IEEE Trans Neural Syst Rehabil Eng. 2018 Apr;26(4):817-829. doi: 10.1109/TNSRE.2018.2811503.
Most active upper-extremity rehabilitation exoskeleton designs incorporate a three sequential rotational shoulder joint with orthogonal axes. This kind of joint has poor conditioning close to singular configurations when all joint axes become coplanar, which reduces its effective range of motion. We investigate an alternative approach of using a redundant non-orthogonal 4R shoulder joint. By inspecting the behavior of the possible nullspace motions, a new method is devised to resolve the redundancy in the differential inverse kinematics (IK) problem. A 1D nullspace global attraction method is used, instead of naive nullspace projection, to guarantee proper convergence. The design of the exoskeleton and the proposed IK method ensure good conditioning, avoid collisions with the human head, arm and trunk, can reach the entire human workspace, and outperforms conventional 3R orthogonal exoskeleton designs in terms of lower joint velocities and no body collisions.
大多数活跃的上肢康复外骨骼设计都包含三个连续旋转的肩关节，这些关节具有正交轴。当所有关节轴共面时，这种关节在接近奇异构型时的条件较差，从而降低了其有效运动范围。我们研究了一种使用冗余非正交 4R 肩关节的替代方法。通过检查可能的零空间运动的行为，设计了一种新的方法来解决微分逆运动学（IK）问题中的冗余问题。使用一维零空间全局吸引方法，而不是幼稚的零空间投影，以保证正确的收敛。外骨骼的设计和所提出的 IK 方法确保了良好的条件，避免与人体头部、手臂和躯干发生碰撞，可以到达整个人体工作空间，并且在较低的关节速度和无身体碰撞方面优于传统的 3R 正交外骨骼设计。
