Combined turbine flowmeter

Abstract

The utility model relates to a combined turbine flowmeter which is provided with a main shell and a differential pressure sensor, a detection cavity is arranged in the main shell, a turbine detection assembly is arranged in the detection cavity and comprises a front guide wheel, a rear guide wheel and blades, the two guide wheels are of turbine structures and are respectively fixed and installed on the inlet side and the outlet side of the detection cavity in a sealed mode, and the turbine detection assembly is arranged in the detection cavity. The blade is located between the two flow guide wheels and is a rectangular straight blade, the blade shaft is arranged in the middle of the blade, the two bearings used for rotatably supporting the blade shaft are arranged in the centers of the inner sides of the two flow guide wheels respectively, an air inlet side pressure tap of the differential pressure sensor is formed in the inlet side of the detection chamber, and an outlet side pressure tap of the differential pressure sensor is formed in the outlet side of the detection chamber or is communicated with the atmosphere. According to the utility model, the sensitivity and the accuracy of the flowmeter under the condition of low flow can be improved, and the flowmeter is better suitable for related cardiopulmonary function detection.

Description

Technical Field

[0001] This utility model relates to a combined turbine flow meter, belonging to the field of fluid detection and medical device technology. Background Technology

[0002] Turbine flow meters are commonly used instruments in spirometry / pulmonary function testing. Inhalation and exhalation airflow drive blades to rotate via guide wheels. Photoelectric detection is used to obtain the blade rotation frequency, thereby calculating the flow rate and volume. For example, Chinese patent document CN117045231A discloses a turbine-type multifunctional spirometer, including a turbine, a turbine rotation signal acquisition module, a handheld housing, a controller, an air pump, a gas measurement chamber, and a carbon dioxide concentration sensor. The turbine and turbine rotation signal acquisition module are both located inside the handheld housing. One end of the air pump is connected to the gas outlet of the handheld housing via a pipe, and the other end is connected to the gas measurement chamber via a pipe. The detection end of the carbon dioxide concentration sensor is located inside the gas measurement chamber. The controller determines the start time of receiving exhaled air based on the output signal of the turbine rotation signal acquisition module, performs spirometry measurement, drives the air pump to start, and obtains the carbon dioxide concentration value of the exhaled air based on the output signal of the carbon dioxide concentration sensor. It simultaneously has spirometry and CO2 concentration detection functions. Chinese patent document CN113520367A discloses a portable pulmonary function testing device and its operating method, including a main unit, a mouthpiece, and a mask. The main unit of the device is improved to make it more portable, and a mask adapted to the main unit is designed. The mask has a fixing component that can be adjusted to effectively prevent the mask from falling off during exercise. An adhesive patch is provided on the inner edge of the mask to ensure a tight connection between the mask and the patient's face, ensuring that all exhaled or inhaled air passes through the turbine flow meter during exercise. The data calculated by the turbine circuit board is the patient's respiratory intensity data during exercise. These turbine flow meters are widely used due to their good noise resistance, low aerodynamic resistance, minimal impact from atmospheric pressure changes, and low production cost. However, in some situations, such as near the end of exhalation, the detection error is relatively large, affecting the accuracy of vital capacity or other related test data.

[0003] To obtain more accurate detection data, several improved technologies have emerged. For example, Chinese patent document CN118310587A discloses a turbine flow meter, including a main body with an internal cavity and a fluid outlet; a rotating shaft located within the cavity and rotatably connected to the main body; a turbine disposed on the rotating shaft and within the cavity; and a probe disposed on the main body, comprising a probe head located within the cavity and on the side of the turbine near the fluid outlet. The probe head is configured to measure the pressure of the fluid after it leaves the turbine, thereby determining the absolute fluid velocity angle after the fluid leaves the turbine based on the pressure. This turbine flow meter can measure the absolute fluid velocity angle after the fluid leaves the turbine while simultaneously measuring the fluid flow rate. This absolute fluid velocity angle can be used to correlate with system losses to improve the accuracy of the turbine flow meter. Chinese patent document CN114224316A discloses a method for calculating pulmonary function parameters based on a turbine-type pulmonary function analyzer, including the following steps: S10, the collected data is processed by moving average to obtain a new data column O(new)n; S20, low-threshold data is removed and the data is processed to be sparse; S30, peak points are found; S40, an adjustment coefficient α is calculated based on the frequency of the peak points. i S50 substitutes the data into the following expiratory volume model: Compared with existing technologies, based on the theoretical basis of the steady-state gas turbine flow model, and based on the dual-blade shaft tip gas flow turbine, a frequency coefficient adjustment algorithm based on peak point detection is proposed, which solves the problem of large expiratory volume calculation error and improves the acceptability of volume calculation results.

