A signal compensation device based on a biological piezoelectric sensor and a compensation method thereof

Abstract

The application relates to a signal compensation device based on a biological piezoelectric sensor, which comprises a control module, the control module is in bidirectional communication with a piezoelectric sensing module, a first signal input end of the control module is connected with an output end of a voltage compensation module, a second signal input end of the control module is connected with an output end of a temperature sensing module, an output end of the control module is connected with an input end of an alarm module, and a power module supplies power to the voltage compensation module and the control module respectively. The application further discloses a compensation method of the signal compensation device based on the biological piezoelectric sensor. In view of piezoelectric attenuation influence caused by degradation materials of the biological piezoelectric sensor, a robust attenuation characteristic formula is added on the basis of a temperature compensation formula to improve compensation accuracy; a zero-crossing detection circuit is added in compensation, compensation voltage is accurately controlled, and the accuracy of the compensation voltage reaches 0.01 mV.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of signal compensation, in particular to a signal compensation device based on a biological piezoelectric sensor and a compensation method thereof. BACKGROUND

[0002] The biological piezoelectric sensor can more effectively collect signals on the surface of an object due to its unique flexibility, sensitivity and environmental friendliness, and has been widely used in detecting physiological signals of the human body. However, due to the influence of environmental factors, especially temperature and the performance loss of the device itself, the signals generated by the biological piezoelectric sensor will be attenuated, which is not conducive to analyzing the physiological health status of the human body through these signals. Therefore, compensation is needed for the sensor signals in this case.

[0003] The existing document, "Research on Piezoelectric Micro-pressure Sensor with Temperature Compensation[D]. Jilin University, 2017" proposes a temperature compensation method based on a thermistor using hardware compensation. The output voltage of the sensor after amplification is loaded to both ends of the NTC thermistor. Because the voltage and the resistance have consistent change rules with the increase of temperature, according to Ohm's law, the ratio of the sensor output voltage to the resistance is less affected by temperature. This method can realize the temperature compensation of the piezoelectric micro-pressure sensor without determining the specific temperature and compensation amount. However, this compensation method is only effective in a small range (5 to 10 Pa), and is not suitable for temperature compensation in a wide range. The existing document "Piezoelectric and Acousto-optic, 2019, 41(03): 445-447" proposes a temperature compensation model based on the least square method using software compensation. This method collects the output voltage of the piezoelectric sensor in the working temperature range, processes the data after temperature change, and uses the least square method to linearly fit the output voltage of each temperature zone to obtain a temperature compensation model. The temperature model error in this method is large, and only considers temperature, which cannot completely compensate the piezoelectric sensor. SUMMARY

[0004] The primary purpose of the present application is to provide a signal compensation device based on a biological piezoelectric sensor that can ensure stable voltage generation of the sensor during use, eliminate the influence of secondary errors, and improve compensation accuracy.

[0005] To achieve the above purpose, the present application adopts the following technical solution: a signal compensation device based on a biological piezoelectric sensor, characterized by comprising

[0006] A power supply module for supplying power to the control module, and a voltage compensation module for compensating the voltage of the piezoelectric sensor;

[0007] A piezoelectric sensing module for detecting stress and generating piezoelectric voltage;

[0008] a temperature sensing module for detecting the ambient temperature in which the biological piezoelectric sensor operates, so as to obtain the decay voltage;

[0009] a control module for detecting the operating voltage of the piezoelectric sensing module, reading the temperature of the temperature sensing module and the zero-crossing point information of the voltage compensation module, controlling the generation of the trigger pulse according to the zero-crossing point information, obtaining the compensated decay voltage, and inputting the compensated decay voltage to the piezoelectric sensing module;

[0010] a voltage compensation module for detecting the zero-crossing point information of the alternating current of the power module;

[0011] an alarm module for prompting whether the voltage compensation is successful;

[0012] The control module is in bidirectional communication with the piezoelectric sensing module, the first signal input end of the control module is connected with the output end of the voltage compensation module, the second signal input end of the control module is connected with the output end of the temperature sensing module, the output end of the control module is connected with the input end of the alarm module, and the power module supplies power to the voltage compensation module and the control module respectively.

