JPS646932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an apparatus for measuring the temperature pattern of resin within a cylinder of an injection molding machine.

In an injection molding machine, in order to manufacture precision injection molded products, it is necessary to accurately control the resin temperature within the cylinder, particularly the resin temperature at the central axis of the cylinder. In order to control the resin temperature, it is necessary to accurately measure the temperature of the resin.

[Prior art]

Conventionally, the extrapolation method and the direct method are known as methods for measuring the temperature of resin within the cylinder of an injection molding machine.

The extrapolation method detects the cylinder temperature at multiple points,
This method estimates the resin temperature near the inner wall of the cylinder by extrapolating the detected value. However, as will be explained in detail later, there is a considerable temperature difference between the temperature of the resin near the inner wall of the cylinder and near the center axis of the cylinder, depending on the flow of the resin and the amount of heat generated by shearing. method cannot measure the actual temperature of the resin. Therefore, in order to accurately estimate the temperature of the resin, it is necessary to measure the resin temperature by some method.

On the other hand, in order to measure resin temperature, in the direct method, one measurement end (for example, temperature measurement with a torpedo) is provided directly in the resin flow. However, this method not only disturbs the flow of the resin, but also has difficulty in directly measuring the true resin temperature due to the heat capacity of the measurement end itself and heat conduction to the cylinder section. Furthermore, actual resin has a temperature distribution, and a value detected by only one measurement end cannot accurately represent the entire resin temperature.

Therefore, if the temperature of the resin is controlled using the resin temperature near the inner wall of the cylinder (extrapolation method) or the resin temperature at one point within the resin (direct method), as in the past,
Since there is a considerable difference in the temperature of the resin near the inner wall of the cylinder and near the center axis of the cylinder, it has been difficult to manufacture precise injection molded products.

[Purpose of the invention]

An object of the present invention is to provide an apparatus that can accurately measure the temperature pattern of resin within a cylinder of an injection molding machine.

[Structure of the invention]

According to the present invention, an injection molding machine having means for detecting the temperature of a cylinder of an injection molding machine and the temperature of resin in the cylinder at a plurality of points, and means for calculating a temperature pattern of the resin using the plurality of detected values. A resin temperature pattern measuring device for a molding machine is obtained.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an injection molding machine to which the present invention is applied, in which resin material from a hopper (not shown) is supplied into a cylinder 11 and kneaded by the rotation of a screw 12. It is sent along the groove to the tip of the cylinder 11 (toward the left in the figure). At this time, the resin 13 is heated by the band heater 14 on the outer periphery of the cylinder 11, and is brought into a molten state by the addition of frictional heat (shear heat generation) generated by the kneading action.

As the molten resin 13 is stored at the tip of the cylinder 11, the screw 12 moves backward (towards the right in the figure).
retreat to. This amount of retraction is regulated by, for example, a limit switch (not shown), and the screw
The injection amount is controlled by stopping the rotation of No. 2 at a fixed position.

The resin 13 in the cylinder 11 is injected into a mold (not shown) by driving the screw 12 forward (to the left in the figure) during injection, solidified, and then taken out from the mold. Ru.

Referring also to FIG. 2 showing the A-A′ cross section of FIG. 1, the temperature sensor 15 according to the present invention has a resin 1
3, a cross-sectional portion of the cylinder 11 with protrusions 16 arranged in the circumferential direction of the cylinder 11, designed to reduce the heat capacity as much as possible and not disturb the flow of the resin 13, that is, the radius of the cylinder 11 and the resin 13. They are arranged taking into consideration the directional temperature distribution. To be more specific, the temperature sensor 15 is connected to the cylinder 1.
1, near the so-called boundary between cylinder 11 and resin 13 (distance (radius) r = r ₀ from the central axis of cylinder 11) and near the outer periphery of cylinder 11 (radius r
= r ₁ ), and a thermocouple 15-1 that detects the temperature between the inner wall of the cylinder 11 (radius r = r ₀ ) and the protrusion 16.
The thermopile 15-2 has a thermopile 15-2 in which thermocouples are connected in series in the circumferential direction of the cylinder 11 to detect the temperature difference between the cylinder and the contact point (radius r= _r2 and _r2 < _r0 ). There is. In the thermopile 15-2, the detected value is amplified even when the temperature difference between two points (radii r = r ₀ and r ₂ ) is small, so the radius r of the resin 13 is accurately determined.
= r ₂ temperature can be detected.

