ITTV20060108A1 - SYSTEM AND METHOD TO DISCRIMINATE AN ANOMALY CONDITION OF OPERATION IN A HOT CHANNEL DEVICE FOR PLASTIC INJECTION MOLDING EQUIPMENT - Google Patents

Description

DESCRIPTION

The present invention relates to a system and a method for discriminating an anomalous operating condition in a hot runner device for plastic material injection molding equipment.

In particular, the present invention relates to a system and a method which allow to detect an anomalous operating condition of a thermocouple installed in a heating unit of a hot runner device for plastic injection molding equipment, in which the heating unit is provided with a pair of heating resistors, to which two respective thermocouples are operationally connected; to which the following discussion will explicitly refer without losing generality.

As is known, some currently known plastic injection molding equipment is provided with a hot runner device, which is arranged in a seat obtained in an injection mold and comprises a series of tubular branches which selectively convey a plastic material in a fluid state towards the injectors which inject it into an impression obtained inside the mold; and a series of heating units, which are installed in the tubular branches, typically in correspondence with the injectors, to heat the plastic material to be injected on command.

In particular, some of the latest generation heating units are each equipped with a pair of resistors! heating elements separate and independent from each other, and of a pair of thermocouples each of which is arranged in the tubular branch at a respective resistor to measure its temperature. For example, the Italian patent application T02001A000399 filed on 27 April 2001 in the name of A.S. Special Equipment S.r.l. describes an injector of a hot runner device provided with a heating unit having a structure of the type described above, in which the two thermocouples of the two resistors are connected to a control unit of the hot runner device, which selectively activates one or more the other of the two resistors! of the heating unit according to their actual functionality.

In the control systems of hot runner devices of the type described above, there is the problem of being able to distinguish in real time an anomalous temperature measurement condition deriving from a malfunctioning state of one of the thermocouples, such as for example a circuit break or a plastic deformation caused by the crushing of the same, by an anomalous measurement condition deriving from an external event, i.e. from a cause that does not derive from a fault in the thermocouple. In this case, this latter condition arises when a fault in the hot runner device causes a leakage of high temperature plastic material, which accidentally depositing on the thermocouple (s) causes a sudden increase in the measured temperature that cannot be interpreted by the control unit.

The possibility of immediately discriminating the two different anomalous conditions described above has become a deeply felt need in the molding equipment sector since, on the one hand, a failure of a thermocouple does not cause significant and immediate irreversible effects on the equipment and can therefore be repaired during any pre-established routine maintenance operation, on the other hand, the loss of hot plastic material from the hot runner device can determine, if prolonged over time, significant damage to the mold with obvious consequences from an economic point of view . It is therefore necessary to ascertain almost immediately any loss of the plastic material from the hot runner device, so as to be able to stop the molding process and repair the hot runner device, thus limiting damage to the mold.

The purpose of the present invention is therefore to provide a control system that is able to immediately discriminate an anomalous condition deriving from a fault in the thermocouple, from an anomalous condition deriving from an "external event", that is, from a non-attributable cause. to a failure of the thermocouple itself, but resulting for example from a loss of material from the hot runner device or a loss of coolant or other causes.

According to the present invention, a system and a method are provided for discriminating an anomalous operating condition of a hot runner device as described in the attached claims.

The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of embodiment, in which:

Figure 1 schematically shows a system for discriminating an anomalous operating condition in a hot runner device for plastic material injection molding equipment, according to the present invention; And

Figures 2a and 2b show a flow diagram of the operations implemented by the system of Figure 1.

With reference to Figure 1, the number 1 indicates as a whole a system suitable for discriminating an anomalous condition deriving from a malfunction of a temperature sensor installed in a hot runner device from an anomalous operating condition of the hot runner device deriving from other generic external causes and events such as for example leaks of hot plastic material between the hot runner device and the relative mold and / or from a loss of cooling liquid of the mold itself.

In particular, the system 1 comprises a plastic material injection molding apparatus 20 comprising, in turn, a hot runner device 2 capable of selectively conveying and injecting the plastic material in the liquid state into a series of injection points. internal to an injection mold 4 (schematically represented with dashed line) to make a product with a predetermined shape; and a control unit 3 of the operation of the hot runner device 2 which comprises at least one memory 3a, and a processing unit 3b connected through known circuit modules (not shown) to the various electrical components included in the hot runner device 2 and described in detail below.

In the example shown in Figure 1, the hot runner device 2 is adapted to be housed in a suitable seat 4a obtained in the body of the injection mold 4 and comprises, in turn, one or more injectors 6 each arranged in a corresponding point injection mold provided in the injection mold 4, and one or more tubular branches 7 (two of which are schematically shown in figure 1}, which convey the liquid plastic material starting from an inlet (not shown) towards the injectors 6.