[0013] The power module is composed of a 5V to 10V alternating current power supply and a bridge rectifier bridge, the piezoelectric sensing module adopts a biological piezoelectric sensor, the temperature sensing module adopts a temperature sensor, the control module adopts a microcontroller MCU, the microcontroller MCU adopts an STM32F103RCT6 chip, the voltage compensation module adopts a zero-crossing detection circuit, and the alarm module adopts a Bluetooth module and an LED lamp.

[0014] The zero-crossing detection circuit comprises resistors R1, R2 and R3 which are connected in series, one end of the resistor R1 is connected with the alternating current, the other end is connected with the non-inverting input end of an operational amplifier U1 through a resistor R4, one end of the resistor R2 is connected with the alternating current, the other end is connected with the inverting input end of the operational amplifier U1 through a resistor R5, the output end of the operational amplifier U1 is connected with one end of a resistor R8, the other end of the resistor R8 is connected with the base of a transistor Q1, one end of a resistor R9 is connected with the collector of the transistor Q1, the other end of the resistor R9 is connected with a power supply VCC, and the emitter of the transistor Q1 is connected with the ground.

[0015] Another object of the present application is to provide a compensation method of the signal compensation device based on the biological piezoelectric sensor, which comprises the following sequential steps:

[0016] (1) power-on stage: the alternating current power supply of the power module supplies power, and the function compensation model facing the temperature sensing module and the piezoelectric sensing module is written into the microcontroller MCU of the control module;

[0017] (2) Working stage: The control module reads the voltage of the piezoelectric sensing module and the temperature of the temperature sensing module, substitutes the voltage and temperature into the microcontroller MCU of the control module, and obtains the attenuation voltage ΔU according to the internal function compensation model of the microcontroller MCU. The formula of the function compensation model is as follows:

[0018]

[0019] In the formula, the first term is the voltage calculation formula related to temperature of the piezoelectric sensing module, where U 00 , K 10 、a 0i 、b 1i is the temperature compensation coefficient, T is the temperature of the experimental environment, U N is the voltage collected for the Nth time; the second term ΔU N =[(9E-08N 2 -(8E-05)N+0.0517)]U N-1 The voltage attenuation calculation formula of the piezoelectric sensing module is: N The attenuation voltage of the piezoelectric sensing module is N, which is automatically increased by 1 each time it is used. N-1 The original voltage collected at the N-1th time, N and U N-1 Recorded and saved by the microcontroller MCU of the control module;

[0020] (3) Compensation stage: The microcontroller MCU of the control module reads the zero-crossing point information of the zero-crossing detection circuit of the voltage compensation module, and controls the time of its own trigger pulse generation according to the size of the attenuation voltage, generates a compensation voltage and compensates it to the piezoelectric sensing module; the microcontroller MCU of the control module reads the voltage U of the piezoelectric sensing module after compensation. C And compared with the uncompensated original acquisition voltage U N Subtract and get the compensated attenuation voltage ΔU C :

[0021] ΔU C =U C -U N (2)

[0022] The compensated attenuation voltage ΔU C Subtract the absolute value from the attenuation voltage ΔU before compensation to obtain the compensation deviation voltage U D :

[0023] U D =|ΔU C -ΔU| (3)

[0024] If the compensation deviation voltage U DIf the compensation is within the set threshold, the alarm module will display that the compensation is successful, otherwise the compensation will continue and the compensation deviation voltage U D The piezoelectric sensing module is compensated. If the continuous compensation fails, the alarm module will sound an alarm, indicating that the piezoelectric sensing module is damaged.

[0025] It can be seen from the above technical solution that the beneficial effects of the present invention are: First, in order to address the piezoelectric attenuation effect caused by the degradation material of the biological piezoelectric sensor, the present invention adds a robust attenuation characteristic formula on the basis of the temperature compensation formula to improve the compensation accuracy; second, the present invention adds a zero-crossing detection circuit to the compensation to accurately control the compensation voltage, so that the accuracy of the compensation voltage reaches 0.01mV. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a block diagram of the system composition of the present invention;

[0027] Figure 2 The relative voltage attenuation rate curve of the biopiezoelectric sensor of the present invention is shown in FIG. 1 , where the horizontal axis represents the number of times the biopiezoelectric sensor is used, and the vertical axis represents the ratio of the piezoelectric voltage generated by the biopiezoelectric sensor for the Nth time to the piezoelectric voltage generated for the N-1th time;

