# Real-Time Physical Prototyping Tool Design Based on Shape-Changing Display
## 5 Conclusions  
In this study, we introduced a closed, surface-based SCD for real-time prototyping. Accordingly, novel algorithms were developed to optimize shape reconstruction and to determine the ideal number and placement of the actuating pins to ensure a robust expression of shapes through the physical device. Validation experiments were conducted to identify the resolution robustness and shape reconstruction expressiveness displayed using the proposed SCD. The results demonstrated that the proposed method can accurately reconstruct an optimized shape. The simulations also revealed that complex organic shapes (rabbits and human faces) and man-made shapes (chairs, cars, and buildings) can be accurately reconstructed by using a closed, surface-based SCD with an optimized number of actuators. Although we used high-fidelity 3D digital models for the validation experiments, the proposed SCD can accommodate 3D models with various levels of detail.  
The contribution of this study is two-fold. Academically, to the best of our knowledge, this is the first study on real-time prototyping using a closed, surface-based SCD that can accurately and instantly create physical reconstructions of digital 3D models. Unlike traditional tabletop SCDs, the proposed method requires solutions of various novel practical problems, such as 3D reconstruction optimization, platform architecture, surface tension, placement rules for actuators, new actuator designs, and interaction software. Our work contributes to the solutions of these problems by proposing a novel shape reconstruction algorithm that can be used even when the type and number of actuators are changed. Thus, we propose a complete component for designing a closed, surface-based SCD for real-time prototyping. The proposed method can be used as a foundation to aid the design  
Figure 15: Comparison of actuating vertex density of the Sydney Opera House constructed using two different center positions (a,b).  
prototyping process. The real-time shape changing quality of the SCD allows designers to immediately check a prototype from multiple viewpoints, thereby enabling them to communicate and provide more effective feedback.  
Developing a more robust SCD requires further research. First, a novel actuator design that can expand the impact of SCDs is required. Currently, actuating pins are connected to gears that occupy a large volume. Thus, the minimization of these actuators can significantly improve the resolution of the display. Additionally, creating a modular SCD would improve the robustness of the 3D model expressions. For example, if we were to assemble more than one SCD, we could reconstruct more dynamic shapes with the display because there would be more than one actuation core. Second, if augmented reality with a head-mounted display was to be adopted for the SCD, the Lycra would not be required. Thus, users could better evaluate design concepts through real-time prototyping by touching and seeing the model. The proposed methods can be used in diverse industries, including architecture, product design, furniture design, and other fields that require 3D prototypes for design evaluations.  
Conceptualization, S.B. and K.H.H.; Data curation, [PERSON]; Formal analysis, [PERSON]; Funding acquisition, K.H.H.; Investigation, [PERSON]; Methodology, S.B. and K.H.H.; Project administration, K.H.H.; Resources, K.H.H.; Software, [PERSON]; Supervision, K.H.H.; Validation, S.B. and K.H.H.; Visualization, S.B. and K.H.H.; Writing--original draft, S.B. and K.H.H.; Writing--review & editing, S.B. and K.H.H. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP: Ministry of Science, ICT and Future Planning) (NRF-2020R1C1C1011974).  
Not applicable.  
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The authors declare no conflict of interest.