A better way is to actuallymeasure commanded vs. actual steps, with traceable, non-contacting external metrology, such as laser interferometers. Sometimes it is suggested to skip this somewhat elaborate process and just excite a frequency in the positioning stage using the positioning systems’s internal sensor and frequency domain measurements to determine resolution and stability. Let’s think about what it means for the above example.
What if a very weak A/C voltage, a continous sinewave, equivalent to 0.1 nm peak-peak motion (red trace in the graph above) was fed into the motor input, and the resulting stage vibration were analyzed using FFT (Fast Fourier Transform) techniques. Would the specific excitation frequency stand out in the random noise spectrum? Very likely.
Would the result indicate the positioning stage be able to execute individual, repeatable steps of 0.1nm magnitude? Unlikely. Here is another example to put this method in perspective.
If a sinewave is played on a smart phone speaker at very low volume, it will cause nanometric vibration on the phone’s screen. The motion can be detected by a laser or even by the phone’s internal accelerometers. When FFT-analyzed, the frequency of the specific sinewave will show up in the spectrum.