User guide

Chapter 6. Following 223
Conditional
Statements Using
PMAS
The master cycle position (PMAS) value may be used in the comparison argument of these
commands:
• WAIT & GOWHEN: If it is desired to WAIT or GOWHEN on a master cycle position of the
next master cycle, one master cycle length (value of FMCLEN) should be added to the master
cycle position specified in the argument. This allows commands that sequence slave events
through a master cycle to be placed in a loop. The WAIT or GOWHEN command at the top
of the loop could execute, even though the actual master travel had not finished the previous
cycle. This is done to allow a PMAS value which is equal to the master cycle length to be
specified and reliably detected.
• IF, UNTIL, & WHILE: These arguments use the instantaneous PMAS value. Be careful to
avoid specifying PMAS values that are nearly equal to the master cycle length (FMCLEN),
because rollover may occur before a PMAS sample is read.
Compiled Motion
Following profiles may be pre-compiled to save processing time. For details, refer to
page 166.
Troubleshooting for Following (see also Chapter 7)
The table below offers some possible reasons for troubles which may be encountered in achieving the desired slave motion.
Symptom Possible Causes
Slaves do not follow master • Improper FOLMAS
• Poor connection if master is encoder
• Master running backward
• No encoder power (when the encoder is selected as the master)
Slave motion is rough • FFILT command value too low
• Unnecessary FPPEN amplifies master roughness
Ratio seems wrong • FOLRN and FOLRD slave-to-master ratio values are inaccurate,
possibly reversed
• SCLD or SCLMAS wrong
• DRES or ERES wrong for encoder step slaves (steppers only)
• Following limited by FMAXV or FMAXA (steppers only)
Slave profile wrong, or un-repeatable • WAIT used where GOWHEN should be
• Too little master travel between GOWHEN and GO1, desired PMAS is
missed
Master/slave alignment drifts over
many cycles
• Roundoff error due to fractional steps resulting from SCLD or SCLMAS
and user's parameters
• Ratios and master distances specified result in fractional slave steps
covered during ramps, constant ratio
Slave lags Following position
(steppers only)
• Inhibited by FMAXV
• FMAXA
clips acceleration peaks resulting from attempt to follow rough
master
Slave dithers, or oscillates about
desired position
(steppers only)
• EPMG too high for encoder step slave
• FMAXA too low for EPMV