CA2054739A1 - Injection control method for injection molder - Google Patents

Abstract

ABSTRACT
The invention relates to an injection control method for controlling the weight of a plasticized synthetic resin injected from the cylinder of the injection molder to fill the cavity of a mold. An object of the invention is to offer the method for keeping the quality of the products constant even if there is an influence by outside disturbances or there is a change in the given conditions, such as the molten resin pressure. Another object is to offer a method wherein a study and an analysis from the beginning is not required, different from the adaptive control, in csse of the change of the mold.
The travel distance SD of the screw to the position for injecting the plasticized synthetic resin by the amount corresponding to the weight value G of a product is calculated by a specified calculation formula and preset.
And the injection of the plasticized synthetic resin into the mold cavity is stopped when the screw has moved for the preset travel distance SD from the stop position immediately before injection.

Description

SPECIFICATION
In~ection Control Method ~or In~ection Molder FIELD OF THE INVENTION
The present invention relates to an inJection control method ~or controlling the weight of the plastlclzed synthetic resin in~ected ~rom a cylinder o~ an ln~ection molder to ~ill a cavity o~ the mold.

BACKGROUND OF THE INVENTION
In the conventional in~ection molding o~ plasticized synthetic resin by an in~ection molder, the welght o~ the inJected plasticized synthetic resin varies with the mplten~
resin pressure, the molten resin speci~ic volume or the~t~
molten resin temperature (including the influence o~ the disturbance on the molding system) etc.. There~ore, it is di~ficult to ~orm products o~ a constant quali ~ To cope with this problem, so-called adaptive control a number o-~proposals have been made. The art disclosed in the Japanese Patent Laid Open Publication No. 84932 of Showa 56 (the year 1981) is an example.
Basically, in the adaptive control method, when the influence o~ a disturbance on the molding system and change in the molten resin pressure, molten resin temperature or mold temperature are detected, a controllable molding condi-tion (pressure, time, etc.) other than the detected factors, ' .... ..
.~ ~ ,. ; .-.- . ,.

.
:, '' .: ~ , ..

~, ~. ': ;~ ~r are changed lnto a control ~actor, thereby assurlng the constant produc-t quality.
However, this control method has the ~ollowing problems:
1Preliminary study and analysis are necessary to determine the correlation between the detected ~actor according to the mold and the product quality and between the control ~actor and -the product quality.
2With the same plasticized synthetic resin, the correlation between the detected ~actor and the product quality and between the control factor and the product quality varies greatly depending on the mold.
There~ore, the stud~ and analysis described in the item 1 above must be repeated each time the mold is changed.
In order to solve a~orementioned problems, the present invention provides an inJection control method o~ an in~ection molder, which assures the products of constant quality even when there is an in~luence to the moldin~
system by the disorder ~rom outside, there is a change in the given condition such as the change o~ the molten resin pressure and which does not require the analysis and the investigation ~rom the beginning as in a case of the adaptive control method even the cavity is changed. the cavity is changed, and o~ers a molder products o~ o~
constant quality.

~ .

.

2~
DISCLOSURE OF THE INVENTI~N
According to the present invention, in order to achleYe the aforementioned obJect, an in~ection control method ~or controlling the weight of the plastlcized synthetic resin in~ected from the cylinder of an in~ection molder to ~ill the cavity of a mold comprises the steps o-~: calculating the travel distance SD of the screw to the position for ln~ecting plastici~ed synthetic resin by the amount corre-sponding to the weight value G of a product by using a specified calculation formula and preset it, on the basis of the weight value G of the product, and terminating the in~ection of the plasticized synthetic resin into the cavity when the screw has moved ~or the preset travel distance SD
~rom the stop position immediately before inJection.
Further, the calculation by using the specified formula for obtaining the travel distance S~ of the screw to the position for in~ecting the plasticized synthetic resln by the amount corresponding to said weight value G o~ a product is carried out at a constant molten resin temperature value T, on the basis of the detected or set molten resin pressure value PI of plasticized synthetic resin immediately before in~ection, the detected or set molten resin pressure value P~ of plasticized synthetic resin during the dwelling process following the in~ection, the detected posltional value SI Of the screw lmmedlately before in~ection, and the PV property relation formula of plasticized synthetic resin, , /

zdsi~9 as follows:
SD = SI ~ S~ = V(P~) {G/A -- SI ~ ~ 1/V(PI) -- 1/V(P~) ] }
wherein S~ : the positional value of the screw durlng t~e dwelling process following the in~ection.
A : pro~ected sectional area of the screw V(PH): the molten resin specific volume value during the dwelling process ~ol:lowing the inJection V(PI): the molten resin specific volume value lmme-diately before the inJection.
Or, the calculation by using the specified formula for obtaining the travel distance SD of the screw to the posi-tlon for inJecting the plasticized synthetic resin by the amount corresponding to said weight value G of a product is carried out on the basis of the detected or set molten resin temperature value T of in~ected plasticized synthetic resin, molten resin pressure value PI of plasticized synthetic resin immediately before in~ection~ molten resin pressure value P~ of plastici7ed synthetic resin during the dwelling process ~ollowing the in~ection, the detected positional value SI of the screw immediately before ln~ection, and the PVT property relation formula of plasticized synthetic resin, as follows:
SD = SI -- S~ = V(PEI~T) {(~/A ~ SI '[1/V(PI .T) ~ 1/V(P~ ,T) ] }
S~ : the positional value of the screw during $he dwelling process ~ollowing the ln~ection .: .

