Page 136 - Human Inspired Dexterity in Robotic Manipulation

134 Human Inspired Dexterity in Robotic Manipulation

Table 7.4 Points where linear behavior was first observed
Initial fluid pressure [kPa] 1.5 2.7 4.0 6.0

Phase change points x l [mm] 11.6 13.8 12.6 10.4
Standard deviation of x l [mm] 0.5 0.3 0.1 0.4

are identified by circles whereas squares mark the points where linear
compression behavior was first observed. It can be seen that the detection
method worked well.

7.3.2.4 Experimental Validation
Fig. 7.24 shows the procedure for the validation of the fracture avoidance
method. The target was tofu weighing at 22.7 g. The fluid fingertip was
pushed against the tofu at a speed of 1.0 mm/s and stopped when the push-
ing distance was x l ¼ 4, 6, 8, 10, 12, and 14 mm. The Z-axis of the stage on
which the tofu was placed was moved in the lower direction for grasping.
After checking whether the tofu was grasped without breaking, a disturbing
force was exerted manually in the direction of the gravitational force, to
observe the stability of grasping. If the tofu did not fall, grasping was deemed
to be stable, otherwise, grasping was adjudged unstable. The initial fluid
pressures in the fingertip when there was no contact were set as 1.5, 2.7,
4.0, and 6.0 kPa. The experiments were conducted three times for each
condition.
Table 7.5 summarizes the results of the experiment. It can be seen that
there was no fracture, and stable grasping was obtained at the points where
compression behavior was linear. At these points, fracture can be avoided.
Moreover, a concentration of the density of tofu occurred, eventually sat-
urated, and the applied force was then transferred, minimizing loss. Stable
grasping was thus obtained. Clearly, it is a good procedure to grasp the tofu
at points where the compression behavior is linear.

Fig. 7.24 Grasping test procedure for soft (Kinugoshi) tofu.