Why use a step motor?

[PopeyeTheSailor]

I would like to know why one would choose to use a step motor over another technology i.e. DC servomotor, Brushless DC servomotor, etc. My understanding of the advantage of a step motor (dated by about 25 years) was the ease of controlling motion/position without shaft position feedback. When I look at the information that is available to me for step motors, I see the use of encoders for feedback. This would seem to take away from that advantage. If you use an incremental encoder, won’t this have problems as far as encoder transitions and step angle (full step mode)? Speaking of full step, I see a lot of step motors being offered with micro stepping as a way to overcome some of the inherent problems with driving the motors through a wide range of speed and torque. I’ll list of some of the things I think make a step motor a desired choice:
1. Longer life (no brushes)---BLDC is same
2. Holding torque (without power, although some of the very small motors do not exhibit much)
3. Ease of control (pulse train to achieve position/speed etc.)
4. Control electronics (a little less complicated than a brushless DC, maybe the same as a mechanically commutated DC motor)
Any insight would be appreciated.

 

[itsmoked]

Stepper motors cost less to manufacture and so cost the user less.

The control is digital. This makes writing the computer control code for them easier.

Most steppers do not have encoders and use only dead reckoning. Lack of an encoder reduces costs significantly.



Keith Cress
kcress -

http://www.flaminsystems.com