A low-coherence interference-based deep-hole surface topography measurement system

Abstract

The application discloses a kind of deep hole surface topography measurement systems based on low coherence interference, including detection part and autocollimation system, detection part includes the white light interference system, specifically 1550nm ASE broadband light source, first mirror, first beam splitter prism, second mirror, reference mirror are sequentially arranged, two sides of first beam splitter prism are respectively provided with to-be-measured deep hole, near-infrared camera, and conical prism is arranged in to-be-measured deep hole;Autocollimation system is arranged between to-be-measured deep hole and first beam splitter prism, and autocollimation system includes sequentially arranged 630nm light source, dichroic prism, second beam splitter prism, third mirror, four-quadrant detector.The application can realize one-time scanning to deep hole surface topography, and multiple measurements are obtained by four-step phase shift algorithm, splicing algorithm and alignment algorithm, to realize the reconstruction of surface three-dimensional topography.In the device, autocollimation system is designed, the error generated by the deflection of the horizontal placement of the rod can be measured and error compensation is carried out.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of precision measurement, and particularly relates to a low-coherence interferometry system for detecting surface topography of a deep hole. BACKGROUND

[0002] In industry, deep holes are important components of various instruments and industrial products, such as deep holes of main shafts and landing gears of airplane engines, deep holes in inner cavities of valve housings of steam turbines, deep holes of tube plates of steam generators, and the like.

[0003] Detection of surface topography of a deep hole mainly includes contact measurement and non-contact measurement, and traditional measurement methods include a surface roughness meter, a roundness meter, and a three-dimensional surface topography meter, and the like. The roundness meter has two measurement structures, one of which is that a measurement head rotates with a main shaft, but it is not suitable for measuring surface topography of a deep hole because of difficulty in vertical or horizontal movement of the measurement head or a rod. The other structure is that the measurement head is stationary and a workpiece rotates with a worktable, and the worktable has poor rotation accuracy. The surface roughness meter has the disadvantages of less measurement parameters, inflexible measurement mode, and low measurement accuracy, and does not meet the standard of high-precision measurement. The three-dimensional surface topography meter can perform three-dimensional reconstruction of surface topography of a deep hole, but is expensive, with a price of 1-2 million yuan RMB per meter.

[0004] In view of the above problems, a non-contact deep hole surface topography profile measurement system and method are invented, which are non-contact and multi-parameter. The non-contact property solves the problem of influence of a measurement head on surface topography in contact measurement. The system can quickly acquire three-dimensional profile of surface topography at one time. The system is low in cost and cheap in price, and is supplemented by a self-collimation system to improve measurement accuracy. SUMMARY

[0005] The present application aims to design a device combining a low-coherence interferometry system and a self-collimation system to measure surface topography profile of a deep hole and detect surface defects and scratches of the deep hole. The device can construct surface profile of the deep hole at one time and realize automatic full inspection, point cloud reconstruction, and automatic evaluation.

[0006] To achieve the above-mentioned purpose, the present application provides a deep hole surface topography measurement system and method based on low-coherence interference, which comprises a detection part and a self-collimation system. The detection part comprises a white light interference system, specifically a 1550nm ASE broadband light source 1, a first mirror 3, a first beam splitting prism 4, a second mirror 7, and a reference mirror 8 arranged in sequence. The two sides of the first beam splitting prism 4 are respectively provided with a deep hole to be measured 5 and a near-infrared camera 10. The deep hole to be measured 5 is provided with a conical prism 6.

[0007] The light beam emitted by the 1550nm ASE broadband light source 1 of the white light interference system passes through the first mirror 3 and enters the beam splitter prism 4, part of the light returns to the beam splitter prism 4 via the reflection of the second mirror 7 after reaching the reference mirror 8, and part of the light returns to the beam splitter prism 4 via the reflection of the conical prism 6, the two light beams realize interference, and the interference pattern is captured by the near-infrared camera 10;

[0008] The autocollimator system is arranged between the to-be-measured deep hole 5 and the first beam splitter prism 4, and the autocollimator system comprises a 630nm light source 11, a dichroic prism 13, a second beam splitter prism 14, a third mirror 15 and a four-quadrant detector 16 arranged in sequence; wherein the dichroic prism 13 and the second beam splitter prism 14 are arranged on the light path between the to-be-measured deep hole 5 and the first beam splitter prism 4.

