Research On Micromanipulation Method And Experiments Based On Traces Of Reagent Dispensing Control

Compared with gravity, adhesion force dominates in the micron grade objectoperation due to size effect and surface effect. How to pick up accurately and releasereliable become critical issues, and this problem increases with the reducing of objectsize. Due to the mechanical contact between the gripper and the microobjects, a highlocal mechanical stress could occur and the microobjects are easily to be damaged whenmechanical tweezers and vacuum tools are applied. Therefore it is necessary toinvestigate new harmless operation method.Based on traces of reagent dispensing control, a new micromanipulation method wasproposed. The liquid bridge formed between drop and microobject could be adjusted bymanipulating the volume of drop, and under the effect of capillary force the microobjectwas picked up. By ejecting out trace volume of drop the releasing process ofmicroobject realized.First, by analyzing typical capillary force model between solid and liquid interfaces, theformula of capillary force within liquid bridge formed between reagent in the capillarytube and microobject was derived. The factors affecting the capillary force and thefeasibility of micromanipulation by controlling capillary force were discussed. Themicromanipulation method based on traces of reagent dispensing control was proposed.Pressure adjustment of reagent at capillary orifice was used to control the meniscus’svolume to pick up microobject and piezoelectric ceramics scheme was put forward toeject traces of reagent drop to release microobject. The working principles of these twoschemes were analysed. By dividing the operation process into various stages, relatedoperation strategies were presented.Second, according to pressure adjustment scheme to control the volume of meniscus topick up microobject, Fluent software was used to simulate the influence of pressure oncapillary meniscus. Based on piezoelectric scheme about ejecting out traces of reagentdrop to release microobject, the simulation was analysed under two different signals:DC(Direct Current) voltage and rectangular pulse voltage. Under DC voltage signal thedeformation of capillary walls were acquired by Ansys software and these deformationdata were imported to Fluent to simulate the appearance of capillary menisci. Underrectangular pulse voltage signal the velocity history of reagent at the capillary nozzleorifice was computed by analytic expression, and the velocity data were used in Fluentto simulate the variation of capillary menisci with different voltage parameters.Finally, the microobject experiment system based on traces of reagent dispensingcontrol was built. Pressure adjustment scheme was adopted to do picking upexperiments of microobjects with various volume parameters of menisci and the effectof pressure on the volume of capillary menisci were discussed. The piezoelectric scheme was applied on releasing experiments of microobjects with different voltageparameters under DC voltage and rectangular pulse voltage signals. The effect ofparametric variation on trace reagent dispensing and microobjects releasing wereconsidered. As a consequence, by using pressure adjustment scheme to pick andpiezoelectric scheme under rectangular pulses to release microobjects, the picking upand releasing experiments of200μm polystyrene ball,200μm solder ball,300μm solderball in diameter and irregular silicon wafer were performed successfully. Themicroobjects gripping operations were executed to verify the micromanipulationmethod. The maximum repetitiveness was8.6μm when releasing300μm solder ball indiameter.