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Patent Searching and Data


Title:
DETERMINING SURFACE LEVELS
Document Type and Number:
WIPO Patent Application WO/2021/061126
Kind Code:
A1
Abstract:
A container is disclosed. The container comprises a wall defining a volume to contain material, a plurality of light sources located within the volume at different heights with respect to a base of the wall, each light source controllable to emit light. The location of the light sources defines a measurement zone to contain the material. The container further comprises a sensor above the measurement zone to receive light emitted by each of the light sources. The container also includes a controller to control a light source to emit light, receive from the sensor data indicative of the emitted light, and determine a surface level of the material based on the height of the light source and the received data.

Inventors:
ZAMORANO ALVEAR JUAN MANUEL (ES)
Application Number:
PCT/US2019/053132
Publication Date:
April 01, 2021
Filing Date:
September 26, 2019
Export Citation:
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Assignee:
HEWLETT PACKARD DEVELOPMENT CO (US)
International Classes:
G01F23/292; B29C64/343
Domestic Patent References:
WO2014200578A22014-12-18
Foreign References:
US8463083B22013-06-11
US8552666B22013-10-08
US20190001575A12019-01-03
US10111992B22018-10-30
Attorney, Agent or Firm:
WOODWORTH, Jeffrey C. et al. (US)
Download PDF:
Claims:
CLAIMS

WHAT IT IS CLAIMED IS:

1. A container comprising: a wall defining a volume to contain material; a plurality of light sources located within the volume at different heights with respect to a base of the wall, each light source being controllable to emit light, wherein the location of the light sources defines a measurement zone to contain the material; a sensor above the measurement zone to receive light emitted by each of the light sources; and a controller to: control a light source from the plurality of light sources to emit light, receive, from the sensor, data indicative of the emitted light, and determine a surface level of the material based on the height of the light source and the received data.

2. The container of claim 1 , wherein a light source from the plurality of light sources is an incoherent light source.

3. The container of claim 1 , wherein the controller is to control the plurality of light sources to be illuminated in a sequence.

4. The container of claim 1 , wherein the controller is to control a subset of consecutive light sources from the plurality of light sources to emit light at a given time.

5. The container of claim 1 , wherein the plurality of light sources is a Light-Emitting Diode strip and the sensor is a photo-sensor. 6. The container of claim 1 , wherein the controller is further to: determine a light power gradient from the data relative to two consecutive received light readings by the sensor; compare the light power gradient with a light power gradient threshold; and determine the surface level of material based on the comparison.

7. The container of claim 1 , wherein the controller is further to control a light source from the plurality of light sources to emit a coded light.

8. The container of claim 7, wherein the code type of the coded light is at least one of a coded pulse wave signal, a color-coded light, a coded intensity value, or a combination thereof.

9. The container of claim 7, wherein the controller is to control the light source to emit light at a wavelength complementary to a color of the material.

10. The container of claim 1 , further comprising: an additional plurality of light sources located in the measurement zone at different heights with respect to the base of the wall, each additional light source controllable to emit light; wherein the plurality of light sources is located at a first location of the wall and the additional plurality of light sources is located at a second location of the wall; and wherein the controller is further to: determine a first surface level of material corresponding to the plurality of light sources and a second surface level of material corresponding to the additional plurality of light sources, and determine that the surface level of build material is non-uniform based on the first surface level of material and the second surface level of material. 11. The container of claim 1 , further comprising a protective transparent element to protect the light source from the material.

12. A build unit comprising: a housing comprising a chamber to contain additive manufacturing material; a plurality of light sources located within the chamber at different predetermined heights with respect to a base of the housing, each light source being controllable to emit light, wherein the location of the light sources defines a measurement zone to contain the material; a sensor above the measurement zone to receive light emitted by each of the light sources that are uncovered by the additive manufacturing material; and a controller to: control a light source from the plurality of light sources to emit light; receive, from the sensor, data indicative of the received light; and determine a surface level of material based on the height of the light source and the received data.

13. The build unit of claim 12, further comprising: a moveable build platform within the housing forming an upper limit of the chamber, wherein the sensor moves along with the platform; and a cleaning element mounted at the moveable build platform to clean a light source from the plurality of light sources as the build platform moves.

