Plastic and nonmetallic article shaping or treating: processes – With step of cleaning – polishing – or preconditioning...
Patent
1989-04-14
1990-12-04
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With step of cleaning, polishing, or preconditioning...
264 401, 264 405, 425136, 425149, 425154, 425155, B29C 4524, B29C 4576
Patent
active
049752278
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention is directed to a method for removing resin clogged in a nozzle of a motor-driven injection molding machine by moving forward a screw of the machine. More particularly, the present invention is directed to a method of this kind adapted to protect a servomotor for driving the screw from being overloaded.
(b) Description of the Related Art
While an injection molding machine is operated, there are occasions when molten resin is cooled and solidified in a nozzle and finally clogs the nozzle. This prevents continuation of injection molding cycles. Particularly in the case where retracting of the nozzle, or a so-called sprue break, is not performed in each injection molding cycle to set the nozzle apart from the mold. The nozzle is readily cooled by the mold contacting the nozzle, resulting in solidification of molten resin at the distal end of the nozzle and hence clogging of the same.
Measures conventionally taken to remove the solidified resin when the nozzle becomes clogged are to disassemble the nozzle, or move the screw forward through manual operation of an injection mechanism to discharge the solidified resin by applying a high pressure thereto.
If the latter-mentioned method for removing the resin in the clogged nozzle is applied to a hydraulic injection molding machine, no particular problems will arise. However, if this method is used with an injection molding machine using a motor, e.g., a servomotor, as the driving power source of the injection mechanism, an excessive load may be placed on the motor when the resin clogged in the nozzle is discharged. On such occasions, a large current flow occurs in the motor for a long period of time. Thus, the motor and the components of an electronic circuit for driving the motor, e.g., power transistors, will have shortened lives or be destroyed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for removing resin clogging a nozzle in a motor-driven injection molding machine, which is capable of discharging resin in the nozzle without an excessive load being continuously applied to a servomotor for driving a screw.
To achieve the above object, the present invention provides a method for removing resin clogging a nozzle in a motor-driven injection molding machine, which comprises the steps of moving a screw forward toward a predetermined axial position at which resin clogged in the nozzle is ensured to be discharged, by actuating a servomotor for driving the screw judging whether the servomotor is in an overload state, during the forward movement of the screw, and definitely stopping the forward movement of the screw when the overload state of the servomotor continues over a predetermined period of time.
Preferably, the method of the invention further comprises the steps of temporarily stopping the forward movement of the screw when the servomotor is judged to be in an overload state, and terminating the temporary stoppage of the forward movement of the screw when the servomotor is released from the overload state. before passage of the predetermined period of time after the temporary stoppage of the forward movement of the screw.
Thus, according to the present invention, the forward movement of the screw is stopped when the servomotor continuously undergoes an overload state for the predetermined time while being actuated to move the screw forward for discharging resin clogged in the nozzle. Clogging of the nozzle can therefore be removed without an excessive load being continuously applied to the servomotor, and the servomotor and the components of an electronic circuit for actuating the servomotor can be protected and thus prolonged in their service life.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of a control program for executing a nozzle clogging removal method according to one embodiment of the invention; and
FIG. 2 is a block diagram of a principal part of a motor-driven injection molding machine to which is applied the nozzle
REFERENCES:
patent: 4816196 (1989-03-01), Otake
patent: 4851171 (1989-07-01), Shimizu et al.
Fanuc Ltd.
Heitbrink Jill L.
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