Automatic control method and system for wall thickness of hollow plastic forming blank

Abstract

The invention discloses a hollow plastic forming blank wall thickness automatic control method which comprises the following steps: presetting a to-be-formed blank wall thickness parameter and a forming equipment parameter, and establishing a parison wall thickness optimization mathematical model according to a nonlinear PID (Proportion Integration Differentiation) operation method; obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model; parison wall thickness control parameters are obtained according to the mouth mold gap curve; and setting the blank wall thickness control parameters to control forming equipment to process the hollow plastic forming blank. An intelligent nonlinear PID control method is introduced through a mathematical model of PLC control software, the large inertia and hysteresis of electro-hydraulic servo are effectively overcome, a closed-loop control system for setting, detection and feedback is rapidly and accurately achieved, and the requirement for parison wall thickness control of hollow plastic forming equipment is met.

Description

Technical Field

[0001] The invention relates to the technical field of hollow plastic molding, and in particular to an automatic control method and system for the wall thickness of a hollow plastic molding blank. Background Art

[0002] The wall thickness control method of the preform used in hollow plastic molding equipment is composed of components such as relays, potentiometers, electronic rulers, hydraulic solenoid valves and switches. It has low control accuracy and poor interference resistance and is easily affected by changes in internal parameters and external environmental factors. For example, changes in time, distance, length, voltage, pressure, temperature, etc. cause fluctuations in the head gap, resulting in poor uniformity of the wall thickness of the product preform, high product scrap rate and unstable quality. Summary of the invention

[0003] In view of the above defects or shortcomings, the object of the present invention is to provide a method and system for automatically controlling the wall thickness of a hollow plastic molding blank.

[0004] To achieve the above purpose, the technical solution of the present invention is:

[0005] A method for automatically controlling the wall thickness of a hollow plastic preform, comprising:

[0006] Preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and establish a mathematical model for optimizing the wall thickness of the blank according to the nonlinear PID calculation method;

[0007] Obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model;

[0008] Obtaining parison wall thickness control parameters according to the die gap curve;

[0009] The blank wall thickness control parameter is set to control the molding equipment to process the hollow plastic molding blank.

[0010] The wall thickness parameters of the blank to be formed and the parameters of the forming equipment are preset, and a mathematical model for optimizing the wall thickness of the blank is established according to a nonlinear PID calculation method, specifically including:

[0011] 1.1. Set the stock setting value and the stock feedback value of the control point. When the actual stock value is not less than the setting value, the wall thickness control starts to run, and the stock setting value and the stock feedback value of each control point are compared and updated. According to the obtained data, the formula (1) is used for calculation:

[0012] 1.2. Define the standard PID controller model as:

[0013]

[0014] In the formula, U(t) is the control variable entering the control object, e(t) is the error signal, T is the sampling period, t is the time point of each calculation, TI is the integral time constant, and TD is the differential time constant;

[0015] 1.3. Discretize the standard PID controller model to obtain:

[0016]

[0017] Wherein, U(k) is the output signal value, e(k) is the difference between the given value and the measured value, j is the error number, and k is the sampling period at the current moment;

[0018] 1.4. Order k d =k p T D Substituting into formula (2), we get:

[0019]

[0020] The step of obtaining the optimal die gap curve according to the parison wall thickness optimization mathematical model specifically includes:

[0021] Each point setting has a mark output and displays the setting value of each point;

[0022] Through stretching and curve fine-tuning, a curve is simulated between two set points to draw a set curve.

[0023] The step of setting the blank wall thickness control parameter to control the molding equipment to process the hollow plastic blank specifically includes:

[0024] Adjust the parison thickness curve so that the PLC controller controls the servo proportional valve to achieve the predetermined die gap after receiving the curve data set by the human-machine interface.

