Page 101 - Human Inspired Dexterity in Robotic Manipulation

Approaching Human Hand Dexterity Through Highly Biomimetic Design 99

Fig. 6.8 Mechanical analogies of the MCP joint of the human fingers. Left: A ball-socket
that allows the closet replica of the MCP joint. Middle: A universal joint that does not
support axial rotation. Right: An elastic joint that has no rigid support in axial direction.

of the ball-socket joint is simpler and only requires two components. In
addition, its structure naturally matches the anatomy of the MCP joint in
the human finger.
Different from the fingers, the varied thumb movements (see Fig. 6.9)
are resulted from the contact between the trapezium and first metacarpal
bones at the CMC joint. Due to the irregular shape of the trapezium bone
(see Fig. 6.10), the CMC joint has been commonly explained as a saddle
joint that allows the thumb a wide ROM—up (adduction) and down
(abduction), bent (flexion) and straightened (extension), and the ability to
move across the palm (opposition).

Fig. 6.9 Illustration drawing showing the range of motion of the human thumb. The
complicated thumb movements are resulted from contact between the trapezium
and first metacarpal bones at the CMC joint.