Patent Publication Number: US-2020298482-A1

Title: Detection of build material in a 3d printing system

Description:
BACKGROUND 
     In 3D (three-dimensional) printing, objects may be generated by forming successive layers of a build material on a build platform or support platform, and selectively solidifying portions of each layer of the build material. 
     Build material may be removed from a feed tray with a vane or plate, and a pile of build material may be placed adjacent a recoater or spreader. The spreader may spread the pile of build material to form a layer of build material on the support platform, over the previous layer that has been selectively solidified. 
    
    
     
       BRIEF DESCRIPTION 
       Some non-limiting examples of the present disclosure will be described in the following with reference to the appended drawings, in which: 
         FIG. 1  is a simplified side view illustration of a build material supply system for a 3D printing system, according to one example; 
         FIG. 2  is a flow diagram outlining an example method for spreading build material in a 3D printing system, according to one example; 
         FIG. 3  is a simplified side view illustration of a 3D printing system according to one example; 
         FIG. 4  is a simplified isometric illustration of a portion of a 3D printing system according to one example; 
         FIGS. 5 and 6  are simplified isometric illustrations of examples of the arrangement of sensors as disclosed herein; 
         FIGS. 7 a  and 7 b    are simplified plan views of a plate of a build material supply systems, according to one example, in two different situations; 
         FIGS. 8 a  and 8 b    are respectively a simplified side view and a simplified, partial plan view of a 3D printing system according to one example; 
         FIG. 8 c    is a graph of the readings of a sensor in the example system of  FIGS. 8 a    and  8   b;    
         FIGS. 9 a  and 9 b    show simplified plan views of a plate of a build material supply system according to one example, in two different situations, and corresponding graphs showing sensor readings in each case; 
         FIG. 10  is a flow diagram outlining a method for spreading build material in a 3D printing system, according to one example; 
         FIGS. 11 a  to 11 c    are schematic side views of a 3D printing system according to one example, illustrating an example method for spreading build material as disclosed herein; 
         FIG. 12  is a flow diagram outlining another example method for spreading build material in a 3D printing system; and 
         FIG. 13  is a block diagram of a controller according to one example. 
     
    
    
     DETAILED DESCRIPTION 
     Some 3D printing systems use build materials that have a powdered, or granular, form, such as for example powdered semi-crystalline thermoplastic materials. 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. 
     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. 
     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. 
     Each layer of build material formed on the support platform is selectively solidified by any suitable build material solidification system, such as fusing agent deposition and heating systems, binder agent deposition systems, laser sintering systems, and the like, before forming the next layer. 
       FIG. 1  shows a portion of a build material supply system for a 3D printing system according to implementations disclosed herein. In  FIG. 1  the build material supply system  100  may comprise a feed tray  110  for containing build material  120 , a vane or plate  130  for removing build material from the feed tray  110  as shown by arrow A, and forming a pile  140  of build material adjacent a spreader or recoater (not shown in  FIG. 1 ) of the 3D printing system. 
     The spreader or recoater may spread the pile  140  of build material in a spreading direction shown by arrow B, forming a layer of build material on a support platform  150  of the 3D printing system, as a first layer of build material or over previous layers which have been selectively solidified. 
     The build material supply system may also comprise a sensor module  160  to detect build material on the plate  130 , as shown by arrow C. 
     With such a build material supply system, implementations of a method for spreading build material in a 3D printing system as disclosed herein may comprise, as illustrated in  FIG. 2 , at  510  providing a pile of build material on a plate adjacent a spreader of the 3D printing system, and at  520  sensing an amount of build material on the plate. Depending on the sensed amount of build material, different actions may be carried out, as will be explained later on. 
     Implementations of build material supply systems and spreading methods as disclosed herein may increase efficiency and reduce defects in the manufactured 3D objects, because a lack of build material, or an insufficient amount of build material, may be detected before spreading a layer, and the printing process may then be paused or stopped, and/or the build material feed process may be adjusted before further layers are formed. 
       FIG. 3  illustrates in side view a portion of a 3D printing system according to implementations disclosed herein, with a build material supply system. For clarity reasons not all the elements of the 3D printing system and the build material supply system are shown in  FIG. 3 .  FIG. 4  is a simplified isometric view of part of the elements shown in  FIG. 3 . 
