Azimuth motion failures dec09,jan10
There was a series of azimuth motion failures
on 07dec09 and again on 31jan10. A motion failure can be caused by
encoder showing that the system moved opposite to the direction
requested. It can also occur if requested motion does not occur after a
specified time interval (assuming the system is active).
Aeronomy had been running for a few days and had
been getting the motion failures. The moved the azimuth from 168 to
168+90 degrees at slew speed for the entire time. The errors occurred
The plots show the azimuth motion
near az=168 degrees (.ps) (.pdf
- azimuth moving at .4 deg/sec and passes 168 degrees.
- azimuth then commanded back to 168
- azimuth overshoots 168 to about 168.06 (this is normal)
- azimuth then approaches 168 but never quite arrives (gets to
- azimuth sits for a 5-90 secs and then moves away from az=168.
This causes the motion failure.
- The plots show the azimuth position for each azimuth swing as it
moves toward az=168 degrees. The vertical axis is the azimuth position.
The horizontal axis is the number of seconds since the azimuth crossed
- Top: This shows the azimuth swings when a motion failure did not
- Bottom: This has the azimuth swings with the motion failure. The
* and dashed vertical line occurs at the motion failure. At each motion
failure the azimuth position jumps up away from azimuth=168 (the
The speed monitor output is used by the PI loop to
control the azimuth. All 8 of the amp velocities are summed to get the
final control command. Looking at one of the amplifiers, it's speed
monitor output had a large dc offset (when the azimuth was stationary).
After replacing the amplifier the az motion failure problem went away
(at least till jan10).
The az motion failure occurred 3 times in the early
morning. The first time was during an astronomy. The last 2 times was
the aeronomy azimuth swings.
The plots show the
azimuth information during the failures (.ps) (.pdf):
- Page 1: azimuth position vs hour of day. The failures are flagged
with red,green,blue lines. The last two failures occurred at 180
degrees when the azimuth was turning around.
- Pages 2-4: azimuth failures 1,2,3
- Top: azimuth position vs time around the failure
- Bottom: az velocity during failure. The red line is computed
from the encoder. The black line is the velocity from the amplifiers
(all 8 amplifiers values are averaged).
- Page 4: Amplifier velocity vs Encoder velocity
- Top: all data 5am to 10am
- bottom: blowup showing abs(vel)< .02 deg/sec.
- There is a large vertical spread in the amplifier velocity
when the encoder velocity is 0.
- Page 5: Encoder Velocity - amp velocity vs time when encoder
velocity < .01 deg/sec.
- The plot shows how velocity difference when the encoder
velocity is small. motion failures 1,2,3 are marked in red,green,
- Failures 2, 3 (green,blue) have a large amplifier offset and
then jump down to 0 when the failure occurs and the motors are shutdown.
- failures 2,3 (the az failures while swinging the azimuth arm)
show motion in the wrong direction. Failure 1 shows no jump.
- All 3 failures show encoder velocity=0 while the amp velocity is
non-zero prior to the failure.
- Probably need to check the individual amplifier speed outputs to
see if one has a dc offset.