The control of dyebath pH in the dyeing of cotton with reactive dyes is critical for batch to batch shade reproducibility, levelness of dyeing and the optimisation of the dyeing process. Conventional controllers have not proved too successful in controlling dyebath pH since it is very difficult to develop a mathematical model for the dyeing process. The relationship between various parameters of dyeing is highly complex, non-linear and exhibits time-varying behaviour. One method to deal with such complex situation is to apply fuzzy control to the dyeing process. Fuzzy control is a modern control method that uses a control algorithm based on human reasoning to take control decisions. In this project work, a fuzzy control system was developed to monitor the pH of the dyebath during the dyeing process. An on-line pH meter and dosing pumps were mounted on a laboratory jet dyeing machine. Various preset pH profiles were used to study the tracking performances of the control system. Simulation and initial experimental results of the system performance proved to be very promising. Further fine-tuning of the system gave very satisfactory tracking performances of the dyebath pH up to pH values of around10.0. Above pH 10.0, the tracking performance degrades. With respect to the dyeing performance, the controller did not significantly improve the colour yield of the dyed fabric. However, results showed a high degree of shade reproducibility between dyed batches when using the proposed controller for the applied preset pH profiles.
