CN110631483A - Orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, detector and detection method thereof - Google Patents

Orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, detector and detection method thereof Download PDF

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CN110631483A
CN110631483A CN201910932300.6A CN201910932300A CN110631483A CN 110631483 A CN110631483 A CN 110631483A CN 201910932300 A CN201910932300 A CN 201910932300A CN 110631483 A CN110631483 A CN 110631483A
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light
orthogonal
detector
spot position
displacement
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CN110631483B (en
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常素萍
吴昊
卢文龙
赵言情
刘晓军
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes

Abstract

The invention belongs to the field of precision measurement, and discloses an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, a detector and a detection method thereof, wherein the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor comprises a light splitting prism, a laser and a first plane reflector which are respectively arranged at the left side and the right side of the light splitting prism, an interference signal detector and an orthogonal transmission grating which are respectively arranged at the upper side and the lower side of the light splitting prism, a second plane reflector which is positioned below the orthogonal transmission grating, and four light spot position detectors which are positioned above the second plane reflector and are in orthogonal arrangement, wherein the second plane reflector is arranged on a magnetic levitation contact pin structure to; the detector comprises a deflection angle calculation module, a displacement calculation module and the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor; the detection method is realized by the detector. The invention can realize the simultaneous measurement of deflection angles in two directions, and can perform current feedback on the support rigidity of the contact pin magnetic suspension shaft, thereby accurately measuring the linear displacement in the vertical direction, and the invention has the advantages of compact structure, high measurement precision and the like.

Description

Orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, detector and detection method thereof
Technical Field
The invention belongs to the field of precision measurement, and particularly relates to an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, a detector and a detection method thereof.
Background
With the continuous development of science and technology, people have higher and higher requirements on the precision of measurement technology, wherein the high-precision optical interferometric measuring device becomes a key technology for the development of numerous fields. Commonly used displacement measuring devices are grating scales and laser interferometry. The grating ruler is used for measuring the displacement of the generated interference fringe number by recording the mutual movement of the static ruler and the movable ruler, and is easily influenced by temperature, the measurement resolution is seriously dependent on the grating constant of the grating ruler, the measurement range is limited, and the maximum allowable speed detected by a single grating ruler is often in inverse proportion to the measurement resolution, so that the contradiction between the measurement speed and the resolution exists. The laser interferometer uses the wavelength of laser in vacuum as the length standard, can reach the nanometer measurement resolution, measures the displacement by using the optical path difference between the reference optical path and the measurement optical path, the coherence length of the laser is large, and the measurement range is far larger than the measurement range of the grating ruler.
At present, there are many devices for utilizing laser interference precision measurement, for example, the line laser phase-shifting interference triangular micro-displacement measuring device and method disclosed in CN108680108B, which combines the phase-shifting interference technology and the laser triangular technology to realize large-range high-precision micro-displacement measurement; for another example, CN105004273A discloses a laser interference displacement measurement system, which uses the polarization optical principle to make the measurement light go in and out of the movable pyramid lens twice in the same direction, so as to implement the relationship between the optical path difference change between the measurement light and the reference light and the eight-fold displacement of the pyramid lens, thereby implementing the optical eight-fold subdivision measurement of the displacement. However, the current laser interference device can only measure the displacement and cannot measure the deflection angle, and for the suspended contact pin, the motion precision of the shaft is directly related to the metering precision of a measuring system, so that the detection and control of the deflection angle are necessary, the support of the shaft is fed back, and the support rigidity of the shaft and the maximum offset in the measuring process are ensured. Therefore, research and design needs to be conducted to obtain a device and a method capable of simultaneously measuring linear displacement and deflection angle.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, a detector and a detection method thereof, aiming at realizing the simultaneous measurement of linear displacement in one direction and deflection angles in two directions (namely three-degree-of-freedom data) through structural design, and having the advantages of compact structure, high measurement precision and the like.
