S.N.A.K.E.: A Dynamically Reconfigurable Artificial Sensate Skin ...

Or,
∆R
=
R3
R3
R3 + RC
(5.2)
However, unit resistance change is a function of strain, so if we re-express Equation 5.2
to reflect this, we can then extract a relationship between the simulated strain and the
shunting resistance necessary to produce it. Unit resistance change is related to strain by:
∆R
= FGε (5.3)
RG
Where RG is the nominal resistance of the strain gage (obtained from Table 5.1), FG is the
gage factor, and ε is the material strain. Now, if we combine Equations 5.2 and 5.3, we can
obtain:
εS =
−R3
FG(R3 + RC)
(5.4)
Where εS is the compressive strain simulated by shunting R3 with RC 1 . Now, we already
mentioned that the minimum bend radius of a multi-layer flex circuit should be of approx-
imately 24 times the total thickness of the substrate, or in the case of the Skin Nodes
24 × 0.0162in = 0.3888in = 0.987552cm. If we take this to be the bending limit of the Skin
Nodes, then the strains experienced by the gages will be extremely small. If we consider
small strains and we solve for RC from Equation 5.4 we can now find a resistance value that
will produce a known strain which we can then use to calibrate the sensors:
RC = R3
FGεS
− R3
Since we expect strains to be small, we can arbitrarily pick a relatively small strain value
and calculate the resistance needed to produce it. For this case a value of 100 −6 strain
1 Although these equations are specific to compressive strain, a similar method can be applied to find
tensile strains by shunting R4 instead of R3
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