A great start: load cells and bed leveling on 3D printers

Published On: November 24 2021

Anyone with a 3D printer knows the problems of getting that all important first layer of print accurate. Often bed leveling (the process of printing onto a completely flat surface) is a matter of making adjustments manually, resulting in multiple print failures. Incorporating laid cells into the printer nozzle can help reduce if not eliminate the manual process, and creating more accurate printed results in the process.

What is bed leveling?

3D printers need to print into a build platform. The challenge is to ensure that the first layer laid down is as accurate as possible. This requires the print nozzle to maintain a constant distance from the build platform during the whole printing process.

As website Hackaday explains:

“If the nozzle is too close to the bed in some places, but too far away in others, that leads to poor quality and failures. Adjusting the printer’s bed until it is parallel to the nozzle’s range of motion is called leveling. (Machinists would correctly call the process tramming, because nothing actually has to be perpendicular to the earth’s gravitational field.)”

First layer calibration involves adjusting the Z-axis offset such that the distance between the tip of the nozzle and the platform surface allows an even layer of plastic (or other printing materials) to be evenly laid down.

The issue is that it’s almost impossible to create a perfectly flat build platform, and in prints that involves measurements in fractions of millimetres, this can be a major problem.

Load cells to the rescue

One solution is to use the tip of the printing nozzle as a sensor. This is achieved by adding a load cell into the extruder above. As the website All3DP explains:

“Prusa has included a load cell sensor embedded within the heat sink that enables nozzle probing of the print surface.”

The slightest change in the nozzle position can be measured, calibrated and used to adjust the mechanism. With the nozzle acting as a hot sensor, multiple measurements can be taken in a grid pattern, and also the Z-axis offset implemented in real time as the printer is printing.

As the Hackaday site reminds users, this works when the nozzle and print surface are clean, and additionally, at a constant temperature. The blog at Prusa printers, explains how the latest generation of their CoreXY 3D printers feature a segmented heatbed. Rather than heat the whole bed, you can turn off individual segments, making it more energy efficient.

The XL Prusa extruder unit also includes a:

“A highly precise load cell sensor to deliver an always-perfect first layer … It is embedded within the solid single-piece heatsink and it allows us to measure the physical load on the heatsink. As a result, we can use the nozzle as a sensor to “probe” the print surface.”

loadcell graph 640x360

The Original Prusa XL nozzle and output from the load cell sensor (Source: Original Prusa)

This system also allows the printer to detect nozzle jams and pause the printing process. As All3DP says:

“The Prusa XL will now detect nozzle jams and pause your prints, giving you time to swap out print heads or clean the jam before continuing your print. The number of failed prints that this tech is likely to prevent is unfathomable, and that’s good news for both wallets and the environment.”

The print heads can be easily swapped out too, with the tool changer unit using another load cell to automatically calibrated new print heads when swapped in.

Custom load cells for innovative solutions

If you’re working on an innovative solution that will help your customers save money (and help the environment too), and you need a load cell, call us. We design, manufacture and distribute our own brand load cells here in the UK. So if you can’t find what you need in our online load cell store, call us. We’ll work with you to design and build custom load cells to your specific requirements. No order is too small – we do this all the time with university students, start-ups and OEMs looking for cost-effective components.