Rotational accuracy measurement system and method for hydrostatic bearing spindle

Abstract

The present invention discloses a system and method for measuring the rotation accuracy of a hydrostatic bearing spindle. The system includes: a standard ball, which is fixed on a hydrostatic bearing spindle to achieve coaxial motion with the hydrostatic bearing spindle; an optical measurement system; and a data processing system. When the hydrostatic bearing spindle rotates, the optical measurement system simultaneously collects the displacement of the outer contour of the standard ball, and the collected displacement data is transmitted to the data processing system for error separation calculation. The present invention measures the rotation error of the hydrostatic bearing spindle by combining laser heterodyne interference with a confocal microscope system, and achieves error separation by a three-point method. Not only does it collect a higher-precision rotation displacement through a highly sensitive optical measurement system, but it also improves the rotation measurement accuracy of the hydrostatic bearing spindle.

Description

Technical Field

[0001] The invention relates to a measuring system and a measuring method, and in particular to a rotation accuracy measuring system and a measuring method for a hydrostatic bearing main shaft. Background Art

[0002] With the development of aerospace, industrial robots, automobiles, aircraft and other industries, the precision requirements for their parts are also getting higher and higher. CNC machine tools and machining centers are precision equipment for manufacturing processing. The precision of machine tools determines the precision quality of parts in other industries. Hydrostatic bearings are widely used in various types of machine tools, affecting the machining accuracy of machine tools. Therefore, the precision level of hydrostatic bearings is an important factor affecting the development of the manufacturing industry. The hydrostatic bearing spindle component is the core component among the main components. The spindle rotation error generated by the hydrostatic bearing spindle during rotation has an important influence on the accuracy of the machine tool, which directly affects the quality of the processed parts. In order to improve the rotation accuracy of the hydrostatic bearing spindle, it is first necessary to measure the hydrostatic bearing spindle rotation error, analyze the measured rotation error, determine the source of the error, and thus suppress the generation of the error.

[0003] The measurement accuracy always affects the accuracy of the error separation results. For non-contact measurement systems, the laser heterodyne interferometer has nanometer-level measurement accuracy, but due to the limitation of its measurement optical path, it cannot be used with a standard ball for rotation accuracy measurement. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a rotation accuracy measurement system and method for a hydrostatic bearing spindle.

[0005] The present invention solves the above technical problems through the following technical solutions: a rotation accuracy measurement system for a hydrostatic bearing spindle, characterized in that it comprises:

[0006] Standard ball: The standard ball is fixed on a hydrostatic bearing main shaft. The center of the standard ball is placed on the central axis of the hydrostatic bearing main shaft to achieve coaxial movement with the hydrostatic bearing main shaft.

[0007] Optical measurement system, including:

[0008] A laser heterodyne interference module comprises a dual-frequency laser transmitter, a first beam splitter prism, and a first photodetector, wherein the dual-frequency laser transmitter is located on the left side of the first beam splitter prism, and the first photodetector is located above the first beam splitter prism; the dual-frequency laser transmitter transmits a light beam containing a first frequency polarized light and a second frequency polarized light perpendicular to each other, and the first beam splitter prism splits the first light beam containing the first frequency polarized light and the second frequency polarized light into a second light beam and a third light beam, wherein the second light beam is a reference light beam containing a difference between the first frequency polarized light and the second frequency polarized light, and is reflected by the first beam splitter prism to the first photodetector to generate a reference signal, and the reference signal is used to calculate a phase difference, and the third light beam is a light beam containing the first frequency polarized light and the second frequency polarized light and is input into a subsequent optical path and optical device;

[0009] A second beam splitter prism, a third beam splitter prism, a first plane reflector, a second plane reflector, and a third plane reflector;

