GB2561113A

GB2561113A - Temperature determination based on emissivity

Info

Publication number: GB2561113A
Application number: GB1809984.6A
Authority: GB
Inventors: h donovan David
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2014-01-16
Filing date: 2014-05-30
Publication date: 2018-10-03
Anticipated expiration: 2034-05-30
Also published as: GB2561113B; DE112014006200T5; GB201809984D0

Abstract

An additive manufacturing system comprising a controller to determine an emissivity of a portion of a layer of build material 302 based on a measured optical property of the portion, or on object design data representing a degree of intended solidification of the portion; and determine a temperature of the portion 322 based on the determined emissivity and a measured radiation distribution 320. A non-transitory computer readable storage medium including executable instructions causing a processor to receive data representing a measured radiation distribution emitted by a portion of material, determine an emissivity of the portion based on a measured absorbance or gloss of the portion 318 or on object design data representing a degree of intended solidification of the portion, and determine a temperature of the portion based on the determined emissivity and a measured radiation distribution. A method of determining temperature in an additive manufacturing system comprising, determining an emissivity of a portion of build material based on measuring an optical property of the portion or object design data, and determine the temperature of the portion based on the emissivity and measuring infra-red energy emitted 322.

Description

I, Patent Fulltext (71) Applicant(s):

Hewlett-Packard Development Company, L.P. 11445 Compaq Center Drive West, Houston, Texas 77070, United States of America (72) Inventor(s):

David H Donovan (74) Agent and/or Address for Service:

Haseltine Lake LLP

Redcliff Quay, 120 Redd iff Street, BRISTOL, BS1 6HU, United Kingdom

Title ofthe Invention: Temperature determination based on emissivity Abstract Title: Temperature determination based on emissivity

An additive manufacturing system comprising a controller to determine an emissivity of a portion of a layer of build material 302 based on a measured optical property ofthe portion, or on object design data representing a degree of intended solidification ofthe portion; and determine a temperature ofthe portion 322 based on the determined emissivity and a measured radiation distribution 320. A non-transitory computer readable storage medium including executable instructions causing a processor to receive data representing a measured radiation distribution emitted by a portion of material, determine an emissivity ofthe portion based on a measured absorbance or gloss ofthe portion 318 or on object design data representing a degree of intended solidification ofthe portion, and determine a temperature ofthe portion based on the determined emissivity and a measured radiation distribution. A method of determining temperature in an additive manufacturing system comprising, determining an emissivity of a portion of build material based on measuring an optical property of the portion or object design data, and determine the temperature ofthe portion based on the emissivity and measuring infra-red energy emitted 322.

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Application No. GB 1809984.6

RTM

Date :25 July 2018

Intellectual

Property

Office

The following terms are registered trade marks and should be read as such wherever they occur in this document:

Sigma Aldrich

Hewlett Packard

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

TEMPERATURE DETERMINATION EASED ON EMISSIVITY

RELATED APPLICATIONS [00011 This· application claims priority to POT Application No. PCT/US2014/032341 filed on March 31, 2014» entitled GENERATING THREE-DIMENSIONAL OBJECTS’*,, the- entire contents of which are hereby incorporated herein by reference, and which itself claims priority to POT Application No. ECT/EP2014/069841 filed on January 16, 2014, entitled GENERATING A THREEDIMENSIONAL OBJECT', the entire contents of which are hereby incorporated herein by reference,

BACKGROUND [00921 Additive manufacturing systems that generate fhrae-dimehSlenai objects on a layer-by-layer basis have been proposed as a potentially convenient way to produce three-dimensional objects in small quantifies. The quality of objects produced by such systems may vary widely depending on the type of additive manufacturing technology used.

BRIEF DESCRIPTION [0993] Some examples are described with respect to the following figures:

[99943 FIG. 1 is a f ew diagram Illustrating a method of determining temperature according to some examples;

[99953 FiG; 2a is a simplified Isometric illustration of an additive manufacturing system according to some examples: and [99063 FIG. 2b is a simplified isometric Illustration of a heMer for an additive manufacturing system according to some examples:

[99973 FIG. 2e is a simplified isometric Illustration of a radiation sensor and am unfocused radiation source in ah additive manufactunng system according to some examples;

[99963 FIG. 2d is a simplified isometric .iilustration: of a radiation sensor and a focused radiation source jn an additive manufacturing system according to some examples;

[9999] FSG. 2e te a Simplified iSOmethc illustration pf two radiation sensors and two focused radiation sburcos in an additive manufacturing system according to some examples;

[00810] FIG. 21 • is a simplified isometric illustration of two radiation sensors and a focused radiation source in an additive manufacturing system according to some examples;

[08011] FIG. 3 is a flow diagram illustrating a method of generating a threedimensional object According to some examples; and [08812] FIGS. 4a-h show a series of cross-sectional side views of layers of build material according to some examples.

DETAILED DESCRIPTION [08813] The following terminology is understood to mean the;following when recited by the specification or the claims. The singular forms to, ton/ and The mean “one or more.” The terms Including and having are intended to have the same inclusive mean ing. as the term comprising.

[88814] Using an additive manufacturing system, a three-dimensional object may be generated through the solidification of portions of one or more successive Sayers of build material. The build material can, for example, be powder-based or be a liquid, and the properties of generated objects may be dependent on the type of build material and the type of solidification mechanism used, in some examples, solidification may be achieved using a liquid binder agent to chemically solidify build material. In ether examples, solidification may he achieved by temporary application of energy to the build materia!. This may, for example.: Involve use of a coalescing agent., which is a material that, when a_: suitable amount of energy is applied to a combination of build material and coalescing agent, may cause the build material to coalesce and solidify: In other examples, ether methods of solidification may be used.

[8881S] Desired object properties, including but not limited to surface roughness, accuracy e.g. existence of deformations, and strength, may depend on the nature of the build rriatenals used, the processes by which build material is solidified to form; a desired threetoimeosicnai object, and temperatures of build materials during such processes- Thus., for example, poo r object properties may resul t . if temperature of build materia! Is not precisely regulated during the build process. For example, in an effect called coalescence bleed, some portions bf build material may achieve undesirable high temperatures sufficient to cause softening, bending, and subsequent un-intended solidification of build material, resulting in deformations. Deformations may extend laterally from the sides of the object, Or below from the bottom of the object. Deformations may also include smaller irregularities in solidification dee to undesired temperature distributions or heat conduction effects across the build material Moreover, spatial or temporal temperature gradients in the build material may decrease object accuracy through inhomogeneous contraction of the object because, for example, some build materials may be optimally processed in very narrow temperature windows.

