A U-shaped turntable coaxiality detection system and method

Abstract

A U-shaped turntable coaxiality detection system and method are disclosed, belonging to the field of photoelectric detection. The system includes: a light source device, a collimation device, a magnification conversion device, a U-shaped turntable, a horizontal axis photoelectric detection device, and a vertical axis photoelectric detection device. The laser beam emitted by the light source device is shaped into parallel light by the collimation device, and the magnification conversion device performs magnification conversion on the parallel light. The horizontal axis photoelectric detection device captures a light spot image on the inner surface of the U-shaped turntable to detect the deviation of the shaft hole of the U-shaped turntable's pitch axis in the horizontal direction. The vertical axis photoelectric detection device captures a light spot image on the inner surface of the U-shaped turntable to detect the deviation of the shaft hole of the U-shaped turntable's pitch axis in the vertical direction. An industrial control computer is connected to the magnification conversion device, the horizontal axis photoelectric detection device, and the vertical axis photoelectric detection device, respectively. This invention has the advantages of online adjustment, high measurement accuracy, high efficiency, low maintenance cost, low requirements on the size of the U-shaped turntable, and measurement results unaffected by ambient temperature.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection technology, and in particular relates to a U-shaped turntable coaxiality detection system and detection method. Background Technology

[0002] High-precision inertial navigation testing equipment such as two-axis and three-axis turntables widely utilize U-shaped frame structures. A two-axis U-shaped frame typically includes azimuth and pitch axes, with bearing mounting holes at both ends of the pitch axis. As the main load-bearing structure, the U-shaped frame provides a stable working platform for the mounted optical equipment, enabling more efficient operation. To meet the high-precision attitude requirements of the equipment, the bearing holes at both ends of the pitch axis of the U-shaped frame must ensure corresponding coaxiality requirements. The coaxiality of the turntable's shaft holes, as a technical indicator in the machining of mechanical parts, is also a crucial precision indicator for the turntable frame, directly affecting the turntable's accuracy and stability.

[0003] There are currently two common methods for detecting coaxiality error. One is contact measurement, which can easily, efficiently, and intuitively detect the coaxiality of the turntable frame. For example, Chinese Patent CN104132605A discloses a device for detecting the coaxiality of a turntable frame. This device adopts a reasonable assembly mechanical structure and uses a dial indicator to obtain the coaxiality of the turntable pitch axis shaft hole. The design is simple, compact, low-cost, and easy to maintain. However, the manual reading error and the scratches on the measured parts caused by contact measurement are unavoidable drawbacks of this device. In addition, Chinese Patent CN109506555A discloses a device and method for measuring the coaxiality of bearing holes of a two-axis U-shaped frame. This method uses left and right mandrels to fit without clearance with the left and right bearing holes of the two-axis U-shaped frame through expansion sleeves. The axial length of the left and right mandrels is greater than the axial length of the left and right bearing holes of the two-axis U-shaped frame. The data is indirectly measured by dialing on the mandrels. The coaxiality is calculated by comparing the measurement data on both sides. This method has a reasonable structure and is easy to use. Although it uses indirect contact measurement to detect coaxiality, it also suffers from problems such as human eye reading errors, additional errors introduced by dial indicators, and scratches caused by indirect contact. Another type is non-contact measurement, which has advantages such as comprehensive information acquisition, high accuracy, and no additional damage to the measured workpiece. Common non-contact measurement methods include ultrasonic testing, eddy current testing, and laser sensing testing. Among these, laser sensing testing is exemplified by a method for measuring coaxiality using a laser sensor, disclosed in Chinese Patent Publication No. CN108827192A. This method first adjusts the coaxiality of the two rotating laser sensors by measuring a standard workpiece. Specifically, the measuring device is adjusted so that the laser sensor extends into the inner hole. Then, point clouds of the two inner hole surfaces are acquired through rotary scanning. The ideal axes on both sides of the standard workpiece are fitted using the least squares method, and the spatial position relationship of the measurement coordinate system of the two laser sensors is calibrated by the coaxiality characteristic of the standard workpiece. When measuring a workpiece, the coordinates of the effective point clouds of the holes on both sides are transformed to the same coordinate system according to the aforementioned coordinate system calibration relationship. Then, the ideal axes and common reference axes of the two holes are fitted respectively, thereby calculating the coaxiality error of the workpiece. The coaxiality detection method based on the above principle has the advantages of high detection accuracy and convenient measurement. However, for complex U-shaped turntable workpieces or workpieces with small pitch axis hole sizes, the rotary scanning mechanism is limited by the rotation radius, making it difficult to extend into the circular hole for scanning and obtain the point cloud data of the inner hole.

