Summary
A new multi degree of freedom (mDOF) metastructure concept that utilizes a hybrid position feedback (HPF) controller is introduced and its characteristics are demonstrated. The concept is based on bistable elements and associated controllers that are unstable-then-stable position feedback controllers. An arbitrary number of bistable segments or so-called “meta elements” are attached to each other in a serial (or parallel) manner to generate a “distributed” multi-stable structure. This new metastructure inherits the multiple bistable positions that its building blocks have; hence, the structure becomes multi-stable. It can hold multiple positions without consuming power and has the capability of achieving many shapes. The proposed concept can be used in various applications: locomotion in bioinspired systems, undulatory motion, morphing aerodynamic surfaces, wave guiding, and vibration attenuation. In this paper, the HPF controller attached to each DOF is modified to ensure the stability of the controller using feedback linearization, and disturbance rejection terms in the control law. With this approach, the chaotic nature of the Duffing oscillation is harnessed, and leveraged to facilitate the necessary state transfer, which is essential for realizing an efficient metastructure properties. The modified HPF controller consist of NPF and PPF controller as in classical HPF scheme. The NPF component functions in the same way as in the classical HPF, while the PPF component is modified by incorporating linearization and disturbance rejection terms. Through this modification, when the system transitions from the stable equilibrium to an unstable state after destabilization from the initial stable equilibrium, the PPF becomes active and stabilizes the system by mitigating disturbances coming from neighboring DOFs and preventing frequency mismatch between the controller and the system, which may arise due to the nonlinear cubic stiffness term. The paper will present the comparison of the responses under conventional and modified HPF controller for 3DOF metastructure scheme.
