Omni-directional Mobile Microrobots on a Millimeter Scale for a Microassembly System

The development of microrobots on a millimeter scale has recently received much attention. The environments in which these robots are supposed to operate are narrow and potentially complicated spaces, such as micro-factory, blood vessel, and micro-satellite. The robots must have omni-directional mobility, high power and high load capacity, within a scale in millimeters, in order to accomplish the work efficiently. Motion principles and actuation mechanisms that combine volume, motion of resolution, and the speed virtues of coarse positioning, are still the challege in the microrobot design. Different principles to drive microrobots have been developed. The Microprocessor and Interface Lab of EPEL developed a 1cm3 car-like microrobot with two Smoovy 3 mm motors. Sandia National Lab developed a 4cm3 volume and 28g weight microrobot for plume tracking with two Smoovy micromotors with a car-like steering (Byrne et al., 2002). AI lab in MIT designed Ants microrobot with a 36.75cm3 volume and 33g weight, driven like a tank with pedrail (Mclurkin, 1996). Caprari and Balmer built another car-like microrobot with 8cm3 volume by watch motor (Caprari et al., 1998). Dario developed a millimeter size microrobot by a novel type of electromagnetic wobble micromotor, with a three-wheel structure (Dario et al., 1998). Besides the normal motors driven principle, other microactuation techniques based on smart materials have been devised, such as piezoelectric actuators, shape memory alloys, etc. The MINIMAN robot and the MiCRoN microrobot have employed these techniques (Schmoeckel & Fatikow, 2000; Brufau et al., 2005). The first walking batch fabricated silicon microrobot, with the 15x5 mm2 size, able to carry loads has been developed and investigated. The robot consists of arrays of movable robust silicon legs having a length of 0.5 or 1 mm. Motion is obtained by thermal actuation of robust polyimide joint actuators using electrical heating (Thorbjörn et al., 1999). Omni-directional mobile robots have kept developing due to inherent agility benefits (Williams et al., 2002). The mechanisms can be divided into two approaches: special wheel designs and conventional wheel designs. Fujisawa et al., Ferriere and Raucent developed the universal wheel for omni-directional mobility (Fujisawa et al., 1997; Ferriere et al., 1998). Muri and Neuman developed the Mecanum wheel similar to the universal one (Muir & Neuman, 1987). West and Asada developed the ball wheel (West & Asada, 1997), while Killough and Pin developed the orthogonal wheel (Killough & Pin, 1994).