[00016] Accordingly, the present disclosure allows accurate temperature measurements of the build, material during the build process to allow temperature to be precisely regulated during the build process, such that build materia! may be maintained in an optimal temperature window. Thus, desired object properties and control of the generation of the fiiree-dimensteha! object may be achieved, Including reduction of deformations, control of mechanical properties, and consistency when generating objects built at different times, Moreover, a greater variety of materiais may be used because materials having narrow temperature windows for optima! processing may still be useable, [08017] Temperature of the build material may be determined· accurately as follows. A temperature sensor may measure a spectrum of infra-red (IR) radiation emitted by a portion of the build material Additionally, emissivity of the portion of the build material maybe determined. The emissivity of a material for a given wavelength is the relative ability of Its surface to emit energy at that wavelength: The emissivity may be any percentage up to 100%. An emissivity of 50% corresponds to a materiel having a given temperature and emitting half the amount of energy emitted by an ideal black body at that same temperature. Generally, emissivity may for example, depend eri the type of material the material's chemical composition, surface characteristics such as degree of roughness, material geometry such as thickness of the material layer, and other factors. The emissivity is generally proportional to its absorptivity: Thus, emissiyity of build material may also depend oh Whether the build material has i/l ) coalesced and solidified, or is coalescing, or (2) has not coalesced and solidified, Some types of build material may exhibit lessor emissivity when coalesced end solidified relative to when they have not coalesced. However, other build materiais may exhibit greater emissivity upon coalescence and solidification. [00018] A materia! with 100% emissivity may omit a biack body distribution, which is based soieiy on trie temperature of the emitting material. However, realistic materials, including build materials, may have less than 100% emissivity, thus the radiant distribution may not be a perfect black body, and the radiation distribution may be based on both temperature and emissivity. Thus, the measured radiant spectrum and the determined emissivity may be used to accurately determine the temperature of build rfiatehals, even if they have fess than 100% emissivity, [00019] The emissivity of the portion of buiid material may be determined in various ways. In some examples, emissivity values of the type of build material may be known for each of the phases of the build material such as different degrees of solidification, for example. In other examples, such as if the type of buiid materia! is, unknown, emissivity of one or more phases of the buiid materia! may be_: measured before starting the build process, [00020] Then, during the build process, the degree of solidification of the portion of the build material may be determined, which may in turn be used to determine the emissivity based on the known relationship between emissivity values and the degree of solidification of the build material, In some examples, the degree of solidification of the portion of the build material may be determined using object design data defining a model of fee object tobe generated, or using agent delivery: control data defining delivery regions where coalescing agent is to be delivered. In other examples, the degree of solidification may be determined by measuring optical properties, such as <5bsorbanee or gloss, from the build material, “Absorbance- also known as “optical density^ is a ratio between radiation failing on a material and radiation transmitted through the materia! or reflected by the mstenai. The absorbance may be calculated according to the formula: ehxoXfimwi? ™ ’-Tog ( an epticsf property of a surface to reflect radiation In a specular, I.e. ηΐίΟοΡίΙΚο, direction. The absorbance and gloss measurements may also, In some examples, be generally unaffected by changes in temperature or thermal properties of the build mateha! throughout the build. Optical properties other than absorbance or gloss may be used as well, [00021] FIG. 1 is a flow diagram illustrating a method 1:00· of generating a threedimensional obiect according to some examples. The method 100 may, for example, be implemented by an additive manufacturing system comprising a controller. At 102, the controller may determine an emissivity of a portion of a layer of build materia! based on a measured optical property of the portion, of based on object design data representing a degree of intended solidification of the portion. At 1M the controller may determine a temperature of the portion based on the determined emissivity and a measured radiation distribution emitted by the portion, [00022] FIG, 2a b a simplified isometric illustration of an additive manufacturing system 200 according to some examples,. The system 200 may be operated, as described further beiow with reference to the flow diagrams: of FIG. 3 to generate a three-dimensional object, [00023] Imsome examples the build material may be a powder-based build material. As used herein the term powder-based materials is intended to encompass both dry and wet powder-based materials, particulate maferiais. and granular materials. In seme examples, the bulid material may include a mixture of air and solid polymer particles, tor example at a ratio of about 40% air and about 60% solid polymer particles. One suitable material may he Nylon 12, which Is available,: for example, from Sigma-Aldnch Co. LLC. Another suitable Nylon 12 material may be PA 2200 which is available from Electro· Optical Systems EOS GmbH. Other examples of suitable build materlais may include, for example, powdered metal materials, powdered composite materials, powdered ceramic materials, powdered glass materials, powdered resin material, powdered polymer materials, and the like, and combinations thereof; it should be understood, however, that the examples described herein are not limited to powder-based materials or to any of the materlais listed above; In other examples the build materlai may be in the form of a paste, liquid or a gel. According to one example a: suitable build material may be a powdered semi-crystalline thermoplastic material.

[00024] in some examples, many of the build materials above, such as powders, may exhlbii different optical properties, such as different absorbance and different gloss,: depending bn the degree of solidification of build .materiel, such as whether the build material is or Is not solidified. This may allow determining, based on measured optical properties, whether build material has solidified as intended. Degree of solidification may be reistsd to a number of other object properties, including density, strength, elastic modulus, and mechanical performance such as the degree ef efohgation the object can sustain without breaking. Thus, based on measured eptlcsi properties, the degree of each of these object properties: may also be determined. For example, the degree of absorbance and the degree of gioss may each be positively correlated: with each of the foregoing object properties.

[00025] In some examples, if the build material is not solidified, then if may exhibit tittle or no absorbance end little or np gloss in the presence of a suitable radiation source that emits radiation to the build material. These optical properties may result because of opacity resulting fropn scattering of radiation between parts of an irregular surface of the build material and between the large number of interfaces between the build material and air, such as between a powder's particles and air voids throughout the powder. If the build material is solidified, then It may exhibit greater absorbance and greater gloss relative to a hon-soiidified build material. Greater absorbance may result because of greater transparency to radiation e.g. infra-red radiation, for example due to reduced scattering of radiation, causing the radiation to travel deeper into the build material and become absorbed therein, causing the solidified area to look darker. Greater gloss may result, for example, because fee build material may have a smoother surface than prior to solidification, [00026] in some examples, coalescing agent is delivered to build material, after which the build material haying the coalescing agent is solidified when energy is applied. Different types of coalescing agents, may have different effects on absorbance, as follows.

[00027] in some examples using a radiation absorbing coalescing agent, the agent may cause additional absorption of radiation that is transmitted within the build material, further darkening the solidified area. For example, after delivering coalescing agent but prior to applying energy for solidifcafipn, the un-sblldified build material may exhibit greater absorbance it ban un-solidifled build material on which coalescing agent was not delivered· This may be because the coalescing agent, updo being delivered into the build material, may be at least partially disposed oh the surface of the build material, such that the coalescing agent may act as an absorber and absorb the radiation, thereby Increasing absorbande. Carbon black, for example, may be an ingredient of a radiation absorbing coalescing agent that may remain at least barfiatly on the:surface of the build material. However, in sbrne examples, the coatescing agent penetrates into the build material or iscovered by additional build material Such that it is buried and interspersed inside the build material. In such cases, the coalescing agent does not affect the hon-soiidified build materiais surface characteristics, which may be responsible for the low absorbance, [00028] After applying energy for solidification, the absorbahoe of the Solidified build material may increase. For example, radiation may pass through the solidified build material's surface, which may he transparent to the radiation after solidification, and reach the coalescing agent buried and interspersed Inside the build material. The coalescing agent may act as an absorber and absorb the radiation, thereby increasing absorbance, in any of these examples, there may remain a significant difference in absorbance in un-soiidified versus solidified build material.

[00020] In examples In which coalescing agent is not used, uh'Solidified build material may, for example, have an absorbance between about 0.1 and about 0.2 optical density (QD) units, and solidified build material may have an absorbance of about 0.4 OD units.

[00030] in examples in which coalescing agent is used that includes carbon black, the change In absorbance between the non-solldified and solidified build material may, for exampie, be greater than above, For example, un-solidified build material on which coalescing agent Iriciuding carbon black has been applied may have an absorbance between about 0.5 and about 1.0 OD units, and solidified build material incorporating carbon black from coalescing agent may have an absorbance between about 1.3 and about 1,8 QD units. This may allow measured: absorbance to serve as an accurate indicator of object properties, [00031] However, In other examples, the absorbance may achieve other values than those listed above.

[00032] In some examples using a coalescing agent that does not absorb the radiation used for detection, such: as visible light, absorbance may not be effected, because the radlailbn may pass through the coalescing agerit Thus, un-solldlfled build rdaferial having coalescing agent may exhibit absorbance; similar to that exhibited by un-solidified build material do which coalescing agent wasnot delivered. Additionally, In some examples, solidified build material having opalescing spent may exhibit absorbance similar to that exhibited by solidified build material on which coalescing agent Was not delivered.

