Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1987-07-24
1989-03-28
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 407, 318632, 364476, 425135, 425149, 425166, B29C 4577
Patent
active
048161969
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection-molding machine, and more particularly, to a method and an apparatus for controlling injection of an injection-molding machine, in which the injection of the injection-molding machine is controlled by means of a numerical control unit.
2. Description of the Related Art
Injection control in an injection-molding machine may be effected by two control methods, as shown in FIGS. 4 and 5. Namely, in a system of the type shown in FIG. 4, speed control is performed from an injection starr position, and, when a screw reaches a switching position for hold, the speed control is changed over to hold pressure control. Thereupon, hold is performed for a predetermined period of time, and a metering block in the next stage is entered. According to the system of FIG. 5, injection control is performed for a predetermined time after the start of injection, and, when the predetermined time for the injection control elapses, the injection control is changed over to the hold pressure control. When the hold time terminates, the metering block in the next stage is entered.
Conventionally, in controlling an injection-molding machine by means of a numerical control unit (hereinafter referred to as NC unit), the system of FIG. 4, not the system of FIG. 5, has been used. However, if the screw cannot inject resin at a predetermined injection speed and cannot, therefore, reach the switching position for hold within a normal required injection time, on account of the viscosity of the resin being too high or any other reason, the time required for the execution of an injection cycle is extended, thus lowering the efficiency of production. Also, the screw cannot follow up an output command, for use as a speed command, so that an error of a command for movement, compared with an actual screw position, is stored in an error register in the NC unit. If the value of the error reaches a predetermined level or higher, the NC unit stops pulse distribution, thereby possibly stopping the whole injection-molding machine in an unexpected manner.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of injection control for an injection-molding machine by means of an NC unit, whereby the aforementioned drawbacks of the prior art are eliminated, and injection control can be performed on the basis of the time elapsed after the start of injection.
In order to achieve the above object, according to the present invention, injection is performed while controlling the injection speed by means of injection-speed control means when an injection command is inputted. At the same time, a first timer for measuring a predetermined time after the start of the injection is started. When the preset time of the first timer is up, hold pressure control is performed by hold pressure control means, and a second timer for measuring a predetermined time after the start of the hold pressure control is started. When the preset time of the second timer is up, pulse distribution is performed until the position of a screw reaches a hold pressure end position, and a follow-up operation is performed by follow-up means so that a value stored in an error register through the pulse distribution becomes zero.
Thus, according to the present invention, injection control can be controlled in a time-based manner, even in an injection-molding machine which is controlled by an NC unit. Accordingly, the injection cycle is fixed. Even if a servomotor, for use as a drive source for the injection, cannot inject resin at a predetermined speed so that the screw cannot reach a switching position for hold, for any reasons, the control mode is switched to hold pressure control and the second timer is actuated when the preset time of the first timer is up. When the preset time of the second timer is up, pulse distribution is performed compulsorily so that the screw apparently reaches the hold pressure end position, and the follow-up operation is accomplished. Accor
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patent: 4325896 (1982-04-01), Rodgers, Jr.
patent: 4411609 (1983-10-01), Yoshii et al.
Fanuc Ltd
Heitbrink Jill L.
Silbaugh Jan H.
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