     The 3D printing system shown in  FIGS. 3 and 4  may comprise a build material supply system  100 . In some implementations the build supply system  100  comprises the feed tray  110 , the plate  130  and the sensor module  160  to detect build material on the plate  130 . The plate  130  may be rotatable around an axis  132 , such as shown by arrow E in  FIG. 4 , but in other examples it may have a different operation. The sensor module  160  may be mounted in several configurations, for example as shown in  FIG. 3  and disclosed later on. In some examples, the sensor module  160  may be to detect the presence or absence of build material on the plate  130 , or it may be to detect the amount of build material on the plate  130 . 
     In some implementations, the sensor module  160  may comprise an optical sensor. For example, the sensor module  160  may comprise a one-dimensional line sensor providing an output signal that is a function of the colour of the sensed surface. 
     A line sensor may comprise a light source and an electro-optical detector. The source illuminates the target surface, in this case the plate  130 , and the detector produces an electrical signal related to the light reflected from the surface. In practice the source may be a light-emitting diode, or sometimes two or more such diodes emitting light of different colours. The light reflected, and therefore the electrical signal generated by the detector, depends e.g. on the colour of the target surface. 
     Thus, if the plate  130  and the build material are not of the same colour, the presence or absence of build material on the plate  130  may be determined from on the electrical signal produced by the line sensor. The amount and/or distribution of build material may also be determined to a certain extent, for example by sensing in several points of an area of the plate and taking into account the different sensor readings. 
     The plate  130  on which the build material is to be detected by the line sensor may be of a colour that contrasts with the colour of the build material: for example, the plate  130  may be of a dark colour, for example black, when the build material is of a light colour, for example white, thereby allowing reliable readings to be obtained from the line sensor. 
     The feed tray  110  forms a generally open container in which build material may be deposited and from which build material may be moved to enable it to be spread over the support platform  150 . In  FIG. 4 , the foreground endplate of the feed tray  110  is not shown so as to allow the internal structure to be visible. 
     The feed tray  110  may have a length that, in some example, is substantially the same as the length of the support platform  150 . In other examples, however, the feed tray  110  may be longer or shorter than the support platform  150 . 
     The support platform  150  may be movable in the z-axis, as indicated by arrow D, to enable it to be lowered as each layer of build material formed thereon is processed by the 3D printing system. 
     In some implementations, build material  120  may be supplied to a delivery zone  112  of the feed tray  110  from a build material store  170 , which may be located below the height of the feed tray  110 , as shown in  FIG. 3 , for example through a feed channel  180 . The feed channel  180  may comprise a feed mechanism, such as for example an auger screw  185 . The delivery zone  112  may be positioned at any suitable position in the feed tray  110 : for example, it may be in a central area along the length of the feed tray  110 . In order to show such an example, in  FIG. 4  the perimeter of the base of the feed tray  110  and the position of the delivery zone  112 , which are not visible in the isometric view, have been schematically depicted in dotted lines. 
     In other examples build material may be delivered to the feed tray  110  using other suitable configurations such as, for example, from an overhead build material hopper. 
     In some implementations a build material distribution element  114  may be provided on the base portion of the feed tray  110 , as shown in  FIGS. 3 and 4 , in order to distribute the build material throughout the feed tray  110 , for example along all the length. 
     The build material distribution element  114  may comprise, in some examples, a mesh-like structure such as schematically represented in  FIG. 4  for the portion that is visible from the end of the feed tray  110 . 
     The build material distribution element  114  may be driven by any suitable drive system, such as a motor (not shown) and in some implementations it may be controlled to reciprocate by a small amount, for example up to about 1 cm, along the base of the feed tray  110  in the direction shown by arrow F, to help distribute the build material. 
     For example, in implementations such as shown in  FIG. 4 , the build material distribution element  114  may cause build material delivered to delivery zone  112  to move progressively along the feed tray  110  towards the two ends thereof, to provide build material along substantially all the length of the feed tray  110 . 
     Thus, when the plate  130  removes build material from the feed tray  110 , it may take up a suitable amount of build material along substantially all the length of the plate  130 . 
     In  FIG. 3 , a pile  140  of build material that has been removed from feed tray  110  to be spread in a layer across the support platform  150  is shown on the plate  130 , adjacent a horizontally movable build material spreader  190  according to implementations disclosed herein. 
     By the expression “adjacent the spreader” it is meant that the pile  140  of build material is in a position, also adjacent to the support platform  150 , generally between the support platform  150  and the spreader  190  when the spreader is in the starting position for the spreading operation, at a level suitably close to level of the lower edge of the spreader  190 , from where the build material of the pile  140  may be spread on the previously spread and selectively solidified layer of build material on the support platform  150 . 
