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
1991-07-02
1992-10-27
Heitbrink, Tim
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
264 407, 425170, B29C 4577
Patent
active
051587831
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a crank driven injection apparatus for an injection molding machine which employs an electric motor as its primary driver.
BACKGROUND ART
Injection molding machines generally include an injection mechanism for forcing molten resin into a mold. Conventional hydraulic injection mechanisms include a hydraulic cylinder and an injection plunger. However, it is difficult to simplify the structure of hydraulic injection mechanisms and much labor is required to maintain the hydraulic cylinders and hydraulic fluid paths. Moreover, it is difficult to precisely control the reciprocation of the injection plunger.
To obviate these difficulties, injection mechanisms using motors as primary drivers have been also developed. A typical motor-driven injection mechanism includes a ball screw/ball nut mechanism having a rotatably mounted ball screw which is coupled to the output shaft of a servomotor, and a ball nut which is threadedly engaged therewith. The ball nut is mounted in such a manner that it is unrotatable relative to but movable in unison with an injection screw. The rotary motion of the motor output shaft is converted into linear motion of the injection screw through the ball screw/ball nut mechanism, so as to drive the screw in the direction of injection. However, motor-driven ball screw/ball nut injection mechanisms are expensive.
Moreover, in such motor-driven injection mechanisms, typically, the servomotor is operatively coupled to the ball screw through the medium of a power transmission which includes respective toothed pulleys fixed on the motor output shaft and the ball screw, and a timing belt stretched between such pulleys. In this connection, the power reduction ratio between the servomotor and the ball screw cannot be increased and in order to drive the injection screw with a desired driving force, in particular, with a great driving force, a servomotor which is high in output torque is required. However, since general-purpose servomotors having high output torque are not readily available, motor-driven injection mechanisms are high-priced.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a crank operated injection apparatus which is low-priced and which is capable of driving an injection screw with a desired driving force, without the need of employing a high output type electric motor.
In order to achieve the aforementioned object, according to the present invention, there is provided a crank operated injection apparatus for use in an injection molding machine which has an elongated injection screw disposed to be movable toward and away from the front face of a stationary plate. The screw has a longitudinal axis and the same is positioned with its longitudinal axis extending along a straight line which passes through the front face of the stationary plate. The screw is mounted for linear reciprocating movement along such line toward and away from the face of the stationary plate. The injection apparatus of the invention includes an electric motor having a rotatable output shaft and the motor is operable to rotate the output shaft in forward and reverse rotational directions. The injection apparatus also includes a reduction gearing mechanism having a rotatable drive shaft and gearing elements which operably interconnect the output shaft of the motor and the drive shaft such that the drive shaft is rotated in forward and reverse directions in coordination with the output shaft of the motor. A crank mechanism operably interconnects the drive shaft and the injection screw for converting forward and reverse rotation of the drive shaft into said reciprocating movement of the injection screw. A control unit is provided for controlling the operation of the electric motor in such a manner that the drive shaft is rotated in said forward and reverse directions within a predetermined rotary angular region corresponding to a predetermined operational region of the crank mechanism which does not contain a dead center position of
REFERENCES:
patent: 4741685 (1988-05-01), Inaba et al.
patent: 4758391 (1988-07-01), Shimizu et al.
Inaba Yoshiharu
Nishimura Koichi
Fanuc Ltd.
Heitbrink Tim
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