Starpak/Levy & Smith have for years manufactured their well known and robust Brandpak single roll wrapping/shrink-wrapping machine. Except for the main PLC, however, the machine was largely mechanical. Although Starpak and its wide customer base were largely happy with the design, managing director Steve Smith knew that the technology was becoming dated.
Because of their mechanical nature the versatility of the machines was limited. This prompted Starpak to redesign the overall control philosophy in order to incorporate synchronised servo and VFD control of the unwinding, film feeding, cutting, indexing and final wrapping stations.
After due consideration of the various options, Starpak decided on utilising an LS GM4 PLC which, with its rack-mounted multi-axis positioning control in combination with four Mecapion servo inverters and five LS open loop vector inverters, offered many options to increase the versatility of the Brandpak.
The LS agents, Ana-Digi Systems, assisted Starpak in specifying and optimising the correct PLC, VFD, Servo Equipment and Planetary Gearboxes to suit the speed, torque and acceleration requirements of the new machine.
According to Steve the commitment received from Ana-Digi Systems gave him the peace of mind to expose his market to a technology. It was vital to Steve however, that the machines were still to remain user friendly and not to 'just use servos for the sake of it', as he put it. He jealously guards the simplicity of his designs, as he believes it is this very feature, in conjunction with careful component selection that has made the Starpak brand so successful.
With this in mind, Starpak rewrote the system programme into the LS GM4 PLC, incorporating the profiled multi-axis parameters of the positioning module, but retaining the basic feel of the original mechanical version.
The various 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 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 in-feed conveyor. This encoder feeds the multi-axis positioning module on the PLC, which then generates the necessary profiles for the three axes to suit the requirements of the various packs.
The conversion has dramatically improved the Brandpak in all operational spheres, namely smoothness, 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.
The finalised machines have been warmly welcomed by the end users, where the quiet, smooth and efficient running of the new ‘Brandpak’ has impressed all concerned.
Starpak itself has found that the new system affords so much more versatility that it can now handle pack sizes previously not considered practical within the same machine geometry.
Starpak and Ana-Digi Systems are presently busy with ongoing refinement of the operating system in order to further improve the machine.
For more information contact Keith Gross, Ana-Digi Systems, +27 (0)21 914 9030, [email protected], www.anadigi.co.za
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