Injection cylinder lower cavity oil supplementing system for electric pre-molding injection molding machine

Abstract

The invention relates to the technical field of injection molding machines, in particular to an injection cylinder lower cavity oil supplementing system for an electric pre-molding injection molding machine, which comprises a hydraulic power source, an oil supplementing oil way and an intelligent control unit, and the hydraulic power source is in fluid connection with a lower cavity of an injection cylinder through the oil supplementing oil way. The intelligent control unit is electrically connected with the oil supplementing electro-hydraulic proportional overflow valve and the electromagnetic directional valve, and is configured as follows: in the material storage process of the injection molding machine, according to a preset oil supplementing pressure-screw position relation curve, the oil supplementing pressure-screw position relation curve is calculated according to the oil supplementing pressure-screw position relation curve, and the oil supplementing pressure-screw position relation curve is calculated according to the oil supplementing pressure-screw position relation curve. And an analog quantity control signal is dynamically output to the oil supplementing electro-hydraulic proportional overflow valve so as to control the oil supplementing pressure of the lower cavity of the correlation cylinder. By means of intelligent pressure control, the problem that oil supplementing vacuum and plasticizing of the lower cavity of the injection cylinder of the electric pre-molding injection molding machine are unstable is effectively solved, vacuum of the lower cavity of the injection cylinder can be effectively eliminated, sufficient oil supplementing is guaranteed, and the plasticizing stability and the product precision are improved.

Description

TECHNICAL FIELD

[0001] The application relates to an oil supplementing system, in particular to an oil supplementing system for the lower cavity of a shooting cylinder of an electric pre-plastic injection molding machine. BACKGROUND

[0002] As a development direction of modern injection molding machines, the electric pre-plastic technology directly drives a screw by a servo motor, and has the advantages of low energy consumption and high control precision. However, in the plasticizing (material storing) process, the servo motor system does not involve a hydraulic oil circuit, and the lower cavity of the shooting cylinder can only be supplemented with oil from the oil tank by self-suction. For large, vertical or high-precision injection molding machines, this method is prone to form a vacuum in the lower cavity of the shooting cylinder, leading to insufficient oil supplementing, a prolonged material storing time, unstable screw retreat, poor plasticizing uniformity and a series of problems, and finally damaging the size precision and weight consistency of products.

[0003] The existing oil supplementing schemes are mostly for hydraulic drive systems, or supplement oil at a constant pressure by simple on-off control, and cannot meet the stringent requirements of the electric pre-plastic technology for precise control. The fundamental problem lies in the failure to deeply couple and intelligently cooperate the oil supplementing control with the core process parameters (such as the screw position and back pressure) of the plasticizing process. SUMMARY

[0004] In view of the above prior art, the technical problems to be solved by the application are how to overcome the vacuum phenomenon caused by insufficient self-suction oil supplementing in the lower cavity of the shooting cylinder of the electric pre-plastic injection molding machine during the material storing process, and how to realize the dynamic cooperative control of the oil supplementing pressure and the screw position and back pressure parameters, so as to solve the problems of unstable screw retreat and poor plasticizing precision.

[0005] To solve the above problems, in a first aspect, the application provides an oil supplementing system for the lower cavity of a shooting cylinder of an electric pre-plastic injection molding machine, which comprises a hardware execution unit, a sensing and detecting unit and an intelligent control unit.

[0006] The hardware execution unit comprises:

[0007] a hydraulic power source: providing stable pressure oil for the entire oil supplementing system;

[0008] an oil supplementing circuit: fluidly connecting the hydraulic power source and the lower cavity of the shooting cylinder, and sequentially connecting an electromagnetic reversing valve (as a total switch for oil supplementing on-off), an oil supplementing electro-hydraulic proportional relief valve (for accurately adjusting the oil supplementing pressure) and a check valve (for preventing oil backflow and ensuring system sealing) on the oil circuit;

[0009] a back pressure control circuit: fluidly connected with the upper cavity of the shooting cylinder, and provided with a back pressure electro-hydraulic proportional relief valve thereon for controlling the plasticizing back pressure.

[0010] The sensing and detecting unit comprises:

[0011] Electronic ruler: for real-time detection of axial displacement of screw;

[0012] First pressure sensor: set in the lower chamber of the cylinder, for real-time detection of oil supplement pressure;

[0013] Second pressure sensor: set in the upper chamber of the cylinder, for real-time detection of back pressure.