In order to achieve the above object, according to a first aspect of the present invention, the present invention provides an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, which includes a light splitting prism, a laser and a first plane mirror respectively disposed at the left and right sides of the light splitting prism, an interference signal detector and an orthogonal transmission grating respectively disposed at the upper and lower sides of the light splitting prism, a second plane mirror located below the orthogonal transmission grating, and four light spot position detectors located above the second plane mirror and orthogonally arranged, wherein the second plane mirror is mounted on a magnetic levitation contact pin structure to be measured; during measurement, laser emitted by a laser is divided into two paths of orthogonal light output through a beam splitter prism, namely transmitted light and reflected light, wherein the transmitted light is reflected by a first plane reflector and returns to the beam splitter prism and then is reflected to an interference signal detector, the reflected light forms a beam of 0-order direct light and four beams of +/-1-order diffracted light after passing through an orthogonal grating, the beam of 0-order direct light directly returns to the interference signal detector through a second plane reflector and forms interference fringes with the transmitted light reflected to the interference signal detector, and the four beams of +/-1-order diffracted light are respectively vertically incident to four corresponding light spot position detectors through the second plane reflector so as to detect the positions of light spots.
Preferably, the interference signal detector is a four-quadrant detector, and four photodiodes with identical performance are manufactured according to the requirements of a rectangular coordinate system.
As a further preferred, the magnetic floating stylus structure comprises a stylus shaft, a stylus mounted below the stylus shaft and a suspension assembly for suspending the stylus shaft.
As further preferred, the suspension subassembly includes square permanent magnet spare, guidance coil, suspension coil and annular permanent magnet, and wherein, square permanent magnet spare is equipped with two sets ofly, divides to locate the outside at both ends about the contact pin axle, and every square permanent magnet spare of group comprises the square permanent magnet that the contact pin axle circumference distributes along the polylith, guidance coil's quantity corresponds with the quantity of square permanent magnet, and is orthogonal arrangement with a plurality of guidance coils in the square permanent magnet spare of group, the annular permanent magnet suit is at the middle part of contact pin axle, suspension coil comprises two upper and lower suspension coils that are parallel to each other and coaxial, and two upper and lower suspension coils suit is in the outside of contact pin axle, and arranges the upper and lower both ends of annular permanent magnet in.
According to a second aspect of the present invention, a suspension shaft displacement detector is provided, which includes a deflection angle calculation module, a displacement calculation module, and the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, where the deflection angle calculation module is configured to receive light spot position information measured by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, and calculate and obtain a deflection angle of the magnetic levitation contact pin structure based on the light spot position information; the displacement calculation module is used for receiving interference fringe information measured by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor and calculating and obtaining the displacement of the magnetic levitation contact pin structure based on the interference fringe information.
Preferably, the displacement calculation module comprises a differential circuit, an amplification shaping circuit, a direction-finding subdivision circuit, an a/D conversion circuit and a computer which are connected in sequence, wherein interference fringe information output by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor is converted into sine and cosine signals with a phase difference of 90 degrees through the differential circuit, one path of the interference fringe information is sent to the amplification shaping circuit to be converted into digital square waves and output to the direction-finding subdivision circuit for four-subdivision counting, and the counting circuit counts fringe movement exceeding 1/4 periods; the other path of the signal passes through an A/D conversion circuit, and the A/D converter is used for subdividing the stripe movement with less than 1/4 cycles; the count values of the two paths of signals are sent to a computer for synchronous addition processing so as to calculate the number of cycles of movement of the interference fringes, and then the displacement of the magnetic suspension contact pin structure is calculated based on the number of cycles of movement of the interference fringes.
According to a third aspect of the present invention, there is provided a three-degree-of-freedom measuring method for an orthogonal grating, comprising the following steps:
s1, dividing the incident laser into two orthogonal light outputs, namely transmitted light and reflected light, by a beam splitter prism;
s2, the transmitted light is reflected by the first plane mirror and returns to the beam splitter prism, and then is reflected to the interference signal detector;
s3 reflected light forms a beam of 0-level direct light and four beams of +/-1-level diffracted light after passing through the orthogonal grating, the 0-level direct light is directly returned to the interference signal detector through the second plane mirror to form interference fringes with transmitted light reflected to the interference signal detector, and the displacement of the magnetic suspension contact pin structure is calculated based on the information of the interference fringes;
and S4, reflecting the four beams of +/-1 st-order diffracted light to four corresponding light spot position detectors through the second plane mirror respectively to detect the light spot positions, and calculating the deflection angle of the second plane mirror, namely the magnetic suspension contact pin structure, based on the light spot positions and the displacement of the magnetic suspension contact pin structure.
