Starpak, previously trading as Levy & Smith, has been manufacturing the well known Brandpac single roll shrink packaging machine for many years. The design incorporated a PLC performing some basic control, however, the machine was largely mechanical.
Although Starpak and its customers were happy with the design, managing director, Steve Smith knew that the technology was becoming dated. The machine’s reliance on mechanical technology limited its versatility. This prompted the company to review the control philosophy, incorporating synchronised servo and variable frequency drive (VFD) control for the unwinding, film feeding, cutting, indexing and final wrapping stations.
After considering its options, Starpak decided to use the LS GM4 PLC, which incorporates multi-axis position control. This was used in combination with four Mecapion servo inverters and five LS open loop vector inverters. This arrangement offered many possibilities for increasing the utility of the packaging machine.
South African LS agents, Ana-Digi Systems, assisted Starpak in specifying and optimising the PLC, VFD, servo equipment and planetary gearboxes to suit the speed, torque and acceleration requirements of the redesign.
Smith is passionate about the simplicity of his designs, as he believes it is this very feature that has made the brand so successful. He was adamant that the machines were still to remain user friendly and not to 'just use servos for the sake of it', as he put it. With this in mind Starpak wrote the PLC application program for the LS GM4 PLC, incorporating the profiled multi-axis parameters of the positioning module. The requirements of the different pack sizes (speed, cut-length, feed rate and profile) were pre-programmed into the PLC and addressed as recipes from an LS PMU-330BTE touch-screen operator interface (HMI). Scope was left for customer inclusion of specialised and experimental recipes.
The original coupled mechanical gear drives were replaced by three Mecapion servo motors, fitted to HPB high precision, high service factor in-line planetary gearboxes. In the case of the cutter, the blade was directly coupled to its own servo motor without a gearbox.
The index and wrapping actions were synchronised to the machine speed by fitting an encoder to the infeed conveyor. This encoder signal is directed to the multi-axis positioning module on the PLC, which then generates and synchronises the necessary profiles for the three axes to suit the requirements of the various packs.
The conversion has dramatically improved the Brandpac in terms of smooth running, silence of operation, adjustment flexibility and ease of set-up.
The PLC system also affords clients production reports and fault analysis by displaying the necessary information on the system HMI. “Put simply, the machine is able to tell you how well a line is operating throughout a given cycle. It is possible to identify any throughput fall-off and more particularly, why this has occurred in any one hour of a cycle of, for example, 500 hours,” says Smith.
The ease of communication of the LS PLC with other makes of equipment will, at a later date, allow the machines to be incorporated into various factory information and control systems.
Starpak has found that the versatility of the new system allows pack sizes previously considered impractical within the same machine geometry. Starpak and Ana-Digi Systems are presently busy with ongoing refinement of the system.
For more information contact Keith Gross, Ana-Digi Systems, +27 (0)21 914 9034, [email protected], www.anadigi.co.za
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