Automatic extruder changer

I had an idea the other day on how to build an extruder changer where the extruder is static, i.e. the build platform moves on all three axes. The design could probably be modified to work on printers where the extruder moves on the x and y axes. Below is an animation I threw together to illustrate the idea:

Each of the extruder blocks would contain a hot-end, hobbed bolt and idler wheel. The motor however is kept separate. To select a new extruder the current one is lifted up, disengaging the motor. The new extruder is moved inline with the motor, then lowered into place. As the extruder lowers the motor re-engages with the new extruder.

There are a couple of challenges however:

• Modified firmware will need to be implemented. This includes remembering the motor angle to prevent jams when re-engaging.
• The extruder needs to be secured into place when lowered. A tapered slot and/or strong magnets could work.
• A method needs to be devised for raising/lowering the extruder. A geared DC motor with a crank type linkage is one solution. The raised and lowered states can be indicated by limit switches.
• A drive mechanism is needed for the extruder "carousel". One method would be to use a rack and pinion configuration. The stopping points can be indicated by using an optical switch and flags on each extruder

I personally have no plans to implement this, but I thought I should put the idea into the public domain so that it will remain free for anyone to use.

Edited 1 time(s). Last edit at 10/06/2013 09:44AM by samp20.

samp20 Wrote:
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> I had an idea the other day on how to build an
> extruder changer where the extruder is static,

Lovely idea.

It might be one less operation if the motor was fixed and the coupling was a pair of gears. As the new head comes down it's gear would mesh with the motor gear.

Many older plotters used to use the X and/or Y limit positions to do interesting things, they would release paper clamps or change pen colours typically. I vaguely remember hearing of a tool or head changer that was actuated by the carriage moving past normal working limits to actuate a mechanical selector. You could possibly do something similar.

Old (Roland) pen plotters used to have a row of pens that would be changed merely by pushing the two pen holders together, the pen would be transferred from one to the other so the current pen would be parked and a new pen fetched with very little effort. With magnets perhaps a push on ans slide off system could work.

Many contemporary CNC mills with tool changes have a parking position and then the head goes to swap the tool, this is a 3D process and there is usually some kind of clamp to hold the tool, larger machines have a pneumatic clamp.

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Kalle
--
Lahti, Finland
The only stable form of government is Open Source Government. - Kalle Pihlajasaari 2013

This is a really awesome idea! I would imagine that once you align all of the hobbed bolts so that they are aligned with the motor shaft it probably wouldn't get too misaligned either if the motor is consistent about how it is aligning the hobbed bolts before it is disengaging. I think there should be a way to engineer the hobbed bolt and motor coupler so that the sides are sloped so that even if it is a little out of alignment it should have some wiggle room to get pushed into the correct position. I have in mind something that sort of looks like a one way screw:
[www.alliedboltinc.com]
It would have to be different obviously because you'd want to move the motor in both directions. Maybe you could have something like this:
[imgur.com]
If it was offset a little, the curve in the female side would allow the male side to correct itself before locking in.

I also had an idea that was similar where I wanted 1 motor and then multiple hobbed sections on a bolt. You would use servos to actuate idlers on each hobbed section so you could get multiple colors with 1 motor + several servos. Just a thought.

I don't think alignment should be too much of an issue since the hobbed bolts are unlikely to rotate when not in use, making it easy to remember their angle. In the animation, although difficult to see, the motor attachment is slightly tapered to help. I really like the idea of using gears instead though. It would completely negate the need to move the motor and would mesh easier too.

I think this could work really well on a H-bot too. Have the motor fixed on the XY gantry, and off to the side have the carousel of extruders. The steps to change the extruder would be as follows:

1. Move the gantry towards the carousel
2. Unlock the extruder
3. Move away to allow the carousel to move
4. Move back to pick up the new extruder
5. Lock it in place and continue printing

For the locking/unlocking a solenoid or servo could be used to insert a pin into the extruder. This whole idea isn't limited to extruders either. I see potential for an automated PCB manufacturing machine which mills, extrudes solder paste and places components without human interaction. You could also have a tool to pick up the final PCB and transport it to a toaster oven for reflowing (I think I'll stop there before I get too carried away).

I'm tempted to see if I can get this idea working with an XZ gantry setup. The major issue is the Z axis is slow, so any movement on that axis to change tool will likely increase print time dramatically. I'm currently building a printer with aluminium extrusion, so it should be easy to bolt additional parts onto it for experimentation. Also I plan to drill a 9x9 grid of tapped holes in my build platform to allow attachment of anything I dream up.