BACKGROUND

[0001] Some three-dimensional (3D) printing systems form objects by selectively solidifying successively formed layers of a particulate build material formed on a build platform within a build chamber.

[0002] Some three-dimensional printing systems apply liquid binder agent, for example from an ink-jet type printhead, to each layer of build material in a pattern corresponding to the cross-section of the object being formed. In some systems the binder agent has to be cured after it is applied, for example through use of heat or ultra-violet energy, to the build material to cause the binder agent to bind particles of the build material together in the desired shape.

[0003] In other three-dimensional printing system objects may be generated by selectively melting portions of successively formed layers of a particulate build material, such as a powdered plastic build material, to form layers of the object.

[0004] After generation of a 3D object formed using such techniques the object has to be cleaned to remove any non-solidified powder that may be adhered to the object.

BRIEF DESCRIPTION

[0005] Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: [0006] Figure 1 is a schematic diagram of a cleaning apparatus according to one example;

[0007] Figure 2 is a flow diagram outlining a method of operating a cleaning apparatus according to one example;

[0008] Figures 3A and 3B are schematic diagrams outlining operation of a cleaning apparatus according to one example; and

[0009] Figures 4A and 4B are schematic diagrams outlining operation of a cleaning apparatus according to one example.

DETAILED DESCRIPTION

[00010] To improve the value proposition of 3D printing, especially for relatively large production runs, the end-to-end object generation process should be highly automated and should minimise the level of human intervention needed to generate final 3D objects. Although 3D objects may be generated by 3D printers in a generally highly automated manner, typically 3D printed objects have to be cleaned after their generation before they can be considered to be final parts. This is particularly the case with objects that have been generated using powder bed 3D printing techniques.

[00011] Objects formed using powder bed techniques are formed by selective solidification of successive layers of a powdered build material, such as a plastic, metal, or ceramic build material within a build unit. After object generation, the object is surrounded in the build unit by a volume of non-solidified and typically free-flowing build material. Furthermore, the object may have additional nonsolidified but non-free flowing build material adhered to the object (for example adhered to the object surface, or accumulated within internal object structures).

[00012] Free-flowing build material surrounding the object may be separated from the object relatively easily, for example using sieving techniques that may be augmented with the addition of vibrations and/or air flows. Adhered build material, however, requires the use of additional build material removal techniques, such as use of relatively high-pressure air flows. However, use of high-pressure air flows can cause objects to move around during clearing which can cause the objects to be damaged. This may be particularly the case with 3D objects known as green parts, which are formed through the application of a binder agent to layers of metal or ceramic build material, and which may have relatively poor strength (e.g. a tensile strength of around 2 to 10 MPa) until they are sintered in a sintering furnace.

[00013] Examples will now be described of a system and method for cleaning 3D printed objects which aim to enhance automated adhered build material removal whilst reducing or eliminating the risk of damage to the objects.

[00014] Referring now to Figure 1 , there is shown a schematic view of a cleaning apparatus 100 for cleaning 3D printed objects. The apparatus 100 comprises an at least partially enclosed housing 102 within which is provided a cleaning platform 104, or a mechanism or interface, such as a set of guide rails, to receive a cleaning platform 104 on which a 3D object 106 to be cleaned may be placed (shown in a side view). The 3D object 106 may be placed on the cleaning platform 104 by a suitable object placement system (not shown), that may include a robotic arm, a conveyor belt, or any other suitable object placing mechanism. In one example, the object is not fixed to the cleaning platform or restrained in any manner. In one example, the housing 102 may include one or multiple openings to allow the cleaning platform 104 to be moved into and out of the housing. As discussed above, the 3D object 106 may initially comprise an object portion and a quantity of adhered build material.

[00015] The apparatus 100 further comprises an imaging system 108, a cleaning module 110, and a controller 120.

[00016] The imaging system 108 comprises one or multiple cameras or other suitable imaging elements, such as a line scanner, to enable a 2D or a 3D image of the object 106 to be generated and also to determine the position of the object 106 on the cleaning platform. In one example, the imaging module 110 comprises a 3D camera to enable a 3D image of the object 106 to be obtained. In another example, the imaging module 110 comprises a movable 2D camera, or a set of fixed 2D cameras to allow a 3D image of the object 106 to be obtained. One or more lights or projectors may also be provided in appropriate positions to suitably illuminate the 3D object 106.

