Visual Servoing Platform  version 3.5.1 under development (2022-07-03)
Tutorial: IBVS with a robot from Universal Robots

This tutorial provides information on controlling robots from Universal Robots using vpRobotUniversalRobots class implemented in ViSP. This class is a wrapper over ur_rtde 3rd party.

This tutorial explains also how to implement an image-based visual-servoing with an UR robot equipped with an Intel Realsense camera.

Prerequisites

Install ur_rtde 3rd party

To use vpRobotUniversalRobots class you need first to install ur_rtde on your remote host that will be used to control the robot.

  • You can either install ur_rtde from existing Ubuntu package
    $ sudo add-apt-repository ppa:sdurobotics/ur-rtde
    $ sudo apt-get update
    $ sudo apt install librtde librtde-dev
    
  • or build ur_rtde from source
    $ cd $VISP_WS/3rdparty
    $ git clone https://gitlab.com/sdurobotics/ur_rtde.git
    $ mkdir ur_rtde/build
    $ cd ur_rtde/build
    $ cmake .. -DCMAKE_BUILD_TYPE=Release
    $ make -j4
    

Build ViSP with ur_rtde support

Once ur_rtde is installed, you need to rebuild ViSP to enable ur_rtde support.

$ cd $VISP_WS/visp-build
$ cmake ../visp -Dur_rtde_DIR=$VISP_WS/3rdparty/ur_rtde/build/ur_rtde

At this point, check if ur_rtde is detected by ViSP:

$ cd $VISP_WS/visp-build
$ grep ur_rtde ViSP-third-party.txt
    Use ur_rtde:                 yes (ver 1.5.0)

If you see Use ur_rtde: no it means that the 3rd party is not detected. You need than to set ur_rtde_DIR,

  • either by setting an environment var like
    $ export ur_rtde_DIR=$VISP_WS/3rdparty/ur_rtde/build/ur_rtde
    $ cmake ../visp
    
  • or setting a cmake var
    $ cmake ../visp -Dur_rtde_DIR=$VISP_WS/3rdparty/ur_rtde/build/ur_rtde
    

Setting up UR robot

For using ur_rtde you need to prepare the robot.

Install the externalcontrol-1.0.5.urcap which can be found here.

Note
For installing this URCap a minimal PolyScope version of 3.7 or 5.1 (in case of e-Series) is necessary.

For installing the necessary URCap and creating a program, please see the individual tutorials on how to setup a CB3 robot or how to setup an e-Series robot.

On our UR5, using the PolyScope Robot User Interface

  • entering "Robot Setup > URCaps" menu we have the following settings
    UR5 URCaps external control settings
  • and entering "Robot Setup > Network" menu we configured the network with static address 192.168.0.100
    UR5 network settings

Setting up remote host

  • Connect an Ethernet cable between your UR robot and your remote host
  • Enter network settings interface and create a new wired profile named for example "Universal Robot" and set a static IP like 192.168.0.77
Remote host network settings

Testing connexion

To test communication between UR robot and your remote host, you can use testUniversalRobotsGetData.cpp

$ cd $VISP_WS/visp-build/modules/robot
$ ./testUniversalRobotsGetData --ip 192.168.0.100
-- Start test 1/3
Robot connected  : yes
Robot mode       : 3
Robot model      : UR5
PolyScope version: 3.15.7.106331
End test 1/3
-- Start test 2/3
To proceed with this test you need to power on the robot
-- Start test 3/3
...

If you can see a similar output it means that all the prerequisites have been successfully fulfilled.

You can now continue powering the robot on. To this end using PolyScope and entering "Initialize Robot" menu, press "ON" button

PolyScope powering robot on

and then run again the test to get robot joint positions:

$ cd $VISP_WS/visp-build/modules/robot
$ ./testUniversalRobotsGetData --ip 192.168.0.100
-- Start test 1/3
Robot connected  : yes
Robot mode       : 5
Robot model      : UR5
PolyScope version: 3.15.7.106331
-- Start test 2/3
Joint position [deg]: -0.05700840128  -89.63515793  91.56270198  -88.23354847  -89.88700067  -0.02810304071
...

Image-based visual servoing

Here we consider that you have an UR robot equipped with a Reasense camera. Our model is a Realsense D435 camera, but the tutorial should work with any other Realsense device.

Our UR5 equipped with a D435 Realsense device

An example of image-based visual servoing using a robot from Universal Robots equipped with a Realsense camera is available in servoUniversalRobotsIBVS.cpp.

  • Attach your Realsense camera to the robot end-effector. To this end, we provide a CAD model of a support that could be 3D printed. The FreeCAD model is available here.
  • Put an Apriltag in the camera field of view
  • If not already done, follow Tutorial: Camera extrinsic calibration to estimate $^e{\bf M}_c$, the homogeneous transformation between robot end-effector and camera frame. We suppose here that the file is located in tutorial/calibration/ur_eMc.yaml.

Now enter in example/servo-universal-robots folder and run servoUniversalRobotsIBVS binary using --eMc to locate the file containing the $^e{\bf M}_c$ transformation. Other options are available. Using --help show them:

$ cd example/servo-universal-robots
$ ./servoUniversalRobotsIBVS --help
./servoUniversalRobotsIBVS [--ip <default 192.168.0.100>] [--tag_size <marker size in meter; default 0.12>] [--eMc <eMc extrinsic file>] [--quad_decimate <decimation; default 2>] [--adaptive_gain] [--plot] [--task_sequencing] [--no-convergence-threshold] [--verbose] [--help] [-h]

Run the binary activating the plot and using a constant gain:

$ ./servoUniversalRobotsIBVS --eMc ../../tutorial/calibration/ur_eMc.yaml --plot

Use the left mouse click to enable the robot controller, and the right click to quit the binary.

At this point the behaviour that you should observe is the following:

Legend: Example of initial position. The goal is here to center the 4 tag corners in the image.
Legend: Example of final position reached after position-based visual servoing. In green, you can see the trajectories in the image of the tag corners. When the camera extrinsic parameters are well estimated these trajectories are straight lines.
Legend: Corresponding visual-features (x and y coordinates of the corner points in the image plane) and velocities applied to the robot in the camera frame. You can observe an exponential decrease of the visual features.

You can also activate an adaptive gain that will make the convergence faster:

$ ./servoUniversalRobotsIBVS --eMc ../../tutorial/calibration/ur_eMc.yaml --plot --adaptive_gain

You can also start the robot with a zero velocity at the beginning introducing task sequencing option:

$ ./servoUniversalRobotsIBVS --eMc ../../tutorial/calibration/ur_eMc.yaml --plot --task_sequencing

And finally you can activate the adaptive gain and task sequencing:

$ ./servoUniversalRobotsIBVS --eMc ../../tutorial/calibration/ur_eMc.yaml --plot --adaptive_gain --task_sequencing

Next tutorial

To learn more about adaptive gain and task sequencing see Tutorial: How to boost your visual servo control law.

To see the differences with a position-based visual-servoing you may also follow Tutorial: PBVS with a robot from Universal Robots.