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Top1. Introduction
Many micro- and nanomanipulation processes have been robotized, facilitating the human access to those micro- and nanospaces with unknown dynamics and properties. The process of robotization creates many problems that have to be resolved. One of them is the development of mechanical constructions that are appropriate for controlling the working tool, that can be applied to the domains of microsurgery and microbiology, and particularly to cell manipulations, microelectronics research, chemistry and investigation of thin films, scanning of micro- and nanosurfaces, microassembly etc. (Fatikow & Rembold, 1997; Pernette & Henein, 1997; Kasper & Heinemann, 1998).
The body of these micromanipulators is constituted of a high-precision mechanical structure which is free from backlash, friction and hysteresis, in order to obtain the required submicron accuracy, (Pernette & Henein, 1997). Mechanisms with closed kinematics chains are suitable for high- precision tasks (Li & Xu, 2005; Yao & Dong, 2008; Prusak & Uhl, 2009). As it is well-known, parallel kinematic mechanisms possess inherent advantages over conventional serial manipulators, such as high rigidity, high load capacity, high velocity, high precision, etc. The high accuracy of such mechanical systems is due to their inherent structural stiffness. The small workspace in the case of cell manipulations is not to their disadvantage, since it is sufficient for the application under consideration.
On the other hand, compliant mechanisms, i.e., flexure-based mechanisms can be employed into parallel mechanisms for high-precision applications (Li & Xu, 2005; Yong & Lu, 2008; Yong & Lu, 2009). Compliant mechanisms exhibit many advantages in terms of vacuum compatibility: they have no backlash property, nor nonlinear friction, and what is more, their structure is simple, and they are easy to manufacture. The use of a compliant mechanism in order to provide motion transfer means that the position accuracy of such micromotion mechanisms depends only on the accuracy of microactuators and on the position sensors. It is possible to use the deformation in the elastic areas to achieve tension in the closed structures as well.
Many actuation principles have been applied to drive the compliant mechanism in micro- and nanorobots. Piezoelectric actuators, electrostatic, electromagnetic and shape memory allow actuators to be utilized to provide fine motions to micro- and nanorobots. Piezoelectric actuators are commonly used to provide fine resolution of input displacements in the subnanometer range (Kasper & Heinemann, 1998; Chu & Fan, 2006; Gao & Swei, 1999; Kasper & Al-Wahab, 2004), since their resolution is dependent solely on the quality of applied voltage signal. Piezoelectric actuators offer substantial advantages for microtechnology applications compared to competitive actuators, e.g. large force, high frequency and small size. Piezoelectric actuators developed in closed kinematical structures are suitable for high-precision tasks in 3D space (Prusak & Uhl, 2009; Ionescu & Kostadinov, 2002). The concept of total decoupling is accepted to isolate and protect the actuators as the presence of unwanted transverse loads may damage some types of motors such as the piezoelectric actuators. Translations in compliant parallel stages, and the design of a totally decoupled parallel micropositioning stages has been proposed (Li & Xu, 2011) in order to eliminate the cross-axial coupling errors between the axes.