What are best practices for achieving good precision with xArm?

xArm/850 Troubleshooting
1

We’ve just purchased our second xArm and are working on the next version of our software. It seems like there have been many SDK improvements since we checked last! We would like to verify that our assumptions concerning precision vs repeatability still are true with the latest xArm software.

We have been assuming that repeatability is the main factor to rely on. Your doc states +/- 0.1 mm for repeatability and as far as we can tell, our xArm6 robot has been achieving this reliably! For more than a year of weekly use! Very impressed!

First, a little background to make sure we’re not confused about anything

Our understanding is that with xArm (and most robots in general), repeatability is high but precision can be much lower. For example:

  1. repeatability is high because repeated move commands take the arm to the same location very closely (to within 0.1 mm, for example).

  2. precision, however, is usually lower because if one specifies an XYZRPY movement target, the actual location arrived at is only accurate in (say) the 1 mm range. Usually this is due to a variety of small manufacturing variations adding up such that the model the controller is using does not exactly match the actual physical dimensions of the robot.

Now, the ACTUAL questions :slight_smile:

What is your recommended procedure to achieve the best precision with xArm?

Provided we are not misunderstanding something:

  1. Is there a procedure to calibrate the xArm internal model to account for small manufacturing variations? This would be a calibration of the forward and backward kinematics. I.e. some method of determining and calibrating the internal model used by the controller in the BASE coordinate system to account for small manufacturing differences in arm link lengths, joint angles, etc.

  2. In a previous email, I asked about TCP calibration procedures, I won’t say more about that here.

In other words, if we wanted to make sure we are using xArm to its maximum precision, what would you recommend we do?

Our ultimate goal would be to plan a TCP path with our own CAD type software and have the xArm perform it with good precision.

Thanks for your attention and a great product!

Andre

2
  1. Each machine will be calibrated for accuracy before leaving the factory, but the accuracy range cannot be guaranteed to be within 1 mm.
  2. Regarding the maximum precision of xArm, we have no recommendations.
3

Do you have any information about my question below? Is it possible to calibrate the internal model of XArm controller itself? (I’m assuming that a significant component of errors is related to small errors in the internal model - is that correct?)

Thanks,

André

4

Hello,
It is impossible to calibrate the internal model of xArm controller itself.

5

Thanks for the info! It is not that important to us right now and we can always work around it with an external IK tool if we need it. Love the product!

-Andre

6

You are welcome.