CN113029006A

CN113029006A - Detection device and detection method based on moire fringes

Info

Publication number: CN113029006A
Application number: CN202110459992.4A
Authority: CN
Inventors: 彭川黔
Original assignee: Chongqing University of Technology
Current assignee: Chongqing University of Technology
Priority date: 2021-04-27
Filing date: 2021-04-27
Publication date: 2021-06-25
Anticipated expiration: 2041-04-27
Also published as: CN113029006B

Abstract

The invention relates to a detection device and a detection method based on moire fringes, wherein the device comprises an area array light source and an area array photoelectric detector, the light source and the photoelectric detector are arranged in parallel and can relatively slide along the plane where the light source and the photoelectric detector are arranged, an imaging lens is also arranged between the light source and the photoelectric detector in parallel, a light beam emitted by the light source is imaged on the photoelectric detector after passing through the imaging lens, and the area array light source is electrically connected with a programming controller so as to control the area array light source to display set content information through the programming controller; the photoelectric detector is electrically connected with the control computer so as to control the photoelectric detector to read signals according to the set reading area through the control computer, and the signals read by the photoelectric detector are processed through the control computer. The invention can realize the displacement measurement application of the moire fringes through simple structure replacement and a corresponding method, does not need a grating and a strict assembly process to ensure the position of a physical structure, has lower cost and is beneficial to ensuring the measurement precision.

Description

Detection device and detection method based on moire fringes

Technical Field

The invention belongs to the technical field of metering by taking an optical method as a characteristic in physical measurement, and particularly relates to a detection device and a detection method based on moire fringes.

Background

The engineering value of moire fringe pattern has been recognized and applied by people, the most widely applied field is relative displacement measurement of grating, and also applied products such as grating ruler, in order to improve the measurement accuracy, the prior art is as follows: CN101571377A, CN102706373A, CN105627921A, CN106556342A, etc., have also been studied and innovated for the subdivision and measurement method of grating stripes and image coding. However, the moire fringes of the current grating ruler application products are utilized, which can be seen in fig. 1, and are all performed by adopting a point light source 100, a lens 101, two metering gratings (one is a scale grating 102 and the other is an indicating grating 103) and a photoelectric element 105, specifically, the point light source, the lens, one metering grating and the photoelectric element are integrated into a reading detection head, the reading detection head moves relative to the other metering grating, a light beam of the point light source passes through the lens, transmitted light shielded by the two metering gratings is imaged on the photoelectric element, an inclination angle theta is formed between a plurality of equally spaced grooves on the two metering gratings, the measurement of geometric quantity (one-dimensional measurement) is realized by utilizing the moire fringe phenomenon of the gratings, that is, the relative movement of the grating makes the intensity of the transmitted light change periodically, the photoelectric element changes the light intensity signal into an electric signal which changes periodically, and the relative displacement of the grating is obtained by the change of the electric signal.

However, the difficulty of processing and manufacturing the measurement grating is high, a large number of parallel slits (nicks, thousands or even tens of thousands of slits are engraved in the width of 1 cm) with equal width and equal spacing are required to be engraved on a glass sheet or a surface coated with a metal layer, the parallel slits are engraved by a precise engraving machine or are obtained by adopting a photoetching copying process of evaporating chrome plating on a glass substrate, and the distance between adjacent scribes is called as the grating pitch, the grating pitch or the grating constant and is the reference of displacement measurement. The cost of the metering grating is high, and the difficulty of further improving the manufacturing precision is also great. In addition, when the grating is assembled as a product, the requirement on the installation precision between the two metering gratings is very high, and the requirement on the relative position of the designed and used assembly must be met, otherwise, the use effect of the product is seriously influenced, so that the assembly process is complex and the operation difficulty is high.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a detection apparatus and a detection method based on moire fringes, which avoid the problem that only a grating is needed to be used in the measurement of geometric quantities based on moire fringes, and realize another effective application of moire fringes through simple structure replacement and a corresponding method.

