Appendix – Anti-Rollback Setup
126
d) Set the brake and turn the drive OFF via normal commands. (In that order, to prevent the car
from drifting away!)
5. Repeat #3 several times and.....
a) Increase the setting of ARB Bandwidth to reduce the amount of initial movement as desired.
But there may be more jerkiness. Reducing the setting will allow more movement, but with
less jerk. Adjust for a good compromise.
b) Reduce the setting of ARB Damping to speed up the position recovery, or increase the setting
for a softer recovery, as desired.
c) If oscillations occur, release the brake and shut down the drive or reduce the setting of ARB
Bandwidth to stop them. This may be a practical limit for position tightness in this particular
hoistway. See the hints below for using the notch filter.
6. Change the reference velocity to run the car at normal speeds. Make several empty single or
multiple floor runs up and down to observe the complete starting action. The adjustments made
so far should not alter landing position accuracy. Ride the car to observe the quality of
adjustment.
7. If weights are available, load the car to payload capacity. Repeat the observations and
adjustments of step 4 with a full load. In this case the initial movement should be downward.
Then repeat floor runs as in step 5 with a full load. Ride the car to verify smoothness.
Adjustment procedure is complete.
ARB Adjustment Hints And Cautions
1. Caution, the ARB function can increase regulator bandwidth far beyond that required for
controlling the speed of the elevator. It does so at only near zero speed, but when the ARB gain
bandwidth is boosted it is possible that one or more mechanical resonant frequencies may
become excited to produce unacceptable vibration. If an annoying vibration does occur, try to
determine the resonant frequency. Then use the notch filter to tune it out if possible. Be aware
that the notch filter does cause additional phase shift lag. This can and will interfere with the
operation of E-Reg and ARB. Tune the notch filter to the resonant frequency and adjust notch
depth to the smallest value that suppresses the vibration. Then turn ARB off and verify or re-tune
E-Reg to yield acceptable performance. Then re-tune ARB settings to control rollback. Some
hoist ways may not be compatible with high gain ARB settings.
2. The adjustment settings for Speed Bandwidth and Per-Unit Inertia are used by both the velocity
regulator (E-Reg) and the velocity control portion of ARB, therefore adjustment of them will alter
the performance of anti-rollback controls. Be sure to tune the velocity controls of the elevator
BEFORE adjusting controls for ARB Bandwidth and Damping. Changing any ARB settings will not
interfere with other velocity control tuning.
3. Elevator rollback is a function of gravity load unbalance of the car. This is what causes the car to
move when the brake is released, even though the reference velocity may still be at zero.
However, there is a finite time required for ARB to measure unwanted car motion via the encoder,
produce a counteracting motor torque, and then return the car to the original position. The
reaction time is controlled by ARB Bandwidth. The smoothness a
nd time to settle is controlled by
ARB Damping. The need for ARB starts only when the elevator brake is actually released, not
when it is told to release. (A subtle difference in electromechanical timing.) But the allotted time
for ARB to function will cease as soon as the velocity reference (internal or external) moves away
from zero speed and crosses the threshold identified by ARB threshold.
a) Ideally, there would be adequate dwell time after release of the brake for ARB settling to
occur. But elevator floor-to-floor time specifications do not necessarily allow for any time
delay. If the resulting ARB time is cut short by release of the velocity reference before position
settling is complete, the car will begin to accelerate toward the next landing from wherever it
may be in the ARB cycle. The position regulator to speed regulator change-over will be
smooth, but the repeatability of velocity profile tracking during acceleration may be altered by
the amount of load unbalance and the value of the threshold set in ARB threshold. Keep this
setting as low as possible for best results.
b) If the threshold is set too low ARB may be terminated too early, particularly when using an
external analog reference. This will result in elevator rollback that could have been prevented.
c) If acceleration of the velocity profile is started and crosses the threshold before the elevator
brake actually releases, ARB will not function and may result in elevator roll-back as
acceleration begins. This, and the jerk or vibration sometimes felt by passengers as the motor
To Next Page
Loading...