Page 110 - Human Inspired Dexterity in Robotic Manipulation

108 Human Inspired Dexterity in Robotic Manipulation

qualitatively conduct the telemanipulation experiments. The experimental
setup, procedures, and results are reported in the following sections.

6.5.1 Fingertip Trajectories
As we briefly mentioned, the ring and little fingers are coupled considering
their collaborative relationship as the grasping fingers. Their flexion and
extension motions are controlled by a pair of Dynamixel servos through a
differential pulley transmission as shown in Fig. 6.17. The benefit of using
such a pulley structure is to provide an extra source of hand compliance in
addition to the build-in compliance at each finger joint, because it allows the
two grasping fingers to conform to the contour of an object by automatically
adjusting the shared string length between the two insertion sites. But the
drawback is that the underactuated mechanism could also become a source
of uncertainty bringing the two fingers into certain unknown postures when
they bend and straighten between the two extreme postures. Thus it is
important to first investigate the repeatability of our proposed mechanism,
especially when the finger’s ROM is controlled in between full flexion and
extension postures.
Compared to the ring and little fingers, the index, middle, and thumb are
each actuated by more than two servos, therefore they can be better con-
trolled in this case. In the fingertip tracking experiment, we chose two
extreme positions for the coupled ring and little fingers, and then controlled

Fig. 6.17 Labeled pictures showing the differential pulley transmission for ring and little
fingers and the locations of the reflective makers. All the marker coordinates were
recorded with respect to the forearm frame.