# 3D Printing > 3D Printer Parts, Filament & Materials >  Ultrasonic Alignment tool for  Bed Leveling+zeroing of stage + Filament monitor

## dsayan

Check this Kickstarter project :


https://www.kickstarter.com/projects...or-3d-printers

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## curious aardvark

I like that. Simple, effective and not tied in to any one machine. 
Are you by any chance looking for beta testers ?

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## Davo

Very nice.

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## wirlybird

Interesting.

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## dsayan

> I like that. Simple, effective and not tied in to any one machine. 
> Are you by any chance looking for beta testers ?



Thanks for your comments, yes it can work on any machine and practically on any bed surfaces! Few beta testers are already in line but more the merrier. Although,all depends on the success of this Kickstarter project,currently we are about 23% funded . Do you have any suggestions on platforms (online, journals, etc..) to get the word out about this product more effectively? And also please share it with your own groups..
Thanks so much !!!

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## dsayan

> Interesting.


Thanks for your comment, hoping fully the project becomes successful - Share the project , so more people gets aware of it , and also any suggestions are very much welcome!

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## dsayan

> Very nice.


Davo, Thanks for the comment- I see you are a staff engineer at HYREL, do you see any possibilities to include alignG in your product lines? Let me know !

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## Davo

dsayan, we've talked about accoustic metrics on bed level and zero position for years (my CTO has a lot of ultrasonic and megasonic experience), but never implemented anything. Since our heads are loaded by the user, their positioning can vary. Sonic detection is very interesting to us. I've forwarded your link to him.

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## wirlybird

> Thanks for your comments, yes it can work on any machine and practically on any bed surfaces! Few beta testers are already in line but more the merrier. Although,all depends on the success of this Kickstarter project,currently we are about 23% funded . Do you have any suggestions on platforms (online, journals, etc..) to get the word out about this product more effectively? And also please share it with your own groups..
> Thanks so much !!!


Count me in as a willing beta tester.  I have four printers.

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## DaveB

> Count me in as a willing beta tester.  I have four printers.


I like Kickstarter.  I've participated in a few. Signed up.

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## dsayan

> dsayan, we've talked about accoustic metrics on bed level and zero position for years (my CTO has a lot of ultrasonic and megasonic experience), but never implemented anything. Since our heads are loaded by the user, their positioning can vary. Sonic detection is very interesting to us. I've forwarded your link to him.


Hey Davo, 

Its glad to know you see the potential of this device and further talked with your CTO. Any update from him yet? And any suggestions to help promote our kickstarter campaign, we truly appreciate your help!

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## curious aardvark

I still don't see how you align the widget exactly with the print nozzle to start with and make sure it lines up with it each time you stick it back on. 

I guess you could get the print nozzle to touch the bed and do the same with the widget, but it'll go out of alignment as soon as you change the print head temp, or the magentic strip shifts. 

I'm obviously missing something :-)

Currently have 2 printers, both have different levelling procedures.

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## dsayan

Hey Curious, good question - for the purpose of bed leveling for your printers. With our sensor the position of the print head in respect to our sensor is not relevant, since we are measuring distance from a height above the bed plane. As long as the sensor is attached to the magnetic strip  and not perturbed on purpose during the bed leveling procedure....Also to be noted the provided magnetic strip is industrial class and one has to really try hard to make it move from its position. It is one of its first kind so i totally understand your misunderstanding - with our device you wont need two different leveling technique for sure!
Hope it clears the confusion. Let me know if you have further questions!
And please suggest ways to get the word out to more people to make this project sucessful!

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## dsayan

Folks, Thanks so much for your support we have reached over 300 supporters of our project and have raised more than 25K, anyways good news is we have made some exciting changes on our project page - prices have been slashed for a limited time - check it out and let us know what you think? Here it is :
https://www.kickstarter.com/projects...or-3d-printers

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## dsayan

> Check this Kickstarter project :
> 
> 
> https://www.kickstarter.com/projects...or-3d-printers


Update : Folks, Thanks so much for your support we have reached over 300 supporters of our project and have raised more than 25K, anyways good news is we have made some exciting changes on our project page - prices have been slashed for a limited time - check it out and let us know what you think?

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## curious aardvark

prices don't look any different to me.

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## ShadowX

The concept seems very interesting.  However, I think it can be a lot more successful and popular with 3D printer users if there is a rigid mount to maintain a fixed position on the print head and the device directly interfaces with the controller card probe interface.

The device should have the option to trigger at some set height above the bed and it should have an output signal that can be directly connected to most 3D printer probe endstops.  If it can do that and maintain accurate/repeatable readings, it would be a great contact-less bed leveling tool that can use the automatic bed leveling systems already built into most modern firmware like Marlin, Repetier, DuetWifi, etc. The location of the probe in reference to the tip of the nozzle is critical and must be a fixed distance. Without a rigid mount, the measurements would not be repeatable if the device moved.

 I honestly can't forsee myself doing a manual bed level each time I print with a separate software on a device that is attached with a magnet.  Watching the video, the locations indicated for each spot is not even clear.  Do you randomly pick a spot?  The firmware in Repetier can probe over 40+ points on a bed and create a contour profile of the entire surface if needed.   It can also do it without user interaction.  Some beds are concave or convex and not planar.  The leveling software in the video demo assumes the bed would be flat.   I run an automatic bed level probing routine each time before I print.  The height can change slightly just with temperature deltas between the hot end and the heated bed.  Some of the changes can be enough to cause poor or too much adhesion on the first layers.

Another problem is most of the parts on or around my hot end are non-ferrous.  I have a hot end cooling fin made of aluminum, a hot end block made of aluminum and fans and shrouds made of plastic.  There is no place that is flat and magnetic for me to attach the device.  I would have to design a custom bracket that is fixed or have magnets to use this device.

I hope you will be successful and become fully funded in your project.  Its definitely a great endeavor.   I would love to be able to use a device like this if it works seamlessly with the controller card.

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## curious aardvark

the device uses an adhesize magnetic strip that attaches to the print head. The measurer then magnetically attaches to the strip. 
ie: no ferrous parts are needed. I've gota roll of magnetic sticky tape in my workshop, useful stuff.

So if the device doesn't need to line up with the printhead - how can you know how far the printhead is from the bed.
I know I'm labouring this point - but I just don't see how it works.

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## wirlybird

I am also a bit confused on how the device gets a registration point to use.  When i used a dial indicator to level I would bring the bed touching the nozzle and then zero the dial.  Back to paper now though!
I could see if the device was a more permanent mount that was a known distance but even then what if I change nozzles and it is a bit different than the last one?

