Control of forces applied by individual fingers engaged in restraint of an active object
Control of forces applied by individual fingers engaged in restraint of an active object
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DOI：
10.1152/jn.1997.78.1.117
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发表时间：
1997-07-01
影响因子：
2.5
通讯作者：
Johansson, RS
中科院分区：
文献类型：
--
作者：
Burstedt, MKO;Birznieks, I;Johansson, RS
我们研究了受试者使用两个手指的指尖来限制具有水平方向的抓握表面的仪器化操作的指尖力的协调。夹持表面相对于手指在远端方向上受到切向拉力。受试者使用右手食指和中指（单手抓握）或双手食指（双手抓握）来抑制操作。为了改变手指-物体界面处的摩擦条件，要么两个抓握表面都覆盖有砂纸，要么一个表面覆盖有砂纸，另一个表面覆盖有人造丝。沿接骨板位置沿着在每个接骨板上分别测量垂直和切向施加到夹持表面的力。受试者可以成功地完成本任务与许多不同的力量分布之间的数字。然而，他们以反映局部数字对象界面摩擦条件的方式分配负载。当两个手指接触砂纸时，它们通常对称地分配载荷，但是当一个手指与人造丝接触而另一个手指与砂纸接触时，接触较不光滑的材料（砂纸）的手指占据了更大部分的载荷。法向力也受摩擦条件的影响，但它们反映的是两个接触点的平均摩擦力，而不是局部摩擦力。也就是说，当手指与物体之间的摩擦力较低时，只有施加在两个手指上的法向力增加。因此，与各自手指-物体界面处的局部摩擦条件相关的感觉信息控制了两个手指的法向力。每个手指的法向：切向力比似乎是一个受控变量。它在每个数字上独立调整到防止摩擦滑动所需的最小比率，保持足够的安全裕度防止滑动。这是通过将法向力缩放到平均摩擦力以及根据数字对象界面之间的摩擦差异划分负载来实现的。总之，通过调整法向：切向力的比例，以当地的摩擦条件下，科目避免过多的法向力在个人的数字对象接口，并通过分区的负载根据摩擦的差异，科目避免高的法向力。因此，在单独的手指-物体界面处的局部摩擦条件是可以强烈影响参与操纵行为的手指之间的力分布的一个因素。
We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the frictional condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the frictional condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the frictional condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local frictional condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local frictional condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the frictional difference, subjects avoided high normal forces. Thus the local frictional condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.