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Stepping out of the shadows

An Unimatic Engineers product story
Edited by the Engineeringtalk editorial team Feb 18, 2004

Stepper motors are fighting back against the current dominance of servo systems and proving that they represent a vibrant, developing technology as relevant to industrial design as any alternative.

Stepper motors are fighting back against the current overdominance of servo systems and proving that they represent a vibrant, developing technology that is as relevant to industrial design as any alternative.

In the past steppers and servos stood comfortably alongside each other, and users selected which ever was appropriate for the task in hand.

But about 10 years ago the big control companies started putting their promotional muscle behind servo systems.

"They naturally like servos because they are used in conjunction with encoders, controllers, PLCs and other control equipment, so generate lots of synergistic sales opportunities", explains Jon Harding of Unimatic Engineers.

"And at that time they were able to use the very persuasive sales pitch of saying that servo prices were falling".

However, what was not said was that stepper prices were falling too, and often the cost of the gearhead and other necessary items were omitted.

"Now we have a situation where many engineers and designers are blinkered into thinking only of servo solutions to what they perceive as precision systems.

But in reality 70% of applications would be better served with a stepper".

Unimatic supplies both stepper and servo technologies and tries to fit the more appropriate option for each application.

However it is notable that many users will barely consider anything other than a servo.

"Servos are indisputably better for high speed dynamic work", concedes Harding, "but that represents less than a third of all the jobs I see.

If what you actually need is point-to-point motion profiles, steppers will almost always serve you better.

And because you don't need to close the control loop, set up is far easier and faster, cheaper and less prone to working out of synchronisation".

Harding thinks that he has detected the beginnings of the return swing of the pendulum, with users once again willing to listen when a stepper solution is suggested.

He thinks that this may be due in part to having to provide service, maintenance and back up to systems and machines that may have to be exported: steppers are so much simpler that local field engineers are more likely to sort out problems on the spot that to try to call an international helpline.

The purchase price differential is quite apparent, and users are increasingly aware of the additional on-costs relating to servo systems.

"Some of the support technologies like digital signal processing make it very apparent that the supposed advantages of servos are often overinflated, and when you look at the performance capabilities of today's high powered steppers you can be left wondering why so many people overlook them in the race to pay for a servo".

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