NL2023320B1 - Method for manufacturing a building and device for automated manufacturing of obiects by means of 3D printing of a material. - Google Patents

Abstract

Device (l) for manufacturing of an object (20) by 3D printing, the device (1) comprising: - a robot unit (3) for the controlled deposition of the material; - a support structure (2), whereby the robot unit (3) is supported by the support structure (2); - a first actuator system for moving the robot unit (3) relative to the support structure (2); - a first controller for outputting a first control signal to the first actuator system to implement movement ofthe robot unit (3); whereby the device (1) further comprises a measuring system (4) for determining the actual position ofthe robot unit (3); whereby the first controller receives the actual position of the robot unit (3) from the measuring system (4) and calculates the first control signal based on the deviation of the actual position ofthe robot unit (3) from a desired position.

Description

Method for manufacturing a building and device for automated manufacturing of objects by means of 3D printing of a material. The present invention relates to a method for manufacturing a building and a device for automated manufacturing of objects by means of 3D printing of a material.

Automated manufacturing of buildings, like housing, foundations and bridges has been developed only recently during the last decade. Additive manufacturing of buildings is usually based on printable concrete and does not require a mould to set concrete ina desired shape. Alternatively moulds for pouring concrete can be created using an automated manufacturing system it is well known to use printing systems with a gantry suspended robot unit comprising a nozzle.

13 Gantry assemblies for additive manufacturing are rigid structures which are usually erected along the edges of a cuboid shape, which defines the space in which the additive manufacturing or printing of the building can be performed. In general the material used is concrete but it could be any other material suitable for a building or for forming a mould later to be used for constructing the building. A robot unit usually comprises a printing unit including ducts and/or reservoirs for the material to be printed and means to extrude the concrete through the printing nozzle at the desired location.

The robot unit is moved by actuators under the control of a controller. Positioning of the nozzle is performed based on displacement reported by the actuators, and is therefore relative to the gantry assembly. In order to obtain the required accuracy, the gantry assemblies need to be very rigid and stable. This is all the more important because the robot units may weigh up to several hundreds of kilograms, so that movement of the robot unit may easily impact the mechanical rigidity of the gantry assembly or the suspension.

This means that, in order to achieve the desired precision, gantry assemblies for 3D printing are large heavy structures, which need to be built up with care and need to be aligned, and which require a perfectly levelled and stabilized based.

Especially on construction sites, such systems are therefore expensive and difficult to implement, and considering that other construction works are ongoing in the vicinity, a stable base is often difficult to guarantee.

An example of such a system is disclosed in US9764378B2. The invention aims to reduce the disadvantages of the known systems and therefore provides for a device for automated manufacturing of an object by means of 3D printing of a material, the device comprising: - a robot unit for the controlled deposition of the material; - a support structure, whereby the robot unit is supported by the support structure; - a first actuator system for moving the robot unit relative to the support structure; - a first controller for outputting a first control signal to the first actuator system in order to implement a desired movement of the robot unit.

In a preferred embodiment the device further comprises a measuring system for determining the actual position of the robot unit relative to a reference point which is fixed, in other words has a fixed spatial position, and which is independent of the support structure, meaning that it does not move if the support structure moves, and the first actuator system, whereby the first controller is arranged to receive the actual position of the robot unit from the measuring system and to calculate the first control signal at least partly based on the actual position of the robot unit.

It should be noted that the position may be measured directly by measuring the position, relative to the reference point, of the robot unit itself, or indirectly by measuring the position, relative to the reference point, of a component which has a known distance to the robot unit.

The advantage is that the support structure may be built from much lighter materials, and may be installed with much less accuracy. The support structure may move with the wind, or move with time, or distort depending on the position of the robot unit, or distort as a consequence of movement of the robot unit, but due to the position measurement of the robot unit relative to an independent reference point, the required printing precision can still be obtained. Furthermore, such a support structure does not need to be properly aligned, and may be different every time. This means that such a support structure is much cheaper to manufacture and much easier to set up than a gantry assembly.

