JPH0383621A - Dwell controlling device of injection molder - Google Patents

Abstract

PURPOSE:To uniformize the quality of molded item by a method wherein changing-over is performed from a closed loop in-mold resin pressure controlling means, which controls the resin pressure in a mold, to a closed loop in-reservoir resin pressure controlling means, which controls the resin pressure in the reservoir of an injection cylinder, so as to directly control the dwell pressure applied to the resin in the mold. CONSTITUTION:During a time, which ranges from the starting time point t1 of swell process to a time point t2, a manipulated variable is controlled by a closed loop in-mold resin pressure controlling means 10. During a time, which ranges from the time point t2 to a time point t3, a manipulated variable is controlled by a changing-over zone controlling means 13. Further, during a time after the time point t3, a manipulated variable is controlled by the closed loop in-reservoir resin pressure controlling means 12. Thus, the changing-over from the closed loop in-mold resin pressure controlling means 10 to the closed loop in-reservoir resin pressure controlling means 12, which controls the resin pressure in the reservoir of an injection cylinder, can be smoothly performed and, at the same time, the dwell pressure to be applied to the resin in the mold can be controlled directly, resulting in uniformizing the quality of a molded item.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an injection molding machine that controls the holding pressure applied to the resin when changing the resin from a molten state to a solidified state after filling a mold with the resin. This relates to a device for

[Prior Art] In an injection molding machine, a device is known in which a pressure detector detects the resin pressure in the mold during the pressure holding process and controls the resin pressure in the mold based only on the detected resin pressure. ing. In this device, the pressure detected by the pressure detector is that on the surface of the molded product molded in the mold, and the pressure distribution of the resin in the mold is uneven over time and position. In the latter stage of the pressure holding process after the resin in the gate part has solidified, the pressure difference between the pressure application part and the pressure detection part becomes large, so excessive pressure is applied to local parts of the molded product, resulting in uneven density. Molded products will be made.

Therefore, conventionally, as a holding pressure control device for injection molding machines,
It has been proposed to switch the control amount from the resin pressure in the mold to the oil pressure in the injection cylinder in the pressure holding process (for example, see Japanese Patent Laid-Open No. 62-261419).

[Issue 8 to be solved by the invention] In conventional devices, when switching the control amount, the hydraulic pressure of the injection cylinder at the end of controlling the resin pressure in the mold is set to We use an arithmetic control means that can replace the pressure command value in the process, but since the compensator for the resin pressure in the mold and the compensator for the oil pressure in the injection cylinder are different, the servo valve or proportional valve is used at the time of switching the control amount. This method has the disadvantage that an inflection point occurs in the control amount (input current value) to, and as a result, an inflection point occurs in the resin pressure in the mold or the oil pressure of the injection cylinder.

In addition, in conventional equipment, the hydraulic pressure of the injection cylinder is controlled in the latter half of the pressure holding process, but in the pressure transmission path that transmits this hydraulic pressure to the resin in the mold, there is a frictional resistance against the screw in the injection cylinder. Due to factors that are difficult to quantify, such as force, resin in the injection cylinder reservoir, and shape of the injection cylinder nozzle, the control of the holding pressure applied to the resin in the mold is indirect, so the quality of the molded part is affected. It has the disadvantage that it is difficult to make it uniform.

An object of the present invention is to switch from an in-mold resin pressure closed loop control means for controlling the resin pressure in the mold to an in-reservoir resin pressure closed loop control means for controlling the resin pressure in the reservoir of an injection cylinder in an injection molding machine. To provide a holding pressure control device which can smoothly perform molding, directly control the holding pressure applied to resin in a mold, and thereby make the quality of molded products uniform. There is a particular thing.

[Means for Solving the Problems] The present invention provides an in-mold resin pressure closed loop that controls the resin pressure in the mold based on the measured value of an in-mold resin pressure detector that detects the resin pressure in the mold. a control means, a resin pressure closed loop control means for controlling the resin pressure in the reservoir based on a measured value of a resin pressure detector for detecting the resin pressure in the reservoir of the injection cylinder, and a switching section for switching between these. control means, and the switching section control means is operated so as not to cause an inflection point between the operation amount by the mold resin pressure closed loop control means and the operation amount by the reservoir resin pressure closed loop control means. It is characterized by controlling to switch the amount.

