Underwater dual manipulators-Part I: Hydrodynamics analysis and computation

1098-1103This paper introduces two 4-DOF underwater manipulators mounted on autonomous underwater vehicle (AUV) with grasping claws, such that the AUV can accomplish the underwater task by using dual manipulators. Mechanical design of the manipulator is briefly presented and the feature of the simple structure of dual manipulators is simulated by using Solid Works. In addition, the hydrodynamics of the manipulator is analyzed, considering drag force, added mass and buoyancy. Then, hydrodynamic simulations of the manipulator are conducted by using 3-D model with Adams software, from which the torque of each joint is calculated. This paper presents an integrated result of computed torques by combining the theoretical calculation and simulation results, which is instrumental in determining the driving torque of the manipulators

RBF-based supervisor path following control for ASV with time-varying ocean disturbance

1028-1036A robust model-free path following controller is developed for autonomous surface vehicle (ASV) with time-varying ocean disturbance. First, the geometrical relationship between ASV and virtual tracking point on the reference path is investigated. The differentiations of tracking errors are described with the relative motion method, which greatly simplified the direct differential of tracking errors. Furthermore, the control law for the desired angular velocity of the vehicle and virtual tracking point are built based on the Lyapunov theory. Second, the traditional proportional-integral-derivative (PID) controller is developed based on the desired velocities and state feedback. The radial basic function (RBF) neural network taking as inputs the desired surge velocity and yaw angular velocity is developed as the supervisor to PID controller. Besides, RBF controller tunes weights according to the output errors between the PID controller and supervisor controller, based on the gradient descent method. Hence, PID controller and RBF supervisor controller act as feedback and feed forward control of the system, respectively. Finally, comparative path following simulation for straight path and sine path illustrate the performance of the proposed supervisor control system. The PID controller term reports loss of control even in the unknown disturbance

Underwater dual manipulators-Part II: Kinematics analysis and numerical simulation

1104-1112This paper introduces dual-arm underwater manipulators mounted on an autonomous underwater vehicle (AUV), which can accomplish the underwater handling task. Firstly, the mechanical structure of the dual-arm system is briefly introduced, wherein each 4-DOF manipulator has an additional grasping function. In addition, the kinematics model of the manipulator is derived by using the improved D-H method. Secondly, the working space of the underwater dual-arm system is analyzed, which is obtained by using Monte Carlo method. The cubic polynomial interpolation and the five polynomial interpolation trajectory planning methods are compared in the joint space. Finally, with the help of the Robotics Toolbox software, the numerical test is conducted to verify the functions of the underwater dual-arm manipulator system

AN EXPERIMENTAL STUDY TOWARDS UNDERWATER PROPULSION SYSTEM USING STRUCTURE BORNE TRAVELING WAVES

The method of generating steady-state structure-borne traveling waves underwater in an infinite media creates abundant opportunities in the field of propulsive applications, and they are gaining attention from several researchers. This experimental study provides a framework for harnessing traveling waves in a 1D beam immersed under quiescent water using two force input methods and providing a motion to an object floating on the surface of the water. In this study, underwater traveling waves are tailored using structural vibrations at five different frequencies in the range of 10Hz to 300Hz. The resulting fluid motion provides a propulsive thrust that moves a 3D-printed bob floating on the surface of the water. The undulatory motion of the floating bob is determined using an image processing approach. In this approach, videos are recorded for image processing to determine the effects of each traveling wave frequency on the object’s motion. Through image processing, observations are drawn regarding the velocity and the distance traveled by the bob for each SBTW frequency. As this is developing research, there is a limited understanding to the relationship between the amplitude of force input, the traveling wave frequency, and the velocity attained by the object. So, with the help of image processing, a general observation about the effects of varied force input on the motion of the object at each frequency is drawn

