User's Manual

PMAC User Manual
92 Setting Up PMAC Commutation
OPEN PLC 1 CLEAR
CMD”#2O0” ; Force zero-magnitude open-loop
P229=I229 ; Save real Phase A bias
P279=I279 ; Save real Phase B bias
IF (I272<128)
I229=-I273 ; Force negative bias into A
I279=I273 ; Force positive bias into B
ELSE ; Ix72>128
I229=I273 ; Force positive bias into A
I279=-I273 ; Force negative bias into B
ENDIF ; This should force to 60 deg
M70=I274*256 ; Starting value for countdown timer
WHILE (M70>0) ; Wait for prescribed time
ENDWHILE
I229=P229 ; Restore real bias to A for 0 deg
M70=I274*256 ; Starting value for countdown timer
WHILE (M70>0) ; Wait for prescribed time
ENDWHILE
M271=0 ; Set phase position to zero
I279=P279 ; Restore real bias to B
CMD “#2J/” ; Close servo loop
DISABLE PLC 1 ; Keep from executing again
CLOSE
Phasing Referenced to Absolute Sensor
With a position sensor that is absolute over at least one commutation cycle of the motor, it is possible to
set the proper phase of the motor on power-up/reset without having to perform a phasing search. Instead,
the absolute sensor is read to determine the location of the motor within its phasing cycle. With this
procedure, the phasing reference only needs to be done once, during the initial development of the
system. Remember that this reading of absolute position is only done at motor reset time; the ongoing
phase position is always read through an encoder counter.
I-Variables
Two I-variables need to be set up properly to perform phasing from an absolute sensor. Ix81 tells PMAC
the address and format of the absolute sensor. If this parameter is greater than zero, PMAC will read
from the specified address in the specified format on power-up/reset to get the absolute position. Ix75
specifies the difference between the sensor's zero position and the phase cycle's zero position, in units of
(counts * Ix70). After reading the power-up/reset position from the absolute sensor, PMAC adds this
value and writes the resulting sum to the phase position register.
Set-up Phasing Search
To set up for the absolute phasing, first do a phasing search on the motor not utilizing the absolute power-
on position. All of the directions for setting up the commutation with an incremental sensor apply here.
These tasks should be done with an unloaded motor for maximum accuracy. Assure that a phasing search
on the motor can be done consistently using the stepper motor method implemented in the PLC program
shown in this manual, and the motor can be turned in both directions with small open-loop commands
(e.g., O5, O-5). This phasing search can also be done with four on-line commands, as shown below.
Once confident that the commutation algorithms with the stepper-motor phasing search are working well,
determine the phasing offset required for phasing with the absolute sensor. First, define an M-variable to
read the absolute sensor. For a resolver read through the Acc-8D Option 7 R/D converter board, this is a
TWR form of M-variable. For a sensor such as an absolute encoder read as parallel bits, usually through
an Acc-14 I/O board, this is a Y form of M-variable.