Air pump control method of electronic sphygmomanometer and electronic sphygmomanometer

Abstract

The application discloses a kind of air pump control method and electronic sphygmomanometer of electronic sphygmomanometer, air pump control method includes steps S1, the battery load voltage when air pump idling is measured, and load voltage is divided into several segments;Step S2, the air pressure in cuff is measured;Step S3, in low pressure section, calculate inflation rate with first frequency and use PID control algorithm to adjust inflation rate;Step S4, in high pressure section, calculate inflation rate with second frequency and use PID control algorithm to adjust inflation rate;Step S5, when the pulse feature extracted from air pressure signal meets the requirement of calculating blood pressure, end measurement and display result;Through the above structure, the problem that conventional PID control algorithm converges slowly when controlling air pump inflation can be solved, and the same cuff can make air pressure rise at a relatively stable rate under different wearing tightness, and the requirement of hardware configuration is lower.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic sphygmomanometers, in particular to a gas pump control method of an electronic sphygmomanometer and the electronic sphygmomanometer. BACKGROUND

[0002] The electronic sphygmomanometer based on the principle of the oscillographic method is the most mainstream electronic sphygmomanometer scheme on the current market, and the main components of the electronic sphygmomanometer include a gas pump, a deflation valve, a gas pressure sensor, a cuff, a control and display circuit and the like; after a user wears the cuff as required, presses a measurement key, the electronic sphygmomanometer can automatically complete the measurement, and the use is very convenient.

[0003] According to different measurement opportunities, the measurement is divided into uplink (pressure type) measurement and downlink (decompression type) measurement; the uplink measurement is completed in the process of gas pump inflation, and it is required that the air pressure in the cuff rises at a relatively constant rate, the inflation is stopped after the blood pressure value is measured, the deflation valve is opened, and the measurement is ended; the downlink measurement is to pressurize the air pressure in the cuff to a relatively high air pressure value, and then realize slow deflation through the deflation valve, and the measurement is completed in the process of deflation; since the cuff is a soft material, the air bag in the cuff is often composed of rubber and has a certain elasticity, and in the process of inflation, the volume of the air bag will have a nonlinear change with the increase of the air pressure, and it is a technical problem in the industry to control the gas pump inflation so that the air pressure in the cuff rises at a relatively stable rate.

[0004] The mainstream method at present is to use the PID principle to control the gas pump, but the conventional PID control needs a certain time to converge, and has high sensitivity to the tightness of the cuff, and it is difficult to ensure that it can quickly converge under different tightness, and for users with lower blood pressure, the inflation rate may not have reached a relatively linear state when the blood pressure measurement is completed, which will affect the accuracy of the blood pressure measurement; therefore, there is an urgent need for a new gas pump control method of an electronic sphygmomanometer and the electronic sphygmomanometer to solve the above problems. Content of the utility model

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a gas pump control method of an electronic sphygmomanometer and the electronic sphygmomanometer.

[0006] The technical solution adopted by an embodiment of the present application to solve its technical problem is: a gas pump control method of an electronic sphygmomanometer, comprising:

[0007] Step S1, keep the deflation valve open, and measure the battery load voltage when the gas pump is idling, divide the battery load voltage into several segments according to the battery type, and set an initial duty ratio, a minimum duty ratio threshold, a maximum duty ratio threshold of a low voltage segment and a maximum duty ratio threshold of a high voltage segment for each voltage segment;

[0008] Step S2, measure the air pressure in the cuff, close the exhaust valve, and keep the air pump working at the initial duty cycle before the air pressure in the cuff reaches the preset value;

[0009] Step S3, in the low-pressure section, calculate the inflation rate at the first frequency and adjust the inflation rate using the PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold of the low-pressure section, limit the current duty cycle to the maximum duty cycle threshold of the low-pressure section; if the new duty cycle is less than the minimum duty cycle threshold, limit the current duty cycle to the minimum duty cycle threshold.

[0010] Step S4, in the high-pressure section, calculate the inflation rate at the second frequency and adjust the inflation rate using the PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold of the high-pressure section, limit the current duty cycle to the maximum duty cycle threshold of the high-pressure section; if the new duty cycle is less than the minimum duty cycle threshold, limit the current duty cycle to the minimum duty cycle threshold, wherein the second frequency is less than the first frequency.

[0011] Step S5, when the pulse feature extracted from the air pressure signal meets the requirement for calculating blood pressure, end the measurement and display the result.

