Optical laser displacement sensor and measurement method

Abstract

The application discloses a kind of optical laser displacement sensors and measurement methods, including including dual-color laser emission module, optical splitter, emission shaping optical component, receiving imaging module, control and processing module;The dual-color laser emission module includes red laser and blue laser, and the receiving imaging module includes imaging lens, image sensor and band-pass filter.This scheme solves the problem of separating the superimposed light spot of the traditional sensor measuring transparent glass through the innovative design of dual-color laser time-sharing emission and spot width feature analysis, realizes the synchronous accurate measurement of thickness and upper and lower surface position, and has strong anti-interference, compact structure and good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of photoelectric measurement and industrial inspection technology, specifically to a laser displacement sensor and measurement method. Background Technology

[0002] When measuring opaque surfaces, traditional triangulation-type laser displacement sensors form a single light spot on the imaging sensor at the receiving end. The center of the light spot can be easily determined by methods such as centroid / peak value, thereby calculating the distance.

[0003] When the object being measured is transparent glass, the incident laser will produce reflected echoes on both the upper and lower surfaces of the glass, theoretically forming two corresponding light spots at the receiving end (representing the upper and lower surfaces respectively). However, under actual structural and imaging conditions, the two reflected light spots often highly overlap on the imaging sensor, appearing as a "superimposed light spot," leading to: 1. Unable to stably separate the center points of the two light spots, thus making it impossible to calculate the positions of the upper and lower surfaces separately; 2. Thickness calculation is unstable or impossible; 3. Changes in glass thickness, reflectivity, and exposure will further cause changes in the shape of the light spot, rendering traditional single-spot algorithms ineffective.

[0004] Therefore, a solution is needed. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an optical laser displacement sensor and measurement method to solve the problems mentioned in the background section.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A laser displacement sensor and measurement method include a dual-color laser emitting module, a beam splitter, an emission shaping optical component, a receiving imaging module, and a control and processing module; The dual-color laser emitting module includes a red laser and a blue laser. The receiving and imaging module includes an imaging lens, an image sensor, and a bandpass filter. The bandpass filter corresponds to the red and blue light bands. The emission shaping optical component is used to form a line spot or a spot spot. The beam splitter combines the red and blue lasers into the same emission optical path to achieve coaxial or near-coaxial projection of the dual-color combined light.

[0007] Preferably, it includes the following steps: a. Control the dual-color laser emitting module to emit red light and blue light in a time-division manner according to a preset time sequence, and simultaneously control the receiving imaging module to acquire images synchronously, so as to obtain red light frame image Ir and blue light frame image Ig respectively; b. Perform automatic exposure control on the red light frame image Ir and the blue light frame image Ig respectively, so that the peak gray level of the light spot is within the preset target range [Hmin, Hmax]; c. Perform background correction and ROI localization on the red light frame image Ir and the blue light frame image Ig after automatic exposure processing; d. Extract the spot width feature Wr from the located red light frame image Ir, and extract the spot width feature Wg from the blue light frame image Ig; e. Calculate the difference in the beam width characteristics ΔW = Wg − Wr or the ratio ρ = Wg / Wr; f. Based on the pre-calibrated functional relationship T=f (ΔW) or T=g (ρ) (where f and g are calibrated polynomial, piecewise linear or lookup table interpolation functions), calculate the thickness T of the transparent glass; g. Combining triangulation geometry, based on the center position of the light spot in the red light frame image Ir or the blue light frame image Ig, and in conjunction with the calculated thickness T, calculate the positions of the upper and lower surfaces of the transparent glass.

[0008] Preferably, the preset timing sequence for time-division emission in step a is that red light is turned on and red light frame image Ir is acquired in the nth frame, and blue light is turned on and blue light frame image Ig is acquired in the (n+1)th frame, or red light is turned on first and then blue light is turned on within the same frame period, and two exposures are completed sequentially, and the laser activation window is precisely aligned with the camera exposure window to avoid light mixing.

[0009] Preferably, the specific process of automatic exposure control in step b is as follows: detect the peak gray value of the light spot in each frame of the image; when the peak gray value is higher than the upper limit of the preset target range Hmax, shorten the exposure time, reduce the gain, or reduce the laser power; when the peak gray value is lower than the lower limit of the preset target range Hmin, extend the exposure time, increase the gain, or increase the laser power. The light spot peak value is normalized through automatic exposure, automatic gain, or laser power closed-loop control, thereby improving the stability of the functional relationship between width features and thickness.

[0010] Preferably, in step c, background correction uses dark field subtraction or background estimation, and ROI is located by precisely cropping the preset expected spot area in the image to eliminate interference from non-spot areas.

