A magnetic insertion control circuit and control method suitable for hard label machine

Abstract

The present invention discloses a magnetic insertion control circuit suitable for a hard label machine and a control method thereof. The control circuit includes an excitation signal source module, a precision resistor R1, a compensation capacitor unit, a single-coil sensitive probe, a signal processing module, and a control unit. The single-coil probe has a simple design structure and is easy to install and debug. The use of a compensation capacitor unit design effectively eliminates the frequency offset problem of a traditional single-coil detection circuit. In the process of controlling the insertion of the magnetic rod, when the control unit detects the minimum value of the digital signal of the AD conversion unit, the magnetic rod can be stopped from being pressed in. The control method is simple. The circuit and its control method provide technical support for the fully automated production of hard labels.

Description

Technical field:

[0001] The invention belongs to the technical field of production and processing of commodity anti-theft hard labels, and in particular relates to a magnetic insertion control circuit applicable to a hard label machine and a control method thereof. Background technology:

[0002] In the Electronic Article Surveillance (EAS) system, electronic anti-theft tags can be divided into two categories: soft tags and hard tags according to their structures. Among them, anti-theft hard tags can be further divided into four categories: bottle tags, buckle tags, can tags and other categories. EAS can be divided into radio frequency systems (4.75MHz / 8.2MHz / 10MHz) and acoustic magnetic systems (58KHz) according to their operating frequencies.

[0003] The internal structure of the electronic tag is mainly an RLC oscillation circuit. One of the criteria for determining whether a tag is qualified is to see whether the tag resonates within the resonant frequency range. At present, in the production process of hard tags, the resonant frequency of the hard tag is adjusted by inserting a magnetic bar into the frame wound with a coil to adjust the inductance value in the resonant circuit of the hard tag so that the resonant frequency of the series circuit composed of the inductance and capacitance of the hard tag meets the industry requirements. This process is called the magnetic insertion process.

[0004] According to the existing literature, the sensing technology that provides the resonant frequency signal of the hard tag for the magnetic insertion control device can be divided into single coil, double coil and three coil types according to the number of probe coils. The paper "Research on Quality Parameter Detection Technology of Three-coil Passive Electronic Tags" explains the detection principle of the three-coil hard tag resonant frequency tag, which can effectively solve the problem of indirect acquisition and test frequency offset of single coil and double coil, but its principle ignores the influence of the hard tag on the left receiving coil. The three patents with patent announcement numbers CN107239079A, CN108268929A and CN108549265A disclose magnetic insertion devices and corresponding control methods based on three-coil sensor probe technology, realize semi-automatic magnetic insertion, and the quality and efficiency of magnetic insertion are better than traditional manual magnetic insertion. However, these three patent technologies also have some shortcomings. First, the assembly, debugging and zeroing of the three-coil probe structure are cumbersome. Second, there is a principle error in the detection of resonant frequency by the three-coil sensor technology. Third, the magnetic insertion control method based on the three-coil sensor probe technology is complex and the control accuracy is not high. Summary of the invention:

[0005] In view of the above technical problems, the present invention adopts a single-coil probe and proposes a circuit and a control method suitable for a hard tag machine to insert magnets to control the resonant frequency of the hard tag.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A magnetic insertion control circuit suitable for a hard tag machine, comprising:

[0008] Excitation signal source module, precision resistor R 1 , compensation capacitor unit, single coil sensitive probe, signal processing module, control unit;

[0009] The excitation signal source module is used to generate a resonant frequency F that the hard tag needs to modulate. 0 AC excitation signal;

[0010] The compensation capacitor unit includes a fixed capacitor C 0 and adjustable capacitor C X , the fixed capacitor C 0 and adjustable capacitor C X Parallel connection;

[0011] The precision resistor R 1 The first end of the fixed capacitor C is connected to the output signal end of the excitation signal source module. 0 and adjustable capacitor C X The first end after parallel connection with the precision resistor R 1 The second end of the fixed capacitor C 0 and adjustable capacitor C X The second end after parallel connection is connected to the first end of the single-coil sensitive probe, and the second end of the single-coil sensitive probe is connected to the signal ground electrical end of the excitation signal source module;

[0012] The total capacitance C of the compensation capacitor unit 总 And the equivalent inductance L of the single coil sensitive probe 1 At the resonant frequency F 0 The corresponding angular frequency w 0 When the corresponding capacitive reactance and inductive reactance are equal, that is, w 0 L 1 =1 / w 0 C 总 .