[0012] Preferably, the PID control algorithm is:

[0013] Output = K p * (V n – V tag ) + K d * [(V n – V tag ) – (V n-1 – V tag )], wherein K p is the proportional gain, K d is the derivative time, V n is the inflation rate at the nth moment, and V tag is the target inflation rate.

[0014] Preferably, in the low-pressure section, the target inflation rate is half of the expected target inflation rate, and when the output result of the PID control algorithm is positive, reduce the duty cycle of the air pump, and the amount of reduction is the absolute value of the output result; when the output result of the PID control algorithm is negative, increase the duty cycle of the air pump, and the amount of increase is the absolute value of the output result.

[0015] Preferably, in the high pressure stage, an adjustment threshold is set, if the absolute value of the output result of the PID control algorithm is greater than the adjustment threshold, the adjustment amount of the duty cycle of the air pump is limited to the adjustment threshold; if the absolute value of the output result of the PID control algorithm is less than the adjustment threshold, the adjustment amount of the duty cycle of the air pump is the absolute value of the output result of the PID control algorithm.

[0016] Preferably, between step S1 and step S2, further comprising:

[0017] Step S1.1, setting a sleeve wearing too tight threshold and a sleeve wearing too loose threshold;

[0018] Step S1.2, integrating the product of the load voltage and the duty cycle of the air pump, and taking the air pressure sampling period as the integration unit, counting the result in the inflation detection stage, if less than the sleeve wearing too tight threshold, judging as wearing too tight, if greater than the sleeve wearing too loose threshold, judging as wearing too loose.

[0019] An electronic sphygmomanometer applying the air pump control method.

[0020] The air pump control method of the electronic sphygmomanometer and the electronic sphygmomanometer, the air pump control method comprising steps S1, keeping the air release valve open, and measuring the battery load voltage when the air pump is idling, dividing the battery load voltage into several segments according to the battery type, setting an initial duty cycle, a minimum duty cycle threshold, a maximum duty cycle threshold of the low pressure stage and a maximum duty cycle threshold of the high pressure stage for each voltage segment; step S2, measuring the air pressure in the sleeve, closing the air release valve, and keeping the air pump working at the initial duty cycle before the air pressure in the sleeve reaches the preset value; step S3, in the low pressure stage, calculating the inflation rate at a first frequency and adjusting the inflation rate using the PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold of the low pressure stage, limiting the current duty cycle to the maximum duty cycle threshold of the low pressure stage; if the new duty cycle is less than the minimum duty cycle threshold, limiting the current duty cycle to the minimum duty cycle threshold; step S4, in the high pressure stage, calculating the inflation rate at a second frequency and adjusting the inflation rate using the PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold of the high pressure stage, limiting the current duty cycle to the maximum duty cycle threshold of the high pressure stage; if the new duty cycle is less than the minimum duty cycle threshold, limiting the current duty cycle to the minimum duty cycle threshold, wherein the second frequency is less than the first frequency; step S5, when the pulse feature extracted from the air pressure signal meets the requirement of calculating blood pressure, ending the measurement and displaying the result; the above structure can solve the problem of slow convergence of the conventional PID control algorithm in controlling the air pump inflation, and make the same sleeve rise at a relatively stable rate under different wearing tightness, and has low requirements for hardware configuration. BRIEF DESCRIPTION OF DRAWINGS

[0021] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings of which:

[0022] Figure 1 A classical circuit for PWM controlled air pump;

[0023] Figure 2 A waveform diagram for PWM control;

[0024] Figure 3 An embodiment for duty cycle limitation;

[0025] Figure 4 A diagram for air pressure change in the cuff;

[0026] Figure 5 A diagram for inflation rate change of the present application. DETAILED DESCRIPTION

[0027] This part will describe the specific embodiments of the present application in detail, the preferred embodiments of the present application are shown in the drawings, the role of the drawings is to supplement the description of the text part with graphics, so that people can intuitively and visually understand each technical feature and the overall technical scheme of the present application, but it cannot be understood as a limitation on the protection scope of the present application.

[0028] In the description of the present application, the meaning of multiple is more than two, greater than, less than, more than, etc. is not included in the number, above, below, within, etc. is included in the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0029] In the description of the present application, it is understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and is not intended to indicate or imply that the device or element indicated must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0030] In the present application, unless otherwise explicitly limited, the words "set", "install", "connect" and the like should be understood broadly, for example, they can be directly connected, or indirectly connected through an intermediate medium; can be fixedly connected, or can be detachably connected, or can be integrally formed; can be mechanically connected; can be the internal communication of two elements or the interaction relationship between two elements. The person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical scheme.

