 Code for indoor environmental pollution control of civil building engineering(2013 Version)" and "GB/T 18883-2002 Indoor air quality standard".In China,the special research on formaldehyde emission detection of wood-based panels and its products has been carried out for many years.The mature detection methods of formaldehyde emission include a perforated extraction,a dryer,a gas analysis,a climate chamber,and a full-scale chamber.Among them,the detection method of the full-scale chamber can maximally simulate the real indoor environment of the building to test the formaldehyde emission status,which is emitted from the whole furniture and wood-based panels and the products of building materials.There is one of the key development directions of formaldehyde emission detection in the industry now and in the future.The core technology of the climate chamber used in the early stage of the formaldehyde emission detection in China is a German method,which is called as constant temperature and humidity method.However,the detection time spends more than ten hours,and the accuracy do not work at a high level.After years of efforts,the Chinese academy of forestry has broken through the key control technology of the climate chamber.The dynamic and accurate tracking control technology of the climate chamber is invented so that the set temperature and humidity conditions of the climate chamber can quickly reach and maintain high precision control.The control precision of the temperature and humidity are ±0.1? and ?±1%respectively,the control precision of the humidity is 30%higher than foreign technologies,which achieve breakthrough results.However,there is a condensation phenomenon occasionally under a series of certain conditions,which using the dynamically precise tracking and control technology of the climate chamber.In order to solve the problem that the result of the formaldehyde emission is inaccurate and the experiment is not reproducible when the formaldehyde emission of wood-based panels and its products is detected in the chamber.In this paper,a 30m3 full-scale chamber is developed for detecting the formaldehyde emission,and a progressive target approximation algorithm is proposed to prevent the occurrence of the condensation in the full-scale chamber,achieving the goal of accurate detection of formaldehyde emission.Firstly,a hardware platform of the full-scale chamber and a piece of high-precision control equipment are developed.By studying the principle of the detection method of the full-scale chamber,an emission chamber,a temperature control system,a humidity control system,a fresh air exchange system,an air circulation system and a control system are respectively designed and realized,according to the function of each component device of the full-scale chamber.At the same time,in order to avoid the temperature and humidity shock in the full-scale chamber caused by the process of the distilled water replenishment into dew point humidity generator in the experiment of 7?28 days,an intelligent feedforward PID water replenishment system is proposed.Otherwise,aiming at the problem of the high-frequency signal noise disturbance generated by the signal acquisition system in the feedback control,a low-pass filter is designed for signal filtering,controlling the full-scale chamber system with high precision in kind of ways.Secondly,the mathematical model of the full-scale chamber is established,and the controllers based on exact feedback linearization,the H? control,and state observer are designed to discuss the high-precision control method and verify the theoretical feasibility of the design control method next section.According to the law of the energy conservation and mass conservation,the dynamic differential equations are established for the temperature of the full-scale chamber,the relative humidity of the full-scale chamber,the temperature of the medium water in the temperature-controlled tank and the temperature of the medium water in the dew point humidity generator.After that,in the fresh air exchange system,the model of the air temperature is described,in which air is blown into the dew-point humidity generator by the air pump,so that the mathematical model of the full-scale chamber is established.In order to avoid unnecessary running with energy waste when the high-power full-scale chamber is working for a long period of the experiment,there are controlled effect of the designed controller and the state response of the full-scale chamber system,which can be considered respectively as follows:1)Based on exact feedback linearization,a linear feedback controller is designed,using a way of the pole assignment.The simulation state response of the full-scale chamber is shown;2)The feedback controller is designed based on H? control with an approximate linearized full-scale chamber nonlinear model.By using a given weight matrix,the feedback gain is calculated by linear matrix inequality,and the state response of the full-scale chamber is simulated.3)For the linearized model,the Luenberger state observer is developed,where the gain of the observer is determined by the pole assignment method,and the system feedback gain is given by the method of a linear quadratic regulator to simulate the state response of the full-scale chamber.At the same time,the proposed control methods are compared with the traditional PID control methods,and the design experience of the anti-condensation constraint controller is summarized,which lays a foundation for the reasonable control algorithm and solution.Finally,the algorithm of the gradual target approximation is designed to satisfy the requirements of the anti-condensation during the process of constraint control.By analyzing the conditions of dewing,the fitting coefficient of the quadratic polynomial is determined by the least square method,so that the mathematical model of the anti-condensation condition is constructed.The control method of a gradual target is designed,and the desired temperature and relative humidity are divided into several sub-targets.For any sub-target,a feedback controller is proposed according to the error between the sub-target value and the real time value.In this part of the control,an H? controller is designed,and the optimal control parameters are calculated by linear matrix inequality so that the condition of the chamber can be reached quickly without the phenomenon of the fog and condensation,and the algorithm is realized by hardware platform and software programThe results of this paper show that:1)The method of the proposed control in this paper has been applied to the identification and detection of the wood-based panel furniture.The algorithm of the gradual objective tracking proposed in this paper can maintain the ability of the anti-condensation during the whole test process so that there is no phenomenon of the fog and condensation in the full-scale chamber;2)When the full-scale chamber works in a steady-state,the maximum deviation of the temperature is ±0.1?,and the relative humidity is ±1%;3)Under different environmental conditions,the time of the process for reaching the stable condition of the full-scale chamber is different:3.3 hours in spring,7.8 hours in summer,3.8 hours in autumn,and 4.4 hours in winter.The designed 30m3 formaldehyde emission detection full-scale chamber achieves the goal of the high precision control.The proposed gradual target approximation control algorithm effectively prevents the occurrence of the condensation in the full-scale chamber,and improves the accuracy and precision of the detection using the method of the full-scale chamber for determining the formaldehyde emitted from wood-based panels and their products.It provides a reliable instrument and control algorithm for detecting the formaldehyde emitted from wood-based panels and its products. |
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