[0028] Figure 3 1 is a circuit diagram of a zero-crossing detection circuit in the present invention;

[0029] Figure 4 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0030] like Figure 1 As shown, a signal compensation device based on a biological piezoelectric sensor is characterized by comprising:

[0031] The power module is used to supply power to the control module and perform voltage compensation on the piezoelectric sensor through the voltage compensation module;

[0032] Piezoelectric sensing module, used to detect stress and generate piezoelectric voltage;

[0033] The temperature sensing module is used to detect the ambient temperature of the bio-piezoelectric sensor and obtain the attenuation voltage;

[0034] The control module is used to detect the operating voltage of the piezoelectric sensing module, read the temperature of the temperature sensing module and the zero-crossing point information of the voltage compensation module, control the generation of the trigger pulse according to the zero-crossing point information, obtain the compensated attenuation voltage, and input it to the piezoelectric sensing module;

[0035] Voltage compensation module, used to detect the zero-crossing information of the AC power of the power module;

[0036] Alarm module, used to prompt whether the voltage compensation is successful;

[0037] The control module communicates bidirectionally with the piezoelectric sensing module, the first signal input end of the control module is connected to the output end of the voltage compensation module, the second signal input end of the control module is connected to the output end of the temperature sensing module, the output end of the control module is connected to the input end of the alarm module, and the power supply module supplies power to the voltage compensation module and the control module respectively.

[0038] The power supply module consists of a 5V to 10V AC power supply and a bridge rectifier bridge, the piezoelectric sensing module adopts a biological piezoelectric sensor, the temperature sensing module adopts a temperature sensor, the control module adopts a microcontroller MCU, and the microcontroller MCU adopts an STM32F103RCT6 chip; the voltage compensation module adopts a zero-crossing detection circuit, and the alarm module adopts a Bluetooth module and an LED light.

[0039] like Figure 3 As shown, the zero-crossing detection circuit includes a resistor R1, a resistor R2, and a resistor R3, which are connected in series. One end of the resistor R1 is connected to the alternating current, and the other end is connected to the non-inverting input terminal of the operational amplifier U1 through the resistor R4. One end of the resistor R2 is connected to the alternating current, and the other end is connected to the inverting input terminal of the operational amplifier U1 through the resistor R5. The output terminal of the operational amplifier U1 is connected to one end of the resistor R8, and the other end of the resistor R8 is connected to the base of the inverter Q1. The collector of the inverter Q1 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the power supply VCC. The emitter of the inverter Q1 is grounded.

[0040] like Figure 4 As shown, the method includes the following steps in order:

[0041] (1) Power-on phase: The AC power supply of the power module is used to write the function compensation model for the temperature sensing module and the piezoelectric sensing module into the microcontroller MCU of the control module;

[0042] (2) Working stage: The control module reads the voltage of the piezoelectric sensing module and the temperature of the temperature sensing module, substitutes the voltage and temperature into the microcontroller MCU of the control module, and obtains the attenuation voltage ΔU according to the internal function compensation model of the microcontroller MCU. The formula of the function compensation model is as follows:

[0043]

[0044] In the formula, the first term is the voltage calculation formula related to temperature of the piezoelectric sensing module, where U 00 , K 10 、a 0i 、b 1i is the temperature compensation coefficient, T is the temperature of the experimental environment, UN is the voltage collected for the Nth time; the second term ΔU N =[(9E-08)N 2 -(8E--05)N+0.0517)]U N-1 The voltage attenuation voltage calculation formula of the piezoelectric sensing module, where ΔU N The attenuation voltage of the piezoelectric sensing module is N, which is automatically increased by 1 each time it is used. N-1 is the original voltage collected for the (N-1)th time, N and U N-1 Recorded and saved by the microcontroller MCU of the control module;

[0045] The first term in formula (1):

[0046]

[0047] It can be expressed as:

[0048] U(T)=K1(T)U N +U0(T) (5)

[0049] K1(T) and U0(T) are the temperature-related scale factor and zero bias voltage, respectively. The mathematical model of the bio-piezoelectric sensor scale factor and zero bias with respect to temperature is:

[0050]