, ' . ' ~ :

A : the pro~ected sectional area o~ screw V(P~,T): the molten resin speci~ic volume value for the molten resin temperature value T and the molten resin pressure value P~ during the dwelling process following the in~ection at the molten resin temperature value T, and V(PI ~T): the molten resin specific volume ~alue for the molten resin temperature value T and the molten resin pressure PI immediately before the in~ec-tion at the molten resin temperature value T.
Thus, according to the inJection control method for an in~ection molder of the present invention, the travel dis-tance of the screw for keeping the predetermined weight value G of the product constant is automatically controlled even there are influences by the disturbance~ from outside or there is a change in the given conditions such as the change of the molten resin pressure, as a result, the constant quality of the products is guaranteed. And differ-ent from the adaptive control, study and analysis from the beginning are required even when the mold is changed. And at the stage of fixing the molding conditions, molten resin pressure value etc. are often changed. In such cases, the $ravel distance o-f the screw is automatically controlled to the specified weight value G, so that the forming condition of a mold is easily fixed.
Furthermore, the fluctuation range of the molten resin ...... . . ............ . ... ...

- ~ :
::

pressure value PI and P~ of the plasticized synthetic resin to be detected immediately before the in~ection and during the dwelling process following the in~ection. respective~Y.
and the molten resin temperature value T of the plasticized synthetic resin to be injected is extremely small during the continual formation in a short period. And in order to improve the detecting accuracy by eliminating the error in a quite a short time, the mean value of the each molten resin pressure value PI. P~ and the molten resin temperature value T to be detected on the basis of the plurality of the injec-tion fillings during the continual formation in a short period can be employed.
In calculating the molten resln specific volume value V
from the molten resin pressure value P and molten resin temperature value T on the basis of the above-mentioned PVT
property relation formula, the plane approximation method can be used on the assumption that the fluctuation of the molten resin pressure value P and molten resin temperature value T is within a specified range.
;:
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1 through 8 are drawings for explaining preferred embodiments of the inJection control method for an inJection molder according to the present invention:
Flgs. l(A) and l(B) are a semi-diagrammatical vertlcal sectional view and a partially enlarged ver~ical sectional , æ~73s view, respectively, of the inJection molder relevant to the present invention;
Figs. 2 and 3 are vertical sectional drawings showing the operation state of the screw in the Example 1 and 2 for the detecting method of the resin property, Fig. 4 is a graph explainin,g the extrapolation method ~or obtaining the molten resin ~volume value remalning in front of the screw;
Fig. 5 is a vertical sectional view showing the opera-tion state of the screw ~or re-ference in obtaining the calculation formula for the travel distance of the screw for inJecting resin of a constant weight value;
Figs. 6 and 7 are semi-diagrammatical Yertical sec-tional views of molding systems to which the first and second embodiments o~ a control method of the present inven-tion are applied.
Fig.8 is a graphical representation for describing the plain approximation method of PVT property relation ~ormula.

' PREFERRED EMBODIMENTS OF THE INVENTION
Some embodiments of the in~ection control method for an ; injection molder according to the present invention are described with reference to attached drawings.
Referring to the Fig. l(A), a schematical view of an entire in~ection molder, in formin~ a product by injection molding, an inJectlon molder 11 is connected through a ``- ' ;

5~9 nozzle 12 with a mold 10 in which *he product is formed. A
screw 19 is contained in the cylinder 13 of the in~ection molder 11. Resin pellets supplled from a hopper 15 are melted and mixed in the cylinder 13 heated by a heater 14 into a plasticized synthetic res:in, while the molten resin is measured and then inJected by the screw 19 through a flow passage 16 ~ormed in the nozzle 12 and $hrough a gate 17 into the cavity 18 of the mold 10. To melt and mlx the resin pellets, the screw 19 is rotated by a screw-driving motor 20. The screw 19 and the screw-driving motor 20 are fixed on a base 21 which is moved laterally in the drawing, by means of pressure oil supplied to a hydraulic piston device 27 through a pipe line 26 from a pressure oil supply 25. To supply the pressure oil, an electromagnetic flow valve 22 and an electromagnetic pressure valve 23 are controlled by a controller 24. In othsr words, the movement of the screw 19 toward and away from the noz~le 12 to measure the molten resin amount to be in~ected and to inJect the measured molten resin into the cavity 18 of the mold 10, and the application of a specified pushing force to the screw 19 to provide a specified molten resin pressure to the molten resin in the cylinder 13 ~re ~ll controlled through the base 21 by the pressure oil supplied to the hydraulic piston device 27. The base 21 is engaged with a screw posi-tion detector 28 for detecting the positional value of the screw 19, which is "0" at the left end~ in the drawing, in ., , ... , .. .. .. ~ ., . ~ ......... .. . . . ..
, ~

3~

the cylinder 13 and increases as the screw 19 moves toward the right. The screw position detector 28 comprises a potentiometer and an encoder etc.. The posltional values o~
the screw 19 detected by the detector 28 minute by minute are sent to the controller 24 as well as to a PVT arithmetic unit 29 which determines the PVT property relation formula for plasticized synthetic resin when detecting the resin property. The PVT arithmet~c unit 29 also operates the PV
property relation formula to calculate the travel distance of the screw 19 and supplies the calculated result to the controller 24, thereby controlling the injection. The molten resin temperature value in the cylinder 13 detected by a resin temperature detector 30 is also transm~tted to the PYT arithmetic unit 29. The oil pressure value for the hydraulic piston device 27, detected by an oil pressure detector 31, is also sent to the arithmetlc unit 29 as the pushing force applied to the screw 19 or the molten resln pressure value P in the cylinder 13. 32 is an external Input unit through which to lnput the measured weight value ~f in~ected molten resin to the PVT unit 29 when detectlng the resin property. The molten resln pressure valu~ P, molten resin temperature value T and other conditional values set for detecting the resin property are also input from the external Input unlt 32 through the PVT arithmetic unit 29 to the controller 24. The target weight value o~
molten resin to be in~ected is also input from this external %05~73~
Input un~t 32 to the PVT arithmetic unit 29.
The flow passage 16 of the no~zle :L2 contains a block valve 33 as a flow path opening/closin~ mechanls~ of the present lnvention so as to interrupt the molten resin flow.
The block valve 33 is operated through an operation lever 35 by an electromagnetic driving unit 34 which is controlled by the controller 24.
As shown in Fig. l(B), a ring-shaped axially slidable valve plug 39 is provided between the conical end portion 36 and the flange proJection 38 at the end of the spiral por-tion 37 of the screw 19. As the molten resin pressure in front of the screw 19 or in the left side of the screw end increases, the slidable valve plug 39 is pressed agalnst the flange pro~ection 38, thus preventing the molten resin from flowing back to the right. Thus, the flange proJection 38 and the ring-shaped slidable valve plug 39 constitute a check valve ~0. It must be noted that even if the screw position detector 28 reads "O" for the position o~ the screw 19, molten plasticized synthetic resin exis~s ln the space between the front end of the screw 19 and the block valve 33, or more specifically between the check valve 40 and the block valve 33.
Now, the detecting method of resin property in fixing the PV(T) property relation formula which is employed in the in~ection control method of an in~ection molder is described in detail re~erring to Example 1.