[0014] Intelligent control unit, preferably programmable logic controller (PLC), which is electrically connected with oil supplement electro-hydraulic proportional overflow valve, electromagnetic reversing valve and sensor detection unit, and is configured to execute intelligent oil supplement control logic: during the storage process, according to the preset oil supplement pressure-screw position relationship curve, the analog quantity control signal is output to the oil supplement electro-hydraulic proportional overflow valve to accurately control the oil supplement pressure of the lower chamber of the cylinder; wherein the oil supplement pressure-screw position relationship curve is configured as: the oil supplement pressure value changes segmentally according to the retraction position of the screw.

[0015] Preferably, the intelligent control unit is further configured to:

[0016] Obtain the real-time position signal of the screw, and query the curve to determine the target oil supplement pressure reference value;

[0017] At the same time, obtain the real-time back pressure signal of the upper chamber of the cylinder, and according to the deviation of the real-time back pressure and the preset back pressure value, the target oil supplement pressure reference value is adjusted in real time through PID control algorithm;

[0018] Finally, output the analog quantity control signal to the oil supplement electro-hydraulic proportional overflow valve based on the adjusted pressure value.

[0019] Preferably, the oil supplement pressure-screw position relationship curve is a three-segment curve, which sets a higher pressure in the initial storage segment to realize fast start, sets a relatively stable pressure in the main storage segment to maintain uniform plasticization, and sets a gradually decreasing pressure in the final storage segment to realize smooth deceleration.

[0020] Further preferably, the oil supplement pressure-screw position relationship curve includes:

[0021] The initial storage segment corresponds to 0-20% stroke of the screw, and the oil supplement pressure linearly decreases from 2.0MPa to 1.5MPa;

[0022] The main storage segment corresponds to 20-80% stroke of the screw, and the oil supplement pressure is constant at 1.5MPa;

[0023] The final storage segment corresponds to 80-100% stroke of the screw, and the oil supplement pressure linearly decreases from 1.5MPa to 0.8MPa.

[0024] Preferably, the intelligent control unit is also configured to perform fault diagnosis function, which generates a fault warning signal when an abnormality occurs by monitoring the real-time fluctuation of the replenishment pressure and comparing it with a pre-stored standard health model.

[0025] Secondly, the present invention provides an intelligent fuel replenishment control method for the above-mentioned system.

[0026] This method is executed by an intelligent control unit, which controls the screw position according to a preset oil replenishment pressure-screw position relationship curve. The curve is configured such that the oil replenishment pressure value changes in segments according to the screw's retraction position.

[0027] The method includes the following steps:

[0028] When material storage begins, activate the oil replenishment circuit;

[0029] The screw position is acquired in real time, the pre-stored PL curve is queried, and the target oil replenishment pressure reference value is determined.

[0030] The back pressure value is acquired in real time, and the target pressure value is fine-tuned through a feedback algorithm;

[0031] Output the final control signal to the oil replenishment proportional valve;

[0032] Optionally, real-time fault monitoring can be performed.

[0033] Compared with the prior art, the present invention has the following significant advantages:

[0034] Eliminate oil replenishment vacuum: The active pressure oil replenishment system fundamentally solves the vacuum problem in the lower chamber of the electro-pre-plasticizing injection cylinder, ensuring sufficient and timely oil replenishment.

[0035] Achieving precise plasticizing control: Through intelligent composite control of "position feedforward + back pressure feedback", the real-time dynamic matching of oil replenishment pressure and plasticizing process is realized, which can effectively suppress fluctuations, make the screw retraction more stable, and greatly improve the consistency of products.

[0036] Intelligent and adaptive: The system has the ability to manage process parameters and can call different PL curves for different raw materials, making it highly adaptable.

[0037] High reliability and maintainability: Integrated online fault diagnosis function can detect system anomalies in a timely manner, realize predictive maintenance, and reduce unplanned downtime. Attached Figure Description

[0038] Figure 1 This is a block diagram illustrating the hydraulic principle and control structure of the lower chamber oil replenishment system for the injection cylinder of the present invention;

[0039] Figure 2 This is a flowchart illustrating the intelligent control method executed by the intelligent control unit of the present invention.