[00033] In some examples, un-solidified build material having coalescing agent may exhibit gloss similar to that exhibited by uri-Solidified build material on which coalescing agent was net delivered. Additionally, In some examples, solidified build material having coalescing agent may exhibit gloss similar to that exhibited by solidified build material oh which eeaiesclhg agent was not delivered. This may be true regardless of whether coalescing agent settles on the surface of the build material, or penetrates into the build material.

[00034] In some examples,.-some build materials, such as liquids, may instead show a negqOye, rather than positive, correlation between degree of solidification and absorbance, and between degree of solidification and gloss, 'This may, for example, be because solidification causes increased roughness on the surface of the liquid build material, [00035] The additive manufacturing system 200 may include a system eontrelier 210, .Any of the operations and methods disclosed herein may be Implemented and controlled in the additive manufacturing system 200 and/or controller 210.

[00030] The controller 210 may include a processor 212 for executing Instructions that may implement the methods desonbed herein. The processor 212 may, for example, be a microprocessor, a microcontroller, a programmable gate array, an application specific infegraiod circuit (ASIC), a computer processor, or the like. The processor 212 may, for example, include multiple cores on a chip, multiple cores across multiple chips, multiple cores across multiple devices, or combinations thereof. In some examples, the processor 212 may include af least one integrated circuit (1C), other control logic,other electronic circuits, or combinations thereof.

[00037] The controller 210 may support direct user interaction, For example, the additive manufacturing system 200 may include user input devices 220 coupled to the processor 212, such as one or more of a keyboard, touchpad, buttons, keypad, dials, mouse, track-ball, card reader, or other input devices. Additionally, the additive manuladtdring system 200 may include output devises 222 coupled to the processor 212, such as one or more of a liquid crystal display (LCD), printer, video; monitor, touch screen display, a light-emitting diode (LED), or other output devices. The output devices 222 may be responsive to instructions to display textual information or graphical data, [00038] The processor 212 may he in communication with a computer-readable storage medium 218 via a communication bus 214. The computer-readable storage medium 216 may include a single· medium or multiple media. For example, the computer readable storage medium 216 may include one or both of a memory of the ASIC, and a separate memory In the controller 210, The computer readable storage medium 210 may be any electronic, magnetic, optical dr other physical storage device, For example, the computef-readable storage medium 218 may be, for example, random access memory (RAM), static memory, read only memory, an x

electrically erasable programmable read-only memory (EEPROM), a hard drive, an optica! drive, a storage drive, a CD, a DVD, and the like. The computer-readable storage medium 216 may foe non-transitory. The computer-readable storage medium 216 may store, encode, or carry computer executable instructions 218 that, when executed by the processor 212, may cause the processor 212 to perform any one or more of the methods or operations diseiosed herein according to various examples. [00630] The system 200 may Include a coalescing agent distributor 202 to selectively deliver coalescing agent to successive layers of build materiel provided on a support member 204, According to one non-limiting example, a suitable coalescing agent may be an ink-type formulation comprising carbon black, such as, for example, the ink formuiation commercially known as CM997A available from Hewlett-Packard Company. In one example such an ink may additionally comprise an Infra-red light absorber. In one example such an ink may additionally comprise a near infra-red light absorber, in one example such an Ink may additionally comprise a visible light absorber, in one example such an ink may additionally comprise a UV light absorber. Examples of inks comprising visible light absorbers are dye based colored ink and pigment based colored ink, such as inks commercially known as CM903A and CE642A available from Hewlett-Packard Company, [00040] The controller 210 controls the selective delivery of coalescing agent to a layer of provided build material in accordance with Instructions comprising agent delivery control data 208, which may, for example, be derived from object design data 206.

[00041] The agent distributor 202 may be a printhead, soch as a thermal inkjet printhead Or a piezo inkjelprinthead, The printhead may have arrays of nozzles. In one example, printheads such as those commonly used in commercially available inkjet printers may be used, in other examples, the agents may be delivered fbrdogh spray nozzles rather than through printheads. Other delivery mechahisms may be used as well. The agent distributor 202 may be used to selectively deliver, e,gl deposit, coalescing agent when in the form of Suitable fluids such as a iiguld- in some examples, fire agent distributor 202 rnay be selected to deliver suitably sized drops of agent at any suitable resolution. In some examples the coalescing agent may comprise a liquid carrier, such as water or any other suitable solvent or dlspersaht, to enable it to be delivered via a printhead. in Some examples the v

printhead may be a drop-on-demand'printhead. in other examples the printhead may he a continuous drop printhead.

[00042] in the example illustrated in FIG. 2a, the agent distributor 202 has a length that enables it to span the whole width of the support member 204 in a so-called page-wide array configuration. In one example this may be achieved through a suitable arrangement of multiple printheads- In ether examples a single printhead having an array of nozzles having a length to enable them to span the width of the support member 204 may be used, in other examples, the agent distributor 202 may have a shorter length that dees not enable them to span the whole width of the support member 204.

[00043] The agent distributor 202 may be mounted on a moveable· carriage to enable it to move bi-directionally across the length of the support 204 along the illustrated vaxis, This enables selective delivery of coalescing agent across the whole width and iength of the support 204 in a single pass, in other examples the agent distributor 202 may he fixed, and the support member 204 may move relative to the agent distributer 202, [00044] it should be noted that the term 'width' used herein is used to generally denote the shortest dimension in the plane parallel to the x and y axes Illustrated in FIG. 2d, whilst the term length' used herein is used to generally denote the longest dimension in this plane. However, it will be understood that in other examples the term; 'width' may be interchangeable with the term; ‘length’. For example; in other examples the agent distributor 202 may have a length that enables It to span the whole iength of the support member 204 whilst the moveable carriage may move bidirectionally across the width of the support 204 .

[00045] In another example the agent distributor 202 does opt have a length that enables if to: span the whole width of the support member but are addifionaiSy movable bi-directionally across the width of the support 204 in the illustrated X-axis. This configuration enables selective delivery of coalescing agent and coalescence modifier agent across the whole width and iength of the support 204 using multiple passes. Other configurations, however, such as a page-wide array configuration, may pnphie three-dimensional objects to be created faster, [00040] The coalescing agent distributor 202 may Include a supply of coalescing agent or may he conneotable to a separate supply of coaieseing agent, ill [00047] The system; 200 may further comprise a. build material distributor 224 to provide_: e.g, deliver and/or deposit, successive layers of build material on tee support member 204. Suitable build material distributors 224 may include, for example, a wiper blade and a roller. Build material may be supplied to foe build material distributor 224 from a hopper or build material store. In the example shown the build material distributor 224 moves across the length (y-axis) of toe support member 204 to deposit a layer of build material. As previously described, a layer of build material will be deposited on the support member 204, whereas subsequent layers of build material will be deposited on a previously deposited layer of build material. The build material distributor 224 may be a fixed part of the system 200, or may not be a fixed part of the system 200, instead being, tor example, a part of a removable module.

[00040] in some examples, the thickness of each layer may have a value selected from the range of between about 50 to about 300 microns, or about 90 to about 110 microns, or about 250 microns, although in other exampies thinner or thicker layers of build material may fee provided. The thickness may be controlled by the controller 210, for example based on the agent delivery control data 205.

