Hi, I'm thinking of putting limit switches on my X Y and Z axes, and am considering using hall-effect sensors on the machine frame with little magnets mounted on the moving axes.
Has anyone done this or have any input on doing this?
It seems to be a good system with no moving parts and since I don't machine ferrous metals I can't see a down side.
One of the best features is that they allow overtravel so I can put them some distance back from the end of the travel. So even if the steppers have had a major misalignment it can be easily detected with no chance of hitting the end stops.
There is some digital type hall effect switches, like allegro A11xx series.
Really simple to use but need 3 wires and not as rugged as simple switches.
They have no bounce but switch position can be tricky to adjust.
Ive considered using prox switches but have yet to start the build
Is the voice in my head bothering you?
read in one of the threads around here that they were popular in the joecnc fourms. might want to check there.
You can definitely get digital output hall sensors like mchabot said. But I'm not bothered by having to hook up a support circuit if it comes to that.
Zygoat- I'll check the joecnc forums, thanks for the tip.
Yes, several people are using them now, and I will also be using them on my new Rack and pinion machine.
joecnc2006 at yahoo
Hey Joe, (please ignore pop-culture Hendrix reference ) do you have a link to a thread etc discussing the sensor types and mounting details?
The only thread I found was a real old one in the general electronics discussion section.
Kent, Made a writeup with pictures for the members which remains on my site for our members, but here is a quick excert from the writeup, with just a little research you can get them working easily.
Hall Effect Limit Switches
A Hall Effect (HE) transistor switches when in the presence of a magnetic field. They can be used to replace micro-switches to implement very accurate and reliable limit switches on a CNC machine. However, if the machine is used to cut ferrous metals, the swarf will be attracted to the magnets which will interfere with the trigger point of the switch. Therefore, they should only be used on machines that do not cut ferrous metals.
I recently implemented HE limit switches on all three axes. The repeatability of these switches is better than I can measure with a dial indicator which means they are performing better than 0.001”. I chose to make the magnet stationary with the HE mounted to the moving carriage (you could also make the switch permanent and the magnet mobile if you prefer). I placed at each end of the axis, thus only one switch was required per axis thereby reducing wiring.
joecnc2006 at yahoo
Suggest you use the low price inductive proximity switches as these do not suffer from fouling with bits of stray steel. These switches are available from China via ebay for arround £6 each and I have been using them for the last 12 months with no problems for both limits and zeroing switches. These switches are available in different styles and are fully fluid proof and contain an indicator light to show the switch state.
Here is a link for a sale that is current.
The point to note is that the distance in the data sheet for different materials is the gap between sensor and the operating block not the switching accuracy.
For my money the inductive and capacitive proximity sensors have replace mechanical microswitches, magnetic hall effect and optical devices for most applications with the possible exception of high speed shaft rotation measurements.
Hope this helps - regards Pat
Last edited by wildwestpat; 02-28-2010 at 02:29 PM. Reason: changed link to one that is China sourced
I'm using them on my machine and they work fantastic! I have them wired directly to my G540, no other circuitry was necessary. I don't have the schematic handy, Mariss told me how to connect them. If you have a G540 contact him and I'm sure he can tell you how to wire them up.