[0040] Figure 3 This is a schematic diagram of a typical oil replenishment pressure-screw position relationship curve of the present invention;

[0041] Figure 4 This is a schematic diagram illustrating the fault diagnosis function performed by the intelligent control unit of the present invention. Detailed Implementation

[0042] The present invention will now be clearly and completely described in conjunction with the accompanying drawings and specific embodiments. The following content is merely a typical example of the present invention and is not intended to limit the present invention.

[0043] Example 1

[0044] like Figure 1 As shown, an oil replenishment system for the lower chamber of an electro-pre-plasticizing injection molding machine includes a hardware execution unit, a sensing and detection unit, and an intelligent control unit.

[0045] The hardware execution unit structure and connection relationships are as follows:

[0046] The hardware execution unit includes:

[0047] Hydraulic power source: provides stable pressurized oil for the entire oil replenishment system;

[0048] Oil replenishment circuit: The hydraulic power source is connected to the fluid in the lower chamber of the injection cylinder. The oil circuit is equipped with an electromagnetic directional valve (as the main switch for oil replenishment), an electro-hydraulic proportional relief valve for oil replenishment (used to precisely adjust the oil replenishment pressure), and a check valve (to prevent oil backflow and ensure system sealing).

[0049] Back pressure control oil circuit: It is fluidly connected to the upper chamber of the injection cylinder and is equipped with a back pressure electro-hydraulic proportional relief valve to control the plasticizing back pressure.

[0050] The hydraulic power source consists of a hydraulic pump driven by an electric motor, and its oil outlet is connected to the oil inlet of a two-position two-way solenoid directional valve through an oil pipe.

[0051] The outlet of the electromagnetic reversing valve is connected to the inlet of the replenishing electro-hydraulic proportional relief valve, and the return port of the replenishing electro-hydraulic proportional relief valve is directly connected back to the oil tank.

[0052] The outlet of the electro-hydraulic proportional relief valve is connected to the inlet of the check valve. The outlet of the check valve is ultimately connected to the lower chamber (rodless chamber) of the injection cylinder via an oil pipe.

[0053] In the back pressure control oil circuit, the oil inlet of the back pressure electro-hydraulic proportional relief valve is connected to the upper chamber (rod chamber) of the injection cylinder, and its oil return port is connected back to the oil tank.

[0054] The sensing and detection unit includes:

[0055] Electronic ruler, used to detect the linear displacement of the screw;

[0056] The first pressure sensor is installed at the inlet of the lower chamber of the injection cylinder to detect the replenishment pressure;

[0057] The second pressure sensor, installed at the inlet of the upper chamber of the injection cylinder, is used to detect back pressure.

[0058] The intelligent control unit (PLC) receives signals from all sensors and outputs switching signals to the solenoid directional valve, and outputs analog control signals (such as 0-10V voltage) to the oil replenishing electro-hydraulic proportional relief valve and the back pressure electro-hydraulic proportional relief valve.

[0059] The core of this invention lies in the intelligent control method executed by the intelligent control unit, the process of which is as follows: Figure 2 As shown.

[0060] 1. Generation and storage of PL curves:

[0061] The oil replenishment pressure-screw position relationship curve (PL curve) is established based on a system dynamics model and process optimization. First, by analyzing the forces acting on the system, the theoretical oil replenishment pressure profile required to overcome the inertia, friction, and back pressure of the molten material to achieve smooth motion is estimated. Subsequently, for different raw materials (such as ABS and PC), experimental calibration and optimization are performed based on the theoretical curve, with fine-tuning aimed at plasticizing uniformity and storage time. Finally, the optimal curve is stored in the formula library of the intelligent control unit.

[0062] A typical PL curve for general ABS raw materials is as follows: Figure 3 As shown, the specific parameters are as follows:

[0063] Initial stage (0-20% stroke): The replenishment pressure decreases linearly from 2.0MPa to 1.5MPa. This stage initially provides a large starting thrust to overcome the maximum static friction, followed by a smooth pressure transition to ensure the screw starts quickly and smoothly from a standstill.

[0064] Main section (20-80% stroke): The replenishment pressure is kept constant at 1.5 MPa. This pressure is the optimal value for maintaining a uniform screw retraction speed and achieving stable plasticization.

[0065] In the final stage (80-100% stroke): the replenishment pressure decreases linearly from 1.5MPa to 0.8MPa. This design allows the screw to decelerate smoothly, effectively preventing overshoot at the end of the storage process and material swelling caused by inertial impact, thus ensuring metering accuracy.

