THE new LUT luminescent scanner from SICK provides help wherever conventional photoelectric sensors come up against their limits with high-contrast backgrounds, fluctuating background colours and, particularly, where optical marks cannot be attached to goods.
Instead of an optically visible minimum contrast, the "mini-lumi" detects natural luminophores and those added or attached for product marking purposes, that are not visible with the naked eye.
The extremely compact design of the LUT 2 permits space-saving mounting. Thanks to its high switching frequency the device, with a range of approximately 12.5mm, is also suitable for high-performance machines.
The LUT 2 uses a maintenance-free and long-lived UV diode as its light source. The emitted ultraviolet light, at a wavelength of 370 nm, hits a fluorescent pigment on the surface, that either occurs naturally in the target good or has been added or attached to it for identification purposes.
This pigment then generates light with a long wavelength between 420nm and 750nm in the visible range. This is detected by the reception element of the LUT 2.
In the process, the electronics check whether the emitted and received light have the same modulation frequency. This ensures that spurious switching, caused by surface or other reflections, or light impinging on the machine, can be reliably prevented.
A new development in the detection of fluorescent markings is the optimum adaptation of sensitivity by means of the static two-point teach-in process. As a result, weak background luminescence can be suppressed, or the sensitivity of the device can be increased by teach-in if there is a low level of pigmentation in the marking.
Devices with a supplementary optical filter are available for stronger background luminescence. If an object has been detected by the luminescence scanner, a signal to the machine control system is triggered.
Fluorescent pigments can be added to almost all substances, e.g. paints, oils, fats and glues. In addition, they can also then be attached to solid materials such as labels and boxes, if these have already been printed with other information.
As the markings can be invisible, they are suitable for attaching validation marks for establishing that the goods, e.g. high-value quality articles, are genuine. Moreover, they have no interfering effect on the labels on consumer articles.
There are numerous opportunities for using the LUT 2 in packaging technology.
Thus, for example, PET bottles can be positioned by means of an invisible control mark on the label in such a way that, after automatic placement in a crate, the labels are positioned to face outwards for effective advertising.
In this and many other applications it is possible to automatically detect target goods with fluorescent visible and invisible marks with the LUT 2, even where space is tight.