AT516879B1 - Method for operating an injection unit and injection unit - Google Patents

Abstract

A method for operating an injection unit for a casting process, wherein - for filling a mold cavity, a melt is displaced by means of an actuator from a melt vessel, - a control and / or control of a movement of the actuator is carried out according to a kinematic parameter, - a measure, which for a pressure of the melt is characteristic, is measured and - is calculated from the measured variable prevailing at a respective future time in the melt pressure with a manipulated variable for the control and / or control of the kinematic parameter taking into account at a respective future time in the Melt prevailing pressure specified and / or corrected and injection unit.

Description

Description [0001] The invention relates to a method for operating an injection unit for a casting process according to the features of the preamble of claim 1 and to an injection unit according to the features of the preamble of claim 13.

In the following, the prior art will be described by way of example in an injection molding process. The statements also apply more generally in relation to other casting processes.

In a generic method is [0004] - to fill a mold cavity a melt by means of an actuator from a

Displacement of the melt vessel, [0005] a control and / or control of a movement of the actuator carried out according to a kinematic parameter and [0006] - a measured variable which is characteristic of a pressure of the melt ge measured.

The mold filling during injection is usually carried out after a predetermined by the operator injection speed (as kinematic size). Depending on the material and shape, the injection pressure is set during mold filling. In addition to the injection speed, an injection pressure limit can be set. This limit value must not be exceeded in order to protect the tool or, at maximum value, the operator and the machine (cylinder, nozzle, worm, lock, etc.).

In a known variant of the speed setting is followed until reaching the injection pressure limit and then the pressure control is activated, whereby the speed is reduced. However, this leads to corresponding overshoots in the pressure at high speeds, especially at steep pressure increases when the mold is already completely filled or e.g. the closing nozzle does not open. (See FIG. 6). Another variant would be to parameterize a PID controller in such a way that it reduces the speed at a pressure increase early, that is, even before reaching the injection pressure limit, thus avoiding the pressure overshoot. However, this design is difficult to parameterize and in some cases leads to an unwanted premature deviation of the injection speed from the specification (and thus longer cycle times).

In EP 1 612 027 A1, the pressure increase during deceleration is predicted as a function of the current pressure change, the speed and a coefficient on the basis of a simple arithmetic expression. If this precalculated pressure exceeds the injection pressure limit, the deceleration of the plasticizing screw is initiated, whereby a constant acceleration (in this case of course a deceleration) is specified.

Due to this constant acceleration cycle time is given away, as a constant delay of the plasticizing screw will of course be ideal only for the few combinations of tool and melt.

The object of the invention is to provide a method for operating an injection unit and an injection unit, which allow a shortened injection time.

With regard to the method, this object is solved by the features of claim 1. This is done by predefining and / or correcting a manipulated variable for the regulation and / or control of the kinematic parameter, taking into account the pressure prevailing in the melt at any future time.

With regard to the injection unit, this object is achieved by the features of claim 13. This is achieved in that the regulating or control unit is designed to predetermine and / or correct a manipulated variable for the regulation and / or control of the kinematic parameter, taking into account the pressure prevailing in the melt at any future time.

Thus, the information that is available from the measurement of the measured variable can also be used during the phase of the control and / or control according to a kinematic parameter. It is thereby achieved that the extension of the injection time, which results from the engagement of the pressure limit regulator in the profile predetermined by the operator, is minimized, whereby at the same time there are no excessive pressures in the melt.

In the measured variable, which is characteristic of a pressure of the melt, it may be, for example, a pressure measurement. As measured variables, any measured variables can be used which can describe the pressure behavior of the melt. For example, measured variables can be used that allow statements about the force exerted by the actuator on the melt (since the geometry of the actuator is usually known). These would be a pressure measurement of the hydraulic fluid in an injection piston or, if the actuator is moved by means of an electric drive, currents and voltages of the electric drive. Of course, melt pressure sensors can also be used in the mold cavity or other areas where the melt reaches. In fact, sensors could also be used which measure the increase in the closing force in a closing unit which serves to close the mold cavity in response to the urging force caused by the pressure of the melt.

