Session: Controls 2

Paper Number: 111497

111497 - Control of Hydraulic Injection Moulding Machine With Electro-Hydraulic Variable-Speed Drive 

Injection moulding machines are traditionally hydraulic driven, however within the last couple of decades electric injection moulding machines are expanding in volume. Electric machines are marketed on their speed and accuracy compared to hydraulic driven machines. These properties are essential as the injection of plastic into a mould requires the machine to operate in both velocity and pressure control and requires an accurate switch-over from velocity to pressure control within each cycle.

In this work a retrofitted hydraulic injection moulding machine is presented, enabling high bandwidth control of a hydraulic injection moulding machine. The focus is placed on the injection cylinder, where the design of the hydraulic system is realized with standard components. The design is based on two permanent magnet synchronous motors connected to two fixed displacement pumps, allowing the control of the injection cylinder without the need for valves in the flow path, removing the dynamic influence of a valve and reducing throttle losses. 

The controller structure is designed from a model-based approach, where the electric motors and associated drive are operated in speed control modes.

A sum and load pressure decoupling control structure is proposed, enabling the possibility to apply SISO control designs for the sum pressure and the injection process separately. For the latter, a cascaded hydraulic drive controller structure is proposed, where the inner loop consists of a pressure controller, and the second loop consists of a velocity controller. A method to smoothly switch from velocity to pressure control is furthermore proposed.

Experimental results comparing injection cycles of an industrial injection moulding machine and the retrofitted injection drive and proposed control are presented, and limitations of the implementation are discussed.

Presenting Author: Rasmus Aagaard Hertz LEGO System A/S

Presenting Author Biography: Rasmus Aagaard Hertz received his M.Sc. in Electro Mechanical System Design from Aalborg University, Denmark, in 2017. With special interest in dynamic modelling and control of hydraulic systems. From 2017 to 2020 he has been working in industry with R&D Moulding, LEGO System A/S. Focusing on data and development of moulding platforms for the internal moulding factories. Since 2020 he has been an Industrial PhD student in cooperation with LEGO System A/S and Aalborg University, Denmark. Topics of interests include injection moulding, with focus on in-line material characterization, dynamic process modelling and control of the injection moulding process.