Re: Questions about creating a Model 3 Driver for stepper motor axis

[Torsten Bögershausen via Tech-talk <tech-talk at aps.anl.gov>]

Hej again Paul-Elie,


On 2024-01-17, 16:25, "Paul-Elie GUILLOT" <peguillot at irelec-alcen.com <mailto:peguillot at irelec-alcen.com>> wrote:


Hello again Torsten,
Thank you for helping me on all of this.
Based on our exchange and your driver, I think I need to implement at least 2 more records to fetch the axis error status and a record to reset the axis error.
I think I ve seen those in your driver as well. 
That is actually implemented:
(We stick to the generation 1 stuff)
<https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/master/ethercatmcApp/src/ethercatmcAxis.cpp/#L944-L949>

<https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/master/ethercatmcApp/src/ethercatmcAxis.cpp/#L1390-L1399>

However, if you say that the driver can do a lot of things, and is hard to read,
yes. We can probably have a zoom meeting to explain more details.



> Not sure, if I understand the question....
> In our world, the encoder and it's scaling are "connected" into the NC, which, once the Axis is commissioned, does everything.
> I think that our test crate019 has still "generation 1" software:
> <https://bitbucket.org/europeanspallationsource/tc_lab_mcu019> <https://bitbucket.org/europeanspallationsource/tc_lab_mcu019&gt;>


Ohhh I see, I was planning on using a simulated encoder on my stepper axis so that way the user can switch between open loop and semi-close loop, with the record functions.
That s how I pictured a driver would want the PLC to behave, as most of its commands are issued in steps.
If you have encoder directly link to your NC task, how do you handle the field UEIP of the records? Do you force it at 1?

Still not sure, if we are on the same page ?
The NC blocks do allow a scaling, something with nominator/denominator.
We never see any steps (well we can see them for debugging), but we don't
sell them to the users.
And yes, we close the loop inside the TwinCAT system.
And no, we can not switch between open loop and close loop from EPICS yet.
It is what it is, discussions are ongoing, if that should be implemented in TwinCAT.
But so far, it isn't implemented.
Is this a requirement from your side ?
(If yes, we really should talk)
> And, by the way, we have a motorRecord with many patches/bug fixes/improvements, which are not part of the upstream version.


Interesting I have downloaded it, I will have a look into it.


On other matter, do you know how modifying the VAL ends up issuing an axis::move()?
This question has been bogging me for some time.
Yes, but that is a new story, for tomorrow __


Thank you for your help.
Best Regards 


Paul-Elie GUILLOT
Technology Manager in Automation and Robotics
Téléphone: +33 (0)4 76 44 98 93






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F-38400 St Martin d’Hères Cedex
Phone : +33 (0)4 76 44 12 96
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-----Message d'origine-----
De : Torsten Bögershausen <torsten.bogershausen at ess.eu <mailto:torsten.bogershausen at ess.eu>> 
Envoyé : mercredi 17 janvier 2024 14:26
À : Paul-Elie GUILLOT <peguillot at irelec-alcen.com <mailto:peguillot at irelec-alcen.com>>; tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov>
Objet : Re: Questions about creating a Model 3 Driver for stepper motor axis






On 2024-01-17 14:03, Paul-Elie GUILLOT wrote:
> Hello Torsten,
> I looked through your driver, it is quite dense.
> it seems you are using ADS to communicate with Beckhoff PLC variables 
> and your function directly write to it and polls them.
> 
> The interface structures that you are talking about are related to the 
> nCommand and nCmdData you seem to manipulate to issue command to the 
> axis, right?


Yes


> 
> I see you have defined lot of records in your ethercatmc.template to 
> replace those of the motor record and accommodate to your driver features?


Yes, there are some additional records defined.
Some of them are not really needed in production, so they can be taken out.




> 
> My application is pretty simple, so for starter I was thinking of 
> using TCP/IP connection to the Beckhoff PLC and issuing command through there.


Yes, that is how we started.
If you want, see this (now historic) repo, which s our "phase 0".
https://github.com/EuropeanSpallationSource/MCAG_Base_Project <https://github.com/EuropeanSpallationSource/MCAG_Base_Project>




> 
> I am using the basic TC2_Motion functions such as MC_MoveAbsolute, 
> MC_MoveRelative, etc…
Yes, that is what we are doing as well.
"Generation 1" has another functionblock on top of these blocks, that what includes "nCommand and nCmdData".


> 
> If you are handling the encoder inside the code, does the record 
> always passes step command to your PLC?


Not sure, if I understand the question....
In our world, the encoder and it's scaling are "connected" into the NC, which, once the Axis is commissioned, does everything.
I think that our test crate019 has still "generation 1" software:
<https://bitbucket.org/europeanspallationsource/tc_lab_mcu019> <https://bitbucket.org/europeanspallationsource/tc_lab_mcu019&gt;>


> 
> How do you use your motor record? Do you use its backlash compensation 
> or do you only use the record as an interface to modify say the dval 
> and your PLC do the rest?


We use the VAL field, or course, JOGF, JOGR, HOMF/HOMR (they do the
same) and a lot of other fields.
Backlash can be used from the motorRecord, that is the easist way, I think.


And, by the way, we have a motorRecord with many patches/bug fixes/improvements, which are not part of the upstream version.


HTH
/Torsten




> 
> Thank you for your help.
> 
> Best Regards
> 
> Paul-Elie GUILLOT
> 
> Technology Manager in Automation and Robotics
> 
> Téléphone: +33 (0)4 76 44 9893
> 
> 20 rue du Tour de l'Eau
> 
> F-38400 St Martin d’Hères Cedex
> 
> Phone : +33 (0)4 76 44 12 96
> 
> irelec-alcen.com <http://www.irelec-alcen.com/en> <http://www.irelec-alcen.com/en&gt;>
> 
> *IRELEC after sales services – please send your request to 
> support at irelec-alcen.zendesk.com <mailto:support at irelec-alcen.zendesk.com> 
> <mailto:support at irelec-alcen.zendesk.com <mailto:support at irelec-alcen.zendesk.com>> *
> 
> Any disclosure, use, dissemination or reproduction (either whole or
> partial) of this message or the information contained herein is 
> strictly prohibited without prior consent of Irelec.
> 
> *De :*Torsten Bögershausen <Torsten.Bogershausen at ess.eu <mailto:Torsten.Bogershausen at ess.eu>> *Envoyé :* 
> mercredi 17 janvier 2024 11:48 *À :* Paul-Elie GUILLOT 
> <peguillot at irelec-alcen.com <mailto:peguillot at irelec-alcen.com>>; tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov> *Objet :* Re: 
> Questions about creating a Model 3 Driver for stepper motor axis
> 
> Salut Paul-Elie,
> 
> welcome to the world of motion and EPICS.
> 
> I try to answer some.
> 
> First of all, we do our microstepping, hadnling the encoder,
> 
> and calculating EGU (mm) inside the Beckhoff, using TwinCAT and
> 
> the motion libraries. (NC in TwinCAT speech).
> 
> (I need to mention that we also have a complete different solution,
> 
> where not TwinCAT is used, but Linux. This does include an EPICS 
> driver
> 
> and everything.
> 
> Please see https://github.com/epics-modules/ecmc <https://github.com/epics-modules/ecmc>
> <https://github.com/epics-modules/ecmc> <https://github.com/epics-modules/ecmc&gt;> )
> 
> If you go for TwinCAT, what do you use ?
> We have defined ‘interface structures’ inside the PLC program,
> 
> and then written a model 3 driver, that talks to the PLC.
> 
> Of course, the PLC program must match the EPICS driver, and vice versa.
> 
> Over the years, there are 2 generations of PLC/EPICS, the first one 
> more
> 
> straightforward, the second one more advanced.
> 
> Both versions of the PLC code are (still) in one EPICS module .
> 
> The first generation of an Axis is here :
> 
> <https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/m <https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/m>
> aster/ethercatmcApp/src/ethercatmcAxis.cpp 
> <https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/m <https://github.com/EuropeanSpallationSource/m-epics-ethercatmc/blob/m>
> aster/ethercatmcApp/src/ethercatmcAxis.cpp>>
> 
> (And then you find the other stuff as well, I think).
> 
> HTH
> /Torsten, happy to answer more questions
> 
> *From: *Tech-talk <tech-talk-bounces at aps.anl.gov <mailto:tech-talk-bounces at aps.anl.gov> 
> <mailto:tech-talk-bounces at aps.anl.gov <mailto:tech-talk-bounces at aps.anl.gov>>> on behalf of Paul-Elie GUILLOT 
> via Tech-talk <tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov> <mailto:tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov>>> 
> *Reply to: *Paul-Elie GUILLOT <peguillot at irelec-alcen.com <mailto:peguillot at irelec-alcen.com> 
> <mailto:peguillot at irelec-alcen.com <mailto:peguillot at irelec-alcen.com>>>
> *Date: *Wednesday, 17 January 2024 at 11:11
> *To: *"tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov> <mailto:tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov>>" 
> <tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov> <mailto:tech-talk at aps.anl.gov <mailto:tech-talk at aps.anl.gov>>>
> *Subject: *Questions about creating a Model 3 Driver for stepper motor 
> axis
> 
> Hello to everyone at tech-talk,
> 
> I am currently working on implementing an EPICS driver for controlling 
> axis which are stepper motors with absolute encoders.
> My hardware controller is a Beckhoff PLC I am programming to interface 
> with. I am planning to use mm as EGU.
> 
> I have read multiple documentation and I have started to implement a 
> driver based on the Model 3 drivers, I have heavily inspired myself 
> from the MCB4B Driver for ACS and the Phytron driver.
> 
> I am starting to get a better understanding on how it works but I 
> still need clarifications on some points. Would you be so kind to help 
> me on those matters?
> 
> First of all,
> 
> * I see that when creating an axis controller using the class
> asynMotorController, it creates a lot of parameters then linked to a
> motor record by their names (the string passed to the createParam()
> function), is that correct?
> * How does each axis has its own set of parameters while connected to
> the same asynMotorController, is it because the asynMotorAxis class
> creates an AsynUser which connects to the controller?
> By doing this, it creates a separate set of parameters for the axis
> with the pasynUser_?
> 
> * I heavily rely on the record programming to carry out advanced
> functions, such as backlash compensation and closed loop motion on
> the encoder.
> Do you have experience in those matters? How will the system reach a
> specific encoder position? Will it use a linear term between encoder
> ticks and motor steps?
> But if the axis is not linear enough, there will be issues in
> reaching the position?
> If I understand correctly, usually motors use the FRAC and RTRY
> mechanism to reach a encoder position with a certain number of retry?
> In practice, how do most people operate with an encoder? Do they
> use the motor in open loop and monitor the encoder, or do they set
> UEIP at 1 and use FRAC motion?
> 
> * My motors are able to do microstepping (decomposing a full step in
> 64 microsteps), should I implement this in the MRES field of the
> record, as not being 200 full steps but 12800 microsteps?
> I think so because I intend to give the motor positions in
> microsteps. Is there a low limit on the MRES value? 
> 
> * On the system, we will be using absolute encoders, in that regard
> the encoder ratio is always 1 to transfer to encoder counts, correct?
> From my understanding, encoder ratio is mainly to interface with
> incremental encoders converting to raw A/B ticks in full encoder tick. 
> 
> Because from what I gathered the motorEncoderPosition_ must be linked 
> to the Field REP and is the hardware counter of the encoder.
> 
> * Is there a filter of some sorts on the encoder counts field or
> should I implement one directly on my Beckhoff controller and then
> use the delayAfterMove parameter to allow the encoder counts to
> stabilize?
> * As I have absolute encoder on all axis, for an axis the parameter
> motorhasEncoder_ is always at 1 as well as the motorStatusHomed_ .
> However, to use and encoder, the record needs to have the record
> field UEIP at 1. 
> 
> Is it defined by the user, or should initialize UEIP at 1, in my 
> template defined in “motor.substitutions.irelec” adding the field UEIP 
> to my .db file (which is derived from basic_asyn_motor.db with some 
> field added)?
> 
> * From what I understand, the motor record is defined by the
> motorRecord.cc and motorRecord.dbd and Model 3 drivers mainly
> interface with the devMotorAsyn.c, is it correct?
> A change on a field of the record will be processed by
> motorRecord.cc and use the different functions I have redefined for
> my Driver (move, poll, etc…), is it correct?
> Does the devMotorAsyn.c defines the support entry table required to
> process the record commands? (with the function start_trans,
> build_trans and end_trans)
> Looking through the code, I understood that for Model 2 Driver and
> Support, one needs to defined the support entry table to process the
> record commands? (ex: MCB4B_build_trans function)
> 
> In Model 3, it seems the asynMotorController directly handles the 
> modification of its parameters by calling the needed function of an 
> axis. How does the record interface with the asynMotorController parameters?
> 
> I can’t find where devMotorAsyn.c writes to the asynMotorController 
> parameters.
> 
> Bottom line of this topic is: Can I use the record advanced functions 
> such as backlash compensation even with a Model 3 Driver?
> 
> * The record always feed steps command to the controller if I
> understood the code correctly.
> However as I don’t have a home routine (due to absolute encoders),
> the open loop (step count) is reset at each hardware controller
> power reset.
> Thus, the user should never do move_absolute in openloop. To disable
> it, I would like the UEIP to be always at 1? Or something should be
> done to set the open loop position using setposition based on the
> absolute encoder at the start of the controller?
> 
> It could be the home procedure, just sending a setposition() to the 
> stepper based on the encoder position? Or does the home position 
> require motion?
> 
> * I noticed there is no process of error catching on the motor and
> error resetting, is that correct?
> Should I always reset an axis in Error on my Beckhoff hardware
> controller or should I include command on my EPICS driver to do so,
> thus adding record for those specific actions?
> Because for example, if my motor reaches a hardware limit switch
> while in motion it will put itself in error state, which then needs
> an error reset using the MC_Reset.
> 
> I need it’s a lot of questions, I hope it is clear enough.
> 
> In any case, thank you for your time and help.
> 
> Paul-Elie GUILLOT
> 
> Technology Manager in Automation and Robotics
> 
> Téléphone: +33 (0)4 76 44 9893
> 
> 20 rue du Tour de l'Eau
> 
> F-38400 St Martin d’Hères Cedex
> 
> Phone : +33 (0)4 76 44 12 96
> 
> irelec-alcen.com <http://www.irelec-alcen.com/en> <http://www.irelec-alcen.com/en&gt;>
> 
> *IRELEC after sales services – please send your request to 
> support at irelec-alcen.zendesk.com <mailto:support at irelec-alcen.zendesk.com> 
> <mailto:support at irelec-alcen.zendesk.com <mailto:support at irelec-alcen.zendesk.com>> *
> 
> Any disclosure, use, dissemination or reproduction (either whole or
> partial) of this message or the information contained herein is 
> strictly prohibited without prior consent of Irelec.
>