[0004] In summary, due to the special nature of the turntable frame structure and the high precision requirements, existing measurement methods are difficult to meet the testing requirements. Although they can achieve good measurement accuracy, they are inefficient, have few sampling points, and are easily affected by environmental factors. The main limitations are as follows: (1) The accuracy of the pitch axis shaft hole is a very important indicator for the U-shaped state. Contact measurement (direct contact / indirect contact) will cause a certain degree of scratches on the pitch axis shaft hole of the measured part; (2) For large-scale high-precision inertial navigation testing equipment, the span of the bearing holes at both ends of the U-shaped frame exceeds 1.5m or even more, while the coaxiality requirement reaches Φ15μm or lower. Current measurement devices or methods cannot meet the requirements in terms of measurement range and accuracy; (3) Due to the size limitations of the current laser sensor, it is impossible to measure the smaller shaft hole of the pitch axis of the U-shaped turntable; (4) Due to the influence of the measurement environment, the coordinate measuring machine with high environmental requirements cannot fully and accurately reflect the test data due to temperature changes during and after the test; (5) The turntable has many frames, and the testing workload is large, which cannot meet the needs of the industrialization development of the turntable. Summary of the Invention

[0005] The purpose of this invention is to provide a U-shaped turntable coaxiality detection system and method to solve the problems existing in the prior art.

[0006] The technical solution adopted by this invention to solve the technical problem is as follows:

[0007] The present invention provides a U-shaped turntable coaxiality detection system, comprising:

[0008] A light source device used to emit a laser beam;

[0009] A collimation device is disposed at the rear end of the light source device, the collimation device being used to shape the laser beam emitted by the light source device into parallel light;

[0010] A magnification conversion device is installed at the rear end of the collimation device, which is used to receive the shaped parallel light and perform magnification conversion on it;

[0011] A U-shaped turntable is installed at the rear end of the rate conversion device;

[0012] A horizontal axis photoelectric detection device is installed above the U-shaped turntable. The horizontal axis photoelectric detection device is used to capture light spot images on the inner surface of the U-shaped turntable and to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable in the horizontal direction.

[0013] A vertical axis photoelectric detection device is installed on the side of the U-shaped turntable. The vertical axis photoelectric detection device is used to capture light spot images on the inner surface of the U-shaped turntable and to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable in the vertical direction.

[0014] An industrial control computer is connected to a magnification conversion device, a horizontal axis photoelectric detection device, and a vertical axis photoelectric detection device.

[0015] Furthermore, the optical axis of the magnification conversion device coincides with the normal of the laser beam.

[0016] Furthermore, the magnification conversion device comprises a first focal length free conversion device, a second focal length free conversion device, and a distance compensation device; both the first and second focal length free conversion devices are mounted on the distance compensation device; the distance compensation device is connected to an industrial control computer; the collimation device, the first focal length free conversion device, and the second focal length free conversion device are arranged sequentially; the optical axes of the light source device, the collimation device, the first focal length free conversion device, the second focal length free conversion device, and the U-shaped turntable are kept coaxial; the optical interval between the first and second focal length free conversion devices is adjusted by moving the first and second focal length free conversion devices along the optical axis direction through the distance compensation device.

[0017] Furthermore, the adjustment amount of the distance compensation device is the difference between the focal length f1 of the first focal length free transformation device before zoom and the focal length f1ˊ of the first focal length free transformation device after zoom, i.e., f1ˊ-f1.

[0018] Furthermore, the focal length f1 of the first focal length free transformation device and the focal length f2 of the second focal length free transformation device satisfy the following relationship:

[0019] (1) The optical interval of the magnification conversion device is L = f1 + f2;

[0020] (2) The required magnification of the rate conversion device is β = f2 / f1;

[0021] (3) The focal length of the first focal length free transformation device is f1 = L / (1+β), and the focal length of the second focal length free transformation device is f2 = βL / (1+β).

[0022] Furthermore, both the first and second focal length free transformation devices are selected from liquid crystal spatial light modulators, deformable mirrors, digital micromirrors, or zoom optical lens groups.

[0023] Furthermore, when both the first and second focal length free transformation devices employ liquid crystal spatial light modulators, their phase diagrams satisfy formula (1):

[0024]

[0025] In the formula, λ is the wavelength of the incident beam, and f is the focal length of the focal length-free transformation device. Let x and y be the coordinate values ​​of the surface to be generated by the liquid crystal spatial light modulator. Substitute the focal length f1 of the first focal length free transformation device and the focal length f2 of the second focal length free transformation device into formula (1) to obtain the surface to be generated by the liquid crystal spatial light modulator.

