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Proximity Detectors
« on: March 29, 2014, 01:17:21 PM »
1. I'm planning to use proximity detectors for limit and home on my mill.  Any suggestions as to which ones to get?
2. I realize this is a Mach 3 forum and question #1 probably belongs somewhere else.  Please point me to your favorite forums for milling machines and controllers. 

thanks much, rex
Re: Proximity Detectors
« Reply #1 on: March 29, 2014, 11:20:23 PM »
Unless you can completely protect them from chips and swarf, you might want to reconsider.  Prox sensors WILL trigger on chips, even aluminum chips.  I would recommend optical sensors, or plain old switches.

Regards,
Ray L.
Regards,
Ray L.
Re: Proximity Detectors
« Reply #2 on: March 30, 2014, 11:29:33 AM »
That was a recommendation from someone else, but what you say makes sense.  I'm still a newbie and looking for the right stuff.  Any recommendations for sensors I should be looking at?
Re: Proximity Detectors
« Reply #3 on: March 30, 2014, 12:22:33 PM »
Unless your'e looking for extreme accuracy (in which case you're probably kidding yourself about the machines capability....), plain old high-quality microswitches work great, and are cheap and simple.  Next step up is optical switches.  Hall Effect switches are also good, but, like prox switches, must be protected.  There are tons of designs available on CNCZone's Benchtop Machines forum, and others.

Regards,
Ray L.
Regards,
Ray L.
Re: Proximity Detectors
« Reply #4 on: March 30, 2014, 12:50:44 PM »
I'm with Ray,

  A good quality sealed snap action microswitch is very practical.
Even the medium quality ones I've used are repeatable to less than .0002"

Russ

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Re: Proximity Detectors
« Reply #5 on: March 30, 2014, 03:43:07 PM »
Thinking that a mechanical switch or optical sensor is going to be more trouble free than a proxy sensor is folly. Any sort of contamination that will interfere with a prox sensor will be at least 100x as good at interfering with a mechanical/optical device. There are some accurate and repeatable mechanical switches out there be prepared to pay about $50 for one. They work well when covered from direct contamination and are simple to wire up but still require a mechanical actuator making installation more difficult. I did some testing a few months ago on three different micro-switches that are commonly used on home brew DNC machines. I put together a rig so I could very precisely measure where the switch actuated and released. You can find the paper I wore on it in the documentation section of my website.

Optical sensor can be very accurate but get dirty very easily and are very sensitive to temperature (one that works great at 70F may not work properly at 40F). If the machine is in a relatively temperature environment and can be kept clean it is a good choice. It still needs a precisely aligned actuator/flag so it is harder to install.

A proxy sensor is sealed, has no mechanical actuator and is easy to mount. They are used on a whole lot of industrial machines as well. In the next few weeks I'm going to set up to test prox sensors shielded and unshielded with different target types to see what the accuracy and repeatability is like.
Happy machining , Jeff Birt
 
Re: Proximity Detectors
« Reply #6 on: March 30, 2014, 04:30:10 PM »
 Any sort of contamination that will interfere with a prox sensor will be at least 100x as good at interfering with a mechanical/optical device.  

There's some real folly for ya. :D

100x ? ? ? Really ?

An inductive or capacitive proximity sensor will see stuff that a button actuated limit switch will not.
A pinched chunk of crap, OK but that would not constitute 100x.  :)

Some folks like to sell the additional hardware sometimes associated with prox's also.

Russ  :)

« Last Edit: March 30, 2014, 06:43:57 PM by Overloaded »
Re: Proximity Detectors
« Reply #7 on: March 30, 2014, 06:27:45 PM »
Thinking that a mechanical switch or optical sensor is going to be more trouble free than a proxy sensor is folly. Any sort of contamination that will interfere with a prox sensor will be at least 100x as good at interfering with a mechanical/optical device. There are some accurate and repeatable mechanical switches out there be prepared to pay about $50 for one. They work well when covered from direct contamination and are simple to wire up but still require a mechanical actuator making installation more difficult. I did some testing a few months ago on three different micro-switches that are commonly used on home brew DNC machines. I put together a rig so I could very precisely measure where the switch actuated and released. You can find the paper I wore on it in the documentation section of my website.

Optical sensor can be very accurate but get dirty very easily and are very sensitive to temperature (one that works great at 70F may not work properly at 40F). If the machine is in a relatively temperature environment and can be kept clean it is a good choice. It still needs a precisely aligned actuator/flag so it is harder to install.

A proxy sensor is sealed, has no mechanical actuator and is easy to mount. They are used on a whole lot of industrial machines as well. In the next few weeks I'm going to set up to test prox sensors shielded and unshielded with different target types to see what the accuracy and repeatability is like.

It is very easy to totally enclose a microswitch, and not much more so an optical sensor.  Totally enclosing a prox sensor, and its inductive "flag" is much more difficult, not least because of their much larger size.  On commercial machines, they are either totally enclosed, or mounted in a location where they are sufficiently protected that such enclosure is not required.  On small machines, mounting options are FAR fewer, due, if nothing else, to the small size of the machines themselves.  A sealed microswitch and enclosure can be very small indeed.

Regards,
Ray L.
Regards,
Ray L.
Re: Proximity Detectors
« Reply #8 on: March 30, 2014, 07:14:10 PM »
I use to have problems with proximity switches on my mill. My work is probably 99.99% in aluminum and if a piece of aluminum would find it's way to the switch, I would get a fault. I rectified the problem by following a tip by Ray L. himself.

Ray mentioned placing the sensor in a protective case. I just super glued a piece of plastic on the sensor, just thick enough to keep aluminum chips from setting off the faults....but, still have the limits work with my steel stops.





Mind you, this works great since all i do is aluminum  ;D

pete