JPH04816B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the control of mold temperature during continuous injection molding operations of an injection molding machine, and particularly to a mold temperature estimation device and mold temperature control used for such control. The present invention relates to a method and a mold temperature control device.

[Prior Art] In general, in order to continuously produce stable and high-quality products during continuous injection molding operations, injection molding machines require precise control of the temperature of the mold. be.

By the way, a molded article is produced by filling a cavity of a molding die with a molten resin as a molding material.

At this time, the temperature T _R [℃] of the molten resin injected from the injection device is generally the temperature θ of the molding die.
Higher than [℃]. For this reason, the temperature of the molding die increases and fluctuates each time the molten resin is injected.

However, in the past, in order to suppress such fluctuations in mold temperature, operators had to adjust the supply device for heat medium such as cooling water to adjust the temperature of the mold through trial and error until the mold stabilized at a predetermined target temperature. was being manipulated.

[Problems to be solved by the invention] As described above, in the conventional technology, the product yield is low because it relies on trial and error by the operator without estimating fluctuations in mold temperature. .

Furthermore, it is difficult to accurately control the temperature of the mold with general automatic control that treats such fluctuations in mold temperature simply as a disturbance.

In addition, in reality, the temperature of the mold is adjusted using cooling water, etc., which has a very slow response speed, as a heat medium. On the contrary, there was a problem in that the control resulted in unstable control.

In view of the above drawbacks, the technical problem of the present invention is to provide a mold temperature estimating device for an injection molding machine that compensates for fluctuations in mold temperature and performs control suitable for controlling a heat medium with a slow response speed. The object of the present invention is to provide a mold temperature control device using the same.

[Means for solving the problem] According to the present invention, a mold temperature estimating device for an injection molding machine is provided for setting the mold temperature of the injection molding machine to a mold temperature suitable for the next injection molding cycle. a mold temperature detection means for detecting an actual measurement value of the mold temperature of the injection molding machine; and a mold temperature detection means for detecting the actual measurement value of the mold temperature,
A mold temperature estimating device for an injection molding machine is obtained, characterized by having a time average temperature calculation means for calculating the time average temperature of the mold for each injection molding cycle based on a predetermined calculation formula.

Further, according to the present invention, in a mold temperature control device having a heat medium temperature control means for controlling the temperature of a heat medium that thermally contacts the mold in order to adjust the temperature of the mold of an injection molding machine. , comprising a mold temperature estimating device and a command value calculation means, the mold temperature estimating device comprising a temperature detecting means for detecting an actual measured value of at least one of the mold temperature and the molten resin temperature of the injection molding machine. and time-average temperature calculation means for calculating the time-average temperature of the mold for each injection molding cycle based on a predetermined calculation formula from the actual measurement value, and the command value calculation means is configured to calculate the time-average temperature and a predetermined mold temperature target value, a command value to the heat medium temperature control means is calculated so that the temperature of the mold in the next molding cycle becomes the target value of the mold temperature. An injection molding machine with a mold temperature control device is obtained.

[Operation] According to this configuration, the mold temperature estimating device calculates the time average temperature for each molding cycle from the actual measurement value of the mold temperature according to a predetermined calculation. Then,
Because the time average is taken for the real-time mold temperature, which changes from moment to moment, the temperature change of the molding die, which rises and fluctuates each time molten resin is injected, is not considered as a disturbance, and the temperature is stable. The temperature value (time average temperature) can be used as a future value. Based on this future value, precise commands are sent to the heating medium temperature control means that controls the temperature of the heating medium that is in thermal contact with the mold so that the mold reaches a predetermined target temperature in the next molding cycle. A value can be given. That is, it is possible to perform precise control that matches the characteristics of a heat medium such as cooling water, which is an actual control target that has a slow response speed.

Furthermore, since the time average temperature of the mold is calculated for each molding cycle, the calculation formula can be made to correspond to the state space expression. Since this state space expression is expressed as a simple calculation formula regarding the temperature at any point in the mold and the thermal conductivity inside the mold, it is a new control system design method that converts from an analog system to a digital system. It can be used as a device for precise and quick control.