[0004] These technologies have unique features that help improve the accuracy of detection data, but they still have certain limitations. One important reason is that turbines inevitably have inertia and frictional resistance. When the airflow is low, they cannot drive the turbine to rotate, or the turbine rotation speed cannot reach the required level, resulting in the detected flow rate being lower than the actual flow rate. Utility Model Content

[0005] The purpose of this invention is to improve the sensitivity and accuracy of the flow meter at low flow rates, making it better suited for related cardiopulmonary function testing.

[0006] The technical solution of this utility model is as follows: a combined turbine flow meter, comprising a main housing and a differential pressure sensor. The main housing contains a detection chamber, and the detection chamber contains a turbine detection assembly. The turbine detection assembly includes two guide wheels and blades. Both guide wheels adopt a turbine structure and are fixed and sealed (the interconnected parts are sealed, that is, the outer circle of the guide wheel is sealed with the inner wall of the detection chamber) and installed on the inlet and outlet sides of the detection chamber. The blades are located between the two guide wheels and are rectangular straight blades (planar blades) with a light-shielding layer on their surface. The blade shaft is located in the middle of the blade and is fixed as a whole with the blade. Two bearings for rotating and supporting the blade shaft are respectively located in the center of the inner side (facing the blade side) of the two guide wheels. The pressure tap of the differential pressure sensor on the inlet side (high pressure side) is opened on the inlet side of the detection chamber, and the pressure tap on the outlet side (low pressure side) is opened on the outlet side of the detection chamber or connected to the atmosphere.

[0007] The guide wheel may have an annular groove on its circumference. There may be one or more annular grooves, and a sealing ring is embedded in the annular groove, thereby achieving a seal between the guide wheel and the inner wall of the detection chamber.

[0008] Preferably, the blade is an ultra-thin blade, for example, the blade thickness is ≤0.05mm.

[0009] Preferably, the blade is made of lightweight plastic, such as PET or similar lightweight plastic.

[0010] Preferably, the surface of the blade is provided with a light-blocking layer to block light. For example, the blade surface is sprayed with a light-blocking paint or other alternative coating.

[0011] Preferably, the blade shaft is a pointed shaft.

[0012] Preferably, the bearing is a sapphire bearing or a polyoxymethylene bearing.

[0013] Preferably, the two guide vanes adopt the same basic structure and have the same swirling direction.

[0014] Preferably, the angle between the airflow direction at the outlet side of the guide vane and the blade plane is 45°-90°.

[0015] Preferably, three sensors are provided for detecting blade rotation, and the detection positions of the three sensors are distributed at equal intervals (angular distances) on the same circumference.

[0016] Preferably, the sensor is a laser sensor (e.g., an infrared laser sensor), which has a transmitter and a receiver. The transmitter and receiver of the same sensor are arranged on the same straight line, with the transmitting end and the receiving end facing inward. The optical paths of the three sensors intersect each other at a 60° angle.

[0017] Preferably, the cavity of the detection cavity (the housing forming the detection cavity) is a transparent cavity or a cavity that can transmit the laser used by the laser sensor, and can be mounted on a bracket.

[0018] Furthermore, the laser sensor (including a transmitter and a receiver) is also mounted on the bracket.

[0019] In use, a lower limit for the frequency (rotational frequency, the same below) of turbine detection (detection performed by the turbine detection component, or detection results calculated based on blade speed / rotational frequency) can be set. When the blade frequency (real-time frequency / measured frequency) is greater than (or not less than) the lower limit of the turbine detection frequency, the flow detection result of the turbine detection component (flow result calculated based on blade frequency) is confirmed as the flow detection result; when the blade frequency is less than (or not greater than) the lower limit of the turbine detection frequency, the flow detection result of the differential pressure sensor (flow result calculated based on differential pressure) is confirmed as the flow detection result.

