Optical Encoder Disc

Our high-precision encoder discs and linear scales are designed for motion control systems requiring absolute accuracy. We utilize chrome-on-glass technology to produce patterns with sub-micron edge definition.
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Manufacturing / Description / Technical Details / Custom Services / Industrial Applications / Use Case / FAQ

Product in details

Optical Encoder Disc Manufacturing

Selba’s optical encoder discs and linear scales are precision photolithographic components that convert rotary or linear motion into high-accuracy electrical signals for motion feedback, control, and measurement applications. Manufactured entirely to customer specification — with no standard catalogue products — they are available on glass, film, and aluminium substrates across diameters from 20 mm to 200 mm, with discs up to 290 mm on special request. Graduation patterns are produced at up to 50,800 dpi, delivering fine-pitch lines with consistent width, sharp edge definition, and micron-level positional accuracy across the full pattern area — accuracy that translates directly into encoder system resolution and measurement performance. Glass substrates provide the dimensional stability and low thermal expansion required to preserve pattern geometry and optical contrast across operating temperature ranges, while aluminium substrates and aluminium-coated film variants address weight-constrained and high-reflectivity applications respectively. Chromium and antireflective chromium coatings are selected to match the optical contrast and signal-to-noise requirements of the customer’s readhead configuration. Long-term reliability is supported by the integration of photolithographic patterning and glass machining within a single facility — eliminating tolerance stack-up between graduation pattern and mechanical geometry, and ensuring that the dimensional, optical, and structural performance of the finished disc remains stable across the service life of the encoder system it supports.

Motion Feedback

Product Description

Selba manufactures incremental and absolute encoder discs and linear scales on glass and film substrates, forming the optical reading element in rotary and linear encoder systems. Our photolithographic process ensures consistent line widths, pitch accuracy, and edge definition — parameters that directly determine encoder resolution and signal quality. Glass substrates are selected for dimensional stability and thermal resistance, while film offers a cost-effective alternative. Custom graduation patterns are developed to client specifications, including track layout, index marks, and aperture geometry.
  • Industrial Automation & Robotics
  • CNC Machining & Precision Manufacturing
  • Aerospace & Defense Systems
  • Medical Devices & Imaging Systems
Selba's optical encoder disc

PRODUCT SPECIFICATIONS

Technical Details

Every Dimension. Every Specification. No Standard Catalogue.

Selba designs and manufactures incremental and absolute encoder discs and linear scales entirely to customer specification — there are no standard products. Graduation patterns, track layouts, index marks, and aperture geometry are defined in close collaboration with the customer’s engineering team to match the exact resolution, signal format, and mechanical interface of the target encoder system.
Encoder discs are available on glass, film, and aluminium substrates across a continuous diameter range from 20 mm to 200 mm, with discs up to 290 mm available upon special request. Glass substrates are specified for applications demanding high dimensional stability and thermal resistance. Film substrates offer a cost-effective alternative for less demanding environments, while aluminium — available in sheets as thin as 0.2 mm — addresses applications where low weight and compact assembly integration are priorities. Aluminium-coated film variants are also available for applications requiring high reflectivity combined with cost-competitive production.
Linear scales are produced on glass and film with pitch accuracy and edge definition governed by Selba’s high-resolution laser photoplotting process, operating at up to 50,800 dpi. Pattern fidelity across the full graduation length is verified as part of the standard inspection protocol.

Substrate Options

Sodalime / Quartz /
Film / Aluminium

Diameter Range

20–200 mm
(up to 290 mm on request)

Plotting Resolution

Up to 50,800 dpi


Aluminium Thickness

Substrates: < 0.1 mm (glass) / 0.2 mm (aluminium)

Linear Scale Base

Controlled in-house


Patterning

Chromium (Standard & AR) /
Film Emulsion

PRODUCT SPECIFICATIONS

Custom Services

From File Review to Finished Component.

Selba’s encoder disc and linear scale service covers the full production workflow, beginning upstream of manufacturing. Every order — whether a single prototype or a production batch — starts with a structured file review carried out by Selba’s R&D experts. Submitted artwork is assessed against the intended substrate, photolithographic process, and mechanical constraints before production is initiated, ensuring that design intent is preserved through to the finished component.
For prototyping and first-article validation, Selba’s integrated photolithography and glass machining capabilities operate within a single facility, allowing rapid turnaround without subcontractor dependencies. As programmes mature into small series or mass production, the same process parameters, substrate materials, and inspection protocols are maintained across batches, providing the repeatability that encoder system integrators require for consistent downstream performance. Full traceability is maintained throughout the production chain, and engineering support remains available at every stage for customers refining track geometry, exploring alternative substrate materials, or scaling production volumes.