[0066] 2. Feedforward-feedback composite control process:

[0067] After material storage begins, the intelligent control unit executes the following steps in a loop:

[0068] S1: Position feedforward:

[0069] Read the electronic ruler signal to obtain the real-time position of the screw (e.g., 50% of the stroke);

[0070] Query the PL curve to obtain the target replenishment pressure reference value at that location. MPa;

[0071] S2: Back pressure feedback acquisition:

[0072] Read the signal from the second pressure sensor to obtain the real-time back pressure value. ;

[0073] The preset target back pressure is ;

[0074] S3: PID feedback fine-tuning:

[0075] Calculate back pressure deviation ;

[0076] The pressure adjustment is calculated using a PID control algorithm.

[0077] ;

[0078] As an example, a set of tuned and effective PID parameters could be: proportional coefficient. Integral coefficient Differential coefficients ;

[0079] Calculated according to the formula ;

[0080] S4: Pressure Synthesis and Output:

[0081] Combine the feedforward value with the feedback adjustment: ;

[0082] The intelligent control unit outputs an analog voltage signal (e.g., 7.7V) corresponding to 1.54MPa to the oil replenishment electro-hydraulic proportional relief valve.

[0083] This composite control strategy ensures that the replenishment pressure can both follow the preset process trajectory and resist back pressure disturbances caused by factors such as changes in melt viscosity in real time.

[0084] Example 2

[0085] The intelligent control unit is also configured to perform fault diagnosis functions, which monitor the real-time fluctuations of the replenishment pressure and compare them with a pre-stored standard health model, generating a fault warning signal when an abnormality occurs.

[0086] like Figure 4 As shown, the fault diagnosis function is implemented through the following steps:

[0087] Model establishment: Under normal system conditions, perform at least 20 standard material storage processes and collect data on replenishment pressure fluctuations. Perform statistical analysis on the data from stable sections (such as the main section), calculate the mean μ and standard deviation σ, and determine the upper and lower envelopes of its normal fluctuation range (e.g., μ ± 2σ). This dataset constitutes the "standard health model".

[0088] Real-time monitoring and judgment: During the production process, the actual standard deviation of the replenishment pressure in the stable range is calculated in real time. Set the fault warning threshold to 3σ. If a fault is detected... If this situation persists for more than three storage cycles, the system is deemed to have an anomaly (such as proportional valve sticking). Simultaneously, if the real-time pressure curve continuously impacts the preset upper and lower envelopes, an early warning is also triggered. The intelligent control unit can provide preliminary indications of the fault type (such as worn seals or leaking check valves) based on the abnormal pattern (such as periodic fluctuations or persistently low pressure).

[0089] The criteria for determining "the real-time pressure curve continuously impacting the normal envelope" are as follows:

[0090] 1. Determination of a single "impact" event:

[0091] An "impact" event is defined as occurring if any of the following conditions are met within a single storage cycle:

[0092] (a) Data point condition: More than 30% of the data points on the real-time pressure curve are located outside the normal envelope within any consecutive 50-millisecond time window;

[0093] (b) Duration condition: The real-time pressure curve remains outside the normal envelope for more than 200 milliseconds.

[0094] 2. Determination of "Sustained Impact" Status:

[0095] If, within three consecutive storage cycles of the system, at least one "impact" event as defined above occurs in each cycle, it is determined to be a "continuous impact" and a fault warning signal is generated.

[0096] Example 3

[0097] To reduce energy consumption, a normally closed two-position two-way solenoid relief valve can be connected in parallel at the output of the hydraulic power source. When the injection molding machine is in a stage where oil replenishment is not required, such as injection, pressure holding, or cooling, the intelligent control unit controls the solenoid relief valve to be energized and open, so that the oil output by the hydraulic pump flows back to the oil tank at a very low pressure, thereby unloading and significantly reducing energy consumption during non-working periods.

[0098] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lower chamber oil replenishment system for an electro-pre-plasticizing injection molding machine, the electro-pre-plasticizing injection molding machine comprising a screw and an injection cylinder driven by a servo motor, characterized in that, include: Hydraulic power source; The oil replenishment circuit connects the hydraulic power source to the lower chamber of the injection cylinder. The oil replenishment circuit is equipped with a solenoid directional valve, an oil replenishment electro-hydraulic proportional relief valve, and a check valve in series. The intelligent control unit is electrically connected to the oil replenishment electro-hydraulic proportional relief valve and the solenoid directional valve; The intelligent control unit is configured to: during the material storage process of the injection molding machine, dynamically output analog control signals to the oil replenishment electro-hydraulic proportional overflow valve according to the preset oil replenishment pressure-screw position relationship curve, so as to control the oil replenishment pressure to the lower chamber of the injection cylinder; The oil replenishment pressure-screw position relationship curve is configured such that the oil replenishment pressure value varies in segments according to the screw's retraction position.

