may I ask how to use the ur_test_interfaces

Hey,

I'm a graduate student in mechanical engineering. I'm working with UR robot for about 3 month. I tried to learn ur_control but most of the code is too complicated and I couldn't test them. I know it's my bad, yet I really want to learn this. I wonder if you could share how to use your ur_test_controller and ur_test_launch.

I changed the ip address of the launch file and I used
roslaunch ur_test_launch ur_test_sinusoid_controller.launch

I noticed there is no add_executable in the cmake file under ur_test_controllers but I didn't get any luck trying to add this executable.

I would really really appreciate your help.

Thank you in advance.

[miguelprada]

I created this just to run some tests related to this issue in ur_modern_driver package.

Unless you are already familiar with ROS and ros_control it is very unlikely you'll be able to make much sense of what I have in this repository. Basically, what you can find in this repo are some controller plugins for ros_control and some ROS launchfiles, which is the mechanism used by ROS to start-up compositions of runtime components.

If you could tell me what you're trying to do maybe I can provide some more specific pointers to try to guide you into places to look for more information.

@miguelprada Thank you for your reply. I did read your post and your post gives a lot of useful info.

I want to control the joint speed. Specifically, we are trying to implement admittance control. I tried to publish to the /joint_speed topic but it doesn't give a good response. I need to include "position" in joint trajectory. What I did is to get the current joint position and add the integral of the velocity over the circle time. Also, I did similar things to the acceleration. But it actually gives some real bad result, it may not even move. In ur_modern_driver, the author says we can

Parses the first JointTracetoryPoint and sends the specified joint speeds and accelerations to the robot

I'm not sure what this means...

Then I checked some of documents on ROS_control but I couldn't understand how to use it. I know perhaps I can use the commend topic and create a publisher. But I'm not sure if this is correct.
I wonder if you may point me to the right direction, if possible, an example? Perhaps try to control the joint velocity to follow a sinusoidal signal. I think then I'm good to go.

Thank you again for your time. I'm the only one in my group, possibly my department, working on this project, and I got no one to ask to be honest with you....

[miguelprada]

Parses the first JointTracetoryPoint and sends the specified joint speeds and accelerations to the robot

I'm not sure what this means...

Quite literally, it means that you need to send messages of JointTrajectory type to this topic. This message type contains an array points of type JointTrajectoryPoint. The driver will only read the velocities field in the first entry in the points array (see here).

I wonder if you may point me to the right direction, if possible, an example? Perhaps try to control the joint velocity to follow a sinusoidal signal. I think then I'm good to go.

You can have a look at test_move.py. This example uses the ROS actionlib interface to send complete trajectories, which may not be the best option if you are trying to implement admittance control, but may help you get started.

For implementing the admittance control you can use the /joint_speed topic as discussed above or implement your own ros_control-based controller which is then run by the driver itself. The first option is much easier (see here for an intro to publishers) although performance will likely be much better doing it the second way, at the cost of a much steeper learning curve. If you want to try to go for it, have a look at ros_controllers, which contains implementations for several generic controller plugins.

Not sure whether this is too obvious to suggest, but if you're not very familiar with ROS, maybe the first step would be to go through the tutorials.

@miguelprada
Thank you so much for you reply.

I guess I would go for the ros_control. I read some of the posts in ur_modern_control and it says ur ros control interface is based on ur script, and these is a limit of what we can do. For example, I can use velocity based position control but I may not have control over the joint torque. I actually checked ros_controller several times. The problem is I'm not sure if I can use them on UR robot.

In your ur_test_interface, I noticed your implemented control plugin in ur_test_vel_sinusoid_controller.launch, but there is no add_executable in the CMakeLists.txt under ur_test_controller. I guess I should do something like this to run the program. But I don't know how to run ur_test_sinusoid_controller.cpp siunce it is not added to the CmakeLists.txt
roslaunch ur_test_launch ur_test_vel_sinusoid_controller.launch
rosrun ur_test_contollers ***ur_test_sinusoid_controller.cpp***
(I haved changed the IP address in the launch file)

I tried to edit the CmakeLists.txt to add the executable, dependence and link_library but it doesn't work for me. I wonder if you may give me some suggestions on how to run this code. This is the only ros_control example I can find online. I would really really appreciate if I can run this sinusoidal test.

Anyway, I still want to thank you for your help and time. I read several of your posts and they really helped me a lot to understand the ur_modern_driver.

[miguelprada]

The ros_control controllers are not meant to be run as executables, but rather as plugins to be loaded by some driver node (e.g. ur_modern_driver in the case of the UR) through the ControllerManager interface. A package implementing a new controller needs the build a shared library from the source code of the plugin. It also needs a special xml file which is exported from the package.xml and describes the plugin to the pluginlib system.

Then, the way to load a controller inside the ur_moder_driver node is to load the configuration of the controller to the parameter server and then call a service to load the controller by name (this is usually achieved via the utility executable scripts spawner or controller_manager (not to be confused with the class of the same name)).

Try to understand how urX_ros_control.launch files start the robot with a certain set of controller plugin configurations, if you want to see more examples.

[MichellPinheiro]

HEY
I'm working in the project and in this projecto i use a UR3 Robot but I don't find documention about URX library.
I teste with an exemple but I have many difficuty for move the UR3 where a can find more documentacion about URX library?
thanks for your attencion

[nag92]

Can these controller be used with Gazebo?