A different multi-extrusion approach - UM tool / printhead changer

[foehnsturm 943]

I've been following this dual extrusion discussion for some weeks now. The more I read the more I get the impression that the usual approach doesn't fit for UMs at all. Too bulky, too heavy and so many well known flaws, like oozing and having the second nozzle knocking down prints. It simply makes no sense to me to carry around a second hotend all the time.

So I suggested independently moving heads or a tool changing mechanism like CNC machines are using.

I couldn't resist ...

Just a proof of concept right now but way better then I expected:

0.0 positioning play within the mount, more than enough clamping force, no additional actuators needed

C'mon, if I can get this far in two days ...

 

Edited April 20, 2015 by TheDeugd

[darkdvd 775]

Prima !

 

[pm_dude 26]

Its taking a lot of space but it looks pretty good . Keep it up!

[drayson 67]

Very interesting concept!!

Please keep us updated - worth taking a deeper look :-)

[Titus 170]

I like seeing this! I really like what you are doing!

Though just some advocate of the devil remarks to tickle you a bit to get an even better result

It takes up so much space

It continues to leak

How is the accuracy of collecting and leaving the head there after 100 times?

If you have a lot of switching between heads it takes so much time

 

[aviphysics 9]

Lovely mechanism. Mostly, it looks like the machine needs to be bigger. I would be very impressed if you got that hot swapping mechanism small enough to not be a giant space hog.

 

[macua85 52]

It never ceases to amaze me what you come up with! This is open source at its best, looking forward to seeing if its workable. I assume the space constraint it the size of the carriage required to carry the direct extrude mechanism you are using? A carriage with bowden only would be much smaller I guess.

 

[foehnsturm 943]

Space requirements:

I'll go for the difficult job as I want my NEMA8 direct extruder to be the tool head. The "cartridge" will measure 30 x 40 mm, not that big for a direct extruder... The final gripper with a cartridge attached will be roughly 55 x 45 mm. The current one is big because I'm using my modular mount to be able switch to my standard printhead within a minute. Of course the parking lots take up some print space. I'll loose 50 mm of one axis.

But that's only a prototype.

If you go for a bowden setup , especially with a tiny hotend like the Merlin, it would be easy to have a cartridge with 20 mm square and the reduction of print space should be approx 30 mm in one direction.

And even better: If you don't need multi extrusion, you could simply take out the parking lots and use the entire printing area.

Oozing:

The final parking places should feature some kind of heat resistant and soft material where the nozzle tip sits. And at least, the oozing doesn't harm the print.

Durability:

PLA printed parts might degrade due to wear and tear. But there are so many tool changers out there which are carrying really heavy tools heads with precision in micron scale. It should be quite easy to find optimum material combinations for this tiny mount (PTFE / Aluminum ?)

Required time:

One could park all heads closely together in a magazine but that would take up a lot of space. Anyway, I think the time for reheating the previously unused hotend is in the same scale as the required time for moving.

 

[foehnsturm 943]

What impressed me most is that the tiny magnets work exactly as intended. There is no need for generating an additional signal or having an actuator. Just a simple movement pattern in the x/y plane.

 

[drayson 67]

AAAhhhh...... magnets - I really like this idea.

how do you plan to add more cartridges? in x or y? ask because I think there is much more space needed when add additional ones.

Another thing is the stepper itself - when having it on each cartridge, it might be possible to also quickplug the stepper cables to add more feeder steppers than supported by the board/FW.

So maybe the second feeder output could be used for a revolver...?

:-)

 

[foehnsturm 943]

Right, you can virtually add any kind of tool head if its z-height is properly adjusted.

I'll use the free space in both right corners. It's a two sided gripper.

There is approx 30 mm clearance between the x/y rods and the frame. So I won't loose noticable y travel. In fact you can use almost full x travel in the middle area you just have to avoid some area near these two corners (like the UM2 bed clamps).

 

[Labern 718]

Good Idea. It can be designed so it doesn't take up much additional space quite easily. Cant say how in words though. I may just have to print one 2 :cool:

 

[Anders Olsson 132]

Nice work! :smile:

It was something like that I had in mind when I wrote "magnetic kinematic mount" in the custom heater block thread.

We use Thorlabs kinematic mounts at work, you can have a look at how those are designed if you consider making a metal version: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1546&pn=KB75/M

Using three ball bearing balls and steel rods like on the Thorlabs mounts makes it both very precise and durable.

There are many interesting possibilities that appear if you can switch heads like that.

For example you might be able to change filament in the parked head while the other one is printing. Or use more than two heads if they are compact.

With a more complex software you could even think of changing from extruding to machining tools, but the software for doing that probably will not be available anytime soon.

 

[danilius 117]

That's a seriously nice design. It would be interesting to see the sort of accuracy/repeatability you get with this setup as-is.

