optical endstops ?

Are optical endstops more accurate than micro switches ?

Thanks Nikki

I think they can be more precise - i.e. repeatable, but it depends on how the opto interruptor and the flag are mounted. The weak spot is the way you adjust it- if it isn't very stable the precision goes away. I used a microswitch for a long time and it was fine, but recently decided to try an opto to see if it behaved any better. One thing I noticed immediately was that unlike microswitches, optos have no hysteresis. Microswitches have some mechanical hysteresis that make zeroing the z axis a little uncertain. With an opto there's nothing equivalent to listening for the click then backing the screw off a little. You zero the bed then adjust the flag/opto position until the opto changes state and you're done.

Edited 1 time(s). Last edit at 06/04/2015 02:41PM by the_digital_dentist.

Optical endstops could in theory be more repeatable than microswitches f mounted correctly (see the previous reply), however they may potentially be affected by bright sunlight - which could make them less repeatable. I don't know how big this effect is, but I do know that sunlight affects other types of IR sensor (i.e. reflective ones) a lot. Painting the tab that interrupts the beam black should make them less likely to be affected by sunlight.

On a non-delta machine, repeatability of the X and Y endstop switches isn't really an issue, assuming you never re-home in the middle of a print. Repeatability of the Z endstop switch is only important if you are relying on it for setting Z=0, instead of using a Z probe.

On a delta machine, repeatability is very important, unless you always use a Z probe to auto-calibrate after homing.

When I was using a microswitch-type Z probe, it was repeatable to within 0.12mm, which corresponds to 1 microstep of the motors and so is as good as can be expected. Your results may vary, especially if you use low-quality microswitches.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I am having problems with my z axis am loosing or gaining 0.16 every time I home it from one side of the axis to the other

Quote
Nikki81
I am having problems with my z axis am loosing or gaining 0.16 every time I home it from one side of the axis to the other

Perhaps it is homing too fast? A common technique is to home at a high speed initially, then back off a small amount and re-home at a slower speed.

For setting of Z=0 just before printing, a Z probe is usually capable of more repeatable results than an endstop switch.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].