CN105328886B - Melt state sensory perceptual system and its detection method in injection mold based on point electrode - Google Patents

Abstract

The invention discloses melt state sensory perceptual system and its detection method in a kind of injection mold based on point electrode, system includes point electrode capacitor sensor and state recognition system, the point electrode capacitor sensor includes point electrode capacitor and capacitance measurement unit, two electrodes of the point electrode capacitor are located at the inner side of mould dynamic model and quiet mould respectively, two electrodes of the point electrode capacitor are connected with capacitance measurement unit, and the output end of the capacitance measurement unit and the input of state recognition system are connected.The system of the present invention employs the point electrode capacitor arrangement that two electrodes are located at the inner side of mould dynamic model and quiet mould respectively, do not influenceed by cavity surface structure, so that point electrode capacitor sensor may be mounted in the complicated mould cavity of surface texture, flexibility ratio is higher and adaptability is wider.It the composite can be widely applied to injection molding art.

Description

Melt state sensing system and detection method in injection mold based on point electrodes

technical field

The invention relates to the field of injection molding, in particular to a point electrode-based melt state sensing system in an injection mold and a detection method thereof.

Background technique

In the polymer molding process, especially the injection molding process, online real-time measurement or detection of the state of the polymer melt in the injection mold plays a vital role in the detection of the entire injection molding process and the prediction of the final product quality.

The state detection methods of the melt in the injection mold in the traditional injection molding process mainly include:

1) Indirectly infer the state of the melt in the mold by measuring other variables such as cavity pressure and cavity surface temperature, but this method is not easy to operate.

2) Install a glass cavity in the mold, and use a high-speed camera to take pictures of the state of the polymer melt in the mold. This method provides better experimental information, but because the flow and heat transfer process of the melt on the glass surface and the metal mold surface used in industry are completely different, this method cannot be applied to industry, and the application range is relatively small.

3) The state of the melt flowing in the mold is detected by the ultrasonic pulse reflection method. This method detects the position of the melt front flowing in the mold according to the different attenuation of ultrasonic waves by polymer and air. In the mold, multiple sensors are installed. When the front of the melt flows to the installation position of the sensor, the amplitude of the ultrasonic pulse reflected back changes immediately, thereby obtaining the position of the melt flowing in the mold. However, this method can only detect the front end of the melt at the position where the sensor is installed, and can only provide intermittent or discrete information on the flow state of the melt, which is not accurate enough.

In order to overcome the above defects, a method of using a flat capacitive sensor (composed of a flat capacitor and a corresponding capacitance measurement circuit) was proposed to detect the state of the melt in the injection mold. The capacitive sensor uses two flat electrodes installed on both sides of the cavity to sense the state of the plastic melt in the cavity. The experimental results found that the plate capacitor can accurately and effectively measure the material state of the plate plastic product in the mold cavity online, but the two poles of the plate capacitor are difficult to install in the mold with complex surface structure (such as the mold with non-planar structure) in this method. Less flexibility and narrower applicability.

Contents of the invention

In order to solve the above technical problems, the purpose of the present invention is to provide a system for sensing the melt state in an injection mold based on point electrodes with high flexibility and wide applicability.

Another object of the present invention is to provide a method for detecting the melt state in an injection mold based on point electrodes with high flexibility and wide applicability.

The technical solution adopted by the present invention to solve its technical problems is:

A point electrode-based melt state perception system in an injection mold includes a point electrode capacitor sensor and a state recognition system, the point electrode capacitor sensor includes a point electrode capacitor and a capacitance measurement unit, and the two electrodes of the point electrode capacitor are respectively located in the mold Inside the moving model and the static model, both electrodes of the point electrode capacitor are connected to the capacitance measuring unit, and the output end of the capacitance measuring unit is connected to the input end of the state recognition system.

Further, one pole of the point electrode capacitor is a point electrode arranged in the static mold of the mold, and the other pole of the point electrode capacitor is a metal electrode arranged on the movable mold of the mould. Both the point electrode and the metal electrode are connected to the capacitance measurement unit connection.

Further, the electrode capacitor sensor also includes a nest and a screw bolt, the upper part of the shoulder in the point electrode cooperates with the positioning hole of the mold to realize the positioning in the upward direction, and the lower part of the shoulder in the point electrode is nested and The cooperation of the screw bolt realizes the positioning in the downward direction.