[Example] Next, an example of the invention will be described with reference to the drawings.

-First Embodiment- As shown in FIG. 1, 1 is a mold, which is composed of a fixed mold and a movable mold. Molten resin is injected from an injection cylinder 2 into a mold 1, and a molded product is formed according to a predetermined injection molding cycle.

At this time, the mold temperature fluctuates due to the heat from the high temperature molten resin. Therefore, the cooling water temperature adjustment device 8, which is a heat medium temperature control means, follows the cooling water temperature command value Θ ^* from the mold temperature control device 14, which will be described later.
The cooling water circulation pump 7 is driven to control the mold 1 so that it reaches a predetermined mold temperature target value θ _r in the next molding cycle.

The mold temperature control device 14 controls the actual measurement value θ of the mold temperature.
The time average temperature θ _{i (av)} of the mold in the current injection molding cycle, which is calculated based on the mold temperature sensor 11 which is a mold temperature detection means for detecting the temperature and its actual measurement value θ, is output as a feedback amount. and an adder 3 that adds up the feedback amount θ _{i (av)} from the feedback compensator 13 sent through the transmission line 12 and a predetermined target value θr of the mold temperature sent through the transmission line 16.
and a series compensator that outputs a cooling water temperature command value Θ ^* to the cooling water temperature adjustment device 8 so that the temperature of the mold 1 in the next injection molding cycle becomes a predetermined set temperature based on the summed value. It consists of 10.

Here, the feedback compensator 13 of this embodiment
(Tanimura, Akashi; 30th Automatic Control Association Conference, preprint manuscript) and the calculation formula that derives the time-average temperature θ _{i (av)} of the mold at the time of injection molding. Arithmetic expressions based on state space representation in a discrete time system with a cycle time as a sampling period will be explained below.

First, when creating a mold thermal property model and approximating the unsteady heat conduction within the mold temperature calculation sphere, the second
Using the diagram, make the following assumptions.

Fixed and movable molds 110 and 112 and fixed and movable platens 114 and 116
A heating device (not shown) is installed near the joint surface with the fixed mold and the movable mold 11 on the joint surface.
In order to compensate for heat dissipation from 0 and 112, this joint surface is treated as a heat insulating surface.

Heat transfer from the molten resin (not shown) to the fixed mold and the movable mold takes place only at the start of resin injection. Assume that it is formed instantaneously on the parting surface of the mold.

The fixed mold and the movable mold 110 and 112 are
Assuming a symmetrical temperature distribution regarding the dividing surface, the dividing surface is treated as an adiabatic surface.

Heat radiation from the fixed mold and movable molds 110 and 112 to the surrounding outside air is ignored.

Assume a plane of cooling water temperature parallel to the dividing plane.

Based on the above main assumptions, as shown in FIG. 2, the areas of the isothermal surface of the molten resin temperature on the heat insulation surface 150 and the isothermal surface of the cooling water temperature near the in-mold cooling water pipe 132 are calculated as follows. Let A ₀ and A ₁ be [m ² ], and let the distance between the two surfaces be r ₁ [m].

Next, as shown in FIG. 3, when the fixed mold 110 is approximated to a sphere, the molding surface 130 of the fixed mold 110
The heat conduction between and the in-mold cooling water pipe 132 is treated as unsteady heat conduction, and the temperature distribution is defined as A ₀ , A ₁ ,
Using r ₁ , it is defined as in the first equation. In addition, r
[m] is a virtual quantity, Δr[m] is the plane thickness of the molten resin temperature, and the temperature distribution is treated as being only in the radial direction.

r ₀ = r ₁ (A ₀ + √ ₀・₁ ) / (A ₁ − A ₀ ), A ₁ > A ₀ …
...(1) Next, the unsteady heat conduction equation of equation (1) is expressed by partial differential equations of equations (2) to (5).

