Hi,

With some breaks I've been working towards an application for my robot where I want to position holes/locations in a product to a specific point in space. I've been digging around and i'd like to check that what I'm trying to do is possible at all, and I hope somebody can confirm if i'm on the right track and if needed nudge me into the right direction. While I've got multiple questions, these all have a common cause, therefore I hope it's OK to pose them all together.

I've made a 4DOF robot where I will pick up different products and bring the holes in that product to a location where a tool will add a feature to that hole. The product cannot be rotated in it's own plane (around its frame z-axis). I would like to position these holes to a specified location one by one. Preferably with Python. I've made a the robot moveit package and a robot_support package Below a simple representation:

After a lot of searching I think I have 2 possible solutions:

• Add a hole frame to my tool0 frame of the end-effector, make that the tip of my kinematics chain and have moveit plan that frame to the specified location.
• I could generate a new tool for each product (with a frame at each hole location) and load them with different launch files, but that would give me a new tool for each new product i want to handle and I'm not sure I want the burden of maintaining all those tools.

One hurdle I encounter at trying to position the end effector (just the robot end effector, no extra frames/product) to a point in space with the ros_commander python api is that I can't get the plan to succeed (I try to follow the moveit tutorial example).

link to gist of plan.py

link to terminal output

but I get errors telling me the plan isn't solvable.

[ INFO] [1493551548.788745043]: Planning request received for MoveGroup action. Forwarding to planning pipeline.
[ INFO] [1493551548.859191599]: Planner configuration 'manipulator[RRTkConfigDefault]' will use planner 'geometric::RRT'. Additional configuration parameters will be set when the planner is constructed.
[ INFO] [1493551548.859571195]: manipulator[RRTkConfigDefault]: Starting planning with 1 states already in datastructure
[ INFO] [1493551558.859673954]: manipulator[RRTkConfigDefault]: Created 114272 states
[ INFO] [1493551558.859745128]: No solution found after 10.000228 seconds
[ INFO] [1493551558.869263246]: Unable to solve the planning problem
[ INFO] [1493551558.987668538]: Planning request received for MoveGroup action. Forwarding to planning pipeline.
[ INFO] [1493551559.063110536]: Planner configuration 'manipulator[RRTkConfigDefault]' will use planner 'geometric::RRT'. Additional configuration parameters will be set when the planner is constructed.
[ INFO] [1493551559.063482002]: manipulator[RRTkConfigDefault]: Starting planning with 1 states already in datastructure
[ INFO] [1493551569.063481304]: manipulator[RRTkConfigDefault]: Created 111517 states
[ INFO] [1493551569.063716649]: No solution found after 10.000282 seconds
[ INFO] [1493551569.081697521]: Unable to solve the planning problem

I guess that's because I cannot get to that position because the robot only has 4 DOF and cannot rotate the part. I've been searchin a lot and I've got a lot pieces of the puzzle, but some final pieces seem missing yet.

planning to a pose consisting of joint values work btw.

pose_1 = [1.9, 0.785, -0.785, -1.57]
group.set_joint_value_target(pose_1)
plan3 = group.plan()
group.go()

moves the robot as expected

My questions in a nutshell:

• Is this 4DOF type of planning of a frame to cartesian coordinates possible at all?
• If I need to provide the exact position of the end effector frame (so also roll/pitch/yaw) for the product ens position, which knowledge/info/examples do I need to consume to implement that.
• regarding planning with just the stock robot (no tools on the end effector) I could add 2 extra DOF to the tip of the end-effector, with zero length links. Would that be a satisfactory setup to get solutions?
• If I were to generate (from CAD) a new tool for each new product. Is there a way to switch tools at run-time instead of in my launch file? Where should I look for further info regarding that.
• As an alternative, can I change link lenghts of the loaded URDF at run-time?
• I know how to add a frame to the tool0 frame of my robot, but It does not seem to be a frame I can use for planning purposes because while it is viewable in Rvis (add tf plugin) it does not show up in the moveit kinematics chain. Is there a way to add and remove links from the kinematics chain? Where do I need to look

Thanks in advance, Regards, Bas

edit 1: Doing a step back, forgetting about the hole locations for now, I've updated (cleaned up) my configuration and I can plan cartesian positions of the eef only in the XZ plane. I've copied a moveit_commander demo file, and when I uncomment this line the plannning will fail

[INFO] [1493987683.375836]: Path planning failed with only 0.5 success after 100 attempts.

updated moveit_configuration

updated support

edit 2: I ended up adding 2 dummy links in addition to the 4 DOF. These links have zero length, and are able to rotate in the 2 "missing" DOF. This way planning for the end effector works for points outside the XZ plane. see these commits: matildamoveitconfig and matilda_support