[00049] in some examples, there may be additional agent distributors, and build material distributors reiative to the distributors shown In FIG. 2a. In some examples, the distributors of system 220 may be located on the same carriage, either adjacent to each other or separated by a short distance. In other examples, two or more carriages each may contain one dr more distributors. For example, each distributor may be located in its Own separate carriage, Any additional distributors may have similar features as those discussed earlier with reference to the coalescing agent distributer 202. However, in some examples, different agent distributers may deliver different coalescing dgents,.· for example, [00050] In (ho example shown the support 204 is moveable in too z-axis such that as new layers of build material are deposited a predetermined gap is maintained between the surface of the most recently deposited layer of baiSd material and lower surface of the agent distributor 202. in ether exampies, however, the support 204 may not be movable sn the z-axis pnd the agent distributor 202 may he movable in the z-axis.

[00051] The system 200 may additionaliy include an energy source 226 to apply energy to build material to cause the solidification of portions of the build material according to where coalescing agent has been delivered or has penetrated. In some examples, the energy source 226 is .an Infra-red OR) radiation source, near infra-red radiation source, halogen radiation source, or a light emitting diode. In some examples, the energy source 226 may be a single energy source that is able to uniformly apply energy to build material deposited on the support 204, In some examples, the energy source 226 may comprise an array of energy sources.

[00062] In some examples, the-energy source 226 Is configured to apply energy In a substantially uniform 'manner to the whole surface ef a layer of build material. In these exampies the energy source 226 may be said to be an·· unfocused energy source. In these exampies, a whole layer may have energy applied thereto simultaneously, which may help increase the speed at which a three-dimensiohai object may fee generated, [00063] In other examples., the energy source 226 is configured to apply energy in a substantially uniform manner to a portion of the whole surface of a layer of build material, for example, the energy seurce:226 may fee configured to apply energy to a strip of the whole surface of a layer of build material. In these examples the energysource may fee moved or scanned across, the layer of build materiai such that a substantially equal amount of energy is ultimately applied across the whole surface of a l ayer of build material.

[00664] In soma examples, the energy source 226 may be mounted on the moveable carriage.

[OOOSS] in other examples, the energy source 226 may apply a variable amduhf of energy ae.it is moved across the layer of build materiai, for example io accordance with agent delivery controi data 208. For example, the controller 210 may control the energy source only to apply energy to portions of build material on which coalescing agent has been applied, [600S6] In further examples, the energy source 226 may be a focused energy source, such as a laser beam, in this example the taser beam may be controlled to scan across tee whole of a portion of a layer of build material, in these exampies tee laser beam may be controlled to scan across a layer of build materiai In aecofdaoGe with agent delivery controi data, for example, the laser beam may be centrOlied to apply .energy to those portions of a layer of on which coalescing agent is delivered.. [OOOS?]The combination of the energy supplied, the build material, add the coalescing agent may be selected such that, excluding the effects of any π

•coalescence bleed; 0 portions of. the build material on which no coalescing agent have been delivered do net coalesce when energy is temporarily applied thereto; ii) portions of the build material on which only coalescing agent has been delivered or has penetrated coalesce when energy is temporarily applied thereto do coalesce. [00050] The system 2QQ may additionally include a beater 230 to emit beat to maintain boil'd material deposited on the support 204 within a predetermined temperature range. The heater 230 may have any suitable configuration. One example is shown In FIG, 2b, which is a simplified isometric ilSustrafloh of a heater 230 for an additive manufacturing system according to seme examples. The heater 230 may have an array of heating elements 232, as shown in Fig. 2B, The heating units 232 may be each be any suitable heating' unit, for example a heat iamp such as an inframod lamp. The heating units 232 may have any suitable shapes or configurations such as rectangular as shown in FIG, 2fe. in other examples they may be circular, rod shaped, or buib shaped, for example, The configuration may be optimized: to provide a homogeneous heat distribution toward the area spanned by the build material. Each heating unit 232, or groups of heating units 232, may have an adjustable current or voltage supply to van ably control the local energy density applied to the build materia! surface, [00053] Each heating unit 232 may correspond to its Own respective area of the build material, such that each heating unit 232 may emit heat substantially toward its own area rather than areas covered by other beating units 232, For example, each of the sixteen heating units 232 in FIG, 2b may heat one of sixteeh different: areas ef the build material, where the sixteen areas oofiaafively Cover the entire area of the build material. However, in some examples, each beatihg unit 232 may also emit, to a lesser extent, some heat which influences an adjacent area.

[00000] in seme examples, additionally br alternatively to the heater 23Q, a heater may be provided below the platen of the support member 204 to conduotivoly hoot the support member 204 end thereby the build material. The conductive boater may be to uniformly heat the build materiel across its area on the Support member 204. [00061] The system 200 may addifionaily include a radiation/sensor 229, tor example a point contactless temperature sensor such as one or more thermopiles, or such as a thermographic camera. In other examples, the sensor 229 may include an array of fixeddecailpn pyrometers which each capture radiation from a single area of the build material. In other examples, the sensor 229 may be e single pyrometer which

S3 rnay be operable to sweep or seen ever the <anflre area of the build maferiai. Other types of sensors may also be used.

[0S0S2] The temperature sensor 229 may be to capture a radiation distribution, for example in the IR range. emitted fey each point of the build material across the area spanned by the build material on the support member 204, The temperature sensor 229 may output the radiation distribution to the controller 210; The radiation distribution data may then be used for calculating temperature of the material,, as will be described relative to FIG. 3.

[00063] The sensor 229 may be oriented generally centrally and facing generally· di racily toward the build material, such thaf the optical axis of the camera targets the center line of the support member 204, to allow a generally symmetric capture of radiation from the build material- This may minimize perspective distortions of the build material surface, thus minimizing the need for corrections, and reducing errors in measured temperature values versus real temperature values: Additionally, the sensor 229 may be abie to (1) capture the image Over a wide region covering an entire layer of build material,for example by using suitable magnification, (2) capture a series of images of the entire layer which are later averaged, er (3) capture a series of images each covering a portion of the layer 'that together cover the entire layer. In some examples, the sensor 229 may be in a fixed ideation relative to the support member 204, but in other examples may be moveable if other components, when moving,, disrupt the line of sight between the camera 229 and the support; member 204, [00064] The system 200 may additionally include a radiation sensor 223 to measure an optical property of the build material: that is correlated with emissivity and/or degree of solidification of the build material. Examples of optical properties include absprbance or glass of the build material, but pfher optical properties may be used. The radiation sensor 228 may be to measure, dig. capture, radiation reflected from the build material on the support member 204. At each area cf the build: material, the measurement of radiation may involve measuring a radietiph distribution that is; a spectral distribution obmprising radiant Intensity values as b function of radiation wavelengths. The radiation sensor 228 may also be to measure the angle of reflection of radiation from the build meterlai. The radiation sensor 228 may output data representing the: measurements to the controller 219, which may determine steps to fee performed by the controller 210 if the build material has not solidified as intended. FIGS, 2c~2f show various examples using a radiation sensor 228.

[08865] The radiation sensor 228 may, for example, fee part of a refiectometer, densitometer, colorimeter, digital camera, gioss meter, or feeze meter. The sensor itself may, for example, compose a photelrenslstoo photodiode, light-to-voltage converter integrated circuit (e.g. a photodiode or phototransistor with support circuitry), contact image sensor, or charge coupled device. The radiation sensor 228 may also comprise lenses and/or filters to help collect and sort light when using any of the above sensors.