As a further preferred, the displacement of the magnetic floating stylus structure in step S3 is calculated by the following formula:
Figure BDA0002220609700000041
as a further preference, the deflection angle in step S4 is determined as follows:
s41, establishing a relation between the offset detected by the spot position detector and the deflection angle:
Figure BDA0002220609700000042
wherein the content of the first and second substances,
Figure BDA0002220609700000043
for the offset directly detected by the spot position detector,
Figure BDA0002220609700000044
is a component caused only by the displacement L in the vertical direction of the magnetic suspension contact pin structure, D is the installation vertical distance from the orthogonal transmission grating to the second plane reflector, L is the displacement of the magnetic suspension contact pin structure in the vertical direction, and thetamIs the angle of diffraction, beta is the angle of deflection, s1The distance between the reflected light on the second plane reflector and the corresponding light spot position detector is obtained;
s42, establishing a relation between the offset and the deflection angle detected by the spot position detector which is symmetrical to the spot position detector in the step S41:
Figure BDA0002220609700000045
wherein the content of the first and second substances,
Figure BDA0002220609700000046
is the offset directly detected by the spot position detector opposite to the spot position detector in step S41, S2The distance between the reflected light on the second plane reflector and the corresponding light spot position detector is obtained;
s43 combines the formulas (I) and (II) to solve beta.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages: the invention divides laser into four beams of orthogonal space laser to match with the light spot position detector for detecting the deflection angle, utilizes interference fringes generated by the laser interference principle to carry out linear movement metering, realizes the detection of deflection error on the traditional metering, and can realize the feedback control of a contact pin shaft based on the deflection error and the linear movement amount so that the shaft is in a central position and is controllable. The invention adopts the combination of the beam splitter prism and the orthogonal transmission grating to realize the detection of three degrees of freedom (deflection angles in two directions and displacement in one direction) of the axis of the suspension contact pin, and has the characteristics of wide range and high precision of interferometric measurement.
Drawings
Fig. 1 is a schematic structural diagram of an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor provided in an embodiment of the present invention;
FIG. 2 is a diagram showing the relationship between the displacement component and the deflection component when the stylus shaft is displaced and yawed according to an embodiment of the present invention;
fig. 3 is a two-dimensional analytic graph of rotation quantity of a contact pin of an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor provided by the embodiment of the invention;
fig. 4 is a measurement schematic diagram of an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor provided by an embodiment of the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein: the device comprises an interference signal detector 1, a beam splitter prism 2, a first plane reflector 3, a orthogonal transmission grating 4, a spot position detector 5, a second plane reflector 6, a guide coil 7, a square permanent magnet 8, a suspension coil 9, an annular permanent magnet 10, a contact pin 11, a workpiece to be measured 12, a contact pin shaft 13 and a laser 14.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, an embodiment of the present invention provides an orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor, which includes a beam splitter prism 2, a laser 14, a first plane mirror 3, an interference signal detector 1, an orthogonal transmission grating 4, a second plane mirror 6, and four light spot position detectors 5, wherein the laser 14 and the first plane mirror 3 are respectively disposed on the left and right sides of the beam splitter prism 2, and a mirror surface of the first plane mirror 3 is parallel to a right side surface of the beam splitter prism 2; the interference signal detector 1 and the orthogonal transmission grating 4 are respectively arranged at the upper side and the lower side of the beam splitter prism 2, the second plane reflector 6 is positioned below the orthogonal transmission grating 4, namely the orthogonal transmission grating 4 is positioned between the beam splitter prism 2 and the second plane reflector 6, and the bottom surface of the beam splitter prism 2 and the reflecting surface of the second plane reflector 6 are both parallel to the working surface of the orthogonal transmission grating 4; the four light spot position detectors 5 are positioned above the second plane reflector 6 and are orthogonally arranged, the four light spot position detectors 5 are the same in structural size and model, and the positions of the four light spot position detectors are determined according to laser reflected light and are used for receiving laser light spots reflected by the second plane reflector 6; the second plane reflector 6 is arranged on a magnetic floating contact pin structure to be measured, and the specific magnetic floating contact pin structure is arranged below the second plane reflector 6.
