# An Extended Functional Design Approach Based on Working Principle and Property and Its Application
## 2 Background  
Conceptual design is a solution process that analyzes functional requirements to generate product solutions; it is innovative, complex, and cognitive [11]. Since functional design is a significant activity in conceptual design, a plethora of studies has been conducted on the theory of functional design methodology. A brief review is given below to illustrate the related work. Among the existing functional design approaches, the systematic design approach proposed by [PERSON] and [PERSON] (2007) [3] is the most significant; it regards functional design as a process that involves decomposing an overall function into sub-functions, searching for suitable solution principles for the sub-functions, and combining the solutions of the sub-functions into a complete technical solution to achieve the desired function. Based on the functional decomposition idea, [PERSON] and [PERSON] (1996) [12] developed a function-based approach for generating principle solutions for mechanical devices; [PERSON] et al. (2000) [13] used formal functional decomposition and three heuristic methods to identify modules for product architectures; [PERSON] et al. (2003) [14] proposed the A-design approach to achieve the functional design of electromechanical systems, which combines multi-objective optimization, multi-agent systems, and automated design synthesis; [PERSON] et al. (2012) [15] developed a knowledge-based framework for the functional design of multi-disciplinary systems; [PERSON] et al. (2016) [16] proposed a hybrid approach to automate the process of functional decomposition of complex mechatronic systems to obtain function structure and solutions; [PERSON] presented a literature review of functional decomposition and morphology (FDM). Elsewhere, a new conceptual design approach was presented that can overcome the drawbacks of FDM; the authors suggested combining creativity-enhancing tools or methods with the FDM process [17,18]. In addition to the above functional decomposition approaches, several other functional design approaches have been developed. [PERSON] et al. (1990, 1996) [19,20] proposed the function-behavior-state model, where the functions are decomposed into sub-functions until they can be associated with physical features. Knowledge of the decomposition of functions and alternative solutions can also be retrieved from a knowledge base; [PERSON] (2001) [6] proposed the axiomatic approach for functional design, where functional design is regarded as a zigzag mapping process between functional requirements and the design parameters of solution concepts; [PERSON] et al. (2004) [21] developed a knowledge-based function decomposition system called the \"function way server\", which provides various decomposition solutions to assist designers to decompose the function; [PERSON] et al. (2014) [22] proposeda systems modeling language (SysML)-based methodology for mechatronic system architectural design, which can assist designers to establish the requirements, identify candidate solutions, and select the final physical architecture of the system; [PERSON] et al. (2015) [23; 24] established a new process model of conceptual design (the need-function-principle-system model, NFPS) based on the proposed conceptual foundation, which elaborates a conceptual design process with five major stages; [PERSON] et al. (2016) [25] presented a constrained function-behavior-structure knowledge cell (CFBS) model to provide a consistent knowledge representation model for the conceptual design process. [PERSON] et al. also proposed a CFBS-based integrated approach for design knowledge reuse, while [PERSON] et al. (2017) [26] introduced a function-behavior-structure knowledge cell as a unified consistent design knowledge representation model. Meanwhile, they proposed a hybrid similarity measure to increase the overall possibility of obtaining useful design knowledge, by considering semantic understanding ability; [PERSON] et al.