Line laser underwater contour measurement correction method based on light path model

Abstract

The invention belongs to the technical field of optical measurement, and particularly relates to a line laser underwater contour measurement correction method based on an optical path model. Comprising the following steps: step 1, carrying out waterproof sealing packaging on a line laser; 2, fixedly installing a line laser in an underwater environment; 3, establishing a first light path mathematical model and a second light path mathematical model; 4, placing a tested block at the water bottom, and measuring the contour of the tested block by using a line laser based on the first light path mathematical model; and step 5, based on the second optical path mathematical model, correcting the measurement contour data obtained in the step 4. The method has the beneficial effects that when the on-line laser is used for measuring the outline of an object underwater, the outline height data error value generated by refraction of the line laser can be accurately obtained only by knowing part of optical and structural parameters of the line laser, and the requirement for precision calibration of workpiece outline measurement of the line laser underwater is met.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, specifically relating to a method for underwater profile measurement and correction of a line laser based on an optical path model. Background Technology

[0002] In the industrial field, line lasers are widely used for 3D measurement and modeling of workpieces. A line laser emits a laser line that covers the workpiece being measured, and then receives the diffusely reflected light from the surface of the workpiece through a receiving end, thereby obtaining the contour information of the workpiece.

[0003] The main components of a line laser are a light source and a lens. The laser light emitted from the light source forms a line laser beam under the influence of the lens. Because the structure of a line laser is fixed, the propagation path of the emitted line laser is also fixed. Currently, line laser contour measurement products in the industrial field are used for contour measurement of workpieces in air. However, when using a line laser to measure workpieces underwater, the optical path model of the laser changes due to refraction by the waterproof medium and the water medium. This results in a significant difference between the measured contour data and the actual contour data when measuring a workpiece underwater.

[0004] To perform contour measurement using a line laser in underwater conditions, the underwater contour measurement data needs to be calibrated. Currently, there are few methods and applications for calibrating underwater line laser contour data. Most methods employ curve fitting of surface and underwater experimental measurement data. However, the calibration results are affected by experimental systematic and random errors, and the calibration accuracy cannot meet industrial requirements. For example, the patent with publication number CN115615355A, "A Data-Based Line Laser Contour Measurement Compensation Method in Liquid Medium," addresses this issue. Summary of the Invention

[0005] The purpose of this invention is to provide a method for underwater profile measurement and correction of line lasers based on an optical path model, which can achieve accurate correction of underwater line laser profile data.

[0006] The technical solution of the present invention is as follows: A method for underwater profile measurement and correction of a line laser based on an optical path model, comprising the following:

[0007] Step 1: Waterproof sealing and encapsulation of the line laser;

[0008] Step 2: Securely install the line laser in the underwater environment, allowing for free height adjustment;

[0009] Step 3: Establish the first optical path mathematical model to describe the equation for height change in line laser underwater measurement, and the second optical path mathematical model to describe the equation for contour correction in line laser underwater measurement;

[0010] Step 4: placing the test block at the bottom of the water, and measuring the profile of the test block using the linear laser based on the first optical path mathematical model;

[0011] Step 5: correcting the measured profile data obtained in step 4 based on the second optical path mathematical model.

[0012] In step 1, the linear laser is waterproofed using a transparent acrylic cuboid box with a thickness of not more than 5mm, and a limiting device is provided in the box to ensure that the linear laser is fixed and immovable in the box, thereby reducing errors caused by movement of the linear laser during profile detection.

[0013] In step 2, the linear laser is fixed on the stand using a screw connection device, and the stand is placed on a water tank with a depth of 700mm, and the height of the linear laser can be adjusted through the screw.

[0014] Step 3 includes obtaining the parameters of the linear laser, and establishing a first optical path mathematical model linear laser underwater measurement height change equation based on the parameters of the linear laser, which is as follows:

[0015]

[0016] In the formula, L(h) is the distance reference of the linear laser when measuring underwater, h is the profile measurement value obtained by the linear laser when measuring underwater, when h=0, L(0)=516.2mm, and when the profile height of the object measured by the linear laser underwater is 0, the profile surface is 516.2mm away from the linear laser;

[0017] A second optical path mathematical model linear laser underwater measurement profile correction equation is established based on the parameters of the linear laser, which is as follows:

[0018]

[0019] In the formula, △N represents the value that needs to be corrected for the profile height obtained by the linear laser when measuring underwater, x is the xth measurement value (x∈[1,3200]), L(h) is the expression obtained by the first optical path mathematical model, and h is the profile measurement value obtained by the linear laser when measuring underwater.

[0020] In step 4, the test block placed at the bottom of the water is a stepped test block, so that the linear laser can obtain stepped profile data when measuring the profile of the test block.