[0026] The present invention provides a method for detecting the coaxiality of a U-shaped turntable, which is implemented using the aforementioned U-shaped turntable coaxiality detection system; the method includes the following steps:

[0027] The laser beam emitted by the light source device is shaped into parallel light by a collimating device. After the parallel light undergoes magnification transformation by a first focal length free transformation device and a second focal length free transformation device, the aperture of the parallel light is adjusted to be the same as the aperture size of the large end shaft hole on the left side of the U-shaped turntable. The beam passes through the large end shaft hole on the left side of the U-shaped turntable and then enters the small end shaft hole on the right side of the U-shaped turntable. Ideally, the beam and the small end shaft hole on the right side of the U-shaped turntable form a concentric ring. When there is a deviation, the beam forms an eccentric ring-shaped light spot or an eccentric crescent-shaped light spot at the small end shaft hole on the right side of the U-shaped turntable. The eccentric light spot images caused by the coaxiality deviation of the shaft holes are collected by the horizontal axis photoelectric detection device and the vertical axis photoelectric detection device, respectively. The optical interval between the first focal length free transformation device and the second focal length free transformation device is adjusted by the distance compensation device driven by the industrial control computer to meet the magnification requirements. Finally, the data of the eccentric light spot image is recorded and processed by the industrial control computer to obtain the coaxiality deviation relationship.

[0028] Furthermore, the specific calculation process for the coaxiality deviation relationship is as follows:

[0029] Obtain the corresponding fitting circle at the small end shaft hole on the right side of the U-shaped turntable, and establish an XY coordinate system at the center of the fitting circle. Use the horizontal axis photoelectric detection device and the vertical axis photoelectric detection device to record the eccentric spot image information of the beam in the horizontal and vertical directions, respectively. The obtained images are eccentric annular spot images or eccentric crescent spot images. The circle containing the eccentric annular spot or eccentric crescent spot is recorded as the calibration circle. Use the center fitting algorithm to fit the center of the calibration circle. Analyze the positional relationship between the center of the fitting circle and the center of the calibration circle to obtain the coaxiality deviation relationship.

[0030] Furthermore, the specific calculation process of the circle center fitting algorithm is as follows:

[0031] The center of the circle is fitted using the least squares method, based on the circle's formula (xA). 2 +(yB) 2 =R 2 The following relation is obtained:

[0032] R 2 =x 2 -2Ax+A 2 +y2 -2By+B 2 (2)

[0033] make:

[0034]

[0035] The simplified general form of a circle is:

[0036] x 2 +y 2 +ax+by+c=0 (4)

[0037] Solving for parameters a, b, and c using formula (4) yields the coordinates of the center (A, B) and the parameters of the radius R:

[0038]

[0039] Sample set (X) i Y i In the sequence ), i∈1, 2, 3, ..., n, the distance from a point to the center of the circle is d. i :

[0040] d i 2 =(X i -A) 2 +(Y i -B) 2 (6)

[0041] Let the distance from the point to the center of the circle be d. i The difference between the square of and the square of the radius R is:

[0042]

[0043] Expanding equation (7) and substituting it into equation (4), we obtain the following relation:

[0044]

[0045] Let F(a, b, c) be Δr i The sum of squares yields the following relationship:

[0046]

[0047] Find the parameters a, b, and c that minimize the value of F(a, b, c); take the partial derivatives of F(a, b, c) with respect to parameters a, b, and c respectively, set the partial derivatives to 0, and compare the function values ​​at all extreme points to obtain the minimum value of F(a, b, c):

[0048]

[0049] Equation (10) can be written in matrix form:

[0050]

[0051] Solving matrix (11) yields the values ​​of parameters a, b, and c, and then the fitted estimates of A, B, and R are obtained:

[0052]

[0053] The obtained A and B values ​​are the center coordinates (A, B) of the fitted circle projected onto the inner surface of the right side of the U-shaped turntable by the large end shaft hole on the left side of the turntable. The positional relationship between the center (A, B) and the origin (0,0) is analyzed to obtain the coaxiality deviation.

[0054] The beneficial effects of this invention are:

[0055] The U-shaped turntable coaxiality detection system of the present invention includes: a light source device, a collimation device, a magnification conversion device, a horizontal axis photoelectric detection device, a U-shaped turntable, a vertical axis photoelectric detection device, and an industrial control computer; through the synergistic effect between the components, high-precision U-shaped turntable coaxiality detection can be achieved, which has the advantages of online adjustment, high measurement accuracy, high efficiency, low maintenance cost, low requirements on the size of the U-shaped turntable, and measurement results are not affected by ambient temperature. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the coaxiality detection system of a U-shaped turntable according to the present invention.