     In implementations of the build material supply system as disclosed herein the sensor module  160  may be displaceable along a scanning path over the plate  130 . 
     The spreader  190  may be mounted on a suitable carriage or gantry  192 , an example of which is depicted very schematically in  FIG. 3 . The spreader  190  may be a roller, although in other examples other suitable forms of spreader, such as a wiper blade, may be used. 
     In some implementations of a build material supply system and of a 3D printing system as disclosed herein, examples of which are shown in  FIG. 3 , the sensor module  160  to detect build material on the plate  130  may be mounted on the spreader carriage  192 . However, the sensor module  160  may also be mounted stationary in the 3D printing system, for example in a position above the plate  130 . 
     The example of  FIG. 3  illustrates that when the sensor module  160  is mounted on the spreader carriage  192  it may be mounted between the spreader  190  and a trailing end  194  of the spreader carriage  192  in the spreading direction B, although in other examples the sensor module  160  may be mounted in other suitable positions on the spreader carriage  192 . 
     When the sensor module  160  is mounted on the spreader carriage  192 , such as in the example of  FIG. 3 , it is displaced together with the spreader  190  over the plate  130 , such that in this example the scanning path is in the spreading direction of arrow B. 
     Some implementations of 3D printing systems as disclosed herein may comprise a sensor module with more than one sensor, for example two sensors, to detect build material on the plate  130 , generally in different positions of the plate  130 . For example, two sensors may be provided in correspondence with two different positions along the plate  130  to detect in each position the presence or absence of build material, or the amount of build material. 
     In some implementations, such as depicted in the examples of  FIGS. 5 and 6 , two sensors  160   a  and  160   b  to detect build material  140  may be provided in two corresponding positions of the plate  130  that are spaced apart at least 50% of the length of the plate. The length of the plate  130  is defined in the longitudinal direction of the plate  130  and of the spreader  190 . The sensors may be fixed, as schematically shown in  FIG. 5 , or they may be displaceable, such as for example mounted on the spreader carriage  192 , as described above and shown in  FIG. 6 . 
     In some examples, the two sensors  160   a  and  160   b  are provided near the ends of the plate, e.g. each at a distance of less than 100 mm from one of the ends of the plate. Providing the sensors near the two ends of the plate  130  allows detecting for example if the build material is being suitably distributed along all the length of the feed tray  110 , for example between the delivery zone  112  ( FIG. 4 ) and the two opposite ends of the feed tray  110 . 
     In some implementations with two or more sensors  160 , a distribution of the build material on the plate  130  may be detected. For example it may be detected if there is a substantially higher amount of build material at one end of the plate  130  than at the other end. 
     In some implementations of a build material supply system as disclosed herein, the sensor module  160 , with one sensor or with several sensors if more than one sensor is provided, may be displaceable along a scanning path. In some examples, as disclosed above, the sensor or sensors may be mounted on the spreader carriage  192 . 
     A scanning path along which the sensors are displaceable may comprise in some implementations a transverse line on the plate  130 , such that build material may be detected at several points across the plate  130 . 
       FIGS. 7 a  and 7 b    schematically show a plate  130  in plan view. On the plate  130  an arrow G 1  represents one scanning path and an arrow G 2  represents another scanning path, respectively for two sensors of a sensor module, such as, for example, the sensors  160   a  and  160   b  shown in  FIG. 6 . 
       FIG. 7 a    represents a situation in which the build material  140  covers substantially all the plate  130 : the two sensors  160   a  and  160   b  will give similar signals, relatively constant along the scanning path G 1  and G 2 . 
       FIG. 7 b    represents a situation in which not all the plate is covered with build material  140 , for example due to a malfunctioning in the build material supply system. A malfunctioning may occur, for example, in the build material distributor element  114  ( FIGS. 3 and 4 ), and may cause the level of build material at one end of the feed tray  110  to be too low, such that the plate  130  does not take build material from the feed tray  110  at this end thereof, or does not take enough build material. 
     In the case of  FIG. 7 b   , the signal outputted by the sensor  160   a  when it is displaced along scanning path G 1  will be similar to that provided in the case of  FIG. 7 a   , but the signal outputted by the sensor  160   b  when it is displaced along scanning path G 2  will be different from the case of  FIG. 7 b   , because the scanning path G 2  is not covered with build material  140 , so the colour detected by the sensor  160   b  is not the same as in the case of  FIG. 7   a.    
