Injection molding machines are widely used in industrial applications. The velocity of injection process and the pressure of dwelling process must be controlled with all products; however, such control is very difficult. In fact, the tuning of the controller parameters needed for high quality or multi-objective production takes a long time and requires a high level skill from the professional field engineer. The tuning can be seen as a pursuit of unknown plant parameters.
This study uses a model reference adaptive control (MRAC) strategy to control the injection molding machine. This method can accommodate the unknown plant parameters and tune controller parameters to make output track a desired reference signal. In this first report, we derive the mathematical models and design, separately, adaptive velocity and pressure controllers for the model circuit used to simulate previous two processes. We then performed and evaluated the hybrid MRAC experiment and process MARC. We also examine the robustness of the proposed controller under parameter change, e.g., nozzle clogging, contraction of molded object, etc. The results confirm the proposed method's efficiency and robustness.

View full abstract

The first report confirmed the design of the adaptive injection and dwelling controller in a simulation model, the robustness for parameter change and the possibilities for application. This paper describes the next step: application to an actual commercial real injection molding machine. We examine hybrid control as well as process control of injection and of the dwelling processes. To clarify the designed strategy performance, we compare the proposed method and a PI controller in a sequence of production processes. The cold start operation, i.e., operating the machine without warm-up routine also examined for actual application. The evaluation of product thickness shows how effective the proposed controller will be in an actual machine.

View full abstract

The minimal control synthesis (MCS) algorithm is a simplified adaptive control strategy, since no prior knowledge of plant dynamic parameters is required. Furthermore it is suitable when a small sampling is required, because of the reduction of on-line calculation. The purpose of this paper is to present implementation results of MCS algorithm on a position control system of a pneumatic horizontal and vertical cylinder using proportional control valves. Introducing a switching friction compensation, two kinds of MCS controller are tested in experiment and the results are compared with the conventional PI controller. In order to investigate the robustness of the MCS algorithm, the supply air pressure is changed during the experiment and the disturbance force is also exerted on the piston. The experimental results reveal the good adaptation and robustness of the MCS algorithm.

View full abstract

Compliance control by a novel hydraulic actuator with built-in compound control function of displacement and thrust, and its applications have been studied. It was realized by measuring the rotational angles of stepping motor shaft and body, and adjusting their feedback weight parameters separately. The explanation of the compliance control function and analysis of static and dynamic characteristics were conducted. Through the preliminary experiments, it is confirmed that the actuator is very effective in the compliance control. Furthermore, as an application, experiment of grasping and lifting a ball was conducted. It was clear that the actuator can be used for the control of displacement, thrust and compliance.

View full abstract