If it isn’t broken, there’s no need to fix it
13 June 2016
Martin McGuffie, of motor repair specialist Euroserv, a company of CP Automation, explains how design engineers can minimise errors during the lifetime of a motor by listening to advice from maintenance teams while at the drawing board.
The first thing to think about is simple; the less complex the motor the better. From a repair perspective, if you can use a standard motor, it will be cheaper to install, there will be less to go wrong and if something does go wrong the repair will be easier and cheaper.
Occasionally there is the need for a sophisticated controller to alter the speed. Equally, it may be that you need an extremely high precision motor for your application. Nevertheless, there are still some tricks of the trade you can employ to make your project cheaper and more effective in the long term.
A low cost and mass produced, but unreliable, motor will never be cost effective because of the frequency of break downs and the high likelihood that it will need to be replaced rather than repaired. There’s also a strong chance that the cheaper units will be sealed, making maintenance extremely difficult. Indeed, sealing often makes the repair process so expensive that it’s cheaper to simply replace the motor.
Inevitably one also has to address the availability of the motor at short notice in the event of a replacement being required. Of course, if spares are kept in stock this may not be necessary and so, ironically, the harder to get hold of motors are sometimes the best option. This isn’t because they are scarce, but rather because they aren’t mass produced and are normally of higher quality. So, while a replacement may not always be easy, a repair often is. In this context, when choosing someone to do the repair job, you should always go to a specialist. If you go to a company that hasn’t carved out a niche, you will find that they will simply sub-contract your repair to a specialist; increasing your bill in the process.
When it comes to choosing peripherals to go with your motor, the first point of call will be control; if it’s required. In the early days of servo motors, the majority of the electronic components were in the drives. As a result, there was less to go wrong with the motor but more to go wrong with the inverter. Now, the more sophisticated servos contain more electronics and inbuilt control. So while the drives are becoming less complicated and cheaper, the servos are going in the opposite direction. The key to designing a product that will require as little maintenance as possible is to ensure that the balance is correct.
Another factor to consider is the environment in which the motor is going to be used. If you are designing for a harsh environment go for a more complex drive that can be boxed away. The design regulations for the industry may demand this anyway, if you are dealing with pharmaceuticals for instance, but the added bonus is that the motor and drive are protected from ingress and damage.
If it’s possible to do so, choose a motor that can be swapped out and replaced with one from a different manufacturer. However, this isn’t always an option; for instance, with servos every manufacturer has its own set up. You don’t want to end up in a situation where you can never replace your Siemens motor with an Indramat motor, to pick two major manufacturers at random. When this happens, the design guidelines laid out in this article will come to the fore – because your maintenance partner will be attempting to repair the motor or looking for easily sourced equivalent parts if a direct replacement cannot be secured in time. So in this context it’s simply a case of the more complex the motor the harder it is to replace.
As a design engineer, when you are anticipating the need to replace the motor, you should consider the potential for obsolescence. The consolidation in the drives industry means that not every supplier that’s around today will be around in the same form in five years time. As a result, there is a chance that their products may have been absorbed into other product lines or discontinued. This is another reason to adopt the maxim simple is best.
For instance, there was recently a customer whose motor was beyond repair but no longer in production. Fortunately, Euroserv were able to find six identical motors in surplus stock elsewhere, which the customer was able to buy. However, when these all fail, the customer will need to re-design their machine – with new drive cables, mechanical fittings and so on, all of which will inevitably be expensive.
The final thing to consider is the bane of the design engineer – over specification. Martin McGuffie has seen countless motors, which are doing an easy job like driving a spindle, specified at a much higher capacity than is required. Sometimes this is to the point that the motor costs £2000 but the same job could be done by a motor costing £1000. He has even known motors to be sent in for an overhaul with problems on parts of the motor that just aren’t being used at all. When the situation is reported to the customer, they are completely unaware of it because it’s a problem with functionality they just didn’t need in the first place. Remember, from a repair perspective it’s unlikely that you can solve the problem of over specification, because the motor’s housing will be designed for it to fit in place from a mechanical perspective. It can’t just be swapped out for a cheaper motor – this has to be considered at the design stage.
In conclusion, while the market is changing, to the point that eventually every motor will have a controller built in; there are some design fundamentals that remain the same. So, the next time you come to choose a motor, bear in mind that faults are inevitable and the key is designing a machine in which the faults can be fixed.
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