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Design of Compliant OmniCrawler modules for Modular robotsAuthor: Enna Sachdeva Date: 2018-07-17 Report no: IIIT/TH/2018/39 Advisor:Abhishek Sarkar AbstractIn this thesis, we discuss the design and development of various Compliant OmniCrawler modules, inspired by the OmniCrawler module developed at Osaka University. The circular cross-section of the module enables a holonomic motion, which adds an extra degree of freedom to the module, in addition to the forward/backward motion as in conventional tank like crawler module. The design capabilities of the module enable it to be integrated into a variety of applications like pipe climbing robot, Quadruped or a Snake robot. The first part of the thesis involves designing and developing an In-Pipe climbing robot using OmniCrawler modules using a series of OmniCrawler modules. The robot consists of a kinematic chain of 3 OmniCrawler modules with a link connected in between 2 adjacent modules via compliant joints. While the tank-like crawler mechanism provides good traction on low friction surfaces, its circular cross-section makes it holonomic. The holonomic motion assists it to re-align in a direction to avoid obstacles during motion as well as overcome pipe turns with a minimal energy posture. Additionally, the modularity enables it to negotiate T-junction without motion singularity. With an objective to negotiate sharp turns in small diameter pipes, the second part of the thesis involves introduction of planar revolute joints within the OmniCrawler module and the characteristics of this module have been exploited for designing an In-Pipe climbing robot-COCrIP. The design of the Compliant module introduces certain functionalities in the robot which enables it to address challenges not tackled by the state-of-the-art in-pipe climbing robots. Furthermore, the introduction of active compliance (using planar revolute joints) in the crawler module with a single chain-lugs assembly is the key novelty of this design which makes this module one of its kind and it possesses property of complying with uneven terrain while crawling at the same time. For the desirable pipe diameter and curvature of the bends, the spring stiffness value for each passive joint is determined by formulating a constrained optimization problem using the quasi-static model of the robot. Moreover, a minimum friction coefficient value between the module-pipe surface which can be vertically climbed by the robot without slipping is estimated. The advantages of OmniCrawler modules are further augmented by the introduction of Omnidirectional joint with-in the module in the later part of this theis, which led to the development of a module- CObRaSO: Compliant Omni-Direction Bendable Hybrid Rigid and Soft OmniCrawler Module. The Omnidirectional bendable property of the module achieves high manoeuvrability and adaptability of the OmniCrawler module on an uneven surface. The Omnidirectional bending is realized by an arrangement of two independent 1-DOF joints aligned at 90 _ with respect to each other. The hybrid soft-rigid structure of the module provides compliant pathways for lug-chain assembly which allows crawling motion even in the bent configuration of the module. This hybrid structure provides compliant pathways for the lug-chain assembly to passively conform with the orientation of the module and crawl in Omnidirectional bent configuration. We show that the unique modular design unveils its versatility in terms of achieving compliance on an uneven surface, demonstrating its applications in different robotic platforms, such as an in-pipeline robot, Quadruped, snake robot, and exhibiting hybrid locomotive traits in various configurations of the robots with the help of simulations and experiments results on real robot prototype. Full thesis: pdf Centre for Robotics |
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