What should incoming inspection of encoder discs check? Visual defects, dimensions and optical parameters
A checklist for incoming inspection of encoder discs: visual defects, dimensions and concentricity, graduation quality and optical parameters, plus the inspection methods, sampling and acceptance criteria to agree with the supplier in advance.
2026-10-04 · Langfang Jingzheng Optoelectronic Technology Co., Ltd.
A single pinhole or broken line on an encoder disc can cause the encoder to miss pulses or show periodic errors. We recommend organizing incoming inspection into four categories of items, with the acceptance criteria agreed with the supplier in writing before the order is placed.
| Category | Inspection items | Common methods |
|---|---|---|
| Visual defects | Edge chipping, cracks, scratches, pinholes, broken lines, adhesive residue, contamination | Stereo microscope, AOI (automated optical inspection) |
| Dimensions | Outer diameter, bore, thickness, pattern-to-bore concentricity | Vision measuring machine, micrometer |
| Graduations | Line width, grating pitch, duty cycle, graduation integrity, index position | Vision measuring machine, microscope, AOI |
| Optical parameters | Transmissive: optical density (OD) of the opaque areas; reflective: reflectance of the high- and low-reflectance areas | Transmission densitometer, spectrophotometer or reflectometer, measured at the readhead wavelength |
Judging defects by zone
Defects within the track zone directly affect the signal, so the requirements there are the strictest; they can be relaxed for the assembly zone outside the tracks. A common practice is to divide the disc into a track zone and a non-track zone and agree on the allowable defect size and number for each, for example “no broken lines or line-crossing pinholes in the track zone”. The specific values are set according to the readhead spot size and signal margin.
Sampling and records
- Inspect 100% of the first lot and of the first lot after any design change; once quality is stable, sample according to the agreed sampling plan
- Require the supplier to ship an inspection report with each delivery, including at least measured values for dimensions, concentricity and optical parameters
- Where possible, mount the disc with your own readhead and measure the signal amplitude and phase over one revolution; this reflects actual performance better than a visual inspection
Packaging and storage
Encoder discs should be packed with separators so they do not rub against each other; glass encoder discs must be protected from drops; wear finger cots when handling, and touch only the outer edge and the bore, never the track zone.
Before shipment, every Jingzheng Optoelectronics disc undergoes AOI inspection for graduation integrity, pitch and surface defects; critical dimensions are verified on a vision measuring machine, and the transparent and opaque areas are tested for optical density.
This article was compiled by the engineering department of Langfang Jingzheng Optoelectronic Technology Co., Ltd. Jingzheng Optoelectronics manufactures glass encoder discs, reflective metal encoder discs, PC encoder discs and custom encoder discs. Website: www.encoderdisk.cn; phone: 0316-8933331.