Page 59 - CNC Robotics

GNG Robotics

APPLICATION NOT E

Figure 5 : A real motor. Multiple poles are norma- phase-on is AClCBlBDIDA and the half step se-
lly employed to reduce the step angleto quence is N AC/C/BCI8JBO/OtDA. Note that the
a practicalvalue. The principle of opera- stepangleforthe motorshownaboveis 15°, not45 0 .
tion and drive sequences remain the As before. pratical motors normally employ multiple
same . po les to give a much smaller step angle. This do es
not , however, affectth e prlrcole of operation of the
drive sequences.

Figure 7 : A variable reluctance motor has a soft
iron rotor with fewer poresthan th e sta-
tor. The step angle is 15 ° for this motor.
•

c

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Figure 6 : A unipolar PM rrotoruses Milar win-
dings to reverse the flux in each phase.
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D ,

GENERATI NG THE PHASE SEQUENCES
The heart of the l297 bloc k diagram, figure 8, is a
block called the translator whic h generatessuilable
phase sequences for half step, one-phase-on fuU
step and two-phase-on full step operation. This
block is controlled by two mode inputs - direction
ICWI CCW) and HALFI FULL - and a step clock
which advances the translator from one step to the
next.
Four out puts are provded by the translator for sub-
sequent processing by the outp ut logic block which
implements the inhibit and chopper functions.
VARIABLE RELUCTANCE MOTORS Internally th e translator con sists of a 3- bit counter
A variable reluctance motor has a non-magnetized plus so me co mbinational logic which generates a
basic eight-step gray code sequence as shown in
soft iron rotor with fewer po les than the stator (fig-
ure 7). Unipolar driveis usedand the motor is step- figure9.Anthree drive sequencescan be generated
easily from this master sequence. This sta te se -
ped by energizing statorpolepairs to alignthe rotor
with the polepieces of the energizedwinding. qu ence correspondsdirectty to half ~mode. se-
lectedby a high level on the HALFI FULL irout.
Onceagainthreedifferentphasesequercesca n be
used. The wave drive sequence is NCIBID ; two-
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