CN100439904C - Smart Metal Detector - Google Patents

Abstract

An intelligent metal detector in the field of non-destructive electromagnetic detection technology. The digital signal processor generates a sine wave through a direct digital synthesis chip, which is sent to the transmitting coil after being amplified by the transmitting circuit, and the receiving coil transmits the signal to the receiving circuit, which is divided into two circuits. The digital signal processor generates two signals through two direct digital synthesis chips and sends them to the two multipliers respectively. The two multipliers pass through two low-pass filters to obtain two separated signals. The two-way signals are sent to the A/D converter, and the data obtained through A/D conversion is sent to the digital signal processor, which analyzes and judges the collected data. device serial communication. The invention adopts DSP and direct digital synthesis technology to replace the analog circuit, and at the same time uses an independent single-chip microcomputer to complete the man-machine dialogue function, which improves the stability and fundamentally changes the defects of the analog circuit.

Description

Smart Metal Detector

technical field

The invention relates to a detector in the technical field of non-destructive electromagnetic detection, in particular to an intelligent metal detector.

Background technique

Metal detectors can be roughly divided into beat type, self-excited induction type, energy consumption type (power absorption type) and balanced type according to the basic principle and detection circuit. Using the balanced type can get relatively high sensitivity, and can detect metal particles below 1mm. Metal detectors currently on the market are basically implemented with analog circuits. The advantage of using an analog circuit is that the circuit is simple and easy to implement. The disadvantage is that the analog system has poor anti-interference and stability. It is difficult to adjust parameters. The use of digital technology can overcome the problems of analog circuits. There are two digital technology solutions for metal detectors: one is basically using analog circuit structure, but in the output part, the output value is sent to the microprocessor for judgment through the A/D converter, and at the same time, man-machine dialogue is added. Function. The other uses a direct digital synthesis method to generate a modulated sine wave, which can control the phase of the sine wave. This method not only improves the resolution of the phase and the stability of the system, but also provides convenience for parameter self-adjustment. At present, most metal detectors on the market are composed of analog circuits. The disadvantages of analog circuits are difficult adjustment and poor stability. Although some metal detectors use microprocessors, they are only used for the output part and man-machine dialogue, without fundamentally changing the defects of analog circuits.

After searching the prior art documents, it was found that U.S. Patent No. 5,786,696, title of invention: METAL DETECTOR FOR IDENTIFYING TARGET ELECTRICAL CHARACTERISTICS, DEPTHAND SIZE, ("a metal detector capable of detecting the type, depth and size of metal objects"). The metal detector uses DSP to process the collected signals, the single-chip microcomputer processes the peripheral interface and liquid crystal display, and uses the fast Fourier method to process and obtain the category of the object. The sine wave used in this patent is not generated by DSP and digital synthesis chip, so the phase cannot be moved and controlled, and cannot be used for parameter adjustment and self-learning.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, and propose an intelligent metal detector, which uses DSP and direct digital synthesis technology to replace the analog circuit, and uses an independent single-chip computer to complete the man-machine dialogue function, which improves the stability. , Fundamentally changed the defects of analog circuits.

The present invention is realized through the following technical solutions, the present invention comprises: digital signal processor (DSP), man-machine dialogue system, three direct digital synthesis chips, two multipliers, two low-pass filters, electrically erasable Memory (E ² PROM), transmitting coil, transmitting circuit, receiving coil, receiving circuit.

The digital signal processor generates a standard sine wave of 50-400kHz through the direct digital synthesis chip, and sends it to the transmitting coil after being amplified by the transmitting circuit to establish an alternating electromagnetic field. The receiving coils are symmetrically distributed on both sides of the transmitting coil. The receiving coil transmits the signal to the receiving circuit, which is divided into two paths and sent to two multipliers respectively. The digital signal processor generates two quadrature signals with a phase difference of 90° through the first direct digital synthesis chip and the second direct digital synthesis chip and sends them to the two multipliers respectively. Two multipliers pass through two low-pass filters to obtain two separate signals sensitive to iron and stainless steel. These two signals are sent to the A/D converter, and the data obtained through A/D conversion is sent to the digital signal. Processor, the digital signal processor analyzes the collected data to determine whether there are metal particles. The man-machine dialogue system consists of a single-chip microcomputer, which communicates serially with a digital signal processor.