In order to solve the technical problems, the invention adopts the following technical scheme:

a detection device based on moire fringes comprises an area array light source and an area array photoelectric detector, wherein the area array light source and the area array photoelectric detector are arranged in parallel and can relatively slide along the plane where the area array light source and the area array photoelectric detector are arranged, an imaging lens is arranged between the area array light source and the area array photoelectric detector in parallel, and light beams emitted by the area array light source are imaged on the area array photoelectric detector after passing through the imaging lens;

the light source of the area array is electrically connected with the programming controller so as to control the light source of the area array to display set content information through the programming controller;

the photoelectric detector is electrically connected with a control computer so as to control the photoelectric detector to read signals according to a set reading area through the control computer, and the control computer is used for processing the signals read by the photoelectric detector.

Further perfecting the technical scheme, the light source of the area array is a planar display screen with pixel point distance meeting the measurement precision requirement; the photoelectric detector is an area array CCD.

Furthermore, the vertical distance from the imaging lens to the light source or the photoelectric detector between the light source and the photoelectric detector of the area array is adjustable.

The invention also relates to a detection method based on the moire fringes, which is implemented based on the detection device based on the moire fringes, and the set content information is a plurality of fringes with equal width and equal spacing; the set reading area is a plurality of equal-width and equal-interval fringe reading bands which correspond to the plurality of equal-width and equal-interval fringes and can obtain moire fringe data; it will be appreciated that, in order to obtain moire data, the fringes and fringe read bands are relatively inclined at an angle θ (which meets the measurement accuracy requirement) so as to obtain moire data;

the light source and the photoelectric detector of the area array slide relatively in the direction perpendicular to the stripe or the stripe reading band, the photoelectric detector reads and obtains moire stripe data, and the linear displacement value between the light source and the photoelectric detector of the area array can be obtained by processing the moire stripe data through the control computer.

Optionally, the set content information is a two-dimensional lattice, and all points in the two-dimensional lattice are equally spaced in the vertical and horizontal directions; the set reading area is a longitudinal and transverse stripe reticular reading band which corresponds to the two-dimensional lattice and can obtain moire fringe data, or a two-dimensional lattice reading band which corresponds to the two-dimensional lattice and can obtain moire fringe data; it is understood that, in order to obtain moire data, the longitudinal and transverse stripe mesh read bands or the two-dimensional lattice read bands have an inclination angle θ (satisfying a measurement accuracy requirement) with respect to the two-dimensional lattice so as to obtain two-dimensional moire data;

the light source and the photoelectric detector of the area array slide relatively, the photoelectric detector can read and obtain two-dimensional moire fringe data, and the two-dimensional relative sliding displacement value between the light source and the photoelectric detector of the area array can be obtained by processing the two-dimensional moire fringe data through the control computer.

Further, the set content information further includes a rough measurement area.

Compared with the prior art, the invention has the following beneficial effects:

according to the detection device based on the moire fringes, the area array light source replaces a point light source and an indication grating in a similar grating ruler basic structure, the area array photoelectric detector and the control computer replace a photoelectric element and a scale grating in the similar grating ruler basic structure, the effective application of the moire fringes can be realized, the manufacturing of a grating with a difficult pure physical structure is not needed, and the cost is lower. When the device is used, the stripes or the two-dimensional dot matrixes are displayed through the light source of the area array, the stripes or the two-dimensional dot matrixes are imaged on the photoelectric detector by the imaging lens, the photoelectric detector is correspondingly screened and read, the width and the distance of the stripes and the dot matrixes can be combined with the control part, and the distance among the light source, the imaging lens and the photoelectric detector is changed to control the display and the reading, the adjustment is flexible, the use is convenient, in addition, the inclination angle theta is also set in a mode of controlling the display, and the situation that the!is not required to be ensured through a strict assembly process! The cost can be further reduced, and the use and measurement precision of the product can be guaranteed and adjusted.

When the invention is applied specifically, the invention can be applied to the measurement of small relative displacement amount by considering that the sizes of the display screen and the CCD are not suitable to be overlong or overlarge. In addition, the device can also be applied to an autocollimator instrument, the angle change of the measured surface is measured by the position change of the reflected light beam of the measured surface imaged on the CCD, the display screen and the CCD do not need to move relatively, the display screen and the CCD are fixed, and the overlarge area is not needed. Other possible applications are not detailed again, nor are they particularly limited.