During measurement, laser emitted by the laser 14 is split into two orthogonal light outputs, namely reflected light R, by the beam splitter prism 2sAnd transmitted light TpWherein, the reflected light forms four beams of plus or minus 1 order diffraction light and one beam of 0 order direct light after passing through the orthogonal grating 4, the emergent angle of the diffraction light is related to the grating constant and accords with the grating equation, the four beams of plus or minus 1 order diffraction light are respectively vertically incident into four corresponding light spot position detectors 5 through a second plane mirror 6 to detect the light spot position (namely, the offset is measured)
Figure BDA0002220609700000061
Or
Figure BDA0002220609700000062
) Calculating the deflection angle of a second plane mirror, namely a magnetic suspension contact pin structure based on the detected light spot position, and directly returning a beam of 0-level direct light to the interference signal detector 1 through the second plane mirror 6; the transmission light is reflected by the first plane reflector 3 and returns to the beam splitter prism 2, and then is reflected to the interference signal detector 1 to form interference fringes with 0-level direct light reflected by the second plane reflector 6, so that interference fringe information is obtained, the vertical direction movement of the second plane reflector changes the optical path difference of the two light beams to cause the movement of the interference fringes, the interference signals are received by the detector, and then are conditioned by a subsequent circuit, the movement quantity can be calculated, and the wave-based optical interference detector can calculate the movement quantity according to the waveAnd long to deduce the precise displacement. Namely, the sensor can simultaneously obtain key information (namely light spot position) for calculating the deflection angle and key information (namely interference fringe) for calculating the displacement value of the magnetic suspension contact pin structure (namely contact pin shaft), and the deflection angle and the displacement of the contact pin shaft can be obtained by performing related operation on the two pieces of key information.
Specifically, the interference signal detector 1 is preferably a four-quadrant detector, which is manufactured by four photodiodes with completely consistent performance according to the requirements of a rectangular coordinate system, so that the forward and reverse counting of interference light striations is facilitated, and the metering accuracy is high.
As shown in fig. 1, the magnetic floating stylus structure includes a stylus shaft 13, a stylus mounted below the stylus shaft 13, and a floating assembly for floating the stylus shaft. Specifically, the suspension subassembly includes square permanent magnet spare, guidance coil 7, suspension coil 9 and annular permanent magnet 10, wherein, square permanent magnet spare is equipped with two sets ofly, the outside at both ends about the contact pin axle 13 is located to the branch, every square permanent magnet spare of group comprises the square permanent magnet 8 that the contact pin axle 13 circumference distributes along the polylith, the quantity of guidance coil 7 corresponds with the quantity of square permanent magnet 8, guidance coil 7 and square permanent magnet 8 one-to-one promptly, and a plurality of guidance coils that correspond in the same square permanent magnet spare of group are the quadrature and arrange, annular permanent magnet 10 suit is in the middle part of contact pin axle 13, suspension coil 9 comprises two upper and lower suspension coils that are parallel to each other and coaxial, two upper and lower suspension coils are the same suit in the outside of contact pin axle, and arrange annular permanent magnet 10's upper and lower both.
Preferably, the contact pin shaft is a hollow square shaft, the square permanent magnets are eight, eight same square permanent magnets 8 are divided into two groups and fixed in four directions in two planes of the square shaft, the guide coils are composed of eight cylindrical iron core winding coils with the same structure size and the same number of turns, the eight same square permanent magnets are orthogonally arranged in the horizontal plane and are opposite to each square permanent magnet face, each suspension coil is composed of two coaxial upper and lower suspension coils which are parallel to each other and arranged at two ends of the upper and lower surfaces of the annular permanent magnet, the annular permanent magnet generates magnetic force under the action of an electromagnetic field to enable the contact pin shaft to suspend, a contact pin arranged at the center of the bottom end of the contact pin shaft is fixedly connected to the contact pin shaft, and the supporting rigidity of the whole sensor can be controlled by the guide coils; the micro displacement of the contact pin shaft reflects two rotations in the horizontal direction and one movement amount in the vertical direction, so that three degrees of freedom of rotation amounts of the contact pin shaft in two directions (x and y directions) in the horizontal plane and measurement of the movement amount in one direction (z direction) are detected based on a measuring part of the orthogonal grating, namely the deflection of the contact pin including deflection angles in the two directions and the displacement amount in one direction can be measured, the deflection of the contact pin is converted into the corresponding current amount, and the guide coil is controlled based on the current amount, so that the rigidity of the suspended contact pin shaft can be subjected to feedback control based on the deflection of the contact pin, and the movement precision is improved.
