RE: OmsAsyn Maxnet Homing

["Pearson, Matthew via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Eddy,

 

The implemented homing procedure [1] of the EPICS module  does not seem to work, probably because there is no home switch. There are only limit switches.

 

That’s fairly common I think. Most controllers won’t support homing to a limit switch, probably because it confuses the function of the switch and the home position would change depending on how fast you move onto the switch.

 

The homing procedure should be:

 

1. Move into lower limit switch

2. Define this position as 0 (at least) in the EPICS motor coordinates.

 

For homing on a limit switch, the homing procedure is ideally:

 

1. Move onto the switch (possibly also widen the software limits)
2. Move off the switch some predefined distance (eg. 2mm)
3. Change the speed to a predefined homing speed (normally a slower speed)
4. Move back onto the switch
5. Define zero
6. Change speed back to what it was before, and set the software limits back to what they were
7. Optionally move to a pre-defined post-home position

 

We tried to figure out a solution based on the command reference [2], but were not that successful. 

This is our current connection and init command:

omsMAXnetConfig("MCONTROL0", 5, "MAXNET0", 20, 200, "AZ;LTL;LMH;ABL;PSO;AT;LTL;LMH;ABL;PSO;AU;LTL;LMH;ABL;PSO;“).

 

As a workaround, the student using the setup developed a Python script using the motor record to do:

 

1. Read out and store .HLM and .LLM

2. Depending on .DIR trigger either .HOMF or .HOMR

3. Wait until .LLS is active

4. Store .RBV

5. Switch to calibration mode via .SET=1

6. Set .VAL to 0

7. Restore .HLM and .LLM from 1.

8. .SET=0

 

You might have to set DVAL directly and not VAL in order to initiate the LOAD_POS in the driver. Also it’s better to work in dial coordinates if you’re setting the controller position. You might also want to ensure that the user offset (OFF) is frozen (by setting FOFF).

 

I don’t know the OMS controllers, but is it possible setting HOMF or HOMR starts the controller home function, but it never completes? Or, is perhaps cancelled when it hits a limit switch?

 

So the question is, if there is a better approach by either directly using Maxnet controller commands or with the motor record itself (is there a „Zero“ command?)

 

Simply setting the user offset (OFF) can ‘zero’ the motor. However if you really want to home on the controller and define the controller position as zero, then it could either be done via a script as above, or in database logic. I have some database logic to do this (as well as supporting screens) if you’re interested.

 

Cheers,

Matt