An adaptive laser triangulation method for suppressing speckle

Abstract

The present invention relates to an adaptively adjustable laser triangulation method for suppressing speckle. Light sources of different wavelengths emit light from different angles. The outgoing light intensity is modulated by a light intensity controller to obtain light spots of different intensities. The light spots are incident on a light combining element, and after light combining, multi-wavelength light spots are generated. The multi-wavelength light spots are projected onto a cylindrical mirror group. After being shaped by the cylindrical mirror, a line laser with low speckle is projected at a reference distance. The line laser is imaged by an imaging system and received by a detector to obtain an image of the surface of the object being measured. The present invention adopts an adaptive adjustment method of a light intensity controller to solve the problem of large speckle generated due to the rough surface of the object being measured. The method can adapt to different surfaces of the object being measured to achieve the optimal de-speckle effect, effectively improve the measurement accuracy of the line laser triangulation instrument, and reduce the measurement uncertainty.

Description

Technical Field

[0001] The present invention relates to an adaptive adjustment high-precision measurement method, and in particular to a multi-wavelength low-speckle laser triangulation measurement method based on light combining by a light combining element. Background Art

[0002] Uncertainty, as an important indicator of laser triangulation instruments, reflects the instrument's stability during multiple measurements. In online laser triangulation instruments, speckle phenomenon, as one of the factors affecting the instrument's measurement uncertainty, limits the instrument's theoretical measurement uncertainty. Therefore, suppressing speckle phenomenon on the surface of the object being measured in a laser triangulation instrument can significantly reduce the instrument's measurement uncertainty and improve measurement accuracy. Chinese invention patent CN 113934012 A proposes a spatially distributed compact speckle suppression device based on angular diversity. The device is arranged behind a laser light source and includes: two parallel and spaced three-dimensional reflective plates for directional and efficient reflection of the laser beam; a rotating light-collecting device for achieving time-sequential selection and spatial separation of the laser beam; a support device for fixing the three-dimensional reflective plates and driving the rotating light-collecting device to rotate; and a beam converging device for converging and temporally superimposing the spatially separated beams, thereby completing the spatial separation and temporal superposition of the beams. Based on the principle of angular diversity, the device efficiently suppresses laser speckle. However, the device is relatively large, making it difficult to integrate into a triangulation system. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the present invention uses a light combining element to merge light beams of different wavelengths. After being shaped by a cylindrical mirror, the linear light spot incident on the object to be measured is modulated by multiple wavelengths to form a smaller speckle. This method provides an adaptive laser triangulation measurement method that suppresses speckle, which can effectively improve measurement accuracy and reduce measurement uncertainty.

[0004] The technical solution for achieving the purpose of the present invention is to provide a method for adaptively adjusting laser triangulation for suppressing speckle, comprising the following steps:

[0005] (1) The narrow-bandwidth light sources with different wavelengths include a first light source, a second light source, and a third light source, whose wavelengths correspond to λ1, λ2, and λ3, respectively, and satisfy the conditions λ2 = 405 nm, λ1-λ2 ≥ λ 2 2 / 2h, λ3-λ2≥λ 2 2 / 2h, h is the average height of the surface of the object being measured; the light emitted by the first light source and the third light source enter the first light intensity controller and the second light intensity controller respectively;

[0006] (2) During the first measurement, the two light intensity controllers do not control the light emitted by the first light source and the third light source, and perform the following steps (3) to (4); during subsequent measurements, the light intensity controllers are controlled to adjust the light intensity of the first light source and the third light source, and perform the following steps;

[0007] (3) The outgoing light from the three light sources is incident on the light combining element at different angles, and the light spots of different wavelengths are combined and emitted in the same direction, and projected onto the cylindrical mirror group. After shaping, low-speckle parallel line light spots are formed at the position of the reference distance plane;

[0008] The light combining element is a grating, the angle between the outgoing light of the first light source and the normal line of the grating surface is α1, the angle between the outgoing light of the second light source and the normal line of the grating surface is α2, and the angle between the outgoing light of the third light source and the normal line of the grating surface is α3, and the condition is satisfied. m is the grating order, d is the grating groove spacing, and β is the angle between the outgoing light after grating light combination and the grating surface normal;

[0009] The cylindrical mirror group includes a first cylindrical mirror, a second cylindrical mirror, and a third cylindrical mirror, which are sequentially arranged in the direction of the outgoing light after the grating light is combined, wherein the generatrix direction of the first cylindrical mirror and the third cylindrical mirror is horizontal, the generatrix direction of the second cylindrical mirror is perpendicular to the generatrix direction of the first cylindrical mirror, and the generatrix direction of the first cylindrical mirror and the generatrix direction of the second cylindrical mirror satisfy the left-hand rule with the direction of the incident light;

