Electric direct-acting die clamping unit of an injection molding machine

An object of the present invention is to provide an electric direct-acting die clamping unit of an injection molding machine whose entire length can be reduced. A movable platen is arranged to face a stationary platen. A stationary die is attached to the stationary platen, whereas a movable die is attached to the movable platen. The movable platen is connected to the front of the backup plate. A nut of a ball screw is fixed at each of diagonally-opposed corners of the backup plate. The threaded rod of the ball screw passes through the backup plate via the nut. The tip portion of the threaded rod is rotatably connected to the stationary platen. The rear end portion of the threaded rod is threaded through a support plate via the bearing and connected to a motor.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 and 2 show schematic structures of the electric direct-acting die clamping unit of an injection-molding machine according to the present invention. FIG. 1 is a front view of the unit and FIG. 2 is a cross sectional view of the unit taken along the threaded rod. The unit shown in the figures has a stationary platen 3 , a movable platen 4 , a stationary die 5 , a movable die 6 , a backup plate 2 , a ball screw 10 , a threaded rod 11 of the ball screw, and a nut 12 of the ball screw. The stationary platen 3 and a support plate 7 are respectively arranged at both ends of a base 1 so as to face each other. The movable platen 4 is arranged in the front of the stationary platen 3 so as to face the stationary platen 3 . The stationary die 5 is attached to the front surface of the stationary platen 3 , whereas the movable die 6 is attached to the front surface of the movable platen 4 . The movable platen 4 is designed to slide on the base 1 . The backup plate 2 is arranged between the support plate 7 and movable platen 4 . The backup plate 2 is designed to move back and forth (left and right in the figure) on the base 1 . The nut 12 of each of the ball screws 10 is fixed at each of the two corners of the back plate 2 on the diagonal line. The threaded rod 11 of each of the ball screws 10 passes through the backup plate 2 via the nut 12 . The tip portion (right end, in the figure) of each of the threaded rods 11 is rotatably connected to the stationary platen 3 . On the other hand, the rear end (left end, in the figure) of each of the threaded rods 11 is rotatably supported by the support plate 7 and passes through the support plate 7 . To the front surface of the backup plate 2 , the movable platen 4 is connected via the load cell 15 . A motor 20 is arranged under the base 1 . A pulley 22 is attached to the rear end portion (left end, in the figure) of the threaded rod 11 of each of the ball screws. A pulley 21 is attached to the shaft of the motor 20 . A timing belt 23 goes around the pulleys 21 and 22 , as described later. FIG. 3 (left side view) shows the detail of the connecting portion between the motor 20 and threaded rod 11 . The pulley 22 is attached to the rear end portion of the threaded rod 11 of each of ball screws. On the other hand, the pulley 21 is attached to the shaft of the motor 20 . A timing belt 23 goes around the pulleys 21 and 22 . FIG. 4 shows a fragmentary view of the ball screw 10 , taken along the line IV-IV of FIG. 3 . The nut 12 of the ball screw 10 is fixed on the backup plate 2 . The threaded rod 11 of the ball screw 10 passes through the backup plate 2 via the nut 12 . The tip portion (right end in the figure) of the threaded rod 11 of the ball screw 10 is rotatably connected to the front surface of the stationary platen 3 via a bearing 17 and a fixing member 18 . The rear end portion (left end in the figure) of the threaded rod 11 is rotatably supported by the support plate 7 via a bearing 19 and passes trough the support plate 7 . The pulley 22 is attached to the rear end portion of the threaded rod 11 . When the threaded rods 11 are rotated by the motor 20 , the nuts 12 move along the threaded rods 11 . Accordingly, the backup plate 2 moves back and forth along the threaded rods 11 . Along with the movement of the backup plate 2 , the movable platen 4 moves, which is connected to the front surface of the backup plate 2 . As mentioned above, the clamping and unclamping operation is performed by moving the ball screws 10 . When dies are clamped, a ball screws 10 are rotated to move the movable platen 4 toward the stationary platen 3 . As a result, the stationary die 5 comes into contact with the movable die 6 . At this time, the reaction force against the clamping force (compressive stress applied to the die surfaces) is applied to the threaded rods 11 by way of the load cell 15 and the backup plate 2 . If it is possible to omit the load cell 15 , the movable platen 4 can be directly connected to the front of the backup plate 2 . In this case, the backup plate 2 and the movable platen 4 can be formed integrally into one body as shown in FIG. 5 . According to the electric direct-acting die clamping unit of the present invention, the threaded rods only rotate but do not move along its axis. It is therefore unnecessary to leave a space at the back of the unit to allow the threaded rods to move backward. Furthermore, the stationary platen and the backup plate can be connected by two ball screws, which are arranged symmetrically to the center axis of the stationary die and the movable die and arranged at different heights. With this structure, the number of parts arranged around the dies can be reduced. As a result, the operator can more easily get access to the dies.