Radio frequency heat sealing adaptive adjustment method, system and medium based on digital frequency generator

Abstract

The present invention relates to a radio frequency heat-sealing adaptive adjustment method, system and medium based on a digital frequency generator, the method comprising the steps of: obtaining voltage signals and current signals of a heat-sealing head collected in real time; calculating power, frequency and impedance through voltage signals and current signals; obtaining the adapted heat-sealing frequency and power through the calculated impedance; comparing the calculated frequency and power with the obtained heat-sealing frequency and power; and adjusting the frequency and power of the output signal through the comparison result. The present invention adopts digital signal generation technology, and through a heat-sealing radio frequency signal adaptive control method, automatically switches among three frequency signals of 13.56MHz, 27.12MHz and 40.68MHz according to the characteristics of the material to improve the heat-sealing effect; and collects the output voltage and current in real time for frequency calculation and power calculation, and through a feedback system, controls the signal frequency and power in real time, without considering the changes in system characteristics, and realizes precise control of heat-sealing power and frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency heat sealing, and particularly to a radio frequency heat sealing adaptive adjustment method, system and medium based on a digital frequency generator. Background Art

[0002] A radio frequency heat sealer applies an alternating electromagnetic field to the object to be heat sealed. In order to comply with the frequency standards specified in the national electromagnetic compatibility standard, high-frequency energy such as 13.56 MHz, 27.12 MHz or 40.68 MHz is usually generated; under the action of an alternating electric field, PVC (Polyvinylchloride) molecules are polarized and charged and oscillate and rub at this frequency to generate heat. When the material melts due to heat, it is squeezed by the heat sealing head clamp to achieve the purpose of sealing and cutting.

[0003] For materials to be heat sealed with different thicknesses, radio frequency heat sealers with different frequencies usually need to be selected. The lower the heat sealing frequency, the greater the heat sealing depth; the higher the heat sealing frequency, the smaller the heat sealing depth. For some objects with larger thicknesses, low-frequency heat sealing is required; in addition, due to the low magnetic permeability of the material to be heat sealed, high-frequency heat sealing is required to improve the heat sealing efficiency. Commonly used radio frequency heat sealers usually adopt a fixed frequency, which can achieve a good heat sealing effect for materials with smaller thicknesses, but for materials with larger thicknesses, the results of incomplete heat sealing or heat sealing failure may occur.

[0004] The core of high-frequency and radio frequency heat sealing is the radio frequency generating device. Currently, ceramic oscillators or crystal oscillators are commonly used to generate high-frequency oscillation signals. However, temperature changes, oscillator aging, fluctuations in excitation level, changes in load capacitance, and fluctuations in power supply voltage may all cause the frequency of the radio frequency signal generated by this open-loop oscillation circuit to drift. Since the change in frequency will affect the heat sealing depth and heat sealing power, affecting the heat sealing effect, and in China, the selection of heat sealing frequency needs to comply with the regulations of the national electromagnetic compatibility standard. In addition, during the entire heat sealing process, too large a heat sealing power will cause material damage, and too small a heat sealing power will cause heat sealing failure. The heat sealing power usually needs to conform to a certain power curve. Some devices ignore this point and use a constant signal for heat sealing. However, during the heat sealing process, the distance between the heat sealing head clamps becomes smaller, resulting in continuous changes in the load impedance, causing impedance mismatch, thereby leading to a decrease in the output power, and it is difficult to control the stable output of the power; in addition, some devices achieve re-matching of the impedance by switching relays, but generally can only achieve segmented impedance matching, with a very slow response speed, unable to control the power in real time, nor can it achieve real-time adjustment of the power according to the set curve. At the same time, parameters such as temperature will also affect the impedance of the load and the performance of the power amplifier, resulting in attenuation of the output power. Summary of the Invention

[0005] To achieve the above objects and other advantages of the present invention, the first object of the present invention is to provide a radio frequency heat sealing adaptive adjustment method based on a digital frequency generator, including the following steps:

[0006] Obtain the voltage signal and current signal of the heat sealing head collected in real time;

[0007] Calculate power, frequency and impedance through the voltage signal and the current signal;

[0008] Obtain the adapted heat sealing frequency and power through the calculated impedance;

[0009] Compare the calculated frequency and power with the obtained heat sealing frequency and power;

[0010] Adjust the frequency and power of the output signal according to the comparison result.

