Laser plane 3D scan measurement technology analysis

Laser plane scan is a 3D profile measurement method (1, and the calibration of the measurement system parameters is its key technology, including the number of camera parameters and optical plane equation parameters, respectively The camera calibration and the light plane equation are determined. Traditional calibration methods use different targets 2 when calibrating two part parameters, especially when calibrating the camera parameters, put the target on the precision rail and moved to different locations to obtain control point pairs, and the operation is particularly complex, not suitable for the site. application. This article places a new calibration target to place it in a space-mounted position, which can realize the quick scale of camera parameters and optical flat equation parameters.
2 Measurement Model and System Parameter
2.1 Working Principle of Measuring System
Based on laser visual measurement principle, a laser plane scanning 3D measurement system is established, mainly from line structural laser sensors and data processing.
Part (computer) is composed, as shown in Figure 1. Line-junction consolidation optical sensor includes linear structuring laminate (LD and column glasses), driving the step of scanning beams and CCD capture machines. The line structure laser emits light plane, projected to the surface of the object to form an undulating numeral, received by the CCD
video, through a certain algorithm to obtain 3D information on the surface of the object carried on the light strip (Z, Y, z). Through the motor driving turntable, the active screen is a 3D information on the surface of the entire object to the surface of the object surface.

2.2 3D Establishment
Optical Planning Equation 3D Measurement Model For Establing Conversion between Computer Screen 2D Coordinates and Space Testing Point 3D Coordinates relation. Including the camera perspective variable die and two parts of the optical plane. The visual imaging of the camera can approximate the needle imaging L4, as shown in Figure 2. O points is the imaging perspective center; OCZ is the optical axis of the camera imaging lens, hangingThe image plane of the CCD camera; 0 is the intersection of the optical axis and the flat surface, is a flat optical center. o and 0 distance plants are effective focal length for imaging. pass . Points as the flat coordinate O-XY, the X-axis is in the pixel direction, the Y axis is perpendicular to the X axis.

At 0 points, the camera coordinate system 0 is z Yz, so that the Z-axis and the Y-axis are parallel to the x-axis and Y axes, respectively. The reasonable imaging point on the image plane is p (x, y) on the image plane, due to optical distortion, the actual imaging point at P (X, YD). The 2D coordinate of the optical center O ("., 730) is O ("., 730). The coordinates under the computer screen coordinate system are p (u,), ie in the frame memory The corresponding pixel (PIXE1) position.

When measuring, the line structure laser light source is opened, the projected light plane intersects the object into a light strip, and the stepping motor drives the light source. The optical plane is scanned in the space, the optical plane interval angle formed in the space is j5. Take the koa light plane as a research object, and its planar equation in the camera coordinate system is

Differences D and D are adjacent photosensitive unit distances of the CCD photosensitive array in the X direction, Y direction. The camera parameters are R ~ R., T, T, T , T, f, and k need to be obtained by the camera. Among them, R ~ R. T, T and T are the conversion matrix element of the spatial coordinate system to the camera coordinate system; k is a distortion coefficient; it is a proportional factor; The mouth, CD, and the light plane equation parameters need to be marked by the light plane equation. By (4), the specified system parameters are utilized, as long as each light plane is known to the surface of the object to intersect the surface of the object. Point imaging the coordinates (",) in the computer coordinate system, can be obtained to fit these points in the camera coordinate system, fitting these points, can obtain the surface of the object continuous in the scan area Point 3D information.

3 Measuring system parametersTypical

3.1 Calibration
takes into account the distortion factor of the camera, using R. Y. Tsai's two-step method, labeled camera parameters, as shown in Figure 1. The radial collimation constraints

combined with a conventional calibration camera's planar disc target and a stereo target of the standard light plane equation parameter, a new calibration target is designed. ,As shown in Figure 3. The target is set from two mutually vertical standard torque, and a plurality of rolls are processed on each surface. The class is similar to the circular target, the circular hole diameter is 20mm, the central spacing is 4ommmmmm, and the standard percentage is ± 0.005 mm. The target length is 300mm, high 300mm, put it in space fixed position, as shown in the figure to establish the right hand coordinate system. o One z is the spatial coordinate system, two planar intersections are OW axes,

where x-sxd- d (u-o); one yd D (V- VO). Using the most DX-multiplication, the orthogonal constraint condition of the joint coordinate conversion matrix can be obtained, and R ~,. . , T, T and S, the remaining camera parameters T, F, and the available formula (1) use iterative method.

3.2 Calibration of the optical plane equation parameters

As shown in FIG. 4, the target is fixed, turned off the background illumination light, opening the wire structure laser light source, The line structure laser is projected onto the calibration target, intersecting the target surface into a light strip, the optical strip is imaged in a computer

screen via the CCD camera. After the image processing is 2 straight, the two optical strip intersection P is on the computer. Sitting on P (,) and the screen coordinates (,), the point of the point on the point of the point on both sides of the intersection, the point corresponding to the point of the point (Z, 0, ZW /), and the other side of the intersection Spatial coordinates (O,). The coordinates of this point of the computer screen coordinates and known space coordinates into the formula (1), and solve the coordinate of each point in the space coordinate system. Then, the light-flat, the space, the space coordinate value, respectively, respectively.The optical plane of the spatial coordinates is

Overpot OEZ and OWY, respectively, and it is vertically in the OW axis. Since the two planes are striped vertically, the OWZ axis is vertical in the OW shaft, so that the space coordinate (Z,,,,,,,,,, Open backlight and CCD camera, shut down laser, target imaging in the calculation screen, the coordinates of each round hole in the computer coordinate system are also determined. This gives a group control point pair {(.27,,), (,)}, substitute equation (6), the equation set is the optical plane equation parameter port under the intercordable coordinate system, C, and then use the camera labeling Determined from the coordinate transformation parameters,. ~ ,. 9, T, T, T, T,, are determined, C, C, and.

4 Measurement System Application Experiment

The lamination of the designer is measured in measurement of a reference plane. Set the initial position of the reference plane to 0, then move the reference plane into one or both of the precision guide to the plane perpendicular to the plane, each moving distance is 25.000 mm. The measurement measurement was performed once per move. Under the measurement coordinate system, the data returned to each measurement is returned to the plane 7, and it is obtained. It is calculated that the distance from the base level is calculated, and the measurement results are recorded each time. The distance value of the returning plane distance from the base level is shown in Table 1, and the maximum value of the returning plane position is 0.059mm, the minimum is 0.019mmm.

5 Conclusion
In the calibration method of existing line structure laser sensors, combined with a flat target for conventional camera labeling The technical needs of the three-dimensional target used by the light plane calibration, and a new stereo target is smart.The calibration process of a set of label scanning 3D measurement system parameters can be determined, and the camera parameters and the light plane parameters of the respective scanned light planes can be determined, and the algorithm is simple, the measurement speed is fast, the steady and high accuracy is moderate.This method performs parameter standard for the lamination plane scanning 3D measurement system, and uses a standard parameter to measure the standard plane, and the space measurement accuracy can reach 0.1 mm, which is fully compliant with 3D measurement.

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