Hi everyone,

Some background: I am quite fresh with ROS. The setup i am using includes ROS (kinetic), an ABB arm, ROS-I along with the abb_driver. Moveit for the motion planning, kinematics etc. Setup with just the arm is working as it is supposed to. The goal now is to control an external axis which is rotating.

As stated in the abb_driver wiki the driver supports up to 4 integrated external linear axis. But in this case the external axis is set in front of the robot on top of a fixed base.

As far as the message part goes, with a quick inspection I saw that a conversion from mm to m and vice-versa is happening at the RAPID side. From ROS side the information for the external axis seems to be incorporated into the joint_message - joint_data system. For the RAPID side, is it as simple as using conversion from degree2rad instead of mm2m in order to support a revolute joint?

Main question: If the message structure for the supported linear axis is possible to be used with a revolute joint, what is the correct way to add the external axis assembly in the URDF and Moveit?

Current idea:

• Add a world frame in the urdf.
• Add both the arm's and positioner's first links as children of the world frame (This will create a branch in the kinematic chain.).
• Place positioner_base in front of the robot with a fixed joint and attach the second link to the positioner_base with a revolute joint.
• Define a new positioner planning group.
• Define a new controller for that group.

I have tried this approach for now and set it up with MSA but as soon as I add the new joint in the joint_names.yaml and execute the plan i get the error:

[ERROR] [1550352562.186055092]: Joint trajectory action failing on invalid joints 

Moreover, IK solver does not like it if I create a planning_group that includes both "manipulator" and "positioner" as subgroups therefore i cannot incorporate them under the same planning_group. Currently i am using the TracIK kinematics plugin and it supports only chains.

If I create the second controller and name both of them accordingly: "manipulator", "positioner". I get the following error:

[ WARN] [1550403869.172061404]: Waiting for manipulator/joint_trajectory_action to come up
[ERROR] [1550403875.172279892]: Action client not connected: manipulator/joint_trajectory_action

Searching other posts for solutions i added two groups (inside robot_interface.launch) in order to define two namespaces (i think at least) to start their own instance of joint_trajectory_action but i still get the error.

Last, if I remove joint_7 (external axis) from the controller_joint_names I can normally plan for the arm but I also get this:

[ WARN] [1550419157.365318143]: The complete state of the robot is not yet known.  Missing joint_7

I am confused at this point since adding a second group which is also trying to connect to the same IP does not seem right (since the external axis is integrated in the abb controller). But how else will i be able to get Moveit side to work and include the external axis in the path planning?

p.s: I do not need to control a simultaneous movement of the arm+positioner or use the external axis to minimize movement of the arm. For now I need to only establish a way to control its angle. Similar to a dual arm concept but both joint states (arm+positioner) are received from the same port.

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Edit 1:

An update. I made it work for use with the industrial_robot_simulator. What i did is the following:

• Added the extra joint in the controller_joint_names parameter in the joint_names.yaml.
• Created two controllers as explain above: "manipulator" and "positioner" in the controllers.yaml.
• I added the industrial_robot_simulator package to my workspace and edited the .launch file to duplicate its functionality into two groups that each of them creates the appropriate namespace (manipulator/positioner).
• Edited the moveit_planning_execution launch file to point to the edited simulator.

At this point i could not execute a plan since both instances of the simulator where looking at the /joint_states topic for the state, therefore i added the following in the beginning of moveit_planning_execution.launch to force the states to the appropriate topic (not sure that is the proper way to do it tho):

<remap from="/manipulator/joint_states" to="/joint_states" /> 
<remap from="/positioner/joint_states" to="/joint_states" />

I will provide another update with the changes to make it work with RobotStudio, but the idea should be the same i guess..

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Edit 2:

Ok, I am having a problem with the concept idea when i am trying to connect it to RobotStudio. Here are two routes that i can think of:

1. Robot and Positioner in the same task (TROB1) and return the full state of the robot+positioner from the `ROSstateServerand accept motion command withROS_motionServer`.

2. Two different tasks in RAPID (TROB1 & TPOS1). Having a second task I need to create the appropriate motion and server files in RAPID. Assign 2 new ports and have Moveit connect to those from each group (namespace).

Following No1: I had to define a new controller " " with all 7 joints included which uses the '/jointtrajectoryaction', since i have only 1 connection. But i get this:

[ERROR] [1550747865.040852330]: Joint trajectory action rejected: waiting for (initial) feedback from controller
[ WARN] [1550747865.041136508]: Controller manipulator failed with error code INVALID_GOAL
[ WARN] [1550747865.041343308]: Controller handle manipulator reports status FAILED

I was initially worried about the /jointstates topic since it publishes all 7 joints together. Not sure if this was my problem i made a "splitter" node thats subscribes to the `/jointstatesand republishes 2 sets, one with the arm joints and one with the positioner joint. But that was not it.. It has to do something with the/jointtrajectoryaction` that expects 7 joints and the "manipulator" controller when I plan-execute in moveit calculates 6 joints instead?

Following No2.: This way Moveit works fine, recieves the corrects joints, plans and executes for the arm. The problem arises with the positioner. Sending back a joint_data message requires values in the 6 axis of the robot at least, this is the bytelength that ROS waits, and if I set up only 1 axis the message unload fails with: "Buffer is smaller than requested byteSize.". If i include "dummy" joints the whole state node crashes.

I am not sure what is the "correct" way to build this, any ideas?