Manipulator Force Feedback

Overview

Each joint of the manipulator arm has a force-torque (FT) sensor. Each of those sensors provide 6 readings: x,y,z forces and x,y,z torques. The purpose of these sensors is to provide as much feedback as possible to operators when manipulating the arm in a low visibility under-water environment.

Location of the sensors

For the oberon7 manipulator arm, there are 6 FT sensors located at the following joints:

• azimuth joint
• shoulder joint
• elbow joint
• roll joint
• pitch joint
• wrist joint
• The other joints in the gripper's do not have the FT sensor.

To see these joints in Gazebo, you can turn on the transparency and joints from the view menu. View > Transparent and View > Joints

Spring demo

The demo sets up an underwater world with a springy plate that demonstrate the functionality of the FT sensors. To run the demo launch the following command.

roslaunch uuv_dave uuv_manipulator_spring_demo.launch

Once Gazebo launches, you will see the rexrov UUV in front of a springy plate.

Visualizing the forces and torques using rqt_plot

Using launch file

Run the following launch command to show an rqt plotter showing the current forces on the gripper joint.

roslaunch uuv_dave plot_manipulator.launch

You can see the status of the other joints by writing their topic names and clicking the + button. Here is the format for the topic names for the FT sensors.

/rexrov/ft_sensor_<joint_name>

So if you want to see the x force on the wrist joint, the topic is

/rexrov/ft_sensor_wrist/wrench/force/x

You can watch this video that demonstrates the feedback functionality in this spring world.

Adding command line arguments to rqt_plot

rosrun rqt_plot rqt_plot /rexrov/ftensor_wrist/wrench/torque/x /rexrov/ft_sensor_wrist/wrench/torque/y /rexrov/ft_sensor_wrist/wrench/torque/z

See this video example for torque sensing.