Transmissive · Chrome on glass
Glass encoder disc
A glass encoder disc is a transmissive code wheel made of optical glass with a chrome (Cr) pattern formed by photolithography and etching. Light passes through the clear areas and is blocked by the chrome; a photodetector on the other side converts this into position signals. Glass is flat and dimensionally stable, so it is the mainstream choice for medium- to high-resolution optical encoders.
Also searched as: glass encoder disk · chrome on glass code wheel · glass codewheel · glass code disc · optical glass grating disc
- Optical glass substrate — low thermal expansion, high dimensional stability
- Photolithographic Cr graduations — uniform pitch, sharp edges, high contrast
- Incremental (A/B + Z index), absolute multi-track and sin/cos patterns
- Laser-cut outer diameter and laser-machined bore
- Every disc inspected by AOI machine vision
Specifications
Values marked [spec TBD] are being finalized. Exact figures depend on your drawing — ask for the current datasheet.
| Parameter | Glass Encoder Disc |
|---|---|
| Substrate | Optical glass — available grades [spec TBD] |
| Optical path | Transmissive (light source and detector on opposite sides) |
| Encoding | Incremental (A/B, Z index) · Absolute (multi-track) · Sine/cosine |
| Pattern process | Cr coating + photolithography + etching |
| Contour machining | Laser OD cutting · laser bore machining |
| Outer diameter range | [spec TBD] |
| Bore range | [spec TBD] |
| Thickness | [spec TBD] |
| Line count range | [spec TBD] — example in production: 2000 P/R |
| Minimum line width / tolerance | [spec TBD] |
| Pattern-to-bore concentricity | [spec TBD] |
| Optical density of opaque areas | [spec TBD] |
| Operating temperature | [spec TBD] |
| Inspection | 100% AOI machine vision; vision measuring machine; optical density testing |
| Capacity | About 30,000 discs per day (all product lines combined) |
What we can customize
- Outer diameter, bore and thickness to drawing
- Line count, track layout and index position
- Absolute code: Gray code or pseudo-random [TBD: confirm both offered]
- Coatings: Cr; anti-reflective or protective layers on request
- Centering reference ring for assembly
- Pattern-to-bore concentricity grade to your accuracy requirement
Ordering information
| Quotation | Engineer reviews your drawing for manufacturability, then quotes with sample and production lead times |
|---|---|
| Minimum order quantity (MOQ) | [TBD: MOQ] |
| Sample lead time | [TBD: sample lead time] |
| Production lead time | [TBD: production lead time] |
| Packaging | [TBD: packaging standard] |
| Trade terms / payment | [TBD: Incoterms and payment terms] |
| Inspection documents | [TBD: inspection report contents shipped with each lot] |
Typical applications
Why glass for high-resolution encoders
Photolithography on glass produces cleaner line edges, more uniform pitch and higher light/dark contrast than mechanical scribing or etched film. These properties feed directly into signal quality: better edges mean a waveform closer to an ideal sine for interpolation, and uniform pitch keeps graduation error low across the revolution.
Glass also stays dimensionally stable. Typical expansion coefficients are about 3.3×10⁻⁶/K for borosilicate glass and about 9×10⁻⁶/K for soda-lime glass, compared with about 16–17×10⁻⁶/K for stainless steel (typical literature values).
Handling and assembly notes
- Glass is sensitive to drops and impact; control clamping stress when mounting.
- Handle discs by the outer edge and bore only, never touch the track zone.
- Bond to the hub with a uniform adhesive layer to avoid eccentricity after temperature cycling. A centering reference ring on the disc helps alignment under a microscope.
Glass vs. reflective metal vs. PC encoder discs
| Criterion | Glass (chrome on glass) | Reflective metal | PC (polycarbonate) |
|---|---|---|---|
| Typical optical path | Transmissive | Reflective (source and detector on the same side) | Transmissive |
| High line counts / absolute multi-track | Easiest | Possible, limited by etching and coating | Moderate resolution |
| Thermal expansion (approx.) | Low — about 3.3 (borosilicate) to 9 (soda-lime) ×10⁻⁶/K | Higher — stainless steel about 16–17 ×10⁻⁶/K | Highest — about 65–70 ×10⁻⁶/K |
| Shock and vibration | Sensitive to drops and impact | Very good — does not shatter | Good — tough, not brittle |
| Encoder height | Needs space on both sides | Can be very thin | Needs space on both sides |
| Relative cost | Higher | Lower than glass | Lowest |
| Best for | CNC, rotary tables, metrology, high-resolution servo | Robot joints, slim servo motors, hollow-shaft encoders | High-volume, cost- and weight-sensitive encoders |
Full comparison: Reflective metal or glass encoder disc? How to choose
Quality control on every disc
- 100% AOI — automated optical inspection of graduation integrity, pitch and surface defects (scratches, spots, chips).
- Vision measuring machine — critical dimensions such as outer diameter, bore and pattern-to-bore concentricity are verified.
- Optical density testing — transparent and opaque areas are measured on transmissive discs.
- ISO 9001 quality management system, certified since 2012.
Frequently asked questions
Why choose a glass encoder disc instead of metal or plastic?
How is a chrome-on-glass encoder disc made?
What line count do I need?
Does temperature affect a glass disc's accuracy?
Downloads
- Glass Encoder Disc datasheet (PDF) — [TBD: datasheet file] · available on request now: sales@enc7.com
- RFQ checklist: 20 parameters to send with your drawing
Last updated 1 January 0001 · ENC7 Engineering Team