[0013] As a preferred embodiment of the above technical solution, the signal processing module includes a differential signal extraction unit, a valid value detection unit and an AD conversion unit;

[0014] The differential signal extraction unit is used to obtain the differential voltage signal across the precision resistor;

[0015] The effective value detection unit converts the output signal of the differential signal extraction unit into a corresponding DC voltage output;

[0016] The AD conversion unit converts the DC voltage output voltage of the effective value detection unit into a digital value and sends it to the control unit.

[0017] As a preferred embodiment of the above technical solution, the control unit adopts an MSP430 single-chip microcomputer.

[0018] As a preferred embodiment of the above technical solution, the excitation signal source module adopts a programmable waveform generator AD9833, and the excitation signal source module works in a sine wave output mode.

[0019] As a preferred embodiment of the above technical solution, the differential signal extraction unit adopts a differential to single-ended amplifier TL1991.

[0020] As a preferred embodiment of the above technical solution, the effective value detection unit adopts a broadband root-mean-square-to-direct-current converter LTC1968.

[0021] As a preferred embodiment of the above technical solution, the AD conversion unit adopts a compatible I 2 C 16-bit high-precision and low-power analog-to-digital converter ADS1115.

[0022] A control method for a magnetic insertion control circuit of a hard tag machine includes the following steps when used:

[0023] S1: The control unit controls the excitation signal source module to generate the resonant frequency F controlled by the hard tag 0 ;

[0024] S2: Use a multimeter to measure the DC voltage output by the effective value detection unit and adjust the adjustable capacitor C X When the multimeter measures the maximum voltage value, stop adjusting. At this time, w 0 L 1 =1 / w 0 C 总 ;;

[0025] S3: Put the hard tag to be frequency modulated into the magnetic insertion base, control the stepper motor to drive the pressing block to press the magnetic bar into the frame of the hard tag to be frequency modulated, and at the same time, the control unit obtains the digital signal of the AD conversion unit. When the digital signal changes from small to large, the control unit immediately controls the stepper motor to stop pressing down. This is the best control point for the insertion depth of the magnetic bar. Then the control unit controls the stepper motor to reverse and rise, completing a magnetic insertion and frequency modulation process;

[0026] S4: Repeat the above step S3 to complete multiple magnetizations.

[0027] The beneficial effects of the present invention are as follows: the single-coil probe has a simple design structure and is easy to install and debug. The compensation capacitor unit design effectively eliminates the frequency offset problem of the traditional single-coil detection circuit. In the process of controlling the insertion of the magnetic rod, when the control unit detects the minimum value of the digital signal of the AD conversion unit, the magnetic rod can be stopped from being pressed in. The control method is simple. The circuit and its control method provide technical support for the fully automated production of hard tags. Description of the drawings:

[0028] The following drawings are intended only to illustrate and explain the present invention, and are not intended to limit the scope of the present invention.

[0029] Figure 1 This is a schematic diagram of the connection of a circuit module of a magnetic insertion control circuit applicable to a hard tag machine according to an embodiment of the present invention;

[0030] Figure 2 A circuit diagram of a magnetic insertion control circuit applicable to a hard tag machine according to an embodiment of the present invention;

[0031] Figure 3 A schematic diagram of an excitation signal source unit circuit according to an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of a differential unit circuit according to an embodiment of the present invention;

[0033] Figure 5 The present invention is a schematic diagram of a true effective value detection unit circuit according to an embodiment of the present invention.

[0034] Figure 6 The present invention is a schematic diagram of an AD conversion unit circuit according to an embodiment of the present invention.

[0035] Figure 7 This is a schematic diagram of the mechanical structure of a hard tag magnetic insertion and frequency modulation according to an embodiment of the present invention.

