JPH01288419A - Method of controlling dwelling pressure of electric injection molding machine - Google Patents

Abstract

PURPOSE:To transmit surely a desired resin pressure into a mold cavity by conducting a dwelling pressure correction by increasing one after another the torque limit value of a servo-motor in a dwelling pressure process, from the torque limit value relative to a set dwelling pressure together with the lapsed time after the dwelling pressure initiation. CONSTITUTION:A pressure gap DELTAp(t) is obtained every lapse of a minimum command time DELTAT, the command torque limit value p(t) of the servo-motor 1 for a screw shaft is set-changed to correct the pressure gap. Consequently, the command torque limit value p(t) of the servo-motor 1 increase gradually in accordance with the lapsed time (t) after dwelling pressure initiation, and the increased part of the torque limit value offsets the solidification of a resin caused by the lapsed time after dwelling pressure initiation and the drop of a resin pressure within a mold cavity due to the increase of a viscosity resistance each other, so that the resin pressure within the mold cavity comes to coincide at all time with a set dwelling pressure P0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a holding pressure control system for an electric injection molding machine.

Conventional technology Control of holding pressure in an electric injection molding machine using a servo motor involves limiting the output torque of the servo motor (hereinafter referred to as the injection servo motor), which drives the screw in the axial direction to perform injection and hold pressure. It is done by doing.

Problem to be Solved by the Invention However, when the pressure holding time is set to be relatively long, the section from the gate of the mold cavity to the sprue,
In other words, in a resin path that is not equipped with a means for heating the resin, the filled molten resin is cooled and gradually solidifies, so especially in the case of oven loop control, the viscosity of the resin immediately after injection is used as a reference. There is a drawback that the set holding pressure is not accurately transmitted into the mold cavity, which tends to cause sink marks and insufficient specific gravity in the molded product.

Furthermore, if the convection time of the resin within the cylinder becomes longer, the viscous resistance of the resin within the cylinder may increase, which may promote poor transmission of resin pressure.

Figure 4 is a diagram qualitatively showing the relationship between the elapsed time after the start of pressure holding ([) and the resin pressure P (t) in the mold cavity in the conventional oven loop control method. For injection (based on the viscosity of the finished direct resin)
When setting the 1-L limit value pO of the Novo motor, the resin pressure P([) in the mold cavity matches the desired holding pressure PO immediately after the start of holding pressure, but the progress after the start of holding pressure As the time (0) increases, the pressure gradually drops and sufficient holding pressure cannot be obtained, so even if the pressure is held for the specified holding time (K), the holding pressure effect for 1 minute cannot be obtained, and the above-mentioned Sink marks and non-recovery of specific gravity occurred.

This situation is the same in the case of semi-closed loop υ1wJ, which detects the reaction force of the resin acting on the screw and gives feedback. In order to completely eliminate the poor transmission of resin pressure caused by the increase, the pressure within the mold cavity should be increased by 1? The only way to do this is to perform complete closed-loop control, such as by installing a green ring, which had the disadvantage of increasing costs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a holding pressure control method using an oven loop control method that can reliably transmit a desired resin pressure into a mold cavity regardless of the elapse of the holding pressure time.

Means for Solving the Problems The present invention provides an electric injection system that applies a torque limit to the servo that drives the screw in the axial direction, limits the C output to 1 torque, and performs open-loop control of the holding pressure. In the pressure control system of the molding machine, the holding pressure force is corrected by sequentially increasing the torque limit value of the servo motor in the holding pressure process from the torque limit value for the set holding pressure with the elapsed time after the start of holding pressure. The above problem was solved.

As time elapses after the start of holding pressure, the torque limit value is increased sequentially from the torque limit value for the set holding pressure.
Drives the injection servo.

As a result, the holding pressure applied to the resin in the mold cavity by the screw driven by the servo motor compensates for the pressure drop caused by assimilation of the resin and increase in viscous resistance, and always maintains the same pressure as at the start of holding pressure. The set holding pressure is applied.

Example An embodiment of the present invention will be described below.

In FIG. 1 showing the main parts of an electric injection molding machine according to an embodiment of the present invention, reference numeral 1 indicates a screw 2 of the injection molding machine that is driven in the axial direction of the screw to perform injection and pressure holding operations. The servo motor 1 is an injection servo motor, and a pulse coder 3 is attached to the motor shaft of the servo motor 1. Note that this electric injection molding machine has a button for each axis such as the screw rotating shaft and clamp shaft, just like a normal machine.
Since these are not directly related to the present invention, their explanation will be omitted.

