Measurement of pull-off force for planar contact at the microscale

At the microscale, surface forces influence the behaviour of micro-objects more than volumic forces. During micro-assembly processes, contacts occur between a microgripper and a micro-object or between a substrate and a micro-object. The pull-off force, which represents the force required to break a contact, is one of the predominant problems in micro-assembly. Current force measurements are mostly focused on sphere-plane geometries, and models are based on nanoscale theories. The aim of this letter is to propose an evaluation of the pull-off force for a planar contact, which is the most frequent kind of contact in micro-assembly. Experimental force measurements based on a capacitive microforce sensor and micro/nano robotic systems are carried out. The proposed device enables the study of pull-off forces according to the preload force and the contact angle. Finally, experimental results are discussed and compared with a model.