Chapter 2. Prehension

B
Chapter 6 - During Contact
I
+ ------- 4;
I slip
277
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------- ----- 3,,,,-,
Figure 6.24 'Baton twirling' manipulation by regrasping using
three fingers. Sequence of finger placement is seen on left, and
force angles ai are plotted over the rotation angle p, caused by the
disturbance. A. Baton is held in stable grasp using finger F1 and
finger F2. Both fingers are perpendicular to the surfaces, so a1
and a2 are zero. B. Finger F3 applies a disturbance force, causing
force angles a1 and 012 increase. Angle a2, the fixed point of
contact, is still within friction cone but a1 goes outside friction
limit. Baton begins to rotate around F2, and finger F1 slides. C.
Finger F1 is removed, and a restoring force brings a1 and a2 back
to the stable zone. D. Finger F1 applies a disturbance force and
rotation occurs around F3, the fixed point of contact. Finger F2
slides to the stable zone (from Fearing, 1986; adapted by
permission).
B