WO2022166037A1

WO2022166037A1 - Tip clearance online measuring device, measuring method, and test bench

Info

Publication number: WO2022166037A1
Application number: PCT/CN2021/095979
Authority: WO
Inventors: 肖志成; 吴亚东; 蒙一鸣; 田杰; 李健萍; 欧阳华
Original assignee: 上海交通大学; 上海交大航空发动机科技有限公司
Priority date: 2021-02-02
Filing date: 2021-05-26
Publication date: 2022-08-11
Also published as: CN112902859B; CN112902859A

Abstract

A tip clearance online measuring device (100), comprising: an optical fiber probe (5), configured as capable of producing a conical light beam; an optical fiber (6), connected at one end to the optical fiber probe (5), the optical fiber (6) comprising a transmitting optical fiber (8) and a receiving optical fiber (7); a control device (9), connected to the other end of the optical fiber (6), the control device (9) being configured as capable of controlling the intensity of a light transmitted by the transmitting optical fiber (8), processing a reflected light received by the receiving optical fiber (7), and identifying the time that a blade being measured uses to pass through the conical light beam. A contactless real-time measurement is implemented with respect to tip clearance and is free of interference from factors such as the blade material and surface properties, thus increasing the reliability of the measurement; at the same time, the measuring device is structurally simple, inexpensive, and convenient to mount and unmount, obviates the need for multipoint calibration, and reduces the difficulty of measuring tip clearance. Also provided are a tip clearance online measuring method and a test bench.

Description

On-line measuring device, measuring method and test bench for blade tip clearance

technical field

The application relates to the field of mechanical measurement, and in particular, to an online measurement device and an online measurement method for blade tip clearance, and a test bench for calibrating the online measurement device.

Background technique

Tip clearance refers to the radial distance between the tip of a rotor blade and the casing. For turbomachinery, tip clearance is an important design parameter. If the blade tip clearance is too small, it will lead to friction between the blade and the casing, resulting in potential safety hazards and equipment failure. Therefore, the online tip clearance measurement technology can improve the operation efficiency of the turbomachinery and reduce the operation risk. Existing technologies fall into many categories.

One is to measure by capacitive sensor. The disadvantage of this method is that it needs to calibrate multiple points to complete the measurement, and is greatly affected by the geometry of the blade tip to be measured and the properties of the impeller working medium, the reliability of long-term work is low, and the portability is limited.

The second is to measure the change of the reflected signal intensity (amplitude) through an optical (including electromagnetic wave) probe. These methods are extremely sensitive to the reflective properties of the blade surface, and slight fouling or tilting can greatly affect the measurement results.

The third is to measure the distance through laser triangulation. This method has high reliability and ease of use, but the sampling frequency is limited and cannot be applied to high-speed turbomachinery. And the size of the product is large, which is not suitable for practical application.

The fourth is the tip timing method (for example, Ye Dechao et al. published the paper "Tip gap measurement technology based on multi-beam tip timing principle" published in "Optoelectronic Laser", Vol. 22, No. 4, 2011, p. 570). The probe of this method has a complex structure and large size, and requires two channels of photoelectric signals for detection.

Therefore, those skilled in the art are committed to developing an on-line measuring device, measuring method and test bench for the tip clearance, which can realize non-contact real-time measurement of the tip clearance without being disturbed by factors such as blade material and surface properties. The measurement reliability is improved, and at the same time, the measurement device is simple in structure, low in cost, convenient in disassembly and assembly, does not need multi-point calibration, and reduces the difficulty of blade tip clearance measurement.

SUMMARY OF THE INVENTION

In order to achieve the above purpose, the present application provides an online measuring device for blade tip clearance, including:

a fiber optic probe configured to form a cone beam;

an optical fiber, one end is connected to the optical fiber probe, and the optical fiber includes a transmitting optical fiber and a receiving optical fiber;

a control device connected to the other end of the optical fiber, the control device configured to be able to control the intensity of the light emitted by the transmitting optical fiber, process the reflected light received by the receiving optical fiber, and identify the blade under test passing through the taper The time spent by the beam.