[00017] The imaging system 108 is configured to distinguish between the object 106 and the cleaning platform 104 using any suitable techniques. In one example, the upper surface of the cleaning platform 104 may have a property that is contrasted to a property of the object 106. In one example the property may be at least one of a colour and a surface reflectivity. In another example, the cleaning platform 104 may have a patterned surface, such as a checkerboard pattern, a line pattern, or the like. This may allow the imaging system 108 to generate an image just of the object 104, without including any portion of the cleaning platform 104.

[00018] The cleaning module 110 comprises an output port 112, such as a nozzle, an array of nozzles, a slot, an air knife, or the like, to enable a flow of cleaning fluid 114, such as air, nitrogen, or the like, to be directed towards the object 106. In one example, the output port 112 may span the width of the cleaning platform 104 to allow a flow of cleaning fluid to be applied simultaneously along a portion spanning the whole length of the object 106. In one example, the cleaning module 110 is connected to a source of pressurized cleaning fluid through a variable flow mechanism (not shown), such as an electromechanical variable valve, to enable the pressure of the cleaning fluid flow 114 as it exits the output port 112 to be controlled by the controller 120.

[00019] The cleaning module 110 is laterally moveable relative to the cleaning platform 104. This may be achieved, for example, by allowing the cleaning module 110 to be movable along an axis, by allowing the cleaning platform 104 to be moveable along the axis, or allowing both the cleaning module 110 and the cleaning platform 104 to be movable along the axis. In one example, the height or distance of the cleaning module 110 may be adjusted relative to the cleaning platform 104. In one example the orientation of the cleaning fluid flow 114 may be adjusted, for example by changing the orientation of one or more or of the cleaning module 110 and the output port 112.

[00020] The controller 120 comprises a processor 122, such as a microprocessor or a microcontroller, coupled to a memory 124. On the memory 124 are stored instructions 126 that, when executed by the processor 122, cause the controller 120 to analyse an image or images generated by the imaging system 108 and to obtain therefrom characteristics of the object 106 on the cleaning platform 104. The memory 124 additionally comprises instructions 128 that, when executed by the processor 122, cause the controller 120 to control the cleaning module 110 based on the obtained object characteristics.

[00021] Example operation of the apparatus 100 will now be described with additional reference to the flow diagram of Figure 2.

[00022] At block 202, the controller 120 controls the imaging system 108 to obtain an image or images of the object 106 on the cleaning platform 104. The imaging system 108 may, for example, generate a point cloud or other data representing the 3D object 106 in a suitable digital format. In another example, the controller 120 processes image data obtained from the imaging system 108 to generate the point cloud or other data representing the 3D object 106. In one example the imaging system 108 is able to generate a full 3D image of the object 106, apart from for any portions of the object 106 which are hidden from the imaging system 108, such as the base of the object 106 which is hidden by the cleaning platform 104.

[00023] The controller 120 then processes the image data to obtain characteristics of the object 106 on the cleaning platform 104. The characteristics may include one or more of: the position of the object 106 relative to a reference point of the cleaning platform 104; the surface geometry of the object 106; the estimated mass of the object 106; the estimated centre of gravity of the object 106; and an estimation of the friction force between the base of the object 106 and the upper surface of the cleaning platform 114. In one example, the controller 120 may estimate the mass of the object 106 based on its determined volume and based on knowledge of the type of build material from which the object 106 is formed. Since the imaging system 108 cannot obtain data about the internal structure of the object 302A the controller 120 may determine characteristics of the object 302A using a set of assumptions, for example assuming that the object is a solid object, assuming that the object has a predetermined density, that the object is made of specific build material, or the like.

[00024] At block 204, the controller 120 controls the cleaning module 110 to clean the object 106 based on the obtained characteristics. By controlling the cleaning module 110 is meant that the controller 120 may control at least one or more of: the distance between the cleaning module 110 above the cleaning platform 104; the lateral position of the cleaning module 110 relative to the cleaning platform 104; the orientation of the cleaning fluid flow 114; and the pressure of the cleaning fluid flow 114 at the output port 112.

[00025] A number of examples will now be described to further aid understanding.

[00026] Referring now to Figure 3A, a schematic side view of the cleaning platform 114 is shown with an object 302A positioned thereon. As discussed above, the object 302A may initially comprise an object portion and a quantity of adhered build material. In this example, the cleaning module 110 has a fixed orientation and a fixed height above the cleaning platform 104. For clarity, only the cleaning module output port 112 is shown. In Figure 3A, the relative position of the output port 112 and the object 302A is shown at different moments in time (labelled from 1 to 6).

