Issues with force torque sensor in impedance control mode

xArm/850 Troubleshooting
1

Hey,

I’m using an Xarm7 (XS130510D43A14) with a Ufactory force-torque sensor (Al13021224008) and I’m facing a few issues while using the arm in impedance control mode:

  1. I notice that sometimes (not necessarily, but mostly after a collision / force-torque sensor overload) the robot does not move to the desired pose set using:
    set_position_aa(axis_angle_pose, speed=50, mvacc=500, is_radian=True, relative=False, wait=True
    but rather starts to move slightly down/in some other direction as well. I’m attaching two videos (with impedance K = 300 and K = 1000) both of which are supposed to go to the handle of the dishwasher (which it goes to in normal operation)

https://imgur.com/a/4wQT8Pa

Please note that the payload setting is correct and was set based on a calibrated value from the force sensor

  1. The arm sometimes goes into an uncontrollable shaking motion and stops due to velocity limits exceeded error:

https://imgur.com/a/kJbTxA5

Please note that the uncontrollable shake sometimes occurs while trying to grasp the handle as well.

  1. The speed in impedance control mode is often slower than the speed in normal mode.

Thank you

2

Force/Torque Sensor Diagnostic Instructions

1. Check if the sensor is functioning properly

  1. Remove the tool/gripper from the sensor.
  2. Move the robot to the home (zero) position.
  3. Open UFACTORY Studio:
    Settings > General > Debugging Tools
  4. Set the following:
    • Mode: Raw Data of 6-Axis Torque Sensor
    • Direction: All
    • Frequency: 200Hz
    • Check Observation
  5. Click Start and observe data for about 10 seconds.

Expected ranges (no load):

  • Force: Fx, Fy, Fz should be within ±60 N
  • Torque: Tx, Ty, Tz should be within ±2 N·m

image

2. Share your equivalent mass parameter

Please provide the equivalent mass (M) value in your script.

3

Hello,

Thank you for your quick reply.

  1. I’ve removed the gripper and and reset the arm to home position, the Fz seems to be quite off (97N) but the other values are fine and there doesn’t seem to be much variation in the observation:

image

  1. The equivalent mass (M) is set to 0.06 in my script and J is set to 0.01 * M

(note that currently, I’m only running impedance on the x,y,z axis and not Rx, Ry, Rz)

4

Thanks for the clarification.

Although the force-torque sensor readings are already out of the factory threshold, it can still be used. You can send it back for inspection and repair when convenient.

In the meantime, try increasing the equivalent mass parameter—e.g., set it to 0.08 kg or higher—and see if it improves the impedance behavior.

Let us know how it goes.

5

Thank you, I’ll try to increase the equivalent mass parameter and update you once done. I’ll send it back for inspection and repair in case that doesn’t work.

6

Sure, in case that you need repairment service, just copy the link of this post, send the link along with your shipping information to the support@ufactory.cc