14. The build unit of claim 12, wherein a light source from the plurality of light sources is an incoherent light source. 15. A method comprising: filling a measurement zone from a build unit inner volume with material, wherein the measurement zone is defined by the presence of a plurality of light sources; emitting light by a set of light sources from the plurality of light sources, wherein each light source is located in the inner volume at different heights with respect to a base of the build unit; receiving, at a sensor located in the inner volume and above the measurement zone, light power associated with the emitted light by the set of light sources; and determining a surface level of material based on the height of the set of light sources and the light power.

Description:
DETERMINING SURFACE LEVELS

BACKGROUND

[0001] Some additive manufacturing or three-dimensional printing systems selectively solidify portions of successive layers of a powdered build material to generate 3D objects. Prior to the generation of the 3D objects, a build unit may be filled with additive manufacturing build material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The present application may be more fully appreciated in connection with the following detailed description of non-limiting examples taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout and in which:

[0003] Figure 1 is a schematic diagram showing an example of a front view of a container to determine a surface level of material.

[0004] Figure 2 is a flowchart of an example method for determining a surface level of material.

[0005] Figure 3 is a flowchart of another example method for determining a surface level of material.

[0006] Figure 4 is a flowchart of another example method for determining a surface level of material.

[0007] Figure 5 is a schematic diagram showing an example of a front view of a build unit to determine a surface level of material.

[0008] Figure 6 is a schematic diagram showing an example of a front view of a container to determine a surface level of material. DETAILED DESCRIPTION

[0009] The following description is directed to various examples of additive manufacturing, or three-dimensional printing, apparatus and processes to generate high quality 3D objects. Throughout the present disclosure, the terms “a” and “an” are intended to denote at least one of a particular element. In addition, as used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on.

[0010] For simplicity, it is to be understood that in the present disclosure, elements with the same reference numerals in different figures may be structurally the same and may perform the same functionality.

[0011] Some examples of additive manufacturing use build material to generate 3D objects by selectively solidifying layers of build material. Suitable powder-based build materials for use in additive manufacturing may include, where appropriate, at least one of polymers, metal powder or ceramic powder. In some examples non- powdered build materials may be used such as gels, pastes, and slurries.

[0012] Some 3D printing systems comprise a 3D printer that selectively solidifies portions of build material layers in the inner volume of a build unit on a layer-by-layer basis. The plurality of build material layers in the build unit are referred to as a build bed. The 3D printer may supply the build bed with build material from a reservoir or container.

[0013] In some examples, it may be required that the build unit may hold enough build material to complete the print job at the beginning of a print job. If a print job is started without enough build material in the container, the incomplete print job may need to be aborted. In some systems, the parts printed from an aborted print job may have to be discarded since they may not meet their respective mechanical requirements. Therefore, accurately measuring the level of build material in the build material reservoir of an additive manufacturing system may reduce the incidence of incomplete and hence aborted print jobs. [0014] The examples herein are directed to containers and build units with additional components that enable the containers and build units to reliably determine a surface level of the contents therein in an automatized manner and without user intervention.

[0015] The examples described may be tolerant of the noisy conditions in which some additive manufacturing systems may need to operate due to noises generated from the systems and noises from the background area where the systems may be located, for example, in a factory.

[0016] The examples may be also tolerant of electromagnetic noise, for example Electromagnetic interference (EMI) or radio-frequency interference (RFI), which may cause a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling or conduction. Electromagnetic noise may cause interference in capacitive sensors and electronics, especially in complex electronic circuits.

[0017] Referring now to the drawings, Figure 1 is a schematic diagram showing an example of a front view vertical cross-section of a container 100 to contain material and includes an additional mechanism to determine a surface level of the material.

[0018] The container 100 comprises a wall 110 enclosing a volume therein. In some examples, the container 100 comprises a single integral wall 110 enclosing the volume therein. In other examples, however, the container 100 comprises a plurality of walls attached together (e.g., welded) that form a single housing. In the illustrated example, the container 100 is depicted as having a constant vertical cross-section. In other examples, however, the vertical cross-section of the container 100 may not be constant.