Referring to FIG. 3, the resin temperature pattern measuring device according to the present invention includes a cylinder 11 as described above.
temperature detector 15 that detects the temperature θ _c of the resin 13 and the temperature θ r of the resin 13 at a plurality of points, and an arithmetic device that uses _these detected values θ _c and θ _r to calculate the temperature pattern of the resin 13 according to a procedure described later. 17, arithmetic unit 1
7 is specifically realized by a microcomputer, an analog computer, or the like.

First, an example of the temperature distribution pattern in the radius r direction of the cylinder 11 and the resin 13 is shown in FIG. Fourth
Figure a shows the cylinder and resin temperature pattern θ _c when the heat generation inside the resin 13 is small, that is, when the flow rate of the resin 13 is slow or when the viscosity coefficient of the resin 13 is low.
(r) and θ _c (r), and FIG. 4b shows the cylinder and resin conditions when the heat generation inside the resin 13 is large, that is, when the flow rate of the resin 13 is high or when the viscosity coefficient of the resin 13 is high. Temperature patterns θ _c (r) and θ _r (r) are shown.

As shown in FIG. 4, the temperature distribution pattern θ _r (r) in the radius r direction of the resin 13 varies greatly depending on the flow of the resin and the amount of heat generated by shearing.
At the interface between the cylinder 11 and the resin 13 (radius r=r ₀ ), the temperature gradient ∂θ _c /∂r|r=r ₀ of the cylinder 11 and the temperature gradient ∂θ _r /∂r|r=r ₀ of the resin 13 are also different. It's on. Therefore, as in the conventional case, the resin temperature θ _r near the inner wall of the cylinder 11
(r ₀ ) (extrapolation method) or the resin temperature θ _{r (} r ₃ ) (0≦r ₃ <r ₀ ) (direct method) at one point in the resin 13.
)
If the representative temperature is used to control the resin temperature, it is difficult to accurately control the entire resin temperature.

In the present invention, the arithmetic unit 17 measures the resin temperature pattern θ _r (r) as shown in FIG. Hereinafter, the temperature distribution pattern calculation device using the calculation device 17 will be described in detail.

First, the cylinder temperature θ _c [℃] and the resin temperature θ _r
Let [°C] be a function of radius r [m] and time t [seconds],
Let θ _c =θ _c (r, t) and θ _r =θ _r (r, t), respectively. At this time, from the thermal relationship, ∂θ _c /∂t=λ _c ∂ ² θ _c /∂r ² +λ _c 1/r ∂θ _c /
∂r ∂θ _r /∂t=λ _r ∂ ² θ _r /∂r ² +λ _r 1/r ∂θ _r /∂r
It is necessary to satisfy the basic partial feature equation of =K _p q _p +f(v)(1). Here, λ _c [m ² /sec] and λ _r [m ² /sec] represent the temperature conductivity of the cylinder 11 and the resin 13, respectively, and q _p
[W/m ³ ] is the shear heating value per unit volume, K _p
[ ^m3 ·°C/J] represents its coefficient, and f(v) [°C/sec] represents a variable caused by the flow. Also, at this time,
At the same time, ∂θ _c ／∂r｜ _r=r1 =K _h q _h −K〓(θ _c ｜ _r=r1 −θ _p ) ∂θ _c ／∂r｜ _r=r0 ＝K〓 _c (θ _cr=r0 +△r−θ _r | _r=r0 ) ∂θ _r /∂r | _r=r0 =K〓 _r (θ _c | _r=r0 −θ _r | _r=r0 −△r
)(2) must be satisfied. Here, △r
[m] (>0) is minute displacement, q _h [W/m ² ] is the heating amount per unit area of heater 14, K _h [m・℃/W]
is its coefficient, θ _p [°C] is the ambient temperature of the cylinder 11,
K〓 [1/m], K〓 _c [1/m], K〓 _r [1/m] are
Each represents a coefficient related to heat transfer.