R&D File Review & Validation
Prototyping to Production
Rapid Prototyping

CUSTOM & MASS PRODUCTION

Industrial Applications

Technical Details

Selba produces encoder discs and linear scales on sodalime glass, quartz (fused silica), film, and aluminium substrates — each selected to match the dimensional stability, thermal, and optical requirements of the target application. Sodalime glass (≈9 ppm/°C) suits the majority of industrial and instrumentation applications, while quartz (≈0.55 ppm/°C) is specified where thermal stability and UV transmission are critical. Graduation patterns are defined photolithographically in standard or antireflective chromium coatings, the latter reducing back-reflection in high-resolution and close-working-distance readhead configurations. Disc diameters span a continuous range from 20 mm to 200 mm — up to 290 mm on special request — with substrate thicknesses down to 0.1 mm on glass and 0.2 mm on aluminium, all defined to customer specification with no standard catalogue formats. Precision is controlled across three levels: graduation line placement and pitch accuracy held to micron-level tolerances via laser photoplotting at up to 50,800 dpi; external geometry and mounting features machined to specification with custom in-house tooling; and pattern-to-geometry registration controlled end-to-end within a single facility, eliminating tolerance stack-up between patterning and machining. Patterned surface quality — coating uniformity, edge sharpness, and freedom from defects — is verified by optical inspection before every disc is released, alongside substrate flatness and machined edge condition, ensuring that both the optical and mechanical performance of the finished component meet the requirements of the encoder system it serves.

Industrial Applications
Selba’s optical encoder discs and linear scales serve demanding motion feedback and position measurement applications across a wide range of industries and technology platforms. In industrial automation and robotics, they provide the closed-loop feedback governing positioning repeatability, path accuracy, and multi-axis coordination in servo drives, conveyor systems, articulated arms, and collaborative robot joints. In CNC machining centres, encoder discs and linear scales deliver the high-resolution angular and linear position data that determines cutting accuracy, surface finish quality, and dimensional repeatability across production runs. Aerospace platforms specify quartz substrate discs for their exceptional thermal stability across extreme temperature ranges, supporting flight control, gimbal positioning, antenna tracking, and deployable structure sensing in airborne and space environments. Medical device applications — including surgical robotics, CT and radiotherapy systems, and laboratory automation — demand the sub-millimetre positional accuracy and batch-to-batch consistency that Selba’s controlled production process and full traceability documentation support. In nanoprinting and nanofabrication equipment, where stage positioning is measured in nanometres, graduation pitch error and signal noise in the encoder disc translate directly into feature placement uncertainty in the printed pattern — making encoder disc quality inseparable from system patterning capability. Photonic systems, including laser beam steering platforms, fibre alignment stages, and interferometers, rely on encoder feedback for the sub-arcsecond angular and nanometre-level linear positioning that governs optical alignment, beam pointing, and measurement repeatability, where signal purity and pattern quality are as critical as positional accuracy.
Custom Services
Selba operates as a fully custom precision manufacturer — there are no standard products, and every encoder disc, linear scale, photomask, calibration plate, or glass component produced leaves the facility to a specification defined in collaboration with the customer. Custom graduation patterns, track layouts, index mark configurations, and substrate formats are developed from the ground up to match the exact optical, mechanical, and dimensional requirements of the target application, with Selba’s R&D team reviewing every submitted artwork file before production is initiated — verifying design integrity, identifying process constraints, and ensuring that the geometry is optimised for the chosen substrate and photolithographic process. This engineering engagement begins at the earliest stage of development: for customers at the prototyping phase, Selba’s integrated photolithography and glass machining capability enables fast first-article turnaround without subcontractor dependencies, allowing design iterations to be validated quickly and cost-effectively. As programmes mature, the same process parameters, substrate materials, and inspection protocols applied during prototyping are maintained through small series and into volume production, ensuring that performance achieved at the development stage is fully reproducible at scale. Throughout the programme lifecycle — from initial design review through first article, qualification, and series supply — Selba’s engineering team remains directly accessible, supporting customers with substrate selection guidance, coating specification, design-for-process optimisation, and artwork revision management, providing a technically grounded long-term partnership rather than a transactional supply relationship.

Use Case

Developing a 200 mm Glass Encoder Disc for a High-Resolution Rotary Encoder System

“Selba’s R&D and glass machining teams developed a dedicated machining process incorporating a chamfered edge profile around the full disc perimeter. “
Read full case study

FAQ

Frequently asked questions

What is an optical encoder disc?

An optical encoder disc is the core optical element of a rotary encoder system, responsible for converting mechanical rotation into a high-resolution electrical signal. It consists of a precision substrate — typically glass, film, or aluminium — carrying a photolithographically produced graduation pattern of opaque and transparent segments arranged with defined geometry around its circumference. Mounted on a rotating shaft, the disc passes through a fixed optical readhead assembly comprising a light source, collimating optics, and a photodetector. The graduation pattern modulates the light reaching the detector as the disc rotates, generating the periodic signal from which the encoder electronics derive angular position, rotational velocity, and direction of travel. The disc is the element in the encoder system where the fundamental limits of resolution, accuracy, and signal quality are set — making the photolithographic precision of its graduation pattern the most critical variable in encoder system performance.