The invention can be preferably used in injection units with an electric drive, wherein the use is also possible in hydraulic drives.

Further advantageous embodiments of the invention are defined in the dependent claims.

It may preferably be provided that a pressure limit is specified as the limit value for the pressure of the melt. This serves to protect the injection unit and the tool, as too high pressures can cause damage. Excessively high pressures can also cause a degradation of the melt. Ultimately, this also serves to increase the safety for the operators.

In many cases, the speed must be reduced only slightly to keep the injection pressure during mold filling below the pressure limit. In the case of methods according to the prior art, however, a relatively large loss in the injection time must also be accepted in these cases.

In a particularly preferred embodiment, it may be provided that the specification and / or the correction of the manipulated variable is carried out if the pre-calculated pressure of the melt is greater than the pressure limit. This procedure enables a further optimized cycle time, since the pressure limit is utilized as well as possible without causing overshoots.

To further improve the control and / or control, it may be provided that a viscosity and / or a compressibility of the melt are taken into account in the precalculation of the pressure prevailing in the melt at any future time.

A particularly simple implementation of the simultaneous control and / or control according to the kinematic parameter and the measured variable can be achieved in that the correction of the manipulated variable is carried out as a feedforward control and / or control according to a kinematic parameter.

It can be provided that the injection pressure limit is specified as a constant, time or path-dependent pressure profile.

As a kinematic parameters, for example, a speed, a position and / or an acceleration can be used.

It can also be provided that an indication is issued to an operator and / or a produced component is declared as rejects and / or production is stopped, if a specification and / or a correction of the manipulated variable in consideration of one each future time in the melt prevailing pressure is performed.

It may preferably be provided to design an injection unit according to the invention so that the executed during the control and / or control of the kinematic parameter specification and / or correction of the manipulated variable can be switched off.

The actuator may comprise an injection piston. The actuator may also comprise a plasticizing screw.

The melt vessel can be designed as plasticizing cylinder.

Protection is also desired for a molding machine with an injection unit according to the invention. Under shaping machines injection molding machines, transfer molding and pressing and the like can be understood.

The injection unit may be particularly suitable for filling a mold cavity with plasticized plastic.

Further advantages and details of the invention are apparent from the figures and the accompanying figures. In the drawings: Figs. 1a and 1b show a pressure diagram and a velocity diagram in two injection events; Fig. 2 shows a flow diagram of an embodiment of an inventive device

Method, Fig. 3 is a diagram of control strategy in an embodiment according to the invention, Fig. 4 is a pressure diagram and a speed diagram with others

FIGS. 5a and 5b show two diagrams for the control concept for the actuator of the injection unit, and FIG. 6 shows a pressure diagram and a velocity diagram, as in the case of FIG

State of the art can occur.

In the example of FIG. 1a, the pre-calculated injection pressure SD reaches the set pressure limit DG, while the measured pressure (ie the measured variable) is still significantly lower. As soon as the pre-calculated injection pressure, but before the measured variable reaches the pressure limit DG (the time is represented by a vertical line), the set velocity profile GP is deviated and the speed manipulated variable SG is reduced to zero under pressure control. This avoids overshooting the pressure in the melt.

The concept of pressure limit control (hereinafter "pressure control") serves to limit the maximum pressure and is often used in injection units with electric drives. In order to fulfill the pressure limiting function due to the high system rigidity and the high injection speeds, a premature reduction of the speed is necessary.

In Fig. 1b, the set maximum pressure (pressure limit DG) is achieved at reduced speed. The speed is reduced to the value needed for the set pressure limit DG. After reaching the pressure limit DG (also "injection pressure limit"), the speed is slowly further reduced by the control to maintain the injection pressure. A reduction of the speed to a standstill in this case would mean that the mold can not be completely filled. The concept of pressure control achieves a higher speed and shortens the injection time.

