How to use the UR5e and Tools/Grabbers (e.g. qb Softhand)?

asked 2020-07-31 07:34:37 -0500

Hey there,

I am new to ros and currently working with the ur5e. I am able to move the robot in a cycle with a simple self written package.

Now I want to Control the QB Softhand from the script i wrote. The docu for the hand is relatively small and not much of help when it comes to writing real applications. It is no problem to open and close the hand with to rqt slider or per commandline. E.g. like this:

rostopic pub /qbhand1/control/qbhand1_synergy_trajectory_controller/command trajectory_msgs/JointTrajectory "{header:{seq: 69, stamp:{ secs: 0, nsecs: 0}, frame_id: ''}, joint_names: [qbhand1_synergy_joint], points: [{ positions: [0.0], velocities: [], accelerations: [], effort: [], time_from_start:{ secs: 1, nsecs: 0}}]}"

I wanted to do pretty much the same inside my script with a publisher (c++). But the problem is that to ur5e and hand do not know each other. I get the error:

[ WARN] [1596196354.965152722]: Unable to transform object from frame 'qbhand1_base_link' to planning frame 'world' (Could not find a connection between 'world' and 'qbhand1_base_link' because they are not part of the same tree.Tf has two or more unconnected trees.)

Until now I don't really know how to handle tf. Basically I am lost and not sure what so look for. Do I need to write a listener and broadcaster for transforms for the qb softhand? Are there other Tools/Grabbers examples from which I can learn? Does anyone else worked with the ur5e and qb softhand?

Thank you very much for your answers!

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