User's Manual

PMAC2 User Manual
Setting Up PMAC2 for Sine-Wave Output Control 37
Establishing Basic Output Operation
A quick test can establish basic operation of the commutation outputs, the drive and motor, and the
feedback. The test uses the output offset variables Ix29 and Ix79 to force current directly into the
particular phases and drive the motor like a stepper motor. The test can be used to verify:
• That output voltages are obtained from the Acc-8E board
• That currents flow in the phases of the motor
• That the currents cause the motor to lock into a position (it only does this well for a synchronous
motor)
• To set the proper polarity of the Ix72 commutation phase angle parameter. (It only does this well for a
synchronous motor. For an asynchronous induction motor, the polarity of Ix72 may have to be
determined by trial and error.)
Executing the Test
This test, which can easily be done from the terminal window of the Executive program by typing in a
few simple commands, is best illustrated by an example, which will use Motor 1. It should first be done
on a bare motor with no load for safety reasons:
M101->X:$C001,24,S ;Encoder 1 phase position register
#1O0 ; Command zero output
I129=2000 ; Positive offset of 2000 bits on 1st phase
M101 ; Request position (after motor settles)
382 ; PMAC responds with position
I179=2000 ; Positive offset of 2000 bits on 2nd phase
M101 ; Request position (after motor settles)
215 ; PMAC responds with position
If the servo-loop feedback has already been established with Ix03, the position query P command, or the
position window in the Executive program, can be used instead of the Mx01 encoder position register.
Verifying Basic Operation
Setting a non-zero value for Ix29 should force a voltage on DACAn, which can be read with a voltmeter
or oscilloscope. It should also force current in the matching phase of the motor, which can be measured
with a current probe. Setting a non-zero value for Ix79 should do the same for Phase B.
A synchronous motor should lock into a position and hold it when an Ix29 offset is given. An induction
motor may lock in briefly for a brief period of time due to short-term eddy currents in the rotor.
When the Ix79 offset is added, a synchronous motor should lock into a new position a fraction of a cycle
away from the earlier position. An induction motor may do this also, but probably not as strongly.
Evaluating the Polarity Match
By looking at the direction of motion between the two steps, we can determine the proper setting of Ix72.
If the position changed in the negative direction, Ix72 should be set less than 128 -- to 85 for a 3-phase
motor, or 64 for a 2- or 4-phase motor. If the position changed in the positive direction, Ix72 should be
set greater than 128 -- to 171 for a 3-phase motor, or 192 for a 2- or 4-phase motor.
For the motor in this example, we conclude that we want a value of 64 if it is a 4-phase motor, or 85 if it
is a 3-phase motor. If the encoder direction is subsequently changed for system reasons, I172 should be
changed as well, to match.