Helicopter tail transmission shaft coaxiality measuring method and system based on laser alignment

Abstract

The invention relates to a helicopter tail transmission shaft coaxiality measurement method and system based on laser alignment, and belongs to the technical field of helicopter tail transmission shaft coaxiality measurement. The method comprises the following steps: firstly, performing zero setting on a measurement system to complete measurement initialization; constructing a measurement model of associated reflection imaging light spot coordinates-target lens displacement parameters-to-be-measured transmission shaft offset; meanwhile, the coincidence deviation of a laser axis and an actual reference axis is considered, and a correlation model between a measured value and an actual value is established by fitting the laser axis and the actual reference axis; according to the position of the high-coaxiality laser source generating device, a to-be-measured point is selected in the forward direction and the backward direction of the high-coaxiality laser source generating device respectively to fix a hollow pyramid, the forward coaxiality deviation and the backward coaxiality deviation are measured respectively, and then the coaxiality deviations of other to-be-measured points are measured in the same mode. According to the invention, the measurement operation steps are simplified, the workload is reduced, the measurement precision can be improved, and the measurement and calibration suggestions are digitized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coaxiality measurement of helicopter tail transmission shaft, and relates to a coaxiality measurement method and system of helicopter tail transmission shaft based on laser collimation. BACKGROUND

[0002] The helicopter must check the coaxiality when the tail transmission shaft (referred to as tail shaft) is replaced. The tail shaft is fixed on the aircraft through a fixing seat, and the fixing seat can place a round gauge. In the current tail shaft transmission shaft maintenance actual operation, the coaxiality is mainly measured according to the crosshair (a special glass lens, referred to as target) arranged in the middle of the round gauge. The target mirror is installed on the input shaft of the other side of the tail shaft fixing seat through a tool support, and the target mirror and the target are head to tail and back to target to adjust the position of the tail shaft. If the deviation occurs, the adjusting shims are added or reduced at the fixing position of the round gauge to adjust the deviation.

[0003] The coaxiality measurement of the tail transmission shaft mainly adopts the optical detection method. The optical detection method is to replace the transmission shaft with the target under the condition that the tail transmission shaft is disassembled, and to measure by using the collimating telescope or observation sighting device. After the optical detection method is used to detect the coaxiality of the helicopter, the coaxiality of the tail transmission shaft is generally adjusted by adjusting the position of the tail transmission shaft round gauge or adjusting the thickness of the shims at the reducer gauge.

[0004] The above is the traditional coaxiality measurement and calibration procedure of the tail transmission shaft. The operation is complex, the transmission shaft needs to be disassembled as a whole, there is no quantitative analysis, the error is large, there is a lack of fixed standard, and it completely relies on the naked eye observation, so the working experience and ability of the calibration personnel are required to be high. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a coaxiality measurement method and system of helicopter tail transmission shaft based on laser collimation, which uses the high collimation of laser and the characteristics of hollow angle cone that is not sensitive to angle deviation, to solve the problems of the traditional coaxiality measurement method of helicopter tail transmission shaft, such as complex operation, no quantitative analysis, large error of measurement results, and high requirements for working experience and ability of calibration personnel.

[0006] To achieve the above purpose, the present application provides a coaxiality measurement system of helicopter tail transmission shaft based on laser collimation, which includes two-way symmetrical high-coaxiality laser source generating device, two-dimensional position sensitive detector, hollow angle cone, angle cone fixing device, data acquisition module and computer.

[0007] The high-coaxiality laser source generating device is arranged on a transmission shaft between a main speed reducer and a tail speed reducer of the helicopter, and is used for generating a forward light beam and a backward light beam which are symmetrically emitted and propagate along the transmission shaft; a hollow corner cone is arranged in front of and behind the high-coaxiality laser source generating device, and is used for reflecting the light beams along the original path; the hollow corner cone is fixed on the transmission shaft through a corner cone fixing device; and a two-dimensional position sensitive detector is used for receiving the reflected light beams, and a light spot position on a photosensitive surface of the two-dimensional position sensitive detector is collected through a data acquisition module, and a coaxiality offset is obtained by a computer.

[0008] Further, the high-coaxiality laser source generating device comprises a laser, a mirror, a lens group, a quarter-plate, a half-plate, a beam splitter, a polarizing beam splitter, an aperture and a Faraday rotation combination.