[0010] The first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, the third laser heterodyne interference displacement measurement module, the second beam splitter prism and the third beam splitter prism are sequentially located between the laser heterodyne interference module and the first laser heterodyne interference displacement measurement module, the first laser heterodyne interference displacement measurement module is located on the right side of the laser heterodyne interference module, the second laser heterodyne interference displacement measurement module is located above the laser heterodyne interference module, the third laser heterodyne interference displacement measurement module is located above the side of the first laser heterodyne interference displacement measurement module, the structure of the first laser heterodyne interference displacement measurement module, the structure of the second laser heterodyne interference displacement measurement module, the third laser heterodyne interference displacement measurement module The structures of the displacement measurement modules are the same. The first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, and the third laser heterodyne interference displacement measurement module all include a polarization beam splitter prism, a fourth beam splitter prism, a second photodetector, a third photodetector, a fourth plane reflector, a first quarter wave plate, a second quarter wave plate, a pinhole, a first lens, a second lens, and an analyzer. The third light beam output from the first beam splitter prism passes through the second beam splitter prism and the third beam splitter prism in sequence and is divided into three light beams containing the first frequency polarized light and the second frequency polarized light, specifically the fourth light beam, the fifth light beam, and the sixth light beam. The fourth light beam is input into the second laser heterodyne interference displacement measurement module, and the fifth light beam is input into the The first beam is input into the first laser heterodyne interference displacement measurement module, the sixth beam is reflected by the first plane reflector, the second plane reflector, and the third plane reflector and then input into the third laser heterodyne interference displacement measurement module; the polarization beam splitter prism divides the fourth beam, the fifth beam, and the sixth beam into two paths again, specifically the seventh beam and the eighth beam, the seventh beam is a beam containing only the first frequency polarized light after being reflected by the beam splitting film of the polarization beam splitter prism, the seventh beam is divided into the ninth beam and the tenth beam, both of which contain the first frequency polarized light, by the fourth beam splitter prism, the ninth beam is converged onto the surface of the constantly moving object to be measured by the first quarter wave plate and the first lens and is reflected by the original path, and then passes through the first lens, the first quarter ... The light beam passes through a quarter wave plate, a polarization beam splitter, and an analyzer to reach the second photodetector; the tenth light beam passes through a second lens and a pinhole to reach the third photodetector as a confocal light intensity signal, and this signal is used to verify whether the sensor is installed correctly; the eighth light beam passes through the beam splitter film of the polarization beam splitter prism to become a light beam containing only second frequency polarized light, the eighth light beam passes through the second quarter wave plate, and is reflected by the fourth plane reflector and then returns to the polarization beam splitter prism along the original path, and after being reflected by the beam splitter film of the polarization beam splitter prism, it passes through the analyzer to reach the second photodetector, and interferes with the first frequency polarized light in the seventh light beam to generate a measurement signal; when the object to be measured moves, the optical path difference is obtained by subdividing the phase value of the measurement signal;

[0011] Data processing system, when the main shaft of the hydrostatic bearing rotates, the optical measurement system simultaneously collects the displacement of the outer contour of the standard ball, and the collected displacement data is transmitted to the data processing system for error separation calculation.

[0012] Preferably, the first laser heterodyne interferometer displacement measurement module, the second laser heterodyne interferometer displacement measurement module, and the third laser heterodyne interferometer displacement measurement module are installed around the same cross section of the standard sphere.

[0013] Preferably, the first beam splitter prism, the second beam splitter prism, the third beam splitter prism and the fourth beam splitter prism are all semi-transmissive and semi-reflective lenses.

[0014] Preferably, the polarization beam splitter prism is a semi-transparent and semi-reflective lens coated with a polarization film.

[0015] Preferably, the first lens and the second lens are both converging lenses.

[0016] Preferably, the hydrostatic bearing spindle is provided with a rotary encoder.

[0017] The present invention also provides a method for measuring the rotation accuracy of a hydrostatic bearing spindle, which is characterized in that it comprises the following steps:

[0018] Step 1: The laser heterodyne interference module collects interference images. At a circumferential position of a certain section of the main shaft of the hydrostatic bearing, a first laser heterodyne interference displacement measurement module, a second laser heterodyne interference displacement measurement module, and a third laser heterodyne interference displacement measurement module are installed at different angle intervals. When the dual-frequency laser interferes, three test signals are formed;

[0019] Step 2: The data processing system calculates the displacement analog signal, records the phase shift changes of the three test signals according to the reference signal, and calculates the analog signal value corresponding to the displacement;

[0020] Step 3: Discretize to obtain the displacement digital signal, perform Nyquist sampling on the three test signals, and obtain three output signals;

[0021] Step 4: Noise removal and filtering. The test signal is an analog signal. The test signal contains valid signals and high-frequency interference signals. Therefore, for the sampled data, the high-order components in the signal must be removed.

