A Turntable-Based Line Structured Light Nonlinear Scanning 3D Data Measurement Method

Abstract

This invention belongs to the field of computer vision, specifically a method for measuring 3D data using line-structured light non-linear scanning based on a turntable. The method includes the following steps: fabricating and installing a turntable calibration ruler; mounting a line-structured light camera directly above the turntable; calibrating the relative pose of the line-structured light emitted by the camera and the turntable to determine the distance between the X-axis origin of the line laser data and the center of the turntable; keeping the line-structured light camera stationary, rotating the turntable one revolution, and triggering the line-structured light through an encoder to complete the scanning of the target on the turntable surface; based on the encoder pulse information, the X-axis coordinates of each frame of data can be converted into polar coordinates, and then calculated into the measured values ​​of the line-structured light in a 3D Cartesian coordinate system relative to the center of the turntable. For line-structured light devices of the same resolution, this invention requires a smaller field of view for rotational scanning than linear scanning, thus achieving higher measurement accuracy at the same resolution and measurement width.

Description

Technical Field

[0001] This invention belongs to the field of computer vision, specifically a method for measuring three-dimensional data using line structured light non-linear scanning based on a turntable. Background Technology

[0002] With the rapid development of science and technology and the continuous improvement of industrial automation in my country, intelligent and flexible production is gradually becoming the future trend. Machine vision, as the "eyes" of machines, plays a crucial role in improving system robustness and flexibility, and has therefore received widespread attention and application. Line structured light, as a high-precision active 3D vision system, provides more height information than traditional 2D vision, enabling it to handle a wider range of application scenarios. Line structured light has been extensively used in projects such as robotic handling, gluing, and polishing.

[0003] Line structured light measurement is an active optical measurement technique. Its basic principle is to project controllable light strips onto the surface of the object being measured using a structured light projector, and an image sensor (such as a camera) captures the image. Then, based on the system's geometric relationships, the object's three-dimensional coordinates are calculated using trigonometric principles. Because line structured light can only collect data points along the laser line, a single frame of data essentially only contains two-dimensional data along the x and z axes. When a complete three-dimensional measurement of the target surface is required, the line structured light device often needs to be moved linearly via a guide rail or a robot end effector, and the y-axis direction information of the three-dimensional data is stitched together from multiple frames. However, this measurement method has certain limitations: although linear scanning allows for unlimited target length, when the target is similar to a circle, with both length and width exceeding the field of view of the line structured light, complete three-dimensional measurement data cannot be obtained. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional measurement method that combines line structured light with turntable rotation to solve the limitation that linear scanning of line structured light does not meet the working range.

[0005] This invention addresses the limitations of linear scanning applications and aims to expand the scanning range of line structured light. It overcomes this limitation by using a scanning method where the line structured light remains stationary while the turntable rotates with the target. Polar coordinate data relative to the turntable's center is acquired by calibrating the relative attitude of the line structured light and the turntable, and the target's three-dimensional Cartesian data is measured through calculation.

[0006] The technical solution adopted by this invention to achieve the above objectives is: a method for measuring three-dimensional data using line structured light non-linear scanning based on a turntable, comprising the following steps:

[0007] 1) Make a calibration ruler for the turntable and install the line structured light camera directly above the turntable; install the calibration ruler so that one end of the calibration ruler coincides with the center of the turntable;

[0008] 2) The relative pose of the line structured light emitted by the line structured light camera and the turntable is calibrated to determine the distance between the X-axis origin of the line laser data and the center of the turntable.

[0009] 3) Keep the line structured light camera stationary and rotate the turntable one revolution. The encoder triggers the line structured light to complete the scanning of the target to be measured on the table. Based on the encoder pulse information, the X-axis coordinate of each frame of data can be converted into polar coordinates, and the result is converted into the measurement value of the line structured light in a three-dimensional rectangular coordinate system relative to the center of the turntable.