The embodiment of the invention also provides a suspension shaft displacement detector which comprises a deflection angle calculation module, a displacement calculation module and the orthogonal grating three-degree-of-freedom magnetic suspension measurement sensor, wherein the deflection angle calculation module is used for receiving the light spot position information measured by the orthogonal grating three-degree-of-freedom magnetic suspension measurement sensor and calculating and obtaining the deflection angle of the magnetic suspension contact pin structure based on the light spot position information; the displacement calculation module is used for receiving interference fringe information measured by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor and calculating and obtaining the displacement of the magnetic levitation contact pin structure based on the interference fringe information.
Specifically, the displacement calculation module comprises a differential circuit, an amplification shaping circuit, a direction-distinguishing subdivision circuit, an A/D conversion circuit and a computer which are connected in sequence, wherein interference fringe information output by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor (specifically, the interference signal detector 1) is converted into sine and cosine signals with the phase difference of 90 degrees through the differential circuit, one path of sine and cosine signals is sent to the amplification shaping circuit to be changed into digital square waves and output to the direction-distinguishing subdivision circuit for four-subdivision counting, and the counting circuit counts fringe movement exceeding 1/4 periods; the other path of sine and cosine signal passes through an A/D conversion circuit and is subjected to subdivision processing on the stripe movement with less than 1/4 cycles through an A/D converter; and the count values of the two paths of signals are sent into a computer for synchronous addition processing so as to calculate and obtain the periodicity N of the movement of the interference fringes, and then the displacement of the magnetic suspension contact pin structure is calculated based on the periodicity N of the movement of the interference fringes.
By combining the effectiveness of actual interference signals, the angular resolution within a quarter period of the signals can reach 2 degrees, the large counts subdivided by four are fused with the small counts subdivided by the A/D converter, and the displacement measurement resolution delta of the invention can reach 0.88 nm:
Figure BDA0002220609700000081
the detection of the displacement of the suspension shaft by adopting the detector of the invention specifically comprises the following steps:
the incident laser of S1 is divided into two paths of orthogonal light output, namely transmitted light and reflected light, by the beam splitter prism 2;
s2 transmitted light is reflected by the first plane mirror 3 and returns to the beam splitter prism 2, and then is reflected to the interference signal detector 1;
s3 reflected light forms a beam of 0-level direct light and four beams of +/-1-level diffracted light after passing through the orthogonal grating 4, the 0-level direct light is directly returned to the interference signal detector 1 through the second plane mirror 6 to form interference fringes with transmitted light reflected to the interference signal detector 1, and the displacement of the magnetic suspension contact pin structure is calculated based on the information of the interference fringes;
s4 four beams of + -1 st order diffraction light are vertically incident on four corresponding light spot position detectors 5 through a second plane mirror 6 respectively to detect the light spot positions, and the deflection angle of the second plane mirror, namely the magnetic suspension contact pin structure, is calculated based on the light spot positions and the displacement of the magnetic suspension contact pin structure.
Specifically, the displacement of the magnetic suspension contact pin structure (i.e. the contact pin shaft) is calculated by the following formula:
Figure BDA0002220609700000091
l is the displacement of the magnetic suspension contact pin structure, N is the periodicity of the movement of the interference fringes, the periodicity is obtained by calculation of the displacement calculation module based on the information of the interference fringes, and lambda is the wavelength of the laser.
