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az encoder1 fail

Azimuth motion failures dec09,jan10

feb10

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).

07dec09:

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 when:

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 about 168.02).
azimuth sits for a 5-90 secs and then moves away from az=168. This causes the motion failure.

The plots show the azimuth motion near az=168 degrees (.ps) (.pdf ):

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 az=169 degrees.
Top: This shows the azimuth swings when a motion failure did not occur.
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 requested position).

Resolution:

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).
processing: x101/091207/agc.pro

31jan10:

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, and blue.
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.

Summary:

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.

processing:x101/100201/aztrouble.pro

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