JPH0796247B2 - Injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention has injection drive means and control means whose transfer function is represented by G _(s), and position control is performed by the injection drive means. The present invention relates to an injection molding machine formed to inject a resin filled in a cylinder into a mold by a piston, and in particular, to improve the quick response of injection control.

[Conventional technology]

As shown in FIG. 10, the conventional injection molding machine includes a mold 16 including a fixed mold 17 and a movable mold 18, a cylinder 11 having a nozzle 12 at the tip, a hopper 13 for supplying resin, and an outer peripheral surface. A metering injection means 10 formed of a piston 14 provided with a screw 15 for metering and feeding in a cylinder, and a piston in a cylinder 11.
Measuring means 20 for rotating 14 (motor 21, detector 2
2) and, for cylinder 11, injection drive means 30 for moving piston 14 together with metering drive means 20 in the left-right direction in the figure.
(The motor 31, the detector 32, the nut member 33, the support rod 34, the ball screw 35) and the cylinder moving drive means 40 (the motor 41, the motor 41,
Detector 42, nut member 43, continuous member 44, ball screw 45)
And a mold moving drive means 50 (a motor 51, a detector for moving the movable mold 18 in the left-right direction in the drawing with respect to the fixed mold 17 of the mold 16).
52, gear train 53, ball screw 55) and each drive means 2
The control means 2 and the position command value generating means are formed so that a predetermined control input can be given to 0, 30, 40 and 50. Further, the control system formed by the respective driving means 20, 30, 40, 50 and the corresponding portions of the control means 2 is shown in FIG. 7, FIG. 8 and FIG. 9 (each drawing is for injection for simplification of the drawing). It can be represented as a so-called soft servo system as shown in (in relation to the driving means 30). That is,
The control system has a position control loop with a relatively low gain (ω _o ) outside the command value and a speed control loop with a relatively high gain (ω _c ) inside. Therefore, since the speed control loop has a high gain (ω _c ), it has high rigidity against disturbances and parameter fluctuations, and the position control loop has a low gain (ω _o ), which causes excessive impact (acceleration) on the mechanical system. It has the advantages that it does not need to be given, and that it does not require special attention when creating a machining program.

Therefore, if each position command value corresponding to each driving means 20, 30, 40, 50 is inputted to the control means 2 from the position command value generating means 1 based on a predetermined program, the mold moving drive means 50
Forms a cavity (not shown) having a predetermined shape so that the movable die 18 is brought into close contact with the fixed die 17 to fill the resin, and the cylinder moving drive means 40 moves the cylinder 11 so that the nozzle 12 of the movable die 18 is an injection port of the fixed die 17. (Not shown). Subsequently, the metering drive means 20 is driven and controlled in advance to rotate the piston 14 to measure the resin supplied from the hopper 13 and drive the injection drive means 30 for the resin filled in the tip side of the cylinder 11. By injecting into the cavity by controlling, i.e. pushing the piston 14 into the cylinder 11. Here, a product having a predetermined shape could be injection-molded in the mold 16.

[Problems to be solved by the invention]

However, the conventional injection molding machine has the following problems.

That is, since the control means 2 and the respective driving means 20, 30, 40, 50 form a soft servo, it is not possible to independently set the quick response and the stability of the system, so either one of them is insufficiently executed. However, there is a drawback in that even if a compromise is made in such a state, a lot of labor and time are spent on the comparative weighing work itself. Further, the maximum value of the gain (ω _o ) of the position control loop is restricted by the allowable large acceleration of the mechanical system and the maximum feed rate, so that there is a problem that the response time cannot be further improved.

In particular, the quality of the molded product depends on the injection state of the resin from the metering injection means 10 into the cavity of the mold 16, and the injection state of the cavity, the inner shape of the cavity, the type of resin, the temperature conditions, the measurement injection means 10 of. The desired product could not be obtained by the simple process of resin injection in a single step, which is restricted by many conditions such as form. For this reason, it was necessary to improve the position response of the injection drive means 30 in comparison with other drive means while establishing the stability of the system, but it was difficult to achieve it due to the above-mentioned soft servo principle. there were.