[Function] The present invention provides the following advantages: 1. at the start of the pressure-holding process; firstly, the manipulated variable is controlled by the in-mold resin pressure closed-loop control means in the time period from to time point t2; first, the manipulated variable is controlled by the switching section control means in the time period from time point t2 to time point t, and
Next, the operation amount is controlled by the resin pressure control means in the reservoir at time t and subsequent times, and the resin pressure in the reservoir at the point on the control operation amount curve for resin pressure in the mold at time t2 and the resin pressure in the reservoir at time t. The operation amount in the switching section indicated by the curve connecting the points on the control operation amount curve is calculated by the switching section control operation amount calculation means, and the switching section control means controls the operation amount based on this calculation value.

[Example] Next, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 1, reference numeral 1 indicates an injection molding machine. This injection molding machine 1 consists of a mold 2 and an injection section 3 that injects resin into the mold. Injection cylinder 3 of this injection part 3
Oil 3b is stored in the rear part of the injection cylinder 3a, and a servo valve 4 is arranged to control the oil pressure of the oil 3b by injecting and discharging the oil 3b into and out of the injection cylinder 3a.

When the oil pressure is changed by this servo valve 4, the position of the screw 3c is changed, and the resin pressure in the injection cylinder 3a and the resin pressure in the mold 2 are changed. The oil pressure may be controlled by a proportional valve instead of the servo valve 4.

An in-mold resin pressure detector 5 is arranged in the mold 2 to detect the resin pressure in the cavity. The injection cylinder 3a
An in-reservoir resin pressure detector 6 is disposed in the reservoir to detect the resin pressure in the reservoir. The outputs of these mold resin pressure detector 5 and reservoir resin pressure detector 6 are controlled by the control bag! given to 17. The control device 7 is connected to a mold resin pressure detector and a target value setting device 8 for inputting information such as a target value of the resin pressure in the reservoir.

A servo valve 4 is connected to an output terminal of the control device 6.

The control device 7 includes an in-mold resin pressure closed loop control means and an in-reservoir resin pressure closed loop control means.

A switching section control means is provided.

The in-mold resin pressure closed loop control means, as shown in FIG. The output of this comparator 9 is applied to the comparator 9, and the output of this comparator 9 is applied to the entire mold resin pressure compensator 1.
0 to the servo valve 4.

The reservoir resin pressure closed loop control means supplies the reservoir resin pressure target value set in the target value setting device 8 and the measured value from the reservoir resin pressure detector 6 to the comparator 11, and 11 output to the resin pressure compensator 1 in the reservoir.
2 to the servo valve 4.

The switching section control means applies the outputs of the entire mold internal resin pressure compensator 10 and the reservoir internal resin pressure compensator 12 to the switching section control operation amount calculation means 13, and.

This switching section control operation amount calculation means 13 performs a predetermined calculation and provides the output to the servo valve 4.

Said whole mold resin pressure compensator 10. The output terminals of the in-reservoir resin pressure compensator 12 and the switching section control operation amount calculation means 13 are connected to the servo valve 4 via the nine control switching means 14. This control switching means 14 includes an in-mold resin pressure compensator 1
0. Separate outputs from the reservoir resin pressure compensator 12 and the switching section control operation amount calculation means 13 are applied to the servo valve 4 only for a predetermined time.

Next, the operation of the holding pressure control device for an injection molding machine of the present invention will be explained based on FIG.

In FIG. 3(a), symbol a is a curve showing the change over time in the resin pressure in the entire mold, and symbol s is a curve showing the change over time in the resin pressure in the reservoir.

