Conductor detection sensor

Abstract

The invention discloses a metal detection sensor, which comprises a signal source connected with a coil and used for applying an excitation signal to the coil so as to excite the coil to generate a primary magnetic field; the delay trigger module is connected with the signal source and is used for detecting the edge of the excitation signal and sending out a control signal after the edge is detected and a preset delay time is delayed; the signal processing circuit is connected with the coil so as to detect the voltage at the two ends of the coil; and the processor responds to the control signal, and is used for outputting the voltage amplitude at the two ends of the coil when the control signal is output or the integral value of the voltage amplitude at the two ends of the coil within a preset period after the control signal is sent out, and judging whether a detected metal object exists in a detection area adjacent to the coil according to the voltage amplitude or the integral value. The sensor is simple in structure and easy to realize. The detection result is not sensitive to the conductivity of a part of objects to be detected, and the method can be suitable for detected metal objects made of various materials.

Description

Technical Field

[0001] The invention relates to the field of sensors, and in particular to a conductor detection sensor. Background Art

[0002] Existing metal sensors usually apply a specific excitation signal through an excitation coil, which generates a specific magnetic field. The magnetic field generates eddy currents in the conductor, which cause secondary magnetic fields. The magnetic field sensor senses the changes in the superposition of the primary and secondary magnetic fields to determine whether there is a metal object near the coil.

[0003] The way existing sensors achieve a constant detection distance for metals is often to oscillate through hardware and then infer the detection distance through the relationship between the oscillation state and the distance to the object to be detected, or to achieve variable detection distance through algorithm recognition feedback.

[0004] There are several types of inductive sensors for metal distance detection: 1) direct measurement inductive sensors, 2) adjustable detection distance inductive sensors, and 3) inductive sensors with special coil structures.

[0005] 1) Direct measurement sensor: Direct measurement sensor is based on the principle of electromagnetic induction. It directly measures the synthetic magnetic field generated by the excitation coil and the eddy current in the object to be measured, and analyzes the distance between the sensor and the object to be measured through changes in amplitude and phase.

[0006] 2) Detection distance adjustable inductive sensor: Based on the principle of oscillation transformer, when the object to be measured approaches, eddy current loss is generated, which changes the oscillation state of the oscillator and realizes the distance detection of the object to be measured.

[0007] 3) Inductive sensor with special coil structure. This sensor uses multiple coils connected in parallel or in series on a low expansion coefficient circuit board, and works in an oscillating manner with an external capacitor. This coil with a special structure can achieve metal detection distance without attenuation for a variety of metals.

[0008] The above prior art has the following disadvantages:

[0009] a) Based on the oscillation principle, the working environment and circuit parameters have high requirements, and it is difficult to ensure the consistency and versatility of the sensor.

[0010] b) Sensor circuits that work via hardware feedback are complex and costly.

[0011] c) The special structure coil has high requirements on process technology, complex circuit design, and it is difficult to ensure consistency and stability. Summary of the invention

[0012] In view of the above-mentioned defects of the prior art, the present invention provides a conductor detection sensor, which comprises:

[0013] A signal source is connected to the coil and is used to apply an excitation signal to the coil to excite the coil to generate a primary magnetic field;

[0014] A delay trigger module, connected to the signal source, for detecting the edge of the excitation signal and delaying the output of the control signal for a predetermined time after the edge is detected;

[0015] A signal processing circuit is connected to the coil to detect the voltage across the coil; in response to the control signal, the signal processing circuit is used to output the voltage amplitude across the coil when the control signal is output or the integral value of the voltage amplitude across the coil within a predetermined period after the control signal is issued, and to determine whether there is a metal object to be detected in the detection area adjacent to the coil based on the voltage amplitude or the integral value.

[0016] A further improvement of the present invention is that the duration of the predetermined time satisfies that: after the edge of the excitation signal appears, after the predetermined time, for the metal objects of various materials within the target material range, the voltage amplitude or integrated value at both ends of the coil is within the predetermined range.

[0017] A further improvement of the present invention is that the target material range includes: 304 stainless steel, brass, and 6061 aluminum alloy.

[0018] A further improvement of the present invention is that: the duration of the predetermined time is 2.5 to 7 us; and the predetermined period for integrating the voltage amplitude is 0.8 to 1.6 us.