[0009] The autocollimator system detects the inclined part of the rod on which the to-be-measured deep hole 5 is located, and specifically, the light beam emitted by the 630nm light source 11 is reflected by the dichroic prism 13 to the second beam splitter prism 14, part of the light is reflected by the third mirror 15 to the four-quadrant detector 16, and part of the light returns to the second beam splitter prism 14 via the reflection of the conical prism 6 and is reflected by the third mirror 15 to the four-quadrant detector 16, if the light spot is not at the center of the four-quadrant detector 16, it indicates that the rod is inclined, and the rod is adjusted until the light spot is at the center of the four-quadrant detector 16.

[0010] Preferably, a first achromatic lens 2 is further arranged between the 1550nm ASE broadband light source 1 and the first mirror 3.

[0011] Preferably, a second achromatic lens 12 is further arranged between the 630nm light source 11 and the dichroic prism 13.

[0012] More preferably, the conical prism 6 comprises a circular conical surface, the head of the circular conical surface is platform-shaped, and the head of the circular conical surface is fused with a plane mirror.

[0013] Further preferably, the reference mirror 8 is fixed on the high-precision displacement table 9.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] This invention patent utilizes a low-cost prism and lens in its low-coherence interference deep hole surface topography measurement system and method. Compared to traditional measuring instruments and equipment, this invention boasts high integration, enabling a single scan of the deep hole surface topography. Multiple measurements are then performed using a four-step phase-shifting algorithm, a stitching algorithm, and an alignment algorithm to obtain the measurement results, achieving three-dimensional reconstruction of the surface topography. A self-collimation system is incorporated into the device to measure and compensate for errors caused by sway when the rod is placed horizontally. Ultimately, this achieves automatic full inspection, point cloud reconstruction, and automatic evaluation. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] Figure 1 This is a schematic diagram illustrating the principle of the deep hole surface morphology measurement system and method based on low coherence interference of the present invention;

[0018] Figure 2 This is the structure of the special conical prism in this invention;

[0019] Figure 3 This refers to the tilting and bending state of a member under the influence of gravity.

[0020] Figure 4 To stitch together the three measurement point clouds using a stitching algorithm. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0022] This invention discloses a deep hole surface topography measurement system and method based on low-coherence interference, including a detection part and a self-collimation system. The detection part includes the white light interferometry system, specifically consisting of a 1550nm ASE broadband light source 1, a first reflecting mirror 3, a first beam-splitting prism 4, a second reflecting mirror 7, and a reference reflecting mirror 8 arranged sequentially. A deep hole 5 to be measured and a near-infrared camera 10 are respectively arranged on both sides of the first beam-splitting prism 4. A conical prism 6 is placed inside the deep hole 5. A first achromatic lens 2 is also arranged between the 1550nm ASE broadband light source 1 and the first reflecting mirror 3. The reference reflecting mirror 8 is fixed on a high-precision displacement stage 9. The conical prism 6 is placed inside the deep hole 5.

[0023] The self-collimation system includes a 630nm light source 11, a dichroic prism 13, a second beam splitter prism 14, a third reflector 15, and a four-quadrant detector 16 arranged sequentially; wherein, the dichroic prism 13 and the second beam splitter prism 14 are arranged in the optical path between the deep hole 5 to be measured and the first beam splitter prism 4; a second achromatic lens 12 is also arranged between the 630nm light source 11 and the dichroic prism 13.

[0024] The first beam-splitting prism 4 is used for beam splitting near-infrared light (700-1100nm), and the second beam-splitting prism 14 is used for beam splitting visible light (400-700nm).

[0025] In the white light interferometer system, the first achromatic lens 2 changes the beam diameter and divergence angle of the broadband light source, and the broadband light source becomes a parallel beam after passing through the first achromatic lens 2; the first reflecting mirror 3 and the second reflecting mirror 7 both change the direction of light propagation and increase the optical path; the reference reflecting mirror 8 fixed on the high-precision displacement stage 9 serves as a reference reflecting arm, and the high-precision displacement stage 9 moves the reference reflecting mirror 8 to achieve scanning of the surface morphology of the deep hole of the rod under test; the near-infrared camera 10 acquires the interference pattern.

[0026] The second achromatic lens 12 in the self-collimation system alters the beam diameter and divergence angle of the broadband light source, transforming it into a parallel beam. The dichroic prism 13 selectively transmits or reflects light based on its wavelength, achieving spectral dispersion. The dichroic prism 13 transmits only near-infrared light in the white light interference system and reflects only visible light in the self-collimation system. The four-quadrant detector 16 can detect the straightness of the rod under test.

