Worked example: from web speed to line rate and bandwidth. A 1,300 mm web is inspected with 4K line-scan cameras such as the HIKROBOT MV-CL042-91GC, which the vendor lists with 4,096 pixels, a maximum line rate of 28 kHz at 8-bit in standard mode and 80 kHz in a high-bandwidth Bayer mode, on Gigabit Ethernet (HIKROBOT MV-CL042-91GC). Along-web pixels are matched to cross-web pixels, so the line rate is web speed divided by pixel size. The data rate is pixels × line rate × 8 bits. The figures are arithmetic for planning; the camera model, mode and count are chosen from your smallest defect and top speed.
Example: line rate and data rate for a 1,300 mm web| Cameras across 1,300 mm | Pixel size | Web speed | Line rate needed | Data per camera (8-bit) | What it means |
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| 1 camera (4,096 px) | 0.32 mm | 150 m/min | about 7.9 kHz | about 260 Mbit/s | Comfortable within the standard mode |
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| 1 camera (4,096 px) | 0.32 mm | 300 m/min | about 15.8 kHz | about 520 Mbit/s | Within the standard mode |
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| 2 cameras (about 8,000 px after overlap) | 0.16 mm | 150 m/min | about 15.4 kHz | about 500 Mbit/s each | Within the standard mode |
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| 2 cameras (about 8,000 px after overlap) | 0.16 mm | 300 m/min | about 30.8 kHz | about 1,000 Mbit/s each | Above the 28 kHz standard mode: needs the high-bandwidth mode, a third camera, or coarser along-web pixels |
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The last row shows the usual trade-off: halving the pixel size doubles both the cameras and the line rate, and the line rate runs into the camera’s and the network’s limits. Exposure time per line also shrinks as the line rate rises, so light power grows with speed.
Light for webs
HIKROBOT’s glossary describes low-angle light, below 45°, as making flat areas dark and rough or raised areas bright, and coaxial light as turning a flat surface into a mirror on which roughness shows clearly; it lists line-scan lights among the sources for both (HIKROBOT light catalogue, glossary). On a web that becomes: transmitted light for holes and gels, coaxial or bright-field reflection for coating faults on foil and film, and low-angle light for creases and scratches.
Interfaces and data
GigE Vision and GenICam are the machine-vision interface standards the camera above is listed against (HIKROBOT MV-CL042-91GC); EMVA hosts GenICam, the generic programming interface that lets software control cameras from different makers the same way (EMVA, GenICam). For a web system that means the software can address each camera’s line rate, exposure and trigger mode, and the encoder input sets the line trigger.
How a web system is accepted
Acceptance metrics for a web inspection system| Metric | How it is measured | Why it matters |
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| Detection rate per defect class | Share of seeded or known defects of each class found in a trial roll | Holes and tears usually first, because they matter most downstream |
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| False alarm rate | Alarms per 1,000 m (or per roll) that turn out to be no defect on review | Too many and operators stop trusting the system |
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| Position accuracy | Difference between the logged position and where the defect is found at rewind or slitting | Decides whether the slitter can cut it out automatically |
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| Classification agreement | Share of logged defects given the same class as the operator’s review | Matters when rolls are graded by defect type |
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For printed packaging, FSSC 22000 version 6 expects packaging manufacturers to control printing, including approval of each run against the master sample and a process to detect and identify printing errors during the run (FSSC 22000 v6, 2.5.2(d)). A web or sheet inspection system with a defect map and a roll report is one way to show that process is in place.