J5 Losing Position

The joint is losing the position after articulation. I am zeroing the robot using the AR4.exe softwares auto-calibrate feature and then exiting and opening a python script that sends serial commands to the AR4. Every joint other than J5 is very repeatable. I have turned off the robot and moved the joint by hand to see if there is any resistance or binding and it moves smoothly across the entire range. I opened the arm to see if the belt, threaded rod or lead screw were binding or had other issues and I couldn't find anything wrong. Any help would be appriciated.

I am sending this serial command to go to the down position:

'RJA0B74C0D0E-74F0J70J80J90Sp75Ac60Dc60Rm100WNLm000000\n'

and sending this command to go back to the home position:

'RJA0B0C0D0E0F0J70J80J90Sp75Ac60Dc60Rm100WNLm000000\n'

Here is a video of the issue. Notice the gripper angle changes with each down/up cycle. https://www.youtube.com/watch?v=YwkHOJSSvv8 Starting Position when home command is sent ('RJA0B0C0D0E0F0J70J80J90Sp75Ac60Dc60Rm100WNLm000000\n')

After the 2 cycles when the same home command is sent ('RJA0B0C0D0E0F0J70J80J90Sp75Ac60Dc60Rm100WNLm000000\n')

Comments (2)

Kyle Montgomery

Jun 22, 2023

Thanks Chris. I tried that but I still see the same offsets occurring. It's looking like that if I send serial commands in quick succession, without waiting for the robot to reach the previous position then it looses its position. I am still investigating and will report back.

Chris Annin

Jun 13, 2023

Does the issue of losing position go away if you put J5 into open loop mode?

ANNIN ROBOTICS