(Example 1~
For the ~irst phase of the method, the followin~ three processes are repeated with various molten resin temperature values Tl , T2 , Ta , . . ., under the constant molten resin pressure value PO, to obtain the molten resin speci~ic volume values VOl, VO~, YO9, ... for the respective molten resin temperature ~alues Tl, T2, T3~ ... (see Fi~. 2).
1) First Process The rotating screw 19 drives the molten plasticized synthetic resin toward the front of the screw 19. In the first process in which the block valve 33 is closed, the screw 19 is moved back because of the pressure of the molten resin existing in front of the screw 19. While the screw 19 is retreated to a preliminarily set initial position, the amount of the molten resin to be in~ected is measured. When the screw 19 has reached the initial position, the screw rotation is stopped. The arrival o-E the scr~w at the inl-tial position is detected by the screw position detector 28 which sends the positional value of the screw 19 at the initial position to the controller 24. On the basis of this positional value, the controller 24 controls the pressure oil supply to the hydraulic piston device 27 so that a specified pushing force value pO is applied to the screw 19.
Under the specified pushing force, the screw 19 makes a forward balancing movement, compressing the molten resin in front of the screw 19 with the aid of the function of the , .

11 ~

. ~ . . . .. ... . . .
:

, .

;20~39 `
check valve 40. Thus, the molten resin pressure in ~he cylinder 13 increases. The screw 19 stops its forward move-ment at a first stop position when the applied pushing force balances the pressure of ths compressed molten resin. The screw position detector 28 detects the positional value of the screw 19 at the first stop position and outputs the value to the PVT arithmetic unit 29. When the screw 19 is at the first stop position, the molten resin pressure value PO in front of the screw 19 is to correspond to the pushing force value pO applled to the screw 19.
2) Second Process The block valve 33 is opened, and the screw 19 is moved for a specified distance by the pushing force applied to the screw 19, so that molten resin is inJected by the amount corresponding to the specified distance. The weight value G
of Amount of in~ected molten resin is measured by an external measuring instrument. The measureed weight value G
is input ~rom the external Input unit 32 to the PVT
arithmetic unit 29.
3) Third Process The block valve 33 is closed again, and with this state, the oil pressure is controlled by the controller 24 in the same manner as in the first process so as to apply the specified pushing force value pO to the screw 19. Due to this pushing force, the screw 19 makes a forward or backward balancing movement, thus compressing the molten .. . . . .
.. . . , , .. ~ . . , , , . . ..... . , . . , .. , , .. ,,.. ,., ., . .. ~ . . . .. . .

5~7~3 resin in front of the screw 19. The screw 19 stops at a second stop position when the applied pushing force balances the compressed molten resin pressure. The screw position detector 28 detects the positional value of the screw 19 at the second stop position and transmits the value to the PVT
arithmetic unit 29.
The PVT arithmetic unit 29 calculates the di~ference S~
between the positional value of the first stop position and that of the second stop position, or in other words, the molten resin volume value corresponding to the weight value ~ of the in~ected molten resin. The calculated molten resin volume value is divided by the weight value G to obtain a molten resin speci-fic volume value V0.
Thus, in the first phase, the series of the processes ls repeated for various molten resin temperature values Tl, T2, T3, ... under a constant specified pushing force value pO (molten resin pressure value P0) to obtain the molten resin specific volume values Vo1, V02, V03, ....
For the second phase, the following two processes are repeated for various molten resin temperature values Tl, T2, T3, ... under various molten resin pressure values P1, P2, P9, ..., to obtain the respective molten resin specific volume values V11, Vzl, V~1, ...; Vl2, Vz2 , V32, . . .; V13 V23, V33, ... (see Fig. 3).
1) First Process Similar to the first process of the first phase, the .. ~ . ,, . . ..... , .. ~ ~ .. . .. .. .... . . . . . . .

