A system for three-dimensional printing of a concrete structure with a fresh cementitious mixture comprising reinforcement means

Abstract

The present invention relates to a system for three-dimensional printing of a concrete structure (2) with a fresh cementitious mixture comprising reinforcement means (3), said system comprising: a robot arrangement (20), said robot having a print head (5) attached thereto as an end effector; a mortar mixing unit (4): a nozzle (6); two or more spools (11), arranged for dispensing said reinforcement means through said nozzle (6), said two or more feeding units (12) comprises a motor for independent speed control of each elongated reinforcement element; wherein said reinforcement means comprise two or more elongated reinforcement elements; a control unit (23); wherein said two or more feeding units (12) is arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material; wherein the said control unit (23) is arranged to control said feeding unit for independent speed control of each elongated reinforcement element to compensate for a difference in distance in said concrete filament along said print path, between said two or more elongated reinforcement elements in curved sections of said print path.

Description

[0001] Title: A system for three-dimensional printing of a concrete structure with a fresh cementitious mixture comprising reinforcement means

[0002] Description:

[0003] The present invention relates, in general to three-dimensional printing of concrete or other cementitious materials. More in particular, the present invention relates to a three-dimensional print head for printing of a wire-filled reinforced cementitious material.

[0004] The traditional construction techniques have long been used to build structures, but they come with limitations such as slow construction time, material waste, and cost inefficiencies. With the advent of three-dimensional (3D) printing technology, the construction industry has been revolutionized. 3D printing of concrete structures presents a unique opportunity to overcome these limitations and offers a new way to construct buildings, bridges, and other structures with greater efficiency, speed, and sustainability.

[0005] The present invention provides a reliable and efficient system and method for 3D printing of concrete structures, which can be used for various applications such as building construction, infrastructure development, and architectural design.

[0006] In the last few years, three-dimensional printing in the construction industry has enjoyed rapid growth.

[0007] A recurring issue that needs to be resolved in 3D printing of concrete used in structural applications is the need to achieve ductility and (flexural) tensile capacity, as the processes that are being applied generally do not yet provide that inherently. 3D concrete printing may typically be used to print concrete as a lost formwork for conventional reinforced concrete. Alternatively, external pre-stressing tendons have been applied to obtain tensile capacity and ductility. This strategy, which comes down to avoiding tensile stresses in the concrete, can also be applied in a different way, namely by designing pure compression structures. What also has been proposed, is reinforced concrete walls in a two-storey house which were made by first erecting a conventional reinforcement mesh and subsequently depositing concrete with a Material Deposition Method (MDM)-type machine, with two large forked print nozzles that can simultaneously print on each side of the reinforcement.

[0008] In the meantime several other approaches have been proposed. However, all these approaches have important drawbacks: they seriously limit the level of formfreedom and automation, which are considered unique and advantageous aspects of 3D printing of concrete. It has been recognised that an alternative to conventional reinforcement would be preferred, and should be incorporated in an automated process without limiting shaping possibilities.

[0009] Hence, in known 3D printing techniques there is a certain trade-off. Printed reinforced cementitious materials with traditional steel reinforcement bars on the one hand provide both high compressive strength and high tensile strength, but allow limited form-freedom and automation. Printed cementitious materials without such traditional steel reinforcement bars, only provide compressive strength, and lack tensile strength, but have improved form-freedom and automation.

[0010] Object of the invention

[0011] It is therefore an object of the present invention to provide a solution to allow 3D printing of concrete or mortar mixtures, which provide both high compressive strength and high tensile strength, and form-freedom and allows automation.

[0012] List of definitions

[0013] The following definitions are used in the present description and claims to define the stated subject-matter. Other terms not cited below are meant to have the generally accepted meaning in the field.

[0014] “Reinforcement means” or more in particular elongated reinforcement means, as used in the present disclosure are any type of elongated reinforcements that are suitable for use in cementitious materials or cementitious mixture such as concrete mixtures and can comprise “wires” and / or “cords” and / or “wire ropes” of any material. Said reinforcement means is sufficiently flexible to follow the print path direction and when introduced into the printed layer stays in the intended location within the layer. Furthermore, the said reinforcement means offers to improve the ductility and tensile strength of the printable concrete or mortar.

[0015] “Aggregates” as used in the present disclosure is defined by standard EN 206-1 (or EN 12620) as a granular material suitable for use in concrete. Aggregates may be natural, artificial or re-cycled from material previously used in construction.

[0016] “Aggregate size” as used in the present disclosure is defined by standard EN 12620 as the designation of aggregate in terms of lower (d) and upper (D) sieve sizes expressed as d / D.

[0017] “Fine aggregates” as used in the present disclosure is defined by standard EN 12620 as the designation given to the smaller aggregate sizes with D less than or equal to 4 mm.