The hot runner device 2 also comprises one or more heating units 8, each of which is arranged in a tubular branch 7 or in correspondence with an injector 6, and comprises a first and a second resistor indicated below respectively with 9 and 10, which are selectively activated by the control unit 3 to transmit a quantity of heat to the plastic material to be injected so as to keep it in the liquid state at a predetermined injection temperature. More in detail, the first and second resistor are housed inside a suitable seat (not shown) obtained in the tubular branch and / or in the injector.

The heating unit 8 also comprises a first and a second thermocouple or other temperature sensor, indicated hereinafter with 11 and 12 respectively, which are housed inside the same seat obtained in proximity to the seat housing the two resistors. 9 and 10 and are suitable for supplying the relative measured temperatures Ti and T2 to the control unit 3.

With reference to figures 2a and 2b, the operating method implemented by the system 1, in particular by the control unit 3, will be described below to discriminate the anomalous condition deriving from the malfunction of the first 11 and / or the second thermocouple 12, from a condition anomalous caused by external events correlated to a loss of plastic material between injector 6 and mold 4 and / or by a loss of the cooling liquid of the mold 4 itself or by other general conditions.

During the molding process, the control unit 3 receives the temperatures Ti and T2 measured by the first 11 and respectively by the second thermocouple 12 (blocks 100 and 110) at the input at regular predetermined intervals.

At each measurement instant ti, the control unit 3 calculates the temperature variations ΔΤΧ and ΔΤ2 measured by the thermocouples 11 and 12, the first of which ΔΤι corresponds to the difference between the temperature Ti detected at the current measurement instant ti and the temperature Tx detected in the instant of measurement ti_i immediately preceding (block 120); while the second temperature variation ΔΤ2 corresponds to the difference between the temperature T2 measured at the current instant ti and the temperature T2 measured at the previous instant ti-i (block 130).

At this point it is checked whether the temperature Tx is greater than a predetermined maximum threshold SM, for example of about 450 ° C (block 140).

If the temperature Tx is higher than the maximum threshold SM (output YES from block 140), the control unit 3 identifies a generic fault condition of the first thermocouple 11 and signals it (block 150); while in the negative case, i.e. if the temperature Ti is less than or equal to the maximum threshold SH (NO output from block 140) the control unit 3 checks whether the following first relation is satisfied:

a) in which S3 is a first comparison threshold set for example at about 10 ° C (block 160), If the first relation is satisfied (YES output from block 160) the control unit 3 detects and signals a fault deriving from a circuit break of the first thermocouple 11 (block 170); while if the relationship is unsatisfied (NO output from block 160) the control unit 3 checks whether the following second relationship is satisfied or not:

b) wherein S4 is a second comparison threshold set for example at about -10 ° C (block 180). If the second relation is satisfied (YES output from block 180), the control unit 3 detects and signals a failure deriving from a plastic deformation of the first thermocouple 11 caused by its squashing (block 190}; while if the second relation turns out to be unsatisfied (NO output from block 180) the control unit 3 checks whether the following third relation is satisfied or not: c) in which S5 is a third comparison threshold set for example at about 0.5 ° C {block 200 }.

If the aforementioned third relationship is satisfied (YES output from block 200), the control unit 3 detects a fault deriving from a plastic deformation of the first thermocouple 11 (block 210), while if the third relationship is unsatisfied (NO output from block 200), the control unit 3 checks whether or not a relationship related to an anomalous condition caused by a loss of material from the hot runner device 2 (block 220 in figure 2b) is satisfied, a condition that will be described in detail afterwards.

Simultaneously with the control and comparison operations of the temperature variation ΔΊι described above (blocks 120-220), the control unit 3 implements similar controls and comparisons by processing the temperature variation ΔΤ2, In detail, following the calculation of the variation of temperature ΔΤ2 the control unit 3 checks whether the temperature T2 is greater than the maximum threshold SM (block 230) and in a positive case it signals a generic fault of the second thermocouple 12 (block 240), while in the negative (NO output from block 230) the control unit control 3 verifies whether the following fourth relation is satisfied:

d) (block 250).

If the aforementioned fourth relation is satisfied (YES output from block 250), the control unit 3 detects and signals a fault condition deriving from a circuit interruption of the second thermocouple 12 (block 260), while if the fourth relation is unsatisfied (NO output from block 250) the control unit 3 checks whether the following fifth relation is satisfied or not:

e) (block 270).