[0011] Preferably, the method for extracting the spot width feature in step d is one of the following: Method A: Take the intensity distribution profile of the light spot and calculate the half-width at half-maximum (FWHM) as the light spot width feature; Method B: Calculate the equivalent width using the second moment as a feature of the spot width; Method C: After thresholding the light spot, calculate the width of the connected components as the light spot width feature.

[0012] Preferably, the process of pre-calibrating the functional relationship in step f is as follows: select multiple standard glass samples with known thicknesses, collect the red light frame image Ir and blue light frame image Ig corresponding to each standard sample, calculate the difference in light spot width ΔW or the ratio ρ corresponding to each standard sample, and obtain the correspondence between thickness T and width difference ΔW or ratio ρ by polynomial fitting, piecewise linear fitting or establishing a lookup table interpolation function.

[0013] Preferably, the specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: first, the upper surface distance Ztop is obtained by mapping the center position xr or xg of the light spot in the red light frame image Ir or the blue light frame image Ig, combined with the triangulation geometric relationship; then, the lower surface distance Zbottom is calculated based on the calculated thickness T and refraction correction parameters.

[0014] Preferably, the specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: the center position xr of the red laser spot is mapped to the upper surface distance Ztop, and the center position xg of the blue laser spot is mapped to the lower surface distance Zbottom, or conversely, the mapping relationship between the center positions of the two-color laser spots and the distances to the upper and lower surfaces is directly established.

[0015] Preferably, the measurement method utilizes the differences in propagation paths and refraction angles of lasers of different wavelengths passing through transparent glass, as well as the imaging differences of the reflected echoes from the upper and lower surfaces at the imaging end. By leveraging the sensitivity of the light spot width characteristics to the thickness, the thickness of the transparent glass and the positions of the upper and lower surfaces can be calculated. Even if the reflected light spots from the upper and lower surfaces overlap at the receiving end, stable measurements can still be taken.

[0016] (III) Beneficial Effects This invention provides an optical laser displacement sensor and a measurement method. It has the following advantages: 1. By employing dual-color laser time-division emission and spot width feature analysis, the thickness of transparent glass can be stably calculated without separating overlapping spots, solving the core pain point of traditional measurement. 2. Through automatic exposure normalization, background correction, and ROI positioning, it effectively resists interference from ambient light and reflectivity changes, thereby improving measurement stability; 3. Leveraging the characteristics of dual-color lasers and multiple solution schemes, it enables simultaneous and precise measurement of the thickness and position of the upper and lower surfaces of transparent glass, adapting to diverse scenarios; 4. It adopts a beam splitter coaxial design, combined with mature industrial components and bandpass filters, resulting in a compact structure, strong anti-stray light capability, and easy mass production. Attached Figure Description

[0017] Figure 1 This is a flowchart of the process of the present invention; Figure 2 This is a schematic diagram of the superposition of light spots in this invention; Figure 3 This is a two-color light reflection diagram of the present invention.

[0018] In the diagram: 1-Dual-color laser emitting module; 11-Red laser; 12-Blue laser; 2-Beam splitter; 3-Emission shaping optical component; 4-Receiver imaging module; 41-Imaging lens; 42-Image sensor; 43-Bandpass filter; 5-Control and processing module. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1-3 The present invention provides a technical solution to achieve this: including a dual-color laser emitting module 1, a beam splitter 2, an emission shaping optical component 3, a receiving imaging module 4, and a control and processing module 5.

[0021] The dual-color laser emitting module 1 includes a red laser 11 (wavelength around 650nm) and a blue laser 12 (wavelength around 520nm). The receiving and imaging module 4 includes an imaging lens 41, an image sensor 42 (CMOS / CCD), and a bandpass filter 43. The bandpass filter 43 corresponds to the red and blue light bands. The emission shaping optical component 3 is used to form a line spot or a spot spot. The red and blue lasers are combined into the same emission optical path through the beam splitter 2 to achieve coaxial or near-coaxial projection of the dual-color combined light.

