FDM 3D printers allow massive creativity in personal products, but their potential has been limited due to inability to manipulating material properties. Previous work had demonstrated that the desired roughness could be presented simply by controlling the spatial density of tiny pins on a printed surface. This article offers a means of providing the desired softness perception of a printed surface and the desired roughness to expand the haptic dimension over which a user can exert control. Specifically, we control the softness by manipulating the infill structures of a printed surface. However, it is known that a skin contact area affects softness perception. The roughness, which is controlled by pins' density, may also affect the perceived softness of a printed surface. Therefore, we investigate how the internal structures and the density of the pins affect softness perception. Through psychophysical experiments, we derive a computational model that estimates the perceived softness from the density of the pins and the infill density of a printed surface. c 2021 Society for Imaging Science and Technology.
We evaluated our previously proposed technique of protecting the copyrights of digital data for 3-D printing. This technique embeds copyright information into not only digital data but also fabricated objects and enables the information to be read to reveal possible copyright violations. The insides of fabricated objects are constructed with fine cavities to embed information into them. In this study, the readability of embedded information relating to the structure parameters of the fine cavities inside fabricated objects was examined to clarify the conditions in which this technique can be applied. The top-view sizes of the cavities, the top-view spaces between cavities, the depths of the cavities themselves, and the depths of the cavities from the surfaces of the objects were changed as experimental parameters. Experimental results clarified the conditions for forming cavities inside the fabricated objects and showed that a sufficient amount of information for copyright (i. e., hundreds of bits) could be embedded if a fabricated object was several centimeters in size.