There are many options for a 3D printer's bed sensor and even more misconceptions about what they can and should do. So after a ton of testing with a custom-built precision test apparatus (TM), 9 myths about these sensors have been examined - and we got a ton of data about how precise each one can be!
🛒 M8, 2mm inductive sensor (5V) http://s.click.aliexpress.com/e/UnYVZFe
🛒 M12, 4mm inductive sensor http://s.click.aliexpress.com/e/e6QJqn6
🛒 M16, 8mm inductive sensor http://s.click.aliexpress.com/e/fuVJu3F
🛒 M16, adjustable distance capacitive sensor http://s.click.aliexpress.com/e/YfIQFie
🛒 M16, 20mm capacitive sensor http://s.click.aliexpress.com/e/ujEuvZf
🛒 David Crocker's IR sensor http://www.escher3d.com/
🛒 SHARP analog sensor http://s.click.aliexpress.com/e/mEMnaQF
🛒 Microswiches http://s.click.aliexpress.com/e/2z3Njm2
🛒 BLTouch http://geni.us/BLTouch
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It is a nice video and I learned something,
but I my expectation was, you would have tested more different types.
Besides, most printers use an optical sensor, which block the light.
For bed leveling, it is often the touch sensor, which you did quicly glance over.
I kinda missed the hal sensor and the piezoelectric sensor.
So, I've been thinking about these results, and I don't believe they can be conclusive for which sensor is actually best for "bed leveling" since that involves sensing at several different places on the bed. This test setup, though certainly useful and helpful, may not be telling the whole story since it continuously tests only one spot on the big aluminum block. A better more conclusive test would test how accurately each sensor can sense the actual flatness of a bed; i.e., at multiple points. Since an aluminum bed, for instance, may not be perfectly uniform across its entirety with respect to its inductive properties, would an inductive sensor actually perform worse than or only as good as a physical touch/contact type sensor in an actual "leveling" application?
I want to address something I've been seeing floating around the internet regarding the inductive/capacitive probes. People keep saying you need a 12 V to 5V voltage divider on the output. This is partially wrong, and may, in fact, introduce more errors in your bed leveling. The sensors do absolutely need to be run from 12 volts to achieve their rated specs, but if you are careful to buy an NPN type sensor, you can simply plug the output directly into the Ramps input pin. This sensors are what is called "open collector drain" output. It means that it doesn't provide an output voltage when trigged, rather it pulls the signal provided to it to ground. The Arduino/Ramps board has internal 20 kohm pull up resistors on all of its pins (enabled in Configurations.h). This pull up provides 5 volts to the output pin of the sensor, when the sensor triggers, it pulls that 5 volt signal to ground. If you use a voltage divider, you might reduce the 5 volts enough to cause unreliable switching in the Arduino. PNP type = needs voltage divider. NPN type = do not use voltage divider.
Thanks for your videos. I have experienced difficulties with sensors. After a few consecutive prints, the levelling of the bed was not accurate, but was accurate again the day after. I now make the levelling when the bed is hot, but the problem still exists. I believe that the sensor close to the bed and the head warms up little by little, and the temperature of the sensor may have some effect of the measurement.
Thanks for your work! But one question:
Is it possible, that a electical heatbed can get a bad influence on these probes?
For e.g. eletric magnetic behaviours? On your test is a "perfect" metal block without heatbed wires etc.
You measured mostly repeatability, and mostly ignored system accuracy due to heating/cooling.
Excellent video, great charts.
Should have had an external digital DTI measure the setups actual position, logging, and dwelled (paused) after contact on the probe.
Then the DTI log would show where the moving piece actually was at probe contact, vs the start position when all was cold.
Likewise, the triggering circuit for probe hit is critical.
I did a lot of work on this, 8 years ago, on testing for lathe spindle index sensors, and we proved conclusively that sensors will give very fuzzy signals, that vary with temp/speed/luck.
A sharp triggering circuit, and a sensor tuned to give a crisp response, will be about 100x more accurate on a range of speeds vs a typical probe "hit".
I also saw that optical sensors will repeat to about 2 microns, with very simple basic cheap sensors.
Why only 5 volt? Are they powered by USB? Since most USB ports are 5 volts? Great video! But you didn't show us stepper motors that have all this stuff built in. Is this just a cheaper method using an external sensor?
I wonder if you can help me with a couple of queries.
