![]() This works perfectly (precision is around a few micrometers). Hence I have introduced a linear regression fit to determine the position at which the force is just zero.It can be compensated for, but this needs to be done manually. This force corresponds to a certain displacement of the nozzle (load cells need to deform to measure anything), which leads to an error. The threshold will correspond to some real force which needs to be applied to the nozzle before recognising it as a contact situation. Even if the the tare compensation is done, a simple threshold has the downside of adding an offset to the result.Frequently here means that this is necessary multiple times even within a single probe measurement. This needs to be compensated by performing a tare measurement quite frequently (measure ADC value without bed contact and subtract this value from subsequent measurements). Depending on the exact mechanical setup, there may be mechanical tension (especially if a heated bed is already switched on) which can lead to slow drifts of the measured ADC value even when actually no external force is applied on the hotend. A simple threshold on the ADC value (i.e.This feature is important for me, since I am using my printer also for CNC milling (the printer is solid enough for light milling operation).įrom that experience I can tell a few things: ![]() It can even be used to probe in X/Y direction, which in principle is mechanically not foreseen. I have developed my implementation based on the experience I have gathered on that printer model. It is using an ADS1100 ADC which can only do 8 Hz at the full resolution (16 bit). It has been released I think in 2015 already (I brought mine in 2016 and started to improve its firmware soon). My printer is a Renkforce RF1000 which is already originally equipped with load cells for probing. The technology is much older than the Prusa XL. I would like to make a few general additions at first: There probably is an ideal chip for this application but finding it on a ready made board is going to be tough. The ADS1256 board is more expensive for no obvious advantage to us.It has 5 differential inputs, I have a tool changer with 4 tools so that’s “enough” inputs.Its available on a relatively cheap board that can be connected to a Pi or an MCU via SPI.I’m going to develop for the ADS1263 because: That is a very narrow margin for success. The sensors with an 80 SPS speed would only allow for 2 samples before they moved farther than the multi-mcu homing distance. Note 3: The resolution for the ADC chips is theoretical and doesn’t include oversampling, which we may well need to do.įrom this chart, only the ADS1256 and ADS1263 have a data rate that approaches the digital endstop pin. ![]()
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