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
1987-07-27
1988-05-03
Woo, Jay H.
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
264 405, 366 78, 425171, 425376B, 425574, 425587, B29C 4580
Patent
active
047416858
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an injection-molding machine, and more specifically, to an injection apparatus of an injection-molding machine, which, using a servomotor as a drive source, performs injection by moving a screw in the axial direction by means of the motor.
BACKGROUND ART
Conventionally, hydraulic pressure has been utilized for a drive source of an injection apparatus which performs injection by moving a screw in the axial direction thereof. Recently have been developed injection-molding machines which use a servomotor as the drive source of the injection apparatus. In this case, the servomotor must be increased in size, in order to make the injection-molding machines large-sized for a higher injection output. If the servomotor is increased in size, then it is a very special motor, which costs high. The moment of inertia, which greatly influences the rise- and fall-time performance of the motor, increases in proportion to the fourth power of the rotor diameter of the motor. If the servomotor used is large-sized, therefore, the moment of inertia is so high that it is very difficult, technically, to obtain a satisfactory acceleration/deceleration characteristic. Thereupon, a system has been proposed in which an injection mechanism is driven by mean of a plurality of motors (see Japanese Patent Disclosure No. 60-125618).
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an injection apparatus of a type in which an injection mechanism is driven, for injection, by means of a plurality of servomotors, so that the injection apparatus can enjoy higher output power, improved acceleration/deceleration characteristic, and lower cost.
In order to achieve the above object, according to the present invention, there is provided an injection drive apparatus for injection molding which is adapted to perform injection by moving a screw in the axial direction by means of ball screw means driven by servomotors. In this apparatus, the ball screw means is driven by means of a plurality of servomotors, and a position detector is attached to only one of the servomotors. A torque command is delivered to power amplifiers, which are provided individually for the servomotors, by a control unit which receives a signal from the position detector, whereby the drive of the individual servomotors is controlled. More specifically, the position of the screw is detected by the position detector, and the control unit delivers the torque command to the power amplifiers of the servomotors in accordance with the detected screw position and an input speed command, thereby driving the individual servomotors in synchronism with one another, for injection-speed control and injection-pressure control of the screw.
Thus, a plurality of servomotors are used to drive the screw for injection, so that a great injection torque can be produced. Since the rotor diameter of each servomotor can be small, moreover, the moment of inertia of each rotor is small. Accordingly, the total moment of inertia of a plurality of servomotors, for use as the drive source of the injection apparatus, can be made much smaller than the moment of inertia of one servomotor which can produce the same torque as that of the drive source according to the present invention. As a result, the acceleration/deceleration characteristic of the injection apparatus is improved, thereby permitting satisfactory injection control with high responsiveness. Despite the use of a plurality of servomotors, moreover, the position detector, such as an pulse encoder, which is expensive, may be one in number. In the control unit for controlling the servomotors, furthermore, only the power amplifiers need be increased in number to accord with the number of servomotors, and only one control circuit is needed besides, thus ensuring high economical efficiency. Further, no large-sized servomotors are needed to produce a large torque, so that the drive source can be composed of commercially available, mass-produced servomotors, which are low-p
Inaba Yoshiharu
Mitoguchi Fumio
Sakamoto Keiji
Sogabe Masatoyo
Fanuc Ltd
Heitbrink Timothy W.
Woo Jay H.
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