Printhead assembly with light emission devices and photon detectors

According to examples, an apparatus may include a printhead assembly containing a housing supporting a printhead. The printhead may have nozzles that are to fire droplets of a functional agent onto a layer of build material particles along respective flight paths to form sections of a 3D object from the build material particles, an array of light emission devices to direct respective light beams in the respective flight paths, and an array of photon detectors to detect respective light beams directed from a light source of the array of light emission devices, the light emission devices and the photon detectors being supported on the housing. The apparatus may also include a controller to determine whether any of the nozzles is operating improperly based upon whether the photon detectors detected the light beams and to output an instruction regarding an improperly operating nozzle in response to a determination that the nozzle is operating improperly.

BACKGROUND

In three-dimensional (3D) printing, an additive printing process is often used to make three-dimensional solid parts from a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short-run manufacturing. Some 3D printing techniques are considered additive processes because they involve the application of successive layers or volumes of material to an existing surface (template or previous layer). This is unlike traditional machining processes, which often rely upon the removal of material to create the final part. 3D printing often requires curing or fusing of the building material, which for some materials may be accomplished using heat-assisted extrusion, melting, or sintering, and for other materials may be accomplished using digital light projection technology. Additive manufacturing techniques typically employ a layering process in which particles of build material are spread into a layer and selectively fused together. Following that process, additional particles are spread into another layer and selectively fused together. This process is repeated over a number of layers to build up a 3D part having a desired configuration.

DETAILED DESCRIPTION

There may be multiple causes for a printhead nozzle to improperly operate, e.g., fail to fire a droplet, fire a droplet having an unintended size, fire droplets at improper times, etc. The causes may include, for instance, an improperly functioning firing element, a blocked or partially blocked nozzle bore, etc. In 3D printing, an improperly operating nozzle may result in 3D objects being formed with partially or improperly fused areas, defects in color, etc. Improperly fused areas may weaken or otherwise cause the formed 3D objects to be defective. As the build material particles as well as the agents used in the printing of 3D objects may be relatively expensive, printing of defective 3D objects may be costly both in terms of monetary costs and the time that it takes to print the 3D objects.

Disclosed herein are apparatuses and methods for detecting a malfunctioning nozzle during 3D object printing operations. The apparatuses disclosed herein may include light emission devices (or equivalently, light sources) and photon detectors (or equivalently, detectors) that are to detect droplets of a functional agent as the droplets are fired from nozzles during a 3D object printing operation. The light emission devices and the photon detectors may be mounted to the same housing as a printhead containing the nozzles to thus enable the light emission devices and the photon detectors to be moved concurrently with the printhead. In this regard, in the apparatuses and methods disclosed herein, droplets may be detected at any point during printing of the 3D object.

According to examples, detection of the droplets during the printing operation may enable real-time detection of malfunctioning nozzles. Real-time detection of malfunctioning nozzles may enable a concurrent determination as to whether to continue with printing of an unfinished 3D object. For instance, when a controller determines that a nozzle has malfunctioned, the controller may stop printing the 3D object and may await further instructions from an operator. In other examples, the controller may implement a mitigation operation that causes another nozzle or other nozzles to deliver droplets onto the locations that the malfunctioning nozzle was intended to deliver the droplets. As such, for instance, through implementation of the apparatuses and methods disclosed herein, defects in printed 3D objects may be reduced and/or the printing of 3D objects may be stopped if it is known to have defects during printing of the 3D objects, which may result in a reduction in wasted build material particles and agents.

Before continuing, it is noted that as used herein, the terms “includes” and “including” mean, but are not limited to, “includes” or “including” and “includes at least” or “including at least.” The term “based on” means, but is not limited to, “based on” and “based at least in part on.”

With reference first toFIGS. 1A and 1B, there are respectively shown a front partially cross-sectional view and a bottom view of a portion of an example apparatus100that may be implemented during part of a 3D printing operation. It should be understood that the apparatus100depicted inFIGS. 1A and 1Bmay include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the apparatus100disclosed herein.

As shown inFIGS. 1A and 1B, the apparatus100may include a printhead assembly102that may contain a housing104supporting a printhead106. The printhead106may include multiple nozzles108arranged along multiple columns (e.g., two columns along a mono-color ink slot) along most or all of a length of the printhead106. A relatively large number of nozzles108positioned in a relatively densely packed arrangement may be provided on the printhead106to enable delivery of liquids, e.g., functional agents, from the nozzles108at a high resolution, e.g., 600 dpi, 1200 dpi, etc. As shown inFIG. 1B, the nozzles108may be arranged in a staggered fashion along the columns of nozzles108as the staggered arrangement may enable the nozzles108to print at a relatively higher resolution. In other examples, the nozzles108in one column may be aligned with the nozzles108in the other column or the nozzles108may be arranged in a single column. In addition or in other examples, a plurality of printheads106may be provided along the housing104.

