| Author: | Li, Jun |
| Title: | Electroadhesive clutches made from high dielectric-constant polymeric materials and flexible electrodes |
| Advisors: | Tao, Xiaoming (ITC) Wong, W. Y. Raymond (ABCT) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Clutches (Machinery) Magnetic clutches Dielectric devices Hong Kong Polytechnic University -- Dissertations |
| Department: | Institute of Textiles and Clothing |
| Pages: | xxiv, 196 pages : color illustrations |
| Language: | English |
| Abstract: | Electroadhesive clutches based on the electrostatic attraction of the two electroadhesive pads have shown promising application in wearable and haptic systems due to their flexibility, fast response, light weight, low power consumption, easy fabrication as compared with the traditional clutch technologies. Electroadhesive clutches could also be easily integrated into the current electrical or robotic systems. Though the electroadhesive clutches have been investigated for several decades, it remains a challenge to develop clutches with large electroadhesive forces at low driving-voltage. Hence this thesis presents a systematic research towards high-performance clutches with an emphasis on material selection and clutch structure optimization. Symmetric clutches made from high dielectric constant P(VDF-TrFE-CFE) terpolymers were firstly developed through direct blade coating on Al foil electrodes followed by annealing at 120 °C overnight. The surface roughness, chemical and dielectric propertiesof the dielectric materials as well as the mechanical properties of the electrodes were systematically investigated. The relationships and response time have been experimentally determined and evaluated including those between the voltage and adhesiveforce, dielectric thickness and force, as well as overlapping area and force. A symmetric-structured electroadhesive clutch could response at 80 V, its electroadhesive force increased dramatically with the increase of applied voltage. A shear stress over 100 kPa was generated at 120 V (DC) with a power consumption as low as 5.56 μW. A new laboratory-made testing apparatus was established for the response time of the clutch. The engage time and release time were ~25 ms and ~324 ms respectively. Furthermore, the change of bending stiffness of the clutch under different working voltages was investigated. The bending stiffness of the clutch at 120 V was about 2-time higher than the non-engaged clutch. In addition, the clutch response to AC square-wave voltage was evaluated for the first time, which was comparable with the clutch's DC-driving performance. To evaluate the influence of the charge characteristics of the dielectric materials to the clutch performance, asymmetric clutches made from PU/PTFE and PU/PI were fabricated by blade coating. Their responses to DC voltage were systematically studied. The electroadhesive force was increased when the polarity of the induced charges is the same as the charge characteristics of dielectric materials. The asymmetric PU25/PI5 clutch exhibited a highest shear stress of ~ 200 kPa at 300 V with an engage time of ~ 20 ms and a release time longer than 15 mins. Reversible chemical adhesion due to the formation of abundant hydrogen bonds at the PU/PI interface was attribute to the clutch performance characteristics. A multi-mechanism of the asymmetric PU/PI clutch was postulated to originate from the integration of interfacial H-bonds, electrostatic attraction and charge characteristics of the dielectric materials. High-k polymer composites with tunable dielectric properties were developed with in situ thermal reduction of GO in P(VDF-TrFE-CFE) matrix. The linear relationship between the dielectric constant (at 100 Hz) and reduction time was observed for the first time. The GO has been demonstrated to be partially reduced (PRGO) at the relatively low reduction temperature of 120 °C by using Raman and FTIR spectra. A relative dielectric constant as high as 1480 with a tan δ of 0.283 at 100 Hz was obtained at a doping ratio of 4 wt%. A clutch-type pressure sensor made of the high-k PRGO/PVDF-FS composites has been demonstrated. The pressure-current relationship at a constant voltage, current-voltage relationship under a constant pressure and pressure sensing behaviour for long time were experimentally determined and analyzed. The pressure sensor exhibited a good linearity at a relatively high pressure range (100 kPa to 1 MPa) but was not favourable for lower pressure range or used for a long time. The mechanism of the current change under external forces was also explored and was attribute to the leakage current of the microcapacitors in the high-k composites. |
| Rights: | All rights reserved |
| Access: | open access |
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