Human hands are able to grasp a wide range of object sizes, shapes, and weights, achieved via reshaping and altering their apparent grasping stiffness between compliant power and rigid precision. Achieving similar versatility in robotic hands remains a challenge, which has often been addressed by adding extra controllable degrees of freedom, tactile sensors, or specialised extra grasping hardware, at the cost of control complexity and robustness. We introduce a novel reconfigurable four-fingered two-actuator underactuated gripper -- the Hydra Hand -- that switches between compliant power and rigid precision grasps using a single motor, while generating grasps via a single hydraulic actuator -- exhibiting adaptive grasping between finger pairs, enabling the power grasping of two objects simultaneously. The mode switching mechanism and the hand's kinematics are presented and analysed, and performance is tested on two grasping benchmarks: one focused on rigid objects, and the other on items of clothing. The Hydra Hand is shown to excel at grasping large and irregular objects, and small objects with its respective compliant power and rigid precision configurations. The hand's versatility is then showcased by executing the challenging manipulation task of safely grasping and placing a bunch of grapes, and then plucking a single grape from the bunch.

翻译：人类手部能够抓取各种尺寸、形状和重量的物体，这是通过重塑并改变其表观抓取刚度（在柔顺强力抓取与刚性精准抓取之间切换）实现的。在机器人手部实现类似的通用性仍是一项挑战，通常通过增加额外的可控自由度、触觉传感器或专用的额外抓取硬件来解决，但代价是控制复杂度和鲁棒性。我们提出了一种新型可重构四指双驱动器欠驱动夹持器——“液压手”，它通过单个电机在柔顺强力抓取与刚性精准抓取之间切换，同时通过单个液压驱动器生成抓取动作——在手指对之间实现自适应抓取，从而能够同时强力抓取两个物体。本文介绍并分析了模式切换机制及手部运动学，并在两个抓取基准上测试了性能：一个专注于刚性物体，另一个专注于衣物。结果表明，液压手在抓取大型不规则物体和小型物体方面表现出色，其对应配置分别为柔顺强力抓取模式和刚性精准抓取模式。随后，通过执行一项具有挑战性的操作任务——安全抓取并放置一串葡萄，然后从串中摘取一颗葡萄——展示了该手部的通用性。