[0036] Explanation of symbols in the figure:

[0037] 1- magnetic base, 2- hard label, 3- magnetic rod, 4- sensitive probe, 5- lead screw, 6- stepping motor, 7- pressing block. Specific implementation method:

[0038] like Figure 1 , Figure 2 As shown, the present invention is a magnetic insertion control circuit suitable for hard label machines, including: an excitation signal source module, a precision resistor R 1 , compensation capacitor unit, single coil sensitive probe, signal processing module, control unit;

[0039] The excitation signal source module is used to generate a resonant frequency F that the hard tag needs to modulate. 0 AC excitation signal;

[0040] The compensation capacitor unit includes a fixed capacitor C 0 and adjustable capacitor C X , the fixed capacitor C 0 and adjustable capacitor C X Parallel connection;

[0041] The precision resistor R 1The first end of the fixed capacitor C is connected to the output signal end of the excitation signal source module. 0 and adjustable capacitor C X The first end after parallel connection with the precision resistor R 1 The second end of the fixed capacitor C 0 and adjustable capacitor C X The second end after parallel connection is connected to the first end of the single-coil sensitive probe, and the second end of the single-coil sensitive probe is connected to the signal ground electrical end of the excitation signal source module;

[0042] The total capacitance C of the compensation capacitor unit 总 And the equivalent inductance L of the single coil sensitive probe 1 At the resonant frequency F 0 The corresponding angular frequency w 0 When the corresponding capacitive reactance and inductive reactance are equal, that is, w 0 L 1 =1 / w 0 C 总 .

[0043] The signal processing module includes a differential signal extraction unit, a valid value detection unit and an AD conversion unit.

[0044] The differential signal extraction unit is used to obtain the differential voltage signal across the precision resistor.

[0045] The effective value detection unit converts the output signal of the differential signal extraction unit into a corresponding direct current voltage output.

[0046] The AD conversion unit converts the DC voltage output voltage of the effective value detection unit into a digital value and sends it to the control unit.

[0047] The control unit adopts MSP430 single chip microcomputer.

[0048] The excitation signal source module adopts a programmable waveform generator AD9833, and the excitation signal source module works in a sine wave output mode.

[0049] The differential signal extraction unit adopts a differential to single-ended amplifier TL1991.

[0050] The effective value detection unit adopts a broadband root-mean-square direct-current converter LTC1968.

[0051] The AD conversion unit adopts compatible I 2 C 16-bit high-precision and low-power analog-to-digital converter ADS1115.

[0052] This embodiment also provides a control method for a magnetic insertion control circuit of a hard tag machine, which is characterized in that it includes the following steps when used:

[0053] S1: The control unit controls the excitation signal source module to generate the resonant frequency F controlled by the hard tag 0 .

[0054] S2: Use a multimeter to measure the DC voltage output by the effective value detection unit and adjust the adjustable capacitor C X When the multimeter measures the maximum voltage value, stop adjusting. At this time, w 0 L 1 =1 / w 0 C 总 ; S3: Place the hard tag to be frequency modulated into the magnetic insertion base, control the stepper motor to drive the pressure block to press the magnetic bar into the skeleton of the hard tag to be frequency modulated, and at the same time, the control unit obtains the digital signal of the AD conversion unit. When the digital signal changes from small to large, the control unit immediately controls the stepper motor to stop pressing down. This is the best control point for the insertion depth of the magnetic bar. After that, the control unit controls the stepper motor to reverse and rise, completing a magnetic insertion and frequency modulation process;

[0055] S4: Repeat the above step S3 to complete multiple magnetizations.

[0056] like Figure 2 As shown, the working principle of the circuit of the present invention is: the circuit structure of the electronic hard tag can be equivalent to Figure 2 The right half of the 2 , C 2 , R 2 Series, L 2 , C 2 , R 2 The resonant angular frequency of the series connection is:

[0057]

[0058] R 1 is the precision resistor, L 1 is the equivalent inductance of the single coil sensitive probe, M is the single coil sensitive probe and the parallel label coil inductance L 2 The mutual inductance coefficient between

[0059] Figure 2 The voltage and current vector relationship of the left and right circuit parts is as follows:

[0060]

[0061]

[0062] Z in formula (2) and (3) 1 For R 1 , C 总 , L 1 Total series impedance, Z 1 For R2 , C 2 , L 2 Total series impedance.

