JP3168289B2 - Pressure control method and pressure control device for injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a resin pressure of an injection molding machine having at least a screw and an injection motor for driving the screw in an injection direction. The invention relates to a pressure control device used for implementing the method.

[0002]

2. Description of the Related Art An injection molding machine is well known in the art without mentioning a document name, and is composed of an injection cylinder, a screw provided in the injection cylinder so as to be freely driven in a rotational direction and an axial direction, and the like. . When the injection molding machine is an electric type, both the plasticizing electric motor for driving the screw to rotate and the injection electric motor for driving in the axial direction are composed of servo motors.

A specific example of such an electric injection molding machine will be described in more detail with reference to FIG. The electric injection molding machine includes an electric motor 1 for plasticizing and an electric motor 2 for injection. The drive shaft 6 is joined to the output shaft of the plasticizing electric motor 1. The drive shaft 6 is supported by a thrust and radial bearing of the intermediate plate 7 and is connected to a screw 8 driven in the rotation direction and the axial direction in the injection cylinder 3. A ball screw 9 is joined to an output shaft of the electric motor 2 for injection via a coupling, and a ball nut provided on an intermediate plate is screwed to the ball screw 9. Ball screw 9
The bearing is supported by a thrust bearing together with the radial bearing, and the movement in the axial direction is restricted. Therefore, when the ball screw 9 is driven to rotate, the intermediate plate 7 moves in the axial direction, and the screw 8 is driven in the injection cylinder 3 in the injection direction.

[0004] Since the electric injection molding machine is constructed as described above, the screw 8 can be rotated in the injection cylinder 3 by the electric motor 1 for plasticizing and metered as conventionally known. Alternatively, the screw 8 can be driven in the axial direction by the electric motor 2 for injection to inject and hold the pressure. By the way, back pressure, injection pressure, holding pressure, etc. when molding while repeating weighing, injection, holding pressure, and weighing as described above affect the quality of a molded product. Detected and controlled. For example, the injection resin pressure is measured by directly measuring the resin pressure by attaching a resin pressure sensor to the tip end of the injection cylinder 3 or a mold, as shown in FIG. Load cell 5
In the electric injection molding machine, since the source of the resin pressure is the torque of the electric motor 2 for injection, the current value of the electric motor 2 is measured, and a constant set in advance to the measured current value is used. Is used.

[0005] The method of detecting the injection resin pressure by attaching a resin pressure sensor to the mold or the injection cylinder 3 has the advantage that it can be applied irrespective of the type of driving device for driving the screw 8 in the injection direction. Is directly measured, so that the accuracy is high, but the resin pressure sensor is relatively expensive. Further, since the resin pressure sensor must be attached to a mold or the like, there is a disadvantage that the structure of the mold is complicated. Since the resin pressure sensor is expensive and the structure of the mold becomes complicated, the cost of the injection molding machine as a whole increases.

Therefore, a method of controlling the torque of the electric motor 2 for injection is adopted in the electric injection molding machine. In this control method, open-loop control is also performed, but generally, feedback control is performed as shown in FIG. This control device 50
First summing point 51, first adjustment portion 52 of the force control gain K _1, a second summing point 53, second adjustment portion 54 of the speed limiter gain K _2, third summing point 55, It comprises a third adjustment / operation unit 56 for the torque constant Kτ, a current control type power converter 57 and the like.

[0007] Then, to the pressure set value P _S in the first summing point 51, and the pressure detection value P _FB detected by the load cell 5 which is provided in connection with the injection shaft 9 'is input It has become. The operation signal obtained by the first summing point 51 is adjusted by the pressure control gain K _1, third
Is added to the addition point 55. This is the third summing point 55, a second addition registration to obtain the operating signal of the speed detection value V ₁ and the speed limit value V ₂ detected by the encoder 4 is attached to the electric motor 2 for injection speed limiter gain K ₂ is multiplied signal to the signal output from the point 53 is also input. The operation signal output from the third addition point 55 is input as a torque command signal from the third adjustment / operation unit 56 to the current control type power converter 57. Then, a predetermined current is supplied from the current control type power converter 57 to the injection electric motor 2. As described above, conventionally, the control of the tree finger pressure is performed by directly controlling the driving force, that is, the torque of the injection electric motor 2.