Drawings

Fig. 1 is a structural schematic diagram of a grating ruler currently applying moire fringes to perform one-dimensional displacement measurement in the background art;

FIG. 2 is a schematic diagram of a moire fringe based detection device according to an exemplary embodiment;

FIG. 3 is a schematic diagram of a display screen with bright stripes in the use (detection method) of the detection device according to the embodiment;

FIG. 4 is a schematic diagram of a fringe reading band set by a CCD in a use (detection method) of the detection apparatus according to the embodiment;

FIG. 5 is a schematic diagram of one-dimensional moire fringe data read by CCD screening in the detection device (detection method) according to an embodiment;

FIG. 6 is a schematic diagram of signals read by the CCD screening method based on FIG. 5;

FIG. 7 is a schematic diagram of signals read by the CCD screening with the addition of rough measurement areas based on FIG. 6;

FIG. 8 is a diagram of a display screen with a set-up two-dimensional array of illuminated dots during use of the detection apparatus (detection method) according to an embodiment;

FIG. 9 is a schematic diagram of a cross-striped mesh read band set by a CCD in a detection apparatus (detection method) according to an embodiment;

fig. 10 is a schematic diagram of two-dimensional moire fringe data positive fringes read by CCD screening in the use of the detection device (detection method) according to the embodiment;

FIG. 11 is a schematic diagram of a two-dimensional matrix reading band set by a CCD in the use (detection method) of the detection apparatus according to the embodiment;

fig. 12 is a schematic view (with an increased rough area) of two-dimensional moire data reverse-fringe read by CCD screening in the use of the detection apparatus (detection method) according to the embodiment;

the device comprises a point light source 100, a lens 101, a scale grating 102, an indication grating 103, a photoelectric element 105, an area array light source 1, an imaging lens 2, a photoelectric detector 3 and a signal area 4.

Detailed Description

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

Referring to fig. 2, a detection apparatus based on moire fringes according to an embodiment includes an area array light source 1 and an area array photodetector 3, where the area array light source 1 and the area array photodetector 3 are arranged in parallel and can relatively slide along a plane where the area array light source 1 and the area array photodetector 3 are located, an imaging lens 2 is further arranged between the area array light source 1 and the area array photodetector 3 in parallel, and a light beam emitted by the area array light source 1 is imaged on the photodetector 3 through the imaging lens 2. During implementation, the light source can be arranged on the sliding carrier, the photoelectric detector and the imaging lens are relatively fixed to serve as fixed items, the vertical distance from the imaging lens to the photoelectric detector is adjustable, and the area array light source image can be zoomed and imaged on the photoelectric detector according to the required proportion, so that the effect of adjusting the stripe distance can be achieved.

The light source 1 of the area array is electrically connected with a programming controller (not shown in the figure) so as to control the light source 1 of the area array to display the set content information through the programming controller;

the photodetector 3 is electrically connected to a control computer (not shown in the figure) to control the photodetector 3 to read signals according to a set reading area through the control computer, and to process the signals read by the photodetector 3 through the control computer.

The light source 1 of the area array is a planar display screen with pixel point distance meeting the measurement precision requirement; the photoelectric detector 3 is an area array CCD.

A display screen having a smaller pixel pitch, for example, 0.1245mm, is preferable.

The invention also provides a detection method of the detection device, and when the device is used in particular, measurement can be conveniently carried out in a one-dimensional or two-dimensional mode.