[0063] From formula (2-3), we can get the precision resistor R 1 The voltage across the two ends is U 0 The vector is:

[0064]

[0065] Obviously, when the excitation signal source U S When the amplitude remains unchanged, the voltage across the precision resistor is related to the signal source frequency w, and the tag coil inductance L 2 related.

[0066] In the present invention, the signal source frequency w is set to control the target hard tag resonant frequency w 0 and by adjusting the adjustable capacitor C X , so that w 0 L 1 =1 / w 0 C 总 In this case, equation (4) is changed to equation (5).

[0067]

[0068] Obviously, according to formula (5), during the magnetization process, L 2 Gradually increases, at the angular frequency w 0 Under the excitation of the signal source, the total impedance of the hard tag changes from capacitive to inductive. The modulus of the total impedance first decreases and then increases. The vector U 0 The effective value also decreases first and then increases. Therefore, when the present invention is used for the hard label machine to insert the magnet to control the resonant frequency of the hard label, the precision resistor R is detected. 1 The voltage across the two ends is U 0 The minimum value can be used to determine whether the magnetic insertion control requirement has been met.

[0069] In this embodiment, the magnetic insertion control circuit of the machine producing 58KHz acoustic magnetic hard label is taken as an example. The schematic diagram of the circuit unit of a preferred embodiment is as follows: Figure 3-6 shown.

[0070] In a preferred embodiment, the excitation signal source module adopts a DDS (Direct Digital Frequency Synthesis) circuit. Figure 3The AD9833 chip is used in the invention. AD9833 is a low-power, DDS device from ADI that can output sine waves, triangle waves, and square waves. AD9833 does not require external components, and the output frequency and phase can be set through software programming, which is easy to adjust. Its frequency register is 28 bits, and its accuracy is 0.1Hz when the main clock is 25MHz. In this embodiment, a 25MHz crystal oscillator is used to provide a clock signal. The three serial interfaces FSYNC, SCLK, and SDATA are connected to the input and output ports of the single-chip microcomputer MSP430. The output of the AD9833 chip is set to a 58KHz sine wave through programming. The signal output terminal of the AD9833 chip pin 10 is electrically connected to the precision resistor R 1 , Figure 2 The equivalent inductance L of the single coil sensitive probe in 1 A commercially available coil with an inner diameter of 33 mm, an outer diameter of 39 mm, a thickness (height): 2.5 mm, a wire diameter of 0.25 mm, and an inductance value of 480 uH may be preferred.

[0071] In the preferred embodiment, the differential signal extraction unit uses the LT1991 chip, which can be configured as a differential amplifier through the pins. In this chip, 8 precision resistors are packaged on the in-phase and inverting input terminals and output terminals. When used, flexible gain selection can be achieved by properly connecting the external pins without adding external resistors. Figure 4 As shown, the gain is set to 4 and the differential input signal is taken across the precision resistor R1.

[0072] In the preferred embodiment, the effective value detection unit uses the LTC1968 chip, which is a true RMS to DC converter. The LTC1968 can accept single-ended or differential input signals and accurately support a peak factor of up to 4. The amplitude of a sine wave up to 500KHz can be measured with an absolute error of less than 1% (independent of the amplitude stability of the circuit). The bandwidth is up to 15MHz. Figure 5 As shown, the differential signal RMS-1 extracted by the differential signal extraction unit is input through the LTC1968 chip pin 2, and the LTC1968 chip pin 2 is grounded.

[0073] In a preferred embodiment, the AD conversion unit uses an ADS1115 chip, which is an I2C-compatible 16-bit high-precision, low-power analog-to-digital converter (ADC). ADS1115 also uses a programmable gain amplifier (PGA), and ADS1115 can perform conversion at a data rate of up to 860 samples per second (SPS). Figure 6As shown, the output A0 signal of the effective value detection unit is input through the ADS1115 chip pin 4. The I2C protocol interface SCL, SDA, can be connected to the input and output ports of the single-chip microcomputer MSP430 to achieve data communication.

