# 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

home_~phil