[ros-users] Joint controller manager

[Edwards, Shaun M.]

Adolfo,

When I originally read your email, I thought it was coming out of Willow.  There are some aspects of the new arm path planning library (MoveIt) that point to a revamped controller manager.  Unfortunately, I don't know any more than you do.

As far as your architecture, I notices that you are utilizing the ROS action interface.  Is there any way to allow for a streaming interface.  I'm thinking of a visual servo application, where you need to close the loop and adjust an actuator position based on some higher level information.  The action interface does not allow for this.

Shaun Edwards
Senior Research Engineer
Manufacturing System Department


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From: ros-users-bounces at code.ros.org [mailto:ros-users-bounces at code.ros.org] On Behalf Of Adolfo Rodríguez Tsouroukdissian
Sent: Monday, January 28, 2013 9:04 AM
To: orocos-users; ros-users
Subject: [ros-users] Joint controller manager

Hello ROS and Orocos users,

This is a call for feedback. I'm currently working on a "joint controller manager", that is, a component that manages joint resources and exposes them to control. For those familiar with the pr2_controller_manager, this would provide similar functionality and interfaces, while relaxing some constraints to allow easy porting to different hardware platforms. Exposing hardware to control (and realtime control in particular) is still a big hurdle, and it would be very desirable to make this at least an order of magnitude easier. Once a minimal set of controller interfaces are made available for a given platform (eg. mobile base controller, spline interpolator, ...), a truckload of higher-level functionality becomes available.

At the moment I have an existing in-house solution that from a ROS API point of view looks pretty much like a pr2_controller_manager, and a design of where I'd like things to go, which is attached to this message in pdf form. As a next step I was planning on setting up a public repo and port the existing design from Orocos 1.x to Orocos 2.x, which adds the expressivity needed to address the missing features. But before that, I'd like to make a pause and ask for some feedback.

- Is there interest in giving this topic a dedicated discussion place, like a mailing list or a ROS special interest group?.

- If you take a look at the attached design, please be critic about it. What would you add or remove?, what would you do differently?.

- What can you not accomplish (or have had trouble accomplishing) with the tools you or your team have used so far?.

Finally, I'd like to be aware of any active and similarly scoped initiative, so please let me know if you're working on the subject. Late last week I found out almost by chance about the yet undocumented ros_control [1] repository, which deferred the writing of this email a day so I could familiarize with it. Its scope is very much aligned with my current objectives, as it consists of a library offering functionality similar to that of the pr2_controller_manager that can be adapted to other robot platforms. I'm looking forward to sharing opinions and use cases with all interested parties, and if possible map interest overlaps to common code. Some questions that come to my mind after reviewing the code in [1]:

- Is it possible to have a controller with multiple interfaces (eg. send position + velocity + effort commands)?.

- If I understand correctly, interfaces are limited by design to position, velocity and effort, and adding a new one (fancy example: stiffness) is not possible, correct?.

- Is it possible to chain controllers as in the attached figure (r_arm_follow_joint_traj + r_arm_pid_controller) from configuration files, ie. without writing code?.

- Controllers running at lower frequency than the manager need to implement this by doing work only one out of every n cycles, as separate controller threads are not supported, correct?.

- Is there any work on decoupling the more common "workhorse" controllers out of the pr2_controller_manager infrastructure (eg. a couple of mobile base implementations, the FollowJointTrtajectory action)?. I've already spent some time factoring out the spline splicing and interpolation code from the FollowJointTrtajectory action, and was planning on writing some unit tests on it. If not, I can also make this available once the cleanup is complete.

That's it for now, thanks for reading.

[1] https://github.com/willowgarage/ros_control

--
Adolfo Rodríguez Tsouroukdissian
Senior robotics engineer
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