The logarithmic spiral is observed as a common pattern in several living beings across kingdoms and species. Some examples include fern shoots, prehensile tails, and soft limbs like octopus arms and elephant trunks. In the latter cases, spiraling is also used for grasping. Motivated by how this strategy simplifies behavior into kinematic primitives and combines them to develop smart grasping movements, this work focuses on the elephant trunk, which is more deeply investigated in the literature. We present a soft arm combined with a rigid robotic system to replicate elephant grasping capabilities based on the combination of a soft trunk with a solid body. In our system, the rigid arm ensures positioning and orientation, mimicking the role of the elephant's head, while the soft manipulator reproduces trunk motion primitives of bending and twisting under proper actuation patterns. This synergy replicates 9 distinct elephant grasping strategies reported in the literature, accommodating objects of varying shapes and sizes. The synergistic interaction between the rigid and soft components of the system minimizes the control complexity while maintaining a high degree of adaptability.

翻译：对数螺旋作为一种常见模式，广泛存在于不同界别和物种的生物体中。典型实例包括蕨类嫩枝、卷缠型尾部以及章鱼腕足与象鼻等柔性肢体。在后述案例中，螺旋运动亦被用于抓取操作。受该策略将复杂行为简化为运动基元并通过组合实现智能抓取的启发，本研究以文献中已有深入研究的象鼻为焦点。我们提出一种结合刚性机械系统的柔性臂装置，通过模拟象鼻与躯干的协同机制来复现其抓取能力。在该系统中，刚性臂负责位姿调控以模拟头部功能，而柔性机械臂则在特定驱动模式下复现象鼻的弯曲与扭转运动基元。通过刚柔协同机制，本系统成功复现了文献记载的9种象鼻抓取策略，可适配不同形状与尺寸的物体。系统刚柔部件间的协同作用在保持高度适应性的同时，有效降低了控制复杂度。