Such a support structure may comprise for example cables, posts, beams, and connectors. The measuring system can for instance be a so called laser tracker, but can also be done by means of triangulation.

In a preferred embodiment the first controller is arranged to calculate the first control signal at least partly from a mathematical model describing the physical behaviour of the support structure and of the robot unit, whereby the mathematical model takes into account the effect of the mass of the robot unit on the dynamic deformation of the support structure.

it is remarked that the dynamic deformation of the support structure is an elastic deformation of the support structure resulting from movement of the robot unit.

This means in effect that a feed-forward control method may be used, in which a control input is calculated from an assumed position of the robot unit relative to the support structure and the modelled physical behaviour of the device, in behaviour of the support structure and the robot unit, allowing a relatively fast movement of the robot unit, faster than with only a feedback-based control.

16 The mathematical model hereby ensure that positioning errors due to deformation of the support structure are reduced. This concerns both static deformation as a consequence of the mass of the robot unit and possibly of components of the support structure, as well as dynamic deformation of the support structure as a consequence of inertia of the robot unit when it is moving. The physical behaviour of the support structure and the robot unit results in the equilibrium state that the system may reach and its dynamic response to deviations from such an equilibrium state. It depends, among others, on the deformation characteristics of the various components, their mass, and the geometric characteristics of the support structure. This feed forward control system is used in combination with the feed-back based control system as specified in the main embodiment, so that the necessary printing precision can also be obtained. Preferably the mathematical model also takes into account the effect of the mass of components of the support structure on other components of the support structure. Preferably the mathematical model also takes into account the effect of forces exerted by components of the support structure on the first actuator system, in particular on delays in the response of the first actuator system to the first control signal. In a preferred embodiment the robot unit comprises a nozzle for depositing the material 5 on an object to be manufactured, whereby the device comprises a second actuator system for moving the nozzle relative to the rest of the robot unit, whereby the device comprises a second controller for outputting a second control signal to the second actuator system in order to implement a desired movement of the nozzle, whereby the second controller is arranged to receive the actual position of the robot unit from the measuring system and to calculate the second control signal based on the actual position of the robot unit. This allows a much more accurate positioning of the nozzle, even if the robot unit itself is not very accurately positioned, or is moving, for instance because of slow vibrations in the support structure, because the nozzle is relatively light and can therefore be moved at much higher speeds, by the second actuator system, than the robot unit itself. The second actuator system will report the relative position of the nozzle with respect to the rest of the robot unit, so that it is not relevant whether the position of the nozzle or of the rest of the robot system is actually measured, because one can be easily calculated from the other. Preferably the second actuator system is a parallel manipulator, more in particular a Stewart platform, These are easily commercially available and have a well known and fast response behaviour to control inputs. Furthermore, this allows adjustment of not only the position, but also the angle of the nozzle. The first controller and the second controller may be the same controller.

Preferably the support structure comprises at least three posts which are erected around the object to be manufactured and one cable from each of the posts to the robot unit. In a preferred embodiment the robot unit comprises a mixing unit for mixing ingredients of the material upstream from the nozzle. This allows a very fast change of the composition of the material that is printed, so that different properties, eg different colours or different insulating properties or different mechanical properties can easily be obtained for different parts of the object to be manufactured. Furthermore, it reduces the amount of waste material when a material composition is changed.

Considering that such a mixing unit has a substantial weight it has a large effect on the movement of the robot unit, so that in general a mixing unit can only be used if the entire device is sufficiently robust with respect to maintaining positional accuracy, which is the case in the present invention due to the technical characteristics of the abovementioned embodiments.

The invention further concerns a method as defined in claims 1 to 7, with analogous advantages to the various embodiments of the device according to the invention.

In both the device and the method according to the invention, the mathematical model also takes into account the effect of dynamic forces on the first actuator system on the response of the first actuator system to control signals.