In some embodiments, optionally, one end of the optical fiber probe is connected to the optical fiber, and the other end is provided with a casing, the casing is provided with an opening, and the center of the opening is the center of the light probe. overlapping; a lens is also arranged in the casing.

In some embodiments, optionally, the optical fibers are bundled fibers.

In some embodiments, optionally, the control device includes an emission light control module, a reflected light processing module and an arithmetic module, the emission light control module is configured to control the intensity of the light emitted by the emission fiber, the reflection light The light processing module is configured to convert the reflected light signal into an electrical signal; the arithmetic module is configured to be able to identify the time taken for the blade under test to pass through the cone beam.

In some embodiments, optionally, the control device further includes a communication module, and the communication module is configured to communicate the control device with the upper computer.

In order to achieve the above purpose, the present application also provides a method for on-line measurement of blade tip clearance using the above-mentioned measuring device, the method comprising the following steps:

Emit a cone beam to irradiate on the tested leaf;

receiving the light reflected by the measured blade;

converting the reflected light into an electrical signal;

Identifying the time when the blade under test passes through the cone beam;

Calculate tip clearance.

In some embodiments, optionally, the step of converting the reflected light into an electrical signal includes: first converting the reflected light into an analog electrical signal, and then converting the analog electrical signal into a digital electrical signal.

In some embodiments, optionally, the tip clearance is calculated according to Equation 1 below:

Wherein, d _lens represents the effective diameter of the lens of the measuring device; c represents the size of the blade tip clearance; v represents the image distance; d _tip represents the thickness of the blade tip; d _focus represents the focal point diameter; rotational speed; r represents the tip radius of the blade to be measured; t represents the time when the control device of the measurement device is triggered when the blade to be measured passes through the cone beam.

In some embodiments, optionally, the formula 1 can be simplified as follows:

c=kwrt-b 2

Where, c represents the tip clearance, k represents the fiber probe constant, w represents the rotational speed of the blade under test, r represents the tip radius of the blade under test, and t represents the blade under test passing through the cone The time when the control device is activated when the beam is on, b represents the constant of the measured blade.

In some embodiments, optionally, the step of identifying when the bladed beam passes through the cone of light comprises:

When the analog electrical signal exceeds a preset trigger voltage threshold, the control device is triggered, and the tested blade starts to pass through the fiber probe;

When the analog electrical signal is lower than the preset trigger voltage threshold, the control device is triggered, and the measured blade leaves the fiber probe.

In some embodiments, optionally, the method further includes:

When the time when the measured blade starts to pass through the optical fiber probe exceeds a preset delay threshold, it is considered that the control device is effectively triggered;

When the time when the measured blade leaves the light probe exceeds the preset delay threshold, it is considered that the control device is effectively triggered.

In some embodiments, optionally, the method further includes:

In the case of the effective triggering, the time difference between the time point when the measured blade passes through the optical fiber probe and the time point when the measured blade leaves the optical fiber probe is taken as the time point when the measured blade passes through the cone The time t at which the control device is activated when the beam is activated.

In some embodiments, optionally, the method further comprises: calibrating the constant k of the fiber probe.

In some embodiments, optionally, the step of calibrating the constant k of the fiber probe is performed on a test bench.

Optionally, in some embodiments, the test bed is configured to enable control of tip clearance.

In some embodiments, optionally, the step of calibrating the constant k of the optical fiber probe includes the following steps:

The impeller of the test stand rotates n times, and the time when each blade of the impeller passes through the fiber probe in each circle is collected;

Calculate the average time that each of the blades passes through the fiber probe based on n rotations of the impeller;

increasing the preset value of the tip clearance in sequence, and repeating the above steps;

Taking the product of the triggering time of the control device and the tip speed of the blade as the horizontal axis, and the tip clearance as the vertical axis, the corresponding variation relationship of each blade is obtained;

Fitting the variation relationship corresponding to each of the blades as a straight line to obtain a slope;

Calculate the average value of the slope, and complete the calibration of the constant k of the fiber probe.

In some embodiments, optionally, a least squares method is used to fit the variation relationship corresponding to each of the blades as a straight line.