[0019] A further improvement of the present invention is that: the excitation signal is a square wave or a pulse wave; and the delay trigger module sends the control signal at a rising edge or a falling edge.

[0020] A further improvement of the present invention is that the coil is a high inductance coil.

[0021] A further improvement of the present invention is that the signal processing circuit comprises a voltage follower module, a filter module, an amplifying circuit and an integrating circuit which are connected in sequence.

[0022] A further improvement of the present invention is that a filter circuit is provided between the integration circuit and the amplification circuit.

[0023] The advantages of the present invention are as follows:

[0024] a) The structure is simple and easy to implement.

[0025] b) The distance between the sensor and the object to be tested has little effect on the detection results, and it can adapt to a variety of metal objects with large differences in conductivity.

[0026] c) It works in non-resonant mode, and does not require high period stability of square waves or pulses. It can directly use RC oscillation circuit to realize the excitation source.

[0027] d) The detection frequency is high. The sensor of the present invention can complete the detection in a single cycle. The detection frequency depends on the time of extracting features, which means that the sensor response rate can be very high, close to MHz.

[0028] e) There are various voltage extraction methods, such as single-point voltage extraction and regional voltage integral extraction, and the extraction method does not require complicated data processing.

[0029] f) Single coil operation, simple analysis, no need to consider the relative position relationship of the double coils. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of a metal detection sensor of the present invention;

[0031] Figure 2 It is the principle block diagram of the signal processing circuit;

[0032] Figure 3 It is the waveform diagram of the voltage signal at both ends of the coil for different objects under test;

[0033] Figure 4 The figure shows the comparison of the voltage amplitudes corresponding to different measured objects at the predetermined time;

[0034] Figure 5 Shown is a comparison chart of the integral values ​​corresponding to different measured objects within a predetermined period;

[0035] Figure 6 is the waveform diagram of the excitation signal;

[0036] Figure 7 This is the waveform diagram of the voltage signal at both ends of another coil corresponding to different objects under test. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0038] While some exemplary embodiments of the present invention have been described for the purpose of illustration, it should be understood that the present invention may be implemented in other ways not specifically shown in the drawings.

[0039] like Figure 1 As shown, this embodiment provides a metal detection sensor, which includes: a signal source, a delay trigger module and a signal processing circuit. Specifically:

[0040] The signal source is connected to the coil and is used to apply an excitation signal to the coil to excite the coil to generate a primary magnetic field; the excitation signal is a square wave or a pulse wave.

[0041] In some embodiments, the signal source drives the coil in a constant pulse current drive mode. Constant pulse current drive means that the maximum current applied to both ends of the coil is constant. When the current flow direction at both ends of the coil is switched, a pulse with a gradually decreasing amplitude will be generated at both ends of the coil and superimposed on the driving current. Constant pulse current drive only requires a voltage-current conversion circuit to realize pulse constant current drive, which can simplify the drive circuit as much as possible.

[0042] like Figure 6 As shown, the delay trigger module is connected to the signal source, and is used to detect the edge of the excitation signal, and send out the control signal after a predetermined delay time after the edge is detected. In this embodiment, the delay trigger module sends the control signal at the rising edge or the falling edge. Figure 6 The characteristic interval in is the interval where the scheduled time is located.

[0043] The signal processing circuit is connected to the coil to detect the voltage across the coil; it responds to the control signal and is used to output the voltage amplitude across the coil when the control signal is output or the integral value of the voltage amplitude across the coil within a predetermined period after the control signal is issued, and judge whether there is a metal object to be detected in the detection area adjacent to the coil based on the voltage amplitude or the integral value.

[0044] like Figure 2 As shown, the signal processing circuit includes a voltage follower module, a filter module, an amplifier circuit and an integration circuit connected in sequence. The amplifier module can respond to the control signal of the delay trigger module and output the voltage amplitude at both ends of the coil at a predetermined time point after the edge of the excitation signal.

[0045] The integration circuit is used to output the integral value of the voltage amplitude at both ends of the coil within a predetermined period after the control signal is sent. The duration of the predetermined time is 3 to 7 us; the predetermined period for integrating the voltage amplitude is 0.8 to 1.6 us. In a specific embodiment, the predetermined time is 4.2 us; the predetermined period is the interval between 3.8 and 4.6 us after the edge (level switching).

[0046] When the integral value output by the integration circuit is used as the judgment parameter, in order to filter out high-frequency noise, a filter circuit may be provided between the integration circuit and the amplification circuit of the signal processing circuit.