[0019] In use, a part of the volume in the container 100 is filled with material 120 which defines a surface level 125. In some examples, the material 120 may be additive manufacturing build material such as powdered build material. In other examples, the material 120 may be a liquid agent used in the generation of a 3D object (e.g., fusing agent, detailing agent, binder agent, coloring agent) or a slurry. In the illustrated example, the surface level is drawn as being completely flat (e.g., parallel to the base of the container), however it is to be understood that, in other examples, the surface level may not be flat. Some examples below are directed to reliably determine the non-flat surface level 125 of the material 120. The material 120 is illustrated in dotted lines to denote that it is an external element that interacts with the container 100, and thereby the material 120 is not an integral part of the container 100 as such.

[0020] The container 100 further comprises a plurality of light sources 130 arranged in an array. The plurality of light sources 130 defines a measuring zone, i.e. a range of possible positions for the surface 125. In use therefore, the plurality of light sources 130 are potentially intended to be covered by material. In the example, the plurality of light sources 130 comprises nine light sources 135A-135I, however it is to be understood that any number of light sources may be used without departing from the scope of the present disclosure, for example, a single light source or ten light sources.

[0021] The plurality of light sources 130 may be located at different known heights with respect to the base of the wall 110. The heights may correspond to heights that meet specific criteria, for example, a height indicative that the surface level 125 of material 120 implies that the container is full, empty, or somewhere in between. In some examples, the plurality of light sources 130 may be substantially equally spaced along the height of the wall 110.

[0022] When the container 100 is in use, and thereby filled or partially filled with material 120, the light sources located below the surface level 125 are covered by the material 125 and the light sources located above the surface level 125 are not covered by the material 125. In the illustrated examples, light sources 135A-E are covered by the material 125 and light sources 135F-I are not covered by the material 125. Light emitted by the light sources covered by the material 120 (e.g., light emitted by light sources 135A-E) may be prevented, at least in part, from traversing the material 120 and reaching the volume of the container 100 not covered by the material 120 (i.e., volume above surface level 125). [0023] Some materials 120 may be abrasive and may damage the light sources 130 covered therein. Therefore, in some additional examples, the plurality of light sources 130 may, at least in part, further comprise a protective transparent covering element (not shown) to protect the plurality of light sources from the material 120. In the examples herein, the term transparent may include any material which allows the transmission of light therethrough. The protective transparent covering element may be a case, for example, a transparent polymeric or glass case or coating covering either the full length of the plurality of light sources 130 or a single light source 135A-I.

[0024] The plurality of light sources 130 may be independently controllable by a controller 150 to emit light. In an example, the controller 150 may be encoded with the height in which each light source 135A-I is located. In other examples, the controller 150 may determine at which height each of the light sources 135A-I is located by reading a look-up table or by controlling additional hardware.

[0025] The plurality of light sources 130 are to emit light. In an example, each of the light sources 135A-135I may emit un-coded light, thereby making no distinction of pulse, color, or intensity between the light emitted by two different light sources from the plurality of light sources 130. In other examples, each of the light sources 135A-135I may emit coded light indicative of the height corresponding to the emitting light source. A coded light source may include a coded pulse wave signal, a color- coded light, a coded intensity value, or a combination thereof.

[0026] The plurality of light sources 130 may be implemented in a number of different ways. In some examples, the plurality of light sources may include coherent light sources (e.g., a laser or a laser array). In other examples, however, the plurality of light sources may comprise a plurality of incoherent light sources. The light sources may have a broad emission cone, e.g., over 15° or 30° aperture angle. An example of plurality of incoherent light source may comprise a Light-Emitting Diode (LED) strip.

[0027] Movement of powdered material 120 in a receptacle or a container, such as a build unit, may lead to the generation of a cloud of material particles that may cause interference to a light beam. Light emitted by light sources having a broader emission cone may be less likely to be suffer interference from clouding of material 120 particles above surface 125 than for instance a laser light source with a narrow emission cone.

[0028] The container 100 may further comprise a sensor 140 to receive the light emitted by the plurality of light sources 130. The sensor 140 may be selected based on the type of light emitted by the plurality of light sources 130. In an example, the sensor is a photo-sensor.

[0029] The sensor 140 is placed within the volume of the container away from the measuring zone, and above the surface level of 125 of material 120 so that, in use, there is no direct contact between the material 120 and the sensor 140. In an example, the sensor 140 is placed at the top inner wall from the container 100. In such configuration, the sensor 140 may receive a strong signal emitted by the light sources located above the surface level 125 (e.g., light sources 135F-I) and a weak signal, or even no signal, from the light sources located below the surface level 125 (e.g., light sources 135A-E). Most of the light power emitted by the light sources located below the surface level 125 may be absorbed by the material 120 and thereby may not reach the sensor 140.