The one-dimensional measurement is: the set content information is a plurality of stripes with equal width and equal interval which meet the measurement precision requirement, namely, the display screen is lighted up according to the stripe areas with equal width and equal interval, which can be seen in fig. 3; the set reading area is a plurality of equal-width and equal-spacing fringe reading bands which correspond to the plurality of equal-width and equal-spacing fringes and can obtain moire fringe data, the width and the spacing of the bands correspond to display fringes of a display screen, and the width and the spacing can be seen in fig. 4, namely, screening reading is carried out on a bright (white) area of a CCD (charge coupled device) according to a graph, and a dark (black) area is omitted; thus, moire fringe data can be screened and read by the CCD, as shown in fig. 5; in the embodiment, the CCD is assumed to be fixed, the display screen moves, the adjustment angle of the bright stripes of the display screen is 0, the stripe reading band and the bright stripes of the display screen form an included angle theta, and the direction of the moire stripes read by the CCD screening and the moving direction of the display screen form an included angle theta/2; in implementation, the moire fringe data image can be extracted by a control computer through an artificial rotation angle-theta/2, referring to fig. 6, so that the extraction of the moire fringe position information can be more convenient.

When the display screen moves for a period T along the moving direction, the moire fringes move for a period along the vertical moving direction, the intensity data of the moire fringes are summed along the fringe direction to obtain periodic variation data, and the phase information of the periodic variation data can be solved through a proper mathematical method (such as fast Fourier transform, function fitting and the like) to obtain the fringe movement amount of the display screen, so that the one-dimensional relative displacement measurement is realized, the solving process is the prior art, and the description is not expanded here. After moving for one period, the image will repeat, and the different periods can be distinguished by special methods, such as: can set up a gross survey region (dark space) at the display screen center, can appear same signal area 4 (dark space) like this on CCD, can see figure 7, when the display screen removed, the dark space will be along with the display screen moves together, and moire fringe moves a cycle, and signal area 4 will move a display screen fringe interval, can conveniently judge through the position gross survey of judging signal area 4 and move the cycle of locating. During implementation, the rough measurement area can be set to be an independent bright area (only the bright area has no stripes), the bright area and the stripe area are alternately displayed by controlling the light source of the area array, the accuracy of bright area position judgment is improved, the difficulty of a bright area position judgment algorithm is reduced, the rough measurement is carried out on the signal area 4 corresponding to the bright area position, and the rough measurement can be selected according to actual needs during specific use.

The two-dimensional measurement is: the set content information is a two-dimensional lattice which meets the requirement of measurement accuracy, all points in the two-dimensional lattice are equal in width and equal in spacing in the longitudinal and transverse directions, namely, bright spots which are displayed in the two-dimensional lattice with equal width and equal in spacing are lighted up on the display screen, and the method can be seen in fig. 8; the set reading area is a crisscross stripe reticular reading band which corresponds to the two-dimensional lattice and can obtain moire fringe data, the crisscross stripe reticular reading band has equal width and equal interval and corresponds to the two-dimensional lattice displayed by the display screen, and referring to fig. 9, namely, a CCD (charge coupled device) is used for screening and reading a bright (white) area according to a diagram, and a dark (black) area is omitted; in this way, the CCD can screen and read the positive stripe data of the two-dimensional moire fringes, as shown in fig. 10 (the artificial rotation angle is performed to extract information);

when the light source and the photoelectric detector of the area array slide relatively, the two-dimensional moire fringe data can be processed by combining the change of the moire fringe intensity data through the control computer, the intensity data changing periodically from X, Y direction can be obtained by summing X, Y directions along the motion direction of the two-dimensional lattice respectively, and then the two-dimensional relative sliding displacement value between the light source and the photoelectric detector is obtained.

During two-dimensional measurement, the set reading area may also be a two-dimensional lattice reading band corresponding to the two-dimensional lattice and capable of obtaining moire fringe data, each reading point of the two-dimensional lattice reading band has equal width and equal interval and corresponds to the two-dimensional lattice displayed on the display screen, as shown in fig. 11, that is, the CCD performs screening reading according to the bright (white) area of the graph, and the dark (black) area is left; in this way, the CCD can screen and read the inverse fringe data of the two-dimensional moire fringes, as shown in fig. 12 (the artificial rotation angle is performed to extract information); the two-dimensional relative slip displacement value between the light source and the photoelectric detector can be obtained through control calculation processing, which is the same as the processing principle of the positive texture.

It will be appreciated that, in order to obtain moire data, the cross-striped mesh or two-dimensional lattice of read bands is inclined at an angle θ relative to the two-dimensional lattice to obtain two-dimensional moire data.

