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Packaging with high speed and quality

Despite the falling popularity of smoking in the UK, tobacco packaging machinery is a major export earner, with active markets in the Americas, Africa and the Far East. A new modular machine packs cigarettes at a rate of 8000/min at the highest quality, thanks to servo motors, drives and motion control technology.

Few areas of packaging technology combine high speeds with sensitive materials and box complexity as is seen in cigarette packaging machinery. The hinge-lid, or flip-top pack of cigarettes is a case with multi-part card and foil materials packaging the tobacco which itself requires gentle handling. The new Molins Optima machine does just that at rates up to 400 packs or 8000 cigarettes a minute. The Molins Optima produces packs with high and consistent quality from a small floor footprint and with easy operator access.

The hinge-lid cigarette packet will be familiar to current and ex-smokers alike. For many it is so familiar that they do not notice the way the card is folded and glued, the way the top is folded with a separate card insert to give it strength. And who notices the tear-off foil wrapping which is embossed, or the way the contents are always accurately aligned in three rows with no marks from the handling process? Smokers expect and get consistent high quality, and this achievement is all the more remarkable as a single Optima machine produces 400 boxes per minute.

The new Optima machine is being manufactured in Coventry as a joint design between Molins Tobacco Machinery and Molins Technologies. Molins is an international company with divisions in packaging machinery, also instrumentation and tobacco machinery. 800 people are employed worldwide. The Optima design team were tasked with creating a modular mach-ine that would easily interface with other Molins machines, allow fast size and format changes, with a small footprint and compet-itive price. It was evident that the speeds and quality requirements demanded a servo drive system. Long-term partner Lenze was brought in to select and supply the servo motors, drives and motion control technology.

The cigarette packaging process starts with an infeed; for example Molins offers a module called a mass tray unloader that takes loose cigarettes from trays and feeds them along a conveyor. All subsequent steps in the Optima machine are synchronised without buffer stocks so smooth handling and reliability is critical. From the conveyor, the cigarettes are collated into three rows then pushed by a servo motor into a former that is shaped as a pack. The motor gives a soft pushing action and a fast withdrawal to prevent tipping in the infeed. A servo driven feed from a reel then wraps the foil which is perforated and embossed, and an inner card frame is inserted to reinforce the final box.

The outer card for the box begins with a stack of blanks that are picked and placed onto a conveyor. Glue spots are added and the blanks are fed to meet the foil wrapped cigarettes. The card blanks are folded to a final box shape with further glueing and then conveyed on to an indexing turret. At this stage the glue has no strength and smooth handling that keeps the final box shape is essential. The servo driven turret indexes every 140 milliseconds and takes the cigarette packets on to outfeed which lifts them away to a film over wrapper module where they arrive with the glue sufficiently dry. Molins project manager Howard Hill explains: “Handling of the packs as the glue is setting is a challenge at these high speeds. We achieve consistent high quality by maintaining a steady but gentle squeeze to the sides of the pack.”

Lenze supplies the drives and motion control based around the 3200C controller. This holds the motion control software and links to the Lenze I/O system as well as communicating to the drives with EtherCAT and the supervisory PLC with PROFINET. The Lenze I/O System 1000 is used both plugged directly to the side of the 3200C and also as a remote station with an EtherCat bus coupler. There are seven servo motors in all, a mix of MCS synchronous and MCA asynchronous servo. All are powered by the Lenze i700 multi-axis servo inverters mounted in a central control cabinet. These servo drives have a linked DC bus, easily connected by swinging steel arms on the front of the drives. The DC bus link allows regenerated power from one drive to be shared amongst the others, so reducing the total power requirement and the machine running costs.

An example of the motion expertise brought in by Lenze is modelling of the main turret drive. This is an unusual servo application where the motor drives through a belt to an index box. Thus the motor runs at a fixed speed but with a rapidly varying torque profile based on a 140ms cycle, corresponding to a line speed of 425 packs per minute. During the cycle the torque loads vary from +300Nm to –330Nm.

The torque profile together with inertias were input to the Lenze DSD Drive Solution Designer modelling software which calculated the peak power requirement of 15.7kW and the RMS value of 7.5kW. This allowed an optimised selection of the motor and the drive taking into account the energy sharing with other drives on the machine. The i700 servo drive was optimised to 11kW saving cost and space, also reducing the power loss to only 160W.

The Octave machine demonstrates the expertise of Molins’ engineers in the high speed handling of sensitive tobacco products. Even at a rate of 8000 cigarettes a minute, every pack is identical with strong construction and unmarked contents. Smooth and synchronised motion control with the Lenze servo system plays a key part here. Octave has proved itself able to deliver the consistent quality demanded by the market together with a small footprint and easy ability to be combined with other machine modules.

Lenze Ltd