Page 127 - Human Inspired Dexterity in Robotic Manipulation

Hand Design—Hybrid Soft and Hard Structures 125

0.8

Contact pressure [MPa]
0.6

0.4

0.2

0
(A) (B) (C)
Fig. 7.13 Derived contact pressure distribution for each fingertip when in contact with a
line surface. (A) Fluid fingertip (fluid pressure at no-contact: 30 kPa). (B) Fluid fingertip
(fluid pressure at no-contact: 10 kPa). (C) Silicon fingertip.

results for the silicone fingertip, relatively high pressures were observed at
the contact area corresponding to the front surface, whereas low pressures
were observed at the contact areas corresponding to the sides. On the other
hand, an almost uniform contact pressure profile was observed when using
fluid fingertips. More uniformity was observed when the no-contact fluid
pressure was at 10 kPa than when it was at 30 kPa. A low, no-contact fluid
pressure is expected to provide low contact pressure and large contact area,
and it is considered to be advantageous for delicate grasping. In the case of
the silicon fingertip, very high pressure was observed at the center and the
entire contact area was small compared to that of the fluid fingertip.

7.2.4 Grasping Test

Fig. 7.14 shows the grasping test results when utilizing a gripper in which the
grippingareaswereconstructedwithfluidfingertips.Itisobservedthatseveral
fragileobjectsweregraspedsuccessfully.Withtheuseofasolidlayerinsidethe
fluid,thegrippershowninFig.7.14Fsucceededingraspinganobject(abottle
of juice) having a weight that cannot be compensated by the fluid layer alone.

7.3 PREVENTIONOFFRACTUREONDUCTILE ANDFRAGILE
OBJECTS (SOFT TOFU) BASED ON PRESSURE PROFILE

As fracture is governed by stress or pressure domain, the fluid pressure cor-
responding to the uniform contact pressure profile, which can be measured