# Research on Three-Dimensional Scanning Path Planning of Casing Parts Based on Industrial Robot
## 1 Introduction
At the same time, some commercial measurement systems, such as those produced by the Beijing Tianyuan 3D Technology Co., Ltd. (Beijing, China); Shanghai Shuzao Technology Co., Ltd. (Shanghai, China); Hangzhou Xianlin 3D Technology Co., Ltd. (Hangzhou, China); and Beijing Bowei Hengxin Technology Development Co., Ltd. (Beijing, China), etc., also launched 3-D measurement systems [11] based on stripe projection technology. In industrial manufacturing, low measurement efficiency will delay the product's production cycle, and the measurement environment needs to maintain a relatively stable state throughout the product's production cycle; therefore, efficiency in the measurement process is needed to achieve automatic measurement. For the measurement of large, complex curved-surface components, the stripe projection sensors are required to measure the measured object in multiple poses, to realize the all-around coverage of the measured area of significant components. The high-precision fringe projection sensor needs to project multiple fringe images and keep the measured object stationary during the measurement process [12; 13]. In addition, when measuring the global control points with the splicing camera based on close-up photogrammetry, it is also necessary to increase the number of poses to capture the global control points on the measured component to ensure accuracy [14]. The traditional close-view photogrammetry systems require manual operation, and the system is complex. Due to the advantages of high automation, high flexibility, and high efficiency of industrial robots, industrial robots were introduced into the measurement system. The fringe projection sensor and the stitching camera based on close-range photogrammetry are installed at the end of the robot through adapters to achieve automatic measurement within the range of motion [15]. Many researchers have optimized the scanning trajectory according to the parameters of the scanning system itself to obtain better scanning results and scanning efficiency. Generally, the scanning path can be generated by determining the point sequence of the scanning direction with the normal surface vector of the CAD model of the known part [16]. [PERSON] [17] proposed a new path planning method that used a conformal map to stretch a 2D surface onto a 3D plane to control the overlap between two adjacent scanning paths. However, this method may cause a sudden change in the direction of the scanner between the two paths. [PERSON] et al. [18] combined industrial robots with high-precision 3D cameras and laser distance sensors to form an automated scanning system to measure ship propeller blades. According to the shooting range of the 3D camera and the optimal proximity distance of the laser sensor, the scanning trajectory of the highly inclined ship propeller blade was planned with a resolution of 0.1 mm. The above research shows that automatic 3D laser scanning is one of the key technologies to improve scanning efficiency and accuracy, and trajectory planning also plays an important role in automated laser-scanning systems. Aiming at the requirement of rapid thickness measurement in the chemical milling of casing parts, in this paper, a general scanning and measuring system composed of a six degrees of freedom industrial robot and tracking 3D scanner was designed. Its core part includes a six degrees of space parallel industrial robot and a three-dimensional tracking scanning system. The specific measurement process is as follows: (1) the three-dimensional point cloud data of the casing were obtained by automatically scanning the casing parts in the working area of the tracker through the six degrees of freedom industrial robot clamping the spherical scanning head; (2) the contoured fitting and post-processing of the point cloud data were carried out to realize the three-dimensional reconstruction of the measured workpiece; (3) the thickness measurement and analysis of the measured position were carried out in the Polyworks measurement software.