If the aforementioned fifth relationship is satisfied (YES output from block 270) the control unit 3 detects and signals a failure deriving from a plastic deformation of the second thermocouple 12 (block 280), while if the fifth relationship is unsatisfied (output no. from block 270) the control unit 3 checks whether the following sixth relation is satisfied or not:

f) (block 290),

If the aforementioned sixth relation is satisfied (YES output from block 290} the control unit 3 detects and signals a failure deriving from a plastic deformation of the second thermocouple 12 (block 300}, while if the sixth relation is unsatisfied (NO output from block 290} the control unit 3 verifies whether or not a relationship correlated to an anomalous condition caused by a loss of material from the hot runner device 2 (block 220) is satisfied.

In particular, in this phase the control unit 3 checks whether the following seventh relation is satisfied or not:

g) (block 220).

In the event that the seventh relationship is satisfied, that is, if both temperature variations ΔΤ] and ΔΤ2 are greater than the first pre-established threshold (YES output from block 220}, the control unit 3 identifies and signals a loss of material from the device a hot runner 2 (block 310}, while if the seventh relationship is unsatisfied (NO output from block 220), the control unit 3 checks an eighth relationship:

h) (block 320);

If the eighth relation h) is satisfied, i.e. if both temperature variations ΔΤι and ΔΤ2 are less than the second predetermined threshold (YES output from block 320), the control unit 3 identifies and signals a loss of material condition from the hot runner device 2 (block 310), while in the event that the eighth relation h) is unsatisfied (NO output from block 320), the control unit 3 verifies a ninth relation:

i) (block 330) in which S6 is a fourth comparison threshold set for example at about 5 ° C (block 330).

In the event that the ninth relation i) is satisfied, i.e. if both temperature variations are greater than the fourth pre-established comparison threshold (YES output from block 330), the control unit 3 identifies and signals a condition of probable loss of material from the hot runner device 2 (block 340), while in the event that the ninth relationship i) is unsatisfied (NO output from block 330), the control unit 3 verifies a tenth relationship:

1) (block 350) in which S7 is a fifth comparison threshold set for example at about -5 ° C (block 350).

In the event that the tenth relationship 1) is satisfied, i.e. if both the temperature variations ΔΤι and ΔΤ2 are less than the fifth predetermined S7 comparison threshold (YES output from block 350), the control unit 3 identifies and signals a probable condition loss of material from the 3⁄4 hot runner device 2 (block 340), while in the event that the tenth relationship 1) is unsatisfied (exit no from block 350), the control unit 3 terminates the implementation of the method which will be repeated instantly ti + i.

According to a different embodiment (not shown), if the first ΔΤι and the second temperature variation ΔΤ2 are both zero ΔΤι = 0 ΔΤ2 = 0 or if the measured temperature is substantially constant at the same time a predetermined variation ΔΕ is detected of the power absorbed by said hot runner device 2 then the control unit 3 identifies and signals an anomalous operating condition deriving from an event not associated with a malfunction of the thermocouples 11 and 12 but deriving from an external event of the type described above. in other words, the control unit 3 identifies and signals an anomalous operating condition deriving from an event not associated with a malfunction of the thermocouples when, during the molding operations, the measured temperature is substantially constant, but oscillations or fluctuations occur. perturbations of absorbed electricity from the hot runner device 2, the latter condition correlated to the presence of leaks of hot plastic material and the leakage of cooling liquid from the mold.

The system 1 described above is extremely advantageous in that it allows a condition of loss of material from the hot runner device to be identified in an extremely rapid time, thus allowing immediate repair of the latter and thus limiting possible conditions of damage to the mold.

The aforementioned discrimination also makes it possible to establish exactly whether the fault condition of the thermocouple (s) corresponding to a plastic deformation or to a circuit interruption of the same, thus allowing an operator to decide the best intervention strategy to be carried out on the hot runner device. according to the type of fault detected.

Finally, it is clear that modifications and variations can be made to the system and method described and illustrated here without departing from the scope of the present invention, defined by the attached claims.

Claims (14)