[0030] The sensor 140 may send data 140 to the controller 150. The data may correspond to the received light power from the plurality of light sources 130. In an example, the sensor 140 may send the data to the controller 150 on demand. In other examples, the sensor 140 may send the data to the controller 150 in a continuous way. In yet another example, the sensor 140 may send the data to the controller 150 periodically.

[0031] The container 100 further includes a controller 150. The controller may be coupled to the plurality of light sources 130 and the sensor 140 via a wired or wireless connection. In these examples, the controller 140 may independently control light emission by the plurality of light sources 130 and the data reception from the sensor 140. The functionality of the controller 150 is disclosed and may be more fully appreciated with reference to the execution of method 200 from Fig. 2, method 300 from Fig. 3, and method 400 from Fig. 4.

[0032] In the examples herein, a controller may be any combinations of hardware and programming that may be implemented in a number of different ways. For example, the programming of modules may be processor-executable instructions stored in at least one non-transitory machine-readable storage medium and the hardware for modules may include at least one processor to execute those instructions. In some examples described herein, multiple modules may be collectively implemented by a combination of hardware and programming. In other examples, the functionalities of the controller may be, at least partially, implemented in the form of an electronic circuitry. The controller may be a distributed controller, a plurality of controllers, and the like.

[0033] The container 100 disclosed above may be any receptacle suitable to contain material. In some examples, however, the container 100 is a build unit from a 3D printing system containing additive manufacturing build material or 3D printing agents. In an example, the container 100 is a build unit removably connectable to a 3D printing processing station and a 3D printer. In other examples, the container 100 is a build unit which is an integral part of a 3D printing processing station. In yet other examples, the container 100 is a build unit which is an integral part of a 3D printer.

[0034] Figure 2 is a flowchart of an example method 200 for determining a surface level 125 of material 120. Method 200 may be executed by the controller 150. The controller 150 may control previously disclosed elements with the like reference numerals.

[0035] At block 220, the controller 150 may control at least one light source 135A-I from the plurality of light sources 130 to emit light. The controller 150 may independently control each of the plurality of light sources 130 to emit light. The light source that is controlled by the controller 150 to emit light is referred hereinafter as the light emitter.

[0036] The light emitted by the light emitter is received by the sensor 140. The sensor 140 is to receive light power from the light emitted by the light emitter. The light power received by the sensor 140 may vary depending on the location of the light emitter. The sensor 140 is to receive light power emitted by the light emitter, if the light emitter is located above the surface level 125 of material 120. However, the sensor 140 is to receive a substantially smaller fraction, if any, of the light power emitted by the light emitter, if the light emitter is located below the surface level 125 of material 120 since most part of the light power emitted may be absorbed by the material 120 before it reaches the sensor 140.

[0037] Once the sensor 140 receives the light power from the light emitted by the light emitter, the sensor 140 may transform the received light power into data indicative of the received light power. The controller 150 may send the data to the controller 150. At block 240, the controller 150 receives, from the sensor 140, the data indicative of the emitted light.

[0038] At block 260, the controller may determine a surface level 125 of the material 120. The controller may determine the surface level 125 of the material based on the data received by the sensor 140 and the height of the light emitter.

[0039] In an example, the controller 150 may be encoded to determine that the light emitter is above the surface level 125, if the data received indicates that the power received by the sensor 140 is above a power threshold. As previously disclosed, the power received by a light emitter which is located below the surface level 125 is low and thereby is not expected to meet the power threshold. Conversely, the power received by a light emitter which is located above the surface level 125 is large and thereby is expected to meet the power threshold.

[0040] Following with the example, the controller 150 may control the plurality of light sources 130 to emit light in a sequence. The controller 150 may thereby control the light source 135A located at the lowest height and receive the data associated with the light emitted by the light source 135A. If the data associated with the light emitted by the light source 135A located at the lowest height does not meet the power threshold, the controller 150 may control the light source 135B located immediately above the previous light source (e.g., light source 135A). The controller 150 may perform the same operation in an iterative manner until it finds the lowest light source that has emitted light that meets the power threshold (e.g., light source 135F).

