Linear hall effect Z-height sensing

Mickyblueeyes

Linear hall effect Z-height sensing
February 13, 2014 09:12AM

Registered: 10 years ago
Posts: 49

One other possibility is using a low cost linear hall effect sensor such as the one detailed in the attachment, this can be used in 2 ways either by embedding small magnets just below the glass or by putting a magnet behind the sensor and sensing a thin layer or strip of magnetic material on or below the glass both methods would be none contact.

I currently use the above to sense movement in an ac coupled sensor design and they have proved to be very reliable.

Regards

Mike

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Attachments:
open | download - 8247.pdf (267.5 KB)

Marc van Beelen

Re: Linear hall effect Z-height sensing
February 13, 2014 11:47AM

Registered: 10 years ago
Posts: 28

Why not? Only remark could be that you need a pretty flat (small) magnets when placed in the bed and detection range should be sufficiant.
Also be aware that is you would like to use the auto bed leveling (G32) that all magnets need to be detected at the same height (I guess positioning exactly in the middle).

Good luck

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Mickyblueeyes

Re: Linear hall effect Z-height sensing
February 13, 2014 11:53AM

Registered: 10 years ago
Posts: 49

For me it would be ideal because I have an aluminium bed fixed at 4 points on a wider set of rails so I only need to set the z height on one corner as the others have been accurately levelled and do not move.

regards

mike

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Radian

Re: Linear hall effect Z-height sensing
February 14, 2014 07:50AM

Registered: 10 years ago
Posts: 300

Might be worth a try, you can get magnetic sheet (A4 inkjet printable for example) that could replace the heat spreader. Not sure how it would stand up to being heated though.

RS Components Reprap Ormerod No. 481

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tru168

Re: Linear hall effect Z-height sensing
February 15, 2014 12:50AM

Registered: 10 years ago
Posts: 176

One problem is, the magnets just under the heated bed will degrade quite fast, because of the heat from heated bed. Unless you print only PLA which require only 60 degree. C .

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Mickyblueeyes

Re: Linear hall effect Z-height sensing
February 15, 2014 04:11AM

Registered: 10 years ago
Posts: 49

Hi tru168 I was more thinking a very thin sheet of steel under the glass and putting a magnet behind the sensor the steel will alter the path of the magnetic field as it aproaxhes the steel plate, the steel can either be just at the corners or over the entire bed.

Regards

Mike

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tru168

Re: Linear hall effect Z-height sensing
February 15, 2014 11:11AM

Registered: 10 years ago
Posts: 176

Hi Mickyblueeyes ,
let us know how it turns out, I have several hall effect sensors in my parts bin, will try to find suitable magnet to experiment with.

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Chris1965

Re: Linear hall effect Z-height sensing
February 18, 2014 10:58AM

Registered: 10 years ago
Posts: 10

Hi
Found this www.reprap.org/wiki/Hall-Endstop if this helps. Found one on eBay to experiment with
I thought of putting removable bed with the magnets in or a small bed that moves with the hot end with the same magnet in.

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Mickyblueeyes

Re: Linear hall effect Z-height sensing
February 19, 2014 09:33AM

Registered: 10 years ago
Posts: 49

Hi Chris1965 I couldn't check the link but it sounds like a hall effect proximity switch which will simply switch an output when a set level is reached, what I was looking for was an analogue output so that the device would replace the current IR sensor and allow for bed compensation.

regards

mike

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Chris1965

Re: Linear hall effect Z-height sensing
February 19, 2014 10:06AM

Registered: 10 years ago
Posts: 10

Hi Mickyblueeyes
This can be used as a digital or analogue and looking at drawing both at the same time.
Try this link [reprap.org]

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Attachments:
open | download - HallOS.JPG (68 KB)
open | download - Endstop600.jpg (120.5 KB)

Mickyblueeyes

Re: Linear hall effect Z-height sensing
February 19, 2014 12:23PM

Registered: 10 years ago
Posts: 49

Hi Thanks for that, the circuit uses the same basic sensor element that I have here but not quite the circuit I need so I will go ahead and design something myself, the main problem with the design shown is that the analogue output change will be fairly small in my application and also I would prefer to have an on board psu to derive the 5V as the sensor is ratiometric it will suffer from variations and noise from the duet 5V supply.

Best regards

Mike

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dc42

Re: Linear hall effect Z-height sensing
February 19, 2014 03:31PM

Registered: 10 years ago
Posts: 14,672

Quote
Mickyblueeyes
Hi Thanks for that, the circuit uses the same basic sensor element that I have here but not quite the circuit I need so I will go ahead and design something myself, the main problem with the design shown is that the analogue output change will be fairly small in my application and also I would prefer to have an on board psu to derive the 5V as the sensor is ratiometric it will suffer from variations and noise from the duet 5V supply.

Don't forget that the ADC on the Duet is ratiometric too. So if you can run your Hall sensor from the 3.3V supply, and amplify the output from it using a 3.3V rail-to-rail op amp, then supply voltage changes will cancel out.

OTOH I'm not sure that you will be able to get a sufficiently consistent magnetic field for a Hall sensor to be a reliable mechanism for height sensing.

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].

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