Scale-inspired layered structure for variable stiffness and shape morphing

Soft robotics represents a shift from traditional rigid systems, offering enhanced adaptability and safer human interaction through the use of compliant materials. However, the inherent softness that enables these advantages also limits load-bearing capacity and precise control. While various approaches exist to achieve either shape morphing or variable stiffness, current solutions typically require complex integration of multiple actuators or separate modules for each function, resulting in bulky designs and complicated control systems. This thesis introduces scale-inspired layered structure (SAILS), a novel soft robotic structure inspired by the scaled surfaces found in nature, such as those of pangolins and fish. SAILS uniquely achieves concurrent shape morphing and variable stiffness capabilities through a single actuation input. The structure consists of a base layer with multiple scales, both featuring programmed surface patterns. When enclosed in a sealed envelope and activated by negative pressure, these patterns engage to transform the structure into predetermined shapes while simultaneously increasing stiffness, achieving up to a 52-fold enhancement in apparent bending modulus. A comprehensive theoretical framework is developed to guide SAILS design, establishing analytical models and design criteria based on geometric parameters including layer thickness, target shape radius, number of scales, and number of periods per scale. Through systematic parametric studies, the effects of material properties (particularly coefficient of friction) and geometric parameters on performance are investigated. This analysis reveals trade-offs between shape morphing capability and variable stiffness, providing crucial insights for optimizing SAILS design. The capabilities of SAILS are demonstrated through multiple practical applications. A SAILS-based amphibious soft robot has been developed to efficiently navigate both terrestrial and aquatic environments, achieving speeds up to 0.34 body lengths per second while swimming and demonstrating the ability to carry loads up to twice its body weight. An adaptive drone landing system showcases SAILS' variable stiffness capabilities through tunable impact absorption, effectively protecting the drone during landing while maintaining a compact profile during flight. Additional applications including a soft gripper, adjustable phone stand, and foldable box further demonstrate the versatility of SAILS across different scales and functions. Furthermore, a bio-inspired control strategy is developed for antagonistic configurations of SAILS, drawing inspiration from muscle coactivation principles in biological systems. The strategy implements a data-driven framework that combines Koopman operator theory with Model Predictive Control, enabling precise motion control without requiring complex analytical models. This control approach is validated through various applications including a versatile gripper capable of handling both rigid and delicate objects, a stiffness sensor, a liquid pump that can transport fluid against gravity, and a reconfigurable bridge structure that adapts to different types of traffic. The results demonstrate significant improvements in motion precision and adaptability compared to conventional control methods. This work provides an integrated solution for shape morphing and variable stiffness in soft robotics, demonstrating its practical utility across diverse applications while maintaining a simple and compact design.