In order to achieve the above purpose, the present application also provides a test bench for calibrating the above-mentioned online measurement device, the test bench includes a bracket, a power component, an impeller and a micro-movement platform, the bracket and the power component Fixed connection, the impeller is connected to the output shaft of the power component, the fiber probe of the online measurement device is fixed on the micro-movement platform, and the tip clearance can be adjusted by adjusting the horizontal position of the micro-movement platform. control.

In some embodiments, optionally, the test bench is arranged on a fixed platform.

In some embodiments, optionally, the micro-movement platform has four degrees of freedom.

Compared with the prior art, the present invention has the following beneficial effects:

1. The blade tip clearance is calculated by using the cone beam to detect the blade, combining the rotational speed and the blade radius;

2. It can realize non-contact real-time measurement of blade tip clearance, and it is not disturbed by factors such as blade material and surface properties, which improves the measurement reliability;

3. The tip clearance measurement is completed by a fiber probe with a lens at the top. The structure is simple, the cost is low, and the disassembly and assembly are convenient. In practical applications, multi-point calibration is not required, thus reducing the difficulty of monitoring the tip clearance;

4. By only measuring the time when the blade passes through the light cone and converting the tip clearance, the measurement can be performed at a very high sampling rate while reducing the amount of data, thereby improving the measurement accuracy and reducing the communication pressure with the host computer.

The concept, specific structure and technical effects of the present application will be further described below with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the present application.

Description of drawings

FIG. 1 is a schematic structural diagram of an online measurement device 100 according to a preferred embodiment of the present application;

Fig. 2 is the composition schematic diagram of the control device;

Fig. 3 is the flow chart of the online measurement method;

Fig. 4 is the light path diagram of the measured blade passing through the cone beam;

Fig. 5 is the schematic flow chart when using formula (2) to measure;

6 is a schematic diagram of a triggering time determination method;

Fig. 7 is the structural representation of the test bench;

Fig. 8 is the schematic flow chart of calibration fiber probe constant k;

9 is a schematic diagram of the corresponding change relationship of each measured blade in the calibration process;

FIG. 10 is a schematic diagram of the measurement results.

Detailed ways

The following describes several preferred embodiments of the present application with reference to the accompanying drawings, so as to make its technical content clearer and easier to understand. The present application can be embodied in many different forms of embodiments, and the protection scope of the present application is not limited to the embodiments mentioned herein.

In the drawings, structurally identical components are denoted by the same numerals, and structurally or functionally similar components are denoted by like numerals throughout. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present application does not limit the size and thickness of each component. In order to make the illustration clearer, the thicknesses of components are appropriately exaggerated in some places in the drawings.

As shown in FIG. 1 , an on-line measurement device 100 for blade tip clearance based on blade tip timing technology includes an optical fiber probe 5 , an optical fiber 6 , and a control device 9 . One end of the fiber probe 5 is connected to the fiber 6, and the other end can emit a light beam, which is a cone beam 2. When the measured blade 1 passes through the cone beam 2, the cone beam 2 can illuminate the measured blade 1. The control device 9 is connected to the other end of the optical fiber 6 , and the control device 9 can control the optical fiber 6 to emit laser light. After the laser light is emitted through the fiber probe 5 , a cone beam 2 is formed. The control device 9 can control the intensity of the emitted laser light. When the blade under test 1 passes through the cone beam 2, the tip area of the blade under test 1 is diffusely reflected, and the reflected light can be converted into an electrical signal after being received by the control device 9. The control device 9 can identify the time it takes for the blade 1 to be tested to pass through the cone beam 2 according to the electrical signal.

The fiber probe 5 can convert the laser light emitted by the fiber 6 into a cone beam 2 . In some embodiments, the fiber probe 5 includes a casing 3, one end of the casing 3 is connected to the optical fiber 6, and the other end is used for emitting a light beam. The end of the casing 3 for emitting the beam is provided with an opening 11 for the laser to emit. The center of the opening 11 overlaps with the center of the fiber probe 5, and a lens 4 is arranged in the casing 3. When the laser is emitted from the optical fiber 6 Outgoing, after passing through the lens 4, a cone beam 2 is formed. It should be understood that other structures that enable the fiber probe 5 to form the cone beam 2 can also be applied in the present application.

