Clever design drives packaging throughput

SEW-Eurodrive Pty Ltd
Friday, 27 August, 2010

When Visy Automation embarked on the development of its second-generation inline VL18 lidder machine for Australia’s largest meat processor, Bindaree Beef, the company called on SEW-Eurodrive to provide an innovative motor and drive solution. All of the new lidder’s motion processes rely on SEW-Eurodrive electronic drive control technology, and servo geared motors. The result is a fast and efficient inline lidder machine, adaptable to nearly any box that comes off the production line.

Visy Automation’s VL18 lidder machine features a clever dual-purpose conveyor design coupled with precision automation and a rapid-fire ‘head compression’ lidding system. Together, they ensure lids are glued onto unlidded boxes at rates of up to 25 per minute.

In operation, unlidded boxes are transferred into the head compression area for lidding via two side-by-side dual-chain conveyors. Each chain conveyor is equipped with two sets of paddles positioned at opposite ends of the chain-set. One of the paddles from the first chain-set is used to push the incoming box into position and hold it in place from the incoming side. Once in position, a paddle from the second chain-set acts as a torque-control paddle, holding the positioned box in place from the opposite side.

The head compression system then delivers and glues the lid to the box in less than one second. Once the lid has been attached, the torque control paddle releases the box by rotating under the conveyor. The first paddle then over-travels, effectively pushing the lidded box off on to the outlet conveyor. This first paddle then takes on the role of the torque control paddle for the next box.

According to Peter Somogyi, Visy Automation Project Manager, the dual functionality of the paddle system is a real feature of the packaging machine. “The fact that each paddle does not have to go back to the start position after each box is lidded is a real time saver,” he says. “By minimising the number and length of machine movements, we have been able to develop an extremely fast lidder machine.”

The VL18 lidder machine is equipped with four SEW-Eurodrive geared servo motors - one on each of the chain conveyors, one on the head compression system and one for the lid-transfer system. Similarly, each of the lidder machine’s four servo motors is combined with its own dedicated SEW-Eurodrive Movidrive B application inverter. All of these drives are linked to a single PLC via an EtherCat network.

According to Spiro Limberakis, SEW-Eurodrive Applications Engineer, the integrated Modulo Function positioning control of the Movidrive B is vital to the operation of the VL18 lidder machine. “The Modulo Function control with encoder feedback is ideal for accurately controlling position in rotating applications such as this one,” he says. “In this case, the drive can direct the chain conveyor to any one of eight paddle positions.”

Here, each motor is equipped with a 24-bit absolute encoder, which by itself is not adequate in such an application - eventually the encoder will overflow, effectively forcing the drive and the chain to go out of position. Importantly, the Movidrive B inverter converts the 24-bit encoder into a 64-bit encoder by counting and storing the overflows in the inverter, eliminating the overflow issue.

“Even after multiple revolutions, the paddles can be taken back to the start position automatically,” says Limberakis. “There is no need for the drive to return to a reference or zero point with this system, even after a power down.”

The drives have been programmed to use the ‘shortest path’ method of positioning. Here, the Movidrive B accepts a chain/paddle destination from the PLC and then determines which paddle should be moved in which direction (clockwise or anti-clockwise) to ensure a paddle is in position in the shortest possible time.

“While this saves time between paddle movements and allows production rates to be optimised, it also presents challenges,” says Somogyi. “There is potential for the two sets of paddles to occupy the same space, so there needs to be a high degree of flexibility within the drives to ensure that paddles from different chains don’t collide.” With this in mind, SEW-Eurodrive implemented a unique control architecture and developed anti-collision software.

“While the paddle position of both chain conveyors is controlled by the PLC via the drives, the drives themselves are in continuous communication with each other in the background, via a dedicated system bus,” says Limberakis. “The drives essentially monitor each other’s position. If the individual paddles get within a certain proximity of each other, the drives will ‘fault out’, avoiding a crash. They then go into recovery mode and travel to a known paddle position before the lidding process is recommenced.”

Visy Automation has also built reliability into the control system. “We’ve set up a handshaking process between all of the drives and the PLC,” says Somogyi. “Each time a message is exchanged between the PLC and any of the drives, an additional confirmation message is sent before any action is taken. This only takes a matter of milliseconds, but adds an extra degree of reliability to the process.”

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