R IV E N D I C A C IO N I 1. Method for discriminating an anomalous operating condition in a hot runner device (2), which is adapted to inject plastic material in the liquid state into a mold (4) for forming a plastic product, and comprises at least an injector (6} adapted to inject said plastic material inside the mold (4), and at least a first (11) and a second temperature sensor (12) respectively arranged on said branch (7) or on said injector (6 ) substantially in the same point to measure the temperatures (Ti) and (T2) of the hot runner device at the same point; said method being characterized by the fact that it comprises the step of discriminating, as a function of the temperature variation (ΔΤι) measured by the first temperature sensor (11) in two successive pre-established measurement instants {ti-lfti) and of the temperature variation (ΔΤ2) measured by the second temperature sensor (12) in the same two measurement instants (ti-i, tj, one condition ne anomalous operation deriving from a failure of at least one of the two temperature sensors (11,12), from an anomalous operating condition of the hot runner device (2) correlated to an external event. Method according to claim 1, comprising the steps of: a) calculating a first variation of the temperature (ΔΤι) measured by the first temperature sensor (11) in the said two successive measurement instants (t ± -i, ti); b) calculating a second variation of the temperature (ΔΤ2) measured by the second temperature sensor (12) in the said two successive measurement instants (ti-i, ti); c) verify whether said first (ΔΊΥ) and second temperature variation (ΔΤ2) both satisfy a predetermined relationship with a predetermined temperature variation (S3; S4); d) detecting anomalous functioning of the hot runner device (2) correlated to an external event not associated with a malfunction of said temperature sensors (11) and 12), when said first (ΔΤχ) and second temperature variations (ΔΤ2) satisfy that predetermined relationship. Method according to claim 2, wherein in step c) said predetermined relationship is satisfied when the first (ΔΤχ) and second temperature variation (ΔΤ2) are each greater than a first predetermined temperature variation (S3). Method according to claims 2 or 3, wherein in step c) said predetermined relationship is satisfied when the first (ATJ and the second temperature variation (ΔΤ2) are less than a second predetermined temperature variation (S4). Method according to any one of claims 3 or 4, comprising the step of detecting an anomalous condition relating to a fault corresponding to a circuit interruption of said temperature sensors {11; 12} when one of the two temperature variations (ΔΤι; ΔΤ2 ) is greater than said first predetermined temperature variation (S3), and the other temperature variation (ΔΤ2; ΔΤι) is less than or equal to said first predetermined temperature variation (S3). 6. Method according to any one of claims 3 to 5, comprising the step of detecting an anomalous condition relating to a failure corresponding to a plastic deformation of one of said temperature sensors (11; 12) when one of the two temperature variations {ΔΤι; ΔΤ2) is less than a second predetermined temperature variation (S4) and the other temperature variation (ΔΤ2; ΔΤχ) is greater than or equal to said second predetermined temperature variation (S4). 7. Method according to any one of claims 3 to 6, comprising the step of detecting an anomalous condition relating to a failure corresponding to a plastic deformation of one of said temperature sensors {11; 12) when both temperature variations (ΔΤι ; ΔΤ2) are greater than a third predetermined temperature change (S5) and one of the two temperature changes (ΔΤι; ΔΤ2) is smaller than the other temperature change (ΔΤ2; ΔΤι). 8. Method according to claim 1 comprising the steps of: d) calculating a first variation of the temperature (ATL) measured by the first temperature sensor (11) in the said two successive measurement instants (ti_i, ti); b) calculating a second temperature variation (ΔΤ2) measured by the second temperature sensor {12) in the said two successive measurement instants (ti-i, ti); c) verify if said first (ΔΤι) and said second temperature variation (ΔΤ2) are both null; d) detecting an anomalous operating condition of the hot runner device {2) correlated to an external event not associated with a malfunction of said temperature sensors (11) and 12) when a predetermined variation (ΔΕ) of the power absorbed by the said hot runner device (2). Method according to any one of the claims characterized in that said first, second and second temperature sensors 12 correspond to thermocouples. 10. Control unit {3) adapted to discriminate an anomalous operating condition in a hot runner device (2), characterized by implementing a method as indicated in any one of the preceding claims. the. Software product that can be loaded into the memory (3a) of a control unit {3} and designed to implement, when performed, the method according to any one of claims 1 to 9. 12. System (1) for discriminating an anomalous operating condition in a hot runner device (2), which is able to inject plastic material in the liquid state into a forming mold (4) and comprises at least one injector (6) adapted to inject the plastic material inside the mold (4); at least one tubular branch (7) for conveying the plastic material towards the injector (6); and at least a first {11} and a second temperature sensor {12} respectively arranged on said branch (7) or on said injector (6) substantially in the same point to measure the temperatures (Ti) and (T2) of the device at hot runner at the same point; said system being characterized in that it comprises a control unit (3) of said device hot runner (2) made according to what is indicated in claim 10. 13. System according to claim 12, said hot runner device (2) comprising a first {9) and a second resistor (10) arranged on said branch {7} or on said injector (6) substantially in the same point to transmit heat to the plastic material in such a way as to bring it and keep it in a liquid state; said first (11) and second temperature sensor (12) being operatively connected to said first (9) and to said second resistor (10) respectively. 14. Apparatus {20) for injection molding of a plastic material comprising a hot runner device (2) capable of selectively conveying and injecting the plastic material in the liquid state into a series of injection points inside a mold {4) injection to make a product with a predetermined shape; and a control unit (3) for the operation of the hot runner device (2); said apparatus (20) being characterized in that said control unit (3) is made according to what is indicated in claim 10.