∂(rθ)/∂t _i =k∂ ² (rθ)/∂r ² ...(2) θ _t1=0 =f _i (r) ...(3) θ _r=a =Θ, a=r ₀ +r _i ...(4) 0≦t _i ≦T ...(5) However, θ [℃] is the temperature of the mold, k [m ² /s] is the temperature conductivity, and Θ [℃] is the cooling water temperature. , f _i (r) [℃]
is the initial condition in the i-th cycle, and T[s] is the injection period.

When the partial differential equations of equations (2) to (5) are solved analytically for each cycle, the temperature θ at time t _i is the 6th
Formula (Kensuke Kawashita: Thermal Conduction Theory, p334, Kawade Shobo 1941)
become that way.

Note that here, f _i (r) is defined using the final state θ _ti=T in the i-1th cycle and equations (7) to (10).

f _i (r)=θ _ti-1=T , 0<r<r ₀ −Δr ……(7) f _i (r)=T _R , r ₀ −Δr≦r≦r ₀ ……(8) f _i (r)=θ _ti-1=T , r ₀ <r≦a ...(9) θ _t0=T =Θ ...(10) However, T _R [° C.] is the temperature of the molten resin.

Furthermore, regarding f _i (r), equations (11) to (13)
Perform interpolation as in Eq.

0=S ₀ <S ₁ <S ₂ ...S _N-1 <SN ...(11) f _i (r)=f _i (S ₁ ), 0<r<S ₁ ...(12) f _i (r )=(f _i (S _j )−f _i (S _j+1 ))/(S _j −S _j+1 )・
r + (S _j・f _i (S _j+1 )−S _j+1・f _i (S _j ))/(S _j −S _j+1
), Sj<r<Sj+1...(13) Using this, the integral of the second term of equation (7) is solved analytically. Here, as an example of the calculation, the solution for the 10th cycle is shown in FIG.

Next, regarding the solution θ of equation (6), the following equation (14)
According to the formula, the time average temperature for each cycle θ _i(av) [℃]
is required.

An example of this calculation is shown in FIG.

Note that the infinite series in Equations (6) and (14) above can be truncated at a finite number of terms in practice.
Furthermore, the degree of compatibility between the actually measured time-average temperature and the calculated value of equation (14) can be improved by adjusting κ and Δr.

Next, we will introduce arithmetic expressions using state space representations (Digital control of dynamic systems; GF Franklin, JD Powell, translated by Hiromasa Haneda, Morikita Publishing,
(1985), pp128-133).

First, the arithmetic expression using the state space expression in this example is Equation (14), which is an expansion of Equation (6) above, and
Furthermore, it is a conversion from an infinite dimension to a finite dimension, that is, from an analog system to a digital system. This is shown in equation (15) below.

X _(i+1) =AX _(i) +bΘ _(i) +eT _R Y _(i)av. =CX (i) + dΘ _(i) +fT _R ... (15) Here, X _(i) , X _{(i +1)} are both estimated values,
Θ _(i) is the cooling water temperature in the i-th injection molding cycle, and T _R is the melting water temperature. The temperature of the resin, Y _{(i) av.,} is the estimated value of the time-average temperature of the mold in the i-th injection molding cycle. In other words, Equation (15) is a state space expression regarding Y _(i)av. , X _(i+1) , X _(i) , Θ _(i) , and _TR . The time average temperature of the mold for each injection molding cycle is given based on a simple calculation formula regarding the detected value of , the detected value of mold temperature, and the heat conduction within the mold.

-Second Embodiment- The second embodiment is shown in FIG. However, those indicated by the same reference numerals as in FIG. 1 have similar functions, and their explanations will be omitted.

