Capacitive sensor with high response frequency

Abstract

The invention discloses a high-response-frequency capacitive sensor, and the sensor comprises a voltage conversion module which is used for supplying power to a signal processing module according to a PWM signal; the signal processing module comprises an oscillation module, a detection module and a comparison output circuit; the oscillation module is used for generating an oscillation signal acting on a polar plate of the capacitor; the detection module is used for detecting the voltage of the polar plate in combination with the PWM signal; the comparison output circuit is used for comparing the detection result with an action threshold value; and the MCU module is used for adjusting the output signal according to the output of the comparison module output circuit, and has the advantages that the response frequency is improved, the requirement of high beat number in the automation industry is met, and the production efficiency is improved. The EMC performance is improved, the anti-interference capability is enhanced, and the stable work of the product in a complex electromagnetic environment is ensured. And the frequency period of the pulse signal can be flexibly modified through the MCU, so that the performance is optimal.

Description

Technical Field

[0001] The invention relates to the field of sensors, and in particular to a high response frequency capacitive sensor. Background Art

[0002] A capacitive sensor is a sensor that converts the change of the measured non-electrical quantity into the change of capacitance. In order to ensure the stability of the signal, traditional capacitive sensors use large capacitors to filter the analog signal passing through the detection module, which restricts its response frequency. At present, the frequency of capacitive sensors is generally low. This technical solution is conducive to improving the response frequency performance of capacitive sensors.

[0003] like Figure 7 As shown, the traditional capacitive sensor rectifies the oscillating signal generated by the plate circuit through a diode, and then uses the charging and discharging characteristics of the capacitor to filter the signal through a large capacitor to obtain a smooth DC level signal. Since there is a capacitor charging and discharging process in its circuit part, in order to have a relatively stable voltage signal, its RC time constant needs to be as large as possible, which means a reduction in the response frequency; the detection frequency of the sensor is very limited.

[0004] Existing capacitive sensors have the following disadvantages:

[0005] a) Traditional capacitive sensors have large filtering parameters to ensure signal stability and low response frequency, which cannot meet high-frequency detection requirements.

[0006] b) Traditional capacitive sensors are very susceptible to interference in strong electromagnetic interference environments, causing false alarms, missed detections, crashes, damage, etc., affecting the normal use of the product.

[0007] c) The existing technical solutions have low sensitivity in converting the change of plate capacitance into the change of voltage and current signals. In addition, the metal shell shields the electric field. Therefore, the detection distance of the traditional capacitive proximity switch is relatively short and long-distance detection cannot be achieved. Summary of the invention

[0008] In view of the above-mentioned defects of the prior art, the present invention provides a high response frequency capacitive sensor to improve the high frequency response frequency, resist strong electromagnetic interference, and extend the detection distance.

[0009] To achieve the above objectives, the present invention provides a high response frequency capacitive sensor, comprising:

[0010] A voltage conversion module, used for supplying power to the signal processing module according to the PWM signal;

[0011] The signal processing module includes an oscillation module, a detection module and a comparison output circuit; the oscillation module is used to generate an oscillation signal to act on the plate of the capacitor; the detection module is used to detect the voltage of the plate in combination with the PWM signal; the comparison output circuit is used to compare the detection result with the action threshold;

[0012] The MCU module is used to adjust the output signal of the sensor according to the output of the comparison module output circuit.

[0013] A further improvement of the present invention is that it also includes a power supply module, which uses a first-level low-voltage difference linear regulator to provide a high-voltage electrical signal for the oscillation module and power the voltage conversion module; and uses a linear voltage regulator module U1 to further stabilize the voltage and power the MCU module.

[0014] A further improvement of the present invention is that it also includes a power supply module, which uses a transistor and a voltage stabilizing circuit to use a resistor voltage divider to adjust the output voltage to provide a high-voltage electrical signal for the oscillation module; and uses a linear voltage stabilizing module U1 to further stabilize the voltage to power the MCU module.

[0015] A further improvement of the present invention is that the PWM signal is generated by an MCU module, or is generated by a logic gate circuit in conjunction with a capacitor charging and discharging circuit.

[0016] A further improvement of the present invention is that the voltage conversion module adopts a common-emitter amplifier circuit to amplify the PWM signal, and the VCC signal and the GND signal outputted by the voltage conversion module are used to supply power to the signal processing module respectively.