[0074] like Figure 7 As shown, this embodiment provides a schematic diagram of a mechanical device for realizing hard tag insertion and frequency modulation in cooperation with the present invention. The sensitive probe 4 is fixed on the pressing block 7. The magnetic rod 3 can be manually or automatically placed into the hard tag 2 to be frequency modulated, and then the hard tag 2 to be frequency modulated can be placed into the magnetic insertion base 1; the stepping motor 6 is controlled to work, and the lead screw 5 rotates to drive the pressing block 7 to press down, and the precision resistor R is detected. 1 The voltage across the two ends is U 0 The minimum value can be used to determine that the magnetic insertion control requirements are completed, stop the stepper motor from pressing down, reverse and rise, and complete a magnetic insertion frequency modulation.

[0075] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A magnetic insertion control circuit suitable for hard tag machines, characterized in that: include: Excitation signal source module, precision resistor R1, compensation capacitor unit, single coil sensitive probe, signal processing module, control unit; The excitation signal source module is used to generate an AC excitation signal having a frequency that is a resonant frequency F0 that the hard tag needs to modulate; The compensation capacitor unit includes a fixed capacitor C0 and an adjustable capacitor C X , the fixed capacitor C0 and the adjustable capacitor C X Parallel connection; The first end of the precision resistor R1 is connected to the output signal end of the excitation signal source module, and the fixed capacitor C0 and the adjustable capacitor C X The first end after parallel connection is connected to the second end of the precision resistor R1, and the fixed capacitor C0 and the adjustable capacitor C X The second end after parallel connection is connected to the first end of the single-coil sensitive probe, and the second end of the single-coil sensitive probe is connected to the signal ground electrical end of the excitation signal source module; The total capacitance C of the compensation capacitor unit 总 When the angular frequency w0 corresponding to the resonant frequency F0 is equal to the equivalent inductance L1 of the single-coil sensitive probe, the corresponding capacitive reactance and inductive reactance should be equal, that is, w0L1=1 / w0C 总 ; The signal processing module includes a differential signal extraction unit, an effective value detection unit and an AD conversion unit; The differential signal extraction unit is used to obtain the differential voltage signal across the precision resistor; The effective value detection unit converts the output signal of the differential signal extraction unit into a corresponding DC voltage output; The AD conversion unit converts the DC voltage output voltage of the effective value detection unit into a digital value and sends it to the control unit; The excitation signal source module adopts a programmable waveform generator AD9833, and the excitation signal source module works in a sine wave output mode.

2. According to claim 1, a magnetic insertion control circuit suitable for a hard tag machine is characterized in that: The control unit adopts MSP430 single chip microcomputer.

3. According to claim 1, a magnetic insertion control circuit suitable for a hard tag machine is characterized in that: The differential signal extraction unit adopts a differential to single-ended amplifier TL1991.

4. The magnetic insertion control circuit for a hard tag machine according to claim 1, characterized in that: The effective value detection unit adopts a broadband root-mean-square direct-current converter LTC1968.

5. The magnetic insertion control circuit for a hard tag machine according to claim 1, characterized in that: The AD conversion unit adopts compatible I 2 C 16-bit high-precision and low-power analog-to-digital converter ADS1115.

6. A control method for a magnetic insertion control circuit of a hard tag machine according to any one of claims 1 to 5, characterized in that: The steps to use include: S1: The control unit controls the excitation signal source module to generate the resonant frequency F0 controlled by the hard tag; S2: Use a multimeter to measure the DC voltage output by the effective value detection unit and adjust the adjustable capacitor C X When the multimeter measures the maximum voltage value, stop adjusting. At this time, w0L1=1 / w0C 总 ; S3: Put the hard tag to be frequency modulated into the magnetic insertion base, control the stepper motor to drive the pressing block to press the magnetic bar into the frame of the hard tag to be frequency modulated, and at the same time, the control unit obtains the digital signal of the AD conversion unit. When the digital signal changes from small to large, the control unit immediately controls the stepper motor to stop pressing down. This is the best control point for the insertion depth of the magnetic bar. Then the control unit controls the stepper motor to reverse and rise, completing a magnetic insertion and frequency modulation process; S4: Repeat the above step S3 to complete multiple magnetizations.

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