force_torque_tools

Overview

Tools for gravity compensation and sensor calibration for wrist-mounted force-torque sensors in robot manipulators.

• force_torque_sensor_calib: calibrates force-torque sensor bias, gripper mass and center of mass of the gripper.
• gravity_compensation: performs gravity compensation to force-torque sensor measurements after calibrating with the force_torque_sensor_calib package.

Installing

Make sure you have a working catkin workspace, as described at: http://www.ros.org/wiki/catkin/Tutorials/create_a_workspace

Also make sure you have git installed:

sudo apt-get install git-core

Change directory to the source folder of your catkin workspace. If, for instance, your workspace is ~/catkin_ws, make sure there is a src/ folder within it, then execute:

cd ~/catkin_ws/src

Download the metapackage from the github repository ( may be `groovy` or `hydro`):

git clone -b <ros_distro> https://github.com/kth-ros-pkg/force_torque_tools.git

Compile your catkin workspace:

cd ~/catkin_ws
catkin_make

force_torque_sensor_calib

Overview

This package can calibrate through least-squares the following parameters related to a wrist-mounted force-torque sensor:

Bias of the F/T sensor
Mass of the gripper
Location of the center of mass of the attached gripper

Running this software assumes that you have an accelerometer/imu whose reference frame is already calibrated with respect to the e.g. base frame of the robot manipulator. It also assumes that you have a manipulator previously configured to be controlled through MoveIt!.

The software calibrates the F/T sensor by moving the manipulator into a number of different poses and using the resulting F/T sensor and accelerometer signals for computing a least-squares estimate of the parameters. Calibration can be done by either manually specifying explicitly the manipulator poses in the parameter server (parameters pose0, pose1, pose2, … poseN) or by executing N random poses.

Running the calibration node

Make sure that the robot is still and other objects don’t obstruct the arms while they move into the calibration poses.

You can look at the configuration/launch files in the config and launch folders for examples on how to set the parameters and launch the software for your robot. For more details on the parameters required to launch the calibration node visit the ROS wiki page of the force_torque_sensor_calib package and the tutorials page.

The calibration software will produce a yaml calibration file that can later be used for gravity compensation. By default the file will be written in the ~/.ros/ft_calib/ directory.

gravity_compensation

Compensates gravity forces measured by a force-torque sensor. Uses the yaml calibration file produced by the force_torque_sensor_calib package and gravity measurements given by an accelerometer whose reference frame has been previously calibrated to the frame of the robot.

You can look at the configuration/launch files in the config and launch folders for examples on how to launch this software.

For more details on running the software visit the package’s [ROS wiki page] [3] and the tutorials page. [3]: http://wiki.ros.org/gravity_compensation

References

Equations are based on “On-line Rigid Object Recognition and Pose Estimation Based on Inertial Parameters”, D. Kubus, T. Kroger, F. Wahl, IROS 2008