[0017] A further improvement of the present invention is that the oscillation module of the signal processing module is powered by the VCC signal and the GND signal output by the voltage conversion module; the oscillation module includes:

[0018] The oscillation module includes: a resistor R28, a high-precision voltage source U6, and a resistor R37 connected in sequence between VCC and GND; an input end of the high-precision voltage source U6 is connected to the first node n1, and an output end thereof is connected to the first node n1 through a capacitor C32, and is connected to GND through a capacitor C34; a ground end of the high-precision voltage source U6 is connected to GND through a resistor R37; a transistor Q4 is a PNP transistor, a base 1 of which is connected to VCC through a resistor R27, an emitter 2 of which is connected to VCC, and a collector 3 of which is connected to the capacitor C34. A plate C- of the capacitance sensor is connected; the plate C- is also connected to the output end of the high-precision voltage source U6 through a resistor R34; another plate C+ of the capacitance sensor is connected to the first node n1 through a resistor R30, and is connected to the base of another transistor Q3; the transistor Q3 is an NPN transistor, whose collector is connected to the base of the transistor Q4, and the emitter of the transistor Q3 is connected to the second node n2 through an inductor L1; the second node n2 is connected to GND through a resistor R32; and the plate C- is also connected to the second node n2.

[0019] A further improvement of the present invention is that the detection module uses an analog switch for detection.

[0020] A further improvement of the present invention is that: the comparison output circuit is a comparator with hysteresis; the hysteresis is adjusted through the adjustable resistance value.

[0021] The advantages of the present invention are as follows:

[0022] a) The response frequency is improved to meet the high cycle requirements of the automation industry and improve production efficiency.

[0023] b) EMC performance is improved and anti-interference ability is enhanced to ensure that the product can work stably in complex electromagnetic environments.

[0024] c) The frequency period of the pulse signal can be flexibly modified through the MCU to achieve optimal performance.

[0025] d) The performance of capacitive sensors is constantly improving, tending towards longer detection distances, higher response frequencies, and more stable detection systems. The present invention has great advantages in improving the performance of capacitive sensors.

[0026] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a principle diagram of a high response frequency capacitive sensor of the present invention;

[0028] Figure 2 This is the schematic diagram of the power module;

[0029] Figure 3 is the schematic diagram of the voltage conversion module;

[0030] Figure 4 is a waveform diagram of the output signal of the voltage conversion module;

[0031] Figure 5 is the circuit diagram of the signal processing module;

[0032] Figure 6 The circuit diagram of the comparison output circuit is shown in FIG.

[0033] Figure 7 It is a schematic diagram of a capacitive sensor in the prior art;

[0034] Figure 8 This is the schematic diagram of another power module;

[0035] Fig. 9 Schematic diagram of the circuit for PWM signal generation. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] like Figure 1 As shown, this embodiment provides a high response frequency capacitive sensor, which includes: a power module, a voltage conversion module, a signal processing circuit, an MCU module and an output circuit. Specifically:

[0039] like Figure 2 As shown, in some embodiments, the power module converts the external DC: 10-30V power supply into a low-dropout linear regulator (LDO) to step down the voltage to VIN, provides a high voltage signal to the oscillation module, increases the plate oscillation amplitude, and then stabilizes the voltage from VIN to VIN1 through the linear regulator U1 to provide voltage for the MCU module.

[0040] like Figure 8As shown, in other embodiments, the power module uses a transistor T1 and a voltage stabilizing circuit to use a resistor divider to adjust the output voltage to provide a high-voltage electrical signal VIN for the oscillation module; and uses a linear voltage stabilizing module U1 to further stabilize the voltage to obtain VIN1 to power the MCU module.

[0041] like Figure 3 As shown, the voltage conversion module removes the DC bias of the 156KHz PWM signal generated by the MCU through the decoupling capacitors C2 and C12 to obtain a square wave signal with a DC reference voltage of 0V. The signal then passes through the common emitter amplifier circuit to generate a square wave voltage signal (VCC) for PGND. The VCC signal passes through the decoupling capacitor C10 to generate a GND signal with the same frequency as VCC but different amplitude. Therefore, GND is used as a reference, and VCC is a fixed voltage signal. This VCC voltage serves as the power supply voltage of the subsequent circuit and provides the oscillation signal of the system; D2, D3, and D4 are clamping diodes. The output waveform of the voltage conversion module is shown in Figure 1. Figure 4 As shown; Figure 4 The red waveform is VCC, and the blue waveform is GND; the frequency and phase of the VCC signal and the GND signal are the same, and the voltage difference is constant. The voltage conversion module can increase the oscillation excitation voltage and improve the detection sensitivity.

[0042] In some embodiments, the PWM signal may not be generated by an MCU, but may be generated by Fig. 9 The circuit uses a logic gate circuit in conjunction with a capacitor charging and discharging circuit to generate a PWM signal of a predetermined frequency.