[0010] The rotary table calibration ruler includes: a calibration ruler body, a positioning through hole, a center graduation line, and a raised structure;

[0011] The calibration ruler body is a cuboid structure, with a positioning through hole at one end for fitting onto a cylinder located at the center of the turntable to fix the turntable calibration ruler; the center of the positioning through hole coincides with the center of the turntable.

[0012] The calibration ruler has a central engraving line on its top surface; the central engraving line is a straight line pointing to the center of the positioning through hole, used to adjust the relative pose rx, ry, rz of the structured light and the turntable.

[0013] The length of the center scribe line is equal to the length of the turntable radius line;

[0014] The protruding structures are multiple and are arranged sequentially along the central etched line. They are used to adjust the relative positions tx, ty, tz of the structured light and the turntable, as well as to determine the distance between the origin of the line structured light measurement data x value and the center of the turntable.

[0015] The protruding structure is an angular protruding structure, and the longitudinal cross-section of the protruding structure is triangular.

[0016] The installation calibration ruler is specifically as follows:

[0017] The positioning through hole of the calibration ruler is fitted onto the central cylinder set at the center of the turntable. At this time, the center of the positioning through hole is the center of the turntable, the center line of the calibration ruler is the radius line of the turntable, and the distance of the protruding structure of the calibration ruler relative to the center is the scale value of the calibration ruler.

[0018] The calibration of the relative pose of the line structured light emitted by the line structured light camera and the turntable includes the following steps:

[0019] 1-1) Adjust the rz attitude of the line structured light camera coordinate system so that the laser line beam points to the center of the turntable;

[0020] 1-2) Adjust the orientation of the line structured light camera coordinate system rx and ry so that the laser plane should be incident perpendicularly on the turntable plane, so as to ensure that the z-axis of the line structured light camera coordinate system is perpendicular to the turntable plane.

[0021] 1-3) Adjust the coordinate system tx, ty, tz of the line structured light camera to establish a relative relationship between the origin of the structured light camera coordinate system and the scale value d, so as to convert the x-axis data of the line structured light camera coordinate system into distance data relative to the center of the turntable.

[0022] 1-4) Data Conversion: After adjusting rx, ry, rz, tx, ty, and tz, the z-axis of the line structured light is perpendicular to the turntable surface, and the x-axis coincides with the turntable radius. Therefore, the x-value of each measurement data point is converted into a distance value R relative to the center of the circle, i.e.:

[0023] R = xd.

[0024] Adjusting the pose of the line structured light camera coordinate system (rx, ry, rz) includes the following steps:

[0025] a. Adjust the rz attitude: make the laser line bar coincide with the center line of the calibration ruler, so that the x-axis of the line structured light camera coordinate system points to the center of the turntable;

[0026] b. Adjusting the RX attitude: When the line structured light device moves up and down perpendicular to the turntable, if the laser line no longer coincides with the center etched line, it is determined that the laser line is not illuminating the table perpendicularly. Adjust the RX and move the laser line back to coincide with the center etched line. Repeat this process until the laser line always coincides with the center etched line when moving up and down. After adjusting the RX attitude, the laser line is now illuminating the table perpendicularly.

[0027] c. Adjust the ry attitude: Take the coordinates of two points, p1(x1, z1) and p2(x2, z2), on the left and right sides of the online structured light data for observation. If the x-axis of the line structured light is to be parallel to the platform, the ry needs to be adjusted so that the coordinates of the two points meet the following conditions:

[0028] z1 = z2.

[0029] Steps 1-3) are specifically as follows:

[0030] Adjust tx, ty, tz; keep the laser line on the center line, and perform a translational motion on the line structured light so that the origin (0, 0) of the line structured light camera coordinate system falls on the appropriate scale position d of the calibration ruler. When the height of the calibration ruler protrusion is h, observe and adjust it until the coordinate value p of the protrusion corner point satisfies the following conditions:

[0031] p(x, z) = (0, h).

[0032] Step 3) specifically includes:

[0033] 3-1) Rotary scanning: the line structured light camera remains stationary, the turntable drives the target to rotate one full revolution, and the encoder sends a pulse signal to trigger the line structured light to complete scanning while rotating; when the number of encoder pulses for one full revolution is known as N, the degree interval angleStep represented by one pulse is calculated by the following formula:

[0034] angleStep=360 / N

[0035] 3-2) Converting polar coordinate data: converting the contour data collected by each frame of line structured light into polar coordinate data relative to the center of the turntable and the rotation starting position. For the i-th frame of data, each measurement contour point p j (x j , z j ) has the polar coordinate ρ j expressed as:

[0036] ρ j =(R j , i*angleStep, z j )

[0037] wherein, 0≤i<N, j is the data point index in each frame of contour data, R j is the distance R relative to the center of the circle calculated by the formula for the j-th point of the current contour;

[0038] 3-3) Converting Cartesian coordinate data: solving and converting the contour data of all collected frames from polar coordinates to Cartesian coordinate values, converting each measurement point's polar coordinate value ρ(r, θ, z) into Cartesian coordinate p out (x, y, z) by the following formula, that is:

[0039] p out =(r*cosθ, r*sinθ, z);

[0040] 3-4) Restoring the data of each frame to the state relative to the scanning starting position, all collected data are converted into measurement value descriptions of the three-dimensional Cartesian coordinate system relative to the center of the turntable, completing the line structured light three-dimensional data measurement based on turntable rotation.

[0041] The present invention has the following beneficial effects and advantages:

[0042] 1. The present invention expands the scanning range of line structured light through rotation of the turntable, increasing the range of measurement width to at least twice the original, and has high practicality when the linear scanning of line structured light cannot meet the field of view requirements.

[0043] 2. For line structured light devices with the same resolution, the present invention requires a smaller field of view to be covered by rotational scanning than by linear scanning. The data point spacing is equal to the field of view divided by the resolution. Therefore, the present invention has higher measurement accuracy under the same resolution and measurement width.

[0044] 3. This invention is more effective for near-circular targets. Near-circular targets reduce the target-free area in the scanning range on the turntable; and when only the outer contour data of the target needs to be measured, targets of any size can be measured without being limited by the field of view of the line structured light equipment, which is of great significance in actual production. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the upper surface of the calibration ruler of the present invention;

[0046] Figure 2 This is a schematic diagram of the calibration ruler side surface of the present invention;

[0047] Figure 3 This is a schematic diagram of the line structured light adjusting rx attitude of the present invention;

[0048] Figure 4 This is a schematic diagram of the line structured light adjustment posture of the present invention;

[0049] Figure 5 This is a schematic diagram of the line structured light adjustment of tx, ty, tz attitudes according to the present invention;

[0050] Figure 6 This is a schematic diagram illustrating the restoration of the line structured light measurement data to its initial position according to the present invention. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0052] The present invention discloses a three-dimensional measurement method combining line structured light and turntable rotation. The method uses a specially designed calibration ruler to calibrate the relative pose of the line structured light and the turntable, and then converts each frame of data obtained by the line structured light scanning of the turntable rotation into polar coordinate data relative to the center of the turntable. Finally, the collected data is converted into three-dimensional measurement data in a Cartesian system through calculation.

[0053] like Figures 1-2 The diagram shown is a structural schematic of the calibration ruler of this invention. The design process of the calibration ruler specifically includes the following steps:

[0054] 1. Design of the calibration scale

[0055] It is used for pose calibration of turntables and line structured light cameras. By using a specially designed calibration ruler, the relative pose relationship between the coordinate system of the line structured light camera and the center of the turntable is established with high precision. The specially designed calibration ruler mainly includes a positioning through hole, several angular protrusions on a fixed scale, and a center line.