In any of the examples discussed above, a respective firing element110may be provided within each of the nozzles108. The firing elements110may be any suitable type of firing element known or as yet to be known to be used in printhead nozzles. Examples of suitable types of firing elements110may include thermal resistors that may become heated to vaporize a functional agent contained in firing chambers of the nozzles108on the firing elements110and form bubbles that force the functional agent out of bores of the nozzles108. Other examples of suitable types of firing elements110may include piezoelectric firing elements that may deform when electricity is applied across the piezoelectric elements, in which the deformation forces a functional agent out of the nozzles108through respective bores. Further examples of suitable types of firing elements110may include mechanical inkjets, which may include solenoid valves that may be opened to provide continuous flow of a functional agent, e.g., deposit the functional agent as a continuous inkjet. Although not shown, the firing chambers may be supplied with the functional agent from an ink delivery system that may include a reservoir containing the functional agent.

The firing elements110, when activated, may cause droplets112of a functional agent to be fired out of the nozzles108and delivered onto a layer of build material particles114. The layer of build material particles114has been depicted with dashed lines to indicate that the layer of build material particles114may not form part of the apparatus100. As shown inFIG. 1A, the droplet112of the functional agent may follow a flight path116from the nozzle108to the layer of build material particles114. In this regard, the droplets112fired from the nozzles108may each follow a respective flight path116from the nozzles108to the build material particles114.

The printhead assembly102may also include an array of light emission devices (or sources)120that may each direct a respective light beam122, which is represented by a dashed line, through a respective flight path116of a droplet112. The light emission devices120may each be any suitable type of light emitting device that is able to generate and/or direct a focused and/or collimated light beam122through the flight path116of a droplet112. By way of particular example, each of the light emission devices120may be a vertical-cavity surface-emitting laser (VCSEL) and the light beam122may be a laser beam. In other examples, the light sources120may be light emitting diodes, laser diodes, or the like.

The printhead assembly102may further include a plurality of photon detectors (or simply detectors)124, e.g., photodetectors, optical detectors, etc., that are to receive the light beams122from respective ones of the light emission devices120. Each of the photon detectors124may be positioned to receive a light beam122from a respective light emission device120. In addition, each of the light sources120may be positioned to direct light beams122across the flight paths116of droplets112fired from each of the nozzles108and each of the photon detectors124may be positioned to receive the light beams122after the light beams have crossed the flight paths116. As shown, the light emission devices120and the photon detectors124may be mounted to the housing104via respective supports126,128.

When a photon detector124receives a light beam122, the photon detector124may generate an electrical signal, e.g., voltage or current, that may correspond to the intensity of the received light beam122. That is, the strength of the electrical signal may be higher for received light that has a higher intensity. In other examples, the photon detector124may generate data corresponding to the detected light intensity, e.g., may generate data that identifies the intensity of the detected light. In any regard, the photon detector124may communicate the generated electrical signal and/or data to a controller130. The intensity of the received light may vary depending upon whether or not a droplet112passes through the light beam122. The intensity of the received light may also vary depending upon the size and/or the composition of the droplet112as the droplet112passes through the light beam122. According to examples, the photon detectors124may be tested and/or calibrated over time or on a periodic basis to ensure that the photon detectors124are operating properly and are accurately detecting the droplets112.

The controller130may be a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), graphics processing unit (GPU), Tensor Processing Unit (TPU), and/or other hardware device and may communicate with the firing elements110, the light sources120, and the detectors124via communication lines. The controller130may determine, from the received electrical signal and/or data, whether a droplet112was properly fired by a particular nozzle108, e.g., the nozzle108that is to fire droplets112along the flight path116that intersects the light beam122. That is, the controller130may determine that a droplet112was properly fired from the particular nozzle108if the received electrical signal or data indicates that the intensity of the light beam122is below a certain threshold level, which may include an indication that the detector124did not receive the light beam122. Likewise, the controller130may determine that a droplet112was properly fired from the particular nozzle108if the received electrical signal or data indicates that the intensity of the light beam122is above the certain threshold level. In other words, the controller130may determine that a droplet112was properly fired if the droplet112is determined to have passed through the light beam122and/or if the droplet112is determined to have certain property, e.g., a volume, a composition, etc., that exceeds a certain level.

