Conducting the bottle minuet
October 2009
Installing intelligent drive and control technology let one Korean maker of blow molding machinery double productivity.
Polyethylene terephthalate is certainly a tongue-twister but it nonetheless makes it far easier to carry soft drinks. Ever since this plastic – better known as PET – revolutionized the range of bottles available, it seems like we’re carrying only the beverage itself; the bottle that holds the liquid weighs almost nothing. What’s tough, by comparison, is producing the featherweight container. A complex sequence of motions has to be coordinated during the process.
Pisko, a Korean manufacturer of machines used to blow mold PET bottles, has reduced cycling times for its newest machine so drastically that it is now twice as productive as its predecessors. The engineers at Pisko and Rexroth have fitted the machine – previously driven by mechanical means – with an intelligent synchronization concept. The system includes Motion Logic Control – the IndraMotion MLC – and an IndraDrive C Package comprising a regulator and servo motor. All this was made possible by two innovative gimmicks: a Virtual Master and Flexprofile.
A faster machine
In the past, a single large drive set the pace and impressed it mechanically, by way of gearing, on all the machine’s various functions. The rigid succession of movements wasted valuable time during the production process. The Virtual Master now takes the place of the mechanical drive. Something like an invisible conductor with his baton, the Master specifies the timing for the five functional axes involved so they play in perfect harmony, each keeping an ear on the other four, so to speak. Here the Master in the electronic control unit imitates the bulky mechanical drive and specifies, like a virtual timing shaft, the motion values for the individual axes. One rotation of the virtual drive corresponds to one machine cycle. Within this cycle the control solution makes it possible for individual shaft motions to overlap, since the starting and final angles are specified for each of the five axial drives. The Virtual Master simply tells the drives what angles they are to assume and when movements are to be executed within the overall sequence of motions. In this way the individual functional steps mesh perfectly. The output rate is increased to 1800 units per hour, thus boosting machine productivity by 100 per cent.
Faster operation
In the past, if the technician setting up the machine wanted to optimize a sequence of motions at just one single point, then it was necessary to edit an entire table with more than a thousand numbers. This was because the control profile imitated a mechanical cam disk. Similar to the camshaft in a car’s engine, the cam disk triggered a predefined function at every point along a revolution. In previous concepts the cam disk was simulated in electronic controls using a table with 1024 entries. This table depicted each of the possible functions.
The Flexprofile concept, by contrast, simplifies retroactive programming changes. This makes it possible to define individual control segments for each axis within the motion sequence. The advantage here is that the operator need not change a thousand values, but just a single number, in order to modify the movement of an axis. In this way the blow molding machine not only saves considerable amounts of time. Its operator can switch to a different product mode by pressing just a single button.
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