During measurement, as described above, the moire fringe intensity data obtained by the CCD periodically changes, and the period T thereof can be calculated by the preset fringe pitch and the fringe inclination angle θ, or can be calculated by performing fourier transform on the data, and after each period T, the intensity data returns to the original state and is repeated. When the displacement between the light source and the photoelectric detector is larger than T, the original shape of the intensity data is repeated, so that the identification and the measurement of the displacement are inconvenient, the displacement corresponding to the periodicity needs to be superposed, if a rough measurement area is preset and displayed on the display screen, the rough measurement area can be a bright spot or a dark area, a corresponding signal area 4 can be obtained on the CCD, please continue to refer to FIG. 12, the period corresponding to the displacement can be conveniently determined, so that the purpose of rough side is achieved, the measurement calculation process is simplified, and the accuracy of the measurement result is improved.

In implementation, the rough measurement region only needs to represent the period of the measured data, that is, only the resolution precision of T needs to be realized. If the magnification of the moire fringes is set to be 10 times and the CCD pixel pitch is set to be 2 micrometers, the moire fringe movement measurement precision of 0.1 pixel can be realized through calculation, and the displacement measurement precision of 20nm can be correspondingly realized.

When in implementation, all points in the two-dimensional lattice are equal in width and equal in spacing in the longitudinal and transverse directions, the width and spacing of the two-dimensional lattice can be set according to the measurement precision requirement, for example, with a pixel pitch of 0.1245mm for the display screen, a pixel pitch of 2 μm for the CCD, assuming a two-dimensional lattice pitch of 4 display screen pixels (0.498 mm), the image of the display screen is reduced to 1/6 through the imaging lens, the image point distance becomes 0.083mm, corresponding to 41.5 pixels on the CCD (in practice, the display screen, the imaging lens and the CCD spacing can be properly adjusted to realize different dot pitches, for example, the dot pitch is just integral multiple of the CCD pixel pitch), by setting theta to be 2.86 degrees and about 0.05rad, the moire fringe spacing is about 1.66mm, and when the relative position movement between the display screen and the CCD is 0.083mm, the moire fringe moves by 1.66mm, and if the measurement precision of the moire fringe position movement is 1 μm, the relative position movement of the display screen and the CCD can realize the measurement precision of 50 nm.

Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.

Claims

1. A moire fringe based detection device, comprising: the imaging device comprises an area array light source and an area array photoelectric detector, wherein the area array light source and the area array photoelectric detector are arranged in parallel and can relatively slide along the plane where the area array light source and the area array photoelectric detector are arranged, an imaging lens is arranged between the area array light source and the area array photoelectric detector in parallel, and light beams emitted by the area array light source are imaged on the photoelectric detector after passing through the imaging lens;

2. A moire pattern based detection device as claimed in claim 1, wherein: the light source of the area array is a planar display screen; the photoelectric detector is an area array CCD.

3. A moire pattern based detection device as claimed in claim 1, wherein: between the light source and the photoelectric detector of the area array, the vertical distance from the imaging lens to the light source or the photoelectric detector is adjustable.

4. A detection method based on moire fringes is characterized in that: the method is implemented based on a detection device based on moire fringes as claimed in any one of claims 1-3, wherein the set content information is a plurality of fringes with equal width and equal spacing; the set reading area is a plurality of equal-width and equal-interval fringe reading bands which correspond to the plurality of equal-width and equal-interval fringes and can obtain moire fringe data;

5. A detection method based on moire fringes is characterized in that: the method is implemented based on a moire fringe based detection device as claimed in any one of claims 1-3, wherein the set content information is a two-dimensional lattice, and all points in the two-dimensional lattice are equally wide and equally spaced in the longitudinal and transverse directions; the set reading area is a longitudinal and transverse stripe reticular reading band which corresponds to the two-dimensional lattice and can obtain moire fringe data, or a two-dimensional lattice reading band which corresponds to the two-dimensional lattice and can obtain moire fringe data;

6. A moire-based detection method as claimed in claim 4 or 5, characterized in that: the set content information further comprises a rough measurement area.