[0022] In detail, the measurement method includes the following steps: a. Control the dual-color laser emitting module 1 to emit red light and blue light in a time-division manner according to a preset time sequence, and simultaneously control the receiving imaging module 4 to acquire images synchronously, so as to obtain red light frame image Ir and blue light frame image Ig respectively; b. Perform automatic exposure control on the red light frame image Ir and the blue light frame image Ig respectively, so that the peak gray level of the light spot is within the preset target range [Hmin, Hmax]; c. Perform background correction and ROI localization on the red light frame image Ir and the blue light frame image Ig after automatic exposure processing; d. Extract the spot width feature Wr from the located red light frame image Ir, and extract the spot width feature Wg from the blue light frame image Ig; e. Calculate the difference in the beam width characteristics ΔW = Wg − Wr or the ratio ρ = Wg / Wr; f. Based on the pre-calibrated functional relationship T=f (ΔW) or T=g (ρ) (where f and g are calibrated polynomial, piecewise linear or lookup table interpolation functions), calculate the thickness T of the transparent glass; g. Combining triangulation geometry, based on the center position of the light spot in the red light frame image Ir or the blue light frame image Ig, and in conjunction with the calculated thickness T, calculate the positions of the upper and lower surfaces of the transparent glass.

[0023] In step a, the preset timing of the time-division emission is that the red light is turned on and the red light frame image Ir is acquired in the nth frame, and the blue light is turned on and the blue light frame image Ig is acquired in the (n+1)th frame, or the red light is turned on first and the blue light is turned on later in the same frame period, and two exposures are completed in sequence. The laser activation window and the camera exposure window are precisely aligned to avoid light mixing.

[0024] The specific process of automatic exposure control in step b is as follows: detect the peak gray value of the light spot in each frame of the image. When the peak gray value is higher than the upper limit of the preset target range Hmax, shorten the exposure time, reduce the gain, or reduce the laser power. When the peak gray value is lower than the lower limit of the preset target range Hmin, extend the exposure time, increase the gain, or increase the laser power. Through automatic exposure, automatic gain, or laser power closed-loop control, the peak value of the light spot is normalized, thereby improving the stability of the functional relationship between the width feature and the thickness.

[0025] In step c, background correction uses either dark field subtraction or background estimation. The ROI is located by precisely cropping the pre-defined expected spot area in the image to eliminate interference from non-spot areas.

[0026] The method for extracting the spot width feature in step d is one of the following: Method A: Take the intensity distribution profile of the light spot and calculate the half-width at half-maximum (FWHM) as the light spot width feature; Method B: Calculate the equivalent width using the second moment as a feature of the spot width; Method C: After thresholding the light spot, calculate the width of the connected components as the light spot width feature.

[0027] The process of pre-calibrating the functional relationship in step f is as follows: Select multiple standard glass samples with known thicknesses, collect the red light frame image Ir and blue light frame image Ig corresponding to each standard sample, calculate the difference in light spot width ΔW or the ratio ρ corresponding to each standard sample, and obtain the correspondence between thickness T and width difference ΔW or ratio ρ by polynomial fitting, piecewise linear fitting or establishing a lookup table interpolation function.

[0028] The specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: first, the upper surface distance Ztop is obtained by mapping the center position xr or xg of the light spot in the red light frame image Ir or the blue light frame image Ig, combined with the triangulation geometric relationship; then, the lower surface distance Zbottom is calculated based on the calculated thickness T and refraction correction parameters.

[0029] The specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: map the center position xr of the red laser spot to the distance Ztop of the upper surface, and map the center position xg of the blue laser spot to the distance Zbottom of the lower surface, or conversely, directly establish the mapping relationship between the center positions of the two-color laser spots and the distances to the upper and lower surfaces.

[0030] The measurement method utilizes the differences in propagation path and refraction angle of lasers of different wavelengths passing through transparent glass, as well as the imaging differences of the reflected echoes from the upper and lower surfaces at the imaging end. By leveraging the sensitivity of the light spot width characteristics to the thickness, the thickness of the transparent glass and the positions of the upper and lower surfaces can be calculated. Even if the reflected light spots from the upper and lower surfaces overlap at the receiving end, the measurement can still be stable.

[0031] Solution Analysis: 1. Solving the core pain points of measurement with transparent glass When measuring transparent glass, traditional triangulation-type laser displacement sensors suffer from highly overlapping reflected light spots on the upper and lower surfaces, making it impossible to stably separate the center of the light spot and causing thickness calculation failures.

[0032] This solution uses time-division emission of dual-color lasers and spot width feature analysis. It does not rely on spot center separation. Even if two spots are highly overlapping, the thickness can be stably calculated by the difference / ratio of the spot widths of lasers of different wavelengths, thus completely solving the measurement problem caused by superimposed spots.

[0033] 2. Improve measurement stability and anti-interference capability Automatic exposure normalization: Automatic exposure control is performed on the red and blue light frame images respectively to ensure that the peak gray level of the light spot is stable within the preset range, avoiding the influence of glass reflectivity changes, ambient light interference, and exposure fluctuations on the shape of the light spot.

[0034] Background correction and ROI localization: Environmental noise is eliminated by dark field subtraction or background estimation, and the spot area is accurately extracted, which further improves the reliability of feature extraction.

