Legged robots can have a unique role in manipulating objects in dynamic, human-centric, or otherwise inaccessible environments. Although most legged robotics research to date typically focuses on traversing these challenging environments, many legged platform demonstrations have also included "moving an object" as a way of doing tangible work. Legged robots can be designed to manipulate a particular type of object (e.g., a cardboard box, a soccer ball, or a larger piece of furniture), by themselves or collaboratively. The objective of this review is to collect and learn from these examples, to both organize the work done so far in the community and highlight interesting open avenues for future work. This review categorizes existing works into four main manipulation methods: object interactions without grasping, manipulation with walking legs, dedicated non-locomotive arms, and legged teams. Each method has different design and autonomy features, which are illustrated by available examples in the literature. Based on a few simplifying assumptions, we further provide quantitative comparisons for the range of possible relative sizes of the manipulated object with respect to the robot. Taken together, these examples suggest new directions for research in legged robot manipulation, such as multifunctional limbs, terrain modeling, or learning-based control, to support a number of new deployments in challenging indoor/outdoor scenarios in warehouses/construction sites, preserved natural areas, and especially for home robotics.

翻译：四足机器人在动态、以人为中心或难以进入的环境中操作物体时可发挥独特作用。尽管迄今为止大多数四足机器人研究通常聚焦于穿越此类复杂环境，但已有诸多四足平台演示将"移动物体"作为执行具体任务的方式。四足机器人可被设计为自主或协同操作特定类型物体（如纸箱、足球或大型家具）。本综述旨在收集并分析这些案例，既梳理学界已有研究成果，又为未来研究指出富有前景的开放方向。本文将现有研究分为四类主要操作方法：无抓取式物体交互、行走腿操作、专用非运动臂操作以及四足机器人团队协作。每种方法在设计与自主性方面各有特点，并通过文献中的典型案例加以说明。基于若干简化假设，我们进一步对操作物体与机器人相对尺寸的可行范围进行了定量比较。综合这些案例，本文提出四足机器人操作研究的新方向，包括多功能肢体、地形建模及基于学习的控制方法，以支持其在仓库/建筑工地、自然保护区的复杂室内外场景中，特别是家庭机器人领域的多方面部署。