2. The oil replenishment system for the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, The intelligent control unit is configured to perform replenishment pressure control including: Obtain the real-time position signal of the screw; Based on the real-time position signal, the oil replenishment pressure-screw position relationship curve is queried to determine the target oil replenishment pressure value; Obtain the real-time back pressure signal of the upper chamber of the injection cylinder; The target oil replenishment pressure value is finely adjusted in real time based on the deviation between the real-time back pressure signal and the preset back pressure value. Based on the finely adjusted target replenishment pressure value, the analog control signal is generated and output to the replenishment electro-hydraulic proportional relief valve.

3. The oil replenishment system for the lower chamber of the injection cylinder in an electro-pre-plasticizing injection molding machine according to claim 2, characterized in that, The intelligent control unit is configured to perform the real-time fine-tuning using a PID control algorithm.

4. The oil replenishment system for the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, The oil replenishment pressure-screw position relationship curve is a three-segment curve, including: During the initial stage of material storage, corresponding to the screw position of 0-20% of the stroke, the oil replenishment pressure decreases linearly from 2.0MPa to 1.5MPa. In the main storage section, corresponding to the screw position at 20-80% of the stroke, the oil replenishment pressure is constant at 1.5MPa; At the end of the material storage stage, corresponding to 80-100% of the screw stroke, the oil replenishment pressure decreases linearly from 1.5MPa to 0.8MPa.

5. The oil replenishment system for the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, The intelligent control unit is also configured to: Monitor real-time fluctuations in oil replenishment pressure during the material storage process; The real-time fluctuation data is compared with a pre-stored standard health model, which includes the average value and standard deviation of the replenishment pressure in the stable range, as well as the upper and lower envelopes of the normal fluctuation range. A fault warning signal is generated when the standard deviation of real-time pressure continuously exceeds the 3σ range of the standard health model, or when the real-time pressure curve continuously impacts the normal envelope.

6. The oil replenishment system for the lower chamber of the injection cylinder in an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, It also includes a back pressure control oil circuit, which is fluidly connected to the upper chamber of the injection cylinder and is equipped with a back pressure electro-hydraulic proportional relief valve; The intelligent control unit is electrically connected to the back pressure electro-hydraulic proportional relief valve and is configured to output another analog control signal to it during material storage to control the back pressure of the upper chamber of the injection cylinder.

7. The oil replenishment system for the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, The hydraulic power source, solenoid directional valve, replenishing electro-hydraulic proportional relief valve, and check valve are connected via the following topology: The outlet of the hydraulic power source is connected to the inlet of the solenoid directional valve; The oil outlet of the electromagnetic reversing valve is connected to the oil inlet of the replenishing electro-hydraulic proportional relief valve. The outlet of the replenishing electro-hydraulic proportional overflow valve is connected to the inlet of the one-way valve; The outlet of the one-way valve is connected to the lower chamber of the injection cylinder.

8. The oil replenishment system for the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine according to claim 1, characterized in that, The intelligent control unit is a programmable logic controller.

9. An injection molding machine, characterized in that, Includes the injection cylinder lower chamber oil replenishment system for an electro-pre-plasticizing injection molding machine as described in any one of claims 1 to 8.

10. A method for controlling oil replenishment in the lower chamber of the injection cylinder of an electro-pre-plasticizing injection molding machine, characterized in that, include: During the material storage process, the oil replenishment pressure is dynamically controlled based on the preset oil replenishment pressure-screw position relationship curve and the real-time position of the screw. The oil replenishment pressure-screw position relationship curve is configured such that the oil replenishment pressure value varies in segments according to the screw's retraction position. The method further includes: Obtain the real-time back pressure signal of the upper chamber of the injection cylinder; Based on the deviation between the real-time back pressure signal and the preset back pressure value, the target oil replenishment pressure value determined based on the curve is finely adjusted in real time. Based on the finely adjusted target replenishment pressure value, the output pressure of the replenishment electro-hydraulic proportional relief valve is controlled.

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