I have bought a LJ12A3-4-Z/BY inductive sensor. It is the 12mm diameter version as I did not have room to fit the larger 18mm version. The problem is that the detection distance is halved to just 4mm. I was wondering if I could power the sensor directly from the power supply and possibly fit either a voltage regulator or resistor voltage divider to reduce the signal back at the board? I also have some 0.1mm stainless steel foil that I am intending to place under the 2mm glass. Will this increase the ability for the sensor to pick up the magnetic field?
One last point, do you know if it is possible to devise a method of using a k type thermocouple instead instead of a thermistor? I know that a thermistor decreases voltage as it heats and a thermocouple works in the opposite direction but i would like to use a PID to control hot end temperature as it better controls better without overrun once heating temperature is achieved.
Hello Peter, this being a year old video chances are Thomas does not answer questions anymore.
The inductive sensor has 3 wires, +V , -V and Signal , +V can be anything from 6-36V DC , the Signal wire is either OC or CC referenced to -V (ground) depending on what status the Sensor is in.
I dont know what Printer you want to add it too but if it's a printer with a micro switch on the Z axis then you should run the Inductive Sensor through an Optocoupler and then hook it up to the wires where the micro switch were.
Depending on what Optocoupler you use you can run it and the Inductive Sensor off the 24V Printer PSU without
and kind of drop down regulator.
The BLTouch manual specifically states the sensor must be run vertically. Since your test rig is horizontal, the results are suspect. It would be good to rerun the BLTouch test with it held vertically.
Another one to try is the piezo force sensor. Mount it in your bed support or (as I did) in your hot-end mount on the carriage and it registers contact of the nozzle to the bed. Zero probe offsets in X, Y and Z, change nozzle and all you have to do is run the auto-level. Super convenient. Precision Piezo do a good rig.
Hello Tom. May I first congratulate you on your clear, informative videos and have now subscribed to you. I am new to 3D printing and Arduino world in general. I have just bought the Ender 3 and having watched various autolevelling videos also purchased the BLtouch sensor. I have added the bootloader to the Ender 3 and now want to download the relevant sketch to control the BLtouch. Can you direct me to any video/information that will help as I am a little confused with what I have seen so far. Many Thanks. Rob
I know this video is over a year old at this point so I hope this is still relevant.
He tested all of these sensors horizontally. The BLTouch specifically states NOT to use it that way. It needs to be hung vertically as it would be mounted on a printer.
I've used a mechanical switch with manual leveling, a mechanical switch that flips up with a servo, capacitive sensors, inductive sensors, glass beds, PEI sheets, Zebra Plate from PRINTinZ, aluminum beds, and even tool steel beds. I've tried a total of 15 different sensors and 11 different beds in my few years of 3D printing. NONE of them were as accurate as simply using the BLTouch. When it is installed correctly, it just works flawlessly. Best of all it doesn't care one bit what surface you have, it will work on anything.
I think it deserves a re-test.
I would love to see this video updated to include Ultrasonic sensors, and name brand inductance sensors like those made by Osram up to say 16mm sensing distance. That being said, this video is so helpful. Thank you for making it.
The only reason I moved from an inductive sensor to David Crocker's IR sensor is because of the bed. If the thickness of the bed varies, or there are holes in it to reduce weight, the induction sensor will trigger at a different height to more/less material being on the bed in one location.
You are talking about 50µm (0.05 millimeters) If your 3d printer i high end maby and i say may your 3d printer has a tolerens of 0.1mm , maby better with out belts, and using ball spindels. 0.05 millimeters is just so unreal.
Mal ne Frage...Kann ich mein Bed ohne Glassplatte leveln, danach zum ersten Mal den Sensor einbauen und dann wieder die Platte aufs Heatbed drauf machen? Oder muss ich irgendetwas verstellen nachdem ich die Platte wieder drauf habe?
I got a 8mm "orange" inductive sensor. It detects from 5mm away at 5V, perfect for my mirror covered bed. Too bad I have deviation between the Z homing distance and the probing distance. Then nozzle homes about 1mm lower than it actually prints at. Same with endstop, that's not the sensor's fault.
Hmm, as detailed your video was, and I consider myself as a reasonably intelligent bloke, I still haven't determined which sensor is the best. Apart from the two that were obviosly way out on the last chart you showed, all the rest performed similarly. So, be brave, which one would YOU choose to use regularly?
Almost 2 years later now and I still adore my BLTouch. Even if it statistically or scientifically isn't the most accurate out there, as you say, it's 'more than good enough'. It's so rare to have a calibration fail.
