Page 122 - Human Inspired Dexterity in Robotic Manipulation

120 Human Inspired Dexterity in Robotic Manipulation

regression model represented the relationship very well, in which the stiff-
ness can be regarded as the gradient at each point of the regression curves.
The results indicate that fingertip stiffness can be controlled by regulating
both the piston of the control unit and fingertip deformation by contact.
Moreover, when contacting with the silicon layer, a large stiffness is
obtained, and a large force can be applied—both useful for grasping rigid
and relatively heavy objects.

7.2.3 Uniform Contact Pressure of Fluid Fingertip
Another benefit of the fluid fingertip is uniform contact pressure. To con-
firm this characteristic, the contact pressure distribution was experimentally
investigated. For comparison, the fluid and silicone fingertips shown in
Fig. 7.6 were utilized. The silicon layer was removed from the fluid fingertip
to avoid unexpected contact with the silicon layer and to see the features of
the incompressible fluid. The silicon fingertip was hemispherical, and its size
and shape were made the same as those of the fluid fingertip. To investigate
the effect of fluid pressure inside the fluid fingertip, we investigated cases
where the fluid pressures at no-contact (pressures before the actual experi-
ments) were 10 and 30 kPa. Note that at a pressure of 30 kPa, the hardness of
the fluid fingertip is close to the hardness of the silicon fingertip.

7.2.3.1 Contact With a Flat Surface
Fig. 7.7 shows the setup for the flat surface contact experiment with the use
of pressure-sensitive paper spread over a Prescale mat (FUJIFILM) which is
in turn placed over a flat surface to measure the contact pressure distribution.
As the fingertip pushed the Prescale mat through the pressure-sensitive paper

Fluid

(A) (B)
Fig. 7.6 Utilized fingertips for investigation of contact pressure distribution. (A) Fluid
fingertip. (B) Silicone fingertip.