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.
Highlights
During micro-assembly, individual micro-sized objects are picked up and placed at a desired destination using a gripping tool
One-finger grippers modify the resultant force acting on the sub-millimetre or micro-sized object during gripping and releasing procedures
The work area setup for the capillary gripping/releasing method is controlled by environmental and surface characteristics to produce a variable capillary force
Summary
During micro-assembly, individual micro-sized objects are picked up and placed at a desired destination using a gripping tool. One-finger grippers modify the resultant force acting on the sub-millimetre or micro-sized object during gripping and releasing procedures. The overview of micro-assembly approaches in Table 1 shows both active and passive approaches, as well as a wide variety and combination of gripping/releasing forces that are used with the approaches presented in this article. With the development of approaches and increased knowledge and experience, the van der Waals force can be successfully used as a releasing force for sub micro-sized objects. The capillary force has been observed to be a very strong surface force with the ability to grip sub-millimetre and micro-sized objects. The work area setup for the capillary gripping/releasing method is controlled by environmental (temperature) and surface characteristics (curvature radius and dimensions) to produce a variable capillary force
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