Reliable and Accurate Release of Micro-Sized Objects with a Gripper that Uses the Capillary-Force Method

Abstract

There have been recent developments in grippers that are based on capillary force and condensed water droplets. These are used for manipulating micro-sized objects. Recently, one-finger grippers have been produced that are able to reliably grip using the capillary force. To release objects, either the van der Waals, gravitational or inertial-forces method is used. This article presents methods for reliably gripping and releasing micro-objects using the capillary force. The moisture from the surrounding air is condensed into a thin layer of water on the contact surfaces of the objects. From the thin layer of water, a water meniscus between the micro-sized object, the gripper and the releasing surface is created. Consequently, the water meniscus between the object and the releasing surface produces a high enough capillary force to release the micro-sized object from the tip of the one-finger gripper. In this case, either polystyrene, glass beads with diameters between 5–60 µm, or irregularly shaped dust particles of similar sizes were used. 3D structures made up of micro-sized objects could be constructed using this method. This method is reliable for releasing during assembly and also for gripping, when the objects are removed from the top of the 3D structure—the so-called “disassembling gripping” process. The accuracy of the release was lower than 0.5 µm.

Multi-scale tarsal adhesion kinematics of freely-walking dock beetles

“…The maximum vertical distance from the glass slide to the claw z M ¼ max (z) ¼ 1:1 [0:7,1:9] mm varied significantly from one step to another. The horizontal speed _ y ¼ 4:2 [1:4,5:5] mm s À1 was one order of magnitude lower than the maximum vertical speed j_ z M j ¼ 28 [10,140] mm s À1 . The average vertical acceleration was € z ≃ À0:64 m s À2 .…”

“…Hexapod adhesion mechanisms are not only interesting for the development of reusable bioinspired adhesives [5][6][7][8]. They also are a promising answer to a current challenge in microrobotics: with conventional prehension (tweezers, vacuum), it is hard to pick and place objects smaller than 100 mm without being impaired by van der Waals forces [9,10]. The reversible adhesion of hexapods does not seem to suffer from this size limit.…”

Design, Analysis and Experimental Investigations of a Double-Arm Based Micro-Gripper for Thin and Flexible Metal Wires Manipulation

“…Alissa et al [12] designed an electric micro-gripper embedded with a metal film heater based on SU-8, with a clamping stroke of 70-90 µm, which can be used to grip and place microsphere objects up to 150 µm in diameter. Uran et al [13] proposed the use of capillary forces to reliably grasp and release tiny objects, which can be used to grasp glass beads between 5 and 60 µm in diameter or irregularly shaped dust particles of similar size with an accuracy of up to 0.5 µm. Zhang et al [14] designed a V-shaped electrothermal driven five bar flexible micro-gripper for grasping, moving and releasing zebrafish embryos.…”

Rupture of Liquid Bridges on Porous Tips: Competing Mechanisms of Spontaneous Imbibition and Stretching

“…In wetted granular materials, e.g., wet sandy soil and humid powders, the capillary force generated by liquid bridges induces the grain-grain cohesion resulting in the increment of shear strength 12 , grain agglomerations 13 and self-assembly 14 . With industrial applications, capillary forces generated by the liquid meniscus between a gripper and objects can be used to handle tiny components 15 , e.g., watch bearings 16 . This capillary gripping presents significant advantages over the tiny-scale manipulations, such as the indirect contact with the objects, self-centering, high compatibility with various shapes and materials.…”