Page 18 - Human Inspired Dexterity in Robotic Manipulation

14 Human Inspired Dexterity in Robotic Manipulation

Thetipofthethumbcanreachtotheotherfourfingertipsduetothiscombined
movement and abduction at the first CMC joint. Flexion, adduction, and
opposition at the first CMC joint are produced by intrinsic muscles of the
thumb(thenarmuscles),extensionbyextrinsicmusclesofthehand,andabduc-
tionbybothmuscles.ActivemovementsatthefirstMPjointarelimitedtoflex-
ion and extension, while those at the second to fifth MP joints are flexion,
extension, abduction, adduction, circumduction, and limited rotation.
The active movements of the interphalangeal joints are flexion and
extension. Flexion at the proximal interphalangeal (PIP, proximal side joint
between two phalangeal bones) joints is controlled by two muscles, while
that at the distal interphalangeal (DIP, distal side joint between two phalan-
geal bones) joints and the interphalangeal (IP, joint between two phalangeal
bones) joint of the thumb is controlled by one muscle. Extension at PIP and
DIP joints of the four fingers are controlled by one muscle. Therefore, PIP
and DIP joints cannot be extended independently. There are accessory
movements (passive movements produced when the active movements
are constrained by external resistance) of a limited range of rotation, abduc-
tion, adduction, and gliding, which allows the thumb and fingers to adapt to
the shape of the object grasped in hand.
The active movements of the four fingers are produced by both extrinsic
and intrinsic muscles. Like the extrinsic muscles of the thumb, those con-
tributing to the movements of the four fingers are originated from the bones
in the upper arm or forearm and inserted in the phalangeal bones. Among
these four fingers, the second and fifth fingers have their own extensor
muscle. Intrinsic muscles contribute to producing the fine movements of
the fingers in cooperation with the extrinsic muscles. The intrinsic muscles
of the second to fourth fingers have a similar structure. It is composed of two
types of intrinsic muscles, one muscle originates from the metacarpal bones,
and the other is from the flexor muscles, and both are inserted in the pha-
langeal bones. In addition to these two intrinsic muscles, the fifth finger has
its own intrinsic muscles (hypothenar muscles) similar to the thumb which
has thenar muscles.
The various motions of the human hand are produced by this complicated
anatomical structure which is composed of bones and muscles. A movement
of one specific joint is produced by more than one muscle. Also, one specific
muscle is contributing to movements of several joints. This makes muscle-
based control of the digital hand extremely difficult. For simplicity, the
digital-hand model usually has a minimum link and joint structure that is
enough to reproduce human-hand motion.