The human-machine dialogue system composed of a single-chip microcomputer cooperates with a dot-matrix liquid crystal display, an electrically erasable memory (E ² PROM), a photoelectric switch and a keyboard, and is used for man-machine dialogue and parameter modification. The max485 serial port is used to connect the MCU and the DSP, and the DSP is the lower computer, which is responsible for executing the commands sent by the MCU. The single-chip microcomputer is the upper computer, which is responsible for realizing the man-machine dialogue, specifically through the keyboard, photoelectric switch, dot-matrix liquid crystal display, and electrically erasable memory (E ² PROM). The dot-matrix liquid crystal display is a dot-matrix type used to display Chinese menus. Photoelectric switch 17 is used for displaying the magnitude of output signal and warning. The keyboard is used for parameter input. Electrically Erasable Memory ( ^E2PROM ) is used to store parameters. The LED and the buzzer used for alarm are connected to the single-chip microcomputer and controlled by the single-chip microcomputer. Realization of self-learning function: In order to improve the intelligence of the metal detector, the present invention adds a parameter self-adjusting function. When the self-learning function is activated, the metal detector can automatically adjust the phase according to the collected signal to suppress the product effect.

According to the electromagnetic field theory, the alternation generated by the transmitting coil generates an induced electromotive force of the same frequency, opposite phase, and equal amplitude in the two differentially connected receiving coils, and the cancellation of the two forms the receiving balance. Due to the eddy current effect (related to electrical conductivity) or magnetic effect (related to magnetic permeability), the metal in the alternating magnetic field will generate additional magnetic fields one by one, destroying the distribution of magnetic force lines of the primary field. The additional magnetic field is also called the secondary field. Non-ferromagnetic metals have high conductivity, which include paramagnets (such as manganese, titanium) and diamagnets (such as gold, silver), which can be considered as conductive and non-magnetic substances, which mainly produce eddy current effects, and the magnetic effects can be ignored; Ferromagnetic metals (such as iron, nickel, and cobalt) have high magnetic permeability and high electrical conductivity. They can be considered as both conductive and magnetic materials, which mainly produce magnetic effects and eddy current effects at the same time. The secondary field generated by the metal target will change the magnitude and phase of the current in the receiving coil, so it can be judged whether there is metal through the signal processing of the receiving coil.

The present invention adopts the method of phase detection, and the specific realization is through two multipliers. The basic principle is: Assume that the output of the receiving coil is Uo=Asin(ωt-φ), and the two modulated inputs are orthogonal sine waves of the same frequency, Us=Bsinωt and Uc=Bsin(ωt+90°).

After passing through the multiplier, the outputs are:

Ur＝Uo*Us＝Asin(ωt-φ)*Bsinωt＝-AB/2[cos(2ωt-φ)-co8φ]

Ux＝Uo*Uc＝Asin(ωt-φ)*Bsin(ωt+90)＝-AB/2[sin(2ωt-φ)-sinφ]

After the low-pass filter, the high-frequency components are filtered out, and the output is:

U _R ＝AB/2cosφ

U _X =AB/2sinφ

Since B is a controllable constant, the size of U _R and U _X depends on the phase φ and amplitude A. Studies have shown that the magnitude is related to the size of the object, while the type of the object is related to the phase. When the object moves with the conveyor belt, it will form a curve passing through U _R and U _X to the speed of the conveyor belt. The type of object can be judged by detecting the magnitude and direction of this curve. In the present invention, the size of the phase φ can be set digitally, and the signal of the metal object to be detected can be highlighted by changing the size of φ for different objects to be detected, thereby detecting the metal object. Here it is basic working principle of the present invention.

The special feature of the present invention is that a single-chip microcomputer, a digital signal processor (DSP) and a direct digital synthesis technique (DDS) are used to generate a sine wave whose frequency and phase can be digitally adjusted.

The invention has a self-learning function, which makes the metal detector intelligent. The learning method is to collect the waveforms of _UR and _UX into the DSP, and then obtain the direction and size of the phase shift through the analysis of the two waveforms. Studies have shown that the two waveforms of ferromagnetic materials are in the same direction, which means that it is the characteristic of iron (fe), and when the waveform is reversed, it shows the characteristics of stainless steel (sus). As long as the initial phase can be set between fe and sus, the size and direction of the initial phase φ can be adjusted according to the size and direction of the collected signal, so that the two signals are below the threshold when the product passes through, which meets the requirements of product effect suppression. Thereby separating metal objects from weakly conductive objects. After the self-learning is completed, the set parameters can meet the purpose of separating the product from the metal object. When the product passes through, the output signal is below the threshold value. When the product mixed with metal passes through, the output signal is above the threshold value. In this way The machine can detect the golden house object.

