Shape-morphing capabilities are essential for enabling multifunctionality in both biological and artificial systems. These capabilities allow structures to adapt their forms and functions in response to varying stimuli, making them highly valuable in numerous applications. Numerous strategies have been proposed for shape morphing in areas such as metamaterials, robotics, Micro-Electro-Mechanical Systems (MEMS), and medical devices. However, many of these approaches have struggled to achieve seamless transformation into a variety of volumetric shapes post-fabrication while maintaining a relatively simple actuation and control mechanism. Conventional shape-morphing structures often suffer from significant limitations. They either have restricted morphing capabilities, offering a limited number of achievable shapes and classifications, or they can reconfigure into numerous shapes but require tedious, time-consuming, and energy-inefficient actuations. These constraints hinder their practicality and limit their deployment in dynamic environments where rapid and efficient shape changes are necessary. To address these issues, we draw inspiration from thick origami and natural hierarchies. We present a hierarchical construction method based on polyhedrons to create an extensive library of compact hierarchical origami metastructures. This innovative approach combines the geometric intricacy of polyhedral shapes with the structural flexibility of origami, resulting in a versatile and adaptive system. Remarkably, starting from just one initial design, a single hierarchical origami structure can reconfigure into over 103 distinct configurations. This is achieved through the unique looped internal folds, which allow for a wide range of shapes with minimal active degrees of freedom (DOF).
One of the key advantages of our design is its simplicity in actuation. Fewer than three active DOFs are required to perform all reconfiguration processes, thanks to simple transition kinematics. This simplicity not only reduces the complexity of the control system but also enhances the efficiency and speed of the reconfiguration process. The versatile shape-morphing capabilities of these origami structures facilitate a wide range of applications. For instance, in robotics, these structures can be used to develop untethered and autonomous robotic transformers capable of various gait-shifting and multidirectional locomotion. This adaptability allows the robots to navigate complex environments, perform diverse tasks, and adjust their configurations as needed. Additionally, the structures can be employed in rapidly self-deployable and self-reconfigurable architecture. These capabilities are exemplified by scalable designs that can extend up to the meter scale, providing robust and versatile solutions for structural applications. Furthermore, without the influence of Earth’s gravity, these hierarchical origami metastructures could serve as ideal candidates for multitask reconfigurable and deployable space robots and habitats. Their adaptability and versatility make them well-suited for space exploration, where they can be used to construct deployable habitats, perform maintenance tasks, or assist in scientific experiments. The ability to reconfigure and adapt to different tasks and environments showcases their potential for a wide range of applications beyond terrestrial boundaries.
Beyond their versatile shape-morphing features, our design strategy introduces structural hierarchy into origami structures, offering significant fundamental insights for origami design. Intrinsically, all origami structures can be equivalently treated as mechanical kinematic mechanisms with or without structural loops. In this work, we design hierarchical origami structures based on the concept of looped spatial mechanical kinematic mechanisms. This approach leverages the inherent properties of origami to create structures that are both flexible and robust. Our hierarchical design scheme fundamentally broadens the design space of origami, as well as mechanical and robotic metamaterials/metastructures. By integrating hierarchical principles, we unlock new possibilities for creating complex, adaptable, and multifunctional structures. This not only enhances the capabilities of origami-based designs but also paves the way for innovative applications in various fields.
This work explores the reconfiguration kinematics of hierarchical origami systems by modeling them as idealized hierarchical rigid mechanisms, neglecting deformation in both cubes and hinges. However, in scenarios where elastic deformations are significant, similar to non-rigidly deformable origami metamaterials, the over-constrained looped kinematic mechanisms become energy scale-dependent. This dependency arises from the complex deformations involved in the cubes, hinges, and architectures during reconfiguration, such as bending, stretching, twisting, shearing, or combinations thereof. Consequently, these rigid mechanisms transform into both reconfigurable and deformable architected materials and structures, coupling kinematics with mechanics. This coupling introduces new kinematic behaviors, mechanical properties, transformed configurations, reconfiguration paths, and reprogrammable mechanical behaviors such as multistability and stiffness anisotropy. Specifically, understanding how the energy scale affects the kinematic bifurcated paths, and how coupled kinematic bifurcation and elasticity alter both the reconfigurations and mechanical responses of bifurcated mechanical metamaterials, remains a critical area of exploration.
We envision that such studies could find broad applications in reprogrammable mechanical computing, mechanical memory, and mechanical metamaterials. For instance, reprogrammable mechanical computing could leverage the dynamic reconfiguration capabilities of these structures to perform complex computations and data storage. Mechanical memory systems could benefit from the stability and robustness of these materials, ensuring reliable data retention even under varying conditions. Additionally, mechanical metamaterials could exploit the unique properties of these structures to develop advanced materials with tailored mechanical responses.
In summary, this work opens a new frontier in the design and application of hierarchical origami metastructures. By leveraging the principles of mechanical kinematic mechanisms and introducing structural hierarchy, we create multifunctional materials and structures with unparalleled adaptability and versatility. The potential applications in robotics, architecture, space exploration, and beyond highlight the transformative impact of this research, paving the way for future innovations in shape-morphing technologies and their applications