Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Positioning of a mold part to form a cavity or controlling...
Patent
1989-10-16
1991-07-09
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Positioning of a mold part to form a cavity or controlling...
26432813, 425145, 425149, 425156, 425159, B29C 4577
Patent
active
050303953
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and an apparatus for pressure control, capable of smoothly effecting multi-stage pressure control in a motor-operated injection-molding machine.
BACKGROUND ART
In an injection-molding machine, multi-stage pressure control is performed to produce good-quality moldings. For example, a pressure hold process is divided into a plurality of pressure hold stages, and target hold pressures for the individual pressure hold stages are set to values different from one another, so that the hold pressures are subjected to multi-stage control. To effect the multi-stage hold pressure control, in a motor-operated injection-molding machine, a torque limit value (target hold pressure) for restricting the output torque of a servomotor for axially driving an injection screw is successively changed with the lapse of time from an instant at which pressure hold is started, so that the hold pressure is subjected to open-loop control. Alternatively, the hold pressure is subjected to closed-loop control (feedback control) in accordance with the difference between the torque limit value thus changed in succession and a detected value of the hold pressure actually acting on resin.
However, the multi-stage pressure control of the injection-molding machine has a problem such that the actual pressure overshoots or undershoots the target pressure at the time of switching the target pressure, due to various factors, including inertia of the screw, inertia of the servomotor, incompatibility of the response output characteristic of the servomotor, and incompatibility of the control gain of a closed-loop control system. The incompatibility of the control gain can be eliminated by adjusting, for example, the proportional, differential, and integral parameters of a PID control section of the control system, without changing the arrangement of the control system. In any control method, however, it is difficult to eliminate unsatisfactory responsiveness attributable to the servomotor or the like. More specifically, in the case of mounting the injection-molding machine with a motor having a response output characteristic compatible with the type and pressure control pattern of the injection-molding machine, or in replacing a once mounted motor with another motor, so as to improve the performance for the actual pressure to follow up the target pressure, it is necessary to provide motors of various specifications and to perform replacement work for the motors. Accordingly, the production and running costs of the injection-molding machine increase considerably. In the case of setting the pressure control pattern agreeable to the motor characteristic, moreover, feasible pressure control patterns are limited, so that there are restrictions on the pressure control. Thus, none of the aforementioned countermeasures are practical for the manufacture of high-quality, low-priced moldings.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an apparatus for pressure control of a motor-operated injection-molding machine, in which a multi-stage pressure control pattern of the injection-molding machine, especially a target pressure switching pattern between adjacent pressure control stages, can be made compatible with the response output characteristic of a servomotor mounted on the injection-molding machine, deterioration of the responsiveness due to the inertia of the servomotor and of an operating part of a pressurization apparatus can be restrained, and various modes of multi-stage pressure control can be smoothly effected without mounting a special servomotor on the injection-molding machine or replacing a once mounted servomotor with another servomotor.
In order to achieve the above object, according to one aspect of the present invention, there is provided a pressure control method applied to a motor-operated injection-molding machine in which an operating part of a pressurization apparatus is driven by a servomotor, the pressure control method comprising
REFERENCES:
patent: 4851170 (1989-07-01), Shimizu et al.
Kamiguchi Masao
Kobayashi Minoru
Neko Noriaki
Fanuc Ltd.
Heitbrink Jill L.
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