面向水下各方向远距离、 大空间作业任务, 提出一种基于变推进力机构的水下近端索驱动机器人。该机器人采用六索及螺旋桨混合驱动形式, 螺旋桨推进力大小和方向均可变, 可等效为1根绳索。首先, 对该机器人进行结构设计, 提出采用近端驱动模式, 并引入可改变推进力方向的A、 B轴转角机构; 其次, 建立机器人的运动学与静力学模型, 进一步针对推进力可变的特点提出一种基于二次规划的力可行工作空间计算方法; 最后, 对恒方向和变方向推进力下机器人的力可行工作空间进行分析。工作空间对比结果表明, 推进力变向机构的引入使机器人的力可行工作空间显著增大, 解决了已有水下多自由度机器人作业空间不足的问题。
Abstract
[Objective] Underwater multiple-degree-of-freedom robots possess a broad range of application potentials in diverse fields such as marine resource exploration, scientific investigation, and engineering construction and maintenance. However, during the execution of large-scale, long-distance underwater tasks, the conventional rigid serial and parallel manipulators frequently face the challenge of inadequate working range. Cable-driven parallel robots offer advantages such as large workspace, small inertia, and strong load capacity. However, prevalent cable-driven parallel robots for underwater applications are typically passively tensioned by gravity or buoyancy with their drive units (winches) mounted on a static platform, which constraints their motion ability and reconfigurability. Hence, a winch-integrated underwater cable-driven parallel robot based on a variable thrust mechanism is presented. The proposed robot adopts a hybrid drive form of six cables and a propeller. The thrust generated by the propeller, equivalent to cable tension, is adjustable in terms of magnitude and direction. [Methods] First, the overall mechanical structure of the robot is examined, and its kinematic and static models are established. On the basis of analyzing the judgment criterion of the wrench-feasible workspace (WFW), the wrench-feasibility testing problem under variable thrust is transformed into a constrained quadratic programming problem through the linear approximation method, and a new WFW calculation method is obtained. Then, a set of structural and force parameters of the robot are provided to evaluate and compare the WFWs of the robot with varied moving platform orientations and external forces under constant- and variable-direction thrusts. In addition, a large-span spiral trajectory is selected, a two-norm force index is implemented to optimize the thrust and cable tensions, and then the changes of all driving forces during the quasi-static motion of the robot on the trajectory are assessed under the two different thrust strategies. [Results] Calculation and analysis reveal that under constant-direction thrust, the WFW of the robot appears columnar. Although the moving platform can extend over 10 meters in the Z direction, its motion ranges in the X and Y directions are small, and the WFW is influenced by the orientation of the moving platform and the external forces, which suggest that the robot is susceptible to out-of-control phenomenon. By contrast, under variable-direction thrust, the WFW becomes a cone-shaped space; compared with the condition of constant-direction thrust, the X and Y direction motion ranges of the moving platform increase, and the volume of the robot workspace remarkably improves. The simulation for spiral trajectory motion also reveals that under constant-direction thrust, the cable tensions vary substantially, which facilitates exceeding the limit and causes problems such as slack. The change of thrust direction can considerably alleviate the variability of the tensions, and guarantee that they remain within feasible limits, hence expanding the robot's range of motion. [Conclusions] Results reveal the remarkable improvement outcome of the variable thrust mechanism on the WFW of the robot, which solves the problem of inadequate working range of the existing underwater multiple-degree-of-freedom robots. This paper can provide a reference for further studies on the design and analysis of underwater cable-driven parallel robots.
关键词
水下装备 /
索并联机构 /
结构设计 /
工作空间
Key words
underwater equipment /
cable-driven parallel mechanism /
structural design /
workspace
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基金
国家自然科学基金面上项目(51975307)
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