Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1989-05-30
1991-03-26
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
425136, 425145, 425170, B29C 4577
Patent
active
050027085
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a drive system abnormality detecting apparatus of an injection-molding machine for detecting an abnormal situation of resin pressure detecting means or screw drive means for axially driving a screw of the injection-molding machine.
2. Background Art
In order to make a resin pressure, e.g., the resin pressure inside a cylinder equal to a set resin pressure, in an injection-molding machine, the resin pressure inside the cylinder is indirectly measured by means of resin pressure detecting means which is disposed at the rear end of a screw. The measured resin pressure is compared with a screw injection pressure set by means of injection pressure setting means. If the resin pressure inside the cylinder is lower than the set screw injection pressure, the screw is driven in the direction to raise the resin pressure inside the cylinder. If the the resin pressure inside the cylinder is higher than the set screw injection pressure, on the other hand, the screw is driven in the direction to lower the resin pressure inside the cylinder. Thus, closed loop drive control is effected.
According to the prior art described above, proper closed-loop control can be accomplished if both the resin pressure detecting means and the screw drive means are in the normal state. If either the resin pressure detecting means of the screw drive means malfunctions, however, proper closed-loop control cannot be achieved.
If the resin pressure detecting means becomes out of order, thus becoming unable to measure the resin pressure inside the cylinder, for example, it is impossible to keep the resin pressure inside the cylinder at the set resin pressure, and the repetition accuracy of pressure control for the molding operation is considerably lowered, thereby inducing the occurrence of defective molding. Moreover, if the screw drive means (hereinafter referred to as injection drive means) for axially driving the screw is compulsorily driven in the direction to raise the resin pressure inside the cylinder, on the basis of a measured value given by the resin pressure detecting means in trouble, the injection drive means is subjected to overload, so that the screw, drive system, dies, etc. are adversely affected. In addition, the resin pressure inside the cylinder increases extraordinarily, thereby creating a very dangerous situation.
In case of trouble in the injection drive means, moreover, the drive means cannot properly respond to feedback input despite the normality thereof. Thus, the same problems as aforesaid are caused.
SUMMARY OF THE INVENTION
The object for the present invention is to provide a drive system abnormality detecting apparatus of an injection-molding machine, capable of detecting an abnormal situation of resin pressure detecting means or injection drive means without delay.
In order to achieve the above-mentioned object, the present invention comprises: resin pressure detecting means for detecting a resin pressure; driving force detecting means for detecting a driving force of screw drive means for driving a screw in an axial direction of the screw; and abnormality detecting means operable to compare values detected by the resin pressure detecting means and the driving force detecting means, and to detect an occurrence of an abnoraml situation when the difference between the compared values exceeds predetermined permissible limits.
According to the present invention, since an abnormal situation caused in the resin pressure detecting means or the injection axis drive means can be automatically detected, lowering of the repetition accuracy of the pressure control can be positively prevented, so that risks such as defective molding, involved in unattended operation of the injection-molding machine, are greatly reduced to ensure reasonable molding operation. Moreover, since incomplete pressure control cannot be caused by the abnormal situation of the resin pressure detecting means or the screw drive means, a screw, drive system, dies, etc. cann
REFERENCES:
patent: 4851171 (1989-07-01), Shimizu et al.
Inaba Yoshiharu
Kamiguchi Masao
Fanuc Ltd.
Heitbrink Jill L.
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