Track relative rotation
Repeated transitions let the encoder electronics accumulate shaft movement from an established reference.
Incremental Encoder Discs
Optical tracks for rotary feedback
An incremental encoder disc carries periodic optical tracks that a readhead converts into motion signals. It supports angular displacement and speed feedback, with an index track available for a defined reference position.
The disc supplies a repeating angular reference to a matched optical readhead. A/B tracks establish direction and relative movement; an index track can establish a repeatable zero.
- Pattern
- A/B + Z
- Count definition
- Periods / pulses / counts
- 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.
Determine direction
A/B track phase lets compatible electronics distinguish clockwise and counterclockwise movement.
Return to a known zero
A drawing-defined index track supplies a repeatable angular reference after homing.
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 |
| PropertyTrack layout | SpecificationRepeated radial divisions with optional A/B, index and commutation tracks |
| PropertyCount convention | SpecificationState whether the value means optical periods, pulses per revolution, quadrature counts or interpolated output |
| PropertyCritical geometry | SpecificationLine count, angular pitch, duty cycle, track radius, phase and index datum |
| PropertySystem boundary | SpecificationThe glass disc is passive; the readhead and electronics determine the electrical signal and interpolation |
Component tolerances do not state the accuracy of the complete encoder. Readhead geometry, eccentricity, bearing motion, interpolation and installation also contribute to system error.
When to choose incremental coding
Choose it when the controller counts motion from a reference and the machine can establish that reference at startup. The periodic track and index layout must match the reader.
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.
- Servo-motor shaft position and speed feedback
- Rotary stages, indexing tables and angular positioning mechanisms
- Robot joints and automated motion-control equipment
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.
Common questions
Does the disc need separate A and B tracks?
Not in every architecture. Some readers generate phase-shifted channels from one periodic track using offset sensing fields; others use distinct tracks. The reader layout determines the artwork.
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
Check angular pitch, line width, duty cycle, index position and code-track concentricity relative to the bore. Where required, verify A/B phase geometry, zero-angle registration and accumulated angular error across the active track.
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
Incremental encoder discs provide repeating radial light-and-dark tracks for relative angle and speed sensing.
Separate optical periods per revolution, A/B phase arrangement and the Z index. State optical line count independently of electronically multiplied counts.
Information for your inquiry
Period count, reading radius, duty cycle, index geometry and angle, bore and readhead layout.
Does line count equal counts per revolution?
Controller multiplication and interpolation determine reported counts. State the optical period count on the drawing and the electronic counting convention in the system specification.