Characterizing Screen-printed Resistive Tactile Sensors
Nummi, Akseli (2020)
2020
Tieto- ja sähkötekniikan kandidaattiohjelma - Degree Programme in Computing and Electrical Engineering, BSc (Tech)
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2020-02-10
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202002041838
https://urn.fi/URN:NBN:fi:tuni-202002041838
Tiivistelmä
This bachelor’s thesis characterizes resistive tactile sensor prototypes made by master’s thesis worker Ahmed Elsayes in Tampere University biomedical engineering laboratory. He has manufactured several sensors but only one is examined in this thesis. The sensor is characterized by drawing a curve illustrating the force–resistance relationship of each element in the sensor. It includes one larger sensing element and two smaller ones that are the same size. The elements are fixed between two layers of flexible plastic film. They are connected to an electrical circuit through thin screen-printed conductors that run inside the sensor. The intention behind the tactile sensors is to create an artificial sense of touch to use in conjunction with a prosthetic hand. They could also be utilized in other flexible electronics and soft robotics applications.
The sensor is used to measure the amount of force that is applied on it. The sensing elements are based on a phenomenon called piezoresistivity where a material’s electrical resistance is proportional to this force. The stress caused by the force is either compressive stress or tensile stress. However, only compressive forces are present in tactile sensing applications. The piezoresistive elements are pieces of insulating fabric doped with conducting nanoparticles. As the fabric is compressed, the distance between the particles inside the material decreases, creating a conductive path through the fabric. Thus, the fabric’s resistance diminishes. There are also other types of piezoresistive materials. Semiconductor materials, such as silicon, have been utilized in piezoresistive sensor for decades.
Using a Stable Micro Systems texture analyzer, different amounts of force were exerted on the sensor. A straightforward voltage divider circuit was used to transform the change in resistance to a voltage signal. The voltage across the series resistor was input to a PC using a National Instruments DAQ device. The voltage curve was then manipulated using MATLAB and Excel to plot the final force–resistance curves.
The characterized sensor indicated promising behavior. The force–resistance relationship of each piezoresistive element is logarithmic, as expected. The measurements were carried out without many errors as there was only one deviation in the data collected. The sensors seem largely suitable for the intended application. However, it was noted that when using extremely low forces, less than 0,5 N, the sensor’s output was sometimes unpredictable. Also, it was not possible to measure forces higher than 5 N with the available laboratory equipment. The results that were gathered show good promise, nonetheless. Further research is of course needed to clarify these uncertainties.
The originality of this thesis has been checked using the Turnitin OriginalityCheck service.
The sensor is used to measure the amount of force that is applied on it. The sensing elements are based on a phenomenon called piezoresistivity where a material’s electrical resistance is proportional to this force. The stress caused by the force is either compressive stress or tensile stress. However, only compressive forces are present in tactile sensing applications. The piezoresistive elements are pieces of insulating fabric doped with conducting nanoparticles. As the fabric is compressed, the distance between the particles inside the material decreases, creating a conductive path through the fabric. Thus, the fabric’s resistance diminishes. There are also other types of piezoresistive materials. Semiconductor materials, such as silicon, have been utilized in piezoresistive sensor for decades.
Using a Stable Micro Systems texture analyzer, different amounts of force were exerted on the sensor. A straightforward voltage divider circuit was used to transform the change in resistance to a voltage signal. The voltage across the series resistor was input to a PC using a National Instruments DAQ device. The voltage curve was then manipulated using MATLAB and Excel to plot the final force–resistance curves.
The characterized sensor indicated promising behavior. The force–resistance relationship of each piezoresistive element is logarithmic, as expected. The measurements were carried out without many errors as there was only one deviation in the data collected. The sensors seem largely suitable for the intended application. However, it was noted that when using extremely low forces, less than 0,5 N, the sensor’s output was sometimes unpredictable. Also, it was not possible to measure forces higher than 5 N with the available laboratory equipment. The results that were gathered show good promise, nonetheless. Further research is of course needed to clarify these uncertainties.
The originality of this thesis has been checked using the Turnitin OriginalityCheck service.
Kokoelmat
- Kandidaatintutkielmat [8235]