Further, the lower part of the shoulder of the point electrode is also provided with a wiring hole connected with the capacitance measuring unit.

Further, an insulating layer is also provided between the point electrodes and the nesting.

Further, the capacitance measurement unit includes a capacitance-voltage conversion circuit, an analog-to-digital converter and an acquisition module, the point electrodes and the metal electrodes are connected to the capacitance-voltage conversion circuit, and the output terminal of the capacitance-voltage conversion circuit passes through the analog-to-digital converter Then it is connected with the input end of the acquisition module.

Further, one pole of the point electrode capacitor is a point electrode arranged on the thimble of the movable mold of the mold, and the other pole of the point electrode capacitor is a metal electrode arranged on the static mold of the mold. Both the point electrode and the metal electrode are connected to the capacitor Measuring unit connection.

Another technical solution adopted by the present invention to solve its technical problems is:

A method for detecting the melt state in an injection mold based on a point electrode, including:

S1. Install the point electrode of the point electrode capacitance sensor at the key point of the injection molding process, and connect the point electrode capacitance sensor with the state recognition system through the capacitance measurement unit, wherein the key point of the injection molding process is located in the mold;

S2. Collect the output voltage of the point electrode capacitive sensor regularly according to the preset sampling period;

S3. Perform state identification according to the collected output voltage and the collection time, so as to detect the state of the melt in the injection mold.

Further, the key points of the injection molding process are the glue inlet, the final filling position or the final cooling position of the injection molding process.

The beneficial effect of the system of the present invention is: the point electrode capacitor structure with two electrodes located on both sides of the movable mold and the static mold of the mold is adopted, which is not affected by the surface structure of the mold cavity, so that the point electrode capacitor sensor can be installed on the surface structure In the complex mold cavity, the flexibility is high and the adaptability is wide. Further, the point electrode capacitor sensor includes a point electrode, a nest and a threaded bolt. The point electrode is positioned by the mutual cooperation between the shoulder, the nest, and the threaded bolt, so that the point electrode can withstand the plastic in the mold cavity. The pressure at the same time ensures that the pole plate does not enter the mold cavity, which is more reliable. Further, directly using the thimble as the point electrode does not need to modify the structure of the mold, which is more convenient and universally applicable.

The beneficial effect of the method of the present invention is: only need to install the point electrode of the point electrode capacitive sensor at the key point of the injection molding process in the mold, and cooperate with the measurement unit and the state recognition system to complete the detection of the state of the melt in the mold, reducing the The influence of the surface structure of the mold cavity on the process of mold state detection is understood, so that the point electrode capacitor sensor can be installed in the mold cavity with complex surface structure, which has high flexibility and wide adaptability.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Fig. 1 is the functional block diagram of the melt state perception system in the injection mold based on the point electrode of the present invention;

Fig. 2 is the structural representation of point electrode capacitor sensor of the present invention;

Fig. 3 is the melt state detection method in the injection mold based on the point electrode of the present invention;

4 is a structural diagram of a one-point electrode capacitor according to an embodiment of the present invention;

Fig. 5 is the structural block diagram of capacitance measurement unit of the present invention;

FIG. 6 is an output voltage-time curve of Embodiment 2 of the present invention.

Reference signs: 1, point electrode; 2, insulating layer; 3, nesting; 4, screw bolt; 5, wiring hole; 6, shaft shoulder; 7, static mold; 8, mold cavity; 9, measuring object; 10. Grounding electrode.

detailed description

Referring to Fig. 1, the melt state sensing system in the injection mold based on point electrodes includes a point electrode capacitor sensor and a state recognition system, the point electrode capacitor sensor includes a point electrode capacitor and a capacitance measurement unit, two of the point electrode capacitor The electrodes are respectively located inside the movable mold and the static mold 7 of the mold. Both electrodes of the point electrode capacitor are connected to a capacitance measurement unit, and the output end of the capacitance measurement unit is connected to the input end of the state recognition system.

Referring to Fig. 2, further as a preferred embodiment, one pole of the point electrode capacitor is a point electrode 1 arranged in the mold static mold 7, and the other pole of the point electrode capacitor 1 is a metal electrode arranged on the mold movable mold , both the point electrode 1 and the metal electrode are connected to the capacitance measuring unit.