[0056] The positioning through-hole is located at one end of the calibration ruler and is used to fit onto a custom cylinder with the same size as the through-hole at the center of the turntable. When the calibration ruler is installed on the turntable, the center of the through-hole coincides with the center of the turntable. When the calibration ruler is installed on the turntable, the center graduation line is a straight line parallel to the turntable plane and pointing to the center of the turntable, used to adjust the relative attitude rx, ry, rz of the structured light and the turntable. Several angular protrusions are machining features with different distances from the center of the through-hole. When the calibration ruler is installed on the turntable, the distance between the center of the angular line of the protrusion and the center of the turntable is the precise value designed and machined by the calibration ruler, used to adjust the relative position tx, ty, tz of the structured light and the turntable, and also used to determine the distance between the origin of the x-value of the line structured light measurement data and the center, thereby converting the x-axis data into distance data relative to the center. The number of protrusions and the graduation interval can be flexibly designed according to the size of the turntable and the field of view width of the line structured light.

[0057] 2. Relative Pose Calibration Method between Line Structured Light and Turntable

[0058] To establish the relative pose relationship between the structured light camera coordinate system and the turntable center, three requirements need to be met: First, adjust the line structured light camera system's coordinate system (rz) so that the laser line beam points towards the turntable center; second, adjust the line structured light camera system's coordinate systems (rx and ry) so that the laser plane is perpendicular to the turntable plane, ensuring that the z-axis of the line structured light camera coordinate system is perpendicular to the turntable plane; third, adjust the line structured light camera system's coordinate systems (tx, ty, and tz) to convert the x-axis data of the line structured light camera coordinate system into distance data relative to the turntable center. The main steps for the relative pose calibration of the line structured light camera and the turntable are as follows:

[0059] (1) Install the calibration ruler: Place the calibration ruler through hole onto the custom cylinder in the center of the turntable. At this time, the center of the calibration ruler through hole is the center of the turntable, the center line of the calibration ruler is the radius line of the turntable, and the distance between the protruding structure of the calibration ruler and the center is the calibration ruler scale value.

[0060] (2) Adjust the rz attitude: Adjust the rz attitude of the line structured light device so that the laser line light stripe coincides with the center line of the calibration ruler, so that the x-axis of the line structured light camera system points to the center of the turntable.

[0061] (3) Adjust the rx attitude: such as Figure 3As shown, the line structured light device moves up and down perpendicular to the turntable. If the laser line no longer coincides with the center etched line, it means that the laser line is not illuminating the turntable perpendicularly. The rx should be adjusted, and the laser line should be moved back to coincide with the center etched line. Repeat this process until the laser line always coincides with the center etched line when moving up and down. This indicates that the rx adjustment is complete and the laser line is illuminating the turntable perpendicularly.

[0062] (4) Adjust the ry posture: such as Figure 4 As shown, the coordinates of two points, p1(x1,z1) and p2(x2,z2), are observed on the left and right sides of the online structured light data. To make the x-axis of the line structured light parallel to the platform, ry should be adjusted so that the coordinates of the two points satisfy the following condition:

[0063] z1=z2 (1)

[0064] (5) Adjust tx, ty, tz: Keep the laser line on the center line, and perform a translational motion on the line structured light so that the origin (0,0) of the line structured light camera system falls on the appropriate scale position d of the calibration scale, such as... Figure 5 As shown, when the height of the calibrated ruler protrusion is h, it should be adjusted until the coordinate value p of the protrusion corner point satisfies the following condition:

[0065] p(x,z) = (0,h) (2)

[0066] (6) Data Conversion: After adjusting rx, ry, rz, tx, ty, and tz, the z-axis of the line structured light is perpendicular to the turntable surface, and the x-axis coincides with the turntable radius. Therefore, the x-value of each measurement data point can be converted into a distance value R relative to the center of the circle.

[0067] R = xd (3)

[0068] 3. Online measurement

[0069] (1) Rotational Scanning: The line structured light equipment remains stationary, while the turntable rotates the target one revolution. Simultaneously, a pulse signal is sent via the turntable encoder to trigger the line structured light to complete the scan. When the number of encoder pulses per revolution is known as N, the degree interval represented by one pulse can be calculated using the following formula: angleStep:

[0070] angleStep=360 / N (4)

[0071] (2) Convert polar coordinate data: Convert the contour data acquired by each frame of line structured light into polar coordinate data relative to the center of the turntable and the starting position of rotation. For the i-th frame of data, each measured contour point p j (x j ,z j The polar coordinates ρ j The expression form is:

[0072] ρ j =(R j ,i*angleStep,z j ) (5)

[0073] wherein, 0≤i<N, j is the data point index in each frame of contour data, R j is the distance of the j-th point on the current contour relative to the circle center calculated by formula (3).

[0074] (3) Converting to rectangular coordinate data: solving all collected frames of contour data from polar coordinates to rectangular coordinate values: converting the polar coordinate value ρ(r,θ,z) of each measurement point to coordinates p in the rectangular coordinate system through the following formula out (x,y,z):

[0075] p out =(r*cosθ,r*sinθ,z) (6)

[0076] After this solving process, the frame data is restored to the state relative to the scanning starting position, as shown in Figure 6 .

[0077] So far, all collected data have been converted into measurement value descriptions in a three-dimensional rectangular coordinate system, and the line structured light three-dimensional data measurement based on turntable rotation is completed.

[0078] In summary, the present invention can realize online, automatic and non-contact measurement combining line structured light and a turntable, with good system flexibility and high precision, and has high practicability when the linear scanning of line structured light cannot meet the field of view requirement.

[0079] The present invention can expand the measurement width without losing the accuracy of line structured light, and is particularly suitable for the measurement of nearly circular objects. When only the measurement of the outer contour data of a target is concerned, the measurement range is not limited by the field of view width of line structured light but only depends on the size of the turntable, which is of great significance in actual industrial production.

[0080] The above description is only the embodiments of the present invention, and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A method for measuring three-dimensional data using line-structured light non-linear scanning based on a turntable, characterized in that, Includes the following steps: 1) Make a calibration ruler for the turntable and install the line structured light camera directly above the turntable; Install the calibration ruler so that one end of the turntable calibration ruler coincides with the center of the turntable; The rotary table calibration ruler includes: a calibration ruler body, a positioning through hole, a center graduation line, and a raised structure; The calibration ruler body is a cuboid structure, with a positioning through hole at one end for fitting onto a cylinder located at the center of the turntable to fix the turntable calibration ruler; the center of the positioning through hole coincides with the center of the turntable. The calibration ruler has a central engraving line on its top surface; the central engraving line is a straight line pointing to the center of the positioning through hole, used to adjust the relative pose rx, ry, rz of the structured light and the turntable. The length of the center scribe line is equal to the length of the turntable radius line; The protruding structures are multiple and are arranged sequentially along the central etched line. They are used to adjust the relative positions tx, ty, tz of the structured light and the turntable, as well as to determine the distance between the origin of the line structured light measurement data x value and the center of the turntable. The protruding structure is an angular protruding structure, and the longitudinal cross-section of the protruding structure is triangular; The installation calibration ruler is specifically as follows: The positioning through hole of the calibration ruler is fitted onto the central cylinder set at the center of the turntable. At this time, the center of the positioning through hole is the center of the turntable, the center line of the calibration ruler is the radius line of the turntable, and the distance between the protruding structure of the calibration ruler and the center is the scale value of the calibration ruler. 2) The relative pose of the line structured light emitted by the line structured light camera and the turntable is calibrated to determine the distance between the X-axis origin of the line laser data and the center of the turntable. 3) Keep the line structured light camera stationary and rotate the turntable one revolution. The encoder triggers the line structured light to complete the scanning of the target to be measured on the table. Based on the encoder pulse information, the X-axis coordinate of each frame of data can be converted into polar coordinates, and the result is calculated into the measurement value of the line structured light in a three-dimensional Cartesian coordinate system relative to the center of the turntable.