These situations can be generated by an operation according to the invention. In the exemplary embodiment described here, first, by means of a model which takes into account the viscosity / compressibility of the melt and the elasticity of the injection unit (or its drive train), it is calculated in advance how high the pressure would rise if the predefined speed profile GP is maintained. (Models which take into account the viscosity / compressibility of the melt are disclosed, for example, in EP 0 478 788 A1 or US 2013/0032961 A1.) In the machine model, the friction and rigidity of the drive train can be described by means of equations of motion. This allows the dynamic limits of the movement of the machine during operation to be taken into account.

If this pressure value of the melt exceeds the pressure limit DG, the pressure regulator intervenes in the control of the actuator.

In the flowchart in Fig. 2, the remaining flow of injection is shown until reaching the switching point. After the start of the injection movement takes place due to the predetermined and measured speed, the control of the injection speed. If there is no intervention of the pressure regulator, the speed control continues until the switchover point.

If the pressure regulator intervenes in the injection process up to the switching point, an information message is displayed on the control screen. Depending on the setting by the operator, further actions can be linked with it.

The pressure control during the engagement of the pressure regulator is carried out in this embodiment with a pilot control of the actuator. For details in this regard, reference is made to FIGS. 5a and 5b.

After the procedure, the pressure control is performed based on the predetermined pressure profile DG and the measured variable (injection pressure).

The process variables during the procedure (pressure, speed and position) are stored for the later optimization. Preferably, only individual values can be determined for specific criteria for the following calculation. After switching to holding pressure, the adaptation of the control parameters is carried out based on the measured variables. The adapted parameters are used for the next cycle.

OPTIMIZATION

As already mentioned, a model for the drive and the injection process is used in a preferred embodiment. With the model, the pressure increases can be precalculated more accurately and the ideal time of intervention of the pressure regulator - that is, as late as possible but without exceeding the pressure limit - be determined. The models of the machine and the drive are usually well-known, but due to the dependence on the tool and the material, the process model is not exactly known in advance.

The controller includes a model for the drive and the process. On the one hand, this can be used to calculate material-specific or tool-specific variables and to carry out a precalculation of the pressure increase during deceleration to the required injection speed. Thereby, the time for activating the pressure regulator can be determined, wherein the model information can also be used for the pressure control.

The model for the process is parameterized in the first step with nominal parameters. These nominal parameters provide a safe function for all tools and material properties, the pressure control is activated in time, the speed is reduced and pressure overshoot can be avoided. Due to the robust parameterization, however, the intervention usually takes place too early (the speed would not have had to be reduced at that time). If it is detected that the intervention takes place too early, the model parameters for the following injection movements are adapted according to a calculation rule on the basis of the measurement data of pressure, position and speed.

In one possible variant embodiment, a deviation of the predicted injection pressure with the measured injection pressure is determined. Depending on the deviation, one or more parameters of the model are adjusted to better match the prediction with the measurement. By way of example, the parameter adaptation can be carried out as follows: Pk + i = f (Pk, pM, pAct, Vaci, c), ie, for example, Pk + 1 = Pk + c * (Pac, -Pm) Pk, Pk + 1 represent the current and adapted model parameters, f is a mathematical function, pM, Pa «is the pressure calculated with the model and the pressure measured, vAct is the measured velocity and c is a coefficient for evaluating the deviation.

This optimization is repeated in the following cycles if necessary.

Since the behavior of the machine changes as a result of this optimization and thus also changes the injection process, the operator can control this optimization.

It can be provided that the estimated model or controlled variables are used for a process or machine monitoring.

An embodiment: During the cycle, a pre-calculated pressure is compared with the measured pressure. The deviation can be used as a factor multiplied model modulator modifier (or model inversion).

ACTIVATION OF OPTIMIZATION

The operator has the option of starting, stopping and resetting the optimization: The operator has the option of activating the optimization of the parameters for the system model stored in the controller as required. In this case, the model parameters are adapted cyclically, based on the measured values of the current injection process, for the subsequent cycle. The optimization process happens without interaction with the operator.

