Driving the stage with 25 nm steps figure_2 it is obvious that the step width shows more variations but in average the value is about 25 ±5 nm. Positioning in the nm range is normally done with piezo drivers. But even with a standard linear stage like PLS-85 and our SMC-controllers it is possible to push the stage in the nm range. In figure 3 you can see the result of programmed 0 nm steps measured by the interferometer. The stage is not moving in regular 0 nm steps but the mirror is pushed in this range. The measurement is limited by the interferometer resolution which was 5 nm. This amazing resolution of the stage is not possible with any axis.

On the other hand the results of a PLS-85 stage shown in figure -3 can be improved by driving the stage in closed loop. One of the advantages of our SMC-controllers is the intelligent control of the stage by using the V peak peak interface of a high resoluting scale. In figure_5 the measurement of a LS-110 stage with a linear scale is shown – the resolution of 50 nm is visible in well defined levels. Even changing the load of the stage doesn´t disturb the positioning. The resolution is limited by the scale system, so using a 2 nm scale enables resolutions of 2 nm influenced by enviromental disturbances like temperature drifts (example: a change of the temperature by 0.0 degree is resulting in expansion of about 0 nm). For these applications we designed our ultraprecision stages UPM-160 and NPE-200 or customized granite based setups using Heidenhain Zerodur scales.

Even with DC servo motors you are not able to drive in the low velocity range in such a linear and smooth way Figure_6 shows the measurement of a PLS-85 stage with linear scale (with encoder resolution of 0 nm). The speed of 100 nm/s was choosen, so 360 µm within one hour or about 10 mm per day. The movement is very smooth. Zooming the first 100 nm travel is shown figure_7.
Here it is important to realize that the interferometer resolution is 5 nm which results in the step-wise diagram. These steps are not coming from the stage, the movement is much more smooth. But its very important to understand that the speed is linear and variations are in the 1 nm/s range which is amazing for a loaded stage with several mm travel range. Also here the results can be improved by using a better encoder resolution. Figure_7 shows an open-loop result of a UPM-160 stage controlled with a speed 45 nm/s. Figure_8 shows zoom-in of figure_7. The movement is very linear! The interferometer resolution is limiting the interpretation in the picometer per second scale.

between wanted and measured position Within a travel range of 100 mm the LS-180 stage is positioning with a positioning error of 32 µm. The measurement shows both travel directions, so that the bidirectional repeatability, which is depending of the backlash, can be seen with a value of .78 µm. For some applications it is important to improve the absolute positioning, whereas the bidirectional repeatability is not important. The problem can be solved by using the deviation measurement for a position correction inside the SMC controller (see option position correction at e.g. SMC corvus). The result is presented in figure_10 which looks crowdy at first. But please realize that the deviation scale is 3 µm. The deviation is minimized by a factor of 0 and without gradiating slope. A cost effective method to get rid of system positioning errors. By using a linear scale system the repeatability and accuracy can be improved further on