Embedded Sensing and Control for High-Speed Electrohydraulic Soft Robots

Soft robotics is a field of robotic system design characterized by materials and structures that exhibit large-scale deformation, high compliance, and rich multifunctionality. The incorporation of soft and deformable structures endows soft robotic systems with the compliance and resiliency that makes them well-adapted for unstructured and dynamic environments. While actuation mechanisms for soft robots vary widely, soft electrostatic transducers such as dielectric elastomer actuators (DEAs) and hydraulically amplified self-healing electrostatic (HASEL) actuators have demonstrated promise due to their muscle-like performance. Despite significant leaps in design and modeling of HASEL actuators thus far, the actuators in and of themselves are limited in terms of estimating their own states and individually lacks useful system-level functionalities. To address the mentioned shortcomings, this body of research has enabled embedded perception and intelligence to electromechanical systems driven by electro-hydraulic actuators, by (i) developing capacitive self-sensing and magnetic sensing techniques to estimate shape changes of electro-hydraulic actuators in real-time; (ii) designing and implementing hardware and software controllers for an array of electrohydraulic actuators to enable complex motions and their collective useful functionalities; and (iii) demonstrating the integration of embedded sensing and control to bring soft robots driven by these actuators closer to practical, real-world applications. While not exhaustive, the introduced system technologies provide the fundamental building blocks for more advanced functionalities and features that can potentially integrate HASEL actuators to augment and enrich our daily lives

A Hyperelastic Porous Media Framework for Ionic Polymer-Metal Composites and Characterization of Transduction Phenomena via Dimensional Analysis and Nonlinear Regression

Ionic polymer-metal composites (IPMC) are smart materials that exhibit large deformation in response to small applied voltages, and conversely generate detectable electrical signals in response to mechanical deformations. The study of IPMC materials is a rich field of research, and an interesting intersection of material science, electrochemistry, continuum mechanics, and thermodynamics. Due to their electromechanical and mechanoelectrical transduction capabilities, IPMCs find many applications in robotics, soft robotics, artificial muscles, and biomimetics. This study aims to investigate the dominating physical phenomena that underly the actuation and sensing behavior of IPMC materials. This analysis is made possible by developing a new, hyperelastic porous media modeling framework for IPMCs. Using the principles of continuum thermodynamics and multiphasic materials, a finite-strain porous media formulation of IPMC materials is developed. The intricate polymer-electrode interface coupling is extended to such a finite-strain model by accounting for charge conservation at deforming material interfaces. Using this new modeling framework, the effects of kinematic nonlinearity are explored, and a partially linearized kinematic model is proposed for capturing rotational deformation in an otherwise linear model. The most comprehensive dimensional analysis of IPMC transduction phenomena is presented, characterizing the IPMC actuator, short-circuit current, and open-circuit voltage response under static and dynamic loading. The information obtained in this analysis is used to construct nonlinear regression models for the transduction response as univariant and multivariant functions. Automatic differentiation techniques are leveraged to linearize the nonlinear regression models in the vicinity of a representative IPMC description and derive the sensitivity of the transduction response with respect to the driving independent variables. Further, the multiphysics model is validated using experimental data collected for the dynamic IPMC actuator and voltage sensor. With data collected from physical samples of IPMC materials in-lab, the regression models developed under the new computational framework are verified. Using these regression models to interpret the experimental data allowed for further material property characterization to occur, demonstrating the capability of using hybrid computational / experimental regression models to extract information regarding material properties that would otherwise be unknown within the data collected. Key values for the mobile concentration and electric potential fields are approximated using order-of-magnitude arguments and the sharpness of the gradients that occur at the polymer-electrode interfaces of IPMC materials. These values allow for approximate reconstruction of the fields themselves, which in turn are leveraged to formulate the internal bending moments and steady-state curvature of the IPMC. Using both an Euler-Bernoulli beam and a constant curvature arc model for the IPMC, the deformation and rotation of the of the order of magnitude model demonstrated impressive performance for being based on rough approximations. The curled shape of IPMCs under large applied potentials with nonlinear deformation are recovered using this simplified model, and the ability to extend the model for dynamic actuation is outlined