System and method for monitoring the closed position of a valve pin

Abstract

A monitoring method for an injection molding system is disclosed. [Solution] A monitoring method for an injection molding system includes the steps of: 1) closing the injection nozzle by moving a valve pin toward the injection nozzle and acquiring data via a sensor indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle; 2) acquiring a comparison value from the acquired data and comparing the comparison value with a reference value; and 3) outputting a signal if the result of the comparison indicates that the actual position is further from the nozzle than the reference value. The warning or alarm signal generated by the system allows for rapid intervention to correct or eliminate any imperfections that prevent the pin from reaching the desired closed position.

Description

Technical Field

[0001] The present invention relates to a system and method for monitoring the closed position of a valve pin used to flow a molten material into a mold cavity through an injection nozzle during an injection molding cycle.

Background Art

[0002] In injection molding, it is known to use a valve pin to adjust the flow of molten material flowing out from a gate nozzle into a mold cavity (see, for example, Patent Document 1). Injection molding of automotive headlights (here taken as an example) is particularly difficult and complex, and the injection position is provided on a large, highly visible, and aesthetically important surface. Therefore, if residues or damage occur in either the injector or the mold components, unacceptable defects will occur in the molded product.

[0003] The valve pin is movable along a stroke composed of a first section closest to the nozzle and a second section farther from the nozzle, and the nozzle is fully opened in the second section.

[0004] The valve pin is moved while being controlled according to different control logics in two sections. That is, it is controlled by position control in the second section and by control of the applied force in the first section. Thereby, the operation of the pin can be adapted according to the current state (real-time state) of the injected material. The purpose of this control is to avoid operations in which excessive force is applied to the pin and prevent damage to one or more components of the hot runner or the mold (excessive force may damage the gate).

[0005] This type of control has a problem in that the actual closed position of the pin can change over time. As a result, burrs may form on the molded part, causing it to be rejected as a defective product. By the time the quality department notices this defect, a large number of molded parts may have been produced, resulting in a lot of wasted material and resources. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent Application Publication No. 23170955 [Overview of the Initiative]

[0007] The main objective of the present invention is to overcome the above-mentioned problems, more specifically to improve the monitoring of defective molded products, and even more specifically to prevent or suppress their occurrence.

[0008] At least one objective is achieved by the claims of this specification.

[0009] One aspect of the present invention is a first monitoring method for an injection molding system. The injection molding system is • A linearly movable valve pin to adjust the flow of molten material out of the (gate) nozzle toward the mold cavity, • An actuator that moves the pin, • A position sensor that detects the position of the pin, • An electronic control unit that drives the actuator, It is equipped with. The monitoring method is, 1) During the nozzle closing process, a step of acquiring data via a sensor indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle, 2) The process involves obtaining a comparison value from the acquired data and comparing the comparison value with a reference value. 3) A step of outputting a signal if the comparison result indicates that the actual position is further from the nozzle than the reference value, This is a monitoring method that includes [specific details about the monitoring method].

[0010] Another aspect of the present invention is a second monitoring method for an injection molding system, 1) A step of closing the injection nozzle by moving the valve pin toward the injection nozzle, and obtaining data via a sensor indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle, 2) A process of obtaining a comparison value from the acquired data and comparing the comparison value with a reference value, 3) A step of outputting a signal if the comparison result indicates that the actual position is further from the nozzle than the reference value, This is a monitoring method that includes [specific details about the monitoring method].

[0011] Another aspect of the present invention is an injection molding apparatus, • Mold cavity and, • An injection nozzle that communicates with the cavity, • A linearly movable valve pin to adjust the flow of molten material out of the nozzle towards the mold cavity, • An actuator that moves the pin, • A position sensor that detects the position of the pin, • Electronic control unit, The electronic control unit is configured to drive an actuator to move the pin toward the nozzle, acquire data via a sensor during the nozzle closing process indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle, acquire a comparison value from the acquired data and compare the comparison value with a reference value, and output a signal if the result of the comparison indicates that the actual position is further from the nozzle than the reference value.

[0012] Each of the above embodiments is subject to the following preferred embodiments, which can be implemented individually or in any combination.

[0013] In one embodiment, the control device is programmed to perform at least one of the main steps of one method and one or each of one or more suitable optional steps defined below.