[0010] (4) The line spot is projected onto the object to be measured, and the scattered light on the surface of the object to be measured is imaged on the detector by the imaging system to obtain a low-speckle image; the detector outputs a signal to the signal processing unit, and the speckle contrast calculation is performed on the image obtained on the detector;

[0011] (5) Repeat steps (2) to (4), and use the lowest speckle contrast in the image obtained on the detector as the adaptive measurement result output.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. The high-precision laser triangulation method provided by the present invention is based on the principle of multi-wavelength fusion to reduce speckle. It combines light of different wavelengths through a light-combining element to form a multi-wavelength light spot. By reducing speckle interference, it improves the measurement accuracy of the triangulation instrument and reduces measurement uncertainty.

[0014] 2. The method of adaptively adjusting the intensity of different light sources incident on the light combining element through the light intensity controller can meet the needs of different measurement surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1This is a workflow diagram of a self-adaptive laser triangulation measurement method for suppressing speckle provided by the present invention;

[0016] Figure 2 This is a schematic diagram of the measurement principle of the laser triangulation instrument;

[0017] Figure 3 、 4 Schematic diagrams of multi-wavelength illumination systems based on reflection grating light combination and transmission grating light combination;

[0018] Figure 5 、 6 These are the light combining principle diagrams based on reflection grating and transmission grating respectively.

[0019] In the figure, 1. first light source; 2. second light source; 3. third light source; 4. first light intensity controller; 5. second light intensity controller; 6. grating; 7. first cylindrical mirror; 8. second cylindrical mirror; 9. third cylindrical mirror; 10. measured surface; 11. light source; 12. lighting system; 13. imaging lens; 14. detector. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1

[0022] See attached Figure 1 , which is a workflow diagram of a method for adaptively adjusting laser triangulation for suppressing speckle provided in this embodiment, including the following steps

[0023] 1. Narrow-bandwidth laser 1 with different wavelengths is the first light source, laser 2 is the second light source, and laser 3 is the third light source. The light emitted by laser 1 and laser 3 passes through light intensity controller 1 and light intensity controller 2 respectively;

[0024] 2. When starting the measurement, the two light intensity controllers do not control the light emitted by the first light source and the third light source, and directly execute the following steps 3 and 4; then, control the two light intensity controllers to adjust the light intensity of the first light source and the third light source, and execute the following steps;

[0025] 3. Three beams of light are incident on the beam splitter (combiner) element at different angles, combining the light spots of different wavelengths and emitting them in the same direction. They are projected onto the cylindrical mirror and, after shaping, form low-speckle parallel line light spots at the reference distance plane.

[0026] 4. A line light spot is projected onto the object being measured. The scattered light from the surface of the object is imaged by the imaging system and formed on the detector, resulting in a low-speckle image. The detector outputs a signal to the signal processing unit, which calculates the speckle contrast of the image obtained on the detector.

[0027] 5. Repeat steps 2, 3, and 4 until the speckle contrast of the image on the detector is lowest, and then output the adaptive measurement results.

[0028] See attached Figure 2 , which is a schematic diagram of the structure of the optical system of the triangulation measuring instrument provided in this embodiment: the light spot emitted by the light source 11 is projected onto the surface of the object to be measured 10 after passing through the illumination system 12, and the scattered or scattered light on the surface of the object to be measured is imaged on the detector 14 through the imaging system 13, and the detector outputs a signal to the signal processing unit

[0029] See attached Figure 3 、 4 , which are schematic diagrams of the structure of the multi-wavelength illumination system based on the combination of reflection grating and transmission grating provided in this embodiment; the light source includes three narrow-band light sources with different wavelengths, namely a first light source 1, a second light source 2 and a third light source 3, and their wavelengths correspond to λ1, λ2 and λ3 respectively; the light intensity controller includes two identical light intensity controllers, which respectively control the intensity of the incident light, the outgoing light of the first light source is incident on the first light intensity controller 4, and the outgoing light of the third light source is incident on the second light intensity controller 5; the light combining element is a grating 6, and this embodiment adopts a reflection grating or a transmission grating, and the cylindrical mirror group includes a first cylindrical mirror 7, a second cylindrical mirror 8 and a third cylindrical mirror 9, which are arranged in the direction of the outgoing light after the grating light is combined, wherein the bus line direction of the first cylindrical mirror and the third cylindrical mirror is horizontal, the bus line direction of the second cylindrical mirror is perpendicular to the bus line direction of the first cylindrical mirror, and the bus line direction of the first cylindrical mirror and the bus line direction of the second cylindrical mirror satisfy the left-hand rule with the incident light direction; the multi-wavelength illumination system based on the combination of reflection grating is projected onto the surface 10 of the object to be measured. The optical axis of the imaging lens forms an angle of 35° with the emission direction of the combined light from the reflection grating.

