BACKGROUND

[0001 ] Additive manufacturing techniques, such as three-dimensional (3D) printing, enable objects to be generated on a layer-by-layer basis. 3D printing techniques may generate layers of an object by forming successive layers of a build material on a build or support platform, and selectively solidifying portions of each layer of the build material. BRIEF DESCRIPTION

[0002] Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0003] Figure 1 is a simplified isometric illustration of a portion of 3D printing system according to one example;

[0004] Figure 2 is a block diagram of a 3D printer controller according to one example;

[0005] Figure 3 is a flow diagram outlining an example method according to one example;

[0006] Figure 4 is a simplified side view illustration of a 3D printing system according to one example;

[0007] Figure 5 is a simplified side view illustration of a 3D printing system according to one example;

[0008] Figure 6 is a simplified side view illustration of a 3D printing system according to one example;

[0009] Figures 7a to 7d are simplified side view illustrations of a 3D printing system according to one example;

[0001 0] Figure 8 is a flow diagram outlining an example method according to one example;

[0001 1 ] Figure 9 is a simplified side view illustration of a 3D printing system according to one example;

[00012] Figure 1 0 is a simplified isometric illustration of a 3D printing system according to one example; and

[0001 3] Figure 1 1 is a flow diagram outlining an example method according to one example. DETAILED DESCRIPTION

[00014] Some 3D printing systems use build material that have a powdered, or granular, form. According to one example a suitable build material may be a powdered semi-crystalline thermoplastic material. One suitable material may be Nylon 12, which is available, for example, from Sigma-Aldrich Co. LLC. Another suitable material may be PA 2200 which is available from Electro Optical Systems EOS GmbH.

[00015] In other examples other suitable build material may be used. Such materials may include, for example, powdered metal materials, powdered plastics materials, powdered composite materials, powdered ceramic materials, powdered glass materials, powdered resin material, powdered polymer materials, and the like.

[00016] Such 3D printing systems typically generate, along a side of a support platform, a quantity of build material to be spread over the support platform. During a 3D printing operation, an initial layer of build material is spread directly on the surface of a support platform, whereas subsequent layers of build material are formed on a previously formed layer of build material. Herein, reference to forming a layer of build material on the support platform may refer to, depending on the context, either forming a layer of build material directly on the surface of the support platform, or forming a layer of build material on a previously formed layer of build material.

[00017] Various examples will now be described that provide a compact and convenient system for providing build material to be spread over a support platform, for example for use in the generation of 3D objects by a 3D printing system. Some examples enable a precise dose of build material to be formed along the edge of a support platform. The dose of build material may then be spread over the build, or support, platform using a build material spreading mechanism. Forming a precise dose of build material may be useful, for example, for reducing the amount of excess build material remaining after a layer of build material has been formed, for ensuring that sufficient build material is provided to enable a complete layer of build material to be formed, and for reducing the amount of build material that could become airborne whilst forming a layer of build material..

[0001 8] Referring now to Figure 1 there is shown an illustration of a portion of a 3D printing system 100 according to one example. For clarity reasons not all the elements of the 3D printing system 100 are shown. For example, the illustrations shown herein do not show any specific build material solidification systems, although any suitable build material solidification systems may be used, such as fusing agent deposition and heating systems, binder agent deposition systems, laser sintering systems, and the like.

[0001 9] The system 100 comprises a build material supply module or supply tray, generally indicated at 102, to provide a quantity of build material to be spread across a support platform 104 by a horizontally movable build material spreader, or build material distributor, 108. The spreader 108 may be mounted on a suitable carriage or gantry (not shown). The support platform 1 04 may be movable in the z-axis, as indicated by arrow 106, to enable it to be lowered as each layer of build material formed thereon is processed by the 3D printing system 1 00. In the example shown the build material spreader 108 is a roller, although in other examples other suitable forms of spreader, such as a wiper blade, may be used. Build material is supplied to the supply module 102 from a build material store (not shown). In one example, as described later, the build material store may be located below the height of the supply module 102.

[00020] The build supply module 1 02 has length that, in one example, is substantially the same as the length of the support module 104. In other examples, however, the supply module 102 may be longer or shorter than the support platform 104.

[00021 ] The supply module 102 forms a generally open container in which build material may be deposited and from which build material may be moved to enable it be spread over the support platform 104. In Figure 1 , the foreground endplate of the supply module 102 is not shown so as to allow the internal structure of the supply module 102 to be visible. The supply module 102 has a cross-section formed from rectangular base portion 1 10, and a curved upper portion 1 12. The curved upper portionl 12 has a cross-section that defines two arcs of a circle having its center located along an axis 1 18 positioned centrally above the longitudinal axis of the base portion 1 10 and about level with the top of the supply module 102, and having a predetermined radius.