In the present application, laser light, preferably single-mode laser light, needs to be emitted through the optical fiber 6 , and at the same time, the light emitted by the blade also needs to be received through the optical fiber 6 . The optical fiber 6 includes a transmitting optical fiber 8 and a receiving optical fiber 7, wherein the transmitting optical fiber 8 is used for emitting laser light, and the receiving optical fiber 7 is used for receiving reflected light. One end of the transmitting fiber 8 and the receiving fiber 7 are both connected to the fiber probe 5 , and the other end is connected to the control device 9 . In some embodiments, the optical fiber 6 is a bundled optical fiber 6, that is, the part of the transmitting optical fiber 8 and the receiving optical fiber 7 connected to the optical fiber probe 5 is arranged in an optical fiber bundle, and then the transmitting optical fiber 8 and the receiving optical fiber 7 are connected to the control device 9. That part can be separated to facilitate the connection of the two to different interfaces of the control device 9 respectively. It should be understood that two separate fibers could also be used.

The control device 9 can control the emitting fiber 8 to emit laser light, and can control the intensity of the emitted laser light. At the same time, after the receiving optical fiber 7 receives the reflected light signal, the control device 9 converts the optical signal received by the receiving optical fiber 7 into an analog electrical signal. For the convenience of processing, the analog electrical signal is further converted from analog to digital. Then, the control device 9 performs arithmetic processing on the converted electrical signal, and can identify the time when the blade 1 under test passes through the cone beam 2 . As shown in FIG. 2 , in some embodiments, the control device 9 includes at least an emission light control module, a reflected light processing module and an arithmetic module, wherein the emission light control module has an optical fiber 6 interface, which is connected to the emission optical fiber 8 and can control the emission optical fiber. 8. Emit single-mode laser and control the laser intensity. The emission light control module may be an existing laser generating device in the prior art. The reflected light processing module has an optical fiber 6 interface, which is connected to the receiving optical fiber 7. When the reflected light signal passing through the receiving optical fiber 7 is converted into an analog electrical signal by the reflected light processing module, it is further converted into a digital signal. The reflected light control module may include a photocell for converting optical signals into electrical signals, and an A/D conversion component for converting analog electrical signals into digital signals. The operation module receives the digital signal from the reflected light processing module, and can perform operation to identify the time when the blade 1 under test passes through the cone beam 2 . At the same time, the operation module can also be connected with the emission light control module, and sends instructions such as the intensity of the laser to be emitted to the emission light control module. In some embodiments, the control device 9 further includes a storage module to store the digital signal, the calculated data, etc. in the control device 9 . In some embodiments, the control device 9 may also integrate subsequent data processing functions, that is, calculate the tip clearance according to the time when the measured blade 1 passes through the cone beam 2 , the rotational speed and the radius of the measured blade 1 . In some embodiments, the control device 9 further includes a communication module, which can communicate with the upper computer 10 to realize data interaction, thereby realizing the remote control of the online measurement device 100, and at the same time, the function of calculating the blade tip clearance can be implemented on the upper computer 10. It is realized to simplify the structure of the control device 9 . The control device 9 may adopt a known processing system, such as an industrial computer, a single-chip microcomputer, an embedded system, etc., and a display component, a human-computer interaction component, etc. may also be integrated on the control device 9 .

The present application also provides a method for on-line measurement of blade tip clearance, as shown in Figure 3, comprising the following steps:

Step S1: emit a cone beam 2 to irradiate the blade 1 under test. The cone-shaped beam 2 can be generated by the above-mentioned online measuring device 100, preferably, the single-mode laser is emitted from the transmitting optical fiber 8, and the cone-shaped beam 2 is formed after passing through the lens 4, and is irradiated on the measured blade 1 through the casing 3;

Step S2: Receive the light reflected by the blade 1 under test. When the measured blade 1 passes through the cone beam 2, diffuse reflection occurs in the blade tip area, and the reflected light is transmitted to the control device 9 through the receiving fiber 7;

Step S3: Convert the reflected light into an electrical signal. After receiving the reflected light, the control device 9 converts the reflected light signal into an analog electrical signal through the reflected light processing module, and further can be converted into a digital signal;

Step S4: Calculate the tip clearance. The control device 9 can process the electrical signal to identify the time when the measured blade 1 passes through the cone beam 2, and then calculate the size of the blade tip gap by combining the blade rotational speed and the blade tip radius.

