Robot doesn't move due to actual.positions being the same as desired.positions in the controller feedback.

[STUPIDTREE]

Affected ROS2 Driver version(s)

2.9.0

Used ROS distribution.

Humble

Which combination of platform is the ROS driver running on.

Linux in a virtual machine

How is the UR ROS2 Driver installed.

Build the driver from source and using the UR Client Library from binary

Which robot platform is the driver connected to.

UR CB3 robot

Robot SW / URSim version(s)

3.14

How is the ROS driver used.

Through the robot teach pendant using External Control URCap

Issue details

Summary

We encountered an issue where the robot does not move after sending trajectory commands using scaled_joint_trajectory_controller. The core problem lies in the feedback from the action server /scaled_joint_trajectory_controller/follow_joint_trajectory. Specifically, the actual.positions in the feedback is always the same as the desired.positions, even though the robot's current position is different.

This behavior causes the robot to remain stationary, as the controller incorrectly assumes that the robot has already reached its target position.

Issue details

1. ros2 launch ur_robot_driver ur_control.launch.py ur_type:=ur10 robot_ip:=192.168.1.1

2. ros2 action send_goal /scaled_joint_trajectory_controller/follow_joint_trajectory control_msgs/action/FollowJointTrajectory "{
   trajectory: {
   joint_names: [shoulder_pan_joint, shoulder_lift_joint, elbow_joint, wrist_1_joint, wrist_2_joint, wrist_3_joint],
   points: [
   { positions: [1.57, -1.57, 1.57, -1.57, -1.57, 0], time_from_start: { sec: 10 } }
   ]
   }
   }" --feedback

3. output log as follow, we can see desired: positions: are the same as actual:positions: ,
   desired:
   positions:

• 1.4702648083500873
• -1.5016473084382875
• 1.4578857600697241
• -1.509482695372137
• -1.5652979063487598
• -0.10027437199636823
  velocities:
• 0.009973520755767828
• -0.006835270246396852
• 0.011211425781250006
• -0.006051731428037476
• -0.0004702094401224377
• 0.01002743879901331
  accelerations:
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
  effort: []
  time_from_start:
  sec: 0
  nanosec: 0
  actual:
  positions:
• 1.470228910446167
• -1.5016472975360315
• 1.457897663116455
• -1.5094226042376917
• -1.5652979055987757
• -0.10032254854311162
  velocities:
• 0.0
• 0.0
• -0.0
• 0.0
• 0.0
• 0.0
  accelerations: []
  effort: []
  time_from_start:
  sec: 0
  nanosec: 0
  error:
  positions:
• 3.589790392033443e-05
• -1.0902255986877663e-08
• -1.1903046730932232e-05
• -6.009113444527259e-05
• -7.499840748437236e-10
• 4.817654674339755e-05
  velocities:
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
  accelerations: []
  effort: []
  time_from_start:
  sec: 0
  nanosec: 0
  multi_dof_joint_names: []
  multi_dof_desired:
  transforms: []
  velocities: []
  accelerations: []
  time_from_start:
  sec: 0
  nanosec: 0
  multi_dof_actual:
  transforms: []
  velocities: []
  accelerations: []
  time_from_start:
  sec: 0
  nanosec: 0
  multi_dof_error:
  transforms: []
  velocities: []
  accelerations: []
  time_from_start:
  sec: 0
  nanosec: 0

4. ros2 topic echo /joint_states, we see actual positions are different with desired.
   header:
   stamp:
   sec: 1758786504
   nanosec: 827778549
   frame_id: base_link
   name:

• shoulder_lift_joint
• elbow_joint
• wrist_1_joint
• wrist_2_joint
• wrist_3_joint
• shoulder_pan_joint
  position:
• -1.5016472975360315
• 1.4578742980957031
• -1.5094588438617151
• -1.5653217474566858
• -0.1003344694720667
• 1.4702528715133667
  velocity:
• 0.0
• -0.0
• 0.0
• 0.0
• 0.0
• 0.0
  effort:
• -3.630066394805908
• -3.5824131965637207
• -0.2355194389820099
• -0.004486084450036287
• -0.0605621412396431
• 0.0732421949505806

Expected Behavior:
actual.positions in the feedback from scaled_joint_trajectory_controller should reflect the robot's actual physical joint positions, matching the data published by /joint_states.
The robot should move to the target position specified in the sent trajectory command.
Actual Behavior:
actual.positions in the feedback is always equal to desired.positions, making the controller think the robot is already at the target position.
As a result, the robot does not move.

Additional Debugging Steps Taken:
Verified that /joint_states publishes correct values, reflecting the physical positions of the robot.
Verified that the hardware interfaces are correctly claimed:
Example ros2 control list_hardware_interfaces output:

command interfaces
shoulder_pan_joint/position [available] [claimed]
...
state interfaces
shoulder_pan_joint/position [available]
...
Verified that scaled_joint_trajectory_controller is active:

scaled_joint_trajectory_controller [active]
joint_state_broadcaster [active]

URCap Version: (externalcontrol-1.0.5.urcap)
robot: UR10

Relevant log output

robot is running state, not hardware question.

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[urfeex]

You didn't include the joint names in your feedback output. The order of the joint array doesn't necessarily have to be the same.

Your joint state says:

-1.5016472975360315   shoulder_lift_joint
1.4578742980957031    elbow_joint
-1.5094588438617151   wrist_1_joint
-1.5653217474566858   wrist_2_joint
-0.1003344694720667   wrist_3_joint
1.4702528715133667    shoulder_pan_joint

If I print your actual values from the feedback with the joint names that I get from a feedback that would be

1.470228910446167     - shoulder_pan_joint                                                                                                                                                                                                                                                                                                        
-1.5016472975360315   - shoulder_lift_joint                                                                                                                                                                                                                                                                                                       
1.457897663116455     - elbow_joint                                                                                                                                                                                                                                                                                                               
-1.5094226042376917   - wrist_1_joint                                                                                                                                                                                                                                                                                                             
-1.5652979055987757   - wrist_2_joint                                                                                                                                                                                                                                                                                                             
-0.10032254854311162  - wrist_3_joint

Those look (almost) the same to me.

Also, the example command you provided works for me (to be honest, tested on Software 5.23 with ROS Rolling at the moment).