Promising results on flexible and large area pressure sensors for human-neuroprostheses and humanneurobotic
interface assessment are presented. Array sensors of 4x4 and 8x8 based on polymer and plastic
electronics have been fabricated and characterized with a resolution of 1 and 0.25 cm<sup>2</sup>. The working pressure
range is between 0 and 1 Kg/cm<sup>2</sup> and the offset measured is around 0.03 Kg/cm<sup>2</sup>. The response time is
around 1 ms.
Tactile sensors have increasing presence in different applications, especially in assistive robotics or medicine
and rehabilitation. They are basically an array of force sensors (tactels) and they are intended to emulate the human skin.
Large sensors must be implemented with large area oriented technologies like screen printing. The authors have
proposed and made some piezoresistive sensors with this technology. They consist of a few layers of conductive tracks
to implement the electrodes and elastomers to insulate them, on a polymer substrate. Another conductive sheet is placed
atop the obtained structure. Pressure distribution in the interface between this conductive sheet and the electrodes has a
direct impact on the sensor performance. The mechanical behavior of the layered topology with conductive tracks,
elastomers and polymers must be studied. For instance, the authors have observed experimentally the existence of
pressure thresholds in the response of their sensors. Finite element simulations with COMSOL explain the reason for
such thresholds as well as the dependence of the pressure distribution profile on the properties of the materials and the
geometry of the tactel. This paper presents results from these simulations and the main conclusions that can be obtained
from them related to the design of the sensor.
This paper presents results from a few tactile sensors we have designed and fabricated. These sensors are based on a
common approach that consists of placing a sheet of piezoresistive material on the top of a set of electrodes. If a force is
exerted against the surface of the so obtained sensor, the contact area between the electrodes and the piezoresistive material
changes. Therefore, the resistance at the interface changes. This is exploited as transconduction principle to measure forces
and build advanced tactile sensors. For this purpose, we use a thin film of conductive polymers as the piezoresistive material.
Specifically, a conductive water-based ink of these polymers is deposited by spin coating on a flexible plastic sheet,
giving as a result a smooth, homogeneous and conducting thin film on it. The main interest in this procedure is it is cheap
and it allows the fabrication of flexible and low cost tactile sensors. In this work we present results from sensors made with
two technologies. First, we have used a Printed Circuit Board technology to fabricate the set of electrodes and addressing
tracks. Then we have placed the flexible plastic sheet with the conductive polymer film on them to obtain the sensor. The
result is a simple, flexible tactile sensor. In addition to these sensors on PCB, we have proposed, designed and fabricated
sensors with a screen printing technology. In this case, the set of electrodes and addressing tracks are made by printing an
ink based on silver nanoparticles. There is a very interesting difference with the other sensors, that consists of the use of an
elastomer as insulation material between conductive layers. Besides of its role as insulator, this elastomer allows the modification
of the force versus resistance relationship. It also improves the dynamic response of the sensor because it implements
a restoration force that helps the sensor to relax quicker when the force is taken off.
A new technology of flexible all-plastic pressure sensors is developed using conducting polymers as electroactive materials on plastic substrates. The lithography of one of the conducting sheets being part of the device makes feasible the construction of a distributed pressure sensor giving not only the cuantitative pressure information but also its spatial distribution. A response time as low as 2 milliseconds, and a lifetime over 1 millions of actuations are obtained. The first demonstrator works in pressure ranges from 3 to 14 Kg/cm<sup>2</sup>. These working pressure ranges can be adjusted by the proper spatial design of conducting and non-conducting paths. The present paper describes the development of an innovative, low cost and flexible technology opening interesting potential opportunities for high-surface applications.
Conducting polymers, due to their property of oxidize and reduce in a reversible way, have largely been studied as adequate materials for constructing actuators. The volume change produced in these processes is used for the stuck of a conducting polymer film on a not-volume-changing layer for the development of artificial muscles. One of the main drawbacks that these multilayer artificial muscles show lies on the fact that they delaminate after several working cycles. In one of our previous works, a simplified, single film, self-supported artificial muscle was developed assembling different polypyrrole structures in the same synthesis process. This produces not only "all-polymeric" but rather "all-conducting-polymer" artificial muscles that are able to move in electrolytic media without showing delamination problems after long cycling times. This new generation of simplified artificial muscles seems to be suitable for biomedical related applications. In the present work, actuator’s basement is explained and design configurations analyzed.