[0043] like Figure 5 As shown, the signal processing module includes an oscillation circuit, a detection module ( Figure 5 U4), comparison output circuit (such as Figure 6 shown).

[0044] VIN indirectly provides a high voltage signal to the oscillator module. Figure 3 The voltage conversion module outputs VCC and GND signals to the oscillation module. Figure 5As shown, in this embodiment, the oscillation module includes: a resistor R28, a high-precision voltage source U6, and a resistor R37 connected in sequence between VCC and GND. The input end of the high-precision voltage source U6 is connected to the first node n1, and its output end is connected to the first node n1 through a capacitor C32, and is connected to GND through a capacitor C34; the ground end of the high-precision voltage source U6 is connected to GND through a resistor R37. The transistor Q4 is a PNP transistor, whose base 1 is connected to VCC through a resistor R27, whose emitter 2 is connected to VCC, and whose collector 3 is connected to a plate C- of the capacitive sensor; the plate C- is also connected to the output end of the high-precision voltage source U6 through a resistor R34. Another electrode plate C+ of the capacitive sensor is connected to the first node n1 through a resistor R30, and is connected to the base of another transistor Q3; the transistor Q3 is an NPN transistor, whose collector is connected to the base of the transistor Q4, and the emitter 2 of the transistor Q3 is connected to the second node n2 through an inductor L1; the second node n2 is connected to GND through a resistor R32; and the electrode plate C- is also connected to the second node n2.

[0045] The detection module U4 includes five pins; its pin 1 is the input end, connected to the second node n2 through the resistor R29; its pin 2 is the output end of the detection module, which is used to Figure 6 In this embodiment, U4 is an analog switch, and detection is implemented by using the analog switch.

[0046] During the detection process, the capacitance value of the plates C- and C+ of the capacitive sensor changes with the distance between them. The oscillation module cooperates with the detection module so that the output of the detection module changes with the distance between the two plates. The specific principle is:

[0047] In the power-on initialization stage, the voltage of each capacitor is 0V. First, C32 and C34 are charged, so that the voltage of the plate C+ rises slowly. The two plates begin to charge until the charging voltage is greater than the conduction voltage of Q3, and the transistor Q3 is turned on. Since the U4 analog switch is a single-channel switch, the control pin is pin 4 (using the voltage fluctuation between PGND and GND, the fluctuation frequency and waveform are the same as the above PWM signal), that is, it is only opened in half a cycle to charge C30. When charging C30, the Ic current of Q3 is large, causing Q4 to turn on, so that the C- voltage is pulled up; in another half cycle, the Ic current of Q3 decreases, and C- returns to the original voltage. At this time, C+ is also pulled down, and Q3 is cut off. The plate C+ continues to be charged through R30, and the C+ potential continues to rise. The charging process is repeated until C30 is full. After C30 is full, the capacitor plate C+ is charged and discharged repeatedly with the switching of the analog switch. The potential of the C+ terminal, i.e. the potential of the C30 pin, is controlled by the size of the capacitor plate C. That is, when a target object approaches, the voltage of the 4th pin of the comparator U5 increases, and when the target object moves away (the distance between the plates C- and C+ becomes farther), the voltage of the 4th pin of the comparator U5 decreases.

[0048] Therefore, the comparison output circuit can judge whether the plates C- and C+ are close by comparing the signal output by the detection module with the reference signal (action threshold). The detection module uses an analog switch to implement sampling according to the beat of the PWM signal, without the need for traditional rectification and filtering circuits, and has a fast response speed.

[0049] like Figure 6 As shown, the comparison output circuit is a comparator with hysteresis, and the reference signal (action threshold) VREF = (R40 / / R41+R39)*VCC / (R35+R43+RP1+R40 / / R41+R39), where " / / " indicates parallel connection. By adjusting the potentiometer RP1, the voltage value of VREF can be adjusted to adjust the sensor distance (the size of the action threshold);

[0050] VP=(R36*VREF) / (R36+R38)+(VO*R38) / (R36+R38)

[0051] The hysteresis can be adjusted by adjusting the resistance values ​​of R36 and R38 and changing the positive feedback voltage value.

[0052] The level signal output by the comparison output circuit is sent to the MCU module for judgment. Since the reference ground of the MCU module is PGND, and the reference ground of the comparator output circuit and the front-end signal is GND, these two ground planes are incompatible. However, the signals at the same input and reverse input of the comparator output circuit are square wave signals with different reference voltages and the same frequency relative to PGND. Therefore, a level signal relative to PGND can be obtained through the comparator and sent to the MCU module for judgment. The MCU module can compare the voltage signal ( Figure 6 Since the PWM beat signal is high, the sensor of the present application can achieve a higher detection frequency.

