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

In this work an industrial hydraulic injection moulding machine, is retrofitted with a electro-hydraulic variable-speed drive. 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 drives are operated in speed control modes. A sum and load pressure decoupling control structure is proposed, enabling the use of SISO control design for the pressure level and the load pressure separately. For the latter, a cascaded hydraulic drive controller structure is proposed, where the inner loop consists of a pressure controller, and the second and third loop consists of a velocity and position controller respectively. 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

Practical Implementation of Secondary Control Principles in an Electro-Hydraulic Speed-Variable Drive Applied to an Injection Moulding Machine

In this work, a hydraulic state of the art injection molding machine is retrofitted with a dual pump drive. The dual pump drive is an electro-hydraulic speed-variable drive, with focus on high bandwidth control through secondary control principles. Secondary control is based on providing the torque references for the electric machines directly, instead of a speed reference. The pressure control loop is based on decoupling of the piston load pressure and sum pressure enabling the possibility to utilize two SISO controllers. The application is the injection cylinder of an industrial injection molding machine, retrofitted with the designed dual pump drive. Experimental results for the proposed secondary control structure are presented and difficulties of implementation are documented, and a large gap between the theoretical achievable bandwidth and the experimental achievable bandwidth is shown. Three possible reasons for this gap are identified, namely amplification of high frequency components from e.g. signal noise on sensors, the use of axial piston pumps which induce pressure pulsations and the influence of the discrete sample time of the digital controller hardware. Lastly future work within the field is considered, including possible methods to minimize the influence of the identified issues

Development and Validation of a 1D Dynamic Model of an Injection Moulding Process and Design of a Model-Based Nozzle Pressure Controller

A 1D model describing the dynamics of an injection moulding machine and the injection process is presented. The model describes an injection cylinder actuated by a dual-pump electro–hydraulic speed-variable drive and the filling, holding and cooling phases of the injection moulding process utilising amorphous polymers. The model is suggested as the foundation for the design of model-based pressure controllers of, e.g., the nozzle pressure. The focus is on using material, mould and machine properties to construct the model, making it possible to analyse and design the dynamic system prior to manufacturing hardware or conducting experiments. Both the presented model and the developed controller show good agreement with experimental results. The proposed method is general in nature and enables the design, analysis and evaluation of the machine, material and mould dynamics for controller design based solely on the physical properties of the system