C 4000 Palletiser: pattern detection improves access protection during automated material transport
Waldkirch, June 2005 ¡V The dynamic, self-learning blanking function of the C 4000 Palletiser safety light curtain offers safety, availability, supplementary functions, and installation and operating cost benefits of up to 40% compared to conventional muting solutions. The device detects persons entering the hazardous areas of machines but permits the transport of material in and out of such areas. Pattern detection, e.g. of pallet feet or goods on pallets, which obviates the need for supplementary sensors and guarding measures, as well as the maximum availability provided by the permanently active light curtain, rapidly lead to enormous cost savings amounting to several thousand euros.
The C 4000 Palletiser electro-sensitive protective equipment corresponds to Type 4 according to IEC 61496 and SIL 3 in compliance with IEC 61508. The safety light curtain is designed for access protection during automated material transport, requiring no additional sensors, swing doors or indicator lamps and thus offering considerable advantages in economic efficiency during planning, construction, mounting, connection and the service work involved with operation. Moreover, the drop in frequency of device faults (corresponding to the reduction in the number of components) results in a significant increase in plant availability.
Goods or pallets ¡V two types of pattern detection
The C 4000 Palletiser has a self-learning, dynamic blanking function for pattern detection with which it reliably differentiates between transported materials and persons during transport into the protected area.
Pattern detection can take place in one of two ways depending on the system version ¡V Standard or Advanced:
„h via the size and closed shape of an object, e.g. the goods on a pallet.
„h via the size and number of several objects, e.g. the feet of a grid box or pallet, or the number of individual goods transported at fixed distances to one another.
In the first case, the blocking of individual light beams and a minimum size are monitored and evaluated. The automatic detection of unitised goods, requiring no complex programming, offers maximum operating flexibility. The difficult adjustment of muting sensors for differing batches, that would otherwise be required, is completely unnecessary. In the second case, self-learning detection of object patterns, e.g. differing pallets, takes place during simultaneous distance monitoring. In addition, the system also carries out a quality inspection during the access process, during which defective pallet or grid box feet (which could impair automated handling) are detected.
Practical supplementary benefits
Both versions of the C 4000 Palletiser are delivered with pattern detection of goods and Europallets already activated. The teaching-in of a new pattern takes place automatically during mixed operation. Moreover, the systems can process transport direction signals. This permits both the detection of the transport direction of goods or pallets, and the switching of the light curtain from pattern detection to protective mode in the case of a belt standstill. Both functions contribute towards minimising the necessary safety distances ¡V important wherever mounting space is limited. The
C 4000 Palletiser can also be used in Ex-zones 2 or 22 with the optional ATEX Kit.
Why person / material differentiation?
The C 4000 Palletiser safety light curtain monitors hazardous areas on automatically operated machines, e.g. robots, turntables, palletisers, insertion equipment or strapping machines. These are often integrated into automated material flow concepts, i.e. objects such as loaded pallets, workpieces, containers or car shells on skids are automatically transported into the working area of the machinery and out again. Such tasks can be easily, flexibly and safely solved with the pattern detection of the C 4000 Palletiser. The permanently active safety light curtain uses the data from the self-learning distance monitoring to reliably differentiate between persons and material. Information on the maximum permissible size of an object, entry into and departure from the protective field, self-learnt object distances within the protective field and their changes, among other data, are used for detection and for differentiating between persons and a transport vehicle, for example. Just one of these switching criteria is sufficient to bring the hazardous machine movement to a stop.
Pattern detection and muting: delineation and complementation
Up to now the usual method for safeguarding these entrance and exit locks has been safety light curtains with their connected muting sensors, muting lamps and sometimes also swing doors. Time-related and logical conditions are checked using muting sensors, on the basis of which the system can distinguish between persons and material. This solution has proven itself in industry but involves greater material and installation costs. Thus both pattern detection and muting have their advantages, based on the particular operating conditions present. There remains, however, the question of which technique is to be used when. The advantages of pattern detection include, above all, minimising installation costs and the number of components, providing maximum availability. Only the actual safety sensor is required. However, an unambiguous detectability of the pattern of goods or transport aids is essential. Therefore muting is the right solution when pattern detection is inappropriate, but objects can be detected by muting sensors and the switching frequency can be evaluated in terms of both time and logic. In practice, both alternatives are often found side by side.