Ser vos or Steppers?
rate stopping. Plus, they still offer the
feedback capabilities servo motors do.
Luckily, it does not have to come with
a servo’s largest disadvantage: the larger
price tag.
The key has always been in the way
open-loop stepper motors work. They
typically have two coils, sometimes five,
with a magnetic balancing act going on
between them. Movement disturbs this
balance, causing the motor’s shaft to
fall behind electrically, but the opera-
tor cannot know how far behind it
falls. The stopping point is repeatable
for open-loop steppers but not for all
loads. Putting an encoder on the stepper
and making it a closed loop provides
some dynamic control. This lets opera-
tors stop on an exact spot under varying
loads.
These benefits from using closed-loop
stepper motors for certain applications
have sharply increased the popularity
of these motors in the motion-control
community. Specifically, in two of the
The open-loop stepper motor is designed to
run at a low speed while still providing high
torque.
C
losed-loop stepper motors offer all the advantages of stepper
motors: ease of use, simplicity, and the ability to run consistently
in low speeds with accurate stopping. Plus, they still offer the feedback
capabilities servo motors do. Luckily, it does not have to come with a
servo’s largest disadvantage: the larger price tag.
52 MAY 2019 MACHINE DESIGN
