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Title:
DEFECT DETECTION
Document Type and Number:
WIPO Patent Application WO/2017/178049
Kind Code:
A1
Abstract:
A defect detection apparatus is provided for detecting defects in a barrier of an imaging device or a three-dimensional printer. The barrier defect detection apparatus comprises a barrier housing to receive a barrier, the barrier comprising a material through which electromagnetic radiation is transmissible and being arranged to provide protection for at least one component of the imaging device. A barrier defect detector is provided, comprising an emitter to emit electromagnetic radiation towards the barrier and a detector to detect electromagnetic radiation received via a predicted path from the barrier. The barrier defect detector has an output port to provide a signal to a controller, which determines if the barrier is defective depending upon a detected level of electromagnetic radiation indicated by the received signal. A corresponding method and machine readable instructions are provided.

Inventors:
BLANCH, Jordi (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
COMAS, Esteve (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
VICENTE, Granados (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
CANO, Emilio Carlos (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
Application Number:
EP2016/058154
Publication Date:
October 19, 2017
Filing Date:
April 13, 2016
Export Citation:
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Assignee:
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P., (11445 Compaq Center Drive West, Houston, Texas, 77070, US)
BLANCH, Jordi (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
COMAS, Esteve (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
VICENTE, Granados (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
CANO, Emilio Carlos (Cami de Can Graells, 1-21, Sant Cugat del Valles, 08174, ES)
International Classes:
H04N1/00; B33Y30/00; G01N21/958
Foreign References:
US20100173096A12010-07-08
EP2572865A12013-03-27
EP2960643A12015-12-30
DE102012112080B32014-03-13
Other References:
None
Attorney, Agent or Firm:
KESTON, Susan (HGF Limited, 50 West Nile Street, Glasgow Strathclyde G1 2NP, G1 2NP, GB)
Download PDF:
Claims:
CLAIMS

1 . A defect detection apparatus for detecting defects in a barrier of an imaging device, the apparatus comprising:

a barrier housing to receive a barrier, the barrier comprising a material through which electromagnetic radiation is transmissible and arranged to provide protection for at least one component of the imaging device;

a barrier defect detector comprising an emitter to emit electromagnetic radiation towards the barrier and a detector to detect electromagnetic radiation received via a predicted path from the barrier;

wherein the barrier defect detector comprises an output port to provide a signal to a controller, the controller to determine the barrier is defective depending upon a detected level of electromagnetic radiation indicated by the received signal.

2. Defect detection apparatus of claim 1 , wherein the imaging device is a two- dimensional printer to create an image by printing or a three-dimensional printer to create an object or a scanner to capture an image by two-dimensional or three dimensional scanning.

3. Defect detection apparatus of claim 1 , wherein at least one of the emitter and the detector are situated within the barrier defect detection apparatus at a predetermined distance from a plane coinciding with a location of the barrier.

4. Defect detection apparatus of claim 1 , wherein the barrier defect detector comprises at least one light emitter and a plurality of light detectors to detect light energy received via a plurality of different respective predicted light paths via the barrier.

5. Defect detection apparatus of claim 4, comprising an equal number of emitters and detectors and wherein at least two of the plurality of emitter and detector pairs are arranged to direct the electromagnetic radiation through the barrier between two differently oriented pairs of edges of the barrier.

6. Defect detection apparatus of claim 1 , comprising at least one reflector to reflect the emitted electromagnetic energy such that the predicted path comprises a plurality of transits of the barrier, the electromagnetic energy being detected by the detector after passing via the at least one reflector.

7. A printer or a scanner comprising the defect detection apparatus of claim 1 and the controller of claim 1.

8. The printer or the scanner of claim 7, wherein the controller is arranged to suspend an imaging operation being performed when it determines that the barrier is defective.

9. A method of detecting a defect in a barrier of an imaging device, the barrier comprising a material through which electromagnetic radiation is transmissible and arranged to provide protection for at least one component of the imaging device, the method comprising:

emitting electromagnetic radiation towards the barrier;

detecting electromagnetic radiation received via a predicted path from the barrier; and

outputting a signal depending upon the detected electromagnetic radiation to a controller;

wherein the signal is used by the controller to determine if the barrier is defective and to suspend operation of at least one component of the imaging device if the controller determines that the barrier is defective.

10. Machine executable instructions stored on a transient or non-transient machine readable medium, the instructions being operable upon execution by one or more processors to perform the method of claim 9.

1 1 . A shielding element housing for an apparatus for generating a three- dimensional object, the shielding element housing comprising:

a shielding element interface to receive a shielding element, the shielding element to provide protection for at least a portion of the apparatus;

a shielding element defect detector comprising an emitter to emit electromagnetic energy to the shielding element and a detector to detect electromagnetic energy received via a predicted transmission path from the shielding element; wherein the shielding element defect detector comprises an output port to output to a controller of the apparatus, a signal depending upon the detected electromagnetic energy and wherein the controller is arranged to control the apparatus to suspend generation of the three-dimensional object depending upon the signal from the output port.

12. The shielding element housing of claim 1 1 , wherein the shielding element housing comprises at least one reflector to reflect the emitted electromagnetic energy through the shielding element to cause the transmission path to traverse the shielding element a plurality of times via non-coincident trajectories to arrive at the detector.

