Precise colour analysis of plastic components
Each part is measured by a colour sensor under the diffuse light of a dome; its L*a*b* values are compared with the reference part to compute ΔE. Shade drift across the batch is followed on a trend chart and an out-of-tolerance part is removed.
The ΔE, ΔL*, Δa*, Δb* values of every part are written to the batch record; an out-of-tolerance part is pushed off the table. The trend chart is shown on the operator display and an alarm goes to the line PLC as the limit approaches.
- 01 Index
- 02 Measure
- 03 ΔE analysis
- 04 Decide
The dial table indexes one step and brings the next part under the measuring head.
- ΔE*ab
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- ΔL*
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- Δb*
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Scenes are illustrative simulations; they are not customer references or performance guarantees.
Need
On a glossy plastic surface glare and shadow mask or exaggerate a shade difference the eye cannot resolve; the same part reads differently as the viewing angle and ambient light change. Shade drift develops slowly across the batch and is invisible on a single part.
Solution approach
The dome light lights the surface evenly from all directions, removing glare and shadow; the sensor looks through the hole at the top of the dome at the same spot and angle. The reading is referenced to a master part measured under the same conditions; ΔE comes from the L*, a*, b* differences. The dial table brings every part to the same spot; the batch trend is charted and drift is seen early.
Process steps
- 01
Index
The dial table indexes one step and brings the next part under the measuring head.
- 02
Measure
The dome light strobes and the sensor measures the surface colour free of glare.
- 03
ΔE analysis
The L*a*b* values are compared with the reference and the result is added to the batch trend.
- 04
Decide
ΔE is compared with the tolerance limit.
Related applications
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