Hereinafter, the position control problem of the injection driving means 30, which has been emphasized more and more in the age of demanding high quality, will be described in detail. The characteristic (G _(s) ) of the position control loop in the conventional position control system shown in FIG. 7 is set so that the gain ω _c of the speed control loop is larger than the gain ω _o of the position control loop (usually 4 to 20 times). Because it is treated as a first-order soft servo, Can be approximated by

Here, the speed response characteristic V _(t) to the stepwise speed command value (V _o / S ₎ is V _(t) = V _o (1-е ^P ) ... (where P is -ω _o t The same applies to the following.) Therefore, the acceleration а _(t) required for this is given by
It was obtained as а _(t) = V _o · ω _o · е ^P.

Therefore, if the maximum feed rate of the mechanical system consisting of the motor 31, the nut member 33, the support frame 34, the ball screw 35, etc. is V _{o max} , the maximum acceleration a _max generated by the position control system is a _max = V _{o max} ω _o …….

On the other hand, from the viewpoint of the mechanical system, the patented maximum acceleration A _max is determined by its configuration, and therefore, in relation to the maximum acceleration а _max , а _max ≤ A _max must be satisfied. Therefore, the maximum value ω _{o max} of the gain of the position control loop is restricted as ω _{o max} = A _max / V _{o max} .

That is, the maximum value of the gain of the position control loop ω _{o max} was restricted by the relationship with the mechanical system as shown in the equation. In other words, in the position control system approximated by the formula, the upper limits of the maximum permissible acceleration A _max and the maximum feed rate V _{o max} determined by the mechanical system are determined, so if the mechanical system (A _max , V _{o max} ) is fixed, the gain Maximum value ω _o
There is a problem that the upper limit of _max is restricted and the gain cannot be further increased, so that further shortening of the response time cannot be achieved.

In this way, in the injection molding machine that adopts the conventional position control system,
Since the responsiveness is controlled by the mechanical system, the injection driving means 30 is drive-controlled to control the injection mode of the resin at a complicated position.
Since it could not be implemented as an ideal state based on the time diagram, it became difficult to achieve high quality.

Therefore, it is an object of the present invention to provide an injection molding machine capable of producing a high-quality injection-molded product by significantly improving the quick response while maintaining the stability of the system.

[Means for solving problems]

The present invention has been made in view of eliminating the above conventional problems, and modifies a mechanical system by introducing a compensation element related to the acceleration time τ to create a new transfer function of the entire system. This is a remarkable improvement in control characteristics.

That is, the transmission completion of the conventional position control system shown in FIG. 7 is G _(s) when the Laplace operator is S, as shown in FIG. Therefore, since the transfer function G _(s) is fixed due to the characteristics of the mechanical system and the like, the above-mentioned conventional problems are inherent. Here, the present invention minimizes the time gap between the ideal position command value R _(s) required from the operation of the injection molding machine and the control target position C _(s) in the conventional position control system. Is aimed at.

Therefore, the transfer function of the position control system is G _(s) and the position command value is
The piston position of the R _(s) and control object serving as injection drive means when a C _(s), position command value system of the entire transmission from R _(s) to a position C _(s) function C _(s) / R _(s) is The series compensating element G _{1 (s)} related to the acceleration time τ is inserted so as to obtain the characteristic represented by, and the quick response is improved.

Here, as a suitable series compensation element G _{1 (s)} , (However, Q is s.τ. The same applies below.) Therefore, the transfer function C _(s) / R _(s) of the entire system is (See FIG. 2).

In addition, the second compensation element G is used to achieve smooth control.
_{2 (s)} can be added.

In this case, the series compensation element G _{1 (s)} is As a result, the transfer function C _(s) / R _(s) of the entire system is (See FIG. 3).

Further, from the viewpoint of deepening the understanding of the present invention, a detailed description will be given from the standpoint of a discrete-time system that is easy to implement.

Now, as shown in FIG. 9, the conventional position control system shown in FIG. 7 and FIG. 8 has a position command value R _(k) generating means 1, a control means 2 and an injection drive which is a controlled object. When represented as output after passing through the zero-order holder, the present invention, as shown in FIGS. 4 and 5, positions command value generating means 1, control means 2, controlled object. The control means 2 is formed of the first calculating means 4 and the first calculating means 3 as the converting means without changing the basic structure of the barrel driving means 30. Note that reference numerals 5 and 6 are samplers placed in front of the zero-order holder.

That is, when Z (= e ^ST ) -transforms the above-mentioned formulas, which are suitable for the series compensation element G _{1 (s)} , and displays them in a discrete time system, the formulas are as follows. .