73~
screw 19 is rotated with the block valve 33 closed. The screw 19 is retreated and stopped at a pre~iminarily set initial position while the molten resin is measured. Then, a specified pushing force value pO ls applied to the s~rew 19 to move the screw 19 forward so that the molten resin is compressed. The screw 19 stops its forward movement at a first stop position when the applied pushing force balances the pressure of the compressed molten resin. The posltional value of the screw 19 at the first stop position is detected by the screw position detector 28 and sent to the PVT arith-metic unit 29. Other operations are the same as those in the first process oE the first phase.
2) Second Process A specified pushing force p is applied to the screw 19 with the block valve 33 closed. This time, the applied specified pushing force value p is increased ~radually from Pl to pz to P9 and so on, with the pushing force value pO in the first process as a reference, thus gradually compressing the molten resin. When each of the pushing forces value p , P2, P9, ... iS applied, the screw 19 makes a balanc~ng movement and stops at second, third, fourth or subsequent stop position. The positional value of each stop position is detected by the screw position detector 28 and sent to the PVT arithmetic unit 29.
The PVT arithmetic unit 29 calculates the difference ST
of the positional value at the second, third, fourth or :

26~ 7~

subsequent stop position from the positlonal value at the first stop position to obtain the molten resin volume value on the basis of the calculated difference. From each o~ the thus obtained molten resin volume values and the molten resin specific volume values Vol tVOz, VO~,...) calculated in the first phase, molten resin specific volume values V11, V21, V91,... ~Vl2~ V22, V32,...: Yl9, Vz3~ V99,...) are obtained by the proportional calculation. This proportional calculation is based on the fact that, for the compressed molten resin of the same molten resin temperature value T
and of the same weight value G, the molten resin specific volume V is obtained from the ratios of molten resin volume values in case that the molten resin pressures value P~(pushing force value p~) is changed to Pl, P2. P9....
(pushing force value Pl. p2, Ps~ --)-Thus, the series of calculation processes is repeatedfor each of the molten resin temperature values Tl, T2, T3,... under each of the pushlng force values pl, p8~ P9~...
applied to the screw 19 (the molten resin pressure values Pl, P2, P3, . . . ), thereby obtaining the molten resin specific volume values V1l, V21, V31,...; V12, V~2 , V32,...; V13, V23, V39,.... In *his calculation process, the molten resin temperature value T is changed by controlling the heater 14 by the controller 24.
Even with the screw 19 at a position of the positional value "O", the molten resin remains between the front end of .

,~ .

~5~73g the screw 19 and the block valve 33. ~s various pushing forces are applled to the screw 19, the remaining molten pressure is compressed. This results in the positional values of the screw 19 at respective stop positions. Ac-cordingly, if the PVT property relation formula established for a particular inJection molder is applied to another inJection molder whose remainlng molten resin volume v~lue is different from that in the particular lnJectlon molder, the calculation result will contain a large error that cannot be ignored.
In such a case, the remaining molten resin volume must be corrected to obtain an accurate molten resln speclfic volume value V. The correction method is described below:
i) When the remaining molten resin volume value is known as a design value for the equipment and given in term of the travel distance SO of the screw 19:
With the molten resin of the sàme molten resin tempera-ture value T and of the same weight value G, pushing force values px and pY are applied sequentially to the screw 19 after the molten resin has been measured. When the molten resin pressure values becomes Px or Py and the screw 19 stops its movement, the positional value ~ or Sy of the screw 19 at the stop posltion is detected. The travel dis-tance SO is added to each of these positional values Sx and Sy to obtain each of corrective positional values Sx (= Sx SO) and Sy ( = Sy + SO). Then, the molten resin specific .. . . . ..... .

2~ 3~
volume values Vx and Vy can be expressed by the following equations, respectively.
Vx = (~/4 DZ Sx)/G -. (1) VY = (~/4 D7 Sy)/G .,. (2) D: diameter of the screw By taking the ratio of these equations, the following equation holds:
Vx/Vy = Sx/Sy ( = tSO ~ SX)/tso + Sy)~ ... t3) If the molten resin speci~ic volume value Vy is the molten resin specific volume values Vo1, Y~2~ Vo~, ...
obtained in the -first phase, the molten resin specific volume value Vx can be calculated easily from the equation (3). Since the present embodiment of the lnvention obtains the molten resin specific volume value V similarly by calcu-lating the ratios, the above method can be used directly in the present example.
ii) When the remaining molten resin volume value is unknown:
As shown on Fig. 4, the compression amount of the molten resin or the travel distance S of the screw 19 for the compression is proportional to the mol*en resin volume before compression or the positional value Sm Of the screw 19 before compression. The graph of a linear function is drawn by changing the positional value Sm Of the screw 19 in steps for a constant molten resin pressure value P and a constant molten resin temperature value T. The travel dis-, ,,. ., , , , ~ . .. ,.~, .. .. . ..

' .

~473~

tance SO is obtained easily by th0 extrapolation on thisgraph. Other opera~ions are the same as those described above.
For the third phase, each o~ the molten resin pressure values PO. Pl. P2........ each of the molten resln specific volume value Vol ~ V02 , V03 , ...; V l ~ V.~z , Yl3....; V21~
V22, V23,... and each o~ the molten resin temperature values Tl, T2, T3,... obtained in the ~irst and second phases are substituted in the general formula for the PVT property, to establish the PVT property relatlon formula.
Meanwhile, it is possible to obtain the following generalized function from the equation (3):
V/VO - f(P/Po) (4) wherein P, V given molten resin pressure value and molten resin specific volume value for the given molten resin pressure value PO~ VO : reference molten resin pressure value and molten resin specific volume value for the reference molten resin pressure value The above molten resin pressure values P and PO and molten resin specific volume values V and VO are given at the same molten resin temperature value T.
From the equation (4), the inventor has found that the PV property can be approximated by the following experimen-tal formula:

t ' ' ` ~
~ ' `, f(P/P0) - exp{a( ~ - 1)} ... (5) wherein a : constant Therefore, if the value for the constant "a" is ob-tained by changing the g~ven molt~,n resin pressure value P, the PV (T = constant) property relation ~ormula can be obtained.
Further, the inventor has found that the value of the constant "a" is a functlon of the molten resin temperature value T and can be approximated as follows:
a(T) = b.T ~ c .. (8) b, c : constants The following general formula can be obtained from the equations (4), (5) and (6):
V = VO~exp{(b~T + c)-(JP/Po - 1)} ... (7) When each of the molten resin pressures values P0, P , Pz,..., each of the molten resin specific volume values Vol, V02, V03 , . . .; Vl~, V12 ~ Vl3,...; Vzl, Vz2 ~ Vz3 , . . . and each of the molten resin temperature values Tl, T2, T3,... ob-tained in the first and second phases are substituted in the equation (7), the constants "b" and "c" are flxed so that the PVT property relation formula can be established.
If the molten resin specific volume value V0 for the reference molten resin pressure value P0 is obtained with the molten resin temperature value T varied, the molten resin temperature value T and the molten resin speclfic i-' ' ~;'`'` '` ~ ..-,.: ``: ' : ::: . :

