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：人类手部能够通过重塑和改变其表面抓取刚度（从柔顺强力抓取到刚性精准抓取），实现对各类尺寸、形状及重量物体的抓取。在机器人手中实现类似的通用性仍是一项挑战，常见的解决方案是增加额外可控自由度、触觉传感器或专用抓取硬件，但这也带来了控制复杂度与鲁棒性方面的代价。我们提出了一种新型可重构四指双驱动欠驱动夹爪——水螅手——它通过单个电机在柔顺强力抓取与刚性精准抓取模式之间切换，并借助单个液压驱动器生成抓取动作，能够实现手指对之间的自适应抓取，从而同时抓取两个物体。文中对该模式切换机构及手部运动学进行了建模与分析，并在两个抓取基准测试上验证其性能：一个侧重于刚性物体，另一个则针对衣物类物品。研究表明，水螅手分别在其柔顺强力与刚性精准配置下，擅长抓取大型不规则物体及小型物体。随后，通过执行安全抓取和放置一串葡萄、再从葡萄串中摘取单粒葡萄这一具有挑战性的操作任务，展示了该手部的通用性。