The invention adopts single-chip microcomputer, digital signal processor (DSP) and direct digital synthesis technology (DDS) to generate a sine wave whose frequency and phase can be adjusted digitally. This structure not only makes parameter setting convenient, but also can obtain frequency and phase linearity. It is very difficult to change the frequency and phase of the sine wave obtained by the analog method, and the change of frequency and phase presents a nonlinear change. In the present invention, DSP is not only used as signal processing, but also used for generating modulated sine waves and the control of I/O ports; according to the direction and size of the signal, the method of tracking is used to obtain the category of the object, and the phase is automatically adjusted accordingly to suppress product effect. The invention has a self-learning function, which makes the metal detector intelligent. In addition, the present invention adopts the structure of DSP and single-chip microcomputer upper and lower computers, the single-chip microcomputer is responsible for man-machine dialogue, and DSP is responsible for generating signals, A/D conversion and signal processing. Greatly enhanced the system's function and expansibility. The invention not only improves the stability and reliability of the metal detector, but also greatly improves the intelligence level of the metal detector, and greatly improves the performance-price ratio of the metal detector, so that the metal detector has stronger market competitiveness. The invention is widely used in food, medicine, weaving, clothing, toys, etc., and can detect and remove metal particles mixed therein to ensure food and personal safety.

Description of drawings

Fig. 1 structural block diagram of the present invention

Figure 2 DDS basic principle block diagram

Figure 3 Connection block diagram of single chip microcomputer, digital signal processor and direct digital synthesis chip

Fig. 4 work flow chart of the present invention

Fig. 5 is the self-study main flowchart of the present invention

Fig. 6 is a schematic diagram of self-learning data acquisition and processing of the present invention

Detailed ways

As shown in Figure 1-3, the present invention comprises: digital signal processor 1, man-machine dialogue system 2, direct digital synthesis chip 3,4,5, multiplier 6,7, low-pass filter 8 and 9, transmitting coil 11. Transmitting circuit 12, receiving coil 13, receiving circuit 14. The digital signal processor 1 generates a standard sine wave of 50-400kHz through the direct digital synthesis chip 3, and sends it to the transmitting coil 11 after being amplified by the transmitting circuit 12 to establish an alternating electromagnetic field. The receiving coils 13 are symmetrically distributed on both sides of the transmitting coil. The receiving coil 13 transmits the signal to the receiving circuit 14, which is divided into two paths and sent to the multiplier 6 and the multiplier 7 respectively. The digital signal processor 1 generates two quadrature signals with a phase difference of 90° through the direct digital synthesis chip 4 and the direct digital synthesis chip 5 and sends them to the multiplier 7 and the multiplier 6 respectively. Multiplier 6 and multiplier 7 pass through low-pass filters 8 and 9 to obtain two separate signals sensitive to iron and stainless steel. These two signals are sent to the A/D converter, and the data obtained through A/D conversion The data is transmitted to the digital signal processor, and the digital signal processor analyzes the collected data to determine whether there are metal particles. The man-machine dialogue system 2 is composed of a single-chip microcomputer, and communicates with the digital signal processor 1 serially.

The man-machine dialogue system 2 that the present invention is made up of single-chip computer connects dot-matrix liquid crystal display 16, electric erasable memory (E ² PROM) 10, LED and buzzer 15, photoelectric switch 17 and keyboard 18 that are used for warning are used to cooperate , used for man-machine dialogue and parameter modification. SCM 2 and DSP1 are connected by max485 serial port, and DSP1 is the lower computer, which is responsible for executing the commands sent by the SCM. The single-chip microcomputer is the upper computer, responsible for realizing the man-machine dialogue, specifically through the keyboard 18, the photoelectric switch 17, the dot-matrix liquid crystal 16, and the electrically erasable memory (E ² PROM) 10 to realize. Liquid crystal 16 is dot-matrix type and is used for displaying Chinese menu. The photoelectric switch 17 is used to display the size of the output signal. The LED and the buzzer 15 that are used for warning are controlled by the single-chip microcomputer, and when the output signal is greater than the set signal, the LED and the buzzer 15 act and buzz. The keyboard is used for parameter input. Electrically erasable memory (E ² PROM) 10 is used to store the sine wave, A/D conversion and signal processing required by the parameter DSP1 output according to the set frequency and phase. Realization of self-learning function: In order to improve the intelligence of the metal detector, the present invention adds a parameter self-adjusting function. When the self-learning function is activated, the metal detector can automatically adjust the phase according to the collected signal to suppress the product effect.

