Page 141 - Human Inspired Dexterity in Robotic Manipulation

138 Human Inspired Dexterity in Robotic Manipulation

Torsion spring
default Releasing pin
Ratchet pawl

Ratchet gear

(A) (B)
Fig. 7.26 Schematic view of ratchet function installed in an underactuated joint to
maintain grasping mode. (A) Shift in grasping mode through contact with an
environment such as a supporting surface. (B) Releasing of pawl by fully opening the
gripper.

is fully opened, the ratchet pawl makes contact with the releasing pin, and
the ratchet is released. When scooping an object, there is a possibility for the
object to move up and the grasp becoming unstable, as illustrated in the
image on the top right of Fig. 7.27. To fix this concern, two separate flexible
belts made of silicone were installed as also illustrated in Fig. 7.27. The flex-
ibility of the belts provide adaptation to the object shape and a stable enve-
loping grasp. The belts were separated such that a tall object can be
conveniently grasped.
Using the design, the three grasping modes illustrated in Fig. 7.28 are
realized. The grasping mode is shifted by utilizing contact with the environ-
ment. Note that these are the primary modes. A combination of two modes
or a partially realized mode, for example, only one finger is rotated, can also
be attained. The three grasping modes are described as follows.

Ratchet pawl

Base belt
Ratchet gear
Fig. 7.27 Schematics of the structure of ratchet and flexible base belts.