Knowledge
Multi-SKU Changeover With One Camera
One camera serving several products is a resolution compromise plus a changeover procedure. The field of view has to contain the largest product while the object-side pixel has to be small enough for the smallest measured feature on any product — and because the object-side pixel is the sensor pixel divided by one magnification, the smallest feature is measured with the same object-side pixel as everything else. That arithmetic, not the optics catalogue, decides whether a single station is feasible.
Part of the POMEAS Machine Vision Inspection Application Cases series — see the Machine Vision Inspection Application Cases index for all 20 articles in this set, grouped by industry.
Sizing the compromise
Work in one direction: largest field required → magnification → object-side pixel → pixels across the smallest feature. With a 3.45 µm pixel and 0.14× the object-side pixel is about 24.6 µm, so a 0.1 mm feature spans only about four pixels — adequate for detection, marginal for measurement. If the tolerance needs ten pixels across that feature, the single-camera option fails on paper and the decision moves up a level: a second station, a zoom lens that changes magnification between product groups, or a higher-resolution sensor. The same arithmetic decides whether the height spread fits the depth of field, with focus at mid-height and a working rule of spread ≤ 0.7 × DOF.
What a changeover really costs
A hardware lens swap costs line downtime, refitting and re-establishing the working distance, refocusing, recalibration, a first-article inspection and the documentation — and it repeats every time. A recipe change on a motorized lens costs seconds and no mechanical intervention, but still needs first-article verification. When changeovers are frequent, the payback of a motorized zoom or a second station is driven by those hours rather than by optical quality; write the comparison with the changeover frequency you actually have, and include the hidden items, or the comparison flatters the manual approach.
Recipes, fixtures and the risk of mixing parts
Treat recipes as controlled documents: zoom, focus, aperture, scale factor, region of interest and illumination settings belong to a revision, and any change should trigger re-verification against a reference feature. Fixtures should guarantee repeatable presentation — indexed adjustable stops or quick-change inserts seating against a hard datum — because a presentation error appears directly in the measurement and looks like process variation. Finally, identify the part automatically (barcode, RFID or vision classification) and refuse to run without a match, so that product A is never measured with the recipe for product B.
Related reading: parts with different heights, industrial lens selection, motorized zoom lens selection, and the machine vision lens range. The questions on resolution compromise, fixtures and recipe control are answered below — send the SKU list and the tolerances and we will check whether one station covers them.
Frequently Asked Questions
How do I check whether one camera can cover every SKU?
Work in one direction: the largest field of view required, then the magnification, then the object-side pixel, then the pixels across the smallest feature. The smallest feature is measured with the same object-side pixel as everything else on the part, so that arithmetic - not the optics catalogue - decides whether a single station is feasible.
With a 3.45 um pixel and 0.14x magnification, how large is the object-side pixel?
About 24.6 um, because the object-side pixel is the sensor pixel divided by the magnification. On that basis a 0.1 mm feature spans only about four pixels, which is adequate for detection but marginal for measurement.
When does the single-camera option fail on paper?
When the tolerance needs about ten pixels across the smallest feature. At that point the option fails on paper and the decision moves up a level: a second station, a zoom lens that changes magnification between product groups, or a higher-resolution sensor.
What does a hardware lens swap cost compared with a recipe change?
A lens swap costs line downtime, refitting and re-establishing the working distance, refocusing, recalibration, a first-article inspection and the documentation, and it repeats every time. A recipe change on a motorized lens costs seconds and no mechanical intervention, but still needs first-article verification.
How do I prevent product A being measured with product B's recipe?
Identify the part automatically by barcode, RFID or vision classification and refuse to run without a match. Treat recipes as controlled documents: zoom, focus, aperture, scale factor, region of interest and illumination settings belong to a revision, and any change triggers re-verification against a reference feature.
What must the fixture guarantee at changeover?
Repeatable presentation - indexed adjustable stops or quick-change inserts seating against a hard datum. A presentation error appears directly in the measurement and looks like process variation.
Related POMEAS product categories
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