~4~;~9 volume value V are approximated as expressed by the follow-ing linear equation:
VO =~ T + ~ ..- (8) ~ constants Therefore, when the equation (8) is substituted in the equation (7), the following equation results:
V = (~-T + ~)~exp{(b~T I c)-~P/PO - 1)~
In the previous process, the constant "a" was approxi-mated ~y a linear equation. When the molten resln tempera-ture value T changes, the constant "a" changes with the molten resin temperature value T as a variable. Therefore, the constant "a" can be modified to be adaptable to actual equipment by using the polynomial approximation of the molten state resin temperature value T as indicated by the following equation:
a(T) = b~Tm + b-~ Tm-l + . ~ bm'~T ~ c' b ~ ~ b ~ bm ~ ~ c~ constants Similarly, with a constant molten resin pressure value P, when the molten resin temperature value T changes, the molten resin specific volume value VO changes with the molten resin temperature value T as a variable. Therefore, it is preferable to employ the following polynomial approxi-mation of the molten resin temperature value T:
VO = ~T~ + ~ T~-1 + ... ~ ~'.T
~', ~'', ... ~', ~' : constants (Example 2) %~'739 Example 2 on a resin property detectlon method accord-ing to *he present inventlon ls described herelna~ter. Only the processes dlfferent from those in the Example 1 are described in the Example 2, wit~h the descrlptlon of the similar processes omitted.
The PVT property relation formula is establlshed by repeating the following three processes for each of the molten resin temperature values Tl, T2, T~,....
1) First Process Similar to the first process of the first phase of the Example 1, the screw 19 is rotated with the block valve 33 closed, and stopped when it has been retreated to a preliminarily set initial position. Then, pushlng force values PBO~ PS1~ pS2~ pS~ are applied sequentially to the screw 19 to compress the molten resin. Under each of these pushing force values p~O, p~, p~2 , . . ., p~ , the screw 19 makes a balanclng movement and stops at a first stop position indicated by the positional value SsO, S~, Ssz~ ..., or Ss~, which is detected by the screw position detector 28 and sent to the PVT arithmetic unit 29. Other operations are the same as those in the first process of the first phase in the Example 1.
2) Second Process A pushing force value p, which is applied lmmediately before in~ection in the ordinary production process, is applied to the screw 19 and the block valve 33 is opened, so ,. .... . - :

:`~

;~ i473~1 that the molten resin o~ the weight for one batch is in~ected into the cavity 18 of the mold 10 to ~orm an actual product. Next, a pushing force value p, which is applied during the dwelling following the in~ection in the ordinary production process, is applled to the screw 19 and the block valve 33 is closed. The weight value G o~ the inJected molten resin is measured by an external measuring instrument and input through the external Input unit 32 to the PVT
arithmetic unit 29.
3) Third Process Similar to the first process, pushing force values Pso, pSl~ pg2~ pS~ are applied sequentially to the screw 19.
Under each of these pushing force values psO, Ps1, Psz,---, ps~ the screw 19 makes a balancing movement and stops at a second stop position indicated by the positlonal value SFO~
SF, SF2 , . . ., or SF~ , which is detected by the screw posi-tion detector 28 and sent to the PYT arithmetic unit 29.
In a series of above-mentioned processes, the molten resin of the weight value G is in~ected "n" times.
Accordingly, for a constant molten resin temperature value T, the followlng equation holds:
G SO + S:qO SO + SFO
A V(PSO.T) V(PSO.T) SO ~ SS1 SO + SF1 V(Ps1,T) V(P~1,T) =

~ . . . . . . . . . .

~0~ 73~
SO ~ SSrl SO + SF~
V(PSn~T) V(P~n~T) G SSr. ~ SF~I A Sr.
( 9 ) A V~P8~,T) V(P~,T) wherein A : proJected sectlonal area o~ the screw 19 SO : travel distance of the screw 19 converted from the remaining molten resin volume value The following equation is obtained by substituting the equation (4) in the equation (5):

V(Ps~.T) = exp{a~( ~s~/PsO - 1)}
V(Pso~T) A S~ SS~ ~ SF~
( = -- ) . . . ( 1 0 ) ~ SO SSO ~ SFO
By operating the above equation (10). the formula for such relation between the molten resin pressure (P) and the weight value G of the molten resin in~ected by one in~ecting operation that will not give an adverse affect on an actual molded product can is obtained.
By substituting the equation (10) in the equation (9), the following equation holds:
G 1 V(P~,T) = ' . . . ( 11 ) : A ~SO exp{a-(~Ps~/PsO - 1)}
The equation (11) is the PV property relation formula for a constant molten resin temperature value T. The PVT
arithmetic unit 29 operates this equation (11) to establish i .
_ ' ,` . ' "` ~ ~ ' ~ ` ' ' -2~S~739 the PV property relation formula for a constant molten resin temperature values T. The similar process is repea*ed for each of the molten resin temperature values T , T2, T~, ...
to establlsh the PVT property relation formula ~or each molten state value.
In the Example 1 and the Example 2, the following equation is used to establish the PVT property relation ~ormula:
V = VO exp{a(T) ~ - 1}
Alternatively, the Spencer & Gilmore's equation as shown below may be used:

R' T
V = + ~ ... (12) p + 7rl wherein T : molten resin temperature value.
, R' : constants determined by the type of plasticized synthetic resin The values for the constants ~ and R' may be ob-tained in the following procedure:
Flrstly, the molten resin specific volume value VO
under a constant molten resin pressure value PO and at a constant molten resin temperature value T~ is obtained in the same method as in the first phase of the Example 1.
Secondly, under the same molten resin pressure value PO, the value for the constant ~is obtained with the molten resin temperature value T varied. Then, at the constant molten ~0~

resin temperature value To, the molten resln volume is obtained with the molten resin pressur.e value P set at Pl.
in the same method as in the second phase of the Example 1, and the molten resin specific volume value Vl under the molten resin pressure value Pl is calculated ~rom the above-,' mentioned molten resin speci~ic volume value VO by the 3 proportional calculation. On the basis of the molten resln pressure values PO and P1. the molten resin speci~lc volume value VO and Vl and the constant ~, the value for the constant ~1 can be calculated by the following equation:
R' ~To Vo ~
Vl - ~1) R ~ To P
Pl + 7 Po + Tr 1 Po + 7rl + ~ p = ( ~ P = Pl - PO) po + Irl ~P
= 1 +
PO + Tr I
When the values for the constans~and ~1 have been obtained, it is possible to calculate the value ~or the constant R' by the equation (12). For other types of plastici~ed synthetic resin, the values for the constants . ~1 and R' may be obtained from the above procedures, if necessary.

i. , '73~

In the above, the method of establlshin~ the PVT
property relation formula by using the Spellcer & Gilmore's equation has been described. Alternatively, the PVT
property relation formula may be established by using the experimental analysis method according to the design of experiment (multivariable se~uential approximation).
The embodiments of an inJection control method accord-ing to the present invention are based on the PVT proper~y relation formula thus established in the above procedure.
Prior to explaining each embodiment of the inJection control method, the calculation formula used to obtain khe travel distance of the screw 19 for inJecting a cons-tant weight value of molten resin is explained with reference to Fig. 5.
First, for plasticized synthetic resin of a constant molten resin temperature value T1, the molten resin pressure value P, the positional value S of the screw 19 and the molten resin specific volume value V immediately before inJection and those during the dwelling after the inJection are set as follows:
The values immediately before in~ection:
Molten resin pressure value : PI1 Positional value of the screw 19 : SI
Molten resin specific volume value : V (PI1. T1) The values during the dwelllng after the inJection:
Molten resin pressure value : P~
Positional value of the screw 19 : S~

... . . . . . ... . . . . . . .......... .

' , ;~05~i~3~
Molten resin speclfic volume value : V (P~.1. T1) The positional values SI1 and S~1 of the screw 19 are based on the distance from the position of the screw 19 lndicated by the positional value "O". These positlonal Ya1UeS SI1 and Ss~1 are corrected values based on the remainlng moltern resin volume.
The weight value G o~ the molten resln inJected by one in~ecting operation into the cavity 18 of the mold 19 can be expressed as follows:

SI1 S~S1 G = A { - - ~ ... (13) V(PI1, T1) V(P~1,T1) J
in which A : proJected sectional area of the screw 19 This equation (13) can be rewritten as follows:

G = A~SI ~ A- -- (SI1 ~ S~S1) V(PI1 ~T1) V(P~1 ~T1) V(P~1 ~T1) ... (14) The travel distance SD of the scre~ 19 to the position : for in~ection is expressed as follows:
SD = SI1 S~1 ' ( 15 ) When the equation (15) is substituted in the equation (14) and rearranged, the following equation is obtained:
SD = SI1 -- S}l1 = V(P~S1 ~T~ SI1- ( 1 ~) A V(PI1~T1) V(P~I1.T1) ... (16) .. . . . . . . .... .. . .. . .

' : ~ , In the eq~ation (16), the proJected sectlonal area A o~
the screw 19 is known. The positional value SI of the screw 19 immediately before inJection is detected by the screw position detector 28. The molten resin specific volume values V(PI1 ~T1) and V(PH1 ~T1) are obt~ined from the PVT property relation formula that has been establlshed in the aforementioned procedure on the basis of the molten resin temperature value T1 and mo:Lten resin pressure values PI1 and P~1 detected by the resin temperature detector 30 and by the oil pressure detector 31, respectively, or on the basis of the molten resin temperature value Tl and molten resin pressure values PI1 and P~1 to be set.
Therefore, by using the equation ~16), it is possible to obtain the travel distance SD of the screw 19 which keeps the in~ected resin weight value G constant.
lFirst Embodiment) An embodiment of the inJection control method according to the present invention is described on the ~ssumption that the screw position detector 28 detects the positional value S~l of the screw 19 immediately be~ore in~ection, the resin temperature detector 30 detects the molten resin temperaturs value T1, and the oil pressure detector 31 detects the molten resin pressures values PI1 and P~l immediately before in~ection and during the dwelling after the in~ection, and that each of these detectors outputs the detected value to the PVT arithmetic unit 29, as shown in Fig. 6.

~S~3~

First, the in~ection welght value G, as the target weight value of a product, is input through the external Input unit 32 to the PVT arithmetic unit 29. The screw 19 i9 rotated and retreated while the amount of molten resin to be in~ected is measured. After the rotation of the screw 19 is stopped, a pushing force is applied to the screw 19.
Then, the screw position detector 28 detects the positional value S~1 o~ the screw 19 immedlately before inJection, wlth the block valve 33 closed. At the same time, the oil pressure detector 31 detects the molten resln pressure values PI1 (or pushing force value pIl)~ and the res~n temperature detector 30 detects the molten resin temperature value Tl. These values are input to the PVT arithmetic unit 29.
The block valve 33 is then opened so that in~ection is started. As the screw 19 is moved forward, the csvity 18 of the mold 10 is filled with the in~ected molten resin. When the cavity 18 has been almost completely filled up, the dwelling process starts. The molten resln pressure value P~1 ~pushing force value P~1) during the dwelling process following the in~ection is also detected by the oil pressure detector 31 and input to the PVT arithmetic unit 29. The PVT arithmetic unit 29 then calculates the travel distance SD of the screw 19 by the equation (16~, from the input positional value SI1, molten resin pressure values PI1 and P~1 and molten resin temperature value Tl, on $he basis of ... . . . . .