Any chances of doing a review of Piezo-electric sensors? Been reading up on them, but most of the hype I've found seems to come from people who work for the company selling commercial versions, so getting third-party reviews would be interesting.
Assuming the data collected is accurate, in order to make probe comparisons, large tolerances must be added to inductive probes that include the build plate tolerance stack for non-conductive top sheets (adhesive, PEI, etc...) . Also the BL Touch is intended to operate vertically, more friction is introduced horizontally. Once all this is considered and included, the BL Touch will compare MUCH better, if not the best. Also, if tossing on a thick G10 build plate for printing Nylon ... only the BL Touch or a micro switch can accommodate that, without having to change the probe z offset value.
I never thought about using such sensors for measuring the bed level. At work I use mostly inductive ones but just for checking if there is an object or not. When I saw your video about the Prusa i3MK3 and its autoleveling I had doubts about the precision, but your video here has told me better. Thank you.
Technically speaking the whole process shouldn't even be called "auto levelling" as the printer doesn't make anything more level after probing. It just compensated with stepper motor movements for the uneven bed.
Lots of great information which in the end was overwhelmingly confusing. Your scripted, rapid fire delivery, in the end just left me confused and without a clear direction as to which sensor I should use. There was no wrap up or recommendation as to which sensor was the best one to use. It seems that you were trying to keep the video as short as possible rather than delivering useable information. I just want a good sensor at a descent price and I still don't know which one to use.
Hello. Where can we read the results please? I am very interested by mecanical switch results (with and without lever)
As I understand, at 7:24; mecanical without lever is more precise than BLTouch ? cool!!
I am looking for someone who has a custom configuration.h file that they are already using, and configured for the BLTouch Sensor, and SKYNET3D that they could put a link in for dropbox or somewhere for my CooCheer 3d Printer. The file needs to be configured for an Anet board with LCD 12864 graphic display. Print Bed Size configuration is W 220 L 270 H 230 mm. If someone would put a link in a reply, I would appreciate it. I'm sure there are other people who could use the file also.
Well i am sure that this aswer had been said again in this video but what the heck!!
2mm thick glass will work on Roko sensor(inductive) prety well, i have not run a perfect test as your's offcourse but it works.
Any chance to give me an idea, how to set up autoleveling in smoothieware, how to level the bed and what gcode should I put in start/end code? I have a 18mm capacitance proximity sensor on hotend carriage.
FYI, you tested the BLTouch in the wrong orientation. I tested mine thoroughly at multiple homing speeds and standard deviation was 0.01mm with the occasional one that that was +/- 0.02mm, on all but really fast homing speeds.
I now do a two step homing with it, once at 1500mm/m, and then a slow home at 100mm/m from ~2mm of the bed.
Some time ago I built a DIY heated bed to my Printrbot Simple Metal. In order to get the sensor to detect the bed through the glass, I had to put a sheet of 1 mm galvanised steel sheet under it. But now, the sensor almost touches the surface of 3mm thick borosilicate glass. Not really useable. I could not find borosilicate glass less than 3 mm thick. I read that plain glass can withstand a certain amount of heating and cooling as long as it happens slowly. But how slowly?
I decided that glass of the type used in picture frames was cheap enough for an experiment and I bought a couple of 200mm square glass frames from a bargain store. This glass, being only 1.5 mm works reliably with the built-in heating setting (I did not have to make the glass heat more slowly) though I must warn that, since I only use PLA, this setup has never been tested above 60c!
Also, borosilicate glass can withstand some downward pressure (when things go slightly wrong) - but picture frame glass cracks immediately. I lost both in the experiment, but have had 6 perfect prints off the third, with one coat of Magigoo on the glass.
I wish your test apparatus also used a layer of glass, typically found on CR-10x's. If the sensor needs to be too close to the glass so as to interfere with prints during printing, then that is a fail. Please account for sensing distance to the detected object.
Hi can anyone help on a question I have? I want to buy the anet a8 3D printer, and I was asking what sensors would work on it, if any. I don't think any of the sensors will work as it requires manual straightening , but can anyone help? Is there any other ways of making the bed straightening automatic on that printer?
Hi Tom, just came across this video while I'm building my i3 clone, great videos! Do you know if there are any 12mm sensors longer than 50mm? My sensor doesn't go close enough to the print surface so doesn't detect the print bed. Would really like to get the printer working, going to watch your clone prusa series now!
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