[0041] The controller 150 may determine the surface level 125 of the material 120 as the height of the lowest light source that has emitted light that meets the power threshold (e.g., light source 135F). In another example, the controller 150 may determine the surface level 125 of the material 120 as somewhere in between the height of the lowest light source that has emitted light that meets the power threshold and the light source immediately below it (e.g., light sources 135E and 135F).

[0042] In another example, the controller 150 may determine that the light emitter is above the surface level 125 by comparing a power gradient, determined based on the received data, with a power gradient threshold.

[0043] In the example, the controller 150 may also control the plurality of light sources 130 to emit light in a sequence. The controller 150 may determine a power gradient as, for example, the difference between the power received between two consecutive light sources. The controller 150 may also compare the determined power gradient with a power gradient threshold to determine whether the surface level 125 is in between the two consecutive light sources.

[0044] If the two consecutive light sources are both below the surface level 125, or both above the surface level 125, the light power received by the sensor 140 from both light sources may be similar, and the determined power gradient is expected to be small, thereby not meeting the power gradient threshold. Conversely, if each of the two consecutive light sources is in the opposite side of the surface level 125, the light power received by the sensor 140 from both light sources may be significantly different, and the determined power gradient is expected to be large, thereby meeting the power gradient threshold.

[0045] In the example, the controller 150 may determine the surface level 125 of the material 120 as somewhere in between the height of the two consecutive light sources that have emitted light that meets the power gradient threshold.

[0046] Figure 3 is a flowchart of another example method 300 for determining a surface level 125 of material 120. Method 300 may be executed by the controller 150. The controller 150 may control previously disclosed elements with the like reference numerals.

[0047] As mentioned above, managing build material in a receptacle or a container, such as a build unit, may lead to the generation of a cloud of material particles. This cloud may interfere in the light beam from a light source to the sensor 140 and cause false negatives in the execution of method 200 from Figure 2. In some examples, the controller 150 may execute method 300 after executing method 200, from Figure 2, resulting without any successful surface level 125 determination.

[0048] To counteract the effects of clouding, the controller may execute method 300 which broadens the light emission aperture of the light sources by incrementing the number of consecutive light sources emitting light at a given time. The broader the light emission aperture is, the more light power the sensor 140 may receive.

[0049] Turning to Figure 3, at block 320 the controller 150 controls a predetermined subset of consecutive, i.e. neighboring, light sources (e.g., light sources 135A and 135B) of the plurality of light sources 130 to emit light. In an example, the controller 150 may control two consecutive light sources at a time. In subsequent iterations, however, the controller 150 may control more than two consecutive light sources, for example, by incrementing one light source in each iteration. Each one of the controlled predetermined subset of consecutive light sources may execute the same operation as the at least one of the plurality of light sources of block 220 from Figure 2.

[0050] By incrementing the number of consecutive light sources emitting light at a time, the overall light emission cone may be incremented as well, thereby being more easily detected by the sensor 140. The sensor 140 may send data associated with the light power received from the light emitted by the predetermined subset of consecutive light sources. At block 340, the controller 150 receives, from the sensor 140, the data.

[0051] At block 360, the controller 150 determines the height of the material (i.e., surface level 125) based on the height of the subset of light sources that emitted light and the received data. The execution of block 360 may be similar as the previously disclosed execution of block 260 from Figure 2 taking into account the data received by the sensor 140 relating to the light emitted by the subset of consecutive light sources.

[0052] Additionally, the controller 150 may determine that the subset of consecutive light sources do not meet the power threshold, and thereby may not determine the surface level 125. In this example, in a subsequent iteration, the controller 150 may control the subsequent subset of consecutive light sources located above (e.g., immediately above) the previous subset of light sources that emitted light (e.g., light sources 135B-C after light sources 135A-B).

[0053] Figure 4 is a flowchart of another example method 400 for determining a surface level 125 of material. Method 400 may be executed by the controller 150. The controller 150 may control previously disclosed elements with the like reference numerals.

[0054] As disclosed above, some examples of light sources emit coded light, for instance using pulse trains, or color, or intensity differences between the light emitted by two different light sources from the plurality of light sources 130. Method 400 is executed to utilize this light source codification capability.

