 | Author | Message | < Off Topics ~ Stepper motor control - part 1 | | eric | | Posted: Thu Oct 12, 2006 10:26 pm Post subject: Stepper motor control - part 1 | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | Just like almost any
other electrically powered
motor, a stepper
motor consists of a
fixed stator and a
moving rotator. However, while the
rotor (and sometimes the stator) is fitted
with electromagnets in dc motors,
the stepper motor has fixed electromagnets
only. The rotor, consisting of
non-magnetic soft iron or a permanent
magnet, rotates as a result of the
field reversals brought about by the
stator magnets. So, before we know
just how a stepper motor works,
we’ve discovered an important
advantage: there is no electricity supply
to the rotor; consequently, the
motor is brushless and therefore practically
free of wear and tear.
The first (inexpensive) stepper
motors were reluctance types with
rotors consisting of cogged wheels
made from soft iron.
Disregarding the
poor torque developed
by these
motors, reluctance
motors lacked ‘rest’ positions of the
shaft because the soft iron did not in
itself act as a magnetic pole. This shortcoming
was overcome with the introduction
of stepper motors employing
permanent magnets. Although the permanently
magnetic rotor did allow rest
positions, these occurred only at relatively
large step angles. This shortcoming
was caused by the limited number
of magnetic poles that could be
arranged on the radially-magnetised
cylindrical rotor. None the less, this
type of stepper motor provides a good
starting point for our purpose.
Figure
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