# An Extended Functional Design Approach Based on Working Principle and Property and Its Application
## 5 Case Study  
In this section, the conceptual design of a self-adaptive luggage transfer device will be taken as an example and discussed using the method proposed above. The conceptual design solution is shown in Figure 7, and has already been granted a Chinese invention patent (No. ZL 201910830749.1) and a United States invention patent (No. US 10968047B2). Generally, passengers' luggage needs to be manually transferred to travel centers, such as airports or ports. For example, after the arrival of flights, the passengers' luggage is stacked on luggage cars; at this time, ground service staff need to carry the stacked luggage one by one from the top of the stack to the ground conveyor belt. The transfer process involves strong working intensity and high labor costs. Figure 6: The cross-mapping model of function and structure. Figure 7: The conceptual design solution model of the self-adaptive luggage transfer device. (In the model shown in Figure 7: 100, the self-adaptive luggage transfer device; 110, the base; 130, the conveyor mechanism; 150, the lifting mechanism; 170, the self-adaptive extendable transfer mechanism; 190, the reverse displacement amplification mechanism). According to the above consideration, in this conceptual design task, the overall function is to transfer luggage from one place to another, and two primary functions are clarified. First, the designed device should relocate the luggage to the designated position, which process comprises horizontal transfer and inclined transfer. Second, the expected device could adjust the horizontal height of the conveyor mechanism to accommodate the luggage being located at different heights. Figure 8 shows the simplified function-structure mapping relation of this self-adaptive luggage transfer device. In the left function domain, the total function \"transfer luggage\" is decomposed into a three-layer function tree. Function modules are located in the middle level, while function units are located in the bottom level. In the right structure domain, specific structure units are mapped to the function units; they are directly generated according to the function units. The structure modules in the middle level are composed of specific structure units. In the middle level, the function modules are realized by structure modules. In the concept generation stage, designers focus on the bottom level--how to generate an available structure unit according to an expected function unit. In this case, the conceptual solutions to the lifting mechanism (150) are chosen to explain the proposed approach, based on Strategy 2 (Processes 2, 3 to 4). The Conceptual Design of the Lifting MechanismWhen considering the function of the lifting mechanism, it is expected to flexibly raise and lower the height of the conveyor mechanism (130). The realization of this function should be dependent on a principle that allows a reciprocating displacement change. Process 2 (F-WP)To realize a reciprocating displacement change, several available working principles could be considered; i.e., the principle of hydraulic transmission, the principle of thermal expansion and contraction, the principle of variable triangles, etc. The principle of hydraulic transmission will directly map onto a hydraulic cylinder device. In a real working space, if a multi-stage hydraulic cylinder is used, it may cause the hydraulic cylinder piston to travel too far and may also lead to a complex structure. Regarding the principles of thermal expansion and contraction, it will not be able to bear the actual workload. Therefore, the above two principles are not selected. Regarding the principle of variable triangles, this could ensure the stability of the structure and provide variable displacement. In addition, the structure's input displacement and output displacement are not in the same direction, which helps to reduce the volume of the structure. Hence, the variable triangles principle can be selected as a candidate working principle to progress to the next design process.