Screw rotating and advancing device for an injection molding machine

A screw rotating and advancing device for an injection molding machine, said device comprising,

• a front fixing plate in which a through hole is formed at the center thereof;
• a rear fixing plate, parallel to said front fixing plate and including at least one ball nut securely mounted on said rear fixing plate;
• at least two sliding rods, parallel to each other and extending between said front and rear fixing plates;
• a movable pressure plate provided on said sliding rods between said front and rear fixing plates and adapted to slide along said sliding rods;
• a screw shaft having one front end and one rear end, in which said front end is formed with screw threads and said rear end thereof passes through said through hole at the center of said front fixing plate and pivotally connected to a first side of said movable pressure plate by a connecting shaft;
• at least one ball screw including one front end and one rear end in which the rear end is formed with threads and is adapted to pass through and threadedly engage with said ball nut of said rear fixing plate, and said front end of the ball screw is pivotally connected to a second opposite side of said movable pressure plate;
• at least one electric injection servomotor fixedly mounted on the first side of said movable pressure plate and is adapted to rotate said ball screw through a first transmission device;
• an electric measuring servomotor fixedly mounted on the second side of said movable pressure plate for rotating said screw shaft through a second transmission device;
• whereby the driving of the electric injection motor provided at the first side of the movable pressure plate rotates the ball screw relative to the ball nut provided on said rear fixing plate and drives the movable pressure plate for movement back and forth along said sliding rods to effectively reduce the space occupied by said ball screw, and whereby the measuring servomotor provided on the second side of said movable pressure plate and rotational speed of the screw shaft can be precisely controlled.