[0020] In use, upper and lower limits of the turbine detection frequency during the transition phase can also be set. When the blade frequency is not less than the upper limit of the turbine detection frequency during the transition phase, the flow detection result of the turbine detection component is confirmed as the flow detection result. When the blade frequency is not greater than the lower limit of the turbine detection frequency during the transition phase, the flow detection result of the differential pressure sensor is confirmed as the flow detection result. When the blade frequency is between the upper and lower limits of the turbine detection frequency during the transition phase, the flow detection result is determined according to the following formula:

[0021]

[0022] in For traffic detection results, The flow detection results are from the turbine detection component. The flow detection results are from the differential pressure sensor. For the blade frequency, This is the upper limit of the frequency for turbine detection during the transition phase. This is the lower limit of the frequency for turbine detection during the transition phase.

[0023] The above thresholds (upper and lower limits) can be set according to the effective detection range of the turbine detection component.

[0024] When using it, you can also set an inertial rotation model that represents the frequency-time curve (function) relationship under the inertial rotation of the blade. During the period when the blade frequency continues to decrease (you can set the shortest duration of this period and ignore cases with a duration shorter than the shortest duration), compare whether the way the blade frequency changes with time is consistent with the inertial rotation model (allowing for differences within the defined error range). If it is consistent with the inertial rotation model, set the blade frequency of this period to zero.

[0025] The beneficial effects of this invention are as follows: Because the rotating component uses straight blades, while ensuring the airflow's pushing effect on the blades, compared to directly using a turbine as the rotating component, the mass (weight) and moment of inertia of the rotating component are effectively reduced, improving the response speed of the rotating component to changes in airflow and enhancing the sensitivity at the beginning and end of the detection process. Because the blade surface is provided with a light-shielding layer, which can be formed by applying a suitable coating with light-shielding properties to the blade surface, a very thin blade thickness is allowed, further effectively reducing the blade's mass (weight). Because a differential pressure flow detection device is set on top of the turbine flow meter, detection data can be obtained using the differential pressure flow meter when the flow rate is below the effective detection limit of the turbine, thereby further reducing detection errors caused by low flow rates at the end of the detection process. Because a three-sensor detection method is used, the rotation direction of the blades can be identified, and changes in the subject's breathing state during the test can be detected at any time, avoiding distortion of the detection results due to changes in breathing state and improving the detection accuracy at the end of the test. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the combined turbine flow meter involved in this utility model;

[0027] Figure 2 This is a schematic diagram (exploded view / separated state view) of the turbine detection component involved in this utility model.

[0028] Figure 3 This is a schematic diagram of the sensor layout under the three-sensor detection method involved in this utility model;

[0029] Figure 4 This is a timing diagram of the three-sensor detection method involved in this utility model;

[0030] Figure 5 This is a frequency-time curve of the blade under inertial rotation, which relates to this utility model.

[0031] The diagram shows: 1. Guide wheel; 2. Bearing; 3. Blade; 4. Blade shaft. Detailed Implementation

[0032] See Figures 1-5 To improve the performance of turbine flow meters, the following improvements can be made to existing turbine flow meters: 1) Set up a guide wheel 1 with a turbine structure and use straight blades 2 as rotating parts; 2) Use a pointed shaft for the blade shaft 4 to reduce the contact area between the shaft and the bearing 3 and achieve near-zero area contact; 3) Use lightweight / low-density blades and shafts; 4) Use the detection data (detection results) of differential pressure flow meters for small flow rates (e.g., <50mL / s); 5) Improve the blade rotation detection method to identify the rotation direction.

[0033] The above improvements can be implemented individually, or in any combination or all at once.

[0034] Further explanation:

[0035] A turbine-structured guide wheel (or guide structure) is used, with straight blades as the rotating parts.

[0036] See Figure 1 and Figure 2 Two turbine-type guide vanes 1 are installed in the detection chamber (the airflow channel in the corresponding part of the housing). Blades 3 are installed between the two guide vanes. The blades are rectangular straight blades (planar blades). The blade shaft is located in the middle of the blade (the blades on both sides of the shaft are symmetrical). The bearings for supporting the two ends of the blade shaft are located in the center of the front and rear guide vanes near the blades (facing the blades). The guide vanes convert the axial intake airflow (the intake air flows along the pipe, which is axial) into a rotating forward (spiral) vortex, which drives the straight blades to rotate. This can significantly reduce the strength standard of the straight blades, reduce the thickness and area of ​​the straight blades, and thus significantly reduce the moment of inertia of the blades.

