GB2508007A

GB2508007A - 3D printer suitable for constructing buildings

Info

Publication number: GB2508007A
Application number: GB1220699.1A
Authority: GB
Inventors: Tim Denholm
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-11-16
Filing date: 2012-11-16
Publication date: 2014-05-21
Also published as: GB201220699D0

Abstract

A 3D printer suitable for printing buildings for domestic habitation comprises a print head 1 adapted to print mortar incrementally upon a base 3. The 3D printer comprises means for mixing at least water and a binding agent to form mortar. First 6 and second 5 guide means are provided which are adapted to jointly control relative horizontal motion of the print head and base along a non-linear (arcuate) guide path. Vertical motion control means, at least one motor and drive train are further provided. The 3D printer preferably comprises a column and at least one arm supporting the print head for substantially pivotal motion around the column and vertical motion up the column. Aprotective tent may be provided to surround the print volume. The print head may be adapted to selectively dispense a mortar and a polymer. A 3D printer wherein the first and second components of motion are non-orthogonal, the first guide means is adapted to pivot about a first vertical axis to affect a circumferential position of the print head and the second guide means controls the radial position of the print head is further provided.

Description

A 3D Printer The present invention relates to a 3D printer for producing a physical 3D object by incremental addition of material, working from the bottom of a print volume upward. The invention is applicable

to the field of 3D printing.

In the past a variety of 3D printers have been described in the literature or marketed which have a print head that deposits a solidifiable material (E.g. molten polymer) which hardens or dries to become solid and contiguous with the 3D object. A second type is known where a material (e.g. powder or liquid) is spread on top of the object and the print head causes the material in desired locations to either melt, solidify, sinter or to otherwise become contiguous with the 3D object, e.g. by application of heat or light. Both of these types of printers involve relative motion between the print head and the object being printed, with the relative motion being independently controllable in three orthogonal linear directions. Typically the print head moves in two independently controllable orthogonal linear axes enabling motion in a horizontal plane, while the object on a platform can be moved in a vertical direction.

One problem with these known arrangements is that three independently controllable servo motors, and three independent orthogonal linear guides are required to control relative motion of the print head and object being printed, which makes them more expensive than 2D printers.

Another problem is that two of the motors and guides need to be controlled to move back and forth repeatedly, so that the motors turn alternately clockwise and anticlockwise. The alternating direction of motor & drive-train motion gives rise to a source of error in the relative positioning of print head and the object being printed. This is known as backlash. The associated repetitive starting, stopping and direction reversal is both a source of wear and requires the motor to be more powerful than A third problem is that the print head needs to be supported by a large, heavy print chassis as wide as the print area, and the printer requires a rigid printer housing surrounding the print volume to hold the print chassis rigidly, which for large objects is quite expensive.

According to a first aspect of the present invention there is provided a 3D printer, for printing physical objects by incremental addition of material thereto, the 3D printer having: a pre-defined printing volume having a base thereof, a print head adapted to add or join printing matter incrementally upon the base to contiguously build up a physical object, the print head having a predetermined maximum horizontal printing thicknesses, a first guide means adapted to control a first component of relative horizontal motion of the print head and base, a second guide means adapted to control a second component of relative horizontal motion of the print head and base, the first and second guide means adapted to jointly control relative horizontal motion of the print head and base along a non-linear horizontal guide path including substantially any position within a horizontal print area, vertical motion control means for controlling relative vertical motion of the print head and the base, at least one motor or like means, at least one drive train arranged to be driven by the at least one motor, and arranged to drive at least one guide means to control relative motion of the print head and the base along the horizontal guide path, and wherein; the first component and second components of relative horizontal motion of the print head and base, are non-orthogonal, and; the first guide means is adapted to pivot about a first vertical axis thereof, to affect a circumferential position of the print head relative to the first vertical axis, such that the first component of relative horizontal motion of the print head and base is an arc coaxial with the first S vertical axis, and the second guide means is adapted to affect at least a radial position of the print head with respect to the first vertical axis.

This printer configuration allows a range of beneficial designs, with several potential benefits depending on the design chosen. For example, designs are possible where the drive train components (e.g. motor & cogs) each turn in one direction throughout the printing process (which minimises backlash positioning errors caused by inaccuracies in manufacture of drive train components, and mitigates wear on components, thereby permitting use of cheaper manufacturing methods and/or materials to achieve a desired printing accuracy and durability). This is more important for small printers e.g. for domestic use. Similarly the described configuration makes it possible to eliminate the rigid and load bearing print housing normally required, so the printer can be less bulky, less heavy and more easily assembled/disassembled, which is more important for large printers. Not all embodiments will achieve all of the benefits described or solve all of the problems described.

