Question re filament detection
I havent received the MK4S I ordered yet, but wondered the operating mode of the sensor. Is it an optical switch, or is it a limit switch of some form. I know that each have their individual pros and cons in use.
As a control engineer, I worked in paper mills;My company was using computer-based control systems in the 1970s, before their use was common. One of the sensors they used to measure the mass of the paper being produced continuously - for most paper, they used a radioactive source (krypton 86) usually above the paper web. And a radiation detector under thw sheet. The heavier the paper, the less radiation would be detected.
Smoke detectors also use radiation to detect smoke in the air. I believe an isotope of americisium is used. A tiny amount of a radioactive isotope, shielded of course, could be used as a missing filament sensor. Ideally, it would be an alpha emitter like tritium, where a sheet of paper could shield you. The sensor could potential
Be used witl all types and sizes of filament, even glass, metal, wood or carbon fiber inpregnated material.
Has anyone heard of radiation being used in this role? An air-gap calibration would need to be periodically done, to re-zero the sensor, as radioactive emissions reduce over time, as it decays naturally..
RE: Question re filament detection
The Mk4S pritner, uses a ball bearing to register filament presence, this interacts with a Magnet and a Hall effect sensor to indicate the presence to the controller board,
the Hall effect / magnet pair, is calibrated as part of the initial configuration.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK
RE: Question re filament detection
For answers to these types of questions I would recommend reviewing the assembly instructions for the MK4S Kit (under the help tab on Prusa3d.com). This will allow you to see in great detail how the mechanical systems of the printer are assembled.
Regards,
Steve
RE: RE: Question re filament detection
My Belated Thanks for the feedback, Steve. I did check the assembly information, as you suggested. I ordered a M4S printer about a month after the original post. The only reason I was questioning the method used was my familiarity with uncommon sensing methods used in continuous manufacturing processes in the pulp/paper, metals, glass and plastic manufacturing arena . The tiny amount of radioactive materials in most smoke detectors allows for sensing the tiny extra mass of smoke particles suspended in the air between the radiation source and detector, while ignoring the slow changes in the air mass due to atmospheric weather events is rather remarkable. There may be a market niche, in the filament manufacture and usage markets, for smoke detector manufacturers, to exploit...actually, two potential markets. One - a low cost, simple filament presence digital sensor, which shouldnt cost any more than a simple smoke detector, and Two - a more expensive analog mass sensor, which would potentially tie in the filament diameter sensor be able to produce a real-time volumetric mass reading, that, among other things, could include the realtime volumetric mass of both the resin and additive fiber or metal fill. For the latter measurement, the sensor whould have to have detailed information of the products mass volume being used in the filament mix, and possibly the filament temperature at point of measurement.
RE: Question re filament detection
if I remember correctly it was something lile this across different mdoels:
It used to be a basic photo sensor diode detection with direct exposure to the filament ( light obstruction by the filament caused sensor to trigger the stage change)t, but it was problematic with transparent filaments. Then they moved to the photosensor where light is obstructed by the metal ball when the filament is inserted.
Current sensors use a metal ball and hall sensor to detect the filament presence by the change of the magnetic field due to ball reposition.
See my GitHub and printables.com for some 3d stuff that you may like.
RE: Question re filament detection
As I recall, the sensor used on the MK3OG (my first printer) was actually a LED/laser mouse sensor (I forget which). It could not only sense the presence of the filament, but could also see if it was moving and how fast. Unfortunately, it had problems with transparent filaments which forced Prusa to change tactics to a gated there/not-there sensor. As you describe, first with the moving flag between an LED/photoDiode pair and then to the current moving magnet to change the magnetic flux sensed by a hall effect sensor in the Nextruder. In both, the ball was just used as the finger to mechanically interact with the filament, basically an axially unconstrained idler.
See my (limited) designs on:
Printables - https://www.printables.com/@Sembazuru
Thingiverse - https://www.thingiverse.com/Sembazuru/designs