[0014] In one embodiment, the nozzle has a stroke composed of a first section close to the nozzle and a second section farther from the nozzle, and the pin is moved toward the nozzle by position control in the second section and by control of the force applied to the pin in the first section.

[0015] For this purpose, the control device is preferably configured to drive an actuator to move the pin toward the nozzle by position control in the second section and by control of the force applied to the pin in the first section.

[0016] In one embodiment, step 1) is only executed when the pin is moving in the first section and is being moved by control of the force applied to the pin.

[0017] In one embodiment, steps 1) to 3) are only executed when the pin is moving in the first section and is being moved by control of the force applied to the pin.

[0018] Real-time control of the pin position can be achieved using different strategies.

[0019] In one embodiment, the comparison value is the position of the pin acquired by the sensor, and the reference value is the reference position.

[0020] The first method is 1) During the nozzle closing process, acquiring, via a sensor, data indicating the actual position of the pin when the pin reaches the movement end position toward the nozzle; 2) Comparing the data with a reference value; 3) Outputting a signal when the result of the comparison indicates that the actual position is farther from the nozzle than the reference value. Includes.

[0021] The second method comprises the following steps: 2) A step of comparing the data with a reference location, 3) A step of outputting a signal if the comparison result indicates that the actual position is further from the nozzle than the reference position, Includes.

[0022] Injection molding equipment, • Mold cavity and, • A nozzle that communicates with the cavity, • To adjust the flow of molten material flowing from the nozzle towards the mold cavity, a linearly movable valve pin is provided along a stroke consisting of a first section closer to the nozzle and a second section further away from the nozzle. • An actuator that moves the pin, • A position sensor that detects the position of the pin, • Control device and The control device drives an actuator and moves the pin toward the nozzle by position control in the second section and by control of the force applied to the pin in the first section. During the nozzle closing process, in the first section, the control device acquires data via a sensor indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle, compares this data with a reference position, and outputs a signal if the comparison indicates that the actual position is further from the nozzle than the reference position.

[0023] In one embodiment, the comparison value is calculated by processing one or more position values ​​acquired by a sensor in the same or subsequent injection cycle, and the reference value is a numerical value representing a threshold position. For example, pin position monitoring can be performed on a basis of statistical criteria, for example, by the following method. • The sensor records the actual position of the pin when it reaches its final destination, as P1, P2, ...P n Obtain multiple N values ​​called [values]. • Calculate the standard deviation σ of N values ​​relative to the mean Vm. • Generate a warning signal if the standard deviation σ exceeds the threshold.

[0024] For example, the mean value Vm can be considered as P0, or it can be newly calculated using the following formula.

[0025]

number

[0026] The value of σ can be calculated, for example, by the following formula.

[0027]

number

[0028] In one embodiment, the data acquired by the sensor refers to, but is not limited to, the tip of the valve pin. Any other point on the pin can be used, as long as the reference position is set accordingly.

[0029] In one embodiment, a signal is output after N times (where N≧2) the comparison result indicates that the actual position is further from the nozzle than the reference position. This allows setting an allowable number N, which represents the number of molding cycles for which the valve pin is allowed to move excessively far from the nozzle, without generating a signal. A signal is generated if the distance exceeds the reference position more than N times. This feature enables preventive maintenance, for example, by notifying the operator before a significant deviation occurs, while allowing accidental and sporadic deviations.

[0030] In a more preferred embodiment, a signal is output after N consecutive occurrences (where N≧2) of the comparison result indicating that the actual position is further away from the nozzle than the actual position.

[0031] The signal in step 3) may be, for example, an audible or visual warning signal displayed on a display device, and / or an SMS or email message, and / or a signal that has the function of stopping the operation of the molding system.

[0032] In one embodiment, the actuator is a motor, most preferably a rotary or linear electric motor.

[0033] The sensor may generally be any type of sensor adapted for detecting position. In one embodiment, the position sensor is a rotary encoder connected to the rotational output shaft of a motor, and the position of the shaft is calculated by detecting the angular position of the shaft, which is detected by the encoder. In one embodiment, the position sensor is a linear encoder.

[0034] In one embodiment, the force applied to the pin is controlled by the torque applied to the shaft by a rotary electric motor, and this torque is detected by a sensor.