Preferably the second guide means is adapted to rotate around a second vertical axis, the horizontal position of the second vertical axis being arranged to be controlled to move in an arc around the first vertical axis by the first guide means, such that the second component is an arc coaxial around the second vertical axis, and the position of the print head is determined by the sum of the first and second components. This provides a simple arrangement whereby the two guide means can jointly position the print head anywhere within the print area. Preferably the first and second guide means are adapted such that in use their motion is mechanically coupled so as to control the print head to follow a path that is pre-determined by the mechanical coupling of the respective motions of the first and second guide means, the pre-determined path being substantially an epicycloid, hypocycloid, epitrochoid, hypotrochoid or spiral, such as to fill the horizontal print area leaving substantially only gaps that are comparable to said maximum horizontal printing thickness.

Preferably the first and second guide means constitute a horizontal arm extending from the first vertical axis, the print head is at a first end of the arm, the first guide means is adapted to control the circumferential position of the first end of the arm, and the second guide means is adapted to extend and retract the arm to control the radial position of the first end of the arm. This provides an alternative simple arrangement whereby the two guide means can jointly position the print head anywhere within the print area. Preferably the two guide means are independently controllable. This enables higher print speeds of objects that do not fill the print volume (e.g. hollow objects), and enables the print head motion to be limited to a non-circular print area.

Preferably the first and second guide means and the vertical motion control means are together substantially driven and controlled either by just one or two motors. This reduces the cost of the 3D printer. Optionally, to further reduce the cost of the 3D printer, the guide means and vertical motion control means may be together driven and controlled by just one motor.

Preferably the vertical control means is controlled in concert with at least one of the first and second guide means. This reduces the cost of the 3D printer.

Preferably the first and second guide means are adapted to control respective circular motions around respective pivots, the second guide means controlling the print head to revolve around it at a radius R2 from it's pivot, the distance between the pivots being Ri, and the ratio R1:R2 being 10, such that the print head is controlled to pass through or underneath the pivot of the first guide means. This ratio provides a simple arrangement whereby the printer is able to print in the centre of the print area without requiring a third guide means (such as a print that can move relative to the second guide means, for example primarily to position either of multiple print heads to a main printing location).

Preferably the base is provided by a print platform, and where one of the first and second guide means is associated with the motion of the print head, and the other guide means is associated with a rotation of the print platform about a vertical axis. This simplifies the motion of a print head cable, avoiding the need for careful positioning of motor cabling to avoid twisting of the cabling and/or mechanisms to compensate for or prevent twisting of the print head cable.

Preferably the vertical control motion means includes a substantially cylindrical print housing with an inner thread. This provides a simple guide mechanism, and by allowing the print platform or print head to move within the print volume, this avoids the need for extra space to accommodate drive train components extending away from the print volume, thus enabling a reduction in size of the printer design.

Preferably the printer is for printing hollow objects (especially but not solely buildings), and the vertical motion control means includes a vertical rod arranged inside the print volume. This is a cheap and simple mechanism, which also permits a reduction in size of the printer design. With this arrangement, preferably the first and second guide means are jointly adapted or controllable to restrict the motion of the print head and support components thereof to a non-circular print area.

This is useful if there is a limited space available for the printer (especially in the case of a building printer), and if the object to be printed is substantially square or rectangular (again especially in the case of a building printer).

Preferably, the print platform is a stationary print platform, and the print head is adapted to move both horizontally and vertically to traverse substantially the whole of the print volume. This is beneficial as the print head and print chassis can be stowed inside the print volume when not in use, and because such printer designs can be cheaper or simpler.

Preferably at least one drive train is arranged such that at least one motor is only required to turn in one direction during printing. This has the advantage that backlash is eliminated from that or those drive train(s), which means that less accurate, and thus less expensive, components can be used to achieve a desired printing accuracy.

Preferably the drive train and/or the first and second guide means are provided as a module adapted to be conveniently interchangeable, in exchange for at least one alternative module, such that a horizontal width of the print volume can be modified and/or such that a density of the guide path can be modified. This has the advantage that a user can select an optimised print area and/or print density for the printing task at hand, thereby reducing the printing duration.