     A case where one of the scanning paths G 1  or G 2  is partly covered with build material is also detectable, because the signal provided by the corresponding sensor will change during the displacement along the scanning path. 
     For practical reasons, in  FIGS. 7 a  and 7 b    the portion of the plate  130  covered with build material  140  has been depicted in a dark colour, while the plate  130  itself has been left white: however, the build material  140  may be white or another clear colour, and the plate  130  may be black or another dark colour. 
     In some implementations, the build material supply system may comprise a sensor verification pattern, in order to check the correct operation of the sensor or sensors in the sensor module  160 . For example, a sensor verification pattern may be provided in the sensor scanning path, and may comprise a number of graphic marks of a predetermined colour set to be detected by the sensor. 
     In implementations such as the example of  FIGS. 3 and 4 , a sensor verification pattern may be placed at the beginning of the travel of the spreader  190 , as schematically shown in  FIG. 8 a   , for example upstream of the feed tray  110 . 
     For example, as shown in  FIG. 8 b   , which is a partial plan view of the arrangement of  FIG. 8 a   , a verification pattern VP may comprise two black lines. 
     Arrow G in  FIG. 8 b    indicates the scanning path of a sensor of sensor module  160  of  FIG. 8 a   : from right to left, in its displacement along the scanning path G the sensor first scans the verification pattern VP, then an intermediate zone  115  corresponding to the exposed part of the feed tray  110 , and then the plate  130 , which in this case is black or similarly dark coloured. 
       FIG. 8 c    is a diagram representing an example of the output signal of a sensor of sensor module  160  for the arrangement of  FIGS. 8 a  and 8 b   , in an implementation in which the sensor is a line sensor, when there is no build material on plate  130 : as shown in the diagram, the output signal is higher when the detected colour is darker. From right to left, the output signal has two peaks corresponding to the two black lines of the verification pattern VP, then a flat zone of low value when the sensor scans the intermediate zone  115  of the feed tray, and then a flat zone of high value when the sensor scans over the dark plate  130 . 
       FIGS. 9 a  and 9 b    show by way of example the output signals in an implementation of a build material supply system with a sensor module comprising two sensors, such as for example as disclosed in  FIGS. 6 and 7   a ,  7   b , and with a verification pattern such as described above, in both scanning paths G 1  and G 2 . 
       FIG. 9 a    represents a situation in which there is white build material along substantially all the length of the black plate  130 , while  FIG. 9 b    represents a situation in which one end of the black plate  130  is devoid of white build material. In the case of  FIG. 9 b    the output signal of one sensor is different from that of the other sensor, showing that sensor  160   b  is detecting the presence of build material on the plate  130 , while  160   a  is not detecting the presence of build material on the plate  130 . 
     The numerical value of the output signal is representative of the detected colour, on a scale given by the sensor itself that may be unrelated to specific physical parameters and is useful for reference and comparison purposes. 
     Implementations of methods for spreading build material in a 3D printing system will now be described by way of example. 
     As described earlier, implementations of the methods may comprise providing a pile of build material on a plate between the spreader and the support platform, and sensing build material on the plate. As disclosed above by way of example and in relation to  FIGS. 3 and 4  and  FIGS. 6 to 9 , the sensing of build material on the plate may comprise displacing over the plate an optical sensor, such as a line sensor, in the spreading direction, to scan the plate along a scanning path. 
     In  FIG. 10 , an implementation of a method for spreading build material comprises at  610  providing a pile of build material on a plate, such as plate  130 , adjacent a spreader of the 3D printing system, at  620  spreading build material from the pile of build material, and at  630  sensing an amount of build material remaining on the plate  130 . 
     The sensing of the build material remaining on the plate  130  may be done at any time after the spreader  190  has left the plate  130  and is spreading build material on the support platform  150 , for example just after the spreader  190 , in its movement, has left the plate  130 . 
       FIGS. 11 a  to 11 c    illustrate an implementation of such a method, which may be carried out for example with a system as disclosed in  FIGS. 3 and 4 . 
     In  FIG. 11 a   , the spreader  190  mounted on its spreader carriage  192  is in a starting position, and the vane or plate  130  is holding a measured amount of build material to be placed adjacent the spreader  190  and to be spread forming a layer over the support platform  150 . 
