It's nearly Summer... So I'm going Probeless

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zombiepantslol
Heh, adding more compensation code is not a big deal, but I personally wouldn't be satisfied with that solution. Using the 623 bearing on the x carriage as a switch in combination with X axis alu replacement parts would be a much cleaner approach IMO.

I've tried this and it didn't work. The force on the runner bearing has to decrease to zero and then the head has to rise some more before contact is lost. Even with the aluminium x-plate, there is still too much elasticity in the system for this to occur at a well-defined point. However, I now have an x-carriage with a slot for a force-sensitive resistor behind the bearing, and I hope to try it out soon. Elasticity should have less effect because we only need to detect a reduction in the contact force, not its complete disappearance.

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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].

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dc42
..I've tried this and it didn't work. The force on the runner bearing has to decrease to zero and then the head has to rise some more before contact is lost...

It's because of the tolerances in the bearing, the way it is made and the vertical position, when the force is released, the balls and the outer ring will keep contact (more or less with a film of grease between) as they move down the inner ring to the relaxed position

Erik

Kim's solution works in essentially the same way by detecting the hotend carriage twisting as the Z axis is driven below zero height, except that it does not require all the force to be off the X runner and it has a more reliable switch with an accurate make/break position.

I have yet to implement it, but it sounds like the easiest and most accurate solution of all. It does not require any reflective spots or limitation in bed coating, it is unaffected by heat, it can probe any position on the bed, and accommodates changes in glass thickness without recalibration. It is also cheap and does not require any firmware changes.

The only shortcoming I can think of is that it will be affected by the X arm twisting when the weight of the hotend is partially removed as the nozzle hits the bed. Such twisting is greater at the outer end than near the Z post - but it also affects the print quality, and so should be minimal by design. If it is too great to allow accurate enough Z probing, I should think that it will affect print quality to the extent that it needs to be attended to - perhaps by fitting an aluminium arm.

Dave
(#106)

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dmould
..The only shortcoming I can think of is that it will be affected by the X arm twisting when the weight of the hotend is partially removed as the nozzle hits the bed....

and difference in the thickness of the acrylic part along the x-axis - measured out to 0.03mm on mine so of no practical consequence
Edit: ups, memory fault sorry, was 0.06, from 4.61 to 4.67mm

Erik

Edited 1 time(s). Last edit at 05/12/2014 03:34PM by ormerod168.

Hi Guys, I'm at work as you know, and things are mad here, so not getting much time to tinker.... or sleep...

I like DCs idea of the force sensor... One question about it would be that actualy printing the new carriage on lots of machines all set slightly differently, where temps alter filament bonding quality, I'm loving the idea, but is it repeatable on other machines....

I have a thought... A pivoted 9mm roller..... The pivot rotates a variable resistor.... In the normal position, the bearing arm would rest on a stop to support the X-carriage rotation, so keeping a regular position.
When the Nozzle rests on the glass, the X-axis tilts, and so the 9mm bearing arm rotates a fraction by a spring, turning the resistor, which tells the Duet that the nozzle is at Z0...
Ok it would be a similar Gcode to the switch, idea, but would we achieve anything? Would a spring loaded 9mm bearing on an arm triggering a microswitch be better?

It's 6 of one, and half a dozen of another I think... LoL my Switch isn't pretty, but it sure works well.

Another idea..... 3M reflective tape on the edge that my switch works on.... Mount the IR Probe so it sees it normally. When the tilt occurs the sensors wouldn't be seeing the reflection of the tape any more, so we then have our trigger point... (hmmm was that a light bulb moment....lol I think that might be bringing the light problem back maybe).

I like the electronic approach, but, what BIG benifit would there be over the switch?

@Les Hi, I use the existing probe wires (two off) to work the Z probe switch as you say... This leaves me now with one spare wire, which I plan to use as half of the wiring for my second fan on BB.
I just need time to run another wire through, and connect it up....

Kim..

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Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete

I've just published the Z-axis MicroSwitch Bracket on ThingyVerse if any one needs one... I've included details of the microswitch in the info...
The Bracket can be found Here..

Kim..

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Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete

I will be releasing Revision 1b of Big Blue later today.
One very minor mod that will save people drilling holes for the Z-Axis MicroSwitch Bracket.
You won't need this revision if your ok with a hand drill and want to use the bracket.

Kim

Edited 1 time(s). Last edit at 05/13/2014 12:09PM by KimBrown.

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Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete