Development of Multi-DOF Forearm Prosthesis

本研究的第一步是开发一种新的驱动器，称为AMA （Antagonistic muscle -样驱动器），它具有与人类关节基本相同的性能，具有拮抗肌肉结构。对AMA控制的理论研究表明，当非线性弹簧组合在AMA中时，AMA能够在大范围内控制关节的刚度。AMA的结构概述如下：一对滚珠丝杠控制一个自由度。它们仅由一个直流电机驱动，而一些驱动模式由齿轮改变，这些齿轮由多个步进电机驱动。(1)单传动：旋转一个滚珠丝杠。(2)同侧传动：一对滚珠丝杠同时沿同一方向旋转。这种模式主要用于调节关节的刚度。(3)对侧传动：一对滚珠丝杠同时沿相反方向旋转。这种模式主要用于转动关节。滚珠丝杠螺母与关节轴线通过非线性弹簧由钢丝连接。该机构最有效的优点是一个AMA可以控制多个自由度，并将其应用于具有严重体积和重量限制的主动假体中。然后介绍了多自由度前臂假体的发展，作为AMA的应用。所研制的多自由度前臂假体共有6个自由度；手腕两个自由度，两个手指四个自由度。只有一个直流电机和一个步进电机驱动和控制整个自由度。非线性弹簧使刚度从几乎完全自由到完全刚性的调整成为可能。手指采用行星齿轮系统的复合四杆机构，使手指的三个关节（PIP DIP和MP关节）能够根据被抓物体的形状自动调整其弯曲角度。控制实验表明，所开发的系统性能良好。

The first step of this research was to develop a new actuator named AMA (Antagonistic Muscle-like Actuator) which has fundamentary identical performance to human articulation with antagonistic muscles structure. Theoretical study of controlling AMA revealed that AMA is able to control the stiffness of joints in the wide range when non-linear springs are combined into it. The structure of the AMA is summarized as follows : A pair of ball-screws controls one degree of freedom. They are driven by only one DC-motor while some driving modes are altered by the gears which are driven by oen stepping motor There are three typical driving modes. (1) Single Driving : One ball-screw is rotated. (2) Ipsilateral Driving : A pair of ball-screws are simultaneously rotated along the same direction. This mode are mainly used to adjust the stiffness of the joint. (3) Contralateral Driving : A pair of ball-screws are simultaneously rotated along the opposite direction. This mode are mainly used to rotate the joint. The ball-screw nuts and the axis of joints are connected by the wire via non-linear springs. The most effective advantage of this mechanism is that one AMA can control some DOFs and this application of the AMA into active prosthesis whch has severe volume and weight limitation. Then it follows the developmen of multi-DOF forearm prosthesis as an application of the AMA.The multi-DOF forearm prosthiesis developed has six DOFs total ; two DOFs for the wrist and four for the two fingers. Only one DC-motor and one stepping motor drive and control the overall DOFs. The non-linear springs enable the adjustment of the stiffniess from almost all free to completly rigid. A finger has compound four bar linkages with planet gears system, which enables three joints of a finger (PIP DIP and MP joints) automatically adjust their flexion angle according to shape of an object to be grasped. The control experiments revealed the developed system performed well.