Biomedical Engineering Reference
In-Depth Information
increases rapidly without significantly changing the grasper angle. In the opening stages,
due to the rigidity of the grasped object, the grasper becomes quickly detached from the
object, causing a force profile similar to a pulse wave. This conclusion is particularly
important for experimental tests on smart graspers. This result confirms that the selection
of a sinusoidal waveform to test the fabricated MIS tactile sensor is the best alternative
in a laboratory test setup. It has always been argued that when a surgeon applies force
to the grasper, no sinusoidal wave is produced, so all experiments using this waveform
would be questionable. But the latter conclusion shows that for soft material, the load
transferred to the grasped object is almost sinusoidal.
Figure 5.13 demonstrates the force - angle relationships for different materials. In these
graphs, the force represents the load that is applied to the handle of the grasper and the
angle is that of the grasper jaws. From Figure 5.13, it can be seen that in the loading phase
of the curves, the average slope is proportional to the softness of the grasped material.
For softer material, the average slope is smaller than that of harder material. Figure 5.14
shows the energy and steepness for four elastomers. Both energy (
E
=
θ
2
θ
1
F (θ) .θ
)
θ
2
θ
1
1
N
F (θ
+
θ)
−
F(θ)
θ
and steepness (
S
=
) criteria plotted in Figure 5.14b,c can easily be
used to arrange the softness of these materials. It is evident that EVA, H1N, A2FR, and
ICF400 are arranged from hard to soft. Figure 5.15 shows the force - angle curves for the
same materials, but the angle at which the energy and steepness are calculated is 25
◦
.
B3 1/2" - 63
EVA 1/2" - 45
ICF400 1/2"
A2 3/4" - 10
30
20
10
0
−45
−40
−35
−30
−25
−20
−15
−10
−5
0
Angle (degrees)
(a)
100
80
60
40
20
0
B3
A2
EVA
ICF400
(b)
2
1
0
B3
A2
EVA
ICF400
(c)
(a) The force - angle curve, energy, and steepness measured at 25
◦
, (b) energy, and
Figure 5.15
(c) steepness
