CN117804348B - Grating displacement sensor based on longitudinal moire fringe correlation calculation - Google Patents
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Abstract
The invention discloses a grating displacement sensor based on longitudinal moire fringe correlation calculation, which comprises a base, a grating adjusting and positioning device, a linear laser, a laser interferometer, a linear array CCD, a grating displacement driving component and a grating displacement calculation system, wherein the linear array CCD is arranged on the base; a fixed indication grating and a scale grating capable of horizontally and transversely moving are arranged in the grating adjusting and positioning device; the linear array CCD is fixedly positioned at the rear side of the light passing hole, the grating displacement driving assembly comprises a diamond displacement driving amplifying mechanism and a piezoelectric actuator, the power output end of the diamond displacement driving amplifying mechanism is fixedly connected with the end part of the scale grating, the grating displacement calculating system comprises an FPGA (field programmable gate array) in communication connection with the linear array CCD and a PC (personal computer) in communication connection with the FPGA, and a normalized cross-correlation algorithm program based on MatLab software is arranged in the PC. Compared with a photoelectric detector adopted by a traditional grating, the grating displacement sensor has the capabilities of high robustness and flexibility, and can realize online accurate position measurement.
Description
Technical Field
The invention relates to the technical field of grating displacement sensors, in particular to a grating displacement sensor based on longitudinal moire fringe correlation calculation.
Background
Micro-displacement sensing measurement technology in micrometer and nanometer level has very wide and important application in various industrial fields such as metering, robots, bioengineering and the like. Among many types of micro displacement sensors, grating displacement sensors based on moire technology theory have been widely used and focused. The grating displacement sensor has good stability and small zero drift because the grating substrate is made of quartz or glass or other materials with low thermal expansion coefficients. In addition, the grating sensor has the remarkable advantages of small volume, good quality and the like. The electromagnetic interference resistance is insensitive to environment, and the method has wide nanometer scale measurement application in the large measurement field and under the conditions of temperature, humidity and pressure change.
At present, two main approaches exist for improving the measurement accuracy and resolution of a grating sensor: one is to increase the number of reticles of the grating, and the other is to use various electronic subdivision techniques (including hardware subdivision and software subdivision). The method for improving the density of the grating lines has the difficulties of high manufacturing process difficulty and high manufacturing cost, and meanwhile, the higher the density of the grating lines is, the greater the requirements on an optical structure system, a circuit processing system and a mechanical structure are; conventional electronic hardware subdivision techniques require complex circuit designs and processes that are costly in terms of both tamper resistance, circuit stability, and bulk. First, moire signals are susceptible to light source fluctuations, harmonic noise, amplitude differences, phase difference shifts, and other factors, and it is difficult to further improve measurement accuracy and resolution. In addition, because of the structural characteristics of the moire fringe acquisition system, the actual fringe signal is not an ideal sine and cosine signal, the phenomena of fluctuation of signal amplitude, non-strict orthogonality of two paths of signals and the like exist, when the grating scale moves at a non-uniform speed, the output moire fringe signal is not a periodic constant signal, and all the factors can influence the subdivision of fringes.
Disclosure of Invention
In order to solve the problems, the invention provides a grating displacement sensor based on longitudinal moire fringe correlation calculation, adopts a longitudinal moire fringe forming mechanism based on equidistant gratings, realizes an accurate position measurement method based on linear array CCD capturing double-grating longitudinal moire fringe movement, and designs a Normalized Cross Correlation (NCC) sub-pixel image registration algorithm.
In order to solve the technical problems, the invention adopts a technical scheme that:
A grating displacement sensor based on longitudinal moire fringe correlation calculation comprises a base, a grating adjusting and positioning device, a linear laser, a laser interferometer, a linear array CCD, a grating displacement driving component and a grating displacement calculation system;
the grating adjusting and positioning device comprises a grating ruler positioning main support and a grating ruler positioning auxiliary support which is arranged opposite to the grating ruler positioning main support, wherein a light passing hole is formed in the middle of the grating ruler positioning main support, two sides of the top and two sides of the bottom of the light passing hole are respectively provided with a transverse adjusting guide pulley with an adjustable vertical position in a rotating mode, an indication grating which is positioned at the front side of the light passing hole is fixedly arranged on the front side surface of the grating ruler positioning main support, a scale grating which is parallel to the front side of the indication grating and can horizontally and transversely move is movably clamped between the upper and lower sets of transverse adjusting guide pulleys, and the scale grating and the indication grating form a grating pair;
The two ends of the front side surface of the grating ruler positioning main support are rotatably provided with at least one main longitudinal adjusting guide pulley which is adjustable in horizontal longitudinal position and in rolling contact with the rear side surface of the grating ruler, and the side surface of the grating ruler positioning auxiliary support is rotatably provided with an auxiliary longitudinal adjusting guide pulley which is arranged in a matched mode with the main longitudinal adjusting guide pulley and in rolling contact with the front side surface of the grating ruler;
The linear laser is positioned at the front side of the scale grating, a point light source is provided for the grating pair, and the grating pair forms longitudinal moire fringes;
the laser interferometer detects the displacement of the scale grating to obtain reference displacement output;
The linear array CCD is arranged in parallel with the indication grating and fixedly positioned at the rear side of the light passing hole, the linear array CCD receives the optical signals of longitudinal moire fringes, and the optical signals are converted and then calculated through a normalized cross correlation algorithm program to obtain the output displacement of the grating displacement sensor;
The grating displacement driving assembly comprises a positioning bracket fixedly arranged at the outer side of one end of the scale grating, the side surface of the positioning bracket is fixedly connected with a diamond displacement driving amplifying mechanism, the internal power input end of the diamond displacement driving amplifying mechanism is provided with a piezoelectric actuator, and the power output end of the diamond displacement driving amplifying mechanism is fixedly connected with the end part of the scale grating;
the grating displacement calculation system comprises an FPGA (field programmable gate array) in communication connection with the linear array CCD and a PC (personal computer) in communication connection with the FPGA, wherein a normalized cross-correlation algorithm program based on MatLab software is arranged in the PC.
Further, the grid ruler positioning main support is provided with a transverse L-shaped lever structure symmetrically distributed on the two sides of the top end and the two sides of the bottom end of the light passing hole, a vertical adjusting screw which is vertically arranged is movably sleeved in the free end of the transverse L-shaped lever structure, the end part of the vertical adjusting screw is in threaded connection with the grid ruler positioning main support, the other end of the transverse L-shaped lever structure is fixedly connected to the top surface or the bottom surface of the grid ruler positioning main support through a flexible hinge structure, and the transverse adjusting guide pulley is rotatably arranged on the front side surface of the free end of the transverse L-shaped lever structure;
the utility model discloses a grid ruler positioning main support, including grid ruler positioning main support, flexible hinge structure, main vertical L type lever structure, main vertical adjusting pulley, main vertical L type lever structure's leading flank tip is provided with at least one main vertical L type lever structure respectively at grid ruler positioning main support's leading flank both ends, movable sleeve is equipped with the main vertical adjusting screw of horizontal vertical setting in the back lateral wall of grid ruler positioning main support, main vertical adjusting screw's tip and the free end threaded connection of main vertical L type lever structure, main vertical L type lever structure's the other end passes through flexible hinge structure fixed connection on grid ruler positioning main support's leading flank tip, main vertical adjusting guide pulley rotates to be installed on main vertical L type lever structure's free end leading flank.