[0053] The output terminal OUT of the comparator input circuit is connected to the MCU module. The MCU module includes an output circuit, which is a circuit attached to the MCU module and is used to output the detection result as the detection result of the sensor. The MCU module can output the detected signal through the output circuit according to the predetermined protocol as required.

[0054] The main characteristics of the sensor of the present invention include:

[0055] 1. High response frequency

[0056] This solution converts the 156KHz PWM signal generated by the MCU into a voltage amplitude, then controls the high-speed switching of a single-channel analog switch, performs detection processing on the oscillation signal, and then compares the signal with the action threshold through a high-speed comparator, and finally transmits the signal to the MCU for processing, thereby achieving the effect of high-speed detection of the detection object.

[0057] 2. Anti-strong electromagnetic interference

[0058] The ground signal GND of the oscillation and detection module is isolated from the ground signal PGND of the product power supply circuit. When subject to common-mode interference, the interference signals can cancel each other out, effectively avoiding interference from harmful electromagnetic fields. At the same time, combined with a high anti-interference software filtering algorithm, it achieves anti-strong electromagnetic interference characteristics.

[0059] 3. Long detection distance

[0060] A wide voltage circuit is used to excite the electrode plate to increase the electric field strength and signal sensitivity. Analog switches and high-speed comparators are used to design a new detection module to achieve effective detection of weak electrical signals and realize long-distance detection.

[0061] 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 high response frequency capacitive sensor, characterized in that include: A voltage conversion module, used for supplying power to the signal processing module according to the PWM signal; A signal processing module, including an oscillation module, a detection module and a comparison output circuit; The oscillation module is used to generate an oscillation signal to act on the plate of the capacitor; the detection module is used to detect the voltage of the plate in combination with the PWM signal; the comparison output circuit is used to compare the detection result with the action threshold; The MCU module is used to adjust the output signal of the sensor according to the output of the comparison module output circuit.

2. A high response frequency capacitive sensor according to claim 1, characterized in that It also includes a power supply module, which uses a first-level low-voltage difference linear regulator to provide a high-voltage electrical signal for the oscillation module and power the voltage conversion module; and uses a linear voltage regulator module U1 to further stabilize the voltage and power the MCU module.

3. A high response frequency capacitive sensor according to claim 1, characterized in that It also includes a power supply module. The power supply module uses a transistor and a voltage stabilizing circuit to use a resistor voltage divider to adjust the output voltage to provide a high-voltage electrical signal for the oscillation module; and uses a linear voltage stabilizing module U1 to further stabilize the voltage to power the MCU module.

4. A high response frequency capacitive sensor according to claim 1, characterized in that: The PWM signal is generated by an MCU module, or by using a logic gate circuit in conjunction with a capacitor charging and discharging circuit.

5. The high response frequency capacitive sensor according to claim 1, characterized in that: The voltage conversion module uses a common-emitter amplifier circuit to amplify the PWM signal, and its output VCC signal and GND signal are used to power the signal processing module respectively; the frequency and phase of the VCC signal and the GND signal are the same.

6. A high response frequency capacitive sensor according to claim 5, characterized in that: The oscillation module of the signal processing module is powered by the VCC signal and the GND signal output by the voltage conversion module; the oscillation module includes: The oscillation module includes: a resistor R28, a high-precision voltage source U6, and a resistor R37 connected in sequence between VCC and GND; an input end of the high-precision voltage source U6 is connected to the first node n1, and an output end thereof is connected to the first node n1 through a capacitor C32, and is connected to GND through a capacitor C34; a ground end of the high-precision voltage source U6 is connected to GND through a resistor R37; a transistor Q4 is a PNP transistor, a base 1 of which is connected to VCC through a resistor R27, an emitter 2 of which is connected to VCC, and a collector 3 of which is connected to the capacitor C34. A plate C- of the capacitance sensor is connected; the plate C- is also connected to the output end of the high-precision voltage source U6 through a resistor R34; another plate C+ of the capacitance sensor is connected to the first node n1 through a resistor R30, and is connected to the base of another transistor Q3; the transistor Q3 is an NPN transistor, whose collector is connected to the base of the transistor Q4, and the emitter of the transistor Q3 is connected to the second node n2 through an inductor L1; the second node n2 is connected to GND through a resistor R32; and the plate C- is also connected to the second node n2.

7. A high response frequency capacitive sensor according to claim 6, characterized in that: The detection module uses an analog switch for detection.

8. The high response frequency capacitive sensor according to claim 1, characterized in that: The comparison output circuit is a comparator with hysteresis; the hysteresis is adjusted through the adjustable resistance value.

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