Three-dimensional correction method for ultra-precision optical profile measurement and measurement device

Abstract

The invention discloses a three-dimensional correction method for ultra-precision optical profile measurement and a measurement device. The method comprises the following steps: recording the center coordinate of a ball head; iteratively converting the center coordinates of the ball head into measurement coordinates; correcting the measurement coordinates to obtain actual measurement coordinates; and correcting the actually measured coordinates to obtain the coordinates of the measured object. Therefore, after the measurement coordinate is obtained based on the conversion of the center coordinate of the ball head, the measurement coordinate is corrected according to the measured data such as the perpendicularity error and the straightness change, the actual measurement coordinate of the contact point of the indication ball head and the surface of the measured object is obtained, and then the coordinate of the measured object is obtained through correction. Inevitable errors existing in the ball head circle center coordinate conversion process are effectively eliminated, and the spatial position of the surface of a measured object is truly reflected.

Description

Technical Field

[0001] The present invention relates to the field of precision measurement technology, and in particular to a three-dimensional correction method and a measuring device for ultra-precision optical profile measurement. Background Art

[0002] When conducting ultra-precision machining production, in addition to the need for the machining equipment to have machining performance of corresponding precision, the workpieces obtained by machining must also be subjected to ultra-precision measurement to ensure that the process meets the standards. If traditional equipment such as micrometers are used for manual measurement, the measurement efficiency is too low, especially when facing workpieces with complex curved surfaces. The number of sampling measurement points will increase significantly compared to workpieces with flat surfaces. In addition, manual measurement relies on the experience of the measurer, and the measurement accuracy is difficult to guarantee. For this reason, there are currently measuring devices that use a ball head to perform contact measurement on the surface of the object being measured. The ball head at the end of the measuring rod traverses the surface of the object being measured, and by measuring the trajectory coordinates of the ball head movement, indirect measurement of the surface of the object being measured is achieved.

[0003] It is understandable that when measuring a horizontal surface, the point of contact between the ball head and the object lies along the vertical axis of the measuring rod. However, when measuring a curved surface, the point of contact between the ball head and the object shifts away from the vertical axis of the measuring rod, toward the side of the ball head. This creates an angle between the line connecting the contact point and the center of the ball head and the vertical axis of the measuring rod. Because existing measuring equipment records the coordinates of the center of the ball head, when measuring objects with free-form surfaces, the coordinates of the contact point cannot be directly calculated based on the coordinates of the center of the ball head. The coordinates of the contact point are the actual measured coordinates of the object being measured. This results in irregular errors that are difficult to correct during ultra-precision measurements. Summary of the Invention

[0004] A first aspect of an embodiment of the present invention discloses a three-dimensional correction method for ultra-precision optical profilometry, specifically comprising:

[0005] Record the center coordinates P of the ball head o (x, y, z);

[0006] The center coordinate P of the ball head o (x, y, z) is iteratively converted to the measured coordinates P1 (x1, y1, z1);

[0007] Correct the measured coordinates P1 (x1, y1, z1) to obtain the measured coordinates (x ′ ,y ′ , z ′ ).

[0008] Correct the measured coordinates (x ′ ,y ′ , z ′ ) obtain the coordinates of the object to be measured (x2, y2, z2).

[0009] As an optional implementation, the method includes:

[0010] The center coordinate P of the ball head o (x, y, z) is measured based on several laser interferometers and nanocapacitive sensors. Let the radius of the ball head be r, let f(x, y) be the surface equation of the free surface of the object being measured, and let f x ′ (x, y) is the first-order partial derivative of f(x, y) with respect to the x-axis, let f y ′ (x, y) is the first-order partial derivative of f(x, y) facing the y-axis, then P o (x, y, z) is expressed as the following coordinate system:

[0011]

[0012] As an optional implementation, the recording ball head center coordinate P o (x, y, z), including:

[0013] The displacement measurement is performed using dual-frequency laser and nanocapacitive sensors to convert the center coordinates of the ball head P o (x, y, z).

[0014] As an optional embodiment, the center coordinate P of the ball head o (x, y, z) is iteratively converted to the measured coordinates P1 (x1, y1, z1), including:

[0015] Setting an iterative target parameter ε, wherein the target parameter ε is used to calibrate the parameter accuracy of the iterative conversion;

[0016] Calculating the absolute difference between the center coordinates of the ball head and the corresponding measurement coordinates;

[0017] If the absolute difference meets ||P o (x, y, z)-P1(x1, y1, z1)||<ε, then the measured coordinate P1(x1, y1, z1) is used to replace the corresponding ball head center coordinate P o (x, y, z).