Among them, in step 4, the principle of calculating the tip clearance is as follows:

As shown in Figure 4, it is a schematic diagram of the optical path of the measured blade 1 passing through the cone beam 2, in which, d _lens represents the effective diameter of the lens 4, x _pass represents the passing length of the blade tip in the area of the cone beam 2, and c represents the blade The size of the tip gap, v is the image distance, d _tip is the thickness of the blade tip, d _focus is the diameter of the focal point, ω is the rotational speed, r is the radius of the blade tip, and t is the control device 9 is triggered when the measured blade 1 passes through the cone beam 2 time. Then the relationship between the tip clearance and the trigger length can be expressed as:

The right-hand side of the formula consists of two parts, the first part

It is an item that is proportional to the time when the control device 9 is triggered when the blade passes through the cone beam 2 . the second part

is a constant related to both the measured object and the probe.

In practice, this formula can be simplified to:

c=kωrt-b (2)

Among them, k is a constant only related to the optical fiber probe 5, which is called the optical fiber probe 5 constant, which needs to be calibrated before actual measurement. And b is a constant related to the measured blade 1, it only affects the specific value of the tip clearance without affecting its variation, so the value of b can be regarded as the measurement zero point and can be specified during the measurement process.

The process of using formula (2) to measure the tip clearance is shown in Figure 5. The constant k of the fiber probe 5 is calibrated, and then the time t when the control device 9 is triggered when the measured blade 1 passes through the cone beam 2 is measured. Radius, and considering b as the zero point, calculate the tip clearance c.

Referring to FIG. 6 , the method for determining the time t when the control device 9 is activated is as follows. The control device 9 is triggered, specifically, the component in the control device 9 that converts the reflected light into an electrical signal is triggered. In some embodiments, the component that converts the reflected light into an electrical signal can use a photocell. The photocell is used as an example for description here. First, set a trigger voltage threshold and noise suppression delay threshold. When the amplitude of the electrical analog signal collected by the control device 9 exceeds the set trigger voltage threshold, it can be considered as starting to trigger, that is, the blade 1 under test starts to pass through the fiber probe 5 . When the amplitude of the analog electrical signal is lower than the trigger voltage threshold, it is regarded as the end of the trigger, that is, the blade under test 1 completely leaves the fiber probe 5 . Considering the noise fluctuation of the electrical analog signal itself, the end trigger whose time exceeds the noise suppression delay threshold after the start trigger is called an effective end trigger. Similarly, the start trigger whose time exceeds the noise suppression delay threshold after the end trigger is regarded as a valid end trigger. is a valid start trigger. The time difference between an effective rising trigger and an effective falling trigger is the time t when the photocell is triggered.

After identifying the time it takes for the blade 1 to pass through the cone beam 2, calculate the equivalent length of the blade 1 to pass through the cone beam 2 according to the blade speed and blade radius, and then calculate the tip clearance according to the equivalent length. That is, one of the two formulas described above can be used for calculation.

For formula (2), the fiber probe constant k can be calibrated by the test bench. In this test rig, the rotational speed and tip clearance of the blade under test can be precisely controlled.

As shown in FIG. 7 , the test bench includes a bracket 22, a power component 21, an impeller 23 and a micro-movement platform 24. The bracket 22 is fixedly connected to the power component 21, and the impeller 23 is connected to the output shaft of the power component 21. The on-line measurement device to be calibrated The fiber probe of 100 is fixed on the micro-movement platform 20. By adjusting the horizontal position of the micro-movement platform 24, the gap between the fiber probe and the tip of the impeller 23 is adjusted to achieve the purpose of accurately controlling the tip gap. At the same time, by controlling the rotational speed of the power component 21 , the purpose of precisely controlling the rotational speed of the impeller 23 is achieved.