Here, it is impossible to obtain an exact solution to the partial partial equation of equation (1) under the boundary condition of equation (2), so θ _c and θ _r are replaced by θ _c ^* (r, t )= _N 〓 ⁱ⁼⁰ a _i P _i (r) θ _r ^* (r, t), _M 〓 ⁱ⁼⁰ b _i Q _i (r) (3) Approximate with a polynomial of radius r. At this time,
Various functions can be considered for P _i (r) and Q _i (r), but P _i (r)= _i 〓 ^j=0 c _j r ^j Q _i (r)= _i 〓 ^j=0 The form d _j r ^j is often used.

Here, the coefficients a _i and b _i in equation (3) are calculated using the following equation (W _ci , R _c )=∫ _r W _ci R _c dr [W _ri , R _r )=∫ _r W _ri R _r dr (4 ) is sought to be minimized. Here, R _c ,
R _r is the residual when θ _c ^* and θ _r ^* in equation (3) are substituted into equation (1), that is, R _c = ∂θ _c ^* / ∂t− [λ _c ∂ ² θ _c ^* / ∂r ² +λ _c 1/r
∂θ _c ^* /∂t] R _r =∂θ _r ^* /∂t− [λ _r ∂ ² θ _r ^* /∂r ² +λ _r 1/r ∂
θ _r ^* /∂r + K _P q _P + f(v)], and W _ci and W _ri represent weight functions.

Ultimately, this problem is reduced to solving the differential equation a = A ₁ a + B ₁ q _h b = B ₂ b + B ₂ q _h (5). These series of calculations are performed using a method of decomposing the object into finite elements and finding an approximate solution instead of finding an analytical solution to a distributed constant system equation such as equation (1).
It is executed using the finite element method and realized using a digital computer or an analog computer. In addition, in equation (5), A ₁ , A ₂ , B ₁ , and B ₂ are coefficient matrices calculated from equations (1) to (4) using the finite element method, and a = (a ₀ a ₁ ...a _N ) ^T , b=
(b ₀ b ₁ ... b _M ) ^T , a = d/dta, b = d/dtb,
The superscript T represents transposition.

From the detected values θ _ci and θ _ri of the temperature detector 15, the initial condition θ _ci (r _i , o) = _N 〓 ⁱ⁼⁰ a _i (o) P _i (r _i ) θ _ri (r _i , o) = _M 〓 ⁱ⁼⁰ b _i (o) Q _i (r _i ) (6) Calculate the initial values of a _i and b _i so as to satisfy the following.
A _i (Δt) and b _i (Δt) are calculated using equation (5) so as to satisfy this initial condition and equations (1) and (2). here,
Δt indicates minute time. As a result, the estimated values θ _c ^* and θ _r ^* of the temperature distribution can be obtained from equation (3).

By the way, the coefficients λ _c , λ _r , K _p , K _h ,
Since K〓, _K〓c , and _K〓r are determined by the thermal properties of the resin 13 and the cylinder 11, the values determined in advance from experiments or physical constant tables cannot be applied to various resins and cylinders. Therefore, in order to increase the accuracy of estimating the temperature distribution pattern, _{the equations (} 1), (2 ) Correct the coefficients of the equation. In reality, the coefficient matrices A ₁ , A ₂ , B ₁ , and B 2 of equation (5) obtained from equations (1) and ( ₂₎ are corrected [system identification]. By repeatedly calculating the estimated values θ _c ^* and θ _r ^* and identifying the system using the detected values θ _ci and θ _ri as shown below, it is possible to accurately calculate the temperature distribution pattern. Become.

Iterative calculation procedure Initial temperature θ _ci (r _i , o) measured by temperature detector 15,
Measurement of θ _ri (r _i , o).

Initial value a of a and b that satisfies equation (6)
(o), determination of b(o).