[0009] The laser emitted by the laser passes through the first mirror, the half-plate, the lens group, the second mirror and the beam splitter in sequence to become the forward light beam and the backward light beam; the backward light beam is reflected by the polarizing beam splitter, passes through the backward aperture, and then reaches the backward hollow corner cone; the backward hollow corner cone reflects the backward light beam along the original path, and the backward light beam passes through the backward aperture, the polarizing beam splitter and the beam splitter in sequence to enter the two-dimensional position sensitive detector; the forward light beam passes through the polarizing beam splitter to reach the Faraday rotation combination, and then is reflected by the polarizing beam splitter, passes through the forward aperture, and then reaches the forward hollow corner cone; the forward hollow corner cone reflects the forward light beam along the original path, and the forward light beam passes through the forward aperture, the polarizing beam splitter, the Faraday rotation combination, the polarizing beam splitter and the beam splitter in sequence to enter the two-dimensional position sensitive detector.

[0010] Further, the Faraday rotation combination comprises a quarter-plate and a high-reflective mirror; the quarter-plate is used for changing the polarization state of the incident light; and the high-reflective mirror is used for reflecting the light beam along the original path.

[0011] Further, the lens group is a collimating lens group, and comprises at least two plano-convex lenses.

[0012] On the other hand, the application provides a helicopter tail transmission shaft coaxiality measurement method based on the above measurement system, which comprises the following steps:

[0013] Initialization of measurement is performed; a plurality of points are selected on the transmission shaft between the main speed reducer and the tail speed reducer of the helicopter; the main speed reducer, the tail speed reducer and each point are taken as a to-be-measured point; a reference position is set; and the measurement system is zeroed through the reference position.

[0014] The measurement system based on zero adjustment constructs a measurement model of the reflected imaging light spot coordinates-target mirror displacement parameter-measured transmission shaft offset; considering the coincidence deviation of the laser axis and the actual reference axis, the correlation model between the measured value and the actual value is established by fitting the laser axis and the actual reference axis;

[0015] According to the position of the high-coaxiality laser source generating device, a hollow corner cone is fixed at each of the selected test points in the forward and backward directions of the high-coaxiality laser source generating device, and the coaxiality deviations in the forward and backward directions are measured, respectively, and then the coaxiality deviations at other test points are measured in the same way.

[0016] Further, the measurement initialization includes:

[0017] Five points on the transmission shaft between the main and tail reducers of the helicopter are selected as the installation points of the corner cone fixing device, and the main reducer, the tail reducer and each point are taken as the test points; the center of the main reducer and the second closest corner cone fixing device installation point from the tail reducer are taken as the reference positions;

[0018] The corner cone fixing devices are installed at the two reference positions, and the hollow corner cones are fixed, and the center line of the two hollow corner cones is the measurement reference axis; the high-coaxiality laser source generating device is arranged on the transmission shaft and adjusted in position, so that the laser beams in two directions coincide with the measurement reference axis, that is, the laser beams in two directions are reflected by the hollow corner cones along the original path and are incident on the center of the two-dimensional position sensitive detector photosensitive surface, and the measurement initialization is completed.

[0019] Further, the measurement system based on zero adjustment constructs a measurement model of the reflected imaging light spot coordinates-target mirror displacement parameter-measured transmission shaft offset:

[0020] The hollow corner cone fixed at the test point is taken as the target mirror, and since the corner cone fixing device and the hollow corner cone are both rigid materials, the displacement of the test point will cause the displacement of the hollow corner cone, and the displacement amounts are equal, that is, the target mirror displacement parameter is equal to the measured transmission shaft offset;

[0021] The incident light direction vector of the hollow corner cone is parallel to the exit light direction vector and is opposite, that is, for any incident direction, the reflection transformation can be represented by the following matrix:

[0022]

[0023] In the formula, v in is the direction vector of the incident light, and R is the reflection transformation matrix;

[0024] If the hollow corner cone is translated by Δx along the x-axis direction, the incident light path is offset by Δx, and the exit light path is also offset by Δx, and finally the exit point P out is the exit point Pout,0 The relationship is:

[0025] P out =P out,0 +(2Δx,0,0)

[0026] Assume the photosensitive surface of the PSD is located in the z=K plane, and the position of the light spot is r. spot The point where the emitted light rays intersect with the screen:

[0027] r spot =P out +sv out

[0028]

[0029] Where s is the propagation distance of the emitted light rays from the screen, and v out Let v be the direction vector of the outgoing ray. out,z Let z be the component of the direction vector of the outgoing ray along the z-axis;

[0030] Let the spot displacement of the photosensitive surface of the two-dimensional position-sensitive detector be: when the hollow cone has not been translated.

