This project has been developed with the goal of creating a system to control the cobot in simulation. Here the Cobot UR3 Series with the attached gripper , simulated in rviz and gazebo, can be controlled from Rviz or as well from the terminal by using scripts written in python.
ROS version : Melodic
O.S : Ubuntu 18.04
- universal_robot - ROS-Industrial
sudo apt-get install ros-$ROS_DISTRO-universal-robot
replace $ROS_DISTRO with melodic
mkdir -p ~/catkin_ws/src
# again here - replace $ROS_DISTRO with the ROS version used
git clone -b $ROS_DISTRO-devel https://github.com/ros-industrial/universal_robot.git
cd $HOME/catkin_ws
#checking dependencies
rosdep update
rosdep install --rosdistro $ROS_DISTRO --ignore-src --from-paths src
#build the workspace
catkin_make (or catkin build)
#source the workspace so you can start using it
source $HOME/catkin_ws/devel/setup.bash
At this moment we have set-up our UR environment, which can be already used but without a gripper.
2F-85 Gripper
In order to download the 3D model of the gripper follow the steps in the screenshot below (in the Download file of the link):
The downloaded file is .STEP format and contains the 3D model of the gripper which has to be converted before attaching to the robot.
In order for the xacro to be processed the format has to be CONVERTED IN .STL OR .DAE
At this time you can use free online converters, freecad or autocad in order to complete this task.
When adding a model into ROS, it has to be splitted in two different sections :
-
visual
-
collision
For more information about differences here
So we will need to add the model to both of them (visual and collision).
#move to the path with the .stl/.dae file
cd /path/where/the/file/has_been_saved_and_converted.stl
#In my case the file is named "efektor_otwarty.stl"
#replace the effector_name with the name of the effector you converted already and copy it into ur_description/meshes/ur3/collision folder
cp efektor_otwarty.stl ~/catkin_ws/src/universal_robot/ur_description/meshes/ur3/collision
#the same has to be done for the visual state, but this time for the visual folder.
cp efektor_otwarty.stl ~/catkin_ws/src/universal_robot/ur_description/meshes/ur3/visual
Now that we added our 3D models to the workspace, we need to call them and attach to the appropriate place. For this scope we need a xacro file which will manage the gripper separately. Then in the next steps we will combine the gripper xacro file to the robot xacro file.
Let's first move to the folder where the urdf files are stored.
cd ~/catkin_ws/src/universal_robot/ur_description/urdf
gedit gripper.xacro
Here we need to create a file xacro which will be generate our model by the input parameters. Paste the following code inside :
<?xml version="1.0" encoding="utf-8"?>
<robot xmlns:xacro="http://ros.org/wiki/xacro">
<!-- Here we define the 2 parameters of the macro -->
<xacro:macro name="measurement_tool" params="prefix connected_to">
<!-- Create a fixed joint with a parameterized name. -->
<joint name="${prefix}measurement_tool_joint" type="fixed">
<!-- The parent link must be read from the robot model it is attached to. -->
<parent link="${connected_to}"/>
<child link="${prefix}measurement_tool"/>
<!-- The effector has to be attached with the following parameteres,otherwise it won't be at the effector position. -->
<origin rpy="1.5708 0 0" xyz="-0.061 0.076 -0.001"/>
</joint>
<link name="${prefix}effector_name_link">
<visual>
<geometry>
<!-- The path to the visual meshes in the package. -->
<mesh filename="package://ur_description/meshes/ur3/visual/efektor_otwarty.stl" scale = "0.0008 0.0008 0.0008" />
</geometry>
</visual>
<collision>
<geometry>
<!-- The path to the collision meshes in the package. -->
<mesh filename="package://ur_description/meshes/ur3/collision/efektor_otwarty.stl" scale = "0.0008 0.0008 0.0008" />
</geometry>
</collision>
</link>
<!-- TCP frame -->
<joint name="${prefix}tcp_joint" type="fixed">
<origin xyz="0 0 0.116" rpy="0 0 0"/>
<parent link="${prefix}effector_name"/>
<child link="${prefix}tcp"/>
</joint>
<link name="${prefix}tcp"/>
</xacro:macro>
</robot>
Save the file and close it.
At this time we can move on and combine the gripper xacro file with the robot xacro file.
Now we need to add the file we have just created to our main xacro file. Basically the ur3_robot.xacro file gets the information from various .xacro and then load them in order to run them together.
gedit ur3_robot.urdf.xacro
You should see something similar to this :
<?xml version="1.0"?>
<robot xmlns:xacro="http://wiki.ros.org/xacro"
name="ur3" >
<xacro:arg name="transmission_hw_interface" default="hardware_interface/PositionJointInterface"/>
<!-- common stuff -->
<xacro:include filename="$(find ur_description)/urdf/common.gazebo.xacro" />
<!-- ur3 -->
<xacro:include filename="$(find ur_description)/urdf/ur3.urdf.xacro" />
<!-- arm -->
<xacro:ur3_robot prefix="" joint_limited="false"
transmission_hw_interface="$(arg transmission_hw_interface)"
/>
<link name="world" />
<joint name="world_joint" type="fixed">
<parent link="world" />
<child link = "base_link" />
<origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0" />
</joint>
</robot>
After
<!-- ur3 -->
<xacro:include filename="$(find ur_description)/urdf/ur3.urdf.xacro" />
add the following text :
<!-- end-effector -->
<xacro:include filename="gripper.xacro" />
<xacro:effector_name prefix="" connected_to="tool0"/>
And save it. Now we need to generate our urdf (it means that the structure will be compiled) , so we will need to call the following command :
rosrun xacro xacro -o gripper.urdf gripper.xacro
In the end we need to catkin_make and source the path of our catkin_ws package
cd ~/catkin_ws
catkin_make # or catkin build
source devel/setup.bash
The only thing that remain to be done is Launch it!
For this step I developed a little script that you can find here , it allows to run in a row all the applications that you need to perform tasks : Gazebo , MoveIt, RviZ.
Maroine Trabelsi , Wrocław University of Science and Technology
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