[0018] As an optional implementation, the correction of the measured coordinates P1 (x1, y1, z1) to obtain the measured coordinates (x ′ ,y ′ , z ′ ),include:

[0019] a represents the perpendicularity error between the X-axis and the Z-axis, b represents the perpendicularity error between the Y-axis and the Z-axis, c represents the perpendicularity error between the X-axis and the Y-axis, zd represents the displacement change measured by the laser interferometer, and Z1, Z2, and Z3 represent the perpendicularity error between the X-axis and the Y-axis. x , Z y Respectively represent the straightness changes measured by each nanocapacitive sensor, and the correction is:

[0020]

[0021] As an optional implementation, the correction of the measured coordinates (x ′ ,y ′ , z ′ ) obtain the coordinates of the object to be measured (x2, y2, z2), including:

[0022] Let α be the angle of rotation of the measured coordinate system around the X axis, let β be the angle of rotation of the measured coordinate system around the Y axis, let γ be the angle of rotation of the measured coordinate system around the Z axis, let t x , t y , t z are the displacements of the measured coordinate system along the X-axis, Y-axis, and Z-axis respectively, and the correction results are:

[0023]

[0024] As an optional implementation, in the correction of the measured coordinates (x ′ ,y ′ , z ′ ) After obtaining the coordinates (x2, y2, z2) of the object to be measured, the method further includes:

[0025] Calculate the surface error e(α, β, γ, t x ,t y ,t z )=z2-f(x2,y2);

[0026] The least square method is used to fit the surface error e(α, β, γ, t x ,t y ,t z );

[0027] Based on the surface error e(α, β, γ, t x ,t y ,t z )Optimize the coordinates (x2, y2, z2) of the object to be measured.

[0028] A second aspect of an embodiment of the present invention discloses a measuring device, comprising:

[0029] A measuring platform for placing the object to be measured, and an XY displacement platform for moving the object to be measured below the measuring platform;

[0030] A measuring rod mounted on the air-bearing Z axis and used to contact the surface of the object being measured above the object being measured, with the end of the measuring rod being a ball head;

[0031] A first nanocapacitive sensor for measuring the linearity change of the XY displacement platform, a second nanocapacitive sensor for measuring the linearity change of the air-bearing Z-axis in the vertical direction, and a third nanocapacitive sensor for measuring the linearity change of the air-bearing Z-axis in the horizontal direction;

[0032] A fixedly set laser generator that outputs a laser beam, an X-axis reflector, a Y-axis reflector, a Z-axis reflector and a measuring rod top reflector that reflect the laser beam, an X-axis laser interferometer that receives the laser beam reflected by the X-axis reflector, a Y-axis laser interferometer that receives the laser beam reflected by the Y-axis reflector, a Z-axis laser interferometer that receives the laser beam reflected by the Z-axis reflector, and a measuring rod top laser interferometer that receives the laser beam reflected by the measuring rod top reflector.

[0033] As an optional embodiment, the first nanocapacitance sensor, the second nanocapacitance sensor and the third nanocapacitance sensor are used to measure the straightness changes of each displacement axis, and the X-axis laser interferometer, the Y-axis laser interferometer, the Z-axis laser interferometer and the laser interferometer on the top of the measuring rod are respectively used to measure the frequency change value of the laser beam and convert it into a displacement value, based on which the coordinates of the center of the ball head of the measuring rod are obtained.

[0034] As an optional embodiment, the coordinates of the center of the ball head are used for iterative conversion into measurement coordinates, and the measurement coordinates are used to indicate the contact point between the ball head and the surface of the object to be measured;

[0035] The measured coordinates are combined with the measured straightness changes and perpendicularity errors of each displacement axis to correct the measured object coordinates indicating the actual position of the measured object surface.

