Reference Manual

PMAC 2 Software Reference
102 PMAC I-Variable Specifiation
Commutation I-Variables
Ix70 Motor x Number of Commutation Cycles (N)
Range
0 .. 255
Units
Commutation cycles
Default
1
Remarks
For a PMAC-commutated motor (Ix01=1), this parameter is used in combination with Ix71
to define the size of the commutation cycle, in encoder counts, as Ix71/Ix70. Usually, this
is set to one, and Ix71 represents the number of counts in a single commutation cycle.
Ix70 only needs to be set greater than one if the number of counts in a single cycle is not
an integer.
A commutation cycle, or electrical cycle, consists of two poles (one pole pair) of a
multiphase motor.
Example
A 6-pole brushless motor has three commutation cycles per mechanical revolution. If a
feedback device is used with 4096 counts per mechanical revolution (a number not
divisible by three), Ix70 should be set to 3, and Ix71 to 4096.
See Also
I-variables Ix01, Ix71-Ix83
Setting Up PMAC Commutation
Ix71 Motor x Encoder Counts per N Commutation Cycles
Range
0 .. 8,388,607
Units
Counts
Default
1000
Remarks
For a PMAC-commutated motor, Ix71 defines the size of a commutation cycle in
conjunction with Ix70 (counts/cycle = Ix71/Ix70). The meaning of a “count” used in this
parameter is defined by the encoder-decode variable for the commutation feedback device
(Encoder I-Variable 0; I900, I905, etc. on a PMAC(1); I9n0 on a PMAC2). If a “times-4”
decode is used, a count is one-fourth of an encoder line.
If a highly interpolated encoder is used (e.g. from an ACC-51P or ACC-8D Opt 8) for
servo loop closure, the digital hardware quadrature counter is usually still used for
commutation, with a resolution of 4 counts per encoder line.
If the commutation feedback comes from a MACRO-node position feedback register, the
position value is usually in units of 1/32 of a count, so Ix71 should be 32 times larger than
it would be for reading a hardware encoder counter directly.
A commutation cycle, or electrical cycle, consists of two poles (one pole pair) of a
multiphase motor.
Example
A four-pole brushless motor with a 1000-line-per-revolution encoder and “times-4” decode
read directly on the PMAC has 2 commutation cycles per revolution and 4000 counts per
revolution. Therefore, either Ix70=2 and Ix71=4000 could be used, or Ix70=1 and
Ix71=2000.
For the same motor and encoder read through a MACRO Station, the units of the position
register read for commutation would be 1/32-count, so there would appear to be 4000*32,
or 128,000 counts per revolution. Therefore, either Ix70=2 and Ix71=128000 could be use,
or Ix70=1 and Ix71=64000.
See Also
I-variables Ix01, Ix70, Ix72-Ix83
Setting Up PMAC Commutation