In literature, research studies (Mehregany, Gabriel, & Trimmer, 1988; Jokiel, Benavides, Bieg, & Allen, 2001) investigate the initial use of Micro Electro-Mechanical Systems technology to design and fabricate parallel mechanisms. Furthermore, a parallel mechanism was built based on MEMS fabrication technology that provided translational motions in three axes as reported in Fan, Wu, Choquette, and Crawford (1997). Motion platforms with two and three degrees of freedom were presented in Jokiel, Benavides, Bieg, and Allen (2001) and Hollar, Bergbreiter, and Pister (2003).
1.1 Parallel Structures
In the design and development of manipulators, it has been realized through several research studies (Merlet, 2000; Gosselin & Angeles, 1991) that parallel structures possess intrinsic advantages over serial manipulators due to their high rigidity, large payload capacity, high velocity and notable precision. However, rigid joints with multi degrees of freedom used in conventional parallel robots affect the precision and accuracy of the system due to backlash, hysteresis and other manufacturing errors. In order to overcome these design constraints, compliant structures have been employed into parallel robots as investigated in Tanikawa, Arai, and Koyachi (1999) where notable precision is desirable at micron levels due to the fact that compliant structures possess simple configuration, do not suffer from backlash and have easy fabrication (Smith, 2000).
Typical development of motion platforms on macro scales comprise of kinematic configurations in which linear piston-like actuators are connected between the top (motion) plate and the bottom (fixed) plate through spherical or universal joints that are difficult to manufacture in MEMS fabrication technology. In literature there is a large body of work (Tsai & Tahmasebi, 1993; Ben-Horin & Shoham, 1996; Ben-Horin, Shoham, & Djerassi, 1998; Honegger, 1998; Wenger & Chablat, 2000; Tsai & Tahmasebi, 1993; Ceccarelli, 1997) that investigates the design and development of such parallel structures which employ passive sub-mechanisms to connect the motion plate.
Through literature studies (Choi, Sreenivasan, & Choi, 2008; Kallio, Lind, Zhou, & Koivo, 1998; Tang, Pham, Li, & Chen, 2004; Wu, Chen, & Chang, 2008; Hudgens & Tesar, 1991) it has been realized that micromanipulators possess potential applications in fields such as optical fiber alignment, micro system assembly and micro-scale experiments in biological research. Therefore more and more micro-robotic systems are developed based upon parallel structures to realize systems with appreciable performance. However, conventional parallel mechanisms found in literature feature fewer degrees of freedom (Choi, Sreenivasan, & Choi, 2008; Kallio, Lind, Zhou, & Koivo, 1998; Tang, Pham, Li, & Chen, 2004; Wu, Chen, & Chang, 2008) that confines their motion envelope. Therefore, design and realization of micro-manipulators with 6-DOF motion capabilities with a reasonable workspace still require further research.