In particular this is useful because due to dynamic forces the displacement caused by the first actuator system may not be as expected based on only static forces, or may be delivered with a delay. In order to illustrate the invention an exemplary embodiment of the invention is explained below, with reference to the following figures, wherein: Fig. 1 shows a perspective view of a device according to the invention; Fig. 2 shows a side view of the device of fig 1; and

Fig. 3 shows an enlargement of the part of fig. 2 indicated by F3.

The device 1 shown in the figures consists mainly of a support structure 2, a 3D printing robot 3 for printing of concrete and other suitable materials, a laser tracker system 4, a first actuator system and an electronic controller, which is not shown in the figures. The first actuator system, the laser tracker system 4 and the robot 3 are connected to the controller so as to allow data communication between the controller and the laser tracker system 4 , the first actuator system and the robot 3.

The support structure 2 supports the robot 3 and comprises four upright posts 5 which are placed on the ground and which are each stabilised by guy lines 6, a vertical support cable 7 which is connected to a crane which is not shown in the figures, and four mainly horizontal steering cables 8.

The posts 5 may move and/or deform due external factors, such a wind, and due to system-specific factors, such as the position and acceleration of the robot 3. Similarly, the steering cables 8 may be strained to a smaller or larger extent as a consequence of these factors. The support structure 2 can therefore not be considered a rigid support structure.

The steering cables 8 are each connected to a first actuator 9 which is arranged to roll up or release the steering cables 8 in a controlled fashion based on instructions from the controller. The four first actuators 9 together form the first actuator system. The first actuators 9 are each arranged to be able to roll up and down the respective posts 5 relatively freely, but are provided with brakes to keep them in a specific vertical position on the posts 5.

The laser tracker system 4 consists of a laser tracker 10 placed outside the support structure 2 and a prism 11 attached to the robot 3. Such a laser tracker system 4 and its operation is well known.

The controller is programmed to contain a mathematical model of the mechanical behaviour of the support structure 2 and the robot 3, so that the response of the robot 3 and the various components of the support structure 2 to control inputs given by the controller to the first actuator system can be predicted. This mathematical model concerns the geometric features of the support structure and additionally the straining behaviour of the steering cables 8, the weight of the steering cables 8 between the robot 3 and the first actuators 4, which obviously depends on the length of the steering cables 8 between the robot 3 and the first actuators 4, the weight of the robot 3 and the effect on the behaviour of the first actuators 9 of forces on the steering cables 8, so that the dynamic behaviour of the entire system may be modelled. The robot 3 comprises a printing nozzle 12 and a main body 13. These are connected by a second actuator system, which is in this example formed by a Stewart platform 14, comprising six second actuators 15 of which only four are shown in fig 3. A hose 16 for concrete runs from the main body 13 to the nozzle 12.

Like most modern actuators the first actuators 9 and second actuators 15 are provided with internal sensors reporting their displacement relative to an internal reference.

The Stewart platform 14 is connected to the controller so as to allow data communication between the controller and the Stewart platform 14.

The main body 13 comprises the necessary components to extrude concrete, and also comprises a feed reservoir for concrete, whereby the feed reservoir contains a mixer, so that different ratios of raw materials may be used depending on the position of the nozzle 12. For instance, in a position where a higher strength concrete is needed, reinforcement fibres may be added to the concrete.

The main body is 13 of the robot 3 is fed by supply hoses which are attached to the support cable 7 but which are not indicted in the figures. The operation of the device 1, in order to build a concrete object 20, eg a wall of a building, is as follows. During the operation of the device 1, the laser tracker system 5 measures the position of the main body 13 of the robot 3 relative to the laser tracker 10 and transmits this position to the controller. The controller also controls the movement and displacement of the nozzle 12 with respect to the main body 13 by means of the Stewart platform 14, so that the actual position of the nozzle 12 can easily be calculated by the controller. The laser tracker 10 forms a fixed reference point for determining the position of the robot 3. In a first stage the device 1, in particular the controller thereof, is calibrated. Even though the controller contains a mathematical model of the components of the support structure, the distance between the posts 5 may be different every time that the support structure 2 is built up, and it is conceivable that the underground has a slope so that not all posts 5 have the same height or are not completely vertical.

Therefore the mathematical model comprises a number of adjustable parameters, in particular related to the positioning of the posts 5, which are determined by applying a certain control signals to the first actuators 9 and determining the response of robot 3 to these control signals.

The laser tracker system 4 is hereby used to determine the position of the robot 3 relative to the laser tracker 10, so that the objective response of the robot 3 to the control signals can be determined.

In a second stage, the robot 3 is used to deposit lines or dots of concrete in order to build up the object 20 layer by layer.

In order to deposit a layer, the robot 3 is placed at the desired height by means of the support cable 7. The brakes of the first actuators 9 are then applied, so that the steering cables 8 are more or less horizontal.

The controller now determines the control inputs on the first actuator system and on the Stewart platform 14 in order to make the nozzle 12 follow a desired path. The control inputs on the first actuator system are determined by a combination of two methods. In the first method, a first control input is calculated by comparing the actual position of the nozzle 12 as determined based on the measurements of the laser tracker system 4 to the desired position, and determining the required control input to effect the desired movement. This first method is a feedback based control method, in which information from the laser tracker system 4 is used to adjust the control input. No use is made of the dynamic modelling of the mechanical behaviour of the support structure 2. The second method takes into account only the mentioned mathematical model and the estimated actual position of the robot as estimated based on the internal displacement sensors of the first actuators 9. In the second method, a second control input is calculated by comparing the estimated actual position of the nozzle 12 to the desired position, and determining, based on the mathematical model, the required control input to effect the desired movement. No information from the laser tracker system 4 is used in this second method. The first control input and second control input are then added up to calculate a first control signal that is fed to the first actuator system to effect a movement of the robot 3, and thereby of the nozzle 12.

Typically, a new first control signal is calculated with a frequency of 10-300 Hz. In order to improve the speed and accuracy of positioning of the nozzle 12, the Stewart platform 14 is also controlled by a feedback based control method.

In order to implement this, the actual position of the nozzle 12, calculated from the actual measured position of the main body 13 of the robot 3 and the displacement of the Stewart platform 14 is compared to the desired position, and a second control signal is calculated by the controller and fed to the Stewart platform 14, so that the nozzle 12 moves relative to the main body 13 of the robot 3. The speed and accuracy of the Stewart platform 14 compensate for any errors that may be left due to imperfections and control delays in the first actuator system and the mathematical model. When deposition of the required layer of concrete is completed, the brakes of the first controllers 4 are released, the crane lifts the robot 3 by the required amount, and the brakes of the first controllers 4 are reapplied, so that a next layer may be deposited.

Even though in the above example the device 1 is set up to print concrete, it is also possible to set it up to print other materials useful for buildings. In particular it is envisaged that the device 1 can be set up to manufacture, in situ, moulds for casting concrete, whereby the moulds are made from a polymer based material, so that complicated concrete structures can be cast in these moulds. This can simply be done by changing the robot 3 to a robot suitable for 3D printing said polymer based material and supplying said material to the robot,

Claims (15)

Conclusions 1.- Method for manufacturing a building, the method comprising a method for the automated manufacture of an object (20) by means of 3D printing, wherein a robot unit (3) is used for the controlled deposition of a material, wherein the robot unit (3) is supported by a support structure (2), wherein the robot unit (3) is movable relative to the support structure (2) by means of a first actuator system, the method comprising the following steps: step A: the measuring the actual position of the robot unit {3} with respect to a reference point which is fixed and which is independent of the support structure (2); step B: calculating a first input to be fed to the first actuator system for effecting a movement of the robot unit {3} from the actual position to a desired position; step C: feeding a first control signal to the first actuator system to obtain movement of the robot unit (3) to the desired position, the first control signal being based at least in part on the calculated first input. Method according to claim 1, characterized in that it further comprises: step D: calculating a second input to be fed to the first actuator system for effecting a movement of the robot unit (3} to the desired position, wherein the second input is calculated from a mathematical model that models the mechanical behavior of the support structure and of the robot unit {3}, where the mathematical model takes into account the effect of the mass of the robot unit (3) on the dynamic deformation of the support structure (2), wherein in step C the first control signal is based at least in part on the calculated second input from step D. Method according to any of the preceding claims, characterized in that the robot unit (3) comprises a main body (13) and comprises a nozzle (12) for depositing the material on an object to be manufactured {20}, wherein the nozzle (12) is movable relative to the main body {13} of the robot unit (3) by means of a second actuator system (14), the method comprising the following steps: step E: determining the actual position of the nozzle { 12}; step F: calculating a third input to be fed to the second actuator system (14) for effecting movement of the nozzle (12) from its actual position to the desired position; step G: feeding a second control signal to the second actuator system (14) to obtain movement of the nozzle {12} to the desired position, the second control signal being based on the calculated third input. Method according to claim 3, characterized in that the second actuator system is a parallel manipulator, more in particular a Stewart platform (14). Method according to any of the preceding claims, characterized in that the supporting construction {2} comprises at least three posts {5} which are arranged around the object to be manufactured. Method according to any of the preceding claims, characterized in that the material in the robot unit (3) is mixed from two or more ingredients that are separately supplied to the robot unit (3). Method according to any of the preceding claims, characterized in that the object (20) is a building and the material is concrete. 8.- Device {1} for the automated production of an object (20) by means of 3D printing of a material, the device comprising: - a robot unit (3) for the controlled deposition of the material; - a support structure (2), wherein the robot unit (3) is carried by the support structure (2); - a first actuator system for moving the robot unit (3) with respect to the support structure (2); - a first controller for outputting a first control signal to the first actuator system to obtain movement of the robot unit (3); characterized in that the device (1) further comprises a measuring system (4) to determine the actual position of the robot unit (3) with respect to a reference point which is fixed and which is independent of the support structure (2), wherein the first controller is arranged to receive the actual position of the robot unit (3) from the measuring system {4} and to calculate the first control signal based at least in part on the deviation of the actual position of the robot unit (3} from a desired position. Device according to claim 8, characterized in that the first controller is arranged to at least partly calculate the first control signal from a mathematical model that models the mechanical behavior of the support structure (2) and of the robot unit (3), wherein the mathematical model takes into account the effect of the mass of the robot unit (3) on the dynamic deformation of the support structure (2). Device according to claim 8 or 9, characterized in that the robot unit (3) comprises a nozzle (12) for depositing the material on an object (20) to be manufactured, wherein the device comprises a second actuator system {14} to move the nozzle (12) relative to the rest (13) of the robot unit (3), the device (1) comprising a second controller for outputting a second control signal to the second actuator system (14) to thereby cause a movement from the nozzle (12), wherein the second controller is arranged to receive the actual position of the robot unit {3} from the measurement system {4} to calculate the second control signal based on the actual position of the robot unit (3) . Device according to claim 10, characterized in that the second actuator system is a parallel manipulator, more in particular a Stewart platform (14). Device according to claim 10 or 11, characterized in that the first controller and the second controller are the same controller. Device according to any of claims 8 to 12, characterized in that the support construction (2) comprises at least three posts (5} which are arranged around the object (20) to be manufactured. Device according to any one of claims 8 to 13, characterized in that the robot unit (3) comprises a mixing unit for mixing ingredients of the material upstream of the nozzle (12). Device according to any of claims 8 to 14, characterized in that the material is concrete.