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## ShadowX

It has to reference to the tip of the nozzle.  Even if the device is accurate in itself, each level would be different if the device moves even slightly.  I have not even factored the issue with the angle in reference to the nozzle tip.  If the probe is at an angle, the distance measurement may change.  It has to be rigidly mounted and the value between the sensor and the nozzle has to fixed.  In fact, it has to be even more accurate than the measurement taken by at least a magnitude of 2 in order to provide accurate measurement.  

i can understand if the device is useful for other types of machines such as CNC or routers, but for 3D printing, the distance of the nozzle to the print bed has to be less than the thickness of the print layer (typically, .2mm or .3mm).  If it can not accurately measure to that level and be repeatable, it will not serve the 3D printing community well.

I provided a link to a typical use case for an automatic level probe in 3D printing.  This is an IR probe that does not contact the bed surface.  However, if this device can perform at the same level of accuracy and repeatability, it would be an interesting device to support.  The IR probe in this video is around $25, so the price has to be competitive to it also.  The IR probe does have limitations such as the the bed surface has to be reflective to the IR and not provide false readings.  The probe also has to be very close to the surface the surface within 3mm.  The ultrasonic sensor would eliminate some of those issues if it can compete at the same level.  It also a tough market since there are other options such as mechanical switches, FSR sensors, and even a direct probe such as BLTouch. 

The sensor may need to be as close to the tip of the nozzle as possible in delta printers.  Delta printer effectors may have a tilt and you want the probe to be as close to the nozzle to minimize the effects of effector tilt.  The size of the device is critical to be able to place it close to the nozzle without interfering with the air from the cooling fans.

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## ShadowX

My effector is round there is no way to attach to it in the current configuration.  Worse case, I can custom design a holder for it. 

  I have a CNC milling machine.  Even with that machine, I don't see how the device would be useful.  Some of my tools are over 3 inches from tip of the Tormach holder to the spindle.  Any slight angle in relation to the tool bit would throw off the measurement.  I use a height gauge to measure the tool tip to the Tormach reference plane on a surface plate and use a spring loaded dial indicator to measure from my reference height to the top surface of the raw stock.   I am able to maintain .001 inch accuracy using that method. In cases like a drill bit or an engraving bit, the tip is so small that I doubt the ultrasonic sensor can detect the tip distance and get a reliable distance measurement.  I really have a hard time trying to think of a useful use case where this device is superior to other methods either in accuracy, cost, or time savings.

In terms of monitoring the spindle, that is what a tachometer is for.  You can use reflective tape or other methods.  I guess you can interface the device with Mach3 and get feedback, but most people don't leave a machine running at full cutting speed without being nearby.  Its dangerous and negligent to not monitor or be near it while its running unless the mill is fully enclosed.




> the device uses an adhesize magnetic strip that attaches to the print head. The measurer then magnetically attaches to the strip. 
> ie: no ferrous parts are needed. I've gota roll of magnetic sticky tape in my workshop, useful stuff.
> 
> So if the device doesn't need to line up with the printhead - how can you know how far the printhead is from the bed.
> I know I'm labouring this point - but I just don't see how it works.

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## dsayan

> I am also a bit confused on how the device gets a registration point to use. When i used a dial indicator to level I would bring the bed touching the nozzle and then zero the dial. Back to paper now though!
> I could see if the device was a more permanent mount that was a known distance but even then what if I change nozzles and it is a bit different than the last one?


The same way that you use an IR sensor or inductive proximity sensor. For bed leveling the offset does not matter. But, it is essential for zeroing.
Apparently, alignG doesn’t know the coordinates of the print head. Through trial and error, only for the first time, you find the best extruder/bed gap; then mount and leave alignG in that spot. You also reset the alignG reading in the software in that position.
We also considered a tapped M3 hole on the back of alignG. You can just mount it using a M3 screw and simple mechanical structure. You can even glue it to the surface if you need a permanent attachment.
Remember that there are two very significant advantages for alignG when comparing with any dial indicator: (1) dial indicators in the price range of alignG always apply a (spring loaded) force to the surface, roughly about 1 Newton (100 grams). To make sure that the force is not displacing the dial indicator, you need a very rigid mounting for the dial. When speaking about 15-micron displacement, 1 Newton force is tremendous. (2) Dial indicators in the price range of alignG weights about 100-150 grams. So, you need to consider that in the structure of the mounting fixture. Besides, the weight of the mounting structure is often more than the weight of dial indicator, do take that into account!
alignG is a non-contact measurement device; so, no worries about the spring-loaded force to displace it. In the other hand, it weighs only 20 grams. A strong magnet tape can simply keep a 20-gram gadget in place for a long time, except if you want to displace it intentionally. For sure, there are many simple ways to permanently attach a 20grams gadget to your extruder, if you want to install it for one time and leave it there.

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## dsayan

> the device uses an adhesize magnetic strip that attaches to the print head. The measurer then magnetically attaches to the strip. 
> ie: no ferrous parts are needed. I've gota roll of magnetic sticky tape in my workshop, useful stuff.
> 
> So if the device doesn't need to line up with the printhead - how can you know how far the printhead is from the bed.
> I know I'm labouring this point - but I just don't see how it works.


The same way that you use an IR sensor or inductive proximity sensor. For bed leveling the offset donot matter. althpugh, it is important for zeroing.
Obviously, alignG doesn’t know the coordinates of the print head. Through trial and error, only for the first time, you find the best extruder/bed gap; then mount and leave alignG in that spot. You also reset the alignG reading in the software for that position.

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## dsayan

> The concept seems very interesting. However, I think it can be a lot more successful and popular with 3D printer users if there is a rigid mount to maintain a fixed position on the print head and the device directly interfaces with the controller card probe interface.
> 
> The device should have the option to trigger at some set height above the bed and it should have an output signal that can be directly connected to most 3D printer probe endstops. If it can do that and maintain accurate/repeatable readings, it would be a great contact-less bed leveling tool that can use the automatic bed leveling systems already built into most modern firmware like Marlin, Repetier, DuetWifi, etc. The location of the probe in reference to the tip of the nozzle is critical and must be a fixed distance. Without a rigid mount, the measurements would not be repeatable if the device moved.
> 
> I honestly can't forsee myself doing a manual bed level each time I print with a separate software on a device that is attached with a magnet. Watching the video, the locations indicated for each spot is not even clear. Do you randomly pick a spot? The firmware in Repetier can probe over 40+ points on a bed and create a contour profile of the entire surface if needed. It can also do it without user interaction. Some beds are concave or convex and not planar. The leveling software in the video demo assumes the bed would be flat. I run an automatic bed level probing routine each time before I print. The height can change slightly just with temperature deltas between the hot end and the heated bed. Some of the changes can be enough to cause poor or too much adhesion on the first layers.
> 
> Another problem is most of the parts on or around my hot end are non-ferrous. I have a hot end cooling fin made of aluminum, a hot end block made of aluminum and fans and shrouds made of plastic. There is no place that is flat and magnetic for me to attach the device. I would have to design a custom bracket that is fixed or have magnets to use this device.
> 
> I hope you will be successful and become fully funded in your project. Its definitely a great endeavor. I would love to be able to use a device like this if it works seamlessly with the controller card.


