Parker TQ10X, Руководство пользователя

Страница: 122 / 139

➅
Troubleshooting 113
Foldback
A mechanical jam in a servo system can cause the motor to overheat. In contrast
to a stepper motor, which does not run hotter when jammed, a servo will apply
full current (for full torque) while it attempts to move as commanded. Usually,
this current will be much higher than the motor can withstand continuously. If it
persists indefinitely, it may damage the motor’s windings.
To help protect the motor from overheating, the TQ10X has a current foldback
circuit. If high motor current persists for too long, the circuit can reduce the
current to a lower level that decreases the rate of motor heating; it can also acti-
vate a fault condition.
Three of the DIP switches on top of the drive allow you to set the maximum
current the drive will produce (“
PEAK CURRENT LIMIT ”) These switches should
be set to a value no greater than three times the continuous current rating (Ics) of
the motor used. This setting is used by the foldback circuitry to help protect the
motor.
Six of the DIP switches configure the foldback circuitry. Three of them set the
time that “high” current will be permitted before the foldback circuitry takes
action. Settings range from 1 to 10 seconds. One switch defines what constitutes
“high” current. This is set according to Ics. One switch will cause a latched fault
to be generated when the selected time at high current is exceeded, otherwise
current is reduced (“folded back”) to 40% of the peak current limit setting. One
switch allows foldback to be disabled entirely. (see Chapter 2—Installation and
Chapter 4—Tuning (Tuning procedure) for instructions on setting the dip
switches.
How Foldback Works
When actual current produced by the drive exceeds the threshold (relative to the
peak current limit) set with SW2-2, the foldback circuit illuminates the
PEAK
CURRENT LED green, and starts a timer. If the current remains above this
threshold for longer than the time set with the time-at-peak dipswitches, the
foldback circuit activates, and the
IN FOLDBACK LED illuminates red. The
circuit can generate: A) A latched fault, if so configured, or B) reduce current to
40% of the peak current limit setting.
In case A (with SW2-1 ON ), the fault will remain until power is cycled, or the
RESET input is asserted. This fault condition will be indicated by a red
MOTOR
FAULT LED, and an active FAULT OUT signal. The IN FOLDBACK LED may go
out when the
MOTOR FAULT
comes on, depending on the load. When faulted, the
motor current will be reduced to zero.
In case B (with SW2-1 OFF ), the current reduction will persist until the command
input goes below the actual current, when the circuit will once again allow the full
current permitted by the peak current limit setting. While foldback is limiting the
current, the
IN FOLDBACK
LED will be red. When the command is reduced, the
LED will go out. The FAULT OUT will not go active, since current foldback is not
considered a fault.
Oscillating currents, such as are seen when a system goes unstable during tuning,
will activate the foldback circuit if the current gets high enough, and the frequency
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com