Calibration method of point laser measuring device

Abstract

The invention discloses a calibration method of a point laser measuring device, which comprises the following steps: constructing a calibration auxiliary device of the point laser measuring device, the calibration auxiliary device comprises a vertical guide shaft, the vertical guide shaft is provided with a mounting back plate which moves in the vertical direction, the mounting back plate is provided with a reflecting plate and a calibration block, and the reflecting plate and the calibration block are arranged on the vertical guide shaft; the reflecting plate is matched with a laser interferometer, and the calibration block is matched with a point laser measuring device; adjusting the positions of the laser interferometer and the point laser measuring device relative to the vertical guide shaft, and ensuring that the laser emission paths of the point laser measuring device and the laser interferometer are parallel to the vertical movement direction of the mounting back plate; dividing the measuring range of a point laser measuring device into n intervals at equal intervals, acquiring real measurement data of n + 1 positions by using the laser interferometer, and acquiring n + 1 original measurement data by using the point laser measuring device; and constructing a cubic function of each interval by using the data.

Description

Technical field

[0001] The present invention relates to the field of measurement technology, and in particular to a calibration method for a point laser measurement device. [Background Technology]

[0002] Point laser measurement devices (such as point laser displacement sensors) are primarily used in industrial inspection environments, where the application environment is complex and some applications require very high measurement accuracy. Due to the high cost control requirements placed on point laser measurement devices, the quality of the optical lenses in point laser measurement devices is generally poor, which leads to large lens distortion. This is reflected in the fact that the measurement data obtained at equally spaced positions using the point laser measurement device (such as raw measurement data of height or displacement) does not change linearly. Directly using the raw measurement data will undoubtedly result in errors. Therefore, it is necessary to design a precise calibration algorithm to ensure that the point laser measurement device can output highly accurate measurement data over the entire range. [Summary of the invention]

[0003] The object of the present invention is to provide a calibration method for a point laser measuring device, so as to solve the problem in the prior art that the original measurement data of the point laser measuring device has large errors due to large lens distortion of the point laser measuring device.

[0004] To achieve the above-mentioned purpose, the calibration method of the point laser measuring device of the present invention comprises the following steps:

[0005] Step 1: Constructing a calibration auxiliary device for a point laser measuring device, the calibration auxiliary device comprising a vertical guide shaft, wherein the vertical guide shaft comprises a mounting back plate, the mounting back plate is moved in a vertical direction by a driving device, a reflector and a calibration block are provided on the mounting back plate, wherein the reflector cooperates with a laser interferometer to obtain an actual travel distance value of the mounting back plate, and the calibration block cooperates with a point laser measuring device to obtain a travel distance measurement value of the mounting back plate through the point laser measuring device;

[0006] Step 2: Adjust the positions of the laser interferometer and the point laser measuring device relative to the vertical guide axis to ensure that the laser emitted by the point laser measuring device irradiates the same position of the calibration block at the maximum and minimum positions of the range of the point laser measuring device, and ensure that the laser emission paths of the point laser measuring device and the laser interferometer are parallel to the vertical movement direction of the mounting backplate;

[0007] Step 3: Data collection step, dividing the measuring range of the point laser measuring device into n preset intervals at equal intervals, causing the mounting back plate to move according to the aforementioned intervals, using the laser interferometer to collect real measurement data at n+1 positions, and using the point laser measuring device to obtain n+1 raw measurement data;

[0008] Step 4: Construct a cubic function for each interval using the actual measurement data of n+1 positions collected by the laser interferometer and the n+1 original measurement data obtained by the point laser measurement device.

[0009] Preferably, the specific steps of constructing the cubic function of each interval segment in step 4 are as follows:

[0010] Divide the range [a,b] of the point laser measuring device into [(x0,x1),(x1,x2),...,(x n-1 ,x n )], where a=x0, b=x n , so there are n+1 points and n intervals. In each interval, a cubic function is used for interpolation. It is required that the first-order derivatives and second-order derivatives of the endpoints are equal. According to the interpolation node function value is equal to the value of the sample point, that is, the left and right sides meet the interpolation conditions. There are 2n equations in total. The first-order derivative is continuous at each node (n-1 equations) and the second-order derivative is continuous at each node (n-1 equations). A total of 4n-2 equations are obtained. In fact, a i ,b i ,c i ,d i There are 4n unknowns in total. These two equations are obtained by setting natural boundary conditions and specifying the second-order derivative at the endpoint as a constant f i ”(x0)=A,f i ”(x n )=B, where the cubic function of each interval is set as:

[0011] f i (x) = a i +b i (xx i )+c i (xx i ) 2 +d i (xx i ) 3 ,i=[0,...,n-1] (1.1)

[0012] The first-order derivative is:

[0013] f i '(x)=b i +2c i (xx i )+3d i (xx i ) 2 ,i=[0,...,n-1] (1.2)

[0014] The second-order derivative is:

[0015] f i ”(x)=2c i +6d i (xx i ),i=[0,...,n-1] (1.3)

[0016] According to the definition of interpolation, the left endpoint of each function is equal to its function value, and n equations can be obtained:

[0017] f i (x i )=a i +b i (x i -x i )+c i (x i -x i ) 2 +d i (x i -x i ) 3 =y i ,i=[0,...,n-1](1.4)

[0018] According to the definition of interpolation, the right endpoint of each function is equal to its function value, and n equations can be obtained:

[0019] f i (x i+1 )=a i +b i (x i+1 -x i )+c i (x i+1 -x i ) 2 +d i (x i+1 -x i ) 3 =y i+1 ,i=[0,...,n-1](1.5)

[0020] Let h i =x i+1 -x i , we can get:

[0021]

[0022] According to the continuity condition of the first-order derivative, except for the first endpoint, the left and right first-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained:

[0023] b i +2ci (x i+1 -x i )+3d i (x i+1 -x i ) 2 =(1.7)

[0024] b i+1 +2c i+1 (x i+1 -x i+1 )+3d i+1 (x i+1 -x i+1 ) 2 ,i=[0,...,n-2]

[0025] From the above h i =x i+1 -x, you get:

[0026]

[0027] According to the continuity condition of the second-order derivative, except for the first endpoint, the left and right second-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained:

[0028] 2c i +6d i (x i+1 -x i )=2c i+1 +6d i+1 (x i+1 -x i+1 ),i=[0,1,...,n-2](1.9)

[0029] From the above h i =x i+1 -x, you get:

[0030] 2c i +6d i h i =2c i+1 ,i=[0,1,...,n-2] (1.10)

[0031] Let f i ”(x i )=m i , where i=[0,1,...n,,] the subsequent steps are around n+1 m i Solve the equations with the value of ; when i=[0,1,...,n-1], we can get from formula (1.3):

[0032] m i =2c i (1.11)

[0033] Substituting equation (1.11) into equation (1.10), we can obtain:

[0034]

[0035] Substituting equations (1.12) and (1.4) into equation (1.6), we can obtain:

[0036]

[0037] Substituting equations (1.11), (1.12), and (1.13) into equation (1.8), we can obtain:

[0038]

[0039] We can get about m i There are n-1 equations in m, and n+1 unknowns. Add two boundary conditions.

[0040] f0”(x0)=0 (1.15)

[0041] f n ” -1 (x n )=0 (1.16)

[0042] Write it in matrix form:

[0043]

[0044] After solving the matrix (1.17), all equation parameters can be obtained:

[0045]

[0046] Through the above method, after the original measurement height is obtained by using the point laser measuring device, the corresponding cubic function can be determined by calling the corresponding coefficient according to the original measurement height within the range of the point laser measuring device, thereby obtaining the original measurement height according to the point laser measuring device and outputting the corrected accurate measurement value.

[0047] Preferably, in step three, the process of obtaining n+1 raw measurement data by using the point laser measurement device includes the steps of turning on automatic exposure and mean filtering, so as to make the data collected by the point laser measurement device more stable.

[0048] Preferably, after calibration using the above method, the step of storing the above-mentioned range interval, cubic function and the corresponding coefficients of the cubic function corresponding to each range interval into the point laser measuring device is also included, so that after the point laser measuring device obtains the original measurement data, the above-mentioned cubic function can be directly used to output the corrected accurate measurement value.

[0049] Compared with the prior art, the calibration method of a point laser measuring device embodying the present invention divides the measuring range of the point laser measuring device into intervals, then uses the actual measurement data corresponding to the starting point of each interval of the laser interferometer and the point laser measuring device to obtain the corresponding original measurement data, and then uses the above data to construct a cubic function corresponding to each interval. In this way, the original measurement data of the point laser measuring device is corrected using this cubic function to obtain accurate measurement values, thereby solving the problem of large errors in the original measurement data of the point laser measuring device due to large lens distortion of the point laser measuring device.