The present invention can install the point electrodes on the static mold of the mould, so that the signal line drawn from the point electrodes does not need to change with the change of the movable mold of the mould, so that the obtained signal is more stable.

Referring to Fig. 2, further as a preferred embodiment, the electrode capacitor sensor also includes a nest 3 and a screw bolt 4, and the upper part of the shoulder 6 in the point electrode 1 cooperates with the positioning hole of the mold to realize the positioning in the upward direction, The lower part of the shoulder 6 of the point electrode 1 realizes the positioning in the downward direction through the cooperation of the nest 3 and the screw bolt 4 .

Referring to FIG. 2 , as a further preferred embodiment, the lower part of the shoulder 6 of the point electrode 1 is further provided with a wiring hole 5 connected with a capacitance measuring unit.

As a further preferred embodiment, an insulating layer 2 is also provided between the point electrode 1 and the nest 3 .

Referring to Fig. 5, further as a preferred embodiment, the capacitance measurement unit includes a capacitance voltage conversion circuit, an analog-to-digital converter and an acquisition module, the point electrodes and the metal electrodes are all connected with the capacitance voltage conversion circuit, and the capacitance voltage conversion circuit The output end of the circuit is further connected with the input end of the acquisition module through an analog-to-digital converter.

Further as a preferred embodiment, one pole of the point electrode capacitor is the point electrode 1 arranged on the movable die thimble of the mold, and the other pole of the point electrode capacitor is a metal electrode arranged on the static mold 7 of the mold. Both the electrode 1 and the metal electrode are connected with the capacitance measuring unit.

In the present invention, the thimble can also be directly used as a point electrode after the thimble is specially designed (for example, an insulating layer is added). In this case, the point electrode is on the movable mold of the mold (because the thimble is generally on the movable mold). At this time, the metal electrode corresponding to the point electrode is directly the metal surface corresponding to the mold, that is, it is in the insulating layer of the point electrode. part of the corresponding area. The advantage of this design is that there is no need to modify the mold (because each mold must have a thimble), which is very convenient and easy to implement.

Referring to Figure 3, the method for detecting the state of the melt in the injection mold based on point electrodes includes:

S1. Install the point electrode of the point electrode capacitance sensor at the key point of the injection molding process, and connect the point electrode capacitance sensor with the state recognition system through the capacitance measurement unit, wherein the key point of the injection molding process is located in the mold;

S2. Collect the output voltage of the point electrode capacitive sensor regularly according to the preset sampling period;

S3. Perform state identification according to the collected output voltage and the collection time, so as to detect the state of the melt in the injection mold.

As a further preferred embodiment, the key points of the injection molding process are the glue inlet, the final filling position or the final cooling position of the injection molding process.

As a further preferred embodiment, the point electrode capacitor sensor is a point electrode capacitor sensor as shown in FIG. 2 .

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Embodiment one

With reference to Fig. 1, Fig. 2, Fig. 4 and Fig. 5, the first embodiment of the present invention:

The point electrode-based melt state perception system in the injection mold of the present invention includes a state identification system and a point electrode capacitance sensor composed of a point electrode capacitor and a capacitance measuring unit. The two parts are introduced respectively below.

(1) Point electrode capacitive sensor

In order to meet the needs of online measurement of flat-shaped products (such as mobile phone casings), some people have designed and processed flat-type capacitive sensors, but flat-type capacitors cannot be installed in plastic product molds with complex cavity surface structures. Based on this requirement, the present invention designs a novel point electrode capacitor sensor to solve the online measurement problem of complex surface plastic products.

The point sensor of the present invention can not only play the role of a flat plate capacitive sensor in the form of an array, but also can be rationally arranged in a mold with a non-planar surface structure, and has wider applicability. The capacitive sensor plate of the present invention is designed as a single-point shape (generally 3~6mm round), which can be respectively arranged at key points of the injection molding process such as the glue inlet, the final filling position, and the final cooling position.