[0057] Figure 2 This is a schematic diagram of the zoom optical lens group structure, which consists of a first focal length free transformation device and a second focal length free transformation device.

[0058] Figure 3 Analysis of coaxiality deviation of U-shaped turntable under eccentric annular light spot.

[0059] Figure 4 Analysis of coaxiality deviation of U-shaped turntable under eccentric crescent-shaped light spot.

[0060] Figure 5 The results of the coaxiality tolerance test of the U-shaped turntable in Specific Implementation Method 1 are shown.

[0061] Figure 6 The results of the coaxiality tolerance test of the U-shaped turntable in Specific Implementation Method 1 are shown.

[0062] In the figure, 1 is the light source device, 2 is the collimation device, 3 is the first focal length free transformation device, 4 is the second focal length free transformation device, 5 is the horizontal axis photoelectric detection device, 6 is the U-shaped turntable, 7 is the vertical axis photoelectric detection device, 8 is the industrial control computer, 9 is the magnification conversion device, 10 is the distance compensation device, 11 is the fitting circle, 12 is the calibration circle, 13 is the eccentric annular light spot, and 14 is the eccentric crescent-shaped light spot. Detailed Implementation

[0063] The present invention will be further described in detail below with reference to the accompanying drawings.

[0064] like Figure 1 As shown, the U-shaped turntable coaxiality detection system of the present invention mainly includes: a light source device 1, a collimation device 2, a magnification conversion device 9, a horizontal axis photoelectric detection device 5, a U-shaped turntable 6, a vertical axis photoelectric detection device 7, and an industrial control computer 8.

[0065] The light source device 1 is placed at the front end of the system and is used to emit a laser beam with a laser output wavelength of 635±2nm and a numerical aperture NA≤0.14.

[0066] The collimation device 2 is placed after the light source device 1, that is, between the light source device 1 and the magnification conversion device 9. The collimation device 2 is used to shape the laser beam emitted by the light source device 1, and can shape it into parallel light with a certain aperture.

[0067] The magnification conversion device 9 is placed after the collimation device 2, that is, between the collimation device 2 and the U-shaped turntable 6. The magnification conversion device 9 is used to receive the shaped beam and perform magnification conversion on it. The optical axis of the magnification conversion device 9 coincides with the normal of the incident beam.

[0068] The magnification conversion device 9 mainly consists of a first focal length free conversion device 3, a second focal length free conversion device 4, and a distance compensation device 10. The first focal length free conversion device 3 and the second focal length free conversion device 4 are both installed on the distance compensation device 10. The first focal length free conversion device 3 is placed after the collimation device 2, and the first focal length free conversion device 3 is placed in front of the second focal length free conversion device 4.

[0069] The distance compensation device 10 drives the first focal length free transformation device 3 and the second focal length free transformation device 4 to move along the optical axis, adjusting the optical interval L between them to ensure a reasonable scaling ratio that matches the aperture size of the large end shaft hole 601 on the left side of the pitch axis of the U-shaped turntable 6. During the scaling process, the first focal length free transformation device 3 and the second focal length free transformation device 4 in the scaling conversion device 9 not only achieve focal length transformation but also eliminate system aberrations and ensure the beam quality of the system.

[0070] The distance compensation device 10 moves in a direction parallel to the optical axis transmission direction. Its adjustment amount is the difference between the focal length f1 of the first focal length free transformation device 3 before zoom and the focal length f1ˊ of the first focal length free transformation device 3 after zoom, i.e., f1ˊ-f1. When the difference is positive, it is adjusted in the opposite direction to the optical transmission direction, moving away from the U-shaped turntable 6; when the difference is negative, it is adjusted in the same direction as the optical transmission direction, moving closer to the U-shaped turntable 6.

[0071] In this embodiment, the distance compensation device 10 can be a mechanism with linear displacement adjustment function driven by a motor, piezoelectric ceramics, etc. Specifically, a piezoelectric inertial driven linear displacement stage with a stroke of 60mm can be used.

[0072] Both the first focal length free-shifting device 3 and the second focal length free-shifting device 4 can be selected from devices such as liquid crystal spatial light modulators, deformable mirrors, digital micromirrors, and zoom optical lens groups. These devices have the function of zooming and can compensate for defocus aberration. The zoom optical lens group composed of the first focal length free-shifting device 3 and the second focal length free-shifting device 4 mainly adopts a Galilean telescope structure, but can also be a transmissive or reflective structure. In this embodiment, as... Figure 2 As shown, the first focal length free transformation device 3 and the second focal length free transformation device 4 are a negative lens and a positive lens, respectively. The focal length f1 of the first focal length free transformation device 3 is less than zero, and the focal length f2 of the second focal length free transformation device 4 is greater than zero.