"The concept seems very interesting. However, I think it can be a lot more successful and popular with 3D printer users if there is a rigid mount to maintain a fixed position on the print head and the device directly interfaces with the controller card probe interface.”


We considered a tapped M3 hole on the back of alignG. You can simply mount it using a M3 screw and simple mechanical structure. You can even glue it to the surface if you need a permanent attachment.
Remember that there are two very important advantages for alignG when comparing with any dial indicator: (1) dial indicators in the price range of alignG always apply a (spring loaded) force to the surface, roughly about 1 Newton (100 grams). To make sure that the force is not displacing the dial indicator, you need a very rigid mounting for the dial. When speaking about 15-micron displacement, 1 Newton force is huge. (2) a dial indicators in the price range of alignG weights about 100-150 grams. So, you need to consider that in the structure of the mounting fixture. In addition, the weight of mounting structure is often more than the weight of dial indicator, take that in account!
alignG is a non-contact measurement device; so, no worries about the spring-loaded force to displace it. In the other hand, it weighs only 20 grams. A strong magnet tape can simply keep a 20 gram gadget in place for a long time, except if you want to intentionally displace it. For sure, there are many ways to permanently attach a 20grams gadget to your extruder, if you want to install it for one time and leave it there. 


“The device should have the option to trigger at some set height above the bed and it should have an output signal that can be directly connected to most 3D printer probe endstops. If it can do that and maintain accurate/repeatable readings, it would be a great contact-less bed leveling tool that can use the automatic bed leveling systems already built into most modern firmware like Marlin, Repetier, DuetWifi, etc. The location of the probe in reference to the tip of the nozzle is critical and must be a fixed distance. Without a rigid mount, the measurements would not be repeatable if the device moved.”


We considered an option for the output port of alignG, providing analog/I2C/USART interface for creative developers to integrate alignG into their system. The precision value reported for alignG (25 micron for alignG-I & alignG-II and 15 microns for alignG-III) are the standard deviation of the measurement. Standard deviation also represents the repeatability of the measurement system. Using alignG, you will have a repeatable reading. 
There is no way that somebody compares a 15-micron precision sensor with an IR sensor or inductive proximity sensors, commonly used in the auto bed leveling systems. Even a high precision premium brand inductive sensor still lack the necessary accuracy. Inductive proximity sensors are limited to the conductive (or magnetic) target materials. If you have a glass bed, probably you need a conductive tape on top of that. Proximity sensors are not measuring the distance; So, your measurement is dependent on the accuracy of the Z-Stage. While using alignG, there is no need to move the Z-stage; because it measures the distance. Inductive proximity sensors have a large hysteresis problem, sometimes up to 20% of their sensing range, look at their datasheet. What inductive proximity sensors measure depends on the target material and even its thickness. If you have a thin aluminum bed, the measurement will depend on its thickness uniformity. It is a small dependence; but when talking about micron precision, it is counted.

“I honestly can't forsee myself doing a manual bed level each time I print with a separate software on a device that is attached to a magnet. Watching the video, the locations indicated for each spot is not even clear. Do you randomly pick a spot? The firmware in Repetier can probe over 40+ points on a bed and create a contour profile of the entire surface if needed. It can also do it without user interaction. Some beds are concave or convex and not planar. The leveling software in the video demo assumes the bed would be flat. I run an automatic bed level probing routine each time before I print. The height can change slightly just with temperature deltas between the hot end and the heated bed. Some of the changes can be enough to cause poor or too much adhesion on the first layers.”

Even if you are always using an auto leveling mechanism, it is always recommended to keep your bed leveled. If the miss-leveling in your bed is comparable with the backlash of the Z-stage, auto bed leveling will not result in an excellent finished surface. So, having an instrument that can check the four corners of the bed in few seconds is always useful.

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## ShadowX

> "The concept seems very interesting. However, I think it can be a lot more successful and popular with 3D printer users if there is a rigid mount to maintain a fixed position on the print head and the device directly interfaces with the controller card probe interface.”
> 
> 
> We considered a tapped M3 hole on the back of alignG. You can simply mount it using a M3 screw and simple mechanical structure. You can even glue it to the surface if you need a permanent attachment.
> Remember that there are two very important advantages for alignG when comparing with any dial indicator: (1) dial indicators in the price range of alignG always apply a (spring loaded) force to the surface, roughly about 1 Newton (100 grams). To make sure that the force is not displacing the dial indicator, you need a very rigid mounting for the dial. When speaking about 15-micron displacement, 1 Newton force is huge. (2) a dial indicators in the price range of alignG weights about 100-150 grams. So, you need to consider that in the structure of the mounting fixture. In addition, the weight of mounting structure is often more than the weight of dial indicator, take that in account!
> alignG is a non-contact measurement device; so, no worries about the spring-loaded force to displace it. In the other hand, it weighs only 20 grams. A strong magnet tape can simply keep a 20 gram gadget in place for a long time, except if you want to intentionally displace it. For sure, there are many ways to permanently attach a 20grams gadget to your extruder, if you want to install it for one time and leave it there. 
> 
> 
> “The device should have the option to trigger at some set height above the bed and it should have an output signal that can be directly connected to most 3D printer probe endstops. If it can do that and maintain accurate/repeatable readings, it would be a great contact-less bed leveling tool that can use the automatic bed leveling systems already built into most modern firmware like Marlin, Repetier, DuetWifi, etc. The location of the probe in reference to the tip of the nozzle is critical and must be a fixed distance. Without a rigid mount, the measurements would not be repeatable if the device moved.”
> ...


Some of your responses do not make any sense.  The response on the force needed on the dial indicator is absolutely ridiculous.  The force required is not the problem with metal tool bits.  The amount of force will not deform the tool bit.  However, if you mean the internal mechanisms inside the indicator may have backlash, that is a different story.  Every indicator has its accuracy levels, but the manufacturer states the accuracy on the spec.  You still haven't answered how an ultrasonic device can detect the tip of a cutting bit in reference to the tool holder (ie tormach, R8, etc).  The z plane is established to the tip of the tool to the top of a raw stock, not the bed on the mill.  

