Topic with the ur_driver/joint_speed in ur_modern_driver

[MinhDangTG]

Summary

Are there any same topics with the ur_driver/joint_speed in the ur_modern_driver package

Versions

• ROS Driver version: 16.04
• Affected Robot Software Version(s): 4.1
• Affected Robot Hardware Version(s): UR3 CB3
• Robot Serial Number:
• UR+ product(s) installed: No
• URCaps Software version(s):

Hello everyone,

I was using the ur_modern_driver package and then I figured out this package had a better checking system with all the stops (safeguard stop, protective stop...) with the new version of the UR Software also when the ur_modern_driver began to be a bit old.

With the ur_modern_driver package, I can publish the joint velocities with accelerations to the ur_driver/joint_speed at the rate of 125Hz. I did the installation of the Universal_Robots_ROS_Driver package so do anyone know which ros_topic has the same usage/benefits as the ur_driver/joint_speed in the ur_modern_driver package?

Thank you

[fmauch]

You can use the joint_group_vel_controller instead of the default scaled_pos_traj_controller. See the controller_manager documentation on how to switch between different controllers.

[tkelestemur]

I was able to send velocity command by switching the controllers:

rosservice call /controller_manager/switch_controller "start_controllers: ['joint_group_vel_controller']
stop_controllers: ['scaled_pos_traj_controller']
strictness: 2
start_asap: false
timeout: 0.0"

But if I don't stop the scaled_pos_traj_controller I cannot start the joint_group_vel_controller. Is there way to use both of the at the same time?

[gavanderhoorn]

But if I don't stop the scaled_pos_traj_controller I cannot start the joint_group_vel_controller. Is there way to use both of the at the same time?

No, that's not how ros_control works.

Can you clarify why you'd want to have both controllers active at the same time?

You can actually ask ros_control to switch the controllers.

[tkelestemur]

In my task, the UR goes to a neutral joint configuration using MoveIt and then it starts executing a linear motion in task space using the cartesian velocity controller that I wrote using the joint_group_vel_controller/command. I guess I can switch between controllers during the execution.

[gavanderhoorn]

Yes, that would be the envisioned flow of events.

The idea is also that this prevents two controllers from trying to control the same resources at the same time. What should happen fi when both the JTC and the velocity controllers get commands at the same time?

See Switching between controllers with ros_control / controller_manager for a related Q&A on ROS Answers. And wiki/controller_manager for more info on the controller_manager.

[MinhDangTG]

Hello fmauch,

what is the script command that the joint_group_vel_controller is using? I used speedj with the ur_modern_driver.

I should explain more. I am using a force-torque sensor at the tcp of the ur3 and an admittance control. I was working alright with ur_modern_driver since I could control the acceleration while using velocity control. When I switched to ur_robot_driver, the movement is jerky and shaking a lot since I can not define the acceleration at all (liked the speedj command). Should I continue using the /joint_group_vel_controller or switch to other controllers?

[fmauch]

The speedj acceleration used with the velocity controllers is currently hard-coded here. While I did have good results with this, that might not be the best choice for every application. Could you try whether changing this can solve your use-case? We could then make this a parameter.

You can modify this by changing this line locally on your PC. The robot controller will request this script each time the "External Control" program node gets started.

[MinhDangTG]

Do you know how I can make the acceleration rate as a parameter/subscriber? I tried to open a socket similar to qd by using URServer class but I have no luck to bind the port together.

I can add another value to write function in URServer class but it will change the driver by a lot (future update will overdrive it as well).

[fmauch]

Sorry, I don't think, I quite understand what you are trying to achieve.Is this related to this issue? Otherwise, please open a new one.

[sunnymints]

The speedj acceleration used with the velocity controllers is currently hard-coded here. While I did have good results with this, that might not be the best choice for every application. Could you try whether changing this can solve your use-case? We could then make this a parameter.

You can modify this by changing this line locally on your PC. The robot controller will request this script each time the "External Control" program node gets started.

Hi fmauch, thank your professional work. I have a question want to ask you. I hope ues joint_group_vel_controller instead of /joint_speed in ur_modern_driver to do visual servoing, but joint_group_vel_controller can not get the smooth vel. I think the reason is that the acceleration is fixed when joint_group_vel_controller calls ros_control.urscript,before. But when I changed the accelertion value from 40 to 1, the effect is still not change(the speed change is not smooth). I want to use joint_group_vel_controller to get the effect of /joint_speed in ur_modern_driver what should I do？