Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Patent
1996-04-15
1998-06-09
Heitbrink, Tim
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
425143, 425144, B29C 4578
Patent
active
057628394
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a temperature control method in injection molding using an injection molding machine.
BACKGROUND ART
In carrying out an injection molding using an injection molding machine, objects of temperature control, such as a plurality of heating regions defined by dividing a cylinder of an injection molding machine, a nozzle and a mold mounted on the injection molding machines are heated by the respective heaters such as band heaters or rod heaters. A temperature of each object of temperature control is detected by a temperature sensor such as a thermocouple and a feedback control of temperature is performed so that the detected temperature coincides with a set temperature. In the conventional art, the temperature control is accomplished by an on/off control. That is, the temperature of each object of temperature control is controlled by adjusting the calorific value generated by the heater per unit time, which is realized by manipulating a turn-on time during which the fixed electric current is supplied to the heater and a turn-off time during which no electric current is supplied to the heater.
In the conventional temperature control method, as the on/off control is employed in which the ratio between the turn-on time for supplying the fixed electric current to the heater and the turn-off time for pausing the electric current to the heater is controlled, the value of the electric current flowing in the heater fluctuates largely and therefore the calorific value generated by the heater fluctuates largely. In the case where the heat capacity of the object of temperature control such as a cylinder and a nozzle is relatively large, a large fluctuation of the calorific value of the heater would give a small influence on change of temperature of the object of temperature control to cause no problem. In the case where the heat capacity of the object of temperature control is relatively small, however, the temperature of the object of temperature control would vary largely in response to a change of the calorific value generated by the heater, thereby causing a problem such that stable temperature control is not realized.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a temperature control method for an injection molding machine capable of performing stable temperature control at all times, irrespective of heat capacity of an object of temperature control.
According to the present invention, a temperature of an object of temperature control, such as a heating region of an injection cylinder, an injection nozzle or a mold, is detected and a feedback control is performed to obtain a command value of an electric current to be supplied to the heater so that the detected temperature coincides with a set value. Based on the obtained command value, the temperature of the object of temperature control is controlled by manipulating the value of the current to be supplied to the heater. When the detected temperature is lower than the set value, the electric current command value increases to raise the electric current flowing in the heater, so that the calorific value generated by the heater increases to cause a rise of temperature of the object of temperature control. Contrarily, when the detected temperature is higher than the set value, the electric current command value decreases to reduce the electric current flowing in the heater, so that the calorific value generated by the heater decreases to cause a drop of the temperature of the object of temperature control. As a result, the temperature of the object of temperature control is kept at the set value.
Further, an actual current flowing in the heater is detected and a feedback control of electric current is performed so that the detected actual current coincides with the command value obtained by the temperature feedback control in order to control the temperature of the object of temperature control more accurately.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of a control appa
REFERENCES:
patent: 5355938 (1994-10-01), Hosoya et al.
patent: 5435711 (1995-07-01), Yamada
patent: 5486105 (1996-01-01), Katsumata
Kamiguchi Masao
Neko Noriaki
Fanuc Ltd.
Heitbrink Tim
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