Internal forces during object manipulation
Internal forces during object manipulation
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DOI：
10.1007/s00221-005-2282-1
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发表时间：
2005-08-01
影响因子：
2
通讯作者：
Zatsiorsky, VM
中科院分区：
文献类型：
--
作者：
Gao, F;Latash, ML;Zatsiorsky, VM
内力是一组不会破坏物体平衡的接触力。内力矢量的元素相互抵消，因此不会对作用在物体上的合力(操纵)起作用。内力和操纵力的数学独立性允许它们在机器人操作器中实现独立(解耦)控制。为了检查人体的内力是否与操作力相耦合，以及表演者使用什么抓握策略，受试者(n=6)被指示用定制的手柄进行周期性的手臂运动。测试了手柄方向和移动方向的六种组合。这些操作包括：平行操作(1)VV任务(垂直方向和垂直移动)和(2)HH任务(水平方向和水平移动)；正交操作(3)VH任务(垂直方向和水平移动)和(4)HV任务(水平方向和垂直移动)；以及对角线操作(5)DV任务(对角方向和垂直移动)和(6)DH任务(对角方向和水平移动)。系统地改变了手柄重量(3.8~13.8N)和运动频率(1~3 Hz)。分析是在拇指-虚拟手指水平上进行的(VF，一种假想的手指，产生的扳手等于所有手指产生的扳手的总和)。在这个层面上，利益的力量可以归结为内力和内力矩。在平行操作中，内力(握力)与操作力(产生物体加速度)耦合，拇指-VF力同步增加或减少：拇指和VF同步工作，以更强或更弱地抓住物体。在正交操作中，拇指-VF力的变化是异相的：内力与物体加速度的曲线图类似于一个倒置的字母V。HV任务是唯一一个拇指和VF的法向力之间的相对相位(耦合)取决于振荡频率的任务。在对角操作中，DV和DH任务中的耦合是不同的。描述了一种新的大量内力矩的观测：由法向指力产生的力矩被切向力产生的力矩抵消，从而所产生的力矩接近于零。讨论了这些发现对把握协同效应这一概念的影响。
Internal force is a set of contact forces that does not disturb object equilibrium. The elements of the internal force vector cancel each other and, hence, do not contribute to the resultant (manipulation) force acting on the object. The mathematical independence of the internal and manipulation forces allows for their independent (decoupled) control realized in robotic manipulators. To examine whether in humans internal force is coupled with the manipulation force and what grasping strategy the performers utilize, the subjects (n=6) were instructed to make cyclic arm movements with a customized handle. Six combinations of handle orientation and movement direction were tested. These involved: parallel manipulations (1) VV task (vertical orientation and vertical movement) and (2) HH task (horizontal orientation and horizontal movement); orthogonal manipulations (3) VH task (vertical orientation and horizontal movement) and (4) HV task (horizontal orientation and vertical movement); and diagonal manipulations (5) DV task (diagonal orientation and vertical movement) and (6) DH task (diagonal orientation and horizontal movement). Handle weight (from 3.8 to 13.8 N), and movement frequency (from 1 to 3 Hz) were systematically changed. The analysis was performed at the thumb-virtual finger level (VF, an imaginary finger that produces a wrench equal to the sum of wrenches produced by all the fingers). At this level, the forces of interest could be reduced to the internal force and internal moment. During the parallel manipulations, the internal (grip) force was coupled with the manipulation force (producing object acceleration) and the thumb-VF forces increased or decreased in phase: the thumb and VF worked in synchrony to grasp the object more strongly or more weakly. During the orthogonal manipulations, the thumb-VF forces changed out of phase: the plots of the internal force vs. object acceleration resembled an inverted letter V. The HV task was the only task where the relative phase (coupling) between the normal forces of the thumb and VF depended on oscillation frequency. During the diagonal manipulations, the coupling was different in the DV and DH tasks. A novel observation of substantial internal moments is described: the moments produced by the normal finger forces were counterbalanced by the moments produced by the tangential forces such that the resultant moments were close to zero. Implications of the findings for the notion of grasping synergies are discussed.