The mold temperature control device 14 of this embodiment includes a mold temperature estimation section (not shown) that calculates the time average temperature of the mold, and a cooling water temperature adjustment device 8 that receives a mold temperature target value from a transmission line 16. A calculation section 24 consisting of a command value calculation section (not shown) that calculates a command value for
and a correction section 25 that corrects the calculation contents of the calculation section 24. Note that, as described later, the calculation section 24 and the correction section 25 are realized by an adaptive observation device.

The calculation unit 24 calculates the temperature of the molten resin detected by the molten resin temperature sensor 20 that detects the temperature of the molten resin.
The time average temperature θ _{i (av)} of the mold for each injection molding cycle, which is the future mold temperature, is calculated and estimated from T _R and the set temperature Θ of the cooling water, and the time average temperature θ _{i ( av)} , a cooling water temperature Θ ^* that can realize a predetermined mold temperature is determined, and this cooling water temperature Θ ^* is output to the cooling water temperature adjustment device 8 as a command value Θ ^* . The cooling water temperature adjustment device 8 adjusts the cooling water temperature so that it follows the command value Θ ^* .

Here, after the end of each injection molding cycle, the correction unit ₂₅ calculates the calculated time average temperature Y _{( i) av.} , and set the parameters in the calculation contents of the calculation unit 24 to the actual measured values.
y _{(i) Correct to correspond to av} . Further, the calculation unit 24 recalculates the cooling water temperature Θ ^* that can realize a predetermined mold temperature every time the parameters are corrected.

In addition, if the fluctuation of the resin temperature T _R is small,
The resin temperature T _R can also be treated as a constant value, and the molten resin temperature sensor 20 can be omitted.

Next, the details of the parameter correction calculation performed by the correction unit 25 will be specifically explained.

First, the time average temperature Y _(i)av. of the mold in the mold temperature estimation section is as described in the first embodiment.
It is expressed by Equation (16) using the state space expression below.

X _(i+t) =A(k)X _(i) +b(k)Θ _(i) +e(k)T _R Y _(i)av. =C(k)X _(i) +d(k)Θ _{( i)} +f(k)T _R ... (16) Similar to equation (15), both X _(i) and X _(i+1) are estimated values, and each A state vector expressing the temperature distribution in the mold immediately before injection, Θ _(i) is the cooling water temperature in the i-th injection molding cycle, T _R is the temperature of the molten resin, and Y _(i)av. is the temperature in the i-th injection molding cycle. is an estimate of the time-average temperature of the mold during the injection molding cycle. Also, A(k), b(k), C
(k), d(k), e(k), and f(k) are matrices with k as a parameter.

On the other hand, the correction unit 25 first measures the time average temperature of the mold in the i-th injection molding cycle from the actual measurement value of the mold temperature from the mold temperature sensor 11 after the end of the i-th injection molding cycle. value y _(i)av.
seek. Next, the actual detected time-average temperature
y _(i)av. and the time average temperature calculated by the calculation unit 24
A correction amount Δk of the parameter k is calculated from the difference with Y _(i)av based on the following equation (17).

Δk=−k・(Y _(i)av. −y _(i)av. /(Xm _(i+1) −Y _(i)
)...(17) However, Xm _{(i+1 )} is _the m-th row element of the vector is the estimated value of the time-average temperature at the location.

Here, Equation (17) is analytically obtained from Equation (14) for determining the time-averaged temperature θ _{i (av)} of the mold. That is, in the i-th injection molding cycle, Δk of parameter k is Δk=−k・(Y _(i)av. −y _(i)av. )/(∂Y _(i)av. /
∂k)...(18) At this time, according to equation (14), ∂Y _(i)av. /∂k can be found analytically, so by substituting it into equation (18), equation (17) becomes can get.

In addition, in the correction rule of equation (17), if the sensitivity of the correction operation of the correction unit 15 is too high, using an appropriate number α such that 0<α<1, Δk=−αk・(Y _{(i) av.} −y _(i)av. )／(Xm _(i+1) −Y
_(i)av. )……(19) may also be used.