[00022] The base portion 1 1 0 may comprise a reciprocating build material distribution element 1 14 movable in the direction shown by arrow 1 15. The build material distribution element 1 14 may be controlled to reciprocate, or slide, along the base of the supply module 102, by a small amount to help distribute build material within the supply module 102, as described further below. In one example the build material distribution element 1 14 may be controlled to slide by up to about 1 cm, although in other examples the build material distribution element 1 14 may be controlled to slide by a greater or smaller amount. In one example the build material distribution element 1 14 may comprise a mesh-like structure and be driven by any suitable drive system, such as a motor.

[00023] The supply module 102 further comprises a vane, or blade, 1 16 that is rotatable about the axis 1 18, as shown by arrow 120. The vane has a height such that during its rotation the base of the vane may form a substantial seal against the curved upper portion 1 1 2, enabling it to move build material from the base portion 1 10 to the curved upper portion 1 12. [00024] The vane 1 16 may be driven by any suitable drive mechanism (not shown), such as a stepper motor, rack and pinion arrangement, or the like and may additionally be coupled to a position determination module (not shown), such as an angular encoder, to enable the angular position of the vane to be accurately controlled and determined.

[00025] In some examples the supply module 102 may further comprise a horizontal protrusion 122 that defines a gap, or void, 124 between the top of the vane 1 1 6 and one longitudinal edge of the protrusion 122. In other examples, however, there may be no protrusion 122 in which case a gap or void 124 may be defined between the top of the vane 1 16 and one side of the supply module 102, as illustrated. In some examples the protrusion 122 may not be horizontal, and may be inclined .

[00026] Operation of the 3D printing system 100 is generally controlled by a controller 1 26, as shown in greater detail in Figure 2.

[00027] The controller 126 comprises a processor 202 coupled to a memory 204. The memory 204 stores build material supply management instructions 206 that, when executed by the processor 202, control the 3D printing system 100 to manage the supply of build material, as described herein.

[00028] Operation of the 3D printing system 1 00 will now be described with reference to the flow diagram of Figure 3 and the drawings of Figures 4 to 10. [00029] At 302, the controller 126 controls the delivery of build material to the supply module 102. One example of how build material may be delivered to the supply module 1 02 is shown in Figure 4. In Figure 4 is shown a main build material store 402 comprising build material 404 and a feed channel 406 to move build material 404 from the build material store 402 to a delivery zone 408. The feed channel 406 comprises a feed mechanism, such as an auger screw 410, or any other suitable feed mechanism.

[00030] In one example the build material feed mechanism 410 may be controlled to deliver a predetermined amount of build material to the supply module 102. For example, if an auger screw mechanism is used as the feed mechanism, the number of rotations of the auger screw may be controlled to deliver the predetermined amount of powder. If an accurate amount of build material can be delivered by the feed mechanism 41 0, then in one example the protrusion 122 may be absent from the supply module 102, as in Figures 4, 5, 6, and 7.

[00031 ] The delivery zone 408 may be positioned at any suitable position along the length of the supply module 102, but in at least some examples the delivery zone 408 does not extend substantially along the length of the supply module. For example, the delivery zone may have a length that is less than about 10% of the length of the supply module 102 in some examples. [00032] The build material store 402 may, in one example, additionally include a vibrator or compactor (not shown) to help ensure that build material 404 within the build material store 402 compacts around the lower end of the feed mechanism 410, to ensure a regular supply of build material to the feed mechanism 410.

[00033] Having a build material store located generally beneath the support platform 104 and supply module 102 enables the footprint of such a 3D printing system to be reduced, compared to having a build material store located at one side of the 3D printing system.

[00034] In other examples build material may be delivered to the supply module 102 using other suitable configurations such as, for example, from an overhead build material hopper.

[00035] At 304, the controller 126 controls the build material distribution element 1 14 to reciprocate to evenly distribute the delivered build material 402 along the length of the supply module 102. In one example, as build material is being delivered to the supply module 102, the controller 126 moves the vane 1 1 6 to a position, such as a horizontal position as shown in Figure 5. In one example when the vane 1 16 is in a horizontal position it is level with the top of the supply module 1 02. [00036] In a further example, illustrated in Figure 6, as build material is being delivered to the supply module 102 the controller 126 may control the vane 1 16 to move from a roughly vertical position, in which the lower edge of the vane is within the rectangular base portion 1 10, to reciprocate, up to about 45 degrees to either side. This may help, in conjunction with the reciprocating build material distribution element 1 14, the rapid and even distribution of build material along the length of the supply module 102. This may also help in maintaining the fluidity of the build material.

