Design and control of a microrobotic system using magnetic levitation

This paper presents a prototype microrobotic system based on magnetic principles. The goal is to build a system in which miniature items can be transported and assembled within hazardous environments. A microrobot can be remotely operate with 3 DOF in an enclosed environment by transferring magnetic energy and optical signals from outside. A magnetic drive unit generates magnetic energy for the microrobot's manipulation. The drive unit consists of eight electromagnets (four pairs), two permanent magnets, a return yoke made from a soft magnetic iron and a special pole piece. The microrobot is manipulated in a workspace under the pole piece by regulating magnetic field. It consists of three main components; magnetic head, body consisting of electronic circuit and batteries and ringers made from two thin ribbons of a copper alloy. A shape memory alloy actuator activates the ringers to grasp or release an object by illuminating/extinguishing several LEDs facing the microrobot. Proportional integral derivative controls were applied for the positioning of the microrobot (with payloads) on the three axes. To cope with uncertainties and variations in payload masses, an adaptive control law was also employed for positioning along the z axis to enable the controller parameters to be adjusted in real-time. Effectiveness of the control was verified by the results of several experiments. The microrobot has a net mass of 8.1 g and it can elevate and manipulate objects with masses up to 1.5 g within a volume of 29 x 29 x 26 mm(3) with a precision of 0.05 mm.