Development of biological-micro-manipulation system in scanning electron microscope

In an application of biological and medical engineering, there are increasing demands of implementing dissection, inspection and/or evaluation at the sub-micron scale. Currently, most of such operations are manually done by highly skilled operators with the assistance of scanning electron microscopes or CCD camera. The limited visible area at a high magnification of SEM makes it more difficult for the operator to trace the target. The operators have also to experience a long time training to familiarize the feeling of micro-scale movements in order to achieve high accuracy. The operations are tedious and time-consuming. It is, therefore, strongly expected to develop a manipulation system possible for unskilled operators to easily execute the desired tasks. Our goal is to develop a manipulation system enabling unskilled operators to deal with biological objects in sub-micro size as easily as to deal with objects in usual size. The scope of this paper includes the conceptual design, the prototype development, field tests and the operability evaluation. The system is modularized into the manipulation unit, the control unit and the man-machine interface. The manipulation unit is further comprised of a twin-arm manipulator mounted on a rotary table and a specimen stage with four degrees of freedom linear along X, Y and Z direction, and rotational around the Z-axis. The manipulator is driven by PZT actuators with magnifier elements and able to cover an envelope as wide as 200 μm for each axis of X, Y and Z. Instead of doing a direct operation, the operator steers the manipulator via user-friendly interface, which is designed to absorb the optical and mechanical variations. The control unit merges the visual information of the SEM and the manipulation information from the user interface and derives the optimum locomotion from the arm for the desired operation. The image processing algorithm of the vision system can capture specified object and auto-locate it with in the scope of SEM (low vacuum type). With this function, the operator is able to concentrate on the operation without paying much attention to the changes in SEM magnification and other conditions. By feeding the force exerted on the tool tip back to the joystick, the operator actually feel the res- istance so that the contact between the tool and the specimen, and force applied to the specimen are identical. The field test has demonstrated that the modules are able to cooperate each other to complete the complicated tasks.