DE102008003499B4 - Method for the detection of a foreign body - Google Patents

Abstract

A method for the detection of a foreign body between mold halves of an injection molding machine during a closing process, an error variable (E) being obtained from a comparison of a measured variable of the current closing process with a reference variable, and a threshold value (S) being established, characterized in that the threshold value is exceeded (S) is detected by a parameter (E) obtained by integrating the error size (E) over a time (t), and that in addition the exceeding of the threshold value (S) is detected by a comparison of a measured variable (F, I) of the current Closing process with a reference size (F) obtained error size (E ') is detected.

Description

The present invention relates to a method for detecting a foreign body between the mold halves of an injection molding machine during a closing process, an error variable being obtained from a comparison of a measured variable of the current closing process with a reference variable, and a threshold value being established.

In the prior art, two basic groups of methods for the detection of objects clamped between the mold halves are known.

The first group is essentially based on limiting the maximum possible force acting on the mold halves (for example in a mold protection area) and / or checking the time required for a specific mold protection section and / or adding the control error to the mold position or speed evaluate.

The second group of methods compares one or more specific signal curve (s) of one or more measured variables with a reference signal in which there was no part in the area between the mold halves. For this purpose, for example, the speed of the movable mold mounting plate, the clamping force signal obtained from a mold protection sensor (combination sensor also for the clamping force) and / or the hydraulic cylinder pressure in injection molding machines with a hydraulic clamping side are used.

In a method for controlling injection molding machines according to JP H06-218,786 A the feedback of a pulse, which is detected by a position detector which detects a rotational position of a servomotor, to a pulse train at the target position as the actual position is carried out, and a control system is used which gives a speed command of the servomotor by its deflection. Then, an integral value of a pulse difference (accumulated pulse) between a pulse system at the target position and a feedback pulse is monitored. The integral value of the accumulated pulse quickly becomes larger than a fixed value even at the time of deceleration of a switching operation of a tool when resistances such as foreign matter being caught in the tool or others occur. Therefore, when the integral value of the accumulated pulse exceeds a fixed value, the individual operations are suspended.

A molding machine and a control method therefor, which can reliably determine whether an abnormality has occurred in the molding machine, provides EP 1 640 136 A1 ready. The molding machine includes an abnormality determining index processing means for obtaining an abnormality determining index for determining whether an abnormality has occurred in the molding machine; Integration processing means for integrating the obtained abnormality determination index to obtain an integral value; and abnormality determination processing means for determining, based on the integral value, whether an abnormality has occurred in the molding machine. In this case, high frequency components included in the abnormality determination index can be removed because the abnormality determination processing is performed based on the integral value of the abnormality determination index. Even if noise is generated in the abnormality determination index due to jumping, time shift, etc., influences of the noise can be canceled. Accordingly, the abnormality determination processing can be accurately performed, and the determination as to whether an abnormality has occurred in the molding machine can be reliably performed.

1. a) Vor dem Start des Produktionsbetriebes der Spritzgießmaschine: Messung des für das Bewegen der beweglichen Werkzeugträgerplatte samt zweiten Teil des Spritzgießwerkzeugs von der Offen-Position bis zur Geschlossen-Position erforderlichen Strombedarfs des Servomotors über dem Verschiebeweg als Offset-Funktion und Abspeichern der gemessenen Werte in der Maschinensteuerung;
2. b) Während des sich anschließenden Produktionsbetriebes der Spritzgießmaschine: Überwachen des während des Bewegens der beweglichen Werkzeugträgerplatte von der Offen-Position bis zur Geschlossen-Position benötigten Strombedarfs des Servomotors über dem Verschiebeweg;
3. c) Umgehende Unterbrechung der Bewegung der beweglichen Werkzeugträgerplatte, sobald der benötigte Strombedarf des Servomotors über dem für die jeweilige Position gemessenen Offsetwertes liegt, wobei eine vorher definierte Toleranzgrenze berücksichtigt wird.

DE 199 25 302 A1 discloses a method for securely closing the clamping unit of a machine for processing injection-mouldable material, in particular a plastic injection molding machine, comprising the following steps:

1. a) Before the start of the production operation of the injection molding machine: Measurement of the power requirement of the servo motor required for moving the movable tool carrier plate including the second part of the injection molding tool from the open position to the closed position via the displacement path as an offset function and storage of the measured values in the machine control;
2. b) During the subsequent production operation of the injection molding machine: monitoring of the power requirement of the servomotor over the displacement path during the movement of the movable tool carrier plate from the open position to the closed position;
3. c) Immediate interruption of the movement of the movable tool carrier plate as soon as the required power requirement of the servomotor is above the offset value measured for the respective position, taking into account a previously defined tolerance limit.

