September 8, 2008 by Chris Stergiou
Every plant has one, a troublesome automated system that’s been around forever. Or perhaps, this machine services a dying product line and replacing it isn’t feasible. Maintenance is high and uptime and reliability are low and it may require an additional operator simply because they’re the only one who “knows” the system. Furthermore, there may be little documentation and no one wants to open that “can of worms.”
This common situation presents a dilemma: how to get more reliability and uptime from this obsolete system without investing huge amounts of money? If a new product line and its accompanying new system aren’t on the horizon, the company may just struggle along.
There is another option however, that can turn the problem into a competitive advantage by looking at cost-justifiable “fixes” that eliminate the headaches. Begin by employing a technique that machine builders use to make a marginal machine design work at the debugging and optimization stage. Engineer a solution that works, accepting the hardware as it is and acknowledging that it’s not optimal.
Performing a detailed survey of the operational system typically reveals a few problem areas, such as a worn part feeder jamming, requiring operator intervention or a worn pneumatic actuator running open loop and based on variations in air pressure or system timing issues doesn’t always make its full stroke. A flaw in PLC logic or no feedback may also cause out of sequence actions under certain conditions. Parts may also regularly jam at some load location, causing a system crash.
These failure modes typically exist because while the design was adequate when new, the functionality was based on the components running at their rated performance and after millions of cycles and infrequent maintenance, normal wear has taken its toll. Replacing those components is the first step. (Often, this can be enough and is indicative of a lack of maintenance rather than deeper wear on the system.)
Beyond the first step, the remaining problem areas will deal with mechanical hardware, which means we will be looking at wear on those items that can’t readily be replaced. For corrective action, we isolate the problem area as if it were a stand-alone module and introduce the appropriate combination of mechanical, electrical and/or control solution that “designs-in” the wear as part of the solution. Accordingly, a “patch” must be engineered.
This solution will most often be low tech, as it will simulate whatever the manual operator intervention that corrects the problem is. For example, if the operator is periodically “poking” a tool at the end of the feeding track to clear a jam, a cylinder can be mounted at that position and perform this operation to 100 per cent of the cycles, as if we are clearing the jam 100 per cent of the time. If the problem is an out of sequence timing issue, the system can be “tricked” by making an artificial interrupt to the logic, mechanically or electrically. If the problem is that the system is open loop and the parts don’t always get there in time, a buffer can be created so that the system can always be ready to deliver the next part. Regardless of the problem, the solution basically designs the flaw into the system and treats it as part of the new design.
By developing this “engineered patch,” something that would be unacceptable in a new design, the problem is solved safely and reliably. The objective is increased machine uptime on a system that is dying by simply prolonging its life, not redesigning the system.
In summary, first accept that this is an end of life system and the objective is to increase uptime/reliability with minimum investment. This can be accomplished by replacing all low-cost worn components to get back into operational specification. Finally, since certain parts of the system are too costly to replace, such as tooling, feeders, controls etc., a creatively-engineered, low-cost “patch” to the problem that accepts and designs in the wear/flaw as part of the new system design will yield increased uptime and reliability from the system without impacting the final output (product) of the system.
Chris Stergiou (firstname.lastname@example.org) is a manufacturing consultant with 25 years of experience. He provides custom automation and consulting services to clients, many of them Fortune 500 companies.
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