[08888] FIG. 2c is a simplified isometric illustration of a radiation sensor 228 and an unfocused radiation source 238 in the additive manufacturing system 200 according to some examples. In this example, the radiation sensor 228 may be used to measure absorbance. Thus, the radiation sensor 228 may, for example, fee part of a refiectometer, densitometer, colorimeter, or digital camera. However, other types of sensors may be used. In these examples, the radiation sensor 228 may include or may be used with an unfocused radiation source 238, For example, if the radiation sensor 228 is a densitometer, the radiation sensor 228 may Inciude the unfocused radiation source 238, [88087] In some examples, the energy source 228 or the heater 230 may be used as the unfocused radiation soume 238, In these examples, the radiation sensor 228 may, for example, include a filter to block a portion of the radiation, e,g, infra-red radiation, from the energy source 226 or the beater 230, such that the radiation sensor 228 defects a visible; fight fail of radiation reflected by the build material, but hot infra-red radiation from the build material. Thus, the infra-red radiation used tor beating or solidification of build materia! may not interfere with the visible light radiation used for detection of solidification» [00868] in some examples, the unfocused radiation source 238 may be Separate from the energy source 228 and the heater 23Q. In these cases, the radiation sensor 228 may similarly include a filter to block a portion Of the radiation, e.g. infra-red radlgtieh, from the energy source 228, heater 23Q, and the build material. Additionally, the unfocused radiation source 238 may, for example, apply radiation in a radiant spectrum that is substantially different than the radiant spectra applied fey the energy source 226 and heater 238. For example, the unfocused radiation source 238 may apply radiation in the visible Sight range, whereas the energy source 228 and heater 230 may -primarily apply radiation In the infra-red range. Thus, Interference may be reduced or prevented between the infra-red radiation used for heating or solidification of build material and the visible tight radiation used for .detection of solidification, [00069] To measure absorbance, the radiation source 238 may apply unfocused radiation 240 to the build material 234, and a radiation distribution 242 reflected from a portion 236 of the build material 234 may be measured by radiation sensor 228. The wavelengths of the unfocused .radiation 240 may be .selected such that the radiation 240 is not absorbed when the portion 238 is not solidified, and such that the radiation 240 is absorbed when the portion 236 is solidified and/or contains coalescing agent therein. The coalescing agent may de selected, for example carbon black, such that it absorbs the wavelengths of the unfocused radiation, [00070] FIG, 2d is a simplified Isometric illustration of a radiation sensor 228 and a focused radiation source 244 in ah additive manufacturing system 200 according to some examples. In this example, the radiation sensor 228 may he used to measure gloss. Thus, the radiation sensor 228 may, for example, be part of a gioss meter, densitometer, ref leoto meter, of digital camera. However, other types of sensors may be used, in these exampies, the radiation sensor 223 may include or may be used with a focused radiation source 244, In some examples, if the energy source 226 is a focused energy source, then if may be used as the focused radiation source 244. In some exampies, the fpoused fadiatibn source 244 may be separate from the energy source 228. In some examples, the focused radiation source 244 may, for example, apply radiation in a radiant: spectrum that is substantially different than the radiant spectra applied by the energy source 220 and heater 230 to reduce or prevent interference between radiation used for heating or solidification of build material and radiation used for detection of solidification.

[00071] To measure gloss, the radiation source 244 may apply focused radiation 246a to a portion 236 of the build material 234 at an angle (0) 260 from the 2mxis, and the radiation sensor 228 may measure any of the radiation 248 that exhibits specular reflection at the opposite and equal angle (0) 260 from the surface of the portion 236/Thus, the overall angular change in the reflected radiation may be twice the angle 250 (20), [00072] In some examples, in measuring gloss, the radiation source 244 may instead 'be unfocused, and the radiation sensor 228 may be fitted with apertures to filter out off-angle radiation, This may be acceptable because the reflection of unfocused radiation from the build material at the. specular angle may substantially exceed radiation scattering from other angles received by the radiation sensor 228,.

[00073] The .radiation sensor 228 and the radiation source 244 may be arranged such that the angle (4) 250 may take on any suitable value, for example any value greater than 0 degrees and less than 90 degrees, or between about 5 and about 85 degrees, or between about 15 ami75 degrees, or between about 20 and about 60 degrees, for example- Thus, the angle (0) 250 may be non-zero.

[00074] In some examples, the radiation sensor 244 may be part of a haze meter. These examples may be similar to above, except that in these examples, the radiation sensor 244 may Instead be placed at a nomspeeular angle, such that it detects non-specuiar refection from the portion 236 to detect radiation. In this case, the degree of nomspeeuiar reflection may negatively correiafe with gloss of the portion. 238, because it may be inferred that increased non-specuiar reflection correlates with decreased specular reflection, [00075] FIG, 2e is a simplified isometric illustration of two radiation sensors 228 and 254 and two focused radiation sources 244 and 252 in an additive manufacturing system 200 according to seme examples, F IG, 2e may Include similar features as those in FIG; 2d, except for the additional rad:afion source 252 and additional radiation sensor 254, The radiation sensor 254 may, for exampie, be part of a gloss meter, densitometer, refiectometer, or digital gamers. The-radiation source 252 may apply focused radiation 258 at an angle (φ) 280 from the z-axls to be specularly reflected by the portion 238 as radiation 258 at the opposite and equal angle (y>) 280. Thus, relative to the radiation sensor 228 and radiation source 244 described earlier, the specular reflection using: radiation sensor 254 and radiation source 2521 may be similar to and may be used similarly in determining solidification of the portion 288Thud, two concurrent gloss measurements may be made involving spbcular refiedtiop at different angles 250 and 280. Thus, reliability of the measurertlent may be Incfeaeed, end errors due to unintended Interference by other light sources may be redudedl In other examples, three or more radiation sensors and three or more radiation sources may be used to concurrently measure specular reflection at three of more different angles.

n [00076] FIG, 2f is a simplified isometric illustration of two radiation sensors 228 and 254 and a focused radiation source 244 in an additive manufacturing system 200 according to some examples. FIG. 2f may include similar features to those in FIG. 2d, except lor the additional radiation sensor 266, The radiation sensor 286 may, for example, be part of a gioss meter, haze meter, densitometer; refieotometer, of digital camera. The radiation sensor 288 may be placed at a nomspecuiar angle (cd 264, la. an angle ether than angle (di In some examples, some of the radiation 248 may be non-specuiarly reflected as radiation 262. The degree of non-specular reflection may be negatively correlated with solidification of the portion 238, Thus, the nonspecular reflection may be used provide fine correction to the gloss measurement represented by the specular refiecffon, in the following ways. In some examples·,, a ratio between the magnitude of the detected radiation 248 and detected radiation 262, or between the detected radiation 248 and detected radiation 282, may provide a precise measure of gloss, in other examples,, the radiation sensor 286 may measure stray radlaflpn from other sources, for example the energy source 228. Thus, the measurement by radiation sensor 228 may be corrected to correct for unintended stray radiation, such that the radiation sensor 228 may acoUfately provide a measurement of specularly reflected radiation 248.

[08877] In any of the examples above in which the waveiength(s) of the energy source 228 used to impart energy to the build material and the wavetengthfs) of the radiation spurpe used to measure the optical property, suehi as absorbance or gloss, of the build material substantially overlap, a differential signal technique can be used tp acquire a signal free of background radiation frdm the energy source 226; The radiation source used for measurement may apply radiation that is pulsed, i.e. turned on and off at a desired ffeguehcy, for example but not ilmlted to a frequency selected from; the range of 1 to 1000 Hz. The radiation sensor may measure a radiation distribution while the radiation source Is on and may also measure a radiation distribution while the radiation source is off. These distributions may be compared, and the difference of these values may represent the desired quantify to be measured with the background radiation removed.