[0008]

As described above, the tree finger pressure can be controlled by controlling the torque of the electric motor 2, but according to the torque control, the reproducibility and response of the pressure are low. There are drawbacks. More specifically, when torque control is performed as shown in FIG.
The pressure transfer equation is as follows. T _P = T _M −J (dω / dt) −Kω−T _R where T _P : pressure transmission torque J: moment of inertia T _M : electric motor generated torque K: running friction coefficient T _R : nonlinear such as static friction torque Loss ω: Injection speed From the above equation, it can be seen that there are various losses before the motor torque is transmitted as the actual finger pressure. Above all, non-linear loss such as static friction becomes a very troublesome disturbance component in feedback control, generates a large phase lag, and makes the system unstable. The instability of the system can be stabilized by reducing the feedback control gain. However, the response speed becomes slow and the system becomes very weak against disturbance. Conversely, if the gain is increased, the system becomes unstable and oscillates easily.
As described above, in the conventional method of directly controlling the driving force, that is, the torque of the electric motor, many disturbance elements and non-linear elements must be considered in order to improve the performance of the pressure control. Is practically almost impossible, and there is no other way but to set an appropriate gain empirically with normal PI control, and there is a drawback that pressure reproducibility and response are low. As described above, if the resin pressure is not controlled according to the set value, the composition of the injected resin is adversely affected, and the quality of the molded product is deteriorated. Therefore, the present invention provides a pressure control method for an injection molding machine and a pressure control device used for implementing the method, which can obtain a high quality molded product with high reproducibility and responsiveness of resin pressure. It is an object.

[0009]

According to the present invention, in order to achieve the above object, pressure is controlled by controlling displacement of a screw. That is, the above object of the present invention is achieved by controlling the pressure generation system as a spring system. The pressure transfer equation in this case is as follows. _{Q 1 = K S ∫ (ω} -ω 1) dt (1) provided that, _{Q 1:} generated pressure omega: screw speed K _S: spring constant omega _1: from Invalid rate above (1), present in the conventional manner It can be seen that the nonlinear element and the pressure loss that have been performed have completely disappeared. Further, it can be seen that if (ω-ω ₁ ) is controlled, the control can always be performed as a spring system. In other words invalid speed omega ₁ if is because a variable that occurs corresponding to the filling state of the resin, indicating that can control the pressure independently of the filling state of the resin. However, disabling speed omega ₁ is because it is the internal state variables that can not be detected directly, by utilizing the actual detection rate and the detection pressure value, the observer (state observer), was estimated by the Kalman filter or the like, (omega-omega ₁₎ Is achieved by controlling Thus, in order to achieve the above object, the present invention provides a method for controlling a resin pressure of an injection molding machine having at least a screw and an injection motor for driving the screw in an injection direction. The injection speed command signal is calculated based on the operation signal with the resin pressure value, and the operation signal as the injection speed command value obtained from the calculated injection speed command signal and the estimated invalid speed estimated value is supplied to the injection motor. It is configured to calculate the input torque. A second aspect of the present invention provides a closed loop control section for resin pressure, a closed loop control section for resin injection speed, a disturbance observer operation section, and a pressure detection for detecting pressure of resin to be injected or pressure corresponding to pressure of resin. Means, and a speed detecting means for detecting an injection speed or a speed corresponding to an injection speed, wherein the closed-loop control section of the resin pressure detects a set resin pressure value and a detected resin pressure value detected by the pressure detecting means. A controller that adjusts the obtained operation signal and outputs an injection speed command signal , wherein the resin injection speed closed loop control unit adjusts the injection pressure command signal adjusted by the resin pressure closed loop control unit. motor for injection from the the injection speed command value is an operation signal obtained from the computed disabled velocity estimates by the disturbance observer calculating unit, the speed detection value detected by said speed detecting means and Comprising a speed controller for calculating a torque,
The injection motor is configured to be controlled by an output signal of a speed controller of the closed loop control unit for the resin injection speed. According to a third aspect of the present invention, the disturbance observer operation unit according to the second aspect adjusts an operation signal obtained from the detected resin pressure value detected by the pressure detecting means and the pressure estimated value to estimate the invalid speed. It is composed of an adjusting unit for obtaining a value, and a pressure / speed transfer function model for obtaining a pressure estimated value from an invalid speed estimated value and a speed detected value detected by speed detecting means.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the right side of a vertical line A indicates a control target, and the left side indicates a control device. The control target is configured as described with reference to FIG. 6, but FIG. 1 schematically shows only the electric motor 2 for injection and the injection cylinder / screw system 3. The electric motor 2 for injection has a speed / torque transfer function of K _m / (1+
As a primary system lag of T _m s), also the injection cylinder screw system 3, the transfer function of the pressure / velocity regarded as spring system are expressed as 1 / T _c s of the integral system. According to the embodiment shown in FIG. 1, the screw speed or the injection speed is detected by the encoder 4 attached to the injection electric motor 2, and the finger pressure value is applied to the screw shaft. It is to be detected by a load cell 5 attached in association.