[0035] 3. Achieve simultaneous and precise measurement of thickness and surface position. Accurate and reliable thickness calculation: Based on the differences in the propagation path and refraction angle of lasers of different wavelengths in glass, the characteristics of the laser spot width are highly sensitive to the thickness. Combined with the pre-calibrated functional relationship, stable thickness calculation can be achieved.

[0036] Flexible and efficient surface position calculation: Two surface position calculation schemes are provided. One can calculate the position by combining the center of a single-wavelength light spot with thickness and refraction correction, while the other can directly use the center of a two-color light spot to map the positions of the upper and lower surfaces respectively, adapting to different application scenarios.

[0037] 4. Compact hardware structure and strong compatibility The design employs a beam splitter and coaxial projection, allowing dual-color lasers to share the same emission path, which simplifies the optical structure and makes the sensor smaller and easier to install.

[0038] The bandpass filter 43 at the receiver corresponds to the red and blue light bands, which can effectively filter ambient stray light and improve imaging quality. Moreover, the core components (image sensor 42, laser, etc.) are all mature industrial devices, with controllable costs and easy mass production.

[0039] Working principle: The control and processing module 5 triggers the dual-color laser emission module 1, causing the red laser 11 and blue laser 12 to output lasers in a time-division manner. After the two beams are combined by the beam splitter 2, they are shaped into a light spot by the emission shaping optical component 3 and projected onto the transparent glass under test. The reflected echoes from the upper and lower surfaces of the glass are captured by the receiving imaging module 4. After the ambient light is filtered by the bandpass filter 43 and focused by the imaging lens 41, the image sensor 42 generates a red / blue light frame image and transmits it to the control and processing module 5. The control and processing module 5 extracts the light spot width features through automatic exposure calibration and image preprocessing. It calculates the glass thickness using the difference or ratio of the light spot width combined with the calibration function. Then, it obtains the position of the upper and lower surfaces of the glass through triangulation or dual-color light spot mapping relationship, and finally outputs the thickness and surface position results.

[0040] Technical effects of implementing this solution: This solution, through an innovative design combining dual-color laser time-division emission and spot width feature analysis, fundamentally solves the core problem of "inseparable superimposed spots" in the measurement of transparent glass using traditional triangulation sensors. It achieves synchronous, stable, and accurate measurement of the thickness and position of the upper and lower surfaces of transparent glass. Furthermore, technologies such as automatic exposure normalization and background correction further enhance the system's anti-interference capability and measurement reliability. Its compact hardware structure also demonstrates promising prospects for industrial applications, providing an efficient and stable solution for the high-precision detection of transparent materials such as transparent glass.

[0041] The present invention comprises: 1-a dual-color laser emitting module; 11-red laser; 12-blue laser; 2-beam splitter; 3-emission shaping optical component; 4-receiving imaging module; 41-imaging lens; 42-image sensor; 43-bandpass filter; 5-control and processing module. These components are all general standard parts or components known to those skilled in the art. Their structure and principle can be learned by those skilled in the art through technical manuals or conventional experimental methods. The problem solved by the present invention is that when the traditional triangulation laser displacement sensor measures transparent glass, the reflected echoes of the incident laser on the upper and lower surfaces of the glass will form highly overlapping superimposed light spots on the imaging sensor at the receiving end. Not only is it impossible to stably separate and obtain the center points of the two light spots to calculate the positions of the upper and lower surfaces, but it also leads to unstable or even impossible glass thickness calculation. Furthermore, changes in glass thickness, reflectivity, and exposure will further change the shape of the light spots, ultimately causing the traditional single-spot algorithm to completely fail. This invention solves the problem of beam separation when measuring transparent glass with traditional sensors by using a novel design of time-division emission of dual-color lasers and beam width feature analysis. It achieves synchronous and accurate measurement of thickness and position of upper and lower surfaces, and has strong anti-interference capabilities, compact structure and good industrial application prospects.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A laser displacement sensor, characterized in that: It includes a dual-color laser emitting module (1), a beam splitter (2), an emission shaping optical component (3), a receiving imaging module (4), and a control and processing module (5). The dual-color laser emitting module (1) includes a red laser (11) and a blue laser (12). The receiving imaging module (4) includes an imaging lens (41), an image sensor (42), and a bandpass filter (43). The bandpass filter (43) corresponds to the red and blue light bands. The emission shaping optical component (3) is used to form a line spot or a spot spot. The red and blue lasers are combined into the same emission optical path through the beam splitter (2) to achieve coaxial or near-coaxial projection of dual-color combined light.