[0073] When the first focal length free transformation device 3 and the second focal length free transformation device 4 use a liquid crystal spatial light modulator, their phase diagrams satisfy the relationship shown in formula (1):

[0074]

[0075] Where λ is the wavelength of the incident beam, and f is the focal length of the focal length-free transformation device. Let x and y be the coordinate values ​​of the surface to be generated by the liquid crystal spatial light modulator. Substitute the focal length f1 of the first focal length free transformation device 3 and the focal length f2 of the second focal length free transformation device 4 into formula (1) to obtain the surface to be generated by the liquid crystal spatial light modulator. The industrial control computer 8 calculates the surface to be generated by the liquid crystal spatial light modulator according to the relationship shown in formula (1) and the requirements of the focal length f1 of the first focal length free transformation device 3 and the focal length f2 of the second focal length free transformation device 4, and controls the liquid crystal spatial light modulator to generate the corresponding surface, thereby realizing the focal length transformation of the first focal length free transformation device 3 and the second focal length free transformation device 4.

[0076] The focal length f1 of the first focal length free transformation device 3 and the focal length f2 of the second focal length free transformation device 4 satisfy the following geometric relationship:

[0077] (1) The optical interval of the magnification conversion device 9 is L = f1 + f2;

[0078] (2) The required magnification of the magnification conversion device 9 is β = f2 / f1;

[0079] (3) The focal length f1 of the first focal length free transformation device 3 is L / (1+β), and the focal length f2 of the second focal length free transformation device 4 is βL / (1+β).

[0080] The distance compensation device 10, horizontal axis photoelectric detection device 5, and vertical axis photoelectric detection device 7 in the magnification conversion device 9 are connected to the industrial control computer 8 via data cables. The industrial control computer 8 controls the operation of the distance compensation device 10, horizontal axis photoelectric detection device 5, and vertical axis photoelectric detection device 7. The U-shaped turntable 6 is positioned after the magnification conversion device 9, the horizontal axis photoelectric detection device 5 is positioned above the U-shaped turntable 6, and the vertical axis photoelectric detection device 7 is positioned to the left of the U-shaped turntable 6. Both the horizontal axis photoelectric detection device 5 and the vertical axis photoelectric detection device 7 are used to capture light spot images. Specifically:

[0081] The horizontal axis photoelectric detection device 5 is placed above the U-shaped turntable 6, according to... Figure 1 The inner surface of the U-shaped turntable 6 is photographed in the direction shown, to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable 6 in the horizontal direction; the vertical axis photoelectric detection device 7 is placed on the side of the U-shaped turntable 6, according to... Figure 1 The inner surface of the U-shaped turntable 6 is photographed in the direction shown, which is used to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable 6 in the vertical direction.

[0082] The following principles apply to the specific placement of the U-shaped turntable 6: When the diameters of the left and right shaft holes (large end shaft hole 601 and small end shaft hole 602) on the pitch axis of the U-shaped turntable 6 are different, the shaft hole with the larger diameter (large end shaft hole 601) should be closer to the second focal length free transformation device 4; when the diameters of the left and right shaft holes (large end shaft hole 601 and small end shaft hole 602) on the pitch axis of the U-shaped turntable 6 are the same, there are no special requirements for the placement.

[0083] During the coaxiality test of the U-shaped turntable, the optical axes of the light source device 1, collimation device 2, first focal length free transformation device 3, second focal length free transformation device 4, and U-shaped turntable 6 must always be kept coaxial.

[0084] The coaxiality deviation of a U-shaped rotary table can be mainly classified into the following types:

[0085] (1) The diameters of the left and right shaft holes (large end shaft hole 601 and small end shaft hole 602) of the pitch axis of the U-shaped turntable 6 are the same or different, and the coaxiality deviation is small, and the spot information presents an eccentric ring shape.

[0086] (2) The diameters of the left and right shaft holes (large end shaft hole 601 and small end shaft hole 602) of the pitch axis of the U-shaped turntable 6 are the same or different, and the coaxiality deviation is large, so the light spot information presents an eccentric crescent shape.