The point electrode capacitor sensor of the present invention includes a point electrode capacitor and a capacitance measuring unit. Among them, the schematic diagram of the measurement structure of the point electrode capacitor is shown in Figure 4, and a capacitor is formed between the point electrode and the ground electrode plate. When the measured plastic melt is placed between the above two electrodes, the melt acts as a medium to replace the air medium, causing the capacitance value to increase. In addition, factors such as the material state, thickness, and mold temperature of the melt will also affect the capacitance value during the injection molding process. Variety. Therefore, applying this configuration in the mold can monitor real-time process information by monitoring the capacitance value in real time. The two metal electrodes of the point electrode capacitor are respectively installed in the two halves of the mold (one half is the static mold, and the other half is the moving mold, as shown in Figure 4. During the closing process of the mold, the static mold does not move, and the moving mold faces the direction of the static mold closed, while the two metal plates are isolated from each other), thus forming the two electrodes of the capacitor.

In addition, because both the plate electrode and the mold are made of metal, in order to reduce the complexity of the design, only the point electrode is designed in the present invention, and the other electrode of the point electrode capacitor is replaced by a moving mold connected to the capacitance measurement unit. As shown in Figure 4, a stainless steel plate is installed in the movable mold to form one pole of the point electrode capacitor, while the static mold part containing the point electrode does not need any modification to form the other pole of the point electrode capacitor.

Considering the small size of the point electrode and the positional relationship between the thimble and the mold, the point electrode sensor of the present invention can also be designed to have the same shape as the thimble instead of the thimble, that is, the point electrode is arranged on the thimble of the movable mold of the mold and the metal The electrodes are arranged on the static mold of the mould. Such a design can be quickly transformed from the existing equipment, without changing the existing mold structure, it can be realized only by improving the thimble, avoiding additional processing of mounting holes on the mold, which is more convenient and universally applicable.

The capacitance measurement unit of the present invention is mainly composed of three parts, as shown in Figure 5, wherein the capacitance-voltage conversion module measures the capacitance value of the point electrode capacitor and converts the capacitance value into an analog voltage output, and the output voltage is the same as The capacitance value has a linear relationship; the analog-to-digital conversion module of the capacitance measurement unit converts the output analog voltage into a digital quantity; the acquisition module of the capacitance measurement unit collects the digital quantity output by the capacitance measurement unit and feeds it back to the state recognition system.

(2) Status recognition system

The state recognition system collects and records the digital output of the capacitance measurement unit at different times to obtain the output voltage-time curve, and then analyzes the curve to identify the state of the melt in the mold.

Embodiment two

With reference to Fig. 2, the second embodiment of the present invention:

For the sake of reliability, the point electrode capacitive sensor of the present invention is divided into three parts, which are respectively point electrodes, nests and bolts. The design of the point electrode needs to consider its working environment. In the mold, the point electrode must not only bear the pressure from the plastic in the mold cavity, but also must ensure that its electrode plate does not enter the mold cavity, so as to avoid affecting the product quality. Therefore, the point electrode plate needs to be positioned in two directions. As shown in Figure 2, the positioning of the point electrode in the present invention is realized by the shaft shoulder, and the upper part of the shaft shoulder cooperates with the positioning hole of the mold to realize the positioning in the upward direction; while the lower part of the shaft shoulder cooperates with the nest, and then the screw bolt passes through The thread cooperates with the static mold to realize the positioning in the downward direction.

The present invention designs the point electrode, the nest and the threaded bolt into a structure that cooperates with each other, so as to realize the positioning and assembly of the point electrode capacitor sensor in the mould. The point electrode relies on nesting to realize the cooperative positioning with the positioning bolt, so as to be fixed in the static mold, and sense the plastic state information in the mold through its surface.

When the point electrode capacitor sensor is installed on the mold, the mold needs to be processed (such as drilling, etc.). into the same structure. In this way, for different products, when different sensor position layouts are required, it is only necessary to process different static mold modules, and then assemble the static mold modules into the grooves of the mold, which effectively reduces production costs and improves the applicability of the mold.

In order to form a capacitor, the two poles of the capacitor must be isolated from each other. The present invention uses an electrical insulator to isolate the point electrode from other parts of the mold, and an insulating layer is set between the point electrode and the nest.