[0047] The selection of the predetermined time and the predetermined period plays an important role in the detection result. The duration of the predetermined time satisfies that: after the edge of the excitation signal appears, after the predetermined time, for the metal objects of various materials within the target material range, the voltage amplitude or integral value at both ends of the coil is within the predetermined range. The "predetermined range" here means that the difference between the maximum value and the minimum value is less than the predetermined value.

[0048] In this embodiment, the signal source gives the coil a square wave or pulse signal as an excitation signal. Here, a 1kHz, 1Vpp (±0.5V) square wave is used as an example. The signal is connected to both ends of the coil (a high inductance coil in this embodiment). Here, a coil with a wire diameter of 0.04mm, 300 turns, an inner diameter of 1mm, a thickness of 1mm, and an outer diameter of 2.5mm is used as an example. At the same time, both ends of the coil are connected to the signal processing circuit as signal output. The signal after filtering and amplification (output 1) is compared as shown in the figure below. Figure 3 .

[0049] Figure 3 The figure shows the voltage across the coil after the coil is suspended in the air (without the object to be tested), on the surface of 304 stainless steel, brass and 6061 aluminum. It can be seen that about 4.2us after the level switching (edge), the metal object under test has a relatively consistent effect on the voltage across the coil, and the voltage is basically the same and within the predetermined range (within the predetermined range means that the difference between the maximum and minimum values ​​at this time is less than the predetermined value). The voltage across the coil of the control group without the object to be tested is significantly higher than the measurement result with the metal object to be tested. By extracting the voltage at this point, the same detection distance sensitivity of the object to be tested can be achieved under different metal objects to be tested, and the classification effect is obvious, such as Figure 4 Therefore, 4.2us is used as the scheduled time.

[0050] Figure 3 The voltage intersection time in is related to the coil inductance parameter. It is necessary to extract the voltage at different intersection times according to the coils with different inductance parameters, such as Figure 7 It can be seen that due to the change in coil inductance, the signal crossover point for detecting different metal objects to be tested is advanced to about 1.4us.

[0051] In the case where the integral value output by the integration circuit is used as the judgment parameter, the predetermined time can be slightly advanced, such as Figure 5 As shown, the predetermined time is selected as 3.8us, the predetermined period is selected as 0.8us (the integration circuit integrates the voltage signal in the interval of 3.8 to 4.6us after the edge) and the integral value is used as the judgment parameter, which can effectively distinguish the metal object to be tested and the situation where there is no object to be tested.

[0052] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A metal detection sensor, Features include: A signal source is connected to the coil and is used to apply an excitation signal to the coil to excite the coil to generate a primary magnetic field; A delay trigger module, connected to the signal source, for detecting the edge of the excitation signal and delaying the output of the control signal for a predetermined time after the edge is detected; A signal processing circuit connected to the coil to detect the voltage across the coil; It responds to the control signal and is used to output the voltage amplitude at both ends of the coil when the control signal is output or the integral value of the voltage amplitude at both ends of the coil within a predetermined period after the control signal is issued, and judge whether there is a metal object to be detected in the detection area adjacent to the coil based on the voltage amplitude or the integral value.

2. A metal detection sensor according to claim 1, Features: The duration of the predetermined time satisfies that: after the edge of the excitation signal appears, after the predetermined time, for the metal objects of various materials within the target material range, the voltage amplitude or integrated value across the coil is within a predetermined range.

3. A metal detection sensor according to claim 2, Features: The target material range includes; 304 stainless steel, brass, and 6061 aluminum alloy.

4. A metal detection sensor according to claim 2, Features: The duration of the predetermined time is 2.5 to 7 us; the predetermined period for integrating the voltage amplitude is 0.8 to 1.6 us.

5. A metal detection sensor according to claim 1, Features: The excitation signal is a square wave or a pulse wave; the delay trigger module sends the control signal at a rising edge or a falling edge.

6. A metal detection sensor according to claim 1, Features: The coil is a high inductance coil.

7. The metal detection sensor according to claim 1, Features: The signal processing circuit comprises a voltage follower module, a filter module, an amplifier circuit and an integration circuit which are connected in sequence.

8. A metal detection sensor according to claim 7, Features: A filter circuit is arranged between the integration circuit and the amplification circuit.

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