THE MEDUSA MACHINE - 3D Printer
Previous 3D Printer Designs
There are very many filament deposition 3D printers on the market today. Generally, these machines have motion of the print build table in one axis and of the extrusion head in the orthogonal axis. A few have a stationary table with the extrusion head moving in both axes using a cross-bearing or a tripod motion for the extrusion head. The printed part is constructed layer by layer under computer control and either the head assembly or the table is moved in the Z direction as each layer is completed.
The earlier machines had the filament drive motor co-located with the extrusion head. Some machines offered two extrusion heads for a choice of colour filament during a print operation. It soon became clear with these machines that one limitation on the speed of printing was the mass of the moving assemblies. The top speed of motion of the head assembly was limited by the maximum acceleration possible.
One improvement adopted was to move the extrusion motor and its feeding mechanism to the fixed frame of the machine and then supply the filament to the extrusion head via a Bowden cable arrangement. With the 'cable' being the filament the outer casing is often PTFE to reduce friction and minimise the force on the cable at the motor end.
Of course, reducing the mass of moving head in the one direction is helpful but the mass of the table with its build load still limits the acceleration and, therefore, speed in the other direction. This is where the cross-bearing and tripod designs have a potential speed advantage as the table is stationary and a Bowden type filament feed is used.
One over-riding feature of all of the above designs is that they are still limited by the rate at which molten filament can be supplied by one extrusion head. Consequently, it is often stated that, because it is slow, filament deposition 3D printing is only suitable for making prototypes or very small numbers of identical parts.
A New Concept of 3D Printer - The Medusa Machine - Dreamed up at The T-Exchange
The Medusa Machine incorroporates an alternative arrangement of motion to previous designs and is designed to provide much faster, quantity production of 3D printed parts by filament deposition. The configuration offers great productivity gains over traditional machines.
In this machine, illustrated in Diagram 1, there are two main structural elements, a frame and a base plate. The frame is a twin column and beam structure supporting the filament reels and a bridge carrying a number of extrusion heads, while a separate base structure carries the printing table. Both structures are mounted on a plane, flat, stiff base plate. The table is arranged to move in both the X and Y directions while the bridge moves only in the Z direction. As the extrusion heads move only a small distance, vertically each time a layer of material is deposited, they do not need a high value of acceleration. This means that the Z-motion support structure can carry a large number of extrusion heads, typically from one to ten or more. In the arrangement shown in the diagram below ten heads are configured in two banks of five.
In operation, each head has its own identical work area and each prints exactly the same object or set of objects owing to the motion of the table. The machine can carry one or two banks of extrusion heads that can be quickly mounted or demounted onto the bridge. The X, Y and Z motions are provided using sliding bearings on ground rods.
The table motion in the Y direction is by a toothed belt drive, where the driving motor and idler pulley are fixed to a stationary base frame attached to the base board. A leadscrew may alternatively be used to provide this motion. The X-axis motion is provided by a second toothed belt drive or leadscrew. The X-axis driving motor is mounted on the Y-carriage.
The bridge, together with the extrusion heads, is raised and lowered by a pair of vertical axis leadscrews. The two Z motion drive motors are synchronised and drive each leadscrew via a timing belt, geared to give a torque increase.
The filament is carried by spools, one for each extrusion head and mounted on the frame with a quick change arrangement. The extrusion heads themselves are mounted in two banks, one on either side of the bridge. Two heads on each side offers one quarter of the work-bed area to each head.
The build table is clad with a glass build surface and heated by an integral element with thermal insulation on the underside. In order to reduce the mass of the print build table, it is constructed as an integrated structure free from clips or clamps.
The design offers considerable advantages in a quantity production situation where, otherwise, a good number of individual single extrusion head machines might be required. With the need for only one control computer, considerably reduced space requirements and only one, rather than several operators, the machine offers significantly greater productivity.
List of Features of The Medusa Machine
The novelty in this new machine design can be described by the following set of features.
1) Within the limits of the overall size of the machine a number of extrusion heads can be mounted in one or two banks each typically carrying between one and six extrusion heads. In principle, the width of the bridge structure and table can be extended to carry ten or more extrusion heads.
2) These banks of extrusion heads are mounted on a bridge that is moved in the Z or vertical direction, generally up and down.
3) This bridge is raised and lowered in the Z direction by synchronised Z motion motors driving leadscrews.
4) The X and Y, or generally orthogonal and horizontal, motions are mounted on a stationary base and carry a sub frame on to which is mounted the build plate.
5) The X and Y motions are provided by two motors working through timing belts or leadscrews.
6) The extrusion head modules each carry a motor driving the feed filament directly into the extrusion head.
7) The extrusion heads have a spring loaded, quick release arrangement to permit simple insertion of a new filament.
8) Filament is supplied to the extrusion heads from reels mounted on supports that can be dropped onto the structure without any fixings required.
9) The print build table is constructed from a glass work-table, a heating element and a block of thermal insulation on the underside together with minor other components to permit stiff mounting of the assembly. All of these parts are bonded together to ensure stiffness and to minimise mass.
10) As is general practice, the machine's thermal conditions, motions and filament feeds are controlled by a micro-computer-controller. In the prototype, an ARM powered Smoothie Board is used.
We have called this concept and design "The Medusa Machine"
because of its multiple snake-like filament feeds and because, to some,
it may resemble a monster.
Diagram showing the main features of The Medusa Machine
The Medusa Machine prototype at the Orkney International Science Festival
Saturday 3rd September 2016
The Medusa Machine prototype at Forres Culture Day
Saturday 24th September 2016