# NPS6D200--A Long Range Nanopositioning Stage with 6D Closed Loop Control
## 3 Setup and Subsystems of the 6D Nanopositioning System
### Vertical Drive System with Aerostatic Guiding and Weight Force Compensation  
The precise vertical displacement of the quartz slider is accomplished by the combined operation of three lifting modules (LAU25) that are located at the corner points. Besides the pure translation in \(z\), this also includes the rotational DOFs \(\varphi_{x}\) and \(\varphi_{y}\). The three modules are identical, and their development for the implementation in the NPS6D200 follows the same approach as earlier realizations for 10 mm vertical stroke as described in [38; 40]. Thereby, an individual lifting module integrates multiple functions into a compact mechanical design. These functions are listed in Table 4 together with the chosen technical realization in the current design.  
Figure 5a illustrates a sectional view of the developed lifting modules where the design implementation of these functions is shown. The cylindrical shape of both the actuators (voice coil and pneumatic) and the guidings (planar and vertical) facilitates a compact concentric arrangement built around the central cylindrical linear guiding. The guided piston is, at the same time, part of the pneumatic actuator that arises from the pressurized chamber below the piston. By precisely controlling the pressure in this chamber, the static weight of the moving body is carried out without substantial heat generation. It is important to note that the sealing of this chamber is designed as a gap-sealing between the precisely manufactured surfaces of the air bushing and thus works without mechanical contact of the parts. In this way, disturbance forces and friction effects are avoided. Ring grooves separate the air bushing from the sealing gap and drain the exhaust air so that it does not leak into the surrounding area. By this means, the thermal disturbance to the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Function** & **Description** & **Design Choice** \\ \hline \multirow{2}{*}{dynamic actuation} & generation of vertical driving & \multirow{2}{*}{voice coil actuator, \multirow{2}{*}{moving coil}} \\  & force with high sensitivity and & \\  & frog with high bandwidth & \\ \hline \multirow{2}{*}{quasistatic actuation} & generation of vertical driving & \multirow{2}{*}{pneumatic actuator with \multirow{2}{*}{contactless sealing}} \\  & force with high sensitivity and & \\  & low bandwidth & \\ \hline \multirow{2}{*}{planar guiding} & frictionless support of the & \multirow{2}{*}{planar air bearing pad} \\  & moving body & \\ \hline \multirow{2}{*}{vertical guiding} & frictionless internal guiding & \multirow{2}{*}{cylindrical air bushing} \\  & for 25 mm vertical stroke & \\ \hline \multirow{2}{*}{displacement measurement} & internal measurement of the & \multirow{2}{*}{optical encoder with \multirow{2}{*}{linear scale}} \\  & LAU displacement & \\ \hline \end{tabular}
\end{table}
Table 4: Lifting module subfunctions.  
Figure 4: Measured effects on the planar drive system due to lifting of the slider (coils remain at initial height). (_black_) —force constant of the linear actuators. (_blue_)—servo error (RMS) in \(x\) (solid) and \(y\) (dashed). (_red_)—required controller current (RMS) in \(x\) (solid) and \(y\) (dashed).  
overall system originating from the pneumatic components in the LAU is minimized. The voice coil works parallel to the pneumatic actuator, and its specific tailored design makes optimal use of the available design space. This Lorentz actuator is intended to generate only a dynamic force and, consequently, operate with zero DC current to minimize the power loss in the coil. In addition to these core components, an auxiliary linear feedback system is provided so that during initialization, an individual operation of each LAU is possible based on this feedback. Table 5 summarizes the characteristics of the LAU25 lifting modules.