[0031] Referring to Figures 1 to 5 A gas pump control method of an electronic sphygmomanometer, comprising:

[0032] Step S1, keep the air release valve open, and measure the battery load voltage when the gas pump idles, divide the battery load voltage into several segments according to the battery type, and set an initial duty cycle, a minimum duty cycle threshold, a maximum duty cycle threshold for the low voltage segment, and a maximum duty cycle threshold for the high voltage segment for each voltage segment;

[0033] Step S2, measure the air pressure in the cuff, close the air release valve, and keep the gas pump working at the initial duty cycle until the air pressure in the cuff reaches a preset value;

[0034] Step S3, in the low voltage segment, calculate the inflation rate at a first frequency and adjust the inflation rate using a PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold for the low voltage segment, limit the current duty cycle to the maximum duty cycle threshold for the low voltage segment; if the new duty cycle is less than the minimum duty cycle threshold, limit the current duty cycle to the minimum duty cycle threshold;

[0035] Step S4, in the high voltage segment, calculate the inflation rate at a second frequency and adjust the inflation rate using a PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold for the high voltage segment, limit the current duty cycle to the maximum duty cycle threshold for the high voltage segment; if the new duty cycle is less than the minimum duty cycle threshold, limit the current duty cycle to the minimum duty cycle threshold, wherein the second frequency is less than the first frequency;

[0036] Step S5, when the pulse feature extracted from the air pressure signal meets the requirement for calculating blood pressure, end the measurement and display the result.

[0037] 1. In the present application, referring to Figures 1-2 , the control of the gas pump on the electronic sphygmomanometer is completed through PWM, Figure 1 The classic circuit for PWM control of the gas pump, the control circuit will generate a square wave of about 10-100 kHz, when the PWM port outputs high level, the transistor is turned on, the gas pump works; when the output is low, the transistor is not turned on, the gas pump does not work.

[0038] When the gas pump is working, the voltage of the battery will be lower than when it is not working, that is, the difference between the no-load voltage and the load voltage. In order to accurately measure the voltage when the gas pump is working, the load voltage must be measured.

[0039] 2、In the beginning of the blood pressure measurement, keep the exhaust valve open, let the air pump work at a fixed duty cycle (for example, 50%) for a period of time, this period of time does not need to measure the pressure in the cuff, only measure the battery voltage, can avoid the difficulty of measuring the pressure and battery voltage at the same time, suitable for use in some solutions that cannot meet the pressure and battery voltage at the same time.

[0040] According to the type of battery, the battery load voltage is segmented, the principle of segmentation is that the performance difference of the air pump in the same segment is not too large, which needs to be determined according to the measured data of different air pumps; For example, using rechargeable lithium battery power supply, the voltage range is 3.6V-4.2V, which can be segmented every 0.2V, that is, V bat ≥4.0, 3.8≤V bat <4.0, 3.6≤V bat <3.8; while using 4 AA batteries for power supply, the voltage range is 4.8-6V, which can be segmented every 0.4V, that is, V bat ≥5.6, 5.2≤V bat <5.6, 4.8≤V bat <5.2.

[0041] Each voltage segment sets 4 duty cycle limits, which are the initial duty cycle, the minimum duty cycle threshold, the maximum duty cycle threshold of the low pressure segment and the maximum duty cycle threshold of the high pressure segment.

[0042] Initial duty cycle: the initial value of the duty cycle when the blood pressure measurement is formally started;

[0043] Minimum duty cycle threshold: the duty cycle of the air pump during the entire measurement process cannot be less than the minimum duty cycle threshold, to avoid the air pump from stopping due to too low duty cycle;

[0044] Maximum duty cycle threshold of low pressure segment: when the air pressure in the cuff is less than a certain value, the duty cycle of the air pump cannot be greater than this threshold, to avoid the PID adjustment range being too large, causing large fluctuations in the adjustment of the inflation rate;

[0045] Maximum duty cycle threshold of high pressure segment: when the air pressure in the cuff is greater than a certain value, the duty cycle of the air pump cannot be greater than this threshold, to avoid the PID adjustment range being too large, causing large fluctuations in the adjustment of the inflation rate;

[0046] The duty cycle limit needs to be adjusted according to the measured data of different air pumps, for reference Figure 3 , which is an embodiment of the duty cycle limit;

[0047] 3. Modify the measurement mode of the ADC from measuring the battery voltage to measuring the air pressure in the cuff; modify the duty cycle of the air pump to be the initial duty cycle, close the air release valve, and maintain the initial duty cycle until the air pressure in the cuff reaches 1 mmHg.

