A customer inquiry reached wenglor concerning the reliable detection of UV print marks on a running textile web. The challenge was to clearly detect a mark of around 12 × 40 mm printed with UV ink at belt speeds of up to 120 m/min. The web itself is black, which makes conventional optical methods even more difficult.
The UV ink used shows its strongest emission at an excitation of 375 nm and radiates with maximum intensity in the range of around 435 nm. Conventional print mark sensors work exclusively with white light and are therefore unable to reliably detect such UV markings. In addition, we are dealing with web material in which the print marks occur at regular intervals of around two meters – the web speed is therefore easy for the sensors to control, but the optical separation of the mark and label material is crucial.
A luminescence sensor is used for this type of task. These sensors specifically excite the UV marking and only evaluate the light emitted by the ink. This allows clear and reproducible switching signals to be generated even on dark or black surfaces.
A suitable solution is the luminescence sensor P1PA001. It detects all luminescent markers that emit light in the wavelength range from 420 to 750 nm. An integrated receiver filter ensures that only the light emitted by the UV mark is detected. The sensors work with a long-life UV LED and have a small, clearly defined light spot – ideal for precise print mark detection on textile webs.
The sensor’s large detection range allows maximum flexibility in the choice of marking color, as all luminescent colors in the visible spectrum can be detected. For applications where optical brighteners in the label material – such as in textiles or paper – could interfere, the P1PA002 a variant with a reduced range of 570 to 750 nm is available. This allows whitening agents to be specifically masked out.
The variably designed light spot offers additional flexibility: at close range of around 30 mm, the diameter is only around 4 mm; at greater working distances of up to 90 mm, it increases to around 9 mm. This means that the sensor can be optimally adapted to different marking sizes and installation situations.
Luminescence sensors are the right choice for reliably detecting UV print marks on black textile webs. The P1PA001 is a robust and reliable solution that delivers clear switching signals even at high belt speeds while offering maximum flexibility in terms of marking color, distance and mark size.
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