[0055] At block 420, the controller 150 controls the plurality of light sources 130 to emit coded light. In some examples, the codification of the plurality of light sources 130 may be implemented as each of the light sources 130 comprising the same code. In other examples, the codification of the plurality of light sources 130 may be implemented as each of the light sources 130 comprising a different distinct code.

[0056] The codification of the plurality of light sources 130 may be executed in a number of different ways. In an example, the codification may be implemented as a coded pulse wave signal in which different light sources are to emit light pulses at different duty cycles, so that an emitted light with a specific duty cycle is indicative of which light source from the plurality of light sources 130 is the emitter light source. In another example, the codification may be implemented as a color-coded map, in which each (or a subset of) light source emits light at a different color, so that the emitted colored light indicative of the emitter light source. The controller 150 may control the color of the light emitted by a given light source by controlling the frequency or the wavelength in which the light source emits the light. In yet another example, the codification may be implemented as a coded intensity, in which each (or a subset of) light source emits light at different intensities received as different optical power readings by the sensor 140, each reading being indicative of the respective emitter light source.

[0057] The sensor 140 receives the coded light emitted from at least one light source from the plurality of light sources 130. The sensor 140 subsequently sends corresponding data to the controller 150. At block 440, the controller 150 receives the data from the sensor 140 and, at block 460, the controller 150 determines the height of the material 120 (e.g., surface level 125) based on the received data. The execution of blocks 440 and 460 may be similar to the respective blocks 240 and 260 from Figure 2, and blocks 340 and 360 from Figure 3, with some modifications due to the nature of the data including codified light information.

[0058] In an example, the controller 150 codifies the plurality of light sources 130 to emit coded light at a wavelength (or its corresponding frequency) which is complementary to the material 120 color. For example, if the color of the material 120 is yellow, the controller 150 may control the plurality of light sources 130 to emit light at a wavelength from the blue section of the visible spectrum (e.g., 490-450 nm). The color of the material 120 may be previously encoded to the controller 150 or may be measured by a colorimeter and then sent to the controller 150. In this example, in the execution of method 400, as opposed to the execution of the method 200 or 300, a larger proportion of the light emitted by each of the plurality of light sources which are located below the surface level 125 (e.g., light sources 135A-E) is absorbed by the material 120. This larger absorption causes less light power to be transmitted from below to above the surface level 125 and, thereby causing fewer false positives to be detected in the reception of the light power by the sensor 140 (block 260 from Figure 2 and block 460 from Figure 4).

[0059] Additionally, or alternatively, the controller 150 controls the plurality of light sources 130 to emit coded light indicative of the height of each of the plurality of light sources. In these examples, each light source 135A-135I is independently controlled to emit light with a unique predefined code for each light source. The sensor 140 is to receive a plurality of codes and send them as data to the controller 150 with its respective light power values (e.g., block 440). In this example, the plurality of light sources 130 may emit their respective coded light simultaneously, as opposed to sequentially, as the examples of methods 200 and 300 from Figures 2 and 3 respectively, thereby speeding the surface level 125 request response time. The controller 150 determines the surface level 125 as the height of the lowest light source that meets the corresponding threshold (see, e.g., block 260 from Figure 2).

[0060] Figure 5 is a schematic diagram showing an example of a front view vertical cross-section of a build unit 500 to contain material and includes an additional mechanism to determine a surface level 125 of material. The build unit 500 comprises previously disclosed elements from Figure 1 with the like reference numerals. In some examples, the build unit 500 may be removably attachable between a 3D printing build material processing station and a 3D printer. In other examples, the build unit 500 may be an integral part of a 3D printer.

[0061] The build unit 500 may be used in the generation of a 3D print job including a plurality of 3D objects to be generated. In an example, the material 120 of the build unit 500 is powdered additive manufacturing build material. Some examples of build units comprise a volume therein split into two sub-volumes through a moveable build platform 560. The build platform 560 may move vertically (e.g., move downwardly throughout the generation of the print job). The first sub-volume may comprise a store of the build material to be used in the subsequent generation of the 3D print job. The second sub-volume may be used to generate the print job. In some examples, the second sub-volume is above the build platform 560. The parts generated (e.g., solidified and not solidified build material) on top of the build platform 560 may be commonly referred to as build bed (not shown for simplicity).