[0051]

[0052] Formula (6) is the relationship between the scale factor and temperature, where T is the ambient temperature, b 1i is the high-order coefficient of T, K 10 is the constant temperature coefficient; Formula (7) is the relationship between the zero bias of the bio-piezoelectric sensor and temperature, a 0i is the high-order coefficient of T, U 00 is a constant temperature coefficient; the coefficients to be determined in formula (6) and formula (7) are specifically solved as follows: in the range of -5℃ to 45℃, at intervals of 10℃, and in the range of 5 to 1500Pa, the piezoelectric potential generated by the bio-piezoelectric sensor of the piezoelectric sensing module is sampled at intervals of 50Pa, and each pressure point is sampled 1000 times to obtain the scale factor and zero-bias voltage at each temperature point. The scale factor and zero-bias voltage at each temperature point are fitted to obtain the relevant temperature coefficients of formula (6) and formula (7); therefore, the output voltage expression of the bio-piezoelectric sensor with respect to temperature is obtained by combining formulas (5), (6), and (7), as shown in formula (4).

[0053] The second term in the function compensation model:

[0054] ΔUN =[(9E-08)N 2 -(8E-05)N+0.0517)]U N-1 (8)

[0055] Formula (8) is the calculation formula for the attenuation voltage of the biopiezoelectric sensor. This formula is related to the relative voltage attenuation rate R of the biopiezoelectric sensor. The relative voltage attenuation rate R can be obtained by performing a 1000-cycle stability test on the biopiezoelectric sensor under the conditions of a pressure of 1000 Pa and an ambient temperature of 25°C, with each group consisting of 200 cycles. After averaging each group, the ratio of the output mean voltages of the two adjacent groups of biopiezoelectric sensors is calculated, and a second-order fitting is performed to obtain the relative voltage attenuation rate curve of the biopiezoelectric sensor, as shown in Formula (9):

[0056] R=(-9E-08)N 2 +(8E-05)N+0.9483 (9)

[0057] Where N is the number of times the bio-piezoelectric sensor is used, and the voltage calculation formula for the Nth attenuation of the bio-piezoelectric sensor is:

[0058] ΔU N =U N-1 -U N-1 R (10)

[0059] Among them, ΔU N is the voltage of the bio-piezoelectric sensor at the Nth decay, U N-1 is the original voltage collected (N-1) times, U N-1 R represents the output voltage of the bio-piezoelectric sensor after the Nth attenuation, which is obtained by integrating formulas (5), (6), (7), (9), and (10) and subtracting the original output voltage U of the bio-piezoelectric sensor collected for the Nth time. N , we get the overall function compensation model, namely formula (1).

[0060] The function compensation model is also an attenuation voltage model. The attenuation voltage of the piezoelectric sensing module can be calculated based on the temperature and the currently collected output voltage of the piezoelectric sensing module. The calculated attenuation voltage is the part that needs to be compensated. The attenuation voltage is generated by the zero-crossing detection circuit and compensated to the piezoelectric sensing module.

[0061] (3) Compensation stage: The microcontroller MCU of the control module reads the zero-crossing point information of the zero-crossing detection circuit of the voltage compensation module, and controls the time of its own trigger pulse generation according to the size of the attenuation voltage, generates a compensation voltage and compensates it to the piezoelectric sensing module; the microcontroller MCU of the control module reads the voltage U of the piezoelectric sensing module after compensation. C And compared with the uncompensated original acquisition voltage UN Subtract and get the compensated attenuation voltage ΔU C :

[0062] ΔU C =U C -U N (2)

[0063] The compensated attenuation voltage ΔU C Subtract the absolute value from the attenuation voltage ΔU before compensation to obtain the compensation deviation voltage U D :

[0064] U D =|ΔU C -ΔU| (3)

[0065] If the compensation deviation voltage U D If the compensation is within the set threshold, the alarm module will display that the compensation is successful, otherwise the compensation will continue and the compensation deviation voltage U D The piezoelectric sensing module is compensated. If the continuous compensation fails, the alarm module will sound an alarm, indicating that the piezoelectric sensing module is damaged.

[0066] The following combination Figure 1 、 2 , 3, and 4 further illustrate the present invention.