[00678] In any of the above examples, although measurement is shown relative Ip portion 236, other portions of the build material 234 mam also he measured, for example the portions bordering to the portion 238,

[000793 Although in FIGS. 2a, 2c, 2d, 2e, and 2b the energy source -22S, heater 230, radiation sensors 228 and 284, and radiation sources 238, 244, and 252 are shown in particular locations above the support member 204, they may each he placed In any suitable location above or around the support member 214, In some examples, one or more: of these components may be in a fixed location relative to the support, member 204, but in other examples may be moveable if other components, when moving, disrupt the line of sight to the support member 204.

<00030] The controller 210 may control selective delivery of agents, such as, coalescing agents, in accordance with instructions comprising agent delivery controi data 208. The controller 210 may also control the energy source 226 to apply a variable amount of energy as It is moved across the layer of build material, for example In accordance With agent delivery control data 208. The agent delivery control data 208 may define for each slice of the three-dimensional object to be generated the portions or the locations oh the build material, if any, at which coalescing agent is to be delivered, in one example the locations or portions ofthe build material at which coalescing agent is to be delivered are defined by way of respective patterns.

[00081] The agent delivery control data 208 may be derived, for example, by a suitable tbrae-dimehsionai object processing system. In some examples the threedimensional object, processing system may be comprised within the additive manuiaotonng system 200, For example, the instructions 218 may additionally include Instructions that, when executed by the processor 212, pause the processor 212 to operate as a three-dimensional object processing system as described herein, in. other examples the Wee-dimensional object processing system may be external to the additive manufsciurthg system 200. For example, the threedlmensipnel object processing system may be s software application, or part of a software application, executable On a computing device separate from the system 200.

[80882] in some examples, the agent delivery control data _;208 may be generated based oh object design data 208 including (1) object model data representing a three-dimensional model of an object to be generated, artd/or (2} pbjeof property data representing properties of the object such as density, surface roughness,: strength, and the like. The object model data may define a degree of intended solidification, e.g, solidified or un-solidified, of each portion of the object, and may be

processed by the three-dimensional object processing system to generate slices of parallel pianos of the model. Each slice may define a portion of a respective layer of build material that is to be solidified by the additive manufacturing system. The object model day may he in any suitable format, for example a raster map or vector map, [00083] The object design data 206 may be received, for example, from a user via an input device 220, as input: from a user, from a software driver, from a software application such as a computer aided design (CAD) application, or may be obtained from a memory storing default er user-defined object design data and object property data, [00084] in some exampies the object processing system may obtain data relating to characteristics of the additive manufacturing system 200, Such characteristics may include, for example, buiid material layer thickness, properties of the coalescing agent, properties of the coalescence modifier agent, properties of the build material, and properties of the energy source 228, properties of the heater 230, and properties of the temperature sensor 228.

[08085] FIG, 3a is a flow diagram Illustrating a method 300 of generating a threedimensional object according to some examples. The method may be computer implemented. In some examples, the orderings shewn may be varied, such that seme steps may occur simultaneously,some steps may foe added, and seme steps may be omitted. In describing FIG; 3a; reference will be made to FIGS, :2 and <a-h, FIGS· 4a-h show a series of cross-sectional side views: of layers of build material according to some examples, [08088] At 302, the emissivity ofW build material for each of a number of degrees of sofidificatidn, such as solidified and un-solidified, may he determined, This may be done, for example, if the type of build material is unknown. The emissivities may be determined according to any of the follow-ng methods.

[08087] in some examples,: the controller 210 may control the build material distributor 224 to provide a layer of build material on the support member 204 by causing the build material distributor 224 to move along the ytexis as discussed earlier., The controller 210 may then cause an agent distributor to selectively deliver go agent having known emissivity to a portion of the layer of build material. The agent may be any of the coalescing agents desonbed earlier such as carbon black,, or may be any other suitable agent with a known emissivity. Then, the layer may be heated using the heater 230 or using the conductive heater beneath the platen of the

3« support member 204, The: heating may be· uniform across tee layer, such that the agent, and the portion not having agent may have the same temperature. The agent may radiate the heat it absorbed, and similarly, the portion of the buiid material hot having the agent may then radiate the heat it absorbed, The radiation emitted by the agent and by the portion without agent may then be separately measured by the radiation sensor 228, The measurement may he made after the amount of emitted radiation stabilizes after heating. The IR energy emitted by a black body at the temperature T is equal to the IR energy actually emitted by a portion divided by the po rti on s em issiv I ty:

/0 blnckbndy energy [T] ~ energy {o,yvnb} / R vner[burtd msieWiffJ eiotrsiarty iagenhj. ummwhy tburtd matertef) [00000] Thus, the emissivity of the portion of build material without agent may be determined by the conf roller 210 by inputting the known vaiue of the emissivity of the agent, and the measured values of the IR energy emitted by the agent and the iR energy emitted by the portion of the build materia! not having the agent, in some examples, to determine emissivities of the build material after various degrees of soiidificaSon, various portions of tho build material may be solidified to various degrees using arty suitable solidification process such as those described eariler, after which a similar process as above may be performed as was done with the unsolldirted portion without agent100009] in other exampies, the temperature In a build area Is known for the partieuiar additive manutectefing system being used. In these examples; the layer may be delivered on the support member 104 as above. Then, build material may radiate heat, which may be measured by the radiation sensor 228, Then, the emissivity of the build material may be determined by the controller 210 using the earlier formula, given the known energy emitted by a hlackbody at the known ternperatore f, and the measured IR energy emitted by the build materiai:

. /8 UtterUv tfotrtM material] emtestertv I build imierridl -_u.

rz? hfarkh.'td'.’ ί>ίϊίί?·«ν 7 [00090] This example .may instead involve measuring the IR energy entitled by the build materia! at two or more different known temperatures of the additive manufacturing: system. Thus, for example, two or more different emissivity values may be determined and averaged, In some examples, to determine emissivities of the build material after various degrees of solidification, various portions of the build .25 materia! may be solidified to various degrees using any suitable solidification process such as those described earlier, after which a similar process as above may be performed as-was done with the urn-solidified build material, [00091] in other examples, the layer may be delivered on the support member 104 as above, and emissivity may be measured using techniques similar to those described earlier reiative to measuring absorbance. However, in these examples, the radiation source may apply IR radiate, and the amount of reflected IR radiation detected fey an IR sensor may be used by the controller 210 to determine the emissivity of the build material.

[00092] in the above examples, the layer used for determining emissivity may be ..cleared off the support prior to starting the build at 306. However, in other examples, the build may begin on top of the layer used for determining emissivity, [00093] In yet other examples, 302 may not be performed, for example if the emissivities are already known because the type of build material Is known, [00094] At 304, (1) each of the determined dr known emissivities may be correlated by the controller 210 to a degree of solidification, arid (2) each of the determined or known emissivities for each degree of solidification may be correlated by the controller 210 to an optical property, such as absorbance or gloss, of the build material having that degree of solidification, The values of the optica! property, such as absorbance or gloss, may be known for the; type of material and stored in the Controiier210,; or In Other exart: pies measurements may be made according to any of the tadhnigdes described earlier relative to FIGS, 2a-2t, for example using the radiation source 238, 244, and/or 262. arid the radiate sensor 228 and/or 284, The radiation sensor 228 and/or 284 may output data representing the measured absorbance and/or gloss to the controller 210, [00095] The efetfelations between emissivity and seiidificatlon, and between emissivity arid various opticas properties such as absorbance and gloss, may thus he stored in the controller 210. The correlations may fee stored in look-up tables, as mathematieal formulae fitted to the known data points of the correlates, or as any other suitable data objects.

[00096] At 308,_; the controller 2W may obtain Object design data 206 and, based thereon, may generate agent delivery centre! data 208.

