# Real-Time Physical Prototyping Tool Design Based on Shape-Changing Display
## 1 Introduction
However, the iteration of generation and materialization of a design idea enables the exploration of potential novel design ideas [31]. According to [PERSON] et al. [32], designers actively collect physical and mental visual samples for inspirational purposes during the design ideation process. [PERSON] et al. [32] also found that professional designers highly rated three-dimensional representations as inspirational stimuli. [PERSON] et al. [28] tested the impact of rapid prototyping in the acceleration of design ideation process with 39 participants. Their results reveal that a group that created more prototypes exhibited improved design outcomes and higher satisfaction than those exhibited by the other group, who were only instructed to create one prototype. [PERSON] and [PERSON] [33] conducted experiments to test the sunk cost effect under five conditions--sketching only, metal-building, plastic-building, metal-constrained sketching, and plastic-constrained sketching--in the idea generation process. The results confirm that building a physical model significantly helped improve the design quality, and the decreased effort in creating the prototype (e.g., a quick model-making process) led to comparatively less design fixation. Even though the technology is called rapid prototyping, the 3D printing process is slow and requires overnight printing of a reasonable-sized model [34]. In this respect, researchers have attempted to streamline rapid prototyping speeds. [PERSON] et al. [34] proposed a WirePrint system that constructs low-fidelity wire-frame previews that significantly reduces the printing duration. [PERSON] and [PERSON] [35] incorporated a laser cutting file-making process with hand sketches to streamline the subtractive manufacturing process. However, despite the advancements in rapid prototyping technologies, methods that enable immediate physical prototyping have been thoroughly researched. If a prototype can be created instantly for designers to sensorially experience a model, they can test and simulate various design ideas during the early design phases. In contrast, a shape-changing display (SCD) can dynamically reconstruct digital information through physical changes, thus enabling real-time prototyping. The shape and volume of the SCD change by extruding the actuator. SCDs provide haptic feedback by transforming a shape through a combination of actuating pins that exert physical force. Thus, unlike conventional rapid prototyping and VR-based prototyping technologies, the SCD can construct a physical prototype in real time. In [PERSON] et al. [36], the visualization of a terrain using 16 actuators to create various 2.5D models with FEELEX has been discussed. Previous studies on SCDs have mainly used tabletop SCDs composed of a series of linear actuators extruding in a single axis and could reconstruct the shape of a surface. SCDs can be used in various applications and are compatible with numerous screen technologies. For example, various shapes can be reconstructed through the display [37], and texture mapping can be used to represent information on a display screen [38]. This demonstrates the potential of SCDs to deliver rich content without physical constraints. Existing state-of-the-art reports on SCDs highlight their numerous possible applications in human-computer interaction; however, tabletop SCDs have morphological limitations. For example, certain tasks are analogous to drawing a picture on a curved wall; however, 3D objects require a closed surface-based reconstruction method for morphological robustness. Unlike the systems proposed in previous literature, we propose a closed surface-based SCD that reconstructs a shape based on a series of linear actuators. Specifically, the display deforms the surface by arranging the actuators radially around a single point. To the best of our knowledge, this is the first study to develop a closed surface-based SCD that instantly constructs a physical prototype of 3D digital models, thereby enabling 360\({}^{\circ}\) evaluations.