Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~phil/pnt/azEncJump15sep02.html
Äàòà èçìåíåíèÿ: Mon May 17 00:18:43 2004
Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 07:29:50 2012
Êîäèðîâêà:

Azimuth encoder jump 15sep02

15sep02

Background:

There are two encoders mounted 180 degrees apart on the azimuth arm. These absolute encoders have a gear on the end of their shaft that is mated to the the azimuth encoder rack gear via a spring. The encoder on the dome side is used for pointing. The encoder on the carriage house side is used to measure any bending in the azimuth arm. This is done by measuring the relative change in the two encoders as the arm swings.

The failure:

The telescope stopped tracking on15sep02 at about 22 hours with an azimuth bending error. The difference between the two encoders got larger than an allowable value. This can happen if:

One side of the azimuth stops while the other continues moving (there are motors on both sides).

One or both encoders lose contact with the encoder rack gear. The azimuth continues to move but the encoder does not turn.

The vertex motor data is logged once a second to a file. This allowed us to go back and look at what was happening during the failure.The figure shows the azimuth motion before and during the jump (.ps) (.pdf). The *'s are the 1 second samples.

The Top figure is the azimuth position versus time. The azimuth is moving at slew rate near az=123 deg. At 21.861 hours the azimuth decelerates and stops.
The middle plot shows the encoder difference AzGr-AzCh in degrees. It shows a jump at 21.861 hours.
The bottom plot has the velocity of the azimuth arm measured from the amplifier/motor resolver in black. This is independent of the encoder. The green line is the velocity computed using the encoder positions measured once a second. There is a dip at 21.861 hours. If this was a real jump in motion then the amplifier velocity should also have jumped.
Figure 2 is a blowup of the AzGr - AzCh encoders. The red lines are linear fits to the data before and after the jump. From these fits the jump was .3973 degrees or 1430.2 arc seconds.

Tracking 2 sources after the jump gave a little circle azimuth offset of 1446 asecs . This differs from 1430 by 16 little circle asecs. The sources were tracked at 12 to 15 deg za. The great circle error difference is 16/(sin(13.5)=3.7 arc seconds.
We need to retrack a source that was done prior to the jump and see what the change in the azimuth error is.

processing: x101/020916/doagc.pro

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