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
1987-11-09
1989-02-21
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
425171, 264 407, B29C 4577
Patent
active
048060895
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to injection control of an injection-molding machine, and more particularly, to acceleration/deceleration control of the injection speed of an injection-molding machine controlled by means of a numerical control unit.
BACKGROUND ART
In injection-molding machines, injection-speed control is generally performed in a manner such that a screw is driven for injection at an optimum injection speed for each of three or four sections, into which the injection stroke of the screw is divided. According to known injection-molding machines, an injection device is driven by means of hydraulic oil pressure. Meanwhile, a system has been developed such that the injection device is driven by means of a servomotor. In the servomotor drive system, however, the screw sometimes cannot force out a rigid resin whose viscosity in a fused state is low. The screw often fails to force out the rigid resin particularly if the acceleration/deceleration time (time constant) for its injecting operation, or the time before the screw reaches a set position, is shortened, that is, if the responsiveness is improved, in order to inject the resin in a short period of time. In such a case, the error between the values of an actual injection speed and an injection-speed command issued to the servomotor increases, so that an alarm may possibly be given. In this situation, it is troublesome, for example, to examine the cause of the alarm. In some cases, injection control should be performed so that the command speed is reached gradually by increasing acceleration/deceleration time, depending on the mold shape.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an injection-molding machine which is free of the aforementioned drawbacks of the known machines, and in which the acceleration/deceleration time for the injection speed can be varied in accordance with parameters associated with injection, such as the properties of the resin to be injected, the shape of the mold used, etc., thereby ensuring injection-speed control under optimum conditions.
In order to achieve the above object of the present invention, there is provided an injection-molding machine controlled by means of a numerical control unit, which comprises setting means for setting an injection speed for each of injection-speed control steps, an injection-speed changing screw position, an injection-to-hold switching screw position, and an injection acceleration/deceleration time; memory means for storing individual set values set by means of the setting means; screw position detecting means for detecting the screw position; discrimination means for discriminating the injection-speed control step to which the screw position detected by the screw position detecting means corresponds, through comparison between the detected screw position and the set injection-speed changing screw position and between the detected screw position and the injection-to-hold switching screw position; pulse distribution means adapted to read the set injection speed of the step discriminated by the discrimination means from the memory means, and to perform pulse distribution corresponding to the read injection speed; and acceleration/deceleration control means for processing the output of the pulse distribution means for acceleration and deceleration in accordance with the set acceleration/deceleration time.
According to the present invention, as described above, the injection is accelerated or decelerated at an optimum acceleration corresponding to the acceleration/deceleration time, set in accordance with the hardness of the resin, at the time of switching the injection speed. Accordingly, the screw can securely avoid a situation such that it fails to force out the resin, and no troubles can be caused due to production of alarms.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the principal part of an injection-molding machine according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating
REFERENCES:
patent: 3767339 (1973-10-01), Hunkar
Fanuc Ltd.
Heitbrink Timothy W.
Woo Jay H.
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