Use move in gripper_action when max_effort is 0

[marcbone]

This PR implements the my suggested workaround from #173.

This PR solves #172.

Now the gripper_action can close the gripper to a smaller width when max_effort is 0. However, since this is a breaking change we want to wait until the following issue is resolved in moveit (@rickstaa):

• #2956 MoveIt: Make max_effort settable in the MoveIt Simple Controller Manager

[rickstaa]

@marcbone Thanks for implementing this. I am currently still trying to fix the gravity compensator (i.e. #160) but I will jump right on it after that is done.

[rickstaa]

@marcbone I implemented the requested functionality in Moveit (see moveit/moveit#2984). It is currently under review. I will let you know when it is merged.

[rickstaa]

@marcbone I tested your pull request, and I think your solution is very intuitive. It works perfectly when the gripper hand is positioned horizontally. Please be aware that the move action is currently broken for non-horizontal gripper hand orientations (see #173 (comment) and #173 (comment)).

[rickstaa]

@marcbone Just a heads-up. moveit/moveit#2984 (comment) has been merged.

[rickstaa]

@marcbone, @gollth Just wondering, do you need me to implement something else on the MoveIt side before this can be merged?

Also, did you already manage to find good PID gains that can control the franka_gripper in the vertical mode that does not break the velocity checking logic in the grasp server (see #173 (comment))?

[gollth]

Also, did you already manage to find good PID gains that can control the franka_gripper in the vertical mode that does not break the velocity checking logic in the grasp server (see #173 (comment))?

Not yet unfortunately but we have it on the radar

[rickstaa]

Great! Thanks a lot!

[marcbone]

Just wondering, do you need me to implement something else on the MoveIt side before this can be merged?

No, basically I am just waiting for the moveit release, since I guess nobody is going to build moveit from source.

[rickstaa]

@marcbone Ha good point! I overlooked that fact. Let's wait for the release then.

[rickstaa]

@marcbone Just a heads up, I tried to rebase this branch on the develop branch but git runs into conflicts of which two are not flagged by git. The following lines are injected by the git merge tool on line 354-355 of the franka_gripper_sim.cpp file without git flagging them:

double width = this->finger1_.getPosition() + this->finger2_.getPosition();  // recalculate
bool ok = goal->width - eps.inner < width and width < goal->width + eps.outer;

This will throw a error, further the following line will be changed from:

result.success = static_cast<decltype(result.success)>(true);

to

result.success = static_cast<decltype(result.success)>(ok);

Which also throws an error. After fixing these lines and solving the other flagged conflicts, the pull request works again (see https://github.com/rickstaa/franka_ros/tree/use-move-in-gripper-action-rebased).