[0067] The control module is used to read the temperature of the temperature sensing module, the voltage of the piezoelectric sensing module, and the zero-crossing point information of the voltage compensation module. In an operating environment where the ambient temperature is -5°C to 45°C and the stress of the biological piezoelectric sensor ranges from 5 to 1500Pa, the compensation voltage is obtained through a function compensation model. The microcontroller MCU of the control module controls the generation of the trigger pulse according to the zero-crossing point information, thereby controlling the thyristor output. The trigger pulse is generated by a high-precision timer inside the microcontroller MCU, so the compensation voltage can be accurately obtained and input into the piezoelectric sensing module.

[0068] Figure 2The figure shows the relative voltage attenuation rate curve generated by the biological piezoelectric sensor of the piezoelectric sensing module when the compensation module is not loaded. The curve is obtained by collecting the voltage generated by the biological piezoelectric sensor 1000 times at a temperature of 25°C and a pressure of 1000Pa. The 1000 collected data are grouped, with each 200 data as a group. The mean value Ui is calculated for each group, and the voltage output ratio R0 between adjacent points is calculated. After fitting the calculated R0, the relative voltage attenuation rate curve of the biological piezoelectric sensor of the piezoelectric sensing module is obtained. The vertical axis represents the percentage of the output voltage generated by the biological piezoelectric sensor twice before and after, and the horizontal axis is the number of uses. The attenuation characteristics of the biological piezoelectric sensor can be obtained through the attenuation curve, that is, as the number of uses increases, the voltage generated by the biological piezoelectric sensor will show different degrees of attenuation trends.

[0069] like Figure 3 As shown, the two levels of the AC signal are respectively limited by resistors R1 and R2, and then connected to the operational amplifier U1 through resistors R4 and R. When the AC input of the operational amplifier U1 exceeds the zero reference voltage, the zero-crossing detection circuit will change the output state of the operational amplifier U1 and input the zero-crossing state to the I / O port of the microcontroller MCU. The microcontroller MCU generates a trigger pulse according to the state to control the size of the compensation voltage.

[0070] The input terminal consists of a series circuit consisting of resistors R1, R2, and R3, which divide the input AC voltage signal. The divided voltage is R3 / (R1+R2+R3) times the original voltage. The resistor sizes are adjusted according to the actual power supply used. For a 5V AC voltage source, R1 and R2 are 2Ω, and R3 is 1Ω. The divided AC signal flows through resistors R4 and R5 and enters the input terminal of op amp U1. Resistors R4 and R5 serve as protection resistors for op amp U1 and must be equal in value. Op amp U1 is powered by VCC, which is divided by resistors R6 and R7, which have the same resistance value. Capacitor C7 is connected in parallel with resistor R7 to filter the voltage, making the VCC power supply more stable. The values ​​of the components can be: VCC is 3.3V, resistors R6 and R7 are 2Ω, and capacitor C7 is 10μf.

[0071] The output end of the operational amplifier U1 rectifies the AC signal and outputs a square wave signal, which is then connected to an inverter circuit consisting of resistors R8, R9, and an inverter Q1. Resistors R8 and R9 have the same resistance value, and Q1 is a CMOS inverter. This circuit mainly buffers the output signal of the operational amplifier U1 to protect the microcontroller MCU. It also reverses the phase. When the AC signal is in the positive half-axis, it outputs a low level, and in the negative half-cycle, it outputs a high level. The edge of the signal is the zero crossing point. The I / O port of the microcontroller MCU can determine the zero crossing time by detecting the edge signal.

[0072] In summary, in response to the piezoelectric attenuation effect caused by the degradation of materials in biological piezoelectric sensors, the present invention adds a robust attenuation characteristic formula on the basis of the temperature compensation formula to improve the compensation accuracy; the present invention adds a zero-crossing detection circuit to the compensation to accurately control the compensation voltage, so that the accuracy of the compensation voltage reaches 0.01mV.