As a result, using Δk obtained by equation (17), the correction unit 25 first changes the parameter k in the calculation contents of the calculation unit 24 (formula (17)) to k
Correct to +Δk. At the same time, the calculation unit 24 recalculates the cooling water temperature Θ ^* (command value) that can realize the target value θr of the predetermined mold temperature every time the parameter k is updated, and outputs it to the cooling water temperature adjustment device 8. be done.

The command value Θ ^* is calculated based on the following equation (20).

X ^* =A(k)X ^* +b(k)Θ ^* +e(k)T _R Q _r =C(k)X ^* +d(k)Θ ^* +e(k)T _R ...(20) However, X ^* is a vector of the same size as X _(i+1) .

In this way, when the correction unit 25 corrects the parameter k of the calculation unit 24, the unknown parameter (k+Δ
A mechanism that estimates the state variable (X _(i+1) ) while identifying

-Third Example- A third example is shown in FIGS. 7 and 8. However, those indicated by the same reference numerals as in FIG. 1 have similar functions, and their explanations will be omitted.

The mold temperature control device 14 of this embodiment includes a molten resin temperature sensor 20, a mold temperature sensor 11, an estimation unit 34 consisting of an adaptive observation device, and a feedback amount based on the estimated temperature distribution inside the mold. It has a feedback amount calculating section 35 for calculating. In addition, a mold temperature average value calculator 18 is built in the estimating unit 34, and the mold temperature average value calculator 18 is used to calculate the actual time average temperature of the mold after the end of the injection molding cycle from the actual value of the mold temperature from the mold temperature sensor 11. Calculating the value y _(i)av.

First, the estimation unit 34 calculates the temperature distribution X _(i) in the mold immediately before injection in the i-th injection molding cycle and the cooling water temperature during the i-th injection molding cycle, as in the first embodiment. Θ, molten resin temperature
From T _R , according to equation (15), the time average temperature Y _(i)av. of the i-th mold and the temperature distribution X _(i+1) in the mold immediately before the i-th injection calculate.

Next, after the end of the i-th injection molding cycle, the mold temperature average value calculator 18 calculates the actual measured value y _(i)av. of the time-average temperature of the i-th mold.

At this time, the estimation unit 34 calculates the time average temperature Y _{(i)av of the i-th mold calculated from the above equation (15).}
The deviation between the actual value y _{(i) av.} of the time average temperature of the mold obtained from the mold temperature average value calculator 18 is multiplied by L, and the temperature in the mold immediately before the i+1st injection is calculated. The distribution X _(i+1) is corrected so that Y _(i)av. matches the measured value y _(i)av . Temperature distribution inside the mold from the estimation unit 34
X _(i+1) is output to the feedback amount calculation section 35 via the transmission line 17.

The feedback amount calculation unit 35 calculates the temperature distribution X (i) in the i-th mold based on the temperature distribution X _{(i+1) in} the mold estimated with sufficient accuracy by multiplying by L. The amount of feedback is calculated by multiplying by K so as to achieve a predetermined target temperature θ _r of the mold.
The obtained feedback amount is returned to the adder 3 via the transmission line 12, added to a predetermined mold target temperature θ _r , and outputted to the cooling water temperature adjustment device 8. However, both K and L are column vectors.

In addition, the method of designing a control system when it has an adaptive observation device corresponding to the estimation unit 34 and a feedback amount calculator 35 is described in ``Digital control of dynamic systems; written by GF Franklin and JD Bauer, translated by Hiromasa Haneda, Morikita Publishing. , (1985), pp139)”
You may also use

Furthermore, in the first, second and third embodiments,
For the cooling water temperature, an actual measured value may be used, or a set value may be used assuming that the cooling water temperature has been adjusted according to the set value. Similarly, for the molten resin temperature, an actually measured value may be used, or a set value may be used assuming that the temperature has been adjusted to a set value.