[0021] In step 4, the height of the linear laser is adjusted using a screw adjustment device based on the results of the first optical path mathematical model, so that the linear laser can obtain the profile data of the measured object when it is 516.2mm away from the measured object.

[0022] The step 5 corrects the profile data obtained in step 4 in the following manner: the true profile value N of the xth measurement value (x [1, 3200]) is h + delta N.

[0023] The present application has the beneficial effect that when the line laser is used to measure the profile of an object underwater, only part of the optical and structural parameters of the line laser need to be known, and the profile height data error value of the line laser caused by refraction can be accurately obtained, solving the need for precision calibration of the line laser when measuring the profile of a workpiece underwater. For underwater profile measurement of large workpieces, the time and cost required for experiments are greatly reduced, and the underwater profile parameter correction of the line laser can be achieved through theoretical derivation. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a line laser waterproof device;

[0025] Figure 2 is a schematic diagram of a line laser measurement test block;

[0026] Figure 3 is a schematic diagram of a line laser structure;

[0027] Figure 4 is a first line laser optical path mathematical model;

[0028] Figure 5 is a second line laser optical path mathematical model;

[0029] Figure 6 is line laser underwater uncorrected profile data collection;

[0030] Figure 7 is line laser underwater corrected profile data collection. DETAILED DESCRIPTION

[0031] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0032] The present application is directed to a correction method for line laser profile measurement underwater based on an optical path model under the condition that the structure of the line laser is known by analyzing the line laser structure and the underwater optical path model, specifically comprising:

[0033] The line laser is waterproof sealed and packaged using a transparent acrylic tool box, ensuring that the line laser can normally emit and receive line laser in an underwater environment, as shown in Figure 1

[0034] A gantry is installed on the experimental water tank, and the line laser sealed tool box can be stably installed on the gantry. A screw rod is provided at the installation position, which can adjust the line laser up and down by shaking the screw rod.

[0035] ​A measurement test block is placed at the bottom of the experimental water tank, and the test block is a long step-shaped test block as shown in Figure 2 The test block is placed directly below the line laser, so that the line laser emitted by the line laser can cover the surface of the test block;

[0036] Tap water is poured into the experimental water tank to ensure that the test block and the line laser can be immersed; according to the principle and structure of the line laser, a first light path mathematical model is established for the emission and reflection of the line laser.

[0037] The line laser used in the present application has a structure as shown in Figure 3 The measurement height range of the line laser is 380mm±60mm, and the measurement width is 210mm. When the line laser measures the test block, the refraction and reflection of the line laser are analyzed to obtain a first light path mathematical model as shown in Figure 4 In Figure 4 , when the laser performs profile measurement on an object, the laser emits laser light at the emission end, and forms a reflection and recycling light end on the non-mirror surface object. The relative distance L between the non-mirror surface measured object and the laser can be obtained by triangulation method. When the line laser is placed underwater to measure the object, the laser passes through the refraction of water, which causes the relative distance L to change.

[0038] The refractive index of water is known to be 1.33, and the refractive index of transparent acrylic material is 1.49. According to the refraction law, the following formula is obtained:

[0039]

[0040] Figure 4 The x in the above formula is a constant value, and the length is:

[0041] X=380*tan17.5°

[0042] Suppose the measurement height of the detection head scanning the profile of the workpiece is h, then the refraction angle γ at different measurement heights is:

[0043]

[0044] When h=0, the laser emission angle γ captured by the light receiving end of the line laser is 17.5°, and the incident angle is less than 17.5°. In order to obtain the true incident angle α, the following formula is obtained:

[0045]

[0046] According to the tangent theorem of triangle, the expression of the actual distance L can be obtained:

[0047]

[0048] According to the above formula, when h = 0, the contour height obtained by the detection head is 0, which means that the measured depth is 380, and the actual depth L is equal to 516.204357.

[0049] A mathematical model of the second optical path is established for the underwater laser optical path, such as... Figure 5 As shown, the line laser emits a line laser from the scanning output end in the figure. After hitting the surface of the object, the light is captured by the line laser after passing through the diffuse reflection recovery end. Figure 3 The laser beam has an emission width and a receiving width of 30mm. The vertically emitted laser line height is 380mm, the height measurement range is ±60mm, the laser line width reaching the object surface is 210mm, and the returned beam forms a 17.5° angle with the emitted beam.

[0050] exist Figure 5 In the process, due to the effect of refraction, when the measurement reference is 380mm, mathematical model I shows that the length of BC is the actual height of 516.2mm. This distance serves as the reference plane for the height detection of the line laser head. The original width of the laser line emitted from the scanning end of the line laser is 30mm. The width of the reflected laser line when measuring the contour of the object being measured is 210*516.2 / 380=285.2mm. Mathematical model I shows that ∠ACB is 13.1° at this point, and AB is perpendicular to BC.

