Limit switch repeatability.

[NC Cams]

If you want digital repeatability, interface a "debounce circuit" with the microswitch as the trigger to either a flip flop (4013 CMOS chip) or perhaps a one shot made from a 555 timer IC.

Once you trigger either with the first time"bounce" from wht microswitch, the circuit will "engage" and repeat as often and as repeatably as the microswitch can/will trigger.

Keep in mind that as the switch ages, either corrosion or detioration from repeated current interuptions may cause the switch to trigger a bit differently over time.

For limit switch use, the position degradation probably won't be that deleterious to peformance and/or repeatability. For a "home" sensing, the same caveat applies.

Again, how much "shift" that can/will occur will have to be quantified. Again, assuming that you're not going to pull too much current (10 or 20 milliamps should not cause any appreciable detioration) thru the microswitch, you should have repeatability that will suffice for all but the most psychotic accuracy requirements.

However, at this low a current, atmospheric induced corrosion could cause the switch to lag a bit over time unless the switch "self cleans" somehow ir the contacts are made of a non-corrosive substance. An occasional shot of contact cleaner might adequately "rejuvenate" the contacts.

[vger]

A physical switch for protection at end of travel is probably the way to go for that. As for home position, an opto interupter will work well. No physical contact, no electrical contacts to wear, and some of them are very very precise.

[Rance]

I think vger has your best solution suggesting an opto switch. If a person was clever enough, they could hack a computer mouse and harvest the two optos in there for limit/home switches. Mice are virtually FREE (my favorite word) and much more precise than a mechanical switch. I have no problem interfacing a plain ole switch to my HCNC, but don't know what extra electronics would be required for an opto. Has anyone done this? Got a schematic?

As a bonus, I'd suggest running a plastic tube from your router motor fan to the opto switches to keep the dust clear of them. Is that overkill?

[Edit: But if you used Widget's setup I referenced in post #11, all the electronics and opto are isolated inside a dust-proof box so dust would not be a problem. I'm beginning to really like this idea. You get the best of both worlds. ]

[vger]

Most of the opto interupters I have come across have 3 leads on them. I've pulled many from old copy machines, printers, scanners, and the like. Internally in the base of them is a little PC board with current limit resistor in series with the IR LED. One lead will be ground that is common to both the LED and the phototransistor. One lead will be power (usually +5 V DC). The third lead will be the output and is generally connected to the collector of the phototransistor. Attaching a resistor (470 ohms) from the output to the + 5 V will make the thing work. When nothing is interupting the beam across the gap, the phototransistor will be turned on and the output lead will be held at, or very near ground level. When the beam is interupted the phototransistor turns off and the resistor will pull the output lead up to 5 volts. This is a logic level signal and can be easily interfaced to computer or controller. If you need to operate a coil based relay with it, an additional circuit will be needed. If you are picking Opto Interupters from used equipment, keep the connector and a fair length of wire that attaches to the opto. As for dust... most of these things are fairly forgiving in that aspect. If moisture is an issue, you could construct a sealed compartment with a spring loaded plunger that could be sealed with an O-ring.

[benergy]

I have high speed routers and face this problem too. Im looking for workable home switches that allow over travel without smashing yet good back-off accuracy. i fear the only option is indeed optical with white spots unless anyone knows another solution. I have built opamp circuits to run photoresistors from old mice but want to return to simplicity so its easily replacable.

[Bob Adams]

Originally Posted by ger21 I believe that is how it works. It moves until the switch trips, than backs off until it opens, which is your zero.

Here's video that shows That.
YouTube - ‪Optical Home Switch Indicator Test‬‏

[ger21]

Im looking for workable home switches that allow over travel without smashing yet good back-off accuracy.

How about these?
http://www.cnczone.com/forums/open_s...made_easy.html

[Al_The_Man]

Originally Posted by ger21 How about these?

One thing to be a ware of with these though is the if they are used in an area of high ferrous metal cuttings or dust, they use a magnet to operate.
Al.

[ger21]

He did say routers, though.

[ssutton]

I used the hall effect switches much like ger21 linked to. However, after soldering the 3 wires to them I potted them in a brass tube with epoxy. This makes them very easy to mount and adjust and makes them very durable to shock and impact. I use them as home sensors on all 3 axis and use limit switches only as travel limits (e-stop, read further). I have found them to be VERY repeatable and because they are non-contact they will not wear out. My mechanical limit switches are really just e-stops, they are wired in series with the e-stop button so that Mach stops the machine any time they are tripped. For some reason that I cannot seem to understand or get an answer on, Mach ignores the limit switches when it is homing. Because I have my limits wires to function as the e-stop, Mach stops my machine ANY time they are tripped.

Scott

[ger21]

Because Mach3 allows a single switch to be used as both a Home and Limit switch, it has to ignore the limits, or it would trigger when homing. Also, many people install their home switches outside of the limit switches, so again, they need to be ignored.