Biomedical Engineering Reference
In-Depth Information
3.10 Discussion and Conclusions
This chapter has dealt with the manner in which the proposed tactile sensor will be
developed, based upon prevailing theoretical and experimental knowledge. Because the
goal is to utilize the mechanical and electromechanical properties of piezoelectric PVDF in
the following designs, the anisotropic behavior of PVDF was the main focus of this study.
The result of this study has provided, not only a sound basis for the development of our
proposed sensor, but it has also contributed to exploring the piezoelectricity phenomena of
PVDF in different configurations, such that they can be used in a variety of applications.
In the theoretical approach, we analyzed the anisotropic behavior of PVDF film using
the FE method effect, which consists of measuring the angle between the material and
global coordinate systems. In addition, consideration was given as to the difference
between uniaxial and biaxial PVDF film, as well as the performance of PVDF film in
thickness mode, when the film is sandwiched between two plates. The main concern in
this case was the effect of friction on the output of the PVDF. Using ANSYS, an FE
contact analysis associated with the modeling of the PVDF piezoelectric was developed
and the results for both uniaxial and biaxial PVDF, for a range of friction coefficients,
were obtained. It is also shown that the PVDF response is greatly influenced by contact
friction. Hence, one of the key reasons for observing contrasting outputs from a struc-
turally similar manufactured sensor could be attributed to the difference in contact friction.
Therefore, extreme care should be paid to the uniformity of the contact surfaces during
the manufacturing process. Simulations show that when a PVDF film is firmly glued to a
surface, it is equivalent to having infinite friction with that surface. This is due to the fact
that the boundary condition (e.g., gluing, etc.) not only affects the output of the sensors,
but also makes it difficult to manufacture a number of similar sensors.
Another benefit of this study was that it enabled the measurement of coefficient of fric-
tion of the contact surfaces. This technique is particularly appropriate for the low-friction
range where accurate measurement is difficult and other available friction measurement
methods might be inadequate.
In experimental approach, the Young's modulus of PVDF film in directions 1 and 2
were obtained. To investigate the dependency of PVDF output to friction, a number of
surfaces were tested in order to determine their coefficients of friction and which were,
subsequently, used in another experimental setup in which PVDF film was sandwiched
between the characterized surfaces.
In practice, based on what we learned from all the force and tactile sensing applications
in this chapter, we recommend that PVDF be used in the following order:
1. Drawn direction
2. Transverse direction
3. Thickness mode.
Although the thickness mode is shown as being the least preferred method, sometimes
the type of application prevents the use of either of the other two methods. In such
cases, the user is advised to pay attention to the boundary conditions, upon which the
output of the sensor is highly dependent.