[0030] The light sources used in this embodiment are three diode light sources, namely the first light source, the second light source and the third light source. They are incident on the same order m of the reflection grating from different directions. Their wavelengths correspond to λ1, λ2 and λ3 respectively, and meet the conditions λ2=405nm, λ1-λ2≥λ 2 2 / 2h, λ3-λ2≥λ 2 2 / 2h, h is the average height of the surface of the object being measured. The wavelengths of the light sources λ2 and λ3 should satisfy the relationship λ2-λ1≥λ1 / h, λ3-λ1≥λ1 / h, and h is the surface roughness of the object being measured.

[0031] See attached Figure 5, is the principle diagram of the reflection grating light combination. According to the grating diffraction principle d(sinα-sinβ)=mλ, the angle between the first light source 1 and the normal line of the reflection grating surface after being regulated by the first light intensity controller is α1, the angle between the output light of the second light source 2 and the normal line of the reflection grating surface is α2, and the angle between the third light source 3 and the normal line of the reflection grating surface after being regulated by the second light intensity controller is α3. When the incident angles of the three lasers meet the conditions The three incident lights obtain the same exit angle after being reflected by the grating, thus completing the light combination of light spots of different wavelengths; m is the grating order, d is the grating groove spacing, and β is the angle between the exiting light after grating light combination and the grating surface normal.

[0032] See attached Figure 6 , is the principle diagram of transmission grating light combination. According to the grating diffraction principle: dsinα=mλ, when the incident angles of the three laser output lights 1, 2, and 3 meet When , the three incident lights satisfying the above relationship will have the same exit angle after passing through the transmission grating, completing the light combination of light spots of different wavelengths.

Claims

1. A self-adaptive laser triangulation method for suppressing speckle, characterized in that The steps include: (1) The narrow-bandwidth light sources with different wavelengths include a first light source (1), a second light source (2), and a third light source (3), whose wavelengths correspond to λ1, λ2, and λ3, respectively, and satisfy the conditions λ2 = 405 nm, λ1-λ2 ≥ λ 2 2 / 2h, λ3-λ2≥λ 2 2 / 2h, where h is the average height of the surface of the object being measured; the light emitted by the first light source and the third light source enter the first light intensity controller (4) and the second light intensity controller (5) respectively; (2) During the first measurement, the two light intensity controllers do not control the light emitted by the first light source and the third light source, and perform the following steps (3) to (4); during subsequent measurements, the light intensity controllers are controlled to adjust the light intensity of the first light source and the third light source, and perform the following steps; (3) The outgoing light from the three light sources is incident on the light combining element at different angles, and the light spots of different wavelengths are combined and emitted in the same direction, and projected onto the cylindrical mirror group. After shaping, low-speckle parallel line light spots are formed at the position of the reference distance plane; The light combining element is a grating (6), the angle between the outgoing light of the first light source and the normal line of the grating surface is α1, the angle between the outgoing light of the second light source and the normal line of the grating surface is α2, and the angle between the outgoing light of the third light source and the normal line of the grating surface is α3, and the condition is satisfied. m is the grating order, d is the grating groove spacing, and β is the angle between the outgoing light after grating light combination and the grating surface normal; The cylindrical mirror group comprises a first cylindrical mirror (7), a second cylindrical mirror (8) and a third cylindrical mirror (9), which are sequentially arranged in the direction of the outgoing light after the grating light is combined, wherein the busbar directions of the first cylindrical mirror and the third cylindrical mirror are horizontal, the busbar direction of the second cylindrical mirror is perpendicular to the busbar direction of the first cylindrical mirror, and the busbar directions of the first cylindrical mirror and the second cylindrical mirror satisfy the left-hand rule with the direction of the incident light; (4) The line spot is projected onto the object to be measured (10), and the scattered light on the surface of the object to be measured is imaged on the detector (14) through the imaging system (13), thereby obtaining a low-speckle image; the detector outputs a signal to the signal processing unit, and the speckle contrast calculation is performed on the image obtained on the detector; (5) Repeat steps (2) to (4), and use the lowest speckle contrast in the image obtained on the detector as the adaptive measurement result output.

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