2~ 3~

the PVT property relation formula. The calculated travel distance SD is sent to the controller 24 where it ls com-pared with the positional value provided by the screw posl-tion detector 28. When the travel distance SD is equal to the positional value, the controller 24 closes the block valve 33, thus terminating the inJection o~ the molten resln into the cavity 1~ of the mold 10.
Thus, according to this embodiment, the travel distance SD for in~ection of the resin of a constant wei~ht value G
can be obtained even if the molten resin pressure values PI1 and PH1 and the molten resin temperature value T1 vary.
(Second Embodiment) Another embodiment of the in~ection control method is described on the assumption that the positional value SI1 of the screw 19 immediately before inJection is detected and transmitted to the PVT arithmetic unit ?9, and that the molten resin pressure values PI1 and PH1 and molten resin temperature value T1 preliminarily set in the controller 24 are also transmitted to the PVT ar~thmetlc unit 29, as shown in Fig. 7. For this embodiment, only the operatlons differ-ent from those in the first embodiment ls described, with the description of same operations omitted.
The controller 24 controls the electromagnetic ~low valve 22 and electromagnetic pressure valve 23 so that set molten resin pressure values PI1 and Plll are obtained. The controller 24 also controls the heater 14 so that set molten ... . ...... , . .. ,..... .. ,, ...... ~ ., ,.. , ....... , . ,.. ,. , .. I

~~ .
` ~, ' .

3~

resin temperature value Tl is obtai~ed. The PVT arlthmetic unlt 29 calculates the travel distance SD ~rom the posi-tional value SI1 of the screw 19 immedlately beYore in~ec-tion input from the screw position detector ~ and the molten resin pressure values PI1 and P~l and molten resin temperature value T1 set in the controller 24, on the basis of the PVT property relation formula. The calculated travel distance SD is sent to the controller 24. Other operations are the same as those in the first embodiment.
In the first embodiment, the travel distance SD Of the screw 19 is calculated based on the m~lten resin pressure value PI1, Pnl and the molten resin temperature value T1 to be detected this time, the fluctuation range of each value PI1, P81. T1 at every in~ection filling during the continual formation process in a short period is extremely small. In other wordsr even if each value PI1~ PK1~ T1 are detected at every in~ection filling, it is often the case that these value PI~ ~ P~1~ T1 are within the detection error and even the calculation is done based on the each value having the error, the actual formation of the molds varies.
Furthermore, the changes in the molten resin pressure and molten resin temperature occur gradually and caused by the change of the outside temperature and water temperature during the continual formation for a long period of time.
Thus, the changed amount is caused not by in~ection filling of five or ten times but by the in~ection filling of hundred ~.

....
: , :

. .

;~ 015i~7~

times or thousand times. Accordingly, in order to lmprove the detecting accuracy on the assumptIon o-f the detecting error of the molten resin pressure and the molten resln temperature, the mean value of the detected vallle PI1~ P~1 Tl in a short period o~ two to ten times can be employed.
Also, instead o~ the PI1, P~ T1 to be detected this time, the detected value of the previou's time PI1~ P~1~ T1 can be employed or the mean value of the PI1~ P81~ T1 from two to ten times up to the previous times can be employed.
In the ~irst and second embodiments, PVT property relation formula which is obtained from the Example 1 and Example 2, in other words, as shown in Fig. 8, PVT property formula forming the PVT curved surface in the three dimen-sional coordinates of the molten resin pressure axls P, molten resin specific volume axis V and the molten resin temperature axis T is directly employed in order to calcu-late the travel distance SD of the screw 19. However, in the actual continual in~ectlon formation, the range of change of the molten resin pressure value P and molten resin temperature value T is quite little, so that the fluctuation range of the molten resin pressure value P and molten resin temperature value T can be dealt with a range of a value which is capable for plaln approximation. Accordingly, instead of directly using the PVT property relation formula obtained in the above-mentioned method, calculation can be done based on 1the formula of plain approximation by setting 2~ ;4~739 the molten resin speciflc volume value V (P,T) as molten resin specific volume value Y (P +QP, T+ ~T). QP and QT are the expected range of ~luctuation within the allowed range.
As to the method of obtaining the molten resin specific volume value V (P~, T) and molten resin ~pecific volume value V (P~, T), the method of substituting the value glven by changing the formula PI ~P~ +aPI~ P~ ) P~ +~P~ T-~T+~T.
forcedly, and the weight value of the formation obtained as a result of changing the ~ormula, directly into the plain approximation formula can be employed.
In the first and the second embodiment, though the travel distance SD Of the screw 19 is calculated using the PVT property relation formula, it can be calculated on the basis of the formula (5) and ~11), using the PVT property relation formula, under the assumption that the fluctuation range of the molten resin temperature value T is small and constant. In using the PV property relation formula, if the positional value S~O, Sno of the screw 19 imidiately before the inJection and during the dwelling process following the in~ection for keeping the inJection weight value G constant in a stable formation, respectively, is known at immediately before the in;ection for keeping the in~ection weight value G constant in a stable formation and at the dwelling process following the in~ection, respectively, of the molten resin pressure values PIO, P~O, as a reference, the travel distance of the screw 19 can be obtained by the follo~ing .. . . . , . ~ . . . . . , ; .. ~ .. . ... . .. . . .... . .. . . . .. .... . .. . .
. ~

