�� . �� : http://www.naic.edu/~phil/td/tdtrouble/td12_largeTqs_ReplaceJack_apr12.html
�� : Thu Apr 19 22:14:20 2012
�� : Tue Feb 5 02:35:42 2013
��:
�� : � � � � � � � � � � � � � � � � � � � � � � �

td12 largeTorquesReplaceJack apr12

td12 needs large torques to move. Jack to be replaced

19apr12

Td 12 stopped moving on 18apr12 around 20:00. The error was cmdSpdErr and foldback.

cmdSpdErr occurs when the motor speed read back from the amplifier differs from the requested speed but a specified number of counts (i think it is currently 300). This could be a a/d input problem (the voltage divider resistor is wrong) or a real error with the tiedowns not moving as instructed.
foldBack errors occur when the requested torques are above the allowable maximum for a period of time.

When foldback and cmdSpdErr happen there is usually a real problem. The jack is not able to move at the requested speed because too much torque is required.

Plots were made of the tiedown data from 01mar12 thru 19apr12 to see if any patterns existed.

The first plots shows the td torques and position vs daynumber of year (.pdf):

The 3 tiedowns are color coded : black td12, red td4, green td8.
Only data when the tiedowns were moving were used
Top: motor current vs daynumber.

You can see that td12 (black) is much larger than the other two td's.

Bottom: Td position vs daynumber.

All 3 jacks moved close to the same positions.

During the nights the jacks were between 14 and 15 inches.

The second plot shows the motor torque vs the tension on each tiedown (.pdf):

The force the motor applies is related to the tension in the cable, the direction of motion, and how fast the tiedown has to move.
The motor torque is proportional to the force the motor applies.
For the same force on each tiedown (say 30 kips) td12 needs 4 to 10 times as much current as the other two motors.

This could be a problem with the current readback from the jack
or it could be a real problem where the friction in the jack motion is much larger than the other 2 tiedowns.

On 19apr12 while testing the tiedowns, loud noises were coming from td12 jack when when tried to pull down on tiedown (increase the tension in the tiedown cable).
These loud noises and the large torque needed to pull on the tiedown point to a broken jack (or transmission)

Summary:

td12 jack stopped moving with foldback errors (and cmdSpdErr) on 18apr12.
Plotting the motor torque vs tiedown tension showed that td12 needed 4 to 10 times as much torque as the other two tiedowns for the same cable tension.

This has been occurring at least since 01mar12.

Loud noises were heard in td12 jack when moving it on 19apr12.

There have been intermittent noises from td12 for the last few months.

td 12 jack needs to be replaced.

processing: x101/120419/td12err.pro

<- page up
home_~phil