[0022] Step 5: Extract synchronous motion errors and asynchronous motion errors, separate the errors according to the three-point method, and use the measured data to solve the model parameters; discretize the mathematical model, and perform Fourier transform and inverse Fourier transform to obtain synchronous components and asynchronous components, where the average measurement is the average profile calculated based on multiple rotations of the data, which is mathematically equivalent to the integer components of the data in the Fourier domain; the remaining data are asynchronous components and correspond to non-integer components in the Fourier domain.

[0023] Preferably, in step three, the radial rotation error of the main shaft of the hydrostatic bearing is measured by using a three-point error separation method, and the DC component, the first-order harmonic component and the higher-order harmonic component are removed from the three output signals.

[0024] The positive progressive effect of the present invention is that the present invention measures the rotation error of the main shaft of the hydrostatic bearing by combining laser heterodyne interference with a confocal microscope system, and realizes error separation by a three-point method. Not only a higher-precision rotation displacement is collected by a highly sensitive optical measurement system, but also the three-point method is used to perform FFT error separation on the collected three-way signals, thereby improving the rotation measurement accuracy of the main shaft of the hydrostatic bearing, which is of great significance to improving the manufacturing of precision parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a partial structural schematic diagram of the rotation accuracy measurement system of the hydrostatic bearing spindle of the present invention.

[0026] Figure 2 It is a structural schematic diagram of the laser heterodyne interference module in the present invention.

[0027] Figure 3 It is a schematic structural diagram of a first laser heterodyne interference displacement measurement module, a second laser heterodyne interference displacement measurement module, and a third laser heterodyne interference displacement measurement module in the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0030] like Figures 1 to 3 As shown, the rotation accuracy measurement system of the hydrostatic bearing spindle of the present invention comprises:

[0031] Standard ball S1, the standard ball is fixed on a hydrostatic bearing spindle, and the center of the standard ball is placed on the central axis of the hydrostatic bearing spindle to achieve coaxial movement with the hydrostatic bearing spindle;

[0032] Optical measurement system, including:

[0033] The laser heterodyne interference module M0 includes a dual-frequency laser transmitter L1, a first beam splitter prism BS1, and a first photodetector D1. The dual-frequency laser transmitter L1 is located on the left side of the first beam splitter prism BS1, and the first photodetector D1 is located above the first beam splitter prism BS1. The dual-frequency laser transmitter L1 emits a light beam containing a first frequency ω1 polarized light and a second frequency ω2 polarized light perpendicular to each other. The first beam splitter prism BS1 splits the first light beam containing the first frequency polarized light and the second frequency polarized light into a second light beam and a third light beam (i.e., into two light beams), wherein the second light beam is a light beam containing the first frequency polarized light. The reference beam having a difference with the second frequency polarized light is reflected by the first beam splitter prism to the first photodetector D1 to generate a reference signal, and the reference signal is used to calculate the phase difference. The third beam is a beam containing the first frequency polarized light and the second frequency polarized light and is input into the subsequent optical path and optical devices (including the second beam splitter prism BS2, the third beam splitter prism BS3, the first plane reflector F1, the second plane reflector F2, the third plane reflector F3, the first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3);

[0034] A second beam splitter prism BS2, a third beam splitter prism BS3, a first plane reflector F1, a second plane reflector F2, and a third plane reflector F3;