[0027] The 1550nm ASE broadband light source 1 of the white light interference system is transformed into a parallel beam by the first achromatic lens 2 and propagates. After passing through the first reflecting mirror 3, it enters the beam splitter prism 4. Part of the light is reflected by the second reflecting mirror 7 and reaches the reference reflecting mirror 8 before returning to the first beam splitter prism 4. Part of the light is reflected by the conical prism 6 and returns to the first beam splitter prism 4. The two beams of light interfere with each other, and the interference pattern is captured by the near-infrared camera 10.

[0028] The position where the interference is strongest at each measurement point is calculated in MATLAB using a four-step phase-shifting algorithm, and the relative height of that point is obtained, thus realizing the reconstruction of the three-dimensional morphology of the surface.

[0029] With λ c The interferogram is captured with a sampling step of / 4, so the phase change between two adjacent interferograms captured by the camera is π / 2. The light intensity corresponding to the pixel in the interferogram is:

[0030]

[0031] The light intensity values of each pixel point of the four continuous interference images are I1, I2, I3 and I4, I0 is the background light intensity value of the camera; A represents the modulation amplitude of each point; and φ represents the phase value of the corresponding point.

[0032] The phase value of the (x, y) point is obtained by simultaneously solving the above four equation groups:

[0033]

[0034] The relative height is:

[0035]

[0036] Wherein, λ is the wavelength of the broadband light source, and N is the number of interference fringes.

[0037] The surface morphology of the deep hole is obtained by three-dimensional surface reconstruction of the obtained interference fringes, including defects and scratches on the surface.

[0038] The 630nm light source 11 of the autocollimator system is converted into a parallel light beam by the second achromatic lens 12 and is propagated, is reflected to the second beam splitting prism 14 through the dichroic prism 13, part of the light is reflected to the four-quadrant detector 16 through the third reflecting mirror 15, and part of the light returns to the second beam splitting prism 14 through the reflection of the conical prism 6 and is reflected to the four-quadrant detector 16 through the third reflecting mirror 15, if the light spot is not in the center of the four-quadrant detector 16, it indicates that the rod is inclined, and the rod is adjusted until the light spot is in the center of the four-quadrant detector 16.

[0039] As Figure 2 The conical prism 6 of the present application is integrated with the plane 601 and the conical surface 602 as a whole, and is used as a special prism for measurement. The surface morphology of the deep hole is obtained by multiple measurements of each point cloud, and the final measurement point cloud is obtained by splicing algorithm.

[0040] The Figure 3That is to use the stitching algorithm to stitch three measurement point clouds. The stitching algorithm derives the process of the final measurement point cloud as follows: the first measurement point cloud 501 is selected as the aligned reference cylinder (RC), and the second measurement point cloud 502 is selected as the misaligned cylinder (MC). First, stitch the first measurement point cloud 501 and the second measurement point cloud 502 as the reconstructed reference measurement point cloud, and then stitch the third measurement point cloud 503 with the reference measurement point cloud, and so on. The final measurement point cloud is obtained by stitching. An overlap area is reserved between adjacent measurement point clouds, and the alignment algorithm is used. The data in the overlap area of the two measurement point clouds has good consistency. The core of the alignment algorithm is to use the least absolute method to calculate the translation and tilt parameters of the cylinder, so as to ignore the abnormal points in the measurement point cloud, recalculate the new radius of each point in the misaligned point cloud to obtain the radius of the aligned point cloud, and make the two measurement point clouds transition smoothly. The measured all measurement point clouds are stitched to reconstruct the inner surface morphology of the deep hole completely. The main formula of the alignment algorithm is as follows:

[0041] By least square method

[0042]

[0043] Wherein, x i , y i and z i are the Cartesian coordinates of the misaligned cylinder; n is the number of misaligned cylinder MC points; (x0, y0) is the point of the misaligned cylinder MC axis passing through the xoy plane of z=0; The values of k x and k y are related to the inclination angle of the misaligned cylinder MC axis relative to the z axis; r0 is the radius of the cylinder; x0, y0 are the values of the rigid body on the x axis and y axis, respectively, which must be aligned with the misaligned cylinder MC when the rigid body is translated.

