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64 • Chapter 6 Programming Motion DMC-2X00
When a Galil controller is configured for step motor operation, the step pulse output by the controller
is internally fed back to the auxiliary encoder register. For SPM the feedback encoder on the stepper
will connect to the main encoder port. Enabling the SPM mode on a controller with YS=1 executes an
internal monitoring of the auxiliary and main encoder registers for that axis or axes. Position error is
then tracked in step pulses between these two registers (QS command).
YC
YBYATP
TDQS
××
−=
Where TD is the auxiliary encoder register(step pulses) and TP is the main encoder register(feedback
encoder). Additionally, YA defines the step drive resolution where YA = 1 for full stepping or YA = 2
for half stepping. The full range of YA is up to YA = 9999 for microstepping drives.
Error Limit
The value of QS is internally monitored to determine if it exceeds a preset limit of three full motor
steps. Once the value of QS exceeds this limit, the controller then performs the following actions:
1. The motion is maintained or is stopped, depending on the setting of the OE command. If OE=0
the axis stays in motion, if OE=1 the axis is stopped.
2. YS is set to 2, which causes the automatic subroutine labeled #POSERR to be executed.
Correction
A correction move can be commanded by assigning the value of QS to the YR correction move
command. The correction move is issued only after the axis has been stopped. After an error
correction move has completed and QS is less than three full motor steps, the YS error status bit is
automatically reset back to 1; indicating a cleared error.
Example: SPM Mode Setup
The following code demonstrates what is necessary to set up SPM mode for a full step drive, a half
step drive, and a 1/64
th
microstepping drive for an axis with a 1.8
o
step motor and 4000 count/rev
encoder. Note the necessary difference is with the YA command.
Full-Stepping Drive, X axis:
#SETUP
OE1; Set the profiler to stop axis upon error
KS16; Set step smoothing
MT-2; Motor type set to stepper
YA1; Step resolution of the full-step drive
YB200; Motor resolution (full steps per revolution)
YC4000; Encoder resolution (counts per revolution)
SHX; Enable axis
WT50; Allow slight settle time
YS1; Enable SPM mode