The controller130may additionally or in other examples determine whether a droplet112crossed the light beam122within a predefined time frame following activation of the firing element110. That is, when the controller130sends a firing instruction to the firing element110of a particular nozzle108, the controller130may also send an activation signal to the light emission device120that is to direct a light beam122through the flight path116of the droplets112corresponding to that nozzle108. The activation signal may be kept active for a duration of time that covers a period of time that it normally takes for a droplet112or for multiple droplets112to be formed and fired from the nozzle108and pass through the light beam122. The duration of time may be determined through testing. The controller130may determine when the firing instruction was sent to the firing element110and when an electrical signal or data was received from the photon detector124. The controller130may determine whether the droplet112crossed the light beam122within the predetermined time frame based upon when an electrical signal or data was received from the photon detector124. If the controller130determines that the droplet112crossed the light beam122within the predetermined time frame, the controller130may determine that the droplet112was properly fired. However, if the controller130determines that the droplet112did not cross the light beam122within the predetermined time frame, the controller130may determine that the droplet112was improperly fired.

A droplet112may be considered as having been improperly fired if the droplet112does not cross the light beam122within the predetermined time frame. In addition, or in other examples, a droplet112may be considered as having been improperly fired if the droplet122crosses the light beam122within the predetermined time frame but has an improper property, e.g., has an improper volume, has an improper composition, etc. In instances in which the controller130determines that the droplet112has been improperly fired, the controller130may determine that the nozzle108that fired the droplet112may be operating improperly or may otherwise be malfunctioning. In response to making this determination, the controller130may output an alert such that a user or operator may be notified of the possibility of the improperly operating nozzle108. In addition, or in other examples, the controller130may implement an operation to mitigate errors caused by the improperly operating nozzle108or cease firing of the droplets112of the functional agent in response to making this determination.

As discussed herein, the functional agent may be a binding agent that is to cause the build material particles114upon which the functional agent has been deposited to bind together. In addition or in other examples, the functional agent may be a fusing agent that is to enhance fusing of the build material particles114upon which functional agent has been deposited. In these examples, when energy is applied, the functional agent may enhance absorption of the energy by the build material particles114upon which the functional agent has been deposited. In other examples, the functional agent may be a detailing agent that is to reduce or inhibit fusing of the build material particles114upon which the functional agent has been applied. In addition or in other examples, the functional agent may be a coloring agent that is to apply color to the build material particles114. In addition or in other examples, the functional agent may change a chemical composition of the build material particles114(e.g., for printed metal, black ink providing carbon may become incorporated into a printed stainless steel, ink containing nanoparticles of metal may be locally added into the printed metal (e.g., Cu into Al-alloy, Cr into Ti-alloy), etc.

In addition or in yet further examples, the functional agent may include energetics ink, e.g., ink containing compounds that release substantial amounts of energy when they decompose at elevated temperatures as may occur during exposure of build material particles114to energy. This additional heat energy may be used for boosting the melting process of the build material particles114, particularly when the build material particles114are metallic particles.

According to examples, the type of light beam122emitted through the flight paths116of the droplets112may depend upon the luminescent properties of the droplets112. That is, for example, in instances in which the droplets112are transparent and may thus absorb infrared light, the light beams122may be infrared light beams. In other examples in which the droplets112are opaque, the light beams122may be between the infrared and the ultraviolet spectrums. In one regard, therefore, the type of light beam122may be tuned to a spectrum that accurately tracks the luminescent properties of the droplets112.

InFIG. 1C, there is shown a front partially cross-sectional view of the apparatus100depicted inFIGS. 1A and 1Baccording to another example. The apparatus100depicted inFIG. 1Cis similar to the apparatus100depicted inFIGS. 1A and 1Bexcept that the path of the light beam122in the apparatus100depicted inFIG. 1Cmay reflect off a surface of the layer of build material particles114. That is, for instance, the light emission devices120may be angled to direct the light beams122in the manner shown inFIG. 1Cand the detectors124may also be angled to receive the light beams122after the light beams122have been reflected off the build material particles114.

