Direct pressure mold clamping apparatus for an injection-molding machine

Claim 1

A direct pressure mold clamping apparatus for an injection-molding machine having a fixed platen and a movable platen, each platen having a die connectable thereto, said direct pressure mold clamping apparatus comprising: a rotatable member and a rectilinear motion member movable in unison with said movable platen; conversion means for converting rotary motion of said rotatable member into rectilinear motion of said rectilinear motion member; a servomotor operatively connected to said rotatable member and generating a rotational force; an induction motor operatively connected to said rotatable member and having a rotating speed and generating torque; transmission means for transmitting the rotational force of said servomotor to said rotatable member; a speed reducer connected to said induction motor for reducing the rotating speed and increasing the torque of said induction motor, and transmitting the increased torque to said transmission means; clutch means, interposed between said speed reducer and said transmission means, for releasably coupling said speed reducer to said transmission means; braking means for braking said induction motor; position detecting means coupled to said servomotor for detecting the moved position of the movable platen and outputting a signal indicative of the speed of said servomotor; numerical control means coupled to said position detecting means, said induction motor, said clutch means, and said braking means for outputting control signals to said numerical control means including a servo circuit for driving said servomotor, said servo circuit including an error register for receiving a pulse signal from said position detecting means and a distributed pulse speed command signal from said numerical control means and outputting an error signal based on a difference between the speed command signal and the servomotor speed signal; said numerical control means for outputting a torque limit command signal which stops operation of the servomotor, and for actuating said clutch means when the movable platen, driven by said servomotor, reaches a first predetermined position in which said dies of the movable platen and the fixed platen touch each other, the movable platen being driven by said induction motor from the first predetermined position to a second position at which a set mold clamping force is produced; said numerical control means outputting a pulse distribution corresponding to movement of the movable platen from the first predetermined position to the second predetermined position; and said numerical control means determining when the movable platen reaches the second predetermined position, and actuating said braking means to lock the movable platen when the error signal of said error register is reduced to zero, the error signal being produced as said servomotor rotates, accompanying the rotation of the induction motor.