[0048] The tightness of the cuff affects the degree of inflation of the cuff after inflation. The greater the degree of inflation, the greater the volume in the cuff. In general, when the cuff is tight, the degree of inflation is small and the volume is small. When the cuff is loose, the degree of inflation is large and the volume is large.

[0049] If the same duty cycle is used, the air pressure in the cuff will rise quickly when the volume is small, and the air pressure in the cuff will rise much more slowly when the volume is large. The rising sphygmomanometer does not want the air pressure in the cuff to rise too quickly, which can lead to inaccurate measurements of low blood pressure. Therefore, a relatively small initial duty cycle is set to ensure that even if the cuff is very tight, the air pressure will not rise too high at the beginning of inflation.

[0050] When the air pressure reaches 1 mmHg, the current inflation rate can be estimated. If the inflation rate is higher than the desired inflation rate, the next step is to reduce the duty cycle of the air pump. If the inflation rate is lower than the desired inflation rate, the next step is to increase the duty cycle of the air pump. This can be done using a PID control algorithm.

[0051] 4. The formula for the classic PID control algorithm: output = K p * error + K i * integral term + K d * derivative term, where K p , K i , and K d represent the proportional gain, integral time, and derivative time, respectively. The proportional gain controls the response speed of the system, but can cause stability problems in the system. The integral time controls the steady-state error of the system, but can cause overshoot and oscillation. The derivative time controls the stability of the system, but can increase the impact of noise. In the measurement of the rising sphygmomanometer, the most important factor is the overshoot and oscillation of the inflation rate. Therefore, K i is set to 0, and the integral time is not considered. The error in the formula is the difference between the current inflation rate and the target inflation rate. The derivative term is the difference between the current inflation rate and the target inflation rate minus the difference between the inflation rate and the target inflation rate at the last adjustment. The inflation rate and the PID output are calculated at a frequency of 16 Hz. The adjustment formula for the PID control algorithm is: output = K p * (V n - V tag ) + K d * [(V n - V tag ) - (V n-1 - Vtag )], wherein, K p is a proportional gain, K d is a differential time, V n is the inflation rate at the nth moment, V tag is the target inflation rate.

[0052] The target inflation rate of the low pressure section is set to half of the desired target inflation rate, that is, if the desired inflation rate of the ascending sphygmomanometer is 6 mmHg / s, then the target inflation rate is set to 3 mmHg / s in the low pressure section, wherein the low pressure section is defined as 1-20 mmHg; the reason for such setting is that when the inflation of the cuff is started, the volume change of the cuff is particularly obvious from a deflated state to an inflated state, and the amount of gas filled is not proportional to the increase of the air pressure, and generally the air pressure needs to reach 30 mmHg before the volume change of the cuff is not so obvious; if 6 mmHg / s is used as the target all the time, when the volume of the cuff is no longer obviously increased, the inflation rate will suddenly increase, resulting in a sudden increase of the air pressure, but the adjustment of the PID control algorithm needs reaction time, and when the overshoot occurs, it needs a period of oscillation to recover to normal, which is easy to cause the inflation to be unstable in the air pressure range of 30-80 mmHg, thereby affecting the blood pressure measurement accuracy; therefore, in the low pressure section of 1-20 mmHg, half of the desired inflation rate is used as the target, which can reduce the overshoot in the high pressure section after 30 mmHg.

[0053] Further, K p in the PID control algorithm is set to 1, K d is set to 0.5, when the output result of the PID control algorithm is positive, the duty cycle of the air pump is reduced by the absolute value of the output result; when the output result of the PID control algorithm is negative, the duty cycle of the air pump is increased by the absolute value of the output result; for example, if the output result of the PID control algorithm is 2, and the current duty cycle is 40%, then the duty cycle needs to be adjusted to 40%-2%=38%.

[0054] In the process of adjusting the PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold of the low pressure section, the maximum duty cycle threshold of the low pressure section is limited to be the current duty cycle; if the new duty cycle is less than the minimum duty cycle threshold, the minimum duty cycle threshold is limited to be the current duty cycle.

