A van der Waals Force-Based Adhesion Model for Micromanipulation

The robotic manipulation of microscopic objects is disturbed directly by the adhesion between the end-effector and the objects. In the microscale, no reliable model of adhesion is available and currently the behaviour of the micro-objects cannot be predicted before experiments. This paper proposes a new model of adhesion based on the analytical resolution of the coupling between the mechanical deformation of the micro-objects and van der Waals forces. In the nanoscale, the impact of the deformation can be neglected and the proposed model is thus similar to the classical expression for van der Waals forces. In the microscale, the deformation induces van der Waals forces to increase significantly and a new analytical expression is proposed. The limit of validity of this 'deformable van der Waals forces' is also discussed. This result can be used as an alternative to classical adhesion–deformation models in literature (Johnson–Kendall–Roberts (JKR) or Derjaguin–Muller–Toporov (DMT)), which have been validated at the macroscale but are not sufficient to describ the interaction forces in the microscale (typically from 100 nm to 500 μm).