CN110806571B - A multi-structured light sensor space attitude calibration component and its calibration method - Google Patents

Abstract

The invention discloses a multi-line structured light sensor spatial attitude calibration method, which belongs to the field of precision measurement. Based on multiple line structured light sensors and special-shaped calibration components, the present invention proposes a calibration component for spatial attitude calibration of multi-structured light sensors and a calibration method thereof. This method is suitable for the measurement of mechanical parts with rotating axes by multiple line-structured light sensors distributed along the circumferential direction. This method uses the least squares method to fit two straight lines, and by analyzing and calculating the coordinate data relationship of the fitting results, it achieves the calibration of the pose relationship of multiple line structure light sensors.

Description

A multi-structured light sensor space attitude calibration component and its calibration method

Technical field

The invention relates to a standard component for spatial attitude calibration of a multi-structured light sensor and a calibration method thereof, and belongs to the field of precision measurement.

Background technique

The line structured light sensor is a sensor developed based on the principle of laser triangulation. It can obtain the distance between the sensor laser zero plane and the surface of the measured object within a certain range. The line structured light sensor is a non-contact measurement. Its fast, high-precision, simple structure and ease of use facilitate industrial applications. The sensor is highly packaged and users can use lasers for precise measurements without having to understand laser knowledge. Under normal circumstances, line structured light sensors output two-dimensional data. After appropriate calibration and calculation, the three-dimensional information of the measured object can be derived.

Before measuring the geometric dimensions of the object surface, the spatial position relationship between the line structured light sensor and the coordinate system of the measured object must be calibrated. The calibration method is closely related to the geometric shape of the measured object and the structure of the measurement system. For rotating measurement mechanisms and systems, the measured object is generally represented by the polar coordinate system (two-dimensional) or the cylindrical coordinate system (three-dimensional), so the coordinate calibration of the line structured light sensor must also be performed in the cylindrical coordinate system. The calibration method in this article is to convert the two-dimensional distance values measured by multiple line structured light sensors into the three-dimensional values of the cylindrical coordinate system of the measured object: (ρ, θ, h).

In the actual measurement process, it is necessary to select an appropriate calibration method according to the characteristics of the object to be measured. This method is aimed at using multiple line structured light sensors to measure rotating parts such as cylindrical parts (cylinders, gears, etc.), and the rotating parts are placed with a rotatable shaft. Attitude calibration of the attached sensor. During the calibration process, a calibration piece needs to be placed in the center of the rotating shaft system. Specific points, lines or surfaces on the calibration piece have been measured and evaluated by other measuring instruments, so that their accuracy information is known. By correlating the measurement data of this calibration piece from the line structured light sensor with the existing accuracy information, the position and results of the line structured light sensor can be calibrated. Different measurement sensors and devices use different calibration parts for calibration. Calibration parts are generally mechanical parts with special shapes, which are generally called heterogeneous calibration parts.

Contents of the invention

In order to solve the coordinate calibration problem of multiple line structure light sensors around the rotation axis, the patent of the present invention proposes a special-shaped calibration piece and a calibration method. This method fixes the high-precision special-shaped calibration piece proposed by the patent of this invention to the rotary shaft system, adjusts the relative position of each line structure light sensor and the special-shaped calibration piece, and aligns the light of the line structure light sensor with a certain angle to the calibration device and makes the laser line Across the groove of the special-shaped calibration piece, the surface of the special-shaped calibration piece is within the range of the sensor, and the measurement value can be read normally. As shown in Figure 1, l is the laser width of the line structure light sensor, and the groove of the calibration device is the deepest. is approximately in the middle of the laser plane. Coordinate calibration is carried out on this basis.

The posture heterosexual calibration component involved in the present invention is based on a cube metal block, with isosceles triangles of the same height cut on its front, rear, left and right sides respectively. A through hole is provided in the center of the calibration component to facilitate the fixation of the chuck. The front, rear, left, and right sides of the anisotropic calibration piece are composed of two sides of an isosceles triangle. Use a three-dimensional coordinate measuring machine or other measuring device to measure the accuracy information.

A method for spatial attitude calibration of multi-line structured light sensors. The specific steps of this method are as follows:

S1. Establish a theoretical position model of the surface of the line structured light sensor and calibration device;

The theoretical positions of the line structure light sensor and anisotropic calibration parts are:

First, the laser plane of the line structured light sensor is perpendicular to the front, rear, left, and right planes of the calibration piece.

Second, the laser plane of the line structure light sensor is bisected by the fixed point of the isosceles triangle, that is, the vertex of the isosceles triangle is at the center of the laser plane.