Further, an auxiliary vertical L-shaped lever structure which is opposite to the main vertical L-shaped lever structure is arranged in the rear side surface of the grid ruler positioning auxiliary support, an auxiliary longitudinal adjusting screw which is horizontally and longitudinally arranged is movably sleeved in the front side wall of the grid ruler positioning auxiliary support, the end part of the auxiliary longitudinal adjusting screw is in threaded connection with the free end of the auxiliary vertical L-shaped lever structure, the other end of the auxiliary vertical L-shaped lever structure is fixedly connected onto the end part of the rear side surface of the grid ruler positioning auxiliary support through a flexible hinge structure, and an auxiliary longitudinal adjusting guide pulley is rotatably arranged on the rear side surface of the free end of the auxiliary vertical L-shaped lever structure.
Furthermore, a laser chuck positioned at the front side of the light transmission hole is fixedly arranged on the top surface of the base, and a linear laser and a laser interferometer are fixedly arranged on the laser chuck.
Further, the middle part of the laser chuck is provided with a through hole, two sides of the bottom of the through hole are respectively provided with a notch groove, the top of the through hole is provided with a through groove penetrating the top of the laser chuck, one side part of the top of the laser chuck is internally provided with a bolt through hole, and the other side part of the top of the laser chuck is internally provided with a threaded connection hole.
Furthermore, the grid ruler positioning main support and the grid ruler positioning auxiliary support are both made of 7075 aluminum alloy materials.
The mechanism comprises an indication grating, a scale grating capable of horizontally and transversely moving and a point light source, wherein the indication grating is fixedly arranged, the scale grating is parallel to the indication grating, the grating period of the scale grating is the same as that of the indication grating, the grating lines of the scale grating and the indication grating are perpendicular to the movement direction of the scale grating, and the point light source is positioned on one side of the scale grating far away from the indication grating;
Under the action of a point light source, the length of the grating pitch of the scale grating with the grating pitch of W 1, which is actually projected to the indication grating with the grating pitch of W 2, is amplified to a certain extent and then is changed into W 11, and the calculation formula of the scale grating is as follows according to a similar principle:
；
two gratings with grating periods of W 2 and W 11 can form longitudinal moire fringes, after the scale grating relatively indicates the distance of one grating period of grating movement, the corresponding relative movement distance is amplified by a grating pair under a point light source, and the fringe width of the longitudinal moire fringes is as follows:
；
Wherein d 1 is the distance between the scale grating and the indication grating, and d 2 is the vertical distance between the point light source and the grating surface of the scale grating;
the displacement resolution of the grating displacement sensor is expressed as:
；
Wherein N is the number of CCD pixels occupied by one longitudinal moire fringe period, and W is one grating period;
The width of each pixel of the whole pixel output result of the linear array CCD is b, and the following relation exists according to the above formula:
。
Further, the grating period of the scale grating is the same as the grating period of the indication grating, i.e. W 1=W2 =w, then
；
The displacement resolution of the grating displacement sensor is expressed as:
。
The invention also provides a grating displacement sensor debugging method based on moire fringe correlation calculation, which comprises the following steps:
s1, adjusting the horizontal pose of the scale grating, enabling grating lines of the scale grating and the indication grating to be perpendicular to the horizontal moving direction of the scale grating, and adjusting the parallel distance between the scale grating and the indication grating;
S2, applying a drive voltage with preset waveforms to the grating displacement drive assembly, and enabling the grating displacement drive assembly to work so as to drive the scale grating to horizontally move relative to the indication grating;
s3, providing a point light source to the surface of the scale grating by the in-line laser, and forming longitudinal moire fringes by the relatively moving grating pair of the point light source;
s4, the linear array CCD receives the optical signals of the longitudinal moire fringes, converts the optical signals into digital signals through the FPGA and transmits the digital signals to the PC;
S5, the PC machine runs a normalized cross-correlation algorithm program, and the acquired data are processed to obtain displacement output of the grating displacement sensor;
s6, detecting reference displacement output of the scale grating by a laser interferometer;
S7, comparing and analyzing the reference displacement output obtained by the laser interferometer with the output displacement of the grating displacement sensor obtained by calculation;
s8, repeating the steps S1 to S7, and obtaining the resolution of the grating sensor corresponding to the light source at different positions and the optimal resolution of the grating sensor by changing the parallel interval between the grating and the light source.
Further, in step S5, before performing correlation calculation by the normalized cross correlation algorithm, sub-pixel interpolation subdivision is performed on the whole pixel output result of each line of the linear array CCD by adopting an interpolation mode.
Further, the interpolation mode adopted by sub-pixel interpolation subdivision of the whole pixel output result of each line of the linear CCD is spline interpolation.
Further, the driving voltage applied to the grating displacement driving assembly is a triangular wave voltage or a step wave voltage.
And provides a normalized cross-correlation sub-pixel registration algorithm applied to a grating sensor, comprising the steps of:
S1, generating longitudinal moire fringes by a grating pair placed in parallel under a proper light source, receiving optical signals of the longitudinal moire fringes by a linear array CCD, processing and converting the optical signals into digital signals, and transmitting the digital signals to a PC;
s2, the PC machine runs a normalized cross-correlation algorithm program, and the acquired data are processed to obtain the output displacement of the grating displacement sensor;
The method comprises the following specific steps:
S2.1, two sub-set time sequences f i=[fp,fp+1,……,fp+m-1],gi=[gq,gq+1,……,gq+m-1 of the same continuous data points with the length of m, which are extracted from two frames of discrete time sequences f= [ f 0,f1,……,fn-1],g=[g0,g1,……,gn-1 ] with n discrete points output by the linear array CCD;
S2.2, a normalized cross-correlation algorithm is defined as:
；
Wherein p, q, m are positive integers, and p, q epsilon [0, n-m+1], m epsilon [2, n ], ，/>Representing two groups of discrete sequences output by linear array CCD，/>；
S2.3, substituting the data of the two subsets of time sequences into a normalized cross-correlation algorithm for calculation.
Further, in step S2.2, before performing correlation calculation by the normalized cross correlation algorithm, sub-pixel interpolation subdivision is performed on the whole pixel output result of each line of the linear array CCD by adopting an interpolation mode.
