# NPS6D200--A Long Range Nanopositioning Stage with 6D Closed Loop Control
## 3 Setup and Subsystems of the 6D Nanopositioning System  
### Stage Concept  
The stage architecture of the NPS6D200 is based on the concept of an integrated planar direct drive for the long-range lateral positioning as it has been realized in earlierdevelopments, see [28]. The main idea for the new development of the NPS6D200 is to extend this concept towards a vertical actuation in a macroscopic travel range with active control of all six degrees of freedom (DOFs). The integration of a high precision vertical actuation thereby leads to enhanced functional capabilities of the machine:  
* Compensate guiding deviations in \(z\), \(\varphi_{x}\), \(\varphi_{y}\);
* Compensate vertical shift at tilted probes;
* Measure 3D objects, tilted surfaces and macroscopic step heights;
* Enable applications that require vertical displacements, e.g. focus height variations in interferometry, contour following mode in atomic force microscopy
* Enable load/unload of the measurement object without having to remove the tool  
In principle, the planar direct drive architecture is well suited to be enhanced by vertical actuation because of the planar arrangement of the drive components. Coils and magnets each are located in horizontal planes so that the slider is free to move vertically. Moreover, compared to a stacked axis arrangement the vertical actuation here can be implemented directly between the stator and the moving part. In this way, it is possible to maintain the advantages of the direct drive principle by continuing to have all actuation forces acting directly on the same body. This body is the so-called slider, and its movement is controlled in six DOFs. The displacements in \(x\), \(y\), \(z\) are available for large-scale movements, whereas the rotational DOFs are regulated to zero. The schematic explosion illustration in Figure 1 shows the system composition and the main components. The slider, as the moving part of the 6D drive system, also carries the reflectors for the 6D feedback system so that these two central functions are incorporated in one and the same solid and rigid body. All drive forces act directly on this very body without any additional transfer elements. The result is a high stiffness in the actuation chain, which means in the mechanical path from the point of force application to the point where the displacement is measured. This high stiffness is linked to a good controllability. It allows for tuning the controller to higher bandwiths with robust phase margins and thereby enables better disturbance rejection and servo errors only at nanometer scale in closed loop control. The whole system follows a triangular configuration, which applies to the arrangement of the planar drive components and the laser interferometers (U, V, W) as planar feedback systems. This configuration also leads to a triangular slider shape with three-point support against the granite stator. These support points are formed by lifting modules (LAU25) which contain the vertical actuation as well as the aerostatic guiding both for the planar and the vertical slider motion. In combination, the three LAU25 represent the vertical drive system to address the \(z\), \(\varphi_{x}\), \(\varphi_{y}\) DOFs of the slider. Parallel to this, a planar direct drive system consisting of magnet arrays at the slider and encapsulated flat coils in the stator generates the required horizontal driving forces to control \(x\), \(y\), and \(\varphi_{z}\). Figure 2 shows a photograph of the NPS6D200, which in summary has the following key features:  
* Nanopositioning platform for \(\diameter 200\,\mathrm{mm}\)\(\times\)\(25\,\mathrm{mm}\) operating range;
* Multiaxial direct drive system with contactless force application to the moving part;
* Pneumatic weight force compensation;
* Frictionless aerostatic guiding;
* High resolution 6D measurement of the slider position;
* 6D closed loop control;
* Scalable design approach;
* Open architecture to implement different applications and sensor tools.