Page 125 - Human Inspired Dexterity in Robotic Manipulation

Hand Design—Hybrid Soft and Hard Structures 123

Table 7.3 Parameter values for the regression curved surface at Fig. 7.9 [22]
Gel-layer fingertip Gel-layer fingertip Silicon
[30 kPa] [10 kPa] fingertip
2
α [kPa/mm ] 0.638 0.650 11.8
2
β [kPa/mm ] 0.151 0.0317 10.2
2
γ [kPa/mm ] 0.312 0.135 0.857
A [mm] 9.32 12.5 9.00
B [mm] 6.99 35.5 8.40
M [MPa] 0.420 0.378 0.696

fingertip had a nearly uniform pressure distribution even when the fluid
pressure was as high as 30 kPa. This suggests that the increase in fluid pres-
sure does not indicate a convergence to the silicone fingertip. Because frac-
ture is governed by a pressure or stress domain, the fact that the fluid fingertip
produces a small contact pressure due to uniform pressure distribution means
that it is suitable for grasping fragile objects without fracture.

7.2.3.2 Contact With a Line Surface
When handling thin objects, humans often choose the edges as grasping
areas for stability, as shown in Fig. 7.10. This is an example of a situation
where uniform pressure distribution cannot be obtained easily. Using the
experimental setup shown in Fig. 7.11, further investigation was then con-
ducted to determine if and where uniformity exists when the fluid fingertip
is in contact with a line surface. The fingertip was attached to a force gauge

Fig. 7.10 Example of a thin object that a human is grasping.