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Mechanical grippers can also be used for manipulating micron-sized components. Sanchez-Salmeron et al. reviewed the existing systems for micro handling and transportation (Sanchez-Salmeron et al., 2005). Fig. 2.6 shows the hangdling of a live cell by a mechanical gripper (Gilbert 2008). Typical manipulation dimensions are in the range of micrometers up to a few millimetres, and the typical location accuracy is in the range of 0.1 to 10 . There are primarily three types of micro grippers: friction, hydraulic, and pneumatic. Gravity shall not be considered as the main force being applied to the part about handling methods at the micro-scale. Unwanted surface forces such as electrostatic, van der Waals and surface tension forces dominate at such scale. All these forces are known as adhesive forces (Fearing et al., 1995). Therefore, the pick-and-place method is difficult in micro-world taking into account of adhesive forces. To solve the problem, sensor control is often required to compensate for the inaccuracies resulting caused by the adhesive forces. Another survey of micro mechanical grippers for biotechnology applications is available in (Ouyang et al., 2008). The authors have pointed out that various microfabrication techniques are being increasingly used to grasp objects of different shapes with high positioning accuracy and a large number of degrees of freedom. |
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