[0031] r spot,0 =P out,0 +s0v out

[0032]

[0033] In the formula, z out,0 Let be the z-coordinate of the exit point; the z-coordinate of the exit point remains unchanged before and after the translation of the hollow cone, and the direction vector of the exit ray remains unchanged, i.e., s = s0. Then the displacement of the light spot before and after the translation is:

[0034] Δr spot =r spot -r spot,0 =(2Δx,0,0)

[0035] Similarly, for the translation Δy of the hollow cone along the y-axis, the offset of the light spot before and after the translation is (0, 2Δy, 0); then, the offset of the light spot caused by the displacement Δr of the hollow cone is:

[0036] Δr′ spot =2PΔr

[0037] In the formula, P is the equivalent scaling factor of the optical system.

[0038] Further, considering the coincidence deviation of the laser axis and the actual reference axis, a correlation model between the measured value and the actual value is established by fitting the laser axis and the actual reference axis: the measured values of two reference positions are (x1, y1) and (x2, y2) respectively; the measured value of a to-be-measured point relative to the measured reference axis is (x, y), and the actual value of the to-be-measured point relative to the actual reference axis is (x', y'); if the distance of the two reference positions is D, and the distance of the to-be-measured point and the front reference position is L, then:

[0039]

[0040] The above formula is the correlation model between the measured value and the actual value.

[0041] The beneficial effects of the present application are:

[0042] (1) The helicopter tail transmission shaft coaxiality measurement method based on laser collimation provided by the present application uses the high collimation characteristics of laser to replace the traditional naked eye observation scheme, can avoid disassembling the helicopter tail transmission shaft components during coaxiality measurement, and through the design of a high coaxiality laser source generation device with two-way symmetrical emission, the reuse of a single light source can be realized, too many optical devices are avoided, the device cost is reduced, the measurement operation steps are simplified, and the workload of single measurement is greatly reduced.

[0043] (2) The present application eliminates installation errors by using the characteristic that the hollow angle cone is not sensitive to the angle deflection of incident light, and at the same time, by using the principle that the incident light and the emitted light of the hollow angle cone are parallel and reverse, a mapping model of the light spot coordinate offset from the bearing offset to the detector photosurface is constructed, combined with a high-precision two-dimensional position sensitive detector, the measurement accuracy is greatly improved, the measurement and calibration are digitized, and the work efficiency is improved.

[0044] (3) The present application ensures that the two-way laser beams have extremely high directional consistency after being split by the fine adjustment of high-precision reference devices, realizes the high coaxiality maintenance of the laser beams under long measurement distance, and provides a solid technical foundation for the application in the fields of laser measurement, communication and the like.

[0045] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, and will be learned from the practice of the present application. The objects and other advantages of the present application can be realized and obtained by the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred detailed description of the present application will be made below in combination with the drawings, in which:

[0047] Figure 1It is a schematic diagram for coaxiality measurement of helicopter tail transmission shaft;

[0048] Figure 2 It is a schematic diagram of a helicopter tail transmission shaft coaxiality measurement system based on laser collimation provided by an embodiment of the present application;

[0049] Figure 3 It is a schematic diagram of a helicopter tail transmission shaft coaxiality measurement method flow provided by an embodiment of the present application. DETAILED DESCRIPTION

[0050] The advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the present application. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and the features in the following embodiments and examples can be combined with each other without conflict.

[0051] The drawings are only used for illustrative explanation, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation of the present application; in order to better illustrate the embodiments of the present application, some components in the drawings are omitted, enlarged or reduced, and do not represent the actual product size; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings can be omitted.

[0052] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for illustrative explanation, and cannot be understood as a limitation of the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific situation.

[0053] In view of the problems of complex operation, large error, lack of fixed standard and complete reliance on naked eye observation in the traditional tail transmission shaft coaxiality measurement and calibration procedure, the present application proposes to use the high collimation of laser, high sensitivity two-dimensional position sensor and the characteristics of hollow angle cone being insensitive to angle offset, and designs a helicopter tail transmission shaft coaxiality measurement method and measurement system based on laser collimation.