 

[foehnsturm 943]

We use Thorlabs kinematic mounts at work, you can have a look at how those are designed if you consider making a metal version: https://www.thorlabs...=1546&pn=KB75/M

 

Holy shit that's precise.

It would be interesting to find out how much clamping force is possible with my lock/unlock idea.

It's basically a linear movement onto a wedge which produces shear force to overcome the break away force of the magnets. Followed by a perpendicular movement to move away (or the other way around).

Right now the stepper / belt setup has no problem at all with the required forces.

 

[foehnsturm 943]

That's a seriously nice design. It would be interesting to see the sort of accuracy/repeatability you get with this setup as-is.

 

That'll be the next step. However I'll have to finish a second NEMA8 / worm gear extruder for that and this will require some free time which I can spend at my lathe. Don't want to disassemble the working one every time.

 

[Daid 283]

This is a seriously cool design! I am wondering about the repeatability, but I'm pretty sure you could manage to get that down to what's required.

 

[Titus 170]

Then one other thing we need to look out for is the height calibration of the two nozzles. Wonder if an "autolevel" with each " revolving" head could be a solution.

Also, about the holding and oozing. If you were to create a nozzle block/shield that keeps it from oozing, not only will your print bed not be a mess, you'd still have plastic in the nozzle when you resume printing with it, and you can leave it hot!

 

[foehnsturm 943]

Yeah, the Merlin hotend is easy to adjust because it features an outside thread and can be rotated against the aluminum mounting part.

The more generic approach of course would be to design a slim mounting adaptor with slotted holes which can be attached to whatever hotend you like. Some procedure like: Mount the hotend with the adaptor to the gripper, loosen the screws, let it drop down to the print bed, retighten screws ...

 

[duesentrieb 0]

Brilliant idea! Love that one. I also like your direct extruder and flexdrive approach. Hope I will soon have the time to start thinkering with my printer as well.

About the garage, that name inspired me to an idea. Thinking about special garages, where you can park one car upon the other, because they have a lift. What if you just had sth. like a lift for the garage with the unused print head? The garage could swing away or just being lifted above the area where the print head moves with a parallelogram type hinge. To operate this lift a very cheap, simple and fast solution would be this motor for a central locking system of a car:

http://www.pollin.de/shop/dt/MTE1OTg2OTk-/Motoren/DC_Getriebemotoren/Stellmotor_fuer_Zentralverriegelung_12_V_.html

Can lift up to 7,5kg, which is more than enough, travels 20mm, is fast and requires only 12V to operate. If you use a spring to keep it in the upper position, all you need to do, if you want to change is, put 12V on the motor for the change time and if no voltage is applied it would lift automatically. Used them on another project and wired them up to an Arduino, with a Transistor amplifing the signal. The only thing is you need an additional I/O pin on the electronics. There are free ones, but im not sure which one is best and if maybe another unused M-code for this PIN exists.

Saves print space, but increases complexity. With this setup you could even change between more than 2 print heads.

Just my 5 cents. Not sure if it is worth the work.

 

[foehnsturm 943]

With a simple lever which increases travel to 60 mm one could lift a tool magazine in a way that it wouldn't interfere with the x/y rods anymore.

 

[meduza 189]

I just started to think about building the mating side as the thorlabs mount, with a printed part that you insert small rods in, and a mating printed part with steel balls, and a magnet in center, should be perfectly realizable and you would not put any wear on the printed parts during switching that would affect the long-term accuracy.

 

[foehnsturm 943]

Sounds good.

You want to have an area within the mounting surface where you can attack with a wedge shaped part for unlocking (or find another way how to break the high holding force of the magnets with comparatively low force). This linear move - wedge - shear force trick is actually the idea I'm really proud of :wink:

 

[foehnsturm 943]

So what is next?

a)

Repeat accuracy testing with a NEMA8 direct extruder cartridge which has to be finished.

b )

Building a second cartridge and cartridge holder

Ideas so far: another identical direct extruder or a direct extruder with 1:20 gear and for 1.75 mm filament or a flexdrive cartridge

1.75 mm is interesting but a later dual extrusion test would require identical filament diameters afaik.

c)

Prepare for dual extrusion: electronics, firmware

I didn't take a closer look into gcode generating for dual extrusion so far. Extruder switching would require a short roundtrip between the two cartridge holders and coming back to the initial position (with the usual dual extrusion offset, as I would use a two sided gripper). Cura Plugin?

d)

Replacing the bulky modular printhead gripper part with a most compact all-in-one design.

e)

laser cartridge, ink / felt tip cartridge for painting perimeters after printing ...

Obstacles: Two main professions ...

[aviphysics 9]

(e) sounds like it would be really cool.

I wonder if something like an inkjet cartridge could be applied in an effective way.