If the operator deactivates the optimization, he has the possibility of having the result

Join part data record (= stop optimization) or discard (= reset).

If the parts data record is saved while the optimization is active, the operator has the option of deciding whether the current state of the optimization is also backed up or not.

If the operator loads a part data record which contains an optimization result, he has the option of using this for the following production cycles. If he uses this option, the optimization is activated and starts with the saved result. In this case too, with automatic activation of the optimization, when the optimization is ended manually, the operator has the choice of linking or rejecting the optimization result with the parts data.

OTHER VARIATIONS FOR START AND DURATION OF OPTIMIZATION

· The optimization runs constantly and checks the criteria for adjusting the parameters internally (no activation by the operator necessary). If no intervention takes place, no adjustment happens. During an intervention it is checked whether the behavior can be improved by a parameter adjustment. If this is positive, the parameters are saved and used for the next shot.

The optimization takes place only once after manually triggering the optimization after an intervention. The operator himself determines whether a change of the controller behavior is permissible. After optimization, the parameters are saved and used for the next shot.

The optimization runs for a certain number of cycles. Within the cycles, the parameters can be adjusted several times. Furthermore, the adjustment can be averaged over several shots. After optimization, the parameters are saved and used for the following molding cycles.

The optimization runs until an optimization criterion or a max. Number of cycles is reached. After optimization, the parameters are saved and used for the following shots.

· Optimization runs continuously after activation until the operator deactivates it again.

The optimized parameters are stored as pieces of data. Thus, the process can be repeated reproducibly with the parameters determined so high product consistency can be achieved.

FIG. 3 shows how the method according to the invention embeds itself in the entire shaping cycle, or which states the pressure regulator (also known as the pressure limit regulator) can assume. First, the control of the actuator according to a kinematic parameter and without intervention of the pressure regulator (monitoring, 1), i. E. without the target profile for the speed of the actuator is changed.

The following steps are carried out in the state "monitoring" in each sampling step: From the measured pressure increase and the model of the compression behavior, the required velocity profile is determined and the course of the injection pressure is precalculated.

It is checked whether the predicted pressure exceeds the pressure limit.

If the pressure limit is not reached, the predetermined profile speed is not changed (no intervention). The pressure regulator thus remains in the "monitor" state.

As soon as the pressure limit DG is reached by the predicted pressure of the melt, the pressure regulator intervenes (braking, 2) and reduces the speed with the aid of the precontrol and the slave controller. (For details, refer again to Figs. 5a and 5b.) As soon as the pressure increase is completed, the follow-up control regulates the pressure according to the predetermined pressure limit (pressure control, 3). As soon as the changeover point has been reached, a predefined pressure profile is traversed by the pressure regulator (without regulation of a kinematic parameter).

During the engagement of the pressure regulator, the speed is reduced by a pilot control. In addition, a slave controller becomes active. If the pressure increase is less than the predicted, the delay is reduced by the pilot control. If the pressure does not increase any further, the speed will not be further reduced by the pilot control.

After completion of the feedforward control, the pressure is kept at the pressure limit with the help of the slave controller. If the current pressure is below the pressure limit, the slave controller increases the speed until the currently valid profile speed is reached.

The intervention is terminated when the pressure has dropped below a certain value and the profile speed is reached again. Thus, the pressure regulator behaves again as before the procedure.

The effect of a pressure limit regulator according to the invention is illustrated in Figure 4, wherein in the first graph, the pressure in the melt and in the second graph, the injection speed is plotted against time. The diagrams contain several examples of different activation times.

In Example I, the speed of the actuator was reduced too early, whereby the pressure limit DG is not reached. It is the task of the controller to increase the speed so that the pressure limit is reached.

In Example III, the actuator is decelerated too late. The pressure regulator (described in FIGS. 5a and 5b) will intervene in this case because the predicted melt pressure exceeds the pressure limit DG.

