A hot summer!
2003 promises to be the summer of the century in Germany. June broke new records and many a drinks producer broke out in a sweat. The weak points along a line often only become evident during continuous operation at full output and it is just then that there is no time to optimise the line. The following serves as an insight into how such weak points can be identified even under these prevailing conditions and the solutions available for such faults which can be frequently observed.
It is annoying when the conveyor motor fails but the cause can be quickly found and rectified with a long-lasting effect. It is much more difficult to find the many small malfunctions which can have a considerable influence on the efficiency of a filling line when added together. A jammed bottle or a valve which has remained closed for a few seconds - these are faults which are hardly noticeable but the consequences of which can result in considerable downtimes. As a rule there is plenty of information available about these malfunctions. Whether it is the PLC for the filler, a temperature probe in the washing machine or the jam switch before the packer - information is collected and processed at many stages or simply only displayed. It is becoming increasingly difficult in modern filling plants to identify the cause of a fault from the information available. For example even if the control photocells of the pressureless combiner, before the sorting of the returned empties, identifies jammed bottles and resolves this situation, by decelerating the conveyor speed, the effect of this occurs a lot later as a lack of bottles at the filler. The information which could help to find the cause of this, that is to say the signals from the conveyor belt control system, is no longer available at this point in time.
It is exactly at this point that the latest products in the field of data acquisition and evaluation become relevant. Signals from sensors, machine controls or control computers of your choice can be stored in a central database. Every fault can be analysed afterwards with the appropriate software if the data has been saved on a central computer. The advantages are obvious. Those of you who have attempted to find the cause of a malfunction have learnt by experience that you were always looking somewhere else at the decisive moment. The database makes it possible to view each situation repeatedly and to observe various positions at the same time. In this way the delayed effect a fault at the unpacker can have on the efficiency of the filler can quickly be seen in a diagram. Further possibilities arise from storing the data. You can take the time to deal with data collected in August in peace and quiet in the autumn, when demand is not so great, if you do not have the time at the moment to analyse the faults because there are more important matters to take care of.
Small converter units make this possible. These are installed in the control cabinet where the signal is generated. They convert digital as well as analog information in such a way that this can be transferred via a network connection to the computer collecting the data. The converters have been miniaturized to such an extent that there is always room for them even in a control cabinet which has been integrated into a machine. Nowadays a single converter can process several signals at the same time and pass these on reducing the time required for installation and wiring considerably.
An Ethernet connection has established itself as quasi-standard for the signal transmission to the central database. Extensively branched networks can be set up without a problem using this technology by using several distribution points which ensures a very high transmission reliability. All functions can be continuously monitored by means of this network.
But how does this work in practice? It is often very noticeable when analysing data that the greatest potential for improvement lies in the transport of the bottles. In many cases dealing with constant jams has become so routine for the operator that it is no longer registered. Whereas a fault to the machine is purposefully eliminated, smaller transport problems are regarded to be normal. In this case the new analysis tools help to locate the cause and to deal with it in practical terms on the basis of the data recorded. If the losses incurred due to a reduction in efficiency are calculated it is soon realized that an investment in optimising the transport of the containers quickly pays for itself.
The sensitive areas in the case of filling lines for returnables often prove to be the sections between the unpacker and the washing machine, the section before and after the filler and the infeed to the packer. Foreign bottles, foreign objects and pieces of broken glass are amongst the causes for interference in the dry area before the washing machine. 90% of all malfunctions can often be eliminated by carrying out a mechanical and control technical revision.
A minus point is scored each time the filler stops in the wet section as far as efficiency is concerned. Modern control systems ensure that the bottle flow runs at full load output for as long as possible by electronically blocking the machines and in the case of a shortage allow the bottles to pass through constantly with reduced power rather than running at full speed to an abrupt stop. The database analysis clearly shows the consequences of such an abrupt stop. In many cases the graphs show a saw-tooth effect after such stops. A constant performance is only achieved again after several starts and stops. By comparison the curve produced in the case of electronic blocking stands out as a harmonious line flow. Efficiency is kept very constant in this case due to the reduced number of stops.
The supply to the packer is the next critical position. Sufficient bottle pressure is required here in order to place the bottle in the correct position otherwise it is exactly this pressure which causes the bottles to become jammed at the laning section. An attempt is made to automatically resolve the jams using vibrating guide rails. This is not always successful. The machine frequently stops until the operator intervenes. Many a person has also wondered whether the vibrating guide rails have even possibly encouraged the jam. However even small jams which are automatically resolved cause minor stops at the packer which are hardly noticeable but are evident later amongst the numbers of produced or to be more precise non-produced bottles. New systems ensure that the bottle inflow is constant. The movement of the bottles is monitored by sensors and if necessary (and only then!) movable guide rails are placed in such a way that jamming and a subsequent break to the bottle flow is prevented. In this way jams can be resolved by purposeful intervention before the bottle pressure has become so great that the situation can only be sorted out by using brute force.
Now is the time to get involved with data acquisition and analysis in order to avoid this sudorific work next summer. You can look forward to the next season more calmly by introducing the resultant measures in the winter. Hopefully you will nevertheless start to sweat again because this summer of the century will most certainly not be the last this century.
This report has been taken from the German magazine "Brauindustrie", published in August 2003 issue 08/2003 page 36.