[0054] As Figure 1The schematic diagram of the coaxiality measurement of the application is shown, wherein the main reduction, tail reduction, No. 1 support, No. 2 support, No. 3 support, No. 4 support and No. 5 support are all to-be-measured points. Considering the complexity of the environment at the back of the helicopter, the light source generating device is placed between the No. 1 support and the No. 2 support, and the side close to the main reduction is called the front light outlet, and the side close to the tail reduction is called the rear light outlet. When measuring, the corner pyramid fixing frame and the hollow corner pyramid are installed on the to-be-measured points. Because the size and shape of the corner pyramid fixing frame are the same as the bearing seat of the original installed tail transmission shaft, the hollow corner pyramid is installed at the center of the corner pyramid fixing frame, so the center of the hollow corner pyramid and the center of the tail transmission shaft are coincident. Because the corner pyramid fixing frame and the hollow corner pyramid are both rigid materials, the displacement of the to-be-measured points will all cause the displacement of the hollow corner pyramid, and the displacement amount is equal. In the actual measurement process, the center line of the main reduction and the center of the No. 4 support is taken as the transmission shaft reference axis, and the measurement values of the remaining measurement positions reflect the coaxiality deviation of the measurement points.

[0055] As shown in the embodiment of the application, a coaxiality measurement system of the tail transmission shaft of a helicopter based on laser collimation is provided, which comprises a two-way symmetrical light source generating device, a two-dimensional position sensitive detector (PSD), a hollow corner pyramid, a corner pyramid fixing device, a data acquisition module and a computer. Figure 2

[0056] The two-way symmetrical light source generating device is used to generate a symmetrical light source with high coaxiality, which is arranged between the No. 1 support and the No. 2 support of the to-be-measured helicopter. The corner pyramid fixing device is installed at each of the to-be-measured points in front of and behind the high coaxiality light source generating device to fix the hollow corner pyramids. The center line of the two hollow corner pyramids is the reference axis. The position of the light source generating device is adjusted so that the two-way laser beams coincide with the reference axis, that is, the front and rear two-way transmitted laser beams hit the center of the hollow corner pyramid.

[0057] The high coaxiality light source generating device comprises a laser, a first mirror DM1, a second mirror DM2, a one-half glass, a lens group, a beam splitter BS, a polarization beam splitter PBS, a one-quarter glass, a high reflection mirror HR and a diaphragm. The laser is a THORLABS HNL050RB type linear polarization helium-neon laser (wavelength 632.8 nm), the diameter of the emitted beam is 0.63 mm, and the divergence angle is 1.3 mrad. The laser has good stability and monochromaticity, and has extremely high linear polarization degree.

[0058] The high coaxiality light source generating device generates front and rear beams in the following manner:

[0059] ​The forward light beam is generated by closing the backward light diaphragm, and the output laser sequentially passes through the first mirror DM1, the half-wave plate, the lens group, the second mirror DM2, and the beam splitter BS to reach the polarizing beam splitter PBS. The polarizing beam splitter PBS adjusts the intensity ratio of the forward and backward light beams and realizes the back-and-forth transmission of the two light beams. After the PBS splits the two light beams, one light beam is blocked by the backward light diaphragm from the backward direction; the other light beam passes through the Faraday rotation combination (including a quarter-wave plate and a high-reflectivity mirror HR, which can be used to change the polarization state of the light beam) to change the polarization state, and is then reflected by the PBS to the forward direction to enter the hollow corner cube in the forward direction of the light source generation device. The forward reflected light beam is reflected back to the light beam carrying the x-axis and y-axis coordinate information along the original path, and the forward reflected light beam with the changed polarization state passes through the PBS along the original path and is guided to the two-dimensional position sensitive detector PSD by the beam splitter BS.

[0060] The backward light beam is generated by closing the forward light diaphragm, and the output laser sequentially passes through the first mirror DM1, the half-wave plate, the lens group, the second mirror DM2, and the beam splitter BS to reach the polarizing beam splitter PBS. After the PBS splits the two light beams, one light beam sequentially passes through the Faraday rotation combination and the PBS to reach the forward light diaphragm, which is blocked by the forward light diaphragm; the other light beam enters the hollow corner cube in the backward direction of the light source generation device from the backward direction, and the backward reflected light beam carrying the x-axis and y-axis coordinate information is reflected back along the original path. The backward reflected light beam passes through the PBS along the original path and is guided to the two-dimensional position sensitive detector PSD by the beam splitter BS.