13. An energy directing unit comprising the shielding element housing of claim 1 1 , wherein the energy directing unit has an interface to receive at least one removably insertable energy generating element to direct energy to a build material for forming the three-dimensional object and wherein the shielding element is arranged to protect the at least one energy generating element from build material during generation of the three dimensional object.

14. The energy directing unit of claim 13, wherein at least one of the emitter and the detector are displaced by at least a predetermined distance from a plane of the shielding element.

15. Apparatus for generating a three dimensional object, comprising the shielding element housing of claim 1 1 .

Description:
DEFECT DETECTION

BACKGROUND

Imaging devices, such as two-dimensional (2D) printers, three-dimensional (3D) printers (or additive manufacturing systems) and 2D and 3D scanners are electronic devices that are in widespread use and the reliability of these devices is desirable to users, with maintenance being an overhead of operation. Some scanners and printers may involve the use of hazardous or flammable chemical agents, or may use environments set apart from the atmosphere. For example, a Selective Laser Sintering (SLS) 3D printer may build up a 3D object layer by layer using a laser to selectively melt a powder on a powder bed in a build chamber filled with an inert gas to prevent oxidation of the melting powder via atmospheric air. The powder form of the build material used in 3D printers should be kept within a temperature range that may conflict with temperatures characteristic of some functional elements of some printing systems.

BRIEF INTRODUCTION OF THE DRAWINGS

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

Figure 1 schematically illustrates an example of a defect detection apparatus for use in an imaging apparatus;

Figure 2 schematically illustrates a 3D printer having an energy directing unit incorporating a shielding element defect detector according to one example;

Figure 3 schematically illustrates a view of one of the energy directing units of the 3D printer of the example of Figure 2;

Figure 4 schematically illustrates an alternative example view of an energy-directing unit relative to the view illustrated in Figure 3;

Figure 5 schematically illustrates an example defect detection apparatus in which a barrier is provided to contain an inert gas;

Figure 6 schematically illustrates a first example of a defect being detected by the defect detection apparatus;

Figure 7a schematically illustrates a second example of a defect being detected by the defect detection apparatus;

Figure 7b schematically illustrates a third example of a defect being detected by the defect detection apparatus; Figure 8 schematically illustrates a fourth example configuration of the defect detection system, showing an emitter and detector arrangement for detecting defects in a barrier;

Figure 9 is a flowchart schematically illustrating an example of a process of detecting a defect in a barrier using the defect detector apparatus in an electronic device;

Figure 10a schematically illustrates empirical results of directing a 1000 milliWatt (mW) green laser light through an edge of a non-laminated glass barrier having no defects; and

Figure 10b schematically illustrates empirical results of the same 1000mW green laser as in the example of Figure 10a being directed through a barrier having a defect.

DETAILED DESCRIPTION

Figure 1 schematically illustrates an example of a defect detection apparatus 100 for use in an imaging apparatus. The imaging apparatus may be, for example, a two-dimensional (2D) printer for creating an image through 2D printing, a three-dimensional (3D) printer (additive manufacturing device) or a 2D or 3D scanner for capturing an image through scanning. In some examples, the defect detection apparatus 100 may be used in a 3D printer such as a Selective Laser Sintering (SLS) 3D printer or a 3D printer that forms a 3D object by selectively fusing portions of successive layers of a build material via application of energy to the layers.

The defect detection apparatus 100 comprises a barrier housing 1 10, a barrier defect detector comprising an emitter 120, a detector 130 and an output port 140. The barrier housing 1 10 holds a barrier (or "shielding element") 150 comprising a material that allows the transmission of electromagnetic (EM) radiation. For example, the barrier may be laminated or non-laminated glass, quartz, soda-lime glass, quartz glass, borosilicate glass, alumina-silicate, ceramic glass, sapphire glass, magnesium fluoride glass, calcium fluoride glass or any other material that is transmissible to the EM energy that the emitter 120 is emitting. The emitter 120 may emit, for example, red laser light or green laser light or infrared light. The barrier 150 may be fixed, or may be removably insertable from the barrier housing 1 10 in order to allow for easier replacement of the barrier in case the barrier should break. The barrier 150 functions to protect at least one component of the imaging device in which it is installed. The imaging device can be at least one of a 2D printer, a 3D printer (additive manufacturing device), a 2D scanner and a 3D scanner. An interface 1 12 in the barrier housing 1 10 comprises a groove or the like for receiving and, in some examples, the barrier may be removably retained. The barrier 150 may have a flat smooth finish, for example a polished finish, at least on an edge where the EM energy is intended to enter the barrier 150 and on an edge where the EM energy is intended to leave the barrier 150. A granulated finish at a point of entry and/or exit of the barrier 150 could result in EM energy being absorbed, whereas a smooth finish should promote good transmission of EM energy through the barrier 150.

In a device such as a printer or scanner, for example, the barrier 150 may protect components of the device such as protecting a heating element or laser from damage from printing liquid or three-dimensional object build material. In some examples, the barrier 150 may be positioned in the device as a safety measure, or to protect the components from damage. For example, the barrier 150 may be used to contain an inert gas within a sealed chamber in the printer/scanner. Alternatively, the barrier 150 may provide thermal shock resistance against the energy of an energy source used to heat build material in a 3D printer and/or to prevent contact between particulate matter corresponding to the build material in a deposition region of the 3D printer and one or more lamps being used as an energy source to fuse the build material. Any damage to or breakage in the barrier 150 may compromise its ability to prevent such events.

