Design, control, modeling, and gait analysis in miniature foldable robotics

Abstract

Miniature or micro robotic platforms are perfect candidates for accomplishing tasks such as inspection, surveillance, and hazardous environment exploration where conventional macro robots fail to serve. Such applications require these robots to potentially traverse uneven terrain, implying legged locomotion to be suitable for their design. However, despite the recent advances in the nascent eld of miniature robotics, the design and capabilities of these robots are very limited as roboticists favor legged morphologies with low degrees of freedom. This limits small robots to work with a single gait set during the design phase, as opposed to legged creatures which bene t from e cient gait modi cation during locomotion. MinIAQ, a 23 g origami-inspired miniature foldable quadruped with individually actuated legs, is designed to address such limitations. The design of the robot is unique in which a high structural integrity is achieved by transforming a single exible thin sheet into a rigid mechanical system through folding. MinIAQ's design novelties help modulate and extend the design standards of origami robots. The actuation independency of MinIAQ enables gait modi cation and exhibits maneuvering capabilities which is another novel quality for a robot at this scale. The design of the compliant four-bar legs is optimized for better foot trajectory in a newer version of the robot, MinIAQ{II, through dimensional synthesis of mechanisms. The resulting robot demonstrates signi cant improvements over its predecessor. For characterization and synchronization of the motors, custom encoders are designed to estimate speed and phase of each leg. Accordingly, a closed-loop feedback control algorithm is applied to follow an envisioned gait pattern. Towards understanding these gaits in robots with passive closed-chain legs, a comprehensive mathematical model is developed to describe the 6-DOF rigid body dynamics of MinIAQ. The proposed dynamics employs a nonlinear viscoelastic spring-damper model to estimate the feet-ground interactions. An interactive GUI is developed based on the model in MATLAB to simultaneously visualize the e ects of design parameters on performance. 3D simulation results closely match with the experiments and e ectively predict locomotion trends on at terrain. Since there is no control on foot placement in such underactuated robots, the model has given an insight into analyzing how close the actual locomotion is to the envisioned gait. This suggests that a comprehensive locomotion study with the model can lead to optimizing the gait and improve performance of miniature legged robots.