Further, the interpolation mode adopted by sub-pixel interpolation subdivision of the whole pixel output result of each line of the linear CCD is spline interpolation.
Compared with the prior art, the invention has the following beneficial effects:
The high-resolution grating displacement sensor based on moire fringe correlation calculation, which is designed by the invention, realizes an accurate position measurement method for capturing double-grating longitudinal moire fringe movement based on a linear array CCD, and designs a Normalized Cross Correlation (NCC) sub-pixel image registration algorithm. When the light intensity changes to cause the direct current drift of moire fringe signals in a certain range, the fringe signals obtained by the linear array CCD drift integrally and still contain accurate phase information, and the influence caused by amplitude fluctuation can be well restrained through a normalization correlation algorithm. Compared with a photoelectric detector adopted by a traditional grating, the grating displacement sensor has the capabilities of high robustness and flexibility, and can realize online accurate position measurement.
Drawings
FIG. 1 is a schematic overall perspective view of the present invention;
FIG. 2 is a schematic view of the overall three-dimensional explosion structure of the present invention;
FIG. 3 is a schematic perspective view of the grid ruler positioning main support and the assembly state of the grid ruler positioning main support;
FIG. 4 is a schematic perspective view of the grid ruler positioning main support and the assembly state of the grid ruler positioning main support;
FIG. 5 is one of the schematic perspective views of the grid ruler positioning main support;
FIG. 6 is a second schematic perspective view of the grid ruler positioning main support;
FIG. 7 is a schematic perspective view of the grid ruler positioning sub-bracket and the assembly state of the grid ruler positioning sub-bracket;
FIG. 8 is a second perspective view of the grid ruler positioning sub-bracket and the assembly state of the grid ruler positioning sub-bracket;
FIG. 9 is a schematic top view of a clamping state of a grating pair on a grating adjusting and positioning device;
FIG. 10 is a schematic perspective view of the laser chuck;
FIG. 11 is a schematic perspective view of a grating displacement drive assembly;
FIG. 12 is a schematic view of the principle of operation of the present invention;
FIG. 13 is a block diagram of the data processing logic of a grating sensor of the present invention;
FIG. 14 is a longitudinal moire image produced by a conventional unequal pitch grating illuminated with parallel light;
FIG. 15 is a schematic diagram of moire fringe imaging principle of an equal-pitch grating under a point light source according to the invention;
FIG. 16 is a schematic representation of the extraction of two subsets of time series according to the present invention;
FIG. 17 is a graph showing the first displacement test result of the grating sensor and the laser interferometer under the triangular wave voltage in the embodiment;
Fig. 18 shows a second displacement test result of the grating sensor and the laser interferometer under the triangular wave voltage in the embodiment:
FIG. 19 is a third example of displacement test results of the grating sensor and the laser interferometer at triangular wave voltage;
FIG. 20 is a graph showing the resolution of a grating sensor tested using a step wave voltage according to an embodiment;
FIG. 21 is a test result of the resolution of the whole pixel of the linear CCD array according to the step wave voltage test in the embodiment;
FIG. 22 is a graph showing the comparison of the results of the step wave test after sub-pixel subdivision in the examples;
FIG. 23 is a step resolution of an embodiment in which sub-pixels are subdivided;
FIG. 24 is a schematic modeling diagram of an optical simulation of the present invention;
fig. 25 is an optical simulation result of the equal pitch longitudinal moire imaging of the present invention.
In the figure: the device comprises a base, a 2-grating adjusting and positioning device, a 21-grating ruler positioning main support, a 211 light-passing hole, a 212 transverse L-shaped lever structure, a 213-main vertical L-shaped lever structure, a 22-grating ruler positioning auxiliary support, a 221-auxiliary vertical L-shaped lever structure, a 23 transverse adjusting guide pulley, a 24-main longitudinal adjusting guide pulley, a 25-auxiliary longitudinal adjusting guide pulley, a 26-vertical adjusting screw, a 27-main longitudinal adjusting screw, a 28-auxiliary longitudinal adjusting screw, a 3-linear CCD (charge coupled device), a 31-linear CCD (charge coupled device), a 4-grating displacement driving component, a 41-position support, a 42-diamond displacement driving and amplifying mechanism, a 43 piezoelectric actuator, a 5-indicating grating, a 6-grating, a 7-laser chuck, a 71 through hole, a 72-notch groove, a 73-passing groove and an 8-laser interferometer.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making clear and defining the scope of the present invention.
It is noted that when an element is referred to as being "mounted to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "secured to" another element, it can be directly secured to the other element or intervening elements may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or/and" as used herein includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1 to 11, a grating displacement sensor based on longitudinal moire fringe correlation calculation comprises a base 1, a grating adjusting and positioning device 2, a linear laser, a laser interferometer 8, a linear array CCD3, a grating displacement driving component 4 and a grating displacement calculation system. Hereinafter, referring to the coordinate system shown in fig. 1, the X-axis direction is the horizontal longitudinal direction, the positive direction is the front side, the negative direction is the rear side, the Y-axis direction is the horizontal lateral direction, the positive direction is the right side, the negative direction is the left side, the Z-axis direction is the vertical direction, the positive direction is the upper side, and the negative direction is the lower side.
The grating adjusting and positioning device 1 comprises a grating ruler positioning main support 21 and a grating ruler positioning auxiliary support 22 which is arranged opposite to the grating ruler positioning main support 21. As shown in fig. 3 to 6, the grid ruler positioning main support 21 is in a square block shape as a whole, and is fixed on the rear side of the top of the base 1 through bolting for adjusting, fixing and flexibly guiding the position of the grid ruler. Square light through holes 211 are formed in the middle of the grating ruler positioning main support 21, so that light emitted by a light source is received by the linear array CCD3 positioned at the rear side of the grating ruler positioning main support 21 after passing through the grating. The indication grating 5 positioned at the front side of the light transmission hole 211 is fixedly (adhesively connected, bolted or clamped) arranged on the front side of the grating ruler positioning main bracket 21.