In some embodiments, the power component 21 may be a servo motor, and it should be understood that other types of motors may also be used.

In some embodiments, in order to precisely control the blade tip clearance, the micro-movement platform 24 can be selected as a four-axis micro-movement platform 24, that is, the micro-movement platform 24 has four degrees of freedom, which can be precisely adjusted in the three directions of XYZ, and the surrounding The angle of the center line of the fiber probe 5 can be precisely adjusted. The micro-moving platform 24 can well control the blade tip clearance, and the control precision can be set to not less than 0.01 mm.

In some embodiments, the test bench can be placed on a platform 20 whose rigidity meets a preset requirement, so as to reduce the interference of the external environment on the calibration.

Referring to Figure 8, the method for calibrating the fiber probe constant is as follows:

S201: Control the rotation of the power component 21 so that the impeller 23 rotates. The impeller 23 rotates n times, and the time t _ij when the jth blade of the ith circle passes through the optical fiber probe is collected;

S202: Calculate the average time for the blades under test of the impeller 23 to pass through the fiber probe based on n rotations of the impeller 23:

S203: Increase the blade tip clearance by a preset value in turn, and repeat steps S201 to S202.

S204: Referring to FIG. 9, the collected data is processed: the product of the triggering time of the control device and the speed of the blade tip

is the horizontal axis, the set tip clearance is plotted as the vertical axis, and the corresponding change relationship of each blade is obtained;

S205: Fit the variation relationship corresponding to each leaf as a straight line to obtain the slope k _j ; wherein, the least squares method can be used for fitting;

S206: Calculate the average value k=∑k _j of the slope, and complete the calibration of the constant k of the fiber probe.

Wherein, the number n of rotations of the impeller 23 can be set to be ≥100, and the gradient of increasing the tip clearance in sequence is 0.2, 0.4, .

In the present application, experiments were carried out using a test rig with 12 blades. The tip clearance was measured in real time under the condition of changing rotational speed, and the results are shown in Figure 10. It can be seen that under the condition of variable speed, the application can accurately reflect the change of the blade tip clearance, and the accuracy is not less than 0.05 mm, which verifies the feasibility of the application.

It should be noted that, in addition to implementing the system, device and each module provided by the present application in the form of pure computer readable program code, the system, device and each module provided by the present application can be implemented by logic gates by logically programming the method steps. , switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers to implement the same program. Therefore, the systems, devices and their respective modules provided in this application can be considered as a kind of hardware components, and the modules included in them for realizing various programs can also be considered as structures in the hardware components; A module for realizing various functions can be regarded as either a software program for realizing a method or a structure within a hardware component.

The preferred specific embodiments of the present application are described in detail above. It should be understood that many modifications and changes can be made according to the concept of the present application without creative efforts by ordinary skills in the art. Therefore, any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the prior art according to the concept of the present application shall fall within the protection scope determined by the claims.

Claims

An on-line measuring device for blade tip clearance, comprising:

a fiber optic probe configured to form a cone beam;

an optical fiber, one end is connected to the optical fiber probe, and the optical fiber includes a transmitting optical fiber and a receiving optical fiber;

a control device connected to the other end of the optical fiber, the control device configured to be able to control the intensity of the light emitted by the transmitting optical fiber, process the reflected light received by the receiving optical fiber, and identify the blade under test passing through the taper The time spent by the beam.
The on-line measuring device for blade tip clearance according to claim 1, wherein one end of the optical fiber probe is connected to the optical fiber, and the other end is provided with a casing, the casing is provided with an opening, and the opening of the opening is The center of the circle overlaps with the center of the light probe; a lens is also arranged in the casing.
The on-line measuring device for blade tip clearance according to claim 1, wherein the optical fiber is a bundled optical fiber.
The on-line measuring device for blade tip clearance according to claim 1, wherein the control device comprises an emission light control module, a reflected light processing module and an arithmetic module, and the emission light control module is configured to control the emission optical fiber the intensity of the emitted light, the reflected light processing module is configured to convert the reflected light signal into an electrical signal; the arithmetic module is configured to be able to identify the time it takes for the blade under test to pass through the cone beam.
The online blade tip clearance measuring device according to claim 4, wherein the control device further comprises a communication module, and the communication module is configured to communicate the control device with a host computer.
A method for on-line measurement of blade tip clearance using the measuring device as claimed in claim 1, wherein the method comprises the steps of:

Emit a cone beam to irradiate on the tested leaf;

receiving the light reflected by the measured blade;

converting the reflected light into an electrical signal;

Identifying the time when the blade under test passes through the cone beam;

Calculate tip clearance.
The method of claim 6, wherein the step of converting the reflected light into an electrical signal comprises: first converting the reflected light into an analog electrical signal, and then converting the analog electrical signal into a digital electrical signal Signal.
The method of claim 6, wherein the tip clearance is calculated according to Equation 1 below:

Wherein, d lens represents the effective diameter of the lens of the measuring device; c represents the size of the blade tip clearance; v represents the image distance; d tip represents the thickness of the blade tip; d focus represents the focal point diameter; rotational speed; r represents the tip radius of the blade to be measured; t represents the time when the control device of the measurement device is triggered when the blade to be measured passes through the cone beam.
The method of claim 8, wherein the formula 1 can be simplified as follows:

c=kwrt-b 2

Where, c represents the tip clearance, k represents the fiber probe constant, w represents the rotational speed of the blade under test, r represents the tip radius of the blade under test, and t represents the blade under test passing through the cone The time when the control device is activated when the beam is on, b represents the constant of the measured blade.
9. The method of claim 8, wherein the step of identifying when the bladed beam passes the cone of light comprises:

When the analog electrical signal exceeds a preset trigger voltage threshold, the control device is triggered, and the tested blade starts to pass through the fiber probe;

When the analog electrical signal is lower than the preset trigger voltage threshold, the control device is triggered, and the measured blade leaves the fiber probe.
The method of claim 10, wherein the method further comprises:

When the time when the measured blade starts to pass through the optical fiber probe exceeds a preset delay threshold, it is considered that the control device is effectively triggered;

When the time when the measured blade leaves the light probe exceeds the preset delay threshold, it is considered that the control device is effectively triggered.
The method of claim 11, wherein the method further comprises:

In the case of the effective triggering, the time difference between the time point when the measured blade passes through the optical fiber probe and the time point when the measured blade leaves the optical fiber probe is taken as the time point when the measured blade passes through the cone The time t at which the control device is activated when the beam is activated.
The method of claim 9, wherein the method further comprises: calibrating the constant k of the fiber probe.
14. The method of claim 13, wherein the step of calibrating the constant k of the fiber probe is performed on a test bench.
15. The method of claim 14, wherein the test stand is configured to control tip clearance.
The method of claim 15, wherein the step of calibrating the constant k of the optical fiber probe comprises the following steps:

The impeller of the test stand rotates n times, and the time when each blade of the impeller passes through the fiber probe in each circle is collected;

Calculate the average time for each of the blades to pass through the fiber probe based on n rotations of the impeller;

sequentially increasing the preset value of the tip clearance, and repeating the above steps;

Taking the product of the triggering time of the control device and the tip speed of the blade as the horizontal axis, and the tip clearance as the vertical axis, the corresponding variation relationship of each blade is obtained;

Fitting the variation relationship corresponding to each of the blades as a straight line to obtain a slope;

The average value of the slope is calculated to complete the calibration of the constant k of the fiber probe.
17. The method of claim 16, wherein the variation relationship corresponding to each of the blades is fitted as a straight line using a least squares method.
A test bench for calibrating the online measurement device according to claim 1, wherein the test bench comprises a bracket, a power component, an impeller and a micro-movement platform, and the bracket is fixedly connected with the power component, The impeller is connected to the output shaft of the power component, the fiber probe of the online measurement device is fixed on the micro-movement platform, and the tip clearance is controlled by adjusting the horizontal position of the micro-movement platform.
The test stand according to claim 18, wherein the test stand is arranged on a fixed platform.
The test stand of claim 18, wherein the micro-movement platform has four degrees of freedom.