The barrier defect detector may detect defects such as scratches, cracks, holes or breakages in the barrier 150. The emitter 120 emits EM radiation (energy) through the barrier 150 such that when the barrier is intact, the EM radiation is expected to follow a predicted path from the emitter 120 to the detector 130, for example by reflection from a surface of the barrier or transmission through the material of the barrier. In this example the EM radiation is visible light, which is refracted and/or reflected through the body of the barrier 150 from one edge to an opposite edge. The EM radiation traverses the barrier 150 and exits the barrier 150 at the detector 130, which is positioned to receive the EM radiation based on the predicted path of the EM radiation. In alternative examples the EM radiation could pass across a surface of the barrier by reflection without necessarily passing through the barrier and emerging from it prior to detection. Thus a predicted transmission path via the shielding element may be, for example, a reflected path such as a single or multi-stage reflected path from a surface of the shielding element or a single or multi-stage path through the material of the shielding element, such as a refracted path. The output port 140 transmits a signal 160 to a controller 170. In some examples, the controller 170 is a component of the barrier defect detector, although this is not necessarily the case. In some examples, the signal 160 includes information on the detected EM radiation, such as an intensity or energy value or the like. The EM radiation may be, for example, visible light, infra-red radiation or ultra-violet radiation. In one example the barrier 150 is made from silicon (silicium) or germanium and is transmissible principally to EM radiation corresponding to far infra-red wavelengths.

The controller 170 comprises a comparator 180 and one or more processor(s). The comparator 180 compares the information from the signal 160 with information regarding the emitted EM radiation. In some examples, the emitter 120 is controlled by the controller 170. If, for example, the energy of the detected EM radiation is less than the energy of the emitted EM radiation by a magnitude of more than a predetermined threshold, the controller 170 may determine that the barrier 150 is defective. In some cases, the controller 170 may trigger suspend circuitry 190, which causes the device, or at least one component thereof, to suspend its operation when it is determined by the controller 170 that the barrier 150 is defective. In an alternative example, the comparator 180 may be provided as part of the barrier defect detector, in which case the signal 160 from the output port 140 may comprise an indication of a difference between emitted and detected EM energy for processing by the controller 170.

In some examples, the controller 170 is coupled to a memory unit 195, where computer program instructions may be stored for controlling the EM emission and detection process and for suspending a scanning or printing operation in the event that it is determined that the barrier 150 is damaged or impaired to the extent that its function is potentially compromised.

Processing circuitry or circuitry such as the circuitry implemented in the controller 170 and the suspend circuitry 190 of the example of Figure 1 may be general purpose processor circuitry configured by program code to perform specified processing functions or special purpose processing circuitry for implementing the corresponding function by modification to the processing hardware. Configuration of the circuitry to perform a specified function may be entirely in hardware, entirely in software or using a combination of hardware modification and software execution. Program instructions may be used to configure logic gates of general purpose or special-purpose processing circuitry to perform a processing function. Program instructions may be provided on a non-transitory medium or via a transitory medium. The transitory medium may be a transmission medium.

Processing hardware may comprise, for example, one or more processors, very large scale integration (VLSI) circuits or field programmable gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. The processing hardware of the controller 170 may comprise a storage medium readable by the processor, including volatile and non-volatile memory and/or storage elements. The volatile and non-volatile memory and/or storage elements may be a random access memory (RAM), erasable programmable read-only memory (EPROM), flash drive, optical drive, magnetic hard drive, or other medium for storing electronic data.

Program code or machine-readable program instructions for performing the defect detection of the barrier 150 may be implemented in a high level procedural or object- oriented programming language. However, the code may be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language, and combined with hardware implementation.

Figure 2 schematically illustrates a 3D printer (an example of an imaging device) having an energy directing unit incorporating a shielding element defect detector according to one example. The 3D printer 200 comprises: a working area 202 where a three-dimensional object is generated; a build material depositor carriage 210 comprising a build-material coater 212 flanked on either side by a pair of energy directing units 214a, 214b; and a detailing/fusing carriage 220 for distributing a detailing agent and a fusing agent onto respective layers of the build material in the working area 202. The detailing/fusing carriage 220 in this example is arranged to traverse the working area 202 between a position 222 and a position 224 and may distribute the detailing and fusing agents using an array of a plurality of jets or nozzles. The build material depositor carriage 210 is arranged in this example to traverse the working area between a top position 232 and a bottom position 234, as shown.

Production (manufacturing) of a 3D object by the 3D printer 200 depends on object- specifying data specifying a 3D shape of the object and also object property data such as strength or roughness corresponding to the whole object or part(s) of the 3D object. The desired 3D object properties may be supplied to the 3D printer via a user interface, via a software driver or via predetermined object property data stored in memory 195, for example.