[0037] The number and shape of turbine blades in the guide vane should take into account both the guiding resistance (including the influence of resistance on the lower limit of eddy current detection and the sensitivity of differential pressure detection) and the driving effect of airflow on straight blades (especially at low flow rates) (depending on the angle between the airflow and the blade plane; the thrust is greatest when perpendicular and zero when parallel). Typically, the angle between the airflow (swirling flow) direction on the outlet side of the guide vane and the blade plane can be 45°-90° to obtain a better overall effect.

[0038] The blade shaft is a pointed shaft, which reduces the contact area between the shaft and the bearing, thereby reducing the contact friction surface and frictional resistance. The bearings used are low-friction bearings that are compatible with the pointed shaft, and any suitable existing technology can be adopted.

[0039] Blades and blade shafts are made from suitable lightweight materials, and bearings with low friction (low coefficient of friction) (e.g., jewel bearings) are used to reduce friction.

[0040] With the development of materials technology, lightweight metals and plastics are becoming increasingly common. Materials with low density and high strength, such as titanium, aluminum, and plastics, can be used to manufacture blades and shafts. By controlling the density or weight of the blades and shafts to reduce inertia, the response of turbine flow meters can be effectively improved. For example, plastics typically have a lower density than metals. Simultaneously, the blade thickness can be appropriately reduced, for example, by using ultra-thin blades. Through engineering experiments, a preferred implementation is to use ultra-thin blades supported by PET material, with a thickness controlled to ≤0.05 mm. The surface of the ultra-thin blades is coated with a light-blocking varnish (or other alternative materials) to achieve infrared radiation blocking, ensuring that infrared laser detectors can effectively detect the blades.

[0041] The blade shaft should be made of a material that is rigid, wear-resistant, and has a small diameter, such as a lightweight steel shaft. Other lightweight and rigid materials can also be selected. The diameter of the shaft can be controlled within 0.3 mm.

[0042] Bearings can be made of materials such as sapphire or POM (polyoxymethylene) plastic, with sapphire being the preferred material.

[0043] Add a differential pressure flow detection device (or differential pressure flow meter) to use the detection results of the differential pressure flow meter at small (very small) flow rates.

[0044] Because the airflow is obstructed by the guide vanes, a pressure difference exists across the turbine detection assembly (blades and front and rear guide vanes), and this pressure difference is positively correlated with the flow rate. Utilizing the principle of pressure difference detection, a pressure difference sensor (e.g., a low-pressure difference sensor) is added. One pressure sampling port for the pressure difference sensor (connected to the high-pressure side interface) is located on the inlet side of the turbine detection assembly, and another pressure sampling port (connected to the low-pressure side interface) is connected to the atmosphere or located on the outlet side of the turbine detection assembly. When the flow rate is below a set turbine detection lower limit (e.g., 50 ml / s), low-flow rate measurement is achieved using the pressure difference principle, compensating for the insufficient accuracy and precision of the turbine flow meter at low flow rates. Testing has shown that with the addition of pressure difference detection, the turbine detection assembly design of this invention can achieve a resolution of 10 mL / s or even lower.

[0045] During the testing process, when the blade frequency (or rotational speed, hereinafter the same) is zero or lower than the set lower limit, the test result obtained from differential pressure detection is used as the test result; when the blade frequency is greater than zero or not lower than the set lower limit, the test result obtained from turbine detection is used as the test result. If necessary, a transition phase between the two test results can be set, during which the two test results are fused. For example, for the blade frequency (or rotational speed), an upper limit for the frequency (or rotational speed) during the transition phase can be set. and lower limit (The lower limit can usually be zero or greater than zero.) When the blade frequency or rotational speed is between the upper and lower limits of the transition phase, the detection result (real-time flow rate) is calculated using the following formula:

[0046]

[0047] in, For the test results, For turbine inspection results, The result is from the differential pressure test. blade frequency ( ), This is the upper limit of the frequency for turbine detection during the transition phase. This is the lower limit of the frequency for turbine detection during the transition phase.

[0048] This method of determining the flow rate during the transition phase is also suitable for situations where the blade frequency enters the transition phase range during the detection process.