In the example apparatus100depicted inFIG. 10, the intensity levels of the light beams122received by the photon detectors124may vary depending upon whether droplets112of a functional agent have been deposited onto intended locations on the surface of the layer of material particles114. In this regard, the light emission devices120may direct light beams122at particular locations with respect to the nozzles108such that the locations at which the light beams122reflect off the surface of a layer of build material particles114are the locations at which the droplets122are intended to land on the surface of the layer of build material particles114. In addition, the controller130may determine whether the droplets112have successfully been deposited at their intended locations on the layer of build material particles114. In response to a determination that a droplet112has not successfully been deposited at its intended location, the controller130may determine that a nozzle108that was instructed to fire the droplets112malfunctioned or otherwise operated improperly. As a result, the controller130may output an alert to indicate the issue, may implement mitigation operations, and/or may cease production of a 3D object.

Turning now toFIGS. 2A and 2B, there are respectively shown a front partially cross-sectional view and a cross-sectional side view of another example apparatus200. It should be understood that the apparatus200depicted inFIGS. 2A and 2Bmay include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the apparatus200disclosed herein.

The apparatus200depicted inFIGS. 2A and 2Bincludes features similar to those contained in the apparatus100depicted inFIGS. 1A and 1B. In the apparatus200, however, the detectors124are depicted as being mounted to the same support126as the light sources120. That is, both the array of light sources120and the array of detectors124are depicted as being positioned on the same side with respect to an array of nozzles108. In this regard, a detector124may detect a light beam122emitted from a light source120after the light beam122has been reflected from a droplet112as shown inFIG. 2A. That is, the detector124may not output a signal or may output a first signal when the detector124does not detect the light beam122reflected or otherwise emitted from the droplet112and the detector124may output a second signal when the detector124detects the light beam122emanating from the droplet112. The controller130may determine whether a particular nozzle108properly fired a droplet112from the received signal from the detector124.

InFIGS. 2A and 2B, a single row of nozzles108are depicted. It should, however, be understood that an additional row of nozzles108may be provided along the printhead106as depicted inFIG. 1B. In this regard, the additional row of nozzles108may be aligned with the light sources120and the detectors124that are not depicted as being aligned with nozzles108inFIG. 2B. The light sources120may emit light beams122having wavelengths that may fall within one or more of a visible spectrum, a UV spectrum, and an IR spectrum.

Turning now toFIG. 3, there is shown an isometric view of an example 3D printer300that may employ either or both of the printhead assemblies102depicted inFIGS. 1A-1C and 2A-2B. It should be understood that the 3D printer300depicted inFIG. 3may include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the 3D printer disclosed herein.

The 3D printer300may include a build area platform302, a build material supply304containing build material particles306, and a spreader308. The build material supply304may be a container or surface that is used to position build material particles306between the spreader308and the build area platform302. The build material supply304may be a hopper or a surface upon which the build material particles306may be supplied, for instance, from a build material source (not shown) located above the build material supply304. Additionally, or alternatively, the build material supply304may include a mechanism to provide, e.g., move, the build material particles306from a storage location to a position to be spread onto the build area platform302or a previously formed layer of build material particles306. For instance, the build material supply304may include a hopper, an auger conveyer, or the like. Generally speaking, 3D objects or parts are to be generated from the build material particles306and the build material particles306may be formed of any suitable material including, but not limited to, polymers, metals, and ceramics. In addition, the build material particles306may be in the form of a powder.

The spreader308may move in directions as denoted by the arrow310, e.g., along the y-axis, over the build material supply304and across the build area platform302to spread a layer314of the build material particles306over a surface of the build area platform302. The layer314may be formed to a substantially uniform thickness across the build area platform302. In an example, the thickness of the layer314may range from about 90 μm to about 110 μm, although thinner or thicker layers may also be used. For example, the thickness of the layer314may range from about 20 μm to about 200 μm, or from about 50 μm to about 200 μm. The spreader308may also be returned to a position adjacent the build material supply304following the spreading of the build material particles306. The spreader308may be a doctor blade, roller, a counter rotating roller or any other device suitable for spreading the build material particles306over the build area platform302.

The 3D printer300may also include a plurality of warming devices320arranged in an array above or below the build area platform302. Each of the warming devices320may be a lamp or other heat source that is used to apply heat onto spread layers314of the build material particles306, for instance, to maintain the build material particles306at or above a predetermined threshold temperature. According to an example, the warming devices320may maintain the temperatures of the build material particles306at a relatively high temperature that facilitates the fusing of the build material particles306at selected locations, e.g., the build material particles306upon which a particular liquid, such as a fusing agent, has been mixed or applied.