Production of a 3D object is performed using the 3D printer 200 by the build material depositor carriage 210 laying down a layer of build material in the working area 202 by passing between the top position 232 and the bottom position 234. After a layer of the build material has been deposited, the detailing/fusing carriage 220 traverses the working area once between positions 222 and 224 and selectively deposits a fusing agent in areas or positions where particles of the build material are to fuse together. A detailing agent may also be selectively applied where the fusing action is to be reduced or amplified. Different detailing agents may be used for fusing and for amplification. For example, the detailing agent may be selectively applied in a pattern relative to the fusing agent such that it reduces fusing at a boundary between build material in an area to be fused and build material not to be fused, which can create sharp smooth edges. Once the detailing agent and the fusing agent have been applied, the build material depositor carriage 210 traverses the work area and at least one of the energy directing units exposes a layer of the deposited build material to fusing energy using one or more heating elements in the respective energy directing unit 214a, 214b. The build material depositor carriage 210 may combine the build material deposition and the fusing energy application in a continuous pass from top to bottom or from bottom to top between positions 232 and 234. A selected one of the pair of energy directing units 214a, 214b may be applied depending upon the direction of travel of the build material depositor carriage 210 across the working area 202. The deposition, fusing/detailing agent and fusing energy application process may be repeated in successive layers until a complete 3D object has been generated. The two carriages 210, 220 may change direction between the application of each layer. This process can operate efficiently by using multiple printhead jets/nozzles to simultaneously apply the fusing and detailing agents to the build material.

Each of the energy directing units 214a, 214b of the 3D printer 200 comprises a shielding element (or a barrier) to protect one or more printer components during the 3D printing process. For example, the shielding element may protect an energy generating element that is used to direct fusing energy on the build material against damage from particulate matter rising up towards the energy directing unit 214a, 214b as it traverses the working area 202 and may also provide a shield between a high temperature (e.g. around 300°C) at and close to a surface of the energy directing element and any accumulation of build material in the working area 202. Characteristics of the build material, the heating and the fusion systems in the 3D printer 200 could potentially give rise to undesirable conditions without a shielding element to separate the hot energy generating element(s) of the energy directing unit 214a, 214b from particles of build material in the work area 202. Thus the shielding element may provide segregation between some portions of the printer arranged to run at a first temperature range, and other portions arranged to run at a second temperature range. The build material may be, for example, polyamide powder and the energy generating element(s) may be, for example, halogen lamps which generate short wave infrared energy.

It is desirable to keep a surface temperature of halogen lamps at a high temperature such as around 300°C because this is known to extend the expected lamp life by reducing an undesirable "blackening effect" that may occur as a result of condensation of halogen lamp filament vapours. However, it may be better to keep build materials such as polyamide powder at a temperature below 240°C when in a cloud state. A cloud state of the build material may be created during the 3D printing process.

Furthermore, the build material may melt at a temperature lower than the chosen operating surface temperature of the halogen lamps (e.g. melting point of around 180- 190°C), which means that, in the absence of a shielding element, or in the event of damage to or failure of the shielding element, particulate matter from build material in the working area of the 3D printer 200 could impinge upon the halogen lamp(s) and cause damage to the 3D printer by melting on them. This could result in interrupted production and even perhaps the need to replace one or more of the halogen lamps.

Figure 3 schematically illustrates a view of one of the energy directing units 214a of the 3D printer 200 of Figure 2. The energy directing unit 214a comprises: a shielding element housing 310 having a shielding element interface 316 to receive a shielding element 318; a first energy generating element 312; a second energy generating element 314; an emitter 342 and a detector 344 of EM energy. In this example, the shielding element is made of non-laminated quartz glass and is removably insertable in the shielding element interface 316 by provision of a shield element receiving groove (not shown) in the shielding element housing 310. In alternative examples the shielding element may be fixed in the interface 316. The first and second energy generating elements 312, 314 direct heating and/or fusing energy down onto the working area 202 where a 3D object 352 is being generated.

The energy generating elements 312, 314 may be halogen lamps arranged to direct infrared energy down onto a layer of the build material to heat (melt) the powder. The halogen lamps 312, 314 are directional but where non-directional halogen lamps are provided to emit energy at 360°, an inner surface 302 of the shielding element housing 310 may be at least partially covered by a reflective material to guide the lamp energy down towards the working area 202. The surfaces of the halogen lamps 312, 314 are at a higher temperature than a desired temperature range of a build material cloud 350 to in a deposition area of the 3D printer. However, the shielding element 318 protects the 3D printer or at least one device component by separating the high temperature lamp surfaces from any build material cloud. To reduce a temperature close to the shielding element 318, one or more cooling fans (not shown) may be provided within a chamber formed by the shielding element housing 310 and the shielding element 318. Damage to the shielding element 318 can arise, for example, due to one of the following reasons:

• Hidden imperfections and internal stresses arising within the material of the shielding element 318.

• As a result of temperature variations caused by the halogen lamps 312, 314 and any associated cooling mechanism (e.g. cooling fan within housing 310 cavity).

• Heating of the shielding element 318 to the point of cracking/breaking due to absorption increases that can arise due to: scratches made during a cleaning process and/or hot spot(s) created by build material (e.g. polymer powder) accumulation giving rise to differential thermal expansion; and/or fingerprints on the shielding element; and/or 3D print process chemicals such as an enhancer agent aerosol.

The emitter 342 and the detector 344 provide a defect detection mechanism to dynamically check for any defects in the shielding element 318 during functional operation of the 3D printing device. The emitter 342 and detector 344 may be controlled by the controller 170 of Figure 1 to monitor continuously for damage to the shielding element 318 whilst the device is switched on, or may monitor periodically or intermittently, for example. In the Figure 3 arrangement, the emitter 342 and the detector 344 are both situated substantially in the same plane as the shielding element 318, which has a length, a width and a finite thickness. This means that EM radiation such as visible light can be emitted through one edge of the shielding element 318 and can be predicted, when the shielding element 318 is undamaged, to follow a straight path through the shielding element 318 emerging at substantially the same displacement along the opposite edge of the shielding element relative to where the emitter 342 emitted the light. In alternative examples, EM radiation may be incident on the edge of the shielding element away from a normal to the edge and may be refracted by the shielding element such that it is predicted to follow a path such that it emerges at a different angle and/or at a different displacement along the opposite edge of the shielding element.