2. A measurement method based on the optical laser displacement sensor according to claim 1, characterized in that: Includes the following steps: a. Control the dual-color laser emitting module (1) to emit red light and blue light in a time-division manner according to a preset time sequence, and simultaneously control the receiving imaging module (4) to collect images synchronously, so as to obtain red light frame image Ir and blue light frame image Ig respectively; b. Perform automatic exposure control on the red light frame image Ir and the blue light frame image Ig respectively, so that the peak gray level of the light spot is within the preset target range [Hmin, Hmax]; c. Perform background correction and ROI localization on the red light frame image Ir and the blue light frame image Ig after automatic exposure processing; d. Extract the spot width feature Wr from the located red light frame image Ir, and extract the spot width feature Wg from the blue light frame image Ig; e. Calculate the difference in the beam width characteristics ΔW = Wg − Wr or the ratio ρ = Wg / Wr; f. Based on the pre-calibrated functional relationship T=f (ΔW) or T=g (ρ) (where f and g are calibrated polynomial, piecewise linear or lookup table interpolation functions), calculate the thickness T of the transparent glass; g. Combining triangulation geometry, based on the center position of the light spot in the red light frame image Ir or the blue light frame image Ig, and in conjunction with the calculated thickness T, calculate the positions of the upper and lower surfaces of the transparent glass.

3. The measurement method according to claim 2, characterized in that: In step a, the preset timing of the time-division emission is that the red light is turned on and the red light frame image Ir is acquired in the nth frame, and the blue light is turned on and the blue light frame image Ig is acquired in the (n+1)th frame, or the red light is turned on first and the blue light is turned on later in the same frame period, and two exposures are completed in sequence. The laser activation window and the camera exposure window are precisely aligned to avoid light mixing.

4. The measurement method according to claim 2, characterized in that: The specific process of automatic exposure control in step b is as follows: detect the peak gray value of the light spot in each frame of the image. When the peak gray value is higher than the upper limit of the preset target range Hmax, shorten the exposure time, reduce the gain, or reduce the laser power. When the peak gray value is lower than the lower limit of the preset target range Hmin, extend the exposure time, increase the gain, or increase the laser power. Through automatic exposure, automatic gain, or laser power closed-loop control, the peak value of the light spot is normalized, thereby improving the stability of the functional relationship between the width feature and the thickness.

5. The measurement method according to claim 2, characterized in that: In step c, background correction uses either dark field subtraction or background estimation. The ROI is located by precisely cropping the pre-defined expected spot area in the image to eliminate interference from non-spot areas.

6. The measurement method according to claim 2, characterized in that: The method for extracting the spot width feature in step d is one of the following: Method A: Take the intensity distribution profile of the light spot and calculate the half-width at half-maximum (FWHM) as the light spot width feature; Method B: Calculate the equivalent width using the second moment as a feature of the spot width; Method C: After thresholding the light spot, calculate the width of the connected components as the light spot width feature.

7. The measurement method according to claim 2, characterized in that: The process of pre-calibrating the functional relationship in step f is as follows: Select multiple standard glass samples with known thicknesses, collect the red light frame image Ir and blue light frame image Ig corresponding to each standard sample, calculate the difference in light spot width ΔW or the ratio ρ corresponding to each standard sample, and obtain the correspondence between thickness T and width difference ΔW or ratio ρ by polynomial fitting, piecewise linear fitting or establishing a lookup table interpolation function.

8. The measurement method according to claim 2, characterized in that: The specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: first, the upper surface distance Ztop is obtained by mapping the center position xr or xg of the light spot in the red light frame image Ir or the blue light frame image Ig, combined with the triangulation geometric relationship; then, the lower surface distance Zbottom is calculated based on the calculated thickness T and refraction correction parameters.

9. The measurement method according to claim 2, characterized in that: The specific method for calculating the positions of the upper and lower surfaces of the transparent glass in step g is as follows: map the center position xr of the red laser spot to the distance Ztop of the upper surface, and map the center position xg of the blue laser spot to the distance Zbottom of the lower surface, or conversely, directly establish the mapping relationship between the center positions of the two-color laser spots and the distances to the upper and lower surfaces.

10. The measurement method according to claim 2, characterized in that: The measurement method utilizes the differences in propagation paths and refraction angles of lasers of different wavelengths passing through transparent glass, as well as the imaging differences of the reflected echoes from the upper and lower surfaces at the imaging end. By leveraging the sensitivity of the light spot width characteristics to the thickness, the method calculates the thickness of the transparent glass and the positions of the upper and lower surfaces. Even if the reflected light spots from the upper and lower surfaces overlap at the receiving end, the measurement can still be stable.

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