[0087] The horizontal axis photoelectric detection device 5 and the vertical axis photoelectric detection device 7 can be photoelectric conversion devices such as four-quadrant sensors, CCD detectors, or CMOS detectors. In this embodiment, both the horizontal axis photoelectric detection device 5 and the vertical axis photoelectric detection device 7 can be CMOS industrial cameras; the specific parameters of the lens end are as follows: resolution of 125 lp / mm, focal length of 90mm, aperture of 4mm, and working distance of 1000mm~∞mm; the specific parameters of the camera end are as follows: maximum resolution of 10000*7000, pixel size of 3.1um*3.1um, effective photosensitive area of ​​31mm*21.7mm, and output color of black and white.

[0088] The present invention provides a method for detecting the coaxiality of a U-shaped turntable, which mainly includes the following steps:

[0089] The light source device 1 emits a laser beam, which is shaped into parallel light with a certain aperture by the collimating device 2. After the parallel light passes through the magnification conversion device 9, where the first focal length free conversion device 3 and the second focal length free conversion device 4 are used, its aperture is adjusted to be the same as the aperture size of the large end shaft hole 601 on the left side of the pitch axis of the U-shaped turntable 6. After passing through the large end shaft hole 601 on the left side of the U-shaped turntable 6, the beam enters the small end shaft hole 602 on the right side of the U-shaped turntable 6. Ideally, the beam and the small end shaft hole 602 on the right side of the U-shaped turntable 6 form a concentric ring. Figure 1As shown; when a deviation exists, the beam forms an eccentric circular or crescent-shaped spot at the small end shaft hole 602 on the right side of the U-shaped turntable 6; then, the horizontal axis photoelectric detection device 5 and the vertical axis photoelectric detection device 7 respectively acquire images of the eccentric spot caused by the coaxiality deviation of the shaft hole. Due to the non-coaxial shooting angle and beam obstruction, dual-angle shooting is used to acquire images; the horizontal axis photoelectric detection device 5 detects the deviation of the small end shaft hole 602 on the right side of the pitch axis of the U-shaped turntable 6 in the horizontal direction, and the vertical axis photoelectric detection device 7 detects the deviation of the small end shaft hole 602 on the right side of the pitch axis of the U-shaped turntable 6 in the vertical direction; the industrial control computer 8 drives the distance compensation device 10 to adjust the optical interval between the first focal length free transformation device 3 and the second focal length free transformation device 4 to meet the magnification requirements; finally, the industrial control computer 8 records and processes the data of the eccentric spot image to obtain the coaxiality deviation relationship. Specifically: First, a fitting circle is obtained at the small end shaft hole 602 on the right side of the U-shaped turntable 6, and a corresponding XY coordinate system is established at the center O′ of the fitted circle 11; second, the eccentric light spot image information in the horizontal and vertical directions is recorded by the horizontal axis photoelectric detection device 5 and the vertical axis photoelectric detection device 7 respectively, and then the corresponding circle center fitting algorithm is used to fit the eccentric circular light spot 13 (e.g., Figure 3 (as shown) or an eccentric crescent-shaped light spot 14 (as shown) Figure 4 The center O of the outer arc (shown) is the center of calibration circle 12; the positional relationship between the fitted center O′ and the initially calibrated center O is analyzed to obtain the coaxiality deviation relationship. The specific calculation process is as follows:

[0090] The center of the circle is fitted using the least squares method, based on the circle's formula (xA). 2 +(yB) 2 =R 2 The following relation is obtained:

[0091] R 2 =x 2 -2Ax+A 2 +y 2 -2By+B 2 (2)

[0092] make:

[0093]

[0094] The simplified general form of a circle is:

[0095] x 2 +y 2 +ax+by+c=0 (4)

[0096] Solving for parameters a, b, and c using formula (4) yields the coordinates of the center (A, B) and the parameters of the radius R:

[0097]

[0098] Sample set (X) i Y i In the sequence ), i∈1, 2, 3, ..., n, the distance from a point to the center of the circle is d. i :

[0099] d i 2 =(X i -A) 2 +(Y i -B) 2 (6)

[0100] Let the distance from the point to the center of the circle be d. i The difference between the square of and the square of the radius R is:

[0101]

[0102] Expanding equation (7) and substituting it into equation (4), we obtain the following relation:

[0103]

[0104] Let F(a, b, c) be Δr i The sum of squares yields the following relationship:

[0105]

[0106] Find the parameters a, b, and c that minimize the value of F(a, b, c); take the partial derivatives of F(a, b, c) with respect to parameters a, b, and c respectively, set the partial derivatives to 0, and compare the function values ​​at all extreme points to obtain the minimum value of F(a, b, c):

[0107]

[0108] Equation (10) can be written in matrix form:

[0109]

[0110] Solving matrix (11) yields the values ​​of parameters a, b, and c, and then the fitted estimates of A, B, and R are obtained:

[0111]

