Machine vision for in-line quality inspection
What vision can inspect, what it cannot replace and how to define the criterion before buying the camera.
Vision inspection is not “a camera that sees defects”. It is an acceptance criterion turned into image, lighting and rules. If the defect cannot be described, shown and repeated, the camera will not solve it.
What types of inspection exist
Presence, dimension, position, sorting, surface defect and assembly verification. Each has different camera, lighting and rule requirements.
| Criterion | What it measures | Limit |
|---|---|---|
| Presence / position | Whether the part is there and where. | Does not measure surface quality. |
| Dimension | Measurements and tolerances with calibration. | Does not replace lab metrology. |
| Surface defect | Scratches, stains, missing areas, color. | Depends on lighting and visual criteria. |
Camera, lighting and lens
The required resolution depends on the smallest defect to be seen. Lighting defines contrast and repeatability; the lens defines field of view and distance. They are not chosen separately.
Acceptance criterion
You must define what is good, bad and uncertain. Borderline parts matter most: if the criterion does not classify them the same way as the customer, inspection does not work.
In-line or end-of-line
In-line inspection runs at production rate and can reject or correct; end-of-line inspects the batch. The first demands more speed and integration; the second, more traceability.
PLC integration and traceability
Vision must tell the PLC what to do with the part and log the result. Retries, uncertain parts and what happens if the camera cannot decide must also be defined.
When not to use vision
When the defect cannot be seen with contrast, when variation exceeds the rule or when contact measurement is more reliable. Vision does not replace a lab.
Frequently asked questions
What can vision inspect?
Presence, position, dimensions, sorting, surface defects and assembly. Each type requires different camera, lighting and rules.
Does it replace metrology?
No. Vision can measure in-line, but does not replace a lab when tolerance or traceability requires it.
How is a defect defined?
With good, bad and uncertain samples and a criterion the customer accepts. If borderline parts are not classified the same way, inspection fails.
In-line or end-of-line?
In-line allows rejection or correction at production rate; end-of-line prioritizes traceability and batch review. The choice changes the architecture.
How does it integrate with the PLC?
Vision provides a result and the PLC decides the action. Retries, uncertain parts and result logging must be defined.
When is vision not a good fit?
When the defect cannot be seen with contrast, variation exceeds the rule or contact measurement is more reliable.