[0011] Further, the obtaining the adapted heat sealing frequency and power through the calculated impedance includes the following steps:

[0012] Establish an electrical model of the heat sealing head, and the electrical model is an adjustable capacitor;

[0013] Obtain the thickness of the sample to be heat sealed through the calculated impedance;

[0014] Adapt the optimal heat sealing frequency and heat sealing power through the calculated thickness.

[0015] Further, the two poles of the heat sealing head are equivalent to a parallel capacitor, and the capacitance calculation formula of the parallel capacitor is

[0016]

[0017] where ε is the dielectric constant, S is the area of the plate facing each other, k is the electrostatic constant, and d is the distance between the plates.

[0018] Further, the obtaining the thickness of the sample to be heat sealed through the calculated impedance includes the following steps:

[0019] Obtain the correlation between impedance and characteristic frequency and characteristic peak;

[0020] Derive the correlation between the plate distance and the characteristic frequency and characteristic peak through the correlation between impedance and characteristic frequency and characteristic peak;

[0021] Use a PWM signal with a duty cycle less than the preset duty cycle to control the heat sealing head to clamp the heat sealing material to avoid its deformation;

[0022] Measure the characteristic peak and characteristic frequency with standard materials of different thicknesses, and fit to obtain a curve;

[0023] According to the fitted curve, the thickness of the material to be heat-sealed is obtained by interpolation.

[0024] Further, the method further includes the following steps:

[0025] Judge whether the thickness of the sample to be heat-sealed exceeds a preset value. If so, reduce the heat-sealing frequency; otherwise, increase the heat-sealing signal power.

[0026] Further, the method further includes the following steps:

[0027] Judge whether the measured characteristic peak value is less than a preset value. If so, it is determined as no-load.

[0028] Judge whether the calculated power exceeds a preset value. If so, it is determined as overload, and an overload protection program is executed.

[0029] The second object of the present invention is to provide a computer or embedded system-readable storage medium, on which program instructions are stored, and when the program instructions are executed, a radio frequency heat-sealing adaptive adjustment method based on a digital frequency generator is implemented.

[0030] The third object of the present invention is to provide a radio frequency heat-sealing adaptive adjustment system based on a digital frequency generator, including a controller, a digital-to-analog converter, and a signal processing circuit. The controller is used to execute a radio frequency heat-sealing adaptive adjustment method based on a digital frequency generator to adjust the frequency and power of the output radio frequency signal in real time. The digital-to-analog converter is used to convert the radio frequency signal output by the controller into an analog signal, and the signal processing circuit is used to process the analog signal output by the digital-to-analog converter and apply the processed signal to the heat-sealing head.

[0031] Further, the signal processing circuit includes a power amplification circuit, a filtering circuit, and an impedance matching circuit, and the analog signal output by the digital-to-analog converter is processed in sequence through the power amplification circuit, the filtering circuit, and the impedance matching circuit.

[0032] Further, the controller is a field programmable gate array, and the digital-to-analog converter is a direct digital frequency synthesizer.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The present invention provides a radio frequency heat-sealing adaptive adjustment method based on a digital frequency generator, which adopts digital signal generation technology. Through a heat-sealing radio frequency signal adaptive control method, according to the characteristics of the material, it automatically switches among three frequency signals of 13.56 MHz, 27.12 MHz, and 40.68 MHz to improve the heat-sealing effect; and it collects the output voltage and current in real time for frequency calculation and power calculation, and through a feedback system, it controls the signal frequency and power in real time, without considering the change of system characteristics, and realizes the precise control of heat-sealing power and frequency.

