Influence of surface topography in electrostatic forces simulations for microassembly

Micro manipulations of objects between 10μm and 1mm by contact are often disturbed by adhesion between the handled object and the gripper. This is due to the presence of the surface forces which overcome gravity and prevent the release of the object. Capillary, electrostatic and van der Waals forces are the main surface forces responsible for this adhesive phenomenon. Several factors may influence these forces such as the materials in contact, the fabrication process, the surface treatments or the surface contaminations. All of these factors contribute to shape the topography of the surface. In this paper simulations are performed on the electrostatic forces for smooth surfaces and for rough surfaces in order to study the influence of surface topography. The results are compared with analytical models for the smooth case and show a good correlation. The rough case simulations use a sphere ended conical tip-plane contact. The discussed roughness models are mainly elementary protuberances and fractal representation using the WeierstrassMandelbrot model. The simulations using fractal representation show an influence of the surface topography at small separation distances. A comparison is also performed with experimental results from the literature.