How does an optical rotary encoder work?
An optical rotary encoder works by reading a precision graduation pattern on a rotating disc to produce a continuous electrical signal proportional to angular position or velocity. As the disc rotates, its graduation pattern — a precisely defined sequence of opaque and transparent segments produced photolithographically at a controlled angular pitch — passes through the optical readhead. The readhead projects light through or onto the graduation, and the alternating opaque and transparent segments modulate the intensity of light reaching the photodetector, generating a periodic electrical signal with a frequency proportional to rotational speed and a period corresponding to the graduation pitch. Incremental encoders generate a repeating signal from which angular displacement is accumulated relative to a known reference position, typically established by a dedicated index mark on the disc. Absolute encoders carry multiple concentric graduation tracks, each encoding a binary or Gray-code bit, which together uniquely identify the angular position of the disc at any point within one revolution — or, in multi-turn absolute systems, across multiple revolutions — without requiring a reference return at power-up. System resolution is determined by the graduation pitch on the disc combined with the electronic interpolation factor applied by the readhead signal processor.
What industries use optical rotary encoders?
Optical rotary encoders are used across virtually every industry where controlled or measured rotational motion is involved. In industrial automation and robotics, they are the primary feedback element in servo motor drives, providing the closed-loop position and velocity data that governs motor torque, speed regulation, and multi-axis coordination in manufacturing equipment, conveyor systems, and articulated robotic arms. CNC machining centres use rotary encoders on spindles and rotary axes to control cutting speed, angular indexing, and coordinated contouring between axes. In aerospace, rotary encoders serve in flight control surface actuation, gimbal and antenna positioning, and rotary joint sensing in deployable satellite structures, where thermal stability and long-term reliability without maintenance access are paramount. Medical devices — including surgical robotic systems, CT scanner gantries, radiotherapy platforms, and motorised diagnostic equipment — rely on rotary encoder feedback for the angular positioning accuracy that directly determines procedural precision and patient safety. Scientific and photonic instrumentation, including telescope mounts, spectrometers, polarimeters, and laser beam steering systems, use rotary encoders for the sub-arcsecond angular positioning that optical alignment and measurement repeatability demand. In semiconductor and nanofabrication equipment, rotary encoders govern the motion of precision stages and wafer handling systems where angular error translates directly into pattern placement uncertainty.
What materials are used for rotary encoder discs?

The substrate material of a rotary encoder disc determines its dimensional stability under thermal and mechanical load, its compatibility with the photolithographic patterning process, and its structural integrity across the operating lifetime of the encoder system. Selba produces rotary encoder discs on four substrate families, selected according to the specific requirements of the application. Sodalime glass is the standard substrate for the majority of industrial and instrumentation encoder discs, offering a well-controlled thermal expansion coefficient of approximately 9 ppm/°C, good surface flatness, and full compatibility with chromium and antireflective chromium photolithographic patterning — delivering the balance of dimensional stability, optical performance, and cost that most encoder applications require. Quartz (fused silica), with a thermal expansion coefficient of approximately 0.55 ppm/°C, is specified for encoder discs deployed in demanding metrology, aerospace, photonic, and scientific instrumentation applications where thermal dimensional change in the disc would introduce systematic angular error in the encoder output. Film substrates provide a cost-effective alternative for applications where glass-grade dimensional stability is not a requirement, and are well suited to prototyping programmes and cost-sensitive production environments. Aluminium substrates — available in sheets as thin as 0.2 mm — serve applications where low rotational inertia, light weight, and compact mechanical integration take priority, while aluminium-coated film variants address systems requiring high reflectivity graduation surfaces alongside cost-competitive production volumes.

What level of precision can be achieved with optical rotary encoder discs?
The precision of a rotary encoder system is ultimately bounded by the accuracy of the graduation pattern on the disc — specifically by the consistency of graduation pitch, the sharpness of line edges, and the positional accuracy of each graduation line relative to the disc’s mechanical centre of rotation. Selba’s rotary encoder discs are produced using high-resolution laser photoplotting at up to 50,800 dpi, enabling fine-pitch graduation patterns with consistent line widths, sharp edge definition, and micron-level positional accuracy across the full disc circumference. At the photolithographic level, line placement error and pitch non-uniformity are held to the tolerances required by the encoder system’s angular accuracy specification — tolerances that are verified by optical inspection before every disc is released. At the mechanical level, Selba’s integrated glass machining operations control disc diameter, thickness uniformity, and the concentricity between the graduation pattern and the disc’s mechanical mounting datum, eliminating the tolerance stack-up that arises when patterning and machining are performed by separate suppliers. Substrate selection extends precision into the thermal domain: sodalime glass substrates are suited to applications tolerating standard industrial thermal variation, while quartz substrates preserve graduation accuracy across the temperature extremes encountered in aerospace, metrology, and scientific instrumentation environments. For the most demanding applications — including precision angle metrology, semiconductor wafer handling, and high-resolution scientific rotary stages — the combination of quartz substrates, antireflective chromium coatings, and Selba’s micron-level patterning process supports rotary encoder systems operating at the limits of achievable angular measurement performance.
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