The controller 170 (see Figure 1 ) is programmed or arranged to detect any difference between the emitted EM radiation and the detected EM radiation and to determine whether or not that difference is indicative of a defect being present in the shielding element 318. Since the position of the emitter 342 and detector 344 may be effective at detecting smaller defects confined to a region of the shielding element 318 close to the predicted path of the EM radiation from emitter 342 to detector 344, a plurality of paths though the shielding element 318 may be probed by allowing for translation of the emitter 342 and/or the detector 344 or by providing a plurality of emitters and/or detectors in different positions such as along different edges of the shielding element 318.

In an alternative example, the energy directing unit 214a of Figure 3 may be implemented in a 2D printer that uses a printing fluid such as a solvent or water-based ink or a latex ink to produce a 2D image. The 2D printer may use, for example thermal printheads or piezo printheads. In this case the lamps 312, 314 may be infrared lamps used to dry latex ink or other printing fluid(s) and the shielding element 318 may serve to avoid damaged parts inside the printer.

In yet further alternative examples, the shielding element 318 may be a viewing window in the printer or scanner, such as a transparent plastic window allowing the viewer to see inside the device, but also providing protection to parts inside the device from being touched or damaged. The emitter 342 and detector 344 of the defect detector system may be used to monitor for any damage to the viewing window and the controller 170 may send a message to a front panel of the device to alert a user to the detected defect as an alternative or in addition to suspending operation of at least one component of the imaging device. A defect such as a scratch, crack or breakage of a barrier such as a viewing window may be detected for user safety reasons, with a warning being sent to a control panel of the device. The barrier defect detection apparatus may be implemented to take account of user safety. For example, a user could be hurt as a result of a crack in a glass barrier.

Figure 4 schematically illustrates an alternative example cross-section of an energy- directing unit relative to the view illustrated in Figure 3. The energy directing unit comprises: a barrier housing 410; first and second lamps 412, 414; a shielding element 418; an emitter 442; a detector 444; an emitter waveguide 462; and a detector waveguide 464. In the arrangement of Figure 3, the emitter 342 and the detector 344 are situated within the barrier defect detection apparatus substantially in the same plane as that corresponding to the shielding element 318, which we shall refer to as the x-y plane. By way of contrast, in the example of Figure 4, the emitter 442 and the detector 444 are displaced by at least a predetermined distance along the z axis, away from the x-y plane of the shielding element 318. This may be desirable, for example, when the plane of the shielding element 318 corresponds to a region where the detector 342 and/or emitter 344 could be exposed to undesirable over-heating due to the action of the lamps 412, 414. In the example of Figure 4, the detector 442 and the emitter 444 are conveniently arranged in respective channels within the walls of the barrier housing 410 and the waveguides 462, 464 are located such that they provide a channel from the emitter to an edge of the shielding element 418 through which the EM radiation is to be emitted and a channel from where the EM radiation emerges from the shielding element 464 directing the EM radiation to the detector 444. In alternative examples, one or both waveguides 462, 464 may be replaced by different optical components such as a mirror and lens combination to direct emitted EM radiation to a desired position where it should enter the shielding element 318 and to direct EM radiation emerging from the shielding element 318 to the displaced detector 444. The controller 170 may be arranged to compensate for any loss in intensity/energy of the detected radiation arising after it has emerged from the shielding mechanism to distinguish any such loss from a loss arising from a defect or breakage of the shielding element 418. Figure 4 also schematically illustrates a cloud 450 of particulate matter corresponding to a build material in a deposition area 454 of a 3D printer. In this example, the shielding element 418 protects against the particulate matter from damaging the heating elements 412 and 414 by settling on their hot surfaces and melting on them. It also allows for some thermal isolation, for example by fan-based cooling within the cavity 416, between the cloud 450 and heat generated by the lamps 412, 414.

Figure 5 schematically illustrates an example defect detection apparatus 500 for an imaging device in which a barrier 510 is provided in a barrier housing 520 to contain an environment filled with an inert gas cloud 530. The inert gas may be, for example, nitrogen and/or argon or another noble gas. For example in an SLS 3D printer, the inert gas environment may be used to shield the melting powder from oxygen contamination and to better maintain the temperature during the process specific to the melting point of the powdered build material of choice. If the barrier 510 should become damaged, this could result in the sealed environment within the housing 520 being breached, allowing oxygen from the atmosphere to ingress. This may result in reduced efficiency in the printing process due to oxidation of the build material powder and/or undesirable variations in temperature within the working region of the device. Accordingly, a barrier defect detection apparatus comprising an emitter 542 and detector 544 is provided so that emission of EM radiation through or onto the barrier 510 and detection of EM radiation emerging from that barrier may be used to dynamically detect any barrier defects and to conditionally suspend operation of the device or at least one component of the device, at least temporarily, when a defect is detected. Figure 6 schematically illustrates a first example of a defect being detected by the defect detection apparatus.

Barrier 650 is shown in a top view in Figure 6. A crack 610 is present in the barrier 650 as an example of a defect. Other defects may be scratches, fractures, breakages, bubbles, or the like. In some examples, barrier 650 may be considered similar to barrier 150 introduced in Figure 1 . The barrier 650 has a length, along an x-axis, a width, along a y- axis and a thickness, along a z-axis. The view shown in Figure 6 is a slice along one value of the z-axis.