[0051] Based on the properties of line lasers and the data acquisition method, it is known that the data of a line laser line at the reflected light end consists of 3200 contour points. For mathematical model II, let ΔN be the distance that needs to be corrected for the x-th contour point (x∈[1,3200]). The derivation process of the expression for ΔN with respect to x and L(h) is given below:

[0052] exist Figure 5 middle,

[0053] LM = 380 * tan17.5°

[0054]

[0055] Spatial incident angle α:

[0056]

[0057] According to the law of refraction, let n be the ratio of the refractive index of air to that of water, the expression for the angle of incidence γ is:

[0058] γ = arcsin(n*sinα)

[0059] at last:

[0060]

[0061] The first optical path mathematical model shows that the reference distance measured by the linear laser in the air is 380mm, and the reference distance measured in water is 516.2mm. The height of the linear laser is adjusted by using a screw device, so that the linear laser is 516mm away from the bottom of the water block to be tested, and the height profile parameters of the test block are measured by using the linear laser, which are recorded as profile measurement values;

[0062] The profile correction values are obtained by correcting the profile measurement values collected in the previous step by using the second optical path mathematical model, and the profile correction of the underwater measurement of the linear laser is completed.

[0063] Figure 6 For the uncorrected profile data of the block to be tested measured by using the linear laser under water, it can be seen that the profile is obviously distorted. Figure 7 For the corrected profile data, it can be seen that the profile data of the test block after correction conforms to the true profile of the block to be tested, and the average error between the true profile data of the test block and the corrected profile data is less than 1mm.

[0064] Based on the present application, the profile data measured under water can be corrected in the case that the basic parameters of the linear laser are known, and the requirement of high-precision measurement of workpieces by the linear laser in the underwater environment can be realized.

Claims

1. A method for underwater profile measurement and correction of a line laser based on an optical path model, characterized in that, Including the following: Step 1: Waterproof sealing and encapsulation of the line laser; Step 2: Securely install the line laser in the underwater environment, allowing for free height adjustment; Step 3: Establish the first optical path mathematical model to describe the equation for height change in line laser underwater measurement, and the second optical path mathematical model to describe the equation for contour correction in line laser underwater measurement; Step 4: Place the test block underwater and use a line laser to measure the contour of the test block based on the first optical path mathematical model; Step 5: Based on the second optical path mathematical model, correct the measurement contour data obtained in Step 4.

2. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 1, characterized in that: In step 1, a transparent acrylic cuboid box with a thickness of no more than 5mm is used to waterproof and seal the line laser. A limiting device is set inside the box to ensure that the line laser is fixed inside the box, thereby reducing the error caused by the movement of the line laser when detecting the contour.

3. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 1, characterized in that: In step 2, a screw connection device is used to fix the line laser onto the stand, which is placed on a water tank with a depth of 700mm. The height of the line laser can be adjusted by the screw.

4. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 1, characterized in that: Step 3 includes acquiring the parameters of the line laser, and establishing a first optical path mathematical model based on the line laser parameters, which is an equation for underwater height measurement using the line laser. The equation is as follows: In the formula, L(h) is the distance reference between the line laser and the object being measured when measuring underwater, and h is the contour measurement value obtained by the line laser when measuring underwater. When h = 0, L(0) = 516.2 mm, which means that when the height of the object contour measured by the line laser underwater is 0, the distance between the contour surface and the line laser is 516.2 mm. Based on the parameters of the line laser, a mathematical model for the second optical path is established, along with the line laser underwater measurement profile correction equation, as follows: In the formula, △N represents the value that needs to be corrected for the profile height obtained by the line laser underwater measurement, x is the xth measurement value (x∈[1,3200]), L(h) is the expression obtained by the optical path mathematical model I, and h is the profile measurement value obtained by the line laser underwater measurement.

5. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 1, characterized in that: In step 4, the test block placed underwater is a stepped test block, so that when the line laser performs contour measurement on the test block, it can obtain stepped contour data.

6. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 4, characterized in that: In step 4, based on the results of the first optical path mathematical model, the height of the line laser is adjusted using a screw adjustment device so that when the line laser is 516.2mm away from the object being measured, the contour data of the object being measured can be obtained.

7. The underwater profile measurement and correction method for a line laser based on an optical path model as described in claim 6, characterized in that: Step 5 corrects the contour data obtained in step 4. The correction method is: the true contour value N of the xth measurement value (x∈[1,3200]) is h + ΔN.

Images