[0035] The first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, the third laser heterodyne interference displacement measurement module M3, the second beam splitter prism BS2, and the third beam splitter prism BS3 are sequentially located between the laser heterodyne interference module M0 and the first laser heterodyne interference displacement measurement module M1, the first laser heterodyne interference displacement measurement module M1 is located on the right side of the laser heterodyne interference module M0, the second laser heterodyne interference displacement measurement module M2 is located above the laser heterodyne interference module M0, the third laser heterodyne interference displacement measurement module M3 is located above the side of the first laser heterodyne interference displacement measurement module M1, and the first laser heterodyne interference displacement measurement module The structures of the first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3 are the same. The first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3 all include a polarization beam splitter prism PBS, a fourth beam splitter prism BS4, a second photodetector D2, a third photodetector D3, a fourth plane reflector F4, a first quarter wave plate QWP1, a second quarter wave plate QWP2, a pinhole PH, a first lens Len1, a second lens Len2, and a polarizer PZ. The third light output from the first beam splitter prism BS1 The beam passes through the second beam splitter prism BS2 and the third beam splitter prism BS3 in sequence and is divided into three beams containing the first frequency polarized light and the second frequency polarized light, specifically the fourth beam, the fifth beam, and the sixth beam. The fourth beam is input into the second laser heterodyne interference displacement measurement module M2, the fifth beam is input into the first laser heterodyne interference displacement measurement module M1, and the sixth beam is reflected by the first plane reflector F1, the second plane reflector F2, and the third plane reflector F3 and then input into the third laser heterodyne interference displacement measurement module M3; the polarization beam splitter prism PBS divides the fourth beam, the fifth beam, and the sixth beam into two again, specifically the seventh beam and the eighth beam. The seventh beam is polarized After being reflected by the beam splitter film of the beam splitter prism PBS, the seventh beam is divided into a ninth beam and a tenth beam, both of which have the first frequency polarized light, by the fourth beam splitter prism BS4. The ninth beam passes through the first quarter wave plate QWP1 and the first lens Len1 and converges onto the surface of the moving object to be measured and is reflected by the original path. Then, it passes through the first lens Len1, the first quarter wave plate QWP1, the polarization beam splitter prism PBS, and the analyzer PZ in sequence to reach the second photodetector D2. The tenth beam passes through the second lens Len2 and the pinhole PH to reach the third photodetector D3 as a confocal light intensity signal, and this signal is used to verify whether the sensor is installed correctly.The eighth light beam is transmitted through the beam splitter film of the polarization beam splitter prism and becomes a light beam containing only the second frequency polarized light. The eighth light beam passes through the second quarter wave plate QWP2, and is reflected by the fourth plane reflector F4 and then returns to the polarization beam splitter prism PBS along the original path. After being reflected by the beam splitter film of the polarization beam splitter prism PBS, the eighth light beam passes through the analyzer PZ and reaches the second photodetector D2, and interferes with the first frequency polarized light in the seventh light beam to generate a measurement signal. When the object to be measured moves, the optical path difference is obtained by subdividing the phase value of the measurement signal.

[0036] Data processing system, when the main shaft of the hydrostatic bearing rotates, the optical measurement system simultaneously collects the displacement of the outer contour of the standard ball, and the collected displacement data is transmitted to the data processing system for error separation calculation.

[0037] The first laser heterodyne interferometer displacement measurement module M1, the second laser heterodyne interferometer displacement measurement module M2, and the third laser heterodyne interferometer displacement measurement module M3 are installed around the same cross section of the standard sphere S1 to facilitate measurement and improve measurement accuracy.

[0038] The first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3 all use laser heterodyne interferometers, which have nanometer-level measurement accuracy. However, due to the limitation of their measurement optical path, they cannot be used in conjunction with standard balls for rotation accuracy measurement. The present invention combines the advantages of laser heterodyne interference nanometer-level displacement measurement accuracy and the positioning accuracy of the confocal optical measurement system, uses laser heterodyne interference technology and standard balls to reflect the measurement beam, realizes nanometer-level displacement measurement of standard balls, and uses phase compensation technology in the system to reduce the influence of the nonlinear error of laser heterodyne interference on the measurement accuracy, thereby improving the measurement accuracy. The present invention collects the outer contour of the spindle, and separates the pure rotation error and roundness error from the collected displacement data through the FFT error separation algorithm of the data processing system, thereby realizing high-dynamic nanometer-level rotation accuracy measurement and characterization. The present invention can improve the measurement accuracy of the rotation error of the hydrostatic bearing spindle, and has broad application prospects in the field of ultra-precision fly cutting.

