Electric prosthetic hands should be lightweight to decrease the burden on the user, shaped like human hands for cosmetic purposes, and designed with motors enclosed inside to protect them from damage and dirt. Additionally, in-hand manipulation is necessary to perform daily activities such as transitioning between different postures, particularly through rotational movements, such as reorienting a pen into a writing posture after picking it up from a desk. We previously developed PLEXUS hand (Precision-Lateral dEXteroUS manipulation hand), a lightweight (311 g) prosthetic hand driven by four motors. This prosthetic performed reorientation between precision and lateral grasps with various objects. However, its controller required predefined object widths and was limited to handling lightweight objects (of weight up to 34 g). This study addresses these limitations by employing motor current feedback. Combined with the hand's previously optimized single-axis thumb, this approach achieves more stable manipulation by estimating the object's width and adjusting the index finger position to maintain stable object holding during the reorientation. Experimental validation using primitive objects of various widths (5-30 mm) and shapes (cylinders and prisms) resulted in a 100% success rate with lightweight objects and maintained a high success rate (>=80) even with heavy aluminum prisms (of weight up to 289 g). By contrast, the performance without index finger coordination dropped to just 40% on the heaviest 289 g prism. The hand also successfully executed several daily tasks, including closing bottle caps and orienting a pen for writing.

翻译：电动假肢手应具备轻量化特性以减轻使用者负担，外形需仿照人手以满足美观需求，并采用电机内置设计以防护损伤与污物。此外，为完成日常活动（例如在不同姿态间转换），手内操作功能不可或缺，特别是通过旋转动作实现物体重定向，如从桌面拾取钢笔后将其调整至书写姿态。我们先前研发了PLEXUS手（精密-侧向灵巧操作手），这是一款由四电机驱动的轻型（311克）假肢手。该假肢手能对不同物体实现精密抓握与侧向抓握间的姿态重定向，但其控制器需预定义物体宽度，且仅能处理轻质物体（重量上限34克）。本研究通过引入电机电流反馈解决了这些局限。结合该假肢手先前优化的单轴拇指设计，该方法通过实时估计物体宽度并调节食指位置，在重定向过程中维持稳定的物体持握状态。使用不同宽度（5-30毫米）与形状（圆柱体与棱柱）的基础物体进行实验验证，结果显示：对轻质物体操作成功率达100%，即使对重达289克的铝制棱柱仍保持高成功率（≥80%）。相比之下，在无食指协同的情况下，对最重289克棱柱的操作成功率骤降至40%。该假肢手还成功完成了多项日常任务，包括旋紧瓶盖与调整钢笔至书写姿态。