[ros-users] cartesian trajectories
Adolfo Rodríguez Tsouroukdissian
adolfo.rodriguez at pal-robotics.com
Wed Jun 5 14:49:46 UTC 2013
On Wed, Jun 5, 2013 at 4:09 PM, Mrinal Kalakrishnan <kalakris at usc.edu>wrote:
> Let me correct that. We actually don't use a specific
> "CartesianTrajectory" msg any more. Instead, we have a generic
> "Trajectory" msg, which has a list of dimension names and
> TrajectoryPoints - which makes it very similar to a JointTrajectory
> msg. We then agree upon a naming scheme, like "r_hand_cart_x",
> "r_hand_cart_force_x", and "r_hand_cart_gain_x" and so on. This allows
> us to synchronize the execution of cartesian positions, forces and
> gains (impedances), on multiple end-effectors if needed. We can also
> send joint trajectories (or null-space joint posture trajectories)
> through the same interface.
> Maybe this is not how you want the CartesianTrajectory msg to look,
> but I just thought I'd mention where we ended up after a few
> iterations, to have all the functionality we needed.
Interesting that you bring this up. The JointTrajectory and JointTolerance
messages are in fact applicable to non-joint data, albeit their name.
Furthermore, the de facto consumer of these messages, the
JointTrajectoryActionController is largely a spline interpolator, and joint
specifics appear in very localized places such as when interfacing with its
inputs/outputs, or to determine whether a joint is continuous (by reading
It makes a lot of sense in my mind to have a more generic interpolator
message and code that leverages it. As an obvious non-joint usecase, we
have some RGB led arrays, and it would be just great to reuse a generic nD
trajectory interpolator to control them.
@Mrinal, does your implementation provide a mechanism for specifying custom
interpolation functions for certain fields?; for example one might want to
interpolate orientation data represented by quaternions, whose components
are best not interpolated independently, but using slerp.
> - Mrinal
> On Wed, Jun 5, 2013 at 11:56 AM, Adolfo Rodríguez Tsouroukdissian
> <adolfo.rodriguez at pal-robotics.com> wrote:
> > On Wed, Jun 5, 2013 at 11:39 AM, Mrinal Kalakrishnan <kalakris at usc.edu>
> > wrote:
> >> We use a simple Cartesian trajectory msg internally at USC. The one
> >> additional thing we have is accelerations at each
> >> CartesianTrajectoryPoint. This allows us to use quintic splines in
> >> cartesian space, for continuous accelerations between segments
> >> (similar to the JointTrajectory msg).
> > +1 for accelerations in the message specification. Also, the more
> > parallelisms we can make with the JointTrajectory msg the better. If
> > used to the look& feel of one, it should be straightforward to use the
> > other.
> > Adolfo.
> >> - Mrinal
> >> On Wed, Jun 5, 2013 at 3:53 AM, Jonathan Bohren
> >> <jonathan.bohren at gmail.com> wrote:
> >> >
> >> > On Tue, Jun 4, 2013 at 9:09 PM, Edwards, Shaun M. <sedwards at swri.org>
> >> > wrote:
> >> >>
> >> >> Are you aware if anybody is currently using a cartesian trajectory
> >> >> (this
> >> >> definition or any other)?
> >> >
> >> >
> >> > There's an old repository of Stu's here:
> >> >
> >> >
> >> >
> >> > I think at one point there was something similar in ros_control or
> >> > moveit,
> >> > too. I put together a minimal cartesian trajectory message which was
> >> > just an
> >> > array of Poses and Twists with associated durations, but I think it
> >> > should
> >> > have some of the features that the aforementioned review describes.
> >> > Other
> >> > than that I don't know.
> >> >
> >> > --
> >> > Jonathan Bohren
> >> > Laboratory for Computational Sensing and Robotics
> >> > http://dscl.lcsr.jhu.edu/People/JonathanBohren
> >> >
> >> >
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> > --
> > Adolfo Rodríguez Tsouroukdissian
> > Senior robotics engineer
> > adolfo.rodriguez at pal-robotics.com
> > http://www.pal-robotics.com
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