[ros-users] [Orocos-Dev] Control system design question.

[Konrad Banachowicz]

My solution splits the trajectory generation into two parts.
One part is hard-RT and do interpolation between two points (with non zero
velocity at both ends). It can be used with sensor feedback (servo vision).
Second part is feeding first one with points along complex trajectory, it do
all "trajectory joining", joints reordering ...

Pozdrawiam
Konrad Banachowicz


2010/9/18 Herman Bruyninckx <Herman.Bruyninckx at mech.kuleuven.be>

> On Fri, 17 Sep 2010, Konrad Banachowicz wrote:
>
>  Hi,
>> I'm working on integration of orocos RT-controller with ROS manipulation
>> pipeline.
>> I already done joint_state_publisher and oro_action_server. Next on my
>> list are
>> joint_trajectory_action and JointSplineTrajectoryController.
>> I have some concerns about real-time behaviours of those, and way of
>> implementation
>> in orocos.
>>
>> joint_trajectory_action :
>> It receive goal containing trajectory (variable size, unbounded size),
>> then check
>> constraints and send to JointSplineTrajectoryController.
>>
>> JointSplineTrajectoryController:
>> It loop generating interpolated position for joint regulator.
>> When it receive new trajectory it reorder joints in received trajectory
>> (memory
>> allocation, iterating on unknown size array) and try to compose current
>> trajectory
>> with newly received (memory allocation, iterating on unknown size array).
>> It have to by done between two sequential interpolations (in my system
>> 1ms).
>>
>> My solution :
>> Data transmited between  joint_trajectory_action and
>> JointSplineTrajectoryController
>> contains only single point (constant size).
>>
>> joint_trajectory_action do joint reordering and compose trajectories and
>> is feeding
>> JointSplineTrajectoryController with trajectory points.
>>
>> JointSplineTrajectoryController interpolate between two points (have one
>> point
>> buffer)
>>
>> This solution should work with trajectories when time between points is >>
>> 1ms.
>>
>> What do you think about doing this this way ?
>> What is alternative solutions ?
>> What do you think about re-usability of this solution in yours systems ?
>>
>
> I do not know whether I fully understand your approach and solution, but
> here are some comments nevertheless about what I have learned about
> trajectories the last 20 years:
> - if you have a system with hard realtime constraints to connect
>  trajectories together within 1ms, it makes sense to add another level of
>  trajectory generation, in the form of a "trajectory joining" component.
>  That component can do the joining already before the trajectory is
>  finished, in a separate thread/process. It will not be a trivial
>  extension to the current approach, though.
> - do you really the kind of joint space trajectories that are currently
>  being used? With 1ms latency, it seems that you are looking for
>  trajectories that can be joined also at non-zero velocity, in contrast to
>  our current implementations...
>  If you have indeed a need for other trajectory types, please start a
>  discussion on this topic, since one of our PhD students. Wilm Decré, is
>  doing his research on this topic; and he has already some results, but
>  they have not yet been integrated in Orocos code.
>
> Herman
> _______________________________________________
> ros-users mailing list
> ros-users at code.ros.org
> https://code.ros.org/mailman/listinfo/ros-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ros.org/pipermail/ros-users/attachments/20100918/a65c7048/attachment-0003.html>