An Underwater Robotic Manipulator with Soft Bladders and Compact Depth-Independent Actuation

Abstract

An underwater manipulator is essential for underwater robotic sampling and other service operations. Conventional rigid body underwater manipulators generally required substantial size and weight, leading to hindered general applications. Pioneering soft robotic underwater manipulators have defied this by offering dexterous and lightweight arms and grippers, but still requiring substantial actuation and control components to withstand the water pressure and achieving the desired dynamic performance. In this work, we propose a novel approach to underwater manipulator design and control, exploiting the unique characteristics of soft robots, with a hybrid structure (rigid frame+soft actuator) for improved rigidity and force output, a uniform actuator design allowing one compact hydraulic actuation system to drive all actuators, and a novel fully customizable soft bladder design that improves performances in multiple areas: (1) force output of the actuator is decoupled from the working depth, enabling wide working ranges; (2) all actuators are connected to the main hydraulic line without actuator-specific control loop, resulting in a very compact actuation system especially for highdexterity cases; (3) dynamic responses were improved significantly compared with the counter system without bladder. A prototype soft manipulator with 4-DOFs, dual bladders, and 15 N payload was developed; the entire system (including actuation, control, and batteries) could be mounted onto a consumer-grade remotely operated vehicle, with depth-independent performances validated by various laboratory and field test results across various climatic and hydrographic conditions. Analytical models and validations of the proposed soft bladder design were also presented as a guideline for other applications.

Soft Robots for Ocean Exploration and Offshore Operations: A Perspective

“…Nevertheless, conducting this study, we did not come across with entirely soft robots capable to perform complex tasks in the environments that we identified as crucial for industrial sustainable development and oceanographic exploration. [51][52][53][54] From our investigation emerged an increasing trend in embedding soft elements into established underwater technologies 45,46,55 (Fig. 5G-I).…”

Underwater Crawling Robot With Hydraulic Soft Actuators

“…Soft robotics is a top-trending area, inspiring paradigm changes in robotic design and actuation, with soft-material bodies of inherent compliance being used both as structural components and as actuators ( Rus and Tolley, 2015 ; Wang et al, 2015 ; Liu et al, 2021 ). There have been many notable attempts in developing underwater soft robots, but mostly focused on the manipulation and sampling end of operations, ranging from underwater soft actuators ( Ku et al, 2009 ; Yim et al, 2007 ), wrist joint ( Kurumaya et al, 2018 ), manipulator arms ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ), and underwater exploration platforms ( Patterson et al, 2020 ). These underwater soft robot designs showcased their advantages for the underwater environment: soft manipulators or grippers composed of simple structural design and modular variants could achieve both a high degree of dexterity and flexibility ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ).…”

“…There have been many notable attempts in developing underwater soft robots, but mostly focused on the manipulation and sampling end of operations, ranging from underwater soft actuators ( Ku et al, 2009 ; Yim et al, 2007 ), wrist joint ( Kurumaya et al, 2018 ), manipulator arms ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ), and underwater exploration platforms ( Patterson et al, 2020 ). These underwater soft robot designs showcased their advantages for the underwater environment: soft manipulators or grippers composed of simple structural design and modular variants could achieve both a high degree of dexterity and flexibility ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ). In particular, the soft actuators’ natural waterproofness, superior environmental adaptability, and flexibility make them ideal for interacting with various marine creatures within the pressurized and corrosive harsh underwater environment ( Calisti et al, 2011 ; Cianchetti et al, 2011 ; Arienti et al, 2013 ; Stilli et al, 2014 ; Stuart et al, 2014 ; Shen et al, 2021 ).…”

“…However, despite their success as manipulators and sampling grippers, existing underwater soft robotic limbs still require conventional robotic vehicles as mounting platforms ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ), while existing soft underwater vehicles or robotic platforms are highly scarce, with highly limited payload or locomotion capabilities ( Ishida et al, 2019 ; Patterson et al, 2020 ), insufficient for carrying soft manipulators. The key bottle neck of soft robots for payload-and-precision demanding tasks such as marine benthic crawling lies in the soft actuators.…”

A review of different designs and control models of remotely operated underwater vehicle

“…The additional equipment are electronic modules and suction arm. 15 In these types of systems, a cable connects the operator and vehicle. The underwater vehicle is powered from the control surface platform.…”