On the basis of the above theoretical position, let the angle between the upper and lower surfaces of the special-shaped calibration piece on the same side be α, and the sensor laser width be l. Assume that under ideal circumstances, the intersection of the sensor laser plane and the plane is perpendicular, and the line structure light sensor and the special-shaped calibration are established. The theoretical position model of the component, then the measurement data of the sensor at this time is shown in Figure 2.

The angle between the two measuring straight lines is α, where

Among them, OA ₀ is the contact depth between the laser direction of the line structure light sensor and the heterogeneous calibration piece, and is the normal distance from the vertex of the isosceles triangle to the line connecting the farthest end of the contact between the laser plane and the heterogeneous calibration piece.

S2. Position and orientation judgment when the laser plane is deflected along the X direction;

Based on the theoretical position model described in S1, when the laser plane is deflected only in the X direction, the left and right distribution of the measurement data in the line structured light sensor remains unchanged, but the measurement data in the Y direction changes, and the maximum value is larger than OA ₀ . As shown in Figure 3, OA is the actual height of the line structure light sensor in contact with the anisotropic calibration piece when the X direction is offset. Then the deflection angle of the laser plane is:

S3. Position and orientation judgment when the laser plane is deflected only in the Y direction;

When the laser plane is deflected only in the Y direction, the measurement data in the line structure light sensor, the maximum value in the Y direction remains unchanged, but the left and right distribution is not equal, as shown in Figure 4, the length on the left is l ₀ and the length on the right is l ₁ , the left-right ratio determines the Y-direction deflection of the sensor. The Y-axis deflection angle α _y of the laser plane is:

S4. Laser plane pose judgment at general positions;

The posture of a linear structured light sensor in a general position will deflect along the X and Y directions simultaneously, and the actual measured values of the special-shaped calibration parts have corresponding errors. The measurement results are shown in Figure 5.

As shown in the figure, the scattered points are the measurement data of the line structure light sensor. Let the left data S ₀ ={x ₀ , x ₁ ,..., x _n } and the right data S ₁ ={x ₀ , x ₁ ,..., x _m }, and the expressions of the two straight lines on the left and right

According to the least squares method, two straight lines are fitted respectively:

After the fitting is completed, then According to the analysis of S2 and S3, it can be obtained that

S5. Fix the special-shaped calibration piece to the rotating coordinate system, such as a high-precision turntable and other equipment, rotate the special-shaped calibration piece, and find the time when the maximum value A in the measured data of the structured light sensor is the smallest, the value is A ₀ ,

but

At this point, the coordinate relationship calibration of the line structured light sensor is completed.

The patent of this invention proposes a special-shaped calibration piece suitable for spatial attitude calibration of multiple line structure light sensors and a corresponding calibration method. The structure is simple and clear, and the current manufacturing technology level can process high-precision geometric features. This special-shaped calibration piece can be used on a universal rotating platform. It uses the linear characteristics of the intersection between the surface of the special-shaped calibration piece and the laser plane of the line structure light sensor to perform coordinate conversion and position and attitude calibration. It has high accuracy and uses least squares to fit the straight line. The technology is mature, the accuracy is high, and it can truly reflect the actual coordinate numerical relationship.

Description of the drawings

Figure 1 is an overall diagram of the calibration principle.

Figure 2 is an illustration of the ideal location layout.

Figure 3 is a schematic diagram of deflection in the X direction.

Figure 4 is a schematic diagram of deflection in the Y direction.

Figure 5 is a schematic diagram of the general position of Y.

Detailed ways

The present invention will be described below with reference to specific calibration examples.

Choose an appropriate method to fix the four line structured light sensors so that their laser planes intersect with the special-shaped calibration parts in an oblique direction. Adjust the relative positions of each line structured light sensor and the special-shaped calibration parts so that each plane of the special-shaped calibration parts is in contact with the online structured light sensor. The vertices of the isosceles triangle within the measurement range and the laser plane spans the front, rear, left, and right directions of the special-shaped calibration piece.

According to the above calibration steps, perform the following operations on each line structured light:

Select _{an appropriate position} to obtain a two-dimensional point set Trigonometric functions calculate OA and OA ₀ , then according to The tilt angle α _x of the line structured light sensor in the x direction can be calculated.

On the basis of step 1, use the relationship between the sides and angles of the triangle to calculate l ₀ and l ₁ , according to The tilt angle α _y of the line structured light sensor in the y direction can be obtained.

