A Birmingham-based health products manufacturer had a major breakdown on one of two machines making sticking plasters. I responded to the call and found that the machine, one I had not seen before, was more than 10 years old and the faulty part was obsolete and no longer available. The machine had been designed and made in-house by the Works Engineer who had since left and records were sketchy. It incorporated a number of servo drives, one of which was a linear motor supplied by Linear Drives Ltd, of Basildon, used for indexing the continuous web of sticky-backed material through the punch and die set which punched out the plasters.
The linear motor comprises a stainless steel tube packed with disc magnets, running through the centre of a thrust block fitted with three integral phase coils that moves relative to the motor tube when the coils are energised in sequence. The motor was powered by a Linear Drives brushless servo amplifier operating in force (current) control mode, to control the tension in the web, and its operation is controlled by a motion controller made by German company Jetter GmbH, for adjusting the length of the indexing stroke which in turn controls the width of the sticking plasters.
The motor coils had burnt out, causing the amplifier to fail. The first problem was that whilst Linear Drives still made an almost identical motor that could be fitted as a direct replacement, they no longer made the amplifier, having been taken over by American automation equipment company which chose to supply its own range of brushless amplifiers. We resolved the problem by fitting a Lenze 9300 servo drive with onboard PLC that was programmed and commissioned and returned the machine to production within three days. Ironically, their sister machine also failed within a few weeks of the first with exactly the same fault. This time, I had it running again within three hours of fitting the replacement servo drive and PLC.