JP2736683B2 - Insulation control device for injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention controls the holding pressure applied to a resin when the resin is changed from a molten state to a solidified state after the resin is filled in a mold in an injection molding machine. The present invention relates to an apparatus for performing the above.

[Prior Art] In an injection molding machine, a device that detects a resin pressure in a mold by a pressure detector in a pressure holding process and controls the resin pressure in the mold based only on the detected resin pressure value is known. Have been. In this device, the pressure detected by the pressure detector is that of the surface of the molded product to be molded with the mold, and the pressure distribution of the resin in the mold is uneven over time and position. In the later process after the resin in the gate part is solidified in the pressure holding process, the pressure difference between the pressure application unit and the pressure detection unit becomes large, so that excessive pressure is applied to the local part of the molded product and the density becomes uneven. To make goods.

In view of the above, conventionally, as a pressure holding control device of an injection molding machine, a device has been proposed in which a control amount is switched from a resin pressure in a mold to a hydraulic pressure of an injection cylinder in a pressure holding process (for example, Japanese Patent Application Laid-Open No. 62-261419) Reference).

[Problems to be Solved by the Invention] In the conventional apparatus, when the control amount is switched, the hydraulic pressure of the injection cylinder at the end of the control of the resin pressure in the mold is controlled in the next process so that no inflection point occurs in the pressure control. Computation control means that can be replaced with the pressure command value is used. However, since the compensator for the resin pressure in the mold and the compensator for the oil pressure of the injection cylinder are different, the servo valve or proportional valve is switched when the control amount is switched. Has a disadvantage in that a control point (input current value) causes a change point, and as a result, a change point occurs in the resin pressure in the mold or the hydraulic pressure of the injection cylinder.

SUMMARY OF THE INVENTION It is an object of the present invention to smoothly switch from a resin pressure control means for controlling a resin pressure in a mold to a hydraulic control means for controlling a hydraulic pressure of an injection cylinder in an injection molding machine, and An object of the present invention is to provide a pressure-holding control device that can make the quality of a molded product uniform.

Means for Solving the Problems The present invention is a resin pressure closed loop control means for controlling a resin pressure based on a measurement value of a resin pressure detector for detecting a resin pressure in a mold, and detecting a hydraulic pressure of an injection cylinder. Closed loop control means for controlling the hydraulic pressure based on the measured value of the hydraulic pressure detector to be changed, and switching section control means for switching between these, wherein the switching section control means is controlled by an operation amount by the resin pressure closed loop control means. It is characterized in that control is performed to switch the operation amount so that no inflection point occurs between the operation amount and the operation amount by the hydraulic closed-loop control means.

[Operation] invention controls the operation amount by the resin pressure closed-loop control means in the time from the start time t ₁ of the pressure holding process to time t _2, then switching section controlled in time from t ₂ to time t ₃ controlling a manipulated variable by means and, at the next time t ₃ after the time be one that controls the operation amount by the hydraulic pressure closed-loop control means, in terms of resin pressure control operation amount curve at time t ₂ and time t ₃ The operation amount in the switching section indicated by the curve connecting the points of the hydraulic control operation amount curve is calculated by the switching section control operation amount calculating means, and the switching section control means controls the operation amount based on the calculated value.

Example Next, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, reference numeral 1 denotes an injection molding machine. The injection molding section 1 includes a mold 2 and an injection section 3 for injecting resin into the mold. The injection cylinder of this injection unit 3
An oil 3b is accommodated in the rear of 3a, and a servo valve 4 for controlling the oil pressure of the oil 3b by injecting and discharging the oil 3b to and from the injection cylinder 3a is arranged. When the hydraulic pressure is changed by the servo valve 4, the position of the screw 3c is changed, and the pressure of the resin in the mold 2 is changed. The hydraulic pressure may be controlled by a series valve instead of the servo valve 4.

The mold 2 is provided with a resin pressure detector 5 for detecting the resin pressure in the cavity. A hydraulic pressure detector 6 for detecting a hydraulic pressure is disposed at the rear of the injection cylinder 3a.
The resin pressure detector 5 and the oil pressure detector 6 are provided to a control device 7. The control device 7 includes a target value setting device 8 for inputting information such as a resin pressure target value and a hydraulic pressure target value.
Is connected. The servo valve 4 is connected to an output terminal of the control device 6.

The control device 7 includes resin pressure closed loop control means, hydraulic closed loop control means, and switching section control means.

As shown in FIG. 2, the resin pressure closed loop control means gives the resin pressure target value set in the target value setting device 8 and the measured value from the resin pressure detector 5 to the comparator 9, and The output of the comparator 9 is provided to the servo valve 4 via the resin pressure compensator 10.

The hydraulic closed loop control means supplies the comparator 11 with the target hydraulic pressure set in the target value setting device 8 and the measured value from the hydraulic pressure detector 6, and outputs the output of the comparator 11 to the hydraulic compensator 12.
To the servo valve 4 via

The switching section control means supplies the outputs of the resin pressure compensator 10 and the hydraulic pressure compensator 12 to the switching section control manipulated variable computing means 13, and the switching section control manipulated variable computing means 13 performs a predetermined computation and The output is given to the servo valve 4.