[0036] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0037] In an embodiment of the present invention, after obtaining the measurement coordinates based on the ball head center coordinate conversion, the measurement coordinates are corrected according to the measured verticality error, straightness change and other data to obtain the actual coordinates of the contact point between the indicating ball head and the surface of the object to be measured, and then the coordinates of the object to be measured are corrected based on this, effectively eliminating the inevitable errors in the ball head center coordinate conversion process, thereby truly reflecting the spatial position of the surface of the object to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 1 is a schematic diagram of the workflow of a three-dimensional correction method for ultra-precision optical profilometry disclosed in an embodiment of the present invention;

[0040] Figure 2 It is a schematic diagram of the three-dimensional structure of a measuring device disclosed in an embodiment of the present invention;

[0041] Figure 3 is another schematic diagram of the three-dimensional structure of a measuring device disclosed in an embodiment of the present invention;

[0042] Figure 4 The present invention is a schematic diagram of a measuring rod of a measuring device disclosed in an embodiment of the present invention measuring a free-form surface of a measured object. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] It should be noted that the terms "first," "second," "third," "fourth," etc. in the description and claims of the present invention are used to distinguish different objects rather than to describe a specific order. The terms "including" and "having," as well as any variations thereof, in the embodiments of the present invention, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, products, or apparatuses.

[0045] Example 1

[0046] See also Figure 1 ,like Figure 1 As shown, a three-dimensional correction method for ultra-precision optical profilometry disclosed in an embodiment of the present invention includes the following steps:

[0047] 101. Record the coordinates P of the center of the ball head o (x, y, z).

[0048] In this embodiment, the accurate coordinates of the center of the ball head can be directly measured by detecting the ball head of the measuring rod. However, when measuring the free-form surface of the object to be measured, the contact point between the ball head and the surface of the object to be measured is not constant, but changes according to the curvature of the free-form surface, and the coordinates of the contact point are not directly measured. Therefore, when measuring the free-form surface, the coordinate data measured by the ball head inevitably have a six-degree-of-freedom measurement error.

[0049] Therefore, in this embodiment, the coordinates of the center of the ball head are first recorded, and relatively accurate measurement coordinates are calculated based on them. Then, correction and calibration are performed in combination with the displacement parameters measured by the external device to obtain the true coordinate data of the surface of the object being measured.

[0050] As an optional implementation, the displacement measurement is performed for the dual-frequency laser and nanocapacitive sensor, and the coordinates of the center of the ball head P are converted. o (x, y, z).

[0051] Specifically, a fixed laser generator emits a laser beam, which illuminates the laser interferometer after reflection to measure the displacement value. At the same time, the nanocapacitive sensor synchronously measures the displacement value and indirectly measures the coordinates of the center of the ball head.

[0052] As an optional implementation, the ball head center coordinate P o (x, y, z) is measured based on several laser interferometers and nanocapacitive sensors. Let the radius of the ball head be r, let f(x, y) be the surface equation of the free surface of the object being measured, and let f′ x (x, y) is the first-order partial derivative of f(x, y) with respect to the x-axis, let f′ y (x, y) is the first-order partial derivative of f(x, y) facing the y-axis, then P o (x, y, z) is expressed as the following coordinate system:

[0053]

[0054] Here, partial derivative calculations are also performed based on the ball head radius and the surface equation of the free-form surface of the object being measured obtained during the measurement process. Based on this, in addition to recording the coordinates of the center of the ball head, the surface data corresponding to each point position is also recorded synchronously for each coordinate of the center of the ball head for subsequent coordinate correction.

[0055] 102. Coordinates P of the center of the ball head o (x, y, z) is iteratively converted to the measured coordinates P1 (x1, y1, z1).

[0056] In this embodiment, the coordinates of the center of the ball head are converted into measurement coordinates. At this time, due to the existence of the ball head radius and the free curved surface, there must be an error value in the measurement coordinates compared with the actual coordinates of the contact point between the ball head and the object to be measured. The coordinate conversion is performed first, and then the error value is eliminated in subsequent steps.

[0057] As an optional implementation, an iteration target parameter ε is set, and the target parameter ε is used to calibrate the parameter accuracy of the iterative conversion;

[0058] Calculate the absolute difference between the coordinates of the center of the ball head and its corresponding measured coordinates;

[0059] If the absolute difference meets ||P o (x, y, z)-P1(x1, y1, z1)||<ε, then the measured coordinate P1(x1, y1, z1) is used to replace the corresponding ball head center coordinate P o (x, y, z).

[0060] Specifically, target parameters are set for the conversion process to ensure that the measurement coordinate error value obtained by the conversion is within a limited range, thereby avoiding numerical fluctuations in the subsequent optimization process.

