Kim Hyunchul, Miller Levi Makaio, Al-Refai Aimen, Brand Moshe, Rosen Jacob
Dept of Electrical Engineering, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
Annu Int Conf IEEE Eng Med Biol Soc. 2011;2011:3471-4. doi: 10.1109/IEMBS.2011.6090938.
The human arm including the shoulder, elbow, wrist joints and exclusion scapular motion has 7 Degrees of Freedom (DOF) while positioning of the wrist in space and orientating the palm is a task that requires 6 DOF. As such it includes one more DOF than is needed to complete the task. Given the redundant nature of the arm, multiple arm configurations can be used to complete a task, which is expressed mathematically by none unique solution for the inverse kinematics. Despite this mathematical difficulty, the motor control provides a unique solution for the arm redundancy as the arm is moved in space. Resolving this redundancy is becoming critical as the human interacts with a wearable robotic system(exoskeleton) which includes the same redundancy as the human arm. Therefore, the inverse kinematics solution resolving the redundancy of these two coupled systems must be identical in order to guarantee a seamless integration. The redundancy of the arm can be formulated kinematically by defining the swivel angle - the rotation angle of the plane including the upper and lower arm around a virtual axis connecting the shoulder and wrist joints which are fixed in space. Analyzing reaching tasks recorded with a motion capture lab indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points the head. Based on these experimental results, selecting the point around the center of the head as a stationary target allows to calculate the swivel angle and in that way to resolve the human arm redundancy. Experimental results indicated that by using the proposed redundancy resolution criteria the error between the predicted swivel angle and the actual swivel angle adopted by the motor control system is less then 5 Deg. This criterion or a synthesis of several additional criteria may improve the synergistic relationships between an operator and a wearable robotic system.
人类手臂（包括肩部、肘部、腕关节且不包括肩胛骨运动）在空间定位时具有7个自由度（DOF），而手腕在空间中的定位以及手掌的定向是一项需要6个自由度的任务。因此，它比完成该任务所需的自由度多一个。鉴于手臂的冗余特性，多种手臂配置可用于完成一项任务，这在数学上表现为逆运动学没有唯一解。尽管存在这个数学难题，但当手臂在空间中移动时，运动控制为手臂冗余提供了唯一的解决方案。随着人类与具有与人类手臂相同冗余度的可穿戴机器人系统（外骨骼）进行交互，解决这种冗余变得至关重要。因此，解决这两个耦合系统冗余的逆运动学解决方案必须相同，以确保无缝集成。手臂的冗余可以通过定义旋转角在运动学上进行公式化——包含上臂和下臂的平面围绕连接肩部和腕关节（在空间中固定）的虚拟轴的旋转角度。对运动捕捉实验室记录的伸手任务进行分析表明，旋转角的选择使得当肘关节弯曲时，手掌指向头部。基于这些实验结果，选择头部中心周围的点作为固定目标，可以计算旋转角，从而解决人类手臂的冗余问题。实验结果表明，通过使用所提出的冗余解决标准，预测的旋转角与运动控制系统采用的实际旋转角之间的误差小于5度。这个标准或几个附加标准的综合可能会改善操作员与可穿戴机器人系统之间的协同关系。
