Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1995-03-23
1998-08-11
Le, Long V.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 2643281, 425145, B29C 4550
Patent
active
057923957
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasticization control method for an injection molding machine in which resin in an injection cylinder is plasticized and measured by rotating a screw thereof.
BACKGROUND ART
There is known an injection molding machine in which a screw disposed in an injection cylinder is rotated at a preset rotational speed for measuring. In the conventional injection molding machine, only the speed of a motor for rotating the screw is preferentially controlled, and the driving torque of the motor is automatically controlled so as to rotate the screw at the set speed by compensating the viscous resistance of resin acting on the screw, various disturbances, etc.
When the injection cylinder is insufficiently heated or foreign material is mixed in the resin, the driving torque of the motor for rotating the screw at the set speed inevitably increases. In the conventional injection molding machine, however, variation of the driving torque of the motor is not taken into account, and insofar as the screw is rotated at the set speed, an abnormal state, such as insufficient heating of the injection cylinder and intrusion of foreign material, cannot be detected by a control system of the motor. Furthermore, when the supply of resin to the injection cylinder is insufficient, the screw rotates more lightly and the driving torque of the motor inevitably decreases. In this case, as the screw rotates easier at the set speed, no abnormality is found with respect to the rotational speed of the screw. Thus, an abnormal state due to the insufficient supply of resin cannot be detected by the motor control system.
In some cases, the screw is rotated with a very large force exceeding its practical strength in order to attain a target rotational speed in accordance with measuring conditions such as the screw rotational speed, back pressure and the kind of resin used. Especially, when the maximum output torque of the motor exceeds the practical strength of the screw, the screw may possibly be broken. This is the case with the situation where screws with different diameters are alternately used. For example, when the screw used is replaced with a screw of a smaller diameter and measuring is carried out with the screw of a smaller diameter, the replaced screw may possibly be broken. In such a case, the maximum output torque of the motor must be restricted, for example, by resetting a torque limit in the control system, but the resetting operation is complicated. Conversely, in the cases where the set rotational speed cannot be attained even though the screw is driven with a maximum output torque of the motor, inaccurate measuring may result or the measuring itself becomes impossible. In some cases, the motor may be overheated.
It is desirable for the user of the injection molding machine to carry out its injection molding operation at the lowest possible running cost, insofar as molded products are of equal quality. It is also desirable for the user to optimize measuring conditions. It is, however, difficult to separately detect the electric power or electric energy used for the measuring. Therefore, it is not possible to know the variations of the running cost due to difference of measuring conditions.
SUMMARY OF THE INVENTION
An object of the present invention is to surely detect the plasticized state of resin during measuring on the basis of the rotating force of a screw, thereby avoiding breakdown of the screw as well as overheating of a motor, and permitting measuring to be properly carried out in consideration of electric power required for the measuring.
A plasticization control method of the present invention comprises the steps of: determining a reference screw rotating force as a reference of rotating force of a screw during measuring operation; setting and storing an allowable range with respect to the reference screw rotating force; successively detecting the rotating force of the screw and determining whether or not the detected rotating force is within the allowable range duri
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Ito Susumu
Yamanaka Katsuyuki
Fanuc Ltd.
Le Long V.
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