CN112082490B - Displacement sensor based on Talbot image and COMS camera structure - Google Patents
Displacement sensor based on Talbot image and COMS camera structure Download PDFInfo
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- CN112082490B CN112082490B CN202011129953.XA CN202011129953A CN112082490B CN 112082490 B CN112082490 B CN 112082490B CN 202011129953 A CN202011129953 A CN 202011129953A CN 112082490 B CN112082490 B CN 112082490B
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- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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Abstract
The invention belongs to the technical field of displacement sensors, and particularly relates to a displacement sensor based on a Talbot image and a COMS camera structure, which comprises a light source, a convex lens, a grating and a COMS camera, wherein the light source is arranged at the focus of the convex lens, scattered light emitted by the light source becomes parallel light beams after passing through the convex lens, the grating is arranged in the light path direction of the parallel light beams, the parallel light beams are subjected to diffraction interference through the grating, the parallel light beams form a Talbot image after the grating, and the COMS camera is arranged on the Talbot image at any level; the invention combines the light source displacement and the Talbot image period through optical design, measures the Talbot image period through the COMS camera so as to realize the measurement of the light source displacement and realize the output of displacement signals, only uses the light source, the convex lens, the grating and the COMS camera device, and has simpler structure; meanwhile, collimation of the light source can be realized through measurement of the Talbot image period, and the positioning precision is further improved. The invention is used for measuring the light micro-displacement.
Description
Technical Field
The invention belongs to the technical field of displacement sensors, and particularly relates to a displacement sensor based on a Talbot image and a COMS camera structure.
Background
Displacement measurement is an important field of modern mechanical industry, and particularly in the field of micro-displacement measurement, a displacement measurement system with high resolution and tiny volume needs to be realized. Among them, the measurement of the nano-grating has the advantages of high precision, high resolution and the like, so that the nano-grating is widely applied. At present, the main principle of a single-layer grating micro-displacement sensor is that a certain level of diffracted light diffracted by a light beam through a grating is overlapped to form interference fringes through a designed light path, so that the displacement is measured. However, this method generally has the following problems at present: 1. polarizing optical elements such as polarizing plates and glass slides are large in number, complex in structure, high in cost and difficult to miniaturize; 2. there is no light source collimation location structure.
Disclosure of Invention
Aiming at the technical problems that the traditional single-layer grating micro-displacement sensor is complex in structure and cannot be used for collimating and positioning a light source, the invention provides the displacement sensor based on the Talbot image and COMS camera structure, which is simple in structure, high in positioning accuracy and high in efficiency.
In order to solve the technical problems, the invention adopts the technical scheme that:
a displacement sensor based on a Talbot image and a COMS camera structure comprises a light source, a convex lens, a grating and a COMS camera, wherein the light source is arranged at the focus of the convex lens, scattered light emitted by the light source passes through the convex lens to become parallel light beams, the grating is arranged in the light path direction of the parallel light beams, the parallel light beams are subjected to diffraction interference by the grating, the parallel light beams form a Talbot image after the grating, and the COMS camera is arranged on the Talbot image of any stage; when the light source is displaced in the direction vertical to the grating, light beams are changed into scattered light after passing through the convex lens, the period of the Talbot image after the grating is changed along with the displacement of the light source, and the COMS camera measures the light intensity of the Talbot image, so that displacement measurement is realized.
The grating is made of silicon, the period of the grating is 800nm, the duty ratio of the grating is 0.5, and the scribing depth of the grating is 765 nm.
The wavelength of the light source is 65nm, and the power of the light source is mW.
The focal length of the convex lens is 55 μm.
Further comprising collimating the light source before the light source is displaced in a direction perpendicular to the grating.
The method for collimating the light source comprises the following steps: when the light source at the focus of the convex lens moves in the plane of the focal plane of the convex lens relative to the grating, the light beam passing through the convex lens forms an included angle with the vertical direction of the grating, the Talbot image generated by the grating is translated in the in-plane direction, and the displacement can be measured by the COMS camera, so that the light source is collimated.
Compared with the prior art, the invention has the following beneficial effects:
the invention combines the light source displacement and the Talbot image period through optical design, measures the Talbot image period through the COMS camera so as to realize the measurement of the light source displacement and realize the output of displacement signals, only uses the light source, the convex lens, the grating and the COMS camera device, and has simpler structure; meanwhile, collimation of the light source can be realized through measurement of the Talbot image period, and the positioning precision is further improved.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a diagram of an optical simulation architecture of the present invention;
FIG. 3 is a Talbot image simulation diagram of the present invention;
FIG. 4 is a graph showing the relationship between the out-of-plane displacement of the light source and the intensity of light received by the COMS camera according to the present invention;
FIG. 5 is a graph showing the relationship between the light source in-plane direction displacement and the Talbot image translation distance.
Wherein: 1 is a light source, 2 is a convex lens, 3 is a grating, and 4 is a COMS camera.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A displacement sensor based on a Talbot image and a COMS camera structure is shown in figure 1 and comprises a light source 1, a convex lens 2, a grating 3 and a COMS camera 4, wherein the light source 1 is arranged at the focus of the convex lens 2, scattered light emitted by the light source 1 passes through the convex lens 2 and then becomes parallel light beams, the grating 3 is arranged in the light path direction of the parallel light beams, the parallel light beams are subjected to diffraction interference through the grating 3, the parallel light beams form a Talbot image after the grating 3, and the COMS camera 4 is arranged on the Talbot image of any level; when the light source 1 is displaced in the direction vertical to the grating 3, light beams are changed into scattered light after passing through the convex lens 2, the period of the Talbot image behind the grating 3 is changed along with the displacement of the light source 1, and the COMS camera 4 measures the light intensity of the Talbot image, so that displacement measurement is realized.