[0035] The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and be implemented in accordance with the content of the specification, the following provides a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. The specific implementation manners of the present invention are given in detail by the following embodiments and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of this application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0037] Figure 1 is the principle of the radio frequency heat sealing adaptive adjustment system based on a digital frequency generator for Embodiment 1 Figure 1 ;

[0038] Figure 2 is the principle of the radio frequency heat sealing adaptive adjustment system based on a digital frequency generator for Embodiment 1 Figure 2 ;

[0039] Figure 3 is the flowchart of the radio frequency heat sealing adaptive adjustment method based on a digital frequency generator for Embodiment 2;

[0040] Figure 4 is a schematic diagram of the impedance model of the heat sealing head for Embodiment 2;

[0041] Figure 5 is a schematic diagram of the impedance simulation curve of the heat sealing head for Embodiment 2;

[0042] Figure 6 is a schematic diagram of the measured impedance curve of the heat sealing head for Embodiment 2;

[0043] Figure 7 is a schematic diagram of the relationship between the pole pitch and the characteristic peak value and characteristic frequency for Embodiment 2;

[0044] Figure 8 is a schematic diagram of a computer or embedded system readable storage medium for Embodiment 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Next, in combination with the accompanying drawings and specific implementation manners, the present invention will be further described. It should be noted that, on the premise of no conflict, any combination of the following described embodiments or technical features can form a new embodiment.

[0046] Embodiment 1

[0047] A radio frequency heat sealing adaptive adjustment system based on a digital frequency generator, such as Figure 1 、 Figure 2As shown, it includes a controller, a digital-to-analog converter, and a signal processing circuit. In this embodiment, the controller is a field programmable gate array, which not only solves the deficiencies of custom circuits but also overcomes the drawback of limited gate circuits in original programmable devices. The digital-to-analog converter is a direct digital frequency synthesizer, which adopts direct digital frequency synthesis technology to improve the frequency stability and accuracy of the signal generator to the same level as the reference frequency and can perform fine frequency adjustment within a wide frequency range. The controller is used to execute the radio frequency heat sealing adaptive adjustment method based on a digital frequency generator, calculate impedance, power, and frequency through the voltage signal and current signal of the heat sealing head collected in real time, estimate the thickness of the sample to be heat sealed according to the change of the heat sealing head impedance, match the best frequency and power according to the thickness of the sample to be heat sealed, compare the calculated power and frequency with the matched power and frequency, and adjust the frequency and power of the output radio frequency signal in real time. For a detailed description of the method, reference can be made to the corresponding description in the following method embodiments, which will not be elaborated here. The digital-to-analog converter is used to convert the radio frequency signal output by the controller into an analog signal, and the signal processing circuit is used to process the analog signal output by the digital-to-analog converter and apply the processed signal to the heat sealing head. Using a field programmable gate array and a direct digital frequency synthesizer to generate radio frequency signals, the frequency is adjustable, the power is adjustable, and the stability is higher.

[0048] The signal processing circuit includes a power amplifier circuit, a filter circuit, and an impedance matching circuit. The analog signal output by the digital-to-analog converter is processed successively through the power amplifier circuit, the filter circuit, and the impedance matching circuit. In this embodiment, the impedance matching circuit is a digital impedance matching array, and the system selects different matching networks according to different heat sealing frequencies.

[0049] Embodiment 2

[0050] The adjustment method of the radio frequency heat sealing adaptive adjustment system based on a digital frequency generator in Embodiment 1 realizes judging the thickness of the material to be heat sealed and can automatically select the heat sealing frequency according to the thickness. As Figure 3 shown, it includes the following steps:

[0051] Obtain the voltage signal and current signal of the heat sealing head collected in real time;

[0052] Calculate power, frequency, and impedance through the voltage signal and current signal; specifically, calculate the power by multiplying the voltage signal and the current signal through a multiplier, calculate the frequency through the sampling time, and calculate the ratio of the voltage signal to the current signal to obtain the impedance.

[0053] Obtain the adapted heat sealing frequency and power through the calculated impedance; specifically, it includes the following steps:

[0054] Establish an electrical model of the heat sealing head. As Figure 4 shown, since the pole pitch of the heat sealing head is variable, an adjustable capacitor C is used.v It is described as follows. The two poles of the heat-sealing head are equivalent to a parallel capacitor, and the capacitance value calculation formula of the parallel capacitor is

[0055]

[0056] Among them, ε is the dielectric constant, S is the facing area of the plates, k is the electrostatic constant, and d is the distance between the plates.