[0039] The first beam splitter prism BS1, the second beam splitter prism BS2, the third beam splitter prism BS3, and the fourth beam splitter prism BS4 are all semi-transparent and semi-reflective lenses, which can be used for light path turning and splitting. The polarization beam splitter prism PBS is a semi-transparent and semi-reflective lens coated with a polarization film, which can perform light path turning and splitting for light of a specific polarization direction. The first quarter wave plate QWP1 and the second quarter wave plate QWP2 can rotate the polarization direction of vertically incident linear polarized light by ninety degrees without changing other light source characteristics. The first lens Len1 can converge the detection light onto the surface of the standard sphere to be measured, thereby increasing the measurement resolution and measurement accuracy. The polarizer PZ uses a quarter wave plate, which can only pass linear polarized light of a specific polarization direction to achieve the light screening effect. The first lens Len1 and the second lens Len2 are both converging lenses, which are used to converge parallel light to achieve high-resolution imaging. The pinhole PH can achieve the imaging selection effect, filter the measured signal located in the defocus, and only pass the non-defocused signal to perform high-resolution imaging and confocal imaging.

[0040] This embodiment establishes a mathematical model for separating the spindle rotation errors using the three-probe method. During measurement, the first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3 are fixed on a bracket. The standard ball rotates along with the hydrostatic bearing spindle, and the data contained in the three sensors are obtained as shown in the following equations (1), (2), and (3):

[0041] m A (θ)=r(θ)+x(θ)……(1)

[0042] m B (θ)=r(θ+α)+x(θ)cosα+y(θ)sinα……(2)

[0043] m C (θ)=r(θ+β)+x(θ)cosβ+y(θ)sinβ……(3)

[0044] Among them, A, B, and C are three displacement sensors with different detection positions, which are respectively equivalent to the first laser heterodyne interference displacement measurement module M1, the second laser heterodyne interference displacement measurement module M2, and the third laser heterodyne interference displacement measurement module M3;

[0045] m A (θ), m B (θ), m C (θ) are the output signals of the three sensors A, B, and C, respectively, representing the periodic spindle profile signal;

[0046] θ: angular amplitude of the main axis rotation;

[0047] α, β: the angles between sensors B, C and A respectively;

[0048] r(θ): roundness error of the tested piece at θ;

[0049] x(θ), y(θ): the components of the rotation error of the spindle at θ in the x-axis and y-axis directions respectively;

[0050] Introducing sensor calibration factor C A , C B , C C , we get the following formula (4)

[0051] C(θ)=C A m A (θ)+C B m B (θ)+C C m C (θ)……(4)

[0052] Eliminate x(θ) and y(θ) to obtain the basic equation for three-point error separation, as shown in equation (5):

[0053] C A m A (θ)+C B m B (θ)+C C m C (θ) = C A r(θ)+C B r(θ+α)+C C r(θ+β)……(5)

[0054] Let C A =1, and a set of characteristic solutions is obtained as follows (6):

[0055] C A =1, C B = sinβ / sin(α-β), C C = sinα / sin(α-β)……(6)

[0056] Let n be the number of points at which the workpiece rotates one circle and k be the number of points at which the workpiece rotates one circle. A , k B , k C The angles at which the three sensors read the data points, Discretize equation (4) to get equation (7):

[0057] C(k A )=C A m A (k A )+C B m B(k B )+C C m C (θk C )……(7)

[0058] where θ xn , α xn , β xn They are the radians of sensors A, B, and C at the xth measuring point (a total of n measuring points in one circle).

[0059] Because m A (k A ) and C(k A ) are both periodic sequences, so discrete Fourier transform is performed on both sides, and C(k A ) is C(N), which is the following equation (8):

[0060]

[0061] The discrete Fourier transform of both ends of equation (6) is as follows:

[0062]

[0063] Taking the inverse Fourier transform of equation (8), the shape contour error m can be obtained: A (k A ), as shown in formula (10):

[0064]

[0065] On an ultra-precision lathe, when the spindle is running, its repeated rotation is not a periodic motion, but the spindle has a very high precision when rotating, and the retention is very good for almost every rotation. The calculated synchronization error can be regarded as the rotation motion error of the spindle, as shown in the following equations (11) and (12):

[0066]

[0067] A syn (n) = m A (k A )-m yn (n)……(12)

[0068] S yn (n) and A syn (n) represent the synchronous component and asynchronous component of the nth measurement point, respectively, m yn (n) represents the discretized syn value.

