# Research on Three-Dimensional Scanning Path Planning of Casing Parts Based on Industrial Robot
## 1 Introduction  
With the continuous development of aero-engine manufacturing technology, under the premise of ensuring the high stability of aero-engines [1], the lightweight design and manufacture of aero-engine casings has become one of the most critical and effective technical means to improve the thrust-weight ratio of aero-engines. The casing is the basic skeleton of an aviation engine, comprising not only the central parts but also the main bearing parts of an aviation engine. The engine casing is a critical component of an aviation engine. Under the harsh conditions of high temperature and high pressure for a long time, it bears the high-temperature load and thrust load of the combustion chamber, and its manufacturing precision and performance requirements are incredibly high. At present, the lightweight problem of aviation engine casing parts is solved mainly by chemical milling after traditional metal cutting [2]. Chemical milling removes the excess metal on the surface of the features, forming reinforcement and structural convex platform characteristics, reducing the weight of the self-structure without affecting the stress state of the casing elements. The chemically milled casing has characteristics of a thin wall, complex reinforced reinforcement structure, high precision, and weak rigid conical shell parts [3]. In the process of chemically milling the casing parts, it is necessary to measure thecasing many times during the chemical milling, to evaluate the machining accuracy of the casing parts and the effectiveness of the chemical milling process. The high concentration of acid corrosion liquid remaining on the surface of the pieces will also constantly corrode the parts during the measurement process [4], thus influencing wall thickness. Currently, this enterprise still uses the traditional ultrasonic thickness measurement method to measure the thickness of the critical position of the casing. In addition to the harsh operating environment, there is low detection efficiency and poor repetition accuracy in the results. The accurate measurement for the chemical milling process has become one of the greatest technological limitations in optimizing the chemical milling process and evaluating its lightweight-forming quality. The surface shape of significant components is complex, and the manufacturing technology is complicated, so the morphology and size measurement has become the bottleneck that restricts the development and technological advancement of large equipment. Under field conditions, measuring the complex surface of significant components must meet the requirements for large scale, high point-cloud density, high precision, and high efficiency. Given the importance of the precision measurement of complex surfaces during the manufacturing of significant components in large equipment, the integrated automatic measurement method applicable to the industrial area has been studied [5]. Realizing the size of complex components requires both measurement accuracy and efficiency. The research background is described in Figure 1.  
As early as the 1980s, Germany began studying 3-D measurement technology in surface-structured light. In 1985, Dr. [PERSON] introduced phase shift interferometry to three-dimensional morphology measurement, establishing a new three-dimensional morphology measurement technology: the phase-measurement contour technique (PMP) [6;7]. Additionally, Dr. [PERSON] and Professor [PERSON] at Germany's Braunschweig Technical University introduced the Steinbichler GmbH COMET 5-3D measurement system [8;9] and the GOM Gmbh Atos structural light 3-D measurement system [10]. In China,  
Figure 1: Research background for the key components of aero-engines. Tsinghua University, Beijing University of Aeronautics and Astronautics, Shanghai Jiao Tong University, Xi'an Jiaotong University, Sichuan University, Huazhong University of Science and Technology, Tianjin University, and many other universities have also conducted systematic research on the stripe projection technology.