JPS61217227A - Back pressure control for injection molding machine - Google Patents

Abstract

PURPOSE:To permit stabilized back pressure control by a method wherein a sensor, measuring resin pressure in the tip end of a heating tube, is provided at he tip end of the heating tube to detect measuring resin pressure of plasticating process and control the speed of a servomotor for injection so that the resin pressure becomes a predetermined pressure at all times. CONSTITUTION:The detecting section of the resin pressure measuring sensor 15 is faced to the inside of tip end of the heating tube 3, the sensor 15 is connected electrically to the servomotor 6 for injection through a resin pressure control unit 16 and detects the molten resin pressure of plasticating process, which is reserved at the tip end of the heating tube by the rotation of a screw 2, the input of the sensor is read by an A/D converter 19 to compare with the value of pressure preset in a setter 17 and the speed of the servomotor 6 for injection is operated by a microcomputer 18 so that the resin pressure of the tip end section A becomes constant. Speed command is sent to an amplifier 20 through a D/A converter 21 while the servomotor 6 drives the screw 2 to retreat it through the amplifier 20 so that he resin pressure becomes the set value. Thus, correct and stabilized back pressure control may be effected and good products may be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a back pressure control method for controlling the back pressure of an injection molding machine so that it always maintains a predetermined pressure.

(Conventional structure and its problems) Conventionally, as a method for controlling the back pressure of a screw in a servo motor-driven injection molding machine, for example, Japanese Patent Laid-Open No. 58-1
As shown in Japanese Patent No. 79631, the screw shaft that drives the screw forward is made to receive the backward force generated in the screw to generate a rotational force in the opposite direction on the screw shaft, and the rotational force is controlled. Since this is performed using a so-called brake mechanism, there is a problem in that the frictional force changes greatly and stable and accurate back pressure control cannot be performed.

(Purpose of the Invention) The present invention was made in view of the above problems, and it is possible to stabilize the resin pressure by directly detecting the resin pressure on the screw tip side without detecting the back pressure of the screw on the screw drive part side. The present invention provides a back pressure control method for an injection molding machine that enables back pressure control.

(Structure of the Invention) In order to achieve the above object, the back pressure control method for an injection molding machine of the present invention is based on a servo motor-driven injection molding machine that uses a sensor installed at the tip of a heating cylinder to measure the resin pressure inside the tip. The system is characterized in that it detects the measured resin pressure in the plasticizing process and controls the speed of the injection servo motor so that the resin pressure always remains at a predetermined value.

(Description of Embodiments) An embodiment of the present invention will be described with reference to the drawings. (1) is a device main body of an injection molding machine, in which a heating cylinder (3) inside which an injection screw (2) is rotatable and slidable back and forth is installed. A heating tube (3) is provided on the upper periphery of the rear end of the heating cylinder (3).
A hopper (4) is installed to supply the raw material resin inside. (5) is the injection screw and the tip nozzle of 2).

(6) is an injection servo motor, and a gear (7) fixed to its rotating shaft 6a is screwed into a screw shaft (9) connected to the rear end of the injection screw (2) via a bearing (8). It meshes with the gear 00).

11 is a screw rotation drive gear attached to the rear end shaft portion 2a of the injection screw (2) via a slide key 12;
It meshes with a gear 14 fixed to the rotating shaft of the drive motor 13.

15 is a heating cylinder (3) in the vicinity of the injection nozzle (5)
A resin pressure measurement sensor is embedded in the tip of the heating cylinder (3), and its detection part is exposed to the inside of the tip of the heating cylinder (3).This sensor 15 is connected to the injection servo motor (6) via a resin pressure control device 16. It is electrically connected to.

As shown in FIG. 2, the resin pressure control device 16 includes a microcomputer 18 equipped with a resin pressure setting device 17, and an analog-digital (A/D) input for the resin pressure detection sensor 15.
) A converter 19, an amplifier 20 for driving the injection servo motor (6), and a Digicrew analog (D/A) converter 21 connected to the amplifier 20 without issuing a command.

With the above configuration, when the drive motor 13 is driven to rotate, the injection screw (2) is rotated through the gears 11 and 14.
The heating cylinder (
3) becomes molten inside, is sent to the tip A, and accumulates in the core A. The accumulated molten resin is transferred from the tip nozzle (5) to the mold 22 by rotating the gear 00) through the rotational drive of the injection servo motor (6) to advance the screw (2) through the screw shaft (9). Press-fit into the cavity between .23 and .23.

In this step, the pressure (back pressure) of the molten resin accumulated at the tip of the screw (2) during the plasticizing process is detected by the sensor 15, and the input is read by the A/D converter 19 and sent to the setting device 17. It is compared with a preset pressure value, and based on the comparison, the speed of the injection servo motor (6) is calculated by the microcomputer 18 so that the resin pressure at the tip A is constant.

The speed command is sent to the amplifier 20 through the D/A converter 21, which drives the servo motor (6) to drive the screw (2) backward so that the resin pressure reaches the set value.

(Effects of the Invention) As described above, according to the back pressure control method in an injection molding machine of the present invention, the resin pressure inside the tip of the heating cylinder is detected by the sensor and fed back to the injection servo motor through the microcomputer, and Since the retraction speed of the screw is controlled so that the resin pressure in the part is always at the set value, accurate and stable back pressure control is possible, and good products can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a longitudinal sectional side view of the device, and FIG. 2 is a block diagram of back pressure control. +1. l...Device main body, (2)...Injection screw, (3)...Heating tube, (5)...Nozzle, (6)...
...Injection servo motor, 13...Drive motor, 15
. . . Resin pressure measurement sensor, 16 . . . Resin pressure control device, 18 . . . Microcomputer.

Claims (1)

[Claims] In an injection molding machine driven by a servo motor, a sensor is installed at the tip of the heating cylinder to measure the resin pressure inside the tip to detect the measured resin pressure during the plasticization process so that the resin pressure is always at a predetermined value. A method for controlling back pressure in an injection molding machine, characterized by controlling the speed of an injection servo motor.