Meaning
Geometric alignment errors quantify the distance between the actual position of a component and its nominal coordinate after calibration and correction algorithms have been applied. In precision metrology, residual spatial offset represents the remaining positional error that cannot be resolved by standard feedback systems. This offset arises from finite sensor resolution and mechanical hysteresis.
It acts as a benchmark for comparing the ultimate accuracy of different motion stages and positioning systems.
Error Source
Non-repeatable mechanical errors and electrical noise in the encoder signals prevent perfect alignment. Thermal expansion of the stage during long duty cycles shifts the reference frame. These factors combine to create a randomized distribution of positioning errors that cannot be pre-programmed out of the motion controller.
Metrology Verification
Laser interferometers measure the position of the moving carriage at multiple points across its full travel. Comparing these measurements with the internal encoder readings reveals the spatial variation. This step is conducted in a temperature-controlled cleanroom to prevent air turbulence from distorting the laser beam.
Assembly Mitigation
Optomechanical stages use low-drift materials like Zerodur to minimize thermal distortion. Symmetric mounting configurations help to distribute mechanical stress evenly and prevent twisting. Fine-tuning the feedback loop gains can also reduce the final offset.
