Reply with QuoteGuys, if any one needs small neodymium magnets, try looking in old CD-rom drives there are two at both sides of the laser.
Excellent! Thanks for the info! Your distinctiveness has been added to our own (sorry that's a little sci-fi joke).
That's a perfect mounting choice for those 6mm magnets (I'm assuming they are the 6mm diameter x 1.5mm thick common Ebay style) as they are high field strength from the front but being thin they give quite a fast field transition then the sensor passes the thin edge (ie slide-by 90' mounting). You could probably detect much better than 0.01mm precision with them.
Guys, if any one needs small neodymium magnets, try looking in old CD-rom drives there are two at both sides of the laser.
Reed switch
Hello, I am not sure a reed switch works the same way as the switch in this thread. I am having problems with a switch that retracts the tool magazine in my machine. The switch is mounted outside the piston cylinder and when it activates the magazine retracts. Would it be a good idea to go DIY?
http://www.boschrexroth.com/pneumati..._p41066_en.pdf
This is the spec sheet for the part number. The machine I have is an Okuma ES-V3016
Thank you.
Reed sensors should work. I've played with the Hamlin reed sensor (see attached) and they work. The accuracy is as good as the hall effect sensor with the added benefit of not having to need a power source. Also, you can get them as Normally Closed vs the Normally Open switch for the hall effect sensor.Originally Posted by brujo
Not sure about effect of temperature but from the searches I've done, reed sensors don't seem to be affected by temperature.
Reed switches will work as home and limit switches but I would never expect the accuracy you can get from the hall sensor.
The reed switch is mechanical and may be subject to contact wear and spring wear, also they are not temperature compensated and because they mechanically move to make a contact they perform differently with different changes in field strength over time, ie if your machine moves fast the reed switch will operate at a slightly different point than if the machine is moving slowly.
I agree their simplicity might make them attractive but really they are a big step down in performance. Considering that the hall switches are only a couple of dollars each (or less) and a few people have already posted DXF files of the mounts you can cut for free, I would really advise just going for the best right from the start.
Reed switches are better suited for simple applications like detecting when the burglar opens your door.
I was originally going to use the hall sensors for my homing switches and the reed sensors for my limit switches. But after testing the reed sensors, I didn't see any difference between the two.
Can you give more specifics on how they are a big step down in performance?
On another topic, I replaced the mechanical relay turning my VFD on/off with an electronic one. But when I turn the VFD on and then turn it off, the VFD just slows down a lot instead of turning completely off. I'm thinking that the relay 'leaks' even if it's turned off? Is this true for electronic relays in general or do I just have a bad one?
Thanks!
Never mind. I was reading your post on my email and somehow the thing is truncated. Now that I'm reading your whole post, I see that you've described why reed switches are inferior to hall effect switches.
The wear and tear should not be a problem for hobbyists as I seem to remember that they last for billions of operations (compared to almost infinite for hall effect sensors). Temperature wise, the specs said that they are not affected unless they're operating outside the specified temperature range. But the speed at which they respond to a fast machine may be a different matter.
I'll take your advise and use hall effect sensors for my homing switches and use the reed sensors for my limit switches. That was my originally plan anyway. :-)
Thanks.
Hi, re the electronic relay some types are not great at switching fussy loads. Your VFD is probably in that category as it's most likely a capacitive or inductive load.
You could try a different type of electronic relay, one specifically rated for motor control or inductive load control. Do you need to switch the VFD off? I assumed they have spinlde on/off control as a standard feature and you would just leave it on.
Re the reed switches, they have failed on me in a few situations. Sometimes corrosion or erosion of the contacts, sometimes they are fussy regarding the amount of current. Too much and the contacts burn, too little and they fail open circuit. And I've seen units mechanically fail from cyclic use in encoders although that is unlikely with the low frequency from machine homing or limits.
Thanks, Roman. I tried another electronic relay and got the same result. Installed my old mechanical relay and the problem went away.
My spindle is turned on and off by the g-code that I'm running that in turn switches the relay on and off.
Why would you switch the incoming power on/off to a VFD other than E-stop etc, every time you run it it has to go through the power up sequence, A contactor style relay should be used on the power input and the run/fwd/rev/ inputs used for control?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I don't switch the incoming power on/off to the VFD using a relay. The VFD is turned on by a manual switch.
The relay is connected to the VFD fwd input that is used to turn on/off the spindle - like you said. Using an electronic relay connected to the VFD FWD input does not turn off my spindle once I turn it on. It stays and couldn't turn it off by g-code or Mach 3. Don't have this problem with an electro-mechanical relay.
Oh, went back to my earlier post and I guess I did say that I'm using a relay to turn my VFD on/off. My bad. I meant my spindle. Sorry for the confusion.
Man 23 pages and I am lost beyond belief. I understand how to make the hall sensors but hooking up to my g540 I am completely and utterly confused.
First if I understand the schematic on the g540 there are only 4 inputs, so how are you guys wiring all 6 sensors, "in series"?????
Also where did everyone figure out how to pull the 5v from the g540, or is there a better way to get the power elsewhere.
These sensors will work from other voltages too, like 12v if that is more readily available for you.
I prefer 5v, and many people obtain a regulated 5v from their PC, from a USB port.
Regarding the multiple sensors, they can be wired in parallel, so the output wires from a number of sensors can be safely joined. Just make sure your software has the ability to know which sensor was tripped, which it needs to calculate based on the direction the machine was moving.
The sensors mentioned are "open drain" so you can wire them in parallel.
Of course, one really simple idea is one sensor, two magnets. Mount the sensor on the moving part of the axis and the magnets on either end of the axis. That gets you to 3 inputs.
I use an external 12V supply. The G540 has an internal pullup resistor to 12V. I'm uncomfortable having the input at a higher voltage than the supply voltage. I just used an old wall wart I had hanging around from some long gone device
Does anyone have a good source for wire to use with these switches?
I know that Roman mentioned microphone wire earlier, but I can't find a source where I know what I am buying...
On top of that, what sort of wire am I looking for? Should I be looking for 3 conductor shielded wire or 2 conductor shielded wire?
I am kind of at a loss here.
Thanks for any help,
Jay
"The bitterness of poor quality remains long after the sweetness of low price is forgotten"
Got mine from ebay. It's a 3-conductor shielded mic wire. Search for microphone wire.
Any electronics outlet should have shielded mic wire.
Shield and 2 conductors is fine, and is probably easier to find and cheaper than shield plus 3 conductors.
If you have choices try to get the non-woven shield. It is rated for more flex cycles, and you don't need very high levels of shielding as this is not an audio or RF application so you don't need woven or foil shield etc.
I posted a part number at McMaster Carr in post 247
Gerry
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Guys,
I will be using the same type switches in my build, home switches (3 wired parallel) but I will be doing it a little different than the most.
Limit switches wired (series) 24V with a relay, not directly connected to the Bob, no shielded wire.
Home switches wired (parallel) 24V with relay, not directly connected to the Bob, no shielded wire.
I don’t use shielded wire and I don’t intend using it.
Any interest read this.
http://www.cnczone.com/forums/genera...tml#post883799
