In everyday life, we often find that we can maintain an object's equilibrium on a tray by adjusting its orientation. Building upon this observation and extending the method we previously proposed to suppress sloshing in a moving vessel, this paper presents a feedforward control approach for transporting objects with a robot that are not firmly grasped but simply placed on a tray. The proposed approach combines smoothing actions and end-effector re-orientation to prevent object sliding. It can be integrated into existing robotic systems as a plug-in element between the reference trajectory generator and the robot control. To demonstrate the effectiveness of the proposed methods, particularly when dealing with unknown reference signals, we embed them in a direct teleoperation scheme. In this scheme, the user commands the robot carrying the tray by simply moving their hand in free space, with the hand's 3D position detected by a motion capture system. Furthermore, in the case of point-to-point motions, the same feedforward control, when fed with step inputs representing the desired goal position, dynamically generates the minimum-time reference trajectory that complies with velocity and acceleration constraints, thus avoiding sloshing and slipping. More information and accompanying videos can be found at https://sites.google.com/view/robotwaiter/

翻译：在日常生活中，我们常通过调整托盘朝向以保持物体平衡。基于此观察，并扩展了我们先前提出的抑制移动容器内液体晃荡的方法，本文提出一种前馈控制方法，用于机器人运输未牢固抓取、仅置于托盘上的物体。该方法将平滑操作与末端执行器重定向相结合，以防止物体滑动。它可作为参考轨迹生成器与机器人控制器之间的插件模块集成至现有机器人系统中。为验证所提方法的有效性（尤其在处理未知参考信号时），我们将其嵌入直接遥操作方案中：用户仅需在自由空间中移动手掌（通过运动捕捉系统检测手部三维位置），即可指令载有托盘的机器人运动。此外，对于点到点运动，当以表示目标位置的阶跃信号作为输入时，相同的前馈控制可动态生成满足速度与加速度约束的最短时间参考轨迹，从而避免液体晃荡与物体滑动。更多信息及配套视频请参见https://sites.google.com/view/robotwaiter/