Printer Z Axis ballscrew brake designs?

CNCModeller

Hi All,
Does anyone know of a printable / DIY brake for a printer z axis ballscrew to stop the axis dropping on power failure? I really don't want the print head crashing into my print now that I'm enabling power loss recovery. I've thought about just using a counterbalance mass hanging inside the spine of my printer but it's not ideal for easily moving the printer around which I tend to do quite regularly.

I did come across the idea of using a spring loaded RC car brake and servo which I to hold it off which I quite like.

I can't find much in terms of off the shelf designs online, so I thought I'd ask before I wade in to designing one from scratch.

Many thanks
Barry M

mrehorstdmd

If you want to resume printing, the bed can't drop more than a few microns. You can get motors with brakes that are held off while there is power and activate when the power is lost, but I don't know if they would act quick enough to stop the bed from moving more than the acceptable few microns.

Counterweights might be workable but can cause backlash.

I used belts to lift my printer's Z axis (the bed) and drive it with a 30:1 worm gear that is irreversible under the loads the printer presents. When power fails the bed doesn't move. Upon power resume, the motor will jump some random amount up to 2 steps in either direction, which in my printer translates to +/-40 um (20 um/ full step), but in the limited testing I have done, I have never seen visible movement, and I haven't mounted a gauge on it to check. Hmmm. Another test to try...

CNCModeller

Thanks @mrehorstdmd,
I like the worm gear idea., Will look into it.

To restart a print I'll be re-homing to z max. So don't need to worry about a small drop as long as it doesn't crush the print significantly.

As long as a counterbalance doesn't totally remove load from the ballscrew it shouldn't introduce backlash as it'll always be loaded in the same direction by gravity.

This printer is a fairly unorthodox design so it has its own design features that need working around lol.

Many thanks again.

Barry M

o_lampe

@cncmodeller said in Printer Z Axis ballscrew brake designs?:

I really don't want the print head crashing into my print now that I'm enabling power loss recovery

How about a second power source?
There are big lithium batteries (4-5S RC-stuff), ready to keep the axis position alive for a long time (no bed heating, sorry)
I've used 'dual-Schottky diodes' to decouple the PSU from the battery. The battery would only come into play, when the PSU voltage is lower than batt-voltage.
RRFs power failure would have to be triggered above batt voltage otherwise the printer would move on.

You can even add an alarm to the batt.

CNCModeller

@o_lampe said in Printer Z Axis ballscrew brake designs?:

@cncmodeller said in Printer Z Axis ballscrew brake designs?:

I really don't want the print head crashing into my print now that I'm enabling power loss recovery

How about a second power source?
There are big lithium batteries (4-5S RC-stuff), ready to keep the axis position alive for a long time (no bed heating, sorry)
I've used 'dual-Schottky diodes' to decouple the PSU from the battery. The battery would only come into play, when the PSU voltage is lower than batt-voltage.
RRFs power failure would have to be triggered above batt voltage otherwise the printer would move on.

You can even add an alarm to the batt.

@o_lampe Yeah I've been looking into a small UPS. Hopefully that'd give time to park and enough time in pause mode with really low power motor settings to hold things in place.

On the other hand it's really annoying to hear the print head crash into the bed when the printer is turned off intentionally. I use a little spring clamp on the rails currently to stop this happening, hence leaping to the brake idea first.

All the best
Barry M

o_lampe

@cncmodeller said in Printer Z Axis ballscrew brake designs?:

I've been looking into a small UPS

An UPS does exactly the same, but on AC side. In my country it's more likely to see the PSU fail (in that case the UPS would be useless) than having a mains power failure, hence the DC-power supply.

Big business means big measures, you might need a small emergency generator too? (fired up from the UPS?)

CNCModeller

@o_lampe if things take off then I'll be building a farm of these printers, in which case you may be right lol. That's a little bit further down the road though, let's just get some reliable long term printing with this MK2 polar design :-), further updates and improvements are already in the pipeline!

Thinking about it you raise an interesting point about power supplies. My bed axis will be running on a different PSU so the main board won't be aware if that fails... Perhaps I need a relay across its output and a trigger in the setup to detect failure of the second PSU and trigger a power failure response.

Food for thought...