::heading=Context
After deploying a palletizer the person in charge will most of the time make a visual check to evaluate the system stability. While visual check is efficient to correct the biggest issues it is not enough to fix all problems. It is for example possible to run a program with wrong payload settings without being able to notice anything wrong.
Non-visible issues can surface after installation and have important consequences like recurrent protective stops and even permanent robot hardware failure.
Application stability can be checked by looking at the joint deviation which tells how far the system is from a protective stop. The article proposes some tools to monitor joint deviation and identify issues.
::note=The importance of checking joint deviation is explained in UR guidelines:
https://www.universal-robots.com/download/manuals-e-seriesur20ur30/installation-guides/good-installation-practices/robot-good-practices-installation-guide-english/
::heading=Write join deviation in UR logs
The most basic way to see if an application is stable is to have the system write in UR logs if the joint deviation goes above a threshold value. If everything is going well you should have a joint deviation under 20%.
To have logs when joint deviation goes above a threshold value, add the following script function in the before start of the program,:
position_deviation_warning(0.2)
UR recommends starting with a threshold of 40% to first identify the biggest issues and then decrease to 20%.
::note=In some cases the joint deviation can be intentionally high. This is for example the case of shaky motions. While those motions should be avoided they are sometimes necessary and tolerated.
::heading=Record real-time data with UR log viewer
Knowing that the joint deviation goes above a threshold value tells you that something is going wrong but it does not tell you why. Additional information like time, robot position, payload, settings, forces, OI status,... is necessary to make a diagnostic. All those data can be collected from robot RTDE registers which can be recorded in real-time using the UR log viewer.
Check the data you want to collect (The more the better :) ), select the sampling frequency (100Hz should be enough) and the auto recording time (Check the time to make a pallet on the configurator), and click on start to collect the data.
Once you have all this data you can look at it and try to understand of the situation.
::important= Additional visual observation can help to make the diagnostic it is recommended to use a camera to get a video of the system (gopro, webcam connected to a PC, smartphone,...)
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