Example II represents the Ideal situation, wherein the pressure limit DG only at the end of the deceleration process to the pressure limit DG - without overshoot - enough.

The task of the pressure regulator is to avoid situation III and to influence the actuator so that situation II sets. An example of such a pressure regulator is given in Fig. 5a and Fig. 5b.

The structure of the cruise control is shown in Figure 5a. The set speed is calculated in the profile generator as a function of the current worm position (x_akt). If no intervention of the pressure limit regulator is necessary, the profile speed (v Prof) corresponds to the set speed (v soll) of the drive. In the pressure limit controller, the current pressure (p_akt), the current injection speed (v_akt) and the current screw position (x_akt) are used as measures for limiting the injection pressure (pJJmit).

FIG. 5b gives an overview of the parameterizable components of this example of a pressure limit regulator and its range of action. Below is a brief description of the individual components. ACTUAL VALUE FILTER: The actual value filter can be designed as a band-stop filter and / or as a low-pass filter. The band-stop filter is a special filter that makes it possible to almost completely suppress a certain (disturbing) frequency. In this control loop, the band-stop filter offers the possibility of suppressing pressure oscillations with a known and approximately constant frequency.

A low-pass filter suppresses all signal components with frequencies that are above the set limit frequency. The signal is smoothed out by filtering out high-frequency components. MODEL: In the model, the precalculation of the pressure takes place based on the model parameters and measured values. Therein, the intervention time and also the input signals for the precontrol and the slave controller are determined. PRELIMINATION: In summary, a pilot control offers the possibility of predetermining the input of the system to be controlled so that its output follows a desired course under ideal conditions. As a result, the system behavior is known in advance and it is possible to use the full dynamics of the system.

When the predicted pressure reaches the pressure limit, the speed is reduced so that the pressure rises to the pressure limit as predicted. When calculating the pressure, the model parameters and the current measured values are taken into account. If the pressure increases more slowly than expected, the deceleration is reduced accordingly so that it does not deviate more than absolutely necessary from the given velocity profile. If the pressure remains constant before reaching the pressure limit, the setpoint speed (v_Vorst) output by the pilot control is also kept constant. FOLLOWER: In the pressure limit controller, the slave controller is used to correct deviations between the set pressure limit and the measured pressure. The sum of the output of the feed forward control and the output of the slave controller is used as the new setpoint speed for the system. If the pressure limit is not reached, the speed is increased again until either the pressure limit or the set profile speed is reached.

OPERATOR INTERFACE

The method according to the invention can result in a speed profile for the actuator entered by the operator being changed by the pressure regulator as a function of the situation. In order to make the behavior of the machine more transparent, in the first step, the operator is informed about the intervention of the pressure control during injection with a message and pointed to possible remedies.

Furthermore, in a preferred embodiment of the invention, it is possible to select further actions in addition to an information message. Material and process fluctuations can cause a change in the operating point, which can lead to an intervention of the pressure regulator.

If the process requires a cyclic intervention of the controller or if the required product quality is achieved despite intervention, the information message can also be deactivated.

[0098] The action when the injection pressure controller intervenes can be determined by a drop-down selection: [0099] o none [00100] o notification message (default) [00101] o declaration of the produced part as scrap (and notification message) [00102] o Production stop (and advice message and reject declaration) The message informs the operator about the intervention of the pressure regulator, which reduces the specified injection speed and points out possible remedies via the help. By specifying the position or the injection volume, for example, the operator can specifically adjust the speed in certain areas.

[00104] An appropriate indication message could include, for example: [00105] - engaging injection pressure regulator reduces speed (possibly indicating the speed of the actuator being intervened); [00106] - Effect: The injection pressure regulator reduces the injection speed, the set injection speed can not be achieved thereby.