In FIG. 3(b), the symbol a' is a mold resin pressure control operation amount curve showing the change over time of the operation amount U to the servo valve 4 by the mold resin pressure closed loop control means, and the symbol b ′
The servo valve 4 is controlled by the resin pressure closed loop control means in the reservoir.
This is a curve of the manipulated variable for controlling the resin pressure in the reservoir showing the change over time in the manipulated variable u2 to the servo valve 4, and the symbol C indicates the change over time in the manipulated variable u (k+1) to the servo valve 4 by the switching section control means. This is a section control operation amount curve. This switching section control operation amount curve C is between point C0 of the mold resin pressure control operation amount curve a' at time t2, which is a predetermined time elapsed from the start point 1° of the pressure holding process, and point C0, which is a predetermined time elapsed from point t2. This is a curve that connects point c2 of resin pressure control operation amount curve b' in the reservoir at time t3.

The operation mu(k+l) shown in the switching section control operation amount curve C
) is calculated by sampling at one time point t
2, and 'rmt2-t9. When τ is the sampling time, the 9th order equation % equation % (1) (2) Based on these equations (1) and (2), the switching section control operation amount calculation means 13 calculates the operation amount u ( k+1
).

In interval A from the start time tl of the pressure holding process to time t2, the operation g1u1 is controlled by the in-mold resin pressure closed loop control means so as to follow the in-mold resin pressure control operation amount curve a'. In interval B from time t2 to time t3, the operation amount u (k+1) is controlled by the switching interval control means so as to follow the switching interval control operation amount curve C. The resin pressure closed loop control means controls the manipulated variable u2 so as to follow the resin pressure control manipulated variable curve b' in the reservoir.

The above-mentioned time points i2+　　i3 are the switching start times.

The time points at which the switching is completed are set in advance in the control device 7, and the time points provided in the control device 7 are measured.

[Effects of the Invention] In an injection molding machine, the present invention provides an in-mold resin pressure closed loop control means for controlling the resin pressure in the mold, and an in-reservoir resin pressure closed loop control means for controlling the resin pressure in the reservoir of the injection cylinder. In addition to being able to smoothly switch to the mold, it is also possible to directly control the holding pressure applied to the resin in the mold.

Moreover, for this reason, the quality of the molded product can be made uniform.

[Brief explanation of 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 present invention in detail. 2... Mold, 3... Injection part, 5... Resin pressure detector in mold, 6... Resin pressure detector in reservoir, 7... Control device. 10...Resin pressure compensator in all molds, 12...Resin pressure compensator in reservoir, 13...Switching section control operation amount calculation means. 14... Control switching means.

Claims (1)

[Claims] (1) Measurement using an in-mold resin pressure detector that detects the resin pressure in the mold, an in-mold resin pressure detector that detects the resin pressure in the reservoir of the injection cylinder, and the above-mentioned in-mold resin pressure detector. an in-mold resin pressure closed loop control means that controls the resin pressure by comparing the value with a target value; and a resin pressure in the reservoir by comparing the measured value by the resin pressure detector in the reservoir with the target value. an in-mold resin pressure control operation amount curve showing changes over time in the operation amounts for control in the reservoir resin pressure closed loop control means and the mold in-mold resin pressure closed loop control means;
At time t_2 when a predetermined time has elapsed from the start time t_1 of the pressure holding process, based on the reservoir resin pressure control operation amount curve showing the change over time of the operation amount for control in the reservoir resin pressure closed loop control means. Switching that calculates the manipulated variable in a switching section indicated by a curve connecting a point on the mold resin pressure control manipulated variable curve and a point on the reservoir resin pressure control manipulated variable curve at time t_3 after a predetermined time has elapsed from time t_2. A section control operation amount calculating means, a switching section control means for controlling the operation amount as shown by the switching section control operation amount curve obtained by this, and a starting point t of the pressure holding process.
The operation amount is controlled by the in-mold resin pressure closed loop control means during the time from _1 to time t_2, and then at time t_2
It is characterized by comprising a control switching means for controlling the manipulated variable by the switching section control means during the time from to time t_3, and then controlling the manipulated variable by the reservoir resin pressure closed loop control means for the time after time t_3. Holding pressure control device for injection molding machines.