The 3D printer300may further include a first printhead assembly330and a second printhead assembly332, which may both be scanned across the build area platform302in both of the directions indicated by the arrow338, e.g., along the x-axis. The first printhead assembly330and the second printhead assembly332may have features similar to those depicted inFIGS. 1A-1CorFIGS. 2A-2Band may extend a width of the build area platform302. That is, the nozzles108of the printheads106in the first printhead assembly330and the second printhead assembly332may deliver droplets112of a functional agent or multiple functional agents across a majority of the surface of a layer314of build material particles306.

In other examples, the first printhead assembly330and the second printhead assembly332may not extend the width of the build area platform302. In these examples, the first printhead assembly330and the second printhead assembly332may also be scanned along the y-axis to enable the first printhead assembly330and the second printhead assembly332to be positioned over a majority of the area above the build area platform302. The first printhead assembly330and the second printhead assembly332may be attached to a moving XY stage or a translational carriage (neither of which is shown) that is used to move the first printhead assembly330and the second printhead assembly332adjacent to the build area platform302in order to deposit respective liquid droplets112in intended locations on a layer314of the build material particles306.

In some examples, the functional agent is a fusing agent that is to enhance absorption of energy by the build material particles306upon which the fusing agent has been deposited. In these examples, a radiation generator334may be implemented to apply fusing radiation onto the layer314of build materials306. The fusing radiation may be in the form of light, electromagnetic radiation, microwaves, or the like. Particularly, for instance, the fusing radiation generator334may be activated and moved across the layer314of build material particles306, for instance, along the directions indicated by the arrow338, to apply fusing radiation in the form of light and/or heat onto the build material particles306. Examples of the radiation generator334may include a UV, IR or near-IR curing lamp, IR or near-IR light emitting diodes (LED), halogen lamps emitting in the visible and near-IR range, microwaves, or lasers with desirable electromagnetic wavelengths. The type of fusing radiation generator334may depend, at least in part, on the type of active material used in the functional agents applied onto the layer314of build material particles306. In addition or in other examples, the light beams122may be composed of radiation having similar types of electromagnetic wavelengths as the fusing radiation generator334. In these examples, the fusing radiation generator334may include the light sources120that may generate larger intensities of light to fuse the build material particles306and may generate smaller intensities of light to detect the droplets112.

Following fusing of the build material particles306in the selected areas, the build area platform302may be lowered as denoted by the arrow312, e.g., along the z-axis. In addition, the spreader308may be moved across the build area platform302to form a new layer314of build material particles306on top of the previously formed layer. Moreover, the first printhead assembly330and the second printhead assembly332may deliver droplets112of a functional agent onto respective selected areas of the new layer of build material particles306. Furthermore, the radiation generator334may be implemented to apply fusing radiation onto the new layer314of the build material particles306and the build area platform302may be lowered. The above-described process may be repeated until a predetermined number of layers have been formed to fabricate a desired 3D part.

As further shown inFIG. 3, the 3D printer300may include a controller350that may control operations of the 3D printer300components including the build area platform302, the build material supply304, the spreader308, the warming devices320, the first printhead assembly330, the second printhead assembly332, and the radiation generator334. Particularly, for instance, the controller350may control firing elements110(not shown) to control various operations of the 3D printer300components. The controller350may be a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), graphics processing unit (GPU), Tensor Processing Unit (TPU), and/or other hardware device. Although not shown, the controller350may be connected to the 3D printer300components via communication lines.

The controller350is also depicted as being in communication with a data store352. The data store352may include data pertaining to a 3D part to be printed by the 3D printer300. For instance, the data may include the locations in each build material layer314that the first printhead assembly330is to deposit droplets of the functional agent. The data store352may also include instructions for determining when nozzles108are functioning improperly based upon signals and/or data received from detectors124in the printhead assemblies330,332and for handling determinations of improperly functioning nozzles108. According to examples, the controller350may be equivalent to the controller130depicted inFIGS. 1A and 2A. In other examples, the controller350may receive data from the controller130and they communicate instructions to the controller130. Various manners in which the controller130and/or the controller350may operate are described in greater detail herein.

With reference now toFIG. 4, there is shown a block diagram of another example apparatus400, which may also be a 3D fabricating device, a 3D printer, or the like, that may be implemented to fabricate 3D objects from build material particles114,306. It should be understood that the apparatus400depicted inFIG. 4may include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the apparatus400disclosed herein. The description of the apparatus400is made with reference toFIGS. 1A-1C, 2A-2B, and 3.