[0049] When the blade frequency is set to zero (because the blade is in an inertial rotation state), differential pressure detection data is used.

[0050] Improve the blade rotation detection method to identify the rotation direction and achieve high flow rate detection.

[0051] Turbine flow meters typically use laser detection devices to detect (or count) blade rotation. The laser detection device can be a split type, where the transmitter beam (or optical path) passes through the blade rotation area and is directed to the receiver. When there are no blades obstructing the view between the two, the receiver receives the optical signal. When the blades rotate between the two, the beam is blocked, and the receiver cannot receive the optical signal. Thus, rotation counting is achieved through photoelectric signal conversion (for example, the resistance value of a photoresistor switches to form different high and low level outputs).

[0052] See Figure 3 This invention employs three infrared laser detection devices (or infrared laser sensors, or infrared laser detectors) and three sets of transmitter-receiver pairs. The angle α between the optical paths (beams) of each transmitter-receiver pair is 60 degrees. All three beams are perpendicular to the blade axis and can typically be located in the same plane, but can also be positioned at different axial locations if necessary. This detection method not only identifies the direction of blade rotation and distinguishes between exhalation and inhalation (airflows in different directions), but also increases detection accuracy.

[0053] Figure 3The numbers outside the outer circle (corresponding to the inner wall of the detection cavity) are used to indicate the position (which can be in scale form), and the inner circle is the trajectory of the blade vertices A and B during rotation. To illustrate the principle, it is assumed that the distance / angular distance between adjacent scales (the positions indicated by the scales) (for example, the distance from scale 9_1 to 9, scale 9 to 9_2, and scale 9_2 to 8_1) is 1 / 36 of a circle.

[0054] The three transmitters are located at 9_2, 1_2, and 5_2, and the three receivers are located at 1_1, 5_1, and 9_1, respectively. The transmitters and receivers are positioned opposite each other, and their beams follow optical paths 1, 2, and 3, respectively. The intersection of each optical path with the plane of blade rotation (trajectory) is the sensor's detection position of the blade. When the blade (any part of the blade) is located at this position, the beam is blocked; when the position is changed and there is no blade, the optical path is open.

[0055] Based on the same principle, any other suitable type of sensor can be used to replace the infrared laser detector, and the detection position can be the same as the detection position of the infrared laser detector.

[0056] For ease of analysis, the following assumptions are made: 1) The blade rotates counterclockwise at a constant speed; 2) The time zero point is the time when the blade passes through position 9_1; 3) A pair of transmitters and receivers at the same position do not affect each other; 4) A high time sequence indicates that the optical path is open, and a low time sequence indicates that the optical path is closed; 5) Time is represented by the scale of the circle traversed by end A of the blade (the numbers below the timing diagram).

[0057] Figure 4 The timing diagram for this detection is shown. The intervals between 9_2 and 7_2 represent 1 / 6 of a circumference, 7_2 and 5_2 represent 1 / 6 of a circumference, and 5_2 and 3_2 represent 1 / 6 of a circumference. This demonstrates that the requirement of one rising edge corresponding to 1 / 6 of a blade rotation is met. This detection method can achieve a 60-degree angle judgment, and when the blade rotates at high speed, the sensitivity for high-speed rotation detection can be further increased. Experiments have shown that this detection method meets the requirements of the YY / T1438 (ISO23747) standard, achieving a maximum flow rate detection of 20 L / s while maintaining sensitivity for low flow rates. At extremely low speeds, because it can identify the 60-degree angle before rotation stops, it can detect even lower rotational speeds.

[0058] Furthermore, the flow meter involved in this utility model can also eliminate natural inertia through algorithms / models, specifically including:

[0059] Derivation of the model / formula for inertial rotation

[0060] The so-called natural inertia refers to the characteristic that when a blade rotates under the drive of airflow, it will continue to rotate even after the driving force suddenly disappears (this can be called inertial rotation). Under the action of resistance, the inertial rotation will gradually stop (this can be called natural stopping). Therefore, after the airflow stops, a certain airflow will still be recorded based on the inertial rotation of the blade, but this airflow is not real.

[0061] The study found that, in cases where airflow suddenly stops, there is a non-linear negative correlation between the natural stopping time and the blade frequency at which the airflow stops. Figure 5 The corresponding frequency-time curves are given, where Fmax is the maximum frequency of blade rotation, F1–F5 represent the five frequency points at which the blade begins its inertial rotational motion, and t4 is the time corresponding to F4.

