Papers by Keyword: Nonlinear Spring

Abstract: Flying robots with flapping wings are preferred over conventionally fixed or rotational wings in terms of hovering capability for a simple mechanical configuration. Until recently, available actuators for such a robot are limited to (1) a conventional motor with four-bar linkage mechanism or (2) a piezo electric actuator, but none of them could provide enough lift because of low flapping frequency, small stroke angles, and/or frequent mechanical failure. A new actuator capable of generating large stroke angles with high frequency is developed. It consists of an out-runner brushless motor with a modified motor driver attached to a torsion spring. The wing is attached directly on the cap of the motor. A prototype is built and preliminary thrust force measurements are performed. Properties of wing materials suitable for powerful and robust actuators will be discussed. The actuator employed in the present study utilizes resonance oscillation, which leads to high energy efficiency. Further study of wing shape and directional stiffness is needed for generating higher lift capability.

Abstract: In-plane characteristics of a single degree of freedom frictional system with a compressed spring are considered. The compressed spring is vertically installed to the mass moving horizontally along the friction interface. The compressed spring can introduce a nonlinear negative stiffness into the in-plane motion. The resulting system has a multiple equilibrium points; an unstable point at the center and two stable points on either side. It is shown that two stable equilibrium points can be separated far apart by increasing the compression ratio and the stiffness of the spring. The friction system is often characterized by stick and slip motions that cause unfavorable effects such as wear, noise, and chatter etc. It is demonstrated that increasing the compression ratio and the stiffness of the spring results in decreasing the size of the stick regions.