Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1990-01-10
1991-07-23
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 425135, 425162, 425166, B29C 4576
Patent
active
050341693
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an injection control method for an electrically-operated injection molding machine.
BACKGROUND ART
Depending on types of molded products, it sometimes is desirable to more sharply increase the injection speed at the beginning of an injection process. To this end, in conventional hydraulic injection molding machines an accumulator is connected to a hydraulic injection cylinder for supplying pressurized operating oil at a large flow rate to the cylinder. On the other hand, electrically-operated injection molding machines employ injection servomotors capable of producing a large output with small inertia. However, injection molding machines equipped with accumulators or injection motors capable of large output with small inertia are costly.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an injection control method for an electrically-operated injection molding machine, whereby the injection speed may be sharply raised even while using a low-priced electric injection molding machine.
To achieve the above-mentioned object, according to the present invention, there is provided an injection control method which is applied to an electrically-operated injection molding machine wherein an injection servomotor driven in accordance with an error between a target value and an actual value of an injection control parameter. The injection control method comprises the steps of: (a) preventing substantial rotational movement of the injection servomotor at an initial stage of injection control, while the target value of the injection control parameter increases; and (b) starting the rotational movement of the injection servomotor when the error between the target value and the actual value of the injection control parameter reaches a predetermined value.
According to the method of the present invention, the injection servomotor is capable of generating a great output torque upon initiation of the rotational movement of the servomotor, even if the servomotor is other than a large output, small inertia type, because the target value of the injection control parameter associated with the rotational movement of the injection servomotor is increased, while substantial rotational movement of the injection servomotor is prevented, and the rotation of the injection servomotor is not started until the error between the target value and the actual value of the injection control parameter reaches a predetermined value. Accordingly, injection speed can rise rapidly even in a less costly injection molding machine, so that injection molding is carried out with a desired injection characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing the operational principles of an injection control method according to an embodiment of the present invention;
FIG. 2 is a block diagram showing the essential parts of an injection molding machine to which the injection control method of FIG. 1 is applied;
FIG. 3 is a block diagram the servo circuit of FIG. 2; and
FIG. 4 is a flowchart showing the injection control process as executed by the control unit of FIG. 2.
BEST MODE OF CARRYING OUT THE INVENTION
The operational principles of an injection control method according to an embodiment of the present invention will be explained with reference to FIG. 1.
Conventionally in injection control methods wherein command pulses are periodically distributed to a servo circuit to provide a target rotational position, for an injection servomotor connected to the servo circuit for driving the same motor which position varies depending on the pulse distribution level, the pulse distribution amount per pulse distribution period is increased at an accelerating rate from the start of an injection process with lapse of time, and at the same time, actual rotational position of the servomotor is immediately caused to follow the target rotational position from the instant at which the injection process is started, so that the axial movement of the injection screw i
REFERENCES:
patent: 4812268 (1989-03-01), Kamiguchi et al.
patent: 4826640 (1989-05-01), Neko
patent: 4849678 (1989-07-01), Kamiguchi et al.
Hosoya Yuichi
Kamiguchi Masao
Neko Noriaki
Taira Takayuki
Fanuc Ltd.
Heitbrink Jill L.
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