[0025] An automatic control system for the wall thickness of a hollow plastic preform, comprising:

[0026] A modeling unit is used to preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and to establish a mathematical model for optimizing the wall thickness of the blank according to a nonlinear PID calculation method;

[0027] A processing unit, used for obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model;

[0028] An acquisition unit, used for acquiring a parison wall thickness control parameter according to the die gap curve;

[0029] The control unit is used to set the blank wall thickness control parameter to control the molding equipment to process the hollow plastic molding blank.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The present invention provides a method and system for automatically controlling the wall thickness of a hollow plastic molding preform. An intelligent nonlinear PID control method is introduced through the mathematical model of a PLC control software, which effectively overcomes the large inertia and hysteresis of an electro-hydraulic servo, and quickly and accurately realizes a closed-loop control system of setting, detection and feedback, meeting the requirements for controlling the wall thickness of a hollow plastic molding equipment preform.

[0032] Automatically control the wall thickness of the parison to avoid the deviation of the parison wall thickness caused by changes in various internal parameters such as time, distance, length, and external interference such as voltage, temperature, and pressure. Through real-time detection, feedback, and closed-loop automatic adjustment and control of the die gap, combined with intelligent control algorithms, the wall thickness of the hollow plastic molded product is within the effective error range, improving product performance and reducing material consumption to ensure stable product performance. It has high reliability and strong adaptability and can be used in various complex and harsh environments. It can realize functions such as precise control of actions, conversion operations of analog quantities, data processing, and I / O signal processing.

[0033] PWS touch-type industrial-grade human-machine interface and PLC control module adopt real-time time-sharing multi-tasking operating system, which can define the priority and cycle time of each task; the cycle time can reach 1 millisecond, and the real-time performance of the whole system can be optimized. Various wall thickness curves and straight lines can be set on the touch screen, making full use of the functions of the PLC control module to realize analog quantity conversion calculation, data processing, online monitoring and closed-loop control, etc., and can achieve fast and accurate control of the wall thickness of the parison. It is simple to operate, easy to implement, and low in cost. It can be applied to hollow plastic molding equipment to improve product performance, reduce material consumption, reduce scrap rate, improve qualification rate, and enhance the performance and automation level of the whole machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the method for automatically controlling the wall thickness of a hollow plastic molding blank of the present invention;

[0035] Figure 2 This is a diagram of an automatic control system for the wall thickness of a hollow plastic molding blank;

[0036] Figure 3 It is a schematic diagram of the hardware structure of the method for controlling the wall thickness of a hollow plastic molding device of the present invention;

[0037] Figure 4 It is a schematic diagram of the structure of the electro-hydraulic servo system of the present invention;

[0038] Figure 5 It is a schematic diagram of setting and detecting the wall thickness curve of the parison of the present invention;

[0039] Figure 6 It is the principle diagram of the intelligent nonlinear PID of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0041] like Figure 1 As shown, the present invention adopts a method for automatically controlling the wall thickness of a hollow plastic preform, comprising:

[0042] S1. Preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and establish a mathematical model for optimizing the wall thickness of the blank according to the nonlinear PID calculation method;

[0043] S2. Obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model;

[0044] S3, obtaining the parison wall thickness control parameter according to the die gap curve;

[0045] S4, setting the blank wall thickness control parameter to control the molding equipment to process the hollow plastic molding blank.

[0046] The wall thickness parameters of the blank to be formed and the parameters of the forming equipment are preset, and a mathematical model for optimizing the wall thickness of the blank is established according to a nonlinear PID calculation method, which specifically includes:

[0047] 1.1. Set the stock setting value and the stock feedback value of the control point. When the actual stock value is not less than the setting value, the wall thickness control starts to run, and the stock setting value and the stock feedback value of each control point are compared and updated. According to the obtained data, the formula (1) is used for calculation:

[0048] 1.2. Define the standard PID controller model as:

[0049]

[0050] In the formula, U(t) is the control variable entering the control object, e(t) is the error signal, T is the sampling period, t is the time point of each calculation, TI is the integral time constant, and TD is the differential time constant;

[0051] 1.3. Discretize the standard PID controller model to obtain:

[0052]

[0053] Wherein, U(k) is the output signal value, e(k) is the difference between the given value and the measured value, kp is the adjustable gain, j is the error number, and k is the sampling period at the current moment;

[0054] 1.4. Order k d =k p T D Substituting into formula (2), we get:

[0055]

[0056] The step of obtaining the optimal die gap curve according to the parison wall thickness optimization mathematical model specifically includes:

[0057] Each point setting has a mark output and displays the setting value of each point;

[0058] Through stretching and curve fine-tuning, a curve is simulated between two set points to draw a set curve.

