Auto Bed Leveling - inductive vs microswitch

Most IR sensors fail to give reproducible trigger height for two reasons:

1. Trigger height is affected by ambient IR, e.g. halogen lighting or direct sunlight. Modulated sensors are less affected by ambient IR that unmodulated sensors, but are still affected, because of the non-linear response of the phototransistor.

2. Trigger height is affected a great deal by the reflectivity of the bed surface. So small differences in the bed surface cause large variations in trigger height.

Most proximity sensors are intended only to detect whether a target is close or not, and it doesn't matter if the sensing distance varies. What we need in 3D printing is a sensor that has a trigger height that is reproducible to better than 0.05mm despite variations in temperature, humidity, bed surface and supply voltage.

That is why my IR sensor uses two IR beams instead of just one.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I think the issue with the cheap IR sensors is repeatability with changing environmental conditions, plus a great deal of sensitivity to the reflecting surface. DC42's is a differential sensor with two transmitters which he designed specifically for repeatability on typical printing surfaces.

Ah, cross posted

Edited 1 time(s). Last edit at 02/03/2016 06:59AM by JamesK.

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realthor

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tjnamtiw
Amazingly, no one that I saw mentioned the BLTOUCH. I have this working now on my FT 2020 for $33 shipping included from S. Korea. It took about 2 weeks to get here. [www.ebay.com]

My biggest problem was that, while it worked right out of the 'box' with my laptop hooked up, it required a separate 5V supply on the ramps board. Some people can run it off of the Ramps power and others like me can't.

We're kind of talking sub $15 solutions here. I'd go for DC42's optical sensor for anything else (besides lasers, electron beams, etc). Moreover, I haven't really saw it adopted on a large scale after the indiegogo campaign. It's so hard to find these days too.

It's not at all hard to find. It's on EBay, as seen above, and you can PAYPAL the inventor and have one in your mailbox in two weeks. There is a lot of chatter lately about them, although it's still in the debugging stage, but that's half the fun, right?

[plus.google.com]

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Folger Tech 2020 i3 and FT-5 as well as modified JGAurora A5 with direct drive E3D/Titan. All running the BLTOUCH.
Great kits. Having fun and running the heck out of them.
Running Marlin 1.1.0 RC8 on the i3 and FT5. Custom firmware on A5.
Folger Tech Wiki board >[folgertech.wikia.com]

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tjnamtiw

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realthor

Quote
tjnamtiw
Amazingly, no one that I saw mentioned the BLTOUCH. I have this working now on my FT 2020 for $33 shipping included from S. Korea. It took about 2 weeks to get here. [www.ebay.com]

My biggest problem was that, while it worked right out of the 'box' with my laptop hooked up, it required a separate 5V supply on the ramps board. Some people can run it off of the Ramps power and others like me can't.

We're kind of talking sub $15 solutions here. I'd go for DC42's optical sensor for anything else (besides lasers, electron beams, etc). Moreover, I haven't really saw it adopted on a large scale after the indiegogo campaign. It's so hard to find these days too.

It's not at all hard to find. It's on EBay, as seen above, and you can PAYPAL the inventor and have one in your mailbox in two weeks. There is a lot of chatter lately about them, although it's still in the debugging stage, but that's half the fun, right?

[plus.google.com]

That would be how much? With shipping to Northern Europe...? I am assuming that by quoting me you answered for the sub $15 requirement?

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff

Good grief, is there no end to the options? Now piezo disks as sensors: [diy3dprinting.blogspot.ca]

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JamesK
Good grief, is there no end to the options? Now piezo disks as sensors: [diy3dprinting.blogspot.ca]

Yes as far as i know they fall in the same ballpark with FSRs so they might have the same properties.

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff

Quote
realthor

Quote
tjnamtiw

Quote
realthor

Quote
tjnamtiw
Amazingly, no one that I saw mentioned the BLTOUCH. I have this working now on my FT 2020 for $33 shipping included from S. Korea. It took about 2 weeks to get here. [www.ebay.com]

My biggest problem was that, while it worked right out of the 'box' with my laptop hooked up, it required a separate 5V supply on the ramps board. Some people can run it off of the Ramps power and others like me can't.

We're kind of talking sub $15 solutions here. I'd go for DC42's optical sensor for anything else (besides lasers, electron beams, etc). Moreover, I haven't really saw it adopted on a large scale after the indiegogo campaign. It's so hard to find these days too.

It's not at all hard to find. It's on EBay, as seen above, and you can PAYPAL the inventor and have one in your mailbox in two weeks. There is a lot of chatter lately about them, although it's still in the debugging stage, but that's half the fun, right?

[plus.google.com]

That would be how much? With shipping to Northern Europe...? I am assuming that by quoting me you answered for the sub $15 requirement?

No, I answered your "Moreover, ....." statement about it being hard to find. Didn't know you were in Europe. Go to the Ebay site for your country to find out. If you insist on sub-$15, then that's ashamed and rather restrictive as to options; however, have fun.

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Folger Tech 2020 i3 and FT-5 as well as modified JGAurora A5 with direct drive E3D/Titan. All running the BLTOUCH.
Great kits. Having fun and running the heck out of them.
Running Marlin 1.1.0 RC8 on the i3 and FT5. Custom firmware on A5.
Folger Tech Wiki board >[folgertech.wikia.com]

The piezo looks good might look into it. If you just fit them under the bed springs then it's an easy fix. Assuming the sensors have holes in the centre the problem of a moving bed knocking them around is no longer a problem.

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JamesK
Good grief, is there no end to the options? Now piezo disks as sensors: [diy3dprinting.blogspot.ca]

I think that they may detect the 'click' sound of the nozzle touching the build stage.
In answer to JamesK's raised eyebrows, I have catalogued 12 different ways of detecting the nozzle to bed distance and am sure that there are many more. I would have published the list but am worried that some people may get a bit irate at having methods they have sweated blood over reduced to two lines in a two page document.

Mike

Edited 1 time(s). Last edit at 02/03/2016 02:48PM by leadinglights.

Publish it it might save a lot of people a lot of time.

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DjDemonD
Publish it it might save a lot of people a lot of time.

O.K., short form below, still a work in progress.
Once again, I apologize for shortening some descriptions so much but he field is wide (and how do you describe synchronous demodulation simply)
Also, I haven't even started on methods using an introduced sensor such as realthor is presently investigating.

Mike

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Bed leveling, tramming, squaring or truing - whatever term is used it means getting the Z axis to be at 90 degrees to both the X axis and the Y axis. This is not the same thing as finding the Z position relative to the bed, but the ideal Z sensor should serve both purposes.

There are a great many ways of sensing the bed, some are suitable for setting the Z zero, others are relative and can't be relied on if the nozzle position relative to the sensor alters - as may occur if the nozzle is changed.

Addressing first the methods which will give the Z zero directly but may or may not be useful for assesing the bed level.

1) Motor stall.
This method requires that the bed be sufficiently firmly mounted to the printer that the Z axis motor will stall. All that is needed is to bring the nozzle down for greater than the total available Z travel so that the motor is stopped. The zero is then set by adding on an adjustment to account for the spring in the system. This method is not easily adapted for bed leveling and cannot be used where there is more than one motor driving movement in the Z axis.

2) Electrical contact sensing.
Zero is detected by sensing a direct electrical contact between the nozzle and the bed. The single requirement of this method is that there is no insulating material between the bed and the nozzle, a requirement that is hard to meet with plastic being extruded from the nozzle.

3) Nozzle to bed capacitance sensing.
The electrical capacitance from the nozzle to the bed can be measured while the nozzle is approaching the bed; the change in capacitance as the nozzle approaches the bed can be used to find their proximity.

4) Contact force sensing.
These methods rely on the nozzle contacting the bed and the force of this contact being sensed. Variations on this include:-
a) The contact force operating a mechanical switch. This can be one on the nozzle or extruder/nozzle combination or one on each of the bed mounts.
b) The contact force operating a force transducer of some sort including strain gauges and force sensitive resistors. As with the mechanical switch this can be either in the nozzle or in each mounting point of the bed.
Note that the condition of having mechanical switches or force transducers at each mounting of the bed is obviated if zero setting is only performed over or very near only one of the mountings. This may be useful if a non-contact method is used to obtain a bed lavel from multiple points.

5) Vibration contact sensing.
If the nozzle is made to vibrate this will be transmitted through to the bed when the nozzle touches the bed and can be detected by a transducer. Vibrators used for pagers would be suitable for this purpose while simple microphones could be used for detection.

