Investigation of capillary forces and capillary bridges between an end-adjusted three-finger microgripper with hydrophobic side surface and a plate

Capillary forces generated by capillary adsorption between varied solids have been widely used in micro-objects manipulation. In present study, capillary forces and capillary bridges between an end-adjusted three-finger capillary microgripper with hydrophobic side surface and a plate were investigated. The effects of the separation distance on capillary forces for three configurations of capillary bridges were analyzed experimentally using a customized platform to verify the effectiveness of the established capillary models. The results show that the capillary forces increased sharply in the initial stage, followed by a decrease. The maximum capillary force of 141.1 μN was obtained for the capillary bridge of Structure A with capillary bridge volume of 0.55 μL. The effects of the capillary bridge volume, radial distance between probes and contact angles on the capillary forces were analyzed based on the established simulation model. The results indicate that the variation of capillary force with capillary bridge volume increasing was not monotonic because of the restriction of the probe edge. The capillary force changing was more sensitive to the variation of the contact angle on the plate than the variation of the contact angle on the probe end surface. Additionally, experimental analysis was conducted on variations in capillary forces for two types of the microgripper with variable relative axial distance between probes. The capillary forces increased as the relative axial distance between the probes increased, and then decreased. The maximum capillary force of 159.15 μN was obtained for Type 1 capillary bridge with capillary bridge volume of 0.45 μL.