Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: JohnHaine on October 10, 2016, 10:50:57 AM

Title: Slotted opto sensors as limit sitches
Post by: JohnHaine on October 10, 2016, 10:50:57 AM

Hello all, a while back, on a different PC, I found someone's website where they had some nice info on using slotted opto sensors as limit switches, referencing a specific type that used laser diodes for a narrow beam and could sense very accurately and repeatably.  Of course I've lost the bookmark - any help or links to such a site or info on using optos in this way would be very welcome please!  The site also had information on making touch-off probes if that helps.

Thanks in advance for your help!

John.

Title: Re: Slotted opto sensors as limit sitches
Post by: Hood on October 10, 2016, 02:51:44 PM

I have used Optek OPB916B and OPB917B sensors and repeatability was excellent.
Hood

Title: Re: Slotted opto sensors as limit sitches
Post by: JohnHaine on October 10, 2016, 03:28:46 PM

Thanks Hood - do you have an actual value for the repeatability please?  This is actually for a pendulum sensing application.

Title: Re: Slotted opto sensors as limit sitches
Post by: Hood on October 10, 2016, 04:57:41 PM

On a Bridgeport with steppers and a rapid of 2500mm/min, homing speed was set to 40%. I had a glass scale DRO on the mill at the time. I homed the machine and zeroed the DRO, moved off and homed and repeated I think about 100 times, only a couple of times did the DRO show other than zero. Now this was on a clapped out retrofitted  Bridgeport and the chances are that the times it was out was more likely to be due to the slop in the axis.
 The switch was a fully enclosed affair that had a rod poking out either side of an Alu case and the flag was attached tp the rod and the rod held central with springs either side of the flag. The switches were originally bought units from some place in the USA, I forget the name of the place but it changed hands and they stopped making them. Anyway the original optos in them gave up the ghost one by one and I just modified the housing and replaced them with the OPB916B.

The optos are cheap, about £6 or £7 here so even if they are not suitable for your job it is no big loss.

Hood

Title: Re: Slotted opto sensors as limit sitches
Post by: JohnHaine on October 11, 2016, 10:46:57 AM

Thanks again - good input.  Actually only £3.94 one-off, even from RS!

Title: Re: Slotted opto sensors as limit sitches
Post by: rcaffin on October 15, 2016, 05:09:09 AM

a specific type that used laser diodes for a narrow beam
I don't think such beasties exist.
LEDs with apertures on both sides to make a narrow beam, yes, hundreds of models and tens of brands, but with a laser? I have never heard of them. Well, unless you get into the hundreds of dollars class.
Be satisfied with LEDs.

Cheers
Roger

Title: Re: Slotted opto sensors as limit sitches
Post by: JohnHaine on October 15, 2016, 11:56:29 AM

Aha! I found the website, http://www.vinland.com/Opto-Interrupter.html

He tested the same type as you Hood, and they don't use lasers, I misremembered!