Follow the pattern through manufacture
The component route links glass preparation, coating, photoresist preparation, exposure or direct writing, development, film etching, resist removal, outline machining and inspection. The order of cutting relative to patterning depends on the part and fixture. Keep the artwork revision and mechanical datum connected through the route so the final bore or edge locates the intended optical reference.
Separate critical dimension from placement
Line width and clear width describe feature size. Edge location, angular pitch and track registration describe placement. A uniform etch bias can change width while leaving some centre locations similar; a placement error can shift a correct-width feature. Evaluate these quantities separately. At radial tracks, give the reading radius and whether the measurement uses edges or feature centres.
Inspect the full reference geometry
A rotary pattern needs the correct period count or code map, track radii, last-to-first closure, index or zero location and pattern-to-datum position. A linear pattern needs local pitch, accumulated intervals, usable travel and reference-mark position. Multi-track codes need relative registration and valid boundary geometry. A sampled CD result does not establish full-circle angular error or full-travel position error.
| Feature | Component inspection quantity |
|---|---|
| Periodic rotary track | Period count, angular spacing, clear fraction and closure. |
| Absolute code tracks | Code map, track registration, transition locations and zero. |
| Linear grating | Local pitch, accumulated interval error and reference-mark coordinates. |
| Mounting geometry | Bore or edge datum, outline, thickness and pattern registration. |
Measure contrast at the actual optical conditions
Transmission acceptance specifies clear-region transmission and blocked-region leakage or optical density at the operating wavelength. Reflection acceptance specifies both reflectance levels at the illumination and collection geometry. Film uniformity, unintended pinholes, broken lines and contamination can affect the signal. An unintended coating pinhole is a defect; an index window is a designed feature and needs its own geometry.
Select the glass with the mounted assembly in mind
Material expansion, substrate thickness, spectral transmission and coating behaviour must be considered with the hub, support and temperature range. For uniform linear expansion, ΔL ≈ αLΔT; a 100 mm span with α = 9 × 10⁻⁶/K changes by about 18 µm over 20 K. That assumed coefficient is a calculation input, not a property assigned to every glass. Uniform expansion of a centred radial pattern does not by itself change its angular divisions, but it can change read radius, gap and mounting stress.
Distinguish component inspection from installed validation
Component records identify the drawing revision, measured features, reference conditions and method. Installed validation adds shaft and bearing runout, sensing gap, real waveform or code transitions, speed and temperature. A declared encoder IP rating belongs to the enclosure; a maximum speed belongs to the supported rotating assembly and signal chain. Dynamic balance concerns the rotating part and hub together where required. Keep these system checks distinct from glass dimensions.
Release geometry, then preserve the optical surface
A production DWG defines units, pattern datums, mounting geometry, active radii or travel and critical tolerances; a controlled code map defines the sequence. Match geometry and revisions when data are converted for the writer. Handle the part at permitted edges, protect the patterned surface and use a cleaning method compatible with the coating, bonded materials and contamination. Solvent compatibility is specific to that construction, so there is no universal solvent or service-life rule for all encoder discs.