[0069] The hydrostatic bearing spindle is equipped with a rotary encoder. The spindle motor and drive can have a significant impact on the synchronous component of the measured data. Therefore, the test hydrostatic bearing spindle was checked without a motor, requiring it to be rotated manually. The rotary encoder is used to trigger data collection at evenly spaced angular increments in the event of spindle speed fluctuations. The hydrostatic bearing spindle is mounted on a precision turntable. The counter-chuck between the workpiece and the hydrostatic bearing spindle has a spherical workpiece guide to facilitate accurate indexing of the workpiece relative to the spindle. The rotary table, hydrostatic bearing spindle, counter-chuck and workpiece are assembled on the same axis to within 400nm. This precise alignment eliminates the need to adjust the displacement sensor standoff distance during turntable indexing. The test hardware is located on a three-axis measurement machine (Moore Universal Measuring Machine) to facilitate alignment and centering of the displacement sensor measurement machine. The laser heterodyne interferometric displacement measurement module is aligned to a standard sphere. The finite radius of the standard sphere causes a slight nonlinearity in the output of the interferometric displacement sensor. In order to obtain the nanometer-level repeatability results shown in the subsequent results, the sensor standoff distance must be kept constant during all measurements of a given error separation step. Therefore adjust the nominal sensor spacing manually if necessary.

[0070] The data processing system includes a low-pass analog filter with a cutoff frequency of 100Hz (equivalent to 100 cycles per revolution at 60rpm) to prevent aliasing and remove higher spectral content from the data. In addition, quasi-static frequency components caused by thermal drift and fluctuations in air bearing supply pressure are removed by high-pass digital filtering at 0.1Hz. These steps are performed according to high-precision rotating axis metrology standards.

[0071] The experimental results are based on radial measurements taken at the equator of a standard sphere at a fixed height from the geometric center of the test spindle stator. Thirty-two revolutions of data are measured to average out the asynchronous effects of noise, vibration and other environmental influences when calculating synchronous error motions. All calculations are performed with a fixed sensitive direction, for fixed tool applications (such as lathes) rather than rotating sensitive direction applications (such as rotary milling cutters).

[0072] The method for measuring the rotation accuracy of a hydrostatic bearing spindle of the present invention comprises the following steps:

[0073] Step 1: The laser heterodyne interference module collects interference images. At the circumferential position of a certain section of the main shaft of the hydrostatic bearing, the first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, and the third laser heterodyne interference displacement measurement module are installed at different angle intervals. When the dual-frequency laser interferes, three test signals M are formed. A 、M B 、M C ;

[0074] Step 2: The data processing system calculates the displacement analog signal and records three test signals M according to the reference signal M0. A 、M B 、M C The phase shift change can be used to calculate the analog signal value corresponding to the displacement;

[0075] Step 3: Discretize the displacement digital signal and transform the three test signals M A 、M B 、M C Perform Nyquist sampling to obtain three output signals m A (θ), m B (θ), m C (θ);

[0076] Step 4: Noise removal and filtering. The test signal is an analog signal. The test signal contains effective signals and high-frequency interference signals. The roundness error of the workpiece is mostly a low-frequency signal. When the harmonic order of the roundness error of the measured part is greater than 22 to 45, it is usually attributed to the surface quality of the part, such as waviness, surface roughness, etc. Therefore, for the sampled data, the high-order components in the signal must be removed. When measuring the radial rotation error of the spindle using the three-point method error separation, the influence of the first-order harmonic component can be ignored. Therefore, the first-order harmonic component in the signal can be directly removed before the error separation. Therefore, the three output signals m A (θ), m B (θ), m C (θ) Remove the DC component (constant value), first-order harmonic component and higher-order harmonic component;

[0077] Step 5: Extract synchronous motion error and asynchronous motion error, separate errors according to the three-point method, and use the measured data to solve the model parameters; discretize the mathematical model, and perform Fourier transform and inverse Fourier transform to obtain synchronous components and asynchronous components, where the average (synchronous) measurement is the average profile calculated based on multiple rotations of the data, which is mathematically equivalent to the integer components of the data in the Fourier domain; the remaining data are asynchronous components and correspond to non-integer components in the Fourier domain. The rotational error motion of the hydrostatic bearing spindle is actually not periodic. For ultra-precision lathes, the rotational accuracy of the hydrostatic bearing spindle is very high, and the rotational error motion of each rotation is basically consistent. The synchronous error S calculated from this yn (n) can be regarded as the rotational motion error of the spindle, using both redundant measurements to obtain the average value and closed loop to reduce measurement uncertainty.

