Underwater vehicles have carried out subsea operations for many decades, and since the 1980s, remotely operated vehicles (ROV) have been essential for the development and maintenance of subsea installations. As the technology has progressed, various types of vehicles have been developed to perform subsea inspection, maintenance, and repair (IMR) operations, including conventional work class ROVs, inspection class ROVs, autonomous underwater vehicles (AUVs), and more recently, intervention AUVs (I-AUVs). The underwater swimming manipulator (USM), presented in this paper, is an innovative, bioinspired addition to the family of underwater robotic vehicles. The overall vision of the USM is to provide a significant impact on how to perform inspection and light intervention tasks. In this paper, we discuss the most important applications for the USM and the main challenges related to modelling, guidance, and control of this innovative vehicle. We provide a detailed description of the concept of the USM, together with a proposed generic motion control framework. A kinematic and a dynamic model of the USM is derived for the purpose of designing control algorithms, and selected task based control approaches are presented, based on inverse kinematic control. We also present the development of a
The underwater swimming manipulator (USM) is a snake-like, multi-articulated, underwater robot that is equipped with thrusters. One of the main purposes of the USM is to act like an underwater floating base manipulator. As such, it is essential to achieve good station-keeping and trajectory tracking performance for the USM by using the thrusters and by using the joints to attain the desired position and orientation of the head and tail of the USM. In this 'paper, we propose a sliding mode control (SMC) law, specifically the super-twisting algorithm with adaptive gains, for the trajectory tracking of the USM's centre of mass. A higher-order sliding mode observer is proposed for state estimation. Furthermore, we show the ultimate boundedness of the tracking errors. We demonstrate the applicability of the proposed control law and show that it leads to better performance than a linear PD-controller.
Abstract-Autonomous underwater vehicles (AUVs) have been used for environmental mapping and surveys of various kinds for some time. More recently, the AUVs have entered the domain of the remotely operated vehicles (ROVs) to tackle some of the lighter subsea operations, such as inspection, maintenance, and repair (IMR) and light intervention tasks. The successful transition to AUVs for inspection of subsea infrastructure has pushed the technology towards AUVs equipped with robotic arms. Some AUVs with attached manipulator arms have demonstrated autonomous light intervention, but the majority of such tasks are still carried out using tethered and expensive ROVs with support vessels. The underwater swimming manipulator (USM) presented in this paper, is a snakelike bio-inspired AUV with exceptional accessibility and flexibility, due to its slender, multi-articulated structure. In this paper, we discuss why the USM is an appropriate system for certain tasks that are normally carried out by conventional ROVs and AUVs. Furthermore, we address the topic of kinematic control of the USM to utilize the inherent redundancy. Finally, we present and make use of a newly developed and versatile simulation environment for USMs to assert the applicability of the USM for performing subsea inspections and light intervention.
Abstract-This paper proposes a novel method for kinematic singularity avoidance for robot manipulators. Using set-based singularity avoidance tasks within the singularity-robust multiple task priority framework, avoidance of kinematic singularities is guaranteed without interfering with the convergence of compatible equality tasks. Non-compatible equality tasks will still be fulfilled to the extent possible. In addition, the method can be used to reconfigure the robot into a more dexterous configuration. The proposed method is applicable to both redundant and nonredundant robots, with both fixed base and floating base. The implementation is generic and independent of the type and number of tasks. Although also applicable for non-redundant fixed base robot manipulators, this novel approach is particularly well suited for highly redundant and/or floating base manipulators, since the robot configuration can be changed to improve the dexterity of the manipulator arm. We demonstrate the method by applying it to an underwater swimming manipulator, which is an innovative and highly redundant underwater floating base manipulator. Furthermore, simulation results are presented that illustrate and validate the proposed method.
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