The apparatus400may include a controller402that may control operations of the apparatus400. The controller402may be a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), graphics processing unit (GPU), Tensor Processing Unit (TPU), and/or other hardware device. The controller402may access a data store404, which may be a Random Access Memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like. The data store404may have stored thereon data pertaining to a 3D object that the apparatus400is to fabricate.

The apparatus400may also include an interface406through which the controller402may communicate instructions to a plurality of components contained in the apparatus400. The interface406may be any suitable hardware and/or software through which the controller402may communicate the instructions. In some examples, the interface406may also enable communication of information from the components to the controller402. In any regard, the components may include a spreader410, a printhead motor412, a plurality of firing elements110414-1to414-N, a plurality of light sources416-1to416-N, an output device418, and a plurality of detectors420-1to420-N. The spreader410may be equivalent to the spreader308depicted inFIG. 3. The firing elements110414-1to414-N may be equivalent to the firing elements110, the light sources416-1to416-N maybe equivalent to the light sources120, and the detectors420-1to420-N may be equivalent to the detectors124depicted inFIGS. 1A-1C and 2A-2B. The variable “N” may represent a value greater than one.

The apparatus400may also include a memory430that may have stored thereon machine readable instructions432-446(which may also be termed computer readable instructions) that the controller402may execute. The memory430may be an electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. The memory430may be, for example, Random Access memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like. The memory430, which may also be referred to as a computer readable storage medium, may be a non-transitory machine-readable storage medium, where the term “non-transitory” does not encompass transitory propagating signals.

The controller402may fetch, decode, and execute the instructions432to access 3D object slices, in which each slice may identify (e.g., contain instructions about) a section of a 3D object that is to be formed in a particular layer314of build material particles114,306. The controller402may fetch, decode, and execute the instructions434to control the spreader410to spread build material particles114,306into a layer314. The controller402may fetch, decode, and execute the instructions436to control the printhead motor412. The controller402may fetch, decode, and execute the instructions438to activate an actuator414-1or multiple firing elements414-1to414-N contained in nozzles108. The controller402may fetch, decode, and execute the instructions440to activate a light source416-1or multiple light sources416-1to416-N. The controller402may fetch, decode, and execute the instructions442to receive signals/data from a detector420-1or multiple detectors420-1to420-N. The controller402may fetch, decode, and execute the instructions444to determine whether any of the nozzles108failed to fire a droplet112as intended. The controller402may fetch, decode, and execute the instructions446to output an instruction regarding a malfunctioning nozzle in response to a determination that the nozzle failed to fire a droplet as intended.

The computer readable storage medium430may be any electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. Thus, the computer readable storage medium430may be, for example, Random Access Memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like. The computer readable storage medium430may be a non-transitory machine-readable storage medium, where the term “non-transitory” does not encompass transitory propagating signals.

Various manners in which the apparatus400may be implemented are discussed in greater detail with respect to the method500depicted inFIG. 5. Particularly,FIG. 5depicts an example method500for detecting a malfunctioning nozzle during a 3D object printing operation with detectors that are mounted to a common housing as a printhead containing the nozzle. It should be apparent to those of ordinary skill in the art that the method500may represent generalized illustrations and that other operations may be added or existing operations may be removed, modified, or rearranged without departing from the scope of the method500.

The description of the method500is made with reference to the apparatuses100,200,400illustrated inFIGS. 1A-1C, 2A-2B, and 4and the 3D printer300illustrated inFIG. 4for purposes of illustration. It should, however, be understood that apparatuses and 3D printers having other configurations may be implemented to perform the method500without departing from a scope of the method500.

At block502, 3D object slices may be accessed. For instance, the controller402may execute the instructions432to access the 3D object slices, in which each slice may identify a section of a 3D object that is to be formed in a particular layer of build material particles114,306. The controller402may access the 3D object slices from the data store404, from a user input, over a network, etc.

At block504, a layer314of build material particles114,306may be spread across the build area platform302. For instance, the controller402may execute the instructions434to control a spreader308,410to spread a pile of build material particles114,306across the build area platform302to form the layer314of build material particles114,306.

