Optically assisted rotor cone monitoring method

Abstract

The invention relates to an optical-assisted rotor cone monitoring method, which comprises the following steps that: targets are arranged at the tip of each blade of a rotor, and the images of the targets are different from each other; irradiating the tip of the rotor blade by using a stroboscopic light source, and observing a target image formed by each target when the rotor blade rotates at a high speed; and judging the same conicity of the rotor wing cone according to the height difference between the target images formed by different targets. By utilizing the human vision inertia principle, the helicopter air cone monitoring can be effectively realized, and the requirements of ground and ship-based cone monitoring can also be met.

Description

Technical Field

[0001] The present invention relates to the field of aviation testing technology, and in particular to an optically assisted rotor cone monitoring method. Background Art

[0002] Checking the uniformity of helicopter rotor cone tapers is a critical and recurring inspection during helicopter production and operation, and a key research project in the development of new helicopters. Uneven rotor cone tapers can deteriorate the helicopter's vibration environment, exacerbate wear on rotating components, shorten their lifespan, and, in severe cases, compromise flight safety. Therefore, monitoring and adjusting helicopter rotor cones is crucial to extending helicopter life and flight safety.

[0003] Currently, helicopter cone monitoring on the ground is mostly accomplished using ground-based methods like "paper cones." However, aerial cone monitoring cannot rely on ground support, and the "paper cone" method cannot meet the requirements for helicopter cone monitoring. To ensure helicopter flight safety, technical research and method implementation of aerial rotor cone monitoring are necessary. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an optically assisted rotor cone monitoring method, which can effectively realize helicopter aerial cone monitoring and also meet the requirements of ground and ship-based cone monitoring.

[0005] The technical solution adopted by the present invention to solve the technical problem is to provide an optically assisted rotor cone monitoring method, comprising:

[0006] A target is set at the tip of each rotor blade, and the images of the targets are different from each other;

[0007] Use a stroboscopic light source to illuminate the tip of the rotor blade and observe the target images formed by each target when the rotor blade rotates at high speed;

[0008] The same taper of the rotor cone is determined based on the height difference between the target images formed by different targets.

[0009] Furthermore, before the step of observing the target images formed by each target when the rotor blades rotate at high speed, the method further includes:

[0010] Set the stroboscopic frequency to the basic frequency F1 so that each target forms a continuous target image at its corresponding position;

[0011] Adjust the distance between the target images formed by each target so that they do not overlap.

[0012] Furthermore, the step of adjusting the spacing between target images formed by the respective targets so as to prevent them from overlapping includes:

[0013] Calculate the time Δt required for the rotor blades to rotate to move the target image by a distance of one target width;

[0014] The period corresponding to the basic frequency F1 is used as the initial time interval t1, and the interval time of the strobe is set to a periodic arithmetic progression with the initial time interval t1 as the first term, the duration Δt as the tolerance, and the rotor speed period as the repetition period.

[0015] Furthermore, the time Δt required for the rotor blades to rotate is given by the formula Calculated, where w is the target width, r is the rotor blade length, and f is the rotor speed frequency.

[0016] Furthermore, the basic frequency F1 is calculated by the formula F1=n×f×m, where f is the rotor speed frequency, m is the magnification factor, and n is the number of rotor blades.

[0017] Furthermore, the product of the basic driving frequency of the stroboscope and the magnification m is greater than the threshold of the critical flicker fusion frequency.

[0018] Furthermore, when setting the targets, they are installed in a reverse order to the direction of rotation of the rotor, and the images of the installed targets are natural integers starting from 1.

[0019] Furthermore, the step of determining the same taper of the rotor cone based on the height difference between the target images formed by different targets includes:

[0020] If the height difference between the targets is less than the set threshold, the rotor cone is judged to be in good condition; otherwise, the cone needs to be adjusted.

[0021] Beneficial effects

[0022] Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention uses high-frequency strong light to illuminate targets of different images installed on the tip of the rotor blade, and uses the principle of human visual inertia to observe continuously appearing target images, and judges the same-taper state of the helicopter rotor cone based on the observed target height difference, which can not only realize helicopter aerial cone monitoring, but also meet the requirements of ground and ship-based cone monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of an optically assisted cone monitoring method according to an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of target spacing before and after adjustment according to an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of optically assisted cone monitoring results according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0027] An embodiment of the present invention relates to an optically assisted rotor cone monitoring method, comprising:

[0028] A target is set at the tip of each rotor blade, and the images of the targets are different from each other;

[0029] Use a stroboscopic light source to illuminate the tip of the rotor blade and observe the target images formed by each target when the rotor blade rotates at high speed;

[0030] The same taper of the rotor cone is determined based on the height difference between the target images formed by different targets.