6) Mechanical transient sensing.
The transient contact 'click' of the nozzle touching the build stage can be detected by a transducer.

Methods which either do not contact the print bed or can not be integrated into the nozzle do not lend themselves to setting the nozzle zero but can be well suited to checking a number of points on the surface to allow bed levelling.

1) Retractable switch.
A switch is connected to an actuator in a manner that allows it to be extended to make contact with the bed while the nozzle is some distance from the bed. The actuator would withdraw the switch after measurments had been taken.

2) Capacitative sensor.
The capacitance between two electrodes is altered by the approach of a dialectric or conductive material.

3) Inductive sensor.
This relies on the bed being of a conductive material. The inductance of an inductor is changed by the presence of the bed.

4) Optical sensor.
Optical sensors use the reflection of light from the bed surface. Differential optical sensors use two emitters so configured that there is a small area of overlap in the optical field where a detector will detect reflection equaly from each emitter.

5) Pneumatic back pressure sensor.
Relying on detecting an increase in the back pressure to a flow of air through an oriface bought near to contact with the build stage.

Nice list, but you missed out a couple that I know of:

6. Switch that is deployed and retracted by moving the head in a particular way. See the Allen key probe used on some Mini Kossels.

7. Ultrasonic measurement of the distance to the bed from a sensor on the hot end. I used to sell a dual IR and ultrasonic height sensor. The ultrasonic works well when the system is cold, but is affected too much by draughts if you probe near the edges of a heated bed.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks DC42, I blush that I forgot the ultrasonic method. (note to reprap :- What no pink embarrassed smiley?)
Mike

An interesting approach, however the last version departed from the simplicity of the initial one.

https://plus.google.com/photos/108444220873455562851/albums/6017207592763461137

Blog about it: http://ei8htohms.tinyparts.net/?p=1111

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff

Quote
tjnamtiw
Amazingly, no one that I saw mentioned the BLTOUCH. I have this working now on my FT 2020 for $33 shipping included from S. Korea. It took about 2 weeks to get here. [www.ebay.com]

My biggest problem was that, while it worked right out of the 'box' with my laptop hooked up, it required a separate 5V supply on the ramps board. Some people can run it off of the Ramps power and others like me can't.

This looks pretty good! I was going to set up a servo and microswitch arrangement for my ABL, however this may be a better (easier?) solution. The microswitch I bought seems to require a bit more pressure to activate than I'd like - the bed is pushed down a bit from the pressure, which would affect leveling readings I would imagine.

How is the BLTouch working for you so far?

Quote
realthor
An interesting approach, however the last version departed from the simplicity of the initial one.

https://plus.google.com/photos/108444220873455562851/albums/6017207592763461137

Blog about it: http://ei8htohms.tinyparts.net/?p=1111

Is this a commercial product?

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DjDemonD

Quote
realthor
An interesting approach, however the last version departed from the simplicity of the initial one.

https://plus.google.com/photos/108444220873455562851/albums/6017207592763461137

Blog about it: http://ei8htohms.tinyparts.net/?p=1111

Is this a commercial product?

I doubt it by the looks of it.

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff

Wow thanks for the wonderful ideas. I have been studying the different options for the past few days and have come to the conclusion that an IR sensor is "the next best thing".

A pressure sensor/strain gauge seems to be the most reliable alternative but this is hardcore stuff to set it up. Definitely looking for something simpler. Inductive sensors are the simplest option but I have glass over a pcb heated bed. So I could use a capacitive sensor - just as easy to set up and good enough accuracy.

IR sensors however can be used on any surface - so I won't have to worry about changing the glass an switching to aluminum in future. Also IR sensors probably provide better accuracy and repeatability.
While I have no doubts that dc42's setup is the best one there is, it is simply too expensive for folks who just want to build a reprap machine in their spare time with their spare money I like to think that the machine I have assembled offers outstanding value for money so slamming a nearly 45 EUR sensor (incl. shipping to Germany) would cause a major disturbance in the force

So has anyone tried this PiBot solution? I guess it would be compatible with all motherboards including my Ramps 1.4. What do you think?

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Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

I sold a mini differential IR sensor a few weeks ago to a person who already had a Pibot which didn't work well enough for him.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].