At block506, a printhead motor412may be controlled to cause a printhead106,330,332to move across the spread layer314of build material particles114,306. The printhead motor412may thus be a motor that may cause a carriage on which the printhead106,330,332is supported to move across the spread layer314. In this regard, activation of the printhead motor412may cause the printhead106,330,332to move in the directions denoted by the arrow338inFIG. 3. In addition, in some examples, activation of the printhead motor412may cause the printhead106,330,332to move along the y-axis as shown inFIG. 3. In any regard, the controller402may execute the instructions436to control the printhead motor412and thus the movement of the printhead106,330,332across the layer314.

At block508, a plurality of firing elements414-1to414-N may selectively be activated to fire droplets112of a functional agent from the nozzles108onto selected locations of the layer314of build material particles114,306. That is, the controller402may execute the instructions438to selectively activate some or all of the firing elements110414-1to414-N as the printhead106,330,332is moved (e.g., scanned) across the layer314of build material particles114,306to cause droplets112of a functional agent to be fired onto selected locations on the layer314. For instance, the controller402may selectively activate the firing elements414-1to414-N as the printhead106,330,332is moved to deliver the droplets112of the functional agent onto the locations on the layer314that are to be fused together. The locations at which the droplets112are to be delivered may be defined by the accessed 3D object slices, e.g., the object slice for a current layer314.

At block510, a plurality of light sources416-1to416-N may be activated to direct respective light beams122to intersect with flight paths116of the droplets112fired from the nozzles108. The controller402may execute the instructions440to activate the light sources416-1to416-N and to keep the light sources416-1to416-N active for a duration of time that covers a period of time that it normally takes for droplets fired by the firing elements414-1to414-N to pass through the respective light beams122. In some examples, the controller402may activate each of the light sources416-1to416-N. In other examples, the controller402may activate those light sources416-1to416-N that direct light beams122in the flight paths116of the firing elements414-1to416-N that are activated. In these examples, the controller402may activate a light source416-1when the controller402activates an actuator414-1that is to fire a droplet112through the light beam122emitted from the light source416-1. In addition, the controller402may deactivate the light source416-1after expiration of a duration of time that covers a period of time that it normally takes for a droplet fired by the actuator414-1to pass through the light beam122.

As discussed above, in some examples, the light sources416-1to416-N may direct the light beams122to cross the droplet112flight paths116prior to the droplets112reaching the layer of build material particles114,306. In addition or in other examples, the light sources416-1to416-N may direct the light beams122to cross the droplet112flight paths116on the surface of the layer of build material particles114,306. That is, for instance, the light beams122may be directed to reflect off the surface of the layer of build material particles114,306at locations on which the droplets112are to land. In still other examples, the light sources416-1to416-N may move the light beams122, e.g., scan the light beams122, in one or more directions, which may enhance detection of the droplets112.

At block512, the controller402may receive signals from the detectors420-1to420-N, in which the signals may correspond to whether or not the droplets112were detected to have been fired from the nozzles108as intended. As discussed herein, the detectors420-1to420-N, which may also be termed photodetectors, may collect light beams122that the light sources416-1to416-N have outputted. That is, each of the detectors420-1to420-N may be positioned to collect a light beam122emitted from a corresponding light source416-1to416-N, e.g., a first detector420-1may be positioned to collect a light beam122emitted from a first light source414-1, a second detector420-2may be positioned to collect a light beam122emitted from a second light source414-2, etc. In addition, or in other examples, light beams122originating from a common light source414-1may be filtered, for instance, with a collimating mechanism or lens, to be directed to the first detector420-1, the second detector420-2, etc.

Each of the detectors420-1to420-N may generate a signal corresponding to the intensity of the light that the detectors420-1to420-N collect and may send the generated signals to the controller402. Thus, for instance, a detector420-1may generate a first signal in response to the collected light being at a first intensity level, may generate a second signal in response to the collected light being at a second intensity level, and so forth. By way of particular example, the detector420-1may generate a first signal if the light beam122directed from the light source416-1corresponding to the detector420-1is collected without interference as may occur when a droplet112does not pass through the light beam122. The detector420-1may generate a second signal if the light beam122is collected with a relatively small amount of interference as may occur when the droplet112is smaller than intended, e.g., has a smaller volume that intended. The detector420-1may generate a third signal if the light beam122is obstructed during collection as may occur when the droplet112has an intended volume.