Reference numeral 10 is a control unit for the electric injection molding machine, and the control unit 10 controls the operation of the entire injection molding machine and each axis 7.
Central processing equipment (hereinafter referred to as CPU) for numerical control (hereinafter referred to as NG) that controls pulse distribution processing etc. of the motor
11 and the position of each axis servo motor based on the command value of NC CP Ull.

The servo CPU 12 for servo control that controls speed, torque $11111, etc. is missing.

The NG CPU 11 includes a ROM 13 that stores a control program J3 that manages the entire injection molding machine, a sequence program that controls the sequence operation of the injection molding machine, a program that controls the servo CPU 12, and a holding pressure process setting maintenance. The pressure pO, the pressure holding time T, the correction coefficient α, the minimum command time Δd which is the setting change cycle of the torque limit value of the injection servo motor 1 within the pressure holding time, various setting values, parameter values, etc. RA memorized
A manual data input device 15 (hereinafter referred to as CRT/MDI) with a CRT display device is connected via a bus 16 to M14 and the RAM 14 for setting various setting values and parameter data.

On the other hand, servo CPtJ12 has NCJ'I'lCPU
command values and various data such as the pulse distribution level to each axis for each distribution cycle, torque limit value, etc. output from 11, and N
The RAM 17 is used to temporarily store the program for controlling the servo CPU 12, which is transferred by the NG CPU 1i through the bus 21 when the power is turned on, and the pulse distribution 0 commanded by the NG CPL 111 is attached to the injection servo motor 1. A speed control circuit 18 that controls the speed of the servo motor 1 based on a signal from the valve coder 3, and a torque that similarly controls the torque of the servo motor 1! 11 control circuit 19 is connected via a bus 20. That is, in this embodiment, the servo CPU 12. Speed control circuit 18. The torque control circuit 19 and the like constitute a servo means, a so-called software servo. In addition, servo CP
U12 and the above NC CPU11 are connected to bus 20.21.1.
6.

Next, the correction calculation method in this embodiment will be briefly explained.

p(t)=pO+Δp(t) ・・・・・・(1)
Δp(t) = cX(t/ΔT) ・・・・・・(
2) Equation (1) calculates the torque limit value p(t) of the screw shaft servo motor in the pressure holding process by the setting holding pressure pO of the holding process, the elapsed time t after the start of pressure holding, and the resin used. This is a correction calculation formula related to the present invention that is calculated using a pressure correction function Δp(t) corresponding to the pressure correction function Δp(t).
[) is a function of the elapsed time t after the start of pressure holding. That is, the pressure correction function Δp(t) is a function indicating the pressure gap between the set holding pressure pO and the resin pressure in the mold cavity, and as shown in equation (1), the holding pressure By supplementing the command holding pressure pO of the process with the value of the pressure correction function Δp(t) that changes with the elapsed time after the start of holding pressure and outputting the torque limit value p(t) of the injection servo motor, the mold Resin pressure in the cavity and set holding pressure pO
I am trying to match the .

Equation (2) is the pressure correction of this embodiment, in which correction is performed assuming that the resin pressure in the mold cavity decreases almost linearly with the elapsed time after the start of pressure holding (see Fig. 4). This is a correction calculation formula showing the function Δp(t), and the correction coefficient α
is the value of the resin pressure in the mold cavity that decreases per unit time, that is, the minimum command time ΔT in the numerical control device 10, and is calculated by dividing the elapsed time t after the start of pressure holding by the minimum command time ΔT. Find the number of six minimum command times corresponding to the elapsed time t, and apply the above correction coefficient α to the number of six minimum command times.
The pressure gap Δp (t) between the set holding pressure pO and the resin pressure in the mold cavity at the elapsed time t after the start of holding pressure is calculated by multiplying by the value of .

Hereinafter, the operation of this embodiment will be explained with reference to a flowchart (see FIG. 2) showing the processing operation of the NC CPLJ 11 in the pressure holding process.

Note that the operator must set the holding pressure p for the holding pressure process in advance.
O2 pressure holding time T, correction coefficient α, minimum command time ΔT, etc.
It is set in the RAM 14 via the RT/MD I 15.

When the injection process is finished and the pressure holding process is started, the C for NC
The PU 11 first reads the torque limit value of the set holding pressure in the holding pressure process from the RAM 14 and stores it in step S1), and then sets the timer R to monitor the elapsed time after the start of holding pressure.
(t) and a timer R(t') that monitors the minimum command time 6 times which is the setting change cycle of the torque limit value is set to O and started to start timing (steps 82 and 83).

