DPM code reading and traceability
Dot-peen, laser and ink-jet Data Matrix codes on parts, read and passed to your PLC or MES.
Technical review: Frank GuoReviewed
A fixed code reader can read Data Matrix codes marked directly on parts by dot-peen, laser or ink-jet, and send the serial and result to the PLC or MES for the part's traceability record. Whether it reads reliably depends mainly on the mark and the lighting: dot-peen usually needs low-angle light, laser marks on shiny metal often need dome or coaxial light. Reading a code is not grading it to the DPM quality standard. We test your marked parts first.
What a DPM reading station does
Three functions. Which you need depends on how your traceability records are kept.
Decode the mark
Reads Data Matrix and other 2D codes marked on the part, at a fixed point in the process.
Check the content
Compares the decoded serial or part number with what the line expects, and flags duplicates already on record.
Write the traceability record
Sends the result to the PLC or MES, linking the serial to the station, time and outcome.
How the marking method affects reading
| Method | How the mark is made | Lighting tried first | Common reading problems |
|---|---|---|---|
| Dot-peen | A stylus punches small dots into the surface; contrast comes from their shape, not colour. | Low-angle (dark-field) | Worn stylus tip, uneven dot spacing, rough or oily surface. |
| Laser | The beam changes the colour or texture of the surface, or removes material. | Diffuse (dome) or coaxial | Low contrast on some alloys, glare, fading after coating or heat treatment. |
| Ink-jet | Ink dots printed on the surface, closer to a code on a label. | Diffuse or bright-field | Smearing, ink spread on oily parts, abrasion in handling. |
A consistent mark matters more than the reader. Marks drift as a stylus wears or laser settings change, so a read straight after marking gives early warning. We do not sell or service markers. Printed date and batch codes are covered under OCR/OCV and code inspection.
Lighting angles for direct part marks
Lighting creates the contrast the reader needs. The geometry is confirmed on your parts.
Low-angle (dark-field)
Light skims the surface, so dot edges light up against a dark background. Usually first choice for dot-peen.
Diffuse (dome)
Even light from all directions hides tooling marks and curvature. Common for laser marks on curved or shiny parts.
Coaxial
Light along the camera axis: flat, shiny areas look bright, marked cells dark. Suits laser marks on flat, polished faces.
Where DPM reading stops
We agree these boundaries before a project starts, so nobody expects the reader to do what it cannot.
Not covered by this station
- Formal DPM grading. Grading to ISO/IEC 29158 needs a calibrated verifier.
- Destroyed or covered marks. Lighting cannot recover a mark filled by paint or scale, or worn away.
- Wrong data at source. If the marker and the MES both hold the wrong serial, they agree and the error passes.
Works reliably when
- The mark is presented the same way. A fixture, stop or robot places the mark at a known angle.
- The marking process is controlled. Stylus, laser settings and part cleanliness stay consistent.
- No-reads have a defined path. Every failed read ends at a NOK station with a record.
How a DPM reading station is laid out
Side view of a typical station after the marker. The real layout follows the site survey.
Swipe sideways to see the whole drawing →
What a pass and a reject look like
Illustrations, not images of real parts or codes. How much the lighting can recover from a weak mark is found on your own parts.
Code read and recorded
Dots are clear under low-angle light; the serial is written to the part's record.
Mark not readable
Faint dots and glare from an oil film. The part goes to NOK for cleaning and a re-read.
Serial already on record
The code reads, but the MES already holds this serial, so the part is stopped.
What the station sends, and where
Who builds each side of the link is agreed at design review.
| Result | Goes to | Used for |
|---|---|---|
| Pass, fail or no-read | Line PLC | Part continues, or goes to NOK. |
| Decoded string | PLC or MES | Starts or updates the serial's record. |
| Duplicate or unexpected serial | MES or station | Stops repeated or out-of-sequence serials. |
| Image of a failed read | Station storage | Shows whether mark, position or lighting failed. |
Protocol support depends on the reader model: HIKROBOT's catalogue lists protocols such as PROFINET, EtherNet/IP and Modbus on specific code reader models (vendor-stated). MES-side changes are made by your MES team or supplier.
How the station is accepted
We define what is measured, and on which parts, before FAT and SAT.
Read rate on your parts
The share of good marks read at line conditions, measured on agreed production parts.
No-read handling
A test that every failed read reaches the NOK station and is logged with its image.
Record integrity
A check that each serial read lands in the right record, including duplicates and link failures.
What to prepare for the sample test
We test marks from your own marker before proposing a station, and confirm quantities and shipping with you first.
Sample preparation guideMarked parts
Production parts, after marking and after later processes.
Difficult marks
Faint, uneven or damaged marks, and parts that fail today.
Mark specification
Marking method, symbol type, data format and mark location drawing.
Line information
Marker, PLC and MES details, and how parts are presented at the read point.
DPM code reading questions
Why does a dot-peen code read on the bench but fail on the line?
Which lighting works best for direct part marks?
Is reading a DPM code the same as verifying it?
Can marks be read after heat treatment, blasting or coating?
What happens when a code cannot be read?
Which hardware do you use?
Sources
- ISO/IEC 29158: Direct Part Mark (DPM) Quality Guideline (standards body page, checked 2026-09-24; replaces ISO/IEC TR 29158 and has since been revised)
- HIKROBOT VisionMaster product page (code reading) (vendor page, checked 2026-09-24)
- HIKROBOT machine vision product navigation (fixed and handheld code readers) (vendor page, checked 2026-09-24)
- HIKROBOT Machine Vision Smart Product Catalog, 2025 Q4 (PDF) (vendor catalogue, checked 2026-09-24; code reader protocol rows)
Request an assessment for this application
Tell us how parts are marked and where the record is kept, and send marked parts, including ones that fail today. We will tell you what a station can read.