Z axis Brake

Hi there,

I am designing a brake for my belt driven Z axis.
The plan is to use a small solenoid wich clamps to an 8mm rod, which is attached to the Z motor using a coupler.

photo of the design in attachment, i will be testing it tomorrow.

It would prevent the Z axis from crashing down when power is cut.
I also need to make sure the Z axis does not crash when turning the power on since the Solenoid retracts when power is on.

To prevent a crash at power on i therefore need the Z axis motor to move just a little bit as soon as the duet2 gets power.

Can anyone explain the easiest way to do so? I suppose it could be something similar to a "resume after power off" code.

Cheers

Edited 3 time(s). Last edit at 08/12/2020 06:51PM by Govahnator.

You could put G91 G1 H2 Z0.1 G90 towards the end of config.g. We don't normally advise putting movement commands in config.g but in this case it seems justified.

I am looking at various options to support motor brakes in RRF. One is to assign a pin as a brake for an axis, and turn it on whenever the axis motors are enabled. Another is to add a command to power up motors without moving them.

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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].

Quote
dc42
You could put G91 G1 H2 Z0.1 G90 towards the end of config.g. We don't normally advise putting movement commands in config.g but in this case it seems justified.

I am looking at various options to support motor brakes in RRF. One is to assign a pin as a brake for an axis, and turn it on whenever the axis motors are enabled. Another is to add a command to power up motors without moving them.

Thanks for the fast response!

Looks like i will have to look into a different design for my brake though, it is not able to hold the 8mm rod, which makes sense if i look at it now.

I'm using a different solution. Maybe it will be helpful to you.
Source(rus)

Quote
Reanimator2k
I'm using a different solution. Maybe it will be helpful to you.
Source(rus)

Interesting! Thanks for sharing.

I will look further into this.
Not sure if i can use it on a Nema23 and Duet2. Also not sure if this combined with 4.7 ohm resistors will do for me.

Quote
Govahnator

Quote
Reanimator2k
I'm using a different solution. Maybe it will be helpful to you.
Source(rus)

Interesting! Thanks for sharing.

I will look further into this.
Not sure if i can use it on a Nema23 and Duet2. Also not sure if this combined with 4.7 ohm resistors will do for me.

It seems to be quite universal. I think the most important thing is to use bipolar stepper motors. A very elegant solution. Thanks for sharing Reanimator2k.

Edited 1 time(s). Last edit at 08/20/2020 06:03PM by Ohmarinus.

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http://www.marinusdebeer.nl/

I tested shorting the Z axis motor in my belt lifted Z axis in UMMD before I installed the worm gear drive. Here's what happened...
The braking action is proportional to the current in the windings. The current is a function of the motor's rotational speed. If the motor doesn't spin, there's no current and no braking. So the motor spins, and the bed drops. Shorting the coils does not prevent the bed from dropping. It's progress is slowed initially, but it accelerates linearly (?) at first, and then gets to some speed where the braking no longer seems to work and it drops hard and fast. Maybe that's a function of the length of the z axis and the mass that's dropping. Maybe in a short Z axis, it will lower itself gently and never accelerate to the point that it crashes. In my 700 mm long Z axis, it definitely got to the point of crashing.

I'm not sure why you'd want to put resistors into the circuit. They will limit the current and the braking. It would be simpler to put springs at the bottom of the Z axis and let the bed drop. The end result is the same. The bed will end up at the bottom of the Z axis when motor current is cut.

Maybe you could couple the bed to some very strong magnets dropping through copper tubes to slow the drop...[www.youtube.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
I tested shorting the Z axis motor in my belt lifted Z axis in UMMD before I installed the worm gear drive. Here's what happened...
The braking action is proportional to the current in the windings. The current is a function of the motor's rotational speed. If the motor doesn't spin, there's no current and no braking. So the motor spins, and the bed drops. Shorting the coils does not prevent the bed from dropping. It's progress is slowed initially, but it accelerates linearly (?) at first, and then gets to some speed where the braking no longer seems to work and it drops hard and fast. Maybe that's a function of the length of the z axis and the mass that's dropping. Maybe in a short Z axis, it will lower itself gently and never accelerate to the point that it crashes. In my 700 mm long Z axis, it definitely got to the point of crashing.

I'm not sure why you'd want to put resistors into the circuit. They will limit the current and the braking. It would be simpler to put springs at the bottom of the Z axis and let the bed drop. The end result is the same. The bed will end up at the bottom of the Z axis when motor current is cut.

Maybe you could couple the bed to some very strong magnets dropping through copper tubes to slow the drop...[www.youtube.com]

This again reminds me of using a counterweight. But the magnets with copper are also a really nice low-tech solution, using the Eddy currents. Aluminium plate or copper plate would suffice, so you can use a tube with the side cut open. Using a full pipe introduces more difficulty since you need a system that runs through it instead of alongside of it. Unless you run the belt through the pipe with a magnet attached to the belt.... Hmm. If you move the Z-axis slowly it won't have much drag from the Eddy currents, but when it drops faster it will definitely slow it down. Also what's nice is that the forces still act on the point of fixture to the Z-carriage that way and are not offset.

Edited 1 time(s). Last edit at 08/21/2020 02:49AM by Ohmarinus.

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http://www.marinusdebeer.nl/