Thread: Hall effect proximity sensors
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24-06-2019 #21
Hey, if you don't need it or want it don't do it! :D
With decent screws and nuts I think a repeatability of 5 microns isn't out of reach, or even difficult, that's where I'm aiming with my next build, machining accuracy is likely to be closer to 15 but if you aim low you're bound to achieve shite results! :DLast edited by magicniner; 24-06-2019 at 05:56 PM.
You think that's too expensive? You're not a Model Engineer are you? :D
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24-06-2019 #22
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24-06-2019 #23
I’ve just skim read this thread (funny in places !) so my answer to the first question which I think was essentially can I use Hall effect sensors instead of proximity sensors for homing -
They require a magnet to get close to the target to trigger and so like all magnets in the workshop will grow metal hairs and become unreliable. I have one to play with on my new E-kart foot throttle. Great if the magnet and sensor can be sealed in a box but I think one part must ride on the gantry for CNC machines if they are the sole sensor so they can’t be protected.
However for the auxiliary use as discussed they can be enclosed on the end of the stepper shaft at the rear of the motor or off the ballscrew and be sealed off. (Like the twist throttle of an electric bike).
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24-06-2019 #24
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24-06-2019 #25
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24-06-2019 #26
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25-06-2019 #27
Just out of interest, I thought I would see where the stepper positions itself with repeated homings using an inductive proximity sensor and a 5mm pitch leadscrew.
https://www.dropbox.com/s/xayeqtbo8l...P0009.AVI?dl=0
The video shows the stepper coming back to the same angular position and I tried it out 6 times with the same result, before I set up the camcorder.
I will leave you to draw your own conclusions about the necessity for a chopper
Cheers
Rob-T
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25-06-2019 #28
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25-06-2019 #29
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25-06-2019 #30
I am sorry that my camcorder was too close (AND TOO CHEAP) to sharply define the image. However, I do believe that the definition was enough to allow you to observe that the stop point of the stepper was within a few degrees. In fact, I thought that it probably stopped at the same point and a stepper motor, when energised by hold current, would settle at the same point on the step. My crude test would probably indicate +/- 1.8 deg and if you regard it as valuable, you may like to repeat the experiment with more accurate indication of the angle that the stepper motor settles on.
I am interested in knowing more about hold points and microstepping, but even if the homing point is one full step either way, then on a 5mm pitch screw you have a positional error of +/-0.025mm, which is good enough for woodwork.
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