We consider the nonprehensile object transportation task known as the waiter's problem, in which a robot must move an object balanced on a tray from one location to another. In contrast to prior works on the robotic waiter's problem, which make the robot tilt a tray rigidly held by its end effector (EE), we use a tray suspended from the EE by ropes, such that it behaves like a three-dimensional pendulum. Some prior works have actuated the robot so that the EE simulates the behavior of a pendulum, because pendular motion reduces the shear forces acting on the transported objects, minimizing the sliding of rigid objects and sloshing in containers of liquid. In contrast, our use of a real hanging tray allows us to obtain the benefits of pendular motion while only actuating a 3 degree-of-freedom (DOF) mobile base, rather than requiring a full 6-DOF manipulator arm. Our experiments in simulation and on real hardware show that the hanging tray substantially reduces both sliding and sloshing compared to a static, rigidly-grasped tray. Furthermore, we integrate the hanging tray into an interactive robot waiter demonstration, which uses computer vision to identify people with a raised hand and visual servoing to steer toward them and allow them to access the tray.

翻译：摘要：本文研究了被称为“服务员问题”的非抓取式物体运输任务，即机器人需将平衡放置在托盘上的物体从一个位置移动到另一个位置。与以往机器人服务员问题研究中机器人倾斜由末端执行器（EE）刚性固定的托盘不同，我们采用绳索将托盘悬挂于EE上，使其表现为三维摆锤系统。部分先前研究通过控制机器人使EE模拟摆锤运动，因为摆动运动能减少作用在运输物体上的剪切力，从而降低刚性物体的滑动和容器内液体的晃荡。相比之下，使用实际悬挂托盘可在仅驱动3自由度（DOF）移动基座而非完整6-DOF机械臂的情况下获得摆动运动的优势。仿真与实物实验表明，相较于静态刚性抓取托盘，悬挂托盘能显著减少滑动与晃荡。此外，我们将悬挂托盘集成到交互式机器人服务员演示系统中，该系统通过计算机视觉识别举手人物，并利用视觉伺服控制机器人转向目标，以便其取用托盘物品。