# Real-Time Physical Prototyping Tool Design Based on Shape-Changing Display
## 2 Related Work
### Advancements in SCD  
Studies focusing on transmitting information or providing new experiences through morphological transformations have been actively conducted in the field of human-computer interaction [40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54]. In addition to studies that describe elements, such as tactile displays [55; 56], tangible interfaces [57], and shape-changing interfaces [58; 59], several studies on actuated surface displays, which can adjust the surface to create various screens, have been conducted. The most common approach for applying digital information to real objects is to include digital information as texture on the object surface [60]. This method, called projection mapping, projects the digital content on the surface of a real object through a projector. This allows us to use complex shapes instead of flat screens. It can cover large areas, such as one side of a building [61], and it can incorporate digital content through projection mapping for various materials, including those that are not rigid, such as fabrics [62] or sand [63]. Projection mapping is a display technology that is widely used in digital art and museums [64; 65]. FEELEX, proposed by [PERSON] et al. [36], is an SCD that was initially used to adjust an actuator to create a specific shape. Its basic form is that of a tabletop, but the upper surface is constructed to actuate vertically to present various 2.5D content. FEELEX is a 240 mm \(\times\) 240 mm display, with a total of 36 pins (6 \(\times\) 6). However, for inFORM, proposed by [PERSON] et al. [37], 30 \(\times\) 30 pins were used for a 381 mm \(\times\) 381 mm display. In this type of SCD, all actuators are oriented in one direction; therefore, the actuator arrangement is also in a 2D plane. In general, the density of the actuators is the same as the resolution of the display, which enables the formation of more complex shapes. In this system configuration, the actuator density per unit area increases as the actuator size decreases. To arrange several actuators in such a narrow area, inFORM uses a system in which the actuator power section and actual moving section are separated. The actuator of inFORM is located at a lower part and makes pins move by receiving force through a linkage. To apply this method to actuating pins arranged in different directions and positions in three dimensions, a more complex linkage system design is required. The display can also convey different types of content and user experiences if the size is varied. For example, [PERSON] et al. [66] utilized small actuating pins for tactile interaction with a mobile phone. The pins were attached to the side of the device, and they output dynamic affordances using various interaction techniques. As indicated, by increasing the display size where the actuators are arranged in a 2D plane, the number of actuators can be increased by simply using additional actuators. However, when the actuating pins are arranged in three dimensions, size determination becomes critical. [PERSON] et al. [67] developed ShapeClip, a modular tool capable of transforming any display along the \(z\)-axis. Owing to its modularity, it enables users to rearrange the SCD into various shapes. However, if the actuating length is fixed, the size of the entire display will, despite its modularity, cause a decrease in the minimum-maximum size variation of the display; this, in turn, affects its ability to express a shape. Thus, a closed surface based SCD must analyze the factors for determining the optimal actuator placement.