Next, the elapsed time t is determined based on equation (2) using the elapsed time t after the start of pressure holding indicated by the timer R(t), the correction coefficient α set in the RAM 14, and the minimum command time ΔK. The pressure gap Δρ(1) between the current resin pressure in the mold cavity and the set holding pressure PO is determined (step 84), and the pressure gap Δp(t) is set to the torque limit value pO of the set holding pressure. The command torque limit value p([) is calculated by adding the corresponding torque limit value (Step S5), and the command torque limit value is stored in RAM1.
7 to rewrite the torque limit value (step 86).

On the other hand, the servo CPU 12 reads the rewritten torque limit value p([) from the RAM 17 and outputs the torque iIIIw.
The torque of the screw shaft servo motor 1 is controlled via the J circuit 19, and the holding pressure is set to the resin in the mold cavity against the solidification of the resin and increase in viscous resistance that occurs over time after the start of holding pressure. The same holding pressure will be applied.

J3, in the first process, it is immediately after the start of holding pressure, and the elapsed time t = o-r indicated by timer R(t)
, pressure gap Δp (Since the calculation result of the t1 term is approximately (), the torque limit value output to the RAM 17 in step S6 becomes virtually equal to the set holding pressure po.

Next, a timer R(t) that monitors the elapsed time after the start of pressure holding
In step S7, it is determined whether the elapsed time t indicated by has reached the set pressure holding time T stored in the RAM 14.
), if the elapsed time t has not reached the set holding pressure time,
Next, it is determined whether the minimum command time ΔF & the value t' of the monitored timer R(t') is the minimum command time ΔT k: '31, and the value of the timer R(t') is the minimum command time 6.
It waits until it reaches the end (step 88).

Thailand? When the value of R(t') reaches the minimum command time of 6 teeth and the torque limit value setting change cycle has elapsed, step S
3, restart the timer R(t') and re-monitor the minimum command time 6, and change the setting of the torque limit value of the screw shaft servo [-1] in the same manner as above. Execute processing.

In this way, the torque limit value setting change process from step 83 to step S8 is repeated every time the minimum command time ΔT elapses.
When it is determined in step 7 that the elapsed time t after the start of pressure holding has reached the set pressure holding time T stored in the RAM 14, the pressure holding process ends.

According to this embodiment, the pressure gap Δp (t) is determined every time the minimum command time of 6 units elapses, and the command 1 hell limit value p (t ), the command torque limit value p of servo motor 1
As shown by the thin line in Figure 3, (t) gradually increases according to the elapsed time 1 after the start of holding pressure, and
~The increase in the limit value offsets the decrease in resin pressure in the mold cavity due to solidification of the resin and increase in viscous resistance that occurs over time after the start of holding pressure, and the resin pressure in the mold cavity is reduced to the value shown in Figure 3. As shown by the solid line, the pressure always matches the set holding pressure PO.

Since the setting of J3 and command l-ruke limit value is changed every cycle, the command torque limit value p([)8 and the corresponding resin pressure in the mold cavity are as shown in Fig. 3. Although J changes discontinuously, the width of the minimum command time ΔT, that is, the command torque limit (a p
By setting the setting change period of (t) even shorter, smooth pressure 1. l III can be performed.

- In the example described in h, the correction coefficient α according to the resin used is
'/I explained the example of inputting from MD115, but N
Equipped with non-volatile RAM in the CPU II for G (set up a 7-T-daple-shaped storage area, and set correction coefficients α, α, ... α, etc. according to the name of each resin) according to various resins. - (Memorize these resin names on the CRT/MD.
115 and select a correction coefficient corresponding to the resin used using soft keys or the like.

Further, in the above embodiment, the process in one stage of pressure holding step is explained, but even in the case where multiple pressure holding stages are set, the process of CPLJII for NG is the same as described above. That is, in the process of the NG CPU 11 shown in FIG. 2, in step S1, the set dollar limit 1-value and the pressure holding time of each stage of holding pressure are read, and the processes from step 82 onwards are executed (-1). In addition, the value of the counter that indicates the number of pressure holding stages is updated each time the pressure holding process of each stage is completed, and the end of the pressure holding process is detected when the counter (illj reaches the set number of pressure holding stages). do it.

Next, step 83 to step S8 (second
Simplify the loop-shaped 1~ru limit setting change processing formed by Another embodiment in which the width of the torque limit value can be set shorter than ever will be explained. According to this embodiment, the step width S of the setting change cycle of the torque limit value is shorter than in the above embodiment, so the pressure control can be performed extremely smoothly.

Hereinafter, the operation of this embodiment will be briefly explained along with a flowchart (see FIG. 5) showing the processing operation of the NC CPU 11. Note that the electric injection molding machine and the numerical control device are the same as those in the above embodiment, so a description thereof will be omitted. Also in this embodiment, the set holding pressure pO2 of the holding pressure process, the holding time T, the correction coefficient α, the minimum command time ΔT
@ is inputted by the operator via the CRT/MD I 15.