[Effects of the Invention] As explained above, according to the mold temperature estimating device for an injection molding machine of the present invention, during continuous injection molding work, the mold time for each injection molding cycle is calculated from the actual value of the mold temperature. Since the average temperature is estimated, temperature fluctuations in the mold can be compensated for without treating them as disturbances, and control suitable for heat media with slow response speed can be performed.

In addition, since the time-average temperature of the mold is used,
State space representation allows for highly accurate estimation with simple formulas.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an injection molding machine equipped with a mold temperature control device according to the first embodiment of the present invention, Fig. 2 is a simplified perspective view of the mold, and Fig. 3 is a diagram showing a fixed mold. A model diagram representing the case of approximation to a sphere, Figure 4 is a diagram showing the change in temperature distribution inside the mold in the 10th cycle, and Figure 5 is a diagram showing the changes in the temperature distribution inside the mold in the 10th cycle. FIG. 6 is a block diagram of an injection molding machine equipped with a mold _temperature control device according to a second embodiment of the present invention.
FIG. 7 is a block diagram of a mold temperature control device according to a third embodiment of the present invention, and FIG. 8 is a block diagram of a mold temperature control device according to a third embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Mold, 2... Injection cylinder, 3... Adder, 7... Cooling water circulation pump, 8... Cooling water temperature adjustment device, 10... Series compensator, 11... Mold temperature sensor, 13... ...Feedback compensator, 14...
...Mold temperature control device, 16...Mold temperature target value transmission line, 18...Mold temperature average value calculator, 20...
...Melted resin temperature sensor, 24...Calculation section, 25...
...correction section, 34...estimation section, 35...feedback amount calculation section.

Claims (1)

[Scope of Claims] 1. A mold temperature estimating device for an injection molding machine for setting the mold temperature of the injection molding machine to a mold temperature suitable for the next injection molding cycle. temperature detection means for detecting an actual measured value of at least one of the temperature and the molten resin temperature, and a time average temperature of the mold for each injection molding cycle is calculated from the actual measured value based on a predetermined calculation formula. 1. A mold temperature estimating device for an injection molding machine, comprising time average temperature calculation means. 2. In the mold temperature estimating device for an injection molding machine according to claim 1, the calculation formula uses a state space expression in a discrete time system with an injection molding cycle time as a sampling period. Molding machine mold temperature estimation device. 3. In a mold temperature control device having a heat medium temperature control means for controlling the temperature of a heat medium in thermal contact with the mold in order to adjust the temperature of the mold of an injection molding machine, a mold temperature estimation device and The mold temperature estimating device includes a temperature detecting means for detecting an actual measured value of at least one of the mold temperature and the molten resin temperature of the injection molding machine, and a and a time average temperature calculation means for calculating the time average temperature of the mold for each injection molding cycle based on the calculated formula, and the command value calculation means calculates the time average temperature and a predetermined mold temperature target value. A mold temperature control device that calculates a command value to the heating medium temperature control means so that the temperature of the mold in the next molding cycle becomes the target value of the mold temperature. 4. The mold temperature control device according to claim 3, wherein the arithmetic expression uses a state space expression in a discrete time system with an injection molding cycle time as a sampling period. . 5. The mold temperature control device according to claim 4, wherein the time average temperature calculation means and the command value calculation means are realized by an adaptive observation device. 6. In the mold temperature control device according to claim 5, after the injection molding cycle has ended, the adaptive observation device is configured to measure the temperature of each injection molding cycle calculated from the actual measured value based on a predetermined calculation formula. The time-average temperature of the mold is compared with the time-averaged mold temperature actually measured in the injection molding cycle, and the parameters of the calculation formula are corrected to correspond to the actually measured mold time-average temperature. Mold temperature control device. 7. In the mold temperature control device according to claim 5, after the end of the injection molding cycle, the adaptive observation device detects the calculated mold time average temperature and the mold time average actually measured in the injection molding cycle. Based on the deviation from the temperature, a feedback amount for the command value given to the heating medium temperature control means is controlled so that the command value realizes the predetermined target value of the mold temperature. mold temperature control device.