[0078] The present invention measures the rotation error of the main shaft of the hydrostatic bearing by combining laser heterodyne interference with a confocal microscope system, and realizes error separation by a three-point method. Not only a higher-precision rotation displacement is collected by a highly sensitive optical measurement system, but also the three-point method is used to perform FFT error separation on the collected three-way signals, thereby improving the rotation measurement accuracy of the main shaft of the hydrostatic bearing, which is of great significance to improving the manufacturing of precision parts.

[0079] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0080] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A rotation accuracy measurement system for a hydrostatic bearing spindle, characterized in that: It includes: Standard ball: The standard ball is fixed on a hydrostatic bearing main shaft. The center of the standard ball is placed on the central axis of the hydrostatic bearing main shaft to achieve coaxial movement with the hydrostatic bearing main shaft. Optical measurement system, including: A laser heterodyne interference module comprises a dual-frequency laser transmitter, a first beam splitter prism, and a first photodetector, wherein the dual-frequency laser transmitter is located on the left side of the first beam splitter prism, and the first photodetector is located above the first beam splitter prism; the dual-frequency laser transmitter transmits a light beam containing a first frequency polarized light and a second frequency polarized light perpendicular to each other, and the first beam splitter prism splits the first light beam containing the first frequency polarized light and the second frequency polarized light into a second light beam and a third light beam, wherein the second light beam is a reference light beam containing a difference between the first frequency polarized light and the second frequency polarized light, and is reflected by the first beam splitter prism to the first photodetector to generate a reference signal, and the reference signal is used to calculate a phase difference, and the third light beam is a light beam containing the first frequency polarized light and the second frequency polarized light and is input into a subsequent optical path and optical device; A second beam splitter prism, a third beam splitter prism, a first plane reflector, a second plane reflector, and a third plane reflector; The first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, the third laser heterodyne interference displacement measurement module, the second beam splitter prism and the third beam splitter prism are sequentially located between the laser heterodyne interference module and the first laser heterodyne interference displacement measurement module, the first laser heterodyne interference displacement measurement module is located on the right side of the laser heterodyne interference module, the second laser heterodyne interference displacement measurement module is located above the laser heterodyne interference module, the third laser heterodyne interference displacement measurement module is located above the side of the first laser heterodyne interference displacement measurement module, the structure of the first laser heterodyne interference displacement measurement module, the structure of the second laser heterodyne interference displacement measurement module, the third laser heterodyne interference displacement measurement module The structures of the displacement measurement modules are the same. The first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, and the third laser heterodyne interference displacement measurement module all include a polarization beam splitter prism, a fourth beam splitter prism, a second photodetector, a third photodetector, a fourth plane reflector, a first quarter wave plate, a second quarter wave plate, a pinhole, a first lens, a second lens, and an analyzer. The third light beam output from the first beam splitter prism passes through the second beam splitter prism and the third beam splitter prism in sequence and is divided into three light beams containing the first frequency polarized light and the second frequency polarized light, specifically the fourth light beam, the fifth light beam, and the sixth light beam. The fourth light beam is input into the second laser heterodyne interference displacement measurement module, and the fifth light beam is input into the The first beam is input into the first laser heterodyne interference displacement measurement module, the sixth beam is reflected by the first plane reflector, the second plane reflector, and the third plane reflector and then input into the third laser heterodyne interference displacement measurement module; the polarization beam splitter prism divides the fourth beam, the fifth beam, and the sixth beam into two paths again, specifically the seventh beam and the eighth beam, the seventh beam is a beam containing only the first frequency polarized light after being reflected by the beam splitting film of the polarization beam splitter prism, the seventh beam is divided into the ninth beam and the tenth beam, both of which contain the first frequency polarized light, by the fourth beam splitter prism, the ninth beam is converged onto the surface of the constantly moving object to be measured by the first quarter wave plate and the first lens and is reflected by the original path, and then passes through the first lens, the first quarter ... The light beam passes through a quarter wave plate, a polarization beam splitter, and an analyzer to reach the second photodetector; the tenth light beam passes through a second lens and a pinhole to reach the third photodetector as a confocal light intensity signal, and this signal is used to verify whether the sensor is installed correctly; the eighth light beam passes through the beam splitter film of the polarization beam splitter prism to become a light beam containing only second frequency polarized light, the eighth light beam passes through the second quarter wave plate, and is reflected by the fourth plane reflector and then returns to the polarization beam splitter prism along the original path, and after being reflected by the beam splitter film of the polarization beam splitter prism, it passes through the analyzer to reach the second photodetector, and interferes with the first frequency polarized light in the seventh light beam to generate a measurement signal; when the object to be measured moves, the optical path difference is obtained by subdividing the phase value of the measurement signal; Data processing system, when the main shaft of the hydrostatic bearing rotates, the optical measurement system simultaneously collects the displacement of the outer contour of the standard ball, and the collected displacement data is transmitted to the data processing system for error separation calculation.

