Add three new anti-windup techniques and a Saturation feature #298
Conversation
ViktorCVS
changed the title
|
This pull request is in conflict. Could you fix it @ViktorCVS? |
|
@christophfroehlich, it appears that no reviewers have been assigned to this PR. Could you please help with that? If you have time, I'd appreciate it if you could also take a look at the changes. |
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
Thx for this thorough PR, but it will need some time to properly review it
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## ros2-master #298 +/- ##
===============================================
- Coverage 78.17% 77.53% -0.65%
===============================================
Files 30 30
Lines 1338 1696 +358
Branches 87 101 +14
===============================================
+ Hits 1046 1315 +269
- Misses 245 327 +82
- Partials 47 54 +7
Flags with carried forward coverage won't be shown. Click here to find out more.
🚀 New features to boost your workflow:
|
|
@ViktorCVS could you please resolve the current conflicts? |
done |
Please add a deprecation notice to the code, as well as a warning on |
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
For the future: Please don't force push to PRs because it makes it harder for reviewers to check the changes since the last review ;) The history does not have to be linear, because we squash that anyways.
We get closer to the finish line, but some of our comments haven't been addressed yet.
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
The tests are failing now, can you have a look please?
|
|
Sorry about that. I tried pushing without force, but Git wouldn’t accept it. I’ll try other methods from now on. |
|
why you rebased and force-pushed again? the diff is strange now because the last commit on master is included here? |
There’s a warning that this branch is out of date with the base branch, so I pulled the latest changes and pushed. This time I didn’t use a force push, so it’s strange that you’re still seeing this message. Whenever the master branch is updated, I can’t push without force. Since you asked me to avoid force pushes, I merged master into my branch before pushing. |
|
alright, I see what I can do to fix it and do the final review round ;) |
Thanks! There are new updates in the master branch. Should I wait before merging them? |
|
I merged them already in, now the diff view looks fixed again. |
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
The API and structure looks good now, thanks! I cross-checked the equations with the cited literature and have some questions, see my comments.
I recently added documentation integrated in control.ros.org. Could you please summarize your changes in
- the release notes. You can use the style from the other repos.
- and add necessary migration steps here. What will be the default after the deprecation cleanup? conditional integration?
Not necessarily in this PR, but could you please summarize the PID class in structured text format and add it here?
control_toolbox/src/pid.cpp
Outdated
| } | ||
| else if (gains.antiwindup_strat_ == AntiwindupStrategy::CONDITIONAL_INTEGRATION) | ||
| { | ||
| if (!(cmd_unsat_ != cmd_ && error * cmd_unsat_ > 0)) |
There was a problem hiding this comment.
maybe we should not compare if two double are equal, let's compare the difference against eps?
control_toolbox/src/pid.cpp
Outdated
| gains.antiwindup_strat_ == AntiwindupStrategy::CONDITIONING_TECHNIQUE && | ||
| !is_zero(gains.i_gain_)) | ||
| { | ||
| i_term_ += dt_s * gains.i_gain_ * (error + 1 / gains.trk_tc_ * (cmd_ - cmd_unsat_)); |
There was a problem hiding this comment.
I don't have access to [2], but in [1] the conditioning technique is described differently (Fig 3.4).
Is there a real benefit in adding all of the three? Or should we skip the CONDITIONING_TECHNIQUE as it is the least known/documented one? I think the other two leave enough choices and tuning possibilities for the user.
There was a problem hiding this comment.
I simplified the material from source [2], but I have researched the CONDITIONING_TECHNIQUE and noticed some discrepancies between sources. In some of them, BACK_CALCULATION and CONDITIONING_TECHNIQUE can have the same effect if we tune Tt in a specific way. Therefore, I agree to remove CONDITIONING_TECHNIQUE. I’ll do this as soon as possible. I’ll also replace [2] with an equivalent but accessible article.
There was a problem hiding this comment.
great thx, let's push this to be merged soon. documentation can be added afterwards, because we don't need to release it
There was a problem hiding this comment.
I’m having a hard time pushing. Git only accepts it with -f, and every time I pull, it erases my changes.
Why? Have you pulled the changes (after my merge via Github UI?). It maybe won't let you pull if you have uncommited changes, either commit them and do a
Let's add the migration notes before we remove it. We will release the changes, wait for the next sync, and then we can remove it. So users have one release cycle to see the deprecation warnings before any behavior changes are applied. |
There was a problem hiding this comment.
Thanks again!
Could you please submit two follow-up PRs:
- One which updates the documentation, basically the summary of your initial message here. But you don't need to document the old behavior, just the result after the deprecation cleanup. Here you can add the migration notes.
- Another one cleaning up the deprecated code. You can draft it for now, and we will merge after the next sync to kilted/rolling.
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
Oh, I see that the downstream PidController tests fail now. Can you have a look please and update ros-controls/ros2_controllers#1585?
Fixed |
Thanks. I see now that |
saikishor
left a comment
saikishor
left a comment
There was a problem hiding this comment.
@ViktorCVS Very good work
I've only one question, what will the bool antiwindup parameter be used for from now on?
Thanks! Until I remove it, it will still maintain the old behavior. This PR just adds more options. I’ll open a follow-up PR soon to remove it. |
In ros2_controllers? I agree. I’ll update the anti-windup parameter description accordingly. |
Should I wait for the merge? |
All legacy constructors and setters that used the Boolean anti-windup flag are now tagged [[deprecated]], while new overloads that take only AntiwindupStrategy provide the forward path; internal calls that still rely on the deprecated forms are wrapped in #pragma GCC diagnostic push / ignored "-Wdeprecated-declarations" / pop, eliminating stderr noise during colcon build without changing runtime behaviour and keeping backward compatibility intact.
christophfroehlich
left a comment
christophfroehlich
left a comment
There was a problem hiding this comment.
Do we need the overloads with the boolean AND the new AntiwindupStrategy?
christophfroehlich
merged commit f652c3d
into
ros-controls:ros2-master
(cherry picked from commit f652c3d) # Conflicts: # control_toolbox/include/control_toolbox/pid.hpp # control_toolbox/include/control_toolbox/pid_ros.hpp # control_toolbox/src/pid.cpp # control_toolbox/src/pid_ros.cpp # control_toolbox/test/pid_tests.cpp # doc/release_notes.rst
|
@ViktorCVS I came to the conlusion with Sai that we merge this and discuss about the saturation in a follow-up PR. Could you please prepare the documentation update first? The deprecation removal has more time, at least until we release the package. |
Co-authored-by: Victor Coutinho Vieira Santos <[email protected]>
|
@ViktorCVS Do you maybe have time and like to open a PR cleaning all the legacy and deprecated behavior now? |
5 participants
Overview
This PR adds three new anti-windup techniques: back‑calculation, the conditioning technique, and conditional integration. It also adds a saturation feature for the PID output. New parameters have been introduced, and additional overloads have been implemented to ensure compatibility.
What was added/changed in this PR
About compatibility
The packages compile correctly and have passed the pre‑commit and colcon tests (packages with dependencies continue to show the same number of failures before and after my modifications). If the new parameters are not used, the package retains its old behavior.
About the older anti-windup technique
My plan, either by the end of this PR or in a subsequent one, is to completely remove the older anti‑windup technique that has been used so far. This method, which is a form of conditional integration, has several disadvantages:
Additionally, regardless of whether the 'antiwindup' parameter is set to true or false, the anti-windup technique is applied (using the same method with a different approach), so the user does not have the option to disable it.
About unit tests
I've added 10 new unit tests for the new features and updated the existing ones to accommodate the new parameters.
Related PR's
Important notes
These three techniques are common anti‑windup strategies used to mitigate the windup effect and are widely employed in control applications: back‑calculation [1], the conditioning technique [1,2], and conditional integration [1,3].
The default values for the tracking time constant are defined in [3,4] for back‑calculation and in [1] for the conditioning technique.
Both back‑calculation and the conditioning technique use forward Euler discretization; this may change before merging this PR.
Graphs
I tested it on ros2_control_demos to better illustrate this feature and test it on simulation to valide the equations. The tests were conducted using a modified version of Example 1: RRBot, which uses a PID controller instead of the default forward position controller. It was tested on Docker, Ubuntu Noble, and Jazzy.
PID values: p = 4.0, i = 25.0, d = 0.5; u_max = 13, u_min = -13; and the tracking time constant was left at its default value.
The standard response with a settling time (ts) of 5.2 seconds, the response affected by saturation, resulting in a settling time (ts_sat) of 8.6 seconds (+65.4% increase) and the response using the back-calculation technique, which improves performance with a settling time (ts_back) of 4.1 seconds (–21.2% decrease), even lower than the standard response.
Those figures compares three anti-windup methods applied to the step response, a zoomed-in view of the step response is provided here to clearly distinguish between the three anti-windup strategies. They are all very similar due to the system and PID values, but they may vary significantly between applications.
The standard control output, the control output affected by saturation, with a recovery time from saturation of 6.8s and the control output using the back-calculation technique, with a recovery time from saturation of 2s (-70.6%).
Those figures compares three control outputs using anti-windup methods, a zoomed-in view of the control output is provided here to clearly distinguish between the three anti-windup strategies. They are all very similar due to the system and PID values, but they may vary significantly between applications.
All the equations have been validated with these simulations, providing a feature with three techniques to address windup.
Final notes
I'm very open to any recommendations to improve this code.
References
[1] VISIOLI, A. Pratical PID Control. London: Springer-Verlag London Limited, 2006. 476 p.
[2] VRANCIC, D et al. Antiwindup, Bumpless, and Conditioned Transfer Techniques for PID Controllers. IEEE Control Systems Magazine, 1996. 16(4):48 - 57.
[3] BOHN, C.; ATHERTON, D. An analysis package comparing pid anti-windup strategies.
IEEE Control Systems Magazine, p. 34–40, 1995.
[4] ASTRöM, K.; HäGGLUND, T. PID Controllers: Theory, Design and Tuning. ISA Press.
Research Triangle Park, USA: Springer-Verlag London Limited, 1995. 343 p.