[0057] The impedance measured under no-load of the heat-sealing head is:

[0058]

[0059] Among them, R 1 is the load resistance, X L1 = j2πfL 1 is the inductive reactance of the load, is the capacitive reactance of the load, C v and L 1 are the load capacitance and load inductance respectively, L 1 can be 0, and f is the signal frequency.

[0060] The thickness of the sample to be heat-sealed is obtained through the calculated impedance; specifically, it includes the following steps:

[0061] Obtain the correlation between the impedance and the characteristic frequency and characteristic peak; Figure 5 For the impedance simulation curve of the heat-sealing head (C v1 <C v2 <C v3 ), Figure 5 in the order from left to right, they are the simulation curves of C v3 , C v2 , C v1 respectively. As Figure 5 shown, the impedance reaches a maximum value at a specific frequency, which is the peak impedance of the heat-sealing head. When C v becomes larger, the frequency of this peak point gradually becomes smaller, and the amplitude also gradually decreases.

[0062] Through the correlation between the impedance and the characteristic frequency and characteristic peak, the correlation between the plate distance and the characteristic frequency and characteristic peak is deduced; the measured impedances when the distances between the two poles of the heat-sealing head are 6mm, 4mm, 2mm, and 0mm are respectively as Figure 6 shown, Figure 6 in the order from top to bottom, they are the measured curves corresponding to the distance between the two poles of the 6mm heat-sealing head, the measured curves corresponding to the distance between the two poles of the 4mm heat-sealing head, the measured curves corresponding to the distance between the two poles of the 2mm heat-sealing head, and the measured curves corresponding to the distance between the two poles of the 0mm heat-sealing head, Figure 6 the measured impedance of the heat-sealing head and Figure 5The simulation impedance is consistent. When the pole pitch becomes smaller, the capacitance value increases, the peak frequency decreases, and the amplitude also decreases. The material thickness has a positive correlation with the characteristic peak and characteristic frequency, and as the pole pitch increases, the characteristic peak and characteristic frequency increase monotonically.

[0063] Use a PWM signal with a duty cycle less than a preset duty cycle (such as 30%) to control the heat-sealing head to clamp the heat-sealing material to avoid its deformation.

[0064] Such as Figure 7 As shown, the characteristic peak and characteristic frequency are measured with standard materials of different thicknesses, and a curve is obtained by fitting. Figure 7 The dotted curve in [[ ]] is the peak curve, and the solid curve is the frequency curve.

[0065] According to the fitted curve, the thickness of the material to be heat-sealed is obtained by interpolation.

[0066] Adapt the optimal heat-sealing frequency and heat-sealing power according to the calculated thickness. Among them, the relationship between thickness and heat-sealing frequency and power can be obtained through experience or experiments.

[0067] When the heat-sealing head touches, the characteristic peak disappears, and the discrimination of the no-load situation can be realized. That is, it is judged whether the measured characteristic peak is less than the preset value. If so, it is determined that it is no-load.

[0068] Judge whether the calculated power exceeds the preset value. If so, it is determined that it is overloaded, and the overload protection program is executed. The function of overload protection can be realized through power detection.

[0069] Calculate the distance between the two poles of the heat-sealing head according to the changes of the characteristic frequency and peak, and judge whether the thickness of the sample to be heat-sealed exceeds the preset value. If so, reduce the heat-sealing frequency, otherwise increase the power of the heat-sealing signal through the field-programmable gate array to control the direct digital frequency synthesizer.

[0070] Compare the calculated frequency and power with the obtained heat-sealing frequency and power.

[0071] Adjust the frequency and power of the output signal according to the comparison result.

[0072] The present invention realizes thickness detection based on impedance change, and can select signals with different frequencies for samples to be heat-sealed of different sizes; adopts closed-loop control to accurately control the heat-sealing frequency and heat-sealing power; can realize no-load and overload judgment without additional circuits.

[0073] Embodiment 3

[0074] A computer or embedded system-readable storage medium, such as Figure 8As shown, program instructions are stored thereon, and a radio frequency thermal welding adaptive adjustment method based on a digital frequency generator is implemented when the program instructions are executed. For a detailed description of the method, reference may be made to the corresponding description in the above method embodiments, which will not be repeated here.

