Page 96 - Human Inspired Dexterity in Robotic Manipulation

94 Human Inspired Dexterity in Robotic Manipulation

The thick ligament formed on the palmar side of the finger is called the
volar plate. Like the collateral ligaments, the volar plate also has insertions on
both sides of the bones. Its function is to prevent the occurrence of finger
deformity from hyperextension. The unlabeled ligaments are called acces-
sory collateral ligaments, their function is to help stabilize the finger joint.
Together with other ligaments and soft tissues, they form an important
structure known as the joint capsule.

6.3.3 Flexor and Extensor Tendons
There are two groups of tendons in the human hand. Named according to
the function of their contraction motion, the ones straightening the fingers
are called extensor tendons, the ones bending the fingers are called flexor
tendons. The contraction motions of the tendons originate from the corre-
sponding muscle groups located in the forearm. If we treat the muscles as the
actuators that output contraction forces, the tendons of the hand serve as the
transmission system that smartly partitions the forces and smoothly delivers
torques to each finger joint. As shown in Fig. 6.4, starting from the wrist, the
extensor tendons branch out and have multiple insertion sites on the dorsal

Fig. 6.4 Illustrations showing the extensor and flexor tendons of the human left hand.
The extensor tendons branch out from the wrist and cover the dorsal side of the finger
bones. The flexor tendons travel through a series of pulley-like tendon sheaths grown
onto the palmar side of the finger bones and eventually insert at the base of the DIP and
PIP joints.