[0112] The obtained A and B values ​​are the center coordinates (A, B) of the fitted circle projected onto the inner surface of the right side of the U-shaped turntable by the large end shaft hole on the left side of the turntable. The positional relationship between the center (A, B) and the origin (0,0) is analyzed to obtain the coaxiality deviation. Specific Implementation Method 1

[0114] The U-shaped turntable 6 has different diameter shaft holes on the left and right sides of its pitch axis. The diameter of the larger shaft hole 601 on the left is 48mm, and the diameter of the smaller shaft hole 602 on the right is 40mm. The laser wavelength emitted by the light source device 1 is 635nm. The collimating device 2 shapes the laser beam emitted by the light source device 1 into a circular beam with a diameter of 6mm. The magnification of the magnification conversion device 9 is β = -8. x The focal length of the first focal length free-changing device 3 is f1 = -6mm, and the focal length of the second focal length free-changing device 4 is f2 = 48mm. At this time, the positional relationship between the projected light spot and the small end shaft hole 602 on the right side of the U-shaped turntable 6 is as follows: Figure 5 As shown, using the detection method of the present invention, the coaxiality tolerance of the U-shaped turntable was measured to be 0.010 mm. Specific Implementation Method Two

[0116] The U-shaped turntable 6 has the same diameter shaft holes on both sides of its pitch axis. The diameter of the shaft hole 601 at the large end on the left and the shaft hole 602 at the small end on the right are both 36mm. The laser wavelength emitted by the light source device 1 is 635nm. The collimating device 2 shapes the laser beam emitted by the light source device 1 into a circular beam with a diameter of 6mm. The magnification of the magnification conversion device 9 is β = -6. x The focal length of the first focal length free-changing device 3 is f1 = -7mm, and the focal length of the second focal length free-changing device 4 is f2 = 42mm. At this time, the positional relationship between the projected light spot and the small end shaft hole 602 on the right side of the U-shaped turntable 6 is as follows: Figure 6 As shown, using the detection method of the present invention, the coaxiality tolerance of the U-shaped turntable was measured to be 0.015 mm.

[0117] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A U-shaped turntable coaxiality detection system, characterized in that, include: A light source device used to emit a laser beam; A collimation device is disposed at the rear end of the light source device, the collimation device being used to shape the laser beam emitted by the light source device into parallel light; A magnification conversion device is installed at the rear end of the collimation device, which is used to receive the shaped parallel light and perform magnification conversion on it; A U-shaped turntable is installed at the rear end of the rate conversion device; A horizontal axis photoelectric detection device is installed above the U-shaped turntable. The horizontal axis photoelectric detection device is used to capture light spot images on the inner surface of the U-shaped turntable and to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable in the horizontal direction. A vertical axis photoelectric detection device is installed on the side of the U-shaped turntable. The vertical axis photoelectric detection device is used to capture the light spot image on the inner surface of the U-shaped turntable and to detect the deviation of the shaft hole of the pitch axis of the U-shaped turntable in the vertical direction. An industrial control computer is connected to a magnification conversion device, a horizontal axis photoelectric detection device, and a vertical axis photoelectric detection device.

2. The coaxiality detection system for a U-shaped turntable according to claim 1, characterized in that, The optical axis of the magnification conversion device coincides with the normal of the laser beam.

3. The coaxiality detection system for a U-shaped turntable according to claim 1, characterized in that, The magnification conversion device consists of a first focal length free conversion device, a second focal length free conversion device, and a distance compensation device; both the first and second focal length free conversion devices are mounted on the distance compensation device; the distance compensation device is connected to an industrial control computer; the collimation device, the first focal length free conversion device, and the second focal length free conversion device are arranged sequentially; the optical axes of the light source device, the collimation device, the first focal length free conversion device, the second focal length free conversion device, and the U-shaped turntable are kept coaxial; the optical interval between the first and second focal length free conversion devices is adjusted by moving the first and second focal length free conversion devices along the optical axis direction through the distance compensation device.

4. The coaxiality detection system for a U-shaped turntable according to claim 3, characterized in that, The adjustment amount of the distance compensation device is the difference between the focal length f1 of the first focal length free transformation device before zoom and the focal length f1ˊ of the first focal length free transformation device after zoom, i.e., f1ˊ- f1.

5. The coaxiality detection system for a U-shaped turntable according to claim 3, characterized in that, The focal length f1 of the first focal length free transformation device and the focal length f2 of the second focal length free transformation device satisfy the following relationship: (1) The optical spacing of the magnification conversion device is L = f1 + f2; (2) The required magnification of the rate conversion device is β=f2 / f1; (3) The focal length of the first focal length free transformation device is f1=L / (1+β), and the focal length of the second focal length free transformation device is f2=βL / (1+β).

6. The coaxiality detection system for a U-shaped turntable according to claim 3, characterized in that, Both the first and second focal length free transformation devices are selected from liquid crystal spatial light modulators, deformable mirrors, digital micromirrors, or zoom optical lens groups.

7. The coaxiality detection system for a U-shaped turntable according to claim 3, characterized in that, When both the first and second focal length free transformation devices use liquid crystal spatial light modulators, their phase diagrams satisfy formula (1): （1）； In the formula, λ is the wavelength of the incident beam, f is the focal length of the focal length free transformation device, φ(x, y) is the surface shape to be generated by the liquid crystal spatial light modulator, and x and y are the coordinate values ​​respectively; by substituting the focal length f1 of the first focal length free transformation device and the focal length f2 of the second focal length free transformation device into the formula (1) respectively, the surface shape to be generated by the liquid crystal spatial light modulator is obtained.

8. A method for detecting the coaxiality of a U-shaped turntable, characterized in that, The method employs the coaxiality detection system of a U-shaped turntable as described in claim 3; the method includes the following steps: The laser beam emitted by the light source device is shaped into parallel light by a collimating device. After the parallel light undergoes magnification transformation by a first focal length free transformation device and a second focal length free transformation device, the aperture of the parallel light is adjusted to be the same as the aperture size of the large end shaft hole on the left side of the U-shaped turntable. The beam passes through the large end shaft hole on the left side of the U-shaped turntable and then enters the small end shaft hole on the right side of the U-shaped turntable. Ideally, the beam and the small end shaft hole on the right side of the U-shaped turntable form a concentric ring. When there is a deviation, the beam forms an eccentric ring-shaped light spot or an eccentric crescent-shaped light spot at the small end shaft hole on the right side of the U-shaped turntable. The eccentric light spot images caused by the coaxiality deviation of the shaft holes are collected by the horizontal axis photoelectric detection device and the vertical axis photoelectric detection device, respectively. The optical interval between the first focal length free transformation device and the second focal length free transformation device is adjusted by the distance compensation device driven by the industrial control computer to meet the magnification requirements. Finally, the data of the eccentric light spot image is recorded and processed by the industrial control computer to obtain the coaxiality deviation relationship.

9. The method for detecting the coaxiality of a U-shaped turntable according to claim 8, characterized in that, The specific calculation process for the coaxiality deviation relationship is as follows: Obtain the corresponding fitting circle at the small end shaft hole on the right side of the U-shaped turntable, and establish an XY coordinate system at the center of the fitting circle. Use the horizontal axis photoelectric detection device and the vertical axis photoelectric detection device to record the eccentric spot image information of the beam in the horizontal and vertical directions, respectively. The obtained images are eccentric annular spot images or eccentric crescent spot images. The circle containing the eccentric annular spot or eccentric crescent spot is recorded as the calibration circle. Use the center fitting algorithm to fit the center of the calibration circle. Analyze the positional relationship between the center of the fitting circle and the center of the calibration circle to obtain the coaxiality deviation relationship.

10. The method for detecting the coaxiality of a U-shaped turntable according to claim 9, characterized in that, The specific calculation process of the circle center fitting algorithm is as follows: The center of the circle is fitted using the least squares method, based on the formula for a circle. The following relation is obtained: (2)； make: (3)； The simplified general form of a circle is: (4)； Solving for parameters a, b, and c using formula (4) yields the coordinates of the center (A, B) and the parameters of the radius R. (5)； Sample set , In the middle, the distance from the point to the center of the circle is : (6)； Let the distance from the point to the center of the circle be... The difference between the square of and the square of the radius R is: (7)； Expanding equation (7) and substituting it into equation (4), we obtain the following relation: (8)； Let F(a, b, c) be Δr i The sum of squares yields the following relationship: (9)； Find the parameters a, b, and c that minimize the value of F(a, b, c); take the partial derivatives of F(a, b, c) with respect to parameters a, b, and c respectively, set the partial derivatives to 0, and compare the function values ​​at all extreme points to obtain the minimum value of F(a, b, c): (10)； Equation (10) can be written in matrix form: (11)； Solving matrix (11) yields the values ​​of parameters a, b, and c, and then the fitted estimates of A, B, and R are obtained: (12)； The obtained values ​​A and B are the center coordinates (A, B) of the fitted circle projected onto the inner surface of the right side of the U-shaped turntable from the large end of the left side shaft hole. The relationship between the center (A, B) and the origin is analyzed. The positional relationship between them is used to obtain the coaxiality deviation.

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