The emitter 620 emits EM radiation, illustrated by emitted EM radiation waveform 660. In some examples, the emitted EM radiation waveform 660 enters the material of the barrier 650 and propagates through the thickness of the barrier 650, toward the opposite side of the barrier 650. In some examples, the emitted EM radiation 660 may propagate toward an adjacent side or face instead of an opposite side or face of the barrier 650. The emitted EM radiation 660 propagates substantially uniformly across the barrier until it reaches the crack 610, at which point some of the EM radiation reflects and/or refracts, illustrated by reflection and refraction lines 680. The remaining EM radiation 670 continues to propagate across the barrier 650, towards the detector 630. The detector 630 then detects the remaining EM radiation 670.

The reflection and/or refraction of EM radiation generally results in a reduction in energy, meaning the energy of the remaining EM radiation 670 is less than the energy of the emitted EM radiation 660. For example, experiments with barriers of a particular material and given a particular EM radiation used in the emitter can be used to determine a predetermined magnitude difference between emitted energy and detected energy likely to be associated with a barrier defect. It may also be possible to determine the degree of the severity of the defect depending upon, for example, the magnitude of a difference between the emitted and the detected energies. Other EM radiation characteristics may also be reduced in the detected values, such as intensity or the like. The reduction in amplitude shown in Figure 6 is merely a schematic visual representation of the loss of energy or intensity or the like, and is not intended to be limiting. Although the EM radiation in this example is shown to be transmitted at a point along the z axis of the barrier 650, in alternative examples the EM radiation maybe transmitted through ay one of the plurality of faces or edges of the barrier 650 or may be reflected one or more times from one or more faces and/or edges between emission and detection. Figure 7a schematically illustrates a second example of a defect being detected by the defect detection apparatus. Similarly to the Figure 6 example, there is a crack 705 through a barrier 710. In this example an emitter 720 and a detector 740 are arranged along the same edge of the barrier 710 and a mirror 730 is provided at an opposite edge of the barrier 710 to reflect light incident from the emitter 720 via the material of the barrier 710, back to the detector 740. In alternative examples a plurality of mirrors may be provided. In the Figure 7a example emitted EM radiation 722 is reflected and/or refracted and/or scattered at a first point 714 where it encounters the crack 705, but an undeflected portion 724 of the incident EM waveform arrives at the mirror 730 having reduced energy (e.g. reduced amplitude) and is scattered and/or refracted and/or reflected again at a point 712 of the crack 705 on its return path to the detector 740. Thus the EM radiation, which is already diminished in energy along path 726 upon leaving the mirror, is further diminished when an undeflected portion 728 emerges from point 712 back towards the detector as waveform 728. An arrangement such as that of Figure 7a may provide better coverage of the barrier 710 to detect localised cracks because the predicted path of the EM radiation spans more of the barrier 710 than it would without the mirror 730 being present.

Figure 7b schematically illustrates a third example of a defect being detected by the defect detection apparatus. In this example, even more coverage of the barrier 710 is achieved than in the arrangement of Figure 6 or Figure 7a, by providing a first mirror 732 at the opposite edge of a barrier 710 from the emitter and a second mirror 734 on the same edge of the barrier 710 as the emitter 720. In this example, the detector 740 is arranged to detect EM radiation emerging from the barrier 710 at the opposite edge from where the emitter 720 emits the EM radiation. Each successive encounter of the crack results in a further reduction in the energy of the EM radiation along the path predicted when assuming an intact barrier 710.

Figure 8 schematically illustrates a fourth example configuration of the defect detection system, showing an emitter and detector arrangement for detecting defects in a barrier 810. Some barrier defects may comprise a crack spanning the barrier from end to end as illustrated in Figure 7a and Figure 7b. However, some cracks may be less extensive, for example, shorter in length and thus localised to a certain area of the barrier. The same is true of small holes, pits or scratches in the barrier, which are different types of defects. Better coverage of more of the barrier to detect defects may be achieved by providing a plurality of stages of reflected EM radiation using mirrors as illustrated in Figure 7b. Alternatively, more of the area of the barrier may be probed by providing a plurality of non- overlapping EM radiation predicted trajectories through the barrier or onto the barrier (via reflection) using a plurality of pairs of emitter and detector at different positions of the barrier. Alternatively, the ability to rotate and/or translate a single emitter and/or detector may serve the same purpose. In the arrangement of Figure 8, two emitters 812, 814 are arranged at different points along an x-axis of the barrier 810 and two corresponding detectors 822, 824 are arranged at opposite edges of the barrier 810. Three emitters 832, 834, 836 are arranged along a y-axis of the barrier 810 of Figure 8 and a respective plurality of three detectors 842, 844, 846 is arranged at corresponding positions at the opposite edge of the barrier 810 according to a predicted trajectory, the predicted trajectory being plotted assuming that the barrier 810 is undamaged. In alternative arrangements a single emitter on a given axis may be arranged to rotate, for example via program instructions executing on the controller 170 (see Figure 1 ) to selectively emit EM radiation to one of a plurality of detector positions at the opposite end of the barrier 810. A beam splitter may also be used in some examples to provide multiple beams or waveforms from a single emitter.

An example of a process of detecting a defect in a barrier using the defect detector apparatus is schematically illustrated in the flowchart of Figure 9.