The top and bottom sides of the light passing hole 211 are rotatably provided with a transverse adjustment guide pulley 23 with an adjustable vertical position, respectively. Specifically, the grid ruler positioning main support 21 is provided with a transverse L-shaped lever structure 212 symmetrically distributed on two sides of the top end and two sides of the bottom end of the light passing hole 211, a vertical adjusting screw 26 vertically arranged is movably sleeved in the free end of the transverse L-shaped lever structure 212, the end part of the vertical adjusting screw 26 is in threaded connection with the grid ruler positioning main support 21, and the other end of the transverse L-shaped lever structure 212 is fixedly connected onto the top surface or the bottom surface of the grid ruler positioning main support 21 through a flexible hinge structure. The transverse adjusting guide pulleys 23 are rotatably mounted on the front side of the free end of the transverse L-shaped lever structure 212, the axes of the transverse adjusting guide pulleys 23 are horizontally and longitudinally arranged and perpendicular to the front side of the grid ruler positioning main support 21, and the four transverse adjusting guide pulleys 23 are symmetrically distributed at the four corners of the outer side of the light through hole 211 in an up-down and left-right mode. The scale grating 6 which is arranged in parallel on the front side of the indication grating 5 and can horizontally and transversely move is movably clamped between the upper group of transverse adjustment guide pulleys 23 and the lower group of transverse adjustment guide pulleys 23, namely the outer circular surface of the transverse adjustment guide pulleys 23 is in rolling contact with the top surface or the bottom surface of the scale grating 6. The four transverse adjustment guide pulleys 23 are mainly used for adjusting the rotation freedom degree of the scale grating 6 on the X axis besides playing a role in guiding the horizontal and transverse movement of the scale grating 6, and are important adjustment means for ensuring that two gratings overlap to generate longitudinal moire fringes under the action of a point light source. Taking the right end position adjustment of the scale grating 6 as an example, by screwing the corresponding vertical adjusting screw 26 on the transverse L-shaped lever structure 212 on the right side of the upper part, the free end of the transverse L-shaped lever structure 212 can rotate right downwards under the action of the flexible hinge, and simultaneously, by unscrewing the corresponding vertical adjusting screw 26 on the transverse L-shaped lever structure 212 on the right side of the lower part, the free end of the transverse L-shaped lever structure 212 can rotate right downwards under the action of the flexible hinge by the same amplitude, so that the right end of the scale grating 6 is driven by the two transverse adjusting guide pulleys 23 on the right side to move downwards for a certain distance, and the left end position of the scale grating 6 is unchanged, so that the X-axis rotation degree of freedom of the scale grating 6 is adjusted.
Preferably, in order to facilitate screwing or unscrewing operations of the four vertical adjusting screws 26, in this embodiment, screw heads of the corresponding vertical adjusting screws 26 on the bottom two horizontal L-shaped lever structures 212 are also disposed on the top surface of the grid ruler positioning main support 21, so that vertically disposed bolt through holes are formed in the upper two horizontal L-shaped lever structures 212 and in the portion of the grid ruler positioning main support 21 located between the free ends of the upper and lower two horizontal L-shaped lever structures 212, threaded connection holes are formed in the bottom surface of the free ends of the lower horizontal L-shaped lever structures 212 and are in threaded connection with the vertical adjusting screws 26 therein, and upper rod ends of the vertical adjusting screws 26 are sleeved in the bolt through holes.
The grating lines of the scale grating 6 (main grating) and the indication grating 5 are always parallel in the relative motion process to generate longitudinal moire fringes, the grating lines are perpendicular to the motion direction of the scale grating 6, and a certain gap is kept between the two gratings, so that the follow-up problem caused by mutual friction of surfaces and grating line abrasion are avoided.
As shown in fig. 7 and 8, at least one main longitudinal adjustment guide pulley 24 with adjustable horizontal longitudinal position and rolling contact with the rear side of the scale grating 6 is rotatably mounted at both ends of the front side of the scale positioning main support 21, and a sub longitudinal adjustment guide pulley 25 which is arranged in pair with the main longitudinal adjustment guide pulley 24 and rolling contact with the front side of the scale grating 6 is rotatably mounted on the side of the scale positioning sub support 22. In this embodiment, the number of main longitudinal adjustment guide pulleys 24 is 2 symmetrically arranged on the left side of the grid ruler positioning main support 21, and one is arranged near the right side of the grid ruler positioning main support 21, and the single main longitudinal adjustment guide pulley 24 on the right side is positioned on or near the symmetry plane of the two main longitudinal adjustment guide pulleys 24 on the left side.
Specifically, the left end of the front side of the grid ruler positioning main support 21 is respectively provided with a main vertical L-shaped lever structure 213 which is arranged in an up-down symmetrical manner, the right end of the front side is provided with a main vertical L-shaped lever structure 213, a main longitudinal adjusting screw 27 which is horizontally and longitudinally arranged is movably sleeved in the rear side wall of the grid ruler positioning main support 21, the end part of the main longitudinal adjusting screw 27 is in threaded connection with the free end of the main vertical L-shaped lever structure 213, the other end of the main vertical L-shaped lever structure 213 is fixedly connected onto the front side end part of the grid ruler positioning main support 21 through a flexible hinge structure, and a main longitudinal adjusting guide pulley 24 is rotatably arranged on the front side of the free end of the main vertical L-shaped lever structure 213. Bolt through holes are formed in the bottom of the grid ruler positioning auxiliary support 22, waist-shaped grooves which are distributed horizontally and longitudinally are formed in two sides of the front end of the top surface of the base 1 respectively, locking bolt pairs sleeved in the bolt through holes are located in the waist-shaped grooves, and position adjustment of the grid ruler positioning auxiliary support 22 in the horizontal and longitudinal directions can be achieved. An auxiliary vertical L-shaped lever structure 221 which is opposite to the main vertical L-shaped lever structure 213 is arranged in the rear side surface of the grid ruler positioning auxiliary support 22, an auxiliary longitudinal adjusting screw 28 which is horizontally and longitudinally arranged is movably sleeved in the front side wall of the grid ruler positioning auxiliary support 22, the end part of the auxiliary longitudinal adjusting screw 28 is in threaded connection with the free end of the auxiliary vertical L-shaped lever structure 221, the other end of the auxiliary vertical L-shaped lever structure 221 is fixedly connected to the end part of the rear side surface of the grid ruler positioning auxiliary support 22 through a flexible hinge structure, and an auxiliary longitudinal adjusting guide pulley 25 is rotatably arranged on the rear side surface of the free end of the auxiliary vertical L-shaped lever structure 221. The three groups of longitudinal pulleys mainly adjust the horizontal and longitudinal positions of the scale grating 6 besides guiding the horizontal and transverse movement of the scale grating 6, so as to adjust the gap between the scale grating and the indication grating. The gap between the two grating rulers cannot be too large, otherwise, the longitudinal moire fringe period is reduced sharply, and the resolution of the sensor is greatly affected.
Taking the right end longitudinal position adjustment of the scale grating 6 as an example, by screwing a corresponding main longitudinal adjusting screw 27 on a main vertical L-shaped lever structure 213 on the right side, the free end of the main vertical L-shaped lever structure 213 can rotate to the right rear side under the action of a flexible hinge, and simultaneously unscrewing a corresponding auxiliary vertical L-shaped lever structure 221 on a auxiliary vertical L-shaped lever structure 221 on the right side can rotate to the right rear side with the same amplitude under the action of the flexible hinge, so that a main longitudinal adjusting guide pulley 24 and an auxiliary longitudinal adjusting guide pulley 25 on the right side drive the right end of the scale grating 6 to move backwards for a certain distance, and the longitudinal position adjustment of the left end of the scale grating 6 can be synchronously adjusted in the same way, thereby adjusting the distance between the scale grating 6 and the indicating grating 5. Through the mutual cooperation between the plurality of transverse adjustment guide pulleys and the longitudinal adjustment guide pulleys, the limitation of 5 degrees of freedom of the scale grating 6 on the grating positioning main support 21 is realized, and the scale grating 6 can only move along the horizontal and the transverse straight lines.