Specifically, the deflection angle is determined as follows:
s41, establishing a relation between the offset detected by the spot position detector and the deflection angle:
Figure BDA0002220609700000092
wherein the content of the first and second substances,
Figure BDA0002220609700000093
for offsets directly detected by the spot position detector (e.g. the left-hand spot position detector),
Figure BDA0002220609700000094
is a component caused only by the displacement L in the vertical direction of the magnetic suspension contact pin structure, D is the installation vertical distance from the orthogonal transmission grating to the second plane reflector, L is the displacement of the magnetic suspension contact pin structure in the vertical direction, and thetamIs the diffraction angle (as an intrinsic parameter), beta is the deflection angle, s1The distance from the reflected light on the second plane reflector to a light spot position detector (a left light spot position detector);
s42, establishing a relation between the offset and the deflection angle detected by the spot position detector which is symmetrical to the spot position detector in the step S41:
Figure BDA0002220609700000095
wherein the content of the first and second substances,
Figure BDA0002220609700000096
is the offset directly detected by the spot position detector relative to the spot position detector in the above equation, e.g. in the above equation
Figure BDA0002220609700000097
Measured by the left spot position detector, then
Figure BDA0002220609700000098
Measured by the spot position detector on the right side, in the above formula
Figure BDA0002220609700000101
Measured by a forward spot position detector, then
Figure BDA0002220609700000102
For rear spot position detector, i.e.And
Figure BDA0002220609700000104
are data measured by two opposing spot position detectors,
Figure BDA0002220609700000105
is a component caused only by the displacement L in the vertical direction of the magnetic suspension contact pin structure, D is the installation vertical distance from the orthogonal transmission grating to the second plane reflector, L is the displacement of the magnetic suspension contact pin structure in the vertical direction, and thetamIs the diffraction angle (as an intrinsic parameter), beta is the deflection angle, s2The distance from the reflected light on the second plane mirror to the spot position detector (the spot position detector on the right side).
S43 finally, combine equations (one) and (two) to solve β, i.e. the two equations are added, and simplified as:
Figure BDA0002220609700000106
in the formula (I), the compound is shown in the specification,
Figure BDA0002220609700000107
D、L、θm、s1and s2All are known parameters, and beta can be solved according to the formula.
The following are specific examples:
the laser 14 adopted in the embodiment is a frequency stabilized helium-neon laser with the wavelength of 632.8 nm; the beam splitter prism 2 is a single-wavelength beam splitter prism with the side length of 25.4 mm; the mirror surface diameter of the first and second plane reflectors 3 and 6 is phi 25.4 mm; the interference signal detector selects a four-quadrant photodiode, and can subdivide the interference fringe four into 1/4 periods of large fringe count; light spotThe position detector 5 selects a four-quadrant detector, but the function of the position detector is different from that of the interference signal detector 1, and the position of the light spot can be calculated through the light currents output by the four quadrants, so that the displacement of the light spot on the photosensitive surface of the four-quadrant detector at a certain moment is obtained. The photocurrent output by the 4 quadrants of each detector is IA,IB,IC,IDThe measured displacement amount thereof
Figure BDA0002220609700000108
Comprises the following steps:
Figure BDA0002220609700000109
or
Figure BDA00022206097000001010
Where k is a coefficient, the amount of displacement
Figure BDA00022206097000001011
Or
Figure BDA00022206097000001012
And can be read directly on the spot position detector.
The deflection angle of the contact pin shaft can be calculated by the light spot position detected by the light spot position detector 5, so that the current of the guide coil 7 is adjusted, the feedback control of the rigidity of the contact pin shaft in the horizontal direction is realized, the deflection error of the contact pin shaft is slight, the light spot position detector 5 is only used for detection, and the precision can be lower than the metering precision of the interference signal detector 1.
In this embodiment, for the displacement in the z direction, the following formula is adopted to calculate:
Figure BDA0002220609700000111
when the moving part is displaced, the optical path difference between the measuring beam and the reference beam is changed to cause the interference fringes to change, and when the optical path difference changes by one wavelength, the interference fringes change alternately in brightness and darknessNext, the process is carried out. According to the characteristics of the grating equation, when the diffraction angle thetamSatisfies the relationship qsin thetamThe interference enhancement occurs when/λ is | m |, where q is the slit pitch, i.e., the grating constant, and m is an integer with values of 0, ± 1, ± 2, … …, and the point of interference enhancement is called the diffraction maximum. Thus, the diffracted light will be at diffraction angle θmTime is extremely large, and when the light is vertically incident:
dsinθm＝mλ (3)
the larger the grating constant is, the smaller the diffraction angle is, and when a grating having q of 1 μm is selected, θm＝39.26°。
Fig. 2 illustrates the relationship between the stylus axis displacement and yaw, the displacement component op, and the yaw component pq or pq'. Fig. 3 is a detailed relationship analysis of the spot position detector on the rotation amount of the stylus shaft, when the stylus shaft rotates, the displacement changes of the spot positions detected by the two symmetrical spot position detectors in different directions and the displacement amounts are different, and for the angle of the stylus shaft in one direction, the deflection angle β is calculated by combining the following equations (5) and (6):
Figure BDA0002220609700000112
Figure BDA0002220609700000113
wherein the content of the first and second substances,
Figure BDA0002220609700000114
the displacement measured by the spot position detector on the left side,
Figure BDA0002220609700000115
the displacement measured by the light spot position detector on the right side; d is the installation vertical distance from the orthogonal transmission grating to the second plane reflector, and s is the distance from the reflected light on the second plane reflector to the detector corresponding to the light spot position;
the deflection angle beta can be calculated through two formulas (5) and (6), the deflection angle beta obtained through calculation of information of the left and right spot position detectors is a deflection angle around a y axis (a direction from the back to the front in a horizontal plane), and the deflection angle beta obtained through calculation of information of the front and back spot position detectors is a deflection angle around an x axis (a direction from the left to the right in the horizontal plane), so that the deflection angles of the touch needle shaft in two directions in the horizontal plane are obtained.