[0035] In one embodiment, the actuator includes an operating member, such as an output shaft, which is connected to a valve pin via a kinematic chain, and converts, for example, the rotational motion of the operating member into the linear motion of the pin.

[0036] In one embodiment, the molding system includes one or more nozzles having corresponding valve pins, and each of the one or more methods is intended to accept a selection from the user to set up a nozzle to perform steps 1) to 3) and related modifications.

[0037] In one embodiment, each of one or more methods is - A step of defining a zero position representing the target closing position for a valve pin, for example, the tip of the valve pin, - A step of defining the maximum allowable distance value from the target closing position for the valve pin, for example, the tip of the valve pin, - The process of defining the reference position as an upstream position that is the same distance from the zero position as the maximum allowable distance, Includes.

[0038] In one embodiment, if Pzero is the zero position, Dmax is the maximum allowable distance value, and Pref is the reference position, then Dmax = |Pref - Pzero|, and therefore, depending on whether the position value is considered to increase in the direction away from the nozzle or in the direction towards the nozzle, Pref = Pzero + Dmax or Pref = Pzero - Dmax.

[0039] In one embodiment, each of one or more methods is • A process of physically moving the valve pin to the reference closed position, • A step of storing the position (or a step of storing the position in memory), • A step of using the stored value as the zero position (or, in general, a step of using the stored value as the above reference value), It is assumed that this will be included.

[0040] This procedure allows for the determination of the zero value of the valve pin position, improving the accuracy of monitoring positional deviations.

[0041] In one embodiment, each of the one or more methods is assumed to include a step of obtaining a value from the user for setting a reference value (or a step of obtaining a value from the user for which a reference value is set).

[0042] In one embodiment, each of one or more methods is assumed to include a step of obtaining a value from a user for setting a maximum allowable distance value, the maximum allowable position deviation of the valve pin relative to the closed zero position.

[0043] The selections and / or values ​​obtained from the user can be acquired in various ways, for example, from a computer's graphical interface or from software, particularly injection molding process simulation software, such as MoldFlow (trademark).

[0044] In one embodiment, a vehicle, such as an automobile headlight, is manufactured in one or more molding cycles.

[0045] In one embodiment, one or more each Steps 1) to 3) of the method are executed via software, for example, by a microcontroller program. Specifically, in step 1), digital values ​​are acquired from the sensor, for example, via ADC conversion, and / or in step 2), the digital values ​​are processed. In particular, one or each of Vm, σ, Pi, Pzero, Dmax, Pref, and Dmax are digital values. [Brief explanation of the drawing]

[0046] The advantages of the present invention will become clearer from the following description of preferred systems. [Figure 1] Figure 1 shows an injection molding system. [Figure 2] Figure 2 shows a graph of the system variables in Figure 1. [Modes for carrying out the invention]

[0047] A known injection molding machine 100 includes known means (e.g., a cylindrical screw 102) for generating a flow of molten material that is injected into the cavity 12 of the mold 10 via a manifold 16.

[0048] The manifold / distributor 16 (commonly called a hot runner) receives molten material from the molding machine 100 and is heated to distribute the molten material to the cavities 12 through one or more nozzles 20 (the mold 10 may contain multiple cavities 12 that are different from or identical to each other).

[0049] The flow of material flowing out of each nozzle 20 is regulated by a corresponding known valve pin 30. The pin 30 is movable in a linear stroke within the manifold 16 and moves between a closed position where no molten material flows out of the nozzle 20 and an open position where the material flows out toward the cavity 12. The position of the pin 30 determines the flow rate of molten material passing through the nozzle 20.

[0050] Each valve pin 30 is driven by a corresponding electric actuator 40 (preferably rotary, linear, or other type of electric motor). Each actuator 40 includes an actuating member 42, such as an output shaft, which is connected to the valve pin 30 via a kinematic chain 50, causing the pin 30 to move linearly back and forth.

[0051] The sensor 60 directly or indirectly detects the position of the valve pin 30. In one embodiment, the sensor 60 is a rotary encoder connected to member 42, which records its angular position, and the position of the valve pin 30 is detected indirectly.

[0052] The electronic control unit 70 reads the signal output from the sensor 60, for example via an ADC converter, and drives the actuator 40 to dynamically displace the pin 30 during the injection cycle.

[0053] Figure 2 schematically shows the stroke of pin 30.