[0031] More specifically, before observing the target images formed by each target when the rotor blades rotate at high speed, the following steps are also included:

[0032] Set the stroboscopic frequency to the basic frequency F1 so that each target forms a continuous target image at its corresponding position;

[0033] Adjust the distance between the target images formed by each target so that they do not overlap.

[0034] The present embodiment will be further described below in conjunction with the principle of human visual inertia.

[0035] The helicopter rotor rotates at high speed, and it is impossible to visually observe any details of the rotor blade tip with the human eye. The present invention uses a target with different images installed on the tip of each blade, and the target image uses a reflective layer. At the same time, a handheld high-frequency strong light emission sensor, i.e., a stroboscope, and a rotor speed sensor can be selected. The rotor speed cycle is measured by the speed sensor, and combined with the number of rotor blades, a stroboscopic drive signal is applied to the stroboscope. Figure 1 As shown, at this time, the handheld stroboscope illuminates the target at the tip of the blade, and the target image will reflect the strong light emitted by the stroboscope. The stroboscope operator can see the target image of each blade and monitor the rotor cone by visually observing the target height difference. It should be noted that the method described in the present invention is not limited to handheld devices or stroboscopes. Any stroboscopic light source with adjustable frequency is within the scope of the present invention. In addition, when observing and judging the same taper of the rotor cone based on the height difference of the target image, it can be done by visual observation by the staff, or the target image can be obtained by category visual monitoring equipment, and the height difference can be automatically identified and calculated for judgment.

[0036] The monitoring method mainly includes two parts. One part is to achieve the repeated appearance of all target images somewhere on the running trajectory of the high-speed rotating rotor blade tip. The other part is to separate the overlapping target images by a certain distance to facilitate the observation of each target image.

[0037] The principle of the repetitive appearance of the rotor blade tip target image is further explained below.

[0038] Helicopter rotor blades are usually evenly distributed, that is, the angles between the blades are equal. Assuming the helicopter rotor speed frequency is f and the number of rotor blades is n, the basic driving frequency F1 of the stroboscope should be:

[0039] F1=n×f

[0040] When the stroboscope is driven at a strobe frequency of F1, the handheld stroboscope illuminates the rotor blade tip's trajectory. Throughout the 360-degree trajectory, the stroboscope operator can see repeated target images on each blade at n locations. When F1 is less than 25, meaning fewer than 25 target images appear per second, the observed target images are considered flashes. To ensure consistent visual inertia and continuous target images observed by the stroboscope operator, the stroboscope drive frequency should be amplified by integer multiples, i.e., F1 = F1 × m (m is an integer), until F1 × m > 25.

[0041] From the above analysis, we can get that the basic driving time interval t1 of the stroboscope is:

[0042]

[0043] When the above conditions are met, the stroboscope operator can see the repeated images of each blade target image at n positions, but the n target images overlap with each other (e.g. Figure 2 As shown in the figure on the right, it is difficult to identify each target image, so the spacing between overlapping target images needs to be adjusted.

[0044] Next, the principle of adjusting the spacing between overlapping target images will be further explained.

[0045] If the target spacing is too small, the targets will overlap and be difficult to identify; however, if the target spacing is too large, it will be difficult to accurately identify the heights of n targets. In addition, the strong light emitted by the stroboscope is focused, and if the spacing is too large, it may not even be possible to illuminate every target, and the stroboscope operator will not be able to observe the images of all targets. Therefore, the adjustment of the target spacing requires weighing multiple factors.

[0046] If the target width is w, the optimal target spacing adjustment method is to select a blade target as the reference, and then horizontally shift the subsequent blade targets left or right by one target width. This connects the left and right edges of all targets, making it easier to visually determine the height difference of the targets. Target spacing adjustment is achieved by fine-tuning the stroboscope drive frequency F1 within a cycle.

[0047] Assuming that the length of the helicopter rotor blade and the radius of the rotor rotation plane are r, when the target moves a distance of target width w, the rotor blade rotates by an angle α in radians.

[0048]

[0049] Then the time Δt required for the blade to rotate α radians is:

[0050]

[0051] In one cycle of the helicopter rotor speed, if the first target stroboscope frequency driving cycle is t1, then the second target stroboscopic time should be delayed by Δt based on t1, that is, t2 = t1 + Δt; the third target stroboscopic time should be delayed by two Δt based on t1, that is, t3 = t1 + 2 × Δt; and so on, the stroboscopic time of the yth target t y =t1+y×Δt, that is

[0052] t y =t1+y×Δt

[0053]

[0054] Where n is the number of rotor blades, f is the rotor speed frequency, m is a constant, Δt is the time required for the target to move one target width, w is the target width, r is the rotor blade length, and y is the target number, with a value range of 0 to n-1.

[0055] Through the above operations, the overlapping target images will be stretched horizontally, such as Figure 2 As shown in the figure on the left.

