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Author Topic: Accuracy or repeatability of homeing switches, something to worry about?  (Read 7168 times)

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Offline Sage

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Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #10 on: November 09, 2008, 07:52:01 PM »
What are the optical switches you mention. I've done a lot of work with optical interrupters which are an infrared LED, and receiver placed across a gap from each other, but they require some electronics to condition them. We used to use them in ticket transports to detect very fast moving tickets. I suppose you might be using a commercially packaged version of those giving an electrical "contact closure" or circuit path.

Sage

Offline Hood

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Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #11 on: November 09, 2008, 08:16:25 PM »
Use Optek OPB917B, only thing you need is a current limiting resistor. Heres how I enclosed the one for the Z axis on the Bridgeport, there are springs to go either side of the flag to keep it centered and 'o'rings go in the housing where the rod protrudes. I could have made it in two parts but didnt have thick enough Alu on hand at the time so just made it up out of thinner plate. The ones on the X and Y were ready made from Industrial Hobbies but I dont think he does them any more.

Hood

Offline Sage

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Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #12 on: November 10, 2008, 03:35:13 PM »
OK. Those are (except for manufacturer) exactly what I'm familiar with. And you are correct, you would only need a resistor for the LED half. I forgot about the BOB having a pullup to 5v on it's input so that would take care of the photo transistor collector side.

Hmm.... now you have me thinking.

I like your hardware to make it swarf proof too.

[edited - removed my comments about using optical switches for limits. The discussion was using them for home switches]

So you say they are "deadly accurate". I know they seemed to be in our old ticket transports but then our firmware used to jocky the ticket edge back and forth a bit in front of the sensor to get it just right.

How fast do you approach the sensors?


Thanks

Sage

« Last Edit: November 10, 2008, 04:06:15 PM by Sage »

Offline Hood

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Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #13 on: November 10, 2008, 03:53:05 PM »
I think I just homed at the normal 40% at that time, it was on my first conversion that I did when I tested them with the glass scale and DRO. On that machine I think it was 4M/min on the X axis so suppose that would be about 1.6M/min homing. 

Hood
Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #14 on: November 10, 2008, 04:01:47 PM »
thanks, I have a bunch of different opto switches from other projects, never thought about using them in this application....I'll have to whip something up now !!!
Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #15 on: November 10, 2008, 07:31:17 PM »
Automation Direct has many types of environmentally sealed limit switches for about $38 each.
They are quality made in Italy units and similar to the original Bridgeport units.
May be a lot easier to go this route than mess with making up optical ones that are sealed.


Scott

Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #16 on: November 14, 2008, 06:45:31 PM »
Mueller I've been using the original limit switches on my Bridgeport for around a year now, I've found them to be quite accurate but it does seam to depend on the speed that you home at.
Give them a try!
Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #17 on: November 14, 2008, 06:51:21 PM »
I've managed to score several Industrial Hobbies optical limit switches at a great price.  I can copy them for the rest I'll need.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #18 on: November 14, 2008, 07:03:16 PM »
They are nice switches Ray but just be carefull with the wires, they are easy to pull off. I put a cable tie (zip tie to you guys I think) round  the wire inside so that there was slack inside even when the cable was taught.

Hood
Re: Accuracy or repeatability of homeing switches, something to worry about?
« Reply #19 on: November 14, 2008, 07:12:55 PM »
They are nice switches Ray but just be carefull with the wires, they are easy to pull off. I put a cable tie (zip tie to you guys I think) round the wire inside so that there was slack inside even when the cable was taught.

Hood

Hood,

    Will do.  Thanks!

Regards,
Ray L.
Regards,
Ray L.