Research On Cable Harness Virtual Assembly Based On Mass-Spring Model

For electromechanical products, with the development direction of informatization, miniaturization, lightweight and electromechanical integration, cables which are used as connectors between electrical equipment and control devices have taken a growing part. Because of the fact of various type of cable, different shape, and limited assemble space, wrong equipment, missing equipment, irrational layout or interference is easily occurred in actual assembly process. Therefore, how to improve the quality and efficiency of the assembly and cable products is an important issue faced by enterprises. Virtual reality technology provides a new idea and method for design and installation of cable products. In this paper, for the study of marine equipment, in the case of cable in separator cables virtual assembly technology-related theories, key technologies and implementation methods have been studied intensively. The main research work includes the following aspects:(1) In the light of the in-depth study on the soft object modeling approach based on physical attributes and in accordance with the requirements of virtual assembly system, there are suppositions that the section where the cable is perpendicular to the centerline tangent to the base vector is a rigid section without deformation and always orthogonal to the centerline, and the cable is in a straight form without original curvature and torsion under a unconstrained and relaxed state. On this basis, the method of conducting cable modeling based on the improved mass-spring method is proposed. The geometry of the cable is a simplified one-dimensional object linked by a number of particles. The cable form is determined by the spatial positions of particles, and the spatial position changes of particles determine the changes of cable form. Particles are linked by three different types of springs:extension spring, bending spring and boundary spring. Extension springs are linear springs, which are used to calculate the elastic tension the particles subjected during deformation, guaranteeing the cable length would not be changed in the deformation process. Bending springs are non-linear springs, representing the bending rigidity of the cable. Boundary springs are also non-linear springs, representing the boundary constraints the cable subjected during installation.(2) The numerical calculation framework of cable deformation simulation was researched. The morphological formation time during cable deformation is required to be as short as possible and the guarantee of stability and physical property performance without distortion in the case of large step size is required. For this purpose, Newmark-β algorithm was adopted to solve the equation of cable deformation. Compared with the explicit integration, implicit integration is characterized by increased time step, reduced number of iterations, shortened calculation time, and higher system stability. The stability and convergence of the numerical calculation framework was approved on the basis of studies on the convergence and stability analysis theory of the single step method for solving differential equations.(3) The modeling techniques in a virtual environment were studied. Since the virtual platform itself is not able to complete modeling of complex parts and morphological changes will occur during cable assembly, the parts in the scene were divided into rigid parts and soft parts for separate processing. The expressions of product model were divided into product level, component level, part level and patch level, and the information expression pattern and descriptive approach of rigid parts and soft parts were provided respectively on this basis. In addition, the rigid-soft correlation model based on the digraph of part level was proposed, and the rigid parts and soft parts were related on the part level to form a complete scene model. An in-depth study on the neutral file format of STEP as well as the entity expression methods on virtual platforms was conducted. The format of STEP was set as the intermediate file to complete the conversion and storage of parts information from commercial CAD models to virtual scenes.(4) The cable assembly process in a virtual environment was studied. The progressive hierarchical collision detection algorithm in a virtual environment was proposed, and the detection process was divided into three major steps:preliminary detection, detailed detection and accurate detection. The OBB-based model of hierarchical bounding volume was applied for preliminary detection; to increase the computational efficiency, random collision detection based on particle swarm optimization (PSO) was applied at the detailed detection stage so as to further reduce the potential scope of collisions; traditional triangle detection was used for accurate detection to find the locations of collisions. Meanwhile, detailed analysis on the results of collision detection was conducted to capture assembly intention. According to the expression of the constrained characteristic parameters, constraint recognition rules were formulated and determination of constraint priority was completed, and accurate positioning of the assembly parts was achieved.(5) As the practice of above-mentioned research, the cables virtual assembly platform was developed. More detailed information of system development background, system structure, function modules and the working process were introduced.