In the following formula, Ψ [] represents Z conversion.

Similarly, the expression, is converted into the expression, respectively.

However, in the formulas, T: sampling period _(sec) τ: acceleration time _(sec) M: τ / T M = 1,2,3, ... (natural number).

By the way, as shown in the above figures, the transfer function G _(s) of the position control system is Is expressed as, the pulse transfer function G _(Z) through the zero-order holder is Becomes

Therefore, the pulse transfer function G _{1 (Z) of} the compensation element shown in the equation
By substituting the expression If you arrange this by algebraic calculation, Becomes

Therefore, if the intermediate position command value is P _(Z) , Then, when substituting the equation into the equation and expressing P by the difference equation of R, Becomes

Therefore, the conventional method has a transfer function G as shown in FIG.
_{While the} position command value R _(k) was directly input to the control means 2 (first calculation means 4) in the position control system _(s) , the present invention shows the same as shown in FIG. As described above, the second computing means 3 as the converting means is provided, and the intermediate position command value P _(k) newly created from the position command value R _(k) and the value M times before it is input and controlled. Is understood.

Therefore, the transfer function of the system has an injection drive unit and a control unit represented by G _(s), and the resin filled in the cylinder by the piston whose position is controlled by the injection drive unit is injected into the mold. In the injection molding machine formed to inject into the control means, the control means is provided with a series compensation element G relating to acceleration time.
_{It is} intended to achieve the above object by inserting _{1 (s)} and changing the entire transfer function to G _{1 (s)} · G _(s) so as to improve the control characteristics of the piston.

In addition, the present invention, the series compensation element G _{1 (s),} when the acceleration time is τ, Is represented by.

Further, the present invention is characterized in that the series compensation element G _{1 (s)} is The second compensation element represented by is added to enable smoother control.

[Action]

Therefore, the present invention can improve the control characteristics without introducing a modification to the mechanical system by introducing the series compensation element G _{1 (s)} into the system, so that the control with improved responsiveness while ensuring stability can be achieved. Since this can be ensured, the injection drive means can be drive-controlled in accordance with a desired position-time diagram to injection-mold a high-quality product.

〔Example〕

An embodiment of an injection molding machine according to the present invention will be described with reference to the drawings.

In this embodiment, the mechanical system has a structure similar to that of the conventional injection molding machine shown in FIG. 10, and the control means 2 and the like have the structure shown in FIG. 5 and the series compensation element G _{1 (s)} As shown in FIG. And set up and configured by computer. Then, the response of the injection drive means 30 when the stepwise position command value (R) is input from the position command value generating means 1 is confirmed.

The result of this embodiment is that even if the stepwise position command signal R is added as shown in FIG. 6, the acceleration of the conventional system (X ₂ ) and the acceleration of the system of the present invention shown in FIGS. Although the maximum value of (Y ₂ ) is almost the same, the response of the control system is significantly different. That is, in the case of the system of the present invention, the response is made at 50 msec with almost the maximum speed (Y ₁ ), whereas the speed of the conventional system (X ₁ ) is decelerated as the command value is approached, and the speed of about 150 msec There is a time delay. Here, it was confirmed that the present invention exerts an excellent effect that the responsiveness can be greatly improved while ensuring the stability without rapidly increasing the maximum acceleration.

The implementation conditions are as follows.

Sampling cycle T = 0.001 sec M = τ / T = 50 times Gain of position control loop ω ₀ = 20 rad / sec Further, gain of conventional system ω ₁ = 20 rad / sec.

As described above, in the present invention, the maximum acceleration is the same as in the conventional system, but the convergence time for the command signal R in the system of the present invention can be shortened to about 1/3 of that in the conventional system. Cylinder 11 of piston 14 by drive means 30
Since the position control can be performed based on a desired position-time diagram, it is possible to establish an injection molding machine having excellent adaptability and handleability as well as product quality improvement.

Therefore, according to each of the above embodiments, the series compensation element G is added to the control system corresponding to the injection driving means 30 having the transfer function G _(s).
Insert _{1 (s)} and set the transfer function of the entire position control system to G _{1 (s)}・ G
_Since it is set to _(s) , the quick response can be dramatically improved compared to the conventional system.

