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
1987-07-09
1988-11-29
Woo, Jay H.
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
264401, 425171, B29C 4577
Patent
active
047878347
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a metering apparatus of an injection molding machine and, more particularly, to a metering apparatus which is mounted on an injection molding machine using a motor as a drive source for rotating a screw and supplying a back pressure by a servo motor used as a drive source for an injection mechanism in metering, thereby correctly performing metering.
In a conventional injection molding machine, a screw is rotated by a motor, or the like, during metering, and a back pressure is applied by a hydraulic piston, or the like. The resin is melted by rotation of the screw. When the molten pressure of the resin exceeds the back pressure, the screw is moved backward. When the screw reaches a metering pin, it is detected by a limit switch, or the like, and the rotation of the screw is stopped. However, even when the screw has reached the metering point and the limit switch is operated, the rotation of the screw is not stopped immediately because of the inertia of the screw rotating mechanism. As a result, the metered injection amount may be excessive. When the actual metering point is set at a position slightly before a logical metering point, considering inertia, the injection amount may be insufficient. Also, because of the preset position error of the limit switch or the operation error, high-precision metering cannot be performed. The metering error causes short shot, a sink mark, or a burr, so that a product having a good quality cannot be obtained.
In order to solve the above problem, as is disclosed in Japanese patent publication No. 52-43869, the screw rotation speed is reduced at a position slightly before the metering point in order to decrease the inertia, and the screw is stopped at the metering point. However, in this method as well, the position of the screw is detected by a limit switch. Therefore, a metering error occurs because of the preset position error and the operation error of the limit switch. Since the error amount generated by the inertia of the screw rotating mechanism differs depending on the rotation speed of the screw, high-precision metering cannot be performed unless the preset position of the limit switch is moved every time the screw rotation speed is changed.
SUMMARY OF THE INVENTION
The present invention has been made in order to eliminate the above drawbacks of the conventional technique and has an object to provide a metering apparatus for an injection molding machine wherein a metering point can be easily set and which can perform metering correctly without being influenced by the inertia of the screw rotating mechanism, even when the preset screw rotation speed is changed in the last stage of the metering process.
In order to achieve the above object, according to the present invention, an injection molding machine is provided which rotates a screw by a screw rotating motor, and supplies a predetermined back pressure by an injection servo motor, for driving an injection mechanism for moving the screw in an axial direction during metering. The position of the screw is detected by a position detecting means based on a position detection output supplied from a position detector of the injection servo motor. Next, a screw position indicating a metering point at which metering is to be ended is stored in a memory means. The screw position detected by the position detecting means and a metering position stored in the memory means are then compared by a metering point detecting means, thereby discriminating whether the screw has reached the metering point. Further, the screw position, detected by the position detecting means, and a decelerating screw position, set at a position slightly before the metering pont, are compared by a screw deceleration point detecting means, thereby discriminating whether the screw has reached a deceleration start position. Finally, a rotation control means decreases the rotation speed of the screw rotating motor, in accordance with a detection output supplied from the screw deceleration poin
Fanuc Ltd.
Heitbrink Timothy W.
Woo Jay H.
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