Surface morphologies of workpieces affect the properties of mechanical system, such as friction and wear, fatigue strength, and corrosion resistance. Precise measurements of surface morphologies are of great significance, which can show the processing quality, guide processing and improve surface performance. The contact measurement method is inefficient, and may cause workpiece damage. Optical non-contact precision measurement methods are developed based on the properties of light, which have the advantages of non-destruction, large area, high precision, high sensitivity, simplicity and efficiency, so they are widely applied. The structured light measurement method is one of the most popular measurement methods, in which different lights with different modes are projected onto a object surface and the 3D morphology is reconstructed by shooting distorted images with a camera. However, when a line laser profilometer is used to measure the 3D morphology of a workpiece, a relatively linear motion is usually needed between them, so the system needs a linear motion module with high precision and occupies a large space. Therefore, it is difficult to achieve precision measurement. To solve these problems, a rotation scanning measurement method with a line laser profilometer is proposed in this paper.

First, the line structured light rotation measurement system (Fig. 10) is built, which can project the laser stripe vertically onto a standard plane. Then, when the laser profilometer rotates with the rotation stage at different angles (Fig. 12), the fixed CMOS camera shoots images of line structured light. By the Matlab programming, the images are processed based on the extremum method, and the motion trajectory of the laser light strip (Fig. 13) is fitted based on the least square method. Then, the eccentricity error of rotation center of profilometer and rotation stage are calculated according to the fitted trajectory. In the next step, by the Java programming, 3D synthesis and polar processing of point cloud data are processed. The run-out and eccentricity errors of the rotation stage and the tilt error of the line laser profilometer are compensated. Finally, the effectiveness of the proposed method is verified by measuring the radius of a standard zirconia ceramic ball and the diameter, width and height of a key.

The line structured light is shot by the CMOS camera, and the eccentric error is calculated by fitting the motion trajectory. After the relative position between the laser profilometer and the rotation stage is adjusted, the minimum error reaches 0.02752 mm (Table 9), which provides a good position for rotation measurement. A high-precision profilometer and the proposed method are used to measure the radius of the standard zirconia ceramic ball (Figs. 18 and 19), the average error of measurement results is 2.99 μm (Table 10). Due to the shortcoming of line structured light in measuring smooth surface, the non-measurement region appears in the spherical crown, but our method still presents high measurement accuracy. When a key surface is measured by the two methods, the measurement range of the proposed method is larger than that of the confocal measurement method. That is to say, when large size features are measured, the confocal measurement method needs multiple measurements and data splicing, which reduces the measurement efficiency and accuracy. The deviations of the measured widths of the key surface at three different positions by the two methods are 2.9 μm, 1.9 μm, 3.3 μm, and the deviations of the measured diameter and height of the key surface by the two methods are 4.2 μm and 2.8 μm(Table 11), respectively. Due to the low machining accuracy and the abrasion and corrosion of the key surface, the large deviation appears in the measurement results.

In this paper, a method for measurement and error compensation of 3D morphology with precision rotation line structured light is proposed. When the proposed method is used to measure the radius of the standard sphere, the error is smaller than 3 μm compared with the measurement result by a precision profilometer, which is close to the limit of measurement accuracy of this instrument set. The CMOS camera is used to capture the images at different positions to fit the motion trajectory of the line structured light when the line structured light rotates with the rotation stage. In this process, it is necessary to keep the camera fixed and a stable lighting environment without stray light interference. After the laser stripe center is extracted by the extremum method, the least square method is used for trajectory fitting, then the relative position between the laser profilometer and the rotation stage is adjusted according to the fitting results. In this process, the gray distribution and fitting regression evaluation index are monitored to ensure the effectiveness of the fitting method. Compared with the confocal measurement method, our method has a larger measurement range and higher efficiency when measuring large features. Meanwhile, the minimum and maximum deviations between the two measurement results are 1.9 μm and 4.2 μm, respectively, which proves the accuracy of the proposed method. The verified results indicate that the proposed method is suit for on-machine precision measurement of 3D workpiece morphologies when the workpiece or motion stage is too large and the precision of the relative motion is not high enough.