URDF2ROBCOGEN {#mainpage}

Authors: Jan Carius (jcarius@ethz.ch) and Ruben Grandia (rgrandia@ethz.ch), based on an earlier version by Diego Pardo (depardo@ethz.ch)

Maintainers: Jan Carius (jcarius@ethz.ch) and Ruben Grandia (rgrandia@ethz.ch)

What is this repository for?

This tool generates the RobCoGen description files (.kindsl & .dtdsl) from a URDF description format.

Building

Dependencies

• Eigen
• Boost
• ros::urdf
• kindr (a kinematics library for robotics)

Build the executable

We use catkin as a build system. To build the bare version use

catkin build urdf2robcogen

Build the documentation

We use rosdoc_lite with doxygen backend to build documentation for this catkin package.

rosdoc_lite /path/to/package

Usage

Two modes of operation are possible.

A) Run as standalone application (plain URDF file)

You must have a URDF description of your robot as a plaintext xml file. This should not contain xacro macros, i.e., you must invoke the xacro command beforehand to produce the URDF file.

To generate the robcogen description, execute

./urdf2robcogen_script RobotName /path/to/description.urdf

The generated files are written into the directory where the executable was executed (i.e., the output of pwd).

B) Using a launch file (xacro urdf file)

The urdf2robcogen.launch file converts a robot description on the parameter server.

roslaunch urdf2robcogen urdf2robcogen.launch robot_name:=myRobot description_name:=robot_description

See xacro_example.launch to see how to integrate this with generation of the robot description.

As a default, output files are placed in the /generated folder of this package.

Main differences between URDF and RobCoGen/Kindsl

• URDF:

  • Frame rotations are extrinsic (rotations about a fixed frame)
  • The axis of rotation of the joints is set with the vector property 'axis' of the joint element
  • There is no concept of Frame
  • Artificial links are used to define frames (a.k.a., link_frames), they may or may not have inertia
  • Artificial Joints (usually fixed) are used to connect link_frames to the real links
  • It is common to find URDF with 'virtual' links for compatibility with other tools
  • Virtual links might have incomplete information (i.e., inertial parameters)
  • The inertial parameters are expressed w.r.t a frame at the CoM of the link

• RobCoGen:

  • Frame rotations are intrinsic (rotations about the current frame)
  • Frame rotation order is x,y,z
  • The axis of rotation of the joint is always Z
  • Links always carry inertia and must have a parent joint that is moving (i.e., not fixed)
  • Additional frames can be defined at any link
  • Inertial parameters are expressed w.r.t. the link frame (i.e., the corresponding joint frame)
  • It includes a special feature to set a different frame for expressing the inertial parameters (ref_frame)

Caveats

• Double-check the ordering of the joints/links in the generated files. They may differ from what you expect.