In process element S901 , EM radiation is emitted by the emitter 120 (see Figure 1 ) toward the barrier 150. The EM radiation may be, for example, visible light, infrared radiation, UV light, or the like. Under the assumption that the barrier 150 is free of defects such as cracks, scratches, bubbles or the like, the path of the EM radiation through the barrier 150 may be predicted. The detector 130 is positioned such that the EM radiation leaving the barrier 150 is detected. In some examples, the detector 130 may be positioned directly adjacent to the barrier 150, although this is not necessarily the case. In some examples, the detector 130 may be positioned elsewhere, and other systems such as waveguides, mirrors and/or lenses are used to direct the EM radiation towards the detector 130 from the barrier 150. In some examples, there may be more than one detector 130, and/or more than one emitter 120.

The EM radiation is detected by the detector 130 after it emerges from the barrier 150 at process element S903. Signal 160 is then output to the controller 170 in process element S905, containing information regarding the EM radiation detected in process element S903. The information in the signal 160 may, for example, relate to the detected EM radiation's energy, intensity or the like. The information transmitted in signal 160 may be used to determine whether or not the barrier 150 is damaged. The presence of scratches, breakages, cracks, bubbles, or the like may impact on the effectiveness of the barrier 150 in providing safety or preventing damage to components of the imaging device such as 3D printer, for example. Process element S907 determines whether the information regarding the detecting EM radiation suggests that a defect may be present. This may be done, for example, by comparing an energy value of the emitted EM radiation to the energy value of the detected EM radiation. In this case, a loss of energy between the emission of the EM radiation and the detection of the EM radiation may indicate that unexpected scattering of EM radiation has taken place, suggesting an imperfection or defect in the barrier 150. Other information may be used to make this determination, such as intensity or the like.

In the event that the controller 170 detects a defect in the barrier 150, the operation of at least one component of the imaging device may be suspended, as shown in process element S91 1 . In some examples, a warning is provided to user(s), which may be visual, audible or the like. In some examples, further safety measures may be triggered.

If the controller 170 does not detect a defect, process element S909 is followed, in which normal functional operation of the device is continued. In some examples, the process may immediately repeat, such that the defect detection system is constantly monitoring for defects, the process may be scheduled to occur at certain times or under certain conditions, or arranged to be performed as specified by a user.

Figure 10a schematically illustrates empirical results of directing a 1000 milliWatt (mW) green laser light through an edge of a non-laminated glass barrier having no defects. The image has been inverted so that the light beam appears as a dark line. The light enters the barrier 1050 at point 1010 and emerges at point 1020 at an opposite end having followed a straight predicted trajectory 1012 through the medium of the barrier 1050. The same effect is achievable by translating the emitter (not shown) along a y-axis

corresponding to a left-hand edge of the barrier as illustrated.

Figure 10b schematically illustrates empirical results of the same 1000mW green laser as in the example of Figure 10a being directed through a barrier 1 150 having a crack 1 154 spanning from top to bottom. Similarly to Figure 10a, the image has been inverted so that dark shading corresponds to light shining and a dark lines correspond to the laser light beam. Laser light enters the barrier 1 150 at point 1 162 on the left hand edge and exits the barrier at point 1 164 on the right-hand edge. At point 1 164 a light spot (a dark spot in the inverted image) is visible as a result of the crack 1 154, which diverts the laser beam from a straight path. In this case some of the laser light is reflected or scattered along path 1 152 back towards the barrier edge where the emitter is situated upon encountering the crack 1 154 so that a portion of the laser beam emerging at a detector position

corresponding to a predicted path has less energy than the known emitted laser energy. In this example, the crack 1 154 has absorbed part of the light beam energy and the glass body corresponding to the barrier 1 150 shines, radiating laser energy away from the detector. In fact in the Figure 10b example, it is apparent that the body of the glass corresponding to the barrier 1 150 is shining, as is the region corresponding to the crack 1 154. This is a result of dispersion of the laser light due to the defect. Empirical results have shown that as a result of a defect such as the crack 1 154, there may also be a change in direction of the emitted beam such that it does not traverse a straight predicted path from emitter to detector. Thus a detector placed according to a predicted straight path will predict reduced or perhaps even no light energy.

Example 1 may comprise a defect detection apparatus for detecting defects in a barrier of an imaging device, the apparatus comprising:

a barrier housing to receive a barrier, the barrier comprising a material through which electromagnetic radiation is transmissible and arranged to provide protection for at least one component of the imaging device;

a barrier defect detector comprising an emitter to emit electromagnetic radiation towards the barrier and a detector to detect electromagnetic radiation received via a predicted path from the barrier;

wherein the barrier defect detector comprises an output port to provide a signal to a controller, the controller to determine the barrier is defective depending upon a detected level of electromagnetic radiation indicated by the received signal.

Example 2 may comprise the defect detection apparatus of example 1 , or some other example herein, wherein the imaging device is a two-dimensional printer to create an image by printing or a three-dimensional printer to create a three-dimensional object.

Example 3 may comprise the defect detection apparatus of example 1 or example 2, or some other example herein, wherein the imaging device is a scanner to capture an image by scanning, such as 2D scanning or 3D scanning. Example 4 may comprise the defect detection apparatus of any one of examples 1 to 3, or some other example herein, wherein at least one of the emitter and the detector are situated within the barrier defect detection apparatus at a predetermined distance from a plane coinciding with a location of the barrier.

