Page 17 - Human Inspired Dexterity in Robotic Manipulation

Digital Hand: Interface Between the Robot Hand and Human Hand 13

Phalangeal bones

Metacarpal bones

Carpal bones

Fig. 2.1 Skeletal structure of the human hand.

The main active movements of the wrist are flexion (palmar flexion),
extension (dorsiflexion), abduction (radial deviation), and adduction (ulnar
deviation) at the radiocarpal joint and midcarpal joint. Circumduction of the
wrist results from consecutive flexion, adduction, extension, and abduction
carried out in this or in the reverse order. Active movements of the wrist are
produced by extrinsic muscles of the hand originating from the bones in the
upper arm or forearm, and inserted into the carpal bones, metacarpal bones,
or palmar aponeurosis.
The second to the fifth metacarpal bones almost lie on a plane, but the
first metacarpal bone lies on the more palmar side than the other four meta-
carpal bones and rotates medially around its longitudinal axis by 90 degrees.
Therefore, its morphologically dorsal surface is directed at the lateral (radial)
direction, and flexion-extension occurs in a plane parallel to the palmar sur-
face. Also, the dominant movements of the thumb are produced at the first
carpometacarpal (CMC, joint between carpal and metacarpal bone) joint,
while dominant movements of the other four fingers are produced at the
second to fifth metacarpophalangeal (MP, joint between metacarpal and
phalangeal bone) joints.
ActivemovementsofthefirstCMCjointareflexion,extension,abduction,
adduction, rotation, and circumduction. In the second to fifth fingers, the
movements of the CMC joints are limited to slight gliding of the articular sur-
faces. The flexion of the first CMC joint is associated with the medial rotation.