[0061] By recording the positions of the light spots on the PSD and comparing them with the target reference standard, the coaxiality offset amounts corresponding to the forward and backward directions can be calculated respectively, so as to complete the accurate measurement of the coaxiality.

[0062] The lens group consists of two plano-convex lenses with a focal length of 750 mm, which is used to collimate the light beam and ensure that the spot diameter is less than or equal to 3 mm within an 8 m light beam path propagation range.

[0063] The beam splitter BS has a splitting ratio of 50 / 50. The two-dimensional position sensitive detector PSD uses the DRX-2DPSD-GJD01-X (9*9mm) type detector from Shenzhen Daruxin Optoelectronic Technology Co., Ltd., with a resolution of 5 μm, a response wavelength range of 400-1050 nm, and a bandwidth of 150 kHz.

[0064] The hollow corner cube is a LB3Au-1 of Lamber optics, which represents an aperture of 1 inch, a beam offset of 3 arcseconds, a gold-coated film, and a wide wavelength range of 0.8-14 μm.

[0065] The angle cone fixing device is a high-precision rigid installation fixing device, and is in a hollow cylindrical shape as a whole, the hollow part is provided with a hollow angle cone with a protective sleeve, the diameter is 40mm, and the outer ring is installed on the helicopter measurement base with a diameter of 89mm.

[0066] The data acquisition module is an acquisition card, and PCIe-6251 of National Instruments Company is adopted, and a supporting wiring box BNC-2110 is adopted, and the acquisition speed can reach 2.8MS / s.

[0067] The computer comprises a processor, a memory, a display and the like components, calculates the coaxiality offset according to the data transmitted by the data acquisition module, and can display relevant information on the display for a user to view.

[0068] The coaxiality measurement system utilizes the insensitivity of the hollow angle cone to the angle deflection of incident light, can effectively separate and eliminate errors introduced by the measurement system and the environment, and ensures the accuracy and reliability of the measurement result; meanwhile, in combination with the high-precision PSD, the measurement precision is greatly improved, the measurement and calibration are digitized, and the work efficiency is improved.

[0069] Another embodiment of the application provides a method for measuring the coaxiality of a helicopter tail transmission shaft by using the coaxiality measurement system, mainly characterized by the following steps:

[0070] 1. Measurement initialization is performed, a plurality of points are selected on the transmission shaft between the helicopter main reducer and the tail reducer, the main reducer, the tail reducer and the points are all taken as to-be-measured points, a reference position is set, and the measurement system is zeroed by the reference position.

[0071] Five points are selected as the angle cone fixing device installation points on the transmission shaft between the helicopter main reducer and the tail reducer, i.e. the No.1 to No.4 supports, the main reducer, the tail reducer and the points are all taken as to-be-measured points, and the main reducer center and the No.4 support are taken as reference positions.

[0072] The angle cone fixing devices are installed and the hollow angle cones are fixed at the two reference positions, the center line of the two hollow angle cones is a measurement reference axis, the high-coaxiality laser source generating device is arranged on the transmission shaft and the position is adjusted, so that the two-way laser beams coincide with the measurement reference axis, i.e. the two-way laser beams are reflected along the original path by the hollow angle cones and are incident on the center of the two-dimensional position sensitive detector photosensitive surface, and the measurement initialization is completed.

[0073] In the embodiment, considering the complexity of the environment at the back of the helicopter, the light source device is arranged between the No.1 support and the No.2 support.

[0074] 2. A measurement model of the reflection imaging spot coordinates-target mirror displacement parameter-to-be-measured transmission shaft offset is constructed.

[0075] The incident light ray and the reflected light ray of the hollow cornered pyramid are parallel and reverse, and the hollow cornered pyramid is composed of three mutually perpendicular reflection surfaces, which are located in the x=0 plane (y-z plane), y=0 plane (x-z plane), and z=0 plane (x-y plane), and are a right-handed rectangular coordinate system.

