= Physik Instrumente
{c}
<Physik Instrumente> makes precision motion equipment used in scientific apparatus. Its archived M-222–M-226 <motorized micrometer> family illustrates a concrete measurement issue: motor-shaft encoder counts and screw geometry give a <design resolution>, while actual motion also depends on mechanics and loading.<High Precision Actuators with Closed-Loop Feedback Motor by Physik Instrumente>[M-221–M-226 description: micrometer screw, gearhead and motor-shaft encoder]{ref}
For a worked reconstruction from the manufacturer's M-222.20 specifications, use screw pitch $p=0.5\,\mathrm{mm}$ per revolution, gear reduction $G=(31/9)^4$ and 60 encoder counts per motor revolution. The nominal linear increment is
$$
\delta x=\frac{0.5\,\mathrm{mm}}{60(31/9)^4}\simeq0.0592\,\mathrm{\mu m}=59.2\,\mathrm{nm}.
$$
This agrees with the listed <design resolution> of $0.059\,\mathrm{\mu m}$. The same table separately lists <minimum incremental motion> of $0.1\,\mathrm{\mu m}$ and <backlash> of $5\,\mathrm{\mu m}$ for that model.<High Precision Actuators with Closed-Loop Feedback Motor by Physik Instrumente>[Technical-data table, M-222.20 column; design resolution, minimum incremental motion, backlash, encoder resolution, drive screw pitch and gear ratio]{ref}
Thus a command corresponding to one encoder count is not evidence for an independently resolved 59 nm movement of the load. The listed <backlash> corresponds to roughly 84 nominal counts, illustrating why reversing direction is a different test from continuing in one direction. These are calculations from a legacy specification, not new performance measurements. In an assembled instrument, compare commanded and independently measured displacement, including reversals, to establish the usable response and its <measurement uncertainty>.
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