Damage and Hole Defect Visual Inspection
Damage and hole visual inspection: for punctures, perforations and missing material in film, non-woven fabric, foam and mesh fabric, transmitted backlight provides the highest contrast, distinguishing designed holes from real damage.
defect Overview
Damage and holes show the highest contrast under transmitted light; the difficulty is distinguishing designed holes from real holes
Damage and holes are local loss of material, including punctures, tears, perforations, and short shots. When the material is light-transmitting or semi-transmitting, backlight/transmitted light creates the strongest contrast between the hole area and the solid material, making it the most effective imaging method. Machine vision judges by connected-component area and shape; the main risk is misjudging the material's own designed holes, mesh openings, or foam texture as damage, so the position and shape of "allowed holes" must first be defined with a template.
Damage and holes appear on the image as an area "where material should be but is missing". For semi-transparent or open-work materials such as film, non-woven fabric, foam, and mesh fabric, use transmitted backlight from behind: the solid areas are dark and the voids are bright (or the reverse), giving far higher contrast than front diffuse light, so even tiny holes can be clearly separated.
These defects are most easily confused with "intentional holes". Punched materials, mesh fabric and breathable films already have regular hole arrays, and grid fabric is made entirely of holes. Judgement must first use a template to register the position, diameter and arrangement of the "allowed holes", and then judge extra holes, joined holes and torn edges that deviate from the template as defects.
Opaque thick materials (such as leather and thick foam) cannot use transmitted light, so here low-angle light or 3D height information is needed to expose the collapsed edge and missing thickness of a hole. For tear-type defects, the irregular burr at the edge versus the clean edge of a punched hole is also an important distinguishing feature.
Occurrence Causes
Only when the cause is known can you decide which station should check for it
- Incoming Material Defects: Holes, Pinholes and Uneven Thickness in the Substrate Itself
- Cutting / punching anomalies: dulled dies or centering offset causing joined holes or tears
- Traction and Tensioning: Tearing from Over-Tight Material Feed, Breakage at Folded Corners
- Designed holes: punched holes, mesh holes and vent holes are normal and must be excluded by template
- Downstream handling: sharp corners puncturing, folding and squeezing causing holes
imaging Key Points
Whether it can be detected depends first on whether it can be captured
Transmitted Backlight
Backlighting gives the strongest contrast between holes and solid material and is best suited to semi-transparent materials such as film / non-woven fabric / foam
Low-Angle Light
For thick opaque materials, use grazing light to emphasize the shadow at the collapsed edge of a hole
3D Height Information
A hole means missing thickness, so a height map helps resolve short shot on opaque materials
Template Registration
Register the designed hole positions and shapes first, and exclude the regular hole array to avoid false rejection
judgement Method
Judgement centers on "material missing from areas that are not part of the design." Template registration first excludes permitted holes and mesh openings, then the remaining void areas are assessed for area, aspect ratio and edge regularity. The irregular burr on a torn edge is the key feature that distinguishes it from a clean punched hole.
Threshold bias: holes are usually unacceptable defects with a high cost of escape, so judgement should lean strict; but too strict will wrongly reject normal mesh openings / micro ventilation holes, so the "allowed hole" template must be accurate. The specific area and shape thresholds are defined quantitatively by the quality department and saved with the recipe.
| Judgement Dimension | Description |
|---|---|
| Position | Whether it is outside the holes / mesh openings allowed by the template; no judgement inside the template |
| Area | Minimum/maximum area thresholds for non-designed holes |
| Edge Regularity | Distinguishing features between clean punched holes and torn burrs |
| shape | Comparison of connected holes and irregular holes with regular holes |
| Material Suitability | Use transmitted light for semi-transparent materials and 3D/low-angle light for opaque materials |
Applicable algorithm
Template Registration and Image Differencing
Register the designed hole template and exclude the regular hole array before searching for extra voids
- Avoid false rejects on mesh / punched holes
- Centering offset must be corrected in sync
Blob and Connected Components
Threshold segmentation on the transmitted image to measure void area and shape
- Filter by area and aspect ratio
- Edge regularity distinguishes tears
3D Short Shot Judgement
For opaque thick materials, use a height map to detect local missing thickness
- Supplements cases where transmitted light is not available
- Collapsed edges as a secondary criterion
Common Materials
Common Industry
Common Question
Why Are Holes Imaged with Transmitted Light?
Will holes in mesh fabric cause false calls?
How Do You Detect Holes in Opaque Thick Materials?
How Do You Distinguish Tears from Clean Punched Holes?
Who Sets the Rejection Threshold for Holes?
What Is the Smallest Hole That Can Be Detected?
Do You Need to Reset When Switching to Different Hole Patterns?
Submit sample testing
Damage and hole inspection uses transmitted light for the highest contrast and uses templates to exclude designed holes and mesh openings.
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Send Us Your Defect Samples and We Will Measure Them and Show You the Results
Whether a defect can be detected depends on whether imaging captures the defect features. Provide OK and NG samples and we will run actual imaging and judgement tests on the equipment.