[0061] 103. Correct the measured coordinates P1(x1, y1, z1) to obtain the measured coordinates (x ′ ,y ′ , z ′ ).

[0062] In this embodiment, in addition to directly measuring and converting the measured coordinates, the verticality error and the straightness change are also measured during the measurement process, and the error value of the measured coordinates is eliminated accordingly.

[0063] As an optional implementation, a represents the perpendicularity error between the X-axis and the Z-axis, b represents the perpendicularity error between the Y-axis and the Z-axis, c represents the perpendicularity error between the X-axis and the Y-axis, zd represents the displacement change measured by the laser interferometer, and Z1, Z2, and Z3 represent the perpendicularity error between the X-axis and the Y-axis. x , Z y Respectively represent the straightness changes measured by each nanocapacitive sensor, and the correction is:

[0064]

[0065] Specifically, the device-side values ​​such as verticality error, displacement change, straightness change, etc. of the detection process measured by external equipment are used to correct the measurement coordinates obtained by conversion, thereby avoiding error offset caused by a single measurement source, achieving mutual verification, and significantly eliminating the error values ​​that are inevitable in the conversion process.

[0066] 104. Correct measured coordinates (x ′ ,y ′ , z ′ ) obtain the coordinates of the object to be measured (x2, y2, z2).

[0067] In this embodiment, the rotation angle of the measuring rod relative to the object to be measured on each coordinate axis can be used to determine the specific contact point between the surface of the object to be measured and the ball head of the measuring rod, so as to correct the actual measured coordinates obtained by conversion to the real coordinates of the object to be measured at the contact point between the ball head and the surface of the object to be measured.

[0068] As an optional implementation, let α be the angle of rotation of the measured coordinate system around the X axis, let β be the angle of rotation of the measured coordinate system around the Y axis, let γ be the angle of rotation of the measured coordinate system around the Z axis, and let t x , t v , t z are the displacements of the measured coordinate system along the X-axis, Y-axis, and Z-axis respectively, and the correction results are:

[0069]

[0070] Here, coordinate correction is performed by adding the rotation angle of the measuring rod relative to the object to be measured on each coordinate axis, so that the corrected coordinates of the object to be measured are more consistent with the real coordinates of the contact point between the ball head and the surface of the object to be measured, eliminating the posture error of the coordinates of the object to be measured relative to the surface of the object to be measured.

[0071] In this embodiment, since the above coordinate parameters are all measured using an optical measurement solution, there are surface errors and they need to be optimized and fitted.

[0072] As an optional implementation, when correcting the measured coordinates (x ′ ,y ′ , z ′ ) After obtaining the coordinates (x2, y2, z2) of the object to be measured, it also includes:

[0073] Calculate the surface error e(α, β, γ, t x ,t y ,t z )=z2-f(x2,y2);

[0074] The least square method is used to fit the surface error e(α, β, γ, t x ,t y ,t z );

[0075] Based on the surface error e(α,β,γ,t x ,t y ,t z )Optimize the coordinates of the object to be measured (x2, y2, z2).

[0076] Here, the least squares method is used to optimize the surface shape error of the coordinates of the object to be measured, so that the coordinates of the object to be measured are more consistent with the actual coordinates of the contact points between the ball head and the surface of the object to be measured.

[0077] It can be seen that after obtaining the measurement coordinates based on the ball head center coordinate conversion, the measurement coordinates are corrected according to the measured verticality error, straightness change and other data to obtain the actual coordinates of the contact point between the indicating ball head and the surface of the object to be measured, and then the coordinates of the object to be measured are corrected, which effectively eliminates the inevitable errors in the ball head center coordinate conversion process and truly reflects the spatial position of the surface of the object to be measured.

