| 摘要 |
The invention relates to a detector for registering marks on moving products as used in the packaging industry, where, for example, printed foil is drawn off a roll and must be cut at a particular point or aligned and folded in accordance with the printed pattern. The products (5), for example the foil or the tube workpieces are provided with a printed mark (6) and the detector has an illumination device (1, 2, 15, 3, 4) which throws two light spots, which are next to one another in the direction of movement, onto the product (5), and an optical device (4, 8) which throws the light reflected from each of the light spots onto in each case one photocell (9a, 9b) which, together with two resistors (16, 17) are connected to form a bridge circuit, one diagonal corner point of which is connected to a direct-voltage source. The signal picked up from the other diagonal corner points passes via a rectifier bridge (20) to a differential amplifier (18), the output signals of which are applied unchanged to an input (23) of a comparator (22) and are supplied via a diode (25) to a smoothing capacitor (26) with parallel-connected resistor. Some of the smoothed voltages are supplied to the other input (24) of the comparator (22) and act as "tracking response threshold", the level of which depends on the respective contrast of the marks (6) with which these marks stand out from the coloured background of the product (5). This results in an improvement in the response reliability, particularly in the case of low-contrast marks. <IMAGE>
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