As one of the important supporting technologies for the construction of CPS(cyber-physical space),the digital twin has been applied in many fields,such as aerospace,intelligent manufacturing,smart city,smart medical care,smart education,etc.However, some problems in the practice process has also appeared: the generalization of the concept of digital twin leads to the misunderstanding,which results in the inconsistency of production,teaching,research and application goals,and the practice results are not recognized by the target users; The lack of general and effective methods in concrete implementation leads to the limitation of the results,which results in the lack of universal practical cases and difficulty in forming recognized typical cases.To solve these problems,it is necessary to restrict the concept boundary of digital twin and extend the boundary of digital twin method,so as to form a new boundary of digital twin,promote the formation of consensus,increase implementation methods and promote its better development. 河北科技大学学报 2021年 第2期 刘〓青，等：数字孪生的新边界 Conceptually,physical entity is a collection of materials with various properties,which is characterized by complexity,authenticity and immediacy,and can dynamically evolve with the change of external conditions according to objective laws.In the study of mapping physical entities to digital twins,it is easy to expand the scope of concept to include simulation (the simulation of dynamic evolution process),data (external conditions),and even physical entities (objects).As a result,the concept of digital twin will lose its core and it is difficult to from a consensus.In terms of methods,based on the detailed investigation and analysis of related applications in multi-scenarios,the existing research on digital twin often goes beyond the perception process of physical entities,and directly relies on the models or modelconstruction methods in the original professional fields.While this method has made some progress,its limitations have already been revealed.Firstly,the existing models are mostly focused on subdivision fields,which can not be used universally among fields.Secondly,there are few existing models that reflect the characteristics of high fidelity,multi-scale and multi-physical fields of the digital twin model,and even less information flow corresponding to the whole life cycle.Direct application can not guarantee the effective realization of digital twin; Thirdly,entering the modeling process directly from the height of existing cognition may cause huge costs.For example,the ADT program,a world recognized typical case of US military,was constructed in ten years and with huge investment in manpower and material resources,which further hinders the industry from entering the practice of digital twin.In order to meet these challenges,in terms of conceptual boundary,this paper proposed that the digital twin should return to the essence of its digital model,and effectively restrict the model as the center,so as to promote the understanding of all parties involved in production,teaching and research to reach an agreement.As for the extension of method boundary,this paper put forward a multi-sensory oriented digital twin model construction method,that is,according to the general process of human understanding of the physical world,firstly obtained perceptual knowledge of features through various perception methods,and then further formed rational knowledge through various cognitive processes,from shallow to deep,from easy to difficult,from simple to complex.At first,the digital twin initial model of physical entity was established by multi-sensory methods,such as visual perception,auditory perception,tactile perception and dynamic perception,gustatory/taste perception,and combination with control data reflecting the change of conditions,thus focusing on the complexity and authenticity of physical entity at the beginning of the model establishment,fully embodying the characteristics of the digital twin model,and effectively enhancing the practicability and universality of the model. Then,the initial model was gradually matched with the existing cognitive knowledge framework,and the control data returned from the physical entity was used for continuous iteration.In this way,information of various property changes,real-time/near-real-time reactions,various objective laws and behavioral logic affecting the physical entity under specific external conditions can be gradually added to the digital twin model according to the actual needs of the research field,thus effectively controled the scale and cost of the model and gradually realized the information flow in the whole life cycle. Third,the optimized digital twin model was further used in theoretical and practical research,such as simulation,planning,optimization,decision-making,etc.,so as to promote the development of various studies.The application prospect of the multi-sensory oriented digital twin model in computer image scanning,cultural heritage protection,medical treatment,education and some special fields was prospected.
河北省创新能力提升计划项目(20551801K); 河北省省级科技计划资助项目(20310802D, 18210109D); 河北省高层次人才资助项目(A2016002015); 石家庄市科学技术研究与发展计划项目（19SCX01006, 191130591A）[ZK)]