[0062] In some examples, the controller 150 may be encoded with instructions to determine whether the amount of build material 120 in the first volume is sufficient to generate the print job through previously determining the surface level 125 of build material 120. In other examples, however, the controller 150 is queried in whether the surface level 125 of build material meets a build material height threshold. In any case, the controller 150 may determine the surface level 125 by executing any of the methods 200, 300, and 400 from Figure 2, 3, and 4 respectively.

[0063] In some examples, the sensor 140 may be fixed under the build platform 560 and move along the build platform 560. In other examples, the sensor 140 may be fixed in another location which enables the reception of light from light sources located under the build platform 560.

[0064] Some light sources from the plurality of light sources 130 are in contact with the build material 120 during the generation of a print job. In an example, some build materials may be abrasive to the plurality of light sources 130 or to the protective transparent element placed thereon. In another example, some build materials may attach to the surface of the plurality of light sources 130 and, thereby block the light emitted therefrom.

[0065] Some examples of build platforms 560 further comprise a cleaning element (not shown) at the edge of the build platform 560 in contact with the wall comprising the plurality of cleaning elements 130. The cleaning element cleans the plurality of light sources 130 from attached build material thereon as the build platform 560 moves vertically. In an example, the cleaning element is a wiping belt to wipe out build material attached to the light sources as the build platform 560 moves vertically. In another example, the cleaning element is a brush to brush out build material attached to the light sources as the build platform 560 moves vertically.

[0066] The controller 150 may be encoded with additional instructions. For example, the controller 150 may be encoded with instructions to receive a print job to be printed and determine the amount of build material 120 to be used to print the received print job and its associated surface level 125. The controller 150 may also comprise instructions to determine the surface level 125 of the actual contents of build material 120 in the build unit, for example, instructions corresponding to method 200, 300, and/or 400 from Figures 2, 3, and 4 respectively. Additionally, the controller 150 may be encoded with instructions to determine whether the determined surface level 125 of build material 120 is compliant with the amount of build material to be used to print the received print job. The controller 150 may also alert a user that there is not enough build material in the build unit inner volume to print the received print job if the determined surface level 125 of build material 120 is not compliant with the amount of build material to be used to print the received print job.

[0067] Figure 6 is a schematic diagram showing an example of a front view vertical cross-section of a container 600 to contain material and includes an additional mechanism to determine a surface level 620 of material. The container 600 comprises previously disclosed elements from Figure 1 with the like reference numerals.

[0068] Some containers comprise material therein that does not form a uniform flat surface level 620. In addition to the plurality of light sources 130, the container 600 further comprises an additional plurality of light sources 630 controllable by the controller 150. In the illustrated example, the additional plurality of light sources 630 comprises nine light sources 635A-I, each of them controlled to perform the same operations as the plurality of light sources 130 with reference to previously disclosed examples. In other examples, the additional plurality of light sources 630 may comprise any other number of light sources, for example, a single light source or ten light sources. Additionally, in some examples, the number of light sources from the plurality of light sources 130 may be different than the number of light sources from the additional plurality of light sources 630. The additional plurality of light sources 630 is placed along the height at a different location of the container than the plurality of light sources 130.

[0069] The controller 150 controls the plurality of light sources 130 according to method 200, 300, or 400 from Figures 2, 3, and 4 to determine a first surface level of material located at the vicinity where the plurality of light sources 130 are located at. Independently, the controller 150 controls the additional plurality of light sources 630 according to method 200, 300, or 400 from Figures 2, 3, and 4 to determine the second surface level of material 625 located at the vicinity where the additional plurality of light sources 630 are located at. In some examples, the controller 150 may control the plurality of light sources 130 and the additional plurality of light sources 630 at different times (e.g., method 200 and 300). In other examples, however, the controller 150 may control the plurality of light sources 130 and the additional plurality of light sources 630 at the same time (e.g., method 400).

[0070] Additionally, in some examples, the controller 150 may compare the first surface level 125 and the second surface level 625 with a predetermined surface uniformity threshold. The uniformity threshold is defined to indicate the minimum surface level difference to identify the overall surface level as non-uniform.

[0071] Furthermore, the controller 150 is to determine the amount of material 120 in the container 600 based on the previously determined surface levels and the horizontal cross-section area of the container 600. In some examples, the controller 150 may render a theoretical non-uniform surface level by executing interpolation operations between the first surface level 125 and the second surface level 625 and determine the amount of material 120 therefrom.

