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Author Topic: Homing switches accuracy  (Read 4545 times)

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Offline Hood

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Re: Homing switches accuracy
« Reply #10 on: April 26, 2013, 05:23:07 PM »
You shouldnt have to worry about such a thing if you have decent snap action switches.
Hood
Re: Homing switches accuracy
« Reply #11 on: May 27, 2013, 09:21:49 AM »
Hood, If I was to enclose 24 V proximity switches in my old balluf limit switch enclosures you think that would give me high accuracy?  I also have to ask, will the angle of the dogs that trip the limit switches have any negative affect on accuracy?  The old limit switch enclosures had these stainless looking plungers spring tensioned and sticking out of the enclosure.  They seem to have been liquid tight and basically they would activate the switches when depressed by a "trip dog ( I think that is what they are called?)"  One "trip dog" is mounted in the max and one in teh Min of an axis motion so only one switch is used.  Is there a more appropriate angle on those trip dogs for homing and another for limit?  I am trying to figure why the machine originally used 2 different switches for homing and limit?   At this point I am thinking of chaining the all together.     

Offline Hood

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Re: Homing switches accuracy
« Reply #12 on: May 27, 2013, 01:45:24 PM »
I have never used prox's for homing switches so not sure what accuracy can be achieved.
They likely are used on some industrial machines however they will not be relying on the switches for the homing accuracy as they will just be using them as a trigger to start looking for the index pulse on the encoder.
 That also is likely the reason your BP had separate homing switches as they would be used to signal the control to look for the index pulse. Likely it did not back off the switch before looking for the index so the home switch had to be separate so as not to trip a limit.

Hood
Re: Homing switches accuracy
« Reply #13 on: May 28, 2013, 06:57:38 AM »
OK, so the angle of teh trip dog is not why they used one set of switches for homing and another for limit?  So basically even if my swictes are top of the line, they were never made to achieve a precise location and never can achieve such a thing?  Sure wish there was an auxiliary board that can combine limit switch inpuit and encoder index signal so mach can read a precise point for homing. 

Offline Hood

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Re: Homing switches accuracy
« Reply #14 on: May 28, 2013, 07:45:00 AM »
They may well be accurate, the honeywell switches I use are accurate enough although I always did index homing anyway. I could do that because my servo drives supported it but on the other machines that I have the CSMIO fitted then it does it so drives with homing capability are not needed.
 Regarding an index homing board, there use to be such a thing, Ed Gilbert made various boards, one of which was just that. He doesnt make them any more as far as I know, in fact I dont think he makes anything now, his company was called CNC Building Blocks. I have a complete breakout board of his on the big lathe and it has the homing to index feature although I do not use that part of it now.

Hood