[0062] Based on the experimental data, the curve function was obtained through fitting:

[0063]

[0064] The zero point of time in the formula is the frequency. The moment (point in time).

[0065] Set the zero point of time to the moment when the airflow stops, and take... The value is 4000 (currently, it is generally believed that the maximum blade rotation frequency of the current measurement system is 4000Hz). Through experimental data fitting / verification, the following frequency-time function of inertial motion (which can be called the inertial rotation model / model formula) is obtained:

[0066] .

[0067] Alternatively, any other suitable method can be used to determine the inertial rotation model / formula. Experimental data for constructing the inertial rotation model / formula can be obtained using appropriate flow meters and standard / higher-precision flow measurement devices.

[0068] Inertia cancellation of waveforms using an inertial rotation model (formula)

[0069] Compare the measured (especially near the end) expiratory frequency-time data (which can be discrete data) with the frequency-time relationship of the inertial rotation model. If the two are consistent (within the allowable error range), the rotation of the blade is considered to be an inertial rotational motion. Set the blade rotation frequency of the corresponding stage to 0. When a differential pressure detection device is also installed, use the differential pressure retrieval result of the corresponding stage as the retrieval result.

[0070] Experiments show that this invention can effectively improve response speed and sensitivity, obtain higher accuracy flow values ​​at low flow rates, achieve plateaus in end-expiratory and end-inspiratory curves, meet the requirements of pulmonary function guidelines for end-expiratory judgment, and allow for an increase in the upper limit of turbine flow rate, with the volume change in the last second of end-expiratory flow being <0.025L, reaching 0.0125L or even lower.

[0071] Unless otherwise specified, the preferred and optional technical means disclosed in this utility model can be arbitrarily combined to form several different specific embodiments when one preferred or optional technical means is a further limitation of another technical means.

Claims

1. A combined turbine flow meter, comprising a main housing, wherein a detection chamber is provided within the main housing, characterized in that... The device is also equipped with a differential pressure sensor. The detection chamber contains a turbine detection assembly, which includes two guide vanes and blades. Both guide vanes are turbine structures and are fixedly and sealed on the inlet and outlet sides of the detection chamber, respectively. The blades are rectangular straight blades located between the two guide vanes and have a light-shielding layer on their surface. The blade shaft is located in the middle of the blade and is fixed to the blade as a whole. Two bearings for rotating and supporting the blade shaft are respectively located in the center of the inner side of the two guide vanes. The pressure tap on the inlet side of the differential pressure sensor is located on the inlet side of the detection chamber, and the pressure tap on the outlet side is located on the outlet side of the detection chamber or connected to the atmosphere.

2. The combined turbine flow meter as described in claim 1, characterized in that... The guide wheel has an annular groove on its circumference. There are one or more annular grooves, and a sealing ring is embedded in the annular groove, thereby achieving a seal between the guide wheel and the inner wall of the detection chamber.

3. The combined turbine flow meter as described in claim 1, characterized in that... The blade is an ultra-thin blade made of lightweight plastic.

4. The combined turbine flow meter as described in claim 1, characterized in that... The surface of the blade is provided with a light-shielding layer.

5. The combined turbine flow meter as described in claim 1, characterized in that... The blade shaft is a pointed shaft, and the bearing is a sapphire bearing or a polyoxymethylene bearing.

6. The combined turbine flow meter as described in claim 1, characterized in that... The two guide vanes use the same basic structure and have the same swirling direction.

7. The combined turbine flow meter as described in claim 6, characterized in that... The angle between the airflow direction at the outlet side of the guide vane and the blade plane is 45°-90°.

8. The combined turbine flow meter as described in any one of claims 1-7, characterized in that... Three sensors are provided to detect the rotation of the blades, and the detection positions of the three sensors are equally spaced on the same circumference.

9. The combined turbine flow meter as described in claim 8, characterized in that... The detection cavity is a transparent cavity or a cavity that can transmit the laser used by the laser sensor. It can be installed on a bracket. The bracket has a laser sensor with a transmitter and a receiver. The transmitter and receiver of the same sensor are arranged on the same straight line, with the transmitting end and the receiving end facing inward. The optical paths of the three sensors intersect each other at a 60° angle.

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