Tokyo Institute of Technology, Institute of Innovative Research, Yokohama, Japan.
Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
Sci Rep. 2020 Jan 15;10(1):379. doi: 10.1038/s41598-019-57267-0.
Humans can increase the endpoint stiffness of their arm to reduce self-generated movement variability and to reject unpredictable perturbations from the environment, like during handheld drilling, thereby increasing movement precision. Existing methods to estimate changes in the endpoint stiffness use robotic interfaces to apply position or force perturbations to measure the arm's dynamic response. We propose an alternative method of measuring changes in the power grasp force to estimate adaptations in the magnitude of the arm's endpoint stiffness. To validate our method, we examined how the strength of the power grasp, when holding onto a robotic manipulandum, affected the arm's endpoint stiffness in three different locations of the workspace. The endpoint stiffness magnitude increased linearly with the grasp force, and this linear relationship did not depend on the arm's posture or position in the workspace. The endpoint stiffness may have increased as a combination of greater grasp stiffness and greater arm stiffness, since larger co-contraction was observed in the elbow and shoulder with a stronger grasp. Changes in the grasp force could serve as a metric in assessing how humans adapt their endpoint stiffness magnitude.
人类可以增加手臂的端点刚度，以减少自身产生的运动可变性，并拒绝来自环境的不可预测的扰动，例如在手持钻孔时，从而提高运动精度。现有的估计端点刚度变化的方法使用机器人接口施加位置或力扰动来测量手臂的动态响应。我们提出了一种测量功率抓握力变化的替代方法，以估计手臂端点刚度大小的适应变化。为了验证我们的方法，我们研究了在机器人操作器上握住时，功率抓握的强度如何影响工作空间中三个不同位置的手臂端点刚度。端点刚度大小与抓握力呈线性关系，并且这种线性关系不依赖于手臂的姿势或在工作空间中的位置。由于观察到更强的抓握时肘部和肩部的更大共收缩，端点刚度可能会随着更大的抓握刚度和更大的手臂刚度的组合而增加。抓握力的变化可以作为评估人类如何适应端点刚度大小的指标。