The author has also identified a further related invention: According to one aspect there is provided a 3D printer, for printing objects by incremental addition of material thereto, the 3D printer having: a pre-defined printing volume having a base thereof, a print head adapted to add or join printing matter incrementally upon the base to contiguously build up a physical object, the print head having a predetermined maximum horizontal printing thicknesses, a first guide means adapted to control a first component of relative horizontal motion of the print head and base, a second guide means adapted to control a second component of relative horizontal motion of the print head and base, the first and second guide means adapted to jointly control relative horizontal motion of the print head and base along a non-linear horizontal guide path including substantially any position within a horizontal print area, vertical motion control means for controlling relative vertical motion of the print head and the base, at least one motor or like means, at least one drive train arranged to be driven by the at least one motor, and arranged to drive at least one guide means to control relative motion of the print head and the base along the horizontal guide path, and wherein; the 3D printer is suitable for printing buildings for domestic habitation, the print head is adapted to print mortar, and the 3D printer comprises means for mixing at least water and a binding agent to form mortar.

This has the advantage that the cost and time required to build a house can be greatly reduced, and the cost of including a variety of typically very expensive style features or complicated design elements is vastly reduced. The 3D printer may advantageously, but not necessarily utilise the invention defined in the first aspect. Mortar has an advantageous combination of properties, including the ability to be extruded, having reasonably low cost and high physical strength for security, while being non-melting and non-flammable.

Preferably the print volume is at least 50 cubic meters (1800 cubic feet), typically greater than 200 cubic meters (7000 cubic feet), and more typically greater than 450 cubic meters (16,000 cubic feet), and typically the print volume is less than 10,000 cubic meters (350,000 cubic feet). The range 450 - 10,000 cubic meters covers the range of print volumes suitable for printers that could print typical houses, however for printing buildings other than houses, the buildings may be of a size that the print volume will be outside that range, for example potentially as low as 50 cubic meters.

The maximum printing thickness is preferably at least 3mm, more preferably at least 10mm, thereby reducing the time required to print buildings. Optionally the print head is adapted to vary the print thickness by at least a factor of 3, preferably at least a factor of 10, so as to both enable fine detail and maximise printing speed.

Optionally, the print head is adapted to selectively (e.g. including alternately) dispense mortar and polymer. This enables waterproof surfaces to be built included in the walls, floors, ceilings and/or roof of the house.

The printer may comprise a column, and at least one arm supporting the print head therefrom for substantially pivotal motion around the column and vertical motion up the column. This enables a much smaller and/or lighter print head support arrangement, which becomes increasingly important for larger buildings.

Optionally the 3D printer has a protective tent and the vertical control means is a central vertical rod within the print volume. This has the advantage of being much cheaper than a rigid, load-bearing housing, while still offering protection from wind and rain during the printing process. The tent may however support cabling from a roof thereof. The rod is preferably segmented and adapted to be disassembled e.g. from within the building.

The term mortar encompasses, fluids adapted to harden into a ceramic, preferably including water, a ceramic filler (such as sand) and either lime or a similar ceramic binder. The mortar may also include additional ingredients such as polymers or surfactants to provide improved flow characteristics. The mortar can be used to create non-flammable, structural support, elements such as pillars, beams, arches, ceilings and walls (ceilings are preferably curved to reduce the material required for the desired strength but more importantly to facilitate printing of a ceiling without any underlying interim support structures. Either the mortar or the polymer can be used to create insulating cellular structures within walls, floors and ceilings. The polymer fluid can be deposited to form layers to mitigate water ingress (for example as a damp proof course or as a coating for a flat roof surface), to create floor surfaces, and/or to create pipework within walls, floors and ceilings as well as guttering and drainpipes outside then walls. Either fluid can be used to print a variety of furniture, utility or decorative items, including kitchen units and pre-plumbed bathroom units. If the polymer and mortar have distinctly different colours or shades (when hardened), then they can be mixed to create contrast and patterns (e.g. faux brickwork, tiling or pebbledash) on exposed surfaces, thus avoiding the need for additional colourants to be printed or mixed within the print head, and avoiding the need for the building to be painted thereafter. If the polymer fluid is adapted to set to be substantially translucent, it can be used to create translucent wall sections, skylights and shower cubicles.

The advantage of a 3D printer, over traditional building construction methods, is that the printer can be left alone for weeks or months thus mostly eliminating construction labour costs. The new process additionally permits design options and features at essentially no extra cost which were previously cost prohibitive. Although mortar is more expensive by weight than bricks and concrete there are several reasons why the cost of building materials may not be much higher, and indeed should be lower than before -a) the 3D printing permits designs that require less material (e.g. arched/concave ceilings that are intrinsically more material efficient than using beams, and cellular structures arranged within walls and floors). B) The reduction in weight of upper floors again reduces the materials required for the ground floor. C) The printing process eliminates the need for pre-fabricated items such as bricks, beams, boards, pipes etc. Even if the 3D printer needs to be left in operation for a few months to build a typical home, this is still far faster than traditional methods.

The methods described above to enable the printer to print on a square print area, are particularly suited to printing buildings, such as a substantially central post and the use of extra mechanisms or independent control of the two rotary guide means.

Sizing a conventional 3D printer design (with orthogonal linear horizontal guides) to construct a building is possible (not illustrated) and has the advantage that it does not require sophisticated software to control it. However, it would be more expensive, heavy and bulky, as a rigid frame is needed around the print volume, to carry the print chassis. The necessary components are large, heavy and expensive. A less bulky printer design may be preferable, and this can be achieved using a central vertical rod to control vertical motion of the print head, whilst one or two arms provide a simple, potentially light-weight, structure for guiding the print head.

Definitions: The term "base" includes a physical print platform surface and a notional surface.

Optionally the base may be exposed so the printer may be placed on any suitable surface (such as a table, floor, tile or sheet of material), for printing onto that surface, but preferably the printer includes a printing platform. The terms "horizontal" and "vertical" refer to an in-use arrangement, which will typically be horizontal and vertical respectively (in which case the base is a floor at the bottom of the print volume), however the 3D printer could theoretically be used to print sideways or even upside down and such arrangements are encompassed too. The term "such that the guide path is curved and fills a horizontal area leaving substantially only gaps that are narrower than or comparable to said maximum printing thickness" is intended to include arrangements for printing (e.g. hollow) objects where the guide path omits a part of the area, such as a centre thereof. This may be to facilitate use of multiple print heads, or if a vertical control means (e.g. screw thread) is arranged within the print volume. The term "rotary guide means" covers cogs and wheels, but also alternative mechanisms such as 4-bar linkages, flexible elements and bearings. Such alternatives to cogs and wheels can of course be substantially non-circular, e.g. providing for elliptical and other more complex rotary motions. The term "substantially epicyclic fashion or similar" is intended to cover systems where a path is defined by the addition of two vectors which rotate at different speeds, and it covers arrangements where the vectors also change length, or where a third rotating vector is additionally added. The term "vertical" is intended to cover variations such and at an angle to the vertical or even a curved path -however typically the print area defined by horizontal motion is positioned and aligned to at least correspond to the base of the print area when arranged to start printing an object. The term "square print area" covers shapes which facilitate time-efficient printing of an object with a square or rectangular footprint' substantially better than a circular print area would. The term "cog means or wheel means" is not limited to circular components, and includes for example an arm driven to rotate around a pivot, having near its centre a cog arranged to be driven by another cog, or having near its centre a wheel arranged to be driven by a pulley or similar arrangement. The term "motor or like means" encompasses rotary and linear electric motors as well as other drive means which may be substituted, such as a hydraulic piston or a hydraulically driven motor (in the case of a building printer) or a solenoid or solid state actuator (in the case of a desktop sized printer), and the term motor used in isolation is intended to cover these alternatives.

Brief description of the drawings.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an illustration of a 3D printer according to the prior art.

Figure 2 is an illustration of a 3D printer according to one embodiment of the present invention, having a cylindrical housing.

Figure 3 is an illustration of a building printer according to one embodiment of the present invention, having a central vertical rod.

Figure 4a is an illustration of a guide means for a 3D printer according to one embodiment of the present invention.

Figure 4b is an illustration of a first and second guide means according to another embodiment of the present invention.

Figure 4c is an illustration of a first and second guide means according to yet another embodiment of the present invention.

Description of the preferred embodiment.

An embodiment of this invention will now be explained with reference to the drawings. Figure 1 shows a prior art 3D printer with a print head (1) controllable on a first axis along a print chassis which in turn is moveable along a second axis orthogonal to the first. A print volume (2) defined at its base in this case by a print platform (3) is moved vertically relative to the print head. Together these three actions, driven by three independently controllable motors (12) allow the print head to be positioned anywhere in the print volume. A typical printing motion involves straight line horizontal movements back and forth to complete a layer (14a), alternating with stepwise upward movements of the platform. A curved path can be approximated (as shown) but generally is formed of either discrete steps in two horizontal axes, or two orthogonal guide means being driven simultaneously at varying speed ratio, combining to result in a curved print head motion.

Figure 2 shows a 3D printer according to one embodiment of the present invention. The housing is generally cylindrical and provided with an internal screw thread (11) such that a generally circular print chassis 6 can be guided very slowly vertically while rotating at a comparatively faster rate. The print chassis supports a print head wheel (5) which rotates at a different speed to the print chassis (6). As an example, the print head wheel might turn 1000 times per rotation of the print chassis which might in turn rotate 1000 times during a full vertical movement of the print chassis through the print volume (2). However, this requires a very fine pitch on the housing's screw thread, so it may be more sensible for the print chassis to include two parts (not shown for simplicity), one which rotates slowly against the housing screw thread, and one which turns comparatively faster to move the print head wheel around the housing.

In this embodiment there is only one motor (12). Three motors are also possible, to independently control the print head wheel (5), the print chassis (6), and vertical motion, or two motors can share these tasks. Where a single motor (12) is used, the position of the motor is of significance. If the motor is on the print chassis there is a danger that the motor power cable and the print head will be twisted together by the rotation of the print chassis. In this embodiment the motor (12) is on the periphery of the print chassis, and prevented from rotating relative to the print housing, in this case by a vertical guide in the print housing. Power from the motor to the drive train is by means of a unison ring (4) arranged around the print chassis so that it can transmit power to it irrespective of its angular position. To avoid the need for the unison ring to be a precision part and precisely held, it is preferable that the unison ring (4) moves quickly compared to the print head wheel (5) and powers the latter via a down-gearing (not shown), so that a large error in position of the unison ring corresponds to a small error in position of the print head wheel. The print head wheel turns to move the print head (1) in a circle above the print platform (3), and can be geared to drive the print chassis to rotate against the housing. In the embodiment illustrated, cogs (8) transfer power from the unison ring, down-gear the motion, and drive the print chassis to rotate slowly against the housing wall. To achieve a repeatable and consistent rotation, it is desirable that either the print housing has cog teeth (not shown) for the print chassis to drive against. Perhaps more conveniently, the print chassis may have cog teeth for a mechanism associated with the motor or unison ring to drive slowly S against. To ensure gradual rather than jerky/stepwise motion, the interface between the print chassis and the screw thread should ideally be greased. Bearings or a ball-thread interface (albeit costly) are possible.

Note that with a conventional 3D printer the object is built up in layers. This is also possible in the present invention, especially if the vertical motion is controlled independently of horizontal motion.

However in this embodiment vertical motion occurs gradually while the print head completes a scan of the horizontal print area. Therefore printing no longer occurs in layers. Similarly in the embodiment of figure 2 where the print head wheel and print chassis movements are coupled, the print head spends more time in some locations than in others. With the print head radius (Ri) and the radius of the print head wheel pivot to the print chassis pivot (R2) having a ratio of 1.0:1.0, and in the absence of additional positioning mechanisms the print area is circular and the print head visits the centre of the print area very frequently. Printer designs with just one motor provide a predetermined and predictable route for the print head to follow in 3D. Print server software is needed to control the printer to deposit (or join) material at suitable times so as to avoid an excess of material at the horizontal locations where the print head spends more time. Such software can be written by a skilled programmer, and at it's simplest in a system with one motor, the software merely identifies the timing of deposition (or joining) of material required to build up the required structure, based on the predetermined 3D route that the print head will follow. As the print head path includes neighbouring sections that vary in their spacing, and are vertically offset, it is beneficial if the print head can dispense (or join) a trail of material of varying thickness. Aside from these differences in software requirements, the 3D printer is generally adapted to be controllable by by a computer (not shown), e.g. via a USB cable, in the customary way in accordance with a suitable data file defining the object to be printed.

Above the print chassis is a printer cartridge and/or electronics module (dotted outline). This preferably does not rotate, as generally it will require a power cable and typically a computer cable too. This module preferably is prevented from rotating via the same guide in the housing shown adjacent the motor (12). Accordingly the print head should not rotate repeatedly relative to the module, otherwise the ink' cable will become twisted. The print head (1) is therefore provided with a pivot, coaxial around the print head, so that it can rotate freely relative to the print head wheel, without affecting the print head location. As an alternative to free rotation constrained by the ink' cable, it is possible for an extensible arm or other means to restrict or control the rotation of the print head.

In this embodiment the print cartridge and/or electronics module (dotted line) stows within the print volume when not in use. To return the print head to the start position may take many hours, therefore it is desirable if the prescribed 3D route can be over-ridden. In this example the screw-thread interface on the print chassis is biased resiliently such that if a user shoves the printing components downwards, the screw-thread interface is overcome, and the module ratchets' quickly to the bottom of the print volume. An automated procedure of bringing the print head back to a starting position whereby further motion is stopped may be sufficient to allow the printer to reset the print head position accurately. Desirably a print head position sensor is additionally used to ensure the start position is achieved precisely. It should be noted that provided the horizontal print head position can be determined, it may not be necessary to know the exact vertical position in embodiments where a rotation of the print chassis corresponds to a vertical movement that is S insignificant compared to the vertical printing thickness. Similarly it may not be of interest to know the print chassis orientation, provided that the print head wheel orientation (relative to the print chassis) is known -e.g. using a print head sensor. This is because it is of no significance what orientation the object gets printed in. A distance sensor, to measure the vertical distance from the print head to the nearest surface, may be useful, as this helps to calibrate the flow of ink' -this may be an optical, physical touch or any other type of sensor.

The print head wheel, print head chassis and associated drive cogs may form a module, to be interchanged with alternate modules (not shown). This enables a user to select a module with a small print area if printing a small object, as then the printer would finish printing more quickly (than one which covers the maximum possible print area). An alternate module might include a smaller print wheel, operating closer to the centre of the print area (e.g. again with Ri:R2 ratio of 1).

Multiple print heads are beneficial, and a print head that can mix print fluids is even better. This could offer different material properties & colours etc as is known in the prior art. It is possible to arrange print heads in a bundle, such that each of them will perform an adequately comprehensive scan of the 3D print volume including the centre point however it is then important to control rotation of the print head bundle e.g. using an extensible tongs' style arm, associated with one side of the print cartridge/electronics module. This does not entirely prevent rotation, but achieves a known and repeatable angular variation.

The method of supporting the print head wheel is of significance. With a fixed relationship between print head wheel motion and the print chassis motion, it is possible to find at least two locations relative to the print chassis whereby thin struts can be provided under the print head wheel, to support it at its centre. These locations might include near the periphery of the print area (where the print head spends more time than necessary), and also near the centre of the print area (again the print head spends more time here than necessary. However, the support struts should not prevent printing at the outermost and innermost printing positions, and instead are beneficially offset slightly to one side or other. The support struts are beneficially very thin (E.g. thin sheet steel) and ideally are as thin as the vertical printing thickness of the print head (i.e. equivalent to a layer' in a conventional 3D printer). Overall the print head path forms an epicycloid (14c) (e.g. a spirograph) path, or in this case more specifically a hypotrochoid (14c) path as the speed Si of the print head wheel is much faster than the speed 52 of the print chassis. Note that it is also entirely possible for S2 to be comparable to Si (e.g. generating a basic epicycloid path) or indeed much faster than Si (e.g. creating a spiral path such as in i4b).

Figure 3 shows a 3D printer according to another embodiment of the present invention. This embodiment utilises a central threaded rod supporting a rotating arm on which a secondary arm rotates. The arms are equivalent to the wheels of the embodiment of figure 2. The system is preferably balanced so that it does not cause the vertical rod to wobble. In this case the object to be printed is a house. Selecting a central rod to support the printing arms makes the printer cheaper than requiring a housing larger than a house (a tent is typically still needed to mitigate rain and wind). The disadvantage of the central rod is that it prevents printing in the centre of the print area.

This can be acceptable, as the house can be designed to have very little of interest in that particular location. The rod can be composed of segments which can be disassembled after completion of the house, leaving perhaps a small section of roof, flooring and foundations to be completed manually.

One other advantage of arms extending from a central column, is that if they are controlled independently, or if they can be varied in length, then it is possible to print on a variety of non- circular (E.g. square or rectangular) plots, without any part of the printer extending beyond the non-circular plot. This would be particularly useful when printing buildings as they tend to be needed on square or rectangular plots which tend to be very close to pre-existing structures such as neighbouring buildings. Again, some margin is needed around the building to accommodate a tent (not shown) to protect the printer and building from rain and wind. Variations in arm length can give rise to a series of superelipses (14d) that together substantially fill the plot, however for a building printer it would be useful to have independent control of the arms at least, thus greatly speeding up printing (especially with buildings which are mostly hollow) by allowing the print head to perform arbitrary and optimised motion, rather than following a fixed path. For example the print head may then trace out the path of walls of any desired building shape (14e).

The print head ink' cable(s) (not shown) may be arranged to feed the print head without undue twisting thereof in a variety of ways. One option is to hang the cable from a central support such as the top of a protective tent, or from the top of the central support rod (for example it may pass down through the rod to an exit at the bottom of the rod). Another option is for the cable to extend along the outer arm, through the centre of the pivot supporting it etc. Another approach is to accommodate rotation of the cable using a connector that permits relative rotation of two sections of the cable. A third approach is to control the two arms independently and prevent one, or both of them from performing repeated rotations in either direction. The outer arm (5) is depicted as vertically above the inner arm (6) as this allows a full rotation of the outer arm without impeding a print head cable (not shown) hanging vertically to the print head -however unless the print head can retract slightly as it passes the inner arm, there is a problem that the thickness of the inner arm may prevent the print head being suitably close to the print object. However, with independent control of the arms, the outer arm can be positioned vertically below the inner arm, alleviating this problem.

Figure 4a shows one design for a rotary means that is not a conventional cog or wheel. The print head (1) is supported by a main array of at least three (in this case four) long arms (15), which limit the motion of the print head to a notional hemisphere, while an extra arm, in this case shorter than the main array, limits the motion to a different hemisphere, together limiting the motion to the intersection of the two hemispheres which constitutes a horizontal circular path. The rate of the motion is preferably controlled by by a cog, wheel, arm or similar. The arms (15) are shown with pivots (ball joints) at either end, but the arm could have short flexible portions at either end instead.

Two such rotary means could be used in conjunction to generate the required epicyclic motion.

Figure 4b shows a design for a central rod mounted first and second guide means. A rotary guide means 6 controls circumferential motion of the print head around the vertical rod 11, while an extendable arm, in this case a sliding arm, (5) controls radial motion of the print head. The sliding arm may also affect circumferential motion to some extent depending on its orientation. This design is suited to embodiments where the first and second guide means are independently controllable, and well suited to use in a building printer where such independent control is useful to improve printing speed. The rotary guide means 6 may include a counterweight, adapted to move oppositely to the sliding arm, preferably is geared to move in sync with the sliding arm and optionally may be heavier and move correspondingly less far, to enable printing adjacent the vertical rod within a non-circular print area.

Figure 4c shows another design whereby the first and second guide means (6,5) jointly control motion of the print head in a horizontal plane. Here, unlike in other embodiments, the motion of the print head 1 does not correspond to a simple addition of the motions of the first and second components (of the first and second guide means), as they interact in a more complicated fashion to determine the print head position.

Claims

Claims: 1. A 3D printer, for printing objects by incremental addition of material thereto, the 3D printer having: a pre-defined printing volume having a base thereof, a print head adapted to add or join printing matter incrementally upon the base to contiguously build up a physical object, the print head having a predetermined maximum horizontal printing thicknesses, a first guide means adapted to control a first component of relative horizontal motion of the print head and base, a second guide means adapted to control a second component of relative horizontal motion of the print head and base, the first and second guide means adapted to jointly control relative horizontal motion of the print head and base along a non-linear horizontal guide path including substantially any position within a horizontal print area, vertical motion control means for controlling relative vertical motion of the print head and the base, at least one motor or like means, at least one drive train arranged to be driven by the at least one motor, and arranged to drive at least one guide means to control relative motion of the print head and the base along the horizontal guide path, and wherein; the 3D printer is suitable for printing buildings for domestic habitation, the print head is adapted to print mortar, the 3D printer comprises means for mixing at least water and a binding agent to form mortar.
2. A 3D printer according claim 1, further adapted according to any one of claims 6 to 21.
3. A 3D printer according to claim 2, comprising a column, and at least one arm supporting the print head therefrom for substantially pivotal motion around the column and vertical motion up the co I urn n.
4. A 3D printer according claim 3, further comprising a protective tent surrounding the print volume.
5. A 3D printer according to any preceding claim where the print head is adapted to selectively dispense a mortar and a polymer.
6. A 3D printer, for printing physical objects by incremental addition of material thereto, the 3D printer having: a pre-defined printing volume having a base thereof, a print head adapted to add or join printing matter incrementally upon the base to contiguously build up a physical object, the print head having a predetermined maximum horizontal printing thicknesses, a first guide means adapted to control a first component of relative horizontal motion of the print head and base, a second guide means adapted to control a second component of relative horizontal motion of the print head and base, the first and second guide means adapted to jointly control relative horizontal motion of the print head and base along a non-linear horizontal guide path including substantially any position within a horizontal print area, vertical motion control means for controlling relative vertical motion of the print head and the base, at least one motor or like means, at least one drive train arranged to be driven by the at least one motor, and arranged to drive at least one guide means to control relative motion of the print head and the base along the horizontal guide path, and wherein; the first component and second components of relative horizontal motion of the print head and base, are non-orthogonal, and the first guide means is adapted to pivot about a first vertical axis thereof, to affect (at least jointly with the second guide means) a circumferential position of the print head relative to the first vertical axis, such that the first component of relative horizontal motion of the print head and base is an arc coaxial with the first vertical axis, and the second guide means is adapted to affect at least a radial position of the print head with respect to the first vertical axis.
7. A 3D printer according to claim 6 where the second guide means is adapted to rotate around a second vertical axis, the horizontal position of the second vertical axis being arranged to be controlled to move in an arc around the first vertical axis by the first guide means, such that the second component is an arc coaxial around the second vertical axis, and the position of the print head is determined by the sum of the first and second components.
8. A 3D printer according to claim 7 where the first and second guide means constitute a horizontal arm extending from the first vertical axis, the print head is at a first end of the arm, the first guide means is adapted to control the circumferential position of the first end of the arm, and the second guide means is adapted to extend and retract the arm to control the radial position of the first end of the arm.
9. A 3D printer according to claim 7 where the two guide means are independently controllable.
10. A 3D printer according to claim 7 where the first and second guide means are adapted such that in use their motion is mechanically coupled so as to control the print head to follow a path that is pre-determined by the mechanical coupling of the respective motions of the first and second guide means, the pre-determined path being substantially an epicycloid, hypocycloid, epitrochoid, hypotrochoid or spiral, such as to fill the horizontal print area leaving substantially only gaps that are comparable to said maximum horizontal printing thickness.
11. A 3D printer according to any one of claims 6 to 10 where the first and second guide means and the vertical motion control means are together substantially driven and controlled either by just one or two motors.
12. A 3D printer according to claim 11 where the guide means and vertical motion control means are together driven and controlled by just one motor.
13. A 3D printer according to any one of claims 6 to 12 where the vertical control means is controlled in concert with at least one of the first and second guide means.
14. A 3D printer according to any one of claims 6 to 13 where the first and second guide means are adapted to control respective circular motions around respective pivots, the second guide means controlling the print head to revolve around it at a radius R2 from it's pivot, the distance between the pivots being Ri, and the ratio R1:R2 being 1.0, such that the print head is controlled to pass through or underneath the pivot of the first guide means.
15. A 3D printer according to claim 6 where the base is provided by a print platform, and where one of the first and second guide means is associated with the motion of the print head, and the other guide means is associated with a rotation of the print platform about a vertical axis.
16. A 3D printer according to any one of claims 6 to 15 where the vertical control motion means includes a substantially cylindrical print housing with an inner thread.
17. A 3D printer according to any one of claims 6 to 15, for printing hollow objects, where the vertical motion control means includes a vertical rod arranged inside the print volume.
18. A 3D printer according to claim 17 where the vertical control means is a vertical rod arranged inside the print volume and the first and second guide means are jointly adapted or controllable to restrict the motion of the print head and support components thereof to a non-circular print area.
19. A 3D printer according to any one of claims 6 to 18 where the print platform is a stationary print platform, and the print head is adapted to move both horizontally and vertically to traverse substantially the whole of the print volume.
20. A 3D printer according to any one of claims 6 to 19 where at least one drive train is arranged such that at least one motor is only required to turn in one direction during printing.
21. A 3D printer according to claim 6 where the drive train and/or the first and second guide means are provided as a module adapted to be conveniently interchangeable, in exchange for at least one alternative module, such that a horizontal width of the print volume can be modified and/or such that a density of the guide path can be modified.