Fighting with computers

Computers are not always friendly.

Thursday, March 27, 2014

Delta 3D printers

Since the presentation of the Rostock 3D printer, I have been amazed on the kind of motion that these machines make to print a part. While I have found quite hypnotic the way layers are deposited to create plastic part using fused filament fabrication, when the process is done by a delta robot instead of by a cartesian robot, the show is even more interesting.

However the Rostock was a big machine, not compatible with the space I have available at home. But when I saw Richard's 3DR printers, I thought it was a good way for me to venture into the interesting world of this type of printers. Contrary to the Rostock, the 3DR had a small footprint so I built one. But that was just part of the challenge.

Delta 3D printers use three vertical parallel carriages linked by a set of rods to a central platform where the hotend is placed. But contrary to some other printers, those vertical axis are not screw-driven but belt-driven, which allows very fast motion. As a result, Delta 3D printers can move the low-inertia effector very fast accurately. Besides, z-axis speed is no longer restricted compared to the other axis speeds, which enables operations like raising the hotend in z-axis when retracting (before a non-extruding movement).

The second part of the challenge is properly calibrating the printer. A bit more difficult that its equivalent on a cartesian bot. But this is an interesting world where smart people are creating cool innovations on a daily basis. A new feature to auto bed-leveling permits not to have to worry about bed-leveling when using a delta. This make its operation simpler but requires to have a way to detect when the head is touching the bed. Several ways have been developed to do that, like a dedicated retractable switch, proximity switches or even force sensitive resistors on the bed. But the most radical idea was to use the printer to probe itself in order to create its own calibration data.  Just run "G30 A" command and wait your printer to create its own calibration values.


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