The control device includes a first closed loop control unit 10 for performing closed loop control of resin pressure, a minor loop control unit 30 for performing closed loop control of injection speed, and a disturbance observer calculation unit 40 for estimating an invalid speed. I have. First
The closed loop control unit 10 includes a first addition point 11, a PI controller 13 that performs a proportional-integral operation, and a second addition point 1.
2, a speed limiter 14, a setting unit 15, and the like. The pressure command value Q set by the setting unit 15 and the pressure detection value Q _FB in which the pressure detected by the load cell 5 is fed back through the pressure detection filter 16 are input to the first addition point 11. Addition point 12 of 2
Is input with the output value of the PI controller 13 and the estimated invalid speed ω ₁ ″ estimated by the disturbance observer operation unit 40.
The speed limiter 14 receives the speed limit values S ₁ and S ₂ in the positive and negative directions set by the setting unit 15, respectively.

The minor loop control unit 30 includes a speed controller 3
1 and a torque limiter 32, and the speed controller 31 has a speed command value ω _m output from the speed limiter 14,
The speed detection value ω _FB detected by the encoder 4 is fed back. Then, the motor torque limit value T ₁ set by the setting unit 15 is input to the torque limiter 32 and is output to the electric motor 2 for injection as the limited torque τ.

[0013] disturbance observer calculating section 40 includes a first and second summing point 41, the adjustment unit 43 of the observer gain _{K g,} the transfer function is represented as the integral system pressure /
And a speed transfer function model 44. At the first and second addition points 41, the pressure detection value _QFB and the pressure
And a pressure estimated value Q "which is estimated by the transfer function model 44 of the force / velocity is input. The signal output from the first summing point 41 is adjusted by the observer gain K _g, and its output signal is disabled The speed estimation value ω ₁ ″ is input to the second addition point 12 of the first closed-loop control unit 10 described above. Note that T ′ _{c of} the pressure / velocity transfer function model 44
Is the transfer function 1 / T _c of the injection cylinder / screw system 3.
The theoretical value of the time constant _Tc of _s, and the spring constant Ks is _Tc = 1
/ Are in a relationship of _{K s.}

Next, the operation will be described. A pressure command value Q, positive and negative speed limit values S ₁ and S ₂ and a motor torque limit value Tτ are set in the setting unit 15. Then, it is measured by an electric motor for plasticization and an electric motor 2 for injection in a well-known manner, and injection and pressure are maintained to obtain a molded product. At this time, the set pressure value or the pressure command value Q and the detected pressure value _QFB detected by the load cell 5 are input to the first addition point 11 of the first closed loop control unit 10, and the operation signal is PI Adjusted by the controller 13, the injection power
The first addition point 1 as the speed command signal of the dynamic motor 2
2 is input. In the disturbance observer operation unit 40,
The detected pressure value Q _FB detected by the load cell 5 and the estimated pressure value Q ″ are input to the first addition point 41, and are adjusted by the observer gain K _g to estimate the invalid speed ω.
₁ ”is obtained and input to the second addition point 12 of the first closed-loop control unit 10. In the disturbance observer calculation unit 40, the estimated invalid speed ω is added to the second addition point 42.
₁ ”and a speed detection value ω _FB detected by the encoder 4, which is used as an effective speed as a pressure / speed transfer function.
The pressure estimation value Q ″ calculated by the model 44 is output to the first addition point 41.

A motor speed command value is output from the second addition point 12 of the first closed loop control unit 10. Then, the motor speed command value ω limited by the speed limiter 14
_m is input to the speed controller 31. The speed detection value ω _FB detected by the encoder 4 is input to the speed controller 31.
Output as motor torque. Then, the torque value τ limited to within the limit value by the torque limiter 32 is applied to the electric motor 2 for injection. Thus, the tree finger pressure is controlled so as to match the set pressure value.

[0016]

【Example】

Example 1: The control method according to the present embodiment was applied to an electric injection molding machine, and a pressure waveform at the time of switching between injection and holding pressure was measured. In FIG. 2, the waveform is shown with the pressure on the vertical axis and the time on the horizontal axis in FIG. From this waveform, hold pressure 1
It can be seen that the pressure set value is quickly settled from the stage, and the control is almost the same as when the pressure is completely filled, that is, the pressure response waveform after the second stage of the holding pressure. For comparison, a pressure waveform at the time of switching between the injection and the holding pressure was similarly measured by the conventional control method shown in FIG. 7, that is, a control method not considering the filling state. FIG. 4 shows the results. According to the conventional method, it can be seen that the pressure waveform at one stage of the holding pressure is greatly disturbed. The reason for this is that near the injection / hold pressure switching point, the change in the filling state is covered by the integral operation of PI control, despite the fact that there is a large change from the incomplete filling state of the resin to the complete filling state. It is because. That is, since there is no correlation between the integration time constant and the change time of the filling state, the response is disturbed according to the degree of change of the system.