The invention adopts the combination of the beam splitter prism and the two-dimensional grating to realize the detection of three degrees of freedom of the suspension contact pin shaft, has the characteristics of wide range and high precision of interferometric measurement, can realize the feedback control of the contact pin shaft based on the data of the three measured degrees of freedom, has strong anti-interference capability, and can reduce the error caused by non-linear motion compared with single-path light beam interference. The sensor of the invention adopts the orthogonal grating diffraction technology, divides the single wavelength laser emitted by the laser into five beams in space, and respectively acts on the rotation error detection in the x and y directions on a plane and the movement displacement measurement in the z direction vertical to the plane, the displacement measurement part adopts the combination of a beam splitter prism, a reflector and a photoelectric detector, and the displacement is measured by utilizing the interference principle.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. The three-degree-of-freedom orthogonal grating magnetic levitation measurement sensor is characterized by comprising a light splitting prism (2), a laser (14) and a first plane reflector (3) which are respectively arranged on the left side and the right side of the light splitting prism (2), interference signal detectors (1) and orthogonal transmission gratings (4) which are respectively arranged on the upper side and the lower side of the light splitting prism (2), a second plane reflector (6) which is positioned below the orthogonal transmission gratings (4) and four light spot position detectors (5) which are positioned above the second plane reflector (6) and are in orthogonal arrangement, wherein the second plane reflector (6) is arranged on a magnetic levitation contact pin structure to be measured; during measurement, laser emitted by a laser (14) is divided into two paths of orthogonal light output, namely transmitted light and reflected light, through a beam splitter prism (2), wherein the transmitted light is reflected back to the beam splitter prism (2) through a first plane reflector (3) and then reflected into an interference signal detector (1), the reflected light forms a beam of 0-order direct light and four beams of +/-1-order diffracted light after passing through an orthogonal grating (4), the 0-order direct light is directly returned into the interference signal detector (1) through a second plane reflector (6) and forms interference fringes with the transmitted light reflected into the interference signal detector (1), and the four beams of +/-1-order diffracted light are respectively reflected into four corresponding spot position detectors (5) through second plane reflectors (6) to detect spot positions.
2. The orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor as claimed in claim 1, wherein the interference signal detector (1) is preferably a four-quadrant detector, which is made of four photodiodes with identical performance according to the requirements of a rectangular coordinate system.
3. The orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor as claimed in claim 1, wherein the magnetic levitation stylus structure comprises a stylus shaft (13), a stylus (11) installed below the stylus shaft (13), and a levitation component for realizing the suspension of the stylus shaft.
4. The orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor as claimed in claim 3, wherein the levitation assembly comprises two groups of square permanent magnet pieces, two guiding coils (7), two levitation coils (9) and two annular permanent magnets (10), wherein the two groups of square permanent magnet pieces are respectively arranged outside the upper and lower ends of the stylus shaft (13), each group of square permanent magnet pieces is composed of a plurality of square permanent magnets (8) distributed along the circumference of the stylus shaft (13), the number of the guiding coils (7) corresponds to the number of the square permanent magnets (8), a plurality of guiding coils in the same group of square permanent magnet pieces are orthogonally arranged, the annular permanent magnets (10) are sleeved on the middle portion of the stylus shaft (13), the levitation coils (9) are composed of two upper and lower levitation coils which are parallel to each other and coaxial, and the two upper and lower levitation coils are sleeved on the outside of the stylus shaft (13), and are arranged at the upper end and the lower end of the annular permanent magnet (10).
