Page 104 - Human Inspired Dexterity in Robotic Manipulation

102 Human Inspired Dexterity in Robotic Manipulation

After cleaning the support materials off from the parts, each robotic fin-
ger can be quickly assembled as explained in Fig. 6.11 (bottom row). Com-
pared to our previously proposed joint design [16], our current design
greatly reduced the fabrication time. As shown in Fig. 6.12, one pair of
the crocheted ligaments is used to mimic the two collateral ligaments located
on the sides of each finger joint. Similarly, the function of the volar plate (see
Fig. 6.3) is replaced by two crocheted ligaments anchored across each joint
(as shown in Fig. 6.12). Instead of using the silicone rubber sleeve, a laser-cut
(80 W CO 2 1100 series laser, Legacy Laser, Defiance, PA) rubber sheet was
used to provide the human-like compliance for the second version of the
joint capsule design. Based on the ROM of each joint, the dimensions of
these components vary in size. The longest joint ligaments can be manually
crocheted within 5 min by using two stitch types (see Fig. 6.12, right). The
laser-cut rubber sheet can be prepared in a few seconds. Coating the ther-
moplastic onto the joint base becomes the most time-consuming part of the
prototyping process. However, it still can be finished within 20 min for each
finger.
The next step is to attach the laser-cut extensor hood onto the dorsal side
of each finger. In the previous section, we have detailed the important roles
of the extensor hood during both finger extension and flexion motions.

Fig. 6.12 Crocheted artificial ligaments used in the biomimetic robotic hand. Left:
Simplified joint capsule (the second version) composed of crocheted Spectra kite
string and laser-cut high strength rubber sheet. Right: Two stitch types (the chain
and single crochet) used in the fabrication of artificial ligaments.