Ever since safety-related components such as the MLD series of safety light barriers from Leuze electronic with AS-i Safety interface have been available, Strema Maschinenbau GmbH in Sulzbach-Rosenberg has been using AS-i Safety-at-Work to efficiently fulfil the high safety requirements at the highest performance level in a network.
The AS-Interface bus system is used by Strema Maschinenbau, one of the most renowned manufacturers of stretch wrapping systems, standard since 1999. The need for its use is explained Klaus Lösch, Head of Electrical Design at the company, is particularly concerned with the increasingly extensive functionalities: „As the number of actuators and sensors increases, so does the need to network them simply, reliably and economically.
Depending on the design and scope of a stretch machine, up to 80 switching standard sensors such as Light switch and Reflection light barriers from Leuze electronic including HRT 96, HRT 46B, HRT 3B and PRK 25B.
Advantages of AS-i
Lösch decided in favour of AS-Interface very early on when selecting a suitable bus system. In addition to a conscientious cost analysis, this is primarily due to the design of the stretch systems: either the pallets to be wrapped are rotated on a stationary stretch head, in which case we speak of Turntable machines. With rotary arm machines, on the other hand, one or two stretch heads are rotated around a pallet on one arm. In either case Slip rings which transfer media such as energy, data and air to the rotor of the machine.
This is where AS-i has advantages, explains Lösch: „When communicating via slip rings, carbon deposits occur on the slip ring paths with the usual energised bus systems such as Profibus or Profinet, despite silver-plated slip ring tracks and silver graphite pick-ups. This causes maintenance work and can lead to faults. With AS-i, on the other hand, the Bit sequences in the form of Current pulses sent. The Permanent current flow keeps the slip ring paths clean.“
AS-i therefore guarantees a high level of transmission reliability in all stretch wrapping machines. The fact that the current-carrying AS-i bus is generally less sensitive to electromagnetic interference, such as that caused by frequency-controlled drives and their supply lines, also contributes to this.
In particular, the terminal box-free design of the I/O level and the simple installation thanks to the so-called penetration technology. This is based on the use of the mostly yellow AS-i cable, a reverse polarity protected flat cable During installation, the piercing pins of the device to be connected drill into the conductors of the cable and establish a reliable contact.
„It couldn't be easier to connect sensors, actuators or modules,“ says Lösch, who also enables the operators of stretch machines to change, add or replace components at any point without tools if required. Lösch says: „This is precisely what makes AS-i so attractive as a simple and economical cabling system for the lower level of industrial communication.“
Increased safety requirements
As the functionality and performance of stretch systems has increased, so too have the safety requirements. A fully automatic rotary arm machine from the A 5000 series packs up to 150 pallets per hour with two stretch heads. The performance level according to the applicable Machinery Directive is PL e, i.e. at highest level.
„Since safety-related components such as the MLD series of Light Beam Safety Devices from Leuze electronic have been available with an AS-i Safety interface, we can also use the existing AS-i network for safety technology,“ says Lösch happily.
Multiple light beam safety devices
The multiple light beam safety devices of the MLD series with integrated AS-i safety interface are connected directly to the AS-i bus without additional coupling modules. In addition to the simple adaptation to the AS-i cable thanks to the penetration technology, the M12 connection technology also ensures quick installation. Even a device change is possible via Plug & Play possible without programming. Simply connect, immediately ready for operation, This is exactly what Lösch means by the charm of AS-i and AS-i Safety [infotext].
About Strema:
Strema Maschinenbau GmbH has been developing and manufacturing stretch wrapping machines and systems for over 30 years, with which pallet loads are wrapped in film for optimum load security. The product portfolio ranges from the simple but very robust Pallet stretch wrapping machine, in which the film slide by hand is operated and the turntable is switched on and off using a foot switch, until the Fully automatic machines with an electronically controlled and infinitely variable variable power stretching system. With enormous innovative strength, the experts place their machines in all performance classes[/infotext].
