Position-word transitions
One changing bit reduces the combinations that can be sampled while crossing a valid boundary. It does not make every reading immune to noise or misalignment.
Compare a four-bit binary and Gray transitionGray Code Encoder Discs
Absolute position, encoded in glass.
Patterned glass encoder componentCustom formats
Product selection
What it is and what it does
A Gray-code disc arranges concentric optical tracks so adjacent valid position words differ by one bit. The reader samples those tracks and converts the Gray word into the position representation used by the controller.
When to choose it
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.
How it differs from related products
Natural binary may change several bits at one boundary. Gray changes one bit between adjacent valid words, but detector thresholds, registration and code conversion still affect the boundary reading.
What can be customised
Bit count, approved Gray sequence, bit-to-track order, code-zero angle, optical polarity and mounting datums can be matched to the decoder.
What you receive
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.
Specifications and inspection
Product configuration
| 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 |
Pattern architecture and system fit
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 | Multi-track Gray-code sequence for absolute angular position |
| Code definition | Bit count, approved sequence, track order and angular reading direction |
| Critical geometry | Track width, track-to-track registration and code-zero datum |
| Readhead interface | Optical spot size, threshold and wavelength matched to the decoder |
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 using a Gray-code sequence for absolute angular-position sensing with a compatible optical readhead and decoder. Adjacent code words ideally change by one bit, reducing ambiguity at a sector boundary when the optical channels are sampled during a transition.
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Reduce ambiguity at adjacent positions
Decoder compatibility
The same bit count can represent different sequences, directions or track orders. The complete code map fixes which angle each word represents.
Define bit order, polarity and angular zeroInspection and acceptance
Verify the code sequence against the approved map, inspect angular transition positions, track-to-track registration and pattern-to-bore concentricity. For critical systems, define how code-word errors and missing or bridged features are reported.
| 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 |
What to include in the drawing
| 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 |
Substrate & optical configuration
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 readoutQuality & Inspection PhotolithographyWhere this product is used
Absolute angular code for a readhead designed for this encoding.
Absolute angular coding with one-bit changes between adjacent ideal code positions.
Absolute code tracks for compatible angular readout systems.
Parallel Gray-code tracks for a matching angular readhead.
Selection notes
Gray-code absolute discs arrange a Gray sequence across optical tracks to identify absolute angular position.
Adjacent standard Gray words change one bit. The artwork must also define bit order, increasing-angle direction and the transition across zero.
Information for your inquiry
Bit count, complete sequence, inner-to-outer bit order, rotation direction, zero and readhead window.
Is bit count enough to define the disc?
The same bit count can use different track order, reading direction and zero position. The complete map establishes how the read word corresponds to angle.