[0044] θ x = atn(k x )

[0045] θ y = atn(k y )

[0046] The angle of the rod caused by gravity is obtained from the above formula, wherein θ x is the angle between the misaligned cylinder MC axis and the z axis in the XZ plane, and θ y is the angle between the misaligned cylinder MC axis and the z axis in the YZ plane.

[0047] After finding the above five parameters, the radius of each point of the misaligned point cloud must be recalculated to generate the aligned point cloud.

[0048] The new radius of each point is obtained from the following formula:

[0049] x1 = -x0 - k x *z[i] - r[i] * cos(0[i])

[0050] y1 = -y0 - k y *z[i] - r[i] * sin(0[i])

[0051] raligh[i] = sqrt(x1 * x1 + y1 * y1)

[0052] where r[i] is the radius of the i-th point of the misaligned point cloud; 0[i] is the polar angle of the i-th point of the misaligned point cloud; z[i] is the z coordinate of the i-th point of the misaligned point cloud; raligh[i] is the radius of the i-th point of the aligned point cloud.

[0053] In the foregoing formula, assuming that all cloud data are stored in a one-dimensional matrix, the value of raligh[i] must cover the value of r[i] before, and the process will produce an aligned cloud, the average value of the radius is unchanged.

[0054] The Figure 4 For the inclined bending state 511 of the rod under the influence of gravity and the ideal state 512 when not affected by gravity, as shown by the dashed line in the figure, the error caused by the inclination of the rod due to gravity during the measurement process can be detected by the autocollimation system. After the error caused by the inclination of the rod due to gravity is known, error compensation can be performed.

[0055] The device can ultimately detect surface defects and scratches of deep holes and can construct the surface profile of deep holes at one time, realize automatic full inspection, point cloud reconstruction and automatic evaluation.

[0056] The above-described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A low-coherence-interference-based deep-hole surface topography measurement system, characterized by, The application relates to a detection device for a deep hole, which comprises a detection part and a collimation system, wherein the detection part comprises a white light interference system, specifically a 1550nm ASE broadband light source (1), a first reflector (3), a first beam splitter prism (4), a second reflector (7), a reference reflector (8) arranged in sequence, and a deep hole (5) and a near-infrared camera (10) arranged on the two sides of the first beam splitter prism (4) respectively, wherein a conical prism (6) is arranged in the deep hole (5). The light beam emitted by the 1550nm ASE broadband light source (1) of the white light interference system enters the beam splitter prism (4) through the first reflector (3), part of the light reaches the reference reflector (8) after being reflected by the second reflector (7) and returns to the beam splitter prism (4) in the original path, part of the light returns to the beam splitter prism (4) in the original path after being reflected by the conical prism (6), and the two light beams realize interference, and the interference pattern is captured by the near-infrared camera (10). The collimation system is arranged between the deep hole (5) and the first beam splitter prism (4), and the collimation system comprises a 630nm light source (11), a dichroic prism (13), a second beam splitter prism (14), a third reflector (15) and a four-quadrant detector (16) arranged in sequence, wherein the dichroic prism (13) and the second beam splitter prism (14) are arranged on the light path between the deep hole (5) and the first beam splitter prism (4). The collimation system detects the inclined part of the rod where the deep hole (5) is located, specifically, the light beam emitted by the 630nm light source (11) is reflected by the dichroic prism (13) to the second beam splitter prism (14), part of the light is reflected by the third reflector (15) to the four-quadrant detector (16), part of the light returns to the second beam splitter prism (14) in the original path after being reflected by the conical prism (6) and is reflected by the third reflector (15) to the four-quadrant detector (16), if the light spot is not in the center of the four-quadrant detector (16), it indicates that the rod is inclined, and the rod is adjusted until the light spot is in the center of the four-quadrant detector (16).

2. The low coherence interferometry based surface profile measurement system for deep hole according to claim 1, wherein, The first achromatic lens (2) is further arranged between the 1550nm ASE broadband light source (1) and the first reflector (3).

3. The low coherence interferometry based surface profile measurement system for deep holes according to claim 1, wherein, The second achromatic lens (12) is further arranged between the 630nm light source (11) and the dichroic prism (13).

4. The low coherence interferometry based surface profile measurement system for deep holes according to claim 1, wherein, The conical prism (6) comprises a circular conical surface, the head of the circular conical surface is platform-shaped, and the head of the circular conical surface is fused with a plane mirror.

5. The low coherence interferometry based surface profile measurement system of claim 1, wherein, The reference reflector (8) is fixed on a high-precision displacement table (9).

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