[0075] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, commodity or device including the element.

[0076] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0077] The above is only for the embodiments of this specification and is not used to limit one or more embodiments of this specification. For those skilled in the art, one or more embodiments of this specification can have various changes and transformations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of one or more embodiments of this specification shall be included within the scope of the claims of one or more embodiments of this specification.

Claims

1. A radio frequency heat sealing adaptive adjustment method based on a digital frequency generator, characterized in that: The following steps are involved: Obtain the voltage signal and current signal of the heat sealing head collected in real time; Calculate power, frequency and impedance through the voltage signal and the current signal; Obtain the appropriate heat-sealing frequency and power through the calculated impedance; Compare the calculated frequency and power with the obtained heat-sealing frequency and power; Adjust the frequency and power of the output signal based on the comparison results; The method of obtaining the adapted heat-sealing frequency and power by calculating the impedance comprises the following steps: Establishing an electrical model of the heat sealing head, wherein the electrical model is an adjustable capacitor; The thickness of the sample to be heat-sealed is obtained through the calculated impedance; The optimal heat sealing frequency and heat sealing power are adapted according to the calculated thickness.

2. The RF heat sealing adaptive adjustment method based on a digital frequency generator according to claim 1, characterized in that: The two electrodes of the heat sealing head are equivalent to parallel capacitors, and the capacitance calculation formula of the parallel capacitor is: Among them, ε is the dielectric constant, S is the area facing the plates, k is the electrostatic force constant, and d is the distance between the plates.

3. The RF heat sealing adaptive adjustment method based on a digital frequency generator according to claim 1, characterized in that: The step of obtaining the thickness of the sample to be heat-sealed by calculating the impedance comprises the following steps: Obtain the correlation between impedance, characteristic frequency and characteristic peak value; Through the correlation between impedance and characteristic frequency and characteristic peak value, the correlation between plate spacing and characteristic frequency and characteristic peak value is derived; A PWM signal with a duty cycle less than a preset duty cycle is used to control the heat sealing head to clamp the heat sealing material to prevent it from deforming; The characteristic peak value and characteristic frequency are measured with standard materials of different thicknesses, and the curve is fitted; According to the fitted curve, the thickness of the material to be heat-bonded is obtained by interpolation.

4. The RF heat sealing adaptive adjustment method based on a digital frequency generator according to claim 3, characterized in that: The following steps are also included: Determine whether the thickness of the sample to be heat-sealed exceeds the preset value. If so, reduce the heat-sealing frequency; otherwise, increase the heat-sealing signal power.

5. The RF heat sealing adaptive adjustment method based on a digital frequency generator according to claim 3, characterized in that: The following steps are also included: Determine whether the measured characteristic peak value is less than the preset value, if so, determine it as no-load; Determine whether the calculated power exceeds the preset value. If so, it is determined to be overloaded and the overload protection program is executed.

6. A computer or embedded system readable storage medium, characterized in that: Program instructions are stored thereon, and when the program instructions are executed, the method according to any one of claims 1 to 5 is implemented.

7. The radio frequency heat sealing adaptive adjustment system based on digital frequency generator is characterized by: It includes a controller, a digital-to-analog converter, and a signal processing circuit. The controller is used to execute the method described in any one of claims 1 to 5, and adjust the frequency and power of the output radio frequency signal in real time. The digital-to-analog converter is used to convert the radio frequency signal output by the controller into an analog signal. The signal processing circuit is used to process the analog signal output by the digital-to-analog converter and apply the processed signal to the heat sealing head.

8. The RF heat sealing adaptive adjustment system based on a digital frequency generator according to claim 7, characterized in that: The signal processing circuit includes a power amplifier circuit, a filter circuit and an impedance matching circuit. The analog signal output by the digital-to-analog converter is processed by the power amplifier circuit, the filter circuit and the impedance matching circuit in sequence.

9. The RF heat sealing adaptive adjustment system based on a digital frequency generator according to claim 7, characterized in that: The controller is a field-editable gate array, and the digital-to-analog converter is a direct digital frequency synthesizer.

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