Identification and Autotuning of Temperature-Control System With Application to Injection Molding

Abstract—Motivated by the practical barrel-temperature con-trol of injection molding, this paper proposes two identification methods and a united control scheme for general temperature con-trol design. Based on the unity step response, corresponding to the full heating response in a temperature-control system, an identi-fication method is developed to obtain an integrating model for heating-up control design. By using a relay test around the set-point temperature, another identification method is proposed to obtain a model of stable or integrating type for control-system de-sign to reject load disturbances during system operation. To en-sure identification robustness, denoising strategies have also been presented for practical applications with measurement noise. For simplicity of implementation, a united control scheme based on the internal-model-control structure is proposed for both heating-up and steady operations against load disturbance. Analytical con-troller-design formulas and tuning rules are correspondingly de-veloped for quantitative regulation of the heating-up response and the load-disturbance response for operation. Examples from the recent literature and a practical application to injection molding are performed to demonstrate the effectiveness and merit of the proposed identification methods and control scheme. Index Terms—Injection-molding machine, integrating model, internal model control (IMC), relay test, step-response identifica-tion, temperature control. I.