An absolute optical disc carries a position code that the matching reader decodes at the current angle. Multi-track Gray and natural-binary patterns are available code arrangements; custom code sequences use their own reading windows and decoding rules.
Choose it when the instrument needs the current single-turn angle after startup without first travelling to an index. The readable code range and zero direction belong to the disc and decoder together.
Absolute describes position identification. Gray, natural binary and pseudo-random sequences describe the code architecture. Turn counting requires additional system mechanisms beyond a single-turn disc.
Code map, bit or sequence arrangement, track radii, fine-track relationship, reading direction, code zero and mounting geometry can be defined as one layout.
A patterned glass disc with the selected track layout, mounting geometry and component inspection records. The light source, readhead, decoder and shaft assembly are defined by the instrument design.
| 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 |
| Maximum disc diameter | 1500 mm |
| Pattern-to-bore concentricity | ≤0.02 mm |
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 angular tracks matched to the optical readhead and decoder |
| Code definition | Gray code, natural binary or a supplied custom code map |
| Critical geometry | Bit count, track radii, track registration and code-zero datum |
| Readhead interface | Reading direction, wavelength, optical window and transition handling |
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.
Multi-track glass encoder discs encode absolute angular position through an approved Gray-code, natural-binary or custom code map. Provide the bit count, track order, reading direction, zero datum and sensor geometry together.
| Product type | When to choose it |
|---|---|
| Gray Code Encoder Discs | Choose it for a decoder that expects a specified Gray sequence, track order and reading direction. It reduces simultaneous bit changes at neighbouring code boundaries. |
| Binary Code Encoder Discs | Choose it for an existing binary-weighted reading architecture with a defined method for sampling and resolving code transitions. |
Each sampled track contributes to the position word. Track order, polarity and the observed side determine how the word is interpreted.
Compare Gray, natural binary and coded-window layoutsA coarse absolute address can be combined with a periodic fine track. Their angular registration is part of the decoding geometry.
Understand single-turn and multi-turn positionExplore code families for direct angular-position identification.
Code patterns for servo systems requiring direct position identification.
Compare absolute code architectures for direct angular identification.
CD is checked against the approved artwork at defined critical features. The finished outline is checked against the mechanical drawing and the tolerance stated in Product configuration. Disc products are additionally checked for pattern-to-bore concentricity; linear scales are checked for pitch, accumulated interval error and reference-mark position.
| 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 transmissive and reflective readoutAbsolute encoder discs map angular positions to readable code words using a defined track pattern.
Supply the code map, track and bit order, read direction and zero reference together. Gray, binary and custom codes require their own definitions.
Bit count, full code table, track radii and widths, readhead window, zero and installation datum.
Their code sequences and transition rules differ. A change also requires the matching decoder convention, readhead geometry and control logic.