Because the hinge part transmits force and displacement through material deformation, and the requirements on the material are both soft and strong (high strength and low Young's modulus), in the embodiment, the grid ruler positioning main support 21 and the grid ruler positioning auxiliary support 22 are both made of 7075 aluminum alloy materials with high strength and Young's modulus.
The linear array CCD3 is arranged in parallel with the indication grating 5 and fixedly positioned at the rear side of the light transmission hole 211. The Charge Coupled Device (CCD) image sensor is a high-performance solid imaging device, can convert optical signals into electric signals, is widely applied to image acquisition and measurement detection systems, has the characteristics of high sensitivity, high resolution, large dynamic range, small volume and the like, and has the characteristics of acquiring grating moire fringes by adopting a linear array CCD module. The linear array CCD module can obtain grating moire fringe signals of the whole period after each measurement, and data processing is carried out on the signals of the whole period, so that average errors are facilitated; when the grating ruler moves at a non-uniform speed, the output signal is a moire fringe signal with equal period, which is beneficial to continuous signal processing; when the stripe signal is subjected to direct current drifting, the obtained stripe signal is wholly drifting, does not undulate in one period and contains accurate phase information.
In this embodiment, the linear array CCD3 is an existing linear array CCD TCD1304 module. The CCD module has 3648 photosensitive elements, each of which has a width of 8 μm, and the total length of the photosensitive elements is about 29.1mm. The internal triggering is to collect photoelectric signals of the linear array CCD by using low-frequency pulses generated by an FPGA internal clock as triggering signals. A linear array CCD box 31 arranged in parallel with the grid ruler positioning main support 21 is fixedly arranged at the rear side of the base 1, and the linear array CCD3 is fixedly connected in the front side surface of the linear array CCD box 31 through a screw.
The in-line laser is fixedly arranged towards the front side of the scale grating 6, a point light source is provided for the grating pair, and the grating pair forms longitudinal moire fringes. The linear array CCD3 is most sensitive to red light with the wavelength between 600nm and 650nm, so that a 650nm red light laser with the power of 0.5mW is adopted as the light source. In addition, in order to reduce interference of the ambient light to the linear CCD3, a narrow band filter (not shown) having a center wavelength of 650nm is also added to the optical path. The laser interferometer 8 (model IDS3010, ATTOCUB) is used as a reference sensor, and the measuring point is located on a target plate fixed on the front side of the scale grating 6, so as to record the displacement output of the target plate on the scale grating 6, and compare with the displacement output result calculated by the system by adopting a related normalization correlation algorithm, thereby further verifying the accuracy of the calculation result.
For this purpose, the top surface of the base 1 is also fixedly provided with a laser chuck 7 located at the front side of the light transmission hole 211, and the laser chuck 7 is fixedly provided with the above-mentioned in-line laser and the laser interferometer 8.
Because the clamping surface in the laser chuck 7 and the outer surface of the probe of the laser interferometer 8 are in interference fit (with interference of 0.02 mm), the clamping surface and the outer surface are in interference fit during assembly, so that the laser chuck 7 adopts an inverted Y-shaped chuck in order to meet the assembly process and the use requirement. Specifically, as shown in fig. 10, a through hole 71 is formed in the middle of the laser chuck 7, notch grooves 72 are formed on two sides of the bottom of the through hole 71, a through groove 73 penetrating the top of the laser chuck 7 is formed in the top of the through hole 71, the top of the laser chuck 7 is equally divided into a left part and a right part by the through groove 73, and the clamping parts on the left side and the right side of the laser chuck 7 form a flexible hinge structure at the notch grooves 72. Wherein, bolt through holes are arranged in one side part of the top of the laser chuck 7, and threaded connection holes are arranged in the other side part of the top. By screwing or unscrewing the bolt arranged in the bolt through hole, the clamping part of the laser chuck 7 can be contracted or expanded, so that the probe of the laser interferometer 8 can be quickly assembled in the laser chuck 7.
The structural design of the laser chuck 7 adopts a flexible hinge structure, so that stress generated during interference fit can be dispersed, in addition, as the shell of the probe of the laser interferometer 8 is made of metal, the thermal expansion coefficient of the shell is larger than that of microcrystalline glass material, and the existence of the hinge can absorb the stress and strain generated by the fact that the thermal expansion coefficient of the metal probe is inconsistent with that of the microcrystalline glass, and the deformation of the probe is reduced; the through hole 71 in the laser chuck 7 is cut into three parts by the flexible hinge, so that six points are in contact with the clamping surface on the surface of the probe of the laser interferometer 8, and the stability of the probe of the laser interferometer is ensured.
As shown in fig. 1and 2, the grating displacement driving assembly 4 includes a positioning support 41 fixedly disposed at the outer side of one end of the scale grating 6, a diamond displacement driving amplifying mechanism 42 is fixedly connected to the side surface of the positioning support 41, a piezoelectric actuator 43 is disposed at the internal power input end of the diamond displacement driving amplifying mechanism 42, and the power output end of the diamond displacement driving amplifying mechanism 42 is fixedly connected with the end of the scale grating 6. In addition to the structural configuration, the driving of the displacement output can also significantly affect the performance of the positioning stage. Piezoelectric actuators (PZT) are widely used for micro-nano positioning due to their advantages of large driving force, nano resolution, and fast response. In this embodiment, piezoelectric ceramics are used as the actuator stage for micro-nano positioning. The scale grating 6 is driven to move by driving a displacement amplifying mechanism to carry out output displacement amplification by adopting a piezoelectric stack (model PSt 150/3.5X3.5/20L, core tomorrow, maximum driving voltage 120V can provide maximum travel of 16 mu m), and the input voltage of the piezoelectric stack is given after the signal generator amplifies by a power amplifier. In some cases, PZT uses a bolt preloading mechanism to achieve high bandwidth. In order to achieve a large working space and compact structural dimensions, it is necessary for the actuator to preload the actuator and amplify the output displacement; however, the limited working space cannot meet the requirement of large stroke positioning, so in order to enlarge the movement stroke, a diamond displacement driving amplifying mechanism (as in the prior art) is adopted at the outer side of the PZT, as shown in FIG. 11. Through COMSOL simulation of the diamond displacement amplifying mechanism 42, a 1um side vertical designated displacement (output by PZT) was added to the inner surface, and a 5.7um horizontal displacement was output at the right end face (left end face fixed), and the displacement amplification factor was about 5.7.
