Design and Experimental Evaluation of a Multivariable Grinding Circuit Control System

Abstract The multivariable control that was designed for the primary grinding in the Vuonos concentrator can control important variables like the final particle size and the density of the cyclone feed. The controller was designed for the plant using an interactive CACSD-software package which included the use of the inverse Nyquist array method. The control algorithms designed were implemented in the control computer in Vuonos and there was good agreement between the simulated results and the full scale tests: Changes of the setpoint of either one controlled output variable produced satisfactory responses, while the other controlled output simultaneously remained close to the desired constant value. The multivariable controller designed has been taken into continuous use in Vuonos. Autocovariance and spectral density functions have been calculated in order to analyse the behaviour of the final particle size and the density of the cyclone feed. According to the results obtained in the design by the inverse Nyquist array method and the experiments at the Vuonos Mill, this technique is suitable for the design of multivariable control of grinding. A practical advantage of this design technique is the simplicity of the final controller and the use of standard control algorithms.