Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Feed control of material en route to shaping area
Patent
1986-11-26
1988-07-05
Chiesa, Richard L.
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Feed control of material en route to shaping area
264 407, 2643281, 425147, 425587, B29C 4550, B29C 4577
Patent
active
047551232
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding machine and, more particularly, to a metering system of an injection molding machine which can control the rotating speed and back pressure of a screw in accordance with the position of the screw when metering is performed.
Background Art
Although most of conventional injection molding machines can variably control the rotating speed of a screw, they apply a back pressure to the screw by a hydraulic pressure when metering is performed. Therefore, it is difficult to switch the value of the back pressure to arbitrary values as needed. When a molding material is to be homogeneously metered, the rotating speed of a screw must be controlled, and a back pressure must also be switched and controlled. Thus, since the conventional injection molding machines cannot easily switch the back pressure to various values, they cannot meter a molding material to sufficient homogeneity.
SUMMARY OF THE INVENTION
It is an object of the present invention to switch the back pressure applied to a screw to an arbitrary value by utilizing a torque limit function of a numerical control unit, in order to enable switching of the rotating speed and the back pressure of the screw in accordance with the position of the screw, thereby obtaining an optimum metering state of a molding material.
In order to achieve the above object, according to the present invention, a numerical control unit is provided which has a first servo motor for driving a screw of an injection molding machine in an axial direction, a second servo motor for rotating the screw, position detecting means for detecting a position of the screw, and memory means for storing a screw rotating speed command value and a torque limit value in correspondence with a screw position; and the numerical control unit also has a torque limit function. The numerical control unit reads out a screw rotating speed command value and a torque limit value from the memory means in accordance with the screw position detected by the position detecting means, and outputs the readout screw rotating speed command value to the second servo motor and the readout torque limit command value to the first motor, so that a predetermined screw rotation and back pressure can be obtained in accordance with a screw position.
In this manner, according to the present invention, drive of the screw in the axial direction and rotating drive of the screw are performed by the servo motors, the torque limit function of the numerical control unit is utilized to switch and control the back pressure in accordance with the screw position, and the rotating speed of the screw is also controlled. Therefore, a homogeneous metering state and an efficient metering can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view for showing an overall configuration of an injection molding machine to which an embodiment of the present invention is applied;
FIG. 2 is a table stored in a non-volatile memory shown in FIG. 1; and
FIG. 3 is an operation flow chart of the injection molding machine shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows an injection molding machine according to an embodiment of the present invention. Referring to FIG. 1, reference numeral 1 denotes a screw of the injection molding machine; 2, a heating cylinder; and 3, a screw shaft of the screw 1. The screw shaft 3 can be rotated by a second servo motor M2 for screw rotation through a transmission mechanism 4. The screw shaft 3 is also moved in the axial direction by a first servo motor M1 for injection through a transmission mechanism 5 so as to perform injection. Reference numeral 7 denotes a servo circuit for driving and controlling the servo motor M2. The servo circuit 7 controls the speed of the motor M2 by a speed command supplied from an input/output circuit 15 of a numerical control unit (to be referred to as a CNC hereinafter) 10 which incorporates a computer, and a feed-back signal supplied from an incremental-type encoder P2. Refe
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Chiesa Richard L.
Fanuc Ltd
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