Biomedical Engineering Reference
In-Depth Information
Fig. 17.8
Example of a portable, 9-tile version of the distributed floor interface of Visell et al. [
39
],
shown without video feedback, as developed by Kemper, Franinovic, Willle, and Visell
community. These make it possible to resolve the locations of contact, forces at the
interface, and the moment about the contact normals using internal force and torque
measurements [
7
] using far fewer sensors than are needed in surface-based tactile
sensing techniques. For simplification, we assume that there is frictionless contact
between the foot and floor and we neglect relative displacement of the suspension
elements in the tile (which is, by design, less than 3 mm [
36
]). We then resolve the
location of the centroid
x
c
associated with the pressure distribution
p
R
(
exerted
by the foot, such that a normal force
F
c
at
x
c
gives rise to the same measurements
as
p
R
(
x
)
)
does [
7
]. For a floor tile with sensor locations
x
j
where measurements
f
j
are taken (
j
indexes the tile sensors),
x
c
and the normal force
F
c
x
=
(
0
,
0
,
F
c
)
can be recovered from scalar measurements
F
j
=
(
0
,
0
,
f
j
)
via force and torque
equilibrium equations,
4
4
f
j
+
F
c
+
f
p
=
0
,
x
j
×
F
j
+
x
c
×
F
c
+
x
p
×
F
p
=
0
.
(17.1)
j
=
1
j
=
1
F
p
=
(
is the weight of the plate and actuator at the tile's center
x
p
.Thethree
nontrivial scalar equalities in (
17.1
) yield:
0
,
0
,
f
p
)
4
4
1
F
c
F
c
=
f
i
−
f
p
,
x
c
=
1
(
x
i
−
x
p
)
f
i
+
f
c
x
p
(17.2)
i
=
1
i
=
