Implementation of vision based 2-DOF underwater Manipulator

Abstract

Abstract. Manipulator is of vital importance to the remotely operated vehicle (ROV), especially when it works in the nuclear reactor pool. Two degrees of freedom (2-DOF) underwater manipulator is designed to the ROV, which is composed of control cabinet, buoyancy module, propellers, depth gauge, sonar, a monocular camera and other attitude sensors. The manipulator can be used to salvage small parts like bolts and nuts to accelerate the progress of the overhaul. It can move in the vertical direction alone through the control of the second joint, and can grab object using its unique designed gripper. A monocular vision based localization algorithm is applied to help the manipulator work independently and intelligently. Eventually, field experiment is conducted in the swimming pool to verify the effectiveness of the manipulator and the monocular vision based algorithm. Keywords: ROV, 2-DOF manipulator, monocular camera, monocular vision segmentation algorithm IntroductionThese guidelines, Underwater research and development has becoming faster and faster during the last decade. However, the extreme conditions such as high water pressure, invisibility and non-oxygen become great barriers for human to access directly [1]. Underwater robots are expected and developed as efficient tools for the operation instead of human beings, and ROV is just one of them. Based on this, the manipulator mounted on the ROV is expected to play an important role for complex tasks, such as grabbing small parts like bolts and nuts in the nuclear reactor pool.There are many manipulators that are developed for industrial purpose but fewer for underwater utility on account of the high sealing requirement in the highpressure underwater environment and complex control method. A visual servoing control system was proposed for a two-link electrically actuated underwater manipulator by Maruthupandi A etc, and its effectiveness had been verified in a laboratory water tank using visual feedback to process the position and tracking control of the 2-link underwater robot manipulator [2]. CC Chang et al. [3] had designed and implemented an intelligent underwater robotic manipulator system, which consisted of a manipulator, ad distance measurement system, water-proof camera, computer, interface technology and task planning technology etc, to enhance the capability of the robotic manipulator to fulfill the need of less-skilled or even non-skilled operators. It has five rotary joints, including waist, shoulder, and elbow, wrist-pitch, and wrist-roll motion, and can accomplish an object grab under water with an ROV system. The 2-DOF manipulator designed and manufactured by us is mounted on an ROV that is used to inspect the reactor pressure vessel and other water-filled infrastructure in the nuclear reactor pool. It has two joints, and can move in the vertical direction alone through the control of the second joint and grab object using its unique designed gripper. A monocular vision based localization algorithm is applied to help the manipulator grab obje...

Research Progress of Underwater Vehicle-manipulator Systems: Configuration, Modeling and Control

“…UVMS 在进行水下接触作业时(如： 采样、 焊接、 搬运等)，不仅要保证末端执行器的精确位置，还需 要考虑末端执行器与环境的交互力/力矩，一些特殊 情况下细小的位置偏差可能导致大的接触力，从而 对任务目标或机械手本体造成损伤。 考虑到 UVMS 进行分析时末端执行器的动态 特性与控制框架，针对末端执行器约束运动和主动 力控制，KHATIB 提出了运动与力的统一控制方 法 [176] 。LAPIERRE 等 [177] 以力控制为基础，保持机 械手在自由或受约束的空间内稳定，通过安装在机 械手基座和本体之间的力传感器来估计机械手所产 生的力/力矩，借助外力控制回路来校正平台的位置 误差。ANTONELLI 等 [178] 提出了一种 UVMS 外力 控制方案，考虑了本体在运动过程中机械手可能出 现的触点失稳问题，采用了动态补偿的自适应运动 控制方案。CUI 和 SARKAR [179] 结合阻抗和混合控 制，提出一种统一的力控制方案，该模型将阻抗控 制与模糊切换方式的力/位置控制相结合，实现了水 下自主控制。BARBALATA 等 [180] 针对力传感器不 可用时， 保证控制律能够处理与环境近似的接触力。 OLGUIN-DIAZ 等 [181] 对于冗余的非惯性 UVMS，提 出了一种基于无源性水下全驱动 UVMS 接触控制 的无模型控制方案。 HESHMATI-ALAMDARI 等 [182] 提出的力/位置跟踪控制方法能够保证响应速度，减 少 最 大 稳 态 误 差 以 及 跟 踪 误 差 。 CATALDI 和 ANTONELLI [183] 采用一种适当的任务优先级逆运动 学控制器，完成了水下交互控制方案--转动阀门 和按按钮。为了实现水下机械手在未知环境下对目 标物进行抓取， 张建军等 [184] 提出了自适应阻抗控制 方法，并结合自适应 PID 控制来调节期望位置，实 现了跟踪目标位置的同时保证了力的要求。段晋军 等 [185] 针对双臂协调搬运中同时存在外部干扰和内 力约束，提出了一种基于变阻抗模型的内外力/位置 混合控制策略，对力约束子空间中的内力约束采用 变阻抗模型进行力跟踪，对位置子空间中的外部干 扰采用阻抗模型进行轨迹跟踪，并进行了仿真和实 验验证。DAI 等 [186] 将滑模阻抗力/位置控制方法应 用在干预型水下机器人上从而解决水下作业问题。 针对末端执行器上的手爪，需要合理的控制加持力 与加持速度，采用带有闭环的位置控制和力反馈有 利于更好地完成任务。 4.6 视觉伺服控制 视觉伺服控制是实现 UVMS 自主控制的关键， 目前常用的水下目标探测与识别技术有声学传感器 (声纳)成像和光学传感器(摄像机)成像 [1] 。基于视觉 引导，手眼协同控制可以实现水下目标的跟踪和自 主操作。针对视觉传感器参数、UVMS 运动学和特 征位置信息等的不确定，LI 等 [187] 提出了一种水下 机器人手眼相机系统的无标定视觉伺服方案并进行 了数值模拟。 通过机器视觉的单目和双目技术，能够辅助完 成悬停 [188] 、特征点提取 [189] ，水下定位 [190] ，水下抓 取 [191] ，双目视觉测距 [192] 等工作任务。GENG 等 [193] 提出了一种基于单目视觉的定位算法，实现了水下 机械手的自主定位，并在水池中进行了试验，验证 了水下机械手和 基 于 单 目 视 觉 算 法 的 有 效 性 。 UVMS 的视觉标定是视觉伺服控制中的难点 [194] ， PALOMER 等 [195] 采用水下三维激光扫描仪与机械 手结合，能够实现相对位置的标定。肖治琥 [196] 设计 了一种基于视觉和超声传感器的水下机械手自主抓 取算法，并进行了相关试验研究。在交互任务中基 于视觉技术可以帮助 UVMS 实现完全自主控制 [197] 。 此外，利用视觉伺服技术还能够实现水下机器人的 自动对接工作 [198] 。 [109] SIMETTI E，CASALINO G，WANDERLINGH F，et al…”