Further, preferably, the material of the grating 3 is silicon, the period of the grating 3 is 800nm, the duty ratio of the grating 3 is 0.5, the scribing depth of the grating 3 is 765nm, the generated Talbot image is ensured to have better effect by setting the grating thickness of the grating 3 to 765 μm, and the sine of the output signal is optimized.
Further, it is preferable that the wavelength of the light source 1 is 635nm and the power of the light source 1 is 1.2 mW.
Further, it is preferable that the focal length of the convex lens 2 is 55 μm.
Further, it comprises collimating the light source 1 before the light source 1 is displaced in a direction perpendicular to the grating 3.
Further, the method for collimating the light source 1 is as follows: when the light source 1 at the focus of the convex lens 2 makes an in-plane motion relative to the grating 3 on the focal plane, an included angle is generated between the light beam passing through the convex lens 2 and the vertical direction of the grating 3, the Talbot image generated by the grating 3 is translated in the in-plane direction, and the displacement can be measured by the COMS camera 4, so that the light source 1 is collimated.
Examples
The specific implementation parameters are as follows:
wavelength of light source: λ 635 nm; power of light source: 1.2 mW; grating period: d is 800 nm; the duty ratio of the grating is as follows: 0.5; grating ruling depth: h is 765 nm; grating material: si; focal length of convex lens used in simulation: f is 55 μm.
The specific analysis is as follows:
wherein, the grating thickness of the grating 3 is set to 765 μm to ensure that the generated Talbot image has better effect and optimize the sine of the output signal.
The structure was simulated and the simulated setup is shown in fig. 2, and it can be seen that when the grating thickness is set to 765 μm, a Talbot image area in the shape of an inverted triangle is seen behind the grating 3, as shown in fig. 3. In the in-plane direction on a certain level of Talbot image, the light intensity is distributed in a sine shape. Therefore, when the light source 1 makes an out-of-plane motion, the scattering angle of light emitted by the convex lens 2 changes, and further the period of the Talbot image in the in-plane direction changes, and light intensity information changing along with the displacement of the light source 1 can be obtained on the COMS camera 4 with the same pixel size and grating period, namely the displacement of the light source 1 and the total light intensity received by the COMS camera are linearly related, so that displacement measurement can be realized, and the simulation result is shown in FIG. 4.
Therefore, the correlation coefficient R of the out-of-plane displacement of the light source of the structure and the light intensity received by the COMS camera2At 0.99304, the relationship between the displacement of the visible light source and the received light intensity is linear, so that the displacement can be measured by the light intensity information received by the COMS camera in the structure.
When spherical waves are incident on the grating, the light intensity on any observation plane behind the grating is
Wherein, a0And a1The amplitudes of 0-order diffraction waves and +/-1-order diffraction waves after the light waves pass through the grating are respectively obtained; l is0The distance between the point light source and the grating; z is the distance between the observation surface and the grating in the optical axis direction; a is the amplitude of the light wave; d is the grating period; x is the distance from the optical axis at a point in the direction perpendicular to the optical axis. When in use
Then, the Talbot distance z ═ z can be obtainedTnThe corresponding Talbot distance formula can be obtained as
In addition, an imaging formula according to a convex lens
Where f is the focal length of the convex lens, u is the object distance, and v is the distance, where v is L0. Therefore, the relationship between the Talbot image distance and the distance between the point light source and the convex lens is
Wherein u is f-x, so
Therefore, when the light source is displaced out of the plane, the period of the generated Talbot image changes correspondingly.
Meanwhile, the Talbot image period D can be obtained by the formula (1)TAlso as the distance between the point source and the grating changes.
Wherein, R is the distance from a certain point on the Talbot image to the image generated by the point light source on the convex lens.
In summary, it can be seen that, when the point light source is displaced on the optical axis of the convex lens, the cmos camera placed on the Talbot image of a certain stage behind the convex lens can receive a varying light intensity, which is linear with the displacement, thereby enabling displacement measurement. Meanwhile, it can be concluded that this is caused by the combined influence of the out-of-plane displacement of the Talbot image caused by the out-of-plane displacement of the point light source and the variation of the period of the Talbot image.
Although only the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art, and all changes are encompassed in the scope of the present invention.
Claims (4)
1. A displacement sensor based on Talbot image and COMS camera structure, its characterized in that: the device comprises a light source (1), a convex lens (2), a grating (3) and a COMS camera (4), wherein the light source (1) is arranged at the focus of the convex lens (2), scattered light emitted by the light source (1) passes through the convex lens (2) and then becomes parallel light beams, the grating (3) is arranged in the light path direction of the parallel light beams, the parallel light beams are subjected to diffraction interference through the grating (3), the parallel light beams form a Talbot image behind the grating (3), and the COMS camera (4) is arranged on the Talbot image of any level; when the light source (1) displaces in the direction vertical to the grating (3), light beams are changed into scattered light after passing through the convex lens (2), the period of a Talbot image behind the grating (3) changes along with the displacement of the light source (1), and the COMS camera (4) measures the light intensity of the Talbot image, so that displacement measurement is realized.
2. A displacement sensor based on Talbot images and COMS camera structure according to claim 1, characterized in that: the grating (3) is made of silicon, the period of the grating (3) is 800nm, the duty ratio of the grating (3) is 0.5, and the scribing depth of the grating (3) is 765 nm.
3. A displacement sensor based on Talbot images and COMS camera structure according to claim 1, characterized in that: the wavelength of the light source (1) is 635nm, and the power of the light source (1) is 1.2 mW.
4. A displacement sensor based on Talbot images and COMS camera structure according to claim 1, characterized in that: the focal length of the convex lens (2) is 55 mu m.
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