Tortuous manipulation tasks like minimally-invasive surgery, rescue missions, inspection through tight spaces present a plethora of technical challenges for researchers and engineers. The author identifies and presents a novel concept that combines the advantages of mobile systems, tethered robots, and tendon-driven continuum robots to address the challenges of tortuous manipulation tasks. Mobile systems like wheeled-robots, aerial vehicles or quadrupeds have the advantage of moving the robots on a macro scale, while continuum robots offer movements that are more refined. On the other hand, tethered systems offer the uncoupling of the actuators from the continuum robot, allowing these actuators to be located from a remote area instead of encumbering the mobile robot. To the author’s best knowledge, such systems have not been formally presented academically.
Therefore, in this thesis, the author presents the development of such a robot, and discusses how the coupling of each component presents technical challenges for a self-contained minimal yet practical implementation of the aforementioned system in detail. This thesis employs the Cosserat rod theory method and constant curvature method. However, the implementation of Cosserat rod theory proves to be more accurate, scalable and versatile. Furthermore, the aerial tendon-driven continuum robot is subjected to the external mechanical phenomena such as friction and disturbances induced from the augmented tethers.
Since the Cosserat rod method is generalised to any slender flexible objects, it is also then used to model the augmented tethers used to connect the tendon-driven continuum robot to the ground. However, the low elastic modulus of these tethers could numerically destabilise the solutions of the Cosserat rod states. Therefore, the multiple shooting method (inspired from numerical optimal control) is proposed to solve the augmented tether’s states instead of existing methods to circumvent the issues of numerical instabilities.
The static friction, determined by Capstan’s theory together with Cosserat rod solutions has provided better Jacobian estimations, which are superior in controlling a 3 stage continuum robot, compared to Jacobians computed without using friction compensation. The friction loss and 6-DOF wrench estimations were also experimentally validated with the proposed multiple shooting method with 0.1679N and 0.0401Nm for RMSE force estimation and torque estimation error respectively, while achieving a 3% mean absolute percentage steady state friction estimation error.
Lastly, the solution of the Cosserat rod equations provides the total curvature, which can be used to solve for frictional hysteresis in both the continuum robot and augmented tethers by updating the curvature terms in modified Dahl’s friction model. These tools have provided the means to determine the tip position of a remote-driven tendon-driven continuum robot and also removed the need for external sensors like Optitrack. The performance in RMSE for tension estimation from friction loss for augmented tethers is 25.2% better compared to the unmodified friction model, while the performance in RMSE for tip position estimation compared to a typical unmodified Cosserat rod method is a 35.8% increase in accuracy.
- Towards a High-Fidelity Model for Practical Tethered Remote-Actuated Tendon-Driven Continuum Robots for Aerial Manipulation
- Jer Luen Chien
- Shaohui Foong - Singapore University of Technology and Design, Engineering Product Development (EPD)
- Singapore University of Technology and Design; Doctor of Philosophy (PHD)
- Doctor of Philosophy (PHD), Singapore University of Technology and Design
- 136
- 9915315509846
- Engineering Product Development (EPD)
- English
- Dissertation