Applying a Fuzzy Gain-Scheduled PID Controller to Dyebath pH

Abstract

One of the factors critical to dyeing levelness in the textile industry is pH control, but it is a difficult problem because of inherent nonlinearity and changing process dynamics. The proportional integral derivative (PID) controller has been widely used in industry. Conventional fixed gains are hard to achieve with dyebath pH control, since it is difficult to model the process and the scheme is not adaptive to time-varying characteristics. Thus, a fuzzy gain-scheduled PID controller is promising for dyebath pH control because of its self-adaptation and robustness. The control scheme uses fuzzy rules and reasoning to autotune PID gains without the need of modeling. A modification to overcome the difficulty in finding the ranges of gains for stability is proposed. Simplified dyeing experiments demonstrate that the proposed controller can track pH set values under the influence of temperature rise, residual alkali, etc.