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Author Topic: Laser limit switch  (Read 357 times)

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Laser limit switch
« on: December 09, 2018, 12:01:44 AM »
Does anyone know of a supplier of limit switches, which utilize a laser (or other light source) and a photo cell to sense when the machine has reached it's limit of travel? I currently use mechanical limit switches, which are not very precise (when homing the Z axis, in particular). And I just thought that light/photo cell system would probably be much more consistent. Thanks in advance, for any help you can offer!
Re: Laser limit switch
« Reply #1 on: December 09, 2018, 06:03:17 AM »
Hey Mate, After alot of trouble with mechanical switches, I've just installed Inductive Proximity Sensors to my machine for homing, the ones that work magnetically when coming close to steel. At around $2.50 on ebay, I thought it was worth a try and i'm super happy with them. They are easy to install and wire up. These ones will run off 5v.
After much umming and aaahing, I ordered these.

https://www.ebay.com.au/itm/5Pcs-TL-Q5MC2-Inductive-Proximity-Switch-Sensor-NPN-Normal-Close-DC-10-30V-AU/182246325347?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I haven't tested the repeatability on them, but from all i've read, they are very accurate. (.01mm), I'll get back to you tomorrow on that one.

Re: Laser limit switch
« Reply #2 on: December 09, 2018, 08:28:07 AM »
"...I haven't tested the repeatability on them, but from all i've read, they are very accurate. (.01mm), I'll get back to you tomorrow on that one."


Thanks for the suggestion. It is the "repeatability" in particular which is the issue. I spent a day, trying to calibrate my machine's Z axis using a touch plate on the stock, and a fixed plate mounted on table. The results kept varying as much as 0.050" I finally concluded that this was the amount of "play" in the microswitch, when homing the machine. And since all movements in Mach 3 are referenced from the (make, or break contact) of the limit switch, then the microswitch must be the variable culprit. I am currently using a ball screw on the Z axis, so I don't think that it's an issue with the mechanical aspects, other than the limit switch movements. What brought it to my attention, was upon re-homing my machine, I noticed that the Machine Coordinate display on the Z axis would always read something other than zero (resetting to zero, of course upon striking the limit switch).

Re: Laser limit switch
« Reply #3 on: December 11, 2018, 03:39:10 AM »
After testing that way about 30 times today, my results were up to .02mm out on the software, but generally about .005mm. To me, that's amazing.
I doubt you're gonna get much better than that without spending big dollars.

BTW, this test was done with my homing speed set at 50%, about 1000mm/min. I also haven't tuned the motors/drivers etc since the day I set the machine up. I'm sure there are ways to get a smoother run up to the limit for better accuracy.

My machine is a full Aliexpress Chinesium homejob.
425 oz longs steppers
1605 ballscrews and supported rails.
2.2kw VFD spindle.
all welded steel frame and gantry though.
Re: Laser limit switch
« Reply #4 on: December 16, 2018, 04:48:58 AM »
Try looking for www.vinland.com/Opto-Interrupter.html for details of how to use opto-interrupters (a standard component) as limit switches and what repeatability can be achieved.