2. The method for measuring three-dimensional data using line-structured light non-linear scanning based on a turntable according to claim 1, characterized in that, The calibration of the relative pose of the line structured light emitted by the line structured light camera and the turntable includes the following steps: 1-1) Adjust the rz attitude of the line structured light camera coordinate system so that the laser line beam points to the center of the turntable; 1-2) Adjust the orientation of the line structured light camera coordinate system rx and ry so that the laser plane should be incident perpendicularly on the turntable plane, so as to ensure that the z-axis of the line structured light camera coordinate system is perpendicular to the turntable plane. 1-3) Adjust the coordinate system tx, ty, tz of the line structured light camera to establish a relative relationship between the origin of the structured light camera coordinate system and the scale value d, so as to convert the x-axis data of the line structured light camera coordinate system into distance data relative to the center of the turntable. 1-4) Data Conversion: After adjusting rx, ry, rz, tx, ty, and tz, the z-axis of the line structured light is perpendicular to the turntable surface, and the x-axis coincides with the turntable radius. Therefore, the x-value of each measurement data point is converted into a distance value R relative to the center of the circle, i.e.: R = x –d.

3. The method for measuring three-dimensional data using line-structured light non-linear scanning based on a turntable according to claim 2, characterized in that, Adjusting the pose of the line structured light camera coordinate system (rx, ry, rz) includes the following steps: a. Adjust the rz attitude: make the laser line bar coincide with the center line of the calibration ruler, so that the x-axis of the line structured light camera coordinate system points to the center of the turntable; b. Adjusting the RX attitude: When the line structured light device moves up and down perpendicular to the turntable, if the laser line no longer coincides with the center etched line, it is determined that the laser line is not illuminating the table perpendicularly. Adjust the RX and move the laser line back to coincide with the center etched line. Repeat this process until the laser line always coincides with the center etched line when moving up and down. After adjusting the RX attitude, the laser line is now illuminating the table perpendicularly. c. Adjust the ry attitude: Take the coordinates of two points, p1(x1, z1) and p2(x2, z2), on the left and right sides of the online structured light data for observation. If the x-axis of the line structured light is to be parallel to the platform, the ry needs to be adjusted so that the coordinates of the two points meet the following conditions: z1 = z2.

4. The method for measuring three-dimensional data using line-structured light non-linear scanning based on a turntable according to claim 2, characterized in that, Steps 1-3 are specifically as follows: Adjust tx, ty, tz; keep the laser line on the center line, and perform a translational motion on the line structured light so that the origin (0, 0) of the line structured light camera coordinate system falls on the appropriate scale position d of the calibration ruler. When the height of the calibration ruler protrusion is h, observe and adjust it until the coordinate value p of the protrusion corner point satisfies the following conditions: p(x, z) = (0, h).

5. The method for measuring three-dimensional data using line-structured light non-linear scanning based on a turntable according to claim 1, characterized in that, Step 3) specifically refers to: 3-1) Rotational Scanning: The line structured light camera remains stationary, while the turntable rotates the target one revolution. Simultaneously, an encoder sends pulse signals to trigger the line structured light to complete the scan. When the number of encoder pulses for one revolution is known as N, the degree interval angleStep represented by one pulse is calculated using the following formula: angleStep = 360 / N 3-2) Conversion of polar coordinate data: convert the profile data collected by each frame of line structured light into polar coordinate data relative to the center of the rotary table and the starting position of rotation. For the i-th frame of data, each measured profile point p j (x j , z j ) is expressed in polar coordinate form as: j ​ ρ j =(R j ,i*angleStep,z j ) wherein 0≤i<N, j is the data point index in the contour data of each frame, R j is the distance R relative to the center of a circle calculated by the formula for the j-th point of the current contour; 3-3) Converting Rectangular Coordinate Data: The contour data of all acquired frames is converted from polar coordinates to rectangular coordinates. For each measurement point, the polar coordinate value ρ(r, θ, z) is converted to rectangular coordinates p using the following formula. out (x, y, z), that is: p out =(r*cosθ,r*sinθ,z); 3-4) The data distance of each frame is restored to the state relative to the starting position of the scan, and all the collected data is converted into a measurement value description in a three-dimensional rectangular coordinate system relative to the center of the turntable, thus completing the three-dimensional data measurement of line structured light based on the rotation of the turntable.

Images