# CAD-Based Feature Recognition for Process Monitoring Planning in Assembly
## 3 Concept  
The following section describes an approach for the automatic identification of process monitoring features in assembled products. As can be seen in Figure 1, a user interaction enables the customization of the identification of the monitoring features and parameters and, thus, the individual monitoring requirements of a new product variant to be assembled.  
The initial situation for the use of the system or the identification of the monitoring requirements is based on the newly planned assembly of a new product variant with high quality demands. In this case, the product and its assembly plan(s), with its production locations (e.g., stations or cells) and operating resources (e.g., robots and grippers), are defined. Multiple assembly plans and assembly sequences can influence the determination of monitoring requirements. Based on the sequence of components to be assembled, different characteristics may form as a result that are necessary for monitoring. This concept considers multiple assembly plans and creates the monitoring requirement individually for the assembly plans (see Figure 1). Different assembly plans and monitoring requirements can have an influence on the generation of monitoring tasks and plans [15]. Therefore, the main objective for using the following system is to identify and define monitoring requirements that must be considered when planning process monitoring. The product information derived from the CAD model of the assembled product and the information from the assembly plan serve as an input for the system to identify the monitoring requirements for assembly processes. The extraction and recognition of the geometric and process-specific features rely heavily on two sub-modules. The sub-module containing templates for monitoring requirements describes known geometric features and process parameter types that are relevant to the successful execution of the assembly processes. These templates must be created manually in advance. The templates are based on existing descriptions (e.g., norms and standards, such as DIN 8593 - \"Manufacturing Processes Joining\") of assembly processes and their relevant characteristics. A more detailed description of the templates can be found in Section 3.2. Depending on the complexity of the process and the company's internal adjustments or additional requirements, the manual setup of a template varies in the time required. These can then be used more frequently for different product alternatives. This recording can be performed in workshops and by experts (e.g., the quality manager or product designer).  
Figure 1: System overview for the identification of process monitoring requirements in assembly products.  
The sub-module for parameterizing the process monitoring requirements assigns the monitoring parameters obtained from the assembly plan information, standard process parameters (e.g., the torque of the screw, the joining force), and user inputs. The extraction and recognition module is the core element of requirement identification and serves as a feature extractor for the product CAD model and for feature recognition. First, the CAD data are extracted. This information is then used for feature recognition to determine and identify the application-specific assembly features. Figure 2 describes the interactions between the individual modules and the user. The generation of process monitoring requirements for a single product can be divided into four phases: 1. the import phase; 2. the feature extraction phase; 3. the feature detection phase; 4. the parameter determination phase. The individual phases and modules are described in the following sections. At the end of the cycle, the user can manually define further monitoring requirements that the system does not recognize or that need to be detailed further.