This means that even if the allowable maximum acceleration and maximum feed rate that determine the maximum value of the position control loop gain are restricted in the same mechanical system as the conventional mechanical system, the maximum value of the position control loop gain is not limited. It is possible to remarkably improve the followability of the moving speed and the position of the piston 14 with respect to the position command signal.

Further, since the series compensation element G _{1 (s)} is said to have introduced the acceleration time τ, it is possible to improve stability and improve quick response.

Furthermore, since the series compensation element G _{1 (s)} can be Z-transformed into a discrete time system, the present invention can be implemented easily and appropriately using a computer. Further, since it can be executed by a computer, it is possible to select a sampling period at an arbitrary time and an extremely short time, so that it is possible to form a control system according to the characteristics of the injection molding machine used.

Furthermore, since the responsiveness can be improved without increasing the capacity of the motor 31 of the injection driving means 30 and without causing excessive collision with the mechanical system, the facility structure and the economic advantage are large.

Furthermore, since the position control characteristics can be improved without modifying the mechanical system, there is an effect that the present invention can be applied to an existing injection molding machine as it is.

In the above embodiment, the series compensation element G _{1 (s)} is However, the series compensating element G _{1 (s)} is provided with an additional second series compensating element G _{2 (s)} for further improving and smoothing a part of the control characteristic so that it can be finely adjusted. Therefore, for example, by adding a first-order lag element, it is possible to provide a control system that does not cause vibration or the like in the mechanical system while significantly improving the quick response to the conventional system.

For example, Is like.

Further, in the above embodiments, the injection driving means 30 of the control means 2 is used.
Although the series compensating element is provided only for the portion corresponding to, the series compensating element is introduced also for the portion corresponding to the measuring driving means 20, the cylinder moving driving means 40, and the mold moving driving means 50. It may be configured to improve similarly to the control characteristics for the driving means 30.

Further, the position command value generating means 1 and the control means 2 are separated from each other, but the point is that the series compensating element G _{1 (s)} is inserted to improve the control characteristics. Not done. Of course, it can be implemented not only in the discrete time system but also in the continuous time system. However, if it is a discrete time system, its implementation is easy and its industrial utility is improved.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The present invention can provide an injection molding machine capable of efficiently producing a high-quality product by improving stability and remarkably improving quick response.

[Brief description of drawings]

FIG. 1 is a block diagram showing a transfer function of injection driving means for carrying out an injection molding machine according to the present invention, FIG. 2, FIG.
The figure is a block diagram showing a transfer function which also clarifies an example of a series compensation element, and particularly FIG. 3 shows a case where a second compensation element is also added. FIGS. 4 and 5 are block diagrams of the position control system when the same is implemented as a discrete time system. FIG. 4 is a block diagram and FIG. 5 is a detailed block diagram.
FIG. 6 is the fifth example of the series compensation element shown in FIG.
The time chart showing the control characteristics by the configuration of the position control system shown in the figure, and FIGS. 7, 8, 9, and 10 relate to a conventional injection molding machine, and FIG. 7 is a block diagram showing the control system. , FIG. 8 is a block diagram showing a transfer function, FIG. 9 is a block diagram of a control system when implemented as a discrete time system, and FIG.
The figure is an overall configuration diagram of an injection molding machine. 1 ... Position command value generating means, 2 ... Control means, 3 ... Second computing means, 4 ... First computing means, 5,6 ... Sampler, 10 ... Metering injection means, 11 ... Cylinder, 14 ... Piston, 16 ... Mold, 30 ... Injection drive means, 31 ... Motor, 32 ... Detector.

Claims (3)

[Claims] Claim: What is claimed is: 1. A resin having a transfer function represented by G _(s) and a control means for injection, wherein the piston is position-controlled by the injection drive means to charge the resin filled in the cylinder with gold. In an injection molding machine configured to inject into a mold, the control means is provided with a series compensating element G relating to acceleration time.
An injection molding machine characterized in that _{1 (s)} is inserted and the entire transfer function is changed to G _{1 (s)} · G _(s) so that the control characteristics of the piston can be improved. 2. In the claim 1, when the series compensation element G _{1 (s)} has an acceleration time of τ, An injection molding machine which is said to be represented as. 3. The claim 1 according to claim 1, wherein the series compensating element G _{1 (s)} has an acceleration time of τ and a second compensating element of G _{2 (s)} , An injection molding machine which is said to be represented as.