[0078] Example 2

[0079] See also Figures 2-4 .like Figures 2-4 As shown, the measuring device may include:

[0080] A measuring platform 100 for placing the object to be measured, and an XY displacement platform 200 for moving the object to be measured below the measuring platform 100;

[0081] A measuring rod 111 is mounted on the air-bearing Z-axis 110 and is used to contact the surface of the object being measured. The end of the measuring rod 111 is a ball head;

[0082] A first nanocapacitive sensor 210 for measuring the linearity change of the XY displacement platform 200, a second nanocapacitive sensor 220 for measuring the linearity change of the air-bearing Z-axis 110 in the vertical direction, and a third nanocapacitive sensor 230 for measuring the linearity change of the air-bearing Z-axis 110 in the horizontal direction;

[0083] A fixedly set laser generator 300 that outputs a laser beam; an X-axis mirror 310, a Y-axis mirror 320, a Z-axis mirror 330 and a measuring rod top mirror 340 that reflect the laser beam; an X-axis laser interferometer 240 that receives the laser beam reflected by the X-axis mirror 310; a Y-axis laser interferometer 250 that receives the laser beam reflected by the Y-axis mirror 320; a Z-axis laser interferometer 260 that receives the laser beam reflected by the Z-axis mirror 330; and a measuring rod top laser interferometer 270 that receives the laser beam reflected by the measuring rod top mirror.

[0084] In this embodiment, the object to be measured is placed above the measurement platform 100. The air-bearing Z-axis 110 is moved to make the ball head at the end of the measuring rod 111 contact the surface of the object to be measured, and then the XY displacement platform 200 is moved. At this time, the ball head moves along the surface of the object to be measured, resulting in displacement changes in the Z-axis direction. The displacement changes are fed back in real time to adjust the movement process of the air-bearing Z-axis 110, ensuring stable pressure during the measurement process and avoiding excessive pressure on the object to be measured.

[0085] As an optional embodiment, the first nanocapacitance sensor 210, the second nanocapacitance sensor 220 and the third nanocapacitance sensor 230 are used to measure the straightness changes of each displacement axis, and the X-axis laser interferometer 240, the Y-axis laser interferometer 250, the Z-axis laser interferometer 260 and the laser interferometer 270 on the top of the measuring rod are respectively used to measure the frequency change value of the laser beam and convert it into a displacement value, based on which the coordinates of the center of the ball head of the measuring rod are obtained.

[0086] In this embodiment, the coordinates of the center of the ball head are used for iterative conversion into measurement coordinates, and the measurement coordinates are used to indicate the contact point between the ball head and the surface of the object to be measured;

[0087] The measured coordinates are combined with the measured straightness changes and perpendicularity errors of each displacement axis to correct the coordinates of the object to be measured that indicate the actual position of the surface of the object to be measured.

[0088] Therefore, the unavoidable six-degree-of-freedom measurement errors when measuring free-form surfaces, the calculation errors generated in the coordinate conversion process, the equipment errors accumulated during the operation of the measuring equipment, and the surface errors existing in optical measurement are eliminated through multi-source detection data and optimization algorithms, so that the coordinates of the object finally obtained can reflect the true coordinate values ​​of the contact points between the ball head and the surface of the object as closely as possible.

[0089] The above is a detailed introduction to the three-dimensional correction method and measuring device for ultra-precision optical contour measurement disclosed in an embodiment of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A three-dimensional correction method for ultra-precision optical profile measurement, characterized in that: The method comprises: Record the center coordinates P of the ball head o (x, y, z); The center coordinate P of the ball head o (x, y, z) is iteratively converted to the measured coordinates P1 (x1, y1, z1); Correct the measured coordinates P1 (x1, y1, z1) to obtain the measured coordinates (x ′ ,y ′ , z ′ ); Correct the measured coordinates (x ′ ,y ′ , z ′ ) obtain the coordinates of the object to be measured (x2, y2, z2).

2. The three-dimensional correction method for ultra-precision optical profilometry according to claim 1, characterized in that: The method comprises: The center coordinate P of the ball head o (x, y, z) is measured based on several laser interferometers and nanocapacitive sensors. Let the radius of the ball head be r, let f(x, y) be the surface equation of the free surface of the object being measured, and let f x ′ (x, y) is the first-order partial derivative of f(x, y) with respect to the x-axis, let f′ y (x, y) is the first-order partial derivative of f(x, y) facing the y-axis, then P o (x, y, z) is expressed as the following coordinate system:

3. The three-dimensional correction method for ultra-precision optical profilometry according to claim 2, characterized in that: The recorded ball head center coordinate P o (x, y, z), including: The displacement measurement is performed using dual-frequency laser and nanocapacitive sensors to convert the center coordinates of the ball head P o (x, y, z).

