Preparation And Electrical Research Of A Piezoelectric-piezoresistive Double-membrane Tactile Sensing Unit

The tactile perception is one of the most important approaches for biological creatures to get information from the external environment, which is also one of the main sensory abilities of human beings. For the disabled, however, they have to use artificial hands to recapture this kind of capacity. In recent years, as the rapid development of tactile sensing technology and intelligent robot technology, the research of tactile sensors that reproduce the tactile perception functions of human hands has become a hotspot. Based on different sensing principles and making use of different sensitive materials, researchers at home and abroad have successfully developed lots of tactile sensors with superior performances, which also have some limitations, though. The purpose of this paper is to design and prepare a novel flexible tactile sensing unit that is able to simultaneously detect both dynamic and static strains, based on simplified tactile perception model of human hands. A design and preparation method of a double-layer sensing unit using piezoelectric material and piezoresistive polymer composite is proposed.In this paper, the histories and application of piezoelectric material and piezoresitive polymer composite have been deeply researched, the sensing principles of piezoelectric materials and conductive mechanisms of polymer composite materials have been emphatically explained, as well as the influence factors. Appropriate sensitive materials have been chosen and detailed preparation process is designed. For the piezoelectric membrane, due to the poor experiment results of PVDF polymer polarization, improved ferroelectric copolymers P(VDF-TrFE) powder is used. The preparation technology is spinning-coating. For the piezoresistive membrane, MWNT/PU polymer composite film is prepared, which consists of PU (substrate), MWNT (conductive doping), and DMF (organic solvent).Before the preparation process, an experiment is firstly conducted to verity the piezoresistive capacity of MWNT. Pure MWNT film sample is prepared and tested, a computing and experimental method of Gauge factor is proposed. Then, through strong acid chemical modification, advanced material MWNT-OH is got, which can be steadily dispersed in organic substrate. MWNT/PU doping concentration is calculated according to the percolation model analysis. The piezoresistive film is prepared by direct solvent evaporation method. At last, coating the double-membrane structure with electrodes and encapsulating with PDMS elastomer, the target flexible sensing unit preparation process is completed.Experiments testing the electric performances of the flexible double-membrane sensing unit have been conducted. Results show that it has good piezoelectric sensitivity, accurate signal output in time and frequency domains; its piezoresistive sensitivity is linear and fair. Based on the test results, improvement scheme research prospects are presented.