[0076] Q is defined as a reflection matrix corresponding to a plane in a three-dimensional space, and is expressed as:

[0077] Q = I - 2nn T (1)

[0078] wherein I is a 3*3 unit matrix, n = (n x , n y , n z ) is a unit normal vector corresponding to the plane, and ||n|| = 1. The expansion form is:

[0079]

[0080] For the xy plane, the normal vector is n = (0, 0, 1), and the reflection matrix is:

[0081]

[0082] The effects are as follows:

[0083]

[0084] Similarly, the following can be obtained:

[0085]

[0086] In summary, when the incident light ray A is reflected by the three surfaces, it is equivalent to the outgoing light ray B obtained after three times of operation with the reflection matrix:

[0087]

[0088] Using this characteristic, the hollow cornered pyramid can be used as a measurement target mirror of the coaxiality offset amount, and the random angle crosstalk when the target mirror is connected with the transmission shaft can be suppressed.

[0089] According to the characteristics that the direction vector of the incident light ray is parallel and reverse to the direction vector of the outgoing light ray, the direction vector of the incident light ray r is v = (v x , v y , v z ), and each reflection can be represented as negation of the corresponding coordinate component.

[0090] Suppose that the hollow cornered pyramid is translated by Δx along the x direction, then the positions of the three reflection surfaces become: x = Δx plane, y = 0 plane, and z = 0 plane.

[0091] For the incident ray r, the parametric equation after reflection is given as: r(t)=r0+tV, where t is the intersection parameter of the incident ray and the reflecting surface, V is the direction vector of the incident ray, and r0=(x0,y0,z0) is the original incident point.

[0092] Calculate the first reflection point, substitute the ray parametric equation into the plane equation x = Δx, and solve for the parameter t1:

[0093]

[0094] Substituting t1 back into the ray equation, the coordinates of the reflection point P1 are:

[0095] (Δx,y0+t1v y ,z0+t1v z (9)

[0096] The direction of light reflection after the first reflection is:

[0097] v1 = (-v x ,v y ,v z (10)

[0098] Similarly, calculate the intersection points of ray r with the planes y=0 and z=0. Due to the reflection characteristics of the hollow pyramid, the path of the incident ray is shifted by Δx due to the translation Δx, and the path of the outgoing ray is also shifted by Δx. Finally, obtain the exit point P of the ray in the hollow pyramid. out Compared to the exit point P before translation out,0 The relationship is:

[0099] P out =P out,0 +(2Δx,0,0)(11)

[0100] Assume the photosensitive surface of the PSD is located in the z=K plane, and the position of the light spot is r. spot The point where the emitted light rays intersect with the screen:

[0101] r spot =P out +sv out (12)

[0102] Where s is the propagation distance of the emitted light rays from the screen, and v out Let be the direction vector of the emitted ray.

[0103] The coordinates of the point of exit of the light after three reflections (x) out,0 ,y out,0 ,z out,0 The spot displacement before translation is:

[0104] rspot,0 = P out,0 + s0v out (13)

[0105]

[0106] The parameter s after translation is:

[0107]

[0108] Since the z coordinate of the exit point does not change before and after the hollow angle cone translation, and the direction vector of the exit light ray also does not change, s = s0, and therefore the spot displacement amount is:

[0109] Δr spot = r spot -r spot,0 = (2Δx, 0, 0) (16)

[0110] It can be concluded that for any incident direction, the reflection transformation can be represented by the following matrix:

[0111]

[0112] Therefore, the spot shift caused by the displacement Δr is:

[0113] Δr′ spot = 2PΔr (18)

[0114] Where P is the equivalent scale factor of the optical system, and under ideal conditions P = 1. When P ≠ 1, it indicates that the optical system (such as a lens group) has a scaling effect on the displacement.

[0115] 3. Considering the coincidence deviation of the laser axis and the actual reference axis, an absolute coordinate system with the PSD photosensitive surface center as the measurement reference is established, and a correlation model between the measurement value and the actual value is established.

[0116] In theory, the two-way symmetric laser light source needs to be coincident with the actual reference axis during measurement, i.e. when measuring the actual reference axis position, the spot should be transmitted back to the PSD photosensitive surface center in the original path, i.e. the forward and backward measurement values are both (0, 0). However, in actual operation, the two-way symmetric laser light source cannot be accurately coincident with the actual reference axis, and there is a certain deviation, so the laser axis needs to be fitted with the actual reference axis (i.e. the axis center of the transmission shaft in the ideal state where there is no deviation of the transmission shaft of the helicopter), to obtain an absolute coordinate system with the PSD photosensitive surface center as the measurement reference.

