- Tiedown 4 stated having problems on sat 02mar13.
- The encoder readout started jumping between the current
value and 24 inches (first time around 11:00). The program
was in tietrk mode at this time (use the distomats to keep
the platform at a fixed height).
- Around 13:00 the mode was switched to tiepos temp (move to
a fixed position and sit there).
- The jump continued intermittently.
- On sunday 03mar13 around 12:00 the tiedowns were turned
off and disabled. For the rest of the day the operators
would enable the tiedowns, move them, and then shut them
The plots show the tiedown status for these two days:
02mar13 td status (.ps) (.pdf)
- page 1: data 0-24 hours sat 02mar13
- top: encoder position. td 4 is in red
- the jumps are at:11,13,14,19 hours
- 2nd: velocity feedback. This is the voltage readback
that is sent to the amplifier
- The bright purple is the requested value for
- 3rd: amplifier speed readback. This voltage provided
by the amp is proportional to the amp speed
- There are large red jumps were td 4 encoder jumped.
This shows that the system tried to follow the encoder
- 4th: drive status. td 4 was off (red value=0) from
14:30 to 16:15
- bottom: drive current from the amplifier. This is
proportional to the motor torque
- There are large jumps in td 4 torque (red) during
the encoder jumps.l\
- page 2: blowup of 14.5 to 14.7 hours (14:30 to
- the 5 frames are the same as page 1
- the longest encoder error lasted from 14.58 to 14.61
(.03 hrs = 108 seconds).
- The motor power was turned off just before this
occurred (frame 4 status = 0).
- The computer continued to command the a/d to follow
the jump (vel feedback -> -1800).
- this shows that the computer was not completely
"messed up" when the encoder failure occurred
(since it was still commanding the amplifier and reading
back the requested voltage). I do wonder why the cpu was
commanding the td if the drive status had been set to
- sun 03mar13 td status (.ps)
- the tiedowns were turned off around 11:30. Around 13:00
emergency stop was set.
- There are encoder jumps at 10:45 and 14:00
- During these jumps there were large torque in td4
- td 4 position readback is jumping from current value to 24
- It could be:
- the encoder or encoder board
- the bus connecting the encoder board to the cpu
- the cpu
- the cpu continued to do some functions while the jumps
occurred so it wasn't completely dead.
- It is important to make sure that the tiedowns are left
off while this problem occurs. You don't want these large
steps in position to be sent to the jack.