[0055] 5、When the air pressure is greater than 20 mmHg, the PID control algorithm of the low pressure section is switched to the PID control algorithm of the high pressure section, specifically:

[0056] Using the desired inflation rate as the target inflation rate, the frequency of the PID control algorithm is changed from 16Hz to 4Hz, and the adjustment frequency is reduced mainly because it is more important to stabilize the inflation rate than to accurately follow the target inflation rate after entering the high pressure section, and only when the inflation rate is approximately stable around the target inflation rate is it necessary to frequently adjust to closely follow the target inflation rate.

[0057] At the same time, the adjustment amplitude can be limited, and if the adjustment amplitude output by the PID control algorithm is greater than 0.5, it can only be adjusted by 0.5, which can further avoid excessive adjustment frequency; for example, the current air pump duty cycle is 50%, the PID control algorithm outputs 2, and the new duty cycle is 50%-0.5%=49.5%; or the current air pump duty cycle is 50%, the PID control algorithm outputs 0.4, and the new duty cycle is 50%-0.4%=49.6%.

[0058] The maximum duty cycle threshold of the high pressure section is greater than that of the low pressure section, because when the air pressure rises to a certain extent, the air pump needs a larger duty cycle to maintain the target inflation rate, and if it is limited too low, the inflation rate will decrease significantly when the air pressure is high.

[0059] 6, keep until the end of the measurement, for the rising sphygmomanometer, as long as the pulse feature extracted from the air pressure signal during the inflation process meets the requirement of calculating blood pressure, the measurement can be ended and the result can be displayed; refer to Figures 4-5 , wherein, in Figure 4 is the change of air pressure in the cuff, the horizontal axis is the sampling point, and the sampling rate is 64Hz; the vertical axis is the air pressure, and the unit is mmHg, the sawtooth appearing in the latter half of the air pressure curve is caused by pulse jumping, and the sphygmomanometer uses this pulse information to calculate the blood pressure value; in Figure 5 , the desired inflation rate is 5.5mmHg / s, the horizontal axis is the sampling point, and the sampling rate is 64Hz; the vertical axis is the inflation rate, and the unit is mmHg / s, from Figure 5 , it can be seen that when the air pressure is less than 20mmHg, the inflation rate is about half of the desired inflation rate, and after greater than 20mmHg, there is a slight shock stabilization process, and gradually converges to the vicinity of the desired inflation rate.

[0060] 7, the advantage of the present application is that the above structure can solve the problem of slow convergence of the conventional PID control algorithm in controlling the inflation of the air pump, and the same cuff can make the air pressure rise at a relatively stable rate under different wearing tightness, and the hardware configuration requirement is low.

[0061] Preferably, the PID control algorithm is:

[0062] Output=K p * (V n- V tag ) + K d * [(V n - V tag ) - (V n-1 - V tag )], wherein K p is a proportional gain, K d is a derivative time, V n is the inflation rate at the n th moment, V tag is a target inflation rate.

[0063] In the low pressure section, the target inflation rate is half of the desired target inflation rate, and when the output result of the PID control algorithm is positive, the duty cycle of the air pump operation is reduced by the absolute value of the output result; when the output result of the PID control algorithm is negative, the duty cycle of the air pump operation is increased by the absolute value of the output result.

[0064] In the high pressure section, an adjustment threshold is set, if the absolute value of the output result of the PID control algorithm is greater than the adjustment threshold, the adjustment amount of the duty cycle of the air pump operation is limited to the adjustment threshold; if the absolute value of the output result of the PID control algorithm is less than the adjustment threshold, the adjustment amount of the duty cycle of the air pump operation is the absolute value of the output result of the PID control algorithm.

[0065] Between step S1 and step S2, there are also:

[0066] Step S1.1, set the sleeve wearing too tight threshold and the sleeve wearing too loose threshold;

[0067] Step S1.2, integrate the product of the load voltage and the air pump operation duty cycle, and take the air pressure sampling period as the integration unit, and count the result in the inflation detection stage, if less than the sleeve wearing too tight threshold, it is judged as wearing too tight, if greater than the sleeve wearing too loose threshold, it is judged as wearing too loose.

