Browsing by Subject "Foldable Robotics"

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Open Access
Design, control, modeling, and gait analysis in miniature foldable robotics
(2018-09) Askari, Mohammad
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 The design of the compliant four-bar legs is optimized for better foot trajectory in a newer version of the robot, MinIAQ{II, through dimensional synthesis of mechanisms.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.
Open Access
Optimization of compliant joints used in miniature foldable robotics
(2018-03) Karakadıoğlu, Cem
In small scale and more specifically in miniature robotics applications, compliant mechanisms are highly preferred because of their advantages such as, less moving parts, friction losses, assembly time and effort, but their biggest challenge need to be addressed which is fatigue failure under cyclic loads. As the first step of this work, a new miniature, foldable, quadruped robot, MinIAQ, was developed whose legs are individually controlled by custom motors and encoders. The locomotion mechanism used in this robot is based on a simple four bar mechanism that consists of flexure joints instead of ideal revolute joints. These joints allow a single degree of freedom rotation provided by the bending of flexure members. Even though they are much more efficient and easier to make in small scale, such compliant joints suffer from fatigue failure, if subjected to long period of cyclic loads. Moreover, flexure joints and their use in robotic applications have not been modeled before using large deflection beam theory methods, which results with a limited understanding of the robot kinematics using compliant joints. In this thesis, elliptic integral solution of nonlinear large deflections are used to model the flexure joints used in miniature compliant mechanisms. The elliptic integral kinematic solutions are verified with experimental and FEA results by using a simple leg mechanism. With varying the geometric parameters for this simple compliant mechanism, results obtained from elliptic integral solution and experiments are presented and discussed. Since flexure joints store strain energy throughout bending, they act as torsion springs. The elliptic integral kinematic solution takes this bending moment into account and the results yield accurate load capacity of the compliant mechanism. The necessary input torque to operate the compliant mechanism can also be predicted in a more accurate manner. Using the model developed, the stresses on a compliant joint can be calculated for any mechanism. As a case study, an optimization is done for MinIAQ’s compliant joints based on its geometric parameters to withstand desired number of cycles before failure.