[0059] The step of setting the blank wall thickness control parameter to control the molding equipment to process the hollow plastic blank specifically includes:

[0060] Adjust the parison thickness curve so that the PLC controller controls the servo proportional valve to achieve the predetermined die gap after receiving the curve data set by the human-machine interface.

[0061] In addition, the present invention also provides a hollow plastic preform wall thickness automatic control system, comprising:

[0062] A modeling unit is used to preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and to establish a mathematical model for optimizing the wall thickness of the blank according to a nonlinear PID calculation method;

[0063] A processing unit, used for obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model;

[0064] An acquisition unit, used for acquiring a parison wall thickness control parameter according to the die gap curve;

[0065] The control unit is used to set the blank wall thickness control parameter to control the molding equipment to process the hollow plastic molding blank.

[0066] For example, Figure 2 The system of the method for controlling the wall thickness of the parison of the hollow plastic molding equipment is shown. Figure 2 It can be seen that the control system hardware includes: PWS touch industrial-grade human-machine interface 1, PLC control module 2, servo displacement sensor 3 that can detect and feedback, actuator electro-hydraulic servo valve 4, servo oil source 5, and spindle 6. Figure 3 and Figure 4It can be seen that the software part includes 1 and 2 and the method of establishing the mathematical model.

[0067] The PWS touch-type industrial-grade human-machine interface is connected to the PLC control module.

[0068] The PLC control module includes a CPU processing unit, an I / O unit, an AI / AO unit, a communication port, a signal processing board, etc. The CPU processor is connected to a human-machine interface through the communication port, and the AI / AO unit is connected to a servo displacement sensor and an electro-hydraulic servo valve.

[0069] The actuator electro-hydraulic servo valve is connected with the signal processing board and the hydraulic system.

[0070] The detection and feedback servo displacement sensor is connected to the signal processing board and the AI / AO unit.

[0071] The detection and feedback servo displacement sensor is connected to the core shaft to detect and feedback the die clearance.

[0072] The software control program directly controls the size of the detection and control die gap, including the establishment and implementation of a mathematical model, the programming of a human-machine interface and a PLC control module.

[0073] For example, Figure 5 As shown, the present invention uses a real-time time-sharing multi-tasking operating system to define the priority and cycle time of each task; 1 is to set various straight and curved lines, adjust the wall thickness curve of the parison and related process parameters, 3 is to display the curve, and can real-time 6 status and other information of the hollow plastic molding equipment, 2 receives the curve data and parameter information set by the human-machine interface to control 4 to achieve the predetermined 7, the whole process requires the control system to respond in milliseconds, it not only has fast hardware computing speed, but also has advanced software and digital control theory algorithms, which meets the requirements of the parison wall thickness control system to respond quickly, 7 precise control, stable and reliable, and real-time detection.

[0074] The working process of the present invention is:

[0075] According to user needs, input the parison wall thickness curve in the human-machine interface. The curve setting method is as follows: Figure 4 As shown, each point setting has a marked output and displays the set value of each point. There are two modes: stretching and curve fine-tuning. Curve fitting is used between two set points. Both the overall and single points can be adjusted. There is a confirmation link for wall thickness graphic modification to avoid misoperation.

[0076] The electro-hydraulic servo system of this control system adopts a jet-type electro-hydraulic servo valve, the most prominent advantages of which are fast response speed, large output power, precise control and high stability. Figure 3 shown.