When the injection process is finished and the pressure holding process is started, the C for NC
The PU 11 first reads the torque limit value of the set holding pressure in the holding pressure process from the RAM 14 and stores it in the register p(
Step 511), a timer R ([) that monitors the elapsed time after the start of pressure holding, and a timer R that monitors the minimum command time ΔT that is the setting change cycle of the torque limit value.
(t') is set to 0, and time counting begins (steps 812 to 513).

Next, the torque limit value of the set holding pressure stored in the register p([) is output to the RAM 17 to set the torque limit value in the holding pressure process (step 514).

Next, a timer R(t) that monitors the elapsed time after the start of pressure holding
In step 51, it is determined whether the elapsed time t indicated by has reached the set pressure holding time T stored in the RAM 14.
5) If the elapsed time t has not reached the set pressure holding time T, then timer R(t') monitors the minimum command time ΔT.
It is determined whether or not the value t' has reached the minimum command time ΔT (step 816).

When the value of timer R(t') reaches the minimum command time ΔT and the torque limit value setting change cycle has elapsed, step 81
7, the correction coefficient α indicates the resin pressure in the mold cavity that decreases during the unit time, that is, the minimum command time ΔT.
is added to the register p(t) and stored to calculate the command torque limit value corrected for the pressure gap corresponding to the elapsed time ΔT after the start of pressure holding (in the case of the first setting change process).Step 817) After returning to step 813 and restarting the timer R(t') that monitors the minimum command time ΔO, the updated command torque limit value p(t) is set to R.
The command torque limit value is outputted to the AM 17 to control the command torque limit value (step 514).

Thereafter, in the same way, every time the minimum command time of 6 teeth elapses, the torque limit value setting change process from step 813 to step 817 is repeated, and the correction coefficient α is added to the register p (t) to set the command torque limit value. The pressure holding process is performed while updating the torque limit value, but since the calculation process in the process of changing the setting of the torque limit value is constituted by a simple addition process (see step 817), the above-mentioned embodiment (Fig. 2 , see step S4).
The processing speed of U11 is increased, and T can be set to be shorter in the step size of the setting change/update cycle of the torque limit value, so that pressure control can be performed extremely smoothly.

In the case of this embodiment as well, when it is determined in step S15 that the elapsed time t after the start of pressure holding has reached the set pressure holding time T stored in the RAM 14, the pressure holding process is terminated.

Also in this embodiment, as in the case of the above-mentioned embodiments, it is possible to select a correction coefficient in a menu format and to set multiple pressure holding stages.

Effects of the Invention In the present invention, the resin in the cylinder solidifies and viscous resistance increases depending on the passage of time after the start of holding pressure, and the holding pressure applied to the resin in the cavity gradually increases. In order to prevent this from decreasing, we applied holding pressure while sequentially correcting the torque limit value of the servo motor that drives the screw, so the resin in the mold 4P and tee is set correctly regardless of the elapsed time. Holding pressure is transmitted.

Therefore, no sink marks or insufficient specific gravity occur in the molded product.

Further, in order to transmit a normal set holding pressure to the resin in the mold cavity, there is no need for rose droop control as in the conventional method, so the cost does not increase.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing essential parts of an electric injection molding machine and its numerical control device according to an embodiment of the present invention that implements the holding pressure control system, and Fig. 2 is a block diagram showing the numerical control device of the same embodiment. 3 shows the relationship between the command pressure and the resin pressure in the mold cavity in the same example with respect to the elapsed time after the start of retention. 4 is a diagram showing the relationship between the command pressure and the resin pressure in the mold cavity in the conventional holding pressure control method with respect to the elapsed time from the beginning of the holding pressure period, and FIG. This is a "F1" chart showing the pressure holding process of the embodiment. 1... Screw, knee axis servo motor, 2... Screw, 3... Pulse encoder, 10... Numerical control. Device, 11... CPtJ for NG, 12... Servo cpu. 13... ROM, 14. 17... RAM, 15...
・Manual data input device with CRT display device, 16, 20. , 21... Bus, 18... Speed control circuit, 19... Torque υIIM] circuit. Area Figure 2 Figure 50

Claims (1)

[Claims] In the pressure control method of an electric injection molding machine, which applies a torque limit to the servo motor that drives the screw in the axial direction to limit the output torque and control the holding pressure in an open loop, the torque limit of the servo motor during the holding pressure process is A holding pressure control method for an electric injection molding machine, characterized in that holding pressure is corrected by gradually increasing the value from a torque limit value for a set holding pressure as time elapses after starting holding pressure.