The output terminals of the resin pressure compensator 10, the hydraulic compensator 12, and the switching section control operation amount calculating means 13 are connected to the servo valve 4 via the control switching means 14. This control switching means 14
Supplies the respective outputs of the resin pressure compensator 10, the hydraulic compensator 12, and the switching section control manipulated variable calculating means 13 to the servo valve 4 only for a predetermined time.

Next, the operation of the pressure holding control device of the injection molding machine according to the present invention will be described with reference to FIG.

In FIG. 3 (a), a symbol a is a curve showing a change over time in resin pressure, and a symbol b is a curve showing a change over time in oil pressure.

In a third diagram (b), reference numeral a 'is a resin pressure control operation amount curve showing the variation with time of the operation amount u ₁ to the servo valve 4 by the resin pressure closed-loop control unit, reference numeral b' is the hydraulic closed-loop control unit by a hydraulic control operation amount curve showing the variation with time of the operation amount u ₂ to the servo valve 4, and reference numeral c is an operation amount to the servo valve 4 by switching section control means u (k + 1)
6 is a switching section control operation amount curve showing a change with time of the switching section. This switching section control manipulated variable curve c is obtained at the start time t _{1 of the} pressure holding process.
A resin pressure control operation amount curve a at the time t ₂ has elapsed a predetermined time and a point c ₂ 'and a point c ₁ of the hydraulic control operation amount curve b at time t ₃ when passed from the time t ₂ for a predetermined time period' It is a connecting curve.

The operation amount u (k + 1) of the switching section control operation amount curve c
, When calculated by sampling a k = 0 at time _{t 2, T = t 2 -t} 3, when the τ sampling time is represented by the following formula.

u (0) = u ₁ (0) (1) u (k + 1) = u (k) + [u ₂ (k) −u ₁ (k)] τ / (T−kτ) (2) Based on these equations (1) and (2), the switching section control manipulated variable computing means 13 computes and determines the manipulated variable u (k + 1).

Hold pressure as disclosed Time resin pressure control operation amount curve a by resin pressure closed-loop control unit in section A from t ₁ to time t ₂ '
To control the operation amount u ₁ along the next time t ₃ from the time t ₂
Until the section to control the manipulated variable along the switching section control amount curve c u (k + 1) by the switching section control means B for, and then the hydraulic pressure controlled by the hydraulic pressure closed-loop control means at the time point t ₃ after the interval C along the operating amount curve b 'for controlling the operation amount u _2.

The time points t ₂ and t ₃ are set in the control device 7 in advance as a switching start time and a switching completion time, and these times are measured by a timer provided in the control device 7.

According to the present invention, in an injection molding machine, switching from resin pressure control means for controlling resin pressure in a mold to hydraulic control means for controlling oil pressure of an injection cylinder can be smoothly performed, and Therefore, the quality of the molded product can be made uniform.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the configuration of the present invention, FIG. 2 is a block diagram showing the configuration of the present invention, and FIG. 3 is a diagram for explaining the operation of the present invention. 2 ... Mold, 3 ... Injection section, 5 ... Resin pressure detector, 6 ... Hydraulic detector, 7 ... Control device, 10 ... Resin pressure compensator, 12 ... Hydraulic compensator, 13 ... ... Switching section control manipulated variable calculating means, 14 ... Control switching means.

Claims (1)

(57) [Claims] 1. A resin pressure detector for detecting a resin pressure in a mold, a hydraulic pressure detector for detecting an oil pressure of an injection cylinder, and a resin pressure detector which compares a measured value of the resin pressure detector with a target value. Pressure closed loop control means for controlling pressure, hydraulic pressure closed loop control means for comparing the measured value of the oil pressure detector with a target value to control oil pressure, and time lapse of an operation amount for control in the resin pressure closed loop control means. It changes the resin pressure control operation amount curves showing, on the basis of the hydraulic control amount curve showing the variation with time of the operation amount for the control in the hydraulic closed-loop control means, predetermined from the starting time t ₁ of the pressure holding process a point of the resin pressure control operation amount curve at time t ₂ the time has elapsed,
A switching section controlled control amount calculating means for calculating a manipulated variable between switching section indicated by the curve connecting the points of the hydraulic control operation amount curve from the time t ₂ at the time t ₃ when the predetermined time has elapsed, thereby obtained a switching section control means for controlling the operation amount as shown between switching section operation amount curve, by controlling the manipulated variable by the resin pressure closed loop control means in the time from the start time t ₁ of the pressure holding process to time t _2, then time from the time t ₂
controlling a manipulated variable by switching section control means in time to t _3, and then characterized by comprising a control switching means for controlling a manipulated variable by the hydraulic pressure closed-loop control unit at time t ₃ after the time injection Pressure control device of molding machine.