Alternate to the Opto Endstop

Could you use a plain Jane low tech limit switch (NO or NC depending on the circuit) to accomplish the same goal? Can't open the schems for the stepper drivers from my work machine. If this question has already been asked I apologize for the repeat, but I am thankful for the link! Thanks.

-Rick

Should be possible; there might be a bit less accuracy, but that would depend on the type of switch.

I think the reason opto switches are used it because they don't really have any moving parts; therefore they're not going to wear out, or change their properties over time. All the paper printers I've dismantled recently seemed to use all opto switches, for what it's worth.

One thing too - I've noticed my Z axis zero point has a very large effect on layer adhesion during prints - changes of even 0.1mm have noticeable effects on the printed object. I have been adjusting the opto by hand, but I think I'm going to move to leaving the opto where it is and changing the offsets in software, to make things more repeatable.

I don't know much about mechanical switches, but I would imagine they're not as accurate or dependable. Switch bounce would be a big problem too.

Wade

Hi guys.

If you find a good quality microswitch it should serve you well - I had a play with one a few years back and had repeatability of better then 0.05mm. I'm not so sure about cheaper ones though...

A point to remember is that there will be some (small) force applied to the switch, which might cause it to slowly move over time. Anchor it well.

Also look out for what will happen if the software stuffs up and the stage keeps travelling? Will it hit the main body of the switch or something more solid first?

For debouncing it's probably easiest to 'suck it and see,' but a few guidelines:
-- Either Normally Open or Normally Closed is fine - it just depends on how you wire up the circuit. Although you could change the firmware to suit either logic high or logic low sensing, I suggest sticking with the current standard so that you don't accidentally wind up updating non-tweaked firmware and wondering why it doesn't work.
-- You probably want to have about 10mA flowing through the switch when it's on. This might seem a lot but remember it'll be in a somewhat noisy electrical environment on flying leads. Additionally switch contact resistances can quite high if there isn't enough current about (saw this in a presentation from Semikron who make MW range power electronics, so I assume they know what they're talking about).
-- Debouncing can be done in software or hardware. The bouncing will probably be over in less than 30ms, a value I've used plenty of times in the past.

Good luck.

Ack! Hadn't considered switch bounce or wear. Bounce I could have probably accounted for, wear...not so much. Looks like opto is the way to go! Thanks for the info, folks.

-Rick

Happy to help.

When you look at optos I suggest that see if you can find the datasheet - some have better repeatability when the vane comes in from the side rather than the top. A little tweak might make things just the tiniest bit better - and I understand that getting the layer height right is quite important.

Also, some plastics (even black ones!) are transparent in the infrared. If you have trouble I seem to recall that Twink (or whiteout fluid or whatever you want to call it) is a pretty good IR blocker.

jbb