Marionette 3D Printer Runs Without Rigid Rails
With a series of spools and pulleys, the Marionette 3D printer pulls an inverted extruder carriage on a slider across a pane of glass.
A 3D printer is a three-axis machine, as the name implies. The most common layout for 3D printers is Cartesian, which means that each axis moves independently of the others. Almost all Cartesian 3D printers have those axes riding on rigid rails, like hardened steel rods or aluminum extrusion. But that isn't a requirement and a 3D printer can abandon the rails and the Cartesian layout altogether. One very interesting example is Dizekat's Marionette 3D printer.
The Marionette 3D printer is extremely unique and we've never seen a design quite like it. The frame of the printer is aluminum extrusion, but almost all of the similarities to a typical 3D printer end there. The kinematics and mechanical setup share more in common with a cable robot than the 3D printers on the consumer market.
To understand how this works, lets first look at the XY plane. Instead of two sets of rails and bearings, the Marionette printer has a simple pane of glass and the extruder carriages moves around on a slider that contacts the glass. This is inverted, so the glass is on top and the carriage is pulled up against it underneath. The friction is low enough that it can slide without issue, so it can move freely in the X and Y axes while being constrained in the Z axis.
The printer moves the carriage slider using a pair of motorized spools that adjust the lengths of the cables that hold the carriage against the glass. Lengthen the left two while shortening the right two, and the carriage will move right on the X axis. Coordinating that movement requires some trigonometry calculations, like with a cable robot. A complex 3D-printed mechanism on top of the glass ensures that the cables maintain proper tension and length, relative to each other.
The Z axis is also unusual. The heated bed raises and lowers using another pulley system that distributes force across the four sides. And even the hot end is unique, as it sits at an angle relative to the bed with a 90-degree nozzle.
The electronics seem to be standard fare, though they certainly required custom firmware to translate standard g-code into the required trigonometric movements.
There are many potential problems with this design that all result from a lack of rigidity and the imprecision of spooled cable. But Dizekat was able to print a Speed Benchy in just under four minutes — though it looks pretty rough. The primary advantage of this Marionette design is cost, as linear rails and bearings are pricey. It also has the potential for high-speed printing, because the moving carriage is very lightweight.