[0077] Input the parison wall thickness curve distribution data and the mold function type, time and other corresponding parameters in the human-machine interface. This control method will use the intelligent nonlinear PID principle to establish a mathematical model for the parison wall thickness optimization of hollow plastic molding equipment, and solve the model to obtain the optimal die gap curve. When the set wall thickness changes, this control system automatically reads the relevant parameters and regenerates a new parison wall thickness curve. The schematic diagram of the intelligent nonlinear PID is shown in the figure below. Figure 6 As shown, Continuous is the setting for continuous wall thickness control, and Accumulator is the setting for accumulator wall thickness control. In continuous wall thickness control, continuous wall thickness control works; in accumulator wall thickness control, accumulator wall thickness control works. Co is the filter constant, which is used by the D part of the PID controller. Act is the feedback of the servo oil port cylinder linear displacement sensor, which enters the PID controller after filtering. The PID controller scan cycle is 2 milliseconds, and the Io scan is also refreshed to complete the output at the same time. The intelligent nonlinear PID system has strong influence ability, good robustness, and certain adaptability, which can realize the automatic control of the wall thickness of the parison.

[0078] It is obvious to those skilled in the art that the above-mentioned specific examples are only preferred embodiments of the present invention. Therefore, the improvements and changes that may be made by those skilled in the art to certain parts of the present invention still embody the principles of the present invention and achieve the purpose of the present invention, and all belong to the scope of protection of the present invention.

Claims

1. A method for automatically controlling the wall thickness of a hollow plastic preform, characterized in that: include: Preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and establish a mathematical model for optimizing the wall thickness of the blank according to the nonlinear PID calculation method; Obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model; Obtaining parison wall thickness control parameters according to the die gap curve; The blank wall thickness control parameter is set to control the molding equipment to process the hollow plastic molding blank.

2. The method for automatically controlling the wall thickness of a hollow plastic preform according to claim 1, characterized in that: The wall thickness parameters of the blank to be formed and the parameters of the forming equipment are preset, and a mathematical model for optimizing the wall thickness of the blank is established according to a nonlinear PID calculation method, specifically including: 1.

1. Set the stock setting value and the stock feedback value of the control point. When the actual stock value is not less than the setting value, the wall thickness control starts to run, and the stock setting value and the stock feedback value of each control point are compared and updated. According to the obtained data, the formula (1) is used for calculation: 1.

2. Define the standard PID controller model as: In the formula, U(t) is the control variable entering the control object, e(t) is the error signal, T is the sampling period, t is the time point of each calculation, TI is the integral time constant, and TD is the differential time constant; 1.

3. Discretize the standard PID controller model to obtain: Wherein, U(k) is the output signal value, e(k) is the difference between the given value and the measured value, kp is the adjustable gain, j is the error number, and k is the sampling period at the current moment; 1.

4. Order k d =k p T D Substituting into formula (2), we get:

3. The method for automatically controlling the wall thickness of a hollow plastic preform according to claim 2, characterized in that: The step of obtaining the optimal die gap curve according to the parison wall thickness optimization mathematical model specifically includes: Each point setting has a mark output and displays the setting value of each point; Through stretching and curve fine-tuning, a curve is simulated between two set points to draw a set curve.

4. The method for automatically controlling the wall thickness of a hollow plastic preform according to claim 1, characterized in that: The step of setting the blank wall thickness control parameter to control the molding equipment to process the hollow plastic blank specifically includes: Adjust the parison thickness curve so that the PLC controller controls the servo proportional valve to achieve the predetermined die gap after receiving the curve data set by the human-machine interface.

5. An automatic control system for the wall thickness of a hollow plastic preform, characterized in that: include: A modeling unit is used to preset the wall thickness parameters of the blank to be formed and the parameters of the forming equipment, and to establish a mathematical model for optimizing the wall thickness of the blank according to a nonlinear PID calculation method; A processing unit, used for obtaining an optimal die gap curve according to the parison wall thickness optimization mathematical model; An acquisition unit, used for acquiring a parison wall thickness control parameter according to the die gap curve; The control unit is used to set the blank wall thickness control parameter to control the molding equipment to process the hollow plastic molding blank.

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