[0056] The following uses a 5-meter-long 4-blade rotor system as an example to illustrate the implementation of the technical solution. It should be noted that the principles and technical solutions of the present invention are applicable to rotor cone monitoring with all rotor blades evenly distributed, as well as to rotor cone monitoring with any number of blades.

[0057] This embodiment specifically includes the following steps:

[0058] Step 1. Select a blade as the reference blade and install a target with image 1 at its tip. The blade immediately adjacent to the reference blade, facing the opposite direction of rotor rotation, is blade 2, with a target with image 2 installed at its tip. The blade immediately adjacent to blade 2 is blade 3, with a target with image 3 installed at its tip. The blade between the reference blade and blade 3 is blade 4, with a target with image 4 installed at its tip.

[0059] Step 2: Measure the rotor speed using a speed sensor to obtain the speed frequency f. Assuming the rotor speed is 360 r / min (revolutions per minute), or 6 Hz, the stroboscope's basic drive frequency is 4 × 6 = 24. Since this is less than 25, it needs to be amplified by an integer multiple. The stroboscope drive frequency is adjusted to 2 × 24 = 28, resulting in a stroboscope drive interval of t1 = 1 / 28 = 0.0357142857 seconds, or 35714.2857 microseconds.

[0060] Step 3: The target width is usually 20 mm. Calculate the time required for the blade tip to travel 20 mm using expression (1):

[0061] Step 4: Drive the stroboscope to flash at a period of 35714.2857 microseconds. The stroboscope operator can see the target image of each blade repeating at 4 positions, that is, the numbers 1, 2, 3, and 4 overlap. Figure 2 As shown in the figure on the right.

[0062] Step 5. Because the rotor has four blades, the stroboscope uses four flashes as a cycle. There is no delay in the first flash, a delay of 106.1033 microseconds is added to the second flash, a delay of 2 times the delay is added to the third flash, that is, 212.2066 microseconds, and a delay of 3 times the delay is added to the fourth flash, that is, 318.3099 microseconds.

[0063] Step 6: Use a handheld stroboscope to illuminate the blade tip target. The stroboscope operator will see four blade target images arranged horizontally in sequence, as shown in the following example: Figure 2 As shown in the figure on the left.

[0064] Step 7: Determine the rotor cone by observing the height difference of the targets. If the height difference of the four targets is less than the height of one target, it means that the rotor cone is in good condition; if the height difference of the four targets is greater than the height of one target, it means that the rotor cone is in poor condition and needs to be adjusted. The results of optically assisted cone monitoring are usually as follows: Figure 3 shown.

[0065] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all such changes or substitutions should fall within the scope of the claims and protection of the present invention.

Claims

1. An optically assisted rotor cone monitoring method, characterized in that: include: A target is set at the tip of each rotor blade, and the images of the targets are different from each other; Use a stroboscopic light source to illuminate the tip of the rotor blade and observe the target images formed by each target when the rotor blade rotates at high speed; The same taper of the rotor cone is determined based on the height difference between the target images formed by different targets.

2. The method according to claim 1, characterized in that Before the step of observing the target images formed by each target when the rotor blades rotate at high speed, the method further includes: Set the stroboscopic frequency to the basic frequency F1 so that each target forms a continuous target image at its corresponding position; Adjust the distance between the target images formed by each target so that they do not overlap.

3. The method according to claim 2, characterized in that The distance between the target images formed by each target is adjusted. So that they do not overlap, include: Calculate the time Δt required for the rotor blades to rotate to move the target image by a distance of one target width; The period corresponding to the basic frequency F1 is used as the initial time interval t1, and the interval time of the strobe is set to a periodic arithmetic progression with the initial time interval t1 as the first term, the duration Δt as the tolerance, and the rotor speed period as the repetition period.

4. The method according to claim 3, characterized in that The time Δt required for the rotor blades to rotate is given by the formula Calculated, where w is the target width, r is the rotor blade length, and f is the rotor speed frequency.

5. The method according to claim 2, characterized in that The basic frequency F1 is calculated by the formula F1=n×f×m, where f is the rotor speed frequency, m is the magnification factor, and n is the number of rotor blades.

6. The method according to claim 5, characterized in that The product of the basic driving frequency of the stroboscope and the magnification m is greater than the threshold of the critical flicker fusion frequency.

7. The method according to claim 1, characterized in that When setting the targets, they are installed in the reverse direction of the rotor rotation direction, and the images of the installed targets are natural integers starting from 1.

8. The method according to claim 1, characterized in that The determining of the same taper of the rotor cone based on the height difference between target images formed by different targets includes: If the height difference between the targets is less than the set threshold, the rotor cone is judged to be in good condition; otherwise, the cone needs to be adjusted.

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