Claims

1. A signal compensation device based on a bio-piezoelectric sensor, characterized in that: include The power module is used to supply power to the control module and perform voltage compensation on the piezoelectric sensor through the voltage compensation module; Piezoelectric sensing module, used to detect stress and generate piezoelectric voltage; The temperature sensing module is used to detect the ambient temperature of the bio-piezoelectric sensor and obtain the attenuation voltage; The control module is used to detect the operating voltage of the piezoelectric sensing module, read the temperature of the temperature sensing module and the zero-crossing point information of the voltage compensation module, control the generation of the trigger pulse according to the zero-crossing point information, obtain the compensated attenuation voltage, and input it to the piezoelectric sensing module; Voltage compensation module, used to detect the zero-crossing information of the AC power of the power module; Alarm module, used to prompt whether the voltage compensation is successful; The control module communicates bidirectionally with the piezoelectric sensing module, the first signal input terminal of the control module is connected to the output terminal of the voltage compensation module, the second signal input terminal of the control module is connected to the output terminal of the temperature sensing module, the output terminal of the control module is connected to the input terminal of the alarm module, and the power supply module supplies power to the voltage compensation module and the control module respectively; The power supply module is composed of a 5V to 10V AC power supply and a bridge rectifier. The piezoelectric sensing module uses a biological piezoelectric sensor, the temperature sensing module uses a temperature sensor, and the control module uses a microcontroller MCU. The microcontroller MCU uses an STM32F103RCT6 chip. The voltage compensation module uses a zero-crossing detection circuit for detecting the zero-crossing information of the AC power. The alarm module uses a Bluetooth module and an LED light. The zero-crossing detection circuit includes a resistor R1, a resistor R2, and a resistor R3, which are connected in series. One end of the resistor R1 is connected to an alternating current, and the other end is connected to a non-inverting input of an operational amplifier U1 through a resistor R4. One end of the resistor R2 is connected to an alternating current, and the other end is connected to an inverting input of the operational amplifier U1 through a resistor R5. The output of the operational amplifier U1 is connected to one end of a resistor R8, the other end of the resistor R8 is connected to the base of an inverter Q1, the collector of the inverter Q1 is connected to one end of a resistor R9, the other end of the resistor R9 is connected to a power supply VCC, and the emitter of the inverter Q1 is grounded.

2. The compensation method of the signal compensation device based on the bio-piezoelectric sensor according to claim 1, characterized in that: The method comprises the following steps in sequence: (1) Power-on phase: The AC power supply of the power module is used to write the function compensation model for the temperature sensing module and the piezoelectric sensing module into the microcontroller MCU of the control module; (2) Working stage: The control module reads the voltage of the piezoelectric sensing module and the temperature of the temperature sensing module, substitutes the voltage and temperature into the microcontroller MCU of the control module, and obtains the attenuation voltage ΔU according to the internal function compensation model of the microcontroller MCU. The formula of the function compensation model is as follows: In the formula, the first term is the voltage calculation formula related to temperature of the piezoelectric sensing module, where U 00 , K 10 、a 0i 、b 1i is the temperature compensation coefficient, T is the temperature of the experimental environment, U N is the voltage collected for the Nth time; the second term ΔU N =[(9E-08)N 2 -(8E-05)N+0.0517)]U N-1 The voltage attenuation calculation formula of the piezoelectric sensing module is: N The attenuation voltage of the piezoelectric sensing module is N, which is automatically increased by 1 each time it is used. N-1 The original voltage collected at the N-1th time, N and U N-1 Recorded and saved by the microcontroller MCU of the control module; (3) Compensation stage: The microcontroller MCU of the control module reads the zero-crossing point information of the zero-crossing detection circuit of the voltage compensation module, and controls the time of its own trigger pulse generation according to the size of the attenuation voltage, generates a compensation voltage and compensates it to the piezoelectric sensing module; the microcontroller MCU of the control module reads the voltage U of the piezoelectric sensing module after compensation. C And compared with the uncompensated original acquisition voltage U N Subtract and get the compensated attenuation voltage ΔU C : ΔU C =U C -U N (2) The compensated attenuation voltage ΔU C Subtract the absolute value from the attenuation voltage ΔU before compensation to obtain the compensation deviation voltage U D : U D =|ΔU C -ΔU| (3) If the compensation deviation voltage U D If the compensation is within the set threshold, the alarm module will display that the compensation is successful, otherwise the compensation will continue and the compensation deviation voltage U D The piezoelectric sensing module is compensated. If the continuous compensation fails, the alarm module will sound an alarm, indicating that the piezoelectric sensing module is damaged.

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