The grating displacement calculation system comprises an FPGA (field programmable gate array) in communication connection with the linear array CCD3 and a PC (personal computer) in communication connection with the FPGA, and a normalized cross-correlation algorithm program based on MatLab software is arranged in the PC. As shown in fig. 12 and 13, the high-speed image acquisition system based on the FPGA and the linear array CCD3 mainly comprises the linear array CCD3, the FPGA and the USB interface circuit. The linear array CCD3 receives the optical signals, the linear array CCD3 performs self-scanning under the control of driving pulses of the FPGA, and each pixel point performs photoelectric conversion to convert the optical signals into electric signals and outputs the electric signals through the shift register. The A/D conversion circuit converts the analog signals output by the linear array CCD3 into corresponding digital signals under the control of a sampling clock generated by the FPGA, the corresponding digital signals are collected by the FPGA, and the FPGA transmits the image data to the PC through the USB controller. In this embodiment, an existing Cylone I FPGA board is selected to provide driving signals for the CCD module, and control and driving signals for the AD sampling chip and the USB interface chip.
Two gratings with unequal grating pitches are placed in parallel, and can generate longitudinal moire fringes under the irradiation of parallel light, as shown in fig. 14, the period calculation formula of the longitudinal moire fringes is as follows:
；
Where d 1,d2 is the pitch of the two gratings, respectively. From the above equation, in order to generate moire fringes with a long period, the difference in the pitch between the two gratings needs to be very small, and the requirements on the processing accuracy of the gratings are high.
The invention does not need to be researched based on the traditional optical gate moire fringes, but adopts two gratings with equal grating pitches to be placed in parallel, namely the grating period of the scale grating 6 is the same as the grating period of the indication grating 5; the linear laser is used as a point light source, longitudinal moire fringes can be generated as well, and the fringe period can be flexibly adjusted.
As shown in fig. 15, a longitudinal moire fringe forming mechanism of an equal-pitch grating comprises an indication grating, a scale grating and a point light source, wherein the indication grating is fixedly arranged, the scale grating can horizontally and transversely move, the scale grating is arranged in parallel with the indication grating, the grating period of the scale grating is identical to that of the indication grating, the grating lines of the scale grating and the indication grating are perpendicular to the movement direction of the scale grating, and the point light source is positioned on one side of the scale grating away from the indication grating.
Under the action of a point light source, the length of the grating pitch of the scale grating 6 with the grating pitch of W 1, which is actually projected to the indication grating 5 with the grating pitch of W 2, is amplified to a certain extent and then is changed into W 11, and the calculation formula of the scale grating is as follows according to a similar principle:
；
The two gratings with the grating pitches of W 2 and W 11 form longitudinal moire fringes, after the scale grating 6 moves by one grating period relative to the indication grating 5, the relative movement distance is amplified by the grating pair under the point light source, and the fringe width of the longitudinal moire fringes is as follows:
；
Wherein d 1 is the distance between the scale grating and the indication grating, and d 2 is the vertical distance between the point light source and the grating surface of the scale grating;
the displacement resolution of the grating displacement sensor is expressed as:
；
Wherein N is the number of CCD pixels occupied by one longitudinal moire fringe period, and W is one grating period;
The width of each pixel of the whole pixel output result of the linear array CCD is b, and the following relation exists according to the above formula:
。
when the grating period of the scale grating 6 is the same as the grating period of the indication grating 5, i.e. W 1=W2 =w, then
；
The displacement resolution of the grating displacement sensor is expressed as:
。
according to the gap d 1 between the scale grating 6 and the indicator grating 5, the effect of the grating distance d 2 of the point light source to the scale grating 6 on the stripe width: if d 2 is increased (the light source is positioned away from the grating), the fringe period is increased, so the fringe period can be increased by adjusting the light source distance d 2, and the resolution can be improved. If d 1 is increased, i.e. d 2 is reduced at the same time, it is found from the experimental results that the change in fringe width can be approximately considered to be linear in the range where the change in gap is small, which also indicates that the displacement of the scale grating 6 in the horizontal longitudinal direction can be measured by the size of the moire period.
And simulating longitudinal moire fringe imaging of the equivalent pitch grating by using Zemax optical simulation software. Setting a pair of gratings with grating pitches of 20um, setting a grating ruler interval d 1 to be 30um, setting a distance d 2 between a light source and a scale grating to be 30mm, adopting a rectangular light source as the light source, setting a residual chord angle to be 1, namely a cosine radiator, also called as a lambertian radiator (Lambert radiator), wherein the radiation intensity of the rectangular light source at different angles can be changed according to a cosine formula, the larger the angle is, the weaker the intensity is, so that a linear laser is simulated, the rectangular light source can be approximately considered, and the simulation experiment parameter data are shown in table 1; a rectangular detector is arranged behind the grating to receive light intensity, so that the linear array CCD is simulated, and an optical modeling schematic diagram is shown in FIG. 24.
Table 1 longitudinal moire imaging simulation experiment parameters of equal pitch grating
And enabling the scale grating to move in parallel relative to the indication grating by taking 5um as a step length, and checking the movement condition of the longitudinal moire fringes. As a result of the calculation, as shown in fig. 25, the grating is shifted by one pitch length, and the corresponding moire fringes are also shifted by one period.
After receiving the facula signals modulated by the longitudinal moire fringes, the linear array CCD3 of the imaging array transmits the output voltage signals to a PC through a USB interface, and related data are read by Matlab in the PC for processing and analysis, and a normalized cross correlation algorithm is adopted for real-time displacement calculation.
After the image signal output by the linear array CCD3 is transmitted into a PC, the number of the moving pixels of each two adjacent frames of the linear array CCD3 is calculated on the PC by utilizing a MatLab Normalized Cross Correlation (NCC) algorithm, and the displacement value of the grating is obtained by continuously accumulating the number of the moving pixels. Cross-correlation functions are commonly used in the fields of signal processing, image processing, pattern recognition, etc. In image processing, cross-correlation functions may be used for target detection and tracking; in speech recognition, a cross-correlation function may be used for the matching of sound signals. According to the correlation definition, covariance provides a measure of the strength of correlation between two sets of numbers (or time series). One serious drawback of covariance is that it depends on the amplitude of the two sequences being compared. The output signal of the linear array CCD3 is affected by noise of the linear array CCD3 and unstable light source, and has fluctuation in amplitude. The main advantage of adopting the normalized form of covariance, namely Normalized Cross Correlation (NCC), is that the method is insensitive to the linear change of the signal amplitude in two comparison signals, and can greatly reduce the influence caused by the linear fluctuation of the signal amplitude. And the correlation coefficient is limited to the range of-1, the detection threshold is set much easier than the cross correlation.
