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
1986-12-30
1988-07-26
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, 425149, 425170, B29C 4577
Patent
active
047597054
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection molding machine and, more particularly, to a switching control system for unit torque control value of a servo motor for an injection molding machine which uses a servo motor as a drive source for driving the injection mechanism.
2. Description of the Related Art
In a conventional injection molding machine, hydraulic pressure drives an injection mechanism and axially moves a screw to perform injection. An injection pressure and a back pressure could be adjusted by controlling the hydraulic pressure. On the other hand, injection molding machines in which a servo motor drives the injection mechanism to perform injection have been developed. In these injection molding machines driven by servo motors to perform injection, the injection pressure or the back pressure must be controlled by controlling the output torque of the servo motor. According to a conventional method of controlling the torque of a servo motor, the torque of the servo motor is limited. Although a back pressure during metering is as low as about 1/10 of a maximum injection pressure during injection, a torque limit command representing a large unit value is supplied to a D/A converter from a control unit. Therefore, it was impossible to set a small unit torque limit value during metering.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a switching control system for a unit torque limit value of a servo motor for an injection molding machine, wherein in response to a torque limit command from a control unit, a unit torque limit value during metering can be set to be smaller than that during injection.
In order to achieve the above object of the present invention, in a control system for an injection molding machine, wherein an injection mechanism is driven by a servo motor to perform injection, a digital torque limit command is converted into an analog signal by a D/A converter, and the torque command supplied from a servo circuit to the servo motor is limited by the analog signal from the D/A converter, a switching control system for a unit torque limit value of a servo motor for an injection molding machine, wherein a level of the output from the D/A converter during metering is set to be smaller by a predetermined value than the level of the output during injection to reduce a unit torque limit value, and a unit limit value of a back pressure during metering is set to be smaller than that of a unit pressure limit value for injection pressure and a holding pressure during injection, thereby allowing setting of a small torque limit value in units of small values.
Thus, in a switch control system for a unit torque limit value of a servo motor for an injection molding machine of the present invention, a torque limit command for a servo motor for driving the injection mechanism changes an output level of the D/A converter for converting the torque limit command into an analog signal to change the torque limit value itself, and can set a torque limit value in substantially the same accuracy in an injection and pressure holding mode as well as a metering mode. Therefore, optimal values for the injection pressure, the holding pressure and the back pressure can be set.
BRIEF DESCRIPTION OF DRAWINGS
The FIGURE is a block diagram of a control system for an injection molding machine according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be described in detail referring to the accompanying drawing. The FIGURE is a block diagram of an embodiment of the present invention. Referring to the drawing, reference numeral 1 denotes a control unit comprising CNC or the like for controlling an injection molding machine (not shown); 2, a central processing unit (to be referred to as a CPU hereinafter); 3, a ROM for storing a control program which controls the entire injection molding machine; 4, a RAM for serving as a temporary memory or the like;
REFERENCES:
patent: 3893792 (1975-07-01), Laczko
patent: 4511319 (1985-04-01), Takayama
Neko Noriaki
Otake Hiromasa
Fanuc Ltd
Heitbrink Timothy W.
Woo Jay H.
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