scheme design includes design requirements analysis, system function analysis, principle scheme design process. This stage mainly starts from the analysis of requirements, determines the overall object (technical system) needed to realize the product function and performance, determines the technical system, realizes the image of the product function and performance to the technical system, and carries on the preliminary evaluation and optimization of the technical system. According to the requirements of the design task book, the designer uses his own knowledge and experience to choose a reasonable technical system and conceive a solution to meet the design requirements.