Embodiment three

Referring to Fig. 3 and Fig. 6, the third embodiment of the present invention:

The realization process of the method for detecting the state of the melt in the injection mold based on the point electrodes of the present invention is as follows:

(1) Install the point electrode of the point electrode capacitive sensor at the key point of the injection molding process, and connect the point electrode capacitive sensor with the state recognition system through the capacitance measurement unit, wherein the key point of the injection molding process is located in the mold, and the point electrode It can be arranged at the key points of the injection molding process, such as the glue inlet, the final filling position, and the final cooling position;

(2) The state recognition system sets the sampling period and regularly collects the output voltage according to the sampling period;

(3) The state recognition system records the collected output voltage and collection time, and obtains the corresponding output voltage-time curve;

(4) The state identification system analyzes the obtained state identification system curve to obtain the state of the melt in the mold.

The following is an analysis of each state of an injection molding cycle according to the output voltage-time curve:

As shown in Figure 6, in the mold closing stage, the moving mold moves closer to the static mold, and the distance between the two plates of the capacitor in the mold becomes shorter. This change causes the capacitance value of the point electrode capacitor to gradually increase; since the output voltage varies linearly with the capacitance, the voltage value output by the capacitance measurement unit also increases correspondingly until the relative distance between the dynamic mode and the static mode no longer changes . In the injection stage, since the polymer dielectric constant is larger than that of air, as the polymer melt is gradually injected into the mold cavity, the capacitance value of the in-mold capacitor gradually increases, and the output voltage value of the capacitance measurement unit also increases; In the pressure holding stage, a small amount of melt is squeezed into the mold cavity to compensate for the shrinkage of the product caused by the cooling of the melt. At this time, the output voltage of the capacitance measurement unit also increases, but compared with the injection stage, the increase in the output voltage at this stage and the rate becomes very slow. Correspondingly, on the voltage-time curve based on the above process, the output characteristics of the above two stages are very different. If the in-mold capacitor sets the electrode at the last filling point of the cavity, then it can be directly based on this difference in output characteristics Detect the switching time point of the above two stages, and then switch the control stage of the injection molding machine in time to avoid the consequences of mold cavity dissatisfaction or overfilling caused by too early or too late switching. After the holding pressure is over, the injection molding process enters the cooling stage, and the capacitance value of the point electrode capacitor does not change significantly; when the product is fully solidified and the mold is opened, the distance between the two poles of the capacitor suddenly increases, causing the capacitance value and output voltage to drop rapidly. Through the above method, the status recognition system can clearly monitor the status of each stage of the injection molding process, and provide data support for the central control system of the injection molding machine.

Embodiment four

This embodiment illustrates the practical application of the point electrode-based melt state sensing system in the injection mold of the present invention in industrial control.

(1) Through the in-mold melt state sensing system of the present invention, the time point for transition from the injection phase to the pressure holding phase can be determined.

When the mold cavity is filled with melt, the injection molding process switches from the injection phase to the pressure holding phase. Correspondingly, at this time point (that is, the switching point of injection pressure), the injection molding process control is switched from the speed control of the injection section to the pressure control of the pressure holding stage. If the switch is too early, it will cause underfilling, that is, the cavity is not filled; if the switch is too late, it will cause overfilling, that is, the melt overflows. Therefore, it is necessary to accurately and timely determine the time point of injection pressure switchover for the successful operation of the injection molding process. And the in-mold melt state sensing system of the present invention can be used to detect the switching time point of the injection holding pressure. The capacitance value of the in-mold capacitor gradually increases with the injection of the melt. When the melt reaches the point electrode in the mold, although the capacitance value continues to increase, the speed is very slow, as shown in Figure 6. The rate at which stage capacitance increases varies widely. Therefore, if the end of the in-mold capacitor plate is covered at the point where the cavity is last filled, the switching point is easily detected by the output of the melt state sensing system in the injection mold.

(2) Through the in-mold melt state sensing system of the present invention, the product weight can be predicted online to provide a measurement basis for online product weight control.