Example 2 Similarly, the control method according to the present embodiment was applied to an electric injection molding machine, and a pressure waveform during back pressure control was measured. In FIG. 3, the waveform is shown with the pressure on the vertical axis and the time on the horizontal axis in FIG. At the time of back pressure control, the filling direction is opposite to that at the time of injection. At the start of back pressure control, a change in the filling state, that is, the weighing speed is input to the pressure control system as a step disturbance, so that overshoot occurs. As shown in FIG. 3, according to the present embodiment, no overshoot is observed. This is because, as is evident from the transfer function obtained from the above-mentioned equation (1), the step disturbance is not affected in principle. On the other hand, the conventional control method shown in FIG.

[0018]

As is evident from the foregoing description, according to the present invention, setting the resin pressure value and on the basis of the operation signal and the detected resin pressure value to calculate the injection speed command signal, the injection speed command signal <br/> that this operation Injection speed command obtained from the estimated invalid speed value
Since the torque input to the injection motor is calculated based on the operation signal as the value , that is, the difference between the screw speed and the invalid speed is controlled so that the pressure value of the injection shaft matches the set pressure value. Pressure control with high reproducibility and responsiveness of resin pressure can be performed without being affected by factors and pressure loss. In particular, the back pressure control and the pressure response at the time of switching between injection and holding pressure, which have been conventionally difficult, are improved, and the effect of obtaining a high-quality molded product is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a pressure waveform at the time of switching between injection and holding pressure according to the embodiment of the present invention.

FIG. 3 is a diagram showing a pressure waveform during back pressure control according to the embodiment of the present invention.

FIG. 4 is a diagram showing a pressure waveform at the time of switching between injection and holding pressure according to a conventional control method.

FIG. 5 is a diagram showing a pressure waveform at the time of switching between injection and holding pressure according to a conventional control method.

FIG. 6 is a front view schematically showing the electric injection machine in a partial cross section.

FIG. 7 is a block diagram showing a conventional control method.

[Explanation of symbols]

Reference Signs List 2 Electric motor for injection 3 Cylinder / screw system 4 Encoder 5 Load cell 10 First closed loop control unit 11, 12 First and second addition point 13 PI controller 30 Minor loop control unit 31 Speed controller 40 Disturbance observer operation unit 43 Regulator 44 pressure / speed transfer function model

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 45/46-45/54 B29C 45/76-45/77

Claims (3)

(57) [Claims] When controlling a resin pressure of an injection molding machine having at least a screw (3) and an injection motor (2) for driving the screw (3) in an injection direction, a set resin pressure value ( Q) and the detected resin pressure value (Q _FB ), the injection speed command signal is calculated based on the operation signal, and the calculated injection speed command signal and the estimated invalid speed estimated value (ω
₁ )), wherein a torque (τ) to be input to the injection motor (2) is calculated based on an operation signal as an injection speed command value obtained from (1)). 2. A closed loop control unit for resin pressure (10),
A closed loop control unit for resin injection speed (30), a disturbance observer calculation unit (40), and a pressure detecting means (5) for detecting a pressure of the injected resin or a pressure corresponding to the pressure of the resin;
And a speed detecting means (4) for detecting an injection speed or a speed corresponding to an injection speed. The closed loop control section (10) for the resin pressure comprises a set resin pressure value (Q) and the pressure detecting means (5). ), A controller (13) for adjusting an operation signal obtained from the detected resin pressure value (Q _FB ) and outputting an injection speed command signal , wherein the closed loop control unit (30) for the resin injection speed comprises: Injection, which is an operation signal obtained from the injection speed command signal adjusted by the resin pressure closed loop control unit (10) and the invalid speed estimated value (ω ₁ ″) calculated by the disturbance observer calculation unit (40). A speed controller (31) for calculating a motor torque (τ) for injection from a speed command value (ω _m ) and a speed detection value (ω _FB ) detected by the speed detection means (4); Motor (2) A pressure control device for an injection molding machine, wherein the pressure control device is controlled by an output signal of a speed controller (31) of a closed loop control section (30) of a resin injection speed. 3. The disturbance observer operation unit according to claim 2,
(40) a detecting resin detected by the pressure detecting means (5);
Pressure value (Q_FB) And the pressure estimate (Q ")
The motion signal is adjusted to estimate the invalid speed (ω₁”)
The node (43) and the invalid speed estimated value (ω₁”) And speed detection
The speed detection value (ω) detected by the means (4)_FB) And pressure
Get force estimate (Q ")Pressure / velocity transfer function model
(44) A pressure control device for an injection molding machine, comprising: