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Author Topic: Automation Direct Photo switch  (Read 6694 times)

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Automation Direct Photo switch
« on: April 22, 2008, 12:17:09 PM »
I am trying to use an NPN photo switch as an X axis home switch.  I have it connected into a Campbell breakout board.  The problem I am running into is that the input is flickering.  I have a couple of thoughts that I am hoping somebody can either verify or kill. 
1)  First, the switch is rated 10-36V.  The board is 11.6V, close to the bottom edge.
2)  The other is the opto isolator may not be able to react appropriately with a 250Hz signal. 
3)  The Campbell board indicates it is setup for inductive or mechanical switches.  I am sensing wood, so inductive is out, and I would prefer non-contact in this application.

I read on one post that a guy put a 1k ohm resistor between the signal and ground to limit the bounce, any thoughts?

Offline Hood

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Re: Automation Direct Photo switch
« Reply #1 on: April 22, 2008, 01:45:37 PM »
Try putting it in at another input if you can, I seem to remember someone having a problem with the Campbell board and an optical switch for the index pulse, think the inputs were too slow.

Hood

Offline Chip

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Re: Automation Direct Photo switch
« Reply #2 on: April 22, 2008, 02:35:39 PM »
Hi, Roger

Do you have a link or diag. for the photo switch.

You may need a pull-up or pull-down resistor "I read on one post that a guy put a 1k ohm resistor between the signal and ground to limit the bounce".

It would stabilize the "off" state until the sw has a solid "on" signal state.


Hood: I think the index pulse needed a mpg input that goes direct to the PP (no opto/direct) on the Campbell breakout board.

Hope this Helps, Chip

Offline Chaoticone

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Re: Automation Direct Photo switch
« Reply #3 on: April 22, 2008, 03:06:46 PM »
rkowash, Post a link to the switch. We use some that measure distance. They put out an analog signal. Just wondering if that is the type you have.

Brett
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Re: Automation Direct Photo switch
« Reply #4 on: April 22, 2008, 05:10:05 PM »
Re: Automation Direct Photo switch
« Reply #5 on: April 22, 2008, 09:03:27 PM »
I think that is a Diffuse Reflective photo sw. with a sensitivity adjustment, out to 2 Meters ! I don't believe it would be a good choice for a Home switch. Might be OK for a limit if you can get it to calm down. The ones I used vary too much, they were nowhere near precise enough for homing.
However, these may be different........
A "Through Beam" or a "Retro-reflective" sensor would probably be a better choice. Still best is probably a snap action limit switch.
Sensing WOOD ? For homing ? Is your machine made of wood ?
RC
Re: Automation Direct Photo switch
« Reply #6 on: April 22, 2008, 09:16:00 PM »
I used a Photo Eye like this on a project last year as a home switch  however, this is how we did it.  The unit we used was the 'reflector style.  We set up the photoeye and reflector at the home position, when the gantry broke the beam, the machine was homed.  From your description thus far, it's hard to tell how your switch is mounted.  Are you using a reflector.  A pic or a drawing would probably help expedite a solution.

Regards,
Sid
Re: Automation Direct Photo switch
« Reply #7 on: April 23, 2008, 10:37:18 AM »
To answer some of the questions on the last two posts.  I am cutting a SIP (structural insulated panel), it is a sandwich of 2 sheets of OSB and styrofoam in the middle.  The parts are 8' x 24', and vary from 4.5" thick to 12.25" thick.  The panels are vertical, and they move in the X, where the saw moves in the Y,Z, Beta, and tilt.  This particular switch is fed off a powered coveyor into the saw.  This trips the sensor.  The X axis then clamps onto the part (now I have stepper precision) and backs the part up until this switch is clear.  This will be my zero position.

I tried the retro-reflective sensors, but the skin of the part varies too much.  I was having the same signaling problem on the Campbell board with a banner 312 photo sensor using through beam fiber optics.  For using a mechanical limit switch, until the part is clamped, there is no guarantee that the part will be close enough to the switch to trigger it. 

Ideally I can get this switch to work.  If it is just too sensitive for the Campbell, I will probably hard wire this switch to the PLC, and code in that as soon as that input is latched, fire an output hooked to the Campbell.  That way I maintain the speed, but can use the PLC to filter the signal.

Hope this helps explain my problem some.
Re: Automation Direct Photo switch
« Reply #8 on: April 25, 2008, 11:22:46 AM »
I tried the 1k resistor, and the sensor went to a constant on.  I went with 100k resistor, and it slowed the pulse, but not enough.  I tried about 10 different values in between, and while they all made a difference, none rocked the world.  Any help would be great.

Roger
Re: Automation Direct Photo switch
« Reply #9 on: April 25, 2008, 11:26:59 AM »
Here's a thought... How about you add a relay to the mix.  Have the photo switch trigger a relay (coil) and then use the switched relay circuit to trigger the BOB?  I know it involves adding another piece of hardware but it's about all I can think of right now...

HTH,

Sid