We propose a method to determine the required performances of the positioning mechanics of the optical elements of a
beamline. Generally, when designing and specifying a beamline, one assumes that the position and orientations of the
optical elements should be aligned to its ideal position. For this, one would generally require six degrees of freedom per
optical element. However, this number is reduced due to symmetries (e.g. a flat mirror does not care about yaw).
Generally, one ends up by motorizing many axes, with high resolution and a large motion range. On the other hand, the
diagnostics available at a beamline provide much less variables than the available motions. Moreover, the actual
parameters that one wants to optimize are reduced to a very few. These are basically, spot size and size at the sample,
flux, and spectral resolution. The result is that many configurations of the beamline are actually equivalent, and therefore
indistinguishable from the ideal alignment in terms of performance.We propose a method in which the effect of
misalignment of each one of the degrees of freedom of the beamline is scanned by ray tracing. This allows building a
linear system in which one can identify and select the best set of motions to control the relevant parameters of the beam.
Once the model is built it provides the required optical pseudomotors as well as the requirements in alignment and
manufacturing, for all the motions, as well as the range, resolution and repeatability of the motorized axes.