[0054] In one embodiment, position control operating in terms of absolute value is implemented. With respect to the X-axis, which is in the direction opposite to the nozzle 20 and is oriented parallel to the longitudinal direction of the pin 30, the current position of the tip of the pin 30 measured by the sensor 60 is defined as Patt. Also, a reference position Pref that the tip of the pin 30 must at least reach is defined in order not to cause an abnormality during the closing process. Therefore, in each molding cycle, the control device 70 detects Patt and confirms that the relational expression Patt < Pref holds at the end of the injection cycle. If this does not hold, the control device 70 generates an alarm signal for the user. In order to avoid false alarms and average out sporadic operation variations, it is preferable that the control device 70 generates an alarm signal only when the condition Patt < Pref is not satisfied N consecutive times, where N is 2 or more, for example, N = 10.

[0055] In one embodiment, in order to simplify the calibration of the system, it is possible and preferable to operate using the acquired value with respect to the desired zero position of the pin 30. Since each type of mold, material, or part to be molded has its own unique characteristics, it is convenient to set the optimal zero closing position for the pin 30 each time and then measure the actual position deviation of the pin 30 during molding.

[0056] Referring to FIG. 2, the zero position of the pin 30 is defined as Pzero, and the deviation Dmax from Pzero is also defined. The deviation Dmax indicates the maximum allowable distance that the pin 30 can take with respect to Pzero at the end of the molding cycle with the nozzle 20 blocked. Here, Pref = Pzero + Dmax.

[0057] Preferably, Pzero and / or Dmax can be set via the control device 70, for example, by physically moving the pin 30 to the desired position and then storing the value generated by the sensor 60 (e.g., in the memory of the control device 70). During each molding cycle, the control device 70 detects Pat via the sensor 60 and verifies that Pat < (Pzero + Dmax) is satisfied at the end of the injection cycle. If this is not satisfied, or if it is not satisfied for N consecutive times, the control device 70 generates an alarm signal to the user.

[0058] The warning or alarm signals generated by the system allow for rapid intervention to correct or eliminate any imperfections that prevent pin 30 from reaching the desired closed position. As a result, the number of discarded parts is significantly reduced.

[0059] When the direction of the X-axis is reversed, the control condition becomes Patt > Pref in the first case, and Patt > Pzero-Dmax in the second case.

[0060] In either case, Dmax = |Pref - Pzero| holds true.

Claims

1. A monitoring method for an injection molding system, 1) A step of closing the injection nozzle by moving the valve pin toward the injection nozzle, and obtaining data via a sensor indicating the actual position of the pin when it reaches the end position of its movement toward the nozzle, 2) A step of obtaining a comparison value from the acquired data and comparing the comparison value with a reference value, 3) A step of outputting a signal when the result of the comparison indicates that the actual position is further from the nozzle than the reference value, A method characterized by including

2. The comparison value is calculated by processing one or more position values ​​acquired by the sensor in the same injection cycle or subsequent injection cycles, and the reference value is a numerical value representing the threshold position. The method according to claim 1, characterized in that

3. The comparison value is the position of the pin acquired by the sensor, and the reference value is the reference position. The method according to claim 1, characterized in that

4. The signal is output after the comparison results indicate that the actual position is further from the nozzle than the reference position, N times (where N ≥ 2). The method according to any one of claims 1 to 3, characterized in that

5. The signal is output after the comparison result indicates that the actual position is further away from the nozzle than the actual position, and this condition occurs N times consecutively (where N ≥ 2). The method according to claim 4, characterized in that

6. The signal in step 3) is an audible or visual warning signal to a human user. The method according to any one of claims 1 to 5, characterized in that

7. The signal in step 3) is a signal that has the function of stopping the operation of the molding system. The method according to any one of claims 1 to 6, characterized in that

8. The valve pin is physically moved to the reference closed position, The location is stored in memory, The stored value is used as the reference value. The method according to any one of claims 1 to 7, characterized in that

9. A value is obtained from the user, and the reference value is set by the value obtained from the user. The method according to any one of claims 1 to 8, characterized in that

10. The nozzle has a stroke consisting of a first section close to the nozzle and a second section further away from the nozzle. The pin is moved toward the nozzle by position control in the second section and by control of the force applied to the pin in the first section. Step 1) is performed only in the first section. The method according to any one of claims 1 to 9, characterized in that

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