From the known pearson correlation coefficient between two sets of one-dimensional signals (variables) X and Y, the formula is:
。
as shown in fig. 16, a normalized cross-correlation sub-pixel registration algorithm applied to a grating sensor includes the steps of:
S1, generating longitudinal moire fringes by a grating pair placed in parallel under a proper light source, receiving optical signals of the longitudinal moire fringes by a linear array CCD, processing and converting the optical signals into digital signals, and transmitting the digital signals to a PC;
s2, the PC machine runs a normalized cross-correlation algorithm program, and the acquired data are processed to obtain the output displacement of the grating displacement sensor;
The method comprises the following specific steps:
S2.1, two sub-set time sequences f i=[fp,fp+1,……,fp+m-1],gi=[gq,gq+1,……,gq+m-1 of the same continuous data points with the length of m, which are extracted from two frames of discrete time sequences f= [ f 0,f1,……,fn-1],g=[g0,g1,……,gn-1 ] with n discrete points output by the linear array CCD;
S2.2, a normalized cross-correlation algorithm is defined as:
；
Wherein p, q, m are positive integers, and p, q epsilon [0, n-m+1], m epsilon [2, n ], ，/>Representing two groups of discrete sequences output by linear array CCD，/>；
S2.3, substituting the data of the two subsets of time sequences into a normalized cross-correlation algorithm for calculation.
And (3) carrying out a test experiment by adopting the device and a normalized cross-correlation algorithm. A triangular wave voltage of 40V and 0.2Hz is applied to the piezoelectric actuator 43, and displacement is output through the diamond displacement amplifying mechanism 42 to push the scale grating 6 to move. In the process, the laser interferometer 8 is used for recording the displacement of the target plate on the scale grating 6, and the displacement output result calculated by the normalized cross-correlation algorithm is compared, as shown in fig. 17. One curve is the displacement output by the laser interferometer, the other curve is the displacement output by the grating sensor, and the result shows that the consistency of the two is better.
And (3) changing the positions of the light source and the grating, and performing multiple groups of experiments, wherein fig. 18 shows the test result that the light source is nearer to the grating, the displacement measured by the laser interferometer in one period is 28635nm, the number of moving pixels corresponding to the grating sensor is 3137, and the displacement corresponding to each pixel point is 9.13nm. Fig. 19 shows the test result after increasing the distance, wherein the displacement measured by the laser interferometer in one period is 28589nm, the number of moving pixels corresponding to the grating sensor is 3332, and the displacement corresponding to each pixel point is 8.58nm.
And (3) testing the resolution of the grating sensor:
a step wave voltage of 1.6V was applied to the piezoelectric actuator 43, and each step-up amplitude was 0.23V.
As shown in fig. 20 and 21, the grating sensor can sense the change of the micro displacement, and can output the jump step of the whole pixel point, and the displacement resolution corresponding to one pixel is about 11.9nm. It can be seen that the number of output steps of the grating sensor is less than the number of steps measured by the laser interferometer at many positions. This is because the pixel number and pixel density of the linear array CCD are limited, the subdivision of the whole pixel can only achieve the effect, the sub-pixel interpolation subdivision is carried out on the whole pixel output result of each line of the linear array CCD by adopting a spline interpolation mode, and then the correlation calculation is carried out by a normalized cross correlation algorithm, so that the result is shown in fig. 22. After the sub-pixel interpolation is carried out, the number of steps which can be reflected by the grating sensor in one period is increased, and the sub-pixel resolution is realized basically in synchronization with the test result of the laser interferometer. As shown in fig. 23, the resolution achievable by the grating sensor is at least 8.6nm, based on the existing test results.
The foregoing description is only illustrative of the present invention and is not intended to limit the scope of the invention, and all equivalent structures or equivalent processes or direct or indirect application in other related technical fields are included in the scope of the present invention.
Claims (9)
1. A grating displacement sensor based on longitudinal moire correlation calculation, characterized in that: the device comprises a base, a grating adjusting and positioning device, a linear laser, a laser interferometer, a linear array CCD, a grating displacement driving component and a grating displacement computing system;
the grating adjusting and positioning device comprises a grating ruler positioning main support and a grating ruler positioning auxiliary support which is arranged opposite to the grating ruler positioning main support, wherein a light passing hole is formed in the middle of the grating ruler positioning main support, two sides of the top and two sides of the bottom of the light passing hole are respectively provided with a transverse adjusting guide pulley with an adjustable vertical position in a rotating mode, an indication grating which is positioned at the front side of the light passing hole is fixedly arranged on the front side surface of the grating ruler positioning main support, a scale grating which is parallel to the front side of the indication grating and can horizontally and transversely move is movably clamped between the upper and lower sets of transverse adjusting guide pulleys, and the scale grating and the indication grating form a grating pair;
The two ends of the front side surface of the grating ruler positioning main support are rotatably provided with at least one main longitudinal adjusting guide pulley which is adjustable in horizontal longitudinal position and in rolling contact with the rear side surface of the grating ruler, and the side surface of the grating ruler positioning auxiliary support is rotatably provided with an auxiliary longitudinal adjusting guide pulley which is arranged in a matched mode with the main longitudinal adjusting guide pulley and in rolling contact with the front side surface of the grating ruler;
The linear laser is fixedly arranged at the front side of the scale grating, a point light source is provided for the grating pair, and the grating pair forms longitudinal moire fringes;
the laser interferometer detects the displacement of the scale grating to obtain reference displacement output;
The linear array CCD is arranged in parallel with the indication grating and fixedly positioned at the rear side of the light transmission hole;
The grating displacement driving assembly comprises a positioning bracket fixedly arranged at the outer side of one end of the scale grating, the side surface of the positioning bracket is fixedly connected with a diamond displacement driving amplifying mechanism, the internal power input end of the diamond displacement driving amplifying mechanism is provided with a piezoelectric actuator, and the power output end of the diamond displacement driving amplifying mechanism is fixedly connected with the end part of the scale grating;
the grating displacement calculation system comprises an FPGA (field programmable gate array) in communication connection with the linear array CCD and a PC (personal computer) in communication connection with the FPGA, wherein a normalized cross-correlation algorithm program based on MatLab software is arranged in the PC.
