Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1988-03-22
1989-03-14
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 264 407, 318632, 364476, 425135, 425149, 425166, B29C 4577
Patent
active
048122688
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a suckback method capable of positively effecting a suckback operation in an injection molding machine which employs a servomotor as an injection axis drive source for axially driving the screw.
2. Description of the Related Art
In metering operation, when a screw receives the back pressure and at the same time is drivingly rotated, resin material in a heating cylinder becomes molten by virtue of thermal energy supplied from a heater and frictional heat generated during screw rotation. As an amount of the molten resin accumulated in the distal end portion of the heating cylinder increases, the screw is subjected to molten resin pressure. This pressure is in the opposite direction of the screw movement and would cause the screw to be moved backward. Thereafter, the screw rotation is stopped when the screw reaches a metering completion position. Then, the socalled suckback operation is effected by slightly moving the screw backward and at the same time eliminating the back pressure so as to disconnect the molten resin material between a sprue bushing and a nozzle to prevent the resin from loosely falling off. An injection molding machine of a type equipped with a hydraulic drive source on its injection axis can easily effect such suckback operation. On the other hand, in an injection molding machine of a different type employing a servomotor as the injection axis drive source and limiting the output torque of the servomotor to provide a controlled back pressure during the metering process, the following drawback can occur. That is, when the torque limit for the servomotor is released to generate a drive force enough to effect suckback operation, the screw is moved forwardly by virtue of the presence of an error amount accumulated in an error register of a servo circuit for driving the servomotor, and hence the suckback operation cannot be smoothly performed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a suckback method in an injection molding machine capable of effecting a smooth suckback operation by preventing forward movement of the screw upon execution of the suckback operation at the last stage of a metering process.
According to the present invention, an injection molding machine includes a servomotor as an injection axis drive source for axially driving a screw a servo circuit adapted to drive the servomotor and including an error register for storing therein an error amount indicative of the difference between a commanded screw position and an actual screw position. A torque limit for the servomotor is effected to apply a set back pressure to resin. In order to achieve the object, a suckback method in an injection molding machine, according to the present invention, comprises the steps of: (a) stopping screw rotation when the screw reaches a metering completion position; (b) reducing an error amount, accumulated in the error register at the time the screw rotation is stopped, to a value less than a predetermined value; (c) releasing torque limit for the servomotor and for applying the preset back pressure; and (d) driving the screw backwardly by means of the servomotor by a predetermined suckback amount. Preferably, a follow-up operation for the error register is carried out in step (b) so that the error amount accumulated in the error register becomes equal to zero.
As mentioned above, according to the present invention, the error amount, accumulated in the error register at the time the metering completion position is reached, is reduced to a value less than the predetermined value, preferably to zero, by carrying out a follow-up operation for the error register, before the screw is driven for suckback operation by means of the servomotor, with the torque limit for the servomotor released. Accordingly, the suckback operation can be accurately and positively carried out.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing an arrangement of a control section of
REFERENCES:
patent: 4524313 (1985-06-01), Kuno et al.
patent: 4710119 (1987-12-01), Otako
patent: 4718841 (1988-01-01), Kiya
patent: 4734025 (1988-03-01), Kawamura et al.
patent: 4755123 (1988-07-01), Otake
patent: 4759705 (1988-07-01), Otake et al.
Kamiguchi Masao
Umemoto Hiroshi
Fanuc Ltd.
Heitbrink Jill L.
Silbaugh Jan H.
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