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Design, analysis, and development of hybrid electrostatic adhesive for wall climbing robot applications
thesisposted on 22.02.2017, 00:41 by Koh, Keng Huat
The ability to climb and manoeuvre on vertical surfaces is seemed as an easy task to nature’s climbers such as geckos and insects. Yet we are still at the initial stage attempting to mimic this remarkable locomotion perfectly. For the past three decades, various climbing machines in the form of robotic devices are developed to solve the climbing problem. Different attachment strategies such as vacuum suction, magnetic adhesion, mechanical grasping, gecko adhesion, electrostatic adhesion, and others have shown promising steps, in spite of some limitations which are intrinsic to each of the mechanism. The objective of this thesis is to develop a method of adhesion in wall climbing robot applications for wide range of surface types. It requires a systematic mechatronic approach, and finally arrives at a solution using hybrid electrostatic and elastomer adhesion. This work begins by experimenting with a 3-layer electrostatic adhesive actuator. When the actuator is placed close to a test surface and driven with high voltage, the electrodes are electrified and subsequently induced bound charges at the dielectric layer by means of polarization. Opposite polarities of the charges between the layer and test surface creates electric field and the attractive force is a result of this phenomena. Parameters that affect the holding force of actuator on test surfaces include the driving voltage, electrode area, surface roughness, and dielectric thickness. It is found that the theoretical quadratic relation of force and voltage is no longer valid at higher electric fields. Saturation that happens at higher fields is caused by leakage current and corona discharge. The key factor in electrostatic adhesion lies at the material compliance to surface, since electrostatic force behaves as a surface-only force. The adhesive actuator is susceptible to external peeling force. To overcome this problem, this thesis suggests the use of flexible and soft material for the entire structure of adhesive actuator. It is shown that elastic film structure with suitable material property exhibits appreciable elastomeric adhesion effect. The resulted hybrid adhesive is shaped into tracks for the robot. This thesis also proposes a novel multiple stages blade coating fabrication method for the hybrid adhesive. The method is simple, scalable, geometrically controllable, and thus suitable for producing such dry adhesive in variety of size for various surface attachment applications. The proposed dynamic climbing template for the robot is designed by analysing gecko’s climbing dynamics. As a result, this thesis presents a proof-of-concept robot prototype, named ELAD. It uses electrostatic, elastomeric, and biomimetic tail forces to simultaneously work together and achieve stable climbing. ELAD is able to ascend, hold position, and descend on smooth surfaces. The hybrid adhesive can be readily scaled to higher payload for future practical applications with modifications on the robot footprint. Future work for improvement on the adhesive has already begun. At conclusion, the next generation ELAD-II which aims at overcoming some limitations of the developed wall climbing robot is also provided in this thesis.