[0117] When measuring the actual reference axis position, the measured values of the forward and backward reference positions are (x1, y1) and (x2, y2) respectively, and the measured values of the actual reference axis in the forward and backward directions should both be (0, 0). In the subsequent actual coaxiality measurement, the measured value (deviation from the laser axis, i.e. the measurement reference axis) of a certain to-be-measured point is (x, y), the actual value (deviation from the actual reference axis) of the to-be-measured point is (x', y'), the distance between the two reference positions is D, and the distance between the to-be-measured point and the front reference position is L. The following can be obtained:

[0118]

[0119] Thus, the deviation (x', y') of the measurement point from the actual reference axis and the spot shift Δr caused by the displacement Δr can be obtained. spot That is, the relationship between the PSD measurement value (x, y) and the spot shift Δr caused by the displacement Δr.

[0120] 4. In the forward and backward of the high-coaxiality laser source generation device, a hollow angle cone is selected at a to-be-measured point, and the coaxiality deviation in the forward direction and the coaxiality deviation in the backward direction are measured respectively, and then the coaxiality deviations at other to-be-measured points are measured in the same way.

[0121] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, and all should be covered in the scope of the claims of the present application.

Claims

1. A coaxiality measurement system for helicopter tail drive shaft based on laser collimation, characterized in that, The system includes a high coaxiality laser source generating device with bidirectional symmetrical emission, a two-dimensional position sensitive detector, a hollow pyramid, a pyramid fixing device, a data acquisition module, and a computer; A high coaxiality laser source generating device is installed on the drive shaft between the helicopter's main gearbox and tail gearbox to generate symmetrically emitted forward and backward beams that propagate along the drive shaft. Hollow cones are set in the front and rear directions of the high coaxiality laser source generating device to reflect the light beam along the original path. The hollow cones are fixed on the drive shaft by a cone fixing device. A two-dimensional position sensitive detector is used to receive the reflected light beam. The position of the light spot on the photosensitive surface of the two-dimensional position sensitive detector is collected by the data acquisition module, and the coaxiality offset is calculated by the computer.

2. The system according to claim 1, characterized in that, The high coaxiality laser source generating device includes a laser, a mirror, a lens group, a quarter glass slide, a half glass slide, a beam splitter, a polarizing beam splitter, an aperture, and a Faraday rotation assembly; The laser emitted by the laser sequentially passes through a first reflecting mirror, a half-glass slide, a lens group, a second reflecting mirror, and a beam splitter to reach a polarizing beam splitter, where it is split into a forward beam and a backward beam. The backward beam is reflected by the polarizing beam splitter, travels along the drive shaft, passes through a backward aperture, and reaches a backward hollow pyramid. The hollow pyramid reflects the backward beam along its original path, and it passes sequentially through the backward aperture, the polarizing beam splitter, and the beam splitter before entering the two-dimensional position-sensitive detector. The forward beam passes through the polarizing beam splitter to reach a Faraday rotation assembly. After its polarization state is changed by the Faraday rotation assembly, it is reflected by the polarizing beam splitter, travels along the drive shaft, passes through a forward aperture, and reaches a forward hollow pyramid. The hollow pyramid reflects the forward beam along its original path, and it passes sequentially through the forward aperture, the polarizing beam splitter, the Faraday rotation assembly, the polarizing beam splitter, and the beam splitter before entering the two-dimensional position-sensitive detector.

3. The system according to claim 2, characterized in that, The Faraday rotation assembly consists of a quarter-glass slide and a high-reflection mirror. The quarter-glass slide is used to change the polarization state of the incident light, and the high-reflection mirror is used to reflect the beam along its original path.

4. The system according to claim 2, characterized in that, The lens group is a collimating lens group, which includes at least two plano-convex lenses.