2. The rotation accuracy measurement system of the hydrostatic bearing spindle according to claim 1, characterized in that: The first laser heterodyne interference displacement measurement module, the second laser heterodyne interference displacement measurement module, and the third laser heterodyne interference displacement measurement module are installed around the same cross section of the standard sphere.

3. The rotation accuracy measurement system of the hydrostatic bearing spindle according to claim 1, characterized in that: The first beam splitter prism, the second beam splitter prism, the third beam splitter prism and the fourth beam splitter prism are all semi-transmissive and semi-reflective lenses.

4. The rotation accuracy measurement system of the hydrostatic bearing spindle according to claim 1, characterized in that: The polarization beam splitting prism is a semi-transparent and semi-reflective lens coated with a polarization film.

5. The rotation accuracy measurement system of the hydrostatic bearing spindle according to claim 1, characterized in that: The first lens and the second lens are both converging lenses.

6. The rotation accuracy measurement system of the hydrostatic bearing spindle according to claim 1, characterized in that: The hydrostatic bearing spindle is provided with a rotary encoder.

7. A method for measuring the rotation accuracy of a hydrostatic bearing spindle, characterized in that: It includes the following steps: Step 1: The laser heterodyne interference module collects interference images. At a circumferential position of a certain section of the main shaft of the hydrostatic bearing, a first laser heterodyne interference displacement measurement module, a second laser heterodyne interference displacement measurement module, and a third laser heterodyne interference displacement measurement module are installed at different angle intervals. When the dual-frequency laser interferes, three test signals are formed; Step 2: The data processing system calculates the displacement analog signal, records the phase shift changes of the three test signals according to the reference signal, and calculates the analog signal value corresponding to the displacement; Step 3: Discretize to obtain the displacement digital signal, perform Nyquist sampling on the three test signals, and obtain three output signals; Step 4: Noise removal and filtering. The test signal is an analog signal. The test signal contains valid signals and high-frequency interference signals. Therefore, for the sampled data, the high-order components in the signal must be removed. Step 5: Extract synchronous motion error and asynchronous motion error, separate the errors according to the three-point method, and use the measured data to solve the model parameters; The mathematical model is discretized and Fourier transformed and inverse Fourier transformed to obtain synchronous and asynchronous components, where the average measurement is the average profile calculated based on multiple rotations of the data, which is mathematically equivalent to the integer component of the data in the Fourier domain; The remaining data are asynchronous components and correspond to non-integer components in the Fourier domain.

8. The method for measuring the rotation accuracy of a hydrostatic bearing spindle according to claim 7, characterized in that: The step three uses the three-point method error separation to measure the radial rotation error of the hydrostatic bearing main shaft, and removes the DC component, the first-order harmonic component and the high-order harmonic component from the three output signals.

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