[0018] “Coarse aggregates” as used in the present disclosure is defined by standard EN 12620 as the designation given to the larger aggregate sizes with D greater than or equal to 4 mm and d greater than or equal to 2 mm.

[0019] “Additives” as used in the present disclosure is defined by the standard EN 197-1 as ingredients added to a dry or fresh mortar / cementitious material to improve the manufacture or properties of the cementitious material or resulting concrete structure.

[0020] “Admixtures” as used in the present disclosure is defined by standard EN 934-2 as ingredients added during the mixing process of dry of fresh mortar / concrete to modify the properties of the cementitious material such as concrete mixtures in the fresh and / or hardened state. “Dry mortar mixture” as used in the present disclosure means a printable mixture of at least one or more mineral binders and fine aggregates and additionally one or more additives.

[0021] “Fresh mortar mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid (e.g. water).

[0022] “Fresh concrete mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid (e.g. water) and coarse aggregates.

[0023] “Fresh fibre reinforced concrete mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid (e.g. water), coarse aggregates and fibres.

[0024] “Rz rotation” as used in the present disclosure means an additional rotational degree of freedom along the z-axis of the print head.

[0025] “Buckling” as used in the present disclosure means a sudden lateral deformation under (concentric) axial compressive load.

[0026] Summary of the invention

[0027] The foregoing object is achieved according to a first aspect of the present invention with a system for three-dimensional printing of a concrete structure with a fresh cementitious mixture comprising reinforcement means, said system comprising: a robot arrangement, comprising a robot framework and a robot attached to said robot framework, said robot having a print head attached thereto as an end effector, and wherein said robot is arranged to move said print head in a predefined space in respect of said robot framework; a mortar mixing unit arranged for mixing a dry mortar mixture with an aqueous liquid into said fresh cementitious mixture; said print head comprising: - a nozzle comprising a nozzle opening arranged for extruding concrete filament comprising two or more orifices arranged for guiding said reinforcement means into said concrete filament in a path parallel to a print path direction;

[0028] - two or more spools, arranged for the storage of the reinforcement means at the print head;

[0029] - two or more feeding units, arranged for dispensing said reinforcement means through said nozzle,

[0030] - wherein said reinforcement means comprise two or more elongated reinforcement elements; a control unit arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material; wherein said two or more feeding units is arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material; and wherein the said control unit is arranged to control said feeding unit for independent speed control of each elongated reinforcement element to compensate for a difference in distance in said concrete filament along said print path, between said two or more elongated reinforcement elements in curved sections of said print path.

[0031] 3D printing of cementitious materials, which is also known as concrete additive manufacturing, is a process of creating 3D objects by depositing layers of cementitious materials as a concrete filament using a robot system such as a gantry robot, robotic arm, or other automated system.

[0032] Before the 3D object is printed, a 3D model is designed, typically with a Computer-Aided Design (CAD) program that allows an engineer to create detailed digital models of the object he or she want to print. The digital model is then converted into a format that can be processed by the 3D printer of the system. The system comprises a robot framework, such as a robotic arm, a gantry robot or other automated system and a print head attached to the robot as material deposition system and a pump unit to pump and supply the cementitious material to the print head. The robot is used to move the deposition system in three dimensions and deposit the concrete layer by layer, following the digital model. The path the print head follows per layer is also known the print path. The cementitious material used for 3D printing is typically specially formulated to have the right consistency and setting time, as well as good flow properties, so that it can be extruded through the deposition system. The mixture therefore may include using additives to improve the workability of the mixture and prevent it from hardening too quickly.

[0033] Throughout the present disclosure, the compound that is printed is referred to as cementitious material. This is to be interpreted in its broadest sense, meaning that various types of cementitious materials that can be used for 3D concrete printing may be applicable, depending on the specific application and requirements. It is expressed that in any of the examples and aspects of the present disclosure, the print head is not limited what so ever to certain types of concrete. The print head of the present disclosure is suitable for any type of cementitious mixture in which reinforcement means are added. Hence, although throughout the description, these mixtures may be referred to as concrete mixture, the skilled person will appreciate that these can also mean any other type of cementitious mixture.

[0034] The most commonly used mixture type for 3D printing is a high- performance concrete (HPC) mix, which typically has a high strength and workability, as well as good flow properties for extrusion through the printing nozzle. Such mixture may comprise at least cement as a basic component of the concrete (e.g. in accordance with EN 197-1) which allows the mixture to harden and gain strength. However, there are alternatives that can partially or fully replace cement in the mixture may also be used. For example, fly ash as a by-product of coal combustion may be used as a partial replacement for cement in the mixture, up to 30% by weight. Fly ash can improve the workability of the mixture and reduce the heat generated during the hydration process. Also ground granulated blast furnace slag (GGBFS) may be used. This is a by-product of the metallurgy industry and can be used as a partial replacement for cement in the mixture, up to 95% by weight (e.g. according to EN 197- 1). GGBS can improve the durability and long-term strength of the concrete. Silica fume is another alternative or additive which may be used in the mixture. This is a by- product of silicon and ferrosilicon alloy production and can be used as a partial replacement for cement in the mixture, up to 10% by weight. Silica fume can improve the strength and durability of the concrete. The mixture may also comprise geopolymers as inorganic polymers that can be used as a substitute for cement in the mixture, resulting in a more sustainable and eco-friendly alternative. Geopolymers can be made from a range of raw materials, such as fly ash, slag, and clay. The skilled person will appreciate which compounds are applicable and may be comprised in the mixture, which are all covered by the present disclosure.

[0035] During the printing process, the layers of concrete are deposited one on top of the other, with each layer being allowed to set before the next one is added. This creates a solid object that is built up layer by layer, according to the digital model.

[0036] The print head thus deposits the cementitious material through nozzle. The nozzle allows precise control of the position of the mixture and the way in which the mixture is set and pressed into the layer below.

[0037] In order to increase the tensile strength, it is required to add some sort of reinforcement. Reinforced cementitious materials may relate to fibres, which increase ductility and tensile strength of the concrete, but may also relate embedding wires, cords, or wire ropes, or a mesh into the concrete in order to increase tensile strength. The present disclosure is directed to the latter, in which the 3D printing system is comprised of an improved print head which is configured to embed a wires, cords, or wire ropes, or a mesh into the cementitious material.

[0038] Steel wire rope or other types of reinforcement can be added into 3D concrete printing to improve the strength and durability of the printed object. The reinforcement is typically placed within the layers of the printed object as it is being printed. This can be achieved through several methods: Typically, steel wire rope or reinforcement mesh is manually placed between layers of the printed object as it is being printed. In such method, the system pauses from time to time, stopping the print head at specified intervals, to allow the operator to insert the reinforcement into the layer. It is however also known to have the reinforcement placed automatically, for example with a robotic arm with an end effector designed to place the reinforcement into the printed object. Yet another known method is to add the reinforcement in-situ. Steel wire rope or other reinforcement can be integrated into the cementitious material itself, and this mixture can be printed using a 3D concrete printer. This can provide a more homogenous distribution of the reinforcement within the printed object.

[0039] The print head plays a crucial role in the reinforcement process, especially in such most technologically advanced in-situ printing, by controlling the flow of the concrete and ensuring that the reinforcement is placed correctly within the layers of the printed object. This requires a specifically designed print head to accommodate the size and shape of the reinforcement being used, and to ensure that the reinforcement is placed in the correct location and orientation, which requirement is challenging.

[0040] It has been found to be beneficial to embed, per layer, multiple reinforcement means, e.g. two elongated reinforcement means such as steel wire ropes in the extruded filament. The print head is preferably arranged to embed for example, and preferably, two, but alternatively three, four or more, elongated reinforcement means into the mixture. The two steel wire ropes, may be disposed off- centre in respect of the cementitious material, in parallel along an axis perpendicular to a direction along which said print head is moved upon printing. The steel wires ropes may for example be positioned such that each wire rope has an approximately similar volume of mixture in which it is embedded.

[0041] The rate at which the mixture is disposed, i.e. the flow-rate, and the rate at which the steel wire rope is fed into the mixture, i.e. the feed speed, are configured in relation to each other and to the speed at which the print head is moved by the robotic system, e.g. the robotic arm.

[0042] For printing mixtures with a straight printing path, such fixed setting of speed of mixture deposition, the steel wire rope feed and print head movement is sufficient. However, once the printing path includes organic shapes the printing becomes challenging. Such an organic printing path refers to the way in which natural objects are mimicked. Such natural forms are not only visually more appealing and aesthetically pleasing, which for example allows the printed object to be more seamlessly blended into the environment, but it also allows more complex forms which may provide constructional benefits such as lowering the required volume of materials, and increase overall strength and stability of the printed structure. In contrast to straight lines, which are linear and rigid, organic pathways, as defined by the present disclosure, may include curves, twists and bends. These may be achieved by having the print head follow a (continuous) arc, spiral or other geometric shape that mimics the natural flow of movements found in nature. In such an organic pathway, corners and radii are not necessarily sharp, and they are preferably smoothed or rounded to create a more flowing, natural look.

[0043] A known print head, which is modified to embed two wires ropes in parallel into the mixture, will suffer from problems with such organic pathways, due to the corners, bends, twists, etc. When the print head follows such a corner, the travel distance of the inner wire is shorter than that of the outer wire, which may result in the outer wire to be pulled inwards into the centre of the deposited mixture, and / or the inner wire to crumple of buckle. To correct for the wider arc of the outer wire, and / or the smaller arc of the inner wire, the present invention, in a first aspect, is arranged to have independent speed control for each wire. Hence, the speed control allows and controls the speed at which the wire is dispensed into the cementitious material, hence, the speed in respect of the print head movement and / or the speed in respect of the flow-rate of the cementitious material. With such individual speed control, each wire may have a different speed setting, such that during corners, bends or any nonlinear section of the print path, the individual wire speed may be controlled to correct for the wider or smaller arc of the respective wire.

[0044] The controlled dispensing of the reinforcement elements (wires) into the cementitious material ensures that an equal distance between the dispensed wires is maintained and that sufficient cementitious material is applied between the wires to cover each wire to ensure proper bonding between the wire and the cementitious material, which thereby ensures the quality required to maintain the performance of the reinforcement over the entire printed geometry. The reinforcement elements should be stiff enough to be pushed through a tube from the feeder to the nozzle, without the issue of buckling occurring. For example, a thin glass fibre or thin glass fibre roving will not be stiff enough and will buckle. The ability to prevent buckling depends on both the material properties (modulus of elasticity) and the geometric properties (e.g., thickness, configuration of the wires in the cable). Also, the reinforcement elements should be flexible enough to follow the curvature of the concrete filaments, and as a result stay at the required position in the freshly-printed concrete structure.

[0045] In the system according to the present disclosure, the entrainment of the reinforcement elements into the fresh cementitious mixture is independent of the properties of the fresh cementitious mixture of the printable concrete related to specific yield stresses, which offers the system according to the present disclosure more flexibility and adaptability thereby reducing any additional material requirements on the cementitious mixture making it cost effective as any cost related on developing special printable concrete can be eliminated.

[0046] In an example, the robot is arranged to move said print head along an x- axis and an y-axis in a predefined space, and to rotate said print head about a z-axis for printing said concrete structure having curved sections in said print path.

[0047] The robot assembly allows the print head to move in a three-dimensional space by using at least a linear motion, but also a rotational motion. The linear motions may defined as the movement of the print head and more precisely, the nozzle along the x-axis and y-axis. The rotational movement provides a z-axis rotation or also referred to as Rz. This rotation axis is defined as the longitudinal axis of the print head and is perpendicular to the x-axis and y-axis. During the curved section of the print path, the rotation along the Rz is controlled and steered accordingly.

[0048] The robot of the robot assembly may typically have several joints, each of which can move in a specific direction, allowing the robot to reach any position within its workspace. The robot assembly may further be arranged to also be arranged for further degrees of freedom, e.g. a fourth, fifth, sixth degrees of rotational or linear movement.

[0049] The robot may for example be a gantry robot, a robotic arm, a cable-driven robot, a telescopic robot or a printing robot in a robot crawler, wherein the print head is used as an end effector of the robot.

[0050] The robot assembly is comprised of a framework and a robot which provides the movement in respect of the framework. The framework in itself can also be a movable framework, e.g. the robot may be attached to a framework which is placed on, or part of a platform that can be moved along a track, or movable for being attached to a vehicle.

[0051] In an example, the nozzle opening has a nozzle width, which is defined by the width of a printed layer concrete filament forming said concrete structure, and wherein aid robot is arranged to rotate said print head for said nozzle opening to remain oriented perpendicular to the print path direction.

[0052] The certain width of the nozzle opening ensures sufficient deposition capacity of the nozzle and defines the width of the concrete filament. In combination with a rectangular shape, the nozzle can allow greater control over the width and height of the filament and therefore the structure, which is beneficial in creating certain shapes and designs.

[0053] In an example, the two or more orifices of said nozzle of said print head, are configured to guide said reinforcement means in a pattern evenly disposed within said concrete filament.

[0054] With the orifices, which can be defined as openings in the nozzle of the print head, the elongated reinforcement means can be guided into the concrete filament. This way the position of the elongated reinforcement means can be controlled more accurately. Also, such orifice guides allow to define certain patterns which define the positions of the elongated reinforcement means in the filament. For example, typically, the elongated reinforcement means are distributed evenly in the filament, such that each elongated reinforcement element has the same amount of concrete surrounding the element. However, for certain applications and even for certain sections or parts of the same structure, the position may be altered, i.e. in accordance with tensile strength requirements for the particular section of part of the structure. To this end, the nozzle may be arranged for changing a guide block having the orifices, which allows switching between patterns of distribution of the elements in the filament. This may be achieved in several manners, for example by having interchangeable guide blocks, or which the nozzle is a monolithic part, interchanging the nozzle or complete print head. Interchanging may be done manually or automatically, for which the orifices are controllable and arranged to be moved in accordance with a certain predefined pattern.

[0055] In an example, the two or more orifices of said nozzle of said print head, are configured to guide said reinforcement means in a pattern with an offset in respect of the centroid of a cross-section of the concrete filament.

[0056] This example provides a non-evenly distributed pattern of elements in the filament as the elements are offset in respect of the centre of centroid of the filament. Such off-centre or offset placement of the reinforcement means in this configuration can help to improve the overall structural properties of the printed structure depending the loading conditions. While placing the wires off-centre at a desired location to make sure each wire ropes will have a minimum required volume of cementitious material surrounding it.

[0057] Furthermore, due to the limitation of the known printhead of embedding only single steel wire rope, it cannot fulfil the conditions of minimum reinforcement for the printed structure to be used for load bearing applications. With the proposed printhead due to its capability of disposing two or more steel wire ropes within the extruded concrete filament at the desired location, helps fulfil the minimum reinforcement conditions for the printed structure to be used for load bearing application. In an example, a cross-section of said nozzle opening is at least substantially circular-shaped or at least substantially rectangular-shaped.

[0058] In an example, the nozzle is a downflow nozzle having a downward orientation for disposing the said concrete filament, or a backflow nozzle having a backwards orientation for disposing the said concrete filament, or a hybrid downflow / backflow nozzle having a combined downward and backward orientation for disposing the said concrete filament.

[0059] A round nozzle opening may allow for a more uniform and controlled flow of material, which can improve the accuracy and quality of the printed object. The circular shape of the nozzle opening provides a smooth and even surface for the cementitious material to flow through. This can also help to prevent clogging or blockages in the nozzle and ensure that the material flows smoothly and consistently during the printing process. Additionally, the circular shape of the nozzle can help to minimize turbulence and eddies in the flow of material, which can also contribute to a more uniform and controlled extrusion process.

[0060] A rectangular shaped nozzle may also allow for a more controlled and precise flow of material, which can improve the accuracy and quality of the printed object. The rectangular shape of the nozzle opening provides a defined and controlled surface for the cementitious material to flow through. This can help to regulate the flow of material and ensure that it is deposited in a precise and consistent manner. Additionally, the rectangular shape of the nozzle can allow for greater control over the width and height of the extruded material, which can be beneficial in creating specific shapes and designs.

[0061] In an example, the feeding unit is configured to dispense said two or more elongated reinforcement elements at a speed which is controlled by said control unit, relative to a speed at which said extruded concrete filament is dispensed through said nozzle opening. There are typically and ideally several speeds to control, one of which may be considered the most important one, e.g. the flow-speed of the extruded concrete filament. These different speeds relate to the speed of the print head in relation to the static environment, e.g. the object to be printed, the substate on which it is printed or the framework to which the print head is attached (via the robot). Another speed is the flow-rate of the material, i.e. the cementitious material and the speed of the wire rope which is embedded into the concrete filament. As there are at least two wires ropes embedded these have individual speed controls such that the speed of one or both may be increased or decreased in relation to the movement of the print head or the flow-rate of the mixture. The flow-speed of the extruded concrete filament can be defined as the volumetric flow rate [m3 / s] which equals the flow velocity [m / s] multiplied by the cross-sectional area [m2].

[0062] In other words: with a fixed flow rate, the flow velocity changes through the printing system, depending on the cross-section the concrete is passing through. The wire velocity should match the concrete filament velocity (through the nozzle) and should match the nozzle velocity.

[0063] Hence, each wire velocity typically matches the centre of nozzle opening but in the present disclosure the individual wire velocities are aligned to the velocity at the exact position of the orifice. Thus, in corners or curved sections these will increase or decrease in respect of the other orifice, depending on the wire to be embedded in the filament in the inside corner or small radius corner, or on an outside corner or larger radius corner.

[0064] In an example, the nozzle opening has a width w in the range of from 5 mm to 100 mm, preferably from 30 mm to 70 mm, more preferably from 40 mm to 60 mm and the said nozzle has a height h in the range of from 5 mm to 100 mm, preferably from 8 mm to 50 mm, more preferably from 10 mm to 20 mm.

[0065] In an example, the two or more feeding units comprises a stepper motor for independent speed control of each elongated reinforcement element. Preferably the feeding units and alternatively or in addition also other driving means, e.g. to rotate around the Rz, are provided by a stepper motor for being accurate, fast and having low power requirements.

[0066] In an example, the print head is arranged for disposing the said concrete filament through said nozzle opening in an organic form having curved sections with radii of below 1500 mm, more preferably below 500 mm, even more preferably below 100 mm and most preferably below 40 mm.

[0067] In an example, the two or more elongated reinforcement elements have a diameter of between 0.1 mm and 5 mm, more preferably between 0.2 mm and 3 mm, even more preferably between 0.3 mm and 2 mm, most preferably, between 0.5 mm and 1 .5 mm.

[0068] In an example, each of said two or more elongated reinforcement elements are comprised of steel, hemp fibre, glass fibre and carbon fibre reinforcement means, more preferably steel or hemp fibre, even more preferably a galvanized steel comprising reinforcement means.

[0069] In an example, the print head comprises two or more cutting units, arranged to cut each of said two or more elongated reinforcement elements at desired location of the filament layer during printing.

[0070] The print head may, in an example, comprise cutting means, preferably one for each elongated reinforcement element. This allows to cut the elements in between sections, layers and / or in between different structures.

[0071] In an example, the print head comprises two or more sensor means for tracking one or more of a feeding speed and slippage in the said elongated reinforcement elements during feeding, and two or more further sensor means for tracking an alignment of cutting means and cutting quality of the said elongated reinforcement elements, and wherein said control unit is further arranged for controlling said feeding and cutting of the said reinforcement means, in correspondence with said measurements of said sensor means.

[0072] With the sensor means, the feeding of the elongated reinforcement elements can be controlled more precisely as there is feedback on speed, slippage and the like. Also the cutting may be controlled more accurately as sensor means may provide feedback on the alignment of the element with the cutting means.

[0073] In an example, the print head further comprises an extrusion tube disposed between said nozzle opening and an input of said mortar mixing unit.

[0074] The extrusion tube extends the nozzle and moves the nozzle opening further away for the print head. This allow more accuracy and flexibility upon printing, similar to more conventional ways of printing.

[0075] In an example, the robot framework is static, or wherein said robot framework is dynamic and configured as a moving platform.

[0076] In an example, the system further comprises: transport means arranged for transporting said fresh cementitious mixture from said mortar mixing unit to said print head.

[0077] In an example, the said transport means comprises a pumping unit.

[0078] In an example, the system further comprises: a concrete mixing unit, arranged for mixing said fresh cementitious mixture with aggregates and fibres in a mixing chamber into a fibre reinforced cementitious mixture; a fibre dosing unit arranged for introducing fibres to said concrete mixing unit; an aggregate dosing unit arranged for introducing said aggregates to said concrete mixing unit; further transport means arranged for transporting said aggregates and said fibres from said respective aggregate dosing unit and fibre dosing unit to said concrete mixing unit.

[0079] Preferably, in the example of the disclosure, the system also has separate fibre dosing units and aggregate dosing units, and transport means to transport the fibres and aggregates from the dosing units to the concrete mixing unit. These way the supply or dosing of each ingredient of the concrete recipe can be controlled more accurately.

[0080] The above-mentioned and other features and advantages of the invention are illustrated in the following description with reference to the enclosed drawings which are provided by way of illustration only and which are not limitative to the present invention.

[0081] Fig. 1 shows, in a schematic and illustrative manner, a system according to an aspect of the present disclosure;

[0082] Fig. 2 shows, in a schematic and illustrative manner, a print head according to an aspect of the present disclosure;

[0083] Fig. 3 shows a perspective view of the print head according to an aspect of the present disclosure;

[0084] Fig. 4 shows, in a schematic and illustrative manner, the print head and a printed concrete filament according to an aspect of the present disclosure;

[0085] Fig. 5 shows, in a schematic and illustrative manner, a system according to another aspect of the present disclosure.

[0086] Fig. 1 shows a system 1 for three-dimensional printing of a concrete structure 2. The structure can have many shapes and designs and typically comprises at least one but mostly several curved sections, meaning that at least some parts of the structure or at least some part or parts of a layer of the structure have curves or corners with a certain radius. The structure is thus comprised of layers of filament or concrete filament, which comprises a fresh cementitious mixture with reinforcement means 3 (shown in more detail in Fig. 4). The reinforcement means are comprised of at least two but may also comprise three, four, five, six, seven or more elongated elements. The elements may be comprised of steel, hemp fibre, glass fibre and carbon fibre reinforcement means, more preferably steel or hemp fibre, even more preferably a galvanized steel comprising reinforcement means.

[0087] The system 1 comprises several components. Fig. 1 shows a robot arrangement 20, comprising a robot framework 21 and a robot 22 attached to the robot framework. The framework can be static, or dynamic or movable, e.g. along a track or freely due to being mounted on a vehicle. The robot has the print head 5 attached thereto as an end effector, by which the robot is arranged to move the print head in a predefined space in respect of the robot framework.

[0088] The system further shows a mortar mixing unit 4 arranged for mixing a dry mortar mixture with an aqueous liquid into said fresh cementitious mixture. For example the dry mortal mixture may be comprised of a dry mixture for making concrete or the like, and by adding water for example, the fresh cementitious mixture is formed. It is expressed that in any of the examples and aspects of the present disclosure, the print head is not limited what so ever to certain types of concrete. Any cementitious mixture in which reinforcement means are added can be used with an embodiment, example or aspect of print head of the present disclosure. Hence, throughout the description, these mixtures may be referred to as concrete mixture but the skilled person will appreciate that these can also mean any other type of cementitious mixture.

[0089] The mortar, once mixed, may be transported with a pump along transport means toward the print head 5.

[0090] The print head 5 is arranged to embed the elongated reinforcement means into the concrete filament. This print head, to this end, has a nozzle having a nozzle opening for extruding the concrete filament (or as indicated above, an alternative printed cementitious based fresh mixture. The nozzle opening has two or more orifices by which the elongated reinforcement means are guided. The number of orifices corresponds to the number of elongated reinforcement elements of which the elongated reinforcement means are comprised of, e.g. two, three, four, five, six, seven, eight or more, but in the examples shown, two.

[0091] The system further comprises a control unit 23. The control unit is shown as a separate unit, located remotely of the robot and print head, but may also be posited elsewhere, or integrated into other components of the system, e.g. may be integrated with the controls of the robot. The control unit is arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material. Hence, the control unit drives the feeding units of the reinforcement means and may also be coupled to the robot to allow alignment with the movement of the robot and thus print head, or the speed of printing the filament.

[0092] The two or more feeding units for feeding the elongated reinforcement elements, are arranged for speed control of the speed at which these two or more elongated reinforcement elements are dispensed into the fresh cementitious material, i.e. the filament. Since these feeding units can be controlled separately, the control unit can control the feeding unit in such a manner that independent speed control of each elongated reinforcement element to compensate for a difference in distance in the concrete filament along said print path, between the two or more elongated reinforcement elements in curved sections of the print path.

[0093] Fig. 2 shows more details of the print head and shows an example of a print head configured to embed two elongated reinforcement elements. The elements are supplied via spools 11 and fed by individual feeding units 12. The feeding units 12 may comprise stepper motors 16 to feed the elements to and out of the nozzle 6, through a nozzle oping. The example shown, shows an extrusion tube, to extend the opening of the nozzle further away from the printer.

[0094] A cutting unit 36 allows the elements to be cut at desired location.

[0095] Further, Fig. 2 shows a stepper motor 35 to drive the print head and provide for the rotation around Rz, for the curved sections in the print path. Further, Fig. 2 shows sensors to determine feeding speed and cutting alignment.

[0096] Fig. 3 shows the print head 5 from a perspective view and shows that the opening of the nozzle 6 is rectangular shaped such that a certain type of filament is extruded for a desired concrete structure 2.

[0097] In Fig. 4 a detail of the nozzle 6 is shown which is arranged for embedding two reinforcement elements into the filament 8. The nozzle opening is shaped rectangularly and has a certain nozzle height 34 defining the layer thickness, and a nozzle width 31 , which defines the width of the structure.

[0098] Each layer of concrete filament 8 has, in the example shown, two reinforcement means, e.g. steel wire ropes. These are offset in respect of the centre of the print path 32, indicated with the centre dotted line of the print path 32. In curved sections, as shown here, the radii 17 of the curved section defines a difference in distance that the individual reinforcement elements have to make. To prevent buckling of the cable or shift of the cable towards or away of the centre line, the individual reinforcement elements are disturbed and thus entered into the filament at different speeds, to compensate for the difference in distance.

[0099] Fig. 5 further shows an aspect in which the system is further comprised of separate dosing units, e.g. for the aggregates and fibres, which can be added to the print head. It is expressed that several combinations may be made of ingredients, e.g. purely comprising a dry mortar mixture with aqueous liquid and reinforcement means, or addition of one or more of aggregates and fibres.

[0100] Modifications and additions to the method and arrangement disclosed above are obvious to those skilled in the art and covered by the scope of the appended claims.

Claims

CLAIMS1. A system (1 ) for three-dimensional printing of a concrete structure (2) with a fresh cementitious mixture comprising reinforcement means (3), said system comprising: a robot arrangement (20), comprising a robot framework (21) and a robot (22) attached to said robot framework, said robot having a print head attached thereto as an end effector, and wherein said robot is arranged to move said print head in a predefined space in respect of said robot framework; a mortar mixing unit (4) arranged for mixing a dry mortar mixture with an aqueous liquid into said fresh cementitious mixture; said print head (5) comprising:- a nozzle (6) comprising a nozzle opening (7) arranged for extruding concrete filament (8) comprising two or more orifices (9) arranged for guiding said reinforcement means into said concrete filament in a path parallel to a print path direction;- two or more spools (11), arranged for the storage of the reinforcement means at the print head;- two or more feeding units (12), arranged for dispensing said reinforcement means through said nozzle, said two or more feeding units comprises a motor for independent speed control of each elongated reinforcement element;- wherein said reinforcement means comprise two or more elongated reinforcement elements; a control unit (23) arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material; wherein said two or more feeding units is arranged for speed control of the speed at which the two or more elongated reinforcement elements are dispensed into the said fresh cementitious material; and wherein the said control unit is arranged to control said feeding unit for independent speed control of each elongated reinforcement element to compensate for a difference in distance in said concrete filament along said print path, betweensaid two or more elongated reinforcement elements in curved sections of said print path.

2. The system according to claim 1 , wherein the robot is arranged to move said print head along an x-axis and an y-axis in a predefined space, and to rotate Rz (30) said print head about a z-axis (z) for printing said concrete structure having curved sections in said print path.

3. The system according to claim 2, wherein said nozzle opening has a nozzle width, which is defined by the width of a printed layer concrete filament forming said concrete structure, and wherein said robot is arranged to rotate said print head for said nozzle opening to remain oriented perpendicular to the print path direction.

4. The system according to any of the claims 1-3, wherein said two or more orifices of said nozzle of said print head, are configured to guide said reinforcement means in a pattern evenly disposed within said concrete filament.

5. The system according to any of the claims 1-3, wherein said two or more orifices of said nozzle of said print head, are configured to guide said reinforcement means in a pattern with an offset in respect of the centroid of a cross-section of the concrete filament.

6. The system according to any of the previous claims, wherein a crosssection of said nozzle opening is at least substantially circular-shaped or at least substantially rectangular-shaped.

7. The system for three-dimensional printing according to any of the previous claims, wherein said nozzle is a downflow nozzle having a downward orientation for disposing the said concrete filament, or a backflow nozzle having a backwards orientation for disposing the said concrete filament, or a hybrid downflow / backflow nozzle having a combined downward and backward orientation for disposing the said concrete filament.

8. The system according to any of the previous claims, wherein said feeding unit is configured to dispense said two or more elongated reinforcement elements at a speed which is controlled by said control unit, relative to a speed at which said extruded concrete filament is dispensed through said nozzle opening.

9. The system according to any of the previous claims, wherein said nozzle opening has a width w (31) in the range of from 5 mm to 100 mm, preferably from 30 mm to 70 mm, more preferably from 40 mm to 60 mm and the said nozzle has a height h (34) in the range of from 5 mm to 100 mm, preferably from 8 mm to 50 mm, more preferably from 10 mm to 20 mm.

10. The system according to any of the previous claims, wherein the motor is a stepper motor.

11. The system according to any of the previous claims, wherein said print head is arranged for disposing the said concrete filament through said nozzle opening in an organic form having curved sections with radii of below 1500 mm, more preferably below 500 mm, even more preferably below 100 mm and most preferably below 40 mm.

12. The system according to any of the previous claims, wherein said two or more elongated reinforcement elements have a diameter of between 0.1 mm and 5 mm, more preferably between 0.2 mm and 3 mm, even more preferably between 0.3 mm and 2 mm, most preferably, between 0.5 mm and 1.5 mm.

13. The system according to any of the previous claims, wherein each of said two or more elongated reinforcement elements are comprised of steel, hemp fibre, glass fibre and carbon fibre reinforcement means, more preferably steel or hemp fibre, even more preferably a galvanized steel comprising reinforcement means.

14. The system according to any of the previous claims, wherein said print head comprises two or more cutting units, arranged to cut each of said two or moreelongated reinforcement elements at desired location of the filament layer during printing.

15. The system according to any of the previous claims, wherein said print head comprises two or more sensor means for tracking one or more of a feeding speed and slippage in the said elongated reinforcement elements during feeding, and two or more further sensor means for tracking an alignment of cutting means and cutting quality of the said elongated reinforcement elements, and wherein said control unit is further arranged for controlling said feeding and cutting of the said reinforcement means, in correspondence with said measurements of said sensor means.

16. The system according to any of the previous claims, wherein said print head further comprises an extrusion tube disposed between said nozzle opening and an input of said mortar mixing unit.

17. The system according to any of the previous claims, wherein said robot framework is static, or wherein said robot framework is dynamic and configured as a moving platform.

18. The system according to any of the previous claims, further comprising: transport means arranged for transporting said fresh cementitious mixture from said mortar mixing unit to said print head.

19. The system according to claim 18, wherein said transport means comprises a pumping unit.

20. The system according to any of the previous claims, wherein said system further comprises: a concrete mixing unit, arranged for mixing said fresh cementitious mixture with aggregates and fibres in a mixing chamber into a fibre reinforced cementitious mixture; a fibre dosing unit arranged for introducing fibres to said concrete mixing unit;an aggregate dosing unit arranged for introducing said aggregates to said concrete mixing unit; further transport means arranged for transporting said aggregates and said fibres from said respective aggregate dosing unit and fibre dosing unit to said concrete mixing unit.

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