[0072] As used herein, the term “substantially” is used to provide flexibility to a range endpoint by providing a degree of flexibility. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.

[0073] The drawings in the examples of the present disclosure are some examples. It should be noted that some units and functions of the procedure may be combined into one unit or further divided into multiple sub-units. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims and their equivalents.

[0074] There have been described example implementations with the following sets of features:

[0075] Feature set 1 : A container comprising: a wall defining a volume to contain material; a plurality of light sources located within the volume at different heights with respect to a base of the wall, each light source being controllable to emit light wherein the location of the light sources defines a measurement zone to contain the material; a sensor above the measurement zone to receive light emitted by each of the light source; and a controller to: control a light source from the plurality of light sources to emit light, receive, from the sensor, data indicative of the emitted light, and determine a surface level of the material based on the height of the light source and the received data.

[0076] Feature set 2: A container with feature set 1 , wherein a light source from the plurality of light sources is an incoherent light source.

[0077] Feature set 3: A container with any preceding feature set 1 to 2, wherein the controller is to control the plurality of light sources to be illuminated in a sequence.

[0078] Feature set 4: A container with any preceding feature set 1 to 3, wherein the controller is to control a subset of consecutive light sources from the plurality of light sources to emit light at a given time.

[0079] Feature set 5: A container with any preceding feature set 1 to 4, wherein the plurality of light sources is a Light-Emitting Diode strip and the sensor is a photo sensor.

[0080] Feature set 6: A container with any preceding feature set 1 to 5, wherein the controller is further to: determine a light power gradient from the data relative to two consecutive received light readings by the sensor; compare the light power gradient with a light power gradient threshold; and determine the surface level of material based on the comparison.

[0081] Feature set 7: A container with any preceding feature set 1 to 6, wherein the controller is further to control a light source from the plurality of light sources to emit a coded light. [0082] Feature set 8: A container with any preceding feature set 1 to 7, wherein the code type of the coded light is at least one of a coded pulse wave signal, a color- coded light, a coded intensity value, or a combination thereof.

[0083] Feature set 9: A container with any preceding feature set 1 to 8, wherein the controller is to control the light source to emit light at a wavelength complementary to a color of the material.

[0084] Feature set 10: A container with any preceding feature set 1 to 9, further comprising: (a) an additional plurality of light sources located in the measurement zone at different heights with respect to the base of the wall, each additional light source controllable to emit light; wherein the plurality of light sources is located at a first location of the wall and the additional plurality of light sources is located at a second location of the wall; and (b) wherein the controller is further to: (i) determine a first surface level of material corresponding to the plurality of light sources and a second surface level of material corresponding to the additional plurality of light sources, and (ii) determine that the surface level of build material is non-uniform based on the first surface level of material and the second surface level of material.

[0085] Feature set 11 : A container with any preceding feature set 1 to 10, further comprising a protective transparent element to protect the light source from the material.

[0086] Feature set 12: A build unit comprising: a housing comprising a chamber to contain additive manufacturing material; a plurality of light sources located within the chamber at different predetermined heights with respect to a base of the housing, each of the light sources being controllable to emit light, wherein the location of the light sources defines a measurement zone to contain material; a sensor above the measurement zone to receive light emitted by each of the light sources that are uncovered by the additive manufacturing material; and a controller to: control a light source from the plurality of light sources to emit light; receive, from the sensor, data indicative of the received light; and determine a surface level of material based on the height of the light source and the received data.

[0087] Feature set 13: A build unit with feature set 12, further comprising: a moveable build platform within the housing forming an upper limit of the chamber, wherein the sensor moves along with the platform; and a cleaning element mounted at the moveable build platform to clean a light source from the plurality of light sources as the build platform moves.

[0088] Feature set 14: A build unit with any preceding feature set 12 or 13, wherein a light source from the plurality of light sources is an incoherent light source.

[0089] Feature set 15: A method comprising, filling a measurement zone from a build unit inner volume with material, wherein the measurement zone is defined by the presence of a plurality of light sources; emitting light by a set of light sources from the plurality of light sources, wherein each light source is located in the inner volume at different heights with respect to a base of the build unit; receiving, at a sensor located in the inner volume and aboe the measurement zone, light power associated with the emitted light by the set of light sources; and determining a surface level of material based on the height of the set of light sources and the light power.




 
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