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Author Topic: Accuracy of Homing Devices? Pro's and Con's of Different Sensors  (Read 30020 times)

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Offline Dan13

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #30 on: October 17, 2012, 04:00:18 PM »
Thanks.

These are single sided, Russ. First intention was making them double sided, but it interfered with the requirement of making them smallest possible and I decided to make them this way. The plunger stroke is 5mm, dimensions are 29x23x14mm. You supply anything between 5 to 15VDC and output is active low. Price is $30.

Hood, yes, they are based on the same concept. The new ones are an entirely different design (round frame with M12x1 external thread - like the industrial proximity switches) and they are single ended as well.

Dan

Offline Hood

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #31 on: October 17, 2012, 04:05:40 PM »
Sounds reasonable Dan, the ones I bought years ago were double sided and $50 so only needed one per axis but that was a lot of years ago, probably 8, so yours are on a par and being plastic probably better.
I had toyed with the idea of making some with  a roller cam operated flag, that way travel accidental overtravel wouldnt be a problem but as I went to Index homing in the drives I never proceeded wit them
Hood

Offline Dan13

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #32 on: October 17, 2012, 04:16:56 PM »
Thanks Hood. These are not plastic however - it's an anodized aluminium there ;)

Mounting them to trigger against an inclined surface could be used to solve the overtavel problem. But I mount them just before the hard stop.

Dan

Offline Hood

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #33 on: October 17, 2012, 04:21:00 PM »
Ah ok, looked plastic and knowing you made the plastic stepper end covers I just presumed they were as well
The roller cam method has a few advantages to my thinking. One is you only need 1 switch per axis if you wish, second is if you wish to have separate home switches (big travel machine etc) then you can do that.
Hood

Offline Dan13

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #34 on: October 17, 2012, 04:24:15 PM »
I agree on the roller type advantages you mentioned, but every additional moving link reduces repeatability in my opinion, that's why I tried to stay away of this.

Dan

Offline Hood

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #35 on: October 17, 2012, 04:29:42 PM »
Not sure if repeatability would be an issue if they were high enough spec. The Honeywell switches I use are very accurate and repeatable but there in lies the problem, they cost a lot because of that. I was going to be making them for myself so cost and effort of making them  was not an issue, you on the other hand are making them to sell so I can see it would likely not be cost effective for you to go that route as it would be very expensive to produce, probably more than 3 or 4 times what you charge for one of your switches.
Hood

Offline Dan13

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #36 on: October 18, 2012, 04:13:34 AM »
True. Do you have a link to the Honeywell switches? What type are they and what accuracy?

Dan
Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #37 on: October 18, 2012, 11:36:19 AM »
If I was to install one of these http://www.ebay.com/itm/110936667967?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 and a disc with one hole in it on the end of my double shaft stepper with a mechanical switch on the axis slide adjusted to switch "on" the ground to the opto device close to the home position, I would have a very accurate and repeatable home, yes?

This assumes that the opto is set up as a normal home switch input in Mach and the mechanical switch does nothing but switch on & off the ground (or power?) to the opto.  If this has been discussed before and I missed it I apologize.  Seems like it ought'a work a treat??
Milton from Tennessee ya'll.

Offline mc

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Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #38 on: October 18, 2012, 12:05:52 PM »
It would depend on how the sensor acts when the ground is disconnected and reconnected. Provided the output goes to high impedence or shorts to +5V when disconnected, and it doesn't do anything daft to the output when powered up (i.e. it remains at 5V, and doesn't spike to gnd), then it should work.

One thing I'd suggest is make the slot in the disc pretty big, otherwise there's a chance you could overshoot the slot if you're homing at a reasonable speed.
Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors
« Reply #39 on: October 18, 2012, 01:05:40 PM »
Ahh, OK thanks.  I figured I'd have to play around with it to get it to work.  Hopefully the sensor electronics don't do anything weird on power up but come to think about I could leave it powered up and just switch the signal?

Being a retro'd ORAC lathe it has little X-axis travel and with a very slow homing feed rate it won't take long at all. ;)
Milton from Tennessee ya'll.