DE 43 45 034 A1 teaches a method for guiding the injection process in an injection molding machine, the injection screw being driven by an electric motor and mechanically translated axially, characterized in that either a speed signal (or path target signal) is selected for a drive as the manipulated variable, and for the pressure - (or holding pressure) and / or the plasticizing phase as target variables, in particular the injection pressure and preferably at the same time the path limitation is controlled or limited, particularly preferably not linearly controlled or the injection pressure, the injection speed and the path limitation is controlled or limited via the speed signal to a drive via a multivariable controller so as to approach the target variable values as closely as possible.

US 2005/0 218 545 A1 shows a method for a mold clamping device in which a clamping position detection mode is provided to obtain a rate of variation (including an amount of variation) in a physical quantity up to a predetermined amount of movement of a movable platen or a cross head and to detect a position as a mold clamping position when the rate of variation reaches a preset ratio. The mold clamping device is operated beforehand in the clamping position detection mode in order to store the mold clamping position at which a target mold clamping force is achieved as a reference value. In the production operation, the mold clamping device is operated in the clamping position detection mode to obtain an actual mold clamping position (detection value). The mold clamping force is corrected based on a deviation of the detection value from the reference value.

For error detection, in the known methods, the difference obtained from the current signal (measured variable) and reference signal is essentially compared with a threshold value. Some modifications are possible (for example shifting the reference signal by a distance or time difference).

It has turned out to be problematic with these methods that they only function unsatisfactorily with regard to the most frequently expected jammed objects, namely plastic parts. Since plastic is a plasticizable material, a progressive plasticization occurs when the mold halves are closed, whereby the clamped plastic part initially offers the mold halves only a low resistance. On the other hand, the plasticized, clamped plastic part can lead to the formation of dents on the mold halves or to a displacement of the mold core.

In order to be able to reliably avoid such damage, the threshold value would have to be chosen to be very low. In order to avoid false detections due to fluctuations in the measurement signal, however, the threshold value is often selected in practice to be significantly higher than the slight increase in the measurement signal to be expected due to the jammed plastic part.

The object of the invention is to develop a generic method in such a way that the presence of a foreign body between the mold halves of an injection molding machine is reliably detected even in the case of a plastic part, without having to accept frequent false triggers due to a threshold value that is too low.

This object is achieved by a method having the features of claim 1 and claim 10.

The basic idea of this method is to control a parameter that is based on the deformation energy applied to the plastic part or on the approximately related integrated or approximately integrated error. This stabilization has the task of ensuring that certain smallest errors in the measured variables, such as those that can occur due to noise in the measured variables, are not added up and thus unintentionally and incorrectly exceed a threshold value.

In this way, regardless of the actual amount of the defect size, the presence of a foreign body between the mold halves (mold protection case) can be detected if the defect size has only been present long enough. In other words, such a measure generates a strictly monotonically increasing signal from the error size (as long as it is genuinely greater than zero), which signal can be detected much more reliably (with regard to a fluctuation in the detection time or location when the error size changes).

Further advantageous developments of the method are defined in the dependent claims.

For example, that point in time at which the measured variable (or the error variable) exceeds a predetermined, adjustable value can be selected as the starting time for the integration of the error variable. The position of the movable platen at this point in time defines the start of the mold protection section.

According to the invention, the course of the measured variable in an earlier closing process, in which no foreign body was present between the mold halves, is used as the reference variable.

A simple embodiment of the method results if it is provided that the threshold value is obtained by adding a predetermined, adjustable amount to the reference variable.

The error size itself can be obtained, for example, by forming the difference between the measured variable and the reference variable.

Various measured values can be used as the measured variable. For example, the measured value of a form protection sensor can be used as the measured variable. A variable of the closing actuator of the injection molding machine, preferably the closing force, or a variable derived from such a variable, for example the current strength or the hydraulic pressure, can also be used as the measured variable.

In order to be able to detect not only plastic parts with a high degree of certainty, in a further advantageous embodiment of the invention it can be provided that the exceeding of the threshold value is additionally detected by an error variable obtained from a comparison of a measured variable of the current closing process with a reference variable. This represents, so to speak, a combination of the further developed method with the method already known from the prior art. In the simplest case, it can be provided that the additionally monitored error size is the same error size from which approximately, stabilized integration over the Time the parameter is obtained.

In order to be able to guarantee a reliable detection of foreign bodies, it is preferably provided that the first exceeding of the threshold value by the parameter or the error size is reported as a detection of a foreign body.

A method embodied in accordance with the above exemplary embodiments is used according to the invention in a method for protecting the mold halves of an injection molding machine during a closing process, namely in that the closing process is stopped after a foreign body has been detected.

• 1a, 1b den zeitlichen Verlauf einer Messgröße bzw. der Fehlergröße für den Fall eines eingeklemmten Kunststoffteils,
• 2a, 2b dieselben Größen für den Fall eines eingelegten Papierstapels (zur Simulation von Einlegeteilen) und
• 3a, 3b eine weitere Messgröße bzw. Fehlergröße für den Fall eines eingeklemmten Kunststoffteils.

