A model predictive controller of plastic sheet temperature for a thermoforming process

This paper presents a method to control the surface temperature of a plastic sheet using model predictive control (MPC). Although control techniques have been developed for the heating phase of the thermoforming process, oven heater temperatures in the thermoforming industry are still largely adjusted by trial and error based on the experience of the operator. MPC is one of the advanced methods for process control that has been used in different plants since the 1980s. Even though the MPC controller can handle a multivariable process, the large number of computations makes it difficult to apply to large systems such as multi-zone temperature control in a thermoforming machine. In this paper, the design of a model predictive controller is reported and implemented on a complex thermoforming oven with a large number of inputs and outputs for precise control of sheet temperatures under hard constraints on heater temperature and their rates.