[00107] - Possible Remedies: [00108] o Check cavities and temperature settings [00109] o increase injection pressure limit [00110] o reduce set injection speed (in the area of the controller intervention) o Activate the optimization of the injection pressure limitation for the process [ 00112] o Deactivation of the information message

Claims (20)

claims 1. A method for operating an injection unit for a casting process, wherein - for filling a mold cavity, a melt is displaced by means of an actuator from a melt vessel, - a control and / or control of a movement of the actuator is carried out according to a kinematic parameter, - a measured variable, which is characteristic of a pressure of the melt, is measured and - from the measured quantity a pressure prevailing in the melt in each future time is precalculated, characterized in that a value of a manipulated variable for the regulation and / or control of the kinematic parameter taking into account is formed and / or corrected at a respective future time in the melt prevailing pressure. 2. The method according to claim 1, characterized in that a pressure limit is set as the limit value for the pressure of the melt. 3. The method according to claim 2, characterized in that the specification and / or the correction of the manipulated variable is performed if the pre-calculated pressure of the melt is greater than the pressure limit. 4. The method according to any one of claims 1 to 3, characterized in that in the pre-calculation of prevailing at a respective future time in the melt pressure, a viscosity and / or compressibility of the melt are taken into account. 5. The method according to any one of claims 1 to 4, characterized in that the correction of the manipulated variable with a feedforward control for the control and / or control is carried out according to a kinematic parameter. 6. The method according to claim 2, characterized in that the pressure limit is specified as a constant, time- and / or path-dependent pressure profile. 7. The method according to any one of claims 1 to 6, characterized in that as a kinematic parameter, a speed, a position and / or an acceleration is used. 8. The method according to any one of claims 1 to 7, characterized in that an indication is issued to an operator and / or a produced component is declared as rejects and / or the production is stopped, if a default and / or a correction of the manipulated variable is carried out taking into account the pressure prevailing in the melt at a future time in each case. 9. The method according to claim 3, characterized in that an indication is issued to an operator and / or a produced component is declared as broke and / or the production is stopped if the pre-calculated pressure of the melt is greater than or equal to the pressure limit , 10. The method according to any one of claims 1 to 9, characterized in that based on a process model, the measured variable and / or measurements of the kinematic parameter adapted control and / or control parameters and / or adapted model parameters are calculated 11. The method according to claim 10, characterized in that the adapted control and / or control parameters and / or the adapted model parameters are used in a subsequent injection process. 12. The method according to claim 10 or 11, characterized in that the adaptation of the parameters controlled by the operator and / or the operator is displayed. 13. Injection unit, in particular operated according to a method of claims 1 to 12, comprising - a melt vessel in which a melt can be provided, - an actuator for displacing a melt from the melt vessel for filling a mold cavity, - a control connected to the actuator or control unit for controlling and / or controlling movements of the actuator according to a kinematic parameter and - a connected to the control unit or control unit for measuring a measured variable which is characteristic of a pressure of the melt, wherein the Regeloder control unit is designed to off the measure to predict a prevailing at any future time in the melt pressure, characterized in that the control or control unit is adapted to a value of a manipulated variable for the control and / or control of the kinematic parameter, taking into account each one in the future to form and / or correct time in the melt of prevailing pressure. 14. Injection unit according to claim 13, characterized in that a connected to the Regeloder control unit memory is provided, in which a pressure limit as the limit value for the pressure of the melt can be stored. 15. Injection unit according to claim 14, characterized in that the control and / or control unit is adapted to perform the specification and / or the correction of the manipulated variable, if the pre-calculated pressure of the melt is greater than the injection pressure limit. 16. Injection unit according to one of claims 13 to 15, characterized in that the executed during the control and / or control according to the kinematic parameter specification and / or correction of the manipulated variable can be switched off. 17. Injection unit according to one of claims 13 to 16, characterized in that the actuator comprises an injection piston. 18. Injection unit according to one of claims 13 to 17, characterized in that the actuator has a plasticizing screw. 19. Injection unit according to one of claims 13 to 18, characterized in that the melt vessel is designed as a plasticizing cylinder. 20. Forming machine with an injection unit according to one of claims 13 to 19. For this 7-sheet drawings