A Scheme of Micromanipulation using a Liquid Bridge
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A Scheme of Micromanipulation using a Liquid Bridge Kenichi J. Obata1, Shigeki Saito1,2, and Kunio Takahashi1 1 Dept. of International Development Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo, 152-8552, Japan 2 Dept. of Material Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307, USA ABSTRACT This paper presents a scheme of micromanipulation with a liquid bridge and an analysis of the capillary forces involved. The following procedure is considered in this article: (a) PICK UP: a probe, with liquid in the tip, approaches the target object. (b) A liquid bridge forms between the object and the tip of the probe. (c) The object is picked up by means of the capillary force of the liquid bridge. (d) TRANSPORT: The probe ascends, moves to the target point, and descends towards a substrate. (e) PLACEMENT: At a given height, a second liquid bridge made from a drop previously applied at the target point on the substrate, forms between the object and the substrate. (f) The probe ascends and the probe-object bridge collapses. The collapse can be predicted through the stability analysis of the bridge and its condition can be controlled by the regulation of the liquid volume. The liquid volumes required for the manipulation, in the first and second liquid bridge, are calculated in this paper.
INTRODUCTION In the micrometer range, it is difficult to manipulate objects with a hand or gripper because the effects of the adhesional forces induced by solid-solid contact is dominant compared to gravitational force at such scales. The object still adheres to any of the fingers even if the gripper opens for releasing it. Manipulation based on the adhesive effects is assumed to be effective. Several studies have attempted to explore the methods for reliable manipulation; i.e., mechanical and electrical methods. The mechanical methods were attach/detaching a micro-object to/from the tool by mechanical interaction between the object and the tool. These methods could be successful solutions for limited tasks. Some problems, however, still might occur, because they require impractically high-mechanical precision and severe control, or because they depend on the operator's skill[1]. The electrical method were attach/detaching a micro-object to/from the tool by electrostatic force generated from an applied electric field. This method must avoid discharging or melting of the micro particle in order to realize a practical and reliable micromanipulation[2,3]. If capillary phenomena could be controlled, we could apply it to counteract the effects of the adhesional forces since capillary force is known to be potentially greater than adhesional force. Tanikawa et. al. have picked/placed an object with a micro-hand and a micro-drop, however, they have not provided any analysis of the capillary force[4]. In the present paper, a numerical investigation is presented and applied to evaluate the force required for the manipulation. Collapse of the liqui
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