2. A grating displacement sensor based on longitudinal moire correlation calculations as defined in claim 1, wherein: the grid ruler positioning main support is provided with a transverse L-shaped lever structure symmetrically distributed on the two sides of the top end and the two sides of the bottom end of the light passing hole, a vertical adjusting screw which is vertically arranged is movably sleeved in the free end of the transverse L-shaped lever structure, the end part of the vertical adjusting screw is in threaded connection with the grid ruler positioning main support, the other end of the transverse L-shaped lever structure is fixedly connected to the top surface or the bottom surface of the grid ruler positioning main support through a flexible hinge structure, and the transverse adjusting guide pulley is rotatably arranged on the front side surface of the free end of the transverse L-shaped lever structure;
the utility model discloses a grid ruler positioning main support, including grid ruler positioning main support, flexible hinge structure, main vertical L type lever structure, main vertical adjusting pulley, main vertical L type lever structure's leading flank tip is provided with at least one main vertical L type lever structure respectively at grid ruler positioning main support's leading flank both ends, movable sleeve is equipped with the main vertical adjusting screw of horizontal vertical setting in the back lateral wall of grid ruler positioning main support, main vertical adjusting screw's tip and the free end threaded connection of main vertical L type lever structure, main vertical L type lever structure's the other end passes through flexible hinge structure fixed connection on grid ruler positioning main support's leading flank tip, main vertical adjusting guide pulley rotates to be installed on main vertical L type lever structure's free end leading flank.
3. A grating displacement sensor based on longitudinal moire correlation calculations as claimed in claim 2, wherein: the auxiliary vertical L-shaped lever structure which is opposite to the main vertical L-shaped lever structure is arranged in the rear side surface of the auxiliary grid ruler positioning support, an auxiliary longitudinal adjusting screw which is horizontally and longitudinally arranged is movably sleeved in the front side wall of the auxiliary grid ruler positioning support, the end part of the auxiliary longitudinal adjusting screw is in threaded connection with the free end of the auxiliary vertical L-shaped lever structure, the other end of the auxiliary vertical L-shaped lever structure is fixedly connected onto the end part of the rear side surface of the auxiliary grid ruler positioning support through a flexible hinge structure, and the auxiliary longitudinal adjusting guide pulley is rotatably arranged on the rear side surface of the free end of the auxiliary vertical L-shaped lever structure.
4. A grating displacement sensor based on longitudinal moire correlation calculations as defined in claim 1, wherein: the laser chuck is fixedly arranged on the top surface of the base and positioned at the front side of the light transmission hole, and a linear laser light source and a laser interferometer are fixedly arranged on the laser chuck.
5. A grating displacement sensor based on longitudinal moire correlation calculations as defined in claim 4, wherein: the middle part of the laser chuck is provided with a through hole, both sides of the bottom of the through hole are respectively provided with a notch groove, the top of the through hole is provided with a through groove penetrating through the top of the laser chuck, one side part of the top of the laser chuck is internally provided with a bolt through hole, and the other side part of the top of the laser chuck is internally provided with a threaded connection hole.
6. A grating displacement sensor based on longitudinal moire correlation calculations as claimed in any one of claims 1 to 5, wherein: the grid ruler positioning main support and the grid ruler positioning auxiliary support are both made of 7075 aluminum alloy materials.
7. A grating displacement sensor based on longitudinal moire correlation calculations as claimed in any one of claims 1 to 5, wherein: under the action of a point light source, the length of the grating pitch of the scale grating with the grating pitch of W 1, which is actually projected to the indication grating with the grating pitch of W 2, is amplified to a certain extent and then becomes W 11, and the calculation formula is as follows:
；
The two gratings with the grating pitches of W 2 and W 11 form longitudinal moire fringes, after the scale grating relatively indicates the grating to move for one grating period, the corresponding relative movement distance is amplified by the grating pair under the point light source, and the fringe width of the longitudinal moire fringes is as follows:
；
Wherein d 1 is the distance between the scale grating and the indication grating, and d 2 is the vertical distance between the point light source and the grating surface of the scale grating;
the displacement resolution of the grating displacement sensor is expressed as:
；
Wherein N is the number of CCD pixels occupied by one longitudinal moire fringe period, and W is one grating period;
The width of each pixel of the whole pixel output result of the linear array CCD is b, and the following relation exists according to the above formula:
。
8. A grating displacement sensor based on longitudinal moire correlation calculations as defined in claim 7, wherein: the grating period of the scale grating is the same as that of the indication grating, i.e. W 1=W2 =W, then
；
The displacement resolution of the grating displacement sensor is expressed as:
。
9. a grating displacement sensor based on longitudinal moire correlation calculations as defined in claim 8, wherein: two subsets of time series of identical consecutive data points of length m extracted from two discrete time series of n discrete points, the normalized cross-correlation algorithm being defined as:
；
Wherein p, q, m are positive integers, and p, q epsilon [0, n-m+1], m epsilon [2, n ], ，/>Representing two groups of discrete sequences output by linear array CCD，/>。
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Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1370307A (en) * | 1970-10-23 | 1974-10-16 | Bendix Corp | Apparatus for and method of determinging displacements using moire fringes |
| JP2000205819A (en) * | 1999-01-13 | 2000-07-28 | Olympus Optical Co Ltd | Optical displacement sensor |
| CN101000252A (en) * | 2006-12-01 | 2007-07-18 | 华中科技大学 | Double-raster displacement sensor |
| JP2008232970A (en) * | 2007-03-23 | 2008-10-02 | Citizen Holdings Co Ltd | Displacement measuring device |
| CN107796310A (en) * | 2017-06-01 | 2018-03-13 | 常州秦宁迈超电子科技有限公司 | The device and its measuring method of grating displacement sensor monocycle error in dipping |
| CN110487219A (en) * | 2019-08-15 | 2019-11-22 | 卢振武 | A kind of detection system and its detection method of movement mechanism straightness |
| CN114018451A (en) * | 2021-12-07 | 2022-02-08 | 台州安奇灵智能科技有限公司 | High-resolution driving shaft torque sensing system based on moire fringe principle |
-
2024
- 2024-03-01 CN CN202410237337.8A patent/CN117804348B/en active Active
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1370307A (en) * | 1970-10-23 | 1974-10-16 | Bendix Corp | Apparatus for and method of determinging displacements using moire fringes |
| JP2000205819A (en) * | 1999-01-13 | 2000-07-28 | Olympus Optical Co Ltd | Optical displacement sensor |
| CN101000252A (en) * | 2006-12-01 | 2007-07-18 | 华中科技大学 | Double-raster displacement sensor |
| JP2008232970A (en) * | 2007-03-23 | 2008-10-02 | Citizen Holdings Co Ltd | Displacement measuring device |
| CN107796310A (en) * | 2017-06-01 | 2018-03-13 | 常州秦宁迈超电子科技有限公司 | The device and its measuring method of grating displacement sensor monocycle error in dipping |
| CN110487219A (en) * | 2019-08-15 | 2019-11-22 | 卢振武 | A kind of detection system and its detection method of movement mechanism straightness |
| CN114018451A (en) * | 2021-12-07 | 2022-02-08 | 台州安奇灵智能科技有限公司 | High-resolution driving shaft torque sensing system based on moire fringe principle |
Non-Patent Citations (1)
| Title |
|---|
| 基于泰伯-莫尔条纹的激光波前曲率半径测量;陈好;张浩;樊红英;蒋泽伟;贾静;胡绍云;孟庆安;;激光技术;20170531(第02期);全文 * |
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