Product weight is a key indicator of product quality. It can usually only be measured off-line, ie after the product has been released from the mold. Offline measurement is only an afterthought and cannot be used to realize online real-time control of product weight. As shown in Figure 6, the output of the in-mold melt capacitive sensor gradually increases with the gradual inflow of melt during the injection stage, and the output continues to increase during the pressure holding stage, but due to the amount of melt flowing into the cavity at this stage Compared with the speed, the injection stage is obviously reduced, so the increase speed of the output of the sensor is also obviously slowed down. When the gate of the injection molding machine condenses (at this time, the melt can no longer flow into the cavity), the amount of melt flowing into the cavity reaches the maximum, and the output of the corresponding in-mold melt sensor also reaches the maximum. Installing a point electrode capacitance sensor at the gate can accurately sense the capacitance change at the gate, and when the gate is solidified, the output of the electrode capacitance sensor will well represent the final weight of the product. Thus, the output of the melt condition sensing system of the present invention can be used to detect and predict final product weight. In the specific implementation process, first obtain the variation between the output of the system before injection and the maximum output, establish a linear model between the variation and the product weight, and then predict the product weight online based on this model, providing a basis for online closed-loop control of product quality basis of measurement.

The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the described embodiments, and those skilled in the art can also make various equivalent deformations or replacements without violating the spirit of the present invention. , these equivalent modifications or replacements are all within the scope defined by the claims of the present application.

Claims (7)

1. melt state sensory perceptual system in the injection mold based on point electrode, it is characterised in that：Including point electrode capacitor sensing Device and state recognition system, the point electrode capacitor sensor include point electrode capacitor and capacitance measurement unit, the point Two electrodes of electrode capacitor are located at mould dynamic model and quiet mould respectively（7）Inner side, two electricity of the point electrode capacitor Extremely it is connected with capacitance measurement unit, the output end of the capacitance measurement unit and the input of state recognition system are connected；

The one of the point electrode capacitor is extremely arranged on the quiet mould of mould（7）Interior point electrode（1）, the point electrode capacitor Another metal electrode being extremely arranged on mould dynamic model, the point electrode（1）Connect with metal electrode with capacitance measurement unit Connect；

Or, the one of the point electrode capacitor is extremely arranged on the point electrode on mould dynamic model thimble（1）, the point electrode electricity The another of container is extremely arranged on the quiet mould of mould（7）On metal electrode, the point electrode（1）Surveyed with metal electrode with electric capacity Measure unit connection；

The point electrode（1）For 3~6mm circle.

2. melt state sensory perceptual system in the injection mold according to claim 1 based on point electrode, it is characterised in that：Institute Stating point electrode capacitor sensor also includes nesting（3）With helical bolt（4）, the point electrode（1）The middle shaft shoulder（6）Top and mould The positioning hole of tool coordinates the positioning for realizing upward direction, the point electrode（1）The middle shaft shoulder（6）Bottom pass through nesting（3）With spiral shell Line bolt（4）Cooperation, realize positioning in downward direction.

3. melt state sensory perceptual system in the injection mold according to claim 2 based on point electrode, it is characterised in that：Institute State point electrode（1）The middle shaft shoulder（6）Bottom be additionally provided with the wiring hole being connected with capacitance measurement unit（5）.

4. melt state sensory perceptual system in the injection mold according to claim 2 based on point electrode, it is characterised in that： The point electrode（1）With it is nested（3）Between be additionally provided with insulating barrier（2）.

5. melt state sensory perceptual system in the injection mold according to claim 2 based on point electrode, it is characterised in that：Institute Stating capacitance measurement unit includes capacitance-voltage conversion circuit, analog-digital converter and acquisition module, the point electrode（1）With metal electricity Extremely it is connected with capacitance-voltage conversion circuit, the output end of the capacitance-voltage conversion circuit is by analog-digital converter and then with adopting Collect the input connection of module.

6. melt state detection method in the injection mold based on point electrode, it is characterised in that：Including：

S1, the point electrode of point electrode capacitor sensor is arranged at the key point of injection moulding process, and by point electrode capacitor Sensor is connected by capacitance measurement unit with state recognition system, wherein, the key point of injection moulding process is in mould；

S2, according to the timing of default sampling period the output voltage of point electrode capacitor sensor is acquired；

S3, the output voltage according to collection and collection moment carry out state recognition, so as to detect the shape of melt in injection mold State；

The point electrode capacitor sensor is point electrode capacitor sensor as claimed in claim 1 or 2.

7. melt state detection method in the injection mold according to claim 6 based on point electrode, it is characterised in that：Institute The key point of injection moulding process is stated for the glue-feeder of injection moulding process, last filling position or position is finally cooled down.