UR Guiding

Overview - A handy device for controlling Universal Robot

To intuitively control UR, I developed a device with AR markers and an IMU unit. The device output absolute pose with respect to base_link, where the position information is givne by AR marker and the orientation is defined by the IMU sensor. The transformation from camera to base is computed on a real-time basis. The setup is illustrated below.

The model is 3d printed and the stl can be found here. You can modify it by changing CAD file.

The trjecotry can be recorded with 6 DOF:

And this can be stored, or it can be used for a real-time follwing:

I further developed it for 3d drawing and robotic welding path planning (check below subsections for detail). The whole program is developed in ROS kinetic, most scripts are in python.

How is it made?

AR marker

We obtained the position of AR marker using the package ar_track_alvar. In our lab, there are two cameras, one kinect mounted at the top and another realsense mounted at the end-effector of robot manipulator. Both can be used for tracking the AR marker and record the trajectory.

IMU

We obtained orientation information form the sensor in ROS. For detail of the sensor and its usage in ROS can be found at jy901-imu-ros.

The algorithm

Filter the path

The motion and detection and introduce considerable noise. Therefore, I used voxel grid for filtering the nearby points. As shown below, the yellow represent the original trajectory and red is the filtered result. This is done online.

Explaination of the nodes

Node	Function
kinect_pen_trajectory.py	use kinect camera to detect AR and generate trajectory
ar_marker_transformation.py	obtain real-time transformation from realsense camera to base_link
rs_pen_trajectory.py	use realsense camera to detect AR and generate trajectory
trajectory_execution.py	execution trajectory using UR
ur_imu.py	control the UR by orientation only
voxel.py	voxel downsampling the trajectory
filtered_trajectory.py	voxel downsampling the trajectory and remap it to 3d space

Command

To visualise the trajectory:

roslaunch ur-guiding trajectory_visual.launch

To filter the trajectory using voxel grid:

roslaunch ur-guiding filtered_trajectory.launch

Application

3d drawing

I packed the tip trajecotry of the device as the marker array and visualised in Rviz:

robotic welding path planning

Same principle, we record the path and then executed it by the manipulator. Three shapes are showed for illustration.

Plane

Tube

Y-shape

Remarks

Related videos can also be found on https://www.youtube.com/playlist?list=PL5FErTrn43DAEZoOoIT-MDyYhVbtMYqoF