Calculate a(△t) and b(△t) using equation (5).

From equation (3), θ _ci ^* (r _i , △t), θ _ri ^* (r _i , △t)
seek.

The temperature detector 15 detects θ _ci (r _i , △t), θ _ri (r _i
,
△t) was measured.

So that the difference between θ _ci ^* and θ _ci and between θ _ri ^* and θ _ri are minimized,
The coefficient matrices A ₁ , A ₂ , B ₁ , and B ₂ in equation (5) are corrected.

Return to the initial values of θ _ci (r _i , Δt) and θ _ri (r _i , Δt).

Repeat the same steps below.

With the device according to the present invention (Fig. 3), the temperature distribution pattern finally determined is a,
It can be obtained by substituting b into the polynomial in equation (3) and calculating θ _c ^* and θ _c ^* for an arbitrary radius r.
The above is the general procedure for calculating a temperature distribution pattern using the detected temperature values θ _ci and θ _ri.As a result, for example, as shown in FIG. 5, the temperature at three points θ _c1 = θ _c (r ₁ ), θ _r1 = θ _r (r ₀ ) (= θ _c2 = θ _c (r ₀
)), θ _r2 =
The overall temperature distribution pattern θ _r ^* can be obtained from θ _r (r ₂ ). That is, through the above repeated calculations, the true temperature distribution pattern shown by the solid line in FIG. 5 can be determined with high accuracy from the temperature distribution pattern shown by the dotted line in FIG.

Note that in order to obtain b from equation (5), it is necessary to know the value of the shear calorific value _qP . Also _, the temperature θ _c ( _{r 0} , _{t 0} ) (= θ _r (r ₀ , _{t 0} ), θ _c (r ₁ , t ₀ ), θ _r
( _r2 , _t0 )
Even if a temperature distribution pattern as shown by the dotted line in Fig. 6 is obtained by measuring , the temperature distribution pattern gradually changes due to heat generation, and the radius r = r ₀ , r at time t = t ₁ . ₁ , r ₂ temperature θ _c (r ₀ , t ₁ ) (= θ _r
(r ₀ , t ₁ )), θ _c (r ₁ , t ₁ ), and θ _r (r ₂ , t ₁ ), resulting in a temperature distribution pattern as shown by the solid line in FIG. Therefore, even if we initially use the experimentally determined value for the shear heating value q _p , we will make the following changes so that the changes will be the same between the actual system and the model system, as shown in Figure 6. As described in , the shear calorific value q _p ^* of the model is corrected.

Fig. 7 is a block diagram showing the method for estimating the shear calorific value q _p , where G _R is a transfer function representing the thermal characteristics of the actual injection molding machine, and G _E is the estimated value θ _r ^* , θ _c ^* . It shows a transfer function representing the thermal characteristics of the model assumed for calculation. Since the heating amount q _h of the heater can be measured, both inputs of the transfer functions G _R and G _E (known quantities) are required.
It has been added as. Although the true shear heat value q _p added to the actual system G _R can be estimated in advance through experiments, it is not an accurate value, so the model system
Give an estimated value q _p ^* as the shear heat value added to G _E.

The temperature measurement values θ _ri , θ _ci which are the outputs of the actual system G _R ,
The estimated temperatures θ _ri ^* and θ _ci ^* , which are the outputs of the model system G _E , are
Since the estimated shear heat value q _p ^* is different from the actual shear heat value q _p , a deviation e=(θ _ri −θ _ri ^* , θ _ci −θ _ri ^* ) occurs. Therefore, using this deviation e, the estimated shear heating value is
Change q _p ^* so that θ _ri ^* = θ _ri and θ _ci ^* = θ _ci .
By repeating this process several times, finally
q _p ^* = q _p , and the actual shear calorific value q _p is estimated. Here, various methods can be considered to correct the estimated shear heat value q _p ^* so that the deviation e becomes zero, but if the actual shear heat value q _p does not change much over time, the deviation e The transfer function H in Fig. 7 takes as input and outputs the estimated shear heating value q _p ^* .
, the integrator K/S as shown in FIG.
is given as an example. Here, K is a constant that defines the speed of estimation.

