Limit switches and encoders

28feb20

Note:
This page got overwritten 09aug18. I grabbed some older data from the td.html page before the limitswitch_encoder
info was moved to their own page. i then went through the x101/yymmdd files to find when the encoder limit info was recorded

Limit switch positions/encoder reference:

Software limits:
The software limits are defined in ~phil/vw/h/tieProg.h. The software will not send a command outside of these. They are rather old and may not correspond to the
current hardware limits. The software limits are defined to be .2 inches inside the software final limits. If you want to measure inside the swPrelimit, you need to use the pcu.

td	swFinalLimit	swPreLimit
12	(22.69,1.43)	(22.49,1.63)
4	(23.24,1.28)	(23.04,1.48)
8	(22.20,1.19)	(22.0,1.39)

**td hardware limits** (encoder inches)
td/date	jack flim	sw final limit	prelimit	tapeMeas inch / bar (when enc=13")
12	lim to jackend (.7" , .84")(h,l)170828 (24+,.313) (24+,.253)	(23.290,1.150) (23.290,1.150) 23apr12 (23.36,1.2) 04feb09 (23.28,0.86) 14aug06 (23.28,0.86) 17mar06 (23.21,1.19) 04aug03	(22.3576,1.83) 200303 (22.278, 1.780) 170828 (22.278,1.780) 23apr12 (22.92,1.81) 04feb09 (22.461,1.668) 14aug06 lost .3"!! (22.69,1.57) 17mar06 (22.62,1.9 ) 04aug03	just ran into prelim vw% 28 1/8 (enc=12")23apr12 26 19/16 04feb09 26 3/8" 18mar05
4	saw 2" prelim to jackEnd200303 (24+,.799)	(23.317,1.487) 24sep12 (23.19,1.37) 13may04	(22.6713,1.957) (22.78,2.03) 24sep12 ( 22.82,2.01) 13may04	bar=11.01 "
8		(23.21,1.19) 30jul03	(22.0, 1.l7836) (22.498,1.907)170830 (22.5,1.9) 30jul03	hlim is my software lim 25 15/16 18mar05

There is a pre and final hardware limit switch for the upper limit and the lower limit on each jack. The actions of the limts are:

The final limit is a relay in the safety chain. When it opens, the safety relay opens causing the power to the motors to be cut off. To drive the jack out of this limit you must use the manual control built into each tiedown.
When the prelimit relay is tripped (or the encoder value is within the pre limit) the program will automatically issue a stop commad. After it is stopped, the program will allow motion requests that move the jack out of the limit. It will limit the dac voltage to the sign that drives the jack in the correct direction. This assumes that the zero offset value for the dac is correct. When new dacs are installed, this value (parameter 19) needs to be updated. To check this, just watch the value of the Ki constant while the jack tracks the current position (eg montie 8). The integrated value needed to keep the jack fixed is the offset that needs to be added to the current value. The prelimit will stop the motion of the jacks if the dacs are controlling the motor amplifier. If the dac is blownout, the tiedown is in autorelease, or the manual control (hagens box) is enabled, then the prelimit will not stop the motion of the jacks (but the final limit will).
There is also a software limit that is .2 inches inside the final limit. The VME software will never request a position outside of this software limit. When moving in rate mode (constant velocity) this limit has no affect.

We have measured the location of the jack at the limit positions using the encoder value and a tape measure (see td manual log section for the reference positions). This has also been done at some interim jack positions. If you lose the encoder position (an encoder fails and the jack moves before a new encoder is installed), then these measurements can be used to calibrate the new encoder. This can be done by:

move to a limit position (when the limit switch triggers) and then adjust the encoder to match the last encoder measurement at this position.
Measure the jack position with a tape measure and then interpolate what the encoder position should by using the encoder reading/tape measuremets and the two limits
Move the jack until the tape measure agrees with a miscLocation measurement and then set the encoder position accordingly.

Using the limit switches is a bit tricky since when they trigger depends on how fast you drive into the limit (you should do it slowly). If you do have to recalibrate an encoder, it is a good idea to remeasure all of the positions (limits,tape, misc) so you can see how close you got to the old position.

Whenever we survey from AO9, we use the current encoder values to determine how to move the tiedowns. So by definition, after an ao9 survey, the tiedown positions are now correct. This is not quiet true since we have been using the focus curves to determine the focus rather than the ao9 survey value.

The table below has the measured values of the position using encoder and tape measure. Encoder values 24 inches is when the jack is fully retracted (high tension). 0 encoder inches is when the jack if fully extended (low tension).The cols in the table below are:

Limits encoder: Encoder readings at the limits (when the switch trips driving into the switch very slowly).
Limits tape: The value measured (see illustration log section of td manual) with the tape measure when the td was at the final limit. The measured stop position for the final limit is a hardware stop (interlock opens). The measured stop position on the prelimit is the position where the software stopped it after seeing the digital bit change (and allowing for the slowdown).
MiscLocations enc/tape . The encoder value, tape measurement at any other position.

Note: The computer displays call the limits at 24 encoder inches (high tension) the down limits while the limts at 0 encoder inches are called the upLimits.

17mar05. Changed the jack td12 for maintenance. Measured positions from bottom of jack to yoke.

before: after:
measured the prelim encoder values with the vme. the final limits and the end of the jack travel were not checked. The final limit was computed from the prelim offsetkkj

28feb05. jack td4 broke. changed jack. Measured positions from bottom jack to yoke. difference before after was?? Looked at encoder values for prelims. Moved lower by about .08 inches. Did not measure the final limits or the end of jack encoder position.

Bar used to set encoder position:

An aluminum bar was made in an L shape. It goes from on top of the center bolt of the jack mount (on top of cement block) to the top of the yoke. When the jack yoke is touching the bar, the encoder value is recorded. This lets us change jacks (which are different lengths) and maintain the correct encoder position.
when all the tiedowns are at 10" and there is tension in the cable (say 10 kips) the laser should read

date/jack	encoder	notes
td4-21sep12	11.01 inces	bar on center bolt.
td12 -23apr12	11.692 inches	bar on center bolt, north side (see photos below)

Laser to measure jack position
170828 .. and later.. used laser to measure jack position, set encoder. procedure

Put all jacks at 10"
put 2x4 on top of yoke, put laser flush against it pointed down to base plate
distance measured was 3260.6 mm= 114.789 inches

Not sure where the ref point is. (inside laser, front of laser, back of laser)?

move jack until laser reads 3260.6 then reset encoder to 10" .. this should be 436633 revs or encoder counts.
Question.

03mar20. td4 at 11.397", measured distance from hor bar at top of yoke (a few inches below the top) and got 124 + 1/4"
This would give 122.853 inches when jack at 10".. so there is an 8 inch discrepancy.
And the tape 124 1/4" is not even from the top of the yoke.. (used the horizontal bar on yoke).
not sure why the difference.

Measured positions for limits/miscPos using encoder and tape measurements.
date	td	hardware limits (encoder inches)	Limits Tape(hi,lo)	MiscLocation encoder, tape
03mar20	4	used tape measure hor bar near top of yoke to base plate left 124 3/8" right 124 3/16" (looking at cabinet). td at 10",11.397",11.689" , az=181.58,za=5.57 with new jack 124" 1/4 left 124 1/4 " .. so 1/8 " lower than original.. left it that way. Then measured limit switches (See table above) just ran into hardware prelimit slowly...
24sep12	4	adjusted limits1091111 downlim 1047891 24" jacklim0=.799 jacklim24= +24.. encCnts:1091111 24"= 1047891 finalLim:(23.317,1.487) prelim:
21sep12	4	installed new jack.Used L bar for encoder.
23apr12	12	jacklim0=.3134 (no tension) jacklim24=24+ (little tension) finalLim(23.290,1.150) these changed a bit each time we drove in. preLim(22.278,1.780) New jack installed. Used bar to transfer old encoder value to new jack bar on top of center bolt (north side of jack) encoder=11.692 (old reading) when bar touches top of yoke encoder=11.2643 (new reading before encoder adjusted. Difference .428 inches.Could be jack height or encoder moved.		12",28 1/8
04feb09	12	jackLim0=.253 measured by running into end of jack throw (with tension in the cables). jackLim24=23.998 and still had 1/4 inch before jacklim finalLim12:(23.36,1.2) preLim(22.92,1.81) full speed motion. limit switces were way off since the aluminum plate holding the limit switches was mounted incorrectly when the jack was replaced 09jan09 . Readjusted the aluminum plate to give the settings above. measured aluminum plate distance before adjusting aluminum plate		13",26 19/16" 13",23 7/8
18mar05	12 4 8	I put all jacks at 13" and then measured the dist from bottom of aluminum plate to top of ridge on jacks (see luis's picture). These look like the old values back in 2001.		13", 26 3/8" 13",27" 13",25 15/16"
17mar05	12	finalLim12:(23.28,0.86 ) preLim(22.69,1.57) finalLim12:(23.21, 1.19) preLim (22.62, 1.9 ) old values final limits computed from previous prelim,flim differences. td 12 jack replaced (see above)
28feb05	4	finalLim4:(23.19,1.37) preLim(22.82,2.01 Prelim measured, flim computed from old flim and distance change for prelim.		13. , 37 "
13may04	4	finalLim4:(23.24,1.28) preLim:(22.87,1.91) jacklimLow: went to .057 inches then stopped. Had not hit limt yet. jackLimHi: went to 23.875 then stopped. currents started to go up.		13" , 36 15/16"
10may04	4	jack broke, had to replace. this required the encoder to be removed as well as the limits.
06aug03	8 4 12			13" , 35 15/16" 13" , 36 13/16" 13" , 36 7/8"
06aug03	4	finalLim4:(23.2,1.2) preLim4:(22.7,x.xx) jackLim0:went to 0" enc , did not hit end of travel. jackLim24: stopped at 23.9998 inches. full speed into final limit stopped at 23.26 full speed into prelimt stopped at 22.77
06aug03	4	rotated limit switches to face away from box. moved mounting bracket for limit switches so previous tape measurements are no longer valid.
04aug03	12	finalLim12:(23.21, 1.19) preLim12:(22.62,1.9) jackLim0:hit endOf travel a little beyone 0"(enc) jackLim24:hit end of travel a little beyond 24"(enc). full speed into final limit (no tension) stopped at 1.177 enc full speed into prelim (no tension) stopped at 1.7 enc. full speed into prelim stopped at 22.72 (enc)
30jul03	8	finalLim8:(23.2088, 1.19) prelimit8:(22.6,1.9) jackLim0:ran jack to 0" (enc) didn't hit end of travel jackLim24:ran jack to 24"(enc) didn't end of travel. Full speed into prelimit (no tension) cpu stopped within about .2 inches.
2003??		replaced all limit switches.Previous limit switch positions no longer valid

24sep01	8	finalLim8:(22.20,1.08)		(13.07, 25 3/4)
	4	finalLim4:(22.82, 1.92)		(14.44, 25 1/4)
	12	finalLim12:(22.29, 1.85		(14.70, 24 7/8)

08feb00	8	finalLim8:(22.20, 1.19)
	4
	12	finalLim12:(22.29, 1.43)

28aug98	8	finalLim8:(21.79 , 1.20)	(17 , 37 9/16)
	4	finalLim4:(23.21 , 1.95)	(16 5/8, 37 7/8)
	12	finalLim12:(22.14 , 1.52)	(17 1/2, 38 1/8)

The software limits used to limit the requested positions are .2 inches inside the final limits. They are in the file /home/phil/h/tieProg.h

software request position limits.

start date td12 td8 td4

08feb00 (22.29,1.43) (22.87,1.93) (22.20,1.19)

xxx (21.79,1.2) (22.14,1.52) (23.21,1.95)

software request position limits.
start date	td12	td8	td4
08feb00	(22.29,1.43)	(22.87,1.93)	(22.20,1.19)
xxx	(21.79,1.2)	(22.14,1.52)	(23.21,1.95)

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