Tuesday, August 07, 2007
Quick change artist
My MSc student Arman has modified his auto-head-changer (which always was for Mendel, not Darwin) to design and make a quick-change plug-unplug mechanism for the Darwin head. You have to take the head off quite often when you're setting up the machine, and also when you're using it. Before, that took about 15 minutes of fiddling with cap screws in hard-to-get-at places. Now it takes a couple of seconds.
The next thing we'll do is to make two heads: one for CAPA and one for HDPE so we can swap them ad-lib for experiments. We'll also put the balloon paste extruder on the same mechanism next to this one for support experiments.
I'm not sure if we want to change the Darwin design at this late stage, but this certainly makes things easy...
Labels: extruder changer
Monday, July 16, 2007
Mendel Preview
We are all working like crazy on RepRap 1.0 "Darwin" of course. But I have an MSc student, Arman Ghandizadehdezfuli, who is looking at Mendel for the future. Here's a video of the prototype extruder changer that he's designed being tested in Darwin. (The slight jerkiness is all from the cheapo webcam software; the actual movements were clean and smooth.)
The idea is to have a row of extruders along one (or more) sides of the machine, and have it pick each up and use it in turn so that many different materials can be incorporated in a single built object.
I had originally thought that each extruder would have its own RepRap controller attached to it. Docking and undocking an extruder would momentarily break, and then re-route, the token ring that allows all the controllers to communicate. But now I think that that would be unreliable. Better to have one controller on the moving carriage, and to connect the drives for the motors and heaters from that to each extruder when it is picked up. The extruder machinery doesn't need clean data during the moment of connection, and so this would be far more robust. Any extruder that needs a controller when it is parked (to keep it at temperature, for example) can have its own controller attached to its docking station that makes contacts in the same way.
Another change will be that the X, Y, and Z flags for the opto endstops will be on each extruder (rather than having just one set on the carriage), so the machine can always zero with precision and get the registration between materials exactly right. The picker-upper grip on the extruder in the carriage is firm, and it doesn't move. But this zeroing scheme would also mean that the grip wouldn't have to grab an extruder in exactly the same place each time.
The idea is to have a row of extruders along one (or more) sides of the machine, and have it pick each up and use it in turn so that many different materials can be incorporated in a single built object.
I had originally thought that each extruder would have its own RepRap controller attached to it. Docking and undocking an extruder would momentarily break, and then re-route, the token ring that allows all the controllers to communicate. But now I think that that would be unreliable. Better to have one controller on the moving carriage, and to connect the drives for the motors and heaters from that to each extruder when it is picked up. The extruder machinery doesn't need clean data during the moment of connection, and so this would be far more robust. Any extruder that needs a controller when it is parked (to keep it at temperature, for example) can have its own controller attached to its docking station that makes contacts in the same way.
Another change will be that the X, Y, and Z flags for the opto endstops will be on each extruder (rather than having just one set on the carriage), so the machine can always zero with precision and get the registration between materials exactly right. The picker-upper grip on the extruder in the carriage is firm, and it doesn't move. But this zeroing scheme would also mean that the grip wouldn't have to grab an extruder in exactly the same place each time.
Labels: extruder changer, multiple materials