Another factor not mentioned is if the sensor has been calibrated against NIST standard instruments to establish your accuracy claims.  The problem I see is the angle of the ultrasonic sensor and detector are fixed, therefore, the arc angle varies in relation to the distance from the tip of the sensor to the surface.  Is this a linear signal that is returned or is the signal a non-linear curve?  If its non-linear, how is it calibrated?  At a fixed location or distance?  A range of distance to establish enough curve for the profile?  Does that accuracy change as a function of distance from the measuring object?  What is the distance range where this accuracy claim is spec'd for? Does the ultrasonic detector compensate for humidity, temperature, barometric pressure, etc that defines air density and compensates?  This is an important factor since the speed of sound varies in relation to air density.  If it doesn't compensate, measurements taken at hot environments with high humidity would not match the results from measurements at cold locations with low humidity.   The advantage that IR sensor has is the speed of light is not affected (or the effects are negligible) by these environmental factors.  The speed of sound, on the other hand, is definitely affected by the environment.

http://www.migatron.com/high-accuracy-sensor/

The reason I mention this is the RPS-412A high-accuracy ultrasonic sensor compensates for all these parameters and cost over $2000, and yet, they can only claim an accuracy of 50um maximum.   I like to see hard concrete accuracy results using established calibrated industry standards before I can accept what is claimed.  I know your spec is for "precision" and not "accuracy".   I understand the difference, but listing just the "precision" is not enough (repeatability of the measurement).  The measurement might be precise in that moment when you measure, but the accuracy could be off.  I would get getting different results on hot days vs cold days.  Getting repeatable measurements is not good enough to level the bed.  The measured distance needs to be accurate (and precise) since I need the sensor to be calibrated against my nozzle tip.  I don't want to keep changing my delta z probe height firmware setting depending on the temperature and humidity of my environment.  In case you didn't know, the IR sensor is spec'd to 0.01mm (10 um), so its more precise than your device.  

https://miscsolutions.wordpress.com/mini-height-sensor-board/

I saw on one of the FAQ that claims the device is accurate to 0.0015 cm (15 um).  Yet, the spec for precision is 15um to 25um.  That absolutely makes no sense at all.  Unless you mean the 15um only applies to the sensor spec'd at 15um and the 25um sensor's accuracy is 25um.  Even then, its a stretch to say the accuracy is higher than the precision level for the 25 um.  I can't be measuring something accurate to 15um when my measurements itself is varying up to 25um from one measurement to the next without moving the carriage.  It just doesn't make any sense.  If you said the sensor is precise to 15um, but only accurate to 25um, that is more believable.  I hope this is more of an oversight in terms of spec'ing the device properly.  A simple temperature cycling test with the device in a controlled chamber cycling between hot and cold (10F to 160F) can easily determine the accuracy claims.  If the measurements are within 15um in that condition, then it would prove the accuracy claims.

The autoleveling mechanism is the tool to keep the bed level.  Not only is the parameters used to calibrate out the level but adjust for any imperfections of the bed.  I don't understand your logic where you have 4 points in the corner (not clearly defied via Gcode) is more accurate than 40 measurements across the bed using precise and repeatable locations defined by the bed leveling algorithms that goes to the same spot every time you level.  In terms of checking each time, the process is to first establish the endstop positions using fixed length of rod (in the case of a delta machine).  At that point, the system will move the carriage to each point and directly read the Z height value on the computer or LCD screen.  You can adjust the endstops as needed if you want a pre-set height.  I don't see how your system is any different in terms of process other than a separate computer program to measure the height.  You can also take the data from the bed leveling and do a least squares fit to adjust for imperfections of the build such as Delta frame angles, the bed tilt, bed warpage, and so on.  The process has to go through several iterations if you want to get the height measurements within a narrow range.  These values are automatically fed back to the firmware to control the delta radius, end stop adjustments.  Every firmware has differences.  I hope you understand this is not just a check four corners and you are ready to go situation.

Adding a analog/I2C/USART interface sounds like a great idea, but why should it be end users or 3rd party developers making tools for it to work on a 3D printer?  If you are trying to sell this to 3D printer users, it should already have a pre-defined interface that works with the existing controller boards like Rumba, Duet, and firmware like Marlin, Reprap, Repetier, etc.  

I absolutely like the idea of having M3 mounting holes.  It would be great for users to mount the sensor in a rigid configuration.  

I am not here to crap on your thread.  I just want to get reasonable answers so other 3D users are informed.

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## Mjolinor

I think that temperature variation will kill it anyway unless you employ some very clever compensation techniques. You have minimum 10% variation in velocity with temperature and velocity is the main factor in any timing that you must use to measure distance. That temperature variation cannot be accounted for because it may go from 100 C at the head through a cold patch at (I guess) around 30C then back up to 60C as the signal approaches the bed. Once you had set the thing with a warm head and bed then the results would be way off with a cold head and bed so it would need setting for every different temperature you use and for every location on the bed as temperatures vary depending on where you are then once you have opened a door or walked round the room the air moves and your readings are wrong again.

You also have a small variation in the velocity depending on frequency so any frequency sweep method would need more compensation tables. If you use eg. 40 kHz then you have lambda of around 8mm. No way on earth can you distinguish how many wavelengths you are away without moving the bed up and down significant amounts and without knowing if the head will crash how can you know if you are one wavelength away or more.

I am watching with interest to see how you overcome some of these (and significant other) problems. I looked at doing this a couple of years ago as I have done significant design work in ultrasonic sensing, I abandoned the idea because the further in you go the more problems arise.

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## ShadowX

I agree.  Its not that it can't be done, but at what cost.  Its interesting that they claim they can compensate for environmental factors with doppler, phase difference, etc. It is a very challenging environment especially on a 3D printer with a heated bed. The hot end near the sensor may be at 240C and the bed is at 110C and the air surrounding the bed is at 25C with a fan blowing over it.  I would be shocked if the air density remains constant between the probe and the bed unless its a very short distance.  At least with a physical mechanical probe, you have a set known distance that shouldn't change.  Here, you are dependent on the sound waves travelling through air onto a hot surface and bouncing back.  It might work in a relatively short distance from the sensor, I just don't know.  They have to prove that it works and its reliable.

The 10F to 160F (-12C to 71C) is actually a very reasonable temperature swing that would accelerate the life cycle testing of the electronics.  Most high reliability electronics can handle those temperature swings within a limited amount of cycles (ie: 30 cycles).  You have to temp cycle it through the range and measure with a fixed calibrated height.  Its the only way you know what the measurements are doing in those environments.  At least you can do a plot and get an idea of the delta in readings and plot the change over time/temperature.  You may find out that its only accurate at a specific temperature range.  The accuracy and precision may even drift with the temperature swings.  If they claim something is accurate or precise to a certain level, the entire device, including sensor and the electronic components has to output a signal within those spec limits.  If the electronic components drift over temperature, even though the sensor is stable, the output would also drift.  You may end up having to source high precision components with low thermal drift to maintain the requirements.

I hope others are asking similar questions and getting honest answers.  I don't mind if someone doesn't know an answer, but if they give me a BS answer, I will be all over them in a short time.  They have three PhD graduates or candidates working on the project, so they should be able to answer some of these technical questions easily.  





> I think that temperature variation will kill it anyway unless you employ some very clever compensation techniques. You have minimum 10% variation in velocity with temperature and velocity is the main factor in any timing that you must use to measure distance. That temperature variation cannot be accounted for because it may go from 100 C at the head through a cold patch at (I guess) around 30C then back up to 60C as the signal approaches the bed. Once you had set the thing with a warm head and bed then the results would be way off with a cold head and bed so it would need setting for every different temperature you use and for every location on the bed as temperatures vary depending on where you are then once you have opened a door or walked round the room the air moves and your readings are wrong again.
> 
> You also have a small variation in the velocity depending on frequency so any frequency sweep method would need more compensation tables. If you use eg. 40 kHz then you have lambda of around 8mm. No way on earth can you distinguish how many wavelengths you are away without moving the bed up and down significant amounts and without knowing if the head will crash how can you know if you are one wavelength away or more.
> 
> I am watching with interest to see how you overcome some of these (and significant other) problems. I looked at doing this a couple of years ago as I have done significant design work in ultrasonic sensing, I abandoned the idea because the further in you go the more problems arise.

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## ralphzoontjens

I like the AlignG for bed leveling but find it a bit of a pricey mod just for that.
So I am wondering what else I can do with it. Any ideas?
It would already add some value if I could detect the neighborhood cat that enters the garden sometimes and starts digging into the flower boxes.

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## curious aardvark

thanks for the answers dsayan. 
I see how it works - it doesn't matter how far from the bed it is - because it lets you set the same distance at all points on the bed. 
And then you zero the device for future calibrations. 
That by itself would really help, particularly with the machine with three central levelling knobs. 

Any idea what the postage to the uk will be ?  presumably that's added to the actual kickstarter price ?

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## Mjolinor

If it works and is stable there is no reason why the signals from it cannot be used to make the Z axis closed loop at all heights rather than just using it for level at the start.

Now that would be an improvement as you could also vary layer height per layer, within the layer, dynamically if you needed to.

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## curious aardvark

> as you could also vary layer height per layer, within the layer, dynamically if you needed to.


and in english ?

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## Mjolinor

> and in english ?


Make a layer tapered.

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## ShadowX

> Make a layer tapered.


That what a slicer is for.  With Simplify 3D, you can define set layer thickness at different heights.   I know you are talking about changes within a layer, but I don't see how that can be accomplished without the slicer telling the controller where to change the height at a specific point.  

I would not trust an instrument like this to establish your z height and use it as a feedback loop for now.  If you calibrated your steps per mm accurately, there is no reason to do what you are saying unless you are skipping steps.  A servo motor control would be a better option.  I am not sure if most firmware even have the ability to use a closed feedback to adjust heights.  I mainly use reprap and I don't believe it has the ability, but I may be wrong.

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## dsayan

> Some of your responses do not make any sense. The response on the force needed on the dial indicator is absolutely ridiculous. The force required is not the problem with metal tool bits. The amount of force will not deform the tool bit. However, if you mean the internal mechanisms inside the indicator may have backlash, that is a different story. Every indicator has its accuracy levels, but the manufacturer states the accuracy on the spec. You still haven't answered how an ultrasonic device can detect the tip of a cutting bit in reference to the tool holder (ie tormach, R8, etc). The z plane is established to the tip of the tool to the top of a raw stock, not the bed on the mill. 
> 
> Another factor not mentioned is if the sensor has been calibrated against NIST standard instruments to establish your accuracy claims. The problem I see is the angle of the ultrasonic sensor and detector are fixed, therefore, the arc angle varies in relation to the distance from the tip of the sensor to the surface. Is this a linear signal that is returned or is the signal a non-linear curve? If its non-linear, how is it calibrated? At a fixed location or distance? A range of distance to establish enough curve for the profile? Does that accuracy change as a function of distance from the measuring object? What is the distance range where this accuracy claim is spec'd for? Does the ultrasonic detector compensate for humidity, temperature, barometric pressure, etc that defines air density and compensates? This is an important factor since the speed of sound varies in relation to air density. If it doesn't compensate, measurements taken at hot environments with high humidity would not match the results from measurements at cold locations with low humidity. The advantage that IR sensor has is the speed of light is not affected (or the effects are negligible) by these environmental factors. The speed of sound, on the other hand, is definitely affected by the environment.
> 
> http://www.migatron.com/high-accuracy-sensor/
> 
> The reason I mention this is the RPS-412A high-accuracy ultrasonic sensor compensates for all these parameters and cost over $2000, and yet, they can only claim an accuracy of 50um maximum. I like to see hard concrete accuracy results using established calibrated industry standards before I can accept what is claimed. I know your spec is for "precision" and not "accuracy". I understand the difference, but listing just the "precision" is not enough (repeatability of the measurement). The measurement might be precise in that moment when you measure, but the accuracy could be off. I would get getting different results on hot days vs cold days. Getting repeatable measurements is not good enough to level the bed. The measured distance needs to be accurate (and precise) since I need the sensor to be calibrated against my nozzle tip. I don't want to keep changing my delta z probe height firmware setting depending on the temperature and humidity of my environment. In case you didn't know, the IR sensor is spec'd to 0.01mm (10 um), so its more precise than your device. 
> 
> https://miscsolutions.wordpress.com/mini-height-sensor-board/
> ...


“Some of your responses do not make any sense. The response on the force needed on the dial indicator is absolutely ridiculous. The force required is not the problem with metal tool bits. The amount of force will not deform the tool bit. However, if you mean the internal mechanisms inside the indicator may have backlash, that is a different story. Every indicator has its accuracy levels, but the manufacturer states the accuracy on the spec. “
Which part of my response is “absolutely ridiculous”? Please be specific about what does not make sense. 
I’m not talking about the effect of applied force on the metal tool bits or backlash or precision of the dial indicator.  
The spring-loaded probe (or plunger) of the dial indicator applies a force (often about 1N - 3N) to the under-test surface. Based on the Newton’s third law of motion, the under-test surface also applies the same force in the opposite direction to the dial indicator. This force can cause the displacement of the dial indicator if it is not mounted very well. So, you need a rigid mounting structure to prevent that. If these 4 sentences look “absolutely ridiculous” to you, please let me know if you need more clarifications.

“You still haven't answered how an ultrasonic device can detect the tip of a cutting bit in reference to the tool holder (ie tormach, R8, etc). The z plane is established to the tip of the tool to the top of a raw stock, not the bed on the mill. “
The ultrasonic sensor, alignG, is a distance measurement sensor, not a tip detector. It measures the distance from any under test (target) surface. Like what a dial indicator does. It does the same job that inductive proximity or IR sensors do; but, with much higher precision. If you want to use it for the zeroing, you need to align it for the first time. Then you zero the reading of the sensor by software and mount the alignG in that position.

“Another factor not mentioned is if the sensor has been calibrated against NIST standard instruments to establish your accuracy claims. The problem I see is the angle of the ultrasonic sensor and detector are fixed, therefore, the arc angle varies in relation to the distance from the tip of the sensor to the surface. Is this a linear signal that is returned or is the signal a non-linear curve? If its non-linear, how is it calibrated? At a fixed location or distance? A range of distance to establish enough curve for the profile? Does that accuracy change as a function of distance from the measuring object? What is the distance range where this accuracy claim is spec'd for? “
It is not a simple narrow beam transmitted and reflected in a direct path. Ultrasonic is a wave, it has a distribution function based on the type of transducer we use. The ultrasonic transmitter transducer is a source of wave; the wave is distributed based on the diffraction theory. A portion of that wave is reflected from the target surface and returns to the received transducer. The received signal is not a single wave. It is the result of constructive and destructive interference of many waves. We know the coordinates of the wave source and the receiver. Knowing the amplitude/phase/Doppler data, we solve the diffraction equations for the distance. There is a complicated physics behind that, I really don’t want to go through all that here.

“Does the ultrasonic detector compensate for humidity, temperature, barometric pressure, etc that defines air density and compensates? This is an important factor since the speed of sound varies in relation to air density. If it doesn't compensate, measurements taken at hot environments with high humidity would not match the results from measurements at cold locations with low humidity. The advantage that IR sensor has is the speed of light is not affected (or the effects are negligible) by these environmental factors. The speed of sound, on the other hand, is definitely affected by the environment.”
alignG compensates for that. It does not mean that there is no effect; but, it is minimized. There are many ways to do that. The parameters that you mentioned, directly affect the transit time based ultrasonic sensors. We are not doing a transit time measurement. For Phase/Doppler measurement, there is a different story. Our measurement is not as simple as sending a pulse and measuring the time that it returns. There are many techniques employed by many researchers during past decades to minimize the effect of sound speed on the Doppler/Phase measurements. A simple search in google or IEEEXplore website will show you many practiced techniques including multi-frequency approach, T&R orientation, …
Any measurement instrument is sensitive to the temperature. We never claimed that we have an ideal sensor that solves all the problems for everybody on any condition. What are the sensors that you can use for auto bed leveling today? Please let me know the available choices. Which of them are not dependent to the temperature? Is an inductive proximity sensor or IR sensor kept several millimeters away from the hot bed not affected by its temp? You can keep alignG 10cm away from the bed and do the measurement.


“http://www.migatron.com/high-accuracy-sensor/
The reason I mention this is the RPS-412A high-accuracy ultrasonic sensor compensates for all these parameters and cost over $2000, and yet, they can only claim an accuracy of 50um maximum.”
The RPS-412A sensor does not cost them $2000, they sell it for $2000! 
However, the link that you posted is not showing what measurement technology is employed in this sensor. But, its structure and the shown parameters obviously (99% but not 100% sure) shows it is a transit time based transducer. A transit time ultrasonic transducer for 50-micron precision must be a high-frequency transducer. High-frequency transducers are expensive + high frequency wave gets damped in the air; so, you need an expensive precision high power system to provide enough energy to compensate for that + fabrication of acoustic lenses in that frequency is much complicated and costly + when designing a precision analog circuit for a 20X higher frequency, it is much more difficault + …  So, it costs them a lot and they sell it $2000
We developed a new measurement technology that allows for precision measurement without using expensive, high frequency transducers and circuits. Should we sell it for $2000 to you to believe its precision ??!! :-)

“ I like to see hard concrete accuracy results using established calibrated industry standards before I can accept what is claimed. I know your spec is for "precision" and not "accuracy". I understand the difference, but listing just the "precision" is not enough (repeatability of the measurement). The measurement might be precise in that moment when you measure, but the accuracy could be off. I would get getting different results on hot days vs cold days. Getting repeatable measurements is not good enough to level the bed. The measured distance needs to be accurate (and precise) since I need the sensor to be calibrated against my nozzle tip. “
The practical accuracy of the alignG is about twice its precision value in the recommended calibrated range of 1cm -10cm. 

“I don't want to keep changing my delta z probe height firmware setting depending on the temperature and humidity of my environment. In case you didn't know, the IR sensor is spec'd to 0.01mm (10 um), so its more precise than your device. 
https://miscsolutions.wordpress.com/...-sensor-board/“
If you really get 10 micron precision from your IR sensor, please forget alignG !
The strong comments and scientific questions that you are asking about our product shows that you have lots of knowledge in electrical engineering and measurement science. I’m surprised how you are that much sure about 10 micron precision of your IR sensor. 
An IR emitter (a temperature dependent P-N junction diode) probably in series connection with a current limiting (temperature dependent) resistor emits the light. In the surface of the bed you have refraction, scattering, and reflection issues; all of them depend on many parameters including the tilt angle of the bed, the surface roughness in that spot, the material ,…. The reflected light is detected by a detector (a temperature dependent P-N junction diode) then it probably has a voltage divider (temperature dependent) resistor and an op-amp to increase the slope and a second op amp to trigger on a threshold voltage. It has 10 micron precision? If you look at the link that you posted on your previous comment you see this sentence: “Reproducibility of repeated probing at same spot: approx. 0.01mm”
What does “at the same spot” mean? remember that we are talking about an optical device with the wavelength of about 800nm. Does your XYZ stage has that much repeatability to keep the sensor at the same spot? What is happening if in the next measurement your sensor is positioned 1 micron away from the previous point? Is scattering of the light on the surface changed? What if your bed is not perpendicular, is it affecting the reflection and changes the intensity of the detected light?
Does IR sensors measure the distance or you move your z-stage to find the zero? What is the accuracy of the Z-stage in your 3D printer? Have you ever measured the backlash of the Z-stage? How can we have 10 micron precision when most of the 3D printers in the market have above 50 micron backlash?

“I saw on one of the FAQ that claims the device is accurate to 0.0015 cm (15 um). Yet, the spec for precision is 15um to 25um. That absolutely makes no sense at all. Unless you mean the 15um only applies to the sensor spec'd at 15um and the 25um sensor's accuracy is 25um. Even then, its a stretch to say the accuracy is higher than the precision level for the 25 um. I can't be measuring something accurate to 15um when my measurements itself is varying up to 25um from one measurement to the next without moving the carriage. It just doesn't make any sense. If you said the sensor is precise to 15um, but only accurate to 25um, that is more believable. I hope this is more of an oversight in terms of spec'ing the device properly. A simple temperature cycling test with the device in a controlled chamber cycling between hot and cold (10F to 160F) can easily determine the accuracy claims. If the measurements are within 15um in that condition, then it would prove the accuracy claims.”
The accuracy of the device is not 15 micron. If it has been written anywhere in our page, certainly it is not true and needs to be corrected, I apologize for that mistake. I highly appreciate if you let me know in what FAQ you observed that. I could not find it. 
“The autoleveling mechanism is the tool to keep the bed level. Not only is the parameters used to calibrate out the level but adjust for any imperfections of the bed. I don't understand your logic where you have 4 points in the corner (not clearly defied via Gcode) is more accurate than 40 measurements across the bed using precise and repeatable locations defined by the bed leveling algorithms that goes to the same spot every time you level. “
We never claimed that a 4 point leveling is more accurate than 40 point measurement. For sure 40 point leveling is much better. 

“In terms of checking each time, the process is to first establish the endstop positions using fixed length of rod (in the case of a delta machine). At that point, the system will move the carriage to each point and directly read the Z height value on the computer or LCD screen. You can adjust the endstops as needed if you want a pre-set height. I don't see how your system is any different in terms of process other than a separate computer program to measure the height. You can also take the data from the bed leveling and do a least squares fit to adjust for imperfections of the build such as Delta frame angles, the bed tilt, bed warpage, and so on. The process has to go through several iterations if you want to get the height measurements within a narrow range. These values are automatically fed back to the firmware to control the delta radius, end stop adjustments. Every firmware has differences. I hope you understand this is not just a check four corners and you are ready to go situation.
Adding a analog/I2C/USART interface sounds like a great idea, but why should it be end users or 3rd party developers making tools for it to work on a 3D printer? If you are trying to sell this to 3D printer users, it should already have a pre-defined interface that works with the existing controller boards like Rumba, Duet, and firmware like Marlin, Reprap, Repetier, etc. “
As explained in my previous post, we have a limited resource, time, and forces here. We can’t build software for every things and release it for end users on April 2016. We will consider that for future updates of our software.

“I absolutely like the idea of having M3 mounting holes. It would be great for users to mount the sensor in a rigid configuration.
I am not here to crap on your thread. I just want to get reasonable answers so other 3D users are informed.”
Thanks for all fantastic questions and comments. We are here to get feedback and learn from people who have experience in working with 3D printer and CNC. I will be more than happy to receive more comments. Thanks for your time.

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## dsayan

> I think that temperature variation will kill it anyway unless you employ some very clever compensation techniques. You have minimum 10% variation in velocity with temperature and velocity is the main factor in any timing that you must use to measure distance. That temperature variation cannot be accounted for because it may go from 100 C at the head through a cold patch at (I guess) around 30C then back up to 60C as the signal approaches the bed. Once you had set the thing with a warm head and bed then the results would be way off with a cold head and bed so it would need setting for every different temperature you use and for every location on the bed as temperatures vary depending on where you are then once you have opened a door or walked round the room the air moves and your readings are wrong again.
> 
> You also have a small variation in the velocity depending on frequency so any frequency sweep method would need more compensation tables. If you use eg. 40 kHz then you have lambda of around 8mm. No way on earth can you distinguish how many wavelengths you are away without moving the bed up and down significant amounts and without knowing if the head will crash how can you know if you are one wavelength away or more.
> 
> I am watching with interest to see how you overcome some of these (and significant other) problems. I looked at doing this a couple of years ago as I have done significant design work in ultrasonic sensing, I abandoned the idea because the further in you go the more problems arise.


I think that temperature variation will kill it anyway unless you employ some very clever compensation techniques. You have minimum 10% variation in velocity with temperature and velocity is the main factor in any timing that you must use to measure distance. That temperature variation cannot be accounted for because it may go from 100 C at the head through a cold patch at (I guess) around 30C then back up to 60C as the signal approaches the bed. Once you had set the thing with a warm head and bed then the results would be way off with a cold head and bed so it would need setting for every different temperature you use and for every location on the bed as temperatures vary depending on where you are then once you have opened a door or walked round the room the air moves and your readings are wrong again.”
alignG compensates for the temperature gradient. It does not mean that there isnt any effect; but, it is minimized. There are many ways to do that. But, please don’t make it that much bold. In the worst condition, after compensation, we may have less than 20% change in the accuracy. In the other hand, it is a systematic error in the measurement; if you always do the measurement on a bed with 120C, you will get an approximately consistent result; so, it does not really matter. But if you plan always to play with the bed temperature during the bed leveling, that’s a different deal. You do not also have to do the measurement when the extruder and bed are hot if you are that much concerned.
The parameters that you mentioned, directly affect the transit time based ultrasonic sensors. We are not doing a transit time measurement. For Phase/Doppler measurement, there is a different story. Our measurement is not as simple as sending a pulse and measuring the time that it returns. There are many techniques employed by many researchers during past decades to minimize the effect of sound speed on the Doppler/Phase measurements. A simple search in google or IEEEXplore website will show you many practiced techniques including multi-frequency approach, T&R orientation, …
Any measurement instrument is sensitive to the temperature. We never claimed that we have an ideal sensor that solves all the problems for everybody on any condition. What are the sensors that you can use for auto bed leveling today? Please let me know the available choices. Which of them are not dependent to the temperature? Is an inductive proximity sensor or IR sensor kept several millimeters away from the hot bed not affected by its temp? You can keep alignG 10cm away from the bed and do the measurement.