[00027] In this example, the controller 120 determines the 3D shape of at least a portion of the object 302A. From this, the controller 120 determines the highest portion of the object 302A above the cleaning platform 104 and sets the height of the output port 112 to be a predetermined distance above the highest portion of the object 302A. The controller 120 also estimates one or more of the mass of the object 106, the estimated centre of gravity of the object 106, and the friction force between the object 302A and the cleaning platform 104. The controller 120 also determines the distance, referred to hereinafter as the cleaning distance, between the output port 112 and the portion of the surface of the object 106 to which the cleaning fluid flow 114 is to be directed. In one example, controller 120 further determines the angle, referred to hereinafter as the cleaning angle between the cleaning fluid flow 114’1 and surface of the object. Using these determined characteristics, the controller 120 can determine a pressure of cleaning fluid flow 114 that is to be applied to a particular portion of the object 302A that is unlikely to cause movement, and hence damage, to the object 302A but that will cause acceptable cleaning of object surface. In one example, a small degree of movement of the object, may be acceptable, providing this is determined not to cause damage to the object.

[00028] For example, at position 112’1 (indicating the position of the output port 112 at position 1 shown in Figure 3A), a first pressure is generated for cleaning fluid flow 114’1 (indicating the cleaning fluid flow 114 at position 1 shown in Figure 3A). For example, at cleaning position 1 , the controller 120 determines the cleaning distance between the output port 112 and the portion of the object 302A to which the cleaning fluid flow 114’1 is directed and further determines the cleaning angle between the cleaning fluid flow 114’1 and surface of the object at that point. As shown in Figure 3A, at this position the cleaning angle is about 45 degrees. Using at least one of determined mass of the object 302A and the estimated friction between the object 302A and the cleaning platform 104, the controller 120 determines a suitable pressure of the cleaning fluid flow 114 at the output port 112 that is sufficient to cause satisfactory cleaning of the object surface but is insufficient to cause the object 302A to move relative to the cleaning platform 104.

[00029] If, for example, the cleaning fluid flow pressure were too high, the force generated by the cleaning fluid flow 114’1 on the object 302A could cause the object 302A to move relative to the cleaning platform 104. Since, however, it is difficult to measure the pressure of the cleaning fluid flow 114 at the surface of object 302A, the pressure of cleaning fluid flow at the surface of object 106 may be estimated, based, for example, on at least one of the pressure of the cleaning fluid flow 114 at the output port 112 or within the cleaning module 110, the cleaning distance, and the cleaning angle. In one example, a maximum estimated pressure of the cleaning fluid 114 at the surface of object 302A may be set. This maximum pressure may be, for example, based on test results for a similar type of object to be cleaned, and is determined to be a maximum pressure of cleaning fluid flow that can be safely applied to the surface of the object 302A without causing damage to the object.

[00030] At cleaning position 2, the controller 120 determines the cleaning distance and the cleaning angle, which is still about 45 degrees. Accordingly, in order to prevent the object 302A from moving relative to the cleaning platform 104, the controller 120 determines that fluid cleaning flow 114’2 is to be generated to have a second pressure lower than the first pressure since the cleaning distance is less than in cleaning position 1.

[00031] At cleaning position 3, the controller 120 determines that the cleaning angle is about 90 degrees, meaning that the fluid flow 114’3 hits the object perpendicular to the object surface. The controller 120 also determines the cleaning distance, and using this data determines a pressure for the cleaning fluid flow 114’3 that is unlikely to generate a force that would cause the object 302A to move relative to the cleaning platform 104. Accordingly, the controller 120 determines that the fluid cleaning flow 114’3 is to be generated to have a third pressure higher than the first or second pressure.

[00032] At each cleaning position, the controller 120 thus determines an appropriate pressure of the cleaning fluid flow 114 so as to avoid causing the object 302A to move relative to the cleaning platform 104. For ease of explanation only a small number of cleaning positions are shown in the drawings. However, it will be appreciated that the relative position of output port 112 and the object 302A may be changed on a continuous basis, or may be changed using small discrete movements. In one example, the speed of relative movement between the output port 112 and the object 302A may be determined to enable satisfactory cleaning of each portion of the object 302A.

[00033] Referring now to Figure 3B, a second example is shown of an object 302B.

[00034] At cleaning position 1 , the controller 120 determines, based on, for example, one or more of the determined object geometry, the determined object centre of gravity, and the determined object mass, that applying too great a pressure for cleaning fluid flow 114’1 could result in the object 302B from toppling over or moving. The controller 120, thus determines a suitable first pressure for the cleaning fluid flow 114’1 that will prevent the object 302 B from moving.

