Sensorless X/Y homing and other Prusa MK3 features
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Regarding the use of Stallguard to detect hard endstops and skipped steps, this is much easier to do when you can choose the motors to match the printer and the drivers - as Prusa can. It's much harder to do when you don't control the motors.
What should be the specs of motors?
Also, Stallguard works over a limited speed range. I am doubtful that the prusa Mk3 is capable of detecting missed steps during slow moves, for example when printing small detail that requires a slow print speed.
Well, don't missing steps mostly occur at high speed? unless there is a collision, of course…
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The ideal motors for stall detection would be high-inductance ones - which is just the opposite of what you need for high speed.
Maybe I should put an experimental stall detect feature in 1.20, with configurable stallguard thresholds and minimum speeds at which it is used.
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That would allow us to make some tests…
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Thinking about it, if it works on a delta with an accurate z probe, as you can even out any inaccuracy in the absolute endstop position by doing autocalibration (so long as you remember, perhaps if endstop-less mode is selected, the firmware could behave as it if is not homed, until a calibration run has taken place?), and the absolute endstop accuracy on cartesian machines is not that important (certainly in x and y) then why not try it?
I imagine it makes recovery from power loss far less likely to be successful. I might ask the Prusa team at TCT, to demonstrate a power loss and recovery, without endstops.
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https://www.youtube.com/watch?v=ROSriVwO0JE
Shows a bit more.
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I have to say it looks good. I started with an i3, never imagined it would be back as probably the most integrated and advanced 3D printer (for quite reasonable money too) a few years later. I really want one now.
Power off recovery is a nice idea, but with ABS printing depending on your surface allowing the bed to cool can be print-ruined, as it won't remain adhered.
I'd like to be able to add these features to my duet controlled machines, and for duet to not only keep pace but to also get ahead. So what do we think we need more than that? Can someone crack an autocalibrating extruder?
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With the filament sensor, if tuned correctly before install, I can't see why an autocalibrating extruder is out of the question.
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True but the filament monitor as Duet use it and from what I can see of it, its the same in Prusa's implementation, can provide data on filament presence and filament movement, in the case of duet's filament monitor currently they have to infer filament presence (if movement is detected) as there is no detector for it, as yet, on the PCB. They are not measuring filament diameter (or as would be required in reality - cross-sectional area) in order to calculate the volume of filament entering the hotend (let alone the density of filament). It's a tricky problem, a pressure sensor in the hotend might do it but no-one has demonstrated one working.
My only idea is a glass section of the bed, at the side perhaps, which assuming a perfect gap could be achieved from nozzle to glass using precise z probes, could optically via a scanner/camera sensor measure the width of an extruded line of filament and then adjust the extrusion multiplier to achieve a predetermined width. This would, in theory, allow loading any filament, hitting calibrate and after printing a few lines the calibration would be complete. Assuming the nozzle to bed gap was precise every time, and with the smarteffector or piezo probe this is possible, assuming the nozzle was exactly the width it was meant to be etc.
If width required too much resolution, perhaps length might be measured instead, so the printer would prime, move to position, begin extruding past a fixed point, then stop after x seconds, and then the length of good extrusion would be measured optically through the glass section. Determining the cutoff point between "good" and stringy extrusion would also have to be carefully determined.
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Their optical filament sensor does look good.
Does it just monitor the presence of filament, or does it track filament motion in both directions as ours does? Detecting out-of-filament is easy; detecting blocked nozzles, jammed extruders drives etc. is much harder.
I didn't see real reply. The new Prusa sensor works like an optical (laser) encoder in a computer mouse. It tracks the motion of the filament, allowing those advanced features you mention.
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Is this sensor accurate? I mean, can it be used to really measure the filament advance? Or is it just some 'order of magnitude'?
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@fma:
Is this sensor accurate? I mean, can it be used to really measure the filament advance? Or is it just some 'order of magnitude'?
Prusa sayd that it actually is a Sensor like a Mouse so it should be work realy well.
Source: https://www.youtube.com/watch?v=mk1u5I5EKvQ -
Yes, I saw that. I would like to know what sensor he is using.
I made some tests, a few weeks ago, with an old mouse sensor (I found old stocks on ali express, with the lens), but it does not work on all filaments…
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I've preordered one so I can play I with the new features. I'm really excited about how much more reliable these sorts of additions will make 3D printing.
I'd be very interested in seeing support for the temperature compensated bed probe. I've been having horrible issues with fluctuations in readings with my inductive probe based on temperature.
I'm also desperate for someone to come out with custom-sized version of the magnetic spring steel bed, but that's a different topic entirely.
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Have you considered other probing options. Smarteffector or piezo probes are not affected by temperature in this way? If prusa are temperature compensating their pinda probe then it must be capacitative, these are not a great choice generally but if you have sufficient control of the entire machine as prusa do they can be made to work. I wonder if they have a humidity sensor too?
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Have you considered other probing options. Smarteffector or piezo probes are not affected by temperature in this way? If prusa are temperature compensating their pinda probe then it must be capacitative, these are not a great choice generally but if you have sufficient control of the entire machine as prusa do they can be made to work. I wonder if they have a humidity sensor too?
I'm 99% sure that Prusa is using inductive sensor like they have in the past. Previously they actually had specific locations on the PCB heater that were also used for calibration. I'm not sure how that will work with the new spring steel print bed.
I've thought about using a different type of sensor, but just haven't had the time to actually follow through on it.
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At TCT today I had a good look at the i3 mk2 and mk3, thinking about buying a mk3. We've been thinking about how to integrate our sensor on an i3. If you were willing to give it a try we'd happily give you one to play with. We were thinking it might be a waste of time given that the sensor on the i3 seems to be very much an integrated part of the machine, with the axis calibration/bed levelling etc.. and I have not heard many complaints from i3 owners so far, but if it is not performing to your expectations, then I am quite sure we can improve upon it. Piezo is just a more reliable way to do it and has the added benefits of no offsets, its independent of the surface being printed on, its light, and permanently mounted.
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Why did Prusa not install a BLTouch?
I orderd one and hope it will work better than my Capacitive Sensor.
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Bltouch is a nice idea but it's not that accurate or repeatable. I suspect it wasn't good enough for Prusa.
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The inductive sensor is used to detect probe points in the bed. Since the beds are precisely manufactured and their position is known, this data can be used to adjust for slanted bed/skewed axis. With a Bltouch or a piezo you'll still be able to do mesh bed leveling (probably to much better precision with the piezo), but no MK2 specific black magic calibration.
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Bltouch is a nice idea but it's not that accurate or repeatable. I suspect it wasn't good enough for Prusa.
Sry i never heard something from a Sensor like this.
Does it use the preasure when the Nozzle touches the Bed or use it some sort of light to measure the Distance?
