Design And Experiments Of A Gripper For Microparts Transfer Based On Microdrop Control

Microparts transfer is the key procedure in microparts assembly, propertymeasurements and characterization of microobjects. In the microparts transfer, due tothe small size and the fragile structure, the microparts are easily to be damaged by theconventional microparts grriper in the picking process. And under the influence of thedominant adhesion force, the microparts are difficult to be released reliably by usinggravity. Therefore，it is significant to explore a new method of nondestructive pickingup and reliable releasing of the microparts in the transfer process.Based on microdrop control, a new microparts transfer method was proposed. Themicroparts will be picked up by the liquid bridge formed atfer the meniscus contactingwith the microparts. And the microparts will be released by breaking the liquid bridge.Since the compliant deformation of the liquid, stress concentration doesn’t exist inpicking microparts. Therefore, the picking of the microparts will be nondestructive inthis method. And also the releasing of the microparts will be reliable by controllingsingle microdrop.Firstly, the simplified models of meniscus and liquid bridge at the end of a capillarywere established. Solved the contour of the meniscus and the liquid bridge as well as thecapillary force, got the influence of pressure difference to the height of the meniscusand the liquid bridge, and to the capillary force. The best pressure difference applied topick up microparts was determined due to the requirements of the liquid bridge, and therelation between best pressure difference and contact angle was disscussed. On the base,the scheme of adjusting the meniscus and microdrop formation was established and thestructure of microparts transfer tool was designed; the process of microparts transferwas divided.Secondly, the simulation models of meniscus controlling and droplet formation werebuilt in COMSOL. Analyzed the influence of the amplitude and loading speed ofpressure difference lo to meniscus, got the curve of meniscus’ volume along with thechange of pressure difference and the critical pressure difference for stable meniscuswere obtained. The pulse voltage waveform forming a single microdrop and therelationship between the speed of the droplet and the voltage amplitude were obtainedthrough the analysis of the influence of pulse voltage waveform to droplet formation.Finally, an experimental system on microparts transfer was established. Therelationship of meniscus volume and liquid level’s height difference was obtained byadjusting the liquid level’s height difference between liquid bottle and nozzle. Theexperiments of droplets formation were conducted under different pulse voltage waveforms and different liquid level’s height difference and the influence of theseparameters to the volume of the droplets was obtained. According to the best pressuredifference determined in the liquid bridge model and the condition forming the smallestmicrodrop in microdrops formation experiment, transfer of tin balls with diameters300)im was realized. The best control condition of transferring tin microballs wasdetermined through analyzing the influence of the parameters of pulse voltagewaveform, the liquid level’s height difference and the releasing height to the reliabilityand accuracy of the tin ball releasing. The microparts transfer tool was proved to beflexible by experiment on tin microballs and polystyrene microballs.