     In  FIG. 11 b   , the spreader  190  has traveled in the spreading direction B to a position in which a forward part of the spreader carriage  192  covers the plate  130 , and the plate  130  has raised to place a pile of build material  140  adjacent the spreader  190 ; the spreader  190  itself has not yet reached the build material. 
     In  FIG. 11 c    the spreader  190  has advanced further in the spreading direction B, has passed over the plate  130 , entraining build material from the pile, and is now spreading the entrained build material on the support platform  150 . The sensor module  160  mounted on the spreader carriage  192 , between the spreader  190  and the trailing edge of the carriage, is now scanning the plate  130  and sensing the build material  142  remaining on the plate  130 . Different actions may be performed depending on the result of the sensing of build material remaining on the plate, as described below. 
       FIG. 12  is a flow diagram of implementations of a method for spreading build material comprising providing at  710  a pile of build material on a plate between the spreader and the support platform, sensing at  720  the build material on the plate, and at  730  determining if there is a malfunction of the 3D printing system, depending on the amount of build material sensed on the plate. 
     If no malfunction is determined at  730 , the operation continues at  740  as it was programmed in the 3D printing system. 
     If a malfunction is determined, at  750  the system may perform at least one correcting action, for example an action selected from: issuing an alarm, issuing a diagnose of the system, pausing operation, providing another pile of build material on the plate, and/or increasing the amount of build material provided on the plate in a subsequent spreading operation. 
     If a malfunction is determined, and depending on the severity of the defect and on variables such as the printing quality, different actions may be performed. 
     In a 3D printing system with a build material supply system such as that disclosed in  FIGS. 3 and 4 , with a build material distribution element  114  in the feed tray  110 , if one of the ends of the plate receives no build material or too little build material, it is likely that the problem is a malfunction of the build material distribution element  114 . The solution to the problem may be to pause or stop the printing operation and perform a maintenance operation on the build material supply system. 
     However, it is also possible to temporarily or permanently increase the supply of build material to the feed tray prior to each layer being formed, such that even if the build material distribution element  114  is not functioning in the optimum manner and provides more build material towards one end of the feed tray than towards the other end, with an increased supply of build material the level is sufficient in all the length of the feed tray to form a suitable pile of build material all along the plate, and therefore defects in the printed object may be avoided. 
     In some cases it may be possible to solve the problem in the current or in successive layers, and continue the printing operation; in other cases it may be more convenient to pause or stop the printing operation without waiting for the object to be finished, so as to prevent the manufacture of an object with defects, and therefore saving time and materials. 
     In some implementations of a method such as shown in  FIG. 12 , the determination at  730  that there is a malfunction may depend on whether the amount of build material sensed on the plate, represented by the value of the sensor signal, is below a predetermined threshold. 
     For example, a malfunction may be determined if the sensor signal falls below 25% of a maximum value corresponding to the situation in which the plate is fully covered with build material. The maximum value depends on the colour of the build material, and may be determined by a simple calibration of the sensors of the sensor module for each build material. 
     In other implementations of a method such as shown in  FIG. 12 , the determination at  730  that there is a malfunction may depend on sensing the amounts of build material in two positions of the plate, determining the difference between the amount of build material sensed in one position and the amount of build material sensed in the other position, represented by the values of the corresponding sensor signals, and determining that there is a malfunction of the 3D printing system if the difference is above a predetermined threshold. 
     The determination may be made for each spread cycle, but it may also be made over a number of spread cycles or layers. For example, a malfunction may be determined if the difference between the readings of the sensors is more than 75% over more than 3 spread cycles. 
     For example, in a system with two sensors such as disclosed above, it may be determined that there is a malfunction if at least one of the sensors detects no build material on the plate, or an amount of build material that is below a predetermined threshold. It may also determined that there is a malfunction if the difference in the amount of build material detected by the two sensors is above a predetermined threshold, that is, if the difference between the readings of the sensors is above a predetermined threshold. 
     Operation of the 3D printing system and build material supply system  100  may be controlled by a controller, such as controller  200  in  FIG. 3 . As shown in greater detail in  FIG. 13 , the controller  200  may comprise a processor  202  coupled to a memory  204 . The memory  204  stores management instructions  206  for the supply and spreading of build material that, when executed by the processor  202 , control the operation of the systems and the methods disclosed herein. 
     Although a number of particular implementations and examples have been disclosed herein, further variants and modifications of the disclosed devices and methods are possible. For example, not all the features disclosed herein are included in all the implementations, and implementations comprising other combinations of the features described are also possible.