5. A suspension shaft displacement detector is characterized by comprising a deflection angle calculation module, a displacement calculation module and the orthogonal grating three-degree-of-freedom magnetic suspension measurement sensor as claimed in any one of claims 1 to 4, wherein the deflection angle calculation module is used for receiving light spot position information measured by the orthogonal grating three-degree-of-freedom magnetic suspension measurement sensor and calculating and obtaining the deflection angle of the magnetic suspension contact pin structure based on the light spot position information; the displacement calculation module is used for receiving interference fringe information measured by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor and calculating and obtaining the displacement of the magnetic levitation contact pin structure based on the interference fringe information.
6. The levitation shaft displacement detector as claimed in claim 5, wherein the displacement calculation module comprises a differential circuit, an amplifying and shaping circuit, a direction-identifying and subdividing circuit, an A/D conversion circuit and a computer, which are connected in sequence, wherein interference fringe information output by the orthogonal grating three-degree-of-freedom magnetic levitation measurement sensor is converted into sine and cosine signals with a phase difference of 90 degrees through the differential circuit, one path of the interference fringe information is sent to the amplifying and reshaping circuit to be converted into digital square waves and output to the direction-identifying and subdividing circuit for four subdivision counting, and the counting circuit counts fringe movement exceeding 1/4 periods; the other path of the signal passes through an A/D conversion circuit, and the A/D converter is used for subdividing the stripe movement with less than 1/4 cycles; the count values of the two paths of signals are sent to a computer for synchronous addition processing so as to calculate the number of cycles of movement of the interference fringes, and then the displacement of the magnetic suspension contact pin structure is calculated based on the number of cycles of movement of the interference fringes.
7. A three-degree-of-freedom measuring method for orthogonal grating is characterized by comprising the following steps:
s1 incident laser is divided into two paths of orthogonal light output, namely transmitted light and reflected light, by the light splitting prism (2);
s2 transmitted light is reflected by the first plane mirror (3) and returns to the beam splitter prism (2), and then is reflected to the interference signal detector (1);
s3 reflected light forms a beam of 0-level direct light and four beams of +/-1-level diffracted light after passing through the orthogonal grating (4), the beam of 0-level direct light directly returns to the interference signal detector (1) through the second plane mirror (6) to form interference fringes with transmitted light reflected to the interference signal detector (1), and the displacement of the magnetic suspension contact pin structure is calculated based on the information of the interference fringes;
s4 four beams of plus or minus 1 order diffraction light are respectively vertically incident on four corresponding light spot position detectors (5) through a second plane mirror (6) to detect the light spot position, and the deflection angle of the second plane mirror, namely the magnetic suspension contact pin structure, is calculated based on the light spot position and the displacement of the magnetic suspension contact pin structure.
8. The orthogonal grating three-degree-of-freedom measurement method as claimed in claim 7, wherein the deflection angle in step S4 is determined as follows:
s41, establishing a relation between the offset detected by the spot position detector and the deflection angle:
Figure FDA0002220609690000031
wherein the content of the first and second substances,
Figure FDA0002220609690000032
for the offset directly detected by the spot position detector,
Figure FDA0002220609690000033
is a component caused only by the displacement L in the vertical direction of the magnetic suspension contact pin structure, D is the installation vertical distance from the orthogonal transmission grating to the second plane reflector, L is the displacement of the magnetic suspension contact pin structure in the vertical direction, and thetamIs the angle of diffraction, beta is the angle of deflection, s1For reflecting light on the second plane mirror to the corresponding spot positionThe distance of the detector;
s42, establishing a relation between the offset and the deflection angle detected by the spot position detector which is symmetrical to the spot position detector in the step S41:
Figure FDA0002220609690000034
wherein the content of the first and second substances,
Figure FDA0002220609690000035
is the offset directly detected by the spot position detector opposite to the spot position detector in step S41, S2The distance between the reflected light on the second plane reflector and the corresponding light spot position detector is obtained;
s43 combines the formulas (I) and (II) to obtain beta.
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