Repeat steps 1 and 2 several times and calculate the average value to obtain the accurate spatial attitude.

Claims (2)

1. A multi-line structured light sensor spatial attitude calibration method. Using the measurement characteristics of the line structured light sensor and the measurement position relationship of the rotating part, a special coordinate position calibration component is designed. On the basis of the high-precision cube, it is based on the standard cube. An isosceles triangle of the same height is cut into the front, back, left and right sides respectively, forming a concave polyhedron, which serves as the measurement plane of the structured light sensor. The measurement result of the sensor is two intersecting straight lines; the laser plane of each structured light sensor is The calibration piece intersects into two straight lines. By accurately fitting these two straight lines, the spatial geometric relationship between each sensor and the calibration piece is obtained. Finally, the coordinate value of each line structure light sensor is converted into a rotational measurement coordinate system; it is characterized by: , including the following steps: Step 1: Fix each line structured light sensor in an appropriate manner so that its plane laser beam intersects with the special-shaped calibration piece from the oblique direction. Adjust the position so that the laser contact area is within the effective measurement area of the line structured light sensor. The measurement data is in the sensor coordinate system. Two-dimensional data, take the average of multiple measurements, and obtain the two-dimensional point set X ₀ = (x _i ,y _i ) Step 2: Select the fitting areas of the two straight lines respectively, and fit the two straight lines respectively to obtain the straight line parameters. Step 3: Calculate the angle between the structured light and the x and y axes of the rotating coordinate system based on the angle between the two straight lines. Step 4: Calculate the angle between the structured light sensor and the z-axis direction of the rotating coordinate system based on the projection of the two straight lines on the x-axis; Step 5: Convert the coordinate data of the line structured light sensor to the rotating coordinate system to complete the coordinate calibration. 2. A multi-line structured light sensor spatial attitude calibration method according to claim 1, characterized in that the specific steps of the method are as follows: S1. Establish a theoretical position model of the surface of the line structured light sensor and calibration device; The theoretical positions of the line structure light sensor and anisotropic calibration parts are: The laser plane of the line structure light sensor is bisected by the vertex of the isosceles triangle, that is, the vertex of the isosceles triangle is at the center of the laser plane; On the basis of the above theoretical position, assume that the angle between the upper and lower surfaces of the special-shaped calibration piece on the same side is α, and the sensor laser width is l. Suppose that under ideal circumstances, the sensor laser plane is perpendicular to the plane intersection of the upper and lower surfaces of the special-shaped calibration piece on the same side, Establish a theoretical position model of the line structure light sensor and anisotropic calibration parts; The angle between two intersecting straight lines is α, where Among them, OA ₀ is the contact depth between the laser direction of the line structure light sensor and the heterogeneous calibration piece, and is the normal distance from the vertex of the isosceles triangle to the line connecting the farthest end of the contact between the laser plane and the heterogeneous calibration piece; S2. Position and orientation judgment when the laser plane is deflected along the X direction; Based on the theoretical position model described in S1, when the laser plane is deflected only in the X direction, the left and right distribution of the measurement data in the line structure light sensor remains unchanged, the measurement data in the Y direction changes, and OA is the shift in the X direction. When , the actual height of the line structured light sensor in contact with the anisotropic calibration piece; then the deflection angle of the laser plane is: S3. Position and orientation judgment when the laser plane is deflected only in the Y direction; When the laser plane is deflected only in the Y direction, the measurement data in the line structure light sensor, the maximum value in the Y direction remains unchanged, the length of the left side of the vertical center of the triangle base l ₀ , the length of the right side of the vertical center of the triangle base l ₁ , left and right The ratio determines the degree of deflection of the sensor in the Y direction. The Y-axis deflection angle α _v of the laser plane is: S4. Laser plane pose judgment at general positions; The posture of a linear structured light sensor in a general position will deflect in both the X and Y directions at the same time, and the actual measured values of the special-shaped calibration parts will have corresponding errors; The scattered points are the measurement data of the line structured light sensor. Let the left data D ₀ ={x ₀ , x ₁ ,..., x _n } and the right data S ₁ ={x ₀ , x ₁ ,..., x _m }, and the expressions of the two straight lines on the left and right According to the least squares method, two straight lines are fitted respectively: After the fitting is completed, then According to the analysis of S2 and S3, it can be obtained that S5. Fix the special-shaped calibration piece to the rotating coordinate system, use a high-precision turntable to rotate the special-shaped calibration piece, and find A ₀ ; but At this point, the coordinate relationship calibration of the line structured light sensor is completed.