Further advantages and details of the invention emerge from the figures and the description of the figures. Show:

• 1a , 1b the temporal course of a measured variable or the error size in the event of a jammed plastic part,
• 2a , 2 B same sizes for the case of an inserted paper stack (to simulate insert parts) and
• 3a , 3b Another measured variable or error variable in the event of a jammed plastic part.

In 1a Fact describes the course of the measured variable of the ongoing closing process as a function of time t. In this case, the closing force of the closing actuator of the injection molding machine was used as the measured variable. FREF denotes the course of the same measured variable as a function of time t from an earlier closing process. Due to the problem-free sequence of the earlier closing process, this curve is used as a reference value.

1b represents the course of the error size E for the current closing process. The error size E is determined by the following formula: E = F _act -F _REF . It can be seen that between times t ₁ and t _{2 there is} a relatively small but constant error size E of approximately 0.5. In order to be able to detect this error size with a conventional method, the threshold value S would have to be selected to be less than or equal to 0.5. This behavior occurs in the case of a jammed plastic part.

As from the 2a and 2 B shows which are analogous to the 1a and 1b represent the same values for the case of an inserted stack of paper (to simulate insert parts), a completely different behavior occurs with a non-plasticifiable foreign body. In this case there is a relatively short-term increase in the error signal E without it having to be present for a long time. Such an increase can easily be detected with a larger threshold value S without damage to the mold halves already occurring.

The 3a and 3b show the course of a measured variable (in this case the motor current I of the closing actuator, which is approximately proportional to the drive torque). In 3b both the previously used defect size E and the parameter EINT obtained by integrating the defect size are shown.

The context applies ${\mathrm{E.}}_{\mathrm{I.}NT}={\displaystyle \int \mathrm{E.}\left(t\right)}dt$

The monotonously increasing behavior of the parameter for the form protection case is clearly recognizable.

Especially for those in the 3a and 3b In the illustrated case, that a variable I of the closing actuator is to be used as a measured variable, the method according to the invention is particularly advantageous. Since a change to the reference signal I _REF due to a trapped foreign body often only occurs after a reaction to a control deviation has taken place, the detection must take place as quickly as possible. In addition, the error size E and thus the time of detection in the method according to the prior art are also heavily dependent on the setting of the controller.

In the case of toggle-lever injection molding machines, the variable toggle-lever transmission ratio results in a position-dependent detection sensitivity. This can be avoided by considering the toggle lever transmission ratio (linearization of the sensitivity). The setting of the threshold value can be adjusted by converting the motor current I to a theoretically corresponding closing force (in the event that a mold protection sensor supplies the closing force).

Claims (10)

A method for the detection of a foreign body between mold halves of an injection molding machine during a closing process, an error variable (E) being obtained from a comparison of a measured variable of the current closing process with a reference variable, and a threshold value (S) being established, characterized in that the threshold value is exceeded (S) is detected by a parameter (E _INT ) obtained by integrating the error size (E) over a time (t), and that the exceeding of the threshold value (S) is also detected by a comparison of a measured variable (F _act , I) of the current closing process with a reference variable (F _REF ) obtained error variable (E ') is detected. Procedure according to Claim 1 , characterized in that the starting time (t ₀ ) for the integration of the error variable (E) is selected as the time at which the measured variable (F, I) and / or the error variable (E) have a predetermined, adjustable value (F ₀ , I ₀ , E ₀ ). Procedure according to Claim 1 or 2 , characterized in that a course of the measured variable (F _REF , I _REF ) in an earlier closing process is used as the reference variable. Method according to one of the Claims 1 to 3 , characterized in that the threshold value (S) is obtained by adding a predetermined, adjustable amount (A) to the reference variable. ' Method according to one of the Claims 1 to 4th , characterized in that the error variable (E) is obtained by forming the difference between the measured variable (F _act , I) and the reference variable. Method according to one of the Claims 1 to 5 , characterized in that the measured value of a form protection sensor is used as the measured variable (F _act ). Method according to one of the Claims 1 to 5 , characterized in that a variable of a closing actuator of the injection molding machine, preferably a closing force, or a variable derived from such a variable is used as the measured variable (F _act , I). Method according to one of the preceding claims, characterized in that the additionally monitored error variable (E ') is the same error variable (E) from which the parameter (E _INT ) is obtained by integration over time (t). Method according to one of the preceding claims, characterized in that the first exceeding of the threshold value (S) is reported by the parameter (E _INT ) or the error size (E ') as a detection of a foreign body. A method for protecting the mold halves of an injection molding machine during a closing process, characterized in that foreign bodies present between the mold halves by a method according to one of the Claims 1 to 9 can be detected and that the closing process is stopped following a successful detection.

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