Example 5 may comprise the defect detection apparatus of example 4, or some other example herein, wherein the barrier defect detector comprises at least one waveguide to direct the emitted electromagnetic radiation between the emitter and the detector.

Example 6 may comprise the defect detection apparatus of any one of examples 1 to 5, or some other example herein, wherein the barrier defect detector comprises at least one light emitter and a plurality of light detectors to detect light energy received via a plurality of different respective predicted light paths via the barrier.

Example 7 may comprise the defect detection apparatus of any one of examples 1 to 6, or some other example herein, wherein the barrier element defect detector comprises a plurality of emitters and a respective plurality of detectors.

Example 8 may comprise the defect detection apparatus of example 6, or some other example herein, wherein at least two of the plurality of emitter and detector pairs are arranged to direct the electromagnetic radiation through the barrier between two differently oriented pairs of edges of the barrier.

Example 9 may comprise the defect detection apparatus of any one of examples 1 to 8, or some other example herein, comprising at least one reflector to reflect the emitted electromagnetic energy such that the predicted path comprises a plurality of transits of the barrier, the electromagnetic energy being detected by the detector after passing via the at least one reflector.

Example 10 may comprise the defect detection apparatus of any one of examples 1 to 9, or some other example herein, wherein the electromagnetic radiation is visible light.

Example 1 1 may comprise the defect detection apparatus of any one of examples 1 to 10, or some other example herein, comprising the barrier. Example 12 may comprise the defect detection apparatus of example 1 1 , or some other example herein, wherein the barrier is formed to have a smooth and substantially flat surface at least at a region of the barrier where the electromagnetic energy is directed from the emitter and in a region of the barrier where electromagnetic energy emerges from the barrier towards the detector.

Example 13 may comprise the printer or a scanner comprising the defect detection apparatus of any one of examples 1 to 12 or some other example herein, and the controller of any one of examples 1 to 12 or some other example herein,.

Example 14 may comprise the printer or the scanner of example 13, or some other example herein, wherein the controller is arranged to suspend an imaging operation being performed when it determines that the barrier is defective.

Example 15 may comprise the method of detecting a defect in a barrier of an imaging device, the barrier comprising a material through which electromagnetic radiation is transmissible and arranged to provide protection for at least one component of the imaging device, the method comprising:

emitting electromagnetic radiation towards the barrier;

detecting electromagnetic radiation received via a predicted path from the barrier; and

outputting a signal depending upon the detected electromagnetic radiation to a controller;

wherein the signal is used by the controller to determine if the barrier is defective and to suspend operation of at least one component of the imaging device or to send a warning to a user display of the imaging device if the controller determines that the barrier is defective.

Example 16 may comprise machine executable instructions stored on a transient or non- transient machine readable medium, the instructions being operable upon execution by one or more processors to perform the method of example 15 or some other example herein,.

Example 17 may comprise a shielding element housing for an apparatus for generating a three-dimensional object, the shielding element housing comprising: a shielding element interface to receive a shielding element, the shielding element to provide protection for at least a portion of the apparatus;

a shielding element defect detector comprising an emitter to emit electromagnetic energy to the shielding element and a detector to detect electromagnetic energy received via a predicted transmission path from the shielding element;

wherein the shielding element defect detector comprises an output port to output to a controller of the apparatus, a signal depending upon the detected electromagnetic energy and wherein the controller is arranged to control the apparatus to suspend generation of the three-dimensional object depending upon the signal from the output port.

Example 18 may comprise the shielding element housing of example 17, or some other example herein, wherein the shielding element housing comprises at least one reflector to reflect the emitted electromagnetic energy through the shielding element to cause the transmission path to traverse the shielding element a plurality of times via non-coincident trajectories to arrive at the detector.

Example 19 may comprise the an energy directing unit comprising the shielding element housing of example 17 or example 18, wherein the energy directing unit has an interface to receive at least one removably insertable energy generating element to direct energy to a build material for forming the three-dimensional object and wherein the shielding element is arranged to protect the at least one energy generating element from build material during generation of the three dimensional object.

Example 20 may comprise he energy directing unit of example 19, or some other example herein, wherein at least one of the emitter and the detector are displaced by at least a predetermined distance from a plane of the shielding element.

Example 21 may comprise the apparatus for generating a three dimensional object, comprising the shielding element housing of example 17 or example 18, or some other example herein.

Example 22 may comprise the method for conditionally suspending operation in an apparatus for generating a three-dimensional object, the method comprising: providing a shielding element in the apparatus to protect at least one component of the apparatus during generation of the three-dimensional object;

emitting light energy from an emitter through the shielding element;

detecting at a detector, light energy received at a predetermined position in the apparatus, the predetermined position depending upon a predicted transmission path via the shielding element;

comparing the emitted light energy and the detected light energy to detect a defect in the shielding element; and

controlling the apparatus to suspend or at least partially suspend generation of the three-dimensional object depending upon the comparison.

Example 23 may comprise the machine executable instructions stored on a transient or non-transient machine readable medium, the instructions being operable upon execution by one or more processors to perform the method of example 22 or some other example herein.

Example 24 may comprise a shielding element defect detector for use in an apparatus for generating a three-dimensional object, the shielding element defect detector comprising an emitter to emit electromagnetic energy to the shielding element and a detector to detect electromagnetic energy received via a predicted transmission path from the shielding element.