[00037] At 306 the controller 126 controls the vane 1 1 6 to move to a pre-feed position, as illustrated in Figure 7a. Since the vane 1 16 has moved through the delivered build material in the supply module 102 it scoops up some of the build material such that a first portion of the scooped up build material is above the top of the supply module 102 and a second portion is below the top of the supply module 1 02. [00038] At 308, the controller 126 controls the build material spreader 108 to move across at least a portion of the support platform 104 and over the void 124 such the first portion of build material is displaced and falls back into the supply module 1 02 leaving a predetermined dose of build material being retained by the vane 1 16, as shown in Figure 7b. The quantity of build material in the predetermined dose may be modified by changing the angular position of the pre-feed position.

[00039] At 310, the controller 1 26 controls the vane 1 16 to move to a feed position, as illustrated in Figure 7c at which the measured dose of build material is positioned level with the top of the supply module 1 02. The measured dose of build material may then be distributed over support platform 104, which may be positioned slightly below the top of the supply module 102, by the build material spreader 108, as shown in Figure 7d. The height of the layer of formed build material may be controlled by the vertical position of the support platform 104.

[00040] The supply module 102 may then be supplied with additional build material in the manner described above. The resupply of additional build material may be performed whilst the 3D printing system is selectively solidifying portions of the build material on the support platform. In this way processing of successive layers of build material may be performed in an efficient and timely manner.

[00041 ] In another example, for example where the feed mechanism is not controllable to deliver an accurate quantity of build material to the supply module 102 the protrusion 122 may be used to determine when a sufficient quantity of build material has been delivered to the build module 102, as described with additional reference to the flow diagram of Figure 8, and the illustration of Figure 9. [00042] At 302, the controller 126 controls the delivery of build material to the supply module 102, for example as described above.

[00043] At 304, the controller 126 controls the build material distribution element 1 14 to reciprocate to evenly distribute the delivered build material 402 along the length of the supply module 102. In one example, as build material is being delivered to the supply module 102, the controller 126 moves the vane 1 1 6 to a position, such as a horizontal position. [00044] At 802, the controller 1 26 controls the vane 1 16 to rotate towards the protrusion 122, as shown in Figure 9. If there is sufficient build material in the supply module 102 some of the build material will be scooped up by the vane 1 16 and will be compressed against the protrusion 1 22. Since the build material is not compressible by any significant amount the vane 1 1 6 becomes blocked at an angular position below the protrusion 122. The controller 126 may then determine the angular position 902 at which the vane 1 1 6 becomes blocked, and, at 804, may thus determine whether a predetermined quantity of build material has been delivered to the supply module 1 02. If not, the controller 126 controls the delivery of additional build material to the supply module 102.

[00045] This routine may be performed periodically until the controller 126 determines that there is sufficient build material in the supply module 102.

[00046] When the controller 126 does determine that sufficient build material has been delivered to the supply module the controller 126 controls, at 806, the build material supply mechanism to stop supplying build material to the supply module 102. The controller 126 may then perform the previously described actions to provide a measured dose of build material ready to be distributed across the support platform 104.

[00047] A yet further example is illustrated in Figure 1 0, which shows an illustration of a portion a portion of a 3D printing system 100 according to one example. In this example a pair of supply modules 102a and 102b are provided on opposite sides of a support platform 1 04. This example enables build material to be supplied to either side of the support platform 104. Furthermore, any excess build material may be returned to the opposite supply module through the aforementioned void.

[00048] In this way, coordination of the control of each supply module 102 may provide enhanced efficiencies when the 3D printing system 1000 is configured to operate in a bi-directional manner. By bi-directional is meant that layer of build material may be formed on the support platform 1 04 by the build material spreader 108 using build material from either of the build modules 102. The 3D printing system 1000 may also be able to selectively solidify portions of a formed layer of build material whilst operating in either direction.

[00049] In one example the support platform 104 may be part of a removable build module that may be insertable into the 3D printing system. Accordingly, reference herein to a support platform will be understood to generally refer to when such a build module is inserted into the 3D printing system.

[00050] In a yet further example, as shown in Figure 1 1 , the controller 126 may dispense with the pre-feed stage 306 and removal of excess build material stage 308 (described above in relation to Figure 3) and may control the vane 1 16 to move it directly to a horizontal feed position. In this example, the dose of quantity of build material provided on the vane 1 1 6 may vary each time the vane 1 16 is moved to the feed position, and any excess build material left over following the forming of a layer of build material on the support platform 1 04 may recuperated, for example in second supply module on the other side of the support platform 104 (as shown in Figure 10).

[00051 ] It will be appreciated that examples described herein can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, some examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, some examples may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection.

[00052] 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.

[00053] 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.