[00035] At cleaning position 2, the controller 120 determines, that a higher pressure may be generated for the cleaning fluid flow 114’2, based on the determined object characteristics, since at cleaning position 2 the object 302B is determined to be relatively stable, and unlikely to be moved by cleaning fluid flow 114’2, even at a relatively higher pressure.

[00036] Referring now to Figure 4A, a side view of the cleaning platform 114 is shown with an object 402A positioned thereon. In this example, the cleaning module 110 or the output port 112 has a variable orientation and a variable height above the cleaning platform 104.

[00037] In this example, the controller 120 controls, based on the determined object characteristics, the orientation of the output port 112 such that the cleaning fluid flow 114 is applied substantially perpendicularly to the object surface, although in other examples the controller 120 may determine that any other suitable angle may be chosen. In some examples, the cleaning angle may be changed during a cleaning operation.

[00038] At cleaning position 1 , the controller 120 positions the cleaning fluid flow 114’1 to be directed towards the base of the object 402A. As described above, the controller 120 determines a suitable pressure of the cleaning fluid flow 114’1 to avoid movement of the object 402A relative to the cleaning platform 104.

[00039] Since in this example the height of the cleaning port 112 is adjustable, the controller 120 may adjust the pressure of the cleaning fluid flow 114 based on the cleaning distance. For example, using a relatively high-pressure cleaning fluid flow at a relatively far distance from the object surface is equivalent to using a relatively low-pressure cleaning fluid flow at a relatively close distance from the object surface. The controller 120 may thus determine a suitable combination of cleaning fluid flow pressure and output port distance, for example based on the determined geometry of the object 402A.

[00040] At cleaning position 2, the controller 120 positions the cleaning fluid flow 114’2 to be directed towards the top of the object 402A. As described above, the controller 120 determines a suitable pressure of the cleaning fluid flow 114’2 to avoid movement of the object 402A relative to the cleaning platform 104.

[00041] At cleaning position 3, the controller 120 positions the cleaning fluid flow 114’3 to be directed towards the top surface of the object 402A. As described above, the controller 120 determines a suitable pressure of the cleaning fluid flow 114’3 to avoid movement of the object 402A relative to the cleaning platform 104.

[00042] Referring now to Figure 4B, a side view of the cleaning platform 114 is shown with an object 402B positioned thereon. In this example, the cleaning module 110 has a variable orientation and a variable height above the cleaning platform 104. At cleaning position 1 , the controller 120 determines, based on, for example, one or more of the determined object geometry, the determined object centre of gravity, and the determined object mass, that applying too great a pressure for cleaning fluid flow 114’1 could result in the object 302B from sliding or from toppling over on the cleaning platform 104. To avoid this, the controller 120 may make different choices. For example, at position 1 , the controller 120 may determine a suitable first pressure for the cleaning fluid flow 114’1 that, when applied perpendicularly to the surface of object 402B will prevent the object 302B from moving.

[00043] Alternatively, the controller 120 may determine that a different pressure cleaning fluid flow 114’1’ may be applied at a shallower cleaning angle. For example, the controller 120 may determine whether a component of the force of the cleaning fluid flow 114’1’ as applied to the object surface is likely to cause the object to move relative to the cleaning platform 104. In one example, the controller 120 may determine a minimum estimated pressure of the cleaning fluid 114 at the surface of object 302A. The minimum estimated pressure may, for example, be a determined minimum pressure that obtains satisfactory cleaning results. In this way, the controller 120 may determine the orientation of the output port 112 to ensure that the minimum pressure is met, whilst at the same time preventing movement of the object 402B.

[00044] The controller 120 may determine then, for example, the position of the output port 112 as it is moved relative to the surface of the object 402B, a suitable output port orientation, and an appropriate cleaning pressure.

[00045] The above-described techniques enable efficient cleaning of objects having a wide-range of object geometry whilst avoiding or limiting movement, and hence damage caused by movement of objects which are placed in an unrestrained manner on a cleaning platform. Being able to place objects on the cleaning platform without having to restrain them helps simplify both the object cleaning workflow and the object cleaning apparatus. The process can be repeated after a first cleaning pass, for example after the object 106 has been repositioned in a different orientation on the cleaning platform by a suitable object placement mechanism.

[00046] It will be appreciated that example described herein can be realized in the form of hardware, software or a combination of hardware and software. [00047] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[00048] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.