Page 105 - Human Inspired Dexterity in Robotic Manipulation

Approaching Human Hand Dexterity Through Highly Biomimetic Design 103

When the finger straightens, the extensor hood acts as a force transmission
mechanism that actively delivers torques at each finger joint. However, most
of the grasping movements of the human hand heavily rely on the contrac-
tion of flexor muscles to execute different types of grips. With the help of
flexor tendons, when cocontraction (like stiffening all the finger joints) of
agonist and antagonist muscles is not required, the extensor hood is mainly
functioning as a passive breaking mechanism that smartly facilitates the
motion during finger flexion. In human hands, these two roles of the exten-
sor hood are perfectly regulated by different groups of muscles controlled by
our brain. Yet it is very challenging to replicate all the behaviors of those
muscles with one set of actuators in robotic hand control. We thus propose
to design a hierarchical extensor mechanism to handle the two roles of
the extensor hood separately.
As shown in Fig. 6.13, a highly resilient rubber sheet was laser cut
into the shape of an extensor hood to mimic the passive behaviors of the
extensor tendons, leaving the active part of control to the electric servos that
enable the finger extension through a cable-driven mechanism. By doing so,
control of the robotic hand can be greatly simplified.

Fig. 6.13 The fully assembled biomimetic hand containing the 3D-printed ABS bones
from the scan of cadaveric hand bones. The wrist of the hand is immobilized because it
is not the focus of this work at this stage.