Method and device for pressure control of electric injection molding machine

Abstract

A rotational angle of a motor operative to propel forward a screw in an injection molding machine is detected at an encoder. An output from the encoder is employed to obtain an angular velocity ω of the motor. From the obtained angular velocity ω, an estimated melt pressure value δˆ that contains no differential term is derived using a certain observer theory. The estimated melt pressure value δˆ is employed to calculate a torque command value TCMD for the motor, which is fed back to the motor. Thus, precise propelling power control unaffected by noises can be executed without the use of a pressure sensor such as a load cell.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for controlling pressure in an electric injection molding machine. BACKGROUND ART [0002] A typical electric molding machine employed in the art senses pressure using a pressure sensor in a control target (such as mold open / close, extrusion, and nozzle touch) and, based on a signal from the pressure sensor, configures a closed-loop control circuit to control the propelling power. [0003] Specifically, for control of injection pressure, a load cell is arranged at the root of a screw, for example, to sense a force that pushes the screw (a forward force) in the form of pressure by the load cell. Then, based on the sensed pressure, feedback control is applied such that the pressure to be sensed at the load cell reaches a desired pressure value, thereby controlling the propelling power of the screw. [0004] A measured signal output from a general pressure sensor such as the load cell is a weak analog signal. An e...

AI Technical Summary

Benefits of technology

[0031] In accordance with the present invention, an angular velocity ω of the motor operative to propel forward the screw in the injection molding machine is obtained. An estimated melt pressure value δˆ is derived from the obtained angular velocity ω using the observer theory. The motor is then controlled such that the estimated melt pressure value δˆ follows the melt pressure setting δREF. Thus, the melt pressure can be controlled precisely without the use of any pressure sensor such as a load cell.

Problems solved by technology

In this case, the propelling power may not be controlled well as a phenomenon.

Nevertheless, it is extremely difficult to completely eliminate such the control failure.

Therefore, depending on adjusters, adjusted conditions may differ subtly and result in individually different controlled conditions as a problem.

As a result, a precise melt pressure control is made difficult as a problem.

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