LOW-COST DEPTH-CAMERA: OPEN-SOURCE 3D DISPLACEMENT MEASUREMENTS FOR 4D PRINTED HYGROSCOPIC COMPOSITES

Abstract. 4D printing (4DP) is a growing branch of 3D printing technology that involves the design of composite material architectures capable of shape-change transformations, which occur post printing, in response to external stimulus. Among these, Wood Polymer Composites (WPCs) change their shape in reaction to changes of moisture content, shrinking or swelling like natural wood until the equilibrium with the environment is reached. Such intrinsic material behavior can be particularly useful in the development of passive moisture airflow controllers that can modulate humidity and airflow in indoor environments to improve air quality. Precise measurement of the time-based stimulus induced shape-change response of these composites is critical to assess the responsiveness, velocity of reaction and overall deformation of the designed 4DP composite mechanisms. Up until now, Digital Image Correlation (DIC) techniques have been widely used for such purpose. However, DIC methods require expensive equipment and costly commercial software. This paper presents a Low-Cost Depth-Camera (LCDC) method that uses a free custom algorithm that returns a 3D coloured displacement map with the corresponding meshes of the acquired object. The LCDC method does not require specialized equipment and allows for an overall understanding of the time-dependent deformation of 4DP actuators, this method also facilitates the comparison between composites with different properties under the same external conditions. This new LCDC method has the potential to further 4DP research by providing an open-source, accessible and reliable tool to assess 3D displacement measurements.