Control-Oriented Energy-Based Modeling of a Screw Extruder Used for 3D Printing

This paper proposes an energy-based approach for modeling a screw extruder used for 3D printing. This approach was used due to the difficulty in measuring the salient variables associated with regulation of the process state. The control-oriented steady-state model for the screw extruder is based on the reliably available process variables of heater current and screw speed, which constitute the manipulated variables. The controlled variable for this extrusion process is the extrusion rate. This model is based on balancing the energy between the work done by the screw, the heat delivered by the heater at the nozzle, and the enthalpy of the extruded product stream. The fine measurement available is the current commanded by the heater control system to maintain a fixed temperature at the nozzle. An array of thermistors are used as feedback for the temperature profile along the extruder. The screw speed is calibrated for a stepping motor used for conveying the material. This steady state model can then be helpful for developing a dynamic model for a controller capable of accurate flow control based on preview of the extrusion rate but with a simple yet robust hardware requirement.