~0~3~
formula:

S D ~ = V ( P H 1 ) ~ -- S I ~L . [ ,~ }
A V ( ]?I 1 ) V ( P~I L ) V(PI1 ) V(P~1 ) V(P~1 ) S:~O ~ _ -- ~ ( SIO ~ S~O ) V ( PT O ) Y ( P}~O ) V ( P~IO ) r V ( P~
-- SIO -- 1 ¦
Y(PIO) J
"`(14) formula ~

~ V ( P ~ 1 ) V ( P ~ ~ ) 1 S I O S M O
G = A-SIO- _ + A~
. V(PIO) V(P~O) V(P~O) : In other words, the values other than positional value SIO~ S~O~ SI1 the screw 19 are indicated as a ratio for the molten resin specific volume value V. The ratio of the molten resin specific volume value V is obtained as a ratio of the molten resin specific volume value in the constant molten resin temperature value T. Thus, when the fluctua-tion range of the molten resin temperature value T is small enough to be ignored, and only the molten resin - pressure value PI~ and P~ fluctuate, the weight value G of a product can be kept constant only by obtaining the compression property of the molten resin to be in~ected, which is measured by the screw 19 in a closed state of the blocked ~ valve 33.
; In another embodiment, in ease that the blocked valve 33 is not installed in the flow passage 16 of the nozzle 12, a shut-off valve installed in the gate 17 of the mold ` 34 .. . .. ..

:

21D5~39 10 can be used as a blocked valve 33.

POTENTIAL INDUSTRIAL APPLICATION
According to the present invention, appropriate travel distance of the screw can be calculated on the basis of the resin property and the formula. Therefore, the in~ection control method of an in~ection molder of the present invention is especially suitable when the mold is changed.

.: :
. . , - . :
; " ' ": :;. :
~, ~ i.: :. .

Claims (7)

WHAT IS CLAIMED IS:

1. An injection control method for an injection molder, for controlling the weight of the plasticized synthetic resin injected from the cylinder of the injection molder to fill the cavity of a mold, comprising the steps of:
calculating the travel distance SD of the screw to the position for injecting the plasticized synthetic resin by the amount corresponding to the weight value G of a product, by using a specified calculation formula;
presetting the thus calculated travel distance SD; and terminating the injection of the plasticized synthetic resin into the mold cavity when the screw has moved for the preset travel distance SD from the stop position immediately before injection.

2. An injection control method for an injection molder as described in Claim 1, wherein said calculation by using the specified formula for obtaining the travel distance SD
of the screw to the position for injecting the plasticized synthetic resin by the amount corresponding to said target weight value G of a product is carried out at a constant molten resin temperature value T, on the basis of the detected or set molten resin pressure value PI of plasticized synthetic resin immediately before injection, the detected or set molten resin pressure value PH of plasticized synthetic resin during the dwelling process following the the injection, the detected positional value SI of the screw immediately before injection, and the PV
property relation formula of plasticized synthetic resin, as follows:

wherein SH: the positional value of the screw during the dwell ing process following the injection, A : the projected sectional area of the screw, V(PH) : the molten resin specific volume value during the dwelling process following the injection, and V(PI): the molten resin specific volume value immediately before injection.

3. An injection control method for an injection molder as described in Claim 2, wherein said molten resin pressure values PI and PH of plasticized synthetic resin detected immediately before injection and during the dwelling process following the injection, respectively, are mean value of each molten resin pressure values PI and PH
detected in a plurality of the injection fillings during the continual formation in a short period can be employed.

4. An injection control method for an injection molder as described in either Claim 2 or 3, wherein if the molten resin pressure value PI of plasticized synthetic resin immediately before injection is equal to the molten resin pressure value PH of plasticized synthetic resin during the dwelling process following the injection, calculation of said weight value G of a product is based on the difference So as shown in the following equation:

wherein A : the projected sectional area of the screw, and .DELTA.So: the difference between the positional value of the screw immediately before injection with the molten resin pressure value PI and the positional value of the screw during the dwelling process following the the injection with the molten resin pressure value PH (= PI).

5. An injection control method for an injection molder as described in Claim 1, wherein said calculation by using the specified formula for obtaining the travel distance SD
of the screw to the position for injecting the plasticized synthetic resin by the amount corresponding to said target weight value G of a product is carried out on the basis of the detected or set molten resin temperature value T of injected plasticized synthetic resin, molten resin pres-sure value PI of plasticized synthetic resin immediately before injection, molten resin pressure value PH, of plasticized synthetic resin during the dwelling process following the the injection, the detected positional value SI of the screw immediately before injection, and the PVT
property relation formula of plasticized synthetic resin, as follows:

wherein SH : the positional value of the screw during the dwelling process following the injection, A : the projected sectional area of the screw, V(PH,T): the molten resin specific volume value for the molten resin temperature value T and the molten resin pressure value PH during the dwelling process following the injection at the molten resin temperature value T, and V(PI,T) : the molten resin specific volume value for the molten resin temperature value T and the molten resin pressure value PT immediately before the injection at the molten resin temperature value T.

6. An injection control method for an injection molder as described in Claim 5, wherein said detected molten resin temperature value T of the injected plasticized synthetic resin and said detected molten resin pressure values PI

and PH of plasticized synthetic resin immediately before injection and during the dwelling process following the injection, respectively, are mean values of each molten resin temperature value T and molten resin pressures value PI and PH detected in a plurality of continuous injection operations for a specified short period of time.

7. An injection control method for an injection molder as described in Claim 5 or 6, wherein said calculation of the molten resin specific volume V on the basis of the PVT
property relation formula from she molten resin pressure value P and molten resin temperature value T uses the plane approximation, on the assumption that the fluctuation of the molten resin pressure value P and of the molten resin temperature value T is withln a specified range.