Abstract:

Objective: Formaldehyde released from wood-based panels and its products is identified as a highly carcinogenic substance by the international health organization, and the emission climate chamber methods is determined as one of detection methods in China. However, there is the phenomenon of the fog and the condensation using the existing climate chamber devices during the test processes, so that the detection results of formaldehyde released from wood-based panels and its products are not enough accurate. Therefore, an algorithm of gradual objective tracking is proposed in this paper, which could make the temperature and relative humidity of chamber without the phenomenon of the fog and the condensation to achieve high precision in the whole processes. Method: The control objective is divided into different segments in this method, f_{C_set}(t)={f_{C_set}(t₀), f_{C_set}(t₁), …, f_{C_set}(t_m-1), f_{C_set}(∞)±ξ, f_{C_set}(∞)}. The control algorithm which starts from the initial value selects the control sub-objective and the control parameters in each segment. The control sub-object f_{C_set}(t_i)(0 ≤ i ≤ m) becomes the next-stage control sub-object f_{C_set}(t_i+1) when a state reaches a neighborhood of the set sub-objective f_{C_set}(t_i). The PID algorithm is used for controlling in each segment, and the parameters of gain K_p, integral K_i and differential K_d are selected under the conditions of the non-condensing constraints, so that the climate chamber temperature and the relative humidity can quickly reach the defined conditions. Meanwhile, there is no phenomenon of the fog or the condensation inside the climate chamber all the time. The method of control proposed in this paper is applied to the designed climate chamber, and the wood-based panel furniture is identified and measured. Experiments have been carried out under the different environmental conditions in four seasons of the year, using the developed controller. Result: 1) The algorithm of the gradual objective tracking proposed in this paper can maintain the ability of anti-condensation during the whole test processes, so that there is no phenomenon of the fog and the condensation inside the climate chamber. 2) When the climate chamber is in a steady state, the maximum deviation of the climate chamber temperature is 0.1℃, and the relative humidity is±3%. 3) The time for the climate chamber to reach the stable detection conditions is different under different environmental conditions, those are 3.3 h, 7.8 h, 3.8 h and 4.4 h in spring, in summer, in autumn and in winter, respectively. Conclusion: With the proposed control method which applied to the 30 m³ climate chamber, the following conclusions could be drawn:1) There is no phenomenon of the fog and the condensation inside the climate chamber. 2) The accuracy of steady-state between 23±0.1℃ and 50%±3% inside climate chamber, which temperature and relative humidity respectively, meeting the ISO 16000-9 standard requirements; 3) The time for the climate chamber to reach the steady state is less than 8 h.

Key words: full-scale chamber, prevent condensation, gradual objective, variable parameter tracking control