Brief Description of the Drawings

[0050] Figure 1 The figure is a flow chart of a calibration method for a point laser measurement device according to the present invention.

[0051] Figure 2 A schematic structural diagram of a calibration auxiliary device used to implement the calibration method of a point laser measurement device of the present invention. [Specific implementation method]

[0052] See also Figure 1 FIG. 1 is a flow chart of a method for calibrating a point laser measuring device according to the present invention. The method for calibrating a point laser measuring device according to the present invention comprises the following steps:

[0053] Step 1: Construct a calibration auxiliary device for a point laser measurement device. The calibration auxiliary device includes a vertical guide shaft 10, wherein the vertical guide shaft 10 includes a mounting backplate 11. The mounting backplate 11 is moved in a vertical direction by a drive device (not shown). A reflector 12 and a calibration block 13 are provided on the mounting backplate 11. The reflector 12 cooperates with a laser interferometer 2 to obtain the actual movement distance value of the mounting backplate 11, and the calibration block 13 cooperates with a point laser measurement device 3 to obtain the movement distance measurement value of the mounting backplate 11 by the point laser measurement device 3 (using triangulation method);

[0054] Step 2: Adjust the positions of the laser interferometer and the point laser measuring device relative to the vertical guide axis to ensure that the laser emitted by the point laser measuring device irradiates the same position of the calibration block at the maximum and minimum positions of the range of the point laser measuring device, and ensure that the laser emission paths of the point laser measuring device and the laser interferometer are parallel to the vertical movement direction of the mounting backplate;

[0055] Step 3: Data collection step, dividing the measuring range of the point laser measuring device into n preset intervals at equal intervals, causing the mounting back plate to move according to the aforementioned intervals, using the laser interferometer to collect real measurement data at n+1 positions, and using the point laser measuring device to obtain n+1 raw measurement data;

[0056] Step 4: Construct a cubic function for each interval using the actual measurement data of n+1 positions collected by the laser interferometer and the n+1 original measurement data obtained by the point laser measurement device.

[0057] In specific implementation, the specific steps of constructing the cubic function of each interval segment in step 4 are as follows:

[0058] Divide the range [a,b] of the point laser measuring device into [(x0,x1),(x1,x2),...,(x n-1 ,x n )], where a=x0, b=x n , so there are n+1 points and n intervals, where a is the first data collected by the above laser interferometer (i.e., the data at the minimum range position), and b is the last data collected by the above laser interferometer (i.e., the data corresponding to the n+1th point, i.e., the data at the maximum range position). In each interval, a cubic function is used for interpolation, requiring the left and right first-order derivatives and second-order derivatives of the endpoints to be equal. According to the interpolation node function value equal to the value of the sample point, that is, the left and right sides meet the interpolation conditions, a total of 2n equations, and the first-order derivative is continuous at each node (n-1 equations) and the second-order derivative is continuous at each node (n-1 equations), a total of 4n-2 equations are obtained. In fact, a i ,b i ,c i ,d i There are 4n unknowns in total. These two equations are obtained by setting natural boundary conditions and specifying the second-order derivative at the endpoint as a constant f i ”(x0)=A,f i ”(x n )=B, where the cubic function of each interval is set as:

[0059] f i (x) = a i +b i (xx i )+c i (xx i ) 2 +d i (xx i ) 3 ,i=[0,...,n-1] (1.1)

[0060] The first-order derivative is:

[0061] f i '(x)=b i +2c i (xx i )+3d i (xx i ) 2 ,i=[0,...,n-1] (1.2)

[0062] The second-order derivative is:

[0063] f i ”(x)=2c i +6d i (xx i ),i=[0,...,n-1] (1.3)

[0064] According to the definition of interpolation, the left endpoint of each function is equal to its function value, and n equations can be obtained:

[0065] f i (x i )=a i +b i (x i -x i )+c i (x i -x i ) 2 +d i (x i -x i ) 3 =y i ,i=[0,...,n-1] (1.4)

[0066] According to the definition of interpolation, the right endpoint of each function is equal to its function value, and n equations can be obtained:

[0067] f i (x i+1 )=a i +b i (x i+1 -x i )+c i (x i+1 -x i ) 2 +d i (x i+1 -x i ) 3 =y i+1 ,i=[0,...,n-1] (1.5)

[0068] Let h i =xi+1 -x i , we can get:

[0069]

[0070] According to the continuity condition of the first-order derivative, except for the first endpoint, the left and right first-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained:

[0071]

[0072] From the above h i =x i+1 -x, you get:

[0073]

[0074] According to the continuity condition of the second-order derivative, except for the first endpoint, the left and right second-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained:

[0075] 2c i +6d i (x i+1 -x i )=2c i+1 +6d i+1 (x i+1 -x i+1 ),i=[0,1,...,n-2] (1.9)

[0076] From the above h i =x i+1 -x, you get:

[0077] 2c i +6d i h i =2c i+1 ,i=[0,1,...,n-2] (1.10)

[0078] Let f i ”(x i )=m i , where i=[0,1,...n,,] the subsequent steps are around n+1 m i Solve the system of equations with the value of ;

[0079] When i = [0, 1, ..., n-1], from formula (1.3) we can get:

[0080] m i =2c i (1.11)

[0081] Substituting equation (1.11) into equation (1.10), we can obtain:

[0082]

[0083] Substituting equations (1.12) and (1.4) into equation (1.6), we can obtain:

[0084]

[0085] Substituting equations (1.11), (1.12), and (1.13) into equation (1.8), we can obtain:

[0086]

[0087] We can get about m i There are n-1 equations in m, and n+1 unknowns. Add two boundary conditions.

[0088] f0”(x0)=0 (1.15)

[0089] f n ” -1 (x n )=0 (1.16)

[0090] Write it in matrix form:

[0091]

[0092] After solving the matrix (1.17), all equation parameters can be obtained:

[0093]

[0094] Through the above method, after the original measurement height is obtained by using the point laser measuring device, the corresponding cubic function can be determined by calling the corresponding coefficient according to the original measurement height within the range of the point laser measuring device, thereby obtaining the original measurement height according to the point laser measuring device and outputting the corrected accurate measurement value.

[0095] In addition, in step three, the process of obtaining n+1 raw measurement data by using the point laser measurement device includes the steps of turning on automatic exposure and mean filtering, so as to make the data collected by the point laser measurement device more stable.

[0096] Furthermore, after calibration using the above method, the above range interval, cubic function and the corresponding coefficients of the cubic function corresponding to each range interval are stored in the point laser measuring device. In this way, after the point laser measuring device obtains the original measurement data, the above cubic function can be directly used to output the corrected accurate measurement value.

[0097] Compared with the prior art, the calibration method of a point laser measuring device embodying the present invention divides the measuring range of the point laser measuring device into intervals, then uses the actual measurement data corresponding to the starting point of each interval of the laser interferometer and the point laser measuring device to obtain the corresponding original measurement data, and then uses the above data to construct a cubic function corresponding to each interval. In this way, the original measurement data of the point laser measuring device is corrected using this cubic function to obtain accurate measurement values, thereby solving the problem of large errors in the original measurement data of the point laser measuring device due to large lens distortion of the point laser measuring device.

[0098] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A calibration method for a point laser measuring device, characterized in that The method comprises the following steps: Step 1: Constructing a calibration auxiliary device for a point laser measuring device, the calibration auxiliary device comprising a vertical guide shaft, wherein a mounting back plate is provided on the vertical guide shaft, the mounting back plate is moved in a vertical direction by a driving device, a reflector and a calibration block are provided on the mounting back plate, wherein the reflector cooperates with a laser interferometer to obtain an actual travel distance value of the mounting back plate, and the calibration block cooperates with a point laser measuring device to obtain a travel distance measurement value of the mounting back plate through the point laser measuring device; Step 2: Adjust the positions of the laser interferometer and the point laser measuring device relative to the vertical guide axis to ensure that the laser emitted by the point laser measuring device irradiates the same position of the calibration block at the maximum and minimum positions of the range of the point laser measuring device, and ensure that the laser emission paths of the point laser measuring device and the laser interferometer are parallel to the vertical movement direction of the mounting backplate; Step 3: Data collection step, dividing the measuring range of the point laser measuring device into n preset intervals at equal intervals, causing the mounting back plate to move according to the aforementioned intervals, using the laser interferometer to collect real measurement data at n+1 positions, and using the point laser measuring device to obtain n+1 raw measurement data; Step 4: Construct a cubic function for each interval using the actual measurement data of n+1 positions collected by the laser interferometer and the n+1 original measurement data obtained by the point laser measurement device.

2. The calibration method of a point laser measuring device according to claim 1, wherein: The specific steps for constructing the cubic function for each interval segment in step 4 are as follows: Divide the range [a,b] of the point laser measuring device into [(x0,x1),(x1,x2),...,(x n-1 ,x n )], where a=x0, b=x n , so there are n+1 points and n intervals. In each interval, a cubic function is used for interpolation. It is required that the first-order derivatives and second-order derivatives of the endpoints are equal. According to the interpolation node function value is equal to the value of the sample point, that is, the left and right sides meet the interpolation conditions. There are 2n equations in total. The first-order derivative is continuous at each node (n-1 equations) and the second-order derivative is continuous at each node (n-1 equations). A total of 4n-2 equations are obtained. In fact, a i ,b i ,c i ,d i There are 4n unknowns in total. These two equations are obtained by setting natural boundary conditions and specifying the second-order derivative at the endpoint as a constant f i ”(x0)=A,f i ”(x n )=B, where the cubic function of each interval is set as: f i (x)=a i +b i (x-x i )+c i (x-x i ) 2 +d i (x-x i ) 3 ,i=[0,...,n-1](1.1) The first-order derivative is: f i '(x)=b i +2c i (x-x i )+3d i (x-x i ) 2 ,i=[0,...,n-1](1.2) The second-order derivative is: f i ”(x)=2c i +6d i (x-x i ),i=[0,...,n-1](1.3) According to the definition of interpolation, the left endpoint of each function is equal to its function value, and n equations can be obtained: f i (x i )=a i +b i (x i -x i )+c i (x i -x i ) 2 +d i (x i -x i ) 3 =y i ,i=[0,...,n-1](1.4) According to the definition of interpolation, the right endpoint of each function is equal to its function value, and n equations can be obtained: f i (x i+1 )=a i +b i (x i+1 -x i )+c i (x i+1 -x i ) 2 +d i (x i+1 -x i ) 3 =y i+1 ,i=[0,...,n-1](1.5) Let h i =x i+1 -x i , we can get: According to the continuity condition of the first-order derivative, except for the first endpoint, the left and right first-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained: From the above h i =x i+1 -x, you get: According to the continuity condition of the second-order derivative, except for the first endpoint, the left and right second-order derivatives of the middle n-1 endpoints are equal, and n-1 equations can be obtained: 2c i +6d i (x i+1 -x i )=2c i+1 +6d i+1 (x i+1 -x i+1 ),i=[0,1,...,n-2](1.9) From the above h i =x i+1 -x, you get: 2c i +6d i h i =2c i+1 ,i=[0,1,...,n-2](1.10) Let f i ”(x i )=m i , where i=[0,1,...n,,] the subsequent steps are around n+1 m i Solve the system of equations with the value of ; When i = [0, 1, ..., n-1], from formula (1.3) we can get: m i =2c i (1.11) Substituting equation (1.11) into equation (1.10), we can obtain: Substituting equations (1.12) and (1.4) into equation (1.6), we can obtain: Substituting equations (1.11), (1.12), and (1.13) into equation (1.8), we can obtain: We can get about m i There are n-1 equations in m, and n+1 unknowns. Add two boundary conditions. f0”(x0)=0(1.15) f n ” -1 (x n )=0(1.16) Write it in matrix form: After solving the matrix (1.17), all equation parameters can be obtained: Through the above method, after the original measurement height is obtained by using the point laser measuring device, the corresponding cubic function can be determined by calling the corresponding coefficient according to the original measurement height within the range of the point laser measuring device, thereby obtaining the original measurement height according to the point laser measuring device and outputting the corrected accurate measurement value.

3. The calibration method of a point laser measuring device according to claim 1, wherein: In step three, the process of obtaining n+1 raw measurement data by using the point laser measurement device includes the steps of turning on automatic exposure and mean filtering, so as to make the data collected by the point laser measurement device more stable.

4. The calibration method of a point laser measuring device according to claim 1, wherein: After calibration is performed using the above method, the method further includes storing the above range intervals, cubic functions and coefficients of the cubic functions corresponding to each range interval in the point laser measuring device.

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