Robotic arms are key components in fruit-harvesting robots. In agricultural settings, conventional serial or parallel robotic arms often fall short in meeting the demands for a large workspace, rapid movement, enhanced capability of obstacle avoidance and affordability. This study proposes a novel hybrid six-degree-of-freedom (DoF) robotic arm that combines the advantages of parallel and serial mechanisms. Inspired by yoga, we designed two sliders capable of moving independently along a single rail, acting as two feet. These sliders are interconnected with linkages and a meshed-gear set, allowing the parallel mechanism to lower itself and perform a split to pass under obstacles. This unique feature allows the arm to avoid obstacles such as pipes, tables and beams typically found in greenhouses. Integrated with serially mounted joints, the patented hybrid arm is able to maintain the end's pose even when it moves with a mobile platform, facilitating fruit picking with the optimal pose in dynamic conditions. Moreover, the hybrid arm's workspace is substantially larger, being almost three times the volume of UR3 serial arms and fourteen times that of the ABB IRB parallel arms. Experiments show that the repeatability errors are 0.017 mm, 0.03 mm and 0.109 mm for the two sliders and the arm's end, respectively, providing sufficient precision for agricultural robots.

翻译：机械臂是果实采摘机器人的关键部件。在农业环境中，传统的串联或并联机械臂往往难以同时满足大工作空间、快速运动、增强避障能力及经济性等多重要求。本研究提出一种新型的六自由度混合机械臂，融合了并联机构与串联机构的优势。受瑜伽动作启发，我们设计了两个可沿单轨道独立移动的滑块，作为“双足”。这些滑块通过连杆与啮合齿轮组相互连接，使并联机构能够降低高度并执行劈叉动作以穿越障碍物下方。这一独特设计使机械臂能够规避温室中常见的管道、桌台和横梁等障碍物。该专利混合机械臂集成了串联安装的关节，即使在移动平台上运动时也能保持末端姿态稳定，从而在动态条件下以最优姿态完成果实采摘。此外，混合机械臂的工作空间显著扩大，其体积约为UR3串联机械臂的3倍、ABB IRB并联机械臂的14倍。实验表明，两个滑块及臂末端的重复定位误差分别为0.017毫米、0.03毫米和0.109毫米，为农业机器人提供了足够的精度。