As shown in Figure 4, the metal detector switch is turned on. After the machine is powered on, the system will perform initialization work, and then after a relatively long period of adjustment, it will enter the selection stage, and a set of parameters are preset in the metal detector. , can be run directly. You can also enter parameter modification, reset the sensitivity and phase, and then store this parameter in E ² PROM for the next call.

As shown in Figure 5, first set the number of learning times to M, and give up if the requirements cannot be met after M times. After starting the self-learning program, the counter, conveyor belt, and AD converter are turned on, and the products flow in. The digital system starts to collect data, and calculates the size and direction of the curve according to the collected data. Then judge the direction and magnitude of the next phase change according to the magnitude and direction of the curve. This is repeated until the signal decreases below the threshold. If the learning is successful, the learned parameters are stored in E ² PROM.

SENSA＝SENSB＝32.4(比值)，阈值＝2V。As shown in Figure 6, according to the waveform data obtained by each sampling, the same direction and the opposite direction are judged, and the direction of increase and decrease is determined. Then judge whether to change the parameter setting according to the amplitude. The phase angle of each increase or decrease is 1/2 of the previous one. After the new parameter setting is changed, it is judged whether the amplitude is below 1.0V. If it is, it means that the setting is successful. , and save the existing parameter settings. The initial conditions are set as:

SENSA = SENSB = 32.4 (ratio), Threshold = 2V.

Claims (5)

1, a kind of intelligent metal detector, comprise: interactive system (2), first multiplier (6), second multiplier (7), first low-pass filter (8), second low-pass filter (9), transmitting coil (11), radiating circuit (12), receiving coil (13) and receiving circuit (14), it is characterized in that, also comprise: digital signal processor (1), the first Direct Digital synthesis chip (3), the second Direct Digital synthesis chip (4) and the 3rd Direct Digital synthesis chip (5), wherein: digital signal processor (1) produces sinusoidal wave by the first Direct Digital synthesis chip (3), through delivering to transmitting coil (11) behind radiating circuit (12) amplifying circuit, receiving coil (13) passes to receiving circuit (14) with signal, be divided into two-way and deliver to first multiplier (6) and second multiplier (7) respectively, digital signal processor (1) produces two paths of signals by the second Direct Digital synthesis chip (4) and the 3rd Direct Digital synthesis chip (5) and delivers to second multiplier (7) and first multiplier (6) respectively, first multiplier (6), second multiplier (7) is through first low-pass filter (8), second low-pass filter (9) obtains the signal that two-way separates, this two paths of signals is sent into A/D converter, import digital signal processor (1) into through the data that A/D is converted to, digital signal processor (1) carries out analysis and judgement to the data of gathering, interactive system (2) is made of single-chip microcomputer, with digital signal processor (1) serial communication.

2, intelligent metal detector according to claim 1, it is characterized in that, the interactive system (2) that is made of single-chip microcomputer also is connected with electricity erasable memorizer (10), the LED and the hummer (15) of usefulness are used to report to the police, dot matrix lcd (16), optoelectronic switch (17) and keyboard (18), adopt the max485 serial ports to connect between single-chip microcomputer (2) and the digital signal processor (1), digital signal processor (1) is a slave computer, be responsible for carrying out the order that single-chip microcomputer (2) transmits, single-chip microcomputer (2) is a host computer, be responsible for realizing man-machine conversation, concrete by keyboard (18), optoelectronic switch (17) and dot lcd (16), electricity erasable memorizer (10) is realized, the LED and the hummer (15) of usefulness of being used to report to the police is subjected to Single-chip Controlling, LCD (16) is a dot matrix, optoelectronic switch (17) is used to show the size of output signal, electricity erasable memorizer (10) is used for stored parameter, and digital signal processor (1) is exported needed sine wave and A/D conversion and signal Processing according to frequency of setting and phase place.

3, intelligent metal detector according to claim 1 is characterized in that, receiving coil (13) is symmetrically distributed in the both sides of transmitting coil (11).

4, intelligent metal detector according to claim 1, it is characterized in that, described digital signal processor (1) produces sinusoidal wave by the first Direct Digital synthesis chip (3), the sine wave that is produced is: the standard sine wave of 50～400kHz, through delivering to transmitting coil (11) behind radiating circuit (12) amplifying circuit, set up the electromagnetic field of an alternation.

5, intelligent metal detector according to claim 1, it is characterized in that, digital signal processor (1) by the second Direct Digital synthesis chip (4) and the 3rd Direct Digital synthesis chip (5) produce two-way mutually the orthogonal signal of 90 ° of phasic differences deliver to first multiplier (6) and second multiplier (7) respectively.

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