[0068] When the sphygmomanometer measures, the tightness of the sleeve is required, and wearing too tight or too loose may affect the measurement result, so the display screen of the sphygmomanometer generally has a prompt whether it is correctly worn; generally, the wearing condition of the sleeve is judged by the time from 0 to 30 mmHg of air pressure, when the time is less than a certain threshold, it is considered that the sleeve is worn too tight, and when the time is greater than a certain threshold, it is considered that the sleeve is worn too loose.

[0069] Here, the product of the measured load voltage before starting measurement and the duty cycle of the air pump is integrated, with the air pressure sampling period as the unit of integration, the result of the integration from 0-30mmHg is counted (i.e. at each time of sampling the air pressure value, the product of the voltage and the duty cycle is accumulated, and the accumulation is continued until the air pressure reaches 30mmHg), and then compared with the thresholds of tight and loose wearing, less than the threshold of tight wearing is tight wearing, and greater than the threshold of loose wearing is loose wearing; this method uses two variables (battery voltage and air pump duty cycle) related to the air pump air output, and the consistency of wearing can be better calculated by the air charge.

[0070] An electronic sphygmomanometer using the air pump control method.

[0071] Of course, the present application is not limited to the above-mentioned embodiments, and those skilled in the art can make equivalent modifications or replacements without departing from the spirit of the present application, and these equivalent modifications and replacements are all included in the scope defined by the claims of the present application.

Claims

1. A method of controlling an air pump of an electronic sphygmomanometer, characterized by, The method comprises the following steps: S1, keeping the air release valve open, measuring the battery load voltage when the air pump is idling, dividing the battery load voltage into several segments according to the battery type, setting an initial duty cycle, a minimum duty cycle threshold, a maximum duty cycle threshold for the low voltage segment, and a maximum duty cycle threshold for the high voltage segment for each voltage segment; S2, measuring the air pressure in the cuff, closing the air release valve, and keeping the air pump working at the initial duty cycle until the air pressure in the cuff reaches a preset value; S3, in the low voltage segment, calculating the inflation rate at a first frequency and adjusting the inflation rate using a PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold for the low voltage segment, limiting the current duty cycle to the maximum duty cycle threshold for the low voltage segment; if the new duty cycle is less than the minimum duty cycle threshold, limiting the current duty cycle to the minimum duty cycle threshold; S4, in the high voltage segment, calculating the inflation rate at a second frequency and adjusting the inflation rate using a PID control algorithm, if the new duty cycle is greater than the maximum duty cycle threshold for the high voltage segment, limiting the current duty cycle to the maximum duty cycle threshold for the high voltage segment; if the new duty cycle is less than the minimum duty cycle threshold, limiting the current duty cycle to the minimum duty cycle threshold, wherein the second frequency is less than the first frequency; S5, when the pulse feature extracted from the air pressure signal meets the requirement for calculating blood pressure, ending the measurement and displaying the result; In the low voltage segment, the target inflation rate is half of the expected target inflation rate, and when the output result of the PID control algorithm is positive, the duty cycle of the air pump is reduced by the absolute value of the output result; when the output result of the PID control algorithm is negative, the duty cycle of the air pump is increased by the absolute value of the output result; In the high voltage segment, an adjustment threshold is set, if the absolute value of the output result of the PID control algorithm is greater than the adjustment threshold, the adjustment amount of the duty cycle of the air pump is limited to the adjustment threshold; if the absolute value of the output result of the PID control algorithm is less than the adjustment threshold, the adjustment amount of the duty cycle of the air pump is the absolute value of the output result of the PID control algorithm.

2. The air pump control method of an electronic sphygmomanometer according to claim 1, wherein The PID control algorithm is: Output = K p * (V n – V tag ) + K d * [(V n – V tag ) – (V n-1 – V tag )], where K p is a proportional gain, K d is a derivative time, V n is the inflation rate at the n-th instant, V tag is the target inflation rate.

3. The air pump control method of an electronic sphygmomanometer according to claim 1, wherein Between step S1 and step S2, the following steps are further included: S1.1, setting a cuff tightness threshold and a cuff looseness threshold; S1.2, integrating the product of the load voltage and the duty cycle of the air pump, and taking the air pressure sampling period as the integration unit, counting the result in the inflation detection stage, if it is less than the cuff tightness threshold, it is judged as tight, if it is greater than the cuff looseness threshold, it is judged as loose.

4. An electronic sphygmomanometer characterized by comprising: The air pump control method according to any one of claims 1-3. The air pump control method according to any one of claims 1-3.

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