4. The three-dimensional correction method for ultra-precision optical profilometry according to claim 2, characterized in that: The center coordinate P of the ball head o (x, y, z) is iteratively converted to the measured coordinates P1 (x1, y1, z1), including: Setting an iterative target parameter ε, wherein the target parameter ε is used to calibrate the parameter accuracy of the iterative conversion; Calculating the absolute difference between the center coordinates of the ball head and the corresponding measurement coordinates; If the absolute difference meets ||P o (x, y, z)-P1(x1, y1, z1)||<ε, then the measured coordinate P1(x1, y1, z1) is used to replace the corresponding ball head center coordinate P o (x, y, z).

5. The three-dimensional correction method for ultra-precision optical profilometry according to claim 1, characterized in that: The measured coordinates P1 (x1, y1, z1) are corrected to obtain the measured coordinates (x ′ ,y ′ , z ′ ),include: a represents the perpendicularity error between the X-axis and the Z-axis, b represents the perpendicularity error between the Y-axis and the Z-axis, c represents the perpendicularity error between the X-axis and the Y-axis, zd represents the displacement change measured by the laser interferometer, and Z1, Z2, and Z3 represent the perpendicularity error between the X-axis and the Y-axis. x , Z y Respectively represent the straightness changes measured by each nanocapacitive sensor, and the correction is:

6. The three-dimensional correction method for ultra-precision optical profilometry according to claim 5, characterized in that: The correction of the measured coordinates (x ′ ,y ′ , z ′ ) obtain the coordinates of the object to be measured (x2, y2, z2), including: Let α be the angle of rotation of the measured coordinate system around the X axis, let β be the angle of rotation of the measured coordinate system around the Y axis, let γ be the angle of rotation of the measured coordinate system around the Z axis, let t x , t y , t z are the displacements of the measured coordinate system along the X-axis, Y-axis, and Z-axis respectively, and the correction results are:

7. The three-dimensional correction method for ultra-precision optical profilometry according to claim 6, characterized in that: In the correction of the measured coordinates (x ′ ,y ′ , z ′ ) After obtaining the coordinates (x2, y2, z2) of the object to be measured, the method further includes: Calculate the surface error e(α, β, γ, t x ,t y ,t z )=z2-f(x2,y2); The least square method is used to fit the surface error e(α, β, γ, t x ,t y ,t z ); Based on the surface error e(α, β, γ, t x ,t y ,t z )Optimize the coordinates (x2, y2, z2) of the object to be measured.

8. A measuring device, characterized in that: include: A measuring platform for placing the object to be measured, and an XY displacement platform for moving the object to be measured below the measuring platform; A measuring rod mounted on the air-bearing Z axis and used to contact the surface of the object being measured above the object being measured, with the end of the measuring rod being a ball head; A first nanocapacitive sensor for measuring the linearity change of the XY displacement platform, a second nanocapacitive sensor for measuring the linearity change of the air-bearing Z-axis along the Y-axis, and a third nanocapacitive sensor for measuring the linearity change of the air-bearing Z-axis along the X-axis; A fixedly set laser generator that outputs a laser beam, an X-axis reflector, a Y-axis reflector, a Z-axis reflector and a measuring rod top reflector that reflect the laser beam, an X-axis laser interferometer that receives the laser beam reflected by the X-axis reflector, a Y-axis laser interferometer that receives the laser beam reflected by the Y-axis reflector, a Z-axis laser interferometer that receives the laser beam reflected by the Z-axis reflector, and a measuring rod top laser interferometer that receives the laser beam reflected by the measuring rod top reflector.

9. A measuring device according to claim 8, characterized in that: include: The first nanocapacitance sensor, the second nanocapacitance sensor, and the third nanocapacitance sensor are used to measure the straightness changes of each displacement axis. The X-axis laser interferometer, the Y-axis laser interferometer, the Z-axis laser interferometer, and the laser interferometer on the top of the measuring rod are respectively used to measure the frequency change value of the laser beam and convert it into a displacement value, based on which the coordinates of the center of the ball head of the measuring rod are obtained.

10. A measuring device according to claim 9, characterized in that: include: The center coordinates of the ball head are used for iterative conversion into measurement coordinates, and the measurement coordinates are used to indicate the contact point between the ball head and the surface of the object to be measured; The measured coordinates are combined with the measured straightness changes and perpendicularity errors of each displacement axis to correct the measured object coordinates indicating the actual position of the measured object surface.

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