In this embodiment, a case is described in which a thermocouple and a thermopile are used as the temperature detector 15.
It goes without saying that a multi-junction thermocouple such as -68704 may be used, or a resistance thermometer, a thermistor thermometer, or the like may be used.

Furthermore, although this embodiment describes a case in which only the temperature distribution in the radius r direction is taken into account, the temperature detector 15 is connected to the cylinder 11 as shown in FIG.
By increasing the number of measurement points, the temperature distribution pattern can be estimated by taking into account not only the heat flow in the radius r direction as shown by the solid line arrow, but also the heat flow from adjacent zones as shown by the dotted line arrow. be able to. At this time, equation (3) is as follows: θ _c ^* (r, z, t) = 〓 ⁱ 〓 ^j a _ij P _1i (r) P _2j (z) θ _r ^* (r, z, t) = 〓 ⁱ 〓 ^j b _ij Q _1i (r)Q _2j (z). Furthermore, when taking into consideration the temperature distribution in the circumferential direction, θ _c ^* (r, z,, t) and θ _r ^* (r, z, , t) may be considered.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, a model is created from the shape of the cylinder given in advance and the physical property values of the cylinder and resin, and the detected location is It is possible to successively estimate the overall temperature distribution pattern of other cylinders and resin with high accuracy. that time,
The physical properties of cylinders and resins vary depending on the type and temperature conditions, so the model used to estimate the temperature distribution pattern is successively modified based on the temporal change (response) of the measured temperature values of the resin and cylinder. Increase accuracy. By incorporating the injection speed and shear heat generation amount into the model, it becomes possible to estimate the temperature distribution pattern with even greater accuracy.

Furthermore, in the present invention, the detection end that directly measures the resin temperature is devised to minimize heat conduction to the cylinder and the heat capacity of the detector itself, and also to prevent errors caused by these and errors in shear heat generation. , skillfully corrects the temperature changes while watching them in real time. In addition, as for the model, it is sufficient to first provide thermal correlations, that is, the shape and initial values of the model, and then the model is modified so that the accuracy improves successively in accordance with the conditions of the injection molding machine.

Therefore, if the temperature of the resin is controlled based on the temperature distribution pattern determined by this device, for example, based on the temperature of the cylinder center shaft, which cannot be directly measured, the resin temperature at the cylinder center shaft can be accurately determined. The accuracy of injection molded products can be improved.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the tip of a cylinder of an injection molding machine to which the present invention is applied, Fig. 2 is a sectional view taken along line A-A' in Fig. 1, and Fig. 3 is a resin temperature pattern measuring device according to the present invention. Block diagram showing the configuration of
The figure shows an example of the temperature distribution pattern of the cylinder and the resin, Figure 5 shows an example of estimating the temperature distribution pattern according to the present invention, and Figure 6 shows an example of a change in the temperature distribution pattern due to heat generation inside the resin. Figure 7 is a block diagram showing the method for estimating the shear heat generation amount, Figure 8 is a diagram showing an example of the transfer function H in Figure 7, and Figure 9 is a diagram showing the method for estimating the shear heat value. FIG. 3 is a cross-sectional view showing an example of determining a temperature distribution pattern by providing measurement points. 11... cylinder, 12... screw, 13...
...Resin, 14...Band heater, 15...Temperature detector, 16...Protrusion, 17...Arithmetic device.

Claims (1)

[Claims] 1. In a resin temperature pattern measuring device used in an injection molding machine that fills and injects resin into a cylinder extending in the axial direction, the temperature of the cylinder at a predetermined cross-sectional position in the axial direction of the cylinder is measured at a plurality of different points in the radial direction. means for measuring, means for measuring the temperature of the resin at the predetermined cross-sectional position at a plurality of different points in the radial direction, and calculating a temperature pattern within the cross-section of the resin at the predetermined cross-sectional position from the measured values of the cylinder and the resin. 1. A resin temperature pattern measuring device for an injection molding machine, comprising means for measuring.