IR Sensor QC: Repeatability test

This article will explain how to perform a repeatability test on your printer's autolevel sensor.  This test works for the R1, R2 and C2 printers; though you will need a different serial monitor to test the R1.  

To get started, log into your printer's Octoprint web interface.  If you haven't visited the Octoprint interface before, you can learn how to connect to it with this article: How to connect to Robo web dashboard.

Once logged in, scroll down the page until you reach the "Printer Terminal" tab on the right side of the screen.  On a freshly loaded browser it will be minimized, so you will need to click on the tab to expand the window.  To make finding the results in the terminal stream easier, find the "Suppress" options located in either the drop down menu button in the top right, or just under the Autoscroll button on the bottom left of the Printer Terminal window (depending on what version of RoboOS you are running).  

Note: Make sure your bed is clear for this test.

Starting the test

To start the test, type in the following commands (one at a time) in the text field next to the Send button and press "Send".

This test comprises of probing the bed 8 times, followed by an analysis of the distance from the bed to the probe that the printer has read during each point.  From these distances, the firmware will calculate both a Standard Deviation and a Range value.  These two values tell us if the Autoleveling is working within an acceptable level of accuracy.

1) First, check you RoboOS Version. You can find the OS version by going to Utilities>Update from your LCD.

1A) For R2 and C2 running RoboOS 2.0-r1.6 or higher:

1. G28 then press 'Send'
2. G35 then press 'Send'
3. M48 then press 'Send'

1B) For R2s and C2s running OS 1.9 or lower, or for all R1's:

1. G28 then press 'Send'
2. G1 X0 Y0 F7000 then press 'Send'
3. M48 then press 'Send'

Reading the results

Once the probing has stopped, the printer will print a response on the serial line that will look like this: 

Recv: Finished!
Recv: Mean: 0.004750 Min: -0.033 Max: 0.023 Range: 0.055
Recv: Standard Deviation: 0.015750

The upper limit for a sensor's Standard Deviation is 0.3.  Anything higher than this will lead to poor mapping of your print surface.  The results above are considered to be within acceptable limits.

A Range of 0.055 means that the accuracy of your probing will vary by 0.055mm across 8 probing points.  Considering your Robo's default first layer thickness is 0.3mm, this variance will not impact your first layer quality.  If you are trying to print a 0.1mm first layer (directly on the bed with no adhesion options such as a raft), you will likely have problems with your print sticking.  By default, all Robo slicers set the first layer to 0.3mm thick, regardless of the print quality chosen.  The rest of the print (after layer 1) will follow the quality thickness.

If your Standard Deviation results are above 0.3, give our Customer Service team a call to further troubleshoot.