At block514, a determination may be made from the received signals as to whether any of the nozzles108malfunctioned. That is, the controller402may execute the instructions444to determine, from the signals received from the detectors420-1to420-N, whether any of the nozzles108failed to fire a droplet112as intended. The controller402may determine that a particular nozzle108failed to fire a droplet112as intended if a firing signal was sent to the actuator414-1of the particular nozzle108, the light source416-1was activated to emit a light beam122, and the detector420-1sent a signal indicative of a droplet112either not crossing through the light beam122or having an insufficient volume within a certain period of time following the transmission of the firing signal. Thus, for instance, the controller402may determine from the signal received from the detector420-1that a droplet112was either not fired from the particular nozzle108or that the fired droplet112was not fired as intended, e.g., with the proper volume.

In response to a determination that a nozzle108and/or multiple nozzles108have malfunctioned at block514, the controller402may execute the instructions446to output an instruction as indicated at block516. In some examples, the controller402may output an instruction to the output device418to issue an alert for an operator to be informed that a nozzle has or that multiple nozzles108have malfunctioned. In these examples, the controller402may cease printing operations until an operator decides to continue with the printing operation. In other examples, the controller402may output an instruction that is to cause a mitigation operation to be performed to compensate for the malfunction nozzle or nozzles108. The mitigation operation may include, for instance, implementing another nozzle or multiple other nozzles108to deposit droplets112of a functional agent onto the locations of the layer of build material particles114,306upon which the malfunctioning nozzle or nozzles108were intended to deposit the droplets112.

According to other examples, and as shown inFIG. 6, the controller402may implement other operations at block516. That is,FIG. 6depicts a flow diagram of a method600that may be implemented as part of or in place of block516inFIG. 5. In this regard, at block602, the controller402may determine that a nozzle or that multiple nozzles108have malfunctioned. In addition, at block604, the controller402may determine a print quality level selected for the 3D object that is in the process of being printed. That is, a user may select to print the 3D object at one of multiple print quality levels, e.g., a high quality level, a low quality level (e.g., a draft mode), etc. The print quality at which the 3D object is to be printed may be based upon various considerations, for instance, the criticality of the 3D object, tolerance adherence requirements, etc.

At block606, the controller402may determine whether the selected print quality level exceeds a certain print quality level. For instance, the controller402may determine at block606whether the selected print quality level is the high quality level or the low quality level. In response to a determination that the selected print quality level exceeds the certain print quality level at block606, e.g., that the 3D object is to be printed at a high quality level, the controller402may cease printing of the 3D object as indicated at block608. That is, the controller402may stop activating the firing elements414-1to414-N to thus stop firing of droplets112onto the layer of build material particles114,306. However, in response to a determination that the selected print quality level falls below the certain print quality level at block606, e.g., that the 3D object is to be printed at a low quality level, the controller402may continue printing of the 3D object as indicated at block610. That is, the controller402may continue activating the firing elements414-1to414-N to thus continue firing droplets112onto the layer of build material particles114,306as the printhead106,330,332is moved across the layer of build material particles114,306. Thus, for instance, the 3D object may continue to be fabricated with defects if the selected quality level for the 3D object is low.

With reference back toFIG. 5, in response to a determination at block514that none of the nozzles108has malfunctioned or following the determination to continue printing at block610inFIG. 6, a determination may be made as to whether the method500is to be continued at block518. The controller402may determine that the method500is to be continued in instances in which additional areas of the layer of build material particles114,306are to be fused together, additional sections of the 3D object are to be formed from additional layers of build material particles114, etc. In response to a determination that the method500is to be continued, the controller402may repeat blocks508-518until a determination that the method500is to be discontinued is made at block518, at which the method500may end as indicated at block520.

According to examples, blocks510-518may be performed each time the firing elements414-1to414-N are activated. In other examples, blocks510-518may be performed at predefined periods of time, once for each of the firing elements414-1to414-N during a printing operation, once for each of the firing elements414-1to414-N during an initial activation of the firing elements414-1to414-N for printing onto a newly formed layer of build material particles114,306, or the like. In addition, the detectors124may undergo testing and/or calibration operations periodically and/or over time to ensure that the detectors124,420-1to420-N are operating properly, e.g., accurately detecting the droplet112.

Some or all of the operations set forth in the methods500and600may be contained as programs or subprograms in any desired computer accessible medium. In addition, the methods500and600may be embodied by computer programs, which may exist in a variety of forms both active and inactive. For example, they may exist as machine readable instructions, including source code, object code, executable code or other formats. Any of the above may be embodied on a non-transitory computer readable storage medium.

Examples of non-transitory computer readable storage media include computer system RAM, ROM, EPROM, EEPROM, and magnetic or optical disks or tapes. It is therefore to be understood that any electronic device capable of executing the above-described functions may perform those functions enumerated above.