[00097] At 308, a layer 402b of build material may be provided, as shown in FIG. 4a; For example, the controller 210 may oontroi the build materia! distributor 224 to >2 provide the layer 402b on a previously completed layer 402a on ihe support member 204 by causing the build material distributor 224 to move along the y-axis as discussed earlier. The completed layer 402a may include a solidified portion 408. Although a completed layer 482a is shown in FIGS, 4a-d for illustrative purposes, it is understood that the steps 308 to: 322 may initially be applied to generate the first layer 402a.

[99898] At 310, the build material may be heated by the heater 230: to heat and/or maintain the build material within a predetermined temperature range. The predetermined temperature range may, for example, be below the temperature at which the build matehel would experience bonding in the presence of coalescing agent 404, for example below the melting point of the build material. For example, the predetermined temperature range may be between about 155 and about 180 degrees Celsius, or the range may be centered at about 180 degrees Celsius. If the build material Is crystalline or semi-crystalline, the predetermined temperature range: may bo between the crystallization temperature pod the melting point of the build mate rial, O ther temperature ranges may be used depending on the type of build material. Pre-heating may help reduce the amount of energy that has to be applied by the energy source 226 to cause coalescence and subsequent solidification of build material on which coalescing agent has been delivered or has penetrated. [90099! in some examples, different portions of the layer 402b may be heated to different amounts by the heating elements 232, based on the temperature distribuflbo across the different portions of the layer 482b that was determined in a previous iteration of 303 to 322, For example, more beat may be applied td portions with lower determined temperatures relative to portions with greater determined temperatures; Thus, a generally uniform temperature: distribution may ho achieved after heating, even if the temperature distribution was nomuhiform before heating;

[008100] in some exbmples, if some portions pf the iayor 402b have temperatures that are too high, these portions may be cooled by a suitable cooling mechanism or agent. Thus, temperature regulation of the build materlai may involve the controller 210 causing a temperature regulating; unit, such as a heater or cooling mechanism, to change the temperature of the build materlai,, e.g. one or both of heating and codling, based oh the temperature determined In a previous iteration of 368 to 322, [008191] At 312, as shown in FiG, 4b, a doaiesoing agent 404 may be 'selectively delivered to the surface of the one or mere portions 491 of the layer 402b, As discussed oarller, the agent 404 may be delivered by agent distributor 202, ter example in tea form of fluids such as liquid droplets. Agent 404 may not be delivered to portions 403 and 405.

[000102] The selective delivery of the agent 404 may be performed in patterns on the portions 401 of the layer 402b that the agent delivery control data 208 may define to become solid to form part of the three-dimensional object being generated. “Selective delivery¹’ means that agent may be delivered to selected portions of the surface layer of the build material ih various patterns. The patterns may be defined by the-agerit delivery control data 200.

[000103] FIG. 4c shows coalescing agent 404 having penetrated substantially completely Into the portions 401 of tee layer 402b of build material, but in other examples, the degree of penetration may be less than 100%, The degree of penetration may depend, for example, on tee quantity of agent delivered, on the nature of the build material, on the nature of the agent, etc.

[000104] However, in some examples, coalescing agent 404 may not be delivered, for example if the solidification of build material is achieved using a focused energy source, [000105] At 314, a predetermined level of energy may be temporarily applied to the layer 402b of build material. In various examples, the energy applied may be Infrared or near intra-red energy, microwave energy, ultra-violet (UV) light, halogen light, ultra-sonic energy, or the like. The length Of time the energy is applied foe Or energy exposure time, may be dependent, for example, on one or more of: characteristics of the energy source: characteristics of the build material; and characteristics of the coalescing agent. The type of energy source used may depend on one or more of: characteristics of the build material: and Characteristics of the coalescing agent. In one example, the energy may be applied for a predetermined length ef time, [000100] The temporary application of energy may cause the portions 401 Of the build material to heat up above the melting point ef the build material and to coalesce, in some examples, the eriergy source may be focused. and ebatesbing agent 404 may net have been provided at 312. In other examples, the energy source may he Unfocused, and the temporary application of energy may cause ted portions 401 of the build materia! on which coalescing agent 404 has been delivered or has penetrated to heat up above the melting point of the build material and to coalesce. For example, tee temperature of sortie or all of the layer 492b may achieve about

220 degrees Celsius. Upon cooling, the portion 401 may coalesce may become solid and form part of the three-dimensional object being generated, as shown in FIG. 4d. [000107] As discussed earlier, one such solidified portion 408; may have been generated in a previous iteration. The heat absorbed during the application of energy may propagate to the previously solidified portion 408 to cause part of portion 408 to heat up above Its melting point, This effect helps creates a portion 410 that has strong infertayer bonding between adjacent layers of solidified build materiai, as shown In FIG, 4d, [000108] At 318, an optical property, such as absorbance and/or gloss, of the surface of the portions 401, 403, and 408 of the layer 402b of build material may be measured. In some examples, as discussed earlier, the measurement may be made after dr during applying the energy at 314, The measurement may be made according to any of the techniques described earlier relative to FIGS, 2a-2f, for example using the radiation source 238, 244, and/or 252, add the radiation sensor 228 and/or 254, One measurement may be made for each portion 401, 403, and 405, or muitipie measurements in different regions of each portion 401, 403, and 405 may be made, for example, [880108] The measured optical property may be used at 318 when determining emissivity of portions of build materiai. However, In ether examples, such as if emissivity is determined based on object design data 208 rather than optical properties, then 318 may not be performed.

[000110] At 313, emissivities of each of the portions 401, 403, and 405 may be determined, [000111] In some examples, the emissivities may be determined using the optical property measurements, such as absorbance and/or gloss measurements, made at 318 and the correlations between emissivity and the optical properties determined or stored et 304. For example, for each portion 401, 403; and 405, the· emissivity may be the emissivity value stored in the correlation table or other date object corresponding to the optical property values measured at 316.

[000112] in some examples, the emissivities may be determined using the object design data 203 and the correlations between emissivity and Sofia if Ication determined or stored at 304, For example, for each portion 401, 403, and 405, the emissivity may be the emissivity value stored in the correlation table or other data object corresponding to the Intended degree of sbildlfication defined on the object design date 206 for the respective portion 461, 403, or 405; Thus, for example,, the object design data may· define that the portion 403 was intended to experience a predetermined degree of seiidifieafien, The correlation data or other data object may map that degree of solidification to an emissivity value[080113] Any of the above methods of determining emissivity may be used in combination, and the emissivity determinations using different methods may be averaged or otherwise malbemaiicaliy combined to provide a determination that Is more accurate and more robust to errors.

[080114] At 320, the sensor 229 may capture an Image representing a radiation distribution, such as IR radiation, emitted by each of one or more areas of the layer 402b, for example including portions 401, 403, and 405. As discussed earlier, in other exampies, a series of images may be token fo generate a composite or averaged image representing the radiation distribution.

[080115] At 322, temperatures across the layer 402b may be determined by the controller 210 based on the emissivities determined at 318 and based on the radiation distributions measured af 320, As discussed earlier, the temperature of a portion of build material may depend on the measured IR radiation distribution, and based bn the emissivity. The methods herein may, in some exampies, allow sufficient resolution such that a large number of temperature determinations may fee made each corresponding to a small area of the layer 402b, Thus, each of the areas far which a temperature: may be determined may fee small enough teat if does not contain both solidified and non-solldlfied materia!; Ror example, for each portion 401, 463, arid 485, one or more temperatures may be determined.