“You also have a small variation in the velocity depending on frequency so any frequency sweep method would need more compensation tables. If you use eg. 40 kHz then you have lambda of around 8mm. No way on earth can you distinguish how many wavelengths you are away without moving the bed up and down significant amounts and without knowing if the head will crash how can you know if you are one wavelength away or more.
I am watching with interest to see how you overcome some of these (and significant other) problems. I looked at doing this a couple of years ago as I have done significant design work in ultrasonic sensing, I abandoned the idea because the further in you go the more problems arise.”
Does the sound velocity depend on its frequency? 
No way on earth? Seriously?

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## dsayan

> I agree. Its not that it can't be done, but at what cost. Its interesting that they claim they can compensate for environmental factors with doppler, phase difference, etc. It is a very challenging environment especially on a 3D printer with a heated bed. The hot end near the sensor may be at 240C and the bed is at 110C and the air surrounding the bed is at 25C with a fan blowing over it. I would be shocked if the air density remains constant between the probe and the bed unless its a very short distance. At least with a physical mechanical probe, you have a set known distance that shouldn't change. Here, you are dependent on the sound waves travelling through air onto a hot surface and bouncing back. It might work in a relatively short distance from the sensor, I just don't know. They have to prove that it works and its reliable.
> 
> The 10F to 160F (-12C to 71C) is actually a very reasonable temperature swing that would accelerate the life cycle testing of the electronics. Most high reliability electronics can handle those temperature swings within a limited amount of cycles (ie: 30 cycles). You have to temp cycle it through the range and measure with a fixed calibrated height. Its the only way you know what the measurements are doing in those environments. At least you can do a plot and get an idea of the delta in readings and plot the change over time/temperature. You may find out that its only accurate at a specific temperature range. The accuracy and precision may even drift with the temperature swings. If they claim something is accurate or precise to a certain level, the entire device, including sensor and the electronic components has to output a signal within those spec limits. If the electronic components drift over temperature, even though the sensor is stable, the output would also drift. You may end up having to source high precision components with low thermal drift to maintain the requirements.
> 
> 
> I hope others are asking similar questions and getting honest answers. I don't mind if someone doesn't know an answer, but if they give me a BS answer, I will be all over them in a short time. They have three PhD graduates or candidates working on the project, so they should be able to answer some of these technical questions easily.


”I agree. Its not that it can't be done, but at what cost. Its interesting that they claim they can compensate for environmental factors with doppler, phase difference, etc. It is a very challenging environment especially on a 3D printer with a heated bed. The hot end near the sensor may be at 240C and the bed is at 110C and the air surrounding the bed is at 25C with a fan blowing over it. I would be shocked if the air density remains constant between the probe and the bed unless its a very short distance. At least with a physical mechanical probe, you have a set known distance that shouldn't change. Here, you are dependent on the sound waves travelling through air onto a hot surface and bouncing back. It might work in a relatively short distance from the sensor, I just don't know. They have to prove that it works and its reliable.
The 10F to 160F (-12C to 71C) is actually a very reasonable temperature swing that would accelerate the life cycle testing of the electronics. Most high reliability electronics can handle those temperature swings within a limited amount of cycles (ie: 30 cycles). You have to temp cycle it through the range and measure with a fixed calibrated height. Its the only way you know what the measurements are doing in those environments. At least you can do a plot and get an idea of the delta in readings and plot the change over time/temperature. You may find out that its only accurate at a specific temperature range. The accuracy and precision may even drift with the temperature swings. If they claim something is accurate or precise to a certain level, the entire device, including sensor and the electronic components has to output a signal within those spec limits. If the electronic components drift over temperature, even though the sensor is stable, the output would also drift. You may end up having to source high precision components with low thermal drift to maintain the requirements.
I hope others are asking similar questions and getting honest answers. I don't mind if someone doesn't know an answer, but if they give me a BS answer, I will be all over them in a short time. They have three PhD graduates or candidates working on the project, so they should be able to answer some of these technical questions easily. “
alignG compensates for the temperature gradient. It does not mean that there is no effect; but, it is minimized. There are many ways to do that. But, please don’t make it that much bold. In the worst condition, after compensation, we may have less than 20% change in the accuracy. In the other hand, it is a systematic error in the measurement; if you always do the measurement on a bed with 120C, you will get an approximately consistent result; so, it is not really matter. But if you plan to always play with the bed temperature during the bed leveling, that’s a different deal. You are not also have to do the measurement when the extruder and bed are hot, if you are that much concerned.
The parameters that you mentioned, directly affect the transit time based ultrasonic sensors. We are not doing a transit time measurement. For Phase/Doppler measurement, there is a different story. Our measurement is not as simple as sending a pulse and measuring the time that it returns. There are many techniques employed by many researchers during past decades to minimize the effect of sound speed on the Doppler/Phase measurements. A simple search in google or IEEEXplore website will show you many practiced techniques including multi-frequency approach, T&R orientation, …
Any measurement instrument is sensitive to the temperature. We never claimed that we have an ideal sensor that solves all the problems for everybody on any condition. What are the sensors that you can use for auto bed leveling today? Please let me know the available choices. Which of them are not dependent to the temperature? Is an inductive proximity sensor or IR sensor kept several millimeters away from the hot bed not affected by its temp? You can keep alignG 10cm away from the bed and do the measurement.

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## Mjolinor

You need to sort out your quoting and your original text, your posts are too long and confusing.

Sound velocity varies with frequency. Air does not always act adiabatically and that makes the velocity change slightly.

Anyway, I am not trying to tell you it won't work I am really just interested to see if you can do it or not.

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## dsayan

> You need to sort out your quoting and your original text, your posts are too long and confusing.
> 
> Sound velocity varies with frequency. Air does not always act adiabatically and that makes the velocity change slightly.
> 
> Anyway, I am not trying to tell you it won't work I am really just interested to see if you can do it or not.


That is true. Unfortunately, when I receive a half a page long comment including 10 different question, I have to write a long response. I highly appreciate if everybody only targets a specific question to have a clearer discussion to learn from each other.

Air does not always act adiabatically and that makes the velocity change slightly. I totally agree with that. But I’m not sure If I understood your point about the frequency sweep. If you are talking about the dependence of the speed on the frequency in dispersive medium, that is not really relevant to our case. On the other hand, I’m not still sure if I understand where does the frequency variation coming from. Why should we have a frequency variation? Are you talking about the Doppler effect? Please be more specific about that question.

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## Mjolinor

There was no question other than "why are you quoting twice" in each response that you make. I was stating some of the easier to understand things that I think you will find hard to do.

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## ralphzoontjens

I have seen discussions on bed leveling at several forums, you may want to reach out there to get more backers, for example the UM forum at https://ultimaker.com/en/community

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