5. A method for measuring the coaxiality of a helicopter tail drive shaft based on the system described in any one of claims 1 to 4, characterized in that, The method includes: Initialize the measurement process by selecting multiple points on the drive shaft between the helicopter's main and tail gearboxes, treating the main and tail gearboxes and each point as the measurement points; set a reference position and zero the measurement system using the reference position. Based on the zero-adjustment measurement system, a measurement model is constructed that combines the coordinates of the reflected imaging spot, the displacement parameter of the target mirror, and the offset of the transmission shaft under test. At the same time, considering the coincidence deviation between the laser axis and the actual reference axis, a correlation model between the measured value and the actual value is established by fitting the laser axis and the actual reference axis. Based on the location of the high coaxiality laser source generating device, a hollow cone is fixed at one test point in front of and one in the back of the high coaxiality laser source generating device. The coaxiality deviation in the front and the coaxiality deviation in the back are measured respectively. Then, the coaxiality deviation at other test points is measured in the same way.

6. The method according to claim 5, characterized in that, Measurement initialization includes: Five points were selected on the drive shaft between the helicopter's main gearbox and tail gearbox as installation points for the bevel fixing device. The main gearbox, tail gearbox, and each point were all used as test points. The center of the main gearbox and the second closest bevel fixing device installation point to the tail gearbox were used as reference positions. A cone fixing device is installed at both reference positions and a hollow cone is fixed therein. The line connecting the centers of the two hollow cones is the measurement reference axis. A high coaxiality laser source generating device is set on the transmission shaft and its position is adjusted so that the two-way laser beams coincide with the measurement reference axis. That is, the two-way laser beams are reflected along the original path by the hollow cones and then incident on the center of the photosensitive surface of the two-dimensional position sensitive detector, thus completing the measurement initialization.

7. The method according to claim 6, characterized in that, Based on the zero-adjustment measurement system, a measurement model is constructed that combines the coordinates of the reflected imaging spot, the target mirror displacement parameter, and the offset of the transmission shaft under test. The hollow cone fixed at the test point is used as the target mirror. Since both the cone fixing device and the hollow cone are made of rigid materials, the displacement of the test point will cause the displacement of the hollow cone, and the displacement amounts are equal. That is, the displacement parameter of the target mirror is equal to the offset of the transmission shaft under test. Taking advantage of the property that the incident ray direction vector and the outgoing ray direction vector of a hollow pyramid are parallel and opposite, the reflection transformation can be represented by the following matrix for any incident direction: In the formula, v in Let R be the direction vector of the incident ray, and let R be the reflection transformation matrix. If the hollow pyramid is translated by Δx along the x-axis, the path of the incident ray will be shifted by Δx due to the translation, and the path of the outgoing ray will also be shifted by Δx, ultimately exiting at point P. out Compared to the exit point P before translation out,0 The relationship is: P out =P out,0 +(2Δx,0,0) Assume the photosensitive surface of the PSD is located in the z=K plane, and the position of the light spot is r. spot The point where the emitted light rays intersect with the screen: r spot =P out +sv out Where s is the propagation distance of the emitted light rays from the screen, and v out Let v be the direction vector of the outgoing ray. out,z Let z be the component of the direction vector of the outgoing ray along the z-axis; Let the spot displacement of the photosensitive surface of the two-dimensional position-sensitive detector be: when the hollow cone has not been translated. r spot,0 =P out,0 +s0v out In the formula, z out,0 Let be the z-coordinate of the exit point; the z-coordinate of the exit point remains unchanged before and after the translation of the hollow cone, and the direction vector of the exit ray remains unchanged, i.e., s = s0. Then the displacement of the light spot before and after the translation is: Δr spot =r spot -r spot,0 =(2Δx,0,0) Similarly, for the translation Δy of the hollow cone along the y-axis, the offset of the light spot before and after the translation is (0, 2Δy, 0); then, the offset of the light spot caused by the displacement Δr of the hollow cone is: Δr′ spot =2PΔr In the formula, P is the equivalent scaling factor of the optical system.

8. The method according to claim 7, characterized in that, Considering the overlap deviation between the laser axis and the actual reference axis, a correlation model between the measured value and the actual value is established by fitting the laser axis and the actual reference axis: Let the measured values ​​of the two reference positions be (x1, y1) and (x2, y2); let the measured value of a certain point to be measured relative to the measurement reference axis be (x, y), and the actual value of the point to be measured relative to the actual reference axis be (x′, y′); if the distance between the two reference positions is D, and the distance between the point to be measured and the previous reference position is L, then: The above formula is the correlation model between the measured value and the actual value.

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