[000116] However, in other examples. ifa; single radiation distribution measurement was made for a region spanning solidified and un-sofidified areas, such as portions 461 arid 403, then the determination of the temperature of each of the portions 491 grid 403 may fee determined based on (1) trie determined emissivity, (21 the measured radiation distribution, (3) known relative sizes of the areas; spanned by the portions 481 arid 463, which may be determined based on the object design dele 208 or based on the emissivity measurements or ether sensor measurements, and (4) in seme examples but hot necessarily all examples, the relative difference In heating typically caused In a solidified portion compared do a non-seiidified portion, the controller 218 may be able to determine the temperatures. The above information may be enough tb determine temperatures of each of the solidified portion 401 and non-soiidlfiod portion 403, despite the temperature measurement spanning both portions.

[000117] Although determining temperatures using the method of 316 to 322 is shown as being performed after applying energy at 314, in other examples, 316 to 322 may be performed continually throughoutthe method 300, may be performed at any other time during the method 300; such as between 308 and 310, between 31Q and 812, and/or between 312 and 314.

[000118] After a layer of build material has been processed as described above in 308 to 322, new layers of build material may be provided on top of the previously processed layer of build material, in this way, the previously processed layer of build matonal acts as a support for a subsequent layer pf build material. The process of 308 id 322 may then be repeated to generate a three-dimensional object Sayer by layer.

[000110] Aii of the features disclosed in ibis specification (including any accompanying claims, abstract and drawings), and/or all ot the steps of any method or process so disclosed,: may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[080120] In the foregoing description, numerous details are set forth to provide an understanding of the subject disclosed herein. However, examples may be practiced without some or al! of these details, Other examples may include modifications and variafio-ns from the details discussed above. It Is Intended that the appended claims cover Such modifications and variations.

2?

Claims

t. An additive manufacturing system comprising: a controller to;

determine an emissivity of a portion of a layer of build material based on e measured optical property of the portion, or based on object design data representing a degree of intended solidification of the portion: and determine a temperature of the portion based on the determined emissivity and a measured radiation distribution emitted by the portion.

2. The additive manufacturing system of claim 1 further comprising:

a first radiation sensor to measure the optica! property of the portion; and a second radiation sensor to measure the radiation distribution emitted by the portion, wherein the controller is to:

receive, from the first radiation sensor, data representing the measured optical property:

determine the emissivity of the portion based On the measured optical property: and receive, from the second radiation sensor, data representing the measured radiation distribution omitted by the portion,

3. The additive manufacturing system of claim 2 wherein the optical property Is absorbance,

4. The additive manufacturing system of claim 3 wherein the controller Is to control an agent distributor to selectively deliver coalescing agent to the portion to cause the portion to coalesce when energy is applied by an energy source, wherein coalescing agent is, to absorb unfocused radiation used for measuring the absorbance, the unfocused radiation being received from the energy source or another fcartiafion source.

5. The additive manufacturing system of claim 2 further comprising' an unfocused radiation source to apply unfocused radiation fp the portion, the build material to reflect the unfocused radiation for detection by the first radiation sensor io measure the absorbance of the portion, the unfocused radiation having a substentlaiiy different radiant spectrum than energy applied by an energy source that is to apply energy to cause the portions of the layer to coalesce and subsequently solidify.

6. The additive manufacturing system of claim 2 wherein the optica! property is

7. The additive manufacturing system of claim 6 further comprising a focused radiation source to apply focused radiation to the build material, the build material to refiecf the focused radiation for detection by the radiation sensor to measure the specular reflection or gloss of the build material the focused radiation having a substantially different radiant spectrum than the energy applied by the energy source,

8. The additive manufacturing system of claim 2 further comprising a radiation source to apply pulsed radiation to the build material, the build material to reflect the pulsed radiation for detection by the first radiation sensor such that the detected pulsed radiation when the radiation source is in the on-state is compared by the first radiation sensor or controller with detected background radiation when the radiation source is in the off-state, the comparison used to remove background noise from the measurement of the optica! property.

§> The additive ntonufacluhng system of claim 1 further comprising:

a radiation sensor to measure the radiatiori distribution emitted by the portlori, wherein the coritroiler Is to:

determine the erilisslvity of the poriion based an the object design data; and receive, from the radiation sensor, data representing the measured radiation distribution emitted b v the portion.

10. The additive manufacturing system of claim 1 wherein the oontroiier is to cause a temperature regulating unit io heat or cool the portion based on the determined temperature.

if. The additive manufacturing system of claim 1 wherein a epmputer-readahip medium of the controiier may store a correlation between emissivity of the build material and (1) a value of the optical property of the build material, or (2) a degree of solidification of the build material,

12, The additive manufacturing system of claim 11 wherein the correlation is based on measurements of the build material prior to genera ting a three-dimensionai object,

13, The additive manufacturing system(of claim f wherein the portion may include a solidified portion end an un-solidified portion, wherein determining the emissivity of the portion comprises:

determining a solidified emissivity of the solidified portion based oh a measured optical property of the solidified portion, or based on object design data representing that the solidified portion is to be solidified; and determining an un-soSidified emissivity of the umsolidlfled portion based on a measured optical property of the un-solidified portion, or based bn object design data representing that the non-solidified portion Is not to he solidified, wherein the temperature of the portion is determined further based on relative sizes of the solidified portion and the non-soildifsed portion.

14, A nph-ffahsltory computer readable storage medlutn including executable instructions that,: when executed by a processor, cause the processor te:

receive data representing the measured radiation distribution emitted by a portion ofa layer of build material:

determine an emissivity of the portion based on a measured absorbance of the portion, based on Pleasured giosS of the portion, or based on object design data representing a degree of intended solidification of the portion; and determine a temperature of the portion based bp the determined emissivity and a measured radiation distribution emitted by the portion.

3«

15, A method of determining temperature of build material io an additive manufeoturlng system, the method comprising:

measure, by a radiation sensor, infra-red energy emitted fey a layer of the build materia!;

measure an opflcsi property of the portion, or determine object design data representing a degree of intended seildiiieation of the portion;

determine an emissivity of a portion of a layer of build material based ona measured optica! property or the object design data; and determine the temperature of the portion based on the determined emissivity and a measured infra-red energy.

Examiner:

Date of search:

gsTjt·*

Intellectual

Property

Office

Application No: Claims searched:

GB 1809984.6 1-15

Miss Evelyn Toalster 25 July 2018

Patents Act 1977: Search Report under Section 17

Documents considered to be relevant:

Category Relevant to claims Identity of document and passage or figure of particular relevance X 1, 7-15 US2009/0152771 Al (PHILIPPI JOCHEN et al.) Paragraphs 0010-0019, 0025, 0029, claims 11-19. X 1-2, 6-8, 10-12, 1415 US5156461 A (MOSLEHI MEHRDAD M et al.) Column 2 line 66 - column 3 line 2, column 4 lines 6-33, column 7 lines 43-59, column 15 line 57 - column 16 line 11. X 1-3, 1012, 14-15 US4956538 A (MOSLEHI MEHRDAD M ) Column 5 line 57 - column 6 line 2, column 6 line 43 - column 7 line 35, column 2 lines 14-30, 50-61, column 3 lines 26-50. X 1-2, 9, 1112, 14-15 US2010/0256945 Al (MURATA RONALD N) Paragraphs 0010, 0027, 0035, 0039, 0049, figure 4, claim 1.

Categories:

X Document indicating lack of novelty or inventive step A Document indicating technological background and/or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.

Field of Search:

Search of GB, EP, WO & US patent documents classified in the following areas of the UKC^X :

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

International Classification:

Intellectual

Property

Office

Subclass Subgroup Valid From B29C 0064/364 01/01/2017 B29C 0064/386 01/01/2017 B33Y 0040/00 01/01/2015 B33Y 0050/02 01/01/2015 G01J 0005/00 01/01/2006 G01N 0021/57 01/01/2006

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo