JPH0511743B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold temperature control device for controlling mold temperature during continuous injection molding operations of an injection molding machine.

[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 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.

[Problem that the invention seeks to solve]

As described above, the conventional technology relies on trial and error by the operator without estimating fluctuations in mold temperature, resulting in a low product yield.

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.

SUMMARY OF THE INVENTION In view of the above drawbacks, a technical object of the present invention is to provide a mold temperature control device that compensates for fluctuations in mold temperature and performs control suitable for controlling a heat medium with a slow response speed.

[Means for solving problems]

According to the present invention, the mold temperature includes a heating medium temperature control means for controlling the temperature of the heating medium that is in thermal contact with the mold for each injection molding cycle in order to adjust the temperature of the mold of the injection molding machine. The control device first controls the temperature of the molten resin injected into the mold of the injection molding machine.
a first temperature detection means for detecting as a detected value;
Let θ _r be the target value of the predetermined mold temperature, Θ ^* be the steady input value, T _R be the temperature of the molten resin, k be the parameter, and the functions of the parameter k be P(k) and Q(k), respectively.
State space equation of only scalar quantities determined in advance as the first arithmetic expression Θ ^* = (θ _r −Q(k)・T _R )/P(k)
Based on the first detected value and a predetermined target value of the mold temperature, a command value to the heat medium temperature control means is calculated so that the temperature of the mold in the injection molding cycle becomes the target value of the mold temperature. The estimated values of the state vector expressing the temperature distribution in the mold immediately before injection in the i- _th and _i+1 -th injection molding cycles are ₎ ,
The cooling water temperature in the i-th injection molding cycle is Θ _(i) , the temperature of the molten resin is T _R , the parameters are A, b, e, C, d, f, the mold in the i-th injection molding cycle Estimate the time-averaged temperature of
Let Y _(i)av. be the linear form of the state space representation defined in advance as the second arithmetic expression X _(i+1) = AX _(i) + bΘ _(i) + eT _R ,
and Y _(i)av. =CX _(i) +dΘ _(i) +fT Based on _R , the first
a mold temperature estimating means that calculates the time average temperature of the mold for each injection molding cycle from the detected value and the command value; and a second temperature detection means that detects the first and second calculations from the actual measured value of the time-average temperature based on the second detected value and the calculated value of the time-average temperature calculated by the second calculation formula. and a correction means for correcting the parameters of the equation to correspond to the actual measured value of the time average temperature, and the heating medium temperature indicating means calculates based on the first calculation equation using the parameters corrected by the correction means. The mold temperature control device has a memory section that stores the command value, and reads out the command value corresponding to at least the first detected value and the target value from the memory section and outputs it to the heat medium temperature indicating means. can get.

〔Example〕

Next, embodiments of the invention will be described with reference to the drawings.

First Embodiment As shown in FIG. 1, a mold 1 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, drives the cooling water circulation pump 7 in accordance with the cooling water temperature command value Θ ^* from the mold temperature control device, which will be described later. is controlled so that it becomes a predetermined mold temperature target value θ _r .

Here, the mold temperature control device controls the cooling water temperature adjustment device 8 to achieve a predetermined mold temperature based on the detected value of the molten resin temperature and the mold temperature target value from the transmission line 16. A cooling water temperature indicating device 17 that calculates a cooling water temperature command value and stores the calculated command value, and a cooling water temperature indication device 17 that stores the calculated command value, A mold temperature estimation device 14 that calculates the time average temperature of the mold compares the time average temperature of the actually measured mold temperature with the time average temperature of the calculated mold temperature, and calculates the time average of the actually measured mold temperature. It mainly comprises a cooling water temperature indicating device 17 and a correction device 15 that corrects parameters in the calculation contents of the mold temperature estimating device 14 so as to correspond to the temperature.

First, the calculation formula (Tanimura, _Akashi ; 30th
The following is an explanation of the calculation formula based on the state space representation in a discrete time system with the injection molding cycle time as the sample period, which is uniquely developed using the relevant calculation formula as a model. do.

First, when modeling the thermal characteristics of the mold and approximating the mold temperature to the unsteady heat conduction within the calculation sphere, the following assumptions are made using FIG.

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 movable molds 110 and 112 occurs only at the start of resin injection, so that the temperature plane of the molten resin has a uniform thickness in the vicinity of the molding cavity. , is assumed to be 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 [m ² ] be, and let the distance between the two surfaces be r1 [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 expressed as A ₀ , A ₁ ,
Using r ₁ , it is defined as in the first equation. Furthermore, r ₀
[m] is a virtual quantity (Δr [m] is the thickness of the plane of the molten resin temperature), and the temperature distribution is treated 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 ₁ =k∂ ² (rθ)/∂r ² …(2) θ _ti=0 =f ₁ (r) …(3) θ _r=a =Θ, a=r ₀ + r ₁ …(4) 0≦t ₁ ≦T …(5) However, θ [℃] is the mold temperature, k [m ² /s] is the temperature conductivity, Θ [℃] is the cooling water temperature, f ₁ ( r) [°C] 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 ₁ is the 6th
Formula (Kensuke Kawashita: Thermal Conduction Theory, p334, Kawade Shobo 1941)
become that way.

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

f ₁ (r)=θ _t1-1=T , 0<r<r ₀ −Δr …(7) f ₁ (r)=T _R , r ₀ −Δr≦r≦r ₀ …(8) f ₁ ( r)=θ _t1-1=T , r ₀ <r≦a (9) θ _tp-T =Θ (10) where T _R [°C] is the temperature of the molten resin.

Further, for f ₁ (r), interpolation is performed as shown in equations (11) to (13).

0=S ₀ <S ₁ <S ₂ ...S _N-1 <S _N ...(11) f ₁ (r)=f ₁ (S ₁ ), 0<r<S ₁ ...〓 f ₁ (r)=( f ₁ (S _J )−f ₁ (S _J+1 ))/(S _J −S _J+1 )・r
+
(S _J・f ₁ (S _J+1 )−S _J+1・f ₁ (S _J ))/(S _J −S _J+1 ),
S _J <r<S _J+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 time average temperature θ _1(av) [° C.] for each cycle is determined by equation (14) below.

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 k 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 embodiment is one that further transforms Equation (14), which is an expansion of Equation (6), from infinite dimension to finite dimension. 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. That is, the first
Equation (15) is a state space expression regarding Y _(i)av. , X _{( i+ t )} , Based on a simple calculation formula regarding the detected value of the mold temperature and the heat conduction within the mold, the time average temperature of the mold for each injection molding cycle is given.

In this way, the mold temperature estimating device 14 determines the future mold temperature from the molten resin temperature T _R detected by the molten resin temperature sensor 10 that detects the temperature of the molten resin and the set temperature Θ of the cooling water. The time average temperature θ _1(av) of the mold for each injection molding cycle is calculated and estimated, and based on the time average temperature θ _1(av) , the cooling water temperature Θ that can realize the predetermined mold temperature is calculated. Find ^* ,
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 in accordance with the command value Θ ^* .

Next, after the end of each injection molding cycle, the correction device ₁₅ calculates the calculated time average temperature Y _{( i)av} . is input, and the parameter k in the calculation contents of the cooling water temperature indicating device 17 and the mold temperature estimating device 14 is corrected so as to correspond to the actual measurement value y _(i)av . The cooling water temperature indicating device 17 recalculates the cooling water temperature Θ ^* that can realize a predetermined mold temperature every time the parameter k is 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 10 can be omitted.

Here, the contents of the correction calculation of the parameter k by the correction device 15 will be specifically explained.

First, the time average temperature Y _(i)av. of the mold in the mold temperature estimating device 14 is expressed by the following equation using the state space expression below, as in equation (15) described above. Ru.

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 they are the i-th and i+1st injection A state vector expressing the temperature distribution in the mold immediately before injection in a molding cycle, 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. It is an estimated value of the time average temperature of the mold in the i-th 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 device 15 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
Find Y _(i)av. Next, from the difference between the actually detected time average temperature y _{(i) av.} and the time average temperature Y _{(i) av.} calculated by the mold temperature estimation device 14, the correction amount Δk of the parameter k is calculated as follows. Calculated based on equation (17).

Δk=−k・(Y _(i)av. −y _(i)av. )/ (Xm ₍₁₊₁₎ −Y _(i)av. ) …(17) However, Xm ₍₁₊₁₎ is The element in the m-th row of the vector X ₍₁₊₁₎ is an estimated value of the temperature at an arbitrary position where the mold temperature sensor 11 detects the temperature of the mold 1.

Here, Equation (17) is analytically obtained from Equation (14), which calculates the time-averaged temperature θ _{i (av)} of the mold. That is, in the i-th injection molding cycle, the correction amount Δk of parameter k is Δk=−(Y _(i)av. −y _(i)av. )/(∂Y _(i)av. /∂k) ...(18) At this time, according to equation (14),
Since ∂Y _(i)av. /∂k can be found analytically,
Substituting it into equation (18), we get equation (18).

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

As a result, using Δk obtained by equation (17), the correction device 15 first calculates the temperature of the cooling water temperature indicating device 1.
7 and calculation contents of the mold temperature estimating device 14 (No. (17)
The parameter k in formula) is corrected to k+Δk. At the same time, the cooling water temperature indicating device 17 recalculates the cooling water temperature Θ ^* (command value) that can realize the target value θ _r of the predetermined mold temperature every time the parameter k is updated, and the cooling water temperature adjusting device 8 is output.

Next, the command value Θ ^* calculated by the cooling water temperature indicating device 17 can also be calculated based on the following equation (20).

X ^* =A(k)X ^* +b(k)Θ ^* +e(k)T _R θ _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 device 15 corrects the parameter k of the cooling water temperature indicator 17 and the mold temperature estimation device 14, the unknown parameter (k+Δk)
The mechanism for estimating the state variable (X _(1+t) ) while identifying is defined as an adaptive observer (adaptive control; Kunihiko Ichikawa et al., Shokodo, (1984) pp. 54).

However, in the calculation of equation (20), the temperature distribution of the mold is assumed to be in a steady state, and a steady input value Θ ^* that satisfies the target value θ _r is obtained, so when deriving Θ ^* , It is necessary to perform an infinite number of calculations using Newton's method or the like.

Therefore, by transforming the state space equation in Equation (20) into the form of a function described only by scalar quantities, the following Equation (21) can be obtained.

Θ _r =P(k)Θ ^* +Q(k)T _R (21) However, P(k) and Q(k) are functions of k.

Furthermore, if this equation (21) is transformed with respect to Θ ^* , Θ ^* = (θ _r −Q(k)·T _R )/P(k) (22) is obtained.

That is, according to equation (22), if T _R , θ _r and k are determined, Θ ^* can be uniquely determined.

Therefore, in the cooling water temperature indicating device 17, T _R , θ _r
Regarding the combination ^of As a result, during actual process operation, the cooling water temperature indicating device 17 can simply read Θ ^* corresponding to the combination from the memory section from the next time, without performing complicated calculations. can be output to.

〔Effect of the invention〕

As described above, according to the present invention, mold temperature control of an injection molding machine is suitable for rapid and precise control of a heat medium with a slow response speed by predicting mold temperature fluctuations and sequentially compensating for them. equipment can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an injection molding machine equipped with a mold temperature control device that is an embodiment of the present invention, Fig. 2 is a simplified perspective view of the mold, and Fig. 3 is a fixed mold with a sphere. Figure 4 is a diagram showing the change in temperature distribution inside the mold in the 10th cycle, Figure 5 is a model diagram showing the change in temperature distribution in the mold in the 10th cycle, and Figure 5 is a diagram showing the change in the temperature distribution in the mold in the 1st to 6th injection molding cycles according to the formula FIG. 3 is a diagram illustrating an example of calculating the time average temperature θ ₁ . In the figure, 1... Mold, 2... Injection cylinder, 7... Cooling water circulation pump, 8... Cooling water temperature adjustment device, 9... Cooling water flow, 10... Molten resin temperature sensor, 11... Mold temperature sensor, 14... Gold Mold temperature estimation device, 15...
Correction device, 16... Mold temperature target value, 17... Cooling water temperature indicating device.

Claims (1)

[Claims] 1. 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 for each injection molding cycle in order to adjust the temperature of the mold of an injection molding machine. A first temperature detection means detects the temperature of the molten resin injected into the mold of the injection molding machine as a first detection value, a target value of a predetermined mold temperature is θ _r , and a steady input value is Θ ^* , the temperature of the molten resin is T _R , the parameter is k, and the functions of the parameter k are P(k) and Q(k), respectively, and a state space equation Θ ^* of only scalar quantities is predetermined as the first calculation equation. = (θ _r −Q(k)・T _R )/P(k), the temperature of the mold in the injection molding cycle is determined from the first detected value and the predetermined target value of the mold temperature. a heat medium temperature instruction means for calculating a command value to the heat medium temperature control means so as to reach a target value of the mold temperature; The estimated values of the state vector expressing the temperature distribution are X _(i) and
X _(i+1) , the temperature of the cooling water in the i-th injection molding cycle is Θ _(i) , and the temperature of the molten resin is
T _R , the parameters are A, b, e, C, d, f, and the estimated value of the time average temperature of the mold in the i-th injection molding cycle is Y _(i)av. The linear form of the state space representation defined as
X _(i+1) =AX _(i) +bΘ _(i) +eT _R , and Y _(i)av. =CX _(i) +
dΘ _(i) +fT _R , a mold temperature estimating means for calculating the time average temperature of the mold for each injection molding cycle from the first detected value and the command value; a second temperature detection means for detecting the temperature of the mold in the injection molding cycle as a second detected value; and a correction means for correcting the parameters of the first and second arithmetic expressions so as to correspond to the actual measured value of the time-average temperature, based on the calculated value of the time-average temperature, and the heat medium temperature indicating means: the first method using the parameters corrected by the correction means;
has a memory section that stores a command value calculated based on the calculation formula, reads out the command value corresponding to at least the first detected value and the target value from the memory section, and outputs it to the heat medium temperature indicating means. A mold temperature control device characterized by: