Generate IKFast Plugin Tutorial¶

In this section, we will walk through configuring an IKFast plugin for MoveIt!

What is IKFast?¶

From Wikipedia: IKFast, the Robot Kinematics Compiler, is a powerful inverse kinematics solver provided within Rosen Diankov’s OpenRAVE motion planning software. Unlike most inverse kinematics solvers, IKFast can analytically solve the kinematics equations of any complex kinematics chain, and generate language-specific files (like C++) for later use. The end result is extremely stable solutions that can run as fast as 5 microseconds on recent processors

MoveIt! IKFast¶

MoveIt! IKFast is a tool that generates a IKFast kinematics plugin for MoveIt using OpenRave generated cpp files. This tutorial will step you through setting up your robot to utilize the power of IKFast. MoveIt! IKFast is tested on ROS Groovy with Catkin using OpenRave 0.8 with a 6dof and 7dof robot arm manipulator. While it works in theory, currently the IKFast plugin generator tool does not work with >7 degree of freedom arms.

Pre-requisites¶

You should have already created a MoveIt! configuration package for your robot, by using the Setup Assistant.

MoveIt! IKFast Installation¶

Install the MoveIt! IKFast package either from debs or from source.

Binary Install

sudo apt-get install ros-indigo-moveit-kinematics

Source

Inside your catkin workspace

git clone https://github.com/ros-planning/moveit.git
cd moveit
git checkout indigo-devel

OpenRAVE Installation¶

Binary Install (only Indigo / Ubuntu 14.04)

sudo apt-get install ros-indigo-openrave

Note: you have to set export PYTHONPATH=$PYTHONPATH:`openrave-config –python-dir` (2016.9.1)

Source Install

Thanks to instructions from Stéphane Caron in https://scaron.info/teaching/troubleshooting-openrave-installation.html

git clone --branch latest_stable https://github.com/rdiankov/openrave.git
cd openrave && mkdir build && cd build
cmake ..
make -j4
sudo make install

Working commit numbers 5cfc7444... confirmed for Ubuntu 14.04 and 9c79ea26... confirmed for Ubuntu 16.04, according to Stéphane Caron.

Please report your results with this on the moveit-users mailing list.

Create Collada File For Use With OpenRave¶

First you will need robot description file that is in Collada or OpenRave robot format.

If your robot is not in this format we recommend you create a ROS URDF file, then convert it to a Collada .dae file using the following command:

rosrun collada_urdf urdf_to_collada <myrobot_name>.urdf <myrobot_name>.dae

where <myrobot_name> is the name of your robot.

Often floating point issues arrise in converting a URDF file to Collada file, so a script has been created to round all the numbers down to x decimal places in your .dae file. Its probably best if you skip this step initially and see if IKFast can generate a solution with your default values, but if the generator takes longer than, say, an hour, try the following:

rosrun moveit_kinematics round_collada_numbers.py <input_dae> <output_dae> <decimal places>

From experience we recommend 5 decimal places, but if the OpenRave ikfast generator takes to long to find a solution, lowering the number of decimal places should help. For example:

rosrun moveit_kinematics round_collada_numbers.py <myrobot_name>.dae <myrobot_name>.rounded.dae 5

To see the links in your newly generated Collada file

You may need to install package libsoqt4-dev to have the display working:

openrave-robot.py <myrobot_name>.dae --info links

This is useful if you have a 7-dof arm and you need to fill in a –freeindex parameter, discussed later.

To test your newly generated Collada file in OpenRave:

openrave <myrobot_name>.dae

Create IKFast Solution CPP File¶

Once you have a numerically rounded Collada file its time to generate the C++ .h header file that contains the analytical IK solution for your robot.

Select IK Type¶

You need to choose which sort of IK you want. See this page for more info. The most common IK type is transform6d.

Choose Planning Group¶

If your robot has more than one arm or “planning group” that you want to generate an IKFast solution for, choose one to generate first. The following instructions will assume you have chosen one <planning_group_name> that you will create a plugin for. Once you have verified that the plugin works, repeat the following instructions for any other planning groups you have. For example, you might have 2 planning groups:

<planning_group_name> = "left_arm"
<planning_group_name> = "right_arm"

Identify Link Numbers¶

You also need the link index numbers for the base_link and end_link between which the IK will be calculated. You can count the number of links by viewing a list of links in your model:

openrave-robot.py <myrobot_name>.dae --info links

A typical 6-DOF manipulator should have 6 arm links + a dummy base_link as required by ROS specifications. If no extra links are present in the model, this gives: baselink=0 and eelink=6. Often, an additional tool_link will be provided to position the grasp/tool frame, giving eelink=7.

The manipulator below also has another dummy mounting_link, giving baselink=1 and eelink=8.

name	index	parents
base_link	0
mounting_link	1	base_link
link1_rotate	2	mounting_link
link2	3	link1_rotate
link3	4	link2
link4	5	link3
link5	6	link4
link6_wrist	7	link5
tool_link	8	link6_wrist

Generate IK Solver¶

To generate the IK solution between the manipulator’s base and tool frames for a 6 dof arm, use the following command format:

python `openrave-config --python-dir`/openravepy/_openravepy_/ikfast.py --robot=<myrobot_name>.dae --iktype=transform6d --baselink=1 --eelink=8 --savefile=<ikfast_output_path>

where <ikfast_output_path> is recommended to be a path that points to a file named ikfast61_<planning_group_name>.cpp.

For a 7 dof arm, you will need to specify a free link:

python `openrave-config --python-dir`/openravepy/_openravepy_/ikfast.py --robot=<myrobot_name>.dae --iktype=transform6d --baselink=1 --eelink=8 --freeindex=4 --savefile=<ikfast_output_path>

The speed and success of this process will depend on the complexity of your robot. A typical 6 DOF manipulator with 3 intersecting axis at the base or wrist will take only a few minutes to generate the IK.

Known issue –freeindex argument is known to have a bug that it cannot handle tree index correctly. Say –baselink=2 –eelink=16 and links index from 3 to 9 is not related to current planning group chain. In that case –freeindex will expect index 2 as link 2, but index 3 as link 10 ... and index 9 as link 16.

You should consult the OpenRAVE mailing list and ROS Answers for information about 5 and 7 DOF manipulators.

Create Plugin¶

Create the package that will contain the IK plugin. We recommend you name the package <myrobot_name>_ikfast_<planning_group_name>_plugin. From here on out we’ll refer to your IKFast package as simply <moveit_ik_plugin_pkg>:

cd ~/catkin_ws/src
catkin_create_pkg <moveit_ik_plugin_pkg>

Build your workspace so the new package is detected (can be ‘roscd’):

cd ~/catkin_ws
catkin_make

Create the plugin source code:

rosrun moveit_kinematics create_ikfast_moveit_plugin.py <myrobot_name> <planning_group_name> <moveit_ik_plugin_pkg> <ikfast_output_path>

Or without ROS:

python /path/to/create_ikfast_moveit_plugin.py <myrobot_name> <planning_group_name> <moveit_ik_plugin_pkg> <ikfast_output_path>

Parameters¶

myrobot_name - name of robot as in your URDF

planning_group_name - name of the planning group you would like to use this solver for, as referenced in your SRDF and kinematics.yaml

moveit_ik_plugin_pkg - name of the new package you just created

ikfast_output_path - file path to the location of your generated IKFast output.cpp file

This will generate a new source file <myrobot_name>_<planning_group_name>_ikfast_moveit_plugin.cpp in the src/ directory, and modify various configuration files.

Build your workspace again to create the ik plugin:

cd ~/catkin_ws
catkin_make

This will build the new plugin library lib/lib<myrobot_name>_<planning_group_name>_moveit_ikfast_moveit_plugin.so that can be used with MoveIt!

Usage¶

The IKFast plugin should function identically to the default KDL IK Solver, but with greatly increased performance. The MoveIt configuration file is automatically edited by the moveit_ikfast script but you can switch between the KDL and IKFast solvers using the kinematics_solver parameter in the robot’s kinematics.yaml file

rosed <myrobot_name>_moveit_config/config/kinematics.yaml

Edit these parts:

<planning_group_name>:
  kinematics_solver: <myrobot_name>_<planning_group_name>_kinematics/IKFastKinematicsPlugin
-INSTEAD OF-
  kinematics_solver: kdl_kinematics_plugin/KDLKinematicsPlugin

Test the Plugin¶

Use the MoveIt Rviz Motion Planning Plugin and use the interactive markers to see if correct IK Solutions are found.

Updating the Plugin¶

If any future changes occur with MoveIt! or IKFast, you might need to re-generate this plugin using our scripts. To allow you to easily do this, a bash script is automatically created in the root of your IKFast package, named update_ikfast_plugin.sh. This does the same thing you did manually earlier, but uses the IKFast solution header file that is copied into the ROS package.

Open Source Feedback

See something that needs improvement? Please open a pull request on this GitHub page