An absolute linear scale carries a code that identifies position within a defined travel. A multi-track code or a coded reading window is paired with the matching detector and decoder.
Choose it when the axis must identify its current position at startup without first moving to a reference mark. The sensing window must contain enough valid code to determine the address.
An absolute address identifies a region; a fine periodic track may resolve position inside it. Both code uniqueness and coarse/fine registration matter in the combined reader.
Code sequence, reading-window length, fine-track registration, active travel, reading direction, absolute zero and mounting references can be coordinated.
A patterned glass scale with the selected measuring length, code or grating layout, reference marks and component inspection records.
| Substrate | B270 / K9 / soda-lime glass; fused silica by request |
|---|---|
| Pattern medium | Chromium-on-glass or a specified clear/opaque pattern |
| Photolithographic line-width tolerance | ±0.2 µm |
| Mechanical cutting accuracy | ±0.02 mm |
| Thickness | ≥0.4 mm |
| Total thickness variation (TTV) | ≤2 µm |
| Surface figure | λ/4 |
| Optical mode | Transmissive or reflective, matched to the readhead wavelength |
| Active scale length | Defined by the approved drawing |
| Reference-mark position | Defined from the mounting datum |
A disc or scale is the passive optical reference inside a larger encoder system. The artwork, readhead and mounting datum must be designed together so that the manufactured pattern is read in the intended direction and at the intended contrast.
| Property | Specification |
|---|---|
| Pattern architecture | Coded glass scale for absolute linear-position identification |
| Code definition | Approved code sequence, reading window, track order and absolute zero |
| Critical geometry | Track registration, active length and position relative to the mounting datum |
| Readhead interface | Decoder convention, optical window and minimum feature size |
System resolution and system accuracy are separate from the manufactured CD and outline values. Interpolation, bearing runout, eccentricity, alignment and electronics contribute to the final error budget.
Custom coded glass scales for absolute linear-position sensing, using a pattern sequence designed for the selected readhead.
The decoder matches the current optical word or sequence window to the approved coordinate map. Repeated codes must not create ambiguous addresses within the required travel.
Define a coded window and a unique coordinate mapWhen a periodic fine track is added, its phase relationship to the absolute address must be defined at transitions and after a direction reversal.
Verify transitions and coarse/fine registrationVerify the full code sequence, code-to-datum position and critical feature placement across the active length.
| Property | Specification |
|---|---|
| Pattern dimensions | Measured CD at agreed locations; report nominal and measured values |
| Outline geometry | Outer diameter, bore or scale length checked to the mechanical drawing |
| Registration | Pattern origin, track-to-bore or pattern-to-datum position |
| Optical defects | Clear/opaque defects, broken lines, pinholes and contamination |
| Traceability | Drawing revision, lot identification, inspection method and report |
| Property | Specification |
|---|---|
| Geometry | Disc outer diameter and bore, or scale length, width and thickness |
| Pattern data | Approved artwork or code map, line count/pitch, polarity and revision |
| Optical interface | Transmissive or reflective mode, wavelength, contrast and readhead gap |
| Datum scheme | Mechanical datum, pattern origin, index/zero position and orientation |
| Acceptance record | CD measurement, cutting dimensions, registration, defects and report format |
Specify substrate material and geometry together with the operating wavelength. For transmissive reading, define clear-area transmission and opaque-track density. Reflective reading also needs the high/low reflectance pair and illumination geometry. Optical contrast must match the readhead, not only the appearance of the part.
Compare glass scale readout and encoding optionsQuality & Inspection PhotolithographyPosition-coded scales matched to a specified decoder.
Absolute linear scales identify position along the scale using a defined optical code.
Specify the complete sequence, reading window, track order, absolute zero and active length so a local observation maps to position.
Code sequence, active length, reading direction, zero, track geometry and decoding convention.
No. Absolute identification also needs the code sequence and decoding relationship. Pitch defines local geometry but cannot replace the code map.