Z Probe losing calibration

Hi.

Sometimes I find the nozzle pushes down on the bed when I home the axes before a print, And then I do a Z axis calibration and find that the value shown by the Z probe is way off. For example, the previous setting was a G31 Z2.0 P603, and now I have to set it to G31 Z3.3 P604 to calibrate it.
Why does it change so much randomly? I havent made any changes to bed height or any other changes. This happens as often as once in a week or two. Is this normal?

Ormerod 1 or 2?

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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].

What type of probe? The original probe was extremely sensitive to ambient light from daylight or incandescent lighting to the extent that it was pretty much unusable except in a room that had no daylight and no incandescent lighting. DC42's probe is far superior.

Dave

also see if the position of the sensor has changed



Erik

Hi.
I am going through a similar maddness.
Every time that I register the z probe zero x heighth as seen on the control web interface, I jot it down, shut the machine down swap over the memory chip, change the config.g code, put the chip back in the ormerod2 then I check the z probe height at the exact position height is now reading approximately 010 higher than it was when I read it. do that ten times and stay sane!!!!

Are any of DC42's chips available? where would i get one, I want ten!! no seriously...

thank you.

Quote
helix
Are any of DC42's chips available? where would i get one, I want ten!! no seriously...

I have 4 partially-assembled boards that I can complete as either dual nozzle, or single nozzle upgradable to dual. I have just one of the original single-nozzle boards left. See [forums.reprap.org] for prices and how to order. I'd love to reduce the prices, but demand is now low (if only I could get RepRapPro to buy them!), so automated assembly is not practical and I have to manufacture them by hand. See [miscsolutions.wordpress.com] for the fitting instructions.

I also have a design for a lower cost sensor-only mini board (see [miscsolutions.wordpress.com]), but the first batch of 10 prototypes sold out almost immediately, and I won't have any more for a few weeks.

I should also point out that if you are using the 3-wire Ormerod 1 proximity sensor, then your problems are probably caused by ambient IR. Upgrading to RRP's modulated sensor (as on Ormerod 2) will help substantially, although not as much as my board does.

Edited 3 time(s). Last edit at 05/24/2015 03:59AM by dc42.

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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].

the mini board is very nice i can really recommend it! I just shoehorned my mini ir sensor board on my ormerod: works nicely. I even "cut" the original x-carriage of RRP up to accommodate the mniboard with components towards the "inside" but have not yet printed this version (as changing the x-carriage is not exactly as easy as e.g. the z-top ;-)
x-carriageMiniIR
many thanks for all your work dc42!

A quick glance through the Ormerod forums shows just what a "repeat offender" Z probing is.

+1 for getting RRP to source David's dual IR. The mini should be economically viable in Qty. >250 I would think.

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RS Components Reprap Ormerod No. 481

Sorry for the late reply guys.
@ dc42: Its an Ormerod 2.
@dmould: I have a 4 wire probe that came with the Ormerod 2. [reprappro.com]
@ormerod168: No. It hasn't moved. Its mounted on the carriage. Nothing ever touches it.

I reckon I am seeing the same problem with a new Ormerod 2. After a few prints, the nozzle sits a fraction too low and smears the extrusion rather than leaving a neat bead of filament. Recalibrating the Z Probe sorts it for a while, then the same thing happens.

Think I need one of your boards too DC42!

Ralph

seem to have the same problem

Quote
rjmusto
I reckon I am seeing the same problem with a new Ormerod 2. After a few prints, the nozzle sits a fraction too low and smears the extrusion rather than leaving a neat bead of filament. Recalibrating the Z Probe sorts it for a while, then the same thing happens.

Think I need one of your boards too DC42!

Ralph

This sounds like it could be the bed warping upwards as it warms through after a couple of prints. The heat spreader plate is firmly bolted to the bed support, both are aluminum, one is heated and the other isn't.
I've seen a +0.1 to +0.2mm offset in the middle compared with the edges when the heater is on. I've been thinking about elongating the holes in the bed support and locking the bolts with extra nuts to allow them to slide

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RS Components Reprap Ormerod No. 481

I'll be glad to sell you a board!

There are a couple of reasons I know why the calibration of the modulated probe changes:

1. The print head of the Ormerod pivots about the X rod. This is an advantage when the nozzle hits the bed or the print, but unfortunately it can lead to the angle of the head varying, for example due to flexing of the acrylic X arm. The standard IR sensor is not in line with the nozzle in the X direction, so any change in head angle will affect the relative heights of the nozzle and the sensor. That is why I mount the sensor on the hot end, with the sensitive area in line with the nozzle in the X direction as closely as possible.

2. The modulated IR sensor is still slightly sensitive to ambient IR, although about 15x less sensitive than the unmodulated sensor of the Ormerod 1 in my tests. So if the machine is in a room that gets direct bright sunlight, the sunlight can affect the calibration.

I still observe a slight variation in trigger height using my IR probe. It is generally within 0.1mm of the calibrated value, just occasionally worse.

Before you do the final Z homing prior to printing, heat the nozzle and the bed to operating temperature. When checking the calibration height, make sure there is no plastic stuck to the bottom of the nozzle.

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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].

Just a quick postscript to this in case its helpful:

I printed a set of herringbone gears for the z axis (iamburny on thingivrse) and have also got in the habit of switching off the strip lights over the workbench during bed calibration.
Since then, I have not had any problems with the z axis.

Ralph