Building large and stable structures from highly irregular stones is among the most challenging construction tasks with excavators. In this letter, we present a method for grasp planning and object manipulation that enables the world's first autonomous assembly of a large-scale stone wall with an unmanned hydraulic excavator system. Our method utilizes point clouds and mesh surface reconstruction of stones in order to plan grasp configurations with a 2-jaw gripper mounted on the excavator. Besides considering the geometry of the stone to sample force closure grasps, the grasp planner also takes into account collision constraints during object pick and place, informed by a LiDAR based point cloud map. Furthermore, we show an approach to reorient arbitrarily shaped objects that are not feasible to be directly placed at the desired location without violating collision constraints. Using a physics engine, we find a settled intermediate pose that allows direct placement and is reachable from the initial stone pose. The applicability of the proposed grasp planning method is demonstrated with the construction of a dry stone wall composed of over one hundred boulders using an autonomous excavator. We show a high primary grasp success rate (82.2 $\%$ ) and illustrate how the system recovers from slippage by relocating the object and re-planning the grasp correspondingly.

中文翻译：

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石材结构自主构造的抓取和对象重新定向

用高度不规则的石头建造大型而稳定的结构是挖掘机最具挑战性的施工任务之一。在这封信中，我们介绍了一种用于掌握计划和对象操作的方法，该方法使世界上第一个具有无人液压挖掘机系统的大型石墙自动组装成为可能。我们的方法利用点云和石头的网状表面重建，以便通过安装在挖掘机上的2爪抓爪计划抓地力配置。除了考虑石头的几何形状以采样力闭合抓紧力外，抓紧计划器还考虑了对象拾取和放置期间的碰撞约束，并基于基于LiDAR的点云图进行了提示。此外，我们展示了一种重新定向任意形状的对象的方法，这些对象在不违反碰撞约束的情况下无法直接放置在所需位置。使用物理引擎，我们找到了一个稳定的中间姿势，该姿势可以直接放置并且可以从初始石头姿势到达。通过使用自动挖掘机建造由一百多块巨石组成的干石墙，证明了所提出的抓握计划方法的适用性。我们显示出较高的主要掌握成功率（82.2 通过使用自动挖掘机建造由一百多块巨石组成的干石墙，证明了所提出的抓握计划方法的适用性。我们显示出较高的主要掌握成功率（82.2 通过使用自动挖掘机建造由一百多块巨石组成的干石墙，证明了所提出的抓握计划方法的适用性。我们显示出较高的主要掌握成功率（82.2$ \％$ ），并说明系统如何通过重新定位对象并相应地重新计划抓地力来从滑移中恢复。