Identify position after startup
A compatible reader identifies the current coded sector without first accumulating repeated increments.
Absolute Encoder Discs
Absolute position encoded in glass
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.
Multiple optical tracks form a code word for each angular sector. The approved code map, bit order, reading direction and zero datum must match the readhead and decoder.
- Code options
- Gray / binary / custom
- Position reference
- Absolute sector
- Line-width tolerance
- ±0.2 µm
- Mechanical cutting
- ±0.02 mm
What the optical pattern does
The code disc supplies a passive optical reference. The readhead, electronics, mechanical mounting and control algorithm determine how that reference becomes a usable position signal.
Retain a defined angular map
The complete code table ties every sector to an approved angular-position convention.
Match existing decoder logic
Track order, polarity and direction can be defined around an established optical and decoding architecture.
Glass, pattern and code
Common manufacturing capability and product-specific code geometry are shown together. Final dimensions and acceptance values follow the approved drawing.
| Property | Specification |
|---|---|
| PropertySubstrate | SpecificationB270 / K9 / soda-lime glass; fused silica by request |
| PropertyPattern medium | SpecificationChromium-on-glass or a specified clear/opaque pattern |
| PropertyPhotolithographic line-width tolerance | Specification±0.2 µm |
| PropertyMechanical cutting accuracy | Specification±0.02 mm |
| PropertyThickness | Specification≥0.4 mm |
| PropertyTotal thickness variation (TTV) | Specification≤2 µm |
| PropertySurface figure | Specificationλ/4 |
| PropertyOptical mode | SpecificationTransmissive or reflective, matched to the readhead wavelength |
| PropertyMaximum disc diameter | Specification1500 mm |
| PropertyPattern-to-bore concentricity | Specification≤0.02 mm |
| PropertyPattern architecture | SpecificationConcentric coded tracks matched to the optical readhead and decoder |
| PropertyCode definition | SpecificationGray code, natural binary or a supplied custom code map |
| PropertyCritical geometry | SpecificationBit count, track radii, track registration and code-zero datum |
| PropertyReadhead interface | SpecificationReading direction, wavelength, optical window and transition handling |
Component tolerances do not state the accuracy of the complete encoder. Readhead geometry, eccentricity, bearing motion, interpolation and installation also contribute to system error.
Choose the matching code family
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.
Supply the actual readhead geometry and decoding convention with the drawing. Matching only the outside diameter is not enough to make two code discs interchangeable.
- Absolute angular feedback for servo and positioning systems
- Robot joints and mechanisms that must identify the current sector
- Surveying and precision instruments with a defined angular code map
Match the disc to the reader
Substrate, chromium pattern, clear and opaque regions, outer geometry and mounting references are reviewed together. Transmissive and reflective reading require different optical definitions.
Substrate and outline
Select the glass, diameter, bore, thickness, edge finish and mounting datum for the mechanical assembly.
Optical contrast
Define clear-area transmission or the reflective contrast pair at the actual readhead wavelength and geometry.
Pattern registration
Relate tracks, transitions and zero marks to the bore or another stable mechanical datum.
Acceptance and drawing inputs
Confirm these items after the code type and core geometry are selected. They define how the finished disc is manufactured, checked and documented.
Inspection and acceptance
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What to provide in the drawing or inquiry
- Outer diameter, bore, thickness, edge format and mechanical datums
- Complete track drawing or code map, polarity and viewing direction
- Track radii, critical line widths, pitch and registration requirements
- Optical mode, operating wavelength, readhead gap and required contrast
- Zero datum, rotation direction and relationship to mounting features
- Inspection items, report format, quantity and drawing revision
Send the complete code map, mechanical drawing and readhead requirements for manufacturing and inspection review.
Discuss your encoder discTechnical reading
Selection notes
Absolute 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.
Information for your inquiry
Bit count, full code table, track radii and widths, readhead window, zero and installation datum.
Can a Gray-code disc replace a binary-code disc directly?
Their code sequences and transition rules differ. A change also requires the matching decoder convention, readhead geometry and control logic.